Estrogenic hormone replacement therapy increases the risk of developing ovarian cancer, and 17-β estradiol accelerates tumour growth in mouse models of this disease. One possible mediator of estrogen action is Growth Regulation by Estrogen in Breast Cancer 1 (GREB1), an estrogen receptor alpha (ESR1)-upregulated protein. GREB1 is required for hormone-driven proliferation of several breast and prostate cancer cell lines, but its role in tumour progression is unknown and its mechanism of action remains unclear. To determine the role of GREB1 in ovarian cancer, its expression and function were examined in ovarian cancer cell lines and mouse models. GREB1 was upregulated by estradiol, and overexpression and/or knockdown of GREB1 showed that GREB1 promotes proliferation and migration in ovarian cancer cells. GREB1 knockdown also slowed tumour growth and prolonged survival in mice engrafted with ovarian cancer cells. GREB1 expression was detected in human ovarian tumours of all major histotypes, with moderate to strong expression in 75-85% of serous, endometrioid, mucinous, and clear cell carcinomas. GREB1 mRNA levels correlated with ESR1 transcripts, but protein levels of GREB1 and ESR1 did not show a correlation in tumours. Serous, endometrioid and mucinous ovarian cancers were almost always positive for either ESR1 or GREB1 (59/60 tumours), which may imply a dependence on estrogen signalling pathways. GREB1 expression in normal tissues is mainly confined to the reproductive tract, suggesting that it may be useful as a diagnostic biomarker. GREB1 combined with PAX8 showed high efficacy in differentiating mucinous tumours of gastrointestinal vs. ovarian origin. Targeting GREB1 may inhibit tumour-promoting pathways downstream of ESR1 and could therefore prove more effective than current anti-estrogen therapies.

Chlamydia trachomatis is a leading cause of bacterial genital infection in the US and worldwide. The chlamydial replication cycle is biphasic, meaning it enters the host cell as an infectious elementary body (EB), differentiates into an actively dividing reticulate body (RB) inside of a vacuole-like compartment, called a chlamydial inclusion, and differentiates back into EB form before exiting the host. Studies have demonstrated that estrogen aids Chlamydia infection in human and swine endometrial cells and in guinea pigs. Our prior data showed that antibody blockage of estrogen receptors or exposure to the ERβ antagonist tamoxifen in vitro decreased the development of chlamydial inclusions. Given these observations, we wanted to further examine the role of ER signaling on chlamydial infection in a murine model. We hypothesized that the absence of estrogen receptors would alter the establishment and/or progression of chlamydial infection in mice. To test this hypothesis, we compared C. muridarum infection in wild type (ERαWT or ERβWT) versus knockout (ERαKO or ERβKO) mice. Groups of eight ERαWT, ERβWT, ERαKO, or ERβKO mice were Depo-Provera treated seven days prior to vaginal infection with C. muridarum. Vaginal swabs were taken every three days for 21 days to monitor infection by EB titer analysis. Interestingly, titer data showed that peak EB shedding occurred earlier in the ERαKO mice compared to the ERαWT. At day 3 pi, EB shedding from ERαKO mice was 12-fold greater than shedding from ERαWT mice. On day 6, however, ERαWT mice shed >3-fold more EB than ERαKO mice. Conversely, there was no significant difference observed in ERβKO versus ERβWT mice or in ERαKO versus ERβKO mice. In a subset of experiments, genital tracts were collected on day 9pi and processed for flow cytometry analysis of the immune response to infection. ERαKO mice had significantly more monocytes and macrophages than ERαWT and ERβKO mice, as well as significantly more T cells than ERβKO mice. There was no significant difference in the immune cells in ERβKO and ERβWT mice. Together, these data suggest that: 1) the absence of ERs in mice does not inhibit chlamydial infection as has been observed in human cells in vitro; and 2) C. muridarum infection progression is affected by ERα signaling, possibly via alterations in the immune response.

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