Transforming growth factor- β mediated regulation of epigenome is required for epithelial to mesenchymal transition associated features in liver cancer cells

Abstract

Hepatocellular carcinoma (HCC) frequently unfolds under an inflammatory condition, which is a hub for a plethora of cytokines. A better understanding of the cytokine functions and their contributions to disease development is key to design of future therapeutic strategies and reduction of global HCC burden. In this context, one of the major cytokines present in the HCC tumour milieu is the transforming growth factor-β (TGF-β). One of its classical functions involve facilitation of epithelial to mesenchymal transition (EMT), in tumour cells, promoting an invasive phenotype. In spite of its clinical relevance, the cellular events associated with TGF-β-induced EMT and its molecular regulation is poorly elucidated. Therefore, as part of this study, we treated HCC cells with TGF-β and characterized the cellular processes associated with EMT. Interestingly, EMT triggered by TGF-β was found to be associated with cytostasis and altered cellular metabolism. TGF-β resulted in down-regulation of cell cycle-associated transcripts, like Cyclin A2 (CCNA2), and metabolic genes, like Glutamic-oxaloacetic transaminase 1 (GOT1) through epigenetic silencing. An overall increase in total histone repressive mark (H3K27me3) associated with a specific enrichment of H3K27me3 at the upstream promoter region of CCNA2 and GOT1 was observed after TGF-β exposure, leading to their down-regulation. Importantly, TGF-β-downstream signalling mediator- SMAD and chromatin repressive complex member-enhancer of zeste homolog 2 (EZH2) were found to co-immunoprecipitate and were required for the above effects. Overall, our findings reflect that HCC cells undergoing EMT, attain cytostasis and modulate metabolic demands to efficiently facilitate the EMT differentiation switch, and these events are regulated at the epigenomic level through TGF-β-mediated signalling. Our results provide better understanding of cellular invasive features which can lead to development of novel therapeutic strategies.