Co-localization of the ketohexokinase and glucokinase regulator genes to a 500-kb region of Chromosome 2p23

The glucokinase regulator (GCKR) is a 65-kDa protein that inhibits glucokinase (hexokinase IV) in liver and pancreatic islet. The role of glucokinase (GCK) as pancreatic β cell glucose sensor and the finding of GCK mutations in maturity onset diabetes of the young (MODY) suggest GCKR as a further candidate gene for type 2 diabetes. The inhibition of GCK by GCKR is relieved by the binding of fructose-1-phosphate (F-1-P) to GCKR. F-1-P is the end product of ketohexokinase (KHK, fructokinase), which, like GCK and GCKR, is present in both liver and pancreatic islet. KHK is the first enzyme of the specialized pathway that catabolizes dietary fructose. We have isolated genomic clones containing the human GCKR and KHK genes. By fluorescent in situ hybridization (FISH), KHK maps to Chromosome (Chr) 2p23.2-23.3, a new assignment corroborated by somatic cell hybrid analysis. The localization of GCKR, originally reported by others as 2p22.3, has been reassessed by high-resolution FISH, indicating that, like KHK, GCKR maps to 2p23.2-23.3. The proximity of GCKR and KHK was further demonstrated both by two-color interphase FISH, which suggests that the two genes lie within 500 kb of each other, and by analysis of overlapping YAC and P1 clones spanning the interval between GCKR and KHK. A new microsatellite polymorphism was used to place the GCKR-KHK locus between D2S305 and D2S165 on the genetic map. The co-localization of these two metabolically connected genes has implications for the interpretation of linkage or allele association studies in type 2 diabetes. It also raises the possibility of coordinate regulation of GCKR and KHK by common cis-acting regulatory elements. Received: 8 December 1995 / Accepted: 27 January 1996     

Screening of mutations and polymorphisms in the glucokinase gene in Czech diabetic and healthy control populations

Glucokinase (GCK) plays a key role in glucose metabolism. GCK mutations are known as a pathogenic cause of maturity-onset diabetes of the young type 2 (MODY2). These mutations are also found in gestational diabetics. The aim of our study was to assess the variability of the GCK gene in the Czech diabetic and control populations. We screened all 10 exons specific for the pancreatic isoform of glucokinase (1a and 2-10) including the intron flanking regions in 722 subjects (in 12 patients with an unrecognised type of MODY and their 10 family members, 313 patients with diabetes mellitus type 2 (DM2), 141 gestational diabetics (GDM), 130 healthy offspring of diabetic parents, and 116 healthy controls without family history of DM2). In two MODY families we identified two mutations in exon 2 of the GCK gene: a novel mutation Val33Ala and the previously described mutation Glu40Lys. In other subgroups (excluding MODY families) we detected only intronic variants and previously described polymorphisms in exons 6 (Tyr215Tyr) and 7 (Ser263Ser), we did not find any known GCK pathogenic mutation. We observed no difference in the frequencies of GCK polymorphisms between Czech diabetic (DM2, GDM) and non-diabetic populations.     

MODY 2: Mutation identification and molecular ancestry in a Brazilian family

Maturity Onset Diabetes of the Young (MODY) is a heterogeneous group of genetic diseases characterized by a primary defect in insulin secretion and hyperglycemia, non-ketotic disease, monogenic autosomal dominant mode of inheritance, age at onset less than 25 years, and lack of auto-antibodies. It accounts for 2–5% of all cases of non-type 1 diabetes. MODY subtype 2 is caused by mutations in the glucokinase (GCK) gene. In this study, we sequenced the GCK gene of two volunteers with clinical diagnosis for MODY2 and we were able to identify four mutations including one for a premature stop codon (c.76C>T). Based on these results, we have developed a specific PCR-RFLP assay to detect this mutation and tested 122 related volunteers from the same family. This mutation in the GCK gene was detected in 21 additional subjects who also had the clinical features of this genetic disease. In conclusion, we identified new GCK gene mutations in a Brazilian family of Italian descendance, with one due to a premature stop codon located in the second exon of the gene. We also developed a specific assay that is fast, cheap and reliable to detect this mutation. Finally, we built a molecular ancestry model based on our results for the migration of individuals carrying this genetic mutation from Northern Italy to Brazil.     

