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阻滞或细胞凋亡程序来对抗多种应激，包括化学诱变剂、电离辐射、缺氧和营养剥夺。所有癌症都必须在p53网络的一个或多个节点上失活才能进展。大多数情况下，p53突变使其在肿瘤中失活。在其他情况下，p53的调节因子被改变，而不是p53本身。通常，在癌细胞中被改变的调节因子参与了泛素/蛋白酶体系统对p53蛋白的正常破坏。p53被泛素/蛋白酶体系统破坏的途径是复杂的，包括单泛素化、多泛素化、多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MDM2单泛素化，先前的研究表明p300/CBP共激活因子是E4酶，催化细胞质中p53的进一步多泛素化。多泛素化的p53可以被hHR23蛋白酶体衔接蛋白家族识别，该蛋白似乎可以在细胞应激（如DNA损伤）后保护p53免受蛋白酶体的破坏，但也可能在正常情况下将p53传递给蛋白酶体。反过来，hHR23蛋白被蛋白酶体的S5a亚基识别，这可能是p53的蛋白酶体的门户，导致其破坏。此更新申请的目的是：1。表征p300/CBP E4活性的p53多泛素化的结构和功能2研究p300/CBP E4和Ub结合活性在p53调控中的作用。研究hHR23和S5a在p53调控中的作用对p53被泛素/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如何通过破坏这一途径形成癌症的认识，也将导致针对这一途径的新型癌症治疗的发展。这种疗法有望在那些携带野生型p53的肿瘤中重新激活p53，从而导致肿瘤内恶性细胞的阻滞或凋亡。

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.