Genomic imprinting and cancer

Food abundance in men before puberty predicts a range of cancers in grandsons

Nutritional conditions early in human life may influence phenotypic characteristics in later generations. A male-line transgenerational pathway, triggered by the early environment, has been postulated with support from animal and a small number of human studies. Here we analyse individuals born in Uppsala Sweden 1915-29 with linked data from their children and parents, which enables us to explore the hypothesis that pre-pubertal food abundance may trigger a transgenerational effect on cancer events. We used cancer registry and cause-of-death data to analyse 3422 cancer events in grandchildren (G2) by grandparental (G0) food access. We show that variation in harvests and food access in G0 predicts cancer occurrence in G2 in a specific way: abundance among paternal grandfathers, but not any other grandparent, predicts cancer occurrence in grandsons but not in granddaughters. This male-line response is observed for several groups of cancers, suggesting a general susceptibility, possibly acquired in early embryonic development. We observed no transgenerational influence in the middle generation.

Tumor Suppressing Subtransferable Candidate 4 Expression Prevents Autophagy-Induced Cell Death Following Temozolomide Treatment in Glioblastoma Cells

Glioblastoma (GBM) is the most common and aggressive type of brain cancer in adults, with temozolomide (TMZ) being widely used as the standard chemotherapy drug for its treatment. However, GBM frequently becomes resistant to TMZ treatment due to various mechanisms including amplification and mutations of the epidermal growth factor receptor (EGFR), where EGFR variant III (EGFRvIII) is the most common EGFR mutation. Autophagy (macroautophagy) is an intracellular “self-degradation” process involving the lysosome. It mainly plays a pro-cell survival role contributing to drug resistance in cancers including GBM, but, under some conditions, it can induce cell death called autophagy-induced cell death (AuICD). We recently published that TSSC4 (tumor suppressing subtransferable candidate 4) is a novel tumor suppressor and a novel autophagy inhibitor that inhibits cancer cell growth through its interacting with the autophagy protein LC3. In this brief research report, we demonstrate that cell death induced by TMZ in GBM cells is inhibited by overexpression of TSSC4. TSSC4 overexpression also prevents TMZ-induced autophagy but not when TSSC4 is mutated in its conserved LC3-interacting region. When EGFRvIII was expressed in GBM cells, TSSC4 protein was increased and TMZ-induced cell death was decreased. Knockout of TSSC4 in EGFRvIII-expressing GBM cells increased TMZ-induced autophagy and cell death. This cell death was decreased by autophagy inhibition, suggesting that TSSC4 downregulation promotes TMZ-induced AuICD. This indicates that TSSC4 is a novel target to sensitize GBM cells to TMZ treatment.

Misregulation of Nucleoporins 98 and 96 leads to defects in protein synthesis that promote hallmarks of tumorigenesis

Nucleoporin 98KD (Nup98) is a promiscuous translocation partner in hematological malignancies. Most disease models of Nup98 translocations involve ectopic expression of the fusion protein under study, leaving the endogenous Nup98 loci unperturbed. Overlooked in these approaches is the loss of one copy of normal Nup98 in addition to the loss of Nup96 - a second Nucleoporin encoded within the same mRNA and reading frame as Nup98 - in translocations. Nup98 and Nup96 are also mutated in a number of other cancers, suggesting that their disruption is not limited to blood cancers. We found that reducing Nup98-96 function in Drosophila melanogaster (in which the Nup98-96 shared mRNA and reading frame is conserved) de-regulates the cell cycle. We found evidence of overproliferation in tissues with reduced Nup98-96, counteracted by elevated apoptosis and aberrant signaling associated with chronic wounding. Reducing Nup98-96 function led to defects in protein synthesis that triggered JNK signaling and contributed to hallmarks of tumorigenesis when apoptosis was inhibited. We suggest that partial loss of Nup98-96 function in translocations could de-regulate protein synthesis, leading to signaling that cooperates with other mutations to promote tumorigenesis.

