BRUCE, a Giant E2/E3 Ubiquitin Ligase and Inhibitor of Apoptosis Protein of the trans-Golgi Network, Is Required for Normal Placenta Development and Mouse Survival

Abstract

BRUCE is a highly conserved 528-kDa peripheral membrane protein of the trans-Golgi network. Owing to the presence of an N-terminal single baculovirus inhibitor repeat, BRUCE functions as an inhibitor of apoptosis protein and blocks apoptosis when overexpressed. In addition, due to the presence of a C-terminal ubiquitin-conjugating domain, BRUCE can covalently attach ubiquitin to substrates. Here we report the generation and characterization of BRUCE-deficient mice. Complete inactivation of the BRUCE gene resulted in perinatal lethality and growth retardation discernible after embryonic day 14. The growth defect is linked to impaired placental development and may be caused by insufficient oxygen and nutrient transfer across the placenta. Chorioallantoic placentation initiated normally, but the mutant placenta showed an impaired maturation of the labyrinth layer and a significant reduction of the spongiotrophoblast. No evidence for an elevated apoptosis rate was detectable in embryonic and extraembryonic tissues and in knockout fibroblasts. Thus, although BRUCE is broadly expressed in embryonic, extraembryonic, and adult mouse tissues, this bifunctional protein might play a unique role in normal trophoblast differentiation and embryonic survival.

Prostaglandin F2α promotes muscle cell survival and growth through upregulation of the inhibitor of apoptosis protein BRUCE

“…We were especially interested in the upregulation of BRUCE mRNA by PGF2a, given the reported role for BRUCE in inhibition of apoptosis. 18,21 Therefore, we confirmed by realtime RT-PCR that BRUCE mRNA expression increases approximately twofold in response to PGF2a treatment (Figure 2b). To determine whether PGF2a treatment increases BRUCE protein expression, we utilized flow cytometry ( Figure 2c) and determined that following 6 h of PGF2a treatment, the proportion of BRUCE þ muscle cells increased 9.8±0.9% relative to vehicle (n ¼ 4, Po0.001).…”

“…37 Multiple groups have generated BRUCE-deficient mice, and all mice are embryonic lethal. [20][21][22] However, whether embryonic lethality associated with loss of BRUCE function is caused by an increase in apoptosis is unclear. Ren et al 22 reported the abundance of apoptotic cells in the placenta and yolk sac in mice lacking the C-terminal half of BRUCE.…”

“…18,19 BRUCE null mice are embryonic lethal, whereas overexpression of either BRUCE or its human ortholog, Apollon, is sufficient to inhibit apoptosis induced by a variety of stimuli. 18,[20][21][22] Despite the significant role for BRUCE in blocking apoptosis, very little is known about the regulation of BRUCE expression.…”

Oncolytic adenovirus-mediated shRNA against Apollon inhibits tumor cell growth and enhances antitumor effect of 5-fluorouracil

“…13,14 Complete inactivation of the Bruce gene in mice results in perinatal lethality and growth deficiencies. 15 In Drosophila, overexpression of dBruce can inhibit cell death induced by the proapoptotic Smac analogs Reaper and Grim. 14 Several lines of evidence show that the Apollon can protect cells against apoptosis and functions as an IAP by binding the active caspases via its single BIR domain.…”

IAPs – the ubiquitin connection

“…35 Several groups have reported deleting BRUCE in mice. [36][37][38] While all agree that deletion of BRUCE results in embryonic lethality, its exact role remains controversial, with suggested activities including preventing p53 activation, 38 directly binding to both unprocessed and mature Smac/DIABLO and both pro-and processed caspase 9, and targeting them for degradation. 36,39,40 Survivin is a BIR containing protein that acts together with INCENP and Aurora kinase B in a complex required for chromosome segregation and cytokinesis during mitosis.…”