Transcriptional Regulation of the Claudin-16 Gene by Mg²⁺Availability

Abstract

Background/Aims: Renal tubular Mg²⁺ reabsorption is mediated predominantly by the tight junction channel protein claudin-16 which is encoded by the gene CLDN16. Hypermagnesemia decreases, whereas hypomagnesemia increases Mg²⁺ reabsorption. This study examines the role of claudin-16 in the adaptive response of the kidney to Mg²⁺ availability. Methods/Results: Mice received a low-, normal- or high Mg²⁺ diet for up to 3 days. Mg²⁺-loaded animals displayed hypermagnesemia with increasing urine Mg²⁺/Ca²⁺ levels paralleled by a decrease in claudin-16 protein and mRNA in the kidney. Mg²⁺- deprived animals developed hypomagnesemia with decreasing urine Mg²⁺/Ca²⁺ levels associated with an increase in claudin-16 protein and mRNA abundance. Mg²⁺ depletion markedly increased and Mg²⁺ load decreased endogenous claudin-16 mRNA levels in calcium-sensing receptor-transfected HEK293 cells compared with native HEK293 cells. The effect of Mg²⁺ availability on the human CLDN16 (hCLDN16) gene promoter was examined. Using a 2.5kb hCLDN16 5′-flanking DNA sequence, we show that magnesium depletion increases and Mg²⁺ load decreases hCLDN16 promoter activity in transfected HEK293 cells. Conclusions: Changes in Mg²⁺ availability may influence claudin-16 mediated Mg²⁺ transport at the transcriptional level. The possible involvement of the cell membrane bound Ca²⁺/Mg²⁺ sensing receptor or the potential role of a hypothetical Mg²⁺ response element on the CLDN16 promoter in the Mg²⁺-induced response remains to be explored.

The claudin‐16 channel gene is transcriptionally inhibited by 1,25‐dihydroxyvitamin D

“…The reduction in the Cldn16 mRNA level in kidneys of mice receiving the combination of 1,25(OH) 2 VitD and low‐Mg 2+ diet contrasts with our previous finding of a marked increase in Cldn16 mRNA in mice receiving low‐Mg 2+ diet alone (Efrati et al . ).…”

“…The more modest inhibition produced by the combination of 1,25(OH) 2 VitD and low Mg 2+ was nonetheless unexpected in view of our previous observation of increased endogenous CLDN16 mRNA in cells exposed to low Mg 2+ alone (Efrati et al . ).…”

“…; Efrati et al . ]. Most of these factors influence both transcellular Mg 2+ transport in the DCT and paracellular Mg 2+ transport in the TAL (Quamme, ; Dai et al .…”

“…We have previously characterized the promoter region of h CLDN16 and have shown that claudin‐16 is transcriptionally regulated by Mg 2+ availability (Efrati et al . , ).…”

Claudins and mineral metabolism

“…Mice fed with low Mg ++ diet had significantly higher expression levels of claudin-16 in the kidney compared to those fed with normal or high Mg ++ diet [35]. The 2.5kb proximal promoter of the claudin-16 gene seems to contain sequences that can directly respond to extracellular Mg ++ alterations [35]. The promoter activity of claudin-16 can also be regulated by 1,25-(OH) 2 vitamin D 3 .…”