Preferential externalization of newly synthesized phosphatidylserine in apoptotic U937 cells is dependent on caspase-mediated pathways

• Published in: Biochimica et biophysica acta 2000-09, Vol.1487 (2), p.296-308
• Main Authors: Yu, Anan, Byers, David M, Ridgway, Neale D, McMaster, Christopher R, Cook, Harold W
• Format: Article
• Language: English
• Subjects: Apoptosis; Camptothecin; Caspase; Caspase Inhibitors; Caspases - metabolism; Cell Membrane - metabolism; Cell-Free System; Enzyme Inhibitors; Exocytosis; Humans; Phosphatidylserine; Phosphatidylserines - biosynthesis; Phosphatidylserines - metabolism; Phospholipid; Tumor Cells, Cultured; U937 cell; U937 Cells; Ultraviolet Rays
• ISSN: 1388-1981; 0006-3002; 1879-2618
• DOI: 10.1016/S1388-1981(00)00100-1

Externalization of phosphatidylserine (PtdSer) is a common feature of programmed cell death and plays an important role in the recognition and removal of apoptotic cells. In this study with U937 cells, PtdSer synthesis from [ 3H]serine was stimulated and newly synthesized PtdSer was transferred preferentially to cell-free medium vesicles (CFMV) from cells when apoptosis was induced with a topoisomerase I inhibitor, camptothecin (CAM). When CAM-induced apoptosis was blocked by a caspase inhibitor, z-VAD-fmk, stimulation of PtdSer synthesis and movement to CFMV were abolished. In contrast, changes in synthesis and transport of sphingomyelin (SM) or phosphatidylethanolamine (PtdEtn) were minor; total phosphatidylcholine (PtdCho) synthesis was below control levels. All phospholipids appeared in CFMV but PtdSer displayed a 6-fold increase relative to controls compared to 3-fold for SM, 2-fold for PtdCho and 1.8-fold for PtdEtn. Even greater effects on specificity of PtdSer synthesis, movement to CFMV and inhibition by z-VAD-fmk were observed in apoptotic cells induced by UV irradiation or tumor necrosis factor-α/cycloheximide treatment. Thus, PtdSer biosynthesis stimulated during apoptosis in U937 cells was specific for this phospholipid and was correlated with caspase-mediated exposure of PtdSer at the cell surface and preferential movement to vesicles during apoptosis.