Adherens and tight junctions: structure, function and connections to the actin cytoskeleton

Connexin43 modulates cell polarity and directional cell migration by regulating microtubule dynamics

Knockout mice deficient in the gap junction gene connexin43 exhibit developmental anomalies associated with abnormal neural crest, primordial germ cell, and proepicardial cell migration. These migration defects are due to a loss of directional cell movement, and are associated with abnormal actin stress fiber organization and a loss of polarized cell morphology. To elucidate the mechanism by which Cx43 regulates cell polarity, we used a wound closure assays with mouse embryonic fibroblasts (MEFs) to examine polarized cell morphology and directional cell movement. Studies using embryonic fibroblasts from Cx43 knockout (Cx43KO) mice showed Cx43 deficiency caused cell polarity defects as characterized by a failure of the Golgi apparatus and the microtubule organizing center to reorient with the direction of wound closure. Actin stress fibers at the wound edge also failed to appropriately align, and stabilized microtubule (Glu-tubulin) levels were markedly reduced. Forced expression of Cx43 with deletion of its tubulin-binding domain (Cx43dT) in both wildtype MEFs and neural crest cell explants recapitulated the cell migration defects seen in Cx43KO cells. However, forced expression of Cx43 with point mutation causing gap junction channel closure had no effect on cell motility. TIRF imaging revealed increased microtubule instability in Cx43KO cells, and microtubule targeting of membrane localized Cx43 was reduced with expression of Cx43dT construct in wildtype cells. Together, these findings suggest the essential role of Cx43 gap junctions in development is mediated by regulation of the tubulin cytoskeleton and cell polarity by Cx43 via a nonchannel function.

FXYD5 (dysadherin) regulates the paracellular permeability in cultured kidney collecting duct cells

FXYD5 (dysadherin or RIC) is a member of the FXYD family of single-span transmembrane proteins associated with the Na(+)-K(+)-ATPase. Several studies have demonstrated enhanced expression of FXYD5 during metastasis and effects on cell adhesion and motility. The current study examines effects of FXYD5 on the paracellular permeability in the mouse kidney collecting duct cell line M1. Expressing FXYD5 in these cells leads to a large decrease in amiloride-insensitive transepithelial electrical resistance as well as increased permeability to 4-kDa dextran. Impairment of cell-cell contact was also demonstrated by staining cells for the tight and adherence junction markers zonula occludens-1 and β-catenin, respectively. This is further supported by large expansions of the interstitial spaces, visualized in electron microscope images. Expressing FXYD5 in M1 cells resulted in a decrease in N-glycosylation of β1 Na(+)-K(+)-ATPase, while silencing it in H1299 cells had an opposite effect. This may provide a mechanism for the above effects, since normal glycosylation of β1 plays an important role in cell-cell contact formation (Vagin O, Tokhtaeva E, Sachs G. J Biol Chem 281: 39573-39587, 2006).

CRSBP-1/LYVE-1 ligands disrupt lymphatic intercellular adhesion by inducing tyrosine phosphorylation and internalization of VE-cadherin

Cell-surface retention sequence (CRS) binding protein (CRSBP-1) is a membrane glycoprotein identified by its ability to bind PDGF-BB and VEGF-A via their CRS motifs (clusters of basic amino acid residues). CRSBP-1 is identical to LYVE-1 and exhibits dual ligand (CRS-containing proteins and hyaluronic acid) binding activity, suggesting the importance of CRSBP-1 ligands in lymphatic function. Here, we show that CRSBP-1 ligands induce disruption of VE-cadherin-mediated intercellular adhesion and opening of intercellular junctions in lymphatic endothelial cell (LEC) monolayers as determined by immunofluorescence microscopy and Transwell permeability assay. This occurs by interaction with CRSBP-1 in the CRSBP-1-PDGFβR-β-catenin complex, resulting in tyrosine phosphorylation of the complex, dissociation of β-catenin and p120-catenin from VE-cadherin, and internalization of VE-cadherin. Pretreatment of LECs with a PDGFβR kinase inhibitor abolishes ligand-stimulated tyrosine phosphorylation of VE-cadherin, halts the ligand-induced disruption of VE-cadherin intercellular adhesion and blocks the ligand-induced opening of intercellular junctions. These CRSBP-1 ligands also induce opening of lymphatic intercellular junctions that respond to PDGFβR kinase inhibitor in wild-type mice (but not in Crsbp1-null mice) as evidenced by increased transit of injected FITC-dextran and induced edema fluid from the interstitial space into lymphatic vessels. These results disclose a novel mechanism involved in the opening of lymphatic intercellular junctions.

Lowe Syndrome protein OCRL1 supports maturation of polarized epithelial cells

Mutations in the inositol polyphosphate 5-phosphatase OCRL1 cause Lowe Syndrome, leading to cataracts, mental retardation and renal failure. We noted that cell types affected in Lowe Syndrome are highly polarized, and therefore we studied OCRL1 in epithelial cells as they mature from isolated individual cells into polarized sheets and cysts with extensive communication between neighbouring cells. We show that a proportion of OCRL1 targets intercellular junctions at the early stages of their formation, co-localizing both with adherens junctional components and with tight junctional components. Correlating with this distribution, OCRL1 forms complexes with junctional components α-catenin and zonula occludens (ZO)-1/2/3. Depletion of OCRL1 in epithelial cells growing as a sheet inhibits maturation; cells remain flat, fail to polarize apical markers and also show reduced proliferation. The effect on shape is reverted by re-expressed OCRL1 and requires the 5'-phosphatase domain, indicating that down-regulation of 5-phosphorylated inositides is necessary for epithelial development. The effect of OCRL1 in epithelial maturation is seen more strongly in 3-dimensional cultures, where epithelial cells lacking OCRL1 not only fail to form a central lumen, but also do not have the correct intracellular distribution of ZO-1, suggesting that OCRL1 functions early in the maturation of intercellular junctions when cells grow as cysts. A role of OCRL1 in junctions of polarized cells may explain the pattern of organs affected in Lowe Syndrome.

The WASp-based actin polymerization machinery is required in somatic support cells for spermatid maturation and release

WASp family proteins serve as conserved regulators of branched microfilament array formation via the Arp2/3 actin polymerization machinery. We have identified a specific role during spermatogenesis for the Drosophila WASp homolog (Wsp) and associated elements. Spermatogenesis within the fly testis is carried out in cysts, where a pair of somatic cyst cells encloses differentiating sperm. The final phase of the process involves the attachment of matured cysts to a specialized epithelium at the base of the testis, followed by release of individual motile spermatids into the adjoining seminal vesicle. Wsp mutant cysts contain fully mature sperm, but spermatid release does not occur, resulting in male sterility. Our data suggest that the Wsp-Arp2/3-based machinery acts in the cyst cells to influence proper microfilament organization and to enable cyst attachment to the base of the testis. Wsp activity in this context is mediated by the small GTPase Cdc42. Involvement of the cell surface protein Sticks and stones and the Wsp adapter protein D-WIP (Vrp1) is also crucial. In parallel, we demonstrate that N-WASp (Wasl), the major mammalian WASp family protein, is required in the somatic Sertoli cells of the mouse testis for sperm maturation. A requirement for WASp-based activity in somatic support cells therefore appears to be a universal feature of spermatogenesis.

Evans blue as a selective dye marker for white-light diagnosis of non-muscle-invasive bladder cancer: an in vitro study

OBJECTIVE

To develop a diagnostic method relying on the preferential accumulation of a dye in non-muscle-invasive bladder cancer (NMIBC) that is visible in conjunction with white-light cystoscopy (WLC).

