PECAM-1 (CD31) functions as a reservoir for and a modulator of tyrosine-phosphorylated beta-catenin

Catenins function as regulators of cellular signaling events in addition to their previously documented roles in adherens junction formation and function. Evidence to date suggests that beta and gamma catenins can act as signaling molecules, bind transcriptional factors and translocate to the nucleus. Beta- and gamma-catenin are also major substrates for protein tyrosine kinases, and tyrosine phosphorylation of junctional proteins is correlated with decreased adhesiveness. One way in which catenin functions are modulated is by dynamic incorporation into junctional complexes which controls, in part, the cytoplasmic levels of catenins. Here we show that: (1) vascular endothelial growth factor (VEGF) induces beta-catenin tyrosine phosphorylation in a time-, and dose-dependent manner and that VEGF receptors co-localize to areas of endothelial cell-cell contact in vitro and in vivo. (2) Platelet-endothelial cell adhesion molecule (PECAM)-1 can function as a reservoir for, and modulator of, tyrosine phosphorylated beta-catenin. (3) PECAM-1 can prevent beta-catenin nuclear translocation in transfected SW480 colon carcinoma cells. We suggest that PECAM-1 may play a role in modulating beta-catenin tyrosine phosphorylation levels, localization and signaling and by doing so, functions as an important modulator of the endothelium.

Egr-1 mediates extracellular matrix-driven transcription of membrane type 1 matrix metalloproteinase in endothelium

Matrix metalloproteinase activity is instrumental in processes of cellular invasion. The interstitial invasion of endothelial cells during angiogenesis is accompanied by up-regulation of several matrix metalloproteinases, including membrane type 1 matrix metalloproteinase (MT1-MMP). In this study, we show that endothelial cells stimulated to undergo angiogenesis by a three-dimensional extracellular matrix environment increase production of the transcription factor Egr-1. Increased binding of Egr-1 to the MT1-MMP promoter correlates with enhanced transcriptional activity, whereas mutations in the Egr-1 binding site abrogate the increased transcription of MT1-MMP in the stimulated cells. These data identify Egr-1-mediated transcription of MT1-MMP as a mechanism by which endothelial cells can initiate an invasive phenotype in response to an alteration in extracellular matrix environment, thus functionally associating MT1-MMP with a growing number of proteins known to be up-regulated by Egr-1 in response to tissue injury or mechanical stress.

Hyperglycemia-induced vasculopathy in the murine vitelline vasculature: correlation with PECAM-1/CD31 tyrosine phosphorylation state

Maternal diabetes mellitus is associated with an increased incidence of congenital abnormalities as well as embryonic and perinatal lethality. In particular, a wide range of cardiovascular abnormalities have been noted in children of diabetic mothers and in the offspring of diabetic animals. The vascular system is the first organ system to develop in the embryo and is critical for normal organogenesis. The organization of mesodermal cells into endothelial and hematopoietic cells and into a complex vascular system is, in part, mediated by a series of specific cell-cell, cell-extracellular matrix, and cell-factor interactions. PECAM-1 expression has been observed during the earliest stages of vasculogenesis, and changes in PECAM-1 tyrosine phosphorylation have been associated with endothelial cell migration, vasculogenesis, and angiogenesis both in vitro and in vivo. In this report we demonstrate that exposure to hyperglycemia during gastrulation causes yolk sac and embryonic vasculopathy in cultured murine conceptuses and in the conceptuses of streptozotocin-induced diabetic pregnant mice. In addition, we correlate the presence of yolk sac and embryonic vasculopathy with the failure of PECAM-1 tyrosine dephosphorylation during the formation of blood islands/vessels from clusters of extra-embryonic and embryonic angioblasts in the murine conceptus using both in vitro and in vivo models. The importance of these findings in the development of vasculopathy in the offspring of diabetic mothers and the potential effects and benefits of glucose regulation during the periods of vasculogenesis/angiogenesis in embryonic development are discussed.

