HUMAN MONONUCLEAR-CELLS EXPRESS 12-LX - COORDINATED MESSENGER-RNA REGULATION WITH 5-LX AND FLAP GENES

Lipoxygenases (LXs) catalyze formation of leukotrienes and hydroxy-eic osatetraenoic acids (HETEs), proinflammatory, and spasmogenic autacoid s that are critical for host defense systems. We studied the expressio n and regulation of LX genes (12-LX, 5-LX, and 15-LX) and the 5-lipoxy genase activating protein (FLAP) in human mononuclear cells (MNC) and granulocytes using a quantitative reverse transcription polymerase cha in reaction (RT-PCR) technique. We show that 12-LX mRNA is constitutiv ely expressed in resting platelet-free MNC. 12-LX gene expression was upregulated by activation with lipopolysaccharide (LPS). The formation of 12-HETE was inducible with ionophore in MNC, as assessed by high-p erformance liquid chromatography (HPLC) and gas chromatography, and in creased after LPS pretreatment. In addition to 12-LX, resting MNC expr essed the genes for 5-LX and FLAP constitutively. Quantitative time co urse analyses of 12-LX, 5-LX, and FLAP gene expression suggested coreg ulation of 12-LX and FLAP mRNAs, and reciprocal regulation of 5-LX and FLAP mRNAs. During cell stimulation with LPS 5-LX mRNA levels remaine d unchanged, whereas FLAP gene expression increased. No 15-LX mRNA exp ression or 15-HETE formation was detectable in unstimulated and activa ted MNC. In contrast to MNC, quantitative RT-PCR mRNA analysis showed intermittent intraindividual expression of the 5-LX and FLAP genes in resting granulocytes, mRNAs for 12-LX and 15-LX were not expressed. On stimulation of granulocytes ex vivo, mRNA expression of 5-LX and FLAP was upregulated. Stimulation by LPS differed from that by ionophore A 23187. Neither LPS nor ionophore induced gene expression of 12-LX or 1 5-LX in granulocytes. Our data indicate that resting human MNC and gra nulocytes express LX and FLAP genes in a cell-specific manner. Cell ac tivation induces coordinated upregulation of 12-LX and FLAP genes in M NC, and 5-LX and FLAP genes in granulocytes, respectively. The constit utive expression of 12-LX mRNA, its upregulation on cell activation, a nd the formation of 12-HETE clearly indicate the presence of a functio nal 12-LX in human MNC. (C) 1996 by The American Society of Hematology .