Abstract
Objective: AT-rich interaction domain 1A (ARID1A), is frequently mutated in cancer, leading to loss-of-function and posing challenges to therapeutic targeting. This study aimed to systematically explore epigenetic regulation of ARID1A, specifically promoter hypermethylation, in gastric cancer (GC) and its functional/immunological consequences. Methods: We employed multi-omics bioinformatics analyses (UALCAN, cBioPortal, MEXPRESS and UCSC Xena) combined with in vitro functional validation in GC cell lines, including pharmacological demethylation using 5-Aza-2'-deoxycytidine (5-aza-CdR) and mechanistic interrogation via AKT agonism (SC79). Results: Promoter hypermethylation was identified as a key mechanism silencing ARID1A transcriptional, showing a significant negative correlation between methylation β-values and mRNA expression (Spearman's ρ = - 0.29, p = 2.06 × 10-8). 5-aza-CdR treatment restored ARID1A expression (p < 0.001), suppressed malignant phenotypes (proliferation, invasion, and apoptosis resistance), and revealed that ARID1A lose activates the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathway (elevated p-AKT, p-mTOR) and upregulates PD-L1. Rescue experiments with SC79 reversed 5-aza-CdR's effects, confirming the ARID1A-PI3K/AKT/mTOR-PD-L1 axis. Integrative analysis linked ARID1A hypermethylation to elevated immune/ESTIMATE scores (p < 0.05). Conclusion: ARID1A promoter hypermethylation drives an epigenetic-immune checkpoint cascade in GC. Combined with its association with immune signatures and PD-L1 upregulation, ARID1A hypermethylation emerges as a candidate biomarker for predicting immune checkpoint blockade (ICB) responsiveness and patient stratification in GC. Future studies should evaluate 5-aza-CdR-ICB-AKT inhibitor regimens in advanced models to guide clinical translation.