Accumulation Of E-cadherin Research Articles

Xiaotan Sanjie recipe, a compound Chinese herbal medicine, inhibits gastric cancer metastasis by regulating GnT-V-mediated E-cadherin glycosylation

ObjectiveXiaotan Sanjie recipe (XTSJ), a Chinese herbal compound medicine, exerts a significant inhibitory effect on gastric cancer (GC) metastasis. This work investigated the mechanism underlying the XTSJ-mediated inhibition of GC metastasis. MethodsThe effect of XTSJ on GC metastasis and the associated mechanism were investigated in vitro, using GC cell lines, and in vivo, using a GC mouse model, by focusing on the expression of Glc-N-Ac-transferase V (GnT-V; encoded by MGAT5). ResultsThe migration and invasion ability of GC cells decreased significantly after XTSJ administration, which confirmed the efficacy of XTSJ in treating GC in vitro. XTSJ increased the accumulation of E-cadherin at junctions between GC cells, which was reversed by MGAT5 overexpression. XTSJ administration and MGAT5 knockdown alleviated the structural abnormality of the cell–cell junctions, while MGAT5 overexpression had the opposite effect. MGAT5 knockdown and XTSJ treatment also significantly increased the accumulation of proteins associated with the E-cadherin-mediated adherens junction complex. Furthermore, the expression of MGAT5 was significantly lower in the lungs of BGC-823-MGAT5 + XTSJ mice than in those of BGC-823-MGAT5 + solvent mice, indicating that the ability of gastric tumors to metastasize to the lung was decreased in vivo following XTSJ treatment. ConclusionXTSJ prevented GC metastasis by inhibiting the GnT-V-mediated E-cadherin glycosylation and promoting the E-cadherin accumulation at cell–cell junctions.

Rap1 coordinates cell-cell adhesion and cytoskeletal reorganization to drive collective cell migration in vivo

Collective cell movements contribute to tissue development and repair and spread metastatic disease. In epithelia, cohesive cell movements require reorganization of adherens junctions and the actomyosin cytoskeleton. However, the mechanisms that coordinate cell-cell adhesion and cytoskeletal remodeling during collective cell migration invivo are unclear. We investigated the mechanisms of collective cell migration during epidermal wound healing in Drosophila embryos. Upon wounding, the cells adjacent to the wound internalize cell-cell adhesion molecules and polarize actin and the motor protein non-muscle myosin II to form a supracellular cable around the wound that coordinates cell movements. The cable anchors at former tricellular junctions (TCJs) along the wound edge, and TCJs are reinforced during wound closure. We found that the small GTPase Rap1 was necessary and sufficient for rapid wound repair. Rap1 promoted myosin polarization to the wound edge and E-cadherin accumulation at TCJs. Using embryos expressing a mutant form of the Rap1 effector Canoe/Afadin that cannot bind Rap1, we found that Rap1 signals through Canoe for adherens junction remodeling, but not for actomyosin cable assembly. Instead, Rap1 was necessary and sufficient for RhoA/Rho1 activation at the wound edge. The RhoGEF Ephexin localized to the wound edge in a Rap1-dependent manner, and Ephexin was necessary for myosin polarization and rapid wound repair, but not for E-cadherin redistribution. Together, our data show that Rap1 coordinates the molecular rearrangements that drive embryonic wound healing, promoting actomyosin cable assembly through Ephexin-Rho1, and E-cadherin redistribution through Canoe, thus enabling rapid collective cell migration invivo.

Ovarian Clear Cell Carcinoma and Markers of Epithelial-Mesenchymal Transition (EMT): Immunohistochemical Characterization of Tumor Budding.

