Multiple Integrin Receptors Research Articles

Abstract 1819: Integrin inhibitor GLPG-0187 promotes T-cell killing of mismatch repair-deficient colorectal cancer cells by suppression of SMAD/TGF-β signaling

Abstract Colorectal cancer is the third leading cause of cancer-related death and the third most common cause of cancer. As the five-year survival with advanced metastatic colorectal cancer (mCRC) is 14%, new treatment strategies are needed. Immune checkpoint blockade which takes advantage of an individual's immune system in order to fight cancer, is a promising future direction of research, although it is only effective and approved for the treatment of mismatch repair (MMR)-deficient CRCs. Long-term outcomes even in MMR-deficient mCRC suggest that most patients are not cured but eventually develop therapy resistance. We hypothesized that targeting TGF- β signaling may enhance immune-mediated T-cell killing by MMR-deficient CRC cells. Using GLPG-0187, an inhibitor of multiple integrin receptors and TGF- β, we demonstrate minimal cytotoxicity against MMR-deficient HCT116 or p53-null HCT116 human CRC cells. However, GLPG-0187 promoted significant immune cell killing of the CRC cells by TALL-104 T lymphoblast cells. GLPG-0187 reduced pSMAD2 in HCT116 p53-null cells either in the absence or presence of exogenous TGF- β. We observed a reduction in CCL20, CXCL5, prolactin, and TRAIL-R3 while GDF-15 was increased in TALL-104 cells treated with a T-cell activating dose of GLPG-0187 (4 μM). Our results suggest that TGF- signaling inhibition by a general integrin receptor inhibitor may boost T-cell killing of MMR-deficient colorectal cancer cells, and suggest that a combination of anti-GDF-15 in combination with TGF- β blockade should be further investigated in the treatment of MMR-deficient mCRC. Our results support the development of a novel immune-based therapeutic strategy to treat colorectal cancer by targeting the TGF-β signaling pathway through integrin receptor blockade. Citation Format: Brooke Verschleiser, William MacDonald, Lindsey Carlsen, Kelsey E. Huntington, Lanlan Zhou, Wafik El-Deiry. Integrin inhibitor GLPG-0187 promotes T-cell killing of mismatch repair-deficient colorectal cancer cells by suppression of SMAD/TGF-β signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1819.

PO-201 Mutant KRAS-driven cancers depend on PTPN11/SHP2 phosphatase

IntroductionThe ubiquitously expressed non-receptor protein tyrosine phosphatase SHP2, encoded by PTPN11, is involved in signal transduction downstream of multiple growth factor, cytokine and integrin receptors. Its requirement for complete RAS-MAPK activation and its role as a negative regulator of JAK-STAT signalling have established SHP2 as an essential player in oncogenic signalling pathways. Recently, novel potent allosteric SHP2-inhibitors have been presented as a viable therapeutic option for RTK-driven cancers, but were shown to be ineffective in KRAS mutant tumour cell lines in vitro.Material and methodsVarious mutant KRAS-driven murine models of pancreatic ductal adenocarcinoma (PDAC) and non-small cell lung cancer (NSCLC) were employed to investigate the contribution of Ptpn11/SHP2 to carcinogenesis and tumour maintenance, and to determine its utility as a therapeutic target for treatment of established tumours in vivo. CRISPR/Cas9 mediated knockout of PTPN11 in human PDAC cell lines, drug-synergy screening and human PDAC organoid and tissue xenograft model therapeutic trials substantiated the rationale of dual SHP2/MEK inhibition in a human context.Results and discussionsWe report a central and indispensable role for SHP2 in oncogenic KRAS-driven tumours. Genetic deletion of Ptpn11 profoundly inhibited tumour development in mutant KRAS-driven murine models PDAC and NSCLC. We provide evidence for a critical dependence of mutant KRAS on SHP2 during carcinogenesis. Deletion or inhibition of SHP2 in established tumours delayed tumour progression but was not sufficient to achieve tumour regression. However, SHP2 was necessary for resistance mechanisms upon blockade of MEK. Synergy was observed when both SHP2 and MEK were targeted, resulting in sustained tumour growth control in murine and human patient-derived organoids and xenograft models of PDAC and NSCLC.ConclusionOur data suggest clinical utility of dual SHP2/MEK inhibition as a targeted therapy approach for KRAS mutant cancers.