Extracellular matrix-driven matrix metalloproteinase production in endothelial cells: implications for angiogenesis

The process of new blood vessel growth, angiogenesis, involves orchestrated alterations in endothelial cell interactions with adjacent cells and with components of the underlying basement membrane matrix. The activity of matrix metalloproteinases (MMPs), proteases that can cleave basement membrane and interstitial matrix molecules, has been shown to be necessary for angiogenesis as it occurs in several different in vivo and in vitro models. This review discusses the potential roles of two particular MMPs, MMP-2 and MT1-MMP, in angiogenesis, with emphasis on current understanding of how endothelial cell-extracellular matrix interactions may regulate the production of these MMPs via matrix-induced signaling leading to transcriptional activation and subsequent formation of active multiprotease complexes on the cell surface.

Distinct signal transduction pathways are utilized during the tube formation and survival phases of in vitro angiogenesis

Angiogenesis, the formation of new blood vessels from pre-existing ones, occurs during development, wound healing and cancer and involves stages that orchestrate a network of cooperative interactions. Peptide growth factors and extracellular matrix (ECM) components are two major groups of angiogenesis mediators. Among the different ECM proteins, collagens have been well-associated with in vivo angiogenesis. Using human umbilical vein endothelial cells (HUVEC) grown in 3-D collagen gels we show that: (1) HUVEC do not survive well in 3-D collagen gels due to rapid induction of apoptosis. (2) VEGF, a potent in vivo angiogenic factor, fails to induce tube formation. (3) PMA was effective in inducing tube formation and survival in HUVEC dispersed in 3-D collagen gels, activating MAP kinase, phosphoinositide 3-OH kinase (PI-3-kinase) and Akt/PKB (protein kinase B) pathways. (4) VEGF was effective in preventing PMA-induced tube-like structure regression after PMA-withdrawal by (5) activating the mitogen activated protein kinase (MAPK), rather than the Akt/PKB, signaling pathway.

The interrelationship of alpha4 integrin and matrix metalloproteinase-2 in the pathogenesis of experimental autoimmune encephalomyelitis

Previous studies have suggested that surface expression of alpha4 integrin by autoreactive T-cell clones is necessary for the clones to induce experimental autoimmune encephalomyelitis (EAE), a mouse model for human multiple sclerosis. To provide direct evidence for this phenomenon, we have transfected alpha4 integrin into C19alpha4-LO, a myelin basic protein-reactive T-cell clone that does not express alpha4 integrin and does not induce EAE when adoptively transferred into a susceptible mouse strain. Transfection of alpha4 integrin converted this clone to an alpha4 integrin-expressing clone that induced EAE. We then examined potential mechanisms by which alpha4 integrin may facilitate the disease process. C19 T-cell clones adhered equally to a monolayer of microvascular endothelial cells, regardless of level of alpha4 integrin expression. However, in contrast to T-cell clones that do not express alpha4 integrin, T-cell clones that express alpha4 integrin (endogenously or by transfection) transmigrated through an endothelial cell layer and subendothelial matrix at an enhanced rate and adhered to recombinant vascular cell adhesion molecule-1 (rVCAM-1) and the CS1 fragment of fibronectin, and after adhesion to these ligands, a matrix-degrading metalloproteinase (MMP-2) was induced and activated. The clones were also shown to constitutively express the membrane-type matrix metalloproteinase (MT1-MMP), an enzyme that activates MMP-2. GM6001 and UK-221,316, inhibitors of metalloproteinases, reduced alpha4 integrin-mediated transmigration and EAE induction by C19 T-cell clones. In addition, we studied a second EAE-inducing T-cell clone, MM4, which constitutively expresses alpha4 integrin and MMP-2. Engagement of alpha4 integrin on the MM4 clone up-regulated the expression and activation of MMP-2, without changing the expression of MT1-MMP. MMP inhibitors also reduced transmigration of and EAE induction by the MM4 T-cell clone. These studies demonstrate directly that expression of alpha4 integrin by autoreactive T-cell clones is required for adoptive transfer of EAE in this model. We also define a role for alpha4 integrin in the disease process in mediating the induction and coordinate activation of a matrix metalloproteinase (MMP-2), which facilitates T-cell transmigration.

