Syndecan binding sites in the laminin alpha1 chain G domain

The laminin alpha1 chain G domain has multiple biological activities. Previously, we identified cell binding sequences in the laminin alpha1 chain G domain by screening 113 synthetic peptide-polystyrene beads for cell attachment activity. Here, we have used a recombinant protein of the laminin alpha1 G domain (rec-alpha1G) and a large set of synthetic peptides to further identify and characterize heparin, cell, and syndecan-4 binding sites in the laminin alpha1 chain G domain. The rec-alpha1G protein promoted both cell attachment and heparin binding (K(D) = 19 nM). Cell attachment to the rec-alpha1G protein was inhibited 60% by heparin and 30% by EDTA. The heparin binding sites were identified by competing heparin binding to the rec-alpha1G protein with 110 synthetic peptides in solution. Only two peptides, AG73 (IC(50) = 147 microM) and AG75 (IC(50) = 206 microM), inhibited heparin binding to rec-alpha1G. When the peptides were compared in a solid-phase heparin binding assay, AG73 showed more heparin binding than AG75. AG73 also inhibited fibroblast attachment to the rec-alpha1G protein, but AG75 did not. Cell attachment to the peptides was studied using peptide-coated plates and peptide-conjugated sepharose beads. AG73 promoted cell attachment in both assays, but AG75 only showed cell attachment activity in the bead assay. Additionally, AG73, but not AG75, inhibited branching morphogenesis of mouse submandibular glands in organ culture. Furthermore, the rec-alpha1G protein bound syndecan-4, and both AG73 and AG75 inhibited this binding. These results suggest that the AG73 and AG75 sites are important for heparin and syndecan-4 binding in the laminin alpha1 chain G domain. These sites may play a critical role in the diverse biological activities involving heparin and syndecan-4 binding.     

Importance of syndecan-4 and syndecan -2 in osteoblast cell adhesion and survival mediated by a tissue transglutaminase-fibronectin complex

Tissue transglutaminase (TG2) has been identified as an important extracellular crosslinking enzyme involved in matrix turnover and in bone differentiation. Here we report a novel cell adhesion/survival mechanism in human osteoblasts (HOB) which requires association of FN bound TG2 with the cell surface heparan sulphates in a transamidase independent manner. This novel pathway not only enhances cell adhesion on FN but also mediates cell adhesion and survival in the presence of integrin competing RGD peptides. We investigate the involvement of cell surface receptors and their intracellular signalling molecules to further explore the pathway mediated by this novel TG-FN heterocomplex. We demonstrate by siRNA silencing the crucial importance of the cell surface heparan sulphate proteoglycans syndecan-2 and syndecan-4 in regulating the compensatory effect of TG-FN on osteoblast cell adhesion and actin cytoskeletal formation in the presence of RGD peptides. By use of immunoprecipitation and inhibitory peptides we show that syndecan-4 interacts with TG2 and demonstrate that syndecan-2 and the α5β1 integrins, but not α4β1 function as downstream modulators in this pathway. Using function blocking antibodies, we show activation of α5β1 occurs by an inside out signalling mechanism involving activation and binding of protein kinase PKCα and phosphorylation of focal adhesion kinase (FAK) at Tyr⁸⁶¹ and activation of ERK1/2.     

Adhesion and protease activity in cell lines from human salivary gland tumors are regulated by the laminin-derived peptide AG73, syndecan-1 and β1 integrin

