Discovering the molecular components of intercellular junctions--a historical view

N-cadherin: A diagnostic marker to help discriminate primary liver carcinomas from extrahepatic carcinomas

Distinguishing primary liver cancer (PLC), namely hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (iCCA), from liver metastases is of crucial clinical importance. Histopathology remains the gold standard, but differential diagnosis may be challenging. While absent in most epithelial, the expression of the adherens junction glycoprotein N-cadherin is commonly restricted to neural and mesenchymal cells, or carcinoma cells that undergo the phenomenon of epithelial-to-mesenchymal transition (EMT). However, we recently established N- and E-cadherin expression as hallmarks of normal hepatocytes and cholangiocytes, which are also preserved in HCC and iCCA. Therefore, we hypothesized that E- and/or N-cadherin may distinguish between carcinoma derived from the liver vs carcinoma of other origins. We comprehensively evaluated E- and N-cadherin in 3359 different tumors in a multicenter study using immunohistochemistry and compared our results with previously published 882 cases of PLC, including 570 HCC and 312 iCCA. Most carcinomas showed strong positivity for E-cadherin. Strong N-cadherin positivity was present in HCC and iCCA. However, except for clear cell renal cell carcinoma (23.6% of cases) and thyroid cancer (29.2%), N-cadherin was only in some instances faintly expressed in adenocarcinomas of the gastrointestinal tract (0%-0.5%), lung (7.1%), pancreas (3.9%), gynecological organs (0%-7.4%), breast (2.2%) as well as in urothelial (9.4%) and squamous cell carcinoma (0%-5.6%). As expected, N-cadherin was detected in neuroendocrine tumors (25%-75%), malignant melanoma (46.2%) and malignant mesothelioma (41%). In conclusion, N-cadherin is a useful marker for the distinction of PLC vs liver metastases of extrahepatic carcinomas (P < .01).

Engagement of α3β1 and α2β1 integrins by hypervirulent Streptococcus agalactiae in invasion of polarized enterocytes

The gut represents an important site of colonization of the commensal bacterium Streptococcus agalactiae (group B Streptococcus or GBS), which can also behave as a deadly pathogen in neonates and adults. Invasion of the intestinal epithelial barrier is likely a crucial step in the pathogenesis of neonatal infections caused by GBS belonging to clonal complex 17 (CC17). We have previously shown that the prototypical CC17 BM110 strain invades polarized enterocyte-like cells through their lateral surfaces using an endocytic pathway. By analyzing the cellular distribution of putative GBS receptors in human enterocyte-like Caco-2 cells, we find here that the alpha 3 (α3) and alpha 2 (α2) integrin subunits are selectively expressed on lateral enterocyte surfaces at equatorial and parabasal levels along the vertical axis of polarized cells, in an area corresponding to GBS entry sites. The α3β1 and α2β1 integrins were not readily accessible in fully differentiated Caco-2 monolayers but could be exposed to specific antibodies after weakening of intercellular junctions in calcium-free media. Under these conditions, anti-α3β1 and anti-α2β1 antibodies significantly reduced GBS adhesion to and invasion of enterocytes. After endocytosis, α3β1 and α2β1 integrins localized to areas of actin remodeling around GBS containing vacuoles. Taken together, these data indicate that GBS can invade enterocytes by binding to α3β1 and α2β1 integrins on the lateral membrane of polarized enterocytes, resulting in cytoskeletal remodeling and bacterial internalization. Blocking integrins might represent a viable strategy to prevent GBS invasion of gut epithelial tissues.

Cell Death, by Any Other Name…

Studies trying to understand cell death, this ultimate biological process, can be traced back to a century ago. Yet, unlike many other fashionable research interests, research on cell death is more alive than ever. New modes of cell death are discovered in specific contexts, as are new molecular pathways. But what is "cell death", really? This question has not found a definitive answer yet. Nevertheless, part of the answer is irreversibility, whereby cells can no longer recover from stress or injury. Here, we identify the most distinctive features of different modes of cell death, focusing on the executive final stages. In addition to the final stages, these modes can differ in their triggering stimulus, thus referring to the initial stages. Within this framework, we use a few illustrative examples to examine how intercellular communication factors in the demise of cells. First, we discuss the interplay between cell-cell communication and cell death during a few steps in the early development of multicellular organisms. Next, we will discuss this interplay in a fully developed and functional tissue, the gut, which is among the most rapidly renewing tissues in the body and, therefore, makes extensive use of cell death. Furthermore, we will discuss how the balance between cell death and communication is modified during a pathological condition, i.e., colon tumorigenesis, and how it could shed light on resistance to cancer therapy. Finally, we briefly review data on the role of cell-cell communication modes in the propagation of cell death signals and how this has been considered as a potential therapeutic approach. Far from vainly trying to provide a comprehensive review, we launch an invitation to ponder over the significance of cell death diversity and how it provides multiple opportunities for the contribution of various modes of intercellular communication.

5α-Hydroxycostic acid inhibits choroidal neovascularization in rats through a dual signalling pathway mediated by VEGF and angiopoietin 2

BACKGROUND

5α-Hydroxycostic acid is a eudemane sesquiterpene that is isolated from the natural plant, Laggera alata. It exerts anti-inflammatory and anti-angiogenic effects on human breast cancer cells, but its role and underlying mechanism in choroidal neovascularization (CNV) are still unclear. We conducted a study to verify that 5α-Hydroxycostic acid can inhibit the formation and leakage of CNV, and describe the possible dual pathway by which it exerts its inhibitory effects in this process.

METHODS

An in vitro model of choroidal neovascularization was established using VEGF164, while a rat model of choroidal neovascularization was established using a 532 nm laser. In both models, the effects of 5α-Hydroxycostic acid in vivo and in vitro were evaluated to determine its inhibitory effect on abnormal cell proliferation, migration and tubule formation, as well as its effect on pathological changes in choroidal tissues and the area of neovascularization leakage in rats. The levels of components in the VEGF/VEGFR and Ang2/Tie2 signaling pathways were measured in tissues and cells.

RESULTS

In vitro experiments have shown that 5α-Hydroxycostic acid can inhibit abnormal cell proliferation, migration and angiogenesis. Additionally, 5α-Hydroxycostic acid enhances cell adhesion by inhibiting the phosphorylation pathways of VEGFR2 and Tie2. In vivo experiments demonstrated that 5α-Hydroxycostic acid has a positive therapeutic effect on choroidal neovascularization in rats. It can effectively reduce vascular leakage, consistent with the results of the cell experiments.

CONCLUSION

5α-Hydroxycostic acid can inhibit choroidal neovascularization by interfering with the VEGF- and Ang2/Tie2-related pathways, and it may be a good candidate drug for treating CNV.

Identification of age-specific gene regulators of La Crosse virus neuroinvasion and pathogenesis

One of the key events in viral encephalitis is the ability of virus to enter the central nervous system (CNS). Several encephalitic viruses, including La Crosse Virus (LACV), primarily induce encephalitis in children, but not adults. This phenomenon is also observed in LACV mouse models, where the virus gains access to the CNS of weanling animals through vascular leakage of brain microvessels, likely through brain capillary endothelial cells (BCECs). To examine age and region-specific regulatory factors of vascular leakage, we used genome-wide transcriptomics and targeted siRNA screening to identify genes whose suppression affected viral pathogenesis in BCECs. Further analysis of two of these gene products, Connexin43 (Cx43/Gja1) and EphrinA2 (Efna2), showed a substantial effect on LACV pathogenesis. Induction of Cx43 by 4-phenylbutyric acid (4-PBA) inhibited neurological disease in weanling mice, while Efna2 deficiency increased disease in adult mice. Thus, we show that Efna2 and Cx43 expressed by BCECs are key mediators of LACV-induced neuroinvasion and neurological disease.

