Biallelic expression of the IGF2 gene in human breast disease

Exploration of the potential roles of m6A regulators in the uterus in pregnancy and infertility

Infertility is a prevalent female reproductive disease worldwide. Currently, there are many unknown etiologies of infertility. N6-methyladenosine (m6A) is the most prevalent modification of eukaryotic mRNA. This study intended to investigate the implications of m6A regulators in the uterus for pregnancy and infertility. Pregnant ICR mice on days (D) 0, 4, 6, 10, and 15 were used to monitor m6A methylation in the uterus by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and then m6A methylation regulators were detected by real-time quantitative PCR (qPCR), western blot and immunohistochemistry (IHC). We found that m6A levels increased and that m6A regulators were expressed differently in the uterus during pregnancy. Then, we acquired expression data from endometrial tissue from women with infertility and recurrent pregnancy loss from the Gene Expression Omnibus (GEO) database. The expression of m6A regulators in infertility was significantly dysregulated according to the data mining technique. Specifically, the mRNA levels of METTL16 (p = 0.0147) and WTAP (p = 0.028) were lower and those of ALKBH5 (p = 0.0432) and IGF2BP2 (p = 0.0016) were higher in the endometrium of infertile patients. Meanwhile, many immunity-related pathways are abnormal in infertility, such as cytokine-cytokine receptor interactions, natural killer cell-mediated cytotoxicity and leukocyte transendothelial migration. In conclusion, we found that the m6A levels in the uterus increased as pregnancy progressed, and these regulators were dysregulated in the endometrium of infertility patients. These results suggest that m6A methylation may be very important in the establishment of implantation and maintenance of pregnancy and may become a new direction for research on infertility.

Genome-Wide DNA Methylation and RNA Analysis Reveal Potential Mechanism of Resistance to Streptococcus agalactiae in GIFT Strain of Nile Tilapia (Oreochromis niloticus )

Streptococcus agalactiae is an important pathogenic bacterium causing great economic loss in Nile tilapia (Oreochromis niloticus) culture. Resistant and susceptible groups sharing the same genome showed significantly different resistance to S. agalactiae in the genetically improved farmed tilapia strain of Nile tilapia. The resistance mechanism is unclear. We determined genome-wide DNA methylation profiles in spleen of resistant and susceptible O. niloticus at 5 h postinfection with S. agalactiae using whole-genome bisulfite sequencing. The methylation status was higher in the spleen samples from resistant fish than in the susceptible group. A total of 10,177 differentially methylated regions were identified in the two groups, including 3725 differentially methylated genes (DMGs) (3129 hyper-DMGs and 596 hypo-DMGs). The RNA sequencing showed 2374 differentially expressed genes (DEGs), including 1483 upregulated and 891 downregulated. Integrated analysis showed 337 overlapping DEGs and DMGs and 82 overlapping DEGs and differentially methylated region promoters. By integrating promoter DNA methylation with gene expression, we revealed four immune-related genes (Arnt2, Nhr38, Pcdh10, and Ccdc158) as key factors in epigenetic mechanisms contributing to pathogen resistance. Our study provided systematic methylome maps to explore the epigenetic mechanism and reveal the methylation loci of pathogen resistance and identified methylation-regulated genes that are potentially involved in defense against pathogens.

DNA methylation in human diseases

Even though the importance of epigenetics was first recognized in light of its role in tissue development, an increasing amount of evidence has shown that it also plays an important role in the development and progression of many common diseases. We discuss some recent findings on one representative epigenetic modification, DNA methylation, in some common diseases. While many new risk factors have been identified through the population-based epigenetic epidemiologic studies on the role of epigenetics in common diseases, this relatively new field still faces many unique challenges. Here, we describe those promises and unique challenges of epigenetic epidemiological studies and propose some potential solutions.

Impairment of IGF2 gene expression in prostate cancer is triggered by epigenetic dysregulation of IGF2-DMR0 and its interaction with KLF4

Background

Human cancer cells often exhibit impaired IGF2 expression and the underlying mechanisms are multifaceted and complex. Besides the well-known imprinting control region IGF2/H19-ICR, the involvement of a differentially methylated region in the promoter P0 of IGF2 gene (IGF2-DMR0) has been suggested. Here, we evaluate several mechanisms potentially leading to up- and/or down-regulation of IGF2 expression in prostate cancer and present a novel role of Kruppel-like factor 4 (KLF4) as a transcriptional regulator of IGF2 binding in IGF2-DMR0.

Methods

Putative binding sites for transcription factors were identified in IGF2-DMR0 using JASPAR CORE database. Gene expressions were analyzed by RT-qPCR in prostate carcinoma and adjacent benign prostate hyperplasia samples obtained by radical prostatectomy (86 RP-PCa and 47 RP-BPH) and BPH obtained by transurethral prostate resection (13 TUR-BPH). Pyrosequencing and qMSP were used for DNA methylation studies in IGF2-DMR0, IGF2/H19-ICR and Glutathione-S-transferase-P1 (GSTP1) promoter. Loss of imprinting (LOI) was analyzed by RFLP. Copy number variation (CNV) test was performed using qBiomarker CNV PCR Assay. KLF4-binding and histone-modifications were analyzed by ChIP-qPCR in prostate cancer cell lines exhibiting differentially methylated IGF2-DMR0 (LNCaP hypomethylated and DU145 hypermethylated). KLF4 protein was analyzed by western blot. Statistical associations of gene expression to methylation, IGF2 LOI and CNV were calculated by Mann-Whitney-U-test. Correlations between gene expression and methylation levels were evaluated by Spearman’s-Rank-Correlation-test.

Results

We found a significant reduction of IGF2 expression in the majority of RP-PCa and RP-BPH in comparison to TUR-BPH. Analyzing potential molecular reasons, we found in RP-PCa and RP-BPH in comparison to TUR-BPH a significant hypomethylation of IGF2-DMR0, which coincided with hypermethylation of GSTP1-promoter, a prominent marker of prostate tumors. In contrast, IGF2 LOI and CNV did not associate significantly with up- and/or down-regulation of IGF2 expression in prostate tumors. By analyzing IGF2-DMR0, we detected a consensus sequence for KLF4 with a z-score of 7.6. Interestingly, we found that KLF4 binds to hypomethylated (17%) IGF2-DMR0 enriched with H3K9me3 and H3K27me3 (LNCaP), but does not bind under hypermethylated (85%) and H3K4me3-enriched conditions (DU145). KLF4 expression was detected in TUR-BPH as well as in RP-BPH and RP-PCa and showed a highly significant correlation to IGF2 expression.

