title: A novel Crumbs3 isoform regulates cell division and ciliogenesis via importin beta interactions.
abstract: The Crumbs family of apical transmembrane proteins regulates apicobasal polarity via protein interactions with a conserved C-terminal sequence, ERLI. However, one of the mammalian Crumbs proteins, Crumbs3 (CRB3) has an alternate splice form with a novel C-terminal sequence ending in CLPI (CRB3-CLPI). We report that CRB3-CLPI localizes to the cilia membrane and a membrane compartment at the mitotic spindle poles. Knockdown of CRB3-CLPI leads to both a loss of cilia and a multinuclear phenotype associated with centrosomal and spindle abnormalities. Using protein purification, we find that CRB3-CLPI interacts with importin beta-1 in a Ran-regulated fashion. Importin beta-1 colocalizes with CRB3-CLPI during mitosis, and a dominant-negative form of importin beta-1 closely phenocopies CRB3-CLPI knockdown. Knockdown of importin beta-1 blocks targeting of CRB3-CLPI to the spindle poles. Our data suggest an expanded role for Crumbs proteins in polarized membrane targeting and cell division via unique interactions with importin proteins.
authors.affiliation: Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
authors.forename: Shuling
authors.initials: S
authors.lastname: Fan
authors.forename: Vanessa
authors.initials: V
authors.lastname: Fogg
authors.forename: Qian
authors.initials: Q
authors.lastname: Wang
authors.forename: Xiao-Wei
authors.initials: XW
authors.lastname: Chen
authors.forename: Chia-Jen
authors.initials: CJ
authors.lastname: Liu
authors.forename: Ben
authors.initials: B
authors.lastname: Margolis
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D002455:Cell Division / Q000502:physiology*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D016764:Cell Polarity; D018385:Centrosome / Q000378:metabolism / Q000648:ultrastructure; D002923:Cilia / Q000502:physiology* / Q000648:ultrastructure; D018390:Gene Targeting; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D008941:Spindle Apparatus / Q000378:metabolism / Q000648:ultrastructure; D028961:beta Karyopherins / Q000235:genetics / Q000378:metabolism*
chemical_list: C472002:CRB3 protein, human; C424166:KPNB1 protein, human; D008562:Membrane Glycoproteins; D020033:Protein Isoforms; D028961:beta Karyopherins