Journal articles: 'Β4'

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Soung, Young, Shane Ford, Cecilia Yan, and Jun Chung. "The Role of Arrestin Domain-Containing 3 in Regulating Endocytic Recycling and Extracellular Vesicle Sorting of Integrin β4 in Breast Cancer." Cancers 10, no. 12 (December 11, 2018): 507. http://dx.doi.org/10.3390/cancers10120507.

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Despite the established role of integrin β4 (ITG β4) in breast cancer progression, the importance of endocytic recycling of ITG β4 and its regulatory mechanism are poorly understood. Here, we found that a sub-population of ITG β4 is sorted into early endosomes, recycled back to the plasma membrane, and secreted in the form of extracellular vesicles (EVs) upon EGF treatment in triple negative breast cancer (TNBC) cells. A metastasis suppressor, ARRDC3 (arrestin domain-containing 3) prevents EGF-driven endocytic recycling of ITG β4 by inducing NEDD4-dependent ubiquitination of ITG β4 and targeting endosomal ITG β4 into lysosomes. Endocytic recycling of ITG β4 is linked to sorting of ITG β4 into EVs (ITG β4+ EVs). ITG β4+ EVs are mainly detectable from supernatants of TNBC cells and their production is inhibited by ARRDC3 expression. ARRDC3 reduces the metastatic potentials of breast cancer cell-derived EVs by reducing ITG β4 levels in EVs. Overall, current studies provide novel mechanistic insights on the regulatory mechanism of ITG β4 recycling, and its importance in invasive potentials of TNBC EVs, thus providing the basis for therapeutic targeting of the ARRDC3/ITG β4 pathway in TNBC.

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Geuijen, Cecile A. W., and Arnoud Sonnenberg. "Dynamics of the α6β4 Integrin in Keratinocytes." Molecular Biology of the Cell 13, no. 11 (November 2002): 3845–58. http://dx.doi.org/10.1091/mbc.02-01-0601.

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The integrin α6β4 has been implicated in two apparently contrasting processes, i.e., the formation of stable adhesions, and cell migration and invasion. To study the dynamic properties of α6β4 in live cells two different β4-chimeras were stably expressed in β4-deficient PA-JEB keratinocytes. One chimera consisted of full-length β4 fused to EGFP at its carboxy terminus (β4-EGFP). In a second chimera the extracellular part of β4 was replaced by EGFP (EGFP-β4), thereby rendering it incapable of associating with α6 and thus of binding to laminin-5. Both chimeras induce the formation of hemidesmosome-like structures, which contain plectin and often also BP180 and BP230. During cell migration and division, the β4-EGFP and EGFP-β4 hemidesmosomes disappear, and a proportion of the β4-EGFP, but not of the EGFP-β4 molecules, become part of retraction fibers, which are occasionally ripped from the cell membrane, thereby leaving “footprints” of the migrating cell. PA-JEB cells expressing β4-EGFP migrate considerably more slowly than those that express EGFP-β4. Studies with a β4-EGFP mutant that is unable to interact with plectin and thus with the cytoskeleton (β4R1281W-EGFP) suggest that the stabilization of the interaction between α6β4 and LN-5, rather than the increased adhesion to LN-5, is responsible for the inhibition of migration. Consistent with this, photobleaching and recovery experiments revealed that the interaction of β4 with plectin renders the bond between α6β4 and laminin-5 more stable, i.e., β4-EGFP is less dynamic than β4R1281W-EGFP. On the other hand, when α6β4 is bound to laminin-5, the binding dynamics of β4 to plectin are increased, i.e., β4-EGFP is more dynamic than EGFP-β4. We suggest that the stability of the interaction between α6β4 and laminin-5 is influenced by the clustering of α6β4 through the deposition of laminin-5 underneath the cells. This clustering ultimately determines whether α6β4 will inhibit cell migration or not.

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Ivanova, V. P. "THE EFFECT OF THYMOSIN β4 ON THE FUNCTIONAL ACTIVITY OF THE IMMUNE AND NERVOUS SYSTEM COMPONENTS." Medical academic journal 19, no. 1S (December 15, 2019): 164–66. http://dx.doi.org/10.17816/maj191s1164-166.

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The data on properties of thymosin β4, a conserved multifunctional polypeptide of mammals is summarized. Attention has been focused on regulatory activity of thymosin β4 in regard to immune and nervous system components. In these systems thymosin β4 is present in different cell types both stationary and mobile ones. Besides intracellular localization thymosin β4 is also located in extracellular fluids. Inside cells, thymosin β4 has been postulated to regulate actin polymerization as a G-actin-sequestering molecule. But molecular mechanisms of thymosin β4 located extra cells on cell functions remain unclear. The structural-functional organization of thymosin β4 is also discussed. Thymosin β4 is a perspective medicine preparation for the therapy of diseases related to immune and neurological disturbances in patients.

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Rima, Mohamad, Marwa Daghsni, Anaïs Lopez, Ziad Fajloun, Lydie Lefrancois, Mireia Dunach, Yasuo Mori, et al. "Down-regulation of the Wnt/β-catenin signaling pathway by Cacnb4." Molecular Biology of the Cell 28, no. 25 (December 2017): 3699–708. http://dx.doi.org/10.1091/mbc.e17-01-0076.

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The β4 isoform of the β-subunits of voltage-gated calcium channel regulates cell proliferation and cell cycle progression. Herein we show that coexpression of the β4-subunit with actors of the canonical Wnt/β-catenin signaling pathway in a hepatoma cell line inhibits Wnt-responsive gene transcription and decreases cell division, in agreement with the role of the Wnt pathway in cell proliferation. β4-subunit–mediated inhibition of Wnt signaling is observed in the presence of LiCl, an inhibitor of glycogen synthase kinase (GSK3) that promotes β-catenin translocation to the nucleus. Expression of β4-subunit mutants that lost the ability to translocate to the nucleus has no effect on Wnt signaling, suggesting that β4-subunit inhibition of Wnt signaling occurs downstream from GSK3 and requires targeting of β4-subunit to the nucleus. β4-subunit coimmunoprecipitates with the TCF4 transcription factor and overexpression of TCF4 reverses the effect of β4-subunit on the Wnt pathway. We thus propose that the interaction of nuclear β4-subunit with TCF4 prevents β-catenin binding to TCF4 and leads to the inhibition of the Wnt-responsive gene transcription. Thereby, our results show that β4-subunit is a TCF4 repressor and therefore appears as an interesting candidate for the regulation of this pathway in neurons where β4-subunit is specifically expressed.

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Pullar, Christine E., Brian S. Baier, Yoshinobu Kariya, Alan J. Russell, Basil A. J. Horst, M. Peter Marinkovich, and R. Rivkah Isseroff. "β4 Integrin and Epidermal Growth Factor Coordinately Regulate Electric Field-mediated Directional Migration via Rac1." Molecular Biology of the Cell 17, no. 11 (November 2006): 4925–35. http://dx.doi.org/10.1091/mbc.e06-05-0433.

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Endogenous DC electric fields (EF) are present during embryogenesis and are generated in vivo upon wounding, providing guidance cues for directional cell migration (galvanotaxis) required in these processes. To understand the role of beta (β)4 integrin in directional migration, the migratory paths of either primary human keratinocytes (NHK), β4 integrin-null human keratinocytes (β4−), or those in which β4 integrin was reexpressed (β4+), were tracked during exposure to EFs of physiological magnitude (100 mV/mm). Although the expression of β4 integrin had no effect on the rate of cell movement, it was essential for directional (cathodal) migration in the absence of epidermal growth factor (EGF). The addition of EGF potentiated the directional response, suggesting that at least two distinct but synergistic signaling pathways coordinate galvanotaxis. Expression of either a ligand binding–defective β4 (β4+AD) or β4 with a truncated cytoplasmic tail (β4+CT) resulted in loss of directionality in the absence of EGF, whereas inhibition of Rac1 blinded the cells to the EF even in the presence of EGF. In summary, both the β4 integrin ligand–binding and cytoplasmic domains together with EGF were required for the synergistic activation of a Rac-dependent signaling pathway that was essential for keratinocyte directional migration in response to a galvanotactic stimulus.

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Schaapveld, Roel Q. J., Luca Borradori, Dirk Geerts, Manuel R. van Leusden, Ingrid Kuikman, Mirjam G. Nievers, Carien M. Niessen, Renske D. M. Steenbergen, Peter J. F. Snijders, and Arnoud Sonnenberg. "Hemidesmosome Formation Is Initiated by the β4 Integrin Subunit, Requires Complex Formation of β4 and HD1/Plectin, and Involves a Direct Interaction between β4 and the Bullous Pemphigoid Antigen 180." Journal of Cell Biology 142, no. 1 (July 13, 1998): 271–84. http://dx.doi.org/10.1083/jcb.142.1.271.

