Estradiol promotes cell survival and induces Greb1 expression in granulosa cell tumors of the ovary through an ERα‐dependent mechanism

Abstract

Granulosa cell tumor (GCT) is a form of ovarian tumor characterized by its tendency to recur years after surgical ablation. Little is known about the mechanisms involved in GCT development and progression. GCTs can produce estradiol (E2), but whether this hormone could play a role in this cancer through its nuclear receptors, i.e. ERα and ERβ, remains unknown. Here, we addressed this issue by cell-based and molecular studies on human GCTs and GCT cell lines. Importantly, we observed that E2 significantly increased the growth of GCT cells by promoting cell survival. The use of selective agonists of each type of receptor, together with Esr1 (ERα) or Esr2 (ERβ)-deleted GCT cells, revealed that E2 mediated its effects through ERα-dependent genomic mechanisms and ERβ/ERα-dependent extra-nuclear mechanisms. Notably, the expression of Greb1, a prototypical ER target gene, was dose-dependently upregulated by E2 specifically through ERα in GCT cells. Accordingly, using GCTs from patients, we found that GREB1 mRNA abundance was positively correlated to intra-tumoral E2 concentrations. Tissue microarray analyses showed that there were various combinations of ER expression in primary and recurrent GCTs, and that ERα expression persisted only in combination with ERβ in $40% of recurrent tumors. Altogether, this study demonstrates that E2 can promote the progression of GCTs, with a clear dependence on ERα. In addition to demonstrating that GCTs can be classified as a hormone-related cancer, our results also highlight that the nature of ER forms present in recurrent GCTs could underlie the variable efficiency of endocrine therapies.

Estradiol Signaling at the Heart of Folliculogenesis: Its Potential Deregulation in Human Ovarian Pathologies

“…In this context wherein ER signaling is inactive, we observed that E2 decreases KGN cell migration through GPER1-mediated ERK1/2 inactivation, therefore possibly preventing GCT metastasis spreading [ 135 ]. Two studies, including ours in a mouse GCT cell line wherein ER signaling is active, support the idea that E2 favors the growth of GCT by promoting cell survival [ 136 , 142 ]. This E2-mediated effect may be triggered by ERα, acting either alone or in combination with ERβ [ 142 ].…”

“…Two studies, including ours in a mouse GCT cell line wherein ER signaling is active, support the idea that E2 favors the growth of GCT by promoting cell survival [ 136 , 142 ]. This E2-mediated effect may be triggered by ERα, acting either alone or in combination with ERβ [ 142 ]. The ERα-dependency for the pro-survival action of E2 in GCT may explain the relatively limited clinical benefits of aromatase inhibitors, since not all GCT express ERα [ 31 , 136 , 139 , 140 , 141 , 142 ].…”

“…Contradicting patterns of GPER1 expression show that 14% to 90% of GCT express GPER1 [ 134 , 135 , 136 ] with either an up-regulation [ 136 ] or an unchanged expression between primary and recurrent tumors [ 134 , 135 ]. On the other hand, ERβ is reported to be preferentially expressed in GCT [ 31 , 136 , 137 ] along with a high expression of AR (59% of positive cells are AR positive [ 138 ]) and PR (98–100% of positive cells are PR positive), while ERα is present at moderate to high levels (20–66% of GCT are ERα positive) in these tumors [ 31 , 136 , 139 , 140 , 141 , 142 ]. These different observations may partly be explained by the small patient samples, the use of arbitrary cutoff points for interpreting positive immunoreactivity, and the lack of valuable antibodies [ 143 ].…”

“…This E2-mediated effect may be triggered by ERα, acting either alone or in combination with ERβ [ 142 ]. The ERα-dependency for the pro-survival action of E2 in GCT may explain the relatively limited clinical benefits of aromatase inhibitors, since not all GCT express ERα [ 31 , 136 , 139 , 140 , 141 , 142 ]. In addition, this effect of ERβ in GCT would be different from that described in other cancers, wherein this receptor is generally described as an anti-proliferative factor that is down-regulated in breast (BC), prostate (PC), and epithelial ovarian cancers (OC) [ 67 , 69 , 149 ].…”

“…However, the role of ERβ as a tumor suppressor is still controversial and may be tissue-dependent. ERβ may have a bi-faceted role as reported in BC cancers, in which ERβ activation either prevents or promotes cell growth, depending on the presence or the absence of ERα, respectively [ 69 ]; when present together with ERα, ERβ generally has a restraining effect on ERα activities [ 69 ], contrasting with its action in GCT [ 142 ]. Since ER homo- and heterodimers regulate different sets of downstream target genes, the ER expression ratios (ERα: ERβ isoforms) may then be an important determinant in ER-mediated signaling pathways.…”