Development of monoclonal antibodies to integrin receptors

Integrins are heterodimeric cell surface receptors composed of an alpha and a beta subunit. They are involved in homotopic and heterotopic cell adhesion and also function as receptors for extracellular matrix molecules such as collagen, fibronectin and laminin. The family to which an integrin belongs is defined by the presence of a particular beta subunit paired with a unique alpha subunit. In this chapter we describe methods to produce monoclonal antibodies to the family of integrin subunits characterized by beta1 and provide detailed instructions for the development of a monoclonal antibody to the alpha6 integrin receptor expressed by human prostate carcinoma cells (PC3 cells). Data are presented that correlate the functional capabilities of an antibody with its biochemical characterization.

The keratinocyte-derived cytokine IL-7 increases adhesion of the epidermal T cell subset to the skin basement membrane protein laminin-5

Human epidermis contains a subset of epidermal T cells that can mount an immune response by migrating through the skin and into the peripheral lymphnodes to proliferate before re-entering the epidermis. The cytokine IL-7 is shown to be localized to the basement membrane of normal human skin. Furthermore, culturing in the presence of IL-7 causes increased adhesion of epidermal T cells but not peripheral blood T cells to the major epidermal basement membrane protein, laminin-5. The mechanism for increased T cell adhesion to laminin-5 is due, at least in part, to an increase in the cell surface expression of the integrin alpha3beta1. Epidermal T cells cultured in IL-7 that are strongly adherent to laminin-5 are shown by flow cytometry to consist of a variety of subsets; therefore, the increase in cell adhesion is not due to an outgrowth of one T cell subset during culturing. We hypothesize that in vivo, exposure to IL-7 is required for epidermal T cell adhesion to laminin-5.

Interactions of type IV collagen and its domains with human mesangial cells

Type IV collagen (COL-IV) interacts with a variety of cell types. We present evidence that human mesangial cells (HMC) bind directly to COL-IV, its major triple helical domain, and the main non-collagenous, NC1 domain. A synthetic peptide, HEP-III, and its triple helical counterpart (THP-III), previously reported to be a heparin-binding domain, also promoted approximately 15% adhesion of HMC. HMC bound to solid-phase-immobilized, intact COL-IV (approximately 75%), isolated NC1 domain (approximately 15%), and a pepsin-derived triple helical fragment,which lacks Hep-III (approximately 65%). We further examined inhibition of HMC adhesion to COL-IV and its domains by using anti-integrin antibodies. Blocking monoclonal antibodies against the alpha2 integrin resulted in 70% inhibition of adhesion to COL-IV and 80% inhibition to HEP-III. Moderate inhibition was observed on the NC1 and triple helical fragments. Anti-alpha1 antibodies inhibited the binding of HMC to COL-IV, the NC1, and triple helical domains, but not to peptide HEP-III. Anti-beta1 antibodies inhibited almost completely (>95%) the adhesion to COL-IV, the NC1, and triple helical fragments; inhibition on HEP-III was approximately 30%. Affinity chromatography studies with solid-phase HEP-III and mesangial cell lysate also demonstrated the presence of integrin alpha2 beta1 along with alpha3 beta1. We conclude that alpha2 beta1 and alpha1 beta1 integrins mediate HMC adhesion to COL-IV. Peptide HEP-III is a major, specific site for alpha2 integrin-mediated binding of mesangial cells to COL-IV. Both the alpha1 beta1 and alpha2 beta1 integrins interact with the NC1 and triple helical fragments of COL-IV. Therefore, we demonstrate that several sites for integrin-mediated interactions exist on several collagenous and non-collagenous domains of COL-IV.

Adhesion of cultured human kidney mesangial cells to native entactin: role of integrin receptors

Entactin is an extracellular matrix glycoprotein which binds to laminin and is found in most renal basement membranes and in the glomerular mesangial matrix. In the present study, we have characterized specific integrin receptors on cultured human mesangial cells (CHMC) responsible for adhesion to native entactin. The integrin receptors alpha 2 beta 1, alpha 3 beta 1, alpha 5 beta 1, alpha v beta 3, alpha v beta 5, and alpha 6 complexed with either beta 1 or beta 4 could be immune precipitated from detergent extracts of metabolically labeled CHMC. Adhesion assays with inhibitory anti integrin monoclonal antibodies (mab) demonstrated that CHMC use both alpha v beta 3 and a beta 1-containing integrin to bind surfaces coated with native entactin. Optimal binding of CHMC to native entactin required the participation of cations. Using wild type and mutant recombinant entactin fragments, the binding site for the alpha v beta 3 receptor was localized to the RGD sequence on the rod or E domain of entactin. CHMC adhesion to mutant full length recombinant entactin ligands lacking the E domain RGD sequence confirmed the presence of ligand binding site(s) for beta 1 integrin receptor(s). Differences in CHMC binding characteristics to recombinant and full length entactin compared to native bovine basement membrane entactin were observed. This suggests that tertiary molecular structure may contribute to entactin ligand binding properties. Primary amino acid residue sequences and tertiary structure of entactin may play roles in forming functional cell attachment sites in native basement membrane entactin.

Mapping epitopes to distinct regions of the extracellular domain of endoglin using bacterially expressed recombinant fragments

Endoglin (CD105) is a homodimeric cell surface component of the TGF-beta 1 receptor complex, which is expressed at high levels on vascular endothelium and at lower levels on activated monocytes. It is also the target gene for the dominantly inherited vascular disorder hereditary hemorrhagic telangiectasia type 1. To date, each family has a distinct endoglin mutation, most of which generate premature stop codons. The purpose of the current study was to identify monoclonal antibodies capable of binding to normal and mutated forms of the protein. We generated stable transfectants of full-length human endoglin in murine fibroblasts and engineered and expressed in bacteria several fragments of the extracellular domain. Relatively pure polypeptides were recovered with good yield from inclusion bodies and were tested by ELISA and Western blot; 11 monoclonal antibodies were shown to react specifically with the endoglin transfectants. Ten of these monoclonal antibodies reacted with the bacterial fragments, and their epitopes were assigned to 3 distinct regions of endoglin. Monoclonal antibodies P3D1, TEC4 and GRE reacted with the N-terminal region of 204 amino acids encoded by exons 1 to 5. Monoclonal antibodies P4A4, 44G4, E-9, MAEND3 and PN-E2 all bound to a region of 54 amino acids encoded mostly by exon 7. Monoclonal antibodies CLE4 and RMAC8 reacted with the C-terminal region of the extracellular domain, coded for by exons 8 to 12. Knowing the localization of these epitopes will facilitate the structural and functional analysis of normal and mutated forms of endoglin.

Monoclonal antibody crosslinking of the alpha 4 or beta 1 integrin inhibits committed clonogenic hematopoietic progenitor proliferation

Adhesion receptors can serve as primary signal transduction molecules that convey information into cells that can affect cell proliferation and differentiation. Since hematopoietic progenitors adhere to marrow stroma and fibronectin via the alpha 4 beta 1 integrin and CD44, we examined the role of these receptors in the transfer of proliferation-regulatory signals to progenitors. Actively proliferating colony-forming cells (CFCs) present in cultured CD34+ cells were incubated with mouse monoclonal antibodies against the alpha 4, beta 1, or CD44 receptors and crosslinking was performed with a secondary goat-anti-mouse antibody. The effect on CFC proliferation was examined with a 3H thymidine suicide assay. Compared with controls (39 to 51% kill), crosslinking the alpha 4 or beta 1 integrins significantly reduced CFC proliferation (12 to 26% kill, p = 0.01), indicating that proliferation-inhibitory signals are transmitted through the VLA-4 integrin. Cytochalasin D, a compound that prevents actin polymerization, prevented not only alpha 4 receptor capping, but also the inhibition of CFC proliferation observed following alpha 4 crosslinking. However, crosslinking of the CD44 receptor with the antibodies Hermes-3 and 50B4, which inhibit adhesion of CFC to fibronectin, failed to cap the CD44 receptor in the majority of CD34+ cells. Furthermore, crosslinking of the CD44 receptor with these antibodies also failed to inhibit proliferation of CFCs. These studies demonstrate that adhesion receptor crosslinking of the alpha 4 beta 1 integrin, together with subsequent changes in F-actin polymerization, negatively regulates hematopoietic progenitor proliferation in a manner independent of the shape change associated with adhesion.

