Distinct molecular mechanisms for protein sorting within immature secretory granules of pancreatic beta-cells.
Distinct molecular mechanisms for protein sorting within immature secretory granules of pancreatic beta-cells.
复制标题
胰腺β细胞未成熟分泌颗粒中蛋白质分类的不同分子机制。
DOI：
10.1083/jcb.126.1.77
复制
发表时间：
1994-07
影响因子：
7.8
通讯作者：
Arvan, P
中科院分区：
文献类型：
--
作者：
Kuliawat, R;Arvan, P
在胰岛的β细胞中，胰岛素作为主要蛋白质储存在储存颗粒内，所述储存颗粒响应于葡萄糖而进行调节性胞吐。通过对β细胞中放射性标记蛋白质缩合的脉冲追踪分析，调节分泌蛋白质的不溶性聚集体的形成滞后于胰岛素原向胰岛素的转化。凝聚发生在未成熟颗粒（IG）内，解释了被动蛋白分选，如通过化学计量过量的胰岛素中新合成的C肽的组成型样分泌所证明的（Kuliawat，R.，和P. Arvan。J. Cell Biol.1992. 118：521 - 529）。在体内的凝聚条件的实验操作揭示了调节分泌蛋白的分选和IGs内的聚合物组装之间的直接关系。相比之下，从trans-Golgi网络进入IGs似乎对受调节的分泌蛋白没有特别的选择性。具体而言，在正常胰岛中，溶酶体酶前体以与胰岛素原相当的效率进入刺激依赖性分泌途径。然而，在合成后2小时内（与胰岛素原加工发生的时间相同），新合成的水解酶相当有效地从刺激依赖性途径中重新定位。在衣霉素处理的胰岛中，虽然新的溶酶体酶进入受调节的分泌途径继续不受干扰，但不发生非糖基化水解酶从该途径的退出。因此，非糖基化水解酶在β细胞中的最终靶向是储存颗粒而不是溶酶体。这些结果暗示后高尔基体机制的积极清除溶酶体水解酶远离浓缩颗粒内容物在存储过程中调节分泌蛋白。
In the beta-cells of pancreatic islets, insulin is stored as the predominant protein within storage granules that undergo regulated exocytosis in response to glucose. By pulse-chase analysis of radiolabeled protein condensation in beta-cells, the formation of insoluble aggregates of regulated secretory protein lags behind the conversion of proinsulin to insulin. Condensation occurs within immature granules (IGs), accounting for passive protein sorting as demonstrated by constitutive-like secretion of newly synthesized C- peptide in stoichiometric excess of insulin (Kuliawat, R., and P. Arvan. J. Cell Biol. 1992. 118:521-529). Experimental manipulation of condensation conditions in vivo reveals a direct relationship between sorting of regulated secretory protein and polymer assembly within IGs. By contrast, entry from the trans-Golgi network into IGs does not appear especially selective for regulated secretory proteins. Specifically, in normal islets, lysosomal enzyme precursors enter the stimulus-dependent secretory pathway with comparable efficiency to that of proinsulin. However, within 2 h after synthesis (the same period during which proinsulin processing occurs), newly synthesized hydrolases are fairly efficiently relocated out of the stimulus- dependent pathway. In tunicamycin-treated islets, while entry of new lysosomal enzymes into the regulated secretory pathway continues unperturbed, exit of nonglycosylated hydrolases from this pathway does not occur. Consequently, the ultimate targeting of nonglycosylated hydrolases in beta-cells is to storage granules rather than lysosomes. These results implicate a post-Golgi mechanism for the active removal of lysosomal hydrolases away from condensed granule contents during the storage process for regulated secretory proteins.