Expression Of Insulin Receptor Isoforms Research Articles

Increased Expression of Insulin Receptor Isoform a (IR-a) and Insulin Receptor Substrate 1 (IRS1) in Poorly Differentiated Colon Cancer Cell Lines and APC MIN/+ Tumors

Increased Expression of Insulin Receptor Isoform a (IR-a) and Insulin Receptor Substrate 1 (IRS1) in Poorly Differentiated Colon Cancer Cell Lines and APC MIN/+ Tumors

Abstract 327: Altered expression of insulin receptor isoforms in breast cancer

Abstract Human insulin receptor (INSR) isoform A (IR-A), one of the two primary isoforms of INSR, constitutes an important therapeutic target for the development of anticancer drugs. There is also crucial need to develop a quick and sensitive method to accurately measure each of the two isoforms in humans. A specific quantitative real-time PCR-based assay has been developed to distinguish IR-A from insulin receptor isoform B (IR-B). This assay provides greater sensitivity, reproducibility, and clinical applicability than previously established methodologies. We used this assay to evaluate the mRNA expression levels of the IR-A and IR-B as well as multiple tumor proliferation markers in breast tumor tissues. Results revealed a significant decrease in IR-B mRNA expression leading to a relative increase in IR-A mRNA proportion in tumor samples compared to normal breast tissue samples. We also identified a novel positive correlation between increased IR-A: IR-B mRNA ratio and cancer proliferation markers, including Ki67. Furthermore, we observed a statistically significant difference of IR-A: IR-B mRNA ratio between luminal-A and -B breast cancer subtypes. These results suggest that IR-A is the predominant isoform of insulin receptor in breast cancer and highlights the potential value of characterizing changes in the IR-A: IR-B mRNA ratio as a therapeutic indicator for drugs that target insulin growth factor. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 327. doi:10.1158/1538-7445.AM2011-327

Expression of insulin receptor isoform A and insulin-like growth factor-1 receptor in human acute myelogenous leukemia: effect of the dual-receptor inhibitor BMS-536924 in vitro.

The insulin receptor (IR) and insulin-like growth factor-1 receptor (IGF1R) are receptor tyrosine kinases that participate in mitogenic and antiapoptotic signaling in normal and neoplastic epithelia. In the present study, immunoblotting and reverse transcription-PCR demonstrated expression of IGF1R and IR isoform A in acute myelogenous leukemia (AML) cell lines as well as in >80% of clinical AML isolates. Treatment with insulin enhanced signaling through the Akt and MEK1/2 pathways as well as survival of serum-starved AML cell lines. Conversely, treatment with BMS-536924, a dual IGF1R/IR kinase inhibitor that is undergoing preclinical testing, inhibited constitutive receptor phosphorylation as well as downstream signaling through MEK1/2 and Akt. These changes inhibited proliferation and, in some AML cell lines, induced apoptosis at submicromolar concentrations. Likewise, BMS-536924 inhibited leukemic colony formation in CD34+ clinical AML samples in vitro. Collectively, these results not only indicate that expression of IGF1R and IR isoform A is common in AML but also show that interruption of signaling from these receptors inhibits proliferation in clinical AML isolates. Accordingly, further investigation of IGF1R/IR axis as a potential therapeutic target in AML appears warranted.

Expression of insulin receptor isoforms in honey bee (Apis mellifera) caste development

Expression of insulin receptor isoforms in honey bee (Apis mellifera) caste development

Differential gene expression of insulin receptor isoforms A and B and insulin receptor substrates 1, 2 and 3 in rat tissues: modulation by aging and differentiation in rat adipose tissue

