Members of the claudin protein family, such as CLDN2, are expressed in an organ-specific manner and regulate the tissue-specific physiologic properties of tight junctions (Sakaguchi et al., 2002).[supplied by OMIM]
Claudin-2 is expressed in cation-leaky epithelia such as that of the kidneyproximal tubule. Mice that are deficient in claudin-2 have reduced reabsorption of Na+ in the proximal tubule, consistent with a role in paracellular transport.
Similar results have been obtained with cultured cells, as overexpression in claudin-2 lacking cells leads to increase of permeability for small cations.
Furthermore, claudin-2 has been shown to form paracellular channels for water.
^Amasheh, S; Meiri, N; Gitter, A. H.; Schöneberg, T; Mankertz, J; Schulzke, J. D.; Fromm, M (2002). "Claudin-2 expression induces cation-selective channels in tight junctions of epithelial cells". Journal of Cell Science. 115 (Pt 24): 4969–76. doi:10.1242/jcs.00165. PMID12432083.
^Rosenthal, R.; Milatz, S.; Krug, S. M.; Oelrich, B.; Schulzke, J. -D.; Amasheh, S.; Gunzel, D.; Fromm, M. (2010). "Claudin-2, a component of the tight junction, forms a paracellular water channel". Journal of Cell Science. 123 (11): 1913–1921. doi:10.1242/jcs.060665. PMID20460438.
Sakaguchi T, Gu X, Golden HM, et al. (2002). "Cloning of the human claudin-2 5'-flanking region revealed a TATA-less promoter with conserved binding sites in mouse and human for caudal-related homeodomain proteins and hepatocyte nuclear factor-1alpha". J. Biol. Chem. 277 (24): 21361–70. doi:10.1074/jbc.M110261200. PMID11934881.
Colegio OR, Van Itallie C, Rahner C, Anderson JM (2003). "Claudin extracellular domains determine paracellular charge selectivity and resistance but not tight junction fibril architecture". Am. J. Physiol., Cell Physiol. 284 (6): C1346–54. doi:10.1152/ajpcell.00547.2002. PMID12700140.
Mankertz J, Hillenbrand B, Tavalali S, et al. (2004). "Functional crosstalk between Wnt signaling and Cdx-related transcriptional activation in the regulation of the claudin-2 promoter activity". Biochem. Biophys. Res. Commun. 314 (4): 1001–7. doi:10.1016/j.bbrc.2003.12.185. PMID14751232.
Escaffit F, Boudreau F, Beaulieu JF (2005). "Differential expression of claudin-2 along the human intestine: Implication of GATA-4 in the maintenance of claudin-2 in differentiating cells". J. Cell. Physiol. 203 (1): 15–26. doi:10.1002/jcp.20189. PMID15389642.