A p120 catenin isoform switch affects Rho activity, induces tumor cell invasion, and predicts metastatic disease

Cigarette smoke extract-induced p120-mediated NF-κB activation in human epithelial cells is dependent on the RhoA/ROCK pathway

Cigarette smoke exposure is a major cause of chronic obstructive pulmonary disease (COPD), but the underlying molecular inflammatory mechanisms remain poorly understood. Previous studies have found that smoke disrupts cell-cell adhesion by inducing epithelial barrier damage to the adherens junction proteins, primarily E-cadherin (E-cad) and p120-catenin (p120). Recently, the anti-inflammatory role of p120 has drawn increasing attention. In this study, we demonstrate that p120 has a role in the cigarette smoke extract-induced inflammatory response, presumably by regulating NF-κB signaling activation. Mechanistically, we show that p120-mediated NF-κB signaling activation in airway epithelial inflammation is partially RhoA dependent and is independent of E-cad. These results provide novel evidence for the role of p120 in the anti-inflammatory response.

The Genome-Wide Analysis of Carcinoembryonic Antigen Signaling by Colorectal Cancer Cells Using RNA Sequencing

Сarcinoembryonic antigen (CEA, CEACAM5, CD66) is a promoter of metastasis in epithelial cancers that is widely used as a prognostic clinical marker of metastasis. The aim of this study is to identify the network of genes that are associated with CEA-induced colorectal cancer liver metastasis. We compared the genome-wide transcriptomic profiles of CEA positive (MIP101 clone 8) and CEA negative (MIP 101) colorectal cancer cell lines with different metastatic potential in vivo. The CEA-producing cells displayed quantitative changes in the level of expression for 100 genes (over-expressed or down-regulated). They were confirmed by quantitative RT-PCR. The KEGG pathway analysis identified 4 significantly enriched pathways: cytokine-cytokine receptor interaction, MAPK signaling pathway, TGF-beta signaling pathway and pyrimidine metabolism. Our results suggest that CEA production by colorectal cancer cells triggers colorectal cancer progression by inducing the epithelial- mesenchymal transition, increasing tumor cell invasiveness into the surrounding tissues and suppressing stress and apoptotic signaling. The novel gene expression distinctions establish the relationships between the existing cancer markers and implicate new potential biomarkers for colorectal cancer hepatic metastasis.

p120 Catenin-Mediated Stabilization of E-Cadherin Is Essential for Primitive Endoderm Specification

E-cadherin-mediated cell-cell adhesion is critical for naive pluripotency of cultured mouse embryonic stem cells (mESCs). E-cadherin-depleted mESC fail to downregulate their pluripotency program and are unable to initiate lineage commitment. To further explore the roles of cell adhesion molecules during mESC differentiation, we focused on p120 catenin (p120ctn). Although one key function of p120ctn is to stabilize and regulate cadherin-mediated cell-cell adhesion, it has many additional functions, including regulation of transcription and Rho GTPase activity. Here, we investigated the role of mouse p120ctn in early embryogenesis, mESC pluripotency and early fate determination. In contrast to the E-cadherin-null phenotype, p120ctn-null mESCs remained pluripotent, but their in vitro differentiation was incomplete. In particular, they failed to form cystic embryoid bodies and showed defects in primitive endoderm formation. To pinpoint the underlying mechanism, we undertook a structure-function approach. Rescue of p120ctn-null mESCs with different p120ctn wild-type and mutant expression constructs revealed that the long N-terminal domain of p120ctn and its regulatory domain for RhoA were dispensable, whereas its armadillo domain and interaction with E-cadherin were crucial for primitive endoderm formation. We conclude that p120ctn is not only an adaptor and regulator of E-cadherin, but is also indispensable for proper lineage commitment.

Roles and Regulation of Epithelial Splicing Regulatory Proteins 1 and 2 in Epithelial-Mesenchymal Transition

The transformation of polarized epithelial cells into cells with mesenchymal characteristics by the morphogenetic process of epithelial-mesenchymal transition (EMT) is a well-characterized process essential for embryonic development and associated with cancer progression. EMT is a program driven by changes in gene expression induced by several EMT-specific transcription factors, which inhibit the expression of cell-cell adhesion proteins and other epithelial markers, causing a characteristic loss of cell-cell adhesion, a switch to mesenchymal cell morphology, and increased migratory capabilities. Recently, it has become apparent that in addition to these transcriptionally regulated changes, EMT may also be regulated posttranscriptionally, that is, by alternative splicing. Specifically, the epithelial splicing regulatory proteins 1 and 2 (ESRP1 and ESRP2) have been described as epithelial-specific splicing master regulators specifically involved in EMT-associated alternative splicing. Here, we discuss the regulation of ESRP activity, as well as the evidence supporting a causal role of ESRPs in EMT.

p120-catenin controls contractility along the vertical axis of epithelial lateral membranes

In vertebrate epithelia, p120-catenin (hereafter referred to as p120; also known as CTNND1) mediates E-cadherin stability and suppression of RhoA. Genetic ablation of p120 in various epithelial tissues typically causes striking alterations in tissue function and morphology. Although these effects could very well involve p120's activity towards Rho, ascertaining the impact of this relationship has been complicated by the fact that p120 is also required for cell-cell adhesion. Here, we have molecularly uncoupled p120's cadherin-stabilizing and RhoA-suppressing activites. Unexpectedly, removing p120's Rho-suppressing activity dramatically disrupted the integrity of the apical surface, irrespective of E-cadherin stability. The physical defect was tracked to excessive actomyosin contractility along the vertical axis of lateral membranes. Thus, we suggest that p120's distinct activities towards E-cadherin and Rho are molecularly and functionally coupled and this, in turn, enables the maintenance of cell shape in the larger context of an epithelial monolayer. Importantly, local suppression of contractility by cadherin-bound p120 appears to go beyond regulating cell shape, as loss of this activity also leads to major defects in epithelial lumenogenesis.

Beyond β-catenin: prospects for a larger catenin network in the nucleus

β-catenin is widely regarded as the primary transducer of canonical WNT signals to the nucleus. In most vertebrates, there are eight additional catenins that are structurally related to β-catenin, and three α-catenin genes encoding actin-binding proteins that are structurally related to vinculin. Although these catenins were initially identified in association with cadherins at cell-cell junctions, more recent evidence suggests that the majority of catenins also localize to the nucleus and regulate gene expression. Moreover, the number of catenins reported to be responsive to canonical WNT signals is increasing. Here, we posit that multiple catenins form a functional network in the nucleus, possibly engaging in conserved protein-protein interactions that are currently better characterized in the context of actin-based cell junctions.

Phosphorylation and isoform use in p120-catenin during development and tumorigenesis

P120-catenin is essential to vertebrate development, modulating cadherin and small-GTPase functions, and growing evidence points also to roles in the nucleus. A complexity in addressing p120-catenin's functions is its many isoforms, including optional splicing events, alternative points of translational initiation, and secondary modifications. In this review, we focus upon how choices in the initiation of protein translation, or the earlier splicing of the RNA transcript, relates to primary sequences that harbor established or putative regulatory phosphorylation sites. While certain p120 phosphorylation events arise via known kinases/phosphatases and have defined outcomes, in most cases the functional consequences are still to be established. In this review, we provide examples of p120-isoforms as they relate to phosphorylation events, and thereby to isoform dependent protein-protein associations and downstream functions. We also provide a view of upstream pathways that determine p120's phosphorylation state, and that have an impact upon development and disease. Because other members of the p120 subfamily undergo similar processing and phosphorylation, as well as related catenins of the plakophilin subfamily, what is learned regarding p120 will by extension have wide relevance in vertebrates.

