Transcriptional and post-transcriptional regulation of the human IGF-II gene expression

IGF2 in memory, neurodevelopmental disorders, and neurodegenerative diseases

Insulin-like growth factor 2 (IGF2) emerged as a critical mechanism of synaptic plasticity and learning and memory. Deficits in IGF2 in the brain, serum, or cerebrospinal fluid (CSF) are associated with brain diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS). Increasing IGF2 levels enhances memory in healthy animals and reverses numerous symptoms in laboratory models of aging, neurodevelopmental disorders, and neurodegenerative diseases. These effects occur via the IGF2 receptor (IGF2R) - a receptor that is highly expressed in neurons and regulates protein trafficking, synthesis, and degradation. Here, I summarize the current knowledge regarding IGF2 expression and functions in the brain, particularly in memory, and propose a novel conceptual model for IGF2/IGF2R mechanisms of action in brain health and diseases.

Isogenic GAA-KO Murine Muscle Cell Lines Mimicking Severe Pompe Mutations as Preclinical Models for the Screening of Potential Gene Therapy Strategies

Pompe disease (PD) is a rare disorder caused by mutations in the acid alpha-glucosidase (GAA) gene. Most gene therapies (GT) partially rely on the cross-correction of unmodified cells through the uptake of the GAA enzyme secreted by corrected cells. In the present study, we generated isogenic murine GAA-KO cell lines resembling severe mutations from Pompe patients. All of the generated GAA-KO cells lacked GAA activity and presented an increased autophagy and increased glycogen content by means of myotube differentiation as well as the downregulation of mannose 6-phosphate receptors (CI-MPRs), validating them as models for PD. Additionally, different chimeric murine GAA proteins (IFG, IFLG and 2G) were designed with the aim to improve their therapeutic activity. Phenotypic rescue analyses using lentiviral vectors point to IFG chimera as the best candidate in restoring GAA activity, normalising the autophagic marker p62 and surface levels of CI-MPRs. Interestingly, in vivo administration of liver-directed AAVs expressing the chimeras further confirmed the good behaviour of IFG, achieving cross-correction in heart tissue. In summary, we generated different isogenic murine muscle cell lines mimicking the severe PD phenotype, as well as validating their applicability as preclinical models in order to reduce animal experimentation.

Identification of the hub genes and transcription factor-miRNA axes involved in Helicobacter pylori-associated gastric cancer

It has been previously reported that transcription factor-microRNA (TF-miRNA) axes play a significant role in the carcinogenesis of several types of malignant tumor. However, there is a lack of research into the differences in the mechanism of Helicobacter pylori (HP)-positive [HP(+)] and HP-negative [HP(−)] gastric cancer. The aim of the present study was to identify the hub genes and TF-miRNA axes, and to determine the potential mechanisms involved in HP-associated gastric cancer. HP-associated mRNA and miRNA data, as well as the corresponding clinical information, was downloaded from The Cancer Genome Atlas database. Differentially expressed genes (DEGs) and DE miRNAs (DEMs) were then identified from the HP(+) and HP(−) cancer mRNA and miRNA datasets, respectively. Subsequently, gene set enrichment analysis and the protein-protein interaction (PPI) networks were investigated using the ClusterProfiler packages. Lastly, TF-miRNA-DEG networks were constructed using the miRWalk online tool. A total of 1,050 DEGs and 13 DEMs were identified from the normalized mRNA and miRNA expression datasets, respectively. In addition, 180 Gene Ontology terms and 30 Kyoto Encyclopedia of Genes and Genomes pathways were found to be enriched, while 6 hub genes were identified from the PPI analysis. Furthermore, 7 TF-miRNA interactions and 181 TF-miRNA-DEG axes were constructed using an integrated bioinformatics approach, while 2 TF-miRNA interactions (ZEB1-miRNA-144-3p and PAX2-miRNA-592) were confirmed using reverse transcription-quantitative PCR in samples from enrolled patients. Moreover, the ZEB1-miRNA-144-3p axis was further validated based on dual luciferase reporter assay results. In summary, an integrated bioinformatics approach was used to screen the significant molecular and regulatory axes, which may provide a novel direction to investigate the pathogenesis of gastric cancer associated with HP.

Insulin-like growth factor-II and bioactive proteins containing a part of the E-domain of pro-insulin-like growth factor-II