Tumor budding, largely considered a manifestation of epithelial-mesenchymal transition (EMT) is an established prognostic marker for several cancers. In a recent study, tumor budding was associated with poor clinical outcomes in early-stage ovarian clear cell carcinoma. Here, we evaluated the immune expression of 3 proteins shown to be associated with EMT (E-cadherin, β-catenin, and glypican-3) in 72 primary tumors of ovarian clear cell carcinoma with median follow-up of 39.47mo. E-cadherin and β-catenin expression was further evaluated in tumor buds in 29 (40%) cases. In the tumor mass, diffuse membranous expression of E-cadherin and β-catenin was seen in 83% (60/72) and 81% (58/72) cases, respectively. Nuclear accumulation of E-cadherin was seen in 7 (10%) cases, while none of the cases showed nuclear β-catenin expression. Glypican-3 expression was diffuse in 33.3% (24/72), patchy in 29.2% (21/72), and absent in 37.5% (27/72) cases. Evaluation of tumor buds showed aberrant patterns of expression (complete loss/cytoplasmic accumulation/diminished, discontinuous incomplete membranous staining) of E-cadherin in 29/29 (100%) and of β-catenin in 26/29 (90%) cases. E-cadherin, β-catenin, and glypican-3 expression in the main tumor mass had no association with stage, lymph node status, recurrent/progressive disease, status at last follow-up, survival and histopathologic features ( P >0.05). Our finding of aberrant expression of both E-cadherin and β-catenin in tumor buds indicates involvement of Wnt signaling pathway/EMT in tumor budding and outlines its significance as a prognostic marker especially for early-stage ovarian clear cell carcinoma.

A meiotic switch in lysosome activity supports spermatocyte development in young flies but collapses with age

SummaryGamete development ultimately influences animal fertility. Identifying mechanisms that direct gametogenesis, and how they deteriorate with age, may inform ways to combat infertility. Recently, we found that lysosomes acidify during oocyte maturation in Caenorhabditis elegans, suggesting that a meiotic switch in lysosome activity promotes female germ-cell health. Using Drosophila melanogaster, we report that lysosomes likewise acidify in male germ cells during meiosis. Inhibiting lysosomes in young-male testes causes E-cadherin accumulation and loss of germ-cell partitioning membranes. Notably, analogous changes occur naturally during aging; in older testes, a reduction in lysosome acidity precedes E-cadherin accumulation and membrane dissolution, suggesting one potential cause of age-related spermatocyte abnormalities. Consistent with lysosomes governing the production of mature sperm, germ cells with homozygous-null mutations in lysosome-acidifying machinery fail to survive through meiosis. Thus, lysosome activation is entrained to meiotic progression in developing sperm, as in oocytes, and lysosomal dysfunction may instigate male reproductive aging.

Force-dependent intercellular adhesion strengthening underlies asymmetric adherens junction contraction

Tissue morphogenesis arises from the culmination of changes in cell-cell junction length. Mechanochemical signaling in the form of RhoA underlies these ratcheted contractions, which occur asymmetrically. The underlying mechanisms of asymmetry remain unknown. We use optogenetically controlled RhoA in model epithelia together with biophysical modeling to uncover the mechanism lending to asymmetric vertex motion. Using optogenetic and pharmacological approaches, we find that both local and global RhoA activation can drive asymmetric junction contraction in the absence of tissue-scale patterning. We find that standard vertex models with homogeneous junction properties are insufficient to recapitulate the observed junction dynamics. Furthermore, these experiments reveal a local coupling of RhoA activation with E-cadherin accumulation. This motivates a coupling of RhoA-mediated increases in tension and E-cadherin-mediated adhesion strengthening. We then demonstrate that incorporating this force-sensitive adhesion strengthening into a continuum model is successful in capturing the observed junction dynamics. Thus, we find that a force-dependent intercellular "clutch" at tricellular vertices stabilizes vertex motion under increasing tension and is sufficient to generate asymmetries in junction contraction.

Knockdown of YAP/TAZ Inhibits the Migration and Invasion of Fibroblast Synovial Cells in Rheumatoid Arthritis by Regulating Autophagy.

