Abstract 1462: Tandem genome-wide and functional screening reveals that MiRNA-29 regulates the proteasome activator PSME4 to promote therapeutic resistance in myeloma

MicroRNAs (miRNAs) are newly recognized, master regulators of the human genome and hence play key roles in cellular pathways that govern proliferation, differentiation and apoptosis during both physiologic and pathologic states. Accordingly, alterations in miRNA levels contribute to myriad diseases including human cancers. MiRNAs have rapidly attracted significant attention as agents with significant potential as diagnostics and therapeutics to improve the outcome of cancer patients. While proteasome inhibitors (PIs) such as bortezomib (Velcade, Millennium-Takeda) have transformed management of the invariably fatal disease multiple myeloma, therapeutic resistance inevitably emerges through mechanisms that remain elusive. A goal of these studies was to investigate the role of individual miRNAs in regulating functional activity of the ubiquitin+proteasome system. Genome-wide expression profiling was performed to identify differentially expressed miRNAs in the PI-resistant cells relative to drug-naive parental cells. A live-cell functional screen that employed a recombinant fluorescent probe comprised of a short-lived reporter bearing a destabilizing modification to promote constitutive proteasomal degradation was used to quantitate the effect of individual miRNAs. MiRNAs-29a/b/c were significantly reduced in the PI-resistant cells and these miRNAs negatively regulated PSME4 which expresses the proteasome activator PA200. Transfection of synthetically-engineered miRNA-29 replacements reduced PSME4 levels, promoted myeloma cell death and overcame drug resistance. Deletion of a nuclear localization signal (NLS) enriched the cytoplasmic distribution and enhanced the functional effect of miRNA-29 replacements. Doxycycline-induced expression of miRNA-29b or miRNA-29 variants that lacked the NLS also dramatically reduced the in vivo growth of subcutaneously injected myeloma tumor cells in NOD/SCID mice. We demonstrate that the loss of a tumor suppressive miRNA activates not only inherently oncogenic pathways to promote the generation of a cancer phenotype but also to promote therapeutic resistance to PIs. We provide a platform to perform a genome-wide interrogation of miRNAs and other non-coding RNAs that regulate the ubiquitin+proteasome system. The significant cytotoxic effect of miRNA-29 replacements observed using MM cell lines and myeloma patient samples as well as ability to reduce tumor growth in vivo validate miRNA-29 replacements as highly effective anti-cancer tools to overcome therapeutic resistance, promote tumor cell death and eventually improve patient outcome. Citation Format: James J. Driscoll, Sajjeev Jagannathan. Tandem genome-wide and functional screening reveals that MiRNA-29 regulates the proteasome activator PSME4 to promote therapeutic resistance in myeloma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1462. doi:10.1158/1538-7445.AM2014-1462