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Predicted expansion of the claudin multigene family
FEBS Letters
Abstract
Claudins (Cldn) are essential membrane proteins of tight junctions (TJs), which form the paracellular permselective barrier. They are produced by a multi-gene family of 24 reported members in mouse and human. Based on a comprehensive search combined with phylogenetic analyses, we identified three novel claudins (claudin-25, -26, and -27). Quantitative RT-PCR revealed that the three novel claudins were expressed in a tissue- and/or developmental stage-dependent manner. Claudins-25 and -26, but not claudin-27, were immunofluorescently localized to TJs when exogenously expressed in cultured MDCK and Eph epithelial cell lines. These findings expand the claudin family to include at least 27 members.
Supplementary resource (1)
Data
October 2023
... Therefore, disrupting CLDN-11 function/localization without the loss of its expression may cause hypomyelination. The second most highly expressed CLDN in oligodendrocytes is CLDN domain containing 1 (CLDND1), more commonly known as CLDN-25 [7,13,14]. The function of CLDN-25 is, however, very poorly understood due to the amino acid sequences of CLDN-25 being particularly unique for a non-classic CLDNs [13]. ...
... The second most highly expressed CLDN in oligodendrocytes is CLDN domain containing 1 (CLDND1), more commonly known as CLDN-25 [7,13,14]. The function of CLDN-25 is, however, very poorly understood due to the amino acid sequences of CLDN-25 being particularly unique for a non-classic CLDNs [13]. CLDN-25 is also expressed abundantly in many tissues and cell types, but its barrier function has been assessed only in brain endothelial cells whose tight junctions are almost exclusively composed of CLDN-5 [15,16]. ...
... To examine whether the A249P mutation in the CLDN25 gene is a pathogenic mutation, the subcellular localization of CLDN-25 A249P in MDCKII cells was elucidated and we also generated nonfunctional C-terminus constructs (Fig. 2b). Wild-type (WT) CLDN-25 is known to localize at cell-cell borders with weak expression in the cytoplasm of MDCKII cells, HEK293 cells and endothelial cells [13,15,16]. As it is a CLDN protein, as expected, GFP-tagged CLDN-25 WT was weakly localized at the cell-cell border (Fig. 2c); however, GFP-tagged mutant CLDN-25 A249P was not, showing that the mutant protein was not able to localize to the cell-cell border. ...
Claudin-25 (CLDN-25), also known as Claudin containing domain 1, is an uncharacterized claudin family member. It has less conserved amino acid sequences when compared to other claudins. It also has a very broad tissue expression profile and there is currently a lack of functional information from murine knockout models. Here, we report a de novo missense heterozygous variant in CLDN25 (c. 745G>C, p. A249P) found in a patient diagnosed with Pelizaeus-Merzbacher-like leukodystrophy and presenting with symptoms such as delayed motor development, several episodes of tonic absent seizures and generalized dystonia. The variant protein does not localize to the cell-cell borders where it would normally be expected to be expressed. Amino acid position 249 is located 4 amino acids from the C-terminal end of the protein where most claudin family members have a conserved binding motif for the key scaffolding protein ZO-1. However, CLDN-25 does not contain this motif. Here, we show that the C-terminal end of CLDN-25 is required for its junctional localization in a ZO-1 independent manner. The A249P mutant protein as well as a deletion mutant lacking its last 5 C-terminal amino acids also failed to localize to the cell-cell border in vitro. Intriguingly, cellular knockout of CLDN25, in vitro, appeared to increase the integrity of the tight junction between 2 contacting cells, while driving highly unusual increased movement of solutes between cells. We propose that the barrier function of CLDN-25 is akin to a decoy claudin, whereby decreasing its expression in “leaky” epithelial cells and endothelial cells will drive dynamic changes in the adhesion and interaction capacity of cell-cell contact points. While it remains unclear how this de novo CLDN-25 mutant induces leukodystrophy, our findings strongly suggest that this mutation induces haploinsufficiency of CLDN-25. Elucidating the function of this uncharacterized claudin protein will lead to a better understanding of the role of claudin proteins in health and disease.
... Cldns polymerize in the cell membrane and form a network of strand-like structures that connect to a similar network on neighboring cells [5,6]. They form a barrier to control the transport of small molecules across epithelia [7][8][9][10][11][12]. Dysregulated cldn expression or function has been identified in various cancers, kidney diseases, and intestinal diseases, underscoring the therapeutic potential for targeting claudins [13,14]. ...
... So far, 27 members (subtypes) of the cldn family have been identified [8]. Beyond determining the barrier or channel properties, the composition of cldn subtypes is observed to influence the morphologies of the TJs and cldn strands [4,7,10,[15][16][17][18][19][20][21][22][23][24]. ...
Claudins are one of the major components of tight junctions (TJs) that polymerize within the cell membrane and form interactions between cells. Some claudins seal the paracellular space, limiting paracellular flux, while others form selectively permeable ion channels that control the paracellular permeability of small ions. Claudin strands are known to be dynamic and reshape within TJs to accommodate large-scale movements and rearrangements of epithelial tissues. Here, we summarize the recent computational and modeling studies on claudin assembly into tetrameric ion channels and their polymerization into μm long strands within the membrane. Computational studies ranging from all-atom molecular dynamics, coarse-grained simulations, and hybrid-resolution simulations elucidate the molecular nature of claudin assembly and function and provide a framework that describes the lateral flexibility of claudin strands.
... Through a combination of cis-and transinteractions they can polymerize into long TJ strands and even more complex meshworks (5,6). 25 different Cldns have been described in humans (7,8). Their expression is tissue-specific, where they provide distinct barrier properties (9). ...
... Scale bar: 1 µm. B, Phylogenetic tree of the Cldn family, following the nomenclature suggested by Mineta et al. (7), demonstrating that meshwork-forming Cldn3, Cldn6 and Cldn9 (in green), and non-meshwork-forming Cldn4, Cldn8 and Cldn17 (in blue) fall into the same cluster. C, Aligned crystal structures of mouse Cldn3 (green) and human Cldn4 (blue) monomers, derived from cCPE-claudin complexes (PDB 6AKE (42), 7KP4 (43)). ...
Tight junctions play a pivotal role in the functional integrity of the human body by forming barriers crucial for tissue compartmentalization and protecting the body from external threats. Essential components of tight junctions are the transmembrane claudin proteins, which can polymerize into tight junction strands and meshworks. This study delves into the structural determinants of claudin polymerization, utilizing the close homology yet strong difference in polymerization capacity between claudin-3 and claudin-4. Through a combination of sequence alignment and structural modeling, critical residues in the second extracellular segment are pinpointed. Molecular dynamics simulations provide insights into the interactions of and the conformational changes induced by the identified extracellular segment 2 residues, shedding light on the intricacies of claudin polymerization. Live-STED imaging demonstrates that introduction of these residues from claudin-3 into claudin-4 significantly enhances polymerization in non-epithelial cells. In tight junction-deficient epithelial cells, mutated claudin-4 not only influences tight junction morphology but also partially restores barrier function. Understanding the structural basis of claudin polymerization is of paramount importance, as it offers insights into the dynamic nature of tight junctions. This knowledge could be applied to targeted therapeutic interventions, offering insight to repair or prevent barrier defects associated with pathological conditions, or introduce temporary barrier openings during drug delivery.
... Through this, they regulate the permeability properties of the paracellular cleft. The TJ proteins that mainly control permeability comprise the family of claudins (Cldn), which, in mammals, comprise 27 members [7]. Besides their general tightening properties, certain claudins mediate the passage of small cations, anions, and water, through this forming selective paracellular channels (for review see [8,9]). ...
The ability of the immune system to combat pathogens relies on processes like antigen sampling by dendritic cells and macrophages migrating through endo-and epithelia or penetrating them with their dendrites. In addition, other immune cell subtypes also migrate through the epithe-lium after activation. For paracellular migration, interactions with tight junctions (TJs) are necessary, and previous studies reported TJ protein expression in several immune cells. Our investigation aimed to characterize, in more detail, the expression profiles of TJ proteins in different immune cells in both naïve and activated states. The mRNA expression analysis revealed distinct expression patterns for TJ proteins, with notable changes, mainly increases, upon activation. At the protein level, LSR appeared predominant, being constitutively present in naïve cell membranes, suggesting roles as a crucial interaction partner. Binding experiments suggested the presence of claudins in the membrane only after stimulation, and claudin-8 translocation to the membrane occurred after stimulation. Our findings suggest a dynamic TJ protein expression in immune cells, implicating diverse functions in response to stimulation, like interaction with TJ proteins or regulatory roles. While further analysis is needed to elucidate the precise roles of TJ proteins, our findings indicate important non-canonical functions of TJ proteins in immune response.
... Various tight junction proteins have been identified in epithelial cells of different species, including claudins, occludin, cingulin, tricellulin, junctional adhesion molecule, and MarvelD3, which form semipermeable transmembrane along with the adapter protein and zona occludens 1, 2, and 3 [57,[60][61][62]. Zona occludens link tight junction transmembrane proteins to actin cytoskeleton and help maintain the structure and functioning of tight junctions [58]. ...
The rumen plays an essential role in the physiology and production of agriculturally important ruminants such as cattle. Functions of the rumen include fermentation, absorption, metabolism, and protection. Cattle are, however, not born with a functional rumen, and the rumen undergoes considerable changes in size, histology, physiology, and transcriptome from birth to adulthood. In this review, we discuss these changes in detail, the factors that affect these changes, and the potential molecular and cellular mechanisms that mediate these changes. The introduction of solid feed to the rumen is essential for rumen growth and functional development in post-weaning calves. Increasing evidence suggests that solid feed stimulates rumen growth and functional development through butyric acid and other volatile fatty acids (VFAs) produced by microbial fermentation of feed in the rumen and that VFAs stimulate rumen growth and functional development through hormones such as insulin and insulin-like growth factor I (IGF-I) or through direct actions on energy production, chromatin modification, and gene expression. Given the role of the rumen in ruminant physiology and performance, it is important to further study the cellular, molecular, genomic, and epigenomic mechanisms that control rumen growth and development in postnatal ruminants. A better understanding of these mechanisms could lead to the development of novel strategies to enhance the growth and development of the rumen and thereby the productivity and health of cattle and other agriculturally important ruminants.
... Table S1: Overview of PS values (blank, all: cell + blank, cell) and permeability values of cell (PC) and cell + blank (PE) from transport studies with NSAIDs; Table S2: Overview of mRNA expression after inflammation studies analysed with a high-throughput (96.96) qPCR chip; Table S3: Overview of physicochemical properties of NSAIDs, accessed on public databases, and calculated permeability coefficients of NSAIDs in this study. References [29,71] are cited in the supplementary materials. ...
Non-steroidal anti-inflammatory drugs (NSAIDs) are one of the most prescribed drugs to treat pain or fever. However, oral administration of NSAIDs is frequently associated with adverse effects due to their inhibitory effect on the constitutively expressed cyclooxygenase enzyme 1 (COX-1) in, for instance, the gastrointestinal tract. A systemic delivery, such as a buccal delivery, of NSAIDs would be beneficial and additionally has the advantage of a non-invasive administration route, especially favourable for children or the elderly. To investigate the transport of NSAIDs across the buccal mucosa and determine their potential for buccal therapeutic usage, celecoxib, diclofenac, ibuprofen and piroxicam were tested using an established oral mucosa Transwell® model based on human cell line TR146. Carboxyfluorescein and diazepam were applied as internal paracellular and transcellular marker molecule, respectively. Calculated permeability coefficients revealed a transport ranking of ibuprofen > piroxicam > diclofenac > celecoxib. Transporter protein inhibitor verapamil increased the permeability for ibuprofen, piroxicam and celecoxib, whereas probenecid increased the permeability for all tested NSAIDs. Furthermore, influence of local inflammation of the buccal mucosa on the transport of NSAIDs was mimicked by treating cells with a cytokine mixture of TNF-α, IL-1ß and IFN-γ followed by transport studies with ibuprofen (+ probenecid). Cellular response to pro-inflammatory stimuli was confirmed by upregulation of cytokine targets at the mRNA level, increased secreted cytokine levels and a significant decrease in the paracellular barrier. Permeability of ibuprofen was increased across cell layers treated with cytokines, while addition of probenecid increased permeability of ibuprofen in controls, but not across cell layers treated with cytokines. In summary, the suitability of the in vitro oral mucosa model to measure NSAID transport rankings was demonstrated, and the involvement of transporter proteins was confirmed; an inflammation model was established, and increased NSAID transport upon inflammation was measured.
... Recently, genome-wide association studies with linkage studies in renal calcium diseases and kidney stone diseases are ongoing and the data obtained from these studies suggest that CasR may play a role in the regulation of water, salt and calcium homeostasis in the kidney, NKCC2, ROMK and ClCkb/Barttin genes in renal salt secretion and CLDN gene family members such as CLDN14, 16 and 19 in renal calcium secretion. CLDN gene family members play a role in paracellular transport of renal tubular epithelium and expression of different klaudin isoforms determines ion selectivity and paracellular permeability of renal epithelium [17,18]. The most striking nding of our study was the statistically signi cant increased expression of CLDN1 gene, which encodes a tight junction protein, in patients with recurrent kidney stones. ...
OBJECTİVES: It is thought that genetic variations observed in members of the Claudin (CLDN) gene family may be responsible for the pathogenesis of recurrent kidney stone disease. In this study, we aimed to evaluate and compare the expression profiles of CLDN gene family members responsible for the mechanism of stone formation in patients with recurrent calcium oxalate stones and in a control group without a history of renal stones.
METHODS: Nineteen patients with recurrent calcium oxalate renal calculi who underwent percutaneous nephrolithotomy and 21 control patients without renal calculi who underwent surgery for other reasons were included in the study. Biopsy samples were taken from the intact renal parenchymal tissue consistent with computerized tomography images of all individuals. Total RNA was isolated from biopsy samples and expression profiles of target genes (Claudin 1-4, 7, 8, 10, 14, 16, 18, 19) were determined by real-time PCR(Polymerase Chain Reaction).
RESULTS: It was determined that CLDN1 gene expression in patients with recurrent calcium oxalate kidney stones was approximately 4 times higher than in the control group, this difference was significant (p<0.050). CLDN1 expression was also strongly positively correlated with CLDN4 (r=0.642), CLDN7 (r=0.753) and CLDN14 (r=0.651)
CONCLUSIONS: We thought that CLDN1 overexpression might play a role in the pathogenesis of recurrent calcium oxalate stone formation. CLDN1 together with CLDN2, CLDN4, CLDN7, and CLDN14 are also probably responsible for this pathogenesis. More studies are needed on CLDN gene family members responsible for the pathogenesis of recurrent calcium oxalate kidney stones
... The claudin family of tight junction proteins defines both pore pathway permeability and barrier function, depending on which of the 27 different claudin genes are expressed (13,20,21). Claudin-2 is a prototypical pore-forming molecule that, in the gut, is downregulated after weaning but upregulated during inflammatory states. ...
Intestinal epithelial expression of the tight junction protein claudin-2, which forms paracellular cation and water channels, is precisely regulated during development and in disease. Here, we show that small intestinal epithelial claudin-2 expression is selectively upregulated in septic patients. Similar changes occurred in septic mice, where claudin-2 upregulation coincided with increased flux across the paracellular pore pathway. In order to define the significance of these changes, sepsis was induced in claudin-2 knockout (KO) and wild-type (WT) mice. Sepsis-induced increases in pore pathway permeability were prevented by claudin-2 KO. Moreover, claudin-2 deletion reduced interleukin-17 production and T cell activation and limited intestinal damage. These effects were associated with reduced numbers of neutrophils, macrophages, dendritic cells, and bacteria within the peritoneal fluid of septic claudin-2 KO mice. Most strikingly, claudin-2 deletion dramatically enhanced survival in sepsis. Finally, the microbial changes induced by sepsis were less pathogenic in claudin-2 KO mice as survival of healthy WT mice injected with cecal slurry collected from WT mice 24 h after sepsis was far worse than that of healthy WT mice injected with cecal slurry collected from claudin-2 KO mice 24 h after sepsis. Claudin-2 upregulation and increased pore pathway permeability are, therefore, key intermediates that contribute to development of dysbiosis, intestinal damage, inflammation, ineffective pathogen control, and increased mortality in sepsis. The striking impact of claudin-2 deletion on progression of the lethal cascade activated during sepsis suggests that claudin-2 may be an attractive therapeutic target in septic patients.
... TJ expression is a key factor in the integrity of the intestinal mechanical barrier. The claudin family forms TJ by polymerization within the plasma membrane and forms paracellular seals by dimerization with claudin on neighboring cells through the extracellular space [29] . Several studies on claudin-1 in this family with intestinal barrier dysfunction and integrity pointed out that increased intestinal permeability was accompanied by decreased claudin-1 expression [30][31] . ...
... The claudin family comprises 30 proteins, at least 26 of which are found in humans (Mineta et al., 2011;Engelund et al., 2012). Functionally, claudins form tight junctions (TJs) between polarized cells, regulating ion transport (Colegio et al., 2002;Koziel et al., 2020). ...
Claudin-11 plays a critical role in multiple physiological processes, including myelination, auditory function, and spermatogenesis. Recently, stop-loss mutations in CLDN11 have been identified as a novel cause of hypomyelinating leukodystrophy (HLD22). Understanding the multifaceted roles of claudin-11 and the potential pathogenic mechanisms in HLD22 is crucial for devising targeted therapeutic strategies. This review outlines the biological roles of claudin-11 and the implications of claudin-11 loss in the context of the Cldn11 null mouse model. Additionally, HLD22 and proposed pathogenic mechanisms, such as endoplasmic reticulum stress, will be discussed.
... In the case of the non-classical claudins (claudins 11-13, 16, 18, 20-24) [58], claudin-12 displayed the highest relative expression levels. Claudin-25, a relatively recently identified family member [59], also showed robust expression levels. In addition to the claudin family members, we detected expression for other proteins of the tight junction complex with tight junction protein-1 (Tjp1, alias Zo-1) showing highest expression levels. ...
This study investigates the intricate composition and spatial distribution of tight junction complex proteins during early mouse neurulation. The analyses focused on the cranial neural tube, which gives rise to all head structures. Neurulation brings about significant changes in the neuronal and non-neuronal ectoderm at a cellular and tissue level. During this process, precise coordination of both epithelial integrity and epithelial dynamics is essential for accurate tissue morphogenesis. Tight junctions are pivotal for epithelial integrity, yet their complex composition in this context remains poorly understood. Our examination of various tight junction proteins in the forebrain region of mouse embryos revealed distinct patterns in the neuronal and non-neuronal ectoderm, as well as mesoderm-derived mesenchymal cells. While claudin-4 exhibited exclusive expression in the non-neuronal ectoderm, we demonstrated a neuronal ectoderm specific localization for claudin-12 in the developing cranial neural tube. Claudin-5 was uniquely present in mesenchymal cells. Regarding the subcellular localization, canonical tight junction localization in the apical junctions was predominant for most tight junction complex proteins. ZO-1 (zona occludens protein-1), claudin-1, claudin-4, claudin-12, and occludin were detected at the apical junction. However, claudin-1 and occludin also appeared in basolateral domains. Intriguingly, claudin-3 displayed a non-canonical localization, overlapping with a nuclear lamina marker. These findings highlight the diverse tissue and subcellular distribution of tight junction proteins and emphasize the need for their precise regulation during the dynamic processes of forebrain development. The study can thereby contribute to a better understanding of the role of tight junction complex proteins in forebrain development.
... Claudins are a large family of 27 members of transmembrane proteins, [34][35][36], which possess four transmembrane (TM1-TM4) domains, two extracellular loops (EC1 and EC2), one cytosolic segment (CS) and the amino and carboxylic termini retained at the cytosolic phase. Among them, two members viz Claudin-16 and Claudin-19 proteins translated from CLDN-16 and CLDN-19 genes, respectively, are found at the tight junctions of the adjacent epithelial cells of thick ascending limb (TAL) in the kidney, retina, and dental enamel [37,38]. ...
Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHNNC) is a rare autosomal recessive renal tubulopathy disorder characterized by excessive urinary loss of calcium and magnesium, polyuria, polydipsia, bilateral nephrocalcinosis, progressive chronic kidney disease, and renal failure. Also, sometimes amelogenesis imperfecta and severe ocular abnormalities are involved. The CLDN-16 and CLDN-19 genes encode the tight junction proteins claudin-16 and claudin-19, respectively, in the thick ascending loop of Henle in the kidney, epithelial cells of the retina, dental enamel, etc. Loss of function of the CLDN-16 and/or CLDN-19 genes leads to FHHNC. We present a case of FHHNC type 1, which was first confused with autosomal dominant hypocalcaemia (ADH) due to the presence of a very low serum parathyroid hormone (PTH) concentration and other similar clinical features before the genetic investigations. After the exome sequencing, FHHNC type 1 was confirmed by uncovering a novel homozygous missense mutation in the CLDN-16 gene (Exon 2, c.374 T > C) which causes, altered protein structure with F55S. Associated clinical, biochemical, and imaging findings also corroborate final diagnosis. Our findings expand the spectrum of the CLDN-16 mutation, which will further help in the genetic diagnosis and management of FHNNC.
... Increased intestinal permeability of luminal antigen that can damage the heart is another mechanism. The most plausible theory is that both illnesses could be caused by autoimmune processes [22]. ...
The prevalence of cardiac complications linked to celiac disease (CD) is on expanding. This study aimed to evaluate the cardiac function in children with CD using two dimensional speckle tracking echocardiography (2D-STE) to detect early myocardial dysfunction, if any. This cross-sectional study included 40 children with CD as the patient group and 40 healthy age- and sex-matched children served as the control group. High sensitive troponin T (Hs-troponin T), anti-tissue transglutaminase immunoglobulin A (tTG-IgA), hemoglobin, ferritin, albumin, and vitamin D levels were measured in all participants. Conventional, tissue Doppler imaging (TDI), and 2D-STE were performed for all included children. Conventional echocardiographic parameters showed no significant difference between the two groups. Left ventricular global longitudinal strain (LV GLS) obtained by 2D-STE was substantially lower in children with CD than the control group; however, myocardial performance index (MPI) obtained by TDI was significantly higher in children with CD. Hs-troponin T levels were comparable in both groups. LV GLS was positively correlated with hemoglobin, ferritin, and albumin level, but it was inversely correlated with the duration of the disease and anti tTG-IgA.
Conclusion: 2D-STE can detect subclinical early cardiac dysfunction in children with CD and this cardiac injury correlated to the duration and severity of the disease and some nutritional deficiency in these children.What is Known:
• The prevalence of cardiac complications linked to celiac disease (CD) is on expanding.
• Only one study evaluated cardiac function in children with CD using two dimensional speckle tracking echocardiography (2D-STE).
What is New:
• Our study found that 2D-STE can detect early subclinical cardiac dysfunction in children with CD. Cardiac injury in theses children correlated to the duration and severity of the disease, hemglobin, ferritin, and albumin levels.
... This, alongside earlier studies into claudin-5 deficient mice showing intact TJs, supports the idea that these proteins can compensate for one another to a certain extent. [41,42]. JAMs are believed to localise ZO-1 and occludin to TJ complexes [43]. ...
The blood–brain barrier (BBB) is a selectively permeable membrane that separates the bloodstream from the brain. While useful for protecting neural tissue from harmful substances, brain-related diseases are difficult to treat due to this barrier, as it also limits the efficacy of drug delivery. To address this, promising new approaches for enhancing drug delivery are based on disrupting the BBB using physical means, including optical/photothermal therapy, electrical stimulation, and acoustic/mechanical stimulation. These physical mechanisms can temporarily and locally open the BBB, allowing drugs and other substances to enter. Focused ultrasound is particularly promising, with the ability to focus energies to targeted, deep-brain regions. In this review, we examine recent advances in physical approaches for temporary BBB disruption, describing their underlying mechanisms as well as evaluating the utility of these physical approaches with regard to their potential risks and limitations. While these methods have demonstrated efficacy in disrupting the BBB, their safety, comparative efficacy, and practicality for clinical use remain an ongoing topic of research.
... Claudins form the structural and functional core of tight junctions. So far, 27 members of the claudin gene family have been identified, which are generally divided into pore-forming and barrier-forming claudins [26,27]. We did not detect any differences between sexes in the expression profiles of different claudins in the whole-bladder tissue samples (based on the unsupervised clustering of RNA sequencing (RNA seq) data; Supp_S5). ...
