Basic TLR4Signaling Plays A Protective Role Against Chemical Carcinogens-induced Hepatocellular Carcinoma Via Induction Of DNA Repair

DNA damage and repair signaling system is indispensabel element for eukaryote genetic integrity. Double-stranded break damage to DNA is introduced into the genome during physiological processes such as lymphocyte development, meiosis and DNA replication, as well as during pathological processes such as viral infection and cellular transformation. So, this type of DNA damage is a continuous threat to genetic integrity and even to the survival of an organism. For example, accumulation of DNA DSB damage in cells could lead to oncogenic chromosomal translocations and eventually, to cancer. The deficiency of DNA repair is related to multiple diseases such as leukemia, breast cancer and immunodeficiency. Recent researches had found that DNA damage and repair signaling system participated various immune response such as the activation of NK cells and autophagy. So, do immune system and immune receptors control the DNA damage and repair signaling system? Here we proposed that TLR4was involvement in DNA damage and repair induced by chemical carcinogens in hepatocarcinogenesis.Liver cancer is the6th most common cancer and the3rd leading cause of cancer deaths in mortality deseases in the world. Chemical carcinogens are the key factors which cause DNA damage, cell mutations and promote hepatocarcinogenesis. Inflammation is a major contrbuting factor to carcinogenesis. HCC represents a classic case of inflammation-linked cancer, and chemically or genetically induced HCC depends on inflammatory signalling. Chronic inflammation not only promote production of ROS, DNA damage and vicious transformation of mutant cells, but also induce the inhibitive immuno-microenvironment, boosting tumor growth and metastasis. Toll-like receptor4(TLR4) is a major pattern recognition receptor to mediate PAMPs and DAMPs to launch immune response. TLR4can mediate multiple pathogen-induced acute hepatic injury. Thus, TLR4deficiency is found to be protective against acute hepatic injury caused by endotoxin, chemical agents and ischemia-reperfusion. Here we report that basal TLR4activity is protective after chemical carcinogens diethylnitrosamine-induced hepatocarcinogenesis. Fifteen-day-old C3H and TLR4deficient mice were injected intraperitoneally with25mg/kg diethylnitrosamine(DEN). We found that genetic inhibition of TLR4significantly increased the diethylnitrosamine-induced animal death and aggravated hepatocarcinogenesis. Six months after DEN injection, all mice were presented typical hepatocellular carcinoma. Visible tumors (>0.5mm)in liver were counted and analyzed. The meanvalue of tumor nodules number in C3H mice was18, and TLR4deficient mice was37. The tumor areas of left lobe in liver of TLR4deficient mice reached up to39.3%, compared with16.8%of C3H mice. In addition, TLR4deficency elevated the ALT in serum, which indicated more aggravated liver injury. The research of animal survival rate found that18months after DEN injection, the livability of C3H mice exceeded60%, but TLR4deficient mice were all dead. TLR4deficiency caused more grievous DNA damage, production of reactive oxgen species and promoted cell proliferation and lowered the apoptosis. Besides, TLR4deficiency inhibited cytokines prodution. Further research proved that TLR4signaling can activate ASK1-p38MAPK signaling pathway, which can eliminate ROS, regulate apoptosis and control proliferation. We found that the decline of DNA repair protein Ku70accounted to the aggravated DNA damage. Experimental cell researches proved that the expression of Ku70was regulated by TLR4signaling. Over-expression of Ku70via adenovirus in TLR4deficient mice can reduce diethylnitrosamine-induced DNA damage and ROS production. Maybe it can influence the process of hepatocarcinogenesis. DNA damage and repair signaling can participate in various immune response, but for the first time our research have immune receptor and DNA damage and repair signaling tied together. Immune receptors are not only the front lines which resist pathogen infection, but also mediate the endogenous danger signals such as DNA damage caused by chemical carcinogens. The activation of immune receptors inhibits cell mutations and oncogenesis.