THR‐687, a potent small molecule integrin antagonist, holds promise as a therapeutic approach for back‐of‐the‐eye vascular pathologies

PurposePathologic neovascularization and vessel leakage are key drivers for vision loss in several back‐of‐the‐eye diseases, such as diabetic retinopathy and age‐related macular degeneration. In the eye, integrin receptors play an important role in (pathological) angiogenesis and vascular leakage. Blocking integrin receptors has the potential to inhibit these processes, independent of anti‐VEGF responsiveness. In this study, we evaluated the integrin‐blocking and anti‐angiogenic properties of THR‐687, a novel small molecule integrin antagonist.MethodsCompetition ELISA assays were used to assess the ability of THR‐687 to compete with the binding of integrin receptors to their natural ligands. The inhibitory effect of THR‐687 on the migration of human umbilical vein endothelial cells (HUVECs) was evaluated in the ORIS cell migration assay. The effect of THR‐687 on blood vessel outgrowth was evaluated in an ex vivo mouse choroidal explant model. Cytotoxicity of THR‐687 on human retinal microvascular endothelial cells (HRMVECs) was evaluated using the CellTox Green assay. The safety profile of THR‐687 was further evaluated using hERG and genotoxicity assays.ResultsTHR‐687 was found to inhibit multiple integrin receptors belonging to the RGD class with IC50 values in the low nanomolar range, including, but not limited to, αvβ3, αvβ5 and α5β1. THR‐687 potently inhibited the migration of HUVECs in the ORIS system (IC50 of 82 ± 11 nM). Ex vivo choroidal vessel sprouting was dose‐dependently inhibited by THR‐687 (IC50 of 1.50 ± 0.27 μM). No relevant cytotoxicity signal was observed on HRMVECs at concentrations ranging from 0.25 nM to 20 μM, and in vitro pharmacological profiling studies indicated a good safety profile.ConclusionsTHR‐687 is a potent drug candidate for the treatment of diabetic eye disease.

Adhesive Peptide Sequences Regulate Valve Interstitial Cell Adhesion, Phenotype and Extracellular Matrix Deposition.

Knowledge of how extracellular matrix (ECM) binding impacts valve interstitial cells (VICs) is critical not only to better understanding the etiology of valvular diseases but also to constructing living valve substitutes that can grow and remodel. Use of ECM-mimicking adhesive peptides with specific affinity to different receptors provides insights into adhesion-mediated cell signaling and downstream outcomes. Expression of adhesion receptors by VICs was assessed by flow cytometry and used to guide the choice of peptides studied. The peptide RGDS with affinity to multiple integrin receptors, and specific receptor-targeting peptides DGEA (integrin α2β1), YIGSR (67kDa laminin/elastin receptor; 67LR), and VAPG (67LR) were incorporated into hydrogels to investigate their effects on VICs. DGEA, YIGSR, and VAPG alone were insufficient to induce stable VIC adhesion. As a result, these peptides were studied in combination with 1 mM RGDS. For VICs cultured on two-dimensional hydrogel surfaces, YIGSR and VAPG down-regulated the expression of smooth muscle α-actin (myofibroblast activation marker); DGEA promoted VIC adhesion and VIC-mediated ECM deposition and inhibited the activity of alkaline phosphatase (osteogenic differentiation marker). Further, YIGSR and DGEA in combination promoted ECM deposition while inhibiting both myofibroblastic and osteogenic differentiation. However, VICs behaved differently to adhesive ligands when cultured within three-dimensional hydrogels, with most VICs assuming a healthy, quiescent phenotype under all peptide conditions tested. DGEA promoted ECM deposition by VICs within hydrogels. Overall, we demonstrate that the presentation of defined peptides targeting specific adhesion receptors can be used to regulate VIC adhesion, phenotype and ECM synthesis.

