Tomasz K. Wojdacz

Methylation-sensitive high resolution melting (MS-HRM): a new approach for sensitive and high-throughput assessment of methylation

In this article, we show that high resolution melting analysis (HRM) is a sensitive and specific method for the detection of methylation. Methylated DNA and unmethylated DNA acquire different sequences after bisulphite treatment resulting in PCR products with markedly different melting profiles. We used PCR to amplify both methylated and unmethylated sequences and assessed HRM for the determination of the methylation status of the MGMT promoter region. Reconstruction experiments showed that MGMT methylation could be detected at levels as low as 0.1%. Moreover, MS-HRM allows for estimation of the methylation level by comparing the melting profiles of unknown PCR products to the melting profiles of PCR products derived from standards with a known unmethylated to methylated template ratio. We used MS-HRM for the analysis of eight cell lines of known methylation status and a panel of colorectal cancer specimens. The simplicity and high reproducibility of the MS-HRM protocol makes MS-HRM the method of choice for methylation assessment in many diagnostic and research applications.

Methylation-sensitive high-resolution melting

The base composition of PCR products derived from sodium bisulfite-modified templates is methylation dependent. Hence, methylated and unmethylated, PCR products show different melting profiles when subjected to thermal denaturation. The methylation-sensitive high-resolution melting (MS-HRM) protocol is based on the comparison of the melting profiles of PCR products from unknown samples with profiles specific for PCR products derived from methylated and unmethylated control DNAs. The protocol consists of PCR amplification of bisulfite-modified DNA with primers designed to proportionally amplify both methylated and unmethylated templates and subsequent high-resolution melting analysis of the PCR product. The MS-HRM protocol allows in-tube determination of the methylation status of the locus of interest following sodium bisulfite modification of template DNA in less than 3 h. Here, we provide a protocol for MS-HRM, which enables highly sensitive, labor- and cost-efficient single-locus methylation studies on the basis of DNA high-resolution melting technology.

Comprehensive Genome Methylation Analysis in Bladder Cancer: Identification and Validation of Novel Methylated Genes and Application of These as Urinary Tumor Markers

Purpose: Epigenetic alterations are common and can now be addressed in a parallel fashion. We investigated the methylation in bladder cancer with respect to location in genome, consistency, variation in metachronous tumors, impact on transcripts, chromosomal location, and usefulness as urinary markers. Experimental Design: A microarray assay was utilized to analyze methylation in 56 samples. Independent validation was conducted in 63 samples by a PCR-based method and bisulfite sequencing. The methylation levels in 174 urine specimens were quantified. Transcript levels were analyzed using expression microarrays and pathways were analyzed using dedicated software. Results: Global methylation patterns were established within and outside CpG islands. We validated methylation of the eight tumor markers genes ZNF154 (P < 0.0001), HOXA9 (P < 0.0001), POU4F2 (P < 0.0001), EOMES (P = 0.0005), ACOT11 (P = 0.0001), PCDHGA12 (P = 0.0001), CA3 (P = 0.0002), and PTGDR (P = 0.0110), the candidate marker of disease progression TBX4 (P < 0.04), and other genes with stage-specific methylation. The methylation of metachronous tumors was stable and targeted to certain pathways. The correlation to expression was not stringent. Chromosome 21 showed most differential methylation (P < 0.0001) and specifically hypomethylation of keratins, which together with keratin-like proteins were epigenetically regulated. In DNA from voided urine, we detected differential methylation of ZNF154 (P < 0.0001), POU4F2 (P < 0.0001), HOXA9 (P < 0.0001), and EOMES (P < 0.0001), achieving 84% sensitivity and 96% specificity. Conclusions: We initiated a detailed mapping of the methylome in metachronous bladder cancer. Novel genes with tumor, chromosome, as well as pathway-specific differential methylation in bladder cancer were identified. The methylated genes were promising cancer markers for early detection of bladder cancer. Clin Cancer Res; 17(17); 5582–92. ©2011 AACR.

Identification and validation of highly frequent CpG island hypermethylation in colorectal adenomas and carcinomas.