Distribution of integrin subunits in human diabetic kidneys

Integrins are cell-surface protein receptors that participate in cell adhesion to multiple extracellular matrix ligands, and consist of alpha and beta chain heterodimers. This study examined altered integrin distribution in diabetic nephropathy by investigating 12 human diabetic kidney biopsies, which were compared with normal human kidney. Diabetic nephropathy is characterized by mesangial expansion and progressive thickening of the glomerular basement membrane. Based on morphometric studies of mesangial expansion, diabetic nephropathy was determined to be moderate or severe. Three different patterns (P) of altered intensity of integrin staining were observed. In the mesangial integrin P, the intensity of integrin subunit staining of mesangial cells (alpha 1, alpha 2, alpha 3, beta 1, alpha V, alpha V beta 5) was increased in moderate diabetic nephropathy and further increased in severe diabetic nephropathy. In the epithelial integrin P, integrin subunits localized to epithelial cells (alpha V, beta 3, alpha V beta 3, alpha V beta 5) were increased to the same extent in moderate and severe diabetic nephropathy. In the endothelial integrin P, integrin subunits localized to endothelial cells (alpha 3, alpha 5, alpha 6, beta 1) were increased in moderate diabetic nephropathy but returned to normal kidney staining intensity in severe diabetic nephropathy. From these observations, it was concluded that there is significant alteration in the expression of integrin subunits in diabetic nephropathy that is related to the severity of diabetic mesangial expansion. Additionally, the spectrum of integrin subunit alteration appears to be unique to individual glomerular cell types. Given the role of integrins in cell-surface interactions with extracellular matrix components, abnormalities in the expression of these molecules may be important in the pathogenesis of diabetic nephropathy.

Expression of alpha 6 and beta 4 integrins in serous ovarian carcinoma correlates with expression of the basement membrane protein laminin

The surface of a normal ovary is covered by a monolayer of epithelial cells that rest on a basement membrane. The glycoprotein laminin is the major noncollagenous protein present in the basement membrane. The integrins alpha 1 beta 1, alpha 2 beta 1, alpha 3 beta 1, alpha 6 beta 1, and alpha 6 beta 4 serve as cell surface receptors for laminin. During the progression of serous ovarian carcinoma, tumor cells are frequently exfoliated from the surface of the ovary, thereby losing contact with the basement membrane. This study was designed to determine whether alterations in integrin expression may be associated with the malignant phenotype of the primary ovarian tumor and exfoliated ovarian carcinoma cells in the ascites fluid. By immunohistochemical staining, the entire surface of epithelial cells of normal ovaries stained positively for beta 1, alpha 2, and alpha 3 integrins, whereas only the basal surface of the epithelial cells, where they are in contact with laminin, stained positively for alpha 6 and beta 4. The entire surface of epithelial cells of solid tumors from patients with serous ovarian carcinoma stained positively for beta 1, alpha 2, and alpha 3 integrins. In most cases, no intact basement membrane surrounded the tumor nests, and staining for alpha 6 and beta 4 was irregular. When present, the basement membrane stained positively for laminin, and the basal surface of the epithelial cells stained positively for alpha 6 and beta 4. Ovarian carcinoma ascites cells exhibited a distinct phenotype, with a significant decrease in expression of the alpha 6 and beta 4 integrin subunits. As alpha 6 and beta 4 integrin subunits are present at the basal surface of many epithelial cells and serve as receptors for laminin, it is possible that ovarian carcinoma epithelial cells may be released from the basement membrane of the ovary due to their deficit of alpha 6 and beta 4 integrin subunits.

Human SY5Y neuroblastoma cell interactions with laminin isoforms: neurite outgrowth on laminin-5 is mediated by integrin alpha 3 beta 1

Laminin (Ln) isoforms may play important roles in neuronal development, particularly axon guidance, but neural receptors mediating interactions with Ln are not entirely understood. In this paper, we have compared the adhesive and process outgrowth activities of a human neuroblastoma cell line SY5Y on various laminin isoforms. Cell adhesion and process outgrowth were examined on murine Ln-1 (Englebreth-Holm-Swarm sarcoma laminin), human placental Ln-1 (human Ln-1[p]), human Ln-2 (merosin), human Ln-5 (kalinin/epiligrin/nicein), and human foreskin keratinocyte extracellular matrix extract (human HFK-ECM). Ln-5 was shown to evoke process outgrowth in amounts comparable to other Ln isoforms. Antibody perturbation experiments showed that adhesion and process outgrowth on murine Ln-1 was primarily mediated by the integrin alpha 1 beta 1, whereas adhesion and outgrowth on human Ln-5 and human HFK-ECM were mediated by alpha 3 beta 1. Adhesion to human Ln-1(p) and Ln-2 was not blocked by addition of anti-alpha 1 or anti-alpha 3 antibodies alone, but adhesion was partially perturbed when these antibodies were added in combination. Process outgrowth on human Ln-1(p) was blocked when either anti-alpha 3 or anti-beta 1 antibodies were added, indicating that alpha 3 beta 1 is the primary integrin heterodimer responsible for process extension on this substrate. These results demonstrate that Ln-5 and other Ln isoforms support comparable levels of adhesion and process outgrowth, but different integrin heterodimers, alone and in combination, are used by SY5Y cells to mediate responses.

REceptors in proximal tubular epithelial cells for tubulointerstitial nephritis antigen

Tubulointerstitial nephritis antigen (TIN-ag) is a novel basement membrane macromolecule that is involved in human antitubular-basement-membrane-mediated tubulointerstitial nephritis. The presence of antibodies to TIN-ag may result in an alteration of proximal tubule epithelial cell interaction with surrounding matrix and contribute to the pathogenesis of immune-mediated tubulointerstitial disease. To study the adhesive interactions between TIN-ag and proximal tubule epithelial cells and the macromolecules that mediate these interactions, an immortalized proximal tubular epithelial cell line from normal adult human kidney (HK-2) was used. Plastic-coated TIN-ag was able to promote adhesion of HK-2 cells in a concentration-dependent manner. the strength of the adhesive interaction was comparable to that of type IV collagen or laminin. to explore which members of the integrin family of cell surface receptors were involved in this interaction, we performed fluorescence activated cell sorting (FACS) analysis and adhesion-inhibition studies using monoclonal antibodies against various integrins. Both approaches suggested that integrins alpha 3 beta 1 and alpha 5 beta 3 are crucial for the adhesion of proximal tubule epithelial cells on TIN-ag, and that they are probably using independent domains of TIN-ag for their action. These data will help us to understand the interactions between proximal tubule epithelial cells and the underlying basement membrane, and will provide tubule clues to the pathogenesis of kidney tubular diseases at the molecular level.

Glucose-induced alteration of integrin expression and function in cultured human mesangial cells

Alteration in mesangial volume, due to an increase of the matrix surrounding mesangial cells, is a hallmark indicator of nephropathy in diabetes. Mesangial cells may also play a significant role in the development of nephropathy. Therefore, we examined the effect of glucose on the expression of integrins by cultured human mesangial cells and their ability to interact with collagen IV, a major component of the mesangial matrix. Human mesangial cells were grown in 5 and 25 mM glucose and their integrin profile was examined by immunoprecipitation and flow cytometry in each experimental condition. The results indicate that when mesangial cells were grown in 25 mM glucose, the expression of integrin subunit alpha 2, was increased, while the alpha 1 subunit was considerably decreased, as compared to cells grown in 5 mM glucose. Additionally, mesangial cells were tested for their ability to adhere to collagen IV in a solid-phase assay in the presence of neutralizing antibodies to integrin subunits. The results of these experiments indicate that both alpha 1 and alpha 2 complexed to beta 1 (alpha 2 beta 1 and alpha 1 beta 1) are major mesangial cell receptors for adhesion to collagen IV both in 5 and 25 mM glucose. The two receptors act in concert to mediate adhesion of mesangial cells to type IV collagen. When cell surface expression of the alpha 1 subunit in 25 mM glucose was reduced, the alpha 2 subunit was involved in adhesion to a greater extent than it was in 5 mM glucose. Immunoperoxidase histochemical studies localized both alpha 1 and alpha 2 integrin subunits in the mesangium of normal adult kidneys, suggesting that in vivo interaction with collagen IV could involve both of these receptors. These observations suggest that glucose-induced alterations in integrin expression may modify the ability of mesangial cells to interact with collagen IV.

Dermabrasive scar revision. Immunohistochemical and ultrastructural evaluation

BACKGROUND

Dermabrasion of facial scars 4-8 weeks after injury frequently completely eliminates visible evidence of scar formation. However, efforts to define the cellular and structural mechanisms by which this phenomenon occurs have been limited in their success.

OBJECTIVE

We investigated wound healing after dermabrasive scar revision.

