Cell Growth & Differentiation, Vol 4, Issue 5 403-410, Copyright © 1993 by American Association of Cancer Research

ARTICLES

Altered glycosylation of the env-sea oncoprotein inhibits intracellular transport and transformation

AJ Crowe and MJ Hayman
Department of Microbiology, State University of New York, Stony Brook 11794.

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.

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				C. Y. Park and M. J. Hayman The Tyrosines in the Bidentate Motif of the env-sea Oncoprotein Are Essential for Cell Transformation and Are Binding Sites for Grb2 and the Tyrosine Phosphatase SHP-2 J. Biol. Chem., March 12, 1999; 274(11): 7583 - 7590. [Abstract] [Full Text] [PDF]