PURINERGIC AGONIST ATP IS A COMITOGEN IN THYROID FRTL-5 CELLS

Several growth factors may stimulate proliferation of thyroid cells. T his effect has, in part, been dependent on calcium entry. In the prese nt study using FRTL-5 cells, we show that in addition to its effect on calcium fluxes, ATP acts as a comitogen in these cells. In medium con taining 5% serum, but no TSH, ATP stimulated the incorporation of H-3- thymidine in a dose- and time-dependent manner in the cells. At least a 24-h incubation with ATP was necessary to observe the enhanced (30-5 0%) incorporation of H-3-thymidine and an increased (30%) cell number. The effect of ATP was dependent on insulin in the incubation medium. Furthermore, ATP enhanced the TSH-mediated incorporation of H-3-thymid ine. The effect of ATP was apparently mediated via a C-protein depende nt mechanism, as no stimulation of thymidine incorporation was observe d in cells treated with pertussis toxin. The effect of ATP was not dep endent on the activation of protein kinase C (PKC), as ATP was effecti ve in cells with downregulated PKC. ATP rapidly phosphorylated mitogen activated protein (MAP) kinase in FRTL-5 cells. In addition, ATP stim ulated the expression of a 62 kDa c-fos dependent protein in a dose- a nd time-dependent manner. Our results thus suggest that extracellular ATP, in the presence of insulin, may be a cofactor in the regulation o f thyroid cell proliferation, probably by phosphorylating MAP kinase a nd stimulating the expression of c-fos. (C) 1996 Wiley-Liss, Inc.