E-cadherin surface levels in epithelial growth factor-stimulated cells depend on adherens junction protein shrew-1

Expression Patterns of Ezrin and AJAP1 and Clinical Significance in Breast Cancer

Ezrin and adherens junction-associated protein 1 (AJAP1) are structural proteins which are involved in numerous human malignancies. However, little is known about the relationship between them in breast cancer. This study was set out to investigate the relationship between them and to further explore the mechanism of AJAP1-mediating cytoskeleton in breast cancer progression. Ezrin and AJAP1 expressions were detected in 377 samples of breast cancer by immunohistochemistry, and different expression patterns between AJAP1 and Ezrin with clinicopathological parameters were analyzed. Besides, univariate and multivariate Cox models were used to evaluate their prognostic potential. Enzyme-linked immunosorbent assay, Western blot, qRT-PCR, and phalloidin staining of F-actin were used to explore the relationship and the mechanism between AJAP1 and Ezrin in cytoskeleton arrangement. 377 cases of breast cancer results showed that AJAP1 expression was negatively related with histological grade and lymph node involvement and could be an independent prognosis marker of breast cancer. AJAP1 expression tended to be higher in the Ezrin-negative expression case. Patients with AJAP1^negative and Ezrin^positive expression had a worse prognosis (p < 0.0001) and shorter DFS (p = 0.015). More importantly, AJAP1 depletion increased the cell ability of F-actin formation through promoting Ezrin expression. AJAP1 depletion might mediate breast cancer malignancy potential through promoting Ezrin expression and cytoskeleton formation.

Phenotypic Consequences of SLC25A40-ABCB1 Fusions beyond Drug Resistance in High-Grade Serous Ovarian Cancer

Simple Summary

Among the plethora of malignancies affecting the female reproductive tract, those concerning the ovary are the most frequently fatal. In particular, chemotherapy-resistant High-Grade Serous Ovarian Cancer (HGSOC) remains a clinically intractable disease with a high rate of mortality. We previously identified SLC25A40-ABCB1 transcriptional fusions as the driving force behind drug resistance in HGSOC. As success in the clinical arena will only be achieved by enhancing our fundamental understanding of the drivers that mediate cellular drug resistance, this report sought to elucidate the phenotypic, metabolomic and transcriptional consequences of SLC25A40-ABCB1 fusions beyond drug resistance. High-throughput FDA drug screening was also undertaken to identify new therapeutic avenues against drug-resistant cellular populations.

Abstract

Despite high response rates to initial chemotherapy, the majority of women diagnosed with High-Grade Serous Ovarian Cancer (HGSOC) ultimately develop drug resistance within 1–2 years of treatment. We previously identified the most common mechanism of acquired resistance in HGSOC to date, transcriptional fusions involving the ATP-binding cassette (ABC) transporter ABCB1, which has well established roles in multidrug resistance. However, the underlying biology of fusion-positive cells, as well as how clonal interactions between fusion-negative and positive populations influences proliferative fitness and therapeutic response remains unknown. Using a panel of fusion-negative and positive HGSOC single-cell clones, we demonstrate that in addition to mediating drug resistance, ABCB1 fusion-positive cells display impaired proliferative capacity, elevated oxidative metabolism, altered actin cellular morphology and an extracellular matrix/inflammatory enriched transcriptional profile. The co-culture of fusion-negative and positive populations had no effect on cellular proliferation but markedly altered drug sensitivity to doxorubicin, paclitaxel and cisplatin. Finally, high-throughput screening of 2907 FDA-approved compounds revealed 36 agents that induce equal cytotoxicity in both pure and mixed ABCB1 fusion populations. Collectively, our findings have unraveled the underlying biology of ABCB1 fusion-positive cells beyond drug resistance and identified novel therapeutic agents that may significantly improve the prognosis of relapsed HGSOC patients.

