title: Decreased catalytic function with altered sumoylation of DNA topoisomerase I in the nuclei of scleroderma fibroblasts.
abstract: BACKGROUND
  Sumoylation is involved in nucleolus-nucleoplasm transport of DNA topoisomerase I (topo I), which may associate with changes of cellular and topo I functions. Skin fibroblasts of patients with systemic sclerosis (SSc) exhibit profibrotic cellular changes. The aims of this study were to examine the catalytic function and sumoylation of topo I in the nuclei of SSc fibroblasts, a major cell type involved in the fibrotic process.
  
  
  METHODS
  Eleven pairs of fibroblast strains obtained from nonlesional skin biopsies of SSc patients and age/sex/ethnicity-matched normal controls were examined for catalytic function of nuclear topo I. Immunoprecipitation (IP)-Western blots were used to examine sumoylation of fibroblast topo I. Real-time quantitative RT-PCR was used to measure transcript levels of SUMO1 and COL1A2 in the fibroblasts.
  
  
  RESULTS
  Topo I in nuclear extracts of SSc fibroblasts generally showed a significantly lower efficiency than that of normal fibroblasts in relaxing equivalent amounts of supercoiled DNA. Increased sumoylation of topo I was clearly observed in 7 of 11 SSc fibroblast strains. Inhibition of SUMO1 with SUMO1 siRNA improved the catalytic efficiency of topo I in the SSc fibroblasts. In contrast, sumoylation of recombinant topo I proteins reduced their catalytic function.
  
  
  CONCLUSIONS
  The catalytic function of topo I was decreased in SSc fibroblasts, to which increased sumoylation of topo I may contribute.
authors.affiliation: Division of Rheumatology, Department of Internal Medicine, University of Texas Health Science Center at Houston, Houston, TX 77030, USA. xiaodong.zhou@uth.tmc.edu
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Zhou
authors.forename: Wei
authors.initials: W
authors.lastname: Lin
authors.forename: Filemon K
authors.initials: FK
authors.lastname: Tan
authors.forename: Shervin
authors.initials: S
authors.lastname: Assassi
authors.forename: Mavin J
authors.initials: MJ
authors.lastname: Fritzler
authors.forename: Xinjian
authors.initials: X
authors.lastname: Guo
authors.forename: Roozbeh
authors.initials: R
authors.lastname: Sharif
authors.forename: Tom
authors.initials: T
authors.lastname: Xia
authors.forename: Syeling
authors.initials: S
authors.lastname: Lai
authors.forename: Frank C
authors.initials: FC
authors.lastname: Arnett
mesh_terms: D055162:Biocatalysis; D015153:Blotting, Western; D002467:Cell Nucleus / Q000201:enzymology*; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D005260:Female; D005347:Fibroblasts / Q000201:enzymology*; D006801:Humans; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D008297:Male; D034741:RNA, Small Interfering; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012595:Scleroderma, Systemic / Q000201:enzymology*; D058207:Sumoylation; D014162:Transfection
chemical_list: D034741:RNA, Small Interfering; D004264:DNA Topoisomerases, Type I; C528909:TOP1 protein, human