Changes in the fibronectin-specific integrin expression pattern modify the migratory behavior of sarcoma S180 cells in vitro and in the embryonic environment

Sarcoma Tumor Microenvironment

Components of the tumor microenvironment (TME) are known to play an essential role during malignant progression, but often in a context-dependent manner. In bone and soft tissue sarcomas, disease-regulatory activities in the TME remain largely uncharacterized. This chapter introduces the cellular, structural, and chemical composition of the sarcoma TME from a pathobiological and therapeutic perspective.Sarcomas are malignant tumors with diverse features when it comes to primary tumor appearance, metastatic potential, and response to treatment. Many of the classic subtypes are mainly composed of malignant cells and are therefore assumed to be committed to autocrine signaling. Some of the tumors are infiltrated by immune cells and contain necrotic areas or excessive amounts of extracellular matrix (ECM) that regulates tissue stiffness and interstitial fluid pressure. Vascular invasion and blood vessel characteristics can in some instances be considered in the prognostic setting.Further insights into the disease-regulatory activities of the sarcoma TME will provide essential knowledge on how to develop successful combination treatments targeting not only malignant cells, but also their routes of nutrition and ability to shield themselves toward existing therapy.

Dexamethasone-Mediated Upregulation of Calreticulin Inhibits Primary Human Glioblastoma Dispersal Ex Vivo

Dispersal of Glioblastoma (GBM) renders localized therapy ineffective and is a major cause of recurrence. Previous studies have demonstrated that Dexamethasone (Dex), a drug currently used to treat brain tumor-related edema, can also significantly reduce dispersal of human primary GBM cells from neurospheres. It does so by triggering α5 integrin activity, leading to restoration of fibronectin matrix assembly (FNMA), increased neurosphere cohesion, and reduction of neurosphere dispersal velocity (DV). How Dex specifically activates α5 integrin in these GBM lines is unknown. Several chaperone proteins are known to activate integrins, including calreticulin (CALR). We explore the role of CALR as a potential mediator of Dex-dependent induction of α5 integrin activity in primary human GBM cells. We use CALR knock-down and knock-in strategies to explore the effects on FNMA, aggregate compaction, and dispersal velocity in vitro, as well as dispersal ex vivo on extirpated mouse retina and brain slices. We show that Dex increases CALR expression and that siRNA knockdown suppresses Dex-mediated FNMA. Overexpression of CALR in GBM cells activates FNMA, increases compaction, and decreases DV in vitro and on explants of mouse retina and brain slices. Our results define a novel interaction between Dex, CALR, and FNMA as inhibitors of GBM dispersal.

A randomized phase II study of cilengitide (EMD 121974) in patients with metastatic melanoma

Cilengitide (EMD 121974) is a selective inhibitor of integrins αvβ3 and αvβ5. The αvβ3 promotes the proliferation of tumor-associated endothelial cells and potentially the survival of melanoma cells. We conducted a randomized phase II trial in patients with metastatic melanoma to evaluate the clinical efficacy of cilengitide. Patients with stage IV or unresectable stage III melanoma who were either chemonaive or who had previously received one systemic therapy were enrolled. Patients were randomly assigned to either 500 or 2000 mg of cilengitide administered intravenously twice weekly. The primary aim of this study was to determine the progression-free survival rate at 8 weeks. Tumor samples and blood samples were collected for pharmacodynamic and pharmacokinetic studies. Twenty-nine patients were enrolled, of whom 26 were treated (14 at 500 mg and 12 at 2000 mg). Among those treated, only three were progression free at 8 weeks: two in the 500 mg arm and one in the 2000 mg arm. One patient in the 2000 mg arm showed a prolonged partial response after an initial 28% enlargement of her target lesions. The treatment was well tolerated without clinically significant adverse events. The sole responder and one of two patients with stable disease had no αvβ3 expression at baseline. Overall, αvβ3 expression was decreased by day 8 of the treatment (P=0.05). Cilengitide was well tolerated by patients in both the treatment arms but had minimal clinical efficacy as a single-agent therapy for metastatic melanoma, and the efficacy was not related to baseline αvβ3 expression.

Lipopeptide with a RGDK tetrapeptide sequence can selectively target genes to proangiogenic alpha5beta1 integrin receptor and mouse tumor vasculature

Integrins, the major class of alphabeta heterodimeric transmembrane glycoprotein receptors, play crucial roles in mediating tumor angiogenesis. Genetic ablation experiments combined with use of antibodies/peptide ligands for blocking either alpha(5) or beta(1) integrins have convincingly demonstrated alpha(5)beta(1) integrin to be unquestionably proangiogenic among the 24 known integrin receptors. Herein, we report on a novel RGDK-lipopeptide 1 that targets selectively alpha(5)beta(1) integrin and is capable of targeting genes to mouse tumor vasculatures.

Volociximab, a chimeric monoclonal antibody that specifically binds alpha5beta1 integrin: a phase I, pharmacokinetic, and biological correlative study

PURPOSE

This study aimed to assess the safety and feasibility of administering volociximab, a chimeric monoclonal antibody that specifically binds to alpha(5)beta(1) integrin, and to determine the pharmacokinetics, pharmacodynamics, and preliminary evidence of antitumor activity.

EXPERIMENTAL DESIGN

Patients with advanced solid malignancies were treated with escalating doses of volociximab i.v. administered over 60 minutes. Blood samples were assayed to determine plasma pharmacokinetic parameters, detect human antichimeric antibody formation, and determine the saturation of alpha5beta1 sites on peripheral blood monocytes.

