Iejimalides A and B inhibit lysosomal vacuolar H+-ATPase (V-ATPase) activity and induce S-phase arrest and apoptosis in MCF-7 cells.
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.
McHenry
Peter
P
Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, South Bend, Indiana 46617, USA.
Wang
Wei-Lin Winnie
WL
Devitt
Edward
E
Kluesner
Nicholas
N
Davisson
Vincent Jo
VJ
McKee
Edward
E
Schweitzer
Dirk
D
Helquist
Paul
P
Tenniswood
Martin
M
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*
D002219:Carbamates; D018942:Macrolides; C520301:iejimalide B; C520300:iejimalide A; D025262:Vacuolar Proton-Translocating ATPases