Crowe A J, Hayman M J
Department of Microbiology, State University of New York, Stony Brook 11794.
Cell Growth Differ. 1993 May;4(5):403-10.
The transforming gene product of the S13 avian erythroblastosis virus, env-sea, is a member of the growth factor receptor class of tyrosine kinases. The env-sea precursor protein gp155env-sea is proteolytically processed into the mature cleavage products gp85env and gp70env-sea, which are subsequently terminally glycosylated and transported to the cell surface. Previous studies have shown that the abnormal glycosylation of gp155env-sea induced by the carbohydrate processing inhibitor castanospermine blocks the proteolytic cleavage of gp155env-sea and impairs its transforming ability. We have shown recently that an uncleaved but fully glycosylated sea-encoded protein retains the ability to transform chicken embryo fibroblasts, indicating that proteolytic processing is not essential for transformation by the env-sea tyrosine kinase. To address the question of how castanospermine blocks transformation by env-sea, differential sucrose gradient centrifugation was performed on env-sea-transformed cells treated with the inhibitor. This report shows that no surface forms of env-sea could be detected in inhibitor-treated cells, suggesting that castanospermine acts by blocking the transport of sea-encoded proteins to the cell surface.
S13禽成红细胞增多症病毒的转化基因产物env-sea是酪氨酸激酶生长因子受体家族的成员。env-sea前体蛋白gp155env-sea经蛋白水解加工成成熟的裂解产物gp85env和gp70env-sea，随后进行终末糖基化并转运至细胞表面。先前的研究表明，碳水化合物加工抑制剂栗精胺诱导的gp155env-sea异常糖基化会阻断gp155env-sea的蛋白水解裂解，并损害其转化能力。我们最近发现，一种未裂解但完全糖基化的sea编码蛋白保留了转化鸡胚成纤维细胞的能力，这表明蛋白水解加工对于env-sea酪氨酸激酶的转化并非必不可少。为了解决栗精胺如何阻断env-sea转化的问题，对用该抑制剂处理的env-sea转化细胞进行了差速蔗糖梯度离心。本报告表明，在抑制剂处理的细胞中未检测到env-sea的表面形式，这表明栗精胺通过阻断sea编码蛋白向细胞表面的转运而起作用。