The purpose of this study was to investigate the effect of knockdown of the yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) on the migration and invasion of the rheumatoid arthritis fibroblast-like synoviocytes (RA-FLS) and to preliminarily elucidate the mechanisms between YAP/TAZ and autophagy in the migration and invasion of RA-FLS. RA-FLS stable knockdown of YAP or TAZ was successfully established by using lentiviral-mediated gene knockdown techniques. Wound healing assay and Transwell assay were used to evaluate the effect of knockdown of YAP or TAZ on the migration and invasion of RA-FLS. Reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) and western blotting assays were performed to examine the expression of indicated genes. The results showed that YAP and TAZ were upregulated in RA-FLS, and knockdown of YAP or TAZ inhibited the migration and invasion, reduced the expression of N-cadherin and Vimentin, and increased the accumulation of E-cadherin and β-catenin in RA-FLS. Our results also demonstrated that knockdown of YAP or TAZ promoted autophagy which increased the accumulation of LC3B-II and ULK1 and decreased the amount of SQSTM1/p62 in RA-FLS. Furthermore, our data displayed that inhibition of autophagy either with 3-MA or CQ can partially reverse the decrease of migration and invasion induced by YAP and TAZ knockdown in RA-FLS. Our experiments preliminarily revealed that YAP/TAZ and autophagy play important roles in the migration and invasion of RA-FLS, which might provide novel targets for the treatment of RA.

AGS3-dependent trans-Golgi network membrane trafficking is essential for compaction in mouse embryos.

Activator of G-protein signaling 3 (AGS3, also known as GPSM1) regulates the trans-Golgi network. The AGS3 GoLoco motif binds to Gαi and thereby regulates the transport of proteins to the plasma membrane. Compaction of early embryos is based on the accumulation of E-cadherin (Cdh1) at cell-contacted membranes. However, how AGS3 regulates the transport of Cdh1 to the plasma membrane remains undetermined. To investigate this, AGS3 was knocked out using the Cas9-sgRNA system. Both trans-Golgi network protein 46 (TGN46, also known as TGOLN2) and transmembrane p24-trafficking protein 7 (TMED7) were tracked in early mouse embryos by tagging these proteins with a fluorescent protein label. We observed that the majority of the AGS3-edited embryos were developmentally arrested and were fragmented after the four-cell stage, exhibiting decreased accumulation of Cdh1 at the membrane. The trans-Golgi network and TMED7-positive vesicles were also dispersed and were not polarized near the membrane. Additionally, increased Gαi1 (encoded by GNAI1) expression could rescue AGS3-overexpressed embryos. In conclusion, AGS3 reinforces the dynamics of the trans-Golgi network and the transport of TMED7-positive cargo containing Cdh1 to the cell-contact surface during early mouse embryo development.

The Tricellular Junction Protein Sidekick Regulates Vertex Dynamics to Promote Bicellular Junction Extension

Remodeling of cell-cell junctions drives cell intercalation that causes tissue movement during morphogenesis through the shortening and growth of bicellular junctions. The growth of new junctions is essential for continuing and then completing cellular dynamics and tissue shape sculpting; however, the mechanism underlying junction growth remains obscure. We investigated Drosophila genitalia rotation where continuous cell intercalation occurs to show that myosin II accumulating at the vertices of a new junction is required for the junction growth. This myosin II accumulation requires the adhesive transmembrane protein Sidekick (Sdk), which localizes to the adherens junctions (AJs) of tricellular contacts (tAJs). Sdk also localizes to and blocks the accumulation of E-Cadherin at newly formed growing junctions, which maintains the growth rate. We propose that Sdk facilitates tAJ movement by mediating myosin II-driven contraction and altering the adhesive properties at the tAJs, leading to cell-cell junction extension during persistent junction remodeling.

Clostridium perfringens Delta-Toxin Damages the Mouse Small Intestine.

Clostridium perfringens strains B and C cause fatal intestinal diseases in animals. The secreted pore-forming toxin delta-toxin is one of the virulence factors of the strains, but the mechanism of intestinal pathogenesis is unclear. Here, we investigated the effects of delta-toxin on the mouse ileal loop. Delta-toxin caused fluid accumulation and intestinal permeability to fluorescein isothiocyanate (FITC)-dextran in the mouse ileal loop in a dose- and time-dependent manner. Treatment with delta-toxin induced significant histological damage and shortening of villi. Delta-toxin activates a disintegrin and metalloprotease (ADAM) 10, leading to the cleavage of E-cadherin, the epithelial adherens junction protein, in human intestinal epithelial Caco-2 cells. In this study, E-cadherin immunostaining in mouse intestinal epithelial cells was almost undetectable 1 h after toxin treatment. ADAM10 inhibitor (GI254023X) blocked the toxin-induced fluid accumulation and E-cadherin loss in the mouse ileal loop. Delta-toxin stimulated the shedding of intestinal epithelial cells. The shedding cells showed the accumulation of E-cadherin in intracellular vesicles and the increased expression of active caspase-3. Our findings demonstrate that delta-toxin causes intestinal epithelial cell damage through the loss of E-cadherin cleaved by ADAM10.

