α-Catenin contributes to the strength of E-cadherin-p120 interactions

3D cell segregation geometry and dynamics are governed by tissue surface tension regulation

Tissue morphogenesis and patterning during development involve the segregation of cell types. Segregation is driven by differential tissue surface tensions generated by cell types through controlling cell-cell contact formation by regulating adhesion and actomyosin contractility-based cellular cortical tensions. We use vertebrate tissue cell types and zebrafish germ layer progenitors as in vitro models of 3-dimensional heterotypic segregation and developed a quantitative analysis of their dynamics based on 3D time-lapse microscopy. We show that general inhibition of actomyosin contractility by the Rho kinase inhibitor Y27632 delays segregation. Cell type-specific inhibition of non-muscle myosin2 activity by overexpression of myosin assembly inhibitor S100A4 reduces tissue surface tension, manifested in decreased compaction during aggregation and inverted geometry observed during segregation. The same is observed when we express a constitutively active Rho kinase isoform to ubiquitously keep actomyosin contractility high at cell-cell and cell-medium interfaces and thus overriding the interface-specific regulation of cortical tensions. Tissue surface tension regulation can become an effective tool in tissue engineering.

Reduction of invasion and cell stemness and induction of apoptotic cell death by Cinnamomum cassia extracts on human osteosarcoma cells

Cinnamomum cassia possesses antioxidative activity and induces the apoptotic properties of various cancer types. However, its effect on osteosarcoma invasion and cancer stemness remains ambiguous. Here, we examined the molecular evidence of the anti-invasive effects of ethanoic C. cassia extracts (CCE). Invasion and migration were obviously suppressed after the expression of urokinase-type plasminogen activator and matrix metalloprotein 2 in human osteosarcoma 143B cells were downregulated. CCE reversed epithelial-to-mesenchymal transition (EMT) induced by transforming growth factor β1 and downregulated mesenchymal markers, such as snail-1 and RhoA. CCE suppressed self-renewal property and the expression of stemness genes (aldehyde dehydrogenase, Nanog, and CD44) in the 143B cells. CCE suppressed cell viability, reduced the colony formation of osteosarcoma cancer cells, and induced apoptotic cell death in the 143B cells, as indicated by caspase-9 activation. The xenograft tumor model of immunodeficient BALB/c nude mice showed that CCE administered in vivo through oral gavage inhibited the growth of implanted 143B cells. These findings indicated that CCE inhibited the invasion, migration, and cancer stemness of the 143B cells. CCE reduced proliferation of 143B cell possibly because of the activation of caspase-9 and the consequent apoptosis, suggesting that CCE is a potential anticancer supplement for osteosarcoma.

Reconstitution of the full transmembrane cadherin-catenin complex

The dynamic regulation of epithelial adherens junctions relies on all components of the E-cadherin-catenin complex. Previously, the complexes have been partially reconstituted and composed only of α-catenin, β-catenin, and the E-cadherin cytoplasmic domain. However, p120-catenin and the full-length E-cadherin including the extracellular, transmembrane, and intra-cellular domains are vital to the understanding of the relationship between extracellular adhesion and intracellular signaling. Here, we reconstitute the complete and full-length cadherin-catenin complex, including full-length E-cadherin, α-catenin, β-catenin, and p120-catenin, into nanodiscs. We are able to observe the cadherin in nanodiscs by cryo-EM. We also reconstitute α-catenin, β-catenin, and p120-catenin with the E-cadherin cytoplasmic tail alone in order to analyze the affinities of their binding interactions. We find that p120-catenin does not associate strongly with α- or β-catenin and binds much more transiently to the cadherin cytoplasmic tail than does β-catenin. Overall, this work creates many new possibilities for biochemical studies understanding transmembrane signaling of cadherins and the role of p120-catenin in adhesion activation.

