title: Caki-1 cells represent an in vitro model system for studying the human proximal tubule epithelium.
abstract: OBJECTIVE
  The human proximal tubule (PT) epithelium is distinguished from other nephron segments via several unique characteristics. Studies assessing PT epithelium increasingly employ cell lines, bypassing the complexity of primary cell cultures. However, few human model systems exist for studying PT cells in vitro. The current work involves an intensive characterization of Caki-1 cells, a commercially available human renal cell line.
  
  
  METHODS
  Caki-1 cells were validated as a representative model system for PT cell research via morphological, physiological and biochemical investigations including light and transmission electron microscopy, transepithelial electrical resistance (TER) measurements and the detection of PT markers.
  
  
  RESULTS
  Morphologically, these cells form a polarized monolayer with apical located microvilli and multiple mitochondria per cell. Low TER ranging from 2 to 28 Omega cm(2) was determined for Caki-1 cells, characteristic of the 'leaky' PT epithelium in vivo. Expression of the PT markers: NHE3, GGT, DPP IV, APM and AP were present in Caki-1 cells. Two epithelial markers, E-cadherin and Na(+)/K(+)-ATPase, were additionally observed.
  
  
  CONCLUSIONS
  The current work is a concise summary which confirms that Caki-1 cells represent well-differentiated polarized PT cells in vitro, regardless of its cancerous origin and multiple passaging. They prove to be a significant contribution to the field of PT research.
authors.affiliation: Institute of Pharmacy, Johannes Gutenberg University, Department of Pharmaceutical Technology, Mainz, Germany.
authors.forename: Natalie
authors.initials: N
authors.lastname: Glube
authors.forename: Andreas
authors.initials: A
authors.lastname: Giessl
authors.forename: Uwe
authors.initials: U
authors.lastname: Wolfrum
authors.forename: Peter
authors.initials: P
authors.lastname: Langguth
mesh_terms: D015415:Biomarkers / Q000378:metabolism; D018938:Caco-2 Cells; D045744:Cell Line, Tumor / Q000737:chemistry / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure*; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure*; D006801:Humans; D007680:Kidney Neoplasms / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure*