Regulation of the retinoblastoma protein by ARF and the role of peptidyl-prolyl isomerase Pin1 in the regulation ofp63.

摘要

The tumor suppressor ARF plays a critical role in regulating cell cycle progression in response to oncogenic stress. ARF binds to and inhibits MDM2 resulting in activation of p53. Recent studies have shown that MDM2 also functions as a critical negative regulator of retinoblastoma protein (Rb). In this study, we showed that ARF inhibition of MDM2 resulted in Rb protein accumulation. Wild-type ARF, but not an ARF mutant defective in MDM2 interaction, stabilized Rb and inhibited colony foci formation independently of p53. In addition, ARF disrupted the interaction of MDM2 and Rb, and inhibited the interaction of MDM2 with the C8 subunit of the 20S proteasome. Furthermore, ablation of Rb impaired ARF-mediated growth suppression. Thus, this study demonstrates that ARF plays a direct role in the regulation of Rb, and suggests that the Rb pathway is an integral part of ARF growth suppression.; Additional studies were performed to examine the role of the peptidyl-prolyl isomerase Pin1 in the regulation of p63, a newly discovered p53 homolog. Our previous work showed that Pin1 interacts with and activates p53 in response to genotoxic stress. In this study, we found that Pin1 was overexpressed in various cancer cell lines, whereas p63 was predominantly overexpressed in squamous cell carcinomas and DMBA-induced mammary tumors. Pin1 interacted with p63 in a phosphorylation-dependent manner. The Ser12-Pro motif in the transactivation domain of TAp63gamma was critical for Pin1-p63 interaction. Pin1, but not a Pin1 mutant defective in p63 interaction, enhanced TAp63 transcriptional activity. Taken together, this study suggests a novel role for Pin1 in the regulation of p63.