Involvement of integrin-induced activation of protein kinase C in the formation of adherens junctions

Blood-testis barrier: a review on regulators in maintaining cell junction integrity between Sertoli cells

The blood-testis barrier (BTB) is formed adjacent to the seminiferous basement membrane. It is a distinct ultrastructure, partitioning testicular seminiferous epithelium into apical (adluminal) and basal compartments. It plays a vital role in developing and maturing spermatocytes into spermatozoa via reorganizing its structure. This enables the transportation of preleptotene spermatocytes across the BTB, from basal to adluminal compartments in the seminiferous tubules. Several bioactive peptides and biomolecules secreted by testicular cells regulate the BTB function and support spermatogenesis. These peptides activate various downstream signaling proteins and can also be the target themself, which could improve the diffusion of drugs across the BTB. The gap junction (GJ) and its coexisting junctions at the BTB maintain the immunological barrier integrity and can be the "gateway" during spermatocyte transition. These junctions are the possible route for toxicant entry, causing male reproductive dysfunction. Herein, we summarize the detailed mechanism of all the regulators playing an essential role in the maintenance of the BTB, which will help researchers to understand and find targets for drug delivery inside the testis.

The role of adhesion molecules in osteocalcin-induced effects on glucose and lipid metabolism in adipocytes

Recent findings suggest that uncarboxylated osteocalcin (GluOC) promotes glucose and lipid metabolism via its putative receptor GPRC6A; however, its direct effect on adipocytes remains elusive. In this study, we elucidated the effects of GluOC on adipocytes, with an emphasis on the role of cell adhesion molecules. We determined that GluOC promoted the expression of adipocyte adhesion molecule (ACAM) and its transcription factor Krüppel-like factor 4 and enhanced the cortical actin filament assembly, which ameliorated lipid droplet hypertrophy. Additionally, GluOC upregulated the expression of integrin αVβ3 and activation of focal adhesion kinase (FAK) and prevented insulin receptor substrate 1 (IRS1) degradation by inhibiting the ubiquitin-proteasome system via the FAK-PLC-PKC axis, which activated IRS1-Akt-mediated glucose transporter 4 (GLUT4) transport. Furthermore, we showed that GluOC elevated the expression of the insulin-independent glucose transporters GLUT1 and GLUT8, which facilitated insulin stimulation-independent glucose transport. The GluOC-induced activation of integrin αVβ3 signaling promoted microtubule assembly, which improved glucose and lipid metabolism via its involvement in intracellular vesicular transport. GluOC treatment also suppressed collagen type 1 formation, which might prevent adipose tissue fibrosis in obese individuals. Overall, our results imply that GluOC promotes glucose and lipid metabolism via ACAM, integrin αVβ3, and GLUT1 and 8 expression, directly affecting adipocytes.

A single injection of periostin decreases cardiac voltage-gated Na+ channel in rat ventricles

Changes in electrophysiological properties, such as ion channel expression and activity, are closely related to arrhythmogenesis during heart failure (HF). However, a causative factor for the electrical remodeling in HF has not been determined. Periostin (POSTN), a matricellular protein, is increased in heart tissues of patients with HF. In the present study, we investigated whether a single injection of POSTN affects the electrophysiological properties in rat ventricles. After male Wistar rats were intravenously injected with recombinant rat POSTN (64 µg/kg, 24 hr), electrocardiogram (ECG) was recorded. Whole-cell patch clamp was performed to measure action potential (AP) and Na⁺ current (I_Na) in isolated ventricular myocytes. Protein expression of cardiac voltage-gated Na⁺ channel (Na_V1.5) in isolated ventricles was examined by Western blotting. In ECG, POSTN-injection significantly increased RS height. POSTN-injection significantly delayed time to peak in AP and decreased I_Na in the isolated ventricular myocytes. POSTN-injection decreased Na_V1.5 expression in the isolated ventricles. It was confirmed that POSTN (1 µg/ml, 24 hr) decreased I_Na and Na_V1.5 protein expression in neonatal rat ventricular myocytes. This study for the first time demonstrated that a single injection of POSTN in rats decreased I_Na by suppressing Na_V1.5 expression in the ventricular myocytes, which was accompanied by a prolongation of time to peak in AP and an increase of RS height in ECG.

