ITGA8

ITGA8 encodes integrin α8, which pairs with β1 to form a heterodimeric cell-surface receptor that mediates cell–extracellular matrix adhesion and transduces outside-in signals across diverse tissue contexts including kidney, liver, vasculature, bladder, and lung. During organogenesis, ITGA8 interacts with the Fraser complex component FRAS1 at the epithelial–mesenchymal interface to drive pharyngeal pouch morphogenesis and craniofacial skeletal development (PMID:27265864), and it marks vascular smooth muscle cells where it is used as a lineage-specific Cre driver that reveals contractile function distinct from visceral smooth muscle (PMID:36424917). In fibrotic disease, ITGA8 exerts context-dependent effects: it attenuates renal fibrosis by suppressing TGF-β/SMAD2/3 signaling and fibroblast activation (PMID:26938996), promotes hepatic fibrosis through COL11A1-dependent ECM remodeling in stellate cells (PMID:40056500), and drives neurogenic bladder fibrosis upon engagement by macrophage-derived fibronectin (Fn1) via FAK/RhoA/ROCK signaling (PMID:41355531). In lung adenocarcinoma, ITGA8 functions as a tumor suppressor by dampening FAK/SRC/AKT/MAPK signaling and suppressing aerobic glycolysis through AMPK-mediated inhibition of mTOR/S6K/4EBP1, thereby sensitizing cells to EGFR tyrosine kinase inhibitors (PMID:39809840, PMID:41731056).

1. 2016 Medium

   Establishing that ITGA8 functions as an anti-fibrotic signal in the kidney by placing it upstream of TGF-β/SMAD2/3 suppression and fibroblast activation, answering how loss of this integrin exacerbates tubulointerstitial injury.

   Evidence Itga8 knockout mice subjected to unilateral ureteral obstruction; immunostaining for pSMAD2/3 and α-SMA

   PMID:26938996

   Open questions at the time

   • Ligand that engages α8β1 in renal interstitium not identified
   • Mechanism by which ITGA8 suppresses SMAD2/3 phosphorylation not resolved
   • Single-lab study without independent replication
2. 2016 High

   Demonstrating that ITGA8 is a functional receptor for the Fraser complex component FRAS1, establishing a direct epithelial–mesenchymal signaling axis required for craniofacial morphogenesis.

   Evidence Zebrafish forward genetic screen and CRISPR alleles; genetic epistasis between itga8 and fras1 single and double mutants

   PMID:27265864

   Open questions at the time

   • Biochemical binding affinity between ITGA8 and FRAS1 not measured
   • Whether this interaction is conserved in mammalian craniofacial development not tested
3. 2020 Medium

   Revealing that ITGA8 is epigenetically silenced by ERα-dependent promoter hypermethylation in ER-positive breast cancer, providing a mechanism for its loss in certain tumors.

   Evidence Methylation-specific PCR; 5-aza-dC demethylation and 17-beta-estradiol treatment in breast cancer cell lines; clinical tissue validation

   PMID:32953793

   Open questions at the time

   • Functional consequence of ITGA8 re-expression in breast cancer cells not assessed
   • Identity of the methyltransferase(s) recruited by ERα not determined
4. 2021 Medium

   Identifying ITGA8 as a surface marker of Schlemm's canal endothelial cells in the eye, linking it to contractile regulation of aqueous humor outflow resistance.

   Evidence Immunofluorescence, FISH, magnetic bead isolation of ITGA8+ cells from trabecular meshwork/Schlemm's canal; gel contraction assay with endothelin-1

   PMID:33961857

   Open questions at the time

   • Whether ITGA8 directly mediates contractility or serves only as a marker not distinguished
   • Relevance to glaucoma pathogenesis not tested in vivo
5. 2022 High

   Validating ITGA8 as a preferential vascular smooth muscle cell marker by generating an Itga8-CreER knock-in and showing that conditional Srf deletion produces vascular contractile incompetence, establishing tissue-selective expression distinct from visceral smooth muscle.

