Altered expression of imprinted genes in Wilms tumors
ABSTRACT Overexpression of insulin-like growth factor 2 (IGF2), an imprinted gene located on chromosome 11p15, has been reported as a characteristic feature in various embryonal tumors, including Wilms tumor (WT). Recent studies specified loss of imprinting (LOI) in a differential methylated region (DMR) of the IGF2/H19 cluster or loss of heterozygosity (LOH), respectively, uniparental disomy (UPD) being responsible for this overexpression. However, the role of other imprinted genes in the genesis of WT is still unknown. In the current study, we analyzed transcriptional activity of the imprinted genes IGF2, H19, NNAT, DLK1, RTL1, MEG3, and MEST as well as the methylation status of the DMR of the IGF2/H19 cluster in a panel of 32 WTs. Except for H19, we detected massive overexpression of all genes in the majority of WTs compared to normal renal tissue, which was most prominent for the paternally expressed genes IGF2, NNAT, and MEST. Alterations of the H19DMR were found in two-thirds of the WTs. Moreover, we have seen a strong correlation between the transcriptional activity of IGF2, NNAT and MEST and LOI/LOH of H19DMR, which was inverse for H19. Expression of DLK1, RTL1 and MEG3 does not correlate with LOI/LOH of H19DMR. Altogether, our findings suggest that over-expression of imprinted genes is common in WTs and correlates at least for some imprinted genes with LOI of H19DMR. Thus, it may be speculated that alterations of the DNA modification machinery drive erroneous setting of methylation marks in imprinting regions throughout the genome, which leads to the concomitant activation of imprinted genes in blastomagenesis.
- SourceAvailable from: Roland Kappler
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- "It is generally accepted that the methylation patterns of binding sites for regulatory proteins are responsible for the transcriptional regulation of many imprinted genes. CTCF is one of the factors that are involved in gene regulation, especially at the H19DMR and is well-studied at this locus , , . By researching the Ensembl database, we detected a regulatory region of the NNAT locus that harbors four putative CTCF binding sites 1.5 kb upstream of the first exon of NNAT (Fig. 2b) and outside of its described promoter . "
ABSTRACT: Aberrant expression of imprinted genes, such as those coding for the insulin-like growth factor 2 (IGF2) and neuronatin (NNAT), is a characteristic of a variety of embryonic neoplasms, including Wilms tumor (WT). In case of IGF2, it is generally accepted that loss of imprinting in a differentially methylated region of the IGF2/H19 locus results in biallelic expression and, thus, upregulation of the gene. In this study we examined methylation pattern at potential regulatory elements of the paternally expressed NNAT gene in a cohort of WT patients in order to further characterize the molecular mechanism causing overexpression of this regulatory gene. We demonstrate that transcriptional upregulation of NNAT in WT is grossly independent of the bladder cancer-associated protein (BLCAP) gene, an imprinted gene within the imprinted domain of the NNAT locus. However, expression of the BLCAP transcript isoform v2a formerly known to be selectively expressed from the paternal allele in brain was associated with high expression of NNAT. This contrasts the situation we found at the IGF2/H19 locus, which shows high overexpression of IGF2 and inversely correlated expression of the H19 gene in WT. An analysis of DNA methylation in two potential regulatory regions of the NNAT locus by pyrosequencing revealed significant hypomethylation of the tumors compared to normal kidney tissue. Interestingly, the difference in DNA methylation was highest at CpGs that were observed within three putative binding sites of the CCCTC-binding factor CTCF. Most importantly, hypomethylation of both NNAT regulatory regions is significantly associated with the upregulation of NNAT expression and the BLCAP_v2a transcript. Our data indicate that the methylation status of a not-yet-described regulatory element within the NNAT locus that contains four potential CTCF binding sites determines the expression level of NNAT and the nearby located BLCAP_v2a transcript, thereby suggesting a functional role in the aberrant upregulation of NNAT in WT.PLoS ONE 06/2013; 8(6):e67605. DOI:10.1371/journal.pone.0067605 · 3.23 Impact Factor
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- "At least one study attempted to define a relationship between imprinting status of IGF2 and expression levels and discovered that LOI of IGF2 correlated significantly with overexpression . Furthermore, the investigators identified two developmentally expressed genes, mesoderm-specific transcript homolog (MEST) and neuronatin (NNAT), which were also correlated with the imprinting status of the DMR of IGF2 . "
ABSTRACT: Among the hypotheses discussing cancer formation, the cancer stem cell (CSC) theory is one receiving widespread support. One version of this theory states that changes in otherwise healthy cells can cause formation of tumor- initiating cells (TICs), which have the potential to create precancerous stem cells that can lead to CSC formation. These CSCs can be rare, in contrast to their differentiated progeny, which give rise to the vast majority of the tumor mass in most cancers. Loss of imprinting (LOI) of the insulin-like growth factor-2 (IGF2) gene is one change that can produce these TICs via an epigenetic progenitor model of tumorigenesis. While IGF2 usually supports normal cellular growth, LOI of IGF2 may lead to overexpression of the gene and moreover global chromatin instability. This modification has been observed in many forms of cancer, and given the effect of LOI of IGF2 and its role in cancer, detecting a loss of imprinting in this gene could serve as a valuable diagnostic tool. Preclinical data has shown some progress in identifying therapeutic approaches seeking to exploit this relationship. Thus, further research surrounding LOI of IGF2 could lead to increased understanding of several cancer types and enhance therapies against these diseases.American Journal of Stem Cells 01/2012; 1(1):59-74.
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ABSTRACT: Epigenetic dysregulation comprising DNA hypermethylation and hypomethylation, enhancer of zeste homologue 2 (EZH2) overexpression and altered patterns of histone modifications is associated with the progression of prostate cancer. DNA methylation, EZH2 and histone modifications also ensure the parental-specific monoallelic expression of at least 62 imprinted genes. Although it is therefore tempting to speculate that epigenetic dysregulation may extend to imprinted genes, expression changes in cancerous prostates are only well documented for insulin-like growth factor 2 (IGF2). A literature and database survey on imprinted genes in prostate cancer suggests that the expression of most imprinted genes remains unchanged despite global disturbances in epigenetic mechanisms. Instead, selective genetic and epigenetic changes appear to lead to the inactivation of a sub-network of imprinted genes, which might function in the prostate to limit cell growth induced via the PI3K/Akt pathway, modulate androgen responses and regulate differentiation. Whereas dysregulation of IGF2 may constitute an early change in prostate carcinogenesis, inactivation of this imprinted gene network is rather associated with cancer progression.Asian Journal of Andrology 02/2012; 14(3):436-50. DOI:10.1038/aja.2011.160 · 2.60 Impact Factor