Overexpression of truncated IκBα induces TNF-α-dependent apoptosis in human vascular smooth muscle cells

Abstract

Dysregulation of apoptosis is one of the likely underlying mechanisms of neointimal thickening, a disorder in which proinflammatory cytokines may influence the function of vascular smooth muscle cells (VSMCs) and contribute to atherogenesis. One of these cytokines, tumor necrosis factor-α (TNF-α), induces 2 possibly conflicting pathways, 1 leading to the activation of nuclear factor-κB (NF-κB) and the other leading to caspase-mediated apoptosis. We investigated whether specific inhibition of NF-κB affects TNF-α-dependent apoptosis in human VSMCs. To inhibit NF-κB activation specifically, we constructed a recombinant adenovirus vector expressing a truncated form of the inhibitor protein IκBα (AdexIκBΔN) that lacks the phosphorylation sites essential for activation of NF-κB. The IκBΔN was overexpressed by adenoviral infection and was resistant to stimulus-dependent degradation. Electromobility gel shift and luciferase assays demonstrated that overexpression of IκBΔN inhibited NF-κB activation induced by TNF-α or interleukin-1β (IL-1β). In cells overexpressing IκBAN, TNF-α dramatically induced apoptosis, whereas IL-1β had no effect. The induction was suppressed by treatment with a selective inhibitor of the caspase-3 family, Z-DEVD-fmk, and the overexpression of IκBΔN induced TNF-α-mediated caspase-3 and caspase-2 activity. These results indicate that overexpression of IκBΔN induces TNF-α-dependent apoptosis by efficient and specific suppression of NF-κB and upregulation of caspase-3 and caspase-2 activity in human VSMCs. Our findings suggest that adenovirus-mediated IκBΔN gene transfer may be useful in the treatment of disorders associated with inflammatory conditions, such as the response to vascular injury and atherosclerosis.