Platelet endothelial cell adhesion molecule-1 expression modulates endothelial cell migration in vitro

Endothelial cell migration is an important process that occurs during embryonic vasculogenesis and angiogenesis, wound healing, and tumor growth and metastasis, and after denudation injury following angioplasty and bypass grafting. Mechanisms regulating this process involve a complex interplay of cytoskeletal reorganization, cell-cell adhesion, and cell-extracellular matrix interactions. Platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31) is constitutively expressed in endothelial cells, leukocytes, monocytes, lymphocytes, and platelets. PECAM-1 undergoes dynamic dephosphorylation during endothelial cell migration in vitro and during vasculogenesis in the murine conceptus. In transfected 3T3 cells, in cultured endothelial cells, and in the murine conceptus undergoing vasculogenesis, the tyrosine phosphorylation state of PECAM-1 Y686 correlates with the migratory state of the cells. In the present study, we investigate the role of PECAM-1 in modulating endothelial cell migration in vitro using retroviral transduction of c-myc epitope-tagged, wild-type, Y686 to F-mutated PECAM-1 and extracellular domain-deleted PECAM-1 constructs in endothelial cells devoid of endogenous PECAM-1 (ECV304 cells) and in endothelial cells expressing high levels of endogenous PECAM-1 (bovine aortic endothelial cells, BAEC). In ECV304 cells, the expression of wild-type PECAM-1 inhibited migration rates, whereas in BAEC, overexpression of wild-type PECAM-1 had no effect. Expression of Y686 to F-mutated PECAM-1 or extracellular domain-deleted PECAM-1 in BAEC increased migration rates. These data support the concept that endothelial cell migration is modulated, in part, by a balance between PECAM-1 cytoplasmic domain-mediated "inside-out" and "outside-out" signaling resulting from PECAM-1-mediated cell-cell interactions and integrin-extracellular matrix interactions.

Immunofluorescence characterization of key extracellular matrix proteins in murine bone marrow in situ

The mechanism of hemopoietic stem cell homing to the bone marrow involves molecular interactions that mediate the recognition and interaction of these cells with the marrow microenvironment, including the extracellular matrix. On selective binding, this environment, in combination with soluble cytokines, regulates stem cell proliferation and differentiation. Using immunofluorescence labeling, we analyzed the location of the prominent extracellular matrix proteins fibronectin, collagen Types I, III, and IV, and laminin in sections of murine femoral bone marrow. Collagen Types I, IV, and fibronectin were localized to the endosteum, the region of the femoral microenvironment for which homing stem cells have a high affinity. The results further demonstrated a strong spatial association of collagen Type IV and laminin with the bone marrow vessels, including arterioles, veins, and sinuses. Fibronectin was distributed throughout the central marrow region, and all the proteins analyzed except collagen Type III were present in the bone, although at different levels. Fibronectin, collagen Types III and IV, and laminin were also present in the periosteum. The distinct locations of particular extracellular matrix proteins support the notion that they may play an important mechanistic role in the homing of engrafting cells.

The synergistic activity of alphavbeta3 integrin and PDGF receptor increases cell migration

Integrins and growth factor receptors act synergistically to modulate cellular functions. The alphavbeta3 integrin and the platelet-derived growth factor receptor have both been shown to play a positive role in cell migration. We show here that a platelet derived growth factor-BB gradient stimulated migration of rat microvascular endothelial cells on vitronectin (9.2-fold increase compared to resting cells) in a alphavbeta3 and RGD-dependent manner. In contrast, this response was not observed on a beta1 integrin ligand, laminin; background levels of migration, in response to a platelet derived growth factor-BB gradient, were observed on this substrate or on bovine serum albumin (2.4- or 2.0-fold, respectively). Comparable results were obtained using NIH-3T3 cells. Platelet derived growth factor-BB did not change the cells' ability to adhere to vitronectin, nor did it stimulate a further increase in proliferation on vitronectin versus laminin. In addition, platelet derived growth factor-BB stimulation of NIH-3T3 cells did not alter the ability of alphavbeta3 to bind RGD immobilized on Sepharose. The alphavbeta3 integrin and the platelet derived growth factor receptor-beta associate in both microvascular endothelial cells and NIH-3T3 cells, since they coprecipitated using two different antibodies to either alphavbeta3 or to the platelet derived growth factor receptor-beta. In contrast, beta1 integrins did not coprecipitate with the platelet derived growth factor receptor-beta. These results point to a novel pathway, mediated by the synergistic activity of alphavbeta3 and the platelet derived growth factor receptor-beta, that regulates cell migration and, therefore, might play a role during neovessel formation and tissue infiltration.