RESULTS

Twenty-one patients received 223 infusions of volociximab at doses ranging from 0.5 to 15 mg/kg i.v. on days 1, 15, 22, 29, and 36; and weekly thereafter. Treatment was well tolerated, and dose-limiting toxicity was not identified over the range examined. Mild (grade 1 or 2), reversible fatigue was the principal toxicity of volociximab at the highest dose levels of 10 and 15 mg/kg. Nausea, fever, anorexia, headache, vomiting, and myalgias were mild and infrequent, and there was no hematologic toxicity. Volociximab had biexponential distribution; clearance was inversely related to increasing dose, and the half-life at 15 mg/kg was estimated as being 30 days. Three patients tested positive for anti-volociximab antibodies. Saturation of monocyte alpha5beta1 integrin sites was dose-dependent up to 15 mg/kg. There was one minor response (renal, 7 months) and one durable stable disease (melanoma, 14 months).

CONCLUSIONS

Volociximab can be safely administered at 15 mg/kg i.v. per week. The absence of severe toxicities and preliminary activity at the highest dose level warrants further disease-directed studies.

Stripes and belly-spots -- a review of pigment cell morphogenesis in vertebrates

Pigment patterns in the integument have long-attracted attention from both scientists and non-scientists alike since their natural attractiveness combines with their excellence as models for the general problem of pattern formation. Pigment cells are formed from the neural crest and must migrate to reach their final locations. In this review, we focus on our current understanding of mechanisms underlying the control of pigment cell migration and patterning in diverse vertebrates. The model systems discussed here - chick, mouse, and zebrafish - each provide unique insights into the major morphogenetic events driving pigment pattern formation. In birds and mammals, melanoblasts must be specified before they can migrate on the dorsolateral pathway. Transmembrane receptors involved in guiding them onto this route include EphB2 and Ednrb2 in chick, and Kit in mouse. Terminal migration depends, in part, upon extracellular matrix reorganization by ADAMTS20. Invasion of the ectoderm, especially into the feather germ and hair follicles, requires specific signals that are beginning to be characterized. We summarize our current understanding of the mechanisms regulating melanoblast number and organization in the epidermis. We note the apparent differences in pigment pattern formation in poikilothermic vertebrates when compared with birds and mammals. With more pigment cell types, migration pathways are more complex and largely unexplored; nevertheless, a role for Kit signaling in melanophore migration is clear and indicates that at least some patterning mechanisms may be highly conserved. We summarize the multiple factors thought to contribute to zebrafish embryonic pigment pattern formation, highlighting a recent study identifying Sdf1a as one factor crucial for regulation of melanophore positioning. Finally, we discuss the mechanisms generating a second, metamorphic pigment pattern in adult fish, emphasizing recent studies strengthening the evidence that undifferentiated progenitor cells play a major role in generating adult pigment cells.

Changes in cholesterol levels in the plasma membrane modulate cell signaling and regulate cell adhesion and migration on fibronectin

The number and distribution of lipid molecules, including cholesterol in particular, in the plasma membrane, may play a key role in regulating several physiological processes in cells. We investigated the role of membrane cholesterol in regulating cell shape, adhesion and motility. The acute depletion of cholesterol from the plasma membrane of cells that were well spread and motile on fibronectin caused the rounding of these cells and decreased their adhesion to and motility on fibronectin. These modifications were less pronounced in cells plated on laminin, vitronectin or plastic, indicating that cholesterol-mediated changes in adhesion and motility are more specific for adhesion mediated by fibronectin-specific integrins, such as alpha5beta1. These changes were accompanied by remodeling of the actin cytoskeleton, the spatial reorganization of paxillin in the membrane, and changes to the dynamics of alpha5 integrin and paxillin-rich focal adhesions. Levels of tyrosine phosphorylation at position 576/577 of FAK and Erk1/Erk2 MAP-kinase activity levels were both lower in cholesterol-depleted than in control cells. These levels normalized only on fibronectin when cholesterol was reincorporated into the cell membrane. Thus, membrane cholesterol content has a specific effect on certain signaling pathways specifically involved in regulating cell motility on fibronectin and organization of the actin cytoskeleton.

Coculture with endothelial cells enhances vascular smooth muscle cell adhesion and spreading via activation of β1-integrin and phosphatidylinositol 3-kinase/Akt

The interactions between endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) play significant roles in the homeostasis of the blood vessel during vascular remodeling. Cell adhesion and spreading are an essential process for VSMC migration, survival and proliferation in the events of vascular physiology and pathophysiology. However, effects of ECs on adhesion and spreading of VSMCs have not been characterized yet. Here, the interaction of ECs and VSMCs on adhesion and spreading of VSMCs were investigated by using a coculture system. The results showed that VSMCs cocultured with ECs exhibited a significant increase in the number of adherent and spreading cells, and much more mRNA (twofold, P<0.01) and protein (threefold, P<0.05) expression of beta(1)-integrin comparing to the control, i.e., VSMCs cultured alone. Furthermore, the enhanced functional activity of beta(1)-integrin expression was confirmed by FACS. A beta(1)-integrin blocking antibody (P5D2) could inhibit the EC-induced VSMC adhesion and spreading. It was demonstrated that in correspondence with enhanced cell adhesion, ECs also prompted focal adhesion complex assembly and stress fiber formation of VSMCs. The phosphatidylinositol 3-kinase (PI3K)/Akt pathway was more pronouncedly activated in response to VSMC attachment. Our results for the first time show that coculture with ECs enhances VSMC adhesion and spreading by up-regulating beta(1)-integrin expression and activating the PI3K/Akt pathway, suggesting that the interaction between ECs and VSMCs serves an important role in vascular homeostasis and remodeling.