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Hemidesmosomes (HDs) are stable anchoring structures that mediate the link between the intermediate filament cytoskeleton and the cell substratum. We investigated the contribution of various segments of the β4 integrin cytoplasmic domain in the formation of HDs in transient transfection studies using immortalized keratinocytes derived from an epidermolysis bullosa patient deficient in β4 expression. We found that the expression of wild-type β4 restored the ability of the β4-deficient cells to form HDs and that distinct domains in the NH2- and COOH-terminal regions of the β4 cytoplasmic domain are required for the localization of HD1/plectin and the bullous pemphigoid antigens 180 (BP180) and 230 (BP230) in these HDs. The tyrosine activation motif located in the connecting segment (CS) of the β4 cytoplasmic domain was dispensable for HD formation, although it may be involved in the efficient localization of BP180. Using the yeast two-hybrid system, we could demonstrate a direct interaction between β4 and BP180 which involves sequences within the COOH-terminal part of the CS and the third fibronectin type III (FNIII) repeat. Immunoprecipitation studies using COS-7 cells transfected with cDNAs for α6 and β4 and a mutant BP180 which lacks the collagenous extracellular domain confirmed the interaction of β4 with BP180. Nevertheless, β4 mutants which contained the BP180-binding region, but lacked sequences required for the localization of HD1/plectin, failed to localize BP180 in HDs. Additional yeast two- hybrid assays indicated that the 85 COOH-terminal residues of β4 can interact with the first NH2-terminal pair of FNIII repeats and the CS, suggesting that the cytoplasmic domain of β4 is folded back upon itself. Unfolding of the cytoplasmic domain may be part of a mechanism by which the interaction of β4 with other hemidesmosomal components, e.g., BP180, is regulated.

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Litjens, Sandy H. M., Jan Koster, Ingrid Kuikman, Sandra van Wilpe, José M. de Pereda, and Arnoud Sonnenberg. "Specificity of Binding of the Plectin Actin-binding Domain to β4 Integrin." Molecular Biology of the Cell 14, no. 10 (October 2003): 4039–50. http://dx.doi.org/10.1091/mbc.e03-05-0268.

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Plectin is a major component of the cytoskeleton and links the intermediate filament system to hemidesmosomes by binding to the integrin β4 subunit. Previously, a binding site for β4 was mapped on the actin-binding domain (ABD) of plectin and binding of β4 and F-actin to plectin was shown to be mutually exclusive. Here we show that only the ABDs of plectin and dystonin bind to β4, whereas those of other actin-binding proteins do not. Mutations of the ABD of plectin-1C show that Q131, R138, and N149 are critical for tight binding of the ABD to β4. These residues form a small cavity, occupied by a well-ordered water molecule in the crystal structure. The β4 binding pocket partly overlaps with the actin-binding sequence 2 (ABS2), previously shown to be essential for actin binding. Therefore, steric interference may render binding of β4 and F-actin to plectin mutually exclusive. Finally, we provide evidence indicating that the residues preceding the ABD in plectin-1A and -1C, although unable to mediate binding to β4 themselves, modulate the binding activity of the ABD for β4. These studies demonstrate the unique property of the plectin-ABD to bind to both F-actin and β4, and explain why several other ABD-containing proteins that are expressed in basal keratinocytes are not recruited into hemidesmosomes.

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Bertotti, Andrea, Paolo M. Comoglio, and Livio Trusolino. "β4 integrin activates a Shp2–Src signaling pathway that sustains HGF-induced anchorage-independent growth." Journal of Cell Biology 175, no. 6 (December 11, 2006): 993–1003. http://dx.doi.org/10.1083/jcb.200605114.

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Despite being a cell–matrix adhesion molecule, β4 integrin can prompt the multiplication of neoplastic cells dislodged from their substrates (anchorage-independent growth). However, the molecular events underlying this atypical behavior remain partly unexplored. We found that activation of the Met receptor for hepatocyte growth factor results in the tyrosine phosphorylation of β4, which is instrumental for integrin-mediated recruitment of the tyrosine phosphatase Shp2. Shp2 binding to β4 enhances the activation of Src, which, in turn, phosphorylates the multiadaptor Gab1 predominantly on consensus sites for Grb2 association, leading to privileged stimulation of the Ras–extracellular signal-regulated kinase (ERK) cascade. This signaling axis can be inhibited by small interfering RNA–mediated β4 depletion, by a β4 mutant unable to bind Shp2, and by pharmacological and genetic inhibition of Shp2 or Src. Preservation of the β4 docking sites for Shp2 as well as the integrity of Shp2, Src, or ERK activity are required for the β4-mediated induction of anchorage-independent growth. These results unravel a novel pathway whereby β4 directs tyrosine kinase–based signals toward adhesion-unrelated outcomes.

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Grimm, P. Richard, Ruth M. Foutz, Robert Brenner, and Steven C. Sansom. "Identification and localization of BK-β subunits in the distal nephron of the mouse kidney." American Journal of Physiology-Renal Physiology 293, no. 1 (July 2007): F350—F359. http://dx.doi.org/10.1152/ajprenal.00018.2007.

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Large-conductance, Ca2+-activated K+ channels (BK), comprised of pore-forming α- and accessory β-subunits, secrete K+ in the distal nephron under high-flow and high-K+ diet conditions. BK channels are detected by electrophysiology in many nephron segments; however, the accessory β-subunit associated with these channels has not been determined. We performed RT-PCR, Western blotting, and immunohistochemical staining to determine whether BK-β1 is localized to the connecting tubule's principal-like cells (CNT) or intercalated cells (ICs), and whether BK-β2-4 are present in other distal nephron segments. RT-PCR and Western blots revealed that the mouse kidney expresses BK-β1, BK-β2, and BK-β4. Available antibodies in conjunction with BK-β1−/− and BK-β4−/− mice allowed the specific localization of BK-β1 and BK-β4 in distal nephron segments. Immunohistochemical staining showed that BK-β1 is localized in the CNT but not ICs of the connecting tubule. The localization of BK-β4 was discerned using an anti-BK-β4 antibody on wild-type tissue and anti-GFP on GFP-replaced BK-β4 mouse (BK-β4−/−) tissue. Both antibodies (anti-BK-β4 and anti-GFP) localized BK-β4 to the thick ascending limb (TAL), distal convoluted tubule (DCT), and ICs of the distal nephron. It is concluded that BK-β1 is narrowly confined to the apical membrane of CNTs in the mouse, whereas BK-β4 is expressed in the TAL, DCT, and ICs.

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Yang, Xiuwei, Oleg V. Kovalenko, Wei Tang, Christoph Claas, Christopher S. Stipp, and Martin E. Hemler. "Palmitoylation supports assembly and function of integrin–tetraspanin complexes." Journal of Cell Biology 167, no. 6 (December 20, 2004): 1231–40. http://dx.doi.org/10.1083/jcb.200404100.

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As observed previously, tetraspanin palmitoylation promotes tetraspanin microdomain assembly. Here, we show that palmitoylated integrins (α3, α6, and β4 subunits) and tetraspanins (CD9, CD81, and CD63) coexist in substantially overlapping complexes. Removal of β4 palmitoylation sites markedly impaired cell spreading and signaling through p130Cas on laminin substrate. Also in palmitoylation-deficient β4, secondary associations with tetraspanins (CD9, CD81, and CD63) were diminished and cell surface CD9 clustering was decreased, whereas core α6β4–CD151 complex formation was unaltered. There is also a functional connection between CD9 and β4 integrins, as evidenced by anti-CD9 antibody effects on β4-dependent cell spreading. Notably, β4 palmitoylation neither increased localization into “light membrane” fractions of sucrose gradients nor decreased solubility in nonionic detergents—hence it does not promote lipid raft association. Instead, palmitoylation of β4 (and of the closely associated tetraspanin CD151) promotes CD151–α6β4 incorporation into a network of secondary tetraspanin interactions (with CD9, CD81, CD63, etc.), which provides a novel framework for functional regulation.

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Wang, Bin, Brad S. Rothberg, and Robert Brenner. "Mechanism of β4 Subunit Modulation of BK Channels." Journal of General Physiology 127, no. 4 (March 27, 2006): 449–65. http://dx.doi.org/10.1085/jgp.200509436.

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Large-conductance (BK-type) Ca2+-activated potassium channels are activated by membrane depolarization and cytoplasmic Ca2+. BK channels are expressed in a broad variety of cells and have a corresponding diversity in properties. Underlying much of the functional diversity is a family of four tissue-specific accessory subunits (β1–β4). Biophysical characterization has shown that the β4 subunit confers properties of the so-called “type II” BK channel isotypes seen in brain. These properties include slow gating kinetics and resistance to iberiotoxin and charybdotoxin blockade. In addition, the β4 subunit reduces the apparent voltage sensitivity of channel activation and has complex effects on apparent Ca2+ sensitivity. Specifically, channel activity at low Ca2+ is inhibited, while at high Ca2+, activity is enhanced. The goal of this study is to understand the mechanism underlying β4 subunit action in the context of a dual allosteric model for BK channel gating. We observed that β4's most profound effect is a decrease in Po (at least 11-fold) in the absence of calcium binding and voltage sensor activation. However, β4 promotes channel opening by increasing voltage dependence of Po-V relations at negative membrane potentials. In the context of the dual allosteric model for BK channels, we find these properties are explained by distinct and opposing actions of β4 on BK channels. β4 reduces channel opening by decreasing the intrinsic gating equilibrium (L0), and decreasing the allosteric coupling between calcium binding and voltage sensor activation (E). However, β4 has a compensatory effect on channel opening following depolarization by shifting open channel voltage sensor activation (Vho) to more negative membrane potentials. The consequence is that β4 causes a net positive shift of the G-V relationship (relative to α subunit alone) at low calcium. At higher calcium, the contribution by Vho and an increase in allosteric coupling to Ca2+ binding (C) promotes a negative G-V shift of α+β4 channels as compared to α subunits alone. This manner of modulation predicts that type II BK channels are downregulated by β4 at resting voltages through effects on L0. However, β4 confers a compensatory effect on voltage sensor activation that increases channel opening during depolarization.