Autophagy inhibition by TSSC4 (tumor suppressing subtransferable candidate 4) contributes to sustainable cancer cell growth

Cancer cell growth is dependent upon the sustainability of proliferative signaling and resisting cell death. Macroautophagy/autophagy promotes cancer cell growth by providing nutrients to cells and preventing cell death. This is in contrast to autophagy promoting cell death under some conditions. The mechanism regulating autophagy-mediated cancer cell growth remains unclear. Herein, we demonstrate that TSSC4 (tumor suppressing subtransferable candidate 4) is a novel tumor suppressor that suppresses cancer cell growth and tumor growth and prevents cell death induction during excessive growth by inhibiting autophagy. The oncogenic proteins ERBB2 (erb-b2 receptor tyrosine kinase 2) and the activation EGFR mutant (EGFRvIII, epidermal growth factor receptor variant III) promote cell growth and TSSC4 expression in breast cancer and glioblastoma multiforme (GBM) cells, respectively. In EGFRvIII-expressing GBM cells, TSSC4 knockout shifted the function of autophagy from a pro-cell survival role to a pro-cell death role during prolonged cell growth. Furthermore, the interaction of TSSC4 with MAP1LC3/LC3 (microtubule associated protein 1 light chain 3) via its conserved LC3-interacting region (LIR) contributes to its inhibition of autophagy. Finally, TSSC4 suppresses tumorsphere formation and tumor growth by inhibiting autophagy and maintaining cell survival in tumorspheres. Taken together, sustainable cancer cell growth can be achieved by autophagy inhibition via TSSC4 expression.ABBREVIATIONS: 3-MA: 3-methyladenine; ACTB: actin beta; CQ: chloroquine; EGFRvIII: epidermal growth factor receptor variant III; ERBB2: erb-b2 receptor tyrosine kinase 2; GBM: glioblastoma multiforme; LIR: LC3-interacting region; MAP1LC3/LC3: microtubule Associated protein 1 light chain 3; TSSC4: tumor suppressing subtransferable candidate 4.

Tumor-Suppressing STF cDNA 3 Overexpression Suppresses Renal Fibrosis by Alleviating Anoikis Resistance and Inhibiting the PI3K/Akt Pathway

BACKGROUND

Myofibroblast (MF) activation is the key event of irreversible renal interstitial fibrosis. Anoikis resistance is the hallmark of active MFs, which is conferred by continuous activation of the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/protein kinase B (Akt) pathway. Our previous study found that tumor-suppressing STF cDNA 3 (TSSC3) enhances the sensitivity of cells to anoikis via the PI3K/Akt pathway. Therefore, we hypothesized that TSSC3 might suppress renal interstitial fibrosis by inducing anoikis via the PI3K/Akt pathway.

METHODS

Cell anoikis was induced by the exogenous addition of RGD-containing peptides or by culturing cells in suspension. MFs were established by stimulating HK-2 renal tubular epithelial cells with transforming growth factor beta 1 (TGF-β1). Lentivirus vectors were to construct a TSSC3 overexpression cell model. The effects of TSSC3 on the anoikis, growth, migration, invasion, and contraction of MFs were determined using annexin V-fluorescein isothiocyanate assays, cell counting kit-8 assays, wound healing migration assays, matrigel invasion assays, and collagen-based contraction assays.

RESULTS

The results demonstrated that TGF-β1, simultaneous with the induction of MF differentiation, confers significant protection against anoikis-induced cell death, which could be partly reversed by treatment with the PI3K/Akt pathway inhibitor, LY294002. Moreover, overexpression of TSSC3 obviously impaired cell growth, cell migration, cell invasion, contraction, and anoikis resistance of MFs, and decreased the activity of the PI3K/Akt pathway and the production of extracellular matrix molecules, all of which could be attenuated by treatment with the PI3K/Akt pathway activator, 740Y-P. Taken together, this study suggested that TSSC3 attenuates the anoikis resistance and profibrogenic ability of TGF-β1-induced MF by regulating the PI3K-Akt pathway.

CONCLUSION

These findings provide a biological basis for further exploration of the therapeutic significance of targeting MF via TSSC3 in renal interstitial fibrosis.

Two Powerful Tests for Parent-of-Origin Effects at Quantitative Trait Loci on the X Chromosome

Parent-of-origin effects, which describe an occurrence where the expression of a gene depends on its parental origin, are an important phenomenon in epigenetics. Statistical methods for detecting parent-of-origin effects on autosomes have been investigated for 20 years, but the development of statistical methods for detecting parent-of-origin effects on the X chromosome is relatively new. In the literature, a class of Q-XPAT-type tests are the only tests for the parent-of-origin effects for quantitative traits on the X chromosome. In this paper, we propose two simple and powerful classes of tests to detect parent-of-origin effects for quantitative trait values on the X chromosome. The proposed tests can accommodate complete and incomplete nuclear families with any number of daughters. The simulation study shows that our proposed tests produce empirical type I error rates that are close to their respective nominal levels, as well as powers that are larger than those of the Q-XPAT-type tests. The proposed tests are applied to a real data set on Turner's syndrome, and the proposed tests give a more significant finding than the Q-C-XPAT test.