Actomyosin contractility modulates Wnt signaling through adherens junction stability.

Actomyosin contractility can influence the canonical Wnt signaling pathway in processes like mesoderm differentiation and tissue stiffness during tumorigenesis. We identified that increased nonmuscle myosin II activation and cellular contraction inhibited Wnt target gene transcription in developing Drosophila imaginal disks. Genetic interactions studies were used to show that this effect was due to myosin-induced accumulation of cortical F-actin resulting in clustering and accumulation of E-cadherin to the adherens junctions. This results in E-cadherin titrating any available β-catenin, the Wnt pathway transcriptional coactivator, to the adherens junctions in order to maintain cell–cell adhesion under contraction. We show that decreased levels of cytoplasmic β-catenin result in insufficient nuclear translocation for full Wnt target gene transcription. Previous studies have identified some of these interactions, but we present a thorough analysis using the wing disk epithelium to show the consequences of modulating myosin phosphatase. Our work elucidates a mechanism in which the dynamic promotion of actomyosin contractility refines patterning of Wnt transcription during development and maintenance of epithelial tissue in organisms.

INDUCTION OF EPITHELIAL-TO-MESENCHYMAL TRANSITION IN MCF-7-SNAI1 CELLS LEADS TO REORGANIZATION OF ADHERENS JUNCTIONS AND ACQUISITION OF MIGRATORY ACTIVITY

Using DIC and confocal microscopy, changes in morphology, migratory characteristics and adherence junctions (AJs) were analyzed in the mammary carcinoma cell line MCF-7-SNAI1 after activation of the EMT transcription factor SNAI1. Western Blot analysis showed that after removal of tetracycline from the cell culture medium expression of SNAI1 reached its peak in 24 hours and then plateaued for 7 days. During the 7 days the cells continued to express E-cadherin; however, tangential AJs typical for cells with stable cell-cell adhesion, changed into radial AJs. The radial AJs continued to accumulate E-cadherin during 24‑72 hours after tetracycline removal. As a result of SNAI1 activation, the cells underwent epithelial-mesenchymal transition (EMT) and became migratory. On a two-dimensional substrate, cells exhibited both individual and collective migration. As the tetracycline washout period progressed, the fraction of the cells capable of migrating through migration chamber membranes increased; on the contrary, cells’ ability to invade an epithelial monolayer decreased. These results demonstrate that retaining a hybrid epithelial/mesenchymal phenotype and accumulation of E-cadherin in AJs during early stages of EMT do not impede disruption of stable cell-cell adhesion and cells’ acquisition of migratory activity.

Junctional E-cadherin/p120-catenin Is Correlated with the Absence of Supporting Cells to Hair Cells Conversion in Postnatal Mice Cochleae

Notch inhibition is known to generate supernumerary hair cells (HCs) at the expense of supporting cells (SCs) in the mammalian inner ear. However, inhibition of Notch activity becomes progressively less effective at inducing SC-to-HC conversion in the postnatal cochlea and balance organs as the animal ages. It has been suggested that the SC-to-HC conversion capacity is inversely correlated with E-cadherin accumulation in postnatal mammalian utricles. However, whether E-cadherin localization is linked to the SC-to-HC conversion capacity in the mammalian inner ear is poorly understood. In the present study, we treated cochleae from postnatal day 0 (P0) with the Notch signaling inhibitor DAPT and observed apparent SC-to-HC conversion along with E-cadherin/p120ctn disruption in the sensory region. In addition, the SC-to-HC conversion capacity and E-cadherin/p120ctn disorganization were robust in the apex but decreased toward the base. We further demonstrated that the ability to regenerate HCs and the disruption of E-cadherin/p120ctn concomitantly decreased with age and ceased at P7, even after extended DAPT treatments. This timing is consistent with E-cadherin/p120ctn accumulation in the postnatal cochleae. These results suggest that the decreasing capacity of SCs to transdifferentiate into HCs correlates with E-cadherin/p120ctn localization in the postnatal cochleae, which might account for the absence of SC-to-HC conversion in the mammalian cochlea.