MATERIALS AND METHODS

We investigated in detail the permeation of Evans blue in urothelial cell carcinoma (UCC) spheroids prepared from T24, J82 and RT-112 human cell lines and spheroids composed of normal human urothelial (NHU) cells. To gain more insight into the differential accumulation, all spheroids were investigated ultrastructurally using transmission electron microscopy (TEM).

RESULTS

We found that, after exposure to Evans blue for 2 h, UCC spheroids accumulated dramatically more dye than spheroids composed of NHU cells. Using TEM it was found that the malignant spheroids contain similar ultrastructural characteristics, i.e. a wide intercellular space and a decreased number of desmosome-like cell attachments, to those from clinical samples of non-papillary carcinoma in situ of the bladder.

CONCLUSION

We believe the present findings could be important for future developments in clinical diagnostics for early bladder cancer detection, staging and grading involving WLC.

The connexin43 carboxyl terminus and cardiac gap junction organization

The precise spatial order of gap junctions at intercalated disks in adult ventricular myocardium is thought vital for maintaining cardiac synchrony. Breakdown or remodeling of this order is a hallmark of arrhythmic disease of the heart. The principal component of gap junction channels between ventricular cardiomyocytes is connexin43 (Cx43). Protein-protein interactions and modifications of the carboxyl-terminus of Cx43 are key determinants of gap junction function, size, distribution and organization during normal development and in disease processes. Here, we review data on the role of proteins interacting with the Cx43 carboxyl-terminus in the regulation of cardiac gap junction organization, with particular emphasis on Zonula Occludens-1. The rapid progress in this area suggests that in coming years we are likely to develop a fuller understanding of the molecular mechanisms causing pathologic remodeling of gap junctions. With these advances come the promise of novel approach to the treatment of arrhythmia and the prevention of sudden cardiac death. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.

Stem cell property epithelial-to-mesenchymal transition is a core transcriptional network for predicting cetuximab (Erbitux™) efficacy in KRAS wild-type tumor cells

Beyond a well-recognized effect of KRAS mutations in determining de novo inefficacy of cetuximab (CTX) in metastatic colorectal cancer, we urgently need a biomarker signature for predicting CTX efficacy in KRAS wild-type (WT) tumors. CTX-adapted EGFR gene-amplified KRAS WT tumor cell populations were induced by stepwise-chronic exposure of A431 epidermoid cancer cells to CTX. Genome-wide analyses of 44K Agilent's whole human arrays were bioinformatically evaluated by Gene Set Enrichment Analysis (GSEA)-based screening of the KEGG pathway database. Molecular functioning of CTX was found to depend on: (i) The occurrence of a positive feedback loop on Epidermal Growth Factor Receptor (EGFR) activation driven by genes coding for EGFR ligands (e.g., amphiregulin); (ii) the lack of a negative feedback on mitogen-activated protein kinase (MAPK) activation regulated by dual-specificity phosphatases (e.g., DUSP6) and; (iii) the transcriptional status of gene pathways controlling the epithelial-to-mesenchymal transition (EMT) and its reversal (MET) program (actin cytoskeleton and cell-cell communication-e.g., keratins-focal adhesion signaling-e.g., integrins-and EMT-inducing cytokines - e.g., transforming growth factor-β). Quantitative real-time PCR, high-content immunostaining, and flow-cytometry analyses confirmed that CTX efficacy depends on its ability to promote: (i) Stronger cell-cell contacts by up-regulating the expression of the epithelial markers E-cadherin and occludin; (ii) down-regulation of the epithelial transcriptional repressors Zeb, Snail, and Slug accompanied by restoration of cortical F-actin; and (iii) complete prevention of the CD44(pos)/CD24(neg/low) mesenchymal immunophenotype. The impact of EGFR ligands/MAPK phosphatases gene transcripts in predicting CTX efficacy in KRAS WT tumors may be tightly linked with the ability of CTX to concurrently reverse the EMT status, a pivotal property of migrating cancer stem cells.

Connexin 43 gap junction plaque endocytosis implies molecular remodelling of ZO-1 and c-Src partners

Gap junctions, through their constitutive proteins, connexins (Cx), are involved in several processes including regulation of cellular proliferation, tissue differentiation, homeostasis and neoplasic transformation. Internalization of the gap junction plaque to form annular gap junction is a dynamic process, which present similarities with endocytosis, and participates in the control of gap junction coupling. Cx43 exhibits dynamic trafficking that needs sequential implication of a large number of protein partners. We have recently shown that ZO-1 localized in both sides of the gap junction plaque was restricted to one side during internalization. The dissociation between ZO-1 and Cx43 particularly occurred on the face where c-Src specifically associated with Cx43 and was abnormally accelerated in response to a carcinogen. In this addendum we summarize and further discuss these results.

Adherens junction proteins in the hamster uterus: their contributions to the success of implantation

The adherens junction (AJ) is important for maintaining uterine structural integrity, composition of the luminal environment, and initiation of implantation by virtue of its properties of cell-cell recognition, adhesion, and establishment of cell polarity and permeability barriers. In this study, we investigated the uterine changes of AJ components E-cadherin, beta-catenin, and alpha-catenin at their mRNA and protein levels, together with the cellular distribution of meprinbeta, phospho-beta-catenin, and active beta-catenin proteins, in hamsters that show only ovarian progesterone-dependent uterine receptivity and implantation. By in situ hybridization and immunofluorescence, we have demonstrated that uterine epithelial cells expressed three of these AJ proteins and their mRNAs prior to and during the initial phase of implantation. Immunofluorescence study showed no change in epithelial expression patterns of uterine AJ proteins from Days 1 to 5 of pregnancy. With advancement of the implantation process, AJ components were primarily expressed in cells of the secondary decidual zone (SDZ), but not in the primary decidual zone (PDZ). In contrast, we noted strong expression of beta-catenin and alpha-catenin proteins in the PDZ, but not in the SDZ, of mice. Taken together, these results suggest that AJ proteins contribute to uterine barrier functions by cell-cell adhesion to ensure protection of the embryo. In addition, cleavage of E-cadherin by meprinbeta might contribute to weakening uterine epithelial cell-cell contact for blastocyst implantation. We also report that the nuclear localization of active beta-catenin from Day 4 onward in hamsters implies that beta-catenin/Wnt-signal transduction is activated in the uterus during implantation and decidualization.

Hypertonic stress promotes the upregulation and phosphorylation of zonula occludens 1

Tight junction molecules form a barrier between adjacent cells and mediate the cells' ability to develop membranes that constitute boundaries of different compartments within the body. Membranes with selective ion and water passage are important for the electrolyte and water homeostasis in the kidney. Due to their role in the urinary concentration process, renal medullary cells are exposed to hyperosmotic stress. Therefore, we were interested in the question of how mouse inner medullary collecting duct cells (mIMCD3) manage to maintain their cell-cell contacts, despite hypertonicity-induced cell shrinkage. Employing mRNA expression analysis, we found that the zonula occludens type 1 (Zo-1), multi-PDZ domain protein 1 (MUPP1) and cortactin mRNA levels were upregulated in a tonicity-dependent manner. Using Western blot analysis, immunoprecipitation and immunofluorescence, we show that the Zo-1 protein is upregulated, phosphorylated and linked to the actin cytoskeleton in response to hypertonic stress. After cell exposure to hypertonicity, rearrangement of the actin cytoskeleton resulted in a stronger colocalization of actin fibres with Zo-1. Urea, which generates hyperosmolality, but no transcellular gradient, did not induce changes in Zo-1 protein expression or actin rearrangement. This data indicates that Zo-1 is a response protein to inner medullary tonicity and that extracellular stressors can promote Zo-1 protein expression, tyrosine phosphorylation and cytoskeleton association.