Adherens junction: the ensemble of specialized cadherin clusters

The cell-cell connections in adherens junctions (AJs) are mediated by transmembrane receptors, type I cadherins (referred to here as cadherins). These cadherin-based connections (or trans bonds) are weak. To upregulate their strength, cadherins exploit avidity, the increased affinity of binding between cadherin clusters compared with isolated monomers. Formation of such clusters is a unique molecular process that is driven by a synergy of direct and indirect cis interactions between cadherins located at the same cell. In addition to their role in adhesion, cadherin clusters provide structural scaffolds for cytosolic proteins, which implicate cadherin into different cellular activities and signaling pathways. The cluster lifetime, which depends on the actin cytoskeleton, and on the mechanical forces it generates, determines the strength of AJs and their plasticity. The key aspects of cadherin adhesion, therefore, cannot be understood at the level of isolated cadherin molecules, but should be discussed in the context of cadherin clusters.

Double mutation of claudin‐1 and claudin‐3 causes alopecia in infant mice

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 (Cldn1^Δ/Δ Cldn3^-/- ) mice. Although hair growth was normal, Cldn1^Δ/Δ Cldn3^-/- 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 Cldn1^Δ/Δ Cldn3^-/- 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.

The urothelium: a multi-faceted barrier against a harsh environment

All mucosal surfaces must deal with the challenge of exposure to the outside world. The urothelium is a highly specialized layer of stratified epithelial cells lining the inner surface of the urinary bladder, a gruelling environment involving significant stretch forces, osmotic and hydrostatic pressures, toxic substances, and microbial invasion. The urinary bladder plays an important barrier role and allows the accommodation and expulsion of large volumes of urine without permitting urine components to diffuse across. The urothelium is made up of three cell types, basal, intermediate, and umbrella cells, whose specialized functions aid in the bladder's mission. In this review, we summarize the recent insights into urothelial structure, function, development, regeneration, and in particular the role of umbrella cells in barrier formation and maintenance. We briefly review diseases which involve the bladder and discuss current human urothelial in vitro models as a complement to traditional animal studies.

Desmosomes undergo dynamic architectural changes during assembly and maturation

Desmosomes are macromolecular cell-cell junctions critical for maintaining adhesion and resisting mechanical stress in epithelial tissue. Desmosome assembly and the relationship between maturity and molecular architecture are not well understood. To address this, we employed a calcium switch assay to synchronize assembly followed by quantification of desmosome nanoscale organization using direct Stochastic Optical Reconstruction Microscopy (dSTORM). We found that the organization of the desmoplakin rod/C-terminal junction changed over the course of maturation, as indicated by a decrease in the plaque-to-plaque distance, while the plaque length increased. In contrast, the desmoplakin N-terminal domain and plakoglobin organization (plaque-to-plaque distance) were constant throughout maturation. This structural rearrangement of desmoplakin was concurrent with desmosome maturation measured by E-cadherin exclusion and increased adhesive strength. Using two-color dSTORM, we showed that while the number of individual E-cadherin containing junctions went down with the increasing time in high Ca²⁺, they maintained a wider desmoplakin rod/C-terminal plaque-to-plaque distance. This indicates that the maturation state of individual desmosomes can be identified by their architectural organization. We confirmed these architectural changes in another model of desmosome assembly, cell migration. Desmosomes in migrating cells, closest to the scratch where they are assembling, were shorter, E-cadherin enriched, and had wider desmoplakin rod/C-terminal plaque-to-plaque distances compared to desmosomes away from the wound edge. Key results were demonstrated in three cell lines representing simple, transitional, and stratified epithelia. Together, these data suggest that there is a set of architectural programs for desmosome maturation, and we hypothesize that desmoplakin architecture may be a contributing mechanism to regulating adhesive strength.

Endothelial barrier dysfunction induced by anthracene and its nitrated or oxygenated derivatives at environmentally relevant levels

Polycyclic aromatic hydrocarbons (PAHs) are epidemiologically associated with cardiovascular diseases characterized by early key events involving in the disruption of endothelial barrier function. Whether PAHs can induce adverse cardiovascular outcome by directly destabilizing endothelial barrier function remains elusive. Herein, we investigated the effect of anthracene (ANT), 9-nitroanthracene (9-NANT), and 9,10-anthraquinone (9,10-AQ) on vascular endothelial barrier functions in human umbilical vein endothelial cells (HUVECs). The integrity of endothelial barrier in HUVECs was disturbed with a 1.15-1.42 fold increase in fluorescein leakage, and 21.8%-58.3% downregulated transendothelial electrical resistance. ANT, 9-NANT and 9,10-AQ promoted paracellular gap formation as revealed by transmission electron microscope. The disrupted cell junctions after 24 h exposure to ANT, 9-NANT and 9,10-AQ at 0.01 μM were indicated by the downregulated mRNA expression of vascular endothelial cadherin (VE-cadherin), zona occludens-1 (ZO-1) and occludin by 33.2%-71.4%, 19.1%-21.0%, and 31.9% respectively, and the downregulated protein expression of ZO-1 and occludin, and by the internalization of VE-cadherin. We demonstrated that ANT and its derivatives at environmentally relevant concentrations induced endothelial barrier dysfunction via the disruption of cell junctions, providing essential in vitro evidence on the association with their adverse cardiovascular outcomes.

Cortisol differentially affects the viability and myogenesis of mono- and co-cultured porcine gluteal muscles satellite cells and fibroblasts

Cortisol is a ubiquitously expressed stress hormone. In this study, we investigated the effects of exogenous cortisol on porcine gluteal muscles primary cultured satellite cells and fibroblasts. Satellite cells and fibroblasts were mono-or co-cultured, and cells in each type of culture were categorized into the control and cortisol-treated (treatment) groups. We selected 28 μmol mL^-1 cortisol for treatment based on their efficacy. Cortisol treatment reduced viability of monocultured satellite cells and fibroblasts. In both monocultured and co-cultured cells, the nucleus in the treatment group was damaged than that control group. Moreover, the total cell cycle duration was shorter in the treatment group than the control group. PAX-7 expression was upregulated in the control group of co-cultured satellite cells and fibroblasts than those remaining groups. Moreover, MyoD expression was downregulated in the cortisol treated group of both mono-and co-cultured satellite cells compared with that in the control group. In co-cultured fibroblasts, MyoD and MyoG expression was upregulated than those remaining groups. The Cyto-C expression was upregulated in the treatment group compared to the control mono-and co-cultured both cells. These results suggest that the selected experimental dose of cortisol reduced cell viability and myogenesis-related gene expression in the monoculture compared to that in the co-culture of satellite cells and fibroblasts.

Impact of Endocytosis Mechanisms for the Receptors Targeted by the Currently Approved Antibody-Drug Conjugates (ADCs)-A Necessity for Future ADC Research and Development

Biologically-based therapies increasingly rely on the endocytic cycle of internalization and exocytosis of target receptors for cancer therapies. However, receptor trafficking pathways (endosomal sorting (recycling, lysosome localization) and lateral membrane movement) are often dysfunctional in cancer. Antibody-drug conjugates (ADCs) have revitalized the concept of targeted chemotherapy by coupling inhibitory antibodies to cytotoxic payloads. Significant advances in ADC technology and format, and target biology have hastened the FDA approval of nine ADCs (four since 2019). Although the links between aberrant endocytic machinery and cancer are emerging, the impact of dysregulated internalization processes of ADC targets and response rates or resistance have not been well studied. This is despite the reliance on ADC uptake and trafficking to lysosomes for linker cleavage and payload release. In this review, we describe what is known about all the target antigens for the currently approved ADCs. Specifically, internalization efficiency and relevant intracellular sorting activities are described for each receptor under normal processes, and when complexed to an ADC. In addition, we discuss aberrant endocytic processes that have been directly linked to preclinical ADC resistance mechanisms. The implications of endocytosis in regard to therapeutic effectiveness in the clinic are also described. Unexpectedly, information on endocytosis is scarce (absent for two receptors). Moreover, much of what is known about endocytosis is not in the context of receptor-ADC/antibody complexes. This review provides a deeper understanding of the pertinent principles of receptor endocytosis for the currently approved ADCs.

First body of evidence suggesting a role of a tankyrase-binding motif (TBM) of vinculin (VCL) in epithelial cells

BACKGROUND

Adherens junctions (AJ) are involved in cancer, infections and neurodegeneration. Still, their composition has not been completely disclosed. Poly(ADP-ribose) polymerases (PARPs) catalyze the synthesis of poly(ADP-ribose) (PAR) as a posttranslational modification. Four PARPs synthesize PAR, namely PARP-1/2 and Tankyrase-1/2 (TNKS). In the epithelial belt, AJ are accompanied by a PAR belt and a subcortical F-actin ring. F-actin depolymerization alters the AJ and PAR belts while PARP inhibitors prevent the assembly of the AJ belt and cortical actin. We wondered which PARP synthesizes the belt and which is the PARylation target protein. Vinculin (VCL) participates in the anchorage of F-actin to the AJ, regulating its functions, and colocalized with the PAR belt. TNKS has been formerly involved in the assembly of epithelial cell junctions.

HYPOTHESIS

TNKS poly(ADP-ribosylates) (PARylates) epithelial belt VCL, affecting its functions in AJ, including cell shape maintenance.

MATERIALS AND METHODS

Tankyrase-binding motif (TBM) sequences in hVCL gene were identified and VCL sequences from various vertebrates, Drosophila melanogaster and Caenorhabditis elegans were aligned and compared. Plasma membrane-associated PAR was tested by immunocytofluorescence (ICF) and subcellular fractionation in Vero cells while TNKS role in this structure and cell junction assembly was evaluated using specific inhibitors. The identity of the PARylated proteins was tested by affinity precipitation with PAR-binding reagent followed by western blots. Finally, MCF-7 human breast cancer epithelial cells were subjected to transfection with Tol2-plasmids, carrying a dicistronic expression sequence including Gallus gallus wt VCL (Tol-2-GgVCL), or the same VCL gene with a point mutation in TBM-II (Tol2-GgVCL/*TBM) under the control of a β-actin promoter, plus green fluorescent protein following an internal ribosome entry site (IRES-GFP) to allow the identification of transfected cells without modifying the transfected protein of interest.

RESULTS AND DISCUSSION

In this work, some of the hypothesis predictions have been tested. We have demonstrated that: (1) VCL TBMs were conserved in vertebrate evolution while absent in C. elegans; (2) TNKS inhibitors disrupted the PAR belt synthesis, while PAR and an endogenous TNKS pool were associated to the plasma membrane; (3) a VCL pool was covalently PARylated; (4) transfection of MCF-7 cells leading to overexpression of Gg-VCL/*TBM induced mesenchymal-like cell shape changes. This last point deserves further investigation, bypassing the limits of our transient transfection and overexpression system. In fact, a 5th testable prediction would be that a single point mutation in VCL TBM-II under endogenous expression control would induce an epithelial to mesenchymal transition (EMT). To check this, a CRISPR/Cas9 substitution approach followed by migration, invasion, gene expression and chemo-resistance assays should be performed.

Effect of X-rays on transcript expression of rat brain microvascular endothelial cells: role of calcium signaling in X-ray-induced endothelium damage

Radiation-induced brain edema is a serious adverse effect of radiotherapy. Although there are many causes of radiation-induced brain edema, the pathogenesis is not clear and clinical treatment is not ideal. Therefore, knowing the differential expression of the brain microvascular endothelial cell (BMEC) transcriptome after brain radiotherapy may shed light on the pathogenesis of radiation-induced brain edema. The present study used RNA-Seq technique to identify 383 BMEC transcripts differentially expressed (many 2-fold or higher; P < 0.05) between control and X-ray–treated primary cultured rat BMECs. Compared with controls, X-ray–treated BMECs had 183 significantly up-regulated transcripts and 200 significantly down-regulated transcripts. The differentially expressed genes were associated with the biological processes of the cell cycle, apoptosis, vascular permeability, and extracellular junctions. The functional changes identified in the X-ray–treated BMECs included Ca²⁺ signaling, phosphoinositide 3-kinase–Akt signaling, and methionine degradation. These results indicated that transcript expression was substantially affected by radiation exposure and the proteins encoded by these differentially expressed genes may play a significant role in radiotherapy-induced brain edema. Our findings provide additional insight into the molecular mechanisms of radiation-induced brain edema and may be helpful in the development of clinical treatment of this adverse reaction to radiotherapy.

Avian intestinal ultrastructure changes provide insight into the pathogenesis of enteric diseases and probiotic mode of action

Epithelial damage and loss of barrier integrity occur following intestinal infections in humans and animals. Gut health was evaluated by electron microscopy in an avian model that exposed birds to subclinical necrotic enteritis (NE) and fed them a diet supplemented with the probiotic Bacillus amyloliquefaciens strain H57 (H57). Scanning electron microscopy of ileal mucosa revealed significant villus damage, including focal erosions of epithelial cells and villous atrophy, while transmission electron microscopy demonstrated severe enterocyte damage and loss of cellular integrity in NE-exposed birds. In particular, mitochondria were morphologically altered, appearing irregular in shape or swollen, and containing electron-lucent regions of matrix and damaged cristae. Apical junctional complexes between adjacent enterocytes were significantly shorter, and the adherens junction was saccular, suggesting loss of epithelial integrity in NE birds. Segmented filamentous bacteria attached to villi, which play an important role in intestinal immunity, were more numerous in birds exposed to NE. The results suggest that mitochondrial damage may be an important initiator of NE pathogenesis, while H57 maintains epithelium and improves the integrity of intestinal mucosa. Potential actions of H57 are discussed that further define the mechanisms responsible for probiotic bacteria’s role in maintaining gut health.

Cell-cell interfaces as specialized compartments directing cell function

Cell-cell interfaces are found throughout multicellular organisms, from transient interactions between motile immune cells to long-lived cell-cell contacts in epithelia. Studies of immune cell interactions, epithelial cell barriers, neuronal contacts and sites of cell-cell fusion have identified a core set of features shared by cell-cell interfaces that critically control their function. Data from diverse cell types also show that cells actively and passively regulate the localization, strength, duration and cytoskeletal coupling of receptor interactions governing cell-cell signalling and physical connections between cells, indicating that cell-cell interfaces have a unique membrane organization that emerges from local molecular and cellular mechanics. In this Review, we discuss recent findings that support the emerging view of cell-cell interfaces as specialized compartments that biophysically constrain the arrangement and activity of their protein, lipid and glycan components. We also review how these biophysical features of cell-cell interfaces allow cells to respond with high selectivity and sensitivity to multiple inputs, serving as the basis for wide-ranging cellular functions. Finally, we consider how the unique properties of cell-cell interfaces present opportunities for therapeutic intervention.

