Activation Of IGF-1 Receptor Signaling Research Articles

Suppression of Cardiac Autophagy by Hyperinsulinemia in Insulin Receptor-Deficient Hearts Is Mediated by Insulin-Like Growth Factor Receptor Signaling.

Aims: Autophagy is a catabolic process required for the maintenance of cardiac health. Insulin and insulin-like growth factor 1 (IGF-1) are potent inhibitors of autophagy and as such, one would predict that autophagy will be increased in the insulin-resistant/diabetic heart. However, autophagy is rather decreased in the hearts of diabetic/insulin-resistant mice. The aim of this study is to determine the contribution of IGF-1 receptor signaling to autophagy suppression in insulin receptor (IR)-deficient hearts. Results: Absence of IRs in the heart was associated with reduced autophagic flux, and further inhibition of autophagosome clearance reduced survival, impaired contractile function, and enhanced myocyte loss. Contrary to the in vivo setting, isolated cardiomyocytes from IR-deficient hearts exhibited unrestrained autophagy in the absence of insulin, whereas addition of insulin was able to suppress autophagy. To investigate the mechanisms involved in the maintenance of the responsiveness to insulin in IR-deficient hearts, we generated mice lacking both IRs and one copy of the IGF-1 receptor (IGF-1R) in cardiac cells and showed that these mice had increased autophagy. Innovation and Conclusion: This study unveils a new mechanism by which IR-deficient hearts can still respond to insulin to suppress autophagy, in part, through activation of IGF-1R signaling. This is a highly significant observation because it is the first to show that systemic hyperinsulinemia can suppress autophagy in IR-deficient hearts through IGF-1R signaling.

Klotho, an anti-aging gene, acts as a tumor suppressor and inhibitor of IGF-1R signaling in diffuse large B cell lymphoma

BackgroundKlotho, is a transmembrane protein, performs as a circulating hormone and upstream modulator of the insulin-like growth factor-1 receptor (IGF-1R), fibroblast growth factor (FGF), and Wnt signaling pathways. These pathways are involved in the development and progression of B cell lymphoma. We aimed to explore the expression pattern and functional mechanism of Klotho in diffuse large B cell lymphoma (DLBCL).MethodsImmunohistochemistry (IHC) and western blotting were performed to detect the expression level of Klotho in DLBCL patients and cell lines. Tumor suppressive effect of Klotho was determined by both in vitro and in vivo studies. Signaling pathway activity was assessed by western blotting.ResultsRemarkable lower expression levels of Klotho were observed in DLBCL patients and cell lines. Enforced expression of Klotho could significantly induce cell apoptosis and inhibit tumor growth in DLBCL. Upregulation of Klotho resulted in declined activation of IGF-1R signaling, accompanied with decreased phosphorylation of its downstream targets, including AKT and ERK1/2. Moreover, xenograft model treated with either Klotho overexpression vector or recombinant human Klotho administration presented restrained tumor growth and lower Ki67 staining.ConclusionsOur findings establish that Klotho performs as a tumor suppressor and modulator of IGF-1R signaling in DLBCL. Targeting Klotho may provide novel strategies for future therapeutic intervention.

Klotho suppresses tumor progression via inhibiting IGF-1R signaling in T-cell lymphoma

Klotho is a transmembrane protein and acts as an upstream modulator of insulin-like growth factor-1 receptor (IGF-1R) signaling, which was indicated to be involved in the pathogenesis of solid cancer and hematological malignancies, including T‑cell lymphoma. Although Klotho was recently identified as a tumor suppressor in several types of human malignancies, the potential role of Klotho in T‑cell lymphoma has not been reported. In the present study, we investigated the expression level and the molecular events of Klotho in T‑cell lymphoma. Significantly lower expression of Klotho was observed in T‑cell lymphoma patient samples compared to normal lymph nodes. Functional analysis after Klotho overexpression revealed significantly inhibited tumor cell viability in T‑cell lymphoma. Moreover, apoptosis of T‑cell lymphoma cells were induced after transfected with Klotho-overexpressing vectors. Forced expression of Klotho resulted in decline of activation of IGF-1R signaling, accompanied by decreased phosphorylation of its downstream targets, including AKT and ERK1/2. These data indicated that Klotho acts as a tumor suppressor via inhibiting IGF-1R signaling, thus suppressing the viability and promoting apoptosis in T‑cell lymphoma. Taken together, Klotho may serve as a potential target for the therapeutic intervention of T‑cell lymphoma.

