Induction of MMP-13 expression in bone-metastasizing cancer cells by type I collagen through integrin α1β1 and α2β1-p38 MAPK signaling

BACKGROUND

Breast cancer cells frequently metastasize to the skeleton and produce and secrete proteinases, such as matrix metalloproteinase-13 (MMP-13), which promote destruction of the bone matrix. However, the mechanism of MMP-13 expression induced in areas of bone metastasis is unknown. Here, the interaction between tumors and type I collagen in bone metastasis was investigated.

MATERIALS AND METHODS

A mouse model of bone metastasis was prepared by inoculating mice with suspensions of cells of the human metastatic breast cancer cell line MDA-MB-231 via the left cardiac ventricle. MMP-13 expression was examined by immunohistochemical, Western blot, and real-time RT-PCR analyses.

RESULTS

MMP-13 expression was highly up-regulated in MDA-MB-231 cells, and attachment of these cells to type I collagen and the induction of MMP-13 were down-regulated by treatment with integrin α1, α2 or β1 neutralizing antibodies. The attachment of MDA-MB-231 cells to type I collagen induced the activation of focal adhesion kinase (FAK) and p38 mitogen-activated protein kinase (MAPK). Inhibition of FAK and p38 MAPK down-regulated type I collagen-induced MMP-13 expression.

CONCLUSION

Our study indicates that metastatic breast cancer cells in the bone microenvironment attached to type I collagen, which stimulated integrins α1β1 and α2β1, via FAK and p38 MAPK pathways, to induce MMP13 expression and further osteolysis.

Saccharomyces boulardii improves intestinal cell restitution through activation of the α2β1 integrin collagen receptor

Intestinal epithelial cell damage is frequently seen in the mucosal lesions of inflammatory bowel diseases such as ulcerative colitis or Crohn's disease. Complete remission of these diseases requires both the cessation of inflammation and the migration of enterocytes to repair the damaged epithelium. Lyophilized Saccharomyces boulardii (Sb, Biocodex) is a nonpathogenic yeast widely used as a therapeutic agent for the treatment and prevention of diarrhea and other gastrointestinal disorders. In this study, we determined whether Sb could accelerate enterocyte migration. Cell migration was determined in Sb force-fed C57BL6J mice and in an in vitro wound model. The impact on α2β1 integrin activity was assessed using adhesion assays and the analysis of α2β1 mediated signaling pathways both in vitro and in vivo. We demonstrated that Sb secretes compounds that enhance the migration of enterocytes independently of cell proliferation. This enhanced migration was associated with the ability of Sb to favor cell-extracellular matrix interaction. Indeed, the yeast activates α2β1 integrin collagen receptors. This leads to an increase in tyrosine phosphorylation of cytoplasmic molecules, including focal adhesion kinase and paxillin, involved in the integrin signaling pathway. These changes are associated with the reorganization of focal adhesion structures. In conclusion Sb secretes motogenic factors that enhance cell restitution through the dynamic regulation of α2β1 integrin activity. This could be of major importance in the development of novel therapies targeting diseases characterized by severe mucosal injury, such as inflammatory and infectious bowel diseases.

Differential proteomic analysis of platelets suggested possible signal cascades network in platelets treated with salvianolic acid B

Background

Salvianolic acid B (SB) is an active component isolated from Danshen, a traditional Chinese medicine widely used for the treatment of cardiovascular disorders. Previous study suggested that SB might inhibit adhesion as well as aggregation of platelets by a mechanism involving the integrin α2β1. But, the signal cascades in platelets after SB binding are still not clear.

Methodology/Principal Findings

In the present study, a differential proteomic analysis (two-dimensional electrophoresis) was conducted to check the protein expression profiles of rat platelets with or without treatment of SB. Proteins altered in level after SB exposure were identified by MALDI-TOF MS/MS. Treatment of SB caused regulation of 20 proteins such as heat shock-related 70 kDa protein 2 (hsp70), LIM domain protein CLP-36, copine I, peroxiredoxin-2, coronin-1 B and cytoplasmic dynein intermediate chain 2C. The regulation of SB on protein levels was confirmed by Western blotting. The signal cascades network induced by SB after its binding with integrin α2β1 was predicted. To certify the predicted network, binding affinity of SB to integrin α2β1 was checked in vitro and ex vivo in platelets. Furthermore, the effects of SB on protein levels of hsp70, coronin-1B and intracellular levels of Ca(2+) and reactive oxygen species (ROS) were checked with or without pre-treatment of platelets using antibody against integrin α2β1. Electron microscopy study confirmed that SB affected cytoskeleton structure of platelets.

Conclusions/Significance

Integrin α2β1 might be one of the direct target proteins of SB in platelets. The signal cascades network of SB after binding with integrin α2β1 might include regulation of intracellular Ca(2+) level, cytoskeleton-related proteins such as coronin-1B and cytoskeleton structure of platelets.

Diet-induced muscle insulin resistance is associated with extracellular matrix remodeling and interaction with integrin alpha2beta1 in mice

OBJECTIVE

The hypothesis that high-fat (HF) feeding causes skeletal muscle extracellular matrix (ECM) remodeling in C57BL/6J mice and that this remodeling contributes to diet-induced muscle insulin resistance (IR) through the collagen receptor integrin α(2)β(1) was tested.

