Molecular scanning of insulin-responsive glucose transporter (GLUT4) gene in NIDDM subjects

We investigated the prevalence of mutations in the gene encoding the major insulin-responsive facilitative glucose transporter (GLUT4) in patients with non-insulin-dependent diabetes mellitus (NIDDM). All 11 exons of the GLUT4 gene from 30 British white subjects with NIDDM were amplified using the polymerase chain reaction and screened for nucleotide sequence variation using the single-stranded conformation polymorphism (SSCP) method. No variation between the study subjects was detected in exons 1-3, 4b-8, and 10. Variant SSCP patterns were detected in exons 4a and 9. SSCP variation in exon 4a was revealed by direct nucleotide sequencing to be due to a common silent polymorphism (AAC----AAT at Asn130). One NIDDM patient demonstrated a variant SSCP pattern in exon 9. This was caused by a point mutation (GTC----ATC) at codon 383, which leads to the conservative substitution of isoleucine for valine in the putative fifth extracellular loop of the transporter. Allele-specific oligonucleotide hybridization was used to examine the frequency of this mutation in 240 Welsh white subjects (160 with NIDDM and 80 controls). The Val----Ile383 mutation was found in the heterozygous state in two diabetic subjects and no control subjects. We conclude that mutations of the GLUT4 coding sequence are very uncommon in this population of subjects with typical NIDDM. Determining whether the Ile383 GLUT4 variant present in 3 diabetic subjects contributes in any way to their disease will require further study.

Analysis of the gene sequences of the insulin receptor and the insulin-sensitive glucose transporter (GLUT-4) in patients with common-type non-insulin-dependent diabetes mellitus

Insulin resistance is a common feature of non-insulin-dependent diabetes mellitus (NIDDM) and "diabetes susceptibility genes" may be involved in this abnormality. Two potential candidate genes are the insulin receptor (IR) and the insulin-sensitive glucose transporter (GLUT-4). To elucidate whether structural defects in the IR and/or GLUT-4 could be a primary cause of insulin resistance in NIDDM, we have sequenced the entire coding region of the GLUT-4 gene from DNA of six NIDDM patients. Since binding properties of the IRs from NIDDM subjects are normal, we also analyzed the sequence of exons 16-22 (encoding the entire cytoplasmic domain of the IR) of the IR gene from the same six patients. When compared with the normal IR sequence, no difference was found in the predicted amino acid sequence of the IR cytoplasmic domain derived from the NIDDM patients. Sequence analysis of the GLUT-4 gene revealed that one patient was heterozygous for a mutation in which isoleucine (ATC) was substituted for valine (GTC) at position 383. Consequently, the GLUT-4 sequence at position 383 was determined in 24 additional NIDDM patients and 30 nondiabetic controls and all showed only the normal sequence. From these studies, we conclude that the insulin resistance seen in the great majority of subjects with the common form of NIDDM is not due to genetic variation in the coding sequence of the IR beta subunit, nor to any single mutation in the GLUT-4 gene. Possibly, a subpopulation of NIDDM patients exists displaying variation in the GLUT-4 gene.

Polymorphism in exon 4a of the human GLUT4/ muscle-fat facilitative glucose transporter gene detected by SSCP

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Molecular biology of mammalian glucose transporters

The oxidation of glucose represents a major source of metabolic energy for mammalian cells. However, because the plasma membrane is impermeable to polar molecules such as glucose, the cellular uptake of this important nutrient is accomplished by membrane-associated carrier proteins that bind and transfer it across the lipid bilayer. Two classes of glucose carriers have been described in mammalian cells: the Na(+)-glucose cotransporter and the facilitative glucose transporter. The Na(+)-glucose cotransporter transports glucose against its concentration gradient by coupling its uptake with the uptake of Na+ that is being transported down its concentration gradient. Facilitative glucose carriers accelerate the transport of glucose down its concentration gradient by facilitative diffusion, a form of passive transport. cDNAs have been isolated from human tissues encoding a Na(+)-glucose-cotransporter protein and five functional facilitative glucose-transporter isoforms. The Na(+)-glucose cotransporter is expressed by absorptive epithelial cells of the small intestine and is involved in the dietary uptake of glucose. The same or a related protein may be responsible for the reabsorption of glucose by the kidney. Facilitative glucose carriers are expressed by most if not all cells. The facilitative glucose-transporter isoforms have distinct tissue distributions and biochemical properties and contribute to the precise disposal of glucose under varying physiological conditions. The GLUT1 (erythrocyte) and GLUT3 (brain) facilitative glucose-transporter isoforms may be responsible for basal or constitutive glucose uptake. The GLUT2 (liver) isoform mediates the bidirectional transport of glucose by the hepatocyte and is responsible, at least in part, for the movement of glucose out of absorptive epithelial cells into the circulation in the small intestine and kidney. This isoform may also comprise part of the glucose-sensing mechanism of the insulin-producing beta-cell. The subcellular localization of the GLUT4 (muscle/fat) isoform changes in response to insulin, and this isoform is responsible for most of the insulin-stimulated uptake of glucose that occurs in muscle and adipose tissue. The GLUT5 (small intestine) facilitative glucose-transporter isoform is expressed at highest levels in the small intestine and may be involved in the transcellular transport of glucose by absorptive epithelial cells. The exon-intron organizations of the human GLUT1, GLUT2, and GLUT4 genes have been determined. In addition, the chromosomal locations of the genes encoding the Na(+)-dependent and facilitative glucose carriers have been determined. Restriction-fragment-length polymorphisms have also been identified at several of these loci.(ABSTRACT TRUNCATED AT 400 WORDS)

