BRCA1 Mutation Status and Follicular Fluid Exposure Alters NFκB Signaling and ISGylation in Human Fallopian Tube Epithelial Cells

Abstract

Germline BRCA1 or BRCA2 mutations (mtBRCA1 and mtBRCA2) increase risk for high-grade serous ovarian cancer (HGSOC), the most commonly diagnosed epithelial ovarian cancer histotype. Other identified risk factors for this cancer, which originates primarily in the distal fallopian tube epithelium (FTE), implicate ovulation, during which the FTE cells become transiently exposed to follicular fluid (FF). To test whether mtBRCA1 or mtBRCA2 nonmalignant FTE cells respond differently to periovulatory FF exposure than control patient FTE cells, gene expression profiles from primary FTE cultures derived from BRCA1 or BRCA2 mutation carriers or control patients were compared at baseline, 24 hours after FF exposure, and 24 hours after FF replacement with culture medium. Hierarchical clustering revealed both FF exposure and BRCA mutation status affect gene expression, with BRCA1 mutation having the greatest impact. Gene set enrichment analysis revealed increased NFκB and EGFR signaling at baseline in mtBRCA1 samples, with increased interferon target gene expression, including members of the ISGylation pathway, observed after recovery from FF exposure. Gene set enrichment analysis did not identify altered pathway signaling in mtBRCA2 samples. An inverse relationship between EGFR signaling and ISGylation with BRCA1 protein levels was verified in an immortalized FTE cell line, OE-E6/E7, stably transfected with BRCA1 cDNA. Suppression of ISG15 and ISGylated protein levels by increased BRCA1 expression was found to be mediated by decreased NFκB signaling. These studies indicate that increased NFκB signaling associated with decreased BRCA1 expression results in increased ISG15 and protein ISGylation following FF exposure, which may be involved in predisposition to HGSOC.

ISG15 induction is required during L1-mediated colon cancer progression and metastasis

“…We found that the mechanism/s downstream of L1 that bring about the increase in ISG15 involve NF-κB signaling, since blocking this pathway by various methods eliminated the ability of L1 to induce ISG15. Increased NF-κB signaling and elevated ISG15 expression were recently observed also in BRCA1 mutants of fallopian tube epithelial cells [19] and in ovarian cancer cells [20]. In addition, cRel, a subunit of NF-κB, was shown to bind and activate the ISG15 gene promoter, supporting the involvement of NF-κB in regulating the transcription of the ISG15 gene [21].…”

HERC5 and the ISGylation Pathway: Critical Modulators of the Antiviral Immune Response

“…HERC5 expression is also regulated by the cytokine interleukin 1 β (IL-1β) and tumor necrosis factor α (TNFα) in distinct signal transduction pathways. Moreover, recent studies have shown that ISG15, UBE1L, UBE2L6 and HERC5 are tightly regulated by nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB)-an immunological protein complex that is involved in controlling diverse cellular responses to viral infection including cytokine production, DNA transcriptional regulation and interferon activation [33].…”

ISG15 Promotes ERK1 ISGylation, CD8+ T Cell Activation and Suppresses Ovarian Cancer Progression

“…Future studies to evaluate the effects of ISG15 on tumor growth and immune response by manipulating the presences of different immune cell types, including NK cells, in animal models could provide valuable insight into the roles of ISG15 in the immune tumor microenvironment. Recently research findings showed that decreased BRCA1 expression resulted in increased ISG15 expression and protein ISGylation in human fallopian epithelial cells [47]. Follow up studies on the relationship between BRCA mutation status and ISG15 expression levels in ovarian cancer cells may help us to understand the underlying genetic components that drive ISG15 expression.…”