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

Abstract

Summary 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 (sPLA2). 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 sPLA2. 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 sPLA2 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 × 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 sPLA2 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.

Modulated mechanism of phosphatidylserine on the catalytic activity of Naja naja atra phospholipase A2 and Notechis scutatus scutatus notexin

“…Consequently, the membrane permeability of propidium iodide does not greatly increase in NnaPLA 2 -and notexin-induced apoptosis of K562, U937 and SK-N-SH cells (Liu et al, 2009;Chen et al, 2010a,b). Nelson et al (2011Nelson et al ( , 2012 also found that A. piscivorus piscivorus PLA 2 did not cause the membrane of ionomycin-and thapsigargin-treated cells to become free permeable for propidium iodide.…”

“…Previous studies suggested that membrane structure contributed to the level of membrane susceptibility to A. piscivorus piscivorus PLA 2 in addition to PS externalization (Bailey et al, 2007(Bailey et al, , 2009Nelson et al, 2011Nelson et al, , 2012. Nevertheless, the effect of membrane-interacted mode of PLA 2 enzymes and membrane compositions on PLA 2 activity does not explore in the studies of Bailey et al (2007Bailey et al ( , 2009 and Nelson et al (2011and Nelson et al ( , 2012. Nelson et al (2011) found that A. piscivorus piscivorus PLA 2 showed different activity on hydrolyzing the membrane of ionomycin-, dexamethasone-or thapsigargin-treated cells.…”

“…Nevertheless, the effect of membrane-interacted mode of PLA 2 enzymes and membrane compositions on PLA 2 activity does not explore in the studies of Bailey et al (2007Bailey et al ( , 2009 and Nelson et al (2011and Nelson et al ( , 2012. Nelson et al (2011) found that A. piscivorus piscivorus PLA 2 showed different activity on hydrolyzing the membrane of ionomycin-, dexamethasone-or thapsigargin-treated cells. Although ionomycin similarly induced PS externalization of normal lymphocytes, Raji human Burkitt's lymphoma cells and S49 mouse lymphoma cells, A. piscivorus piscivorus PLA 2 differently hydrolyzed the membrane of ionomycin-treated lymphocytes, Raji cells and S49 cells (Nelson et al, 2012) Collectively, these findings suggest the notion that membrane compositions and/or membrane-bound conformation of PLA 2 enzymes should be important for the susceptibility of apoptotic cells for PLA 2 .…”

“…Previous research has reported that the membranes of cells undergoing apoptosis are susceptible to human secreted PLA 2 enzymatic activity (Atsumi et al, 1997). Bell and his colleagues suggest that PS externalization in concert with alteration of membrane structure increase the susceptibility of apoptotic cells to Agkistrodon piscivorus piscivorus PLA 2 and human secreted PLA 2 s (Harris et al, 2001;Bailey et al, 2007Bailey et al, , 2009Nelson et al, 2011Nelson et al, , 2012. In their studies, ionomycin, dexamethasone or thapsigargin are used to induce apoptosis of cells, and thus the direct effect of these reagents on membrane structure and PLA 2 activity could not exclude out (Harris et al, 2001;Bailey et al, 2007Bailey et al, , 2009Nelson et al, 2011Nelson et al, , 2012.…”

“…Bell and his colleagues suggest that PS externalization in concert with alteration of membrane structure increase the susceptibility of apoptotic cells to Agkistrodon piscivorus piscivorus PLA 2 and human secreted PLA 2 s (Harris et al, 2001;Bailey et al, 2007Bailey et al, , 2009Nelson et al, 2011Nelson et al, , 2012. In their studies, ionomycin, dexamethasone or thapsigargin are used to induce apoptosis of cells, and thus the direct effect of these reagents on membrane structure and PLA 2 activity could not exclude out (Harris et al, 2001;Bailey et al, 2007Bailey et al, , 2009Nelson et al, 2011Nelson et al, , 2012. Our previous studies revealed that Naja naja atra PLA 2 (NnaPLA 2 ) induced apoptosis of human leukemia K562 and U937 cells (Liu et al, 2009;Chen et al, 2010a), while Notechis scutatus scutatus notexin (presynaptic PLA 2 neurotoxin) induced apoptosis of human neuroblastoma SK-N-SH cells (Chen et al, 2010b).…”