DEMETHYLATION OF A REPETITIVE DNA-SEQUENCE IN HUMAN CANCERS

To detect DNA alterations in unknown regions in human cancers, we have performed restriction landmark genomic scanning (RLGS) analysis of DN A isolated from cancer and normal cells. One spot with a highly intens ified signal was detected in DNA from all six malignant melanoma cell lines, two of five colon cancer cell lines and one of six pancreatic c ancer cell lines analyzed. In DNA from normal cells, two placentas and seven cultured lymphocytes, the signal of this spot was not intense. The DNA fragment corresponding to the spot was cloned. By nucleotide s equence analysis, the DNA fragment was revealed to be a part of a repe ating unit of a 13 kbp nucleotide sequence of which 200 copies were lo cated in chromosome 8q21. Southern blotting analysis using the cloned fragment as a probe demonstrated that the intensified signal for the D NA fragment observed in cancer cells was due to demethylation in the r ecognition sequence of the NotI restriction enzyme. The results sugges t that marked demethylation in the repeating units might be associated with the genesis or progression of some types of cancers.