Journal articles: 'Exocyst Subunit Sec6'

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Morgera, Francesca, Margaret R. Sallah, Michelle L. Dubuke, Pallavi Gandhi, Daniel N. Brewer, Chavela M. Carr, and Mary Munson. "Regulation of exocytosis by the exocyst subunit Sec6 and the SM protein Sec1." Molecular Biology of the Cell 23, no. 2 (January 15, 2012): 337–46. http://dx.doi.org/10.1091/mbc.e11-08-0670.

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Trafficking of protein and lipid cargo through the secretory pathway in eukaryotic cells is mediated by membrane-bound vesicles. Secretory vesicle targeting and fusion require a conserved multisubunit protein complex termed the exocyst, which has been implicated in specific tethering of vesicles to sites of polarized exocytosis. The exocyst is directly involved in regulating soluble N-ethylmaleimide–sensitive factor (NSF) attachment protein receptor (SNARE) complexes and membrane fusion through interactions between the Sec6 subunit and the plasma membrane SNARE protein Sec9. Here we show another facet of Sec6 function—it directly binds Sec1, another SNARE regulator, but of the Sec1/Munc18 family. The Sec6–Sec1 interaction is exclusive of Sec6–Sec9 but compatible with Sec6–exocyst assembly. In contrast, the Sec6–exocyst interaction is incompatible with Sec6–Sec9. Therefore, upon vesicle arrival, Sec6 is proposed to release Sec9 in favor of Sec6–exocyst assembly and to simultaneously recruit Sec1 to sites of secretion for coordinated SNARE complex formation and membrane fusion.

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Chavez-Dozal, Alba A., Stella M. Bernardo, Hallie S. Rane, and Samuel A. Lee. "Functional Analysis of the Exocyst Subunit Sec15 in Candida albicans." Eukaryotic Cell 14, no. 12 (October 9, 2015): 1228–39. http://dx.doi.org/10.1128/ec.00147-15.

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ABSTRACTIn prior studies of exocyst-mediated late secretion inCandida albicans, we have determined that Sec6 contributes to cell wall integrity, secretion, and filamentation. A conditional mutant lackingSEC6expression exhibits markedly reduced lateral hyphal branching. In addition, lack of the related t-SNAREs Sso2 and Sec9 also leads to defects in secretion and filamentation. To further understand the role of the exocyst in the fundamental processes of polarized secretion and filamentation inC. albicans, we studied the exocyst subunit Sec15. SinceSaccharomyces cerevisiae SEC15is essential for viability, we generated aC. albicansconditional mutant strain in whichSEC15was placed under the control of a tetracycline-regulated promoter. In the repressed state, cell death occurred after 5 h in the tetR-SEC15 strain. Prior to this time point, the tetR-SEC15 mutant was markedly defective in Sap and lipase secretion and demonstrated increased sensitivity to Zymolyase and chitinase. Notably, tetR-SEC15 mutant hyphae were characterized by a hyperbranching phenotype, in direct contrast to strain tetR-SEC6, which had minimal lateral branching. We further studied the localization of the Spitzenkörper, polarisomes, and exocysts in the tetR-SEC15 and tetR-SEC6 mutants during filamentation. Mlc1-GFP (marking the Spitzenkörper), Spa2-GFP (the polarisome), and Exo70-GFP (exocyst) localizations were normal in the tetR-SEC6 mutant, whereas these structures were mislocalized in the tetR-SEC15 mutant. Following alleviation of gene repression by removing doxycycline, first Spitzenkörper, then polarisome, and finally exocyst localizations were recovered sequentially. These results indicate that the exocyst subunits Sec15 and Sec6 have distinct roles in mediating polarized secretion and filamentation inC. albicans.

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Synek, Lukáš, Roman Pleskot, Juraj Sekereš, Natalia Serrano, Nemanja Vukašinović, Jitka Ortmannová, Martina Klejchová, et al. "Plasma membrane phospholipid signature recruits the plant exocyst complex via the EXO70A1 subunit." Proceedings of the National Academy of Sciences 118, no. 36 (September 1, 2021): e2105287118. http://dx.doi.org/10.1073/pnas.2105287118.

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Polarized exocytosis is essential for many vital processes in eukaryotic cells, where secretory vesicles are targeted to distinct plasma membrane domains characterized by their specific lipid–protein composition. Heterooctameric protein complex exocyst facilitates the vesicle tethering to a target membrane and is a principal cell polarity regulator in eukaryotes. The architecture and molecular details of plant exocyst and its membrane recruitment have remained elusive. Here, we show that the plant exocyst consists of two modules formed by SEC3–SEC5–SEC6–SEC8 and SEC10–SEC15–EXO70–EXO84 subunits, respectively, documenting the evolutionarily conserved architecture within eukaryotes. In contrast to yeast and mammals, the two modules are linked by a plant-specific SEC3–EXO70 interaction, and plant EXO70 functionally dominates over SEC3 in the exocyst recruitment to the plasma membrane. Using an interdisciplinary approach, we found that the C-terminal part of EXO70A1, the canonical EXO70 isoform in Arabidopsis, is critical for this process. In contrast to yeast and animal cells, the EXO70A1 interaction with the plasma membrane is mediated by multiple anionic phospholipids uniquely contributing to the plant plasma membrane identity. We identified several evolutionary conserved EXO70 lysine residues and experimentally proved their importance for the EXO70A1–phospholipid interactions. Collectively, our work has uncovered plant-specific features of the exocyst complex and emphasized the importance of the specific protein–lipid code for the recruitment of peripheral membrane proteins.

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Songer, Jennifer A., and Mary Munson. "Sec6p Anchors the Assembled Exocyst Complex at Sites of Secretion." Molecular Biology of the Cell 20, no. 3 (February 2009): 973–82. http://dx.doi.org/10.1091/mbc.e08-09-0968.

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The exocyst is an essential protein complex required for targeting and fusion of secretory vesicles to sites of exocytosis at the plasma membrane. To study the function of the exocyst complex, we performed a structure-based mutational analysis of the Saccharomyces cerevisiae exocyst subunit Sec6p. Two “patches” of highly conserved residues are present on the surface of Sec6p; mutation of either patch does not compromise protein stability. Nevertheless, replacement of SEC6 with the patch mutants results in severe temperature-sensitive growth and secretion defects. At nonpermissive conditions, although trafficking of secretory vesicles to the plasma membrane is unimpaired, none of the exocyst subunits are polarized. This is consistent with data from other exocyst temperature-sensitive mutants, which disrupt the integrity of the complex. Surprisingly, however, these patch mutations result in mislocalized exocyst complexes that remain intact. Our results indicate that assembly and polarization of the exocyst are functionally separable events, and that Sec6p is required to anchor exocyst complexes at sites of secretion.

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Dubuke, Michelle L., Stephanie Maniatis, Scott A. Shaffer, and Mary Munson. "The Exocyst Subunit Sec6 Interacts with Assembled Exocytic SNARE Complexes." Journal of Biological Chemistry 290, no. 47 (October 7, 2015): 28245–56. http://dx.doi.org/10.1074/jbc.m115.673806.

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Chavez-Dozal, Alba A., Stella M. Bernardo, Hallie S. Rane, Gloria Herrera, Vibhati Kulkarny, Jeanette Wagener, Iain Cunningham, Alexandra C. Brand, Neil A. R. Gow, and Samuel A. Lee. "The Candida albicans Exocyst Subunit Sec6 Contributes to Cell Wall Integrity and Is a Determinant of Hyphal Branching." Eukaryotic Cell 14, no. 7 (May 22, 2015): 684–97. http://dx.doi.org/10.1128/ec.00028-15.

