Integration of hormone signaling in the regulation of human 25(OH)D₃24-hydroxylase transcription

Abstract

. In these cells, cotreatment with the PKC activator TPA and 1,25(OH)2D3 yielded a 27-fold increase in luciferase activity, which was 2-to 3-fold greater than activation obtained with 1,25(OH)2D3 alone (P Ͻ 0.05). Similar results were observed using LLCPK-1 kidney cells, suggesting that the previously observed enhancement of 1,25(OH)2D3-induced renal 24(OH)ase mRNA and activity by PKC activation occurs at the level of transcription. The functional cooperation between PKC activation and VDR was not found to be mediated by the AP-1 site in the h24(OH)ase promoter or by enhanced binding of GRIP or DRIP205 to VDR and was also not due to PKC-mediated phosphorylation of VDR on Ser 51 . Our study demonstrates that, in LLCPK-1 kidney cells, the PKC enhancement of 1,25(OH)2D3-stimulated transcription may be due, in part, to an increase in VDR concentration. In addition, inhibitors of the MAPK pathway were found to decrease the TPA enhancement (P Ͻ 0.05). Because activation of MAPK has been reported to result in the phosphorylation of SRC-1 and in functional cooperation between SRC-1 and CREB binding protein, we propose that the potentiation of VDR-mediated transcription may also be mediated through changes in the phosphorylation of specific VDR coregulators. , and the production of 1,24,25(OH) 3 D 3 is believed to be the initial step in the catabolism of 1,25(OH) 2 D 3 to calcitroic acid (46). Recent studies using the 24(OH)ase-null mutant mouse provided the first direct in vivo evidence that the C-24 pathway, initiated by the 24(OH)ase enzyme, is the major catabolic process that functions to regulate the physiological levels of 1,25(OH) 2 D 3 , thereby preventing the accumulation of toxic levels of the hormone (53). Thus 1,25(OH) 2 D 3 , by inducing the 24(OH)ase enzyme, stimulates its own deactivation.The cloning of the rat and human 24(OH)ase gene promoters has made possible, for the first time, studies related to the regulation of this major target of 1,25(OH) 2 D 3 action (7,30,39,59). The 24(OH)ase gene is the most transcriptionally responsive 1,25(OH) 2 D 3 -inducible gene identified to date. It is the first vitamin D-responsive gene to be controlled by two independent VDREs (7,30,59). Although a number of studies by us and others (4,13,14,22,45) have defined factors that affect rat 24(OH)ase transcription, very little work has been done to examine molecular mechanisms by which 1,25(OH) 2 D 3 and other factors affect the regulation of human 24(OH)ase transcription. In previous studies, two VDREs have been defined and a putative activating protein-1 (AP-1) site has been identified by sequence homology in the human

New insights into the function and regulation of vitamin D target proteins

“…Our findings indicate functional cooperation between C/EBP proteins, CBP (CREB binding protein) and VDR in regulating 24(OH)ase [10]. We also found cooperation between protein kinase C and VDR in the regulation of 24(OH)ase [30]. Our results indicate that the protein kinase C enhancement of 1,25(OH) 2 D 3 stimulated 24(OH)ase transcription may be due, in part, to an increase in VDR concentration and may also be mediated through changes in phosphorylation of VDR coregulators [30].…”

“…We also found cooperation between protein kinase C and VDR in the regulation of 24(OH)ase [30]. Our results indicate that the protein kinase C enhancement of 1,25(OH) 2 D 3 stimulated 24(OH)ase transcription may be due, in part, to an increase in VDR concentration and may also be mediated through changes in phosphorylation of VDR coregulators [30]. In addition, using the human 24(OH)ase promoter, we found that transcriptional activation of VDR from patients with HVDRR (1,25(OH) 2 D 3 resistant rickets; mutant H305Q) can be enhanced by inhibition of phosphatase 1 and 2A ( Fig.…”

An architectural perspective of vitamin D responsiveness

“…One of the most pronounced effects of vitamin D is to induce the expression of the 25-hydroxy vitamin D3 24-hydroxylase [24(OH)ase] gene, which encodes an enzyme that metabolizes vitamin D. It has been generally believed that vitamin D-mediated transcription of the 24(OH) ase gene is controlled by VDREs located in the proximal promoter region [17,48,49]. However, recent reports indicate that additional upstream VDR binding regions (see Figure 3A) may be also contributing to full vitamin D-responsiveness by the 24(OH)ase gene in osteoblastic cells [50].…”

CYP24 Promoter Activity is Affected by Mechanical Stress and Mitogen-Activated Protein Kinase in MG63 Osteoblast-like Cells

“…Vitamin D acting through the VDR reacts with the CYP24 promoter region at two positions, -150bp and -250bp. 7 Regulation of CYP24 mRNA depends on the level of circulating 1,25(OH) 2 D 3 . 8 Dwivedi et al reported that ERK1/2 and ERK5 in the MAPK signaling pathway participated in CYP24 promoter induction in monkey kidney fibroblast COS-1 cells.…”