Detection of Imprinting Effects for Quantitative Traits on X Chromosome Using Nuclear Families with Multiple Daughters

Genomic imprinting is an epigenetic phenomenon in which the expression of an allele copy depends on its parental origin. This mechanism has been found to play an important role in many complex diseases. Statistical tests for imprinting effects have been developed for more than 15 years, but they are only suitable for autosomes. It was not until recently that the parental-asymmetry test on the X chromosome (XPAT) was proposed to test for imprinting effects. However, this test can only be used for qualitative traits. Therefore, in this article, we propose a class of PAT-type tests to test for imprinting for quantitative traits on the X chromosome in the presence of association, namely, Q-XPAT(c), Q-1-XPAT(c) and Q-C-XPAT(c), where c is a constant. These methods can accommodate complete and incomplete nuclear families with an arbitrary number of daughters. Extensive simulation studies demonstrate that the proposed tests control the size well under the null hypothesis of no imprinting effects and are powerful under various family structures. Moreover, by setting the inbreeding coefficient in females to be nonzero and using the assortative mating pattern in simulations, the proposed tests are shown to be valid under Hardy-Weinberg disequilibrium.

Epigenetic modifications at DMRs of placental genes are subjected to variations in normal gestation, pathological conditions and folate supplementation

Invasive placentation and cancer development shares many similar molecular and epigenetic pathways. Paternally expressed, growth promoting genes (SNRPN, PEG10 and MEST) which are known to play crucial role in tumorogenesis, are not well studied during placentation. This study reports for the first time of the impact of gestational-age, pathological conditions and folic acid supplementation on dynamic nature of DNA and histone methylation present at their differentially methylated regions (DMRs). Here, we reported the association between low DNA methylation/H3K27me3 and higher expression of SNRPN, PEG10 and MEST in highly proliferating normal early gestational placenta. Molar and preeclamptic placental villi, exhibited aberrant changes in methylation levels at DMRs of these genes, leading to higher and lower expression of these genes, respectively, in reference to their respective control groups. Moreover, folate supplementation could induce gene specific changes in mRNA expression in placental cell lines. Further, MEST and SNRPN DMRs were observed to show the potential to act as novel fetal DNA markers in maternal plasma. Thus, variation in methylation levels at these DMRs regulate normal placentation and placental disorders. Additionally, the methylation at these DMRs might also be susceptible to folic acid supplementation and has the potential to be utilized in clinical diagnosis.

Modeling familial cancer with induced pluripotent stem cells

In vitro modeling of human disease has recently become feasible with induced pluripotent stem cell (iPSC) technology. Here, we established patient-derived iPSCs from a Li-Fraumeni syndrome (LFS) family and investigated the role of mutant p53 in the development of osteosarcoma (OS). LFS iPSC-derived osteoblasts (OBs) recapitulated OS features including defective osteoblastic differentiation as well as tumorigenic ability. Systematic analyses revealed that the expression of genes enriched in LFS-derived OBs strongly correlated with decreased time to tumor recurrence and poor patient survival. Furthermore, LFS OBs exhibited impaired upregulation of the imprinted gene H19 during osteogenesis. Restoration of H19 expression in LFS OBs facilitated osteoblastic differentiation and repressed tumorigenic potential. By integrating human imprinted gene network (IGN) into functional genomic analyses, we found that H19 mediates suppression of LFS-associated OS through the IGN component DECORIN (DCN). In summary, these findings demonstrate the feasibility of studying inherited human cancer syndromes with iPSCs.

Stability of genomic imprinting in human induced pluripotent stem cells

BACKGROUND

hiPSCs are generated through epigenetic reprogramming of somatic tissue. Genomic imprinting is an epigenetic phenomenon through which monoallelic gene expression is regulated in a parent-of-origin-specific manner. Reprogramming relies on the successful erasure of marks of differentiation while maintaining those required for genomic imprinting. Loss of imprinting (LOI), which occurs in many types of malignant tumors, would hinder the clinical application of hiPSCs.

