A Sustained Reduction in IκB-β May Contribute to Persistent NF-κB Activation in Human Endothelial Cells

It is concluded that TNF causes persistent activation of NF-κB in human EC and that this may result from sustained reductions in IκB-β levels.

Abstract

The responses of vascular endothelial cells (EC) to tumor necrosis factor-α (TNF), interleukin-1α (IL-1), and phorbol myristate acetate (PMA) were compared with respect to the kinetics of (i) NF-κB activation, (ii) IκB-α and IκB-β degradation, and (iii) NF-κB-dependent cell surface molecule expression. TNF rapidly (≤20 min) and persistently (>20 h) activates NF-κB; IL-1 rapidly activates NF-κB, but activity declines by 3 h and further by 20 h; PMA slowly and transiently activates NF-κB. Untreated EC contain the inhibitory proteins IκB-α and IκB-β. The onset of NF-κB activation correlates with degradation of IκB-α, but IκB-α reappears by 4 h without resequestration of NF-κB. TNF causes a rapid but partial (50%) reduction in IκB-β, which does not recover by 22 h; IL-1 and PMA cause slower and less sustained reductions in IκB-β. All three agonists induce de novo expression of E-selectin (CD62E) and vascular cell adhesion molecule-1 (CD106) and increase expression of intercellular adhesion molecule-1 (CD54) at 4 h. TNF induces sustained increases in vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 and increases human leukocyte antigen class I molecules at 24 h. We conclude that TNF causes persistent activation of NF-κB in human EC and that this may result from sustained reductions in IκB-β levels. The responses of vascular endothelial cells (EC) to tumor necrosis factor-α (TNF), interleukin-1α (IL-1), and phorbol myristate acetate (PMA) were compared with respect to the kinetics of (i) NF-κB activation, (ii) IκB-α and IκB-β degradation, and (iii) NF-κB-dependent cell surface molecule expression. TNF rapidly (≤20 min) and persistently (>20 h) activates NF-κB; IL-1 rapidly activates NF-κB, but activity declines by 3 h and further by 20 h; PMA slowly and transiently activates NF-κB. Untreated EC contain the inhibitory proteins IκB-α and IκB-β. The onset of NF-κB activation correlates with degradation of IκB-α, but IκB-α reappears by 4 h without resequestration of NF-κB. TNF causes a rapid but partial (50%) reduction in IκB-β, which does not recover by 22 h; IL-1 and PMA cause slower and less sustained reductions in IκB-β. All three agonists induce de novo expression of E-selectin (CD62E) and vascular cell adhesion molecule-1 (CD106) and increase expression of intercellular adhesion molecule-1 (CD54) at 4 h. TNF induces sustained increases in vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 and increases human leukocyte antigen class I molecules at 24 h. We conclude that TNF causes persistent activation of NF-κB in human EC and that this may result from sustained reductions in IκB-β levels.