Altered imprinting, promoter usage, and expression of insulin-like growth factor-II gene in gestational trophoblastic diseases

Lentivirus-mediated RNA interference targeting the H19 gene inhibits cell proliferation and apoptosis in human choriocarcinoma cell line JAR

Background

H19 is a paternally imprinted gene that has been shown to be highly expressed in the trophoblast tissue. Results from previous studies have initiated a debate as to whether noncoding RNA H19 acts as a tumor suppressor or as a tumor promotor in trophoblast tissue. In the present study, we developed lentiviral vectors expressing H19-specific small interfering RNA (siRNA) to specifically block the expression of H19 in the human choriocarcinoma cell line JAR. Using this approach, we investigated the impact of the H19 gene on the proliferation, invasion and apoptosis of JAR cells. Moreover, we examined the effect of H19 knockdown on the expression of insulin-like growth factor 2 (IGF2), hairy and enhancer of split homologue-1 (HES-1) and dual-specific phosphatase 5 (DUSP5) genes.

Results

H19 knockdown inhibited apoptosis and proliferation of JAR cells, but had no significant impact on cell invasion. In addition, H19 knockdown resulted in significant upregulation of HES-1 and DUSP5 expression, but not IGF2 expression in JAR cells.

Conclusions

The finding that H19 downregulation could simultaneously inhibit proliferation and apoptosis of JAR cells highlights a putative dual function for H19 in choriocarcinoma and may explain the debate on whether H19 acts as a tumor suppressor or a tumor promotor in trophoblast tissue. Furthermore, upregulation of HES-1 and DUSP5 may mediate H19 downregulation-induced suppression of proliferation and apoptosis of JAR cells.

Increased insulin resistance and C-reactive protein in women with complete hydatidiform mole

OBJECTIVE

To evaluate (i) insulin resistance and C-reactive protein (CRP) levels in women with complete hydatidiform mole (CHM) and (ii) whether there were any correlations between these parameters and CHM.

METHODS

Thirty-two women with CHM and 30 healthy pregnant women were enrolled in the study. Fasting serum glucose and insulin levels, low-density lipoprotein (LDL), high-density lipoprotein (HDL), total cholesterol (TC), and triglyceride (TG) and C-reactive protein (CRP) were measured. Insulin resistance was calculated by the homeostasis model assessment ratio (HOMA-IR).

RESULTS

Fasting glucose, insulin, HOMA-IR, CRP, and TG levels were higher, and HDL was lower among patients with CHM compared with healthy pregnant group (p < 0.05 for all). There were positive associations between CHM status and glucose, insulin, HOMA-IR, CRP, TG levels and had a negative correlation with HDL (p < 0.05 for all). The receiver operating characteristic curve (ROC) analysis value for HOMA-IR in CHM was 0.96 (95% confidence interval (CI) = 0.92-1.00), sensitivity = 94%, and specificity = 87%. The area under ROC curve value for CRP was 0.72 (95% confidence interval (CI) = 0.58-0.84), sensitivity = 82%, and specificity = 60% in CHM.

CONCLUSIONS

Insulin resistance and CRP were found to be higher among patients with CHM. These parameters were also closely associated with CHM. Further studies are needed to investigate the nature of this link in this group.

Epigenetics and the placenta

BACKGROUND

The placenta is of utmost importance for intrauterine fetal development and growth. Deregulation of placentation can lead to adverse outcomes for both mother and fetus, e.g. gestational trophoblastic disease (GTD), pre-eclampsia and fetal growth retardation. A significant factor in placental development and function is epigenetic regulation.

METHODS

This review summarizes the current knowledge in the field of epigenetics in relation to placental development and function. Relevant studies were identified by searching PubMed, Medline and reference sections of all relevant studies and reviews.

RESULTS

Epigenetic regulation of the placenta evolves during preimplantation development and further gestation. Epigenetic marks, like DNA methylation, histone modifications and non-coding RNAs, affect gene expression patterns. These expression patterns, including the important parent-of-origin-dependent gene expression resulting from genomic imprinting, play a pivotal role in proper fetal and placental development. Disturbed placental epigenetics has been demonstrated in cases of intrauterine growth retardation and small for gestational age, and also appears to be involved in the pathogenesis of pre-eclampsia and GTD. Several environmental effects have been investigated so far, e.g. ethanol, oxygen tension as well as the effect of several aspects of assisted reproduction technologies on placental epigenetics.

CONCLUSIONS

Studies in both animals and humans have made it increasingly clear that proper epigenetic regulation of both imprinted and non-imprinted genes is important in placental development. Its disturbance, which can be caused by various environmental factors, can lead to abnormal placental development and function with possible consequences for maternal morbidity, fetal development and disease susceptibility in later life.

