title: Mitochondrial dysfunction represses HIF-1α protein synthesis through AMPK activation in human hepatoma HepG2 cells.
abstract: BACKGROUND
  Hypoxia-inducible factor-1α (HIF-1α) is an important transcription factor that modulates cellular responses to hypoxia and also plays critical roles in cancer progression. Recently, somatic mutations and decreased copy number of mitochondrial DNA (mtDNA) were detected in hepatocellular carcinoma (HCC). These mutations were shown to have the potential to cause mitochondrial dysfunction. However, the effects and mechanisms of mitochondrial dysfunction on HIF-1α function are not fully understood. This study aims to explore the underlying mechanism by which mitochondrial dysfunction regulates HIF-1α expression.
  
  
  METHODS
  Human hepatoma HepG2 cells were treated with various mitochondrial respiration inhibitors and an uncoupler, respectively, and the mRNA and protein expressions as well as transactivation activity of HIF-1α were determined. The role of AMP-activated protein kinase (AMPK) was further analyzed by compound C and AMPK knock-down.
  
  
  RESULTS
  Treatments of mitochondrial inhibitors and an uncoupler respectively reduced both the protein level and transactivation activity of HIF-1α in HepG2 cells under normoxia or hypoxia. The mitochondrial dysfunction-repressed HIF-1α protein synthesis was associated with decreased phosphorylations of p70(S6K) and 4E-BP-1. Moreover, mitochondrial dysfunction decreased intracellular ATP content and elevated the phosphorylation of AMPK. Treatments with compound C, an AMPK inhibitor, and knock-down of AMPK partially rescued the mitochondrial dysfunction-repressed HIF-1α expression.
  
  
  CONCLUSIONS
  Mitochondrial dysfunctions resulted in reduced HIF-1α protein synthesis through AMPK-dependent manner in HepG2 cells.
  
  
  CONCLUSIONS
  Our results provided a mechanism for communication from mitochondria to the nucleus through AMPK-HIF-1α. Mitochondrial function is important for HIF-1α expression in cancer progression.
authors.affiliation: Department and Institute of Pharmacology, National Yang-Ming University, Taiwan.
authors.forename: Chia-Chi
authors.initials: CC
authors.lastname: Hsu
authors.forename: Chun-Hui
authors.initials: CH
authors.lastname: Wang
authors.forename: Ling-Chia
authors.initials: LC
authors.lastname: Wu
authors.forename: Cheng-Yuan
authors.initials: CY
authors.lastname: Hsia
authors.forename: Chin-Wen
authors.initials: CW
authors.lastname: Chi
authors.forename: Pen-Hui
authors.initials: PH
authors.lastname: Yin
authors.forename: Chun-Ju
authors.initials: CJ
authors.lastname: Chang
authors.forename: Ming-Ta
authors.initials: MT
authors.lastname: Sung
authors.forename: Yau-Huei
authors.initials: YH
authors.lastname: Wei
authors.forename: Shing-Hwa
authors.initials: SH
authors.lastname: Lu
authors.forename: Hsin-Chen
authors.initials: HC
authors.lastname: Lee
mesh_terms: D000263:Adenylate Kinase / Q000378:metabolism*; D001483:Base Sequence; D006528:Carcinoma, Hepatocellular / Q000201:enzymology* / Q000473:pathology; D017931:DNA Primers; D004789:Enzyme Activation; D056945:Hep G2 Cells; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000096:biosynthesis* / Q000235:genetics; D008113:Liver Neoplasms / Q000201:enzymology* / Q000473:pathology; D008928:Mitochondria / Q000502:physiology*; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D017931:DNA Primers; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D000263:Adenylate Kinase
keywords: AMP-activated protein kinase; AMPK; Adenosine monophosphate-activated protein kinase; CAIX; CCCP; DMEM; Dulbecco's modified Eagle medium; HCC; HIF-1α; Hypoxia-inducible factor-1α; LDHA; Mitochondrial dysfunction; Protein synthesis; ROS; RT-PCR; carbonic anhydrase IX; carbonyl cyanide m-chlorophenyl hydrazine; hepatocellular carcinoma; hypoxia-inducible factor-1α; lactate dehydrogenase A; mitochondrial DNA; mtDNA; reactive oxygen species; reverse transcription-polymerase chain reaction