G9a 表达上调在肝癌中的功能和临床意义

Hepatocellular carcinoma, HCC is the major type of primary liver cancer. HCC ranks as the fifth most common cancer in the world and is one of the leading causes of cancer death in our population. Most of HCC patients are diagnosed at late stages of cancer progression and therefore not eligible for curative surgical resection. For this reason, the development of reliable early diagnostic modalities and effective therapeutic interventions are of urgent need. The causal role of genetic alterations in human carcinogenesis has been intensively investigated in the past few decades. In recent years, increasing evidence strongly suggested that epigenetic alterations are also playing a major role in cancer development. Among various types of epigenetic alterations, previous studies have primarily focused on promoter DNA hypermethylation. However, our current knowledge about the pathological implications of histone modifications, another major epigenetic event, in human carcinogenesis remains elusive. Epigenetic regulation is a sophisticated process and involves multiple regulatory enzymes and complexes. In this study, we analyzed the expression changes of 591 epigenetic regulators by transcriptome sequencing (RNA-Seq) in human HCC samples. Our preliminary data revealed that G9a, a SET domain containing histone methyltransferase was one of the most frequently up-regulated genes in human HCC. G9a is a H3K9-specific histone methyltransferase responsible for transcriptional gene silencing in euchromatin region. Recent studies reported that G9a is a key regulator in stem cell renewal and cell fate determination. Deregulation of G9a has also been implicated in human carcinogenesis. However, little is known about the functional and pathological roles of G9a in human HCC. In this proposed project, we aim to thoroughly investigate the pathological roles of G9a in human HCC by 1) determining the expression changes of G9a in human HCC samples and establishing the clinicopathological significance of G9a deregulation in human HCC; 2) characterizing the oncogenic functions of G9a in HCC with in vitro and in vivo models; 3) investigating the mechanisms contributed to the frequent G9a up-regulation in human HCC; and 4) delineating the down-stream targets of G9a and the molecular mechanisms underlying G9a mediated liver carcinogenesis; 5) evaluating the therapeutic potential of G9a inhibitor. We believe our proposed study will enhance our current knowledge to the molecular basis of hepatocarcinogenesis and may provide new insights to facilitate the development of new diagnostic and therapeutic modalities.

肝细胞癌（HCC）是世界第五大常见的高致死率原发性癌症。早期诊疗方法亟待发展。近年来，有证据显示表观遗传改变在人体癌变中也起着重要作用。我们通过转录组高通量测序（RNA-Seq）分析了人肝癌样本中591种表观遗传调节因子的表达谱。我们发现，G9a在肝癌中表达上调程度最高。G9a组蛋白甲基化酶，负责特异性地甲基化H3K9，并引起常染色质中的基因转录沉默。有研究指出G9a在干细胞再生，分化及人类癌变过程中十分重要。然而，G9a在人肝癌中的病理作用却所知甚少。此研究旨在：1）确定G9a在人肝癌样本中的表达变化并分析其临床病理意义; 2）描绘G9a在体外和体内模型中的致癌作用; 3）研究G9a在人类肝癌中失调的上游分子机理；4）鉴定G9a的下游靶点及其在肝癌发展转移中的作用；及5）评估G9a抑制剂治疗肝癌的潜力。我们相信此项研究会提升关于肝癌发生发展分子机理的认识，并促进开发新的诊疗方法。

肝细胞癌（HCC）是全球主要的癌症之一，尤其是在中国很常见。表观遗传失调是人类肝癌的共同特征。在这项研究中，我们确定了G9a是人类HCC中经常被上调的组蛋白甲基转移酶。 G9a的上调与HCC进展和侵袭性临床病理特征显着相关。在功能上，我们证明了通过RNAi敲低，CRISPR / Cas9敲除和药理学抑制作用使G9a失活，在体外和体内模型中均显着消除了H3K9二甲基化并抑制了HCC细胞增殖和转移。从机制上讲，我们表明人类HCC中G9a的频繁上调归因于6p21染色体上的基因拷贝数增加。此外，我们确定了miR-1是G9a的负调控因子。 miR-1的缺失减轻了G9a的转录后抑制，并促进了其在人类HCC中的上调。利用RNA测序，我们确定了肿瘤抑制因子RARRES3是G9a的关键靶标。 RARRES3的表观遗传沉默有助于G9a的致癌功能。总之，我们的研究结果发现miR-1 / G9a / RARRES3轴在肝癌发生中频繁失调。我们的发现还强调了G9a的病理学意义及其在HCC治疗中的治疗潜力。