EIF2AK3, encoding translation initiation factor 2-alpha kinase 3, is mutated in patients with Wolcott-Rallison syndrome

Neonatal and very-early-onset diabetes mellitus

Transient (TNDM) and permanent neonatal diabetes mellitus (PNDM) are rare conditions occurring in one in 400,000-500,000 live births. In TNDM, growth-retarded infants develop diabetes in the first few weeks of life only to go into remission in a few months with later relapse as permanent type 2 diabetes, often around the time of adolescence. We believe that pancreatic dysfunction in this condition is maintained throughout life with relapse initiated at times of metabolic stress such as puberty or pregnancy. The mechanisms involved in this rare condition may inform on fetal pancreatic development, islet cell physiology and predisposition to type 2 diabetes. In PNDM, insulin secretory failure occurs in the early postnatal period. A number of conditions are associated with PNDM, some of which have been elucidated at the molecular level. Insulin therapy is difficult to manage in the neonatal period, and in experienced hands, the insulin pump may provide a valuable tool to administer insulin.

Evidence for linkage on chromosome 4p16.1 in Type 1 diabetes Danish families and complete mutation scanning of the WFS1 (Wolframin) gene

AIMS

To investigate whether the WFS1 gene, the gene for Wolfram syndrome, is a susceptibility gene for more common forms of diabetes in the Danish population.

METHODS

One hundred and fifty-two Danish Type 1 diabetes mellitus sib-pair families were genotyped for two microsatellite markers situated within 5 cM of the WFS1 gene and analysed for linkage and association using the sib-TDT. The entire coding region, the 5'UTR and 3'UTR of the WFS1 gene, were screened for mutations by direct sequencing in 29 selected Type 1 diabetes patients. Four of the identified mutations were tested for linkage and association in 255 Danish Type 1 diabetes families (including 103 simplex families).

RESULTS

Evidence for linkage to Type 1 diabetes was found as the second most frequent allele of the marker D4S394 were transmitted 137 times (T = 61%) and not transmitted 88 times to affected offspring (Puc = 0.0011). Twelve mutations were found in the coding region and three mutations in the 3'UTR. No evidence for linkage and association to Type 1 diabetes was found testing four of the identified amino acid substitutions.

CONCLUSIONS

Evidence of linkage to Type 1 diabetes was observed in the Danish family collection. However, no evidence of linkage and association was observed for any of the analysed polymorphisms, suggesting that other variations must be responsible for the observed evidence of linkage in the region.

Activating transcription factor 3 is integral to the eukaryotic initiation factor 2 kinase stress response

In response to environmental stress, cells induce a program of gene expression designed to remedy cellular damage or, alternatively, induce apoptosis. In this report, we explore the role of a family of protein kinases that phosphorylate eukaryotic initiation factor 2 (eIF2) in coordinating stress gene responses. We find that expression of activating transcription factor 3 (ATF3), a member of the ATF/CREB subfamily of basic-region leucine zipper (bZIP) proteins, is induced in response to endoplasmic reticulum (ER) stress or amino acid starvation by a mechanism requiring eIF2 kinases PEK (Perk or EIF2AK3) and GCN2 (EIF2AK4), respectively. Increased expression of ATF3 protein occurs early in response to stress by a mechanism requiring the related bZIP transcriptional regulator ATF4. ATF3 contributes to induction of the CHOP transcriptional factor in response to amino acid starvation, and loss of ATF3 function significantly lowers stress-induced expression of GADD34, an eIF2 protein phosphatase regulatory subunit implicated in feedback control of the eIF2 kinase stress response. Overexpression of ATF3 in mouse embryo fibroblasts partially bypasses the requirement for PEK for induction of GADD34 in response to ER stress, further supporting the idea that ATF3 functions directly or indirectly as a transcriptional activator of genes targeted by the eIF2 kinase stress pathway. These results indicate that ATF3 has an integral role in the coordinate gene expression induced by eIF2 kinases. Given that ATF3 is induced by a very large number of environmental insults, this study supports involvement of eIF2 kinases in the coordination of gene expression in response to a more diverse set of stress conditions than previously proposed.

eIF2B-related disorders: antenatal onset and involvement of multiple organs

Leukoencephalopathy with vanishing white matter, also called "childhood ataxia with central nervous system hypomyelination," is the first human disease related to mutations in any of the five genes encoding subunits of eukaryotic initiation factor eIF2B or any translation factor at all. eIF2B is essential in all cells of the body for protein synthesis and the regulation of this protein synthesis under different stress conditions. It is surprising that mutations in the eIF2B genes have been reported to lead to abnormalities of the white matter of the brain only, although it has been shown recently that ovarian failure may accompany the leukoencephalopathy. Another surprising observation is that the onset of the disease varies from early childhood to adulthood, with the exception of Cree leukoencephalopathy, a disease related to a particular mutation in one of the eIF2B genes, which invariably has its onset within the first year of life. We analyzed the eIF2B genes of nine patients with an antenatal- or early-infantile-onset encephalopathy and an early demise and found mutations in eight of the patients. In addition to signs of a serious encephalopathy, we found oligohydramnios, intrauterine growth retardation, cataracts, pancreatitis, hepatosplenomegaly, hypoplasia of the kidneys, and ovarian dysgenesis. Until now, no evidence had been found for a genotype-phenotype correlation, but the consistently severe phenotype in affected siblings among our patients and in Cree encephalopathy patients suggests an influence of the genotype on the phenotype.