GPR161 RECEPTOR AS A NOVEL TARGET FOR ANTIBODY-BASED IMMUNOTHERAPY OF TRIPLE-NEGATIVE BREAST CANCER

Triple-negative breast cancer is a rare type of breast cancer, accounting for 20% of all women diagnosed with the adenocarcinoma. Triple-negative breast cancer cells are mainly characterized by the absence of estrogen receptors, progesterone receptors, and human epidermal growth factor receptors. Moreover, these cells do not respond to hormonal and targeted treatment with monoclonal antibodies. A literature review revealed several receptors in the oncogenic cells of this phenotype with potential to serve as a novel target for therapy. In particular, the G-protein coupled receptor (GPR) 161 was found to be overexpressed in triple-negative breast cancer cells, and correlated with a poor prognosis of the disease. In addition, overexpression of GPR161 in human mammary epithelial cells resulted in increased cell proliferation, migration, intracellular accumulation of E-cadherin, and the formation of multiple structures in a three-dimensional cell culture. Activation of the receptor reduces the phosphorylation of GTPase-activating protein 1 proteins, thereby enhancing mammalian target of rapamycin signaling pathways.
 GPCRs belong to a family of cell membrane proteins that transform extracellular signals into intracellular signaling pathways. These receptors play a key role in many important physiological processes whose malfunction may lead to various diseases, including cancer. Several currently produced drugs target different members of the GPCR family and have shown excellent therapeutic advantages.
 Therefore, huge efforts are focused on developing new drugs based on GPCRs, particularly for the treatment of cancer. This article provides an overview of data that show great promise in new opportunities for the treatment of triple-negative breast cancer. In particular, research on GPCRs is highlighted as promising targets for monoclonal antibodies and, after humanization, as therapeutic drugs

Selective serotonin reuptake inhibitor, fluoxetine, impairs E-cadherin-mediated cell adhesion and alters calcium homeostasis in pancreatic beta cells

Selective serotonin reuptake inhibitors (SSRIs) are the most commonly prescribed drugs for mood disorders. Long term use of SSRIs is associated with an increased risk of diabetes, but the underlying mechanism(s) remains elusive. E-cadherin-mediated cell-cell adhesion and elevated [Ca2+]i are important for insulin release and pancreatic β cell functions. This study aims to investigate whether a SSRI, fluoxetine (Prozac), induces pancreatic β cell dysfunction through affecting E-cadherin and/or [Ca2+]i. Here we show that fluoxetine significantly reduces glucose stimulated insulin secretion (GSIS). MIN6 cells, an established murine immortalized β cell line, form smaller colonies of loosely packed cells with reduced cell-cell contact after fluoxetine treatment. Immunofluorescence staining reveals that fluoxetine increases cytoplasmic accumulation of E-cadherin and reduces the membrane-localized E-cadherin probably due to increase of its endocytosis. Fluoxetine inhibits spreading of β cells on E-cad/Fc coated slides and also disrupts E-cadherin-mediated actin filaments. Additionally, fluoxetine significantly suppresses endoplasmic reticulum (ER) calcium release and store-operated calcium entry (SOCE) activation, probably through reduction of ER calcium storage and inhibition of stromal interaction molecule 1 (STIM1) trafficking. These data suggest that exposure to fluoxetine results in impaired β cell functions, occurring in concert with reduction of E-cadherin-dependent cell adhesion and alterations of calcium homeostasis.

Receptor-Type Guanylyl Cyclase at 76C (Gyc76C) Regulates De Novo Lumen Formation during Drosophila Tracheal Development.