We studied the induction of protease activity by the laminin alpha1-derived peptide AG73 in cells from adenoid cystic carcinoma (CAC2) and myoepithelioma (M1), respectively a malignant and a benign salivary gland tumors. Laminin alpha1 chain and MMP9 were immunolocalized in adenoid cystic carcinoma and myoepithelioma in vivo and in vitro. Cells grown inside AG73-enriched laminin-111 exhibited large spaces in the extracellular matrix, suggestive of remodeling. The broad spectrum MMP inhibitor GM6001 decreased spaces induced by AG73 in CAC2 and M1 cells. This result strongly suggests that AG73-mediated matrix remodeling involves matrix metalloproteinases. CAC2 and M1 cells cultured on AG73 showed a dose-dependent increase of MMP9 secretion, as detected by zymography. Furthermore, siRNA silencing of MMP9 decreased remodeling in 3D cultures. We searched for AG73 receptors regulating MMP9 activity in our cell lines. CAC2 and M1 cells grown on AG73 exhibited colocalization of syndecan-1 and beta1 integrin. siRNA knockdown of syndecan-1 expression in these cells resulted in decreased adhesion to AG73 and reduced protease and remodeling activity. We investigated syndecan-1 co-receptors in both cell lines. Silencing beta1 integrin inhibited adhesion to AG73, matrix remodeling and protease activity. Double-knockdown experiments were carried out to further explore syndecan-1 and beta1 integrin cooperation. CAC2 cells transfected with both syndecan-1 and beta1 integrin siRNA oligos showed significant decrease in adhesion to AG73. Simultaneous silencing of receptors also induced a decrease in protease activity. Our results suggest that syndecan-1 and beta1 integrin signaling downstream of AG73 regulate adhesion and MMP production by CAC2 and M1 cells.     

Endothelial cell migration on RGD-peptide-containing PEG hydrogels in the presence of sphingosine 1-phosphate

Sphingosine 1-phosphate (S1P) is a potent chemokinetic agent for endothelial cells that is released by activated platelets. We previously developed Arg-Gly-Asp (RGD)-containing polyethylene glycol biomaterials for the controlled delivery of S1P to promote endothelialization. Here, we studied the effects of cell adhesion strength on S1P-stimulated endothelial cell migration in the presence of arterial levels of fluid shear stress, since an upward shift in optimal cell adhesion strengths may be beneficial for promoting long-term cell adhesion to materials. Two RGD peptides with different integrin-binding specificities were added to the polyethylene glycol hydrogels. A linear RGD bound primarily to β₃ integrins, whereas a cyclic RGD bound through both β₁ and β₃ integrins. We observed increased focal adhesion formation and better long-term adhesion in flow with endothelial cells on linear RGD peptide, versus cyclic RGD, even though initial adhesion strengths were higher for cells on cyclic RGD. Addition of 100 nM S1P increased cell speed and random motility coefficients on both RGD peptides, with the largest increases found on cyclic RGD. For both peptides, much of the increase in cell migration speed was found for smaller cells (<1522 μm² projected area), although the large increases on cyclic RGD were also due to medium-sized cells (2288-3519 μm²). Overall, a compromise between high cell migration rates and long-term adhesion will be important in the design of materials that endothelialize after implantation.     

Cell type-specific differences in glycosaminoglycans modulate the biological activity of a heparin-binding peptide (RKRLQVQLSIRT) from the G domain of the laminin alpha1 chain

AG73 (RKRLQVQLSIRT), a peptide from the G domain of the laminin alpha1 chain, has diverse biological activities with different cell types. The heparan sulfate side chains of syndecan-1 on human salivary gland cells were previously identified as the cell surface ligand for AG73. We used homologous peptides from the other laminin alpha-chains (A2G73-A5G73) to determine whether the bioactivity of the AG73 sequence is conserved. Human salivary gland cells and a mouse melanoma cell line (B16F10) both bind to the peptides, but cell attachment was inhibited by glycosaminoglycans, modified heparin, and sized heparin fragments in a cell type-specific manner. In other assays, AG73, but not the homologous peptides, inhibited branching morphogenesis of salivary glands and B16F10 network formation on Matrigel. We identified residues critical for AG73 bioactivity using peptides with amino acid substitutions and truncations. Fewer residues were critical for inhibiting branching morphogenesis (XKXLXVXXXIRT) than those required to inhibit B16F10 network formation on Matrigel (N-terminal XXRLQVQLSIRT). In addition, surface plasmon resonance analysis identified the C-terminal IRT of the sequence to be important for heparin binding. Structure-based sequence alignment predicts AG73 in a beta-sheet with the N-terminal K (Lys(2)) and the C-terminal R (Arg(10)) on the surface of the G domain. In conclusion, we have determined that differences in cell surface glycosaminoglycans and differences in the amino acids in AG73 recognized by cells modulate the biological activity of the peptide and provide a mechanism to explain its cell-specific activities.     

