Molecular basis of cell cycle control: p300 and pRb

[摘要] The retinoblastoma protein (pRb) and p300 are transcriptional co-repressor and co-activator respectively, playing key roles in regulating the cell cycle. Both molecules are targeted by a number of viral oncoproteins, suggesting that the functional inactivation of these molecules is required for oncogenicity. Furthermore, p300 has an intrinsic histone acetyltransferase activity (HAT), which is crucial to its function. Here, studies were performed to understand how acetylation and de-acetylation may influence cell cycle regulation. I demonstrated that pRb is a substrate of p300 HAT activity. Furthermore, adenovirus E1A re-directs p300 HAT activity and enhances pRb acetylation. Acetylated pRb preferentially binds to proto-oncoprotein MDM2, indicating the functional relevance of this modification in regulating pRb function. Acetylation of pRb also influences its phosphorylation pattern, implying a certain level of 'cross-talk' between these two post-translational modification events. In an attempt to understand the underlying mechanism of p300-mediated transcriptional co-activation, I investigated its interaction with a newly identified binding-partner NAP-2 (nucleosome assembly protein 2). First, the domains of interaction between these two proteins were studied. Subsequently, both NAP-2 and p300 were found to augment in transcriptional regulation. Overall, the results suggested a mechanism by which p300 and NAP family proteins co-operate in chromatin-remodeling related mechanisms in regulating transcription. Finally, a series of pRb B pocket mutants were created, one of which was significantly compromised in binding to LXCXE peptide motif, including histone deacetylases (HDACs). pRb's growth suppressive function was correlated to its intrinsic repressive activity on transcription. At least in part, this intrinsic repressive activity was described by its association with HDACs. Using this mutant, I analysed the necessity of EQDAC association for pRb mediated G1 arrest. Surprisingly, the results suggested that HD AC may be dispensable for such function. Therefore, it readdresses the question of the functional significance of the pRb-HDAC interaction.

[发布机构] University:University of Glasgow

[关键词] Cellular biology, Molecular biology