Protein kinase C beta1 is implicated in the regulation of neuroblastoma cell growth and proliferation

To investigate a putative involvement of protein kinase C (PKC) isoforms in supporting neuroblastoma cell proliferation, SK-N-BE(2) neuroblastoma cells were transfected with expression vectors coding for the C2 and V5 regions from different PKC isoforms. These structures have been suggested to inhibit the activity of their corresponding PKC isoform. The PKC fragments were fused to enhanced green fluorescent protein to facilitate the detection of transfected cells. Expression of the C2 domain from a classical PKC isoform (PKCalpha), but not of C2 domains from novel PKCdelta or PKCepsilon, suppressed the number of neuroblastoma cells positive for cyclin A and bromodeoxyuridine incorporation. This indicates a role for a classical isoform in regulating proliferation of these cells. Among the V5 fragments from PKCalpha, PKCbetaI, and PKCbetaII, the PKCbetaI V5 had the most suppressive effect on proliferation markers, and this fragment also displaced PKCbetaI from the nucleus. Furthermore, a PKCbeta-specific inhibitor, LY379196, suppressed the phorbol ester- and serum-supported growth of neuroblastoma cells. There was a marked enhancement by LY379196 of the growth-suppressive and/or cytotoxic effects of paclitaxel and vincristine. These results indicate that PKCbetaI has a positive effect on the growth and proliferation of neuroblastoma cells and demonstrate that inhibition of PKCbeta may be used to enhance the effect of microtubule-interacting anticancer agents on neuroblastoma cells.