Epigenetic silencing of LDHB to promote hepatocellular carcinoma by remodeling the tumor microenvironment.

Abstract

e16220 Background: Hepatocellular carcinoma (HCC) is a deadly disease with limited therapeutic options. Low expression of the LDHB has been associated with poor prognosis of HCC patients, but the role and underlying mechanism remains unclear. Methods: The HCC dada from The Cancer Genome Atlas (TCGA) and GEO were obtained to analyze the LDHB expression and DNA methylation levels. Next, the correlation between LDHB and Hallmark gene sets was analyzed by GO and KEGG. RNA-seq, Western blotting, Immunohistochemistry, and Bisulfite DNA sequencing were performed to explore the relationship between DNA methylation and LDHB expression. CCK8 and colony formation assay were used to evaluate the effect of overexpression of LDHB on the proliferation of hepatocellular carcinoma cells in vitro. Finally, the role of LDHB in HCC tumor immunity was assessed in multiple mouse models in vivo. Results: Here, we found that down-regulation of LDHB was coupled with the promoter hypermethylation and knocking down the DNMT 3A restored LDHB expression levels in HCC cell lines. Bioinformatics analysis of the HCC cohort from The Cancer Genome Atlas revealed a significant positive correlation between LDHB expression and immune regulatory signaling pathways and immune cell infiltrations. Notably, HCC patients with high LDHB expression responded better to immune checkpoint inhibitors. Finally, we demonstrated that there was no difference in the tumor growth rate between the LDHB-expressing tumors and the control tumors in immunodeficient BALB/c nude mice. However, the LDHB-expressing tumors were significantly inhibited in immunocompetent C57BL/6 mice, suggesting that the host immune system was involved in the LDHB-medicated tumor suppression. Moreover, as compared with the LDHB+/+ mice, LDHB-/- mice showed promoted tumor growth in an NRAS/shp53 plasmid-induced primary liver tumor model. Conclusions: Overall, our findings indicate that DNMT3A-mediated epigenetic silencing of LDHB may contribute to HCC progression through remodeling the tumor immune microenvironment, and LDHB may become a potential prognostic biomarker and target for HCC immunotherapy.