title: Degradation of filamin induces contraction of vascular smooth muscle cells in type-I collagen matrix honeycombs.
abstract: BACKGROUND
  Dedifferentiated rabbit vascular smooth muscle cells (SMCs) exhibit similar features to differentiated SMCs when cultured in three-dimensional matrices of type-I collagen called "honeycombs," but the mechanism is unknown. The role of filamin, an actin-binding protein that links actin filaments in SMCs, was investigated.
  
  
  METHODS
  Filamin and other related proteins were detected by western blot analysis and immunofluorescence staining. Honeycomb size was measured to confirm the contraction of SMCs.
  
  
  RESULTS
  Full-length filamin was expressed in subconfluent SMCs cultured on plates; however, degradation of filamin, which might be regulated by calpain, was observed in confluent SMCs cultured on plates and in honeycombs. While filamin was co-localized with β-actin in subconfluent SMCs grown on plates, filamin was detected in the cytoplasm in SMCs cultured in honeycombs, and degraded filamin was mainly detected in the cytoplasmic fraction of these cells. In addition, β-actin expression was low in the cytoskeletal fraction of SMCs cultured in honeycombs compared with cells cultured on plates, and the size of the honeycombs used for culturing SMCs was significantly reduced.
  
  
  CONCLUSIONS
  These data suggest that degradation of filamin in SMCs cultured in honeycombs induces structural weakness of β-non-muscle actin filaments, thereby permitting SMCs in honeycombs to achieve contractility.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Uchida
authors.forename: Itsuko
authors.initials: I
authors.lastname: Ishii
authors.forename: Kaori
authors.initials: K
authors.lastname: Hirata
authors.forename: Fumiko
authors.initials: F
authors.lastname: Yamamoto
authors.forename: Kaori
authors.initials: K
authors.lastname: Tashiro
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Suzuki
authors.forename: Yuji
authors.initials: Y
authors.lastname: Nakayama
authors.forename: Noritaka
authors.initials: N
authors.lastname: Ariyoshi
authors.forename: Mitsukazu
authors.initials: M
authors.lastname: Kitada
mesh_terms: D000818:Animals; D001483:Base Sequence; D024042:Collagen Type I / Q000378:metabolism*; D003285:Contractile Proteins / Q000378:metabolism*; D017931:DNA Primers; D064448:Filamins; D008297:Male; D051379:Mice; D008840:Microfilament Proteins / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D011817:Rabbits; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D024042:Collagen Type I; D003285:Contractile Proteins; D017931:DNA Primers; D064448:Filamins; D008840:Microfilament Proteins