E-Cadherin Regulates Mitochondrial Membrane Potential in Cancer Cells

Epithelial cancer cells often have unusually higher mitochondrial membrane potential (ΔΨ_m) than their normal counterparts, which has been associated with increased invasiveness in vitro and higher metastatic potential in vivo. However, the mechanisms by which ΔΨ_m in cancer cells is regulated in tumor microenvironment (TME) remain unclear. In this study, we used an in vitro micropatterning platform to recapitulate biophysical confinement cues in the TME and investigated the mechanisms by which these regulate cancer cell ΔΨ_m. We found that micropatterning resulted in a spatial distribution of ΔΨ_m, which correlated with the level of E-cadherin mediated intercellular adhesion. There was a stark contrast in the spatial distribution of ΔΨ_m in the micropattern of E-cadherin-negative breast cancer cells (MDA-MB-231) compared to that of the high E-cadherin expressing (MCF-7) cancer cells. Disruption and knockout of E-cadherin adhesions rescued the low ΔΨ_m found at the center of MCF-7 micropatterns with high E-cadherin expression, while E-cadherin overexpression in MDA-MB-231 and MCF-7 cells lowered their ΔΨ_m at the micropattern center. These results show that E-cadherin plays an important role in regulating the ΔΨ_m of cancer cells in the context of biophysical cues in TME.

AJAP1 affects behavioral changes and GABABR1 level in epileptic mice

Adherens junction-associated protein-1 (AJAP1), also called SHREW1, was first discovered as a novel component of adherens junctions in 2004. In later studies, AJAP1 was found to suppress invasion and predict recurrence of some tumors. Apart from its function as a putative tumor suppressor, AJAP1 is still poorly understood. Schwenk et al. recently found that AJAP1 was tightly associated with the γ-Aminobutyric acid type B receptor subunit 1(GABABR1). It is well known that GABABR plays a vital role in epilepsy as an inhibitory transmitter receptor. Structurally adjacent, possibly functionally interacting, therefore, we hypothesize that AJAP1 participates in the onset and progression of epilepsy. We designed this experiment to investigate the expression and location of AJAP1 in temporal lobe epilepsy (TLE) patients and kainic acid(KA)-induced epilepsy animal models by immunofluorescence and Western blot analyses. We overexpressed and inhibited AJAP1 through lentiviruses in KA-induced models and observed the corresponding effects on epileptic animals. Double-label immunofluorescence showed that AJAP1 was expressed mainly in neurons. Western blot analysis revealed that AJAP1 expression was downregulated in the neocortex of TLE patients and the hippocampus and neocortex of epileptic animal models. The overexpression of AJAP1 can reduce the frequency of spontaneous seizures, whereas the inhibition of AJAP1 expression can increase the incidence rate. Our study demonstrated that AJAP1 may be involved in the pathogenic process of epilepsy and may represent a novel antiepileptic target.

Genome-wide association study and a post replication analysis revealed a promising genomic region and candidate genes for chicken eggshell blueness

The eggshell blueness is an interesting object for chicken genetic studies and blue-shelled chicken industry, especially after the discovery of the causative mutation of chicken blue eggshell. In the present study, genome wide association study (GWAS) was conducted in Chinese Dongxiang blue-shelled chicken underlying four traits of blue eggshell pigments: quantity of biliverdin (QB), quantity of protoporphyrin (QP), quantity of total pigment (QT), and color density trait (CD). A total of 139 individuals were randomly collected for GWAS. We detected two SNPs in genome-wise significance and 35 in suggestive significance, 24 out of the 37 SNP were located either within intron/exon or near 15 genes in a range of ~1.17 Mb on GGA21. For further confirmation of the identified SNP loci by GWAS, the follow-up replication studies were performed in two populations. A total of 146 individuals of the second generation derived from the former GWAS population, as well as 280 individuals from an alternative independent population were employed for genotyping by MALDI-TOF MS in a genotype-phenotype association study. Eighteen SNPs evenly distributed on the GGA21 significant region were successfully genotyped in the two populations, of which 4 and 6 SNP loci were shown significantly associated with QB, QT and QP in the two repeat populations, respectively. Further, the SNPs were narrowed down to a region of ~ 653.819 Kb on GGA21 that harbors five candidate genes: AJAP1, TNFRSF9, C1ORF174, CAMTA1, and CEP104. Shell gland of chickens laying dark and light blue eggshell was chosen for detection of mRNA expression of the five candidate genes. The results showed differential expression levels of these genes in the two groups. The specific function of these genes has not yet been defined clearly in chickens and further in-depth studies are needed to explore the new functional role in chicken eggshell blueness.

