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.

Laron syndrome - A historical perspective.

Laron Syndrome (LS) [OMIm#262500], or primary GH insensitivity, was first described in 1966 in consanguineous Jewish families from Yemen. LS is characterized by a typical phenotype that includes dwarfism, obesity and hypogenitalism. The disease is caused by deletions or mutations of the GH-receptor gene, causing high serum GH and low IGF-I serum levels. We studied 75 patients from childhood to adult age. After early hypoglycemia due to the progressive obesity, patients tend to develop glucose intolerance and diabetes. The treatment is by recombinant IGF-I, which improves the height and restores some of the metabolic parameters. An unexpected finding was that patients homozygous for GH-R defects are protected from malignancy lifelong, not so heterozygotes or double heterozygote subjects. We estimate that there are at least 500 patients worldwide, unfortunately only few treated.

Identification of thioredoxin-interacting protein (TXNIP) as a downstream target for IGF1 action.

Laron syndrome (LS), or primary growth hormone (GH) insensitivity, is the best-characterized entity among the congenital insulin-like growth factor 1 (IGF1) deficiencies. Life-long exposure to minute endogenous IGF1 levels is linked to low stature as well as a number of endocrine and metabolic abnormalities. While elevated IGF1 is correlated with increased cancer incidence, epidemiological studies revealed that patients with LS do not develop tumors. The mechanisms associated with cancer protection in LS are yet to be discovered. Recent genomic analyses identified a series of metabolic genes that are overrepresented in patients with LS. Given the augmented expression of these genes in a low IGF1 milieu, we hypothesized that they may constitute targets for IGF1 action. Thioredoxin-interacting protein (TXNIP) plays a critical role in cellular redox control by thioredoxin. TXNIP serves as a glucose and oxidative stress sensor, being commonly silenced by genetic or epigenetic events in cancer cells. Consistent with its enhanced expression in LS, we provide evidence that TXNIP gene expression is negatively regulated by IGF1. These results were corroborated in animal studies. In addition, we show that oxidative and glucose stresses led to marked increases in TXNIP expression. Supplementation of IGF1 attenuated TXNIP levels, suggesting that IGF1 exerts its antiapoptotic effect via inhibition of TXNIP Augmented TXNIP expression in LS may account for cancer protection in this condition. Finally, TXNIP levels could be potentially useful in the clinic as a predictive or diagnostic biomarker for IGF1R-targeted therapies.

MicroRNA 132-3p Is Upregulated in Laron Syndrome Patients and Controls Longevity Gene Expression.

The growth hormone (GH)-insulin-like growth factor-1 (IGF1) endocrine axis is a central player in normal growth and metabolism as well as in a number of pathologies, including cancer. The GH-IGF1 hormonal system, in addition, has emerged as a major determinant of lifespan and healthspan. Laron syndrome (LS), the best characterized entity under the spectrum of the congenital IGF1 deficiencies, results from mutation of the GH receptor (GHR) gene, leading to dwarfism, obesity and other defects. Consistent with the key role of IGF1 in cellular proliferation, epidemiological studies have shown that LS patients are protected from cancer development. While reduced expression of components of the GH-IGF1 axis is associated with enhanced longevity in animal models, it is still unknown whether LS is associated with an increased lifespan. MicroRNAs (miRs) are endogenous short non-coding RNAs that regulate the expression of complementary mRNAs. While a number of miRs involved in the regulation of IGF components have been identified, no previous studies have investigated the differential expression of miRs in congenital IGF1 deficiencies. The present study was aimed at identifying miRs that are differentially expressed in LS and that might account for the phenotypic features of LS patients, including longevity. Our genomic analyses provide evidence that miR-132-3p was highly expressed in LS. In addition, we identified SIRT1, a member of the sirtuin family of histone deacetylases, as a target for negative regulation by miR-132-3p. The data was consistent with the notion that low concentrations of IGF1 in LS lead to elevated miR-132-3p levels, with ensuing reduction in SIRT1 gene expression. The impact of the IGF1-miR-132-3p-SIRT1 loop on aging merits further investigation.

Insulin: A Growth Hormone and Potential Oncogene.

