Watanabe N, Kuriyama H, Sone H, Neda H, Yamauchi N, Maeda M, Niitsu Y
Department of Internal Medicine, Sapporo Medical College, Japan.
J Biol Chem. 1988 Jul 25;263(21):10262-6.
The cell dynamics of the receptor for tumor necrosis factor (TNF) were examined in TNF-sensitive KYM cells derived from human myosarcoma. With receptor synthesis inhibited by cycloheximide, the half-life of the surface TNF receptor was 2 h in the absence of TNF and 30 min in its presence, suggesting that the TNF receptor is non-recycling and that its internalization is accelerated by TNF. During cell incubation with TNF receptor degradation suppressed by chloroquine, the number of surface TNF receptors remained approximately constant, but the total number of surface and internal TNF receptors increased gradually, at 3 h reaching 1.5 times the initial number, thus suggesting continuous synthesis, externalization, internalization, and degradation of the TNF receptor in the absence of cycloheximide. On cell incubation with 125I-TNF, the intracellular quantity of the pulse-labeled TNF-receptor complex promptly increased, reaching a maximum at 20 min, and then gradually declined, thus confirming that the TNF receptor is internalized as a TNF-receptor complex in the presence of TNF. During incubations with protein synthesis suppressed by cycloheximide following surface TNF receptor digestion by trypsin, TNF receptors reappeared on the cell surface, increasing in number to a peak at 60 min and gradually decreasing, and cells previously exposed to cycloheximide with or without TNF showed no recurrence of surface TNF receptors, suggesting that the TNF receptor is non-recycling. The results of the study thus suggest that the TNF receptor is continuously internalized and degraded intracellularly by lysosomes without being recycled regardless of the presence or absence of TNF and, further, that its internalization is accelerated when it is part of the TNF-receptor complex.
在源自人肌肉肉瘤的对肿瘤坏死因子（TNF）敏感的KYM细胞中，研究了TNF受体的细胞动力学。在用环己酰亚胺抑制受体合成的情况下，在无TNF时表面TNF受体的半衰期为2小时，在有TNF时为30分钟，这表明TNF受体不会再循环，且TNF可加速其内化。在用氯喹抑制TNF受体降解的细胞孵育过程中，表面TNF受体的数量大致保持恒定，但表面和细胞内TNF受体的总数逐渐增加，3小时时达到初始数量的1.5倍，这表明在无环己酰亚胺的情况下，TNF受体持续进行合成、外化、内化和降解。在用125I-TNF孵育细胞时，脉冲标记的TNF受体复合物的细胞内含量迅速增加，在20分钟时达到最大值，然后逐渐下降，这证实了在有TNF存在时，TNF受体作为TNF-受体复合物被内化。在用胰蛋白酶消化表面TNF受体后，用环己酰亚胺抑制蛋白质合成进行孵育时，TNF受体重新出现在细胞表面，数量在60分钟时增加到峰值，然后逐渐减少，且之前暴露于有或无TNF的环己酰亚胺的细胞未出现表面TNF受体的再次出现，这表明TNF受体不会再循环。因此，该研究结果表明，无论有无TNF，TNF受体都会持续被内化并在细胞内被溶酶体降解，不会再循环，此外，当它作为TNF-受体复合物的一部分时，其内化会加速。
