Protein kinase Cμ downregulation of tumor-necrosis-factor-induced apoptosis correlates with enhanced expression of nuclear-factor-κB-dependent protective genes

Abstract

Protein kinase Cμ (PKCμ) 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 PKCμ in signal-transduction pathways, stable PKCμ 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-κB-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 PKCμ transfectants. In support of a PKCμ action on NF-κB, we show enhancement and downregulation of TNF-induced expression of a NF-κB- dependent reporter gene by transient overexpression of wild-type and kinase- negative mutants of PKCμ, respectively. Interestingly, no significant changes were found m an electrophoretic mobility shift assay, indicative of PKCμ action downstream of IκB degradation, probably by modulation of the transactivation capacity of NF-κB The dominant negative action of the kinase-negative mutant further suggest a regulatory role of PKCμ for NF- κB-dependent gene expression.