Insulin-like growth factor I receptor gene structure

Activation of the insulin receptor by insulin-like growth factor 2

Insulin receptor (IR) controls growth and metabolism. Insulin-like growth factor 2 (IGF2) has different binding properties on two IR isoforms, mimicking insulin's function. However, the molecular mechanism underlying IGF2-induced IR activation remains unclear. Here, we present cryo-EM structures of full-length human long isoform IR (IR-B) in both the inactive and IGF2-bound active states, and short isoform IR (IR-A) in the IGF2-bound active state. Under saturated IGF2 concentrations, both the IR-A and IR-B adopt predominantly asymmetric conformations with two or three IGF2s bound at site-1 and site-2, which differs from that insulin saturated IR forms an exclusively T-shaped symmetric conformation. IGF2 exhibits a relatively weak binding to IR site-2 compared to insulin, making it less potent in promoting full IR activation. Cell-based experiments validated the functional importance of IGF2 binding to two distinct binding sites in optimal IR signaling and trafficking. In the inactive state, the C-terminus of α-CT of IR-B contacts FnIII-2 domain of the same protomer, hindering its threading into the C-loop of IGF2, thus reducing the association rate of IGF2 with IR-B. Collectively, our studies demonstrate the activation mechanism of IR by IGF2 and reveal the molecular basis underlying the different affinity of IGF2 to IR-A and IR-B.

Radio-immunotherapy by 188Re-antiCD20 and stable silencing of IGF-IR in Raji cells, new insight in treatment of lymphoma

Hematologic malignancies such as Non-Hodgkin's lymphoma (NHL), remain a serious threat to human health due to their heterogeneity and complexity. The inherent genetic heterogeneity of NHL B-cells, as well as the instability of lymphoma cancer cells, results in drug resistance in lymphoma, posing a fundamental challenge to NHL treatment. Burkitt lymphoma (including Raji cell line) is a rare and highly aggressive form of B-cell NHL. Since overexpression of the insulin-like growth factor-1 receptor (IGF-1R) playing a prominent role in the development and transformation of different malignancies, especially lymphoma malignancies, we have explored the role of IGF-1R in the development and progression of Raji cells and the stable silencing of IGF-1R by lentivirus-mediated RNA interference (RNAi). We have shown that stable silencing of the IGF-1R gene in Raji cells using lentivirus-mediated-RNAi have resulted in a significant reduction in Raji cell proliferation. Moreover, the results of the cell viability assays indicatedhigh resistance of Raji cells to rituximab. However, coupling rituximab to 188Re potentially leads to specific targeting of Raji cells by 188Re, improving the therapeutic efficacy. We found that the synergistic effect of using a gene therapy-based system in combination with radioimmunotherapy could be a promising therapeutic strategy in the future. To the best of our knowledge, this is the first study that reports the knock down of IGF-1R via lentiviral-mediated shRNA in Raji cells.

The IGF1 Signaling Pathway: From Basic Concepts to Therapeutic Opportunities

Insulin-like growth factor 1 (IGF1) is a peptide growth factor with important functions in multiple aspects of growth, development and metabolism. The biological actions of IGF1 are mediated by the IGF1 receptor (IGF1R), a cell-surface protein that is evolutionarily related to the insulin receptor (InsR). The effects of IGF1 are moderated by a group of binding proteins (IGFBPs) that bind and transport the ligand in the circulation and extracellular fluids. In mechanistic terms, IGF1R function is linked to the MAPK and PI3K signaling pathways. Furthermore, IGF1R has been shown to migrate to cell nucleus, where it functions as a transcriptional activator. The co-localization of IGF1R and MAPK in the nucleus is of major interest as it suggests novel mechanistic paradigms for the IGF1R-MAPK network. Given its potent anti-apoptotic and pro-survival roles, and in view of its almost universal pattern of expression in most types of cancer, IGF1R has emerged as a promising molecular target in oncology. The present review article provides a concise overview of key scientific developments in the research area of IGF and highlights a number of more recent findings, including its nuclear migration and its interaction with oncogenes and tumor suppressors.

Structural basis of the alkaline pH-dependent activation of insulin receptor-related receptor

The insulin receptor (IR) family is a subfamily of receptor tyrosine kinases that controls metabolic homeostasis and cell growth. Distinct from IR and insulin-like growth factor 1 receptor, whose activation requires ligand binding, insulin receptor-related receptor (IRR)-the third member of the IR family-is activated by alkaline pH. However, the molecular mechanism underlying alkaline pH-induced IRR activation remains unclear. Here, we present cryo-EM structures of human IRR in both neutral pH inactive and alkaline pH active states. Combined with mutagenesis and cellular assays, we show that, upon pH increase, electrostatic repulsion of the pH-sensitive motifs of IRR disrupts its autoinhibited state and promotes a scissor-like rotation between two protomers, leading to a T-shaped active conformation. Together, our study reveals an unprecedented alkaline pH-dependent activation mechanism of IRR, opening up opportunities to understand the structure-function relationship of this important receptor.

Molecular basis for the role of disulfide-linked αCTs in the activation of insulin-like growth factor 1 receptor and insulin receptor

The insulin receptor (IR) and insulin-like growth factor 1 receptor (IGF1R) control metabolic homeostasis and cell growth and proliferation. The IR and IGF1R form similar disulfide bonds linked homodimers in the apo-state; however, their ligand binding properties and the structures in the active state differ substantially. It has been proposed that the disulfide-linked C-terminal segment of α-chain (αCTs) of the IR and IGF1R control the cooperativity of ligand binding and regulate the receptor activation. Nevertheless, the molecular basis for the roles of disulfide-linked αCTs in IR and IGF1R activation are still unclear. Here, we report the cryo-EM structures of full-length mouse IGF1R/IGF1 and IR/insulin complexes with modified αCTs that have increased flexibility. Unlike the Γ-shaped asymmetric IGF1R dimer with a single IGF1 bound, the IGF1R with the enhanced flexibility of αCTs can form a T-shaped symmetric dimer with two IGF1s bound. Meanwhile, the IR with non-covalently linked αCTs predominantly adopts an asymmetric conformation with four insulins bound, which is distinct from the T-shaped symmetric IR. Using cell-based experiments, we further showed that both IGF1R and IR with the modified αCTs cannot activate the downstream signaling potently. Collectively, our studies demonstrate that the certain structural rigidity of disulfide-linked αCTs is critical for optimal IR and IGF1R signaling activation.

Analysis of whole-genome re-sequencing data of ducks reveals a diverse demographic history and extensive gene flow between Southeast/South Asian and Chinese populations

BACKGROUND

The most prolific duck genetic resource in the world is located in Southeast/South Asia but little is known about the domestication and complex histories of these duck populations.

