Decoding the PTM Code of cGAS-STING in Gastric Cancer: From Innate DNA Sensing to Precision Combination Therapy
核心洞察
The cGAS (搜索)-STING (搜索) pathway plays a dual role in gastric cancer (搜索), mediating both antitumor immunity and immune escape depending on post-translational modifications (PTMs) such as ubiquitination, phosphorylation, and acetylation.
TRIM6 (搜索)-mediated K27-linked ubiquitination of cGAS (搜索) drives proteasomal degradation and immune evasion in microsatellite-stable gastric cancers, while USP35 (搜索) deubiquitination of STING (搜索) paradoxically promotes peritoneal metastasis via HIF-1α/FAK signaling.
HER2 (搜索)-positive gastric cancers suppress cGAS (搜索)-STING (搜索) through an HER2-AKT1 (搜索)-TBK1 axis, and HER2-targeted agents like T-DXd can restore pathway activity and CD8+ T cell infiltration.
The cGAS (搜索)-STING (搜索) pathway, a cornerstone of innate immune sensing of cytosolic DNA, has emerged as a critical determinant of gastric cancer (搜索) progression and therapeutic response. A comprehensive review published in Frontiers in Immunology systematically decodes how post-translational modifications (PTMs) — including ubiquitination, phosphorylation, acetylation, methylation, SUMOylation, and palmitoylation — govern the dual antitumor and pro-tumor functions of this pathway in gastric cancer, revealing novel precision therapeutic opportunities that extend beyond conventional STING agonism.
The Dual Face of cGAS (搜索)-STING (搜索) in Gastric Carcinogenesis
The cGAS (搜索)-STING (搜索) pathway is deeply embedded in gastric cancer (搜索) biology through multiple etiological mechanisms. Chronic Helicobacter pylori infection, a major risk factor for gastric malignancies, induces DNA double-strand breaks and activates cGAS-STING signaling. H. pylori upregulates ACVR1, which inhibits the DNA repair enzyme POLD1, leading to cytosolic DNA accumulation. Simultaneously, the pathogen suppresses IRF3 activation and induces TRIM proteins to inhibit STING, thereby evading innate immune sensing. H. pylori-induced oxidative stress also upregulates SUMOylation enzymes (SAE1, SUMO1, SUMO2/3), which conjugate SUMO onto lysine residues 335, 372, and 382 of cGAS, suppressing its DNA-binding capacity and enzymatic activity.
Epstein-Barr virus (EBV)-associated gastric cancer (搜索) (EBVaGC) presents a distinct regulatory landscape. EBV infection increases cGAS (搜索) expression and STING (搜索) phosphorylation, driving CD47 expression as an immune escape signal while simultaneously inducing OLFM4 via the cGAS-STING pathway to promote YAP activation and tumor proliferation. Notably, cGAS and STING expression levels are significantly elevated in EBVaGC compared to EBV-negative tumors and correlate with increased CD8+ T cell infiltration and PD-L1 expression, suggesting pathway activation shapes an immunocompetent yet checkpoint-regulated microenvironment.
HER2 (搜索)-Mediated Suppression and Therapeutic Restoration
In HER2 (搜索)-positive gastric cancer (搜索), the HER2 intracellular domain directly binds the C-terminal fragment of STING (搜索) on the endoplasmic reticulum and selectively recruits AKT1 (搜索) to the STING signalosome complex. AKT1 directly phosphorylates TBK1, attenuating STING phosphorylation and reducing IRF3 and NF-κB target gene transcription, ultimately limiting type I interferon and chemokine secretion. Clinical specimens confirm that HER2-high lesions exhibit lower STING levels and fewer CD8+ tumor-infiltrating lymphocytes, while elevated total STING predicts unfavorable prognosis.
HER2 (搜索)-targeted therapies can reverse this suppression. Trastuzumab deruxtecan (T-DXd) induces cytosolic DNA accumulation via its TOP1-inhibiting payload to activate cGAS (搜索)-STING (搜索) signaling and enhance CD8+ T cell-mediated antitumor immunity. Small-molecule HER2 inhibitors disrupt the HER2-AKT1 (搜索) axis to restore STING signaling and improve intratumoral immune infiltration.