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BALLWEBER, Edda, Ewald HANNAPPEL, Thomas HUFF, and Hans Georg MANNHERZ. "Mapping the binding site of thymosin β4 on actin by competition with G-actin binding proteins indicates negative co-operativity between binding sites located on opposite subdomains of actin." Biochemical Journal 327, no. 3 (November 1, 1997): 787–93. http://dx.doi.org/10.1042/bj3270787.

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The β-thymosins are small monomeric (G-)actin-binding proteins of 5 kDa that are supposed to act intracellularly as actin-sequestering factors stabilizing the cytoplasmic monomeric pool of actin. The binding region of thymosin β4 was determined by analysing the binding of thymosin β4 to actin complexed with DNase I, gelsolin or gelsolin segment 1. Binding was analysed by determining the increase in the critical concentration of actin polymerization by native gel electrophoresis or chemical cross-linking. The formation of a ternary complex including thymosin β4 should indicate that the actin-binding proteins attach to different sites on actin. Competition would be indicative of binding to identical or overlapping sites on actin or of a negative co-operative linkage between the two binding sites. Competition of thymosin β4 for actin binding was observed in the presence of intact gelsolin or the N-terminal gelsolin fragment, segment 1, indicating that thymosin β4 binds to a site close to or identical with the gelsolin segment 1-binding site. The ternary complex of actin-DNase I-thymosin β4 was obtained only when using the chemically cross-linked actin-thymosin β4 complex, indicating that thymosin β4 is dissociated by the binding of DNase I to actin. It is suggested that the dissociation of thymosin β4 by DNase I binding to actin is caused by negative co-operativity between their spatially separated binding sites on actin. A similar negative co-operativity was observed between DNase I and gelsolin segment 1 binding to actin. The results therefore indicate that the respective binding sites for DNase I and segment 1 on subdomains 1 and 2 of actin are linked in a negative co-operative manner.

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Oldak, Monika, Radoslaw B. Maksym, Tanya Sperling, Moshe Yaniv, Hans Smola, Herbert J. Pfister, Jacek Malejczyk, and Sigrun Smola. "Human Papillomavirus Type 8 E2 Protein Unravels JunB/Fra-1 as an Activator of the β4-Integrin Gene in Human Keratinocytes." Journal of Virology 84, no. 3 (November 18, 2009): 1376–86. http://dx.doi.org/10.1128/jvi.01220-09.

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ABSTRACT The papillomavirus life cycle parallels keratinocyte differentiation in stratifying epithelia. We have previously shown that the human papillomavirus type 8 (HPV8) E2 protein downregulates β4-integrin expression in normal human keratinocytes, which may trigger subsequent differentiation steps. Here, we demonstrate that the DNA binding domain of HPV8 E2 is sufficient to displace a cellular factor from the β4-integrin promoter. We identified the E2-displaceable factor as activator protein 1 (AP-1), a heteromeric transcription factor with differentiation-specific expression in the epithelium. β4-Integrin-positive epithelial cells displayed strong AP-1 binding activity. Both AP-1 binding activity and β4-integrin expression were coregulated during keratinocyte differentiation suggesting the involvement of AP-1 in β4-integrin expression. In normal human keratinocytes the AP-1 complex was composed of JunB and Fra-1 subunits. Chromatin immunoprecipitation assays confirmed that JunB/Fra-1 proteins interact in vivo with the β4-integrin promoter and that JunB/Fra-1 promoter occupancy is reduced during keratinocyte differentiation as well as in HPV8 E2 positive keratinocytes. Ectopic expression of the tethered JunB/Fra-1 heterodimer in normal human keratinocytes activated the β4-integrin promoter, while coexpression of HPV8 E2 reverted the JunB/Fra-1 effect. In summary, we identified a novel mechanism of human β4-integrin regulation that is specifically targeted by the HPV8 E2 protein mimicking transcriptional conditions of differentiation. This may explain the early steps of how HPV8 commits its host cells to the differentiation process required for the viral life cycle.

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Wang, Bin, Brad S. Rothberg, and Robert Brenner. "Mechanism of Increased BK Channel Activation from a Channel Mutation that Causes Epilepsy." Journal of General Physiology 133, no. 3 (February 9, 2009): 283–94. http://dx.doi.org/10.1085/jgp.200810141.

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Concerted depolarization and Ca2+ rise during neuronal action potentials activate large-conductance Ca2+- and voltage-dependent K+ (BK) channels, whose robust K+ currents increase the rate of action potential repolarization. Gain-of-function BK channels in mouse knockout of the inhibitory β4 subunit and in a human mutation (αD434G) have been linked to epilepsy. Here, we investigate mechanisms underlying the gain-of-function effects of the equivalent mouse mutation (αD369G), its modulation by the β4 subunit, and potential consequences of the mutation on BK currents during action potentials. Kinetic analysis in the context of the Horrigan-Aldrich allosteric gating model revealed that changes in intrinsic and Ca2+-dependent gating largely account for the gain-of-function effects. D369G causes a greater than twofold increase in the closed-to-open equilibrium constant (6.6e−7→1.65e−6) and an approximate twofold decrease in Ca2+-dissociation constants (closed channel: 11.3→5.2 µM; open channel: 0.92→0.54 µM). The β4 subunit inhibits mutant channels through a slowing of activation kinetics. In physiological recording solutions, we established the Ca2+ dependence of current recruitment during action potential–shaped stimuli. D369G and β4 have opposing effects on BK current recruitment, where D369G reduces and β4 increases K1/2 (K1/2 μM: αWT 13.7, αD369G 6.3, αWT/β4 24.8, and αD369G/β4 15.0). Collectively, our results suggest that the D369G enhancement of intrinsic gating and Ca2+ binding underlies greater contributions of BK current in the sharpening of action potentials for both α and α/β4 channels.

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Koster, J., S. van Wilpe, I. Kuikman, S. H. M. Litjens, and A. Sonnenberg. "Role of Binding of Plectin to the Integrin β4 Subunit in the Assembly of Hemidesmosomes." Molecular Biology of the Cell 15, no. 3 (March 2004): 1211–23. http://dx.doi.org/10.1091/mbc.e03-09-0697.

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We have previously shown that plectin is recruited into hemidesmosomes through association of its actin-binding domain (ABD) with the first pair of fibronectin type III (FNIII) repeats and a small part of the connecting segment (residues 1328–1355) of the integrin β4 subunit. Here, we show that two proline residues (P1330 and P1333) in this region of the connecting segment are critical for supporting β4-mediated recruitment of plectin. Additional binding sites for the plakin domain of plectin on β4 were identified in biochemical and yeast two-hybrid assays. These sites are located at the end of the connecting segment (residues 1383–1436) and in the region containing the fourth FNIII repeat and the C-tail (residues 1570–1752). However, in cells, these additional binding sites cannot induce the assembly of hemidesmosomes without the interaction of the plectin-ABD with β4. Because the additional plectin binding sites overlap with sequences that mediate an intramolecular association of the β4 cytoplasmic domain, we propose that they are not accessible for binding and need to become exposed as the result of the binding of the plectin-ABD to β4. Furthermore, these additional binding sites might be necessary to position the β4 cytoplasmic domain for an optimal interaction with other hemidesmosomal components, thereby increasing the efficiency of hemidesmosome assembly.

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Wyczółkowska, Janina, Aurelia Walczak-Drzewiecka, Waldemar Wagner, and Jarosław Dastych. "Thymosin β4 and thymosin β4-derived peptides induce mast cell exocytosis." Peptides 28, no. 4 (April 2007): 752–59. http://dx.doi.org/10.1016/j.peptides.2007.01.004.

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App, Christine, Jana Knop, Thomas Huff, Heinrich Sticht, and Ewald Hannappel. "Thymosin β4 and Tissue Transglutaminase. Molecular Characterization of Cyclic Thymosin β4." Protein Journal 32, no. 6 (August 2013): 484–92. http://dx.doi.org/10.1007/s10930-013-9507-0.

