Suppression of the phosphorylation of receptor tyrosine phosphatase-α on the Src-independent site tyrosine 789 by reactive oxygen species

Oxidation of receptor protein tyrosine phosphatase-alpha (RPTP alpha) is emerging as an important yet poorly characterized regulatory mechanism for RPTP alpha signaling in cells. RPTP alpha has been shown to be reversibly oxidized and inhibited by reactive oxygen species. However, it is not known whether oxidative stress could regulate the phosphorylation of Tyr789, a critical tyrosine residue for RPTP alpha signaling that modulates the function of Grb2 and the activation of Src family kinases. In the present study, we have taken advantage of a phosphospecific antibody against Tyr789-phosphorylated RPTP alpha and characterized the phosphorylation of RPTP alpha Tyr789 in various cultured cells, including SYF cells lacking all three ubiquitously expressed members (Src, Yes, and Fyn) of Src family kinases. We have obtained substantial evidence indicating that the phosphorylation of RPTP alpha Tyr789 is regulated predominantly by an Src kinase inhibitor, protein phosphatase 1 (PP1)-sensitive but Src/Yes/Fyn- independent tyrosine kinase, in cells. We further reported a novel finding that, besides the inhibition of RPTP alpha's activity, H2O2 at low to moderate concentrations (50-250 mu M) markedly suppressed the phosphorylation of RPTP alpha Tyr789 and the association of RPTP alpha with Grb2 in cultured cells, which may result from inhibition of such a PP1- sensitive but Src/Yes/Fyn-independent tyrosine kinase. Because Tyr789 plays an important role in RPTP alpha signaling, our findings may provide new insights into the functional regulation of RPTP alpha by oxidative stress in cells.