Discovery of a novel site regulating glucokinase activity following characterization of a new mutation causing hyperinsulinemic hypoglycemia in humans

Type 2 diabetes is a global problem, and current ineffective therapeutic strategies pave the way for novel treatments like small molecular activators targeting glucokinase (GCK). GCK activity is fundamental to beta cell and hepatocyte glucose metabolism, and heterozygous activating and inactivating GCK mutations cause hyperinsulinemic hypoglycemia (HH) and maturity onset diabetes of the young (MODY) respectively. Over 600 naturally occurring inactivating mutations have been reported, whereas only 13 activating mutations are documented to date. We report two novel GCK HH mutations (V389L and T103S) at residues where MODY mutations also occur (V389D and T103I). Using recombinant proteins with in vitro assays, we demonstrated that both HH mutants had a greater relative activity index than wild type (6.0 for V389L, 8.4 for T103S, and 1.0 for wild type). This was driven by an increased affinity for glucose (S(0.5), 3.3 ± 0.1 and 3.5 ± 0.1 mm, respectively) versus wild type (7.5 ± 0.1 mm). Correspondingly, the V389D and T103I MODY mutants had markedly reduced relative activity indexes (<0.1). T103I had an altered affinity for glucose (S(0.5), 24.9 ± 0.6 mm), whereas V389D also exhibited a reduced affinity for ATP and decreased catalysis rate (S(0.5), 78.6 ± 4.5 mm; ATP(K(m)), 1.5 ± 0.1 mm; K(cat), 10.3 ± 1.1s(-1)) compared with wild type (ATP(K(m)), 0.4 ± <0.1; K(cat), 62.9 ± 1.2). Both Thr-103 mutants showed reduced inhibition by the endogenous hepatic inhibitor glucokinase regulatory protein. Molecular modeling demonstrated that Thr-103 maps to the allosteric activator site, whereas Val-389 is located remotely to this position and all other previously reported activating mutations, highlighting α-helix 11 as a novel region regulating GCK activity. Our data suggest that pharmacological manipulation of GCK activity at locations distal from the allosteric activator site is possible.     

A polymorphic (CA)n repeat element maps the human glucokinase gene (GCK) to chromosome 7p.

A compound imperfect dinucleotide repeat element, [CA]4TTTGT[CT]7[CA]9AA[CA]4CCACATA[CA]3, was found approximately 10 kb 3' to the human glucokinase gene (GCK) from analysis of contiguous genomic DNA obtained from a bacteriophage lambda chromosome walk. Direct human genomic sequencing revealed the source of polymorphism to be variable numbers of CT and CA repeats. Altogether six alleles that range in length from +10 to -15 nucleotides compared to the most common (Z) allele have been identified. Alleles Z, Z + 2, and Z + 4 were present in American Blacks, Pima Indians, and Caucasians, with somewhat varied frequencies among the groups. Two alleles, Z + 10 and Z - 15, appear to be unique to American Blacks, while a Z + 6 allele was observed only in the Caucasian population studied. Observed heterozygosity of the polymorphism in the CEPH reference pedigree collection is 44% and the PIC 0.44. The polymorphism is assayed by PCR amplification and resolution of 32P-end-labeled products (ranging in length from 180 to 205 bp) on denaturing polyacrylamide sequencing gels. Using the PCR assay, the human glucokinase gene was physically localized to chromosome 7 in a panel of rodent/human somatic cell lines. Genetic analysis in CEPH pedigrees placed the dinucleotide repeat element, and thereby the human glucokinase gene, on chromosome 7p between TCRG and a RFLP locus D7S57. The glucokinase dinucleotide repeat genetic marker can now be used to assess the role of the glucokinase gene in diabetes by population association studies. In addition, this repeat marker and others flanking it on chromosome 7 can be used in linkage studies with families segregating the disorder.     

Glucokinase gene mutations: structural and genotype-phenotype analyses in MODY children from South Italy

Background

Maturity onset diabetes of the young type 2 (or GCK MODY) is a genetic form of diabetes mellitus provoked by mutations in the glucokinase gene (GCK).

Methodology/Principal Findings

We screened the GCK gene by direct sequencing in 30 patients from South Italy with suspected MODY. The mutation-induced structural alterations in the protein were analyzed by molecular modeling. The patients'' biochemical, clinical and anamnestic data were obtained. Mutations were detected in 16/30 patients (53%); 9 of the 12 mutations identified were novel (p.Glu70Asp, p.Phe123Leu, p.Asp132Asn, p.His137Asp, p.Gly162Asp, p.Thr168Ala, p.Arg392Ser, p.Glu290X, p.Gln106_Met107delinsLeu) and are in regions involved in structural rearrangements required for catalysis. The prevalence of mutation sites was higher in the small domain (7/12: ∼59%) than in the large (4/12: 33%) domain or in the connection (1/12: 8%) region of the protein. Mild diabetic phenotypes were detected in almost all patients [mean (SD) OGTT = 7.8 mMol/L (1.8)] and mean triglyceride levels were lower in mutated than in unmutated GCK patients (p = 0.04).

