Abstract 2418: Characterization of the PAX8 regulatory network in epithelial ovarian cancer

Abstract

Abstract PAX8 is a lineage-restricted transcription factor expressed in a large proportion of epithelial ovarian cancers (EOCs). PAX8 is commonly upregulated in EOCs relative to precursor tissues, suggesting it functions as an oncogene. However, the biological role of PAX8 during cancer initiation and development is poorly understood, and the genome-wide transcriptional targets have yet to be comprehensively catalogued. Using stable models of PAX8 knockdown in HEYA8 and IGROV1 EOC cell lines we show that PAX8 knockdown reduces cell proliferation in vitro and tumor growth in vivo. To understand how PAX8 regulates neoplastic phenotypes in cancer cells we performed RNA expression profiling by microarray in HEYA8 and IGROV1 before and after PAX8 knockdown. We also performed chromatin immunoprecipitation followed by next generation sequencing (ChIP-seq) for PAX8 and a marker of active chromatin (H3K27ac) in both cell lines. De novo motif discovery in the ChIP-seq profiles identified a PAX-like binding motif and several potential PAX8 cofactors in IGROV1 that are not enriched in HEYA8. These cofactors include members of the TEAD and Sp/KLF families of transcription factors. We divided the genes from our differential expression (DE) analysis in PAX8 knockdown into three non-overlapping categories: (a) direct regulatory targets (RTs), i.e. DE genes with PAX8 binding sites in their promoter regions; (b) putative enhancer RTs, where DE genes and PAX8 binding sites reside within the same topological association domain (TAD) defined from embryonic stem cells; and (c) indirect RTs. Our findings reveal that PAX8 can function as either an activator or a repressor, and that PAX8 regulates a very different set of genes in each cell line, as only a small fraction RTs (~50) is shared between HEYA8 and IGROV1. Nonetheless, independent pathway enrichment analysis reveals four pathways downstream of PAX8 that are common to both cell lines: DNA replication, cellular response to lipopolysaccharides, TNFA signaling via NFKB and anatomical structure morphogenesis. Individually, we discovered enrichment for G2M checkpoint and EMT signaling in HEYA8, and tissue morphogenesis and mesenchymal cell development in IGROV1. Collectively, our results suggest that PAX8 regulates cell proliferation and cancer promoting processes via highly tissue-specific regulation of common oncogenic pathways. Citation Format: Rosario I. Corona, Emily Adler, Janet M. Lee, Norma Rodriguez-Malave, Paulette Mhawech-Fauceglia, Heidi Sowter, Dennis J. Hazelett, Kate Lawrenson, Simon A. Gather. Characterization of the PAX8 regulatory network in epithelial ovarian cancer [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 2418. doi:10.1158/1538-7445.AM2017-2418