PROHIBITION GENE IN GROWTH CONTROL AND TUMOR SUPPRESSION

这一建议的主要焦点是了解禁止素的肿瘤抑制特性，该基因位于人类染色体17q21上，靠近BRACA1基因座。Prohibitin可以诱导细胞中的G1/S停滞，并且已经在散发性乳腺癌的亚群中发现了禁止素突变。目前还没有关于禁止素导致G1/S阻滞的机制的信息。我们最近的研究表明，禁止素可以与RB家族蛋白以及重要的信号分子Raf-1发生物理相互作用。Prohibitin能够抑制多种细胞系中克隆的形成；这种抑制可以被Raf-1逆转。此外，禁止素可以抑制E2F的转录活性，E2F是Rb蛋白的主要下游靶标。Prohibitin介导的对B细胞E2F活性的抑制可以通过刺激IgM受体来逆转。本申请中提出的实验旨在了解禁止素导致细胞生长停滞的分子机制。将对禁止素进行详细的突变分析，以确定参与影响生长抑制、对Raf-1蛋白的反应以及抑制E2F活性的禁止素区域。将详细研究禁止素介导的抑制E2F的机制，特别是HDAC1在这一过程中的作用。此外，还将试图了解上游信号，特别是Raf-1和MAP激酶通路是如何调节禁止素功能的。在同样的背景下，将确定禁止素在IgM受体介导的信号传递中的作用。最后，我们将评估禁止素基因和蛋白在人类肿瘤和肿瘤衍生细胞系中的状态。我们将重点研究禁忌素失活在乳腺癌和B细胞淋巴瘤中的作用，并将评估该突变是否导致生长控制的丧失。我们相信，这项提案中描述的研究将有助于阐明一个知之甚少的肿瘤抑制基因在肿瘤发生中的作用，并将为设计抗癌药物确定新的靶点。

The major focus of this proposal is to understand the tumor suppressive properties of prohibitin, a gene located on human chromosome 17q21 close to the BRACA1 locus. Prohibitin can induce a G1/S arrest in cells, and prohibitin mutations have been found in a subset of sporadic breast cancers. No information is available on the mechanisms by which prohibitin induces a G1/S arrest. Our recent studies have shown that prohibitin can physically interact with the Rb family proteins, as well as Raf- 1, a vital signaling molecule. Prohibitin is capable of suppressing the formation of colonies in a variety of cell lines; this suppression can be reversed by Raf-1. Further, prohibitin can repress the transcriptional activity of E2F, a major down- stream target of the Rb protein. Prohibitin mediated repression of E2F activity in B-cell lines can be reversed by stimulating the IgM receptors. The experiments proposed in this application aim at understanding the molecular mechanisms by which prohibitin induces growth arrest in cells. A detailed mutational analysis of prohibitin will be conducted, to identify the region of prohibitin involved in effecting growth suppression, response to Raf-1 protein as well as inhibition of E2F activity. The mechanisms involved in prohibitin-mediated repression of E2F will be studied in detail, with special emphasis on the role of HDAC1 in this process. Attempts will also be made to understand how prohibitin function is regulated by upstream signals, especially Raf-1 and MAP kinase pathway. In the same context, the role of prohibitin in IgM receptor-mediated signaling will be established. Lastly, we will assess the status of prohibitin gene and protein in human tumors and tumor derived cell lines. We will focus on the role of prohibitin inactivation in breast carcinomas as well as B-cell lymphomas, and it will be assessed whether the mutation has contributed to a loss of growth control. We believe that the studies described in this proposal will throw light on the role of a poorly understood tumor suppressor gene in oncogenesis, and will identify novel targets for designing anti-cancer agents.