Effect of Radiation and Repeated Sub-culturing on the Transforming Growth Factor-beta 1 Signaling Pathway in FRTL-5 Cells

摘要

Background/Aim: Fisher rat thyroid cells (FRTL-5) display increased proliferation, reduced follicularization and decreased thyroxin release with repeated sub-culturing. These changes occur earlier and more rapidly following exposure to ionizing radiation. We hypothesized that altered transforming growth factor-beta 1 (TGF-beta 1) signaling contributes to these differences. Materials and Methods: Assessments included FRTL-5 cell growth rate and quantification of TGF-beta 1 ligand and receptors. The levels and activity of Smads2, 3 and 4 were measured by western blotting and the ability of TGF-beta 1 to regulate cyclin A and plasminogen activator inhibitor type 1 (PAI-1) activity was assessed using transfection assays. Results: TGF-beta 1 production increased after radiation but returned to control levels after repeated sub-culturing. There was no difference in TGF-beta 1 levels between un-irradiated cells at low versus high-passage number. TGF-beta 1 receptors and basal levels of Smads2, 3 and 4 remained unchanged. However, there were significant changes in cell proliferation, TGF-beta 1-mediated Smads2 and 3 activation and in TGF-beta 1's ability to regulate cyclin A and PAI-1 transcription in irradiated and repeatedly sub-cultured cells (p<0.05). Conclusion: Collectively, these results support the conclusion that alterations in the TGF-beta 1 pathway contribute to phenotypic changes in FRTL-5 cells as a function of passage number and radiation.