RGD-independent cell adhesion via a tissue transglutaminase-fibronectin matrix promotes fibronectin fibril deposition and requires syndecan-4/2 and {alpha}5{beta}1 integrin co-signaling

Fibronectin (FN) deposition mediated by fibroblasts is an important process in matrix remodeling and wound healing. By monitoring the deposition of soluble biotinylated FN, we show that the stress-induced TG-FN matrix, a matrix complex of tissue transglutaminase (TG2) with its high affinity binding partner FN, can increase both exogenous and cellular FN deposition and also restore it when cell adhesion is interrupted via the presence of RGD-containing peptides. This mechanism does not require the transamidase activity of TG2 but is activated through an RGD-independent adhesion process requiring a heterocomplex of TG2 and FN and is mediated by a syndecan-4 and β1 integrin co-signaling pathway. By using α5 null cells, β1 integrin functional blocking antibody, and a α5β1 integrin targeting peptide A5-1, we demonstrate that the α5 and β1 integrins are essential for TG-FN to compensate RGD-induced loss of cell adhesion and FN deposition. The importance of syndecan-2 in this process was shown using targeting siRNAs, which abolished the compensation effect of TG-FN on the RGD-induced loss of cell adhesion, resulting in disruption of actin skeleton formation and FN deposition. Unlike syndecan-4, syndecan-2 does not interact directly with TG2 but acts as a downstream effector in regulating actin cytoskeleton organization through the ROCK pathway. We demonstrate that PKCα is likely to be the important link between syndecan-4 and syndecan-2 signaling and that TG2 is the functional component of the TG-FN heterocomplex in mediating cell adhesion via its direct interaction with heparan sulfate chains.     

Syndecan-2 overexpression regulates adhesion and migration through cooperation with integrin α2

Syndecan-2, a transmembrane heparan sulfate proteoglycan, is known to serve as an adhesion receptor, but details of the regulatory mechanism governing syndecan-2 cell adhesion and migration remain unclear. Here, we examined this regulatory mechanism, showing that overexpression of syndecan-2 enhanced collagen adhesion, cell migration and invasion of normal rat intestinal epithelial cells (RIE1), and increased integrin α2 expression levels. Interestingly, RIE1 cells transfected with either syndecan-2 or integrin α2 showed similar adhesion and migration patterns, and a function-blocking anti-integrin α2 antibody abolished syndecan-2-mediated adhesion and migration. Consistent with these findings, transfection of integrin α2 siRNA diminished syndecan-2-induced cell migration in HCT116 human colon cancer cells. Taken together, these results demonstrate a novel cooperation between syndecan-2 and integrin α2β1 in adhesion-mediated cell migration and invasion. This interactive dynamic might be a possible mechanism underlying the tumorigenic activities of colon cancer cells.     

Syndecan-1 and -4 differentially regulate oncogenic K-ras dependent cell invasion into collagen through α2β1 integrin and MT1-MMP

Syndecans function as co-receptors for integrins on different matrixes. Recently, syndecan-1 has been shown to be important for α2β1 integrin-mediated adhesion to collagen in tumor cells by regulating cell adhesion and migration on two-dimensional collagen. However, the function of syndecans in supporting α2β1 integrin interactions with three-dimensional (3D) collagen is less well studied. Using loss-of-function and overexpression experiments we show that in 3D collagen syndecan-4 supports α2β1-mediated collagen matrix contraction. Cell invasion through type I collagen containing 3D extracellular matrix (ECM) is driven by α2β1 integrin and membrane type-1 matrix metalloproteinase (MT1-MMP). Here we show that mutational activation of K-ras correlates with increased expression of α2β1 integrin, MT1-MMP, syndecan-1, and syndecan-4. While K-ras-induced α2β1 integrin and MT1-MMP are positive regulators of invasion, silencing and overexpression of syndecans demonstrate that these proteins inhibit cell invasion into collagen. Taken together, these data demonstrate the existence of a complex interplay between integrin α2β1, MT1-MMP, and syndecans in the invasion of K-ras mutant cells in 3D collagen that may represent a mechanism by which tumor cells become more invasive and metastatic.     