Insulin-like growth factor (IGF)-II is considered to function as an important fetal growth factor, which is structurally and functionally related to IGF-I and proinsulin. At least in vitro, IGF-II actions are mediated through the IGF-I receptor and to a lesser extent the insulin receptor. After birth, the function of IGF-II is less clear although in adults the serum level of IGF-II exceeds that of IGF-I several fold. The IGF-II gene is maternally imprinted, with exception of the liver and several parts of the brain, where it is expressed from both alleles. The regulation, organization, and translation of the IGF-II gene is complex, with five different putative promotors leading to a range of noncoding and coding mRNAs. The 180-amino acid pre-pro-IGF-II translation product can be divided into five domains and include a N-terminal signal peptide of 24 amino acid residues, the 67 amino acid long mature protein, and an 89 residues extension at the COOH terminus, designated as the E-domain. After removal of the signal peptide, the processing of pro-IGF-II into mature IGF-II requires various steps including glycosylation of the E-domain followed by the action of endo-proteases. Several of these processing intermediates can be found in the human circulation. There is increasing evidence that, besides IGF-II, several incompletely processed precursor forms of the protein, and even a 34-amino acid peptide (preptin) derived from the E-domain of pro-IGF-II, exhibit distinct biological activities. This review will focus on the current insights regarding the specific roles of the latter proteins in cancer, glucose homeostasis, and bone physiology. To address this topic clearly in the right context, a concise overview of the biological and biochemical properties of IGF-II and several relevant aspects of the IGF system will be provided.

Big Insulin-like Growth Factor 2-Producing Tumor in a Hypoglycemic Dog

A 10-year-old female Papillon dog that had previously developed a mammary tumor was admitted for treatment of a hypoglycemic attack. Blood examination showed severe hypoglycemia and decreased blood insulin concentration. Computed tomography indicated multiple tumors in the cranial and caudal lobes of the right lung. These tumors were resected surgically and diagnosed as pulmonary adenocarcinomas by histopathologic examination. Hypoglycemia was temporarily improved after the resection, but a hypoglycemic event occurred 2 months after the surgery. Immunohistochemistry of the tumor demonstrated the expression of insulin-like growth factor 2 in tumor cells. Western blot analysis revealed the expression of high-molecular-weight (big)-insulin-like growth factor 2 in the tumor region. Insulin-like growth factor 2 mRNA expression was also confirmed in the tumor using reverse transcription-polymerase chain reaction. These findings indicate the diagnosis of non-islet cell tumor-induced hypoglycemia caused by big-insulin-like growth factor 2 produced by the tumor in the dog. This report provides information on differentiating tumors that cause paraneoplastic hypoglycemia.

The insulin-like growth factor 2 gene in mammals: Organizational complexity within a conserved locus

The secreted protein, insulin-like growth factor 2 (IGF2), plays a central role in fetal and prenatal growth and development, and is regulated at the genetic level by parental imprinting, being expressed predominantly from the paternally derived chromosome in mice and humans. Here, IGF2/Igf2 and its locus has been examined in 19 mammals from 13 orders spanning ~166 million years of evolutionary development. By using human or mouse DNA segments as queries in genome analyses, and by assessing gene expression using RNA-sequencing libraries, more complexity was identified within IGF2/Igf2 than was annotated previously. Multiple potential 5’ non-coding exons were mapped in most mammals and are presumably linked to distinct IGF2/Igf2 promoters, as shown for several species by interrogating RNA-sequencing libraries. DNA similarity was highest in IGF2/Igf2 coding exons; yet, even though the mature IGF2 protein was conserved, versions of 67 or 70 residues are produced secondary to species-specific maintenance of alternative RNA splicing at a variable intron-exon junction. Adjacent H19 was more divergent than IGF2/Igf2, as expected in a gene for a noncoding RNA, and was identified in only 10/19 species. These results show that common features, including those defining IGF2/Igf2 coding and several non-coding exons, were likely present at the onset of the mammalian radiation, but that others, such as a putative imprinting control region 5’ to H19 and potential enhancer elements 3’ to H19, diversified with speciation. This study also demonstrates that careful analysis of genomic and gene expression repositories can provide new insights into gene structure and regulation.

The insulin-like growth factor 2 gene and locus in nonmammalian vertebrates: Organizational simplicity with duplication but limited divergence in fish

The small, secreted peptide, insulin-like growth factor 2 (IGF2), is essential for fetal and prenatal growth in humans and other mammals. Human IGF2 and mouse Igf2 genes are located within a conserved linkage group and are regulated by parental imprinting, with IGF2/Igf2 being expressed from the paternally derived chromosome, and H19 from the maternal chromosome. Here, data retrieved from genomic and gene expression repositories were used to examine the Igf2 gene and locus in 8 terrestrial vertebrates, 11 ray-finned fish, and 1 lobe-finned fish representing >500 million years of evolutionary diversification. The analysis revealed that vertebrate Igf2 genes are simpler than their mammalian counterparts, having fewer exons and lacking multiple gene promoters. Igf2 genes are conserved among these species, especially in protein-coding regions, and IGF2 proteins also are conserved, although less so in fish than in terrestrial vertebrates. The Igf2 locus in terrestrial vertebrates shares additional genes with its mammalian counterparts, including tyrosine hydroxylase (Th), insulin (Ins), mitochondrial ribosomal protein L23 (Mrpl23), and troponin T3, fast skeletal type (Tnnt3), and both Th and Mrpl23 are present in the Igf2 locus in fish. Taken together, these observations support the idea that a recognizable Igf2 was present in the earliest vertebrate ancestors, but that other features developed and diversified in the gene and locus with speciation, especially in mammals. This study also highlights the need for correcting inaccuracies in genome databases to maximize our ability to accurately assess contributions of individual genes and multigene families toward evolution, physiology, and disease.

Similarity and variation in the insulin-like growth factor 2 - H19 locus in primates

Insulin-like growth factor 2 (IGF2), a small, secreted protein, is critical for fetal and prenatal growth in humans and other mammals. The IGF2 gene and its mouse homolog comprise part of a conserved linkage group that is regulated by parental imprinting, with IGF2/ Igf2 being expressed from the paternal chromosome, and the adjacent H19 gene from the maternal chromosome. By using information extracted from public genomic and gene expression databases, I have now analyzed this locus in nine nonhuman primate species representing over 60 million years of evolutionary divergence from a common progenitor. Both IGF2 and H19 genes and the entire locus have been conserved among these primates. Each primate IGF2 gene except for gibbon and marmoset is composed of 10 exons and contains five potential promoters, each with distinctive 5'-untranslated exons. Similarly, except for marmoset and mouse lemur, H19 consists of six exons and has two promoters. DNA sequence conservation is high, not only in orthologous exons and promoters, but also in a putative imprinting control region located 5' to H19 and in multiple potential distal enhancer elements found 3' to H19. Collectively, these results support the hypothesis that common regulatory processes shaped the IGF2 - H19 locus before the onset of primate speciation more than 85 million years ago. This study also leads to the conclusion that inaccuracies in data presentation in genetic repositories could limit our ability to develop novel insights about roles of individual genes and multigene loci in mammalian physiology and disease.

The complex genetics of human insulin-like growth factor 2 are not reflected in public databases

Recent advances in genetics present unique opportunities for enhancing knowledge about human physiology and disease susceptibility. Understanding this information at the individual gene level is challenging and requires extracting, collating, and interpreting data from a variety of public gene repositories. Here, I illustrate this challenge by analyzing the gene for human insulin-like growth factor 2 (IGF2) through the lens of several databases. IGF2, a 67-amino acid secreted peptide, is essential for normal prenatal growth and is involved in other physiological and pathophysiological processes in humans. Surprisingly, none of the genetic databases accurately described or completely delineated human IGF2 gene structure or transcript expression, even though all relevant information could be found in the published literature. Although IGF2 shares multiple features with the mouse Igf2 gene, it has several unique properties, including transcription from five promoters. Both genes undergo parental imprinting, with IGF2/Igf2 being expressed primarily from the paternal chromosome and the adjacent H19 gene from the maternal chromosome. Unlike mouse Igf2, whose expression declines after birth, human IGF2 remains active throughout life. This characteristic has been attributed to a unique human gene promoter that escapes imprinting, but as shown here, it involves several different promoters with distinct tissue-specific expression patterns. Because new testable hypotheses could lead to critical insights into IGF2 actions in human physiology and disease, it is incumbent that our fundamental understanding is accurate. Similar challenges affecting knowledge of other human genes should promote attempts to critically evaluate, interpret, and correct human genetic data in publicly available databases.

Increased motor neuron resilience by small molecule compounds that regulate IGF-II expression

The selective vulnerability of motor neurons in amyotrophic lateral sclerosis (ALS) is evident by sparing of a few subpopulations during this fast progressing and debilitating degenerative disease. By studying the gene expression profile of resilient vs. vulnerable motor neuron populations we can gain insight in what biomolecules and pathways may contribute to the resilience and vulnerability. Several genes have been found to be differentially expressed in the vulnerable motor neurons of the cervical spinal cord as compared to the spared motor neurons in CNIII/IV. One gene that is differentially expressed and present at higher levels in less vulnerable motor neurons is insulin-like growth factor II (IGF-II). The motor neuron protective effect of IGF-II has been demonstrated both in vitro and in SOD1 transgenic mice. Here, we have screened a library of small molecule compounds and identified inducers of IGF-II mRNA and protein expression. Several identified compounds significantly protected motor neurons from glutamate excitotoxicity in vitro. One of the compounds, vardenafil, resulted in a complete motor neuron protection, an effect that was reversed by blocking receptors of IGF-II. When administered to naïve rats vardenafil was present in the cerebrospinal fluid and increased IGF-II mRNA expression in the spinal cord. When administered to SOD1 transgenic mice, there was a significant delay in motor symptom onset and prolonged survival. Vardenafil also increased IGF-II mRNA and protein levels in motor neurons derived from healthy subject and ALS patient iPSCs, activated a human IGF-II promoter and improved survival of ALS-patient derived motor neurons in culture. Our findings suggest that modulation of genes differentially expressed in vulnerable and resilient motor neurons may be a useful therapeutic approach for motor neuron disease.

Doege-Potter syndrome: A review of the literature including a new case report

RATIONALE

We reviewed 76 published cases of Doege-Potter syndrome, and non-islet cell tumor hypoglycemia (NICTH) secondary to a solitary fibrous tumor (SFT) between 1989 and 2016, to study disease pathogenesis, diagnosis, and treatment of this rare paraneoplastic disease. Further, we report 1 new case of a patient presenting with Doege-Potter syndrome.

PATIENTS CONCERNS

The tumors originated from the pleural cavity, lung, pelvis, liver, retroperitoneum, kidney, mediastinal, the sella, uterus, bladder, intestine, mandibular, and the thigh. The most common location was the pleural cavity (left 12 cases and right 28 cases). Moreover, 28/71 (39.4%) were benign and 43/71 (60.6%) were malignant. SFTs with NICTH were more likely to be malignant and present at a higher rate than previously published (5%-10.4%). The malignancy rate of extrathoracic SFTs was higher than that of thoracic SFTs, 20 (66.7%) as compared with 23 (56.1%). Age of onset varied from 24 to 85 years (mean 59 years), with 47 males and 28 females, and gender unavailable for 1 case. When comparing clinical characteristics of patients with benign as compared malignant tumors, no significant differences in the age of onset, gender, or size of tumor were seen. Among 15/19 cases, the insulin-like growth factor II (IGF-II)/IGF-I ration was >10.0. Complete tumor resection remained the only definitive treatment.

OUTCOMES AND LESSENS

Glucocorticoids dose-dependently reduce the frequency and severity of hypoglycemic episodes. Low doses of prednisone were ineffective at relieving hypoglycemia. The effect of neoadjuvant treatment, consisting of chemoradiation, and consecutive selective embolization of vessels feeding the tumor were not identified.

The role of the insulin‑like growth factor (IGF) axis in osteogenic and odontogenic differentiation

The insulin-like growth factor (IGF) axis is a multicomponent molecular network which has important biological functions in the development and maintenance of differentiated tissue function(s). One of the most important functions of the IGF axis is the control of skeletal tissue metabolism by the finely tuned regulation of the process of osteogenesis. To achieve this, the IGF axis controls the activity of several cell types—osteoprogenitor cells, osteoblasts, osteocytes and osteoclasts to achieve the co-ordinated development of appropriate hard tissue structure and associated matrix deposition. In addition, there is an increasing awareness that the IGF axis also plays a role in the process of odontogenesis (tooth formation). In this review, we highlight some of the key findings in both of these areas. A further understanding of the role of the IGF axis in hard tissue biology may contribute to tissue regeneration strategies in cases of skeletal tissue trauma.

The insulin and igf-I pathway in endocrine glands carcinogenesis

Endocrine cancers are a heterogeneous group of diseases that may arise from endocrine cells in any gland of the endocrine system. These malignancies may show an aggressive behavior and resistance to the common anticancer therapies. The etiopathogenesis of these tumors remains mostly unknown. The normal embryological development and differentiation of several endocrine glands are regulated by specific pituitary tropins, which, in adult life, control the function and trophism of the endocrine gland. Pituitary tropins act in concert with peptide growth factors, including the insulin-like growth factors (IGFs), which are considered key regulators of cell growth, proliferation, and apoptosis. While pituitary TSH is regarded as tumor-promoting factor for metastatic thyroid cancer, the role of other pituitary hormones in endocrine cancers is uncertain. However, multiple molecular abnormalities of the IGF system frequently occur in endocrine cancers and may have a role in tumorigenesis as well as in tumor progression and resistance to therapies. Herein, we will review studies indicating a role of IGF system dysregulation in endocrine cancers and will discuss the possible implications of these findings for tumor prevention and treatment, with a major focus on cancers from the thyroid, adrenal, and ovary, which are the most extensively studied.

Severe hypoglycemia with "Big"-IGF-2 oversecretion by a giant phyllode tumor of the breast: a rare case of non-islet cell tumor-induced hypoglycemia (NICTH)

OBJECTIVE

We report an exceptional case of non-islet cell tumor-induced hypoglycemia (NICTH) secondary to "Big"-IGF-2 oversecretion due to a giant phyllode tumor of the breast.

CLINICAL PRESENTATION

A 49-year-old woman was admitted in emergency for brutal neurologic defect revealing severe hypoglycemia. Several similar episodes were observed throughout hospitalization, requiring continue perfusion of hypertonic glucose solution. Beside these metabolic disorders, we observed a giant and hard tumor of the left breast (about 30cm in diameter).

INTERPRETATION

Supplementary blood analysis revealed serum levels of C-peptide and insulin suppressed during hypoglycemia, excluding the possibility of either endogenous or exogenous hyperinsulinism. Low plasma levels of GH and IGF-1 were found, suggesting a negative feedback loop on somatotroph axis function. Therefore, the hypothesis of an insulinomimetic compound released by tumor cells was evoked because of abnormal presence of high-weight and immature form of IGF-2 (called "Big"-IGF-2) in the serum identified by western immunoblot analysis. A left mastectomy was performed and completely restored glucose homeostasis and confirmed the paraneoplastic origin of hypoglycemia because of markedly elevated expression of IGF-2 mRNA (qPCR) within the tumor cells. Finally, the anatomopathology analysis diagnosed a mesenchymatous tumor, namely a high-grade phyllode sarcoma of the breast.

CONCLUSION

Although NICTH due to "Big"-IGF-2 overproduction is a rare phenomenon, mainly observed in case of mesenchymatous tumor, it should be considered in presence of severe hypoglycemia with voluminous tumor and without hyperinsulinism.

Cohesin is required for higher-order chromatin conformation at the imprinted IGF2-H19 locus

Cohesin is a chromatin-associated protein complex that mediates sister chromatid cohesion by connecting replicated DNA molecules. Cohesin also has important roles in gene regulation, but the mechanistic basis of this function is poorly understood. In mammalian genomes, cohesin co-localizes with CCCTC binding factor (CTCF), a zinc finger protein implicated in multiple gene regulatory events. At the imprinted IGF2-H19 locus, CTCF plays an important role in organizing allele-specific higher-order chromatin conformation and functions as an enhancer blocking transcriptional insulator. Here we have used chromosome conformation capture (3C) assays and RNAi-mediated depletion of cohesin to address whether cohesin affects higher order chromatin conformation at the IGF2-H19 locus in human cells. Our data show that cohesin has a critical role in maintaining CTCF-mediated chromatin conformation at the locus and that disruption of this conformation coincides with changes in IGF2 expression. We show that the cohesin-dependent, higher-order chromatin conformation of the locus exists in both G1 and G2 phases of the cell cycle and is therefore independent of cohesin's function in sister chromatid cohesion. We propose that cohesin can mediate interactions between DNA molecules in cis to insulate genes through the formation of chromatin loops, analogous to the cohesin mediated interaction with sister chromatids in trans to establish cohesion.

PPAR-γ agonists and their effects on IGF-I receptor signaling: Implications for cancer

It is now well established that the development and progression of a variety of human malignancies are associated with dysregulated activity of the insulin-like growth factor (IGF) system. In this regard, promising drugs have been developed to target the IGF-I receptor or its ligands. These therapies are limited by the development of insulin resistance and compensatory hyperinsulinemia, which in turn, may stimulate cancer growth. Novel therapeutic approaches are, therefore, required. Synthetic PPAR-γ agonists, such as thiazolidinediones (TZDs), are drugs universally used as antidiabetic agents in patients with type 2 diabetes. In addition of acting as insulin sensitizers, PPAR-γ agonists mediate in vitro and in vivo pleiotropic anticancer effects. At least some of these effects appear to be linked with the downregulation of the IGF system, which is induced by the cross-talk of PPAR-γ agonists with multiple components of the IGF system signaling. As hyperinsulinemia is an emerging cancer risk factor, the insulin lowering action of PPAR-γ agonists may be expected to be also beneficial to reduce cancer development and/or progression. In light of these evidences, TZDs or other PPAR-γ agonists may be exploited in those tumors "addicted" to the IGF signaling and/or in tumors occurring in hyperinsulinemic patients.

IGF and insulin receptor signaling in breast cancer

Major molecular abnormalities in breast cancer include the deregulation of several components of the IGF system. It is well recognized that the epithelial breast cancer cells commonly overexpress the IGF-I receptor while IGF-II is expressed by the tumor stroma. In view to the fact that the IGF-IR has mitogenic, pro-invasive and anti-apoptotic effects and mediates resistance to a variety of anti-cancer therapies, breast cancer is expected to be a candidate to therapeutic approaches aimed to inhibit the IGF-IR. However, there is increasing awareness that IGF system in cancer undergoes signal diversification by various mechanisms. One of these mechanisms is the aberrant expression of insulin receptor (IR) isoform A (IR-A), which is a high affinity receptor for both insulin and IGF-II, in breast cancer cells. Moreover, overexpression of both IGF-IR and IR-A in breast cancer cells, leads to overexpression of hybrid IR/IGF-IR receptors (HRs) as well. Upon binding to IGF-II, both IR-A and HRs may activate unique signaling patterns, which predominantly mediate proliferative effects. A better understanding of IGF system signal diversification in breast cancer has important implications for cancer prevention measures, which should include control of insulin resistance and associated hyperinsulinemia. Moreover, in addition to the IGF-IR, both IR-A and HRs should be also considered as molecular targets for anti-cancer therapies.

Examination of IGF2 and H19 loss of imprinting in bladder cancer

Loss of imprinting (LOI) is a common epigenetic event in cancer and may serve as an early biomarker in some cancers. To obtain a better understanding of LOI, we studied 41 bladder tumors and their adjacent normal bladder mucosa. We found 2/9 (22.2%) cases that displayed LOI of IGF2 and 2/16 (12.5%) that had LOI of H19, as determined by the evaluation of mRNA for biallelic expression. In addition, we examined allele-specific methylation of the differentially methylated regions (DMR) of IGF2 and H19 using a new allele-specific pyrosequencing assay. We found that DNA methylation changes were a common finding (21/30, 70%) in the DMR regions, but could not clearly link DNA methylation changes with LOI as measured by biallelic expression. LOI and allele-specific DNA methylation changes are present in bladder cancer; however, a better understanding of the biology of LOI and its relationship to DNA methylation changes is needed before its use as an epigenetic biomarker.

Transcriptional regulation and biological significance of the insulin like growth factor II gene

The insulin like growth factors I and II are the most ubiquitous in the mammalian embryo. Moreover they play a pivotal role in the development and growth of tumours. The bioavailability of these growth factors is regulated on a transcriptional as well as on a posttranslational level. The expression of non-signalling receptors as well as binding proteins does further tune the local concentration of IGFs. This paper aims at reviewing how the transcription of the IGF genes is regulated. The biological significance of these control mechanisms will be discussed.

IGF-II promoter methylation and ovarian cancer prognosis

PURPOSE

The insulin-like growth factor-II (IGF-II) gene has four promoters that produce distinct transcripts which vary by tissue type and developmental stage. Dysregulation of normal promoter usage has been shown to occur in cancer; DNA methylation regulates promoter use. Thus, we sought to examine if DNA methylation varies among IGF-II promoters in ovarian cancer and if methylation patterns are related to clinical features of the disease.

STUDY DESIGN

Tumor tissue, clinical data, and follow-up information were collected from 215 patients diagnosed with primary epithelial ovarian cancer. DNA extracted from tumor tissues was analyzed for IGF-II promoter methylation with seven methylation specific PCR (MSP) assays: three for promoter 2 (P2) and two assays each for promoters 3 and 4 (P3 and P4).

RESULTS

Methylation was found to vary among the seven assays: 19.3% in P2A, 45.6% in P2B, 50.9% in P2C, 48.4% in P3A, 13.1% in P3B, 5.1% in P4A, and 6.1% in P4B. Methylation in any of the three P2 assays was associated with high tumor grade (P = 0.043), suboptimal debulking (P = 0.036), and disease progression [hazards ratio (HR) = 1.73, 95% confidence interval (CI) 1.09-2.74]. When comparing promoter methylation patterns, differential methylation of P2 and P3 was found to be associated with disease prognosis; patients with P3 but not P2 methylation were less likely to have disease progression (HR = 0.39, 95% CI 0.17-0.91) compared to patients with P2 but not P3 methylation.

CONCLUSIONS

This study shows that methylation varies among three IGF-II promoters in ovarian cancer and that this variation seems to have biologic implications as it relates to clinical features and prognosis of the disease.

Biological activity of rainbow trout Ea4-peptide of the pro-insulin-like growth factor (pro-IGF)-I on promoting attachment of breast cancer cells (MDA-MB-231) via alpha2- and beta1-integrin

E-peptide of pro-IGF-I was considered as biologically inactive. We have demonstrated that rainbow trout (rt) Ea4-peptide exerted biological activities in several established tumor cell lines [Chen et al., 2002; Kuo and Chen, 2002]. Here we report the activity of rtEa4-peptide in promoting attachment of human breast cancer cells (MDA-MB-231). While rtEa2-, rtEa3-, and rtEa4-peptides enhanced the attachment of MDA-MB-231 cells in a dose dependent manner, rtEa4-peptide possessed the highest activity. Antibodies specific to alpha2 and beta1 integrins significantly inhibited the attachment of cells to rtEa4-peptide coated-plates by 40%. In addition, rtEa4-peptide induced the expression of fibronectin 1 and laminin receptor genes in MDA-MB-231 cells. Blocking new protein synthesis by cycloheximide significantly reduced the attachment of MDA-MB-231 cells to rtEa4-peptide coated wells by 50%. These results suggest that rtEa4-peptide may promote cell attachment by interacting with alpha2/beta1 integrin receptors at the cell surface and by inducing the expression of fibronectin 1 and laminin receptor genes. Expression of fibronectin 1 gene induced by rtEa4-peptide in MDA-MB-231 cells was abolished by inhibitors of PI3K, PKC, Mek1/2, JNK1/2, and p38 MAPK signaling transduction molecules. These results suggested that induction of fibronectin 1 gene expression in MDA-MB-231 cells by rtEa4-peptide may be mediated via PI3K, PKC, Mek1/2, JNK1/2, and p38 MAPK signal transduction molecules.

H19 sense and antisense transgenes modify insulin-like growth factor-II mRNA levels

The oppositely-imprinted genes insulin-like growth factor-II (IGF2) and H19, a putative tumor suppressor, often show coordinate, reciprocal regulation and are believed to play a role in carcinogenesis. To explore the possible interactions between these genes, we stably transfected diHepG2 cells with a plasmid containing either the sense or the antisense H19 cDNA sequences and verified their expression by Northern analysis and by RNase protection analysis. Levels of H19, IGF2 and gamma-actin mRNA were quantified by competitive RT-PCR analysis. Although H19 sense transgene overexpression (n = 24 clones) did not decrease the low, basal levels of IGF2 mRNA compared to control cells, levels of IGF2 mRNA were positively correlated with the levels of H19 antisense mRNA (P < 0.0001, n = 40 clones). Furthermore, the increase in IGF2 mRNA level was accompanied by an elevation of IGF-II peptide in conditioned media. To see if H19 mRNA had a specific effect on transcription, we also performed transient transfections with reporter gene constructs containing IGF2 promoter 3 in the presence of sense or antisense H19 cDNA sequences under control of a cytomegalovirus promoter. We show a lower reporter gene activity from reporter gene constructs in the presence of sense H19 cDNA than from those with antisense or neomycin. Our results suggest that H19 participates in the repression of IGF2, at least in part through effects on IGF2 transcription, an effect which may contribute to its action as a tumor suppressor.

