1α,25‐Dihydroxycholecalciferol activates binding of CREB to a CRE site in the CD14 promoter and drives promoter activity in a phosphatidylinositol‐3 kinase‐dependent manner

1,25‐Dihydroxycholecalciferol, also known as 1α,25‐dihydroxyvitamin D 3 or calcitriol, regulates the differentiation and functional properties of mononuclear phagocytes. Many of these effects involve nongenomic signaling pathways, which are not fully understood. Activation of CD14 expression, a monocyte differentiation marker and coreceptor with TLR‐2 for bacterial LPS, by calcitriol was shown previously to be PI‐3K‐dependent [1]; however, the mechanism of gene activation remained undefined. Using a transcription factor‐binding array screen coupled with EMSA, we found evidence for PI‐3K‐dependent activation of CREB in THP‐1 cells incubated with calcitriol. Furthermore, analysis of the proximal promoter of human CD14 identified regions that contained up to seven sequences, which showed significant similarity to a canonical CRE sequence, 5′‐TGACGTCA‐3′. Treatment of THP‐1 cells with calcitriol activated CREB binding to one of these regions at Positions −37 to −55, relative to the transcription start site in a PI‐3K‐dependent manner. This 19‐mer region also became transcriptionally active in a reporter assay in response to calcitriol, again dependent on PI‐3K. Mutation of the CRE within the 19‐mer abolished this activity. Taken together, these results show that calcitriol signaling, leading to activation of the CD14 promoter, involves CREB activation downstream of PI‐3K.