Exosomal Complement Factor H Promotes Liver Cancer Metastasis by Inhibiting Complement-dependent Cytotoxicity of Tumor Cells

Hepatocellular carcinoma (HCC), the seventh most common malignancy in the world, can cause deaths of approximately 780,000 patients each year. Although a large number of studies have been conducted for a long time, the current treatment level of HCC is very limited, and many treatments are only effective for early HCC. However, most HCC are diagnosed in the advanced stage. Usually, patients with advanced stage have extrahepatic metastasis. This metastasis is not a random process. Therefore, studying the mechanism of HCC metastasis is beneficial to the early diagnosis of patients and the development of novel therapeutic strategy.<br> <br>Many recent studies have found that exosomes play an important role in intercellular communication. Exosomes transfer their contents, causing localized effects of cancer cells on surrounding cells and systemic effects on distant cells. Our results indicate that exosomes derived from metastatic HCC cells increased the migratory and invasive potentials of liver cancer cells and metastasis in animal models. Further analysis of exosomal proteins by proteomic analysis revealed that complement factor H (CFH) is highly expressed in exosomes of metastatic HCC cells.<br> <br>CFH is a major inhibitor of the immune defense complement system. We generated stable CFH knockdown clones in metastatic HCC cells. It was confirmed that reduced CFH expression was observed in the total cell lysates and exosomes of the stable clones, resulting in the decreased oncogenic properties of cells and exosomes. We also showed that HCC cells treated with exosomes of non-target control cells had a decrease in complement-mediated cytotoxicity when compared to the cells treated with exosomes derived from CFH knockdown cells suggesting that CFH protects HCC cells by evading complement attack.<br> <br>Based on the above, we hypothesize that exosomal CFH inhibits complement activation in the tumor microenvironment to promote HCC tumorigenesis and metastasis. Although we do not fully understand the role of CFH in tumor development, our study provides new insights into the functional role of CFH in HCC and provides a basis for further study of other potential roles of CFH in carcinogenesis.<br><br>

肝细胞癌（Hepatocellular carcinoma, HCC）是全球第七大常见恶性肿瘤，每年约导致78万名患者死亡。尽管长期以来开展了大量研究，但当前肝细胞癌的治疗水平仍十分有限，多数疗法仅对早期肝细胞癌有效。然而，大部分肝细胞癌患者在确诊时已处于晚期，且通常伴随肝外转移。此类转移并非随机过程，因此研究肝细胞癌转移的机制，有助于实现患者的早期诊断，并推动新型治疗策略的开发。

近年来诸多研究表明，外泌体（exosomes）在细胞间通讯中发挥重要作用。外泌体可通过传递自身内容物，使癌细胞对周围细胞产生局部效应，同时对远端细胞造成全身影响。本研究结果显示，源自转移性肝癌细胞的外泌体可增强肝癌细胞的迁移与侵袭能力，并可促进动物模型中的肿瘤转移。通过蛋白质组学分析对外泌体蛋白进行深入解析后发现，补体因子H（complement factor H, CFH）在转移性肝癌细胞的外泌体中呈高表达状态。

补体因子H是免疫防御补体系统的主要抑制因子。本研究在转移性肝癌细胞中构建了稳定的CFH敲低克隆株，经证实，这些稳定克隆的总细胞裂解液及外泌体中CFH的表达水平均显著降低，进而削弱了细胞与外泌体的致瘤特性。研究同时发现，与经CFH敲低细胞来源外泌体处理的肝癌细胞相比，经非靶向对照细胞来源外泌体处理的肝癌细胞，其补体介导的细胞毒性有所降低，这表明CFH可通过逃避补体攻击来保护肝癌细胞。

基于上述发现，本研究提出假说：外泌体携带的CFH可通过抑制肿瘤微环境中的补体激活，进而促进肝细胞癌的发生与转移。尽管目前尚未完全阐明CFH在肿瘤发生发展中的完整作用，但本研究为理解CFH在肝细胞癌中的功能角色提供了新视角，也为后续探究CFH在癌变过程中的其他潜在作用奠定了基础。