title: Topoisomerase I is differently phosphorylated in two sublines of L5178Y mouse lymphoma cells.
abstract: Two sublines of LY murine lymphoma, differing in sensitivity to CPT, served as source of topoisomerase I in order to compare the enzyme's properties. The activity of topoisomerase I isolated from LY-S cells of reduced sensitivity to CPT increased about 2-times more upon phosphorylation with casein kinase but was inhibited to a lesser extent upon dephosphorylation with alkaline phosphatase than the enzyme from the CPT-sensitive LY-R cells. The in vitro phosphorylation of LY-S enzyme restored its sensitivity to CPT. The in vitro incorporation of 32P into topoisomerase protein was about 1.7-times higher in LY-S than in LY-R enzyme. A reversed incorporation ratio was observed upon metabolic labelling. The level of topoisomerase I protein, determined by Western blot analysis using scleroderma anti-topoisomerase I antibodies, was about 1.5-times higher in LY-S than in LY-R cells. The level of topoisomerase I mRNA was similar in both sublines. These results indicate that the reduced sensitivity of LY-S cells to CPT is based on the lowered phosphorylation of topoisomerase I protein but does not depend on the expression of topoisomerase I gene.
authors.affiliation: Institute of Biochemistry, Warsaw University, Poland.
authors.forename: K
authors.initials: K
authors.lastname: Staron
authors.forename: B
authors.initials: B
authors.lastname: Kowalska-Loth
authors.forename: J
authors.initials: J
authors.lastname: Zabek
authors.forename: R M
authors.initials: RM
authors.lastname: Czerwinski
authors.forename: K
authors.initials: K
authors.lastname: Nieznanski
authors.forename: I
authors.initials: I
authors.lastname: Szumiel
mesh_terms: D000818:Animals; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000378:metabolism*; D008223:Lymphoma / Q000201:enzymology; D051379:Mice; D010766:Phosphorylation; D012333:RNA, Messenger / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D012333:RNA, Messenger; D004264:DNA Topoisomerases, Type I