Linking endoplasmic reticulum stress to polyploidy in ovarian cancer cells

Polyploid giant cancer cells (PGCCs) have been observed in epithelial ovarian tumors and have the ability to survive to antimitotic drugs. Their appearance can result from paclitaxel treatment or hypoxia, two conditions known to induce unfolded protein response (UPR) activation. PGCCs produced under hypoxia may be formed by cell fusion and can contribute by bursting and budding to the generation of cancer stem-like cells which have a more aggressive phenotype than the parental cells. Despite the fact that PGCCs may contribute to tumor maintenance and recurrence, they were poorly studied. Here, we confirmed that PGCCs could derive, at least in part, from cell fusion. We also observed that PGCCs nuclei were able to fuse. The resulting cells were able to proliferate by mitosis and were more invasive than the parental cancer cells. Using two different ovarian cancer cell lines (COV318 and SKOV3), we showed that UPR activation with chemical inducers increased cell fusion and PGCCs appearance. Down-regulation of the UPR-associated protein PERK expression partially reversed the UPR-induced PGCCs formation, suggesting that the PERK arm of the UPR is involved in ovarian PGCCs onset.