title: Intramitochondrial recruitment of endolysosomes mediates Smac degradation and constitutes a novel intrinsic apoptosis antagonizing function of XIAP E3 ligase.
abstract: Intrinsic apoptosis involves BH3-only protein activation of Bax/Bak-mediated mitochondrial outer membrane permeabilization (MOMP). Consequently, cytochrome c is released from the mitochondria to activate caspases, and Smac (second mitochondria-derived activator of caspases) to inhibit XIAP-mediated caspase suppression. Dysfunctional mitochondria can be targeted for lysosomal degradation via autophagy (mitophagy), or directly through mitochondria-derived vesicle transport. However, the extent of autophagy and lysosomal interactions with apoptotic mitochondria remains largely unknown. We describe here a novel pathway of endolysosomal processing of mitochondria, activated in response to canonical BH3-only proteins and mitochondrial depolarization. We report that expression of canonical BH3-only proteins, tBid, BimEL, Bik, Bad, and mitophagy receptor mutants of atypical BH3-only proteins, Bnip3 and Bnip3L/Nix, leads to prominent relocalization of endolysosomes into inner mitochondrial compartments, in a manner independent of mitophagy. As an upstream regulator, we identified the XIAP E3 ligase. In response to mitochondrial depolarization, XIAP actuates Bax-mediated MOMP, even in the absence of BH3-only protein signaling. Subsequently, in an E3 ligase-dependent manner, XIAP rapidly localizes inside all the mitochondria, and XIAP-mediated mitochondrial ubiquitylation catalyses interactions of Rab membrane targeting components Rabex-5 and Rep-1 (RFP-tagged Rab escort protein-1), and Rab5- and Rab7-positive endolysosomes, at and within mitochondrial membrane compartments. While XIAP-mediated MOMP permits delayed cytochrome c release, within the mitochondria XIAP selectively signals lysosome- and proteasome-associated degradation of its inhibitor Smac. These findings suggest a general mechanism to lower the mitochondrial apoptotic potential via intramitochondrial degradation of Smac.
authors: 1] Lysosomal Systems Biology, German Cancer Research Center (DKFZ), Heidelberg, Germany [2] Bioquant, University of Heidelberg, Heidelberg, Germany.
authors: A
authors: A
authors: Hamacher-Brady
authors: 1] Bioquant, University of Heidelberg, Heidelberg, Germany [2] Systems Biology of Cell Death Mechanisms, German Cancer Research Center (DKFZ), Heidelberg, Germany [3] Department of Surgery, Heidelberg University Hospital, Heidelberg, Germany.
authors: S C
authors: SC
authors: Choe
authors: 1] Bioquant, University of Heidelberg, Heidelberg, Germany [2] Department of Virology, Hygiene Institute, University of Heidelberg Medical School, Heidelberg, Germany.
authors: J
authors: J
authors: Krijnse-Locker
authors: 1] Bioquant, University of Heidelberg, Heidelberg, Germany [2] Systems Biology of Cell Death Mechanisms, German Cancer Research Center (DKFZ), Heidelberg, Germany [3] Department of Surgery, Heidelberg University Hospital, Heidelberg, Germany.
authors: N R
authors: NR
authors: Brady
mesh_terms: D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D011992:Endosomes / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism*; D061986:MCF-7 Cells; D053078:Membrane Potential, Mitochondrial; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000378:metabolism*; D063306:Mitophagy; D021381:Protein Transport; D059748:Proteolysis; D022161:Transport Vesicles; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D054875:Ubiquitination; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000378:metabolism*
chemical_list: D051017:Apoptosis Regulatory Proteins; C412403:DIABLO protein, human; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D044767:Ubiquitin-Protein Ligases; C111567:parkin protein