Separation Force Measurements Reveal Different Types of Modulation of E-cadherin-based Adhesion by Nectin-1 and -3

Nectins are Ca2+-independent cell adhesion molecules found at cadherin-based adherens junctions. We used a dual pipette assay that measures the forces required to separate cell doublets to determine how nectins affect the formation and strength of cell-cell adhesion. Less force was required to separate doublets of L cells expressing nectin-1 or nectin-3 than to separate doublets of E-cadherin-expressing cells. Heterodimers formed between cells expressing nectin-1 or nectin-3 adhered more strongly than homodimers. Nectin-3 that does not trans-interact with nectin-1 inhibited E-cadherin-mediated adhesion. However, the extracellular fragment of nectin-1 did not have an agonistic effect on E-cadherin-dependent cell adhesion when it trans-interacted with nectin-3, expressed at high levels in cells. In contrast, the extracellular fragment of nectin-3 had a significant agonistic effect on cadherin-based adhesion when it interacted with endogenous nectin-1, expressed at low levels in cells. Our results indicate that E-cadherin is the key molecule involved in cell adhesion and that the regulation of E-cadherin-based adhesion involving cellular nectin-1 trans-interacting with nectin-3 is qualitatively different from that involving cellular nectin-3 trans-interacting with nectin-1 and depends on the nectin levels expressed by cells.

Force measurements in E-cadherin-mediated cell doublets reveal rapid adhesion strengthened by actin cytoskeleton remodeling through Rac and Cdc42

We have used a modified, dual pipette assay to quantify the strength of cadherin-dependent cell–cell adhesion. The force required to separate E-cadherin–expressing paired cells in suspension was measured as an index of intercellular adhesion. Separation force depended on the homophilic interaction of functional cadherins at the cell surface, increasing with the duration of contact and with cadherin levels. Severing the link between cadherin and the actin cytoskeleton or disrupting actin polymerization did not affect initiation of cadherin-mediated adhesion, but prevented it from developing and becoming stronger over time. Rac and Cdc42, the Rho-like small GTPases, were activated when E-cadherin–expressing cells formed aggregates in suspension. Overproduction of the dominant negative form of Rac or Cdc42 permitted initial E-cadherin–based adhesion but affected its later development; the dominant active forms prevented cell adhesion outright. Our findings highlight the crucial roles played by Rac, Cdc42, and actin cytoskeleton dynamics in the development and regulation of strong cell adhesion, defined in terms of mechanical forces.

TGF-beta1-promoted epithelial-to-mesenchymal transformation and cell adhesion contribute to TGF-beta1-enhanced cell migration in SMMC-7721 cells

Transforming growth factor-b1 (TGF-beta1), a multi-function polypeptide, is a double-edged sword in cancer. For some tumor cells, TGF-beta1 is a potent growth inhibitor and apoptosis inducer. More commonly, TGF-beta1 loses its growth-inhibitory and apoptosis-inducing effects, but stimulates the metastatic capacity of tumor cells. It is currently little known about TGF-beta1-promoted cell migration in hepatocellular carcinoma (HCC) cells, let alone its mechanism. In this study, we found that TGF-beta1 lost its tumor-suppressive effects, but significantly stimulated cell migration in SMMC-7721 human HCC cells. By FACS and Western blot analysis, we observed that TGF-beta1 enhanced the expression of alpha5beta1 integrin obviously, and subsequently stimulated cell adhesion onto fibronectin (Fn). Furthermore, we observed that TGF-beta1 could also promote SMMC-7721 cells adhesion onto laminin (Ln). Our data also provided evidences that TGF-beta1 induced epithelial-to-mesenchymal transformation (EMT) in SMMC-7721 cells. First, SMMC-7721 cells clearly switched to the spindle shape morphology after TGF-beta1 treatment. Furthermore, TGF-beta1 induced the down-regulation of E-cadherin and the nuclear translocation of beta-catenin. These results indicated that TGF-beta1-promoted cell adhesion and TGF-beta1-induced epithelial-to-mesenchymal transformation might be both responsible for TGF-beta1-enhanced cell migration.

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.

Inhibition of alpha4-integrin stimulates epicardial-mesenchymal transformation and alters migration and cell fate of epicardially derived mesenchyme

Epithelial-mesenchymal transformation of the embryonic epicardium produces the subepicardial mesenchyme that is essential for normal coronary vascular development. Gene targeting experiments in mice have demonstrated an essential role for alpha4-integrin in normal epicardial development, but the precise cellular consequences of alpha4-integrin loss remain uncertain. To better understand the function of alpha4-integrin in epicardial development, we constructed a replication-incompetent adenovirus (AdlacZalpha4AS) that expresses antisense chicken alpha4-integrin as the 3' untranslated region of a lacZ reporter gene. This construct effectively labeled cells while greatly reducing levels of alpha4-integrin mRNA and protein. In quail chick chimeras, transplanted epicardial cells infected with AdlacZalpha4AS adhered to the heart and were incorporated into the epicardium, but 4 days after grafting, were largely absent from the epicardial epithelium, recapitulating the defect in alpha4-null mice. This did not result from epicardial cell apoptosis or anomalous migration of epicardial cells to extracardiac sites. Rather, AdlacZalpha4AS-infected epicardial cells were particularly invasive, being three to four times more likely to migrate to the interstitium of the myocardium than AdlacZ-infected epicardial cells. Accelerated epicardial-mesenchymal transformation and migration of alpha4-negative epicardium was observed in an organ culture system that does not require prior culture of epicardial cells. Remarkably, AdlacZalpha4AS infection also prevented targeting of epicardially derived mesenchyme to the media of developing coronary vasculature in the myocardial interstitium. This study provides evidence that epicardial alpha4-integrin normally restrains epicardial-mesenchymal transformation, invasion, and migration and is essential for correct targeting of epicardially derived mesenchyme to the developing coronary vasculature.

