Abstract 293: TGF-b regulates Par-4 expression through XIAP in ovarian and endometrial cancers.

Abstract

Abstract The lethality of gynecological malignancies can be explained by their propensity to develop chemioresistance and metastases. The loss of apoptotic pathways is one of the major underlying mechanisms by which tumors become resistant to treatments. This loss can be explained by the silencing of pro-apoptotic proteins that would normally contrive the cell into suicide. Par-4 is a tumor suppresor protein that is widely expressed but only functionally silenced in most endometrial cancer. This protein presents the unique ability to induce apoptosis selectively in cancer cells. We have recently demonstrated that Par-4 is a substrate of caspase-3 and the resulting cleaved fragment retains its apoptotic-inducing capabilities. We have also evidenced that TGF-β, a known instigator of EMT, regulates the invasiveness of endometrial cancer cells and Par-4 expression. TGF-β has also been shown to increase the expression of XIAP, an important promoter of cell survival and invasiveness in endometrial cancer. In this study, we have investigated the effect of TGF-ß and XIAP on Par-4 expression in ovarian and endometrial cancer. We have performed rescue experiment in which MEFs cells from XIAP KO mice were cultured and transfected with either an empty plasmid, a wild-type XIAP plasmid or a XIAP mutated RING domain plasmid. We have then submitted these cells to cisplatin treatment. In the empty vector transfectants, we have found that the absence of XIAP results in Par-4 cleavage, increased cleaved caspase-3 and cleaved PARP. The rescue of XIAP inhibited the apoptotic machinery and Par-4 cleavage thus resulting in increased chemoresistance. This effect was reversed using the mutated XIAP plasmid. We have also treated endometrial cancer cells (HeLa, KLE) with TGF-ß3 and observed an higher expression of EMT markers such as Snail, Vimentin and N-Cadherin; Par-4 was also upregulated by TGF-ß3. Finally, we have overexpressed ovarian A2780 cancer cells with Par-4 plasmid, which resulted in the upregulation of Snail and Vimentin. We confirmed these results using Par-4 siRNA and found that Snail and Vimentin expression were reduced. Altogether, results of the present study shed new light in the underlying mechanisms of Par-4 regulation and apoptosis induction. The assembled data also suggests that TGF-β plays a cardinal role in the regulation of Par-4 expression, which regulates EMT in gynecological cancers. Citation Format: Francois Fabi, Sophie Parent, Valérie Leblanc, Eric Asselin. TGF-b regulates Par-4 expression through XIAP in ovarian and endometrial cancers. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 293. doi:10.1158/1538-7445.AM2013-293