The effects of insulin-like growth factors on tumorigenesis and neoplastic growth

Several decades of basic and clinical research have demonstrated that there is an association between the insulin-like growth factors (IGFs) and neoplasia. We begin with a brief discussion of the function and regulation of expression of the IGFs, their receptors and the IGF-binding proteins (IGFBPs). A number of investigational interventional strategies targeting the GH or IGFs are then reviewed. Finally, we have assembled the available scientific knowledge about this relationship for each of the major tumor types. The tumors have been grouped together by organ system and for each of the major tumors, various key elements of the relationship between IGFs and tumor growth are discussed. Specifically these include the presence or absence of autocrine IGF-I and IGF-II production; presence or absence of IGF-I and IGF-II receptor expression; the expression and functions of the IGFBPs; in vitro and in vivo experiments involving therapeutic interventions; and available results from clinical trials evaluating the effect of GH/IGF axis down-regulation in various malignancies.

Cloning of breakpoints in and downstream the IGF2 gene that are associated with overexpression of IGF2 transcripts in colorectal tumours

The human IGF2 gene belongs to a group of imprinted genes clustered on the short arm of chromosome 11, band p15.5. It contains 9 exons and spans over 30 kb. IGF2 mRNA overexpression has been reported in human tumours and in some inherited growth disorders. It was recently demonstrated that IGF2 mRNA overexpression contributes to tumour progression and that loss of parental imprinting as well as altered transcription factors are contributing to this overexpression. We have reported structural alterations in the 3' region of the IGF2 gene in two colorectal tumours that overexpressed the IGF2 transcript by 200- and 800-fold. We cloned by the vectorette-PCR strategy, genomic DNA fragments containing the breakpoints from these tumours. The sequencing of these fragments positioned the breakpoint 2 kb downstream the IGF2 gene in one tumour, and in exon 9 in the second. Both breakpoints occurred in regions containing repetitive elements: a TGGA repeat we have identified downstream the gene, and the (CA)n repetition in exon 9. We hypothesize that a negative regulatory element, located downstream the IGF2 gene, has been deleted following these structural alterations and leads to IGF2 gene overexpression.

Basic fibroblast growth factor induces proteolysis of secreted and cell membrane-associated insulin-like growth factor binding protein-2 in human neuroblastoma cells

Insulin-like growth factor (IGF) action in the brain is modulated by IGF-binding proteins (IGFBPs) whose abundance can be altered by other locally expressed growth factors. However, the mechanisms involved are unclear. We here employed the neuroblastoma cell line SK-N-MC as a model to define the mechanisms involved in modulation of IGFBPs in neuronal cells. Western ligand blotting analysis and immunoprecipitation of conditioned media (CM) from SK-N-MC cells showed that in these cells, as in the brain, the most abundantly expressed IGFBP was IGFBP-2. However, IGFBP-2 was barely detectable in CM from cells treated with basic fibroblast growth factor (bFGF) without a change in IGFBP-2 messenger RNA (mRNA) abundance. These CM contained specific IGFBP-2 proteolytic activity, resulting in two IGFBP-2 fragments of 14 and 22 kDa. The activity was inhibited by EDTA/phenylmethylsulfonyl fluoride or aprotinin. Competitive binding studies indicated that IGFBP-2 fragments had reduced binding affinity for IGF-I. bFGF induced IGFBP-3 mRNA and protein. Affinity cross-linking of [125I]IGF-I to neuroblastoma cell membranes followed by immunoprecipitation revealed a approximately 38 kDa [125I]IGF-I/IGFBP-2 complex. Cell surface-associated IGFBP-2 was also susceptible to bFGF-induced proteolysis, with the appearance of a single cross-linked 21-kDa complex with low affinity for IGF-I. These findings indicate that intact IGFBP-2 and the 14-kDa, but not the 22-kDa fragment, bind to the cell surface. Our data suggest that induction of IGFBP-2 proteolysis on neuronal cell surface is a novel mechanism whereby IGF availability is modulated by the local growth factor bFGF.

