Camussi G, Biancone L, Iorio E L, Silvestro L, Da Col R, Capasso C, Rossano F, Servillo L, Balestrieri C, Tufano M A
Dipartimento di Biochimica e Biofisica, I Facoltá di Medicina e Chirurgia, Universitá di Napoli, Italy.
Kidney Int. 1992 Dec;42(6):1309-18. doi: 10.1038/ki.1992.422.
Porins, a family of hydrophobic proteins located in the outer membrane of the cell wall of gram-negative bacteria and lipopolysaccharide (LPS), were shown to stimulate the synthesis of platelet activating factor (PAF), a phospholipid mediator of inflammation and endotoxic shock, by cultured human glomerular mesangial cells (MC). The synthesis of PAF induced by porins was rapid (peak at 20 min) and independent either from contamination by LPS or from generation of an endotoxin-induced cytokine such as tumor necrosis factor (TNF) since it was not prevented by cycloheximide, an inhibitor of protein synthesis or anti-TNF blocking antibodies. LPS also stimulated PAF synthesis by MC. However, the kinetic of PAF synthesis induced by LPS was biphasic with an early and transient peak at 10 minutes and a second and sustained peak at three to six hours. This second peak required an intact protein synthesis and was prevented by anti-TNF antibodies, suggesting the dependency on LPS-induced synthesis of TNF. Experiments with labeled precursors demonstrated that in MC, either after stimulation with porins or LPS, PAF was synthesized via the remodeling pathway that involves acetylation of 1-0-alkyl-sn-glyceryl-3-phosphorylcholine (2-lyso-PAF) generated from 1-0-alkyl-2-acyl-sn-glyceryl-3-phosphorylcholine by phospholipase A2 (PLA2) activity. Porins and LPS, indeed, induced PLA2-dependent mobilization of [14C]-arachidonic acid that was inhibited by p-bromodiphenacylbromide (PBDB). PBDB, an inhibitor of PLA2, also blocked PAF synthesis by preventing the mobilization of 2-lyso-PAF, the substrate for PAF-specific acetyltransferase.(ABSTRACT TRUNCATED AT 250 WORDS)
孔蛋白是位于革兰氏阴性菌细胞壁外膜和脂多糖（LPS）中的一类疏水蛋白，已证实其可刺激培养的人肾小球系膜细胞（MC）合成血小板活化因子（PAF），PAF是一种炎症和内毒素休克的磷脂介质。孔蛋白诱导的PAF合成迅速（20分钟达到峰值），且独立于LPS污染或内毒素诱导的细胞因子（如肿瘤坏死因子（TNF））的产生，因为蛋白质合成抑制剂环己酰亚胺或抗TNF阻断抗体均不能阻止其合成。LPS也刺激MC合成PAF。然而，LPS诱导的PAF合成动力学呈双相性，在10分钟时有一个早期短暂峰值，在三到六小时时有第二个持续峰值。第二个峰值需要完整的蛋白质合成，且可被抗TNF抗体阻止，这表明其依赖于LPS诱导的TNF合成。用标记前体进行的实验表明，在MC中，无论是用孔蛋白还是LPS刺激后，PAF都是通过重塑途径合成的，该途径涉及由磷脂酶A2（PLA2）活性将1-0-烷基-2-酰基-sn-甘油-3-磷酸胆碱转化生成的1-0-烷基-sn-甘油-3-磷酸胆碱（2-溶血-PAF）的乙酰化。实际上，孔蛋白和LPS诱导了依赖PLA2的[14C]-花生四烯酸的动员，该动员被对溴二苯甲酰溴（PBDB）抑制。PBDB是一种PLA2抑制剂，它还通过阻止2-溶血-PAF（PAF特异性乙酰转移酶的底物）的动员来阻断PAF的合成。（摘要截短于250字）
