9‐cis retinoic acid accelerates calcitriol‐induced osteocalcin production and promotes degradation of both vitamin D receptor and retinoid X receptor in human osteoblastic cells

Abstract

vitamin D receptor (VDR) and retinoid X receptor (RXR) heterodimerize to mediate the genomic actions of 1alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3), calcitriol), the biologically active form of vitamin D(3). In this study, we show that 9-cis retinoic acid (9-cisRA), the ligand for RXR, accelerates calcitriol-induced expression of osteocalcin gene, the marker for mature osteoblasts. Calcitriol and its synthetic analog KH1060 (1 nM) induced osteocalcin secretion after a 96-h incubation period as detected by radioimmunoassay. When these compounds were used together with 9-cisRA, osteocalcin protein secretion was, however, detected already after 72 and 48 h, respectively. Detection of osteocalcin mRNA with quantitative PCR revealed elevated mRNA levels already after a 4-h treatment of the cells with calcitriol, KH1060, or 9-cisRA compared with untreated cells. In combination treatments, 9-cisRA rapidly stimulated osteocalcin mRNA synthesis induced by the different vitamin D(3) compounds. In MG-63 cells treated with calcitriol or KH1060, the stimulation was maximal after the first 4 h and diminished thereafter. In fact, after the 48-h incubation 9-cisRA reduced osteocalcin mRNA levels in KH1060-treated cells, the amount of mRNA being only 44% of the levels obtained with KH1060 alone. The reduction was accompanied by an increased degradation rate of both VDR and RXRbeta in the presence of 9-cisRA. Furthermore, 9-cisRA increased the formation of RXRbeta-VDR-VDRE complex on the osteocalcin gene VDRE. These results suggest that 9-cisRA accelerates calcitriol-induced osteocalcin production in human osteoblastic cells through increased formation of transcriptionally active chromatin complexes and, subsequently, promotes degradation of the heterodimeric complex of VDR and RXR.

Demographics and Characterization of 10,282 Randall Plaque-Related Kidney Stones

“…The osteocalcin gene has a classical VDR response element in promoter region, and is considered as a hallmark feature of VDR activation. 31 , 32 Taken together, our results suggest that patients prone to develop plaques have an increased biological response to 1,25-dihydroxyvitamin D implying VDR. In turn, VDR activation increases calcium absorption by intestinal epithelial cells and eventually calcium renal excretion.…”

Osteoporose – die unterschätzte und untertherapierte Volkskrankheit

“…B. 4000 I. E./d) ist für die Knochengesundheit sowie für die Bildung Vitamin-K-abhängiger Proteine unerlässlich 22 23 24 .…”