Regulation of thyroid follicular cell function by intracellular redox-active copper

Pyrrolidine dithiocarbamate (PDTC) is a metal-chelating compound that exert s prooxidant or antioxidant effects and is widely used to study redox regul ation of cell function. In the present study, we investigated effects of PD TC on the function of rat thyroid follicular FRTL-5 cells. Treatment of the cells with PDTC resulted in a marked decrease in Pax-8 messenger RNA level and its DNA-binding activity. This decrease was associated with a signific ant reduction in thyroperoxidase (TPO) messenger RNA level. Expression of T TF-1 and thyroglobulin was not affected by PDTC. Treatment with PDTC also d ecreased DNA-binding activity of p53, a tumor suppressor protein, and incre ased cell proliferation rates. These changes were not observed by the treat ment with another antioxidant, N-acetyl-L-cysteine, suggesting that the met al-chelating, prooxidant property of PDTC is responsible for its effects. I ndeed, the intracellular level of copper was significantly increased by PDT C. Treatment with batho-cuproinedisulfonic acid, a noncell-permeable chelat or of Cu1+, abrogated the copper increase by PDTC and its effects on Pax-8 and TPO expression as well as on p53 binding. Taken together, these results indicate that the intracellular level of redox-active copper is crucial fo r Pax-8 and TPO expression and for proliferation of thyroid follicular cell s.