AJAP1 expression modulates glioma cell motility and correlates with tumor growth and survival

Glioblastoma multiforme (GBM) is one of the most common primary malignant brain tumors. Unraveling the molecular and genetic complexity that determines GBM's pronounced migratory property could provide new options for therapeutic targeting that may significantly complement current surgical and chemoradiation therapy and alter the current poor outcome. In this study, we establish stable AJAP1 overexpressing glioma cells in order to examine in vivo tumor growth. We examine AJAP1 localization by confocal microscopy and AJAP1's functional effect on migration and invasion across surfaces coated with laminin. Finally, analysis of AJAP1 expression in murine xenografts and GBM primary tumors revealed its association with tumor growth and survival. Stable overexpression of AJAP1 promotes adherence, decreases invasion of glioma cells through an extracellular-like matrix, and slows migration in the presence of laminin. These observations are reversed by gene knockdown using multiple siRNAs. Additionally, overexpression of AJAP1 decreases colony formation in glioma cells, and leads to smaller tumor growth with increased survival in glioma xenograft mice. Loss of AJAP1 protein expression predicts worse survival in GBM patients. AJAP1 overexpression decreases cell motility in the presence of laminin and decreases tumor growth in xenografts. Its loss of expression predicts worse survival in patients. This study extends our prior observations and implicates AJAP1 as a potential prognostic marker and a viable target for therapeutic intervention in GBM.

Endogenous AJAP1 associates with the cytoskeleton and attenuates angiogenesis in endothelial cells

The adherens junction associated protein 1 (AJAP1, aka shrew-1) is presumably a type-I transmembrane protein localizing and interacting with the E-cadherin-catenin complex. In various tumors, AJAP1 expression is reduced or lost, including hepatocellular and esophageal squamous cell carcinoma, and glial-derived tumors. The aberrant expression of AJAP1 is associated with alterations in cell migration, invasion, increased tumor growth, and tumor vascularization, suggesting AJAP1 as a putative tumor suppressor. We show that AJAP1 attenuates sprouting angiogenesis by reducing endothelial migration and invasion capacities. Further, we show for the first time that endogenous AJAP1 is associated with the microtubule cytoskeleton. This linkage is independent from cell confluency and stable during angiogenic sprouting in vitro Our work suggests that AJAP1 is a putative negative regulator of angiogenesis, reducing cell migration and invasion by interfering with the microtubule network. Based on our results and those of other authors, we suggest AJAP1 as a novel tumor suppressor and diagnostic marker.

Growth hormone-releasing hormone (GHRH) promotes metastatic phenotypes through EGFR/HER2 transactivation in prostate cancer cells

The involvement of growth hormone-releasing hormone (GHRH) in several relevant processes that contribute to prostate cancer progression was analyzed. Firstly, we evaluated GHRH effects on cell proliferation and adhesion in human cancer prostate cell lines, LNCaP and PC3, by using specific assays (BrdU incorporation and collagen adhesion). The expression levels of the main marker molecules of these processes were measured by RT-PCR, Western blotting and zymography assays. GHRH increased both cell proliferation and proliferating cell nuclear antigen (PCNA) levels in LNCaP cells and in PC3 cells; however, such a rise was faster in the PC3 cells that represent the most aggressive stage of prostate cancer. Furthermore, GHRH significantly reduced cell adhesion and E-cadherin levels in LNCaP and PC3 cells and up-regulated the total and nuclear expression of β-catenin in PC3 cells. In addition, we assessed cell cycle, cell migration and VEGF secretion in PC3 cells. GHRH augmented the number of cells in G2/M-phase but diminished that corresponding to G1-phase. Cell-cycle specific markers were evaluated since GHRH effects may be related to their differential expression; we observed a decrease of p53, p21, and Bax/Bcl2 ratio. Furthermore, GHRH increased the expression of CD44, c-myc and cyclin D1, MMP-2 and MMP-9 activity, and VEGF secretion. We also observed that EGFR and/or HER2 transactivation is involved in cell adhesion, cell migration and VEGF secretion produced by GHRH. Consequently, present results define GHRH as a proliferative, anti-apoptotic and migratory agent in prostate cancer.