Three-dimensional type I collagen lattices induce coordinate expression of matrix metalloproteinases MT1-MMP and MMP-2 in microvascular endothelial cells

Matrix metalloproteinases (MMPs) are hypothesized to play a key role in the processes of endothelial cell migration and matrix remodeling during angiogenesis. We utilized an in vitro model of microvascular endothelial cell angiogenesis, cells cultured within a collagen matrix, to investigate the MMP profile of endothelial cells undergoing angiogenesis. We demonstrated by gelatin zymography that monolayer cultures (two-dimensional) of endothelial cells constitutively expressed low levels of latent MMP-2, but that culture in a three-dimensional collagen matrix increased the total amount of MMP-2 mRNA and protein. Furthermore, 51% of total MMP-2 protein was activated in the three-dimensional culture lysates, compared with 3.5% in two-dimensional culture. The mRNA and protein of MT1-MMP, the putative activator of MMP-2, were up-regulated in endothelial cells cultured in three-dimensional as compared with two-dimensional culture. Treatment of cultures with MMP inhibitors blocked activation of MMP-2 and inhibited formation of endothelial cell networks within the collagen gel. Induction of MT1-MMP and MMP-2 appeared to be specific to collagen, inasmuch as culture of the endothelial cells on top of, or within, a Matrigel(R) matrix neither increased total MMP-2 nor increased activation of MMP-2. These results suggest that MT1-MMP activation of MMP-2 occurs in endothelial cells undergoing angiogenesis, that this activation has a functional role in endothelial cell organization, and that specific matrix interactions may be critical for the increased expression of MT1-MMP and MMP-2.

Nitric oxide production contributes to the angiogenic properties of vascular endothelial growth factor in human endothelial cells

Vascular endothelial growth factor (VEGF) is a regulator of vasculogenesis and angiogenesis. To investigate the role of nitric oxide (NO) in VEGF-induced proliferation and in vitro angiogenesis, human umbilical vein endothelial cells (HUVEC) were used. VEGF stimulated the growth of HUVEC in an NO-dependent manner. In addition, VEGF promoted the NO-dependent formation of network-like structures in HUVEC cultured in three dimensional (3D) collagen gels. Exposure of cells to VEGF led to a concentration-dependent increase in cGMP levels, an indicator of NO production, that was inhibited by nitro-L-arginine methyl ester. VEGF-stimulated NO production required activation of tyrosine kinases and increases in intracellular calcium, since tyrosine kinase inhibitors and calcium chelators attenuated VEGF-induced NO release. Moreover, two chemically distinct phosphoinositide 3 kinase (PI-3K) inhibitors attenuated NO release after VEGF stimulation. In addition, HUVEC incubated with VEGF for 24 h showed an increase in the amount of endothelial NO synthase (eNOS) protein and the release of NO. In summary, both short- and long-term exposure of human EC to VEGF stimulates the release of biologically active NO. While long-term exposure increases eNOS protein levels, short-term stimulation with VEGF promotes NO release through mechanisms involving tyrosine and PI-3K kinases, suggesting that NO mediates aspects of VEGF signaling required for EC proliferation and organization in vitro.

