Protein-tyrosine phosphatase D1, a potential regulator and effector for Tec family kinases

Etk, also named Bmx, is a member of the Tec tyrosine kinase family, which i s characterized by a multimodular structure including a pleckstrin homology (PH) domain, an SH3 domain, an SH2 domain, and a catalytic domain. The sig naling mechanisms regulating Etk kinase activity remain largely unknown. To identify factor(s) regulating Etk activity, we used the PH domain and a li nker region of Etk as a bait for a yeast two-hybrid screen. Three independe nt clones encoding protein-tyrosine phosphatase D1 (PTPD1) fragments were i solated. The binding of PTPD1 to Etk is specific since PTPD1 cannot associa te with either the Akt PH domain or lamin. In vitro and in vivo binding stu dies demonstrated that PTPD1 can interact with Etk and that residues 726-84 8 of PTPD1 are essential for this interaction. Deletion analysis of Etk ind icated that the PH domain is essential for PTPD1 interaction. Furthermore, the Etk-PTPD1 interaction stimulated the kinase activity of Etk, resulting in an increased phosphotyrosine content in both factors. The Etk-PTPD1 inte raction also increased Stat3 activation. The-effect of PTPD1 on Etk activat ion is specific since PTPD1 cannot potentiate Jak2 activity upon Stat3 acti vation In addition, Tec (but not Btk) kinase can also be activated by PTPD1 . Taken together, these findings indicate that PTPD1 can selectively associ ate with and stimulate Tec family kinases and modulate Stat3 activation.