Nuclear Accumulation of Cyclin D1 and Oncogenesis

描述（由申请人提供）：本研究的长期目标是阐明细胞周期蛋白D1/CDK 4激酶触发肿瘤发生的机制。我们目前的研究集中在生长信号通路如何调节有丝分裂反应的D型细胞周期蛋白，更具体地说，这些途径如何调节正常细胞与癌细胞中活性的核细胞周期蛋白D1依赖性激酶的积累。细胞周期蛋白D1在多种人类癌症中的过度表达突出了阐明调节细胞周期蛋白D1活性的机制的重要性。在涉及细胞周期蛋白D1活性失调的各种癌症中，套细胞淋巴瘤（MCL）是最具破坏性的癌症之一。由于11：14染色体易位，细胞周期蛋白D1在MCL中异常表达。MCL是B细胞淋巴瘤的一个独特类别，表现为累及骨髓、脾脏，有时累及胃肠道的播散性疾病。我们已经开发了D1驱动的B细胞淋巴瘤的小鼠模型，其类似于人类MCL，基因组不稳定，并表现出与人类疾病相关的矛盾;保留野生型p53。由于p53的作用是限制基因组不稳定细胞的扩增，因此MCL必须绕过p53而不选择功能丧失突变。我们已经证明，细胞周期蛋白D1/CDK 4激活PRMT 5甲基转移酶，我们提出的初步证据表明，它可以抑制p53依赖性细胞凋亡提供了一个潜在的机制，在野生型p53背景下的肿瘤发展。MCL的特征还在于包含编码ATM的基因座的染色体缺失。ATM的丧失预计会通过DNA损伤消除p53的激活，从而提供逃避p53监视的第二种机制。在3个特定目标的背景下描述的实验将直接确定致癌细胞周期蛋白D1绕过内在肿瘤监视机制以触发肿瘤生长的分子机制。目的1将确定PRMT 5/MEP 50与致癌细胞周期蛋白D1 T286 A合作诱导肿瘤生长的能力;目的2将确定PRMT 5/MEP 50在表达核细胞周期蛋白D1/CDK 4的细胞中绕过p53依赖性凋亡的作用;目的3将评估ATM作为DNA损伤传感器在抑制D1驱动的恶性肿瘤中的作用。 公共卫生相关性：细胞周期蛋白D1在人类癌症中的过度表达经常发生，这是破坏细胞周期蛋白D1蛋白的机制突变的结果。为了开发有效的治疗方法来对抗这些事件，有必要确定由细胞周期蛋白D1指导的触发肿瘤发展的分子机制。我们已经确定了机器的关键组成部分，PRMT 5/MEP 50精氨酸甲基转移酶。PRMT 5不仅修饰组蛋白，而且还可以修饰和潜在地调节p53以响应DNA损伤。本提案中描述的实验将评估PRMT 5在肿瘤发展和进展中的生物化学和生物学作用。

DESCRIPTION (provided by applicant): The long-term objective of my research is the elucidation of the mechanisms whereby the cyclin D1/CDK4 kinase triggers tumorigenesis. Our current studies focus on how growth-signaling pathways regulate the mitogenically responsive D-type cyclins and more specifically, how these pathways regulate accumulation of an active, nuclear cyclin D1-dependent kinase in normal versus cancerous cells. The noted overexpression of cyclin D1 in multiple human cancers highlights the importance of elucidating the mechanisms that regulate cyclin D1 activity. Of the various cancers in which deregulated cyclin D1 activity is implicated, mantle cell lymphoma (MCL) is one of the most devastating. Cyclin D1 is aberrantly expressed in MCL due to the 11:14 chromosomal translocation. MCL represents a distinct category of B-cell lymphoma that presents as a disseminated disease with involvement of bone marrow, spleen, and, sometimes, gastrointestinal tract. We have developed a mouse model of D1-driven B-cell lymphoma, which similar to human MCL, is genomically unstable and exhibits a paradox associated with human disease; retention of wild type p53. Because p53 functions to limit expansion of genomically unstable cells, MCL must bypass p53 without selection for loss of function mutations. We have demonstrated that cyclin D1/CDK4 activates the PRMT5 methyltransferase, and we present preliminary evidence that it can inhibit p53-dependent apoptosis providing a potential mechanism for tumor development in a wild type p53 background. MCL is also characterized by chromosomal deletions that encompass the locus encoding ATM. Loss of ATM is expected to abrogate p53 activation by DNA damage, providing a second mechanism of escape from p53 surveillance. The experiments described in the context of 3 Specific Aims will directly determine the molecular mechanisms whereby oncogenic cyclin D1 bypasses intrinsic tumor surveillance mechanisms to trigger neoplastic growth. Aim 1 will determine the ability of PRMT5/MEP50 to cooperate with oncogenic cyclin D1T286A to induce neoplastic growth; Aim 2 will determine the role of PRMT5/MEP50 in bypassing p53-dependent apoptosis in cells expressing nuclear cyclin D1/CDK4; Aim 3 will assess the role of ATM, as a sensor of DNA damage, in the suppression of D1-driven malignancy. PUBLIC HEALTH RELEVANCE: Overexpression of cyclin D1 in human cancer occurs frequently as a consequence of mutations in the machinery that destroys the cyclin D1 protein. In order to develop effective therapies that counter these events, it is necessary to identify molecular mechanisms directed by cyclin D1 to trigger the development of neoplasia. We have identified a critical component of the machinery, the PRMT5/MEP50 arginine methyltransferase. PRMT5 not only modifies histones, but can also modify and potentially regulate p53 in response to DNA damage. The experiments described in this proposal will evaluate the biochemical and biological role of PRMT5 in tumor development and progression.