Organization and partial sequence of the hepatocyte nuclear factor-4 alpha/MODY1 gene and identification of a missense mutation, R127W, in a Japanese family with MODY

High prevalence of copy number variations in the Japanese participants with suspected MODY

Maturity-Onset Diabetes of the Young (MODY) is a diabetes mellitus subtype caused by a single gene. The detection rate of the responsible gene is 27% in the United Kingdom, indicating that the causative gene remains unknown in the majority of clinically diagnosed MODY cases. To improve the detection rate, we applied comprehensive genetic testing using whole exome sequencing (WES) followed by Multiplex Ligation-dependent Probe Amplification (MLPA) and functional analyses. Twenty-one unrelated Japanese participants with MODY were enrolled in the study. To detect copy number variations (CNVs), WES was performed first, followed by MLPA analysis for participants who were negative on the basis of WES. Undetermined variants were analyzed according to their functional properties. WES identified 7 pathogenic and 3 novel likely pathogenic variants in the 21 participants. Functional analyses revealed that 1 in 3 variants was pathogenic. MLPA analysis applied to the remaining 13 undetermined samples identified 4 cases with pathogenic CNVs: 3 in HNF4A and 1 in HNF1B. Pathogenic variants were identified in 12 participants (12/21, 57.1%) - relatively high rate reported to date. Notably, one-third of the participants had CNVs in HNF4A or HNF1B, indicating a limitation of WES-only screening.

Plasma Proteins Associated with Chronic Histopathologic Lesions on Kidney Biopsy

Key Points

Proteomic profiling identified 35 blood proteins associated with chronic histopathologic lesions in the kidney. Testican-2 was expressed in the glomerulus, released by the kidney into circulation, and inversely associated with glomerulosclerosis severity. NELL1 was expressed in tubular epithelial cells, released by the kidney into circulation, and inversely associated with interstitial fibrosis and tubular atrophy severity.

Background

The severity of chronic histopathologic lesions on kidney biopsy is independently associated with higher risk of progressive CKD. Because kidney biopsies are invasive, identification of blood markers that report on underlying kidney histopathology has the potential to enhance CKD care.

Methods

We examined the association between 6592 plasma protein levels measured by aptamers and the severity of interstitial fibrosis and tubular atrophy (IFTA), glomerulosclerosis, arteriolar sclerosis, and arterial sclerosis among 434 participants of the Boston Kidney Biopsy Cohort. For proteins significantly associated with at least one histologic lesion, we assessed renal arteriovenous protein gradients among 21 individuals who had undergone invasive catheterization and assessed the expression of the cognate gene among 47 individuals with single-cell RNA sequencing data in the Kidney Precision Medicine Project.

Results

In models adjusted for eGFR, proteinuria, and demographic factors, we identified 35 proteins associated with one or more chronic histologic lesions, including 20 specific for IFTA, eight specific for glomerulosclerosis, and one specific for arteriolar sclerosis. In general, higher levels of these proteins were associated with more severe histologic score and lower eGFR. Exceptions included testican-2 and NELL1, which were associated with less glomerulosclerosis and IFTA, respectively, and higher eGFR; notably, both of these proteins demonstrated significantly higher levels from artery to renal vein, demonstrating net kidney release. In the Kidney Precision Medicine Project, 13 of the 35 protein hits had cognate gene expression enriched in one or more cell types in the kidney, including podocyte expression of select glomerulosclerosis markers (including testican-2) and tubular expression of several IFTA markers (including NELL1).

Conclusions

Proteomic analysis identified circulating proteins associated with chronic histopathologic lesions, some of which had concordant site-specific expression within the kidney.

Molecular mechanism of HNF-1A-mediated HNF4A gene regulation and promoter-driven HNF4A-MODY diabetes

Monogenic diabetes is a gateway to precision medicine through molecular mechanistic insight. Hepatocyte nuclear factor 1A (HNF-1A) and HNF-4A are transcription factors that engage in crossregulatory gene transcription networks to maintain glucose-stimulated insulin secretion in pancreatic β cells. Variants in the HNF1A and HNF4A genes are associated with maturity-onset diabetes of the young (MODY). Here, we explored 4 variants in the P2-HNF4A promoter region: 3 in the HNF-1A binding site and 1 close to the site, which were identified in 63 individuals from 21 families of different MODY disease registries across Europe. Our goal was to study the disease causality for these variants and to investigate diabetes mechanisms on the molecular level. We solved a crystal structure of HNF-1A bound to the P2-HNF4A promoter and established a set of techniques to probe HNF-1A binding and transcriptional activity toward different promoter variants. We used isothermal titration calorimetry, biolayer interferometry, x-ray crystallography, and transactivation assays, which revealed changes in HNF-1A binding or transcriptional activities for all 4 P2-HNF4A variants. Our results suggest distinct disease mechanisms of the promoter variants, which can be correlated with clinical phenotype, such as age of diagnosis of diabetes, and be important tools for clinical utility in precision medicine.

Spontaneous episodic inflammation in the intestines of mice lacking HNF4A is driven by microbiota and associated with early life microbiota alterations

The inflammatory bowel diseases (IBD) occur in genetically susceptible individuals who mount inappropriate immune responses to their microbiota leading to chronic intestinal inflammation. Whereas IBD clinical presentation is well described, how interactions between microbiota and host genotype impact early subclinical stages of the disease remains unclear. The transcription factor hepatocyte nuclear factor 4 alpha (HNF4A) has been associated with human IBD, and deletion of Hnf4a in intestinal epithelial cells (IECs) in mice (Hnf4aΔIEC) leads to spontaneous colonic inflammation by 6-12 mo of age. Here, we tested if pathology in Hnf4aΔIEC mice begins earlier in life and if microbiota contribute to that process. Longitudinal analysis revealed that Hnf4aΔIEC mice reared in specific pathogen-free (SPF) conditions develop episodic elevated fecal lipocalin 2 (Lcn2) and loose stools beginning by 4-5 wk of age. Lifetime cumulative Lcn2 levels correlated with histopathological features of colitis at 12 mo. Antibiotic and gnotobiotic tests showed that these phenotypes in Hnf4aΔIEC mice were dependent on microbiota. Fecal 16S rRNA gene sequencing in SPF Hnf4aΔIEC and control mice disclosed that genotype significantly contributed to differences in microbiota composition by 12 mo, and longitudinal analysis of the Hnf4aΔIEC mice with the highest lifetime cumulative Lcn2 revealed that microbial community differences emerged early in life when elevated fecal Lcn2 was first detected. These microbiota differences included enrichment of a novel phylogroup of Akkermansia muciniphila in Hnf4aΔIEC mice. We conclude that HNF4A functions in IEC to shape composition of the gut microbiota and protect against episodic inflammation induced by microbiota throughout the lifespan. IMPORTANCE The inflammatory bowel diseases (IBD), characterized by chronic inflammation of the intestine, affect millions of people around the world. Although significant advances have been made in the clinical management of IBD, the early subclinical stages of IBD are not well defined and are difficult to study in humans. This work explores the subclinical stages of disease in mice lacking the IBD-associated transcription factor HNF4A in the intestinal epithelium. Whereas these mice do not develop overt disease until late in adulthood, we find that they display episodic intestinal inflammation, loose stools, and microbiota changes beginning in very early life stages. Using germ-free and antibiotic-treatment experiments, we reveal that intestinal inflammation in these mice was dependent on the presence of microbiota. These results suggest that interactions between host genotype and microbiota can drive early subclinical pathologies that precede the overt onset of IBD and describe a mouse model to explore those important processes.

Structural insights into the HNF4 biology

Hepatocyte Nuclear Factor 4 (HNF4) is a transcription factor (TF) belonging to the nuclear receptor (NR) family that is expressed in liver, kidney, intestine and pancreas. It is a master regulator of liver-specific gene expression, in particular those genes involved in lipid transport and glucose metabolism and is crucial for the cellular differentiation during development. Dysregulation of HNF4 is linked to human diseases, such as type I diabetes (MODY1) and hemophilia. Here, we review the structures of the isolated HNF4 DNA binding domain (DBD) and ligand binding domain (LBD) and that of the multidomain receptor and compare them with the structures of other NRs. We will further discuss the biology of the HNF4α receptors from a structural perspective, in particular the effect of pathological mutations and of functionally critical post-translational modifications on the structure-function of the receptor.