IGF2 Is Up-regulated by Epigenetic Mechanisms in Hepatocellular Carcinomas and Is an Actionable Oncogene Product in Experimental Models

Effective treatments are urgently needed for hepatocellular carcinoma (HCC), which is usually diagnosed at advanced stages. Signaling via the insulin-like growth factor (IGF) pathway is aberrantly activated in HCC by IGF2 overexpression. We aimed to elucidate the mechanism of IGF2 overexpression and its oncogenic activities and evaluate the anti-tumor effects of reducing IGF2 signaling. We obtained 228 HCC samples from patients who underwent liver resection, 168 paired non-tumor adjacent cirrhotic liver samples, and 10 non-tumor liver tissues from patients undergoing resection for hepatic hemangioma. We analyzed gene expression, microRNA, and DNA methylation profiles for all samples, focusing on genes in the IGF signaling pathway. IGF2 was expressed in SNU449 and PLC5 HCC cells and knocked down with small hairpin RNAs in Hep3B and Huh7 cell lines. We analyzed these cells for proliferation, apoptosis, migration, and colony formation. We performed studies in mice engineered to express Myc and Akt1 in liver, which develop liver tumors, with or without hepatic expression of Igf2. Mice with xenograft tumors grown from HCC cells were given a monoclonal antibody against IGF1 and IGF2 (xentuzumab), along with sorafenib; tumor growth was measured and tissues were analyzed by immunohistochemistry and immunoblots. Levels of IGF2 messenger RNA and protein were increased >20-fold in 15% of human HCC tissues compared with non-tumor liver tissues. Methylation at the fetal promoters of IGF2 was reduced in the HCC samples and cell lines that overexpressed IGF2, compared with those that did not overexpress this gene, and non-tumor tissues. Tumors that overexpressed IGF2 had gene expression patterns significantly associated with hepatic progenitor cell features, stellate cell activation, NOTCH signaling, and an aggressive phenotype (P < .0001). In mice engineered to express Myc and Akt1 in liver, co-expression of Igf2 accelerated formation of liver tumors, compared to mice with livers expressing only Myc and Akt1, and shortened survival times (P= .02). The antibody xentuzumab blocked phosphorylation of IGF1 receptor in HCC cell lines and reduced their proliferation and colony formation. In mice with xenograft tumors, injection of xentuzumab, with or without sorafenib, slowed tumor growth and increased survival times compared to vehicle or sorafenib alone. Xentuzumab inhibited phosphorylation of IGF1 receptor and AKT and reduced decreased tumor vascularization compared with vehicle. A large proportion of HCC samples were found to overexpress IGF2, via demethylation of its fetal promoter. Overexpression of IGF2 accelerates formation of liver tumors in mice with hepatic expression of MYC and AKT1, via activation of IGF1 receptor signaling. An antibody against IGF1 and IGF2 slows growth of xenograft tumors and increases survival of these mice.