Central role of the alpha4beta1 integrin in the coordination of avian truncal neural crest cell adhesion, migration, and survival

Based on functional and histological studies, the fibronectin receptor of the integrin family alpha4beta1 has been ascribed a critical role during neural crest cell migration in the vertebrate embryo. In the present study, because integrins have been shown to participate in multiple basic cellular processes, including cell adhesion, migration, survival, proliferation, and differentiation, we have reexamined in detail the role of alpha4beta1 during avian truncal neural crest cell migration. RT-PCR and immunocytochemical studies revealed that migrating neural crest cells but not premigratory cells explanted in vitro expressed detectable levels of alpha4 messengers and proteins suggesting that alpha4beta1 expression was induced at the time of the initiation of the migration phase. In agreement with this observation, antibody inhibition of alpha4beta1 activity in vitro resulted in a strong, immediate and sustained reduction of neural crest cell motion on fibronectin, as judged on videomicroscopy analyses, but apparently did not prevent their delamination from the neural tube. However, alpha4beta1 appeared to exhibit a broader role in the control of cell migration on a variety of extracellular matrix molecules, presumably by regulating cellular events downstream from integrins. Moreover, blocking alpha4beta1 function caused a severe increase in apoptotic cell death among the neural crest population without influencing notably cell proliferation. Collectively, these results indicate that, notwithstanding its critical implication in cell motion, alpha4beta1 integrin could play a central role in neural crest cell development by coordinating multiple cellular events, such as cell adhesion, locomotion, and survival.

Integrin receptors are required for cell survival and proliferation during development of the peripheral glial lineage

Proliferation and survival of Schwann cells are important for nerve development and for disease processes in peripheral nerves. We have analyzed embryos lacking alpha4- or alpha5-integrins and show here that these integrins contribute to the control of glial cell numbers. To overcome early embryonic lethality an explant and grafting system that allows the study of isolated glial progenitor cells both in vitro and in vivo was used. Schwann cells differentiate in the absence of alpha5 but their numbers and the proliferation rate of early progenitor cells are reduced, suggesting that alpha5 is essential for normal proliferation. Survival, rather than proliferation, is compromised in alpha4-deficient explants. Conditional immortalization allowed further characterization and revealed that alpha4 contributes to survival in a cell-density-dependent fashion. In addition, transplants into chicken embryos were used to analyze in vivo cell migration and showed that cell death occurs mainly in highly motile, individually migrating cells. The cell death patterns in vitro and in vivo argue that alpha4-integrins play a role in survival during cell migration. Neural crest migration has been suggested to require these integrins; however, no defects in migration were observed in the absence of alpha4 or alpha5. We conclude that integrins can complement growth factors in the control of glial cell numbers.

Transplantation of mammalian olfactory progenitors into chick hosts reveals migration and differentiation potentials dependent on cell commitment

In vertebrates, interneurons of the olfactory bulb are continuously generated postnatally and throughout life at the subventricular zone of the forebrain. From there, the neuronal progenitors migrate tangentially in a typical chain-like structure to the olfactory bulb in which they differentiate as interneurons. We have used a mouse/chick xenograft strategy to explore the migration and differentiation potential of the mouse olfactory progenitors in a heterochronic and heterotypic environment. We compared the migration of primary cells derived from the subventricular zone of adult or newborn lateral ventricule with the behavior of in vitro amplified cells derived from the same structures. We show that in the chick environment, olfactory bulb progenitors from newborn brain tissue perform chain migration along the neural crest cell routes, whereas grafted neurosphere-derived-cells migrate as isolated cells. These results, together with in vitro observations, allow us to propose that neuronal chain migration is a community effect independent of environmental cues but which is closely regulated by the differentiation program of the cells. We established that the progenitor cells performing chain migration are already committed, while neurosphere-derived-cells are able to integrate and differentiate as components of the peripheral nervous system.

TGF-beta 1 modulated the expression of alpha 5 beta 1 integrin and integrin-mediated signaling in human hepatocarcinoma cells

Integrins are a family of cell surface adhesion molecules which mediate cell adhesion and initiate signaling pathways that regulate cell spreading, migration, differentiation, and proliferation. TGF-beta is a multifunctional factor that induces a wide variety of cellular processes. In this study, we show that, TGF-beta 1 treatment enhanced the amount of alpha 5 beta 1 integrin on cell surface, the mRNA level of alpha 5 subunit, and subsequently stimulated cell adhesion onto a fibronectin (Fn) and laminin (Ln) matrix in SMMC-7721 cells. TGF-beta 1 could also promote cell migration. Furthermore, our results showed that TGF-beta1 treatment stimulated the tyrosine phosphorylation level of FAK, which can be activated by the ligation and clustering of integrins. PTEN can directly dephosphorylate FAK, and the results that TGF-beta 1 could down-regulate PTEN at protein level suggested that TGF-beta 1 might stimulate FAK phosphorylation through increasing integrin signaling and reducing dephosphorylation of FAK. These studies indicated that TGF-beta 1 and integrin-mediated signaling act synergistically to enhance cell adhesion and migration and affect downstream signaling molecules of hepatocarcinoma cells.

