The first extracellular domain of claudin-7 affects paracellular Cl− permeability

• Published in: Biochemical and biophysical research communications Vol. 357; no. 1; pp. 87 - 91
• Main Authors: Alexandre, Michele D., Jeansonne, Beverly G., Renegar, Randall H., Tatum, Rodney, Chen, Yan-Hua
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 25.05.2007
• Subjects: Animals; Cell Line; Cell Membrane Permeability - physiology; Chlorine - metabolism; Claudin-7; Claudins; Cl− permeability; Dilution potentials; Epithelial Cells - metabolism; Extracellular Fluid - chemistry; Extracellular Fluid - metabolism; LLC-PK1 cells; Membrane Proteins - chemistry; Membrane Proteins - metabolism; Paracellular charge selectivity; Protein Structure, Tertiary; Static Electricity; Structure-Activity Relationship; Swine; Tight junctions; Tight Junctions - metabolism; Claudin-7; Tight junctions; Dilution potentials; Cl− permeability; Paracellular charge selectivity; LLC-PK1 cells
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2007.03.078

Tight junctions (TJ) constitute paracellular diffusion channels regulating the passage of ions and solutes across epithelia. We recently demonstrated that overexpression of the TJ membrane protein claudin-7 in LLC-PK1 cells decreases paracellular permeability to Cl− and increases paracellular permeability to Na+. To investigate the effect of charged amino acid residues in extracellular domains (ED) of claudin-7 on paracellular charge selectivity, we created claudin-7 mutants by replacing negatively charged amino acids on ED with positively charged amino acids. Immunofluorescence light microscopy showed that these mutant proteins were correctly targeted to the cell junction. Ultrastructure examination of TJ morphology did not reveal any difference between cells expressing wildtype (WT) and mutant claudin-7. However, electrophysiological studies showed increased Cl− permeability in cells expressing first extracellular domain (ED1) mutants, but not second extracellular domain (ED2) mutants, compared to that of WT claudin-7. Our results demonstrate that negatively charged amino acids in ED1 of claudin-7 are involved in modulating paracellular Cl− permeability.