Staron K, Kowalska-Loth B, Zabek J, Czerwinski RM, Nieznanski K, Szumiel I. Topoisomerase I is differently phosphorylated in two sublines of L5178Y mouse lymphoma cells.
BIOCHIMICA ET BIOPHYSICA ACTA 1995;
1260:35-42. [PMID:
7999792 DOI:
10.1016/0167-4781(94)00175-3]
[Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
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.
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