GENOMIC SEQUENCING INDICATES A CORRELATION BETWEEN DNA HYPOMETHYLATION IN THE 5'-REGION OF THE PS2 GENE AND ITS EXPRESSION IN HUMAN BREAST-CANCER CELL-LINES

The methylation status of the cytosines located on the 5' region of th e pS2 gene have been investigated in two human breast cancer cell line s. The genomic sequencing method used is based on an oxydative deamina tion by NaHSO3 of the unmethylated cytosines, but not 5-methylcytosine . Data obtained indicate that in the DNA extracted from the pS2-expres sing cell line, MCF7, the CpG located at the 5' flanking sequence of p S2 are unmethylated. In contrast in the non-expressing cell line, BT20 , these CpG are largely methylated. However, this correlation is not o bserved at all CpG sites, since a significant portion of the cloned PC R fragments obtained from BT20 cells are unmethylated at specific CPG sites. These results suggest that the methylation status of only some of the CpG located at the 5' flanking sequences of pS2 might differ be tween expressing and nonexpressing cell lines.