The Expression of the Zonula Adhaerens Protein PLEKHA7 Is Strongly Decreased in High Grade Ductal and Lobular Breast Carcinomas

PLEKHA7 is a junctional protein, which participates in a complex that stabilizes E-cadherin at the zonula adhaerens. Since E-cadherin is involved in epithelial morphogenesis, signaling, and tumor progression, we explored PLEKHA7 expression in cancer. PLEKHA7 expression was assessed in invasive ductal and lobular carcinomas of the breast by immunohistochemistry, immunofluorescence and quantitative RT-PCR. PLEKHA7 was detected at epithelial junctions of normal mammary ducts and lobules, and of tubular and micropapillary structures within G1 and G2 ductal carcinomas. At these junctions, the localization of PLEKHA7 was along the circumferential belt (zonula adhaerens), and only partially overlapping with that of E-cadherin, p120ctn and ZO-1, as shown previously in rodent tissues. PLEKHA7 immunolabeling was strongly decreased in G3 ductal carcinomas and undetectable in lobular carcinomas. PLEKHA7 mRNA was detected in both ductal and lobular carcinomas, with no observed correlation between mRNA levels and tumor type or grade. In summary, PLEKHA7 is a junctional marker of epithelial cells within tubular structures both in normal breast tissue and ductal carcinomas, and since PLEKHA7 protein but not mRNA expression is strongly decreased or lost in high grade ductal carcinomas and in lobular carcinomas, loss of PLEKHA7 is a newly characterized feature of these carcinomas.

Pro-Tumorigenic Phosphorylation of p120 Catenin in Renal and Breast Cancer

Altered protein expression and phosphorylation are common events during malignant transformation. These perturbations have been widely explored in the context of E-cadherin cell-cell adhesion complexes, which are central in the maintenance of the normal epithelial phenotype. A major component of these complexes is p120 catenin (p120), which binds and stabilizes E-cadherin to promote its adhesive and tumor suppressing function. However, p120 is also an essential mediator of pro-tumorigenic signals driven by oncogenes, such as Src, and can be phosphorylated at multiple sites. Although alterations in p120 expression have been extensively studied by immunohistochemistry (IHC) in the context of tumor progression, little is known about the status and role of p120 phosphorylation in cancer. Here we show that tyrosine and threonine phosphorylation of p120 in two sites, Y228 and T916, is elevated in renal and breast tumor tissue samples. We also show that tyrosine phosphorylation of p120 at its N-terminus, including at the Y228 site is required for its pro-tumorigenic potential. In contrast, phosphorylation of p120 at T916 does not affect this p120 function. However, phosphorylation of p120 at T916 interferes with epitope recognition of the most commonly used p120 antibody, namely pp120. As a result, this antibody selectively underrepresents p120 levels in tumor tissues, where p120 is phosphorylated. Overall, our data support a role of p120 phosphorylation as a marker and mediator of tumor transformation. Importantly, they also argue that the level and localization of p120 in human cancer tissues immunostained with pp120 needs to be re-evaluated.

Detection of recurrent alternative splicing switches in tumor samples reveals novel signatures of cancer

The determination of the alternative splicing isoforms expressed in cancer is fundamental for the development of tumor-specific molecular targets for prognosis and therapy, but it is hindered by the heterogeneity of tumors and the variability across patients. We developed a new computational method, robust to biological and technical variability, which identifies significant transcript isoform changes across multiple samples. We applied this method to more than 4000 samples from the The Cancer Genome Atlas project to obtain novel splicing signatures that are predictive for nine different cancer types, and find a specific signature for basal-like breast tumors involving the tumor-driver CTNND1. Additionally, our method identifies 244 isoform switches, for which the change occurs in the most abundant transcript. Some of these switches occur in known tumor drivers, including PPARG, CCND3, RALGDS, MITF, PRDM1, ABI1 and MYH11, for which the switch implies a change in the protein product. Moreover, some of the switches cannot be described with simple splicing events. Surprisingly, isoform switches are independent of somatic mutations, except for the tumor-suppressor FBLN2 and the oncogene MYH11. Our method reveals novel signatures of cancer in terms of transcript isoforms specifically expressed in tumors, providing novel potential molecular targets for prognosis and therapy. Data and software are available at: http://dx.doi.org/10.6084/m9.figshare.1061917 and https://bitbucket.org/regulatorygenomicsupf/iso-ktsp.

The Rho GTPase Rnd1 suppresses mammary tumorigenesis and EMT by restraining Ras-MAPK signalling

We identified the Rho GTPase Rnd1 as a candidate metastasis suppressor in basal-like and triple-negative breast cancer through bioinformatics analysis. Depletion of Rnd1 disrupted epithelial adhesion and polarity, induced epithelial-to-mesenchymal transition, and cooperated with deregulated expression of c-Myc or loss of p53 to cause neoplastic conversion. Mechanistic studies revealed that Rnd1 suppresses Ras signalling by activating the GAP domain of Plexin B1, which inhibits Rap1. Rap1 inhibition in turn led to derepression of p120 Ras-GAP, which was able to inhibit Ras. Inactivation of Rnd1 in mammary epithelial cells induced highly undifferentiated and invasive tumours in mice. Conversely, Rnd1 expression inhibited spontaneous and experimental lung colonization in mouse models of metastasis. Genomic studies indicated that gene deletion in combination with epigenetic silencing or, more rarely, point mutation inactivates RND1 in human breast cancer. These results reveal a previously unappreciated mechanism through which Rnd1 restrains activation of Ras-MAPK signalling and breast tumour initiation and progression.

RhoGTPases, actomyosin signaling and regulation of the epithelial Apical Junctional Complex

Epithelial cells form regulated and selective barriers between distinct tissue compartments. The Apical Junctional Complex (AJC) consisting of the tight junction (TJ) and adherens junction (AJ) control epithelial homeostasis, paracellular permeability and barrier properties. The AJC is composed of mutliprotein complexes consisting of transmembrane proteins that affiliate with an underlying perijunctional F-actin myosin ring through cytoplasmic scaffold proteins. AJC protein associations with the apical actin-myosin cytoskeleton are tightly controlled by a number of signaling proteins including the Rho family of GTPases that orchestrate junctional biology, epithelial homeostasis and barrier function. This review highlights the vital relationship of Rho GTPases and AJCs in controlling the epithelial barrier. The pathophysiologic relationship of Rho GTPases, AJC, apical actomyosin cytoskeleton and epithelial barrier function is discussed.

DIPA-family coiled-coils bind conserved isoform-specific head domain of p120-catenin family: potential roles in hydrocephalus and heterotopia

Isoform-specific expression of p120 affects cell motility and migration during development and tumor progression. The DIPA coiled-coil protein is a novel binding partner to the conserved isoform 1–specific head domain of p120 family members. Zebrafish data suggest that DIPA is mechanistically linked to p120 isoform–specific function in development.

p120-catenin (p120) modulates adherens junction (AJ) dynamics by controlling the stability of classical cadherins. Among all p120 isoforms, p120-3A and p120-1A are the most prevalent. Both stabilize cadherins, but p120-3A is preferred in epithelia, whereas p120-1A takes precedence in neurons, fibroblasts, and macrophages. During epithelial-to-mesenchymal transition, E- to N-cadherin switching coincides with p120-3A to -1A alternative splicing. These isoforms differ by a 101–amino acid “head domain” comprising the p120-1A N-terminus. Although its exact role is unknown, the head domain likely mediates developmental and cancer-associated events linked to p120-1A expression (e.g., motility, invasion, metastasis). Here we identified delta-interacting protein A (DIPA) as the first head domain–specific binding partner and candidate mediator of isoform 1A activity. DIPA colocalizes with AJs in a p120-1A- but not 3A-dependent manner. Moreover, all DIPA family members (Ccdc85a, Ccdc85b/DIPA, and Ccdc85c) interact reciprocally with p120 family members (p120, δ-catenin, p0071, and ARVCF), suggesting significant functional overlap. During zebrafish neural tube development, both knockdown and overexpression of DIPA phenocopy N-cadherin mutations, an effect bearing functional ties to a reported mouse hydrocephalus phenotype associated with Ccdc85c. These studies identify a novel, highly conserved interaction between two protein families that may participate either individually or collectively in N-cadherin–mediated development.

