Antibodies to small nuclear RNAs complexed with proteins are produced by patients with systemic lupus erythematosus

Abstract

Patients with systemic lupus erythematosus often possess antibodies against two nuclear antigens called Sm and RNP (ribonucleoprotein). We have established the molecular identity of these antigens by analyzing immune precipitates of nuclear extracts from mouse Ehrlich ascites cells labeled with 32P and 35S. Anti-Sm serum selectively precipitates six small nuclear RNA molecules (snRNAs); anti-RNP serum reacts with only two of these; and a third serum, characterized as mostly anti-RNP, precipitates a subset of three snRNA bands. Three of the six RNAs are identified by fingerprint analysis as the previously characterized and highly abundant nucleoplasmic snRNA species Ula (171 nucleotides), Ulb, and U2 (196 nucleotides). The other three RNAs (U4, U5, and U6) likewise are uridine rich and contain modified nucleotides, but they are smaller, with lengths of about 145, 120, and 95 residues, respectively. Each of the six snRNAs is complexed with and apparently antigenic by virtue of association with specific proteins. All three sera precipitate an identical complement of seven different polypeptides ranging in molecular weight from 12,000 to 35,000; these proteins are abundant in nuclear extracts, but are neither histones nor the major polypeptides comprising the 30S heterogeneous nuclear RNP particles of mammalian nuclei. Our data argue that each of the six snRNAs exists in a separate small nuclear ribonucleoprotein (snRNP) complex with a total molecular weight of about 175,000. We find that human antisera also precipitate snRNAs from a wide range of vertebrate species and from arthropods. We discuss the antigenic snRNPs in relation to the published literature on snRNAs and nuclear RNPs and consider possible functions of snRNPs in nuclear processes.Systemic lupus erythematosus (SLE) is an autoimmune disease of unknown etiology (see refs. 1 and 2 for reviews). Antibodies to nuclear components, many of which have been identified as known macromolecules or macromolecular assemblies, are a hallmark of the disease. Antibodies directed against DNA, RNA, and nucleohistones are common. However, the molecular nature of two other antigens commonly precipitated by sera from patients with SLE, called ribonucleoprotein (RNP) and Sm, has remained obscure.Previous work on the RNP and Sm antigens has established that they are highly conserved nuclear components (3, 4). Immunodiffusion experiments using anti-RNP and anti-Sm sera have detected crossreacting material in a wide variety of mammalian tissues (3). Immunofluorescence studies (3, 4) have localized RNP entirely within the interphase nucleus, whereas Sm is reported to be largely, but not exclusively, nuclear. Most striking is the observation that the activity of RNP, as measured by immunodiffusion assays, can be destroyed by either RNase or trypsin (3-5). Sm is sensitive only to trypsin and is less heat labile, but appears antigenically related to RNP (3, 4, 6). Finally, velocity centrifugation and gel filtration studies (3, 4) have assigned a sedimentation constant of 7...

Human autoantibodies against the 70‐kd polypeptide of u1 small nuclear rnp are associated with hla‐dr4 among connective tissue disease patients

“…Sm is an antigenic complex consisting of U1, U2, U4/U6. and U5 (U1-6) RNAs associated with proteins designated B'/B and D (8,9,11). Autoantibodies against these proteins are typically found in the sera of approximately 30% of patients with SLE (10,12,13).…”

Synthesis of U1 RNA in isolated nuclei from sea urchin embryos: U1 RNA is initiated at the first nucleotide of the RNA.

“…This RNA forms a characteristic ribonucleoprotein particle which can be immunoprecipitated with anti-RNP or anti-Sm antisera from patients with the autoimmune disease lupus erythematosus (18,19). The sequence of this RNA has been highly conserved in evolution, with only a 25 to 30% difference between Ul RNA from such diverse organisms as rats, drosophila, and sea urchins (3,5,28).…”

Identification of autoantibodies to the I protein of the heterogeneous nuclear ribonucleoprotein complex in patients with systemic sclerosis

“…Complex structures are common targets of autoimmunity in connective tissue diseases, so that antibodies directed to different proteins of a unique complex can be found in a single patient and in patients with the same disease (2)(3)(4). The data presented herein reveal that hnRNP proteins A/B and I are distinct targets of different autoimmune responses.…”