Claudin-18 is a tight junction protein expressed as lung- and stomach-specific isoforms which are generated by alternative splicing of the claudin-18 gene.1 The lung-specific form is a downstream target gene regulated by the T/EBP/NKX2.1 transcription factor.1 A splice variant lacking the C-terminal cytoplasmic domain also exists in mouse, but has not been confirmed in human.1 Human claudin-18 demonstrates 88% amino acid sequence identity to the mouse protein.1 Immunohistochemical studies have demonstrated complete membrane localization of claudin-18 in lung and stomach epithelial cells, while electron microscopy has shown that it is concentrated in the cell-cell borders of these cells.1 These features suggest a potentially important role for claudin-18 in the structure and function of tight junctions in the lung and stomach.1 Claudin-18 expression has also been reported in the inner ear.2
Intended for research use only. Not for use in human, therapeutic, or diagnostic applications.