Invadolysin, a novel and essential metalloprotease, is involved in the activation of apoptosis. Michal M. Janiszewski, Christopher G. Mills, Catherine M. Rose, Cristina Aguilar, Samantha J. Littler, Margarete M. S. Heck. University/BHF Centre for Cardiovascular Science, University of Edinburgh, Edinburgh, United Kingdom.

   Induction of programmed cell death in Drosophila requires the activity of three closely linked genes: reaper, hid, and grim. It has been previously established that these proteins activate apoptosis by inhibiting the anti-apoptotic activity of the Drosophila IAP1 (dIAP-1) protein. Here we show that invadolysin, a novel and essential metalloprotease, plays a crucial role in the activation of apoptosis. Invadolysin shares residues in common with other IAP antagonists in flies at what we are predicting to be N-terminus of cleaved full-length protein. In a genetic modifier screen, invadolysin mutants strongly suppressed reaper-, hid- and grim-induced apoptosis. Significantly, RT-PCR analysis of lines overexpressing reaper, hid, or grim all showed an increase in the level of both invadolysin transcript and protein. In addition, invadolysin accumulates upon heat-shock activation of hid and reaper. Finally, dcp-1 and dronc caspase mutants suppress and diap-1 mutant enhances an invadolysin-induced rough eye phenotype, which could suggest a genetic interaction between pro- and anti-apoptotic genes and invadolysin. As invadolysin is highly conserved amongst eukaryotes, we also analyzed the localization of invadolysin in HeLa cells undergoing apoptosis. Staurosporine-induced apoptosis revealed relocalization of invadolysin from the cytoplasm to the nucleus with a strong concentration in apoptotic bodies, similar to what is observed with cleaved caspase-3 staining. Taken together, our data suggest that invadolysin may be involved in the activation and/or regulation of apoptosis.