Reciprocal Regulation of DAPK

Abstract

The tumor suppressor death-associated protein kinase (DAPK) functions by inhibiting cell adhesion and migration and promoting apoptosis. It is positively regulated by calmodulin and is thought to inactivate integrins, thus preventing cell adhesion-induced survival signals. Wang et al . sought to determine the mechanism of regulation of DAPK. Yeast two-hybrid screening identified leukocyte common antigen-related protein (LAR), a receptor-like tyrosine phosphatase, as a binding partner for the ankyrin repeat domain of DAPK. This interaction was confirmed by coimmunoprecipitation studies in 293T cells. Western blotting showed that DAPK was a substrate for LAR and, using DAPK mutants, the authors identified Tyr 491 and Tyr 492 as the target dephosphorylation sites. In vitro kinase assays demonstrated that the kinase activity of DAPK was increased in 293T transfectants coexpressing LAR but not in cells expressing a phosphatase-deficient mutant LAR. 293T cells cotransfected with DAPK and LAR performed poorly in adhesion assays compared with 293T cells transfected with DAPK alone. Adhesion of cells to fibronectin resulted in the phosphorylation of DAPK, which was reduced by inhibitors of Src tyrosine kinases. Western blotting revealed that Src phosphorylated DAPK at the same residues targeted by LAR, and Src-mediated phosphorylation of DAPK promoted cell adhesion and migration. Epidermal growth factor (EGF) activates Src and decreases the abundance of LAR at the membrane. Treatment of epithelial carcinoma cells with EGF resulted in DAPK inactivation and increased EGF-stimulated migration. Immunohistochemistry demonstrated a correlation between the incidence of hyperphosphorylated, inactivated DAPK and increased Src activity in tumor cells. Together, these data establish a possible link between EGF-induced tumorigenesis and DAPK inactivation through the reciprocal regulation of DAPK by LAR and Src. W.-J. Wang, J.-C. Kuo, W. Ku, Y.-R. Lee, F.-C. Lin, Y.-L. Chang, Y.-M. Lin, C.-H. Chen, Y.-P. Huang, M.-J. Chiang, S.-W. Yeh, P.-R. Wu, C.-H. Shen, C.-T. Wu, R.-H. Chen, The tumor suppressor DAPK is reciprocally regulated by tyrosine kinase Src and phosphatase LAR. Mol. Cell 27 , 701-716 (2007). [PubMed]