Inhibition of Macrophage Ca2+-independent Phospholipase A2 by Bromoenol Lactone and Trifluoromethyl Ketones

Abstract

A novel Ca(2+)-independent phospholipase A2 (PLA2) has recently been purified from the murine macrophage-like cell line P388D1 (Ackermann, E. J., Kempner, E. S., and Dennis, E. A. (1994) J. Biol. Chem. 269, 9227-9233). This enzyme is now shown to be inhibited by palmitoyl trifluoromethyl ketone (PACOCF3), arachidonyl trifluoromethyl ketone (AACOCF3), and a bromoenol lactone (BEL). Both PACOCF3 and AACOCF3 were found to inhibit the macrophage PLA2 in a concentration-dependent manner. PACOCF3 was found to be approximately 4-fold more potent than AACOCF3, with IC50 values of 3.8 microM (0.0075 mol fraction) and 15 microM (0.028 mol fraction), respectively. Reaction progress curves in the presence of either inhibitor were found to be linear, and the PACOCF3.PLA2 complex rapidly dissociated upon dilution. BEL was also found to inhibit the macrophage PLA2 in a concentration-dependent manner, with half-maximal inhibition observed at 60 nM after a 5-min preincubation at 40 degrees C. Inhibition was not reversed after extensive dilution of the enzyme into assay buffer. Treatment of the PLA2 with BEL resulted in a linear, time-dependent inactivation of activity, and the rate of this inactivation was diminished in the presence of PACOCF3. In addition, PLA2 treated with [3H]BEL resulted in the covalent labeling of a major band at M(r) 80,000. Inactivation of the PLA2 by 5,5'-dithiobis(2-nitrobenzoic acid) prior to treatment with [3H]BEL resulted in the near complete lack of labeling consistent with covalent irreversible suicide inhibition of the enzyme. The labeling of a M(r) 80,000 band rather than a M(r) 40,000 band upon treatment with [3H]BEL distinguishes the macrophage Ca(2+)-independent PLA2 from a previously identified myocardial Ca(2+)-independent PLA2 and provides strong evidence that the M(r) 80,000 protein is the catalytic subunit.

Hydrogen peroxide generated at the level of mitochondria in response to peroxynitrite promotes U937 cell death via inhibition of the cytoprotective signalling mediated by cytosolic phospholipase A2

“…26 It would appear that, in our system, AACOCF 3 acts as a cPLA 2 inhibitor since its effects were not reproduced by HELSS, an iPLA 2 inhibitor. 26,27 The notion that cPLA 2 is specifically involved in the cytoprotective signalling opposing peroxynitrite toxicity was further established using antisense oligonucleotides downregulating either cPLA 2 ( Figure 6) or iPLA 2 ( Figure 7).…”

“…26 It would appear that, in our system, AACOCF 3 acts as a cPLA 2 inhibitor since its effects were not reproduced by HELSS, an iPLA 2 inhibitor. 26,27 The notion that cPLA 2 is specifically involved in the cytoprotective signalling opposing peroxynitrite toxicity was further established using antisense oligonucleotides downregulating either cPLA 2 ( Figure 6) or iPLA 2 ( Figure 7). Cells transfected with the respective nonsense oligonucleotides were used as a negative control and, in both toxicity and DHR oxidation studies, responded to peroxynitrite alone, or associated with various treatments, as the nontransfected cells.…”

2,2′,4,4′-Tetrachlorobiphenyl upregulates cyclooxygenase-2 in HL-60 cells via p38 mitogen-activated protein kinase and NF-κB

“…Exposure to 2244-TCB produced a significant increase in 3 H-AA release (Table 1). BEL, an inhibitor of the calcium-independent PLA 2 (Ackermann et al 1995), attenuated the 2244-TCB-mediated increase in 3 H-AA release. Incubation with either OP, an inhibitor of the cytosolic and secretory isoforms of PLA 2 (Magolda and Galbraith, 1989), or SB-202190, an inhibitor of p38 MAP kinase (Lee et al 1994), had no effect on 2244-TCBinduced 3 H-AA release.…”

Polychlorinated biphenyls induce arachidonic acid release in human platelets in a tamoxifen sensitive manner via activation of group IVA cytosolic phospholipase A2-α

“…Pyrrolidine-1 is a potent and selective inhibitor of cPLA 2 -α [48,49]. BEL is an inhibitor of iPLA 2 [56,57] whereas AACOCF 3 inhibits both cPLA 2 -α and iPLA 2 [56,58]. Furthermore, AACOCF 3 is known to inhibit thrombin-and calcium ionophore-induced arachidonic acid release and 12-HETE synthesis in human platelets [54,59].…”