PRMT9通过TGF-β/lncRPCM激活巨噬细胞并反馈促进肝癌侵袭转移的机制研究

The regulation mechanisms between tumor-associated macrophages (TAM) in hepatocellular carcinoma (HCC) remain to be elucidate. We have recently reported that protein arginine methyltransferase 9 (PRMT9) is overepressed in HCC and promotes HCC invasion and metastasis. In this project, our preliminary data showed that PRMT9 could promote the expression and secretion of TGF-β from HCC cells. TGF-β could activate macrophages to TAM probably through lncRPCM. Exosomes derived from TAM could promote HCC cells migration and invasion. Therefore, we hypothesize that the aberrantly high expression of PRMT9 in HCC cells can induce macrophage M2 polarization through TGFβ/lncRPCM pathway. The induced TAM then promotes HCC invasion and metastasis. Our project will employ ChIP and in vitro methylation assays to explore the mechanism by which PRMT9 regulates the expression and secretion of TGF-β from HCC cells through histones modification. Besides, we will also perform ChIRP and RNA pull-down assays to identify the downstream targets of TGFβ/lncRPCM, clarifying the mechanism by which TGFβ/lncRPCM regulate the polarization of macrophages. In addition, our project will explore how exosomes derived from TAM promote HCC cells invasion and metastasis. In conclusion, our research will help to further clarify the regulation relationship between HCC cells and TAM, and provide scientific evidences in developing new therapeutic targets for HCC.

肝细胞癌（HCC）与肿瘤相关巨噬细胞（TAM）的相互作用机制尚未完全阐明。我们已发表文献表明HCC细胞中精氨酸甲基转移酶PRMT9与侵袭转移密切相关。本项目预实验发现PRMT9可促进HCC细胞表达分泌TGFβ，TGFβ可能通过lncRPCM激活巨噬细胞为TAM，TAM释放的外泌体可促进HCC细胞迁移侵袭。据此我们提出：HCC细胞中异常表达的PRMT9通过TGFβ/lncRPCM使巨噬细胞极化为TAM，后者反馈促进HCC侵袭转移。本项目拟通过ChIP和体外甲基化等实验明确PRMT9通过组蛋白修饰调控TGFβ表达的机制；通过ChIRP和RNA pull-down实验鉴定TAM中lncRPCM的下游靶点，明确TGFβ/lncRPCM调节巨噬细胞极化的机制；以及明确TAM通过释放外泌体促进HCC侵袭转移的机制。研究成果将进一步解释HCC细胞与TAM的相互作用关系，为寻找HCC治疗新靶点提供依据。

PRMT9是蛋白质精氨酸甲基转移酶家族的一个成员，本课题组前期已发表的研究显示其在肝细胞癌（HCC）中行使明显的促癌作用，引起广泛关注，但其对HCC的影响及机制仍有许多未知。本项目在执行过程中主要探讨PRMT9在HCC细胞中过表达后促进肿瘤微环境中巨噬细胞向M2型极化的机制，以及这些受HCC细胞特殊刺激而极化的巨噬细胞对HCC细胞的反馈作用及其机制。本项目的主要发现为：1. PRMT9在肝癌细胞中可通过与PYCR2结合，激活NOTCH通路，进而促进Fibronectin表达并分泌至细胞外；2.PRMT9-PYCR2-Fibronectin通路可刺激巨噬细胞，使其向M2型极化并可进一步促进肝癌的进展。这些成果有助于从肿瘤微环境和表观遗传学角度上进一步理解HCC发生发展的分子机制，并为HCC的诊治提供潜在靶点。