Received for publication October 20, 2005.
Revised February 27, 2006.
Accepted for publication February 27, 2006.

Suppression of the Phosphorylation of Receptor Tyrosine Phosphatase- on a Src-independent Site Tyrosine-789 by Reactive Oxygen Species

Abstract

Oxidation of receptor protein tyrosine phosphatase- (RPTP) is emerging as an important, yet poorly characterized, regulatory mechanism for RPTP signaling in cells. RPTP 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 Tyr-789, a critical tyrosine residue for RPTP signaling that modulates the function of Grb2 and the activation of Src family kinases. In the present study, we have taken advantage of a phospho-specific antibody against Tyr-789-phosphorylated RPTP and characterized the phosphorylation of RPTP Tyr-789 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 Tyr-789 is regulated predominantly by a Src kinase inhibitor PP1-sensitive but Src/Yes/Fyn-independent tyrosine kinase in cells. We further reported a novel finding that, besides the inhibition of RPTP activity, H₂O₂ at low to moderate concentrations (50-250 µM) markedly suppressed the phosphorylation of RPTP Tyr-789 and the association of RPTP with Grb2 in cultured cells, which may result from inhibition of such a PP1-sensitive but Src/Yes/Fyn-independent tyrosine kinase. Since Tyr-789 plays an important role in RPTP signaling, our findings may provide new insights into the functional regulation of RPTP by oxidative stress in cells.

Key words: Protein tyr Phosphatases, Src and other nonreceptor tyrosine kinases, Oxidative stress