Myosin Vb uncoupling from RAB8A and RAB11A elicits microvillus inclusion disease

Microvillus inclusion disease (MVID) is a severe form of congenital diarrhea that arises from inactivating mutations in the gene encoding myosin Vb (MYO5B). We have examined the association of mutations in MYO5B and disruption of microvillar assembly and polarity in enterocytes. Stable MYO5B knockdown (MYO5B-KD) in CaCo2-BBE cells elicited loss of microvilli, alterations in junctional claudins, and disruption of apical and basolateral trafficking; however, no microvillus inclusions were observed in MYO5B-KD cells. Expression of WT MYO5B in MYO5B-KD cells restored microvilli; however, expression of MYO5B-P660L, a MVID-associated mutation found within Navajo populations, did not rescue the MYO5B-KD phenotype but induced formation of microvillus inclusions. Microvilli establishment required interaction between RAB8A and MYO5B, while loss of the interaction between RAB11A and MYO5B induced microvillus inclusions. Using surface biotinylation and dual immunofluorescence staining in MYO5B-KD cells expressing mutant forms of MYO5B, we observed that early microvillus inclusions were positive for the sorting marker SNX18 and derived from apical membrane internalization. In patients with MVID, MYO5B-P660L results in global changes in polarity at the villus tips that could account for deficits in apical absorption, loss of microvilli, aberrant junctions, and losses in transcellular ion transport pathways, likely leading to the MVID clinical phenotype of neonatal secretory diarrhea.

Molecular mechanisms of epithelial-mesenchymal transition

The transdifferentiation of epithelial cells into motile mesenchymal cells, a process known as epithelial-mesenchymal transition (EMT), is integral in development, wound healing and stem cell behaviour, and contributes pathologically to fibrosis and cancer progression. This switch in cell differentiation and behaviour is mediated by key transcription factors, including SNAIL, zinc-finger E-box-binding (ZEB) and basic helix-loop-helix transcription factors, the functions of which are finely regulated at the transcriptional, translational and post-translational levels. The reprogramming of gene expression during EMT, as well as non-transcriptional changes, are initiated and controlled by signalling pathways that respond to extracellular cues. Among these, transforming growth factor-β (TGFβ) family signalling has a predominant role; however, the convergence of signalling pathways is essential for EMT.

Exo70 isoform switching upon epithelial-mesenchymal transition mediates cancer cell invasion

Epithelial-mesenchymal transition (EMT) is an important developmental process hijacked by cancer cells for their dissemination. Here, we show that Exo70, a component of the exocyst complex, undergoes isoform switching mediated by ESRP1, a pre-mRNA splicing factor that regulates EMT. Expression of the epithelial isoform of Exo70 affects the levels of key EMT transcriptional regulators such as Snail and ZEB2 and is sufficient to drive the transition to epithelial phenotypes. Differential Exo70 isoform expression in human tumors correlates with cancer progression, and increased expression of the epithelial isoform of Exo70 inhibits tumor metastasis in mice. At the molecular level, the mesenchymal-but not the epithelial-isoform of Exo70 interacts with the Arp2/3 complex and stimulates actin polymerization for tumor invasion. Our findings provide a mechanism by which the exocyst function and actin dynamics are modulated for EMT and tumor invasion.

Genome-wide activities of RNA binding proteins that regulate cellular changes in the epithelial to mesenchymal transition (EMT)

The epithelial to mesenchymal transition (EMT) and reverse mesenchymal to epithelial transition (MET) are developmentally conserved processes that are essential for patterning of developing embryos and organs. The EMT/MET are further utilized in wound healing, but they can also be hijacked by cancer cells to promote tumor progression and metastasis. The molecular pathways governing these processes have historically focused on the transcriptional regulation and networks that control them. Indeed, global profiling of transcriptional changes has provided a wealth of information into how these networks are regulated, the downstream targets, and functional consequence of alterations to the global transcriptome. However, recent evidence has revealed that the posttranscriptional landscape of the cell is also dramatically altered during the EMT/MET and contributes to changes in cell behavior and phenotypes. While studies of this aspect of EMT biology are still in their infancy, recent progress has been achieved by the identification of several RNA binding proteins (RBPs) that regulate splicing, polyadenylation, mRNA stability, and translational control during EMT. This chapter focuses on the global impact of RBPs that regulate mRNA maturation as well as outlines the functional impact of several key posttranscriptional changes during the EMT. The growing evidence of RBP involvement in the cellular transformation during EMT underscores that a coordinated regulation of both transcriptional and posttranscriptional changes is essential for EMT. Furthermore, new discoveries into these events will paint a more detailed picture of the transcriptome during the EMT/MET and provide novel molecular targets for treatment of human diseases.

PTP-PEST targets a novel tyrosine site in p120 catenin to control epithelial cell motility and Rho GTPase activity

Tyrosine phosphorylation is implicated in regulating the adherens junction protein, p120 catenin (p120), however, the mechanisms are not well defined. Here, we show, using substrate trapping, that p120 is a direct target of the protein tyrosine phosphatase, PTP-PEST, in epithelial cells. Stable shRNA knockdown of PTP-PEST in colon carcinoma cells results in an increased cytosolic pool of p120 concomitant with its enhanced tyrosine phosphorylation and decreased association with E-cadherin. Consistent with this, PTP-PEST knockdown cells exhibit increased motility, enhanced Rac1 and decreased RhoA activity on a collagen substrate. Furthermore, p120 localization is enhanced at actin-rich protrusions and lamellipodia and has an increased association with the guanine nucleotide exchange factor, VAV2, and cortactin. Exchange factor activity of VAV2 is enhanced by PTP-PEST knockdown whereas overexpression of a VAV2 C-terminal domain or DH domain mutant blocks cell motility. Analysis of point mutations identified tyrosine 335 in the N-terminal domain of p120 as the site of PTP-PEST dephosphorylation. A Y335F mutant of p120 failed to induce the 'p120 phenotype', interact with VAV2, stimulate cell motility or activate Rac1. Together, these data suggest that PTP-PEST affects epithelial cell motility by controlling the distribution and phosphorylation of p120 and its availability to control Rho GTPase activity.

p120 catenin: an essential regulator of cadherin stability, adhesion-induced signaling, and cancer progression

p120 catenin is the best studied member of a subfamily of proteins that associate with the cadherin juxtamembrane domain to suppress cadherin endocytosis. p120 also recruits the minus ends of microtubules to the cadherin complex, leading to junction maturation. In addition, p120 regulates the activity of Rho family GTPases through multiple interactions with Rho GEFs, GAPs, Rho GTPases, and their effectors. Nuclear signaling is affected by the interaction of p120 with Kaiso, a transcription factor regulating Wnt-responsive genes as well as transcriptionally repressing methylated promoters. Multiple alternatively spliced p120 isoforms and complex phosphorylation events affect these p120 functions. In cancer, reduced p120 expression correlates with reduced E-cadherin function and with tumor progression. In contrast, in tumor cells that have lost E-cadherin expression, p120 promotes cell invasion and anchorage-independent growth. Furthermore, p120 is required for Src-induced oncogenic transformation and provides a potential target for future therapeutic interventions.

