title: Nucleo-cytoplasmic shuttling of Id2, a negative regulator of basic helix-loop-helix transcription factors.
abstract: Id proteins function as negative regulators for basic helix-loop-helix transcriptional factors that play important roles in cell fate determination. They preferentially associate with ubiquitously expressed E proteins of the basic helix-loop-helix family and prevent them from binding to DNA and activating transcription. Although their small size suggests that Id proteins enter and exit the nucleus by passive diffusion, several studies have indicated that other pathways may regulate their subcellular localization. In this study, we obtained evidence that Id2 has the ability to shuttle between the nucleus and the cytoplasm. When passive diffusion was prevented by fusion with green fluorescent protein (GFP), Id2 was predominantly localized in the cytoplasm. Using GFP fusion constructs, we demonstrated that the C-terminal region is required for cytoplasmic localization. Nuclear accumulation of GFP-Id2 in cells treated with the nuclear export inhibitor leptomycin B suggests that the nuclear export receptor chromosome region maintenance protein 1 mediates the cytoplasmic localization of Id2. Id2 contains two putative leucine-rich nuclear export signals, and the nuclear export signal in the C-terminal region is essential for nuclear export. On the other hand, the helix-loop-helix domain is important for nuclear localization. Finally, experiments using reporter assays revealed an inverse correlation between nuclear export and transcriptional repression via the E-box sequence. Based on all these findings, we propose that nucleo-cytoplasmic shuttling is a novel mechanism for the regulation of Id2 function.
authors.affiliation: Department of Molecular Genetics, School of Medicine, University of Fukui, 23-3, Shimoaizuki, Matsuoka, Fukui 910-1193, Japan.
authors.forename: Hisanori
authors.initials: H
authors.lastname: Kurooka
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Yokota
mesh_terms: D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D019070:Cell Lineage; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism*; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D017353:Gene Deletion; D049452:Green Fluorescent Proteins / Q000378:metabolism; D018257:Helix-Loop-Helix Motifs; D047468:Immunoprecipitation; D051797:Inhibitor of Differentiation Protein 2; D007930:Leucine / Q000737:chemistry; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012097:Repressor Proteins / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D004268:DNA-Binding Proteins; D005231:Fatty Acids, Unsaturated; C497452:Idb2 protein, mouse; D051797:Inhibitor of Differentiation Protein 2; D012097:Repressor Proteins; D014157:Transcription Factors; D049452:Green Fluorescent Proteins; D004247:DNA; D008156:Luciferases; D007930:Leucine; C038753:leptomycin B