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Summary Recent studies have revealed that newly emerging transformed cells are often eliminated from epithelial tissues via cell competition with the surrounding normal epithelial cells. This cancer preventive phenomenon is termed epithelial defense against cancer (EDAC). However, it remains largely unknown whether and how EDAC is diminished during carcinogenesis. In this study, using a cell competition mouse model, we show that high-fat diet (HFD) feeding substantially attenuates the frequency of apical elimination of RasV12-transformed cells from intestinal and pancreatic epithelia. This process involves both lipid metabolism and chronic inflammation. Furthermore, aspirin treatment significantly facilitates eradication of transformed cells from the epithelial tissues in HFD-fed mice. Thus, our work demonstrates that obesity can profoundly influence competitive interaction between normal and transformed cells, providing insights into cell competition and cancer preventive medicine. [ABSTRACT FROM AUTHOR]

ErbB2 and ErbB3, members of the EGF receptor/ErbB family, form a heterodimer upon binding of a ligand, inducing the activation of Rac small G protein and Akt protein kinase for cell movement and survival, respectively. The enhanced ErbB3/ ErbB2 signaling causes tumorigenesis, invasion, and metastasis. We found here that the ErbB3/ErbB2 signaling is regulated by immunoglobulin-like Necl-2, which is down-regulated in various cancer cells and serves as a tumor suppressor. The extracellular region of ErbB3, but not ErbB2, interacted in cis with that of Necl-2. This interaction reduced the ligand-induced, ErbB2-catalyzed tyrosine phosphorylation of ErbB3 and inhibited the consequent ErbB3-mediated activation of Rac and Akt, resulting in the inhibition of cancer cell movement and survival. These inhibitory effects of Necl-2 were mediated by the protein-tyrosine phosphatase PTPN13 which interacted with the cytoplasmic tail of Necl-2. We describe here this novel mechanism for silencing of the ErbB3/ErbB2 signaling by Necl-2. [ABSTRACT FROM AUTHOR]

Nectins are Ca2+-independent Ig-like cell adhesion molecules (CAMs) which homophilically and heterophilically interact in trans with nectins and form cell–cell adhesion. This cell–cell adhesion is involved in the formation of many types of cell–cell junctions such as adherens junctions, tight junctions, and synaptic junctions, cooperatively with other CAMs such as cadherins and claudins. Nectins transduce signals cooperatively with integrin αvβ3, and regulate formation of cell–cell junctions. In addition, nectin interacts in cis with PDGF receptor and regulates its signaling for anti-apoptosis. Furthermore, nectin interacts in trans with nectin-like molecule-5 (Necl-5) and regulate cell movement and proliferation. We describe cooperative roles of nectins with other CAMs and growth factor receptors. [Copyright &y& Elsevier]

Integrin αvβ3, which forms focal complexes at leading edges in moving cells, is up-regulated in cancer cells and so is implicated in their invasiveness. Necl-5, originally identified as a poliovirus receptor and also up-regulated in cancer cells, co-localizes with integrin αvβ3 at leading edges in moving cells and enhances growth factor-induced cell movement. Here, we show that Necl-5 interacts directly, in cis, with integrin αvβ3, and enhances integrin αvβ3 clustering and focal complex formation at leading edges in NIH3T3 cells. The extracellular region of Necl-5, but not the cytoplasmic region, is necessary for its inter- action with integrin αvβ3 however, both regions are necessary for its action. An interaction between integrin αvβ3 and vitronectin and PDGF-induced activation of Rac are also necessary for integrin αvβ3 clustering. The interaction between Necl-5 and integrin αvβ3 enhances PDGF-induced Rac activation, facilitating integrin αvβ3 clustering presumably in a feedback amplification manner. Thus, Necl-5 has a critical role in integrin αvβ3 clustering and focal complex formation. [ABSTRACT FROM AUTHOR]

Cell migration plays roles in invasion of transformed cells and scattering of embryonic mesenchymal cells into surrounding tissues. We have found that Ig-like Necl-5/Tage4 is up-regulated in NIH3T3 cells transformed by an oncogenic Ras (V12Ras-NIH3T3 cells) and heterophilically trans-interacts with a Ca2+-independent Ig-like cell adhesion molecule nectin-3, eventually enhancing their intercellular motility. We show here that Nec1-5 furthermore enhances cell migration in a nectin-3-independent manner. Studies using L fibroblasts expressing various mutants of Necl-5, NIH3T3 cells, and V12Ras-NIH3T3 cells have revealed that Necl-5 enhances serum, and platelet-derived growth factor-induced cell migration. The extracellular region of Necl-5 is necessary for directional cell migration, but not for random cell motility. The cytoplasmic region of Necl-5 is necessary for both directional and random cell movement. Necl-5 colocalizes with integrin αvβ3 at leading edges of migrating cells. Analyses using an inhibitor or an activator of integrin αvβ3 or a dominant negative mutant of Necl-5 have shown the functional association of Necl-5 with integrin αvβ3 in cell motility. Cdc42 and Rac small G proteins are activated by the action of Necl-5 and required for the serum-induced, Necl-5-enhanced cell motility. These results indicate that Necl-5 regulates serum, and platelet-derived growth factor-induced cell migration in an integrin-dependent, nectin-3-independent manner, when cells do not contact other cells. We furthermore show here that enhanced motility and metastasis of V12Ras-NIH3T3 cells are at least partly the result of up-regulated Necl-5. [ABSTRACT FROM AUTHOR]