Beta-catenin versus the other armadillo catenins: assessing our current view of canonical Wnt signaling

The prevailing view of canonical Wnt signaling emphasizes the role of beta-catenin acting downstream of Wnt activation to regulate transcriptional activity. However, emerging evidence indicates that other armadillo catenins in vertebrates, such as members of the p120 subfamily, convey parallel signals to the nucleus downstream of canonical Wnt pathway activation. Their study is thus needed to appreciate the networked mechanisms of canonical Wnt pathway transduction, especially as they may assist in generating the diversity of Wnt effects observed in development and disease. In this chapter, we outline evidence of direct canonical Wnt effects on p120 subfamily members in vertebrates and speculate upon these catenins' roles in conjunction with or aside from beta-catenin.

Epithelial-mesenchymal transition: focus on metastatic cascade, alternative splicing, non-coding RNAs and modulating compounds

Epithelial-mesenchymal transition (EMT) is a key process in embryonic development and metastases formation during malignant progression. This review focuses on transcriptional regulation, non-coding RNAs, alternative splicing events and cell adhesion molecules regulation during EMT. Additionally, we summarize the knowledge with regard to the small potentially druggable molecules capable of modulating EMT for cancer therapy.

p120catenin alteration in cancer and its role in tumour invasion

Since its discovery in 1989 as a substrate of the Src oncogene, p120catenin has been revealed as an important player in cancer initiation and tumour dissemination. p120catenin regulates a wide range of cellular processes such as cell-cell adhesion, cell polarity and cell proliferation and plays a pivotal role in morphogenesis, inflammation and innate immunity. The pleiotropic effects of p120catenin rely on its interactions with numerous partners such as classical cadherins at the plasma membrane, Rho-GTPases and microtubules in the cytosol and transcriptional modulators in the nucleus. Alterations of p120catenin in cancer not only concern its expression level but also its intracellular localization and can lead to both pro-invasive and anti-invasive effects. This review focuses on the p120catenin-mediated pathways involved in cell migration and invasion and discusses the potential consequences of major cancer-related p120catenin alterations with respect to tumour spread.

Concomitant loss of p120-catenin and β-catenin membrane expression and oral carcinoma progression with E-cadherin reduction

The binding of p120-catenin and β-catenin to the cytoplasmic domain of E-cadherin establishes epithelial cell-cell adhesion. Reduction and loss of catenin expression degrades E-cadherin-mediated carcinoma cell-cell adhesion and causes carcinomas to progress into aggressive states. Since both catenins are differentially regulated and play distinct roles when they dissociate from E-cadherin, evaluation of their expression, subcellular localization and the correlation with E-cadherin expression are important subjects. However, the same analyses are not readily performed on squamous cell carcinomas in which E-cadherin expression determines the disease progression. In the present study, we examined expression and subcellular localization of p120-catenin and β-catenin in oral carcinomas (n = 67) and its implications in the carcinoma progression and E-cadherin expression using immunohitochemistry. At the invasive front, catenin-membrane-positive carcinoma cells were decreased in the dedifferentiated (p120-catenin, P < 0.05; β-catenin, P < 0.05) and invasive carcinomas (p120-catenin, P < 0.01; β-catenin, P < 0.05) and with the E-cadherin staining (p120-catenin, P < 0.01; β-catenin, P < 0.01). Carcinoma cells with β-catenin cytoplasmic and/or nuclear staining were increased at the invasive front compared to the center of tumors (P < 0.01). Although the p120-catenin isoform shift from three to one associates with carcinoma progression, it was not observed after TGF-β, EGF or TNF-α treatments. The total amount of p120-catenin expression was decreased upon co-treatment of TGF-β with EGF or TNF-α. The above data indicate that catenin membrane staining is a primary determinant for E-cadherin-mediated cell-cell adhesion and progression of oral carcinomas. Furthermore, it suggests that loss of p120-catenin expression and cytoplasmic localization of β-catenin fine-tune the carcinoma progression.

Posttranscriptional regulation by RNA-binding proteins during epithelial-to-mesenchymal transition

Epithelial-to-mesenchymal transition (EMT), one of the crucial steps for carcinoma cells to acquire invasive capacity, results from the disruption of cell–cell contacts and the acquisition of a motile mesenchymal phenotype. Although the transcriptional events controlling EMT have been extensively studied, in recent years, several posttranscriptional mechanisms have emerged as critical in the regulation of EMT during tumor progression. In this review, we highlight the regulation of posttranscriptional events in EMT by RNA-binding proteins (RBPs). RBPs are responsible for controlling pre-mRNA splicing, capping, and polyadenylation, as well as mRNA export, turnover, localization, and translation. We discuss the most relevant aspects of RBPs controlling the metabolism of EMT-related mRNAs, and describe the implication of novel posttranscriptional mechanisms regulating EMT in response to different signaling pathways. Novel insight into posttranscriptional regulation of EMT by RBPs is uncovering new therapeutic targets in cancer invasion and metastasis.

Interaction of p190RhoGAP with C-terminal domain of p120-catenin modulates endothelial cytoskeleton and permeability

p120-catenin is a multidomain intracellular protein, which mediates a number of cellular functions, including stabilization of cell-cell transmembrane cadherin complexes as well as regulation of actin dynamics associated with barrier function, lamellipodia formation, and cell migration via modulation of the activities of small GTPAses. One mechanism involves p120 catenin interaction with Rho GTPase activating protein (p190RhoGAP), leading to p190RhoGAP recruitment to cell periphery and local inhibition of Rho activity. In this study, we have identified a stretch of 23 amino acids within the C-terminal domain of p120 catenin as the minimal sequence responsible for the recruitment of p190RhoGAP (herein referred to as CRAD; catenin-RhoGAP association domain). Expression of the p120-catenin truncated mutant lacking the CRAD in endothelial cells attenuated effects of barrier protective oxidized phospholipid, OxPAPC. This effect was accompanied by inhibition of membrane translocation of p190RhoGAP, increased Rho signaling, as well as suppressed activation of Rac1 and its cytoskeletal effectors PAK1 (p21-activated kinase 1) and cortactin. Expression of p120 catenin-truncated mutant lacking CRAD also delayed the recovery process after thrombin-induced endothelial barrier disruption. Concomitantly, RhoA activation and downstream signaling were sustained for a longer period of time, whereas Rac signaling was inhibited. These data demonstrate a critical role for p120-catenin (amino acids 820-843) domain in the p120-catenin·p190RhoGAP signaling complex assembly, membrane targeting, and stimulation of p190RhoGAP activity toward inhibition of the Rho pathway and reciprocal up-regulation of Rac signaling critical for endothelial barrier regulation.

RhoA is down-regulated at cell-cell contacts via p190RhoGAP-B in response to tensional homeostasis

p190RhoGAP-B mediates Rho activity and ductal morphogenesis in response to 3D collagen stiffness. p190B associates with p120-catenin at cell–cell contacts, where RhoA activity is decreased compared to cell–ECM adhesions. This suggests that Rho is in an inactive pool at cell–cell contacts and is recruited to cell–ECM contacts in stiff matrices.

