title: αvβ5 integrin promotes dedifferentiation of monolayer-cultured articular chondrocytes.
abstract: OBJECTIVE
  When cultured in monolayers, articular chondrocytes undergo an obvious phenotypic change. Although the involvement of integrins has been suggested, the exact mechanisms of the change have not been determined. This study was undertaken to clarify the mechanisms underlying the loss of chondrocyte phenotype early after plating.
  
  
  METHODS
  Primary cultured human articular chondrocytes were used for the experiments. Involvement of respective integrins in the phenotypic change was investigated in RNA interference (RNAi) experiments. A signaling pathway involved in the change was identified in experiments using specific inhibitors and adenoviruses encoding mutated genes involved in the pathway. Adenoviruses carrying mutated GTPases were used to determine the involvement of small GTPases in the process.
  
  
  RESULTS
  In monolayer-cultured chondrocytes, suppression of αv or β5 integrin expression by RNAi inhibited morphologic changes in the cells and increased (or prevented a reduction in) the expression of various cartilage matrix genes. Consistent results were obtained in experiments using a blocking antibody and a synthetic inhibitor of αvβ5 integrin. The decrease in cartilage matrix gene expression in chondrocytes after plating was mediated by ERK signaling, which was promoted primarily by αvβ5 integrin. In articular chondrocytes, the affinity of αvβ5 integrin for ligands was regulated by the small GTPase R-Ras. R-Ras was gradually activated in monolayer-cultured chondrocytes after plating, which caused a gradual decline in cartilage matrix gene expression through enhanced αvβ5 integrin activation and the subsequent increase in ERK signaling.
  
  
  CONCLUSIONS
  Our findings indicate that αvβ5 integrin may be involved in the change that occurs in monolayer-cultured chondrocytes after plating.
authors.affiliation: National Hospital Organization Sagamihara Hospital, Sagamihara, Japan. n-fukui@sagamihara-hosp.gr.jp
authors.forename: Naoshi
authors.initials: N
authors.lastname: Fukui
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Ikeda
authors.forename: Nobuho
authors.initials: N
authors.lastname: Tanaka
authors.forename: Masahiro
authors.initials: M
authors.lastname: Wake
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Yamaguchi
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Mitomi
authors.forename: Satoru
authors.initials: S
authors.lastname: Ishida
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Furukawa
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Hamada
authors.forename: Yoshinari
authors.initials: Y
authors.lastname: Miyamoto
authors.forename: Motoji
authors.initials: M
authors.lastname: Sawabe
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Tashiro
authors.forename: Yozo
authors.initials: Y
authors.lastname: Katsuragawa
authors.forename: Shigeto
authors.initials: S
authors.lastname: Tohma
mesh_terms: D000704:Analysis of Variance; D015153:Blotting, Western; D002358:Cartilage, Articular / Q000166:cytology / Q000378:metabolism*; D054337:Cell Dedifferentiation / Q000502:physiology*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D034622:RNA Interference; D019030:Receptors, Vitronectin / Q000235:genetics / Q000378:metabolism*
chemical_list: D019030:Receptors, Vitronectin; C064660:integrin alphaVbeta5