BACTERIAL O6-METHYLGUANINE-DNA METHYLTRANSFERASE REDUCES N-METHYL-N'-NITRO-N-NITROSOGUANIDINE INDUCTION OF PLASMINOGEN-ACTIVATOR IN MER(-) HUMAN GLIOBLASTOMA A1235 CELL-LINE

The alkylation repair deficient (Mer(-) phenotype) cells produce high levels of proteolytic enzyme plasminogen activator (PA) after treatmen t with alkylation agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). B oth, in Escherichia coli and in mammalian cells O-6-methylguanine (O-6 -MeG) is repaired by analogues O-6-methylguanine-DNA methyltransferase (MGMT). In E. coli MGMT is product of ada gene. To investigate the ef fect of bacterial MGMT expression on the induction of PA activity in h uman cells, we have transfected ada-alkB operon into Mer- human A1235 cells that are known to produce high levels of PA after MNNG treatment . We have shown here that A4 and A8 transformants that harbour ada gen e become resistant to killing by MNNG. In addition, MNNG produced indu ction of extracellular PA activity was much less pronounced in A4 and A8 transformants (induction ratio 3.42 and 3.74, respectively) than in control A1235 and Aneo-1 cells (induction ratio 11.04 and 9.11, respe ctively). However, changes of intracellular PA activity were not signi ficant. It appears, therefore, that induction of extracellular PA acti vity is inversely related to the cell capacity to repair the DNA lesio ns induced by alkylation agents. (C) 1998 Elsevier Science B.V. All ri ghts reserved.