title: Vacuolar H+-ATPase inhibitors overcome Bcl-xL-mediated chemoresistance through restoration of a caspase-independent apoptotic pathway.
abstract: The anti-apoptotic oncoproteins Bcl-2 and Bcl-xL play crucial roles in tumorigenesis and chemoresistance, and are thus therapeutic cancer targets. We searched for small molecules that disturbed the anti-apoptotic function of Bcl-2 or Bcl-xL, and found vacuolar H(+)-ATPase (V-ATPase) inhibitors, such as bafilomycin A1 (BMA), that showed such activity. Bcl-xL-overexpressing Ms-1 cells displayed resistance to anticancer drugs, but underwent apoptosis following treatment with a combination of V-ATPase inhibitors at doses similar to those that caused inhibitory activities of V-ATPase. We investigated the apoptosis mechanism induced by cotreatment of Bcl-xL-overexpressing Ms-1 cells with BMA as a V-ATPase inhibitor and taxol (TXL) as an anticancer drug. With BMA, TXL triggered mitochondrial membrane potential loss and cytochrome c release, whereas downstream caspase activation was not observed. In contrast, pronounced nuclear translocation of mitochondrial apoptosis-inducing factor and endonuclease G, known as effectors of caspase-independent apoptosis, was observed with BMA and TXL cotreatment. Moreover, depletion of apoptosis-inducing factor and endonuclease G using each siRNA significantly rescued cells from BMA- and TXL-induced apoptosis. Hence, the apoptosis-inducing factor- and endonuclease G-dependent pathway was critical for apoptosis induction by BMA and TXL cotreatment. Our data suggest that V-ATPase inhibitors could not only suppress anti-apoptotic Bcl-2 nor Bcl-xL but could also facilitate the caspase-independent apoptotic pathway. V-ATPase inhibition will be a promising therapeutic approach for Bcl-2- or Bcl-xL-overexpressing malignancies.
authors.affiliation: Department of Biosciences and Informatics, Faculty of Science and Technology, Keio University, Yokohama, Japan.
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Sasazawa
authors.forename: Yushi
authors.initials: Y
authors.lastname: Futamura
authors.forename: Etsu
authors.initials: E
authors.lastname: Tashiro
authors.forename: Masaya
authors.initials: M
authors.lastname: Imoto
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000378:metabolism; D017209:Apoptosis / Q000502:physiology*; D051033:Apoptosis Inducing Factor / Q000378:metabolism; D020169:Caspases / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D003574:Cytochrome c Group / Q000378:metabolism; D004338:Drug Combinations; D019008:Drug Resistance, Neoplasm; D004706:Endodeoxyribonucleases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics; D018942:Macrolides / Q000037:antagonists & inhibitors; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D017239:Paclitaxel / Q000378:metabolism; D055752:Small Cell Lung Carcinoma / Q000235:genetics; D025262:Vacuolar Proton-Translocating ATPases / Q000037:antagonists & inhibitors*; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D051033:Apoptosis Inducing Factor; D003574:Cytochrome c Group; D004338:Drug Combinations; D004791:Enzyme Inhibitors; D018942:Macrolides; D051020:bcl-X Protein; C076615:cytochrome c''; C040929:bafilomycin A1; D004706:Endodeoxyribonucleases; C052391:endonuclease G; D020169:Caspases; D025262:Vacuolar Proton-Translocating ATPases; D017239:Paclitaxel