Distinct phospholipases A2 regulate the release of arachidonic acid for eicosanoid production and superoxide anion generation in neutrophils

PK Tithof, M Peters-Golden, PE Ganey - The Journal of Immunology, 1998 - journals.aai.org
PK Tithof, M Peters-Golden, PE Ganey
The Journal of Immunology, 1998journals.aai.org
Arachidonic acid (AA) released from membrane phospholipids by phospholipase A 2 (PLA
2) is important as a substrate for eicosanoid formation and as a second messenger for
superoxide anion (O 2−) generation in neutrophils. Different isoforms of PLA 2 in neutrophils
might mobilize AA for different functions. To test this possibility, we sought to characterize the
PLA 2 s that are activated by the neutrophil stimuli, Aroclor 1242, a mixture of
polychlorinated biphenyls, and A23187, a calcium ionophore. Both Aroclor 1242 and …
Abstract
Arachidonic acid (AA) released from membrane phospholipids by phospholipase A 2 (PLA 2) is important as a substrate for eicosanoid formation and as a second messenger for superoxide anion (O 2−) generation in neutrophils. Different isoforms of PLA 2 in neutrophils might mobilize AA for different functions. To test this possibility, we sought to characterize the PLA 2 s that are activated by the neutrophil stimuli, Aroclor 1242, a mixture of polychlorinated biphenyls, and A23187, a calcium ionophore. Both Aroclor 1242 and A23187 caused release of [3 H] AA; however, O 2− production was seen only in response to Aroclor 1242. Eicosanoids accounted for> 85% of the radioactivity recovered in the supernatant of A23187-stimulated cells but< 20% of the radioactivity recovered from cells exposed to Aroclor 1242. Omission or chelation of calcium abolished A23187-induced AA release, but did not alter AA release in Aroclor 1242-stimulated neutrophils. AA release and O 2− production in response to Aroclor 1242 were inhibited by bromoenol lactone (BEL), an inhibitor of calcium-independent PLA 2. BEL, however, did not alter A23187-induced release of AA. Cell-free assays demonstrated both calcium-dependent and calcium-independent PLA 2 activity. Calcium-independent activity was inhibited> 80% by BEL, whereas calcium-dependent activity was inhibited< 5%. Furthermore, calcium-independent, but not calcium-dependent, PLA 2 activity was significantly enhanced by Aroclor 1242. These data suggest that Aroclor 1242 and A23187 activate distinct isoforms of PLA 2 that are linked to different functions: Aroclor 1242 activates a calcium-independent PLA 2 that releases AA for the generation of O 2−, and A23187 activates a calcium-dependent PLA 2 that mobilizes AA for eicosanoid production.
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