Yu A, Byers D M, Ridgway N D, McMaster C R, Cook H W
Atlantic Research Centre, Departments of Pediatrics and Biochemistry and Molecular Biology, 5849 University Avenue, Dalhousie University, B3H 4H7, Halifax, NS, Canada.
Biochim Biophys Acta. 2000 Sep 27;1487(2-3):296-308. 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 [(3)H]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-alpha/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.
磷脂酰丝氨酸（PtdSer）外化是程序性细胞死亡的一个共同特征，在凋亡细胞的识别和清除中起重要作用。在这项针对U937细胞的研究中，当用拓扑异构酶I抑制剂喜树碱（CAM）诱导凋亡时，[（3）H]丝氨酸合成PtdSer受到刺激，新合成的PtdSer优先从细胞转移至无细胞培养基囊泡（CFMV）中。当用半胱天冬酶抑制剂z-VAD-fmk阻断CAM诱导的凋亡时，PtdSer合成的刺激以及向CFMV的转移均被消除。相比之下，鞘磷脂（SM）或磷脂酰乙醇胺（PtdEtn）的合成及转运变化较小；总磷脂酰胆碱（PtdCho）合成低于对照水平。所有磷脂均出现在CFMV中，但与对照相比，PtdSer增加了6倍，而SM增加了3倍，PtdCho增加了2倍，PtdEtn增加了1.8倍。在紫外线照射或肿瘤坏死因子-α/环己酰亚胺处理诱导的凋亡细胞中，观察到对PtdSer合成特异性、向CFMV转移以及z-VAD-fmk抑制的影响更大。因此，U937细胞凋亡过程中刺激的PtdSer生物合成对这种磷脂具有特异性，并且与半胱天冬酶介导的凋亡过程中PtdSer在细胞表面的暴露以及向囊泡的优先转移相关。