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ABSTRACTThe yeast exocyst is a multiprotein complex comprised of eight subunits (Sec3, Sec5, Sec6, Sec8, Sec10, Sec15, Exo70, and Exo84) which orchestrates trafficking of exocytic vesicles to specific docking sites on the plasma membrane during polarized secretion. To studySEC6function inCandida albicans, we generated a conditional mutant strain in whichSEC6was placed under the control of a tetracycline-regulated promoter. In the repressed state, the tetR-SEC6mutant strain (denoted tSEC6) was viable for up to 27 h; thus, all phenotypic analyses were performed at 24 h or earlier. Strain tSEC6 under repressing conditions had readily apparent defects in cytokinesis and endocytosis and accumulated both post-Golgi apparatus secretory vesicles and structures suggestive of late endosomes. Strain tSEC6 was markedly defective in secretion of aspartyl proteases and lipases as well as filamentation under repressing conditions. Lack ofSEC6expression resulted in markedly reduced lateral hyphal branching, which requires the establishment of a new axis of polarized secretion. Aberrant localization of chitin at the septum and increased resistance to zymolyase activity were observed, suggesting thatC. albicansSec6 plays an important role in mediating trafficking and delivery of cell wall components. The tSEC6 mutant was also markedly defective in macrophage killing, indicating a role ofSEC6inC. albicansvirulence. Taken together, these studies indicate that the late secretory protein Sec6 is required for polarized secretion, hyphal morphogenesis, and the pathogenesis ofC. albicans.

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Shin, Dong Min, Xiao-Song Zhao, Weizhong Zeng, Marina Mozhayeva, and Shmuel Muallem. "The Mammalian Sec6/8 Complex Interacts with Ca2+ Signaling Complexes and Regulates Their Activity." Journal of Cell Biology 150, no. 5 (September 4, 2000): 1101–12. http://dx.doi.org/10.1083/jcb.150.5.1101.

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The localization of various Ca2+ transport and signaling proteins in secretory cells is highly restricted, resulting in polarized agonist-stimulated Ca2+ waves. In the present work, we examined the possible roles of the Sec6/8 complex or the exocyst in polarized Ca2+ signaling in pancreatic acinar cells. Immunolocalization by confocal microscopy showed that the Sec6/8 complex is excluded from tight junctions and secretory granules in these cells. The Sec6/8 complex was found in at least two cellular compartments, part of the complex showed similar, but not identical, localization with the Golgi apparatus and part of the complex associated with Ca2+ signaling proteins next to the plasma membrane at the apical pole. Accordingly, immunoprecipitation (IP) of Sec8 did not coimmunoprecipitate βCOP, Golgi 58K protein, or mannosidase II, all Golgi-resident proteins. By contrast, IP of Sec8 coimmunoprecipitates Sec6, type 3 inositol 1,4,5-trisphosphate receptors (IP3R3), and the Gβγ subunit of G proteins from pancreatic acinar cell extracts. Furthermore, the anti-Sec8 antibodies coimmunoprecipitate actin, Sec6, the plasma membrane Ca2+ pump, the G protein subunits Gαq and Gβγ, the β1 isoform of phospholipase C, and the ER resident IP3R1 from brain microsomal extracts. Antibodies against the various signaling and Ca2+ transport proteins coimmunoprecipitate Sec8 and the other signaling proteins. Dissociation of actin filaments in the immunoprecipitate had no effect on the interaction between Sec6 and Sec8, but released the actin and dissociated the interaction between the Sec6/8 complex and Ca2+ signaling proteins. Hence, the interaction between the Sec6/8 and Ca2+ signaling complexes is likely mediated by the actin cytoskeleton. The anti-Sec6 and anti-Sec8 antibodies inhibited Ca2+ signaling at a step upstream of Ca2+ release by IP3. Disruption of the actin cytoskeleton with latrunculin B in intact cells resulted in partial translocation of Sec6 and Sec8 from membranes to the cytosol and interfered with propagation of agonist-evoked Ca2+ waves. Our results suggest that the Sec6/8 complex has multiple roles in secretory cells including governing the polarized expression of Ca2+ signaling complexes and regulation of their activity.

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van Gisbergen, Peter A. C., Shu-Zon Wu, Mingqin Chang, Kelli A. Pattavina, Madelaine E. Bartlett, and Magdalena Bezanilla. "An ancient Sec10–formin fusion provides insights into actin-mediated regulation of exocytosis." Journal of Cell Biology 217, no. 3 (January 26, 2018): 945–57. http://dx.doi.org/10.1083/jcb.201705084.

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Exocytosis, facilitated by the exocyst, is fundamentally important for remodeling cell walls and membranes. Here, we analyzed For1F, a novel gene that encodes a fusion of an exocyst subunit (Sec10) and an actin nucleation factor (formin). We showed that the fusion occurred early in moss evolution and has been retained for more than 170 million years. In Physcomitrella patens, For1F is essential, and the expressed protein is a fusion of Sec10 and formin. Reduction of For1F or actin filaments inhibits exocytosis, and For1F dynamically associates with Sec6, another exocyst subunit, in an actin-dependent manner. Complementation experiments demonstrate that constitutive expression of either half of the gene or the paralogous Sec10b rescues loss of For1F, suggesting that fusion of the two domains is not essential, consistent with findings in yeast, where formin and the exocyst are linked noncovalently. Although not essential, the fusion may have had selective advantages and provides a unique opportunity to probe actin regulation of exocytosis.

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Wu, Jiandong, Xiaoyun Tan, Chengyun Wu, Kun Cao, Yan Li, and Yiqun Bao. "Regulation of Cytokinesis by Exocyst Subunit SEC6 and KEULE in Arabidopsis thaliana." Molecular Plant 6, no. 6 (November 2013): 1863–76. http://dx.doi.org/10.1093/mp/sst082.

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Ding, Yu, Juan Wang, John Ho Chun Lai, Vivian Hoi Ling Chan, Xiangfeng Wang, Yi Cai, Xiaoyun Tan, et al. "Exo70E2 is essential for exocyst subunit recruitment and EXPO formation in both plants and animals." Molecular Biology of the Cell 25, no. 3 (February 2014): 412–26. http://dx.doi.org/10.1091/mbc.e13-10-0586.

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In contrast to a single copy of Exo70 in yeast and mammals, the Arabidopsis genome contains 23 paralogues of Exo70 (AtExo70). Using AtExo70E2 and its GFP fusion as probes, we recently identified a novel double-membrane organelle termed exocyst-positive organelle (EXPO) that mediates an unconventional protein secretion in plant cells. Here we further demonstrate that AtExo70E2 is essential for exocyst subunit recruitment and for EXPO formation in both plants and animals. By performing transient expression in Arabidopsis protoplasts, we established that a number of exocyst subunits (especially the members of the Sec family) are unable to be recruited to EXPO in the absence of AtExo70E2. The paralogue AtExo70A1 is unable to substitute for AtExo70E2 in this regard. Fluorescence resonance energy transfer assay and bimolecular fluorescence complementation analyses confirm the interaction between AtExo70E2 and Sec6 and Sec10. AtExo70E2, but not its yeast counterpart, is also capable of inducing EXPO formation in an animal cell line (HEK293A cells). Electron microscopy confirms the presence of double-membraned, EXPO-like structures in HEK293A cells expressing AtExo70E2. Inversely, neither human nor yeast Exo70 homologues cause the formation of EXPO in Arabidopsis protoplasts. These results point to a specific and crucial role for AtExo70E2 in EXPO formation.

