beta(II) protein kinase C is required for the G(2)/M phase transition of cell cycle

Entry into mitosis requires the coordinated action of multiple mitotic protein kinases, In this report, we investigate the involvement of protein kinase C in the control of mitosis in human cells, Treatment of synchronized HL60 cells with the highly selective protein kinase C (PKC) inhibitor chelerythrine chloride leads to profound cell cycle arrest in G(2) phase. The cellular effects of chelerythrine are not due to either direct or indirect inhibition of the known mitotic regulator p34(cdc2)/cyclin B kinase, Rather, several lines of evidence demonstrate that chelerythrine-mediated G(2) phase arrest results from selective inhibition and degradation of beta(II) protein kinase C. First, chelerythrine causes dose-dependent inhibition of beta(II) PKC in vitro with an IC50 identical to that for G(2) phase blockade in whole cells, Second, chelerythrine specifically inhibits beta(II) PKC-mediated lamin B phosphorylation and mitotic nuclear lamina disassembly, Third, chelerythrine leads to selective loss of beta(II) PKC during G, phase in synchronized cells, Fourth, chelerythrine mediates activation-dependent degradation of PKC, indicating that beta(II) PKC is selectively activated during G, phase of cell cycle, Taken together, these data demonstrate that beta(II) PKC activation at G(2) phase is required for mitotic nuclear lamina disassembly and entry into mitosis and that beta(II) PKC-mediated phosphorylation of nuclear lamin B is important in these events.