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Kedmi, Merav, and Avi Orr-Urtreger. "Differential brain transcriptome of β4 nAChR subunit-deficient mice: is it the effect of the null mutation or the background strain?" Physiological Genomics 28, no. 2 (January 2007): 213–22. http://dx.doi.org/10.1152/physiolgenomics.00155.2006.

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Studies using mice with β4 nicotinic acetylcholine receptor (nAChR) subunit deficiency (β4−/− mice) helped reveal the roles of this subunit in bradycardiac response to vagal stimulation, nicotine-induced seizure activity and anxiety. To identify genes that might be related to β4-containing nAChRs activity, we compared the mRNA expression profiles of brains from β4−/− and wild-type mice using Affymetrix U74Av2 microarray. Seventy-seven genes significantly differentiated between these two experimental groups. Of them, the two most downregulated were spastic paraplegia 21 (human) homolog ( Spg21) and 6-pyruvoyl-tetrahydropterin synthase ( Pts) genes. Since the targeted mutagenesis of the β4 nAChR subunit was done by using two mouse strains, 129SvEv and C57BL/6J, it is possible that the genes closely linked to the mutated β4 gene represent the 129SvEv allele and not the control C57BL/6J-driven allele. We examined this possibility by using public database and quantitative RT-PCR. The expression levels of Spg21 and Pts genes that, like the β4 gene, are localized on mouse chromosome 9, as well as the expression levels of other genes located on this chromosome, were dependent on the mouse background strain. The 67 differentially expressed genes that are not located on chromosome 9 were further analyzed for overrepresented functional annotations and transcription regulatory elements compared with the entire microarray. Genes encoding for proteins involved in tyrosine phosphatase activity, calcium ion binding, cell growth and/or maintenance, and chromosome organization were overrepresented. Our data enhance the understanding of the molecular interactions involved in the β4 nAChR subunit function. They also emphasize the need for careful interpretation of expression microarray studies done on genetically manipulated animals.

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Kedmi, Merav, Arthur L. Beaudet, and Avi Orr-Urtreger. "Mice lacking neuronal nicotinic acetylcholine receptor β4-subunit and mice lacking both α5- and β4-subunits are highly resistant to nicotine-induced seizures." Physiological Genomics 17, no. 2 (April 13, 2004): 221–29. http://dx.doi.org/10.1152/physiolgenomics.00202.2003.

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Nicotine, the main addictive component of tobacco, evokes a wide range of dose-dependent behaviors in rodents, and when administrated in high doses, it can induce clonic-tonic seizures. Nicotine acts through the nicotinic acetylcholine receptors (nAChRs). Mutations in the human α4- and the β2-nAChR subunit genes cause autosomal dominant nocturnal frontal lobe epilepsy. Using transgenic mice with mutations in nAChR subunits, it was demonstrated previously that the α4-, α5-, and α7-subunits are involved in nicotine-induced seizures. To examine the possibility that the β4-subunit is also involved in this phenotype, we tested mice with homozygous β4-subunit deficiency. The β4 null mice were remarkably resistant to nicotine-induced seizures compared with wild-type and α5 null mice. We also generated mice with double deficiency of both α5- and β4-nAChR subunits and demonstrated that they were more resistant to nicotine’s convulsant effect than either the α5 or the β4 single mutant mice. In addition, the single α5 mutants and the double α5β4-deficient mice exhibited a significantly shorter latency time to seizure than that of the wild-type mice. Our results thus show that β4-containing nAChRs have a crucial role in the pathogenesis of nicotine-induced seizures. Furthermore, by comparing multiple mutant mice with single and double subunit deficiency, we suggest that nicotinic receptors containing either α5- or β4-subunits are involved in nicotine-induced seizures and that receptors containing both subunits are likely to contribute to this phenomena as well. However, the α5-subunit, but not the β4-subunit, regulates the rate of response to high doses of nicotine.

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Blain, E. J., D. J. Mason, and V. C. Duance. "The effect of thymosin β4 on articular cartilage chondrocyte matrix metalloproteinase expression." Biochemical Society Transactions 30, no. 6 (November 1, 2002): 879–82. http://dx.doi.org/10.1042/bst0300879.

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Mechanical loading is paramount in regulating both the anabolic and catabolic activities of articular cartilage chondrocytes, essential for the matrix to retain its functional integrity. We have identified thymosin β4 as a putative mechanically regulated gene that may mediate load-enhanced synthesis and activation of matrix metalloproteinases (MMPs) 2 and 9 in articular cartilage. The objective of this study was to confirm the mechanical regulation of thymosin β4 and determine its effect on cartilage chondrocyte MMP production. Thymosin β4 mRNA expression, analysed by quantitative PCR, revealed a significant 20-fold increase in cartilage loaded for 10 min which was still evident after 30 min of loading. Treatment of primary chondrocytes with 2 and 4 μg · ml-1 thymosin β4 peptide for 4 h significantly increased pro-MMP 9 expression and activation. We postulate a functional role for load-induced thymosin β4 in modulating the cytoskeletal organization of articular cartilage chondrocytes to affect MMP expression.

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Chen, Weiguo, Saad Sammani, Sumegha Mitra, Shwu Fan Ma, Joe G. N. Garcia, and Jeffrey R. Jacobson. "Critical role for integrin-β4 in the attenuation of murine acute lung injury by simvastatin." American Journal of Physiology-Lung Cellular and Molecular Physiology 303, no. 4 (August 15, 2012): L279—L285. http://dx.doi.org/10.1152/ajplung.00361.2011.

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The statins are a class of 3-hydroxy-3-methylglutaryl-coenzyme A-reductase inhibitors that are recognized to have pleiotropic properties. We previously reported the attenuation of LPS-induced murine acute lung injury (ALI) by simvastatin in vivo and identified relevant effects of simvastatin on endothelial cell (EC) signaling, activation, and barrier function in vitro. In particular, simvastatin induces the upregulation of integrin-β4, which in turn inhibits EC inflammatory responses via attenuation of MAPK signaling. The role of integrin-β4 in murine ALI protection by simvastatin, however, is unknown. We initially confirmed a time- and dose-dependent effect of simvastatin on increased integrin-β4 mRNA expression in human lung EC with peak protein expression evident at 16 h. Subsequently, reciprocal immunoprecipitation demonstrated an attenuation of LPS-induced integrin-β4 tyrosine phosphorylation by simvastatin (5 μM, 16 h). Increased expression of EC inflammatory cytokines [IL-6, IL-8, monocyte chemoattractant protein (MCP)-1, regulated on activation normal T cell expressed and secreted (RANTES)] by LPS (500 ng/ml, 4 h) was also significantly attenuated by simvastatin pretreatment (5 μM, 16 h), but this effect was reversed by cotreatment with an integrin-β4-blocking antibody. Finally, although simvastatin (20 mg/kg) conferred significant protection in murine ALI as evidenced by decreased bronchoalveolar lavage fluid cell counts, protein, inflammatory cytokines (IL-6, IL-1β, MCP-1, RANTES), decreased Evans blue dye albumin extravasation in lung tissue, and changes on lung histology, these effects were reversed by the integrin-β4-blocking antibody (IV, 1 mg/kg, 2 h before LPS). These findings support integrin-β4 as an important mediator of ALI protection by simvastatin and implicate signaling by integrin-β4 as a novel therapeutic target in patients with ALI.

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Conlon, J. M., L. Grimelius, G. Wallin, and L. Thim. "Isolation and structural characterization of thymosin-β4 from a human medullary thyroid carcinoma." Journal of Endocrinology 118, no. 1 (July 1988): 155–59. http://dx.doi.org/10.1677/joe.0.1180155.

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ABSTRACT An extract of a tumour metastases from a human medullary thyroid carcinoma contained a high concentration (at least 2·9 nmol/g wet weight) of the immunoregulatory peptide, thymosin-β4. The peptide was isolated as a mixture of two components with free and blocked NH2-terminal amino acid residues, the latter form predominating (approximately 98% of the total). The primary structure of the peptide was established by automated Edman degradation after cleavage with cyanogen bromide. The amino acid sequence of human thymosin-β4 was identical to thymosin-β4 previously isolated from calf thymus. Further studies are warranted to determine whether thymosin-β4 production is a useful marker for thyroid and other tumours. J. Endocr. (1988) 118, 155–159

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Frijns, Evelyne, Ingrid Kuikman, Sandy Litjens, Marcel Raspe, Kees Jalink, Michael Ports, Kevin Wilhelmsen, and Arnoud Sonnenberg. "Phosphorylation of threonine 1736 in the C-terminal tail of integrin β4 contributes to hemidesmosome disassembly." Molecular Biology of the Cell 23, no. 8 (April 15, 2012): 1475–85. http://dx.doi.org/10.1091/mbc.e11-11-0957.

