COA-INDEPENDENT TRANSACYLASE ACTIVITY IS INCREASED IN HUMAN NEUTROPHILS AFTER TREATMENT WITH TUMOR-NECROSIS-FACTOR-ALPHA

CoA-independent transacylase (CoA-IT) appears to play a critical role in lipid mediator generation by rapidly moving arachidonate (AA) betwe en phospholipid pools during cell activation. Tumor necrosis factor-cu (TNF) pretreatment of human neutrophils increases agonist-induced pro duction of inflammatory mediators. The current study tested if the TNF -induced increase in lipid mediator production may be, in part, due to altered CoA-IT activity. Neutrophils were treated with TNF (250 U/ml, 30 min), homogenates prepared, and CoA-IT activity measured by the ab ility of these homogenates to acylate 1-[H-3]alkyl-2-lyso-sn-glycero-3 -phosphocholine (GPC). There was an increased CoA-IT activity, from 9. 1 +/- 1.1 to 13.7 +/- 1.4 pmol/mg per min in control vs. TNF-treated s amples, respectively. Varying the concentration of 1-alkyl-2-lyso-GPC revealed an increased CoA-IT activity in microsomes that was due to an increased V-max, from 26 to 54 pmol/mg per min. The ability of TNF to increase CoA-IT activity was concentration-dependent, with maximal re sponse observed at 25 U/ml. This effect on CoA-IT appears to be specif ic, in that TNF treatment of neutrophils had no effect on CoA-dependen t acylation of 1-acyl-2-lyso-sn-glycero-3-phosphocholine using either AA-CoA or linolenoyl-CoA as substrates. In the intact cell, the moveme nt of [H-3]AA from other phospholipids into PE in fMLP-stimulated neut rophils was greatly enhanced after TNF treatment, demonstrating a func tional consequence of increased CoA-IT activity. In addition, TNF trea tment doubled platelet-activating factor production in response to the chemotactic peptide fMLP, as measured by [H-3]acetate incorporation, while the response to A23187 remained unchanged. Taken together, these results provide the first evidence of modulation of CoA-IT activity b y a proinflammatory cytokine and suggest that one mechanism for augmen ted lipid mediator formation is through increases in CoA-IT activity.