The role of periostin in neoplastic processes

Periostin, also called osteoblast-specific factor 2 (OSF-2), is a multifunctional glycoprotein that belongs to the group of matricellular proteins. Due to its characteristic molecular structure containing integrin-binding domains, periostin is capable of binding to multiple integrin receptors (αvβ3, αvβ5, α6β4), thus affecting the regulation of the intracellular signaling pathways associated with protein kinases PI3K/AKT and focal adhesion kinase (FAK). This protein thus plays a role in the adhesion process, in the migration of many cells, and importantly, epithelial-mesenchymal transition of cancer cells. Periostin also participates in the processes of angiogenesis and lymphangiogenesis, metastases of cancer cells, and remodeling of the extracellular matrix. Increased expression of periostin has been observed in various tumor types, including breast, NSCLC, colorectal, pancreatic, prostate, and ovarian cancers, as well as tumors of the head and neck, and glioblastomas. Many groups have recently reported on periostin's key role in tumor progression, which suggests that periostin can be considered a potential therapeutic target.

Evidence for a regulatory role of α4 – integrins in the maturation of eosinophils generated from the bone marrow in the presence of dexamethasone

Although eosinophils co-express multiple integrin receptors, the contributions of integrins to eosinophil development have not been explored. We previously described extensive aggregation and cytological immaturity in eosinophils developing in bone-marrow (BM) cultures exposed to dexamethasone. Here we examined the relationship of alpha 4 integrins with these effects of dexamethasone. We evaluated: (a) the effects of exposure to dexamethasone in BM culture on eosinophil expression of alpha 4 integrin receptors and ligands; (b) the contribution of alpha 4 integrins to eosinophil aggregation and maturation. Cultures were established with IL-5 (alone or with dexamethasone) for up to 7 days, and eosinophil production, alpha 4 integrin receptor/ligand expression, aggregation and morphology were evaluated before and after targeting alpha 4 integrin-dependent adhesions. Because prostaglandin E2 (PGE2) modifies the effects of dexamethasone on eosinophilopoiesis, PGE2 effects on alpha 4 integrin expression and function were also evaluated. Dexamethasone increased the yield of eosinophils up to day 7. The frequency of eosinophils expressing alpha 4, beta1 and beta 7 integrin receptors at day 7 was also increased by dexamethasone. Eosinophils also expressed the alpha 4 beta 1 ligand, VCAM-1. Dexamethasone increased the expression of alpha 4 integrin and VCAM-1 in aggregates containing eosinophils as early as day 3. PGE2, added up to day 3, modified the effects of dexamethasone to suppress the expression of alpha 4 integrin, decrease aggregation and promote cytological maturation of eosinophils recovered at day 7. Dissociation of immature eosinophils from clusters present at day 3 by reagents targeting alpha 4 or beta1 integrins or VCAM-1 also induced cytological maturation. The concordant effects of targeting alpha 4 integrins with drugs and antibodies support a relationship between alpha 4-mediated aggregation and maturational arrest. These observations support a novel role for alpha 4 integrin receptors and ligands in eosinophilopoiesis. In addition, increased alpha 4 expression following glucocorticoid exposure may contribute to the retention and accumulation of eosinophils in haemopoietic tissue.

Engineering Clustered Ligand Binding Into Nonviral Vectors: αvβ3 Targeting as an Example

The development of techniques to efficiently deliver genes using nonviral approaches can broaden the application of gene delivery in medical applications without the safety concerns associated with viral vectors. Here, we designed a clustered integrin-binding platform to enhance the efficiency and targetability of nonviral gene transfer to HeLa cells with low and high densities of alpha(v)beta(3) integrin receptors. Arg-Gly-Asp (RGD) nanoclusters were formed using gold nanoparticles functionalized with RGD peptides and used to modify the surface of DNA/poly(ethylene imine) (PEI) polyplexes. DNA/PEI polyplexes with attached RGD nanoclusters resulted in either 5.4- or 35-fold increase in gene transfer efficiency over unmodified polyplexes for HeLa cells with low- or high-integrin surface density, respectively. The transfection efficiency obtained with the commercially available vector jetPEI-RGD was used for comparison as a vector without clustered binding. JetPEI-RGD exhibited a 1.2-fold enhancement compared to unmodified jetPEI in cells with high densities of alpha(v)beta(3) integrin receptors. The data presented here emphasize the importance of the RGD conformational arrangement on the surface of the polyplex to achieve efficient targeting and gene transfer, and provide an approach to introduce clustering to a wide variety of nanoparticles for gene delivery.

