Myositis
Abstract Number 1241 - Autoantibodies to Transcriptional Intermediary Factor 1-gamma (TIF1-g) in Dermatomyositis
Authors: Ira N. Targoff1, Edward P. Trieu2, Mauricio Levy-Neto2, Therapol Prasertsuntarasai3, Frederick W. Miller4. 1University of Oklahoma HSC, VAMC, OMRF, Oklahoma City, OK; 2Oklahoma Medical Research Foundation, Oklahoma City, OK; 3University of Oklahoma HSC, Oklahoma City, OK; 4NIEHS, NIH, DHHS, Bethesda, MD
PURPOSE: Autoantibodies (autoabs) have been associated with polymyositis (PM) and dermatomyositis (DM), some with relative specificity for these conditions. Anti-Mi-2 is the only established myositis-specific autoantibody found predominantly in DM. Preliminary reports, however, described anti-p155 in 29% of adult and juvenile DM, but rarely in PM or other diseases. Anti-p155, identified by immunoprecipitation (IPP), reacted with a 155kd protein and showed a nuclear pattern by indirect immunofluorescence, but the nature of the p155 antigen was unknown. The intent of this study was to further characterize p155 and develop better detection methods.
METHODS: Anti-p155 autoabs were confirmed by IPP-blots (IPP-WB) using K562 cell extract. Some anti-p155-positive sera were known to react by IPP but not by WB. Patient sera were therefore used for the IPP step, and anti-p155 reference serum (p155-1) and rabbit antiserum or controls were used for WB. P155 antigen was prepared by affinity-purification and SDS-PAGE. The gel band was digested with trypsin followed by HPLC of peptides and mass spectrometry. Rabbit antibody (anti-TIFp), affinity-purified with MAP, was used to coat wells for capture-ELISA. Wells were incubated with K562 extract, then patient antibody, then rabbit anti-human IgG conjugate.
RESULTS: Mascot analysis of the mass spectrometry gave a score of 81 for human TIF-1g, with scores >47 considered significant. Other significant scores were only seen with related proteins and trypsin. By IPP-WB, rabbit anti-TIFp blotted a 155kd protein band in IPPs prepared with p155-1 serum, similar to the band blotted by p155-1 serum. Similarly, p155-1, but not normal serum, blotted a 155kd protein in IPPs prepared with rabbit anti-TIFp.
CONCLUSION: These studies identify a target of anti-p155 autoantibodies as TIF-1g, a transcriptional co-regulator. Thus, two DM-associated autoantibodies (anti p 155 and anti Mi-2) target nuclear, transcription-regulating proteins, while autoantibodies often seen in PM such as anti-synthetases target cytoplasmic translation-related proteins.
COMMENT: This work points out a novel anti-nuclear autoantigenic target in dermatomyositis. Additional work by this group also determined that this autoantigen may be seen more often in myositis associated with malignancy. Thus, anti-p 155 may serve as a diagnostic antibody as well as one that may help to identify patients who are at risk for malignancy. Determining more specific phenotypic elements related to the association with this newly described autoantibody may be helpful for the clinician.