Nectins are Ca[sup 2+]-independent immunoglobulin-like cell-cell adhesion molecules that play roles in organization of a variety of cell-cell junctions in cooperation with or independently of cadherins. Four nectins have been identified. Five nectin-like molecules, which have domain structures similar to those of nectins, have been identified, and we characterized here nectin-like molecule-2 (Necl-2)/IGSF4/RA175/SgIGSF/TSLC1/SynCAM1. Necl-2 showed Ca[sup 2+]-independent homophilic cell-cell adhesion activity. It furthermore showed Ca[sup 2+]-independent heterophilic cell-cell adhesion activity with Nec;l-1/TSLL1/SynCAM3 and nectin-3. Necl-2 was widely expressed in rat tissues examined. Necl-2 localized at the basolateral plasma membrane in epithelial cells of the mouse gall bladder, but not at specialized cell-cell junctions, such as tight junctions, adherens junctions, and desmosomes. Nectins bind afadin, whereas Necl-2 did not bind afadin but bound Pals2, a membrane-associated guanylate kinase family member known to bind Lin-7, implicated in the proper localization of the Let-23 protein in Caenorhabditis elegans, the homologue of mammalian epidermal growth factor receptor. These results indicate the unique localization of Necl-2 and its possible involvement in localization of a transmembrane protein(s) through Pals2. [ABSTRACT FROM AUTHOR]

Malignant transformation of cells causes disruption of cell-cell adhesion, enhancement of cell motility, and invasion into surrounding tissues. Nectins have both homophilic and heterophilic cell-cell adhesion activities and organize adherens junctions in cooperation with cadherins. We examined here whether Tage4, which was originally identified to be a gene overexpressed in colon carcinoma and has a domain structure similar to those of nectins, is involved in cell adhesion and/or migration. Tage4 heterophilically trans-interacted with nectin-3, but not homophilically with Tage4. Expression of Tage4 was markedly elevated in NIH3T3 cells transformed by an oncogenic Ki-Ras (V12Ras-NIH3T3 cells) as compared with that of wild-type NIH3T3 cells. trans-Interaction of Tage4 with nectin-3 enhanced motility of V12RasNIH3T3 cells. Tage4 did not bind afadin, a nectin- and actin filament-binding protein that connects nectins to the actin cytoskeleton and cadherins through catenins. Thus, Tage4 heterophilically trans-interacts with nectin-3 and regulates cell migration. Tage4 is tentatively re-named here nectin-like molecule-5 (necl-5) on the basis of its function and domain structure similar to those of nectins. [ABSTRACT FROM AUTHOR]

Examines the direct binding of cell polarity protein PAR-3 to cell-cell adhesion molecule nectin at neuroepithelial cells of developing mouse. Role of nectin in the localization of JAM-1 in mammalian epithelial cells and in the organization of adherens junctions; Results indicating that nectin-e and -3 are involved in the localization of PAR-3 at adherens junctions in the neuroepithelial cells of the embryonic telecenphalon.

Tight junctions (TJs) and adherens junctions (AJs) are major junctional apparatuses in epithelial cells. Claudins and junctional adhesion molecules (JAMs) are major cell adhesion molecules (CAMs) at TJs, whereas cadherins and nectins are major CAMs at AJs. Claudins and JAMs are associated with ZO proteins, whereas cadherins are associated with β- and α-catenins, and nectins are associated with afadin. We previously showed that nectins first form cell-cell adhesions where the cadherin-catenin complex is recruited to form AJs, followed by the recruitment of the JAM-ZO and claudin-ZO complexes to the apical side of AJs to form TJs. It is not fully understood how TJ components are recruited to the apical side of AJs. We studied the roles of afadin and ZO-1 in the formation of TJs in Madin-Darby canine kidney (MDCK) cells. Before the formation of TJs, ZO-1 interacted with afadin through the two proline-rich regions of afadin and the SH3 domain of ZO-1. During and after the formation of TJs, ZO-1 dissociated from afadin and associated with JAM-A. Knockdown of afadin impaired the formation of both AJs and TJs in MDCK cells, whereas knockdown of ZO-1 impaired the formation of TJs, but not AJs. Re-expression of full-length afadin restored the formation of both AJs and TJs in afadin-knockdown MDCK cells, whereas re-expression of afadin-ΔPR1-2, which is incapable of binding to ZO-1, restored the formation of AJs, but not TJs. These results indicate that the transient interaction of afadin with ZO-1 is necessary for the formation of TJs in MDCK cells. [ABSTRACT FROM AUTHOR]