Human prodynorphin gene generates several tissue-specific transcripts

The present study analyzes the transcription of the human prodynorphin gene. Transfection experiments indicate that promoter activity for the 2.8 kb 'brain-type' human prodynorphin mRNA resides in the DNA region located 140-180 b upstream of the exon 1/intron A boundary and not 1.2 kb further upstream, as proposed by others [S. Horikawa, T. Takai, M. Toyosato, H. Takahashi, M. Noda, H. Kakidani, T. Kubo, T. Hirose, S. Tanayama, H. Hayashida, T. Miyata, S. Numa, Isolation and structural organization of the human preproenkephalin B gene, Nature 306, 1983, pp. 611-614]. The new data locates the human prodynorphin gene promoter for the brain-type mRNA in a position corresponding to the position of the rat prodynorphin gene promoter [J. Douglass, C.T. McMurray, J.E. Garett, J.P. Adelman, L. Calavetta, Characterization of the rat prodynorphin gene, Mol. Endocrinol. 3, 1989, pp. 2070-2078]. Three previously not described types of human prodynorphin mRNA of the same size, 2.8 kb, one expressed in fetal brain and two others in testis, were characterized in this study. These mRNAs are generated by alternative splicing of novel 5'-uppermost exons and transcription is probably initiated from other promoters. Human neuroblastoma SH-SY5Y and SK-N-MC cell lines previously used in studies of gene transcription have the 2.8 kb prodynorphin mRNA of adult brain alongside a more abundant, shorter 2.3 kb transcript. The latter transcript was also found in testis and in fetal brain. It lacked the 5'-part of the 2.8 kb mRNA including the signal peptide encoding sequence. The complex pattern of prodynorphin gene expression and its functional consequences are issues for further studies.

Alterations in DNA methylation: a fundamental aspect of neoplasia

Neoplastic cells simultaneously harbor widespread genomic hypomethylation, more regional areas of hypermethylation, and increased DNA-methyltransferase (DNA-MTase) activity. Each component of this "methylation imbalance" may fundamentally contribute to tumor progression. The precise role of the hypomethylation is unclear, but this change may well be involved in the widespread chromosomal alterations in tumor cells. A main target of the regional hypermethylation are normally unmethylated CpG islands located in gene promoter regions. This hypermethylation correlates with transcriptional repression that can serve as an alternative to coding region mutations for inactivation of tumor suppressor genes, including p16, p15, VHL, and E-cad. Each gene can be partially reactivated by demethylation, and the selective advantage for loss of gene function is identical to that seen for loss by classic mutations. How abnormal methylation, in general, and hypermethylation, in particular, evolve during tumorigenesis are just beginning to be defined. Normally, unmethylated CpG islands appear protected from dense methylation affecting immediate flanking regions. In neoplastic cells, this protection is lost, possibly by chronic exposure to increased DNA-MTase activity and/or disruption of local protective mechanisms. Hypermethylation of some genes appears to occur only after onset of neoplastic evolution, whereas others, including the estrogen receptor, become hypermethylated in normal cells during aging. This latter change may predispose to neoplasia because tumors frequently are hypermethylated for these same genes. A model is proposed wherein tumor progression results from episodic clonal expansion of heterogeneous cell populations driven by continuous interaction between these methylation abnormalities and classic genetic changes.

Switch from monoallelic to biallelic human IGF2 promoter methylation during aging and carcinogenesis

We have previously linked aging, carcinogenesis, and de novo methylation within the promoter of the estrogen receptor (ER) gene in human colon. We now examine the dynamics of this process for the imprinted gene for insulin-like growth factor II (IGF2). In young individuals, the P2-4 promoters of IGF2 are methylated exclusively on the silenced maternal allele. During aging, this promoter methylation becomes more extensive and involves the originally unmethylated allele. Most adult human tumors, including colon, breast, lung, and leukemias, exhibit increased methylation at the P2-4 IGF2 promoters, suggesting further spreading during the neoplastic process. In tumors, this methylation is associated with diminished or absent IGF2 expression from the methylated P3 promoter but maintained expression from P1, an upstream promoter that is not contained within the IGF2 CpG island. Our results demonstrate a remarkable evolution of methylation patterns in the imprinted promoter of the IGF2 gene during aging and carcinogenesis, and provide further evidence for a potential link between aberrant methylation and diseases of aging.

Rat B-50 gene transcription and translation

Previously we reported that the rat B-50/GAP-43 gene contains two promoters (P1 and P2). This study describes the contribution of these two promoters to the mRNA population in several paradigms leading to an altered B-50 mRNA expression. In 8-day-old rat brain we found that P1 transcripts (1676 +/- 50 nt) account for 5% and P2 transcripts (1462 +/- 46 nt) for 95% of the B-50 mRNAs. The expression of P1 and P2 derived transcripts is high at postnatal day 8 and the ratio between the amount of transcripts derived from P1 and P2 did not change during (embryonal and postnatal) development or aging. After peripheral nerve crush or transection B-50 mRNA expression in induced in the distal nerve stump. The amount of transcript in the nerve stump distal of the lesion derived from both P1 and P2 was increased and the ratio between P1 and P2 transcripts was not altered. To determine whether both P1 and P2 transcripts are translated, a polyribosomal profile from 8-day-old rat brain was generated. Northern analysis showed that both transcripts were associated with approximately four ribosomes. Since no change could be found in the activity in either of the two promoters under the different circumstances tested, we conclude that the activity of the two rat B-50 gene promoters is regulated by a similar mechanism.