title: Tumor suppressor protein Lgl mediates G1 cell cycle arrest at high cell density by forming an Lgl-VprBP-DDB1 complex.
abstract: Lethal giant larvae (Lgl) is an evolutionarily conserved tumor suppressor whose loss of function causes disrupted epithelial architecture with enhanced cell proliferation and defects in cell polarity. A role for Lgl in the establishment and maintenance of cell polarity via suppression of the PAR-aPKC polarity complex is established; however, the mechanism by which Lgl regulates cell proliferation is not fully understood. Here we show that depletion of Lgl1 and Lgl2 in MDCK epithelial cells results in overproliferation and overproduction of Lgl2 causes G1 arrest. We also show that Lgl associates with the VprBP-DDB1 complex independently of the PAR-aPKC complex and prevents the VprBP-DDB1 subunits from binding to Cul4A, a central component of the CRL4 [VprBP] ubiquitin E3 ligase complex implicated in G1- to S-phase progression. Consistently, depletion of VprBP or Cul4 rescues the overproliferation of Lgl-depleted cells. In addition, the affinity between Lgl2 and the VprBP-DDB1 complex increases at high cell density. Further, aPKC-mediated phosphorylation of Lgl2 negatively regulates the interaction between Lgl2 and VprBP-DDB1 complex. These results suggest a mechanism protecting overproliferation of epithelial cells in which Lgl plays a critical role by inhibiting formation of the CRL4 [VprBP] complex, resulting in G1 arrest.
authors.affiliation: Department of Molecular Biology, Graduate School of Medical Science, Yokohama City University, Yokohama 236-0004, Japan.
authors.forename: Kazunari
authors.initials: K
authors.lastname: Yamashita
authors.affiliation: Department of Molecular Biology, Graduate School of Medical Science, Yokohama City University, Yokohama 236-0004, Japan.
authors.forename: Mariko
authors.initials: M
authors.lastname: Ide
authors.affiliation: Department of Molecular Biology, Graduate School of Medical Science, Yokohama City University, Yokohama 236-0004, Japan.
authors.forename: Kana T
authors.initials: KT
authors.lastname: Furukawa
authors.affiliation: Department of Molecular Biology, Graduate School of Medical Science, Yokohama City University, Yokohama 236-0004, Japan Molecular Cellular Biology Laboratory, Graduate School of Medical Life Science, Yokohama City University, Yokohama 230-0045, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Suzuki
authors.affiliation: Supramolecular Biology, International Graduate School of Arts and Sciences, Yokohama City University, Yokohama 230-0045, Japan.
authors.forename: Hisashi
authors.initials: H
authors.lastname: Hirano
authors.affiliation: Department of Molecular Biology, Graduate School of Medical Science, Yokohama City University, Yokohama 236-0004, Japan ohnos@med.yokohama-cu.ac.jp.
authors.forename: Shigeo
authors.initials: S
authors.lastname: Ohno
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002452:Cell Count; D002460:Cell Line; D016764:Cell Polarity / Q000502:physiology; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004285:Dogs; D029721:Drosophila Proteins / Q000378:metabolism*; D059585:G1 Phase Cell Cycle Checkpoints / Q000502:physiology; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D061985:Madin Darby Canine Kidney Cells; D025581:Neurofibromin 2 / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D025521:Tumor Suppressor Proteins / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases
chemical_list: D002352:Carrier Proteins; C091435:DDB1 protein, human; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D025581:Neurofibromin 2; D025521:Tumor Suppressor Proteins; C081435:l(2)gl protein, Drosophila; D044767:Ubiquitin-Protein Ligases; C530533:DCAF1 protein, human; D017346:Protein Serine-Threonine Kinases