Black Virginia H, Sanjay Archana, van Leyen Klaus, Lauring Brett, Kreibich Gert
Department of Cell Biology and Kaplan Cancer Center, New York University School of Medicine, 550 First Avenue, New York, New York 10016, USA.
Endocrinology. 2005 Oct;146(10):4234-49. doi: 10.1210/en.2005-0372. Epub 2005 Jun 9.
Steroid-secreting cells are characterized by abundant smooth endoplasmic reticulum whose membranes contain many enzymes involved in sterol and steroid synthesis. Yet they have relatively little morphologically identifiable rough endoplasmic reticulum, presumably required for synthesis and maintenance of the smooth membranes. In this study, we demonstrate that adrenal smooth microsomal subfractions enriched in smooth endoplasmic reticulum membranes contain high levels of translocation apparatus and oligosaccharyltransferase complex proteins, previously thought confined to rough endoplasmic reticulum. We further demonstrate that these smooth microsomal subfractions are capable of effecting cotranslational translocation, signal peptide cleavage, and N-glycosylation of newly synthesized polypeptides. This shifts the paradigm for distinction between smooth and rough endoplasmic reticulum. Confocal microscopy revealed the proteins to be distributed throughout the abundant tubular endoplasmic reticulum in these cells, which is predominantly smooth surfaced. We hypothesize that the broadly distributed translocon and oligosaccharyltransferase proteins participate in local synthesis and/or quality control of membrane proteins involved in cholesterol and steroid metabolism in a sterol-dependent and hormonally regulated manner.
分泌类固醇的细胞的特征是有丰富的滑面内质网，其膜上含有许多参与甾醇和类固醇合成的酶。然而，它们在形态上可识别的粗面内质网相对较少，而粗面内质网大概是合成和维持滑面膜所必需的。在本研究中，我们证明富含滑面内质网膜的肾上腺滑面微粒体亚组分含有高水平的转位装置和寡糖基转移酶复合物蛋白，这些蛋白以前被认为只存在于粗面内质网中。我们进一步证明，这些滑面微粒体亚组分能够对新合成的多肽进行共翻译转位、信号肽切割和N-糖基化。这改变了区分滑面内质网和粗面内质网的范例。共聚焦显微镜显示这些蛋白分布在这些细胞中丰富的管状内质网中，内质网主要是光滑表面的。我们推测，广泛分布的转位子和寡糖基转移酶蛋白以甾醇依赖和激素调节的方式参与胆固醇和类固醇代谢相关膜蛋白的局部合成和/或质量控制。
