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Published on: October 28, 2014
Inhibition of calcitriol receptor binding to vitamin D response elements by uremic toxins
S R Patel1, H Q Ke, R Vanholder
1Nephrology Division, University of Michigan Medical School, Ann Arbor 48109-0364, USA.
Abstract:
The genomic action of calcitriol (1,25-dihydroxy-vitamin D3) is mediated through the interaction of the calcitriol receptor (VDR) with vitamin D response elements (VDREs). Although renal failure is associated with resistance to the action of calcitriol, the mechanism of this resistance is not well understood. Therefore, we used the electrophoretic mobility shift assay to compare the ability of VDRs from normal and renal failure rats to bind to the osteocalcin gene VDRE. The results indicate that VDRs from renal failure rats have only half the DNA binding capacity as VDRs from control rats, despite identical calcitriol binding. Furthermore, incubation of normal VDRs with a uremic plasma ultrafiltrate resulted in a loss of > 50% of the binding sites for the osteocalcin VDRE. When VDRs bound to DNA as heterodimers with retinoid X receptors, the inhibitory effect of the uremic ultrafiltrate was due to a specific interaction with the VDR, not retinoid X receptors. In addition, uremic ultrafiltrate blocked calcitriol-induced reporter gene activity in transfected JEG-3 cells. Taken together, the results indicate that an inhibitory effect of a uremic toxin(s) on VDR-VDRE binding could underlie the calcitriol resistance of renal failure.
Insights
Renal failure reduces vitamin D receptor (VDR) DNA binding capacity, impairing calcitriol
Area of Science:
- Endocrinology
- Molecular Biology
- Renal Medicine
Background:
- Calcitriol (1,25-dihydroxy-vitamin D3) genomic actions are mediated by the vitamin D receptor (VDR) binding to vitamin D response elements (VDREs).
- Renal failure is characterized by resistance to calcitriol, but the underlying mechanisms remain unclear.
Purpose of the Study:
- To investigate the effect of renal failure on VDR-VDRE binding capacity.
- To identify potential inhibitory factors in uremic plasma affecting VDR function.
Main Methods:
- Electrophoretic mobility shift assay (EMSA) to compare VDR DNA binding in normal and renal failure rats.
- Incubation of normal VDRs with uremic plasma ultrafiltrate.
- Reporter gene assays in transfected JEG-3 cells.
Main Results:
- VDRs from renal failure rats exhibited 50% less DNA binding capacity compared to controls, despite similar calcitriol binding.
- Uremic plasma ultrafiltrate significantly reduced VDR binding to the osteocalcin VDRE.
- The inhibitory effect was specific to VDR, not retinoid X receptors, and blocked calcitriol-induced reporter gene activity.
Conclusions:
- Uremic toxins may inhibit VDR-VDRE binding, contributing to calcitriol resistance in renal failure.
- This impaired VDR function could explain the reduced efficacy of calcitriol in patients with kidney disease.
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