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During wound healing, hemidesmome disassembly enables keratinocyte migration and proliferation. Hemidesmosome dynamics are altered downstream of epidermal growth factor (EGF) receptor activation, following the phosphorylation of integrin β4 residues S1356 and S1364, which reduces the interaction with plectin; however, this event is insufficient to drive complete hemidesmome disassembly. In the studies reported here, we used a fluorescence resonance energy transfer–based assay to demonstrate that the connecting segment and carboxy-terminal tail of the β4 cytoplasmic domain interact, which facilitates the formation of a binding platform for plectin. In addition, analysis of a β4 mutant containing a phosphomimicking aspartic acid residue at T1736 in the C-tail suggests that phosphorylation of this residue regulates the interaction with the plectin plakin domain. The aspartic acid mutation of β4 T1736 impaired hemidesmosome formation in junctional epidermolysis associated with pyloric atresia/β4 keratinocytes. Furthermore, we show that T1736 is phosphorylated downstream of protein kinase C and EGF receptor activation and is a substrate for protein kinase D1 in vitro and in cells, which requires its translocation to the plasma membrane and subsequent activation. In conclusion, we identify T1736 as a novel phosphorylation site that contributes to the regulation of hemidesmome disassembly, a dynamically regulated process involving the concerted phosphorylation of multiple β4 residues.

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Germain, Emily C., Tanya M. Santos, and Isaac Rabinovitz. "Phosphorylation of a Novel Site on the β4 Integrin at the Trailing Edge of Migrating Cells Promotes Hemidesmosome Disassembly." Molecular Biology of the Cell 20, no. 1 (January 2009): 56–67. http://dx.doi.org/10.1091/mbc.e08-06-0646.

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Hemidesmosomes (HDs) are multiprotein structures that anchor epithelial cells to the basement membrane. HD components include the α6β4 integrin, plectin, and BPAGs (bullous pemphigoid antigens). HD disassembly in keratinocytes is necessary for cells to migrate and can be induced by EGF through β4 integrin phosphorylation. We have identified a novel phosphorylation site on the β4 integrin: S1424. Preventing phosphorylation by mutating S→A1424 results in increased incorporation of β4 into HDs and resistance to EGF-induced disassembly. In contrast, mutating S→D1424 (mimicking phosphorylation) partially mobilizes β4 from HDs and potentiates the disassembly effects of other phosphorylation sites. In contrast to previously described sites that are phosphorylated upon growth factor stimulation, S1424 already exhibits high constitutive phosphorylation, suggesting additional functions. Constitutive phosphorylation of S1424 is distinctively enriched at the trailing edge of migrating keratinocytes where HDs are disassembled. Although most of this S1424-phosphorylated β4 is found dissociated from HDs, a substantial amount can be associated with HDs near the cell margins, colocalizing with plectin but always excluding BPAGs, suggesting that phospho-S1424 might be a mechanism to dissociate β4 from BPAGs. S1424 phosphorylation is PKC dependent. These data suggest an important role for S1424 in the gradual disassembly of HDs induced by cell retraction.

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Xu, Xiaohong, Michael M. Scott, and Evan S. Deneris. "Shared Long-Range Regulatory Elements Coordinate Expression of a Gene Cluster Encoding Nicotinic Receptor Heteromeric Subtypes." Molecular and Cellular Biology 26, no. 15 (August 1, 2006): 5636–49. http://dx.doi.org/10.1128/mcb.00456-06.

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ABSTRACT The nicotinic acetylcholine receptor (nAChR) β4/α3/α5 gene cluster encodes several heteromeric transmitter receptor subtypes that are essential for cholinergic synaptic transmission in adrenal gland, autonomic ganglia, pineal gland, and several nuclei in the central nervous system. However, the transcriptional mechanisms coordinating expression of these subunit genes in different cell populations are unknown. Here, we used transgenic methods to investigate long-range transcriptional control of the cluster. A 132-kb P1-derived artificial chromosome (PAC) encoding the rat cluster recapitulated the neurally- and endocrine-restricted expression patterns of the endogenous β4/α3/α5 genes. Mutation of ETS factor binding sites in an enhancer, β43′, embedded in the β4 3′-untranslated exon resulted in greatly diminished β4, α3, and α5 expression in adrenal gland and to a lesser extent in the superior cervical ganglion (SCG) but not in other tissues. Phylogenetic sequence analyses revealed several conserved noncoding regions (CNRs) upstream of β4 and α5. Deletion of one of them (CNR4) located 20 kb upstream of β4 resulted in a dramatic decrease in β4 and α3 expression in the pineal gland and SCG. CNR4 was sufficient to direct LacZ transgene expression to SCG neurons, which express the endogenous β4α3α5 subunits, and pineal cells, which express the endogenous β4α3 combination. Finally, CNR4 was able to direct transgene expression to major sites of expression of the endogenous cluster in the brain. Together, our findings support a model in which cell type-specific shared long-range regulatory elements are required for coordinate expression of clustered nAChR genes.

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Wang, S. S., B. S. H. Wang, J. K. Chang, T. L. K. Low, and A. L. Goldstein. "SYNTHESIS OF THYMOSIN β4." International Journal of Peptide and Protein Research 18, no. 4 (January 12, 2009): 413–15. http://dx.doi.org/10.1111/j.1399-3011.1981.tb03000.x.

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Martin, R. K., and T. R. Jackson. "Centaurin β4 in cancer." Biochemical Society Transactions 33, no. 6 (October 26, 2005): 1282–84. http://dx.doi.org/10.1042/bst0331282.

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Centaurin β4 proteins are products of the DDEF1 (development and differentiation-enhancing factor 1) locus on human chromosome 8q24.1-24.2. Recent reports have indicated that this region and its products are amplified during development of several human cancers. Centaurins are GAPs (GTPase-activating proteins) that, together with GEFs (guanine nucleotide-exchange factors), regulate cyclic activation of Arfs (ADP-ribosylation factors), members of the Ras GTPase superfamily. Centaurin β4 proteins associate with a variety of cellular signalling components implicated in control of growth, survival and movement and may act to direct assembly and/or disassembly of molecular complexes in concert with Arf, lipid and protein phosphorylation signalling pathways.

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Jackson, T. R., and R. K. Martin. "Centaurin β4 in cancer." Biochemical Society Transactions 33, no. 6 (December 1, 2005): 1282. http://dx.doi.org/10.1042/bst20051282.

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Nikolopoulos, Sotiris N., Pamela Blaikie, Toshiaki Yoshioka, Wenjun Guo, Claudia Puri, Carlo Tacchetti, and Filippo G. Giancotti. "Targeted Deletion of the Integrin β4 Signaling Domain Suppresses Laminin-5-Dependent Nuclear Entry of Mitogen-Activated Protein Kinases and NF-κB, Causing Defects in Epidermal Growth and Migration." Molecular and Cellular Biology 25, no. 14 (July 2005): 6090–102. http://dx.doi.org/10.1128/mcb.25.14.6090-6102.2005.

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ABSTRACT The α6β4 integrin—a laminin-5 receptor—mediates assembly of hemidesmosomes and recruitment of Shc and phosphoinositide 3-kinase through the unique cytoplasmic extension of β4. Mice carrying a targeted deletion of the signaling domain of β4 develop normally and do not display signs of skin fragility. The epidermis of these mice contains well-structured hemidesmosomes and adheres stably to the basement membrane. However, it is hypoplastic due to reduced proliferation of basal keratinocytes and undergoes wound repair at a reduced rate. Keratinocytes from β4 mutant mice undergo extensive spreading but fail to proliferate and migrate in response to epidermal growth factor (EGF) on laminin-5. EGF causes significant phosphorylation of extracellular signal-regulated kinase (ERK) and Jun N-terminal protein kinase (JNK) and phosphorylation and degradation of IκB in β4 mutant cells adhering to laminin-5. Unexpectedly, however, ERK, JNK, and NF-κB remain in the cytoplasm in β4 mutant cells on laminin-5, whereas they enter effectively into the nucleus in the same cells on fibronectin or in wild-type cells on both matrix proteins. Inhibitor studies indicate that α6β4 promotes keratinocyte proliferation and migration through its effect on NF-κB and P-JNK. These findings provide evidence that β4 signaling promotes epidermal growth and wound healing through a previously unrecognized effect on nuclear translocation of NF-κB and mitogen-activated protein kinases.

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Holtzclaw, J. David, Liping Liu, P. Richard Grimm, and Steven C. Sansom. "Shear stress-induced volume decrease in C11-MDCK cells by BK-α/β4." American Journal of Physiology-Renal Physiology 299, no. 3 (September 2010): F507—F516. http://dx.doi.org/10.1152/ajprenal.00222.2010.