CCN2 promotes keratinocyte adhesion and migration via integrin α5β1

Background

CCN2, (a.k.a. connective tissue growth factor and CTGF) has emerged as a regulator of cell migration. While the importance of CCN2 for the fibrotic process in wound healing has been well studied, the effect of CCN2 on keratinocyte function is not well understood. In this study, we investigated the mechanism behind CCN2-driven keratinocyte adhesion and migration.Materials and methods: Adhesion assays were performed by coating wells with 10 μg/ml fibronectin (FN) or phosphate-buffered saline (PBS). Keratinocytes were seeded in the presence or absence of 200 ng/ml CCN2, 5 mmol/l ethylenediaminetetraacetic acid, 10 mmol/l cations, 500 μl arginine–glycine–aspartic acid (RGD), 500 μM arginine–glycine–glutamate–serine (RGES), and 10 μg/ml anti-integrin blocking antibodies. Migration studies were performed using a modified Boyden chamber assay. Quantitative PCR was used to study the effect of CCN2 on integrin subunit mRNA expression. To block intracellular pathways, keratinocytes were pretreated with 20 μM PD98059 (MEK-1 inhibitor) or 20 μM PF573228 (FAK inhibitor) for 60 min prior the addition of CCN2. Western blot was used to measure CCN2, p-ERK1/2, and ERK1/2.Results: CCN2 enhanced keratinocyte adhesion to fibronectin via integrin α5β1. The addition of anti-integrin α5β1 antibodies reduced CCN2-mediated keratinocyte migration. In addition, CCN2 regulated mRNA and protein expression of integrin subunits α5 and β1. CCN2 activated the FAK-MAPK signaling pathway, and pretreatment with MEK1-specific inhibitor PD98059 markedly reduced CCN2-induced keratinocyte migration.Conclusions: Our results demonstrate that CCN2 enhances keratinocyte adhesion and migration through integrin α5β1 and activation of the FAK-MAPK signaling cascade.     

Structure of the integrin alpha2beta1-binding collagen peptide

We have determined the 1.8 Å crystal structure of a triple helical integrin-binding collagen peptide (IBP) with sequence (Gly-Pro-Hyp)₂-Gly-Phe-Hyp-Gly-Glu-Arg-(Gly-Pro-Hyp)₃. The central GFOGER hexapeptide is recognised specifically by the integrins α2β1, α1β1, α10β1 and α11β1. These integrin/collagen interactions are implicated in a number of key physiological processes including cell adhesion, cell growth and differentiation, and pathological states such as thrombosis and tumour metastasis. Comparison of the IBP structure with the previously determined structure of an identical collagen peptide in complex with the integrin α2-I domain (IBP^c) allows the first detailed examination of collagen in a bound and an unbound state. The IBP structure shows a direct and a water-mediated electrostatic interaction between Glu and Arg side-chains from adjacent strands, but no intra-strand interactions. The interactions between IBP Glu and Arg side-chains are disrupted upon integrin binding. A comparison of IBP and IBP^c main-chain conformation reveals the flexible nature of the triple helix backbone in the imino-poor GFOGER region. This flexibility could be important to the integrin-collagen interaction and provides a possible explanation for the unique orientation of the three GFOGER strands observed in the integrin-IBP^c complex crystal structure.     

A novel integrin alpha5beta1 antagonistic peptide, A5-1, screened by Protein Chip system as a potent angiogenesis inhibitor

Integrin α5β1 immobilized on a ProteoChip was used to screen new antagonistic peptides from multiple hexapeptide sub-libraries of the positional scanning synthetic peptide combinatorial library (PS-SPCL). The integrin α5β1-Fibronectin interaction was demonstrated on the chip. A novel peptide ligand, A5-1 (VILVLF), with high affinity to integrin α5β1 was identified from the hexapeptide libraries with this chip-based screening method on the basis of a competitive inhibition assay. A5-1 inhibits the integrin-fibronectin interaction in a dose-dependent manner (IC₅₀; 1.56 ± 0.28 μM. In addition, it inhibits human umbilical vein endothelial cell proliferation, migration, adhesion, tubular network formation, and bFGF-induced neovascularization in a chick chorioallantoic membrane. These results suggest that A5-1 will be a potent inhibitor of neovascularization.     