Conclusions

Our study demonstrated that in human prostate cancer the impairment of IGF2 expression is accompanied by hypomethylation of IGF2-DMR0. We revealed that KLF4 is a putative transcriptional regulator of IGF2, which binds in IGF2-DMR0 in dependence of the prevailing epigenetic state in this region. Herewith we provide complementary new insights into IGF2 dysregulation mechanisms as a critical process in prostate tumorigenesis.

Loss of imprinting of IGF2 in fibroadenomas and phyllodes tumors of the breast

Loss of imprinting (LOI) of insulin-like growth factor 2 (IGF2) is thought to be implicated in the pathogenesis of some tumors by upregulating IGF2 mRNA but its role in the pathogenesis of fibroadenomas (FAs) and phyllodes tumors (PTs) of the breast is yet to be studied. LOI of IGF2 was investigated in 25 FAs and 17 PTs which were heterozygous for Apa I polymorphism, and was found to be present in 13 FAs and 12 PTs. IGF2 mRNA expression was more upregulated in FAs and PTs than in paired surrounding normal tissues and laser microdissection showed that IGF2 mRNA expression was significantly higher in the stromal than the epithelial cells. LOI was not associated with upregulation of IGF2 mRNA, nor were MED12 mutations and methylation status of the differentially methylated region 0 (DMR0) of IGF2. These results demonstrate that IGF2 mRNA expression is more upregulated in FAs and PTs than in normal tissues, especially in their stromal cells, but such an upregulation is not related to LOI of IGF2, and that hypomethylation of DMR0 is unlikely to be involved in induction of LOI.

Aberrant methylation of imprinted genes is associated with negative hormone receptor status in invasive breast cancer

Epigenetic regulation of imprinted genes enables monoallelic expression according to parental origin, and its disruption is implicated in many cancers and developmental disorders. The expression of hormone receptors is significant in breast cancer because they are indicators of cancer cell growth rate and determine response to endocrine therapies. We investigated the frequency of aberrant events and variation in DNA methylation at nine imprinted sites in invasive breast cancer and examined the association with estrogen and progesterone receptor status. Breast tissue and blood from patients with invasive breast cancer (n = 38) and benign breast disease (n = 30) were compared with those from healthy individuals (n = 36), matched with the cancer patients by age at diagnosis, ethnicity, body mass index, menopausal status and familial history of cancer. DNA methylation and allele-specific expression were analyzed by pyrosequencing. Tumor-specific methylation changes at IGF2 DMR2 were observed in 59% of cancer patients, IGF2 DMR0 in 38%, DIRAS3 DMR in 36%, GRB10 ICR in 23%, PEG3 DMR in 21%, MEST ICR in 19%, H19 ICR in 18%, KvDMR in 8% and SNRPN/SNURF ICR in 4%. Variation in methylation was significantly greater in breast tissue from cancer patients compared with that in healthy individuals and benign breast disease. Aberrant methylation of three or more sites was significantly associated with negative estrogen-alpha (Fisher's exact test, p = 0.02) and progesterone-A (p = 0.02) receptor status. Aberrant events and increased variation in imprinted gene DNA methylation, therefore, seem to be frequent in invasive breast cancer and are associated with negative estrogen and progesterone receptor status, without loss of monoallelic expression.

Expression of Intratumoral IGF-II Is Regulated by the Gene Imprinting Status in Triple Negative Breast Cancer from Vietnamese Patients

African American women suffer higher incidence and mortality of triple negative breast cancer (TNBC) than Caucasian women. TNBC is very aggressive, causing the worst clinical outcome. We previously demonstrated that tumors from these patients express high IGF-II and exhibit high activation of the IGF signaling pathways. IGF-II gene expression is imprinted (monoallelic), promotes tumor progression, and metastasis and regulates Survivin, a TNBC prognostic marker. Since BC mortality has increased among young Vietnamese women, we analyzed 48 (paired) TNBC samples from Vietnamese patients to assess IGF-II expression. We analyzed all samples by qrtPCR for identification of IGF-II heterozygosity and to determine allelic expression of the IGF-II gene. We also analyzed the tissues for proIGF-II and Survivin by RT-PCR and Western blotting. A total of 28 samples displayed IGF-II heterozygosity of which 78% were biallelic. Tumors with biallelic IGF-II gene expression exhibited the highest levels of proIGF-II and Survivin. Although 100% of these tissues corresponding normal samples were biallelic, they expressed significantly lower levels of or no proIGF-II and Survivin. Thus, IGF-II biallelic gene expression is differentially regulated in normal versus tumor tissues. We propose that intratumoral proIGF-II is dependent on the IGF-II gene imprinting status and it will promote a more aggressive TNBC.

Co-targeting the IGF system and HIF-1 inhibits migration and invasion by (triple-negative) breast cancer cells

Background:

Metastatic triple-negative breast cancer is mostly incurable, due to lack of suitable drug targets. The insulin-like growth factor (IGF) system could provide such a target, and IGF-1 receptor (IGF-1R)-directed agents are already available, but seem unable to control all the complexities of the system, including crosstalk with hypoxia-inducible pathways.

Methods:

Migration of triple-negative MDA-231 breast cancer cells and its modulation by IGFs, the IGF-1R inhibitor NVP-AEW541 and the IGF-2-sequestering monoclonal antibody MAB292 were assessed by the scratch wound healing and Boyden chamber assays; the effect of topotecan (inhibiting hypoxia-inducible factor-1 (HIF-1)) under hypoxia was also evaluated. Constitutive as well as drug-modulated levels of components of the IGF and HIF-1 pathways were evaluated by western blotting and qPCR.

Results:

IGF-induced migration of MDA-231 cells was not abrogated by the IGF-1R inhibitor NVP-AEW541, whereas IGF-2 sequestration by MAB292 significantly reduced cell migration. Under hypoxia, topotecan was also effective, likely by reducing HIF-1-induced IGF-2 release. Simultaneous targeting of IGF-1R and IGF-2 or HIF-1 completely abolished cell migration.

