title: Hypoxia induced HMGB1 and mitochondrial DNA interactions mediate tumor growth in hepatocellular carcinoma through Toll-like receptor 9.
abstract: OBJECTIVE
  The mechanisms of hypoxia-induced tumor growth remain unclear. Hypoxia induces intracellular translocation and release of a variety of damage associated molecular patterns (DAMPs) such as nuclear HMGB1 and mitochondrial DNA (mtDNA). In inflammation, Toll-like receptor (TLR)-9 activation by DNA-containing immune complexes has been shown to be mediated by HMGB1. We thus hypothesize that HMGB1 binds mtDNA in the cytoplasm of hypoxic tumor cells and promotes tumor growth through activating TLR9 signaling pathways.
  
  
  METHODS
  C57BL6 mice were injected with Hepa1-6 cancer cells. TLR9 and HMGB1 were inhibited using shRNA or direct antagonists. HuH7 and Hepa1-6 cancer cells were investigated in vitro to determine how the interaction of HMGB1 and mtDNA activates TLR9 signaling pathways.
  
  
  RESULTS
  During hypoxia, HMGB1 translocates from the nucleus to the cytosol and binds to mtDNA released from damaged mitochondria. This complex subsequently activates TLR9 signaling pathways to promote tumor cell proliferation. Loss of HMGB1 or mtDNA leads to a defect in TLR9 signaling pathways in response to hypoxia, resulting in decreased tumor cell proliferation. Also, the addition of HMGB1 and mtDNA leads to the activation of TLR9 and subsequent tumor cell proliferation. Moreover, TLR9 is overexpressed in both hypoxic tumor cells in vitro and in human hepatocellular cancer (HCC) specimens; and, injection in mice to knockdown either HMGB1 or TLR9 from HCC cells suppressed tumor growth in vivo.
  
  
  CONCLUSIONS
  Our data reveals a novel mechanism by which the interactions of HMGB1 and mtDNA activate TLR9 signaling during hypoxia to induce tumor growth.
authors: Department of Surgery, University of Pittsburgh Cancer Institute, Pittsburgh, PA, United States; Department of Gastroenterology, The First Affiliated Hospital of Gannan Medical College, China.
authors: Yao
authors: Y
authors: Liu
authors: Department of Surgery, University of Pittsburgh Cancer Institute, Pittsburgh, PA, United States; Department of Gastroenterology, Huazhong University of Science and Technology, China.
authors: Wei
authors: W
authors: Yan
authors: Department of Surgery, University of Pittsburgh Cancer Institute, Pittsburgh, PA, United States.
authors: Samer
authors: S
authors: Tohme
authors: Department of Surgery, University of Pittsburgh Cancer Institute, Pittsburgh, PA, United States.
authors: Man
authors: M
authors: Chen
authors: Department of Gastroenterology, Huazhong University of Science and Technology, China.
authors: Yu
authors: Y
authors: Fu
authors: Department of Gastroenterology, Huazhong University of Science and Technology, China.
authors: Dean
authors: D
authors: Tian
authors: Department of Surgery, University of Pittsburgh Cancer Institute, Pittsburgh, PA, United States.
authors: Michael
authors: M
authors: Lotze
authors: Department of Surgery, University of Pittsburgh Cancer Institute, Pittsburgh, PA, United States.
authors: Daolin
authors: D
authors: Tang
authors: Department of Surgery, University of Pittsburgh Cancer Institute, Pittsburgh, PA, United States. Electronic address: Tsunga@upmc.edu.
authors: Allan
authors: A
authors: Tsung
mesh_terms: D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D004272:DNA, Mitochondrial / Q000235:genetics*; D004273:DNA, Neoplasm / Q000235:genetics*; D005434:Flow Cytometry; D024243:HMGB1 Protein / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D000860:Hypoxia / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D008113:Liver Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D008114:Liver Neoplasms, Experimental / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D004272:DNA, Mitochondrial; D004273:DNA, Neoplasm; D024243:HMGB1 Protein; C582808:HMGB1 protein, mouse
keywords: DAMPs; HMGB1; Hepatocellular carcinoma; Hypoxia; Liver; Mitochondrial DNA