Abstract
BACKGROUND: Epigenetic reprogramming, particularly DNA methylation mediated by DNA-methyltransferase 1 (DNMT1), plays a crucial role in the pathogenesis of hepatocellular carcinoma (HCC). However, the regulatory mechanisms underlying DNMT1 overexpression and its relationship with immune infiltration in HCC remain unclear. This study aimed to investigate the expression pattern, prognostic significance, and regulatory network of DNMT1 in HCC, as well as its correlation with the tumor immune microenvironment. METHODS: A pan-cancer analysis of DNMT1 expression and prognosis was conducted using The Cancer Genome Atlas (TCGA) data. A cohort of 102 pairs of HCC and adjacent normal tissues from patients who underwent surgical resection was analyzed by immunohistochemistry (IHC). Upstream regulatory non-coding RNAs (ncRNAs) were identified by bioinformatics analyses, including an expression correlation analysis, survival analysis, and competing endogenous RNA (ceRNA) network construction. The relationship between DNMT1 expression and immune cell infiltration was evaluated using multiple algorithms, including TIMER, CIBERSORT, and xCell. A Gene Set Enrichment Analysis (GSEA) was performed to identify the DNMT1-associated functional pathways. RESULTS: DNMT1 was significantly overexpressed in the HCC tissues compared to the normal control tissues, and was correlated with poor overall survival (OS) and relapse-free survival (RFS). High DNMT1 expression was associated with advanced histological grade, elevated alpha-fetoprotein (AFP) levels, and older age (P<0.001). SNHG3 was confirmed to be an upstream long non-coding RNA (lncRNA) that competitively binds to hsa-miR-148a-3p, forming the SNHG3/hsa-miR-148a-3p/DNMT1 regulatory axis. DNMT1 expression was significantly positively correlated with the infiltration of multiple immune cell types, including B cells, CD8(+) T cells, CD4(+) T cells, macrophages, neutrophils, and dendritic cells (DCs). Moreover, DNMT1 expression was significantly positively correlated with immune checkpoint molecules, including programmed cell death protein 1 (PD-1), programmed death ligand 1 (PD-L1), and cytotoxic T lymphocyte antigen 4 (CTLA-4). The GSEA results revealed that high DNMT1 expression was enriched in epithelial-mesenchymal transition (EMT), E2F targets, the G2M checkpoint, and inflammatory response pathways. CONCLUSIONS: The SNHG3/miR-148a-3p/DNMT1 axis represents a novel regulatory pathway in hepatocarcinogenesis. DNMT1 overexpression could serve as a biomarker for poor prognosis, and is closely associated with enhanced immune cell infiltration and immune checkpoint expression in HCC. These findings suggest that DNMT1 may serve as a potential therapeutic target for both conventional treatment and immunotherapy in HCC patients.