title: MAP-1 is a mitochondrial effector of Bax.
abstract: Apoptotic stimuli induce conformational changes in Bax and trigger its translocation from cytosol to mitochondria. Upon assembling into the mitochondrial membrane, Bax initiates a death program through a series of events, culminating in the release of apoptogenic factors such as cytochrome c. Although it is known that Bax is one of the key factors for integrating multiple death signals, the mechanism by which Bax functions in mitochondria remains controversial. We have previously identified modulator of apoptosis-1 (MAP-1) as a Bax-associating protein, but its functional relationship with Bax in contributing to apoptosis regulation remains to be established. In this study, we show that MAP-1 is a critical mitochondrial effector of Bax. MAP-1 is a mitochondria-enriched protein that associates with Bax only upon apoptotic induction, which coincides with the release of cytochrome c from mitochondria. Small interfering RNAs that diminish MAP-1 levels in mammalian cell lines confer selective inhibition of Bax-mediated apoptosis. Mammalian cells with stable expression of MAP-1 small interfering RNAs are resistant to multiple apoptotic stimuli in triggering apoptotic death as well as in inducing conformation change and translocation of Bax. Similar to Bax-deficient cells, MAP-1-deficient cells exhibit aggressive anchorage-independent growth. Remarkably, recombinant Bax- or tBid-mediated release of cytochrome c from isolated mitochondria is significantly compromised in the MAP-1 knockdown cells. We propose that MAP-1 is a direct mitochondrial target of Bax.
authors.affiliation: Institute of Molecular and Cell Biology, 61 Biopolis Drive (Proteos), Singapore 138673, Republic of Singapore.
authors.forename: Kuan Onn
authors.initials: KO
authors.lastname: Tan
authors.forename: Nai Yang
authors.initials: NY
authors.lastname: Fu
authors.forename: Sunil K
authors.initials: SK
authors.lastname: Sukumaran
authors.forename: Shing-Leng
authors.initials: SL
authors.lastname: Chan
authors.forename: Jiunn Hian
authors.initials: JH
authors.lastname: Kang
authors.forename: Kar Lai
authors.initials: KL
authors.lastname: Poon
authors.forename: Bin Shun
authors.initials: BS
authors.lastname: Chen
authors.forename: Victor C
authors.initials: VC
authors.lastname: Yu
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism*; D002458:Cell Fractionation; D045304:Cytochromes c / Q000378:metabolism; D005347:Fibroblasts; D019084:Fluorescent Antibody Technique, Indirect; D015151:Immunoblotting; D047468:Immunoprecipitation; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D051028:bcl-2-Associated X Protein / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; C494827:Bax protein, mouse; C492394:Moap1 protein, mouse; D034741:RNA, Small Interfering; D051028:bcl-2-Associated X Protein; D045304:Cytochromes c