RETINOIC ACID DECREASES THYROID-HORMONE RECEPTOR EXPRESSION IN PITUITARY GH1 CELLS

Retinoic acid produced a time and dose-dependent depletion of thyroid hormone receptors in GH1 cells without modifying their affinity for triiodothyronine (T3). A maximal decrease (50-70%) was obtained after 24-48h incubation with 5-10 μM retinoic acid. Treatment with 0.8 nM T3 for 24 h caused a similar reduction and did not potentiate the decrease produced by these concentrations of retinoic acid. However, the combination of sub-maximally effective doses of both ligands had an additive effect on receptor levels. The reduction of receptor caused by retinoic acid is accompanied by a decreased expression of c-erbA α1 and α2 mRNAs, but the retinoid did not reduce the abundance of c-erbA β mRNA. In contrast, T3 decreased the levels of both α and β transcripts. © 1991 Academic Press, Inc.