Fibroblast growth factor-2 suppression of tumor necrosis factor alpha-mediated apoptosis requires Ras and the activation of mitogen-activated protein kinase

Treatment of L929 cells with tumor necrosis factor a (TNF alpha) activates a programmed cell death pathway resulting in apoptosis. We investigated the intracellular signaling pathways activated in L929 cells by TNF alpha. TNF alpha 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 TNF alpha 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 TNF alpha. FGF-2 substantially activated the Raf/MEK/MAPK (where MER is mitogen-activated protein kinase kinase) pathway but did not affect TNF alpha activation of JNK. These results indicate that although JNK may play an important role in transmitting the TNF alpha 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 TNF alpha 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 TNF alpha-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 TNF alpha-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.