METHODS

The surgical scars of seven patients were abraded 6-8 weeks after injury. Comparative electron microscopic and immunohistochemical studies were performed on punch biopsy specimens taken before and after the dermabrasion. Ultrastructural changes in the basement membrane components and dermal structures were evaluated. Monoclonal antibody staining techniques were used to observe the presence, location, and temporal expression of tenascin, epiligrin, cadherins, and integrin subunits.

RESULTS

We observed: 1) an increase in collagen bundle density and size with a tendency toward unidirectional orientation of fibers parallel to the epidermal surface, 2) an upregulation of tenascin expression throughout the papillary dermis, and 3) expression of alpha-6/beta-4 integrin subunit on the keratinocytes throughout the stratum spinosum.

CONCLUSIONS

The mechanisms by which dermabrasive scar revision alters the events of primary cicatrix formation include modification of extracellular ligand expression, thereby influencing epithelial cell-cell interaction, and reorganization of connective tissue.

Selective assembly of laminin variants by human carcinoma cells

BACKGROUND

The laminins are heterotrimeric basement membrane glycoproteins. Eight subunits that can be assembled into laminins have been characterized and are known as: A, B1, B2, S, M, K, B2t, B1k laminin chains. Although many neoplastic cells secrete laminins and some of them even assemble basement membranes, the pattern of production of various laminin subunits remains to be explored.

EXPERIMENTAL DESIGN

The expression of laminin was examined in several human carcinoma cells using a panel of specific cDNA probes as well as polyclonal and chain specific monoclonal antibodies. For this purpose a human laminin S chain 2 kb cDNA was isolated and characterized and used together with existing probes for laminin chains.

RESULTS

All carcinoma cell lines had a high level of expression of three light chains (B1, S and B2) mRNA. In contrast, the heavy chains of laminin, A and M, were expressed in negligible amounts as detected by Northern blotting and PCR. The only exception was the HU-1 lung adenocarcinoma cell line which expressed significant quantities of laminin M chain mRNA and lower levels of laminin A chain mRNA. The presence in the HU-1 cells of translated polypeptides was demonstrated by immunofluorescence staining. The cells contained both B1 and S chain laminin in the cell layer, but preferentially secreted the B1 chain into the culture supernatant as shown by Western blotting. The 300 to 400 kDa M chain immunoreactive band was found in laminin secreted into the culture medium of HU-1 cells. Immunoprecipitation of biosynthetically labeled proteins showed that the M chain was synthesized as a complex with B chains. Little or no A chain laminin was detected in the culture medium supernatant. HU-1 cells also synthesized the newly described laminin variant, epiligrin which was secreted into the medium. Thus, the HU-1 cells secreted two laminin variants: M-B1-B12 laminin and epiligrin into the culture medium. Immunostaining of HU-1 nude mice tumors showed that tumor basement membranes contained M, B1, and B2 laminin and epiligrin immunoreactivity but apparently no S chain.

CONCLUSIONS

All human carcinoma cell lines produced laminin chains B1, B2 and S, but no or little A or M. The only exception was the lung carcinoma cell line HU-1. Human HU-1 carcinoma cells in culture synthesize several homologous laminin chains and regulate the process of assembly, secretion and deposition of laminin variants into tumor basement membranes. These data indicate that the tumor cells vary among themselves with regards to laminin production and that some of them, like HU-1 may produce essentially all laminin chains simultaneously.

Chlamydia trachomatis does not bind to alpha beta 1 integrins to colonize a human endometrial epithelial cell line cultured in vitro

Chlamydia trachomatis is the leading cause of bacterially acquired sexually transmitted diseases in the United States and Europe. As an obligate intracellular pathogen, this bacterium must invade epithelial cells in order to survive and grow. Thus, multiple strategies probably exist for initial binding of chlamydiae to their target cells. Since a variety of bacteria have exploited integrins to colonize tissues, and a precedent existed for the involvement of extracellular matrix components in chlamydial attachment, this study first analyzed, by flow cytometry, integrins expressed by the human endometrial epithelial cell line HEC-1B. The genital cells were then exposed to monoclonal antibodies directed against those integrins and assayed for chlamydial attachment and inclusion development. Monoclonal antibodies bound to the alpha and/or beta 1 subunit of classic integrin receptors displayed by HEC-1B cells were not able to prevent colonization and infection of the epithelial cells by a genital isolate of C. trachomatis.

Activation of 72-kDa type IV collagenase/gelatinase by normal fibroblasts in collagen lattices is mediated by integrin receptors but is not related to lattice contraction

The matrix metalloproteinase 72-kDa type IV collagenase (also known as gelatinase A) is thought to be involved in both normal connective tissue remodeling and invasive pathological processes. Like other matrix metalloproteinases, 72-kDa type IV collagenase is secreted by fibroblast monolayers as an inactive proenzyme, but is unique among this enzyme family in that it is not activated by serine proteinases such as plasmin. However, when fibroblasts are cultured in a collagen lattice, a situation thought to better approximate in vivo conditions, we have invariably found much of the secreted 72-kDa type IV collagenase in its enzymatically active 62-kDa form. Although collagen lattice contraction appeared to be required for the activation of 72-kDa type IV collagenase, we have found that the process of contraction can be dissociated from proenzyme activation. Both cytochalasin D and alpha-methylmannoside completely blocked lattice contraction, but not proenzyme activation. Furthermore, the monoclonal antibody M-13, which is directed against the beta 1 integrin chain, blocked collagen lattice contraction but not 72-kDa type IV procollagenase activation. At concentrations significantly higher than required to block lattice contraction or cell adhesion to collagen, M-13 was able to inhibit proenzyme activation. A second monoclonal antibody to the beta 1 integrin, P5D2, had little effect on collagen lattice contraction at low concentrations, but could significantly inhibit the activation of 72-kDa type IV procollagenase. Antibodies to the integrin alpha 2 chain also inhibited proenzyme activation. These data show that the activation of 72-kDa type IV collagenase proenzyme, like collagen lattice contraction, is mediated by beta 1 integrin receptors, possibly alpha 2 beta 1. Although both anti-beta 1 antibodies used are directed to the same site on the integrin chain, the fact that each antibody preferentially blocks a different event, either lattice contraction or activation of 72-kDa type IV collagenase, suggests the existence of branch points in the receptor-mediated signal transduction pathway.

Interferon-alpha restores normal adhesion of chronic myelogenous leukemia hematopoietic progenitors to bone marrow stroma by correcting impaired beta 1 integrin receptor function

Treatment of chronic myelogenous leukemia (CML) with interferon-alpha frequently results in normalization of peripheral blood counts and, in up to 20% of patients, reestablishment of normal hematopoiesis. We hypothesize that interferon-alpha may restore normal adhesive interactions between CML progenitors and the bone marrow microenvironment and restore normal growth regulatory effects resulting from these progenitor-stroma interactions. We demonstrate that treatment with interferon-alpha induces a significant, dose-dependent increase in the adhesion of primitive long-term culture initiating cells and committed colony-forming cells (CFC) from CML bone marrow to normal stroma. Adhesion of CFC seen after interferon-alpha treatment could be inhibited by blocking antibodies directed at the alpha 4, alpha 5, and beta 1 integrins and vascular cell adhesion molecule, but not CD44 or intracellular adhesion molecule, suggesting that interferon-alpha induces normalization of progenitor-stroma interactions in CML. Because FACS analysis showed that the level of alpha 4, alpha 5, and beta 1 integrin expression after interferon-alpha treatment is unchanged, this suggests that interferon-alpha may restore normal beta 1 integrin function. Normalization of interactions between CML progenitors and the bone marrow microenvironment may then result in the restoration of normal regulation of CML progenitor proliferation, and explain, at least in part, the therapeutic efficacy of interferon-alpha in CML.

The decreased adhesion of Y79 retinoblastoma cells to extracellular matrix proteins is due to a deficit of integrin receptors

PURPOSE

This study was designed to determine whether the Y79 retinoblastoma cell line, a prototype for retinoblastoma cells, exhibits differential adhesive properties toward extracellular matrix (ECM)/basement membrane (BM) proteins compared to normal human retinal (NHR) cells. A second goal was to determine whether differences in adhesion are related to differences in the expression of integrin subunits.

METHODS

Y79 cells and NHR cells were tested for their ability to adhere and spread in microtiter wells adsorbed with the ECM/BM proteins laminin, fibronectin, and type IV collagen, as well as fragments of these proteins. The presence of cell surface integrins was determined by flow cytometry, using monoclonal antibodies (mAbs) against integrin subunits. For inhibition assays, cells were preincubated with mAbs against integrin subunits before the adhesion assays.

