Differential distribution and modulation of expression of alpha 1/beta 1 integrin on human endothelial cells

Monocyte activation: rapid induction of alpha 1/beta 1 (VLA-1) integrin expression by lipopolysaccharide and interferon-gamma

Monocytes play a key role in inflammation, tissue injury and remodelling and wound healing, and most monocyte effector functions are dependent on adhesive interactions. We have analyzed the changes in the pattern of beta 1 integrin expression that take place during monocyte activation and demonstrated that lipopolysaccharide (LPS) and interferon (IFN)-gamma specifically induce the expression of the alpha 1/beta 1 integrin, which was detectable on the monocyte membrane as early as 12 h after monocyte activation. The up-regulated alpha 1/beta 1 expression was not dependent on monocyte adherence to solid surfaces, and Northern blot analysis revealed that LPS and IFN-gamma induce the alpha 1 mRNA de novo. Monocyte deactivating cytokines such as interleukin (IL)-4 or IL-10, could only minimally inhibit the LPS- or IFN-gamma mediated up-regulation of alpha 1/beta 1, suggesting that cytokine release subsequent to monocyte activation does not play a major role in the integrin induction. Interestingly, the LPS-induced expression of alpha 1/beta 1 was found to be dependent on the redox state of the cell, since it was inhibited by antioxidants which also altered the morphological changes that take place during monocyte culture in vitro. The rapid induction of alpha 1 in LPS-activated monocytes suggests that alpha 1/beta 1 might be involved not only in monocyte/extracellular matrix interactions during inflammatory reactions, but also in contributing to further monocyte activation and cytokine production during septic shock syndrome.

Human dermal microvascular endothelial cells produce matrix metalloproteinases in response to angiogenic factors and migration

Matrix metalloproteinases (MMPs) are a family of inducible enzymes that degrade extracellular matrix components, allowing cells to traverse connective tissue structures efficiently. Specific tissue inhibitors (TIMPs) function as physiologic inhibitors of MMP activity. Because neovascularization may require various proteinases, we characterized the profile of metalloenzyme production by microvascular endothelial cells (MEC) and the modulation of expression by phorbol esters (PMA) and by the physiologically relevant cytokines tumor necrosis factor-alpha (TNF-alpha), basic fibroblast growth factor, and interferon-gamma. MMP expression by MEC and large-vessel human umbilical vein endothelial cells (HUVEC) was determined by enzyme-linked immunosorbent assay, immunoprecipitation, Northern hybridization, and transfection assays. Constitutive expression of MMPs by endothelial cells was low. PMA stimulated the production of collagenase, stromelysin, 92-kDa gelatinase, and TIMP-1 in both endothelial cell types. TIMP-2 was constitutively expressed by MEC and HUVEC, but was down-regulated by PMA. TNF-alpha induced an endothelial-cell-specific up-regulation of collagenase with a concomitant inhibition of PMA-induced TIMP-1 up-regulation, a response that is distinct from that of fibroblasts. Interferon-gamma up-regulated TIMP-1 production by MEC and blocked PMA and TNF-induced up-regulation of collagenase. Northern hybridization assays showed pretranslational control of PMA-, basic fibroblast growth factor-, and TNF-alpha-induced MMP expression. Collagenase-promoter CAT constructs containing 2.28 kb of the 5' region of the collagenase gene demonstrated transcriptional regulation. The potential physiologic relevance of such regulation was shown in an in vitro migration assay. MEC were stimulated to migrate by wounding and exposure to TNF-alpha. Collagenase mRNA was prominently expressed by the migrating cells, as shown by in situ hybridization. In sum, MEC have a unique profile of MMP expression and regulation compared with other cell types, which may be important for wound healing and angiogenesis, particularly during the early phase of migration.

Comparison of cell adhesion molecule expression between glioblastoma multiforme and autologous normal brain tissue

We investigated glioblastoma multiforme (GBM) for a pattern of consistent alterations in cell adhesion molecules (CAM) expression that might distinguish tumor from normal autologous brain tissue. We used frozen section immunohistochemistry with anti-CAM and computerized image analysis to quantify staining intensity which we expressed as relative intensity units (RIU). Our results showed that normal brain tissue generally did not express alpha 1 beta 1, intercellular CAM-1 (ICAM-1), and sialylated Lewisx, slightly expressed alpha 2, alpha 4, alpha 5, alpha 6 beta 1, alpha v beta 3, lymphocyte function-associated antigen-3 (LFA-3), Lewisx, sialylated LewisLewisx, had a good expression of alpha 3 beta 1 and CD44, and strongly expressed neural CAM (NCAM). GBM expressed alpha 2, alpha 3, alpha 5, alpha 6 beta 1, alpha v beta 3, ICAM-1, LFA-3, CD44, Lewisx, sialylated Lewisx, and sialylated LewisLewisx significantly higher (2-11-fold RIU) than normal brain tissue. ICAM-1 and LFA-3 were the most distinctive markers of GBM. The small blood vessel endothelial cells of the normal brain and the GBM showed a few differences. The tumor endothelium expression of alpha 2 beta 1, alpha 4 beta 1, and LFA-3 RIU appeared twice higher than in normal endothelium and alpha 6 beta 1 showed an average of 40% RIU decrease in comparison to normal. These results show that the expression of several CAM is consistently altered in GBM and its microvasculature when compared with autologous normal brain tissue.