Evaluation of Evidence for Pathogenicity Demonstrates That BLK, KLF11, and PAX4 Should Not Be Included in Diagnostic Testing for MODY

Maturity-onset diabetes of the young (MODY) is an autosomal dominant form of monogenic diabetes, reported to be caused by variants in 16 genes. Concern has been raised about whether variants in BLK (MODY11), KLF11 (MODY7), and PAX4 (MODY9) cause MODY. We examined variant-level genetic evidence (cosegregation with diabetes and frequency in population) for published putative pathogenic variants in these genes and used burden testing to test gene-level evidence in a MODY cohort (n = 1,227) compared with a control population (UK Biobank [n = 185,898]). For comparison we analyzed well-established causes of MODY, HNF1A, and HNF4A. The published variants in BLK, KLF11, and PAX4 showed poor cosegregation with diabetes (combined logarithm of the odds [LOD] scores ≤1.2), compared with HNF1A and HNF4A (LOD scores >9), and are all too common to cause MODY (minor allele frequency >4.95 × 10-5). Ultra-rare missense and protein-truncating variants (PTV) were not enriched in a MODY cohort compared with the UK Biobank population (PTV P > 0.05, missense P > 0.1 for all three genes) while HNF1A and HNF4A were enriched (P < 10-6). Findings of sensitivity analyses with different population cohorts supported our results. Variant and gene-level genetic evidence does not support BLK, KLF11, or PAX4 as a cause of MODY. They should not be included in MODY diagnostic genetic testing.

Clinical profiling and screening for HNF4α and GCK gene mutations in Kashmiri patients with maturity-onset diabetes of the young (MODY)

AIM

Maturity-onset Diabetes of Young (MODY) is a monogenic form of diabetes affecting 1-5% of young (often ≤25 years) diabetic patients exhibiting an autosomal dominant mode of inheritance. Considering the significance of genetic polymorphisms in a variety of diseases, this study aimed to determine the association between HNF4α and GCK gene polymorphisms and the risk of MODY in the Kashmir community, as well as their clinical differences.

METHOD

The study was conducted on clinically confirmed MODY patients (n = 50), and age and gender-matched controls (25 T1DM and 25 non-diabetic) recruited from the endocrinology department of the hospital, for evaluating the HNF4α and GCK mutation. Under standard conditions, PCR-mediated amplification was done to evaluate the respective exons. Preliminary mutations were detected using restriction enzymes (BfaI and HhaI), which were then followed by sequencing of representative samples. The diabetic history, clinical and biochemical data were obtained after proper consent.

RESULTS

Our data revealed no association of HNF4α (exon7) and GCK (exon8) gene mutation with MODY disease susceptibility in the Kashmiri population. On diagnosis, no MODY patient was given immediate insulin; instead, metformin (68%) or sulphonyl-urea (28%) and dietary changes (4%) were recommended. Later in life, 54% of MODY patients develop insulin dependency. The MODY probability was calculated to be 73.88% (±4.56). HbA1c levels were lower [7.48% (±1.64)] than in T1DM [9.17(±2.29%)].

CONCLUSIONS

Young early-onset diabetic patients were able to keep their HbA1c and blood glucose levels stable with a modified diet and metformin/sulphonyl-urea, but they may become insulin-dependent in the future, as seen in our study. As a result, prompt diagnosis and management are essential for avoiding complications. Furthermore, no HNF4α (exon7) or GCK (exon 8) mutations were found in MODY patients or T1DM/healthy non-diabetic controls.

Disruption of Tumor Suppressors HNF4α/HNF1α Causes Tumorigenesis in Liver

The hepatocyte nuclear factor-4α (HNF4α) and hepatocyte nuclear factor-1α (HNF1α) are transcription factors that influence the development and maintenance of homeostasis in a variety of tissues, including the liver. As such, disruptions in their transcriptional networks can herald a number of pathologies, such as tumorigenesis. Largely considered tumor suppressants in liver cancer, these transcription factors regulate key events of inflammation, epithelial-mesenchymal transition, metabolic reprogramming, and the differentiation status of the cell. High-throughput analysis of cancer cell genomes has identified a number of hotspot mutations in HNF1α and HNF4α in liver cancer. Such results also showcase HNF1α and HNF4α as important therapeutic targets helping us step into the era of personalized medicine. In this review, we update current findings on the roles of HNF1α and HNF4α in liver cancer development and progression. It covers the molecular mechanisms of HNF1α and HNF4α dysregulation and also highlights the potential of HNF4α as a therapeutic target in liver cancer.

Persistent or Transient Human β Cell Dysfunction Induced by Metabolic Stress: Specific Signatures and Shared Gene Expression with Type 2 Diabetes

Pancreatic β cell failure is key to type 2 diabetes (T2D) onset and progression. Here, we assess whether human β cell dysfunction induced by metabolic stress is reversible, evaluate the molecular pathways underlying persistent or transient damage, and explore the relationships with T2D islet traits. Twenty-six islet preparations are exposed to several lipotoxic/glucotoxic conditions, some of which impair insulin release, depending on stressor type, concentration, and combination. The reversal of dysfunction occurs after washout for some, although not all, of the lipoglucotoxic insults. Islet transcriptomes assessed by RNA sequencing and expression quantitative trait loci (eQTL) analysis identify specific pathways underlying β cell failure and recovery. Comparison of a large number of human T2D islet transcriptomes with those of persistent or reversible β cell lipoglucotoxicity show shared gene expression signatures. The identification of mechanisms associated with human β cell dysfunction and recovery and their overlap with T2D islet traits provide insights into T2D pathogenesis, fostering the development of improved β cell-targeted therapeutic strategies.

Comprehensive genetic screening: The prevalence of maturity-onset diabetes of the young gene variants in a population-based childhood diabetes cohort

BACKGROUND

Maturity-onset diabetes of the young (MODY) is caused by autosomal dominant mutations in one of 13 confirmed genes. Estimates of MODY prevalence vary widely, as genetic screening is usually restricted based on clinical features, even in population studies. We aimed to determine prevalence of MODY variants in a large and unselected pediatric diabetes cohort.

METHODS

MODY variants were assessed using massively parallel sequencing in the population-based diabetes cohort (n = 1363) of the sole tertiary pediatric diabetes service for Western Australia (population 2.6 million). All individuals were screened, irrespective of clinical features. MODY variants were also assessed in a control cohort (n = 993).

RESULTS

DNA and signed consent were available for 821 children. Seventeen children had pathogenic/likely pathogenic variants in MODY genes, two diagnosed with type 2 diabetes, four diagnosed with antibody-negative type 1 diabetes (T1DM), three diagnosed with antibody-positive T1DM, and eight previously diagnosed with MODY. Prevalence of MODY variants in the sequenced cohort was 2.1%, compared to 0.3% of controls.

CONCLUSIONS

This is the first comprehensive study of MODY variants in an unselected population-based pediatric diabetes cohort. The observed prevalence, increasing access to rapid and affordable genetic screening, and significant clinical implications suggest that genetic screening for MODY could be considered for all children with diabetes, irrespective of other clinical features.

Genetic basis of early-onset, maturity-onset diabetes of the young-like diabetes in Japan and features of patients without mutations in the major MODY genes: Dominance of maternal inheritance

BACKGROUND

Causative mutations cannot be identified in the majority of Asian patients with suspected maturity-onset diabetes of the young (MODY).

OBJECTIVES

To elucidate the genetic basis of Japanese patients with MODY-like diabetes and gain insight into the etiology of patients without mutations in the major MODY genes.

SUBJECTS

A total of 263 Japanese patients with early-onset, non-obese, MODY-like diabetes mellitus referred to Osaka City General Hospital for diagnosis.

METHODS

Mutational analysis of the four major MODY genes (GCK, HNF1A, HNF4A, HNF1B) by Sanger sequencing. Mutation-positive and mutation-negative patients were further analyzed for clinical features.

RESULTS

Mutations were identified in 103 (39.2%) patients; 57 mutations in GCK; 29, HNF1A; 7, HNF4A; and 10, HNF1B. Contrary to conventional diagnostic criteria, 18.4% of mutation-positive patients did not have affected parents and 8.2% were in the overweight range (body mass index [BMI] >85th percentile). HOMA-IR at diagnosis was elevated (>2) in 15 of 66 (22.7%) mutation-positive patients. Compared with mutation-positive patients, mutation-negative patients were significantly older (P = 0.003), and had higher BMI percentile at diagnosis (P = 0.0006). Interestingly, maternal inheritance of diabetes was significantly more common in mutation-negative patients (P = 0.0332) and these patients had significantly higher BMI percentile as compared with mutation-negative patients with paternal inheritance (P = 0.0106).

