ITGB8

ITGB8 (integrin β8) is a transmembrane receptor subunit that activates latent TGF-β1 and transduces extracellular matrix signals through FAK-dependent intracellular cascades to regulate cell adhesion, lineage commitment, and osteoclastogenesis. In uterine luminal epithelium, ITGB8 activates latent TGF-β1 to drive SMAD2/3 phosphorylation required for embryo implantation, and independently signals through a FAK→VAV→RAC1 axis to promote endometrial epithelial cell adhesion to the blastocyst (PMID:25788663, PMID:28507287). In bone biology, osteoblast-derived osteomodulin engages ITGB8 on osteoclast precursors to suppress RhoA, increase YAP phosphorylation, repress RRM2 transcription, and thereby limit mitochondrial bioenergetics and osteoclastogenesis, while in mesenchymal stem cells ITGB8 activates a FAK–ERK–RUNX2 cascade that favors osteogenic over adipogenic differentiation (PMID:41813908, PMID:41878635). ITGB8 expression is directly repressed by multiple miRNAs including miR-199a-3p and miR-187 via 3′-UTR binding, and is transcriptionally regulated by EBF1 in marrow stromal cells where it contributes to bone marrow fibrosis (PMID:29436681, PMID:34973644, PMID:41756923).

1. 2015 High

   Establishing that ITGB8 activates latent TGF-β1 in the uterine epithelium to drive SMAD2/3 signaling and embryo implantation answered how the maternal endometrium generates active TGF-β at the implantation site.

   Evidence In vivo neutralizing antibody and siRNA silencing of Itgb8 in mouse uterus with SMAD2/3 phosphorylation and implantation rate readouts

   PMID:25788663

   Open questions at the time

   • Whether ITGB8 pairs with αv or another α subunit for TGF-β1 activation in this tissue was not dissected
   • Structural basis of ITGB8-mediated latent TGF-β1 release not resolved
   • Downstream transcriptional targets of SMAD2/3 in the implantation context not identified
2. 2017 High

   Demonstration that ITGB8 signals through FAK→VAV→RAC1 to promote blastocyst attachment established a TGF-β-independent intracellular signaling axis for ITGB8 in endometrial epithelial cells.

   Evidence siRNA knockdown of ITGB8, FAK inhibitor treatment, Western blot for p-FAK/p-VAV, RAC1-GTP pulldown, and JAr spheroid attachment assay in Ishikawa cells

   PMID:28507287

   Open questions at the time

   • Identity of the ligand and α-subunit partner driving FAK activation not determined
   • Relationship between the FAK-VAV-RAC1 axis and the TGF-β1–SMAD2/3 axis in the same tissue not clarified
3. 2018 Medium

   Validation of ITGB8 as a direct miR-199a-3p target via 3′-UTR binding identified a post-transcriptional regulatory mechanism controlling ITGB8 abundance and linked it to cisplatin resistance in ovarian cancer.

   Evidence Luciferase reporter assay confirming 3′-UTR binding, overexpression rescue, and in vivo orthotopic ovarian cancer mouse model

   PMID:29436681

   Open questions at the time

   • Downstream effectors of ITGB8 mediating drug resistance were not defined
   • Whether miR-199a-3p–ITGB8 regulation operates in non-cancer contexts was not tested
4. 2020 Medium

   Linking ITGB8 to MEK/ERK activation downstream of a PVT1/miR-145-5p ceRNA axis in NSCLC showed that ITGB8 can serve as a proliferative effector of oncogenic lncRNA programs.

   Evidence siRNA knockdown, luciferase reporter assay, Western blot for p-MEK/p-ERK, and xenograft tumor model in NSCLC cells

   PMID:32202906

   Open questions at the time

   • Direct physical interaction between ITGB8 and MEK/ERK pathway components not shown
   • Whether ITGB8-mediated MEK/ERK activation requires FAK was not tested
5. 2021 Medium

   Identification of miR-187 as a second direct negative regulator of ITGB8 in goat endometrial cells, with FAK as the functional readout, reinforced the generality of miRNA-mediated ITGB8 control during implantation across species.

   Evidence 3′-UTR luciferase reporter assay, miR-187 inhibitor transfection, Western blot for FAK in primary goat endometrial epithelial cells

   PMID:34973644

   Open questions at the time

   • Cross-species conservation of miR-187–ITGB8 regulation in human endometrium not established
   • Whether miR-187 inhibition phenocopies ITGB8 overexpression in implantation not tested in vivo
6. 2023 Medium

   Placing ITGB8 within an F-actin/TRIM59/AKT/mTOR/glycolysis cascade in 3D-cultured bladder cancer cells revealed a mechanotransduction role for ITGB8 linking biomechanical cues to metabolic reprogramming and tumorigenic softness.

   Evidence Microfluidic soft-cell isolation, 3D Matrigel culture, Western blot for pathway components, clinical tissue immunostaining, xenograft model

   PMID:37390491

   Open questions at the time

   • Direct epistasis between ITGB8 and each downstream node (TRIM59, AKT, mTOR) not individually reconstituted
   • Whether ITGB8 directly binds TRIM59 or signals indirectly was not determined
7. 2026 High

   Multi-level dissection of an OMD→ITGB8→RhoA⊣→YAP/TEAD→RRM2 axis established how osteoblast-derived osteomodulin restrains osteoclastogenesis by suppressing mitochondrial bioenergetics via integrin β8 engagement.

   Evidence Inducible global and cell-type-specific Omd/Itgb8 knockout mice, ITGB8-neutralizing antibody, RhoA activity assay, YAP phosphorylation, ChIP, Seahorse respiration, ovariectomy and LPS bone-loss models

   PMID:41813908

   Open questions at the time

   • How ITGB8 engagement by OMD mechanistically suppresses RhoA GTPase activity is unknown
   • Whether this axis operates in human osteoclasts not shown
   • Identity of the α-subunit partner for ITGB8 in osteoclast precursors not determined
8. 2026 High

   Demonstrating that ITGB8 activates FAK–ERK–RUNX2 signaling to drive osteogenic differentiation of BMSCs, under direct negative regulation by miR-199a-3p, unified the miRNA-target relationship with a specific lineage-commitment pathway.

   Evidence Dual-luciferase reporter assay, miR-199a-3p mimic/antagomiR, ITGB8 overexpression/silencing, Western blot for FAK/ERK/RUNX2, SONFH rat model with local antagomiR delivery

   PMID:41878635

   Open questions at the time

   • Whether FAK–ERK–RUNX2 is the sole downstream effector of ITGB8 in BMSCs or operates in parallel with other cascades not resolved
   • Structural basis of ITGB8-mediated FAK activation not defined

• The identity of the α-subunit partner(s) for ITGB8 in each tissue context (endometrium, bone, tumor), the structural mechanism by which ITGB8 activates latent TGF-β1 versus FAK-dependent intracellular signaling, and the extent to which these two arms operate simultaneously or are context-exclusive remain unresolved.
• No structural model of ITGB8 signaling complex in any context
• Relative contribution of TGF-β1 activation versus direct FAK signaling across tissues not compared
• Systematic identification of ITGB8 extracellular ligands beyond OMD and latent TGF-β1 not performed