ERK-like MAPK signaling and cytochrome c response to oleic acid in two-liquid-phase suspension cultures of Taxus cuspidata

To elucidate the underlying signal mechanisms of Taxus cuspidata in response to oleic acid (OA) in two-liquid-phase suspension cultures (TLPSCs), the mitogen-activated protein kinase (MAPK) activation and release of cytochrome c (CytC) from mitochondria in TLPSC T. cuspidata were investigated with Western blot. The results showed that a long-term treatment with 4% (v/v) OA caused apoptosis and release of CytC from mitochondria and inhibited the activation of extracellular signal-regulated kinase-like (ERK-like) MAPK (approximately 46 kDa) in TLPSC of T. cuspidata, but a short-term treatment significantly increased the ERK-like MAPK activity. These findings suggest that the coordinate expression of p-ERK and CytC is fundamentally involved in cell survival or death in TLPSC T. cuspidata. Further investigation confirmed that anthracene-9-carboxylate (an ion-channel blocker) and suramin (a G-protein inhibitor) markedly blocked the ERK-like MAPK activity, inhibited DNA ladder formation and O2− burst and reduced Taxol production. Although diphenyliodonium (an inhibitor of O2− formation) successfully blocked DNA ladder formation and decreased Taxol production, it did not significantly affect the ERK-like MAPK activity, indicating that the ERK-like MAPK activation should depend on the OA-stimulated G-protein and ion-channel activity, but not on the oxidative burst during the apoptosis and Taxol production in TLPSC T. cuspidata cells.