CREB-independent regulation by CBP is a novel mechanism of human growth hormone gene expression
Laurie E. Cohen, … , Fredric Wondisford, Sally Radovick
Laurie E. Cohen, … , Fredric Wondisford, Sally Radovick
Published October 15, 1999
Citation Information: J Clin Invest. 1999;104(8):1123-1130. https://doi.org/10.1172/JCI7308.
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Article

CREB-independent regulation by CBP is a novel mechanism of human growth hormone gene expression

Abstract

Hypothalamic growth hormone–releasing hormone (GHRH) stimulates growth hormone (GH) gene expression in anterior pituitary somatotrophs by binding to the GHRH receptor, a G-protein–coupled transmembrane receptor, and by mediating a cAMP-mediated protein kinase A (PKA) signal-transduction pathway. Two nonclassical cAMP-response element motifs (CGTCA) are located at nucleotides –187/–183 (distal cAMP-response element; dCRE) and –99/–95 (proximal cAMP-response element; pCRE) of the human GH promoter and are required for cAMP responsiveness, along with the pituitary-specific transcription factor Pit-1 (official nomenclature, POU1F1). Although a role for cAMP-response element binding protein (CREB) in GH stimulation by PKA has been suggested, it is unclear how the effect may be mediated. CREB binding protein (CBP) is a nuclear cofactor named for its ability to bind CREB. However, CBP also binds other nuclear proteins. We determined that CBP interacts with Pit-1 and is a cofactor for Pit-1–dependent activation of the human GH promoter. This pathway appears to be independent of CREB, with CPB being the likely target of phosphorylation by PKA.

Authors

Laurie E. Cohen, Yukiko Hashimoto, Kerstin Zanger, Fredric Wondisford, Sally Radovick

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CBP and Pit-1 synergistic activation of the hGH promoter after GHRH stim...
CBP and Pit-1 synergistic activation of the hGH promoter after GHRH stimulation does not require the presence of CREs. CV-1 cells were transfected with hGHRH receptor and SV-40 expression vectors (pSG5) containing either Pit-1 or CBP cDNAs in the presence of (a) 195 bp of the hGH promoter (b) mutation of the pCRE, or (c) deletion of an additional 55 bp of the hGH promoter, with loss of the dCRE. Stimulation was with hGHRH(1-29)-NH2 for 6 hours, or with BSA as a control. Data are expressed as mean fold activation ± SEM relative to EV Pit-1 plus EV CBP after stimulation with BSA. Significant activation was not seen without cotransfection of the GHRH receptor (data not shown).