Claudins in lung diseases

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Abstract

Tight junctions are the most apically localized part of the epithelial junctional complex. They regulate the permeability and polarity of cell layers and create compartments in cell membranes. Claudins are structural molecules of tight junctions. There are 27 claudins known, and expression of different claudins is responsible for changes in the electrolyte and solute permeability in cells layers. Studies have shown that claudins and tight junctions also protect multicellular organisms from infections and that some infectious agents may use claudins as targets to invade and weaken the host's defense. In neoplastic diseases, claudin expression may be up- or downregulated. Since their expression is associated with specific tumor types or with specific locations of tumors to a certain degree, they can, in a restricted sense, also be used as tumor markers. However, the regulation of claudin expression is complex involving growth factors and integrins, protein kinases, proto-oncogens and transcription factors. In this review, the significance of claudins is discussed in lung disease and development.

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Claudin-1 and -2: Novel Integral Membrane Proteins Localizing at Tight Junctions with No Sequence Similarity to Occludin

Mikio Furuse, Kohji Fujita, Takashi Hiiragi … (1998)

Occludin is the only known integral membrane protein localizing at tight junctions (TJ), but recent targeted disruption analysis of the occludin gene indicated the existence of as yet unidentified integral membrane proteins in TJ. We therefore re-examined the isolated junction fraction from chicken liver, from which occludin was first identified. Among numerous components of this fraction, only a broad silver-stained band ∼22 kD was detected with the occludin band through 4 M guanidine-HCl extraction as well as sonication followed by stepwise sucrose density gradient centrifugation. Two distinct peptide sequences were obtained from the lower and upper halves of the broad band, and similarity searches of databases allowed us to isolate two full-length cDNAs encoding related mouse 22-kD proteins consisting of 211 and 230 amino acids, respectively. Hydrophilicity analysis suggested that both bore four transmembrane domains, although they did not show any sequence similarity to occludin. Immunofluorescence and immunoelectron microscopy revealed that both proteins tagged with FLAG or GFP were targeted to and incorporated into the TJ strand itself. We designated them as “claudin-1” and “claudin-2”, respectively. Although the precise structure/function relationship of the claudins to TJ still remains elusive, these findings indicated that multiple integral membrane proteins with four putative transmembrane domains, occludin and claudins, constitute TJ strands.

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Direct Binding of Three Tight Junction-Associated Maguks, Zo-1, Zo-2, and Zo-3, with the Cooh Termini of Claudins

Masahiko Itoh, Mikio Furuse, Kazumasa Morita … (1999)

ZO-1, ZO-2, and ZO-3, which contain three PDZ domains (PDZ1 to -3), are concentrated at tight junctions (TJs) in epithelial cells. TJ strands are mainly composed of two distinct types of four-transmembrane proteins, occludin, and claudins, between which occludin was reported to directly bind to ZO-1/ZO-2/ZO-3. However, in occludin-deficient intestinal epithelial cells, ZO-1/ZO-2/ZO-3 were still recruited to TJs. We then examined the possible interactions between ZO-1/ZO-2/ZO-3 and claudins. ZO-1, ZO-2, and ZO-3 bound to the COOH-terminal YV sequence of claudin-1 to -8 through their PDZ1 domains in vitro. Then, claudin-1 or -2 was transfected into L fibroblasts, which express ZO-1 but not ZO-2 or ZO-3. Claudin-1 and -2 were concentrated at cell–cell borders in an elaborate network pattern, to which endogenous ZO-1 was recruited. When ZO-2 or ZO-3 were further transfected, both were recruited to the claudin-based networks together with endogenous ZO-1. Detailed analyses showed that ZO-2 and ZO-3 are recruited to the claudin-based networks through PDZ2 (ZO-2 or ZO-3)/PDZ2 (endogenous ZO-1) and PDZ1 (ZO-2 or ZO-3)/COOH-terminal YV (claudins) interactions. In good agreement, PDZ1 and PDZ2 domains of ZO-1/ZO-2/ZO-3 were also recruited to claudin-based TJs, when introduced into cultured epithelial cells. The possible molecular architecture of TJ plaque structures is discussed.

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Structure and function of claudins.

Gerd Krause, Lars Winkler, Sebastian Mueller … (2008)

Claudins are tetraspan transmembrane proteins of tight junctions. They determine the barrier properties of this type of cell-cell contact existing between the plasma membranes of two neighbouring cells, such as occurring in endothelia or epithelia. Claudins can completely tighten the paracellular cleft for solutes, and they can form paracellular ion pores. It is assumed that the extracellular loops specify these claudin functions. It is hypothesised that the larger first extracellular loop is critical for determining the paracellular tightness and the selective ion permeability. The shorter second extracellular loop may cause narrowing of the paracellular cleft and have a holding function between the opposing cell membranes. Sequence analysis of claudins has led to differentiation into two groups, designated as classic claudins (1-10, 14, 15, 17, 19) and non-classic claudins (11-13, 16, 18, 20-24), according to their degree of sequence similarity. This is also reflected in the derived sequence-structure function relationships for extracellular loops 1 and 2. The concepts evolved from these findings and first tentative molecular models for homophilic interactions may explain the different functional contribution of the two extracellular loops at tight junctions.

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Journal

Journal ID (nlm-ta): Respir Res

Title: Respiratory Research

Publisher: BioMed Central

ISSN (Print): 1465-9921

ISSN (Electronic): 1465-993X

Publication date (Print): 2011

Publication date (Electronic): 27 May 2011

Volume: 12

Issue: 1

Page: 70

Affiliations

[1 ]Department of Pathology and Forensic Medicine, Institute of Clinical Medicine, Pathology and Forensic Medicine, School of Medicine, University of Eastern Finland, Cancer Center of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio, Finland

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Publisher ID: 1465-9921-12-70

DOI: 10.1186/1465-9921-12-70

PMC ID: 3128860

PubMed ID: 21619599

SO-VID: a6670f68-411b-4ed9-9e30-99af5bc80b06

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This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Claudins in lung diseases

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Inflamed lung in vitro co-culture models

Most cited references 101

Claudin-1 and -2: Novel Integral Membrane Proteins Localizing at Tight Junctions with No Sequence Similarity to Occludin

Direct Binding of Three Tight Junction-Associated Maguks, Zo-1, Zo-2, and Zo-3, with the Cooh Termini of Claudins

Structure and function of claudins.

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