Regulation and function of cdk5 and ezrin in senescence

cdk5和ezrin在衰老过程中的调控和功能

• 批准号: 7105738
• 负责人: Philip W. Hinds
• 金额: $ 25.75万
• 依托单位: TUFTS MEDICAL CENTER
• 依托单位国家: 美国
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-09-07 至 2011-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7105738
• 关键词: actin binding protein; actins; athymic mouse; cell line; cell morphology; cell proliferation; cell senescence; cytogenetics; cytoskeletal proteins; gene induction /repression; genetic promoter element; messenger RNA; molecular dynamics; neoplasm /cancer genetics; neoplastic cell; neoplastic transformation; protein protein interaction; transfection; tumor suppressor proteins

DESCRIPTION (provided by applicant): Cellular senescence is a tumor-suppressive process characterized by an irreversible cell cycle exit, a unique morphology, and expression of senescence-associated-beta-galactosidase (SA-beta-gal). Passage of normal cells in culture leads to senescence, as do cellular stresses including ras oncoprotein expression and activation of the pRb tumor suppressor pathway. Despite the potential biological importance of cellular senescence, little is known of the mechanisms leading to the senescent phenotype in cultured cells, nor is it clear to what extent these processes occur in vivo. We have recently discovered a role for cdk5 in induction of SA-beta-gal expression and senescent cytoskeletal changes. Cdk5 activity increases in senescing cells and repression of the activity of the GTPase Rac1 by cdk5 is required for expression of SA-beta-gal. Cdk5 regulation of Pad activity is also necessary for actin polymerization accompanying senescent morphology in response to expression of pRb, activated ras, or continuous passage. Inhibition of cdk5 attenuates SA-beta-gal expression and blocks actin polymerization. We have further discovered that one substrate for cdk5 in senescent cells is the ERM protein ezrin. Expression of active pRb induces expression and altered localization of ezrin, an actin-binding protein involved in membrane-cytoskeletal signaling. pRb expression results in the stimulation of cdk5-mediated phosphorylation of ezrin with subsequent membrane association and induction of cell shape changes, linking pRb activity to cytoskeletal regulation in senescent cells. These results begin to illuminate the mechanisms underlying induction of senescence and the senescent shape change and describe new pathways that may contribute to the ability of senescent cells to influence tumor growth. In order to more clearly understand the role of cdk5 and ERMs in senescence and tumor suppression, three specific aims are proposed: 1) Determine the mechanism of activation of cdk5 in senescent cells. 2) Determine how pRb activates transcription of the ezrin gene and use this information to understand transcriptional responses to pRb in senescent cells. 3) Ascertain the effects of constitutive cdk5 or ERM "knock-down" or loss on proliferation and tumorigenesis.

描述（申请人提供）：细胞衰老是一种肿瘤抑制过程，其特征是不可逆的细胞周期退出、独特的形态以及衰老相关β-半乳糖苷酶（SA-β-gal）的表达。培养中正常细胞的传代会导致衰老，细胞应激也会导致衰老，包括 ras 癌蛋白表达和 pRb 肿瘤抑制途径激活。尽管细胞衰老具有潜在的生物学重要性，但人们对培养细胞中导致衰老表型的机制知之甚少，也不清楚这些过程在体内发生的程度。我们最近发现 cdk5 在诱导 SA-β-gal 表达和衰老细胞骨架变化中的作用。衰老细胞中的 Cdk5 活性增加，并且 cdk5 抑制 GTPase Rac1 的活性是 SA-β-gal 表达所必需的。 Cdk5 对 Pad 活性的调节对于肌动蛋白聚合也是必要的，伴随着响应 pRb 表达、激活 ras 或连续传代的衰老形态。抑制 cdk5 可减弱 SA-β-gal 表达并阻断肌动蛋白聚合。我们进一步发现衰老细胞中cdk5的一种底物是ERM蛋白ezrin。活性 pRb 的表达会诱导埃兹蛋白 (ezrin) 的表达并改变其定位，埃兹蛋白是一种参与膜细胞骨架信号传导的肌动蛋白结合蛋白。 pRb 表达导致刺激 cdk5 介导的埃兹蛋白磷酸化，随后发生膜结合并诱导细胞形状变化，将 pRb 活性与衰老细胞中的细胞骨架调节联系起来。这些结果开始阐明诱导衰老和衰老形状变化的潜在机制，并描述可能有助于衰老细胞影响肿瘤生长的能力的新途径。为了更清楚地了解cdk5和ERM在衰老和肿瘤抑制中的作用，提出了三个具体目标：1）确定衰老细胞中cdk5的激活机制。 2) 确定 pRb 如何激活 ezrin 基因的转录，并利用该信息来了解衰老细胞中 pRb 的转录反应。 3) 确定组成型cdk5或ERM“敲低”或缺失对增殖和肿瘤发生的影响。