Molecular mechanism of oncogenic programming by histone demethylase GASC1

描述（由申请人提供）：本申请的长期目标是阐明组蛋白去甲基化酶GASC 1（鳞状细胞癌1中扩增的基因，也称为JMJD 2C和KDM 4C）的失调促进肿瘤发生的基本机制，并为开发该蛋白作为乳腺癌的新治疗靶点奠定基础。GASC 1基因最初是从食管癌细胞中9 p24的扩增区域克隆的。后来的研究表明，GASC 1在大约15%的乳腺癌中扩增，过表达在侵袭性基底型乳腺癌中更为普遍。GASC 1蛋白是组蛋白去甲基化酶的关键成员，其在调节染色质结构和基因表达中起重要作用;并且与肿瘤发生有关。GASC 1主要催化组蛋白H3赖氨酸9（H3 K9 me 3/me 2）表观遗传抑制标记的三甲基化和二甲基化形式的去甲基化。然而，GASC 1依赖的染色质调控转化为致癌性和癌症进展的分子机制仍然知之甚少。有趣的初步证据表明，GASC 1在靶基因启动子区域显著富集，并且GASC 1向特定基因组位点的募集需要GASC 1 Tudor和植物同源结构域（PHD）。研究表明Tudor和PHD结构域具有在启动子区域结合H3 K4 me 3活性标记的潜力。重要的是，我们证明了GASC 1靶基因参与多种信号通路和生物过程，包括关键基因，如参与泛素化的S期激酶相关蛋白2（SKP 2）。本申请的中心假设是，GASC 1通过其组蛋白结合结构域被募集到含有H3 K4 me 3活性标记的基因启动子区域，随后H3 K9 me 3/me 2抑制标记的去甲基化诱导一组关键泛素化途径基因的转录，这些基因最终促进肿瘤发生。基于这一假设，选择性改变GASC 1组蛋白募集的策略作为侵袭性GASC 1扩增的乳腺癌和食管癌的靶向治疗具有很大的希望。在本申请中，将追求两个具体目标。在目标1中，我们将阐明GASC 1介导其募集到靶基因启动子区的分子机制和结构细节。在目标2中，我们将确定GASC 1如何影响组蛋白甲基化状态和靶基因的表达，这些靶基因负责介导GASC 1在体外和异种移植动物模型中乳腺肿瘤发生中的作用。值得注意的是，拟议的研究将从根本上增加我们对GASC 1被招募到基因组位点的机制以及GASC 1的遗传扩增如何改变表观遗传编程并触发癌症下游致癌途径的理解。这些方面在基于GASC 1机制的疗法的开发中具有转化意义，以靶向广泛的癌症，特别是GASC 1扩增的基底乳腺癌。

DESCRIPTION (provided by applicant): The long-term goal of this application is to elucidate the fundamental mechanism by which dysregulation of the histone demethylase, GASC1 (Gene Amplified in Squamous Cell Carcinoma 1, also known as JMJD2C and KDM4C), contributes to tumorigenesis, and to lay a foundation for the development of this protein as a new therapeutic target against breast cancer. The GASC1 gene was originally cloned from an amplified region at 9p24 in esophageal cancer cells. Later studies demonstrated that GASC1 is amplified in approximately 15% of breast cancers with overexpression more prevalent in aggressive, basal-type breast cancer. The GASC1 protein is a key member of histone demethylases that play an essential role in regulating chromatin architecture and gene expression; and is implicated in tumorigenesis. GASC1 mainly catalyzes demethylation of tri- and di-methylated forms of histone H3 lysine 9 (H3K9me3/me2) epigenetic repressive marks. However, the molecular mechanisms by which GASC1-dependent chromatin regulation translates to oncogenicity and cancer progression remain poorly understood. Intriguing preliminary evidence indicated that GASC1 is significantly enriched at target gene promoter regions, and that recruitment of GASC1 to specific genomic loci requires the GASC1 Tudor and Plant Homeo Domains (PHD). Studies indicate that the Tudor and PHD domains have the potential to bind H3K4me3 active marks at promoter regions. Importantly, we demonstrated that GASC1 target genes are involved in multiple signaling pathways and biological processes, including critical genes such as the S-phase kinase-associated protein 2 (SKP2) which participates in ubiquitination. The central hypothesis of this application is that GASC1 is recruited to gene promoter regions containing H3K4me3 active marks via its histone-binding domains, and the subsequent demethylation of H3K9me3/me2 repressive marks induces the transcription of a set of key ubiquitination pathway genes that ultimately promote tumorigenesis. Based on this hypothesis, strategies that selectively alter the GASC1 histone recruitment hold great promise as targeted therapies for aggressive, GASC1-amplified breast and esophageal cancers. In this application, two specific aims will be pursued. In Aim 1, we will elucidate the molecular mechanism and structural details of GASC1 that mediate its recruitment to promoter regions of target genes. In Aim 2, we will determine how GASC1 impacts the histone methylation status and expression of target genes responsible for mediating GASC1's role in breast tumorigenesis in vitro and in xenograft animal models. Significantly, the proposed research will fundamentally increase our understanding of the mechanisms by which GASC1 is recruited to genomic loci and how genetic amplification of GASC1 alters epigenetic programming and triggers downstream oncogenic pathways in cancer. These aspects have translational implications in the development of GASC1 mechanism-based therapies to target a wide range of cancers, particularly GASC1-amplified basal breast cancer.