Inhibition of transforming growth factor-beta signaling in normal lung epithelial cells confers resistance to ionizing radiation

Int J Radiat Oncol Biol Phys. 2007 May 1;68(1):187-95. doi: 10.1016/j.ijrobp.2006.12.057.

Abstract

Purpose: To address the functional role of radiation-induced transforming growth factor-beta (TGF-beta) signaling in a normal epithelial background, we selected a spontaneously immortalized lung epithelial cell line derived from the normal lung tissue of a dominant-negative mutant of the TGF-beta RII (DeltaRII) transgenic mouse that conditionally expressed DeltaRII under the control of the metallothionein promoter (MT-1), and assessed this cell line's response to radiation.

Methods and materials: A spontaneously immortalized lung epithelial cell culture (SILECC) was established and all analyses were performed within 50 passages. Colony-forming and terminal transferase dUPT nick end labeling (TUNEL) assays were used to assess clonogenic inhibition and apoptosis, respectively. Western-blot analysis was performed to assess the kinetics of p21, bax, and RII proteins. Transforming growth factor-beta-responsive promoter activity was measured using dual-luciferase reporter assay.

Results: Exposure to ZnSO(4) inhibited TGF-beta signaling induced either by recombinant TGF-beta1 or ionizing radiation. The SILECC, treated with either ZnSO(4) or neutralizing antibody against TGF-beta, showed a significant increase in radio-resistance compared to untreated cells. Furthermore, the expression of DeltaRII inhibited the radiation-induced up-regulation of the TGF-beta effector gene p21(waf1/cip1).

Conclusions: Our findings imply that inhibition of radiation-induced TGF-beta signaling via abrogation of the RII function enhances the radio-resistance of normal lung epithelial cells, and this can be directly attributed to the loss of TGF-beta signaling function.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis
  • Cell Line
  • Colony-Forming Units Assay
  • Cyclin-Dependent Kinase Inhibitor p21 / genetics
  • Cyclin-Dependent Kinase Inhibitor p21 / metabolism
  • Epithelial Cells / drug effects
  • Epithelial Cells / metabolism
  • Epithelial Cells / radiation effects*
  • Keratins / metabolism
  • Lung / cytology
  • Lung / metabolism
  • Lung / radiation effects*
  • Metallothionein / genetics
  • Mice
  • Mice, Transgenic
  • Protein-Serine-Threonine Kinases
  • Radiation Tolerance*
  • Radiation, Ionizing
  • Receptor, Transforming Growth Factor-beta Type II
  • Receptors, Transforming Growth Factor beta / genetics
  • Receptors, Transforming Growth Factor beta / physiology*
  • Signal Transduction / drug effects
  • Signal Transduction / physiology*
  • Signal Transduction / radiation effects
  • Transforming Growth Factor beta / antagonists & inhibitors*
  • Transforming Growth Factor beta / genetics
  • Transforming Growth Factor beta / metabolism
  • Up-Regulation
  • Zinc Sulfate / pharmacology

Substances

  • Cyclin-Dependent Kinase Inhibitor p21
  • Receptors, Transforming Growth Factor beta
  • Transforming Growth Factor beta
  • Keratins
  • Zinc Sulfate
  • Metallothionein
  • Protein-Serine-Threonine Kinases
  • Receptor, Transforming Growth Factor-beta Type II