Inhibition of EZH2 triggers the tumor suppressive miR-29b network in multiple myeloma

// Maria Angelica Stamato 1, * , Giada Juli 1, * , Enrica Romeo 1 , Domenica Ronchetti 2, 3 , Mariamena Arbitrio 4 , Daniele Caracciolo 1 , Antonino Neri 2, 3 , Pierosandro Tagliaferri 1 , Pierfrancesco Tassone 1, 5 and Nicola Amodio 1 1 Department of Experimental and Clinical Medicine, Magna Graecia University of Catanzaro, Catanzaro, Italy 2 Department of Oncology and Hemato-oncology, University of Milan, Milan, Italy 3 Hematology, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy 4 ISN-CNR, Roccelletta di Borgia, Catanzaro, Italy 5 Sbarro Institute for Cancer Research and Molecular Medicine, Center for Biotechnology, College of Science and Technology, Temple University, Philadelphia, PA, US * These authors contributed equally to this work Correspondence to: Pierfrancesco Tassone, email: tassone@unicz.it Nicola Amodio, email: amodio@unicz.it Keywords: miR-29b; microRNA; miRNA; multiple myeloma; EZH2 Received: August 31, 2017 Accepted: October 29, 2017 Published: November 20, 2017 ABSTRACT Downregulation of tumor suppressor (TS) microRNAs (miRNAs) commonly occurs in human cancer, including multiple myeloma (MM). We previously demonstrated that miR-29b is a relevant TS miRNA, whose expression in MM cells is inhibited by HDAC4-dependent deacetylation. Here, we provide novel insights into epigenetic mechanisms suppressing miR-29b in MM. In MM patient-derived plasma cells, we found inverse correlation between miR-29b and EZH2 mRNA expression. Both siRNAs and pharmacologic inhibitors of EZH2 led to miR-29b upregulation, and this effect was ascribed to reduced H3K27-trimethylation (H3K27me3) of miR-29a/b-1 promoter regions. Induction of miR-29b upon EZH2 inhibition occurred together with downregulation of major miR-29b pro-survival targets, such as SP1, MCL-1 and CDK6. Knock-down of the EZH2-interacting long non-coding RNA MALAT1 also reduced H3K27me3 of miR-29a/b-1 promoter, along with induction of miR-29b and downregulation of miR-29b targets. Importantly, inhibition of miR-29b by antagomiRs dramatically reduced in vitro anti-MM activity of small molecule EZH2-inhibitors, indicating that functional miR-29b is crucial for the activity of these compounds. Altogether, these results disclose novel epigenetic alterations contributing to the suppression of miR-29b molecular network, which can be instrumental for the development of rationally designed miRNA-based anti-MM therapeutics.