Hexachlorobutadiene exposure promotes hepatocellular carcinoma progression via CD8+ T dysfunction and VDR-mediated PI3K/AKT activation: An integrated multi-omics and experimental study

Hexachlorobutadiene (HCBD), a persistent organic pollutant listed under the Stockholm Convention, has raised increasing concern due to its potential health risks; however, its role in hepatocellular carcinoma (HCC) progression remains unclear. In this study, we systematically investigated the toxicological effects and underlying mechanisms of HCBD in HCC progression using an integrated computational and experimental framework. Network toxicology analysis identified 139 shared targets between HCBD exposure and HCC, which were enriched in pathways related to xenobiotic metabolism, oncogenic signaling, and immune regulation. Single-cell transcriptomic analysis further revealed that HCBD targets were associated with CD8⁺ T cell differentiation toward an exhaustion-associated phenotype in HCC patients, which was validated by flow cytometry showing increased expression of exhaustion markers (PD-1, TIM-3, and TIGIT). Through Mendelian randomization and Bayesian colocalization analyses, genetically regulated VDR expression was identified as a key mediator causally linked to HCC risk from the 139 shared target genes. Molecular docking and dynamics simulations suggested stable interaction between HCBD and VDR protein. Mechanistically, HCBD exposure upregulated VDR expression, which transcriptionally activated IGF1 and subsequently triggered PI3K/AKT signaling, promoting HCC cell proliferation, migration, and invasion. These effects were significantly attenuated by VDR knockdown or PI3K inhibition. These findings provide preliminary mechanistic evidence linking HCBD exposure to HCC progression and establish an integrated framework for elucidating health effects of persistent organic pollutants.