The insulin receptor (IR) occurs as two alternatively spliced isoforms, IR-A (exon 11-) and IR-B (exon 11+), which exhibit functional differences and are expressed in a tissue-specific manner. The IR substrate (IRS) proteins 1, 2 and 3 also differ in function and tissue distribution. Here we show the differential gene expression of IRs and IRSs in several rat target tissues of insulin action. IR-B is significantly higher than IR-A in epididymal white adipose tissue and adipogenesis induces a shift in the alternatively spliced species of IR from the A to the B isoform. Moreover, since aging in the rat is associated with the development of insulin resistance we looked for alterations of expression of these proteins in adipocytes from old rats. Our results reveal that there is a specific decrease in the expression of the IR-B isoform, as well as both mRNA and protein levels of IR, IRS-1 and IRS-3 being significantly decreased, in epididymal adipose tissue from old compared with adult rats. It is concluded that the down-regulation of early components of the insulin transduction pathway in a primary insulin target tissue could be related to the insulin resistance of aging.

Insulin and messenger ribonucleic acid expression of insulin receptor isoforms in ovarian follicles from nonhirsute ovulatory women and polycystic ovary syndrome patients.

Insulin action is mediated by two insulin receptor (IR) isoforms, differing in mitogenic and metabolic function. IR isoform expression might occur in human granulosa cells and could be altered in polycystic ovary syndrome (PCOS) from hyperinsulinemia. To determine the relationship between granulosa cell IR isoform expression and follicular fluid insulin concentration in individual follicles, 18 normal women and seven PCOS patients receiving gonadotropins for in vitro fertilization were studied. Glucose tolerance testing was performed before pituitary desensitization, and fasting serum insulin was measured at oocyte retrieval. Granulosa cells and fluid aspirated from the first follicle were used to determine IR isoform mRNA expression and insulin concentration, respectively. IR isoform A mRNA expression was greater than that of IR isoform B expression in normal mural granulosa and cumulus cells, without a cell type effect. Intrafollicular insulin levels increased with adiposity and serum insulin levels at oocyte-retrieval but did not predict IR mRNA expression. Total IR mRNA expression, but not intrafollicular insulin levels, was elevated in PCOS patients, whereas intrafollicular insulin levels were increased in women with impaired glucose tolerance. Granulosa cell IR heterogeneity, together with adiposity-dependent intrafollicular insulin availability, introduces a novel mechanism by which insulin may affect granulosa cell function within the follicle.

The mRNA expression of insulin receptor isoforms (IR-A and IR-B) and IGFR-2 in the bovine corpus luteum during the estrous cycle, pregnancy, and induced luteolysis.

Isoform A of the human insulin receptor and the IGF-receptor type 2 (IGFR-2) are both receptors for insulin- like growth factor II (IGF II), which plays a major role in luteal development and function in bovine species. The objective of this study was to determine if both insulin receptor isoforms and IGFR-2 were expressed in the bovine corpus luteum (CL) and if they were regulated during the estrous cycle, pregnancy, and induced luteolysis. CL were collected at the slaughterhouse. For induced luteolysis, CL were obtained by transvaginal ovariectomy at 2, 4, 12, 48, and 64 h after prostaglandin (PG) F2alpha-injection. Real-time RT-PCR was applied to investigate mRNA expression. Two alternatively spliced transcripts encoding the insulin receptor were detected in bovine CL. These two isoforms corresponded to the known isoforms A (IR-A) and B (IR-B) in humans. IR-A mRNA predominated in bovine CL and was significantly down-regulated on d 5-7. IR-B mRNA was significantly up-regulated in the late luteal stage and during early pregnancy. IR-A showed a significant down-regulation at 48 h after PGF2. IGFR-2 mRNA was significantly up-regulated in mid and late luteal stages (d 8-18). It is proposed that the differential mRNA expression of IR-A and IGFR-2, both binding IGF II, may play a role in the development and function of the bovine corpus luteum.

