Cell adhesion: a new target for therapy

Combinatory Nanovesicle with siRNA-Loaded Extracellular Vesicle and IGF-1 for Osteoarthritis Treatments

Extracellular vesicles (EVs) have been found to have the characteristics of their parent cells. Based on the characteristics of these EVs, various studies on disease treatment using mesenchymal stem cell (MSC)-derived EVs with regenerative activity have been actively conducted. The therapeutic nature of MSC-derived EVs has been shown in several studies, but in recent years, there have been many efforts to functionalize EVs to give them more potent therapeutic effects. Strategies for functionalizing EVs include endogenous and exogenous methods. In this study, human umbilical cord MSC (UCMSC)-derived EVs were selected for optimum OA treatments with expectation via bioinformatics analysis based on antibody array. And we created a novel nanovesicle system called the IGF-si-EV, which has the properties of both cartilage regeneration and long-term retention in the lesion site, attaching positively charged insulin-like growth factor-1 (IGF-1) to the surface of the UCMSC-derived Evs carrying siRNA, which inhibits MMP13. The downregulation of inflammation-related cytokine (MMP13, NF-kB, and IL-6) and the upregulation of cartilage-regeneration-related factors (Col2, Acan) were achieved with IGF-si-EV. Moreover, the ability of IGF-si-EV to remain in the lesion site for a long time has been proven through an ex vivo system. Collectively, the final constructed IGF-si-EV can be proposed as an effective OA treatment through its successful MMP13 inhibition, chondroprotective effect, and cartilage adhesion ability. We also believe that this EV-based nanoparticle-manufacturing technology can be applied as a platform technology for various diseases.

EPB41L5 Mediates TGFβ-Induced Metastasis of Gastric Cancer

PURPOSE

Because of disease heterogeneity, limited studies on effective chemotherapies and therapeutic agents for advanced gastric cancer are available. Erythrocyte membrane protein band 4.1-like 5 (EPB41L5) has critical roles in renal and breast cancer metastasis. However, its role in metastatic gastric cancer remains unknown.

EXPERIMENTAL DESIGN

The specimens of 78 gastric cancer patients were analyzed by oligonucleotide microarray and survival analysis. In vitro experiments and metastatic mice models were used to assess the effects of EPB41L5 on gastric cancer metastasis.

RESULTS

Gastric cancer patients with high EPB41L5 levels had poor prognosis and low survival rate. Further, TGFβ1-induced EPB41L5 expression promoted gastric cancer cell migration and invasion by Smad-dependent TGFβ signaling. Phospho-Smad3 recruitment to the EPB41L5 promoter was significantly inhibited by a TGFβ inhibitor. EPB41L5 overexpression increased lung metastasis of gastric cancer cells in nude mice, which was completely reversed by anti-EPB41L5 monoclonal antibody treatment. Importantly, p120-catenin knockdown abolished EPB41L5-enhanced gastric cancer cell metastasis. Anti-EPB41L5 monoclonal antibody treatment blocked the association of EPB41L5 with p120-catenin.

CONCLUSIONS

TGFβ/EPB41L5/p120-catenin axis regulates gastric cancer cell metastasis, and EPB41L5 is a promising therapeutic target for advanced gastric cancer.

Induction of PNAd and N-acetylglucosamine 6-O-sulfotransferases 1 and 2 in mouse collagen-induced arthritis

BACKGROUND

Leukocyte recruitment across blood vessels is fundamental to immune surveillance and inflammation. Lymphocyte homing to peripheral lymph nodes is mediated by the adhesion molecule, L-selectin, which binds to sulfated carbohydrate ligands on high endothelial venules (HEV). These glycoprotein ligands are collectively known as peripheral node addressin (PNAd), as defined by the function-blocking monoclonal antibody known as MECA-79. The sulfation of these ligands depends on the action of two HEV-expressed N-acetylglucosamine 6-O-sulfotransferases: GlcNAc6ST-2 and to a lesser degree GlcNAc6ST-1. Induction of PNAd has also been shown to occur in a number of human inflammatory diseases including rheumatoid arthritis (RA).

