Distinct Regulation of Hepatic Nuclear Factor 1α by NKX6.1 in Pancreatic Beta Cells

Abstract

Hepatic nuclear factor 1␣ (HNF1␣) is a key regulator of development and function in pancreatic beta cells and is specifically involved in regulation of glycolysis and glucose-stimulated insulin secretion. Abnormal expression of HNF1␣ leads to development of MODY3 (maturity-onset diabetes of the young 3). We report that NK6 homeodomain 1 (NKX6.1) binds to a cis-regulatory element in the HNF1␣ promoter and is a major regulator of this gene in beta cells. We identified an NKX6.1 recognition sequence in the distal region of the HNF1␣ promoter and demonstrated specific binding of NKX6.1 in beta cells by electrophoretic mobility shift and chromatin immunoprecipitation assays. Site-directed mutagenesis of the NKX6.1 core-binding sequence eliminated NKX6.1-mediated activation and substantially decreased activity of the HNF1␣ promoter in beta cells. Overexpression or small interfering RNA-mediated knockdown of the Nkx6.1 gene resulted in increased or diminished HNF1␣ gene expression, respectively, in beta cells. We conclude that NKX6.1 is a novel regulator of HNF1␣ in pancreatic beta cells. This novel regulatory mechanism for HNF1␣ in beta cells may provide new molecular targets for the diagnosis of MODY3. Hepatic nuclear factor 1␣ (HNF1␣)2 is a key transcription factor involved in glucose-stimulated insulin secretion (GSIS) and is the major factor involved in most cases of maturity-onset diabetes of the young (MODY), which accounts for ϳ1% of worldwide diabetes cases (1, 2). Precise cellular concentrations of HNF1␣ are required to maintain normal beta cell function, and both underexpression and overexpression have been shown to lead to diabetes (3-9).HNF1␣ is an important gene involved in the developmental regulation of the liver, pancreas, kidneys, stomach, and intestines (10 -14). This transcription factor is essential for control of mature cellular phenotype in these tissues. In pancreatic beta cells, HNF1␣ is involved in regulating the transcription of several genes that are involved in glycolysis and GSIS such as insulin (15), the Glut2 glucose transporter (16), pyruvate kinase (17), aldolase B (18), HNF3␥ (19), and HNF4␥ (19). Although the regulation of HNF1␣ has been well characterized in hepatocytes, its regulation in beta cells has not been studied in detail, and this gene is assumed to be regulated based on mechanistic studies from hepatocytes (20).HNF1␣ has an HNF4␣-binding site in its proximal promoter that has been shown to be sufficient for its activation in hepatocytes (21, 22), but evidence exists to suggest that the mechanism for regulation of HNF1␣ may different in beta cells. First, HNF1␣ is expressed as three isoforms (A, B, and C) that have tissue-specific distribution ratios (14). HNF1␣A is the predominant form in hepatocytes, whereas HNF1␣B is predominant in pancreatic islets. It has been shown that HNF1␣B and HNF1␣C have greater transactivation potential than HNF1␣A (23). Second, the major regulator of this gene, HNF4␣, is predominantly expressed from the P1 promoter in hepatocytes, whereas in th...

HNF1A variant, energy‐reduced diets and insulin resistance improvement during weight loss: The POUNDS Lost trial and DIRECT

“…Maturity‐onset diabetes of the young (MODY) is a heritable, monogenic form of diabetes . The majority of patients with MODY have mutations in the hepatocyte nuclear factor 1α ( HNF1A ) gene (HNF1A diabetes or MODY3), which result in reduced concentrations of ATP in β cells, and in turn lower insulin secretion . Furthermore, ~20% of white people with HNF1A mutations are obese or overweight, and the HNF1A locus predisposes obese young people to diabetes, implying a link between HNF1A and obesity.…”

Genomic Control Processes in Adult Body Part Formation

“…Sources: For references to linkages that had been established earlier, see caption to predecessor of this GRN (Davidson, 2006, p. 179). More recent sources of data supporting the linkages shown in this GRN model, both positive and negative, are as follows: PTF1 to ptf1a, PTF1 to exocrine genes, PTF1 to RBP-JL (Beres et al, 2006); (ptf1a, RBP-JL) to pdx1 (Miyatsuka et al, 2007;Wiebe et al, 2007); (mafa, mafb) to pdx1 (Vanhoose et al, 2008); (foxa1, foxa2) to pdx1 (Gao et al, 2008); (foxa, nkx2.2, pdx1) to mafa (Raum et al, 2006); glis3 to mafa, glis3 to insulin, glis3 to pdx1, glis3 to ngn3 (Fernandez-Zapico et al, 2009;Kang et al, 2009); (islet1, hnf4a) to insulin, (Eeckhoute et al, 2006;Zhang et al, 2009);(meis, pbx1, pbx2) to pax6 (Zhang et al, 2006;Delporte et al, 2008); nkx6.1 to hnf1α (Donelan et al, 2010); (nkx2.2, ngn3) to neuroD (Anderson et al, 2009); (pdx1, gata4) to gata4 (Rojas et al, 2009);(nkx6.1, pdx1, pax6) to mafa (Raum et al, 2010); foxa to gata4 (Rojas et al, 2010); pax6 to mafb, pax6 to c-maf, pax6 to neuroD1, and (mafb, neuroD1, foxa1, foxa2) to glucagon (Gosmain et al, 2010); islet1 to arx (Liu et al, 2011); dac to cyc21 (Kalousova et al, 2010); hnf1a to mafa ; pdx1 to pax6 (Delporte et al, 2008); ngn3 to ia1 (Mellitzer et al, 2006); hnf4a to hnf1α (Lu et al, 2008); pax6 to glucagon (Grapp et al, 2009); pbx1 to glucagon (Liu et al, 2006); (pax6, cmaf) to glucagon ; nk6.1 to glucagon (Gauthier et al, 2007); brn4 to glucagon, (pdx1, mafa, neuroD) to pander (Burkhardt et al, 2008); alx3 to insulin (Mirasierra and Vallejo, 2006;Mirasierra et al, ...…”

Exploring the role of theHNF-1αG319S polymorphism in β cell failure and youth-onset type 2 diabetes: Lessons from MODY andHnf-1α-deficient animal models

“…Recently, it was demonstrated that Hnf-1␣ expression is directly activated by Nkx6.1 binding to a newly identified cisregulatory element in the distal region of the Hnf-1␣ promoter (Donelan et al 2010). Nkx6.1 is a homeodomain transcription factor that plays a role in pancreatic development as well as maintenance of ␤ cell function in mature ␤ cells (Lyttle et al 2008).…”