TUMOR-SPECIFIC DEMETHYLATION OF HETEROCHROMATIC REPETITIVE DNA IN GASTROINTESTINAL CANCER

DNA methylation appears to play an important role in both physiologica l and experimentally modified gene expression. Alterations in DNA meth ylation have been described in animal tumour models, in transformed ce lls and tumour cell lines, usually for single copy DNA sequences. By a pplying the isoschizomeres HpaII and MspI the methylation status of tw o classes of repetitive sequences (D22Z2 - a member of the alphoid rep eats and D22Z3 which belongs to the HinfI repeats) in colon and stomac h carcinoma were tested. A strong demethylation of both types of repet itive sequences in stomach carcinoma in comparison to healthy stomach mucosa was detected. In colon carcinoma, only minor signs of demethyla tion occured for the same repetitive DNA.