Overexpression of truncated I kappa B alpha induces TNF-alpha-dependent apoptosis in human vascular smooth muscle cells

Dysregulation of apoptosis is one of the likely underlying mechanisms of ne ointimal thickening, a disorder in which proinflammatory cytokines may infl uence the function of vascular smooth muscle cells (VSMCs) and contribute t o atherogenesis. One of these cytokines, tumor necrosis factor-alpha (TNF-a lpha), induces 2 possibly conflicting pathways, 1 leading to the activation of nuclear factor-kappaB (NF-kappaB) and the other leading to caspase-medi ated apoptosis. We investigated whether specific inhibition of NF-kappaB af fects TNF-alpha -dependent apoptosis in human VSMCs. To inhibit NF-kappaB a ctivation specifically, we constructed a recombinant adenovirus vector expr essing a truncated form of the inhibitor protein I kappaB alpha (AdexI kapp aB DeltaN) that lacks the phosphorylation sites essential for activation of NF-kappaB. The I kappaB DeltaN was overexpressed by adenoviral infection a nd was resistant to stimulus-dependent degradation. Electromobility gel shi ft and luciferase assays demonstrated that overexpression of I kappaB Delta N inhibited NF-kappaB activation induced by TNF-alpha or interleukin-1 beta (IL-1 beta). In cells overexpressing I kappaB DeltaN, TNF-alpha dramatical ly induced apoptosis, whereas IL-1 beta had no effect. The induction was su ppressed by treatment with a selective inhibitor of the caspase-3 family, Z -DEVD-fmk, and the overexpression of I kappaB DeltaN induced TNF-alpha -med iated caspase-3 and caspase-2 activity. These results indicate that overexp ression of I kappaB DeltaN induces TNF-alpha -dependent apoptosis by effici ent and specific suppression of NF-kappaB and upregulation of caspase-3 and caspase-2 activity in human VSMCs. Our findings suggest that adenovirus-me diated I kappaB DeltaN gene transfer may be useful in the treatment of diso rders associated with inflammatory conditions, such as the response to vasc ular injury and atherosclerosis.