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Large-conductance, calcium-activated potassium channels (BK) are expressed in principal cells (PC) and intercalated cells (IC) in mammalian nephrons as BK-α/β1 and BK-α/β4, respectively. IC, which protrude into the lumens of tubules, express substantially more BK than PC despite lacking sufficient Na-K-ATPase to support K secretion. We previously showed in mice that IC exhibit size reduction when experiencing high distal flows induced by a high-K diet. We therefore tested the hypothesis that BK-α/β4 are regulators of IC volume via a shear stress (τ)-induced, calcium-dependent mechanism, resulting in a reduction in intracellular K content. We determined by Western blot and immunocytochemical analysis that C11-Madin-Darby canine kidney cells contained a predominance of BK-α/β4. To determine the role of BK-α/β4 in τ-induced volume reduction, we exposed C11 cells to τ and measured K efflux by flame photometry and cell volume by calcein staining, which changes inversely to cell volume. With 10 dynes/cm2, calcein intensity significantly increased 39% and monovalent cationic content decreased significantly by 37% compared with static conditions. Furthermore, the shear-induced K loss from C11 was abolished by the reduction of extracellular calcium, addition of 5 mM TEA, or BK-β4 small interfering (si) RNA, but not by addition of nontarget siRNA. These results show that BK-α/β4 plays a role in shear-induced K loss from IC, suggesting that BK-α/β4 regulate IC volume during high-flow conditions. Furthermore, these results support the use of C11 cells as in vitro models for studying BK-related functions in IC of the kidney.

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Yang, Haoyu, Zixuan Xu, Yuqian Peng, Jiali Wang, and Yang Xiang. "Integrin β4 as a Potential Diagnostic and Therapeutic Tumor Marker." Biomolecules 11, no. 8 (August 12, 2021): 1197. http://dx.doi.org/10.3390/biom11081197.

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Integrin β4 (ITGβ4) is a class of transmembrane adhesion molecules composed of hemidesmosomes (HDs). Its unique long intracellular domain provides intricate signal transduction functions. These signal transduction effects are especially prominent in tumors. Many recent studies have shown that integrin β4 is differentially expressed in various tumors, and it plays a vital role in tumor invasion, proliferation, epithelial–mesenchymal transition, and angiogenesis. Therefore, we categorize the research related to integrin β4, starting from its structure and function in tumor tissues, and provide a basic description. Based on its structure and function, we believe that integrin β4 can be used as a tumor marker. In clinical practice, it is described as a diagnostic marker for the targeted treatment of cancer and will be helpful in the clinical diagnosis and treatment of tumors.

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Geerts, Dirk, Lionel Fontao, Mirjam G. Nievers, Roel Q. J. Schaapveld, Patricia E. Purkis, Grant N. Wheeler, E. Birgitte Lane, Irene M. Leigh, and Arnoud Sonnenberg. "Binding of Integrin α6β4 to Plectin Prevents Plectin Association with F-Actin but Does Not Interfere with Intermediate Filament Binding." Journal of Cell Biology 147, no. 2 (October 18, 1999): 417–34. http://dx.doi.org/10.1083/jcb.147.2.417.

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Hemidesmosomes are stable adhesion complexes in basal epithelial cells that provide a link between the intermediate filament network and the extracellular matrix. We have investigated the recruitment of plectin into hemidesmosomes by the α6β4 integrin and have shown that the cytoplasmic domain of the β4 subunit associates with an NH2-terminal fragment of plectin that contains the actin-binding domain (ABD). When expressed in immortalized plectin-deficient keratinocytes from human patients with epidermol- ysis bullosa (EB) simplex with muscular dystrophy (MD-EBS), this fragment is colocalized with α6β4 in basal hemidesmosome-like clusters or associated with F-actin in stress fibers or focal contacts. We used a yeast two-hybrid binding assay in combination with an in vitro dot blot overlay assay to demonstrate that β4 interacts directly with plectin, and identified a major plectin-binding site on the second fibronectin type III repeat of the β4 cytoplasmic domain. Mapping of the β4 and actin-binding sites on plectin showed that the binding sites overlap and are both located in the plectin ABD. Using an in vitro competition assay, we could show that β4 can compete out the plectin ABD fragment from its association with F-actin. The ability of β4 to prevent binding of F-actin to plectin explains why F-actin has never been found in association with hemidesmosomes, and provides a molecular mechanism for a switch in plectin localization from actin filaments to basal intermediate filament–anchoring hemidesmosomes when β4 is expressed. Finally, by mapping of the COOH-terminally located binding site for several different intermediate filament proteins on plectin using yeast two-hybrid assays and cell transfection experiments with MD-EBS keratinocytes, we confirm that plectin interacts with different cytoskeletal networks.

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Wen, Donghai, Ryan J. Cornelius, Yang Yuan, and Steven C. Sansom. "Regulation of BK-α expression in the distal nephron by aldosterone and urine pH." American Journal of Physiology-Renal Physiology 305, no. 4 (August 15, 2013): F463—F476. http://dx.doi.org/10.1152/ajprenal.00171.2013.

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In the distal nephron, the large-conductance Ca-activated K (BK) channel, comprised of a pore-forming-α (BK-α) and the BK-β4 subunit, promotes K excretion when mice are maintained on a high-K alkaline diet (HK-alk). We examined whether BK-β4 and the acid-base status regulate apical membrane expression of BK-α in the cortical (CCD) and medullary collecting ducts (MCD) using immunohistochemical analysis (IHC) and Western blot. With the use of IHC, BK-α of mice on acontrol diet localized mostly cytoplasmically in intercalated cells (IC) of the CCD and in the perinuclear region of both principle cells (PC) and IC of the MCD. HK-alk wild-type mice (WT), but not BK-β4 knockout mice (β4KO), exhibited increased apical BK-α in both the CCD and MCD. When given a high-K acidic diet (HK-Cl), BK-α expression increased but remained cytoplasmic in the CCD and perinuclear in the MCD of both WT and β4KO. Western blot confirmed that total BK-α expression was enhanced by either HK-alk or HK-Cl but only increased in the plasma membrane with HK-alk. Compared with controls, mice drinking NaHCO3 water exhibited more apical BK-α and total cellular BK-β4. Spironolactone given to mice on HK-alk significantly reduced K secretion and decreased total cellular BK-α but did not affect cellular BK-β4 and apical BK-α. Experiments with MDCK-C11 cells indicated that BK-β4 stabilizes surface BK-α by inhibiting degradation through a lysosomal pathway. These data suggest that aldosterone mediates a high-K-induced increase in BK-α and urinary alkalinization increases BK-β4 expression, which promotes the apical localization of BK-α.

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Wang, Longwang, Jun Zhao, Chenlu Yang, Renrui Kuang, Gallina Kazobinka, Zili Pang, and Teng Hou. "Prognostic Implication of Urothelial Stem Cell Markers Differs According to Primary Tumour Location in Non-Muscle-Invasive Bladder Cancer." Cellular Physiology and Biochemistry 48, no. 6 (2018): 2364–73. http://dx.doi.org/10.1159/000492652.

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Background/Aims: This study aimed to validate the value of urothelial stem cell (USC) markers ΔNp63, integrin β4, CD47, and CD44v6 in predicting the prognosis of non-muscle invasive bladder cancer (NMIBC) located in different anatomic regions of bladder. Methods: The study reviewed the clinicopathologic data of 169 patients with NMIBC. Using real-time PCR and immunohistochemistry, the expression of ΔNp63, integrin β4, CD47, and CD44v6 in archived specimens of patients with NMIBC were validated. Kaplan–Meier analysis and Cox proportional hazards model were used to assess the prognostic impact of USC markers for recurrent-free survival (RFS). Results: The Real-time PCR data showed that the expression of USC markers were higher in tumors located in the trigone and posterior wall than that in other regions of bladder (P< 0.05). Statistical analysis showed that high expression of ΔNp63 was correlated with tumor stage (P=0.023) and tumor size (P=0.001), that high expression of integrin β4 was correlated with tumor stage (P=0.026), tumor grade (P=0.005) and tumor size (P=0.003), and that high integrin β4, CD47, and CD44v6 expression were significantly associated with tumor recurrence (P=0.032, P=0.010, and P=0.043, respectively). Moreover, high expression of ΔNp63 and integrin β4 was correlated with poor RFS in patients with tumors located in the trigone (P=0.025 and P=0.023, respectively). High expression of integrin β4, CD47, and CD44v6 was correlated with poor RFS in patients with tumors in the posterior wall (P=0.017, P=0.033 and P=0.047, respectively). High expression of integrin β4 and CD47 was correlated with poor RFS in patients with tumors in the trigone/posterior wall area (P=0.002 and P=0.005, respectively). Conclusion: Our results suggest that USC markers are linked with poor prognosis of NMIBC patients, especially in patients with tumors in the trigone and posterior wall.

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Litjens, Sandy H. M., Kevin Wilhelmsen, José M. de Pereda, Anastassis Perrakis, and Arnoud Sonnenberg. "Modeling and Experimental Validation of the Binary Complex of the Plectin Actin-binding Domain and the First Pair of Fibronectin Type III (FNIII) Domains of the β4 Integrin." Journal of Biological Chemistry 280, no. 23 (April 6, 2005): 22270–77. http://dx.doi.org/10.1074/jbc.m411818200.

