Abstract 4968: microRNA-mediated silencing of COP1 and altered ubiquitination of key oncogenic transcription factors promote cancer stem cell (CSC) phenotype and prostate cancer progression

Abstract

Abstract Mutations and deletions of ubiquitin ligase complex proteins are emerging as important mechanisms driving tumorigenesis. In this study we report an alternative mechanism, depending on microRNA-mediated post-transcriptional silencing, leading to altered ubiquitination of key oncogenic proteins and induction of tumorigenic and CSC properties in prostate epithelial cells (PrECs). We found that increased expression of miR-424 promotes malignant transformation of normal PrECs by targeting the E3 ubiquitin ligase COP1. miR-424 was upregulated in primary prostate cancers and prevalently in ERG negative tumors. Bioinformatics and functional analysis demonstrated that miR-424 targeted COP1 mRNA in PrECs drastically reducing its protein level. Moreover, miR-424 and COP1 expression were inversely correlated in prostate tumors and associated with enrichment of CSC features. Functionally, over-expression of miR-424 or knockdown of COP1 in PrECs increased anchorage-independent growth, cell migration and prostatosphere formation under CSC selective conditions. Consistently, inhibition of miR-424 or over-expression of COP1 prevented these phenotypic changes in normal PrECs and prostate cancer cell lines. Moreover, COP1 knockdown reproduced closely the effects of miR-424 upregulation in PrECs. Mechanistically, we found that silencing of COP1 by miR-424 resulted in reduced turnover and increased level of several oncogenic transcription factors, including known COP1 substrates like c-JUN and ETV1. Furthermore, we identified STAT3 as a novel substrate of the miR-424/COP1 axis. Consistently, miR-424 upregulation and COP1 silencing increased STAT3 protein level and enhanced basal and cytokine induced STAT3 activity in PrECs and prostate cancer cells. These effects were blocked by miR-424 inhibition and COP1 overexpression. These results establish the miR-424/COP1 axis as a relevant oncogenic pathway acting through deregulation of key transcription factors and with important prognostic and therapeutic implications. Citation Format: Cecilia Dallavalle, Domenico Albino, Gianluca Civenni, Laura Curti, Paola Ostano, Maurizia Mello-Grand, Ramon Garcia-Escudero, Giovanna Chiorino, Carlo V. Catapano, Giuseppina M. R. Carbone. microRNA-mediated silencing of COP1 and altered ubiquitination of key oncogenic transcription factors promote cancer stem cell (CSC) phenotype and prostate cancer progression. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4968. doi:10.1158/1538-7445.AM2015-4968