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Overdijk, Elysa J. R., Vera Putker, Joep Smits, Han Tang, Klaas Bouwmeester, Francine Govers, and Tijs Ketelaar. "Phytophthora infestans RXLR effector AVR1 disturbs the growth of Physcomitrium patens without affecting Sec5 localization." PLOS ONE 16, no. 4 (April 8, 2021): e0249637. http://dx.doi.org/10.1371/journal.pone.0249637.

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Plant pathogens often exploit a whole range of effectors to facilitate infection. The RXLR effector AVR1 produced by the oomycete plant pathogen Phytophthora infestans suppresses host defense by targeting Sec5. Sec5 is a subunit of the exocyst, a protein complex that is important for mediating polarized exocytosis during plant development and defense against pathogens. The mechanism by which AVR1 manipulates Sec5 functioning is unknown. In this study, we analyzed the effect of AVR1 on Sec5 localization and functioning in the moss Physcomitrium patens. P. patens has four Sec5 homologs. Two (PpSec5b and PpSec5d) were found to interact with AVR1 in yeast-two-hybrid assays while none of the four showed a positive interaction with AVR1ΔT, a truncated version of AVR1. In P. patens lines carrying β-estradiol inducible AVR1 or AVR1ΔT transgenes, expression of AVR1 or AVR1ΔT caused defects in the development of caulonemal protonema cells and abnormal morphology of chloronema cells. Similar phenotypes were observed in Sec5- or Sec6-silenced P. patens lines, suggesting that both AVR1 and AVR1ΔT affect exocyst functioning in P. patens. With respect to Sec5 localization we found no differences between β-estradiol-treated and untreated transgenic AVR1 lines. Sec5 localizes at the plasma membrane in growing caulonema cells, also during pathogen attack, and its subcellular localization is the same, with or without AVR1 in the vicinity.

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SAITO, Tetsuya, Tadao SHIBASAKI, and Susumu SEINO. "Involvement of Exoc3l, a protein structurally related to the exocyst subunit Sec6, in insulin secretion." Biomedical Research 29, no. 2 (2008): 85–91. http://dx.doi.org/10.2220/biomedres.29.85.

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Brejšková, Lucie, Michal Hála, Anamika Rawat, Hana Soukupová, Fatima Cvrčková, Florence Charlot, Fabien Nogué, Samuel Haluška, and Viktor Žárský. "SEC6 exocyst subunit contributes to multiple steps of growth and development of Physcomitrella ( Physcomitrium patens )." Plant Journal 106, no. 3 (April 2021): 831–43. http://dx.doi.org/10.1111/tpj.15205.

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RIEFLER, Gary M., Gaithri BALASINGAM, Kenyatta G. LUCAS, Sheng WANG, Shu-Chan HSU, and Bonnie L. FIRESTEIN. "Exocyst complex subunit sec8 binds to postsynaptic density protein-95 (PSD-95): a novel interaction regulated by cypin (cytosolic PSD-95 interactor)." Biochemical Journal 373, no. 1 (July 1, 2003): 49–55. http://dx.doi.org/10.1042/bj20021838.

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The PDZ domains of postsynaptic density (PSD) protein-95 play a role in the localization of PSD-95 and binding partners to neuronal synapses. The identification of binding partners to these PDZ domains can help us in understanding how signalling complexes are assembled. We observed that one of the subunits in the sec6/8 or exocyst complex, sec8, contains a C-terminal consensus sequence for PDZ binding. Sec8 binds to PDZ1–2 of PSD-95, and this binding can be competed with a peptide that binds to PDZ1 and PDZ2 in the peptide-binding site. In addition, binding of sec8 is dependent on its C-terminal-binding sequence namely Thr-Thr-Val (TTV). Immunoblotting of rat tissue extracts shows that sec8 and PSD-95 are enriched in the same brain regions, and sec8 and PSD-95 have the same subcellular distribution in pheochromocytoma cells, suggesting that these proteins may interact in vivo. Immunoprecipitation studies of sec8 and PSD-95 in brain provide further evidence of a sec8 and PSD-95 interaction. Furthermore, the cytosolic PSD-95 interactor competes with sec8 for interaction with PSD-95. Taken together, our results suggest that the cytosolic PSD-95 interactor may function to regulate the ability of sec8 to bind to PSD-95.

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Tang, Han, Jeroen de Keijzer, Elysa J. R. Overdijk, Els Sweep, Maikel Steentjes, Joop E. M. Vermeer, Marcel E. Janson, and Tijs Ketelaar. "Exocyst subunit Sec6 is positioned by microtubule overlaps in the moss phragmoplast prior to cell plate membrane arrival." Journal of Cell Science 132, no. 3 (January 11, 2019): jcs222430. http://dx.doi.org/10.1242/jcs.222430.

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Tan, Xiaoyun, Yihong Feng, Yulong Liu, and Yiqun Bao. "Mutations in exocyst complex subunit SEC6 gene impaired polar auxin transport and PIN protein recycling in Arabidopsis primary root." Plant Science 250 (September 2016): 97–104. http://dx.doi.org/10.1016/j.plantsci.2016.06.001.

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Overgaard, Christian E., Kaitlin M. Sanzone, Krystle S. Spiczka, David R. Sheff, Alexander Sandra, and Charles Yeaman. "Deciliation Is Associated with Dramatic Remodeling of Epithelial Cell Junctions and Surface Domains." Molecular Biology of the Cell 20, no. 1 (January 2009): 102–13. http://dx.doi.org/10.1091/mbc.e08-07-0741.

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Stress-induced shedding of motile cilia (autotomy) has been documented in diverse organisms and likely represents a conserved cellular reaction. However, little is known about whether primary cilia are shed from mammalian epithelial cells and what impact deciliation has on polarized cellular organization. We show that several chemically distinct agents trigger autotomy in epithelial cells. Surprisingly, deciliation is associated with a significant, but reversible increase in transepithelial resistance. This reflects substantial reductions in tight junction proteins associated with “leaky” nephron segments (e.g., claudin-2). At the same time, apical trafficking of gp80/clusterin and gp114/CEACAM becomes randomized, basal-lateral delivery of Na,K-ATPase is reduced, and expression of the nonciliary apical protein gp135/podocalyxin is greatly decreased. However, ciliogenesis-impaired MDCK cells do not undergo continual junction remodeling, and mature cilia are not required for autotomy-associated remodeling events. Deciliation and epithelial remodeling may be mechanistically linked processes, because RNAi-mediated reduction of Exocyst subunit Sec6 inhibits ciliary shedding and specifically blocks deciliation-associated down-regulation of claudin-2 and gp135. We propose that ciliary autotomy represents a signaling pathway that impacts the organization and function of polarized epithelial cells.

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Chavez-Dozal, Alba A., Stella M. Bernardo, Hallie S. Rane, Gloria Herrera, Vibhati Kulkarny, Jeanette Wagener, Iain Cunningham, Alexandra C. Brand, Neil A. R. Gow, and Samuel A. Lee. "Retraction for Chavez-Dozal et al., The Candida albicans Exocyst Subunit Sec6 Contributes to Cell Wall Integrity and Is a Determinant of Hyphal Branching." Eukaryotic Cell 14, no. 12 (December 2015): i. http://dx.doi.org/10.1128/ec.00001-16.