RESULTS

In order to identify an animal model suitable for investigating the role of PNAd in chronic inflammation, we examined the expression of PNAd as well as GlcNAc6ST-1 and -2 in collagen-induced arthritis in mice. Here we show that PNAd is expressed in the vasculature of arthritic synovium in mice immunized with collagen but not in the normal synovium of control animals. This de novo expression of PNAd correlates strongly with induction of transcripts for both GlcNAc6ST-1 and GlcNAc6ST-2, as well as the expression of GlcNAc6ST-2 protein.

CONCLUSION

Our results demonstrate that PNAd and the sulfotransferases GlcNAc6ST-1 and 2 are induced in mouse collagen-induced arthritis and suggest that PNAd antagonists or inhibitors of the enzymes may have therapeutic benefit in this widely-used mouse model of RA.

Influence of the cytoplasmic domain of E-cadherin on endogenous N-cadherin expression in malignant melanoma

E-cadherin is known to be an important molecule in epithelial-mesenchymal transition (EMT). Malignant transformation of melanocytes frequently attends with loss of E-cadherin expression and induction of expression of mesenchymal molecules like N-cadherin. The switch of the cadherin class is an interesting phenomenon of melanoma cells and in EMT in general. Therefore, we analysed the capacity of E-cadherin to regulate expression of N-cadherin in melanocytic cells. Our experiments revealed that melanoma cells downregulate endogenous N-cadherin expression after transient transfection of full-length E-cadherin, but also of the cytoplasmic domain of E-cadherin. Therefore, we concluded that the extracellular domain of E-cadherin and cell-cell contacts are not necessary for negative regulation of N-cadherin. Melanoma cells re-expressing full-length or cytoplasmatic E-cadherin have reduced NFkappaB activity in comparison to mock-transfected cells. Downregulation of NFkappaB activity, either directly or by re-expression of E-cadherin, led to a suppression of N-cadherin promoter activity and N-cadherin expression. Consequently, an NFkappaB-binding site in the N-cadherin promoter was characterized. In summary, our results suggest that N-cadherin is directly regulated by E-cadherin. Loss of E-cadherin induces NFkappaB activity and N-cadherin expression in tumorigenic EMT.

Reversal of melanocytic malignancy by keratinocytes is an E-cadherin-mediated process overriding beta-catenin signaling

Loss of E-cadherin in melanoma cells frees them from keratinocytes-mediated proliferation and phenotypic control, which can be restored by forced E-cadherin expression. In this study, E-cadherin and its derivatives were introduced into metastatic melanoma line 1205Lu. E-cadherin and E-cadherin-alpha-catenin fusion protein were functional in mediating cell adhesion, downregulating MCAM(4) in coculture, and inhibiting proliferation regardless of beta-catenin expression levels and activation status. In contrast, cytoplasmic domain-deleted (E-cadDeltaCYT) derivative was not able to reverse malignancy. The results indicate that E-cadherin-mediated cell adhesion is required for keratinocyte-mediated control of melanocytic cells, which can override proliferative activity of beta-catenin.

Adhesion mechanisms of endothelial cells

Endothelial cells express a diverse and exquisite array of adhesion molecules and cell surface receptors. Adhesion molecules expressed on endothelial cells not only maintain structural integrity of the vasculature, but also mediate more dynamic processes such as the highly regulated movement of leukocytes from free flow into different tissue compartments. Recent studies have focused on the molecular processes that mediate endothelial cell function and their ability to respond rapidly to changes in their immediate microenvironment, as well as maintaining routine cell trafficking through specialist tissue compartments. Adhesion molecules expressed on the endothelium mediate the movement of leukocytes into the underlying extravasculature to mediate a diverse array of functions including immune effector responses, cellular interactions in specialist lymphatic microenvironments and recirculation back into the vasculature. The true diversity and capacity of adhesion molecules capable of being expressed on the endothelium is now beginning to emerge, demonstrating new levels of complexity as specialist subsets of endothelium are characterised that define specific, yet diverse functions. In this chapter, the role of cell adhesion molecules in mediating endothelial cell function is discussed, from how their different physiochemical properties contribute to function, to how specific ligand interactions expressed on leukocyte cell populations contribute to functions ranging from constitutive cell trafficking to inflammation.

Michael Mason prize essay 2003. Why do leucocytes accumulate within chronically inflamed joints?

Chronic inflammation is characterized by the accumulation of leucocytes within tissues. In rheumatoid arthritis the inflammatory infiltrate shares many architectural features with lymphoid tissue. For example, CD4 T cells and B cells accumulate in perivascular lymphoid structures within synovial tissue. CD8 T cells and neutrophils are found predominantly within synovial fluid. What drives these distinctive lymphoid microstructures and the relative contribution of lymphocytes and stromal cells such as fibroblasts to this process is the subject of this review. Cellular interactions between leucocytes and stromal cells such as macrophages and fibroblasts are important in generating tumour necrosis factor-alpha within the inflamed synovium. Therefore understanding how leucocytes accumulate within the inflamed synovium is likely to provide new therapeutic approaches to modify the inflammatory process. We have found that fibroblasts play a dominant role in defining the disordered synovial microenvironment in rheumatoid arthritis. Through their production of a variety of cytokines (interferon-beta, transforming growth factor-beta) and constitutive chemokines (stromal cell-derived factor-1, CXCL12) they directly alter the behaviour of lymphocytes that accumulate within chronically inflamed joints leading to their inappropriate survival and retention. We have extended these observations to another chronic persistent rheumatic disease, Sjögren's syndrome, and found that ectopic production of the constitutive B cell-attracting chemokine BCA-1 (CXCL13) is associated with lymphocyte accumulation and lymphoid tissue formation. These findings suggest that stromal cells such as fibroblasts play an important role in the switch from acute resolving to chronic persistent arthritis by allowing lymphocytes to accumulate in the wrong place at the wrong time.

Characterization of human mucin gene MUC4 promoter: importance of growth factors and proinflammatory cytokines for its regulation in pancreatic cancer cells

The human mucin gene MUC4 encodes a large transmembrane mucin that is thought to play important roles in tumor cell biology and that is overexpressed in human pancreatic carcinomas. In this report, we describe the structure and functional activity of the 5'-flanking region, including 1.0 kilobase of the promoter. The long 5'-untranslated region (2.7 kilobases) is characterized by a high content of GC in its 3'-end. The first TATA box was located at -2672/-2668. Multiple transcription start sites and a high density of putative binding sites for Sp1 (GC and CACCC boxes), AP-1/-2/-4, cAMP-responsive element-binding protein, GATA, GR, and STAT transcription factors were found within the 5'-flanking region. Transcriptional activity of the promoter was assessed using pGL3-luciferase deletion mutants in two MUC4-expressing (CAPAN-1 and CAPAN-2) and one nonexpressing (PANC-1) pancreatic cancer cell line. Two highly active fragments (-219/-1 and -2781/-2572) that drive MUC4 transcription in CAPAN-1 and CAPAN-2 cells were identified. Gel retardation assays indicated that Sp1 and Sp3 bind to cognate cis-elements found in the 5'-flanking region and that Sp1 transactivates, whereas Sp3 inhibits the GC-rich region (-464/-1) in CAPAN-2 cells. Activation of protein kinase C with phorbol ester and treatment of cells with epidermal growth factor and transforming growth factor-alpha resulted in up-regulation of the promoter. Tumor necrosis factor-alpha and interferon (IFN)-gamma inflammatory cytokines had no or mild effect on MUC4 transcriptional activity when used alone. However, a very strong synergistic effect (10-12-fold activation) between IFN-gamma and tumor necrosis factor-alpha or IFN-gamma and transforming growth factor-alpha was obtained in CAPAN-2 cells. Altogether these results demonstrate that the 5'-flanking region of MUC4 contains epithelial cell-specific, positive, and negative regulatory cis-elements, that Sp1/Sp3 are important regulators of MUC4 basal expression, and that its regulation in pancreatic cancer cells involves complex interplay between several signaling pathways.

Fibroblasts regulate the switch from acute resolving to chronic persistent inflammation

Fibroblasts are important sentinel cells in the immune system and, here, it is proposed that these cells play a critical role in the switch from acute inflammation to adaptive immunity and tissue repair. It is suggested that chronic inflammation occurs because of disordered fibroblast behaviour in which failure to switch off their inflammatory programme leads to the inappropriate survival and retention of leukocytes within inflamed tissue.

