title: The BRCA1-binding protein BRAP2 can act as a cytoplasmic retention factor for nuclear and nuclear envelope-localizing testicular proteins.
abstract: Regulation of nuclear protein import is central to many cellular processes such as development, with a key mechanism being factors that retain cargoes in the cytoplasm that normally localize in the nucleus. The breast cancer antigen BRCA1-binding protein BRAP2 has been reported as a novel negative regulator of nuclear import of various nuclear localization signal (NLS)-containing viral and cellular proteins, but although implicated in differentiation pathways and highly expressed in tissues including testis, the gamut of targets for BRAP2 action in a developmental context is unknown. As a first step towards defining the BRAP2 interactome, we performed a yeast-2-hybrid screen to identify binding partners of BRAP2 in human testis. Here we report characterization for the first time of three of these: the high mobility group (HMG)-box-domain-containing chromatin component HMG20A, nuclear mitotic apparatus protein NuMA1 and synaptic nuclear envelope protein SYNE2. Co-immunoprecipitation experiments indicate association of BRAP2 with HMG20A, NuMA1, and SYNE2 in testis, underlining the physiological relevance of the interactions, with immunohistochemistry showing that where BRAP2 is co-expressed with HMG20A and NuMA1, both are present in the cytoplasm, in contrast to their nuclear localization in other testicular cell types. Importantly, quantitative confocal microscopic analysis of cultured cells indicates that ectopic expression of BRAP2 inhibits nuclear localization of HMG20A and NuMA1, and prevents nuclear envelope accumulation of SYNE2, the first report of BRAP2 altering localization of a non-nuclear protein. These results imply for the first time that BRAP2 may have an important role in modulating subcellular localization during testicular development.
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia.
authors.forename: Rebecca G
authors.initials: RG
authors.lastname: Davies
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia.
authors.forename: Kylie M
authors.initials: KM
authors.lastname: Wagstaff
authors.affiliation: Priority Research Centre in Chemical Biology and Reproductive Science, University of Newcastle, Callaghan, NSW, Australia.
authors.forename: Eileen A
authors.initials: EA
authors.lastname: McLaughlin
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia; Department of Anatomy and Developmental Biology, Monash University, Clayton, Victoria, Australia.
authors.forename: Kate L
authors.initials: KL
authors.lastname: Loveland
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia. Electronic address: david.jans@monash.edu.
authors.forename: David A
authors.initials: DA
authors.lastname: Jans
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D034961:Antigens, Nuclear / Q000378:metabolism; D019313:BRCA1 Protein / Q000378:metabolism*; D019556:COS Cells; D018797:Cell Cycle Proteins; D002522:Chlorocebus aethiops; D006609:High Mobility Group Proteins / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D008840:Microfilament Proteins / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009685:Nuclear Envelope / Q000378:metabolism*; D034521:Nuclear Matrix-Associated Proteins / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism*; D011485:Protein Binding; D021381:Protein Transport; D013737:Testis / Q000166:cytology / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D034961:Antigens, Nuclear; D019313:BRCA1 Protein; D018797:Cell Cycle Proteins; C408987:HMG20A protein, human; D006609:High Mobility Group Proteins; C507322:Hmg20a protein, mouse; D008840:Microfilament Proteins; C050045:NUMA1 protein, human; D009419:Nerve Tissue Proteins; D034521:Nuclear Matrix-Associated Proteins; D009687:Nuclear Proteins; C489080:Numa1 protein, mouse; C485904:SYNE2 protein, human; C485903:Syne2 protein, mouse; C111164:BRAP protein, human; C586509:Brap protein, mouse; D044767:Ubiquitin-Protein Ligases
keywords: BRAP2; BRAP2/Imp; BRCA1; BRCA1 Associated Protein 2/Impedes Mitogenic Signal Propagation; Breast Cancer Type I Susceptibility Protein; CLSM; Cytoplasmic retention factor; HMG20A; High Mobility Group Protein 20A; NCBI; NLS; National Centre for Biotechnology Information; NuMA1; Nuclear Mitotic Apparatus Protein 1; Nuclear transport; SYNE2; Simian Virus 40 Large Tumor Antigen; Synaptic Nuclear Envelope Protein 2; T-ag; confocal laser scanning microscopy; nuclear localization signal