title: Phosphorylation of mammalian DNA topoisomerase I and activation by protein kinase C.
abstract: The influence of mammalian DNA topoisomerase I phosphorylation on enzyme activity has been investigated. Dephosphorylation by calf intestine alkaline phosphatase abolished the DNA relaxing activity of DNA topoisomerase I and the sensitivity of the enzyme to its specific inhibitor, camptothecin. DNA topoisomerase I could be reactivated by incubation with purified protein kinase C. DNA topoisomerase I was then able to relax supercoiled DNA processively, like the native enzyme, and to cleave 32P-end-labeled SV40 DNA fragments at the same sequences as the native enzyme in the presence of camptothecin. These results show that active DNA topoisomerase I is a phosphoprotein and suggest a possible regulatory role of protein kinase on topoisomerase I activity and on its sensitivity to camptothecin.
authors.affiliation: Laboratory of Molecular Pharmacology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Y
authors.initials: Y
authors.lastname: Pommier
authors.forename: D
authors.initials: D
authors.lastname: Kerrigan
authors.forename: K D
authors.initials: KD
authors.lastname: Hartman
authors.forename: R I
authors.initials: RI
authors.lastname: Glazer
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D002166:Camptothecin / Q000494:pharmacology; D002417:Cattle; D002460:Cell Line; D006224:Cricetinae; D004264:DNA Topoisomerases, Type I / Q000302:isolation & purification / Q000378:metabolism*; D004278:DNA, Superhelical / Q000378:metabolism; D004789:Enzyme Activation; D007422:Intestines / Q000201:enzymology; D008970:Molecular Weight; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D059004:Topoisomerase I Inhibitors
chemical_list: D004278:DNA, Superhelical; D059004:Topoisomerase I Inhibitors; D011493:Protein Kinase C; D000469:Alkaline Phosphatase; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin