title: AMPK regulates metabolism and survival in response to ionizing radiation.
abstract: OBJECTIVE
  AMPK is a metabolic sensor and an upstream inhibitor of mTOR activity. AMPK is phosphorylated by ionizing radiation (IR) in an ATM dependent manner, but the cellular consequences of this phosphorylation event have remained unclear. The objective of this study was to assess whether AMPK plays a functional role in regulating cellular responses to IR.
  
  
  METHODS
  The importance of AMPK expression for radiation responses was investigated using both MEFs (mouse embryo fibroblasts) double knockout for AMPK α1/α2 subunits and human colorectal carcinoma cells (HCT 116) with AMPK α1/α2 shRNA mediated knockdown.
  
  
  RESULTS
  We demonstrate here that IR results in phosphorylation of both AMPK and its substrate, ACC. IR moderately stimulated mTOR activity, and this was substantially exacerbated in the absence of AMPK. AMPK was required for IR induced expression of the mTOR inhibitor REDD1, indicating that AMPK restrains mTOR activity through multiple mechanisms. Likewise, cellular metabolism was deregulated following irradiation in the absence of AMPK, as evidenced by a substantial increase in oxygen consumption rates and lactate production. AMPK deficient cells showed impairment of the G1/S cell cycle checkpoint, and were unable to support long-term proliferation during starvation following radiation. Lastly, we show that AMPK proficiency is important for clonogenic survival after radiation during starvation.
  
  
  CONCLUSIONS
  These data reveal novel functional roles for AMPK in regulating mTOR signaling, cell cycle, survival and metabolic responses to IR.
authors.affiliation: Ontario Cancer Institute and Campbell Family Institute for Cancer Research, University Health Network, Canada.
authors.forename: Vanessa E
authors.initials: VE
authors.lastname: Zannella
authors.forename: Dan
authors.initials: D
authors.lastname: Cojocari
authors.forename: Susan
authors.initials: S
authors.lastname: Hilgendorf
authors.forename: Ravi N
authors.initials: RN
authors.lastname: Vellanki
authors.forename: Stephen
authors.initials: S
authors.lastname: Chung
authors.forename: Bradly G
authors.initials: BG
authors.lastname: Wouters
authors.forename: Marianne
authors.initials: M
authors.lastname: Koritzinsky
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000704:Analysis of Variance; D000818:Animals; D002470:Cell Survival / Q000528:radiation effects; D015179:Colorectal Neoplasms / Q000378:metabolism* / Q000532:radiotherapy*; D004307:Dose-Response Relationship, Radiation; D005434:Flow Cytometry; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D010100:Oxygen / Q000378:metabolism; D010766:Phosphorylation / Q000528:radiation effects; D011839:Radiation, Ionizing; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism
chemical_list: C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D010100:Oxygen