NF-κB activation in tumor necrosis factor α-stimulated neutrophils is mediated by protein kinase Cδ -: Correlation to nuclear IκBα

The transcription factor NF-kappaB is critical for the expression of multiple genes involved in inflammatory responses and apoptosis. However, the signal transduction pathways regulating NF-kappaB activation in human neutrophils in response to stimulation with tumor necrosis factor-alpha (TNF alpha) are undefined. Since recent studies implicated activation of NP-kappaB as well as protein kinase C-delta (PKC delta) in neutrophil apoptosis, we investigated involvement of PKC delta in the activation of NF-kappaB in TNF alpha -stimulated neutrophils. Specific inhibition of PKC delta by rottlerin prevented I kappaB alpha degradation and NF-kappaB activation in TNF alpha -stimulated neutrophils. This regulation of NF-kappaB activation by PKC delta was specific only for TNF alpha signaling, since lipopolysaccharide- or interleukin-1 beta -induced NF-kappaB activation and I kappaB alpha degradation were not inhibited by rottlerin. In addition, we show that in human neutrophils, but not monocytes, I kappaB alpha localizes in significant amounts in the nucleus of unstimulated cells, and the amount of I kappaB alpha in the nucleus, as well as in the cytoplasm, correlates with the NF-kappaB DNA binding. These results suggest that in human neutrophils, the presence of I kappaB alpha in the nucleus may function as a safeguard against initiation of NF-kappaB dependent transcription of pro-inflammatory and anti-apoptotic genes, and represents a distinct and novel mechanism of NF-kappaB regulation.