title: Phosphorylation of DNA topoisomerase I is increased during the response of mammalian cells to mitogenic stimuli.
abstract: DNA topoisomerase I is phosphorylated after mitogenic stimulation of 3T3-L1 mouse fibroblasts by 12-O-tetradecanoylphorbol 13-acetate (TPA), a phorbol ester tumor promoter. In vivo labeling with [32P]orthophosphate and immunoprecipitation with an anti-DNA topoisomerase I antibody has demonstrated an increase in the phosphorylation of DNA topoisomerase I in Swiss/3T3 mouse fibroblasts treated with epidermal growth factor (EGF) and H35 rat hepatoma cells treated with insulin. The only phosphorylated form of DNA topoisomerase I observed was the 100-kDa protein Digestion of DNA topoisomerase I with trypsin revealed two phosphopeptides. In addition, VT-1, a non-responsive genetic variant of 3T3-L1, and the DNA topoisomerase I inhibitor camptothecin were used to further study TPA-induced DNA topoisomerase I phosphorylation. Our results indicate that the phosphorylation of DNA topoisomerase I may be an ubiquitous response of cultured mammalian cells to mitogenic agents, even in the absence of DNA replication.
authors.affiliation: Department of Molecular and Cellular Biology, University of Arizona, Tucson.
authors.forename: D S
authors.initials: DS
authors.lastname: Samuels
authors.forename: Y
authors.initials: Y
authors.lastname: Shimizu
authors.forename: T
authors.initials: T
authors.lastname: Nakabayashi
authors.forename: N
authors.initials: N
authors.lastname: Shimizu
mesh_terms: D016475:3T3 Cells; D000818:Animals; D002166:Camptothecin / Q000494:pharmacology; D002455:Cell Division; D004247:DNA / Q000096:biosynthesis; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D006133:Growth Substances / Q000494:pharmacology; D051379:Mice; D008934:Mitogens / Q000494:pharmacology*; D010766:Phosphorylation; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014158:Transcription, Genetic
chemical_list: D006133:Growth Substances; D008934:Mitogens; D004247:DNA; D004264:DNA Topoisomerases, Type I; D013755:Tetradecanoylphorbol Acetate; D002166:Camptothecin