Conclusions

The prevalence of GCK MODY is high in southern Italy, and the GCK small domain is a hot spot for MODY mutations. Both the severity of the GCK mutation and the genetic background seem to play a relevant role in the GCK MODY phenotype. Indeed, a partial genotype-phenotype correlation was identified in related patients (3 pairs of siblings) but not in two unrelated children bearing the same mutation. Thus, the molecular approach allows the physician to confirm the diagnosis and to predict severity of the mutation.     

Functional characterization of MODY2 mutations in the nuclear export signal of glucokinase

Glucokinase (GCK) plays a key role in glucose homeostasis. Heterozygous inactivating mutations in the GCK gene cause the familial, mild fasting hyperglycaemia named MODY2. Besides its particular kinetic characteristics, glucokinase is regulated by subcellular compartmentation in hepatocytes. Glucokinase regulatory protein (GKRP) binds to GCK, leading to enzyme inhibition and import into the nucleus at fasting. When glucose concentration increases, GCK-GKRP dissociates and GCK is exported to the cytosol due to a nuclear export signal (NES). With the aim to characterize the GCK-NES, we have functionally analysed nine MODY2 mutations located within the NES sequence.Recombinant GCK mutants showed reduced catalytic activity and, in most cases, protein instability. Most of the mutants interact normally with GKRP, although mutations L306R and L309P impair GCK nuclear import in cotransfected cells. We demonstrated that GCK-NES function depends on exportin 1. We further showed that none of the mutations fully inactivate the NES, with the exception of mutation L304P, which likely destabilizes its α-helicoidal structure. Finally, we found that residue Glu300 negatively modulates the NES activity, whereas other residues have the opposite effect, thus suggesting that some of the NES spacer residues contribute to the low affinity of the NES for exportin 1, which is required for its proper functioning.In conclusion, our results have provided functional and structural insights regarding the GCK-NES and contributed to a better knowledge of the molecular mechanisms involved in the nucleo-cytoplasmic shuttling of glucokinase. Impairment of this regulatory mechanism by some MODY2 mutations might contribute to the hyperglycaemia in the patients.     

Maturity-onset diabetes of the young

Maturity-onset diabetes of the young (MODY) is a subtype of noninsulin dependent diabetes mellitus (NIDDM). It is characterized by an early age of onset and autosomal dominant mode of inheritance. These features and the availability of large multigenerational pedigrees make MODY useful for genetic studies of diabetes. In the large, 5-generational RW pedigree, MODY is tightly linked to genetic markers on chromosome 20q. Affected subjects in this family show abnormalities of carbohydrate metabolism varying from impaired glucose tolerance (IGT) to severe diabetes. Approximately 30% of diabetic subjects become insulin requiring and vascular complications occur. MODY is also linked to the glucokinase gene on chromosome 7p and many different mutations associated with MODY have been identified in this gene. MODY due to mutations in the glucokinase gene is a relatively mild form of diabetes with mild fasting hyperglycemia and IGT in the majority. It is rarely insulin requiring and rarely has vascular complications. Clinical studies indicate that the genetic or primary defect in MODY is characterized by deranged and deficient insulin secretion and not by insulin resistance and that there are quantitative and qualitative differences in insulin secretory defects which differentiate subjects with MODY due to glucokinase mutations from those with mutations in the gene on chromosome 20q. These differences correlate with the severity of diabetes between these two genetic forms of MODY.     

