TGFbeta-1 dependent fast stimulation of ATM and p53 phosphorylation following exposure to ionizing radiation does not involve TGFbeta-receptor I signalling

Radiother Oncol. 2007 Jun;83(3):289-95. doi: 10.1016/j.radonc.2007.05.013. Epub 2007 Jun 8.

Abstract

Background and purpose: It has been proposed that radiation induced stimulation of ATM and downstream components involves activation of TGFbeta-1 and that this may be due to TGFbeta-1-receptor I-Smad signalling. Therefore, the aim of this study was to clarify the distinct role of TGFbeta-1-receptor I-Smad signalling in mediating ATM activity following radiation exposure.

Materials and methods: A549 cells were stably transfected with a conditionally regulatable TGFbeta-1 antisense construct (Tet-on-system) to test clonogenic activity following irradiation. Phosphorylation profile of ATM, p53, and chk2 was determined in non-cycling, serum-starved cells by immunoblotting. Likewise, A549 wild type cells were used to identify cell cycle distribution as a function of irradiation with or without pretreatment with CMK, a specific inhibitor of furin protease involved in activation of latent TGFbeta-1. Furthermore Western and immunoblot analyses were performed on serum-starved cells to investigate the dependence of ATM- and p53-stimulation on TGFbeta-1-receptor I-Smad signalling by applying a specific TGFbeta-1-receptor I inhibitor.

Results: Knock down of TGFbeta-1 by an antisense construct significantly increased clonogenic cell survival following exposure to ionizing radiation. Likewise, CMK treatment diminished the radiation induced G1 arrest of A549 cells. Moreover, both TGFbeta-1-knock down as well as CMK treatment inhibited the fast post-radiation phosphorylation of ATM, p53, and chk2. However, as shown by the use of a specific inhibitor TGFbeta-1-receptor I-Smad signalling was not involved in this fast activation of ATM and p53.

Conclusions: We confirm that TGFbeta-1 plays a critical role in the stimulation of ATM- and p53 signalling in irradiated cells. However, this fast stimulation seems not to be dependent on activation of TGFbeta-1-receptor I-Smad signalling as recently proposed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ataxia Telangiectasia Mutated Proteins
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism*
  • Cell Cycle Proteins / radiation effects
  • Cell Line
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • DNA-Binding Proteins / radiation effects
  • Flow Cytometry
  • Humans
  • Kinetics
  • Phosphorylation
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism*
  • Protein-Serine-Threonine Kinases / radiation effects
  • Radiation, Ionizing
  • Receptors, Transforming Growth Factor beta / drug effects*
  • Signal Transduction / drug effects*
  • Signal Transduction / radiation effects*
  • Smad2 Protein / metabolism
  • Smad2 Protein / radiation effects
  • Time Factors
  • Transforming Growth Factor beta1 / pharmacology*
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / metabolism*
  • Tumor Suppressor Protein p53 / radiation effects
  • Tumor Suppressor Proteins / genetics
  • Tumor Suppressor Proteins / metabolism*
  • Tumor Suppressor Proteins / radiation effects
  • Up-Regulation

Substances

  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • Receptors, Transforming Growth Factor beta
  • SMAD2 protein, human
  • Smad2 Protein
  • Transforming Growth Factor beta1
  • Tumor Suppressor Protein p53
  • Tumor Suppressor Proteins
  • ATM protein, human
  • Ataxia Telangiectasia Mutated Proteins
  • Protein-Serine-Threonine Kinases