TY - JOUR T1 - Effect of Radiation and Repeated Sub-culturing on the Transforming Growth Factor-β1 Signaling Pathway in FRTL-5 Cells JF - In Vivo JO - In Vivo SP - 5 LP - 15 VL - 29 IS - 1 AU - CHERYL G. BURRELL AU - DAILA S. GRIDLEY AU - LETICIA S. ORTLOFF AU - SHELTON M. CHARLES AU - LORA M. GREEN Y1 - 2015/01/01 UR - http://iv.iiarjournals.org/content/29/1/5.abstract N2 - 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-β1 (TGF-β1) signaling contributes to these differences. Materials and Methods: Assessments included FRTL-5 cell growth rate and quantification of TGF-β1 ligand and receptors. The levels and activity of Smads2, 3 and 4 were measured by western blotting and the ability of TGF-β1 to regulate cyclin A and plasminogen activator inhibitor type 1 (PAI-1) activity was assessed using transfection assays. Results: TGF-β1 production increased after radiation but returned to control levels after repeated sub-culturing. There was no difference in TGF-β1 levels between un-irradiated cells at low versus high-passage number. TGF-β1 receptors and basal levels of Smads2, 3 and 4 remained unchanged. However, there were significant changes in cell proliferation, TGF-β1-mediated Smads2 and 3 activation and in TGF-β1'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-β1 pathway contribute to phenotypic changes in FRTL-5 cells as a function of passage number and radiation. ER -