Roles of Cyclin D3 in Neoplastic Proliferation

描述（由申请人提供）：大量人类和实验性癌症显示激活g1控制激酶（CDK4和CDK6）的遗传改变。在这个过程中，异常水平的d型细胞周期蛋白比正常细胞提供了生长优势。虽然细胞周期蛋白D1和D2在细胞增殖中的作用已经确定，但最近的数据表明，细胞周期蛋白D3 （cyc D3）在分化和生长停滞中起着额外的作用。这一数据与我们的初步结果相吻合，表明周期D3是角质形成细胞增殖的负调节因子。值得注意的是，这种细胞周期蛋白的过度表达可以抑制肿瘤的发展，减少恶性进展为鳞状细胞癌（SCC）。对原代角质形成细胞的分析表明，cyc D3的过度表达导致cyc D2蛋白水平的强烈降低，而在cyc D3缺失的小鼠中观察到cyc D2水平升高。因此，我们假设cyc D3通过下调cyc D2的翻译后机制负向调节角化细胞增殖。支持这一假设的是，角质形成细胞、乳头状瘤和鳞状细胞衍生的细胞系，除鳞状细胞外，在所有细胞系中都显示出周期D3的稳定性增加，而鳞状细胞衍生的细胞系显示出周期D1的稳定性升高，这表明这两种细胞周期蛋白发挥相反的作用。为了确定d型细胞周期蛋白作为治疗干预靶点的潜在应用，有必要了解每个成员的作用。这项应用导致了许多与d型细胞周期蛋白在肿瘤发展和表皮稳态中的作用相关的问题。然而，为了保持重点，我们将集中于周期D3和周期D2在肿瘤发生中的作用。基于该应用获得的初步结果，我们提出了两种假设：1- Cyc D3表达通过翻译后机制抑制肿瘤发生，导致Cyc D2水平降低，改变表皮细胞的增殖能力。2- Cyc D3表达通过正向调节分化过程抑制癌变。为了验证这些假设，我们提出以下具体目的：SA 1：确定d型细胞周期蛋白不平衡表达在肿瘤发生中的作用。SA 2：确定调节细胞周期蛋白D2水平的翻译后机制。SA 3：确定细胞周期蛋白D3/CDK6复合物在正常和肿瘤增殖以及角化细胞分化中的作用。

DESCRIPTION (provided by applicant): A large number of human and experimental cancers display genetic alterations that activate G1-control kinases (CDK4 and CDK6). In this process, aberrant levels "of D-type cyclins provide a growth advantage over normal cells. Whereas a role for cyclin D1 and D2 in cell proliferation have been established, recent data suggests that cyclin D3 (cyc D3) plays additional roles in differentiation and growth arrest. This data correlates well with our preliminary results suggesting a role of cyc D3 as a negative regulator of keratinocyte proliferation. Notably, overexpression of this cyclin results in inhibition of tumor development and decreased malignant progression to squamous cell carcinomas (SCC). Analysis of primary keratinocytes shows that overexpression of cyc D3 results in strong reduction of the cyc D2 protein levels, whereas elevated levels of cyc D2 was observed in cyc D3 null mice. Thus, we have hypothesized that cyc D3 negatively regulate keratinocyte proliferation through a posttranslational mechanism downregulating cyc D2. Supporting this hypothesis, cell lines derived from keratinocytes, papillomas and SCC, showed increased cyc D3 stability in all but the SCC cell lines, whereas cell lines derived from SCC showed elevated stability of cyc D1 suggesting that these two cyclins play opposing roles. To determine the potential application of D-type cyclins as target for therapeutic intervention it is essential to understand the role of each member. The work performed for this application has led to a number of relevant questions related to the roles of D-type cyclins in neoplastic development and epidermal homeostasis. However, in order to remain focused, we will concentrate on the role of cyc D3 and cyc D2 in tumorigenesis. Based on the preliminary results obtained for this application, we proposed two hypotheses: 1- Cyc D3 expression inhibits tumorigenesis through a posttranslational mechanism that results in decreased levels of cyc D2 changing the proliferative capacity of epidermal cells. 2- Cyc D3 expression inhibits carcinogenesis by positive regulation of the differentiation process. In order to investigate these hypotheses, we propose the following specific aims: SA 1: To determine the effect of unbalanced expression of D-type cyclins in tumorigenesis. SA 2: To determine the posttranslational mechanism that regulates the levels of cyclin D2. SA 3: To determine the role of cyclin D3/CDK6 complexes in normal and neoplastic proliferation, and keratinocyte differentiation.