Fibronectin induces ureteric bud cells branching and cellular cord and tubule formation

The extracellular matrix (ECM) protein fibronectin is involved in several stages of embryogenesis. Fibronectin exerts its effect through interaction with cellular integrin and nonintegrin receptors. We investigated the effect of fibronectin on branching and tubulogenesis of ureteric bud cells in a three-dimensional gel culture system. Primary ureteric bud cells from mouse embryos at gestation 11 days (E11) were isolated and established in culture. Fibronectin and integrin subunits were localized using immunoperoxidase staining. In three-dimensional collagen type I gel culture of ureteric bud cell, fibronectin dose dependently induces cord and tubule formation. Both ureteric bud cells and ureteric bud branches in embryonic kidney express the same multiple integrin subunits that include beta(1), beta(3), alpha(3), alpha(4) and alpha(v). Embryonic kidneys examined at E12, E14, and E16 days of gestation express fibronectin in the undifferentiated mesenchyme especially next to ureteric bud branches and in the interstitium around glomerulotubular structures and blood vessels. Fibronectin expression was similar at the tips and stalks of branching ureteric bud. Fibronectin expression is maximum at E12 and decreases with advanced gestation. Cultured ureteric bud cells also express fibronectin. RGD peptides inhibit cord and tubular formation in the three-dimensional gel. Anti-alpha(3)beta(1) antibody partially inhibits fibronectin-induced cord and tubule formation. Hepatocyte growth factor (HGF), fibroblast growth factor (FGF), and glial cell line-derived neurotrophic factor (GDNF) induce ureteric bud cell cord formation in three-dimensional gel. The effects of growth factors are delayed and quantitatively less compared to the effect of fibronectin. Fibronectin induces ureteric bud cells branching and tubulogenesis through interaction with multiple integrin receptors. Cultured ureteric bud cells express fibronectin and the origin of fibronectin at mesenchyme-ureteric bud interface is likely both the metanephric mesenchyme and ureteric bud epithelium. Addition of individual neutralizing antibodies to beta(1), beta(3), alpha(3), alpha(4,)alpha(6) and alpha(v) integrin subunits does not block the effect of fibronectin. Only an antibody to alpha(3)beta(1) integrin substantially blocks the effect of fibronectin. Other mechanisms, including unidentified integrins, are likely involved in fibronectin-induced cord and tubule formation.

Fibroblast Migration on Fibronectin Requires Three Distinct Functional Domains

Mesenchymal cell movement is normally constrained; however, fibronectin can provide a pathway for stromal cell migration during embryogenesis, morphogenesis, and wound healing. Cells can adhere to fibronectin via integrin and nonintegrin receptors, which bind multiple unique peptide sequences. Synthetic peptides and recombinant proteins were used to delineate the functional domains needed for human fibroblast migration over fibronectin. The 9th and 10th fibronectin type III repeats, which contain RGD and PHSRN synergy cell attachment sequences, support almost maximal fibroblast attachment, but not migration of primary dermal fibroblasts. Specific sequences within the heparin domain and the IIICS region are also required for migration. These findings predict and additional data confirm the necessity for the cooperation of multiple integrin and nonintegrin receptors for fibroblast migration on fibronectin. Such stringency of migration most likely imposes an immense constraint on normal mesenchymal cell mobility in unperturbed tissue. Loss of such restraint may be critical for the migration cancer cells through the extracellular matrix.

Strategies for the purification of laminin-10 for studies on colon cancer metastasis.

Signals from the epidermal growth factor (EGF) receptor family are thought to combine with integrin-dependent adhesion to laminins to contribute to disease progression and metastasis in cancer. To date, little is known about the mechanisms by which these signals interact. Recently, we have shown that the colon cancer cell line LIM1215 secretes and adheres to laminin-10 through multiple integrin receptors, and that EGF stimulates spreading and migration of these cells on the same substrate. Additionally laminin-10/11 has been shown by immunohistochemistry to be present at the invasive edge of moderately differentiated colon cancers. To enable detailed structure-function studies to be undertaken, it is important to be able to rapidly obtain highly purified native laminin-10 from bulk biological samples in reasonable yield. The development of a multidimensional micropurification scheme to achieve this is presented and compared with other reported methods for the purification of laminins.

Osteopontin--a molecule for all seasons.

