title: Recruitment of topoisomerase I (Scl-70) to nucleoplasmic proteasomes in response to xenobiotics suggests a role for altered antigen processing in scleroderma.
abstract: OBJECTIVE
  Scleroderma, also known as systemic sclerosis (SSc), is a chronic, life-threatening autoimmune disease characterized by a wide spectrum of manifestations and a variable evolution. The presence of particular antinuclear antibodies is often predictive of the clinical expression and prognosis of the disease, but the molecular mechanisms of the immune responses remain unclear. Recently, we have shown xenobiotic-induced recruitment of nuclear autoantigens to proteasomes in the cell nucleus in cell culture and in animal models in correlation with a unique autoantibody response. In this study, we attempted to validate our findings in patients with SSc.
  
  
  METHODS
  Using indirect immunofluorescence microscopy, run-on replication and transcription assays, immunoblotting, and proteasome activity assays, we analyzed the nuclear structure, function, and proteasomal proteolysis in HEp-2 cells treated with xenobiotics or left untreated. Blood dendritic cells (DCs) were isolated from 30 patients with SSc and age- and sex-matched control subjects to determine the subcellular localization of SSc autoantigens in relation to proteasomes.
  
  
  RESULTS
  Xenobiotics induced a relocation of the SSc autoantigen DNA topoisomerase I (Scl-70, topo I) to nucleoplasmic clusters, where proteasomes degrade topo I. Colocalization of topo I with proteasomes occurred exclusively in DCs from patients with SSc who developed antibodies against this autoantigen. Neither centromeres nor other SSc autoantigens colocalized with proteasomes in DCs from patients with SSc or from control subjects.
  
  
  CONCLUSIONS
  Alteration of nuclear structure and function by xenobiotics induces recruitment of the nuclear autoantigen topo I for proteasomal processing. This event may, in turn, lead to subsequent presentation of the resulting peptides on the cell surface and the autoimmune responses against topo I in SSc.
authors.affiliation: Heinrich-Heine-University Düsseldorf, Dusseldorf, Germany.
authors.forename: Min
authors.initials: M
authors.lastname: Chen
authors.forename: Assemgul
authors.initials: A
authors.lastname: Dittmann
authors.forename: Annegret
authors.initials: A
authors.lastname: Kuhn
authors.forename: Thomas
authors.initials: T
authors.lastname: Ruzicka
authors.forename: Anna
authors.initials: A
authors.lastname: von Mikecz
mesh_terms: D017951:Antigen Presentation / Q000276:immunology*; D002478:Cells, Cultured; D004264:DNA Topoisomerases, Type I / Q000276:immunology*; D003713:Dendritic Cells / Q000276:immunology; D006801:Humans; D009687:Nuclear Proteins / Q000276:immunology; D046988:Proteasome Endopeptidase Complex / Q000276:immunology*; D012595:Scleroderma, Systemic / Q000276:immunology*; D015262:Xenobiotics / Q000276:immunology*
chemical_list: D009687:Nuclear Proteins; C048100:Scl 70 antigen, human; D015262:Xenobiotics; D046988:Proteasome Endopeptidase Complex; D004264:DNA Topoisomerases, Type I