Adhesion and migration of avian neural crest cells on fibronectin require the cooperating activities of multiple integrins of the (beta)1 and (beta)3 families

Based on genetic, functional and histological studies, the extracellular matrix molecule fibronectin has been proposed to play a key role in the migration of neural crest cells in the vertebrate embryo. In the present study, we have analyzed in vitro the repertoire and function of integrin receptors involved in the adhesive and locomotory responses of avian truncal neural crest cells to fibronectin. Immunoprecipitation experiments showed that neural crest cells express multiple integrins, namely (alpha)3(beta)1, (alpha)4(beta)1, (alpha)5(beta)1, (alpha)8(beta)1, (alpha)v(beta)1, (alpha)v(beta)3 and a (beta)8 integrin, as potential fibronectin receptors, and flow cytometry analyses revealed no major heterogeneity among the cell population for expression of integrin subunits. In addition, the integrin repertoire expressed by neural crest cells was found not to change dramatically during migration. At the cellular level, only (alpha)v(beta)1 and (alpha)v(beta)3 were concentrated in focal adhesion sites in connection with the actin microfilaments, whereas the other integrins were predominantly diffuse over the cell surface. In inhibition assays with function-perturbing antibodies, it appeared that complete abolition of cell spreading and migration could be achieved only by blocking multiple integrins of the (beta)1 and (beta)3 families, suggesting possible functional compensations between different integrins. In addition, these studies provided evidence for functional partitioning of integrins in cell adhesion and migration. While spreading was essentially mediated by (alpha)v(beta)1 and (alpha)8(beta)1, migration involved primarily (alpha)4(beta)1, (alpha)v(beta)3 and (alpha)8(beta)1 and, more indirectly, (alpha)3(beta)1. (alpha)5(beta)1 and the (beta)8 integrin were not found to play any major role in either adhesion or migration. Finally, consistent with the results of inhibition experiments, recruitment of (alpha)4(beta)1 and (alpha)v(beta)3, individually or in combination using antibodies or recombinant VCAM-1 and PECAM-1 molecules as a substratum, was required for migration but was not sufficient to produce migration of the cell population as efficiently as with fibronectin. In conclusion, our study indicates that neural crest cells express a multiplicity of fibronectin-binding integrins and suggests that dispersion of the cell population requires cooperation between distinct integrins regulating different events of cell adhesion, locomotion and, possibly, proliferation and survival.

Migration of lymphocytes on fibronectin-coated surfaces: temporal evolution of migratory parameters

Lymphocytes typically interact with implanted biomaterials through adsorbed exogenous proteins. To provide a more complete characterization of these interactions, analysis of lymphocyte migration on adsorbed extracellular matrix proteins must accompany the commonly performed adhesion studies. We report here a comparison of the migratory and adhesion behavior of Jurkat cells (a T lymphoblastoid cell line) on tissue culture treated and untreated polystyrene surfaces coated with various concentrations of fibronectin. The average speed of cell locomotion showed a biphasic response to substrate adhesiveness for cells migrating on untreated polystyrene and a monotonic decrease for cells migrating on tissue culture-treated polystyrene. A modified approach to the persistent random walk model was implemented to determine the time dependence of cell migration parameters. The random motility coefficient showed significant increases with time when cells migrated on tissue culture-treated polystyrene surfaces, while it remained relatively constant for experiments with untreated polystyrene plates. Finally, a cell migration computer model was developed to verify our modified persistent random walk analysis. Simulation results suggest that our experimental data were consistent with temporally increasing random motility coefficients.

A novel model to study the dorsolateral migration of melanoblasts

Melanocytes derived from pluripotent neural crest cells migrate initially in the dorsolateral pathway between the ectoderm and dermomyotome. To understand the role of specific proteins involved in this cell migration, we looked for a cellular model that mimics the in vivo behavior of melanoblasts, and that allows functional studies of their migration. We report here that wild-type embryonic stem (ES) cells are able to follow the ventral and dorsolateral neural crest pathways after being grafted into chicken embryos. By contrast, a mutant ES cell line deficient for beta1 integrin subunits, proteins involved in cell-extracellular interactions, had a severely impaired migratory behavior. Interestingly, ES cells deficient for Kit, the tyrosine kinase receptor for the stem cell factor (SCF), behaved similarly to wild-type ES cells. Thus, grafting mouse ES cells into chicken embryos provides a new cellular system that allows both in vitro and in vivo studies of the molecular mechanisms controlling dorsolateral migration.

Differential function of N-cadherin and cadherin-7 in the control of embryonic cell motility

Similar amounts of N-cadherin and cadherin-7, the prototypes of type I and type II cadherin, induced cell-cell adhesion in murine sarcoma 180 transfectants, Ncad-1 and cad7-29, respectively. However, in the initial phase of aggregation, Ncad-1 cells aggregated more rapidly than cad7-29 cells. Isolated Ncad-1 and cad7-29 cells adhered and spread in a similar manner on fibronectin (FN), whereas aggregated cad7-29 cells were more motile and dispersed than aggregated Ncad-1 cells. cad7-29 cells established transient contacts with their neighbors which were stabilized if FN-cell interactions were perturbed. In contrast, Ncad-1 cells remained in close contact when they migrated on FN. Both beta-catenin and cadherin were more rapidly downregulated in cad7-29 than in Ncad-1 cells treated with cycloheximide, suggesting a higher turnover rate for cadherin-7-mediated cell-cell contacts than for those mediated by N-cadherin. The extent of FN-dependent focal adhesion kinase phosphorylation was much lower if the cells had initiated N-cadherin-mediated rather than cadherin-7-mediated cell adhesion before plating. On grafting into the embryo, Ncad-1 cells did not migrate and remained at or close to the graft site, even after 48 h, whereas grafted cad7-29 cells dispersed efficiently into embryonic structures. Thus, the adhesive phenotype of cadherin-7-expressing cells is regulated by the nature of the extracellular matrix environment which also controls the migratory behavior of the cells. In addition, adhesions mediated by different cadherins differentially regulate FN-dependent signaling. The transient contacts specifically observed in cadherin- 7-expressing cells may also be important in the control of cell motility.