During epithelial junctional development, both vesicle transport and reorganization of the actin cytoskeleton must be spatiotemporally regulated. Coordination of these cellular functions is especially important, but the precise mechanism remains elusive. Previously, we identified junctional Rab13- binding protein (JRAB)/molecules interacting with CasL-like 2 (MICAL-L2) as an effector of the Rab13 smallGprotein, and we found that the Rab13-JRAB system may be involved in the formation of cell-cell adhesions via transport of adhesion molecules. Here, we showed that JRAB interacts with two actin-binding proteins, actinin-1 and -4, and filamentous actin via different domains and regulates actin cross-linking and stabilization through these interactions. During epithelial junctional development, JRAB is prominently enriched in the actin bundle at the free border; subsequently, JRAB undergoes a Rab13-dependent conformational change that is required for maturation of cell-cell adhesion sites. These results suggest that Rab13 and JRAB regulate reorganization of the actin cytoskeleton throughout epithelial junctional development from establishment to maturation of cell-cell adhesion [ABSTRACT FROM AUTHOR]

In normal epithelial cells, integrin α6β4 is abundantly expressed and forms hemidesmosomes, which is a cellular structure that mediates cell-extracellular matrix binding. In many types of cancer cells, integrin α6β4 is up-regulated, laminin is cleaved, and hemidesmosomes are disrupted, eventually causing an enhancement of cancer cell movement and facilitation of their invasion. We previously showed that the immunoglobulin-like cell adhesion molecule Necl-2 (Nectin-like molecule 2), known as a tumor suppressor, inhibits cancer cell movement by suppressing the ErbB3/ErbB2 signaling. We show here that Necl-2 interacts in cis with integrin α6β4. The binding of Necl-2 with integrin β4 was mediated by its extracellular region. In human colorectal adenocarcinoma Caco-2 cells, integrin α6β4 was localized at hemidesmosomes. Small interfering RNA-mediated suppression of Necl-2 expression enhanced the phorbol ester-induced disruption of the integrin α6β4 complex at hemidesmosomes, whereas expression of Necl-2 suppressed the disruption of this structure. These results indicate that tumor-suppressive functions of Necl-2 are mediated by the stabilization of the hemidesmosome structure in addition to the inhibition of the ErbB3/ErbB2 signaling. [ABSTRACT FROM AUTHOR]

Focal complexes are continuously formed and transformed into focal adhesions during cell movement. We previously demonstrated that Necl-5 co-localizes with integrin αvβ3 at focal complexes, whereas Necl-5 does not localize at focal adhesions in moving NIH3T3 cells, suggesting that Necl-5 may be dissociated from integrin αvβ3 during the transformation of focal complexes into focal adhesions, but the underlying mechanism remains unknown. Here, we explore the roles of Necl-5 and Rho-associated kinase (ROCK) in the regulation of the transformation of focal complexes into focal adhesions. We found that inhibition of Necl-5 expression and expression of a constitutively active mutant of ROCK! enhanced, whereas treatment with a ROCK inhibitor Y-27632 inhibited the transformation of focal complexes into focal adhesions. In HEK293 cells ectopically expressing Necl-5 and integrin αvβ3 treatment of cells with Y-27632 increased the binding of Necl-5 to clustered integrin αvβ3. The experiments using inhibitors of myosin ATPase and actin polymerization revealed that actomyosin-driven contractility exerts a similar function as ROCK. The phosphorylation of integrin β3 at Tyr747, which is known to be critical for the formation of focal adhesions, plays a pivotal role for the interaction between Necl-5 and integrin αvβ3. These results indicate that the transformation of focal complexes into focal adhesions is negatively and positively regulated by Necl-5 and ROCK, respectively, and that ROCK-dependent actomyosin-driven contractility is a critical determinant for the regulation of the interaction between Necl-5 and integrin αvβ3. [ABSTRACT FROM AUTHOR]

Abstract: Objective:: The development and maturation of the ovarian follicles are characterized by structural changes that require components involved in cell–cell adhesion systems. Recently a novel group of cell adhesion molecules named nectins has been identified. The present study examined expression and cell-specific localization of nectins during mouse follicular development. Study design:: Expression of nectins in mouse ovary was investigated by immnuoblot analysis and immunohistochemistry. More precise localization was determined by electron microscopy. Results:: Immunoblot analysis revealed expression of nectin-2 and nectin-3 but not nectin-1 in ovarian granulosa cells. Immunohistochemistry demonstrated expression of nectin-2 at cell–cell adhesion sites of granulosa cell layer in the primary and preantral follicles. Especially, intense immunoreactivity of nectin-2 accumulated around the zona pellucida. In antral follicles, the intensity of nectin-2 expression on granulosa cells was decreased. By electron microscopy nectin-2 was detected not only on thin extensions of granulosa cells penetrating the zona pellucida, but also on the attachment sites between thin extensions of granulosa cells and oocyte surface. Conclusion:: The restricted expression of nectin-2 in the granulosa cells of primary and preantral follicles might reflect some of the molecular changes in cell–cell adhesion during early follicular development. [Copyright &y& Elsevier]

Identifies an afadin-binding protein using yeast two-hybrid screening. Association of the actin filament afadin with the cytoplasmic tail of nectin; Localization of afadin and nectin at cell-cell adherens junctions undercoated with F-actin bundles; Involvement in the formation of adherens junctions in cooperation with E-cadherin in epithelial cells.