H4K5 lactylation - ENO2 loop drives glycolysis and HCC progression

BACKGROUND & AIMS: Histone lactylation is a lactate-dependent epigenetic modification driven by glycolysis. Although elevated histone lactylation occurs in various cancers, the biological relevance of histone H4 lactylation in hepatocellular carcinoma (HCC) remains unclear. The aim of this study was to investigate the clinicopathological relevance of histone H4 lysine 5 lactylation (H4K5la) and its role in regulating lactate metabolism to promote HCC progression. METHODS: H4K5la, H3K18la, and panKla (global lactylated lysine) expression levels were evaluated by immunohistochemistry in HCC tissues (n = 104). RNA sequencing and chromatin immunoprecipitation qPCR analyses were performed in HCC cells treated with lactate to identify downstream target genes regulated by H4K5la. Functional validation of these targets was conducted using knockdown and overexpression experiments, and biological effects were assessed in vitro and in vivo. RESULTS: Elevated H4K5la, H3K18la, and panKla levels were associated with poor prognosis, and H4K5la was identified as an independent prognostic factor of overall survival (p = 0.0064). Upon lactate treatment, four genes including the glycolytic enzyme enolase 2 (ENO2) were identified in three HCC cell lines, showing enrichment of H4K5la in their promoter regions. ENO2 knockdown reduced intracellular lactate and H4K5la levels, and in vivo tumorigenicity in HCC cells (p