RESEARCH DESIGN AND METHODS

The association between IR and ECM remodeling was studied in mice fed chow or HF diet. Specific genetic and pharmacological murine models were used to study effects of HF feeding on ECM in the absence of IR. The role of ECM-integrin interaction in IR was studied using hyperinsulinemic-euglycemic clamps on integrin α(2)β(1)-null (itga2(-/-)), integrin α(1)β(1)-null (itga1(-/-)), and wild-type littermate mice fed chow or HF. Integrin α(2)β(1) and integrin α(1)β(1) signaling pathways have opposing actions.

RESULTS

HF-fed mice had IR and increased muscle collagen (Col) III and ColIV protein; the former was associated with increased transcript, whereas the latter was associated with reduced matrix metalloproteinase 9 activity. Rescue of muscle IR by genetic muscle-specific mitochondria-targeted catalase overexpression or by the phosphodiesterase 5a inhibitor, sildenafil, reversed HF feeding effects on ECM remodeling and increased muscle vascularity. Collagen remained elevated in HF-fed itga2(-/-) mice. Nevertheless, muscle insulin action and vascularity were increased. Muscle IR in HF-fed itga1(-/-) mice was unchanged. Insulin sensitivity in chow-fed itga1(-/-) and itga2(-/-) mice was not different from wild-type littermates.

CONCLUSIONS

ECM collagen expansion is tightly associated with muscle IR. Studies with itga2(-/-) mice provide mechanistic insight for this association by showing that the link between muscle IR and increased collagen can be uncoupled by the absence of collagen-integrin α(2)β(1) interaction.

Syndecan- and integrin-binding peptides synergistically accelerate cell adhesion

Integrins and syndecans mediate cell adhesion to extracellular matrix and their synergistic cooperation is implicated in cell adhesion processes. We previously identified two active peptides, AG73 and EF1, from the laminin alpha1 chain LG4 module, that promote cell attachment through syndecan- and alpha2beta1 integrin-binding, respectively. Here, we examined time-dependent cell attachment on the mixed peptides AG73/EF1. The AG73/EF1 promoted stronger and more rapid cell attachment, spreading, FAK phosphorylation that reached a maximum at 20 min than that on AG73 (40 min) or EF1 (90 min) supplied singly. Thus, the syndecan- and alpha2beta1 integrin-binding peptides synergistically affect cells and accelerate cell adhesion.

The tetraspanins CD9 and CD81 regulate CD9P1-induced effects on cell migration

CD9P-1 is a cell surface protein with immunoglobulin domains and an unknown function that specifically associates with tetraspanins CD9 and CD81. Overexpression of CD9P-1 in HEK-293 cells induces dramatic changes in cell spreading and migration on various matrices. Experiments using time-lapse videomicroscopy revealed that CD9P-1 expression has led to higher cell motility on collagen I but lower motility on fibronectin through a beta1-integrins dependent mechanism. On collagen I, the increase in cell motility induced by CD9P-1 expression was found to involve integrin alpha2beta1 and CD9P-1 was observed to associate with this collagen receptor. The generation of CD9P-1 mutants demonstrated that the transmembrane and the cytoplasmic domains are necessary for inducing effects on cell motility. On the other hand, expression of tetraspanins CD9 or CD81 was shown to reverse the effects of CD9P-1 on cell motility on collagen I or fibronectin with a concomitant association with CD9P-1. Thus, the ratio of expression levels between CD9P-1 and its tetraspanin partners can regulate cell motility.

Different regions of the class P-III snake venom metalloproteinase jararhagin are involved in binding to alpha2beta1 integrin and collagen

SVMPs are multi-domain proteolytic enzymes in which disintegrin-like and cysteine-rich domains bind to cell receptors, plasma or ECM proteins. We have recently reported that jararhagin, a P-III class SVMP, binds to collagen with high affinity through an epitope located within the Da-disintegrin sub-domain. In this study, we evaluated the binding of jararhagin to alpha(2)beta(1) integrin (collagen receptor) using monoclonal antibodies and recombinant jararhagin fragments. In solid phase assays, binding of jararhagin to alpha(2)beta(1) integrin was detectable from concentrations of 20 nM. Using recombinant fragments of jararhagin, only fragment JC76 (residues 344-421), showed a significant binding to recombinant alpha(2)beta(1) integrin. The anti-jararhagin monoclonal antibody MAJar 3 efficiently neutralised binding of jararhagin to collagen, but not to recombinant alpha(2)beta(1) integrin nor to cell-surface-exposed alpha(2)beta(1) integrin (alpha(2)-K562 transfected cells and platelets). The same antibody neutralised collagen-induced platelet aggregation. Our data suggest that jararhagin binding to collagen and alpha(2)beta(1) integrin occurs by two independent motifs, which are located on disintegrin-like and cysteine-rich domains, respectively. Moreover, toxin binding to collagen appears to be sufficient to inhibit collagen-induced platelet aggregation.

Transcapillary exchange: role and importance of the interstitial fluid pressure and the extracellular matrix

This review will summarize current knowledge on the role of the extracellular matrix (ECM) in general and on the interstitial fluid pressure (P(if)) in particular with regard to their importance in transcapillary exchange. The fluid volume in the interstitial space is normally regulated within narrow limits by automatic re-adjustment of the interstitial hydrostatic and colloid osmotic pressures in response to perturbations in capillary filtration and by the lymphatics. Contrary to this commonly accepted view, P(if) can become an active force and create a fluid flux across the capillaries in several inflammatory reactions and trauma situations rather than limit the changes occurring. The molecular mechanisms involved in the lowering of P(if) include the release of cellular tension exerted on the collagen and microfibril networks in the connective tissue via the collagen-binding beta(1)-integrins, thereby allowing the glycosaminoglycan ground substance, which is normally underhydrated, to expand and take up fluid. Several growth factors and cytokines, including the platelet-derived growth factor BB, are able to reverse a lowering of P(if) and restore the normal compaction of the ECM. The magnitude of the lowering of P(if) varies with the inflammatory response. In several inflammatory reactions, a lowering of P(if) to -5 to -10 mmHg is seen, which will increase capillary filtration by 10-20 times since the normal capillary filtration pressure is usually 0.5-1 mmHg (skin and skeletal muscle). Unless this lowering of P(if) is taken into account, the enhanced solute flux resulting from an inflammatory response will be ascribed to an increased capillary permeability.

Bone marrow osteoblastic niche: a new model to study physiological regulation of megakaryopoiesis

Background

The mechanism by which megakaryocytes (Mks) proliferate, differentiate, and release platelets into circulation are not well understood. Growing evidence indicates that a complex regulatory mechanism, involving cellular interactions, composition of the extracellular matrix and physical parameters such as oxygen tension, may contribute to the quiescent or permissive microenvironment related to Mk differentiation and maturation within the bone marrow.

Methodology/Principal Findings

Differentiating human mesenchymal stem cells (hMSCs) into osteoblasts (hOSTs), we established an in vitro model for the osteoblastic niche. We demonstrated for the first time that the combination of HSCs, Mks and hypoxia sustain and promote bone formation by increasing type I collagen release from hOSTs and enhancing its fibrillar organization, as revealed by second harmonic generation microscopy. Through co-culture, we demonstrated that direct cell-cell contact modulates Mk maturation and differentiation. In particular we showed that low oxygen tension and direct interaction of hematopoietic stem cells (HSCs) with hOSTs inhibits Mk maturation and proplatelet formation (PPF). This regulatory mechanism was dependent on the fibrillar structure of type I collagen released by hOSTs and on the resulting engagement of the alpha2beta1 integrin. In contrast, normoxic conditions and the direct interaction of HSCs with undifferentiated hMSCs promoted Mk maturation and PPF, through a mechanism involving the VCAM-1 pathway.

Conclusions/Significance

By combining cellular, physical and biochemical parameters, we mimicked an in vitro model of the osteoblastic niche that provides a physiological quiescent microenvironment where Mk differentiation and PPF are prevented. These findings serve as an important step in developing suitable in vitro systems to use for the study and manipulation of Mk differentiation and maturation in both normal and diseased states.

Suboptimal activation of protease-activated receptors enhances alpha2beta1 integrin-mediated platelet adhesion to collagen

Thrombin and fibrillar collagen are potent activators of platelets at sites of vascular injury. Both agonists cause platelet shape change, granule secretion, and aggregation to form the primary hemostatic plug. Human platelets express two thrombin receptors, protease-activated receptors 1 and 4 (PAR1 and PAR4) and two collagen receptors, the alpha(2)beta(1) integrin (alpha(2)beta(1)) and the glycoprotein VI (GPVI)/FcRgamma chain complex. Although these receptors and their signaling mechanisms have been intensely studied, it is not known whether and how these receptors cooperate in the hemostatic function of platelets. This study examined cooperation between the thrombin and collagen receptors in platelet adhesion by utilizing a collagen-related peptide (alpha2-CRP) containing the alpha(2)beta(1)-specific binding motif, GFOGER, in conjunction with PAR-activating peptides. We demonstrate that platelet adhesion to alpha2-CRP is substantially enhanced by suboptimal PAR activation (agonist concentrations that do not stimulate platelet aggregation) using the PAR4 agonist peptide and thrombin. The enhanced adhesion induced by suboptimal PAR4 activation was alpha(2)beta(1)-dependent and GPVI/FcRgamma-independent as revealed in experiments with alpha(2)beta(1)- or FcRgamma-deficient mouse platelets. We further show that suboptimal activation of other platelet G(q)-linked G protein-coupled receptors (GPCRs) produces enhanced platelet adhesion to alpha2-CRP. The enhanced alpha(2)beta(1)-mediated platelet adhesion is controlled by phospholipase C (PLC), but is not dependent on granule secretion, activation of alpha(IIb)beta(3) integrin, or on phosphoinositol-3 kinase (PI3K) activity. In conclusion, we demonstrate a platelet priming mechanism initiated by suboptimal activation of PAR4 or other platelet G(q)-linked GPCRs through a PLC-dependent signaling cascade that promotes enhanced alpha(2)beta(1) binding to collagens containing GFOGER sites.

Mechanism of betulinic acid inhibition of collagen biosynthesis in human endometrial adenocarcinoma cells

Collagen as a ligand for integrin receptors plays important role in the integrin - dependent regulation of cellular metabolism. Since betulinic acid (BA) evokes anticancer activity, its effect on collagen biosynthesis was studied in cultured endometrial adenocarcinoma cells. Confluent cells were treated with different concentrations of BA for 24 hours. It was found that BA inhibit collagen biosynthesis ([3H] proline incorporation assay). The mechanism of this phenomenon was found at the level of insulin-like growth factor-I receptor (IGF-IR) and alpha2 integrin signalling (Western immunoblot analysis). The expressions of IGF-I receptor and alpha2 integrin subunit as well as integrin activated focal adhesion kinase (FAK) were decreased in the cells treated with BA. It was accompanied by a parallel decrease in the expression of Sos protein and phosphorylated MAP-kinases (ERK1, ERK2) and up - regulation of NF-kappaB. The data suggest that BA-dependent inhibition of collagen biosynthesis in cultured human endometrial adenocarcinoma cells undergoes through alpha2 integrin and IGF-IR signaling that activate NF-kappaB, potent inhibitor of collagen gene expression.

Rap1b is critical for glycoprotein VI-mediated but not ADP receptor-mediated alpha2beta1 activation

BACKGROUND

The platelet alpha2beta1 integrin functions as both an adhesion and signaling receptor upon exposure to collagen. Recent studies have indicated that alpha2beta1 function can be activated via inside-out signaling, similar to the prototypical platelet integrin alphaIIbbeta3. However, signaling molecules that regulate alpha2beta1 activation in platelets are not well defined. A strong candidate molecule is the small GTPase Rap1b, the dominant platelet isoform of Rap1, which regulates alphaIIbbeta3 activation.

OBJECTIVES

We hypothesized that Rap1b positively regulates alpha2beta1 during agonist-induced platelet activation.

METHODS

To test whether Rap1b activates alpha2beta1 downstream of glycoprotein (GP)VI or other platelet receptors, we stimulated platelets purified from Rap1b-/- or wild-type mice with diverse agonists and measured alpha2beta1 activation using fluorescein isothiocyanate-labeled monomeric collagen. We also examined the role of Rap1b in outside-in signaling pathways by analyzing adhesion and spreading of Rap1b-/- or wild-type platelets on monomeric, immobilized collagen. Finally, we monitored the activation status of related Rap GTPases to detect changes in signaling pathways potentially associated with Rap1b-mediated events.

RESULTS

Rap1b-/- platelets displayed comparable ADP-induced or thrombin-induced alpha2beta1 activation as wild-type platelets, but reduced convulxin-dependent alpha2beta1 activation. Rap1b-/- platelets exhibited increased spreading on immobilized collagen but similar adhesion to immobilized collagen compared to wild-type platelets. Rap1b-/- platelets also showed Rap1a and Rap2 activation upon agonist stimulation, possibly revealing functional compensation among Rap family members.

CONCLUSIONS

Rap1b is required for maximal GPVI-induced but not ADP-induced activation of alpha2beta1 in murine platelets.

Selective binding of integrins from different renal cell types to the NC1 domain of alpha3 and alpha1 chains of type IV collagen

BACKGROUND

Cells interact with type IV collagen (Col IV) via integrins through the triple-helical and NC1 domains. We examined interactions of human glomerular and proximal tubular epithelial cells with recombinant alpha1 and alpha3 NC1 chains of Col IV, to explore the ability of different cell types to interact with Col IV of different trimer composition.

METHODS

Interactions of TSV-40-immortalized human glomerular epithelial cells (HGECs), HPV-16-immortalized human proximal tubular epithelial (HK-2) cells and primary human mesangial cells (MES) with recombinant alpha1 and alpha3 NC1 chains of Col IV were examined by affinity chromatography and solid-phase binding assays. The expression of integrin-regulated metalloproteinases was examined by zymography.

RESULTS

HGECs bound to both alpha3 and alpha1(IV)NC1, albeit there was preferential binding to alpha3(IV)NC1, through the alpha3beta1 and alpha2beta1 integrin receptors; HK-2 cells and MES bound almost exclusively to alpha1(IV)NC1 via the alpha3beta1/alphavbeta3 and alpha1beta1/alpha2beta1 receptors, respectively. It was demonstrated that the expression of MMP-2 and MMP-9 by HGECs was down-regulated in the presence of alpha3(IV)NC1.

CONCLUSIONS

The observed data indicate that the isoform NC1 chains of Col IV serve for selective, integrin-mediated cell binding which probably triggers different signaling mechanisms, resulting in the activation of specific transcription factors and the modulation of gene expression.