RESULTS

We examined the imprinting status, expression levels and DNA methylation status of eight imprinted genes in five independently generated hiPSCs. We found a low frequency of LOI in some lines. Where LOI was identified in an early passage cell line, we found that this was maintained through subsequent passages of the cells. Just as normal imprints are maintained in long-term culture, this work suggests that abnormal imprints are also stable in culture.

CONCLUSIONS

Analysis of genomic imprints in hiPSCs is a necessary safety step in regenerative medicine, with relevance both to the differentiation potential of these stem cells and also their potential tumorigenic properties.

Rare allelic forms of PRDM9 associated with childhood leukemogenesis

One of the most rapidly evolving genes in humans, PRDM9, is a key determinant of the distribution of meiotic recombination events. Mutations in this meiotic-specific gene have previously been associated with male infertility in humans and recent studies suggest that PRDM9 may be involved in pathological genomic rearrangements. In studying genomes from families with children affected by B-cell precursor acute lymphoblastic leukemia (B-ALL), we characterized meiotic recombination patterns within a family with two siblings having hyperdiploid childhood B-ALL and observed unusual localization of maternal recombination events. The mother of the family carries a rare PRDM9 allele, potentially explaining the unusual patterns found. From exomes sequenced in 44 additional parents of children affected with B-ALL, we discovered a substantial and significant excess of rare allelic forms of PRDM9. The rare PRDM9 alleles are transmitted to the affected children in half the cases; nonetheless there remains a significant excess of rare alleles among patients relative to controls. We successfully replicated this latter observation in an independent cohort of 50 children with B-ALL, where we found an excess of rare PRDM9 alleles in aneuploid and infant B-ALL patients. PRDM9 variability in humans is thought to influence genomic instability, and these data support a potential role for PRDM9 variation in risk of acquiring aneuploidies or genomic rearrangements associated with childhood leukemogenesis.

High-throughput detection of aberrant imprint methylation in the ovarian cancer by the bisulphite PCR-Luminex method

BACKGROUND

Aberrant DNA methylation leads to loss of heterozygosity (LOH) or loss of imprinting (LOI) as the first hit during human carcinogenesis. Recently we developed a new high-throughput, high-resolution DNA methylation analysis method, bisulphite PCR-Luminex (BPL), using sperm DNA and demonstrated the effectiveness of this novel approach in rapidly identifying methylation errors.

RESULTS

In the current study, we applied the BPL method to the analysis of DNA methylation for identification of prognostic panels of DNA methylation cancer biomarkers of imprinted genes. We found that the BPL method precisely quantified the methylation status of specific DNA regions in somatic cells. We found a higher frequency of LOI than LOH. LOI at IGF2, PEG1 and H19 were frequent alterations, with a tendency to show a more hypermethylated state. We detected changes in DNA methylation as an early event in ovarian cancer. The degree of LOI (LOH) was associated with altered DNA methylation at IGF2/H19 and PEG1.

CONCLUSIONS

The relative ease of BPL method provides a practical method for use within a clinical setting. We suggest that DNA methylation of H19 and PEG1 differentially methylated regions (DMRs) may provide novel biomarkers useful for screening, diagnosis and, potentially, for improving the clinical management of women with human ovarian cancer.

Upregulation of imprinted genes in mice: an insight into the intensity of gene expression and the evolution of genomic imprinting

Imprinted genes are expressed monoallelically because one of the two copies is silenced epigentically in a parent-of-origin pattern. This pattern of expression is controlled by differential marking of parental alleles by DNA methylation and chromatin modifications, including both suppressive and permissive histone acetylation and methylation. Suppressive histone modifications mark silenced alleles of imprinted genes, while permissive histone modifications mark the active alleles, suggesting the possibility that imprinted genes would show upregulation in gene expression. However, it is currently unknown whether imprinted genes show such upregulation. To address this question in mice, we estimated the intensity of expression of 59 genes relative to the rest of the genome by analyzing microarray data. Expression levels of 24 genes were validated using quantitative real-time PCR (qPCR). Expression of imprinted genes was found to be upreguled in various adult and embryonic mouse tissues. Consistent with their functions in growth and development, imprinted genes were found to be highly expressed in extraembryonic tissues and progressively upregulated during early embryonic development. In conclusion, upregulation of imprinted genes found in this study is similar to the dosage compensation (twofold upregulation) recently reported for X-linked genes. It has been proposed that the twofold upregulation of X-linked genes has been coupled with low transcriptional variation (noise) which could lead to deleterious effects on the organism. Results of this study suggest a general need for imprinted genes in the mouse to be upregulated to certain levels in order to avoid deleterious effects of variation in gene expression.