RESULTS

NHR cells adhered to and spread on laminin, fibronectin, and type IV collagen, whereas Y79 cells only adhered moderately to fibronectin. NHR cells expressed high levels of beta 1, alpha 1, alpha 2, alpha 3, alpha 4, alpha 5, alpha 6, and alpha v integrin subunits, and they used these integrin subunits to adhere to all three ECM proteins. In contrast, Y79 cells expressed high levels of only the alpha 4 and beta 1 integrin subunits, used to adhere to fibronectin.

CONCLUSIONS

Y79 cells have decreased adhesive capabilities toward ECM/BM proteins, compared to NHR cells. These differences can be attributed, in part, to their significantly lower levels of alpha 1, alpha 2, alpha 3, and alpha 5 integrin subunits, which serve as receptors for type IV collagen, laminin, and fibronectin.

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.

Expression and functional significance of alternatively spliced CS1 fibronectin in rheumatoid arthritis microvasculature

Expression of fibronectin (FN) isoforms containing CS1, a 25-amino acid sequence present within the alternatively spliced IIICS region of FN, has been analyzed in rheumatoid arthritis (RA) synovium. Unexpectedly, CS1-containing FN variants were exclusively found on endothelium but not extracellular matrix (ECM) of RA synovium. Lumenal expression of CS1 on RA endothelial cells, as observed by electron microscopy, correlated with inflammation in RA, since normal synovium expressed little CS1 without appreciable decrease in ECM FN. CS1 expression on human endothelial cells was further shown by FN mRNA analyses. In adhesion assays on frozen RA synovial sections, T lymphoblastoid cells expressing functionally activated alpha 4 beta 1 integrin specifically attached to the intravascular surface of RA endothelium. Binding was abrogated by both anti-alpha 4 integrin and CS1 peptides. Our observations suggest direct involvement of CS1-containing FN in recruitment of alpha 4 beta 1-expressing mononuclear leukocytes in synovitis, and provide basis for therapeutic intervention in RA.

Integrin alpha 4 beta 1 and glycoprotein IV (CD36) are expressed on circulating reticulocytes in sickle cell anemia

The abnormal adherence of red blood cells, especially circulating reticulocytes (erythrocyte precursors), to the endothelium is believed to contribute to vascular occlusion observed in patients with sickle cell disease. Although several plasma proteins including von Willebrand factor and fibronectin have been proposed to mediate this adhesion, the mechanism of sickle cell adhesion to the endothelium remains unknown. Using flow cytometry, we screened sickle red blood cells with monoclonal antibodies (MoAbs) against known adhesion receptors and detected integrin subunits alpha 4 and beta 1 and the nonintegrin glycoprotein IV on reticulocytes but not on erythrocytes. No reactivity was detected against integrin subunits alpha 2, alpha 3, alpha 5, alpha 6, alpha v, beta 2, beta 3, integrin alpha IIb beta 3, or the nonintegrin glycoprotein Ib. Immunoprecipitation of reticulocytes with either alpha 4- or beta 1-specific antibodies identified the alpha 4 beta 1 complex (alpha 4(70) and alpha 4(80) forms), a receptor for fibronectin and vascular cell adhesion molecule-1. An antibody against glycoprotein IV, a receptor reported to bind thrombospondin and collagen, immunoprecipitated an 88-kD protein consistent with its reported M(r). MoAbs against alpha 4 and glycoprotein IV bound to an average of 4,600 and 17,500 sites per reticulocyte, respectively. Identification of alpha 4 beta 1 and glycoprotein IV on reticulocytes suggests both plasma-dependent and independent mechanisms of reticulocyte adhesion to endothelium and exposed extracellular matrix.

Epiligrin, a component of epithelial basement membranes, is an adhesive ligand for alpha 3 beta 1 positive T lymphocytes

The cutaneous T cell lymphomas (CTCL), typified by mycosis fungoides, and several chronic T cell mediated dermatoses are characterized by the migration of T lymphocytes into the epidermis (epidermotropism). Alternatively, other types of cutaneous inflammation (malignant cutaneous B cell lymphoma, CBCL, or lymphocytoma cutis, non-malignant T or B cell type) do not show evidence of epidermotropism. This suggests that certain T lymphocyte subpopulations are able to interact with and penetrate the epidermal basement membrane. We show here that T lymphocytes derived from patients with CTCL (HUT 78 or HUT 102 cells), adhere to the detergent-insoluble extracellular matrix prepared from cultured basal keratinocytes (HFK ECM). HUT cell adhesion to HFK ECM was inhibitable with monoclonal antibodies (mAbs) directed to the alpha 3 (P1B5) or beta 1 (P4C10) integrin receptors, and could be up-regulated by an activating anti-beta 1 mAb (P4G11). An inhibitory mAb, P3H9-2, raised against keratinocytes identified epiligrin as the ligand for alpha 3 beta 1 positive T cells in HFK ECM. Interestingly, two lymphocyte populations could be clearly distinguished relative to expression of alpha 3 beta 1 by flow cytometry analysis. Lymphokine activated killer cells, alloreactive cytotoxic T cells and T cells derived from patients with CTCL expressed high levels of alpha 3 beta 1 (alpha 3 beta 1high). Non-adherent peripheral blood mononuclear cells, acute T or B lymphocytic leukemias, or non-cutaneous T or B lymphocyte cell lines expressed low levels of alpha 3 beta 1 (alpha 3 beta 1low). Resting PBL or alpha 3 beta 1low T or B cell lines did not adhere to HFK ECM or purified epiligrin. However, adhesion to epiligrin could be up-regulated by mAbs which activate the beta 1 subunit indicating that alpha 3 beta 1 activity is a function of expression and affinity. In skin derived from patients with graft-vs.-host (GVH) disease, experimentally induced delayed hypersensitivity reactions, and CTCL, the infiltrating T cells could be stained with mAbs to alpha 3 or beta 1 and were localized in close proximity to the epiligrin-containing basement membrane. Infiltrating lymphocytes in malignant cutaneous B disease (CBCL) did not express alpha 3 beta 1 by immunohistochemical techniques and did not associate with the epidermal basement membrane. The present findings clearly define a function for alpha 3 beta 1 in T cells and strongly suggest that alpha 3 beta 1 interaction with epiligrin may be involved in the pathogenesis of cutaneous inflammation.

Regulation of human B-cell precursor adhesion to bone marrow stromal cells by cytokines that exert opposing effects on the expression of vascular cell adhesion molecule-1 (VCAM-1)

Self-renewal and differentiation of B-cell precursors is dependent on interactions with bone marrow (BM) stromal cells and associated extracellular matrix. We have recently developed an interleukin (IL)-7-dependent, BM-derived stromal cell culture that supports the growth of normal human B-cell precursors. In the current study, we have characterized the constitutive expression, cytokine-regulated expression, and function of adhesion molecules on BM stromal cells that are critical for adhesion of B-cell precursors. Flow cytometric analysis showed that cultured adult BM stromal cells expressed higher constitutive levels of vascular cell adhesion molecule (VCAM)-1 than intercellular adhesion molecule (ICAM)-1 (CD54). IL-1 beta upregulated VCAM-1 and CD54 in a dose-dependent manner, whereas IL-4 upregulated VCAM-1, but had no effect on CD54. In contrast, transforming growth factor (TGF)-beta decreased the level of BM stromal cell VCAM-1. Using an assay to measure the adhesion of 51Cr-labeled B-cell precursors to BM stromal cells, we observed a direct correlation between cytokine-regulated levels of VCAM-1 and the capacity of stromal cells to support the adhesion of B-cell precursors. Blocking studies using a panel of monoclonal antibodies (MoAb) showed that adhesion of B-cell precursors to untreated and cytokine-treated (IL-1 beta, IL-4) BM stromal cells was mediated by very late antigen (VLA)-4 (CD49d/CD29) and VCAM-1. Adhesion of B-cell precursors could also be enhanced by direct stimulation with MoAb to the CD29 subunit. Our collective results indicate that B-cell precursor/BM stromal cell adhesion is mediated by a VLA-4-VCAM-1 interaction, which in turn can be regulated at the level of the BM stromal cell by cytokines that specifically increase or decrease cell surface VCAM-1.

