Nitric oxide and superoxide inhibit platelet-derived growth factor receptor phosphotyrosine phosphatases

Platelet derived growth factor receptor (PDGFR) became tyrosine autophospho rylated in rat mesangial cells shortly after platelet derived growth factor (PDGF) ligation in a tyrosine kinase inhibitor (tyrphostin AG 1296) sensit ive manner. Ligand-independent, massive tyrosine PDGFR phosphorylation was achieved by diverse NO releasing compounds. Phosphorylation was slow compar ed to PDGF, revealed a concentration- and time-dependency, and was not mimi cked by lipophilic cyclic-GMP analogues. Interleukin-1 beta / cAMP activate d mesangial cells released NO and in turn showed PDGFR phosphorylation. A N O-synthase involvement was assured by L-N-G-nitroarginine methyl ester inhi bition. PDGFR phosphorylation was also achieved by the redox cycler 2,3-dim ethoxy-1,4-naphthoquinone. NO- and O-2(.-)-evoked PGDFR phosphorylation was N-acetylcysteine reversible. Cell free dephosphorylation assays revealed P DGFR dephosphorylation by tyrosine phosphatases. Receptor dephosphorylation by cytosolic phosphatases was completed within 30 min and was sensitive to the readdition of NO donors or orthovanadate. In addition, phosphatase act ivity determined in a direct dephosphorylation assay using the substrate pa ra-nitrophenyl phosphate was attenuated by NO or vanadate. We conclude that cytosolic protein tyrosine phosphatases are targeted by exogenously suppli ed or endogenously generated NO in mesangial cells. Radical (NO. or O-2(.-) ) formation shifts the phosphorylation dephosphorylation equilibrium toward s phosphorylation, thus integrating redox-mediated responses into establish ed signal transducing pathways. (C) 1999 Elsevier Science Inc.