Disdier M, Morrissey J H, Fugate R D, Bainton D F, McEver R P
Department of Medicine, St. Francis Medical Research Institute, University of Oklahoma Health Sciences Center, Oklahoma City.
Mol Biol Cell. 1992 Mar;3(3):309-21. doi: 10.1091/mbc.3.3.309.
P-selectin (CD62), formerly called GMP-140 or PADGEM, is a membrane protein located in secretory storage granules of platelets and endothelial cells. To study the mechanisms responsible for the targeting of P-selectin to storage granules, we transfected its cDNA into COS-7 and CHO-K1 cells, which lack a regulated exocytic pathway, or into AtT20 cells, which are capable of regulated secretion. P-selectin was expressed on the plasma membrane of COS-7 and CHO-K1 cells but was concentrated in storage granules of AtT20 cells. Immunogold electron microscopy indicated that the electron-dense granules containing P-selectin in AtT20 cells also stored the endogenous soluble hormone ACTH. Activation of AtT20 cells with 8-Br-cAMP increased the surface expression of P-selectin, consistent with agonist-induced fusion of granule membranes with the plasma membrane. Deletion of the last 23 amino acids of the 35-residue cytoplasmic domain resulted in delivery of P-selectin to the plasma membrane of AtT20 cells. Replacement of the cytoplasmic tail of tissue factor, a plasma membrane protein, with the cytoplasmic domain of P-selectin redirected the chimeric molecule to granules. We conclude that the cytoplasmic domain of P-selectin is both necessary and sufficient for sorting of membrane proteins into the regulated pathway of secretion.
P选择素（CD62），以前称为GMP-140或血小板活化依赖性颗粒外膜蛋白，是一种位于血小板和内皮细胞分泌性储存颗粒中的膜蛋白。为了研究P选择素靶向储存颗粒的机制，我们将其cDNA转染到缺乏调节性胞吐途径的COS-7和CHO-K1细胞中，或转染到能够进行调节性分泌的AtT20细胞中。P选择素在COS-7和CHO-K1细胞的质膜上表达，但在AtT20细胞的储存颗粒中浓缩。免疫金电子显微镜显示，AtT20细胞中含有P选择素的电子致密颗粒也储存内源性可溶性激素促肾上腺皮质激素（ACTH）。用8-溴环磷酸腺苷（8-Br-cAMP）激活AtT20细胞可增加P选择素的表面表达，这与激动剂诱导颗粒膜与质膜融合一致。缺失35个氨基酸的胞质结构域的最后23个氨基酸导致P选择素转运到AtT20细胞的质膜上。用P选择素的胞质结构域替换组织因子（一种质膜蛋白）的胞质尾巴，可使嵌合分子重新定向到颗粒中。我们得出结论，P选择素的胞质结构域对于将膜蛋白分选到调节性分泌途径中既是必要的也是充分的。
