TUMOR-NECROSIS-FACTOR-ALPHA (TNF-ALPHA) AND TRANSFORMING GROWTH-FACTOR-BETA-1 (TGF-BETA-1) INHIBIT THE EXPRESSION AND ACTIVITY OF NA+ K+-ATPASE IN FRTL-5 RAT-THYROID CELLS/

We recently reported that tumor necrosis factor-alpha (TNF-alpha) indu ction of the synthesis and secretion of transforming growth factor (TG F)-beta 1 by FRTL-5 cells is a thyroid-stimulating hormone (TSH)-depen dent and age-dependent process.((9)) TNF-alpha is only cytotoxic to ag ed (>40 passages) FRTL-5 cells grown in TSH-containing medium, whereas TGF-beta induces programmed cell death (apoptosis) in epithelial cell s but not in FRTL-5 cells, which otherwise retain many properties of n ormal thyroid follicular cells. This cell line is, therefore, a conven ient model for studies on the TSH-dependent and age-dependent inhibito ry effects of these cytokines on epithelial cell growth, viability, an d function. One prominent effect of TNF-alpha (and TGF-beta 1) on FRTL -5 cell function is suppression of iodide uptake, which is markedly st imulated by TSH. In aged FRTL-5 cells, iodide uptake is only about 10% that of young control cells, Na+/K+-ATPase activity, which drives iod ide uptake by thyroid cells, is inhibited by TNF-alpha and TGF-beta. T he following experiments quantitate the effects of TSH, aging, TNF-alp ha and TGF-beta 1 on the expression and activity of Na+/K+-ATPase acti vity in FRTL-5 cells. Young (<20 passages) and aged (>40 passages) FRT L-5 cells were treated with various doses (0-100 ng/ml) of recombinant human TNF-alpha or TGF-beta 1 for various times (0-3 days) with and w ithout 2 U/liter TSH. These treatments reduced the rate-limiting Na+/K +-ATPase beta 1 mRNA level and Na+/K+-ATPase activity in parallel in a dose-dependent and time-dependent fashion, Aged FRTL-5 cells were mor e sensitive to the inhibitory effects of TNF-alpha, whereas young cell s were more sensitive to the suppressive effects of TGF-beta 1 on the expression and activity of Na+/K+-ATPase, We conclude that inhibition of Na+/K+-ATPase activity by TNF-alpha and TGF-beta in FRTL-5 cells is differentially affected by aging and that this inhibitory effect can be dissociated from effects on cell viability.