title: pH, Lactate, and Hypoxia: Reciprocity in Regulating High-Affinity Monocarboxylate Transporter Expression in Glioblastoma.
abstract: Highly malignant brain tumors harbor the aberrant propensity for aerobic glycolysis, the excessive conversion of glucose to lactic acid even in the presence of ample tissue oxygen. Lactic acid is rapidly effluxed to the tumor microenvironment via a group of plasma-membrane transporters denoted monocarboxylate transporters (MCTs) to prevent "self-poisoning." One isoform, MCT2, has the highest affinity for lactate and thus should have the ability to respond to microenvironment conditions such as hypoxia, lactate, and pH to help maintain high glycolytic flux in the tumor. Yet, MCT2 is considered to not respond to hypoxia, which is counterintuitive. Its response to tumor lactate has not been reported. In this report, we experimentally identify the transcription initiation site/s for MCT2 in astrocytes (normal) and glioma (tumor). We then use a BACmid library to isolate a 4.2-kbp MCT2 promoter-exon I region and examine promoter response to glycolysis-mediated stimuli in glioma cells. Reporter analysis of nested-promoter constructs indicated response of MCT2 to hypoxia, pH, lactate, and glucose, the major physiological "players" that facilitate a tumor's growth and proliferation. Immunoblot analysis of native MCT2 expression under altered pH and hypoxia reflected the reporter data. The pH-mediated gene-regulation studies we describe are the first to record H+-based reporter studies for any mammalian system and demonstrate the exquisite response of the MCT2 gene to minute changes in tumor pH. Identical promoter usage also provides the first evidence of astrocytes harnessing the same gene regulatory regions to facilitate astrocyte-neuron lactate shuttling, a metabolic feature of normal brain.
authors.affiliation: Department of Neurosurgery, Wayne State University School of Medicine, Detroit, MI 48201; Program in Biophysics, University of Michigan, Ann Arbor, MI 48109.
authors.forename: James P
authors.initials: JP
authors.lastname: Caruso
authors.affiliation: Department of Neurosurgery, Wayne State University School of Medicine, Detroit, MI 48201; Department of Biochemistry and Molecular Biology, Rollins College, Winter Park, FL 32789.
authors.forename: Brandon J
authors.initials: BJ
authors.lastname: Koch
authors.affiliation: Department of Neurosurgery, Wayne State University School of Medicine, Detroit, MI 48201.
authors.forename: Philip D
authors.initials: PD
authors.lastname: Benson
authors.affiliation: Department of Physics & Astronomy, Wayne State University College of Liberal Arts & Sciences, Detroit, MI, 48201.
authors.forename: Elsa
authors.initials: E
authors.lastname: Varughese
authors.affiliation: Department of Neurosurgery & Basic Medical Sciences Program, Wayne State University School of Medicine, Detroit, MI 48201.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Monterey
authors.affiliation: Department of Neurosurgery, Wayne State University School of Medicine, Detroit, MI 48201.
authors.forename: Amy E
authors.initials: AE
authors.lastname: Lee
authors.affiliation: Department of Neurosurgery, Wayne State University School of Medicine, Detroit, MI 48201.
authors.forename: Ajal M
authors.initials: AM
authors.lastname: Dave
authors.affiliation: Department of Neurosurgery, Wayne State University School of Medicine, Detroit, MI 48201.
authors.forename: Sam
authors.initials: S
authors.lastname: Kiousis
authors.affiliation: Department of Neurological Surgery, University Hospitals-Case Medical Center & Case Comprehensive Cancer Center, Cleveland, OH 44106.
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Sloan
authors.affiliation: Department of Neurosurgery and Karmanos Cancer Institute, Wayne State University School of Medicine, Detroit, MI 48201. Electronic address: ah1244@wayne.edu.
authors.forename: Saroj P
authors.initials: SP
authors.lastname: Mathupala
mesh_terms: D001253:Astrocytes / Q000378:metabolism; D015687:Cell Hypoxia / Q000235:genetics; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D015870:Gene Expression; D015972:Gene Expression Regulation, Neoplastic; D017930:Genes, Reporter; D005909:Glioblastoma / Q000235:genetics / Q000378:metabolism; D005910:Glioma / Q000235:genetics / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D000860:Hypoxia / Q000235:genetics / Q000378:metabolism*; D019344:Lactic Acid / Q000378:metabolism*; D027501:Monocarboxylic Acid Transporters / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D011401:Promoter Regions, Genetic; D024363:Transcription Initiation Site; D014158:Transcription, Genetic
chemical_list: D027501:Monocarboxylic Acid Transporters; C490427:SLC16A7 protein, human; D019344:Lactic Acid