Two axes in platelet-derived growth factor signaling: tyrosine phosphorylation and reactive oxygen species

The tyrosine phosphorylation cascade is a hallmark of platelet-derived growth factor (PDGF)- induced signal transduction. The amplitude and propagation of the tyrosine phosphorylation signal relies on the balance between tyrosine kinase and tyrosine phosphatase. The tyrosine kinase is latent in the absence of stimulation, whereas the tyrosine phosphatase is highly and constitutively active. Therefore, the kinase activation should be accompanied by temporal and spatial inactivation of tyrosine phosphatase to achieve the robust amplification of tyrosine phosphorylation. For the past decade, reactive oxygen species have been receiving a great deal of attention with regard to their ability to shut down tyrosine phosphatase activities in a reversible manner. In this article, the crosstalk between tyrosine phosphorylation and reactive oxygen species in PDGF signaling is discussed. Received 2 October 2006; received after revision 13 November 2006; accepted 27 November 2006