RESULTS

Based on whole-genome resequencing data of 78 ducks (Anas platyrhynchos) and 31 published whole-genome duck sequences, we detected three geographic distinct genetic groups, including local Chinese, wild, and local Southeast/South Asian populations. We inferred the demographic history of these duck populations with different geographical distributions and found that the Chinese and Southeast/South Asian ducks shared similar demographic features. The Chinese domestic ducks experienced the strongest population bottleneck caused by domestication and the last glacial maximum (LGM) period, whereas the Chinese wild ducks experienced a relatively weak bottleneck caused by domestication only. Furthermore, the bottleneck was more severe in the local Southeast/South Asian populations than in the local Chinese populations, which resulted in a smaller effective population size for the former (7100-11,900). We show that extensive gene flow has occurred between the Southeast/South Asian and Chinese populations, and between the Southeast Asian and South Asian populations. Prolonged gene flow was detected between the Guangxi population from China and its neighboring Southeast/South Asian populations. In addition, based on multiple statistical approaches, we identified a genomic region that included three genes (PNPLA8, THAP5, and DNAJB9) on duck chromosome 1 with a high probability of gene flow between the Guangxi and Southeast/South Asian populations. Finally, we detected strong signatures of selection in genes that are involved in signaling pathways of the nervous system development (e.g., ADCYAP1R1 and PDC) and in genes that are associated with morphological traits such as cell growth (e.g., IGF1R).

CONCLUSIONS

Our findings provide valuable information for a better understanding of the domestication and demographic history of the duck, and of the gene flow between local duck populations from Southeast/South Asia and China.

A Comprehensive Cohort Analysis Comparing Growth and GH Therapy Response in IGF1R Mutation Carriers and SGA Children

CONTEXT

IGF1 receptor mutations (IGF1RM) are rare; however, patients exhibit pronounced growth retardation without catch-up. Although several case reports exist, a comprehensive statistical analysis investigating growth profile and benefit of recombinant human growth hormone (rhGH) treatment is still missing.

OBJECTIVE AND METHODS

Here, we compared IGF1RM carriers (n = 23) retrospectively regarding birth parameters, growth response to rhGH therapy, near final height, and glucose/insulin homeostasis to treated children born small for gestational age (SGA) (n = 34). Additionally, health profiles of adult IGF1RM carriers were surveyed by a questionnaire.

RESULTS

IGF1RM carriers were significantly smaller at rhGH initiation and had a diminished first-year response compared to SGA children (Δ height standard deviation score: 0.29 vs. 0.65), resulting in a lower growth response under therapy. Interestingly, the number of poor therapy responders was three times higher for IGF1RM carriers than for SGA patients (53 % vs. 17 %). However, most IGF1RM good responders showed catch-up growth to the levels of SGA patients. Moreover, we observed no differences in homeostasis model assessment of insulin resistance before treatment, but during treatment insulin resistance was significantly increased in IGF1RM carriers compared to SGA children. Analyses in adult mutation carriers indicated no increased occurrence of comorbidities later in life compared to SGA controls.

CONCLUSION

In summary, IGF1RM carriers showed a more pronounced growth retardation and lower response to rhGH therapy compared to non-mutation carriers, with high individual variability. Therefore, a critical reevaluation of success should be performed periodically. In adulthood, we could not observe a significant influence of IGF1RM on metabolism and health of carriers.

Nuclear localization and actions of the insulin-like growth factor 1 (IGF-1) system components: Transcriptional regulation and DNA damage response

Insulin-like growth factor (IGF) system stimulates growth, proliferation, and regulates differentiation of cells in a tissue-specific manner. It is composed of two insulin-like growth factors (IGF-1 and IGF-2), six insulin-like growth factor-binding proteins (IGFBPs), and two insulin-like growth factor receptors (IGF-1R and IGF-2R). IGF actions take place mostly through the activation of the plasma membrane-bound IGF-Rs by the circulating ligands (IGFs) released from the IGFBPs that stabilize their levels in the serum. This review focuses on the IGF-1 part of the system. The IGF-1 gene, which is expressed mainly in the liver as well as in other tissues, comprises six alternatively spliced exons that code for three protein isoforms (pro-IGF-1A, pro-IGF-1B, and pro-IGF-1C), which are processed to mature IGF-1 and E-peptides. The IGF-1R undergoes autophosphorylation, resulting in a signaling cascade involving numerous cytoplasmic proteins such as AKT and MAPKs, which regulate the expression of target genes. However, a more complex picture of the axis has recently emerged with all its components being translocated to the nuclear compartment. IGF-1R takes part in the regulation of gene expression by forming transcription complexes, modifying the activity of chromatin remodeling proteins, and participating in DNA damage tolerance mechanisms. Four IGFBPs contain a nuclear localization signal (NLS), which targets them to the nucleus, where they regulate gene expression (IGFBP-2, IGFBP-3, IGFBP-5, IGFBP-6) and DNA damage repair (IGFBP-3 and IGFBP-6). Last but not least, the IGF-1B isoform has been reported to be localized in the nuclear compartment. However, no specific molecular actions have been assigned to the nuclear pro-IGF-1B or its derivative EB peptide. Therefore, further studies are needed to shed light on their nuclear activity. These recently uncovered nuclear actions of different components of the IGF-1 axis are relevant in cancer cell biology and are discussed in this review.

Building the Case for Insulin-Like Growth Factor Receptor-I Involvement in Thyroid-Associated Ophthalmopathy

The pathogenesis of orbital Graves' disease (GD), a process known as thyroid-associated ophthalmopathy (TAO), remains incompletely understood. The thyrotropin receptor (TSHR) represents the central autoantigen involved in GD and has been proposed as the thyroid antigen shared with the orbit that could explain the infiltration of immune cells into tissues surrounding the eye. Another cell surface protein, insulin-like growth factor-I receptor (IGF-IR), has recently been proposed as a second antigen that participates in TAO by virtue of its interactions with anti-IGF-IR antibodies generated in GD, its apparent physical and functional complex formation with TSHR, and its necessary involvement in TSHR post-receptor signaling. The proposal that IGF-IR is involved in TAO has provoked substantial debate. Furthermore, several studies from different laboratory groups, each using different experimental models, have yielded conflicting results. In this article, we attempt to summarize the biological characteristics of IGF-IR and TSHR. We also review the evidence supporting and refuting the postulate that IGF-IR is a self-antigen in GD and that it plays a potentially important role in TAO. The putative involvement of IGF-IR in disease pathogenesis carries substantial clinical implications. Specifically, blocking this receptor with monoclonal antibodies can dramatically attenuate the induction by TSH and pathogenic antibodies generated in GD of proinflammatory genes in cultured orbital fibroblasts and fibrocytes. These cell types appear critical to the development of TAO. These observations have led to the conduct of a now-completed multicenter therapeutic trial of a fully human monoclonal anti-IGF-IR blocking antibody in moderate to severe, active TAO.

A New Homozygous IGF1R Variant Defines a Clinically Recognizable Incomplete Dominant form of SHORT Syndrome

Here, we describe a child, born from consanguineous parents, with clinical features of SHORT syndrome, high IGF1 levels, developmental delay, CNS defects, and marked progeroid appearance. By exome sequencing, we identified a new homozygous c.2201G>T missense mutation in the IGF1R gene. Proband's parents and other relatives, all heterozygous carriers of the mutation, presented with milder phenotype including high IGFI levels, short stature, and type 2 diabetes. Functional studies using patient's cell lines showed a lower IGF1R expression that leads to the alteration of IGF1R-mediated PI3K/AKT/mTOR downstream pathways, including autophagy. This study defines a clinically recognizable incomplete dominant form of SHORT syndrome, and provides relevant insights into the pathophysiological and phenotypical consequences of IGF1R mutations.

