How do cell contacts regulate the expression of their components?

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Epithelial cells are specialized cells that line body cavities in the kidney, gut, lung and other internal organs. They prevent free exchange of molecules between the organism and its environment. Their functions require that their top and bottom differs (polarized structure). This difference is maintained by specialized proteins connecting two epithelial cells together at the intercellular junctions (junction proteins). The junctions themselves are regulated by the cell's internal frame, the cytoskeleton. Alteration in the protein composition of junctions can be brought about by different chemical and physical signals, but we do not understand how these regulate how much of each protein is present in the junctions. Changes in the levels of give junction proteins affect various functions, including barrier formation and movement of cells. We found that as junctions are assembled in a growing epithelial layer, the presence of one important protein, claudin-2 increases. This suggests the existence of a feed-back mechanism that reports the presence of newly formed junctions to the cell nucleus and causes the turning on of claudin-2 production. Claudin-2 is an important determinant of permeability of the epithelial layers for water and sodium, and it also regulates cell movement. Using cultured kidney cells, we will explore how the junctions regulate how much Claduin-2 is present in the cells. Our methods will include biochemical assays, state-of-the-art microscopic methods and an electrical method to measure how cells grow and junctions form (ECIS). We will specifically interfere with functions of proteins that are suspected to be involved in mediating effects on Claudin-2 production. Finally, we will ask how the presence of Cld-2 affects cell migration by exploring key signaling pathways in control cells and in cells where Cld-2 production is inhibited. We expect that these experiments will provide a better understanding of regulation of junctions and vital epithelial functions.