Role Of HNF-1α Research Articles

Hepatic Nuclear Factor 1 Alpha (HNF-1α) In Human Physiology and Molecular Medicine.

The transcription factors (TFs) play a crucial role in the modulation of specific gene transcription networks. One of the hepatocyte nuclear factors (HNFs) family's member, hepatocyte nuclear factor-1α (HNF-1α) has continuously become a principal TF to control the expression of genes. It is involved in the regulation of a variety of functions in various human organs including liver, pancreas, intestine, and kidney. It regulates the expression of enzymes involved in endocrine and xenobiotic activity through various metabolite transporters located in the above organs. Its expression is also required for organ-specific cell fate determination. Despite two decades of its first identification in hepatocytes, a review of its significance was not comprehended. Here, the role of HNF-1α in the above organs at the molecular level to intimate molecular mechanisms for regulating certain gene expression whose malfunctions are attributed to the disease conditions has been specifically encouraged. Moreover, the epigenetic effects of HNF-1α have been discussed here, which could help in advanced technologies for molecular pharmacological intervention and potential clinical implications for targeted therapies. HNF-1α plays an indispensable role in several physiological mechanisms in the liver, pancreas, intestine, and kidney. Loss of its operations leads to the non-functional or abnormal functional state of each organ. Specific molecular agents or epigenetic modifying drugs that reactivate HNF-1α are the current requirements for the medications of the diseases.

Acetaminophen-induced reduction in glutathione-S-transferase A1 in hepatocytes: A role for hepatic nuclear factor 1α and its response element

The role of hepatic nuclear factor 1α (HNF-1α) and its response element in the expression of glutathione S-transferase A1 (GSTA1) was investigated in hepatocytes cells injury induced by acetaminophen (APAP). Treatment of hepatocytes with C2-ceramide exacerbated cells injury with GSTA1 mRNA level reducing. Contrastingly, administration of oltipraz alleviated cells damage with GSTA1 mRNA level elevating relative to hepatotoxicity induced by APAP. Western blot analysis showed that C2-ceramide decreased the translocation of HNF-1α and expression of GSTA1 protein, while oltipraz increased nuclear HNF-1α level and transactivation of GSTA1. The role of HNF-1α on GSTA1 expression was confirmed by transfection experiment and dual-luciferase reporter assay system. In the cells transfected with pGSTA1-1298-LUC vector in which HNF-1 response element (HRE) was contained, the luciferase activity decreased with reduction of nuclear HNF-1α and increased with elevation of nuclear HNF-1α. However, the luciferase activity had no change with the variation of nuclear HNF-1α when the cells transfected with the plasmid of pGSTA1-ΔHNF1-LUC in which the HRE was mutated. In conclusion, HNF-1α could affect the transcription of GSTA1 and HNF-1 response element in the GSTA1 promoter region, which is functionally active for the GSTA1 transcription.

Hepatocyte nuclear factor 1α downregulates HBV gene expression and replication by activating the NF-κB signaling pathway.

The role of hepatocyte nuclear factor 1α (HNF1α) in the regulation of gene expression and replication of hepatitis B virus (HBV) is not fully understood. Previous reports have documented the induction of the expression of viral large surface protein (LHBs) by HNF1α through activating viral Sp1 promoter. Large amount of LHBs can block the secretion of hepatitis B surface antigen (HBsAg). Here we found that HNF1α overexpression inhibited HBV gene expression and replication in Huh7 cells, resulting in marked decreases in HBsAg, hepatitis B e antigen (HBeAg) and virion productions. In contrast, knockdown of endogenous HNF1α expression enhanced viral gene expression and replication. This HNF1α-mediated inhibition did not depend on LHBs. Instead, HNF1α promoted the expression of NF-κB p65 and slowed p65 protein degradation, leading to nuclear accumulation of p65 and activation of the NF-κB signaling, which in turn inhibited HBV gene expression and replication. The inhibitor of the NF-κB signaling, IκBα-SR, could abrogate this HNF1α-mediated inhibition. While the dimerization domain of HNF1α was dispensable for the induction of LHBs expression, all the domains of HNF1α was required for the inhibition of HBV gene expression. Our findings identify a novel role of HNF1α in the regulation of HBV gene expression and replication.

