Cisplatin-induced oxidative stress regulates YAP to modulate epigenome promoting survival of osteosarcoma cells

The widely used chemotherapeutic drug cisplatin (CDDP) is an integral part of the pre-operative chemotherapy protocol for high-grade osteosarcoma (OS). However, despite an aggressive treatment regimen, drug refractoriness is a major hindrance to successful therapy. We previously identified key transcriptomic alterations essential for the survival of OS cells following CDDP exposure. In the present study, we further demonstrate that CDDP treatment resulted in a ROS-dependent enrichment of the repressive histone mark H3K27me3 at the upstream promoter regions of growth-promoting genes such as CCNA2, and on the promoter of the negative regulator of Yes-Associated Protein (YAP)-LATS1, thereby contributing to their transcriptional repression. This was associated with a growth arrest, and quenching of ROS with N-acetyl cysteine (NAC) reversed it. Importantly, repression of LATS1 led to an increased nuclear localization of YAP, while pharmacological or genetic ablation of YAP reduced CDDP-mediated induction of repressive marks. YAP was further found to co-localize and co-immunoprecipitate with the Polycomb Repressive Complex 2 (PRC2) catalytic member-the histone methyl transferase-EZH2, indicating its putative role in mediating transcriptional repression. In lieu of the above, inhibition of YAP or reversal of the repressive chromatin state using a histone deacetylase (HDAC) inhibitor sensitized OS cells to a low-dose CDDP treatment as well. Overall, the present study demonstrates an interplay between oxidative stress, epigenetics, and YAP in modulating OS cell fate post CDDP exposure.