IGF-II regulates metastatic properties of choriocarcinoma cells through the activation of the insulin receptor

Choriocarcinoma is a highly malignant tumor that can arise from trophoblasts of any type of gestational event but most often from complete hydatidiform mole. IGF-II plays a fundamental role in placental development and may play a role in gestational trophoblastic diseases. Several studies have shown that IGF-II is expressed at high levels in hydatidiform moles and choriocarcinoma tissues; however, conflicting data exist on how IGF-II regulates the behaviour of choriocarcinoma cells. The purpose of this study was to determine the contribution of the receptors for IGF-I and insulin to the actions of IGF-II on the regulation of choriocarcinoma cells metastasis. An Immuno Radio Metric Assay was used to analyse the circulating and tissue levels of IGF-I and IGF-II in 24 cases of hydatidiform mole, two cases of choriocarcinoma and eight cases of spontaneous abortion at the same gestational age. The JEG-3 choriocarcinoma cell line was used to investigate the role of IGF-II in the regulation of cell invasion. We found that mole and choriocarcinoma tissue express high levels of IGF-II compared to first trimester placenta. Both IGF-I and IGF-II regulate choriocarcinoma cell invasion in a dose dependent manner but through a different mechanism. IGF-II effects involve the activation of the InsR while IGF-I uses the IGF-IR. The positive effects of IGF-II on invasion are the result of enhanced cell adhesion and chemotaxis (specifically towards collagen IV). The actions of IGF-II but not those of IGF-I were sensitive to inhibition by the insulin receptor inhibitor HNMPA(AM)3. Our results demonstrate that the insulin receptor regulates choriocarcinoma cell invasion.

Loss of imprinting and cancer

Imprinting is defined as the parental allele-specific expression of a very limited set of genes (about 50-80). This regulation depends upon an epigenetic marking of parental alleles during gametogenesis. Monoallelic expression ensures that the levels of the proteins encoded by imprinted genes, important factors of embryonic growth, placental growth or adult metabolism, are assured. Without precise control of their expression, developmental abnormalities result, as is shown by a number of hereditary over-growth syndromes, including Beckwith-Wiedemann syndrome. The regulation of imprinted genes is largely dependent on methylation marks, which are laid down during embryological development of germ cells. Once in place, the methylation status of precise chromosomal regions, Imprinting Control Regions (ICRs), is read by either of two mechanisms, chromatin barrier formation or untranslated RNAs, thereby ensuring that only the maternal or paternal allele is expressed. Each imprinted gene is classified as maternal or paternal according to the expressed allele. The stability of the marked regions in somatic cells is maintained through each cellular replication by a methylation enzyme complex containing Dnmt1. Although the major reading mechanisms of imprinted status are known, chromatin boundary formation by CTCF and untranslated RNAs, the molecules elaborating the initial ICR methylation, are just being uncovered. Mis-regulation of imprinted gene expression (loss of imprinting [LOI]) is seen frequently and precociously in a large variety of human tumours, making LOI a potentially valuable tool for both diagnosis and treatment. In fact, LOI is presently considered the most abundant and most precocious alteration in cancer. The present review proposes a mechanism responsible for LOI, as well as its eventual value in tumour diagnosis and prognosis.

Non-random, individual-specific methylation profiles are present at the sixth CTCF binding site in the human H19/IGF2 imprinting control region

Expression of imprinted genes is classically associated with differential methylation of specific CpG-rich DNA regions (DMRs). The H19/IGF2 locus is considered a paradigm for epigenetic regulation. In mice, as in humans, the essential H19 DMR—target of the CTCF insulator—is located between the two genes. Here, we performed a pyrosequencing-based quantitative analysis of its CpG methylation in normal human tissues. The quantitative analysis of the methylation level in the H19 DMR revealed three unexpected discrete, individual-specific methylation states. This epigenetic polymorphism was confined to the sixth CTCF binding site while a unique median-methylated profile was found at the third CTCF binding site as well as in the H19 promoter. Monoallelic expression of H19 and IGF2 was maintained independently of the methylation status at the sixth CTCF binding site and the IGF2 DMR2 displayed a median-methylated profile in all individuals and tissues analyzed. Interestingly, the methylation profile was genetically transmitted. Transgenerational inheritance of the H19 methylation profile was compatible with a simple model involving one gene with three alleles. The existence of three individual-specific epigenotypes in the H19 DMR in a non-pathological situation means it is important to reconsider the diagnostic value and functional importance of the sixth CTCF binding site.

Differential expression profiling of genes in a complete hydatidiform mole using cDNA microarray analysis

OBJECTIVES

To gain a better understanding of the genes involved in the pathogenesis of gestational trophoblastic diseases, we evaluated the genome-wide expression levels of genes in complete hydatidiform mole (H-mole) as compared to normal placenta using cDNA microarray technique.

METHODS

The expression profiles of complete H-mole tissues were compared with those of normal placenta using cDNA microarray technique. The data obtained from 10,305 human genes were normalized by the print-tip-based LOWESS method. Significance analysis of microarray (SAM) was used to identify genes with statistically significant changes in expression. The expression levels of genes which showed significant differences between normal early placenta and complete H-mole tissues were further confirmed by RT-PCR.

