Structural and functional analyses of E-face-associated tight junction strands formed by expression of claudin-1 mutant in the second extracellular loop in MDCKII cells

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When epithelial cells are observed by freeze-fracture electron microscopy, continuous tight junction strands consisted of intramembranous particles and complementary grooves without particles are observed in the protoplasmic (P)-face and exoplasmic (E)-face, respectively (P-type tight junction). In contrast, tight junction particles of endothelial cells of peripheral venules are located on the grooves in the E-face (E-type tight junction). Claudins are integral membrane proteins at tight junctions, consist of at least 24 members, and reconstitute tight junction strands in fibroblasts without occludin. Claudins consist of four transmembrane domains with both NH2-and COOH-termini located in the cytoplasm, two extracellular loops (ECL1 and ECL2), and one cytoplasmic loop. It is thought that structure and function of tight junctions may be determined by combination and mixing ratio of claudin species expressed in the tight junction. We constructed expression vectors containing claudin-1 wi … More th a myc-epitope at the COOH-terminus (1CLmyc), 1CLmyc deleted two amino acids (151P152L) in the ECL2(1CLAPLmyc), and claudin-10 with a myc-epitope at the COOH-terminus (10CLmyc), and claudin-10 itself. We then expressed them in MDCK I or II cells. When 1CLmyc-expressing cells were observed by freeze-fracture electron microscopy, P-type tight junctions were detected in lateral plasma membranes. 10CLmyc formed E-type tight junction in lateral membranes. However, 1CLAPLmyc formed intermediate type of tight junction whose intramembranous particles were associated equally with the P- and E-face. Transepithelial electrical resistances of 1CLmyc-and 1CLAPLmyc-expressing cells were significantly increased, but that of claudin-10 was significantly decreased. These results suggest that the ECL2 of claudin-1 is involved in determining whether tight junction particles associate with the P- or E-face, and that P-type and intermediate-type tight junctions increased transepithelial electrical resistance but E-type tight junction decreased transepithelial electrical resistance. Less