The SNARE Sec22b has a non-fusogenic function in plasma membrane expansion

Petković, Maja; Jemaiel, Aymen; Daste, Frédéric; Specht, Christian G.; Izeddin, Ignacio; Vorkel, Daniela; Verbavatz, Jean‐Marc; Darzacq, Xavier; Triller, Antoine; Pfenninger, Karl H.; Tareste, David; Jackson, Catherine; Galli, Thierry

doi:10.1038/ncb2937

Cited by 129 publications

(178 citation statements)

References 74 publications

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“…In response to strong elevations of cytosolic Ca 2+ , the recruitment of E-Syt1 to the cell cortex correlated with a reduction of the length of E-Syt1-dependent ER to PM tethers indicating a dynamic conformational change (shortening) of the cytosolic portion of E-Syt1. Modulation of ER-PM distance by tethering molecules also was previously reported by other studies (11,31). Because we previously have shown that the C2C domain of E-Syt1 is required for the binding of E-Syt1 to the PM in a cytosolic Ca 2+ -dependent manner (20), we speculate that the reduction of ER-PM distance in E-Syt1-mediated contacts upon elevation of cytosolic Ca 2+ could be accounted by the interaction of its C2C domain with the PM.…”

Section: Discussionsupporting

confidence: 84%

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Three-dimensional architecture of extended synaptotagmin-mediated endoplasmic reticulum–plasma membrane contact sites

Fernández-Busnadiego

Saheki

Camilli

2015

Proc. Natl. Acad. Sci. U.S.A.

204

251

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The close apposition between the endoplasmic reticulum (ER) and the plasma membrane (PM) plays important roles in Ca 2+ homeostasis, signaling, and lipid metabolism. The extended synaptotagmins (E-Syts; tricalbins in yeast) are ER-anchored proteins that mediate the tethering of the ER to the PM and are thought to mediate lipid transfer between the two membranes. E-Syt cytoplasmic domains comprise a synaptotagmin-like mitochondrial-lipidbinding protein (SMP) domain followed by five C2 domains in E-Syt1 and three C2 domains in E-Syt2/3. Here, we used cryo-electron tomography to study the 3D architecture of E-Syt-mediated ER-PM contacts at molecular resolution. In vitrified frozen-hydrated mammalian cells overexpressing individual E-Syts, in which E-Sytdependent contacts were by far the predominant contacts, ER-PM distance (19-22 nm) correlated with the amino acid length of the cytosolic region of E-Syts (i.e., the number of C2 domains). Elevation of cytosolic Ca 2+ shortened the ER-PM distance at E-Syt1-dependent contacts sites. E-Syt-mediated contacts displayed a characteristic electron-dense layer between the ER and the PM. These features were strikingly different from those observed in cells exposed to conditions that induce contacts mediated by the stromal interaction molecule 1 (STIM1) and the Ca 2+ channel Orai1 as well as store operated Ca 2+ entry. In these cells the gap between the ER and the PM was spanned by filamentous structures perpendicular to the membranes. Our results define specific ultrastructural features of E-Syt-dependent ER-PM contacts and reveal their structural plasticity, which may impact on the cross-talk between the ER and the PM and the functions of E-Syts in lipid transport between the two bilayers.T he endoplasmic reticulum (ER) consists of a complex network of tubules and cisternae that extends throughout the cell and forms close appositions ("contact sites") with other membranous organelles and with the plasma membrane (PM) (1, 2). The best characterized function of ER-PM contacts is in Ca 2+ homeostasis, as ER-PM contacts mediate the excitationcontraction coupling in muscle and store-operated Ca 2+ entry (SOCE) in all metazoan cells. In SOCE, upon depletion of Ca 2+ in the ER, the ER protein stromal interaction molecule 1 (STIM1) oligomerizes, binds, and activates Orai1 Ca 2+ channels at the PM to drive influx of extracellular Ca 2+ , thereby allowing homeostatic regulation of ER Ca 2+ levels (3, 4). However, growing evidence suggests that ER-PM contacts also play more general roles, including signaling (5, 6) and the regulation of both lipid metabolism and transport between bilayers (1, 7-17).We recently have shown that the three mammalian extended synaptotagmins (E-Syts), homologs of the yeast tricalbins (18,19), act as ER-PM tethers (20). E-Syts are ER-anchored proteins (via an N-terminal hairpin) containing a synaptotagmin-like mitochondrial-lipid-binding protein (SMP) domain followed by five (E-Syt1) or three (E-Syt2/3) C2 domains. SMP domains are present in proteins that loc...

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Section: Discussionsupporting

confidence: 84%

“…ER-PM contacts are observed frequently in neurons (25,(28)(29)(30)(31). Thus, to complement our overexpression experiments, we analyzed native ER-PM contacts in untransfected neurons cultured on EM grids.…”

Section: Significancementioning

confidence: 99%

Three-dimensional architecture of extended synaptotagmin-mediated endoplasmic reticulum–plasma membrane contact sites

Fernández-Busnadiego

Saheki

Camilli

2015

Proc. Natl. Acad. Sci. U.S.A.