Cloning and characterization of the major insulin-responsive glucose transporter expressed in human skeletal muscle and other insulin-responsive tissues

Complementary DNA clones encoding a facilitative glucose transporter-like protein have been isolated from human small intestine and muscle cDNA libraries. This 509-amino acid protein has 65.3, 54.3, and 57.5% identity with the previously described human erythrocyte/HepG2, liver, and fetal muscle glucose transporter/transporter-like proteins, respectively. RNA blotting studies indicate that transcripts encoding this protein are very abundant in adult human skeletal muscle and subcutaneous fat. The adult skeletal muscle glucose transporter-like protein was expressed in vitro by cDNA-directed transcription and cell-free translation of the synthetic mRNA. The in vitro-synthesized protein reacted with a monoclonal antibody, 1F8, which recognizes the insulin-regulatable glucose transporter expressed in rat skeletal muscle, heart, and adipocytes. In contrast, in vitro-synthesized erythrocyte/HepG2 and fetal muscle glucose transporters did not react with 1F8. The high levels in adult skeletal muscle and subcutaneous fat of mRNA encoding the adult skeletal muscle glucose transporter and its specific reactivity with monoclonal antibody 1F8 suggest that this protein is the major insulin-regulatable glucose transporter expressed in skeletal muscle and other insulin-responsive tissues.

T-cell antigen receptor alpha chain polymorphisms in insulin-dependent diabetes

Insulin-dependent diabetes is a chronic autoimmune disease probably mediated by T cells. We examined the alpha chain of the T-cell antigen receptor in two models of this illness (man and BB rat) to determine any association with autoimmune diabetes. We conducted a population study in man, using a human alpha chain probe, pGA-5, and restriction enzyme Bgl 11. Two allelic forms and three RFLP patterns, 2.8 and 3.0 kb homozygous and 2.8/3.0 heterozygous, were detected. There was no difference in the frequency of these RFLPs among the 50 Type I diabetic patients and 48 controls tested. BB rats develop a spontaneous T-cell mediated autoimmune diabetes. The diabetes has been linked in several breeding studies to an undetermined autosomal recessive gene causing T-cell lymphopenia. We were able to differentiate the T-cell antigen receptor alpha chain of the diabetic BB and control BBN rats using the restriction enzyme EcoR1 and a murine alpha chain probe, TT11. The BB rat had a haplotype characterized by the presence of 4.7 and 5.8 kb bands, and the absence of 1.4, 2.2, 2.6, 3.6, 3.9, 4.1, and 6.1 kb bands. In a breeding study with BB and BBN rats, diabetic animals of the F2 generation demonstrated no linkage with the BBs' alpha chain, nor was lymphopenia linked to the alpha chain of the BB rat. These results suggest that autoimmune diabetes is not linked to the T-cell antigen receptor alpha chain in the BB rat, nor is it associated with alpha chain constant region polymorphisms in Type I diabetes in man.

The NOD mouse: recessive diabetogenic gene in the major histocompatibility complex

Examination of the histocompatibility region of the nonobese diabetic (NOD) mouse with antibodies against class II glycoproteins (products of immune response genes of the major histocompatibility complex I-A and I-E), hybrid T-cell clones, and mixed-lymphocyte cultures and analysis of restriction fragment length polymorphisms indicate that the NOD mouse has a unique class II major histocompatibility complex with no expression of surface I-E, no messenger RNA for I-E alpha, and an I-A not recognized by any monoclonal antibodies or hybrid T-cell clones studied. In crosses of NOD mice with control C3H mice, the development of diabetes was dependent on homozygosity for the NOD mouse's unique major histocompatibility region.

