Burgess T L, Craik C S, Kelly R B
J Cell Biol. 1985 Aug;101(2):639-45. doi: 10.1083/jcb.101.2.639.
The exocrine protein rat anionic trypsinogen has been expressed and is secreted from the murine anterior pituitary tumor cell line AtT-20. We examined which secretory pathway trypsinogen takes to the surface of this endocrine-derived cell line. The "constitutive" pathway externalizes proteins rapidly and in the absence of an external stimulus. In the alternate, "regulated" pathway, proteins are stored in secretory granules until the cells are stimulated to secrete with 8-Br-cAMP. On the basis of indirect immunofluorescence localization, stimulation of release, and subcellular fractionation, we find that trypsinogen is targeted into the regulated secretory pathway in AtT-20 cells. In contrast, laminin, an endogenous secretory glycoprotein, is shown to be secreted constitutively. Thus it appears that the transport apparatus for the regulated secretory pathway in endocrine cells can recognize not only endocrine prohormones, but also the exocrine protein trypsinogen, which suggests that a similar sorting mechanism is used by endocrine and exocrine cells.
外分泌蛋白大鼠阴离子胰蛋白酶原已在小鼠垂体前叶肿瘤细胞系AtT-20中表达并分泌。我们研究了胰蛋白酶原通过何种分泌途径到达这种内分泌来源细胞系的表面。“组成型”途径可在无外部刺激的情况下快速将蛋白质转运至细胞外。在另一种“调节型”途径中，蛋白质储存在分泌颗粒中，直到细胞受到8-溴环磷酸腺苷刺激才分泌。基于间接免疫荧光定位、释放刺激和亚细胞分级分离，我们发现胰蛋白酶原在AtT-20细胞中靶向进入调节型分泌途径。相比之下，内源性分泌糖蛋白层粘连蛋白则以组成型方式分泌。因此，内分泌细胞中调节型分泌途径的转运装置似乎不仅能识别内分泌前体激素，还能识别外分泌蛋白胰蛋白酶原，这表明内分泌细胞和外分泌细胞使用了类似的分选机制。