A novel gene for neonatal diabetes maps to chromosome 10p12.1-p13

We report a genomewide linkage analysis of a large consanguineous family segregating autosomal recessively inherited neonatal diabetes and the identification of a novel neonatal diabetes locus. Neonatal diabetes was characterized by low levels of circulating C-peptide with very low to undetectable levels of insulin in the presence of severe hyperglycemia unresponsive to insulin infusion. A dense genomewide linkage search of the family was undertaken using a first generation 10K single nucleotide polymorphism chip containing 10,044 markers. A region of homozygosity harboring the neonatal diabetes disease gene on chromosome 10p12.1-p13 was identified (multipoint logarithm of odds score 3.25). There is a strong history of type 2 diabetes in carriers of the disease gene. It is likely that chromosome 10p12.1-p13 may harbor a maturity-onset diabetes of the young or type 2 diabetes gene.

Phosphorylation of the alpha subunit of eukaryotic initiation factor 2 is required for activation of NF-kappaB in response to diverse cellular stresses

Nuclear factor kappaB (NF-kappaB) serves to coordinate the transcription of genes in response to diverse environmental stresses. In this report we show that phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2) is fundamental to the process by which many stress signals activate NF-kappaB. Phosphorylation of this translation factor is carried out by a family of protein kinases that each respond to distinct stress conditions. During impaired protein folding and assembly in the endoplasmic reticulum (ER), phosphorylation of eIF2alpha by PEK (Perk or EIF2AK3) is essential for induction of NF-kappaB transcriptional activity. The mechanism by which NF-kappaB is activated during ER stress entails the release, but not the degradation, of the inhibitory protein IkappaB. During amino acid deprivation, phosphorylation of eIF2alpha by GCN2 (EIF2AK4) signals the activation of NF-kappaB. Furthermore, inhibition of general translation or transcription by cycloheximide and actinomycin D, respectively, elicits the eIF2alpha phosphorylation required for induction of NF-kappaB. Together, these studies suggest that eIF2alpha kinases monitor and are activated by a range of stress conditions that affect transcription and protein synthesis and assembly, and the resulting eIFalpha phosphorylation is central to activation of the NF-kappaB. The absence of NF-kappaB-mediated transcription and its antiapoptotic function provides an explanation for why eIF2alpha kinase deficiency in diseases such as Wolcott-Rallison syndrome leads to cellular apoptosis and disease.

PERK eIF2alpha kinase regulates neonatal growth by controlling the expression of circulating insulin-like growth factor-I derived from the liver

Humans afflicted with the Wolcott-Rallison syndrome and mice deficient for PERK (pancreatic endoplasmic reticulum eIF2alpha kinase) show severe postnatal growth retardation. In mice, growth retardation in Perk-/- mutants is manifested within the first few days of neonatal development. Growth parameters of Perk-/- mice, including comparison of body weight to length and organ weights, are consistent with proportional dwarfism. Tibia growth plates exhibited a reduction in proliferative and hypertrophic chondrocytes underlying the longitudinal growth retardation. Neonatal Perk-/- deficient mice show a 75% reduction in liver IGF-I mRNA and serum IGF-I within the first week, whereas the expression of IGF-I mRNA in most other tissues is normal. Injections of IGF-I partially reversed the growth retardation of the Perk-/- mice, whereas GH had no effect. Transgenic rescue of PERK activity in the insulin- secreting beta-cells of the Perk-/- mice reversed the juvenile but not the neonatal growth retardation. We provide evidence that circulating IGF-I is derived from neonatal liver but is independent of GH at this stage. We propose that PERK is required to regulate the expression of IGF-I in the liver during the neonatal period, when IGF-I expression is GH-independent, and that the lack of this regulation results in severe neonatal growth retardation.

Genetic epidemiology of type 1 diabetes

Family and twin studies indicate that a substantial fraction of susceptibility to type 1 diabetes is attributable to genetic factors. These and other epidemiologic studies also implicate environmental factors as important triggers. Although the specific environmental factors that contribute to immune-mediated diabetes remain unknown, several of the relevant genetic factors have been identified using two main approaches: genome-wide linkage analysis and candidate gene association studies. This article reviews the epidemiology of type 1 diabetes, the relative merits of linkage and association studies, and the results achieved so far using these two approaches. Prospects for the future of type 1 diabetes genetics research are considered.

Transcriptional and translational control in the Mammalian unfolded protein response

Cells monitor the physiological load placed on their endoplasmic reticulum (ER) and respond to perturbations in ER function by a process known as the unfolded protein response (UPR). In metazoans the UPR has a transcriptional component that up-regulates expression of genes that enhance the capacity of the organelle to deal with the load of client proteins and a translational component that insures tight coupling between protein biosynthesis on the cytoplasmic side and folding in the ER lumen. Together, these two components adapt the secretory apparatus to physiological load and protect cells from the consequences of protein malfolding.