Both in vitro and in vivo experimental studies proved that insulin has an important anabolic role. This physiological function of insulin is reflected in its well documented involvement in protein metabolism and in acceleration of cell proliferation. Support for a growth promoting action of insulin is further provided by clinical studies that revealed that children with hypoinsulinemia have a decreased growth rate whereas, on the other hand, children with hyperinsulinemia have an accelerated growth. While it was initially assumed that the growth activities of insulin are facilitated via cross-talk with the closely related insulin-like growth factor-1 receptor (IGF-1R), it is now clear that the vast majority of these activities are mediated via direct interaction with the insulin receptor (IR). The present article provides an overview of the growth and proliferative actions of insulin, with an emphasis on a number of pathological conditions, including cancer.

Identification of nucleolar protein NOM1 as a novel nuclear IGF1R-interacting protein.

The insulin-like growth factor-1 receptor (IGF1R) mediates the biological actions of both IGF1 and IGF2. In recent years, evidence has accumulated showing that, in addition to its classical cell-surface distribution, IGF1R translocates to cell nucleus via an apparently SUMO-1-dependent mechanism. While the role of IGF1R in nucleus has not yet been settled, available information suggests that the nuclear receptor displays activities usually linked to transcription factors, including DNA binding and transcription regulation. To gain insight into the biological pathways associated with nuclear IGF1R action we conducted a mass spectrometry-based proteomic analysis aimed at identifying interactors of IGF1R in nucleus of both benign and malignant breast cells. The nucleolar NOM1 molecule belongs to a family of proteins that contain the middle domain of eukaryotic initiation factor 4G (MIF4G) and/or interaction module (MA3), and functions in translation, cell growth and proliferation. Using a combination of co-immunoprecipitation and silencing assays we provide evidence of a complex, bi-directional interplay between nuclear IGF1R and nucleolar protein NOM1. Inhibition of nuclear IGF1R translocation by dansylcadaverine reduced NOM1 levels in nuclei of MCF7 cells. On the other hand, IGF1R overexpression enhanced NOM1 levels in the nuclear fraction. Of interest, NOM1 silencing led to a major increase in IGF1R biosynthesis. In summary, results are consistent with a physiologically-relevant interplay between the nuclear IGF1 signaling pathway and nucleolar protein NOM1.

[THE PROLIFERATIVE EFFECT OF DENDRITIC CELLS IN OVARIAN CANCER AND THE RELATIONSHIP WITH THE IGF SIGNALING PATHWAY].

INTRODUCTION: Epithelial ovarian cancer (EOC) is the principal cause of death from gynecologic cancer in developed countries. While surgery and chemotherapy can improve survival, the mortality and morbidity rates remain significantly high. The insulin-like growth factor (IGF) axis has been shown to play an important part in carcinogenesis of several human malignancies. Preclinical studies reported a significant anti-proliferative activity of IGF1 receptor (IGF1R) inhibitors in ovarian malignancies, however, clinical studies have shown variable response rates. Recent data indicate that immunotherapy could hold promise in improving EOC treatment. Dendritic cells (DCs) which are antigen presenting cells evoke a positive immune response. Moreover, a recent study shows that IGF treatment can inhibit DC maturation. AIMS: To investigate the involvement of IGF1R signaling in DCs and the effect of combined DCs and IGF1R inhibitor treatment on EOC cells growth. METHODS: HL-60 leukemic cells were differentiated to DCs and ligand induced phosphorylated IGF1R levels were measured by Western blotting. Next, inhibition of IGF1R in DCs was applied and the effect of this inhibition on EOC cell lines ES2 and SKOV3 was examined using the migration assay method. RESULTS: The differentiation of HL-60 into DCs was associated with decreased levels of both IGF1R phosphorylation and total IGF1R protein. In addition, in-vitro growth assays (scratch assay) demonstrated an increased growth of both ES2 and SKOV3 cells into the scratch zone when co-cultured with DCs which were not pre-treated with IGF1R inhibitor as compared to treated DCs. CONCLUSIONS: Preliminary data suggest that DC differentiation is associated with IGF1R signaling downregulation. Moreover, inhibition of IGF1R signaling in DCs might decrease EOC growth.

Oncogenic fusion proteins adopt the insulin-like growth factor signaling pathway.

