IL5RA

IL5RA encodes the IL-5-specific alpha subunit of the IL-5 receptor and is the central determinant of IL-5 responsiveness across hematopoietic and, more recently, epithelial cells (PMID:1833065, PMID:8630733). The high-affinity receptor is a heterodimer in which the IL5RA alpha chain confers ligand specificity and the signaling beta chain (βc), shared with the GM-CSF receptor, is recruited in an ordered fashion: βc binds with moderate affinity and a fast off-rate to the preformed IL-5:IL5RA binary complex but not to either component alone (PMID:1833065, PMID:12202242). The gene produces both a signaling-competent transmembrane isoform and a secreted/soluble isoform that antagonizes IL-5 signaling, with isoform output and overall expression controlled by two promoters (P1, P2) acting through GATA-1, PU.1, C/EBP, and cooperating EOS1/AP-1 elements during eosinophil development; the splicing decision itself is IL-5-independent (PMID:1833065, PMID:8585949, PMID:9742933, PMID:34638583, PMID:16856933). Genetically, IL5RA is required for IL-5-driven eosinophilopoiesis and B-1 cell development, with loss eliminating IL-5-induced eosinophil production, depleting B-1 cells, lowering serum IgM/IgG3, and impairing antiparasite immunity (PMID:8630733). The receptor is also expressed and functional on neutrophils, where airway pathogens drive its surface display from intracellular stores (PMID:34391897). Beyond normal immunity, IL5RA participates in disease-associated signaling: it is phosphorylated by Lyn within a FIP1L1-PDGFRA/JAK2/Lyn/Akt complex in eosinophilic leukemia (PMID:29029406), drives epithelial-mesenchymal transition via JAK2/STAT3 in pulmonary fibrosis (PMID:38191068), and is upregulated through an MDM2/p53 axis to confer chemotherapy resistance in uveal melanoma (PMID:35468881).

1. 1991 High

   Established the molecular identity of the IL-5 receptor, resolving that IL-5 specificity is conferred by a dedicated alpha chain partnered with a shared beta chain, and that an antagonistic soluble form exists.

   Evidence cDNA cloning, receptor binding and functional antagonism assays in eosinophilic cells

   PMID:1833065

   Open questions at the time

   • Did not resolve the order or kinetics of subunit assembly
   • Regulation of soluble vs transmembrane isoform production not defined
2. 1996 High

   Defined IL5RA as physiologically required for IL-5-dependent eosinophil and B-1 cell development, moving it from a biochemical receptor to an in vivo lineage determinant.

   Evidence Knockout mouse with colony assays, flow cytometry, and in vivo parasite challenge

   PMID:8630733

   Open questions at the time

   • Does not address roles outside eosinophil/B-1 lineages
   • Downstream signaling effectors in vivo not dissected
3. 1996 Medium

   Began mapping how lineage-restricted IL5RA transcription is achieved by identifying the EOS1 enhancer element and its cooperation with a proximal AP-1 site.

   Evidence Promoter mutagenesis, EMSA, and methylation interference

   PMID:8585949

   Open questions at the time

   • Identity of the EOS1-binding factor not determined
   • Single-study promoter analysis
4. 1998 Medium

   Identified the transcription factors binding the AP-1 site (cJun, CREB, CREM) and showed combinatorial dependence with EOS1 for eosinophil-specific promoter activity.

   Evidence Promoter reporter assays, EMSA, site-directed mutagenesis in HL-60 cells

   PMID:9742933

   Open questions at the time

   • Endogenous chromatin occupancy not confirmed
   • Does not connect promoter activity to isoform choice
5. 2002 High

   Resolved the assembly mechanism, showing βc is recruited sequentially with moderate affinity to a preformed IL-5:IL5RA complex, supporting an ordered receptor model.

   Evidence Surface plasmon resonance binding kinetics with soluble βc ectodomain

   PMID:12202242

   Open questions at the time

   • Performed with soluble ectodomains, not full-length membrane receptors
   • Conformational basis of ordered binding not structurally resolved
6. 2006 Medium

   Determined that the transmembrane-vs-soluble isoform splicing decision is IL-5-independent, ruling out ligand-driven feedback control of isoform ratios.

   Evidence Quantitative RT-PCR in IL-5 gene-deleted vs wild-type mice during Schistosoma infection

   PMID:16856933

   Open questions at the time

   • Does not identify what does control the splicing decision
   • Negative finding limited to the infection model tested
7. 2007 Low

   Linked a promoter polymorphism (c.-5091G>A) to differential IL5RA surface expression on eosinophils, connecting genetic variation to receptor density.

   Evidence Eosinophil flow cytometry and SNP genotyping in asthmatic patients and controls

   PMID:17983872

   Open questions at the time

   • No direct promoter functional assay confirming causality
   • Single method (flow cytometry), association only
8. 2016 Medium

   Placed IL5RA within an oncogenic signaling complex, showing Lyn associates with and phosphorylates it downstream of FIP1L1-PDGFRA in eosinophilic leukemia.

   Evidence Co-immunoprecipitation, phosphorylation assays, and dual JAK2/Lyn inhibition in EOL-1 and imatinib-resistant cells

   PMID:29029406

   Open questions at the time

   • Direct vs indirect IL5RA-Lyn interaction not distinguished
   • Single lab, no reciprocal in vivo validation
9. 2021 Medium

   Expanded IL5RA's cellular reach by demonstrating functional surface expression on neutrophils with pathogen-induced mobilization from intracellular stores.

   Evidence Flow cytometry, immunohistochemistry, and functional stimulation of blood and BAL neutrophils

   PMID:34391897

   Open questions at the time

   • Physiological consequence of neutrophil IL-5 signaling in vivo unclear
   • Whether βc co-engages on neutrophils not shown
10. 2021 Medium

    Defined the dual-promoter (P1/P2) program and transcription-factor inputs that time isoform expression across human eosinophilopoiesis, with soluble mRNA peaking early and transmembrane later.

    Evidence Promoter reporter assays, ChIP in primary eosinophil cultures, isoform qRT-PCR

    PMID:34638583

    Open questions at the time

    • Causal contribution of each factor to isoform switching not isolated
    • Single-lab dataset
11. 2024 Medium

    Extended IL5RA function to non-hematopoietic disease, showing epithelial IL5RA drives EMT and ECM production via JAK2/STAT3 in pulmonary fibrosis.

    Evidence Single-cell analysis, in vitro/in vivo loss- and gain-of-function, pathway inhibition

    PMID:38191068

    Open questions at the time

    • Whether epithelial signaling requires βc and IL-5 ligand not defined
    • Single lab
12. 2022 Medium

    Identified an upstream regulatory axis (JMJD2C/MDM2/p53) controlling IL5RA expression to confer cisplatin resistance, framing IL5RA as a chemoresistance effector.

    Evidence ChIP, p53/ubiquitin Co-IP, knockdown, and xenograft in uveal melanoma cells

    PMID:35468881

    Open questions at the time

    • Mechanism by which IL5RA mediates resistance downstream not defined
    • Direct p53-IL5RA regulatory link not shown

• How IL5RA signaling specificity and isoform balance are coordinated across its diverse contexts (eosinophils, B-1 cells, neutrophils, epithelium, tumor cells) remains unresolved.
• No structural model of the full-length signaling complex
• Factors controlling the IL-5-independent splicing decision unidentified
• Whether epithelial/tumor IL5RA functions require canonical βc/IL-5 engagement is unknown