DHX9 transcriptional upregulation and lactylation at K1024 fuels a glycolysis–histone lactylation loop in osteosarcoma

BACKGROUND: Histone lactylation, a novel posttranslational modification driven by glycolytic lactate, has emerged as a key regulator of tumorigenesis. However, its role in osteosarcoma (OS) progression and the underlying metabolic‒epigenetic crosstalk remain poorly understood. METHODS: Using immunohistochemistry, molecular biology, and functional assays in vitro and in vivo, we investigated lactylation levels, DHX9 regulation, Lactylation and glycolytic activity in osteosarcoma models. Techniques included CUT&Tag, LC-MS/MS, site-directed mutagenesis, and xenograft studies. RESULTS: Here, we show global lactylation levels were significantly elevated in OS tissues compared with paracancerous controls. Glycolysis inhibition suppressed H3K9la and impeded OS malignancy. CUT&Tag identified H3K9la enrichment at the DHX9 promoter. DHX9 knockdown inhibited proliferation, migration, and invasion (in vitro) and tumor growth (in vivo), whereas DHX9 overexpression had the opposite effects. LC‒MS/MS revealed K1024 as a functional lactylation site on DHX9-K1024R mutation (lactylation-deficient) disrupted a feedforward loop: (1) reduced PKM2/LDHA expression → impaired glycolysis → decreased H3K9la; and (2) suppressed malignant phenotypes. Conversely, DHX9-K1024T (lactylation mimetic) partially rescued glycolytic enzyme expression and H3K9la levels. CONCLUSION: We elucidated a self-amplifying H3K9la-DHX9-K1024la-glycolysis circuit that drives OS progression. DHX9 lactylation at K1024 serves as a critical metabolic‒epigenetic interface, suggesting that K1024 lactylation may represent a potential therapeutic target, warranting further investigation.