Two novel monoclonal antibodies to fibronectin that recognize the Hep II and CS-1 regions respectively: their differential effect on lymphocyte adhesion

We have obtained two new mAbs to the carboxy-terminal region of fibronectin, namely P3D4 and P1F11, and have studied their binding sites and their ability to block lymphocyte adhesion to fibronectin. ELISA and Western blot analyses showed that P3D4 reacts with both fibronectin chains and both Hep II-containing fragments (58 kDa and 38 kDa). P1F11, raised against the synthetic peptide CS-1, reacted with the 38 kDa fragment and with a 190 kDa fragment derived from the A chain of fibronectin. P1F11 did not react with the 58 kDa fragment thus clearly establishing that 58 kDa comes from the B chain of fibronectin and lacks the CS-1 sequence. mAbs P3D4 and P1F11 were used to evaluate the contribution of the Hep II and CS-1 sites in cell attachment to fibronectin. P3D4 effectively inhibited B cell adhesion to 38 kDa, 58 kDa and fibronectin; P1F11 however produced only limited inhibition, suggesting that lymphocyte interaction with Hep II may modulate further binding to the CS-1 site.

Coordinate role for cell surface chondroitin sulfate proteoglycan and alpha 4 beta 1 integrin in mediating melanoma cell adhesion to fibronectin

Cellular recognition and adhesion to the extracellular matrix (ECM) has a complex molecular basis, involving both integrins and cell surface proteoglycans (PG). The current studies have used specific inhibitors of chondroitin sulfate proteoglycan (CSPG) synthesis along with anti-alpha 4 integrin subunit monoclonal antibodies to demonstrate that human melanoma cell adhesion to an A-chain derived, 33-kD carboxyl-terminal heparin binding fragment of human plasma fibronectin (FN) involves both cell surface CSPG and alpha 4 beta 1 integrin. A direct role for cell surface CSPG in mediating melanoma cell adhesion to this FN fragment was demonstrated by the identification of a cationic synthetic peptide, termed FN-C/H-III, within the fragment. FN-C/H-III is located close to the amino terminal end of the fragment, representing residues #1721-1736 of intact FN. FN-C/H-III binds CSPG directly, can inhibit CSPG binding to the fragment, and promotes melanoma cell adhesion by a CSPG-dependent, alpha 4 beta 1 integrin-independent mechanism. A scrambled version of FN-C/H-III does not inhibit CSPG binding or cell adhesion to the fragment or to FN-C/H-III, indicating that the primary sequence of FN-C/H-III is important for its biological properties. Previous studies have identified three other synthetic peptides from within this 33-kD FN fragment that promote cell adhesion by an arginyl-glycyl-aspartic acid (RGD) independent mechanism. Two of these synthetic peptides (FN-C/H-I and FN-C/H-II) bind heparin and promote cell adhesion, implicating cell surface PG in mediating cellular recognition of these two peptides. Additionally, a third synthetic peptide, CS1, is located in close proximity to FN-C/H-I and FN-C/H-II and it promotes cell adhesion by an alpha 4 beta 1 integrin-dependent mechanism. In contrast to FN-C/H-III, cellular recognition of these three peptides involved contributions from both CSPG and alpha 4 integrin subunits. Of particular importance are observations demonstrating that CS1-mediated melanoma cell adhesion could be inhibited by interfering with CSPG synthesis or expression. Since CS1 does not bind CSPG, the results suggest that CSPG may modify the function and/or activity of alpha 4 beta 1 integrin on the surface of human melanoma cells. Together, these results support a model in which the PG and integrin binding sites within the 33-kD fragment may act in concert to focus these two cell adhesion receptors into close proximity on the cell surface, thereby influencing initial cellular recognition events that contribute to melanoma cell adhesion on this fragment.

Requirement of the integrin beta 3 subunit for carcinoma cell spreading or migration on vitronectin and fibrinogen

FG human pancreatic carcinoma cells use integrin alpha v beta 5 as their primary vitronectin receptor since they fail to express integrin alpha v beta 3. These cells are unable to form focal contacts, spread, or migrate on vitronectin but readily do so on collagen in a beta 1 integrin-dependent manner. Transfection of FG cells with a cDNA encoding the integrin beta 3 subunit results in the surface expression of a functional integrin alpha v beta 3 heterodimer providing these cells with novel adhesive and biological properties. Specifically, FG cells expressing beta 3 acquire the capacity to attach and spread on vitronectin as well as fibrinogen with beta 3 localization to focal contacts. Moreover, these cells gain the capacity to migrate through a porous membrane in response to either vitronectin or fibrinogen. These results demonstrate that the beta 3 and beta 5 integrin subunits when associated with alpha v, promote distinct cellular responses to a vitronectin extracellular environment.

Activation-dependent recognition by hematopoietic cells of the LDV sequence in the V region of fibronectin

It has been shown that the alpha 4 beta 1 integrin is the lymphocyte receptor for the carboxy terminal cell-binding domain of fibronectin which comprises adhesion sites in Hep 2 and a high affinity site, CS-1, in the type III connecting segment or V (for variable) region. In the present studies, using a series of peptides derived from CS-1, we identify the tripeptide leu-asp-val (LDV), as the minimal peptide capable of supporting stable lymphocyte or melanoma cell adhesion. However, only cells which expressed an active form of the alpha 4 beta 1 complex were capable of attaching to and spreading on LDV peptide. On a molar basis, LDV minimal peptides were either not active or 10-20 times less active than intact CS-1 in promoting the adhesion of lymphocytes expressing the resting form of the receptor. In cells which express the high avidity form of the receptor, LDV and CS-1 were equally effective in promoting cell adhesion and spreading. The avidity of the alpha 4 beta 1 complex could be altered with mAbs to beta 1 which specifically activate beta 1 dependent function. The high avidity form of the alpha 4 beta 1 complex could be induced on U937 cells, T, and B lymphoblastoid cell lines, or PHA-stimulated T cell blasts. Resting PBL could not be induced to bind LDV peptide conjugates by activating antibodies to beta 1 implying that two signals are required for LDV recognition by T cells. In conclusion, these data show clearly that the minimal peptide for the alpha 4 beta 1 complex in CS-1 is the LDV sequence. Although numerous cell populations can interact with intact CS-1 only cells which express an active alpha 4 beta 1 complex can bind the LDV sequence. This implies that cell interaction with the carboxy terminal cell-binding domain of fibronectin can be regulated at several levels: (a) alpha 4 beta 1 expression; (b) activation of the alpha 4 beta 1 complex; and (c) alternate splicing of CS-1 into V+ isoforms of fibronectin.

B lymphocyte fibronectin receptors: expression and utilization

Lymphocytes adhere to fibronectin (FN) via multiple receptors of the VLA (beta 1, CD29 integrin) family. The cellular requirement for the variety of FN receptors (FNR) which have been described is unclear, but they may be associated with differential signalling processes, cooperative effects which may stabilize cellular attachment, or cell homing and retention processes. The present study was undertaken to examine the FN adherence properties and receptor utilization patterns of human B cells. Of ten B-cell culture lines which were studied, six demonstrated a significant adherence to FN. Among these, four employed alpha 4 beta 1, (CD49d/29) and two employed alpha 4 beta 1/alpha 5 beta 1, (CD49d/29, CD49e/29). There was no apparent correlation between the differentiation status of the lines and their FNR utilization patterns. Furthermore, expression of FNR alone was not sufficient to confer FN binding potential. Freshly isolated tonsil B cells did not display significant adherence to FN. Following stimulation, a marked increase in VLA antigens was observed, and the capacity to attach to FN-coated surfaces was co-acquired. Analysis of the induced bulk B-cell population demonstrated that both alpha 4 beta 1 and alpha 5 beta 1 were used for adherence. These results clearly indicate that activated B cells, similar to T cells, may express and utilize alpha 5 beta 1 as a FNR.

Integrins alpha v beta 3 and alpha v beta 5 contribute to cell attachment to vitronectin but differentially distribute on the cell surface

We investigated the role of the integrins alpha v beta 3 and alpha v beta 5 in mediating vitronectin adhesion of three phenotypically distinct cell types. M21 human melanoma cells and H2981 lung carcinoma cells use both alpha v-containing integrins in adhering to vitronectin while UCLA-P3 lung carcinoma cells adhere exclusively with alpha v beta 5. Specifically, monoclonal antibodies directed to functional epitopes on both receptors were required to block adhesion of M21 or H2981 cells while adhesion of UCLA-P3 cells to vitronectin could be blocked with a monoclonal antibody to alpha v beta 5. Although both receptors are involved in M21 and H2981 cell adhesion to vitronectin, only alpha v beta 3 can be detected in focal contacts, colocalizing with vinculin, talin, and the ends of actin filaments, while alpha v beta 5 shows a distinct, nonfocal contact, distribution on the cell surface. These results provide the first evidence that two homologous integrins that recognize the same ligand distribute differentially on the cell surface.

