Mutations of the human insulin receptor gene

Restricted feed intake in lactating primiparous sows. II. Effects on subsequent litter sex ratio and embryonic gene expression

Expression of panels of candidate genes controlling myogenesis, angiogenesis and gender-specific imprinting of development were analysed in embryonic, placental and endometrial tissues recovered at Day 30 of gestation from a subset of primiparous sows that were either feed restricted (Restrict; n=17) or fed to appetite (Control; n=15) during the last week of the previous lactation. Embryos were also sex typed to investigate gender bias in response to treatments. Average embryonic weight was lower in the subset of Restrict compared with Control litters (1.38±0.07vs 1.59±0.08g, respectively) and the male:female sex ratio was higher (P<0.05) in embryos (litters) recovered from Restrict sows. Treatment affected (P≤0.05) the expression of embryonic and placental genes involved in insulin-like growth factor (IGF) 2 signalling, including IGF2, INSR and IGF2R. Embryonic expression of ESR1 was also affected by treatment (P<0.03) and sex×treatment interactions were observed for the expression of embryonic ESR1 (P<0.05) and placental ANGPT2 (P<0.03). At the molecular level, these results support the suggestion that changes in placental function are not the primary mechanism mediating detrimental effects of previous sow catabolism on early embryonic development in the feed-restricted lactational sow model. However, perturbations in the IGF2 system are implicated as mediators of these effects.

Modulation of expression of insulin and IGF-I receptor by Epstein-Barr virus and its gene products LMP and EBNA-2 in lymphocyte cell lines

The receptors for insulin and insulin-like growth factor I (IGF-I) are two closely related integral membrane glycoproteins involved in signalling of cell growth and metabolism. We have used the unique paradigm of pairs of Burkitt lymphoma cell lines (BLO2, BL30, BL41) with or without Epstein-Barr Virus (EBV) infection and cells transfected with EBV-related genes to examine effects of EBV on expression of these receptors at the gene and protein functional level. In BL30 and BL41 cells, EBV infection increased surface insulin binding and total receptor number by 2- and 18-fold, respectively. By contrast, EBV infection decreased total IGF-I receptors by 29 to 87% in all three cell lines. In general, there was a correlation between total receptor concentration and the level of insulin or IGF-I receptor mRNAs, although in one cell line insulin binding increased while receptor mRNA levels decreased slightly, suggesting posttranslational effects. BL41 cells transfected with a vector expressing the EBV latent membrane protein (LMP) exhibited a 2.6- to 3.2-fold increase in insulin receptor expression, whereas cells transfected with EBNA-2 (one of the EBV nuclear antigens) alone exhibited no effect. However, EBNA-2 appears to be required for the EBV effect on insulin receptor expression since cells infected with a mutant virus, P3JHRI, which lacks the EBNA-2 gene failed to show an increase in insulin receptor number. These data indicate that EBV infection of lymphocytes increases expression of insulin receptors while simultaneously decreasing expression of IGF-I receptors. The magnitude and sometimes even the direction of change, depends on host cell factors. A maximal increase in insulin receptors appears to require the coordinate action of several of the EBV proteins including LMP and EBNA-2.

Anti-oncogenic activity of signalling-defective epidermal growth factor receptor mutants

Overexpression and autocrine activation of the epidermal growth factor receptor (EGF-R) cause transformation of cultured cells and correlate with tumor progression in cancer patients. Dimerization and transphosphorylation are crucial events in the process by which receptors with tyrosine kinase activity generate normal and transforming cellular signals. Interruption of this process by inactive receptor mutants offers the potential to inhibit ligand-induced cellular responses. Using recombinant retroviruses, we have examined the effects of signalling-incompetent EGF-R mutants on the growth-promoting and transforming potential of ligand-activated, overexpressed wild-type EGF-R and the v-erbB oncogene product. Expression of a soluble extracellular EGF-R domain had little if any effect on the growth and transformation of NIH 3T3 cells by either tyrosine kinase. However, both a kinase-negative EGF-R point mutant (HERK721A) and an EGF-R lacking 533 C-terminal amino acids efficiently inhibited wild-type EGF-R-mediated, de novo DNA synthesis and cell transformation in a dose-dependent manner. Furthermore, coexpression with the v-erbBES4 oncogene product in NIH 3T3 cells resulted in transphosphorylation of the HERK721A mutant receptor and reduced soft-agar colony growth but had no effect in a focus formation assay. These results demonstrate that signalling-defective receptor tyrosine kinase mutants differentially interfere with oncogenic signals generated by either overexpressed EGF-R or the retroviral v-erbBES4 oncogene product.

