1alpha,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 1alpha,25-dihydroxyvitamin D3 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.
Moeenrezakhanlou
Alireza
A
Department of Medicine, University of British Columbia, Rm. 452D, 2733 Heather St., Vancouver, BC, Canada, V5Z 3J5.
Nandan
Devki
D
Shephard
Lindsay
L
Reiner
Neil E
NE
D001483:Base Sequence; D001665:Binding Sites; D002117:Calcitriol / Q000494:pharmacology*; D002460:Cell Line; D017362:Cyclic AMP Response Element-Binding Protein / Q000187:drug effects* / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D018950:Lipopolysaccharide Receptors / Q000096:biosynthesis / Q000235:genetics*; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011485:Protein Binding / Q000187:drug effects; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D013329:Structure-Activity Relationship
D017362:Cyclic AMP Response Element-Binding Protein; D018950:Lipopolysaccharide Receptors; D019869:Phosphatidylinositol 3-Kinases; D002117:Calcitriol