The Transcriptional Targets of Mutant FOXL2 in Granulosa Cell Tumours

Abstract

BackgroundDespite their distinct biology, granulosa cell tumours (GCTs) are treated the same as other ovarian tumours. Intriguingly, a recurring somatic mutation in the transcription factor Forkhead Box L2 (FOXL2) 402C>G has been found in nearly all GCTs examined. This investigation aims to identify the pathogenicity of mutant FOXL2 by studying its altered transcriptional targets.MethodsThe expression of mutant FOXL2 was reduced in the GCT cell line KGN, and wildtype and mutant FOXL2 were overexpressed in the GCT cell line COV434. Total RNA was hybridised to Affymetrix U133 Plus 2 microarrays. Comparisons were made between the transcriptomes of control cells and cells altered by FOXL2 knockdown and overexpression, to detect potential transcriptional targets of mutant FOXL2.ResultsThe overexpression of wildtype and mutant FOXL2 in COV434, and the silencing of mutant FOXL2 expression in KGN, has shown that mutant FOXL2 is able to differentially regulate the expression of many genes, including two well known FOXL2 targets, StAR and CYP19A. We have shown that many of the genes regulated by mutant FOXL2 are clustered into functional annotations of cell death, proliferation, and tumourigenesis. Furthermore, TGF-β signalling was found to be enriched when using the gene annotation tools GATHER and GeneSetDB. This enrichment was still significant after performing a robust permutation analysis.ConclusionGiven that many of the transcriptional targets of mutant FOXL2 are known TGF-β signalling genes, we suggest that deregulation of this key antiproliferative pathway is one way mutant FOXL2 contributes to the pathogenesis of adult-type GCTs. We believe this pathway should be a target for future therapeutic interventions, if outcomes for women with GCTs are to improve.

FOXL2 molecular status in adult granulosa cell tumors of the ovary: A study of primary and metastatic cases

“…Computer modeling suggests that the presence of tryptophan does not disrupt the folding of the forkhead domain or its ability to interact with DNA, but that it may affect the interaction with other transcription factors (9). Actually, previous unbiased whole transcriptome analyses of GCT patient samples and cell lines indicated that FOXL2 with p.C134W mutation is unable to downregulate genes involved in the control of the cell cycle, and does not upregulate (as wild-type FOXL2) genes involved in cell death (30,31).…”

Adult granulosa cell tumours (GCT): Clinicopathological outcomes including FOXL2 mutational status and expression

“…A recurring somatic mutation in this gene has been described as a potential 'driver' in the pathogenesis of adult-type GCTs [7]. A few studies have investigated the effect of the mutant allele, including studying its transcriptional targets [8][9][10][11][12]. The identification of a recurring mutation reported to be present in up to 94-97% of adult-type tumours may serve as another diagnostic tool for GCTs, alongside traditional pathological and immunohistochemical features.…”

Involvement of FOXL2 and RSPO1 in Ovarian Determination, Development, and Maintenance in Mammals

“…In the context of this disease, it has been shown that this mutation alters the expression of different factors comprising aromatase Fleming et al, 2010;Kim et al, 2011;Rosario et al, 2012]; however, the mechanisms through which FOXL2 mutation induces these cancers remain a mystery.…”

“…Indeed, genes related to steroid production or signaling have been shown to be FOXL2 targets. StAR , CYP11A , CYP17A1, and HSD17B3 were described to be downregulated by FOXL2, limiting androgen production in the ovary [Pisarska et al, 2004;Park et al, 2010;Rosario et al, 2012;Elzaiat et al, 2014]. In contrast, a direct activating effect has been demonstrated on CYP19A1 , which favors female hormone synthesis through the conversion of androgens into estrogens [Pannetier et al, 2006;Fleming et al, 2010].…”

“…Consequences on downstream pathways were observed in vivo at different stages of ovarian development (from early fetal differentiation until adulthood). They were also observed in vitro on immortalized or primary cultured granulosa cells in different mammalian species such as mice, goats, and humans [Batista et al, 2007;Garcia-Ortiz et al, 2009;Uhlenhaut et al, 2009;Escudero et al, 2010;Rosario et al, 2012;Elzaiat et al, 2014;Georges et al, 2014b]. Comparisons of these different studies have been attempted [Escudero et al, 2010;Caburet et al, 2012].…”