In our study, whole‐genome methylation arrays were applied to identify novel genes with tumor specific DNA methylation of promoter CpG islands in pre‐malignant and malignant colorectal lesions. Using a combination of Illumina HumanMethylation27 beadchips, Methylation‐Sensitive High Resolution Melting (MS‐HRM) analysis, and Exon arrays (Affymetrix) the DNA methylation pattern of ∼14,000 genes and their transcript levels were investigated in six normal mucosas, six adenomas and 30 MSI and MSS carcinomas. Sixty eight genes with tumor‐specific hypermethylation were identified (p < 0.005). Identified hypermethylated sites were validated in an independent sample set of eight normal mucosas, 12 adenomas, 40 MSS and nine MSI cancer samples. The methylation patterns of 15 selected genes, hypermethylated in adenomas and carcinomas (FLI1, ST6GALNAC5, TWIST1, ADHFE1, JAM2, IRF4, CNRIP1, NRG1 and EYA4), in carcinomas only (ABHD9, AOX1 and RERG), or in MSI but not MSS carcinomas (RAMP2, DSC3 and MLH1) were validated using MS‐HRM. Four of these genes (MLH1, AOX1, EYA4 and TWIST1) had previously been reported to be hypermethylated in CRC. Eleven genes, not previously known to be affected by CRC specific hypermethylation, were identified and validated. Inverse correlation to gene expression was observed for six of the 15 genes with Spearman correlation coefficients ranging from −0.39 to −0.60. For six of these genes the altered methylation patterns had a profound transcriptional association, indicating that methylation of these genes may play a direct regulatory role. The hypermethylation changes often occurred already in adenomas, indicating that they may be used as biomarkers for early detection of CRC.

A new approach to primer design for the control of PCR bias in methylation studies

Primer design for PCR-based methylation analysis following bisulfite conversion of DNA is considerably more complex than primer design for regular PCR. The choice of the optimal primer set is critical to the performance and correct interpretation of the results. Most methodologies in methylation analysis utilize primers that theoretically amplify methylated and unmethylated templates at the same time. The proportional amplification of all templates is critical but difficult to achieve due to PCR bias favouring the amplification of the unmethylated template. The focus of this brief communication is to point out the important criteria needed for the successful choice of primers that will enable the control of PCR bias in bisulfite based methylation-screening protocols.

Primer design versus PCR bias in methylation independent PCR amplifications

Many protocols in methylation studies utilize one primer set to generate a PCR product from bisulfite modified template regardless of its methylation status (methylation independent amplification MIP). However, proportional amplification of methylated and unmethylated alleles is hard to achieve due to PCR bias favoring amplification of unmethylated relatively GC poor sequence. Two primer design systems have been proposed to overcome PCR bias in methylation independent amplifications. The first advises against including any CpG dinucleoteides into the primer sequence (CpG-free primers) and the second, recently published by us, is based on inclusion of a limited number of CpG sites into the primer sequence. Here we used the Methylation Sensitive High Resolution Melting (MS-HRM) technology to investigate the ability of primers designed according to both of the above mentioned primer design systems to proportionally amplify methylated and unmethylated templates. Ten “CpG-free” primer pairs and twenty primers containing limited number of CpGs were tested. In reconstruction experiments the “CpG-free” primers showed primer specific sensitivity and allowed us to detect methylation levels in the range from 5 to 50%. Whereas while using primers containing limited number of CpG sites we were able to consistently detect 1–0.1% methylation levels and effectively control PCR amplification bias. In conclusion, the primers with limited number of CpG sites are able to effectively reverse PCR bias and therefore detect methylated templates with significantly higher sensitivity than CpG free primers.

Reversal of PCR bias for improved sensitivity of the DNA methylation melting curve assay

In the range of currently used methodologies in methylation studies (reviewed in Reference 1), sequencing of bisulfite-treated DNA (2) can be considered the gold standard, as it reveals the methylation status of each CpG dinuclotide. Nevertheless, this technique is relatively expensive, therefore it has rarely been used in large-scale experiments. By contrast, the simplicity of design and easy performance of methylation-specific PCR (MSP) (3) has made it the most widely used technique in the investigation of methylation status of the genes. However, MSP is prone to false positive results and may lead to an overestimation of the number of methylated samples (4).