Ubiquitination and Deubiquitination: Confirmed PTMs in Gastric Cancer (搜索)
Two pivotal PTM events have been directly validated in gastric cancer (搜索) models. TRIM6 (搜索), a RING-type E3 ubiquitin ligase markedly upregulated in microsatellite-stable (MSS) and immunologically "cold" gastric cancers, utilizes its PRY-SPRY domain to interact with the C-terminal catalytic region of cGAS (搜索) and catalyzes K27-linked polyubiquitination. This modification triggers proteasomal degradation of cGAS, dismantling the cGAS-STING (搜索)-IFN-β signaling cascade. TRIM6 depletion stabilizes cGAS, reactivates innate immune responses, promotes CD8+ T cell infiltration, and sensitizes refractory MSS gastric tumors to anti-PD-1/PD-L1 immune checkpoint blockade.
Conversely, USP35 (搜索), a highly expressed deubiquitinase in gastric cancer (搜索), directly deubiquitinates and stabilizes STING (搜索). However, rather than eliciting canonical antitumor immunity, stabilized STING constitutively activates the HIF-1α/FAK signaling pathway, promoting aerobic glycolysis and enhancing adhesion of gastric cancer cells to peritoneal mesothelial cells. Furthermore, gastric cancer cell-derived exosomes carrying USP35 induce mesothelial-to-mesenchymal transition in peritoneal mesothelial cells, facilitating peritoneal dissemination.
Proposed PTM Mechanisms from Pan-Cancer Evidence
Several additional PTM mechanisms, while not yet directly validated in gastric cancer (搜索), are supported by compelling evidence from other tumor types. PRMT1, highly expressed in gastric cancer and correlated with poor prognosis, catalyzes asymmetric dimethylation at the conserved Arg133 residue of cGAS (搜索), impairing cGAS dimerization and enzymatic activity. CDK1, a key driver of gastric cancer proliferation, can phosphorylate cGAS at the S291 site during mitosis, inhibiting DNA sensing. The AKT kinase network, consistently hyperactivated in gastric cancer through HER2 (搜索) amplification, PTEN loss, and H. pylori-induced oxidative stress, may exert multi-tiered inhibitory phosphorylation on cGAS and STING (搜索).
Acetylation regulation involves multiple enzymes: HDAC3, highly expressed in gastric cancer (搜索), may deacetylate cGAS (搜索) inhibitory sites while simultaneously downregulating STING (搜索) expression through histone deacetylation at its promoter. HAT1 may inhibit cytoplasmic pathway activity by enhancing cGAS nuclear translocation, while SIRT2 may suppress cGAS activation by deacetylating G3BP1. Palmitoylation of cGAS at C474 by ZDHHC18 reduces DNA binding affinity, while STING palmitoylation at Cys88 and Cys91 by DHHC3, DHHC7, and DHHC15 is essential for TBK1 and IRF3 recruitment.
Precision PTM Targeting: Beyond Pan-STING (搜索) Agonism
Conventional pan-STING (搜索) agonists such as diABZI and ADU-S100, while promising in specific settings, carry risks of excessive systemic inflammation and narrow therapeutic windows. The review authors argue that precision interventions targeting specific PTM-modifying enzymes represent a paradigm shift. Small interfering RNA (siRNA) or short hairpin RNA (shRNA) therapeutics targeting TRIM6 (搜索) could abrogate K27-linked ubiquitination of cGAS (搜索), restore protein stability, and reactivate endogenous antitumor immunity, potentially converting MSS gastric tumors from immunologically "cold" to "hot" when combined with immune checkpoint blockade.
Conversely, silencing USP35 (搜索) via RNA interference in patients at risk for peritoneal metastasis could deprive STING (搜索) of deubiquitination protection, leading to its degradation and disrupting the HIF-1α/FAK-mediated metabolic reprogramming that drives peritoneal dissemination.
Challenges and Future Directions
The review identifies several critical challenges: dMMR/MSI-H and EBV-positive tumors exhibit higher intrinsic cGAS (搜索)-STING (搜索) activity, whereas MSS and HER2 (搜索)-positive settings are more immunologically suppressed, meaning PTM-targeted strategies are unlikely to behave uniformly across subtypes. Most candidate interventions — including HDAC inhibitors, AKT inhibitors, PRMT inhibitors, and palmitoylation inhibitors — regulate numerous substrates beyond cGAS or STING, complicating attribution of therapeutic responses. Direct validation of PTM sites in human gastric cancer (搜索) tissues remains rare, and few studies integrate phosphoproteomics, ubiquitinomics, acetylomics, or SUMO-proteomics with functional immune readouts. Future work should prioritize residue-level PTM mapping in gastric cancer specimens, define subtype-specific PTM signatures, and test whether these signatures predict response to immune checkpoint blockade, chemotherapy, or radiotherapy.