Associations of polymorphisms in GHRL, GHSR, and IGF1R genes with feed efficiency in chickens

The ghrelin (GHRL), ghrelin receptor (GHSR), and insulin-like growth factor 1 receptor (IGF1R) genes have crucial effects on body weight (BW), body weight gain (BWG), feed intake (FI), and feed conversion ratio (FCR) in many species. However, few studies on associations of GHRL, GHSR, and IGF1R with BWG, FI, and FCR have been reported in chickens. In this study, 16 SNPs in GHRL, GHSR, and IGF1R genes were genotyped by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The objective of this study was to examine the associations of GHRL, GHSR, and IGF1R genes polymorphisms with BW at 49 days (BW49) and 70 days (BW70) of age, BWG, FI, and FCR in the interval in two yellow meat-type populations with a total of 724 birds. The results showed that rs15675067 of GHRL was significantly associated with BW70, BWG, and FCR (P < 0.05). For GHSR, rs16675844 had significant effects on FI and FCR (P < 0.01), and that rs14678932 showed significant association with BWG and FI (P < 0.05). Rs14011780 of IGF1R was strongly associated with BW49, BW70, and FCR (P < 0.05). Furthermore, haplotypes based on three SNPs of rs14986828, rs15675067, and rs15675065 in GHRL were significantly associated with BW70 and FCR (P < 0.05). Meanwhile, a three-SNP haplotype comprising rs14011783, rs14011780, and rs14011776 in IGF1R showed significant effects on BW49, BW70, and FCR (P < 0.05). Therefore, it was concluded that the identified SNPs and analyzed haplotypes in this study might be useful for broiler breeding programs.

Posttranscriptional regulation of insulin family ligands and receptors

Insulin system including ligands (insulin and IGFs) and their shared receptors (IR and IGFR) are critical regulators of insulin signaling and glucose homeostasis. Altered insulin system is associated with major pathological conditions like diabetes and cancer. The mRNAs encoding for these ligands and their receptors are posttranscriptionally controlled by three major groups of regulators; (i) alternative splicing regulatory factors; (ii) turnover and translation regulator RNA-binding proteins (TTR-RBPs); and (iii) non-coding RNAs including miRNAs and long non-coding RNAs (lncRNAs). In this review, we discuss the influence of these regulators on alternative splicing, mRNA stability and translation. Due to the pathological impacts of insulin system, we also discussed the possibilities of discovering new potential regulators which will improve understanding of insulin system and associated diseases.

Insulin-like growth factors in the gastrointestinal tract and liver

The liver is a major source of insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) that are present in the circulation and have important endocrine activities relating to energy metabolism, body size, carcinogenesis, and various organ-specific functions. Although IGFs have only minor effects on the normal liver itself, production of IGFs and IGFBPs in a tissue-specific manner in the gastrointestinal tract exert important regulatory effects on cellular proliferation, survival, and apoptosis. IGFs and IGFBPs play important regulatory roles in the response of both the liver and the gastrointestinal tract to inflammation and in the development of neoplasia.

Insulin-like growth factor system on adrenocortical tumorigenesis

The insulin-like growth factor (IGF) signaling pathway has many important roles in normal cell growth and development. Remarkably, all of the components of this system (IGFs, receptors, and binding proteins) are expressed in human fetal adrenals. Beckwith-Wiedemann syndrome, a congenital overgrowth disorder characterized by a high risk of development of childhood tumors, is also distinguished by a high incidence of adrenocortical carcinomas. This disease has been associated with structural abnormalities at the 11p15 locus, which harbors the IGF2 gene as well as the genes coding for insulin, H19, and p57kip2. Notably, rearrangements at the 11p15 locus and overexpression of IGF2 were also described in sporadic adrenocortical tumors. In addition, the IGF2 overexpression was exclusively demonstrated in adults with adrenocortical tumors as a frequent feature of the malignant state. More recent studies demonstrated that the interaction of IGF-2 with IGF receptor type 1 (IGF-1R) plays also a pivotal role in adrenocortical tumorigenesis. IGF1R expression levels were significantly higher in pediatric adrenocortical carcinomas, suggesting that IGF1R expression represents a potential prognostic marker in this group of patients. These findings indicate that the IGF system is an important pathway for autonomous growth of adrenocortical cells and potential inhibitors of this system could be a rational therapeutic target for adrenocortical tumors.

Plasma and tissue insulin-like growth factor-I receptor (IGF-IR) as a prognostic marker for prostate cancer and anti-IGF-IR agents as novel therapeutic strategy for refractory cases: a review

Cancer database analysis indicates that prostate cancer is one of the most seen cancers in men meanwhile composing the leading cause of morbidity and mortality among developed countries. Current available therapies are surgery, radiotherapy and androgene ablation for prostate carcinoma. The response rate is as high nearly 90% however, most of these recur or become refractory and androgene independent (AI). Therefore recent studies intensified on molecular factors playing role on development of prostate carcinoma and novel treatment strategies targetting these factors and their receptors. Insulin-like growth factor-I (IGF-I) and its primary receptor insulin-like growth factor receptor-I (IGF-IR) are among these factors. Biologic functions and role in malign progression are primarily achieved via IGF-IR which is a type 2 tyrosine kinase receptor. IGF-IR plays an important role in mitogenesis, angiogenesis, transformation, apoptosis and cell motility. It also generates intensive proliferative signals leading to carcinogenesis in prostate tissue. So IGF-IR and its associated signalling system have provoked considerable interest over recent years as a novel therapeutic target in cancer. In this paper it is aimed to sum up the lately published literature searching the relation of IGF-IR and prostate cancer in terms of incidence, pathologic features, and prognosis. This is followed by a discussion of the different possible targets within the IGF-1R system, and drugs developed to interact at each target. A systems-based approach is then used to review the in vitro and in vivo data in the published literature of the following compounds targeting IGF-1R components using specific examples: growth hormone releasing hormone antagonists (e.g. JV-1-38), growth hormone receptor antagonists (e.g. pegvisomant), IGF-1R antibodies (e.g. CP-751,871, AVE1642/EM164, IMC-A12, SCH-717454, BIIB022, AMG 479, MK-0646/h7C10), and IGF-1R tyrosine kinase inhibitors (e.g. BMS-536942, BMS-554417, NVP-AEW541, NVP-ADW742, AG1024, potent quinolinyl-derived imidazo (1,5-a)pyrazine PQIP, picropodophyllin PPP, nordihydroguaiaretic acid Insm-18/NDGA). And the other end point is to yield an overview on the recent progress about usage of this receptor as a novel anticancer agent of targeted therapies in treatment of prostate carcinoma.

Organ-specific defects in insulin-like growth factor and insulin receptor signaling in late gestational asymmetric intrauterine growth restriction in Cited1 mutant mice

Late gestational placental insufficiency resulting in asymmetric intrauterine organ growth restriction (IUGR) is associated with an increased incidence of diabetes, cardiovascular and renal disease in adults. The molecular mechanisms mediating these defects are poorly understood. To explore this, we investigated the mechanisms leading to IUGR in Cited1 knockout mice, a genetic model of late gestational placental insufficiency. We show that loss of placental Cited1 leads to asymmetric IUGR with decreased liver, lung, and kidney sizes and preservation of fetal brain weight. IGF and insulin signaling regulate embryonic organ growth. IGF-I and IGF-II protein and mRNA expression are reduced in livers, lungs, and kidneys of embryonic d 18.5 embryos with IUGR. Decreased IGF-I is associated with reduced activating phosphorylation of the type 1 IGF receptor (pIGF-IR) in the kidney, whereas reduced IGF-II is associated with decreased phosphorylation of the insulin receptor (pIR) in the lung. In contrast, decreased pIR is associated with reduced IGF-I but not IGF-II in the liver. However, pancreatic β-cell mass and serum insulin levels are also decreased in mice with IUGR, suggesting that hepatic IR signaling may be regulated by alterations in fetal insulin production. These findings contrast with observations in IUGR fetal brains in which there is no change in IGF-IR/IR phosphorylation, and IGF-I and IGF-II expression is actually increased. In conclusion, IUGR disrupts normal fetal IGF and insulin production and is associated with organ-specific defects in IGF-IR and IR signaling that may regulate asymmetric IUGR in late gestational placental insufficiency.

