title: A novel BAT3 sequence generated by alternative RNA splicing of exon 11B displays cell type-specific expression and impacts on subcellular localization.
abstract: BACKGROUND
  The human lymphocyte antigen (HLA) encoded BAT3/BAG6 recently attracted interest as a regulator of protein targeting and degradation, a function that could be exerted in the cytosol and in the nucleus. The BAT3 gene was described to consist of 25 exons. Diversity of transcripts can be generated by alternative RNA splicing, which may control subcellular distribution of BAT3.
  
  
  RESULTS
  By cDNA sequencing we identified a novel alternatively spliced sequence of the BAT3 gene located between exons 11 and 12, which was designated as exon 11B. Using PCR and colony hybridization we identified six cDNA variants, which were produced by RNA splicing of BAT3 exons 5, 11B and 24. In four examined cell types the content of BAT3 splice variants was examined. Most of the cDNA clones from monocyte-derived dendritic cells contain exon 11B, whereas this sequence was almost absent in the B lymphoma Raji. Exon 5 was detected in most and exon 24 in approximately half of the cDNA clones. The subcellular distribution of endogenous BAT3 largely correlates with a cell type specific splicing pattern. In cells transfected with BAT3 variants, full-length and Δ24 BAT3 displayed nearly exclusive nuclear staining, whereas variants deleted of exon 11B showed substantial cytosolic expression. We show here that BAT3 is mainly expressed in the cytosol of Raji cells, while other cell types displayed both cytosolic and nuclear staining. Export of BAT3 from the nucleus to the cytosol is inhibited by treatment with leptomycin B, indicating that the Crm1 pathway is involved. Nuclear expression of BAT3 containing exon 11B suggests that this sequence plays a role for nuclear retention of the protein.
  
  
  CONCLUSIONS
  Cell type-specific subcellular expression of BAT3 suggests distinct functions in the cytosol and in the nucleus. Differential expression of BAT3 variants may reconcile the multiple roles described for BAT3.
authors.affiliation: Division of Immunobiology, Institute of Genetics, University of Bonn, Bonn, Germany. nadine.kaemper@uni-bonn.de
authors.forename: Nadine
authors.initials: N
authors.lastname: Kämper
authors.forename: Jörg
authors.initials: J
authors.lastname: Kessler
authors.forename: Sebastian
authors.initials: S
authors.lastname: Temme
authors.forename: Claudia
authors.initials: C
authors.lastname: Wegscheid
authors.forename: Johannes
authors.initials: J
authors.lastname: Winkler
authors.forename: Norbert
authors.initials: N
authors.lastname: Koch
mesh_terms: D017398:Alternative Splicing / Q000187:drug effects / Q000235:genetics*; D001483:Base Sequence; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D005091:Exons / Q000235:genetics*; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D018832:Molecular Chaperones / Q000235:genetics* / Q000378:metabolism; D009928:Organ Specificity / Q000235:genetics*; D021381:Protein Transport / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D014162:Transfection
chemical_list: C092009:BAG6 protein, human; D005231:Fatty Acids, Unsaturated; D018832:Molecular Chaperones; D012333:RNA, Messenger; C038753:leptomycin B