Conclusions:

IR activation may account for the failure of NVP-AEW541 to suppress MDA-231 cell migration. Ligand-targeting compounds, or co-inhibition of the IGF and HIF-1 systems, may prevent activation of compensatory signalling, thereby providing a valuable addition to IGF-1R inhibitor-based therapies.

Evaluation of the expression and role of IGF pathway biomarkers in human sarcomas

Recent studies have shown that insulin-like growth factor (IGF) signaling components have been involved in the pathogenesis and progression of different types of sarcomas. There has been some evidence to indicate the differential expression of IGF2 and insulin-like growth factor 1 receptor (IGF1R) in human sarcomas. The present study utilized immunohistochemistry (IHC) and in situ hybridization (ISH) to determine the expression of IGF2 and IGF1R in eighty-two cases of human sarcoma specimens and eight cases of non-tumor tissue (NTT). IGF2/IGF1R signaling was blocked by recombinant adenovirus-mediated IGF1R small hairpin RNA (shIGF1R), which was used to transfect into human osteosarcoma (OS) MG-63 cells. The expression of IGF2, IGF1R, matrix metallopeptidase-2 (MMP-2) and MMP-9 was detected by Real-time PCR. Cell migration was evaluated by wound healing assay. As a consequence, the expression of IGF1R and IGF2 was found in human OS with higher strong reactivity rate compared with the NTT (85.0 percent vs 50.0 percent, P=0.022; 95.0 percent vs 100.0 percent, P=0.042), elevating with the ascending order of tumor malignancy. Also, IGF1R had differential expression in different types of sarcomas (P=0.002), while IGF2 had no significant difference (P=0.105). Targeted blockade of IGF2/IGF1R signaling decreased the expression of IGF2, IGF1R, and MMP-2/-9, and diminished the migration capabilities of MG-63 cells. In conclusion, IGF1R is differentially-expressed in different types of human sarcomas, and targeted blockade of IGF1R pathway may inhibit human OS migration through down-regulation of MMP-2/-9 expression. IGF1R pathway may represent a significant therapeutic modality for the treatment of sarcomas.

Leukocyte DNA as surrogate for the evaluation of imprinted Loci methylation in mammary tissue DNA

There is growing interest in identifying surrogate tissues to identify epimutations in cancer patients since primary target tissues are often difficult to obtain. Methylation patterns at imprinted loci are established during gametogenesis and post fertilization and their alterations have been associated with elevated risk of cancer. Methylation at several imprinted differentially methylated regions (GRB10 ICR, H19 ICR, KvDMR, SNRPN/SNURF ICR, IGF2 DMR0, and IGF2 DMR2) were analyzed in DNA from leukocytes and mammary tissue (normal, benign diseases, or malignant tumors) from 87 women with and without breast cancer (average age of cancer patients: 53; range: 31-77). Correlations between genomic variants and DNA methylation at the studied loci could not be assessed, making it impossible to exclude such effects. Methylation levels observed in leukocyte and mammary tissue DNA were close to the 50% expected for monoallellic methylation. While no correlation was observed between leukocyte and mammary tissue DNA methylation for most of the analyzed imprinted genes, Spearman's correlations were statistically significant for IGF2 DMR0 and IGF2 DMR2, although absolute methylation levels differed. Leukocyte DNA methylation levels of selected imprinted genes may therefore serve as surrogate markers of DNA methylation in cancer tissue.

The epidemiology and molecular mechanisms linking obesity, diabetes, and cancer

The worldwide epidemic of obesity is associated with increasing rates of the metabolic syndrome and type 2 diabetes. Epidemiological studies have reported that these conditions are linked to increased rates of cancer incidence and mortality. Obesity, particularly abdominal obesity, is associated with insulin resistance and the development of dyslipidemia, hyperglycemia, and ultimately type 2 diabetes. Although many metabolic abnormalities occur with obesity and type 2 diabetes, insulin resistance and hyperinsulinemia appear to be central to these conditions and may contribute to dyslipidemia and altered levels of circulating estrogens and androgens. In this review, we will discuss the epidemiological and molecular links between obesity, type 2 diabetes, and cancer, and how hyperinsulinemia and dyslipidemia may contribute to cancer development. We will discuss how these metabolic abnormalities may interact with estrogen signaling in breast cancer growth. Finally, we will discuss the effects of type 2 diabetes medications on cancer risk.

Impact of body mass index on breast cancer in accordance with the life-stage of women

A large amount of epidemiological evidence suggests that the impact of body weight on breast cancer risk should be heterogeneous throughout the life-stage of women. At birth, high weight has been positively associated with an increased risk of breast cancer. While, the body mass index (a relative body weight; BMI kg/m²) has been inversely associated with breast cancer risk among pre-menopausal women. The inverse trend had been observed in both Western and Asian population, with a relatively lower percentage of obesity and higher percentage of leanness, suggested that the inverse trend could be explained not only by the protective impact due to obesity, but also by the increased risk of breast cancer due to leanness. Among post-menopausal women, however, an elevated BMI has been positively associated with the development of breast cancer, particularly in the cases of estrogen receptor-positive (ER+) and progesterone receptor-positive (PR+) tumors. Currently, the mechanisms underlying the heterogeneous impacts between BMI on breast cancer risk and the life-stage of women remain poorly understood. We reviewed several proposed biological mechanisms that may contribute to the various impacts of relative body weight on breast cancer risk across life-stage. We also discussed the impact of BMI upon the outcome of endocrine therapy, particularly for aromatase inhibitor, in breast cancer patients. To prevent breast cancer incidence and recurrence, the desirable BMI of women may differ throughout their life-stage. To define the underlying mechanism for the various impacts of BMI in the context of breast cancer across various female life stages, further studies will be required.

Biology and significance of signalling pathways activated by IGF-II

Insulin-like growth factor-II (IGF-II) affects many aspects of cellular function through its ability to activate several different receptors and, consequently, numerous intracellular signalling molecules. Thus, IGF-II is a key regulator of normal foetal development and growth. However, abnormalities in IGF-II function are associated with cardiovascular disease and cancer. Here, we review the cellular mechanisms by which IGF-II's physiological and pathophysiological actions are exerted by discussing the involvement of the type 1 and type 2 IGF receptors (IGF1R and IGF2R), the insulin receptor and the downstream MAP kinase, PI-3 kinase and G-protein-coupled signalling pathways in mediating IGF-II stimulated cellular proliferation, survival, differentiation and migration.