Generation of N-ethyl-N-nitrosourea (ENU) diabetes models in mice demonstrates genotype-specific action of glucokinase activators

We performed genome-wide mutagenesis in C57BL/6J mice using N-ethyl-N-nitrosourea to identify mutations causing high blood glucose early in life and to produce new animal models of diabetes. Of a total of 13 new lines confirmed by heritability testing, we identified two semi-dominant pedigrees with novel missense mutations (Gck(K140E) and Gck(P417R)) in the gene encoding glucokinase (Gck), the mammalian glucose sensor that is mutated in human maturity onset diabetes of the young type 2 and the target of emerging anti-hyperglycemic agents that function as glucokinase activators (GKAs). Diabetes phenotype corresponded with genotype (mild-to-severe: Gck(+/+) < Gck(P417R/+), Gck(K140E)(/+) < Gck(P417R/P417R), Gck(P417R/K140E), and Gck(K140E/K140E)) and with the level of expression of GCK in liver. Each mutant was produced as the recombinant enzyme in Escherichia coli, and analysis of k(cat) and tryptophan fluorescence (I(320/360)) during thermal shift unfolding revealed a correlation between thermostability and the severity of hyperglycemia in the whole animal. Disruption of the glucokinase regulatory protein-binding site (GCK(K140E)), but not the ATP binding cassette (GCK(P417R)), prevented inhibition of enzyme activity by glucokinase regulatory protein and corresponded with reduced responsiveness to the GKA drug. Surprisingly, extracts from liver of diabetic GCK mutants inhibited activity of the recombinant enzyme, a property that was also observed in liver extracts from mice with streptozotocin-induced diabetes. These results indicate a relationship between genotype, phenotype, and GKA efficacy. The integration of forward genetic screening and biochemical profiling opens a pathway for preclinical development of mechanism-based diabetes therapies.     

Characterization of glucokinase polymorphisms associated with Maturity-Onset Diabetes of the Young (MODY2) in Jordanian population

Maturity-Onset Diabetes of the Young (MODY) is a monogenic form of Diabetes Mellitus (DM) characterized by an autosomal dominant inheritance, onset usually before 25 years of age and a primary defect in glucose-stimulated insulin secretion, Glucokinase (GCK) acts as a glucose sensor in the pancreatic beta cell and regulates insulin secretion. The mutation in the gene encoding GCK results in enzyme inactivation cause MODY2. Functional studies of naturally occurring GCK mutations associated with hyperglycaemia provide further insight into the biochemical basis of glucose sensor regulation. In this study 100 diabetic Jordanian patients with MODY2 phenotype and 150 Normal control subjects were screened for the presence of GCK gene mutations including the missense mutations at position Thr228Ala in exon 7, Gly299Arg in exon 8 and nonsense mutation Ser383Ter in exon 9, utilizing polymerase chain reaction with restriction fragment length polymorphism (PCR-RFLP) analysis. The results shows no Thr228Ala, Gly299Arg and Ser383Ter mutations were detected in both groups, which was differ from the results obtained for Italian and Caucasian from the Oxford region in UK MODY2 patients. Our data indicated that the previously studied mutations in Italian and Caucasian patients in the GCK gene are not common in MODY Jordanian population, suggesting a racial difference can be found in the frequency of the GCK polymorphism.     

Investigating Maturity Onset Diabetes of the Young

Maturity Onset Diabetes of Young (MODY) is a monogenic and autosomal dominant form of diabetes mellitus with onset of the disease often before 25 years of age. It is due to dysfunction of pancreatic ß cells characterised by non-ketotic diabetes and absence of pancreatic auto-antibodies. It is frequently mistaken for type 1 or type 2 diabetes mellitus. Diagnosis of MODY is important as the GCK subtype has better prognosis and may not require any treatment. Subtypes HNF1A and HNF4A are sensitive to sulfonylureas, however diabetes complications are common if not treated early. Moreover, there is genetic implication for the patient and family. Rare MODY subtypes can be associated with pancreatic and renal anomalies as well as exocrine dysfunction of the pancreas. So far there are six widely accepted subtypes of MODY described but the list has grown to nine. Although the majority of diabetes mellitus in youth remains type 1 and the incidence of type 2 is rising, MODY should be considered in patients with non-ketotic diabetes at presentation, and in patients with a strong family history of diabetes mellitus without pancreatic auto-antibodies. Furthermore the diagnosis must be confirmed by molecular studies. With advancement in genomic technology, rapid screening for MODY mutations will become readily available in the future.     

