Promoter polymorphisms regulating corticotrophin-releasing hormone transcription in vitro

To investigate whether polymorphisms in the corticotrophin-releasing hormone (CRH) promoter are associated with altered CRH gene regulation, we studied the reactivity of three recently described promoter variants in vitro. The 3625 bp variants A1B1, A2B1 and A2B2 of the human CRH promoter were cloned in the 5' region to a luciferase reporter gene and transiently transfected into both mouse anterior pituitary cells AtT-20D16vF2 and pheochromocytoma cells PC12. Incubation with 8-Br-cAMP alone or in combination with cytokines significantly enhanced the promoter activity in both cell lines studied by up to 22-fold. However, dexamethasone antagonised cAMP effects on CRH expression in AtT-20 cells while showing no effect on PC12 cells, indicating that tissue-specific factors play a crucial role. Among the haplotypes studied, A1B1 exhibited the greatest reactivity on various stimuli. Electric mobility shift assay (EMSA) was performed to study whether the described polymorphic nucleotide sequences in the 5' region of the hCRH gene interfere with binding of nuclear proteins. A specific DNA protein complex was detected at position -2353 bp for the wild type sequence only, possibly interfering with a binding site for the activating transcription factor 6 (ATF6). Taken together, this is the first study to demonstrate that CRH promoter reactivity varies between the compound promoter alleles.