INSULIN-RECEPTOR AUTOPHOSPHORYLATION SITES TYROSINE-1162 AND TYROSINE-1163 CONTROL BOTH INSULIN-DEPENDENT AND INSULIN-INDEPENDENT RECEPTOR INTERNALIZATION PATHWAYS

We previously reported that Chinese hamster ovary (CHO) cell lines ove rexpressing mutated human insulin receptors (hIRs) in which the tyrosi ne residues 1162 and 1163 were replaced by phenylalanines (CHO-Y2) exh ibited a marked defect in hormone-induced receptor internalization as compared to CHO transfectants overexpressing wild-type hIRs (CHO-R). T hese two cell lines are now used to compare the role of tyrosines 1162 -1163 in basal and ligand-stimulated receptor internalization as well as in receptor turnover. We show here that (1) in CHO-Y2 cells, basal endocytosis, like insulin-induced internalization, was markedly altere d despite normal receptor turnover and (2) in both CHO-R and CHO-Y2 ce lls, basal receptor endocytosis was altered by tunicamycin, an inhibit or of protein N-glycosylation, whereas insulin-induced internalization was not. These results support a role for tyrosines 1162-1163 of the IR beta subunit major autophosphorylation domain in both basal and lig and-stimulated receptor endocytosis and provide evidence that the two processes follow distinct pathways.