title: SUN1 interacts with nuclear lamin A and cytoplasmic nesprins to provide a physical connection between the nuclear lamina and the cytoskeleton.
abstract: Nuclear migration and positioning within cells are critical for many developmental processes and are governed by the cytoskeletal network. Although mechanisms of nuclear-cytoskeletal attachment are unclear, growing evidence links a novel family of nuclear envelope (NE) proteins that share a conserved C-terminal SUN (Sad1/UNC-84 homology) domain. Analysis of Caenorhabditis elegans mutants has implicated UNC-84 in actin-mediated nuclear positioning by regulating NE anchoring of a giant actin-binding protein, ANC-1. Here, we report the identification of SUN1 as a lamin A-binding protein in a yeast two-hybrid screen. We demonstrate that SUN1 is an integral membrane protein located at the inner nuclear membrane. While the N-terminal domain of SUN1 is responsible for detergent-resistant association with the nuclear lamina and lamin A binding, lamin A/C expression is not required for SUN1 NE localization. Furthermore, SUN1 does not interact with type B lamins, suggesting that NE localization is ensured by binding to an additional nuclear component(s), most likely chromatin. Importantly, we find that the luminal C-terminal domain of SUN1 interacts with the mammalian ANC-1 homologs nesprins 1 and 2 via their conserved KASH domain. Our data provide evidence of a physical nuclear-cytoskeletal connection that is likely to be a key mechanism in nuclear-cytoplasmic communication and regulation of nuclear position.
authors.affiliation: Department of Genetics, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom.
authors.forename: Farhana
authors.initials: F
authors.lastname: Haque
authors.forename: David J
authors.initials: DJ
authors.lastname: Lloyd
authors.forename: Dawn T
authors.initials: DT
authors.lastname: Smallwood
authors.forename: Carolyn L
authors.initials: CL
authors.lastname: Dent
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Shanahan
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Fry
authors.forename: Richard C
authors.initials: RC
authors.lastname: Trembath
authors.forename: Sue
authors.initials: S
authors.lastname: Shackleton
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism*; D003598:Cytoskeletal Proteins; D003599:Cytoskeleton / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D034904:Lamin Type A / Q000378:metabolism*; D051379:Mice; D008856:Microscopy, Fluorescence; D008869:Microtubule-Associated Proteins / Q000737:chemistry / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D020798:Two-Hybrid System Techniques
chemical_list: D003598:Cytoskeletal Proteins; D034904:Lamin Type A; D008869:Microtubule-Associated Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; C464932:SUN1 protein, mouse; C485901:Syne1 protein, mouse; C485903:Syne2 protein, mouse