CONCLUSIONS

Contrary to the conventional diagnostic criteria, de novo diabetes, overweight, and insulin-resistance are common in Japanese patients with mutation-positive MODY. A significant fraction of mutation-negative patients had features of early-onset type 2 diabetes common in Japanese, and non-Mendelian inheritance needs to be considered for these patients.

Derivation and molecular characterization of pancreatic differentiated MODY1-iPSCs

Maturity onset diabetes of the young (MODY) is a hereditary form of diabetes mellitus presenting at childhood or adolescence, which eventually leads to pancreatic β-cells dysfunction. The underlying genetic basis of MODY disorders is haploinsufficiency, where loss-of-function mutations in a single allele cause the diabetic phenotype in heterozygous patients. MODY1 is a type of MODY disorder resulting from a mutation in the transcription factor hepatocyte nuclear factor 4 alpha (HNF4α). In order to establish a human based model to study MODY1, we generated patient-derived induced pluripotent stem cells (iPSCs). Differentiation of these pluripotent cells towards the pancreatic lineage enabled to evaluate the effects of the MODY1 mutation and its impact on endodermal and pancreatic cells. Analyzing the gene expression profiles of differentiated MODY1 cells, revealed the outcome of HNF4α haploinsufficiency on its targets. This molecular analysis suggests that the differential expression of HNF4α target genes in MODY1 is affected by the number of HNF4α binding sites, their distance from the transcription start site, and the number of other transcription factor binding sites. These features may help explain the molecular manifestations of haploinsufficiency in MODY1 disease.

Quantitative proteomics reveals that distant recurrence-associated protein R-Ras and Transgelin predict post-surgical survival in patients with Stage III colorectal cancer

Surgical resection supplemented with adjuvant chemotherapy is the current preferred treatment for Stage III colorectal cancer (CRC). However, as many as 48% of patients who undergo curative resection eventually suffer from incurable distant recurrence. To investigate the molecular mechanisms involved in Stage III CRC post-surgical distant recurrence, we identified a total of 146 differentially expressed proteins (DEPs) associated with distant recurrence in Stage III CRC using TMT-based quantitative mass spectrometry. Among these DEPs, the altered expressions of R-Ras and Transgelin were then validated in 192 individual specimens using immunohistochemistry (IHC). Furthermore, Kaplan-Meier analysis revealed that the levels of R-Ras and Transgelin were significantly associated with 5-year overall survival (OS) and disease-free survival (DFS), and multivariate Cox-regression analyses revealed that R-Ras and Transgelin were independent prognostic factors for OS and DFS, respectively. In conclusion, this study identified potential biochemical players involved in distant recurrence and indicates that R-Ras and Transgelin are potential post-surgical prognostic biomarkers for Stage III CRC. This proteomics data have been submitted to Proteome Xchange under accession number PXD002903.

The Common p.R114W HNF4A Mutation Causes a Distinct Clinical Subtype of Monogenic Diabetes

HNF4A mutations cause increased birth weight, transient neonatal hypoglycemia, and maturity onset diabetes of the young (MODY). The most frequently reported HNF4A mutation is p.R114W (previously p.R127W), but functional studies have shown inconsistent results; there is a lack of cosegregation in some pedigrees and an unexpectedly high frequency in public variant databases. We confirm that p.R114W is a pathogenic mutation with an odds ratio of 30.4 (95% CI 9.79-125, P = 2 × 10(-21)) for diabetes in our MODY cohort compared with control subjects. p.R114W heterozygotes did not have the increased birth weight of patients with other HNF4A mutations (3,476 g vs. 4,147 g, P = 0.0004), and fewer patients responded to sulfonylurea treatment (48% vs. 73%, P = 0.038). p.R114W has reduced penetrance; only 54% of heterozygotes developed diabetes by age 30 years compared with 71% for other HNF4A mutations. We redefine p.R114W as a pathogenic mutation that causes a distinct clinical subtype of HNF4A MODY with reduced penetrance, reduced sensitivity to sulfonylurea treatment, and no effect on birth weight. This has implications for diabetes treatment, management of pregnancy, and predictive testing of at-risk relatives. The increasing availability of large-scale sequence data is likely to reveal similar examples of rare, low-penetrance MODY mutations.

Transcriptional Regulation of X-Box-binding Protein One (XBP1) by Hepatocyte Nuclear Factor 4α (HNF4Α) Is Vital to Beta-cell Function

The transcription factor, X-box-binding protein-1 (XBP1), controls the development and maintenance of the endoplasmic reticulum (ER) in multiple secretory cell lineages. We show here that Hepatocyte Nuclear Factor 4α (HNF4α) directly induces XBP1 expression. Mutations in HNF4α cause Mature-Onset Diabetes of the Young I (MODYI), a subset of diabetes characterized by diminished GSIS. In mouse models, cell lines, and ex vivo islets, using dominant negative and human- disease-allele point mutants or knock-out and knockdown models, we show that disruption of HNF4α caused decreased expression of XBP1 and reduced cellular ER networks. GSIS depends on ER Ca(2+) signaling; we show that diminished XBP1 and/or HNF4α in β-cells led to impaired ER Ca(2+) homeostasis. Restoring XBP1 expression was sufficient to completely rescue GSIS in HNF4α-deficient β-cells. Our findings uncover a transcriptional relationship between HNF4α and Xbp1 with potentially broader implications about MODYI and the importance of transcription factor signaling in the regulation of secretion.

Transcriptional Factors Mediating Retinoic Acid Signals in the Control of Energy Metabolism

Retinoic acid (RA), an active metabolite of vitamin A (VA), is important for many physiological processes including energy metabolism. This is mainly achieved through RA-regulated gene expression in metabolically active cells. RA regulates gene expression mainly through the activation of two subfamilies in the nuclear receptor superfamily, retinoic acid receptors (RARs) and retinoid X receptors (RXRs). RAR/RXR heterodimers or RXR/RXR homodimers bind to RA response element in the promoters of RA target genes and regulate their expressions upon ligand binding. The development of metabolic diseases such as obesity and type 2 diabetes is often associated with profound changes in the expressions of genes involved in glucose and lipid metabolism in metabolically active cells. RA regulates some of these gene expressions. Recently, in vivo and in vitro studies have demonstrated that status and metabolism of VA regulate macronutrient metabolism. Some studies have shown that, in addition to RARs and RXRs, hepatocyte nuclear factor 4α, chicken ovalbumin upstream promoter-transcription factor II, and peroxisome proliferator activated receptor β/δ may function as transcriptional factors mediating RA response. Herein, we summarize current progresses regarding the VA metabolism and the role of nuclear receptors in mediating RA signals, with an emphasis on their implication in energy metabolism.

Localization of hepatocyte nuclear factor-4α in the nucleolus and nucleus is regulated by its C-terminus

Aims/Introduction:  Mutations in hepatocyte nuclear factor‐4α (HNF4α) lead to various diseases, among which C‐terminal deletions of HNF4α are exclusively responsible for maturity onset diabetes of the young 1 (MODY1). MODY is an autosomal dominant disease characterized by a primary defect in insulin response to glucose, suggesting that the C‐terminus of HNF4α is important for pancreatic β‐cell function. To clarify the role of the C‐terminus of HNF4α, changes in cellular localization and the binding ability to its regulator were examined, specifically in the region containing Q268, which deletion causes MODY1.

Materials and Methods:  Cellular localization of mutant HNF4α were examined in monkey kidney 7 (COS7), Chinese hamster ovary, rat insulinoma and mouse insulinoma cells, and their binding activity to other proteins were examined by fluorescence resonance energy transfer (FRET) in COS7 cells.

Results:  Although wild‐type HNF4α was localized in the nucleoplasm in transfected cultured cells, Q268X‐HNF4α was located predominantly in the nucleolus. Deletion analysis of the C‐terminus of HNF4α showed that the S337X‐HNF4α mutant, and other mutants with shorter amino acid sequences (S337‐K194), were mostly localized in the nucleolus. HNF4α mutants with amino acid sequences shorter than the W192X‐HNF4α mutant gradually spread to the nucleoplasm in accordance with their lengths. The A250X‐HNF4α mutant was capable of causing the accumulation of HNF4α or the small heterodimer partner (SHP), one of the HNF4α regulators, in the nucleolus. However, the R154X‐HNF4α mutant did not have binding ability to wild‐type HNF4α or SHP, and thus was seen in the nucleus.