An in vitro three-dimensional coculture model of cerebral microvascular angiogenesis and differentiation

The microvasculature of the developing brain is plastic and responds differently to the many insults associated with preterm birth. We developed three-dimensional in vitro culture models for the study of the responses of the developing cerebral microvasculature. Beagle brain microvascular endothelial cells (BBMEC) were isolated by differential centrifugation from newborn beagle pups on postnatal Day 1 and placed in three-dimensional culture dispersed in a collagen gel. Alternatively, BBMEC were placed in a three-dimensional coculture with neonatal rat forebrain astrocytes. Cultures were analyzed for extracellular matrix components at 1 and 6 d, and total RNA was extracted for Northern analyses. Urokinase plasminogen activator activity was assayed in both mono- and cocultures of the two cell types. Studies of three-dimensional BBMEC/astrocyte cocultures demonstrated progressive tube formation with only low levels of endothelial proliferation. By 6 d in three-dimensional coculture, the BBMEC formed capillarylike tubes with a wrapping of glial processes, and basement membrane protein synthesis was noted. Urokinase plasminogen zymography suggested intercellular signaling by the two cell types. These data suggest that the three-dimensional beagle brain germinal matrix microvascular endothelial cell/neonatal rat astrocyte coculture provides a good model for the investigation of microvascular responses in the developing brain.

Involvement of endothelial PECAM-1/CD31 in angiogenesis

The adhesive interactions of endothelial cells with each other and the adhesion receptors that mediate these interactions are probably of fundamental importance to the process of angiogenesis. We therefore studied the effect of inhibiting the function of the endothelial cell-cell adhesion molecule, PECAM-1/ CD31, in rat and murine models of angiogenesis. A polyclonal antibody to human PECAM-1, which cross-reacts with rat PECAM-1, was found to block in vitro tube formation by rat capillary endothelial cells and cytokine-induced rat corneal neovascularization. In mice, two monoclonal antibodies against murine PECAM-1 prevented vessel growth into subcutaneously implanted gels supplemented with basic fibroblast growth factor (bFGF). Taken together these findings provide evidence that PECAM-1 is involved in angiogenesis and suggest that the interactions of endothelial cell-cell adhesion molecules are important in the formation of new vessels.

Platelet endothelial cell adhesion molecule-1 is phosphorylatable by c-Src, binds Src-Src homology 2 domain, and exhibits immunoreceptor tyrosine-based activation motif-like properties

Platelet endothelial cell adhesion molecule-1 (PECAM-1) is 130-kDa member of the immunoglobulin gene superfamily that localizes to cell-cell borders of confluent endothelial cells and has been shown to play a role in the control of endothelial sheet migration and leukocyte transmigration through the endothelium. The cytoplasmic tail plays an important role in the modulation of PECAM-1 function. Mutation of tyrosine 663 or 686 in the cytoplasmic tail reduces phosphorylation and mutation of 686 is associated with a reduction in PECAM-1-mediated inhibition of cell migration (1). We have previously noted that these two tyrosine residues are surrounded by consensus sequences for Src homology 2 (SH2) domain binding (1, 2), and the experiments presented explore the potential for PECAM-1-Src and PECAM-1-SH2 domain interactions. PECAM-1 is more highly phosphorylated in endothelial cells overexpressing c-Src, and in in vitro kinase assays, c-Src can phosphorylate a glutathione S-transferase (GST)-PECAM cytoplasmic tail fusion protein. The phosphorylated fusion protein associates with the bead-bound c-Src. This association appears to be mediated by Src-SH2 domain, because PECAM-1 can be precipitated by a GST-Src-SH2 affinity matrix. The binding to the GST-Src-SH2 affinity matrix correlates directly with the level of PECAM-1 phosphorylation, because more PECAM-1 is precipitated from c-Src overexpressors and from wild-type rather than Tyr663 --> Phe and Tyr686 --> Phe mutant PECAM-1 expressors. Yet unidentified phosphoproteins can also be coimmunoprecipitated with wild-type but not mutant PECAM-1. Finally, we note the similarity of the PECAM-1 cytoplasmic domain sequence to the immunoreceptor tyrosine-based activation motif. Our data begin to delineate how tyrosines 663 and 686 may play a role in mediating PECAM-1 signal transduction.

