Abstract
Alterations of the DNA methylation pattern have been related to generalized chromosomal disruption and inactivation of multiple tumor suppressor genes in neoplasia. To screen for tumor-specific alterations and to make a global assessment of methylation status in cancer cells, we have modified the methylated CpG island amplification method to generate easily readable fingerprints representing the cell's DNA methylation profile. The method is based on the differential cleavage of isoschizomers with distinct methylation sensitivity. Specific adaptors are ligated to the methylated ends of the digested genomic DNA. The ligated sequences are amplified by PCR using adaptor- specific primers extended at the 3' end with two to four arbitrarily chosen nucleotidic residues to reduce the complexity of the product. Fingerprints consist of multiple anonymous bands, representing DNA sequences flanked by two methylated sites, which can be isolated and individually characterized. Hybridization of the whole product to metaphase chromosomes revealed that most bands originate from the isochore H3, which identifies the regions of the genome with the highest content of CpG islands and genes. Comparison of the fingerprints obtained from normal colon mucosa, colorectal carcinomas and cell lines revealed tumor-specific alterations that are putative recurrent markers of the disease and include tumor-specific hypo- and hypermethylations.