Oncoviruses and Pathogenic MicroRNAs in Humans

For disease prognosis, the functional significance of the oncoviral integration locus in oncogenesis has remained enigmatic. The locus encodes several transcripts without protein products, but microRNAs (miRNAs) have recently been identified from a common oncoviral integration locus. miRNA is an endogenous, non-coding small RNA by which gene expression is suppressed. Although miRNA genes, such as let-7 in the nematode, have orthologs among animals, the relationship between miRNAs and tumorigenesis or tumor suppression has been mainly discovered in several human cancers. On the contrary, this review clearly demonstrates the potential for human tumorigenesis of both miRNA genes from oncoviral integration sites and other cellular onco-microRNA genes, and we conclude that alteration of the miRNA profile of cells can be defined as tumorigenic or tumor suppressive. Thus, we explain here that virally-pathogenic miRNAs could also be partly responsible for oncogenesis or oncogene suppression to confirm' the RNA wave', with the miRNAs hypothesized as a mobile and functional genetic element.

At least ten genes define the imprinted Dlk1-Dio3 cluster on mouse chromosome 12qF1

Background

Genomic imprinting is an exception to Mendelian genetics in that imprinted genes are expressed monoallelically, dependent on parental origin. In mammals, imprinted genes are critical in numerous developmental and physiological processes. Aberrant imprinted gene expression is implicated in several diseases including Prader-Willi/Angelman syndromes and cancer.

Methodology/Principal Findings

To identify novel imprinted genes, transcription profiling was performed on two uniparentally derived cell lines, androgenetic and parthenogenetic primary mouse embryonic fibroblasts. A maternally expressed transcript termed Imprinted RNA near Meg3/Gtl2 (Irm) was identified and its expression studied by Northern blotting and whole mounts in situ hybridization. The imprinted region that contains Irm has a parent of origin effect in three mammalian species, including the sheep callipyge locus. In mice and humans, both maternal and paternal uniparental disomies (UPD) cause embryonic growth and musculoskeletal abnormalities, indicating that both alleles likely express essential genes. To catalog all imprinted genes in this chromosomal region, twenty-five mouse mRNAs in a 1.96Mb span were investigated for allele specific expression.

Conclusions/Significance

Ten imprinted genes were elucidated. The imprinting of three paternally expressed protein coding genes (Dlk1, Peg11, and Dio3) was confirmed. Seven noncoding RNAs (Meg3/Gtl2, Anti-Peg11, Meg8, Irm/“Rian”, AK050713, AK053394, and Meg9/Mirg) are characterized by exclusive maternal expression. Intriguingly, the majority of these noncoding RNA genes contain microRNAs and/or snoRNAs within their introns, as do their human orthologs. Of the 52 identified microRNAs that map to this region, six are predicted to regulate negatively Dlk1, suggesting an additional mechanism for interactions between allelic gene products. Since several previous studies relied heavily on in silico analysis and RT-PCR, our findings from Northerns and cDNA cloning clarify the genomic organization of this region. Our results expand the number of maternally expressed noncoding RNAs whose loss may be responsible for the phenotypes associated with mouse pUPD12 and human pUPD14 syndromes.

An evaluation of evidence for the carcinogenic activity of bisphenol A

The National Institutes of Health (NIEHS, NIDCR) and the United States Environmental Protection Agency convened an expert panel of scientists with experience in the field of environmental endocrine disruptors, particularly with knowledge and research on bisphenol A (BPA). Five subpanels were charged to review the published literature and previous reports in five specific areas and to compile a consensus report with recommendations. These were presented and discussed at an open forum entitled "Bisphenol A: An Expert Panel Examination of the Relevance of Ecological, In Vitro and Laboratory Animal Studies for Assessing Risks to Human Health" in Chapel Hill, NC on 28-30 November 2006. The present review consists of the consensus report on the evidence for a role of BPA in carcinogenesis, examining the available evidence in humans and animal models with recommendations for future areas of research.

