Inhibition of EHMT2/G9a epigenetically increases the transcription of Beclin-1 via an increase in ROS and activation of NF-κB.

Sang Eun Park,Jae-Young Koh,Yun-Yong Park,Seong-Yun Jeong,Hye Jin Yi,Choung-Soo Kim,Nayoung Suh,Dong-Hyung Cho,Jung Jin Hwang

doi:10.18632/oncotarget.9290

Sang Eun Park, Jae-Young Koh + Show 7 more

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https://doi.org/10.18632/oncotarget.9290

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Abstract

We previously reported that BIX-01294 (BIX), a small molecular inhibitor of euchromatic histone-lysine N-methyltransferase 2 (EHMT2/G9a), induces reactive oxygen species (ROS)-dependent autophagy in MCF-7 cells. Herein, we analyzed the epigenetic mechanism that regulates the transcription of Beclin-1, a tumor suppressor and an autophagy-related gene (ATG). Inhibition of EHMT2 reduced dimethylation of lysine 9 on histone H3 (H3K9me2) and dissociated EHMT2 and H3K9me2 from the promoter of Beclin-1. To this promoter, RNA polymerase II and nuclear factor kappa B (NF-κB) were recruited in a ROS-dependent manner, resulting in transcriptional activation. Moreover, treatment with BIX reversed the suppression of Beclin-1 by the cooperative action of EHMT2 and DNA methyltransferase 1 (DNMT1). Accordingly, a combination treatment with BIX and 5-Aza-2′-deoxycytidine (5-Aza-Cd), a DNMT1 inhibitor, exerted a synergistic effect on Beclin-1 expression. Importantly, high levels of EHMT2 expression showed a significant association with low levels of Beclin-1 expression, which was related to a poor prognosis. These findings suggest that EHMT2 can directly repress Beclin-1 and that the inhibition of EHMT2 may be a useful therapeutic approach for cancer prevention by activating autophagy.

Highlights

Autophagy contributes to tumor suppression by removing damaged organelles and misfolded proteins, whereby it acts as a guardian of the genome [1, 2]
Knockdown of EHMT2 expression with siRNA increased Beclin-1 expression (Figure 1e), and the ectopic overexpression of EHMT2 significantly suppressed Beclin-1 expression in MCF-7 cells (Figure 1f). These findings suggest that autophagy induced by EHMT2 inhibition was coupled with the transcription of Beclin-1
We found that the binding of H3K9me2 and EHMT2 to the Beclin-1 promoter was reduced, whereas the interaction of RNA polymerase II was increased by BIX and EHMT2 siRNA treatment in MCF-7 cells (Figure 2c and 2d)

Summary

Introduction

Autophagy contributes to tumor suppression by removing damaged organelles and misfolded proteins, whereby it acts as a guardian of the genome [1, 2]. We analyzed the epigenetic mechanism that regulates the transcription of Beclin-1, a tumor suppressor and an autophagy-related gene (ATG). We previously reported that inhibiting EHMT2 activates autophagy and increases the expression of LC3 and Beclin-1 in MCF-7 cells [31].

Results

Conclusion