The genetics of adiponectin

Adiponectin encoded by the APMI gene is one of the adipocyte-expressed proteins that function in the homeostatic control of glucose, lipid, and energy metabolism. Its dysregulation has been suggested to be involved in disorders covering the metabolic X syndrome, such as insulin resistance, obesity, type 2 diabetes, and coronary artery disease. Recent data present evidence of a genetic modulation of the adiponectin level, and linkage of the 3q27 locus, where the APMI gene lies, with diabetes and features of the metabolic X syndrome playing a putative role of the APMI gene in this syndrome. In this article, we present an overview of the results available to date and discuss positive evidence for a role of genetic variants of the APMI gene and questions that genetic data raise.

An integrated stress response regulates amino acid metabolism and resistance to oxidative stress

Eukaryotic cells respond to unfolded proteins in their endoplasmic reticulum (ER stress), amino acid starvation, or oxidants by phosphorylating the alpha subunit of translation initiation factor 2 (eIF2alpha). This adaptation inhibits general protein synthesis while promoting translation and expression of the transcription factor ATF4. Atf4(-/-) cells are impaired in expressing genes involved in amino acid import, glutathione biosynthesis, and resistance to oxidative stress. Perk(-/-) cells, lacking an upstream ER stress-activated eIF2alpha kinase that activates Atf4, accumulate endogenous peroxides during ER stress, whereas interference with the ER oxidase ERO1 abrogates such accumulation. A signaling pathway initiated by eIF2alpha phosphorylation protects cells against metabolic consequences of ER oxidation by promoting the linked processes of amino acid sufficiency and resistance to oxidative stress.

Protein synthesis and endoplasmic reticulum stress can be modulated by the hepatitis C virus envelope protein E2 through the eukaryotic initiation factor 2alpha kinase PERK

The hepatitis C virus envelope protein, E2, is an endoplasmic reticulum (ER)-bound protein that contains a region of sequence homology with the double-stranded RNA-activated protein kinase PKR and its substrate, the eukaryotic translation initiation factor 2 (eIF2). We previously reported that E2 modulates global translation through inhibition of the interferon-induced antiviral protein PKR through its PKR-eIF2alpha phosphorylation site homology domain (PePHD). Here we show that the PKR-like ER-resident kinase (PERK) binds to and is also inhibited by E2. At low expression levels, E2 induced ER stress, but at high expression levels, and in vitro, E2 inhibited PERK kinase activity. Mammalian cells that stably express E2 were refractory to the translation-inhibitory effects of ER stress inducers, and E2 relieved general translation inhibition induced by PERK. The PePHD of E2 was required for the rescue of translation that was inhibited by activated PERK, similar to our previous findings with PKR. Here we report the inhibition of a second eIF2alpha kinase by E2, and these results are consistent with a pseudosubstrate mechanism of inhibition of eIF2alpha kinases. These findings may also explain how the virus promotes persistent infection by overcoming the cellular ER stress response.

The mammalian endoplasmic reticulum as a sensor for cellular stress

The recent elucidation of the mammalian unfolded protein response pathway has revealed a unique and transcriptionally complex signal transduction pathway that protects cells from a variety of physical and biochemical stresses that can occur during normal development and in disease states. Although the stress conditions are monitored in the endoplasmic reticulum, the beneficial effects of this pathway are extended to other cellular organelles and to the organism itself.

When translation meets metabolism: multiple links to diabetes

Type 2 diabetes is a polygenic disorder characterized by multiple biochemical defects including transcriptional, translational, and posttranslational abnormalities. Although major progress has been made in elucidation of factors at the transcriptional and posttranslational levels, defects at the translational level remain elusive. Mutation of a kinase that regulates translation initiation has been implicated in the etiology of a monogenic form of diabetes known as Wolcott-Rallison syndrome. Characterization of mice rendered deficient in eukaryotic initiation factors has provided model systems to study the involvement of translation in regulating insulin synthesis and secretion, hepatic function, peripheral insulin resistance, and diabetic complications. Recent progress in the understanding of endoplasmic reticulum overload by unfolded proteins has begun to uncover mechanisms leading to pancreatic beta-cell exhaustion. Future advances in this area may lead to identification of the missing links in the pathogenesis of beta-cell failures due to conditions such as hyperinsulinemia, hyperglycemia, and long-term treatment with sulfonylureas, and thus may identify novel therapeutic targets for diabetes.

Transient neonatal diabetes, a disorder of imprinting

Transient neonatal diabetes (TND) is a rare but distinct type of diabetes. Classically, neonates present with growth retardation and diabetes in the first week of life. Apparent remission occurs by 3 months but there is a tendency for children to develop diabetes in later life. Evidence suggests it is the result of overexpression of an imprinted and paternally expressed gene/s within the TND critical region at 6q24. Two imprinted genes, ZAC (zinc finger protein associated with apoptosis and cell cycle arrest) and HYMAI (imprinted in hydatidiform mole) have been identified as potential candidates. Three genetic mechanisms have been shown to result in TND, paternal uniparental isodisomy of chromosome 6, paternally inherited duplication of 6q24, and a methylation defect at a CpG island overlapping exon 1 of ZAC/HYMAI.

