Bussolino F, Camussi G, Baglioni C
Cattedra di Chimica e Propedeutica Biochimica, Università di Torino, Italy.
J Biol Chem. 1988 Aug 25;263(24):11856-61.
Human endothelial cells synthesize large amounts of platelet-activating factor (PAF) after 30-min treatment with recombinant tumor necrosis factor (TNF). Synthesis of PAF peaks at 4-6 h, whereas in endothelial cells treated with interleukin 1 alpha (IL-1) it peaks at 8-12 h. More than twice as much PAF is synthesized in response to optimal concentrations of TNF than in response to IL-1. However, PAF synthesis is stimulated by lower molar concentrations of IL-1 than TNF. About 30% of PAF produced in response to either TNF or IL-1 is released into the medium, whereas approximately 70% remains cell-associated. Experiments with labeled precursors show that PAF is synthesized de novo in response to TNF. This activity of TNF is inhibited by treating endothelial cells with the inhibitors of protein or RNA synthesis cycloheximide or actinomycin D. This finding may be explained by the observation that TNF induces in endothelial cells an acetyltransferase required for PAF synthesis. The induction of this enzymatic activity precedes the peak of PAF synthesis in TNF-treated cells. After prolonged incubation with either TNF or IL-1, endothelial cells no longer respond to the same monokine, but are still capable of producing PAF when treated with the other monokine. The finding that these monokines do not show reciprocal tachyphylaxis in endothelial cells may be explained by their binding to different receptors. In cells treated simultaneously with different concentrations of TNF and IL-1, PAF synthesis is stimulated in an additive rather than synergistic way. This suggests that PAF is synthesized by the same pathway in response to TNF or IL-1.
用重组肿瘤坏死因子（TNF）处理人内皮细胞30分钟后，其会合成大量血小板活化因子（PAF）。PAF的合成在4 - 6小时达到峰值，而在用白细胞介素1α（IL - 1）处理的内皮细胞中，其峰值出现在8 - 12小时。与最佳浓度的IL - 1相比，TNF刺激合成的PAF量多出两倍以上。然而，刺激PAF合成所需的IL - 1摩尔浓度低于TNF。对TNF或IL - 1作出反应而产生的PAF中，约30%释放到培养基中，而约70%仍与细胞相关。用标记前体进行的实验表明，PAF是对TNF作出反应而重新合成的。用蛋白质或RNA合成抑制剂环己酰亚胺或放线菌素D处理内皮细胞可抑制TNF的这种活性。这一发现可能可以通过以下观察结果来解释：TNF在内皮细胞中诱导出PAF合成所需的乙酰转移酶。这种酶活性的诱导先于TNF处理细胞中PAF合成的峰值。用TNF或IL - 1长时间孵育后，内皮细胞不再对相同的单核因子作出反应，但在用另一种单核因子处理时仍能够产生PAF。这些单核因子在内皮细胞中未表现出相互快速耐受性这一发现，可能可以通过它们与不同受体结合来解释。在用不同浓度的TNF和IL - 1同时处理的细胞中，PAF合成以相加而非协同的方式受到刺激。这表明PAF是通过相同途径对TNF或IL - 1作出反应而合成的。
