title: A non-tight junction function of claudin-7-Interaction with integrin signaling in suppressing lung cancer cell proliferation and detachment.
abstract: BACKGROUND
  Claudins are a family of tight junction (TJ) membrane proteins involved in a broad spectrum of human diseases including cancer. Claudin-7 is a unique TJ membrane protein in that it has a strong basolateral membrane distribution in epithelial cells and in tissues. Therefore, this study aims to investigate the functional significance of this non-TJ localization of claudin-7 in human lung cancer cells.
  
  
  METHODS
  Claudin-7 expression was suppressed or deleted by lentivirus shRNA or by targeted-gene deletion. Cell cycle analysis and antibody blocking methods were employed to assay cell proliferation and cell attachment, respectively. Electron microscopy and transepthelial electrical resistance measurement were performed to examine the TJ ultrastructure and barrier function. Co-immunolocalization and co-immunoprecipitation was used to study claudin-7 interaction with integrin β1. Tumor growth in vivo were analyzed using athymic nude mice.
  
  
  RESULTS
  Claudin-7 co-localizes and forms a stable complex with integrin β1. Both suppressing claudin-7 expression by lentivirus shRNA in human lung cancer cells (KD cells) and deletion of claudin-7 in mouse lungs lead to the reduction in integrin β1 and phospho-FAK levels. Suppressing claudin-7 expression increases cell growth and cell cycle progression. More significantly, claudin-7 KD cells have severe defects in cell-matrix interactions and adhere poorly to culture plates with a remarkably reduced integrin β1 expression. When cultured on uncoated glass coverslips, claudin-7 KD cells grow on top of each other and form spheroids while the control cells adhere well and grow as a monolayer. Reintroducing claudin-7 reduces cell proliferation, upregulates integrin β1 expression and increases cell-matrix adhesion. Integrin β1 transfection partially rescues the cell attachment defect. When inoculated into nude mice, claudin-7 KD cells produced significantly larger tumors than control cells.
  
  
  CONCLUSIONS
  In this study, we identified a previously unrecognized function of claudin-7 in regulating cell proliferation and maintaining epithelial cell attachment through engaging integrin β1.
authors.affiliation: School of Medicine, Hangzhou Normal University, Hangzhou, 310036, China. zhelu84@126.com.|Department of Anatomy and Cell Biology, Brody School of Medicine, East Carolina University, Greenville, NC, 27834, USA. zhelu84@126.com.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Lu
authors.affiliation: Department of Anatomy and Cell Biology, Brody School of Medicine, East Carolina University, Greenville, NC, 27834, USA. KIMDO11@students.ecu.edu.
authors.forename: Do Hyung
authors.initials: DH
authors.lastname: Kim
authors.affiliation: Department of Anatomy and Cell Biology, Brody School of Medicine, East Carolina University, Greenville, NC, 27834, USA. fjmelite@163.com.
authors.forename: Junming
authors.initials: J
authors.lastname: Fan
authors.affiliation: Department of Anatomy and Cell Biology, Brody School of Medicine, East Carolina University, Greenville, NC, 27834, USA. luq@ecu.edu.|Leo Jenkins Cancer Center, Brody School of Medicine, East Carolina University, Greenville, NC, 27834, USA. luq@ecu.edu.
authors.forename: Qun
authors.initials: Q
authors.lastname: Lu
authors.affiliation: Leo Jenkins Cancer Center, Brody School of Medicine, East Carolina University, Greenville, NC, 27834, USA. VERBANACK@ecu.edu.|Department of Surgery, Brody School of Medicine, East Carolina University, Greenville, NC, 27834, USA. VERBANACK@ecu.edu.
authors.forename: Kathryn
authors.initials: K
authors.lastname: Verbanac
authors.affiliation: Department of Anatomy and Cell Biology, Brody School of Medicine, East Carolina University, Greenville, NC, 27834, USA. dinglei1005@126.com.
authors.forename: Lei
authors.initials: L
authors.lastname: Ding
authors.affiliation: Department of Anatomy and Cell Biology, Brody School of Medicine, East Carolina University, Greenville, NC, 27834, USA. RENEGARRA@ecu.edu.
authors.forename: Randall
authors.initials: R
authors.lastname: Renegar
authors.affiliation: Department of Anatomy and Cell Biology, Brody School of Medicine, East Carolina University, Greenville, NC, 27834, USA. cheny@ecu.edu.|Leo Jenkins Cancer Center, Brody School of Medicine, East Carolina University, Greenville, NC, 27834, USA. cheny@ecu.edu.
authors.forename: Yan-Hua
authors.initials: YH
authors.lastname: Chen
mesh_terms: D000818:Animals; D002448:Cell Adhesion; D002453:Cell Cycle; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D057167:Claudins / Q000235:genetics / Q000378:metabolism*; D004195:Disease Models, Animal; D015870:Gene Expression; D055785:Gene Knockdown Techniques; D064593:Heterografts; D006801:Humans; D019012:Integrin beta1 / Q000235:genetics / Q000378:metabolism; D016023:Integrins / Q000235:genetics / Q000378:metabolism*; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D011485:Protein Binding; D015398:Signal Transduction
chemical_list: C473255:CLDN7 protein, human; D057167:Claudins; D019012:Integrin beta1; D016023:Integrins