Activation of human thymocytes induces the phosphorylation of protein tyrosine phosphatase 1C

Phosphorylation of docking proteins is essential for signal transduction. In this report we provide evidence that activation of human thymocytes in culture induces the phosphorylation of the protein tyrosine phosphatase 1C (PTP 1C). Thymocytes were activated with Con A, PMA or Con A+PMA. The enzyme is phosphorylated on its serine and threonine residues. Phosphorylation occurs within 5 min and lasts for 24 h. PTP 1C is phosphorylated by PKC in vivo and in vitro; however, phosphopeptide mapping suggests that in addition to PKC other kinases phosphorylate the enzyme. On the maps of tryptic digests of cultured thymocytes more radiolabeled phosphopeptides are visualized than on the maps of digests of PTP 1C phosphorylated with partially purified PKC alpha or beta. Phosphorylation of PTP 1C decreases its activity, whereas dephosphorylation increases its activity, suggesting that phosphorylation of PTP 1C takes part in the regulation of signal transduction.