Marshall Misty R, Pattu Varsha, Halimani Mahantappa, Maier-Peuschel Monika, Müller Martha-Lena, Becherer Ute, Hong Wanjin, Hoth Markus, Tschernig Thomas, Bryceson Yenan T, Rettig Jens
Cellular Neurophysiology, Center for Integrative Physiology and Molecular Medicine, Saarland University, 66421 Homburg, Germany Department of Medicine, Center For Infectious Medicine, 14186 Stockholm, Sweden.
Cellular Neurophysiology, Center for Integrative Physiology and Molecular Medicine, Saarland University, 66421 Homburg, Germany.
J Cell Biol. 2015 Jul 6;210(1):135-51. doi: 10.1083/jcb.201411093. Epub 2015 Jun 29.
Cytotoxic T lymphocytes (CTLs) eliminate infected and neoplastic cells through directed release of cytotoxic granule contents. Although multiple SNARE proteins have been implicated in cytotoxic granule exocytosis, the role of vesicular SNARE proteins, i.e., vesicle-associated membrane proteins (VAMPs), remains enigmatic. VAMP8 was posited to represent the cytotoxic granule vesicular SNARE protein mediating exocytosis in mice. In primary human CTLs, however, VAMP8 colocalized with Rab11a-positive recycling endosomes. Upon stimulation, these endosomes rapidly trafficked to and fused with the plasma membrane, preceding fusion of cytotoxic granules. Knockdown of VAMP8 blocked both recycling endosome and cytotoxic granule fusion at immune synapses, without affecting activating signaling. Mechanistically, VAMP8-dependent recycling endosomes deposited syntaxin-11 at immune synapses, facilitating assembly of plasma membrane SNARE complexes for cytotoxic granule fusion. Hence, cytotoxic granule exocytosis is a sequential, multivesicle fusion process requiring VAMP8-mediated recycling endosome fusion before cytotoxic granule fusion. Our findings imply that secretory granule exocytosis pathways in other cell types may also be more complex than previously appreciated.
细胞毒性T淋巴细胞（CTLs）通过定向释放细胞毒性颗粒内容物来清除受感染细胞和肿瘤细胞。尽管多种SNARE蛋白与细胞毒性颗粒胞吐作用有关，但囊泡SNARE蛋白，即囊泡相关膜蛋白（VAMPs）的作用仍不清楚。VAMP8被认为是介导小鼠细胞毒性颗粒胞吐作用的囊泡SNARE蛋白。然而，在原代人CTL中，VAMP8与Rab11a阳性再循环内体共定位。受到刺激后，这些内体迅速运输到质膜并与之融合，先于细胞毒性颗粒的融合。敲低VAMP8可阻断免疫突触处再循环内体和细胞毒性颗粒的融合，而不影响激活信号。从机制上讲，VAMP8依赖性再循环内体在免疫突触处沉积Syntaxin-11，促进质膜SNARE复合物组装以便细胞毒性颗粒融合。因此，细胞毒性颗粒胞吐作用是一个顺序性的多泡融合过程，在细胞毒性颗粒融合之前需要VAMP8介导的再循环内体融合。我们的研究结果表明，其他细胞类型中的分泌颗粒胞吐途径可能也比之前认为的更为复杂。
