Background: Ovarian granulosa cell tumours (GCT) are hormonally-active neoplasms characterised by endocrine manifestation, an indolent course and late relapse. Chemotherapy and hormonal therapy have proved not to be effective. Nuclear receptors (NR) play a central pathogenic role in endocrine malignancy and are potential targets for therapeutic intervention. Estrogen receptor β (ERβ) is the predominant ER in GCT. Evidence suggests that ERβ is an anti-proliferative and pro-differentiative transcription factor. Our lab has reported that estrogen (E2)-mediated ERβ signalling is transrepressed by constitutive activation of nuclear factor kappa B (NFκB) signalling in GCT1. NFκB constitutive activities often a feature of many tumour types. The mechanisms involved in NFκB transrepression of ERβ are unknown. We hypothesise that constitutive NFκB signalling in GCT prevents the anti-proliferative effects of ERβ activation.
Methods: Two GCT-derived cell lines, COV434 and KGN were used to perform ligand-dependent transactivation assays and proliferation assays. Cells were transfected with an estrogen responsive reporter, and treated with either E2, or the ERβ-selective agonist diarylpropionitrile (DPN), in the absence or presence of an NFκB inhibitor (BAY11-7082).
Results: NFκB transrepressesion of E2-mediated ERβ signalling was confirmed as previously reported1. Surprisingly, we observed that DPN-mediated ERβ transactivation is not transrepressed by NFκB, as a 2-fold induction of the reporter was observed in the absence of NFκB inhibition. However, when cells were treated with either E2 or DPN, no significant change in proliferation for either ligand was observed.
Conclusion: The lack of NFκB transrepression of DPN-bound ERβ suggests that DPN and E2 induce different conformational changes in ERβ upon ligand binding. We are performing co-immunoprecipitation studies to investigate if these different conformational changes are responsible for whether ERβ is transrepressed by NFκB or not. Additionally, given that DPN had no effect on proliferation, targeting ERβ is unlikely to be a therapeutic option for GCT treatment.