Mechanism of Monocarboxylate Transporter 1 and Its Methylation in Nasopharyngeal Carcinoma Pathogenesis

<b><i>Objective:</i></b> This study explored the role of monocarboxylate transporter 1 (<i>MCT1</i>) in nasopharyngeal carcinoma (NPC) metastasis and its regulation via DNA methyltransferase 3B (<i>DNMT3B</i>)-mediated methylation, to identify therapeutic targets for NPC. <b><i>Methods:</i></b> <i>MCT1/DNMT3B</i> expression was analyzed in NPC (<i>n</i> = 30) and normal tissues (<i>n</i> = 30) using quantitative polymerase chain reaction (qPCR) and immunohistochemistry. <i>DNMT3B</i> overexpression plasmids were transfected into NPC cells to assess <i>MCT1</i> expression and promoter methylation via bisulfite sequencing PCR. Luciferase and chromatin immunoprecipitation (ChIP) assays identified <i>DNMT3B-MCT1</i> promoter interactions. Migration/invasion assays and Western blot evaluated functional impacts of <i>MCT1</i> silencing on metastasis-related pathways. Bioinformatic validation utilized GEO datasets. <b><i>Results:</i></b> <i>MCT1</i> mRNA/protein levels were significantly elevated in NPC versus normal tissues (***<i>p</i> < 0.001), whereas <i>DNMT3B</i> was downregulated. <i>DNMT3B</i> overexpression reduced <i>MCT1</i> expression (*<i>p</i> < 0.05) and increased <i>MCT1</i> promoter methylation (**<i>p</i> < 0.01). Luciferase assays revealed that <i>DNMT3B</i> suppressed wild-type <i>MCT1</i> promoter activity, dependent on an 80 bp CpG island (**<i>p</i> < 0.01). ChIP confirmed <i>DNMT3B</i> enrichment at hypermethylated <i>MCT1</i> promoter regions (**<i>p</i> < 0.01). <i>MCT1</i> silencing inhibited NPC cell migration/invasion (*<i>p</i> < 0.05) and downregulated p-AKT, p-mTOR, and p-NFκB (*<i>p</i> < 0.05). High <i>MCT1</i> correlated with Epstein-Barr virus (EBV)-associated EBNA1BP2 (**<i>p</i> < 0.01), but not PD-L1 markers. <i>DNMT3B</i> inversely correlated with <i>MCT1</i> (*<i>p</i> < 0.05) and was upregulated in advanced-stage NPC (Stage III + IV vs. I + II, ***<i>p</i> < 0.001), indicating stage-specific epigenetic dysregulation. <b><i>Conclusion:</i></b> <i>MCT1</i> promotes NPC metastasis via NF-κB and PI3K/AKT/mTOR pathways, regulated by <i>DNMT3B</i>-driven promoter methylation. The <i>MCT1-DNMT3B</i> axis, linked to EBV-associated metabolic reprogramming, represents a prognostic biomarker and therapeutic target for advanced NPC.