Identification of the first prokaryotic collagen sequence motif that mediates binding to human collagen receptors, integrins alpha2beta1 and alpha11beta1

Many pathogenic bacteria interact with human integrins to enter host cells and to augment host colonization. Group A Streptococcus (GAS) employs molecular mimicry by direct interactions between the cell surface streptococcal collagen-like protein-1 (Scl1) and the human collagen receptor, integrin alpha2beta1. The collagen-like (CL) region of the Scl1 protein mediates integrin-binding, although, the integrin binding motif was not defined. Here, we used molecular cloning and site-directed mutagenesis to identify the GLPGER sequence as the alpha2beta1 and the alpha11beta1 binding motif. Electron microscopy experiments mapped binding sites of the recombinant alpha2-integrin-inserted domain to the GLPGER motif of the recombinant Scl (rScl) protein. rScl proteins and a synthetic peptide harboring the GLPGER motif mediated the attachment of C2C12-alpha2+myoblasts expressing the alpha2beta1 integrin as the sole collagen receptor. The C2C12-alpha11+myoblasts expressing the alpha11beta1 integrin also attached to GLPGER-harboring rScl proteins. Furthermore, the C2C12-alpha11+cells attached to rScl1 more efficiently than C2C12-alpha2+cells, suggesting that the alpha11beta1 integrin may have a higher binding affinity for the GLPGER sequence. Human endothelial cells and dermal fibroblasts adhered to rScl proteins, indicating that multiple cell types may recognize and bind the Scl proteins via their collagen receptors. This work is a stepping stone toward defining the utilization of collagen receptors by microbial collagen-like proteins that are expressed by pathogenic bacteria.

Nitric oxide specifically inhibits integrin-mediated platelet adhesion and spreading on collagen

BACKGROUND

Nitric oxide (NO) inhibits platelet adhesion to collagen, although the precise molecular mechanisms underlying this process are unclear.

OBJECTIVES

Collagen-mediated adhesion is a multifaceted event requiring multiple receptors and platelet-derived soluble agonists. We investigated the influence of NO on these processes.

RESULTS

S-nitrosoglutathione (GSNO) induced a concentration-dependent inhibition of platelet adhesion to immobilized collagen. Maximal adhesion to collagen required platelet-derived ADP and TxA(2). GSNO-mediated inhibition was lost in the presence of apyrase and indomethacin, suggesting that NO reduced the availability of, or signaling by, ADP and TxA(2). Exogenous ADP, but not the TxA(2) analogue U46619, reversed the inhibitory actions of GSNO on adhesion. Under adhesive conditions NO inhibited dense granule secretion but did not influence TxA(2) generation. These data indicated that NO may block signaling by TxA(2) required for dense granule secretion, thereby reducing the availability of ADP. Indeed, we found TxA(2)-mediated activation of PKC was required to drive dense granule secretion, a pathway that was inhibited by NO. Because our data demonstrated that NO only inhibited the activation-dependent component of adhesion, we investigated the effects of NO on individual collagen receptors. GSNO inhibited platelet adhesion and spreading on alpha(2)beta(1) specific peptide ligand GFOGER. In contrast, GSNO did not inhibit GPVI-mediated adhesion to collagen, or adhesion to the GPVI specific ligand, collagen related peptide (CRP).

CONCLUSIONS

NO targets activation-dependent adhesion mediated by alpha(2)beta(1), possibly by reducing bioavailability of platelet-derived ADP, but has no effect on activation-independent adhesion mediated by GPVI. Thus, NO regulates platelet spreading and stable adhesion to collagen.

Collagen-mimetic peptides mediate flow-dependent thrombus formation by high- or low-affinity binding of integrin alpha2beta1 and glycoprotein VI

BACKGROUND

Collagen acts as a potent surface for platelet adhesion and thrombus formation under conditions of blood flow. Studies using collagen-derived triple-helical peptides have identified the GXX'GER motif as an adhesive ligand for platelet integrin alpha2beta1, and (GPO)(n) as a binding sequence for the signaling collagen receptor, glycoprotein VI (GPVI).

OBJECTIVE

The potency was investigated of triple-helical peptides, consisting of GXX'GER sequences within (GPO)(n) or (GPP)(n) motifs, to support flow-dependent thrombus formation.

RESULTS

At a high-shear rate, immobilized peptides containing both the high-affinity alpha2beta1-binding motif GFOGER and the (GPO)(n) motif supported platelet aggregation and procoagulant activity, even in the absence of von Willebrand factor (VWF). With peptides containing only one of these motifs, co-immobilized VWF was needed for thrombus formation. The (GPO)(n) but not the (GPP)(n) sequence induced GPVI-dependent platelet aggregation and procoagulant activity. Peptides with intermediate affinity (GLSGER, GMOGER) or low-affinity (GASGER, GAOGER) alpha2beta1-binding motifs formed procoagulant thrombi only if both (GPO)(n) and VWF were present. At a low-shear rate, immobilized peptides with high- or low-affinity alpha2beta1-binding motifs mediated formation of thrombi with procoagulant platelets only in combination with (GPO)(n).

CONCLUSIONS

Triple-helical peptides with specific receptor-binding motifs mimic the properties of native collagen I in thrombus formation by binding to both platelet collagen receptors. At a high-shear rate, either GPIb or high-affinity (but not low-affinity) GXX'GER mediates GPVI-dependent formation of procoagulant thrombi. By extension, high-affinity binding for alpha2beta1 can control the overall platelet-adhesive activity of native collagens.

Distinct roles of beta1 metal ion-dependent adhesion site (MIDAS), adjacent to MIDAS (ADMIDAS), and ligand-associated metal-binding site (LIMBS) cation-binding sites in ligand recognition by integrin alpha2beta1

Integrin-ligand interactions are regulated in a complex manner by divalent cations, and previous studies have identified ligand-competent, stimulatory, and inhibitory cation-binding sites. In collagen-binding integrins, such as alpha2beta1, ligand recognition takes place exclusively at the alpha subunit I domain. However, activation of the alphaI domain depends on its interaction with a structurally similar domain in the beta subunit known as the I-like or betaI domain. The top face of the betaI domain contains three cation-binding sites: the metal-ion dependent adhesion site (MIDAS), the ADMIDAS (adjacent to MIDAS), and LIMBS (ligand-associated metal-binding site). The role of these sites in controlling ligand binding to the alphaI domain has yet to be elucidated. Mutation of the MIDAS or LIMBS completely blocked collagen binding to alpha2beta1; in contrast mutation of the ADMIDAS reduced ligand recognition but this effect could be overcome by the activating monoclonal antibody TS2/16. Hence, the MIDAS and LIMBS appear to be essential for the interaction between alphaI and betaI, whereas occupancy of the ADMIDAS has an allosteric effect on the conformation of betaI. An activating mutation in the alpha2 I domain partially restored ligand binding to the MIDAS and LIMBS mutants. Analysis of the effects of Ca(2+), Mg(2+), and Mn(2+) on ligand binding to these mutants showed that the MIDAS is a ligand-competent site through which Mn(2+) stimulates ligand binding, whereas the LIMBS is a stimulatory Ca(2+)-binding site, occupancy of which increases the affinity of Mg(2+) for the MIDAS.

Integrin alpha2beta1 plays a critical role in osteoblast response to micron-scale surface structure and surface energy of titanium substrates

Efforts to improve bone response to biomaterials have focused on ligands that bind alpha5beta1 integrins. However, antibodies to alpha5beta1 reduce osteoblast proliferation but do not affect differentiation when cells are grown on titanium (Ti). beta1-silencing blocks the differentiation stimulus of Ti microtopography, suggesting that other beta1 partners are important. Stably alpha2-silenced MG63 human osteoblast-like cells were used to test whether alpha2beta1 specifically mediates osteoblast response to Ti surface micron-scale structure and energy. WT and alpha2-silenced MG63 cells were cultured on tissue culture polystyrene (TCPS) and Ti disks with different surface microtopographies: machined pretreatment (PT) surfaces [mean peak to valley roughness (R(a)) < 0.02 microm], PT surfaces that were grit-blasted and acid-etched (SLA; R(a) = 4 microm), and SLA with high surface energy (modSLA). Alkaline phosphatase (ALP), alpha2 and beta1 mRNA, but not alpha5, alpha v, beta3, type-I collagen, or osteocalcin, increased on SLA and modSLA at 6 days. Alpha2 increased at 8 days on TCPS and PT, but remained unchanged on SLA and modSLA. Alpha2-protein was reduced 70% in alpha2-siRNA cells, whereas alpha5-mRNA and protein were unaffected. Alpha2-knockdown blocked surface-dependent increases in beta1 and osteocalcin and decreases in cell number and increases in ALP and local factors typical of MG63 cells grown on SLA and modSLA [e.g., prostaglandin E(2), osteoprotegerin, latent and active TGF-beta1, and stimulatory effects of 1alpha,25(OH)(2)D(3) on these parameters]. This finding indicates that alpha2beta1 signaling is required for osteoblastic differentiation caused by Ti microstructure and surface energy, suggesting that conclusions based on cell behavior on TCPS are not predictive of behavior on other substrates or the mechanisms involved.

[Molecular mechanisms of Glanzmann thrombasthenia caused by alpha II b L721R and Q860X compound heterozygous mutation]

OBJECTIVE

To explore the molecular mechanisms of Glanzmann thrombasthenia caused by alpha II b L721R and Q860X compound heterozygous mutation.

METHODS

All exons and exon-intron boundaries of alpha II b and beta3 gene were amplified by PCR and analyzed by direct DNA sequencing. Gene polymorphisms were excluded by direct DNA sequencing. Alpha II b L721R and Q860X mutants expressing vectors were constructed by in vitro site-directed mutagenesis. The expression of alpha II b L721R and Q860X mutants on transfected cell membrane were analyzed by flow cytometry and the whole expression level was confirmed by Western blot. The subcellular localizations of alpha II b L721R and Q860X mutants were determined by immunofluorescent confocal scanning microscopy.

RESULTS

The alpha II b compound heterozygous mutations, T2255G (L721R) and C2671T (Q860X), were identified in the proband, the former being inherited from the maternal side and the latter the paternal side. The 293T cells cotransfected with mutated alpha II b L721R and wild-type beta3 expression plasmids expressed 2.1% of normal amount of alpha II b on the cell surface as shown by FACS, in contrast to 31.9% of normal amount of alpha II b on the cells cotransfected with cDNAs of mutated alpha II b Q860X and wildtype beta3 expression plasmids. Western blot of the cell lysates showed no detectable mature alpha II b in cells lysates with L721R mutant. While, truncated alpha II b protein was detected in cell lystes with Q860X mutant. Immunofluorescence studies demonstrated that both L721R and Q860X mutant pro-alpha II bbeta33 complex colocalized in endoplasmic reticulum, but a little in Golgi.

