HNF-1B specifically regulates the transcription of the γa-subunit of the Na+/K+-ATPase.
Hepatocyte nuclear factor-1B (HNF-1B) is a transcription factor involved in embryonic development and tissue-specific gene expression in several organs, including the kidney. Recently heterozygous mutations in the HNF1B gene have been identified in patients with hypomagnesemia due to renal Mg(2+) wasting. Interestingly, ChIP-chip data revealed HNF-1B binding sites in the FXYD2 gene, encoding the γ-subunit of the Na(+)/K(+)-ATPase. The γ-subunit has been described as one of the molecular players in the renal Mg(2+) reabsorption in the distal convoluted tubule (DCT). Of note, the FXYD2 gene can be alternatively transcribed into two main variants, namely γa and γb. In the present study, we demonstrated via two different reporter gene assays that HNF-1B specifically acts as an activator of the γa-subunit, whereas the γb-subunit expression was not affected. Moreover, the HNF-1B mutations H69fsdelAC, H324S325fsdelCA, Y352finsA and K156E, previously identified in patients with hypomagnesemia, prevented transcription activation of γa-subunit via a dominant negative effect on wild type HNF1-B. By immunohistochemistry, it was shown that the γa- and γb-subunits colocalize at the basolateral membrane of the DCT segment of mouse kidney. On the basis of these data, we suggest that abnormalities involving the HNF-1B gene may impair the relative abundance of γa and γb, thus affecting the transcellular Mg(2+) reabsorption in the DCT.
Department of Physiology, Radboud University Nijmegen Medical Centre, The Netherlands.
Silvia
S
Ferrè
Gert Jan C
GJ
Veenstra
Rianne
R
Bouwmeester
Joost G J
JG
Hoenderop
René J M
RJ
Bindels
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D005786:Gene Expression Regulation; D049452:Green Fluorescent Proteins / Q000235:genetics; D051539:Hepatocyte Nuclear Factor 1-beta / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007668:Kidney / Q000201:enzymology; D007686:Kidney Tubules, Distal / Q000201:enzymology; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D009154:Mutation; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic
C496495:HNF1B protein, human; C485184:enhanced green fluorescent protein; D051539:Hepatocyte Nuclear Factor 1-beta; D049452:Green Fluorescent Proteins; C416502:FXYD2 protein, human; D000254:Sodium-Potassium-Exchanging ATPase