Identification of PKP 2/3 as potential biomarkers of ovarian cancer based on bioinformatics and experiments

Background

Plakophilins (PKPs) are widely involved in gene transcription, translation, and signal transduction, playing a crucial role in tumorigenesis and progression. However, the function and potential mechanism of PKP1/2/3 in ovarian cancer (OC) remains unclear. It’s of great value to explore the expression and prognostic values of PKP1/2/3 and their potential mechanisms, immune infiltration in OC.

Methods

The expression levels, prognostic values and genetic variations of PKP1/2/3 in OC were explored by various bioinformatics tools and databases, and PKP2/3 were selected for further analyzing their regulation network and immune infiltration. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes pathways (KEGG) enrichment were also conducted. Finally, the expression and prognosis of PKP2 were validated by immunohistochemistry.

Results

The expression level and prognosis of PKP1 showed little significance in ovarian cancer, and the expression of PKP2/3 mRNA and protein were upregulated in OC, showing significant correlations with poor prognosis of OC. Functional enrichment analysis showed that PKP2/3 and their correlated genes were significantly enriched in adaptive immune response, cytokine receptor activity, organization of cell–cell junction and extracellular matrix; KEGG analysis showed that PKP2/3 and their significantly correlated genes were involved in signaling pathways including cytokine-mediated signaling pathway, receptor signaling pathway and pathways in cancer. Moreover, PKP2/3 were correlated with lymphocytes and immunomodulators. We confirmed that high expression of PKP2 was significantly associated with advanced stage, poor differentiation and poor prognosis of OC patients.

Conclusion

Members of plakophilins family showed various degrees of abnormal expressions and prognostic values in ovarian cancer. PKP2/3 played crucial roles in tumorigenesis, aggressiveness, malignant biological behavior and immune infiltration of OC, and can be regarded as potential biomarker for early diagnosis and prognosis evaluation in OC.

The Urothelium: Life in a Liquid Environment

The urothelium, which lines the renal pelvis, ureters, urinary bladder, and proximal urethra, forms a high-resistance but adaptable barrier that surveils its mechanochemical environment and communicates changes to underlying tissues including afferent nerve fibers and the smooth muscle. The goal of this review is to summarize new insights into urothelial biology and function that have occurred in the past decade. After familiarizing the reader with key aspects of urothelial histology, we describe new insights into urothelial development and regeneration. This is followed by an extended discussion of urothelial barrier function, including information about the roles of the glycocalyx, ion and water transport, tight junctions, and the cellular and tissue shape changes and other adaptations that accompany expansion and contraction of the lower urinary tract. We also explore evidence that the urothelium can alter the water and solute composition of urine during normal physiology and in response to overdistension. We complete the review by providing an overview of our current knowledge about the urothelial environment, discussing the sensor and transducer functions of the urothelium, exploring the role of circadian rhythms in urothelial gene expression, and describing novel research tools that are likely to further advance our understanding of urothelial biology.

Modeling Cell-Cell Interactions from Spatial Molecular Data with Spatial Variance Component Analysis

Technological advances enable assaying multiplexed spatially resolved RNA and protein expression profiling of individual cells, thereby capturing molecular variations in physiological contexts. While these methods are increasingly accessible, computational approaches for studying the interplay of the spatial structure of tissues and cell-cell heterogeneity are only beginning to emerge. Here, we present spatial variance component analysis (SVCA), a computational framework for the analysis of spatial molecular data. SVCA enables quantifying different dimensions of spatial variation and in particular quantifies the effect of cell-cell interactions on gene expression. In a breast cancer Imaging Mass Cytometry dataset, our model yields interpretable spatial variance signatures, which reveal cell-cell interactions as a major driver of protein expression heterogeneity. Applied to high-dimensional imaging-derived RNA data, SVCA identifies plausible gene families that are linked to cell-cell interactions. SVCA is available as a free software tool that can be widely applied to spatial data from different technologies.

PERP-ing into diverse mechanisms of cancer pathogenesis: Regulation and role of the p53/p63 effector PERP

The tetraspan plasma membrane protein PERP (p53 apoptosis effector related to PMP22) is a lesser-known transcriptional target of p53 and p63. A member of the PMP22/GAS3/EMP membrane protein family, PERP was originally identified as a p53 target specifically trans-activated during apoptosis, but not during cell-cycle arrest. Several studies have since shown downregulation of PERP expression in numerous cancers, suggesting that PERP is a tumour suppressor protein. This review focusses on the important advances made in elucidating the mechanisms regulating PERP expression and its function as a tumour suppressor in diverse human cancers, including breast cancer and squamous cell carcinoma. Investigating PERP's role in clinically-aggressive uveal melanoma has revealed that PERP engages a positive-feedback loop with p53 to regulate its own expression, and that p63 is required beside p53 to achieve pro-apoptotic levels of PERP in this cancer. Furthermore, the recent discovery of the apoptosis-mediating interaction of PERP with SERCA2b at the plasma membrane-endoplasmic reticulum interface demonstrates a novel mechanism of PERP stabilisation, and how PERP can mediate Ca²⁺ signalling to facilitate apoptosis. The multi-faceted role of PERP in cancer, involving well-documented functions in mediating apoptosis and cell-cell adhesion is discussed, alongside PERP's emerging roles in epithelial-mesenchymal transition, and PERP crosstalk with inflammation signalling pathways, and other signalling pathways. The potential for restoring PERP expression as a means of cancer therapy is also considered.

CLDN6-mediates SB431542 action through MMPs to regulate the invasion, migration, and EMT of breast cancer cells

Our previous research confirmed the repression of SMADs signaling pathway inhibits the invasion, migration, and EMT in breast cancer MCF-7 and SKBR-3 cell lines by DNMT1 up-regulating CLDN6, but the mechanism is unclear. Western blot was performed to detect the expression of SMAD2, SMAD3, P-SMAD2, and P-SMAD3. Then RT-PCR was carried out to examine the expression of tight junctions and cell adhesion molecule E-cadherin. According to the gene sequence of Claudin6, shRNA was linked with the green fluorescent protein-expressing eukaryotic expression vector pGC silencer TMΜ6/Neo/GFP, and it was transfected into breast cancer MCF-7 cells and SKBR-3 cells. RT-PCR and western blot were applied to verify the Claudin6 gene-silencing effect. We observed cellular morphology with inverted microscope, analyzed the capacity for clone formation, and detected transepithelial electrical resistance. The level of MMP2, and MMP9 in the cells treated with or without SB431542 and MCF-7-shGFP, MCF-7-shClaudin-6, SKBR-3-shGFP, and SKBR-3-shClaudin-6 cells pretreated with SB431542 were examined by RT-PCR and western blot. The expressions of Claudin-6, occludin, and cell adhesion molecule E-cadherin were enhanced by SB431542. SB431542 transformed mesenchymal cell morphology into epithelial cell morphology, inhibited capacity for clone formation, increased transepithelial electrical resistance, and downregulated the expression of MMP2 and MMP9. Knock down of Claudin6 can abolish SB431542 effects. We conclude that Claudin6 mediates the effects of SB431542 on the biologic phenotypes of the breast cancer cells we studied. We speculate Claudin6-mediated the SB431542 inhibition of invasion, migration, and EMT in breast cancer cells via MMP2/9.

Transition of podosomes into zipper-like structures in macrophage-derived multinucleated giant cells

Macrophage fusion resulting in the formation of multinucleated giant cells (MGCs) is a multistage process that requires many adhesion-dependent steps and involves the rearrangement of the actin cytoskeleton. The diversity of actin-based structures and their role in macrophage fusion is poorly understood. In this study, we revealed hitherto unrecognized actin-based zipper-like structures (ZLSs) that arise between MGCs formed on the surface of implanted biomaterials. We established an in vitro model for the induction of these structures in mouse macrophages undergoing IL-4–mediated fusion. Using this model, we show that over time MGCs develop cell–cell contacts containing ZLSs. Live-cell imaging using macrophages isolated from mRFP- or eGFP-LifeAct mice demonstrated that ZLSs are dynamic formations undergoing continuous assembly and disassembly and that podosomes are precursors of these structures. Immunostaining experiments showed that vinculin, talin, integrin α_Mβ₂, and other components of podosomes are present in ZLSs. Macrophages deficient in WASp or Cdc42, two key molecules involved in actin core organization in podosomes, as well as cells treated with the inhibitors of the Arp2/3 complex, failed to form ZLSs. Furthermore, E-cadherin and nectin-2 were found between adjoining membranes, suggesting that the transition of podosomes into ZLSs is induced by bridging plasma membranes by junctional proteins.

Mechanosensation of Tight Junctions Depends on ZO-1 Phase Separation and Flow

Cell-cell junctions respond to mechanical forces by changing their organization and function. To gain insight into the mechanochemical basis underlying junction mechanosensitivity, we analyzed tight junction (TJ) formation between the enveloping cell layer (EVL) and the yolk syncytial layer (YSL) in the gastrulating zebrafish embryo. We found that the accumulation of Zonula Occludens-1 (ZO-1) at TJs closely scales with tension of the adjacent actomyosin network, revealing that these junctions are mechanosensitive. Actomyosin tension triggers ZO-1 junctional accumulation by driving retrograde actomyosin flow within the YSL, which transports non-junctional ZO-1 clusters toward the TJ. Non-junctional ZO-1 clusters form by phase separation, and direct actin binding of ZO-1 is required for stable incorporation of retrogradely flowing ZO-1 clusters into TJs. If the formation and/or junctional incorporation of ZO-1 clusters is impaired, then TJs lose their mechanosensitivity, and consequently, EVL-YSL movement is delayed. Thus, phase separation and flow of non-junctional ZO-1 confer mechanosensitivity to TJs.

Tracing the Evolutionary Origin of Desmosomes

Cadherin-based cell-cell junctions help metazoans form polarized sheets of cells, which are necessary for the development of organs and the compartmentalization of functions. The components of the protein complexes that generate cadherin-based junctions have ancient origins, with conserved elements shared between animals as diverse as sponges and vertebrates. In invertebrates, the formation and function of epithelial sheets depends on classical cadherin-containing adherens junctions, which link actin to the plasma membrane through α-, β- and p120 catenins. Vertebrates also have a new type of cadherin-based intercellular junction called the desmosome, which allowed for the creation of more complex and effective tissue barriers against environmental stress. While desmosomes have a molecular blueprint that is similar to that of adherens junctions, desmosomal cadherins - called desmogleins and desmocollins - link intermediate filaments (IFs) rather than actin to the plasma membrane through protein complexes comprising relatives of β-catenin (plakoglobin) and p120 catenin (plakophilins). In turn, desmosomal catenins interact with members of the IF-binding plakin family to create the desmosome-IF linking complex. In this Minireview, we discuss when and how desmosomal components evolved, and how their ability to anchor the highly elastic and tough IF cytoskeleton endowed vertebrates with robust tissues capable of not only resisting but also properly responding to environmental stress.

Desmosomes: Essential contributors to an integrated intercellular junction network

The development of adhesive connections between cells was critical for the evolution of multicellularity and for organizing cells into complex organs with discrete compartments. Four types of intercellular junction are present in vertebrates: desmosomes, adherens junctions, tight junctions, and gap junctions. All are essential for the development of the embryonic layers and organs as well as adult tissue homeostasis. While each junction type is defined as a distinct entity, it is now clear that they cooperate physically and functionally to create a robust and functionally diverse system. During evolution, desmosomes first appeared in vertebrates as highly specialized regions at the plasma membrane that couple the intermediate filament cytoskeleton at points of strong cell–cell adhesion. Here, we review how desmosomes conferred new mechanical and signaling properties to vertebrate cells and tissues through their interactions with the existing junctional and cytoskeletal network.

The cell-cell junctions of mammalian testes. III. Absence of an endothelial cell layer covering the peritubular wall of the seminiferous tubules-an immunocytochemical correction of a 50-year-old error in the literature

In the molecular biological and ultrastructural studies of the peritubular wall cells encasing the seminiferous tubules of mammalian testes, we found it necessary to characterize the outermost cell layer bordering on the interstitial space in detail. For half a century, the extremely thin cells of this monolayer have in the literature been regarded as part of a lymphatic endothelium, in particular in rodents. However, our double-label immunofluorescence microscopical results have shown that in all six mammalian species examined, including three rodent ones (rat, mouse, guinea pig), this classification is not correct: the very attenuated cells of this monolayer are not of lymphatic endothelial nature as they do not contain established endothelial marker molecules. In particular, they do not contain claudin-5-positive tight junctions, VE-cadherin-positive adherens junctions, "lymph vessel endothelium hyaluronan receptor 1" (LYVE-1), podoplanin, protein myozap and "von Willebrand Factor" (vWF). By contrast and as controls, all these established marker molecules for the lymphatic endothelial cell type are found in the endothelia of the lymph and-partly also-blood vessels located nearby in the interstitial space. Thus, our results provide evidence that the monolayer cells covering the peritubular wall do not contain endothelial marker molecules and hence are not endothelial cells. We discuss possible methodological reasons for the maintenance of this incorrect cell type classification in the literature and emphasize the value of molecular analyses using multiple cell type-specific markers, also with respect to physiology and medical sciences.

Control of cellular responses to mechanical cues through YAP/TAZ regulation

To perceive their three-dimensional environment, cells and tissues must be able to sense and interpret various physical forces like shear, tensile, and compression stress. These forces can be generated both internally and externally in response to physical properties, like substrate stiffness, cell contractility, and forces generated by adjacent cells. Mechanical cues have important roles in cell fate decisions regarding proliferation, survival, and differentiation as well as the processes of tissue regeneration and wound repair. Aberrant remodeling of the extracellular space and/or defects in properly responding to mechanical cues likely contributes to various disease states, such as fibrosis, muscle diseases, and cancer. Mechanotransduction involves the sensing and translation of mechanical forces into biochemical signals, like activation of specific genes and signaling cascades that enable cells to adapt to their physical environment. The signaling pathways involved in mechanical signaling are highly complex, but numerous studies have highlighted a central role for the Hippo pathway and other signaling networks in regulating the YAP and TAZ (YAP/TAZ) proteins to mediate the effects of mechanical stimuli on cellular behavior. How mechanical cues control YAP/TAZ has been poorly understood. However, rapid progress in the last few years is beginning to reveal a surprisingly diverse set of pathways for controlling YAP/TAZ. In this review, we will focus on how mechanical perturbations are sensed through changes in the actin cytoskeleton and mechanosensors at focal adhesions, adherens junctions, and the nuclear envelope to regulate YAP/TAZ.

