NFκB Signaling in Posthypoxic Endothelial Cells: Relevance to E-Selectin Expression and Neutrophil Adhesion

Abstract

Our previous studies have implicated the nuclear transcription factor ĸB (NFĸB) in the regulation of adhesion molecule expression in endothelial cells exposed to anoxia-reoxygenation (A/R) or a redox imbalance. The objectives of this study were (1) to define the kinetics of NFĸB activation by examining IĸBα degradation and the nuclear translocation of p65 in response to A/R or redox imbalance (induced by treatment of cells with diamide and buthionine sulfoximine) and (2) to determine whether the signal for IĸBα degradation, nuclear translocation of p65, and E-selectin-mediated neutrophil adhesion is related to the activity of protein tyrosine kinase (PTK), protein tyrosine phosphatase (PTPase) and/or protein kinase C (PKC). The results demonstrate that both A/R and redox imbalance led to IĸBα degradation within 30 min and the concomitant appearance of p65 in the nucleus, consistent with rapid cytosolic activation of NFĸB and subsequent nuclear translocation of the activated p65 subunit. Inhibition of PKC blocked IĸBα degradation and p65 translocation in A/R-challenged, but not redox-altered, endothelial cells. However, both A/R- and redox-induced NFĸB activation was blocked by inhibition of PTK. Similarly, A/R-induced E-selectin expression and neutrophil-endothelial cell adhesion were blocked by inhibition of PKC or PTK, while only PTK inhibited the redox-induced adhesion response. Pretreatment of cells with N-acetyl cysteine effectively blocked A/R- or redox-induced IĸB degradation and significantly attenuated the respective neutrophil adhesion responses. Collectively, these findings indicate that A/R-induced E-selectin expression and neutrophil-endothelial cell adhesion are mediated by both PKC and PTK, which signal rapid activation of NFĸB. This A/R-induced NFĸB signaling response appears to be mediated, at least in part, by intracellular redox imbalance.