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HNF1B as a New Transcriptional Activator of the Renal KIR4.1/KIR5.1 Potassium Channel
Author(s) -
Kompatscher Andreas,
Baaij Jeroen H.F.,
Aboudehen Karam,
Hoefnagels Anke P.W.M.,
Igarashi Peter,
Bindels Rene J.M.,
Veenstra Gertjan J.C.,
Hoenderop Joost G.J.
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.854.7
Subject(s) - hnf1b , gene knockdown , transcription factor , biology , homeobox , gene , microbiology and biotechnology , genetics
Background Hepatocyte nuclear factor 1 homeobox B ( HNF1B) is an essential transcription factor for the development and functioning of the kidney. Mutations in HNF1b cause autosomal dominant tubulointerstitial kidney disease (ADTKD‐HNF1B), which is characterized by renal cysts and maturity‐onset diabetes of the young (MODY). Moreover, patients suffer from a severe electrolyte phenotype consisting of hypomagnesemia and hypokalemia. Until now, genes that are regulated by HNF1B are only partially known and do not fully explain the phenotype of the patients. Methods Therefore, a chromatin immunoprecipitation and sequencing (chIP‐seq) was executed in immortalized mouse kidney cells (mpkDCT) to identify HNF1B binding sites at a genome‐wide scale. Luciferase‐promoter assays, siRNA‐mediated knockdown of Hnf1b in DCT cells and RT‐qPCR on HNF1B mutant mouse kidneys were performed to assess the transcriptional regulation of Hnf1b on candidate genes in vitro and in vivo . Results In total 7,421 HNF1B binding sites were identified, including several genes involved in electrolyte transport and diabetes. A highly specific and conserved HNF1B site was identified in the promoter of Kcnj16 , encoding the potassium channel Kir5.1. Luciferase‐promoter assays showed a 2.2 fold increase in Kcnj16 expression when HNF1B was present. Expression of the Hnf1b p.Lys156Glu mutant that was previously identified in a ADTKD‐HNF1B patient, did not activate Kcnj16 expression. Knockdown of Hnf1b in mpkDCT cells significantly reduced the expression of Kcnj16 (Kir5.1) and Kcnj10 (Kir4.1) by 38% and 37%, respectively. These results were confirmed in a HNF1B renal knockout mouse, exhibiting downregulation of Kcnj16 , Kcnj10 and Slc12a3 transcripts in the kidney by 78%, 83% and 76%, respectively, compared to HNF1B wild‐type mice. Conclusion HNF1B has been identified as a transcriptional activator of Kcnj16 . Consequently patients with HNF1B mutations may have a reduced Kir5.1 activity in the kidney, resulting in hypokalemia and hypomagnesemia.