The human ptk6 is a cytoplasmic tyrosine kinase, evolutionarily distinct from the src family members and interacting with a 20-kda tyrosine- phosphorylated protein

The human PTK6 (also known as brk) polypeptide deduced from its fulllength cDNA represents a non-receptor protein tyrosine kinase (PTK), containing SH3, SH2, and tyrosine kinase catalytic domains, closely related to src family members. We have analyzed the organization of the human PTK6 gene to examine evolutionary relationship with src family members. The human PTK6 gene of the coding region consists of 8 exons. The exon/intron junctions of the PTK6 gene were quite different from those of the src family genes, which are evolutionarity conserved. This result suggests that PTK6 constitute a new family of non-receptor PTKs, evolutionarily distinct from src family members. In addition, we have generated anti-human PTK6 antibody by immunizing rabbits with a PTK6-specific oligopeptide conjugated to BSA. Immunoblot analysis with the antibody detected an expected 52-kDa band in various mammalian cell lines. Immunoprecipitation and immunoblot analyses demonstrated that PTK6 is phosphorylated on tyrosine residue(s) and interacts with an approximately 20-kDa tyrosine-phosphorylated polypeptide, which is most likely a substrate of PTK6, in breast carcinoma T47-D cells. lmmunofluorescence analysis demonstrated that PTK6 is localized throughout the cytoplasm of T47-D cells. These results support a possible role for PTK6 in the intracellular signal transduction through tyrosine phosphorylation. [Supported by a grant from GERF of MOE of Korea].