The insulin-like growth factor-1 receptor (IGF1R) has been identified as a potent anti-apoptotic, pro-survival tyrosine kinase-containing receptor. Overexpression of the IGF1R gene constitutes a typical feature of most human cancers. Consistent with these biological roles, cells expressing high levels of IGF1R are expected not to die, a quintessential feature of cancer cells. Tumor specific chromosomal translocations that disrupt the architecture of transcription factors are a common theme in carcinogenesis. Increasing evidence gathered over the past fifteen years demonstrate that this type of genomic rearrangements is common not only among pediatric and hematological malignancies, as classically thought, but may also provide a molecular and cytogenetic foundation for an ever-increasing portion of adult epithelial tumors. In this review article we provide evidence that the mechanism of action of oncogenic fusion proteins associated with both pediatric and adult malignancies involves transactivation of the IGF1R gene, with ensuing increases in IGF1R levels and ligand-mediated receptor phosphorylation. Disrupted transcription factors adopt the IGF1R signaling pathway and elicit their oncogenic activities via activation of this critical regulatory network. Combined targeting of oncogenic fusion proteins along with the IGF1R may constitute a promising therapeutic approach.

Molecular insights into the transcriptional regulatory role of thyroid hormones in ovarian cancer.

The regulation of cancer-relevant genes by the thyroid hormones, 3, 5, 3'-Triiodo-L-thyronine (T3) and L-thyroxine (T4), was recently acknowledged. However, limited data exists on the hormonal effects on gene expression in ovarian cancer, a gynecological malignancy associated with a low cure rate. The expression of fifteen genes involved in DNA repair, cell cycle, apoptosis, and tumor suppression was evaluated in OVCAR-3 and A2780 cell lines, using real-time PCR following short incubation with T3 (1 nM) or T4 (100 nM). The thyroid hormones downregulated the expression of the majority of genes examined. Support for the involvement of the MAPK and PI3K in thyroid hormone-mediated gene expression was shown for a set of genes. FAS expression was inhibited in A2780 cells, while an unexpected induction was demonstrated in OVCAR-3 cells. An analogous effect on the protein levels of FAS receptor and its soluble form was demonstrated by Western blotting. We further established, using primer sets that discriminate between the different RNA isoforms, that the hormones increase the mRNA levels of both coding and non-coding FAS mRNAs. The prevalence of these isoforms, using The Cancer Genome Atlas (TCGA) analysis, was significantly more abundant in 17 cancer types, including ovarian cancer, compared to normal tissues. Our results highlight the role of thyroid hormones in the expression of cancer-relevant-genes in ovarian cancer and provide an important insight into the pathways by which mitogenic and anti-apoptotic effects are exerted.

Prolactin - Not Only a "Milk Hormone" Prolactin - Growth Hormone Relationships with Emphasis on Cancer.

Prolactin (PRL) is a hormone secreted by lactotrophic cells in the anterior pituitary gland and its main function is the stimulation of lactogenesis. Research in recent years has revealed that PRL is also related to cancer development and plays a role in autoimmune diseases. PRL and Growth Hormone (GH) belong to the same cytokine family, both are, at least in part, secreted by the same somatomammotrophic cells in the anterior pituitary, and share similar signaling pathways. These common features raise the question whether PRL and GH share also joint actions especially in the pathogenesis of cancer.

New therapeutic targets for endometrial cancer: a glimpse into the preclinical sphere.

INTRODUCTION: Endometrial cancer (EC) is the only gynecologic malignancy showing increasing trends in incidence and mortality. While standard treatment has been effective primarily for early-stage EC, precision medicine with tailored therapy has revolutionized the management of this disease. Genome sequencing analyses have identified four sub-types of EC. Treatments for primary and metastatic disease can now be tailored more accurately to achieve better oncologic results. AREAS COVERED: This review provides an overview of the most relevant and updated evidence in the literature regarding EC molecular analysis and its role in risk classification, prognostication, and guidance for tailored and target therapies in early and advanced/metastatic stages. In addition, it provides updated information on optimal surgical management based on molecular classification and highlights key advances and future strategies. EXPERT OPINION: EC molecular analysis yields the potential of tailoring adjuvant treatment by escalating or deescalating therapy, as shown for POLE-mutated and p53-mutated tumors. Moreover, the expression of specific molecular signatures offers the possibility to employ novel target therapies, such as immune-checkpoint inhibitors that have demonstrated a significant benefit on prognosis. New treatment guidelines are still being established, and ongoing studies are exploring the potential prognostic role of further sub-stratifications of the four molecular classes and treatment options.