Phosphorylated insulin-like growth factor 1 receptor is implicated in resistance to the cytostatic effect of gefitinib in colorectal cancer cells

INTRODUCTION

The ability of certain cancer cells to maintain signaling via the phosphoinositide-3-kinase/Akt and/or Ras/mitogen-activated protein kinase (MAPK) pathways has been repeatedly involved in resistance to epidermal growth factor receptor (EGFR) inhibition.

DISCUSSION

We investigated the potential mechanisms of the uncoupling of EGFR from its downstream signals in colorectal cancer (CRC) cells. Alternative growth factor receptors and regulation of downstream pathways in different gefitinib-responsive cell lines were determined. Basal insulin-like growth factor receptor-1β (IGFR-1β) phosphorylation was undetectable or present at very low levels in highly gefitinib-responsive cell lines and was present at strikingly high levels in less responsive cell lines. Further analysis of cell lines representing the most sensitive (Lovo), moderately sensitive (HT29), and most resistant (HCT116) strains was treated with an IGFR-1 inhibitor (AG1024), gefitinib, or both, revealing that elevated IGFR-1β phosphorylation can compensate for the loss of EGFR signaling function. Increased insulin-like growth factor II expression induced by gefitinib or heterodimerization of EGFR and IGFR-1β may trigger IGFR-1β signal transduction via activation of Akt and MAPK. In addition, high levels of EGFR and IGFR-1β phosphorylation were detected in CRC tumor tissue. We also showed that gefitinib- and/or AG1024-induced cytostatic effects could be mediated by glycogen synthase kinase-3β (GSK-3β) activation. Our data suggest that the crosstalk between EGFR and IGFR-1β signaling are likely to contribute to resistance of CRC cells to gefitinib and that measurement of GSK-3β activation may present a potential biomarker for evaluating the antitumor efficacy of receptor tyrosine kinase inhibition.

Mapping a new spontaneous preterm birth susceptibility gene, IGF1R, using linkage, haplotype sharing, and association analysis

Preterm birth is the major cause of neonatal death and serious morbidity. Most preterm births are due to spontaneous onset of labor without a known cause or effective prevention. Both maternal and fetal genomes influence the predisposition to spontaneous preterm birth (SPTB), but the susceptibility loci remain to be defined. We utilized a combination of unique population structures, family-based linkage analysis, and subsequent case-control association to identify a susceptibility haplotype for SPTB. Clinically well-characterized SPTB families from northern Finland, a subisolate founded by a relatively small founder population that has subsequently experienced a number of bottlenecks, were selected for the initial discovery sample. Genome-wide linkage analysis using a high-density single-nucleotide polymorphism (SNP) array in seven large northern Finnish non-consanginous families identified a locus on 15q26.3 (HLOD 4.68). This region contains the IGF1R gene, which encodes the type 1 insulin-like growth factor receptor IGF-1R. Haplotype segregation analysis revealed that a 55 kb 12-SNP core segment within the IGF1R gene was shared identical-by-state (IBS) in five families. A follow-up case-control study in an independent sample representing the more general Finnish population showed an association of a 6-SNP IGF1R haplotype with SPTB in the fetuses, providing further evidence for IGF1R as a SPTB predisposition gene (frequency in cases versus controls 0.11 versus 0.05, P = 0.001, odds ratio 2.3). This study demonstrates the identification of a predisposing, low-frequency haplotype in a multifactorial trait using a well-characterized population and a combination of family and case-control designs. Our findings support the identification of the novel susceptibility gene IGF1R for predisposition by the fetal genome to being born preterm.

Mechanism of growth inhibition by MicroRNA 145: the role of the IGF-I receptor signaling pathway

MicroRNA 145 (miR145) has been proposed as a tumor suppressor. It was previously shown that miR145 targets the 3' UTR of the insulin receptor substrate-1 (IRS-1) and dramatically inhibits the growth of colon cancer cells. miR145 also targets the type 1 insulin-like growth factor receptor (IGF-IR). We show here that an IRS-1 lacking its 3' UTR is no longer down-regulated by miR145 and rescues colon cancer cells from miR145-induced inhibition of growth. An IGF-IR resistant to miR145 (again by elimination of its 3' UTR) is not down-regulated by miR145 but fails to rescue colon cancer cells from growth inhibition. These and other results, taken together, indicate that down-regulation of IRS-1 plays a significant role in the tumor suppressor activity of miR145.

Familial short stature caused by haploinsufficiency of the insulin-like growth factor i receptor due to nonsense-mediated messenger ribonucleic acid decay

BACKGROUND

IGF-I, essential for normal human growth in utero and postnatally, mediates its effects through the IGF-I receptor (IGF1R), a widely expressed, cell surface tyrosine kinase receptor. Five cases of heterozygous mutations in the IGF1R gene have been identified in patients with varying degrees of intrauterine and postnatal growth retardation.

OBJECTIVE

The objective of the study was the analysis of the IGF1R gene in a short-statured patient and his affected family members.

PATIENT

The male patient, with a height of -3.1 sd score (SDS; aged 12 yr), had normal circulating levels of GH binding protein, IGF-I, and IGF binding protein-3. His mother (-4.6 SDS), one of his siblings (-1.94 SDS), and several other maternal family members were also short statured.

RESULTS

The patient, his mother, and the short-statured sibling carry a novel heterozygous 19-nucleotide duplication within exon 18 of the IGF1R gene, which introduces a premature termination codon at codon 1106 of the IGF1R open reading frame on one allele. Analyses of the primary dermal fibroblasts derived from the patient and family members indicated that the IGF1R mRNA expressed from the mutant allele was degraded through the nonsense-mediated mRNA decay pathway, resulting in reduced amount of wild-type IGF1R protein and, subsequently, diminished activation of the IGF1R pathway.

CONCLUSIONS

The mutation results in haploinsufficiency of IGF1R protein due to nonsense-mediated mRNA decay and is associated with familial short stature.

Polymorphisms in the IGF1 and IGF1R genes and children born small for gestational age: results of large population studies

Small for gestational age (SGA) is the term used to describe a group of children born with a birth weight and/or birth length below the normal range of a reference population, corrected for their gestational age. Although animal models have shown that insulin-like growth factor 1 (IGF1) and insulin-like growth factor 1 receptor (IGF1R) genes are important candidates for reduced pre- and postnatal growth, only limited case reports have been published describing mutations. This might suggest that IGF1 and IGF1R are such crucial growth factors that only common genetic polymorphisms are allowed to survive. Common IGF1 and IGF1R gene polymorphisms, such as single nucleotide polymorphisms and variable number of tandem repeats, have been investigated with conflicting results with respect to SGA-related outcomes. The exact contribution of these polymorphisms to clinical practice remains to be elucidated.

