DNA Hypermethylation-induced LRRC4 downregulation: a driver of glycolysis and lung adenocarcinoma progression

BACKGROUND: Lung adenocarcinoma (LUAD) remains a significant health threat, with high incidence and mortality rates that necessitate innovative treatment strategies. A critical step forward is to elucidate the molecular mechanisms driving LUAD progression. Although LRRC4 has been well-documented as a tumor suppressor in gliomas, its role in LUAD remains largely unknown, suggesting a need for further investigation. METHODS: In LUAD and normal tissues, LRRC4 expression were examined using TCGA data. Methylation differences were assessed using the MethylMix package, and CpG island distribution in the LRRC4 promoter was predicted with MethPrimer. Gene set enrichment analysis (GSEA) was performed to identify pathways associated with LRRC4 and its correlation with key glycolytic genes. LRRC4 mRNA levels were measured by qPCR, and protein expression was detected by western blot for LRRC4 and glycolysis-related proteins. Methylation-specific PCR (MSP) was used to analyze methylation status in normal and LUAD cells. Cellular functions, specifically viability, proliferation, and invasiveness, were evaluated via CCK-8, colony formation, and Transwell assays. Glycolytic activity was determined through glucose consumption, lactate production, ATP levels, and Seahorse XF analysis. RESULTS: LRRC4 was steeply downregulated in LUAD, with a strong negative correlation between its expression and methylation levels. Multiple CpG sites were identified in the promoter region, and MSP demonstrated higher methylation in LUAD cells compared to normal cells. Functionally, LRRC4 acted as a suppressor of LUAD cell viability, proliferation, and invasiveness. GSEA indicated that LRRC4 was enriched in the glycolysis pathway and negatively correlated with key glycolytic genes. LRRC4 also inhibited glucose consumption, lactate and ATP production, and facilitated a metabolic shift toward oxidative phosphorylation. CONCLUSION: Promoter hypermethylation of LRRC4 triggers its downregulation, which promotes glycolysis and fuels the aggressive progression of LUAD.