Disease relevance of SFRS1

• Furthermore, expression of high levels of SF2/ASF inhibits Rev function and impairs HIV replication in vivo [1].
• We have shown previously that ASF/SF2 inhibits adenovirus IIIa pre-mRNA splicing by binding to an intronic repressor element [2].
• Here, we show that the SR protein SF2/ASF is part of a complex that forms upon the 79-nucleotide negative regulatory element (NRE) that is thought to be pivotal in posttranscriptional regulation of late gene expression in human papillomavirus type 16 (HPV-16) [3].
• Functional coexpression of serine protein kinase SRPK1 and its substrate ASF/SF2 in Escherichia coli [4].
• Long-lasting protection, requiring only three immunizations, was achieved against a low-dose challenge with the SF2 strain of HIV-1 and a subsequent high-dose SF2 challenge administered 1 year later without an intervening boost [5].

High impact information on SFRS1

• We first show that in vivo depletion of ASF/SF2 results in a hypermutation phenotype likely due to DNA rearrangements, reflected in the rapid appearance of DNA double-strand breaks and high-molecular-weight DNA fragments [6].
• Inactivation of the SR protein splicing factor ASF/SF2 results in genomic instability [6].
• Here we provide evidence that a prototypical SR protein, ASF/SF2, is unexpectedly required for maintenance of genomic stability [6].
• Our results support a model by which recruitment of ASF/SF2 to nascent transcripts by RNA polymerase II prevents formation of mutagenic R loop structures [6].
• ASF/SF2-regulated CaMKIIdelta alternative splicing temporally reprograms excitation-contraction coupling in cardiac muscle [7].

Chemical compound and disease context of SFRS1

• Binding sites for Rev and ASF/SF2 map to a 55-nucleotide purine-rich exonic element in equine infectious anemia virus RNA [8].
• CTL generated by immunization of mice with syngeneic cells expressing either the native or V3 loop-deleted (delta V3) envelope glycoprotein from HIV-1 IIIB were able to recognize and specifically lyse Hu/Dd target cells infected with the HIV-1 prototypic isolates IIIB, MN, WMJ II, SF2, and CC as well as several HIV-1 clinical isolates [9].
• Assuming a common nucleoside triphosphate-binding fold, we have generated a structural model of this domain based on the X-ray structures of the hepatitis C virus and Bacillus stearothermophilus (SF2) helicases [10].
• The treatment with R115777 decreased by 45% the SF2 value of the more radioresistant glioma cell lines (SF763 and U87) without any significant effect on the radioresistance of the radiosensitive ones (SF767 and U251-MG) [11].
• The kinetics of inactivation of four different strains of HIV-1 (RF, MN, SF2 and IIIB) by beta-propiolactone (BPL) and binary ethylenimine (BEI) were studied under various conditions [12].

Biological context of SFRS1

• ASF/SF2 stimulates exon 6A splicing through specific interaction with the enhancer sequence [13].
• We propose that in some cases the ratio of SF2/ASF to hnRNP A1 may play a role in regulating alternative splicing by exon inclusion or skipping through the antagonistic effects of these proteins on alternative splice site selection [14].
• With appropriate alternative exons, an excess of SF2/ASF promotes exon inclusion, whereas an excess of hnRNP A1 causes exon skipping [14].
• Deletion analysis mapped the phosphorylation sites to a region containing an (Arg-Ser)8 repeat beginning at residue 204, and far-Western analysis showed that the region is required for binding of SRPKs to SF2/ASF [15].
• Moreover, cross-linking experiments show that both ASF/SF2 and SC35 are able to displace binding of hnRNP A1 to the G-rich element, suggesting that the binding sites for these proteins are overlapping [16].

