Exosomes specifically regulate macrophages to enhance anti-tumor effects

Abstract

Hepatocellular carcinoma (HCC), the seventh most common malignancy in the world, causes deaths of approximately 780,000 patients each year. Although a large number of studies have been conducted for a long time, the current treatment options of HCC are very limited, and many treatments are only effective for early HCC. However, most HCC are diagnosed in the advanced stage, thus patients are precluded from curative treatment. Usually, HCC patients at the advanced stage have extrahepatic metastasis. Therefore, understanding the mechanism of HCC metastasis is urgently needed to facilitate the early diagnosis of patients and the development of novel therapeutic strategy.

Many recent studies have found that exosomes play an important role in intercellular communication. Exosomes transfer their contents to the recipient cells influencing their properties and signaling. Compelling evidence has shown the critical role of exosomes of tumor cells in causing the localized effects of neighboring cells and the systemic effects in the distant sites. Our results indicated that exosomes derived from metastatic HCC cells increased the migratory and invasive potentials of immortalized liver and non-metastatic HCC cells as well as metastasis and pre-metastatic niche formation in animal models. Further analysis of exosomal proteins by proteomic analysis revealed that complement factor H (CFH) was highly expressed in the exosomes of metastatic HCC cells but not in exosomes of liver and non-metastatic HCC cells.

CFH is a major inhibitor of the immune defense complement system. We generated stable CFH knockdown clones in two HCC cell lines. It was confirmed that reduced CFH expression was observed in the total cell lysates and exosomes of the stable CFH knockdown clones. Exosomes with reduced CFH levels were found to exert diminished promoting capacity in growth, motility and metastasis of treated cells. The impact of CFH-regulated complement system was further explored. The data showed that 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. This data suggest that CFH protected HCC cells by evading complement attack. Lastly, we also demonstrated the therapeutic efficacy of anti-CFH antibody in suppressing HCC motility in cell culture and metastasis in an experimental metastasis model.

In conclusion, this study unraveled the role of CFH, secreted in the form of exosomes, in facilitating HCC metastasis by evading cells from complement-mediated cell lysis. The accomplishment of this study also provided insights into therapeutic intervention by the blockage of exosome-mediated signaling.