A switch from histone methyltransferase-EZH2 to demethylase KDM6A activity marks reinitiation of proliferation of drug treated colorectal cancer cells

Abstract

Colorectal cancer (CRC) is one of the deadliest cancers, ranking third in cancer incidence worldwide. These tumor cells often adopt unique strategies under drug stress to attain a reversible drug-tolerant state and evade cell death. However, the molecular adaptations associated with this transitory emergence of the drug-tolerant state remain elusive. Herein, epigenetic alterations often dictate such reversible dynamic changes, and this study aims to characterize the role of specific epigenetic modifiers governing CRC cell survival under drug pressure and their subsequent relapse. We observed that under drug stress there is a drastic increase in the histone-repressive mark-H3K27me3, linked to an enhanced expression of EZH2 driving transcriptional inhibition of cell proliferation-associated genes and a proliferative arrest. Interestingly, drug-induced oxidative stress increased the expression of the P65 protein, which was found to interact and regulate EZH2 expression. Quenching of ROS, drug vacation, or P65 inactivation compromised EZH2 activity concurrent with a re-initiation of cell proliferation. Interestingly, this reversal to proliferative state was associated with an elevated activity of the histone lysine demethylase-KDM6A. The promoter elements of the proliferative genes were now occupied by KDM6A instead of EZH2. Accordingly, a genetic knockdown or pharmacological inhibition of KDM6A in vitro not only resulted in increased cell death but also prevented emergence of the re-proliferative CRC cells. Furthermore, KDM6A inhibition in combination with chemotherapy drug, resulted in an increased tumor regression in vivo. Our study thus highlights the importance of KDM6A as a therapeutic target in preventing CRC growth and relapse which can have future therapeutic implications.