Isabelle Guilleret

Hypermethylation of the human telomerase catalytic subunit (hTERT) gene correlates with telomerase activity

DNA methylation is an epigenetic process involved in embryonic development, differentiation and aging. It is 1 of the mechanisms resulting in gene silencing in carcinogenesis, especially in tumor suppressor genes (e.g., p16, Rb). Telomerase, the DNA polymerase adding TTAGGG repeats to the chromosome end, is involved in the regulation of the replicative life span by maintaining telomere length. This enzyme is activated in germ and stem cells, repressed in normal somatic cells and reactivated in a large majority of tumor cells. The promoter region of the hTERT gene, encoding for the catalytic subunit of human telomerase, has been located in a CpG island and may therefore be regulated at least in part by DNA methylation. We analyzed the methylation status of 27 CpG sites within the hTERT promoter core region by methylation‐sensitive single‐strand conformation analysis (MS‐SSCA) and direct sequencing using bisulfite‐modified DNA in 56 human tumor cell lines, as well as tumor and normal tissues from different organs. A positive correlation was observed among hypermethylation of the hTERT promoter, hTERT mRNA expression and telomerase activity (p < 0.00001). Furthermore, this correlation was confirmed in normal tissues where hypermethylation of the hTERT promoter was found exclusively in hTERT‐expressing telomerase‐positive samples and was absent in telomerase‐negative samples (p < 0.00002). Since tumor tissues contain also nonneoplastic stromal elements, we performed microdissection to allow confirmation that the hTERT promoter methylation truly occurred in tumor cells. Our results suggest that methylation may be involved in the regulation of hTERT gene expression. To our knowledge, this is the first gene in which methylation of its promoter sequence has been found to be positively correlated with gene expression.

Epigenetic alteration of the Wnt inhibitory factor-1 promoter occurs early in the carcinogenesis of Barrett's esophagus

The role of Wnt antagonists in the carcinogenesis of esophageal adenocarcinoma (EAC) remains unclear. We hypothesized that downregulation of the Wnt inhibitory factor‐1 (WIF‐1) might be involved in the neoplastic progression of Barretts esophagus (BE). We analyzed the DNA methylation status of the WIF‐1 promoter in normal, preneoplastic, and neoplastic samples from BE patients and in EAC cell lines. We investigated the role of WIF‐1 on EAC cell growth and the chemosensitization of the cells to cisplatin. We found that silencing of WIF‐1 correlated with promoter hypermethylation. EAC tissue samples showed higher levels of WIF‐1 methylation compared to the matched normal epithelium. In addition, we found that WIF‐1 hypermethylation was more frequent in BE samples from patients with EAC than in BE samples from patients who had not progressed to EAC. Restoration of WIF‐1 in cell lines where WIF‐1 was methylation‐silenced resulted in growth suppression. Restoration of WIF‐1 could sensitize the EAC cells to the chemotherapy drug cisplatin. Our results suggest that silencing of WIF‐1 through promoter hypermethylation is an early and common event in the carcinogenesis of BE. Restoring functional WIF‐1 might be used as a new targeted therapy for the treatment of this malignancy. (Cancer Sci 2008; 99: 46–53)

Detection of malignant effusions: Comparison of a telomerase assay and cytologic examination

Telomerase is inactive in most somatic cells, but has been found to be reactivated in a majority of cancers. Our principal goal was to test whether the presence of telomerase activity concurred with positive cytology, and was thus of potential use in detecting cancer cells in effusions. The telomeric repeat amplification protocol (TRAP) assay and cytological examination were performed in a blinded fashion on 91 unselected effusions, for which laboratory processing was done according to standard procedures. In our series, 30% (27/91) of samples were found to be malignant by cytology. Of these, 19 (70%) were also positive in the TRAP assay. Of the 8 telomerase‐negative cytology‐positive samples, RNA integrity was generally poor, indicating suboptimal sample conservation for molecular analysis. Negative cytology in the presence of telomerase activity was observed in 17 effusions. Of these, 11 were from patients with advanced cancer, and thus a diagnosis of malignant effusion should be suspected. The TRAP assay for telomerase activity holds promise in the analysis of effusions, but its routine use as an adjunct to cytology awaits further confirmation of its positive predictive value. Diagn. Cytopathol. 2001;24:174–180.

Imprinting of tumor-suppressor genes in human placenta.

