Cell–Cell Signaling: The ins and outs of receptor tyrosine phosphatases

Many cellular processes including proliferation, differentiation, motility and the outgrowth of processes are regulated by tyrosine phosphorylation of critical substrates. The catalytically opposed activities of proteintyrosine kinases and protein-tyrosine phosphatases maintain an essential balance of phosphorylation levels. In general, tyrosine phosphatases have higher constitutive activity than tyrosine kinases, suggesting that they may maintain a low level of tyrosine phosphorylation that is punctuated by bursts of tyrosine kinase activity.