Relationship between membrane permeability and specificity of human secretory phospholipase A2 isoforms during cell death

• Published in: Biochimica et biophysica acta 2011-07, Vol.1808 (7), p.1913-1920
• Main Authors: Nelson, Jennifer, Gibbons, Elizabeth, Pickett, Katalyn R., Streeter, Michael, Warcup, Ashley O., Yeung, Celestine H.-Y., Judd, Allan M., Bell, John D.
• Format: Article
• Language: English
• Subjects: Apoptosis; Fluorescence spectroscopy; Membrane biophysics; Merocyanine 540; Propidium iodide
• ISSN: 0005-2736; 0006-3002; 1879-2642
• DOI: 10.1016/j.bbamem.2011.04.003

During apoptosis, a number of physical changes occur in the cell membrane including a gradual increase in permeability to vital stains such as propidium iodide. This study explored the possibility that one consequence of membrane changes concurrent with early modest permeability is vulnerability to degradation by secretory phospholipase A2. The activity of this hydrolytic enzyme toward mammalian cells depends on the health of the cell; healthy cells are resistant, but they become susceptible early during programmed death. Populations of S49 lymphoma cells during programmed death were classified by flow cytometry based on permeability to propidium iodide and susceptibility to secretory phospholipase A2. The apoptotic inducers thapsigargin and dexamethasone caused modest permeability to propidium iodide and increased staining by merocyanine 540, a dye sensitive to membrane perturbations. Various secretory phospholipase A2 isozymes (human groups IIa, V, X, and snake venom) preferentially hydrolyzed the membranes of cells that displayed enhanced permeability. In contrast, cells exposed briefly to a calcium ionophore showed the increase in cell staining intensity by merocyanine 540 without accompanying uptake of propidium iodide. Under that condition, only the snake venom and human group X enzymes hydrolyzed cells that were dying. These results suggested that cells showing modest permeability to propidium iodide during the early phase of apoptosis are substrates for secretory phospholipase A2 and that specificity among isoforms of the enzyme depends on the degree to which the membrane has been perturbed during the death process. This susceptibility to hydrolysis may be important as part of the signal to attract macrophages toward apoptotic cells. ► Early apoptotic cells display modest permeability to propidium iodide ► These cells are susceptible to hydrolysis by secretory phospholipase A2 (sPLA2) ► Cells dying by acute calcium loading do not show the modest permeability ► The differences in permeability corresponds to specificity of human sPLA2 isoforms