Insulin Receptor Alternative Splicing Research Articles

FK506-Binding Protein 51 (FKBP51) Suppresses PPARα Activity and Shifts the Insulin Receptor Alternative Splicing Driving Hepatic Insulin Resistance

FK506-binding protein-51 (FKBP51) is a molecular chaperone protein that has great potential to serve as a treatment target for non-alcoholic fatty liver disease (NAFLD) and type II diabetes (T2DM). FKBP51 has been known to regulate nuclear receptors such as glucocorticoid receptor (GR) and peroxisome proliferator-activated receptor γ (PPARγ). However, the connections between FKBP51 and other PPAR family members, such as peroxisome proliferator-activated receptor α (PPARα), are yet to be identified. FKBP51 can also inhibit protein kinase B (AKT) activation, which may impact the insulin receptor signaling pathway. It has been reported that FKBP51 knockout mice presented less adiposity, reduced liver steatosis, and increased insulin sensitivity and insulin clearance, indicating that FKBP51 plays a role in insulin resistance and fatty liver development. However, how FKBP51 regulates insulin resistance, especially in the liver, still needs to be unveiled. It has been shown that insulin receptor (IR) alternative splicing is associated with insulin sensitivity and that PPARα activation is critical in reducing insulin resistance. Thus, we hypothesize that FKBP51 can regulate hepatic insulin resistance through insulin receptor alternative splicing and PPARα suppression. To test this hypothesis, we developed an FKBP51 knockout mouse hepatocyte cell line, 51KO AML12, and treated the cells with insulin for 1hr. We measured RNA and protein expressions in the cells through RT-PCR and western blotting and found that 51KO AML12 had increased phospho-AKT Ser473 (pAKT S473) and IR isoform B (IR-B), indicating increased insulin signaling activity. We also found increased IR isoform A (IR-A) and IR-B expression in 51KO AML12. In addition, we found an increased ratio of IR-B: IR-A in 51KO AML12 treated with insulin. These data indicate a great potential for FKBP51 to be a novel treatment target for hepatic insulin resistance and T2DM. This research is supported by the National Institute of Health R01DK121797 (T.D.H.), R01DA058933 (T.D.H.), and Start-Up funds from the University of Kentucky (T.D.H.). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Current Studies on Molecular Mechanisms of Insulin Resistance.

Diabetes is a metabolic disease that raises the risk of microvascular and neurological disorders. Insensitivity to insulin is a characteristic of type II diabetes, which accounts for 85-90 percent of all diabetic patients. The fundamental molecular factor of insulin resistance may be impaired cell signal transduction mediated by the insulin receptor (IR). Several cell-signaling proteins, including IR, insulin receptor substrate (IRS), and phosphatidylinositol 3-kinase (PI3K), have been recognized as being important in the impaired insulin signaling pathway since they are associated with a large number of proteins that are strictly regulated and interact with other signaling pathways. Many studies have found a correlation between IR alternative splicing, IRS gene polymorphism, the complicated regulatory function of IRS serine/threonine phosphorylation, and the negative regulatory role of p85 in insulin resistance and diabetes mellitus. This review brings up-to-date knowledge of the roles of signaling proteins in insulin resistance in order to aid in the discovery of prospective targets for insulin resistance treatment.