RESULTS

A cDNA microarray analysis consisting of 10,305 human genes revealed significant changes in the expression of 213 genes, with 91 genes being upregulated and 122 being downregulated. SAM revealed significant changes in gene expression, including those associated with signal transduction, cell structure, transcription, and apoptosis. Further RT-PCR analysis of altered gene expression in mole tissues supported the microarray analysis results. We confirmed the upregulation of TLE4, CAPZA1, PRSS25, RNF130, and USP1 in complete H-mole tissues. Moreover, our study provides the first evidence that ELK3, LAMA3, LNK, STAT2, and TNFRSF25 are downregulated in complete H-mole compared to normal early placenta tissues.

CONCLUSIONS

These findings provide a large body of information regarding gene expression profiles associated with complete H-mole tumorigenesis and allow the identification of potential targets for tumor prevention or therapy.

Familial hydatidiform molar pregnancy: the germline imprinting defect hypothesis?

Imprinting is the uniparental expression of a set of genes. Somatic cells carry two haploid sets of chromosomes, one maternal and one paternal, while germ cells contain only one of the two forms of chromosomes, male or female. This implies that during early embryogenesis the cells committed for developing the future germ cell lineage, the primordial germ cells, which are diploid, have to undergo a total chromosome reprogramming process. This process is delicately controlled during gametogenesis to ensure that males and females have only their respective form of gametes. The machinery involved in this process is yet poorly defined. Familial hydatidiform molar (HM) pregnancy is an abnormal form of pregnancy characterized by hydropic degeneration of placental villi and abnormal, or absence of, embryonic development. To date, the molecular defect causing this condition is unknown. However, in a few studied cases, the presence of paternal methylation patterns on the maternal chromosomes was observed. In this chapter, we summarize what is known about methylation aberrations in HMs and examine more closely the proposed hypothesis of a maternal germline imprinting defect.

Biallelic methylation and silencing of paternally expressed gene 3 (PEG3) in gynecologic cancer cell lines

OBJECTIVE

To measure mRNA expression levels of paternally expressed gene 3 (PEG3) in gynecologic cancer cell lines and to determine if DNA methylation is involved in the control of PEG3 expression.

METHODS

PEG3 mRNA levels were measured with real-time PCR from 28 gynecologic cancer cell lines and compared to normal tissues. PEG3 mRNA expression was correlated to promoter methylation levels measured by real-time methylation-specific PCR. Polymorphism-specific restriction digestion was employed to analyze PEG3 allele distribution.

RESULTS

While expressed in normal gynecologic tissues, PEG3 is silenced in all endometrial and cervical cancer cell lines studied. In the eight ovarian cancer cell lines, five were found to be PEG3 negative, the remaining three express low levels of PEG3 mRNA. In contrast, loss of maternal imprinting and relatively high PEG3 expression levels were detected in all four choriocarcinomas cell lines studied. No cell line confirmed to contain two copies of PEG3 expressed PEG3 mRNA, suggesting that PEG3 downregulation is not due to genetic deletion. PEG3 mRNA expression was, however, quantitatively correlated to its promoter methylation status. Treatment of PEG3 negative cells with DNA methyltransferase inhibitor 5'-aza-deoxycytidine led to partial promoter demethylation and biallelic reactivation of PEG3 transcription, confirming the methylation-mediated mechanism for PEG3 silencing.

CONCLUSION

PEG3 silencing is associated with DNA hypermethylation but not gene deletion in cell lines tested. These results suggest that loss of PEG3 expression may be a frequent event in gynecologic cancers. Given the known role of PEG3 in p53-mediated apoptosis, it is possible that PEG3 functions as a tumor suppressor.

The changes of gene expression profiles in hydatidiform mole and choriocarcinoma with hyperplasia of trophoblasts

The purpose of this study is to investigate changes of gene expression profiles in hydatidiform moles (HM) and choriocarcinoma and to explore causes of trophoblastic hyperplasia. Using cDNA microarray, 4,096 genes were analyzed in two pairs of the tissues of HM versus normal villi and in two pairs of normal primary culture trophoblasts versus JAR cell line of choriocarcinoma. The expressions of two genes in normal villi and HM, as well as in JAR and JEG-3, were examined with the help of immunohistochemistry, immunoblot, and reverse transcriptase-polymerase chain reaction in order to confirm the findings of cDNA microarray. Twenty-four genes were upregulated and 65 genes were downregulated in all HM. Four hundred thirty-three genes were upregulated and 380 genes were downregulated in JAR. Forty-six genes were upregulated in both HM and choriocarcinoma, whereas 13 genes were downregulated. Genes associated with the inhibition of cell proliferation were significantly downregulated, whereas genes associated with cell proliferation, malignant transformation, metastasis, and drug resistance were upregulated. Thymidine kinase-1 (TK-1) and small subunit ribonucleotide reductase (RRM-2) were overexpressed in HM, JAR, and JEG-3. The expressions of TK-1 and RRM-2 in moles were positively correlated with proliferative index of trophoblasts. Our results suggest that altered expression of genes exist in HM and choriocarcinoma. Trophoblastic hyperplasia may be involved in the overexpression of DNA synthetic enzymes.