The modulation of PCNA ubiquitination by p21 and its significance for DNA repair

描述（由申请人提供）：虽然体外实验着重证明了p21对PCNA依赖性DNA复制和修复的抑制作用，但在细胞中进行的实验中很难得出类似的结论。这可能至少部分取决于阻止p21在S期上调的趋同信号。我们发现了一个有趣的现象，即许多诱导S期短暂或永久停滞的基因毒性治疗协同促进p21下调和PCNA泛素化。此外，稳定的p21表达负调控PCNA泛素化，这是一种与DNA修复对相关的滑动钳转录后修饰。这一观察结果促使我们对p21调控PCNA的新方面进行研究。我们建议探索紫外线照射后p21依赖性抑制PCNA凋亡的机制。这也将有助于识别其他调节PCNA泛素化的分子，这些分子是p21的靶标。p21降解和PCNA泛素化之间的联系也将有助于识别协调这些事件的上游途径。在上述基因毒性治疗过程中，p21稳定表达对细胞存活的影响可能揭示了p21下调的生物学相关性，并可能对癌症治疗具有重要意义。

DESCRIPTION (provided by applicant): While in vitro experiments emphatically demonstrated the inhibitory effect of p21 on PCNA dependent DNA replication and repair it was much harder to arrive to similar conclusions in experiments performed in cells. This might depend, at least in part, on the convergent signals that prevent p21 up-regulation in S phase. We have come across the intriguing observation that a number of genotoxic treatments that induce transient or permanent arrest in S phase coordinately promote p21 down-regulation and PCNA ubiquitination. Moreover, stable p21 expression negatively modulates PCNA ubiquitination, a post-transcriptional modification of the sliding clamp relevant for its DNA re pair-related activities. This observation prompt us to the study of novels aspects of PCNA regulation by p21. We propose to explore the mechanisms for p21 dependent inhibition of PCNA ubqiutination after UV irradiation. This will also facilitate the identification of other molecules that modulate PCNA ubiquitination and are targets of p21. The link between p21 degradation and PCNA ubiquitination will also allow the identification of pathways upstream that coordinate these events. The effects on cell survival of a stable p21 expression during the above mentioned genotoxic treatments might reveal the biological relevance of p21 down-regulation and might be significant for cancer therapy.