A novel mechanism for cyclic adenosine 3 ',5 '-monophosphate regulation ofgene expression by CREB-binding protein

The pituitary-specific transcription factor, Pit-1, is necessary to mediate protein kinase A (PKA) regulation of the GH, PRL, and TSH-beta subunit gen es in the pituitary. Since these target genes lack classical cAMP DNA respo nse elements (CREs), the mechanism of this regulation was previously unknow n. We show that ORES binding protein (CBP), through two cysteine-histidine rich domains (C/H1 and C/H3), specifically and constitutively interacts wit h Pit-1 in pituitary cells. Pit-1 and CBP synergistically activate the PRL gene after PKA stimulation in a mechanism requiring both an intact Pit-1 am ino-terminal and DNA-binding domain. A CBP construct containing the C/H3 do main [amino acids (aa) 1678-2441], but not one lacking the C/H3 domain (aa 1891-2441), is sufficient to mediate this response. Neither construct augme nts PKA regulation of ORE-containing promoters. Fusion of either CBP fragme nt to the GAL4 DNA-binding domain transferred complete PKA regulation to a heterologous promoter. These findings provide a mechanism for ORES-independ ent regulation of gene expression by cAMP.