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Kwon, Min Jin, Mark Arentshorst, Markus Fiedler, Florence L. M. de Groen, Peter J. Punt, Vera Meyer, and Arthur F. J. Ram. "Molecular genetic analysis of vesicular transport in Aspergillus niger reveals partial conservation of the molecular mechanism of exocytosis in fungi." Microbiology 160, no. 2 (February 1, 2014): 316–29. http://dx.doi.org/10.1099/mic.0.074252-0.

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The filamentous fungus Aspergillus niger is an industrially exploited protein expression platform, well known for its capacity to secrete high levels of proteins. To study the process of protein secretion in A. niger, we established a GFP-v-SNARE reporter strain in which the trafficking and dynamics of secretory vesicles can be followed in vivo. The biological role of putative A. niger orthologues of seven secretion-specific genes, known to function in key aspects of the protein secretion machinery in Saccharomyces cerevisiae, was analysed by constructing respective gene deletion mutants in the GFP-v-SNARE reporter strain. Comparison of the deletion phenotype of conserved proteins functioning in the secretory pathway revealed common features but also interesting differences between S. cerevisiae and A. niger. Deletion of the S. cerevisiae Sec2p orthologue in A. niger (SecB), encoding a guanine exchange factor for the GTPase Sec4p (SrgA in A. niger), did not have an obvious phenotype, while SEC2 deletion in S. cerevisiae is lethal. Similarly, deletion of the A. niger orthologue of the S. cerevisiae exocyst subunit Sec3p (SecC) did not result in a lethal phenotype as in S. cerevisiae, although severe growth reduction of A. niger was observed. Deletion of secA, secH and ssoA (encoding SecA, SecH and SsoA the A. niger orthologues of S. cerevisiae Sec1p, Sec8p and Sso1/2p, respectively) showed that these genes are essential for A. niger, similar to the situation in S. cerevisiae. These data demonstrate that the orchestration of exocyst-mediated vesicle transport is only partially conserved in S. cerevisiae and A. niger.

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Seixas, Cecília, Soo Young Choi, Noemi Polgar, Nicole L. Umberger, Michael P. East, Xiaofeng Zuo, Hugo Moreiras, et al. "Arl13b and the exocyst interact synergistically in ciliogenesis." Molecular Biology of the Cell 27, no. 2 (January 15, 2016): 308–20. http://dx.doi.org/10.1091/mbc.e15-02-0061.

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Arl13b belongs to the ADP-ribosylation factor family within the Ras superfamily of regulatory GTPases. Mutations in Arl13b cause Joubert syndrome, which is characterized by congenital cerebellar ataxia, hypotonia, oculomotor apraxia, and mental retardation. Arl13b is highly enriched in cilia and is required for ciliogenesis in multiple organs. Nevertheless, the precise role of Arl13b remains elusive. Here we report that the exocyst subunits Sec8, Exo70, and Sec5 bind preferentially to the GTP-bound form of Arl13b, consistent with the exocyst being an effector of Arl13b. Moreover, we show that Arl13b binds directly to Sec8 and Sec5. In zebrafish, depletion of arl13b or the exocyst subunit sec10 causes phenotypes characteristic of defective cilia, such as curly tail up, edema, and abnormal pronephric kidney development. We explored this further and found a synergistic genetic interaction between arl13b and sec10 morphants in cilia-dependent phenotypes. Through conditional deletion of Arl13b or Sec10 in mice, we found kidney cysts and decreased ciliogenesis in cells surrounding the cysts. Moreover, we observed a decrease in Arl13b expression in the kidneys from Sec10 conditional knockout mice. Taken together, our results indicate that Arl13b and the exocyst function together in the same pathway leading to functional cilia.

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Oztan, Asli, Mark Silvis, Ora A. Weisz, Neil A. Bradbury, Shu-Chan Hsu, James R. Goldenring, Charles Yeaman, and Gerard Apodaca. "Exocyst Requirement for Endocytic Traffic Directed Toward the Apical and Basolateral Poles of Polarized MDCK Cells." Molecular Biology of the Cell 18, no. 10 (October 2007): 3978–92. http://dx.doi.org/10.1091/mbc.e07-02-0097.

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The octameric exocyst complex is associated with the junctional complex and recycling endosomes and is proposed to selectively tether cargo vesicles directed toward the basolateral surface of polarized Madin-Darby canine kidney (MDCK) cells. We observed that the exocyst subunits Sec6, Sec8, and Exo70 were localized to early endosomes, transferrin-positive common recycling endosomes, and Rab11a-positive apical recycling endosomes of polarized MDCK cells. Consistent with its localization to multiple populations of endosomes, addition of function-blocking Sec8 antibodies to streptolysin-O–permeabilized cells revealed exocyst requirements for several endocytic pathways including basolateral recycling, apical recycling, and basolateral-to-apical transcytosis. The latter was selectively dependent on interactions between the small GTPase Rab11a and Sec15A and was inhibited by expression of the C-terminus of Sec15A or down-regulation of Sec15A expression using shRNA. These results indicate that the exocyst complex may be a multipurpose regulator of endocytic traffic directed toward both poles of polarized epithelial cells and that transcytotic traffic is likely to require Rab11a-dependent recruitment and modulation of exocyst function, likely through interactions with Sec15A.

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Novick, P., M. Medkova, G. Dong, A. Hutagalung, K. Reinisch, and B. Grosshans. "Interactions between Rabs, tethers, SNAREs and their regulators in exocytosis." Biochemical Society Transactions 34, no. 5 (October 1, 2006): 683–86. http://dx.doi.org/10.1042/bst0340683.

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Sec2p is the exchange factor that activates Sec4p, the Rab GTPase controlling the final stage of the yeast exocytic pathway. Sec2p is recruited to secretory vesicles by Ypt32-GTP, a Rab controlling exit from the Golgi. Sec15p, a subunit of the octameric exocyst tethering complex and an effector of Sec4p, binds to Sec2p on secretory vesicles, displacing Ypt32p. Sec2p mutants defective in the region 450–508 amino acids bind to Sec15p more tightly. In these mutants, Sec2p accumulates in the cytosol in a complex with the exocyst and is not recruited to vesicles by Ypt32p. Thus the region 450–508 amino acids negatively regulates the association of Sec2p with the exocyst, allowing it to recycle on to new vesicles. The structures of one nearly full-length exocyst subunit and three partial subunits have been determined and, despite very low sequence identity, all form rod-like structures built of helical bundles stacked end to end. These rods may bind to each other along their sides to form the assembled complex. While Sec15p binds Sec4-GTP on the vesicle, other subunits bind Rho GTPases on the plasma membrane, thus tethering vesicles to exocytic sites. Sec4-GTP also binds Sro7p, a yeast homologue of the Drosophila lgl (lethal giant larvae) tumour suppressor. Sro7 also binds to Sec9p, a SNAP25 (25 kDa synaptosome-associated protein)-like t-SNARE [target-membrane-associated SNARE (soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor)], and can form a Sec4p–Sro7p–Sec9p ternary complex. Overexpression of Sec4p, Sro7p or Sec1p (another SNARE regulator) can bypass deletions of three different exocyst subunits. Thus promoting SNARE function can compensate for tethering defects.

