Figure 2.

CBP and Pit-1 synergistically activate the proximal hGH promoter after stimulation of the hGHRH receptor by hGHRH, which requires both Pit-1 binding sites. 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 proximal Pit-1 binding site, GH1; (c) mutation of the distal Pit-1 binding site, GH2; or (d) mutation of both Pit-1 binding sites to nonbinding sites. 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).