EVIDENCE AGAINST DEPHOSPHORYLATION OF INSULIN-ELICITED PHOSPHOTYROSINE PROTEINS IN-VIVO BY THE PHOSPHATASE PTP2C

In order to determine whether the tyrosine phosphatase PTP2C dephospho rylates insulin-elicited phosphotyrosine proteins in vivo, we have com pared the patterns of protein tyrosine phosphorylation and its reversa l in the kidney 293 cell line with those in 293 cell lines overexpress ing PTP2C and a catalytically inactive point mutant of PTP2C. In all t hree cell types insulin caused the rapid tyrosine phosphorylation of a 160 kD protein, which was shown not to be the insulin receptor substr ate 1 (IRS-1) and may be the recently described IRS-2 as well as that of a 100 kD polypeptide, which is probably a mixture of the beta subun its of the insulin and insulinlike growth factor I receptors. There wa s no difference among the three cell lines in the extent of tyrosine p hosphorylation or in the rate of its reversal upon insulin withdrawal. These results indicate that PTP2C does not function to dephosphorylat e these proteins significantly in vivo. (C) 1995 Academic Press, Inc.