Transcription factor HNF1β controls a transcriptional network regulating kidney cell structure and tight junction integrity.

Abstract

Mutations in the hepatocyte nuclear factor (HNF)1β 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, hypomagnesemia, and hypokalemia. The electrolyte disturbances may develop in the distal part of the nephron, which is important for fine-tuning of Mg²⁺ and Ca²⁺ reabsorption. Therefore, we aimed to study the transcriptional network directed by HNF1β in the distal part of the nephron. We combined HNF1β chromatin immunoprecipitation-sequencing and mRNA expression data to identify direct targets of HNF1β 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 indirectly regulated by HNF1β within these pathways included members of the apical and basolateral polarity complexes including Crumbs protein homolog 3 (Crb3), partitioning defective 6 homolog-β (Pard6b), and LLGL Scribble cell polarity complex component 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 HNF1β 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)1β cause a heterogeneous disease characterized by electrolyte disturbances, kidney cysts, and diabetes. By combining RNA-sequencing and HNF1β chromatin immunoprecipitation-sequencing data, we identified new HNF1β targets that were enriched for cell polarity pathways. Newly discovered 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.