A common haplotype of the glucokinase gene alters fasting glucose and birth weight: association in six studies and population-genetics analyses

Fasting glucose is associated with future risk of type 2 diabetes and ischemic heart disease and is tightly regulated despite considerable variation in quantity, type, and timing of food intake. In pregnancy, maternal fasting glucose concentration is an important determinant of offspring birth weight. The key determinant of fasting glucose is the enzyme glucokinase (GCK). Rare mutations of GCK cause fasting hyperglycemia and alter birth weight. The extent to which common variation of GCK explains normal variation of fasting glucose and birth weight is not known. We aimed to comprehensively define the role of variation of GCK in determination of fasting glucose and birth weight, using a tagging SNP (tSNP) approach and studying 19,806 subjects from six population-based studies. Using 22 tSNPs, we showed that the variant rs1799884 is associated with fasting glucose at all ages in the normal population and exceeded genomewide levels of significance (P=10-9). rs3757840 was also highly significantly associated with fasting glucose (P=8x10-7), but haplotype analysis revealed that this is explained by linkage disequilibrium (r2=0.2) with rs1799884. A maternal A allele at rs1799884 was associated with a 32-g (95% confidence interval 11-53 g) increase in offspring birth weight (P=.002). Genetic variation influencing birth weight may have conferred a selective advantage in human populations. We performed extensive population-genetics analyses to look for evidence of recent positive natural selection on patterns of GCK variation. However, we found no strong signature of positive selection. In conclusion, a comprehensive analysis of common variation of the glucokinase gene shows that this is the first gene to be reproducibly associated with fasting glucose and fetal growth.     

Association of glucokinase regulatory protein polymorphism with type 2 diabetes and fasting plasma glucose: a meta-analysis

Glucokinase regulatory protein (GCKR) which binds to glucokinase (GCK) in the nucleus and inhibits its activity in the presence of fructose-6-phosphate is critical for glucose metabolism. In the past few years, a number of case–control studies have been carried out to investigate the relationship between the GCKR polymorphism and type 2 diabetes (T2D) since it was first identified to be associated with fasting plasma glucose levels, insulin resistance through genome-wide association approach. After that, a number of studies reported that the rs780094 polymorphism in GCKR has been implicated in T2D risk. However, these studies have yielded contradictory results. To investigate this inconsistency, we performed a meta-analysis of 19 studies involving a total of 298,977 subjects for GCKR rs780094 to evaluate its effect on genetic susceptibility for T2D. In a combined analysis, the summary per-allele odds ratio for T2D of the rs780094 polymorphism was 1.11 (95 % CI: 1.07–1.14, P < 10^?5). Significant results were also observed using dominant (OR = 1.18, 95 % CI: 1.05–1.34, P < 10^?5) or recessive genetic model (OR = 1.20, 95 % CI: 1.12–1.28, P < 10^?5). Significant results were found in Asians and Caucasians when stratified by ethnicity. Besides, the polymorphism was found to be significantly associated with increased fasting plasma glucose level. There was strong evidence of heterogeneity, which largely disappeared after stratification by ethnicity. This meta-analysis suggests that the rs780094 polymorphism in GCKR is associated with elevated T2D risk, but these associations vary in different ethnic populations.     

Metabolic Profiling in Maturity-Onset Diabetes of the Young (MODY) and Young Onset Type 2 Diabetes Fails to Detect Robust Urinary Biomarkers

It is important to identify patients with Maturity-onset diabetes of the young (MODY) as a molecular diagnosis determines both treatment and prognosis. Genetic testing is currently expensive and many patients are therefore not assessed and are misclassified as having either type 1 or type 2 diabetes. Biomarkers could facilitate the prioritisation of patients for genetic testing. We hypothesised that patients with different underlying genetic aetiologies for their diabetes could have distinct metabolic profiles which may uncover novel biomarkers. The aim of this study was to perform metabolic profiling in urine from patients with MODY due to mutations in the genes encoding glucokinase (GCK) or hepatocyte nuclear factor 1 alpha (HNF1A), type 2 diabetes (T2D) and normoglycaemic control subjects. Urinary metabolic profiling by Nuclear Magnetic Resonance (NMR) and ultra performance liquid chromatography hyphenated to Q-TOF mass spectrometry (UPLC-MS) was performed in a Discovery set of subjects with HNF1A-MODY (n = 14), GCK-MODY (n = 17), T2D (n = 14) and normoglycaemic controls (n = 34). Data were used to build a valid partial least squares discriminate analysis (PLS-DA) model where HNF1A-MODY subjects could be separated from the other diabetes subtypes. No single metabolite contributed significantly to the separation of the patient groups. However, betaine, valine, glycine and glucose were elevated in the urine of HNF1A-MODY subjects compared to the other subgroups. Direct measurements of urinary amino acids and betaine in an extended dataset did not support differences between patients groups. Elevated urinary glucose in HNF1A-MODY is consistent with the previously reported low renal threshold for glucose in this genetic subtype. In conclusion, we report the first metabolic profiling study in monogenic diabetes and show that, despite the distinct biochemical pathways affected, there are unlikely to be robust urinary biomarkers which distinguish monogenic subtypes from T2D. Our results have implications for studies investigating metabolic profiles in complex traits including T2D.     

