Reactive nitrogen species regulate autophagy through ATM-AMPK-TSC2-mediated suppression of mTORC1

Proc Natl Acad Sci U S A. 2013 Aug 6;110(32):E2950-7. doi: 10.1073/pnas.1307736110. Epub 2013 Jul 22.

Abstract

Reactive intermediates such as reactive nitrogen species play essential roles in the cell as signaling molecules but, in excess, constitute a major source of cellular damage. We found that nitrosative stress induced by steady-state nitric oxide (NO) caused rapid activation of an ATM damage-response pathway leading to downstream signaling by this stress kinase to LKB1 and AMPK kinases, and activation of the TSC tumor suppressor. As a result, in an ATM-, LKB1-, TSC-dependent fashion, mTORC1 was repressed, as evidenced by decreased phosphorylation of S6K, 4E-BP1, and ULK1, direct targets of the mTORC1 kinase. Decreased ULK1 phosphorylation by mTORC1 at S757 and activation of AMPK to phosphorylate ULK1 at S317 in response to nitrosative stress resulted in increased autophagy: the LC3-II/LC3-I ratio increased as did GFP-LC3 puncta and acidic vesicles; p62 levels decreased in a lysosome-dependent manner, confirming an NO-induced increase in autophagic flux. Induction of autophagy by NO correlated with loss of cell viability, suggesting that, in this setting, autophagy was functioning primarily as a cytotoxic response to excess nitrosative stress. These data identify a nitrosative-stress signaling pathway that engages ATM and the LKB1 and TSC2 tumor suppressors to repress mTORC1 and regulate autophagy. As cancer cells are particularly sensitive to nitrosative stress, these data open another path for therapies capitalizing on the ability of reactive nitrogen species to induce autophagy-mediated cell death.

Keywords: cancer therapy; signal transduction.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • AMP-Activated Protein Kinases / metabolism*
  • Animals
  • Ataxia Telangiectasia Mutated Proteins
  • Autophagy / drug effects
  • Autophagy / physiology*
  • Blotting, Western
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism*
  • Cells, Cultured
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Embryo, Mammalian / cytology
  • Fibroblasts / cytology
  • Fibroblasts / drug effects
  • Fibroblasts / metabolism
  • HeLa Cells
  • Humans
  • MCF-7 Cells
  • Mice
  • Mice, Knockout
  • Models, Biological
  • Multiprotein Complexes / metabolism
  • Nitric Oxide / metabolism
  • Nitric Oxide / physiology
  • Nitric Oxide Donors / metabolism
  • Nitric Oxide Donors / pharmacology
  • Phosphorylation / drug effects
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism*
  • Reactive Oxygen Species / metabolism*
  • Signal Transduction / drug effects
  • Spermine / analogs & derivatives
  • Spermine / metabolism
  • Spermine / pharmacology
  • TOR Serine-Threonine Kinases / metabolism*
  • Tuberous Sclerosis Complex 2 Protein
  • Tumor Suppressor Proteins / genetics
  • Tumor Suppressor Proteins / metabolism*

Substances

  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • Multiprotein Complexes
  • Nitric Oxide Donors
  • Reactive Oxygen Species
  • TSC2 protein, human
  • Tsc2 protein, mouse
  • Tuberous Sclerosis Complex 2 Protein
  • Tumor Suppressor Proteins
  • spermine nitric oxide complex
  • Spermine
  • Nitric Oxide
  • STK11 protein, human
  • TOR Serine-Threonine Kinases
  • ATM protein, human
  • Ataxia Telangiectasia Mutated Proteins
  • Atm protein, mouse
  • Protein-Serine-Threonine Kinases
  • AMP-Activated Protein Kinases