Abstract 297: Epigenetic activation of IGF1R signaling promotes resistance to momelotinib and MEK inhibition in KRAS-driven lung cancer

Abstract KRAS is the most frequently mutated oncogene in non-small cell lung cancer (NSCLC), yet remains resistant to targeted therapy. Previously, we reported that RAL-TBK1 activation downstream of KRAS promotes an autocrine cytokine circuit that fuels tumorigenesis. Interruption of this signaling by treatment with momelotinib, an inhibitor of TBK1/IKKϵ and JAK kinases, together with MEK inhibition, was effective in the aggressive Kras-p53 (KP) mouse lung cancer model. These findings have prompted a human clinical trial of momelotinib and trametinib in advanced refractory KRAS mutant NSCLC. Because this combination leads to acquired resistance in mice, we sought to understand additional pathways that could compensate for TBK1/JAK and MEK inhibition. Receptor tyrosine kinase (RTK) profiling of A549 cells treated with momelotinib revealed delayed activation of IGF1 receptor (IGF1R) signaling. Indeed, IGF1 supplementation partially rescued momelotinib-induced growth arrest of A549 cells, while combination of momelotinib with the dual IGF1R/insulin receptor (IR) inhibitor linsitinib cooperated to impair cell viability, which was more pronounced in KRAS/STK11 (encoding LKB1) mutant cell lines compared with LKB1 wild type cell lines. Triple momelotinib/trametinib/linsitinib therapy also improved tumor shrinkage in Kras-Lkb1 (KL) mice compared with KP mice. However, chronic treatment with this triple combination required pulse therapy due to toxicity, and was inferior to momelotinib/trametinib dosed daily, which itself promoted deep responses in KL mice lasting 6 weeks. In parallel, we analyzed mediators of acquired resistance to chronic momelotinib and MEK inhibitor exposure in A549 cells. Interestingly, IGF1 expression was dramatically upregulated in resistant cells, in contrast to IGF2, and enhanced autocrine activation of IGF1R signaling. Importantly, both IGF1 upregulation and inhibitor resistance were completely reversible after drug withdrawal for several passages, yet reappeared quickly upon drug readdition, suggesting epigenetic reprogramming. Consistent with this hypothesis, whereas global H3K27 histone acetylation was decreased in resistant cells, this epigenetic mark was strongly enriched at the IGF1 promoter and linked tightly with both IGF1 levels and drug resistance. Treatment of resistant A549 cells with the BRD4 inhibitor JQ1 completely suppressed IGF1 expression and downstream IGF1R activation, and impaired cell viability. Combination JQ1 treatment also prevented momelotinib/MEK inhibitor induction of IGF1 in A549 cells, synergized to reduce outgrowth of resistant cells, and was well tolerated as daily triple combination therapy in mice. Together, these findings suggest the potential of BET inhibition to synergize with and prevent the development of acquired resistance to momelotinib and MEK inhibitor treatment in KRAS mutant NSCLC. Citation Format: Shunsuke Kitajima, Hajime Asahina, Jillian D. Cavanaugh, Ting Chen, Ashley A. Merlino, Thai C. Tran, Kwonk-Kin Wong, David A. Barbie. Epigenetic activation of IGF1R signaling promotes resistance to momelotinib and MEK inhibition in KRAS-driven lung cancer. [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 297.

Angelica Sinensis polysaccharides stimulated UDP-sugar synthase genes through promoting gene expression of IGF-1 and IGF1R in chondrocytes: promoting anti-osteoarthritic activity.