The dark side of cohesin: the carcinogenic point of view

Genome instability is a hallmark of cancer cells and how it arises is still not completely understood. Correct chromosome segregation is a pre-requisite for preserving genome integrity. Cohesin helps to ensure faithful chromosome segregation during cell cycle, however, much evidence regarding its functions have come to light over the last few years and suggest that cohesin plays multiple roles in the maintenance of genome stability. Here we review our rapidly increasing knowledge on the involvement of cohesin pathway in genome stability and cancer.

The role of insulin-like growth factor system in soft tissue sarcomas: from physiopathology to targeted therapeutic approaches

Purpose/Results. Although surgical, chemo- and radiotherapeutic treatment regimens in patients with soft tissue sarcomas have constantly been refined over the past two decades, the survival rate for these patients is rather low.

Discussion. There is a great need to investigate the mechanisms for oncogenesis and to identify the factors involved in malignant transformation in sarcomas. Among these factors, IGFs are thought to play a pivotal role as progression factors in various types of sarcomas. The dysregulation of the IGF-II synthesis, e.g. by loss of imprinting which occurs in most types of sarcomas, is a permissive effect through the suppression of cell death. In addition, cells that overexpress the type I IGF receptors are more susceptible to transformation by oncogenes. As TP53 suppresses the activity of IGF-II P3 and P4, as well as the type I IGF receptor promoter, mutations of TP53 in sarcomas may alternatively lead to the activation of these factors. Finally, the phenomenon of non-islet cell tumour hypoglycaemia that occurs in patients with sarcomas, and which is related to the secretion of IGF-II prohormones, is discussed. Future therapeutic strategies may be based upon the application of antibodies or antisense oligonucleotides directed against the type I IGF receptors, with the common goal of inducing apoptosis in sarcoma cells. Ultimately, these and other therapeutic approaches may lead to a better outcome in patients suffering from sarcoma.

Relationship of folate, vitamin B12 and methylation of insulin-like growth factor-II in maternal and cord blood

BACKGROUND/OBJECTIVE

One of the speculated mechanisms underlying fetal origin hypothesis of breast cancer is the possible influence of maternal environment on epigenetic regulation, such as changes in DNA methylation of the insulin-like growth factor-2 (IGF2) gene. The aim of the study is to investigate the relationship between folate, vitamin B(12) and methylation of the IGF2 gene in maternal and cord blood.

SUBJECTS/METHODS

We conducted a cross-sectional study to measure methylation patterns of IGF2 in promoters 2 (P2) and promoters 3 (P3).

RESULTS

The percentage of methylation in IGF2 P3 was higher in maternal blood than in cord blood (P<0.0001), whereas the methylation in P2 was higher in cord blood than in maternal blood (P=0.016). P3 methylation was correlated between maternal and cord blood (P<0.0001), but not P2 (P=0.06). The multivariate linear regression model showed that methylation patterns of both promoters in cord blood were not associated with serum folate levels in either cord or maternal blood, whereas the P3 methylation patterns were associated with serum levels of vitamin B(12) in mother's blood (mean change (MC)=-0.22, P=0.0014). Methylation patterns in P2 of maternal blood were associated with serum levels of vitamin B(12) in mother's blood (MC=-0.23, P=0.012), exposure to passive smoking (MC=0.46, P=0.034) and mother's weight gain during pregnancy (MC=0.23, P=0.019).

CONCLUSIONS

The study suggests that environment influences methylation patterns in maternal blood, and then the maternal patterns influence the methylation status and levels of folate and vitamin B(12) in cord blood.

Birth weight-breast cancer revisited: is the association confounded by familial factors?

PURPOSE

The study aimed to investigate whether the association between birth weight and the risk of breast cancer can be confounded by familial factors, such as shared environment and common genes.

MATERIALS AND METHODS

Eligible were all female like-sexed twins of the Swedish Twin Registry, born during the period 1926-1958 and alive in 1973. Data were obtained from birth records, and the final study population with reliable birth weight data was made up of 11,923 twins. Hazard ratios (HR) for breast cancer according to birth weight were estimated through Cox regression, using robust SE to account for the dependence within twin pairs. Paired analysis was done to account for potential confounding by familial factors.

RESULTS

In the cohort analysis, a birth weight >or=3,000 g was associated with an increased risk of breast cancer diagnosed at or before 50 years [adjusted HR, 1.57; 95% confidence interval (95% CI), 1.03-2.42] but not with breast cancer with a later onset (adjusted HR, 0.80; 95% CI, 0.57-1.12). From >or=2,500 g, a 500-g increase in birth weight conferred a HR of 1.62 (95% CI, 1.16-2.27) for breast cancer diagnosed at or before 50 years. This risk remained in analysis within twin pairs (HR, 1.57; 95% CI, 1.00-2.48).

CONCLUSION

In the present study, findings indicate that the association between birth weight and breast cancer risk, seen only in women diagnosed early (<or=50 years), is not confounded by familial factors.

Urinary insulin-like growth factor 2 identifies the presence of urothelial carcinoma of the bladder

OBJECTIVE

To examine urinary insulin-like growth factor 2 (IGF-2) levels in patient urine samples and determine the potential of IGF-2 as a marker for the presence of urothelial carcinoma of the bladder (UCB).

PATIENTS AND METHODS

The current gold standard for diagnosis of UCB is cystoscopy and cytological analysis. The identification of an accurate urine marker for UCB with the potential to replace unnecessary cystoscopy would benefit patients with UCB and others investigated after detecting haematuria. In the present study, we analysed 65 urine samples, and optimized an enzyme-linked immunosorbent assay-based approach to measure urinary levels of IGF-2.

