Decreased catalytic function with altered sumoylation of DNA topoisomerase I in the nuclei of scleroderma fibroblasts
1 Division of Rheumatology, Department of Internal Medicine, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
2 Department of Medicine, University of Calgary, Calgary, AB T2N 1N4, Canada
3 Rice University, Houston, Post Office Box 1892, TX 77030, USA
4 Departmant of Pathology, Baylor College of Medicine, Houston, TX 77030, USA
Arthritis Research & Therapy 2011, 13:R128 doi:10.1186/ar3435Published: 9 August 2011
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.
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.
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.
The catalytic function of topo I was decreased in SSc fibroblasts, to which increased sumoylation of topo I may contribute.