Abstract
Abstract: :
Purpose: The integrity of the corneal epithelium and endothelium layers is highly important for proper cornea function and it is dependent on cytoskeleton organization that may includes Actin, Focal adhesion kinase (FAK), Vinculin and Cortactin p80/85. In this study we explored the involvement of Cortactin in this function. Methods: Cytoskeleton proeins level and cellular localization in cultured endothelial cells were determined by immunoblot and immunofluorescence techniques, respectively. Immunohistochemistry determined the localization of these proteins in human cornea. Results: Anti Cortactin antibody identified in western blot 4 bands of Cortactin in cultured endothelial cells: the known 80/85KDa bands and two other bands corresponding to 87/89 KDa. Cell detachment, due to exposure to EDTA, resulted in a decrease of FAK and Cortactin protein level of 80–90%, while vinculin's protein level decreased by 40%. Through a reattachment process, a gradual increase in the level of these proteins was observed. In order to identify the cellular localization of these proteins the soluble fraction was separated from the in–soluble fraction by Triton X–100 solution. Vinculin and FAK were detected in the soluble fraction only, while Cortactin p80/85 and Actin segregated evenly in both fractions. Immunofluorescence staining of confluent cultures demonstrated the localization of Cortactin at cell–cell contacts as a fine line marking the cells borders. Vinculin showed a similar pattern, while FAK demonstrated a diffuse distribution all over the cell area. Actin staining demonstrated a heavy line of staining at the cortical area of each cell close to the cell–cell contacts leaving a fine line between every two adjacent cells at which Cortactin, α–Catenin and phosphotyrosine staining appeared. In contrast, in sub–confluent cultures Cortactin appeared as fibrilar structures, probably along the Actin stress–fibers, and also at focal adhesion sites, co–localized with FAK. Immunohistochemistry of Cortactin was preformed on paraffin embedded normal and abnormal human corneas. This staining demonstrated that Cortactin is localized at cell borders of epithelial basal columnar cells but not wing cells, and also in endothelial cells. When endothelial and epithelial cells loose their normal morphology, Cortactin staining disappeared. Conclusions: In this study we show that Cortactin, known as an actin–associated protein, is located at cell–cell contacts in confluent corneal endothelial and epithelial cells. Upon cells detachment from each other, Cortactin protein level decreases and it moves from cell–cell contacts to focal contacts and stress fibers.
Keywords: cornea: basic science • cell adhesions/cell junctions • cytoskeleton