title: Initiation of carcinogenesis dependence upon MNNG-induced release of the G1 block of density-inhibited Syrian hamster cells.
abstract: After N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) treatment of density-inhibited postconfluent (DDIR) Syrian hamster embryo cell cultures, only a small population of the cells incorporate [3H]-thymidine within the next 10-20 h. The transformed colonies, observed subsequent to reseeding, are derived from the population incorporating [3H]-thymidine. This study demonstrates that MNNG-induced thymidine incorporation resulted from semiconservative DNA synthesis as analyzed by DNA density gradients. Furthermore, cell cycle distributions at selected times after treatment indicate that the MNNG-responsive population was released from the density-dependent G1 block, proceeded through S, and became blocked again at G2 or M. These results indicate that DNA synthesis is temporally related to an early step in carcinogenesis.
mesh_terms: D000818:Animals; D002471:Cell Transformation, Neoplastic / Q000187:drug effects*; D002478:Cells, Cultured; D006224:Cricetinae; D004247:DNA / Q000096:biosynthesis; D004622:Embryo, Mammalian; D005434:Flow Cytometry; D007399:Interphase / Q000187:drug effects*; D007700:Kinetics; D008647:Mesocricetus; D008769:Methylnitronitrosoguanidine / Q000494:pharmacology*; D013936:Thymidine / Q000378:metabolism
chemical_list: D008769:Methylnitronitrosoguanidine; D004247:DNA; D013936:Thymidine