The urothelium is a vital permeability barrier that prevents the uncontrolled flow of urinary components into and out of the bladder interstitium. Our study addressed the question of possible sex-specific variations in the urothelium of healthy mice and their impact on chronic bladder inflammation. We found that healthy female bladders have a less robust barrier function than male bladders, as indicated by significant differences in transepithelial electrical resistance (TEER) values. These differences could be attributed to detected higher claudin 2 mRNA expression and a less pronounced glycocalyx in females than in males. In addition, TEER measurements showed delayed barrier recovery in chronically inflamed female bladders. We found subtle differences in the expressions of genes involved in the regulation of the actin cytoskeleton between the sexes, as well as pronounced urothelial hyperplasia in females compensating for attenuated barrier function. The identified genetic variations in glycosylation pathways may also contribute to this divergence. Our findings add to the growing body of literature on the intricate sex-specific nuances of urothelial permeability function and their implications for chronic bladder inflammation. Understanding these differences could lead to tailored diagnostic and therapeutic approaches in the treatment of bladder disorders in the future.
... The efficiency of these transcellular fluxes also depends on the paracellular permeability of the epithelium, which is dictated by the tight junction claudins. In humans, claudins form a 26-member family of transmembrane proteins that are localized in tight junctions [2]. They span the membrane 4 times and determine the tight junctions' selective permeability. ...
In the renal collecting ducts, chloride reabsorption occurs through both transcellular and paracellular pathways. Recent literature highlights a functional interplay between both pathways. We recently showed that in polarized inner medullary collecting duct cells, expression of the basolateral kidney anion exchanger 1 (kAE1) results in a decreased transepithelial electrical resistance (TEER), in a claudin-4 dependent pathway. Claudin-4 is a paracellular sodium blocker and chloride pore. Here, we show that kAE1 expression in mouse inner medullary collecting duct cells triggers WNK4, SPAK and claudin-4 phosphorylation. Expression of a functionally dead kAE1 E681Q mutant has no effect on phosphorylation of these proteins. Expression of a catalytically inactive WNK4 D321A or chloride-insensitive WNK4 L319F mutant abolishes kAE1 effect on TEER, supporting a contribution of WNK4 to the process. We propose that variations of the cytosolic pH and chloride concentration upon kAE1 expression alter WNK4 kinase activity and tight junction properties.
... Relatively low claudin-1 levels were observed in the high-intensity exercise group. Claudins consist of 27 members, (22) which are required for intercellular tight junctions, physically occlude the paracellular space, create ion pores between cells, and maintain cell polarity. (23) Claudin-1 is widely expressed in the intestinal epithelium has barrier-forming abilities, and plays an important role in tight junction integrity. ...
The intestine functions as a barrier preventing the entry of extrinsic factors into the body. This barrier function is disrupted by oxidative damage along with an impaired mucosal layer. Excessive exercise can generate oxidative stress in the intestinal tissue; however, the effect of exercise-induced oxidative stress on intestinal permeability is unclear. In this study, we examined the involvement of oxidative stress in barrier function of the ileum of mice following high-intensity exercise. Male ICR mice (12-week-old) were divided into sedentary and exercise groups. Mice in the exercise group underwent a single bout of treadmill running, and the ileum was collected for histological and biochemical analyses. Plasma fluorescence intensity level after oral administration of fluorescein isothiocyanate-dextran gradually increased until 30 min after exercise in response to intensity of exercise. Relatively high levels of oxidative proteins and low level of claudin-1, a tight-junction protein, were observed in the exercise group. Treatment with a xanthine oxidase inhibitor suppressed exercise-induced increases in intestinal permeability. Moreover, excessive exercise training for two weeks led to relatively high intestinal permeability at rest. These results suggest that high-intensity exercise increases intestinal permeability and tight junction damage, which may be mediated by oxidative stress.
... The important structural components belong to the protein families claudin (CLDN), occludin, and junctional adhesion molecules, whereas the adaptor molecules, including zonula occludens 1, 2, and 3; cingulin; and afadin link the TJ complex to the cytoskeleton and various signaling cascades to maintain dynamic cell integrity [63,68,69]. The exact composition of TJs can change dynamically in a given tissue, depending on many factors, including age, tissue type, differentiation state, and external and intracellular signals and stimuli [70,71]. In particular, the CLDN content of a cell type is highly regulated spatially and temporally and can change significantly within hours through a process called CLDN switching. ...
The skin is a tightly regulated, balanced interface that maintains our integrity through a complex barrier comprising physical or mechanical, chemical, microbiological, and immunological components. The skin’s microbiota affect various properties, one of which is the establishment and maintenance of the physical barrier. This is achieved by influencing multiple processes, including keratinocyte differentiation, stratum corneum formation, and regulation of intercellular contacts. In this review, we summarize the potential contribution of Cutibacterium acnes to these events and outline the contribution of bacterially induced barrier defects to the pathogenesis of acne vulgaris. With the combined effects of a Westernized lifestyle, microbial dysbiosis, epithelial barrier defects, and inflammation, the development of acne is very similar to that of several other multifactorial diseases of barrier organs (e.g., inflammatory bowel disease, celiac disease, asthma, atopic dermatitis, and chronic rhinosinusitis). Therefore, the management of acne requires a complex approach, which should be taken into account when designing novel treatments that address not only the inflammatory and microbial components but also the maintenance and strengthening of the cutaneous physical barrier.
... Despite the specific expression of the claudin gene in any other tissue, a tissue may simultaneously appear multiple types of claudin antigens. [8][9][10] Neoplastic cells often show structural and functional defects in tight junctions, which destroys them.. [11] Several studies show the impairment of claudin expression in various cancers, including breast cancer, [12,13] claudin-1 in colon carcinoma, [14] claudin-4 in the colon and gastric cancer, [15] and claudins 1 and 7 in prostate cancer, [16] esophageal cancer, [17] and ovarian cancer. [18] Claudin is a tight junctional protein of epithelial cells that makes the epithelial cells close to each Background: Triple-negative breast cancer is a heterogeneous subtype of breast cancer. ...
... Despite the specific expression of the claudin gene in any other tissue, a tissue may simultaneously appear multiple types of claudin antigens. [8][9][10] Neoplastic cells often show structural and functional defects in tight junctions, which destroys them.. [11] Several studies show the impairment of claudin expression in various cancers, including breast cancer, [12,13] claudin-1 in colon carcinoma, [14] claudin-4 in the colon and gastric cancer, [15] and claudins 1 and 7 in prostate cancer, [16] esophageal cancer, [17] and ovarian cancer. [18] Claudin is a tight junctional protein of epithelial cells that makes the epithelial cells close to each Background: Triple-negative breast cancer is a heterogeneous subtype of breast cancer. ...
... Despite the specific expression of the claudin gene in any other tissue, a tissue may simultaneously appear multiple types of claudin antigens. [8][9][10] Neoplastic cells often show structural and functional defects in tight junctions, which destroys them.. [11] Several studies show the impairment of claudin expression in various cancers, including breast cancer, [12,13] claudin-1 in colon carcinoma, [14] claudin-4 in the colon and gastric cancer, [15] and claudins 1 and 7 in prostate cancer, [16] esophageal cancer, [17] and ovarian cancer. [18] Claudin is a tight junctional protein of epithelial cells that makes the epithelial cells close to each Background: Triple-negative breast cancer is a heterogeneous subtype of breast cancer. ...
... A family of multiple-gene transmembrane proteins called claudins has at least 27 members (Mineta et al., 2011;Zhu et al., 2019). For the purpose of signaling, claudin proteins are connected to tight junctions in cell-cell communication between the plasma membranes of two interacting cells (Krause et al., 2008). ...
The claudin multigene family is associated with various aberrant physiological and cellular signaling pathways. However, the association of claudins with survival prognosis, signaling pathways, and diagnostic efficacy in colon cancer remains poorly understood.
Methods: Through the effective utilization of various bioinformatics methods, including differential gene expression analysis, gene set enrichment analysis protein-protein interaction (PPI) network analysis, survival analysis, single sample gene set enrichment analysis (ssGSEA), mutational variance analysis, and identifying receiver operating characteristic curve of claudins in The Cancer Genome Atlas colon adenocarcinoma (COAD).
Results: We found that: CLDN2, CLDN1, CLDN14, CLDN16, CLDN18, CLDN9, CLDN12, and CLDN6 are elevated in COAD. In contrast, the CLDN8, CLDN23, CLDN5, CLDN11, CLDN7, and CLDN15 are downregulated in COAD. By analyzing the public datasets GSE15781 and GSE50760 from NCBI-GEO (https://www.ncbi.nlm.nih.gov/geo/), we have confirmed that CLDN1, CLDN2, and CLDN14 are significantly upregulated and CLDN8 and CLDN23 are significantly downregulated in normal colon, colon adenocarcinoma tumor, and liver metastasis of colon adenocarcinoma tissues from human samples. Various claudins are mutated and found to be associated with diagnostic efficacy in COAD.
Conclusion: The claudin gene family is associated with prognosis, immune regulation, signaling pathway regulations, and diagnosis of COAD. These findings may provide new molecular insight into claudins in the treatment of colon cancer.
... They serve as a barrier regulating the passage of ions, water and different macromolecules to maintain homeostasis, and work as a fence to keep cell polarity by regulating the separate passages of molecules in the apical and basolateral membrane. At least 27 different CLDN members are known today, all of which are thought to vary in expression depending on location and cell type [5,6]. Altered expression of different CLDNs was found in a wide variety of human malignancies, and in many tumor types it had prognostic significance [7,8]. ...
Background: Although the expression of tight junction protein claudins (CLDNs) is well known in common histological subtypes of lung cancer, it has not been investigated in rare lung cancers. The aim of our study was to examine the expression of different CLDNs in pulmonary salivary gland tumors.
Methods: 35 rare lung cancers including pathologically confirmed 12 adenoid cystic carcinomas (ACCs) and 23 mucoepidermoid carcinomas (MECs) were collected retrospectively. Immunohistochemical (IHC) staining was performed on formalin fixed paraffin embedded (FFPE) tumor tissues, and CLDN1, -2, -3, -4, -5, -7, and -18 protein expressions were analyzed. The levels of immunopositivity were determined with H-score. Certain pathological characteristics of ACC and MEC samples (tumor grade, presence of necrosis, presence of blood vessel infiltration, and degree of lymphoid infiltration) were also analyzed.
Results: CLDN overexpression was observed in both tumor types, especially in CLDN2, -7, and -18 IHC. Markedly different patterns of CLDN expression were found for ACC and MEC tumors, especially for CLDN1, -2, -4, and -7, although none of these trends remained significant after correction for multiple testing. Positive correlations between expressions of CLDN2 and -5, CLDN3 and -4, and CLDN5 and -18 were also demonstrated. Tumors of never-smokers presented lower levels of CLDN18 than tumors of current smokers (p-value: 0.003).
Conclusion: This is the first study to comprehensively describe the expression of different CLDNs in lung ACC and MEC. Overexpression of certain CLDNs may pave the way for targeted anti-claudin therapy in these rare histological subtypes of lung cancer.
... In the BBB, AJs are highly differentiated cells that lie beneath TJs, initiate cell-cell adhesion, and connect to the underlying actin cytoskeleton (7,8). TJs are composed of claudin (CLDN, with 27 members) and TJ-associated MARVEL proteins (TAMP, e.g., occludin, tricellulin, and marvelD3) (9,10). Tricellulin is a protein found in the tricellular junction which helps maintain the impermeability of the BBB to macromolecules (11). ...
Objectives:
Intracerebroventricular (ICV) injections of mesenchymal stem cells (MSCs) may improve the function and structure of blood-brain barrier (BBB), possibly by preserving the BBB integrity. This study examined the impact of Wharton's jelly (WJ)-MSCs on cognitive dysfunction and BBB disruption following a protracted hypoxic state.
Materials and methods:
Twenty-four male Wistar rats were randomly studied in four groups: Control (Co): Healthy animals, Sham (Sh): Rats were placed in the cage without hypoxia induction and with ICV injection of vehicle, Hypoxic (Hx)+vehicle: Hypoxic rats with ICV injection of vehicle (5 μl of PBS), and Hx+MSCs: Hypoxic rats with ICV injection of MSCs. Spatial learning and memory were evaluated one week after WJ-MSCs injection, and then animals were sacrificed for molecular research.
Results:
Hypoxia increased latency and lowered the time and distance required reaching the target quarter, according to the findings. Furthermore, hypoxic rats had lower gene expression and protein levels of hippocampus vascular endothelial (VE)-cadherin, claudin 5, and tricellulin gene expression than Co and Sh animals (P<0.05). Finally, administering WJ-MSCs after long-term hypoxia effectively reversed the cognitive deficits and prevented the BBB breakdown via the upregulation of VE-cadherin, claudin 5, and tricellulin genes (P<0.05).
