Chilcote T J, Galli T, Mundigl O, Edelmann L, McPherson P S, Takei K, De Camilli P
Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510.
J Cell Biol. 1995 Apr;129(1):219-31. doi: 10.1083/jcb.129.1.219.
There is strong evidence to indicate that proteins of the synaptobrevin family play a key role in exocytosis. Synaptobrevin 1 and 2 are expressed at high concentration in brain where they are localized on synaptic vesicles. Cellubrevin, a very similar protein, has a widespread tissue distribution and in fibroblasts is localized on endosome-derived, transferin receptor-positive vesicles. Since brain cellubrevin is not detectable in synaptic vesicles, we investigated whether cellubrevin and the synaptobrevins are differentially targeted when co-expressed in the same cell. We report that in the nervous system cellubrevin is expressed at significant levels only by glia and vascular cells. However, cellubrevin is coexpressed with the two synaptobrevins in PC12 cells, a neuroendocrine cell line which contains synaptic vesicle-like microvesicles. In PC12 cells, cellubrevin has a distribution very similar to that of synaptobrevin 1 and 2. The three proteins are targeted to neurites which exclude the transferrin receptor and are enriched in synaptic-like microvesicles and dense-core granules. They are recovered in the synaptic-like microvesicle peak of glycerol velocity gradients, have a similar distribution in isopycnic fractionation and are coprecipitated by anti-synaptobrevin 2 immunobeads. Finally, cellubrevin, like the synaptobrevins, interact with the neuronal t-SNAREs syntaxin 1 and SNAP-25. These results suggest that cellubrevin and the synaptobrevins have similar function and do not play a specialized role in constitutive and regulated exocytosis, respectively.
有强有力的证据表明，突触小泡蛋白家族的蛋白质在胞吐作用中起关键作用。突触小泡蛋白1和2在大脑中高浓度表达，定位于突触小泡上。细胞ubrevin是一种非常相似的蛋白质，具有广泛的组织分布，在成纤维细胞中定位于内体来源的、转铁蛋白受体阳性的小泡上。由于在突触小泡中检测不到脑细胞ubrevin，我们研究了在同一细胞中共表达时，细胞ubrevin和突触小泡蛋白是否有不同的靶向定位。我们报告，在神经系统中，细胞ubrevin仅在神经胶质细胞和血管细胞中高水平表达。然而，细胞ubrevin与两种突触小泡蛋白在PC12细胞中共表达，PC12细胞是一种神经内分泌细胞系，含有突触小泡样微泡。在PC12细胞中，细胞ubrevin的分布与突触小泡蛋白1和2非常相似。这三种蛋白质靶向于不含转铁蛋白受体且富含突触样微泡和致密核心颗粒的神经突。它们在甘油速度梯度的突触样微泡峰中回收，在等密度分级分离中有相似的分布，并被抗突触小泡蛋白2免疫磁珠共沉淀。最后，细胞ubrevin与突触小泡蛋白一样，与神经元t-SNARE蛋白 syntaxin 1和SNAP-25相互作用。这些结果表明，细胞ubrevin和突触小泡蛋白具有相似的功能，在组成型和调节型胞吐作用中不分别发挥特殊作用。
