Sequence of physical changes to the cell membrane during glucocorticoid-induced apoptosis in S49 lymphoma cells.
During apoptosis, physical changes in the plasma membrane prepare the cell for clearance by phagocytes and hydrolysis by secretory phospholipase A(2) (sPLA(2)). The relationships among these changes have not been adequately established, especially for hormone-stimulated apoptosis. This study addresses these issues for glucocorticoid-induced apoptosis in S49 lymphoma cells. Flow cytometry, microscopy, and fluorescence spectroscopy were used to assess merocyanine 540 emission, laurdan generalized polarization, phosphatidylserine exposure, caspase activation, and membrane permeability to propidium iodide in the absence and presence of sPLA(2). The earliest event observed was activation of cellular caspases. Results with membrane probes suggest that interlipid spacing also increases early during apoptosis and precedes transbilayer migration of phosphatidylserine, DNA fragmentation, and a general increase in lipid order associated with blebbing and dissolution of the cells. The activity of sPLA(2) appeared to be linked more to lipid spacing than to loss of membrane asymmetry. The early nature of some of these events and their ability to promote activity of a proinflammatory enzyme suggests the possibility of an inflammatory response during T-lymphocyte apoptosis.
Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah, USA.
Rachel W
RW
Bailey
Thaothanh
T
Nguyen
Leslie
L
Robertson
Elizabeth
E
Gibbons
Jennifer
J
Nelson
Ryan E
RE
Christensen
Jacob P
JP
Bell
Allan M
AM
Judd
John D
JD
Bell
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects* / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects; D004798:Enzymes / Q000378:metabolism; D005434:Flow Cytometry; D005456:Fluorescent Dyes / Q000378:metabolism; D005938:Glucocorticoids / Q000494:pharmacology*; D006868:Hydrolysis; D050356:Lipid Metabolism / Q000187:drug effects; D008223:Lymphoma / Q000378:metabolism / Q000473:pathology*; D008853:Microscopy; D010718:Phosphatidylserines / Q000378:metabolism; D054467:Phospholipases A2 / Q000378:metabolism; D011744:Pyrimidinones / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013997:Time Factors; D014867:Water / Q000378:metabolism
D004798:Enzymes; D005456:Fluorescent Dyes; D005938:Glucocorticoids; D010718:Phosphatidylserines; D011744:Pyrimidinones; D014867:Water; C003954:merocyanine dye; D054467:Phospholipases A2