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

The molecules that mediate cell-matrix recognition, such as fibronectins (FN) and integrins, modulate cell behavior. We have previously demonstrated that FN and the beta 1-integrins are used during neural crest cell (NCC) migration in vitro as well as in vivo, and that the FN cell-binding domains I and II exhibit functional specificity in controlling either NCC attachment, spreading, or motility in vitro. In the present study, we have analyzed the effect of changes in the integrin expression patterns on migratory cell behavior in vivo. We have generated, after stable transfection, S180 cells expressing different levels of alpha 4 beta 1 or alpha 5 beta 1 integrins, two integrins that recognize distinct FN cell-binding domains. Murine S180 cells were chosen because they behave similarly to NCC after they are grafted into the NCC embryonic pathways in the chicken embryo. Thus, they provide a model system with which to investigate the mechanisms controlling in vitro and in vivo migratory cell behavior. We have observed that either the overexpression of alpha 5 beta 1 integrin or the induction of alpha 4 beta 1 expression in transfected S180 cells enhances their motility on FN in vitro. These genetically modified S180 cells also exhibit different migratory properties when grafted into the early trunk NCC migratory pathways. We observe that alpha 5 and low alpha 4 expressors migrate in both the ventral and dorsolateral paths simultaneously, in contrast to the parental S180 cells or the host NCC, which are delayed by 24 h in their invasion of the dorsolateral path. Moreover, the alpha 4 expressors exhibit different migratory properties according to their level of alpha 4 expression at the cell surface. Cells of the low alpha 4 expressor line invade both the ventral and dorsolateral pathways. In contrast, the high expressors remain as an aggregate at the graft site, possibly the result of alpha 4 beta 1-dependent homotypic aggregation. Thus, changes in the repertoire of FN-specific integrins enable the S180 cells to exploit different pathways in the embryo and regulate the speed with which they disperse in vivo and in culture. Our studies correlate well with known changes in integrin expression during neural crest morphogenesis and strongly suggest that neural crest cells that migrate into the dorsolateral path, i.e., melanoblasts, do so only after they have upregulated the expression of FN receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

In situ expression of beta 1, beta 3 and beta 4 integrin subunits in non-neoplastic endothelium and vascular tumours

Endothelial cells play an important role in adhesive interactions between circulating cells and extracellular matrix proteins. In vitro studies have shown that many of these processes are mediated by a superfamily of alpha beta heterodimeric transmembrane glycoproteins called integrins. The distribution patterns of beta 1, beta 3 and beta 4 integrin subunits in endothelial cells (EC) in situ were examined immunohistochemically on serial frozen sections of a wide range of non-neoplastic tissues and of vascular tumours, both benign and malignant. Expression of the beta 1 subunit was a constitutive feature of EC. Among the beta 1-associated alpha subunits, alpha 5 and alpha 6 were broadly distributed in EC, irrespective of vessel size and microenvironment. The alpha 3 subunit displayed intermediate levels of expression with a slight preference for small vessel EC. Presence of alpha 1 was confined to EC of capillaries and venules/small veins. Expression of alpha 2 in EC was inconsistent. With rare exceptions, the alpha 4 chain was absent in EC. The beta 3 and alpha v subunits were expressed in most EC, though not always concomitantly. In contrast to the beta 1 chain, however, these integrin subunits were absent in EC of glomerular capillaries and were expressed variably in sinusoidal EC. The beta 4 chain was evenly present in the great majority of EC, except for those of large vessels. In vascular tumours, the patterns of beta 1 and alpha 1 to alpha 6 subunit expression generally corresponded to those found in their non-neoplastic counterparts. Expression of beta 3, alpha v and beta 4 chains, however, decreased in neoplasia, especially in angiosarcomas. These data show that EC dispose of broad and at the same time differential repertoires of integrin subunits that presumably reflect vessel-type associated functional differences among these cells. In vascular tumours, the orthologous distribution patterns of beta 1 and alpha 1 to alpha 6 chains are conserved in most instances while the amounts of beta 3, alpha v and beta 4 subunits expressed in EC tend to decrease in the course of malignant transformation.

