Abstract 1066: Synthetic miR-22 inhibits alternative non homologous end-joining DNA repair and increases sensitivity to PARP-inhibition in multiple myeloma cells
Authors: Caracciolo Daniele , Morelli Eugenio , Di Martino Maria Teresa , Talarico Daniela , Botta Cirino , Amodio Nicola , Federico Cinzia , Altomare Emanuela , Biamonte Lavinia , Stamato Maria Angelica , Tagliaferri Pierosandro , Tassone Pierfrancesco 
Published: July 2016

Abstract
Multiple Myeloma (MM) is an incurable hematologic malignancy characterized by deep genomic instability. Alternative non-homologous end-joining (A-NHEJ) DNA repair is up-regulated in a significant fraction of cancers and it is more error-prone than the major LIG4-dependent NHEJ repair pathway (classic-NHEJ). Principal components of A-NHEJ (PARP1, POLQ and LIG3) represent therefore a new class of cancer cell-specific therapeutic targets.
There is Increasing evidence that microRNAs take actively part in the regulation of the DNA damage/repair network. Based on this rationale, we aimed to elucidate the role of miRNAs in the regulation of A-NHEJ-driven genomic instability in MM.
We first examined the prognostic role of DNA Ligases involved in NHEJ pathways interrogating the public MM gene expression dataset GSE9782, which revealed higher expression of LIG3 in patients with shorter survival; conversely LIG4 expression was not associated with worse prognosis, thus supporting the idea that LIG3 has a pivotal role in genomic instability and progression of MM. Next, we aimed to identify LIG3-targeting miRNAs by an integrated approach that predicted miR-22 as negative regulator of LIG3 in MM patients. On this basis we evaluated miR-22 and LIG3 expression in a panel of MM cell lines and primary samples compared to plasma cells from healthy donors. We detected significant down-regulation of miR-22 and up-regulation of LIG3, strictly correlated to disease progression. Subsequently, we induced miR-22 overexpression (by transduction or transfection) in a panel of MM cell lines and we found cell growth inhibition, apoptosis induction and cell cycle arrest. Importantly, transfection of miR-22 mimics reduced the viability of primary MM cells but not of HD-PBMCs. We next examined the effects of enforced overexpression of miR-22 on DNA-damage response and we observed an increase of the DNA damage marker yH2AX, reduction of LIG3 at mRNA and protein level, and decrease of LIG3-3’UTR luciferase activity, indicating specific 3’ UTR targeting. Importantly, we observed inhibition of A-NHEJ repair by a functional assay based on the plasmid EJ2-GFP.
Finally, miR-22 mimics potentiated cytotoxic effects of PARP-inhibitor Olaparib (Selleckchem), both in vitro and in vivo, confirming that co-inhibition of LIG3 and PARP-1 have a synergistic effect on A-NHEJ dependent MM cells.
Taken together, our preliminary findings indicate that miR-22 inhibits A-NHEJ by specific targeting of LIG-3 and modulates sensitivity to PARP inhibition. Further investigations could shed new light on A-NHEJ in MM pathogenesis and define a role for miR-22 as therapeutic agent in this still incurable disease.
Acknowledgement: This work has been supported by Italian Association for Cancer Research (AIRC). PI: PT. “Special Program Molecular Clinical Oncology - 5 per mille” n.9980, 2010/15
Citation Format: Daniele Caracciolo, Eugenio Morelli, Maria Teresa Di Martino, Daniela Talarico, Cirino Botta, Nicola Amodio, Cinzia Federico, Emanuela Altomare, Lavinia Biamonte, Maria Angelica Stamato, Pierosandro Tagliaferri, Pierfrancesco Tassone. Synthetic miR-22 inhibits alternative non homologous end-joining DNA repair and increases sensitivity to PARP-inhibition in multiple myeloma cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1066.