TiO2 nanoparticles induce omphalocele in chicken embryo by disrupting Wnt signaling pathway

Titanium dioxide nanoparticles (TiO₂ NPs) are among abundantly used metal oxide NPs but their interactions with biomolecules and subsequent embryonic toxicity in higher vertebrates is not extensively reported. Physicochemical interactions of TiO₂ NPs with egg albumen reveals that lower doses of TiO₂ NPs (10 and 25 µg/ml) accounted for higher friccohesity and activation energy but an increment in molecular radii was recorded at higher doses (50 and 100 µg/ml). FTIR analysis revealed conformational changes in secondary structure of egg albumen as a result of electrostratic interactions between egg albumen and TiO₂ NPs. The morphometric data of chicken embryo recorded a reduction at all the doses of TiO₂ NPs, but toxicity and developmental deformity (omphalocele and flexed limbs) were recorded at lower doses only. Inductively coupled plasma optical emission spectrometry (ICP-OES) confirmed presence of Ti in chicken embryos. mRNA levels of genes involved in canonical and non-canonical Wnt signaling were lowered following TiO₂ NPs treatment resulting in free radical mediated disruption of lateral plate mesoderm and somite myogenesis. Conformational changes in egg albumen and subsequent developmental deformity in chicken embryo following TiO₂ NPs treatment warrants detailed studies of NP toxicity at lower doses prior to their biomedical applications.

Large-scale phosphotyrosine proteomic profiling of rat renal collecting duct epithelium reveals predominance of proteins involved in cell polarity determination

Although extensive phosphoproteomic information is available for renal epithelial cells, previous emphasis has been on phosphorylation of serines and threonines with little focus on tyrosine phosphorylation. Here we have carried out large-scale identification of phosphotyrosine sites in pervanadate-treated native inner medullary collecting ducts of rat, with a view towards identification of physiological processes in epithelial cells that are potentially regulated by tyrosine phosphorylation. The method combined antibody-based affinity purification of tyrosine phosphorylated peptides coupled with immobilized metal ion chromatography to enrich tyrosine phosphopeptides, which were identified by LC-MS/MS. A total of 418 unique tyrosine phosphorylation sites in 273 proteins were identified. A large fraction of these sites have not been previously reported on standard phosphoproteomic databases. All results are accessible via an online database: http://helixweb.nih.gov/ESBL/Database/iPY/. Analysis of surrounding sequences revealed four overrepresented motifs: [D/E]xxY*, Y*xxP, DY*, and Y*E, where the asterisk symbol indicates the site of phosphorylation. These motifs plus contextual information, integrated using the NetworKIN tool, suggest that the protein tyrosine kinases involved include members of the insulin- and ephrin-receptor kinase families. Analysis of the gene ontology (GO) terms and KEGG pathways whose protein elements are overrepresented in our data set point to structures involved in epithelial cell-cell and cell-matrix interactions ("adherens junction," "tight junction," and "focal adhesion") and to components of the actin cytoskeleton as major sites of tyrosine phosphorylation in these cells. In general, these findings mesh well with evidence that tyrosine phosphorylation plays a key role in epithelial polarity determination.

Enhanced functional properties of corneal epithelial cells by coculture with embryonic stem cells via the integrin β1-FAK-PI3K/Akt pathway

Adult stem cells are important cell sources in regenerative medicine, but isolating them is technically challenging. This study employed a novel strategy to generate stem-like corneal epithelial cells and promote the functional properties of these cells by coculture with embryonic stem cells. The primary corneal epithelial cells were labelled with GFP and cocultured with embryonic stem cells in a transwell or by direct cell-cell contact. The embryonic stem cells were pre-transfected with HSV-tk-puro plasmids and became sensitive to ganciclovir. After 10 days of coculture, the corneal epithelial cells were isolated by treating the cultures with ganciclovir to kill the embryonic stem cells. The expression of stem cell-associated markers (ABCG2, p63) increased whereas the differentiation mark (Keratin 3) decreased in corneal epithelial cells isolated from the cocultures as evaluated by RT-PCR and flow cytometry. Their functional properties of corneal epithelial cells, including cell adhesion, migration and proliferation, were also enhanced. These cells could regenerate a functional stratified corneal epithelial equivalent but did not form tumors. Integrin β1, phosphorylated focal adhesion kinase and Akt were significantly upregulated in corneal epithelial cells. FAK Inhibitor 14 that suppressed the expression of phosphorylated focal adhesion kinase and Akt inhibited cell adhesion, migration and proliferation. LY294002 that suppressed phosphorylated Akt but not phosphorylated focal adhesion kinase inhibited cell proliferation but had no effect on cell adhesion or migration. These findings demonstrated that the functional properties of stem-like corneal epithelial cells were enhanced by cocultured embryonic stem cells via activation of the integrin β1-FAK-PI3K/Akt signalling pathway.

