Protein kinase Cmu downregulation of tumor-necrosis-factor-induced apoptosis correlates with enhanced expression of nuclear-factor-kappaB-dependent protective genes.

Protein kinase Cmu (PKCmu) represents a new subtype of the PKC family characterized by the presence of a pleckstrin homology (PH) domain and an amino-terminal hydrophobic region. In order to analyse the potential role of PKCmu in signal-transduction pathways, stable PKCmu transfectants were established with human and murine cell lines. All transfectants showed a reduced sensitivity to tumor-necrosis-factor (TNF)-induced apoptosis, which correlated with the amount of transgene expressed and with an enhanced basal transcription rate of NF-kappaB-driven genes including the inhibitor of apoptosis protein 2 (cIAP2) and TNF-receptor-associated protein 1 (TRAF1). Sensitivity to apoptosis induced by the lipid mediator ceramide was unchanged in PKCmu transfectants. In support of a PKCmu action on NF-kappaB, we show enhancement and downregulation of TNF-induced expression of a NF-kappaB-dependent reporter gene by transient overexpression of wild-type and kinase-negative mutants of PKCmu, respectively. Interestingly, no significant changes were found in an electrophoretic mobility shift assay, indicative of PKCmu action downstream of IkappaB degradation, probably by modulation of the transactivation capacity of NF-kappaB. The dominant negative action of the kinase-negative mutant further suggest a regulatory role of PKCmu for NF-kappaB-dependent gene expression.