Characterization of downstream transcriptional targets ofp53 involved in tumor growth suppression

The ability of p53 to transactivate specific genes in cell cycle control and apoptosis is important for its role as a tumor suppressor gene. We analyzed the effects of Butyrolactone I (BL) on the stability of the well characterized p53 target gene, p21, and the consequences towards cell cycle checkpoints. Furthermore, we identified novel p53 regulated genes using microarrays hybridized with cRNA from two related p53 temperature-sensitive cell lines.; While a large body of evidence exists characterizing the p53-mediated transcriptional regulation of the cyclin dependent kinase inhibitor, p21, relatively little is known with respect to its post-translational stability. We identified BL as an inducer of p21 degradation. BL targets p21 for proteolytic degradation, requiring the C-terminal region or full-length p21, and this effect can be blocked by treatment with a proteasomal inhibitor. Furthermore, BL induced the degradation of both endogenously induced p21 expression and exogenously induced p21. We have found that BL can be used to study p21 degradation and consequences towards p21 mediated checkpoints.; Microarray analysis revealed BID as a putative p53 regulated gene. BID expression is induced by p53 in vitro and in vivo . Both the murine and human genomic loci contain functional p53-DNA binding elements. Interestingly, BID deficient MEFs were resistant to treatment with chemotherapeutic agents compared to wild-type MEFs. This suggests a potential model where the induction of BID by p53 may help to sensitize the cell to treatment with chemotherapeutic agents.; TRAF4, a member of the TRAF family of adaptor proteins, was identified as a novel p53 regulated gene by microarray analysis. TRAF4 expression is upregulated by p53 both in vitro and in vivo. The promoter region of TRAF4 contains a functional p53-DNA binding element. Interestingly, overexpression of TRAF4 induces apoptosis and suppresses colony formation, suggesting this molecule may play a role in p53-mediated apoptosis.; Taken together, both the characterization of the post-translational stability of p21 and the identification of BID and TRAF4 as novel p53 regulated genes further characterizes the role of p53 in tumor suppression.