Gardner A M, Johnson G L
Division of Basic Sciences, National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206, USA.
J Biol Chem. 1996 Jun 14;271(24):14560-6. doi: 10.1074/jbc.271.24.14560.
Treatment of L929 cells with tumor necrosis factor alpha (TNFalpha) activates a programmed cell death pathway resulting in apoptosis. We investigated the intracellular signaling pathways activated in L929 cells by TNFalpha. TNFalpha robustly activates Jun kinase (JNK), a member of the mitogen-activated protein kinase (MAPK) family. In addition, p42(MAPK) is activated, but a 10-fold greater concentration of TNFalpha was required for substantial MAPK activation than was needed for maximal JNK stimulation. Simultaneous treatment of L929 cells with fibroblast growth factor (FGF-2) significantly reduced the apoptotic response to TNFalpha. FGF-2 substantially activated the Raf/MEK/MAPK (where MEK is mitogen-activated protein kinase kinase) pathway but did not affect TNFalpha activation of JNK. These results indicate that although JNK may play an important role in transmitting the TNFalpha signal from the cell surface to the nucleus, activation of the JNK pathway is not sufficient to induce apoptosis. Expression of dominant-negative Asn-17 Ras in L929 cells diminished the FGF-2 stimulation of p42(MAPK) and eliminated the protective effect of FGF-2. Asn-17 Ras expression did not affect JNK activity and had no effect on TNFalpha activation of JNK. Pharmacological inhibition of MEK-1 activity by incubation of cells with the compound PD 098059 blocked p42(MAPK) activation and FGF-2 protection against apoptosis. Interestingly, activated Val-12 Ras expression substantially enhanced TNFalpha-mediated apoptosis in L929 cells, but Val-12 Ras did not constitutively activate MAPK in L929 cells and FGF-2 partially protected Val-12 Ras-expressing cells from TNFalpha-mediated apoptosis. Our data indicate that activation of the MAPK pathway mediates an FGF-2 protective effect against apoptosis and highlights the important role that integration of multiple intracellular signaling pathways plays in the regulation of cell growth and death.
用肿瘤坏死因子α（TNFα）处理L929细胞会激活程序性细胞死亡途径，导致细胞凋亡。我们研究了TNFα在L929细胞中激活的细胞内信号通路。TNFα能强力激活丝裂原活化蛋白激酶（MAPK）家族成员Jun激酶（JNK）。此外，p42（MAPK）也被激活，但与最大程度激活JNK相比，大量激活MAPK所需的TNFα浓度要高10倍。用成纤维细胞生长因子（FGF-2）同时处理L929细胞可显著降低对TNFα的凋亡反应。FGF-2能大量激活Raf/MEK/MAPK（其中MEK是丝裂原活化蛋白激酶激酶）途径，但不影响TNFα对JNK的激活。这些结果表明，尽管JNK可能在将TNFα信号从细胞表面传递到细胞核中起重要作用，但JNK途径的激活不足以诱导细胞凋亡。在L929细胞中表达显性负性Asn-17 Ras可减弱FGF-2对p42（MAPK）的刺激，并消除FGF-2的保护作用。Asn-17 Ras的表达不影响JNK活性，对TNFα激活JNK也无影响。用化合物PD 098059孵育细胞对MEK-1活性进行药理学抑制可阻断p42（MAPK）的激活以及FGF-2对细胞凋亡的保护作用。有趣的是，激活的Val-12 Ras表达可显著增强L929细胞中TNFα介导的细胞凋亡，但Val-12 Ras在L929细胞中不会组成性激活MAPK，且FGF-2可部分保护表达Val-12 Ras的细胞免受TNFα介导的细胞凋亡。我们的数据表明，MAPK途径的激活介导了FGF-2对细胞凋亡的保护作用，并突出了多种细胞内信号通路的整合在细胞生长和死亡调节中所起的重要作用。
