Phosphorylation of mammalian DNA topoisomerase I and activation by protein kinase C |
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Authors: | Y Pommier D Kerrigan K D Hartman R I Glazer |
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Institution: | Laboratory of Molecular Pharmacology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892. |
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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. |
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