Osteopontin (OPN) is a multifunctional protein, and although highly expressed in bone, it is also expressed by various cell types including macrophages, endothelial cells, smooth muscle cells and epithelial cells.1,,2 OPN is involved in diverse biological processes and the aim of this review is to give a broad outline of some important aspects of the biology of OPN. Although this review is written primarily from a renal perspective, it is hoped that the reader will appreciate that OPN is involved in both physiological and pathological processes in multiple organs and tissues including biomineralization, inflammation, leukocyte recruitment and cell survival. OPN is a negatively‐charged acidic hydrophilic protein of approximately 300 amino acid residues, and is secreted into all body fluids. The OPN cDNA from various mammalian species exhibits a high degree of sequence homology. There is evidence of alternative splicing, although the functional significance of this is unclear at present. The molecule undergoes considerable post‐translational modification, and is phosphorylated and glycosylated. OPN has an arginine‐glycine‐aspartic acid (RGD) cell binding sequence, a calcium binding site and two heparin binding domains. Cells may bind OPN via multiple integrin receptors including the vitronectin receptor ( α v β 3) as well as various β 1 and β 5 integrins. Integrin binding may be RGD‐dependent or ‐independent (e.g. via the motif SVVYGLR). OPN does not bind the standard form of CD44 (hyaluronic acid receptor) but does bind various isoforms of CD44. These CD44 isoforms bind OPN via multiple sites. OPN may be cleaved by thrombin, resulting in the exposure of additional cryptic binding sites as well as the production of functional chemotactic fragments.3 The regulation of OPN expression is incompletely understood at present and may differ between various cell types. Studies indicate that the OPN promoter contains various motifs including a purine‐rich …

Laminin-10 Mediates Basal and EGF-Stimulated Motility of Human Colon Carcinoma Cells via α3β1 and α6β4 Integrins

Signals from the epidermal growth factor (EGF) receptor and integrin-dependent adhesion to laminin contribute to the progression and metastasis of colonic tumors. However, little is know about the mechanisms by which these signals cooperate. Recently, we have reported that the colon cancer cell line LIM1215 secretes and adhere to autocrine laminin-10 via multiple integrin receptors and that EGF stimulates spreading of these cells on the same substrate. In this report, we investigate the effect of EGF and laminin-10 on colon cancer cell migration in vitro. EGF stimulates migration of LIM1215 cells in a wound healing assay. The response to EGF is inhibited by anti-EGF receptor antibody 528, the EGF receptor kinase inhibitor AG-1478, or the MAP kinase kinase inhibitor PD98059 but not the PI3-K inhibitor wortmannin. Using Transwell migration chambers, we demonstrate that laminin-10 but not collagen-I, collagen-IV, or a commercial preparation of human placental laminin is a potent motility factor for LIM1215 cells. The migration response to laminin-10 is increased upon stimulation of the cells with EGF and correlates with the up-regulation of α6β4 integrin expression as measured by analysis of Triton X-100-soluble cellular extracts. The results from integrin inhibition experiments indicate that basal migration on laminin-10 is mediated by α3β1 but not α2β1 nor α6β4 integrins. Alpha3 blocking antibodies also inhibited EGF-stimulated chemokinetic migration of LIM1215 cells on laminin-10. However, in contrast to unstimulated cells, α6 or β4 integrin-blocking antibodies inhibited the migration of EGF-stimulated cells by up to 50%. Taken together, these results support the cooperative role of EGF receptor and laminin-10 on colon cancer cell motility and suggest a critical role for both the α3β1 and the α6β4 integrins in this process.

Colon Cancer Cells Adhesion and Spreading on Autocrine Laminin-10 Is Mediated by Multiple Integrin Receptors and Modulated by EGF Receptor Stimulation

Epidermal growth factor (EGF) receptor ligands such as EGF and transforming growth factor-α (TGF-α) play an important role in controlling the proliferation, survival, morphology, and motility of colonic epithelial cells. There is also increasing evidence that growth factors and extracellular matrix (ECM) proteins cooperate to regulate these cellular processes. We have reported previously that autocrine TGF-α and an unidentified ECM protein in the serum-free conditioned medium of the human colon carcinoma cell line LIM1215 synergize to induce spreading of these cells in low-density cultures. We have now purified the ECM protein secreted by LIM1215 cells and show that it synergizes with EGF to induce spreading of LIM1215 cells and other human cell lines from the colon and other tissues. The purified ECM migrated as a single protein band with an apparent molecular mass of approximately 800 kDa on SDS–PAGE under nonreducing conditions and, under reducing conditions, as three protein bands of approximately 360, 210, and 200 kDa. Immunoblotting experiments and mass spectrometry analysis of tryptic digests on the purified protein identified the 360-, 210-, and 200-kDa protein bands as laminin α5, β1, and γ1 chains, respectively, indicating that LIM1215 cells secrete laminin-10 (α5β1γ1). In serum-free medium, LIM1215 cells adhere to laminin-10 primarily via α2β1 and α3β1 integrin receptors. EGF-induced spreading of LIM1215 cells on laminin-10 is partially inhibited by pretreatment of the cells with blocking antibodies directed against integrin α3 or β1 but not α2, α6, or β4 subunits. Spreading is almost completely inhibited by blocking α3 + α2, α3 + α6, or β1 + β4 integrin chains and results in cell death. Increased spreading in the presence of EGF correlates with up-regulation of α6β4 integrins in these cells after exposure to EGF. These results indicate that colon cancer cells attach and spread on laminin-10 via multiple integrin receptors and suggest a critical role for α3β1 integrins in the spreading response. Together, our results support the concept that the adhesive properties of colon cancer cells are modulated by autocrine production of TGF-α and laminin-10 and autocrine induction of appropriate integrins.

Extracellular matrix and integrin signalling: the shape of things to come

The extracellular matrix (ECM) and integrins collaborate to regulate gene expression associated with cell growth, differentiation and survival. Biochemical and molecular analyses of integrin signalling pathways have uncovered several critical cytoplasmic proteins that link the ECM and integrins to intracellular pathways that may contribute to anchorage-dependent growth. A large body of evidence now indicates that the non-receptor protein kinases focal adhesion kinase (FAK) and specific members of the mitogen-activated protein kinases (MAPKs), including the extracellular-signal-regulated kinases (ERKs), mediate these ECM- and integrin-derived signalling events. However, little is known about how FAK and MAPKs contribute to biological processes other than cell proliferation or migration. In addition, remarkably little is known concerning the signalling events that occur in cells that adhere to complex multivalent extracellular matrices via multiple integrin receptors. Given the stringent requirement for attaining a proper morphology in ECM/integrin-directed cell behaviour, it is still not clear how cell shape and tissue architecture impact upon intracellular signalling programmes involving FAK and MAPKs. However, the recent discovery that members of the Rho family of small GTPases are able to regulate ECM/integrin pathways that modulate both cell shape and intracellular signalling provides new insights into how cell morphology and signal transduction become integrated, especially within three-dimensional differentiated tissues.

Extracellular matrix and integrin signalling: the shape of things to come

The extracellular matrix (ECM) and integrins collaborate to regulate gene expression associated with cell growth, differentiation and survival. Biochemical and molecular analyses of integrin signalling pathways have uncovered several critical cytoplasmic proteins that link the ECM and integrins to intracellular pathways that may contribute to anchorage-dependent growth. A large body of evidence now indicates that the non-receptor protein kinases focal adhesion kinase (FAK) and specific members of the mitogen-activated protein kinases (MAPKs), including the extracellular-signal-regulated kinases (ERKs), mediate these ECM- and integrin-derived signalling events. However, little is known about how FAK and MAPKs contribute to biological processes other than cell proliferation or migration. In addition, remarkably little is known concerning the signalling events that occur in cells that adhere to complex multivalent extracellular matrices via multiple integrin receptors. Given the stringent requirement for attaining a proper morphology in ECM/integrin-directed cell behaviour, it is still not clear how cell shape and tissue architecture impact upon intracellular signalling programmes involving FAK and MAPKs. However, the recent discovery that members of the Rho family of small GTPases are able to regulate ECM/integrin pathways that modulate both cell shape and intracellular signalling provides new insights into how cell morphology and signal transduction become integrated, especially within three-dimensional differentiated tissues.

Human colonic cancer cells synthesize and adhere to laminin-5. Their adhesion to laminin-5 involves multiple receptors among which is integrin alpha2beta1.