Quality assessment of DNA derived from up to 30 years old formalin fixed paraffin embedded (FFPE) tissue for PCR-based methylation analysis using SMART-MSP and MS-HRM

BackgroundThe High Resolution Melting (HRM) technology has recently been introduced as a rapid and robust analysis tool for the detection of DNA methylation. The methylation status of multiple tumor suppressor genes may serve as biomarkers for early cancer diagnostics, for prediction of prognosis and for prediction of response to treatment. Therefore, it is important that methodologies for detection of DNA methylation continue to evolve. Sensitive Melting Analysis after Real Time - Methylation Specific PCR (SMART-MSP) and Methylation Sensitive - High Resolution Melting (MS-HRM) are two methods for single locus DNA methylation detection based on HRM.MethodsHere, we have assessed the quality of DNA extracted from up to 30 years old Formalin Fixed Paraffin Embedded (FFPE) tissue for DNA methylation analysis using SMART-MSP and MS-HRM. The quality assessment was performed on DNA extracted from 54 Non-Small Cell Lung Cancer (NSCLC) samples derived from FFPE tissue, collected over 30 years and grouped into five years intervals. For each sample, the methylation levels of the CDKN2A (p16) and RARB promoters were estimated using SMART-MSP and MS-HRM assays designed to assess the methylation status of the same CpG positions. This allowed for a direct comparison of the methylation levels estimated by the two methods for each sample.ResultsCDKN2A promoter methylation levels were successfully determined by SMART-MSP and MS-HRM in all 54 samples. Identical methylation estimates were obtained by the two methods in 46 of the samples. The methylation levels of the RARB promoter were successfully determined by SMART-MSP in all samples. When using MS-HRM to assess RARB methylation five samples failed to amplify and 15 samples showed a melting profile characteristic for heterogeneous methylation. Twenty-seven of the remaining 34 samples, for which the methylation level could be estimated, gave the same result as observed when using SMART-MSP.ConclusionMS-HRM and SMART-MSP can be successfully used for single locus methylation studies using DNA derived from up to 30 years old FFPE tissue. Furthermore, it can be expected that MS-HRM and SMART-MSP will provide similar methylation estimates when assays are designed to analyze the same CpG positions.

Rapid detection of methylation change at H19 in human imprinting disorders using methylation-sensitive high-resolution melting†

Beckwith Wiedemann syndrome (BWS) and Russell Silver syndrome (RS) are growth disorders with opposing epimutations affecting the H19/IGF2 imprinting center at 11p15.5. Overgrowth and tumor risk in BWS is caused by aberrant expression of the paternally expressed, imprinted IGF2 gene, occurring as a consequence of mosaic hypermethylation within the imprinting center, or to mosaic paternal uniparental disomy (UPD). RS is characterized by severe intrauterine growth retardation (IUGR). A subset of RS cases were recently shown to have mosaic hypomethylation within the H19/IGF2 imprinting center, predicted to silence paternally expressed IGF2 in early development. Molecular diagnosis for BWS and RS involves methylation analysis of the H19 locus, enabling discrimination of allelic methylation patterns. In this study, methylation‐sensitive high‐resolution melting analysis (MS‐HRM) was used to analyze methylation within the intergenic region of the H19 locus. A total of 36 samples comprising normal control (11), BWS (19), and RS (six) DNA were analyzed in a blinded study and scored as hypermethylated, normal, or hypomethylated. Results were compared with those derived by methylation‐sensitive Southern blotting using the restriction enzymes Rsa I and Hpa II. A total of 100% concordance was obtained for the Southern blotting and MS‐HRM scores. A total of three samples with paternal duplication affecting the H19/IGF2 region were scored as equivocal by both methods; however, 33 out of 36 (92%) the samples were unambiguously scored as being hypermethylated, hypomethylated, or normally methylated using MS‐HRM. We conclude that MS‐HRM is a rapid, cost‐effective, and sensitive method for screening mosaic methylation changes at the H19 locus in BWS and RS. Hum Mutat 0,1–6, 2008.

Limitations and advantages of MS-HRM and bisulfite sequencing for single locus methylation studies.

The methylation-sensitive high-resolution melting (MS-HRM) protocol, as described by Wojdacz and Dobrovic, enables detection of a methylated template in an unmethylated background, with sensitivity similar to that of methylation-specific PCR (MSP). Furthermore, MS-HRM-based methylation screening is cost, labor and time efficient in contrast to direct bisulfite sequencing, which, therefore, is unsuitable as a screening method, but is still required to reveal the methylation status of individual CpG sites. In some experiments, detailed information on the methylation status of individual CpGs may be of interest for at least a subset of samples from MS-HRM-based methylation screening. For those samples, sequencing-based methodology has to be coupled with the MS-HRM protocol to investigate the methylation status of single CpG sites within the locus of interest. In this article, we review the limitations and advantages of MS-HRM and bisulfite sequencing protocols for single-locus methylation studies. Furthermore, we provide the insights into interpretation of the results obtained when a combination of the protocols is used for single-locus methylation studies.