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. The lung-specific form is a downstream target gene regulated by the T/EBP/NKX2.1 transcription factor. A splice variant lacking the C-terminal cytoplasmic domain also exists in mouse, but has not been confirmed in human. Human claudin-18 demonstrates 88% amino acid sequence identity to the mouse protein. 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. These features suggest a potentially important role for claudin-18 in the structure and function of tight junctions in the lung and stomach. Claudin-18 expression has also been reported in the inner ear.
Background References
1. Wan YL. et. al. miR-767-3p Inhibits Growth and Migration of Lung Adenocarcinoma Cells by Regulating CLDN18. Oncol Res. 2018 May 7;26(4):637-644.
2. Yao F. et. al. Recurrent Fusion Genes in Gastric Cancer: CLDN18-ARHGAP26 Induces Loss of Epithelial Integrity. Cell Rep. 2015 Jul 14;12(2):272-85.
Western blot analysis of Claudin 18 on 293T cell lysates. Proteins were transferred to a PVDF membrane and blocked with 5% BSA in PBS for 1 hour at room temperature. The primary antibody (HA500131, 1/1,000) was used in 5% BSA at room temperature for 2 hours. Goat Anti-Rabbit IgG - HRP Secondary Antibody (HA1001) at 1:200,000 dilution was used for 1 hour at room temperature.
Immunohistochemical analysis of paraffin-embedded human gastric carcinoma tissue using anti-Claudin 18 antibody. The section was pre-treated using heat mediated antigen retrieval with Tris-EDTA buffer (pH 9.0) for 20 minutes.The tissues were blocked in 5% BSA for 30 minutes at room temperature, washed with ddH2O and PBS, and then probed with the primary antibody (HA500131, 1/200) for 30 minutes at room temperature. The detection was performed using an HRP conjugated compact polymer system. DAB was used as the chromogen. Tissues were counterstained with hematoxylin and mounted with DPX.
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