Conclusions:  The C‐terminus sites might play a key role in facilitating the nucleolar and subnucleolar localization of HNF4α. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2012.00210.x, 2012)

Hepatocyte nuclear factor 4-alpha involvement in liver and intestinal inflammatory networks

Hepatocyte nuclear factor 4-alpha (HNF4-α) is a nuclear receptor regulating metabolism, cell junctions, differentiation and proliferation in liver and intestinal epithelial cells. Mutations within the HNF4A gene are associated with human diseases such as maturity-onset diabetes of the young. Recently, HNF4A has also been described as a susceptibility gene for ulcerative colitis in genome-wide association studies. In addition, specific HNF4A genetic variants have been identified in pediatric cohorts of Crohn’s disease. Results obtained from knockout mice supported that HNF4-α can protect the intestinal mucosae against inflammation. However, the exact molecular links behind HNF4-α and inflammatory bowel diseases remains elusive. In this review, we will summarize the current knowledge about the role of HNF4-α and its isoforms in inflammation. Specific nature of HNF4-α P1 and P2 classes of isoforms will be summarized. HNF4-α role as a hepatocyte mediator for cytokines relays during liver inflammation will be integrated based on documented examples of the literature. Conclusions that can be made from these earlier liver studies will serve as a basis to extrapolate correlations and divergences applicable to intestinal inflammation. Finally, potential functional roles for HNF4-α isoforms in protecting the intestinal mucosae from chronic and pathological inflammation will be presented.

Digenic heterozygous HNF1A and HNF4A mutations in two siblings with childhood-onset diabetes

Monogenic diabetes due to mutations in the transcription factor genes hepatocyte nuclear factor 1A (HNF1A) and HNF4A is characterized by islet cell antibody negative, familial diabetes with residual insulin secretion. We report two sisters with childhood onset diabetes who are both heterozygous for the most common mutation in each of two transcription factors, HNF1A, and HNF4A. The proband was diagnosed with diabetes at 7 yr of age and treated with insulin for 4 yr. Her genetic diagnosis resulted in transition to sulfonylureas for one and a half years before insulin therapy was re-initiated due to declining glycemic control. Her sister was diagnosed with diabetes at 14 yr of age, treated initially with insulin but has been well controlled on oral sulfonylurea therapy for over 2 yr. Both sisters inherited the HNF4A gene mutation R127W from their mother and the HNF1A gene mutation P291fsinsC (c.872dup) from their father. The father was diagnosed with diabetes at 45 yr of age. Their brother is heterozygous for the HNF4A R127W mutation. Both the brother and mother have normal glucose tolerance at the ages of 16 and 46 yr, respectively. Digenic inheritance of HNF1A and HNF4A mutations is very rare and has only been reported in two families where conclusive evidence for the pathogenicity of their mutations was lacking. Follow-up studies in this family co-segregating the two most commonly reported HNF1A/HNF4A mutations will be informative for understanding the effect of digenic inheritance upon phenotypic severity and response to sulfonylurea therapy.

Can hepatoma cell lines be redifferentiated to be used in drug metabolism studies?

Knowledge of metabolism, enzymes so far involved, and potential enzyme-inhibiting or enzyme-inducing properties of new compounds is a key issue in drug development. Primary cultured hepatocytes, cytochrome P450 (CYP)-engineered cells and hepatoma cell lines are currently being used for this purpose, but only primary cultures can produce a metabolic profile of a drug similar to that found in vivo and can respond to inducers. Because of their limited accessibility, alternatives to replace human hepatocytes are currently being explored, including the immortalisation of hepatocytes by using different strategies (i.e. SV40 T-large antigen, conditionally immortalised hepatocytes, transfection with c-myc, cH-ras, N-ras oncogenes, transgenic animals over-expressing growth factors or oncogenes and cre-lox recombination/excision). However, none of the resulting cells has the desirable phenotypic characteristics to replace primary cultures in drug metabolisms studies. We investigated why these differentiated human hepatomas do not express CYP genes and found that the levels of certain key transcription factors clearly differ from those found in hepatocytes. It was then conceivable that re-expression of one (or more) of these transcription factors could lead to an efficient transcription of CYP genes. The feasibility of this hypothesis was demonstrated by genetic engineering of Hep G2 cells with liver-enriched transcription factors followed by the analysis of the expression of the most relevant human CYPs.

The transcription factor Myt3 acts as a pro-survival factor in β-cells

Aims/Hypothesis

We previously identified the transcription factor Myt3 as specifically expressed in pancreatic islets. Here, we sought to determine the expression and regulation of Myt3 in islets and to determine its significance in regulating islet function and survival.

Methods

Myt3 expression was determined in embryonic pancreas and adult islets by qPCR and immunohistochemistry. ChIP-seq, ChIP-qPCR and luciferase assays were used to evaluate regulation of Myt3 expression. Suppression of Myt3 was used to evaluate gene expression, insulin secretion and apoptosis in islets.

Results

We show that Myt3 is the most abundant MYT family member in adult islets and that it is expressed in all the major endocrine cell types in the pancreas after E18.5. We demonstrate that Myt3 expression is directly regulated by Foxa2, Pdx1, and Neurod1, which are critical to normal β-cell development and function, and that Ngn3 induces Myt3 expression through alterations in the Myt3 promoter chromatin state. Further, we show that Myt3 expression is sensitive to both glucose and cytokine exposure. Of specific interest, suppressing Myt3 expression reduces insulin content and increases β-cell apoptosis, at least in part, due to reduced Pdx1, Mafa, Il-6, Bcl-xl, c-Iap2 and Igfr1 levels, while over-expression of Myt3 protects islets from cytokine induced apoptosis.

Conclusion/Interpretation

We have identified Myt3 as a novel transcriptional regulator with a critical role in β-cell survival. These data are an important step in clarifying the regulatory networks responsible for β-cell survival, and point to Myt3 as a potential therapeutic target for improving functional β-cell mass.

Expression of HNF4alpha variants in pancreatic islets and Ins-1 beta cells

BACKGROUND

Hepatocyte nuclear factor (HNF4alpha) is a nuclear receptor essential for endodermal differentiation and cell functions in the adult pancreas, liver, and other tissues. Mutations in the HNF4A gene cause MODY1. Up to nine protein variants arise from two developmentally regulated promoters. Because some variants lack the N-terminal activation function 1 (AF-1) and/or C-terminal inhibitory F domain, defining their tissue-specific regulation and function is important for understanding pancreatic beta cell behaviour.

METHODS

Expression of HNF4alpha variants in islets, rat Ins-1 insulinoma cells, and human Hep3B hepatocellular carcinoma cells was assessed using a long-range reverse transcription-polymerase chain reaction (RT-PCR) strategy capable of recognizing each combination of mRNA termini. Protein expression was verified by immuno-blotting with terminus-specific antibodies and DNA-binding assays.

RESULTS

Mouse islets and both cell lines express HNF4alpha9, which lacks both AF-1 and the F domain. Islets also expressed the HNF4alpha P1 promoter variants HNF4alpha1/alpha2, and Hep3B cells expressed HNF4alpha3. When ectopically expressed in COS-7 cells, HNF4alpha1, alpha3, alpha7, and alpha9 each stimulated an HNF4alpha-dependent promoter. Variants containing exon 1B (HNF4alpha4 - alpha6) were not detected. Lack of canonical splicing signals and species conservation argues against exon 1B usage.

CONCLUSIONS

This is the first report of HNF4alpha9 expression in any tissue. Our findings extend our understanding of HNF4alpha gene transcription and function. This knowledge may be useful in efforts to recover or establish regulated insulin secretion.

Autosomal inheritance of diabetes in two families characterized by obesity and a novel H241Q mutation in NEUROD1

BACKGROUND

The aim of the study was to search for mutations in the NEUROD1 and IPF-1 genes in patients with clinical characteristics of maturity-onset diabetes of the young (MODY) but with no mutations in the HNF-4A (MODY1), GCK (MODY2) and TCF1 (MODY3) genes.

METHODS

We studied 30 unrelated Czech probands with a clinical diagnosis of MODY (median age at testing, 18 yr; median age at the recognition of hyperglycaemia, 16 yr). The promoter, exons and exon/intron boundaries of the NEUROD1 and IPF-1 genes were examined by polymerase chain reaction-denaturing high performance liquid chromatography and direct sequencing.

