Single nucleotide polymorphisms in the human corticosteroid-binding globulin promoter alter transcriptional activity.

Corticosteroid-binding globulin (CBG) is a high-affinity plasma protein that transports glucocorticoids and progesterone. Others and we have reported non-synonymous single nucleotide polymorphisms (SNPs) that influence CBG production or steroid-binding activity. However, no promoter polymorphisms affecting the transcription of human CBG gene (Cbg) have been reported. In the present study we investigated function implications of six promoter SNPs, including -26 C/G, -54 C/T, -144 G/C, -161 A/G, -205 C/A, and -443/-444 AG/-, five of which are located within the first 205 base pairs of 5'-flanking region and close to the highly conserved footprinted elements, TATA-box, or CCAAT-box. Luciferase reporter assays demonstrated that basal activity of the promoter carrying -54 T or -161 G was significantly enhanced. The first three polymorphisms, -26 C/G, -54 C/T, and -144 G/C located close to the putative hepatic nuclear factor (HNF) 1 binding elements, altered the transactivation effect of HNF1β. We also found a negative promoter response to dexamethasone-activated glucocorticoid receptor (GR) α, although none of the SNPs affected its transrepression function. Our results suggest that human Cbg -26 C/G, -54 C/T, -144 G/C, and -161 A/G promoter polymorphisms alter transcriptional activity, and further studies are awaited to explore their association with physiological and pathological conditions.