title: Mobilization of lysosomal calcium regulates the externalization of phosphatidylserine during apoptosis.
abstract: A hallmark of apoptotic cells is the Ca2+-dependent appearance of phosphatidylserine (PS) at the cell surface as a result of its redistribution from the inner-to-outer plasma membrane leaflet. Although endoplasmic reticulum and mitochondrial Ca2+ are known to participate in apoptosis, their role in PS externalization has not been established. In this study, several organelle-specific fluorescent markers and Ca2+-sensitive probes were used to identify the source of Ca2+ critical to PS externalization. By employing Rhod-2AM, fluorescein-labeled high molecular weight dextran, and Calcium Green 1, we provide evidence that lysosomes respond to apoptotic stimuli by releasing their luminal Ca2+ to the cytosol. Cells treated with the cytosolic phospholipase A2 inhibitor, cPLA2alpha, had no effect on caspase activation but exhibited a significant decrease in lysosomal Ca2+ release and externalization of PS in response to apoptotic stimuli. Similarly, cells depleted of lysosomal Ca2+ underwent programmed cell death yet failed to externalize PS. These data indicate that although Ca2+ release from other intracellular organelles to the cytosol is adequate for apoptosis, the release of Ca2+ from lysosomes is critical for PS externalization.
authors.affiliation: Department of Cancer Biology, University of Texas, M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: Banafsheh
authors.initials: B
authors.lastname: Mirnikjoo
authors.forename: Krishnakumar
authors.initials: K
authors.lastname: Balasubramanian
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Schroit
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D020169:Caspases / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D054513:Group IV Phospholipases A2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism*; D051379:Mice; D015335:Molecular Probes / Q000494:pharmacology; D010718:Phosphatidylserines / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D015335:Molecular Probes; D010718:Phosphatidylserines; D054513:Group IV Phospholipases A2; D020169:Caspases; D002118:Calcium