EXPRESSION OF PLASMA PLATELET-ACTIVATING-FACTOR ACETYLHYDROLASE IS TRANSCRIPTIONALLY REGULATED BY MEDIATORS OF INFLAMMATION

Platelet-activating factor (PAF) is a potent phospholipid with diverse physiological and pathological actions, and it is inactivated by PAF acetylhydrolase, In this study, we analyzed the tissue distribution of the plasma PAF acetylhydrolase mRNA in humans. We isolated a 3,5-kilo base fragment containing the 5' genomic sequence of the plasma PAF ace tylhydrolase gene and fun-ther characterized the promoter activity, We detere mined the transcriptional initiation site by primer extension. We then prepared constructs containing various lengths of 5' genomic fragments fused to a luciferase reporter gene and transfected these co nstructs into COS-7 cells, We found that there is more than one region in the 1.3-kilobase 5' genomic sequence conferring promoter activity and that a very short 5'-flanking region (72 base pairs) is sufficient for more than 65% of the basal activity. in parallel, we examined the regulation of expression of the PAF acetylhydrolase gene, We found th at interferon-gamma (IFN gamma) and lipopolysaccharide (LPS) significa ntly inhibited synthesis of PAF acetylhydrolase, whereas other cytokin es, including IFN alpha, interleukin (IE) 1 alpha, IL4, IL6, tumor nec rosis factor-alpha, granulocyte/macrophage colony-stimulating factor, and macrophage colony-stimulating factor, had a smaller or no effect i n human monocyte-derived macrophages. Furthermore, transfection of the promoter/reporter construct into macrophage RAW264.7 cells revealed t hat IFN gamma and LPS decreased the promoter activity by 35% and 50%, respectively, whereas PAF stimulated it by 52% via its receptor, The p romoter activity was much lower in monocytic U937 cells compared with the basal level in COS-7 cells, wile the activities in P388DI and RAW2 64.7 macrophagic cells were considerably higher than the basal level i n COS-7 cells. There are multiple regions in the PAF acetylhydrolase p romoter that contain responsive elements for signal transducer and act ivators of transcription-related proteins, and also for myeloid-specif ic transcription factors. Our data indicate that the opposite of mRNA expression in monocytes versus macrophages is due to inhibition of the promoter activity in the former and activation in the latter cells.