Role of tyrosine phosphorylation in the regulation of the interaction of heterogenous nuclear ribonucleoprotein K protein with its protein and RNA partners

The heterogeneous nuclear ribonucleoprotein K protein recruits a diversity of molecular partners and may act as a docking platform involved in such pr ocesses as transcription, RNA processing, and translation. We show that K p rotein is tyrosine-phosphorylated in vitro by Src and Lck. Treatment with H 2O2/Na3VO4, which induces oxidative stress, stimulated tyrosine phosphoryla tion of K protein in cultured cells and in intact livers. Tyrosine phosphor ylation increased binding of Lck and the proto-oncoprotein Vav to K protein in vitro, Oxidative stress increased the association of K protein with Lck and Vav, suggesting that tyrosine phosphorylation regulates the ability of K protein to recruit these effecters in vivo, Translation-based assay show ed that K protein is constitutively bound to many mRNAs in vivo. Native imm unoprecipitated K protein-mRNA complexes were disrupted by tyrosine phospho rylation, suggesting that the in vine binding of K protein to mRNA may be r esponsive to the extracellular signals that activate tyrosine kinases, This study shows that tyrosine phosphorylation of K protein regulates K protein -protein and K protein-RNA interactions, These data are consistent with a m odel in which functional interaction of K protein is responsive to changes in the extracellular environment, Acting as a docking platform, K protein m ay bridge signal transduction pathways to sites of nucleic acid-dependent p rocess such as transcription, RNA processing, and translation.