Penta-acetyl geniposide-induced apoptosis involving transcription of NGF/p75 via MAPK-mediated AP-1 activation in C6 glioma cells

We have demonstrated the herbal derivative penta-acetyl geniposide ((Ac)5GP) induces C6 glioma cell apoptosis through the critical sphingomyelinase (SMase)/nerve growth factor (NGF)/p75 and its downstream signals. It has been reported mitogen-activated protein kinase (MAPK) mediates NGF synthesis induced by SMase activation. In this study, ERK, p38 and JNK are shown to mediate (Ac)5GP-induced glioma cell apoptosis and elevation of NGF and p75. Treatment of PD98059 (ERK-specific inhibitor), SB203580 (p38 MAPK inhibitor) and SP600125 (JNK inhibitor) decreases the elevation of NGF and p75 mRNA induced by (Ac)5GP, indicating possible transcription regulation via MAPKs. The results of nuclear extract blotting and EMSA further confirm (Ac)5GP maximally increases AP-1 and NF-κB DNA binding at 6 h. Inhibition of ERK, p38 and JNK block the activation of AP-1 and NF-κB, suggesting these MAPKs are involved in (Ac)5GP-induced transcription regulation. We thereby used RT-PCR to analyze cells treated with (Ac)5GP, with or without AP-1 or NF-κB inhibitors. AP-1 inhibitor NDGA decreases NGF/p75 and expression of FasL and caspase 3 induced by (Ac)5GP, suggesting the importance of AP-1 in mediating NGF/p75 and their downstream apoptotic signals. However, FasL and caspase 3 do not change with the NF-κB inhibitor PDTC; NF-κB might be linked to other cellular events. Overall, we demonstrate that MAPK mediates (Ac)5GP-induced activation of AP-1, promoting the transcription of NGF/p75 and downstream apoptotic signals. These results further highlight the potential therapeutic effects of (Ac)5GP in chemoprevention or as an anti-tumor agent.