Distinct functions of alpha3 and alpha(v) integrin receptors in neuronal migration and laminar organization of the cerebral cortex

Changes in specific cell-cell recognition and adhesion interactions between neurons and radial glial cells regulate neuronal migration as well as the establishment of distinct layers in the developing cerebral cortex. Here, we show that alpha3beta1 integrin is necessary for neuron-glial recognition during neuronal migration and that alpha(v) integrins provide optimal levels of the basic neuron-glial adhesion needed to maintain neuronal migration on radial glial fibers. A gliophilic-to-neurophilic switch in the adhesive preference of developing cortical neurons occurs following the loss of alpha3beta1 integrin function. Furthermore, the targeted mutation of the alpha3 integrin gene results in abnormal layering of the cerebral cortex. These results suggest that alpha3beta1 and alpha(v) integrins regulate distinct aspects of neuronal migration and neuron-glial interactions during corticogenesis.

VLA-5 is expressed by mouse and human long-term repopulating hematopoietic cells and mediates adhesion to extracellular matrix protein fibronectin

Fibronectin (FN), an extracellular matrix protein, is involved in the adhesion and migration of hematopoietic cells and has been shown to enhance retroviral gene transfer into primitive hematopoietic cells by co-localization of target cells and retrovirus when used as a substrate in vitro. We have previously found that mouse hematopoietic stem cells could be transduced on a FN fragment that included the recognition sequence Arg-Gly-Asp (RGD), suggesting that stem cells may express the integrin very late antigen (VLA)-5. To address this, we investigated the binding of mouse and human hematopoietic cells to recombinant peptides that contained one or a combination of the three principle cell-binding domains of FN. These domains included the VLA-5- binding sequence RGD, the VLA-4-binding site CS1, and the high affinity heparin-binding domain. Here we show that mouse long-term in vivo repopulating stem cells, as well as primitive human NOD/SCID mouse repopulating cells, can bind extracellular matrix protein FN by using integrin VLA-5 in vitro. This binding is specific and can be inhibited by antibodies to VLA-5. In addition, preincubation of BM cells with peptide CH-296, which contains all three primary FN-binding domains, decreased the engraftment of cells in the bone marrow in vivo, while intravenous injection of the same peptide induced an increase of progenitor cells in the spleen. In summary, our data demonstrate that VLA-5 is expressed on primitive mouse and human hematopoietic cells and suggest that there may be significant cooperation between integrin receptors and proteoglycan molecules in the engraftment of bone marrow cells and hematopoietic cell adhesion in vivo.

Neural crest development: the interplay between morphogenesis and cell differentiation

The final pattern of tissues established during embryogenesis reflects the outcome of two developmental processes: differentiation and morphogenesis. Avian neural crest cells are an excellent system in which to study this interaction. In the first phase of neural crest cell migration, neural crest cells separate from the neural epithelium via an epithelial-mesenchymal transformation. We present three models to account for this process: (1) separation by asymmetric mitosis, (2) separation by generating tractional force in order to rupture cell adhesions and (3) loss of expression or function of cell-cell adhesion molecules that keep the presumptive neural crest cells tethered to the neural epithelium. Evidence is presented that the segregation of the neural crest lineage apart from the neural epithelium is caused by the epithelial-mesenchymal transformation. Once they have detached from the neural tube, neural crest cells take two pathways in the trunk of the chick embryo: (1) the ventral path between the neural tube and somite, where neural crest cells give rise to neurons and glial cells of the peripheral nervous systems, and (2) the dorsolateral path between the ectoderm and dermamyotome of the somite, where they differentiate into pigment cells of the skin. We present data to suggest that the migration and differentiation along the ventral path is controlled primarily by environmental cues, which we refer to as the environment-directed model of neural crest morphogenesis. Conversely, only melanoblasts can migrate into the dorsolateral space, and the ability to invade that path is dependent upon their early specification as melanoblasts. We call this the phenotype-directed model for neural crest cell migration and suggest that this latter model for the positioning of neural crest derivatives in the embryo may be more common than previously suspected. These observations invite a re-examination of patterning of other crest derivates, which previously were believed to be controlled by environmental cues.

RGDS glycosylated peptides as inhibitors of cell-attachment and platelet aggregation

Glycopeptides derived from the GRGDS sequence were synthesized to study the effect of the sugar residue on the activity of these peptides. The peptides were tested as inhibitors of cell adhesion to fibronectin and of platelet aggregation. The sugar moiety was found to reduce the biological activity of the parent compounds except for the cyclic derivatives P37 and P38 where the inhibition of platelet aggregation was increased. Some interesting differences were observed between the peptides bearing sugar residues with free hydroxyl groups and those with peracetylated sugars.

Beta3-integrins rather than beta1-integrins dominate integrin-matrix interactions involved in postinjury smooth muscle cell migration

BACKGROUND

Smooth muscle cell (SMC) migration is a vital component in the response of the arterial wall to revascularization injury. Cell surface integrin-extracellular matrix interactions are essential for cell migration. SMCs express both beta1- and beta3-integrins. In this study, we examined the relative functional roles of beta1- and beta3-integrin-matrix interactions in postinjury SMC migration.