Similarities and differences between insulin and IGF-I: structures, receptors, and signalling pathways

Insulin and the insulin-like growth factors (IGF-I, IGF-II) are pleiotropic hormones that have multiple roles in regulating vital metabolic and developmental processes. Although most early data suggested that insulin is mainly involved in metabolic activities (e.g. control of sugar levels) and IGF-I/II control growth and differentiation events (e.g. bone elongation, cell division), today, it is clear that there is cross-talk between the various ligands and receptors of the IGF family. As a result of these complex interactions, the spectrum of activities that were classically assigned to insulin or IGF-I/II has greatly expanded, and the signalling events mediated by the insulin and IGF receptors is the subject of intensive research. This review provides a comparative analysis of the structures, receptors, and signalling pathways of insulin and IGF-I.

Diversification of the insulin receptor family in the helminth parasite Schistosoma mansoni

Insulin signalling is a very ancient and well conserved pathway in metazoan cells, dependent on insulin receptors (IR) which are transmembrane proteins with tyrosine kinase activity. A unique IR is usually present in invertebrates whereas two IR members are found with different functions in vertebrates. This work demonstrates the existence of two distinct IR homologs (SmIR-1 and SmIR-2) in the parasite trematode Schistosoma mansoni. These two receptors display differences in several structural motifs essential for signalling and are differentially expressed in parasite tissues, suggesting that they could have distinct functions. The gene organization of SmIR-1 and SmIR-2 is similar to that of the human IR and to that of the IR homolog from Echinococcus multilocularis (EmIR), another parasitic platyhelminth. SmIR-1 and SmIR-2 were shown to interact with human pro-insulin but not with pro-insulin-like growth factor-1 in two-hybrid assays. Phylogenetic results indicated that SmIR-2 and EmIR might be functional orthologs whereas SmIR-1 would have emerged to fulfil specific functions in schistosomes.

IGF-1R tyrosine kinase expression and dependency in clones of IGF-1R knockout cells (R−)

Insulin-like growth factor 1 receptor (IGF-1R) plays many crucial roles in cancer, like anti-apoptotic activity and necessity for transformation. IGF-1R knockout cells (R-) represent a useful tool for molecular mapping of biological properties of the receptor. R- cells have been shown to be refractory to transformation by viral and cellular oncogenes, highlighting the necessity of this receptor for transformation. Surprisingly, more recent studies have shown that these cells can undergo spontaneous transformation. This observation raises the question as whether R- cells over the years have acquired some properties mimicking those of IGF-1R. Using an IGF-1R inhibitor (cyclolignan PPP) we have identified clones of R- (R-s) that are sensitive to this compound. Since, PPP is closely related to podophyllotoxin, which is an efficient microtubule inhibitor, we first investigated if such a mechanism could explain the sensitivity to PPP. However, highly purified PPP showed no or very slight tubulin binding. Further analysis of R-s revealed expression of a 90 kDa protein being reactive to IGF-1R beta-subunit antibodies. This protein was weakly but constitutively tyrosine phosphorylated and was downregulated by siRNA targeting IGF-1R. This downregulation was paralleled by decreased R-s survival. Taken together, our study suggests that clones of R- express IGF-1R activity and dependency, which in turn may explain that R- can undergo spontaneous transformation.

Neuroendocrinology of protochordates: Insights from Ciona genomics

The genome for two species of Ciona is available making these tunicates excellent models for studies on the evolution of the chordates. In this review most of the data is from Ciona intestinalis, as the annotation of the C. savignyi genome is not yet available. The phylogenetic position of tunicates at the origin of the chordates and the nature of the genome before expansion in vertebrates allows tunicates to be used as a touchstone for understanding genes that either preceded or arose in vertebrates. A comparison of Ciona, a sea squirt, to other model organisms such as a nematode, fruit fly, zebrafish, frog, chicken and mouse shows that Ciona has many useful traits including accessibility for embryological, lineage tracing, forward genetics, and loss- or gain-of-function experiments. For neuroendocrine studies, these traits are important for determining gene function, whereas the availability of the genome is critical for identification of ligands, receptors, transcription factors and signaling pathways. Four major neurohormones and their receptors have been identified by cloning and to some extent by function in Ciona: gonadotropin-releasing hormone, insulin, insulin-like growth factor, and cionin, a member of the CCK/gastrin family. The simplicity of tunicates should be an advantage in searching for novel functions for these hormones. Other neuroendocrine components that have been annotated in the genome are a multitude of receptors, which are available for cloning, expression and functional studies.

Transcriptional regulation of the insulin-like growth factor-I receptor gene in breast cancer

The insulin-like growth factor-I receptor (IGF-IR) has an important role in normal mammary gland growth and morphogenesis. In addition, the IGF-IR has been implicated in the initiation and progression of breast cancer. Previous studies have indicated that acquisition of the malignant phenotype in breast cancer is initially IGF-IR dependent. Most breast cancer-derived cell lines and primary tumors express high levels of IGF-IR mRNA and protein, whereas metastatic stages are usually associated with a decrease in IGF-IR levels. Transcription of the IGF-IR gene is controlled by complex interactions involving DNA-binding and non DNA-binding transcription factors. This review highlights selected examples of tumor suppressors, including BRCA1, p53, and WT1, whose mechanism of action involves regulation of IGF-IR gene expression.

Association between IGF-IR gene polymorphisms and productive and reproductive traits in Holstein cows

The association between single-strand conformation polymorphism (SSCP) in the gene of insulin-like growth factor-I receptor (IGF-IR) and age at first calving (AFC), calving interval (CI), lactation length (LL), and milk yield (MY) was studied using 106 graded Holstein females. The polimerase chain reaction (PCR) with specific initiating oligonucleotides, resulted an amplified fragment of 335pb. The population genotypes frequencies were 82.1% and 17.9%, for AA and AB genotypes, respectively. The frequency of A allele was 0.91 and 0.09 of B allele. No association between the identified polymorphism and AFC, CI, and MY was observed. The LL was positively associated (P<0.05) with the absence of B allele. Animals carrying the AA genotype presented a longer lactation period.

Mutation at cleavage site of insulin-like growth factor receptor in a short-stature child born with intrauterine growth retardation

CONTEXT

Mouse knockout models have clearly demonstrated the critical importance of IGF-I and IGF receptor type 1 (IGF-IR) for embryonic growth as well as postnatal growth.

OBJECTIVE

We hypothesized that mutations of IGF-IR gene might predispose to short stature in children born with intrauterine growth retardation (IUGR).

PATIENTS

Twenty-four children with unexplained IUGR (birth weight < -1.5 SD) and short stature (<-2.0 SD) were screened for abnormalities of the IGF-IR gene.

METHODS

Direct DNA sequencing was used to identify IGF-IR gene mutations. Unprocessed IGF-IR proreceptor in fibroblasts was detected by immunoblot analysis. Functions of mutated IGF-IR in fibroblasts were evaluated by IGF-I binding, and IGF-I-stimulated DNA synthesis and beta-subunit autophosphorylation.