Bacteroides fragilis Toxin Induces Intestinal Epithelial Cell Secretion of Interleukin-8 by the E-Cadherin/β-Catenin/NF-κB Dependent Pathway

Enterotoxigenic Bacteroides fragilis (ETBF) has emerged as a gut microbiome pathogen that can promote colitis associated cancer in humans. ETBF secretes the metalloprotease, B. fragilis toxin (BFT), which can induce ectodomain cleavage of E-cadherin and IL-8 secretion through the β-catenin, NF-κB, and MAPK pathways in intestinal epithelial cells. However, it is still unclear whether E-cadherin cleavage is required for BFT induced IL-8 secretion and the relative contribution of these signaling pathways to IL-8 secretion. Using siRNA knockdown and CRISPR knockout studies, we found that E-cadherin cleavage is required for BFT mediated IL-8 secretion. In addition, genetic ablation of β-catenin indicates that β-catenin is required for the BFT induced increase in transcriptional activity of NF-κB, p65 nuclear localization and early IL-8 secretion. These results suggest that BFT induced β-catenin signaling is upstream of NF-κB activation. However, despite β-catenin gene disruption, BFT still activated the MAPK pathway, suggesting that the BFT induced activation of the MAPK signaling pathway is independent from the E-cadherin/β-catenin/NF-κB pathway. These findings show that E-cadherin and β-catenin play a critical role in acute inflammation following ETBF infection through the inflammatory response to BFT in intestinal epithelial cells.

Sorting of cadherin-catenin-associated proteins into individual clusters

The cytoplasmic tails of classical cadherins form a multiprotein cadherin-catenin complex (CCC) that constitutes the major structural unit of adherens junctions (AJs). The CCC in AJs forms junctional clusters, "E clusters," driven by cis and trans interactions in the cadherin ectodomain and stabilized by α-catenin-actin interactions. Additional proteins are known to bind to the cytoplasmic region of the CCC. Here, we analyze how these CCC-associated proteins (CAPs) integrate into cadherin clusters and how they affect the clustering process. Using a cross-linking approach coupled with mass spectrometry, we found that the majority of CAPs, including the force-sensing protein vinculin, interact with CCCs outside of AJs. Accordingly, structural modeling shows that there is not enough space for CAPs the size of vinculin to integrate into E clusters. Using two CAPs, scribble and erbin, as examples, we provide evidence that these proteins form separate clusters, which we term "C clusters." As proof of principle, we show, by using cadherin ectodomain monoclonal antibodies (mAbs), that mAb-bound E-cadherin forms separate clusters that undergo trans interactions. Taken together, our data suggest that, in addition to its role in cell-cell adhesion, CAP-driven CCC clustering serves to organize cytoplasmic proteins into distinct domains that may synchronize signaling networks of neighboring cells within tissues.

Deciphering molecular mechanisms of metastasis: novel insights into targets and therapeutics

BACKGROUND

The transition of a primary tumour to metastatic progression is driven by dynamic molecular changes, including genetic and epigenetic alterations. The metastatic cascade involves bidirectional interactions among extracellular and intracellular components leading to disintegration of cellular junctions, cytoskeleton reorganization and epithelial to mesenchymal transition. These events promote metastasis by reprogramming the primary cancer cell's molecular framework, enabling them to cause local invasion, anchorage-independent survival, cell death and immune resistance, extravasation and colonization of distant organs. Metastasis follows a site-specific pattern that is still poorly understood at the molecular level. Although various drugs have been tested clinically across different metastatic cancer types, it has remained difficult to develop efficacious therapeutics due to complex molecular layers involved in metastasis as well as experimental limitations.

CONCLUSIONS

In this review, a systemic evaluation of the molecular mechanisms of metastasis is outlined and the potential molecular components and their status as therapeutic targets and the associated pre-clinical and clinical agents available or under investigations are discussed. Integrative methods like pan-cancer data analysis, which can provide clinical insights into both targets and treatment decisions and help in the identification of crucial components driving metastasis such as mutational profiles, gene signatures, associated pathways, site specificities and disease-gene phenotypes, are discussed. A multi-level data integration of the metastasis signatures across multiple primary and metastatic cancer types may facilitate the development of precision medicine and open up new opportunities for future therapies.

The multifarious regulation of the apical junctional complex

Epithelial cells form highly organized polarized sheets with characteristic cell morphologies and tissue architecture. Cell–cell adhesion and intercellular communication are prerequisites of such cohesive sheets of cells, and cell connectivity is mediated through several junctional assemblies, namely desmosomes, adherens, tight and gap junctions. These cell–cell junctions form signalling hubs that not only mediate cell–cell adhesion but impact on multiple aspects of cell behaviour, helping to coordinate epithelial cell shape, polarity and function. This review will focus on the tight and adherens junctions, constituents of the apical junctional complex, and aims to provide a comprehensive overview of the complex signalling that underlies junction assembly, integrity and plasticity.