Conclusion:
These findings suggest that prolonged hypoxia induces spatial learning and memory dysfunction and increases BBB disruption, the potential mechanism of which might be via reducing VE-cadherin, claudin 5, and tricellulin genes. Hence, appropriate treatment with WJ-MSCs could reverse ischemia adverse effects and protect the BBB integrity following prolonged hypoxia.
... Numerous studies indicate that their expression is increased in many human cancers, including PA. Of the 27 members of this family [9], Claudins -3, -4 and -7 are most frequently dysregulated in epithelial cancers, their functional importance in their progression being well established [10,11]. ...
Claudins are a family of essential tight junction proteins, abnormally expressed in human carcinomas. The studies that indicated the involvement of claudins in tumor biology and progression suggest the possibility of their utility as markers for diagnosis or prognosis, but also as possible targets for therapy. We investigated 50 prostate adenocarcinomas (PAs) for which we followed the expression of Claudins -3, -4 and -7 in relation to International Society of Urological Pathology (ISUP) grades. We observed the positivity for Claudin-3, Claudin-4, and Claudin-7 in 76%, 74% and 46% of cases. Analysis of the immunoexpression pattern revealed the cytoplasmic and nuclear translocation for Claudins -3 and -4, and only cytoplasmic for Claudin-7. For all claudins investigated, we noted a final staining score with significantly higher values or at the limit of statistical significance for PA belonging to ISUP groups 1-4. The internalization of Claudins -3, -4 and -7 expression, regardless of the degree of PA, indicates their involvement in prostate carcinogenesis. In addition, the similar immunoexpression patterns of the three investigated claudins and their positive linear correlation suggest a coordinated regulation and indicate the possibility of a targeted treatment strategy.
... Here, the intercellular space is eliminated and the outer leaflets of apposing plasma membranes seem to fuse [4]. Proteins of the claudin family (CLDNx) [5], which are encoded by~27 genes in mammals [6][7][8], form the characteristic TJ strands that are observed in freeze-fracture electron microscopy [9], and determine the tightness and size-and charge-selective permeability of the epithelium [1,5,8,10]. Throughout the gastrointestinal tract, expression patterns of claudins vary depending on the permeability demands of the epithelium (stomach: CLDN1 to −4, −7, −18.2, −23; small intestine: Cldn1 to −5, −7, −8, −10, −12, −15, −23; colon: 1, −3, −4, −5, −7, −8, 12, −15, −23 [11,12]). ...
Claudins regulate paracellular permeability, contribute to epithelial polarization and are dysregulated during inflammation and carcinogenesis. Variants of the claudin-binding domain of Clostridium perfringens enterotoxin (cCPE) are highly sensitive protein ligands for generic detection of a broad spectrum of claudins. Here, we investigated the preferential binding of YFP- or GST-cCPE fusion proteins to non-junctional claudin molecules. Plate reader assays, flow cytometry and microscopy were used to assess the binding of YFP- or GST-cCPE to non-junctional claudins in multiple in vitro and ex vivo models of human and rat gastrointestinal epithelia and to monitor formation of a tight junction barrier. Furthermore, YFP-cCPE was used to probe expression, polar localization and dysregulation of claudins in patient-derived organoids generated from gastric dysplasia and gastric cancer. Live-cell imaging and immunocytochemistry revealed cell polarity and presence of tight junctions in glandular organoids (originating from intestinal-type gastric cancer and gastric dysplasia) and, in contrast, a disrupted diffusion barrier for granular organoids (originating from discohesive tumor areas). In sum, we report the use of cCPE fusion proteins as molecular probes to specifically and efficiently detect claudin expression, localization and tight junction dysregulation in cell lines, tissue explants and patient-derived organoids of the gastrointestinal tract.
... To determine mediators of increased pore pathway permeability after ethanol/CLP, TJ mediators were compared between water/CLP and ethanol/CLP. The claudin family of TJ proteins defines pore pathway permeability and barrier function, depending on which claudins are expressed (15,33,34). Claudin 4 levels were markedly decreased in ethanol/CLP compared with water/ CLP (Fig. 4A). ...
Alcohol use disorder is associated with increased mortality in septic patients. Murine studies demonstrate that ethanol/sepsis is associated with changes in gut integrity. This study examined intestinal permeability following ethanol/sepsis and investigated mechanisms responsible for alterations in barrier function. Mice were randomized to drink either 20% ethanol or water for 12 weeks and then were subjected to either sham laparotomy or cecal ligation and puncture (CLP). Intestinal permeability was disproportionately increased in ethanol/septic mice via the pore, leak and unrestricted pathways. Consistent with increased permeability in the leak pathway, jejunal MLCK expression and the ratio of phospho-MLC to total MLC were both increased in ethanol/CLP. Gut permeability was altered in MLCK-/- mice in water/CLP; however, permeability was not different between WT and MLCK-/- mice in ethanol/CLP. Similarly, jejunal IL-1β levels were decreased while systemic IL-6 levels were increased in MLCK-/- mice in water/CLP but no differences were identified in ethanol/CLP. While we have previously shown that mortality is improved in MLCK-/- mice following water/CLP, mortality was significantly worse in MLCK-/- mice following ethanol/CLP. Consistent with an increase in the pore pathway, claudin 4 levels were also selectively decreased in ethanol/CLP WT mice. Further, mRNA expression of jejunal TNF and IFN-γ were both significantly increased in ethanol/CLP. The frequency of CD4+ cells expressing TNF and IL-17A and the frequency of CD8+ cells expressing IFN-γ in Peyer's Patches were also increased in ethanol/CLP. Thus, there is an ethanol-specific worsening of gut barrier function following CLP that impacts all pathways of intestinal permeability, mediated, in part, via changes to the tight junction. Differences in the host response in the setting of chronic alcohol use may play a role in future precision medicine approaches toward the treatment of sepsis.
... They have a molecular weight of 22-28 kDa and are expressed in a tissue-specific manner in epithelial and endothelial cells [6, 10,11]. Claudins are proposed to have a similar structure comprising four transmembrane domains, two extracellular segments (ECS1 and ECS2), an intracellular loop, a short intracellular N-terminal, and a long intracellular C-terminal [12] ( Figure 1A). ...
Claudin-2 is a tight junction protein expressed in leaky epithelia where it forms paracellular pores permeable to cations and water. The paracellular pore formed by claudin-2 is important in energy-efficient cation and water transport in the proximal tubules of the kidneys. Mounting evidence now suggests that claudin-2 may modulate cellular processes often altered in disease, including cellular proliferation. Also, dysregulation of claudin-2 expression has been linked to various diseases, including kidney stone disease and renal cell carcinoma. However, the mechanisms linking altered claudin-2 expression and function to disease are poorly understood and require further investigation. The aim of this review is to discuss the current understanding of the role of claudin-2 in kidney function and dysfunction. We provide a general overview of the claudins and their organization in the tight junction, the expression, and function of claudin-2 in the kidney, and the evolving evidence for its role in kidney disease.
... Thus, understanding the mechanism of tumor progression and treatment resistance in ESCC is essential. Claudin5 (coded by CLDN5 gene) is a member of the claudin protein family, which includes 27 integral membrane proteins [4]. Accumulated evidence suggests that claudin proteins are key regulator of carcinogenesis and metastasis [5]. ...
Background
Esophageal squamous cell carcinoma (ESCC) is a highly prevalent and aggressive cancer with poor treatment outcomes. Despite the critical role of tight junction proteins in tumorigenesis, the involvement of Claudin5 in ESCC remains poorly understood. Thus, this study aimed to investigate the role of Claudin5 in ESCC malignant progression and radioresistance, as well as the underlying regulatory mechanisms.
Methods
The expression of Claudin5 was evaluated in esophageal cancer tissue using both public databases and 123 clinical samples. CCK-8, transwell invasion, wound healing and clonogenic survival assays were used to examine the proliferation, invasion, migration and radiosensitivity of ESCC cells in vitro. Xenograft and animal lung metastasis experiments were conducted to examine the impact of Claudin5 on tumor growth and lung metastasis in vivo. The effect of Claudin5 on autophagy was detected via transmission electron microscopy, western blotting and autophagy flux. Immunohistochemical staining was used to detect Claudin5 expression in ESCC patient samples. The statistical difference was assessed with Student t test or one-way ANOVA. The correlation between Claudin5 expression and radiotherapy response rate was performed by the Chi-square test. The significance of Kaplan–Meier curves was evaluated by the Logrank test.
Results
Claudin5 expression was downregulated in ESCC tissues. Downregulation of Claudin5 promoted ESCC cell proliferation, invasion, and migration both in vitro and in vivo. Downregulation of Claudin5 decreased the radiosensitivity of ESCC cells. Moreover, downregulation of Claudin5 promoted autophagy and the expression of Beclin1. Beclin1 knockdown reversed the effect of Claudin5 downregulation on autophagy induction and the promotion of ESCC cell malignant progression and radioresistance. Additionally, low expression of Claudin5 in ESCC cancer tissues was associated with poor radiotherapy response and prognosis.
Conclusions
In summary, these findings suggest that downregulation of Claudin5 promotes ESCC malignant progression and radioresistance via Beclin1-autophagy activation and may serve as a promising biomarker for predicting radiotherapy response and patient outcome in ESCC.
... It has been suggested that the expression of claudin, another transmembrane protein in tight junctions, increases because of inflammation, unlike occludin, in biopsies from patients with Crohn's disease and ulcerative colitis [34,35]. Claudins are a large family, comprised of at least 27 members, that show specific localisation in the gastrointestinal tract [36,37]. Plasma claudin-5 levels, a part of the endothelial tight junction, are increased in patients with haemorrhagic shock in the early course after polytrauma [26]. ...
Purpose
In an effort to better manage critically ill patients hospitalised in the intensive care unit (ICU) after experiencing multiple traumas, the present study aimed to assess whether plasma levels of intestinal epithelial cell barrier proteins, including occludin, claudin-1, junctional adhesion molecule (JAM-1), tricellulin and zonulin, could be used as novel biomarkers. Additional potential markers such as intestinal fatty acid-binding protein (I-FABP), d-lactate, lipopolysaccharide (LPS) and citrulline were also evaluated. We also aimed to determine the possible relationships between the clinical, laboratory, and nutritional status of patients and the measured marker levels.
Methods
Plasma samples from 29 patients (first, second, fifth and tenth days in the ICU and on days 7, 30 and 60 after hospital discharge) and 23 controls were subjected to commercial enzyme-linked immunosorbent assay (ELISA) testing.
Results
On first day (admission) and on the second day, plasma I-FABP, d-lactate, citrulline, occludin, claudin-1, tricellulin and zonulin levels were high in trauma patients and positively correlated with lactate, C-reactive protein (CRP), number of days of ICU hospitalisation, Acute Physiology and Chronic Health Evaluation II (APACHE II) score and daily Sequential Organ Failure Assessment (SOFA) scores (P < 0.05–P < 0.01).
Conclusion
The results of the present study showed that occludin, claudin-1, tricellulin and zonulin proteins, as well as I-FABP, d-lactate and citrulline, may be used as promising biomarkers for the evaluation of disease severity in critically ill trauma patients, despite the complexity of the analysis of various barrier markers. However, our results should be supported by future studies.
... The first tight junction protein to be discovered was zonula occludens 1 (ZO-1) 33 ( Fig. 1), followed by the two related proteins ZO-2 and ZO-3, and the unrelated protein cingulin [34][35][36][37] , though all of these proteins are intracellular peripheral membrane proteins. These discoveries were followed by the discovery of the tetraspan transmembrane tight junction proteins occludin 38 and the claudins, which are encoded by 27 genes in mammals 39,40 . When expressed in non-epithelial cells, claudins can self-assemble into large polymers to form structures that are reminiscent of tight junction strands seen by freeze-fracture electron microscopy 41 (Fig. 1). ...
Epithelial tight junctions define the paracellular permeability of the
intestinal barrier. Molecules can cross the tight junctions via two
distinct size-selective and charge-selective paracellular pathways:
the pore pathway and the leak pathway. These can be distinguished by
their selectivities and differential regulation by immune cells. However,
permeability increases measured in most studies are secondary to
epithelial damage, which allows non-selective flux via the unrestricted
pathway. Restoration of increased unrestricted pathway permeability
requires mucosal healing. By contrast, tight junction barrier loss
can be reversed by targeted interventions. Specific approaches are
needed to restore pore pathway or leak pathway permeability increases.
Recent studies have used preclinical disease models to demonstrate the
potential of pore pathway or leak pathway barrier restoration in disease.
