Mutations in the PTEN gene are the most common genetic defects in endometrioid endometrial carcinoma and seen in more than 50% of tumors. PTEN, a tumor suppressor gene, negatively regulates PI3K/Akt-driven cell growth and survival. Previously, we have shown that levels of the forkhead protein, FOX01, a direct target of AKT, were significantly lower in endometrial carcinoma and overexpression of this gene in endometrial cancer cell lines resulted in decreased cell proliferation and increased apoptosis. Interestingly, the function of FOX01 in this context was determined by the progesterone receptor isoform that was expressed, strongly implicating the regulatory role of the progesterone receptor predictably at the transcription level. In this study, we aimed to look at the effects of an AKT inhibitor (APi59) on endometrial cancer cells and the influence of PRA or PRB on its efficacy.

The cell viability assay revealed a decrease in the number of viable PRA and PRB cells treated with APi59 for 48 hours, while the progestin, R5020, alone did not affect cell viability. In addition, more cell death was observed in the PRA cells compared to the PRB cells. APi59 treatment promoted apoptosis, as measured by cleaved PARP levels, in both PRA and PRB cells, with increased apoptosis in PRA cells compared to the PRB cells. R5020 treatment alone did not cause apoptosis as compared to control. In order to further investigate the increased levels of apoptosis in the PRA cells, a real time PCR array focused on genes associated with apoptosis was used to identify potential genes involved in this differential response. The most highly upregulated gene specifically expressed in PRB cells in response to R5020 was BIRC3 (ciap2). BIRC3 was upregulated 13-fold with R5020 treatment in PRB cells where its expression in PRA cells was unaffected. Given that BIRC3 is a member of the inhibitor of apoptosis genes (IAP), we hypothesized that the increased expression of BIRC3 in PRB cells attenuated APi59-mediated apoptosis. Thus, PR was silenced using transient transfection of siRNA specific to PR and cells were treated with APi59 and R5020. Upon PR silencing, there was an increase in apoptosis as measured by cleaved PARP in APi59 treated cells along with a concomitant decrease in BIRC3 protein. To determine if the attenuation in apoptosis through BIRC3 occurred with other cytotoxic agents, PRB cells were treated with 10nm paclitaxel and R5020. Again, apoptosis in response to paclitaxel was attenuated, as shown by lower cleaved PARP levels when R5020 was added. In conclusion, not only can the AKT inhibitor, APi59, promote apoptosis in endometrial cancer cells, but liganded PRB can blunt the apoptotic response through increased expression of BIRC3, an inhibitor of apoptosis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1196.