The Role of FOXL2 in the Pathogenesis of Ovarian Granulosa Cell Tumours

Abstract

Granulosa cell tumours of the ovary (GCTs) comprise only a small proportion of all ovarian neoplasms, and our understanding of their aetiology and molecular pathogenesis has been limited due to their rarity. Currently women with GCTs receive the same treatment as women with the more common ovarian epithelial tumour, even though granulosa cells are unique and highly specialised, and are completely different to ovarian epithelial tissue. As a result, a significant number of women with GCTs suffer from recurrent disease, ultimately causing the death of approximately 80% of patients. FOXL2 is an ovarian specific transcription factor that has been shown to be specifically mutated in adult-type GCTs. Furthermore, this gene has been demonstrated to be absent, or have reduced expression in juvenile-type GCTs. Therefore the aim of this thesis was to use molecular approaches to identify genes that are relevant in the pathogenesis of GCTs, with a particular focus on the role of FOXL2. Adopting a transcriptomic approach, we have revealed that many of the genes regulated by mutant FOXL2 are clustered into functional annotations of cell death, proliferation and tumourigenesis. In addition, these genes are significantly enriched for TGF-β signalling, thus deregulation of this key antiproliferative pathway is perhaps one way mutant FOXL2 contributes to the pathogenesis of adult-type GCTs. Through investigating miRNAs in juvenile-type tumours, we have demonstrated the endogenous regulation of FOXL2’s 3’UTR and the indirect involvement of the miR-17 family of miRNAs in this gene regulation, particularly in the juvenile-type cell line COV434. Lastly, we have confirmed the value of FFPE tissue samples as a resource in the research of rare cancers such as GCTs, by using FFPE isolated nucleic acids to investigate the diagnostic potential of the FOXL2 mutation and the prognostic significance of FOXL2 expression. Moreover, using targeted next generation sequencing, we have uncovered variants in GCTs that may be involved in tumourigenesis. However these variants have yet to be validated using traditional methods in a larger cohort. This research may enable us to better comprehend the processes underlying malignant transformation in these granulosa cells, highlighting suitable targets for the development of GCT-specific therapies, in addition to alternative diagnostic and prognostic markers. Such research is necessary if outcomes for women with GCTs are to be improved.