Requirements for Normal Rb Function In Vivo

视网膜母细胞瘤肿瘤抑制基因（Rb 1）的突变导致儿童癌症视网膜母细胞瘤，并导致大多数类型的人类癌症。尽管它在肿瘤发生中起着核心作用，但旨在靶向这一途径的治疗方法发展缓慢。对Rb 1介导的肿瘤抑制的分子机制的详细了解将促进此类疗法的发展。这个持续项目的长期目标是识别和表征这些分子机制。Rb 1蛋白（pRb）是细胞周期的负调控因子，这种细胞周期调控活性有助于肿瘤抑制。多种机制可能有助于pRb介导的细胞周期控制，包括涉及pRb与E2 F转录因子结合导致细胞周期进程所需基因转录抑制的充分表征的机制。另一种可能的机制涉及pRb对Skp 2的靶向降解和随后的p27 Kip 1的稳定。pRb调节E2 F转录因子的能力与其降解Skp 2的能力在遗传上是分离的。我们假设pRb介导的Skp 2降解和p27 Kip 1稳定有助于体内前列腺肿瘤抑制。我们的工作模型是p27 Kip 1（p27）的翻译后稳定通常会对致癌应激产生衰老样反应，从而减少肿瘤的发生和进展。在pRb不存在的情况下，这种肿瘤抑制反应是沉默的。本申请的目的是使用体外和体内实验模型系统来检验假设。我们已经创建了一个小鼠品系含有突变Rb 1等位基因（R654 W），其编码的蛋白质是缺乏E2 F的结合和调节，但可能有能力靶向Skp 2降解。我们建议使用这种突变等位基因来评估pRb/E2 F和pRb/p27机制对体内前列腺肿瘤抑制的相对贡献。提出了两个具体目标：1）测试R654 W pRb是否可以抑制小鼠中的前列腺肿瘤发生; 2）表征pRb/Skp 2/p27机制对前列腺肿瘤发生的贡献。 R654 W pRb肿瘤抑制活性。这些特定目标的成功完成将确定一个新的机制，有助于Rb 1肿瘤抑制，并提出新的治疗策略，以治疗前列腺癌。

Mutation of the retinoblastoma tumor suppressor gene (Rb1) causes the pediatric cancer retinoblastoma and contributes to most types of human cancer. Despite its central role in tumorigenesis, therapies designed to target this pathway have been slow to develop. A detailed understanding of the molecular mechanisms underlying Rb1 mediated tumor suppression will facilitate the development of such therapies. The long-term goal of this continuing project is to identify and characterize these molecular mechanisms. Rb1 protein (pRb) is a negative regulator of the cell cycle, and this cell cycle regulatory activity contributes to tumor suppression. Multiple mechanisms likely contribute to pRb mediated cell cycle control, including the well characterized mechanism involving binding of pRb to E2F transcription factors resulting in transcriptional repression of genes required for cell cycle progression. Another possible mechanism involves targeted degradation of Skp2 by pRb and consequent stabilization of p27Kip1. The ability of pRb to regulate E2F transcription factors is genetically separable from its ability to degrade Skp2. We hypothesize that pRb mediated degradation of Skp2 and stabilization of p27Kip1 contributes to prostate tumor suppression in vivo. Our working model is that post translational stabilization of p27Kip1 (p27) normally enforces a senescence like response to oncogenic stress, thereby curtailing tumor initiation and progression. In the absence of pRb, this tumor suppressive response is muted. The goal of this application is to test the hypothesis using in vitro and in vivo experimental model systems. We have created a mouse strain containing a mutant Rb1 allele (R654W) whose encoded protein is deficient for E2F binding and regulation, but may be competent to target Skp2 for degradation. We propose to use this mutant allele to assess the relative contribution of the pRb/E2F and pRb/p27 mechanisms to prostate tumor suppression in vivo. Two specific aims are proposed: 1) Test whether R654W pRb can suppress prostate tumorigenesis in the mouse; 2) Characterize the contribution of the pRb/Skp2/p27 mechanism to R654W pRb tumor suppressor activity. Successful completion of these specific aims will identify a new mechanism contributing to Rb1 tumor suppression and suggest new therapeutic strategies to treat prostate cancer.