Endoplasmic reticulum stress and the development of diabetes: a review

The early steps of insulin biosynthesis occur in the endoplasmic reticulum (ER), and the beta-cell has a highly developed and active ER. All cells regulate the capacity of their ER to fold and process client proteins and they adapt to an imbalance between client protein load and folding capacity (so-called ER stress). Mutations affecting the ER stress-activated pancreatic ER kinase (PERK) and its downstream effector, the translation initiation complex eukaryotic initiation factor 2 (eIF2), have a profound impact on islet cell development, function, and survival. PERK mutations are associated with the Wolcott-Rallison syndrome of infantile diabetes and mutations that prevent the alpha-subunit of eIF2 from being phosphorylated by PERK, block beta-cell development, and impair gluconeogenesis. We will review this and other rare forms of clinical and experimental diabetes and consider the role of ER stress in the development of more common forms of the disease.

Translational control of gene expression and disease

In the past decade, translational control has been shown to be crucial in the regulation of gene expression. Research in this field has progressed rapidly, revealing new control mechanisms and adding constantly to the list of translationally regulated genes. There is accumulating evidence that translational control plays a primary role in cell-cycle progression and cell differentiation, as well as in the induction of specific cellular functions. Recently, the aetiologies of several human diseases have been linked with mutations in genes of the translational control machinery, highlighting the significance of this regulatory mechanism. In addition, deregulation of translation is associated with a wide range of cancers. Current research focuses on novel therapeutic strategies that target translational control, a promising concept in the treatment of human diseases.

Traffic jams II: an update of diseases of intracellular transport

As more details emerge on the mechanisms that mediate and control intracellular transport, the molecular basis for variety of human diseases has been revealed. In turn, disease pathology and physiology shed light on the intricate controls that regulate intracellular transport to assure proper cellular and tissue function and homeostasis. We previously listed a number of diseases that are the result of defects in intracellular transport, or cause defects in intracellular transport. (Aridor M, Hannan LA. Traffic Jam: A compendium of human diseases that affect intracellular transport processes. Traffic 2000; 1: 836-851). This Toolbox updates the previous list to include additional disorders that were recently identified to be related to intracellular trafficking. In the time since we have published our first list there have been significant advances in understanding of the molecular basis of these defects. Such advances will pave the way to future effective therapeutics.

Pushing the limits of the scanning mechanism for initiation of translation

Selection of the translational initiation site in most eukaryotic mRNAs appears to occur via a scanning mechanism which predicts that proximity to the 5' end plays a dominant role in identifying the start codon. This "position effect" is seen in cases where a mutation creates an AUG codon upstream from the normal start site and translation shifts to the upstream site. The position effect is evident also in cases where a silent internal AUG codon is activated upon being relocated closer to the 5' end. Two mechanisms for escaping the first-AUG rule--reinitiation and context-dependent leaky scanning--enable downstream AUG codons to be accessed in some mRNAs. Although these mechanisms are not new, many new examples of their use have emerged. Via these escape pathways, the scanning mechanism operates even in extreme cases, such as a plant virus mRNA in which translation initiates from three start sites over a distance of 900 nt. This depends on careful structural arrangements, however, which are rarely present in cellular mRNAs. Understanding the rules for initiation of translation enables understanding of human diseases in which the expression of a critical gene is reduced by mutations that add upstream AUG codons or change the context around the AUG(START) codon. The opposite problem occurs in the case of hereditary thrombocythemia: translational efficiency is increased by mutations that remove or restructure a small upstream open reading frame in thrombopoietin mRNA, and the resulting overproduction of the cytokine causes the disease. This and other examples support the idea that 5' leader sequences are sometimes structured deliberately in a way that constrains scanning in order to prevent harmful overproduction of potent regulatory proteins. The accumulated evidence reveals how the scanning mechanism dictates the pattern of transcription--forcing production of monocistronic mRNAs--and the pattern of translation of eukaryotic cellular and viral genes.

The ribosome filter hypothesis

A variety of posttranscriptional mechanisms affects the processing, subcellular localization, and translation of messenger RNAs (mRNAs). Translational control appears to occur primarily at the initiation rather than the elongation stage. It has been suggested that translation is mediated largely by means of a cap-binding/scanning mechanism. On the basis of recent findings, we propose here that differential binding of particular mRNAs to eukaryotic 40S ribosomal subunits before translation may also selectively affect rates of polypeptide chain production. In this view, ribosomal subunits themselves are considered to be regulatory elements or filters that mediate interactions between particular mRNAs and components of the translation machinery. Differences in these interactions affect how efficiently individual mRNAs compete for ribosomal subunits. These competitive interactions would depend in part on the complementarity between sequences in mRNA and rRNA, as well as on structural differences among ribosomes in different cell types. By these means, translation may either be enhanced through increased recruitment of ribosomes or inhibited through strong interactions that sequester mRNAs. We propose that ribosomal filters may be important in cell differentiation and describe experimental tests for the filter hypothesis.