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Shen, David, Hua Yuan, Alex Hutagalung, Avani Verma, Daniel Kümmel, Xudong Wu, Karin Reinisch, James A. McNew, and Peter Novick. "The synaptobrevin homologue Snc2p recruits the exocyst to secretory vesicles by binding to Sec6p." Journal of Cell Biology 202, no. 3 (July 29, 2013): 509–26. http://dx.doi.org/10.1083/jcb.201211148.

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A screen for mutations that affect the recruitment of the exocyst to secretory vesicles identified genes encoding clathrin and proteins that associate or colocalize with clathrin at sites of endocytosis. However, no significant colocalization of the exocyst with clathrin was seen, arguing against a direct role in exocyst recruitment. Rather, these components are needed to recycle the exocytic vesicle SNAREs Snc1p and Snc2p from the plasma membrane into new secretory vesicles where they act to recruit the exocyst. We observe a direct interaction between the exocyst subunit Sec6p and the latter half of the SNARE motif of Snc2p. An snc2 mutation that specifically disrupts this interaction led to exocyst mislocalization and a block in exocytosis in vivo without affecting liposome fusion in vitro. Overexpression of Sec4p partially suppressed the exocyst localization defects of mutations in clathrin and clathrin-associated components. We propose that the exocyst is recruited to secretory vesicles by the combinatorial signals of Sec4-GTP and the Snc proteins. This could help to confer both specificity and directionality to vesicular traffic.

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Bendezú, Felipe O., and Sophie G. Martin. "Actin cables and the exocyst form two independent morphogenesis pathways in the fission yeast." Molecular Biology of the Cell 22, no. 1 (January 2011): 44–53. http://dx.doi.org/10.1091/mbc.e10-08-0720.

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Cell morphogenesis depends on polarized exocytosis. One widely held model posits that long-range transport and exocyst-dependent tethering of exocytic vesicles at the plasma membrane sequentially drive this process. Here, we describe that disruption of either actin-based long-range transport and microtubules or the exocyst did not abolish polarized growth in rod-shaped fission yeast cells. However, disruption of both actin cables and exocyst led to isotropic growth. Exocytic vesicles localized to cell tips in single mutants but were dispersed in double mutants. In contrast, a marker for active Cdc42, a major polarity landmark, localized to discreet cortical sites even in double mutants. Localization and photobleaching studies show that the exocyst subunits Sec6 and Sec8 localize to cell tips largely independently of the actin cytoskeleton, but in a cdc42 and phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2)–dependent manner. Thus in fission yeast long-range cytoskeletal transport and PIP2-dependent exocyst represent parallel morphogenetic modules downstream of Cdc42, raising the possibility of similar mechanisms in other cell types.

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Fendrych, Matyáš, Lukáš Synek, Tamara Pečenková, Edita Janková Drdová, Juraj Sekereš, Riet de Rycke, Moritz K. Nowack, and Viktor Žárský. "Visualization of the exocyst complex dynamics at the plasma membrane of Arabidopsis thaliana." Molecular Biology of the Cell 24, no. 4 (February 15, 2013): 510–20. http://dx.doi.org/10.1091/mbc.e12-06-0492.

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The exocyst complex, an effector of Rho and Rab GTPases, is believed to function as an exocytotic vesicle tether at the plasma membrane before soluble N-ethylmaleimide–sensitive factor attachment protein receptor (SNARE) complex formation. Exocyst subunits localize to secretory-active regions of the plasma membrane, exemplified by the outer domain of Arabidopsis root epidermal cells. Using variable-angle epifluorescence microscopy, we visualized the dynamics of exocyst subunits at this domain. The subunits colocalized in defined foci at the plasma membrane, distinct from endocytic sites. Exocyst foci were independent of cytoskeleton, although prolonged actin disruption led to changes in exocyst localization. Exocyst foci partially overlapped with vesicles visualized by VAMP721 v-SNARE, but the majority of the foci represent sites without vesicles, as indicated by electron microscopy and drug treatments, supporting the concept of the exocyst functioning as a dynamic particle. We observed a decrease of SEC6–green fluorescent protein foci in an exo70A1 exocyst mutant. Finally, we documented decreased VAMP721 trafficking to the plasma membrane in exo70A1 and exo84b mutants. Our data support the concept that the exocyst-complex subunits dynamically dock and undock at the plasma membrane to create sites primed for vesicle tethering.

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Roumanie, Olivier, Hao Wu, Jeffrey N. Molk, Guendalina Rossi, Kerry Bloom, and Patrick Brennwald. "Rho GTPase regulation of exocytosis in yeast is independent of GTP hydrolysis and polarization of the exocyst complex." Journal of Cell Biology 170, no. 4 (August 15, 2005): 583–94. http://dx.doi.org/10.1083/jcb.200504108.

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Rho GTPases are important regulators of polarity in eukaryotic cells. In yeast they are involved in regulating the docking and fusion of secretory vesicles with the cell surface. Our analysis of a Rho3 mutant that is unable to interact with the Exo70 subunit of the exocyst reveals a normal polarization of the exocyst complex as well as other polarity markers. We also find that there is no redundancy between the Rho3–Exo70 and Rho1–Sec3 pathways in the localization of the exocyst. This suggests that Rho3 and Cdc42 act to polarize exocytosis by activating the exocytic machinery at the membrane without the need to first recruit it to sites of polarized growth. Consistent with this model, we find that the ability of Rho3 and Cdc42 to hydrolyze GTP is not required for their role in secretion. Moreover, our analysis of the Sec3 subunit of the exocyst suggests that polarization of the exocyst may be a consequence rather than a cause of polarized exocytosis.

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Sakurai-Yageta, Mika, Chiara Recchi, Gaëlle Le Dez, Jean-Baptiste Sibarita, Laurent Daviet, Jacques Camonis, Crislyn D'Souza-Schorey, and Philippe Chavrier. "The interaction of IQGAP1 with the exocyst complex is required for tumor cell invasion downstream of Cdc42 and RhoA." Journal of Cell Biology 181, no. 6 (June 9, 2008): 985–98. http://dx.doi.org/10.1083/jcb.200709076.

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Invadopodia are actin-based membrane protrusions formed at contact sites between invasive tumor cells and the extracellular matrix with matrix proteolytic activity. Actin regulatory proteins participate in invadopodia formation, whereas matrix degradation requires metalloproteinases (MMPs) targeted to invadopodia. In this study, we show that the vesicle-tethering exocyst complex is required for matrix proteolysis and invasion of breast carcinoma cells. We demonstrate that the exocyst subunits Sec3 and Sec8 interact with the polarity protein IQGAP1 and that this interaction is triggered by active Cdc42 and RhoA, which are essential for matrix degradation. Interaction between IQGAP1 and the exocyst is necessary for invadopodia activity because enhancement of matrix degradation induced by the expression of IQGAP1 is lost upon deletion of the exocyst-binding site. We further show that the exocyst and IQGAP1 are required for the accumulation of cell surface membrane type 1 MMP at invadopodia. Based on these results, we propose that invadopodia function in tumor cells relies on the coordination of cytoskeletal assembly and exocytosis downstream of Rho guanosine triphosphatases.

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Arasaki, Kohei, Hana Kimura, Mitsuo Tagaya, and Craig R. Roy. "Legionella remodels the plasma membrane–derived vacuole by utilizing exocyst components as tethers." Journal of Cell Biology 217, no. 11 (October 1, 2018): 3863–72. http://dx.doi.org/10.1083/jcb.201801208.

