Protein kinase C isoenzymes in human neuroblasts involvement of PKCε in cell differentiation

AbstractAlthough neuronal cells are a major target of phorbol ester action, the activity of the various protein kinase C (PKC) isoenzymes have not been studied in detail in human neuroblasts. Differentiation of the LAN-5 human neuroblastoma cell line by interferon-γ (IFN-γ) is accompanied by a twofold increase in PKC activity. Since PKC is a multigene family, we investigated which isoforms were expressed in control and differentiated cells, and which of these isoenzymes is involved in neuronal differentiation. We found that: (1) PKC activity is higher in differentiated than in undifferentiated cells; (2) RT-PCR analysis showed the expression of mRNA for PKCα, -γ, -δ -ε and-ζ and the absence of mRNA for β in untreated LAN-5 cells; (3) Western blot evaluation with PKC isoform-specific antibodies showed the same pattern of PKC expression in non-differentiated cells; (4) Expression of PKCε mRNA was significantly enhanced by IFN-γ-induced differentiation, while the other isoforms were not affected; (5) Differentiation of LAN-5 cells with IFN-γ or retinoic acid induced overexpression of the PKCε protein, while inhibition of cell proliferation by fetal calf serum starvation was without effect. These findings suggest that expression of PKCε isoform is tightly coupled with neuronal differentiation and may play a role in the maintenance of the differentiated state

Poliovirus morphogenesis. I. Identification of 80S dissociable particles and evidence for the artefactual production of procapsids

The current model of poliovirus morphogenesis postulates a fundamental role for procapsid, 80S shells that, upon interaction with viral RNA and subsequent proteolytic cleavage, give rise to complete virus particles. Although 80S sedimenting particles can, indeed, be isolated from cytoplasmic extracts of infected cells, their physical properties differ from those reported for procapsids. Far from being stable structures, they can be dissociated by pH 8.5 and 0.1% sodium dodecyl sulfate into slower-sedimenting subunits. The reasons for this discrepancy were investigated, and two main modalities leading to the appearence of procapsids in vitro were identified. The first involves a temperature-mediated conversion of dissociable 80S particles into stable 80S procapsids, and the second involves the self-assembly of endogenous 14S subunits, also primed by an increase in the temperature of cytoplasmic extracts