Increased CK5/CK8-positive intermediate cells with stromal smooth muscle cell atrophy in the mice lacking prostate epithelial androgen receptor

Results from tissue recombination experiments documented well that stromal androgen receptor (AR) plays essential roles in prostate development, but epithelial AR has little roles in prostate development. Using cell specific knockout AR strategy, we generated pes-ARKO mouse with knock out of AR only in the prostate epithelial cells and demonstrated that epithelial AR might also play important roles in the development of prostate gland. We found mice lacking the prostate epithelial AR have increased apoptosis in epithelial CK8-positive luminal cells and increased proliferation in epithelial CK5-positive basal cells. The consequences of these two contrasting results could then lead to the expansion of CK5/CK8-positive intermediate cells, accompanied by stromal atrophy and impaired ductal morphogenesis. Molecular mechanism dissection found AR target gene, TGF-β₁, might play important roles in this epithelial AR-to-stromal morphogenesis modulation. Collectively, these results provided novel information relevant to epithelial AR functions in epithelial-stromal interactions during the development of normal prostate, and suggested AR could also function as suppressor in selective cells within prostate.

Spectrin-adducin membrane skeleton: A missing link between epithelial junctions and the actin cytoskeletion?

Adherens junctions (AJs) and tight junctions (TJs) represent key adhesive structures that regulate the apico-basal polarity and barrier properties of epithelial layers. AJs and TJs readily undergo disassembly and reassembly during normal tissue remodeling and disruption of epithelial barriers in diseases. Such junctional plasticity depends on the orchestrated dynamics of the plasma membrane with its underlying F-actin cytoskeleton, however the interplay between these cellular structures remains poorly understood. Recent studies highlighted the spectrin-adducin-based membrane skeleton as an emerging regulator of AJ and TJ integrity and remodeling. Here we discuss new evidences implicating adducin, spectrin and other membrane skeleton proteins in stabilization of epithelial junctions and regulation of junctional dynamics. Based on the known ability of the membrane skeleton to link cortical actin filaments to the plasma membrane, we hypothesize that the spectrin-adducin network serves as a critical signal and force transducer from the actomyosin cytoskeleton to junctions during remodeling of AJs and TJs.

Should I stay or should I go? Shedding of RPTPs in cancer cells switches signals from stabilizing cell-cell adhesion to driving cell migration

Dissolution of cell-cell adhesive contacts and increased cell-extracellular matrix adhesion are hallmarks of the migratory and invasive phenotype of cancer cells. These changes are facilitated by growth factor binding to receptor protein tyrosine kinases (RTKs). In normal cells, cell-cell adhesion molecules (CAMs), including some receptor protein tyrosine phosphatases (RPTPs), antagonize RTK signaling by promoting adhesion over migration. In cancer, RTK signaling is constitutive due to mutated or amplified RTKs, which leads to growth factor independence, or autonomy. An alternative route for a tumor cell to achieve autonomy is to inactivate cell-cell CAMs such as RPTPs. RPTPs directly mediate cell adhesion and regulate both cadherin-dependent adhesion and signaling. In addition, RPTPs antagonize RTK signaling by dephosphorylating molecules activated following ligand binding. Both RPTPs and cadherins are downregulated in tumor cells by cleavage at the cell surface. This results in shedding of the extracellular, adhesive segment and displacement of the intracellular segment, altering its subcellular localization and access to substrates or binding partners. In this commentary we discuss the signals that are altered following RPTP and cadherin cleavage to promote cell migration. Tumor cells both step on the gas (RTKs) and disconnect the brakes (RPTPs and cadherins) during their invasive and metastatic journey.

The blood-testis barrier: the junctional permeability, the proteins and the lipids

The elucidation of how individual components of the Sertoli cell junctional complexes form and are dismantled to allow not only individual cells but whole syncytia of germinal cells to migrate from the basal to the lumenal compartment of the seminiferous epithelium without causing a permeability leak in the blood-testis barrier is amongst the most enigmatic yet, challenging and timely questions in testicular physiology. The intriguing key event in this process is how the barrier modulates its permeability during the periods of formation and dismantling of individual Sertoli cell junctions. The purpose of this review is therefore to first provide a reliable account on the normal formation, maintenance and dismantling process of the Sertoli cells junctions, then to assess the influence of the expression of their individual proteins, of the cytoskeleton associated with the junctions, and of the lipid content in the seminiferous tubules on the regulation of the their permeability barrier function. To help focus on the formation and dismantling of the Sertoli cell junctions, several considerations are based on data gleaned not only from rodents but from seasonal breeders as well because these animal models are characterized by exhaustive periods of junction assembly during development and the onset of the seasonal re-initiation of spermatogenesis as well as by an extensive junction dismantling period at the beginning of testicular regression, something unavailable in normal physiological conditions in continual breeders. Thus, the modulation of the permeability barrier function of the Sertoli cell junctions is analyzed in the physiological context of the blood-epidydimis barrier and in particular of the blood-testis barrier rather than in the context of a detailed account of the molecular composition and signalisation pathways of cell junctions. Moreover, the considerations discussed in this review are based on measurements performed on seminiferous tubule-enriched fractions gleaned at regular time intervals during development and the annual reproductive cycle.

Rack1 promotes epithelial cell-cell adhesion by regulating E-cadherin endocytosis

E-cadherin and its cytoplasmic partners, catenins, mediate epithelial cell-cell adhesion. Disruption of this adhesion allows cancer cells to invade and metastasize. Aberrant activation of the Src tyrosine kinase disrupts cell-cell contacts through an E-cadherin/catenin-dependent mechanism. Previously we showed that Rack1 regulates the growth of colon cells by suppressing Src activity at G(1) and mitotic checkpoints, and in the intrinsic apoptotic and Akt cell survival pathways. Here we show that Rack1, partly by inhibiting Src, promotes cell-cell adhesion and reduces the invasive potential of colon cancer cells. Rack1 stabilizes E-cadherin and catenins at cell-cell contacts by inhibiting the Src phosphorylation of E-cadherin, the ubiquitination of E-cadherin by the E3 ligase Hakai and the endocytosis of E-cadherin. Upon depletion and restoration of extracellular calcium, Rack1 facilitates the re-assembly of E-cadherin-containing cell-cell contacts. Rack1 also blocks HGF-induced endocytosis of E-cadherin, disruption of cell-cell contacts and cell scatter. Our results uncover a novel function of Rack1 in maintaining the junctional homeostasis of intestinal epithelial cells by regulation of the Src- and growth factor-induced endocytosis of E-cadherin.

Integration of tight junctions and claudins with the barrier functions of the retinal pigment epithelium

The retinal pigment epithelium (RPE) forms the outer blood-retinal barrier by regulating the movement of solutes between the fenestrated capillaries of the choroid and the photoreceptor layer of the retina. Blood-tissue barriers use various mechanisms to accomplish their tasks including membrane pumps, transporters, and channels, transcytosis, metabolic alteration of solutes in transit, and passive but selective diffusion. The last category includes tight junctions, which regulate transepithelial diffusion through the spaces between neighboring cells of the monolayer. Tight junctions are extraordinarily complex structures that are dynamically regulated. Claudins are a family of tight junctional proteins that lend tissue specificity and selectivity to tight junctions. This review discusses how the claudins and tight junctions of the RPE differ from other epithelia and how its functions are modulated by the neural retina. Studies of RPE-retinal interactions during development lend insight into this modulation. Notably, the characteristics of RPE junctions, such as claudin composition, vary among species, which suggests the physiology of the outer retina may also vary. Comparative studies of barrier functions among species should deepen our understanding of how homeostasis is maintained in the outer retina. Stem cells provide a way to extend these studies of RPE-retinal interactions to human RPE.

