Fukuda Mitsunori, Kowalchyk Judith A, Zhang Xiaodong, Martin Thomas F J, Mikoshiba Katsuhiko
Laboratory for Developmental Neurobiology, Brain Science Institute, RIKEN (The Institute of Physical and Chemical Research), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
J Biol Chem. 2002 Feb 15;277(7):4601-4. doi: 10.1074/jbc.C100588200. Epub 2001 Dec 21.
Synaptotagmin (Syt) I-deficient phaeochromocytoma (PC12) cell lines show normal Ca(2+)-dependent norepinephrine (NE) release (Shoji-Kasai, Y., Yoshida, A., Sato, K., Hoshino, T., Ogura, A., Kondo, S., Fujimoto, Y., Kuwahara, R., Kato, R., and Takahashi, M. (1992) Science 256, 1821-1823). To identify an alternative Ca(2+) sensor, we searched for other Syt isoforms in Syt I-deficient PC12 cells and identified Syt IX, an isoform closely related to Syt I, as an abundantly expressed dense-core vesicle protein. Here we show that Syt IX is required for the Ca(2+)-dependent release of NE from PC12 cells. Antibodies directed against the C2A domain of either Syt IX or Syt I inhibited Ca(2+)-dependent NE release in permeable PC12 cells indicating that both Syt proteins function in dense-core vesicle exocytosis. Our results support the idea that Syt family proteins that co-reside on secretory vesicles may function cooperatively and redundantly as potential Ca(2+) sensors for exocytosis.
突触结合蛋白（Syt）I缺陷的嗜铬细胞瘤（PC12）细胞系显示出正常的钙（Ca2+）依赖性去甲肾上腺素（NE）释放（庄司-笠井，Y.，吉田，A.，佐藤，K.，星野，T.，小仓，A.，近藤，S.，藤本，Y.，桑原，R.，加藤，R.，以及高桥，M.（1992年）《科学》256，1821 - 1823）。为了鉴定另一种钙（Ca2+）传感器，我们在Syt I缺陷的PC12细胞中寻找其他Syt异构体，并鉴定出Syt IX，一种与Syt I密切相关的异构体，作为一种大量表达的致密核心囊泡蛋白。在此我们表明，Syt IX是PC12细胞中钙（Ca2+）依赖性NE释放所必需的。针对Syt IX或Syt I的C2A结构域的抗体抑制了可渗透PC12细胞中钙（Ca2+）依赖性NE释放，表明这两种Syt蛋白在致密核心囊泡胞吐作用中发挥作用。我们的结果支持这样一种观点，即共同存在于分泌囊泡上的Syt家族蛋白可能作为胞吐作用的潜在钙（Ca2+）传感器协同且冗余发挥作用。
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