An optochemical tool for light-induced dissociation of adherens junctions to control mechanical coupling between cells

The cadherin-catenin complex at adherens junctions (AJs) is essential for the formation of cell-cell adhesion and epithelium integrity; however, studying the dynamic regulation of AJs at high spatio-temporal resolution remains challenging. Here we present an optochemical tool which allows reconstitution of AJs by chemical dimerization of the force bearing structures and their precise light-induced dissociation. For the dimerization, we reconstitute acto-myosin connection of a tailless E-cadherin by two ways: direct recruitment of α-catenin, and linking its cytosolic tail to the transmembrane domain. Our approach enables a specific ON-OFF switch for mechanical coupling between cells that can be controlled spatially on subcellular or tissue scale via photocleavage. The combination with cell migration analysis and traction force microscopy shows a wide-range of applicability and confirms the mechanical contribution of the reconstituted AJs. Remarkably, in vivo our tool is able to control structural and functional integrity of the epidermal layer in developing Xenopus embryos.

αE-catenin is a candidate tumor suppressor for the development of E-cadherin-expressing lobular-type breast cancer

Although mutational inactivation of E-cadherin (CDH1) is the main driver of invasive lobular breast cancer (ILC), approximately 10-15% of all ILCs retain membrane-localized E-cadherin despite the presence of an apparent non-cohesive and invasive lobular growth pattern. Given that ILC is dependent on constitutive actomyosin contraction for tumor development and progression, we used a combination of cell systems and in vivo experiments to investigate the consequences of α-catenin (CTNNA1) loss in the regulation of anchorage independence of non-invasive breast carcinoma. We found that inactivating somatic CTNNA1 mutations in human breast cancer correlated with lobular and mixed ducto-lobular phenotypes. Further, inducible loss of α-catenin in mouse and human E-cadherin-expressing breast cancer cells led to atypical localization of E-cadherin, a rounded cell morphology, and anoikis resistance. Pharmacological inhibition experiments subsequently revealed that, similar to E-cadherin-mutant ILC, anoikis resistance induced by α-catenin loss was dependent on Rho/Rock-dependent actomyosin contractility. Finally, using a transplantation-based conditional mouse model, we demonstrate that inducible inactivation of α-catenin instigates acquisition of lobular features and invasive behavior. We therefore suggest that α-catenin represents a bona fide tumor suppressor for the development of lobular-type breast cancer and as such provides an alternative event to E-cadherin inactivation, adherens junction (AJ) dysfunction, and subsequent constitutive actomyosin contraction. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

P120-Catenin Regulates Early Trafficking Stages of the N-Cadherin Precursor Complex

It is well established that binding of p120 catenin to the cytoplasmic domain of surface cadherin prevents cadherin endocytosis and degradation, contributing to cell-cell adhesion. In the present work we show that p120 catenin bound to the N-cadherin precursor, contributes to its anterograde movement from the endoplasmic reticulum (ER) to the Golgi complex. In HeLa cells, depletion of p120 expression, or blocking its binding to N-cadherin, increased the accumulation of the precursor in the ER, while it decreased the localization of mature N-cadherin at intercellular junctions. Reconstitution experiments in p120-deficient SW48 cells with all three major isoforms of p120 (1, 3 and 4) had similar capacity to promote the processing of the N-cadherin precursor to the mature form, and its localization at cell-cell junctions. P120 catenin and protein tyrosine phosphatase PTP1B facilitated the recruitment of the N-ethylmaleimide sensitive factor (NSF), an ATPase involved in vesicular trafficking, to the N-cadherin precursor complex. Dominant negative NSF E329Q impaired N-cadherin trafficking, maturation and localization at cell-cell junctions. Our results uncover a new role for p120 catenin bound to the N-cadherin precursor ensuring its trafficking through the biosynthetic pathway towards the cell surface.