Breast epithelial cells cultured in three-dimensional (3D) collagen gels undergo ductal morphogenesis when the gel is compliant and they can achieve tensional homeostasis. We previously showed that this process requires down-regulation of Rho in compliant collagen gels, but the mechanism remains undefined. In this study, we find that p190RhoGAP-B, but not p190RhoGAP-A, mediates down-regulation of RhoA activity and ductal morphogenesis in T47D cells cultured in compliant 3D collagen gels. In addition, both RhoA and p190RhoGAP-B colocalize with p120-catenin at sites of cell–cell contact. The association between p190RhoGAP-B and p120-catenin is regulated by matrix compliance such that it increases in compliant vs. rigid collagen gels. Furthermore, knockdown of p120-catenin disrupts ductal morphogenesis, disregulates RhoA activity, and results in loss of p190B at cell–cell contacts. Consistent with these findings, using a RhoA-specific FRET biosensor (RhoA-FLARE.sc), we determined spatial RhoA activity to be significantly decreased at cell–cell contacts versus cell–ECM adhesions, and, of importance, spatial RhoA activity is regulated by p190B. This finding suggests that RhoA exists as an inactive pool at cell–cell contacts and is recruited to cell–ECM contacts within stiff matrices. Overall, these results demonstrate that RhoA is down-regulated at cell–cell contacts through p190RhoGAP-B, which is localized to cell–cell contacts by association with p120-catenin that is regulated by tensional homeostasis.

Cyclin-dependent kinase 5 promotes the stability of corneal epithelial cell junctions

PURPOSE

Although cyclin-dependent kinase 5 (Cdk5) inhibits the formation of junctions containing N-cadherin, the effect of Cdk5 on junctions containing E-cadherin is less clear. The present study investigates the functional significance of Cdk5 in forming and maintaining cell-cell stability in corneal epithelial cells.

METHODS

A Cdk5-deficient human corneal limbal epithelial cell line was generated by lentiviral transduction of small hairpin RNA specific for Cdk5 (shCdk5-HCLE cells). A blasticidin-inducible vector for expression of Cdk5-specific short hairpin RNA (ShCdk5) was generated by recombination and packaged into non-replicative lentiviral particles for transduction of human corneal limbal epithelial (HCLE) cells. Blasticidin-resistant cells were isolated for analysis. Cell aggregations were performed using HCLE, Cdk5 inhibitor olomoucine, ShCdk5, and MDA-MB 231 cells in the presence and absence of calcium, and particle size was measured using image analysis software. Relative protein concentrations were measured with immunoblotting and quantitative densitometry. Total internal reflection fluorescence (TIRF) microscopy was performed on cells transfected with green fluorescent protein (GFP)-E-cadherin or GFP-p120, and internalization of boundary-localized proteins was analyzed with particle tracking software. The stability of surface-exposed proteins was determined by measuring the recovery of biotin-labeled proteins with affinity chromatography. Rho and Rac activity was measured with affinity chromatography and immunoblotting.

RESULTS

Examining the effect of Cdk5 on E-cadherin containing epithelial cell-cell adhesions using a corneal epithelial cell line (HCLE), we found that Cdk5 and Cdk5 (pY15) coimmunoprecipitate with E-cadherin and Cdk5 (pY15) colocalizes with E-cadherin at cell-cell junctions. Inhibiting Cdk5 activity in HCLE or suppressing Cdk5 expression in a stable HCLE-derived cell line (ShHCLE) decreased calcium-dependent cell adhesion, promoted the cytoplasmic localization of E-cadherin, and accelerated the loss of surface-biotinylated E-cadherin. TIRF microscopy of GFP-E-cadherin in transfected HCLE cells showed an actively internalized sub-population of E-cadherin, which was not bound to p120 as it was trafficked away from the cell-cell boundary. This population increased in the absence of Cdk5 activity, suggesting that Cdk5 inhibition promotes dissociation of p120/E-cadherin junctional complexes. These effects of Cdk5 inhibition or suppression were accompanied by decreased Rac activity, increased Rho activity, and enhanced binding of E-cadherin to the Rac effector Ras GTPase-activating-like protein (IQGAP1). Cdk5 inhibition also reduced adhesion in a cadherin-deficient cell line (MDA-MB-231) expressing exogenous E-cadherin, although Cdk5 inhibition promoted adhesion when these cells were transfected with N-cadherin, as previous studies of Cdk5 and N-cadherin predicted. Moreover, Cdk5 inhibition induced N-cadherin expression and formation of N-cadherin/p120 complexes in HCLE cells.

CONCLUSIONS

These results indicate that loss of Cdk5 activity destabilizes junctional complexes containing E-cadherin, leading to internalization of E-cadherin and upregulation of N-cadherin. Thus, Cdk5 activity promotes stability of E-cadherin-based cell-cell junctions and inhibits the E-cadherin-to-N-cadherin switch typical of epithelial-mesenchymal transitions.

Regulatory networks defining EMT during cancer initiation and progression

Epithelial to mesenchymal transition (EMT) is essential for driving plasticity during development, but is an unintentional behaviour of cells during cancer progression. The EMT-associated reprogramming of cells not only suggests that fundamental changes may occur to several regulatory networks but also that an intimate interplay exists between them. Disturbance of a controlled epithelial balance is triggered by altering several layers of regulation, including the transcriptional and translational machinery, expression of non-coding RNAs, alternative splicing and protein stability.

Phosphorylation-mediated 14-3-3 protein binding regulates the function of the rho-specific guanine nucleotide exchange factor (RhoGEF) Syx

Syx is a Rho-specific guanine nucleotide exchange factor (GEF) that localizes at cell-cell junctions and promotes junction stability by activating RhoA and the downstream effector Diaphanous homolog 1 (Dia1). Previously, we identified several molecules, including 14-3-3 proteins, as Syx-interacting partners. In the present study, we show that 14-3-3 isoforms interact with Syx at both its N- and C-terminal regions in a phosphorylation-dependent manner. We identify the protein kinase D-mediated phosphorylation of serine 92 on Syx, and additional phosphorylation at serine 938, as critical sites for 14-3-3 association. Our data indicate that the binding of 14-3-3 proteins inhibits the GEF activity of Syx. Furthermore, we show that phosphorylation-deficient, 14-3-3-uncoupled Syx exhibits increased junctional targeting and increased GEF activity, resulting in the strengthening of the circumferential junctional actin ring in Madin-Darby canine kidney cells. These findings reveal a novel means of regulating junctional Syx localization and function by phosphorylation-induced 14-3-3 binding and further support the importance of Syx function in maintaining stable cell-cell contacts.

Neural Wiskott-Aldrich syndrome protein (N-WASP)-mediated p120-catenin interaction with Arp2-Actin complex stabilizes endothelial adherens junctions

Stable adherens junctions (AJs) are required for formation of restrictive endothelial barrier. Vascular endothelial cadherin from contiguous endothelial cells forms AJs, which are stabilized intracellularly by binding of p120-catenin and cortical actin. Mechanisms inducing cortical actin formation and enabling its linkage with p120-catenin remain enigmatic. We altered the function of neural Wiskott-Aldrich syndrome protein (N-WASP), which induces actin polymerization through actin-related protein 2/3 complex (Arp2/3), to address the role of N-WASP in regulating AJ stability and thereby endothelial permeability. We show that depletion of N-WASP in endothelial cells impaired AJ adhesion and favored the organization of actin from cortical actin to stress fibers, resulting thereby in formation of leaky endothelial barrier. Exposure of the N-WASP-depleted endothelial cell monolayer to the permeability-increasing mediator, thrombin, exaggerated AJ disruption and stress fiber formation, leading to an irreversible increase in endothelial permeability. We show that N-WASP binds p120-catenin through its verprolin cofilin acid (VCA) domain, induces cortical actin formation through Arp2, and links p120-catenin with cortical actin. The interaction of N-WASP with p120-catenin, actin, and Arp2 requires phosphorylation of N-WASP at the Tyr-256 residue by focal adhesion kinase. Expression of the VCA domain of N-WASP or phosphomimicking (Y256D)-N-WASP mutant in endothelial cells stabilizes AJs and facilitates barrier recovery after thrombin stimulation. Our study demonstrates that N-WASP, by mediating p120-catenin interaction with actin-polymerizing machinery, maintains AJs and mitigates disruption of endothelial barrier function by edemagenic agents, therefore representing a novel target for preventing leaky endothelial barrier syndrome.

