树突状细胞分化过程中ARG1的表达调控及功能研究

L-arginine is a conditional essential amino acid for adults mammals, ARG1 is one of its key metabolizing enzymes. Recent studies suggest that L-arginine and its metabolizing enzymes play important roles in regulation of immune responses, in addition to its essential role in protein synthesis. Dendritic cell (DC) is one of the most potent antigen presenting cells. Our preliminary results showed that expression of ARG1 was dramatically induced during differentiation of mouse bone marrow derived dendritic cells, histone acetylation participated in the regulation of its expression; modulation of ARG1 level in hematopoietic progenitor cells affected its capability to differentiation into dendritic cells. Therefore we propose that ARG1 represents a novel regulator of dendritic cell differentiation. In order to test this hypothesis, our specific research aims include: to investigate the mechanism of ARG1 regulation by histone acetylation, to determine the effect of ARG1 on differentiation of dendritic cells and functional activity, to identify the molecular mechanism of ARG1 mediated L-arginine metabolism in dendritic cell, to evaluate the pathogenic significance of ARG1 in abnormal dendritic cells in cancer. Our project is expected to establish ARG1 as novel regulator of dendritic cell differentiation, also will provide unique strategy for DC-based immunotherapy in cancer.

精氨酸是人体条件性必需氨基酸的一种，ARG1是代谢精氨酸的主要分子之一。研究表明除了参与蛋白质合成外，精氨酸及其代谢酶具有重要的免疫调节功能。树突状细胞是机体最重要的抗原提呈细胞。预实验结果表明，ARG1 的表达在树突状细胞分化过程中逐渐上调，而乙酰化组蛋白参与了ARG1的表达调控；敲除造血祖细胞中ARG1的表达可抑制其向树突状细胞分化，而过表达ARG1则促进树突状细胞的分化进程。因而我们推测"精氨酸酶ARG1是树突状细胞分化的重要调控因子"。为验证此科学假说，我们拟首先以乙酰化组蛋白为切入点研究ARG1的表达调控机制，进而研究ARG1对树突状细胞分化和功能的影响，并进一步探讨ARG1是否通过参与精氨酸代谢而调控树突状细胞分化及其分子机制，最后在肿瘤中验证其病理意义。本项目的实施将阐明ARG1对树突状细胞分化的作用及其分子机制，为树突状细胞介导的肿瘤免疫治疗提供新策略。

精氨酸属于机体非必需氨基酸，当机体发生外伤，感染，或妊娠等特殊情况时需要从外源摄入。研究表明，精氨酸及其代谢酶具有重要的免疫调节功能，包括参与了髓系细胞的生物学功能调控（巨噬细胞和髓系抑制性细胞）。在本项目的资助下，我们发现：精氨酸代谢酶ARG1是树突状细胞（dendritic cells, DCs）分化调控的新分子。在单核细胞分化为DC的过程中，ARG1的表达出现明显上调；过表达ARG1可促进DC分化进程，包括GM-CSG培养体系及Flt3L培养体系。敲除ARG1的表达则可抑制DC分化。我们进一步对ARG1的调控机制进行了研究，发现在DC分化的过程中，组蛋白去乙酰化酶HDAC4与ARG1启动子的结合逐渐增强，是诱导ARG1表达的重要机制。HDAC4的结合可抑制转录因子STAT6及组蛋白的乙酰化水平，进而转录激活ARG1。进而确定STAT6结合位点介导了STAT3及HDAC4对ARG1的调控作用。过表达ARG1可逆转HDAC抑制剂TSA对DC分化的抑制作用。以上研究表明，HDAC4通过与STAT6相互作用，共同调控ARG1的表达，从而促进DC分化进程。项目的研究成果揭示了DC分化调控的新机制，及精氨酸代谢酶的新的免疫调节功能。