MDM2 AS A NEGATIVE REGULATOR OF P21 WAF1/CIP1

项目描述（由申请人提供）：本项目的长期目标是确定MDM2致癌基因在p21调控中的作用，评估MDM2和p21作为癌症化学预防和化疗新靶点的潜力，并将这些发现转化为更合理的人类癌症预防和治疗。p21的表达受p53的控制。然而，p21也受p53独立通路的调控。MDM2致癌基因在许多人类癌症中过度表达，MDM2水平与肿瘤进展和不良预后相关。MDM2在p53的稳定性和活性调控中起作用。此外，MDM2还具有不依赖p53的活性，这可能与其致癌特性有关。初步研究表明，MDM2在p21的调控中具有重要作用。用靶向MDM2的抗MDM2反义寡核苷酸或siRNA抑制MDM2可显著提高癌细胞中p21蛋白的水平（p53无效）。相反，过表达MDM2可降低p21水平，缩短p21半衰期。MDM2促进p21降解，不依赖于MDM2的泛素化和E3连接酶功能。相反，MDM2通过促进p21与蛋白酶体c8亚基的结合来促进p21的降解。MDM2作为p21的负调节因子，其作用独立于p53和泛素化。本申请旨在进一步阐明MDM2癌基因作为p21负调节因子的作用和机制，包括三个具体目的：1)。确定MDM2在转录水平调控p21的机制；2)在翻译后水平确定MDM2调控p21的机制；3)测定MDM2和p21对人肿瘤生长进展的体内外活性。这些研究将有助于了解MDM2不依赖p53的致癌活性的机制，并评估这些途径在人类癌症预防和治疗中的潜力。

DESCRIPTION (provided by applicant): The long-term objectives of this project are to determine the role of MDM2 oncogene in p21 regulation, to evaluate the potential of MDM2 and p21as novel targets for cancer chemoprevention and chemotherapy, and to translate these findings into more rational prevention and treatment of human cancers. The expression of p21 is under the control of p53. However, p21 is also regulated by p53-independent pathways. The MDM2 oncogene is overexpressed in many human cancers, with the MDM2 levels being associated with tumor progression and poor prognosis. MDM2 has a role in the regulation of p53 stability and activity. In addition, MDM2 also has p53-independent activity, which may be associated with its carcinogenic properties. Preliminary studies have indicated that MDM2 has an important role in regulation of p21. The inhibition of MDM2 with anti-MDM2 antisense oligonucleotide or siRNA targeting MDM2 significantly elevates p21 protein levels in cancer cells (p53 null). In contrast, overexpression of MDM2 diminishes the p21 level, shortening the p21 half-life. MDM2 facilitates p21 degradation independent of ubiquitination and the E3 ligase function of MDM2. Instead, MDM2 promotes p21 degradation by facilitating binding of p21 with the proteasomal C8-subunit. MDM2 functions as a negative regulator of p21, an effect independent of both p53 and ubiquitination. This application seeks to further clarify the role and mechanisms of MDM2 oncogene as a negative regulator of p21, including three Specific Aims: 1). To determine the mechanisms by which MDM2 regulates p21 at transcriptional level; 2) To determine the mechanisms by which MDM2 regulates p21 at post-translational level; and 3) To determine the in vitro and in vivo activity of MDM2 and p21 human cancer growth and progression. These studies will generate knowledge on the mechanisms responsible for the p53-independent carcinogenic activities of MDM2 and evaluate the potential of these pathways for human cancer prevention and treatment.