Vascular endothelial growth factor mediates reactive angiogenesis in the postnatal developing brain

Although chronic sublethal hypoxia has been shown to promote angiogenesis in the developing brain, the pathogenesis of this response is unknown. We hypothesized that this response may be mediated in part by vascular endothelial growth factor (VEGF). We reared newborn rats (P3) in a chamber with FIO2 of 9.5 +/- 1% (exposed, E). At P33, the animals were removed from the chamber and the brains prepared for immunohistochemistry, mRNA extraction, or horseradish peroxidase (HRP) permeability studies. We also isolated beagle brain germinal matrix endothelial cells from PND 1 beagle pups and placed them in three-dimensional (3-D) coculture with PND 1 rat forebrain astrocytes. Cultures were grown for 6 days in 11% O2 and compared to control 3-D cocultures. When compared to age-matched controls, the experimental rats had significantly increased cortical vascular density (vessels/mm2: 518 +/- 18 vs. 400 +/- 15, P = 0.025). HRP studies demonstrated significantly increased permeability in all cortical vessels examined in experimental rats compared to controls. Compared to controls, VEGF mRNA from hypoxic pups was increased 2.4 times, and immunohistochemical studies of VEGF protein confirmed this finding. Similarly, when compared to controls, hypoxic cocultures of brain microvascular endothelial cells and astrocytes demonstrated significant increase in tubelike structures representing in vitro angiogenesis. Additionally, astrocyte VEGF protein levels increased 4.4-fold in hypoxic compared to control astrocyte cultures and VEGF protein levels increased 1.7-fold in hypoxic compared to control cocultures. Finally, addition of VEGF (10 ng/ml culture medium) to BBMEC alone in 3-D culture elicited not only significant proliferation (P = 0.001) but also increased tube formation. These data demonstrate that the developing brain responds to chronic sublethal hypoxia with increases in permeability and angiogenesis and suggest that VEGF mediates this response.

Platelet-endothelial cell adhesion molecule-1 (PECAM-1/CD31) tyrosine phosphorylation state changes during vasculogenesis in the murine conceptus

Vasculogenesis, the differentiation of mesodermal cells to angioblasts and the subsequent formation of blood islands and blood vessels by angioblasts in the conceptus, is a dynamic process modulated, in part, by cell-extracellular matrix and cell-cell interactions in the presence of a variety of growth factors and morphogens. In this report we demonstrate differential tyrosine phosphorylation of platelet-endothelial cell adhesion molecule-1 (PECAM-1) during the formation of blood islands and vessels from clusters of extraembryonic and embryonic angioblasts in the murine conceptus. In addition, we identify the phosphorylation of a particular tyrosine residue in the PECAM-1 cytoplasmic domain, Tyr686, which has the potential of mediating binding to Src homology 2 domain-containing proteins, affecting PECAM-1 cellular localization and endothelial cell migration.

Nitric oxide synthase inhibitors attenuate transforming-growth-factor-beta 1-stimulated capillary organization in vitro

Angiogenesis is a complex process involving endothelial cell (EC) proliferation, migration, differentiation, and organization into patent capillary networks. Nitric oxide (NO), an EC mediator, has been reported to be antigenic as well as proangiogenic in different models of in vivo angiogenesis. Our aim was to investigate the role of NO in capillary organization using rat microvascular ECs (RFCs) grown in three-dimensional (3D) collagen gels. RFCs placed in 3D cultures exhibited extensive tube formation in the presence of transforming growth factor-beta 1. Addition of the NO synthase (NOS) inhibitors L-nitro-arginine methylester (L-NAME, 1 mmol/L) or L-monomethyl-nitro-l-arginine (1 mmol/L) inhibited tube formation and the accumulation of nitrite in the media by approximately 50%. Incubation of the 3D cultures with excess L-arginine reversed the inhibitory effect of L-NAME on tube formation. In contrast to the results obtained in 3D cultures, inhibition of NO synthesis by L-NAME did not influence RFC proliferation in two-dimensional (2D) cultures or antagonize the ability of transforming growth factor-beta 1 to suppress EC proliferation in 2D cultures. Reverse transcriptase-polymerase chain reaction revealed the constitutive expression of all three NOS isoforms, neuronal, inducible, and endothelial NOSs, in 2D and 3D cultures. Moreover, Western blot analysis demonstrated the presence of immunoreactive protein for all NOS isoforms in 3D cultures of RFCs. In addition, in the face of NOS blockade, co-treatment with the NO donor sodium nitroprusside or the stable analog of cGMP, 8-bromo-cGMP, restored capillary tube formation. Thus, the autocrine production of NO and the activation of soluble guanylate cyclase are necessary events in the process of differentiation and in vitro capillary tube organization of RFCs.

