RESUMO
In FRTL-5 cells, methimazole (MMI) and propylthiouracil (PTU), both thyroid peroxidase (TPO) inhibitors, increase thyroglobulin (Tg) mRNA levels and Tg accumulation in the medium. An increase in Tg mRNA levels and in Tg accumulation was observed after 2-4 h and 8 h incubation with 10,000 microM MMI or PTU, respectively. Glutamate dehydrogenase mRNA levels, which corresponded with total RNA levels, were not affected. The concentrations of these drugs at which stimulation occurs are higher than the concentrations required for complete inhibition of TPO activity. The stimulatory effects of MMI and PTU can be suppressed by iodide and do not occur when protein synthesis is inhibited by cycloheximide. The effect of MMI on Tg gene expression is not dependent on thyrotropin (TSH) or insulin and MMI does not change the TSH-induced cAMP production. We conclude that MMI and PTU interfere in a regulatory pathway for Tg gene expression.
Assuntos
Expressão Gênica/efeitos dos fármacos , Metimazol/farmacologia , Propiltiouracila/farmacologia , Tireoglobulina/genética , Linhagem Celular , Humanos , Insulina/fisiologia , Iodetos/farmacologia , Cinética , RNA Mensageiro/metabolismo , Transcrição Gênica/efeitos dos fármacosRESUMO
Methimazole (1-methyl-2-mercaptoimidazole; MMI) increases thyroglobulin mRNA and thyroid peroxidase mRNA concentration in human thyroid cells and in FRTL-5 cells. MMI (1-10,000 microM) gives a dose-dependent increase of thyroglobulin concentration in the medium of human thyroid cells and FRTL-5 cells. The stimulation by MMI has no effect on the TSH-induced cAMP production and occurs in the presence or absence of thyrotropin (TSH). TSH increases the thyroglobulin and thyroid peroxidase mRNA synthesis in human thyroid cells and FRTL-5 cells. The accumulation of thyroglobulin in the medium has an optimum at 100 microU TSH/ml in FRTL-5 cells. This optimum can also be found in most human thyroid cell cultures.
Assuntos
Iodeto Peroxidase/genética , Metimazol/farmacologia , RNA Mensageiro/metabolismo , Tireoglobulina/genética , Glândula Tireoide/efeitos dos fármacos , Northern Blotting , Linhagem Celular , Células Cultivadas , AMP Cíclico/metabolismo , Humanos , Iodeto Peroxidase/metabolismo , Hibridização de Ácido Nucleico , RNA Mensageiro/biossíntese , Tireoglobulina/metabolismo , Glândula Tireoide/citologia , Glândula Tireoide/metabolismo , Tireotropina/metabolismo , Tireotropina/farmacologiaRESUMO
This study shows that the Fisher rat thyroid cell line (FRTL-5) can iodinate thyroglobulin (Tg) in an selective way. The Tg-iodination is TSH dependent and shows a optimum at 10-100 microU TSH/ml. Intracellularly, Tg and various other non Tg-related proteins are iodinated in a TSH dependent fashion. Tg added to the medium is specifically iodinated, this occurs already in microgram amounts, in contrast to many other proteins present in the medium. Only albumin, present in mg amounts is clearly iodinated in a lower degree than Tg. Albumin iodination is not clearly dependent of TSH. Since catalase added to the medium prevents the iodination of albumin but not of newly synthesized Tg we suggest that intracellular iodination must exist.
Assuntos
Iodetos/metabolismo , Tireoglobulina/metabolismo , Glândula Tireoide/metabolismo , Tireotropina/farmacologia , Animais , Linhagem Celular , Radioisótopos do Iodo , RNA Mensageiro/efeitos dos fármacos , RNA Mensageiro/genética , Ratos , Tireoglobulina/genética , Glândula Tireoide/efeitos dos fármacosRESUMO
This study shows that the Fisher rat thyroidal cell line (FRTL-5) can iodinate newly synthesized thyroglobulin. Iodinated thyroglobulin was found intra- and extracellularly. Both the synthesis of thyroglobulin and its subsequent iodination were found to be thyrotropin (TSH) dependent, with optimal activity at 10-100 microU TSH/ml. Thyroglobulin was the only protein in the culture medium, that was iodinated with high specificity and in a TSH-dependent fashion. Albumin, which was abundantly present in the culture medium, was only weakly iodinated. Various proteins, including thyroglobulin, were found to be iodinated intracellularly. Of these iodoproteins only thyroglobulin appeared in the medium suggesting selective secretion of iodinated thyroglobulin. It was shown that the other intracellular iodoproteins were no thyroglobulin breakdown products. Their function is as yet unknown.