Epigenetic silencing of the imprinted gene ZAC by DNA methylation is an early event in the progression of human ovarian cancer

ZAC is a paternally expressed, imprinted gene located on chromosome 6q24, within a region known to harbor a tumor suppressor gene for several types of neoplasia, including human ovarian cancer (HOC). We have failed to identify genetic mutations in the ZAC gene in tumor material. Many imprinted genes contain differentially allele-specific-methylated regions (DMR) and harbor promoter activity that is regulated by the DNA methylation. Aberrant DNA methylation is a common feature of neoplasia and changes in DNA methylation at the ZAC locus have been reported in some cases of HOC. We investigated the DNA methylation and ZAC mRNA expression levels in a larger sample of primary HOC material, obtained by laser capture microdissection. ZAC mRNA expression was reduced in the majority of samples and this correlated with hypermethylation of the ZAC-DMR. Treatment of hypermethylated cells lines with a demethylating agent restored ZAC expression. Our studies indicate that transcriptional silencing of ZAC is likely to be caused by DNA methylation in HOC. Forced expression of ZAC resulted in a reduction in proliferation and marked induction of apoptotic cell death. The ZAC-mediated apoptosis signal is p53-independent and eliminated by inhibitors of caspase 3, 8 and 9. Reduced expression of ZAC would therefore favor tumor progression. As there were no significant differences in either DNA methylation or expression of ZAC mRNA between localized and advanced tumors, our data indicates that loss of ZAC is a relatively early event in HOC. (Supplementary material for this article can be found on the International Journal of Cancer website at http://www.interscience.wiley.com/jpages/0020-7136/suppmat/index.html.)

Specificity and significance of expression of imprinted gene PEG10 in hepatocellular carcinoma

AIM: To study the specificity and significance of the expression of imprinted gene PEG10 in hepatocellular carcinoma (HCC) and to evaluate the feasibility for PEG10 as a novel molecular target of gene therapy for HCC.

METHODS: The total RNA was extracted from different tumor cell lines (liver cancer HepG2, gastric cancer SGC7901, colorectal cancer Lovo, pancreatic cancer PC3, melanoma A375 and T lymphoma Jurkat cells), normal human fetal liver cell line L02, human HCC (n = 32) and the corresponding cancer-adjacent tissues (n = 32), benign liver tissues (n = 10) and peripheral blood cells (n = 10). Then the expression of PEG10 was detected by reverse transcription polymerase chain reaction (RT-PCR). Simultaneously, AFP expression was detected in human HCC and the corresponding cancer-adjacent tissues.

RESULTS: After amplification, the length of PEG10 and AFP fragment was 455 bp and 140 bp respectively. PEG10 was markedly expressed in HepG2 cells, and weakly expressed in SGC7901, PC3, Lovo cells. PEG10 expression was found negative in L02 and other tumor cell lines. The positive rates of PEG10 expression in HCC and the corresponding tissues were 78.1% and 0%, but the ones for AFP were 93.8% and 59.4% respectively. There was no significant difference between PEG10 and AFP expression in HCC tissues (P>0.05), whereas the expression of AFP (19/32) was significantly higher than that of PEG10 in cancer-adjacent tissues (0/32) (c²_0.01,1 = 17.05, P<0.01). PEG10 wasn't detected in benign liver tissues and normal peripheral blood cells.

CONCLUSION: PEG10 is more specifically expressed in HCC than AFP, which provides evidence for PEG10 as a novel molecular target of gene therapy for HCC.

Paternal and maternal genomes confer opposite effects on proliferation, cell-cycle length, senescence, and tumor formation

Loss of imprinting is the silencing of active imprinted genes or the activation of silent imprinted genes, and it is one of the most common epigenetic changes associated with the development of a wide variety of tumors. Here, we have analyzed the effects that global imprinted gene expression has on cell proliferation and transformation. Primary mouse embryonic fibroblasts (MEFs), whose entire genome is either exclusively paternal (androgenetic) or maternal (parthenogenetic), exhibit dramatically contrasting patterns of growth. In comparison with biparental MEFs, andro-genetic proliferation is characterized by a shorter cell cycle, increased saturation density, spontaneous transformation, and formation of tumors at low passage number. Parthenogenetic MEFs reach a lower saturation density, senesce, and die. The maternally expressed imprinted genes p57kip2 and M6P/Igf2r retard proliferation and reduce the long-term growth of MEFs. In contrast, the paternally expressed growth factor Igf2 is essential for the long-term proliferation of all genotypes. Increased Igf2 expression in primary MEFs not only stimulates proliferation, but also results in their rapid conversion to malignancy with tumor formation of short latency. Our results reveal that paternally expressed imprinted genes, in the absence of maternal imprinted genes, predispose fibroblasts to rapid transformation. A potent factor in their transformation is IGF2, which on increased expression results in the rapid conversion of primary cells to malignancy. These results reveal a route by which malignant choriocarcinoma may arise from molar pregnancies. They also suggest that the derivation of stem cells from parthenogenetic embryos, for the purposes of therapeutic cloning, may be ineffective.

