Abstract 1471: miR-148a-3p regulation of OTX2 and PRC2 in group 3 and 4 medulloblastoma

Abstract

Four different molecular subgroups are recognized in medulloblastoma (MB). Among these subgroups, Group 3 and 4 tumors are the most aggressive malignancies with few effective therapies. New therapies are likely to be most effective if they target molecular alterations that mediate the formation and growth of these malignancies. We searched the public cancer microarray database Oncomine and found that the expression of OTX2, c-Myc, polycomb repressor complex 2 (PRC2) subunits EZH2 and SuZ12 are significantly higher in Groups 3 and 4 as compared to the SHH subgroups. Moreover, Immunohistochemical staining of a medulloblastoma tissue array showed that H3k27me3 expression is higher in Group 3 and 4 compared with the SHH groups. These findings suggest that these distinct molecular alterations could represent promising therapeutic targets. In this study, we identify miRNAs with the potential to serve as therapeutic agents for Groups 3 and 4 by targeting oncogene pathway OTX2 and c-Myc as well as targeting PRC2 and modulating H3k27me3-targeted tumor suppressors. Using TargetScan, Pictar and miRanda prediction algorithms, miR-148a-3p is predicted to target OTX2. We show that enforced miR-148a-3p potently inhibits protein expression of OTX2 and c-Myc in medulloblastoma cells. Luciferase reporter analysis shows that miR-148a-3p expression downregulates OTX2 luciferase activities, and overexpressing OTX2 cDNA that lack the respective 3’-UTR region recognized by miR-148a-3p significantly rescues OTX2 downregulation by miR-148a-3p. Furthermore, we show for the first time that enforced miR-148a-3p expression can down-regulate the expression of the PRC2 methylase EZH2 and the PRC2 regulatory subunit SUZ12 in multiple MB cell lines. Conversely, silencing endogenous miR-148a-3p expression up-regulates the expression of EZH2 and SUZ12. Furthermore, enforced OTX2 expression attenuates the expression of miR-148a-3p-downregulated PRC2 subunit EZh2 and Suz12. Consistent with the effects of miR-148a-3p on EZH2 and SUZ12, miR-148a-3p was found to modulate H3k27me3 levels and restore the expression of H3k27me3-targeted tumor suppressors. We also show that enforced miR-148a-3p increases the sensitivity of Group 3 and 4 medulloblastoma cells to radiation and chemotherapy. Together, our findings show that miR-148a-3p has the potential to modulate Group 3 and 4 medulluloblastoma malignancy and chemo/radiation sensitivity by (1) reversing H3k27me3 modifications and thereby potentially restoring tumor suppressor expression; and (2) down-regulating OTX2 and leading to the inhibition of c-Myc-dependent oncogenes. Citation Format: Qingfu Xu, Kimberly Wang, Sama Ahsan, Fausto Rodriguez, Charles Eberhart, Yugang Jiang, John Laterra, Yunqing Li. miR-148a-3p regulation of OTX2 and PRC2 in group 3 and 4 medulloblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1471. doi:10.1158/1538-7445.AM2017-1471