Abstract 3450: Impact of BRCA1 on glucocorticoid signaling in fallopian tube epithelial cells

Abstract

Abstract Background: High-grade serous ovarian cancer (HGSC), the most predominant ovarian cancer histotype, originates in the fallopian tube epithelium (FTE). Women with germline BRCA1 mutations are at high risk for this cancer subtype. Our previous work indicates that FTE cells from BRCA1 mutation carriers (mtBRCA1) have increased EGFR and NFκB signaling compared to FTE from control patients, and that glucocorticoid receptor (GR) signaling may be impaired in BRCA1-deficient cells. Glucocorticoids are potent anti-inflammatory steroids that inhibit NFκB signaling. Studies using breast cancer cells report that BRCA1 increases microRNA miR-146 expression, which targets transcripts for EGFR and activators of NFκB. In this study, we examined the impact of BRCA1 deficiency on GR expression and signaling, and on miR-146 expression. Methods: Primary FTE cells were derived from mtBRCA1 carriers or control patients. Immortalized human FTE OE6/7 cells were engineered to overexpress BRCA1. UWB1.289 and UWB1.289+BRCA1 HGSC cells were obtained from ATCC. Levels of GRα, GRβ (splice variant isoform that acts as a dominant-negative of GRα), inflammatory cytokines, and GR-regulated genes were quantified using qPCR and western blotting. miR146 was quantified using miR PCR assays. Results: FTE and HGSC cells express both GR isoforms. GR mRNA levels in primary cultured FTE cells from mtBRCA1 carriers were similar to FTE cells from mtBRCA2 and control patients, although mtBRCA1 FTE cells had increased GRα:GRβ transcript ratios. In contrast, BRCA1 overexpression in OE6/7 cells and UWB1.1 289 cells increased the GRα:GRβ transcript ratio. Total GR protein levels were similar in UWB1.289 and UWB1.289+BRCA1 cells; however, BRCA1 expression associated with increased dexamethasone (DEX)-induced GR transactivation. GR target genes SGK1 and GILZ were upregulated by DEX similarly regardless of BRCA1 expression. TNFα was decreased in OE6/7 and UWB1.1 289 cells expressing higher levels of BRCA1 and was further decreased by DEX. miR-146 levels were elevated, rather than suppressed, in BRCA1-deficient cells, and correlated with decreased expression of targeted NFκB activators. Conclusions: These data indicate GR signaling is affected by BRCA1 and that both GRα and GRβ are expressed in FTE cells. BRCA1 expression alters relative isoform expression ratios raising the possibility of altered response to glucocorticoids that could impact NFκB signaling. Furthermore, these studies indicate that mechanisms other than decreased miRNA-146 underlie increased NFκB and EGFR signaling in mtBRCA1 FTE cells. Citation Format: Kasra Khalaj, Alexandra Kollara, Julia Hollingsworth, Vladimir Djedovic, Theodore J. Brown. Impact of BRCA1 on glucocorticoid signaling in fallopian tube epithelial cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3450.