RESULTS

While no mutations were found in the IPF-1 gene, a novel H241Q substitution of NEUROD1 gene was identified in two unrelated families. In the first proband, the H241Q mutation led to early diagnosed (20 yr) hyperglycaemia followed by development of diabetic microvascular complications by the age of 32 yr. The second proband suffered from slowly progressing hyperglycaemia detected at the age of 30 yr. Affected members of both families were obese. The overall prevalence of the variant among the general population was 4 of 13 568 chromosomes.

CONCLUSIONS

We report a novel disease-associated variant in NEUROD1 identified among a set of MODYX families. The variant seems to precipitate type-2-like diabetes in excessively obese individuals.

Function of HNF1 in the pathogenesis of diabetes

The importance of hepatocyte nuclear factors (HNFs), as well as other transcription factors in β-cell development and function, was underlined by the characterization of human mutations causing maturity-onset diabetes of the young (MODY). HNF1A and HNF1B mutations lead to MODY forms 3 and 5, respectively. Thus, transcriptional control is an essential mechanism underlying the precise metabolic control exerted by β-cells in regulating insulin release. The diabetes phenotype of MODY3 (HNF1α) and the phenotypes of MODY5 (HNF1β), which can also include renal disease and genitourinary malformations, as well as neonatal diabetes and pancreatic agenesis, have now been described. However, detailed molecular pathology remains elusive. The large array of dominant-negative and deletion mutations, and the lack of structure-phenotype relationships for most mutations, have not helped us to formulate a mechanistic understanding. Further molecular studies of HNF1 actions and gene regulation are anticipated to provide useful insights into β-cell biology and potential therapeutic tools.

HNF4A genetic variants: role in diabetes

PURPOSE OF REVIEW

Variants in the hepatocyte nuclear factor 4alpha (HNF4A) gene play a role in the development of diabetes mellitus. Although genetic variation in and around HNF4A regulatory regions has received considerable attention, the significance of these variants in the common type 2 diabetes varies in the literature. This review will provide a general overview of recent genetic studies involving the evaluation of HNF4A as a contributor to the risk and pathophysiology of diabetes mellitus and related risk factors.

RECENT FINDINGS

These studies report newly identified variants, evaluate previously reported polymorphisms that were associated with type 2 diabetes in several distinct populations with maturity-onset diabetes of the young, type 2 diabetes, gestational diabetes, and diabetes related risk factors, and propose a role for HNF4A in insulin secretion via the potassium ATP channel.

SUMMARY

HNF4A variants identified so far appear to modestly contribute to predisposition for type 2 diabetes. Continued identification and especially functional characterization of variants, however, will be critical in future studies to enhance our understanding of the metabolic impact of this gene.

Differential regulation of constitutive androstane receptor expression by hepatocyte nuclear factor4alpha isoforms

Constitutive androstane receptor (CAR; NR1I3) controls the metabolism and elimination of endogenous and exogenous toxic compounds by up-regulating a battery of genes. In this work, we analyzed the expression of human CAR (hCAR) in normal liver during development and in hepatocellular carcinoma (HCC) and investigated the effect of hepatocyte nuclear factor 4alpha isoforms (HNF4alpha1 and HNF4alpha7) on the hCAR gene promoter. By performing functional analysis of hCAR 5'-deletions including mutants, chromatin immunoprecipitation in human hepatocytes, electromobility shift and cotransfection assays, we identified a functional and species-conserved HNF4alpha response element (DR1: ccAGGCCTtTGCCCTga) at nucleotide -144. Both HNF4alpha isoforms bind to this element with similar affinity. However, HNF4alpha1 strongly enhanced hCAR promoter activity whereas HNF4alpha7 was a poor activator and acted as a repressor of HNF4alpha1-mediated transactivation of the hCAR promoter. PGC1alpha stimulated both HNF4alpha1-mediated and HNF4alpha7-mediated hCAR transactivation to the same extent, whereas SRC1 exhibited a marked specificity for HNF4alpha1. Transduction of human hepatocytes by HNF4alpha7-expressing lentivirus confirmed this finding. In addition, we observed a positive correlation between CAR and HNF4alpha1 mRNA levels in human liver samples during development, and an inverse correlation between CAR and HNF4alpha7 mRNA levels in HCC. These observations suggest that HNF4alpha1 positively regulates hCAR expression in normal developing and adult livers, whereas HNF4alpha7 represses hCAR gene expression in HCC.

Mutations in the genes encoding the transcription factors hepatocyte nuclear factor 1 alpha (HNF1A) and 4 alpha (HNF4A) in maturity-onset diabetes of the young

Maturity-onset diabetes of the young (MODY) is a monogenic form of diabetes mellitus characterized by autosomal dominant inheritance, early age of onset (often <25 years of age), and pancreatic beta-cell dysfunction. MODY is both clinically and genetically heterogeneous, with six different genes identified to date; glucokinase (GCK), hepatocyte nuclear factor-1 alpha (HNF1A, or TCF1), hepatocyte nuclear factor-4 alpha (HNF4A), insulin promoter factor-1 (IPF1 or PDX1), hepatocyte nuclear factor-1 beta (HNF1B or TCF2), and neurogenic differentiation 1 (NEUROD1). Mutations in the HNF1A gene are a common cause of MODY in the majority of populations studied. A total of 193 different mutations have been described in 373 families. The most common mutation is Pro291fs (P291fsinsC) in the polycytosine (poly C) tract of exon 4, which has been reported in 65 families. HNF4A mutations are rarer; 31 mutations reported in 40 families. Sensitivity to treatment with sulfonylurea tablets is a feature of both HNF1A and HNF4A mutations. The identification of an HNF1A or 4A gene mutation confirms a diagnosis of MODY and has important implications for clinical management.

Mechanisms of mutual functional interactions between HNF-4alpha and HNF-1alpha revealed by mutations that cause maturity onset diabetes of the young

Hepatic nuclear factor (HNF)-4alpha and HNF-1alpha are key endodermal transcriptional regulators that physically and functionally interact. HNF-4alpha and HNF-1alpha cooperatively activate genes with binding sites for both factors, whereas suppressive interactions occur at regulatory sequences with a binding site for only one factor. The liver fatty acid binding protein gene (Fabp1) has binding sites for both factors, and chromatin precipitation assays were utilized to demonstrate that HNF-4alpha increased HNF-1alpha Fabp1 promoter occupancy during cooperative transcriptional activation. The HNF4 P2 promoter contains a HNF-1 but not HNF-4 binding site, and HNF-4alpha suppressed HNF-1alpha HNF4 P2 activation and decreased promoter HNF-1alpha occupancy. The apolipoprotein C III (APOC3) promoter contains a HNF-4 but not HNF-1 binding site, and HNF-1alpha suppressed HNF-4alpha APOC3 activation and decreased HNF-4alpha promoter occupancy. Maturity onset diabetes of the young (MODY) as well as defects in hepatic lipid metabolism result from mutations in either HNF-4alpha or HNF-1alpha. We found that MODY missense mutant R127W HNF-4alpha retained wild-type individual Fabp1 activation and bound to HNF-1alpha better than wild-type HNF-4alpha, yet did not cooperate with HNF-1alpha or increase HNF-1alpha Fabp1 promoter occupancy. The R127W mutant was also defective in both suppressing HNF-1alpha activation of HNF4 P2 and decreasing HNF-1alpha promoter occupancy. The HNF-1alpha R131Q MODY mutant also retained wild-type Fabp1 activation and bound to HNF-4alpha as well as the wild type but was defective in both suppressing HNF-4alpha APOC3 activation and decreasing HNF-4alpha promoter occupancy. These results suggest HNF-1alpha-HNF-4alpha functional interactions are accomplished by regulating factor promoter occupancy and that defective factor-factor interactions may contribute to the MODY phenotype.