Deregulated AJAP1/β-catenin/ZEB1 signaling promotes hepatocellular carcinoma carcinogenesis and metastasis

Adherens junctions-associated protein 1 (AJAP1) is an integral membrane protein that is thought to function as a tumor suppressor in various malignancies. Downregulation of AJAP1 mRNA levels may predict recurrence in hepatocellular carcinoma (HCC) patients, but the underlying molecular mechanism is unknown. This was addressed in the present study by examining the role of AJAP1 in HCC cell proliferation, migration, and invasion in vitro as well as in human specimens and mouse xenograft model. We found that AJAP1 expression was reduced in HCC cells and human HCC tissue, which was associated with metastasis. AJAP1 overexpression inhibited HCC progression and metastasis, while its silencing had the opposite effect both in vitro and in vivo. Furthermore, AJAP1 blocked epithelial-to-mesenchymal transition by interacting with β-catenin and inhibiting its nuclear translocation, which suppressed zinc finger E-box binding homeobox 1 (ZEB1) transcription. These results indicate that AJAP1 inhibits HCC metastasis, and is thus a potential therapeutic target for HCC treatment.

Alternative exon usage creates novel transcript variants of tumor suppressor SHREW-1 gene with differential tissue expression profile

Shrew-1, also called AJAP1, is a transmembrane protein associated with E-cadherin-mediated adherence junctions and a putative tumor suppressor. Apart from its interaction with β-catenin and involvement in E-cadherin internalization, little structure or function information exists. Here we explored shrew-1 expression during postnatal differentiation of mammary gland as a model system. Immunohistological analyses with antibodies against either the extracellular or the cytoplasmic domains of shrew-1 consistently revealed the expression of full-length shrew-1 in myoepithelial cells, but only part of it in luminal cells. While shrew-1 localization remained unaltered in myoepithelial cells, nuclear localization occurred in luminal cells during lactation. Based on these observations, we identified two unknown shrew-1 transcript variants encoding N-terminally truncated proteins. The smallest shrew-1 protein lacks the extracellular domain and is most likely the only variant present in luminal cells. RNA analyses of human tissues confirmed that the novel transcript variants of shrew-1 exist in vivo and exhibit a differential tissue expression profile. We conclude that our findings are essential for the understanding and interpretation of future functional and interactome analyses of shrew-1 variants.

Summary: Transcripts of the tumor suppressor gene SHREW-1 exist in various splice variants in human and mouse encoding proteins with a differential expression and intracellular localization profile.

DDR1 promotes E-cadherin stability via inhibition of integrin-β1-Src activation-mediated E-cadherin endocytosis

Discoidin domain receptor 1 (DDR1), a receptor tyrosine kinase of collagen, is primarily expressed in epithelial cells. Activation of DDR1 stabilises E-cadherin located on the cell membrane; however, the detailed mechanism of DDR1-stabilised E-cadherin remains unclear. We performed DDR1 knockdown (Sh-DDR1) on Mardin-Darby canine kidney cells to investigate the mechanism of DDR1-stabilised E-cadherin. Sh-DDR1 decreased junctional localisation, increased endocytosis of E-cadherin, and increased physical interactions between E-cadherin and clathrin. Treatment of the dynamin inhibitor Dyngo 4a suppressed Sh-DDR1-induced E-cadherin endocytosis. In addition, the phosphorylation level of Src tyrosine 418 was increased in Sh-DDR1 cell junctions, and inhibition of Src activity decreased Sh-DDR1-induced E-cadherin endocytosis. To characterise the molecular mechanisms, blocking integrin β1 decreased Src activity and E-cadherin junctional localisation in Sh-DDR1 cells. Photoconversion results showed that inhibition of Src activity rescued E-cadherin membrane stability and that inhibition of integrin β1-Src signalling decreased stress fibres and rescued E-cadherin membrane stability in Sh-DDR1 cells. Taken together, DDR1 stabilised membrane localisation of E-cadherin by inhibiting the integrin β1-Src-mediated clathrin-dependent endocytosis pathway.

