Cytokeratin 8 associates with the external leaflet of plasma membranes in tumour cells.

We reported the identification of tumour-associated antigens from head and neck carcinomas, including cytokeratin 8 (CK8). These antigens were isolated based on the humoral immune response they elicit in vivo using the antibody-mediated identification of antigens technology. Unlike healthy squamous epithelium, tumour cells displayed CK8 at the plasma membrane. However, the actual presence of CK8 at the plasma membrane is still a matter of debate. Here, we have analyzed the expression of CK8 in detail using confocal laser scanning microscopy and circumstantiated its localization at the plasma membrane of carcinoma cells. Healthy human tissues were devoid of CK8 at the membrane, with the exception of hepatocytes. Moreover, membrane-associated CK8 molecules experienced a re-distribution throughout mitosis, which was associated with phosphorylation at serine 73. Phosphorylated CK8 redistributed into dense speckles and relocated to the plasma membrane upon cytokinesis. Thus, CK8 possesses genuine extracellular epitopes on tumour cells, which may represent valuable targets for therapy.