In this Review, we focus on the two paracellular flux pathways that are
dependent on the tight junction. We discuss the latest evidence that
highlights tight junction components, structures and regulatory
mechanisms, their impact on gut health and disease, and opportunities
for therapeutic intervention.
... To explore the reason why Ruminococcaceae are considered BW-associated bacteria, we focused our discussion on Cldn22, which had the highest frequency of occurrence as a gene, showing a correlation coefficient > 0.8 (Fig. 5d) between the gut microbiota abundance and GEL of the host genes associated with gut microorganism-mediated BW regulation (Table 2). Although the function of CLDN22 has not yet been elucidated, it is inferred to represent a component of the tight junction chain 57-59 as it encodes a member of the claudin family 60,61 . Tight junctions are thought to function as physical and chemical barriers that prevent food components and intestinal bacteria from freely passing through intercellular spaces between the epithelial and endothelial cell sheets 62,63 . ...
We aimed to identify gut microbiota that influences body weight by elucidating the association with diets and host genes. Germ-free (GF) mice with and without fecal microbiota transplant (FMT) were fed a normal, high-carbohydrate, or high-fat diet. FMT mice exhibited greater total body weight; adipose tissue and liver weights; blood glucose, insulin, and total cholesterol levels; and oil droplet size than the GF mice, regardless of diet. However, the extent of weight gain and metabolic parameter levels associated with gut microbiota depended on the nutrients ingested. For example, a disaccharide- or polysaccharide-rich diet caused more weight gain than a monosaccharide-rich diet. An unsaturated fatty acid-rich diet had a greater microbial insulin-increasing effect than a saturated fatty acid-rich diet. Perhaps the difference in microbial metabolites produced from substances taken up by the host created metabolic differences. Therefore, we analyzed such dietary influences on gut microbiota, differentially expressed genes between GF and FMT mice, and metabolic factors, including body weight. The results revealed a correlation between increased weight gain, a fat-rich diet, increased Ruminococcaceae abundance, and decreased claudin 22 gene expression. These findings suggest that weight regulation might be possible through the manipulation of the gut microbiota metabolism using the host’s diet.
... The various expression patterns of the 27 CLDN family proteins make up organ-specific barriers, with some critical differences, subtle or notable, in paracellular barrier function and context-dependent associations of permselectivities to maintain the homeostasis of tissues and organs in humans and mice. [2][3][4][5][6][7][8][9] A series of studies have demonstrated that a lack of specific CLDNs can cause pathological conditions owing to aberrant paracellular barrier functions in various organs. [10][11][12][13][14][15][16][17][18] The skin barrier is built and regulated by the epidermis, the outermost layer of which is the stratum corneum. ...
Hair follicles (HFs) undergo cyclic phases of growth, regression, and rest in association with hair shafts to maintain the hair coat. Nonsense mutations in the tight junction protein claudin (CLDN)‐1 cause hair loss in humans. Therefore, we evaluated the roles of CLDNs in hair retention. Among the 27 CLDN family members, CLDN1, CLDN3, CLDN4, CLDN6, and CLDN7 were expressed in the inner bulge layer, isthmus, and sebaceous gland of murine HFs. Hair phenotypes were observed in Cldn1 weaker knockdown and Cldn3‐knockout (Cldn1Δ/ΔCldn3−/−) mice. Although hair growth was normal, Cldn1Δ/ΔCldn3−/− mice showed striking hair loss in the first telogen. Simultaneous deficiencies in CLDN1 and CLDN3 caused abnormalities in telogen HFs, such as an aberrantly layered architecture of epithelial cell sheets in bulges with multiple cell layers, mislocalization of bulges adjacent to sebaceous glands, and dilated hair canals. Along with the telogen HF abnormalities, which shortened the hair retention period, there was an enhanced proliferation of the epithelium surrounding HFs in Cldn1Δ/ΔCldn3−/− mice, causing accelerated hair regrowth in adults. Our findings suggested that CLDN1 and CLDN3 may regulate hair retention in infant mice by maintaining the appropriate layered architecture of HFs, a deficiency of which can lead to alopecia.
Claudin 1 is a transmembrane protein known as a key component of the tight junctions playing a pivotal role in cell-cell interaction and homeostasis of epithelial cells. In breast cancer, the expression of claudin 1 is absent or strongly diminished in 76% of triple-negative breast cancer (TNBC). These tumors constitute the most aggressive subtype of breast cancer. They are a heterogeneous group of breast tumors that do not express estrogen receptor (ER) α, progesterone receptor (PR), and human epidermal growth factor receptor-2 (HER2). Therefore, TNBC patients are not eligible for targeted therapies that have been developed for other breast cancer subtypes. TNBCs have a higher tendency to form metastasis and they rapidly acquire chemo-resistance. Therefore, TNBCs represent a major challenge in cancerology, and the main goal of cancer research is to characterize potential specific targets to treat these tumors lacking efficient therapies. Clinical studies reported that a loss of claudin 1 expression correlates with increased aggressiveness and metastasis potential associated with recurrence of disease in invasive breast carcinoma patients. Although the role of claudin 1 in breast cancer is not clearly defined, several in vitro studies suggested that claudin 1 functions as a tumor suppressor. The reexpression of claudin 1 in some TNBC cell line was shown to be sufficient to induce apoptosis, suggesting that claudin 1 expression could constitute a new therapeutic option in “claudin 1–low” TNBC. This review summarizes the role of claudin 1 in TNBC cancer and its impact on developing novel strategies to treat breast cancer.
This review addresses the role of tight junction proteins at the blood-brain barrier (BBB). Their expression is described, and their role in physiological and pathological processes at the BBB is discussed. Based on this, new approaches are depicted for paracellular drug delivery and diagnostics in the treatment of cerebral diseases. Recent data provide convincing evidence that, in addition to its impairment in the course of diseases, the BBB could be involved in the aetiology of CNS disorders. Further progress will be expected based on new insights in tight junction protein structure and in their involvement in signalling pathways.
Claudins (CLDN1–CLDN24) are a family of tight junction proteins whose dysregulation has been implicated in tumorigeneses of many cancer types. In colorectal cancer (CRC), CLDN1, CLDN2, CLDN4, and CLDN18 have been shown to either be upregulated or aberrantly expressed. In the normal colon, CLDN1 and CLDN3–7 are expressed. Although a few claudins, such as CLDN6 and CLDN7, are expressed in CRC their levels are reduced compared to the normal colon. The present review outlines the expression profiles of claudin proteins in CRC and those that are potential biomarkers for prognostication.
The intestinal microbiota is closely related to liver diseases via the intestinal barrier and bile secretion to the gut. Impairment of the barrier can translocate microbes or their components to the liver where they can contribute to liver damage and fibrosis. The components of the barrier are discussed in this review along with the other elements of the so-called gut–liver axis. This bidirectional relation has been widely studied in alcoholic and non-alcoholic liver disease. However, the involvement of microbiota in the pathogenesis and treatment of viral liver diseases have not been extensively studied, and controversial data have been published. Therefore, we reviewed data regarding the integrity and function of the intestinal barrier and the changes of the intestinal microbioma that contribute to progression of Hepatitis B (HBV) and Hepatitis C (HCV) infection. Their consequences, such as cirrhosis and hepatic encephalopathy, were also discussed in connection with therapeutic interventions such as the effects of antiviral eradication and the use of probiotics that may influence the outcome of liver disease. Profound alterations of the microbioma with significant reduction in microbial diversity and changes in the abundance of both beneficial and pathogenic bacteria were found.
The early and intermediate age-related macular degeneration (AMD) is characterized by the presence of drusen and pigmentary abnormalities in the retinal pigment epithelial (RPE) cells which form the outer blood retinal barrier (oBRB). Fluid leakage through the disrupted oBRB from the choroid to the neural retina has been implicated in the pathogenesis of AMD, however; the molecular mechanisms still remain unclear. The family of four transmembrane proteins, claudins are known to form tight junctions (TJs) in the oBRB. Nonetheless, there are few reports showing how they function in the oBRB in vivo. We found that claudin-1 is dominantly expressed in TJs of the mouse RPE. To investigate the role of claudin-1 in the RPE, we generated RPE-specific Cldn1 conditional knockout mice (Best1-Cre+/- Cldn1flox/flox mice: Cldn1 cKO mice). Deficiency of Cldn1 led to age-related lipid deposits such as subretinal drusenoid deposits (SDD), increased lipid droplets in the RPE, basal lamellar deposits (BlamD) and membranous debris in the Bruch's membrane. In addition, pigmentary abnormalities such as RPE hypertrophy, multilayered-RPE cells, and ectopic pigment granules outside the RPE were observed in Cldn1 cKO mice. Our study provides new insights into the possible association of the TJ protein claudin-1 with lipid metabolism and cellular ageing in the RPE contributing to the early onset of AMD.
Tight junctions, also called zonula occludens, are supramolecular cell–cell adhesion complexes crucial for the architecture of epithelial tissues and selective gates that regulate the paracellular diffusion of ions and solutes. These tight connections prevent the intermixing of apical and basolateral membrane components by generating intramembrane diffusion barriers. Tight junction complexes of adjacent cells also create paracellular channels because of how closely they are spaced, which enables the selective diffusion of ions and solutes through the extracellular environment. Tight junctions are also connected to various cell behaviors and functions, such as controlling cell growth and differentiation, through the transmission of information to the cytoskeleton, nucleus, and different cell adhesion complexes. In addition to inherent genetic changes, recent studies have shown that bacterial toxins, cytokines, hormones, and drugs modify tight junction protein complexes, thus affecting their cellular functions. Recent studies have broadened our understanding of tight junction molecular architecture, biogenesis, and regulation mechanisms. Here we discuss the architecture and functions of this supramolecular complex and its alteration in gene expression and structural architecture in disease states.
Proper functioning of the neural retina relies on the unique retinal environment regulated by the blood–retinal barrier (BRB), which restricts the passage of solutes, fluids, and toxic substances. BRB impairment occurs in many retinal vascular diseases and the breakdown of BRB significantly contributes to disease pathology. Understanding the different molecular constituents and signaling pathways involved in BRB development and maintenance is therefore crucial in developing treatment modalities. This review summarizes the major molecular signaling pathways involved in inner BRB (iBRB) formation and maintenance, and representative animal models of eye diseases with retinal vascular leakage. Studies on Wnt/β-catenin signaling are highlighted, which is critical for retinal and brain vascular angiogenesis and barriergenesis. Moreover, multiple in vivo and in vitro methods for the detection and analysis of vascular leakage are described, along with their advantages and limitations. These pre-clinical animal models and methods for assessing iBRB provide valuable experimental tools in delineating the molecular mechanisms of retinal vascular diseases and evaluating therapeutic drugs.
Background:
High expression of CLDN6 in hepatocellular carcinoma (HCC) has been widely reported. During this research, CLDN6's effect on the infiltration, migration, and apoptosis of HCC cells was investigated.
Methods:
Initially, the knockdown and overexpression of CLDN6 in HCC cells were carried out by short interfering RNA (siRNA) and plasmid transfection. The transfection efficiency was detected by means of a quantitative real-time polymerase chain reaction (qRT-PCR) assay, immunofluorescence staining, and Western blot analysis. Transwell and wound-healing assays were employed for the detection of invasion and migration ability. CCK-8 assay and flow cytometry were utilized for the detection of apoptosis. Finally, analysis of the expression of pathway-related proteins (JAK2, STAT3, p-JAK2, and p-STAT3) and the regulation of apoptotic responses (by measurement of cleaved caspase-3, Bax, and Bcl-2 levels) was carried out.
Results:
When CLDN6 was knocked down, the cellular invasion and migration ability decreased, and apoptosis increased, which decreased p-JAK2, p-STAT3, and anti-apoptotic protein bcl-2 expression. Furthermore, an elevation was observed in cleaved caspase-3 and Bax expression levels. Contrarily, upon overexpression of CDLN6, the aforementioned experimental results were reversed.
Conclusions:
CLDN6 knockdown results in the inhibition of HCC cells' infiltration and migration and promotes apoptosis via downregulation of the JAK2/STAT3 signaling pathway.