204

251

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“…VAMP7 and Sec22b contain a C-terminal transmembrane domain, whereas Ykt6 is targeted to membranes through two lipid anchors and also exists as a soluble cytosolic pool (Figs 1 and 2). These three proteins are enriched in neurons, where they have important functions such as plasma membrane expansion during neuronal development (Rossi et al, 2004;Petkovic et al, 2014). Interestingly, the pollen VAMP7-like protein PiVAMP726 also mediates membrane fusion during pollen tube tip growth in plants (Guo and McCubbin, 2012), suggesting that longin SNAREs perform specialized functions related to membrane growth and remodelling that are conserved across different kingdoms.…”

Section: Longin-snare Proteinsmentioning

confidence: 99%

“…Similarly, the vacuoles of dendritic cells that contain the parasite Toxoplasma gondii require Sec22b to mature and function properly (Cebrian et al, 2011). We have recently shown that Sec22b also plays an important physiological role in neurons because it is required for plasma membrane expansion during neuronal development (Petkovic et al, 2014). To perform this function, Sec22b interacts with the plasma membrane t-SNARE syntaxin1A to bring the ER and plasma membranes into close proximity, but without inducing their fusion.…”

Section: Sec22bmentioning

confidence: 99%

Structure and function of longin SNAREs

Daste

Galli

Tareste

2015

Journal of Cell Science

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Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins constitute the core membrane fusion machinery of intracellular transport and intercellular communication.A little more than ten years ago, it was proposed that the long N-terminal domain of a subset of SNAREs, henceforth called the longin domain, could be a crucial regulator with multiple functions in membrane trafficking. Structural, biochemical and cell biology studies have now produced a large set of data that support this hypothesis and indicate a role for the longin domain in regulating the sorting and activity of SNAREs. Here, we review the first decade of structurefunction data on the three prototypical longin SNAREs: Ykt6, VAMP7 and Sec22b. We will, in particular, highlight the conserved molecular mechanisms that allow longin domains to fold back onto the fusioninducing SNARE coiled-coil domain, thereby inhibiting membrane fusion, and describe the interactions of longin SNAREs with proteins that regulate their intracellular sorting. This dual function of the longin domain in regulating both the membrane localization and membrane fusion activity of SNAREs points to its role as a key regulatory module of intracellular trafficking.

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“…Specifically, mouse Sec22b has been demonstrated to localize to the ER-Golgi intermediate compartment (ERGIC) to deliver ER proteins to phagosomes in dendritic cells (Cebrian et al 2011). In addition, human Sec22b as well as S. cerevisiae Sec22 can mediate ER-plasma membrane contact in a nonfusogenic manner, facilitating membrane expansion during cell growth (Petkovic et al 2014). In C. elegans, SEC-22 has not previously been investigated apart from the observation that SEC-22 depletion by RNAi results in increased accumulation of α-synuclein:: GFP aggregates and neurodegeneration in a Parkinson model (Hamamichi et al 2008).…”

Section: Resultsmentioning

confidence: 99%

The conserved SNARE SEC-22 localizes to late endosomes and negatively regulates RNA interference in Caenorhabditis elegans

Zhao

Holmgren

Hinas

2016

RNA

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Small RNA pathways, including RNA interference (RNAi), play crucial roles in regulation of gene expression. Initially considered to be cytoplasmic, these processes have later been demonstrated to associate with membranes. For example, maturation of late endosomes/multivesicular bodies (MVBs) is required for efficient RNAi, whereas fusion of MVBs to lysosomes appears to reduce silencing efficiency. SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) mediate membrane fusion and are thus at the core of membrane trafficking. In spite of this, no SNARE has previously been reported to affect RNAi. Here, we demonstrate that in Caenorhabditis elegans, loss of the conserved SNARE SEC-22 results in enhanced RNAi upon ingestion of double-stranded RNA. Furthermore, SEC-22 overexpression inhibits RNAi in wild-type animals. We find that overexpression of SEC-22 in the target tissue (body wall muscle) strongly suppresses the sec-22(−) enhanced RNAi phenotype, supporting a primary role for SEC-22 in import of RNAi silencing signals or cell autonomous RNAi. A functional mCherry::SEC-22 protein localizes primarily to late endosomes/MVBs and these compartments are enlarged in animals lacking sec-22. SEC-22 interacts with late endosome-associated RNA transport protein SID-5 in a yeast two-hybrid assay and functions in a sid-5-dependent manner. Taken together, our data indicate that SEC-22 reduces RNAi efficiency by affecting late endosome/MVB function, for example, by promoting fusion between late endosomes/MVBs and lysosomes. To our knowledge, this is the first report of a SNARE with a function in small RNA-mediated gene silencing.

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The SNARE Sec22b has a non-fusogenic function in plasma membrane expansion

Cited by 129 publications

References 74 publications

Three-dimensional architecture of extended synaptotagmin-mediated endoplasmic reticulum–plasma membrane contact sites

Three-dimensional architecture of extended synaptotagmin-mediated endoplasmic reticulum–plasma membrane contact sites

Structure and function of longin SNAREs

The conserved SNARE SEC-22 localizes to late endosomes and negatively regulates RNA interference in Caenorhabditis elegans

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