Endometrial cancer (EC) is the only female cancer that is increasing among women. While the usual treatments work best when the disease is caught early, new advances in genetic studies have greatly improved the management of the disease. Four sub-types of EC have been identified. They are called: POLE-mutated, MMR-deficient, p53-abnormal, and no specific molecular profile. Treatments for EC can now be tailored more accurately to achieve better results. This review gives an overview of the most new and important evidence in the scientific literature about the molecular analysis of EC and how it can be used to help tailor the best treatments and surgeries for women with EC.

Insulin-like growth factor-I receptor (IGF-IR) translocates to nucleus and autoregulates IGF-IR gene expression in breast cancer cells.

The insulin-like growth factor (IGF) system plays an important role in mammary gland biology as well as in the etiology of breast cancer. The IGF-I receptor (IGF-IR), which mediates the biological actions of IGF-I and IGF-II, has emerged in recent years as a promising therapeutic target. The IGF and estrogen signaling pathways act in a synergistic manner in breast epithelial cells. The present study was aimed at investigating 1) the putative translocation of IGF-IR and the related insulin receptor (IR) to the nucleus in breast cancer cells, 2) the impact of IGF-IR and IR levels on IGF-IR biosynthesis in estrogen receptor (ER)-positive and ER-depleted breast cancer cells, and 3) the potential transcription factor role of IGF-IR in the specific context of IGF-IR gene regulation. We describe here a novel mechanism of autoregulation of IGF-IR gene expression by cellular IGF-IR, which is seemingly dependent on ER status. Regulation of the IGF-IR gene by IGF-IR protein is mediated at the level of transcription, as demonstrated by 1) binding assays (DNA affinity chromatography and ChIP) showing specific IGF-IR binding to IGF-IR promoter DNA and 2) transient transfection assays showing transactivation of the IGF-IR promoter by exogenous IGF-IR. The IR is also capable of translocating to the nucleus and binding the IGF-IR promoter in ER-depleted, but not in ER-positive, cells. However, transcription factors IGF-IR and IR display diametrically opposite activities in the context of IGF-IR gene regulation. Thus, whereas IGF-IR stimulated IGF-IR gene expression, IR inhibited IGF-IR promoter activity. In summary, we have identified a novel mechanism of IGF-IR gene autoregulation in breast cancer cells. The clinical implications of these findings and, in particular, the impact of IGF-IR/IR nuclear localization on targeted therapy require further investigation.

Letter to the Editor - responses to Weisntein D, Simon M, Yehezkel E, Laron Z, Werner H. Insulin analogues display IGF-I-like mitogenic and antiactivity in cultured cancer cells.

We thank the team of Eli Lilly and Company for their critical appraisal of our study and for giving us the opportunity to clarify a number of points [1]. We agree with Kazda et al. that randomized clinical trials will best address any direct relationship between insulin analogues and cancer in man. We do not question the fact that tight control of blood glucose has dramatically advanced the lives of patients with diabetes. This article is protected by copyright. All rights reserved.

IGF-1 and BRCA1 signalling pathways in familial cancer.

The insulin-like growth factor (IGF) system has a direct effect on cellular proliferation and survival, and interacts with genetic and environmental factors implicated in causing cancer. Experimental, clinical, and epidemiological evidence show that the IGF signalling pathways are important mediators in the biochemical and molecular chain of events that lead from a phenotypically normal cell to one harbouring neoplastic traits. BRCA1 and BRCA2 have an important role in the development of hereditary and sporadic breast and ovarian cancer. Recent evidence suggests that risk of cancer conferred by BRCA mutations can be modified by genetic and environmental factors, including ambient concentrations of IGF-1 and polymorphisms in IGF system components. This Review addresses interactions between the IGF and BRCA1 signalling pathways, and emphasises the convergence of IGF-1-mediated cell survival, proliferative pathways, and BRCA1-mediated tumour protective pathways. Understanding the complex interactions between these signalling pathways might improve our understanding of basic molecular oncology processes and help to identify new molecular targets, predictive biomarkers, and approaches for optimising cancer therapies.

Administration of insulin like growth factor I (IGFI) lowers serum lipoprotein(a)-impact on atherosclerotic cardiovascular disease.

Insulin like growth factor I (IGFI) secreted by the liver upon stimulation by pituitary growth hormone (GH) acts as the most important growth stimulating hormone in children. The present review presents evidence that among its additional metabolic effects, IGF-I suppresses the synthesis of lipoprotein(a) [Lp(a)], an independent risk factor for atherosclerotic cardiovascular disease. In view of this property, it is suggested that the addition of IGF-I to the armamentarium of hyperlipoproteinemia treatment should be considered.