Phorbol ester-induced differentiation of U937 cells enhances attachment to fibronectin and distinctly modulates the alpha 5 beta 1 and alpha 4 beta 1 fibronectin receptors

Monocyte interaction with fibronectin (Fn) involves specific cell surface receptors and results in cell attachment and differentiation. We have studied the regulation of these receptors using the promonocytic cell line U937 and its PMA-induced differentiation as a model. We recently reported that U937 cells interact with two sites in Fn, RGD and CS-1, via two independent receptors (O. C. Ferreira, A. Garcia-Pardo, and C. Bianco (1990) J. Exp. Med. 171, 351). In this study we have determined the effects of PMA on the interaction of U937 cells with both sites in Fn. PMA-U937 cells showed an enhanced attachment to Fn and to an RGD-containing 80-kDa Fn fragment. This enhancement paralleled a two- to threefold increase in the surface expression of the RGD-dependent receptor alpha 5 beta 1. An anti-alpha 5 beta 1 mAb completely inhibited cell adhesion to Fn and to the 80-kDa fragment. alpha 5 beta 1 receptors from untreated and PMA-treated U937 cells were isolated on 80-kDa-Sepharose columns and shown to contain a similar complex of 152/125-kDa proteins, although proteins from PMA-treated cells had slightly faster mobility on SDS-gels. In contrast, the total number of PMA-U937 cells adhering to a 38-kDa Fn fragment (containing the CS-1 site) was lower when compared to that of untreated cells. This decrease was accompanied by a 50% loss of cell surface alpha 4 beta 1, the specific receptor for CS-1. Our results indicate that differentiation of U937 cells enhances adhesion to Fn primarily by up-regulating the alpha 5 beta 1 Fn receptor. PMA also induces a down-regulation of alpha 4 beta 1, suggesting that these two integrins play different roles during monocyte differentiation.

Distinct functions for integrins alpha 3 beta 1 in focal adhesions and alpha 6 beta 4/bullous pemphigoid antigen in a new stable anchoring contact (SAC) of keratinocytes: relation to hemidesmosomes

Basal cells of stratified epidermis are anchored to the basement membrane zone (BMZ) of skin via hemidesmosomes. We previously identified integrin alpha 3 beta 1, in focal adhesions (FAs), of cultured human keratinocytes (HFKs) as a mediator of HFK adhesion to secreted BMZ-like extracellular matrix (ECM; Carter, W.G., E.A. Wayner, T.S. Bouchard, and P. Kaur. 1990. J. Cell Biol. 110: 1387-1404). Here, we have examined the relation of integrins alpha 6 beta 4 and alpha 3 beta 1, to bullous pemphigoid antigen (BPA), a component of hemidesmosomes. We conclude that alpha 6 beta 4 in HFKs localizes in a new stable anchoring contact (SAC) that cooperates with alpha 3 beta 1-FAs to mediate adhesion to ECM, based on the following. (a) Comparison of secreted ECM, with exogenous laminin, fibronectin and collagen identified ECM as the preferred ligand for HFK adhesion and spreading and for formation of both alpha 6 beta 4-SACs and alpha 3 beta 1-FAs. (b) Inhibition of HFK adhesion with combined anti-alpha 3 beta 1 (P1B5) and anti-alpha 6 beta 4 (GoH3) antibodies indicated that both receptors were functional in adhesion to ECM while alpha 3 beta 1 played a dominant role in spreading. (c) alpha 6 beta 4 colocalized with BPA in SACs that were proximal to but excluded from FAs. Both alpha 6 beta 4-SACs and alpha 3 beta 1-FAs were in contact with the adhesion surface as indicated by antibody exclusion and interference reflection microscopy. (d) In contrast to alpha 3 beta 1-FAs, alpha 6 beta 4-SACs were present only in nonmotile cells, not associated with stress fibers, and were relatively stable to detergents and urea, suggesting a nonmotile, or anchoring function for SACs and motility functions for alpha 3 beta 1-FAs. (e) alpha 6 beta 4 formed a detergent-insoluble complex with exogenous ECM in an affinity isolation procedure, confirming the ability of an unidentified ECM ligand to interact with alpha 6 beta 4. (f) We suggest that alpha 6 beta 4/BPA-SACs in culture restrict migration of HFKs on ECM while alpha 3 beta 1-FAs form dynamic adhesions in spreading and migrating cells. alpha 6 beta 4/BPA-SACs in culture bear functional and compositional similarities to hemidesmosomes in skin.

Identification of surface proteins mediating adherence of CD11/CD18-deficient lymphoblastoid cells to cultured human endothelium

Patients with the severe form of leukocyte adhesion deficiency syndrome do not express the CD11/CD18 adhesion complex on any of their leukocytes. Nevertheless, their lymphocytes, unlike their phagocytes, emigrate to extravascular sites of inflammation, demonstrating that surface proteins other than CD11/CD18 can mediate lymphocyte adherence to endothelium. Using a B-lymphoblastoid cell line (B-LCL) established from a CD11/CD18-deficient patient and cultured human umbilical vein endothelial cells (HEC), we investigated the CD11/CD18-independent mechanism(s) of lymphocyte adherence to endothelium. Monoclonal antibodies directed to the alpha 4 polypeptide (CD49d) and the beta 1 polypeptide (CD29) of the lymphocyte VLA-4 integrin receptor (CD49d/CD29), and to vascular cell adhesion molecule-1 (VCAM-1) on the endothelial cell significantly inhibited the adherence of the CD11/CD18-deficient B-LCL to untreated HEC and to HEC treated with recombinant human tumor necrosis factor-alpha. We suggest that the interaction of the lymphocyte receptor VLA-4 with the endothelial ligand VCAM-1 induced by cytokines at sites of inflammation or immune reaction represents a CD11/CD18-independent pathway of lymphocyte emigration.

Human B lymphocytes define an alternative mechanism of adhesion to fibronectin. The interaction of the alpha 4 beta 1 integrin with the LHGPEILDVPST sequence of the type III connecting segment is sufficient to promote cell attachment

In this report we have studied the mechanism of human B lymphocyte adhesion to fibronectin and to proteolytic fragments of this protein. B cells adhered to fibronectin and to a 38-kDa fragment, derived from the A chain, containing the Hep II domain and most of the type III connecting segment, IIICS, of fibronectin. Cells did not bind to an 80-kDa fragment containing the RGD adhesive sequence of fibronectin. Attachment to fibronectin or to the 38-kDa fragment was not affected by the 80-kDa fragment, the GRGDSPC synthetic peptide, or by a mAb specific for the alpha chain of the RGD-dependent fibronectin receptor, alpha 5 beta 1. However, B cell adhesion to fibronectin was inhibited by the synthetic peptides CS-1, comprising the first 25 amino acids of IIICS and B12, containing the sequence LHGPEILDVPST of CS-1 (residues 14-25). Moreover, this sequence was shown to be sufficient to induce stable cell adhesion when coated on plastic surfaces. A mAb specific for the alpha-subunit of the alpha 4 beta 1 integrin, completely inhibited B cell attachment to B12, CS-1, 38 kDa, and fibronectin coated substrata. These data clearly indicate that adhesion of B lymphocytes to fibronectin is exclusively mediated by the interaction of alpha 4 beta 1 with residues 14-25 of the IIICS region in fibronectin. Therefore this interaction constitutes an alternative pathway of adhesion to fibronectin, independent of RGD and alpha 5 beta 1.

Human B lymphocytes define an alternative mechanism of adhesion to fibronectin. The interaction of the alpha 4 beta 1 integrin with the LHGPEILDVPST sequence of the type III connecting segment is sufficient to promote cell attachment

In this report we have studied the mechanism of human B lymphocyte adhesion to fibronectin and to proteolytic fragments of this protein. B cells adhered to fibronectin and to a 38-kDa fragment, derived from the A chain, containing the Hep II domain and most of the type III connecting segment, IIICS, of fibronectin. Cells did not bind to an 80-kDa fragment containing the RGD adhesive sequence of fibronectin. Attachment to fibronectin or to the 38-kDa fragment was not affected by the 80-kDa fragment, the GRGDSPC synthetic peptide, or by a mAb specific for the alpha chain of the RGD-dependent fibronectin receptor, alpha 5 beta 1. However, B cell adhesion to fibronectin was inhibited by the synthetic peptides CS-1, comprising the first 25 amino acids of IIICS and B12, containing the sequence LHGPEILDVPST of CS-1 (residues 14-25). Moreover, this sequence was shown to be sufficient to induce stable cell adhesion when coated on plastic surfaces. A mAb specific for the alpha-subunit of the alpha 4 beta 1 integrin, completely inhibited B cell attachment to B12, CS-1, 38 kDa, and fibronectin coated substrata. These data clearly indicate that adhesion of B lymphocytes to fibronectin is exclusively mediated by the interaction of alpha 4 beta 1 with residues 14-25 of the IIICS region in fibronectin. Therefore this interaction constitutes an alternative pathway of adhesion to fibronectin, independent of RGD and alpha 5 beta 1.