Kv7.1 surface expression is regulated by epithelial cell polarization

The potassium channel KV7.1 is expressed in the heart where it contributes to the repolarization of the cardiac action potential. In addition, KV7.1 is expressed in epithelial tissues where it plays a role in salt and water transport. Mutations in the kcnq1 gene can lead to long QT syndrome and deafness, and several mutations have been described as trafficking mutations. To learn more about the basic mechanisms that regulate KV7.1 surface expression, we have investigated the trafficking of KV7.1 during the polarization process of the epithelial cell line Madin-Darby Canine Kidney (MDCK) using a modified version of the classical calcium switch. We discovered that KV7.1 exhibits a very dynamic localization pattern during the calcium switch. When MDCK cells are kept in low calcium medium, KV7.1 is mainly observed at the plasma membrane. During the first hours of the switch, KV7.1 is removed from the plasma membrane and an intracellular accumulation in the endoplasmic reticulum (ER) is observed. The channel is retained in the ER until the establishment of the lateral membranes at which point KV7.1 is released from the ER and moves to the plasma membrane. Our data furthermore suggest that while the removal of KV7.1 from the cell surface and its accumulation in the ER could involve activation of protein kinase C, the subsequent release of KV7.1 from the ER depends on phosphoinositide 3-kinase (PI3K) activation. In conclusion, our results demonstrate that KV7.1 surface expression is regulated by signaling mechanisms involved in epithelial cell polarization in particular signaling cascades involving protein kinase C and PI3K.

Junctional music that the nucleus hears: cell-cell contact signaling and the modulation of gene activity

Cell-cell junctions continue to capture the interest of cell and developmental biologists, with an emerging area being the molecular means by which junctional signals relate to gene activity in the nucleus. Although complexities often arise in determining the direct versus indirect nature of such signal transduction, it is clear that such pathways are essential for the function of tissues and that alterations may contribute to many pathological outcomes. This review assesses a variety of cell-cell junction-to-nuclear signaling pathways, and outlines interesting areas for further study.

Disruption of noncanonical Wnt/CA2+ pathway in the cadmium-induced omphalocele in the chick model

PURPOSE

Cadmium (Cd) has been found to cause ventral body wall defects (VBWDs) in the chick embryo similar to human omphalocele. The earliest detectable histologic changes in Cd-induced VBWD chick model have been observed 4 hours posttreatment. The exact mechanism by which Cd acts in the early embryogenesis remains unclear. Wnt proteins play a key role during embryogenesis, and altered Wnt signaling has been linked to developmental defects. Noncanonical Wnt/Ca(2+) pathway has been implicated in regulating embryogenesis by controlling cell movement and adhesion. Wnt11 can activate protein kinase C (PKC) and calcium/calmodulin-dependent kinase II (CaMKII) in the Wnt/Ca(2+) pathway. We hypothesized that the Wnt11, PKCalpha, and CaMKII gene expression is downregulated in the Cd-induced VBWD during early embryogenesis.

METHODS

After 60 hours of incubation, chick embryos were harvested 1 hour (1H), 4H, and 8H after treatment of saline or cadmium and divided into 2 groups: control and Cd (n = 8 at each time-point, respectively). Real-time polymerase chain reaction was performed to evaluate the messenger RNA (mRNA) expression of Wnt11, PKCalpha, and CaMKII in the Cd-induced VBWD chick model.

RESULTS

The mRNA expression levels of Wnt11, PKCalpha, and CaMKII were significantly decreased at 1H in Cd group compared to controls (P < .05). However, there were no significant differences in the other time-points.

CONCLUSION

Downregulation of Wnt11, PKCalpha, and CaMKII gene expression during the narrow window of early embryogenesis may cause VBWD, interfering with cell movement and adhesion, disrupting Wnt/Ca(2+) pathway.