BackgroundOsteoarthritis (OA) is a chronic joints disease characterized by progressive degeneration of articular cartilage due to the loss of cartilage matrix. Previously, we found, for the first time, that an acidic glycan from Angelica Sinensis Polysaccharides (APSs), namely the APS-3c, could protect rat cartilage from OA due to promoting glycosaminoglycan (GAG) synthesis in chondrocytes. In the present work, we tried to further the understanding of ASP-3c’s anti-OA activity.Methodology/Principal FindingsHuman primary chondrocytes were treated with APS-3c or/and recombinant human interleukin 1β (IL-1β). It turned out that APS-3c promoted synthesis of UDP-xylose and GAG, as well as the gene expression of UDP-sugar synthases (USSs), insulin like growth factor 1 (IGF1) and IGF1 receptor (IGF1R), and attenuated the degenerative phenotypes, suppressed biosynthesis of UDP-sugars and GAG, and inhibited the gene expression of USSs, IGF1 and IGF1R induced by IL-1β. Then, we induced a rat OA model with papain, and found that APS-3c also stimulated GAG synthesis and gene expression of USSs, IGF1 and IGF1R in vivo. Additionally, recombinant human IGF1 and IGF1R inhibitor NP-AEW541 were applied to figure out the correlation between stimulated gene expression of USSs, IGF1 and IGF1R induced by APS-3c. It tuned out that the promoted GAG synthesis and USSs gene expression induced by APS-3c was mediated by the stimulated IGF1 and IGF1R gene expression, but not through directly activation of IGF1R signaling pathway.Conclusions/SignificancesWe demonstrated for the first time that APS-3c presented anti-OA activity through stimulating IGF-1 and IGF1R gene expression, but not directly activating the IGF1R signaling pathway, which consequently promoted UDP-sugars and GAG synthesis due to up-regulating gene expression of USSs. Our findings presented a better understanding of APS-3c’s anti-OA activity and suggested that APS-3c could potentially be a novel therapeutic agent for OA.

Role of Insulin-Like Growth Factor-1 Signaling Pathway in Cisplatin-Resistant Lung Cancer Cells

The development of drug-resistant phenotypes has been a major obstacle to cisplatin use in non-small-cell lung cancer. We aimed to identify some of the molecular mechanisms that underlie cisplatin resistance using microarray expression analysis. H460 cells were treated with cisplatin. The differences between cisplatin-resistant lung cancer cells and parental H460 cells were studied using Western blot, MTS, and clonogenic assays, in vivo tumor implantation, and microarray analysis. The cisplatin-R cells were treated with human recombinant insulin-like growth factor (IGF) binding protein-3 and siRNA targeting IGF-1 receptor. Cisplatin-R cells illustrated greater expression of the markers CD133 and aldehyde dehydrogenase, more rapid in vivo tumor growth, more resistance to cisplatin- and etoposide-induced apoptosis, and greater survival after treatment with cisplatin or radiation than the parental H460 cells. Also, cisplatin-R demonstrated decreased expression of insulin-like growth factor binding protein-3 and increased activation of IGF-1 receptor signaling compared with parental H460 cells in the presence of IGF-1. Human recombinant IGF binding protein-3 reversed cisplatin resistance in cisplatin-R cells and targeting of IGF-1 receptor using siRNA resulted in sensitization of cisplatin-R-cells to cisplatin and radiation. The IGF-1 signaling pathway contributes to cisplatin-R to cisplatin and radiation. Thus, this pathway represents a potential target for improved lung cancer response to treatment.

Abstract A35: A role for drug resistance in hepatocellular carcinoma: Upregulatation of CD133, activation of IGF-1R signaling, and IGF-1R nuclear translocation

