Abstract PR04: Epigenetic silencing of CDR1as drives IGF2BP3-mediated melanoma invasion and metastasis

Metastasis is the primary cause of death of cancer patients. Dissecting mechanisms governing metastatic spread may uncover new biology and/or yield promising therapeutic insights. Here we investigated the role of circular RNAs (circRNAs), a class of noncoding RNAs lacking characterized functions, in metastasis, using melanoma as a model aggressive tumor. We analyzed RNA-seq of melanocytes and melanoma short-term cultures to characterize the landscape of circRNA in melanocytic cells. We observed silencing of Cerebellar Degeneration Related 1 (CDR1as), a neuronal-enriched circRNA and known regulator of the microRNA miR-7, in melanoma cell lines and short-term cultures compared to cultured melanocytes, and progressive loss from primary to metastatic disease in melanoma patient samples. Moreover, low CDR1as expression in primary tumors associates with poor prognostic histopathologic indicators and patient outcomes. We find that CDR1as loss results from H3K27me3-mediated silencing of its originating lincRNA LINC00632. We observed abundant H3K27me3, the repressive chromatin mark deposited by the PRC2 complex, in regulatory regions of LINC00632 in cell lines lacking CDR1as expression, and pharmacologic inhibition of EZH2 restored expression of both transcripts. Phenotypically, CDR1as depletion in vitro and in vivo enhances melanoma invasion and metastasis, with limited effect on cell proliferation or tumor growth. Surprisingly, we did not observe miR-7 regulation to be a catalyst of the proinvasive effects of CDR1as depletion in our models. Instead, we identified IGF2BP3 as a novel interactor of CDR1as and critical mediator downstream of CDR1as silencing. Finally, we find that CDR1as abundance associates with previously defined cellular states that engender distinct therapeutic responses to MAPK and GPX4 inhibitors. Collectively, our study reveals CDR1as silencing as a hallmark of melanoma progression; documents novel functional, prognostic and predictive roles for CDR1as; and exposes circRNAs as key players in metastasis. This abstract is also being presented as Poster A29. Citation Format: Douglas Hanniford, Alejandro Ulloa-Morales, Beatriz Sanchez-Sendra, Alcida Karz, Rana Moubarak, Tommaso Tabaglio, Maria Gabriela Berzoti-Coelho, Veronica Davalos, Pamela Wu, Varshini Vasudevaraja, Andreas Kloetgen, Karin Lilja, Jochen Imig, Carlos Monteagudo, Ernesto Guccione, Aristotelis Tsirigos, Iman Osman, Iannis Aifantis, Eva Hernando. Epigenetic silencing of CDR1as drives IGF2BP3-mediated melanoma invasion and metastasis [abstract]. In: Proceedings of the AACR Special Conference on Melanoma: From Biology to Target; 2019 Jan 15-18; Houston, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(19 Suppl):Abstract nr PR04.