RBFOX2 is an important regulator of mesenchymal tissue-specific splicing in both normal and cancer tissues

Alternative splicing provides a critical and flexible layer of regulation intervening in many biological processes to regulate the diversity of proteins and impact cell phenotype. To identify alternative splicing differences that distinguish epithelial from mesenchymal tissues, we have investigated hundreds of cassette exons using a high-throughput reverse transcription-PCR (RT-PCR) platform. Extensive changes in splicing were noted between epithelial and mesenchymal tissues in both human colon and ovarian tissues, with many changes from mostly one splice variant to predominantly the other. Remarkably, many of the splicing differences that distinguish normal mesenchymal from normal epithelial tissues matched those that differentiate normal ovarian tissues from ovarian cancer. Furthermore, because splicing profiling could classify cancer cell lines according to their epithelial/mesenchymal characteristics, we used these cancer cell lines to identify regulators for these specific splicing signatures. By knocking down 78 potential splicing factors in five cell lines, we provide an extensive view of the complex regulatory landscape associated with the epithelial and mesenchymal states, thus revealing that RBFOX2 is an important driver of mesenchymal tissue-specific splicing.

Upon Wnt stimulation, Rac1 activation requires Rac1 and Vav2 binding to p120-catenin

A role for Rac1 GTPase in canonical Wnt signaling has recently been demonstrated, showing that it is required for β-catenin translocation to the nucleus. In this study, we investigated the mechanism of Rac1 stimulation by Wnt. Upregulation of Rac1 activity by Wnt3a temporally correlated with enhanced p120-catenin binding to Rac1 and Vav2. Vav2 and Rac1 association with p120-catenin was modulated by phosphorylation of this protein, which was stimulated upon serine/threonine phosphorylation by CK1 and inhibited by tyrosine phosphorylation by Src or Fyn. Acting on these two post-translational modifications, Wnt3a induced the release of p120-catenin from E-cadherin, enabled the interaction of p120-catenin with Vav2 and Rac1, and facilitated Rac1 activation by Vav2. Given that p120-catenin depletion disrupts gastrulation in Xenopus, we analyzed p120-catenin mutants for their ability to rescue this phenotype. In contrast to the wild-type protein or other controls, p120-catenin point mutants that were deficient in the release from E-cadherin or in Vav2 or Rac1 binding failed to rescue p120-catenin depletion. Collectively, these results indicate that binding of p120-catenin to Vav2 and Rac1 is required for the activation of this GTPase upon Wnt signaling.

Making alternative splicing decisions during epithelial-to-mesenchymal transition (EMT)

Alternative splicing generates multiple mRNAs from a single transcript and is a major contributor to proteomic diversity and to the control of gene expression in complex organisms. Not surprisingly, this post-transcriptional event is tightly regulated in different tissues and developmental stages. An increasing body of evidences supports a causative role of aberrant alternative splicing in cancer. However, very little is known about its impact on cellular processes crucially involved in tumor progression. The aim of this review is to discuss the link between alternative splicing and the epithelial-to-mesenchymal transition (EMT), one of the major routes by which cancer cells acquire invasive capabilities and become metastatic. We begin with a brief overview of alternative splicing. Next, we discuss alternative splicing factors that regulate EMT. Finally, we provide examples of target genes presenting alternative splicing changes that contribute to the morphological conversions in the EMT process.

Bone marrow mesenchymal stem cells stimulated by TNF-α enhance the apoptosis of hepatic stellate cells

AIM: To observe the effect of rat bone marrow mesenchymal stem cells (BMSCs) stimulated by TNF-α on apoptosis of rat hepatic stellate cells (HSCs) in a co-culture system and to explore the possible mechanisms involved.

METHODS: BMSCs from SD rats were isolated, cultured, and purified by the whole bone marrow adherence method. BMSCs at passages 3-4 were stimulated by TNF-α and then co-cultured with HSCs in a Transwell co-culture system. Cells were divided into HSCs blank group, BMSCs blank group, normal co-culture group, and TNF-α-stimulated co-culture group. Apoptosis of HSCs was detected by flow cytometry; expression of RhoA and HGF mRNAs and proteins was tested by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot, respectively; and concentration of hepatocyte growth factor (HGF) in cell supernatants was determined by ELISA.

RESULTS: Compared to the normal co-culture group and HSCs blank group, the expression of RhoA protein (24 h: 0.864 ± 0.006, 48 h: 0.688 ± 0.013) and mRNA (24 h: 0.809 ± 0.004, 48 h: 0.494 ± 0.010) in HSCs was significantly lower in the TNF-α-stimulated co-culture group (all P < 0.01). The expression of HGF protein (24 h: 1.032 ± 0.003, 48 h: 1.060 ± 0.003) and mRNA (24 h: 0.857 ± 0.004, 48 h: 1.195 ± 0.010) in BMSCs was significantly higher in the TNF-α-stimulated co-culture group than in the normal co-culture group (all P < 0.05). The apoptosis rate of HSCs was significantly increased in the TNF-α-stimulated co-culture group (24 h: 6.583% ± 0.091%; 48 h: 29.960% ± 0.223%) compared to the normal co-culture group (24 h: 4.700% ± 0.168%, 48 h: 23.140% ± 0.115%; both P < 0.01).

CONCLUSION: BMSCs stimulated by TNF-α enhance the apoptosis of HSCs possibly via paracrine production of HGF by BMSCs to down-regulate RhoA signaling in HSCs.

N-cadherin expression level as a critical indicator of invasion in non-epithelial tumors

Cancer cell dissemination away from the primary tumor and their ability to form metastases remain the major causes of death from cancer. Understanding the molecular mechanisms triggering this event could lead to the design of new cancer treatments. The establishment and the maintenance of tissue architecture depend on the coordination of cell behavior within this tissue. Cell-cell interactions must form adhesive structures between neighboring cells while remaining highly dynamic to allow and control tissue renewal or remodeling. Among intercellular junctions, cadherin-based adherens junctions mediate strong physical interactions and transmit information from the cell microenvironment to the cytoplasm. Disruption of these cell-cell contacts perturbs the polarity of epithelial tissues leading to their disorganization and ultimately to aggressive carcinomas. In non-epithelial tissues, the role of cadherins in the development of cancer is still debated. We recently found that downregulation of N-cadherin in malignant glioma-the most frequent primary brain tumor-results in cell polarization defects leading to abnormal motile behavior with increased cell speed and decreased persistence in directionality. Re-expression of N-cadherin in glioma cells restores cell polarity and limits glioma cell migration, providing a potential therapeutic tool for diffuse glioma.