The role of integrins alpha 2 beta 1 and alpha 3 beta 1 in cell-cell and cell-substrate adhesion of human epidermal cells

We have examined cultures of neonatal human foreskin keratinocytes (HFKs) to determine the ligands and functions of integrins alpha 2 beta 1, and alpha 3 beta 1 in normal epidermal stratification and adhesion to the basement membrane zone (BMZ) in skin. We used three assay systems, HFK adhesion to purified extracellular matrix (ECM) ligands and endogenous secreted ECM, localization of integrins in focal adhesions (FAs), and inhibition of HFK adhesion with mAbs to conclude: (a) A new anti-alpha 3 beta 1 mAb, P1F2, localized alpha 3 beta 1 in FAs on purified laminin greater than fibronectin/collagen, indicating that laminin was the best exogeneous ligand for alpha 3 beta 1. However, in long term culture, alpha 3 beta 1 preferentially codistributed in and around FAs with secreted laminin-containing ECM, in preference to exogenous laminin. Anti-alpha 3 beta 1, mAb P1B5, detached prolonged cultures of HFKs from culture plates or from partially purified HFK ECM indicating that interaction of alpha 3 beta 1 with the secreted laminin-containing ECM was primarily responsible for HFK adhesion in long term culture. (b) In FA assays, alpha 2 beta 1 localized in FAs conincident with initial HFK adhesion to exogenous collagen, but not laminin or fibronectin. However, in inhibition assays, anti-alpha 2 beta 1 inhibited initial HFK adhesion to both laminin and collagen. Thus, alpha 2 beta 1 contributes to initial HFK adhesion to laminin but alpha 3 beta 1 is primarily responsible for long-term HFK adhesion to secreted laminin-containing ECM. (c) Serum or Ca2(+)-induced aggregation of HFKs resulted in relocation of alpha 2 beta 1 and alpha 3 beta 1 from FAs to cell-cell contacts. Further, cell-cell adhesion was inhibited by anti-alpha 3 beta 1 (P1B5) and a new anti-beta 1 mAb (P4C10). Thus, interaction of alpha 3 beta 1 with either ECM or membrane coreceptors at cell-cell contacts may facilitate Ca2(+)-induced HFK aggregation. (d) It is suggested that interaction of alpha 3 beta 1 with a secreted, laminin-containing ECM in cultured HFKs, duplicates the role of alpha 3 beta 1 in basal cell adhesion to the BMZ in skin. Further, relocation of alpha 2 beta 1 and alpha 3 beta 1 to cell-cell contacts may result in detachment of cells from the BMZ and increased cell-cell adhesion in the suprabasal cells contributing to stratification of the skin.

Affinity chromatographic isolation of the melanoma adhesion receptor for the IIICS region of fibronectin and its identification as the integrin alpha 4 beta 1

Eukaryotic cells adhere to at least two different regions of the fibronectin molecule: a central domain present in all fibronectin isoforms, and the type III connecting segment domain (IIICS), the expression of which is controlled by complex alternative splicing of precursor mRNA. Using affinity chromatography on a matrix containing a synthetic peptide ligand (CS1) representing the strongest active site within the IIICS, we have isolated the human melanoma cell receptor recognizing this region of fibronectin. The receptor is a complex of two polypeptides with subunit molecular masses of 145 and 125 kDa. This heterodimeric structure resembles that of receptors for other extracellular matrix proteins. Immunological analysis with specific antibodies identified these polypeptides as the integrin subunits alpha 4 and beta 1. In addition, antifunctional monoclonal antibodies directed against either alpha 4 or beta 1, but not against other integrin subunits, were potent inhibitors of CS1-mediated melanoma cell spreading. Furthermore, when the function of the central cell-binding domain was blocked, anti-alpha 4 and anti-beta 1 antibodies abolished spreading of A375-M cells on fibronectin, indicating that alpha 4 beta 1 is an authentic fibronectin receptor. Taken together, these results identify the human fibronectin IIICS receptor as the integrin heterodimer alpha 4 beta 1.

Identification and characterization of the T lymphocyte adhesion receptor for an alternative cell attachment domain (CS-1) in plasma fibronectin

Using mAb technology (Wayner, E. A., W. G. Carter, R. Piotrowicz, and T. J. Kunicki. 1988. J. Cell Biol. 107:1881-1891), we have identified a new fibronectin receptor that is identical to the integrin receptor alpha 4 beta 1. mAbs P3E3, P4C2, and P4G9 recognized epitopes on the alpha 4 subunit and completely inhibited the adhesion of peripheral blood and cultured T lymphocytes to a 38-kD tryptic fragment of plasma fibronectin containing the carboxy-terminal Heparin II domain and part of the type III connecting segment (IIICS). The ligand in IIICS for alpha 4 beta 1 was the CS-1 region previously defined as an adhesion site for melanoma cells. The functionally defined mAbs to alpha 4 partially inhibited T lymphocyte adhesion to intact plasma fibronectin and had no effect on their attachment to an 80-kD tryptic fragment containing the RGD (arg-gly-asp) adhesion sequence. mAbs (P1D6 and P1F8) to the previously described fibronectin receptor, alpha 5 beta 1, completely inhibited T lymphocyte adhesion to the 80-kD fragment but had no effect on their attachment to the 38-kD fragment or to CS-1. Both alpha 4 beta 1 and alpha 5 beta 1 localized to focal adhesions when fibroblasts that express these receptors were grown on fibronectin-coated surfaces. These findings demonstrated a specific interaction of both receptors with fibronectin at focal contacts. In conclusion, these findings show clearly that cultured T lymphocytes use two independent receptors during attachment to fibronectin and that (a) alpha 5 beta 1 is the receptor for the RGD containing cell adhesion domain, and (b) alpha 4 beta 1 is the receptor for a carboxy-terminal cell adhesion region containing the Heparin II and IIICS domains. Furthermore, these data also show that T lymphocytes express a clear preference for a region of molecular heterogeneity in IIICS (CS-1) generated by alternative splicing of fibronectin pre-mRNA and that alpha 4 beta 1 is the receptor for this adhesion site.

Mechanism of fibronectin-mediated cell migration: dependence or independence of cell migration susceptibility on RGDS-directed receptor (integrin)

Cell migration on fibronectin (FN)-coated substrata was studied using 10 cell lines, of which only 2 showed clear enhancement and 1 showed marginal enhancement of cell migration. The migration of the other 7 cell lines was not affected on FN-coated substrata, although they all showed FN-dependent cell adhesion. The migration-enhancing activity of FN was found in the fragment including the cell-adhesion and Hep-2 domains, but not other domains (Hep-1/Fib-1, Gel, Fib-2). No difference in the migration-enhancing effect was seen among FNs from plasma, fibroblasts, or transformed cells. FN-dependent cell migration was inhibited by polyclonal antibodies directed to the C-terminal half region including the cell binding domain, but not by antibodies directed to five other domains. Since these results indicated that FN-mediated cell migration could be controlled by the cell-adhesion domain of FN and its receptor, studies were then focused on the effect of antibodies directed to receptors for FN and collagen, and on the effect of tetrapeptide sequences recognized by these receptors. It was found that (i) cell migration on FN-coated surfaces was specifically inhibited by anti-FN receptor antibody P1F8 but not by anticollagen receptor antibody P1H5; (ii) the migration was strongly inhibited by Arg-Gly-Asp-Ser but not by other oligopeptide sequences. However, the majority of those cell lines not susceptible to FN-dependent cell migration were characterized by having FN receptors and the ability to adhere on FN-coated matrix. Based on these findings, it was concluded that FN-dependent cell migration shares the same recognition mechanism as FN-dependent cell adhesion, but that the majority of cell lines not exhibiting FN-dependent migration still show FN-dependent cell adhesion and express the FN receptor (integrin); i.e., cell migration and adhesion involve the same receptor and the same FN loci, but migration is controlled by still-unidentified cellular factors which determine the susceptibility of the cell to the dynamic function of the FN receptor (integrin) unit.