Anatomical context of SFRS1

• Employing transient transfection of human myometrial smooth muscle cells and HeLa cells, as well as in vitro splicing assays, we have provided evidence that the antagonistic splicing factors SF2/ASF and hnRNPA1 act as potent regulators of G alpha(s) isoform expression in these cells [17].
• Somatic cell hybrid mapping of the human ASF/SF2 gene (SFRS1 locus) reveals that it resides on chromosome 17, and fluorescence in situ hybridization refines this localization to 17q21.3-q22 [18].
• These SR proteins, which include SC35 and SF2/ASF, are conserved from Drosophila to man, are required for early steps of spliceosome assembly and can influence splice-site selections [19].
• Using a genetically modified chicken B-cell line, DT40-ASF, we now show that ASF/SF2 inactivation results in a G2-phase cell cycle arrest and subsequent programmed cell death [20].
• The level of expression and extent of phosphorylation of SF2/ASF are upregulated with epithelial differentiation, as is subcellular distribution, specifically in HPV-16-infected epithelial cells, and expression levels are controlled, at least in part, by the virus transcription regulator E2 [3].

Associations of SFRS1 with chemical compounds

• These and other results suggest a central role for ASF/SF2 in the function of purine-rich splicing enhancers [21].
• A domain within this segment, which begins with Arg240 and ends with Asp270, was shown to bind specifically to the arginine/serine domain of ASF/SF2 using a yeast two-hybrid system and a far Western assay [22].
• It has been clearly documented that the arginine/serine domain of ASF/SF2 is responsible for binding to the U1 70k protein [22].
• Depletion of ASF/SF2 from the cells by tetracycline greatly decreased viral RNA expression and RNA splicing at the proximal 3' splice site while increasing use of the distal 3' splice site in the remaining viral RNAs [23].
• We have screened for similar proteins in plants by using monoclonal antibodies specific for a phosphoserine epitope of the SR proteins (mAb1O4) or for SF2/ASF [24].

Physical interactions of SFRS1

• Based upon a model of SRPK1 bound to a segment encompassing the docking motif and active-site peptide of ASF/SF2, we suggest a mechanism for processive phosphorylation and propose that the atypical resiliency we observed is critical for SRPK1's processive activity [25].

Co-localisations of SFRS1

• Furthermore, immunofluorescence studies indicate that the majority of endogenous p52 is colocalized with ASF/SF2 in the nucleoplasm of HeLa cells [26].

Regulatory relationships of SFRS1

• We found that an excess of SF2/ASF effectively prevents inappropriate exon skipping and also influences the selection of mutually exclusive tissue-specific exons in natural beta-tropomyosin pre-mRNA [14].
• 5. SF2/ASF and SRp40 activate the ESE and are required for efficient 3' splice site usage and binding of the U1 snRNP to the downstream 5' splice site no [27].

Other interactions of SFRS1

• Mass spectrometric and kinetic analysis of ASF/SF2 phosphorylation by SRPK1 and Clk/Sty [28].
• Finally, activation by ASF/SF2 and 9G8 was found to be independent of the RS domain [29].
• Expression of an SRPK2 kinase-inactive mutant caused accumulation of SF2/ASF in the cytoplasm [15].
• Interaction between the N-terminal domain of human DNA topoisomerase I and the arginine-serine domain of its substrate determines phosphorylation of SF2/ASF splicing factor [30].
• Modulation of exon skipping and inclusion by heterogeneous nuclear ribonucleoprotein A1 and pre-mRNA splicing factor SF2/ASF [14].

Analytical, diagnostic and therapeutic context of SFRS1

• Indirect immunofluorescence analysis revealed that endogenous hPRP4 was distributed in a nuclear speckled pattern and colocalized with SF2/ASF in HeLa S3 cells [31].
• Analyses involving UV cross-linking and immunoprecipitation indicated that only four (SRp30a, SRp40, SRp55, and SRp75) of six essential splicing factors known as SR proteins bind to the active enhancer RNA [32].
• RT-PCR analysis revealed a marked induction of SC35 and ASF/SF2 as well as mRNA levels in malignant ovarian tissue [33].
• Molecular cloning, polymorphism and mapping of the porcine SFRS1 gene [34].
• SF1, SF2, and SF4B appear to be required for cleavage of the pre-mRNA at the 5' splice site and lariat formation, whereas SF3 and SF4A are only required for cleavage at the 3' splice site and exon ligation [35].

References