title: Decreased camptothecin sensitivity of the stem-cell-like fraction of Caco2 cells correlates with an altered phosphorylation pattern of topoisomerase I.
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.
authors: Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark.
authors: Amit
authors: A
authors: Roy
authors: Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark.
authors: Cinzia
authors: C
authors: Tesauro
authors: Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark.
authors: Rikke
authors: R
authors: Frøhlich
authors: Zymonostics ApS, Aarhus, Denmark.
authors: Marianne S
authors: MS
authors: Hede
authors: Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark.
authors: Maria J
authors: MJ
authors: Nielsen
authors: Hemodiagnostic Laboratory, Cancercytogenetic Section, Aarhus University Hospital, Aarhus, Denmark.
authors: Eigil
authors: E
authors: Kjeldsen
authors: Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark.
authors: Bjarne
authors: B
authors: Bonven
authors: Department of Pathology, Aarhus University Hospital, Aarhus, Denmark.
authors: Magnus
authors: M
authors: Stougaard
authors: Genome Integrity Unit, Proteomics in Cancer, Danish Cancer Research Center, Danish Cancer Society, Copenhagen, Denmark.
authors: Irina
authors: I
authors: Gromova
authors: Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark.
authors: Birgitta R
authors: BR
authors: Knudsen
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D018938:Caco-2 Cells; D002166:Camptothecin / Q000494:pharmacology*; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism; D014411:Neoplastic Stem Cells / Q000187:drug effects; D010766:Phosphorylation / Q000187:drug effects
chemical_list: D000972:Antineoplastic Agents, Phytogenic; C497483:CD44 protein, human; D018960:Hyaluronan Receptors; D004264:DNA Topoisomerases, Type I; C528909:TOP1 protein, human; D002166:Camptothecin