Memelilerde vücudun bazı özel bölümlerindeki molleküllerin kan ve dokular arasındaki hareketi “kan-doku bariyeri” adı verilen yapılar tarafından kontrol edilir. Bu bariyerlerin başlıcaları kan-beyin, -plasenta, -retina, -timus, -testis ve - epididimis bariyerleridir. Kan-testis bariyeri (BTB) ve kan-epididimis bariyeri (BEB) erkek üreme sistemindeki iki önemli hücresel bariyerdir. Seminifer epitelde yerleşen ve komşu Sertoli hücreleri arasında bulunan BTB, tight junction, gap junction (geçit bağlantıları), desmozom (macula adherens) ve adherens junction (bazal ektoplazmik özelleşme-testise özgü bir yapışma bağlantısı) tipi bağlantılar tarafından oluşturulur. Bu bariyer gelişmekte olan germ hücrelerini, özellikle postmayotik spermatidleri, kan ve lenf yoluyla buraya taşınan zararlı ajanlardan (ilaçlar, toksik kimyasallar ve mutajen- ler gibi) koruyan ve farklılaşmış germ hücrelerine karşı oluşabilecek otoimmun tepkileri önleyen biyokimyasal ve immünolojik bir mikro çevre oluşturur. BTB seminifer tübül epitelini bazal ve adluminal bölmelere ayırarak hücre polaritesi sağlar ve tübül lümenindeki sıvının kimyasal bileşiminin korunmasına yardımcı olur. BTB spermatogenez sırasında yeniden yapılanmaya uğrar, ancak bütünlüğü bozulmaz. Böylece germ hücreleri bu benzersiz yapı sayesinde seminifer epitel boyunca taşınır. Bariyeri oluşturan bileşenlerden herhangi birinde bozulma olması durumunda germ hücreleri gelişimlerini tamamlayamaz ve erkeklerde infertilite şekillenir. Ayrıca, gelişmemiş germ hücreleri sekonder oositi dölle- yemediğinden dişi fertilitesi de dolaylı olarak bu durumdan etkilenebilir. Özetle bu bariyer germ hücrelerinin hayatta kalması ve normal spermatogenezin devamlılığı için kritik bir öneme sahiptir. Bu derlemenin amacı, memelilerde erkek infertilitesinde önemli rol oynayan kan-testis bariyerini oluşturan bağlantı komplekslerinin moleküler bileşenleri hakkında bilgi vermektir.
The blood-brain barrier （BBB） is a major obstacle to the delivery of drugs to the central nervous system. In the BBB, the spaces between adjacent brain microvascular endothelial cells are sealed by multiprotein complexes known as tight junctions （TJs）. Claudin-5 （CLDN-5） is the essential protein for TJ in the BBB, which restricts the influx of small molecules up to approximately 800 Da. Thus, among the many components of the TJs, CLDN-5 has received the most attention as a target for drug delivery to the brain by loosening the TJ seal. Many researchers have attempted to develop technologies to selectively inhibit the CLDN-5 and open TJ in the BBB. In this review, we introduce the use of CLDN-5 binders have been shown to enhance the permeation of small molecules from the blood into the brain without apparent adverse effects and the safety concerns of CLDN-5-targeted technologies with respect to their clinical application.
As biologics used in the clinic outpace the number of new small molecule drugs, an important challenge for their efficacy and widespread use has emerged, namely tissue penetrance. Macromolecular drugs - bulky, high-molecular weight, hydrophilic agents - exhibit low permeability across biological barriers. Epithelial and endothelial layers, for example within the gastrointestinal tract or at the blood-brain barrier, present the most significant obstacle to drug transport. Within epithelium, two subcellular structures are responsible for limiting absorption: cell membranes and intercellular tight junctions. Previously considered impenetrable to macromolecular drugs, tight junctions control paracellular flux and dictate drug transport between cells. Recent work, however, has shown tight junctions to be dynamic, anisotropic structures that can be targeted for delivery. This review aims to summarize new approaches for targeting tight junctions, both directly and indirectly, and to highlight how manipulation of tight junction interactions may help usher in a new era of precision drug delivery.
The ingested proteins are catabolized to di/tri-peptides and amino acids (AAs), which are absorbed through various transporters in the small intestinal and colonic epithelial cells. Tight junctions (TJs) are formed between neighboring cells and restrict paracellular fluxes to mineral ions and aqueous molecules. However, it is unknown whether the TJs are implicated in the control of paracellular fluxes to AAs. The paracellular permeability is controlled by claudins (CLDNs), which comprise a family of over 20 members. Here, we found that CLDN8 expression is decreased by AAs deprivation in normal mouse colon-derived MCE301 cells. The reporter activity of CLDN8 was not significantly changed by AAs deprivation, whereas the stability of CLDN8 protein was decreased. MicroRNA analysis showed that AAs deprivation increases the expression of miR-153-5p which targets CLDN8. The AAs deprivation-induced decline of CLDN8 expression was reversed by a miR-153-5p inhibitor. The CLDN8 silencing enhanced the paracellular fluxes to AAs, especially middle molecular size AAs. The expression levels of colonic CLDN8 and miR-153-5p in aged mice were lower and higher than those in young mice, respectively. We suggest that AAs deprivation downregulates CLDN8-dependent barrier function, mediated by the elevation of miR-153-5p expression in the colon, in order to enhance the AAs absorption.
The BLAST programs are widely used tools for searching protein and DNA databases for sequence similarities. For protein comparisons, a variety of definitional, algorithmic, and statistical refinements permits the execution time of the BLAST programs to be decreased substantially while enhancing their sensitivity to weak similarities. A new criterion for triggering the extension of word hits, combined with a new heuristic for generating gapped alignments, yields a gapped BLAST program that runs at approximately three times the speed of the original. In addition, a method is described for automatically combining statistically significant alignments produced by BLAST into a position-specific score matrix, and searching the database using this matrix. The resulting Position Specific Iterated BLAST (PSLBLAST) program runs at approximately the same speed per iteration as gapped BLAST, but in many cases is much more sensitive to weak but biologically relevant sequence similarities.
Entrez Gene (http://www.ncbi.nlm.nih.gov/gene) is National Center for Biotechnology Information (NCBI)’s database for gene-specific information. Entrez Gene maintains
records from genomes which have been completely sequenced, which have an active research community to submit gene-specific
information, or which are scheduled for intense sequence analysis. The content represents the integration of curation and
automated processing from NCBI’s Reference Sequence project (RefSeq), collaborating model organism databases, consortia such
as Gene Ontology and other databases within NCBI. Records in Entrez Gene are assigned unique, stable and tracked integers
as identifiers. The content (nomenclature, genomic location, gene products and their attributes, markers, phenotypes and links
to citations, sequences, variation details, maps, expression, homologs, protein domains and external databases) is available
via interactive browsing through NCBI’s Entrez system, via NCBI’s Entrez programming utilities (E-Utilities) and for bulk
transfer by FTP.
Tight junction (TJ)–like structures have been reported in Schwann cells, but their molecular composition and physiological function remain elusive. We found that claudin-19, a novel member of the claudin family (TJ adhesion molecules in epithelia), constituted these structures. Claudin-19–deficient mice were generated, and they exhibited behavioral abnormalities that could be attributed to peripheral nervous system deficits. Electrophysiological analyses showed that the claudin-19 deficiency affected the nerve conduction of peripheral myelinated fibers. Interestingly, the overall morphology of Schwann cells lacking claudin-19 expression appeared to be normal not only in the internodal region but also at the node of Ranvier, except that TJs completely disappeared, at least from the outer/inner mesaxons. These findings have indicated that, similar to epithelial cells, Schwann cells also bear claudin-based TJs, and they have also suggested that these TJs are not involved in the polarized morphogenesis but are involved in the electrophysiological “sealing” function of Schwann cells.
MicroRNAs have emerged as key post-transcriptional regulators of gene expression, involved in various physiological and pathological processes. It was found that several miRNAs are directly involved in human cancers, including lung, breast, brain, liver, colon cancer and leukemia. In addition, some miRNAs may function as oncogenes or tumor suppressors in tumor development. Furthermore, a widespread down-regulation of miRNAs is commonly observed in human cancers and promotes cellular transformation and tumorigenesis. More than 50% of miRNA genes are located in cancer-associated genomic regions or in fragile sites, frequently amplified or deleted in human cancer, suggesting an important role in malignant transformation. A better understanding of the miRNA regulation and misexpression in cancer may ultimately yield further insight into the molecular mechanisms of tumorigenesis and new therapeutic strategies may arise against cancer. Here, we discuss the occurrence of the deregulated expression of miRNAs in human cancers and their importance in the tumorigenic process.
Whether or not significant amounts of water pass the tight junction (TJ) of leaky epithelia is still unresolved, because it is difficult to separate transcellular water flux from TJ-controlled paracellular water flux. Using an approach without differentiating technically between the transcellular and paracellular route, we measured transepithelial water flux with and without selective molecular perturbation of the TJ to unequivocally attribute changes to the paracellular pathway. To this end, MDCK C7 cells were stably transfected with either claudin-2 or claudin-10b, two paracellular cation-channel-forming TJ proteins that are not endogenously expressed in this cell line. Claudin-2 is typical of leaky, water-transporting epithelia, such as the kidney proximal tubule, whereas claudin-10b is present in numerous epithelia, including water-impermeable segments of the loop of Henle. Neither transfection altered the expression of endogenous claudins or aquaporins. Water flux was induced by an osmotic gradient, a Na(+) gradient or both. Under all conditions, water flux in claudin-2-transfected cells was elevated compared with vector controls, indicating claudin-2-mediated paracellular water permeability. Na(+)-driven water transport in the absence of an osmotic gradient indicates a single-file mechanism. By contrast, claudin-10b transfection did not alter water flux. We conclude that claudin-2, but not claudin-10b, forms a paracellular water channel and thus mediates paracellular water transport in leaky epithelia.
Intestinal barrier function is reduced in inflammatory bowel disease (IBD). Tumor necrosis factor (TNF) and interleukin (IL)-13,
which are up-regulated in IBD, induce barrier defects that are associated with myosin light chain kinase (MLCK) activation
and increased claudin-2 expression, respectively, in cultured intestinal epithelial monolayers. Here we report that these
independent signaling pathways have distinct effects on tight junction barrier properties and interact in vivo. MLCK activation alters size selectivity to enhance paracellular flux of uncharged macromolecules without affecting charge
selectivity and can be rapidly reversed by MLCK inhibition. In contrast, IL-13-dependent claudin-2 expression increases paracellular
cation flux in vitro and in vivo without altering tight junction size selectivity but is unaffected by MLCK inhibition in vitro. In vivo, MLCK activation increases paracellular flux of uncharged macromolecules and also triggers IL-13 expression, claudin-2 synthesis,
and increased paracellular cation flux. We conclude that reversible, MLCK-dependent permeability increases cause mucosal immune
activation that, in turn, feeds back on the tight junction to establish long-lasting barrier defects. Interactions between
these otherwise distinct tight junction regulatory pathways may contribute to IBD pathogenesis.
Jalview Version 2 is a system for interactive WYSIWYG editing, analysis and annotation of multiple sequence alignments. Core features include keyboard and mouse-based editing, multiple views and alignment overviews, and linked structure display with Jmol. Jalview 2 is available in two forms: a lightweight Java applet for use in web applications, and a powerful desktop application that employs web services for sequence alignment, secondary structure prediction and the retrieval of alignments, sequences, annotation and structures from public databases and any DAS 1.53 compliant sequence or annotation server.
Availability: The Jalview 2 Desktop application and JalviewLite applet are made freely available under the GPL, and can be downloaded from www.jalview.org
Contact: g.j.barton@dundee.ac.uk
The BLAST programs are widely used tools for searching protein and DNA databases for sequence similarities. For protein comparisons,
a variety of definitional, algorithmic and statistical refinements described here permits the execution time of the BLAST
programs to be decreased substantially while enhancing their sensitivity to weak similarities. A new criterion for triggering
the extension of word hits, combined with a new heuristic for generating gapped alignments, yields a gapped BLAST program
that runs at approximately three times the speed of the original. In addition, a method is introduced for automatically combining
statistically significant alignments produced by BLAST into a position-specific score matrix, and searching the database using
this matrix. The resulting Position-Specific Iterated BLAST (PSIBLAST) program runs at approximately the same speed per iteration
as gapped BLAST, but in many cases is much more sensitive to weak but biologically relevant sequence similarities. PSI-BLAST
is used to uncover several new and interesting members of the BRCT superfamily.
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 approximately 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.