Drugs, inflammation and cell adhesion receptors

The cell adhesion receptors that participate in the extravasation and migration of leucocytes towards inflammatory foci mainly include the selectins and different members of the integrin and immunoglobulin superfamilies. These adhesion receptors mediate the sequential steps of leucocyte-endothelial cell interaction and, together with chemoattractant molecules (e.g., chemokines), direct the influx of inflammatory cells and define the characteristics of the cell infiltrate. Many different drugs, including non-steroidal anti-inflammatory drugs (NSAIDs), glucocorticoids, rheumatoid arthritis disease-modifying agents and phosphodiesterase inhibitors, interfere with the expression and/or function of cell adhesion receptors and this effect accounts for, at least in part, their anti-inflammatory activity. In recent years, novel approaches for the modulation of the cell membrane receptors involved in inflammation have been active areas in pharmaceutical research. Upgraded synthetic blocking compounds, chimeric monoclonal antibodies or improved antisense oligonucleotides represent important advances in this field. The proper development of these novel approaches, as well as other alternative strategies, will allow a better and more specific pharmacological modulation of the inflammatory phenomenon.

Carbohydrate sulfotransferases: novel therapeutic targets for inflammation, viral infection and cancer

Effective direct inhibition of adhesion receptors by small molecules has been hampered by extended receptor-ligand interfaces as well as the entropic penalties often associated with inhibition of cell adhesion. Therefore, alternative strategies have targeted enzymes that are centrally involved in the biosynthesis of recognition epitopes, which are crucial for productive adhesion. Two classes of enzymes shown to play a pivotal role in cell-cell and cell-matrix adhesions are the protein-tyrosine and carbohydrate sulfotransferases, which impart crucial sulfate moieties onto glycoproteins. The carbohydrate sulfotransferases will be discussed in terms of target validation and small-molecule inhibitor discovery.

COX-2 inhibitors vs. NSAIDs in gastrointestinal damage and prevention

Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit production of protective gastric mucosal prostaglandins and also have a direct topical irritant effect. In some patients this results in dyspepsia and development of gastroduodenal erosions and ulceration. The risk of ulcer complications, such as bleeding, perforation and death is increased approximately 4-fold in NSAID users. Patients at high risk of ulcer complications include the elderly, those taking anticoagulants, steroids and aspirin, those with a previous history of peptic ulceration and patients with concomitant serious medical problems. The interaction of NSAIDs with Helicobacter pylori (the major cause of peptic ulceration in non-NSAID users) is controversial and some studies suggest that H. pylori infection may even protect against NSAID-induced ulceration. Selective inhibitors of the inducible cyclooxygenase-2 (COX-2) enzyme spare COX-1 in the gastric mucosa and, hence, do not inhibit production of mucosal prostaglandins. COX-2-selective inhibitors are associated with a significant reduction in gastroduodenal damage compared with traditional NSAIDs. Proton pump inhibitors (PPI) are probably the best agents for healing and prevention of NSAID-induced ulcers. Preliminary studies suggest that COX-2 selective inhibitors, like traditional NSAIDs, may prevent lower gastrointestinal cancer. Further studies are needed but they may be useful in individuals at high risk of certain types of lower gastrointestinal malignancy with increased gastrointestinal tolerability and safety.

Focal adhesion kinases: interest in immunoendocrinology, developmental biology, and cancer

The research field on focal adhesion-related kinases started a decade ago, but the term focal adhesion was introduced for the first time nearly 20 yr before. Since its identification, many studies have enlightened the role of the first intermediate of focal adhesion-related signals in a large number of biologic and physiologic processes. In this review, we try to integrate the most recent data about the known focal adhesion-related kinases, and we focus on three topics in which they deserve great interest: neuroendocrine-immune interactions, developmental biology, and proliferative diseases.

Regulation of ICAM-1-mediated fibroblast-T cell reciprocal interaction: implications for modulation of gut inflammation

BACKGROUND & AIMS

Immune-nonimmune cell interactions modulate mucosal immunity. We investigated the expression of adhesion molecules by intestinal fibroblasts, the effect of immune cell-derived factor on fibroblast binding of T cells, and the consequences of interfering with adhesion molecule expression on fibroblast-T cell interaction.

METHODS

Expression of fibroblast intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 surface and messenger RNA (mRNA) was measured before and after exposure to immune cell-derived supernatants. Fibroblasts were treated with antibodies to ICAM-1 or VCAM-1, or ICAM-1 antisense oligonucleotide Isis 2302, before a T-cell adhesion assay.