Role of E-cadherin in the pathogenesis of gastroesophageal reflux disease

OBJECTIVES

An early event in the pathogenesis of gastroesophageal reflux disease (GERD) is an acid-induced increase in junctional (paracellular) permeability in esophageal epithelium (EE). The molecular events that account for this change are unknown. E-cadherin is a junctional protein important in barrier function in EE. Therefore, defects in barrier function in EE were sought in GERD as well as whether their presence correlated with abnormalities in e-cadherin.

METHODS

Endoscopic biopsies of EE from GERD (n=20; male 10; female 10; mean age 50 ± 10 years) and subjects with a healthy esophagus (controls; n=23; male 11; female 12; mean age 51 ± 11 years) were evaluated in mini-Ussing chambers and by western blot and immunochemistry; and serum analyzed by enzyme-linked immunosorbent assay (ELISA). A role for e-cadherin was also assessed using a unique conditional knockout of e-cadherin in adult mouse esophagus.

RESULTS

EE from GERD patients had lower electrical resistance and higher fluorescein flux than EE from controls; and the findings in GERD associated with cleavage of e-cadherin. Cleavage of e-cadherin in GERD was documented in EE by the presence of a 35-kDa, C-terminal fragment of the molecule on western blot and by an increase in soluble N-terminal fragments of the molecule in serum. Activation of the membrane metalloproteinase, A Disintegrin And Metalloproteinase (ADAM-10), was identified as a likely cause for cleavage of e-cadherin by western blot and immunostaining and a role for e-cadherin in the increased junctional permeability in EE from GERD supported by showing increased permeability after deletion of e-cadherin in mouse EE.

CONCLUSIONS

The EE in GERD has increased junctional permeability and this is in association with proteolytic cleavage of e-cadherin. As loss of e-cadherin can, alone, account for the increase in junctional permeability, cleavage of e-cadherin likely represents a critical molecular event in the pathogenesis of GERD, and identification of cleaved fragments may, if confirmed in larger studies, be valuable as a biomarker of GERD.

The protease allergen Pen c 13 induces allergic airway inflammation and changes in epithelial barrier integrity and function in a murine model

Fungal allergens are associated with the development of asthma, and some have been characterized as proteases. Here, we established an animal model of allergic airway inflammation in response to continuous exposure to proteolytically active Pen c 13, a major allergen secreted by Penicillium citrinum. In functional analyses, Pen c 13 exposure led to increased airway hyperresponsiveness, significant inflammatory cell infiltration, mucus overproduction, and collagen deposition in the lung, dramatically elevated serum levels of total IgE and Pen c 13-specific IgE and IgG1, and increased production of the Th2 cytokines IL-4, IL-5, and IL-13 by splenocytes stimulated in vitro with Pen c 13. To examine the mechanisms involved in the regulation of allergenicity by Pen c 13, we performed two-dimensional fluorescence difference gel electrophoresis analysis combined with nano-LC-MS/MS, followed by bioinformatics analysis to identify potential targets that associated with allergic inflammation, which suggested that galectin-3 and laminin might be involved in novel pathogenic mechanisms. Finally, we focused on junctional proteins between cells, because, in addition to opening of the epithelial barrier by environmental proteases possibly being the initial step in the development of asthma, these proteins are also associated with actin rearrangement. Taken together, our findings indicate that Pen c 13 exposure causes junctional structure alterations and actin cytoskeletal rearrangements, resulting in increased permeability and airway structural changes. These effects probably change the lung microenvironment and foster the development of allergic sensitization.

Dynamics of zonula occludens-2 expression during preimplantation embryonic development in the hamster

The objective was to study the expression of zonula occludens-2, a tight junction protein, during preimplantation hamster embryonic development, to predict its possible localization, source, and roles in trophectoderm differentiation and blastocyst formation in this species. Comparison of zonula occludens-2 expression pattern between the hamster and mouse preimplantation embryos from the zygote up to the blastocyst stage was also an objective of this study. Zonula occludens-2 localization was noted in nuclei of blastomeres in all stages of hamster and mouse embryonic development. Compared to mice, where zonula occludens-2 was first localized in the interblastomere membrane at the morula stage, hamster embryos had membranous zonula occludens-2 localization from the 2-cell stage onwards. Based on combined results of immunolocalization study in parthenogenic embryos and ovarian and epididymal sections, and quantitative PCR done in oocytes and all developmental stages of preimplantation embryos, perhaps there was a carry-over of zonula occludens-2 proteins or mRNA from the dam to the embryo. Based on these findings, we inferred that maternally derived zonula occludens-2 was involved in nuclear functions, as well as differentiation of blastomeres and blastocoel formation during preimplantation embryonic development in the hamster.

Review: molecular pathogenesis of blood-brain barrier breakdown in acute brain injury

Historically, the blood-brain barrier (BBB) was considered to be at the level of cerebral endothelium. Currently, the interaction of endothelium with other components of the vessel wall and with neurones and glial cells is considered to constitute a functional unit, termed the neurovascular unit that maintains cerebral homeostasis in steady states and brain injury. The emphasis of this review is on cerebral endothelium, the best-studied component of the neurovascular unit, and its permeability mechanisms in health and acute brain injury. Major advances have been made in unravelling the molecular structure of caveolae and tight junctions, both of which are components of the structural barrier to the entry of plasma proteins into brain. Time course studies suggest that caveolar changes precede junctional changes in acute brain injury. Additional factors modulating BBB permeability in acute brain injury are matrix metalloproteinases-2 and 9 and angiogenic factors, the most notable being vascular endothelial growth factor-A and angiopoietins (Ang) 1 and 2. Vascular endothelial growth factor-A and Ang2 have emerged as potent inducers of BBB breakdown while Ang1 is a potent anti-leakage factor. These factors have the potential to modulate permeability in acute brain injury and this is an area of ongoing research. Overall, a combination of haemodynamic, structural and molecular alterations affecting brain endothelium results in BBB breakdown in acute brain injury.

Epithelial cell polarity and tumorigenesis: new perspectives for cancer detection and treatment

Loss of cell-cell adhesion and cell polarity is commonly observed in tumors of epithelial origin and correlates with their invasion into adjacent tissues and formation of metastases. Growing evidence indicates that loss of cell polarity and cell-cell adhesion may also be important in early stage of cancer. In first part of this review, we delineate the current understanding of the mechanisms that establish and maintain the polarity of epithelial tissues and discuss the involvement of cell polarity and apical junctional complex components in tumor pathogenesis. In the second part we address the clinical significance of cell polarity and junctional complex components in cancer diagnosis and prognosis. Finally, we explore their potential use as therapeutic targets in the treatment of cancer.

Salmonella Interaction with and Passage through the Intestinal Mucosa: Through the Lens of the Organism

Salmonella enterica serotypes are invasive enteric pathogens spread through fecal contamination of food and water sources, and represent a constant public health threat around the world. The symptoms associated with salmonellosis and typhoid disease are largely due to the host response to invading Salmonella, and to the mechanisms these bacteria employ to survive in the presence of, and invade through the intestinal mucosal epithelia. Surmounting this barrier is required for survival within the host, as well as for further dissemination throughout the body, and subsequent systemic disease. In this review, we highlight some of the major hurdles Salmonella must overcome upon encountering the intestinal mucosal epithelial barrier, and examine how these bacteria surmount and exploit host defense mechanisms.