Basic fibroblast growth factor increases expression of the alpha v beta 3 integrin complex on human microvascular endothelial cells

Modulation of the expression of the alpha v beta 3 complex on human dermal microvascular endothelial cells (HDMEC) may be crucial in wound healing and angiogenesis. Therefore, we examined the influence of basic fibroblast growth factor (bFGF), transforming growth factor beta, and interferon-gamma (IFN-gamma) on the expression of this complex. Stimulation of HDMEC with bFGF increased cell surface expression of both alpha v and beta 3 in a dose- and time-dependent manner associated with the development of a spindled, elongated cell morphology. Northern blot analysis of HDMEC stimulated with bFGF demonstrated a marked increase in beta 3 but not alpha v mRNA expression. Incubation of HDMEC with transforming growth factor-beta or interferon-gamma alone resulted in modest decreases in cell surface alpha v beta 3, and co-incubation of HDMEC with bFGF and transforming growth factor-beta or interferon-gamma inhibited bFGF-induced changes in cell morphology, increases in cell surface alpha v beta 3 expression, and increases in beta 3 mRNA. These data demonstrate that both growth factors and pro-inflammatory cytokines alter the expression of alpha v beta 3 on microvascular endothelial cells and that these alterations correlate with changes in cell morphology.

Synoviocytes in chronic synovitis in situ and cytokine stimulated synovial cells in vitro neo-express alpha 1, alpha 3 and alpha 5 chains of beta 1 integrins

The expression of the beta 1 integrins was examined immunohistochemically in synoviocytes from normal synovitis membrane and from chronic synovitis of different aetiology and intensity. Normal synoviocytes were alpha 6 beta 1-positive but lacked alpha 1 through alpha 5. In mild inflammation type A synoviocytes neo-expressed alpha 1, alpha 3, and alpha 5 chains. In severe inflammation both type A and B synoviocytes expressed alpha 3, alpha 4, alpha 5, and alpha 6 chains. The effects of inflammatory cytokines, as single agents or in combination, on the beta 1 integrin expression in cultured normal synoviocytes was determined by immunocytochemistry and flow cytometry. The alpha 1 chain, while absent in unstimulated synoviocytes, was induced by interleukin-1 beta (IL-1 beta), tumour necrosis factor-alpha (TNF-alpha), and interferon-gamma (IFN-gamma). This effect was enhanced by combining IL-1 beta and TNF-alpha. Expression of the alpha 3 chain was up-regulated by IL-1 beta and, more intensely, by IFN-gamma. Transforming growth factor beta (TGF-beta) inhibited the up-regulating effect of IL-1 beta and antagonized the effect of IFN-gamma on alpha 3 chain expression. Expression of the alpha 5 chain was up-regulated significantly by co-stimulation through IL-1 beta together with TGF-beta or TNF-alpha. Thus, the beta 1 integrin profile of cytokine activated synoviocytes in vitro resembled that of synoviocytes in synovitis in situ. These data suggest that IL-1 beta, TNF-alpha, IFN-gamma, and TGF-beta are likely to be among the effectors regulating beta 1 integrin expression in synoviocytes in vivo.

Regulation of vitronectin receptor expression by retinoic acid on human melanoma cells

The integrin family of adhesion receptors is likely to be important for tumor cell invasion and dissemination. We have studied the effects of the differentiating agents retinoic acid on integrin expression by the human melanoma cell line MeWo. Our results show that this agent inhibits cellular proliferation, increases melanin content and induces morphological changes in MeWo cells. Functionally, these alterations are associated with an enhanced adhesion to matrix protein vitronectin and higher levels of expression of vitronectin receptor on the cell surface. This is accompanied by increased levels of alpha v integrin mRNA. Although the mechanism by which retinoic acid regulates the expression of vitronectin receptor in MeWo cells needs further examination, this system may represent a good model for understanding the role of this receptor in melanoma progression, as well the molecular basis for retinoic acid therapy in these tumors.

Loss of alpha 1 beta 1 and reduced expression of other beta 1 integrins and CAM in lung adenocarcinoma compared with pneumocytes

