Influence of cytokines on growth and differentiated function of FRTL5 cells

A functioning rat thyroid cell line (FRTL5) was used to study interactions of TSH with interferon-gamma (IFN gamma) and tumor necrosis factor-alpha (TNF alpha). We examined effects on growth and differentiated function. Growth was assessed by DNA, incorporation of [3H]thymidine ([3H]Tdr) into DNA, and cell number; uptake of 125I (I- uptake) and the concentration of cAMP were measured simultaneously with growth assessment. IFN gamma stimulated the 30-min I- uptake and enhanced the effect of TSH. TNF alpha had minimal effects on growth indices (slight increase in [3H]Tdr incorporation) and had no influence on I- uptake; it inhibited TSH stimulation of both growth and I- uptake. When combined, IFN gamma and TNF alpha synergized in inhibiting TSH-stimulated growth. By itself TNF alpha inhibited stimulation of I- uptake by TSH, but augmented the enhancement seen with IFN gamma. The influence of calf serum (CS) was to increase the rate of incorporation of [3H]Tdr, but a similar qualitative pattern for the actions of the cytokines remained. A reverse profile (stimulation by IFN gamma, inhibition by TNF alpha, and stimulation by the combination) was seen for I- uptake, with CS increasingly diminishing all values. TSH stimulation of growth was progressively effective with increments of CS in the medium, but consistently there was inhibition that was greater with IFN gamma than with TNF alpha and was almost total with the combined cytokines. Stimulation of I- uptake by TSH was enhanced by IFN gamma, reduced by TNF alpha, and, when serum was present, increased to a degree that was greater than additive by the combined cytokines. Growth stimulation by insulin or insulin-like growth factor-I was inhibited partially by the individual cytokines and completely by the combination. Both insulin and insulin-like growth factor-I inhibited TSH stimulation of I- uptake, but similar stimulation by the cytokines was not affected. Simultaneous with inhibition of TSH-stimulated growth, both IFN gamma and TNF alpha enhanced cAMP accumulation. The mechanism of these multiple effects of IFN gamma and TNF alpha, especially on the actions of TSH, may not currently be fully explained, but they almost certainly reflect differing modes of action. The relevance to thyroid function in man is conjectural. Especially in Graves' disease, where thyroid infiltration with cells that secrete these cytokines is common, it seems probable that both IFN gamma and TNF alpha will have significant influences on both growth and differentiated cell function.