T cell adhesion to endothelial cells and extracellular matrix is modulated upon transendothelial cell migration

During inflammation, T cells transmigrate from the bloodstream into perivascular tissues. As T cells transmigrate, they undergo a series of attachments to and detachments from the endothelium and then extravasate into the extracellular matrix (ECM). T cell migration into the ECM involves a number of mechanisms that influence cell-ECM interactions. The modulation of integrin expression and affinity are two such mechanisms in which cells can alter their ability to interact with other cells and ECM. We show in vitro that transmigrated T cells exhibit down-regulation of very late activation antigen-4 and leukocyte function-associated antigen-1 integrin surface expression and a decrease in binding to recombinant vascular cell adhesion molecule-1 and recombinant intercellular adhesion molecule-1. Also, transmigrated T cells displayed an increase in binding to collagens I and IV and fibronectin. Further, brain sections of experimental autoimmune encephalomyelitis mice demonstrated that as T cells migrated farther into the tissue, very late activation antigen-4 expression was lost while CD4 expression remained unchanged. The significance of these findings in the modulation of the inflammatory response is discussed.

Integrin engagement mediates tyrosine dephosphorylation on platelet-endothelial cell adhesion molecule 1

Platelet-endothelial cell adhesion molecule 1 (PECAM-1, CD31) is a 130-kDa member of the immunoglobulin gene superfamily expressed on endothelial cells, platelets, neutrophils, and monocytes and plays a role during endothelial cell migration. Phosphoamino acid analysis and Western blot analysis with anti-phosphotyrosine antibody show that endothelial PECAM-1 is tyrosine-phosphorylated. Phosphorylation is decreased with endothelial cell migration on fibronectin and collagen and with cell spreading on fibronectin but not on plastic. Cell adhesion on anti-integrin antibodies is also able to specifically induce PECAM-1 dephosphorylation while concurrently inducing pp125 focal adhesion kinase phosphorylation. Inhibition of dephosphorylation with sodium orthovanadate suggests that this effect is at least partially mediated by phosphatase activity. Tyr-663 and Tyr-686 are identified as potential phosphorylation sites and mutated to phenylalanine. When expressed, both mutants show reduced PECAM-1 phosphorylation but Phe-686 mutants also show significant reversal of PECAM-1-mediated inhibition of cell migration and do not localize PECAM-1 to cell borders. Our results suggest that beta 1-integrin engagement can signal to dephosphorylate PECAM-1 and that this signaling pathway may play a role during endothelial cell migration.

Regulation of human colonic cell line proliferation and phenotype by sodium butyrate

Colonic butyrate may maintain mucosal differentiation and oppose carcinogenesis. We characterized butyrate effects on differentiation, proliferation, and matrix interactions in Caco-2 and SW620 human colonic cells. Differentiation was assessed by brush border enzyme activity and doubling time by serial cell counts. Motility across matrix proteins was quantitated by monolayer expansion and correlated with adhesiveness to matrix. Integrin subunit surface pools were measured by immunoprecipitation. Butyrate-stimulated differentiation inhibited proliferation and was significantly more potent than acetate in this regard. Butyrate also inhibited motility across collagen I, collagen IV, and laminin, as well as decreasing adhesiveness to these matrices and beta 1, alpha 1, and alpha 2 integrin subunit surface expression. Butyrate acts in cultured cells at clinically relevant concentrations to oppose classical malignant behavior, inhibiting proliferation and motility while promoting differentiation. Since butyrate is derived from fermentation of dietary fiber, such mechanisms may contribute to the apparent protective action of fiber against colon carcinogenesis.

