Brion C, Miller S G, Moore H P
Department of Cell and Molecular Biology, University of California, Berkeley 94720.
J Biol Chem. 1992 Jan 25;267(3):1477-83.
Many neural and endocrine cells possess two pathways of secretion: a regulated pathway and a constitutive pathway. Peptide hormones are stored in granules which undergo regulated release whereas other surface-bound proteins are externalized constitutively via a distinct set of vesicles. An important issue is whether proper function of these pathways requires continuous protein synthesis. Wieland et al. (Wieland, F.T., Gleason, M.L., Serafini, T.A., and Rothman, J.E. (1987) Cell 50, 289-300) have shown that a tripeptide containing the sequence Asn-Tyr-Thr can be glycosylated in intracellular compartments and secreted efficiently from Chinese hamster ovary and HepG2 cells, presumably via the constitutive secretory pathway. Secretion is not affected by cycloheximide, suggesting that operation of this pathway does not require components supplied by new protein synthesis. In this report we determined the effects of protein synthesis inhibitor on membrane traffic to the regulated secretory pathway in the mouse pituitary AtT-20 cells. We examined transport of glycosaminoglycan chains since previous studies have shown that these chains enter the regulated secretory pathways and are packaged along with the hormone adrenocorticotropin (ACTH). We found that cycloheximide treatment severely impairs the cell's ability to store and secrete glycosaminoglycan chains by the regulated secretory pathway. In marked contrast, constitutive secretion of glycosaminoglycan chains remains unhindered in the absence of protein synthesis. The differential requirements for protein synthesis indicate differences in the mechanisms for sorting and/or transport of molecules through the constitutive and the regulated secretory pathways. We discuss the possible mechanisms by which protein synthesis may influence trafficking of glycosaminoglycan chains to the regulated secretory pathway.
调节性途径和组成性途径。肽类激素储存在颗粒中，通过调节性释放，而其他表面结合蛋白则通过一组不同的囊泡持续地被转运到细胞外。一个重要的问题是这些途径的正常功能是否需要持续的蛋白质合成。维兰德等人（维兰德，F.T.，格里森，M.L.，塞拉菲尼，T.A.，和罗斯曼，J.E.（1987年）《细胞》50卷，289 - 300页）已经表明，一个含有天冬酰胺 - 酪氨酸 - 苏氨酸序列的三肽可以在内细胞区室中被糖基化，并从中国仓鼠卵巢细胞和肝癌细胞系HepG2细胞中有效地分泌出来，大概是通过组成性分泌途径。分泌不受放线菌酮的影响，这表明该途径的运作不需要新蛋白质合成所提供的成分。在本报告中，我们确定了蛋白质合成抑制剂对小鼠垂体AtT - 20细胞中调节性分泌途径的膜转运的影响。我们研究了糖胺聚糖链的转运，因为先前的研究表明这些链进入调节性分泌途径，并与促肾上腺皮质激素（ACTH）一起被包装。我们发现，放线菌酮处理严重损害了细胞通过调节性分泌途径储存和分泌糖胺聚糖链的能力。与之形成鲜明对比的是，在没有蛋白质合成的情况下，糖胺聚糖链的组成性分泌仍然不受阻碍。对蛋白质合成的不同需求表明，分子通过组成性和调节性分泌途径进行分选和/或转运的机制存在差异。我们讨论了蛋白质合成可能影响糖胺聚糖链向调节性分泌途径转运的可能机制。
