SHISA3

SHISA3 is a tumor-suppressive antagonist of Wnt/β-catenin signaling that also engages receptor tyrosine kinase and innate immune pathways to restrain tumor growth, invasion, and metastasis (PMID:25036006, PMID:31222549). It inhibits Wnt signaling by blocking maturation and transport of Frizzled receptors to the cell surface, preventing Wnt3a-induced nuclear translocation of β-catenin and expression of the target gene Axin2, and by accelerating β-catenin degradation (PMID:25036006, PMID:31222549). In carcinoma cells SHISA3 suppresses invasion and metastasis by impeding TRIM21-mediated ubiquitination and degradation of SGSM1, thereby dampening MAPK pathway activation (PMID:30573520), and it interacts with FGFR1 and FGFR3 to inhibit AKT/mTOR signaling, suppress cancer stem cell properties, and reverse EGFR-TKI resistance (PMID:31801598). Its expression is silenced by promoter hypermethylation in breast cancer cells and restored by demethylation (PMID:32692756). Beyond its tumor-suppressor role, SHISA3 forms a complex with HSPA8 in macrophages to activate NF-κB signaling and maintain M1 polarization, enhancing phagocytosis, antigen presentation, and CD8+ T cell-mediated antitumor immunity (PMID:39054639). Transcriptionally, SHISA3 is controlled by KLF15-Wnt networks in the heart and induced by DAMP/PAMP-driven NF-κB signaling in immune cells (PMID:31582141, PMID:39054639).

1. 2014 Medium

   Established SHISA3 as a functional tumor suppressor by linking it mechanistically to Wnt/β-catenin signaling, answering whether its anti-tumor effect had a defined pathway readout.

   Evidence Microarray/pathway analysis, in vitro invasion assays, and orthotopic mouse tumor models with β-catenin degradation readout in lung cancer

   PMID:25036006

   Open questions at the time

   • Did not resolve the molecular step at which SHISA3 promotes β-catenin degradation
   • No direct binding partner identified
2. 2018 High

   Defined a metastasis-suppressing axis by placing SHISA3 upstream of TRIM21-SGSM1-MAPK, explaining how it blocks invasion independent of Wnt.

   Evidence Co-IP, ubiquitination assays, and SGSM1 knockdown rescue in nasopharyngeal carcinoma with in vitro and in vivo metastasis models

   PMID:30573520

   Open questions at the time

   • Mechanism by which SHISA3 inhibits TRIM21-mediated ubiquitination of SGSM1 not structurally defined
   • Direct SHISA3-TRIM21 vs SHISA3-SGSM1 binding hierarchy not fully resolved
3. 2019 Medium

   Clarified the cell-biological mechanism of Wnt antagonism by showing SHISA3 blocks Frizzled receptor maturation/trafficking, while KO mice revealed family redundancy.

   Evidence Adenoviral overexpression, β-catenin translocation and Axin2 assays in osteoblasts, plus Shisa3 KO mouse phenotyping

   PMID:31222549

   Open questions at the time

   • No bone phenotype in KO leaves the in vivo role uncertain due to Shisa family redundancy
   • Direct SHISA3-Frizzled interaction not biochemically demonstrated
4. 2019 Medium

   Extended SHISA3 function to RTK signaling by identifying FGFR1/3 interaction that suppresses AKT/mTOR and cancer stem cell traits, connecting it to drug resistance.

   Evidence Co-IP, Western blot of AKT/mTOR, sphere formation, and in vivo NOD-SCID models in lung adenocarcinoma

   PMID:31801598

   Open questions at the time

   • Whether FGFR binding and Wnt antagonism are independent or coupled is unresolved
   • Single-lab interaction without reciprocal structural validation
5. 2019 Medium

   Placed SHISA3 within a tissue transcriptional network by showing KLF15-Wnt control of its expression in vascular cells of fetal and remodeling hearts.

   Evidence Transcriptomics, Klf15 KO mice, Wnt-modulated and pressure-overload/ischemia models, and human KLF15 KO stem cell-derived myocardium

   PMID:31582141

   Open questions at the time

   • Functional consequence of SHISA3 expression in cardiac vascular cells not determined
   • Whether cardiac SHISA3 acts through the same Frizzled/β-catenin mechanism not tested
6. 2024 Medium

   Revealed a non-cancer-cell role: SHISA3 partners with HSPA8 to activate NF-κB and sustain M1 macrophage polarization, linking it to antitumor immunity.

   Evidence mRNA delivery, SHISA3-HSPA8 co-IP, NF-κB and phagocytosis/antigen presentation assays, and Shisa3 KO combination immunotherapy in vivo

   PMID:39054639

   Open questions at the time

   • Molecular mechanism by which the SHISA3-HSPA8 complex activates NF-κB is undefined
   • Reconciliation of NF-κB-activating immune role with Wnt-antagonist tumor-cell role not addressed

• How SHISA3's distinct activities — Frizzled trafficking blockade, FGFR binding, TRIM21-SGSM1 regulation, and HSPA8-NF-κB complex formation — are integrated within a single protein and across cell types remains unresolved.
• No structural model defining the domains responsible for each interaction
• No unifying explanation for context-dependent (tumor-suppressive vs immune-activating) functions