Thyroid-stimulating hormone transcriptionally regulates the thiol-specific antioxidant gene

Thiol-specific antioxidant (TSA) plays an important role in regulating cell differentiation and proliferation by modulating the hydrogen peroxide (H2O2) mediated responses in a variety of mammalian cells. Thyroid cells are constantly exposed to the actions of reactive oxygen species (ROS), because they produce high levels of H2O2 in response to the physiological action of TSH (thyroid-stimulating hormone). Thyrocytes have several defense mechanisms against ROS, including TSA and SOD (superoxide anion dismutase). Using Northern blot hybridization, we tested the effects of TSH on TSA gene expression in FRTL-5 cells derived from rat thyroids. TSA mRNA expression increased following treatment of cells with TSH at concentrations greater than 10(-9) M. This effect was observed within 6 hours following treatment, and peaked at 8 hours. The effect was blocked by actinomycin D, but not by cycloheximide. The half-life of TSA mRNA was approximately 5.5 hours in the presence or absence of TSH, and that was not affected by TSA mRNA stability. The effects on TSA gene expression were specific to TSH. Other growth factors (e.g., insulin, transferrin and hydrocortisone) did not alter TSA expression. Our results are the first indication that TSH regulates the expression of TSA transcriptionally in thyrocytes.