title: Mouse Noxa uses only the C-terminal BH3-domain to inactivate Mcl-1.
abstract: Noxa is a member of the pro-apoptotic BH3-only group of Bcl-2 proteins that is known to bind specifically to anti-apoptotic Mcl-1 and A1, antagonizing their function. Mcl-1 has been reported to have a short half-life, and Noxa up-regulation accelerates Mcl-1 degradation by the proteasome. Unlike human Noxa, mouse Noxa has two BH3-domains, which both have affinity for Mcl-1. We here investigate two aspects of the molecular function of Noxa, namely the requirements for the two BH3-domains in mouse Noxa and the role of Noxa in Mcl-1-degradation. We found that only the C-terminal BH3-domain of mouse Noxa is active in neutralizing Mcl-1. This was the result of the targeting of Noxa to the outer mitochondrial membrane through its C-terminal alpha-helix, which allowed Mcl-1-neutralization only when the BH3-domain was immediately N-terminal of the membrane anchor. However, the N-terminal BH3-domain enhanced interaction with Mcl-1 and A1. The Noxa-dependent degradation of Mcl-1 was independent of the kinase GSK3 and the deubiquitinase Usp9x in mouse embryonic fibroblasts. These data show that Noxa is targeted to the mitochondrial membrane where it neutralises Mcl-1 via its C-terminal BH3-domain and suggest that Noxa is co-degraded with Noxa, in a way independent of ubiquitin-modifying enzymes described for Mcl-1.
authors.affiliation: Institute of Medical Microbiology and Hygiene, University Hospital Freiburg, 79104, Freiburg, Germany.
authors.forename: Arnim
authors.initials: A
authors.lastname: Weber
authors.forename: David
authors.initials: D
authors.lastname: Ausländer
authors.forename: Georg
authors.initials: G
authors.lastname: Häcker
mesh_terms: D000818:Animals; D006801:Humans; D051379:Mice; D051336:Mitochondrial Membranes / Q000378:metabolism; D064549:Myeloid Cell Leukemia Sequence 1 Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D059748:Proteolysis; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: C579094:Mcl1 protein, mouse; D064549:Myeloid Cell Leukemia Sequence 1 Protein; C408009:Pmaip1 protein, mouse; D019253:Proto-Oncogene Proteins c-bcl-2