MMP20 cleaves E-cadherin and influences ameloblast development

Dental enamel development occurs in stages as observed by the changing morphology of the ameloblasts that are responsible for enamel formation. During the secretory stage of development, proteins including MMP20 are secreted into the enamel matrix. MMP20 is required for proper enamel formation as mutation of the Mmp20 gene causes autosomal recessive amelogenesis imperfecta. Here, we examined in detail the morphology of the Mmp20-null ameloblast cell layer. Intriguingly, we found that the Mmp20-null mouse secretory stage ameloblasts retract their Tomes' processes as if preparing to enter the maturation stage but later reextend their Tomes' processes as if resuming the secretory stage. We also demonstrated that MMP20 cleaves epithelial cadherin, i.e. E-cadherin. Cadherins are transmembrane proteins with extracellular domains that provide adhesive contacts between neighboring cells. Their intracellular domains bind to the cell cytoskeleton through catenins, including β-catenin. When specific MMPs cleave the cadherin extracellular domain, β-catenin is released and may locate to the cell nucleus as a transcription factor. Therefore, MMP20 may influence ameloblast developmental progression through hydrolysis of cadherin extracellular domains with associated release of transcription factor(s).

Quantification of the forces driving self-assembly of three-dimensional microtissues

In a nonadhesive environment, cells will self-assemble into microtissues, a process relevant to tissue engineering. Although this has been recognized for some time, there is no basis for quantitative characterization of this complex process. Here we describe a recently developed assay designed to quantify aspects of the process and discuss its application in comparing behaviors between cell types. Cells were seeded in nonadhesive micromolded wells, each well with a circular trough at its base formed by the cylindrical sidewalls and by a central peg in the form of a right circular cone. Cells settled into the trough and coalesced into a toroid, which was then driven up the conical peg by the forces of self-assembly. The mass of the toroid and its rate of upward movement were used to calculate the cell power expended in the process against gravity. The power of the toroid was found to be 0.31 ± 0.01 pJ/h and 4.3 ± 1.7 pJ/h for hepatocyte cells and fibroblasts, respectively. Blocking Rho kinase by means of Y-27632 resulted in a 50% and greater reduction in power expended by each type of toroid, indicating that cytoskeletal-mediated contraction plays a significant role in the self-assembly of both cell types. Whereas the driving force for self-assembly has often been viewed as the binding of surface proteins, these data show that cellular contraction is important for cell-cell adhesion. The power measurement quantifies the contribution of cell contraction, and will be useful for understanding the concerted action of the mechanisms that drive self-assembly.

Loss of Smad5 leads to the disassembly of the apical junctional complex and increased susceptibility to experimental colitis

The regulation of intestinal epithelial cell adhesion and migratory properties is often compromised in inflammatory bowel disease (IBD). Despite an increasing interest in bone morphogenetic protein (Bmp) signaling in gut pathologies, little is known of the specific roles played by individual Smads in intestinal epithelial functions. In the present study, we generated a mouse model with deletion of Smad5 transcriptional effector of the Bmp signaling pathway exclusively in the intestinal epithelium. Proliferation, migration, and apical junctional complex (AJC) protein expression were analyzed by immunofluorescence and Western blot. Human intestinal biopsies from control and IBD patients were analyzed for SMAD5 gene transcript expression by quantitative PCR (qPCR). Smad5(ΔIEC) and control mice were subjected to dextran sulfate sodium (DSS)-induced experimental colitis, and their clinical and histological symptoms were assessed. Loss of Smad5 led to intestinal epithelial hypermigration and deregulation of the expression of claudin-1 and claudin-2. E-cadherin was found to be equally expressed but displaced from the AJC to the cytoplasm in Smad5(ΔIEC) mice. Analysis of SMAD5 gene expression in human IBD patient samples revealed a significant downregulation of the gene transcript in Crohn's disease and ulcerative colitis samples. Smad5(ΔIEC) mice exposed to experimental DSS colitis were significantly more susceptible to the disease and had impaired wound healing during the recovery phase. Our results support that Smad5 is partly responsible for mediating Bmp signals in intestinal epithelial cells. In addition, deficiency in epithelial Smad5 leads to the deregulation of cell migration by disassembling the AJC with increasing susceptibility to experimental colitis and impairment in wound healing.

Adhesion molecule signalling: not always a sticky business

The signalling activity of cell adhesion molecules (CAMs) such as cadherins, immunoglobulin-like CAMs or integrins has long been considered to be a direct consequence of their adhesive properties. However, there are physiological and pathological processes that reduce or even abrogate the adhesive properties of CAMs, such as cleavage, conformational changes, mutations and shedding. In some cases these 'adhesion deficient' CAMs still retain signalling properties through their cytoplasmic domains and/or their mutated or truncated extracellular domains. The ability of CAMs to activate signal transduction cascades in the absence of cell adhesion significantly extends their range of biological activities.

The function of e-cadherin in stem cell pluripotency and self-renewal

Embryonic stem (ES) and induced-pluripotent stem (iPS) cells can be grown indefinitely under appropriate conditions whilst retaining the ability to differentiate to cells representative of the three primary germ layers. Such cells have the potential to revolutionize medicine by offering treatment options for a wide range of diseases and disorders as well as providing a model system for elucidating mechanisms involved in development and disease. In recent years, evidence for the function of E-cadherin in regulating pluripotent and self-renewal signaling pathways in ES and iPS cells has emerged. In this review, we discuss the function of E-cadherin and its interacting partners in the context of development and disease. We then describe relevant literature highlighting the function of E-cadherin in establishing and maintaining pluripotent and self-renewal properties of ES and iPS cells. In addition, we present experimental data demonstrating that exposure of human ES cells to the E-cadherin neutralizing antibody SHE78.7 allows culture of these cells in the absence of FGF2-supplemented medium.

Yersinia enterocolitica induces epithelial barrier dysfunction through regional tight junction changes in colonic HT-29/B6 cell monolayers

Yersinia enterocolitica is a common cause of acute gastroenteritis. This study aimed to clarify the mechanisms leading to barrier dysfunction and diarrhea. Exposure of human colonic HT-29/B6 cells to Y. enterocolitica resulted in a decrease in transepithelial resistance from 404±23 to 163±21 Ω cm² (P<0.001) in parallel with an increase in mannitol (182 Da) and fluorescein (332 Da) permeability, whereas short circuit current did not change. This effect was time dependent, required the presence of living bacteria, could not be triggered by bacterial supernatants and was not due to Yersinia outer proteins. Concomitantly, Y. enterocolitica induced necrosis as indicated by an increase in lactate dehydrogenase-release, whereas epithelial apoptosis was not upregulated. Local changes in conductivity were detected by conductance scanning, indicating 'leaky regions' within the epithelium that were visualized by biotinylation and confocal microscopy. In these regions, claudin-3 and -4 and, especially claudin-8, were redistributed off the tight junction (TJ) into the cytoplasm. In addition, the expression of claudin-2, -3, -8, -10 and ZO-1 was diminished as quantified by immunoblotting. Moreover, we found claudin-8 to be regulated by the c-Jun N-terminal kinase, the inhibition of which attenuated the Y. enterocolitica-induced decrease in transepithelial resistance and restored claudin-8 protein level. In conclusion, barrier dysfunction in Y. enterocolitica infection is due to circumscribed epithelial TJ protein changes and necrotic cell loss, as a consequence of which leak flux diarrhea and antigen-uptake provoking extraintestinal arthritis may be triggered.

