Maf1, a novel negative transcriptional regulator of the TATA binding protein

描述（由申请人提供）：在之前的资助期内，我们意外发现表皮生长因子受体家族成员对中心转录起始因子TBP的表达有差异调节，并定义了调节TBP表达的新信号通路和转录因子。除了确定TBP的阳性调节因子外，我们还发现了一种新的人类蛋白Maf1，它可以抑制TBP的转录。Maf1是一种重要的转录抑制因子，独特地靶向RNA pol II-和pol iii -转录基因，促进致癌转化。我们的新结果支持了Maf1是PTEN的关键靶点，对其肿瘤抑制功能至关重要的观点。PTEN缺失导致Maf1表达显著降低；在PTEN-缺陷细胞中，Maf1表达增加抑制细胞转化；在pten缺失的小鼠和人前列腺癌中，核Maf1表达减少。我们的总体目标是了解Maf1的分子和生物学功能，并通过小鼠模型确定PTEN缺失导致的Maf1表达降低是否有助于前列腺癌的发展。目的1将鉴定原代人前列腺上皮细胞中Maf1占据的全基因组区域。鉴于我们新发现的Maf1与转录因子中介CDK8亚复合物之间的相互作用，我们将进一步验证Maf1阻断该亚复合物诱导RNA pol II和iii依赖性基因表达的能力的新假设。这些研究将定义来自不同RNA聚合酶的转录被共同抑制的新范式，从而阐明重要的基因抑制途径。鉴于CDK8是一种有效的癌蛋白，Aim 2将进一步评估Maf1是否会消除CDK8介导的致癌转化。我们将建立转基因小鼠模型来验证恢复pten缺陷小鼠前列腺中Maf1的表达能否阻断或延缓前列腺上皮内瘤变和肿瘤发生。Maf1的表征将为细胞如何抑制转化表型和定义新的PTEN靶标提供一个新的范例，其缺失对前列腺癌的发展至关重要。

DESCRIPTION (provided by applicant): In the previous grant period, we made the unexpected discovery that members of the epidermal growth factor receptor family differentially regulate expression of the central transcription initiation factor, TBP, and defined new signaling pathways and transcription factors that regulate TBP expression. In addition to identifying positive regulators of TBP, we discovered a novel human protein, Maf1, which represses TBP transcription. Maf1 is an important transcriptional repressor that uniquely targets both RNA pol II- and pol III-transcribed genes that promote oncogenic transformation. Our new results support the idea that Maf1 is a key target of PTEN that is critical for its tumor suppressor function. Loss of PTEN results in a marked decrease in Maf1 expression; increased Maf1 expression suppresses cellular transformation in PTEN- deficient cells; and nuclear Maf1 expression is diminished in both mouse and human prostate cancers that are PTEN-deficient. Our overall goal is to understand the molecular and biological function of Maf1, and to use mouse models to determine whether the resultant decrease in Maf1 expression, by loss of PTEN, contributes to the development of prostate cancer. Aim 1 will identify Maf1 occupied regions genome- wide in primary human prostate epithelial cells. Given our newly identified interaction between Maf1 and the transcription factor Mediator CDK8 subcomplex, we will further test the novel hypothesis that Maf1 blocks the ability of this subcomplex to induce both RNA pol II- and III-dependent gene expression. These studies will define new paradigms by which transcription from different RNA polymerases are co-repressed, thus elucidating important gene repression pathways. Given that CDK8 is a potent oncoprotein, Aim 2 will further assess whether Maf1 abrogates CDK8-mediated oncogenic transformation. A transgenic mouse model will be established to test the idea that restoring Maf1 expression in PTEN-deficient mouse prostate will block or delay prostate intraepithelial neoplasia and tumorigenesis. Characterization of Maf1 will provide a new paradigm for how cells suppress a transformed phenotype and define a novel PTEN target whose loss is critical to the development of prostate cancer.