Aspirin inhibits mTOR signaling, activates AMP-activated protein kinase, and induces autophagy in colorectal cancer cells

Gastroenterology. 2012 Jun;142(7):1504-15.e3. doi: 10.1053/j.gastro.2012.02.050. Epub 2012 Mar 6.

Abstract

Background & aims: 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • AMP-Activated Protein Kinases / drug effects
  • AMP-Activated Protein Kinases / metabolism*
  • Adaptor Proteins, Signal Transducing / metabolism
  • Animals
  • Anti-Inflammatory Agents, Non-Steroidal / pharmacology*
  • Aspirin / pharmacology*
  • Autophagy / drug effects*
  • Cell Cycle Proteins
  • Cell Line, Tumor
  • Colorectal Neoplasms / metabolism*
  • Female
  • Humans
  • Intestinal Mucosa / metabolism
  • Mice
  • Mice, Knockout
  • Phenformin / pharmacology
  • Phosphoproteins / metabolism
  • Phosphorylation / drug effects
  • Ribosomal Protein S6 / metabolism
  • Ribosomal Protein S6 Kinases, 70-kDa / metabolism
  • Signal Transduction / drug effects*
  • TOR Serine-Threonine Kinases / antagonists & inhibitors
  • TOR Serine-Threonine Kinases / metabolism*
  • Transcription Factors / metabolism

Substances

  • Adaptor Proteins, Signal Transducing
  • Anti-Inflammatory Agents, Non-Steroidal
  • CRTC2 protein, human
  • Cell Cycle Proteins
  • EIF4EBP1 protein, human
  • Phosphoproteins
  • Ribosomal Protein S6
  • Transcription Factors
  • Phenformin
  • TOR Serine-Threonine Kinases
  • Ribosomal Protein S6 Kinases, 70-kDa
  • ribosomal protein S6 kinase, 70kD, polypeptide 1
  • AMP-Activated Protein Kinases
  • Aspirin