Mechanism of p53-dependent Tumor Suppression

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Project Summary/Abstract p53 tumor suppressor is frequently mutated in cancer, and mutant p53 is an oncogene. Upon exposure to a stress signal, such as DNA damage, p53 transcription factor is activated and then induces an array of pro-survival and pro-death genes. Among these is Rbm38, a RNA-binding protein. Interestingly, we showed that Rbm38 represses p53 mRNA translation by preventing eIF4E from binding to p53 m7G cap. Thus, p53 and Rbm38 constitutes a feedback loop. To determine the significance of the p53-Rbm38 loop, we showed that:(1) phosphorylation of serine-195 and substitution of S195 with aspartic acid (S195D) prevent Rbm38 from interacting with eIF4E, which converts Rbm38 from a repressor to an activator of p53 translation; (2) an 8-aa peptide derived from Rbm38 (Pep8: YPYAAS195PA) and a 23- aa peptide derived from eIF4E (Pep23: aa 195-217) are able to disrupt the Rbm38-eIF4E complex to increase p53 expression. These observations prompt us to hypothesize that the Rbm38-eIF4E pathway, which is regulated by S195 phosphorylation and mutations in Rbm38, plays a critical role in p53- mediated tumor suppression. To test this, we will determine: (1) how p53-dependent tumor suppression is regulated by the Rbm38-eIF4E pathway; (2) whether the Rbm38-eIF4E pathway can be targeted to kill tumor cells carrying wild-type p53.