Role of G1-Cdks in immortalization and oncogenesis

描述（由申请人提供）：大量人类癌症显示异常激活g1控制激酶，细胞周期蛋白d相关Cdk4和Cdk6的遗传改变，表明这些蛋白在致癌转化中起关键作用。摆脱衰老是转变的必要条件。Ras激活或持续体外增殖诱导的衰老伴随着p16ink4a和ARF的表达增加。p16ink4a抑制Cdk4和Cdk6，导致Rb的生长抑制作用增强。ARF稳定p53，导致诱导另一种Cdk抑制剂p21Cip1/Waf1。这些衰老相关通路对肿瘤抑制至关重要。cdk4缺失的小鼠胚胎成纤维细胞（MEF）正常增殖，但在Ras激活、p53抑制或Ink4a/ARF破坏时，MEF对癌性转化具有抗性。没有ARF-p53功能的衰老导致了这种转化潜力的缺乏。此外，cdk4缺失小鼠对致癌物或辐射诱导的肿瘤发生的易感性降低。因此，Cdk4的破坏可以有效地使细胞对转化不敏感，在正常的细胞永生条件下诱导衰老。长期目标是为肿瘤转化的治疗干预奠定基础。本提案将评估细胞需要异常激活cyclin D/Cdk4和cyclin D/Cdk6来克服衰老依赖的肿瘤抑制机制，从而导致永生化和肿瘤发生的假设。具体目标是：(1)通过研究Cdk4缺失MEF中的衰老/永生化相关蛋白，确定Cdk4破坏如何在ARF-p53通路的抑制下导致MEF衰老；(2)通过检测具有乳腺特异性Cdk4破坏的MMTV-Ras转基因小鼠，确定ras诱导的小鼠乳腺上皮癌变是否需要Cdk4；(3)通过检测Cdk6-null MEF和小鼠，确定Cdk4和Cdk6在永生化、转化和肿瘤发生中的相互作用。这些研究有望阐明细胞周期蛋白d依赖性激酶在肿瘤发生过程中的重要作用。该项目采用创新的方法，使用独特的小鼠和细胞模型，使我们能够更好地理解Cdk4和Cdk6与衰老依赖的肿瘤抑制途径的致癌相互作用。

DESCRIPTION (provided by applicant): A large number of human cancers display genetic alterations that aberrantly activate the G1-control kinases, cyclin D-associated Cdk4 and Cdk6, suggesting critical roles for these proteins in oncogenic transformation. Escape from senescence is requisite for transformation. Senescence induced by Ras activation or continuous in vitro proliferation is accompanied by increased expression of p16ink4a and ARF. p16ink4a inhibits Cdk4 and Cdk6, leading to enhance growth-inhibitory action of Rb. ARF stabilizes p53, resulting in induction of another Cdk inhibitor, p21Cip1/Waf1. These senescence-associated pathways are critical for tumor suppression. Cdk4-null mouse embryonic fibroblasts (MEF) proliferate normally, but are resistant to oncogenic transformation upon Ras activation with p53 inhibition or Ink4a/ARF disruption. Senescence without ARF-p53 function accounts for this lack of transformation potential. Furthermore, Cdk4-null mice display reduced susceptibility to carcinogen- or radiation-induced tumorigenesis. Thus, Cdk4 disruption may effectively render cells insensitive to transformation, by inducing senescence under conditions that normally immortalize cells. The long-term goal is to establish the basis for therapeutic intervention of oncogenic transformation. This proposal will evaluate the hypothesis that aberrant activation of cyclin D/Cdk4 and cyclin D/Cdk6 is required for a cell to overcome the senescence-dependent tumor suppressive mechanism, leading to immortalization and tumorigenesis. The specific aims are: (1) Determine how Cdk4 disruption leads MEF to senescence under inhibition of the ARF-p53 pathway, by investigating senescence/immortalization-associated proteins in Cdk4-null MEF; (2) Determine whether Cdk4 is required for Ras-induced carcinogenesis of the mammary epithelium in mice, by examining MMTV-Ras transgenic mice with mammary-specific Cdk4 disruption; (3) Determine how Cdk4 and Cdk6 interact in immortalization, transformation and oncogenesis, by examining Cdk6-null MEF and mice. These studies are expected to clarify essential roles of the cyclin D-dependent kinases during oncogenesis. This program takes innovative approaches that should lead us to better understanding of the oncogenic interplay of Cdk4 and Cdk6 with the senescence-dependent tumor suppressive pathways, using unique mouse and cell models.