Anti-(U1) small nuclear RNA antibodies in anti-small nuclear ribonucleoprotein sera from patients with connective tissue diseases.

Abstract

Small nuclear ribonucleoprotein (snRNP) particles are a class of RNA-containing particles in the nucleus of eukaryotic cells. Sera from patients with connective tissue diseases often contain antibodies against the proteins present in these snRNPs. Antibodies against the RNA components of snRNPs, the U snRNAs, are thought to be rare.We tested 118 anti-snRNP sera for the presence of antisnRNA antibodies and found them in 45 sera (38%). In all sera the antibodies (IgG and F(ab)2 fragments thereof) were exclusively directed against Ul snRNA.The anti-(Ul)RNA antibodies were always accompanied by anti-(Ul)RNP antibodies but were not found in sera which contain antibodies of the Sm serotype directed against all nucleoplasmic U snRNP particles. Like anti-RNP antibodies, anti-Ul RNA activity is confined to sera from patients with SLE or SLE overlap syndromes and is rarely found in patients with other connective tissue diseases. By analyzing binding to subfragments of Ul snRNA made in vitro, it was demonstrated that anti-(Ul)RNA antibodies recognize epitopes distributed throughout the Ul RNA molecule. In most sera, however, either the second or the fourth hairpin loop is the main target of the antibody.The possible mechanisms that could lead to the production of this new type of autoantibody are discussed. (J. Clin. Invest.

Synthetic antibodies for specific recognition and crystallization of structured RNA

“…Thus, as a crystallization chaperone, Fab2 plays an important role in crystal packing via interactions with both protein and RNA. (14,44) and rheumatoid arthritis (15). The successful isolation of synthetic Fabs that bind tightly to ⌬C209 P4-P6 and to a diverse panel of other structured RNAs (J.-D.Y., Y. Koldobskaya, J. Min, and J.A.P., unpublished work) suggests that the paucity of available anti-RNA antibodies probably reflects nucleolytic instability of RNA during in vivo immunization, rather than some fundamental limitation in the ability of natural antibody repertoires to bind RNA.…”

“…A large number of these RNAs adopt complex three-dimensional architectures that frequently act in complex with proteins to mediate their biological function (12,13). Nevertheless, with the exception of a handful of examples, mostly isolated from the sera of autoimmune patients (14)(15)(16)(17), we know little about anti-RNA antibodies and their recognition of nucleic acids. This dearth of information reflects our inability to elicit antibodies against RNA by using traditional approaches.…”

Epitope regions on U1 small nuclear RNA recognized by anti-U1RNA-specific autoantibodies.

“…For example, antibodies directed to the GTPase activity center of 28S rRNA have been found to coexist with anti-ribosomal P protein antibodies (6) and, in PM patients, antibodies directed to an alanyl-tRNA synthetase as well as its cognate tRNA' have been shown to occur (5). Also in patients who contain antibody directed to Ul RNP, the presence of both anti-U 1 RNP protein and anti-U 1 RNA antibody has been demonstrated (7,8). Surprisingly, antibodies directed to other (U)RNAs were not detected (8).…”

Caspase-dependent cleavage of nucleic acids

“…60,71 All proteins remain associated with the U1 snRNP complex in apoptotic cells. 71 The U1 snRNA molecule itself is a major target of autoimmunity in SLE-overlap syndromes, 72 and it has been shown that changes in the titer of anti-U1 snRNA autoantibodies may correlate with the severity of the disease. 73 The most immunodominant epitopes of the autoantigenic U1 snRNA molecule are located in stemloop II (nts 49 ± 65 and 76 ± 90) and stemloop IV (nts 150 ± 153), 74 and were recently characterized in more detail using several recombinant human monoclonal antibodies (scFvs).…”