Caspase-9 processing by caspase-3 via a feedback amplification loop in vivo

In contrast to the autoprocessing of caspase-9, little is known about the b iological significance of caspase-9 processing by caspase-3 via a feedback loop in vivo. We prepared antisera against mouse caspase-9 cleavage sites s o that only the activated form of mouse caspase-9 was recognized. Using the se antisera and caspase-9- and caspase-3-deficient mouse embryonic fibrobla sts, we demonstrated that mouse caspase-9 is initially autoprocessed at D-3 53 and D-368 at low levels during staurosporine-induced apoptosis, whereupo n the D-368 and D-168 sites are preferentially processed over D-353 by acti vated caspase-3 as part of a feedback amplification loop. Ac-DEVD-MCA (casp ase-3-like) and Ac-LEHD-MCA (caspase-9-like) cleavage activities clearly sh owed that caspase-9 autoprocessing was necessary for the activation of casp ase-3, whereas full activation of caspase-3 and caspase-9 was achieved only through the feedback amplification loop, This feedback amplification loop also played a predominant role during programmed cell death of dorsal root ganglia neurons at mouse embryonic day 11.5.