title: Aspirin inhibits mTOR signaling, activates AMP-activated protein kinase, and induces autophagy in colorectal cancer cells.
abstract: OBJECTIVE
  Aspirin reduces the incidence of and mortality from colorectal cancer (CRC) by unknown mechanisms. Cancer cells have defects in signaling via the mechanistic target of rapamycin (mTOR), which regulates proliferation. We investigated whether aspirin affects adenosine monophosphate-activated protein kinase (AMPK) and mTOR signaling in CRC cells.
  
  
  METHODS
  The effects of aspirin on mTOR signaling, the ribosomal protein S6, S6 kinase 1 (S6K1), and eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1) were examined in CRC cells by immunoblotting. Phosphorylation of AMPK was measured; the effects of loss of AMPKα on the aspirin-induced effects of mTOR were determined using small interfering RNA (siRNA) in CRC cells and in AMPK(α1/α2-/-) mouse embryonic fibroblasts. LC3 and ULK1 were used as markers of autophagy. We analyzed rectal mucosa samples from patients given 600 mg aspirin, once daily for 1 week.
  
  
  RESULTS
  Aspirin reduced mTOR signaling in CRC cells by inhibiting the mTOR effectors S6K1 and 4E-BP1. Aspirin changed nucleotide ratios and activated AMPK in CRC cells. mTOR was still inhibited by aspirin in CRC cells after siRNA knockdown of AMPKα, indicating AMPK-dependent and AMPK-independent mechanisms of aspirin-induced inhibition of mTOR. Aspirin induced autophagy, a feature of mTOR inhibition. Aspirin and metformin (an activator of AMPK) increased inhibition of mTOR and Akt, as well as autophagy in CRC cells. Rectal mucosal samples from patients given aspirin had reduced phosphorylation of S6K1 and S6.
  
  
  CONCLUSIONS
  Aspirin is an inhibitor of mTOR and an activator of AMPK, targeting regulators of intracellular energy homeostasis and metabolism. These could contribute to its protective effects against development of CRC.
authors.affiliation: Colon Cancer Genetics Group and Academic Coloproctology, Institute of Genetics and Molecular Medicine, University of Edinburgh and Medical Research Council Human Genetics Unit, Western General Hospital Edinburgh, United Kingdom. Farhat.Din@igmm.ed.ac.uk
authors.forename: Farhat V N
authors.initials: FV
authors.lastname: Din
authors.forename: Asta
authors.initials: A
authors.lastname: Valanciute
authors.forename: Vanessa P
authors.initials: VP
authors.lastname: Houde
authors.forename: Daria
authors.initials: D
authors.lastname: Zibrova
authors.forename: Kevin A
authors.initials: KA
authors.lastname: Green
authors.forename: Kei
authors.initials: K
authors.lastname: Sakamoto
authors.forename: Dario R
authors.initials: DR
authors.lastname: Alessi
authors.forename: Malcolm G
authors.initials: MG
authors.lastname: Dunlop
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism*; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology*; D001241:Aspirin / Q000494:pharmacology*; D001343:Autophagy / Q000187:drug effects*; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000378:metabolism*; D005260:Female; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D010629:Phenformin / Q000494:pharmacology; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D038601:Ribosomal Protein S6 / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000894:Anti-Inflammatory Agents, Non-Steroidal; C493245:CRTC2 protein, human; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D010750:Phosphoproteins; D038601:Ribosomal Protein S6; D014157:Transcription Factors; D010629:Phenformin; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; C448901:ribosomal protein S6 kinase, 70kD, polypeptide 1; D055372:AMP-Activated Protein Kinases; D001241:Aspirin