Biochemical and genetic interactions between Drosophila caspases and the proapoptotic genes rpr, hid, and grim

In Drosophila melanogaster, the induction of apoptosis requires three close ly linked genes, reaper (rpr), head involution defective (hid), and grim. T he products of these genes induce apoptosis by activating a caspase pathway . Two very similar Drosophila caspases, DCP-1 and drICE. have been previous ly identified. We now show that DCP-1 has a substrate specificity that is r emarkably similar to those of human caspase 3 and Caenorhabditis elegans CE D-3, suggesting that DCP-1 is a death effector caspase. drICE and DCP-1 hav e similar yet different enzymatic specificities. Although expression of eit her in cultured cells induces apoptosis, neither protein was able to induce DNA fragmentation in Drosophila SL2 cells. Ectopic expression of a truncat ed form of dcp-1 (Delta N-dcp-1) in the developing Drosophila retina under an eye-specific promoter resulted in a small and rough eye phenotype, where as expression of the full-length dcp-1 (fl-dcp-1) had little effect. On the other hand, expression of either full-length drICE (fl-drICE) or truncated drICE (Delta N-drICE) in the retina showed no obvious eye phenotype. Altho ugh active DCP-1 protein cleaves full-length DCP-1 and full-length drICE in vitro, GMR-Delta N-dcp-1 did not enhance the eye phenotype of GMR-fl-dcp-1 or GMR-fl-drICE flies. Significantly, GMR-rpr and GMR-grim, but not GMR-hi d, dramatically enhanced the eye phenotype of GMR-fl-dcp-1 flies. These res ults indicate that Reaper and Grim, but not HID, can activate DCP-1 in vivo .