CONCLUSIONS

The L721R and Q860X mutations of alpha II b prevent transport of the pro-alpha II bbeta3 complex from the endoplasmic reticulum to the Golgi, hindering its maturation and surface expression. The impaired alpha II bbeta3 transport is responsible for the thrombasthenia.

Integrin alphavbeta3 is not significantly implicated in the anti-migratory effect of anti-angiogenic urokinase kringle domain

The recombinant kringle domain (UK1) of urokinase-type plasminogen activator (uPA) has been shown to possess anti-angiogenic activity in vitro and in vivo. It has also been found to inhibit in vivo malignant glioma growth. In contrast, direct interaction of the kringle domain of uPA and integrin alphavbeta3 has been reported to be involved in plasminogen and leukocyte activation by uPA. Since integrin alphavbeta3 is involved in tumor angiogenesis, we investigated whether integrin alphavbeta3 is involved in the inhibitory function of UK1 in angiogenesis, by examining its anti-migratory activity. In a modified Boyden chamber assay, the Pichia-expressed UK1 dose-dependently inhibited the VEGF-induced migration of human umbilical vein endothelial cells (HUVECs). However, in the absence of growth factor stimulation, soluble UK1 alone did not induce or inhibit HUVEC migration. In cell adhesion, immobilized UK1 promoted HUVEC adhesion and spreading which were compared to BSA. Pretreatment of the anti-alphavbeta3 integrin antibody, significantly inhibited HUVEC binding to immobilized UK1, whereas neither anti-alpha2beta1 nor anti-alpha5beta1 integrin antibody had any effect, although pre-treatment of the soluble UK1 showed no marked alteration of the binding level of anti-alphavbeta3 antibody to HUVECs in FACS analysis. In a modified Boyden chamber assay, the function blocking antibodies against integrins alphavbeta3, alpha2beta1 and alpha5beta1 did not completely prevent the inhibitory effect of UK1 in HUVEC migration. These results suggest that UK1 interacts with integrin alphavbeta3, but its anti-migratory activity on endothelial cells is not significantly mediated by integrin alphavbeta3.

Divalent cations modulate the integrin-mediated malignant phenotype in pancreatic cancer cells

We have previously demonstrated that pathophysiological shifts in the concentrations of extracellular Mg(2+) and Ca(2+) activate the alpha(2)beta(1) integrin-mediated malignant phenotype on type I collagen in pancreatic cancer cells, as evidenced by increased adhesion, migration and proliferation. In the present study, we examined the integrin and divalent cation specificity of pancreatic cancer cell interactions with other physiologically relevant extracellular matrix proteins, including fibronectin, type IV collagen, laminin and vitronectin. Our results indicate that, like alpha(2)beta(1) integrin-mediated interactions with type I collagen, beta(1) integrin-mediated adhesion to fibronectin, type IV collagen and laminin are promoted by Mg(2+) but not by Ca(2+). On vitronectin, cells attach via alpha(v)beta(5) and beta(1) integrins, and in the presence of either divalent cation. We also demonstrate that, like type I collagen, pancreatic cancer cell migration and proliferation on fibronectin, laminin and type IV collagen is maximal when Mg(2+) is present at concentrations that promote optimal adhesion and Ca(2+) is present at concentrations less than Mg(2+). On vitronectin, Panc-1 cell migration is maximal with decreased Mg(2+) and increased Ca(2+), but the reverse is true for BxPC-3 cells. Both cell lines exhibited maximal proliferation with increased Mg(2+) and decreased Ca(2+), however. Together with evidence indicating that the in vivo local tumor microenvironment contains increased Mg(2+) and decreased Ca(2+), our studies demonstrate that such divalent cation shifts could activate the integrin-mediated malignant phenotype in pancreatic cancer.

Potent oncolytic activity of human enteroviruses against human prostate cancer

BACKGROUND

Oncolytic virotherapy offers a unique treatment modality for prostate cancer, especially stages that are resistant to current therapies, with the additional benefit of preferentially targeting tumor cells amongst an environment of healthy tissue. Herein, the low pathogenic enteroviruses; Coxsackievirus A21 (CVA21), as well as a bio-selected variant of Coxsackievirus A21 (CVA21-DAFv) and Echovirus 1 (EV1) are evaluated as novel oncolytic agents against human prostate cancer.

METHODS

The surface expression of viral receptors required for enterovirus cell attachment/entry, including intercellular adhesion molecule-1 (ICAM-1), decay-accelerating factor (DAF) and integrin alpha(2)beta(1) on a number of human prostate cancer lines was assessed by flow cytometry. Susceptibility to viral oncolysis was determined via in vitro cell lysis assays performed on cell monolayers cultured in micro titer plates. The in vivo oncolytic efficacy of the enteroviruses was assessed using xenograft models in immune compromised SCID-mice following systemic challenge.

