title: A role for PKCzeta in potentiation of the topoisomerase II activity and etoposide cytotoxicity by wortmannin.
abstract: Enhanced cytotoxicity of etoposide by wortmannin, an inhibitor of enzymes holding a phosphatidylinositol 3-kinase domain, was investigated in eight cell lines proficient or deficient for DNA double-strand break repair. Wortmannin stimulated the decatenating activity of topoisomerase II, promoted etoposide-induced accumulation of DNA double-strand breaks, shifted the specificity for cell killing by etoposide from the S to G1 phase of the cell cycle, and potentiated the cytotoxicity of etoposide through two mechanisms. (a) Sensitization to high, micromolar amounts of etoposide required integrity of the nonhomologous end-joining repair pathway. (b) Wortmannin dramatically increased the susceptibility to low, submicromolar amounts of etoposide in a large fraction of the cell population irrespective of the status of ATM, Ku86, and DNA-PKCS. It is shown that this process correlates depression of phosphatidylinositol 3-kinase-dependent phosphorylation of the atypical, zeta isoform of protein kinase C (PKCzeta). Stable expression of a dominant-negative, kinase-dead mutant of PKCzeta in a tumor cell line reproduced the hypersensitivity pattern induced by wortmannin. The results are consistent with up-regulation of the topoisomerase II activity in relation to inactivation of PKCzeta and indicate that PKCzeta may be a useful target to improve the efficiency of topoisomerase II poisons at low concentration.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale U612, Orsay, France.
authors.forename: Caroline
authors.initials: C
authors.lastname: Reis
authors.forename: Nicole
authors.initials: N
authors.lastname: Giocanti
authors.forename: Christophe
authors.initials: C
authors.lastname: Hennequin
authors.forename: Frédérique
authors.initials: F
authors.lastname: Mégnin-Chanet
authors.forename: Marie
authors.initials: M
authors.lastname: Fernet
authors.forename: Rodolphe
authors.initials: R
authors.lastname: Filomenko
authors.forename: Ali
authors.initials: A
authors.lastname: Bettaieb
authors.forename: Eric
authors.initials: E
authors.lastname: Solary
authors.forename: Vincent
authors.initials: V
authors.lastname: Favaudon
mesh_terms: D000730:Androstadienes / Q000494:pharmacology*; D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D045744:Cell Line, Tumor; D006224:Cricetinae; D003412:Cricetulus; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004357:Drug Synergism; D005047:Etoposide / Q000494:pharmacology*; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011817:Rabbits; D059005:Topoisomerase II Inhibitors; D014162:Transfection; D020298:U937 Cells; D000077191:Wortmannin; D000099221:Protein Kinase C zeta
chemical_list: D000730:Androstadienes; D004250:DNA Topoisomerases, Type II; D005047:Etoposide; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C; D047428:Protein Kinase Inhibitors; D059005:Topoisomerase II Inhibitors; D000077191:Wortmannin; D000099221:Protein Kinase C zeta