Abstract Introduction: Hepatocellular carcinoma (HCC) is an aggressive neoplasm that is resistant to chemotherapy with mechanisms underlying this drug resistance not well understood. CD133 is a known cancer stem cell (CSC) marker whose high expression is associated with aggressive tumor behavior and poor prognosis. The insulin-like growth factor 1 receptor (IGF-1R) signaling pathway has been shown to play a significant role in tumor behavior. To examine possible mechanisms of drug resistance in HCC, we investigated the role of CD133 expression and IGF-1R signaling activation using geftinib. Methods: We evaluated and separated five different human HCC cell lines (Mahlavu, Huh7, HepG2, Hep3B, PLC/PRF/5) using based on CD133 expression. We subjected these cells to geftinib at different doses, and determined IGF-1R signaling pathway activation using immunoblotting against relevant proteins in the pathway. CD133 mRNA level was examined using quantitative real-time PCR and its expression level was detected using immunofluorescence imaging and flow cytometry after drug treatment. Cell viability and sensitivity to drug treatment were measured using the MTT assay. Results: HCC cell lines showed variable percentages of total cell populations expressing CD133: Mahlavu 0.12 %, HepG2 46 %, Huh7 80.2 %, Hep3B 98.2 %, and PLC/PRF/5 83.5 %. Mahlavu and PLC/PRF/5 were found to be the most resistant cell lines even at higher doses (17.5 uM). Since Mahlavu cells displayed reduced CD133 expression, experiments were focused on this cell line to evaluate the CD133 expression changes after geftinib treatment. After three rounds (9 days) of high dose geftinib treatment, CD133 expression was increased in a dose dependent manner; the percentages of total cell populations expressing CD133 increased to 43.9 % at 10 uM concentration and 52.9 % at 15 uM concentration as compared to 0.12 % in untreated cells. In addition, we found a significant increase in IGF-1R and AKT phosphorylation as well as IGFBP3 expression in those geftinib treated cells. Furthermore, after cell sorting of Huh7 cells by CD133 expression using flow cytometry, we observed that CD133 positive cells showed more resistant to geftinib treatment. Immunofluorescence imaging analysis demonstrated that increased IGF-1R protein translocated to nuclei after geftinib treatment. Conclusion: Geftinib treatment enhanced CD133 expression level and activated IGF-1R signaling in HCC Mahlavu cells, one of the possible mechanism could be the nuclear translocation of IGF-1R. Our findings underscore the importance of a combined therapeutic approach with geftinib and IGF-1R blockage in the treatment of human HCC. Citation Information: Cancer Prev Res 2011;4(10 Suppl):A35.

CCN6 (WISP3) decreases ZEB1-mediated EMT and invasion by attenuation of IGF-1 receptor signaling in breast cancer

During progression of breast cancer, CCN6 protein exerts tumor inhibitory functions. CCN6 is a secreted protein that modulates the insulin-like growth factor-1 (IGF-1) signaling pathway. Knockdown of CCN6 in benign mammary epithelial cells triggers an epithelial to mesenchymal transition (EMT), with upregulation of the transcription factor ZEB1/δEF1. How CCN6 regulates ZEB1 expression is unknown. We hypothesized that CCN6 might regulate ZEB1, EMT and breast cancer invasion by modulating IGF-1 signaling. Exogenously added human recombinant CCN6 protein was sufficient to downregulate ZEB1 mRNA and protein levels in CCN6-deficient (CCN6 KD) HME cells and MDA-MB-231 breast cancer cells. Recombinant CCN6 protein decreased invasion of CCN6 KD cells compared with controls. We discovered that knockdown of CCN6 induced IGF-1 secretion in HME cells cultivated in serum-free medium to higher concentrations than found in MDA-MB-231 cells. Treatment with recombinant CCN6 protein was sufficient to decrease IGF-1 protein and mRNA to control levels, rescuing the effect of CCN6 knockdown. Specific inhibition of IGF-1 receptors using the pharmacological inhibitor NVP-AE541 or short hairpin shRNAs revealed that ZEB1 upregulation due to knockdown of CCN6 requires activation of IGF-1 receptor signaling. Recombinant CCN6 blunted IGF-1-induced ZEB1 upregulation in MDA-MB-231 cells. Our data define a pathway in which CCN6 attenuates IGF-1 signaling to decrease ZEB1 expression and invasion in breast cancer. These results suggest that CCN6 could be a target to prevent or halt breast cancer invasion.

Abstract A248: Substituted 4-amino-1H-pyrazolo[3,4-d]pyrimidines as multitargeted inhibitors targeting insulin-like growth factor-1 receptor (IGF1R) and members of ErbB-family receptor tyrosine kinases