Tissue-specific differences in insulin receptor m-RNA isoform ratio in two dairy cow breeds

The insulin receptor (IR) is one participant in the partitioning of absorbed nutrients to, and between, the insulin-responsive tissues of animals. We previously reported the alternative splicing of a 36 base pair exon 11 segment of the sheep IR gene and found differences in the ratio of the resultant 11 m-RNA and 11+m-RNA isoforms between muscle and fat depots in crossbred, but not purebred, Texel lambs (McGrattan et al., 1998). Because the IR isoforms, when expressed in cultured cell lines, differ in affinity for insulin by two fold or more (McClain, 1991), variations in the ratio of IR isoform expression may have practical significance for the partitioning of nutrients between tissues and thus for differences in lean and fat gain between the purebred and crossbred lambs. Similarly, variation in IR m-RNA isoform ratios amongst the adipose depots in different breeds of dairy cow could have practical significance for differences in the ability of the breeds to store and mobilise energy and thus for differences in lactational performance between dairy breeds. This study is a preliminary investigation of this hypothesis.

The sulfonylurea glimepiride regulates intracellular routing of the insulin-receptor complexes through their interaction with specific protein kinase C isoforms.

Sulfonylureas may stimulate glucose metabolism by protein kinase C (PKC) activation. Because interaction of insulin receptors with PKC plays an important role in controlling the intracellular sorting of the insulin-receptor complex, we investigated the possibility that the sulfonylurea glimepiride may influence intracellular routing of insulin and its receptor through a mechanism involving PKC, and that changes in these processes may be associated with improved insulin action. Using human hepatoma Hep-G2 cells, we found that glimepiride did not affect insulin binding, insulin receptor isoform expression, and insulin-induced receptor internalization. By contrast, glimepiride significantly increased intracellular dissociation of the insulin-receptor complex, degradation of insulin, recycling of internalized insulin receptors, release of internalized radioactivity, and prevented insulin-induced receptor down-regulation. Association of PKC-betaII and -epsilon with insulin receptors was increased in glimepiride-treated cells. Selective depletion of cellular PKC-betaII and -epsilon by exposure to 12-O-tetradecanoylphorbol-13-acetate (TPA) or treatment of cells with PKC-betaII inhibitor G06976 reversed the effect of glimepiride on intracellular insulin-receptor processing. Glimepiride increased the effects of insulin on glucose incorporation into glycogen by enhancing both sensitivity and maximal efficacy of insulin. Exposing cells to TPA or G06976 inhibitor reversed these effects. Results indicate that glimepiride increases intracellular sorting of the insulin-receptor complex toward the degradative route, which is associated with both an increased association of the insulin receptor with PKCs and improved insulin action. These data suggest a novel mechanism of action of sulfonylurea, which may have a therapeutic impact on the treatment of type 2 diabetes.

Expression of the two insulin receptor isoforms is not altered in the skeletal muscle and liver of diabetic rats

Alternative splicing of the 36—base pair exon 11 of the human insulin receptor (IR) gene and of the corresponding domain of the rat IR gene results in the synthesis of two IR isoforms with distinct functional characteristics. Altered expression of these IR isoforms has been previously demonstrated in the skeletal muscle of patients with non—insulin-dependent diabetes mellitus (NIDDM); however, this observation was not confirmed by other studies and is still a matter of debate. To assess whether the reported altered isoform expression is due to the secondary metabolic derangement of diabetes, we examined alternative splicing of IR mRNAs (IR36 + and IR36 −, corresponding to human Ex11 + and Ex11 −) in the skeletal muscle and liver of 6-hour fasting 90% pancreatectomized insulin-resistant diabetic and control Sprague-Dawley rats, using the reverse transcriptase—polymerase chain reaction (PCR) technique. Both diabetic and control rats showed the same pattern of IR mRNA expression: the liver exclusively expressed IR36 + mRNA, whereas only IR36 − mRNA was detected in muscle. In conclusion, diabetes mellitus per se does not alter the expression of IR isoforms in the liver and skeletal muscle, and therefore, at least in this animal model of NIDDM, impaired insulin action develops independently from a relative increase in IR36 + mRNA expression in skeletal muscle.

