Regulation of Npt2b gene promoter activity by RAR/RXR-C/EBP
Takei, Yuichiro Tokushima University|University of Kochi
Nakahashi, Otoki Tokushima University|Tokushima Bunri University
Adachi, Yuichiro Tokushima University
Miyazaki, Makoto University of Colorado Denver
all-trans retinoic acid (ATRA)
gene promoter analysis
CCAAT-enhancer-binding protein (C/EBP)
retinoic acid receptor (RAR)
type IIb sodium-dependent phosphate co-transporter (Npt2b)
Inorganic phosphate (Pi) homeostasis is regulated by intestinal absorption via type II sodium-dependent co-transporter (Npt2b) and by renal reabsorption via Npt2a and Npt2c. Although we previously reported that vitamin A-deficient (VAD) rats had increased urine Pi excretion through the decreased renal expression of Npt2a and Npt2c, the effect of vitamin A on the intestinal Npt2b expression remains unclear. In this study, we investigated the effects of treatment with all-trans retinoic acid (ATRA), a metabolite of vitamin A, on the Pi absorption and the Npt2b expression in the intestine of VAD rats, as well as and the underlying molecular mechanisms. In VAD rats, the intestinal Pi uptake activity and the expression of Npt2b were increased, but were reduced by the administration of ATRA. The transcriptional activity of reporter plasmid containing the promoter region of the rat Npt2b gene was reduced by ATRA in NIH3T3 cells overexpressing retinoic acid receptor (RAR) and retinoid X receptor (RXR). On the other hand, CCAAT/enhancer-binding proteins (C/EBP) induced transcriptional activity of the Npt2b gene. Knockdown of the C/EBP gene and a mutation analysis of the C/EBP responsible element in the Npt2b gene promoter indicated that C/EBP plays a pivotal role in the regulation of Npt2b gene transcriptional activity by ATRA. EMSA revealed that the RAR/RXR complex inhibits binding of C/EBP to Npt2 b gene promoter. Together, these results suggest that ATRA may reduce the intestinal Pi uptake by preventing C/EBP activation of the intestinal Npt2b gene.
Portland Press|The Biochemical Society
This is not the final published Version of Record.
The final authenticated version is available online at: https://doi.org/10.1042/BCJ20190716.
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