METHODS AND RESULTS

Flow cytometry and fluorescence microscopy of migrating SMCs immunostained with anti-beta1 and anti-alpha(v)beta3/5 antibodies (Abs) revealed expression of both beta1- and beta3-integrins, with beta1 observed as linear streaks and beta3 found in focal contacts. In a scrape-wound migration assay, anti-beta1 Abs (92.0+/-10.7% of control, P=.1) and 0.5 mmol/L linear RGD (105+/-5% of control, P=.2) did not alter SMC migration at 48 hours after injury. Beta3-blockade, however, via Abs (anti-beta3/5 35.7+/-4.5% of control, anti-beta3 61+/-12% of control, both P<.001) and cyclic RGD (0.5 mmol/L) (12+/-10% of control, P<.001) decreased migration. Neither beta1- nor beta3-inhibition altered postinjury [3H]thymidine incorporation. In the rat carotid injury model, local adventitial polymer-based delivery of radiolabeled linear or cyclic RGD led to uptake and retention of label, for both peptides, over a 72-hour period after injury. Local arterial wall beta1-blockade via polymer-based delivery of linear RGD had no effect on SMC migration at 4.5 days (11.5+/-3.2 versus 12.8 SMCs per x600 field [control], P=.6) or on neointimal thickening at 14 days (I/M area ratio, 0.664+/-0.328 versus 1.179+/-0.324 [control], P=.6) after injury. In contrast, local beta3-blockade via cRGD limited migration (0.8+/-0.8 versus 12.8+/-4.4 SMCs per x600 field [control], P<.01) and thickening (I/M area ratio, 0.004+/-0.008 versus 1.179+/-0.324 [control], P<.01).

CONCLUSIONS

In postinjury migrating SMCs, beta3- rather than beta1-integrin-matrix interactions are of greater functional significance in adhesive processes essential for SMC migration in vitro and in vivo. Blockade of dominant SMC integrin (beta3)-matrix interactions may be a valuable approach for limiting injury-induced SMC migration and late arterial renarrowing.

Mesodermal defects and cranial neural crest apoptosis in alpha5 integrin-null embryos

Alpha5beta1 integrin is a cell surface receptor that mediates cell-extracellular matrix adhesions by interacting with fibronectin. Alpha5 subunit-deficient mice die early in gestation and display mesodermal defects; most notably, embryos have a truncated posterior and fail to produce posterior somites. In this study, we report on the in vivo effects of the alpha5-null mutation on cell proliferation and survival, and on mesodermal development. We found no significant differences in the numbers of apoptotic cells or in cell proliferation in the mesoderm of alpha5-null embryos compared to wild-type controls. These results suggest that changes in overall cell death or cell proliferation rates are unlikely to be responsible for the mesodermal deficits seen in the alpha5-null embryos. No increases in cell death were seen in alpha5-null embryonic yolk sac, amnion and allantois compared with wild-type, indicating that the mutant phenotype is not due to changes in apoptosis rates in these extraembryonic tissues. Increased numbers of dying cells were, however, seen in migrating cranial neural crest cells of the hyoid arch and in endodermal cells surrounding the omphalomesenteric artery in alpha5-null embryos, indicating that these subpopulations of cells are dependent on alpha5 integrin function for their survival. Mesodermal markers mox-1, Notch-1, Brachyury (T) and Sonic hedgehog (Shh) were expressed in the mutant embryos in a regionally appropriate fashion. Both T and Shh, however, showed discontinuous expression in the notochords of alpha5-null embryos due to (1) degeneration of the notochordal tissue structure, and (2) non-maintenance of gene expression. Consistent with the disorganization of notochordal signals in the alpha5-null embryos, reduced Pax-1 expression and misexpression of Pax-3 were observed. Anteriorly expressed HoxB genes were expressed normally in the alpha5-null embryos. However, expression of the posteriormost HoxB gene, Hoxb-9, was reduced in alpha5-null embryos. These results suggest that alpha5beta1-fibronectin interactions are not essential for the initial commitment of mesodermal cells, but are crucial for maintenance of mesodermal derivatives during postgastrulation stages and also for the survival of some neural crest cells.

A novel region of the alpha4 integrin subunit with a modulatory role in VLA-4-mediated cell adhesion to fibronectin

The integrin VLA-4 (alpha4 beta1) is a receptor for fibronectin and vascular cell-adhesion molecule 1 (VCAM-1). Four functionally different epitopes, designated A, B1, B2 and C, have previously been defined on the alpha4 subunit. Using K562 alpha4 mutant transfectants we found that alpha4 amino acids Tyr151, Gln152, Asp153, Tyr154 and Val155 are important for the structure of the epitope B2. Mutations at alpha4 Gln152 substantially impaired the transfectant adhesion to a CS-1-containing fragment of fibronectin (FN-H89), whereas this adhesion was not affected on the other alpha4 mutant transfectants. None of the alpha4 mutations significantly altered the adhesion of the different alpha4 transfectants to VCAM-1. In addition, we have identified residues Gln152, Asp153 and Tyr154 as part of the alpha4 epitope B2 involved in homotypic cell aggregation. The decrease in adhesion to FN-H89 shown by Gln152 alpha4 mutant transfectants was the result of an inefficient binding of FN-H89 by VLA-4 mutated at this residue. Also, mutant VLA-4 displayed an altered reactivity with HUTS-21, an anti-beta1 monoclonal antibody that reacts with functionally active VLA integrins. Adhesion to FN-H89 was not restored unless stimuli that increase the ligand-binding affinity of VLA heterodimers were added, suggesting that cell adhesion was affected in the initial phases. These results indicate that alpha4 Gln152 modulates cell adhesion to FN-H89 by playing important roles in the maintenance and/or the acquisition of an active state of VLA-4, an integrin that is normally expressed on the cell surface in a range of multiple activation states. The location of the alpha4 Gln152 residue on a loop of the upper surface of the proposed beta-propeller structure suggests a close association with potential ligand-binding sites.

Identification of a fibronectin-like molecule on Eimeria tenella

The attachment of Eimeria tenella to its target cells as an obligatory intracellular pathogen is essential for the development of disease. Previous reports have established that other intracellular protozoa parasites have either fibronectin, an adhesion protein, or fibronectin receptors, both of which are involved in the interaction with the host cells. In this current research, studies have been undertaken to visualize a surface component that may be involved in the attachment of E. tenella to host cells. For this purpose, monoclonal antibodies, both anti-chicken and anti-human fibronectin, and also anti-chicken integrin were used. Our results show a fibronectin-like molecule with an apparent molecular weight of 110 kDa in mature schizonts and microgametes. Staining with serum directed against chicken integrin revealed immunoreactivity within mature schizonts. Both the fibronectin-like molecule and the integrin may play an important role in the parasite stage-cell interaction and the promotion of parasite uptake.

