Induction of plasminogen activator by N-methyl-N'-nitro-N-nitrosoguanidine in mer+ and mer- human tumour cell strains.

Plasminogen activator (PA) synthesis in alkylation DNA repair deficient (mer-) and proficient (mer+) human tumour cell strains exposed to an alkylating agent, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), has been studied. MNNG enhanced the production of PA in mer- cell strains (U87MG, A1235, A1336, A172), but not in mer+ strains (TE85, HT29, U178MG, A288), which reactivated and supported well the growth of alkylation damaged adenovirus 3. Several mer+ strains (A549 and A2182), which are highly susceptible to killing by MNNG, produced moderately elevated enzyme levels after alkylating treatment. In the alkylation repair defective strains, enhanced production of both intra and extracellular PA occurred with 2-10 microM MNNG causing a 20-40% inhibition of [3H]thymidine incorporation. Maximum PA induction was observed 30-48 h after alkylation treatment and the levels of enzyme produced were 5-10 times as high as those of untreated control levels. As shown by electrophoretic analysis, MNNG enhances in mer- cells the synthesis of 40,000-50,000 Dalton of human urokinase type PA which is also present in lower amounts in untreated cells. This alkylation induced PA production by mer- cells required RNA and protein synthesis because it did not occur in the presence of actinomycin D or cycloheximide. PA induction by MNNG occurred throughout the cell cycle of synchronized mer- cells indicating that blockage of DNA synthesis is not responsible for enzyme induction and that it may result from DNA transcription on a damaged template. It was thus concluded that PA induction is causally associated with deficient DNA repair, which makes it useful as a sensitive assay for identification of alkylation repair deficient cell strains.