title: Effect of radiation and repeated sub-culturing on the transforming growth factor-β1 signaling pathway in FRTL-5 cells.
abstract: OBJECTIVE
  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.
  
  
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Basic Sciences, Division of Radiation Research, Loma Linda University School of Medicine, Loma Linda, CA, U.S.A. Department of Biology, Wake Forest University, Winston-Salem, NC, U.S.A. burrelcg@wfu.edu.
authors.forename: Cheryl G
authors.initials: CG
authors.lastname: Burrell
authors.affiliation: Department of Basic Sciences, Division of Radiation Research, Loma Linda University School of Medicine, Loma Linda, CA, U.S.A.
authors.forename: Daila S
authors.initials: DS
authors.lastname: Gridley
authors.affiliation: Department of Basic Sciences, Division of Radiation Research, Loma Linda University School of Medicine, Loma Linda, CA, U.S.A.
authors.forename: Leticia S
authors.initials: LS
authors.lastname: Ortloff
authors.affiliation: Department of Obstetrics and Gynecology, Wake Forest Baptist Health, Winston-Salem, NC, U.S.A.
authors.forename: Shelton M
authors.initials: SM
authors.lastname: Charles
authors.affiliation: Department of Basic Sciences, Division of Radiation Research, Loma Linda University School of Medicine, Loma Linda, CA, U.S.A. Molecular Immunology, J.L. Pettis Memorial Veterans Medical Center Research Service-151, Loma Linda, CA, U.S.A.
authors.forename: Lora M
authors.initials: LM
authors.lastname: Green
mesh_terms: D000818:Animals; D018929:Cell Culture Techniques; D002460:Cell Line; D049109:Cell Proliferation / Q000528:radiation effects; D002478:Cells, Cultured; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays; D015870:Gene Expression; D010766:Phosphorylation; D011829:Radiation Dosage; D051381:Rats; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000528:radiation effects*; D051785:Smad Proteins / Q000378:metabolism; D013961:Thyroid Gland / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*
chemical_list: D018125:Receptors, Transforming Growth Factor beta; D051785:Smad Proteins; D053773:Transforming Growth Factor beta1
keywords: Transforming growth factor-beta 1 (TGF-β1); ionizing radiation; sub-culturing; thyroid cells