Novel Genetic Variations and Haplotypes of Hepatocyte Nuclear Factor 4α(HNF4A) Pound in Japanese Type II Diabetic Patients

Thirty-nine single nucleotide variations, including 16 novel ones, were found in the 5' promoter region, all of the exons and their surrounding introns of HNF4A in 74 Japanese type II diabetic patients. The following novel variations were identified (based on the amino acid numbering of splicing variant 2): -208G>C in the 5' promoter region; 1154C>T (A385V) and 1193T>C (M398T) in the coding exons; 1580G>A, 1852G>T, 2180C>T, 2190G>A, and 2362_2380delAAGAATGGTGTGGGAGAGG in the 3'-untranslated region, and IVS1+231G>A, IVS2-83C>T, IVS3+50C>T, IVS3-54delC, IVS5+173_176delTTAG, IVS5-181_-180delAT, IVS8-106A>G, and IVS9-151A>C in the introns. The allele frequencies were 0.311 for 2362_2380delAAGAATGGTGTGGGAGAGG, 0.054 for 1580G>A, 0.047 for 1852G>T, 0.020 for IVS1+231G>A, 0.014 for IVS9-151A>C, and 0.007 for the other 11 variations. In addition, one known nonsynonymous single nucleotide polymorphism, 416C>T (T139I), was detected at a 0.007 frequency. Based on the linkage disequilibrium profiles, the region analyzed was divided into three blocks. Haplotype analysis determined/inferred 10, 16, and 12 haplotypes for block 1, 2, and 3, respectively. Our results on HNF4A variations and haplotypes would be useful for pharmacogenetic studies in Japanese.

Dysregulated expression of P1 and P2 promoter-driven hepatocyte nuclear factor-4α in the pathogenesis of human cancer

Hepatocyte nuclear factor-4alpha (HNF4alpha) exists in multiple isoforms that are generated by alternative promoter (P1 and P2) usage and splicing. Here we establish monoclonal antibodies (mAbs) for detecting P1 and P2 promoter-driven HNF4alpha, and evaluate their expression in normal adult human tissues and surgically resected carcinomas of different origins. Using immunohistochemical analysis, we demonstrate that, while P1 promoter-driven HNF4alpha is expressed in hepatocytes, small intestine, colon, kidney and epididymis, P2 promoter-driven HNF4alpha is expressed in bile duct, pancreas, stomach, small intestine, colon and epididymis. Altered expression patterns of P1 and P2 promoter-driven HNF4alpha were observed in gastric, hepatocellular and colorectal carcinomas. HNF4alpha was expressed in lung metastases from renal cell, hepatocellular and colorectal carcinoma but was not observed in lung tumours. The P1 and P2 promoter-driven HNF4alpha expression pattern of tumour metastases correlated with the primary site of origin. P1 promoter-driven HNF4alpha was also found in intestinal metaplasia of the stomach. These data provide evidence for the tissue distribution of P1 and P2 promoter-driven HNF4alpha at the protein level and suggest that HNF4alpha may be a novel diagnostic marker for metastases of unknown primary. We propose that the dysregulation of alternative promoter usage of HNF4alpha is associated with the pathogenesis of certain cancers.

The position of premature termination codons in the hepatocyte nuclear factor -1 beta gene determines susceptibility to nonsense-mediated decay

The nonsense-mediated decay (NMD) pathway is an mRNA surveillance mechanism that detects and degrades transcripts containing premature termination codons. The position of a truncating mutation can govern the resulting phenotype as mutations in the last exon evade NMD. In this study we investigated the susceptibility to NMD of six truncating HNF-1beta mutations by allele-specific quantitative real-time PCR using transformed lymphoblastoid cell lines. Four of six mutations (R181X, Q243fsdelC, P328L329fsdelCCTCT and A373fsdel29) showed evidence of NMD with levels of mutant transcript at 71% (p=0.009), 24% (p=0.008), 22% (p=0.008) and 3% (p=0.016) of the wild-type allele respectively. Comparable results were derived from lymphoblastoid cells and renal tubule cells isolated from a patient's overnight urine confirming that cell lines provide a good model for mRNA analysis. Two mutations (H69fsdelAC and P159fsdelT) produced transcripts unexpectedly immune to NMD. We conclude that truncating mutant transcripts of the HNF-1beta gene do not conform to the known rules governing NMD susceptibility, but instead demonstrate a previously unreported 5' to 3' polarity. We hypothesise that this may be due to reinitiation of translation downstream of the premature termination codon. Our study suggests that reinitiation of translation may be an important mechanism in the evasion of NMD, but that other factors such as the distance from the native initiation codon may also play a part.

The functional Thr130Ile and Val255Met polymorphisms of the hepatocyte nuclear factor-4alpha (HNF4A): gene associations with type 2 diabetes or altered beta-cell function among Danes

HNF4A encodes an orphan nuclear receptor that plays crucial roles in regulating hepatic gluconeogenesis and insulin secretion. The aim of the present study was to examine two rare missense polymorphisms of HNF4A, Thr130Ile and Val255Met, for altered function and for association with type 2 diabetes (T2D). We have examined these polymorphisms 1) by in vitro transactivation studies and 2) by genotyping the variants in 1409 T2D patients and in 4726 glucose-tolerant Danish white subjects. When tested in COS7 cells, both the Thr130Ile and the Val255Met variants showed a significant decrease in transactivation activity compared with wild-type (73% of wild-type, P = 0.02, and 76%, P = 0.04, respectively). The Thr130Ile variant had a significantly increased carrier frequency among T2D patients compared with glucose-tolerant subjects [odds ratio, 1.26 (1.01-1.57); P = 0.04]. The rare Val255Met polymorphism had a similar frequency among T2D patients and glucose-tolerant subjects. Heterozygous glucose-tolerant carriers of the variant showed, however, decreased levels of fasting serum C-peptide (76%; P = 0.03) and decreased fasting serum triglyceride (58%; P = 0.02). In conclusion, The Thr130Ile and the Val255Met polymorphisms decrease the transcriptional activity of HNF4A, and the Thr130Ile polymorphism associates with T2D, whereas the Val255Met variant associates with a decrease in fasting serum C-peptide.

Molecular genetics and phenotypic characteristics of MODY caused by hepatocyte nuclear factor 4alpha mutations in a large European collection

AIMS/HYPOTHESIS

Heterozygous mutations in the gene of the transcription factor hepatocyte nuclear factor 4alpha (HNF-4alpha) are considered a rare cause of MODY with only 14 mutations reported to date. The description of the phenotype is limited to single families. We investigated the genetics and phenotype of HNF-4alpha mutations in a large European Caucasian collection.

METHODS

HNF-4alpha was sequenced in 48 MODY probands, selected for a phenotype of HNF-1alpha MODY but negative for HNF-1alpha mutations. Clinical characteristics and biochemistry were compared between 54 HNF-4alpha mutation carriers and 32 familial controls from ten newly detected or previously described families.

RESULTS

Mutations in HNF-4alpha were found in 14/48 (29%) probands negative for HNF-1alpha mutations. The mutations found included seven novel mutations: S34X, D206Y, E276D, L332P, I314F, L332insCTG and IVS5nt+1G>A. I314F is the first reported de novo HNF-4alpha mutation. The average age of diagnosis was 22.9 years with frequent clinical evidence of sensitivity to sulphonylureas. Beta cell function, but not insulin sensitivity, was reduced in diabetic mutation carriers compared to control subjects (homeostasis model assessment of beta cell function 29% p<0.001 vs controls). HNF-4alpha mutations were associated with lower apolipoprotein A2 (p=0.001), A1 (p=0.04) and total HDL-cholesterol (p=0.02) than in control subjects. However, in contrast to some previous reports, levels of triglycerides and apolipoprotein C3 were normal.

CONCLUSIONS/INTERPRETATION

HNF-4alpha mutations are common when no HNF-1alpha mutation is found in strictly defined MODY families. The HNF-4alpha clinical phenotype and beta cell dysfunction are similar to HNF-1alpha MODY and are associated with reduced apolipoprotein A2 levels. We suggest that sequencing of HNF-4alpha should be performed in patients with clinical characteristics of HNF-1alpha MODY in whom mutations in HNF-1alpha are not found.

Functional characterization of the HNF4α isoform (HNF4α8) expressed in pancreatic β-cells

Mutations in the hepatocyte nuclear factor (HNF) 4alpha gene cause a form of maturity-onset diabetes of the young (MODY1), which is a monogenic form of type 2 diabetes characterized by impaired insulin secretion by pancreatic beta-cells. HNF4alpha is a transcription factor expressed in the liver, kidney, intestine, and pancreatic islet. Multiple splice variants of the HNF4alpha gene have been identified and an isoform of HNF4alpha8, an N-terminal splice variant, is expressed in pancreatic beta-cells. However, expression levels of HNF4alpha protein in pancreatic beta-cells and the transcriptional activity of HNF4alpha8 are not yet understood. In the present study, we investigated the expression of HNF4alpha in beta-cells and examined its functional properties. Western blotting and immunohistochemical analysis revealed that the expression of HNF4alpha protein in pancreatic islets and INS-1 cells was much lower than in the liver. A reporter gene assay showed that the transactivation potential of HNF4alpha8 was significantly weaker than that of HNF4alpha2, which is a major isoform in the liver, suggesting that the total level of HNF4alpha activity is very weak in pancreatic beta-cells. We also showed that the N-terminal A/B region of HNF4alpha8 possessed no activation function and C-terminal F region negatively regulated the transcriptional activity of HNF4alpha8. The information presented here would be helpful for the better understanding of MODY1/HNF4alpha diabetes.

