Molecular scanning of the insulin receptor substrate-1 (IRS-1) gene in Japanese patients with NIDDM: identification of five novel polymorphisms

Abstract

Since the insulin receptor substrate-1 (IRS-1) is the major substrate of the insulin receptor tyrosine kinase and has been shown to activate phosphatidylinositol (PI) 3-kinase and promote GLUT4 translocation, the IRS-1 gene is a potential candidate for development of non-insulin-dependent diabetes mellitus (NIDDM). In this study, we have identified IRS-1 gene polymorphisms, evaluated their frequencies in Japanese subjects, and analysed the contribution of these polymorphisms to the development of NIDDM. The entire coding region of the IRS-1 gene of 94 subjects (47 NIDDM and 47 control subjects) was screened by polymerase chain reaction-single stranded conformation polymorphism (PCR-SSCP) analysis. Seven SSCP polymorphisms were identified. These corresponded to two previously identified polymorphisms [Gly971 --> Arg (GGG --> AGG) and Ala804 (GCA --> GCG)] as well as five novel polymorphisms [Pro190 --> Arg (CCC --> CGC), Met209 --> Thr (ATG --> ACG), Ser809 --> Phe (TCT --> TTT), Leu142 (CTT --> CTC), and Gly625 (GGC --> GGT)]. Although the prevalence of each of these polymorphisms was not statistically different between NIDDM and control subjects, the prevalence of the four IRS-1 polymorphisms with an amino acid substitution together was significantly higher in NIDDM than in control subjects (23.4 vs 8.5%, p < 0.05), and two substitutions (Met 209 --> Thr and Ser809 --> Phe) were found only in NIDDM patients. Equilibrium glucose infusion rates during a euglycaemic clamp in NIDDM and control subjects with the IRS-1 polymorphisms decreased by 29.5 and 22.0%, respectively on the average when compared to those in comparable groups without polymorphisms, although they were not statistically significant. Thus, IRS-1 polymorphisms may contribute in part to the insulin resistance and development of NIDDM in Japanese subjects; however, they do not account for the major part of the decrease in insulin-stimulated glucose uptake which is observed in subjects with clinically apparent NIDDM.

Insulin Sensitivity Is Not Affected by Mutation of Codon 972 of the Human IRS-1 Gene

“…Several polymorphisms including a codon 972 mutation of the IRS-1 gene have been reported but their diabetogenic effects are still unclear [4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18]. In this study we found that the frequency of the codon 972 mutation is 4.6% in type-2 DM patients and 4.9% in healthy control subjects.…”

“…Concerning insulin sensitivity, it was previously reported that subjects with the mutant allele have low insulin sensitivity compared to subjects without the mutation [17]. Clausen et al [10]reported on a Dannish white man who was homozygous for the mutation.…”

“…IRS-1 knockout mice showed insulin resistance [1]and animals with a simultaneous defect of glucokinase or mice with double heterozygous alleles for IRS-1 and insulin receptor genes have overt diabetes [2, 3]. In humans, several genetic variations in the coding region of IRS-1 have been identified, the most common polymorphism is the single base substitution of codon 972 (GGG→AGG) [4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18]. Dysfunction of IRS-1 by the Gly972Arg mutation was demonstrated by Almind et al [19].…”

Molecular scanning for mutations in the insulin receptor substrate-1 (IRS-1) gene in Mexican Americans with Type 2 diabetes mellitus

“…To date, several amino acid variants in the IRS-1 gene have been identi®ed in humans [31±34]. These include Ala512Pro and Gly971Arg [31], Pro170Arg, Ser809Phe and Met209Thr [32], Ser892Gly [33], and Gly819Arg and Arg1221Cys [34]. With the exception of Gly971Arg, all are rare, and are thus not likely to be major determinants of Type 2 diabetes.…”

A novel spontaneous mutation of Irs1 in mice results in hyperinsulinemia, reduced growth, low bone mass and impaired adipogenesis

“…The investigators reported a 40 % reduction in the basal levels and function of IRS -1 protein in the skeletal muscle of patients carrying this variant (Rung, Cauchi et al 2009). Likewise, there are numerous studies in humans demonstrating polymorphisms in the IRS-1 gene associated with variable responsiveness to insulin signaling (Imai, Fusco et al 1994; Ura, Araki et al 1996; Le Fur, Le Stunff et al 2002). The most common polymorphism, the G972R variant, has also been associated with type II diabetes mellitus (Almind, Bjørbaek et al 1993; Sesti 2000; Tok, Ertunc et al 2006).…”