Trans-endocytosis elicited by nectins transfers cytoplasmic cargo, including infectious material, between cells

Here, we show that cells expressing the adherens junction protein nectin-1 capture nectin-4-containing membranes from the surface of adjacent cells in a trans-endocytosis process. We find that internalized nectin-1-nectin-4 complexes follow the endocytic pathway. The nectin-1 cytoplasmic tail controls transfer: its deletion prevents trans-endocytosis, while its exchange with the nectin-4 tail reverses transfer direction. Nectin-1-expressing cells acquire dye-labeled cytoplasmic proteins synchronously with nectin-4, a process most active during cell adhesion. Some cytoplasmic cargo remains functional after transfer, as demonstrated with encapsidated genomes of measles virus (MeV). This virus uses nectin-4, but not nectin-1, as a receptor. Epithelial cells expressing nectin-4, but not those expressing another MeV receptor in its place, can transfer infection to nectin-1-expressing primary neurons. Thus, this newly discovered process can move cytoplasmic cargo, including infectious material, from epithelial cells to neurons. We name the process nectin-elicited cytoplasm transfer (NECT). NECT-related trans-endocytosis processes may be exploited by pathogens to extend tropism. This article has an associated First Person interview with the first author of the paper.

Vinculin is critical for the robustness of the epithelial cell sheet paracellular barrier for ions

Vinculin in the apical junctional complex maintains the paracellular barrier function specifically for ions, but not for large solutes, by buffering mechanical fluctuations.

The paracellular barrier function of tight junctions (TJs) in epithelial cell sheets is robustly maintained against mechanical fluctuations, by molecular mechanisms that are poorly understood. Vinculin is an adaptor of a mechanosensory complex at the adherens junction. Here, we generated vinculin KO Eph4 epithelial cells and analyzed their confluent cell-sheet properties. We found that vinculin is dispensable for the basic TJ structural integrity and the paracellular barrier function for larger solutes. However, vinculin is indispensable for the paracellular barrier function for ions. In addition, TJs stochastically showed dynamically distorted patterns in vinculin KO cell sheets. These KO phenotypes were rescued by transfecting full-length vinculin and by relaxing the actomyosin tension with blebbistatin, a myosin II ATPase activity inhibitor. Our findings indicate that vinculin resists mechanical fluctuations to maintain the TJ paracellular barrier function for ions in epithelial cell sheets.

Extracellular Vesicles: Delivery Vehicles of Myokines

Movement and regular physical activity are two important factors that help the human body prevent, reduce and treat different chronic diseases such as obesity, type 2 diabetes, heart diseases, hypertension, sarcopenia, cachexia and cancer. During exercise, several tissues release molecules into the blood stream, and are able to mediate beneficial effects throughout the whole body. In particular, contracting skeletal muscle cells have the capacity to communicate with other organs through the release of humoral factors that play an important role in the mechanisms of adaptation to physical exercise. These muscle-derived factors, today recognized as myokines, act as endocrine and paracrine hormones. Moreover, exercise may stimulate the release of small membranous vesicles into circulation, whose composition is influenced by the same exercise. Combining the two hypotheses, these molecules related to exercise, named exer-kines, might be secreted from muscle cells inside small vesicles (nanovesicles). These could act as messengers in tissue cross talk during physical exercise. Thanks to their ability to deliver useful molecules (such as proteins and miRNA) in both physiological and pathological conditions, extracellular vesicles can be thought of as promising candidates for potential therapeutic and diagnostic applications for several diseases.

Cep128 associates with Odf2 to form the subdistal appendage of the centriole

The mother centriole in a cell has two appendages, the distal appendage (DA) and subdistal appendage (SDA), which have roles in generating cilia and organizing the cellular microtubular network, respectively. In the knockout (KO) cells of Odf2, the component of the DA and SDA, both appendages simultaneously disappear. However, the molecular mechanisms by which the DA and SDA form independently but close to each other downstream of Odf2 are unknown. Here, using super-resolution structured illumination microscopy (SR-SIM), we found that the signal for GFP-tagged Odf2 overlapped considerably with that of immunofluorescently labeled Cep128. We further found that Cep128 knockdown (KD) caused the dissociation of other SDA components from the centriole, including centriolin, Ndel1, ninein and Cep170, whereas Odf2 was still associated with the centriole. In contrast, the DA components remained associated with the centriole in Cep128 KD cells. Consistent with this observation, we identified Cep128 as an Odf2-interacting protein by immunoprecipitation. Taken with the finding that Cep128 deletion decreased the stability of centriolar microtubules, our results indicate that Cep128 associates with Odf2 in the hierarchical assembly of SDA components to elicit the microtubule-organizing function.

Claudin-3 regulates bile canalicular paracellular barrier and cholesterol gallstone core formation in mice

BACKGROUND & AIMS

Most cholesterol gallstones have a core consisting of inorganic and/or organic calcium salts, although the mechanisms of core formation are poorly understood. We examined whether the paracellular permeability of ions at hepatic tight junctions is involved in the core formation of cholesterol gallstones, with particular interest in the role of phosphate ion, a common food additive and preservative.

METHODS

We focused on claudin-3 (Cldn3), a paracellular barrier-forming tight junction protein whose expression in mouse liver decreases with age. Since Cldn3-knockout mice exhibited gallstone diseases, we used them to assess the causal relationship between paracellular phosphate ion permeability and the core formation of cholesterol gallstones.

RESULTS

In the liver of Cldn3-knockout mice, the paracellular phosphate ion permeability through hepatic tight junctions was significantly increased, resulting in calcium phosphate core formation. Cholesterol overdose caused cholesterol gallstone disease in these mice.

CONCLUSION

We revealed that in the hepatobiliary system, Cldn3 functions as a paracellular barrier for phosphate ions, to help maintain biliary ion homeostasis. We provide in vivo evidence that elevated phosphate ion concentrations play a major role in the lifestyle- and age-related risks of developing cholesterol gallstone disease under cholesterol overdose.

LAY SUMMARY

Herein, we reveal a new mechanism for cholesterol gallstone formation, in which increased paracellular phosphate ion permeability across hepatobiliary epithelia causes calcium phosphate core formation and cholesterol gallstones. Thus, altered phosphate ion metabolism under cholesterol overdose plays a major role in the lifestyle- and age-related risks of developing cholesterol gallstone disease.

AMPK-dependent phosphorylation of cingulin reversibly regulates its binding to actin filaments and microtubules

Cytoskeletal organization is essential for the precise morphogenesis of cells, tissues, and organs. Cytoskeletons, bound to scaffolding proteins, regulate the apical junction complex (AJC), which is composed of tight and adherens junctions, and located at the apical side of epithelial cell sheets. Cingulin is a tight junction-associated protein that binds to both actin filaments and microtubules. However, how cingulin binds to microtubules and whether cingulin can bind to actin and microtubules simultaneously are unclear. Here we examined the mechanisms behind cingulin’s cytoskeleton-binding properties. First, using total internal reflection fluorescence microscopy, we detected cingulin at microtubule cross points. We then found the interdomain interactions in cingulin molecules. Notably, we found that this interaction was regulated by AMPK-dependent phosphorylation and changed cingulin’s conformation and binding properties to actin filaments and microtubules. Finally, we found that the AMPK-regulated cingulin properties regulated the barrier functions of epithelial cell sheets. We propose that the cellular metabolic state, which involves AMPK, can contribute to the organization and maintenance of epithelial tissues through cingulin’s tight junction/cytoskeleton regulation.

