Journal Article

Phosphorylation of topoisomerase I in L5178Y-S cells is associated with poly(ADP-ribose) metabolism

Krzysztof Staron, Barbara Kowalska-Loth, Krzysztof Nieznanski and Irena Szumiel

in Carcinogenesis

Volume 17, issue 3, pages 383-387
Published in print March 1996 | ISSN: 0143-3334
e-ISSN: 1460-2180 | DOI:
Phosphorylation of topoisomerase I in L5178Y-S cells is associated with poly(ADP-ribose) metabolism

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The reason for different phosphorylation of topoisomerase I in two sublines of L5178Y murine lymphoma (LY cells) was investigated. Camptothecin-resistant LY-S cells show increased poly(ADP-ribose) level and lowered topoisomerase I phosphorylation compared to camptothecin-sensitive LY-R cells. In this study diminished phosphorylation of LY-S topoisomerase I was observed for sites recognized by casein kinase 2 but not for those phosphorylated by protein kinase C. Tryptic digests of LY-S topoisomerase I labeled in vitro by casein kinase 2 indicated that phosphorylation was similarly lowered at different sites. Activity of casein kinase 2 measured in nuclear extracts was about 1.7 times lower for LY-S than LY-R cells. This difference was diminished or eliminated by increasing casein concentration, diluting the extract or increasing the ionic strength. Activity of poly(ADP-ribose) polymerase was 5.3 times higher in LY-S than in LY-R nuclei. When the activity of the polymerase was inhibited by treatment of LY-S cells with benzamide, casein kinase 2-catalyzed phosphorylation of topoisomerase I increased. This was accompanied by an increase in sensitivity to camptothecin as reflected in the diminished viability of LY-S cells.

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Subjects: Clinical Cytogenetics and Molecular Genetics

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