Expression of protein kinase C isoforms in euxanthone-induced differentiation of neuroblastoma cells

Euxanthone, a potent neuritogenic compound isolated from the roots of the medicinal herb Polygala caudata, has recently been shown to induce the differentiation of murine neuroblastoma Neuro 2A (BU-1) cells. In this study, the role of protein kinase C (PKC) and the expression of various PKC isoforms in euxanthone-treated BU-1 cells were examined, mRNA phenotyping using the reverse-transcription polymerase chain reaction (RT-PCR) showed that BU-1 cells express six different PKC isoforms, namely PKC-α, -β, -δ, -ε, -λ, and -ζ, Differential regulation and expression of PKC isoforms was observed in BU-1 cells treated with 100 μM euxanthone. PKC-α, -β, -δ, -λ, and -ζ were all up-regulated, with 1.7- to 9.5-fold increase, at around 30 to 60 minutes after euxanthone treatment. The expression level of PKC-ε remained relatively constant during the treatment. PKC-γ -η, and -Θ were not detected in both untreated and euxanthone-treated BU-1 cells. Staurosporine, a broad spectrum PKC inhibitor, was found to inhibit both spontaneous and euxanthone-induced neuritogenesis in BU-1 cells. A significant reduction of the euxanthone-induced neuritogenic effect was also observed when the PKC isoform-specific inhibitor Go6976 was included in the culture. These results suggest that the euxanthone-induced differentiation of the neuroblastoma BU-1 cells may be mediated through the differential expression of PKC-α, -β, -δ, -λ and -ζ isoforms.