Inhibition of transforming growth factor-beta signaling in normal lung epithelial cells confers resistance to ionizing radiation.
OBJECTIVE
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
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.
Reeves
Anna
A
Weis Center for Research, Geisinger Clinic, Danville, PA 17822-2616, USA.
Zagurovskaya
Marianna
M
Gupta
Seema
S
Shareef
Mohammed M
MM
Mohiuddin
Mohammed
M
Ahmed
Mansoor M
MM
D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D003114:Colony-Forming Units Assay; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects*; D007633:Keratins / Q000378:metabolism; D008168:Lung / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects*; D008668:Metallothionein / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D017346:Protein Serine-Threonine Kinases; D011836:Radiation Tolerance; D011839:Radiation, Ionizing; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D016212:Transforming Growth Factor beta / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation; D019287:Zinc Sulfate / Q000494:pharmacology
D050759:Cyclin-Dependent Kinase Inhibitor p21; D018125:Receptors, Transforming Growth Factor beta; D016212:Transforming Growth Factor beta; D007633:Keratins; D019287:Zinc Sulfate; D008668:Metallothionein; D017346:Protein Serine-Threonine Kinases; D000077294:Receptor, Transforming Growth Factor-beta Type II