title: Insulin-like growth factor binding protein-6 (IGFBP-6) interacts with DNA-end binding protein Ku80 to regulate cell fate.
abstract: Insulin-like growth factor binding protein-6 (IGFBP-6) is a growth inhibitory protein that regulates the availability of insulin-like growth factors (IGFs). We recently reported that IGFBP-6 exerts intracellular actions via its translocation to the nucleus. We now show that IGFBP-6 co-purifies by tandem-affinity with nuclear proteins involved in DNA stability and repair such as Ku80, Ku70, histone H2B and importin-alpha. Furthermore, this report shows that IGFBP-6 and Ku80 interact specifically using two active binding sites for Ku80 in IGFBP-6. One of the binding sites [196RKR199], as part of the NLS-sequence in IGFBP-6 also binds importin-alpha which may selectively compete with Ku80 regulating its trafficking to the nucleus. Moreover, IGFBP-6 co-localized with Ku80 based on a cell cycle pattern. Overexpression of IGFBP-6 increased the nuclear Ku80 in mitotic cells and reduced it post-mitosis. It is known that if highly expressed IGFBP-6 induces apoptosis and in our model, the down-regulation of Ku80 by specific siRNAs enhanced the apoptotic effect caused by the IGFBP-6 overexpression. This study demonstrates that IGFBP-6 alters cell survival by potentially regulating the availability of Ku80 for the DNA-repair process. This action represents a novel mechanism by which growth inhibitory proteins such as IGFBP-6 regulate cell fate.
authors.affiliation: Department of Pediatrics, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada.
authors.forename: Cristiana
authors.initials: C
authors.lastname: Iosef
authors.forename: Gregory
authors.initials: G
authors.lastname: Vilk
authors.forename: Theofanis
authors.initials: T
authors.lastname: Gkourasas
authors.forename: Kyung-Jong
authors.initials: KJ
authors.lastname: Lee
authors.forename: Benjamin P C
authors.initials: BP
authors.lastname: Chen
authors.forename: Ping
authors.initials: P
authors.lastname: Fu
authors.forename: Leon A
authors.initials: LA
authors.lastname: Bach
authors.forename: Gilles
authors.initials: G
authors.lastname: Lajoie
authors.forename: Madhulika B
authors.initials: MB
authors.lastname: Gupta
authors.forename: Shawn S C
authors.initials: SS
authors.lastname: Li
authors.forename: Victor K
authors.initials: VK
authors.lastname: Han
mesh_terms: D034961:Antigens, Nuclear / Q000032:analysis / Q000302:isolation & purification / Q000378:metabolism*; D017209:Apoptosis; D001665:Binding Sites; D002460:Cell Line; D004247:DNA / Q000378:metabolism; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000032:analysis / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D018976:Insulin-Like Growth Factor Binding Protein 6 / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D000072200:Ku Autoantigen; D008938:Mitosis; D009687:Nuclear Proteins / Q000302:isolation & purification
chemical_list: D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; D018976:Insulin-Like Growth Factor Binding Protein 6; D009687:Nuclear Proteins; D004247:DNA; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen