Galli T, Zahraoui A, Vaidyanathan V V, Raposo G, Tian J M, Karin M, Niemann H, Louvard D
Centre National de la Recherche Scientifique Unité Mixte de Recherche 144 "Compartimentation et Dynamique Cellulaires," Institut Curie, F-75248 Paris Cedex 05, France.
Mol Biol Cell. 1998 Jun;9(6):1437-48. doi: 10.1091/mbc.9.6.1437.
The importance of soluble N-ethyl maleimide (NEM)-sensitive fusion protein (NSF) attachment protein (SNAP) receptors (SNAREs) in synaptic vesicle exocytosis is well established because it has been demonstrated that clostridial neurotoxins (NTs) proteolyze the vesicle SNAREs (v-SNAREs) vesicle-associated membrane protein (VAMP)/brevins and their partners, the target SNAREs (t-SNAREs) syntaxin 1 and SNAP25. Yet, several exocytotic events, including apical exocytosis in epithelial cells, are insensitive to numerous clostridial NTs, suggesting the presence of SNARE-independent mechanisms of exocytosis. In this study we found that syntaxin 3, SNAP23, and a newly identified VAMP/brevin, tetanus neurotoxin (TeNT)-insensitive VAMP (TI-VAMP), are insensitive to clostridial NTs. In epithelial cells, TI-VAMP-containing vesicles were concentrated in the apical domain, and the protein was detected at the apical plasma membrane by immunogold labeling on ultrathin cryosections. Syntaxin 3 and SNAP23 were codistributed at the apical plasma membrane where they formed NEM-dependent SNARE complexes with TI-VAMP and cellubrevin. We suggest that TI-VAMP, SNAP23, and syntaxin 3 can participate in exocytotic processes at the apical plasma membrane of epithelial cells and, more generally, domain-specific exocytosis in clostridial NT-resistant pathways.
可溶性N - 乙基马来酰亚胺（NEM）敏感融合蛋白（NSF）附着蛋白（SNAP）受体（SNAREs）在突触小泡胞吐作用中的重要性已得到充分证实，因为已经证明梭菌神经毒素（NTs）可蛋白酶解小泡SNAREs（v - SNAREs）——小泡相关膜蛋白（VAMP）/布雷文蛋白及其伙伴，即靶标SNAREs（t - SNAREs）—— syntaxin 1和SNAP25。然而，包括上皮细胞顶端胞吐作用在内的几种胞吐事件对多种梭菌NTs不敏感，这表明存在不依赖SNAREs的胞吐机制。在本研究中，我们发现syntaxin 3、SNAP23以及一种新鉴定出的VAMP/布雷文蛋白——破伤风神经毒素（TeNT）不敏感的VAMP（TI - VAMP），对梭菌NTs不敏感。在上皮细胞中，含有TI - VAMP的小泡集中在顶端区域，通过超薄冷冻切片上的免疫金标记在顶端质膜上检测到了该蛋白。Syntaxin 3和SNAP23在顶端质膜上共分布，在那里它们与TI - VAMP和细胞布雷文蛋白形成了依赖NEM的SNARE复合物。我们认为TI - VAMP、SNAP23和syntaxin 3可以参与上皮细胞顶端质膜的胞吐过程，更普遍地说，可以参与梭菌NTs抗性途径中的区域特异性胞吐作用。
