IL6ST regulates liver tumorigenesis via the regulation of mitophagy

다국어 초록 (Multilingual Abstract)

Hepatocellular carcinoma (HCC) is the sixth most commonly occurring cancer in the world and the third largest cause of cancer mortality. There is increasing evidence that the inflammatory process is inherently associated with many different cancer types, including HCC. Cytokines are released in response to a diverse range of cellular stresses, including carcinogen-induced injury, infection, and inflammation. A number of cytokines that are produced in the tumor microenvironment have an important role in cancer pathogenesis. Among them, there are IL-6 family cytokines that share the common receptor subunit IL6ST. IL6ST regulates cell survival, growth, and proliferation through the regulation of JAK-Stat3 and PI3K-mTORC1. Both downstream pathways have been linked with autophagy and mitochondrial function. Moreover, mitophagy contributes to metabolic dysfunction syndrome and chronic liver diseases such as NAFLD, NASH, and HCC. However, the mechanism of how IL6ST modulates hepatocyte mitophagy and HCC development remains unclear. IL6ST activated Stat3 and mTORC1 signaling in HCC, as evidenced by the controls phosphorylation of Stat3 (Tyr705), P70S6K(T389), EIF4E(S209), and RPS6(S235). Interestingly, IL6ST prevents mitochondrial stress and improves cell viability by inhibition of Stat3 and mTORC1-ULK1 mediated mitophagy and apoptosis. In genetically engineered mouse models of HCC (TAK1ΔHep), hepatocyte-specific deletion of IL6ST suppressed the multiplicity and maximum size of naturally occurring cancer. In conclusion, IL6ST governs parallel activation of carcinogenic STAT3 along with mTORC1 in the pathogenesis of HCC by regulation of mitophagy-dependent apoptosis and cancer cell survival.