In the mature gut, laminin-5 is expressed at the basal aspect of the differentiating epithelial cells. In vitro, we show that three more or less differentiated human colonic cancer HT29 cell lines produce and deposit laminin-5; they predominantly synthesize and secrete the 440 kDa form of laminin-5 that comprises the unprocessed 155 kDa gamma2 chain, as determined by immunoprecipitation analysis. In contrast, the highly differentiated colon carcinoma Caco-2 cells produce almost no laminin-5. Using anti-integrin antibodies, we show that adhesion of the two colonic cancer cell lines to laminin-5 is mediated by multiple integrin receptors including those for alpha3beta1, alpha6beta1 and alpha6beta4 integrins like in other cell types. In addition, the implication of integrin alpha2beta1 in this adhesion process is demonstrated for the first time. This has been shown by cell adhesion inhibition experiments, solid phase assays and confocal analysis. Together with previous in situ observations, these data provide a baseline knowledge for the understanding of the regulation of laminin-5 in normal and pathological intestine.

Triflavin, an Arg-Gly-Asp-containing peptide, inhibits the adhesion of tumor cells to matrix proteins via binding to multiple integrin receptors expressed on human hepatoma cells.

Integrins are a superfamily of cell surface glycoproteins that promote cellular adhesion. The interaction of integrins with extracellular matrices such as fibronectin and vitronectin has been shown to be mediated through an arginine-glycine-aspartic acid (RGD) sequence within adhesive proteins. Triflavin, a 7.5-kDa cysteine-rich polypeptide purified from Trimeresurus flavoviridis snake venom, belongs to a family of RGD-containing peptides, termed disintegrins. Disintegrins have been isolated from the venom of various vipers and have been shown to be potent inhibitors of platelet aggregation. In this study, we found that human hepatoma cell adhesion to immobilized matrix proteins (i.e. fibronectin, collagen, laminin, and vitronectin) was differentially affected by various anti-integrin monoclonal antibodies (mAbs) (i.e., alpha3beta1, alpha5beta1, alpha6beta1, and alpha v beta3) as well as by the peptide GRGDS. Indirect flow cytometric analysis of hepatoma cells with anti-integrin mAbs demonstrated that alpha6beta1 was uniformly expressed at a high density, while alpha3beta1, and alpha5beta1 were moderately expressed and alpha v beta3 was expressed in small amounts on hepatoma cells, consistent with the results obtained from immunofluorescence microscopic analysis. When immobilized on plastic wells, triflavin promoted hepatoma cell attachment; this cell attachment was inhibited by either GRGDS or mAbs against integrins alpha3beta1, alpha5beta1 and alpha v beta3). In addition, the binding of FITC-conjugated triflavin to hepatoma cells was inhibited by GRGDS, anti-alpha3beta1, antialpha5beta1, and anti-alpha v beta3 mAbs. Among these mAbs, anti-alpha5beta1 exerted the most pronounced inhibitory effect (>70%) on the binding of triflavin to hepatoma cells. Taken together, these results suggest that triflavin binds via its RGD sequence to multiple integrin receptors (i.e., alpha5beta1, alpha3beta1, and alpha v beta3) expressed on the surface of hepatoma cells, resulting in inhibition of hepatoma cell adhesion to extracellular matrices (i.e., fibronectin and vitronectin).

Differential Effects of the Integrins α9β1, αvβ3, and αvβ6 on Cell Proliferative Responses to Tenascin: ROLES OF THE β SUBUNIT EXTRACELLULAR AND CYTOPLASMIC DOMAINS

Members of the integrin family manifest considerable overlap in ligand specificity, and many cells have the capacity to express multiple integrin receptors for the same ligand. For example, at least 5 different integrins recognize tenascin as a ligand, and 4 of these bind to the same region of the protein, the third fibronectin type III repeat (TNfn3). We utilized colon carcinoma cells (SW480) that do not normally attach to TNfn3 to examine the possibility that ligation of different integrin receptors for this ligand would induce different effects on cell behavior and intracellular signaling. Heterologous expression of the tenascin receptors alphavbeta3 and alpha9beta1 produced comparable effects on cell adhesion and spreading on TNfn3, but alphavbeta3-transfectants proliferated considerably better on each concentration examined. alphavbeta6-transfectants attached (although less avidly), but completely failed to spread or proliferate. Expression of a chimeric beta subunit composed of the beta3 extracellular domain fused to the beta6 transmembrane and cytoplasmic domains resulted in adhesion and spreading similar to that seen with beta3-transfectants, but considerably less proliferation. When the same cell lines were plated on fibronectin, alphavbeta6-transfectants spread and proliferated as well as cells transfected with the chimeric beta3/beta6 subunit, but, again, neither cell line proliferated as well as cells expressing alphavbeta3. Cell proliferation was always associated with spreading and with phosphorylation of the focal adhesion kinase, paxillin, and the mitogen-activated kinase, Erk2, but cell attachment in the absence of spreading or proliferation was not associated with phosphorylation of any of these proteins. These data suggest that different integrin receptors for a single ligand can produce markedly different effects on cell proliferation, and that both the extracellular and cytoplasmic domains of integrin beta subunits contribute to these differences.

