title: Iejimalides A and B inhibit lysosomal vacuolar H+-ATPase (V-ATPase) activity and induce S-phase arrest and apoptosis in MCF-7 cells.
abstract: Iejimalides are novel macrolides that are cytostatic or cytotoxic against a wide range of cancer cells at low nanomolar concentrations. A recent study by our laboratory characterized the expression of genes and proteins that determine the downstream effects of iejimalide B. However, little is known about the cellular target(s) of iejimalide or downstream signaling that lead to cell-cycle arrest and/or apoptosis. Iejimalides have been shown to inhibit the activity of vacuolar H(+)-ATPase (V-ATPase) in osteoclasts, but how this inhibition may lead to cell-cycle arrest and/or apoptosis in epithelial cells is not known. In this study, MCF-7 breast cancer cells were treated with iejimalide A or B and analyzed for changes in cell-cycle dynamics, apoptosis, lysosomal pH, cytoplasmic pH, mitochondrial membrane potential, and generation of reactive oxygen species. Both iejimalides A and B sequentially neutralize the pH of lysosomes, induce S-phase cell-cycle arrest, and trigger apoptosis in MCF-7 cells. Apoptosis occurs through a mechanism that involves oxidative stress and mitochondrial depolarization but not cytoplasmic acidification. These data confirm that iejimalides inhibit V-ATPase activity in the context of epithelial tumor cells, and that this inhibition may lead to a lysosome-initiated cell death process.
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, South Bend, Indiana 46617, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: McHenry
authors.forename: Wei-Lin Winnie
authors.initials: WL
authors.lastname: Wang
authors.forename: Edward
authors.initials: E
authors.lastname: Devitt
authors.forename: Nicholas
authors.initials: N
authors.lastname: Kluesner
authors.forename: Vincent Jo
authors.initials: VJ
authors.lastname: Davisson
authors.forename: Edward
authors.initials: E
authors.lastname: McKee
authors.forename: Dirk
authors.initials: D
authors.lastname: Schweitzer
authors.forename: Paul
authors.initials: P
authors.lastname: Helquist
authors.forename: Martin
authors.initials: M
authors.lastname: Tenniswood
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000188:drug therapy / Q000473:pathology*; D002219:Carbamates / Q000494:pharmacology* / Q000627:therapeutic use; D045744:Cell Line, Tumor; D004847:Epithelial Cells / Q000187:drug effects / Q000473:pathology; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008247:Lysosomes; D018942:Macrolides / Q000494:pharmacology* / Q000627:therapeutic use; D053078:Membrane Potential, Mitochondrial; D018384:Oxidative Stress; D016196:S Phase / Q000187:drug effects*; D025262:Vacuolar Proton-Translocating ATPases / Q000037:antagonists & inhibitors*
chemical_list: D002219:Carbamates; D018942:Macrolides; C520301:iejimalide B; C520300:iejimalide A; D025262:Vacuolar Proton-Translocating ATPases