Candela M, Barker S C, Ballou L R
Research and Medical Service, Veterans Affairs Medical Center, Memphis, Tennessee.
J Exp Med. 1991 Dec 1;174(6):1363-9. doi: 10.1084/jem.174.6.1363.
Sphingosine is a biologically active derivative of sphingomyelin. It affects diverse cellular functions and its mechanism(s) of action is poorly defined. Tumor necrosis factor alpha (TNF alpha) has recently been shown to rapidly induce sphingomyelin turnover, implicating this metabolic pathway in TNF alpha signal transduction. Because TNF alpha is known to induce prostaglandin E2 (PGE2) production in human fibroblasts, we tested the effect of sphingosine on TNF alpha-induced PGE2 production. We found that sphingosine enhanced TNF alpha-induced PGE2 production by as much as 18-fold over TNF alpha alone. Sphingosine appeared to stimulate TNF alpha-induced PGE2 production independent of TNF alpha-mediated interleukin 1 (IL-1) production, because anti-IL-1 antibodies and IL-1 receptor antagonist protein (IRAP) did not inhibit TNF alpha-induced PGE2 production or the stimulatory effect of sphingosine. TNF alpha stimulated PGE2 production to the same degree in normal and protein kinase C (PKC) downregulated cells in the presence and absence of sphingosine, indicating that neither TNF alpha nor sphingosine require active PKC to elicit their respective effects. The sphingosine analogues stearylamine and stearoyl-D-sphingosine had little or no effect on TNF alpha-mediated PGE2 production, supporting a specific role for sphingosine in the activation process. Short-term (1 min) exposure of cells to sphingosine dramatically increased TNF alpha-induced PGE2 production. A potential mechanism by which sphingosine could increase TNF alpha-induced PGE2 production involves enhancement of phospholipase A2 (PLA2) and/or cyclooxygenase (Cox) activity, the rate-limiting enzymes in PGE2 production. We found that both TNF alpha and sphingosine alone enhanced these enzymatic activities, and that sphingosine additively increased the effect of TNF alpha on phospholipase A2 activity. It appears that sphingosine affects TNF alpha-induced PGE2 production via a mechanism that is independent of PKC involvement, and that sphingosine may function as an endogenous second messenger capable of modulating the responsiveness of the cell to external stimuli.
鞘氨醇是鞘磷脂的一种生物活性衍生物。它影响多种细胞功能，但其作用机制尚不清楚。肿瘤坏死因子α（TNFα）最近已被证明能迅速诱导鞘磷脂周转，提示该代谢途径参与TNFα信号转导。由于已知TNFα能诱导人成纤维细胞产生前列腺素E2（PGE2），我们测试了鞘氨醇对TNFα诱导的PGE2产生的影响。我们发现，鞘氨醇使TNFα诱导的PGE2产生比单独使用TNFα时增加了多达18倍。鞘氨醇似乎能刺激TNFα诱导的PGE2产生，而与TNFα介导的白细胞介素1（IL-1）产生无关，因为抗IL-1抗体和IL-1受体拮抗剂蛋白（IRAP）并不能抑制TNFα诱导的PGE2产生或鞘氨醇的刺激作用。在有和没有鞘氨醇的情况下，TNFα在正常细胞和蛋白激酶C（PKC）下调的细胞中刺激PGE2产生的程度相同，这表明TNFα和鞘氨醇都不需要活性PKC来发挥各自的作用。鞘氨醇类似物硬脂胺和硬脂酰-D-鞘氨醇对TNFα介导的PGE2产生几乎没有影响，这支持了鞘氨醇在激活过程中的特定作用。细胞短期（1分钟）暴露于鞘氨醇会显著增加TNFα诱导的PGE2产生。鞘氨醇增加TNFα诱导的PGE2产生的一个潜在机制涉及增强磷脂酶A2（PLA2）和/或环氧化酶（Cox）的活性，这是PGE2产生中的限速酶。我们发现，单独的TNFα和鞘氨醇都能增强这些酶活性，并且鞘氨醇能累加增加TNFα对磷脂酶A2活性的影响。似乎鞘氨醇通过一种独立于PKC参与的机制影响TNFα诱导的PGE2产生，并且鞘氨醇可能作为一种内源性第二信使，能够调节细胞对外界刺激的反应性。
