Receptor tyrosine kinase EphA2 is regulated by p53-family proteins and induces apoptosis

The p53 tumor suppressor protein is mutated in more than 50% of all human c ancers, which makes the study of its functions and activities critical for the understanding and management of cancer. In response to cellular stresse s, p53 is activated and can mediate cell cycle arrest and/or apoptosis via the upregulation of numerous target genes. Here, we have identified EphA2 a s a target gene of the p53 family, that is, p53, p73, and p63. We also foun d that an increase of EphA2 transcript levels correlated with an increase o f EphA2 protein expression, and induction of EphA2 in response to DNA damag e corresponded with p53 activation. Furthermore, we identified a p53 respon se element located within the EphA2 promoter that is responsive to wild-typ e p53, p73, and p63, but not mutant p53. Interestingly, the ligand for EphA 2, ephrin-A1, is also regulated by p53. EphA2 and ephrin-A1 are members of the Eph family of receptor tyrosine kinases and ligands, which are implicat ed in a number of developmental processes. To analyse the role of EphA2 in p53-mediated tumor suppression, we generated stable cell lines capable of e xpressing exogenous EphA2 in a tetracycline-repressible system. We found th at EphA2 expression resulted in an increase in apoptosis. Thus, we hypothes ize that the activated EphA2 may serve to impair anti-apoptotic signaling, perhaps by disrupting focal adhesions and thereby sensitize cells to pro-ap optotic stimuli.