Intermediate filaments (IFs) are cytoskeletal polymers formed by a large family of proteins that are expressed in a cell differentiation and tissue specific manner. Keratins (K) are the IF proteins present in epithelial cells. They are known to provide structural supports to cells and play roles in maintaining cellular integrity against mechanical and toxic stresses. More recently, keratins have been recognized to play non-mechanical functions which include the regulation of signaling pathways that control cell growth and survival. In tumor pathology, K8 and K18 which are the only keratin present in hepatocytes were, for a long time, just considered as cell type markers. However, in recent years various studies have provided evidence that keratins should be considered as regulators of cancer cell signaling. For instance, K8/18 loss is a hallmark of epithelial mesenchymal transition (EMT) but their role in tumor progression is unclear. In an attempt to bring more insight into the function of keratins in this process, we first investigated whether K8/18 expression played an active role in EMT. Using shRNA, we produced new K8/18 stable knockdown cell lines (human endometrial carcinoma KLE, human hepatocellular carcinoma HepG2 and human cervical carcinoma HeLa cell). Our K8/18 stable knockdown model presented a hyperactivation of the PI3K/Akt/NF-κB axis. Moreover, these changes were associated with an increase in collective cell migration and invasiveness. Because of these results, we considered whether NF-κB and its activators (PI3K, Akt (1, 2, 3), pAkt, IKK (α, β, γ), IκB-α and pIκB-α) are associated with keratins in epithelial cells. Using immunoprecipitation and immunofluorescence, our current results show that pAkt, NF-κB and IKKβ are indeed associated with keratins. Taken together, these results support the hypothesis that keratin intermediate filament proteins provide a platform for these proteins involved in signal transduction. Further studies will be done to determine if posttranslational modifications that affect keratins (K8/18 phosphorylation on specific serines and/or K18 O-glycosylation) interfere with their association to signaling protein and transcription factors previously found. Changes in K8/18 posttranlational modifications and their association with different proteins could be important determinants in cancer progression of epithelial cells. This work was supported by CRSNG grants to MC and EA.
Citation Format: Stephanie Lamontagne, Anne-Marie Fortier, Sophie Parent, Eric Asselin, Monique Cadrin. Interaction between keratin intermediate filament proteins K8/18 and cancer related signal transduction proteins in epithelial cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1958. doi:10.1158/1538-7445.AM2015-1958