Some gastric tumors are effectively invisible to checkpoint immunotherapy. This study identifies TRIM6 as a molecular brake: remove it, and the cGAS-STING immune alarm becomes active again. Gastric cancers are classified into four molecular subtypes: Epstein-Barr virus-positive, microsatellite instability-high, chromosomal instability, and genomically stable.

Unlike microsatellite instability-high gastric cancer, genomically stable and chromosomal instability subtypes have immunologically inert microenvironments and show minimal response to immune checkpoint blockade. Gastric cancer ranks as the fifth most frequently diagnosed malignancy and the fourth leading cause of cancer-related mortality worldwide.

Among the subtypes, Epstein-Barr virus-positive and microsatellite instability-high gastric cancers show remarkable sensitivity to immunotherapy, while genomically stable and chromosomal instability types show minimal response to immune checkpoint blockade. Clinical trials showed a one-hundred-percent overall response rate for Epstein-Barr virus-positive gastric cancer and an eighty-five-point-seven-percent overall response rate for microsatellite instability-high gastric cancer with pembrolizumab.

In contrast, genomically stable and chromosomal instability subtypes show limited or no response to anti-PD-1 or PD-L1 therapy, reflecting immunologically cold tumor microenvironments. The molecular basis for immunotherapy resistance in microsatellite-stable gastric carcinomas remains poorly understood.

Weighted gene co-expression network analysis of TCGA-STAD data identified TRIM6 as a RING-type E3 ligase inversely correlated with microsatellite instability-high status. TRIM6 shows hypermethylation-associated downregulation in microsatellite instability-high versus microsatellite-stable tumors and negatively correlates with cytotoxic T lymphocyte infiltration and pembrolizumab response.

Mechanistically, TRIM6 promotes proteasomal degradation of cGAS, suppressing the cGAS-STING pathway. The TCGA-STAD dataset included data from three hundred seventy-four gastric cancer patients, and weighted gene co-expression network analysis examined more than three hundred fifty-six E3 ligases.

Coexpression analysis identified brown and blue modules significantly associated with MSI MANTIS scores, a metric reflecting the microsatellite instability status of patient tumors. The blue module showed a strong negative correlation with MANTIS scores, with an r value of negative zero-point-two-three and a p value of three times ten to the negative fourth.

Among the top ten MANTIS-negatively-associated genes, TRIM6 was selected as the lead candidate because it had the strongest negative correlation with overall survival in gastric cancer patients. TRIM6 expression was validated against microsatellite instability-high and microsatellite-stable status in different gastric cancer datasets.

TRIM6 messenger RNA levels were significantly lower in microsatellite instability-high tumors from the TCGA-STAD and ACRG cohorts than in microsatellite-stable tumors. TRIM6 expression was positively associated with MLH1 expression in gastric cancer.

The TRIM6 promoter contains a CpG island from negative eight hundred fifty-one to negative seven hundred two relative to the transcription start site. Bisulfite sequencing found that TRIM6 promoter methylation was significantly increased in microsatellite instability-high gastric tumor samples compared with microsatellite-stable tumor tissues, and the result was verified in the TCGA-STAD methylation database.

TRIM6 was depleted in MTC cells, and tumorigenesis was observed in immune-competent and immune-deficient mice. TRIM6 depletion retarded MTC tumor growth in immunocompetent C57BL/6J mice, whereas this suppression was compromised in nude mice. Figure two tests TRIM6 in several tumor models and mouse backgrounds.

TRIM6 knockout slowed MTC and B16F10 tumor growth in immunocompetent mice, while this effect was reduced or not significant in nude mice; it also increased MTC sensitivity to anti-PD-L1 treatment. Conversely, TRIM6 overexpression enhanced MFC tumor growth in immune-competent 615 mice but not nude mice, supporting an immune-dependent role for TRIM6 in tumor progression and immunotherapy response.

TRIM6 depletion sensitized MTC tumors to anti-PD-L1 antibody treatment in C57BL/6J mice. TRIM6 overexpression enhanced MFC tumorigenesis in immunocompetent 615 mice but not in nude mice, and it conferred MFC cell resistance to anti-PD-L1 treatment in 615 mice.

TRIM6 depletion inhibited B16F10 melanoma tumor growth in syngeneic mice and increased their response to anti-PD-L1 treatment. These data suggest that TRIM6 is a critical regulator of immune checkpoint blockade resistance in gastric cancer, and that genetic ablation of TRIM6 substantially sensitizes gastric tumors to anti-PD-L1 therapy.

The study analyzed tumor-infiltrating lymphocytes by flow cytometry in MTC tumors with TRIM6 depletion and MFC tumors with TRIM6 overexpression under anti-PD-L1 treatment. Deletion of TRIM6 combined with anti-PD-L1 treatment increased the proportions of CD8-positive and CD8-positive GZMB-positive T cells, but not CD4-positive T cells, in MTC tumors.

TRIM6 overexpression decreased effective CD8-positive T-cell infiltration in MFC tumors under anti-PD-L1 treatment. Blocking CD8-positive T cells with an anti-CD8 antibody significantly reversed the inhibition of tumor growth in the TRIM6-knockout MTC model.

Figure three links TRIM6 loss to a more active antitumor immune environment. In MTC tumors, Trim6 deletion combined with anti-PD-L1 treatment increased infiltrating CD8-positive and GZMB-positive CD8-positive T cells, without a clear change in CD4-positive cells; the MFC overexpression model shows corresponding CD8-positive, interferon-gamma-positive, and GZMB-positive measurements.

