Investigation of signalling cascades induced by neurotrophic synaptolepis factor K7 reveals a critical role for novel PKCε

Abstract

This study elucidates signalling cascades involved in the neurotrophic effects induced by an active compound of Synaptolepis kirkii, a plant that is used against snakebites and for treatment of epilepsy. The active compound of this plant, synaptolepis factor K7 (K7), is suggested to exert anti-tumoral and neurotrophic actions via modulation of PKC. In SH-SY5Y cells synthesis of the neuronal marker growth-associated protein 43 was increased upon 48h treatment with K7. Immunofluorescent staining of neurites revealed an increased neurite formation by synaptolepis factor K7. Short-term signal transduction events were followed at the level of extracellular-regulated kinase phosphorylation. Extracellular-regulated kinase (ERK) phosphorylation was transiently increased upon stimulation with synaptolepis factor K7 (300nM) with a maximal effect at 30min. Use of the general PKC inhibitor bisindolylmaleimide I blocked the K7-induced ERK phosphorylation suggesting involvement of PKC. Conversely, inhibition of conventional PKCs, α, β and γ by treatment with Go6976 did not inhibit ERK phosphorylation up to 1μM. Use of a specific-PKCε translocation inhibitor peptide or RNAi-mediated knockdown of PKC-epsilon (ε) abolished the K7-induced ERK phosphorylation implicating PKCε in K7 function. This was confirmed by the observed increase in PKCε translocation and autophosphorylation induced by the compound. These data show that synaptolepis factor K7 induces neuronal differentiation of SH-SY5Y cells concomitant with a transient increase in ERK phosphorylation that is mediated by activation of PKCε.