title: BAX supports the mitochondrial network, promoting bioenergetics in nonapoptotic cells.
abstract: The dual functionality of the tumor suppressor BAX is implied by the nonapoptotic functions of other members of the BCL-2 family. To explore this, mitochondrial metabolism was examined in BAX-deficient HCT-116 cells as well as primary hepatocytes from BAX-deficient mice. Although mitochondrial density and mitochondrial DNA content were the same in BAX-containing and BAX-deficient cells, MitoTracker staining patterns differed, suggesting the existence of BAX-dependent functional differences in mitochondrial physiology. Oxygen consumption and cellular ATP levels were reduced in BAX-deficient cells, while glycolysis was increased. These results suggested that cells lacking BAX have a deficiency in the ability to generate ATP through cellular respiration. This conclusion was supported by detection of reduced citrate synthase activity in BAX-deficient cells. In nonapoptotic cells, a portion of BAX associated with mitochondria and a sequestered, protease-resistant form was detected. Inhibition of BAX with small interfering RNAs reduced intracellular ATP content in BAX-containing cells. Expression of either full-length or COOH-terminal-truncated BAX in BAX-deficient cells rescued ATP synthesis and oxygen consumption and reduced glycolytic activity, suggesting that this metabolic function of BAX was not dependent upon its COOH-terminal helix. Expression of BCL-2 in BAX-containing cells resulted in a subsequent loss of ATP measured, implying that, even under nonapoptotic conditions, an antagonistic interaction exists between the two proteins. These findings infer that a basal amount of BAX is necessary to maintain energy production via aerobic respiration.
authors.affiliation: Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, 6900 Lake Nona Blvd., Orlando, FL 32827, USA.
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Boohaker
authors.forename: Ge
authors.initials: G
authors.lastname: Zhang
authors.forename: Adina Loosley
authors.initials: AL
authors.lastname: Carlson
authors.forename: Kathleen N
authors.initials: KN
authors.lastname: Nemec
authors.forename: Annette R
authors.initials: AR
authors.lastname: Khaled
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D019069:Cell Respiration / Q000502:physiology*; D002478:Cells, Cultured; D004734:Energy Metabolism; D055785:Gene Knockdown Techniques; D022781:Hepatocytes / Q000166:cytology; D006801:Humans; D053078:Membrane Potential, Mitochondrial; D051379:Mice; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000378:metabolism*; D010101:Oxygen Consumption; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D034741:RNA, Small Interfering; D051028:bcl-2-Associated X Protein; D000255:Adenosine Triphosphate