N-terminal 1-54 amino acid sequence and Armadillo repeat domain are indispensable for P120-catenin isoform 1A in regulating E-cadherin

P120-catenin (p120ctn) exerts important roles in regulating E-cadherin and invasiveness in cancer cells. However, the mechanisms by which p120ctn isoforms 1 and 3 modulate E-cadherin expression are poorly understood. In the current study, HBE, H460, SPC and LTE cell lines were used to examine the effects of p120ctn isoforms 1A and 3A on E-cadherin expression and cell invasiveness. E-cadherin was localized on the cell membrane of HBE and H460 cells, while it was confined to the cytoplasm in SPC and LTE cells. Depletion of endogenous p120ctn resulted in reduced E-cadherin expression; however, p120ctn ablation showed opposite effects on invasiveness in the cell lines by decreasing invasiveness in SPC and LTE cells and increasing it in HBE and H460 cells. Restitution of 120ctn isoform 1A restored E-cadherin on the cell membrane and blocked cell invasiveness in H460 and HBE cells, while it restored cytoplasmic E-cadherin and enhanced cell invasiveness in SPC and LTE cells. P120ctn isoform 3A increased the invasiveness in all four cell lines despite the lack of effect on E-cadherin expression, suggesting a regulatory pathway independent of E-cadherin. Moreover, five p120ctn isoform 1A deletion mutants were constructed and expressed in H460 and SPC cells. The results showed that only the M4 mutant, which contains N-terminal 1–54 amino acids and the Armadillo repeat domain, was functional in regulating E-cadherin and cell invasiveness, as observed in p120ctn isoform 1A. In conclusion, the N-terminal 1–54 amino acid sequence and Armadillo repeat domain of p120ctn isoform 1A are indispensable for regulating E-cadherin protein. P120ctn isoform 1A exerts opposing effects on cell invasiveness, corresponding to the subcellular localization of E-cadherin.

Regulation of adherens junctions by Rho GTPases and p120-catenin

The molecular mechanisms leading to tumor progression and acquisition of a metastatic phenotype are highly complex and only partially understood. The spatiotemporal regulation of E-cadherin-mediated adherens junctions is essential for normal epithelia function and tissue integrity. Perturbation of the E-cadherin complex assembly is a key event in epithelial-mesenchymal transition and is directed by a huge number of mechanisms that differ greatly with regard to cell types and tissues. The reduction in intercellular adhesion interferes with tissue integrity and allows cancer cells to disseminate from the primary tumor thereby initiating cancer metastasis. In the present review we will summarize the current findings about the influence of Rho GTPases on the formation and maintenance of adherens junction and will then proceed to discuss the involvement of p120-catenin on cell-cell adhesion and tumor cell migration.

Complex changes in alternative pre-mRNA splicing play a central role in the epithelial-to-mesenchymal transition (EMT)

The epithelial-to-mesenchymal transition (EMT) is an important developmental process that is also implicated in disease pathophysiology, such as cancer progression and metastasis. A wealth of literature in recent years has identified important transcriptional regulators and large-scale changes in gene expression programs that drive the phenotypic changes that occur during the EMT. However, in the past couple of years it has become apparent that extensive changes in alternative splicing also play a profound role in shaping the changes in cell behavior that characterize the EMT. While long known splicing switches in FGFR2 and p120-catenin provided hints of a larger program of EMT-associated alternative splicing, the recent identification of the epithelial splicing regulatory proteins 1 and 2 (ESRP1 and ESRP2) began to reveal this genome-wide post-transcriptional network. Several studies have now demonstrated the truly vast extent of this alternative splicing program. The global switches in splicing associated with the EMT add an important additional layer of post-transcriptional control that works in harmony with transcriptional and epigenetic regulation to effect complex changes in cell shape, polarity, and behavior that mediate transitions between epithelial and mesenchymal cell states. Future challenges include the need to investigate the functional consequences of these splicing switches at both the individual gene as well as systems level.

Genome-wide determination of a broad ESRP-regulated posttranscriptional network by high-throughput sequencing

Tissue-specific alternative splicing is achieved through the coordinated assembly of RNA binding proteins at specific sites to enhance or silence splicing at nearby splice sites. We used high-throughput sequencing (RNA-Seq) to investigate the complete spectrum of alternative splicing events that are regulated by the epithelium-specific splicing regulatory proteins ESRP1 and ESRP2. We also combined this analysis with direct RNA sequencing (DRS) to reveal ESRP-mediated regulation of alternative polyadenylation. To define binding motifs that mediate direct regulation of splicing and polyadenylation by ESRP, SELEX-Seq analysis was performed, coupling traditional SELEX with high-throughput sequencing. Identification and scoring of high-affinity ESRP1 binding motifs within ESRP target genes allowed the generation of RNA maps that define the position-dependent activity of the ESRPs in regulating cassette exons and alternative 3' ends. These extensive analyses provide a comprehensive picture of the functions of the ESRPs in an epithelial posttranscriptional gene expression program.

The three-dimensional structure of the cadherin-catenin complex

The cadherin-catenin complex is the major building block of the adherens junction. It is responsible for coupling Ca(2+)-dependent intercellular junctions with various intracellular events, including actin dynamics and signaling pathways. Determination of three-dimensional structures of cadherins, p120 catenin, β-catenin and α-catenin at atomic-level resolution has allowed us to examine how the structure and function of cell adhesion molecules are further modulated by protein-protein interactions. Structural studies of cadherins revealed the strand-swap-dependent and -independent trans-dimerization mechanisms, as well as a potential mechanism for lateral clustering of cadherin trans-dimers. Crystallographic and NMR analyses of p120 catenin revealed that it regulates the stability of cadherin-mediated cell-cell adhesion by associating with the majority of the E-cadherin juxtamembrane domain, including residues implicated in clathrin-mediated endocytosis and Hakai-dependent ubiquitination. Crystal structures of the β-catenin/E-cadherin complex and the β-/α-catenin chimera revealed extensive interactions necessary to form the cadherin/β-catenin/α-catenin ternary complex. Structural characterization of α-catenin has revealed conformational changes within the N-terminal and modulatory domains that are crucial for its role as a mechanosensor of cell-cell adhesion. Further insights into the connection between the cadherin-catenin complex and the actin cytoskeleton are integral to better understand how adjoining cells communicate through cell-cell adhesion.

Overexpression of small GTPases directly correlates with expression of δ-catenin and their coexpression predicts a poor clinical outcome in nonsmall cell lung cancer

δ-catenin can affect cytoskeletal assembly, and promote cell migration by regulating the activity of small GTPases. While many malignancies have been shown to be positive for δ-catenin, it is still unclear whether δ-catenin and small GTPases are coexpressed in tumor cells, and so is the relationship between their coexpression and prognosis in the tumor patients. In this study, immunohistochemistry was performed to examine expressive levels of δ-catenin, cdc42, and Rac1 in 135 cases of nonsmall cell lung cancer (NSCLC), including 60 cases with follow-up records. Thirty samples of paired lung cancer tissues and adjacent normal lung tissues were collected to analyze mRNA and protein expression of δ-catenin and small GTPases. The effects of δ-catenin on small GTPases expression and invasive ability of lung cancer cells were also evaluated. Compared with normal lung tissues, both mRNA and protein levels of δ-catenin and small GTPases were increased in lung cancer tissues (P < 0.05), and the expression of small GTPases directly correlated with that of δ-catenin (P < 0.001). In addition, δ-catenin and small GTPases tended to be coexpressed in lung adenocarcinoma, advanced stages, and primary tumors with lymph node metastasis (all P < 0.05). The patients with coexpression of δ-catenin and small GTPases had a shorter survival time than those without coexpression (P < 0.05). Furthermore, δ-catenin overexpression could enhance invasive ability of lung cancer cells by upregulating protein and transcriptional level of small GTPases. Therefore, δ-catenin likely upregulates the activity of small GTPases at transcriptional level, and their coexpression may predict a poor clinical outcome in NSCLC patients.

