GSE131680
Loss of histone macroH2A1 in hepatocellular carcinoma cells promotes paracrine-mediated chemoresistance and CD4+CD25+ T regulatory cells activation
We recently described the phenotype of HepG2 and Huh-7, hepatocellular carcinoma cells, knocked down for histone variant macroH2A1. Both cell lines acquire a cancer stem cell phenotype (Lo Re O et al., Hepatology 2017, PMID: 28913935; Lo Re O et al., Epigenetics 2018, PMID: 30165787). We found that short hairpin RNA-mediated macroH2A1 knockdown induced acquisition of CSC-like features, including the growth of significantly larger and less differentiated tumors when injected into nude mice. MacroH2A1-depleted HCC cells also exhibited reduced proliferation, resistance to chemotherapeutic agents, and stem-like metabolic changes consistent with enhanced hypoxic responses and increased glycolytic pathways. As macroH2A1 is a potent transcriptional modifier we asked how KD of this histone variant might affect patterns of gene expression, and whether we could identify potential mechanistic links to the observed in vitro and in vivo HCC phenotypes.   Here we used RNA-Seq to gain deep mechanistic insight into the distinct functions of macroH2A1 KD and conditioned medium (CM)-exposed Huh-7 cells. Heatmap analysis of the differentially expressed genes between the three groups revealed a similar transcriptomic profile between KD and CM, compared to the control condition. Genes were considered differentially expressed between groups if their expression values significantly differed by >2 fold. Statistical differences in gene expression were assessed by the ANOVA test. Correction for multiple test was achieved by the Benjamini-Hochberg procedure. The significance threshold was set to 0.05.  Using a cut-off of 2 fold change, assessment of differentially expressed genes for Huh-7 macroH2A1 KD  or Huh-7 CM KD versus CTL showed no transcriptional overlap between the different Huh-7 cell lines. 783 and 987 genes were instead significantly differentially-expressed in macroH2A1 KD or CM KD versus control cells, respectively. Interestingly, the significantly enriched transcripts over-represented in KD and CM-exposed cells compared to control cells were implicated in a number of functions and diseases that were also shared between CM versus control comparisons. Specifically, Ingenuity pathway analysis (IPA) identified categories of cancer, gastrointestinal diseases, lipid metabolism, cell-to-cell signaling, nucleic acid metabolism, cell death & survival and others, in common between KD versus CTL and CM versus CTL. These data support a paracrine modulation of gene expression by macroH2A1 KD in HCC cells. Overall design: Profiling the transcriptome of hepatocellular carcinoma cells Huh-7 control, knocked-down (KD) for macroH2A1,  or exposed to conditioned medium from KD cells, using RNA-Seq.