RESULTS

The majority of prostate cancer lines tested expressed surface ICAM-1 and/or DAF, or alpha(2)beta(1), facilitating significant degrees of oncolysis following in vitro viral challenge. Systemic delivery of each of the three viruses induced reduction of xenograft tumor burdens in vivo, and a therapeutic dose-response was demonstrated for escalating doses of EV1 in the LNCaP animal model.

CONCLUSION

Enteroviruses CVA21, CVA21-DAFv, and EV1 are potentially potent oncolytic agents against human prostate cancer.

Effect of brefeldin A on membrane localization of MUC1 mucin and adhesive properties of cancer cells

Transmembrane glycoproteins play a significant role in cancer cells adhesion and metastatic process, just for that reason the glycosylation inhibitors are used to change the glycan structure and in this way the membrane expression of glycoproteins. The inhibitory effect of brefeldin A (BFA) on the expression of some glycoproteins: MUC1 mucin and alpha2beta1 integrin on cell surface of breast (MCF-7 and MDA-MB-231 lines) and endometrial (Ishikawa line) cancer cells was evaluated in our study. In MCF-7 and MDA-MB-231 cells, a decrease in MUC1 expression depended on brefeldin A concentration and equaled about 40% in cells treated with 1mg% of drug. In Ishikawa cells, a decrease in MUC1 expression was lower and amounted to about 25%. The expression of alpha2beta1 integrin was greatly inhibited in brefeldin-treated MCF-7 and Ishikawa cells, though it was unchanged in MDA-MB-231 cells. A decrease in MUC1 mucin and alpha2beta1 integrin level reduced the adhesive properties of BFA-treated cells. Adhesion to type I collagen was greatly diminished in BFA-treated MCF-7 and Ishikawa cells (above 70%), and to a lesser degree in MDA-MB-231 cells (about 50%); which was mainly caused by the inhibited integrin expression. These findings have proved that brefeldin A, by changing the surface glycoproteins level, can alter carcinoma cells adhesion to extracellular matrix proteins.

The role of androgen in determining differentiation and regulation of androgen receptor expression in the human prostatic epithelium transient amplifying population

Abnormal differentiation in epithelial stem cells or their immediate proliferative progeny, the transiently amplifying population (TAP), may explain malignant pathogenesis in the human prostate. These models are of particular importance as differing sensitivities to androgen among epithelial cell subpopulations during differentiation are recognised and may account for progression to androgen independent prostate cancer. Androgens are crucial in driving terminal differentiation and their indirect effects via growth factors from adjacent androgen responsive stroma are becoming better characterised. However, direct effects of androgen on immature cells in the context of a prostate stem cell model have not been investigated in detail and are studied in this work. In alpha2beta1hi stem cell enriched basal cells, androgen analogue R1881 directly promoted differentiation by the induction of differentiation-specific markers CK18, androgen receptor (AR), PSA and PAP. Furthermore, treatment with androgen down-regulated alpha2beta1 integrin expression, which is implicated in the maintenance of the immature basal cell phenotype. The alpha2beta1hi cells were previously demonstrated to lack AR expression and the direct effects of androgen were confirmed by inhibition using the anti-androgen bicalutamide. AR protein expression in alpha2beta1hi cells became detectable when its degradation was repressed by the proteosomal inhibitor MG132. Stratifying the alpha2beta1hi cells into stem (CD133(+)) and transient amplifying population (TAP) (CD133(-)) subpopulations, AR mRNA expression was found to be restricted to the CD133(-) (TAP) cells. The presence of a functional AR in the TAP, an androgen independent subpopulation for survival, may have particular clinical significance in hormone resistant prostate cancer, where both the selection of immature cells and functioning AR regulated pathways are involved.

Scl1-dependent internalization of group A Streptococcus via direct interactions with the alpha2beta(1) integrin enhances pathogen survival and re-emergence

The molecular pathogenesis of infections caused by group A Streptococcus (GAS) is not fully understood. We recently reported that a recombinant protein derived from the collagen-like surface protein, Scl1, bound to the human collagen receptor, integrin alpha(2)beta(1). Here, we investigate whether the same Scl1 variant expressed by GAS cells interacts with the integrin alpha2beta(1) and affects the biological outcome of host-pathogen interactions. We demonstrate that GAS adherence and internalization involve direct interactions between surface expressed Scl1 and the alpha2beta(1) integrin, because (i) both adherence and internalization of the scl1-inactivated mutant were significantly decreased, and were restored by in-trans complementation of Scl1 expression, (ii) GAS internalization was reduced by pre-treatment of HEp-2 cells with anti-alpha2 integrin-subunit antibody and type I collagen, (iii) recombinant alpha2-I domain bound the wild-type GAS cells and (iv) internalization of wild-type cells was significantly increased in C2C12 cells expressing the alpha2beta(1) integrin as the only collagen-binding integrin. Next, we determined that internalized GAS re-emerges from epithelial cells into the extracellular environment. Taken together, our data describe a new molecular mechanism used by GAS involving the direct interaction between Scl1 and integrins, which increases the overall capability of the pathogen to survive and re-emerge.