Abstract Insulin-like growth factor-1 receptor (IGF1R) and members of ErbB family (eg. EGFR, ErbB2) are receptor tyrosine kianses that play significant roles in cancer and have been pursued as drug targets for cancer therapy. There is substantial evidence for the existence of reciprocal cross-talk between IGF1R axis and ErbB axis of cellular signaling. Acquired resistance to EGFR inhibitors gefitinib and erlotinib or ErbB2 inhibitor trastuzumab has been linked to activation of IGF1R signaling through induced overexpression of IGF1R or loss of IGF binding- proteins. Additionally, synergy between IGF1R inhibition and ErbB inhibition has been demonstrated in cancer cell growth inhibition and in xenograft models. Thus, molecules targeting both IGF1R and ErbB-family might have superior anti-tumor efficacy. This poster describes the lead discovery, optimization and biological characterization of a series of substituted 4-amino-1H-pyrazolo[3,4-d]pyrimidines as potent inhibitors of IGF1R, EGFR and ErbB2. The leading compound, A-923573, showed IGF1R IC50 of 12 nM, EGFR (L858R) IC50 of 31 nM and ErbB2 IC50 of 11 nM, potent activity in cellular functional assays and anti-proliferation assays, as well as in an in vivo pharmacodynamic assay. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A248.

Glucagon-Like Peptide-1 Protects β-Cells Against Apoptosis by Increasing the Activity of an Igf-2/Igf-1 Receptor Autocrine Loop

OBJECTIVEThe gluco-incretin hormones glucagon-like peptide (GLP)-1 and gastric inhibitory peptide (GIP) protect β-cells against cytokine-induced apoptosis. Their action is initiated by binding to specific receptors that activate the cAMP signaling pathway, but the downstream events are not fully elucidated. Here we searched for mechanisms that may underlie this protective effect.RESEARCH DESIGN AND METHODSWe performed comparative transcriptomic analysis of islets from control and GipR−/−;Glp-1-R−/− mice, which have increased sensitivity to cytokine-induced apoptosis. We found that IGF-1 receptor expression was markedly reduced in the mutant islets. Because the IGF-1 receptor signaling pathway is known for its antiapoptotic effect, we explored the relationship between gluco-incretin action, IGF-1 receptor expression and signaling, and apoptosis.RESULTSWe found that GLP-1 robustly stimulated IGF-1 receptor expression and Akt phosphorylation and that increased Akt phosphorylation was dependent on IGF-1 but not insulin receptor expression. We demonstrated that GLP-1–induced Akt phosphorylation required active secretion, indicating the presence of an autocrine activation mechanism; we showed that activation of IGF-1 receptor signaling was dependent on the secretion of IGF-2. We demonstrated, both in MIN6 cell line and primary β-cells, that reducing IGF-1 receptor or IGF-2 expression or neutralizing secreted IGF-2 suppressed GLP-1–induced protection against apoptosis.CONCLUSIONSAn IGF-2/IGF-1 receptor autocrine loop operates in β-cells. GLP-1 increases its activity by augmenting IGF-1 receptor expression and by stimulating secretion; this mechanism is required for GLP-1–induced protection against apoptosis. These findings may lead to novel ways of preventing β-cell loss in the pathogenesis of diabetes.

Age‐related differences in insulin‐like growth factor‐1 receptor signaling regulates Akt/FOXO3a and ERK/Fos pathways in vascular smooth muscle cells

Advanced age is a major risk factor for atherosclerosis, but how aging per se influences pathogenesis is not clear. Insulin-like growth factor-1 receptor (IGF-1R) promotes aortic vascular smooth muscle cell (VSMC) growth, migration, and extracellular matrix formation, but how IGF-1R signaling changes with age in VSMC is not known. We previously found age-related differences in the activation of Akt/FOXO3a and ERK1/2 pathways in VSMC, but the upstream signaling remains unclear. Using explanted VSMC from Fischer 344/Brown Norway F1 hybrid rats shown to display age-related vascular pathology similar to humans, we compared IGF-1R expression in early passages of VSMC and found a constitutive activation of IGF-1R in VSMC from old compared to young rats, including IGF-1R expression and its tyrosine kinase activity. The link between IGF-1R activation and the Akt/FOXO3a and ERK pathways was confirmed through the induction of IGF-1R with IGF-1 in young cells and attenuation of IGF-1R with an inhibitor in old cells. The effects of three kinase inhibitors: AG1024, LY294002, and TCN, were compared in VSMC from old rats to differentiate IGF-1R from other upstream signaling that could also regulate the Akt/FOXO and ERK pathways. Genes for p27kip-1, catalase and MnSOD, which play important roles in the control of cell cycle arrest and stress resistance, were found to be FOXO3a-targets based on FOXO3a-siRNA treatment. Furthermore, IGF-1R signaling modulated these genes through activation of the Akt/FOXO3a pathway. Therefore, activation of IGF-1R signaling influences VSMC function in old rats and may contribute to the increased risk for atherosclerosis.

An aging pathway controls the TrkA to p75NTR receptor switch and amyloid β-peptide generation

Aging of the brain is characterized by marked changes in the expression levels of the neurotrophin receptors, TrkA and p75(NTR). An expression pattern in which TrkA predominates in younger animals switches to one in which p75(NTR) predominates in older animals. This TrkA-to-p75(NTR) switch is accompanied by activation of the second messenger ceramide, stabilization of beta-site amyloid precursor protein-cleaving enzyme-1 (BACE1), and increased production of amyloid beta-peptide (Abeta). Here, we show that the insulin-like growth factor-1 receptor (IGF1-R), the common regulator of lifespan and age-related events in many different organisms, is responsible for the TrkA-to-p75(NTR) switch in both human neuroblastoma cell lines and primary neurons from mouse brain. The signaling pathway that controls the level of TrkA and p75(NTR) downstream of the IGF1-R requires IRS2, PIP3/Akt, and is under the control of PTEN and p44, the short isoform of p53. We also show that hyperactivation of IGF1-R signaling in p44 transgenic animals, which show an accelerated form of aging, is characterized by early TrkA-to-p75(NTR) switch and increased production of Abeta in the brain.

Hsp10 and Hsp60 Suppress Ubiquitination of Insulin-like Growth Factor-1 Receptor and Augment Insulin-like Growth Factor-1 Receptor Signaling in Cardiac Muscle: IMPLICATIONS ON DECREASED MYOCARDIAL PROTECTION IN DIABETIC CARDIOMYOPATHY

We have investigated the effects of two heat shock proteins, Hsp10 and Hsp60, on insulin-like growth factor-1 receptor (IGF-1R) signaling in cardiac muscle cells. Neonatal cardiomyocytes were transduced with Hsp10 or Hsp60 via adenoviral vector. Compared with the cells transduced with a control vector, overexpression of Hsp10 or Hsp60 increased the abundance of IGF-1R and IGF-1-stimulated receptor autophosphorylation. Thus, Hsp10 and Hsp60 overexpression increased the number of functioning receptors and amplified activation of IGF-1R signaling. IGF-1 stimulation of MEK, Erk, p90Rsk, and Akt were accordingly augmented. Transducing cardiomyocytes with antisense Hsp60 oligonucleotides reduced Hsp60 expression, decreased the abundance of IGF-1R, attenuated IGF-1R autophosphorylation, and suppressed the pro-survival action of IGF-1 in cardiomyocytes. Using cycloheximide to inhibit protein synthesis did not alter the effect of Hsp60 on IGF-1R signaling, and IGF-1R mRNA levels were not up-regulated by Hsp10 or Hsp60. Additional experiments showed that Hsp10 and Hsp60 suppressed polyubiquitination of IGF-1 receptor. These data indicate that Hsp10 and Hsp60 can modulate IGF-1R signaling through post-translational modification. In animal models of diabetes, diabetic myocardium is associated with decreased abundance of Hsp60, increased ubiquitination of IGF-1R, and lower level of IGF-1R protein. Declined myocardial protection is a major feature of diabetic cardiomyopathy. These data suggest that decreased Hsp60 expression and subsequent decline of IGF-1R signaling may be a fundamental mechanism underlying the development of diabetic cardiomyopathy.