Novel genetic and epigenetic alterations in ... - Ous-research.no

GASTROENTEROLOGY 2007;132:1631–1639CORRESPONDENCEReaders are encouraged to write letters to the editor concerning articles that have been published in GASTROENTEROLOGY. Letters that include original,unpublished data will not be considered. Letters should be typewritten and submitted electronically to http://www.editorialmanager.com/gastro/DNA Hypermethylation of MAL: APromising Diagnostic Biomarker forColorectal TumorsDear Sir:We found the article by Mori et al 1 recently publishedin GASTROENTEROLOGY of great interest. In this paper,several novel promoter methylation target genes wereidentified in colon cancer and among them, MAL, encodinga T-cell differentiation protein. This gene was alsoidentified as a potential target in a recent study from ourgroup using the same methodologic approach as Mori etal (microarray-based gene expression analyses before andafter 5-aza-2=-deoxycytidine treatment of cell lines). 2Only responding genes with concomitant reduced expressionin in vivo tumors were selected for detailed DNAmethylation analysis. We report here hypermethylationof MAL in an exceptionally high frequency among malignant(83%; 40 of 48 carcinomas) as well as in benignlarge bowel tumors (73%; 43 of 59 adenomas) as assessedby methylation-specific polymerase chain reaction (MSP)analysis (Figure 1; primers given on request).This high methylation frequency of MAL is in contrastto the 6% methylation (2 of 34 samples) reported by Moriet al 1 using real-time MSP. However, they did not performan independent validation assay for the methylationstatus of the gene in question, opting for cautionconcerning the correctness of the initial frequency. Bydirect bisulphite sequencing of colon cancer cell lines, wehave confirmed the DNA methylation status establishedby MSP in the present report, and show that the majorityof CpG sites were indeed methylated in the samplesidentified as methylated by MSP. Furthermore, the majorityof normal mucosa samples were unmethylated,only 2 of 18 normal mucosa samples taken from distantsites from the primary carcinoma, and 1 of 23 normalFigure 1. Representative methylation-specific polymerase chain reaction(MSP) results from the analysis of MAL in 3 normal mucosa samples,3 adenomas, and 3 carcinomas. A visible PCR product in lanes Uindicates the presence of unmethylated alleles whereas a PCR productin lanes M indicates the presence of methylated alleles. Abbreviations:A, adenoma; C, carcinoma, N normal mucosa; POS, positive controlconsisting of normal blood (control for unmethylated samples) and invitro methylated DNA (control for methylated samples); NEG, negativecontrol (containing water as template); U, lane for unmethylated MSPproduct; M, lane for methylated MSP product. The illustration is a mergeof 2 gel panels as the adenomas were run on a separate gel.mucosa samples from large bowels without cancershowed weak methylation (seen as a low-intensity bandcompared with the positive control after gel electrophoresis).The frequency found among normal sampleswas significantly less than in primary adenomas (P .0001) and carcinomas (P .0001). These results suggestthat hypermethylation of MAL is suitable as an earlydiagnostic marker of primary or recurrent colorectal tumors.Early detection of disease can result in improved clinicaloutcome for most types of cancer and identificationof cancer-associated aberrant gene methylation representspromising novel biomarkers. 3 For colorectal cancer,initial studies have identified the presence of aberrantlymethylated DNA in patient blood and feces. To ourknowledge, only 2 of the genes screened for methylationin fecal DNA, VIM (vimentin) and SFRP2, have shownhigh sensitivity and specificity. 4,5 In general, the sensitivityand specificity of existing early markers remain suboptimal,independent of whether they are detecting DNAsequence changes or DNA modifications by methylation.Genes aberrantly hypermethylated at high frequenciesalready in benign tumors and only rarely in normalmucosa are good candidate diagnostic biomarkers owingto the potential clinical benefit of early detection ofhigh-risk adenomas as well as early stages of carcinomas.Promoter hypermethylation of MAL, shown to be presentin the vast majority of colorectal adenomas and carcinomasand only rarely in normal mucosa, therefore representsanother promising early diagnostic marker thatshould be further studied in fecal and serum DNA samplesand possibly included in a panel of biomarkers fornoninvasive testing.GURO E. LINDTERJE AHLQUISTRAGNHILD A. LOTHEDepartment of Cancer PreventionInstitute for Cancer ResearchRikshospitalet–Radiumhospitalet Medical Centreand Centre for Cancer BiomedicineUniversity of OsloOslo, Norway1. Mori Y, Cai K, Cheng Y, Wang S, Paun B, Hamilton JP, Jin Z, SatoF, Berki AT, Kan T, Ito T, Mantzur C, Abraham JM, Meltzer SJ. Agenome-wide search identifies epigenetic silencing of somatostatin,tachykinin-1, and 5 other genes in colon cancer. Gastroenterology2006;131:797–808.2. Lind GE, Kleivi K, Meling GI, Teixeira MR, Thiis-Evensen E, RognumTO, Lothe RA. ADAMTS1, CRABP1, and NR3C1 identified as epigeneticallyderegulated genes in colorectal tumorigenesis. CellOncol 2006;28:259–272.