Role of p300/CBP and hHR23 Proteins in p53 Regulation

描述（由申请人提供）：p53肿瘤抑制因子通过激活生长停滞或凋亡程序对抗广泛的应激，包括化学诱变剂、电离辐射、缺氧和营养缺乏。所有癌症都必须在一个或多个节点上破坏p53网络才能进展。最常见的是，p53突变，使其在肿瘤中失活。在其他情况下，p53的调节子被改变而不是p53本身。通常，癌细胞中改变的调节剂参与泛素/蛋白酶体系统对p53蛋白的正常破坏。泛素/蛋白酶体系统破坏p53的途径是复杂的，包括单泛素化、多聚泛素化、多聚泛素结合蛋白的识别以及蛋白酶体的识别和降解。p53被E3连接酶MDM 2单泛素化，并且来自在先授权的工作已经表明p300/CBP共活化剂是催化细胞质中p53的进一步多泛素化的E4酶。多泛素化的p53可以被蛋白酶体衔接蛋白的hHR 23家族识别，其似乎在细胞应激（例如DNA损伤）后保护p53免受蛋白酶体破坏，但也可以正常地将p53递送至蛋白酶体。hHR 23蛋白又被蛋白酶体的S5 a亚基识别，S5 a亚基可能是p53进入蛋白酶体的通道，导致p53的破坏。本续期申请的目的是：1.表征p300/CBP E4活性2的p53多聚泛素化的结构和功能。研究p300/CBP E4和Ub结合活性在p53调节中的作用3.研究hHR 23和S5 a在p53调控中的作用对泛素/蛋白酶体系统破坏p53的途径的坚定和完整的理解将增加我们对癌症如何通过破坏这一途径形成的知识，并导致针对这一途径的新型癌症治疗方法的发展。这种治疗方法有望在那些携带野生型p53的肿瘤中重新激活p53，导致肿瘤内恶性细胞的停滞或凋亡。 所有癌症都会破坏一种叫做p53的保护蛋白的功能。细胞通常会控制p53，直到需要它时才制造并立即破坏它。当需要它时，例如细胞变恶性时，它的破坏会停止，p53水平会增加。在一些肿瘤中，这种破坏系统是永久性的，因此p53不能被激活来对抗癌症。对p53通过泛素/蛋白酶体系统破坏的途径的坚定和完整的理解将增加我们对癌症如何通过破坏该途径形成的知识，并且还导致针对该途径的新型癌症治疗剂的开发。这种疗法有望在p53破坏途径被破坏的肿瘤中重新激活p53，从而通过癌细胞自身的自杀程序破坏癌细胞。

DESCRIPTION (provided by applicant):The p53 tumor suppressor counters a wide range of stresses, including chemical mutagens, ionizing radiation, hypoxia, and nutrient deprivation, by activating growth arrest or apoptosis programs. All cancers must inactivate the p53 network at one or more of its nodes to progress. Most often, p53 is mutated such that it is inactivated in tumors. In other cases, regulators of p53 are altered instead of p53 itself. Frequently, the regulators that are altered in cancer cells participate in the normal destruction of p53 protein by the ubiquitin/proteasome system. The pathway of p53 destruction by the ubiquitin/proteasome system is complex, involving monoubiquitination, polyubiquitination, recognition by polyubiquitin-binding proteins, and recognition and degradation by the proteasome. p53 is monoubiquitinated by the E3 ligase MDM2, and work from the prior grant has shown that the p300/CBP coactivators are E4 enzymes catalyzing further polyubiquitination of p53 in the cytoplasm. Polyubiquitinated p53 can be recognized by the hHR23 family of proteasome adaptor proteins, which appear to shield p53 from proteasome destruction after cell stress such as DNA damage, but may also normally deliver p53 to the proteasome. hHR23 proteins, in turn, are recognized by the S5a subunit of the proteasome, which may be the gateway to the proteasome for p53, leading to its destruction. The Aims of this renewal application are to: 1. Characterize the structure and function for p53 polyubiquitination of a p300/CBP E4 activity 2. Investigate the role of p300/CBP E4 and Ub binding activities in p53 regulation 3. Investigate the role of hHR23 and S5a in p53 regulation A firm and complete understanding of the pathway of p53 destruction by the ubiquitin/proteasome system will increase our knowledge of how cancers form through disruption of this pathway, and also lead to the development of novel cancer therapeutics targeting this pathway. Such therapeutics hold the hope of reactivating p53 in those tumors harboring wild type p53, leading to the arrest or apoptosis of malignant cells within. PUBLIC HEALTH RELEVANCE: All cancers disrupt the function of a protective protein called p53. Cells normally keep p53 in check until it is needed by manufacturing and immediately destroying it. When it is needed, such as the case when a cell is turning malignant, its destruction is halted and the p53 levels build up. In some tumors, this destruction system is permanently "on" so that p53 cannot be activated to battle the cancer. A firm and complete understanding of the pathway of p53 destruction by the ubiquitin/proteasome system will increase our knowledge of how cancers form through disruption of this pathway, and also lead to the development of novel cancer therapeutics targeting this pathway. Such therapeutics hold the hope of reactivating p53 in those tumors where the p53 destruction pathway is disrupted, leading to the destruction of cancer cells by their own suicide program.