IL13RA2

IL13RA2 is a high-affinity decoy receptor for IL-13 that functions as a negative regulator of IL-13/IL-4 signaling across multiple tissue contexts. It sequesters IL-13 at the cell surface and inhibits STAT6 activation both through ligand sequestration and through direct physical interaction of its short intracellular domain with the cytoplasmic domain of IL-4Rα, thereby blocking STAT6 docking (PMID:11861389); N-linked glycosylation of its extracellular domain is required for optimal inhibitory activity (PMID:17023392). The predominantly intracellular pool of IL13RA2 is continuously trafficked to the surface, where it is shed as a soluble form via MMP-8-mediated ectodomain cleavage in humans (PMID:16751396, PMID:20007572). IL13RA2 negatively regulates pro-fibrotic JAK/STAT6 signaling in fibroblasts and pro-survival AKT/NF-κB signaling in breast cancer, while in certain contexts such as intestinal fibrosis it can transduce IL-13 signals via TGF-β1 and downstream effectors (PMID:36757802, PMID:40663259, PMID:18938165).

1. 1997 High

   Establishing the signaling receptor complex for IL-13 revealed that IL-13Rα1/IL-4Rα heterodimerization is required for STAT6 activation, setting the stage for understanding how IL13RA2 competes for IL-13 binding outside this signaling complex.

   Evidence CHO cell reconstitution with ligand binding assays and EMSA for STAT6

   PMID:9013879

   Open questions at the time

   • Does not address IL13RA2 function directly
   • Affinity measurements limited to one heterologous system
2. 2002 High

   The central mechanistic question—whether IL13RA2 is merely a passive sink for IL-13 or actively inhibits signaling—was resolved by showing it functions as a decoy receptor that both sequesters IL-13 and physically interacts with IL-4Rα's cytoplasmic domain to block STAT6 activation independently of ligand binding.

   Evidence Transient transfection in glioblastoma cells, STAT6 activation assays, co-immunoprecipitation of intracellular domains

   PMID:11861389

   Open questions at the time

   • Co-IP of intracellular domains not confirmed by reciprocal endogenous pulldown
   • Structural basis of intracellular domain interaction unknown
3. 2005 Medium

   IL13RA2 was established as the primary IL-13 binding and internalization receptor on glioblastoma cells, explaining why these tumors are selectively targeted by IL-13-based cytotoxins.

   Evidence Antisense and siRNA knockdown with ligand binding and cytotoxin sensitivity assays; gene transfer rescue in low-expressing cells

   PMID:15838375

   Open questions at the time

   • Internalization mechanism not defined
   • Relevance to normal (non-tumor) cells unclear
4. 2006 High

   Two key properties of IL13RA2 were established: its predominantly intracellular distribution with continuous surface trafficking and shedding, and the requirement for N-linked glycosylation of its extracellular domain for optimal IL-13 inhibitory activity.

   Evidence Subcellular fractionation, flow cytometry, recombinant glycosylated vs. non-glycosylated ECD production, PNGase F deglycosylation with STAT6 phosphorylation readouts

   PMID:16751396 PMID:17023392

   Open questions at the time

   • Specific glycosylation sites contributing to function not mapped
   • Identity of proteases responsible for surface shedding not yet known at this point
5. 2008 Medium

   Contrary to its established decoy role, IL13RA2 was shown to transduce IL-13 signals in intestinal fibrosis, activating a TGF-β1/IGF-I/Egr-1 program that drives collagen deposition—revealing context-dependent signaling capacity.

   Evidence siRNA blockade in TNBS colitis mouse model with downstream pathway analysis by ELISA and Western blot

   PMID:18938165

   Open questions at the time

   • Adaptor proteins linking IL13RA2 short cytoplasmic tail to TGF-β1 induction not identified
   • Whether this signaling mode operates outside the gut is unknown
6. 2009 High

   The mechanism generating soluble IL13RA2 was resolved: in humans, MMP-8-mediated ectodomain cleavage of the membrane form is the sole source, whereas mice use an alternatively spliced transcript.

   Evidence Isoform-specific siRNA, broad-spectrum and selective MMP inhibitors, Western blot and ELISA

   PMID:20007572

   Open questions at the time

   • Cleavage site not mapped at residue level
   • Physiological regulation of MMP-8 activity toward IL13RA2 not characterized
7. 2010 Medium

   Transcriptional regulation of IL13RA2 in glioblastoma was mapped to multiple promoters, with NFAT and AP-1 (c-JUN/c-FOS) identified as necessary and sufficient drivers of a tumor-specific transcript.

   Evidence Promoter cloning, deletion/mutagenesis analysis, JNK inhibition, transcription factor binding assays in GBM cell lines

   PMID:20448330

   Open questions at the time

   • Epigenetic regulation not addressed
   • Whether NFAT/AP-1 regulation extends beyond GBM unknown
8. 2019 Medium

   IL13RA2 was shown to promote epithelial-mesenchymal transition and migration in papillary thyroid carcinoma, expanding its functional repertoire beyond cytokine decoy activity to direct regulation of cell motility programs.

   Evidence Reciprocal siRNA knockdown and overexpression with EMT marker and migration assays

   PMID:31290966

   Open questions at the time

   • Downstream signaling pathway mediating EMT induction not fully delineated
   • Ligand dependence of this EMT-promoting function not tested
9. 2023 Medium

   IL13RA2 was established as a negative regulator of fibrotic signaling in human fibroblasts: its loss in keloid tissue leads to STAT6 hyperactivation and fibrosis, while re-expression suppresses fibrotic phenotypes.

   Evidence Reciprocal gain/loss-of-function in patient-derived keloid fibroblasts, xenograft model, STAT6 inhibitor rescue

   PMID:36757802

   Open questions at the time

   • Whether IL13RA2 loss is cause or consequence of keloid pathogenesis not resolved
   • Mechanism of IL13RA2 downregulation in keloid tissue unknown
10. 2024 Medium

    IL13RA2 was shown to suppress vascular calcification by inhibiting STAT3 and WNT3/β-catenin signaling in aortic smooth muscle cells, extending its negative-regulatory role to a new tissue context and additional signaling axes.

    Evidence Cellular thermal shift assay for direct binding, transcriptional profiling, knockdown/overexpression in vascular calcification models in vitro and in vivo

    PMID:38432393

    Open questions at the time

    • Direct binding partners identified by thermal shift not fully characterized
    • Whether STAT3 inhibition is direct or indirect not determined
11. 2025 Medium

    CRISPR knockout studies in breast cancer cells resolved that IL13RA2 acts as a negative regulator of AKT/NF-κB pro-survival signaling, and its loss drives metastatic growth that can be rescued by AKT inhibition.

    Evidence CRISPR KO in human and murine TNBC lines, Western blot for p-AKT/NF-κB, intracardiac metastasis model, pathway inhibitor sensitivity

    PMID:40663259

    Open questions at the time

    • Molecular mechanism linking IL13RA2 to AKT suppression not defined
    • Whether this function depends on IL-13 ligand not tested

• The molecular mechanism by which IL13RA2's short intracellular domain transduces or inhibits intracellular signals remains unresolved—no adaptor proteins or kinases directly recruited to the cytoplasmic tail have been identified, and no structural model of IL13RA2 in complex with IL-4Rα or signaling partners exists.
• No crystal or cryo-EM structure of IL13RA2 alone or in complex
• Adaptor proteins recruited to the 17-amino-acid cytoplasmic tail unknown
• Mechanistic basis for context-dependent switch between decoy and signaling functions unresolved