Reaper is regulated by IAP-mediated ubiquitination.
In most cases, apoptotic cell death culminates in the activation of the caspase family of cysteine proteases, leading to the orderly dismantling and elimination of the cell. The IAPs (inhibitors of apoptosis) comprise a family of proteins that oppose caspases and thus act to raise the apoptotic threshold. Disruption of IAP-mediated caspase inhibition has been shown to be an important activity for pro-apoptotic proteins in Drosophila (Reaper, HID, and Grim) and in mammalian cells (Smac/DIABLO and Omi/HtrA2). In addition, in the case of the fly, these proteins are able to stimulate the ubiquitination and degradation of IAPs by a mechanism involving the ubiquitin ligase activity of the IAP itself. In this report, we show that the Drosophila RHG proteins (Reaper, HID, and Grim) are themselves substrates for IAP-mediated ubiquitination. This ubiquitination of Reaper requires IAP ubiquitin-ligase activity and a stable interaction between Reaper and the IAP. Additionally, degradation of Reaper can be blocked by mutating its potential ubiquitination sites. Most importantly, we also show that regulation of Reaper by ubiquitination is a significant factor in determining its biological activity. These data demonstrate a novel function for IAPs and suggest that IAPs and Reaper-like proteins mutually control each other's abundance.
Olson
Michael R
MR
Department of Pharmacology and Cancer Biology, Duke University, Durham, North Carolina 27710, USA.
Holley
Christopher L
CL
Yoo
Soon Ji
SJ
Huh
Jun R
JR
Hay
Bruce A
BA
Kornbluth
Sally
S
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004330:Drosophila; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D006868:Hydrolysis; D017403:In Situ Hybridization; D051034:Inhibitor of Apoptosis Proteins; D019476:Insect Proteins / Q000502:physiology*; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000378:metabolism; D009841:Oligonucleotides; D046988:Proteasome Endopeptidase Complex; D011506:Proteins; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism*
D029721:Drosophila Proteins; D051034:Inhibitor of Apoptosis Proteins; D019476:Insect Proteins; D009097:Multienzyme Complexes; D009841:Oligonucleotides; D011506:Proteins; D011994:Recombinant Proteins; D025801:Ubiquitin; C086973:rpr protein, Drosophila; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex