title: Regulated nuclear entry of over-expressed Setdb1.
abstract: Setdb1 is a histone H3-lysine 9 (H3K9)-specific methyltransferase that interacts with various transcriptional regulators to induce local heterochromatin formation and participates as an indispensable component in building promyelocytic leukemia nuclear body (PML-NB), which is involved in various biological processes. We studied the effects of Setdb1 over-expression. We unexpectedly observed that exogenously expressed GFP-Setdb1 was retained in the cytoplasm, whereas endogenous Setdb1 showed a punctate nuclear signal. Leptomycin B (LMB) treatment, which blocks protein export from the nucleus, showed that entry of GFP-Setdb1 to the nucleus was regulated and that GFP-Setdb1 in the nucleus could localize at PML-NB as endogenous Setdb1. An analysis of Setdb1 deletion constructs showed that the N-terminal region was related to the nuclear export of Setdb1; supporting this, we detected two nuclear export signal motifs in this region. This N-terminal region had a SUMO interaction motif (SIM) whose mutation greatly reduced the ability of Setdb1 to associate with PML-NB and thus resulted in the disaggregation of PML-NB structure. We therefore presume that the cytoplasmic retention of over-expressed Setdb1 occurs as part of a regulatory mechanism to set a tight limit on the nuclear activity of Setdb1, whose excess activity might result in random and haphazard chromatin modifications that cause globally aberrant gene expression.
authors.affiliation: Development and Differentiation Research Center, KRIBB, 111 Gwahangno, Yuseong-gu, Daejeon 305-806, South Korea.
authors.forename: Sunwha
authors.initials: S
authors.lastname: Cho
authors.forename: Jung Sun
authors.initials: JS
authors.lastname: Park
authors.forename: Yong-Kook
authors.initials: YK
authors.lastname: Kang
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism*; D005786:Gene Expression Regulation; D011495:Histone-Lysine N-Methyltransferase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D051379:Mice; D041681:NIH 3T3 Cells; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000071156:Promyelocytic Leukemia Protein; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000378:metabolism
chemical_list: D009687:Nuclear Proteins; C513293:Pml protein, mouse; D000071156:Promyelocytic Leukemia Protein; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D011495:Histone-Lysine N-Methyltransferase; C516239:SETDB1 protein, mouse