Divergence in the anti-apoptotic signalling pathways used by nerve growth factor and basic fibroblast growth factor (bFGF) in PC12 cells: rescue by bFGF involves protein kinase Cδ

The mechanisms whereby nerve growth factor (NGF) and basic fibroblast growth factor (bFGF) block apoptosis in serum-deprived PC12 cells were investigated. NGF, but not bFGF, strongly activated Akt/protein kinase B, a downstream effector of phosphoinositide (phosphatidylinositol) 3-kinase (PI 3-kinase). In addition, inhibition of PI 3-kinase by LY294002 partially blocked inhibition of apoptosis by NGF, but not that by bFGF, suggesting divergence in NGF and bFGF anti-apoptotic signalling pathways. Both growth factors strongly activated mitogen-activated protein (MAP) kinases, but blockade of signalling through this pathway, either by the expression of dominant-negative Ras or by treatment with the MAP kinase/ERK kinase (MEK) inhibitor U0126, partially inhibited only bFGF, but not NGF, anti-apoptotic signalling. Use of isoform-specific protein kinase C (PKC) inhibitors such as bisindoylmaleimide-I and Gö 6983 suggested that PKCδ is a likely component of bFGF trophic signalling. A role for PKCδ was confirmed in PC12 cells expressing a dominant-negative PKCδ fragment, in which reversal of apoptosis by bFGF was partially blocked. The PKCδ signal was not mediated by the MAP kinase cascade, as bFGF activation of this pathway was not affected in cells expressing the dominant-negative PKCδ fragment. Full inhibition of bFGF anti-apoptotic signalling occurred when both the PKCδ and Ras/MAP kinase pathways were inhibited. Together, these data demonstrate that inhibition of apoptosis by bFGF in PC12 cells operates differently from that mediated by NGF, requiring the addition of signals from both the Ras/MAP kinase and PKC signalling pathways.