Effect of NF-kappa B inhibition on TNF-alpha-induced apoptosis in human RPE cells.

Abstract

In many cell types, tumor necrosis factor (TNF)-alpha-induced apoptosis is prevented by production of TNF-alpha-induced antiapoptotic protein, a process mediated by nuclear transcription factor (NF)-kappa B. TNF-alpha is widely expressed in proliferative vitreoretinopathy (PVR) membranes and is present in the vitreous of eyes with PVR. To understand mechanisms responsible for RPE cell survival and death in this disease, this study was conducted to determine whether specific NF-kappa B blockade by mutant inhibitory (I)-kappa B (I kappa B) affects TNF-alpha-induced cell death. Cultured human RPE cells and T-98G cells were infected with adenovirus encoding either beta-galactosidase or mutant I kappa B and then treated with TNF-alpha or interleukin (IL)-1 beta. I kappa B, inhibitor of apoptosis protein (IAP)-1, and cellular Fas-associated death domain-like interleukin-1 beta-converting enzyme-like inhibitory protein (c-FLIP) expression was determined by Western blot. Functional NF-kappa B activation was examined by luciferase reporter assay. Cell viability was evaluated by trypan blue exclusion assay. Caspase-3 activity and DNA fragmentation was measured with an enzyme-linked immunosorbent assay. Mutant I kappa B expression blocked cytokine-induced I kappa B degradation and NF-kappa B transcriptional activity in RPE cells and T-98G cells. RPE cells were resistant to TNF-alpha-induced apoptosis, even after NF-kappa B activation was specifically blocked. In contrast, TNF-alpha dramatically induced apoptosis in T-98G cells after NF-kappa B inhibition. c-IAP1 expression was not affected by TNF-alpha or mutant I kappa B, and mutant I kappa B abolished TNF-alpha-induced c-FLIP induction in RPE cells. RPE cells are resistant to TNF-alpha-induced cell death, even after NF-kappa B activation is specifically blocked. RPE cell resistance to apoptotic signals present in eyes with PVR, mediated by survival factors such as c-FLIP and c-IAP1, may help to explain unwanted and unchecked cell proliferation in this disease.