THYROTROPIN-RELEASING-HORMONE AND C-FOS C-JUN GENES ARE COLOCALIZED IN RAT ANTERIOR-PITUITARY-CELLS - STIMULATION OF TRANSCRIPTION BY GLUCOCORTICOIDS/

We recently reported that glucocorticoids (GC) enhance the level of TR H peptide and messenger RNA in anterior pituitary cells. However, the regulating mechanism is as yet unclear. The protooncogenes c-fos/-jun. belong to the class of immediate early genes that are activated in ne urons by a variety of stimuli, including GC. Fos protein acts as an in tracellular third messenger, regulating gene transcription of neurotra nsmitters. To determine whether c-fos/c-jun are involved in regulating the effect of GC on TRH in rat anterior pituitary cells, the coexpres sion and nuclear transcription activity of TRH and c-fos/c-jun after d examethasone (DEX) stimulation (7 days) were investigated. The double labeled in situ hybridization results demonstrated that TRH and c-fos/ c-jun are coexpressed in anterior pituitary cells and that DEX (10(-8) M) enhanced the cell intensity for TRH and c-fos/c-jun. The mean cell intensity of treatment vs. control was 2.4-fold for TRH, 1.4-fold for c-fos, and 1.4-fold for c-jun (n = 24; P < 0.01). The Northern blot a nalysis also showed that DEX increased the messenger RNA level of TRH 5.1-fold (n = 4; P < 0.01), that of c-fos 1.8-fold (n = 5; P < 0.01), and that of c-jun 4.2-fold (n = 4; P < 0.01). The nuclear run-on analy sis indicated that DEX increased the nuclear transcription activity of TRH 3.3-fold, that of c-jun 3.2-fold, and that of c-fos 3-fold (n = 3 ; P < 0.01) vs. the control value. The coexpression of TRH and c-fos/c -jun in anterior pituitary cells as well as the enhancement of transcr iption after DEX treatment raise the possibility that c-fos/c-jun coul d mediate the effect of GC on TRH gene transcriptional activity.