Hepatocyte Nuclear Factor 4α Regulates the Expression of Pancreatic β-Cell Genes Implicated in Glucose Metabolism and Nutrient-induced Insulin Secretion

Abstract

Mutations in the HNF4␣ gene are associated with the subtype 1 of maturity-onset diabetes of the young (MODY1), which is characterized by impaired insulin secretory response to glucose in pancreatic ␤-cells. Hepatocyte nuclear factor 4␣ (HNF4␣) is a transcription factor critical for liver development and hepatocytespecific gene expression. However, the role of HNF4␣ in the regulation of pancreatic ␤-cell gene expression and its correlation with metabolism secretion coupling have not been previously investigated. The tetracycline-inducible system was employed to achieve tightly controlled expression of both wild type (WT) and dominantnegative mutant (DN) of HNF4␣ in INS-1 cells. The induction of WT-HNF4␣ resulted in a left shift in glucose-stimulated insulin secretion, whereas DN-HNF4␣ selectively impaired nutrient-stimulated insulin release. Induction of DN-HNF4␣ also caused defective mitochondrial function substantiated by reduced [ 14 C]pyruvate oxidation, attenuated substrate-evoked mitochondrial membrane hyperpolarization, and blunted nutrient-generated cellular ATP production. Quantitative evaluation of HNF4␣-regulated pancreatic ␤-cell gene expression revealed altered mRNA levels of insulin, glucose transporter-2, L-pyruvate kinase, aldolase B, 2-oxoglutarate dehydrogenase E1 subunit, and mitochondrial uncoupling protein-2. The patterns of HNF4␣-regulated gene expression are strikingly similar to that of its downstream transcription factor HNF1␣. Indeed, HNF4␣ changed the HNF1␣ mRNA levels and HNF1␣ promoter luciferase activity through altered HNF4␣ binding. These results demonstrate the importance of HNF4␣ in ␤-cell metabolism-secretion coupling.The hepatocyte nuclear factor 4␣ (HNF4␣), 1 a transcription factor of the nuclear hormone receptor superfamily, is expressed in liver, kidney, gut, and pancreatic islets (1-3). Mutations in the human HNF4␣ gene lead to maturity onset diabetes of the young subtype 1 (MODY1), which is characterized by autosomal dominant inheritance and impaired glucosestimulated insulin secretion from pancreatic ␤-cells (4 -6). These MODY1 mutations located in various domains of the HNF4␣ protein result in defective function of the transcription factor (6). The clinical phenotype of MODY1 patients is indistinguishable from that of MODY3 patients who carry mutations in the HNF1␣ gene (5, 6). HNF4␣ acts upstream of HNF1␣ in a transcriptional cascade that drives liver-specific gene expression and hepatocyte differentiation (7-9). A naturally occurring mutation in the HNF4␣-binding site of the HNF1␣ promoter identified in a MODY3 family (10) suggests that the transcriptional hierarchy could also be involved in pancreatic ␤-cell gene expression and function.HNF4␣ defines the expression of liver-specific genes encoding apolipoproteins, serum factors, cytochrome P-450 isoforms, and proteins involved in the metabolism of glucose, fatty acids, and amino acids (reviewed in Ref. 11). However, clinical characterization of MODY1 subjects reveals that the primary defect is impaired glucose-stimula...

Glucose concentration and AMP-dependent kinase activation regulate expression of insulin receptor family members in rat islets and INS-1E beta cells

“…AICAR is taken up by cells and converted to its monophosphate, ZMP, which than acts in an AMP-like way on all levels of AMPdependent activation of AMPK [24]. In pancreatic beta cells, activation of AMPK by low glucose or by AICAR decreased the expression of metabolic genes, including solute carrier family 2 (facilitated glucose transporter), member 2 (SLC2A2), aldolase B (ALDOB), liver-type pyruvate kinase (PKLR) or preproinsulin (INS) [24,25]. The nuclear transcription factor hepatocyte nuclear factor-4α (HNF4α), but also the newly discovered carbohydrateresponse-element-binding protein, were found to be downstream targets of AMPK [26,27].…”

A transcription factor regulatory circuit in differentiated pancreatic cells

“…Previous data (34) has already indicated binding of hnf4 to the pklr promoter in pancreas. Furthermore, inhibition of hnf4␣ in cultured tumor ␤ cells results in reduced expression of glut2 and pklr (35), and hnf4␣ Ϫ/Ϫ embryoid bodies fail to express glut2 despite only partial reduction of hnf1␣ mRNA (36). Thus, silencing of glut2 and pklr genes selectively in islet cells of hnf1␣ Ϫ/Ϫ mice could result from the aggregate tissue-specific failure of a set of transcriptional regulators required for its expression, including hnf1␣, hnf4␣, and plausibly others.…”

Identification of 9- cis -retinoic acid as a pancreas-specific autacoid that attenuates glucose-stimulated insulin secretion

“…Pdx-1 induces glucokinase, Glut2, and insulin gene expression in the mature pancreas (28,29). HNF4α regulates insulin release through controlling mitochondrial metabolism of glucose and HNF1α, Glut2, and insulin gene expression (30,31).…”