Transcriptional deregulation in cancer has been shown to be associated with epigenetic alterations, in particular to tumor-suppressor-gene (TSG) promoters. In contrast, DNA methylation of TSGs is not considered to be present in normal differentiated cells. Nevertheless, we previously showed that the promoter of the tumor-suppressor gene APC is methylated, for one allele only, in normal gastric cells. Recently, RASSF1A has been shown to be imprinted in normal human placenta. To clarify putative TSG methylation in the placenta, 23 normal placental tissues from the first trimester, both decidua and villi, and four normal non-gestational endometrium were screened for DNA methylation by methylation-sensitive single-strand conformation analysis (MS-SSCA) and sequencing after bisulfite modification, on a panel of 12 genes known to be implicated in carcinogenesis. In all placental villi, 4 TSG promoters - APC, SFRP2, RASSF1A and WIF1 - were hypermethylated, whereas all decidua and normal endometrium did not show any methylation. Allele-specific methylation analysis revealed that this methylation was monoallelic. Furthermore, comparison with maternal DNA indicated that APC and WIF1 were methylated on the maternal allele, whereas SFRP2 was methylated on the paternal allele. Sequence analysis of WIF1 mRNA revealed that only the unmethylated paternal allele was transcribed. The imprinting status of these TSGs is conserved during pregnancy. These results indicate that TSG imprinting is pre-existent in normal human placenta and should not be confused with carcinogenesis or pathology-induced methylation.

DNA methylation profiling of esophageal adenocarcinoma using Methylation Ligation-dependent Macroarray (MLM).

Most types of cancer cells are characterized by aberrant methylation of promoter genes. In this study, we described a rapid, reproducible, and relatively inexpensive approach allowing the detection of multiple human methylated promoter genes from many tissue samples, without the need of bisulfite conversion. The Methylation Ligation-dependent Macroarray (MLM), an array-based analysis, was designed in order to measure methylation levels of 58 genes previously described as putative biomarkers of cancer. The performance of the design was proven by screening the methylation profile of DNA from esophageal cell lines, as well as microdissected formalin-fixed and paraffin-embedded (FFPE) tissues from esophageal adenocarcinoma (EAC). Using the MLM approach, we identified 32 (55%) hypermethylated promoters in EAC, and not or rarely methylated in normal tissues. Among them, 21promoters were found aberrantly methylated in more than half of tumors. Moreover, seven of them (ADAMTS18, APC, DKK2, FOXL2, GPX3, TIMP3 and WIF1) were found aberrantly methylated in all or almost all the tumor samples, suggesting an important role for these genes in EAC. In addition, dysregulation of the Wnt pathway with hypermethylation of several Wnt antagonist genes was frequently observed. MLM revealed a homogeneous pattern of methylation for a majority of tumors which were associated with an advanced stage at presentation and a poor prognosis. Interestingly, the few tumors presenting less methylation changes had a lower pathological stage. In conclusion, this study demonstrated the feasibility and accuracy of MLM for DNA methylation profiling of FFPE tissue samples.

Abstract 3023: Rapid methylation profiling of multiple genes at the same time using the methylation ligation-dependent macroarray (MLM)

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Background: Aberrant methylation of multiple promoter CpG islands is a common event in human cancers. Methylation profile of cancer-related genes has extraordinary potential in basic research as well as translational medicine. The aim of this study was to replace the tedious and inefficient bisulfite-based methods with a simple technology which could permit a rapid and robust analysis of large numbers of genes in large numbers of tumor samples simultaneously. Materials and methods: Genomic DNA was first sonicated, then couples of primers for each specific gene promoter were annealed to this DNA. In a one-step reaction, the CfoI methylation-sensitive enzyme digested unmethylated DNA, whereas the Taq ligase joined primers annealed to the methylated sequence. Tagged ligation products were amplified by PCR and finally hybridized to a nylon membrane macroarray. Methylation Ligation-dependent Macroarray (MLM) allows the establishment of DNA methylation profiles on many samples (up to 21) and on many gene promoters (up to 45) in a simple reaction in 2-3 days. To validate this novel method, we used it to detect aberrant methylation in 14 cell lines and in DNA samples of 40 patients with a colorectal cancer. Results: In tumor cell lines, among the 42 genes investigated 23.7 (11-32) were found methylated whereas only 9 have been observed methylated in a normal fibroblast cell line (BJ). In normal colorectal tissues, about 12/40 gene promoters were found methylated; in colorectal cancers 16 to 36 genes were methylated. Methylated gene promoters identified in colorectal cancers were ADAMTS18 (78%), APC (28%), CDKN2A (20%), DKK2 (50%), GPx3 (48%), Mal (72%), MLH1 (30%), NELL1 (72%), SFRP4 (35%), SFRP5 (52%) and WRN (20%): Conclusion: The MLM is a fast, non expensive and reliable technology that profiles the DNA methylation status of >40 promoter CpG islands in various human samples. This technology can be used in research for rapid methylation profiling of numerous samples and for identification of new epigenetic biomarkers, but also in clinic for rapid cancer diagnosis, for predictive response to cancer therapy and for distinction between progressive and non-progressive diseases. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3023. doi:10.1158/1538-7445.AM2011-3023