The lncRNA–DNA Methylation Axis in Hepatocellular Carcinoma: Mechanisms, Epigenetic Plasticity, and Biological Implications

DNA methylation is a fundamental epigenetic regulator in hepatocellular carcinoma (HCC). However, a key paradox remains: how do ubiquitously expressed enzymes like DNMTs and TETs achieve locus-specific regulation without intrinsic sequence specificity? This review aims to elucidate the "lncRNA-DNA methylation axis," examining how long non-coding RNAs (lncRNAs) confer specificity and plasticity to methylation machinery. We synthesized current literature focusing on the structural mechanisms (e.g., R-loops, DNA:RNA triplexes) by which lncRNAs interact with DNMTs and TETs. We further analyzed the bidirectional regulation between lncRNAs and methylation enzymes and their impact on HCC phenotypes. lncRNAs function as modular scaffolds and guides, directing methylation machinery to specific genomic loci. Rather than binary switches, they act as an "epigenetic rheostat," fine-tuning methylation intensity to balance stability with plasticity. Crucially, a reciprocal feedback loop exists: aberrant DNA methylation suppresses tumor-suppressive lncRNAs, which in turn unleashes DNMT activity, locking cells into a malignant state. This axis drives proliferation, metastasis, metabolic reprogramming, and therapeutic resistance. The lncRNA-DNA methylation axis is a central determinant of epigenetic heterogeneity in HCC. Moving beyond descriptive cataloging to a mechanistic understanding of this network offers new perspectives for developing targeted epigenetic therapies and biomarkers.