Membrane Modifications in Human Erythroleukemia K562 Cells During Induction of Programmed Cell Death by Transforming Growth Factor β1 or Cisplatin

Abstract

Transforming growth factor Pl (TGFP1) and cisplatin induce apoptosis (programmed cell death, PCD) in human erythroleukemia K562 cells in an additive manner. After PCD was induced in K.562 cells, analysis of phospholipid composition, fatty acids and cholesterol content in their membranes showed a decrease in phosphatidylethanolamine and an increase in phosphatidylserine, cardiolipin and phosphatidic acid. Moreover, cisplatin but not TGFPl enhanced sphingomyeline levels in apoptotic cells, whereas TGFPl increased the amount of linoleic acid and, more remarkably, of cholesterol. The combination TGFPl fcisplatin produced membrane changes similar to those provoked by each inducer individually. Furthermore, the specific activities of 5-lipoxygenase and cytosolic phospholipase A,, both modulating the physical properties of membranes and membrane-lipid-mediated intracellular signalling, were enhanced by treatment with TGFPI or TGFP1 +cisplatin. These findings highlight the profound changes in cell membranes during the biochemical events of the apoptotic pathway.Keywords: programmed cell death ; biomembrane ; cholesterol ; lipoxygenase ; phospholipase A,.The mechanism of apoptosis (programmed cell death, PCD) remains to be fully elucidated. Despite the large array of inducers and effectors of apoptosis, the morphological features of PCD are highly conserved, suggesting a common sequence of final events. Even though the most defining parameters of apoptosis are nuclear changes, another morphological hallmark of apoptosis is the cell shrinkage associated with membrane blebbing [l, 21. Several PCD pathways require signal-transduction systems based on membrane receptors [Z] and membranederived lipid precursors of second messengers [3]. While the role of membranes in cell injury has been long recognized [4], major modifications should be expected in membranes of cells undergoing apoptosis, which might allow their specific recognition and elimination by macrophages [5].In the following study, we investigated the changes in membrane lipid composition during the induction of PCD in human erythroleukemia K.562 cells. Transforming growth factor PI (TGFPI) and/or cisplatin were used to induce apoptosis. TGFPl induces PCD in several cell lines [6, 71 by interacting with specific receptors on the cell surface [S]. Cisplatin, however, forces Abbreviations. PCD, programmed cell death ; TGFb1, transforming growth factor Dl ; sPLA,, secretory phospholipase A,; cPLA,, cytosolic phospholipase A, ; d,Ach, arachidonic acid; 5-HPA4Ach, 5-hydroperoxyarachidonic acid; G C N S , gas chromatography-mass spectrometry.Enzymes. Lipoxygenase (EC 1.13.11.12); phospholipase A, (EC 3.1 .I .4). cells into apoptosis [9] by forming complexes with nuclear DNA [lo]. We also assayed the activities of membrane-related enzymes in apoptotic cells, namely lipoxygenase and phospholipase A,. Several lipoxygenases are able to directly oxygenate biological membranes, introducing peroxides in the lipid bilayer [ l l -131. In particular, 5-lipoxygenase plays a role in ...

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