Increases in 5-lipoxygenase activating protein expression account for enhanced capacity for 5-lipoxygenase metabolism that accompanies differentiation of peripheral blood monocytes into alveolar macrophages.
The capacity for 5-lipoxygenase (5-LO) metabolism of endogenous arachidonic acid (AA) is greater in alveolar macrophages (AM) than in their circulating precursors, peripheral blood monocytes (PBM); however, the ability of PBM to metabolize exogenous AA to 5-LO products is comparable to that of AM. In the present study, we examined the enzymatic mechanisms by which 5-LO metabolism of AA is altered during differentiation of PBM in the lung. Resting human AM exhibited greater steady-state levels of 5-LO (7-fold) and LTA4 hydrolase (2-fold) proteins than autologous PBM; moreover, they differed from PBM in that they contained a significant amount of 5-LO associated with the particulate fraction. Importantly, AM contained 40-fold more 5-lipoxygenase activating protein (FLAP) than did PBM, which correlated well with the relative abilities of intact AM and PBM to metabolize endogenous AA to leukotrienes. The FLAP inhibitor MK-886 was unable to block leukotriene synthesis from exogenous AA in the two cell types, despite its ability to completely inhibit 5-LO metabolism of endogenous AA. These observations indicate that, although FLAP is essential for the synthesis of leukotrienes from endogenous AA, perhaps by presenting AA to 5-LO, it is not required for 5-LO metabolism of exogenous AA. The differing roles of FLAP in 5-LO metabolism of endogenous versus exogenous AA are consistent with the conclusion that it is the markedly greater expression of FLAP, rather than of 5-LO, that is primarily responsible for the increased leukotriene synthesis from endogenous AA that accompanies PBM differentiation into AM.
Coffey
M J
MJ
Department of Internal Medicine, University of Michigan Medical School, Ann Arbor.
Wilcoxen
S E
SE
Peters-Golden
M
M
D058927:5-Lipoxygenase-Activating Proteins; D000328:Adult; D001094:Arachidonate 5-Lipoxygenase / Q000378:metabolism*; D016718:Arachidonic Acid / Q000378:metabolism; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000378:metabolism; D002454:Cell Differentiation; D002458:Cell Fractionation; D002478:Cells, Cultured; D015777:Eicosanoids / Q000378:metabolism; D004789:Enzyme Activation; D004851:Epoxide Hydrolases / Q000378:metabolism; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D020024:Leukotriene Antagonists; D016676:Macrophages, Alveolar / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D008565:Membrane Proteins / Q000096:biosynthesis* / Q000378:metabolism; D009000:Monocytes / Q000166:cytology* / Q000378:metabolism*; D012016:Reference Values; D013347:Subcellular Fractions / Q000201:enzymology; D002722:Chlorobenzenes
D058927:5-Lipoxygenase-Activating Proteins; D001094:Arachidonate 5-Lipoxygenase; D016718:Arachidonic Acid; D002352:Carrier Proteins; D015777:Eicosanoids; D004851:Epoxide Hydrolases; D007211:Indoles; D020024:Leukotriene Antagonists; D008565:Membrane Proteins; C548592:ALOX5AP protein, human; C060893:MK-886; D002722:Chlorobenzenes; C043134:leukotriene A4 hydrolase