RESULTS

We found the following results: 1) a heterozygous mutation (R709Q) changing the cleavage site from Arg-Lys-Arg-Arg to Arg-Lys-Gln-Arg was identified in a 6-yr-old Japanese girl (case 1) and her mother who also had IUGR with short stature (case 2); 2) fibroblasts from case 2 contained more IGF-IR proreceptor protein (189 +/- 26% of normal) and less mature beta-subunit protein (63 +/- 12%); 3) [125I]IGF-I binding to fibroblasts from case 2 was reduced, compared with normal control (0.61 +/- 0.16 x 10(6) vs. 1.14 +/- 0.12 x 10(6) sites per cell; P < 0.05); and 4) both IGF-I-stimulated [3H]thymidine incorporation and IGF-IR beta-subunit autophosphorylation were low in fibroblasts from case 2, compared with those of control (P < 0.05).

CONCLUSIONS

These findings strongly suggest that this mutation leads to failure of processing of the IGF-IR proreceptor to mature IGF-IR and causes short stature and IUGR.

Nitric oxide decreases IGF-1 receptor function in vitro; glutathione depletion enhances this effect in vivo

Insulin-like growth factor-1 (IGF) helps maintain healthy articular cartilage; however, arthritic cartilage becomes less responsive to the anabolic actions of IGF. We previously showed that high concentrations of nitric oxide (NO) decrease IGF receptor tyrosine phosphorylation and response to IGF in intact chondrocytes. The current studies evaluate direct effects of NO on IGF receptor kinase (IGF-RK) in vitro. NO from S-nitroso-N-acetyl-d,l-penicillamine (SNAP) or 1-hydroxy-2-oxo-3-(N-3-methyl-aminopropyl)-3-methyl-1-triazene (NOC-7) inhibits IGF-RK auto- and substrate phosphorylation in a dose and time dependent manner. There is a linear correlation between inhibition of auto- and substrate phosphorylation (r(2)=0.98). Increasing either dithiothreitol or reduced glutathione (GSH) content of the phosphorylation buffer to protect thiol groups blocks NO inhibition of IGF-RK substrate phosphorylation. Increased S-nitrosylation of cysteines in IGF-RK after exposure to SNAP suggests that NO may react with sulfhydryl groups, form S-nitrosothiols, which may result in functional modifications. NO blockade of IGF-1 stimulated proteoglycan synthesis in intact cells is enhanced when chondrocyte glutathione is depleted. The in vitro system shows that there can be direct effects of NO on IGF-RK that modify receptor function; the intact cell studies suggest that the mechanisms identified in vitro may be important in intact chondrocyte insensitivity to IGF-1 in cells exposed to NO.

IGF-I receptor mutations resulting in intrauterine and postnatal growth retardation

BACKGROUND

Approximately 10 percent of infants with intrauterine growth retardation remain small, and the causes of their growth deficits are often unclear. We postulated that mutations in the gene for the insulin-like growth factor I receptor (IGF-IR) might underlie some cases of prenatal and postnatal growth failure.

METHODS

We screened two groups of children for abnormalities in the IGF-IR gene. In one group of 42 patients with unexplained intrauterine growth retardation and subsequent short stature, we used single-strand conformation polymorphism analysis, followed by direct DNA sequencing of any abnormalities found. A second cohort consisted of 50 children with short stature who had elevated circulating IGF-I concentrations. Complete sequencing of the IGF-IR gene was performed with DNA from nine children. We also studied a control group of 43 children with normal birth weights.

RESULTS

In the first cohort, we identified one girl who was a compound heterozygote for point mutations in exon 2 of the IGF-IR gene that altered the amino acid sequence to Arg108Gln in one allele and Lys115Asn in the other. Fibroblasts cultured from the patient had decreased IGF-I-receptor function, as compared with that in control fibroblasts. No such mutations were found in the 43 controls. In the second group, we identified one boy with a nonsense mutation (Arg59stop) that reduced the number of IGF-I receptors on fibroblasts. Both children had intrauterine growth retardation and poor postnatal growth.

CONCLUSIONS

Mutations in the IGF-IR gene that lead to abnormalities in the function or number of IGF-I receptors may also retard intrauterine and subsequent growth in humans.

Expression and distribution of insulin-like growth factor-1 receptor in human carcinomas

The insulin-like growth factor-1 receptor (IGF1-R) is a cellular receptor overexpressed in many tumor cell lines and in some human tumors that seems to play a critical role in transformation, tumorigenicity, and metastasis. To date, a comprehensive evaluation of tissue distribution of IGF1-R in human carcinomas from different anatomical sites has been lacking. Using stage-oriented human cancer tissue microarrays, we studied IGF1-R expression and distribution in a group of 152 human carcinomas from a variety of anatomical sites and from 63 normal tissues through immunohistochemistry. The tumors included carcinomas from breast (8), ovary (9), endometrium (7), esophagus (5), stomach (7), pancreas (7), liver (4), colon (10), kidney (14), bladder (17), prostate (11), head and neck (31), salivary glands (8), lung (13), and skin (1). Formalin-fixed, paraffin embedded tissues of each case were immuno-stained using the avidin-biotin peroxidase method and an anti-IGF1-R rabbit polyclonal antibody. High-membranous IGF1-R staining was observed in 7 of 8 (87.5%) breast carcinomas, in 9 of 9 (100%) ovarian carcinomas, in 7 of 7 (100%) endometrial carcinomas, in 5 of 7 (71.1%) gastric carcinomas, in 4 of 7 (57.1%) pancreatic carcinomas, in 9 of 10 (90%) colon adenocarcinomas, in 11 of 13 (84.6%) lung carcinomas, in 6 of 11 (54.5%) prostatic adenocarcinomas, and in 17 of 17 (100%) transitional cell carcinomas of the bladder. Only a minority of squamous cell carcinomas of the head and neck and esophagus (34), salivary gland tumors (5), and renal cell carcinomas (14) were IGF1-R positive. This study demonstrates the overexpression of IGF1-R across a wide variety of human carcinomas of glandular or transitional cell origin.

Oncogenic pathways implicated in ovarian epithelial cancer

Characterization of intracellular signaling pathways should lead to a better understanding of ovarian epithelial carcinogenesis and provide an opportunity to interfere with signal transduction targets involved in ovarian tumor cell growth, survival, and progression. Challenges toward such an effort are significant because many of these signals are part of cascades within an intricate and likely redundant intracellular signaling network (Fig.1). For instance, a given signal may activate a dual intracellular pathway (ie, MEK1-MAPK and PI3K/Akt required for fibronectin-dependent activation of matrix metalloproteinase 9). A single pathway also may transduce more than one biologic or oncogenic signal (ie, PI3K signaling in epithelial and endothelial cell growth and sprouting of neovessels). Despite these challenges, evidence for therapeutic targeting of signal transduction pathways is accumulating in human cancer. For instance, the EGF-specific tyrosine kinase inhibitor ZD 1839 (Iressa) may have a beneficial therapeutic effect on ovarian epithelial cancer. Therapy of this cancer may include inhibitors of PI kinase (quercetin), ezrin and PIP kinase (genistein). The G protein-coupled family of receptors, including LPA, also is an attractive target to drugs, although their frequent pleiotropic functions may be at times toxic and lack specificity. Because of the lack of notable toxicity, PI3K/Akt pathway inhibitors such as FTIs are a promising targeted therapy of ovarian epithelial cancer. Increasing insight into the oncogenic pathways involved in ovarian epithelial cancer also is helping clinicians to understand better the phenomenon of chemoresistance in this malignancy. Oncogenic activation of gamma-synuclein promotes cell survival and provides resistance to paclitaxel, but such a resistance is partially overcome by an MEK inhibitor that suppresses ERK activity. Ovarian epithelial cancer is a complex group of neoplasms with an overall poor prognosis. Comprehension of this cancer pathobiology suffers because of an incomplete understanding of precursor lesions and the absence of an orthotopic animal model until very recently. It can be predicted with confidence, however, that the discovery of potent inhibitors of signal transduction and the development of discovery tools, such as proteomics and metabolomics, may change the way by which clinicians may now address basic biomedical questions in this insidious and lethal disease.