Major histocompatibility complex restriction fragment length polymorphisms define three diabetogenic haplotypes in BB and BBN rats

Class I and II major histocompatibility complex (MHC) probes can be used to subdivide diabetes-prone BB rats and their BBN control strain, coderived from the same outbred colony by selection against diabetes. Class II probes (A-alpha in particular) distinguish four restriction fragment length polymorphisms (RFLP), termed 1a, 1b, 2a, and 2b, in the BBN population, only one of which (2a) is found in BB rats. The degree of class II RFLP in the population studied is RT1.B-alpha greater than or equal to RT1.B-beta greater than RT1.D-alpha greater than or equal to RT1.D-beta, suggesting that intra-class II region dynamics may be different in rats compared with mice. A class I probe (S16) absolutely distinguished BB from BBN rats, since all BB rats exhibit an RFLP pattern termed 2a0, while 2a BBN rats can be subdivided into 2a1 and 2a2 forms. Serologic evaluation has shown that 2a0, 2a1, and 2a2 rats express RT1.AuBu, 1a rats express RT1.AaDa, and 1b rats express neither RT1a nor RT1u at the loci tested. A breeding study was carried out to determine the diabetogenicity of the MHC-defined RFLP's. As expected, the BB-derived 2a0 is diabetogenic. The BBN-derived 2a1 and 2a2 RFLPs are also diabetogenic, while 1a and 1b rats do not carry MHC-linked diabetogenic genes. The MHC-linked diabetes gene acts in a functionally recessive manner, since there is a 10-fold higher incidence in homozygotes than in heterozygotes. Analysis of the RFLP patterns leads us to hypothesize that the 2a1 RFLP results from a crossover between 1a and 2a0 MHCs and that the diabetogenic MHC-linked gene is on the class II side of Qa and T1. The availability of three diabetogenic MHC haplotypes should help localize the MHC-linked diabetogenic gene of rats.

Specific class II histocompatibility gene polymorphism in BB rats

The BB rat spontaneously develops insulin-dependent diabetes mellitus of autoimmune etiology. From breeding studies, one of the genes necessary for the development of diabetes in these animals is linked to RT1, the rat major histocompatibility complex. To better define the BB rat's RT1-linked diabetogenic gene (RT1-DM), we have used restriction endonucleases BamH1 and EcoR1 in conjunction with an I-A alpha (class II mouse major histocompatibility complex) gene probe to study RT1 class II gene polymorphisms among diabetes-prone BB rats and the related non-diabetes-prone BBN rats. Both BB and BBN rats are indistinguishable RT1u by serologic methods. Four polymorphic chromosome types (la, lb, lla, and llb) were recognized among the control BBN rats. In contrast, all BB rats were homozygous (lla/lla). From the multiple breeding programs involved, we hypothesize that the BB rat's RT1-linked diabetogenic gene is linked to an l-A alpha-defined gene of the type lla chromosome. The ability to split the RT1u of BB rats will provide a powerful tool to localize and characterize RT1-DM.

Class I, II and III major histocompatibility complex gene polymorphisms in BB rats

The BB rat spontaneously develops insulin-dependent diabetes mellitus of autoimmune aetiology. From breeding studies, one of the genes necessary for the development of diabetes in these animals is linked to RT1, the rat's major histocompatibility complex. To study further the RT1 linked diabetogenic gene of the BB rat, we have studied restriction fragment length polymorphism using 32P-labelled DNA probes of the major histocompatibility complex genes. As we have previously reported, an I-A alpha probe (mouse class II gene) defines four chromosome types in the control BBN population, only one of which is found among diabetes prone BB rats. All BB rats we have studied are homozygous for the type IIa chromosome. Here we examine restriction fragment length polymorphisms using three other DNA probes. Using a DC beta-probe (human class II), the same pattern of polymorphisms (though different molecular weights) is found as with the I-A alpha probe. An H-2d C4 (fourth component of complement, mouse class III) defines no polymorphisms among or between BB and BBN rats. Using H-2 LdC-2 domain probe (mouse class I) many polymorphisms are apparent and in a limited series distinguishes I-A alpha defined IIa/IIa BBN rats from IIa/IIa BB rats. These studies provide the basis to subtype the RT1u identical BB and BBN animals and should aid in the localization and characterization of the RT1 linked diabetogenic gene of the BB rat.

Two genes required for diabetes in BB rats. Evidence from cyclical intercrosses and backcrosses

The BB rat develops a syndrome of autoimmune diabetes similar to Type I diabetes of man. It also has a severe T cell lymphopenia. As part of an ongoing breeding program to transfer the diabetogenic genes of the BB rat onto inbred rat strain backgrounds, diabetic animals were used in a backcross (BC)- intercross (IC)-backcross breeding scheme with Brown Norway (BN), Lewis (L), and Wistar-Furth (WF) inbred rats. We have used monoclonal antibodies to analyze both lymphopenia and major histocompatibility (MHC) antigens (the RT1 locus in the rat) in relation to the development of diabetes. To examine T cell subsets we used a panel of monoclonal antibodies, in particular W3/25 and OX19 , which discriminate the abnormal phenotype better than W3/13. In our breeding program, at least two independent genes or gene complexes are required for the expression of diabetes. One gene determines the lymphopenia, is inherited by simple autosomal recessive genetics and is not linked to the MHC. The second gene is linked to the MHC. Both genes are necessary, but neither gene is sufficient by itself for the development of diabetes.