Insulin receptors: structure and function

Evaluation of rs10811661 polymorphism in CDKN2A / B in colon and gastric cancer

One of the causes of colon and gastric cancer is the dysregulation of carcinogenic genes, tumor inhibitors, and micro-RNA. The purpose of this study is to apply rs10811661 polymorphism in CDKN2A /B gene as an effective biomarker of colon cancer and early detection of gastric cancer. As a result,400 blood samples, inclusive of 200 samples from healthy individuals and 200 samples (100 samples from intestinal cancer,100 samples from stomach cancer) from the blood of someone with these cancers, to determine the genotype of genes in healthful and ill people through PCR-RFLP approach and Allelic and genotypic tests of SPSS software. To observe the connection between gastric cancer and bowel cancer risk and genotypes, the t-student test for quantitative variables and Pearson distribution for qualitative variables have been tested and the results have been evaluated using the Chi-square test. The effects confirmed that the highest frequency of TT genotypes is in affected individuals and CC genotype is in healthful individuals. In addition, it confirmed that women were more inclined than men to T3 tumor invasion and most grade II and III colon cancers, and in older sufferers with gastric cancer, the grade of tumor tended to be grade I. Among genetic variety and rs10811661, with invasiveness, there is a tumor size and degree in the affected person. In summary, our findings suggest that the rs10811661 polymorphism of the CDKN2A / B gene is strongly associated with the occurrence of intestinal cancer and stomach is linked to its potential role as a prognostic biomarker for the management of bowel cancer and stomach.

Polymorphism of the insulin gene is associated with increased prostate cancer risk

High insulin levels are linked with increased cancer risk, including prostate cancer. We examined the associations between prostate cancer with polymorphisms of the insulin gene (INS) and its neighbouring genes, tyrosine-hydroxylase and IGF-II (TH and IGF2). In this study, 126 case-control pairs matched on age, race, and countries of origin were genotyped for +1127 INS-PstI in INS, -4217 TH-PstI in TH, and +3580 IGF2-MspI in IGF2. The homozygous CC genotype of +1127 INS-PstI occurred in over 60% of the population. It was associated with an increased risk of prostate cancer in nondiabetic Blacks and Caucasians (OR=3.14, P=0.008). The CC genotype was also associated with a low Gleason score <7 (OR=2.60, P=0.022) and a late age of diagnosis (OR=2.10, P=0.046). Markers in the neighbouring genes of INS showed only null to modest associations with prostate cancer. The polymorphism of INS may play a role in the aetiology of prostate cancer. Given the high prevalence of the CC genotype and its association with late age of onset of low-grade tumours, this polymorphism may contribute to the unique characteristics of prostate cancer, namely a high prevalence of indolent cancers and the dramatic increase in incidence with age.

Hormones and prostate cancer: current perspectives and future directions

Prostate cancer is the most commonly diagnosed non-skin cancer in men in most western countries. Despite the high morbidity and mortality from prostate cancer, its etiology remains obscure. Although compelling laboratory data suggest a role for androgens in prostate carcinogenesis, most epidemiologic data on humans are inconclusive. To provide insights and directions for future epidemiologic research on hormones and prostate cancer, this review focuses on current perspectives of serum-based studies and polymorphisms in relevant hormone-related genes. We highlight the importance of methodologic studies and investigations of hormone levels in the prostatic tissue to help clarify the often-contradictory data on serologic studies. We recommend careful analysis and cautious interpretation of studies of genetic markers, including repeats and single nucleotide polymorphisms (SNPs), as false positive and negative results may arise in many current and future studies with limited statistical power and non-representative samples from the population. The review also highlights the reasons to perform functional analyses of SNPs, a critical and often under-appreciated component of molecular epidemiologic investigations. The time is ripe for large-scale multidisciplinary investigations that incorporate molecular genetics, biochemistry, histopathology, and endocrinology into traditional epidemiologic studies. Such collaboration will lead to a deeper understanding of the etiologic pathways of prostate cancer, ultimately yielding better preventive, diagnostic, and therapeutic strategies.

Characterization of a novel receptor in toad retina with dual specificity for insulin and insulin-like growth factor I

The biochemical properties of insulin receptors from toad retinal membranes were examined in an effort to gain insight into the role this receptor plays in the retina. Competition binding assays revealed that toad retinal membranes contained binding sites that displayed an equal affinity for insulin and insulin-like growth factor I (IGF-I). Affinity labeling of toad retinal membrane proteins with 125I-insulin resulted in the specific labeling of insulin receptor alpha-subunits of approximately 105 kDa. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of partially reduced (alpha beta-heterodimer) receptors affinity-labeled with 125I-insulin indicated the presence of a disulfide-linked beta-subunit of approximately 95 kDa. Endoglycosidase F digestion of the affinity-labeled alpha-subunits increased their mobility by reducing their apparent mass to approximately 83 kDa. This receptor was not detected by immunoblot analysis with a site-specific antipeptide antibody directed against residues 657-670 of the carboxy terminal of the human insulin receptor alpha-subunit, whereas this antibody did label insulin receptor alpha-subunits from pig, cow, rabbit, and chick retinas. In in vitro autophosphorylation assays insulin stimulated the tyrosine phosphorylation of toad retina insulin receptor beta-subunits. These data indicate that toad retinal insulin receptors have a heterotetrameric structure whose alpha-subunits are smaller than other previously reported neuronal insulin receptors. They further suggest that a single receptor may account for both the insulin and IGF-I binding activities associated with toad retinal membranes.

Impaired insulin action but normal insulin receptor activity in diabetic rat liver: effect of vanadate

In vivo insulin resistance is a characteristic of the liver and peripheral tissues in 10-wk-old female rats with non-insulin-dependent diabetes induced by streptozotocin given on day 5 after birth. Oral administration of vanadate (0.2 mg/ml) for 20 days in the diabetic rats lowered their plasma glucose levels to normal values without affecting their basal plasma insulin levels. In the basal state as well as after submaximal or maximal hyperinsulinemia (euglycemic clamp studies), peripheral glucose utilization and hepatic glucose production in vivo were normalized in the diabetic rats after the vanadate treatment. In wheat germ agglutinin purified receptors, 125I-labeled porcine insulin binding, basal and insulin-stimulated insulin receptor kinase activities for both the autophosphorylation of the beta-subunit and the phosphorylation of the artificial substrate poly (Glu-Tyr) 4:1, were found identical in diabetic and control rats, treated or not with vanadate. Liver phosphoenolpyruvate carboxykinase activity was significantly enhanced in untreated diabetic rats (P less than 0.01) as compared with control rats and returned to normal values after the 20-day vanadate treatment. Thus, in that model of non-insulin-dependent diabetes, 1) oral vanadate exerts a corrective insulin-like effect on impaired insulin action both at the level of liver and peripheral tissues, 2) impaired insulin action with no alteration of the insulin receptor tyrosine kinase is observed in the liver of untreated rats, and 3) corrective effect of vanadate on liver glucose metabolism is probably distal to the insulin receptor kinase activity.

Insulin binding and insulin receptor tyrosine kinase activity are not altered in the liver of rats with non-insulin-dependent diabetes

Using the insulin-glucose clamp technique, we have previously shown that an increased sensitivity to insulin in vivo is a characteristic of the liver in rats with non-insulin-dependent diabetes induced by neonatal streptozotocin administration. We have thus studied the properties of liver insulin receptor in that model. 125I-porcine insulin binding was found normal both in isolated plasma membranes and in solubilized, wheat germ agglutinin purified receptors prepared from livers of rats with non-insulin-dependent diabetes, when compared to controls. Basal and insulin-stimulated insulin receptor kinase activities were also found normal for both the autophosphorylation of the beta subunit of the insulin receptor and the phosphorylation of the artificial substrate poly (Glu-Tyr) 4:1. Thus, in that model of chronic insulin deficiency and mild hyperglycemia: 1) liver insulin receptors are not up-regulated; 2) tyrosine kinase activity remains unaffected. This last observation supports the hypothesis that the increased insulin effect in the liver of rats with non-insulin-dependent diabetes is probably distal to the insulin receptor kinase.

Comparison of ovine and rat muscle-derived satellite cells: response to insulin

A chemically defined medium has been formulated which supports the growth (proliferation and differentiation) of rat- and ovine-derived myogenic satellite cells in vitro. Utilization of this medium in a direct comparison study in which satellite cells from both species were exposed to insulin resulted in the following observations: (1) insulin promoted the dose-dependent proliferation of primary cultures of ovine-derived but not rat-derived satellite cells and (2) rat-derived satellite cells fused to form multinucleated myotubes when exposed to increasing levels of insulin. Collectively, these observations suggest that the rat satellite cell culture system may not be an appropriate model system for extrapolating in vitro growth data to variables of ruminant skeletal muscle growth.

Specificity of tyrosine protein kinases of the structurally related receptors for insulin and insulin-like growth factor I: Tyr-containing synthetic polymers as specific inhibitors or substrates

The receptors for insulin and insulin-like growth factor (IGF) I are structurally similar transmembrane proteins. Ligand binding to the extracellular domain of the receptor stimulates its cytoplasmic tyrosine protein kinase which phosphorylates its own beta subunit as well as exogenous substrates. It is believed, from several lines of evidence, that tyrosine-specific protein kinases are mediating some or all of the actions of insulin (or IGF-I). In order to gain insights into the substrate specificity of the structurally related insulin and IGF-I receptor kinases, we have studied the action of highly purified receptors isolated from human placental membranes. Present studies using selected tyrosine-containing polymers have revealed: (i) Polymers such as (Y,A,E)n and (Y-A-E)n inhibit beta subunit autophosphorylation and exogenous substrate phosphorylation by autophosphorylated receptors. (ii) Insulin receptor kinase is at least 10 times more sensitive to these inhibitors than IGF-I receptor kinase. (iii) (Y-A-E)n is approximately 8 times more potent an inhibitor than (Y,A,E)n toward both receptors. (iv) While (E4,Y1)n and (E6,A3,Y1)n are good substrates for both receptor kinases, the ratio of phosphate incorporation into the former to the latter is characteristically high (approximately 4) for the IGF-I receptor and low (approximately 1) for the insulin receptor. These results imply that the substrate specificity and enzymatic action of these two receptor kinases are distinct.