RESULTS

Based on a threshold of 5.4 ng/mL, patients with UCB have significantly elevated levels of urinary IGF-2 (P = 0.009) and this difference remained significant after adjustment for age and sex (P = 0.04). Sensitivity and specificity values of 80% and 52%, respectively, were determined for urinary IGF-2 alone and when combined with nuclear matrix protein 22 (NMP22; an approved biomarker for detection of UCB). There was a positive correlation between urinary IGF-2 levels and NMP22 levels in patient urine samples and the combined assay improved the detection of UCB (sensitivity 85% and specificity 52%).

CONCLUSION

Substantiated evidence has identified IGF-2 as a valuable marker for UCB. In addition, the novel observations of the present study have shown that aberrant levels of IGF-2 occurring in the presence of UCB, can now be determined through a simple and inexpensive urine assay.

Igf2r improves the survival and transmission ratio of Igf2 transgenic mice

Mammals with excess insulin-like growth factor 2 (IGFII) during embryogenesis have developmental defects that can lead to perinatal lethality. In adults, higher levels of IGFII increase the risk of cancer and may accelerate the development of atherosclerosis. IGFII can be increased as a consequence of genetic abnormalities and polymorphisms, and through epigenetic mechanisms. Decreasing IGFII levels thus can benefit human health. Degradation of IGFII is mediated by the insulin-like growth factor type 2 receptor (IGF2R). The growth-stimulatory effects of IGFII, and their attenuation by the IGF2R, are considered important for the evolution of IGFII/IGF2R interaction and imprinting. The IGFII/IGF2R interactions during development have been previously examined in mice carrying knock-out alleles of these genes or their regulators. Here we tested the ability of the IGF2R to ameliorate the negative effects of IGFII on development and survival in crosses between Igf2 and Igf2r transgenic mice, which may be a better model for natural variations in the levels of these genes' products. A fraction of hemizygous Igf2 transgenic mice die in the perinatal period, some with cleft palates, with an ensuing reduction in the frequency of transgenic mice among the surviving offspring. The Igf2r transgene lowers the frequency of cleft palate and increases the percentage of Igf2 transgenic mice among the live offspring. These findings draw attention to the fact that Igf2-associated lethality selects for the retention of IGFII/IGF2R binding in present day mammals; it may have played a similar role in the acquisition of IGFII/IGF2R binding in ancient mammals.

Genetic predisposition to idiopathic recurrent spontaneous abortion: contribution of genetic variations in IGF-2 and H19 imprinted genes

PROBLEM

Recurrent spontaneous abortion (RSA) is a common clinical problem with a complex etiology of genetic and non-genetic causes, which remains to be fully determined. IGF-2 stimulates trophoblast invasion, proliferation and maturation of placenta, while H19 RNA suppresses growth. As genomic imprinting plays a critical role in the development of placenta and embryo, our aim was to evaluate the possible role of variations in IGF-2 and H19 imprinted genes as factors of predisposition for RSA.

METHOD OF STUDY

A case-control study was conducted to determine the association between IGF-2 and H19 gene polymorphisms and the susceptibility to RSA in 113 couples with RSA and 226 controls. PCR/RFLP were performed to analyze IGF-2 ApaI and H19 HhaI polymorphisms.

RESULTS

We found a statistically significant difference in the genotype frequency distribution of IGF-2 ApaI polymorphism between males from couples with RSA and healthy males (chi2(2) = 45.12; P < 0.0001). There were no differences in the genotype and allele distribution of H19 polymorphism frequencies, or for the IGF-2 ApaI polymorphism between female groups.

CONCLUSION

The presence of IGF-2 ApaI polymorphism in partners of RSA women could affect IGF-2 level of expression in placenta and embryo and represent a risk factor for RSA susceptibility.

IGF2: epigenetic regulation and role in development and disease

Insulin-like growth factor II (IGF2) is perhaps the most intricately regulated of all growth factors characterized to date. Its gene is imprinted--only one allele is active, depending on parental origin--and this pattern of expression is maintained epigenetically in almost all tissues. IGF2 activity is further controlled through differential expression of receptors and IGF-binding proteins (IGFBPs) that determine protein availability. This complex and multifaceted regulation emphasizes the importance of accurate IGF2 expression and activity. This review will examine the regulation of the IGF2 gene and what it has revealed about the phenomenon of imprinting, which is frequently disrupted in cancer. IGF2 protein function will be discussed, along with diseases that involve IGF2 overexpression. Roles for IGF2 in sonic hedgehog (Shh) signaling and angiogenesis will also be explored.

Microarray-based comparative genomic hybridisation of breast cancer patients receiving neoadjuvant chemotherapy

We analysed the molecular genetic profiles of breast cancer samples before and after neoadjuvant chemotherapy with combination doxorubicin and cyclophosphamide (AC). DNA was obtained from microdissected frozen breast core biopsies from 44 patients before chemotherapy. Additional samples were obtained before the second course of chemotherapy (D21) and after the completion of the treatment (surgical specimens) in 17 and 21 patients, respectively. Microarray-based comparative genome hybridisation was performed using a platform containing approximately 5800 bacterial artificial chromosome clones (genome-wide resolution: 0.9 Mb). Analysis of the 44 pretreatment biopsies revealed that losses of 4p, 4q, 5q, 12q13.11-12q13.12, 17p11.2 and 17q11.2; and gains of 1p, 2p, 7q, 9p, 11q, 19p and 19q were significantly associated with oestrogen receptor negativity. 16q21-q22.1 losses were associated with lobular and 8q24 gains with ductal types. Losses of 5q33.3-q4 and 18p11.31 and gains of 6p25.1-p25.2 and Xp11.4 were associated with HER2 amplification. No correlations between DNA copy number changes and clinical response to AC were found. Microarray-based comparative genome hybridisation analysis of matched pretreatment and D21 biopsies failed to identify statistically significant differences, whereas a comparison between matched pretreatment and surgical samples revealed a statistically significant acquired copy number gain on 11p15.2-11p15.5. The modest chemotherapy-driven genomic changes, despite profound loss of cell numbers, suggest that there is little therapeutic selection of resistant non-modal cell lineages.