Cell adhesion molecules nectins and associating proteins: Implications for physiology and pathology

Nectins have recently been identified as new cell adhesion molecules (CAMs) consisting of four members. They show immunoglobulin-like structures and exclusively localize at adherens junctions (AJs) between two neighboring cells. During the formation of cell-cell junctions, nectins function in cooperation with or independently of cadherins, major CAMs at AJs. Similar to cadherins, which are linked to the actin cytoskeleton by binding to catenins, nectins also bind to afadin through their C-terminal region and are linked to the actin cytoskeleton. In addition to nectins, there are nectin-like molecules (Necls), which resemble nectins in their structures and consist of five members. Nectins and Necls are involved in the formation of various kinds of cell-cell adhesion, and also play key roles in diverse cellular functions including cell movement, proliferation, survival, and differentiation. Thus, nectins and Necls are crucial for physiology and pathology of multicellular organisms.(Communicated by Shigetada NAKANISHI, M.J.A.).

An occludin-focal adhesion kinase protein complex at the blood-testis barrier: a study using the cadmium model

Several integral membrane proteins that constitute the blood-testis barrier (BTB) in mammalian testes, in particular rodents, are known to date. These include tight junction (TJ) proteins (e.g. occludin, junctional adhesion molecule-A, claudins), basal ectoplasmic specialization proteins (e.g. N-cadherin), and gap junction proteins (e.g. connexin43). However, the regulators (e.g. protein kinases and phosphatases) that affect these proteins, such as their interaction with the cytoskeletal actin, which in turn confer cell adhesion at the TJ, remain largely unknown. We report herein that focal adhesion kinase (FAK) is a putative interacting partner of occludin, but not claudin-11 or junctional adhesion molecule-A. Immunohistochemistry and fluorescence microscopy studies illustrated that the expression of FAK in the seminiferous epithelium of adult rat testes was stage specific. FAK colocalized with occludin at the BTB in virtually all stages of the seminiferous epithelial cycle but considerably diminished in stages VIII-IX, at the time of BTB restructuring to facilitate the transit of primary leptotene spermatocytes. Using Sertoli cells cultured in vitro with established TJ-permeability barrier and ultrastructures of TJ, basal ectoplasmic specialization and desmosome-like junction that mimicked the BTB in vivo, FAK was shown to colocalize with occludin and zonula occludens-1 (ZO-1) at the Sertoli-Sertoli cell interface. When these Sertoli cell cultures were treated with CdCl(2) to perturb the TJ-barrier function, occludin underwent endocytic-mediated internalization in parallel with FAK and ZO-1. Thus, these findings demonstrate that FAK is an integrated regulatory component of the occludin-ZO-1 protein complex, suggesting that functional studies can be performed to study the role of FAK in BTB dynamics.

The immunoglobulin-like cell adhesion molecule nectin and its associated protein afadin

Nectins are immunoglobulin-like cell adhesion molecules (CAMs) that compose a family of four members. Nectins homophilically and heterophilically interact in trans with each other to form cell-cell adhesions. In addition, they heterophilically interact in trans with other immunoglobulin-like CAMs. Nectins bind afadin, an actin filament (F-actin)-binding protein, at its cytoplasmic tail and associate with the actin cytoskeleton. Afadin additionally serves as an adaptor protein by further binding many scaffolding proteins and F-actin-binding proteins and contributes to the association of nectins with other cell-cell adhesion and intracellular signaling systems. Nectins and afadin play roles in the formation of a variety of cell-cell junctions cooperatively with, or independently of, cadherins. Cooperation between nectins and cadherins is required for the formation of cell-cell junctions; cadherins alone are not sufficient. Additionally, nectins regulate many other cellular activities (such as movement, proliferation, survival, differentiation, polarization, and the entry of viruses) in cooperation with other CAMs and cell surface membrane receptors.

HPA-1a alloantibodies reduce endothelial cell spreading and monolayer integrity

Maternal human platelet antigen (HPA)-1a alloantibodies causing neonatal alloimmune thrombocytopenia can bind also to endothelium, via the beta3-integrin (CD61). The aim of this study was to investigate the effect of HPA-1a Abs on endothelial cell function, with emphasis on monolayer integrity. We used a CD61 mAb as a model for the HPA-1a alloantibodies and confirmed the results with purified IgG fractions from HPA-1a alloimmunized women. The effect of these antibodies was examined by monitoring the adhesion, spreading, and monolayer integrity of primary HUVECs with conventional adhesion assays as well as electrical cell-substrate impedance sensing. We found that both the mAb CD61 and the HPA-1a antibodies caused a significant reduction in HUVEC spreading. Moreover, addition of the mAb CD61 and the HPA-1a antibodies prior to or following formation of a stable endothelial monolayer negatively affected endothelial monolayer integrity, which was accompanied by a redistribution of junctional proteins. Our data suggest that HPA-1a alloantibodies have a direct effect on endothelial cell spreading and monolayer integrity, which could contribute to the increased bleeding tendency in children with neonatal alloimmune thrombocytopenia.

