RNASE2

RNASE2 (EDN) is an eosinophil-derived secretory ribonuclease of the RNase A superfamily that functions at the interface of antiviral defense and immune signaling, combining catalytic RNA cleavage with non-catalytic recognition activities (PMID:9826755, PMID:35347428). Its antiviral activity against single-stranded RNA virions, notably RSV, requires ribonucleolytic activity but is not explained by catalysis alone: an active-site mutant competitively inhibits wild-type EDN and an N-terminal segment confers specific virion interaction, establishing that unique structural features beyond the catalytic center mediate target recognition (PMID:9826755). The contribution of the N-terminal region to non-catalytic recognition is reinforced by an atomic-resolution structure of an N-terminally extended variant, in which the modified terminus repositions the catalytic His129 and the extension itself drives cellular recognition independent of RNase activity (PMID:11916383). As an enzyme, RNASE2 selectively cleaves tRNAs at anticodon- and D-loop positions with base specificity (U/C at B1, A at B2), generating tRNA-derived fragments during RSV infection, and its loss reduces macrophage survival after infection (PMID:35347428); the substrate selectivity is governed by a defined set of binding-site residues including Arg36, Asn39, Gln40, Asn65, Arg68, and Arg132 (PMID:38228145). Beyond direct antiviral action, RNASE2 acts in immune signaling: it is a selective chemoattractant for dendritic cells acting through a pertussis-toxin-sensitive (Gi-coupled) receptor and p42/44 MAPK activation (PMID:12855582), and it operates upstream of monocyte-derived IL-10 to promote age-associated B cell expansion (PMID:35265065). The protein is both stored in eosinophil granules and displayed at the granulocyte surface via a GPI anchor, distributing across granular and extragranular compartments (PMID:12606041, PMID:23053729). Its lineage-restricted expression is controlled by a promoter–intronic enhancer architecture engaging PU.1, C/EBP, and an NFAT-1 consensus site, with HNF4–Sp1 interplay providing differential regulation (PMID:8647842, PMID:9490699, PMID:10534126, PMID:19115260).

1. 1996 Medium

   Established how the EDN gene achieves high, lineage-restricted expression, identifying an intronic enhancer cooperating with the promoter rather than promoter elements alone.

   Evidence CAT reporter transfection of promoter/exon1/intron constructs in eosinophilic HL-60 and other hematopoietic cell lines

   PMID:8647842

   Open questions at the time

   • Specific factors binding the AP-1 and NF-ATp consensus sites not yet identified
   • Single-lab reporter system
2. 1997 Medium

   Mapped the intronic enhancer activity to an NFAT-1 consensus sequence, but showed the responsible binding factor is not NFAT-1 itself, leaving the trans-acting protein unresolved.

   Evidence Reporter assay, gel shift, site-directed mutagenesis, and negative supershift with anti-NFAT-1 in HL-60 cells

   PMID:8999843

   Open questions at the time

   • Identity of the nuclear protein binding the GGAGAA site unknown
   • Negative supershift leaves the factor uncharacterized
3. 1998 Medium

   Identified PU.1 as a direct activator binding a tandem site in the intronic enhancer, linking EDN expression to myeloid/eosinophilic transcription factor programs.

   Evidence Reporter assay, gel shift, DNA affinity precipitation, and mutagenesis in differentiated eosinophilic HL-60 cells

   PMID:9490699

   Open questions at the time

   • Combinatorial logic with other intronic factors not resolved
   • Single-lab study
4. 1998 High

   Resolved that EDN's antiviral activity against RSV requires but is not sufficiently explained by ribonucleolysis, pointing to N-terminal structural elements that mediate specific virion recognition.

   Evidence In vitro antiviral assay with active-site mutant (K38), competitive inhibition, and chimeric human/monkey constructs

   PMID:9826755

   Open questions at the time

   • Virion target/receptor of the N-terminal segment not identified
   • Mechanism coupling binding to virion destruction not detailed
5. 1999 Medium

   Extended transcriptional control of EDN to the proximal promoter, defining a functional C/EBP site, confirmed in primary eosinophils.