Role of birthweight in the etiology of breast cancer

Breast cancer may originate in utero. We reviewed the available evidence on the association between birthweight and the risk of breast cancer. To date, 26 research papers addressing this issue have been published. The majority of studies identified a positive link between birthweight and premenopausal, but not postmenopausal, breast cancer. The relative risk estimate for breast cancer comparing women with high birthweight to women with low birthweight combining all studies including both pre- and postmenopausal breast cancer was 1.23 (95% confidence interval 1.13-1.34). The mechanisms underlying this association likely include elevated levels of growth factors that may increase the number of susceptible stem cells in the mammary gland or initiate tumors through DNA mutations. Loss of imprinting (LOI) of growth hormone genes relevant for intrauterine growth, such as insulin-like growth factor 2 (IGF2), leads to abnormally high levels of these hormones evidenced by high birthweight. LOI of IGF2 has also been found in mammary tumor tissue. The role of environmental factors that stimulate such epigenetic regulation of gene expression remains to be elucidated.

Delayed Onset ofIgf2-Induced Mammary Tumors inIgf2rTransgenic Mice

The insulin-like growth factor-II (IGF-II) receptor (IGF2R) regulates the level or activity of numerous proteins, including factors that control growth and differentiation. Frequent loss or inactivation of this receptor in a diverse group of tumors indicates that it may act as a tumor suppressor, but it is not known which functions of this receptor are selected against in the tumors. Lysosomal targeting and degradation of the growth-promoting IGF-II has been proposed as a mechanism for the tumor suppressor effects of IGF2R. As a genetic test of this hypothesis in vivo, we have produced Igf2r transgenic mice that ubiquitously express the transgene and have crossed these mice with mice that develop mammary tumors as a consequence of Igf2 overexpression. Our findings indicate that the presence of the Igf2r transgene delays mammary tumor onset and decreases tumor multiplicity in Igf2 transgenic mice. These findings are relevant to human tumors and preneoplastic conditions accompanied by altered IGF2 expression.

Mutations in the IGF-II pathway that confer resistance to lytic reovirus infection

BACKGROUND

Viruses are obligate intracellular parasites and rely upon the host cell for different steps in their life cycles. The characterization of cellular genes required for virus infection and/or cell killing will be essential for understanding viral life cycles, and may provide cellular targets for new antiviral therapies.

RESULTS

A gene entrapment approach was used to identify candidate cellular genes that affect reovirus infection or virus induced cell lysis. Four of the 111 genes disrupted in clones selected for resistance to infection by reovirus type 1 involved the insulin growth factor-2 (IGF-II) pathway, including: the mannose-6-phosphate/IGF2 receptor (Igf2r), a protease associated with insulin growth factor binding protein 5 (Prss11), and the CTCF transcriptional regulator (Ctcf). The disruption of Ctcf, which encodes a repressor of Igf2, was associated with enhanced Igf2 gene expression. Plasmids expressing either the IGF-II pro-hormone or IGF-II without the carboxy terminal extension (E)-peptide sequence independently conferred high levels of cellular resistance to reovirus infection. Forced IGF-II expression results in a block in virus disassembly. In addition, Ctcf disruption and forced Igf2 expression both enabled cells to proliferate in soft agar, a phenotype associated with malignant growth in vivo.

CONCLUSION

These results indicate that IGF-II, and by inference other components of the IGF-II signalling pathway, can confer resistance to lytic reovirus infection. This report represents the first use of gene entrapment to identify host factors affecting virus infection. Concomitant transformation observed in some virus resistant cells illustrates a potential mechanism of carcinogenesis associated with chronic virus infection.

Adipocyte-secreted factors synergistically promote mammary tumorigenesis through induction of anti-apoptotic transcriptional programs and proto-oncogene stabilization

Mammary epithelial cells are embedded in a unique extracellular environment to which adipocytes and other stromal cells contribute. Mammary epithelial cells are critically dependent on this milieu for survival. However, it remains unknown which adipocyte-secreted factors are required for the survival of the mammary epithelia and what role these adipokines play in the process of ductal carcinoma tumorigenesis. Here, we take a systematic molecular approach to investigate the multiple ways adipocytes and adipokines can uniquely influence the characteristics and phenotypic behavior of malignant breast ductal epithelial cells. Microarray analysis and luciferase reporter assays indicate that adipokines specifically induce several transcriptional programs involved in promoting tumorigenesis, including increased cell proliferation (IGF2, FOS, JUN, cyclin D1), invasive potential (MMP1, ATF3), survival (A20, NFkappaB), and angiogenesis. One of the key changes in the transformed ductal epithelial cells associated with the cell cycle involves the induction of NFkappaB (five-fold) and cyclin D1 (three-fold). We show that by regulating the transcription of these molecules, the synergistic activity of adipocyte-derived factors can potentiate MCF-7 cell proliferation. Furthermore, compared to other stromal cell-secreted factors, the full complement of adipokines shows an unparalleled ability to promote increased cell motility, migration, and the capacity for angiogenesis. Adipocyte-secreted factors can affect tumorigenesis by increasing the stabilization of pro-oncogenic factors such as beta-catenin and CDK6 as a result of a reduction in the gene expression of their inhibitors (i.e. p18). An in vivo coinjection system using 3T3-L1 adipocytes and SUM159PT cells effectively recapitulates the host-tumor interactions in primary tumors. Type VI collagen, a soluble extracellular matrix protein abundantly expressed in adipocytes, is further upregulated in adipocytes during tumorigenesis. It promotes GSK3beta phosphorylation, beta-catenin stabilization, and increased beta-catenin activity in breast cancer cells and may critically contribute towards tumorigenesis when not counterbalanced by other factors.

IGF-2 is a mediator of prolactin-induced morphogenesis in the breast

The mechanisms by which prolactin controls proliferation of mammary epithelial cells (MECs) and morphogenesis of the breast epithelium are poorly understood. We show that cyclin D1(-/-) MECs fail to proliferate in response to prolactin and identify IGF-2 as a downstream target of prolactin signaling that lies upstream of cyclin D1 transcription. Ectopic IGF-2 expression restores alveologenesis in prolactin receptor(-/-) epithelium. Alveologenesis is retarded in IGF-2-deficient MECs. IGF-2 and prolactin receptor mRNAs colocalize in the mammary epithelium. Prolactin induces IGF-2 mRNA and IGF-2 induces cyclin D1 protein in primary MECs. Thus, IGF-2 is a mediator of prolactin-induced alveologenesis; prolactin, IGF-2, and cyclin D1, all of which are overexpressed in breast cancers, are components of a developmental pathway in the mammary gland.