Human endothelial cells express integrin receptors on the luminal aspect of their membrane

Endothelial cells (EC) form a dynamic interface between blood and the rest of the body. EC surface properties promoting adhesion of reactive plasma proteins and/or circulating cells might be of pivotal importance for the homeostasis of blood and tissues. EC express multiple integrin receptors that promote their attachment to the subendothelial matrix proteins. Among these receptors, alpha v beta 3 is of particular relevance on EC, since it is abundantly expressed and can bind many different matrix and plasma proteins. It is still unknown whether integrin receptors are selectively located to the basal side of EC membrane or may also be exposed on the cell surface in contact with blood. This issue was addressed using different experimental approaches. First, selective surface radioiodination using lactoperoxidase (LPO)-latex beads and immunoprecipitation analysis were performed. We found that cultured EC, similarly to human skin fibroblasts (HSF), expose alpha v beta 3 on both their apical (free) and basal (substratum-attached) surfaces. This held also for other integrins such as alpha 2 beta 1, alpha 3 beta 1, alpha 5 beta 1, and alpha 6 beta 1. Immunoprecipitation data were verified by morphological techniques. Immunofluorescence and immunogold-staining of EC with alpha v beta 3, as well as with beta 1 subfamily antibodies, showed a diffuse and granular distribution of these integrins on EC surface. alpha v beta 3 and beta 1 integrins were also detected on the apical membrane of EC at higher magnification by scanning electron microscopy (SEM). Finally, data obtained on cultured EC were confirmed in vivo on immunogold-labeled ultrathin cryosections of human vessels by transmission electron microscopy (TEM). Data indicate, that in addition to their role in promoting EC attachment to extracellular matrix proteins, integrin receptors of EC can be exposed to blood-stream and eventually be available for binding of plasma proteins and circulating cells.

Human Endothelial Cells Express Integrin Receptors on the Luminal Aspect of Their Membrane

Abstract Endothelial cells (EC) form a dynamic interface between blood and the rest of the body. EC surface properties promoting adhesion of reactive plasma proteins and/or circulating cells might be of pivotal importance for the homeostasis of blood and tissues. EC express multiple integrin receptors that promote their attachment to the subendothelial matrix proteins. Among these receptors, alpha v beta 3 is of particular relevance on EC, since it is abundantly expressed and can bind many different matrix and plasma proteins. It is still unknown whether integrin receptors are selectively located to the basal side of EC membrane or may also be exposed on the cell surface in contact with blood. This issue was addressed using different experimental approaches. First, selective surface radioiodination using lactoperoxidase (LPO)-latex beads and immunoprecipitation analysis were performed. We found that cultured EC, similarly to human skin fibroblasts (HSF), expose alpha v beta 3 on both their apical (free) and basal (substratum-attached) surfaces. This held also for other integrins such as alpha 2 beta 1, alpha 3 beta 1, alpha 5 beta 1, and alpha 6 beta 1. Immunoprecipitation data were verified by morphological techniques. Immunofluorescence and immunogold-staining of EC with alpha v beta 3, as well as with beta 1 subfamily antibodies, showed a diffuse and granular distribution of these integrins on EC surface. alpha v beta 3 and beta 1 integrins were also detected on the apical membrane of EC at higher magnification by scanning electron microscopy (SEM). Finally, data obtained on cultured EC were confirmed in vivo on immunogold-labeled ultrathin cryosections of human vessels by transmission electron microscopy (TEM). Data indicate, that in addition to their role in promoting EC attachment to extracellular matrix proteins, integrin receptors of EC can be exposed to blood-stream and eventually be available for binding of plasma proteins and circulating cells.