Lumen formation and maintenance are important for the development and function of essential organs such as the lung, kidney and vasculature. In the Drosophila embryonic trachea, lumena form de novo to connect the different tracheal branches into an interconnected network of tubes. Here, we identify a novel role for the receptor type guanylyl cyclase at 76C (Gyc76C) in de novo lumen formation in the Drosophila trachea. We show that in embryos mutant for gyc76C or its downsteam effector protein kinase G (PKG) 1, tracheal lumena are disconnected. Dorsal trunk (DT) cells of gyc76C mutant embryos migrate to contact each other and complete the initial steps of lumen formation, such as the accumulation of E-cadherin (E-cad) and formation of an actin track at the site of lumen formation. However, the actin track and E-cad contact site of gyc76C mutant embryos did not mature to become a new lumen and DT lumena did not fuse. We also observed failure of the luminal protein Vermiform to be secreted into the site of new lumen formation in gyc76C mutant trachea. These DT lumen formation defects were accompanied by altered localization of the Arf-like 3 GTPase (Arl3), a known regulator of vesicle-vesicle and vesicle-membrane fusion. In addition to the DT lumen defect, lumena of gyc76C mutant terminal cells were shorter compared to wild-type cells. These studies show that Gyc76C and downstream PKG-dependent signaling regulate de novo lumen formation in the tracheal DT and terminal cells, most likely by affecting Arl3-mediated luminal secretion.

Three mechanisms control E-cadherin localization to the zonula adherens.

E-cadherin localization to the zonula adherens is fundamental for epithelial differentiation but the mechanisms controlling localization are unclear. Using the Drosophila follicular epithelium we genetically dissect E-cadherin transport in an in vivo model. We distinguish three mechanisms mediating E-cadherin accumulation at the zonula adherens. Two membrane trafficking pathways deliver newly synthesized E-cadherin to the plasma membrane. One is Rab11 dependent and targets E-cadherin directly to the zonula adherens, while the other transports E-cadherin to the lateral membrane. Lateral E-cadherin reaches the zonula adherens by endocytosis and targeted recycling. We show that this pathway is dependent on RabX1, which provides a functional link between early and recycling endosomes. Moreover, we show that lateral E-cadherin is transported to the zonula adherens by an apically directed flow within the plasma membrane. Differential activation of these pathways could facilitate cell shape changes during morphogenesis, while their misregulation compromises cell adhesion and tissue architecture in differentiated epithelia.

FilGAP, a Rho-ROCK-regulated GAP for Rac, controls adherens junctions in MDCK cells.

Rho family small GTPases are essential for the formation of adherens junctions in epithelial cells. Here, we found that FilGAP (also known as ARHGAP24), a Rac-specific Rho GTPase-activating protein, promoted the formation of adherens junctions in Madin-Darby canine kidney (MDCK) cells. Knockdown of FilGAP by siRNA stimulated the disassembly and migration of MDCK cells induced by hepatocyte growth factor (HGF). By contrast, forced expression of FilGAP induced accumulation of E-cadherin at adherens junctions. Endogenous FilGAP colocalized with E-cadherin at adherens junctions, and depletion of FilGAP reduced the amount of E-cadherin expressed at the surface. The Rac GAP domain of FilGAP was necessary for the suppression of cell scattering induced by HGF. In agreement with this, siRNA-mediated knockdown of both Rac1 and FilGAP suppressed cell scattering induced by HGF. Forced expression of Rho kinase (ROCK, of which there are two isoforms ROCK1 and ROCK2) induced the accumulation of E-cadherin at the adherens junction, and depletion of FilGAP prevented the accumulation of E-cadherin. Moreover, wild-type FilGAP but not a non-phosphorylatable FilGAP mutant rescued the accumulation of E-cadherin at adherens junctions. These results suggest that FilGAP might regulate cell-cell adhesion through inactivation of Rac downstream of Rho-ROCK-signaling in MDCK cells.

The antimicrobial protein S100A7/psoriasin enhances the expression of keratinocyte differentiation markers and strengthens the skin's tight junction barrier.