Roles of cell adhesion molecules nectin and nectin-like molecule-5 in the regulation of cell movement and proliferation

In response to chemoattractants, migrating cells form protrusions, such as lamellipodia and filopodia, and structures, such as ruffles over lamellipodia, focal complexes and focal adhesions at leading edges. The formation of these leading edge structures is essential for directional cell movement. Nectin-like molecule-5 (Necl-5) interacts in cis with PDGF receptor and integrin alpha(v)beta(3), and enhances the activation of signalling molecules associated with these transmembrane proteins, which results in the formation of leading edge structures and enhancement of directional cell movement. When migrating cells come into contact with each other, cell-cell adhesion is initiated, resulting in reduced cell velocity. Necl-5 first interacts in trans with nectin-3. This interaction is transient and induces down-regulation of Necl-5 expression at the cell surface, resulting in reduced cell movement. Cell proliferation is also suppressed by the down-regulation of Necl-5, because the inhibitory effect of Necl-5 on Sprouty2, a negative regulator of the Ras signalling, is diminished. PDGF receptor and integrin alpha(v)beta(3), which have interacted with Necl-5, then form a complex with nectin, which initiates cell-cell adhesion and recruits cadherin to the nectin-based cell-cell adhesion sites to form stable adherens junctions. The formation of adherens junctions stops cell movement, in part through inactivation of integrin alpha(v)beta(3) caused by the trans-interaction of nectin. Thus, nectin and Necl-5 play key roles in the regulation of cell movement and proliferation.

Protein kinase C beta in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a disease with few therapeutic options. Protein kinase C beta (PKCbeta) is involved in important cellular functions. Enzastaurin (LY317615.HCl) is a novel inhibitor of PKC in clinical development. MPM cell lines (7) and patient tumor tissues (24) were evaluated for expression of PKCbeta by immunoblotting and immunohistochemistry, respectively. In-vitro cell growth assays were performed with enzastaurin with or without cisplatin. Cell migration was evaluated with the wound healing assay. Downstream signaling (survival and focal adhesion pathways) was studied by immunoblotting for related molecules in the presence of phorbol ester with or without enzastaurin. Expression for PKCbeta1 was seen in all cases, with a mean integrated optical density of 152.5 (standard deviation=95.47, n=24), whereas PKCbeta2 expression was less intense, with a mean integrated optical density of 11.45 (standard deviation=16.27, n=21). There was a trend toward lower overall survival among patients expressing above-median PKCbeta1 (P=0.064), but not PKCbeta2. Robust expression of PKCbeta1 and low expression of PKCbeta2 were observed in MPM cell lines. Treatment of MPM cell lines with enzastaurin revealed an IC50 of 5 micromol/l, and strong synergism was observed when combined with cisplatin. Wound healing assay revealed that treatment of H2461 cells with enzastaurin reduced migration by 59.2%. Enzastaurin treatment led to disruption of F-actin architecture. Downstream signaling showed reduced phosphorylation of AKT, FAK (focal adhesion kinase), p130Cas, S6 ribosomal protein, and paxillin. PKCbeta1 was expressed in the majority of MPM samples. Enzastaurin has preclinical activity against MPM, and exhibited synergism with cisplatin. PKCbeta inhibition in MPM might be able to reduce the invasiveness of MPM by affecting cytoskeletal function.

Nectins and nectin-like molecules: roles in contact inhibition of cell movement and proliferation

Nectins and nectin-like molecules (Necls) are immunoglobulin-like transmembrane cell adhesion molecules that are expressed in various cell types. Homophilic and heterophilic engagements between family members provide cells with molecular tools for intercellular communications. Nectins primarily regulate cell-cell adhesions, whereas Necls are involved in a greater variety of cellular functions. Recent studies have revealed that nectins and NECL-5, in cooperation with integrin alphavbeta3 and platelet-derived growth factor receptor, are crucial for the mechanisms that underlie contact inhibition of cell movement and proliferation; this has important implications for the development and tissue regeneration of multicellular organisms and the phenotypes of cancer cells.

