FIG. 8.

p30 is enzymatically active and the new model of procaspase-8 activation at the CD95 DISC. (A) SKW6.4 cells were stimulated with LZ-CD95L for 1 h. BioVAD pulldown was analyzed by Western blotting using the anti-caspase-8 MAb C15 (*, unspecific band). (B) Procaspase-8 activation at the DISC involves two parallel cleavage pathways, which occur simultaneously and lead to the generation of the active p10₂-p18₂ heterotetramer. The first pathway of procaspase-8 processing comprises the well-described two-step mechanism (right side). The first cleavage occurs between the p18 and p10 subunits, which is followed by the second cleavage between the prodomain and the p18 subunit. The alternative second pathway of procaspase-8 activation involves the novel pathway described in this article (left side). In this pathway, the first cleavage occurs between the prodomain and the protease subunit of p18, which results in p30 generation. Subsequently, p30 is processed to p10 and p18. As the final step in both activation pathways, the active heterotetramer p10₂-p18₂ is formed, which is then released into the cytosol to propagate the apoptotic signal.