Regulation of Vitamin D hydroxylases gene expression by 1,25-dihydroxyvitamin D3 and cyclic AMP in cultured human syncytiotrophoblasts

2007 ◽  
Vol 103 (1) ◽  
pp. 90-96 ◽  
Author(s):  
Euclides Avila ◽  
Lorenza Díaz ◽  
David Barrera ◽  
Ali Halhali ◽  
Isabel Méndez ◽  
...  
Keyword(s):  
Gene Expression ◽  
Vitamin D ◽  
Cyclic Amp ◽  
Dihydroxyvitamin D3 ◽  
1,25 Dihydroxyvitamin D3

Retinoid X receptors stimulate and 9-cis retinoic acid inhibits 1,25-dihydroxyvitamin D3-activated expression of the rat osteocalcin gene

1993 ◽  
Vol 13 (9) ◽  
pp. 5907-5917
Author(s):  
P N MacDonald ◽  
D R Dowd ◽  
S Nakajima ◽  
M A Galligan ◽  
M C Reeder ◽  
...  
Keyword(s):  
Gene Expression ◽  
Vitamin D ◽  
Retinoic Acid ◽  
Transcriptional Level ◽  
Mobility Shift ◽  
Dihydroxyvitamin D3 ◽  
Retinoid X Receptors ◽  
1,25 Dihydroxyvitamin D3 ◽  
Osteocalcin Gene ◽  
X Receptors

The vitamin D receptor (VDR) binds the vitamin D-responsive element (VDRE) as a heterodimer with an unidentified receptor auxiliary factor (RAF) present in mammalian cell nuclear extracts. VDR also interacts with the retinoid X receptors (RXRs), implying that RAF may be related to the RXRs. Here we demonstrate that highly purified HeLa cell RAF contained RXR beta immunoreactivity and that both activities copurified and precisely coeluted in high-resolution hydroxylapatite chromatography. Furthermore, an RXR beta-specific antibody disrupted VDR-RAF-VDRE complexes in mobility shift assays. These data strongly indicate that HeLa RAF is highly related to or is identical to RXR beta. Consequently, the effect of the 9-cis retinoic acid ligand for RXRs was examined in 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]-activated gene expression systems. Increasing concentrations of 9-cis retinoic acid (1 nM to 1 microM) markedly reduced 1,25(OH)2D3-dependent accumulation of osteocalcin mRNA in osteoblast-like ROS 17/2.8 cells. All-trans retinoic acid also interfered with vitamin D responsiveness, but it was consistently less potent than the 9-cis isomer. Transient transfection studies revealed that attenuation by 9-cis retinoic acid was at the transcriptional level and was mediated through interactions at the osteocalcin VDRE. Furthermore, overexpression of both RXR beta and RXR alpha augmented 1,25(OH)2D3 responsiveness in transient expression studies. Direct analysis of VDRE binding in mobility shift assays demonstrated that heteromeric interactions between VDR and RXR were enhanced by 1,25(OH)2D3 and were not affected appreciably by 9-cis retinoic acid, except that inhibition was observed at high retinoid concentrations. These data suggest a regulatory mechanism for osteocalcin gene expression that involves 1,25(OH)2D3-induced heterodimerization of VDR and unliganded RXR. 9-cis retinoic acid may attenuate 1,25(OH)2D3 responsiveness by diverting RXRs away from VDR-mediated transcription and towards other RXR-dependent transcriptional pathways.

scholarly journals Retinoid X receptors stimulate and 9-cis retinoic acid inhibits 1,25-dihydroxyvitamin D3-activated expression of the rat osteocalcin gene.

1993 ◽  
Vol 13 (9) ◽  
pp. 5907-5917 ◽  
Author(s):  
P N MacDonald ◽  
D R Dowd ◽  
S Nakajima ◽  
M A Galligan ◽  
M C Reeder ◽  
...  
Keyword(s):  
Gene Expression ◽  
Vitamin D ◽  
Retinoic Acid ◽  
Transcriptional Level ◽  
Mobility Shift ◽  
Dihydroxyvitamin D3 ◽  
Retinoid X Receptors ◽  
1,25 Dihydroxyvitamin D3 ◽  
Osteocalcin Gene ◽  
X Receptors

The vitamin D receptor (VDR) binds the vitamin D-responsive element (VDRE) as a heterodimer with an unidentified receptor auxiliary factor (RAF) present in mammalian cell nuclear extracts. VDR also interacts with the retinoid X receptors (RXRs), implying that RAF may be related to the RXRs. Here we demonstrate that highly purified HeLa cell RAF contained RXR beta immunoreactivity and that both activities copurified and precisely coeluted in high-resolution hydroxylapatite chromatography. Furthermore, an RXR beta-specific antibody disrupted VDR-RAF-VDRE complexes in mobility shift assays. These data strongly indicate that HeLa RAF is highly related to or is identical to RXR beta. Consequently, the effect of the 9-cis retinoic acid ligand for RXRs was examined in 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]-activated gene expression systems. Increasing concentrations of 9-cis retinoic acid (1 nM to 1 microM) markedly reduced 1,25(OH)2D3-dependent accumulation of osteocalcin mRNA in osteoblast-like ROS 17/2.8 cells. All-trans retinoic acid also interfered with vitamin D responsiveness, but it was consistently less potent than the 9-cis isomer. Transient transfection studies revealed that attenuation by 9-cis retinoic acid was at the transcriptional level and was mediated through interactions at the osteocalcin VDRE. Furthermore, overexpression of both RXR beta and RXR alpha augmented 1,25(OH)2D3 responsiveness in transient expression studies. Direct analysis of VDRE binding in mobility shift assays demonstrated that heteromeric interactions between VDR and RXR were enhanced by 1,25(OH)2D3 and were not affected appreciably by 9-cis retinoic acid, except that inhibition was observed at high retinoid concentrations. These data suggest a regulatory mechanism for osteocalcin gene expression that involves 1,25(OH)2D3-induced heterodimerization of VDR and unliganded RXR. 9-cis retinoic acid may attenuate 1,25(OH)2D3 responsiveness by diverting RXRs away from VDR-mediated transcription and towards other RXR-dependent transcriptional pathways.

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