CD8 depletion altered tumor-growth curves, while RNA sequencing and GSEA associated Trim6 loss with innate immune and interferon-beta pathways. Transcriptomic profiling of wild-type and Trim6-knockout MTC tumors was performed using RNA sequencing.

Gene Ontology enrichment analysis revealed multiple pathways related to immune-response and inflammatory-response pathways when Trim6 was depleted. Gene set enrichment analysis revealed enrichment of the innate immune response and positive regulation of the interferon-beta production pathway in Trim6-knockout MTC tumors.

Immunoprecipitation used MKN28 gastric cancer cells expressing Flag-tagged TRIM6 or a truncation mutant lacking the PRY-SPRY domain, which is responsible for TRIM6 substrate binding. IP-MS showed that cGAS, OASL, USP10, DLST, KHDRBS1, and ZNF638 were immunoprecipitated by wild-type TRIM6 but not by its PRY-SPRY-domain-truncated mutants.

TRIM6 attenuated cGAS protein abundance in a dose-dependent manner in 293T cells. In MKN28 and SNU668 gastric cancer cell lines, TRIM6 knockdown elevated cGAS protein levels while leaving cGAS messenger RNA expression unaffected.

The protein abundance of cGAS increased after MG132 treatment, and the half-life of cGAS was prolonged in shTRIM6 cells. TRIM6 significantly inhibited activation of the cGAS-STING-activated interferon-beta signal in a dose-dependent manner, whereas catalytically inactivated TRIM6 C43A failed to do so.

TRIM6 depletion increased messenger RNA levels of IFNB1 and its downstream genes CXCL10 and ISG15, or Ccl5, under HT-DNA treatment in mouse and human gastric cancer cells, and simultaneous cGAS knockout abolished these effects. Phosphorylated STING, TBK1, and IRF3 proteins increased in three distinct TRIM6-knockout cell lines, but this increase was abrogated upon cGAS depletion.

Figure five tests how TRIM6 affects cGAS–STING signaling. Reporter assays, gene-expression measurements, immunoblots, and cGAMP assays show that TRIM6 status is examined in engineered MTC and MKN28 cells after HT-DNA stimulation, while tumor-growth curves extend the comparison to mouse models.

The co-immunoprecipitation experiment also examines whether TRIM6 associates with cGAS, STING, TBK1, or IRF3, supporting the authors’ focus on TRIM6 as a regulator of this interferon pathway. cGAMP was robustly elevated when TRIM6 was depleted in MTC and MKN28 cells, and this elevation was completely abrogated in TRIM6 and cGAS double-knockout cells.

TRIM6 and cGAS double-knockout cells substantially abrogated the tumor-growth-suppressive effect observed in TRIM6-knockout cells transplanted into C57BL/6J mice. Co-immunoprecipitation showed that TRIM6 does not physically interact with STING, TBK1, or IRF3.

These data suggest that TRIM6 attenuates cGAS-STING-dependent type one interferon responses through degradation of cGAS, facilitating tumor immune evasion and accelerating tumor progression. Immunoblotting revealed increased activation of the cGAS-STING pathway in Trim6-depleted tissues, shown by elevated protein levels of cGAS, phosphorylated TBK1, and phosphorylated IRF3.

These data indicate that Trim6 loss triggers innate immune signaling through cGAS-STING in vivo and suggest a mechanism by which Trim6 deficiency enhances immune-mediated suppression of gastric tumorigenesis. Figure six extends the TRIM6–cGAS mechanism into an in vivo gastric cancer model.

The authors generated epithelial-specific Trp53 and Trim6 conditional knockout mice, induced tumors with Myc and cGAS-STING pathway stimulation, and compared gross tumor morphology, H and E tissue staining, and signaling proteins between genotypes. The schematic summarizes the proposed effect: removing TRIM6 permits cGAS activity and cGAMP production, leading to STING, interferon beta, and interferon-stimulated gene signaling associated with tumor suppression.

Elevated TRIM6 characterizes microsatellite-stable gastric cancers and inversely correlates with microsatellite instability status. High TRIM6 levels associate with reduced cytotoxic T lymphocyte infiltration and poorer response to pembrolizumab therapy. TRIM6 mediates K27-linked polyubiquitination and subsequent proteasomal degradation of cGAS, suppressing innate immune signaling.

TRIM6 deletion restores cGAS protein stability, reactivates the cGAS-STING-interferon-beta signaling axis, and enhances antitumor immunity in gastric cancer cell lines and murine models. The findings suggest that TRIM6 targeting could potentially convert immunologically cold gastric tumors into immunotherapy-responsive hot phenotypes.

Recent efforts to enhance immunotherapy efficacy in microsatellite-stable tumors have primarily focused on colorectal cancer, with limited exploration of microsatellite-stable gastric cancer. TRIM6 is identified as a critical negative regulator of the cGAS-STING innate immune pathway in microsatellite-stable gastric tumors, revealing a potential therapeutic vulnerability.

Future research should prioritize TRIM6-targeted agents and evaluate their safety and combinatorial efficacy with immune checkpoint blockade in preclinical microsatellite-stable models. The study links high TRIM6 to immune-cold, treatment-resistant gastric cancer and shows that TRIM6 loss activates cGAS-STING, increases CD8-positive T-cell infiltration, and improves anti-PD-L1 responses in models.