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The binding of plectin to the β4 subunit of the α6β4 integrin is a critical step in the formation of hemidesmosomes. An important interaction between these two proteins occurs between the actin-binding domain (ABD) of plectin and the first pair of fibronectin type III (FNIII) domains and a small part of the connecting segment of β4. Previously, a few amino acids, critical for this interaction, were identified in both plectin and β4 and mapped on the crystal structures of the ABD of plectin and the first pair of FNIII domains of β4. In the present study, we used this biochemical information and protein-protein docking calculations to construct a model of the binary complex between these two protein domains. The top scoring computational model predicts that the calponin-homology 1 (CH1) domain of the ABD associates with the first and the second FNIII domains of β4. Our mutational analysis of the residues at the proposed interface of both the FNIII and the CH1 domains is in agreement with the suggested interaction model. Computational simulations to predict protein motions suggest that the exact model of FNIII and plectin CH1 interaction might well differ in detail from the suggested model due to the conformational plasticity of the FNIII domains, which might lead to a closely related but different mode of interaction with the plectin-ABD. Furthermore, we show that Ser-1325 in the connecting segment of β4 appears to be essential for the recruitment of plectin into hemidesmosomes in vivo. This is consistent with the proposed model and previously published mutational data. In conclusion, our data support a model in which the CH1 domain of the plectin-ABD associates with the groove between the two FNIII domains of β4.

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Sanvito, Francesca, Simonetta Piatti, Antonello Villa, Mario Bossi, Giovanna Lucchini, Pier Carlo Marchisio, and Stefano Biffo. "The β4 Integrin Interactor p27BBP/eIF6 Is an Essential Nuclear Matrix Protein Involved in 60S Ribosomal Subunit Assembly." Journal of Cell Biology 144, no. 5 (March 8, 1999): 823–38. http://dx.doi.org/10.1083/jcb.144.5.823.

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p27BBP/eIF6 is an evolutionarily conserved protein that was originally identified as p27BBP, an interactor of the cytoplasmic domain of integrin β4 and, independently, as the putative translation initiation factor eIF6. To establish the in vivo function of p27BBP/eIF6, its topographical distribution was investigated in mammalian cells and the effects of disrupting the corresponding gene was studied in the budding yeast, Saccharomyces cerevisiae. In epithelial cells containing β4 integrin, p27BBP/eIF6 is present in the cytoplasm and enriched at hemidesmosomes with a pattern similar to that of β4 integrin. Surprisingly, in the absence and in the presence of the β4 integrin subunit, p27BBP/eIF6 is in the nucleolus and associated with the nuclear matrix. Deletion of the IIH S. cerevisiae gene, encoding the yeast p27BBP/eIF6 homologue, is lethal, and depletion of the corresponding gene product is associated with a dramatic decrease of the level of free ribosomal 60S subunit. Furthermore, human p27BBP/eIF6 can rescue the lethal effect of the iihΔ yeast mutation. The data obtained in vivo suggest an evolutionarily conserved function of p27BBP/eIF6 in ribosome biogenesis or assembly rather than in translation. A further function related to the β4 integrin subunit may have evolved specifically in higher eukaryotic cells.

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Gleason, Brianna, Brian Adley, M. Sambasiva Rao, and Leslie K. Diaz. "Immunohistochemical Detection of the β4 Integrin Subunit in Pancreatic Adenocarcinoma." Journal of Histochemistry & Cytochemistry 53, no. 6 (June 2005): 799–801. http://dx.doi.org/10.1369/jhc.4b6522.2005.

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The expression of the β4 integrin subunit protein in pancreatic cancer was investigated using routine immunohistochemical methods on paraffin-embedded archival material. Forty-eight cases of pancreatic ductal adenocarcinoma were immunostained with a monoclonal antibody to the β4 integrin subunit, and the extent of staining was compared with that seen in non-cancerous pancreatic tissues, including 15 separate cases of chronic pancreatitis and 6 sections from normal pancreas. We found that the β4 integrin subunit protein was overexpressed in the majority of pancreatic carcinoma cases tested, whereas chronic pancreatitis and normal pancreas did not display substantial levels of expression.

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Targosova, Katarina, Matej Kucera, Zuzana Kilianova, Lubica Slobodova, Kristina Szmicsekova, and Anna Hrabovska. "Cardiac nicotinic receptors show β-subunit-dependent compensatory changes." American Journal of Physiology-Heart and Circulatory Physiology 320, no. 5 (May 1, 2021): H1975—H1984. http://dx.doi.org/10.1152/ajpheart.00995.2020.

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Nicotinic receptors (NRs) play an important role in the cholinergic regulation of heart functions, and converging evidence suggests a diverse repertoire of NR subunits in the heart. A recent hypothesis about the plasticity of β NR subunits suggests that β2-subunits and β4-subunits may substitute for each other. In our study, we assessed the hypothetical β-subunit interchangeability in the heart at the level of mRNA. Using two mutant mice strains lacking β2 or β4 NR subunits, we examined the relative expression of NR subunits and other key cholinergic molecules. We investigated the physiology of isolated hearts perfused by Langendorff‘s method at basal conditions and after cholinergic and/or adrenergic stimulation. Lack of β2 NR subunit was accompanied with decreased relative expression of β4-subunits and α3-subunits. No other cholinergic changes were observed at the level of mRNA, except for increased M3 and decreased M4 muscarinic receptors. Isolated hearts lacking β2 NR subunit showed different dynamics in heart rate response to indirect cholinergic stimulation. In hearts lacking β4 NR subunit, increased levels of β2-subunits were observed together with decreased mRNA for acetylcholine-synthetizing enzyme and M1 and M4 muscarinic receptors. Changes in the expression levels in β4−/− hearts were associated with increased basal heart rate and impaired response to a high dose of acetylcholine upon adrenergic stimulation. In support of the proposed plasticity of cardiac NRs, our results confirmed subunit-dependent compensatory changes to missing cardiac NRs subunits with consequences on isolated heart physiology. NEW & NOTEWORTHY In the present study, we observed an increase in mRNA levels of the β2 NR subunit in β4−/− hearts but not vice versa, thus supporting the hypothesis of β NR subunit plasticity that depends on the specific type of missing β-subunit. This was accompanied with specific cholinergic adaptations. Nevertheless, isolated hearts of β4−/− mice showed increased basal heart rate and a higher sensitivity to a high dose of acetylcholine upon adrenergic stimulation.

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Britto, Luiz R. G., Scott W. Rogers, Dânia E. Hamassaki-Britto, and Robert M. Duvoisin. "Nicotinic acetylcholine receptors in the ground squirrel retina: Localization of the β4 subunit by immunohistochemistry and in situ hybridization." Visual Neuroscience 11, no. 3 (May 1994): 569–77. http://dx.doi.org/10.1017/s0952523800002479.

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AbstractImmunohistochemical and in situ hybridization techniques were used to localize the β4 subunit of the neuronal nicotinic acetylcholine receptors (nAChRs) in the ground squirrel retina. The β4 nAChR subunit was detected in both transverse and horizontal sections of the retina using a subunit-specific antiserum and the avidin-biotin complex technique. Two bands of labeled processes were seen in the inner plexiform layer, corresponding approximately to the laminae where the cholinergic cells arborize. Labeled cells were found in the ganglion cell layer and the inner third of the inner nuclear layer. The cells in the ganglion cell layer were medium- to large-sized and were frequently observed to give rise to axon-like processes. Most of the labeled neurons in the inner nuclear layer were small presumptive amacrine cells, but a few medium-to-large cells were also labeled. These could constitute a different class of amacrine cells or displaced ganglion cells. The latter possibility is supported by the existence of nAChR-containing displaced ganglion cells in the avian retina. In situ hybridization with a 35S-labeled cRNA probe revealed the expression of mRNA coding for the nAChR β4 subunit in the ganglion cell layer and the inner third of the inner nuclear layer. This finding confirmed the immunohistochemical data of the cellular localization of β4 nAChR subunit.These results indicate that the β4 nAChR subunit is expressed by specific subtypes of neurons on the ground squirrel retina. As the expression of that particular nAChR subunit appears to be very limited in the brain, the present data suggest that the retina might represent a useful model to study the function of nAChRs containing the β4 subunit.

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Fan, Ying-Xin, Lily Wong, Jinhui Ding, Nikolay A. Spiridonov, Richard C. Johnson, and Gibbes R. Johnson. "Mutational Activation of ErbB2 Reveals a New Protein Kinase Autoinhibition Mechanism." Journal of Biological Chemistry 283, no. 3 (November 26, 2007): 1588–96. http://dx.doi.org/10.1074/jbc.m708116200.

