Thyroid-stimulating hormone inhibits Fas antigen-mediated apoptosis of human thyrocytes in vitro.

Abstract

The mechanisms of TSH-induced growth stimulation of thyrocytes in vivo have yet to be elucidated. We examined the antiapoptotic effect of TSH toward Fas antigen-mediated apoptosis of thyrocytes. Fas antigen was expressed on approximately 40% of unstimulated thyrocytes, and the expression was significantly inhibited by the addition of TSH in a dose-dependent manner. Treatment of thyrocytes with 8-bromo-cAMP mimicked the effect of TSH, suggesting that the inhibitory effect of TSH on Fas antigen expression was mediated by activating protein kinase A. In contrast, treatment of thyrocytes with either interleukin-1 beta (IL-1 beta) or interferon- gamma (IFN gamma) markedly increased Fas antigen expression on thyrocytes, and these effects were inhibited in the presence of TSH. The expression of the protooncogene product Bcl-2 did not change after the addition of TSH, 8-bromo-cAMP, IL-1 beta, IFN gamma, or a combination of TSH and IL-1 beta or IFN gamma. When thyrocytes stimulated with either IL-1 beta or IFN gamma were treated with anti-Fas IgM mAb, the cells were committed to apoptosis, whereas this apoptotic process was significantly inhibited by the addition of TSH. These results indicate that the Fas antigen is functionally expressed on the surface of thyrocytes, and TSH inhibits Fas antigen-mediated apoptosis of thyrocytes through the inhibitory effect of Fas antigen expression, resulting in the promotion of growth of the thyroid gland.

Modulation of Fas-mediated apoptosis of human thyroid epithelial cells by IgG from patients with Graves' disease (GD) and idiopathic myxoedema

“…Among these, Fas has been identified as the putative molecule capable of transducing apoptotic signals into cells [6]. We have recently reported that Fas is functionally expressed on thyrocytes and that anti-Fas-induced apoptosis of thyrocytes is significantly suppressed by treating cells with TSH [7]. Our data indicated that the growth-promoting activity of TSH on the thyroid glands may, in part, be achieved by the inhibitory effect of Fas-mediated apoptosis of thyrocytes.…”

“…The experimental protocol was approved by the Hospital Human Ethics Review Committee and a signed consent was obtained from each patient. The method used for the isolation of thyrocytes was described previously in detail [7,17]. The resultant thyrocyte preparations were < 1% reactive with MoAbs, CD3, CD20, CD14, and anti-von Willebrand factor, which, respectively, define an antigen on all mature T cells, pan-B cells, monocytes/macrophages, and on vascular endothelial cells.…”

“…To investigate the expression of Bcl-2 on thyrocytes, cells were permeabilized with digitonin as described previously [7,18]. Following confirmation of the adequacy of permeabilization by trypan blue uptake, permeabilized cells were incubated with FITC-conjugated antiBcl-2 MoAb and examined by a flow cytometer.…”

“…Following confirmation of the adequacy of permeabilization by trypan blue uptake, permeabilized cells were incubated with FITC-conjugated antiBcl-2 MoAb and examined by a flow cytometer. To check the adequacy of permeabilization on flow cytometric analysis, we used anti-a-tubulin MoAb (Cedarlane Labs, Ontario, Canada) as positive control antibody [7,18]. More than 99% of cells were positive with anti-a-tubulin MoAb.…”

“…Thyrocytes were cultured in RPMI 1640 containing 2% BSA in the presence or absence of various reagents listed above, then treated with anti-Fas IgM (1000 ng/ml) or control IgM (1000 ng/ml) for 18 h as previously described [7]. After detaching the cells from the plate, the cells were fixed with 70% ethanol and treated with 100 mg/ml of RNAse (Sigma), and then stained with 100 mg/ml of propidium iodide (Sigma) for 30 min on ice.…”