Decreased camptothecin sensitivity of the stem-cell-like fraction of caco2 cells correlates with an altered phosphorylation pattern of topoisomerase I

Amit Roy, Cinzia Tesauro, Rikke Frøhlich, Marianne S Hede, Maria J Nielsen, Eigil Kjeldsen, Bjarne Bonven, Magnus Stougaard, Irina Gromova, Birgitta R Knudsen

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Abstract

The CD44+ and CD44- subpopulations of the colorectal cancer cell line Caco2 were analyzed separately for their sensitivities to the antitumor drug camptothecin. CD44+ cells were less sensitive to camptothecin than CD44- cells. The relative resistance of CD44+ cells was correlated with (i) reduced activity of the nuclear enzyme topoisomerase I and (ii) insensitivity of this enzyme to camptothecin when analyzed in extracts. In contrast, topoisomerase I activity was higher in extracts from CD44- cells and the enzyme was camptothecin sensitive. Topoisomerase I from the two subpopulations were differentially phosphorylated in a manner that appeared to determine the drug sensitivity and activity of the enzyme. This finding was further supported by the fact that phosphorylation of topoisomerase I in CD44+ cell extract by protein kinase CK2 converted the enzyme to a camptothecin sensitive, more active form mimicking topoisomerase I in extracts from CD44- cells. Conversely, dephosphorylation of topoisomerase I in extracts from CD44- cells rendered the enzyme less active and camptothecin resistant. These findings add to our understanding of chemotherapy resistance in the Caco2 CD44+ cancer stem cell model.

Original languageEnglish
Article numbere99628
JournalPLOS ONE
Volume9
Issue6
Number of pages11
ISSN1932-6203
DOIs
Publication statusPublished - 2014

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