The role of HNF4A variants in the risk of type 2 diabetes

Genes influence susceptibility to type 2 diabetes mellitus (T2DM), and both positional cloning and candidate gene approaches have been used to identify these genes. Linkage analysis has generated evidence for T2DM-predisposing variants on chromosome 20q in studies of Caucasians, Asians, and Africans, and fine-mapping recently identified a likely susceptibility gene, hepatocyte nuclear factor 4-alpha (HNF4A). Rare loss-of-function mutations in HNF4A cause maturity-onset diabetes of the young and now common noncoding variants have been found to be associated with T2DM.

Genetic and clinical characteristics of maturity-onset diabetes of the young in Chinese patients

In Caucasians, maturity-onset diabetes of the young (MODY) is mostly caused by mutations in the hepatocyte nuclear factor (HNF)-1alpha (MODY3) and glucokinase (MODY2) genes. Most Japanese MODY patients, however, are not linked to known MODY genes. In this study, we examined the genetic and clinical characteristics of Chinese subjects with MODY. The study included 146 unrelated families fulfilling the minimum criteria for MODY: two consecutive generations of type II diabetes with at least one member diagnosed under the age of 25. We screened for mutations in the HNF-4alpha (MODY1), MODY2 and MODY3 genes by direct sequencing. Antibody to glutamic acid decarboxylase (GAD-Ab) was measured in subjects with MODY of unknown cause (MODYX). Insulin resistance index and other clinical data were compared in sex-, age- and duration-matched MODY3 and MODYX patients. In all, 13 families had MODY3 mutations and two had MODY2 mutations. No MODY1 mutation was found. Four of the 12 different MODY3 mutations were newly identified novel mutations (Q243E, A311D, P379R and P488fsdelC). In subjects with MODYX, 3% were GAD-Ab positive and 60% were overweight. Compared to MODY3 patients, MODYX patients had higher body mass index (P<0.02), higher insulin resistance index (P=0.001) and triglyceride level (P<0.02), lower HDL level (P=0.001) and more hypertension (P<0.05), but no significant difference in the prevalence of diabetic complications. In conclusion, MODY3 and MODY2 account for only 9 and 1%, respectively, of Chinese MODY. A majority of Chinese MODY patients are due to defects in unknown genes and appear to be characterized by insulin resistance.

SREBP-1 interacts with hepatocyte nuclear factor-4 alpha and interferes with PGC-1 recruitment to suppress hepatic gluconeogenic genes

The hepatocyte nuclear factor-4alpha (HNF-4alpha)/PGC-1 pathway plays a crucial role in the transcriptional regulation of hepatic gluconeogenic enzymes such as phosphoenolpyruvate carboxykinase (PEPCK) and Glc-6-Pase, genes that are activated at fasting and suppressed in a fed state. SREBP-1c dominates the nutritional regulation of lipogenic genes inverse to gluconeogenesis. Here we show the mechanism by which SREBP-1 suppresses expression of gluconeogenic genes. A series of luciferase reporter assays demonstrated that SREBP-1a and -1c effectively inhibited the PEPCK promoter activity that was induced by HNF-4alpha. The HNF-4alpha-binding site in the glucocorticoid-response unit was responsible for the SREBP-1 inhibition, although SREBP-1 did not bind to the PEPCK promoter as demonstrated by electrophoretic mobility shift assays. The inhibitory effect was more potent in the isoform of SREBP-1a than SREBP-1c and was eliminated by deletion of the amino-terminal transactivation domain of SREBP-1. Coimmunoprecipitation experiments demonstrated that these two transcription factors directly interact through the transactivation domain of SREBP-1 and the ligand binding/AF2 domains of HNF-4alpha. Estimation of coactivator recruitment using HNF-4alpha-Gal4DBD fusion assay showed that SREBP-1 competitively inhibited PGC-1 recruitment, a requirement for HNF-4alpha activation. Consistent with these results, hepatic PEPCK and Glc-6-Pase mRNA levels are suppressed by overexpression of SREBP-1a and -1c in the transgenic mice. Our data indicate that SREBP-1 has a novel role as negative regulator of gluconeogenic genes through a cross-talk with HNF-4alpha interference with PGC-1 recruitment.

T130I mutation in HNF-4alpha gene is a loss-of-function mutation in hepatocytes and is associated with late-onset Type 2 diabetes mellitus in Japanese subjects

AIMS/HYPOTHESIS

Mutations in hepatocyte nuclear factor (HNF)-4alpha gene cause a form of maturity-onset diabetes of the young (MODY1). The T130I mutation is a rare missense mutation, which affects a conserved amino acid in a DNA binding domain. This mutation can be found in the general population, so this variant alone does not cause MODY. However, its significance in the development of late-onset Type 2 diabetes is not known.

METHODS

We screened 423 unrelated Japanese patients with late-onset Type 2 diabetes and 354 unrelated non-diabetic control subjects for the T130I mutation in the HNF-4alpha gene. The transactivation ability of T130I-HNF-4alpha was assessed using reporter gene assay.

RESULTS

The frequency of the T130I mutation was higher in Type 2 diabetic patients ( p=0.015, odds ratio 4.3, 95%CI 1.24-14.98) than control subjects. The serum HDL-cholesterol concentration was lower in Type 2 diabetic patients with the T130I mutation compared with those without this mutation ( p=0.006). Reporter gene analysis showed that T130I-HNF-4alpha transcriptional activity was not impaired compared with wild-type HNF-4alpha in Hela and MIN6 cells, but it was reduced in HepG2 and primary cultured mouse hepatocytes (27-78% of wild type, p<0.05).

CONCLUSION/INTERPRETATION

Our findings suggest that T130I-HNF-4alpha is a loss-of-function mutation in hepatocytes and that this mutation is associated with late-onset Type 2 diabetes in Japanese subjects. The T130I mutation in the HNF-4alpha gene might be involved in the development of Type 2 diabetes in the Japanese population.

Genetic epidemiology of MODY in the Czech republic: new mutations in the MODY genes HNF-4alpha, GCK and HNF-1alpha

AIMS/HYPOTHESIS

The aim of this study was to examine the prevalence and nature of mutations in HNF4alpha/MODY1, GCK/MODY2 and HNF-1alpha/MODY3 genes in Czech subjects with clinical diagnosis of MODY.

METHODS

We studied 61 unrelated index probands of Czech origin (28 males, 33 females) with a clinical diagnosis of MODY and 202 family members. The mean age of probands was 22.7+/-12.0 years (range, 6-62) and the mean age at the first recognition of hyperglycaemia was 14.7+/-6.0 years (range, 1-25). The promotor and coding regions inclusive intron exon boundaries of the HNF-4alpha, GCK and HNF-1alpha genes were examined by PCR-dHPLC (HNF-1alpha and GCK) and direct sequencing.

RESULTS

We identified 20 different mutations in the HNF-4alpha, GCK and HNF-1alpha in 29 families (48% of all families studied), giving a relative prevalence of 5% of MODY1, 31% of MODY2 and 11.5% of MODY3 among the Czech kindred with MODY. Three of 3, 10 of 11 and 1 of 6 of the mutations identified in HNF-4alpha, GCK and HNF-1alpha respectively, were new.

CONCLUSION/INTERPRETATION

Of the families 48% carried mutations in the MODY1-3 genes and of the identified mutations 70% were new. In 52% of Czech families with clinical characteristics of MODY, no mutations were found in the analysed genes. This finding shows that the majority of MODY mutations in a central European population are local and that other MODY genes could be responsible for autosomal dominant transmission of diabetes mellitus.

Hepatocyte nuclear factor-4 alpha/gamma and hepatocyte nuclear factor-1 alpha as causal factors of interindividual difference in the expression of human dihydrodiol dehydrogenase 4 mRNA in human livers

Human dihydrodiol dehydrogenase (DD) catalyses the oxidation of trans-dihydrodiols of polycyclic aromatic hydrocarbons and the reduction of several ketone-containing drugs. About 40-fold interindividual difference in DD activities has been noted. Recently, we found that transcriptional factors, hepatocyte nuclear factor (HNF)-1 alpha, HNF-4 alpha and HNF-4 gamma were essential for the expression of DD4 mRNA, which is a major form of DDs. Thus, to clarify a possible mechanism(s) underlying the interindividual difference in DD activities, we investigated the sequences of genes and the expression levels of mRNA for DD4 and HNFs in human livers. We found no clear relationship between the genotypes of DD4 and HNF genes and the expression levels of DD4 mRNA in the subjects. The expression level of DD4 mRNA significantly correlated with that of HNF-1 alpha, HNF-4 alpha or HNF-4 gamma. These results suggest that the expression level of DD4 mRNA is cooperatively regulated by the amounts of HNF-1 alpha, HNF-4 alpha and HNF-4 gamma.

Activation of the insulin gene promoter through a direct effect of hepatocyte nuclear factor 4 alpha

Maturity onset diabetes of the young, subtype 1 (MODY1), is associated with defective glucose-dependent insulin secretion from pancreatic beta cells. MODY1 is caused by mutation in the transcription factor hepatocyte nuclear factor 4 alpha (HNF4 alpha). To understand better the MODY1 phenotype, we tested whether HNF4 alpha was able to modulate directly the insulin gene promoter. Transfection of cultured 293T cells with an HNF4 alpha expression vector led to 10-fold activation of a cotransfected reporter plasmid containing the rat insulin I gene promoter. Computer analysis revealed a potential HNF4 alpha-binding site between nucleotides -57 and -69 of the promoter; mutation of this sequence led to reduced ability of HNF4 alpha to activate the promoter. The ability of HNF4 alpha to bind this sequence was confirmed using gel shift analysis. In transfected INS-1 beta cells, mutation of either the HNF1 alpha site or the HNF4 alpha site in the insulin gene promoter led to 50-75% reduction in reporter gene activity; expression of dominant negative HNF4 alpha led to significant reduction in the activity of wild type and both mutated promoters. Thus, in addition to the previously described indirect action of HNF4 alpha on insulin gene expression mediated through elevated HNF1 alpha levels, HNF4 alpha also activates the insulin gene directly, through a previously unrecognized cis element.

Genome-wide search for type 2 diabetes in Japanese affected sib-pairs confirms susceptibility genes on 3q, 15q, and 20q and identifies two new candidate Loci on 7p and 11p

The genetic background that predisposes the Japanese population to type 2 diabetes is largely unknown. Therefore, we conducted a 10-cM genome-wide scan for type 2 diabetes traits in the 359 affected individuals from 159 families, yielding 224 affected sib-pairs of Japanese origin. Nonparametric multipoint linkage analyses performed in the whole population showed one suggestive linked region on 11p13-p12 (maximum logarithm of odds score [MLS] 3.08, near Pax6) and seven potentially linked regions (MLS >1.17) at 1p36-p32, 2q34, 3q26-q28, 6p23, 7p22-p21, 15q13-q21, and 20q12-q13 (near the gene for hepatocyte nuclear factor-4alpha [HNF-4alpha]). Subset analyses according to maximal BMI and early age at diagnosis added suggestive evidence of linkage with type 2 diabetes at 7p22-p21 (MLS 3.51), 15q13-q21 (MLS 3.91), and 20q12-q13 (MLS 2.32). These results support previous indication for linkage found on chromosome 3q, 15q, and 20q in other populations and identifies two new potential loci on 7p and 11p that may confer genetic risk for type 2 diabetes in the Japanese population.

Expression of HNF4alpha isoforms in mouse liver development is regulated by sequential promoter usage and constitutive 3' end splicing

Hepatocyte nuclear factor 4alpha (HNF4alpha) is essential for the establishment and maintenance of liver-specific gene expression. The HNF4alpha gene codes for several isoforms whose developmental and physiological relevance has not yet been explored. HNF4alpha1 and HNF4alpha7 originate from different promoters, while alternative splicing in 3' leads to HNF4alpha2 and HNF4alpha8, respectively. HNF4alpha7/alpha8 were abundantly expressed in embryonic liver and fetal-like hepatoma cells. HNF4alpha1/alpha2 transcripts were up-regulated at birth and represented the only isoforms in adult-like hepatoma cells. In line with its expression profile, HNF4alpha7 activated more avidly than HNF4alpha1 reporter plasmids for genes that are expressed early. The expression patterns of both isoforms together with the differences observed in their transcriptional activities provide elements accounting for fine-tuning of the activity of HNF4alpha. The sequential expression of HNF4alpha7/alpha8 and HNF4alpha1/alpha2 during mouse liver development is the only modification in liver-enriched transcription factors thus far recorded, which parallels the transition from the fetal to the adult hepatic phenotype.

A high-resolution 6.0-megabase transcript map of the type 2 diabetes susceptibility region on human chromosome 20

Recent linkage studies and association analyses indicate the presence of at least one type 2 diabetes susceptibility gene in human chromosome region 20q12-q13.1. We have constructed a high-resolution 6.0-megabase (Mb) transcript map of this interval using two parallel, complementary strategies to construct the map. We assembled a series of bacterial artificial chromosome (BAC) contigs from 56 overlapping BAC clones, using STS/marker screening of 42 genes, 43 ESTs, 38 STSs, 22 polymorphic, and 3 BAC end sequence markers. We performed map assembly with GraphMap, a software program that uses a greedy path searching algorithm, supplemented with local heuristics. We anchored the resulting BAC contigs and oriented them within a yeast artificial chromosome (YAC) scaffold by observing the retention patterns of shared markers in a panel of 21 YAC clones. Concurrently, we assembled a sequence-based map from genomic sequence data released by the Human Genome Project, using a seed-and-walk approach. The map currently provides near-continuous coverage between SGC32867 and WI-17676 ( approximately 6.0 Mb). EST database searches and genomic sequence alignments of ESTs, mRNAs, and UniGene clusters enabled the annotation of the sequence interval with experimentally confirmed and putative transcripts. We have begun to systematically evaluate candidate genes and novel ESTs within the transcript map framework. So far, however, we have found no statistically significant evidence of functional allelic variants associated with type 2 diabetes. The combination of the BAC transcript map, YAC-to-BAC scaffold, and reference Human Genome Project sequence provides a powerful integrated resource for future genomic analysis of this region.

Mutations in the coding region of the neurogenin 3 gene (NEUROG3) are not a common cause of maturity-onset diabetes of the young in Japanese subjects

Mutations in transcription factors that play a role in the development of the endocrine pancreas, such as insulin promoter factor-1 and NeuroD1/BETA2, have been associated with diabetes. Cell type-specific members of the basic helix-loop-helix (bHLH) family of transcription factors play essential roles in the development and maintenance of many differentiated cell types, including pancreatic beta-cells. Neurogenin 3 is a bHLH transcription factor that is expressed in the developing central nervous system and the embryonic pancreas. Mice lacking this transcription factor fail to develop any islet endocrine cells and die postnatally from diabetes. Because neurogenin 3 is required for the development of beta-cells and other pancreatic islet cell types, we considered it a candidate diabetes gene. We screened the coding region of the human neurogenin 3 gene (NEUROG3) for mutations in a group of unrelated Japanese subjects with maturity-onset diabetes of the young (MODY). We found three sequence variants: a deletion of 2-bp in the 5'-untranslated region (NEUROG3-g.-44-45delCA), a G-to-A substitution in codon 167 (g.499G/ A), resulting in a Gly-to-Arg replacement (G/R167), and a T-to-C substitution in codon 199 (g.596T/C), resulting in a Phe/Ser polymorphism F/S199. These polymorphisms were not associated with MODY, thereby suggesting that mutations in NEUROG3 are not a common cause of MODY in Japanese patients.

The gene for hepatocyte nuclear factor (HNF)-4alpha is activated by glucocorticoids and glucagon, and repressed by insulin in rat liver

The gene for a transcription factor hepatocyte nuclear factor-4alpha (HNF-4alpha) is responsible for maturity-onset diabetes of the young, type 1. We examined hormonal regulation of the HNF-4alpha gene in the liver. Stimulation of primary-cultured rat hepatocytes with dexamethasone or glucagon led to induction of HNF-4alpha mRNA, being antagonized by insulin. In the liver of streptozotocin-induced diabetic rat, mRNA and protein levels for HNF-4alpha were elevated, and were normalized by insulin treatment. Therefore, HNF-4alpha in the liver is likely to be involved in the regulation of glucose metabolism in response to these hormones.