A dual role of EZH2 in regulating A-to-I RNA editing and mRNA stability through ADAR.

Adenosine-to-inosine (A-to-I) RNA editing, catalyzed by adenosine deaminases acting on RNA (ADARs), is a widespread modification in metazoans. Cumulative evidence has revealed the altered A-to-I editing profiles in cancers, but the underlying mechanism remains unclear. Here, we discover the well-known histone lysine methyltransferase enhancer of zeste homologue 2 (EZH2) as an unexplored ADAR interactor and editing regulator in prostate cancer (PCa). Through competing with interleukin enhancer binding factor 2 (ILF2) for ADAR1 binding, EZH2 reshapes the substrate selectivity of ADAR1 and thus exhibits a bidirectional role in editing regulation. Moreover, EZH2 depletion induces the translational repression of transportin-1 (TRN1), which further results in the accumulation of cytoplasmic ADAR1p110 isoform to protect many oncogenic transcripts from degradation. Consistently, depletion of ADAR1 dramatically enhances the sensitivity of cancer cells and tumors to EZH2 selective degraders. Collectively, our study sheds new light on a link between two layers of epigenetic regulations at histone modification and RNA editing levels, demonstrates a previously uncharacterized role of EZH2 in RNA editing and mRNA stability independently of its lysine methyltransferase activity, and reveals the significance of EZH2-ADAR1 cascade in governing RNA editing and mRNA stability, which may provide additional perspectives for the advancement of EZH2-targeting cancer therapies.