Association of the interferon-dependent tyrosine kinase Tyk-2 with the hematopoietic cell phosphatase

The tyrosine kinase Tyk-2 is physically associated with the Type I interferon (IFN) receptor complex and is rapidly activated during IFNα stimulation. We report that Tyk-2 forms stable complexes with the SH2- containing hematopoietic cell phosphatase (HCP) in several hematopoietic cell lines in vivo, and that the IFNα-induced tyrosine-phosphorylated form of Tyk-2 is a substrate for the phosphatase activity of HCP in in vitro assays. Furthermore, treatment of cells with the phosphatase inhibitor sodium orthovanadate induces tyrosine phosphorylation of Tyk-2 and an associated 115-kDa protein. Altogether, these data suggest that HCP regulates tyrosine phosphorylation of the Tyk-2 kinase, and thus its function may be important in the transmission of signals generated at the Type I IFN receptor level.