α-Catenin-mediated cadherin clustering couples cadherin and actin dynamics

The function of the actin-binding domain of α-catenin, αABD, including its possible role in the direct anchorage of the cadherin-catenin complex to the actin cytoskeleton, has remained uncertain. We identified two point mutations on the αABD surface that interfere with αABD binding to actin and used them to probe the role of α-catenin-actin interactions in adherens junctions. We found that the junctions directly bound to actin via αABD were more dynamic than the junctions bound to actin indirectly through vinculin and that recombinant αABD interacted with cortical actin but not with actin bundles. This interaction resulted in the formation of numerous short-lived cortex-bound αABD clusters. Our data suggest that αABD clustering drives the continuous assembly of transient, actin-associated cadherin-catenin clusters whose disassembly is maintained by actin depolymerization. It appears then that such actin-dependent αABD clustering is a unique molecular mechanism mediating both integrity and reassembly of the cell-cell adhesive interface formed through weak cis- and trans-intercadherin interactions.

Cadherin controls nectin recruitment into adherens junctions by remodeling the actin cytoskeleton

The mechanism that coordinates activities of different adhesion receptors is poorly understood. We investigated this mechanism by focusing on the nectin-2 and E-cadherin adherens junction receptors. We found that, cadherin was not required for the basic process of nectin junction formation because nectin-2 formed junctions in cadherin-deficient A431D cells. Formation of nectin-2 junctions in these cells, however, became regulated by cadherin as soon as E-cadherin was re-expressed. E-cadherin recruited nectin-2 into adherens junctions, where both proteins formed distinct but tightly associated clusters. Live-cell imaging showed that the appearance of E-cadherin clusters often preceded that of nectin-2 clusters at sites of junction assembly. Inactivation of E-cadherin clustering by different strategies concomitantly suppressed the formation of nectin clusters. Furthermore, cadherin significantly increased the stability of nectin clusters, thereby making them resistant to the BC-12 antibody, which targets the nectin-2 adhesion interface. By testing different E-cadherin-α-catenin chimeras, we showed that the recruitment of nectin into chimera junctions is mediated by the actin-binding domain of α-catenin. Our data suggests that E-cadherin regulates assembly of nectin junctions through α-catenin-induced remodeling of the actin cytoskeleton around the cadherin clusters.

Dynamics and regulation of epithelial adherens junctions: recent discoveries and controversies

Adherens junctions (AJs) are evolutionarily conserved plasma-membrane structures that mediate cell-cell adhesions in multicellular organisms. They are organized by several types of adhesive integral membrane proteins, most notably cadherins and nectins that are clustered and stabilized by a number of cytoplasmic scaffolds. AJs are key regulators of tissue architecture and dynamics via control of cell proliferation, polarity, shape, motility, and survival. They are absolutely critical for normal tissue morphogenesis and their disruption results in pathological abnormalities in different tissues. Although the field of adherens-junction research dramatically progressed in recent years, a number of important questions remain controversial and poorly understood. This review outlines basic principles that regulate organization of AJs in mammalian epithelia and discusses recent advances and standing controversies in the field. A special attention is paid to the regulation of AJs by vesicle trafficking and the intracellular cytoskeleton as well as roles and mechanisms of adherens-junction disruption during tumor progression and tissue inflammation.

Guilt by association: what p120-catenin has to hide

Members of the p120-catenin family associate with cadherins and regulate their stability at the plasma membrane. How p120-catenin limits cadherin endocytosis has long remained a mystery. In this issue, Nanes et al. (2012. J. Cell Biol. doi:10.1083/jcb.201205029) identify a conserved acidic motif within cadherins that acts as a physical platform for p120-catenin binding. However, in the absence of p120-catenin, the motif acts as an endocytic signal. These results provide new insight into p120-catenin's role as guardian of intercellular junction dynamics.

Adherens junction assembly

Classical cadherins are a family of transmembrane proteins that mediate cell-cell adhesion at adherens junctions. A complex chain of cis- and trans- interactions between cadherin ectodomains establishes a cadherin adhesive cluster. A principal adhesive interaction in such clusters is an exchange of β strands between the first extracellular cadherin domains (EC1). The structure of cadherin adhesive clusters can be modified by other adherens junction proteins including additional transmembrane proteins, nectins and various intracellular proteins that directly or indirectly interact with the intracellular cadherin region. These interactions determine the dynamics and stability of cadherin adhesive structures.