Lyn tyrosine kinase inhibits nuclear export of the p53 tumor suppressor

The p53 tumor suppressor is activated in the cellular response to stress. Mdm2 inhibits p53-dependent transactivation and promotes degradation of p53 by the ubiquitin-proteosome pathway. The present studies demonstrate that p53 binds directly to the nuclear Lyn tyrosine kinase. Lyn increases p53 levels and stimulates p53-mediated transcription by a kinase-independent mechanism. The results also demonstrate that Lyn increases nuclear levels of ubiquitinated p53 by inhibiting export of p53 to the cytoplasm. In concert with these results, Lyn reverses Mdm2-mediated degradation of p53 and increases p53-dependent apoptosis. Our findings support a previously undefined role for nuclear Lyn in both activation and Mdm2-mediated regulation of p53.