A regulated nucleocytoplasmic shuttle contributes to Bright's function as a transcriptional activator of immunoglobulin genes.
Bright/ARID3a has been implicated in mitogen- and growth factor-induced up-regulation of immunoglobulin heavy-chain (IgH) genes and in E2F1-dependent G1/S cell cycle progression. For IgH transactivation, Bright binds to nuclear matrix association regions upstream of certain variable region promoters and flanking the IgH intronic enhancer. While Bright protein was previously shown to reside within the nuclear matrix, we show here that a significant amount of Bright resides in the cytoplasm of normal and transformed B cells. Leptomycin B, chromosome region maintenance 1 (CRM1) overexpression, and heterokaryon experiments indicate that Bright actively shuttles between the nucleus and the cytoplasm in a CRM1-dependent manner. We mapped the functional nuclear localization signal to the N-terminal region of REKLES, a domain conserved within ARID3 paralogues. Residues within the C terminus of REKLES contain its nuclear export signal, whose regulation is primarily responsible for Bright shuttling. Growth factor depletion and cell synchronization experiments indicated that Bright shuttling during S phase of the cell cycle leads to an increase in its nuclear abundance. Finally, we show that shuttle-incompetent Bright point mutants, even if sequestered within the nucleus, are incapable of transactivating an IgH reporter gene. Therefore, regulation of Bright's cellular localization appears to be required for its function.
Kim
Dongkyoon
D
University of Texas at Austin, Molecular Genetics and Microbiology, 1 University Station A5000, Room ESB-532, Austin, TX 78712-0162, USA.
Tucker
Philip W
PW
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism / Q000473:pathology; D002467:Cell Nucleus / Q000378:metabolism*; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D005786:Gene Expression Regulation; D006801:Humans; D007136:Immunoglobulins / Q000235:genetics*; D028884:Karyopherins / Q000235:genetics / Q000378:metabolism; D045170:Matrix Attachment Regions; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals; D009857:Oncogenes / Q000187:drug effects / Q000235:genetics; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism; D016196:S Phase / Q000235:genetics; D015534:Trans-Activators / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors; D014407:Tumor Cells, Cultured; D000097606:Exportin 1 Protein
D016895:Culture Media, Serum-Free; D004268:DNA-Binding Proteins; D005231:Fatty Acids, Unsaturated; D007136:Immunoglobulins; D028884:Karyopherins; D019913:Nuclear Localization Signals; D018160:Receptors, Cytoplasmic and Nuclear; D015534:Trans-Activators; D014157:Transcription Factors; D000097606:Exportin 1 Protein; C097532:Arid3a protein, mouse; C038753:leptomycin B