Effect of O super(6)-methylguanine-DNA methyltransferase gene activity on repair in human cells transformed by a regulatable ada) gene

To assess the biological role of DNA methylation at the O super(6) position of guanine (O super(6)MeG) a human cell line was created that contains a regulatable gene of the O super(6)MeG-DNA methyl-transferase (MT), a repair activity that removes O super(6)MeG adducts from the DNA. MT-deficient HeLa MR cells were transformed with an SV40-based expression vector in which the bacterial MT gene ada) was put under the control of a glucocorticoid-inducible MMTV promoter. In response to dexamethasone (Dex), pSV MTV ada cells actively accumulated MT protein to reach a constant level after 10-12 h of similar to 15,000 MT molecules per cell. Co-induction by Dex and 12-O-tetradecanoylphorbol-13-acetate (TPA) further accelerated this synthesis similar to 2-fold and, as a result, higher final MT levels were achieved.