Integrin binding human antibody constant domains--probing the C-terminal structural loops for grafting the RGD motif

Recently, it has been demonstrated that loops of the crystallizable fragment of IgG1 (IgG1-Fc) can be engineered to form antigen-binding sites. In this work C-terminal structural loops in the CH3 domains of homodimeric IgG1-Fc have been functionalized to form integrin-binding sites in order to probe the effect of engineering on structural integrity and thermal stability of IgG1-Fc as well as on binding to the ligands Protein A, CD16 and FcRn, respectively. The peptide sequence GCRGDCL - a disulfide-bridged cyclic heptapeptide that confers binding to human αvβ3 integrin was introduced into AB, CD and/or EF loops and single and double mutants were heterologously expressed in Pichia pastoris. Integrin binding of engineered IgG-Fc was tested using both binding to coated αvβ3 integrin in ELISA or to αvβ3-expressing K562 cells in FACS analysis. Additionally, blocking of αvβ3-mediated cell adhesion to vitronectin was investigated. The data presented in this report demonstrate that bioactive integrin-binding peptide(s) can be grafted on the C-terminal loops of IgG-Fc without impairing binding to effector molecules. Observed differences between the investigated variants in structural stability and integrin binding are discussed with respect to the known structure of IgG-Fc and its structural loops.     

Substance P plays an important role in cell adhesion molecule 1-mediated nerve–pancreatic islet α cell interaction

Autonomic neurons innervate pancreatic islets of Langerhans and maintain blood glucose homeostasis by regulating hormone levels. We previously showed that cell adhesion molecule 1 (CADM1) mediated the attachment and interaction between nerves and aggregated pancreatic islet α cells. In this study, we cocultured αTC6 cells, a murine α cell line, with mouse superior cervical ganglion (SCG) neurons. The oscillation of intracellular Ca²⁺ concentration ([Ca²⁺]_i) was observed in 27% and 14% of αTC6 and CADM1-knockdown αTC6 cells (αTC6^siRNA-CADM1 cells) in aggregates, respectively, within 1 min after specific SCG nerve stimulation with scorpion venom. In αTC6^siRNA-CADM1 cells, the responding rate during 3 min after SCG nerve stimulation significantly increased compared with that within 1 min, whereas the increase in the responding rate was not significantly different in αTC6 cells. This indicated that the response of αTC6 cells according to nerve stimulation occurred more rapidly and effectively than that of αTC6^siRNA-CADM1 cells, suggesting CADM1 involvement in promoting the interaction between nerves and α cells and among α cells. In addition, because we found that neurokinin (NK)-1 receptors, which are neuropeptide substance P receptors, were expressed to a similar extent by both cells, we investigated the effect of substance P on nerve–α cell interaction. Pretreatment with CP99,994 (0.1 μg/ml), an NK-1 receptor antagonist, reduced the responding rate of both cells, suggesting that substance P released from stimulated neurites was a mediator to activate αTC6 cells. In addition, α cells that were attached to neurites in a CADM1-mediated manner appeared to respond effectively to neurite activation via substance P/NK-1 receptors.     

Identification of cell adhesive sequences in the N-terminal region of the laminin α2 chain

The laminin α2 chain is specifically expressed in the basement membrane surrounding muscle and nerve. We screened biologically active sequences in the mouse laminin N-terminal region of α2 chain using 216 soluble peptides and three recombinant proteins (rec-a2LN, rec-a2LN+, and rec-a2N) by both the peptide- or protein-coated plate and the peptide-conjugated Sepharose bead assays. Ten peptides showed cell attachment activity in the plate assay, and 8 peptides were active in the bead assay. Seven peptides were active in the both assays. Five peptides promoted neurite outgrowth with PC12 cells. To clarify the cellular receptors, we examined the effects of heparin and EDTA on cell attachment to 11 active peptides. Heparin inhibited cell attachment to 10 peptides, and EDTA significantly affected only A2-8 peptide (YHYVTITLDLQQ, mouse laminin α2 chain, 117-128)-mediated cell attachment. Cell attachment to A2-8 was also specifically inhibited by anti-integrin β1 and anti-integrin α2β1 antibodies. These results suggest that A2-8 promotes an integrin α2β1-mediated cell attachment. The rec-a2LN protein, containing the A2-8 sequence, bound to integrin α2β1 and cell attachment to rec-a2LN was inhibited by A2-8 peptide. Further, alanine substitution analysis of both the A2-8 peptide and the rec-a2LN+ protein revealed that the amino acids Ile-122, Leu-124, and Asp-125 were involved in integrin α2β1-mediated cell attachment, suggesting that the A2-8 site plays a functional role as an integrin α2β1 binding site in the LN module. These active peptides may provide new insights on the molecular mechanism of laminin-receptor interactions.     