The role of the gap junction perinexus in cardiac conduction: Potential as a novel anti-arrhythmic drug target

Cardiovascular disease remains the single largest cause of natural death in the United States, with a significant cause of mortality associated with cardiac arrhythmias. Presently, options for treating and preventing myocardial electrical dysfunction, including sudden cardiac death, are limited. Recent studies have indicated that conduction of electrical activation in the heart may have an ephaptic component, wherein intercellular coupling occurs via electrochemical signaling across narrow extracellular clefts between cardiomyocytes. The perinexus is a 100-200 nm-wide stretch of closely apposed membrane directly adjacent to connexin 43 gap junctions. Electron and super-resolution microscopy studies, as well as biochemical analyses, have provided evidence that perinexal nanodomains may be candidate structures for facilitating ephaptic coupling. This work has included characterization of the perinexus as a region of close inter-membrane contact between cardiomyocytes (<30 nm) containing dense clusters of voltage-gated sodium channels. Here, we review what is known about perinexal structure and function and the potential that the perinexus may have novel and pivotal roles in disorders of cardiac conduction. Of particular interest is the prospect that cell adhesion mediated by the cardiac sodium channel β subunit (Scn1b) may be a novel anti-arrhythmic target.

Spatial and temporal organization of cadherin in punctate adherens junctions

Adherens junctions (AJs) play a fundamental role in tissue integrity; however, the organization and dynamics of the key AJ transmembrane protein, E-cadherin, both inside and outside of AJs, remain controversial. Here we have studied the distribution and motility of E-cadherin in punctate AJs (pAJs) of A431 cells. Using single-molecule localization microscopy, we show that pAJs in these cells reach more than 1 μm in length and consist of several cadherin clusters with crystal-like density interspersed within sparser cadherin regions. Notably, extrajunctional cadherin appears to be monomeric, and its density is almost four orders of magnitude less than observed in the pAJ regions. Two alternative strategies of tracking cadherin motion within individual junctions show that pAJs undergo actin-dependent rapid-on the order of seconds-internal reorganizations, during which dense clusters disassemble and their cadherins are immediately reused for new clusters. Our results thus modify the classical view of AJs by depicting them as mosaics of cadherin clusters, the short lifetimes of which enable stable overall morphology combined with rapid internal rearrangements.

HMP-1/α-catenin promotes junctional mechanical integrity during morphogenesis

Adherens junctions (AJs) are key structures regulating tissue integrity and maintaining adhesion between cells. During morphogenesis, junctional proteins cooperate closely with the actomyosin network to drive cell movement and shape changes. How the junctions integrate the mechanical forces in space and in time during an in vivo morphogenetic event is still largely unknown, due to a lack of quantitative data. To address this issue, we inserted a functional Fluorescence Resonance Energy Transfer (FRET)-based force biosensor within HMP-1/α-catenin of Caenorhabditis elegans. We find that the tension exerted on HMP-1 has a cell-specific distribution, is actomyosin-dependent, but is regulated differently from the tension on the actin cortex during embryonic elongation. By using time-lapse analysis of mutants and tissue-specific rescue experiments, we confirm the role of VAB-9/Claudin as an actin bundle anchor. Nevertheless, the tension exerted on HMP-1 did not increase in the absence of VAB-9/Claudin, suggesting that HMP-1 activity is not upregulated to compensate for loss of VAB-9. Our data indicate that HMP-1 does not modulate HMR-1/E-cadherin turnover, is required to recruit junctional actin but not stress fiber-like actin bundles. Altogether, our data suggest that HMP-1/α-catenin acts to promote the mechanical integrity of adherens junctions.

Narrower insight to SIRT1 role in cancer: A potential therapeutic target to control epithelial-mesenchymal transition in cancer cells

The epithelial-mesenchymal transition (EMT) is a highly networked cellular process which involves cell transition from the immotile epithelial to the motile mesenchymal phenotype, whereby cells lose their cell-cell adhesion and cell polarity. This important process is one of the underlying mechanisms for enabling invasion and metastasis of cancer cells which is considered as malignant phase of tumor progression. However, the molecular mechanisms of this process are not fully clarified. It is reported that Sirtuin1 (SIRT1), a NAD+ dependent class III histone deacetylase is associated with tumor metastasis through positive regulation of EMT in several types of cancers. Recent studies confirmed that up and down regulation of SIRT1 expression remarkably change the migration ability of different cancer cells in vitro and tumor metastasis in vivo. Also, according to this fact that carcinomas as the main human solid tumors, originate from different epithelial cell types, SIRT1 role in EMT has received a great attention due to its potential role in tumor development and metastasis. Therefore, SIRT1 has been proposed as a key regulator of cancer metastasis by promoting EMT, although little is known about the cleared effect of SIRT1 in this transition. Our aim in this review is to explain in more detail the role of SIRT1 in various signaling pathways related to carcinogenesis, with the focus on the promoting role of SIRT1 in EMT as a potential therapeutic target to control EMT and to prevent cancer progression.

Defenders and Challengers of Endothelial Barrier Function

Regulated vascular permeability is an essential feature of normal physiology and its dysfunction is associated with major human diseases ranging from cancer to inflammation and ischemic heart diseases. Integrity of endothelial cells also play a prominent role in the outcome of surgical procedures and organ transplant. Endothelial barrier function and integrity are regulated by a plethora of highly specialized transmembrane receptors, including claudin family proteins, occludin, junctional adhesion molecules (JAMs), vascular endothelial (VE)-cadherin, and the newly identified immunoglobulin (Ig) and proline-rich receptor-1 (IGPR-1) through various distinct mechanisms and signaling. On the other hand, vascular endothelial growth factor (VEGF) and its tyrosine kinase receptor, VEGF receptor-2, play a central role in the destabilization of endothelial barrier function. While claudins and occludin regulate cell-cell junction via recruitment of zonula occludens (ZO), cadherins via catenin proteins, and JAMs via ZO and afadin, IGPR-1 recruits bullous pemphigoid antigen 1 [also called dystonin (DST) and SH3 protein interacting with Nck90/WISH (SH3 protein interacting with Nck)]. Endothelial barrier function is moderated by the function of transmembrane receptors and signaling events that act to defend or destabilize it. Here, I highlight recent advances that have provided new insights into endothelial barrier function and mechanisms involved. Further investigation of these mechanisms could lead to the discovery of novel therapeutic targets for human diseases associated with endothelial dysfunction.

Neural Progenitor Cell Polarity and Cortical Development

Neurons populating the cerebral cortex are generated during embryonic development from neural stem and progenitor cells in a process called neurogenesis. Neural stem and progenitor cells are classified into several classes based on the different location of mitosis (apical or basal) and polarity features (bipolar, monopolar and non-polar). The polarized architecture of stem cells is linked to the asymmetric localization of proteins, mRNAs and organelles, such as the centrosome and the Golgi apparatus (GA). Polarity affects stem cell function and allows stem cells to integrate environmental cues from distinct niches in the developing cerebral cortex. The crucial role of polarity in neural stem and progenitor cells is highlighted by the fact that impairment of cell polarity is linked to neurodevelopmental disorders such as Down syndrome, Fragile X syndrome, autism spectrum disorders (ASD) and schizophrenia.