Integrin regulation by endogenous expression of 18-kDa fibroblast growth factor-2

The three high molecular weight (HMW) forms of fibroblast growth factor-2 (FGF-2) have a distinct intracellular localization and differentially affect cell mobility and growth compared with the fourth 18-kDa form. To characterize further the effects of the 18-kDa and HMW forms of FGF-2, we have examined their ability to modulate integrin expression. Transfected NIH 3T3 cells expressing only 18-kDa FGF-2 exhibited increased cell surface levels of alpha5beta1, whereas cells expressing only HMW FGF-2 exhibited cell surface alpha5beta1 levels similar to parental cells. When cells synthesizing 18-kDa FGF-2 were transfected with a cDNA encoding a dominant negative FGF receptor, alpha5beta1 cell surface levels decreased. Immunoprecipitation of biosynthetically labeled cells indicated that expression of 18-kDa FGF-2 increased the biosynthesis and rate of maturation of alpha5. Northern blot analysis showed that 18-kDa FGF-2 increases the level of the alpha5 subunit mRNA but does not affect beta1 subunit transcript levels. Experiments utilizing luciferase reporter gene activity revealed increased alpha5 promoter activity in cells expressing 18-kDa FGF-2 indicating that the enhanced alpha5 transcript level is due to modulation of the transcription rate. Therefore, interaction of 18-kDa FGF-2 with FGF receptors results in changes in alpha5beta1 biosynthesis and processing. In contrast, endogenous expression of HMW FGF-2 does not mediate this effect.

The L1 adhesion molecule is a cellular ligand for VLA-5

The L1 adhesion molecule is a member of the immunoglobulin superfamily shared by neural and immune cells. In the nervous system L1 can mediate cell binding by a homophilic mechanism. To analyze its function on leukocytes we studied whether L1 could interact with integrins. Here we demonstrate that VLA-5, an RGD-specific fibronectin receptor on a wide variety of cell types, can bind to murine L1. Mouse ESb-MP cells expressing VLA-5 and L1 could be induced to aggregate in the presence of specific mAbs to CD24 (heat-stable antigen), a highly and heterogeneously glycosylated glycophosphatidylinositol-linked differentiation antigen of hematopoietic and neural cells. The aggregation was blocked by both mAbs to L1 and VLA-5, respectively. Aggregation was blocked also by a synthetic RGD-containing peptide derived from the Ig-domain VI of the L1 protein. ESb-MP subclones with low L1 expression could not aggregate. In heterotypic binding assays mouse bone marrow cells could adhere in an L1-dependent fashion to platelets that expressed VLA-5. Also purified L1 coated to polystyrene beads could bind to platelets. The binding of L1-beads was again inhibited by mAbs to L1 and VLA-5, by soluble L1 and the L1-RGD peptide in a dose-dependent manner. Thymocytes or human Nalm-6 tumor cells expressing VLA-5 could adhere to affinity-purified L1 and to the L1-derived RGD-containing peptide coated to glass slides. The adhesion was strongly enhanced in the presence of Mn(2+)-ions and blocked by mAbs to VLA-5. We also demonstrate a direct L1-VLA-5 protein interaction. Our results suggest a novel binding pathway, in which the VLA-5 integrin binds to L1 on adjacent cells. Given its rapid downregulation on lymphocytes after induction of cell proliferation, L1 may be important in integrin-mediated and activation-regulated cell-cell interactions.

Cooperative interactions between extracellular matrix, integrins and parathyroid hormone-related peptide regulate parietal endoderm differentiation in mouse embryos

The outgrowth of parietal endoderm (PE) cells from precursor endodermal cells is one of the first differentiation events that occur in mouse embryos. We have analyzed the molecular determinants of this process by placing isolated inner cell masses (ICMs) on defined extracellular matrix substrata in microdrop cultures. Differentiation and outgrowth of PE required a fibronectin substratum. Laminin supported the adhesion and outgrowth of visceral endoderm (VE) and actively suppressed the differentiation of PE in mixtures of fibronectin and laminin. Collagen type IV, gelatin, vitronectin or entactin supported little or no endodermal outgrowth. Trophectoderm (TE) cells have been implied to be important in PE induction in vivo. We found that recombination of ICMs in culture with TE cells, or with medium conditioned by TE cells, greatly increased the differentiation of PE. TE cells stimulated PE outgrowth on substrata other than fibronectin. One cytokine secreted by trophoblast and endodermal cells, parathyroid hormone-related peptide (PTHrP), was critical for outgrowth on any substratum. A function-perturbing antibody to PTHrP reduced the number of PE cells, whereas the addition of PTHrP increased that number. Furthermore, addition of PTHrP changed the substratum requirements for outgrowth, making laminin, vitronectin and low concentrations of fibronectin permissive for PE outgrowth. Immunostaining with anti-integrin antibodies showed that fully differentiated PE cells outgrowing on fibronectin expressed alpha 5, alpha 6 and alpha v beta 3 integrins. However, analysis of outgrowths in the presence of function-perturbing antibodies to alpha 5, alpha 6 and alpha v beta 3 integrins showed that these integrins directed PE outgrowth only on fibronectin, laminin and vitronectin substrata, respectively. We have shown that there is a cooperative interplay of extracellular matrix, integrins and PTHrP that modulates PE outgrowth.