Defects in insulin binding and receptor kinase in cells from a woman with type A insulin resistance and from her family

Abstract

Summary.Defects in insulin receptor function lead to impairment of the insulin response. We treated a patient with the typical phenotype of type A syndrome of insulin resistance whose insulin receptor seemed to lack the transmembrane region and cytoplasmic domain. Hyperinsulinaemia and resistance to exogenous insulin were evident, and insulin binding to cells and uptake of 2-deoxyglucose into fibroblasts were greatly decreased. Molecular weight of the c~-subunit of the insulin receptor was normal, but autophosphorylation and kinase activity were impaired. In the pedigree analysis, defects in insulin binding were also observed in the mother, maternal grandfather and two maternal aunts, corresponding with the abnormality of the insulin receptor gene and mild insulin resistance. In the mother, much the same kinase defects as were seen in the patient became evident. However, no relatives had clinical symptoms similar to those seen in the patient. In the father there was a mild insulin resistance in the glucose clamp study and a borderline impaired glucose tolerance. Although insulin binding to cells was normal in the father, both autophosphorylation and kinase activity were reduced. Our findings suggest that insulin resistance in the patient may be caused by the defects in insulin receptor kinase activity as well as by a reduction in insulin binding activity.Key words: Insulin receptor, type A syndrome of insulin resistance, insulin binding, autophosphorylation, kinase activity.The action of insulin at the cellular level is initiated by insulin binding to its receptor, with which the kinase is activated [1]. These events result in phosphorylation of the ~3-subunit on the tyrosine residues, and in an increase in kinase activity toward exogenous substrates. Therefore, a defect in insulin binding and/or receptor kinase activity is closely linked to impairment of insulin action at the cellular level.Type A syndrome of insulin resistance is characterized by hyperinsulinaemia, resistance to exogenous insulin, acanthosis nigricans, polycystic ovaries and hyperandrogenism [2]. The pathogenesis of these disorders has not been clarified but alterations in the insulin receptor have been noted on both freshly isolated and cultured cells from these patients. This would suggest that a primary defect at the cellular level exists in these patients. In most patients with type A syndrome of insulin resistance, there is a decrease in the kinase activity in proportion to a decrease in receptor number [3][4][5]. In some patients, however, there is a decrease in kinase activity without alteration in insulin binding [4][5][6][7]. The complementary DNA for the insulin receptor was cloned [8,9], and genetic defects in these patients were examined by analysing the insulin receptor gene [10][11][12][13][14][15][16]. The deletion in the ATP binding site of the tyrosine kinase domain of the insulin receptor gene in patients with type A variant syndrome of insulin resistance was found to result in a decrease in kinase activity [13].In the presen...

Lipoatrophic diabetes

“…Patients with acanthosis nigricans show a type A of insulin resistance similar to that in our patient with a decreased binding of insulin [12,30,36,43,60,61] to its receptor. More is known about the insulin receptor and insulin resistance in acanthosis nigricans, which is often found in patients with lipoatrophic diabetes.…”

“…Fat tissue has now been determined to be as a target organ for the action of insulin. Reports on decreased insulin binding to its receptor and possible postreceptor defects emphasize the topical interest in this [1,12,21,30,36,43,45,48,[59][60][61]. Reports on decreased insulin binding to its receptor and possible postreceptor defects emphasize the topical interest in this [1,12,21,30,36,43,45,48,[59][60][61].…”

Insulin resistance and increased pancreatic β-cell proliferation in mice expressing a mutant insulin receptor (P1195L)

“…The tyrosine kinase domain of the IR is initially phosphorylated by insulin binding and greatly augmented by insulin-stimulated autophosphorylation (White & Kahn 1994). Various mutations in the IR gene have been identified in human subjects (Taira et al 1989, Shimada et al 1990, Suzuki et al 1991, Tritos & Mantzoros 1998, and some patients with a mutation in the tyrosine kinase domain of the IR b-subunit show hyperinsulinemia and insulin resistance. Alterations in the IR gene result in varying degrees of glucose homeostasis.…”

Abnormal messenger ribonucleic acid (mRNA) transcribed from a mutant insulin receptor gene in a patient with type A insulin resistance

“…Cloning of the normal 12 kb and abnormal 10.8 kb fragments revealed that one allele of the insulin receptor gene inherited from her mother contained a 1.2 kb deletion, including the 14th exon, and that the proband was a heterozygote of the mutant allele. Four other members of her family with the same mutation presented neither acanthosis nigricans nor hirsultism and only the proband was obese [4,5].…”

“…The structure of this gene has also been characterized [3], it is composed of 22 exons and contains over 100 kilobases (kb). We examined a patient with type A insulin resistance and found evidence for a 1.2 kb deletion in the insulin receptor gene (IR-Yamanashi) [4,5]. Several types of mutations in the insulin receptor genes have been identified in patients with insulin resistance [6][7][8][9][10][11][12][13].…”