Tight junction (TJ)-like structures have been reported in Schwann cells, but their molecular composition and physiological function remain elusive. We found that claudin-19, a novel member of the claudin family (TJ adhesion molecules in epithelia), constituted these structures. Claudin-19-deficient mice were generated, and they exhibited behavioral abnormalities that could be attributed to peripheral nervous system deficits. Electrophysiological analyses showed that the claudin-19 deficiency affected the nerve conduction of peripheral myelinated fibers. Interestingly, the overall morphology of Schwann cells lacking claudin-19 expression appeared to be normal not only in the internodal region but also at the node of Ranvier, except that TJs completely disappeared, at least from the outer/inner mesaxons. These findings have indicated that, similar to epithelial cells, Schwann cells also bear claudin-based TJs, and they have also suggested that these TJs are not involved in the polarized morphogenesis but are involved in the electrophysiological "sealing" function of Schwann cells.
NCBI's reference sequence (RefSeq) database (http://www.ncbi.nlm.nih.gov/RefSeq/) is a curated non-redundant collection of sequences representing genomes, transcripts and proteins. The database includes
3774 organisms spanning prokaryotes, eukaryotes and viruses, and has records for 2 879 860 proteins (RefSeq release 19). RefSeq
records integrate information from multiple sources, when additional data are available from those sources and therefore represent
a current description of the sequence and its features. Annotations include coding regions, conserved domains, tRNAs, sequence
tagged sites (STS), variation, references, gene and protein product names, and database cross-references. Sequence is reviewed
and features are added using a combined approach of collaboration and other input from the scientific community, prediction,
propagation from GenBank and curation by NCBI staff. The format of all RefSeq records is validated, and an increasing number
of tests are being applied to evaluate the quality of sequence and annotation, especially in the context of complete genomic
sequence.
The recently-developed statistical method known as the "bootstrap" can be used to place confidence intervals on phylogenies. It involves resampling points from one's own data, with replacement, to create a series of bootstrap samples of the same size as the original data. Each of these is analyzed, and the variation among the resulting estimates taken to indicate the size of the error involved in making estimates from the original data. In the case of phylogenies, it is argued that the proper method of resampling is to keep all of the original species while sampling characters with replacement, under the assumption that the characters have been independently drawn by the systematist and have evolved independently. Majority-rule consensus trees can be used to construct a phylogeny showing all of the inferred monophyletic groups that occurred in a majority of the bootstrap samples. If a group shows up 95% of the time or more, the evidence for it is taken to be statistically significant. Existing computer programs can be used to analyze different bootstrap samples by using weights on the characters, the weight of a character being how many times it was drawn in bootstrap sampling. When all characters are perfectly compatible, as envisioned by Hennig, bootstrap sampling becomes unnecessary; the bootstrap method would show significant evidence for a group if it is defined by three or more characters.
A new method called the neighbor-joining method is proposed for reconstructing phylogenetic trees from evolutionary distance data. The principle of this method is to find pairs of operational taxonomic units (OTUs [= neighbors]) that minimize the total branch length at each stage of clustering of OTUs starting with a starlike tree. The branch lengths as well as the topology of a parsimonious tree can quickly be obtained by using this method. Using computer simulation, we studied the efficiency of this method in obtaining the correct unrooted tree in comparison with that of five other tree-making methods: the unweighted pair group method of analysis, Farris's method, Sattath and Tversky's method, Li's method, and Tateno et al.'s modified Farris method. The new, neighbor-joining method and Sattath and Tversky's method are shown to be generally better than the other methods.
The recently-developed statistical method known as the "bootstrap" can be used to place confidence intervals on phylogenies. It involves resampling points from one's own data, with replacement, to create a series of bootstrap samples of the same size as the original data. Each of these is analyzed, and the variation among the resulting estimates taken to indicate the size of the error involved in making estimates from the original data, In the case of phylogenies, it is argued that the proper method of resampling is to keep all of the original species while sampling characters with replacement, under the assumption that the characters have been independently drawn by the systematist and have evolved independently. Majority-rule consensus trees can be used to construct a phylogeny showing all of the inferred monophyletic groups that occurred in a majority of the bootstrap samples. If a group shows up 95% of the time or more, the evidence for it is taken to be statistically significant. Existing computer programs can be used to analyze different bootstrap samples by using weights on the characters, the weight of a character being how many times it was drawn in bootstrap sampling. When all characters are perfectly compatible, as envisioned by Hennig, bootstrap sampling becomes unnecessary; the bootstrap method would show significant evidence for a group if it is defined by three or more characters.
Entrez Gene (www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=gene) is NCBI's database for gene-specific information. Entrez Gene includes records from genomes that have been completely sequenced,
that have an active research community to contribute gene-specific information or that are scheduled for intense sequence
analysis. The content of Entrez Gene represents the result of both curation and automated integration of data from NCBI's
Reference Sequence project (RefSeq), from collaborating model organism databases and from other databases within NCBI. Records
in Entrez Gene are assigned unique, stable and tracked integers as identifiers. The content (nomenclature, map location, gene
products and their attributes, markers, phenotypes and links to citations, sequences, variation details, maps, expression,
homologs, protein domains and external databases) is provided via interactive browsing through NCBI's Entrez system, via NCBI's
Entrez programing utilities (E-Utilities), and for bulk transfer by ftp.
Whether or not significant amounts of water pass the tight junction (TJ) of leaky epithelia is still unresolved because it is difficult to separate transcellular from TJ-controlled paracellular water flux. Using an alternative approach, we measured transepithelial water flux with and without selective molecular perturbation of the TJ to unequivocally attribute changes to the paracellular pathway. To this end, MDCK C7 cells were stably transfected with either claudin-2 or claudin-10b, two paracellular cation channel-forming TJ proteins, which were not endogenously expressed in that cell line. Claudin-2 is typical for leaky, water-transporting epithelia like proximal tubule, while claudin-10b is present in numerous epithelia, including water-impermeable segments of Henle's loop. Both transfections did not alter the expression of endogenous claudins or aquaporins. Water flux was induced by an osmotic gradient, a Na(+) gradient, or both. Under all conditions, water flux in claudin-2-transfected cells was elevated compared to vector controls, indicating claudin-2-mediated paracellular water permeability. Na(+)-driven water transport in the absence of an osmotic gradient indicates a single-file mechanism. In contrast, claudin-10b transfection did not alter water flux. We conclude that claudin-2, but not claudin-10b, forms a paracellular water channel and by this mediates the paracellular part of water transport in leaky epithelia.
The claudin multigene family encodes tetraspan membrane proteins that are crucial structural and functional components of tight junctions, which have important roles in regulating paracellular permeability and maintaining cell polarity in epithelial and endothelial cell sheets. In mammals, the claudin family consists of 24 members, which exhibit complex tissue-specific patterns of expression. The extracellular loops of claudins from adjacent cells interact with each other to seal the cellular sheet and regulate paracellular transport between the luminal and basolateral spaces. The claudins interact with multiple proteins and are intimately involved in signal transduction to and from the tight junction. Several claudin mouse knockout models have been generated and the diversity of phenotypes observed clearly demonstrates their important roles in the maintenance of tissue integrity in various organs. In addition, mutation of some claudin genes has been causatively associated with human diseases and claudin genes have been found to be deregulated in various cancers. The mechanisms of claudin regulation and their exact roles in normal physiology and disease are being elucidated, but much work remains to be done. The next several years are likely to witness an explosion in our understanding of these proteins, which may, in turn, provide new approaches for the targeted therapy of various diseases.
Claudins are transmembrane tight junction proteins that form paracellular pores. Claudins regulate the permeability of small inorganic ions and are selective on the basis of charge. We have developed an inducible expression system to measure the permeability of claudin-2 and have found that claudin-2 forms highly cation-selective paracellular pores. The basis of this charge selectivity is likely to be the presence of a negatively charged binding site within the lumen of the pore. This may be a general mechanism by which claudins achieve selectivity.
Belt-like tight junctions (TJs), referred to as zonula occludens, have long been regarded as a specialized differentiation of epithelial cell membranes. They are required for cell adhesion and paracellular barrier functions, and are now thought to be partly involved in fence functions and in cell polarization. Recently, the molecular bases of TJs have gradually been unveiled. TJs are constructed by TJ strands, whose basic frameworks are composed of integral membrane proteins with four transmembrane domains, designated claudins. The claudin family is supposedly composed of at least 24 members in mice and humans. Other types of integral membrane proteins with four transmembrane domains, namely occludin and tricellulin, as well as the single transmembrane proteins, JAMs (junctional adhesion molecules) and CAR (coxsackie and adenovirus receptor), are associated with TJ strands, and the high-level organization of TJ strands is likely to be established by membrane-anchored scaffolding proteins, such as ZO-1/2. Recent functional analyses of claudins in cell cultures and in mice have suggested that claudin-based TJs may have pivotal functions in the regulation of the epithelial microenvironment, which is critical for various biological functions such as control of cell proliferation. These represent the dawn of 'Barriology' (defined by Shoichiro Tsukita as the science of barriers in multicellular organisms). Taken together with recent reports regarding changes in claudin expression levels, understanding the regulation of the TJ-based microenvironment system will provide new insights into the regulation of polarization in the respect of epithelial microenvironment system and new viewpoints for developing anticancer strategies.
A new method called the neighbor-joining method is proposed for reconstructing phylogenetic trees from evolutionary distance data. The principle of this method is to find pairs of operational taxonomic units (OTUs [= neighbors]) that minimize the total branch length at each stage of clustering of OTUs starting with a starlike tree. The branch lengths as well as the topology of a parsimonious tree can quickly be obtained by using this method. Using computer simulation, we studied the efficiency of this method in obtaining the correct unrooted tree in comparison with that of five other tree-making methods: the unweighted pair group method of analysis, Farris's method, Sattath and Tversky's method, Li's method, and Tateno et al.'s modified Farris method. The new, neighbor-joining method and Sattath and Tversky's method are shown to be generally better than the other methods.
Two related integral membrane proteins, claudin-1 and -2, recently were identified as novel components of tight junction (TJ) strands. Here, we report six more claudin-like proteins, indicating the existence of a claudin gene family. Three of these were reported previously as RVP1, Clostridium perfringens enterotoxin receptor, and TMVCF, but their physiological functions were not determined. Through similarity searches followed by PCR, we isolated full length cDNAs of mouse RVP1, Clostridium perfringens enterotoxin receptor, and TMVCF as well as three mouse claudin-like proteins and designated them as claudin-3 to -8, respectively. All of these claudin family members showed similar patterns on hydrophilicity plots, which predicted four transmembrane domains in each molecule. Northern blotting showed that the tissue distribution pattern varied significantly, depending on claudin species. Similarly to claudin-1 and -2, when these claudins were HA-tagged and introduced into cultured Madin-Darby canine kidney cells, all showed a tendency to concentrate at TJs. Immunofluorescence and immunoelectron microscopy with polyclonal antibodies specific for claudin-3, -4, or -8 revealed that these molecules were exclusively concentrated at TJs in the liver and/or kidney. These findings indicated that multiple claudin family members are involved in the formation of TJ strands in various tissues.
We describe and validate a new membrane protein topology prediction method, TMHMM, based on a hidden Markov model. We present a detailed analysis of TMHMM's performance, and show that it correctly predicts 97-98 % of the transmembrane helices. Additionally, TMHMM can discriminate between soluble and membrane proteins with both specificity and sensitivity better than 99 %, although the accuracy drops when signal peptides are present. This high degree of accuracy allowed us to predict reliably integral membrane proteins in a large collection of genomes. Based on these predictions, we estimate that 20-30 % of all genes in most genomes encode membrane proteins, which is in agreement with previous estimates. We further discovered that proteins with N(in)-C(in) topologies are strongly preferred in all examined organisms, except Caenorhabditis elegans, where the large number of 7TM receptors increases the counts for N(out)-C(in) topologies. We discuss the possible relevance of this finding for our understanding of membrane protein assembly mechanisms. A TMHMM prediction service is available at http://www.cbs.dtu.dk/services/TMHMM/.
Tight junctions are one mode of cell–cell adhesion in epithelial
and endothelial cellular sheets. They act as a primary barrier to the diffusion
of solutes through the intercellular space, create a boundary between the
apical and the basolateral plasma membrane domains, and recruit various cytoskeletal
as well as signalling molecules at their cytoplasmic surface. New insights
into the molecular architecture of tight junctions allow us to now discuss
the structure and functions of this unique cell–cell adhesion apparatus
in molecular terms.
An amphiphilicity index of amino acid residues was developed for improving the method of transmembrane helix prediction.