Wolcott-Rallison syndrome in two siblings with isolated central hypothyroidism

Two sibs with an infantile onset of hyperglycemia, recurrent hepatitis, renal insufficiency, developmental delay, and skeletal epiphyseal dysplasia are described. Clinical presentation and radiological features are suggestive of Wolcott-Rallison syndrome, a rare autosomal recessive disease. In both of our cases we found evidence of central hypothyroidism, which appears to be an associated feature of this syndrome. Hypothyroidism should be suspected and screened for in all cases of Wolcott-Rallison syndrome.

Genetics of type 1 diabetes mellitus

At least 20 different chromosomal regions have been linked to type 1 diabetes (T1D) susceptibility in humans, using genome screening, candidate gene testing, and studies of human homologues of mouse susceptibility genes. The largest contribution from a single locus (IDDM1) comes from several genes located in the MHC complex on chromosome 6p21.3, accounting for at least 40% of the familial aggregation of this disease. Approximately 30% of T1D patients are heterozygous for HLA-DQA1*0501-DQB1*0201/DQA1*0301-DQB1*0302 alleles (formerly referred to as HLA-DR3/4 and for simplification usually shortened to HLA-DQ2/DQ8), and a particular HLA-DQ6 molecule (HLA-DQA1*0102-DQB1*0602) is associated with dominant protection from the disease. There is evidence that certain residues important for structure and function of both HLA-DQ and DR peptide-binding pockets determine disease susceptibility and resistance. Independent confirmation of the IDDM2 locus on chromosome 11p15.5 has been achieved in both case-control and family-based studies, whereas associations with the other potential IDDM loci have not always been replicated. Several possibilities to explain these variable results from different studies are discussed, and a key factor affecting both linkage and association studies is that the genetic basis of T1D susceptibility may differ between ethnic groups. Some future strategies to address these problems are proposed. These include increasing the sample size in homogenous ethnic groups, high throughput genotyping and genomewide linkage disequilibrium (LD) mapping to establish disease associated ancestral haplotypes. Elucidation of the function of particular genes ('functional genomics') in the pathogenesis of T1D will be a most important element in future studies in this field, in addition to more sophisticated methods of statistical analyses.

Loss of kinase activity in a patient with Wolcott-Rallison syndrome caused by a novel mutation in the EIF2AK3 gene

Wolcott-Rallison syndrome (WRS) is an autosomal recessive disorder characterized by neonatal or early infancy type 1 diabetes, epiphyseal dysplasia, and growth retardation. Mutations in the EIF2AK3 gene, encoding the eukaryotic initiation factor 2alpha-kinase 3 (EIF2AK3), have been found in WRS patients. Here we describe a girl who came to our attention at 2 months of age with severe hypertonic dehydration and diabetic ketoacidosis. A diagnosis of type 1 diabetes was made and insulin treatment initiated. Growth retardation and microcephaly were also present. Anti-islet cell autoantibodies were negative, and mitochondrial diabetes was excluded. Imaging revealed a hypoplastic pancreas and typical signs of spondylo-epiphyseal dysplasia. The diagnosis of WRS was therefore made at age 5 years. Sequencing analysis of her EIF2AK3 gene revealed the presence of a homozygous T to C exchange in exon 13 leading to the missense serine 877 proline mutation. The mutated kinase, although it partly retains the ability of autophosphorylation, is unable to phosphorylate its natural substrate, eukaryotic initiation factor 2alpha (eIF2alpha). This is the first case in which the pathophysiological role of EIF2AK3 deficiency in WRS is confirmed at the molecular level. Our data demonstrate that EIF2AK3 kinase activity is essential for pancreas islet function and bone development in humans, and we suggest EIF2AK3 as a possible target for therapeutic intervention in diabetes.

The PERK eukaryotic initiation factor 2 alpha kinase is required for the development of the skeletal system, postnatal growth, and the function and viability of the pancreas

Phosphorylation of eukaryotic initiation factor 2 alpha (eIF-2 alpha) is typically associated with stress responses and causes a reduction in protein synthesis. However, we found high phosphorylated eIF-2 alpha (eIF-2 alpha[P]) levels in nonstressed pancreata of mice. Administration of glucose stimulated a rapid dephosphorylation of eIF-2 alpha. Among the four eIF-2 alpha kinases present in mammals, PERK is most highly expressed in the pancreas, suggesting that it may be responsible for the high eIF-2 alpha[P] levels found therein. We describe a Perk knockout mutation in mice. Pancreata of Perk(-/-) mice are morphologically and functionally normal at birth, but the islets of Langerhans progressively degenerate, resulting in loss of insulin-secreting beta cells and development of diabetes mellitus, followed later by loss of glucagon-secreting alpha cells. The exocrine pancreas exhibits a reduction in the synthesis of several major digestive enzymes and succumbs to massive apoptosis after the fourth postnatal week. Perk(-/-) mice also exhibit skeletal dysplasias at birth and postnatal growth retardation. Skeletal defects include deficient mineralization, osteoporosis, and abnormal compact bone development. The skeletal and pancreatic defects are associated with defects in the rough endoplasmic reticulum of the major secretory cells that comprise the skeletal system and pancreas. The skeletal, pancreatic, and growth defects are similar to those seen in human Wolcott-Rallison syndrome.

