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Tyrosine nitration by peroxynitrite can affect signal transduction pathways involving tyrosine phosphorylation. The present study was undertaken to investigate the effects of peroxynitrite-induced protein tyrosine nitration on insulin-stimulated tyrosine phosphorylation in HepG2 cells. We show here that exposure of HepG2 cells to peroxynitrite led to a dose-dependent increase in tyrosine nitration of cellular proteins, mainly membrane and nuclear proteins. Furthermore, peroxynitrite induced differential responses in tyrosine phosphorylation of membrane proteins as well as cytosolic proteins according to peroxynitrite concentrations used. Our findings indicate at low concentrations peroxynitrite upregulates the insulin signaling and may operate as a signaling molecule, but at higher concentrations peroxynitrite downregulates the insulin signaling and may be involved in insulin resistance, suggesting peroxynitrite plays a dual role in regulation of the insulin signaling.

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