title: Overexpression of the atypical protein kinase C zeta reduces topoisomerase II catalytic activity, cleavable complexes formation, and drug-induced cytotoxicity in monocytic U937 leukemia cells.
abstract: In this study, we evaluated the influence of protein kinase C zeta (PKC zeta) on topoisomerase II inhibitor-induced cytotoxicity in monocytic U937 cells. In U937-zeta J and U937-zeta B cells, enforced PKC zeta expression, conferred by stable transfection of PKC zeta cDNA, resulted in total inhibition of VP-16- and mitoxantrone-induced apoptosis and decreased drug-induced cytotoxicity, compared with U937-neo control cells. In PKC zeta-overexpressing cells, drug resistance correlated with decreased VP-16-induced DNA strand breaks and DNA protein cross-links measured by alkaline elution. Kinetoplast decatenation assay revealed that PKC zeta overexpression resulted in reduced global topoisomerase II activity. Moreover, in PKC zeta-overexpressing cells, we found that PKC zeta interacted with both alpha and beta isoforms of topoisomerase II, and these two enzymes were constitutively phosphorylated. However, when human recombinant PKC zeta (rH-PKC zeta) was incubated with purified topoisomerase II isoforms, rH-PKC zeta interacted with topoisomerase II beta but not with topoisomerase II alpha. PKC zeta/topoisomerase II beta interaction resulted in phosphorylation of this enzyme and in decrease of its catalytic activity. Finally, this report shows for the first time that topoisomerase II beta is a substrate for PKC zeta, and that PKC zeta may significantly influence topoisomerase II inhibitor-induced cytotoxicity by altering topoisomerase II beta activity through its kinase function.
authors.affiliation: INSERM E9910, Institut Claudius Régaud, 20 rue du Pont Saint Pierre, 31052 Toulouse cedex, France. plo@icr.fnclcc.fr
authors.forename: Isabelle
authors.initials: I
authors.lastname: Plo
authors.forename: Hélène
authors.initials: H
authors.lastname: Hernandez
authors.forename: Glenda
authors.initials: G
authors.lastname: Kohlhagen
authors.forename: Dominique
authors.initials: D
authors.lastname: Lautier
authors.forename: Yves
authors.initials: Y
authors.lastname: Pommier
authors.forename: Guy
authors.initials: G
authors.lastname: Laurent
mesh_terms: D000970:Antineoplastic Agents / Q000633:toxicity*; D002470:Cell Survival / Q000187:drug effects; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000302:isolation & purification / Q000378:metabolism; D005047:Etoposide / Q000633:toxicity; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007700:Kinetics; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology; D008942:Mitoxantrone / Q000633:toxicity; D009363:Neoplasm Proteins / Q000302:isolation & purification / Q000378:metabolism; D011493:Protein Kinase C / Q000235:genetics*; D011994:Recombinant Proteins / Q000378:metabolism; D059005:Topoisomerase II Inhibitors; D020298:U937 Cells; D000099221:Protein Kinase C zeta
chemical_list: D000970:Antineoplastic Agents; D004250:DNA Topoisomerases, Type II; D004273:DNA, Neoplasm; D005047:Etoposide; D008942:Mitoxantrone; D009363:Neoplasm Proteins; D011493:Protein Kinase C; D011994:Recombinant Proteins; D059005:Topoisomerase II Inhibitors; D000099221:Protein Kinase C zeta