PROHIBITIN GENE IN GROWTH CONTROL AND TUMOR SUPPRESSION

描述（由申请人提供）：哺乳动物细胞通过增殖、分化或凋亡对多种细胞外信号作出反应。这些事件受到信号分子、肿瘤抑制蛋白、转录因子及其下游靶点组成的复杂机制的严格调控。本文将重点讨论一种潜在的肿瘤抑制蛋白Prohibitin在上述过程中的作用。禁止蛋白基因位于染色体17q21上，在散发性乳腺癌中发现其突变。我们前期的研究表明，prohibition可以与视网膜母细胞瘤肿瘤抑制蛋白结合，抑制E2F家族成员的转录活性。这是禁止素抑制细胞增殖所必需的。我们最近的研究表明，禁止素可以增强p53的转录活性。基于这些发现，我们将研究转录共抑制因子HP1和SUV39H是否参与了禁止素介导的E2F1活性抑制，以及禁止素是否参与了细胞衰老过程中异染色质的形成。我们将尝试了解禁止蛋白是如何调控YY1启动子的，以及它是如何调控细胞增殖的。接下来，我们将研究禁止蛋白促进p53向启动子募集并导致其激活的机制。我们将重点关注禁止蛋白是否影响p53的四聚化及其翻译后修饰。最后一个具体目标将集中在体内模型上研究禁止素的功能。我们在乳腺上皮细胞中培养了过表达禁止素的转基因小鼠。我们将研究禁止素对乳腺发育的影响以及致癌物和Ras诱导的乳腺癌。实验正在进行中，以产生有条件的禁止基因敲除小鼠。我们期望这些实验将有助于阐明禁止素介导的生长控制和肿瘤抑制的分子机制。

DESCRIPTION (provided by applicant): Mammalian cells respond to a variety of extracellular signals by undergoing proliferation, differentiation or apoptosis. These events are stringently regulated by a complex machinery comprising of signaling molecules, tumor suppressor proteins, transcription factors and their downstream targets. This proposal will focus on the role of Prohibitin, a potential tumor suppressor protein, in the above processes. Prohibitin gene is located on chromosome 17q21 and its mutations have been found in sporadic breast cancers. Our earlier studies had shown that prohibitin could bind to the retinoblastoma tumor suppressor protein and repress the transcriptional activity of E2F family members. This was necessary for prohibitin to inhibit cell proliferation. Our recent studies show that prohibitin could enhance the transcriptional activity of p53. Based on these findings, we will examine whether the transcriptional co-repressors HP1 and SUV39H contribute to prohibitin-mediated repression of E2F1 activity and whether prohibitin contributes to heterochromatin formation during cellular senescence. Attempts will be made to understand how prohibitin regulates the YY1 promoter and how this contributes to regulation of cell proliferation. We will next examine the mechanisms by which prohibitin facilitates the recruitment of p53 to promoters, leading to its activation. We will focus on whether prohibitin influences the tetramerization of p53 as well as its post-translational modifications. The last specific aim will focus on in vivo models to study prohibitin function. We have generated transgenic mice over-expressing prohibitin in mammary epithelial cells. We will examine the effects of prohibitin on mammary gland development as well as carcinogen and Ras induced breast carcinoma. Experiments are in progress to generate a conditional prohibitin knock-out mice. We expect that these experiments will help elucidate the molecular mechanisms involved in prohibitin-mediated growth control and tumor suppression.