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 pathogenesis of autoimmune thyroid disease, as it is known to exert diverse effects on thyroid metabolism. These include induction of human leukocyte antigen class II expression, inhibition of gene expression of thyroglobulin and thyroid peroxidase, as well as inhibition of cellular proliferation. However, the mechanism of action of IFN gamma in thyrocytes has not been clearly defined. We studied the action of IFN gamma on the production of inositol phosphates and intracellular Ca2+ mobilization 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 intracellular Ca2+ ([Ca2+](i)) at 37 C. Preincubation with 12-O-tetradecanoylphorbol-13-acetate,which activate, protein kinase C, resulted in the abolition of the IFN gamma response, suggesting that protein kinase C was involved in a negative feedback loop resulting in inhibition of IFN gamma-induced [Ca2+](i) rise. Prior release of intracellularly stored Ca2+ with thapsigargin, the microsomal Ca2+ pump inhibitor, also abolished the response of IFN gamma. Mobilization of [Ca2+](i) resulted in Ca2+ entry across the plasma membrane, which could be blocked by La3+ the inorganic Ca2+ antagonist. The tyrosine protein kinase inhibitor, genistein, inhibited the production of inositol phosphates and the elevation of [Ca2+](i) induced by IFN gamma, but had no effect on ATP, suggesting that tyrosine protein kinase is involved in the signaling transduction of IFN gamma. We conclude that the mobilization of intracellular Ca2+ and the production of inositol phosphates are two important signaling events for the action of IFN gamma in human thyrocytes.