title: Nrdp1-mediated degradation of the gigantic IAP, BRUCE, is a novel pathway for triggering apoptosis.
abstract: Degradation of certain inhibitor of apoptosis proteins (IAPs) appears to be critical in the initiation of apoptosis, but the factors that regulate their degradation in mammalian cells are unknown. Nrdp1/FLRF is a RING finger-containing ubiquitin ligase that catalyzes degradation of the EGF receptor family member, ErbB3. We show here that Nrdp1 associates with BRUCE/apollon, a 530 kDa membrane-associated IAP, which contains a ubiquitin-carrier protein (E2) domain. In the presence of an exogenous E2, UbcH5c, purified Nrdp1 catalyzes BRUCE ubiquitination. In vivo, overexpression of Nrdp1 promotes ubiquitination and proteasomal degradation of BRUCE. In many cell types, apoptotic stimuli induce proteasomal degradation of BRUCE (but not of XIAP or c-IAP1), and decreasing Nrdp1 levels by RNA interference reduces this loss of BRUCE. Furthermore, decreasing BRUCE content by RNA interference or overexpression of Nrdp1 promotes apoptosis. Thus, BRUCE normally inhibits apoptosis, and Nrdp1 can be important in the initiation of apoptosis by catalyzing ubiquitination and degradation of BRUCE.
authors.affiliation: Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA. xqui@hms.harvard.edu
authors.forename: Xiao-Bo
authors.initials: XB
authors.lastname: Qiu
authors.forename: Shirley L
authors.initials: SL
authors.lastname: Markant
authors.forename: Junying
authors.initials: J
authors.lastname: Yuan
authors.forename: Alfred L
authors.initials: AL
authors.lastname: Goldberg
mesh_terms: D017209:Apoptosis / Q000502:physiology*; D020169:Caspases / Q000378:metabolism; D002461:Cell Line, Transformed; D045744:Cell Line, Tumor; D004789:Enzyme Activation; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D009363:Neoplasm Proteins / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D034741:RNA, Small Interfering / Q000096:biosynthesis / Q000378:metabolism; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*
chemical_list: C401541:BIRC6 protein, human; D051034:Inhibitor of Apoptosis Proteins; D009363:Neoplasm Proteins; D034741:RNA, Small Interfering; C097310:UBE2D3 protein, human; D044763:Ubiquitin-Conjugating Enzymes; C452580:RNF41 protein, human; D044767:Ubiquitin-Protein Ligases; D020169:Caspases; D046988:Proteasome Endopeptidase Complex