Association of Rho-associated protein kinase 1 with E-cadherin complexes is mediated by p120-catenin

The dynamic functional linkage of cadherins with the underlying actin cytoskeleton is tightly regulated to achieve proper cell-cell adhesion. p120-catenin (p120) regulates both cadherin stability and actin dynamics, but the relationship between these two functions remains unclear. Using a novel proteomic approach called reversible cross-link immunoprecipitation, or ReCLIP, we previously identified a physical interaction between p120 and Rho-associated protein kinase 1 (ROCK1), a major effector of RhoA. In this paper, we show that a discrete fraction of cellular ROCK1 coimmunoprecipitates with p120 and precisely colocalizes to adherens junctions (AJs). Manipulation of AJs using a calcium-switch assay and cadherin-blocking antibodies indicates direct recruitment of ROCK1 to newly forming junctions. Importantly, we find that p120 links ROCK1 to the cadherin complex, as ROCK1 coimmunoprecipitates with wild-type but not p120-uncoupled E-cadherin. Moreover, depletion of ROCK1 using short-hairpin RNA results in dramatic mislocalization of the cadherin complex and junctional actin. These data are consistent with a model in which p120 dynamically regulates Rho-GTPase activity at the cadherin complex through transient interaction with several of its up- and downstream effectors, including ROCK1.

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

Cadherin–catenin interactions play an important role in cadherin adhesion. In the cadherin complex, α-catenin contributes to the binding strength of another catenin, p120, to the same complex. The data suggest that α-catenin–p120 contact within the cadherin–catenin complex can regulate cadherin trafficking.

Cadherin–catenin interactions play an important role in cadherin-mediated adhesion. Here we present strong evidence that in the cadherin–catenin complex α-catenin contributes to the binding strength of another catenin, p120, to the same complex. Specifically, we found that a β-catenin–uncoupled cadherin mutant interacts much more weakly with p120 than its full-size counterpart and that it is rapidly endocytosed from the surface of A-431 cells. We also showed that p120 overexpression stabilizes this mutant on the cell surface. Examination of the α-catenin–deficient MDA-MB-468 cells and their derivates in which α-catenin was reintroduced showed that α-catenin reinforces E-cadherin–p120 association. Finally, a cross-linking analysis of the cadherin–catenin complex indicated that a large loop located in the middle of the p120 arm-repeat domain is in close spatial vicinity to the amino-terminal VH1 domain of α-catenin. The six amino acid–long extension of this loop, caused by an alternative splicing, weakens p120 binding to cadherin. The data suggest that α-catenin–p120 contact within the cadherin–catenin complex can regulate cadherin trafficking.

Slug (SNAI2) expression in oral SCC cells results in altered cell-cell adhesion and increased motility

The Snail family of zinc finger transcription factors plays an important role in epithelial to mesenchymal transition (EMT) in a variety of tissues and systems. Slug (SNAI2) expression has been shown to directly contribute to a subset of events required for EMT in events such as re-epithelialization during wound healing and neural crest cell migration. In addition, slug expression was shown to correlate with disease recurrence in head and neck squamous cell carcinoma (HNSCC) patients. Based on this association we chose to specifically examine the effects of exogenous slug expression in HNSCC cells and specifically assess adhesive junction assembly and the motility characteristics in these cells. Slug expression led to changes in adherens junction and desmosome assembly characterized by a classical cadherin switch and loss of desmosome assembly. Additionally, we performed gene expression profiling to identify novel slug dependent gene expression changes in a HNSCC cell line. In addition to genes known to be altered during EMT, we identified a novel set of Slug responsive genes that will provide a better understanding of slug overexpression during EMT and HNSCC progression.

Wnt controls the transcriptional activity of Kaiso through CK1ε-dependent phosphorylation of p120-catenin

p120-catenin is an E-cadherin-associated protein that modulates E-cadherin function and stability. In response to Wnt3a, p120-catenin is phosphorylated at Ser268 and Ser269, disrupting its interaction with E-cadherin. Here, we describe that Wnt-induced p120-catenin phosphorylation at Ser268 and Ser269 also enhances its binding to the transcriptional factor Kaiso, preventing Kaiso-mediated inhibition of the β-catenin–Tcf-4 transcriptional complex. Kaiso-mediated repression of this complex is due to its association not only with Tcf-4 but also with β-catenin. Disruption of Tcf-4–Kaiso and β-catenin–Kaiso interactions by p120-catenin not only releases Tcf-4 and β-catenin enabling its mutual association and the formation of the transcriptional complex but also permits Kaiso binding to methylated CpG islands, an interaction that is weakly inhibited by p120-catenin. Consequently, Wnt stimulates Kaiso association to the CDKN2A promoter, which contains CpG sequences, in cells where these sequences are extensively methylated, such as HT-29 M6, an effect accompanied by decreased expression of its gene product. These results indicate that, when released from E-cadherin by Wnt3a-stimulated phosphorylation, p120-catenin controls the activity of the Kaiso transcriptional factor, enhancing its binding to repressed promoters and relieving its inhibition of the β-catenin–Tcf-4 transcriptional complex.

p120 catenin is required for normal renal tubulogenesis and glomerulogenesis

Defects in the development or maintenance of tubule diameter correlate with polycystic kidney disease. Here, we report that absence of the cadherin regulator p120 catenin (p120ctn) from the renal mesenchyme prior to tubule formation leads to decreased cadherin levels with abnormal morphologies of early tubule structures and developing glomeruli. In addition, mutant mice develop cystic kidney disease, with markedly increased tubule diameter and cellular proliferation, and detached luminal cells only in proximal tubules. The p120ctn homolog Arvcf is specifically absent from embryonic proximal tubules, consistent with the specificity of the proximal tubular phenotype. p120ctn knockdown in renal epithelial cells in 3D culture results in a similar cystic phenotype with reduced levels of E-cadherin and active RhoA. We find that E-cadherin knockdown, but not RhoA inhibition, phenocopies p120ctn knockdown. Taken together, our data show that p120ctn is required for early tubule and glomerular morphogenesis, as well as control of luminal diameter, probably through regulation of cadherins.

Involvement of the TGF-beta and beta-catenin pathways in pelvic lymph node metastasis in early-stage cervical cancer

PURPOSE

Presence of pelvic lymph node metastases is the main prognostic factor in early-stage cervical cancer patients, primarily treated with surgery. Aim of this study was to identify cellular tumor pathways associated with pelvic lymph node metastasis in early-stage cervical cancer.

EXPERIMENTAL DESIGN

Gene expression profiles (Affymetrix U133 plus 2.0) of 20 patients with negative (N(0)) and 19 with positive lymph nodes (N(+)), were compared with gene sets that represent all 285 presently available pathway signatures. Validation immunostaining of tumors of 274 consecutive early-stage cervical cancer patients was performed for representatives of the identified pathways.

RESULTS

Analysis of 285 pathways resulted in identification of five pathways (TGF-β, NFAT, ALK, BAD, and PAR1) that were dysregulated in the N(0), and two pathways (β-catenin and Glycosphingolipid Biosynthesis Neo Lactoseries) in the N(+) group. Class comparison analysis revealed that five of 149 genes that were most significantly differentially expressed between N(0) and N(+) tumors (P < 0.001) were involved in β-catenin signaling (TCF4, CTNNAL1, CTNND1/p120, DKK3, and WNT5a). Immunohistochemical validation of two well-known cellular tumor pathways (TGF-β and β-catenin) confirmed that the TGF-β pathway (positivity of Smad4) was related to N(0) (OR: 0.20, 95% CI: 0.06-0.66) and the β-catenin pathway (p120 positivity) to N(+) (OR: 1.79, 95%CI: 1.05-3.05).

CONCLUSIONS

Our study provides new, validated insights in the molecular mechanism of lymph node metastasis in cervical cancer. Pathway analysis of the microarray expression profile suggested that the TGF-β and p120-associated noncanonical β-catenin pathways are important in pelvic lymph node metastasis in early-stage cervical cancer.