title: UVB irradiation-induced changes in the 27-kd heat shock protein (HSP27) in human corneal epithelial cells.
abstract: OBJECTIVE
  This study investigated the presence of the 27-kd heat shock protein (HSP27) and its responses to ultraviolet B (UVB) irradiation in human corneal epithelium and in cultured corneal epithelial cells.
  
  
  METHODS
  Human corneal epithelial cells including presumed corneal epithelial stem cells were cultured in vitro. HSP27 expression and intracellular localization in normal corneas or cultured corneal cells were examined using immunofluorescence staining. The expression of HSP27 in cultured corneal cells was also detected using western blotting, and the phosphorylated isoforms of HSP27 were identified using isoelectric focusing.
  
  
  RESULTS
  In normal corneal tissue, HSP27 was present in limbal basal and suprabasilar epithelial cells. In cultured epithelial corneal cells, HSP27 expression was heterogeneous: Some cells expressed virtually no HSP27 and others showed relatively strong expression. HSP27 was localized to the cytoplasm in nonstressed cells and translocated to the perinuclear and nuclear areas after UVB irradiation. UVB irradiation also induced the phosphorylation of HSP27, resulting in the increase in monophosphorylated isoform and formation of biphosphorylated isoform. UV induced the phosphorylation of HSP27 apparently through activation of p38 mitogen-activated protein kinase.
  
  
  CONCLUSIONS
  HSP27 is present mainly as a nonphosphorylated isoform in corneal epithelium and cultured corneal epithelial cells under nonstressed conditions. The constitutional expression of HSP27 suggests that it plays a physiologic role in the cornea. After UVB irradiation, HSP27 undergoes rapid phosphorylation and translocation. This stress response may be related to a protective role of HSP27 for survival of UVB-exposed corneal cells.
authors.affiliation: Department of Dermatology, University of California Davis School of Medicine, Davis, CA 95616, USA.
authors.forename: Biao
authors.initials: B
authors.lastname: Shi
authors.forename: Bin
authors.initials: B
authors.lastname: Han
authors.forename: Ivan R
authors.initials: IR
authors.lastname: Schwab
authors.forename: R Rivkah
authors.initials: RR
authors.lastname: Isseroff
mesh_terms: D015153:Blotting, Western; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D019573:Epithelium, Corneal / Q000378:metabolism / Q000528:radiation effects*; D019084:Fluorescent Antibody Technique, Indirect; D055551:HSP27 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000378:metabolism / Q000528:radiation effects*; D006801:Humans; D007526:Isoelectric Point; D018832:Molecular Chaperones; D009363:Neoplasm Proteins / Q000378:metabolism / Q000528:radiation effects*; D010766:Phosphorylation; D021381:Protein Transport / Q000528:radiation effects; D014466:Ultraviolet Rays; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D055551:HSP27 Heat-Shock Proteins; C057725:HSPB1 protein, human; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D009363:Neoplasm Proteins; D048051:p38 Mitogen-Activated Protein Kinases