IGFs and IGF-binding proteins as diagnostic markers and biological modulators in brain tumors

The insulin-like growth factors (IGFs) play a pivotal role in brain tumor growth and inhibition of apoptosis. Specific IGF binding proteins (IGFBPs) may enhance or inhibit tumor growth. Moreover, IGFBPs represent tumor markers and their expression correlates with tumor grading and patient survival. Understanding the role IGFs play for the proliferation of brain tumors is a prerequisite for modulating the biology of tumorigenesis. Novel antisense strategies targeting IGF-I or the Type I IGF receptor may offer additional options to patients suffering from malignant gliomas and other CNS malignancies. Clinical trials are currently underway that should demonstrate whether a beneficial effect is achievable in these patients.

Regulation of the H19 imprinting gene expression in human nasopharyngeal carcinoma by methylation

In East Asia and Singapore, the human nasopharyngeal carcinoma (NPC) presented clinically is mainly of the undifferentiated type. In contrast, the well-differentiated squamous NPC is more commonly detected in the West. To study the potential differences in carcinogenesis between undifferentiated and differentiated human NPC, we employed cDNA microarrays to isolate genes that might be specific for human undifferentiated NPC. One of the genes identified to be specifically upregulated in the undifferentiated human NPC cell line CNE-2 is the human imprinting gene H19. Interestingly, H19 is not expressed in the well-differentiated human HK1 NPC cells. Northern blot and in situ hybridization analyses also confirmed that the H19 gene is strongly expressed in the undifferentiated CNE-2 human NPC cell line but not in the well-differentiated HK1 human NPC cell line. In situ hybridization and reverse transcriptase-polymerase chain reaction also demonstrated that H19 is specifically expressed in NPC biopsies and not in non-NPC human tissue biopsies. Furthermore, we demonstrated that deregulation of H19 gene expression in the well-differentiated human HK1 NPC cells could be induced by the hypomethylation of CpG sites of the H19 promoter region. Hypermethylation of gene promoter regions might therefore be an important epigenetic event that plays a role in the differentiation of human NPC cells and the transcriptional silencing of imprinted genes.

NUP98 gene fusions in hematologic malignancies

Acute leukemia is associated with a wide spectrum of recurrent, non-random chromosomal translocations. Molecular analysis of the genes involved in these translocations has led to a better understanding of both the causes of chromosomal rearrangements as well as the mechanisms of leukemic transformation. Recently, a number of laboratories have cloned translocations involving the NUP98 gene on chromosome 11p15.5, from patients with acute myelogenous leukemia (AML), myelodysplastic syndrome (MDS), chronic myelogenous leukemia (CML), and T cell acute lymphoblastic leukemia (T-ALL). To date, at least eight different chromosomal rearrangements involving NUP98 have been identified. The resultant chimeric transcripts encode fusion proteins that juxtapose the N-terminal GLFG repeats of NUP98 to the C-terminus of the partner gene. Of note, several of these translocations have been found in patients with therapy-related acute myelogenous leukemia (t-AML) or myelodysplastic syndrome (t-MDS), suggesting that genotoxic chemotherapeutic agents may play an important role in generating chromosomal rearrangements involving NUP98.

The IGF/IGFBP system in CNS malignancy

The insulin-like growth factor (IGF) system includes IGF-I and IGF-II, the type I and type II IGF receptors, and specific IGF binding proteins (IGFBP-1 to IGFBP-6). These factors regulate both normal and malignant brain growth. Enhanced expression of IGF-I and IGF-II mRNA transcripts has been demonstrated in gliomas, meniningiomas, and other tumours. Abnormal imprinting of IGF-II occurs in gliomas, medulloblastomas, and meningiomas. Both types of IGF receptor are expressed in gliomas and, in particular, the type I IGF receptor appears to be upregulated in malignant brain tissue. Antisense IGF-I receptor mRNA induces an antitumour response, resulting in complete brain tumour regression. Clinical trials for the treatment of brain tumours in humans based on a gene transfer protocol using IGF-I receptor antisense are under way. All six IGFBPs are expressed to a variable extent in brain tumours. High concentrations of IGFBP-2 are found in cerebrospinal fluid from patients with malignant central nervous system tumours; therefore, IGFBP-2 might be a useful marker for these tumours. IGFBP-4 appears to be a negative regulator of tumour proliferation. Both in vitro and in vivo experiments suggest that the IGF system represents an important target for the treatment of malignant central nervous system tumours and the ongoing trials should provide valuable information for future therapeutic approaches.