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During the initial stage of infection, Legionella pneumophila secretes effectors that promote the fusion of endoplasmic reticulum (ER)–derived vesicles with the Legionella-containing vacuole (LCV). This fusion leads to a remodeling of the plasma membrane (PM)–derived LCV into a specialized ER-like compartment that supports bacterial replication. Although the effector DrrA has been shown to activate the small GTPase Rab1, it remains unclear how DrrA promotes the tethering of host vesicles with the LCV. Here, we show that Sec5, Sec15, and perhaps Sec6, which are subunits of the exocyst that functions in the tethering of exocytic vesicles with the PM, are required for DrrA-mediated, ER-derived vesicle recruitment to the PM-derived LCV. These exocyst components were found to interact specifically with a complex containing DrrA, and the loss of Sec5 or Sec15 significantly suppressed the recruitment of ER-derived vesicles to the LCV and inhibited intracellular replication of Legionella. Importantly, Sec15 is recruited to the LCV, and Rab1 activation is necessary for this recruitment.

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Fais, Milena, Giovanna Sanna, Manuela Galioto, Thi Thanh Duyen Nguyen, Mai Uyên Thi Trần, Paola Sini, Franco Carta, et al. "LRRK2 Modulates the Exocyst Complex Assembly by Interacting with Sec8." Cells 10, no. 2 (January 20, 2021): 203. http://dx.doi.org/10.3390/cells10020203.

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Mutations in LRRK2 play a critical role in both familial and sporadic Parkinson’s disease (PD). Up to date, the role of LRRK2 in PD onset and progression remains largely unknown. However, experimental evidence highlights a critical role of LRRK2 in the control of vesicle trafficking, likely by Rab phosphorylation, that in turn may regulate different aspects of neuronal physiology. Here we show that LRRK2 interacts with Sec8, one of eight subunits of the exocyst complex. The exocyst complex is an evolutionarily conserved multisubunit protein complex mainly involved in tethering secretory vesicles to the plasma membrane and implicated in the regulation of multiple biological processes modulated by vesicle trafficking. Interestingly, Rabs and exocyst complex belong to the same protein network. Our experimental evidence indicates that LRRK2 kinase activity or the presence of the LRRK2 kinase domain regulate the assembly of exocyst subunits and that the over-expression of Sec8 significantly rescues the LRRK2 G2019S mutant pathological effect. Our findings strongly suggest an interesting molecular mechanism by which LRRK2 could modulate vesicle trafficking and may have important implications to decode the complex role that LRRK2 plays in neuronal physiology.

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Boyd, Charles, Thom Hughes, Marc Pypaert, and Peter Novick. "Vesicles carry most exocyst subunits to exocytic sites marked by the remaining two subunits, Sec3p and Exo70p." Journal of Cell Biology 167, no. 5 (December 6, 2004): 889–901. http://dx.doi.org/10.1083/jcb.200408124.

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Exocytosis in the budding yeast Saccharomyces cerevisiae occurs at discrete domains of the plasma membrane. The protein complex that tethers incoming vesicles to sites of secretion is known as the exocyst. We have used photobleaching recovery experiments to characterize the dynamic behavior of the eight subunits that make up the exocyst. One subset (Sec5p, Sec6p, Sec8p, Sec10p, Sec15p, and Exo84p) exhibits mobility similar to that of the vesicle-bound Rab family protein Sec4p, whereas Sec3p and Exo70p exhibit substantially more stability. Disruption of actin assembly abolishes the ability of the first subset of subunits to recover after photobleaching, whereas Sec3p and Exo70p are resistant. Immunogold electron microscopy and epifluorescence video microscopy indicate that all exocyst subunits, except for Sec3p, are associated with secretory vesicles as they arrive at exocytic sites. Assembly of the exocyst occurs when the first subset of subunits, delivered on vesicles, joins Sec3p and Exo70p on the plasma membrane. Exocyst assembly serves to both target and tether vesicles to sites of exocytosis.

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Liu, Dongmei, Xia Li, David Shen, and Peter Novick. "Two subunits of the exocyst, Sec3p and Exo70p, can function exclusively on the plasma membrane." Molecular Biology of the Cell 29, no. 6 (March 15, 2018): 736–50. http://dx.doi.org/10.1091/mbc.e17-08-0518.

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The exocyst is an octameric complex that tethers secretory vesicles to the plasma membrane in preparation for fusion. We anchored each subunit with a transmembrane (TM) domain at its N- or C-terminus. Only N-terminally anchored TM-Sec3p and C-terminally anchored Exo70p-TM proved functional. These findings orient the complex with respect to the membrane and establish that Sec3p and Exo70p can function exclusively on the membrane. The functions of TM-Sec3p and Exo70p-TM were largely unaffected by blocks in endocytic recycling, suggesting that they act on the plasma membrane rather than on secretory vesicles. Cytosolic pools of the other exocyst subunits were unaffected in TM-sec3 cells, while they were partially depleted in exo70-TM cells. Blocking actin-dependent delivery of secretory vesicles in act1-3 cells results in loss of Sec3p from the purified complex. Our results are consistent with a model in which Sec3p and Exo70p can function exclusively on the plasma membrane while the other subunits are brought to them on secretory vesicles.

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Prigent, Magali, Thierry Dubois, Graça Raposo, Valérie Derrien, Danièle Tenza, Carine Rossé, Jacques Camonis, and Philippe Chavrier. "ARF6 controls post-endocytic recycling through its downstream exocyst complex effector." Journal of Cell Biology 163, no. 5 (December 8, 2003): 1111–21. http://dx.doi.org/10.1083/jcb.200305029.

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The small guanosine triphosphate (GTP)–binding protein ADP-ribosylation factor (ARF) 6 regulates membrane recycling to regions of plasma membrane remodeling via the endocytic pathway. Here, we show that GTP–bound ARF6 interacts with Sec10, a subunit of the exocyst complex involved in docking of vesicles with the plasma membrane. We found that Sec10 localization in the perinuclear region is not restricted to the trans-Golgi network, but extends to recycling endosomes. In addition, we report that depletion of Sec5 exocyst subunit or dominant inhibition of Sec10 affects the function and the morphology of the recycling pathway. Sec10 is found to redistribute to ruffling areas of the plasma membrane in cells expressing GTP-ARF6, whereas dominant inhibition of Sec10 interferes with ARF6-induced cell spreading. Our paper suggests that ARF6 specifies delivery and insertion of recycling membranes to regions of dynamic reorganization of the plasma membrane through interaction with the vesicle-tethering exocyst complex.

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Fabian, Lacramioara, Ho-Chun Wei, Janet Rollins, Tatsuhiko Noguchi, J. Todd Blankenship, Kishan Bellamkonda, Gordon Polevoy, et al. "Phosphatidylinositol 4,5-bisphosphate Directs Spermatid Cell Polarity and Exocyst Localization in Drosophila." Molecular Biology of the Cell 21, no. 9 (May 2010): 1546–55. http://dx.doi.org/10.1091/mbc.e09-07-0582.