Splice-switching of the insulin receptor pre-mRNA alleviates tumorigenic hallmarks in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is an aggressive pediatric tumor with a poor prognosis for metastasis and recurrent disease. Large-scale sequencing endeavors demonstrate that Rhabdomyosarcomas have a dearth of precisely targetable driver mutations. However, IGF-2 signaling is known to be grossly altered in RMS. The insulin receptor (IR) exists in two alternatively spliced isoforms, IR-A and IR-B. The IGF-2 signaling molecule binds both its innate IGF-1 receptor as well as the insulin receptor variant A (IR-A) with high affinity. Mitogenic and proliferative signaling via the canonical IGF-2 pathway is, therefore, augmented by IR-A. This study shows that RMS patients express increased IR-A levels compared to control tissues that predominantly express the IR-B isoform. We also found that Hif-1α is significantly increased in RMS tumors, portraying their hypoxic phenotype. Concordantly, the alternative splicing of IR adapts to produce more IR-A in response to hypoxic stress. Upon examining the pre-mRNA structure of the gene, we identified a potential hypoxia-responsive element, which is also the binding site for the RNA-binding protein CUG-BP1 (CELF1). We designed Splice Switching Oligonucleotides (SSO) against this binding site to decrease IR-A levels in RMS cell lines and, consequently, rescue the IR-B expression levels. SSO treatment resulted in a significant reduction in cell proliferation, migration, and angiogenesis. Our data shows promising insight into how impeding the IGF-2 pathway by reducing IR-A expression mitigates tumor growth. It is evident that Rhabdomyosarcomas use IR alternative splicing as yet another survival strategy that can be exploited as a therapeutic intervention in conjunction with already established anti-IGF-1 receptor therapies.

Tissue‐specific expression of insulin receptor isoforms in obesity/type 2 diabetes mouse models

The two insulin receptor (IR) isoforms IR‐A and IR‐B are responsible for the pleiotropic actions of insulin and insulin‐like growth factors. Consequently, changes in IR isoform expression and in the bioavailability of their ligands will impact on IR‐mediated functions. Although alteration of IR isoform expression has been linked to insulin resistance, knowledge of IR isoform expression and mechanisms underlying tissue/cell‐type‐specific changes in metabolic disease are lacking. Using mouse models of obesity/diabetes and measuring the mRNA of the IR isoforms and mRNA/protein levels of total IR, we provide a data set of IR isoform expression pattern that documents changes in a tissue‐dependent manner. Combining tissue fractionation and a new in situ mRNA hybridization technology to visualize the IR isoforms at cellular resolution, we explored the mechanism underlying the change in IR isoform expression in perigonadal adipose tissue, which is mainly caused by tissue remodelling, rather than by a shift in IR alternative splicing in a particular cell type, e.g. adipocytes.

Abstract B39: Modulation of insulin receptor alternative splicing to develop cancer therapeutics

Abstract Insulin receptor (IN-R) undergoes alternative splicing to produce two isoforms: the full-length IN-RB and exon 11 skipped IN-RA isoform. While IN-RB has high affinity for insulin and much lower affinity for IGF1 or IGF2 ligands, IN-RA binds both insulin and IGF2 with high affinity and as such it exploits the IGF pathway to accelerate the onset of tumor-cell hallmarks such as proliferation and angiogenesis. Our data show that there is a significantly increased expression of IN-RA levels in multiple cancer patient cohorts, including rhabdomyosarcoma (RMS) and osteosarcoma (OS). We also found this increased IN-RA expression in tumor cell lines derived from multiple different pediatric tumor types such as RMS, OS, and Ewing’s sarcoma as compared to the control samples. Additionally, our data show that cellular stress such as hypoxia increases the expression of the IN-RA isoform. Adaptation to hypoxic environments is a hallmark of the neoplastic phenotype, and pediatric sarcomas exhibit an intrinsically hypoxic physiology. However, how the INR alternatively spliced mRNAs are regulated is not well understood, nor is the role that these isoforms play in the initiation and progression and therapeutic resistance of human cancer. Our central hypothesis is that hypoxia alters the expression of splicing factors, leading to the generation of the IN-RA isoform, which contributes to cancer progression beyond the micrometastatic stage. We used an insulin receptor mini-gene system to identify a binding site for the RNA binding protein cugbp, critical for the hypoxia-induced splicing regulation of IN-R. We targeted the cugbp binding site using an antisense oligonucleotide (ASO) walk to identify an ASO that binds to the cugbp binding site in the intron 10 of INR gene and modulates the levels of endogenous IN-RA. To allow the possibility for therapeutic intervention, we utilized this ASO in OS cell lines. We found that the application of ASO shifts the IN-R splicing towards IN-RB and significantly reduces proliferation, migration, and angiogenesis in cancer cell lines. In order to delineate the downstream consequences of this splicing change, we subjected the control and ASO-treated cells to mass spectrometric analysis. Preliminary analysis of this data reveals that proliferation markers such as Ki67, PI3-kinase pathway components, protein clusters such as cell-cell adhesion, and cell division, among others, are significantly downregulated in cells treated with ASO where the splicing has been restored to the IN-RB isoform. Our data open a new paradigm of how alternative splicing regulates cell signaling to mediate cancer-causing changes, and our ASO compounds show promising insight into how we can reinstate the splicing pattern and impede tumorigenesis. Citation Format: Safiya Khurshid, Matias Montes, Brianne Sanford, Peter Houghton, Frank Rigo, Dawn Chandler. Modulation of insulin receptor alternative splicing to develop cancer therapeutics [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr B39.

