title: Side population in LX2 cells decreased by transforming growth factor-β.
abstract: OBJECTIVE
  Side population (SP) cells are known to be enriched in stem/progenitor-like cells. Transforming growth factor (TGF)-β signaling is associated with extracellular matrix (ECM) production in hepatic stellate cells. We hypothesized that the SP fraction in LX2 cells is associated with ECM deposition, which is regulated through TGF-β signaling.
  
  
  METHODS
  We investigated the relationship between SP cells and TGF-β signaling in the hepatic stellate cell line LX2. The effects of TGF-β and SB431542 on the SP fraction and expression of collagen type I and phospho-Smad2 was determined.
  
  
  RESULTS
  We identified 0.8-3% SP cells in LX2 cells. The growth rate of sorted SP and non-SP cells was similar to that of the original LX2 population, but population of the G0/G1 phase was increased in SP cells. Treatment of LX2 cells with TGF-β decreased the SP fraction in a dose-dependent manner and increased the production of collagen type I. Treatment of LX2 cells with SB431542 blocked the effect of TGF-β on the SP fraction and the expression of collagen type I. We cultured LX2 cells on collagen-coated dishes to observe the effect of ECM deposition on the SP fraction. The growth rate and cell cycle distribution was similar to that observed on normal tissue culture dishes, but the SP fraction was decreased when LX2 cells were cultured on collagen-coated plates.
  
  
  CONCLUSIONS
  These results show that LX2 cells contain an SP fraction and that TGF-β signaling is involved in the induction of ECM deposition as well as the number of SP cells.
authors.affiliation: Department of Internal Medicine and Liver Research Institute, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Jong Bin
authors.initials: JB
authors.lastname: Kim
authors.forename: Yeon Hwa
authors.initials: YH
authors.lastname: Ann
authors.forename: Seo Young
authors.initials: SY
authors.lastname: Park
authors.forename: Hyeon-Gun
authors.initials: HG
authors.lastname: Jee
authors.forename: Hye Ri
authors.initials: HR
authors.lastname: Kim
authors.forename: Jeong-Hoon
authors.initials: JH
authors.lastname: Lee
authors.forename: Su Jong
authors.initials: SJ
authors.lastname: Yu
authors.forename: Hyo-Suk
authors.initials: HS
authors.lastname: Lee
authors.forename: Yoon Jun
authors.initials: YJ
authors.lastname: Kim
keywords: LX2 cells; hepatic stellate cells; side population; stem cells; transforming growth factor-β