RESULTS

Fibroblast activation by immune cell-derived cytokines enhanced ICAM-1 and VCAM-1 surface expression and mRNA as well as adhesiveness for T cells. Blockade with neutralizing antibodies showed that binding was almost exclusively dependent on ICAM-1. Isis 2302 specifically reduced fibroblast ICAM-1 mRNA and dose-dependently inhibited ICAM-1 surface expression and T-cell binding.

CONCLUSIONS

ICAM-1 is essential for intestinal fibroblast binding of T cells, a phenomenon that is efficiently and specifically disrupted by ICAM-1 antisense oligonucleotides. These observations emphasize the crucial regulatory role of fibroblasts in mucosal immunity and their potential as targets for therapeutic intervention in intestinal inflammation.

Regulation of E-cadherin: does hypoxia initiate the metastatic cascade?

The ability of tumours to metastasis is regarded as one of the hallmarks of malignancy. The process through which tumours evolve to achieve this has been termed the metastatic cascade. This cascade has been the subject of much investigation over many years. One of the vital events identified by these investigations is the reduction of adhesion between tumour cells facilitating invasion of the surrounding tissues and vascular channels, ultimately leading to the development of a distant metastasis. E-cadherin and its associated catenin complex have been identified as key molecules in cell adhesion. This review looks at the structure and interaction of the E-cadherin-catenin complex and the factors that appear to regulate E-cadherin expression and thus cell adhesion. From the data gathered, it has become possible to propose the hypothesis that the development of tumour hypoxia is the initiating factor that sets the tumour on the road to metastasis.

Pathogenesis of inflammatory bowel disease

In spite of expanding knowledge of cellular and molecular mechanisms of intestinal inflammation, the etiology and pathogenesis of inflammatory bowel disease (IBD) remain obscure. The link between the environment and IBD is still circumstantial, but definite progress is occurring in defining genetic susceptibility loci for Crohn's disease (CD) and ulcerative colitis (UC). The notion that normal enteric flora play a role in initiating or maintaining IBD is gaining momentum. Some components of the flora may act as noxious agents, whereas others (probiotics) seem to have a protective effect. The importance of the mucosal immune system to IBD is established, and evidence is accumulating that nonimmune components, such as epithelial, mesenchymal, and endothelial cells, also contribute to gut inflammation. The effect of cytokines in intestinal immunity is being elucidated by studies on their molecular mechanism, particularly the activation of nuclear factor (NF)-kappaB. Finally, the beneficial effects of cytoprotective prostaglandins and cell adhesion molecule (CAM) blockade promise novel therapeutic opportunities derived from an improved understanding of IBD pathogenesis.

Tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta down-regulate intercellular adhesion molecule (ICAM)-2 expression on the endothelium

Leukocyte recruitment is a crucial step in inflammation. Inflammatory stimuli upregulate the expression of some endothelial adhesion molecules, such as E-selectin or ICAM-1, but not of others such as ICAM-2. ICAM-2, a constitutively expressed endothelial ligand for beta2 integrins LFA-1 and Mac-1, is involved in leukocyte adhesion to resting endothelium and in transmigration in vitro, however its role in inflammation is unclear. We have studied the effect of TNF-alpha and IL-1beta on ICAM-2 expression on human umbilical vein endothelial cells (HUVECs). Prolonged treatment (24 h) of HUVECs with TNF-alpha (10 ng/ml) or IL-1beta (34 ng/ml) reduced ICAM-2 surface expression to 50% of control, while interferon (IFN)-gamma had no effect. The loss in ICAM-2 surface expression correlated with a reduction of ICAM-2 mRNA to approximately 40% of control after 24 h of cytokine treatment. The activity of an ICAM-2 promoter reporter plasmid transfected into HUVECs was down-regulated by TNF-alpha and IL-1beta to similar values. Thus inflammatory cytokines inhibit ICAM-2 transcription, despite the absence of known cytokine-responsive elements in the promoter. Immunocytochemistry on HUVEC monolayers showed that ICAM-2 expression, mainly at the cell junctions in resting cells, was markedly decreased by cytokine treatment. This data suggest that ICAM-2 expression on the endothelium may be regulated during inflammation.

