In silico identification of novel transcription factors associated with CYP27B1 transcriptional regulation in LPS-challenged mononuclear phagocytes

Abstract

Renal and extrarenal production of the active form of vitamin D, 1,25-dihydroxyvitamin D (1,25(OH)2D), is catalyzed by CYP27B1, an enzyme also called 1-α-hydroxylase. The overproduction of 1,25(OH)2D has been described in granulomatous diseases. High circulating concentrations of 1,25(OH)2D can lead to hypercalcemia. The aim of this work was to characterize the transcriptional regulation of CYP27B1 in human mononuclear phagocytes exposed to LPS due to its relevance to understanding the hypercalcemia and ectopic calcifications associated with chronic inflammatory diseases such as tuberculosis and other granulomatous diseases. The human CYP27B1 promoter analysis identified binding sites for published TF, SNPs, novel putative TFBS and conserved sites compared to mice. Then, using microarray data, a meta-analysis was performed to obtain a global view of the gene expression in LPS-challenged dendritic cells, monocytes and macrophages. Finally, two experiments, GSE40885 and time series GSE19765, were analyzed in-depth using differential expression analysis which permitted the identification of TF co-expressed with CYP27B1. This work allowed us to formulate a CYP27B1 transcriptional regulation model for LPS-challenged monocytes/macrophages. The importance of two TF families, NFKB and CEBPB, was confirmed. Data also suggests that PLAGL2 and STAT4 which are novel TF could participate in the CYP27B1 transcriptional regulation in cells exposed to LPS. These TF, in turn, would be interacting with regions that present polymorphisms in the general population which might explain the pathological phenotypes associated with altered vitamin D metabolism.