Anti-oncogenic activity of signalling-defective epidermal growth factor receptor mutants

Overexpression and autocrine activation of the epidermal growth factor receptor (EGF-R) cause transformation of cultured cells and correlate with tumor progression in cancer patients. Dimerization and transphosphorylation are crucial events in the process by which receptors with tyrosine kinase activity generate normal and transforming cellular signals. Interruption of this process by inactive receptor mutants offers the potential to inhibit ligand-induced cellular responses. Using recombinant retroviruses, we have examined the effects of signalling-incompetent EGF-R mutants on the growth-promoting and transforming potential of ligand-activated, overexpressed wild-type EGF-R and the v-erbB oncogene product. Expression of a soluble extracellular EGF-R domain had little if any effect on the growth and transformation of NIH 3T3 cells by either tyrosine kinase. However, both a kinase-negative EGF-R point mutant (HERK721A) and an EGF-R lacking 533 C-terminal amino acids efficiently inhibited wild-type EGF-R-mediated, de novo DNA synthesis and cell transformation in a dose-dependent manner. Furthermore, coexpression with the v-erbBES4 oncogene product in NIH 3T3 cells resulted in transphosphorylation of the HERK721A mutant receptor and reduced soft-agar colony growth but had no effect in a focus formation assay. These results demonstrate that signalling-defective receptor tyrosine kinase mutants differentially interfere with oncogenic signals generated by either overexpressed EGF-R or the retroviral v-erbBES4 oncogene product.

A leucine to proline mutation at position 233 in the insulin receptor inhibits cleavage of the proreceptor and transport to the cell surface

We have previously shown that a homozygous mutation encoding a substitution of proline for leucine at position 233 in the insulin receptor is linked with the syndrome of leprechaunism, being a lethal form of insulin resistance in newborn children. Specific binding of insulin and insulin-stimulated autophosphorylation of the insulin receptor are nearly absent in fibroblasts from the leprechaun patient. To examine the molecular basis of the observed insulin receptor abnormalities, CHO cell lines overexpressing mutant insulin receptors were made by transfection. The results show that the mutation inhibits cleavage and transport of the proreceptor from intracellular sites to the cell surface. As the mutant receptor is poorly precipitated by two different monoclonal antibodies recognizing epitopes on undenatured wild-type alpha-subunits, the mutation probably affects overall folding of the alpha-subunit. The mutant proreceptor is unable to bind insulin and exhibits no insulin-stimulated autophosphorylation. These data explain the abnormalities seen in the patient's fibroblasts. Pulse-chase labeling experiments on transfected cells show that the mutant precursor has an extended half-life (approximately 5 h) compared to the precursor of wild-type insulin receptors (approximately 2 h). This mutation is the first example of a naturally occurring mutation in the insulin receptor which completely blocks cleavage of the proreceptor and transport to the cell surface.

Five mutant alleles of the insulin receptor gene in patients with genetic forms of insulin resistance

The nucleotide sequence was determined for all 22 exons of the insulin receptor gene from three patients with genetic syndromes associated with extreme insulin resistance. In all three patients, insulin resistance was caused by decreased insulin binding to the cell surface. The patient with leprechaunism (leprechaun/Winnipeg) came from a consanguineous pedigree and was homozygous for a missense mutation substituting arginine for His209 in the alpha-subunit of the insulin receptor. The other two patients were both compound heterozygotes with a nonsense mutation in one allele of the insulin receptor gene, and a missense mutation in the other allele. In the patient with the Rabson-Mendenhall syndrome (patient RM-1), the missense mutation substituted lysine for Asn15 in the alpha-subunit. In the patient with type A extreme insulin resistance (patient A-1), the missense mutation substituted serine for Asn462 in the alpha-subunit. Both nonsense mutations markedly reduced the levels of insulin receptor mRNA transcribed from the alleles with the nonsense mutation as compared to the transcripts from the other allele. The reduction in the level of mRNA would be predicted to greatly reduce the rate at which the truncated receptors would be synthesized. Furthermore, the truncated receptors would be severely impaired in their ability to mediate insulin action.