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During spermiogenesis, Drosophila melanogaster spermatids coordinate their elongation in interconnected cysts that become highly polarized, with nuclei localizing to one end and sperm tail growth occurring at the other. Remarkably little is known about the signals that drive spermatid polarity and elongation. Here we identify phosphoinositides as critical regulators of these processes. Reduction of plasma membrane phosphatidylinositol 4,5-bisphosphate (PIP2) by low-level expression of the PIP2 phosphatase SigD or mutation of the PIP2 biosynthetic enzyme Skittles (Sktl) results in dramatic defects in spermatid cysts, which become bipolar and fail to fully elongate. Defects in polarity are evident from the earliest stages of elongation, indicating that phosphoinositides are required for establishment of polarity. Sktl and PIP2 localize to the growing end of the cysts together with the exocyst complex. Strikingly, the exocyst becomes completely delocalized when PIP2 levels are reduced, and overexpression of Sktl restores exocyst localization and spermatid cyst polarity. Moreover, the exocyst is required for polarity, as partial loss of function of the exocyst subunit Sec8 results in bipolar cysts. Our data are consistent with a mechanism in which localized synthesis of PIP2 recruits the exocyst to promote targeted membrane delivery and polarization of the elongating cysts.

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Hutagalung, Alex H., Jeff Coleman, Marc Pypaert, and Peter J. Novick. "An Internal Domain of Exo70p Is Required for Actin-independent Localization and Mediates Assembly of Specific Exocyst Components." Molecular Biology of the Cell 20, no. 1 (January 2009): 153–63. http://dx.doi.org/10.1091/mbc.e08-02-0157.

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The exocyst consists of eight rod-shaped subunits that align in a side-by-side manner to tether secretory vesicles to the plasma membrane in preparation for fusion. Two subunits, Sec3p and Exo70p, localize to exocytic sites by an actin-independent pathway, whereas the other six ride on vesicles along actin cables. Here, we demonstrate that three of the four domains of Exo70p are essential for growth. The remaining domain, domain C, is not essential but when deleted, it leads to synthetic lethality with many secretory mutations, defects in exocyst assembly of exocyst components Sec5p and Sec6p, and loss of actin-independent localization. This is analogous to a deletion of the amino-terminal domain of Sec3p, which prevents an interaction with Cdc42p or Rho1p and blocks its actin-independent localization. The two mutations are synthetically lethal, even in the presence of high copy number suppressors that can bypass complete deletions of either single gene. Although domain C binds Rho3p, loss of the Exo70p-Rho3p interaction does not account for the synthetic lethal interactions or the exocyst assembly defects. The results suggest that either Exo70p or Sec3p must associate with the plasma membrane for the exocyst to function as a vesicle tether.

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Kampmeyer, Caroline, Antonina Karakostova, Signe M. Schenstrøm, Amanda B. Abildgaard, Anne-Marie Lauridsen, Isabelle Jourdain, and Rasmus Hartmann-Petersen. "The exocyst subunit Sec3 is regulated by a protein quality control pathway." Journal of Biological Chemistry 292, no. 37 (August 1, 2017): 15240–53. http://dx.doi.org/10.1074/jbc.m117.789867.

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Baek, Kyuwon, Andreas Knödler, Sung Haeng Lee, Xiaoyu Zhang, Kelly Orlando, Jian Zhang, Trevor J. Foskett, Wei Guo, and Roberto Dominguez. "Structure-Function Study of the N-terminal Domain of Exocyst Subunit Sec3." Journal of Biological Chemistry 285, no. 14 (February 5, 2010): 10424–33. http://dx.doi.org/10.1074/jbc.m109.096966.

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Knop, Michael, K. Juha Miller, Massimiliano Mazza, DeJiang Feng, Marion Weber, Sirkka Keränen, and Jussi Jäntti. "Molecular Interactions Position Mso1p, a Novel PTB Domain Homologue, in the Interface of the Exocyst Complex and the Exocytic SNARE Machinery in Yeast." Molecular Biology of the Cell 16, no. 10 (October 2005): 4543–56. http://dx.doi.org/10.1091/mbc.e05-03-0243.

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In this study, we have analyzed the association of the Sec1p interacting protein Mso1p with the membrane fusion machinery in yeast. We show that Mso1p is essential for vesicle fusion during prospore membrane formation. Green fluorescent protein-tagged Mso1p localizes to the sites of exocytosis and at the site of prospore membrane formation. In vivo and in vitro experiments identified a short amino-terminal sequence in Mso1p that mediates its interaction with Sec1p and is needed for vesicle fusion. A point mutation, T47A, within the Sec1p-binding domain abolishes Mso1p functionality in vivo, and mso1T47A mutant cells display specific genetic interactions with sec1 mutants. Mso1p coimmunoprecipitates with Sec1p, Sso1/2p, Snc1/2p, Sec9p, and the exocyst complex subunit Sec15p. In sec4-8 and SEC4I133 mutant cells, association of Mso1p with Sso1/2p, Snc1/2p, and Sec9p is affected, whereas interaction with Sec1p persists. Furthermore, in SEC4I133 cells the dominant negative Sec4I133p coimmunoprecipitates with Mso1p–Sec1p complex. Finally, we identify Mso1p as a homologue of the PTB binding domain of the mammalian Sec1p binding Mint proteins. These results position Mso1p in the interface of the exocyst complex, Sec4p, and the SNARE machinery, and reveal a novel layer of molecular conservation in the exocytosis machinery.

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De Craene, Johan-Owen, Jeff Coleman, Paula Estrada de Martin, Marc Pypaert, Scott Anderson, John R. Yates, Susan Ferro-Novick, and Peter Novick. "Rtn1p Is Involved in Structuring the Cortical Endoplasmic Reticulum." Molecular Biology of the Cell 17, no. 7 (July 2006): 3009–20. http://dx.doi.org/10.1091/mbc.e06-01-0080.

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The endoplasmic reticulum (ER) contains both cisternal and reticular elements in one contiguous structure. We identified rtn1Δ in a systematic screen for yeast mutants with altered ER morphology. The ER in rtn1Δ cells is predominantly cisternal rather than reticular, yet the net surface area of ER is not significantly changed. Rtn1-green fluorescent protein (GFP) associates with the reticular ER at the cell cortex and with the tubules that connect the cortical ER to the nuclear envelope, but not with the nuclear envelope itself. Rtn1p overexpression also results in an altered ER structure. Rtn proteins are found on the ER in a wide range of eukaryotes and are defined by two membrane-spanning domains flanking a conserved hydrophilic loop. Our results suggest that Rtn proteins may direct the formation of reticulated ER. We independently identified Rtn1p in a proteomic screen for proteins associated with the exocyst vesicle tethering complex. The conserved hydophilic loop of Rtn1p binds to the exocyst subunit Sec6p. Overexpression of this loop results in a modest accumulation of secretory vesicles, suggesting impaired exocyst function. The interaction of Rtn1p with the exocyst at the bud tip may trigger the formation of a cortical ER network in yeast buds.

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Fölsch, Heike, Marc Pypaert, Sandra Maday, Laurence Pelletier, and Ira Mellman. "The AP-1A and AP-1B clathrin adaptor complexes define biochemically and functionally distinct membrane domains." Journal of Cell Biology 163, no. 2 (October 27, 2003): 351–62. http://dx.doi.org/10.1083/jcb.200309020.

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Most epithelial cells contain two AP-1 clathrin adaptor complexes. AP-1A is ubiquitously expressed and involved in transport between the TGN and endosomes. AP-1B is expressed only in epithelia and mediates the polarized targeting of membrane proteins to the basolateral surface. Both AP-1 complexes are heterotetramers and differ only in their 50-kD μ1A or μ1B subunits. Here, we show that AP-1A and AP-1B, together with their respective cargoes, define physically and functionally distinct membrane domains in the perinuclear region. Expression of AP-1B (but not AP-1A) enhanced the recruitment of at least two subunits of the exocyst complex (Sec8 and Exo70) required for basolateral transport. By immunofluorescence and cell fractionation, the exocyst subunits were found to selectively associate with AP-1B–containing membranes that were both distinct from AP-1A–positive TGN elements and more closely apposed to transferrin receptor–positive recycling endosomes. Thus, despite the similarity of the two AP-1 complexes, AP-1A and AP-1B exhibit great specificity for endosomal transport versus cell polarity.

