cAMP response element-binding protein-binding protein mediates thyrotropin-releasing hormone signaling on thyrotropin subunit genes

Transcription of pituitary alpha -glycoprotein hormone subunit (alpha -GSU) and thyrotropin beta subunit (TSH-beta) genes is stimulated by thyrotropin -releasing hormone (TRH). Since cAMP response element-binding protein (CREB )-binding protein (CBP) integrates a number of cell signaling pathways, we investigated whether CBP is important for TRH stimulation of the TSH subuni t genes. Cotransfection of E1A in GH(3) cells completely blocked TRH stimul ation of the TSH subunit genes, suggesting that CBP is a key factor for TRH signaling in the pituitary. CBP and Pit-1 acted synergistically in TRH sti mulation of the TSH-beta promoter, and amino acids 1-450 of CBP were suffic ient for the TRH effect. In contrast, on the human alpha -GSU promoter, CRE B and P-Lim mediated TRH signaling. Intriguingly, CREB was phosphorylated u pon TRH stimulation, leading to CBP recruitment to the alpha -GSU promoter. CBP also interacted with P-Lim in a TRH-dependent manner, suggesting that P-Lim is an important factor for non-cAMP response element-mediated TRH sti mulation of this promoter. Distinct domains of CBP were required for TRH si gnaling by CREB and P-Lim on the alpha -GSU promoter, amino acids 450-700 a nd 1-450, respectively. Thus, the amino terminus of CBP plays a critical ro le in TRH signaling in the anterior pituitary via both Pit-1-dependent and -independent pathways, yielding differential regulation of pituitary gene p roducts.