Susceptibility of S49 lymphoma cell membranes to hydrolysis by secretory phospholipase A(2) during early phase of apoptosis

During cell death, plasma membranes of cells become vulnerable to attack by extracellular secretory phospholipase A(2). The purpose of this study was to identify the timing of this phenomenon relative to other events that occ ur during the process of cell death. Death was induced in S49 murine lympho ma cells by treatment with dexamethasone, dibutyryl cAMP, ionomycin, thapsi gargin, or heat shock (1 h at 43 degrees C). The appearance of membrane sus ceptibility to secretory phospholipase A(2) was compared to the following a poptotic events: loss of mitochondrial membrane potential, phosphatidylseri ne exposure in the outer leaflet of the cell membrane, early DNA damage ass essed by the comet assay, and changes in cell size and internal complexity assessed by flow cytometry. Each inducer of death was distinct in the time course of events produced. Although dead cells were susceptible to the acti on of phospholipase A(2), live cells (impermeable to propidium iodide) also became vulnerable to the enzyme during characteristic time courses after e xposure to each inducer. In fact, susceptibility to sPLA(2) was observed in each case prior to or concurrent with the earliest of the markers of apopt osis. These results demonstrate that the onset of susceptibility to sPLA(2) is an early event in apoptosis suggesting that changes in membrane structu re may be relevant to initial aspects of the apoptotic process. (C) 2000 El sevier Science B.V. All rights reserved.