Hypoxia mediates mitochondrial biogenesis in hepatocellular carcinoma to promote tumor growth through HMGB1 and TLR9 interaction

Abstract

The ability of cancer cells to survive and grow under hypoxic conditions has been known for decades, but the mechanisms remain poorly understood. Under certain conditions, cancer cells undergo changes in their bioenergetic profile to favor mitochondrial respiration by activating the peroxisome proliferator-activated receptor gamma (PGC-1α) and upregulating mitochondrial biogenesis. In this study, we hypothesized that augmented mitochondrial biogenesis plays a critical role for cancer cells to survive hypoxia. Consistent with this hypothesis, both hypoxic human hepatocellular carcinoma (HCC) tumors and HCC cell lines subjected to hypoxia increase mitochondrial biogenesis. Silencing of PGC-1α in hypoxic HCC cell lines halts their proliferation. Mechanistic investigations in vitro indicated that intracellular High Mobility Group Box (HMGB)-1 protein, a nuclear protein overexpressed in HCC, is essential for the process. Silencing of HMGB1 in hypoxic HCC cell lines resulted in a significant decrease in PGC-1α activation and mitochondrial biogenesis. Without HMGB1, hypoxic HCC cells had significantly reduced ATP production and decreased cellular proliferation and increased apoptosis. In a diethynitrosamine (DEN)-induced murine model of HCC, genetic blocking of HMGB1 in the hypoxic tumors resulted in a significant decrease in tumor growth. Tumors lacking HMGB1 had a significant reduction in mitochondrial biogenesis and a significant increase in mitochondrial dysfunction. Further in vitro mechanistic experiments indicated that, during hypoxia, HMGB1 translocates from the nucleus to the cytoplasm and binds to cytoplasmic Toll-like receptor (TLR)-9. This binding leads to the activation of p38 and subsequent phosphorylation of PGC-1α with resultant upregulation of mitochondrial biogenesis. Conclusion Taken together, our findings suggest that during hypoxia HMGB1 upregulates mitochondrial biogenesis in HCC cancer cells promoting tumor survival and proliferation.

High‐Mobility Group Box‐1 and Liver Disease

“…In a follow‐up publication, they established that tumors lacking HMGB1 had a significant reduction in mitochondrial biogenesis and increased mitochondrial dysfunction. In these studies, they showed that in hypoxic conditions HMGB1 that translocated from the nucleus to the cytoplasm interacted with TLR9, activated p38, and phosphorylated peroxisome proliferator‐activated receptor gamma coactivator 1α with subsequent up‐regulation of mitochondrial biogenesis …”

“…In these studies, they showed that in hypoxic conditions HMGB1 that translocated from the nucleus to the cytoplasm interacted with TLR9, activated p38, and phosphorylated peroxisome proliferator-activated receptor gamma coactivator 1α with subsequent up-regulation of mitochondrial biogenesis. (57) An area that remains to be investigated is the likely possibility that specific HMGB1 isoforms may have a dominant role in the onset and progression of HCC. Likewise, the signaling cascades that they could activate and whether they drive the phenotype of cancer stem cells remain elusive.…”

“…(12)(13)(14) In this latter role, HMGB1 acts as a proinflammatory cytokine that contributes to multiple injuries, including those from the liver, such as warm and cold ischemia/reperfusion (I/R) injury, (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27) sepsis, (23,(28)(29)(30)(31)(32) acetaminophen (APAP) intoxication, (23,(33)(34)(35)(36)(37)(38)(39)(40) alcoholic liver disease (ALD), (41)(42)(43) fibrosis, (44)(45)(46)(47)(48)(49) nonalcoholic steatohepatitis (NASH), (50)(51)(52) and hepatocellular carcinoma (HCC). (53)(54)(55)(56)(57)…”

The role of high‐mobility group protein box 1 in lung cancer

“…HMGB1-TLR9 could promote mitochondrial biogenesis in hepatocellular carcinoma to induce tumor growth mediated by hypoxia. 20,[60][61][62][63][64][65][66][67][68] TIM-3 Inhibits nucleic acid-mediated antitumor immunity in DCs. 19…”

Predictive value of hypoxia, metabolism and immune factors for prognosis in hepatocellular carcinoma: a retrospective analysis and multicenter validation study

“…Among them, a 15-gene signature appears to perform the best [19]. Many previous studies have validated that hypoxia promotes HCC cell growth, migration and invasion [34][35][36]. Furthermore, a meta-analysis documented that higher levels of hypoxia-inducible factor-1 alpha protein expression indicate a greater possibility of vascular invasion and a poorer clinical outcome in HCC [37].…”