Partitioning apoptosis: a novel form of the execution phase of apoptosis.
Apoptosis is characterized by chromatin condensation, DNA cleavage, redistribution of phosphatidylserine, and apoptotic body formation via an actin-dependent process. We describe a novel form of the execution phase of apoptosis in human multiple myeloma cells that is morphologically and mechanistically distinct from classical apoptosis, but is caspase-dependent and inhibited by IL-6 and overexpression of Bcl-2. Electron microscopic analysis of these cells demonstrated chromatin condensation without nuclear fragmentation, and 'partitioning' of cell constituents into two components: a single, large bleb containing soluble protein and free ribosomes, and a region containing the nucleus, organelles, and RER. In some cases, the bleb separated, becoming a free vesicle exhibiting random kinetic motion. These morphologic features occurred despite inhibition of the actin and tubulin cytoskeletal systems. This novel form of apoptosis, called partitioning apoptosis, was observed in a variety of tumor cell types and in primary cells. The execution phase of apoptosis can occur in a manner that is morphologically and mechanistically distinct from classical apoptosis.
Zhang
B
B
University of Maryland Greenebaum Cancer Center, University of Maryland Medical System, Baltimore, MD 21201, USA.
Arany
Z
Z
Mann
D
D
Rhee
J G
JG
Fenton
R G
RG
D017209:Apoptosis; D020169:Caspases / Q000378:metabolism*; D002451:Cell Compartmentation; D002478:Cells, Cultured; D002843:Chromatin / Q000473:pathology*; D006801:Humans; D008854:Microscopy, Electron; D009101:Multiple Myeloma / Q000473:pathology* / Q000648:ultrastructure*
D002843:Chromatin; D020169:Caspases