Decreased expression of p57(KIP2)mRNA in human bladder cancer

To identify targets of genetic and epigenetic alterations on chromosome 11p15.5 in human bladder cancer, expression of the imprinted KIP2, IGF2 and H19 genes was studied by quantitative RT-PCR in 24 paired samples of urothelial carcinomas and morphologically normal mucosa obtained by cystectomy, and in bladder carcinoma cell lines. The most frequent alteration in tumour tissue was decreased expression of KIP2 identified in 9/24 (37%) specimens. Decreased IGF2 and H19 mRNA levels were found in five (21%) and three (13%) tumours, respectively. One tumour each overexpressed IGF2 and H19. Loss of H19 expression was only found associated with loss of KIP2 expression, whereas decreased expression of IGF2 mRNA occurred independently. Almost all bladder carcinoma cell lines showed significant changes in the expression of at least one gene with diminished expression of KIP2 mRNA as the most frequent alteration. IGF2 mRNA levels were diminished in several lines, but increased in others. The KIP2 gene could be an important target of genetic and epigenetic alterations in bladder cancer affecting the maternal chromosome 11p15.5. However, reminiscent of the situation in Wilms' tumours, expression of the IGF2 gene on the paternal chromosome can also be disturbed in bladder cancers.

Loss of IGF-II imprinting in endometrial tumors: overexpression in carcinosarcoma

The genomic imprinting of the maternal allele defines the monoallelic expression of the IGF-II gene in most human tissues. The loss of imprinting (LOI) leading to biallelic overexpression of IGF-II has been reported in several human malignancies, including uterine leiomyosarcoma. To ascertain if LOI occurs in endometrial malignancies, the allelic expression of the IGF-II gene was examined in samples of normal human endometrium (n=22) and endometrial tumors (n=12) by assessing the ApaI polymorphism in cDNA segments amplified by RT-PCR. The biallelic overexpression of IGF-II mRNA, involving activation of all four (P1-P4) promoters, was detected in one normal endometrium and in one endometrial carcinosarcoma. Low level biallelic expression of IGF-II was also detected in two samples of hormone-unresponsive/Type II endometrial carcinomas. The level of IGF-I mRNA in these four samples was low. The IGF-IR mRNA was overexpressed in all endometrial cancers including the carcinosarcoma sample, but not in normal endometrium. These data suggest that LOI associated with overexpression of IGF-II and concomitant overexpression of IGF-IR may play a role in the rare carcinosarcoma of the endometrium.

Relaxation of IGF2 imprinting in Wilms tumours associated with specific changes in IGF2 methylation

Relaxation of IGF2 imprinting occurs in Wilms tumours and many other cancers, but the mechanism of loss of imprinting (LOI) remains unknown. To investigate the role of altered DNA methylation in LOI, we examined the pattern of methylation of the human insulin-IGF2 region in Wilms tumours and the normal kidney. The analysis included regions homologous to three 'differentially methylated regions' of the mouse Igf2 gene (dmrs 0, 1 and 2). In tumours displaying normal IGF2 imprinting, and in the normal kidney, maternal allele-specific DNA methylation was identified spanning exons 2 and 3. This region is homologous to dmr 0, a site of maternal-specific differential methylation in the mouse. In Wilms tumours with relaxed imprinting or 11p15.5 LOH this region was unmethylated. No other differential methylation was identified. In particular, two sites of paternal methylation in the mouse (dmrs 1 and 2), and all three imprinted IGF2 promoters were not methylated in the kidney or in Wilms tumours. We postulate that LOI in Wilms tumours is associated with loss of maternal allele-specific methylation from a region located upstream of the imprinted IGF2 promoters. This region may contain cis acting sequences that coordinately influence imprinting.

Expression and imprinting of insulin-like growth factor II (IGF2) and H19 genes in uterine leiomyomas

Genomic imprinting is defined as a gamete of origin-specific epigenetic modification of DNA leading to differential gene expression in the zygote. Several imprinted genes have been identified and some of them are associated with tumor development. We investigated the expression and the imprinting status of IGF2 and H19 genes in 47 uterine leiomyomas. Using allelic transcription assay, we detected the expression of the IGF2 gene in 10 of a total of 15 informative cases. No loss of imprinting, as determined by the finding of biallelic expression, was detected in any case. The expression of H19 gene was detected in 10 of 20 informative cases and the imprinting pattern was also maintained in all of them. Our data suggest that alterations in IGF2 and H19 genes expression by loss of imprinting do not occur in uterine leiomyomas.

Genomic imprinting and chromatin insulation in Beckwith-Wiedemann syndrome

Genes are recognized as undergoing genomic imprinting when they are capable of being expressed only from the paternal or only from the maternal chromosome. The process can occur coordinately within large physical domains in mammalian chromosomes. One interesting facet of the study of genomic imprinting is that it offers insight into the regulation of large chromosomal regions. Understanding this regulation involves elucidating the cis-acting regulators of gene expression and defining the elements that maintain chromatin insulation, both required for understanding more practically applicable areas of biological research, such as efficient transgene production. This review is focused on the regulation of the imprinted domain of human chromosome 11p15.5, responsible for Beckwith-Wiedemann syndrome (BWS). Recent findings indicate that the maintenance of imprinting within this domain is critically dependent on the stable maintenance of chromatin insulation.

Analysis of IGF2 gene imprinting in breast and colorectal cancer by allele specific-PCR

The insulin-like growth factor II (IGF2) gene is imprinted with the paternal allele expressed and the maternal one silent. Loss of imprinting (LOI) of IGF2 has been suggested to play a role in the development of tumours, but the reported incidence of IGF2 LOI in tumours shows considerable variation, which may stem from different methodologies employed. In particular, partial digestion of reverse transcriptase-polymerase chain reaction (RT-PCR) products by restriction enzymes can lead to inaccurate measurements. To overcome the problem of partial enzymatic digestion, a novel method termed allele specific-polymerase chain reaction (AS-PCR) has recently been reported, which provides a significant advance over enzymatic digestion. A second problem with measurements of biallelic IGF2 transcription is that the co-amplification of contaminating genomic DNA during the RT-PCR step can lead to an overestimation of the frequency of biallelic IGF2 expression. To investigate the extent of this problem, total RNA from breast and colorectal cancer was analysed using two methods. The first method involved a first-round PCR using cDNA generated with primers spanning exons 8 and 9 (exon connection), followed by a second round of AS-PCR using primers from within exon 9. The second method used only AS-PCR with primers from within exon 9. The result was that the exon-connection approach was more accurate, thereby highlighting a significant problem in imprinting analyses where genomic DNA contamination cannot be completely ruled out.

