Genetic evidence that HNF-1α–dependent transcriptional control of HNF-4α is essential for human pancreatic β cell function

Abstract

Mutations in the genes encoding hepatocyte nuclear factor 4α (HNF-4α) and HNF-1α impair insulin secretion and cause maturity onset diabetes of the young (MODY). HNF-4α is known to be an essential positive regulator of HNF-1α. More recent data demonstrates that HNF-4α expression is dependent on HNF-1α in mouse pancreatic islets and exocrine cells. This effect is mediated by binding of HNF-1α to a tissue-specific promoter (P2) located 45.6 kb upstream from the previously characterized Hnf4α promoter (P1). Here we report that the expression of HNF-4α in human islets and exocrine cells is primarily mediated by the P2 promoter. Furthermore, we describe a G → A mutation in a conserved nucleotide position of the HNF-1α binding site of the P2 promoter, which cosegregates with MODY. The mutation results in decreased affinity for HNF-1α, and consequently in reduced HNF-1α–dependent activation. These findings provide genetic evidence that HNF-1α serves as an upstream regulator of HNF-4α and interacts directly with the P2 promoter in human pancreatic cells. Furthermore, they indicate that this regulation is essential to maintain normal pancreatic function

A Novel −192c/g Mutation in the Proximal P2 Promoter of the Hepatocyte Nuclear Factor-4α Gene (HNF4A) Associates With Late-Onset Diabetes

“…Promoter functional analyses. The Ϫ192 variant was introduced in a luciferase reporter plasmid containing the P2 promoter sequence from positions Ϫ371 to Ϫ37 relative to the initiator codons (P2.371) and assessed by transient transfection analysis in MIN6 and CaCo cells as described (3). Electrophoretic mobility shift assays.…”

“…utations in the coding region and the P2 promoter of the hepatocyte nuclear factor (HNF)-4␣ gene (HNF4A) cause maturity-onset diabetes of the young (MODY) (1)(2)(3). Interestingly, studies in Caucasian populations have shown linkage between late-onset type 2 diabetes and the 20q region (4 -10), in which the HNF4A gene is located.…”

“…However, only a few studies have examined the HNF4A P2 promoter for variation associated with diabetes. We and others have previously identified mutations in the P2 promoter causing MODY or forms of early-onset diabetes (2,3,16). Furthermore, Mitchell et al (17) have examined 25 MODYX probands and 48 early-onset type 2 diabetic patients for variants in 534 bp covering the minimal HNF4A P2 promoter and exon 1D.…”

Regulation of Pancreatic .BETA.-cell Function by the HNF Transcription Network: Lessons from Maturity-Onset Diabetes of the Young (MODY)

“…Using these two promoter systems, at least nine distinct isoforms are generated (HNF-4a1 to HNF-4a9). Pancreatic b-cells contain three isoforms, which are HNF-4a7 (corresponding to 4a1 in the liver), HNF-4a8 (corresponding to 4a2), and HNF-4a9 (corresponding to 4a3) [33]. The P2 promoter includes both an IPF-1-binding site and a HNF-1-binding site.…”

“…The P2 promoter includes both an IPF-1-binding site and a HNF-1-binding site. Interestingly, mutations of these binding sites (HNF-1a; -181G to A, and IPF-1; -146T to C) in the P2 promoter cause MODY [32,33]. In addition, hepatic expression of HNF-4a mRNA was normal in HNF-1a knockout mice, but its expression was abolished in the pancreas [28].…”