Expression of the O6-methylguanine-DNA methyltransferase gene MGMT in MER+ and MER- human tumor cells.

DNA probes prepared from human O6-methylguanine-DNA methyltransferase complementary DNA were hybridized to mRNA isolated from human liver and fifteen human tumor cell lines proficient (Mer+) or deficient (Mer-) in transferase activity. Liver and Mer+ cells contained levels of transferase-specific mRNA that correlated with their transferase activity levels, whereas Mer- cells contained undetectable amounts of transferase mRNA. The mRNA levels were not induced in human cells by treatments that induce other DNA damage-inducible genes. These results demonstrate that in human cells the transferase gene is constitutively expressed, that its expression is related to activity levels, and that in Mer- tumor cells the expression of the transferase gene is probably blocked at the level of mRNA production.