Alterations in expression of various cell-adhesion molecules have been reported in a variety of malignant tissues. However, little is known about how lung adenocarcinomas differ in CAM expression from the normal lung. We analyzed the expression of integrins alpha 1 beta 1 through alpha 6 beta 1, intercellular adhesion molecule (ICAM)-1, neural cell adhesion molecule (NCAM), and lymphocyte function antigen (LFA)-3, CD44, and the two carbohydrate antigens, Lewisx (Le(x)) and sialosyl-Le-Le(x) of lung adenocarcinoma cells, and compared them with autologous pneumocytes. CAM expression was studied by an immunohistochemical method using monoclonal antibodies, and computerized image analysis was used to quantify the immunoperoxidase-staining intensity. The normal lung alveolar cells strongly expressed the integrins alpha 1 beta 1 and alpha 3 beta 1, and fairly expressed alpha 2 beta 1, alpha 4 beta 1, alpha 5 beta 1, and alpha 6 beta 1. ICAM-1, LFA-3, and CD44 were strongly expressed, whereas NCAM, the Le(x) and sialosyl-Le-Le(x) antigens, were expressed weakly. In contrast, we did not detect expression of the alpha 1 beta 1 integrin on any autologous lung adenocarcinoma cells, and they showed on average a 50% reduction in labeling relative intensity units for the integrin common chain marker beta 1, the specific integrins alpha 3 beta 1, alpha 5 beta 1, and alpha 6 beta 1, and ICAM-1, and LFA-3. Examination of the adjacent small blood vessel endothelium in malignant lung tissues did not reveal any major alterations in CAM expression, the small vessel endothelium of the normal and malignant lung tissues appeared with a similar CAM profile. These results suggest that lung adenocarcioma cells have a lack of alpha 1 beta 1 expression and significant reduction in some other integrin beta 1 and CAM expression in comparison with their autologous pneumocytes. This aberration in CAM expression by the lung adenocarcinoma cells may be involved in their loss of proliferation control and may interfere with leukocyte adhesion to tumor cells, enabling the tumor to escape immunodestruction.

Focal adhesion kinase is abundant in developing blood vessels and elevation of its phosphotyrosine content in vascular smooth muscle cells is a rapid response to angiotensin II

Focal adhesion kinase (FAK) is a structurally unique nonreceptor protein-tyrosine kinase that localizes to focal adhesion plaques. Regulation of its activity has been implicated in diverse signaling pathways, including those mediated by extracellular matrix/integrin interactions, G-protein coupled receptors for mitogenic neuropeptides, and certain oncogene products. To gain evidence for specific processes in which FAK may be involved in vivo, a study was initiated to determine its expression pattern during mouse development. FAK expression was detected in early embryos and appeared to be distributed throughout all cell types at about the time of neurulation. Subsequent to neural tube closure, expression became particularly abundant in the developing vasculature. This included expression in the medial layer of arteries populated by smooth muscle cells. In vitro studies using cultured rat aortic vascular smooth muscle cells demonstrate that FAK phosphotyrosine content is dramatically elevated in response to plating cells onto the adhesive glycoprotein, fibronectin. Also, enhanced tyrosine phosphorylation of FAK is observed in these cells upon stimulation with the vasoconstrictor angiotensin II. Thus, in vascular smooth muscle cells, like fibroblasts, FAK appears to play a role in signaling mechanisms induced by extracellular matrix components as well as G-protein coupled receptor agonists. The combined results of this study suggest that signaling through FAK may play an important role in blood vessel morphogenesis and function.

Integrin-mediated signal transduction in human endothelial cells: analysis of tyrosine phosphorylation events

Adhesion of human umbilical endothelial cells to fibronectin resulted in increased tyrosine phosphorylation of a group of proteins with molecular mass ranging from 100 to 130 kDa and of a 70 kDa protein. This pattern of tyrosine phosphorylation was also observed when endothelial cells adhered to vitronectin, collagen IV, collagen I and laminin or to culture dishes coated with antibodies directed to either beta 1, alpha 3, alpha 5, alpha 6 or beta 3 integrin subunits. Increased phosphorylation of the 100-130 kDa proteins was detectable as early as 30 sec after adhesion, reached maximal level after 15 min, and remained high as long as the cells adhere to culture dishes. The 70 kDa protein was phosphorylated with a slower kinetics and its phosphorylation increased over a period of 3 h. Using specific monoclonal antibodies, the major component of the 100-130 kDa complex was identified as the focal adhesion tyrosine kinase p125FAK. The phosphorylation of the p125FAK was also observed by inducing beta 1 integrin clustering in non adherent HEC, indicating that this is a primary signalling event induced by integrins. Using tyrosine kinase inhibitors, we show a direct correlation between integrin-stimulated tyrosine kinases and assembly of focal adhesions and actin fibres.