S100A7/psoriasin is a member of the S100 protein family and is encoded in the epidermal differentiation complex, which contains genes for markers of epidermal differentiation. S100A7/psoriasin is overexpressed in hyperproliferative skin diseases, where it is believed not only to exhibit antimicrobial functions, but also to induce immunomodulatory activities, including chemotaxis and cytokine/chemokine production. To evaluate the effect of S100A7/psoriasin on keratinocyte differentiation and regulation of the tight junction (TJ) barrier. Expression of differentiation markers and TJ proteins in human keratinocytes was determined by real-time polymerase chain reaction and Western blot. The changes in TJ barrier function were assessed by transepithelial electrical resistance and paracellular permeability assays. Glycogen synthase kinase-3 (GSK-3) and mitogen-activated protein kinase (MAPK) activation was analysed by Western blot, whereas β-catenin and E-cadherin activation was evaluated by Western blot and immunofluorescence. S100A7/psoriasin enhanced the expression of several differentiation markers and selectively increased the expression of TJ proteins (e.g. claudins and occludin), which are known to strengthen the TJ barrier. Furthermore, S100A7/psoriasin increased β-catenin and E-cadherin accumulation at cell-cell contact, and enhanced transepithelial electrical resistance while reducing the paracellular permeability of keratinocyte layers. The data suggest that S100A7/psoriasin-mediated regulation of the TJ barrier was via both the GSK-3 and MAPK pathways, as evidenced by the inhibitory effects of inhibitors for GSK-3 and MAPKs. Our finding that S100A7/psoriasin regulates differentiation and strengthens TJ barrier function provides novel evidence that, in addition to antimicrobial and immunoregulatory activities, S100A7/psoriasin is involved in skin innate immunity.

Receptor protein tyrosine phosphatase RPTPα controls epithelial adherens junctions, linking E-cadherin engagement to c-Src signaling to cortactin

Epithelial junctions are fundamental determinants of tissue organization, subject to regulation by tyrosine phosphorylation. Homophilic binding of E-cadherin activates tyrosine kinases, such as Src, that control junctional integrity. Protein tyrosine phosphatases (PTPs) also contribute to cadherin-based adhesion and signaling, but little is known about their specific identity or functions at epithelial junctions. Here, we report that the receptor PTP RPTPα (human gene name PTPRA) is recruited to epithelial adherens junctions at the time of cell-cell contact, where it is in molecular proximity to E-cadherin. RPTPα is required for appropriate cadherin-dependent adhesion and for cyst architecture in three-dimensional culture. Loss of RPTPα impairs adherens junction integrity, as manifested by defective E-cadherin accumulation and peri-junctional F-actin density. These effects correlate with a role for RPTPα in cellular (c)-Src activation at sites of E-cadherin engagement. Mechanistically, RPTPα is required for appropriate tyrosine phosphorylation of cortactin, a major Src substrate and a cytoskeletal actin organizer. Expression of a phosphomimetic cortactin mutant in RPTPα-depleted cells partially rescues F-actin and E-cadherin accumulation at intercellular contacts. These findings indicate that RPTPα controls cadherin-mediated signaling by linking homophilic E-cadherin engagement to cortactin tyrosine phosphorylation through c-Src.

Abstract A236: The orphan G-protein coupled receptor GPR161 is an oncogene in triple negative breast cancer.

Abstract Triple negative breast cancer (TNBC) accounts for 20% of breast cancer in women and lacks an effective targeted therapy. Therefore, finding common vulnerabilities in these tumors represents an opportunity for more effective treatment. Recent large-scale analyses of hundreds of tumor samples have provided a deluge of information on the genetic changes occurring during tumorigenesis. However, determining which changes drive tumor initiation and progression, and which are bystanders remains a difficult biological problem. Utilizing this genomic information we have discovered that the orphan G-protein coupled receptor (GPCR) GPR161 is overexpressed specifically in TNBC. TNBC patients expressing higher levels of GPR161 have an increased probability of disease relapse. Overexpression of GPR161 in human non-transformed mammary epithelial cells increases cell proliferation and multiacinar structure formation in three-dimensional (3D) culture through activation of mTORC1 signaling. Knockdown of GPR161 impairs proliferation of a human basal breast cancer cell line. Furthermore, GPR161 expression induces cell migration and invasion of cells in 3D culture. This is accompanied by disrupted cell adhesion and intracellular accumulation of E-cadherin. Cells overexpressing GPR161 show a reduction in IQGAP1 phosphorylation, consistent with mTOR activation and E-cadherin disruption. Furthermore, we find GPR161 in a signaling complex with the scaffold proteins β-arrestin 2 and IQGAP1. These results suggest that GPR161 may provide prognostic value and serve as a potential drug target in TNBC. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A236. Citation Format: Michael E. Feigin, Bin Xue, Molly Hammell, Senthil K. Muthuswamy. The orphan G-protein coupled receptor GPR161 is an oncogene in triple negative breast cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A236.