The unfolded protein response in nutrient sensing and differentiation

Eukaryotic cells coordinate protein-folding reactions in the endoplasmic reticulum with gene expression in the nucleus and messenger RNA translation in the cytoplasm. As the rate of protein synthesis increases, protein folding can be compromised, so cells have evolved signal-transduction pathways that control transcription and translation -- the 'unfolded protein response'. Recent studies indicate that these pathways also coordinate rates of protein synthesis with nutrient and energy stores, and regulate cell differentiation to survive nutrient-limiting conditions or to produce large amounts of secreted products such as hormones, antibodies or growth factors.

Genetic and molecular analyses of complex metabolic disorders: genetic linkage

Wide efforts have taken place with complex metabolic disorders to emulate the success that linkage analysis has had in explaining the nature of monogenic metabolic diseases such as MODY (maturity-onset diabetes of the young) and FH (familial hypercholesterolemia). New linkage methods are being specifically developed and tested for complex disorders since some of the basic assumptions of traditional linkage analysis used with Mendelian traits are not valid. The nature of complex diseases precludes the use of extended families under the hypothesis that the same disease allele acts in most affected individuals throughout a pedigree. Rather, a multitude of genes and of rare and common alleles creates an apparently chaotic pattern of heterogeneity within and between families. Therefore, very simple family structures, in many studies even isolated sibling pairs, form the basis of efforts to compare the inheritance of disease with that of the chromosomal regions under investigation. Also, assumptions about how individual loci contribute to the overall disease inheritance used for the models applied in linkage computation have to be kept to a minimum. The overall effect of this, together with the potentially weak influence of many loci, is a heavy toll on the statistical power to detect individual contributing genes. This may be the reason why very few scans so far have yielded disease loci that meet genome-wide significance criteria. The confirmation of original loci in secondary studies has proven, as predicted, to be very difficult. Nevertheless, the overall emerging picture is very encouraging: one of the genome scans in type 2 diabetes has been carried through to the positional cloning of the underlying genetic variant, namely, the calpain 10-associated polymorphism in type 2 diabetes. Several other loci have been detected repeatedly throughout studies in various human racial groups, such as the chromosome 1q and 20q diabetes loci, and have become the target of collaborative fine-mapping efforts. Modifications to present methodology are in development with the goal to increase statistical power: examples are the use of intermediate traits with potentially increased genetic homogeneity, the investigation of admixed populations, and the study of linkage disequilibrium over wide genomic regions.

ASK1 is essential for endoplasmic reticulum stress-induced neuronal cell death triggered by expanded polyglutamine repeats

Expansion of CAG trinucleotide repeats that encode polyglutamine is the underlying cause of at least nine inherited human neurodegenerative disorders, including Huntington's disease and spinocerebellar ataxias. PolyQ fragments accumulate as aggregates in the cytoplasm and/or in the nucleus, and induce neuronal cell death. However, the molecular mechanism of polyQ-induced cell death is controversial. Here, we show the following: (1) polyQ with pathogenic repeat length triggers ER stress through proteasomal dysfunction; (2) ER stress activates ASK 1 through formation of an IRE1-TRAF2-ASK1 complex; and (3) ASK1(-/-) primary neurons are defective in polyQ-, proteasome inhibitor-, and ER stress-induced JNK activation and cell death. These findings suggest that ASK1 is a key element in ER stress-induced cell death that plays an important role in the neuropathological alterations in polyQ diseases.

Dimerization and release of molecular chaperone inhibition facilitate activation of eukaryotic initiation factor-2 kinase in response to endoplasmic reticulum stress

Phosphorylation of eukaryotic initiation factor-2 (eIF2) by pancreatic eIF2 kinase (PEK), induces a program of translational expression in response to accumulation of malfolded protein in the endoplasmic reticulum (ER). This study addresses the mechanisms activating PEK, also designated PERK or EIF2AK3. We describe the characterization of two regions in the ER luminal portion of the transmembrane PEK that carry out distinct functions in the regulation of this eIF2 kinase. The first region mediates oligomerization between PEK polypeptides, and deletion of this portion of PEK blocked induction of eIF2 kinase activity. The second characterized region of PEK facilitates interaction with ER chaperones. In the absence of stress, PEK associates with ER chaperones GRP78 (BiP) and GRP94, and this binding is released in response to ER stress. ER luminal sequences flanking the transmembrane domain are required for GRP78 interaction, and deletion of this portion of PEK led to its activation even in the absence of ER stress. These results suggest that this ER chaperone serves as a repressor of PEK activity, and release of ER chaperones from PEK when misfolded proteins accumulate in the ER induces gene expression required to enhance the protein folding capacity of the ER.