   Evidence Itga8-CreER knock-in mice compared with Myh11-CreER; conditional Srf knockout; vascular contractility and blood pressure assays

   PMID:36424917

   Open questions at the time

   • Intrinsic role of ITGA8 in VSMC contractility (beyond its use as a Cre driver) not dissected
   • Regulation of Itga8 expression in vascular versus visceral SMC lineages unknown
6. 2024 Medium

   Placing ITGA8 downstream of a circTMCO3/miR-515-5p competing endogenous RNA axis in ovarian cancer, where ITGA8 upregulation promotes tumor malignancy — revealing a pro-oncogenic role contrasting with its tumor-suppressive function in lung cancer.

   Evidence circTMCO3 knockdown and miR-515-5p manipulation; ITGA8 overexpression rescue; nude mouse xenograft

   PMID:38755265

   Open questions at the time

   • Downstream signaling pathway activated by ITGA8 in ovarian cancer not characterized
   • Context-dependent oncogenic versus tumor-suppressive switch mechanism not explained
7. 2025 High

   Identifying macrophage-secreted Fn1 as the ligand engaging ITGA8 on fibroblasts and delineating a FAK/RhoA/ROCK pro-fibrotic signaling cascade in neurogenic bladder fibrosis, answering how immune–stromal crosstalk drives ITGA8-dependent fibrosis.

   Evidence Single-cell RNA-seq; Col1a2-CreERT; Itga8fl/fl conditional knockout; macrophage depletion; FAK/RhoA/ROCK pathway analysis; bladder voiding assessment

   PMID:41355531

   Open questions at the time

   • Whether Fn1-ITGA8 engagement is direct or requires co-receptors not resolved
   • How the same integrin attenuates fibrosis in kidney but promotes it in bladder remains unexplained
8. 2025 Medium

   Demonstrating that ITGA8 promotes hepatic fibrosis via COL11A1 upregulation in stellate cells, extending the pro-fibrotic role beyond the bladder and identifying a specific ECM target.

   Evidence CCl4 liver fibrosis model; AAV2/6-shItga8 knockdown; proteomics identifying COL11A1; collagen contraction assay

   PMID:40056500

   Open questions at the time

   • Signaling pathway connecting ITGA8 to COL11A1 transcription not identified
   • Single-lab study; independent validation needed
9. 2025 Medium

   Establishing ITGA8 as a tumor suppressor in lung adenocarcinoma that dampens FAK/SRC/AKT/MAPK signaling and sensitizes cells to EGFR-TKIs, directly linking integrin signaling to therapeutic response.

   Evidence Genome-wide CRISPR-Cas9 screen; ITGA8 KD/OE in H1975 cells; xenograft models; Western blot for pathway components

   PMID:39809840

   Open questions at the time

   • Mechanism by which ITGA8 inhibits rather than activates FAK not resolved
   • Patient stratification by ITGA8 expression for TKI response not validated clinically
10. 2026 Medium

    Extending the tumor-suppressive mechanism by showing ITGA8 activates AMPK to inhibit mTOR/S6K/4EBP1 signaling and suppress aerobic glycolysis, providing a metabolic explanation for growth suppression in lung adenocarcinoma.

    Evidence ITGA8 overexpression; Seahorse ECAR; glucose uptake/lactate assays; AMPK pharmacological inhibition rescue; xenograft models

    PMID:41731056

    Open questions at the time

    • How ITGA8 activates AMPK (direct interaction, calcium flux, or other) not determined
    • Whether metabolic suppression and FAK/SRC inhibition are parallel or sequential pathways unclear

• The fundamental question of how ITGA8 exerts opposing effects on fibrosis (anti-fibrotic in kidney, pro-fibrotic in bladder and liver) and opposing roles in cancer (tumor-suppressive in lung, oncogenic in ovary) remains mechanistically unexplained.
• No structural model of α8β1 engagement with different ligands (nephronectin, Fn1, FRAS1) to explain context-dependent signaling
• Tissue-specific co-receptor or adaptor usage not characterized
• Systematic comparison of ITGA8 signaling outputs across cell types not performed