   Evidence Reporter assay, gel shift, DNA affinity precipitation, mutagenesis, and transfection in eosinophils differentiated from CD34+ cells

   PMID:10534126

   Open questions at the time

   • Which C/EBP family member dominates in vivo unclear
   • Interplay with intronic enhancer not dissected
6. 2002 High

   Provided atomic-resolution structural insight showing how an N-terminal extension repositions the catalytic His129 and drives cellular recognition independent of catalysis, mechanistically separating EDN's enzymatic and recognition functions.

   Evidence 1 Å X-ray crystallography of (-4)EDN plus cytotoxicity assays on Kaposi's sarcoma and endothelial cell lines

   PMID:11916383

   Open questions at the time

   • Physiological prevalence of the N-terminally extended form unclear
   • Cellular receptor recognizing the extension not identified
7. 2003 High

   Defined a non-antiviral immune role for EDN as a selective dendritic cell chemoattractant signaling through a Gi-coupled receptor and MAPK, requiring RNase activity.

   Evidence In vitro chemotaxis with pertussis toxin and RNase inhibitor blockade, p42/44 MAPK assay, in vivo air pouch, and mEAR2 N-terminal mutagenesis

   PMID:12855582

   Open questions at the time

   • The Gi-coupled receptor on dendritic cells not molecularly identified
   • How RNase activity is mechanistically required for chemotaxis unresolved
8. 2003 Medium

   Showed EDN is not solely a granule protein but is displayed at the granulocyte surface via a GPI anchor, expanding its potential sites of action.

   Evidence PI-PLC treatment, flow cytometry, PNH patient granulocyte comparison, and metabolic labeling with GPI anchor components

   PMID:12606041

   Open questions at the time

   • Functional consequence of surface display not established
   • Mechanism of GPI attachment to a secretory ribonuclease unclear
9. 2009 Medium

   Explained differential regulation between RNase2 (EDN) and RNase3 (ECP) through an HNF4–Sp1 switch acting on the promoter.

   Evidence Supershift, ChIP, DNA affinity precipitation, HNF4 overexpression reporter, and Sp1 depletion

   PMID:19115260

   Open questions at the time

   • In vivo relevance of HNF4 in eosinophils not established
   • Single-lab study
10. 2013 Medium

    Refined the subcellular distribution of EDN, demonstrating an extragranular vesicular/cytosolic/membrane-associated pool beyond specific granules.

    Evidence Sucrose density gradient fractionation and immuno-gold electron microscopy of human eosinophils

    PMID:23053729

    Open questions at the time

    • Functional role of the extragranular pool not defined
    • Trafficking route to this compartment unknown
11. 2022 High

    Established RNase2 as a generator of tRNA-derived fragments in macrophages during RSV infection and showed its loss compromises infected-cell survival, linking catalytic RNA cleavage to antiviral outcome.

    Evidence CRISPR knockout in THP-1 macrophages, cP-RNAseq, recombinant protein cleavage, and tRF/tiRNA array screening

    PMID:35347428

    Open questions at the time

    • Downstream immunoregulatory function of the tRFs not defined
    • Mechanism linking tRF generation to survival unresolved
12. 2022 Medium

    Placed RNASE2 upstream of monocyte-derived IL-10 in a pathway driving age-associated B cell expansion, adding an autoimmunity-relevant function.

    Evidence siRNA knockdown in THP-1/primary monocytes, monocyte-B cell co-culture, cytokine measurement, and recombinant IL-10 rescue

    PMID:35265065

    Open questions at the time

    • Mechanism by which RNASE2 controls IL-10 production unknown
    • Whether catalytic activity is required not tested
13. 2024 High

    Defined the structural basis of RNase2 tRNA anticodon-loop cleavage selectivity, identifying the substrate-binding residues that confer B1/B2 base specificity.

    Evidence In vitro cleavage of synthetic tRNA/hairpin substrates and mutants, tRF product sequencing, and MD simulations of protein-hairpin complexes

    PMID:38228145

    Open questions at the time

    • No experimental high-resolution co-structure of protein bound to tRNA substrate
    • Physiological tRF targets in cells not mapped to these residues

• The molecular identity of the Gi-coupled dendritic cell receptor and of the RSV virion target recognized by the N-terminal segment, and the mechanism linking RNase2-generated tRFs to antiviral and immunoregulatory outcomes, remain unresolved.
• No receptor identified for chemotactic or virion-binding activity
• Functional pathway from tRFs to phenotype not established
• Catalytic-vs-recognition contributions to each phenotype not separately quantified in vivo