CD147 monoclonal antibodies induce homotypic cell aggregation of monocytic cell line U937 via LFA-1/ICAM-1 pathway

CD147 is a 50 000-60 000 MW glycoprotein of the immunoglobulin superfamily broadly expressed on haemopoietic cell lines and peripheral blood cells. In the present study, six monoclonal antibodies (mAbs) directed against the CD147 protein were generated. The antigen defined by the generated CD147 mAbs is widely expressed on haemopoietic cell lines, peripheral blood cells and is a lymphocyte activation-associated cell surface molecule. The generated CD147 mAbs precipitated a broad protein band from U937 cells of 45 000-65 000 MW under reducing conditions. Functional analysis indicated that the CD147 mAbs markedly induced homotypic cell aggregation of U937 cells, but not K562 cells. The CD147 mAb-induced cell aggregation was inhibited by leucocyte function-antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1) mAbs. However, the expression of LFA-1 and ICAM-1 molecules on U937 was not altered by CD147 mAb treatment. The U937 cell aggregation induced by CD147 mAb was also inhibited by ethylenediamine tetra-acetic acid (EDTA), sodium azide and when incubated at 4 degrees. We therefore propose that the binding of CD147 mAb to CD147 molecule, which mimics the natural ligand binding, may generate intracellular signals that activate LFA-1/ICAM-1 intercellular adhesion pathway.

Aryl C-glycosides: physiologically stable glycomimetics of sialyl Lewis X

In the course of the search for physiologically stable, structurally simple, and low molecular weight sLeX mimetics, aryl C-glycosides with carboxylic acid functionality 2 were found to be extremely potent inhibitors against L- and P-selectins with IC50 in the low microM range.

Adhesion molecules in inflammatory diseases

Cell adhesion molecules (CAM) have a key role in the inflammatory response. Selectins, integrins and immunoglobulin (Ig) gene superfamily adhesion receptors mediate the different steps of the migration of leucocytes from the blood-stream towards inflammatory foci. The activation of endothelial cells (EC) upregulates the expression of several CAM and triggers the interaction of these cells with leucocytes. Selectins are involved in the initial interactions (tethering/rolling) of leucocytes with activated endothelium, whereas integrins and Ig superfamily CAM mediate the firm adhesion of these cells and their subsequent extravasation. During rolling, leucocytes are activated through the intracellular signals generated by CAM and chemokine receptors. Blockade of the function or expression of CAM has emerged as a new therapeutic target in inflammatory diseases. Different drugs are able to interfere with cell adhesion phenomena. In addition, new antiadhesion therapeutic approaches (blocking monoclonal antibodies, soluble receptors, synthetic peptides, peptidomimetics, etc.) are currently in development.

Cell adhesion: more than just glue (review)

The ability of cells to interact with each other and their surroundings in a co-ordinated manner depends on multiple adhesive interactions between neighbouring cells and their extracellular environment. These adhesive interactions are mediated by a family of cell surface proteins, termed cell adhesion molecules. Fortunately these adhesion molecules fall into distinct families with adhesive interactions varying in strength from strong binding involved in the maintenance of tissue architecture to more transient, less avid, dynamic interactions observed in leukocyte biology. Adhesion molecules are extremely versatile cell surface receptors which not only stick cells together but provide biochemical and physical signals that regulate a range of diverse functions, such as cell proliferation, gene expression, differentiation, apoptosis and migration. In addition, like many other cell surface molecules, they have been usurped as portals of entry for pathogens, including prions. How the mechanical and chemical messages generated from adhesion molecules are integrated with other signalling pathways (such as receptor tyrosine kinases and phosphatases) and the role that aberrant cell adhesion plays in developmental defects and disease pathology are currently very active areas of research. This review focuses on the biochemical features that define whether a cell surface molecule can act as an adhesion molecule, and discusses five specific examples of how cell adhesion molecules function as more than just 'sticky' receptors. The discussion is confined to the signalling events mediated by members of the integrin, cadherin and immunoglobulin gene superfamilies. It is suggested that, by controlling the membrane organization of signalling receptors, by imposing spatial organization, and by regulating the local concentration of cytosolic adapter proteins, intercellular and cell-matrix adhesion is more than just glue holding cells together. Rather dynamic 'conversations' and the formation of multi-protein complexes between adhesion molecules, growth factor receptors and matrix macromolecules can now provide a molecular explanation for the long-observed but poorly understood requirement for a number of seemingly distinct cell surface molecules to be engaged for efficient cell function to occur.