Functional identification of integrin laminin receptors that mediate process outgrowth by human SY5Y neuroblastoma cells

Treatment of the human neuroblastoma cell line SY5Y with nerve growth factor (NGF) induces terminal neuronal differentiation of a subpopulation of cells which can be selected by treatment with a DNA synthesis inhibitor. We have examined the interactions of naive (untreated) and NGF-differentiated SY5Y cells with laminin, and identified integrin receptors that mediate laminin-induced process outgrowth. Differentiated cells displayed a greater capacity for process extension, which correlated with increased expression of integrin laminin receptors. Both naive and differentiated cells expressed integrins alpha 1/beta 1, alpha 2/beta 1, and alpha 3/beta 1 but the differentiated population expressed about 5-fold higher levels of alpha 1/beta 1 and about 2-fold more alpha 2/beta 1 and alpha 3/beta 1 on their surface. Function blocking monoclonal antibodies were used to identify integrin receptors mediating process outgrowth. The anti-alpha 1 monoclonal antibody SR84 was shown to block alpha 1 function and inhibit process outgrowth on laminin. Despite the presence of multiple integrins which have been shown to bind laminin in other cell types, alpha 1/beta 1 mediated the majority of process outgrowth in both naive and differentiated cells, with a minor role played by alpha 3/beta 1. These data indicate that alpha 1/beta 1 function is required for process outgrowth on laminin by SY5Y cells and suggest that increased expression may be a crucial aspect of neuronal differentiation.

Formation of hemidesmosomes in cells of a transformed murine mammary tumor cell line and mechanisms involved in adherence of these cells to laminin and kalinin

Keratinocytes attach to an underlying basement membrane by adhesion junctions called hemidesmosomes. We have characterized a cell line, RAC-11P/SD, established from a murine mammary tumor, which differentiates into squamous epithelium and forms well defined hemidesmosomes. These hemidesmosomes contain the integrin alpha 6 beta 4 as well as the hemidesmosomal plaque proteins BP230 and HD1 and are associated with a matrix containing kalinin and laminin. We examined how these cells adhere to laminin and to kalinin present in matrices as well as immunopurified kalinin. We show that adhesion to laminin is energy dependent but does not require an intact actin-containing cytoskeleton. The affinity for kalinin proved to be greater and binding to kalinin was still observed when cells had been treated with deoxyglucose and azide to inhibit metabolic energy. Binding to laminin (or fragment E8), but not to kalinin was partially blocked by a monoclonal antibody specific for the integrin alpha 6 subunit, and only in the initial phase of adhesion. The antibody efficiently blocked adhesion to laminin of cells treated with the microfilament disrupting drug cytochalasin B, but only partially blocked the adhesion of cytochalasin B-treated cells to kalinin, while adherence of cells treated with deoxyglucose and azide to kalinin was blocked completely. The integrin alpha 6 beta 4 is redistributed to the basal surface during adhesion and then is organized into ring-like structures when cells are bound to laminin and localized into hemidesmosomes in cells adhered to kalinin. We suggest that anti-alpha 6 hinders the binding of the alpha 6 beta 4 integrins to its ligands laminin and kalinin, but cannot prevent adhesion when clustering of the integrin has become complete. In addition, there is evidence that adhesion to kalinin is mediated by a second receptor, which associates with the actin-containing cytoskeleton. The presence of such a second receptor is suggested because the cells can spread on kalinin, but not when they have been treated with cytochalasin B. On laminin spreading does not occur, irrespective of whether cells have been treated with cytochalasin B or not. The integrin alpha 3 beta 1, which has been identified as a receptor for kalinin but not for laminin, is strongly expressed in RAC-11P/SD cells and it seems likely that this integrin is responsible for spreading of cells on kalinin.

Involvement of protein kinase C and protein tyrosine kinase pathways in tumor necrosis factor-alpha-induced clustering of ovarian theca-interstitial cells

Tumor necrosis factor-alpha (TNF) induces clustering of theca-interstitial cells (TIC) isolated from immature, hypophysectomized rats, while inhibiting luteinizing hormone (LH)-stimulated androstenedione in vitro. Stimulators of PKC, 1-oleoyl-2-acetyl-sn-glycerol (OAG, 50 and 100 microM) and phorbol-12-myristate-13-acetate (PMA, 50 nM), caused TIC clustering by 6 days in vitro. Clustering induced by these compounds resembled that induced by TNF. The protein kinase inhibitor, staurosporine at 1 and 10 nM, impaired TNF-induced TIC clustering for 6 days, as did the protein kinase inhibitor, 1-(5-isoquinolinesulfonyl)-2-methylpiperizine dihydrochloride (H-7); conversely, the protein kinase inhibitor, chelerythrine chloride (0.1, 1.0 or 10 microM), did not attenuate TNF-directed clustering. The protein kinase inhibitors did not reverse the suppression of LH-stimulated androstenedione by TNF. Inhibitors of the EGF receptor PTK, A23 (10, 50, or 100 microM) and A46 (0.1, 1.0, 10, or 50 microM), impaired TNF-induced TIC clustering, while TNF suppression of LH-directed androstenedione was unaffected. EGF-induced TIC clustering was also impaired by A46, while A23 was less effective. Both A23 and A46 blocked EGF attenuation of LH-directed androstenedione after 4 days. When challenged with TNF (1 ng/ml) or PMA (50 nM), PKC activity increased in TIC. A23 (50 microM) and A46 (10 microM) each alone blocked the TNF-associated increase in PKC activity; however, PKC activity attributable to PMA was unaffected by A46. Together, these results suggest that TNF-induced TIC clustering involves activation of PTK which directs subsequent increases in PKC activity; however, mechanisms by which TNF inhibits LH-stimulated steroidogenesis remains elusive.

Basic fibroblast growth factor modulates integrin expression in microvascular endothelial cells

During angiogenesis capillary endothelial cells undergo a coordinated set of modifications in their interactions with extracellular matrix components. In this study we have investigated the effect of the prototypical angiogenic factor basic fibroblast growth factor (bFGF) on the expression and function of several integrins in microvascular endothelial cells. Immunoprecipitation experiments with antibodies to individual subunits indicated that microvascular cells express at their surface several integrins. These include the alpha 1 beta 1, alpha 2 beta 1, and alpha 3 beta 1 laminin/collagen receptors; the alpha 6 beta 1 laminin receptor; the alpha 5 beta 1 and alpha v beta 1 fibronectin receptors; the alpha 6 beta 4 basement membrane receptor; and the alpha v beta 3 and alpha v beta 5 vitronectin receptors. Treatment with bFGF caused a significant increase in the surface expression of the alpha 2 beta 1, alpha 3 beta 1, alpha 5 beta 1, alpha 6 beta 1, alpha 6 beta 4, and alpha v beta 5 integrins. In contrast, the level of expression of the alpha 1 beta 1 and alpha v beta 3 integrins was decreased in bFGF-treated cells. Immunoprecipitation of metabolically labeled cells indicated that bFGF increases the biosynthesis of the alpha 3, alpha 5, alpha 6, beta 4, and beta 5 subunits and decreases the production of the alpha v and beta 3 subunits. These results suggest that bFGF modulates integrin expression by altering the biosynthesis of individual alpha or beta subunits. In accordance with the upregulation of several integrins observed in bFGF-treated cells, these cells adhered better to fibronectin, laminin, vitronectin, and type I collagen than did untreated cells. The largest differences in beta 1 integrin expression occurred approximately 72 h after exposure to bFGF, at a time when the expression of the endothelial cell-to-cell adhesion molecule endoCAM was also significantly upregulated. In contrast, a shorter exposure to bFGF (24-48 h) was required for the maximal induction of plasminogen activator production in the same cells. Taken together, these results show that bFGF causes significant changes in the level of expression and function of several integrins in microvascular endothelial cells.

Integrin-mediated neurite outgrowth in neuroblastoma cells depends on the activation of potassium channels

Electrical signals elicited by integrin interaction with ECM components and their role in neurite outgrowth were studied in two clones (N1 and N7) isolated from 41A3 murine neuroblastoma cell line. Although the two clones similarly adhered to fibronectin (FN) and vitronectin (VN), this adhesion induced neurite outgrowth in N1 but not in N7 cells. Patch clamp recordings in whole cell configuration showed that, upon adhesion to FN or VN but not to platelet factor 4 (PF4), N1 cells undergo a marked (approximately equal to 20 mV) hyperpolarization of the resting potential (Vrest) that occurred within the first 20 min after cell contact with ECM, and persisted for approximately 1 h before reverting to the time zero values. This hyperpolarization was totally absent in N7 cells. A detailed analysis of the molecular mechanisms involved in N1 and N7 cell adhesion to ECM substrata was performed by using antibodies raised against the FN receptor and synthetic peptides variously competing with the FN or VN binding to integrin receptor (GRGDSP and GRGESP). Antibodies, as well as GRGDSP, abolished adhesion of N1 and N7 clones to FN and VN, revealing a similar implication of integrins in the adhesion of these clones to the ECM proteins. However, these anti-adhesive treatments, while ineffective on Vrest of N7 cells, abolished in N1 cells the FN- or VN-induced hyperpolarization and neurite outgrowth, that appeared therefore strictly associated and integrin-mediated phenomena. The nature of this association was deepened through a comparative analysis of the integrin profiles and the ion channels of N1 and N7 cells. The integrin immunoprecipitation profile resulted very similarly in the two clones, with only minor differences concerning the alpha V containing complexes. Both clones possessed Ca2+ and K+ delayed rectifier (KDR) channels, while only N1 cells were endowed with inward rectifier K+ (KIR) channels. The latter governed the Vrest, and, unlike KDR channels, were blocked by Ba2+ and Cs+. By moving patched cells in contact with FN-coated beads, it was shown that KIR channel activation was responsible for the FN-mediated hyperpolarization of Vrest. Treatment with Pertuxis toxin (PTX) abolished this hyperpolarization and neurite outgrowth, indicating that a G protein is interposed between integrins and KIR channels and that the activation of these channels is required for neuritogenesis. In fact, the block of KIR channels by Cs+ abolished both hyperpolarization and neurite outgrowth, provided that the cation was supplied during the first two hours after N1 cell contact with FN.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of in vitro capillary tube formation by anti-integrin antibodies

