Toll-like receptor 4 activity protects against hepatocellular tumorigenesis and progression by regulating expression of DNA repair protein Ku70 in mice. 
Hepatocellular carcinoma (HCC) is a devastating consequence of chronic inflammatory liver diseases.  The goal of this study was to investigate whether Toll-like receptor 4 (TLR4) activity contributes to HCC initiation and progression in mice.  A mouse model of diethylnitrosamine (DEN)-induced HCC was generated with wild-type and TLR4 mutant mice, and the development and progression of HCC and senescent responses were assessed using morphologic, immunological, and biochemical criteria.  We found that genetic or pharmacologic blocking of TLR4 increased susceptibility to DEN-induced HCC carcinogenesis and progression, which was indicated by increases in number of tumor nodules, tumor volume, and animal death.  The enhanced HCC was associated with a broad-spectrum reduction of immune response to DEN liver injury, as indicated by decreases in the liver-infiltrating F4/80+ macrophages, the apoptosis signal-regulating kinase 1/p38 mitogen-activated protein kinase/NF-κB and IRF3 signaling activities, and the expression of inflammatory cytokines.  Suppressed immune networks resulted in a halt of cellular senescence induction in TLR4 mutant liver tissue, which promoted proliferation and suppressed programmed cell death.  Moreover, TLR4 mutation resulted in a suppressed capacity of DNA repair due to a decrease in TLR4-medicated expression of DNA repair proteins Ku70/80 in liver tissue and cells.  Isotopic expression of Ku70 in TLR4 mutant mice restored senescence and interrupted the positive feedback loop of DNA damage and oxidative stress, which reversed TLR4 mutation-deteriorated HCC carcinogenesis and progression.  TLR4 plays an integrated defense role against HCC carcinogenesis by enhancing the expression and function of DNA repair protein Ku70.  Our studies provide novel insight into TLR4 activity in the regulation of HCC tumorigenesis, which may be useful for the prevention of HCC development.