Leda-1/Pianp is targeted to the basolateral plasma membrane by a distinct intracellular juxtamembrane region and modulates barrier properties and E-Cadherin processing

Leda-1/Pianp is a type-I transmembrane protein which is sorted to the basolateral membrane domain of polarized epithelial cells. Here, we investigated trafficking mechanisms and functions of Leda-1/Pianp in MDCK and MCF-7 cells. Basolateral sorting and posttranslational modifications depended on the intracellular juxtamembrane region. Functionally, Leda-1/Pianp increased the transepithelial electrical resistance generated by a polarized cell sheet. Furthermore, resistance to junctional destabilization by tumor cells was enhanced by Leda-1/Pianp indicating increased stability and tightness of intercellular junctions. While Claudin 1 and 4 expression and activities of small GTPases were not affected, γ-Secretase-mediated cleavage of E-Cadherin was attenuated by Leda-1/Pianp. Regulation of proteolytic processing is thus a molecular mechanism by which Leda-1/Pianp can affect junctional integrity and function.

Tbx5 is required for avian and Mammalian epicardial formation and coronary vasculogenesis

RATIONALE

Holt-Oram syndrome is an autosomal dominant heart-hand syndrome caused by mutations in the TBX5 gene. Overexpression of Tbx5 in the chick proepicardial organ impaired coronary blood vessel formation. However, the potential activity of Tbx5 in the epicardium itself, and the role of Tbx5 in mammalian coronary vasculogenesis, remains largely unknown.

OBJECTIVE

To evaluate the consequences of altered Tbx5 gene dosage during proepicardial organ and epicardial development in the embryonic chick and mouse.

METHODS AND RESULTS

Retroviral-mediated knockdown or upregulation of Tbx5 expression in the embryonic chick proepicardial organ and proepicardial-specific deletion of Tbx5 in the embryonic mouse (Tbx5(epi-/)) impaired normal proepicardial organ cell development, inhibited epicardial and coronary blood vessel formation, and altered developmental gene expression. The generation of epicardial-derived cells and their migration into the myocardium were impaired between embryonic day (E) 13.5 to 15.5 in mutant hearts because of delayed epicardial attachment to the myocardium and subepicardial accumulation of epicardial-derived cells. This caused defective coronary vasculogenesis associated with impaired vascular smooth muscle cell recruitment and reduced invasion of cardiac fibroblasts and endothelial cells into myocardium. In contrast to wild-type hearts that exhibited an elaborate ventricular vascular network, Tbx5(epi-/-) hearts displayed a marked decrease in vascular density that was associated with myocardial hypoxia as exemplified by hypoxia inducible factor-1α upregulation and increased binding of hypoxyprobe-1. Tbx5(epi-/-) mice with such myocardial hypoxia exhibited reduced exercise capacity when compared with wild-type mice.

CONCLUSIONS

Our findings support a conserved Tbx5 dose-dependent requirement for both proepicardial and epicardial progenitor cell development in chick and in mouse coronary vascular formation.

E-cadherin couples death receptors to the cytoskeleton to regulate apoptosis

Epithelial-to-mesenchymal transition (EMT) is a cellular process essential to the development and maintenance of solid tissues. In cancer, EMT suppresses apoptosis, but the mechanisms remain unclear. EMT selectively attenuated apoptosis signaling via the death receptors DR4 and DR5. Loss of the epithelial cell adhesion protein E-cadherin recapitulated this outcome, whereas homotypic E-cadherin engagement promoted apoptotic signaling via DR4/DR5, but not Fas. Depletion of α-catenin, which couples E-cadherin to the actin cytoskeleton, or actin polymerization inhibitors similarly attenuated DR4/DR5-induced apoptosis. E-cadherin bound specifically to ligated DR4/DR5, requiring extracellular cadherin domain 1 and calcium. E-cadherin augmented DR4/DR5 clustering and assembly of the death-inducing signaling complex (DISC), increasing caspase-8 activation in high molecular weight cell fractions. Conversely, EMT attenuated DR4/DR5-mediated DISC formation and caspase-8 stimulation. Consistent with these findings, epithelial cancer cell lines expressing higher E-cadherin levels displayed greater sensitivity to DR4/DR5-mediated apoptosis. These results have potential implications for tissue homeostasis as well as cancer therapy.

AJAP1 is dysregulated at an early stage of gliomagenesis and suppresses invasion through cytoskeleton reorganization

AIMS

Down-regulation of AJAP1 in glioblastoma multiforme (GBM) has been reported. However, the expression profiles of AJAP1 in gliomas and the underlying mechanisms of AJAP1 function on invasion are still poorly understood.

METHODS

The gene profiles of AJAP1 in glioma patients were studied among four independent cohorts. Confocal imaging was used to analyze the AJAP1 localization. After AJAP1 overexpression in GBM cell lines, cellular polarity, cytoskeleton distribution, and antitumor effect were investigated in vitro and in vivo.

RESULTS

AJAP1 expression was significantly decreased in gliomas compared with normal brain in REMBRANDT and CGCA cohorts. Additionally, low AJAP1 expression was associated with worse survival in GBMs in REMBRANDT and TCGA U133A cohorts and was significantly associated with classical and mesenchymal subtypes of GBMs among four cohorts. Confocal imaging indicated AJAP1 localized in cell membranes in low-grade gliomas and AJAP1-overexpressing GBM cells, but difficult to assess in high-grade gliomas due to its absence. AJAP1 overexpression altered the cytoskeleton and cellular polarity in vitro and inhibited the tumor growth in vivo.

CONCLUSIONS

AJAP1 is dysregulated at an early stage of gliomagenesis and may suppress glioma cell invasion and proliferation, which suggests that AJAP1 may be a potential diagnostic and prognostic marker for gliomas.

Proteolytic cleavage of LEDA-1/PIANP by furin-like proprotein convertases precedes its plasma membrane localization

Liver endothelial differentiation-associated protein-1 (LEDA-1/PIANP) is a type-I-transmembrane protein first identified by us as a putative junctional protein in liver sinusoidal endothelial cells. Others have shown that LEDA-1/PIANP binds and activates immune inhibitory receptor PILRα in trans, a process that requires sialidation of LEDA-1/PIANP. Here we show that LEDA-1/PIANP is subject to O-glycosylation and sialidation as demonstrated in brain tissue as well as in LEDA-1 expressing cell lines by using anti-LEDA-1/PIANP C-terminal antibodies. In addition, analysis of LEDA-1/PIANP processing with His-tags inserted at different positions in the extracellular domain revealed that multiple steps of proteolytic cleavage occur during maturation of the protein. Proteolytic cleavage between aa59 and aa83 preceded sorting of the protein to the plasma membrane. Deletion of aa75-79 and inhibition with Furin inhibitor I confirmed that LEDA-1/PIANP is processed by a Furin-like proprotein convertase. In summary, these findings show that Furin-like proprotein convertase-dependent processing precedes plasma membrane localization of LEDA-1/PIANP that is a pre-requisite of functional receptor-ligand interactions in vitro and in vivo.

Adherens junctions and cancer

Cadherins and catenins are the central cell-cell adhesion molecules in adherens junctions (AJs). This chapter reviews the knowledge concerning the role of cadherins and catenins in epithelial cancer and examines the published literature demonstrating the changes in the expression and function of these proteins in human cancer and the association of these changes with patient outcomes. The chapter also covers the mechanistic studies aiming at uncovering the significance of changes in cadherin and catenin expression in cancer and potential molecular mechanisms responsible for the causal role of AJs in cancer initiation and progression.