Genomic imprinting and cancer; new paradigms in the genetics of neoplasia

The role of epigenetic modification of gene expression is becoming increasingly important in how we understand the loss of tumour suppressor gene function in a variety of tumours and tumour predisposing syndromes. This review explores the importance of epimutation in Beckwith-Wiedemann syndrome and Wilms' tumour and focuses on genomic methylation in both imprinted and non-imprinted genes as a key mechanism in the development of cancer.

Alterations of H19 imprinting and IGF2 replication timing are infrequent in Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is an overgrowth disorder resulting from dysregulation of multiple imprinted genes through a variety of distinct mechanisms. A frequent alteration in BWS involves changes in the imprinting status of the coordinately regulated IGF2 and H19 genes on 11p15. Patients have been categorized according to alterations in the imprinted expression, allele-specific methylation, and regional replication timing of these genes. In this work, IGF2/H19 expression, H19 DNA methylation, and IGF2 regional replication timing were studied in nine karyotypically normal BWS fibroblasts and two BWS patients with maternally inherited 11p15 chromosomal rearrangements. Informative patients (9/9) maintained normal monoallelic H19 expression/methylation, despite biallelic IGF2 expression in 6/9. Replication timing studies revealed no changes in the pattern of asynchronous replication timing for both a patient with biallelic IGF2 expression and a patient carrying an 11p15 inversion. In contrast, a patient with a chromosome 11;22 translocation and normal H19 expression/methylation exhibited partial loss of asynchrony and a shift toward earlier replication times. These results indicate that in BWS, (1) H19 imprinting alterations are less frequent than previously estimated, (2) IGF2 imprinting and H19 imprinting are not necessarily coordinated, and (3) alterations in regional replication timing are generally not correlated with either chromosomal rearrangements or the imprinting status of IGF2 and H19.

Genomic imprinting of IGF2 and H19 in human meningiomas

A number of genes, including IGF2 and H19, are normally imprinted with preferential expression of the paternal or maternal allele, respectively. Loss of imprinting (LOI) of IGF2 and H19 is found in a number of tumours, suggesting that LOI of IGF2 and/or H19 may play an important role in tumorigenesis. The IGF2 gene codes for a fetal growth factor and the H19 gene is likely to act as an RNA with an antitumour effect. We investigated the imprinting status of IGF2 and H19 in human meningiomas. The normally imprinted IGF2 gene lacks imprint in the leptomeninges and choroid plexus of the brain. To examine the imprinting status of IGF2 and H19 in human meningiomas we used the ApaI polymorphism in exon 9 for the IGF2 gene and the AluI polymorphism in exon 5 for the H19 gene. In total, 24 meningiomas of WHO grade I, II and III were analysed. 15 meningiomas (63%) were informative for the ApaI polymorphism in the IGF2 gene. Monoallelic expression (MAE) for IGF2 was found in 11 out of 15 tumours (73%) which is in contrast to the lack of imprinting status of IGF2 in leptomeninges. Ten cases (42%) were heterozygous for the H19 gene and biallelic expression was found in 3 out of 10 meningiomas (30%). These results indicate that modulation of the imprinting status of IGF2 and H19 may play an important role for the development of meningiomas.

Prader Willi and Angelman syndromes: exemplars of genomic imprinting

The molecular phenomenon genomic imprinting provides an explanation for why two clinically distinct syndromes share genetic etiologies. Increased understanding of genomic imprinting is affecting diagnostics. Use of improved diagnostic tests can enable early, syndrome-specific, and anticipatory interventions and consequently, improved quality of life; however, these tests are of little use unless clinicians are able to identify at-risk patients. Nurses knowledgeable about Prader Willi and Angelman syndromes and their associated genetic mechanisms can play a significant role in early identification, referral, and intervention of patients with these conditions.