Belka C, Wiegmann K, Adam D, Holland R, Neuloh M, Herrmann F, Krönke M, Brach M A
Abteilung für Medizinische Onkologie und Angewandte Molekularbiologie, Freie Universität Berlin, Germany.
EMBO J. 1995 Mar 15;14(6):1156-65. doi: 10.1002/j.1460-2075.1995.tb07099.x.
TNF-alpha mediates proliferation, functional activation and apoptotic death of cells depending upon its concentration and target cell type. The signaling pathways used by TNF-alpha to mount these responses are, at present, not completely understood. We report here that TNF-alpha promotes dose- and time-dependent phosphorylation and activation of the c-raf-1 kinase engaging the type I p55 TNF receptor (TNF-R). c-raf-kinase activation was duplicated by an agonistic monoclonal antibody directed against the p55 TNF-R. Moreover, ectopic expression of the human p55 TNF-R in murine pre-B 70Z/3 cells was sufficient to confer c-raf-1-kinase activation by human TNF-alpha. By inhibiting intracellular activation of acidic sphingomyelinase (SMase) and by using deleted forms of the type I TNF-R it was shown that the neutral, but not the acidic SMase, participated in TNF-alpha-mediated phosphorylation and activation of the c-raf kinase. TNF-alpha-induced transcriptional activation of a heterologous promoter construct harboring the AP-1 binding site was also mediated by the type I p55 TNF-R. In this case the initiation of transcription required the same cytoplasmic domain as that responsible for activation of c-raf-1 kinase and was liberated in the presence of a dominant negative mutant of c-raf-1.
肿瘤坏死因子-α（TNF-α）根据其浓度和靶细胞类型介导细胞的增殖、功能激活和凋亡死亡。目前，TNF-α引发这些反应所使用的信号通路尚未完全明确。我们在此报告，TNF-α通过与I型p55肿瘤坏死因子受体（TNF-R）结合，促进c-raf-1激酶的剂量和时间依赖性磷酸化及激活。针对p55 TNF-R的激动性单克隆抗体可复制c-raf激酶的激活。此外，在小鼠前B细胞70Z/3细胞中异位表达人p55 TNF-R足以使人TNF-α激活c-raf-1激酶。通过抑制酸性鞘磷脂酶（SMase）的细胞内激活并使用I型TNF-R的缺失形式，结果表明中性而非酸性SMase参与了TNF-α介导的c-raf激酶的磷酸化和激活。TNF-α诱导的含有AP-1结合位点的异源启动子构建体的转录激活也由I型p55 TNF-R介导。在这种情况下，转录起始需要与负责激活c-raf-1激酶相同的细胞质结构域，并且在c-raf-1的显性负突变体存在时被释放。
