Hepatocyte nuclear factor 4 alpha regulates the expression of pancreatic beta-cell genes implicated in glucose metabolism and nutrient-induced insulin secretion

Mutations in the HNF4 alpha gene are associated with the subtype 1 of matur ity-onset diabetes of the young (MODY1), which is characterized by impaired insulin secretory response to glucose in pancreatic beta -cells. Hepatocyt e nuclear factor 4 alpha (HNF4 alpha) is a transcription factor critical fo r liver development and hepatocyte-specific gene expression. However, the r ole of HNF4 alpha in the regulation of pancreatic beta -cell gene expressio n and its correlation with metabolism secretion coupling have not been prev iously investigated. The tetracycline-inducible system was employed to achi eve tightly controlled expression of both wild type (WT) and dominant-negat ive mutant (DN) of HNF4 alpha in INS-1 cells. The induction of WT-HNF4 alph a resulted in a left shift in glucose-stimulated insulin secretion, whereas DN-HNPF4 alpha selectively impaired nutrient-stimulated insulin release, I nduction of DN-HNF4 alpha also caused defective mitochondrial function subs tantiated by reduced [C-14]pyruvate oxidation, attenuated substrate-evoked mitochondrial membrane hyperpolarization, and blunted nutrient-generated ce llular ATP production. Quantitative evaluation of HNF4 alpha -regulated pan creatic p-cell gene expression revealed altered mRNA levels of insulin, glu cose transporter-2, L-pyruvate kinase, aldolase B, 2-oxoglutarate dehydroge nase El subunit, and mitochondrial uncoupling protein-2, The patterns of HN F4a-regulated gene expression are strikingly similar to that of its downstr eam transcription factor HNF1 alpha, Indeed, HNF4a changed the HNF1 alpha m RNA levels and HNF1 alpha promoter luciferase activity through altered HNF4 alpha binding. These results demonstrate the importance of HNF4 alpha in b eta -cell metabolism-secretion coupling.