title: Regulation of HAX-1 anti-apoptotic protein by Omi/HtrA2 protease during cell death.
abstract: Omi/HtrA2 is a nuclear-encoded mitochondrial serine protease that has a pro-apoptotic function in mammalian cells. Upon induction of apoptosis, Omi translocates to the cytoplasm and participates in caspase-dependent apoptosis by binding and degrading inhibitor of apoptosis proteins. Omi can also initiate caspase-independent apoptosis in a process that relies entirely on its ability to function as an active protease. To investigate the mechanism of Omi-induced apoptosis, we set out to isolate novel substrates that are cleaved by this protease. We identified HS1-associated protein X-1 (HAX-1), a mitochondrial anti-apoptotic protein, as a specific Omi interactor that is cleaved by Omi both in vitro and in vivo. HAX-1 degradation follows Omi activation in cells treated with various apoptotic stimuli. Using a specific inhibitor of Omi, HAX-1 degradation is prevented and cell death is reduced. Cleavage of HAX-1 was not observed in a cell line derived from motor neuron degeneration 2 mice that carry a mutated form of Omi that affects its proteolytic activity. Degradation of HAX-1 is an early event in the apoptotic process and occurs while Omi is still confined in the mitochondria. Our results suggest that Omi has a unique pro-apoptotic function in mitochondria that involves removal of the HAX-1 anti-apoptotic protein. This function is distinct from its ability to activate caspase-dependent apoptosis in the cytoplasm by degrading inhibitor of apoptosis proteins.
authors.affiliation: Biomolecular Science Center, Burnett College of Biomedical Sciences, University of Central Florida, Orlando, Florida 32826, USA.
authors.forename: Lucia
authors.initials: L
authors.lastname: Cilenti
authors.forename: Mangala M
authors.initials: MM
authors.lastname: Soundarapandian
authors.forename: George A
authors.initials: GA
authors.lastname: Kyriazis
authors.forename: Valerie
authors.initials: V
authors.lastname: Stratico
authors.forename: Supriya
authors.initials: S
authors.lastname: Singh
authors.forename: Sanjeev
authors.initials: S
authors.lastname: Gupta
authors.forename: Joseph V
authors.initials: JV
authors.lastname: Bonventre
authors.forename: Emad S
authors.initials: ES
authors.lastname: Alnemri
authors.forename: Antonis S
authors.initials: AS
authors.lastname: Zervos
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D000074923:High-Temperature Requirement A Serine Peptidase 2; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D024101:Mitochondrial Proteins; D011506:Proteins / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C104759:HAX1 protein, human; C491295:Hs1bp1 protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D011506:Proteins; D012697:Serine Endopeptidases; C000615914:HTRA2 protein, human; D000074923:High-Temperature Requirement A Serine Peptidase 2; C000615915:Htra2 protein, mouse