Temporal relationships between FSH receptor, type 1 insulin-like growth factor receptor, and aromatase expression during FSH-induced differentiation of bovine granulosa cells maintained in serum-free culture

A serum-free culture system has been developed in ruminants that allows gonadotrophin-responsive induction of oestradiol (E2) production by non-differentiated granulosa cells (GC) from small antral follicles. Critical determinants are dose of FSH and insulin-like growth factor (IGF), and the plating density of the GC. Over the first 16 h of culture when cells remained as a dispersed monolayer, expression declined in FSH receptors (FSHr) (P <0.001), IGF type 1 receptor (IGF-1r) (P <0.08) and p450 arom (CYP19, P <0.001). Characteristic GC clusters formed from 16 h and further enlarged between 24 and 48 h, accompanied by marked increases in FSHr (P <0.01), IGF-1r (P <0.05), and p450 arom (P <0.01) expression, and preceded induction and subsequent peak E2 production, at 96 and 144 h, respectively (P <0.01). In conclusion, isolation and dispersion of GC appears to induce reversion to an immature state resulting in loss of receptor expression. Re-establishment of cell-cell communications in the presence of FSH and IGF results in receptor up-regulation and induction of cellular differentiation.

Organization of the human PTK7 gene encoding a receptor protein tyrosine kinase-like molecule and alternative splicing of its mRNA

Protein tyrosine kinase-7 (PTK7) is a receptor protein tyrosine kinase (RPTK)-like molecule that contains a catalytically inactive tyrosine kinase domain. We report here the genomic structure of the human PTK7 gene by screening a BAC library and DNA sequencing. The PTK7 gene is organized into 20 exons. All of the splicing junctions followed the conserved GT/AG rule. The exon-intron structure of the PTK7 gene in the region that encodes the catalytic domain was distinct from those of other RPTKs with strong homology. The 5'-flanking sequence of the PTK7 gene contains two GC boxes that concatenate Sp1 binding motifs, but does not contain either the TATA or CAAT consensus sequence. Using a luciferase reporter assay, it was demonstrated that the 883-bp 5'-flanking sequence is functional as a promoter of the PTK7 gene. We identified four new splicing variants in testis that could be derived from alternative splicing of exons 8-10, 10, a part of 12-13, and 16. The expression patterns of the splicing variants in the hepatoma and colon cancer cells were different from those of the testis. Our findings suggest that PTK7 is evolutionarily distinct from other RPTKs, and that the alternative splicing of PTK7 mRNA may contribute to its diverse function in cell signaling.

Structural biology of insulin and IGF1 receptors: implications for drug design

Type 2 diabetes mellitus -- in which the body produces insufficient amounts of insulin or the insulin that is produced does not function properly to control blood glucose -- is an increasingly common disorder. Prospective clinical studies have proven the benefits of tighter glucose control in reducing the frequency and severity of complications of the disease, leading to the advocation of earlier and more aggressive use of insulin therapy. Given the reluctance of patients with type 2 diabetes to inject themselves with insulin, orally active insulin mimetics would be a major therapeutic advance. Here, we discuss recent progress in understanding the structure-function relationships of the insulin and insulin-like growth factor 1 (IGF1) receptors, their mechanism of activation and their implications for the design of insulin-receptor agonists for diabetes therapy and IGF1-receptor antagonists for cancer therapy.

Zebrafish insulin-like growth factor-I receptor: molecular cloning and developmental expression

The biological actions of the insulin-like growth factors (IGFs) are mediated primarily by the IGF-I receptor (IGF-IR), and the IGF family has been highly conserved throughout vertebrate evolution. In this study we report the isolation of a 3 kb cDNA clone for the zebrafish IGF-IR that includes the complete 3' untranslated region and polyA tail and mapping of the receptor gene to zebrafish linkage group 7. The open reading frame deduced from the cDNA sequence encompasses the juxtamembrane and protein tyrosine kinase portions of the receptor, and is 70 and 67% identical to the corresponding regions of the IGF-IRs of the turbot and Xenopus, respectively. By RT-PCR, zebrafish IGF-IR expression was detected from early blastula to early larval stages of development. Using whole mount in situ hybridization, IGF-IR expression was detected after gastrulation. Expression was evident in most tissues but was particularly evident in the tail, in eye and ear primordia and in the brain.

Cloning of porcine IGF1 receptor cDNA and detection of sequence polymorphisms using RT-PCR

A cDNA encoding the porcine type 1 insulin-like growth factor receptor (IGF1R) was amplified by reverse transcriptase-polymerase chain reaction (RT-PCR). The sequence of a 4.2-kb product was determined and had an open reading frame, encoding 1367 amino acids with 98.1 and 95.2% sequence similarity to the human and rat IGF1R, respectively. In the comparison of RT-PCR derived IGF1R sequences from 12 unrelated pigs, 12 silent sequence variants were found.

Mechanism of STAT3 activation by insulin-like growth factor I receptor

Recent evidence indicates that STAT proteins can be activated by a variety of receptor and non-receptor protein-tyrosine kinases. Unlike cytokine-induced activation of STATs, where JAKs are known to play a pivotal role in phosphorylating STATs, the mechanism for receptor protein-tyrosine kinase-mediated activation of STATs remains elusive. In this study, we investigated the activation of STAT proteins by the insulin-like growth factor I receptor (IGF-IR) in vitro and in vivo and assessed the role of JAKs in the process of activation. We found that STAT3, but not STAT5, was activated in response to IGF-I in 293T cells cotransfected with IGF-IR and STAT expression vectors. Moreover, tyrosine phosphorylation of STAT3, JAK1, and JAK2 was increased upon IGF-I stimulation of endogenous IGF-IR in 293T cells transfected with the respective STAT or JAK expression vector. Supporting the observation in 293T cells, endogenous STAT3 was tyrosine-phosphorylated upon IGF-I stimulation in the muscle cell line C2C12 as well as in various embryonic and adult mouse organs during different stages of development. Dominant-negative JAK1 or JAK2 was able to block the IGF-IR-mediated tyrosine phosphorylation of STAT3 in 293T cells. A newly identified family of proteins called SOCS (suppressor of cytokine signaling), including SOCS1, SOCS2, SOCS3 and CIS, was able to inhibit the IGF-I-induced STAT3 activation as well with varying degrees of potency, in which SOCS1 and SOCS3 appeared to have the higher inhibitory ability. Inhibition of STAT3 activation by SOCS could be overcome by overexpression of native JAK1 and JAK2. We conclude that IGF-I/IGF-IR is able to mediate activation of STAT3 in vitro and in vivo and that JAKs are essential for the process of activation.

Studies of the variability of the genes encoding the insulin-like growth factor I receptor and its ligand in relation to type 2 diabetes mellitus

Insulin-like growth factor I (IGF-I) is an important regulator of many aspects of growth, differentiation, and development, and as low birth weight has been associated with impaired glucose tolerance and overt type 2 diabetes in adult life, we considered the genes encoding the IGF-I and the IGF-I receptor (IGF-IR) as candidates for low birth weight, insulin resistance, and type 2 diabetes. Here we report the mutational analysis of the coding regions of the IGF-I and IGF-IR performed on genomic DNA from probands of 82 Danish type 2 diabetic families. No mutations predicting changes in the amino acid sequences of the IGF-I or IGF-IR genes were detected, but several silent and intronic polymorphisms were found. The impact of the most prevalent polymorphism, GAG1013GAA of the IGF-IR, was evaluated in a population-based sample of 349 young healthy subjects, where the variant had an allele frequency of 0.44 (95% confidence interval, 0.40-0.48). No significant relationships between this variant and birth weight, birth length, or insulin sensitivity index were detected. In addition, we did not observe any significant differences in allelic frequencies of the codon 1013 variant between 395 type 2 diabetic patients (allele frequency, 0.52; 95% confidence interval, 0.49-0.55) and 238 matched glucose-tolerant control subjects (allelic frequency, 0.47; 95% confidence interval, 0.43-0.50). In conclusion, variability in the coding regions of IGF-I and the IGF-IR does not associate with reduced birth weight, insulin sensitivity index, or type 2 diabetes in the Danish population.

Insulin and insulin-like growth factor-1 receptors in an evoluted fish, the turbot: cDNA cloning and mRNA expression

The insulin receptor (IR) and the structurally related insulin-like growth factor type 1 receptor (IGF-1R) belong to the tyrosine kinase (TK) receptor family. In this study, we have carried out the molecular characterization of both receptors from turbot (Psetta maxima), an evoluted teleost flatfish. The cDNA encoding the precursors of IGF-1R and the nearly entire IR (only the first 16 amino acids of the alpha subunit are missing when compared to the published human sequence) were cloned from an embryonic cDNA library. The deduced polypeptides contain all the topological features characterizing the insulin/IGF-1 receptor family. They are highly conserved compared to their mammalian counterparts, particularly within domains involved in the catalytic activity and in the transduction pathways. Nevertheless, some differences in the primary sequences, especially in the carboxy-terminal domain of the precursors, may affect the functions fulfilled by these receptors. As in mammals, the long IGF-1R 5'-untranslated sequence contains open reading frames and potential Sp1 binding sites. Northern blot analyses have revealed a major IR transcript of 11 kb, which is approximately the size of IGF-1R transcript (Eliès, G., Groigno, L., Wolff, J., Boeuf, G., Boujard, D., 1996. Characterization of the insulin-like growth factor type 1 receptor messenger in two teleost species. Mol. Cell. Endocrinol. 124, 131-140.). If IR and IGF-1R transcripts are detected by RT-PCR at all developmental stages and in all tissues examined, in situ hybridization studies have shown that these mRNA can be visualized as ubiquitous signals only in young larvae, whereas IGF-1R and IR expression appears weaker during later development and in adult tissues.

Expression of insulin-like growth factor-1 receptor in human colorectal cancer

The activation of the insulinlike growth factor 1/IGF-1 receptor system (IGF1/IGF1-R) has recently emerged as critical event in transformation and tumorigenicity of several murine and human tumors. Expression of IGF1 and of IGF1-R has been demonstrated in normal and neoplastic intestinal cell lines of rats and humans. However, the modulation of IGF1-R expression during the progression from normal colonic mucosa to adenoma, to carcinoma, and to metastasis, has not been evaluated. In this retrospective study, we investigated the expression of IGF1-R in 12 colonic adenomas (AD), 36 primary colorectal adenocarcinomas (CA), and in 27 corresponding metastases (MT). Normal colonic mucosa (N) was adjacent to the CA in 34 cases. Formalin-fixed, paraffin-embedded tissues of each case were immunostained using the avidin-biotin-peroxidase method. We used an anti-IGF1-R rabbit polyclonal antibody (Santa Cruz Biotechnology, CA; dilution 1:100). Positive staining was quantitated by CAS-200. Moderate to strong cytoplasmic immunostaining was observed in 34 of 36 CA (96%), and in 25 of 27 MT (93%). In all of the positive MTs, the intensity of the staining was always strong. In 10 of 12 ADs (83%), only a faint cytoplasmic stain was identified. Normal mucosa when present was negative. Strong IGF1-R positivity correlated with higher grade and higher-stage tumors (P < .01). These data suggest a role of IGF1-R expression during the progression of colorectal adenoma to carcinoma. An increased number of IGF1-R receptors may favor the metastasis of colorectal cancer.

Genomic structure and expression of the mouse growth factor receptor related to tyrosine kinases (Ryk)

We report the genomic organization of the mouse orphan receptor related to tyrosine kinases (Ryk), a structurally unclassified member of the growth factor receptor family. The mouse RYK protein is encoded by 15 exons distributed over a minimum of 81 kilobases. Genomic DNA sequences encoding a variant protein tyrosine kinase ATP-binding motif characteristic of RYK are unexpectedly found in two separate exons. A feature of the gene is an unmethylated CpG island spanning exon 1 and flanking sequences, including a TATA box-containing putative promoter and single transcription start site. Immunohistochemical examination of RYK protein distribution revealed widespread but developmentally regulated expression, which was spatially restricted within particular adult organs. Quantitative reduction of Southern blotting stringency for the detection of Ryk-related sequences provided evidence for a retroprocessed mouse pseudogene and a more distantly related gene paralogue. Extensive cross-species reactivity of a mouse Ryk kinase subdomain probe and the cloning of a Ryk orthologue from Caenorhabditis elegans demonstrate that Ryk and its relatives encode widely conserved members of a novel receptor tyrosine kinase subfamily.

Insulin-like growth factor-I expression in normal and diseased endometrium

While the role of steroid hormones in the regulation of endometrial proliferation and differentiation is well established, the effects of growth factors and their receptors in normal and neoplastic endometrium remain a matter of debate. Previous studies have documented the positive effects of insulin-like growth factor-I (IGF-I) on epithelial cell proliferation and the active production of this growth factor in endometrial tissues. In view of decreased expression of transforming growth factor-beta1 (TGF-beta1), an antagonist of IGF-I, in endometrial carcinoma, we investigated the expression of IGF-I, at both the mRNA and protein levels, and the immunoreactivity for type I IGF-I receptor in 30 formalin-fixed, paraffin-embedded tissue samples of normal and neoplastic endometrium, in order to possibly clarify the role of IGF-I in endometrial proliferation and differentiation. Our results demonstrate a reduced expression of IGF-I mRNA in endometrial carcinomas compared with non-neoplastic tissues, despite equivalent immunohistochemical expression of IGF-I and IGF-I receptor. Our data suggest that IGF-I and its corresponding receptor may not be directly involved in endometrial cancer cell proliferation and differentiation in vivo, though other components of the IGF-I system (e.g., IGF binding proteins) may affect endometrial malignant transformation and tumor progression.