title: Gadd45a expression induces Bim dissociation from the cytoskeleton and translocation to mitochondria.
abstract: Gadd45a, a p53- and BRCA1-regulated stress protein, has been implicated in the maintenance of genomic fidelity, probably through its roles in the control of cell cycle checkpoint and apoptosis. However, the mechanism(s) by which Gadd45a is involved in the induction of apoptosis remains unclear. We show here that inducible expression of Gadd45a protein causes dissociation of Bim, a Bcl2 family member, from microtubule-associated components and translocation to mitochondria. The Bim accumulation in mitochondria enhances interaction of Bim with Bcl-2, relieves Bax from Bcl-2-bound complexes, and subsequently results in release of cytochrome c into the cytoplasm. Suppression of endogenous Bim greatly inhibits Gadd45a induction of apoptosis. Interestingly, Gadd45a interacts with elongation factor 1alpha (EF-1alpha), a microtubule-severing protein that plays an important role in maintaining cytoskeletal stability, and inhibits EF-1alpha-mediated microtubule bundling, indicating that the interaction of Gadd45a with EF-1alpha disrupts cytoskeletal stability. A mutant form of Gadd45a harboring a deletion of EF-1alpha-binding domain fails to inhibit microtubule stability and to induce Bim translocation to mitochondria. Furthermore, coexpression of EF-1alpha antagonizes Gadd45a's property of suppressing cell growth and inducing apoptosis. These findings identify a novel link that connects stress protein Gadd45a to the apoptotic machinery and address the importance of cytoskeletal stability in apoptotic response to DNA damage.
authors.affiliation: State Key Laboratory of Molecular Oncology, Chinese Academy of Medical Sciences, Cancer Institute, Beijing 100021, People's Republic of China.
authors.forename: Tong
authors.initials: T
authors.lastname: Tong
authors.forename: Junfang
authors.initials: J
authors.lastname: Ji
authors.forename: Shunqian
authors.initials: S
authors.lastname: Jin
authors.forename: Xianxing
authors.initials: X
authors.lastname: Li
authors.forename: Wenhong
authors.initials: W
authors.lastname: Fan
authors.forename: Yongmei
authors.initials: Y
authors.lastname: Song
authors.forename: Minrong
authors.initials: M
authors.lastname: Wang
authors.forename: Zhihua
authors.initials: Z
authors.lastname: Liu
authors.forename: Min
authors.initials: M
authors.lastname: Wu
authors.forename: Qimin
authors.initials: Q
authors.lastname: Zhan
mesh_terms: D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D045304:Cytochromes c / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism*; D017353:Gene Deletion; D006367:HeLa Cells; D006801:Humans; D047468:Immunoprecipitation; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D020648:Peptide Elongation Factor 1 / Q000378:metabolism; D021381:Protein Transport; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D000097642:GADD45 Proteins
chemical_list: D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D045304:Cytochromes c; D008565:Membrane Proteins; D009687:Nuclear Proteins; D020648:Peptide Elongation Factor 1; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; C000606775:BCL2L11 protein, human; C439070:GADD45A protein, human; D000097642:GADD45 Proteins