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Quantifying the functional effects of complex disease risk variants can provide insights into mechanisms underlying disease biology. Genome wide association studies (GWAS) have identified 39 regions associated with risk of epithelial ovarian cancer (EOC). The vast majority of these variants lie in the non-coding genome, suggesting they mediate their function through the regulation of gene expression by their interaction with tissue specific regulatory elements (REs). In this study, by intersecting germline genetic risk data with regulatory landscapes of active chromatin in ovarian cancers and their precursor cell types, we first estimated the heritability explained by known common low penetrance risk alleles. The narrow sense heritabilityof both EOC overall and high grade serous ovarian cancer (HGSOCs) was estimated to be 5-6%. Partitioned SNP-heritability across broad functional categories indicated a significant contribution of regulatory elements to EOC heritability. We collated epigenomic profiling data for 77 cell and tissue types from public resources (Roadmap Epigenomics and ENCODE), and H3K27Ac ChIP-Seq data generated in 26 ovarian cancer-relevant cell types. We identified significant enrichment of risk SNPs in active REs marked by H3K27Ac in HGSOCs. To further investigate how risk SNPs in active REs influence predisposition to ovarian cancer, we used motifbreakR to predict the disruption of transcription factor binding sites. We identified 469 candidate causal risk variants in H3K27Ac peaks that break TF motifs (enrichment P-Value < 1×10−5compared to control variants). The most frequently broken motif was REST (P-Value = 0.0028), which has been reported as both a tumor suppressor and an oncogene. These systematic functional annotations with epigenomic data highlight the specificity of the regulatory landscape and demonstrate functional annotation of germline risk variants is most informative when performed in highly relevant cell types.

Clear cell ovarian and kidney cancers are rare but aggressive cancers characterized by resistance to traditional chemotherapies. The transcriptional drivers of these tumors are poorly understood, but the histologic similarities suggest that a subset of common factors may drive differentiation of the clear cell phenotype, agnostic of anatomic origin. Master transcription factors (MTFs) are the essential transcriptional regulators that create interconnected auto-regulatory circuits critical for tumor cell survival. Candidate MTFs can be identified due to their characteristic high level, tissue-specific expression, functional essentiality in tumor models, and participation in interconnected core regulatory transcriptional circuits. We collated 5 high grade serous ovarian cancer, 5 clear cell ovarian cancer, 5 papillary renal cell cancer and 11 clear cell renal cell cancer primary tissue and 27 cell line data sets for clear cell ovarian and kidney cancers, and non-clear cell tumors of the same organs. We integrated gene expression, super-enhancer landscapes and global maps of open chromatin to identify candidate MTFs specific to clear cell tumors. This identified known Hepatocyte nuclear factor-1-beta (HNF1B), commonly over-expressed in >90% of clear cell cancers and other novel candidates, including RARA, which encodes retinoic acid receptor alpha. Clear cell kidney and ovarian cancer cell lines are often co-dependent on sustained expression of HNF1B and RARA for survival, suggesting perturbed retinoic acid signaling represents a novel therapeutic target for clear cell tumors. Transcriptional inhibitors provide a novel therapeutic target for many cancers that may otherwise be chemoresistant. Clear cell lines are particularly sensitive to general transcriptional inhibitors in in-vitro models; functional analyses are ongoing to determine the role of RARA, HNF1B and other factors in explaining these responses. Citation Format: Marla Elizabeth Scott, Robbin Nameki, Forough Abbasi, Marcos Abraao de Souza Fonseca, Rosario (Ivetth) Corona de la Fuente, Kate Lawrenson. Core regulatory circuits of clear cell ovarian and kidney cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2433.