Bifunctional killing activity encoded by conserved reaper proteins.
Drosophila activators of apoptosis mapping to the Reaper region function, in part, by antagonizing IAP proteins through a shared RHG motif. We isolated Reaper from the Blowfly L. cuprina, which triggered extensive apoptosis in Drosophila cells. Conserved regions of Reaper were tested in the context of GFP fusions and a second killing activity, distinct from the RHG, was identified. A 20 amino-acid peptide, designated R3, conferred targeting to a focal compartment and promoted membrane blebbing. Killing by the R3 fragment did not correlate with translational suppression or with reduced DIAP1 levels. Likewise, R3-induced cell deaths were only modestly suppressed by silencing of Dronc and involved no detectable association with DIAP1. Instead, a second IAP-binding domain, distinct from the R3, was identified at the C terminus of Reaper that bound to DIAP1 but failed to trigger apoptosis. Collectively, these findings are inconsistent with single effector models for cell killing by Reaper and suggest, instead, that Reaper encodes conserved bifunctional death activities that propagate through distinct effector pathways.
Department of Cell Biology, UT Southwestern Medical Center, Dallas, TX 75390, USA.
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D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D017124:Conserved Sequence; D004175:Diptera / Q000737:chemistry; D004330:Drosophila / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D029721:Drosophila Proteins / Q000737:chemistry* / Q000378:metabolism*; D015723:Gene Library; D049452:Green Fluorescent Proteins / Q000378:metabolism; D051034:Inhibitor of Apoptosis Proteins; D019476:Insect Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D011233:Precipitin Tests; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions
C111891:DIAP1 protein, Drosophila; D029721:Drosophila Proteins; D051034:Inhibitor of Apoptosis Proteins; D019476:Insect Proteins; D011506:Proteins; D011993:Recombinant Fusion Proteins; C086973:rpr protein, Drosophila; D049452:Green Fluorescent Proteins; D020169:Caspases; C118731:dronc protein, Drosophila