Disease relevance of SNRP70

• We have previously identified an epitope at residues 131-151 of the U1-70K snRNP protein, recognized by IgG antibodies and CD4+ T cells from at least two strains of lupus mice [1].
• Anti-Sm (Sm: U1-U6 RNA-protein complex) antibodies are usually considered highly specific for systemic lupus erythematosus (SLE), while anti-U1RNP (U1RNP: U1RNA-protein complex) are thought of as diagnostic criteria for the mixed connective tissue disease (MCTD) [2].
• The splicing of the first and second leader exons of adenovirus late RNA was inhibited only by those sera that reacted with U1 RNP [3].
• Circulating immune complexes containing histones were observed only in patients with autoimmune chronic active hepatitis-associated sicca syndrome; those containing U1-RNP were restricted to patients with autoimmune chronic active hepatitis associated with kidney disease [4].
• HLA class II alleles were determined by genotyping in 49 Japanese rheumatic disease patients with anti-U1 RNP antibody and 43 race-matched healthy controls [5].

High impact information on SNRP70

• Functional expression of cloned human splicing factor SF2: homology to RNA-binding proteins, U1 70K, and Drosophila splicing regulators [6].
• The neonatal lupus syndrome associated with U1RNP (nRNP) antibodies [7].
• The carboxy-terminal portion of U1-70K-encompassing repeats of Arg/Ser, Arg/Glu, and Arg/Asp localizes to the nucleus independently of U1 RNA and was responsible for these inhibitory effects [8].
• Correspondingly, splicing and nucleocytoplasmic transport of a coexpressed mRNA substrate was reduced by overexpression of U1-70K [8].
• These findings are compatible with models that propose that direct interaction between U1-70K and SR proteins play a regulatory role in early events of spliceosome assembly [8].

Biological context of SNRP70

• The human U1-70K snRNP protein: cDNA cloning, chromosomal localization, expression, alternative splicing and RNA-binding [9].
• We have isolated and sequenced cDNA clones encoding the human U1-70K snRNP protein, and have mapped this locus (U1AP1) to human chromosome 19 [9].
• Human U1-70K ribonucleoprotein antigen gene: organization, nucleotide sequence, and mapping to locus 19q13.3 [10].
• Comparison of the predicted amino acid sequences of animal U1-70K proteins reveals a high degree of conservation, particularly in the region of the RNP consensus domain [10].
• We have mapped the U1-70K gene to the distal portion of chromosome 19, at band q13 [10].

Anatomical context of SNRP70

• To obtain more insight in the mechanism responsible for this U1RNA-specific antibody formation and to use the antibodies eventually as a tool to study U1RNA-protein (U1RNP) interactions, the B cell epitopes on U1RNA were mapped [11].
• Expression of the recombinant human U1-70K protein in COS cells resulted in its rapid transport to the nucleus, even when binding to U1 RNA was debilitated [12].
• Immunoreactivities to U1 RNP constituent proteins (70K, A, B/B', and C) were detected by immunoblots using purified HeLa cell Sm antigen, and antibody titer was determined by passive hemagglutination assay [5].
• Absorption studies showed that the antibody reacting with this antigen cannot be absorbed by sheep red blood cells coated with extracts of rabbit thymus that contain U1-RNP [13].
• RESULTS: Human sera that recognize U1-70 kd (U1-70K) and La by immunoblotting also recognized multiple novel species when they were used to immunoblot lysates of UVB-irradiated keratinocytes or HeLa cells [14].

Associations of SNRP70 with chemical compounds

• In this study, autoantibody recognition of native U1 snRNPs was investigated by dissociating the particle into four components (U1-70K, U1-A, U1-C, and the Sm core particle) using 1 M MgCl2 or ribonuclease treatment [15].
• The ICE-like protease inhibitor, benzyloxycarbonyl-Val-Ala-Asp (OMe) fluoromethyl ketone (Z-VAD.FMK), inhibited apoptosis and cleavage of Ich-1, CPP32, Mch3alpha, Mch2alpha, PARP, U1-70K, and lamins [16].
• All anti-U1 RNP-positive patients had either a DQB1*0601, *0602, *0301, *0302, or *0303 allele, which share tyrosine at position 30, and the amino acid sequence Thr, Arg, Ala, Glu, Leu, Asp, and Thr at positions 71-77 in the DQB1 beta 1 domain [5].
• The epitope recognized by mAb U1 70K was previously shown to be a repeating arginine/aspartate (RD) dipeptide [17].
• Antibodies to nRNP (U1-RNP/snRNP); Sm; SS-A; SS-B; Scl-70; thyroid microsome; immunoglobulin (Ig)G, IgM, and IgA antibodies to cardiolipin; and antibodies to native and denatured human types I and II collagen were measured by enzyme-linked immunosorbent assay [18].

Physical interactions of SNRP70

• These findings indicate the CRP binds to the U1-RNP snRNP particle [19].
• Changes in levels of antibodies against the 70 kDa and a polypeptides of the U1RNP complex in relation to exacerbations of systemic lupus erythematosus [20].

Co-localisations of SNRP70

• Indeed, hADI1 specifically co-localized with the splicing factor U1-70K to the nucleus but not with another splicing factor, SC35 [21].

Other interactions of SNRP70

• Yeast two-hybrid analysis and immunoprecipitation indicated interaction of ZNF265 with the essential splicing factor proteins U1-70K and U2AF(35) [22].
• Domain fusion analysis of the Rosetta stone protein linked WAC to splicing factor SNRP70 [23].
• An snRNP-associated kinase activity which phosphorylates all U1-70K isoelectric variants was identified [24].
• Conservation of the U1 70K inhibitory domains suggests that polyadenylation regulation via PAP inhibition may be more widespread than previously thought [25].
• Individual crosslinks between the U1-70K and the common D2 or B'/B protein, as well as between U1-C and B'/B, were detected [26].

Analytical, diagnostic and therapeutic context of SNRP70

• These reactions were directed to the unfolded A and D proteins measurable in Western blot since these monoclonals (and several of the human anti-nDNA populations) failed to react with native U1RNP in ELISA or in RNA immunoprecipitation experiments [27].
• Site-directed mutagenesis of the RNA recognition motif NLS demonstrated that the U1-70K protein can be transported independently of U1 RNA and that its association with the U1 small nuclear ribonucleoprotein particle can occur in the nucleus [12].
• HLA typing revealed HLA-B7 and DR1; these have been reported to be increased in Japanese patients with rheumatic diseases who have autoantibodies to U1 RNP [28].
• Induction of apoptosis by SSZ was confirmed by TUNEL analysis and by the detection of cleaved U1-70K, a substrate of caspase 3 [29].
• Immunoelectron microscopy employing anti-stemloop IV antibodies and purified, complete U1snRNP particles showed that stemloop IV is located within the body of the U1RNP complex, which also comprises the Sm site and the common Sm proteins [30].

References