The ability of various inhibitors of lipoxygenase (LOX) enzymes and 5-lipoxygenase-activating protein (FLAP) to induce apoptosis has implicated these pathways in the mechanism(s) of this form of cell death. Although FLAP plays an important role in 5-LOX activity, this protein is found at high levels in some cells lacking LOX, suggesting it might mediate other effects. Furthermore, the concentration of MK886, a FLAP inhibitor, required to induce apoptosis is approximately 100-fold more than that required to inhibit LOX, and this compound remains effective in cells lacking LOX. The present study examines the role of FLAP in MK886-induced apoptosis. MK886 induced apoptosis in WSU cells, a human chronic lymphocytic leukaemia cell line that lacks FLAP protein and mRNA, suggesting that this agent is acting independently of FLAP. This conclusion was further supported by the fact that a more specific FLAP inhibitor, MK591, induced only minimal apoptosis in FL5.12 cells, a murine prolymphoid cell line containing FLAP. The role of FLAP was examined more directly by decreasing its expression by more than 50% in FL5.12 cells treated with 10 microM of an antisense oligonucleotide for 48h. This change in FLAP was not accompanied by any increase in apoptosis. Furthermore, FLAP-depleted cells exhibited the same level of apoptosis 8 h after treatment with 10 microM MK886, as did control cells. The increased fluorescence seen in MK886-treated cells loaded with carboxydichlorofluorescein indicates that oxidative reactions are stimulated by this compound, possibly via the release of fatty acids from fatty acid-binding proteins and their subsequent oxidation.
[1]
F. V. van Nieuwenhoven,et al.
Role of membrane-associated and cytoplasmic fatty acid-binding proteins in cellular fatty acid metabolism.
,
1997,
Prostaglandins, leukotrienes, and essential fatty acids.
[2]
F. Spener,et al.
Fatty acids in cell signalling: modulation by lipid binding proteins.
,
1995,
Prostaglandins, leukotrienes, and essential fatty acids.
[3]
J. Harris,et al.
Induction of apoptosis in blood cells from a patient with acute myelogenous leukemia by SC41661A, a selective inhibitor of 5-lipoxygenase.
,
1993,
Prostaglandins, leukotrienes, and essential fatty acids.
[4]
J. Harris,et al.
A 5-lipoxygenase inhibitor at micromolar concentration raises intracellular calcium in U937 cells prior to their physiologic cell death.
,
1997,
Prostaglandins, leukotrienes, and essential fatty acids.
[5]
D. Cistola,et al.
Cytoplasmic fatty acid binding protein: significance for intracellular transport of fatty acids and putative role on signal transduction pathways.
,
1993,
Prostaglandins, leukotrienes, and essential fatty acids.
[6]
E. Coligan.
Current protocols in immunology
,
1991
.