Keratins are epithelial-specific intermediate filament (IF) proteins, which are expressed in a tissue-specific manner. As part of the cytoskeleton, keratins are important for the mechanical stability and integrity of epithelial cells and tissues. Moreover, a number of keratins are involved in intracellular signalling pathways which regulate response to injuries and non-mechanical stresses, cell growth, cell death and cancer progression. Keratins 8 and 18 (K8/18) are typically co-expressed as the primary keratin pair in simple epithelial cells and their expression are maintained during malignant transformation, hence their use as diagnostic marker in tumor pathology. However, in recent years different studies have shown that IF should not be considered only as markers proteins but also as regulators of cancer cell signaling and that they might play an active role in malignant transformation. In the present study, we addressed the question as to whether K8/18 expression affects tumor fate and behaviour. Our results show that K8/18 stable knockdown using shRNA increases cisplatin sensitivity in three different epithelial cancer cell lines. Indeed, western blot analysis of caspases activation and flow cytometry analysis of AnnexinV/PI staining show that K8/18 knockdown sensitizes cells to cisplatin-induce apoptosis. Increased FasL expression and FasR membrane targeting suggest that apoptosis is enhanced via the death receptor pathway. Moreover, using in vitro wound healing and transwell invasion assays, we observed that K8/18-knockdowned cancer cells display an increased cellular motility and invasion. Interestingly, we observed that these cells present higher PIP3 levels in the plasma membrane as determined by both fluorescence microscopy and flow cytometry analysis. Consequently, the K8/18-shRNA clones show PI3K/Akt/PKC/NFkB pathways hyperactivation and increased MMP-9 expression. Furthermore, these processes are shown to be partially regulated by the tight junction's protein claudin-1, which is highly increased in K8/18-shRNA clones. To our knowledge, these results represent the first indication that K8/18 can influence the phenotype of epithelial cancer cells. Knockdown of K8/18 increases cisplatin sensitivity and invasive potential of epithelial cancer cell lines through the regulation of different cell signaling pathways, involving claudin-1 dependent PI3K activation and NFkB transcription activity. These results support the hypothesis that modulation of K8/18 expression plays an active role in cancer progression.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 174. doi:1538-7445.AM2012-174