Inhibition of ubiquitin-mediated degradation of MOAP-1 by apoptotic stimuli promotes Bax function in mitochondria

Abstract

The multidomain proapoptotic protein Bax of the Bcl-2 family is a central regulator for controlling the release of apoptogenic factors from mitochondria. Recent evidence suggests that the Baxassociating protein MOAP-1 may act as an effector for promoting Bax function in mitochondria. Here, we report that MOAP-1 protein is rapidly up-regulated by multiple apoptotic stimuli in mammalian cells. MOAP-1 is a short-lived protein (t1 ͞2 Ϸ 25 min) that is constitutively degraded by the ubiquitin-proteasome system. Induction of MOAP-1 by apoptotic stimuli ensues through inhibition of its polyubiquitination process. Elevation of MOAP-1 levels sensitizes cells to apoptotic stimuli and promotes recombinant Bax-mediated cytochrome c release from isolated mitochondria. Mitochondria depleted of short-lived proteins by cycloheximide (CHX) become resistant to Bax-mediated cytochrome c release. Remarkably, incubation of these mitochondria with in vitrotranslated MOAP-1 effectively restores the cytochrome c releasing effect of recombinant Bax. We propose that apoptotic stimuli can facilitate the proapoptotic function of Bax in mitochondria through stabilization of MOAP-1.apoptosis ͉ Bcl-2 family ͉ proteasome ͉ DNA damage

Molecular and functional analysis of the stem cell compartment of chronic myelogenous leukemia reveals the presence of a CD34− cell population with intrinsic resistance to imatinib

“…Moreover, our data confirmed the upregulation of the anti-apoptotic gene BCL2 23,31 in CML Lin Ϫ CD34 ϩ and more mature normal and leukemic Lin ϩ CD34 ϩ and BCLXL 32 in CML Lin ϩ CD34 ϩ progenitors, whereas the proapoptotic genes BAX, 33 ENO1, 31 and MOAP1 32 5 were down-regulated if compared with normal cells (supplemental Figure 2C).…”

Expression of the kinetochore protein Hec1 during the cell cycle in normal and cancer cells and its regulation by the pRb pathway

“…To have new insights into Hec1 regulation in cancer cells we first examined the rate of protein turnover in colorectal cancer (HCT116) and normal fibroblast (MRC5) cells by inhibiting de novo protein synthesis with cycloheximide (CHX). 22 Cells were treated with 50 μg/ml CHX and the remaining quantity of Hec1 was assessed by western blot analysis at different time points. In the presence of the drug, Hec1 levels were reduced by 50% at approximately 4 h post-inhibition of protein synthesis in HCT116 cells (Fig.…”

“…An increased recruitment of Hec1 at kinetochores was also observed in cancer cells. Most eukaryotic kinetochores are large protein assemblies containing multiple (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) attachment sites for the plus-end of spindle MT. 6,7 Between six and eight Ndc80 complexes are thought to encircle each attachment site and function as a dynamic grasp for MT.…”

Interaction of diphtheria toxin (fragment A) with actin

“…Thus, Bax-associating protein, MOAP-1, with a high turnover rate (t 1/2 $25 min) is constitutively degraded by the ubiquitin-proteasome system. 12,13 Stabilization and/ or induction of MOAP-1 by apoptotic stimuli can lead to Bax-mediated cytochrom C release from isolated mitochondria. 12,13 On the other hand, the inhibition of protein synthesis by cycloheximide results in a rapid degradation of another short-lived member of the Bcl-2 family, that is the prosurvival protein Mcl-1.…”

“…the short-lived members of Bcl-2 family. 12,13 Thus, protein synthesis inhibition itself is necessary, but additional mechanisms may come into play to unfold the cytotoxic effect. 10,14 The clarification of these mechanism(s) is necessary in order to gain further insight into the sequence of DT-promoted events leading to cell death.…”