Mapping of potent and specific binding motifs, GLOGEN and GVOGEA, for integrin α1β1 using collagen toolkits II and III

Integrins are well characterized cell surface receptors for extracellular matrix proteins. Mapping integrin-binding sites within the fibrillar collagens identified GFOGER as a high affinity site recognized by α2β1, but with lower affinity for α1β1. Here, to identify specific ligands for α1β1, we examined binding of the recombinant human α1 I domain, the rat pheochromocytoma cell line (PC12), and the rat glioma Rugli cell line to our collagen Toolkit II and III peptides using solid-phase and real-time label-free adhesion assays. We observed Mg(2+)-dependent binding of the α1 I domain to the peptides in the following rank order: III-7 (GLOGEN), II-28 (GFOGER), II-7 and II-8 (GLOGER), II-18 (GAOGER), III-4 (GROGER). PC12 cells showed a similar profile. Using antibody blockade, we confirmed that binding of PC12 cells to peptide III-7 was mediated by integrin α1β1. We also identified a new α1β1-binding activity within peptide II-27. The sequence GVOGEA bound weakly to PC12 cells and strongly to activated Rugli cells or to an activated α1 I domain, but not to the α2 I domain or to C2C12 cells expressing α2β1 or α11β1. Thus, GVOGEA is specific for α1β1. Although recognized by both α2β1 and α11β1, GLOGEN is a better ligand for α1β1 compared with GFOGER. Finally, using biosensor assays, we show that although GLOGEN is able to compete for the α1 I domain from collagen IV (IC(50) ～3 μm), GFOGER is much less potent (IC(50) ～90 μm), as shown previously. These data confirm the selectivity of GFOGER for α2β1 and establish GLOGEN as a high affinity site for α1β1.     

Engineered Cystine-Knot Peptides that Bind αvβ3 Integrin with Antibody-Like Affinities

The α_vβ₃ integrin receptor is an important cancer target due to its overexpression on many solid tumors and the tumor neovasculature and its role in metastasis and angiogenesis. We used a truncated form of the Agouti-related protein (AgRP), a 4-kDa cystine-knot peptide with four disulfide bonds and four solvent-exposed loops, as a scaffold for engineering peptides that bound to α_vβ₃ integrins with high affinity and specificity. A yeast-displayed cystine-knot peptide library was generated by substituting a six amino acid loop of AgRP with a nine amino acid loop containing the Arg-Gly-Asp integrin recognition motif and randomized flanking residues. Mutant cystine-knot peptides were screened in a high-throughput manner by fluorescence-activated cell sorting to identify clones with high affinity to detergent-solubilized α_vβ₃ integrin receptor. Select integrin-binding peptides were expressed recombinantly in Pichia pastoris and were tested for their ability to bind to human cancer cells expressing various integrin receptors. These studies showed that the engineered AgRP peptides bound to cells expressing α_vβ₃ integrins with affinities ranging from 15 nM to 780 pM. Furthermore, the engineered peptides were shown to bind specifically to α_vβ₃ integrins and had only minimal or no binding to α_vβ₅, α₅β₁, and α_iibβ₃ integrins. The engineered AgRP peptides were also shown to inhibit cell adhesion to the extracellular matrix protein vitronectin, which is a naturally occurring ligand for α_vβ₃ and other integrins. Next, to evaluate whether the other three loops of AgRP could modulate integrin specificity, we made second-generation libraries by individually randomizing these loops in one of the high-affinity integrin-binding variants. Screening of these loop-randomized libraries against α_vβ₃ integrins resulted in peptides that retained high affinities for α_vβ₃ and had increased specificities for α_vβ₃ over α_iibβ₃ integrins. Collectively, these data validate AgRP as a scaffold for protein engineering and demonstrate that modification of a single loop can lead to AgRP-based peptides with antibody-like affinities for their target.     