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Autoinhibition plays a key role in the control of protein kinase activity. ErbB2 is a unique receptor-tyrosine kinase that does not bind ligand but possesses an extracellular domain poised to engage other ErbBs. Little is known about the molecular mechanism for ErbB2 catalytic regulation. Here we show that ErbB2 kinase is strongly autoinhibited, and a loop connecting the αC helix and β4 sheet within the kinase domain plays a major role in the control of kinase activity. Mutations of two Gly residues at positions 776 and 778 in this loop dramatically increase ErbB2 catalytic activity. Kinetic analysis demonstrates that mutational activation is due to ∼10- and ∼7-fold increases in ATP binding affinity and turnover number, respectively. Expression of the activated ErbB2 mutants in cells resulted in elevated ligand-independent ErbB2 autophosphorylation, ErbB3 phosphorylation, and stimulation of mitogen-activated protein kinase. Molecular modeling suggests that the ErbB2 kinase domain is stabilized in an inactive state via a hydrophobic interaction between the αC-β4 and activation loops. Importantly, many ErbB2 human cancer mutations have been identified in the αC-β4 loop, including the activating G776S mutation studied here. Our findings reveal a new kinase regulatory mechanism in which the αC-β4 loop functions as an intramolecular switch that controls ErbB2 activity and suggests that loss of αC-β4 loop-mediated autoinhibition is involved in oncogenic activation of ErbB2.

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Frolikova, Michaela, Eliska Valaskova, Jiri Cerny, Audrey Lumeau, Natasa Sebkova, Veronika Palenikova, Noemi Sanches-Hernandez, Alzbeta Pohlova, Pavla Manaskova-Postlerova, and Katerina Dvorakova-Hortova. "Addressing the Compartmentalization of Specific Integrin Heterodimers in Mouse Sperm." International Journal of Molecular Sciences 20, no. 5 (February 26, 2019): 1004. http://dx.doi.org/10.3390/ijms20051004.

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Integrins are transmembrane cell receptors involved in two crucial mechanisms for successful fertilization, namely, mammalian intracellular signaling and cell adhesion. Integrins α6β4, α3β1 and α6β1 are three major laminin receptors expressed on the surface of mammalian cells including gametes, and the presence of individual integrin subunits α3, α6, β1 and β4 has been previously detected in mammalian sperm. However, to date, proof of the existence of individual heterodimer pairs in sperm and their detailed localization is missing. The major conclusion of this study is evidence that the β4 integrin subunit is expressed in mouse sperm and that it pairs with subunit α6; additionally, there is a detailed identification of integrin heterodimer pairs across individual membranes in an intact mouse sperm head. We also demonstrate the existence of β4 integrin mRNAs in round spermatids and spermatogonia by q-RT-PCR, which was further supported by sequencing the PCR products. Using super-resolution microscopy accompanied by colocalization analysis, we located integrin subunits as follows: α6/β4-inner apical acrosomal membrane and equatorial segment; α3, α6/β1, β4-plasma membrane overlaying the apical acrosome; and α3/β1-outer acrosomal membrane. The existence of α6β4, α3β1 and α6β1 heterodimers was further confirmed by proximity ligation assay (PLA). In conclusion, we delivered detailed characterization of α3, α6, β1 and β4 integrin subunits, showing their presence in distinct compartments of the intact mouse sperm head. Moreover, we identified sperm-specific localization for heterodimers α6β4, α3β1 and α6β1, and their membrane compartmentalization and the presented data show a complexity of membranes overlaying specialized microdomain structures in the sperm head. Their different protein compositions of these individual membrane rafts may play a specialized role, based on their involvement in sperm-epithelium and sperm-egg interaction.

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Kaur, Harmanpreet, and Bulent Mutus. "Platelet function and thymosin β4." Biological Chemistry 393, no. 7 (July 1, 2012): 595–98. http://dx.doi.org/10.1515/hsz-2012-0131.

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Abstract Thymosin β4 (Tβ4) is a small, low-molecular-weight peptide ubiquitously expressed in all cells and extracellular fluids. It is a major actin sequestering protein present in the cells. In addition to this, Tβ4 has also been shown to be involved in endothelial cell migration, angiogenesis, corneal wound healing, and stem cell differentiation. It is also released by platelets after activation. The amount of Tβ4 increases at sites of injury and thus suggests an important role of this biopeptide in wound healing. Herein, we provide an overview of the role of Tβ4 in thrombosis and platelet aggregation.

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Shrivastava, Santwana, Deepak Srivastava, Eric N. Olson, J. Michael DiMaio, and Ildiko Bock-Marquette. "Thymosin β4 and cardiac repair." Annals of the New York Academy of Sciences 1194, no. 1 (May 2010): 87–96. http://dx.doi.org/10.1111/j.1749-6632.2010.05468.x.

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Malinda, Katherine M., Hynda K. Kleinman, Gurmel S. Sidhu, Haresh Mani, Krishna Banaudha, Radha K. Maheshwari, and Allan L. Goldstein. "Thymosin β4 Accelerates Wound Healing." Journal of Investigative Dermatology 113, no. 3 (September 1999): 364–68. http://dx.doi.org/10.1046/j.1523-1747.1999.00708.x.

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Su, Le, Xin Lv, and JunYing Miao. "Integrin β4 in Neural Cells." NeuroMolecular Medicine 10, no. 4 (May 31, 2008): 316–21. http://dx.doi.org/10.1007/s12017-008-8042-1.

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Gilchrist, John M., Samir Das, Filip Va Petegemn, and Frank Bosmans. "β4 Modulates NaV1.2 Toxin Pharmacology." Biophysical Journal 106, no. 2 (January 2014): 36a. http://dx.doi.org/10.1016/j.bpj.2013.11.276.

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Wilhelmsen, Kevin, Sandy H. M. Litjens, Ingrid Kuikman, Coert Margadant, Jacco van Rheenen, and Arnoud Sonnenberg. "Serine Phosphorylation of the Integrin β4 Subunit Is Necessary for Epidermal Growth Factor Receptor–induced Hemidesmosome Disruption." Molecular Biology of the Cell 18, no. 9 (September 2007): 3512–22. http://dx.doi.org/10.1091/mbc.e07-04-0306.

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Hemidesmosomes (HDs) are multiprotein adhesion complexes that promote attachment of epithelial cells to the basement membrane. The binding of α6β4 to plectin plays a central role in their assembly. We have defined three regions on β4 that together harbor all the serine and threonine phosphorylation sites and show that three serines (S1356, S1360, and S1364), previously implicated in HD regulation, prevent the interaction of β4 with the plectin actin-binding domain when phosphorylated. We have also established that epidermal growth factor receptor activation, which is known to function upstream of HD disassembly, results in the phosphorylation of only one or more of these three residues and the partial disassembly of HDs in keratinocytes. Additionally, we show that S1360 and S1364 of β4 are the only residues phosphorylated by PKC and PKA in cells, respectively. Taken together, our studies indicate that multiple kinases act in concert to breakdown the structural integrity of HDs in keratinocytes, which is primarily achieved through the phosphorylation of S1356, S1360, and S1364 on the β4 subunit.

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Kapurniotu, Afroditi, and Wolfgang Voelter. "Totalsynthese von Thymosin β4, 1. Klassische Synthese des Fragments [11–19] von Thymosin β4." Liebigs Annalen der Chemie 1991, no. 12 (December 12, 1991): 1251–57. http://dx.doi.org/10.1002/jlac.1991199101216.

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Kapurniotu, Afroditi, and Wolfgang Voelter. "Totalsynthese von Thymosin β4, 2. Klassische Synthese des Fragments [20–30] von Thymosin β4." Liebigs Annalen der Chemie 1992, no. 4 (April 13, 1992): 361–70. http://dx.doi.org/10.1002/jlac.199219920164.

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Wang, Bangchen, Jun Wang-France, Huaqing Li, and Steven C. Sansom. "Furosemide reduces BK-αβ4-mediated K+ secretion in mice on an alkaline high-K+ diet." American Journal of Physiology-Renal Physiology 316, no. 2 (February 1, 2019): F341—F350. http://dx.doi.org/10.1152/ajprenal.00223.2018.

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Special high-K diets have cardioprotective effects and are often warranted in conjunction with diuretics such as furosemide for treating hypertension. However, it is not understood how a high-K diet (HK) influences the actions of diuretics on renal K+ handling. Furosemide acidifies the urine by increasing acid secretion via the Na+-H+ exchanger 3 (NHE3) in TAL and vacuolar H+-ATPase (V-ATPase) in the distal nephron. We previously found that an alkaline urine is required for large conductance Ca2+-activated K+ (BK)-αβ4-mediated K+ secretion in mice on HK. We therefore hypothesized that furosemide could reduce BK-αβ4-mediated K+ secretion by acidifying the urine. Treating with furosemide (drinking water) for 11 days led to decreased urine pH in both wild-type (WT) and BK-β4-knockout mice (BK-β4-KO) with increased V-ATPase expression and elevated plasma aldosterone levels. However, furosemide decreased renal K+ clearance and elevated plasma [K+] in WT but not BK-β4-KO. Western blotting and immunofluorescence staining showed that furosemide treatment decreased cortical expression of BK-β4 and reduced apical localization of BK-α in connecting tubules. Addition of the carbonic anhydrase inhibitor, acetazolamide, to furosemide water restored urine pH along with renal K+ clearance and plasma [K+] to control levels. Acetazolamide plus furosemide also restored the cortical expression of BK-β4 and BK-α in connecting tubules. These results indicate that in mice adapted to HK, furosemide reduces BK-αβ4-mediated K+ secretion by acidifying the urine.

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Journal articles on the topic 'Β4'

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