Abstract 2639: Insulin receptor alternative splicing during development and cancer

Abstract It has been shown that alternative splicing of some genes changes during development from embryogenesis to adulthood. Intriguingly, transformation of cells is also often accompanied by a reversion to the embryonic spliced isoforms. Insulin receptor (IN-R) undergoes alternative splicing to produce two isoforms: the full-length IN-RB isoform and the exon 11-skipped IN-RA isoform. The IN-RB isoform encodes a receptor with high affinity for insulin, while the IN-RA isoform has high affinity for both insulin & IGF2 growth hormones. IN-RAexploits the IGF pathway to accelerate growth, proliferation and angiogenesis. It is known that during embryogenesis the IN-R gets spliced to primarily express the INR-A form. Recently, the A isoform has has also been shown to be expressed in certain cancer types. Because the insulin receptor signaling converges on the mTOR/AKTpathway that is one of the most critical pathways for organismal development as well in cancer, it is important to understand the expression of these isoforms and their role in signaling and cellular fate. However, a tissue and a temporal description of the expression of these two isoforms is lacking. Towards this end we have shown that the mouse insulin receptor gene is spliced similarly to the human gene and have used the mouse model to study IR splicing during development. We harvested tissues from mice at different developmental stages (E10, E18, P1, P7, 3 months and 6 months) and performed RT-PCR for the insulin receptor gene. Our data confirmed that the whole embryos at embryonic day 10 (E10) express mostly IN-RA (90%). However, as the embryo develops and we can obtain discrete tissues we are able to detect tissue-specific profiles of IN-Rsplicing. For example, in bone at E18 as well as postnatal day P1 and 7, IN-RBis highly expressed (65%) and decreases to (40%) as the mouse reaches 6 months of age. Likewise, the liver and pancreas, which are primarily involved with metabolic functions, express mostly IN-RB(90%) from postnatal day P1 and into adult hood (6 months). In contrast, when we analyzed IR-splicing in human cancers, we find that in both liver cancer and cancers of the bone (osteosarcoma and Ewing’s sarcoma) there is a shift toward increased levels of the pro-proliferative isoform, IN-RA. We believe that understanding the molecular underpinnings of the splicing regulation during development will provide us with knowledge that will help us better understand the transformation process and how to control it, possibly through splicing corrective therapy. Citation Format: Safiya Khurshid. Insulin receptor alternative splicing during development and cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2639.

P.274 - Post-receptor abnormalities contribute to peripheral insulin resistance in myotonic dystrophy type 1 and type 2

Myotonic dystrophies are autosomal dominant disorders characterized by a variety of multisystemic features including metabolic dysfunctions such as insulin resistance, hyperinsulinemia and a fourfold higher risk of developing Diabetes mellitus type 2. DMs are caused by expanded CTG or CCTG repeats which lead to nuclear accumulation of mutant transcripts deregulating the activity of some splicing regulators and leading to aberrant alternative splicing of different genes. Splicing alteration of insulin receptor (IR) gene is considered one of the causes of metabolic dysfunctions, however it cannot be excluded that post-receptor signalling abnormalities could also contribute to this feature of DM. The aim of this work is to investigate the mechanisms that contribute to the peripheral insulin resistance in DMs. The basal activation of several proteins involved in the insulin pathway has been analysed by western blot in proximal and distal muscles from 6 DM1, 5 DM2 and 7 healthy subjects. Insulin receptor alternative splicing has been analysed by RT-PCR. Our results indicate that DM skeletal muscle exhibits high basal activation of some proteins involved in the insulin pathway. To study if these changes are accompanied by a lack of further insulin stimulation the analysis of insulin pathway activation was performed on myotubes derived from myoblasts isolated from muscle biopsies of 5 DM1, 5 DM2, 5 healthy 2 T2DM subjects. Our results indicate that, despite the similar expression of foetal IR isoform, insulin action appears to be impaired in DM myotoubes in terms of protein activation and glucose uptake. In conclusion, these data indicate that post receptor signalling abnormalities might contribute to DM insulin resistance. Further investigations will be necessary to identify novel biomarkers that could be target for therapeutic intervention to improve the quality of life of DM patients.