Human endothelial cells are induced to form an anastomosing network of capillary tubes on a gel of collagen I in the presence of PMA. We show here that the addition of mAbs, AK7, or RMAC11 directed to the alpha chain of the major collagen receptor on endothelial cells, the integrin alpha 2 beta 1, enhance the number, length, and width of capillary tubes formed by endothelial cells derived from umbilical vein or neonatal foreskins. The anti-alpha 2 beta 1 antibodies maintained the endothelial cells in a rounded morphology and inhibited both their attachment to and proliferation on collagen but not on fibronectin, laminin, or gelatin matrices. Furthermore, RMAC11 promoted tube formation in collagen gels of increased density which in the absence of RMAC11 did not allow tube formation. Neither RMAC11 or AK7 enhanced capillary formation in the absence of PMA. Lumen structure and size were also altered by antibody RMAC11. In the absence of antibody the majority of lumina were formed intracellularly from single cells, but in the presence of RMAC11, multiple cells were involved and the lumen size was correspondingly increased. Endothelial cells were also induced to undergo capillary formation in fibrin gels after PMA stimulation. The addition of anti-alpha v beta 3 antibodies promoted tube formation in fibrin gels and inhibited EC adhesion to and proliferation on a fibrinogen matrix. The enhancement of capillary formation by the anti-integrin antibodies was matrix specific; that is, anti-alpha v beta 3 antibodies only enhanced tube formation on fibrin gels and not on collagen gels while anti-alpha v beta 1 antibodies only enhanced tubes on collagen and not on fibrin gels. Thus we postulate that changes in the adhesive nature of endothelial cells for their extracellular matrix can profoundly effect their function. Anti-integrin antibodies which inhibit cell-matrix interactions convert endothelial cells from a proliferative phenotype towards differentiation which results in enhanced capillary tube formation.

Expression of integrin family of cell adhesion receptors in rheumatoid synovium. Alpha 6 integrin subunit in normal and hyperplastic synovial lining cell layer

Integrins are heterodimeric cell adhesion receptors. The beta 1 integrin subunit can be in a complex with multiple a subunits and form receptors for collagen, laminin, fibronectin, and vitronectin. We have characterized the distribution of eight integrin subunits in rheumatoid synovium, with special interest in the lining cell layer. The beta 1 integrin subunit was found in abundance in synovial stroma and in lining cells. The only alpha subunit seen constantly in lining cells was alpha 6. In complex with alpha beta subunit, alpha 6 forms a laminin receptor usually seen in epithelial or endothelial cells or in macrophages. The fact that laminin was found in the extracellular matrix around synovial cells suggests the importance of alpha 6 integrin in the adhesion of synovial lining cells. Furthermore, alpha 6 expression was noticeably weaker in strongly proliferative lining cell layers, indicating that the inflammatory process may regulate integrin expression. A potential connection between altered expression of cell adhesion receptors and the pathological behavior of rheumatoid lining cells is suggested.

Expression of beta 1 integrin complexes on the surface of unfertilized mouse oocyte

Integrins are a family of cell surface receptors that mediate cell-cell and cell-matrix interactions in a variety of different cellular systems. Here we show that unfertilized mouse oocytes express beta 1 class integrins both at mRNA and protein levels. Using the reverse transcription polymerase chain reaction and oligonucleotide primers based on the DNA sequence of mouse integrins, the RNA transcripts for the beta 1, alpha 5 and alpha 6 subunits were detected in unfertilized oocytes. The expression of the mRNAs is paralleled by the expression of the corresponding proteins, in fact, the alpha 5/beta 1 and the alpha 6/beta 1 complexes can be immunoprecipitated with specific antibodies form 125I-surface-labeled oocytes. Using subunit-specific antibodies we also demonstrate the presence of the alpha 3/beta 1 at the oocyte surface but alpha 1, alpha 2, alpha 4 or alpha V subunits were not detectable. Since the mouse alpha 3 DNA sequence is not available, we have not tested for the corresponding transcript. Integrin subunits alpha 6 and beta 1 were differently distributed on the oocyte surface, as visualized by immunofluorescence staining and by immunoelectron microscopy. alpha 6 antigen was mainly confined to the microvillous area of the oocyte surface, while beta 1 was more homogeneously distributed over the whole oolemma. These data demonstrate for the first time the expression of three beta 1 integrin complexes in unfertilized mouse oocytes. Such proteins may have a role in sperm-egg interaction or during very early steps of embryogenesis.

