Background information
Protein kinases comprise a large group of encoded factors that regulate cellular processes by catalyzing the transfer of a phosphate group to a hydroxyl acceptor in serine, threonine or tyrosine residues (1,2). Kinases are capable of influencing the oncogenic potential of cell sytems at the level of oncoprotein or tumor suppressor protein phosphorylation states (1,2). STAP-2 is a protein that contains a pleckstrin homology (PH) domain and an SH2 domain, and associates with BRK (3). BRK (breast tumor kinase, Sik) is a 451 amino acid, nonreceptor protein-tyrosine kinase that is overexpressed in breast tumors and metastatic melanoma cell lines (4). Similar to the Src family of intracellular kinses, BRK is comprised of an SH3 domain, an SH2 domain, and a catalytic domain (5). STAP-2 is susceptiple to tyrosine phosphorylation and may be invovled in tyrosine kinase-mediated signaling cascades, whose aberrant function may lead to metastis (3).
