English B K, Weaver W M, Wilson C B
Department of Pediatrics, University of Washington, Seatle.
J Biol Chem. 1991 Apr 15;266(11):7108-13.
Lymphotoxin (LT) and tumor necrosis factor (TNF) are related cytokines that share many biological effects. The genes for LT and TNF are adjacent to each other on chromosome 6 in man, but previous data indicate that the kinetics of their production differ markedly. To explain the mechanisms for this difference, we compared the regulation of these two genes in human T lymphocytes, isolated from peripheral blood, after stimulation with the mitogens concanavalin A and phorbol myristate acetate. Differences in the kinetics of protein secretion were paralleled by differences in cognate mRNA accumulation. TNF mRNA accumulated rapidly after stimulation, peaked by 6 h, and returned to unstimulated (base-line) levels by 24 h. In contrast, LT mRNA accumulated slowly after stimulation, usually peaked at approximately 18 h, and remained increased above base-line levels at 48-72 h. By nuclear transcription run-on assays, increased transcription of TNF mRNA and LT mRNA was demonstrated after stimulation. However, TNF transcription peaked earlier and appeared to be 4-10 times greater than that of the LT gene. In contrast, the half-life of LT mRNA was 8-10-fold longer than that of TNF mRNA as demonstrated by actinomycin D pulse-chase experiments. Cycloheximide did not block LT or TNF mRNA accumulation, indicating that new protein synthesis was not required for induction of either gene. These results suggest strongly that the LT and TNF genes are regulated differently in human T lymphocytes after mitogen stimulation. TNF mRNA accumulates rapidly primarily because of increased transcription and decreases rapidly related to its brief half-life. In contrast, LT mRNA accumulates more slowly but persists much longer; the accumulation of this mRNA appears to be controlled largely by post-transcriptional mechanisms.
淋巴毒素（LT）和肿瘤坏死因子（TNF）是具有许多共同生物学效应的相关细胞因子。在人类中，LT和TNF的基因在6号染色体上彼此相邻，但先前的数据表明它们产生的动力学有显著差异。为了解释这种差异的机制，我们比较了从外周血分离的人T淋巴细胞在受到促有丝分裂原刀豆球蛋白A和佛波酯刺激后这两个基因的调控情况。蛋白质分泌动力学的差异与相应mRNA积累的差异平行。刺激后TNF mRNA迅速积累，6小时达到峰值，24小时回到未刺激（基线）水平。相比之下，LT mRNA在刺激后积累缓慢，通常在大约18小时达到峰值，并在48 - 72小时保持高于基线水平。通过核转录连续分析，刺激后证明TNF mRNA和LT mRNA的转录增加。然而，TNF转录峰值出现得更早，似乎比LT基因的转录大4 - 10倍。相反，放线菌素D脉冲追踪实验表明，LT mRNA的半衰期比TNF mRNA长8 - 10倍。放线菌酮不阻断LT或TNF mRNA的积累，表明这两个基因的诱导不需要新的蛋白质合成。这些结果强烈表明，在有丝分裂原刺激后人T淋巴细胞中LT和TNF基因的调控方式不同。TNF mRNA迅速积累主要是因为转录增加，并且由于其短暂的半衰期而迅速下降。相比之下LT mRNA积累较慢但持续时间长得多；这种mRNA的积累似乎在很大程度上受转录后机制控制。
