Transcription factor HNF1b controls a transcriptional network regulating kidney cell structure and tight junction integrity

Mutations in the hepatocyte nuclear factor (HNF)18 gene (HNF1B) cause autosomal dominant tubulointerstitial kidney disease, a rare and heterogeneous disease characterized by renal cysts and/or malformation, maturity-onset diabetes of the young, hypo-magnesemia, and hypokalemia. The electrolyte disturbances may develop in the distal part of the nephron, which is important for fine-tuning of Mg2 thorn and Ca2 thorn reabsorption. Therefore, we aimed to study the transcriptional network directed by HNF18 in the distal part of the nephron. We combined HNF18 chromatin immunoprecipitation-sequencing and mRNA expression data to identify direct targets of HNF18 in a renal distal convoluted tubule cell line (mpkDCT). Gene Ontology term pathway analysis demonstrated enrichment of cell polarity, cell-cell junction, and cytoskeleton pathways in the dataset. Genes directly and indi-rectly regulated by HNF18 within these pathways included members of the apical and basolateral polarity complexes including Crumbs protein homolog 3 (Crb3), partitioning defective 6 homolog-8 (Pard6b), and LLGL Scribble cell polarity complex compo-nent 2 (Llgl2). In monolayers of mouse inner medullary collecting duct 3 cells expressing dominant negative Hnf1b, tight junction integrity was compromised, as observed by reduced transepithelial electrical resistance values and increased permeability for fluorescein (0.4 kDa) compared with wild-type cells. Expression of dominant negative Hnf1b also led to a decrease in height (30%) and an increase in surface (58.5%) of cells grown on membranes. Moreover, three-dimensional spheroids formed by cells expressing dominant negative Hnf1b were reduced in size compared with wild-type spheroids (30%). Together, these findings demonstrate that HNF18 directs a transcriptional network regulating tight junction integrity and cell structure in the distal part of the nephron.NEW & NOTEWORTHY Genetic defects in transcription factor hepatocyte nuclear factor (HNF)18 cause a heterogeneous disease characterized by electrolyte disturbances, kidney cysts, and diabetes. By combining RNA-sequencing and HNF18 chromatin immunoprecipitation-sequencing data, we identified new HNF18 targets that were enriched for cell polarity pathways. Newly dis-covered targets included members of polarity complexes Crb3, Pard6b, and Llgl2. Functional assays in kidney epithelial cells demonstrated decreased tight junction integrity and a loss of typical cuboidal morphology in mutant Hnf1b cells.

Automated summary

Mutations in the HNF18 gene cause a rare and heterogeneous disease characterized by renal cysts, diabetes, and electrolyte disturbances. This study identified new targets of HNF18 that are involved in cell polarity pathways. Functional experiments showed that mutant Hnf1b cells had decreased tight junction integrity and altered cell morphology. These findings highlight the importance of HNF18 in regulating tight junction integrity and cell structure in the distal part of the nephron.