Abstract 49: Modulating insulin receptor splicing as a potential therapeutic approach for rhabdomyosarcoma

Abstract The insulin receptor (IN-R) is subject to alternative splicing to produce two isoforms: the full-length IN-R B isoform and an isoform lacking exon 11 known as IN-R A which is the predominant isoform expressed in sarcoma cells. This short exon encodes for 12 amino acids but the resulting receptor has high affinity for a growth hormone called insulin-like growth factor 2 (IGF2), which exquisitely responds to autocrine and paracrine signaling. Increased IN-R A levels observed in rhabdomyosarcoma (RMS) coupled with increased expression of IGF2, programs the tumor cell for enhanced growth and angiogenesis, two important factors in tumorigenesis. Furthermore, IGF2 can maintain angiogenesis through IN-R A when the cognate receptor for IGF2, the IGF-1 receptor, is blocked. Interestingly we have shown that hypoxia increases alternative splicing to produce more IN-R A. This is an interesting finding since adaptation to the hypoxic environment is a hallmark of the neoplastic phenotype. Therefore, we hypothesize that expression of splicing factors is altered under hypoxic conditions which leads to increased alternative splicing and generation of IN-R A, allowing the cancer cells a growth advantage which contributes to metastasis beyond the micrometastatic phase. To characterize sequence elements and splicing factors involved in the regulation of IN-R alternative splicing, we have developed a hypoxia-inducible splicing system, which recapitulates the splicing patterns observed in tumors. We have shown that sequence elements preceding exon 11 are critical to the increased alternative splicing we see under hypoxic conditions. As such, we have targeted these regions for antisense oligonucleotide (ASO) development to increase full-length splicing of IN-R, with the goal of restricting proliferative signaling by IGF2 activation of IN-R A. We performed an ASO walk to target regions important for exon inclusion or exclusion and have successfully targeted a region known to be a binding site for the splicing factor CUGBP1. RMS-derived cell lines almost exclusively express IN-R A but when treated with our lead ASO compound we see a dramatic decrease in alternative splicing resulting in increased levels of the full-length insulin receptor. We have also shown that RMS-derived cells treated with our splice modulating ASO exhibit reduced cell proliferation and migratory properties. With these promising data we postulate that modulation of IN-R splicing can be used in conjunction with already established anti-IGF-1 receptor therapies in the treatment of RMS. Citation Format: Brianne Sanford, Chelsea Brown, Hemant Bid, Thomas Beebe, Daniel Comiskey, Frank Rigo, Peter Houghton, Dawn Chandler. Modulating insulin receptor splicing as a potential therapeutic approach for rhabdomyosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 49. doi:10.1158/1538-7445.AM2017-49

Insulin receptor alternative splicing is regulated by insulin signaling and modulates beta cell survival.

Type 2 Diabetes (T2DM) affects more than 300 million people worldwide. One of the hallmarks of T2DM is peripheral insulin resistance, in part due to unproductive insulin signaling through the insulin receptor. The insulin receptor (INSR) exists as two isoforms, INSR-A and INSR-B, which results from skipping or inclusion of exon 11 respectively. What determines the relative abundance of the different insulin receptor splice variants is unknown. Moreover, it is not yet clear what the physiological roles of each of the isoforms are in normal and diseased beta cells. In this study, we show that insulin induces INSR exon 11 inclusion in pancreatic beta cells in both human and mouse. This occurs through activation of the Ras-MAPK/ERK signaling pathway and up-regulation of the splicing factor SRSF1. Induction of exon 11 skipping by a splice-site competitive antisense oligonucleotide inhibited the MAPK-ERK signaling pathway downstream of the insulin receptor, sensitizing the pancreatic β-cell line MIN6 to stress-induced apoptosis and lipotoxicity. These results assign to insulin a regulatory role in INSR alternative splicing through the Ras-MAPK/ERK signaling pathway. We suggest that in beta cells, INSR-B has a protective role, while INSR-A expression sensitizes beta cells to programmed cell death.