Mesothelium of the murine allantois exhibits distinct regional properties

The rodent allantois is thought to be unique amongst mammals in not having an endodermal component. Here, we have investigated the mesothelium, or outer surface, of murine umbilical precursor tissue, the allantois (∼7.25-8.5 days postcoitum, dpc) to discover whether it exhibits the properties of an epithelium. A combination of morphology, challenge with biotinylated dextran amines (BDAs), and immunohistochemistry revealed that the mesothelium of the mouse allantois exhibits distinct regional properties. By headfold stages (∼7.75-8.0 dpc), distal mesothelium was generally squamous in shape, and highly permeable to BDA challenge, whereas ventral proximal mesothelium, referred to as "ventral cuboidal mesothelium" (VCM) for the characteristic cuboidal shape of its cells, was relatively impermeable. Although "dorsal cuboidal mesothelium" (DCM) resembled the VCM in cell shape, its permeability to BDA was intermediate between the other two regions. Results of immunostaining for Zonula Occludens-1 (ZO-1) and Epithelial-cadherin (E-cadherin), together with transmission electron microscopy (TEM), suggested that impermeability in the VCM may be due to greater cellular contact area between cells and close packing rather than to maturity of tight junctions, the latter of which, by comparison with the visceral yolk sac, appeared to be rare or absent from the allantoic surface. Both VCM and DCM exhibited an ultrastructure more favorable for protein synthesis than did the distal squamous mesothelium; however, at most stages, VCM exhibited robust afadin (AF-6), whereas the DCM uniquely contained alpha-4-integrin. These observations demonstrate that the allantoic mesothelium is not a conventional epithelium but possesses regional ultrastructural, functional and molecular differences that may play important roles in the correct deployment of the umbilical cord and its associated vascular, hematopoietic, and other cell types.

Glut1/SLC2A1 is crucial for the development of the blood-brain barrier in vivo

OBJECTIVE

The overall permeability of the blood-brain barrier (BBB) is regulated by specialized cerebral endothelial cells and their junctional complexes, consisting of adherens junctions (AJs) and tight junctions (TJs). Among the members of the glucose transporters (Glut), Glut1 is a unique molecule expressed in the cerebral endothelial cells. Glut1 and the junctional proteins are concomitantly downregulated in situations in which breakdown of the BBB has taken place. We hypothesized that the expression of Glut1 may play a significant role in the development of the cerebral microvasculature with BBB properties. To date, there is no information on the role of Glut1 during the development of BBB. In the present study, the in vivo effects of Glut1 knockdown on the cerebral vascular development were investigated.

METHODS

Zebrafish was used as a model organism. We confirmed that the structure of the zebrafish homologue of Glut1 is highly similar to the human Glut1 and that the function of the Glut1-mediated cerebral uptake of glucose is evolutionally conserved.

RESULTS

In the Glut1 knockdown model, we observed loss of the cerebral endothelial cells, with concomitant downregulation of the junctional proteins important for intactness of the AJs/TJs and impaired cerebral circulation. The resulting leaky BBB caused vasogenic brain edema.

INTERPRETATION

The data suggest a crucial role of Glut1 in the development of the cerebral endothelial cells with BBB properties in vivo. The findings suggest that modulation of Glut1 expression and function may open new directions of research for therapeutic strategies to prevent vasogenic brain edema.

Structure and function of ABCG2-rich extracellular vesicles mediating multidrug resistance

Multidrug resistance (MDR) is a major impediment to curative cancer chemotherapy. The ATP-Binding Cassette transporters ABCG2, ABCB1 and ABCC2 form a unique defense network against multiple structurally and functionally distinct chemotherapeutics, thereby resulting in MDR. Thus, deciphering novel mechanisms of MDR and their overcoming is a major goal of cancer research. Recently we have shown that overexpression of ABCG2 in the membrane of novel extracellular vesicles (EVs) in breast cancer cells results in mitoxantrone resistance due to its dramatic sequestration in EVs. However, nothing is known about EVs structure, biogenesis and their ability to concentrate multiple antitumor agents. To this end, we here found that EVs are structural and functional homologues of bile canaliculi, are apically localized, sealed structures reinforced by an actin-based cytoskeleton and secluded from the extracellular milieu by the tight junction proteins occludin and ZO-1. Apart from ABCG2, ABCB1 and ABCC2 were also selectively targeted to the membrane of EVs. Moreover, Ezrin-Radixin-Moesin protein complex selectively localized to the border of the EVs membrane, suggesting a key role for the tethering of MDR pumps to the actin cytoskeleton. The ability of EVs to concentrate and sequester different antitumor drugs was also explored. Taking advantage of the endogenous fluorescence of anticancer drugs, we found that EVs-forming breast cancer cells display high level resistance to topotecan, imidazoacridinones and methotrexate via efficient intravesicular drug concentration hence sequestering them away from their cellular targets. Thus, we identified a new modality of anticancer drug compartmentalization and resistance in which multiple chemotherapeutics are actively pumped from the cytoplasm and highly concentrated within the lumen of EVs via a network of MDR transporters differentially targeted to the EVs membrane. We propose a composite model for the structure and function of MDR pump-rich EVs in cancer cells and their ability to confer multiple anticancer drug resistance.

Neural integrity is maintained by dystrophin in C. elegans

The dystrophin protein complex, an important regulator of muscle membrane integrity, also maintains neural organization through interactions with the L1CAM family member SAX-7.

The dystrophin protein complex (DPC), composed of dystrophin and associated proteins, is essential for maintaining muscle membrane integrity. The link between mutations in dystrophin and the devastating muscle failure of Duchenne’s muscular dystrophy (DMD) has been well established. Less well appreciated are the accompanying cognitive impairment and neuropsychiatric disorders also presented in many DMD patients, which suggest a wider role for dystrophin in membrane–cytoskeleton function. This study provides genetic evidence of a novel role for DYS-1/dystrophin in maintaining neural organization in Caenorhabditis elegans. This neuronal function is distinct from the established role of DYS-1/dystrophin in maintaining muscle integrity and regulating locomotion. SAX-7, an L1 cell adhesion molecule (CAM) homologue, and STN-2/γ-syntrophin also function to maintain neural integrity in C. elegans. This study provides biochemical data that show that SAX-7 associates with DYS-1 in an STN-2/γ-syntrophin–dependent manner. These results reveal a recruitment of L1CAMs to the DPC to ensure neural integrity is maintained.

Su(dx) E3 ubiquitin ligase-dependent and -independent functions of polychaetoid, the Drosophila ZO-1 homologue

Zona occludens (ZO) proteins are molecular scaffolds localized to cell junctions, which regulate epithelial integrity in mammals. Using newly generated null alleles, we demonstrate that polychaetoid (pyd), the unique Drosophila melanogaster ZO homologue, regulates accumulation of adherens junction-localized receptors, such as Notch, although it is dispensable for epithelial polarization. Pyd positively regulates Notch signaling during sensory organ development but acts negatively on Notch to restrict the ovary germline stem cell niche. In both contexts, we identify a core antagonistic interaction between Pyd and the WW domain E3 ubiquitin ligase Su(dx). Pyd binds Su(dx) directly, in part through a noncanonical WW-binding motif. Pyd also restricts epithelial wing cell numbers to control adult wing shape, a function associated with the FERM protein Expanded and independent of Su(dx). As both Su(dx) and Expanded regulate trafficking, we propose that a conserved role of ZO proteins is to coordinate receptor trafficking and signaling with junctional organization.

Morphology and properties of brain endothelial cells

The molecular advances in various aspects of brain endothelial cell function in steady states are considerable and difficult to summarize in one chapter. Therefore, this chapter focuses on endothelial permeability mechanisms in steady states and disease namely vasogenic edema. The morphology and properties of caveolae and tight junctions that are involved in endothelial permeability to macromolecules are reviewed. Endothelial transport functions are briefly reviewed. Diseases with alterations of endothelial permeability are mentioned and details are provided of the molecular alterations in caveolae and tight junctions in vasogenic edema. Other factors involved in increased endothelial permeability such as the matrix metalloproteinases are briefly discussed. Of the modulators of endothelial permeability, angioneurins such as the vascular endothelial growth factors and angiopoietins are discussed. The chapter concludes with a brief discussion on delivery of therapeutic substances across endothelium.

