Further characterization and subcellular localization of Sm and U1 ribonucleoprotein antigens.
Sera from patients with systemic autoimmune diseases often contain antibodies against small nuclear ribonucleoprotein (snRNP) particles. Anti-Sm antibodies react with the entire set of U1, U2, U4, U5 and U6 (U1-U6) RNP particles whereas anti-(U1)RNP sera specifically recognize particles containing U1 RNA. Here we performed semi-quantitative immunoblotting using 16 human anti-Sm, 15 human anti-(U1)RNP sera and two mouse monoclonal antibodies to establish which snRNA-associated proteins carry antigenic determinants. Almost every (15/16) human anti-Sm sera recognized epitopes present on a 28-kDa (B/B') protein doublet and on a 16-kDa (D) polypeptide. Nine anti-(U1)RNP sera also recognized the B/B' doublet, but in all cases a much stronger reaction was observed with one or more of the specifically U1 RNA-associated 70 kDa, A or C antigens. With affinity-purified antibody fractions eluted from individual antigen bands on nitrocellulose blots it is shown that the anti-Sm-reactive polypeptides B/B' and D contain common epitopes. We also report the finding of one human anti-Sm serum with exclusive specificity for the B/B' doublet and a mouse monoclonal anti-Sm antibody recognizing only the D protein, indicating that these antigens also carry unique epitopes. In immunoprecipitation assays, purified anti-B/B' and -D antibodies react with (U1-U6) RNP while purified anti-70 kDa, anti-A and anti-C antibodies precipitate exclusively U1 RNP particles. Finally, we established the subcellular localization of Sm and U1 RNP antigens using a biochemical cell fractionation procedure. Part of the 70 kDa and B/B' antigens were found in a nuclease and high salt-resistant nuclear substructure, usually referred to as nuclear matrix, while the A and D antigens could be extracted completely from HeLa nuclei by ribonuclease treatment and subsequent high salt extraction.
W J
WJ
Habets
J H
JH
Berden
S O
SO
Hoch
W J
WJ
Van Venrooij
D000918:Antibody Specificity; D002451:Cell Compartmentation; D000939:Epitopes; D006801:Humans; D007163:Immunosorbent Techniques; D008180:Lupus Erythematosus, Systemic / Q000276:immunology; D008947:Mixed Connective Tissue Disease / Q000276:immunology; D008970:Molecular Weight; D012261:Ribonucleoproteins / Q000276:immunology* / Q000378:metabolism; D017411:Ribonucleoproteins, Small Nuclear; D013347:Subcellular Fractions / Q000276:immunology / Q000378:metabolism
D000939:Epitopes; D012261:Ribonucleoproteins; D017411:Ribonucleoproteins, Small Nuclear