Phosphatidylinositol 4,5-Bisphosphate Mediates the Targeting of the Exocyst to the Plasma Membrane for Exocytosis in Mammalian Cells □ D

Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018, USA.
Molecular Biology of the Cell (Impact Factor: 4.47). 12/2007; 18(11):4483-92. DOI: 10.1091/mbc.E07-05-0461
Source: PubMed


The exocyst is an evolutionarily conserved octameric protein complex that tethers post-Golgi secretory vesicles at the plasma membrane for exocytosis. To elucidate the mechanism of vesicle tethering, it is important to understand how the exocyst physically associates with the plasma membrane (PM). In this study, we report that the mammalian exocyst subunit Exo70 associates with the PM through its direct interaction with phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)). Furthermore, we have identified key conserved residues at the C-terminus of Exo70 that are crucial for the interaction of Exo70 with PI(4,5)P(2). Disrupting Exo70-PI(4,5)P(2) interaction abolished the membrane association of Exo70. We have also found that wild-type Exo70 but not the PI(4,5)P(2)-binding-deficient Exo70 mutant is capable of recruiting other exocyst components to the PM. Using the ts045 vesicular stomatitis virus glycoprotein trafficking assay, we demonstrate that Exo70-PI(4,5)P(2) interaction is critical for the docking and fusion of post-Golgi secretory vesicles, but not for their transport to the PM.

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    • "Interestingly, it can form two stable subcomplexes. The subunits Exo70 and Sec3 are anchored to the plasma membrane via Rab and Rho GTPases and the phosphoinositide PI(4,5)P 2 , whereas the hexameric subcomplex of the other six subunits is thought to bind via Sec4 to the vesicle [109] [110] [111]. "
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    ABSTRACT: The HOPS multisubunit tethering factor (MTC) is a macromolecular protein complex composed of six different subunits. It is one of the key components in the perception and subsequent fusion of multivesicular bodies and vacuoles. Electron microscopy studies indicate structural flexibility of the purified HOPS complex. Inducing higher rigidity into HOPS by biochemically modifying the complex declines the potential to mediate SNARE-driven membrane fusion. Thus, we propose that integral flexibility seems to be not only a feature, but of essential need for the function of HOPS. This review focuses on the general features of membrane tethering and fusion. For this purpose, we compare the structure and mode of action of different tethering factors to highlight their common central features and mechanisms. Copyright © 2015. Published by Elsevier B.V.
    FEBS letters 06/2015; DOI:10.1016/j.febslet.2015.06.001 · 3.17 Impact Factor
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    • "Next, we examined the migration properties of MDA-MB-231 cells by wound healing assays (Figures 3C and 3D). We have previously generated siRNA oligos that selectively knock down Exo70 (Zuo et al., 2006; Liu et al., 2007, 2009). Here, we found that cells with their endogenous Exo70 knocked down by siRNA took more time for wound closure than control cells. "
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    ABSTRACT: Epithelial-mesenchymal transition (EMT) is an important developmental process hijacked by cancer cells for their dissemination. Here, we show that Exo70, a component of the exocyst complex, undergoes isoform switching mediated by ESRP1, a pre-mRNA splicing factor that regulates EMT. Expression of the epithelial isoform of Exo70 affects the levels of key EMT transcriptional regulators such as Snail and ZEB2 and is sufficient to drive the transition to epithelial phenotypes. Differential Exo70 isoform expression in human tumors correlates with cancer progression, and increased expression of the epithelial isoform of Exo70 inhibits tumor metastasis in mice. At the molecular level, the mesenchymal-but not the epithelial-isoform of Exo70 interacts with the Arp2/3 complex and stimulates actin polymerization for tumor invasion. Our findings provide a mechanism by which the exocyst function and actin dynamics are modulated for EMT and tumor invasion.
    Developmental Cell 12/2013; 27(5):560-573. DOI:10.1016/j.devcel.2013.10.020 · 9.71 Impact Factor
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    • "The fully assembled exocyst complex localizes to growth cones in neurons where it plays an important role in membrane addition (59). The plasma membrane recruitment of exocyst is mediated through interactions of exocyst subunits Exo70 and Sec3 with GTPases (Rho and cdc42 family) and the phosphoinositide lipid PI(4,5)P2 (60, 61). "
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    ABSTRACT: CAPS (Calcium-dependent Activator Protein for Secretion, aka CADPS) and Munc13 (Mammalian Unc-13) proteins function to prime vesicles for Ca(2+)-triggered exocytosis in neurons and neuroendocrine cells. CAPS and Munc13 proteins contain conserved C-terminal domains that promote the assembly of SNARE complexes for vesicle priming. Similarities of the C-terminal domains of CAPS/Munc13 proteins with Complex Associated with Tethering Containing Helical Rods domains in multi-subunit tethering complexes (MTCs) have been reported. MTCs coordinate multiple interactions for SNARE complex assembly at constitutive membrane fusion steps. We review aspects of these diverse tethering and priming factors to identify common operating principles.
    Frontiers in Endocrinology 12/2013; 4:187. DOI:10.3389/fendo.2013.00187
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