RESUMO
BACKGROUND: Peroxiredoxins (Prx) play an important role in regulating cellular differentiation and proliferation in several types of mammalian cells. One mechanism for this action involves modulation of hydrogen peroxide (H2O2)-mediated cellular responses. This report examines the expression of Prx I and Prx II in thyroid cells and their roles in eliminating H2O2 produced in response to TSH. METHODS: The expression of Prx-I and Prx-II were quantiated in FRTL-5 after stimulation with Thyroid stimulating hormone (TSH), Forskolin (FSK), Methimazole (MMI) and hydrogen peroxide (H2O2). Transient transfections were carried out with FRTL-5 cells at 80% confluency and 20microgram of pCRprx I and pCRprx II or equivalent molar amounts of the pCR3.1TM basic vector. Transient transfection used an electroporation technique. Intracellular H2O2 was assayed in FRTL-5 cells with a fluorescent dye, 2', 7'-dichlorofluoresceindiacetate (DCFH-DA). Apoptosis of cells were evaluated by using an detection kit (Promega, Inc., Madison, WI). RESULTS: Prx I and Prx II are constitutively expressed in FRTL-5 thyroid cells. Prx I expression, but not Prx II expression, is stimulated by exposure to TSH and H2O2. In addition, methimazole (MMI) induces a high level of Prx I mRNA and protein in these cells. Overexpression of Prx I and Prx II enhance the elimination of H2O2 produced by TSH in FRTL-5 cells. Treatment with 500microM H2O2 causes apoptosis in FRTL-5 cells as evidenced by standard assays of apoptosis (i.e., terminal deoxynucleotidyl transferase deoxyuridine triphosphate-biotin nick end-labeling (TUNEL), BAX expression and PARP cleavage. Overexpression of Prx I and Prx II reduces the amount of H2O2-induced apoptosis measured by these assays. CONCLUSION: These results suggest that Prx I and Prx II are involved in the removal of H2O2 in thyroid cells, and can protect these cells from undergoing apoptosis. These proteins are likely to be involved in the normal physiological response to TSH-induced production of H2O2 in thyroid cells.