Role of microvascular endothelial cells in inflammation

Endothelial cells are critical elements in the evolution of all types of cutaneous inflammation. They participate through the synthesis and secretion of pro-inflammatory cytokines, including interleukin 1 (IL-1), IL-6, and IL-8, as well as M-CSF, G-CSF, GM-CSF, gro alpha, and MCP. They also express a series of cell-surface proteins and glycoproteins known as cell adhesion molecules that allow circulating leukocytes to bind to endothelial cells and allow endothelial cells to bind to matrix proteins. The regulated expression of these molecules, including those in the integrin, immunoglobulin gene, and selection families, allows for the precise trafficking of circulating leukocytes to sites of inflammation, injury, or immunologic stimulation in the skin. Furthermore, emerging evidence clearly indicates that selected differences exist between endothelial cells of the microvasculature and those that line large blood vessels. These include differences in secreted products, differences in the expression of cell adhesion molecules, and differences in cytokine-induced regulation of commonly expressed cell adhesion molecules, among others. Thus, a precise delineation of the biology of cutaneous microvascular endothelial cells is important to our understanding of cutaneous inflammation.

Expression of alpha 1 integrin, a laminin-collagen receptor, during myogenesis and neurogenesis in the avian embryo

In this study, we have examined the spatiotemporal distribution of the alpha 1 integrin subunit, a putative laminin and collagen receptor, in avian embryos, using immunofluorescence microscopy and immunoblotting techniques. We used an antibody raised against a gizzard 175 × 10(3) M(r) membrane protein which was described previously and which we found to be immunologically identical to the chicken alpha 1 integrin subunit. In adult avian tissues, alpha 1 integrin exhibited a very restricted pattern of expression; it was detected only in smooth muscle and in capillary endothelial cells. In the developing embryo, alpha 1 integrin subunit expression was discovered in addition to smooth muscle and capillary endothelial cells, transiently, in both central and peripheral nervous systems and in striated muscles, in association with laminin and collagen IV. alpha 1 integrin was practically absent from most epithelial tissues, including the liver, pancreas and kidney tubules, and was weakly expressed by tissues that were not associated with laminin and collagen IV. In the nervous system, alpha 1 integrin subunit expression occurred predominantly at the time of early neuronal differentiation. During skeletal muscle development, alpha 1 integrin was expressed on myogenic precursors, during myoblast migration, and in differentiating myotubes. alpha 1 integrin disappeared from skeletal muscle cells as they became contractile. In visceral and vascular smooth muscles, alpha 1 integrin appeared specifically during early smooth muscle cell differentiation and, later, was permanently expressed after cell maturation. These results indicate that (i) the expression pattern of alpha 1 integrin is consistent with a function as a laminin/collagen IV receptor; (ii) during avian development, expression of the alpha 1 integrin subunit is spatially and temporally regulated; (iii) during myogenesis and neurogenesis, expression of alpha 1 integrin is transient and correlates with cell migration and differentiation.

Hyaluronan-binding protein in endothelial cell morphogenesis

Previous studies from several laboratories have provided evidence that interaction of hyaluronan (HA) with the surface of endothelial cells may be involved in endothelial cell behavior. We have recently characterized a mAb, mAb IVd4, that recognizes and neutralizes HA-binding protein (HABP) from a wide variety of cell types from several different species (Banerjee, S. D., and B. P. Toole. 1991. Dev. Biol. 146:186-197). In this study we have found that mAb IVd4 inhibits migration of endothelial cells from a confluent monolayer after "wounding" of the monolayer. HA hexasaccharide, a fragment of HA with the same disaccharide composition as polymeric HA, also inhibits migration. In addition, both reagents inhibit morphogenesis of capillary-like tubules formed in gels consisting of type I collagen and basement membrane components. Immunocytology revealed that the antigen recognized by mAb IVd4 becomes localized to the cell membrane of migrating cells, including many of their lamellipodia. Treatment with high concentrations of HA hexamer causes loss of immunoreactivity from these structures. We conclude that HABP recognized by mAb IVd4 is involved in endothelial cell migration and tubule formation.

Adhesive interactions in angiogenesis and metastasis

A variety of adhesive interactions must take place between the tumor cell and the host vasculature in order to potentiate both tumor expansion and metastatic tumor spread. The study of tumor cell and blood vessel adhesive interactions becomes essential for our understanding of the malignant process, especially with regard to organ-specific tumor metastasis. In this article we will review recent progress made in our understanding of the nature of (i) receptor mediated adhesion of endothelial cells to extracellular matrix components and (ii) adhesion of tumor cells to endothelial adhesion molecules and to components of the subendothelial basement membrane.