Abstract LB-014: Targeting insulin receptor splicing as a therapeutic intervention for pediatric rhabdomyosarcoma

Abstract The insulin receptor (IN-R) alternatively spliced variant A, encoding a receptor lacking exon 11, is the predominant isoform expressed in both pediatric sarcoma cells and vascular endothelial cells. Exon 11 of the IN-R gene is composed of 36 nucleotides that encode 12-amino acids that reside at the carboxyl terminus of the alpha subunit. Though only a small change in the protein composition, deletion of these 12 amino acids results in a receptor that has increased binding affinity for the IGF-2 growth factor and is exquisitely capable of responding to autocrine and paracrine signaling. Cells expressing both the IN-R A variant and the IGF-2 growth factor are therefore programmed for growth and angiogenesis, two essential steps in tumorigenesis. Furthermore, the IGF-2 can maintain angiogenesis through IN-R A when the IGF-1 receptor is blocked. We also demonstrate that hypoxia induces IN-R alternative splicing. This finding is particularly intriguing since recent studies have shown that adaptation to hypoxic environments is a hallmark of the neoplastic phenotype. We therefore hypothesize that the expression of splicing factors is altered by hypoxia leading to the generation of the IN-R A isoform, which contributes to cancer progression beyond the micrometastatic stage. To characterize sequence elements and RNA binding proteins in the regulation of IN-R alternative splicing, we have designed a hypoxia-induced splicing system that recapitulates the IN-R splicing seen in tumors. We have shown that sequence elements flanking the regulated exon are important for the hypoxia-induced splicing changes. Furthermore, have performed an antisense oligonucleotide (ASO) walk to target these splicing enhancer and repressor sequences to interfere with IN-R splicing. We have successfully targeted the CUGBP1 negative regulator of splicing that resides in intron 10 to increase the IN-R B full-length isoform. We have shown that an ASO used to drive production of the IN-R B isoform in a rhabdomyosarcoma (RMS) cell line, which normally expresses the IN-R A isoform, affects cancer cell behavior to induce reduced motility and cell migration. We therefore postulate that modulation of the splicing of the IN-R, alone or in conjunction with IGF-1R blocking antibodies, could be used as a therapeutic intervention in pediatric RMS cells. Citation Format: Dawn S. Chandler, Chelsea Brown, Hemant Bid, Thomas Bebee, Daniel F. Comiskey, Frank Rigo, Peter J. Houghton. Targeting insulin receptor splicing as a therapeutic intervention for pediatric rhabdomyosarcoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-014.

Abstract 4238: Exploring the therapeutic potential of IR and IGF-1R/IR (co-)targeting in ovarian cancer

