INTERFERON-GAMMA INCREASES INTRACELLULAR CALCIUM AND INOSITOL PHOSPHATES IN PRIMARY HUMAN THYROID-CELL CULTURE

Interferon-gamma (IFN gamma) is believed to play a role in the pathoge nesis of autoimmune thyroid disease, as it is known to exert diverse e ffects on thyroid metabolism. These include induction of human leukocy te antigen class II expression, inhibition of gene expression of thyro globulin and thyroid peroxidase, as well as inhibition of cellular pro liferation. However, the mechanism of action of IFN gamma in thyrocyte s has not been clearly defined. We studied the action of IFN gamma on the production of inositol phosphates and intracellular Ca2+ mobilizat ion in primary cultures of human thyrocytes using the fluorescent Ca2 indicator Eura-2. IFN gamma increased the production of inositol mono -, bis-, and trisphosphates and caused a dose-dependent increase in in tracellular Ca2+ ([Ca2+](i)) at 37 C. Preincubation with 12-O-tetradec anoylphorbol-13-acetate,which activate, protein kinase C, resulted in the abolition of the IFN gamma response, suggesting that protein kinas e C was involved in a negative feedback loop resulting in inhibition o f IFN gamma-induced [Ca2+](i) rise. Prior release of intracellularly s tored Ca2+ with thapsigargin, the microsomal Ca2+ pump inhibitor, also abolished the response of IFN gamma. Mobilization of [Ca2+](i) result ed in Ca2+ entry across the plasma membrane, which could be blocked by La3+ the inorganic Ca2+ antagonist. The tyrosine protein kinase inhib itor, genistein, inhibited the production of inositol phosphates and t he elevation of [Ca2+](i) induced by IFN gamma, but had no effect on A TP, suggesting that tyrosine protein kinase is involved in the signali ng transduction of IFN gamma. We conclude that the mobilization of int racellular Ca2+ and the production of inositol phosphates are two impo rtant signaling events for the action of IFN gamma in human thyrocytes .