Role of plasminogen activator inhibitor in the reciprocal regulation of bovine aortic endothelial and smooth muscle cell migration by TGF-beta 1

Vascular endothelial and smooth muscle cells exhibit reciprocal migratory responses after transforming growth factor (TGF)-beta 1 treatment. Endothelial cells exhibit a decreased migratory rate and smooth muscle cells exhibit an increased migratory rate. Previous studies have demonstrated increases in extracellular matrix and integrin synthesis and expression in response to TGF-beta 1. In this report, we illustrate the roles of plasminogen activator inhibitor in modulating the migratory rates in these two cell types. Endothelial cells appear to require a proteolytic phenotype for rapid migration, whereas vascular smooth muscle cells appear to require an anti-proteolytic phenotype. Modulation of proteinase/anti-proteinase activity ratios was accomplished via TGF-beta 1 induction, addition of exogenous plasminogen activator inhibitor, addition of anti-catalytic antibodies directed against urokinase plasminogen activator, overexpression of plasminogen activator inhibitor utilizing stable transfectants, and the use of vitronectin as a substratum. The reciprocal migratory behaviors exhibited by these two vascular cell types in response to TGF-beta 1 is discussed in the context that these two vascular cell types utilize distinct adhesive and signaling pathways in their interactions with extracellular matrix components and responsiveness to proteolytic activity.

Amelioration of lupus-like autoimmune disease in NZB/WF1 mice after treatment with a blocking monoclonal antibody specific for complement component C5

New Zealand black x New Zealand white (NZB/W) F1 mice spontaneously develop an autoimmune syndrome with notable similarities to human systemic lupus erythematosus. Female NZB/WF1 mice produce high titers of antinuclear antibodies and invariably succumb to severe glomerulonephritis by 12 months of age. Although the development of the immune-complex nephritis is accompanied by abundant local and systemic complement activation, the role of proinflammatory complement components in disease progression has not been established. In this study we have examined the contribution of activated terminal complement proteins to the pathogenesis of the lupus-like autoimmune disease. Female NZB/W F1 mice were treated with a monoclonal antibody (mAb) specific for the C5 component of complement that blocks the cleavage of C5 and thus prevents the generation of the potent proinflammatory factors C5a and C5b-9. Continuous therapy with anti-C5 mAb for 6 months resulted in significant amelioration of the course of glomerulonephritis and in markedly increased survival. These findings demonstrate an important role for the terminal complement cascade in the progression of renal disease in NZB/W F1 mice, and suggest that mAb-mediated C5 inhibition may be a useful approach to the therapy of immune-complex glomerulonephritis in humans.

Laminin promotes differentiation of NB4 promyelocytic leukemia cells with all-trans retinoic acid

The promyelocytic leukemia cell line, NB4, carries the t(15; 17) translocation and undergoes limited maturation in response to differentiation agents. Growth on laminin enhanced the ability of all-trans retinoic acid (ATRA) to promote morphologic maturation of these cells. Although exposure to ATRA in suspension yielded minimal maturation beyond the myelocyte stage, after 72 hours of exposure to ATRA on laminin the cells acquired the histologic appearance of metamyelocytes, band forms, and segmented neutrophils. After 96 hours, some cells acquired a spindle shape and became tightly adherent. Growth on collagen types I, III, IV, or fibronectin did not have this effect, although some cells did adhere to fibronectin. NB4 cells treated with ATRA in suspension or on laminin acquired the equivalent ability to reduce nitroblue tetrazolium or cytochrome C. Despite the improved morphologic maturation on laminin, the cells did not express secondary granule proteins such as lactoferrin or neutrophil collagenase. In addition, growth on laminin abolished cell proliferation in the presence of ionomycin. Growth on laminin and/or with ATRA induced new expression of alpha 6 integrin, a laminin receptor, as assessed by reverse transcription-polymerase chain reaction. Different conditions of growth (laminin or differentiation agent) resulted in specific patterns of expression of the alpha 6A and alpha 6B isoforms. Treatment with ATRA also resulted in the acquisition of high-level surface expression of alpha 6 integrin, as assessed by flow cytometry. Thus, treatment of NB4 promyelocytic leukemia cells with ATRA induced expression of alpha 6 integrin (a laminin receptor alpha-chain) and enabled more advanced maturation when the cells were grown on the extracellular matrix component, laminin, compared with tissue culture plastic.