Tubular proteinuria in patients with HNF1α mutations: HNF1α drives endocytosis in the proximal tubule

Hepatocyte nuclear factor 1α (HNF1α) is a transcription factor expressed in the liver, pancreas, and proximal tubule of the kidney. Mutations of HNF1α cause an autosomal dominant form of diabetes mellitus (MODY-HNF1A) and tubular dysfunction. To gain insights into the role of HNF1α in the proximal tubule, we analyzed Hnf1a-deficient mice. Compared with wild-type littermates, Hnf1a knockout mice showed low-molecular-weight proteinuria and a 70% decrease in the uptake of β2-microglobulin, indicating a major endocytic defect due to decreased expression of megalin/cubilin receptors. We identified several binding sites for HNF1α in promoters of Lrp2 and Cubn genes encoding megalin and cubilin, respectively. The functional interaction of HNF1α with these promoters was shown in C33 epithelial cells lacking endogenous HNF1α. Defective receptor-mediated endocytosis was confirmed in proximal tubule cells from these knockout mice and could be rescued by transfection of wild-type but not mutant HNF1α. Transfection of human proximal tubule HK2 cells with HNF1α was able to upregulate megalin and cubilin expression and to increase endocytosis of albumin. Low-molecular-weight proteinuria was consistently detected in individuals with HNF1A mutations compared with healthy controls and patients with non-MODY-HNF1A diabetes mellitus. Thus, HNF1α plays a key role in the constitutive expression of megalin and cubilin, hence regulating endocytosis in the proximal tubule of the kidney. These findings provide new insight into the renal phenotype of individuals with mutations of HNF1A.

Genomics Meets Glycomics—The First GWAS Study of Human N-Glycome Identifies HNF1α as a Master Regulator of Plasma Protein Fucosylation

Over half of all proteins are glycosylated, and alterations in glycosylation have been observed in numerous physiological and pathological processes. Attached glycans significantly affect protein function; but, contrary to polypeptides, they are not directly encoded by genes, and the complex processes that regulate their assembly are poorly understood. A novel approach combining genome-wide association and high-throughput glycomics analysis of 2,705 individuals in three population cohorts showed that common variants in the Hepatocyte Nuclear Factor 1α (HNF1α) and fucosyltransferase genes FUT6 and FUT8 influence N-glycan levels in human plasma. We show that HNF1α and its downstream target HNF4α regulate the expression of key fucosyltransferase and fucose biosynthesis genes. Moreover, we show that HNF1α is both necessary and sufficient to drive the expression of these genes in hepatic cells. These results reveal a new role for HNF1α as a master transcriptional regulator of multiple stages in the fucosylation process. This mechanism has implications for the regulation of immunity, embryonic development, and protein folding, as well as for our understanding of the molecular mechanisms underlying cancer, coronary heart disease, and metabolic and inflammatory disorders.

Metabolomic analysis of the Hepatocyte Nuclear Factor 1 Alpha knockout mouse

Genomic mutations in the transcription factor hepatocyte nuclear factor 1 alpha (HNF1α) result in maturity‐onset diabetes of the young type 3 (MODY3), a form of non‐insulin dependent diabetes mellitus (NIDDM). In addition, Hnf1α was identified as a critical factor in the expression of many transporters of the liver, intestine, and kidney. In order to identify the physiological impact of Hnf1α regulation of transporter proteins, metabolomic analysis was performed on urine from Hnf1α+/+ and Hnf1α −/− using ultra‐performance liquid chromatography (UPLC) coupled with accurate mass determination by time‐of‐flight mass spectrometry (TOFMS). Multivariate analysis revealed clear separation of urinary metabolites between Hnf1α +/+ and Hnf1α −/− mice. Amino acid derived compounds were elevated in the urine of Hnf1α −/− mice suggesting a defect in apical reabsorption in the proximal tubules of the kidney. mRNA expression of members of the imino‐glycine family of transporters was also reduced in Hnf1α −/− mice. In addition to amino acid excretion, steroid hormones associated with adrenal gland function were elevated in the urine of knockout mice. Adrenal glands of Hnf1α −/− were 3‐fold heavier than Hnf1α +/+ and histology showed hyperplasia and reduced lipid content indicating a role for Hnf1α in the endocrine system. Research funded by NIGMS PRAT program and NCI Intramural Research Grants.

