Expression and localization of claudins during caco-2 cells differentiation

Abstract

The paracellular transport of water and solutes between epithelial and endothelial cells is determined by the presence of tight junctions. Claudins are the main structural components of tight junctions. They allow the passage of solutes on the basis of size and charge. The interactions between claudins and other integral proteins lead to the formation of paracellular pores. However, so far, it remains obscure how claudins form these pores at the molecular level. Claudins also interact with signaling molecules that regulate cellular proliferation, differentiation and polarization. Previously, our group studied the change in the mRNA expression of claudins during the time course of caco-2 cells differentiation. The aim of the current work is to complement the mRNA data and to study claudin expression at the protein level by Western Blotting experiments. Moreover, immunofluorescence experiments were conducted in order to study the localization of claudins. Another aim was to determine the influence of the extracellular matrix on protein expression. For this purpose, Caco-2 cells were grown for twenty days in order to differentiate on both plastic and permeable filter supports. Our results showed an increase in transepithelial electrical resistance throughout caco-2 cells differentiation, indicating the formation of tight junctions. This increase in resistance was accompanied by changes in the protein expression of claudins 1, 2 and 14. Western blot data also show the involvement of the extracellular matrix in protein expression. Preliminary immunostaining experiments showed that claudins-1, -2 and -14 are localized in part to plasma membranes where they might influence paracellular permeability. Our studies shed light on the involvement of these claudins in tight junction formation in differentiating caco-2 cells.