title: Expression and function of PEPT2 during transdifferentiation of alveolar epithelial cells.
abstract: OBJECTIVE
  The purpose of this study was to clarify the expression and function of peptide transporter 2 (PEPT2) in primary cultured alveolar type II epithelial cells and in transdifferentiated type I-like cells.
  
  
  METHODS
  Real-time PCR analysis, uptake study of [(3)H]Gly-Sar, and immunostaining were performed in alveolar epithelial cells.
  
  
  RESULTS
  The expression of PEPT2 mRNA in type II cells isolated from rat lungs was highest at day 0, and decreased rapidly during culture of the cells. In accordance with this change, PEPT2 activity estimated as cefadroxil-sensitive [(3)H]Gly-Sar uptake also decreased along with transdifferentiation. The expression of PEPT2 protein in type II cells was confirmed by immunostaining and Western blot analysis. The uptake of [(3)H]Gly-Sar in type II cells was time- and pH-dependent. In contrast, minimal time-dependence and no pH-dependence of [(3)H]Gly-Sar uptake were observed in type I-like cells. The maximal [(3)H]Gly-Sar uptake was observed at pH6.0, and the uptake decreased at higher pHs in type II cells. The uptake of [(3)H]Gly-Sar in type II cells was inhibited by cefadroxil in a concentration-dependent manner, the IC50 value being 4.3 μM. On the other hand, no significant inhibition by cefadroxil was observed in type I-like cells. In addition, [(3)H]Gly-Sar uptake in type II cells was saturable, the Km value being 72.0 μM.
  
  
  CONCLUSIONS
  PEPT2 is functionally expressed in alveolar type II epithelial cells, but the expression decreases along with transdifferentiation, and PEPT2 would be almost completely lost in type I cells.
authors.affiliation: Department of Pharmaceutics and Therapeutics, Graduate School of Biomedical & Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan. Electronic address: takanom@hiroshima-u.ac.jp.
authors.forename: Mikihisa
authors.initials: M
authors.lastname: Takano
authors.forename: Taishi
authors.initials: T
authors.lastname: Horiuchi
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Sasaki
authors.forename: Yuki
authors.initials: Y
authors.lastname: Kato
authors.forename: Junya
authors.initials: J
authors.lastname: Nagai
authors.forename: Ryoko
authors.initials: R
authors.lastname: Yumoto
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002434:Cefadroxil / Q000494:pharmacology; D054338:Cell Transdifferentiation / Q000187:drug effects / Q000502:physiology*; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D015870:Gene Expression / Q000187:drug effects / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D008168:Lung / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D008297:Male; D061251:Primary Cell Culture; D051381:Rats; D027981:Symporters / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000502:physiology*; D013997:Time Factors
chemical_list: D027981:Symporters; C093694:hydrogen-coupled oligopeptide transporter PepT2; D002434:Cefadroxil
keywords: Alveolar epithelial cells; Gly-Sar uptake; Oligopeptide transporter; PEPT2; Transdifferentiation