No difference in the proportion of insulin receptor exon 11 +/- isoform mRNA in the liver of rats after development of hypertension.

1. There are two functionally different isoforms of the insulin receptor in humans and rats. We hypothesized that a change in their relative proportion could be of relevance to insulin resistance in hypertension. 2. A reverse-transcriptase polymerase chain reaction technique was established for the detection of mRNA for the exon 11+ and exon 11- isoforms and the proportion of each was determined in 3, 6, 9 and 12 week old spontaneously hypertensive rats and Wistar-Kyoto rats, as well as adrenocorticotrophin (ACTH)-induced hypertensive rats and controls. 3. The proportion of the exon 11+ form (approximately 95%) and exon 11- form (approximately 5%) was similar in the liver of all rats studied. 4. We conclude that there is no change in insulin receptor isoform expression in the liver in the models of hypertension studied.

Insulin- and insulin-like growth-factor-I receptor tyrosine-kinase activities in human renal carcinoma.

We studied expression and functional characteristics of the insulin- and insulin-like-growth-factor-I (IGF-I) receptors in human renal carcinoma. Ligand-binding properties and tyrosine-kinase activity of both receptors, as well as the expression of the 2 isoforms of the human insulin receptor (HIR-A and -B) were analyzed in renal carcinoma and normal adjacent kidney tissue of 8 adult patients. Partially purified insulin- and IGF-I receptors from normal and renal cell carcinoma tissue possessed identical affinities for their ligands. Renal cell carcinoma, however, contained 3- to 4-fold more specific insulin-binding sites and 2-fold more IGF-I binding sites than adjacent normal kidney tissue. In addition, we determined the relative content of insulin/IGF-I receptor hybrids in both tissues. Renal cell carcinoma and adjacent normal tissue revealed similar amounts of insulin/IGF-I receptor hybrids, i.e., 44 +/- 8.2% of tracer IGF-I binding in normal tissue and 46 +/- 12.0% in renal cell carcinoma. When equal amounts of insulin- and IGF-I receptor protein were studied, we found significantly increased receptor autophosphorylation and elevated substrate phosphorylation in carcinoma tissue. To assess whether the differences in insulin-receptor tyrosine-kinase activity were caused by an altered pattern of insulin receptor isoform expression, we determined mRNA levels for HIR-A and -B. The 2 insulin receptor isoforms were, however, expressed in highly variable ratios in both normal and tumor tissue. Our experiments show that renal carcinoma expresses an elevated amount of insulin- and IGF-I receptor protein with increased specific autophosphorylation and tyrosine-kinase activity each. The increase of insulin-receptor tyrosine-kinase activity in renal carcinoma cannot be explained by an altered expression pattern of insulin receptor isoforms.

Relative expression of insulin receptor isoforms does not differ in lean, obese, and noninsulin-dependent diabetes mellitus subjects.

The insulin receptor is expressed as two isoforms that differ by a 12-amino acid region at the carboxy-terminus of the alpha-subunit encoded by exon 11. These isoforms are produced by tissue-specific alternate splicing of the insulin receptor mRNA. To determine whether the relative expression of the isoforms is altered in skeletal muscle in two insulin-resistant states, NIDDM and obesity, relative mRNA levels were measured using a polymerase chain reaction technique. There were no differences in the relative amounts of skeletal muscle mRNA encoding the exon 11-containing form compared to the exon 11-lacking form of the insulin receptor among lean normal (30 +/- 2% Ex11-), obese nondiabetic (32 +/- 2%), and NIDDM (31 +/- 1%) subjects. We conclude that altered expression of insulin receptor isoform mRNAs does not account for skeletal muscle insulin resistance in NIDDM and obesity.

Relative expression of insulin receptor isoforms does not differ in lean, obese, and noninsulin-dependent diabetes mellitus subjects

Relative expression of insulin receptor isoforms does not differ in lean, obese, and noninsulin-dependent diabetes mellitus subjects