Cell-cell adhesion in metazoans relies on evolutionarily conserved features of the α-catenin·β-catenin-binding interface

Stable tissue integrity during embryonic development relies on the function of the cadherin·catenin complex (CCC). The Caenorhabditis elegans CCC is a useful paradigm for analyzing in vivo requirements for specific interactions among the core components of the CCC, and it provides a unique opportunity to examine evolutionarily conserved mechanisms that govern the interaction between α- and β-catenin. HMP-1, unlike its mammalian homolog α-catenin, is constitutively monomeric, and its binding affinity for HMP-2/β-catenin is higher than that of α-catenin for β-catenin. A crystal structure shows that the HMP-1·HMP-2 complex forms a five-helical bundle structure distinct from the structure of the mammalian α-catenin·β-catenin complex. Deletion analysis based on the crystal structure shows that the first helix of HMP-1 is necessary for binding HMP-2 avidly in vitro and for efficient recruitment of HMP-1 to adherens junctions in embryos. HMP-2 Ser-47 and Tyr-69 flank its binding interface with HMP-1, and we show that phosphomimetic mutations at these two sites decrease binding affinity of HMP-1 to HMP-2 by 40-100-fold in vitro. In vivo experiments using HMP-2 S47E and Y69E mutants showed that they are unable to rescue hmp-2(zu364) mutants, suggesting that phosphorylation of HMP-2 on Ser-47 and Tyr-69 could be important for regulating CCC formation in C. elegans Our data provide novel insights into how cadherin-dependent cell-cell adhesion is modulated in metazoans by conserved elements as well as features unique to specific organisms.

The role of apical cell-cell junctions and associated cytoskeleton in mechanotransduction

Tissues of multicellular organisms are characterised by several types of specialised cell-cell junctions. In vertebrate epithelia and endothelia, tight and adherens junctions (AJ) play critical roles in barrier and adhesion functions, and are connected to the actin and microtubule cytoskeletons. The interaction between junctions and the cytoskeleton is crucial for tissue development and physiology, and is involved in the molecular mechanisms governing cell shape, motility, growth and signalling. The machineries which functionally connect tight and AJ to the cytoskeleton comprise proteins which either bind directly to cytoskeletal filaments, or function as adaptors for regulators of the assembly and function of the cytoskeleton. In the last two decades, specific cytoskeleton-associated junctional molecules have been implicated in mechanotransduction, revealing the existence of multimolecular complexes that can sense mechanical cues and translate them into adaptation to tensile forces and biochemical signals. Here, we summarise the current knowledge about the machineries that link tight and AJ to actin filaments and microtubules, and the molecular basis for mechanotransduction at epithelial and endothelial AJ.

Memory of cell shape biases stochastic fate decision-making despite mitotic rounding

Cell shape influences function, and the current model suggests that such shape effect is transient. However, cells dynamically change their shapes, thus, the critical question is whether shape information remains influential on future cell function even after the original shape is lost. We address this question by integrating experimental and computational approaches. Quantitative live imaging of asymmetric cell-fate decision-making and their live shape manipulation demonstrates that cellular eccentricity of progenitor cell indeed biases stochastic fate decisions of daughter cells despite mitotic rounding. Modelling and simulation indicates that polarized localization of Delta protein instructs by the progenitor eccentricity is an origin of the bias. Simulation with varying parameters predicts that diffusion rate and abundance of Delta molecules quantitatively influence the bias. These predictions are experimentally validated by physical and genetic methods, showing that cells exploit a mechanism reported herein to influence their future fates based on their past shape despite dynamic shape changes.

Cell shape influences function but during mitotic cell rounding the original shape is lost. Here the authors show that the cellular eccentricity of progenitor cell biases stochastic fate-decisions using a combination of quantitative live imaging, genetic manipulations and computational simulations.

Synaptopodin couples epithelial contractility to α-actinin-4-dependent junction maturation

A novel tension-sensitive junctional protein, synaptopodin, can relay biophysical input from cellular actomyosin contractility to induce biochemical changes at cell–cell contacts, resulting in structural reorganization of the junctional complex and epithelial barrier maturation.

The epithelial junction experiences mechanical force exerted by endogenous actomyosin activities and from interactions with neighboring cells. We hypothesize that tension generated at cell–cell adhesive contacts contributes to the maturation and assembly of the junctional complex. To test our hypothesis, we used a hydraulic apparatus that can apply mechanical force to intercellular junction in a confluent monolayer of cells. We found that mechanical force induces α-actinin-4 and actin accumulation at the cell junction in a time- and tension-dependent manner during junction development. Intercellular tension also induces α-actinin-4–dependent recruitment of vinculin to the cell junction. In addition, we have identified a tension-sensitive upstream regulator of α-actinin-4 as synaptopodin. Synaptopodin forms a complex containing α-actinin-4 and β-catenin and interacts with myosin II, indicating that it can physically link adhesion molecules to the cellular contractile apparatus. Synaptopodin depletion prevents junctional accumulation of α-actinin-4, vinculin, and actin. Knockdown of synaptopodin and α-actinin-4 decreases the strength of cell–cell adhesion, reduces the monolayer permeability barrier, and compromises cellular contractility. Our findings underscore the complexity of junction development and implicate a control process via tension-induced sequential incorporation of junctional components.

Microtubules Inhibit E-Cadherin Adhesive Activity by Maintaining Phosphorylated p120-Catenin in a Colon Carcinoma Cell Model

Tight regulation of cadherin-mediated intercellular adhesions is critical to both tissue morphogenesis during development and tissue homeostasis in adults. Cell surface expression of the cadherin-catenin complex is often directly correlated with the level of adhesion, however, examples exist where cadherin appears to be inactive and cells are completely non-adhesive. The state of p120-catenin phosphorylation has been implicated in regulating the adhesive activity of E-cadherin but the mechanism is currently unclear. We have found that destabilization of the microtubule cytoskeleton, independent of microtubule plus-end dynamics, dephosphorylates p120-catenin and activates E-cadherin adhesion in Colo 205 cells. Through chemical screening, we have also identified several kinases as potential regulators of E-cadherin adhesive activity. Analysis of several p120-catenin phosphomutants suggests that gross dephosphorylation of p120-catenin rather than that of specific amino acids may trigger E-cadherin adhesion. Uncoupling p120-catenin binding to E-cadherin at the membrane causes constitutive adhesion in Colo 205 cells, further supporting an inhibitory role of phosphorylated p120-catenin on E-cadherin activity.

Claudin-21 Has a Paracellular Channel Role at Tight Junctions

Claudin protein family members, of which there are at least 27 in humans and mice, polymerize to form tight junctions (TJs) between epithelial cells, in a tissue- and developmental stage-specific manner. Claudins have a paracellular barrier function. In addition, certain claudins function as paracellular channels for small ions and/or solutes by forming selective pores at the TJs, although the specific claudins involved and their functional mechanisms are still in question. Here we show for the first time that claudin-21, which is more highly expressed in the embryonic than the postnatal stages, acts as a paracellular channel for small cations, such as Na(+), similar to the typical channel-type claudins claudin-2 and -15. Claudin-21 also allows the paracellular passage of larger solutes. Our findings suggest that claudin-21-based TJs allow the passage of small and larger solutes by both paracellular channel-based and some additional mechanisms.