Objective To study the role of high-mobility group protein 1 (HMGB1) in the promotion of diethylnitrosamine-induced liver cancer formation in C57BL/6 mice and its mechanism.Methods HMGB1loxp/loxp/Alb-Cre+/-were used as a liver-specific knockout (KO) of HMGB1 gene in mice.HMGB1loxp/loxp/Alb-Cre-/-,HMGB1loxp/WT/Alb-Cre+/-and HMGB1loxp/WT/Alb-Cre-/-born in the same litter were wild-type mice.Six 12-day-old male WT and KO mice were separated and given a single intraperitoneal injection of diethylnitrosamine (25 mg/kg).Six months later,HE staining was used to evaluate the histopathological changes and then the incidence of liver cancer in each mice group was calculated.Serum samples were taken from each mice group to determine alanine aminotransferase levels.Immunohistochemical staining was used to detect the expression and intracellular localizations of HMGB1 protein status in tumor tissue of the two groups of mice.Western blot was used to detect the expressional condition of mitochondrial biogenesis in tumor tissue of the two groups of mice.RT-PCR was used to detect mitochondrial DNA copy number of tumor tissue and normal liver tissue in the two groups of mice.Intra and inter group data comparison was compared using t-tests and one one-way analysis of variance.Results Compared with WT mice,the liver/body weight ratio of KO mice was decreased significantly (t =2.634,P =0.0225).Serum alanine aminotransferase levels in both groups of mice were increased,and the difference was not statistically significant (t =0.4062,P =0.6932).There were many visible gray-white nodules of different sizes on the liver surface of WT mice,and the histological type was hepatocellular carcinoma.There was no statistically significant difference in the incidence of liver cancer among different genotypes of WT mice (P ＞ 0.05).The incidence rate of liver cancer in KO mice was significantly reduced (t =8.521,P ＜ 0.001).Compared with WT mice,the expression levels of HMGB1 and mitochondrial biogenesis (PGC-1α and NRF1) was significantly reduced (t =6.238,4.852,P =0.0335,0.041) in tumor tissue of KO mice.Mitochondrial DNA copy number was decreased significantly (t =9.211,P ＜ 0.01).Mitochondrial DNA copy number in tumor tissue of WT mice was significantly higher than that in normal liver tissue (t =8.305,P =0.0142).Conclusion HMGB1 promotes the formation of diethylnitrosamine-induced liver cancer by inducing mitochondrial biogenesis.

BACKGROUNDThe extracellular release of the danger signal high mobility group box-1 (HMGB1) has been implicated in the pathogenesis and outcomes of sepsis. Understanding the mechanisms responsible for HMGB1 release can lead to the identification of targets that may inhibit this process. The transcription factor interferon regulatory factor-1 (IRF-1) is an important mediator of innate immune responses and has been shown to participate in mortality associated with endotoxemia; however, its role in mediating the release of HMGB1 in these settings is unknown.

METHODSMale IRF-1 knockout (KO) and age matched C57BL/6 wild type (WT) mice were given intraperitoneal (IP) injections of lipopolysaccharide (LPS). In some experiments, 96 hours survival rates were observed. In other experiments, mice were sacrificed 12 hours after LPS administration and sera were harvested for future analysis. In in vitro study, RAW 264.7 murine monocyte/macrophage-like cells or primary peritoneal macrophage obtained from IRF-1 KO and WT mice were cultured for LPS mediated HMGB1 release analysis. And the mechanism for HMGB1 release was analyzed by immune-precipitation.

RESULTSIRF-1 KO mice experienced less mortality, and released less systemic HMGB1 compared to their WT counterparts. Exogenous administration of recombinant HMGB1 to IRF-1 KO mice returned the mortality rate to that seen originally in IRF-1 WT mice. Using cultures of peritoneal macrophages or RAW264.7 cells, in vitro LPS stimulation induced the release of HMGB1 in an IRF-1 dependent manner. And the janus associated kinase (JAK)-IRF-1 signal pathway appeared to participate in the signaling mechanisms of LPS-induced HMGB1 release by mediating acetylation of HMGB1.

CONCLUSIONIRF-1 plays a role in LPS induced release of HMGB1 and therefore may serve as a novel target in sepsis.

Animals ; Cell Line ; Cells, Cultured ; Endotoxemia ; chemically induced ; metabolism ; HMGB1 Protein ; genetics ; metabolism ; Immunoprecipitation ; Interferon Regulatory Factor-1 ; genetics ; metabolism ; Lipopolysaccharides ; toxicity ; Male ; Mice ; Mice, Inbred C57BL ; Mice, Knockout ; Reverse Transcriptase Polymerase Chain Reaction