title: MNNG-induced partial phenotypic reversion of Mer- cells.
abstract: The effect of pretreatment with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) on MNNG sensitivity of the surviving population was compared in two HeLa lines, one of the Mer+ phenotype (HeLa S3) and one of the Mer- phenotype (HeLa MR). Whereas MNNG pretreatment of HeLa Mer+ cells had no effect on the MNNG sensitivity of surviving cells, Mer- cells surviving a first exposure to MNNG became much more resistant to MNNG. Comparison of the sensitivity of individual HeLa MR clones with their MNNG-pretreated population and analysis of the composition of the pretreated population showed that the majority of cells surviving the MNNG pretreatment now displayed the Mer+ phenotype in respect to sensitivity to MNNG. One MNNG-resistant clone derived from a pretreated HeLa MR population (Cl 4) was characterized further. It had a similar sensitivity to the Mer+ line to all monofunctional alkylating agents, but was as sensitive as the Mer- line to the crosslinking agent chloroethylnitrosourea. Cl 4 cells, like the Mer- cells, did not repair O6-methylguanine (O6MeG). The results suggest that the two characteristics which are usually coupled with the Mer- phenotype--lack of O6MeG repair and hypersensitivity to MNNG--can be separated.
mesh_terms: D000477:Alkylating Agents / Q000494:pharmacology; D004260:DNA Repair / Q000187:drug effects; D004351:Drug Resistance; D006147:Guanine / Q000031:analogs & derivatives / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008769:Methylnitronitrosoguanidine / Q000494:pharmacology*; D010641:Phenotype
chemical_list: D000477:Alkylating Agents; D008769:Methylnitronitrosoguanidine; D006147:Guanine; C008449:O-(6)-methylguanine