Lumican inhibits cell migration through α2β1 integrin

Lumican, an extracellular matrix protein of the small leucine-rich proteoglycan family, has been shown to impede melanoma progression by inhibiting cell migration. In the present study, we show that lumican targets α2β1 integrin thereby inhibiting cell migration. A375 melanoma cells were transfected with siRNA directed against the α2 integrin subunit. Compared to A375 control cells, the anti-migratory effect of lumican was abrogated on transfected A375 cells. Moreover, lumican inhibited the chemotactic migration of Chinese hamster ovary (CHO) cells stably transfected with α2 integrin subunit (CHO-A2) but not that of wild-type CHO cells (CHO-WT) lacking this subunit. In contrast to CHO-WT cells, we observed in time-lapse microscopy a decrease of CHO-A2 cell migration speed in presence of lumican. Focal adhesion kinase phosphorylated at tyrosine-397 (pFAK) and total FAK were analysed in CHO-WT and CHO-A2 cells. A significant decrease of the ratio pFAK/FAK was shown in presence of recombinant human lumican. Using solid phase assays, a direct binding between lumican and the α2β1 integrin was demonstrated. This interaction did not involve the glycan moiety of lumican and was cation independent. Lumican was also able to bind the activated I domain of the α2 integrin subunit with a K_d ≥ 200 nM. In conclusion, we demonstrated for the first time that the inhibition of cell migration by lumican depends on a direct binding between the core protein of lumican and the α2β1 integrin.     

Preparation of (1 → 3)-β-d-glucan oligosaccharides by hydrolysis of curdlan with commercial α-amylase

Water soluble (1 → 3)-β-d-glucan oligosaccharides were prepared by hydrolyzing curdlan with α-amylase. The hydrolysis process was monitored by the DE values of the hydrolysates. Under the optimized conditions (pH, 5.98; temperature, 55.92 °C; α-amylase amount, 31.94 mg α-amylase/500 mL of reaction mixture containing 5 g curdlan; reaction time, 30 min), maximum DE value (15.62%) was obtained. The resulting products were composed of (1 → 3)-β-d-glucan oligosaccharides of DP 2-9. The hydrolysates were filtered, concentrated to ∼20% (w/v), and precipitated with 5 volumes of ethanol, which were then freeze dried to yield a water soluble powder. The (1 → 3)-β-d-glucan oligosaccharides content of the product and the yield were 97.7% and 97.6% (w/w), respectively.     

Integrin-dependent cell behavior on ECM peptide-conjugated chitosan membranes

Extracellular matrix (ECM) plays an important role in tissue regeneration by promoting cell adhesion, migration, proliferation, and differentiation. ECM mimetics are of importance for tissue engineering because of their functions as scaffolds for cells. Previously, we developed bioactive laminin-derived peptide-conjugated chitosan membranes and demonstrated their cell- and peptide-type specific functions. Here, we conjugated twelve integrin-binding peptides derived from ECM proteins onto chitosan membranes and examined biological activity. Seven peptide-chitosan membranes promoted human foreskin fibroblast attachment. Additionally, FIB1 (YAVTGRGDSPAS; from fibronectin), A99 (AGTFALRGDNPQG; from laminin alpha1 chain), EF1zz (ATLQLQEGRLHFXFDLGKGR, X = Nle; from laminin alpha1 chain), and 531 (GEFYFDLRLKGDKY; from collagen alpha1 (IV) chain) conjugated chitosan membranes promoted integrin-dependent cell adhesion. Various integrins, including alphav, beta1, and beta3, were involved in the cell adhesion to the peptide-chitosan membranes. Further, only the FIB1- and A99-chitosan membranes promoted neurite outgrowth with PC12 rat pheochromocytoma cells. These data demonstrate that peptide-chitosan membranes can regulate specific integrin-mediated cell responses and are useful constructs as ECM mimetics.