title: Characterization of the ubinuclein protein as a new member of the nuclear and adhesion complex components (NACos).
abstract: BACKGROUND
  We characterized previously a cellular protein through its interaction with cellular and viral transcription factors from the bZip family. The corresponding mRNA was detected in a wide range of cell types and the protein was highly expressed in the nucleus of human keratinocytes. On the basis of these observations, we named this protein ubinuclein.
  
  
  RESULTS
  Using a specific monoclonal antibody, we have shown in the present study that, although endogenous ubinuclein was mainly nuclear in sparse MDCK (Madin-Darby canine kidney) cells, it was exclusively present in the cell-cell junctions in confluent MDCK cultures or in polarized HT29 cells, where it co-localized with the tight junction marker ZO-1 (zonula occludens 1). In accordance with this, we have shown that ubinuclein interacted with ZO-1 in vitro and in vivo. In cultures of undifferentiated human keratinocytes, ubinuclein was essentially nuclear, but in differentiated cells, in which involucrin and periplakin reside at the apical cell membrane and at the cell-cell junctions, ubinuclein staining was observed at the lateral cell-cell borders. In human skin, ubinuclein appeared as a thread-like pattern between the upper granular cell layer and the cornified cell layer. In mouse epithelia, including bile canaliculi, bronchioli, salivary gland ducts, and oral and olfactory epithelium, ubinuclein co-localized with tight junction markers. Ubinuclein was, however, not present in endothelial cell-cell junctions. In addition, when overexpressed, ubinuclein localized to the nucleus and prevented MDCK cells from entering cytokinesis, resulting in multinucleated giant cells after several cycles of endoreplication.
  
  
  CONCLUSIONS
  Ubinuclein mRNA and its corresponding protein are expressed in almost all cell types. Analyses have revealed that in most cells ubinuclein occurred in the nucleoplasm, but in cells forming tight junctions it is recruited to the plaque structure of the zonula occludens. This recruitment appeared to be dependent on cell density. Therefore ubinuclein is a new NACos (nuclear and adhesion complex component) protein.
authors.affiliation: Department of Dermatology and Cutaneous Biology, Thomas Jefferson University, Philadelphia, PA, USA.
authors.forename: Sirpa
authors.initials: S
authors.lastname: Aho
authors.forename: Julien
authors.initials: J
authors.lastname: Lupo
authors.forename: Pierre-Alain
authors.initials: PA
authors.lastname: Coly
authors.forename: Amélie
authors.initials: A
authors.lastname: Sabine
authors.forename: Marc
authors.initials: M
authors.lastname: Castellazzi
authors.forename: Patrice
authors.initials: P
authors.lastname: Morand
authors.forename: Alain
authors.initials: A
authors.lastname: Sergeant
authors.forename: Evelyne
authors.initials: E
authors.lastname: Manet
authors.forename: Véronique
authors.initials: V
authors.lastname: Boyer
authors.forename: Henri
authors.initials: H
authors.lastname: Gruffat
mesh_terms: D000818:Animals; D002460:Cell Line; D004285:Dogs; D004847:Epithelial Cells / Q000737:chemistry*; D006801:Humans; D007365:Intercellular Junctions / Q000737:chemistry; D015603:Keratinocytes / Q000737:chemistry; D051379:Mice; D009687:Nuclear Proteins / Q000032:analysis* / Q000235:genetics; D012867:Skin / Q000166:cytology; D014157:Transcription Factors / Q000032:analysis* / Q000235:genetics
chemical_list: D009687:Nuclear Proteins; D014157:Transcription Factors; C406814:UBN1 protein, human; C541352:ubinuclein protein, mouse