Celine J. Guigon

Pharmacologic Inhibition of SIRT1 Limits the Growth of Tumoral and Metastatic Granulosa Cells by Affecting mTOR, Myc, and E2F Pathways

Abstract Clinical management of patients with ovarian granulosa cell tumor (GCT) remains poor. Sirtuin-1 (SIRT1), a deacetylase enzyme involved in the regulation of tumor growth and metastasis, may represent a therapeutic target because of the availability of selective pharmacologic inhibitors with minimal toxicity. We assessed the possible overexpression of SIRT1 during tumorigenesis by Western blotting and IHC. We tested the effects of SIRT1 inhibition by EX-527 on growth, proliferation, death, migration, metabolism, and gene expression by RNA sequencing in vitro on three GCT cell lines (AT29, KGN, and COV434). Tumor growth in response to EX-527 treatment was examined in nude mice carrying subcutaneous GCT cell grafts using an electronic caliper and in GCT of AT83 mice by three-dimensional ultrasound imaging system. SIRT1 abundance increased during tumorigenesis. In vitro treatment with EX-527 efficiently reduced cell growth, either by inducing apoptosis or by inhibiting proliferation. EX-527 induced alterations in mTOR-, Myc-, and E2F-driven pathways, and in those controlling cell metabolism and oxidative stress. The administration of this treatment for 4 weeks efficiently reduced tumor progression in vivo. Inhibition of SIRT1 activity may have GCT growth suppressive effects, providing a rationale for evaluating the therapeutic potential of drugs targeting SIRT1 in patients.

Aberrant granulosa cell-fate related to inactivated p53/Rb signaling contributes to granulosa cell tumors and to FOXL2 downregulation in the mouse ovary

Ovarian granulosa cell tumors (GCTs) are indolent tumors of the ovary affecting women at all ages and potentially displaying late recurrence. Even if there is still little information regarding the mechanisms involved in GCT development and progression, FOXL2 would be a major tumor suppressor gene in granulosa cells. We analyzed the mechanisms underlying GCT initiation and progression by using mice with targeted expression of SV40 large T-antigen in granulosa cells (AT mouse), which develop GCTs. Consistent with patients, AT mice with developing GCTs displayed increased levels in circulating anti-Müllerian hormone (AMH), estradiol and androgens, as well as decreased FOXL2 protein abundance. Very few mice developed metastases (1 out of 30). In situ analyses revealed that GCT initiation resulted from both increased granulosa cell survival and proliferation in large antral follicles. Tumorigenesis was associated with the combined inactivation of p53 and Rb pathways, as shown by the impaired expression of respective downstream targets regulating cell apoptosis and proliferation, i.e., Bax, Bak, Gadd45a, Ccna2, Ccne1, E2f1, and Orc1. Importantly, the expression of FOXL2 was still present in newly developed GCTs and its downregulation only started during GCT growth. Collectively, our experiments provide evidence that disrupted p53/Rb signaling can drive tumor initiation and growth. This model challenges the current paradigm that impaired FOXL2 signaling is a major switch of granulosa cell tumorigenesis, albeit possibly contributing to tumor growth.

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

AbstractGranulosa 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. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.