Selective sensitization to tumor necrosis factor-α-induced apoptosis by blockade of NF-κB in primary glomerular mesangial cells

Recent data have implicated nuclear factor kappa B (NF-kappa B) in the prevention of apoptosis in transformed cell lines exposed to tumor necrosis factor alpha (TNF-alpha). However, it is obscure whether NF-kappa B plays an anti-apoptotic role in nontransformed cells, and it is not clear whether NF-kappa B inhibits apoptosis triggered by other mediators. We investigated the effect of specific inhibition of NF-kappa B on cytokine-induced apoptosis of glomerular mesangial cells, which is important in determining the outcome of glomerulonephritis. Cultured rat mesangial cells were stably transfected with the dominant negative mutant inhibitor of NF-kappa B (I kappa B alpha M), I kappa B alpha M was resistant to stimulus-dependent degradation and suppressed NF-kappa B activation induced by TNF-alpha (10 ng/ml) or IL-1 beta (10 ng/ml), I kappa B alpha M significantly sensitized mesangial cells to TNF-alpha-induced apoptosis in a dose- and time-dependent manner but had no significant effects on the level of apoptosis in the presence of proinflammatory or apoptosis-inducing stimuli including Fas ligand, IL-1 alpha, IL-1 beta, hydrogen peroxide, lipopolysaccharide, cycloheximide, or serum deprivation, Moreover, I kappa B alpha M-mediated sensitization to TNF-alpha overcame the protective effect of mesangial cell survival factors present in serum, which usually inhibit killing of mesangial cells by the proapoptotic stimuli used. These data show that inhibition of NF-kappa B selectively sensitizes primary adult glomerular mesangial cells to TNF-induced apoptosis but not to other mediators of cell death including the Fas ligand.