Bigda J, Beletsky I, Brakebusch C, Varfolomeev Y, Engelmann H, Bigda J, Holtmann H, Wallach D
Department of Membrane Research and Biophysics, Weizmann Institute of Science, Rehovot, Israel.
J Exp Med. 1994 Aug 1;180(2):445-60. doi: 10.1084/jem.180.2.445.
Whereas there is ample evidence for involvement of the p55 tumor necrosis factor (TNF) receptor (p55-R) in the cytocidal effect of TNF, the role of the p75 TNF receptor (p75-R) in this effect is a matter of debate. In this study, we probed the function of p75-R in cells sensitive to the cytotoxicity of TNF using a wide panel of antibodies (Abs) against the receptor's extracellular domain. Two distinct Ab effects were observed. The Abs triggered signaling for cytotoxicity. This effect: (a) was correlated with the extent of p75-R expression by the cells; (b) was dependent on receptor cross-linking by the Abs; (c) occurred in HeLa cells, but not in A9 cells transfected with human p75-R or in HeLa cells expressing cytoplasmically truncated p75-R mutants, indicating that it involves cell-specific activities of the intracellular domain of the receptor; (d) was synergistic with the cytocidal effect of Abs against p55-R. Moreover, it seemed to reverse induced desensitization to the cytocidal effect of anti p55-R Abs, suggesting that it involves mechanisms different from those of the signaling by the p55 TNF-R. In addition, the Abs affected the response to TNF in a way that does not involve the signaling activity of p75-R. These effects: (a) could be observed also in cells in which only p55-R signaled for the cytocidal effect; (b) were not dependent on receptor cross-linking by the Abs; (c) varied according to the site at which the Abs bound to the receptor; and (d) were correlated inversely with the effects of the Abs on TNF binding to p75-R. That is, Abs binding to the membrane-distal part of the receptor's extracellular domain displaced TNF from the p75 receptor and enhanced cytocidal effect, whereas Abs that bind to the membrane-proximal part of the extracellular domain--a region at which a conformational change seems to take place upon TNF binding--decreased the dissociation of TNF from p75-R and inhibited its cytocidal effect. The above findings suggest that p75-R contributes to the cytocidal effect of TNF both by its own signaling and by regulating the access of TNF to p55-R.
虽然有充分证据表明p55肿瘤坏死因子（TNF）受体（p55-R）参与TNF的细胞杀伤作用，但p75 TNF受体（p75-R）在此作用中的角色仍存在争议。在本研究中，我们使用一系列针对该受体胞外域的抗体，探究了p75-R在对TNF细胞毒性敏感的细胞中的功能。观察到两种不同的抗体效应。这些抗体引发了细胞毒性信号。这种效应：（a）与细胞中p75-R的表达程度相关；（b）依赖于抗体对受体的交联作用；（c）在HeLa细胞中出现，但在转染了人p75-R的A9细胞或表达胞质截短型p75-R突变体的HeLa细胞中未出现，表明它涉及受体胞内域的细胞特异性活性；（d）与针对p55-R的抗体的细胞杀伤效应具有协同作用。此外，它似乎能逆转对抗p55-R抗体的细胞杀伤效应的诱导脱敏，提示其涉及的机制不同于p55 TNF-R的信号传导机制。另外，这些抗体以一种不涉及p75-R信号活性的方式影响对TNF的反应。这些效应：（a）在仅p55-R发出细胞毒性信号的细胞中也能观察到；（b）不依赖于抗体对受体的交联作用；（c）根据抗体与受体结合的位点不同而变化；（d）与抗体对TNF与p75-R结合的影响呈负相关。也就是说，与受体胞外域膜远端部分结合的抗体将TNF从p75受体上置换下来并增强细胞杀伤效应，而与胞外域膜近端部分结合的抗体（TNF结合时似乎会发生构象变化的区域）则减少TNF从p75-R上的解离并抑制其细胞杀伤效应。上述发现表明，p75-R通过自身的信号传导以及调节TNF与p55-R的结合来促进TNF的细胞杀伤作用。
