Finding the balance. EpCAM signaling in health and disease

PhD ceremony: Ms. U. Schnell, 14.30 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Finding the balance. EpCAM signaling in health and disease

Promotor(s): prof. D. Hoekstra

Faculty: Medical Sciences

The epithelial cell adhesion molecule EpCAM, originally identified as a tumor marker, is involved in cell-cell adhesion and cell proliferation. High expression levels of EpCAM can be found in most carcinomas, but also during morphogenesis. Absence of EpCAM due to gene mutations impairs the normal development of the intestinal epithelium, resulting in fatal congenital tufting enteropathy (CTE). As yet, the variety of published observations regarding EpCAM’s function and signaling properties cannot be merged into a unified concept. In my thesis, I aimed to shed light on the mechanism of EpCAM signaling in health and disease. Analysis of EpCAM mutations identified in CTE showed that the cell surface localization of EpCAM is crucial for its normal function. To address recent models of EpCAM-mediated proliferation in cancer, we characterized the protein biochemically. Besides previously described proteolytic peptides, we identified novel EpCAM-derived fragments. Furthermore, we find that EpCAM does not display typical cell-cell adhesion protein features, and that it can be cleaved in tetraspanin-enriched microdomains (TEMs), combining two models of EpCAM signaling. We conclude that EpCAM proteolysis at multiple sites and its spatiotemporal localization in TEMs are important factors in the regulation of EpCAM signaling. In addition, we performed methodological studies on different microscopy techniques. In a critical investigation of routine immunostaining protocols, we emphasize the importance of fluorescent proteins in living cells as controls to avoid and become aware of artifacts induced by the fixation and permeabilization of cells.