NUMB-ing down cancer by more than just a NOTCH

The protein Numb does not live up to its name. This passive-sounding protein is anything but spent. Originally identified as a cell-fate determinant in Drosophila development, Numb received a good deal of attention as an inhibitor of the Notch receptor signaling pathway. It turns out, however, that Numb does a lot more than simply regulate Notch. It has been implicated in a variety of biochemical pathways connected with signaling (it regulates Notch-, Hedgehog- and TP53-activated pathways), endocytosis (it is involved in cargo internalization and recycling), determination of polarity (it interacts with the PAR complex, and regulates adherens and tight junctions), and ubiquitination (it exploits this mechanism to regulate protein function and stability). This complex biochemical network lies at the heart of Numb's involvement in diverse cellular phenotypes, including cell fate developmental decisions, maintenance of stem cell compartments, regulation of cell polarity and adhesion, and migration. Considering its multifaceted role in cellular homeostasis, it is not surprising that Numb has been implicated in cancer as a tumor suppressor. Our major goal here is to explain the cancer-related role of Numb based on our understanding of its role in cell physiology. We will attempt to do this by reviewing the present knowledge of Numb at the biochemical and functional level, and by integrating its apparently heterogeneous functions into a unifying scenario, based on our recently proposed concept of the "endocytic matrix". Finally, we will discuss the role of Numb in the maintenance of the normal stem cell compartment, as a starting point to interpret the tumor suppressor function of Numb in the context of the cancer stem cell hypothesis.

Heparanase Modulates Shh and Wnt3a Signaling in Human Medulloblastoma Cells

The pathogenesis of medulloblastoma (MB), the most common and aggressive brain tumor in children, is poorly understood. MB tumors respond to factors secreted by cerebellar Purkinje neurons such as Sonic hedgehog (Shh) and Wnt3a. Understanding the modulation of Shh/Wnt signaling is critical to developing new MB treatments. Shh and Wnt3a induce MB cell proliferation, and bind heparan sulfate glycosaminoglycan chains (HS-GAG). HS-GAG are components of syndecans: cell surface HS proteoglycans (HSPG) which act as co-receptors for extracellular matrix based ligands, and are targets of heparanase (HPSE). We hypothesized that extracellular HPSE activity can modulate MB intracellular signaling of Shh/Wnt3a, involving syndecans 1/4 carboxy terminal-associated proteins and downstream targets. We compared the regulation of Shh/Wnt3a signaling subsequent to treatment with exogenous human active HPSE in MB lines possessing increased invasive abilities. We identified GEF-H1, a small GTPase guanine nucleotide exchange factor, as a new component of a syndecan signaling complex. Secondly, we demonstrated that HPSE modulated Shh/Wnt3 dependent expression and intracellular distribution of GEF-H1, β-catenin, and N-Myc. Thirdly, HPSE modulated Shh/Wnt3a - dependent gene expression of HSPG and Gli transcription factors. Fourthly, pretreatment with HPSE, alone or prior to Shh/Wnt3a exposure, altered small GTPase (Rac1/RhoA) activities differentially, and promoted RhoA activation. Finally, the differential regulation of Rac1/RhoA activities by HPSE affected MB cell proliferation and invasion. Our results indicate that the HPSE/HSPG axis is implicated in critical MB cell signaling pathways with potential relevance for MB treatment.

Annexin A6 contributes to the invasiveness of breast carcinoma cells by influencing the organization and localization of functional focal adhesions

The interaction of annexin A6 (AnxA6) with membrane phospholipids and either specific extracellular matrix (ECM) components or F-actin suggests that it may influence cellular processes associated with rapid plasma membrane reorganization such as cell adhesion and motility. Here, we examined the putative roles of AnxA6 in adhesion-related cellular processes that contribute to breast cancer progression. We show that breast cancer cells secrete annexins via the exosomal pathway and that the secreted annexins are predominantly cell surface-associated. Depletion of AnxA6 in the invasive BT-549 breast cancer cells is accompanied by enhanced anchorage-independent cell growth but cell-cell cohesion, cell adhesion/spreading onto collagen type IV or fetuin-A, cell motility and invasiveness were strongly inhibited. To explain the loss in adhesion/motility, we show that vinculin-based focal adhesions in the AnxA6-depleted BT-549 cells are elongated and randomly distributed. These focal contacts are also functionally defective because the activation of focal adhesion kinase and the phosphoinositide-3 kinase/Akt pathway were strongly inhibited while the MAP kinase pathway remained constitutively active. Compared with normal human breast tissues, reduced AnxA6 expression in breast carcinoma tissues correlates with enhanced cell proliferation. Together this suggests that reduced AnxA6 expression contributes to breast cancer progression by promoting the loss of functional cell-cell and/or cell-ECM contacts and anchorage-independent cell proliferation.

The NF2 tumor suppressor, Merlin, regulates epidermal development through the establishment of a junctional polarity complex

The neurofibromatosis type 2 (NF2) tumor suppressor, Merlin, is a FERM (Four point one, Ezrin, Radixin, Moesin) domain-containing protein whose loss results in defective morphogenesis and tumorigenesis in multiple tissues. Like the closely related ERM proteins (Ezrin, Radixin, and Moesin), Merlin may organize the plasma membrane by assembling membrane protein complexes and linking them to the cortical actin cytoskeleton. We previously found that Merlin is a critical mediator of contact-dependent inhibition of proliferation and is required for the establishment of stable adherens junctions (AJs) in cultured cells. Here, we delineate the molecular function of Merlin in AJ establishment in epidermal keratinocytes in vitro and confirm that a role in AJ establishment is an essential function of Merlin in vivo. Our studies reveal that Merlin can associate directly with α-catenin and link it to Par3, thereby providing an essential link between the AJ and the Par3 polarity complex during junctional maturation.

Use of fluorescein isothiocyanate-human serum albumin for the intravesical photodiagnosis of non-muscle-invasive bladder cancer: an in vitro study using multicellular spheroids composed of normal human urothelial and urothelial cell carcinoma cell lines

OBJECTIVE

• To evaluate human serum albumin (HSA), fluorescently labelled with fluorescein isothiocyanate (FITC), as a potential intravesical photodiagnostic method for the early detection of non-muscle-invasive bladder cancer.

PATIENTS AND METHODS

• By using multicellular spheroids prepared from normal human urothelial (NHU) cells and from different urothelial cell carcinoma (UCC) cell lines (T24, J82), we simulated three-dimensionally the normal urothelium and non-muscle-invasive UCCs present in the bladder of patients. • The distribution of FITC-HSA in these spheroids was investigated.

RESULTS

• Our data showed that fluorescently labelled albumin is quite evenly dispersed throughout the spheroids. However, in the case of the 10 mg/mL incubations, the fluorescence intensity seems to increase slightly towards the spheroid core. • Using 1 mg/mL, the penetration of FITC-HSA in T24 differed significantly from the penetration in NHU spheroids, but this was not the case for J82 spheroids. • When the concentration of FITC-HSA was increased 10-fold, all UCC spheroids exhibited a significantly different accumulation of FITC-HSA.

CONCLUSIONS

• As spheroids represent a suitable in vitro model for predicting the in vivo behaviour of compounds, our data suggest that FITC-HSA could be used for the early detection of non-muscle-invasive bladder cancer. • Human serum albumin conjugates of new or already available intravesical drugs could be generated to create alternative bladder cancer therapies with increased selectivity.

