The Role Of IL-6/PGRN/MTOR Pathway In Hepatocellular Carcinoma

The primary liver cancer is one of the most common malignant tumors. The world health organization reported that primary liver cancer is the sixth most common neoplastic disease, and the second cause of cancer death worldwide, with an estimated 782500 new cases and 745000 deaths in 2012. China alone accounts for about 50％of the total number of cases and deaths. Primary liver cancer includes hepatocellular carcinoma(HCC), cholangiocarcinoma, hepatoblastoma,bile duct cystadenocarcinoma and haemangiosarcoma. HCC is the most common in these tumors. It accounts for approximately 80％to 85％of all primary liver cancer. Chronic infection of HBV and HCV, alcoholism, nonalcoholic fatty liver disease is the most important risk factors of primary liver cancer.Progranulin (PGRN) is a 593 amino acids-composed growth factor which contains seven and one half granulin-like domains. PGRN plays an important role in various physiological processes, and is widely involved in many kinds of diseases, such as autoimmune diseases, cancer, atherosclerosis, obesity and neurodegenerative diseases. In a variety of human cancers, the expression of PGRN is elevated. It is generally believed that PGRN can promote tumor progression. PGRN has been shown to activate PI3K/Akt and MEK/Erk signaling, which are essential for the proliferation, survival and migration of cancer cells. In addition, PGRN can phosphorylate p70S6K, a downstream molecule of the PI3K/Akt/mTOR signaling pathway.Previous reports have confirmed that the mRNA and protein levels of PGRN are found overexpressed in more than 70％of liver cancer tissues. The in vitro studies indicated that PGRN is closely related with cell proliferation, migration, invasion, and chemotherapy tolerance of HCC. Comparing with the heathy controls, the level of PGRN was up-regulated in the serum and tumor tissues from patients with cholangiocarcinoma, the second most common cancer of primary liver cancer. The expression of Interleukin-6 (IL-6) in cholangiocarcinoma is also increased. IL-6 drives the expression of PGRN through Erk/RSK1/C/EBPβ signaling pathways. In addition, PGRN plays growth-promoting effect in cholangiocarcinoma by inhibiting FOXO1 via PI3K/Akt signaling pathway.IL-6 is also called B cell differentiation factor (BCDF/BSF2), is a pleiotropic cytokine. It can be secreted by a variety of cells including macrophages, B cells, T cells, syncytial trophoblast, fibroblast, cuticle forming cells, mononuclear cells, endothelial cells and stromal cells. As a cytokine, IL-6 can activate downstream signaling pathways through the receptor-ligand interaction. IL-6 combines with the IL-6 receptor IL-6R, and further interacts with gp130, subquently activates JAK/STAT3, MAP kinase and PI3K signaling pathway. As a multifunctional cytokine, IL-6 plays important role in many physiological and pathological processes, such as temperature regulation, inflammatory response, liver cell regeneration, proliferation and invasion of tumor cells, emotional memory consolidation and muscle reconstruction.A series of studies showed that IL-6 is closely related with the occurrence and development a variety of cancers. However, the role of IL-6 induced PGRN and mTOR signaling pathway in the development hepatocellular carcinoma promoted by IL-6 is still unclear.Objective:This study aimed to investigate the the effect of IL-6 on the expression of PGRN in HCC, and the role of PGRN/mTOR signaling in IL-6-driven malignancy of HCC.Methods:We use immunohistochemistry to study the expression of PGRN and IL-6 in the HCC and normal liver tissues. Using the real time RT-PCR and western blot assays to detect the mRNA and protein levels of PGRN in HCC cells HepG2 and Be17402 treated with recombination human IL-6. To investigate the mechanism of IL-6-regulated PGRN expression, the inhibitor of MEK/Erk, U-1026, and small interfering RNA (si-RNA) targeting C/EBPβ are employed. Furthermore, Cell Counting Kit 8, cell cycle, wound healing and transwell assays are performed to explore the mode of action of IL-6/PGRN/mTOR pathway in proliferation, migration and invasion of HCC cells.Results:The immunohistochemistry staining showed enhanced expression of IL-6 and PGRN in HCC tissues compared with that in normal liver tissues. Importantly, the expression of IL-6 and PGRN in HCC tissues was positive correlated. Western blot assay revealed that IL-6 promoted the expression of PGRN in HCC cells in an Erk/C/EBPβ signaling pathway dependent manner. Cell behaviors analysis indicated that IL-6 stimulated the proliferation, migration and invasion of HepG2 cells, which were partially impaired by the lowering expression of PGRN. In addition, IL-6 or PGRN-stimulated proliferation, migration and invasion of HepG2 cells were inhibited by mTOR inhibitor, rapamycin.Conclusion:IL-6 can promote the expression of PGRN through Erk/C/EBPβ signaling pathway. PGRN contributes to IL-6-driven malignancy of HCC. Moreover, inhibition of mTOR signaling pathway protects against PGRN and IL-6-stimulated malignancy of HCC.In summary, our study demonstrated that IL-6 has a synergistic relationship with PGRN in HCC. We firstly verified the role of PGRN/mTOR pathway in IL-6-regualted pathogenesis of HCC. Our study provided a better understanding of the biological activities of the IL-6/PGRN/mTOR cascade in the carcinogenesis of HCC, and suggested that IL-6-driven PGRN and PGRN-activated mTOR signaling pathway may be a potential target in the treatment of HCC.