Role of HNF-1α in regulating the expression of genes involved in cellular growth and proliferation in pancreatic beta-cells

Hepatocyte nuclear factor (HNF)-1α is a homeodomain-containing transcription factor. Humans heterozygous for mutations in the HNF-1α gene develop maturity-onset diabetes of the young (MODY3), which is associated with reduced insulin secretion. The mechanisms responsible for defective glucose-induced insulin secretion due to HNF-1α deficiency are complex. In order to explore the relationship between HNF-1α and beta-cell proliferation, we have created a novel animal model. Mice lacking one allele of the HNF-1α gene were crossed with transgenic mice expressing the large T antigen driven by the rat insulin II promoter (RIP). The resulting mouse strains allowed us to study the effect of HNF-1α deficiency on the extensive beta-cell proliferation that occurs in these mice. Our results indicate that deficiency of HNF-1α severely constrains the extent of beta-cell proliferation occurring in RIP-Tag mice leading to significant changes in blood glucose concentrations as a result of reduced beta-cell number, insulin content, insulin secretion and intracellular responses in Ca 2+. Furthermore expression profiling studies using immortalized cell lines generated from HNF-1α/RIP-Tag mice showed changes in expression of genes involved in cellular growth and proliferation. These results provide insights into the mechanisms whereby HNF-1α affects beta-cell function.

Role of HNF-1α and HNF-1β on insulin, IGF-1 and other potential target genes

Hepatocyte nuclear factor (HNF)-1α and HNF-1β are transcription factors that regulate many target genes in various tissues including liver, pancreas and kidney. Heterozygous mutations in the HNF-1α and HNF-1β genes result in maturity-onset diabetes of the young (MODY)3 and MODY5, respectively. The discovery of these ‘hepatocyte nuclear factors’ as MODY-responsible genes provided a breakthrough in the field of diabetes. Patients with HNF-1α and HNF-1β mutations, as well as their model mice, show impaired pancreatic β-cell function. The mechanism of impaired β-cell function and the target genes has been intensively investigated by considerable in vitro and in vivo studies. The insulin gene is one of the target genes of HNF-1α and HNF-1β in the β-cells, and may contribute to the diabetes. The IGF-1 gene is also regulated by HNF-1α and HNF-1β, and its decreased expression may contribute to growth failure and impaired β-cell proliferation. Mutations in HNF-1β result in symptoms in multiple organs, including kidney and liver, and several target genes have been reported to be involved in the pathogenesis. HNF-1α and HNF-1β may be one of the master regulators of hepatocyte and islet transcription, and further investigations by microarray and genome-scale analyses are providing information for the better understanding of the complex transcriptional network involving HNF-1α and -1β.

The role of HNF1alpha, HNF3gamma, and cyclic AMP in glucose-6-phosphatase gene activation.

The gene for glucose-6-phosphatase (G6Pase), the key enzyme in glucose homeostasis, is expressed in a tissue-specific manner in the liver and kidney. To understand the molecular mechanisms regulating liver-specific expression of the G6Pase gene, we characterized G6Pase promoter activity by transient expression assays. The G6Pase promoter is active in HepG2 hepatoma cells, but inactive in JEG3 choriocarcinoma or 3T3 cells. DNA elements essential for optimal and liver-specific expression of the G6Pase gene were contained within nucleotides -234 to +3. Deletion analysis revealed that the G6Pase promoter contained three activation elements (AEs) at nucleotides -234 to -212 (AE-I), -146 to -125 (AE-II), and -124 to -71 (AE-III). AE-I contains binding sites for hepatocyte nuclear factors (HNF) 1 and 4. Electromobility shift and cotransfection assays demonstrated that HNF1alpha, but not HNF4, bound to its cognate site and transactivated G6Pase gene expression. The G6Pase promoter contained five HNF3 motifs, 1 (-180/-174), 2 (-139/-133), 3 (-91/-85), 4 (-81/-75), and 5 (-72/-66), and all five sites bound HNF3gamma with high affinity. Transient expression and cotransfection assays showed that HNF3 site 1 is not required for basal promoter activity, but is essential for HNF3gamma-activated transcription from the G6Pase promoter. We further showed that HNF3 sites 3, 4, and 5 were essential for basal G6Pase promoter activity and transactivation by HNF3gamma. AE-II contains, in addition to a HNF3 motif, a cAMP-response element (CRE) and a C/EBP half-site. The G6Pase(-146/-116) DNA containing AE-II formed multiple protein-DNA complexes with HepG2 nuclear extracts, including HNF3gamma, CRE-binding protein (CREB), C/EBPalpha, and C/EBPbeta. We showed that AE-II mediated transcription activation of the G6Pase gene by cAMP.