Abstract Ovarian cancer is the most lethal gynecological malignancy. Despite high response rates to platinum based therapies most patients relapse with resistant disease. For these patients novel therapeutic strategies are needed. Hyper-activation of the insulin-like growth factor receptor (IGF-1R) has been implicated in the development, progression and platinum resistance of ovarian cancer. However, targeting the IGF-1R has shown limited clinical benefit. The insulin receptor (IR), highly homologous to the IGF-1R, confers resistance to IGF-1R targeted therapies. Furthermore, in ovarian cancer alternative splicing results in the expression of IR-A & IR-B isoforms, while in normal adult tissues IR-B is the predominant isoform. Therefore targeting the IR or IR-A may be of clinical importance. In this study we determined the therapeutic potential of IR targeting in ovarian cancer. First, the expression levels of the IR isoforms, IGF-1R and stimulatory ligands IGF-I & II were determined in a panel of ovarian cancers and ovarian cancer cell lines of different histological subtype (endometrioid, clear cell, serous) using RT-PCR. IR isoforms and IGF-1R were expressed in 96% (43/44) and 78% (35/44) of the ovarian cancers compared to 89% (8/9) and 100% (9/9) of the ovarian cancer cell lines. IGF-I and IGF-II were expressed in all the ovarian cancers compared to 11% (1/9) and 0% (0/9) of the ovarian cancer cell lines, indicating the presence of an autocrine loop. In addition, all cell lines showed membrane receptor expression and functional downstream signaling upon IGF-I, IGF-II & insulin, via PI3K as determined by western blot and flow cytometry. Subsequently, we investigated which splicing factors may be involved in the IR alternative splicing. Expression of splicing factors (hnRNPA1A, hnRNA2B1, CELF1, SRSF1, hnRNPH, hnRNPF) were determined by qRT-PCR. However, expression levels did not correlate with IR isoform levels, indicating a more complex regulation of IR splicing. Finally, we determined the effect of IR, IGF-1R and IR/IGF-1R (co-)targeting by S961 (1000nM), MAB391 (20µg) and OSI906 (10µM), respectively on ovarian cancer cell survival by MTT and clonogenic assays. IR inhibition by S961 resulted in a decrease in cell viability up to 40% in 7/9 ovarian cancer cell lines. Preliminary data showed similar results upon IGF-1R/IR inhibition with OSI906. IGF-1R inhibition by MAB391 did not affect cell viability. Furthermore a reduction in clonogenic capacity (75%) by OSI906 is observed in 2/3 ovarian cancer cell lines tested. In conclusion, in ovarian cancer functional IR and IGF-1R signaling as well as the presence of a possible autocrine loop may contribute to ovarian cancer pathogenesis and progression. Targeting IR signaling with the IR-antagonist S961 and co-targeting IR/IGF-1R signaling by OSI906 reduced ovarian cancer cell viability, indicating its therapeutic potential in ovarian cancer. Funded by the Dutch Cancer Foundation: Grant RUG 2011-5231 Citation Format: Jolanda A.L. Visser, Roelien A.M. Meijering, Anne K.L. Reyners, Ate G.J. van der Zee, Steven de Jong. Exploring the therapeutic potential of IR and IGF-1R/IR (co-)targeting in ovarian cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4238. doi:10.1158/1538-7445.AM2014-4238

Regulation of chloride ion conductance during skeletal muscle development and in disease. Focus on “Chloride channelopathy in myotonic dystrophy resulting from loss of posttranscriptional regulation for CLCN1”

productive investigations of disease mechanisms that also reveal new information about normal regulation elicit a particularly satisfying sense of a two-for-one deal. In the case of Lueck et al. (Ref. [13][1]; see page 1291 of this issue), a detailed study of the molecular basis for the myotonia (

Aberrant regulation of insulin receptor alternative splicing is associated with insulin resistance in myotonic dystrophy.

Myotonic dystrophy type 1 (DM1) is caused by a CTG trinucleotide expansion in the 3' untranslated region of the DM protein kinase gene. People with DM1 have an unusual form of insulin resistance caused by a defect in skeletal muscle. Here we demonstrate that alternative splicing of the insulin receptor (IR) pre-mRNA is aberrantly regulated in DM1 skeletal muscle tissue, resulting in predominant expression of the lower-signaling nonmuscle isoform (IR-A). IR-A also predominates in DM1 skeletal muscle cultures, which exhibit a decreased metabolic response to insulin relative to cultures from normal controls. Steady-state levels of CUG-BP, a regulator of pre-mRNA splicing proposed to mediate some aspects of DM1 pathogenesis, are increased in DM1 skeletal muscle; overexpression of CUG-BP in normal cells induces a switch to IR-A. The CUG-BP protein mediates this switch through an intronic element located upstream of the alternatively spliced exon 11, and specifically binds within this element in vitro. These results support a model in which increased expression of a splicing regulator contributes to insulin resistance in DM1 by affecting IR alternative splicing.