The anti-cancer effects of (-)-epigallocatechin-3-gallate on the signaling pathways associated with membrane receptors in MCF-7 cells

(-)-Epigallocatechin-3-gallate (EGCg) has been implicated in cancer chemo-prevention in studies using many different kinds of cancer cells. The present study measured cell viability, osteopontin (OPN) secretion, fatty acid synthase (FAS) expression, and cytosolic Ca(2+) and verified the anti-cancer activities of EGCg in MCF-7 human breast cancer cells. EGCg-induced apoptosis was evidenced by nuclear condensation, increased protein levels of activated caspase-3, down-regulation of gelsolin and tropomyosin-4 (Tm-4), and up-regulation of tropomyosin-1(Tm-1). By disrupting adherens junction formation, EGCg caused accumulation of extra-nuclear β-catenin aggregates in the cytosol and alterations of the protein content and mRNA expression of E-cadherin and β-catenin, but not N-cadherin, in MCF-7 cells. To identify the putative mechanisms underlying the EGCg signaling pathways, EGFP (enhanced green fluorescence protein) was ectopically expressed in MCF-7 cells. This allowed us to monitor the EGCg-induced fluorescence changes associated with the effects of Triton X-100 (to remove plasma membrane) or the addition of laminin, anti-laminin receptor (LR) antibody, epidermal growth factor (EGF), and genistein on the cells. Our results indicated that EGCg acts via the signaling pathways associated with cell membrane to suppress cell proliferation, provoke apoptosis, and disturb cell-cell adhesion in MCF-7 cells. The altered events include the EGFR, LR, FAS, intracellular Ca(2+) , OPN secretion, caspace-3, gelsolin, Tm-4, Tm-1, and adherens junction proteins, E-cadherin and β-catenin.

Numb controls E-cadherin endocytosis through p120 catenin with aPKC

Cadherin trafficking controls tissue morphogenesis and cell polarity. The endocytic adaptor Numb participates in apicobasal polarity by acting on intercellular adhesions in epithelial cells. However, it remains largely unknown how Numb controls cadherin-based adhesion. Here, we found that Numb directly interacted with p120 catenin (p120), which is known to interact with E-cadherin and prevent its internalization. Numb accumulated at intercellular adhesion sites and the apical membrane in epithelial cells. Depletion of Numb impaired E-cadherin internalization, whereas depletion of p120 accelerated internalization. Expression of the Numb-binding fragment of p120 inhibited E-cadherin internalization in a dominant-negative fashion, indicating that Numb interacts with the E-cadherin/p120 complex and promotes E-cadherin endocytosis. Impairment of Numb induced mislocalization of E-cadherin from the lateral membrane to the apical membrane. Atypical protein kinase C (aPKC), a member of the PAR complex, phosphorylated Numb and inhibited its association with p120 and α-adaptin. Depletion or inhibition of aPKC accelerated E-cadherin internalization. Wild-type Numb restored E-cadherin internalization in the Numb-depleted cells, whereas a phosphomimetic mutant or a mutant with defective α-adaptin-binding ability did not restore the internalization. Thus, we propose that aPKC phosphorylates Numb to prevent its binding to p120 and α-adaptin, thereby attenuating E-cadherin endocytosis to maintain apicobasal polarity.

H1 and PAR2 receptors enhance delivery of immune-competent cells and molecules by interrupting E-cadherin adhesion in epithelia

The lung's epithelial surface is at the same time vitally exchanging gas with the environment and acting as a barrier that protects the organism from the environment. We hypothesized that activation of epithelial-cell G-protein-coupled receptors for immune-defense molecules would temporarily interrupt cadherin-dependent cell-cell adhesion of epithelial cells and thereby focally and temporarily compromise the epithelial barrier to facilitate delivery of other immune molecules and cells to challenged sites. Activation of type 1 histamine or type 2 PAR receptors on the basolateral surface of primary airway epithelial cells or L-cells expressing E-cadherin interrupted cadherin adhesion and caused approximately a 50% decrease in the epithelial barrier for 2-3 minutes. Given basic biochemical observations of others, we further hypothesized that activation of the receptors altered the barrier by phosphorylating tyrosines on an essential cadherin-complex component, beta-catenin. Y-F mutations in beta-catenin completely blocked the effects of activating the same receptors on cadherin-dependent adhesion and on the epithelial barrier. Hence, G-protein-coupled receptors responding to immune-defense molecules temporarily and focally interrupt the lung epithelial barrier by compromising cadherin-based adhesion.