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

描述(申请人提供)：在之前的资助期间，我们意外地发现，表皮生长因子受体家族的成员对中央转录起始因子TBP的表达进行了差异调节，并定义了调节TBP表达的新的信号通路和转录因子。除了鉴定TBP的正调控因子外，我们还发现了一种新的人类蛋白Maf1，它抑制TBP的转录。Maf1是一种重要的转录抑制因子，它针对促进致癌转化的RNA PolII和PolIII转录基因。我们的新结果支持这样的观点，即Maf1是PTEN的一个关键靶点，而PTEN对其肿瘤抑制功能至关重要。PTEN的缺失导致Maf1的表达显著降低；Maf1的表达增加抑制了PTEN缺失细胞的细胞转化；在PTEN缺失的小鼠和人类前列腺癌中，核Maf1的表达都减少了。我们的总体目标是了解Maf1的分子和生物学功能，并使用小鼠模型来确定PTEN缺失导致的Maf1表达减少是否有助于前列腺癌的发展。目标1将在原代人类前列腺上皮细胞中鉴定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亚复合体之间的相互作用，我们将进一步检验这一新的假设，即Maf1阻断该亚复合体诱导RNA PolII和III依赖的基因表达的能力。这些研究将定义不同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是否取消了CDK8介导的致癌转化。将建立转基因小鼠模型，以测试在PTEN缺陷的小鼠前列腺中恢复Maf1表达将阻止或延缓前列腺上皮内瘤变和肿瘤发生的想法。Maf1的特性将为细胞如何抑制转化的表型提供一个新的范例，并定义一个新的PTEN靶点，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.