[Insulin-dependent neonatal and infant diabetes: genetics and physiopathology]

Insulin-dependent neonatal diabetes (ND) mellitus is uncommon with a frequency of 1/500,000 neonates in Europe. ND is characterised by hyperglycaemia, very low or undetectable insulin levels associated with intrauterine growth retardation and malformations. HLA haplotypes of juvenile diabetes or autoimmunity are not present in ND patients. Sporadic and familial forms are observed. ND could be persistent (PND) or transient (TND). Diabetes relapses occur in approximately 40% of TND patients. Hypothesis for ND aetiology such as pancreatic or beta pancreatic islets of Langerhans immaturity or abnormalities of pancreas organogenesis are postulated. Different genetic basis underlie transient or permanent forms though their clinical features do not allow to distinguish them. TND may in about 20-30% of the cases be associated with chromosome 6 paternal uniparental disomy. A candidate locus for an imprinted gene is mapped to 6q24. The permanent forms are less understood. Homozygous mutations of the IPF1/PDX1 (MODY4) and of the Glucokinase (GK, MODY2) genes have been reported. The association of a ND with a macroglossia should be a strong indicator for genetic testing. The genetic findings of a paternal disomy uniparental allows the prediction of a transient rather than a permanent form. Mutation in the Glucokinase gene should be sought in an infant with ND whose first degree relatives have glucose intolerance.

Molecular etiologies of MODY and other early-onset forms of diabetes

Maturity-onset diabetes of the young (MODY) are monogenic forms of type 2 diabetes that are characterized by an early disease onset, autosomal-dominant inheritance, and defects in insulin secretion. Genetic studies have identified mutations in at least eight genes associated with different forms of MODY. The majority of the MODY subtypes are caused by mutations in transcription factors that include hepatocyte nuclear factor (HNF)-4 alpha, HNF-1 alpha, PDX-1, HNF-1 beta, and NEURO-DI/BETA-2. In addition, genetic defects in the glucokinase gene, the glucose sensor of the pancreatic beta cells, and the insulin gene also lead to impaired glucose tolerance. Biochemical and genetic studies have demonstrated that the MODY genes are functionally related and form an integrated transcriptional network that is important for many metabolic pathways.

The mammalian endoplasmic reticulum as a sensor for cellular stress

The recent elucidation of the mammalian unfolded protein response pathway has revealed a unique and transcriptionally complex signal transduction pathway that protects cells from a variety of physical and biochemical stresses that can occur during normal development and in disease states. Although the stress conditions are monitored in the endoplasmic reticulum, the beneficial effects of this pathway are extended to other cellular organelles and to the organism itself.

Targeted disruption of the Chop gene delays endoplasmic reticulum stress-mediated diabetes

Overload of pancreatic beta cells in conditions such as hyperglycemia, obesity, and long-term treatment with sulfonylureas leads to beta cell exhaustion and type 2 diabetes. Because beta cell mass declines under these conditions, apparently as a result of apoptosis, we speculated that overload kills beta cells as a result of endoplasmic reticulum (ER) stress. The Akita mouse, which carries a conformation-altering missense mutation (Cys96Tyr) in Insulin 2, likewise exhibits hyperglycemia and a reduced beta cell mass. In the development of diabetes in Akita mice, mRNAs for the ER chaperone Bip and the ER stress-associated apoptosis factor Chop were induced in the pancreas. Overexpression of the mutant insulin in mouse MIN6 beta cells induced Chop expression and led to apoptosis. Targeted disruption of the Chop gene delayed the onset of diabetes in heterozygous Akita mice by 8-10 weeks. We conclude that ER overload in beta cells causes ER stress and leads to apoptosis via Chop induction. Our findings suggest a new therapeutic approach for preventing the onset of diabetes by inhibiting Chop induction or by increasing chaperone capacity in the ER.

Gene-specific regulation by general translation factors

Protein synthesis is the ultimate step of gene expression and a key control point for regulation. In particular, it enables cells to rapidly manipulate protein production without new mRNA synthesis, processing, or export. Recent studies have enhanced our understanding of the translation initiation process and helped elucidate how modifications of the general translational machinery regulate gene-specific protein production.

Targeted disruption of the Chop gene delays endoplasmic reticulum stress-mediated diabetes

Overload of pancreatic beta cells in conditions such as hyperglycemia, obesity, and long-term treatment with sulfonylureas leads to beta cell exhaustion and type 2 diabetes. Because beta cell mass declines under these conditions, apparently as a result of apoptosis, we speculated that overload kills beta cells as a result of endoplasmic reticulum (ER) stress. The Akita mouse, which carries a conformation-altering missense mutation (Cys96Tyr) in Insulin 2, likewise exhibits hyperglycemia and a reduced beta cell mass. In the development of diabetes in Akita mice, mRNAs for the ER chaperone Bip and the ER stress-associated apoptosis factor Chop were induced in the pancreas. Overexpression of the mutant insulin in mouse MIN6 beta cells induced Chop expression and led to apoptosis. Targeted disruption of the Chop gene delayed the onset of diabetes in heterozygous Akita mice by 8-10 weeks. We conclude that ER overload in beta cells causes ER stress and leads to apoptosis via Chop induction. Our findings suggest a new therapeutic approach for preventing the onset of diabetes by inhibiting Chop induction or by increasing chaperone capacity in the ER.

