Kinetic evaluation of cell membrane hydrolysis during apoptosis by human isoforms of secretory phospholipase A2.
Some isoforms of secretory phospholipase A(2) (sPLA(2)) distinguish between healthy and damaged or apoptotic cells. This distinction reflects differences in membrane physical properties. Because various sPLA(2) isoforms respond differently to properties of artificial membranes such as surface charge, they should also behave differently as these properties evolve during a dynamic physiological process such as apoptosis. To test this idea, S49 lymphoma cell death was induced by glucocorticoid (6-48 h) or calcium ionophore. Rates of membrane hydrolysis catalyzed by various concentrations of snake venom and human groups IIa, V, and X sPLA(2) were compared after each treatment condition. The data were analyzed using a model that evaluates the adsorption of enzyme to the membrane surface and subsequent binding of substrate to the active site. Results were compared temporally to changes in membrane biophysics and composition. Under control conditions, membrane hydrolysis was confined to the few unhealthy cells present in each sample. Increased hydrolysis during apoptosis and necrosis appeared to reflect substrate access to adsorbed enzyme for the snake venom and group X isoforms corresponding to weakened lipid-lipid interactions in the membrane. In contrast, apoptosis promoted initial adsorption of human groups V and IIa concurrent with phosphatidylserine exposure on the membrane surface. However, this observation was inadequate to explain the behavior of the groups V and IIa enzymes toward necrotic cells where hydrolysis was reduced or absent. Thus, a combination of changes in cell membrane properties during apoptosis and necrosis capacitates the cell for hydrolysis differently by each isoform.
Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah 84602, USA.
Erin D
ED
Olson
Jennifer
J
Nelson
Katalyn
K
Griffith
Thaothanh
T
Nguyen
Michael
M
Streeter
Heather A
HA
Wilson-Ashworth
Michael H
MH
Gelb
Allan M
AM
Judd
John D
JD
Bell
D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D017209:Apoptosis; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology / Q000473:pathology*; D002463:Cell Membrane Permeability; D003907:Dexamethasone / Q000494:pharmacology; D005434:Flow Cytometry; D054501:Group II Phospholipases A2 / Q000378:metabolism*; D054505:Group V Phospholipases A2 / Q000378:metabolism*; D054509:Group X Phospholipases A2 / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D007476:Ionophores / Q000494:pharmacology; D007700:Kinetics; D008223:Lymphoma / Q000201:enzymology / Q000473:pathology*; D008560:Membrane Fluidity; D009336:Necrosis; D054497:Phospholipases A2, Secretory / Q000378:metabolism*; D012910:Snake Venoms / Q000201:enzymology
D000893:Anti-Inflammatory Agents; D007476:Ionophores; D012910:Snake Venoms; D003907:Dexamethasone; D054501:Group II Phospholipases A2; D054505:Group V Phospholipases A2; D054509:Group X Phospholipases A2; D054497:Phospholipases A2, Secretory; D002118:Calcium