Bcl-2 prevents CD95 (Fas/APO-1)-induced degradation of lamin B and poly (ADP-ribose) polymerase and restores the NF-κB signaling pathway

Abstract

In the study presented here, we investigated the possible interactions between CD95 (Fas/APO-1) and Bcl-2 by studying the effects of Bcl-2 on the modulation of cellular pathways activated by CD95 using HeLa cells as a model system. We report that stable expression of Bcl-2 in HeLa cells is associated with multiple phenotypic changes. Treatment of HeLa cells with anti-CD95 monoclonal antibody (mAb) resulted in preferential degradation of lamin B compared with lamins A and C. Significant lamin B degradation was detected as early as 1 h after anti-CD95 mAb treatment. In contrast, lamins A and C as well as actin remained unchanged until 4 h after treatment with anti-CD95 mAb, a time point that correlated with the period of DNA fragmentation. These results indicate that selective degradation of lamin B is an early cellular event in response to activation of the CD95 pathway and that it precedes DNA fragmentation. Overexpression of Bcl-2 resulted in prevention of lamin B degradation and DNA fragmentation into oligonucleosome fragments in response to the apoptotic signal by anti-CD95 mAb. In addition, in Bcl-2-overexpressing cells that were protected against apoptosis, anti-CD95 mAb-induced cleavage of poly(ADP-ribose) polymerase was completely blocked. Overexpression of Bcl-2 also resulted in restoration of the CD95-mediated signaling pathway involving activation of the transcription factor NF-κB (p50/RelA). These findings suggest that Bcl-2 prevents apoptosis in part by preventing the degradation of major nuclear polypeptides such as lamin B and poly(ADP-ribose) polymerase. In addition, our results demonstrate that CD95-mediated signaling involves activation of NF-κB (p50/RelA).