hSMG-1 and ATM sequentially and independently regulate the G1 checkpoint during oxidative stress

Oncogene. 2008 Jul 3;27(29):4065-74. doi: 10.1038/onc.2008.48. Epub 2008 Mar 10.


Genotoxic stress activates the phosphatidylinositol 3-kinase-like kinases (PIKKs) that phosphorylate proteins involved in cell cycle arrest, DNA repair and apoptosis. Previous work showed that the PIKK ataxia telangiectasia mutated (ATM) but not ATM and Rad3 related phosphorylates p53 (Ser15) during hyperoxia, a model of prolonged oxidative stress and DNA damage. Here, we show hSMG-1 is responsible for the rapid and early phosphorylation of p53 (Ser15) and that ATM helps maintain phosphorylation after 24 h. Despite reduced p53 phosphorylation and abundance in cells depleted of hSMG-1 or ATM, levels of the p53 target p21 were still elevated and the G(1) checkpoint remained intact. Conditional overexpression of p21 in p53-deficient cells revealed that hyperoxia also stimulates wortmannin-sensitive degradation of p21. siRNA depletion of hSMG-1 or ATM restored p21 stability and the G(1) checkpoint during hyperoxia. These findings establish hSMG-1 as a proximal regulator of DNA damage signaling and reveal that the G(1) checkpoint is tightly regulated during prolonged oxidative stress by both PIKK-dependent synthesis and proteolysis of p21.

Publication types

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

MeSH terms

  • Androstadienes / pharmacology
  • Apoptosis / drug effects
  • Apoptosis / physiology
  • Ataxia Telangiectasia Mutated Proteins
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism*
  • Cell Line, Tumor
  • DNA Damage / drug effects
  • DNA Damage / physiology
  • DNA Repair / drug effects
  • DNA Repair / physiology
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • G1 Phase / drug effects
  • G1 Phase / physiology*
  • Humans
  • Hyperoxia / genetics
  • Hyperoxia / metabolism
  • Oxidative Stress / drug effects
  • Oxidative Stress / physiology*
  • Phosphatidylinositol 3-Kinases / genetics
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Phosphodiesterase Inhibitors / pharmacology
  • Phosphorylation / drug effects
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism*
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / metabolism
  • Tumor Suppressor Proteins / genetics
  • Tumor Suppressor Proteins / metabolism*
  • Wortmannin


  • Androstadienes
  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • Phosphodiesterase Inhibitors
  • TP53 protein, human
  • Tumor Suppressor Protein p53
  • Tumor Suppressor Proteins
  • ATM protein, human
  • Ataxia Telangiectasia Mutated Proteins
  • Protein-Serine-Threonine Kinases
  • SMG1 protein, human
  • Wortmannin