C/EBPα and the Vitamin D Receptor Cooperate in the Regulation of Cathelicidin in Lung Epithelial Cells

1,25-Dihydroxyvitamin D-3 (1,25(OH)(2)D-3) and the vitamin D receptor (VDR) have been reported to have an important role in the regulation of innate immunity. We earlier reported that the antimicrobial peptide cathelicidin is induced by 1,25(OH)(2)D-3 in normal human bronchial epithelial cells with a resultant increase in antimicrobial activity against airway pathogens. In this study, we demonstrate that C/EBP alpha (C/EBP alpha) is a potent enhancer of human cathelicidin antimicrobial peptide (CAMP) gene transcription in human lung epithelial cells. In addition we found that C/EBP alpha functionally cooperates with VDR in the regulation of CAMP transcription. A C/EBP binding site was identified at -627/-619 within the CAMP promoter, adjacent to the vitamin D response element (VDRE; -615/-600). Mutation of this site markedly attenuated the transcriptional response to C/EBP alpha as well as to 1,25(OH)(2)D-3, further indicating cooperation between these two factors in the regulation of CAMP. ChIP analysis using 1,25(OH)(2)D-3 treated human lung epithelial cells showed C/EBP alpha and VDR binding to the CAMP promoter. C/EBP alpha has previously been reported to cooperate with Brahma (Brm), an ATPase that is component of the SWI/SNF chromatin remodeling complex. We found that dominant negative Brm significantly inhibited C/EBP alpha as well as 1,25(OH)(2)D-3 mediated induction of CAMP transcription, suggesting the functional involvement of Brm. These findings define novel mechanisms involving C/EBP alpha, SWI/SNF, and 1,25(OH)(2)D-3 in the regulation of CAMP in lung epithelial cells. These mechanisms of enhanced activation of the CAMP gene in lung epithelial cells suggest potential candidates for the development of modulators of innate immune responses for adjunct therapy in the treatment of airway infections. (C) 2014 Wiley Periodicals, Inc.