Claudin proteins

Alveolar epithelial cells (AECs) are connected with each other by various epithelial cell-cell contacts (i.e., tight junctions, adherens junctions and others). These contacts comprise several groups of proteins, such as occludin, zonula occludens (ZO-1, -2, -3), claudins, tricellulin, E-cadherin and intercellular adhesion molecule-1 (ICAM-1) [13-15], Their regulation and interplay, which has influence on epithelial barrier properties, however, is largely unknown to date. 

Furuse M, Fujita K, Hiiragi T, Fujimoto K, and Tsukita S [1998] Claudin-1 and -2 Novel integral membrane proteins localizing at tight junctions with no sequence similarity to occludin. J Cell Biol 141 1539-1550... 

Morita K, Furuse M, Fujimoto K, and Tsukita S [1999] Claudin multigene family encoding four-transmembrane domain protein components of tight junction strands. Proc Natl Acad Sci USA 96 511-516... 

Heiskal M, Peterson PA, and Yang Y [2000] The roles of claudin superfamily proteins in paracellular transport. Traffic 2 92-98... 

Kubota K, Furuse M, Sasaki H, Sonoda N, Fujita K, Nagafuchi A, and Tsukita S [1999] Ca2" " -independent cell-adhesion activity of claudins, a family of integral membrane proteins localized at tight junctions. Curr Biol 9 1035-1038... 

Tight junctions form selective barriers that regulate paracellular transport across epithelia and endothelia. Tight junctions are composed of transmembrane proteins (occludin, claudins, and JAMs) linked to the actin cytoskeleton through cytoplasmic ZO proteins, whereas adherence junctions are composed of the nectin-afadin system and the E-cadhcrin catenin system [143]. These cell cell adhesion proteins create the barrier and regulate electrical resistance, size, and ionic charge selectivity [144], Several experimental procedures have... 

Duffy, H. S., John, G. R., Lee, S. C., Brosnan, C. F., and Spray, D. C. (2000). Reciprocal regulation of the junctional proteins claudin-1 and connexin43 by interleukin-1 beta in primary human fetal astrocytes. J. Neurosci. 20, RC114. 

Mitic LL, van Itallie CM (2001) Occludin and claudins transmembrane proteins of the tight junction. In Cereijido M, Anderson JM (eds) Tight Junctions (2nd edn.). CRC, Boca Raton, pp 213-230... 

The TJPs form an intricate complex of transmembrane (occludin, claudins, junctional adhesion molecule-1) and cytoplasmic (zona occludens-1 and -2, cingulin, AF-6, and 7H6) proteins linked to the cytoskeleton (Hawkins and Davis, 2005) (Fig. 1). Occludin was the first TJP discovered. It is a 60- to 65-kDa protein with four transmembrane domains and two extracellular loops that span the cleft between adjacent endothelial cells (Furuse et al., 1993 Hirase et al., 1997 Hawkins and Davis, 2005). Occludin is highly expressed in cerebral endothelium (Fig. 2) and sparsely distributed in nonneural endothelia (Hirase et al., 1997). The phosphorylation state of occludin regulates its association with the cell membrane (Hirase et al., 2001). In experimental autoimmune encephalomyelitis, a model of multiple sclerosis, occludin dephosphorylation precedes the neurological deterioration and increased leakage of plasma proteins across the BBB (Morgan et al., 2007). The C-terminal cytoplasmic domain of occludin is involved in its association with the cytoskeleton via accessory proteins such as zona occludens ZO-1 and ZO-2 (Furuse et al, 1993). 

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