The role of alkylphosphocholines in retinal Müller glial cell proliferation

PURPOSE

Alkylphosphocholines (APCs) are investigated for their effect on Müller glial cell proliferation and F-actin stress fiber distribution in vitro.

MATERIALS AND METHODS

Müller cells were incubated with APCs (C18:1-PC and C22:1-PC) +/- fetal calf serum. Proliferation was assessed by BrdU labeling and with the tetrazolium dye-reduction assay. Toxicity was measured using the trypan blue exclusion assay. The distribution of F-actin stress fibers was determined using FITC-phalloidin staining.

RESULTS

APCs are effective inhibitors of human and rat Müller glial cell proliferation and hypoxia-induced up-regulation of F-actin stress fibers in vitro in non-toxic concentrations.

CONCLUSIONS

APCs might prevent intraretinal changes as a result of serum stimulation and hypoxia following retinal detachment.

Involvement of the nectin-afadin complex in PDGF-induced cell survival

The nectin-afadin complex is involved in the formation of cell-cell junctions, such as adherens junctions (AJs) and tight junctions (TJs). Nectins are Ca2+-independent immunoglobulin-like cell-cell adhesion molecules, whereas afadin is an intracellular nectin-binding protein that connects nectins to the cadherin-catenin system at AJs and to the claudin–zona-occludens (ZO) protein system at TJs. Afadin–/– mice show embryonic lethality, resulting from impaired migration and improper differentiation of cells due to disorganization of cell-cell junctions during gastrulation. However, it remains to be elucidated whether disruption of afadin affects apoptosis. In the present study, we first found that embryoid bodies derived from afadin-knockout embryonic stem (ES) cells contained many more apoptotic cells than those derived from wild-type ES cells. We also revealed that apoptosis induced by serum starvation or Fas-ligand stimulation was increased in cultured NIH3T3 cells when afadin or nectin-3 was knocked down. The nectin-afadin complex was involved in the platelet-derived growth factor (PDGF)-induced activation of phosphatidylinositol 3-kinase (PI3K)-Akt signaling for cell survival. This complex was associated with PDGF receptor on the plasma membrane at cell-cell adhesion sites. Thus, the nectin-afadin complex is involved in PDGF-induced cell survival, at least through the PI3K-Akt signaling pathway.

Cross-talk among integrin, cadherin, and growth factor receptor: roles of nectin and nectin-like molecule

Integrin, cadherin, and growth factor receptor are key molecules for fundamental cellular functions including cell movement, proliferation, differentiation, adhesion, and survival. These cell surface molecules cross-talk with each other in the regulation of such cellular functions. Nectin and nectin-like molecule (Necl) have been identified as cell adhesion molecules that belong to the immunoglobulin superfamily. Nectin and Necl play important roles in the integration of integrin, cadherin, and growth factor receptor at the cell-cell adhesion sites of contacting cells and at the leading edges of moving cells, and thus are also involved in the fundamental cellular functions together with integrin, cadherin, and growth factor receptor. This chapter describes how newly identified cell adhesion molecules, nectin and Necl, modulate the cross-talk among integrin, cadherin, and growth factor receptor and how these integrated molecules act in the regulation of fundamental cellular functions.

The roles of nectins in cell adhesions: cooperation with other cell adhesion molecules and growth factor receptors

Nectins are Ca(2+)-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 alpha(v)beta(3), 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.

Nectin and nectin-like molecules: biology and pathology

Nectins and nectin-like molecules (Necls) are structurally related transmembrane proteins primarily involved in cell adhesion. Nectins and afadin, the adaptor or anchoring protein, stabilize the epithelium and endothelium and establish apical-basal polarity of epithelial cells, independently or in cooperation with other cell adhesion molecules. Necls facilitate cell-cell communication implicated in cell movement and proliferation, immune responses, and cancer cell phenotypes. Necls interact with nectins and specific ligands at cell-cell contacts, whereas Necls associate with integrin alpha v beta 3 and growth factor receptors on the same cell surface. Besides their roles in cell adhesion, nectins regulate the activities of Rho family small G proteins which play critical roles in maintaining the apical junctions of epithelial cells through reorganization of the actin cytoskeleton. Since mice lacking the Rho GDP-dissociation inhibitor (GDI)alpha show massive proteinuria and degeneration of renal epithelial cells, nectins and other cell adhesion molecules may play roles in the structural and functional aspects of renal diseases. Here we summarize our knowledge of nectins and Necls and discuss cell adhesion biology in the kidney.