BRIT 1: Roles in Immortalization, Checkpoints and Cancer

描述（由申请方提供）：细胞周期检查点控制的丧失和无限期增殖能力的获得构成了癌症发展所需的两个基本变化。BRIT 1（BRCT-Repeat Inhibitor of hTERT expression）是一个通过我们增强的逆转录病毒突变筛选鉴定为hTERT功能阻遏物的新基因，与细胞永生化有关。我们的初步数据表明，BRIT 1有额外的功能，调节内S和G2/M检查点，这在一定程度上，可能是由于其调节BRCA 1和Chk 1的表达，其直接作用于DNA损伤信号的传输。此外，BRIT 1位于染色体8p23.1上，基于洛和CGH分析，其与包括乳腺癌和卵巢癌在内的几种恶性肿瘤的发生有关。当通过DNA阵列分析时，BRIT 1的表达在这两种癌症类型中也显著降低。因此，我们推测BRIT 1可能通过双重功能发挥肿瘤抑制基因的作用：抑制细胞永生化和维持基因组稳定性。 将在以下步骤中检验此假设。(1)我们将确定BR T1在防止细胞永生化的作用，通过使用正常的人类细胞，有条件地表达小发夹RNA对BRIT 1，我们将调查的机制，介导BRIT 1的hTERT表达的功能。(2)我们将使用BRIT 1缺失的细胞来研究BRIT 1在应对遗传毒性应激、维持基因组完整性和细胞转化中的作用;我们将通过使用比较基因组杂交（CGH）和光谱核型分析（SKY）检测染色体改变来评估基因组不稳定性;我们将研究BRIT 1如何调节BRCA 1和Chk 1的启动子活性，以及BRIT 1如何在DNA损伤信号的传递中发挥直接作用;我们将建立BRIT 1条件性敲除小鼠模型，以评估BRIT 1在体内维持基因组完整性和抑制肿瘤形成的功能。(3)我们将鉴定和表征乳腺癌和卵巢癌样本中BRIT 1的畸变，以确定BRIT 1是否可作为癌症的预后标志物或治疗靶点。作为一个必然的结果，BRIT 1的功能和它的畸变在癌症患者的分析将有助于提高对癌症的发生和发展的关键病理学改变的理解，并开发新的，有效的癌症治疗方法。

DESCRIPTION (provided by applicant): Loss of cell cycle checkpoint control and acquisition of the ability to proliferate indefinitely constitute two of the fundamental changes required for the development of cancer. BRIT1 (BRCT-Repeat Inhibitor of hTERT expression), a novel gene identified through our enhanced retroviral mutation screen as a repressor of hTERT function, is implicated in cellular immortalization. Our preliminary data indicate that BRIT1 has additional functions-regulating both the intra-S and G2/M checkpoints-that, in part, may result from its regulation of BRCA1 and Chk1 expression and its direct role in the transmission of DNA damage signals. Moreover, BRIT1 is located on chromosome 8p23.1, which has been implicated in the development of several malignancies, including breast cancer and ovarian cancer, based on LOH and CGH analyses. The expression of BRIT1 also was significantly reduced in these two cancer types when analyzed by DNA arrays. Thus, we hypothesize that BRIT1 may function as a tumor suppressor gene through dual functions: repressing cellular immortalization and maintaining genomic stability. This hypothesis will be tested in the following steps. (1) We will determine the role of BR T1 in preventing cellular immortalization by using normal human cells that conditionally express small hairpin RNA against BRIT1, and we will investigate the mechanisms mediating BRIT1's function on hTERT expression. (2) We will use BRIT 1-depleted cells to study the role of BRIT1 in the response to genotoxic stress, maintenance of genomic integrity, and cellular transformation; we will assess genomic instability by detecting chromosome alterations using comparative genomic hybridization (CGH) and spectral karyotyping (SKY); we will study how BRIT1 regulates the promoter activities of BRCA1 and Chk1 and how BRIT1 may play a direct role in transmission of DNA damage signal; and we will develop a BRIT1 conditional knockout mouse model to assess the BRIT1's function in vivo in maintaining genomic integrity and suppressing tumor formation. (3) We will identify and characterize the aberrations of BRIT1 in breast and ovarian cancer samples to determine if BRIT1 serves as a prognostic marker or as a therapeutic target in cancer. As a corollary, an analysis of the function of BRIT1 and its aberrations in cancer patients will contribute to an improved understanding of the key pathological alterations in cancer initiation and progression and to the development of novel, effective therapeutic approaches for cancer.