GP73通过调控内质网应激影响肿瘤微环境的分子机制研究

The tumor microenvironment, characterized by low oxygen supply and nutrient deprivation, can evoke the endoplasmic reticulum (ER) stress response in tumor cells. Transmissible ER stress plays important role by priming macrophages to recapitulate, amplify, and expand inflammation. Golgi membrane protein 73 (GP73), also known as Golph2, is a residential Golgi-specific membrane protein, whose expression was found to be strongly upregulated in hepatocytes from patients with viral or non-viral liver diseases. Previous studies showed that GP73 may be a new serum biomarker for diagnosing hepatocellular carcinoma (HCC). However, the functional relevance of GP73 expression changes during hepatocyte cancer development and progression remains unknown. Our previous studies showed that GP73 deficiency blocks UPR response, inhibits ER Stress transmission from tumor cell line HepG2 to HepG2 or from HepG2 to THP-1 macrophages, with decreased inflammatory levels in tumor microenvironment. Interestingly, both intracellular and secrected forms of GP73 were significantly upregulated in response to ER stress chemical inducer. Importantly, GP73 bind to GRP78, a central player in ERS-UPR signaling. We therefore prostulated that the upregulated GP73 in response to ER stress regulate UPR activation and ER stress transmission by interacting with intracellular GRP78 and cell surface GRP78 in neighbouring cells including tumor cell and macrophages. Based on those findings, we would like to explore further the function of GP73 in regulationg ERS-UPR activation and transmission, elucidating the molecular mechanism of GP73 in HCC cancer development by identifying its downstream target, and finally, to uncover the importance of GP73 as a new predictive marker of HCC and a therapeutic target for hepatocarcinoma cancer.

肿瘤细胞由于长期处于缺氧且营养匮乏的微环境中，导致其内质网应激的激活。内质网应激信号在肿瘤微环境中各种细胞间的传递，对肿瘤的发生发展和转移十分重要，但内质网应激的传递机制尚不十分明确。我们前期研究发现，高尔基体糖蛋白GP73敲低能够抑制内质网应激信号通路的激活、抑制内质网应激信号在肿瘤细胞之间以及肿瘤细胞-巨噬细胞间的传递，进而抑制肿瘤微环境中多种炎性因子的释放。在内质网应激压力刺激下，GP73的表达水平迅速上调，GP73与GRP78之间能够发生相互作用。以上结果提示我们：内质网压力下，GP73通过与细胞内以及临近细胞表面的GRP78相互作用，调控内质网应激信号在肿瘤细胞中的激活以及在临近细胞间的传递，进而影响肿瘤微环境中炎性因子的释放。本项目拟进一步研究GP73参与调控内质网应激激活、传递以及肿瘤微环境的分子机制，并阐明其参与肿瘤发生发展的可能机制，为GP73的临床应用研究提供理论基础。

肿瘤细胞能将未折叠蛋白反应信号传递给邻近的巨噬细胞，并激活未折叠蛋白反应的靶基因及前炎症细胞因子，进而发生促肿瘤炎症反应。然而，内质网应激信号传递的分子机制尚不完全清楚。本研究中，我们发现对肝癌的生长和侵袭至关重要的分泌形式的GP73，能介导细胞间内质网应激信号的传递。此外，内质网应激压力能上调细胞GP73的表达。分泌形式的GP73通过与GRP78相互作用能激活邻近的巨噬细胞也发生内质网应激，肿瘤相关巨噬细胞（TAMs）发生内质网应激后释放炎症趋化因子和细胞因子。通过分析我们发现，肝癌患者的肝癌组织标本中GRP78的表达水平、TAMs的富集程度与GP73水平呈正相关，同时高表达GP73与CD206的肝癌患者预后不良。中和GP73后，两种肝癌模型小鼠组织中TAMs的富集程度降低，肿瘤生长受到抑制，小鼠生存时间明显延长。本研究深入阐述了细胞外GP73引发和传递内质网应激信号的分子机制。