Pober J S
Boyer Center for Molecular Medicine, Yale University School of Medicine, New Haven, CT 06536, USA.
Pathol Biol (Paris). 1998 Mar;46(3):159-63.
Vascular endothelial cells (EC) are primary cellular targets for the actions of pro-inflammatory cytokines such as tumor necrosis factor (TNF). We have studied the signaling pathways used by TNF that lead to new gene expression (endothelial cell activation) or apoptosis (endothelial cell injury). Both responses are initiated by ligand binding to TNFR-I (the p55 receptor). TNF initiates transcription of the E-selectin gene by activation of the transcription factors NF-kappa B and c-Jun/ATF-2. NF-kappa B is activated following degradation of I kappa B alpha and I kappa B-beta. Activation of c-Jun/ATF-2 involves new c-Jun synthesis, and more importantly, phosphorylation of the amino terminus of c-Jun by Jun N-terminal kinase (JNK). Studies in transiently transfected human umbilical vein endothelial cells have revealed that NF-kappa B activation is initiated through the adaptor protein TRAF-2. The activation of JNK also depends upon TRAF-2 and probably involves a kinase cascade initiated by the small G proteins Rac-1 and/or cdc-42. Normally, TNF does not injure human EC. However, TNF can cause apoptosis of EC when cells are co-treated with either the protein synthesis inhibitor cycloheximide (CHX) or the lipid mediator ceramide (cer). The pathways leading to apoptosis following treatment with TNF + CHX and TNF + cer are different since only TNF + CHX is blocked by the caspase inhibitors crmA protein or the peptide zVAD.fmk while only TNF + cer is blocked by the anti apoptotic proteins Bcl-2, Bcl-XL or Al. Both pathways may be inhibited by the anti-apoptotic protein A-20. TNF does not cause the liberation of cer in EC, perhaps because of limited expression of neutral sphingomyelinase-activating adaptor protein FAN. These observations suggest that TNF normally acts as an activator of EC but may change from an activator to a killer of EC when combined with agents that release ceramide, such as u.v. irradiation or cytotoxic drugs, or with ceramide mimetics such as lipopolysaccharide. The activation and injury of endothelial cells induced by TNF and other proinflammatory cytokines may underlie the local effects of these mediators in vivo.
血管内皮细胞（EC）是肿瘤坏死因子（TNF）等促炎细胞因子作用的主要细胞靶点。我们研究了TNF所使用的导致新基因表达（内皮细胞活化）或凋亡（内皮细胞损伤）的信号通路。这两种反应均由配体与TNFR-I（p55受体）结合引发。TNF通过激活转录因子NF-κB和c-Jun/ATF-2来启动E-选择素基因的转录。IκBα和IκB-β降解后NF-κB被激活。c-Jun/ATF-2的激活涉及新的c-Jun合成，更重要的是，c-Jun的氨基末端被Jun氨基末端激酶（JNK）磷酸化。对瞬时转染的人脐静脉内皮细胞的研究表明，NF-κB的激活是通过衔接蛋白TRAF-2启动的。JNK的激活也依赖于TRAF-2，可能涉及由小G蛋白Rac-1和/或cdc-42启动的激酶级联反应。正常情况下，TNF不会损伤人内皮细胞。然而，当细胞与蛋白质合成抑制剂环己酰亚胺（CHX）或脂质介质神经酰胺（cer）共同处理时，TNF可导致内皮细胞凋亡。TNF + CHX和TNF + cer处理后导致凋亡的途径不同，因为只有TNF + CHX被半胱天冬酶抑制剂crmA蛋白或肽zVAD.fmk阻断，而只有TNF + cer被抗凋亡蛋白Bcl-2、Bcl-XL或Al阻断。两种途径都可能被抗凋亡蛋白A-20抑制。TNF不会导致内皮细胞中神经酰胺的释放，这可能是因为中性鞘磷脂酶激活衔接蛋白FAN的表达有限。这些观察结果表明，TNF通常作为内皮细胞的激活剂，但当与释放神经酰胺的药物（如紫外线照射或细胞毒性药物）或神经酰胺模拟物（如脂多糖）联合使用时，可能从激活剂转变为内皮细胞的杀手。TNF和其他促炎细胞因子诱导的内皮细胞激活和损伤可能是这些介质在体内局部作用的基础。
