title: The PI3K/Akt Pathway Regulates Oxygen Metabolism via Pyruvate Dehydrogenase (PDH)-E1α Phosphorylation.
abstract: Inhibition of the PI3K/Akt pathway decreases hypoxia within SQ20B human head and neck cancer xenografts. We set out to understand the molecular mechanism underlying this observation. We measured oxygen consumption using both a Clark electrode and an extracellular flux analyzer. We made these measurements after various pharmacologic and genetic manipulations. Pharmacologic inhibition of the PI3K/mTOR pathway or genetic inhibition of Akt/PI3K decreased the oxygen consumption rate (OCR) in vitro in SQ20B and other cell lines by 30% to 40%. Pharmacologic inhibition of this pathway increased phosphorylation of the E1α subunit of the pyruvate dehydrogenase (PDH) complex on Ser293, which inhibits activity of this critical gatekeeper of mitochondrial respiration. Expressing wild-type PTEN in a doxycycline-inducible manner in a cell line with mutant PTEN led to an increase in PDH-E1α phosphorylation and a decrease in OCR. Pretreatment of SQ20B cells with dichloroacetate (DCA), which inhibits PDH-E1α phosphorylation by inhibiting dehydrogenase kinases (PDK), reversed the decrease in OCR in response to PI3K/Akt/mTOR inhibition. Likewise, introduction of exogenous PDH-E1α that contains serine to alanine mutations, which can no longer be regulated by phosphorylation, also blunted the decrease in OCR seen with PI3K/mTOR inhibition. Our findings highlight an association between the PI3K/mTOR pathway and tumor cell oxygen consumption that is regulated in part by PDH phosphorylation. These results have important implications for understanding the effects of PI3K pathway activation in tumor metabolism and also in designing cancer therapy trials that use inhibitors of this pathway.
authors.affiliation: Department of Radiation Oncology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: George J
authors.initials: GJ
authors.lastname: Cerniglia
authors.affiliation: Department of Radiation Oncology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Souvik
authors.initials: S
authors.lastname: Dey
authors.affiliation: Department of Radiation Oncology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Shannon M
authors.initials: SM
authors.lastname: Gallagher-Colombo
authors.affiliation: Pharmacology Graduate Group, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Natalie A
authors.initials: NA
authors.lastname: Daurio
authors.affiliation: Department of Radiation Oncology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Stephen
authors.initials: S
authors.lastname: Tuttle
authors.affiliation: Department of Radiation Oncology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Theresa M
authors.initials: TM
authors.lastname: Busch
authors.affiliation: Department of Radiation Oncology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Alexander
authors.initials: A
authors.lastname: Lin
authors.affiliation: Department of Radiation Oncology, Ohio State University School of Medicine, Columbus, Ohio.
authors.forename: Ramon
authors.initials: R
authors.lastname: Sun
authors.affiliation: Department of Biochemistry and Biophysics, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Tatiana V
authors.initials: TV
authors.lastname: Esipova
authors.affiliation: Department of Biochemistry and Biophysics, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Sergei A
authors.initials: SA
authors.lastname: Vinogradov
authors.affiliation: Department of Radiation Oncology, Ohio State University School of Medicine, Columbus, Ohio.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Denko
authors.affiliation: Department of Radiation Oncology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Constantinos
authors.initials: C
authors.lastname: Koumenis
authors.affiliation: Department of Radiation Oncology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania. maity@uphs.upenn.edu.
authors.forename: Amit
authors.initials: A
authors.lastname: Maity
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D055785:Gene Knockdown Techniques; D006258:Head and Neck Neoplasms / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051379:Mice; D010101:Oxygen Consumption; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D030481:Pyruvate Dehydrogenase (Lipoamide) / Q000378:metabolism*; D034622:RNA Interference; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors
chemical_list: D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D030481:Pyruvate Dehydrogenase (Lipoamide); D058570:TOR Serine-Threonine Kinases; C065640:pyruvate dehydrogenase E1alpha subunit