title: Trim17-mediated ubiquitination and degradation of Mcl-1 initiate apoptosis in neurons.
abstract: Short-term proteasome inhibition has been shown to prevent neuronal apoptosis. However, the key pro-survival proteins that must be degraded for triggering neuronal death are mostly unknown. Here, we show that Mcl-1, an anti-apoptotic Bcl-2 family member, is degraded by the proteasome during neuronal apoptosis. Using primary cultures of cerebellar granule neurons deprived of serum and KCl, we found that ubiquitination and proteasomal degradation of Mcl-1 depended on its prior phosphorylation by GSK3, providing the first insight into post-translational regulation of Mcl-1 in neurons. In a previous study, we have reported that the E3 ubiquitin-ligase Trim17 is both necessary and sufficient for neuronal apoptosis. Here, we identified Trim17 as a novel E3 ubiquitin-ligase for Mcl-1. Indeed, Trim17 co-immunoprecipitated with Mcl-1. Trim17 ubiquitinated Mcl-1 in vitro. Overexpression of Trim17 decreased the protein level of Mcl-1 in a phosphorylation- and proteasome-dependent manner. Finally, knock down of Trim17 expression reduced both ubiquitination and degradation of Mcl-1 in neurons. Moreover, impairment of Mcl-1 phosphorylation, by kinase inhibition or point mutations, not only decreased ubiquitination and degradation of Mcl-1, but also blocked the physical interaction between Trim17 and Mcl-1. As this stabilization of Mcl-1 increased its neuroprotective effect, our data strongly suggest that Trim17-mediated ubiquitination and degradation of Mcl-1 is necessary for initiating neuronal death.
authors.affiliation: Institut de Génétique Moléculaire de Montpellier UMR 5535 CNRS, Montpellier, France.
authors.forename: M M
authors.initials: MM
authors.lastname: Magiera
authors.forename: S
authors.initials: S
authors.lastname: Mora
authors.forename: B
authors.initials: B
authors.lastname: Mojsa
authors.forename: I
authors.initials: I
authors.lastname: Robbins
authors.forename: I
authors.initials: I
authors.lastname: Lassot
authors.forename: S
authors.initials: S
authors.lastname: Desagher
mesh_terms: D000818:Animals; D017209:Apoptosis; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D016297:Mutagenesis, Site-Directed; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D000070584:Tripartite Motif Proteins; D044767:Ubiquitin-Protein Ligases; D054875:Ubiquitination
chemical_list: D002352:Carrier Proteins; C579094:Mcl1 protein, mouse; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D000070584:Tripartite Motif Proteins; C485451:Trim17 protein, mouse; D044767:Ubiquitin-Protein Ligases; D038362:Glycogen Synthase Kinase 3; D046988:Proteasome Endopeptidase Complex