Reduction of endothelial tight junction proteins is related to cerebral aneurysm formation in rats

OBJECTIVE

The formation of cerebral aneurysms is associated with endothelial damage and macrophage migration. Hypothesizing that the opening of tight junctions due to the disappearance of the tight junction proteins occludin and zona occludens-1 (ZO-1) in damaged endothelia allows macrophage migration, leading to cerebral aneurysm formation, we investigated the role of tight junction proteins.

METHODS

The vascular wall of female rats subjected to hypertension, oophorectomy (OVX), and hemodynamic stress to induce cerebral aneurysms was evaluated morphologically, immunohistochemically, and by quantitative RT-PCR. We also assessed the regulation of tight junction proteins in human brain endothelial cells (HBECs).

RESULTS

In the very early stage before aneurysm formation, the expression of occludin and ZO-1 was reduced in injured endothelial cell junctions exhibiting gaps. In the course of aneurysmal progression their reduction progressed and was correlated with macrophage migration. In hypertension along with OVX rats we observed an increase in angiotensin II and the degradation molecules matrix metalloproteinase-9 (MMP-9), nicotinamide-adenine dinucleotide phosphate oxidases and monocyte chemoattractant protein-1. The mineralocorticoid receptor blocker eplerenone increased occludin and ZO-1 expression; this was associated with a reduction in angiotensin II and the degradation molecules and resulted in the inhibition of macrophage exudation and aneurysm formation. In HBECs, occludin and ZO-1 downregulation by angiotensin II and estrogen deficiency was reversed by eplerenone, the MMP inhibitor SB3CT, and apocynin. Our results suggest that macrophage migration is associated with the reduction in tight junction proteins induced by the degradation molecules.

CONCLUSION

In rats, the destruction of tight junctions may facilitate macrophage migration and cerebral-aneurysm formation.

ZO-1 determines adherens and gap junction localization at intercalated disks

The disruption of the spatial order of electromechanical junctions at myocyte-intercalated disks (ICDs) is a poorly understood characteristic of many cardiac disease states. Here, in vitro and in vivo evidence is provided that zonula occludens-1 (ZO-1) regulates the organization of gap junctions (GJs) and adherens junctions (AJs) at ICDs. We investigated the contribution of ZO-1 to cell-cell junction localization by expressing a dominant-negative ZO-1 construct (DN-ZO-1) in rat ventricular myocytes (VMs). The expression of DN-ZO-1 in cultured neonatal VMs for 72 h reduced the interaction of ZO-1 and N-cadherin, as assayed by colocalization and coimmunoprecipitation, prompting cytoplasmic internalization of AJ and GJ proteins. DN-ZO-1 expression in adult VMs in vivo also reduced N-cadherin colocalization with ZO-1, a phenomenon not observed when the connexin-43 (Cx43)-ZO-1 interaction was disrupted using a mimetic of the ZO-1-binding ligand from Cx43. DN-ZO-1-infected VMs demonstrated large GJs at the ICD periphery and showed a loss of focal ZO-1 concentrations along plaque edges facing the disk interior. Additionally, there was breakdown of the characteristic ICD pattern of small interior and large peripheral GJs. Continuous DN-ZO-1 expression in VMs over postnatal development reduced ICD-associated Cx43 GJs and increased lateralized and cytoplasmic Cx43. We conclude that ZO-1 regulation of GJ localization is via an association with the N-cadherin multiprotein complex and that this is a key determinant of stable localization of both AJs and GJs at the ICD.

The integrity of the esophageal mucosa. Balance between offensive and defensive mechanisms

Heartburn is the most common and characteristic symptom of gastroesophageal reflux disease. It ultimately results from contact of refluxed gastric acid with nociceptors within the esophageal mucosa and transmission of this peripheral signal to the central nervous system for cognition. Healthy esophageal epithelium provides an effective barrier between refluxed gastric acid and esophageal nociceptors; but this barrier is vulnerable to attack and damage, particularly by acidic gastric contents. How gastric acid is countered by defensive elements within the esophageal mucosa is a major focus of this discussion. When the defense is successful, the subject is asymptomatic and when unsuccessful, the subject experiences heartburn. Those with heartburn commonly fall into one of three endoscopic types: nonerosive reflux disease, erosive esophagitis and Barrett's esophagus. Although what determines endoscopic type remains unknown; it is proposed herein that inflammation plays a key, modulating role.

Streptolysin S contributes to group A streptococcal translocation across an epithelial barrier

Group A Streptococcus pyogenes (GAS) is a human pathogen that causes local suppurative infections and severe invasive diseases. Systemic dissemination of GAS is initiated by bacterial penetration of the epithelial barrier of the pharynx or damaged skin. To gain insight into the mechanism by which GAS penetrates the epithelial barrier, we sought to identify both bacterial and host factors involved in the process. Screening of a transposon mutant library of a clinical GAS isolate recovered from an invasive episode allowed identification of streptolysin S (SLS) as a novel factor that facilitates the translocation of GAS. Of note, the wild type strain efficiently translocated across the epithelial monolayer, accompanied by a decrease in transepithelial electrical resistance and cleavage of transmembrane junctional proteins, including occludin and E-cadherin. Loss of integrity of intercellular junctions was inhibited after infection with a deletion mutant of the sagA gene encoding SLS, as compared with those infected with the wild type strain. Interestingly, following GAS infection, calpain was recruited to the plasma membrane along with E-cadherin. Moreover, bacterial translocation and destabilization of the junctions were partially inhibited by a pharmacological calpain inhibitor or genetic interference with calpain. Our data indicate a potential function of SLS that facilitates GAS invasion into deeper tissues via degradation of epithelial intercellular junctions in concert with the host cysteine protease calpain.

An in vitro triple cell co-culture model with primary cells mimicking the human alveolar epithelial barrier

A triple cell co-culture model was recently established by the authors, consisting of either A549 or 16HBE14o- epithelial cells, human blood monocyte-derived macrophages and dendritic cells, which offers the possibility to study the interaction of xenobiotics with those cells. The 16HBE14o- containing co-culture model mimics the airway epithelial barrier, whereas the A549 co-cultures mimic the alveolar type II-like epithelial barrier. The goal of the present work was to establish a new triple cell co-culture model composed of primary alveolar type I-like cells isolated from human lung biopsies (hAEpC) representing a more realistic alveolar epithelial barrier wall, since type I epithelial cells cover >93% of the alveolar surface. Monocultures of A549 and 16HBE14o- were morphologically and functionally compared with the hAEpC using laser scanning microscopy, as well as transmission electron microscopy, and by determining the epithelial integrity. The triple cell co-cultures were characterized using the same methods. It could be shown that the epithelial integrity of hAEpC (mean ± SD, 1180 ± 188 Ω cm(2)) was higher than in A549 (172 ± 59 Ω cm(2)) but similar to 16HBE14o- cells (1469 ± 156 Ω cm(2)). The triple cell co-culture model with hAEpC (1113 ± 30 Ω cm(2)) showed the highest integrity compared to the ones with A549 (93 ± 14 Ω cm(2)) and 16HBE14o- (558 ± 267 Ω cm(2)). The tight junction protein zonula occludens-1 in hAEpC and 16HBE14o- were more regularly expressed but not in A549. The epithelial alveolar model with hAEpC combined with two immune cells (i.e. macrophages and dendritic cells) will offer a novel and more realistic cell co-culture system to study possible cell interactions of inhaled xenobiotics and their toxic potential on the human alveolar type I epithelial wall.