Glucokinase (GCK) mutations and their characterization in MODY2 children of southern Italy

Type 2 Maturity Onset Diabetes of the Young (MODY2) is a monogenic autosomal disease characterized by a primary defect in insulin secretion and hyperglycemia. It results from GCK gene mutations that impair enzyme activity. Between 2006 and 2010, we investigated GCK mutations in 66 diabetic children from southern Italy with suspected MODY2. Denaturing High Performance Liquid Chromatography (DHPLC) and sequence analysis revealed 19 GCK mutations in 28 children, six of which were novel: p.Glu40Asp, p.Val154Leu, p.Arg447Glyfs, p.Lys458_Cys461del, p.Glu395_Arg397del and c.580-2A>T. We evaluated the effect of these 19 mutations using bioinformatic tools such as Polymorphism Phenotyping (Polyphen), Sorting Intolerant From Tolerant (SIFT) and in silico modelling. We also conducted a functional study to evaluate the pathogenic significance of seven mutations that are among the most severe mutations found in our population, and have never been characterized: p.Glu70Asp, p.His137Asp, p.Phe150Tyr, p.Val154Leu, p.Gly162Asp, p.Arg303Trp and p.Arg392Ser. These seven mutations, by altering one or more kinetic parameters, reduced enzyme catalytic activity by >40%. All mutations except p.Glu70Asp displayed thermal-instability, indeed >50% of enzyme activity was lost at 50°C/30 min. Thus, these seven mutations play a pathogenic role in MODY2 insurgence. In conclusion, this report revealed six novel GCK mutations and sheds some light on the structure-function relationship of human GCK mutations and MODY2.     

Hepatic glucokinase promoter polymorphism is associated with hepatic insulin resistance in Asian Indians.

Background  

The role of glucokinase (GCK) in the pathogenesis of maturity-onset diabetes of the young is well established. However, its role in the common form of type 2 diabetes is far from convincing. We investigated the role of the G-to-A polymorphism in the hepatic GCK promoter on insulin sensitivity and beta cell function in 63 normotensive Asian Indians with normal glucose tolerance. As proposed by Matsuda and DeFronzo, hepatic insulin sensitivity (ISI_H) and total body insulin sensitivity (ISI_M) were estimated from the oral glucose tolerance test. Beta cell function was estimated using %B from the Homeostasis Model Assessment and insulingenic index (dI/dG).     

Chronic Ethanol Consumption-induced Pancreatic β-Cell Dysfunction and Apoptosis through Glucokinase Nitration and Its Down-regulation

Chronic ethanol consumption is known as an independent risk factor for type 2 diabetes, which is characterized by impaired glucose homeostasis and insulin resistance; however, there is a great deal of controversy concerning the relationships between alcohol consumption and the development of type 2 diabetes. We investigated the effects of chronic ethanol consumption on pancreatic β-cell dysfunction and whether generated peroxynitrite participates in the impaired glucose homeostasis. Here we show that chronic ethanol feeding decreases the ability of pancreatic β-cells to mediate insulin secretion and ATP production in coordination with the decrease of glucokinase, Glut2, and insulin expression. Specific blockade of ATF3 using siRNA or C-terminally deleted ATF3(ΔC) attenuated ethanol-induced pancreatic β-cell apoptosis or dysfunction and restored the down-regulation of glucokinase (GCK), insulin, and pancreatic duodenal homeobox-1 induced by ethanol. GCK inactivation and down-regulation were predominantly mediated by ethanol metabolism-generated peroxynitrite, which were suppressed by the peroxynitrite scavengers N^γ-monomethyl-l-arginine, uric acid, and deferoxamine but not by the S-nitrosylation inhibitor DTT, indicating that tyrosine nitration is the predominant modification associated with GCK down-regulation and inactivation rather than S-nitrosylation of cysteine. Tyrosine nitration of GCK prevented its association with pBad, and GCK translocation into the mitochondria results in subsequent proteasomal degradation of GCK following ubiquitination. This study identified a novel and efficient pathway by which chronic ethanol consumption may induce GCK down-regulation and inactivation by inducing tyrosine nitration of GCK, resulting in pancreatic β-cell apoptosis and dysfunction. Peroxynitrite-induced ATF3 may also serve as a potent upstream regulator of GCK down-regulation and β-cell apoptosis.