Complementary signaling pathways regulate the unfolded protein response and are required for C. elegans development

The unfolded protein response (UPR) is a transcriptional and translational intracellular signaling pathway activated by the accumulation of unfolded proteins in the lumen of the endoplasmic reticulum (ER). We have used C. elegans as a genetic model system to dissect UPR signaling in a multicellular organism. C. elegans requires ire-1-mediated splicing of xbp-1 mRNA for UPR gene transcription and survival upon ER stress. In addition, ire-1/xbp-1 acts with pek-1, a protein kinase that mediates translation attenuation, in complementary pathways that are essential for worm development and survival. We propose that UPR transcriptional activation by ire-1 as well as translational attenuation by pek-1 maintain ER homeostasis. The results demonstrate that the UPR and ER homeostasis are essential for metazoan development.

beta-Cell death during progression to diabetes

The hallmark of type 1 diabetes is specific destruction of pancreatic islet beta-cells. Apoptosis of beta-cells may be crucial at several points during disease progression, initiating leukocyte invasion of the islets and terminating the production of insulin in islet cells. beta-Cell apoptosis may also be involved in the occasional evolution of type 2 into type 1 diabetes.

Subunits of the translation initiation factor eIF2B are mutant in leukoencephalopathy with vanishing white matter

Leukoencephalopathy with vanishing white matter (VWM) is an inherited brain disease that occurs mainly in children. The course is chronic-progressive with additional episodes of rapid deterioration following febrile infection or minor head trauma. We have identified mutations in EIF2B5 and EIF2B2, encoding the epsilon- and beta-subunits of the translation initiation factor eIF2B and located on chromosomes 3q27 and 14q24, respectively, as causing VWM. We found 16 different mutations in EIF2B5 in 29 patients from 23 families. We also found two distantly related individuals who were homozygous with respect to a missense mutation in EIF2B2, affecting a conserved amino acid. Three other patients also had mutations in EIF2B2. As eIF2B has an essential role in the regulation of translation under different conditions, including stress, this may explain the rapid deterioration of people with VWM under stress. Mutant translation initiation factors have not previously been implicated in disease.

A genomewide scan for type 1-diabetes susceptibility in Scandinavian families: identification of new loci with evidence of interactions

Type 1 diabetes mellitus (TIDM) has a multifactorial etiology, with major genetic-susceptibility determinants located in the HLA and insulin-gene (INS) regions. Linkage data implicating other disease-susceptibility loci are conflicting. This is likely due to (1) the limited power for detection of contributions of additional susceptibility loci, given the limited number of informative families available for study, (2) factors such as genetic heterogeneity between populations, and (3) potential gene-gene and gene-environment interactions. To circumvent some of these problems, we have conducted a genomewide linkage analysis for T1DM-susceptibility loci in 408 multiplex families from Scandinavia, a population expected to be homogeneous for genetic and environmental factors. In addition to verifying the HLA and INS susceptibility loci, the study provides confirmation of IDDM15 on chromosome 6q21. Suggestive evidence of additional susceptibility loci was found on chromosomes 2p, 5q, and 16p. For some loci, the support for linkage increased substantially when families were stratified on the basis of HLA or INS genotypes, with statistically significant heterogeneity between the stratified subgroups. Our data support both the existence of non-HLA genes of significance for T1DM and interaction between HLA and non-HLA loci in the determination of the T1DM phenotype.

Computational analysis of human disease-associated genes and their protein products

The complete genome sequences for human, Drosophila melanogaster and Arabidopsis thaliana have been reported recently. With the availability of complete sequences for many bacteria and archaea, and five eukaryotes, comparative genomics and sequence analysis are enabling us to identify counterparts of many human disease genes in model organisms, which in turn should accelerate the pace of research and drug development to combat human diseases. Continuous improvement of specialized protein databases, together with sensitive computational tools, have enhanced the power and reliability of computational prediction of protein function.

Mitochondrial diabetes, DIDMOAD and other inherited diabetes syndromes

Inherited diabetes syndromes are individually rare but collectively make up a significant proportion of patients attending diabetes clinics, some of whom have multiple handicaps. This chapter focuses on syndromes in which major advances have been made in our understanding of the underlying molecular genetics. These conditions demonstrate novel genetic mechanisms such as maternal inheritance and genetic imprinting. They are also fascinating as they aid our understanding of insulin metabolism, both normal and abnormal. As the causative genes are identified, future issues will be the availability of genetic testing, their contribution to the genetic heterogeneity of the more common types of diabetes, and functional studies of the relevant proteins. It is probable that other subtypes of diabetes will be identified as the relevant metabolic pathways are characterized. This is an exciting time to be a diabetes physician as diabetology returns to being a diagnostic rather than a mainly management-based speciality.

Protein synthesis. The perks of balancing glucose

What do the regulation of translation initiation and glucose metabolism have to do with each other? Quite a lot, it seems, according to Sonenberg and Newgard in their Perspective. They discuss new findings that identify the kinase responsible for inactivating eIF2--a factor that is required for translation initiation (and hence protein synthesis)--when the endoplasmic reticulum is under stress. Loss of this kinase results in destruction of insulin-producing b cells in the pancreas and dysregulation of glucose homeostasis.