Nectins are Ca2؉ -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 2؉ -independent homophilic cell-cell adhesion activity. It furthermore showed Ca 2؉ -independent heterophilic cell-cell adhesion activity with Necl-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.

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 V12Ras-NIH3T3 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.In multicellular organisms, cell adhesion and migration are critical for many events, including tissue patterning, morphogenesis, and maintenance of normal tissues (1-3). They also play roles in malignant transformation of cells (4). Adhesion and migration of non-transformed normal cells are dynamic and well regulated (2). Cells disrupt cell-cell adhesion and start to migrate in response to extracellular cues, such as growth factors, cytokines, and extracellular matrix molecules (4). When migrating cells contact other cells, they stop migration and proliferation and adhere to each other to become confluent (5, 6). This phenomenon is known for a long time as contact inhibition of cell movement and proliferation. Transformation of cells causes disruption of cell-cell adhesion, increase of cell motility, and loss of contact inhibition of cell movement and proliferation, eventually leading the transformed cells to invasion into surrounding tissues and metastasis to other organs (4, 7). However, molecular mechanisms underlying these physiological or pathological processes are not fully understood.Cell-cell adherens junctions (AJs) 1 play major roles in cellcell adhesion in fibroblasts and epithelial cells (1, 2). Cadherins are key Ca 2ϩ -dependent cell-cell adhesion molecules at AJs (1, 2). Cadherins are associated with the actin cytoskeleton through peripheral membrane proteins, including ␣-and ␤-catenins, in fibroblasts and epithelial cells (1). This association strengthens the cell-cell adhesion activity of cadherins (1). Nectins and afadin constitute another cell-cell adhesion unit that localizes at cell-cell AJs and regulates organization of AJs in cooperation with cadherins in fibroblasts and epithelial cells (8). Nectins are Ca 2ϩ -independent Ig-like cell-cell adhesion molecules. Afadin is a nectin-and actin filame...

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 Ca 2؉ -independent Ig-like cell adhesion molecule nectin-3, eventually enhancing their intercellular motility. We show here that Necl-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 ␣ V ␤ 3 at leading edges of migrating cells. Analyses using an inhibitor or an activator of integrin ␣ V ␤ 3 or a dominant negative mutant of Necl-5 have shown the functional association of Necl-5 with integrin ␣ V ␤ 3 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.In multicellular organisms, cell migration is essential for normal development and responses to tissue damages and infection throughout life (1, 2). Cell migration is also observed in many diseases, such as cancer and atherosclerosis (3, 4). Cells migrate as individuals or as groups; leukocytes, lymphocytes, and fibroblasts migrate as individuals, whereas epithelial and endothelial cells migrate as groups. Cell migration is divided into at least four mechanistically separate steps: extension of protrusions, formation of new cell-matrix adhesions, contraction of cell body, and tail detachment (1, 5). Cell migration is normally directed and controlled by extracellular cues, such as growth factors, cytokines, and extracellular matrix molecules. These cues stimulate cell surface receptors to initiate intracellular signaling through second messengers, protein kinases, protein phosphatases, and heterotrimeric large and monomeric small G proteins to regulate the multiple steps. When migrating cells contact other cells, they stop migration and proliferation (6, 7). This phenomenon is known for a long time as contact inhibition of cell movement and proliferation. Transformation of cells causes disruption of cell-cell adhesion, increase of cell motility, and loss of contact inhibition of cell movement and proliferation, eventually leading transformed cells to invasion into surrounding t...

Background : Nectin is a Ca 2+ -independent immunoglobulin-like cell-cell adhesion molecule at the E-cadherin-based cell-cell adherens junctions (AJs), and comprises a family consisting of four members, nectin-1, -2, -3, and -4. Nectin and E-cadherin are associated with afadin and α α α α -catenin, actin filament

Necl-5/Tage4/poliovirus receptor/CD155 has been shown to be the poliovirus receptor and to be up-regulated in rodent and human carcinoma. We have found previously that mouse Necl-5 regulates cell motility. We show here that mouse Necl-5 is furthermore involved in the regulation of cell proliferation. Studies using a specific antibody against Necl-5 and a dominant negative mutant of Necl-5 revealed that Necl-5 enhanced the serum-induced proliferation of NIH3T3, Swiss3T3, and mouse embryonic fibroblast cells. Necl-5 enhanced the serum-induced activation of the Ras-Raf-MEK-ERK signaling, up-regulated cyclins D2 and E, and down-regulated p27 Kip1 Necl-5/Tage4/poliovirus receptor (PVR) 1 /CD155 is an immunoglobulin (Ig)-like molecule having a domain structure consisting of one extracellular region with three Ig-like loops, one transmembrane region, and one cytoplasmic region (1-4). Human PVR/CD155 was originally identified as the human PVR (1, 2), whereas rodent Tage4 was originally identified as the product of a gene overexpressed in rat and mouse colon carcinoma (3, 4). PVR/CD155 has also been shown to be overexpressed in human colorectal carcinoma and malignant glioma (5, 6). The PVR/CD155 gene has thus far been found only in the primates, and the Tage4 gene has thus far been found only in the rodent, but these genes are likely to be derived from the common ancestor gene (7,8) and tentatively renamed nectinlike molecule-5, Necl-5 (for a review, see Ref. 9). Nectin-like molecules (Necls) have been named for a group of Ig-like molecules whose domain structures are similar to, but slightly different from, those of nectins (9). Nectins are Ca 2ϩ -independent Ig-like cell-cell adhesion molecules that constitute a family of four members, nectin-1, -2, -3, and -4 (for reviews, see Refs. 9 and 10). Nectins form cis-dimers followed by formation of trans-dimers (trans-interaction), eventually causing cell-cell adhesion. Nectins first form cell-cell adhesion where cadherins are recruited, resulting in formation of adherens junctions in epithelial cells and fibroblasts. Nectins are associated with the actin cytoskeleton through afadin, a nectin-and actin filamentbinding protein, as cadherins are associated with the actin cytoskeleton through ␣-and ␤-catenins (for a review, see Ref. 11). Necl-5 is one member of the Necl family consisting of five members, Necl-1, -2, -3, -4, and -5 (9). Although they have domain structures similar to those of nectins, they do not directly bind afadin.Nectin-3 forms not only homo-trans-dimers but also heterotrans-dimers (heterophilic trans-interaction) with either nectin-1 or -2 (9, 10). Nectin-4 forms hetero-trans-dimers with nectin-1, but nectin-1 does not form hetero-trans-dimers with nectin-2. These hetero-trans-dimers show much higher cell-cell adhesion activity than the homo-trans-dimers. In contrast to nectins, Necl-5 does not show homophilic cell-cell adhesion activity (12, 13). Thus, the role of Necl-5 as the PVR has been established, but its physiological role remained unknown for a...