Genomic imprinting: implications for human disease

Genomic imprinting refers to an epigenetic marking of genes that results in monoallelic expression. This parent-of-origin dependent phenomenon is a notable exception to the laws of Mendelian genetics. Imprinted genes are intricately involved in fetal and behavioral development. Consequently, abnormal expression of these genes results in numerous human genetic disorders including carcinogenesis. This paper reviews genomic imprinting and its role in human disease. Additional information about imprinted genes can be found on the Genomic Imprinting Website at http://www.geneimprint.com.

Loss of imprinting of IGF2 and not H19 in breast cancer, adjacent normal tissue and derived fibroblast cultures

Insulin-like growth factors are involved in the paracrine growth regulation of human breast tumor cells. IGF2 is imprinted in most tissues, and shows expression of the paternal allele only. To investigate whether disruption of this monoallelic IGF2 expression is involved in breast cancer development, a series of primary tumors and adjacent, histologically normal, breast tissue samples, as well as matched primary in vitro fibroblast cultures were studied. Biallelic expression (partial) of IGF2 was found in the majority of in vivo samples, and corresponding fibroblast cultures, while monoallelic expression was found in a normal breast sample. In contrast, H19, a closely apposed, but reciprocally imprinted gene, assumed to be regulated by a common control element, showed retention of monoallelic H19 expression in all in vivo and in the majority of in vitro samples. These data indicate that IGF2, but not H19, is prone to loss of imprinting in breast cancer.

Genomic imprinting and cancer

Genomic imprinting is the phenomenon by which individual alleles of certain genes are expressed differentially according to their parent of origin. The alleles appear to be differentially marked during gametogenesis or during the early part of development. This mark is heritable but reversible from generation to generation, implying a stable epigenetic modification. Approximately 25 imprinted genes have been identified to date, and dysregulation of a number of these has been implicated in tumour development. The normal physiological role of many imprinted genes is in the control of cell proliferation and fetal growth, indicating potential mechanisms of action in tumour formation. Both dominant and recessive modes of action have been postulated for the role of imprinted genes in neoplasia, as a result of effective gene dosage alterations by epigenetic modification of the normal pattern of allele specific transcription. The aim of this review is to assess the importance of imprinted genes in generating tumours and to discuss the implications for novel mechanisms of transforming mutation.

Promoter-specific insulin-like growth factor 2 gene imprinting in human fetal liver and hepatoblastoma

Insulin-like growth factor 2 (IGF2) gene imprinting has been demonstrated to be promoter-specific, in that expression from the P1 promoter is biallelic whereas that from the P2-P4 promoters is monoallelic. In the present study, in order to investigate IGF2 gene imprinting status at the cellular level, allelic analysis was performed of IGF2 gene expression transcribed from the P1 and P3 promoters, using reverse transcription polymerase chain reaction (RT-PCR) on human fetal liver and hepatoblastoma. In situ hybridization was also undertaken, to obtain information about the cellular localization of transcripts expressed from the P1 and P3 promoters. The results indicated that transcripts expressed from the P1 and P3 promoters co-localized in the same fetal or neoplastic hepatocytes. These data should provide information regarding the molecular basis of genomic imprinting, suggesting that an imprint recognized for the differential expression may be strictly local and localized downstream of the IGF2 P1 promoter.

The MAS proto-oncogene is imprinted in human breast tissue

The human MAS proto-oncogene is situated at 6q25.3-q26, a region that is homologous to mouse chromosome 17 where two parentally imprinted genes (Mas and Igf2r) have previously been identified. We investigated the imprinting status of MAS in adult lesions to establish the imprinting status of this gene in humans, as certain imprinted genes are known to have altered imprinting phenotypes in cancer. Of 14 breast samples demonstrating a MAS RT-PCR product, 4 were informative for a polymorphic marker. In all 4 cases, expression of the MAS gene was found to be mono-allelic, indicating the presence of a functional imprint at this locus in human breast tissue.

Insulin-like growth factor 2 gene imprinting in clear cell sarcoma of the kidney

We examined the expression of insulin-like growth factor 2 (IGF2) transcripts and allelic-specificity in four cases of clear cell sarcoma of the kidney (CCSK). All cases contained abundant IGF2 transcripts in the cytoplasm of tumor cells detected by in situ mRNA hybridization. The level of IGF2 expression was comparable with that of Wilms tumor. The IGF2 gene imprinting status was analysed by using DNA/RNA extracted from one frozen tumor tissue and three archival tumor and kidney tissue. The allele-specific analysis using Apa1 polymorphism in the 5'-untranslated region of the IGF2 gene showed that two out of four tumors were heterozygous at the IGF2 locus. The result showed that one of two informative heterozygous tumors showed biallelic IGF2 expression whereas the other showed monoallelic expression. The data show that disruption of IGF2 gene imprinting occurs in CCSK.

Novel splicing of an IGF2 polymorphic region in human adrenocortical carcinomas

The human IGF2 gene lies on chromosome 11p15.5 and encodes for a mitogenic peptide. IGF2 is often overexpressed in many tumours including adrenal carcinomas. In this study while screening 12 adrenocortical carcinomas for heterozygosity at the Apa I and (CA)n repeat polymorphisms we observed a novel splicing event in two samples which showed both an allelic expression imbalance and preferential splicing for one of the alleles. Further examination revealed that the splicing was not confined to one particular site. Three of such splice products were isolated and cloned. Using RNase protection analysis the presence of this splicing event was demonstrated for both adrenocortical carcinoma samples and also in a Hep3B cell line. This suggested that the event may be occurring in all the samples. The presence of this splicing was then confirmed in all 12 adrenocortical carcinoma samples by PCR. These data suggest that the splicing event may be a general feature for IGF2 transcripts.