The transfer energy of a hydrocarbon stem group beyond the gamma-carbon was calculated from the accessible surface area, and used to index the amphiphilicity of the residue. Non-zero amphiphilicity index values were obtained for lysine, arginine, histidine, glutamic acid, glutamine, tyrosine and tryptophan. Those residues were found to be abundant in the end regions of transmembrane helices, indicating their preference for the membrane-water interface. The moving average of the amphiphilicity index actually showed significant peaks in the end regions of most transmembrane helices. A dispersion diagram of average amphiphilicity index versus average hydrophobicity index was devised to facilitate discrimination of transmembrane helices.
The amphiphilicity index has been incorporated into a system, SOSUI, for the discrimination of membrane proteins and the prdiction of tranmembrane helical regions (http://sosui.proteome.bio.tuat.ac.jp/sosuiframe0.html).
Epithelia separate tissue spaces by regulating the passage of ions, solutes, and water through both the transcellular and paracellular pathways. Paracellular permeability is defined by intercellular tight junctions, which vary widely among tissues with respect to solute flux, electrical resistance, and ionic charge selectivity. To test the hypothesis that members of the claudin family of tight junction proteins create charge selectivity, we assessed the effect of reversing the charge of selected extracellular amino acids in two claudins using site-directed mutagenesis. Claudins were expressed in cultured Madin-Darby canine kidney cell monolayers under an inducible promoter, and clones were compared with and without induction for transmonolayer electrical resistance and dilution potentials. Expression and localization of claudins were determined by immunoblotting, immunofluorescence microscopy, and freeze-fracture electron microscopy. We observed that substituting a negative for a positive charge at position 65 in the first extracellular domain of claudin-4 increased paracellular Na+ permeability. Conversely, substituting positive for negative charges at three positions in the first extracellular domain of claudin-15, singly and in combination, reversed paracellular charge selectivity from a preference for Na+ to Cl-. These results support a model where claudins create charge-selective channels in the paracellular space.
Since the initial report by Ussing and Windhager ([2][1]) in 1964 of an extracellular pathway for ion flow across frog skin, investigators have speculated about the nature of this route. As the evidence accumulated for such “shunt” paths in a wide variety of epithelia, it was apparent that all
Microarray analyses combined with laser-capture microdissection have been applied for risk assessments of gastric cancer as well as for identification of novel genes associated with gastric cancer. EST AA393089 derived from an unknown gene has been reported to be frequently down-regulated in intestinal-type gastric cancer. Here, we identified and characterized the gene corresponding to EST AA393089 by using bioinformatics. EST AA393089 overlapped with BC016047 cDNA, and BC016047 overlapped with EST BM821052. Because the mRNA determined by assembling BM821052 and BC016047 was derived from a novel Claudin (CLDN) family gene, the gene corresponding to EST AA393089 was designated CLDN23. Human CLDN23 mRNA was expressed in germinal center B cells, placenta, stomach as well as in colon tumor. Mouse AK009330 and AK037108 cDNAs were derived from mouse Cldn23 gene. Human CLDN23 (292 aa) and mouse Cldn23 (296 aa) were four-transmembrane proteins, showing 79.5% total-amino-acid identity. WWCC motif, defined by W-X(17-22)-W-X(2)-C-X(8-10)-C, was conserved among four-transmembrane proteins of CLDN family. CLDN23 gene, linked to MFHAS1 and PPP1R3B genes, was mapped to human chromosome 8p23.1. CLDN21, CLDN22, and CLDN24 genes were also identified in this study. CLDN21 and CLDN22 genes were located within human genomic contig NT_022792.13. CLDN24 gene on human chromosome 11q23 was located within human genomic contig NT_033899.3. Among 23 CLDN family genes within the human genome, CLDN1 and CLDN16 genes were clustered on human chromosome 3q28, CLDN3 and CLDN4 on 7q11, CLDN6 and CLDN9 on 16p13.3, CLDN8 and CLDN17 on 21q22.11, CLDN21 and CLDN22 on 4q35.1. This is the first report on comprehensive characterization of CLDN23 gene, a candidate tumor suppressor gene implicated in intestinal-type gastric cancer.
The National Center for Biotechnology Information (NCBI) Reference Sequence (RefSeq) database (http://www.ncbi.nlm.nih.gov/RefSeq/) provides a non-redundant collection of sequences representing genomic data, transcripts and proteins. Although the goal
is to provide a comprehensive dataset representing the complete sequence information for any given species, the database pragmatically
includes sequence data that are currently publicly available in the archival databases. The database incorporates data from
over 2400 organisms and includes over one million proteins representing significant taxonomic diversity spanning prokaryotes,
eukaryotes and viruses. Nucleotide and protein sequences are explicitly linked, and the sequences are linked to other resources
including the NCBI Map Viewer and Gene. Sequences are annotated to include coding regions, conserved domains, variation, references,
names, database cross-references, and other features using a combined approach of collaboration and other input from the scientific
community, automated annotation, propagation from GenBank and curation by NCBI staff.
Tight junctions form continuous intercellular contacts controlling solute movement through the paracellular pathway across epithelia. Paracellular barriers vary among epithelia in electrical resistance and behave as if they are lined with pores that have charge and size selectivity. Recent evidence shows that claudins, a large family (at least 24 members) of intercellular adhesion molecules, form the seal and its variable pore-like properties. This evidence comes from the study of claudins expressed in cultured epithelial cell models, genetically altered mice, and human mutants. We review information on the structure, function, and transcriptional and posttranslational regulation of the claudin family as well as of their evolutionarily distant relatives called the PMP22/EMP/MP20/claudin, or pfam00822, superfamily.
A fundamental question in cell and developmental biology is how epithelial cells construct the diffusion barrier allowing them to separate different body compartments. Formation of tight junction (TJ) strands, which are crucial for this barrier, involves the polymerization of claudins, TJ adhesion molecules, in temporal and spatial manners. ZO-1 and ZO-2 are major PDZ-domain-containing TJ proteins and bind directly to claudins, yet their functional roles are poorly understood. We established cultured epithelial cells (1(ko)/2(kd)) in which the expression of ZO-1/ZO-2 was suppressed by homologous recombination and RNA interference, respectively. These cells were well polarized, except for a complete lack of TJs. When exogenously expressed in 1(ko)/2(kd) cells, ZO-1 and ZO-2 were recruited to junctional areas where claudins were polymerized, but truncated ZO-1 (NZO-1) containing only domains PDZ1-3 was not. When NZO-1 was forcibly recruited to lateral membranes and dimerized, claudins were dramatically polymerized. These findings indicate that ZO-1 and ZO-2 can independently determine whether and where claudins are polymerized.
In an attempt to develop a novel strategy for the identification of new members of protein families by in silico approaches, we have developed a semi-automated procedure of consecutive PSI-BLAST (Position-Specific-Iterated Basic Local Alignment Search Tool) searches incorporating identificiation as well as subsequent validation of putative candidates. For a proof of concept study we chose the search for novel members of the claudin family. The initial step was an iterated PSI-BLAST search starting with the PMP22_Claudin domain of each known member of the claudin family against the human part of the RefSeq Database. Putative new claudin domains derived from the converged list were evaluated by a validating PSI-BLAST in which each sequence was assessed for finding back the starting set of known claudin domains. The local PSI-BLAST searches and validation were automated by a set of PERL scripts. With this strategy a total of three additional putative claudin domains in three different proteins were identified. One of them was subjected to further characterization and was shown to exhibit claudin-like features in terms of protein structure and expression pattern. The strategy we present is an efficient and versatile tool to identify novel members of domain-sharing protein families. Low rates of false positives achieved by inclusion of a validation step into the in silico procedure make this strategy particularly attractive to select candidates for subsequent labor-intensive wet bench characterization.
The Clustal W and Clustal X multiple sequence alignment programs have been completely rewritten in C++. This will facilitate
the further development of the alignment algorithms in the future and has allowed proper porting of the programs to the latest
versions of Linux, Macintosh and Windows operating systems.
Availability: The programs can be run on-line from the EBI web server: http://www.ebi.ac.uk/tools/clustalw2. The source code and executables for Windows, Linux and Macintosh computers are available from the EBI ftp site ftp://ftp.ebi.ac.uk/pub/software/clustalw2/
Contact: clustalw{at}ucd.ie
A high level of structural organization of functional membrane domains in very narrow regions of a plasma membrane is crucial for the functions of plasma membranes and various other cellular functions. Conventional proteomic analyses are based on total soluble cellular proteins. Thus, because of insolubility problems, they have major drawbacks for use in analyses of low-abundance proteins enriched in very limited and specific areas of cells, as well as in analyses of the membrane proteins in two-dimensional gels. We optimized proteomic analyses of cell-cell adhering junctional membrane proteins on gels. First, we increased the purity of cell-cell junctions, which are very limited and specific areas for cell-cell adhesion, from hepatic bile canaliculi. We then enriched junctional membrane proteins via a guanidine treatment; these became selectively detectable on two- dimensionally electrophoresed gels after treatment with an extremely high concentration of NP-40. The framework of major junctional integral membrane proteins was shown on gels. These included six novel junctional membrane proteins of type I, type II, and tetraspanin, which were identified by mass spectrometry and by a database sequence homology search, as well as 12 previously identified junctional membrane proteins, such as cadherins and claudins.
Tight junctions (TJ) regulate paracellular ionic charge selectivity and conductance across epithelial tissues and cell lines. These properties vary among epithelia, and recent evidence implicates the claudins, a family of TJ transmembrane proteins, as important determinants of both characteristics. To test the hypothesis that each claudin contributes a characteristic charge discrimination to the TJ, we expressed claudins-2, -4, -11, and -15 in both cation-selective Madin-Darby canine kidney (MDCK) II cells and in anion-selective LLC-PK1 cells and examined changes in transepithelial electrical resistance (TER) and paracellular charge selectivity. Regulated expression and localization were verified by immunoblot analysis and immunofluorescence microscopy, respectively. Expression of claudin-4 increased TER in both cell lines, whereas effects of the others on TER were variable. Claudin-4 and -11 decreased paracellular permeability for Na+ in MDCK II cells, whereas neither claudin-2 nor -15 had an effect. Conversely, in LLC-PK1 cells, claudin-2 and -15 increased the permeability for Na+, whereas claudin-4 and -11 were without effect. We conclude that the contribution of each claudin is most easily detectable when it reverses the direction of monolayer charge selectivity. These results are consistent with a model in which exogenous claudins add new charge-selective pores, leading to a physiological phenotype that combines endogenous and exogenous contributions. Additionally, it is possible to rationalize the direction of charge selectivity conferred by the individual claudins on the basis of electrostatic effects of the charged amino acids in their first extracellular loops.
l; prediction of membrane protein topology; membrane proteins in genomes; protein structure prediction Introduction The prediction of transmembrane helices in integral membrane proteins is an important aspect of bioinformatics. The most successful methods to date not only predict individual transmembrane helices, but rather attempt to predict the full topology of the protein, i.e. the total number of trans- membrane helices and their in/out orientation relative to the membrane (von Heijne, 1999). Reliable methods for discrimination between mem- brane proteins and soluble proteins and for topology prediction have important applications in genome analysis, and can be used to extract global Present address: B. Lirsson, Department of Quantum Chemistry, AIM Research School, Box 518, SE-75120 Uppsala, Sweden. Abbreviations used: Nin, N terminus inside; Nout, N terminus outside; TM, transmembrane; HMM, hidden Markov model. E-mail address of the corresponding author: krogh@cbs.dtu.dk
Multifunctional strands in tight junctions
- S Tsukita
- M Furuse
- M Itoh
Tsukita, S., Furuse, M. and Itoh, M. (2001) Multifunctional strands in tight
junctions. Nat. Rev. Mol. Cell Biol. 2, 285–293.
Transmembrane protein display software
- S J Johns
Johns, S.J. TOPO2, Transmembrane protein display software. <http://
www.sacs.ucsf.edu/TOPO2/>.
Claudins create charge-selective channels in the paracellular pathway between epithelial cells
- O Colegio
- C Van Itallie
- H Mccrea
- C Rahner
- J M Anderson
Colegio, O., Van Itallie, C., McCrea, H., Rahner, C. and Anderson, J.M. (2002)
Claudins create charge-selective channels in the paracellular pathway
between epithelial cells. Am. J. Physiol. Cell Physiol. 283, C142-C147.
Claudins and epithelial paracellular transport
- Van Itallie
Van Itallie, C.M. and Anderson, J.M. (2006) Claudins and epithelial paracellular
transport. Annu. Rev. Physiol. 68, 403-429.
Claudins create charge-selective channels in the paracellular pathway between epithelial cells
- Colegio
Multifunctional strands in tight junctions
- Tsukita
Tight junction-based epithelial microenvironment and cell proliferation
- Tsukita