Congenital IGF-1 deficiency protects from cancer: lessons from Laron syndrome.

Many clinical and experimental studies have implicated the growth hormone (GH)-insulin-like growth factor (IGF-1) axis with the progression of cancer. The epidemiological finding that patients with Laron syndrome (LS), the best-characterized disease under the spectrum of congenital IGF-1 deficiencies, do not develop cancer is of major scientific and translational relevance. The evasion of LS patients from cancer emphasizes the central role of the GH-IGF-1 system in cancer biology. To identify genes that are differentially expressed in LS and that might provide a biological foundation for cancer protection, we have recently conducted genome-wide profiling of LS patients and normal controls. Analyses were performed on immortalized lymphoblastoid cell lines derived from individual patients. Bioinformatic analyses identified a series of genes that are either over- or under-represented in LS. Differential expression was demonstrated in a number of gene families, including cell cycle, metabolic control, cytokine-cytokine receptor interaction, Jak-STAT and PI3K-AKT signaling, etc. Major differences between LS and controls were also noticed in pathways associated with cell cycle distribution, apoptosis, and autophagy. The identification of novel downstream targets of the GH-IGF-1 network highlights the biological complexity of this hormonal system and sheds light on previously unrecognized mechanistic aspects associated with GH-IGF-1 action in the cancer cell.

Insulin-like growth factors and aging: lessons from Laron syndrome.

The growth hormone (GH)-insulin-like growth factor-1 (IGF1) signaling pathway emerged in recent years as a key determinant of aging and longevity. Disruption of this network in different animal species, including flies, nematodes and mouse, was consistently associated with an extended lifespan. Epidemiological analyses have shown that patients with Laron syndrome (LS), the best-characterized disease under the umbrella of the congenital IGF1 deficiencies, seem to be protected from cancer. While aging and cancer, as a rule, are considered diametrically opposite processes, modern lines of evidence reinforce the notion that aging and cancer might, as a matter of fact, be regarded as divergent manifestations of identical biochemical and cellular underlying processes. While the effect of individual mutations on lifespan and health span is very difficult to assess, genome-wide screenings identified a number of differentially represented aging- and longevity-associated genes in patients with LS. The present review summarizes recent data that emerged from comprehensive analyses of LS patients and portrays a number of previously unrecognized targets for GH-IGF1 action. Our article sheds light on complex aging and longevity processes, with a particular emphasis on the role of the GH-IGF1 network in these mechanisms.

BRCA1 is expressed in uterine serous carcinoma (USC) and controls insulin-like growth factor I receptor (IGF-IR) gene expression in USC cell lines.

OBJECTIVE: The insulin-like growth factor I receptor (IGF-IR) and BRCA1 affect cell growth and apoptosis. Little information is available about BRCA1 activity on the IGF signaling pathway. This study evaluated the effect of BRCA1 on IGF-IR expression. METHODS: BRCA1 and IGF-IR immunohistochemistry on archival tissues (35 uterine serous carcinomas [USCs] and 17 metastases) were performed. USPC1 and USPC2 cell lines were transiently cotransfected with an IGF-IR promoter construct driving a luciferase reporter gene and a BRCA1 expression plasmid. Endogenous IGF-IR levels were evaluated by Western immunoblotting. RESULTS: We found high BRCA1 and IGF-IR protein expression in primary and metastatic USC tumors. All samples were immunostained for BRCA1-71% strongly stained; and 33/35 (94%) were stained positive for IGF-IR-2 (6%) strongly stained. No difference in BRCA1 and IGF-IR staining intensity was noted between BRCA1/2 mutation carriers and noncarriers. Metastatic tumors stained more intensely for BRCA1 than did the primary tumor site (P = 0.041) and with borderline significance for IGF-IR (P = 0.069). BRCA1 and IGF-IR staining did not correlate to survival. BRCA1 expression led to 35% and 54% reduction in IGF-IR promoter activity in the USPC1 and USCP2 cell lines, respectively. Western immunoblotting showed a decline in phosphorylated IGF-IR and phosphorylated AKT in both transiently and stably transfected cells. CONCLUSIONS: BRCA1 and IGF-IR are highly expressed in USC tumors. BRCA1 suppresses IGF-IR gene expression and activity. These findings suggest a possible biological link between the BRCA1 and the IGF-I signaling pathways in USC. The clinical implications of this association need to be explored.