Lipopolysaccharide-Induced Toll-Like Receptor 4 Signaling in Cancer Cells Promotes Cell Survival and Proliferation in Hepatocellular Carcinoma

Abstract

Recent studies have shown that toll-like receptor 4 (TLR4) is involved in hepatocarcinogenesis. However, the significance of TLR4 signaling in cancer development and progression remains unclear. The purpose of this study was to investigate the role of TLR4 in cancer cell survival and proliferation in hepatocellular carcinoma (HCC). Fifty-three HCC and ten normal liver specimens were analyzed by immunohistochemistry, and three cell lines (HL-7702, PLC/PRF/5 and HepG2) were used for in vitro studies. Lipopolysaccharide (LPS), a specific ligand of TLR4, was used to activate TLR4 signaling. The effects of LPS-TLR4 signaling on cell survival, proliferation and invasion were examined. Specific inhibitors of NF-κB and MAPK (JNK, ERK and p38) signaling pathways were used to explore the role of each pathway in LPS-TLR4 signaling. TLR4 was overexpressed in HCC cell lines and in human HCC tissues, where it correlated with Ki-67 expression. LPS-induced activation of TLR4 signaling promoted cancer cell survival and proliferation. LPS-TLR4 signaling was associated with regulation on the activation of NF-κB and MAPK signaling pathways. LPS-TLR4-induced activation of ERK and JNK signaling promotes cell proliferation through regulating Bax translocation to mitochondria. Activation of NF-κB and p38 mediates cytotoxicity of LPS, and inhibition on these two pathways promotes cell proliferation in HCC cells. Our results indicate that TLR4 signaling in cancer cells promotes cell survival and proliferation in HCC.