title: Arkadia-Smad7-mediated positive regulation of TGF-beta signaling in a rat model of tubulointerstitial fibrosis.
abstract: OBJECTIVE
  Upregulation of transforming growth factor beta (TGF-beta)/Smad signaling has been implicated in the primary pathogenesis of renal fibrosis. The ubiquitin-proteasome pathway has an important influence on TGF-beta signaling through regulating Smad degradation. As E3 ubiquitin ligases, both Arkadia and Smurf2 are involved in this prosess. In this study, we focused on Arkadia, Smurf2, Smad7, and TGF-beta type I receptor (TbetaRI), principal molecules in the regulation of TGF-beta signaling, to understand the regulatory mechanism of ubiquitin-proteasomal degradation of TGF-beta signaling in the pathogenesis of renal fibrosis.
  
  
  METHODS
  A unilateral ureteral obstruction (UUO) model was employed, and sham-operated rats were used as controls. Renal lesions and the expression of Arkadia, Smurf2, Smad7, TbetaRI, TGF-beta1, and type 1 collagen (COL-1) were detected by Western blot, immunoprecipitation, immunohistochemistry, and/or reverse transcription-polymerase chain reaction.
  
  
  RESULTS
  The results indicated progressive tubulointerstitial fibrosis, high expression levels of Arkadia, Smurf2, TbetaRI, TGF-beta1 mRNA, type 1 collagen mRNA, and Smad7 mRNA, and low levels of Smad7 protein in the kidneys of rats with unilateral ureteral obstruction, in which Smurf2 interacted with both Smad7 and TbetaRI, and Arkadia only interacted with Samd7 but not with TbetaRI.
  
  
  CONCLUSIONS
  Reduction of Smad7 resulting from ubiquitin-dependent degradation may be mainly attributed to Arkadia, and Arkadia-Smad7-mediated positive regulation of TGF-beta signaling may play a promoting role in the progression of tubulointerstitial fibrosis.
authors.affiliation: Department of Nephrology, Second Xiangya Hospital of the Central South University, Changsha, China. xiaozhaosun@hotmail.com
authors.forename: Fu-You
authors.initials: FY
authors.lastname: Liu
authors.forename: Xiao-Zhao
authors.initials: XZ
authors.lastname: Li
authors.forename: You-Ming
authors.initials: YM
authors.lastname: Peng
authors.forename: Hong
authors.initials: H
authors.lastname: Liu
authors.forename: Ying-Hong
authors.initials: YH
authors.lastname: Liu
mesh_terms: D030201:Activin Receptors, Type I / Q000096:biosynthesis; D000818:Animals; D004195:Disease Models, Animal; D005355:Fibrosis; D007674:Kidney Diseases / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology; D008297:Male; D017346:Protein Serine-Threonine Kinases; D051381:Rats; D017207:Rats, Sprague-Dawley; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000096:biosynthesis; D015398:Signal Transduction; D051906:Smad7 Protein / Q000096:biosynthesis*; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000096:biosynthesis*
chemical_list: D018125:Receptors, Transforming Growth Factor beta; D051906:Smad7 Protein; D016212:Transforming Growth Factor beta; D044767:Ubiquitin-Protein Ligases; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I; C000625843:Tgfbr1 protein, rat