Volume 6 Supplement 1
Involvement of SUMO-1 in the regulation of apoptosis in prosthesis loosening fibroblasts
© The Author(s) 2004
Received: 16 January 2004
Published: 24 February 2004
Prosthesis loosening fibroblasts (PLF) contribute significantly to the pathogenesis of aseptic prosthesis loosening (APL) and show similarities to rheumatoid arthritis synovial fibroblasts (RA-SF). Based on data that have linked the increased expression of the small ubiquitin-like modifier SUMO-1 to the resistance of RA-SF against apoptosis, we investigated the expression of SUMO-1 in APL and used gene transfer of the SUMO protease SENP1 to study consequences of SUMOylation in PLF.
We used in situ hybridization (ISH) to study the expression of SUMO-1 in APL interface tissues. Quantitative PCR and Western blot were applied to measure the expression of SUMO-1 in PLF in comparison with RA-SF. Confocal microscopy of PLF transfected with GFP-labeled wild type (wt) or mutant (mt) gene constructs of SENP1 was performed to investigate the cellular localization of SUMO-1. To study the functional contribution of SUMO-1 to the apoptosis of PLF, SENP1wt-, SENP1mt- and mock-transfected PLF were stimulated with FasL, and apoptosis was determined by a histon fragmentation assay.
ISH revealed marked expression of SUMO-1 in all tissues, with most prominent staining at sites attached to bone. The expression of SUMO-1 in PLF was comparable with that in RA-SF. Confocal microscopy revealed localization of SUMO-1 mainly in nuclear PML-bodies. After transfection of PLF with SENP1, high levels of SENP1 mRNA were measured (up to 472-fold versus endogenous SENP-1). Transfection of PLF with SENP1wt decreased the nuclear staining for SUMO-1, and increased significantly FasL-induced apoptosis (155% versus SENP-1mt). Spontaneous cell death remained unaffected.
The data suggest that SUMO-1 is involved in the activation of PLF and RA-SF by preventing these cells from Fas-induced apoptosis. The modification of nuclear proteins by SUMO-1 appears to contribute to the antiapoptotic effects of SUMO-1. By de-conjugating SUMO-1 from its nuclear substrates, SENP1 can regulate the apoptotic response of PLF.