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

描述（由申请人提供）：在先前的授权期间，我们意外地发现表皮生长因子受体家族的成员差异调节中心转录起始因子TBP的表达，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抑制TBP转录的人类蛋白Maf 1。Maf 1是一种重要的转录抑制因子，其独特地靶向促进致癌转化的RNA pol II和pol III转录基因。我们的新结果支持Maf 1是PTEN的关键靶点的观点，这对其肿瘤抑制功能至关重要。PTEN的缺失导致Maf 1表达的显著降低; Maf 1表达的增加抑制了PTEN缺陷型细胞中的细胞转化;并且在PTEN缺陷型的小鼠和人前列腺癌中，核Maf 1表达都减少。我们的总体目标是了解Maf 1的分子和生物学功能，并使用小鼠模型来确定由于PTEN的缺失而导致的Maf 1表达的降低是否有助于前列腺癌的发展。目的1将在原代人前列腺上皮细胞中鉴定Maf 1占据的全基因组区域。考虑到我们新发现的Maf 1和转录因子介体CDK 8亚复合物之间的相互作用，我们将进一步测试Maf 1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。这些研究将定义新的范例，通过这些范例，来自不同RNA聚合酶的转录被共阻遏，从而阐明重要的基因阻遏途径。鉴于CDK 8是一种有效的癌蛋白，Aim 2将进一步评估Maf 1是否消除CDK 8介导的致癌转化。将建立转基因小鼠模型来测试在PTEN缺陷小鼠前列腺中恢复Maf 1表达将阻断或延迟前列腺上皮内瘤形成和肿瘤发生的想法。Maf 1的表征将为细胞如何抑制转化的表型提供新的范例，并定义一种新的PTEN靶点，其丢失对前列腺癌的发展至关重要。 公共卫生相关性：这项提案将描述一种新的蛋白质Maf 1，它选择性地抑制驱动肿瘤发生的基因的表达。重要的是，Maf 1抑制所有三种核RNA聚合酶的转录。这种功能的关键是Maf 1调节中央转录起始因子TBP表达的能力。此外，Maf 1表达在癌症中通过肿瘤抑制因子PTEN的失活而失调。阐明Maf 1的功能将大大增强我们对细胞如何保持非转化状态的理解，并为不同的RNA聚合酶系统如何协调调节提供新的范例。

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. PUBLIC HEALTH RELEVANCE: This proposal will characterize a novel protein, Maf1, which selectively represses the expression of genes that drive oncogenesis. Importantly, Maf1 acts to repress transcription from all three nuclear RNA polymerases. Key to this function is the ability of Maf1 to regulate the expression of the central transcription initiation factor, TBP. Furthermore, Maf1 expression is deregulated in cancer through the inactivation of the tumor suppressor, PTEN. Elucidating the function of Maf1 will greatly enhance our understanding of how cells maintain a non-transformed state and provide a new paradigm for how distinct RNA polymerase systems are coordinately regulated.