THYROTROPIN-INDUCED NITRIC OXIDE (NO) ACTS AS INHIBITORY SIGNAL ON THYROID-SPECIFIC GENE EXPRESSION AND PROLIFERATION IN FRTL-5 CELLS.

FOZZATTI LAURA; VELEZ MARIA LAURA; MACCIÓ DANIELA; LUCERO ARIEL MAXIMILIANO; ROTH GERMAN; MASINI-REPISO ANA MARIA

Buenos Aires.

Congreso; 13th INTERNATIONAL THYROID CONGRESS; 2005

Sociedad Latinoamericana de Tiroides (SLAT), AOTA, ATA y ETA.

NO is a free radical that mediates a wide array of cellular functions in many tissues. It is generated from L-arginine by NO-synthases (NOS), with additional production of L-citrulline. NOS isoforms have been demonstrated in thyroid tissue. Previous reports indicate that NO donors induce thyroid dedifferentiation. However, the functional significance of thyrocyte-produced endogenous NO has not been examined. This work aimed to explore the role of endogenously produced NO on expression of thyroid-specific genes and proliferation in FRTL-5 cells. The incubation of FRTL-5 cells with L-NAME 1mM increase of the TSH-stimulated iodide uptake and thyroglobulin (TG) mRNA expression. Treatment of cells with TSH for 24-48 h increased NO (14C-citrulline; maximum TSH 200µUI/ml, 24 h, 2-fold, p<0.05) indicating a TSH-dependent NO production. To analyse the NO action on TG gene expression at transcriptional level, minimal TG promoter region (-168 to +36 bp) was transfected. An increment of TSH (200µUI/ml)-stimulated activity of TG promoter after incubation with two NOS inhibitors, L-NAME and L-NMMA (0.05mM) for 12-24 h was evidenced (maximum 24h, 1.8-fold, p<0.05). The presence of L-NAME also induced an increase of TSH-induced NIS mRNA expression (Northern-Blot; 48h, 2-fold, p<0.001). A significant increase of TSH-induced transcriptional activity of a NIS promoter region (-2841 to +13 bp) was obtained in presence of L-NMMA (24h, 2-fold, p<0.05). We also analyzed the action of endogenous NO on cell proliferation. The presence of the NOS inhibitor, L-NMMA (0.1mM), induced an increase of the TSH (100-300 µUI/ml)-stimulated cell proliferation (3H-thymidine incorporation) in a concentration-dependent manner at 24-48 h (maximum 24h, 2-fold, p<0.001). In conclusion, our data indicate that NO could act as a negative signal for TSH-stimulated expression of specific genes and proliferation in thyroid cell. Since TSH induced NO production, a novel physiological role of NO to regulate the stimulating action of TSH could be proposed.