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Yamashita, Masami, Kazuo Kurokawa, Yusuke Sato, Atsushi Yamagata, Hisatoshi Mimura, Azusa Yoshikawa, Ken Sato, Akihiko Nakano, and Shuya Fukai. "Structural basis for the Rho- and phosphoinositide-dependent localization of the exocyst subunit Sec3." Nature Structural & Molecular Biology 17, no. 2 (January 10, 2010): 180–86. http://dx.doi.org/10.1038/nsmb.1722.

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Sivaram, Mylavarapu V. S., Melonnie L. M. Furgason, Daniel N. Brewer, and Mary Munson. "The structure of the exocyst subunit Sec6p defines a conserved architecture with diverse roles." Nature Structural & Molecular Biology 13, no. 6 (May 14, 2006): 555–56. http://dx.doi.org/10.1038/nsmb1096.

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Kulich, Ivan, Rex Cole, Edita Drdová, Fatima Cvrčková, Aleš Soukup, John Fowler, and Viktor Žárský. "Arabidopsis exocyst subunits SEC8 and EXO70A1 and exocyst interactor ROH1 are involved in the localized deposition of seed coat pectin." New Phytologist 188, no. 2 (July 2, 2010): 615–25. http://dx.doi.org/10.1111/j.1469-8137.2010.03372.x.

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Wiederkehr, Andreas, Yunrui Du, Marc Pypaert, Susan Ferro-Novick, and Peter Novick. "Sec3p Is Needed for the Spatial Regulation of Secretion and for the Inheritance of the Cortical Endoplasmic Reticulum." Molecular Biology of the Cell 14, no. 12 (December 2003): 4770–82. http://dx.doi.org/10.1091/mbc.e03-04-0229.

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Sec3p is a component of the exocyst complex that tethers secretory vesicles to the plasma membrane at exocytic sites in preparation for fusion. Unlike all other exocyst structural genes, SEC3 is not essential for growth. Cells lacking Sec3p grow and secrete surprisingly well at 25°C; however, late markers of secretion, such as the vesicle marker Sec4p and the exocyst subunit Sec8p, localize more diffusely within the bud. Furthermore, sec3Δ cells are strikingly round relative to wild-type cells and are unable to form pointed mating projections in response to α factor. These phenotypes support the proposed role of Sec3p as a spatial landmark for secretion. We also find that cells lacking Sec3p exhibit a dramatic defect in the inheritance of cortical ER into the bud, whereas the inheritance of mitochondria and Golgi is unaffected. Overexpression of Sec3p results in a prominent patch of the endoplasmic reticulum (ER) marker Sec61p-GFP at the bud tip. Cortical ER inheritance in yeast has been suggested to involve the capture of ER tubules at the bud tip. Sec3p may act in this process as a spatial landmark for cortical ER inheritance.

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Cole, Rex A., Lukás Synek, Viktor Zarsky, and John E. Fowler. "SEC8, a Subunit of the Putative Arabidopsis Exocyst Complex, Facilitates Pollen Germination and Competitive Pollen Tube Growth." Plant Physiology 138, no. 4 (July 22, 2005): 2005–18. http://dx.doi.org/10.1104/pp.105.062273.

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Overdijk, Elysa J. R., Han Tang, Jan Willem Borst, Francine Govers, and Tijs Ketelaar. "Time-gated confocal microscopy reveals accumulation of exocyst subunits at the plant-pathogen interface." Journal of Experimental Botany, October 26, 2019. http://dx.doi.org/10.1093/jxb/erz478.

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Abstract Polarized exocytosis is essential for plant development and defence. The exocyst, an octameric protein complex that tethers exocytotic vesicles to the plasma membrane, targets exocytosis. Upon pathogen attack, secreted materials form papillae to halt pathogen penetration. To determine if the exocyst is directly involved in targeting exocytosis to infection sites, information about its localization is instrumental. Here, we investigated exocyst subunit localization in the moss Physcomitrella patens upon pathogen attack and infection by Phytophthora capsici. Time-gated confocal microscopy was used to eliminate autofluorescence of deposited material around infection sites allowing the visualization of the subcellular localization of exocyst subunits and of v-SNARE Vamp72A1-labeled exocytotic vesicles during infection. This showed that exocyst subunits Sec3a, Sec5b, Sec5d and Sec6 accumulated at sites of attempted pathogen penetration. Upon pathogen invasion, the exocyst subunits accumulated on the membrane surrounding papilla-like structures and hyphal encasements. Vamp72A1-labeled vesicles were found to localize in the cytoplasm around infection sites. The re-localization of exocyst subunits to infection sites suggests that the exocyst is directly involved in facilitating polarized exocytosis during pathogenesis.

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Yang, Shuai, Xin Zhou, Pingting Guo, Yaqi Lin, Qingwen Fan, Qussai Zuriegat, Songmao Lu, et al. "The Exocyst Regulates Hydrolytic Enzyme Secretion at Hyphal Tips and Septa in the Banana Fusarium Wilt Fungus Fusarium odoratissimum." Applied and Environmental Microbiology 87, no. 17 (August 11, 2021). http://dx.doi.org/10.1128/aem.03088-20.

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The exocyst complex is a multisubunit tethering complex (MTC) for secretory vesicles at the plasma membrane and contains eight subunits, Sec3, Sec5, Sec6, Sec8, Sec10, Sec15, Exo70, and Exo84. While the exocyst complex is well defined in eukaryotes from yeast to humans, the exocyst components in filamentous fungi show different localization patterns in the apical tips of hyphae, which suggests that filamentous fungi have evolved divergent strategies to regulate endomembrane trafficking.

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Van Bergen, Nicole J., Syed Mukhtar Ahmed, Felicity Collins, Mark Cowley, Annalisa Vetro, Russell C. Dale, Daniella H. Hock, et al. "Mutations in the exocyst component EXOC2 cause severe defects in human brain development." Journal of Experimental Medicine 217, no. 10 (July 8, 2020). http://dx.doi.org/10.1084/jem.20192040.

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The exocyst, an octameric protein complex, is an essential component of the membrane transport machinery required for tethering and fusion of vesicles at the plasma membrane. We report pathogenic variants in an exocyst subunit, EXOC2 (Sec5). Affected individuals have severe developmental delay, dysmorphism, and brain abnormalities; variability associated with epilepsy; and poor motor skills. Family 1 had two offspring with a homozygous truncating variant in EXOC2 that leads to nonsense-mediated decay of EXOC2 transcript, a severe reduction in exocytosis and vesicle fusion, and undetectable levels of EXOC2 protein. The patient from Family 2 had a milder clinical phenotype and reduced exocytosis. Cells from both patients showed defective Arl13b localization to the primary cilium. The discovery of mutations that partially disable exocyst function provides valuable insight into this essential protein complex in neural development. Since EXOC2 and other exocyst complex subunits are critical to neuronal function, our findings suggest that EXOC2 variants are the cause of the patients’ neurological disorders.

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Journal articles on the topic 'Exocyst Subunit Sec6'

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