Isolation and DNA sequence of a cDNA clone encoding a lymphocyte adhesion receptor for high endothelium

The migration of lymphocytes from the bloodstream into the secondary lymphoid organs, which is necessary for a successful immune response, occurs primarily within postcapillary venules that are characterized by high-walled endothelial cells. Lymphocyte adhesion to and extravasation at these sites is associated with the expression of specific lymphoid receptors for this specialized venule endothelium. We report here the molecular cloning from a baboon lymphoid cell line of a cDNA that encodes an adhesion receptor for HEV. The 362-amino acid protein encoded by this cDNA is not present in any of the data bases examined. The mature protein, resulting from the cleavage of a putative 20-amino acid signal peptide, has a calculated molecular mass of only 37 kDa, indicating that the 90-kDa cell surface protein is highly modified. The 342 amino acids, which lack any repeated sequences of significant length, encompass an extracellular domain (250 amino acids), a putative transmembrane domain (20 amino acids), and a cytoplasmic domain (72 amino acids).

The fibronectin receptor is organized by extracellular matrix fibronectin: implications for oncogenic transformation and for cell recognition of fibronectin matrices

Cells interact with extracellular fibronectin (FN) via adhesive fibronectin receptors (FNRs) that are members of the very late antigens (VLAs) subgroup of the integrin family. In stationary fibroblasts, the FNR is highly organized and distributed identically to extracellular FN fibrils. However, in highly migratory neural crest cells and embryonic somatic fibroblasts, this organization is lost and the FNR appears diffuse. Similarly, oncogenic transformation typically leads to disorganization of the FN receptor and loss of matrix FN. Two models can account for these observations. First, the FN matrix may organize the FN receptor at extracellular matrix contacts on the cell surface. Motile cells not depositing FN matrices thus lack organized receptors. Alternatively, as the FNR is required for optimal FN matrix assembly, (McDonald, J. A., B. J. Quade, T. J. Broekelmann, R. LaChance, K. Forseman, K. Hasegawa, and S. Akiyama. 1987. J. Biol. Chem. 272:2957-2967; Roman, J. R. M. LaChance, T. J. Broekelmann, C. J. R. Kennedy, E. A. Wayner, W. G. Carter, J. A. McDonald. 1989. J. Cell Biol. 108:2529-2543) and has putative cytoskeletal links, it could be organized from within the cell helping to position newly forming FN fibrils. To study this question, we developed peptide antibodies specifically recognizing the alpha 5 subunit of the FNR. Using these antibodies, we examined the organization of FN and of the FNR in normal, matrix assembly inhibited, and SV40-transformed human fibroblasts. On FN-coated substrates, the FNR is found in focal contacts rather than diffusely on the basal cell surface, suggesting FNR interaction with intracellular components. However, when FN fibrils are deposited, the FNR is co-distributed with these fibrils. Preventing FN matrix assembly prevents organization of the FNR. Moreover, when fibroblasts with well established FN matrices and co-distributed FNR are incubated briefly with monoclonal antibodies that block FNR binding to FN, the FNR is no longer co-distributed with the FN matrix. Thus, the FN receptor is organized in fibrils on the cell surface in response to extracellular FN. Because exogenous FN restores a FN matrix and receptor organization to SV40-transformed cells, the diffuse FN receptor phenotype appears to be related to loss of the FN matrix rather than to impaired FNR function. These results explain diffusely distributed FNRs in migratory neural crest and embryonic fibroblasts lacking well organized FN matrices and emphasize the existence of separate but related systems controlling FN deposition and recognition by receptor-armed cells.

Structural homology between lymphocyte receptors for high endothelium and class III extracellular matrix receptor

We have identified extensive structural homology between one type of heterotypic adhesion receptor (HAR) involved in lymphocyte interactions with high endothelium in lymphoid organs and a collagen-binding protein, termed class III extracellular matrix receptor (ECMRIII), expressed on most nucleated cell types. Both receptors have been described as heterogeneous 90-kDa transmembrane glycoproteins, referred to here as gp90. Monoclonal anti-HAR antibodies, Hermes-1 and Hutch-1, and monoclonal anti-ECMRIII antibodies, P1G12 and P3H9, were utilized to compare the two receptors. (i) All these monoclonal antibodies immunoprecipitated major gp90 components as well as uncharacterized additional higher molecular mass antigens of 120-200 kDa in human and macaque fibroblasts and peripheral blood mononuclear cells. (ii) Competitive binding analyses with the antibodies identified distinct epitopes present on gp90. (iii) Enzymatic and chemical digestions generated identical peptide fragments from all the antigens in human and macaque fibroblasts and peripheral blood mononuclear cells. (iv) Sequential immunoprecipitation with P1G12 followed by the other monoclonal antibodies indicated that all gp90 species reactive with Hermes-1 and Hutch-1 also expressed the P1G12 defined epitope. In reciprocal experiments, Hermes-1 and Hutch-1 immunoprecipitation did not completely remove all P1G12-reactive gp90 from cellular extracts. One inference from these data would be that gp90 is serologically heterogeneous, encompassing HARs as a major subset of this broadly expressed class of molecules.

The membrane glycoprotein Ia-IIa (VLA-2) complex mediates the Mg++-dependent adhesion of platelets to collagen

We have purified the platelet membrane glycoprotein Ia-IIa complex by detergent solubilization and sequential affinity chromatography on Concanavalin A-Sepharose and collagen-Sepharose. The complex, which is identical to the VLA-2 complex of lymphocytes and other cells and contains subunits of 160 and 130 kD on SDS-PAGE, was labeled with 125I and incorporated into phosphatidyl choline liposomes. The liposomes, like intact platelets, adhered to collagenous substrates in an Mg++-dependent manner with a K'a(Mg++) of 3.5 mM. Little adhesion of the liposomes to collagen occurred when Mg++ was replaced by Ca++ or EDTA. Calcium ions inhibited the Mg++-dependent adhesion with a K'i(Ca++) of 5.5 mM. Liposomes containing the Ia-IIa complex adhered to substrates composed of types I, II, III, and IV collagen, but did not effectively adhere to substrates composed of type V collagen or gelatin. Adhesion to collagen was specific. The liposomes did not adhere to fibronectin, vitronectin, laminin, thrombospondin, fibrinogen, or von Willebrand factor substrates. The monoclonal antibody P1H5, which specifically immunoprecipitated the Ia-IIa complex, also specifically inhibited the Mg++-dependent adhesion of both platelets and Ia-IIa-containing liposomes to collagen substrates. These findings provide additional evidence that the platelet membrane Ia-IIa complex is the mediator of Mg++-dependent platelet adhesion to collagen and suggest that the VLA-2 complex may also function as an Mg++-dependent collagen receptor in other cells.

Effects of interferon-gamma on expression of cell surface receptors for collagen and deposition of newly synthesized collagen by cultured human lung fibroblasts

We used cultured human diploid lung fibroblasts as a model system to examine the effects of recombinant IFN-gamma on synthesis of collagen, matrix deposition of newly synthesized collagen, and the expression of cell surface receptors for collagen. Using [3H]proline-labeled cells we found that IFN-gamma resulted in dose-dependent inhibition of fibroblast collagen synthesis. Pulse-chase experiments to analyze compartmentalization of newly synthesized collagen showed that the decrease in collagen synthesis was confined to the soluble pool of procollagen in the medium, while extracellular matrix associated collagen was not changed, indicating that a larger proportion of newly synthesized collagen was deposited into the matrix in IFN-gamma exposed fibroblasts (34.2 vs. 25.3%). This increase in the efficiency of collagen matrix deposition was associated with enhanced expression of a cell surface receptor for collagen as detected by indirect immunofluorescence labeling and analysis by flow cytometry. Fibroblasts (IMR-90) cultured in the presence of IFN-gamma (1,000 U/ml) exhibited a twofold increase in mean linear fluorescence intensity compared with cells cultured under control conditions. The distribution of log fluorescence intensity in both control and IFN-gamma exposed cells was normally distributed about the mean, indicating that discrete subpopulations with respect to receptor expression were not present. Increased fluorescence intensity and log normal distribution of fluorescence intensity also were identified in IFN-gamma-treated lung fibroblasts from a normal adult individual and two strains obtained from patients with pulmonary fibrosis. These results indicate that IFN-gamma modulates fibroblast collagen matrix deposition as well as collagen synthesis. The associated increase in collagen receptors suggests that cytokine-mediated modulation of the cell surface maybe a contributing factor in regulation of fibroblast collagen accumulation in the extracellular matrix or in cellular interaction with collagen-containing matrix. Such an effect could modulate the interaction of fibroblasts with extracellular matrix at sites of inflammation and play an important role in the remodeling of matrix during repair from tissue injury.

The function of multiple extracellular matrix receptors in mediating cell adhesion to extracellular matrix: preparation of monoclonal antibodies to the fibronectin receptor that specifically inhibit cell adhesion to fibronectin and react with platelet glycoproteins Ic-IIa

We have identified monoclonal antibodies that inhibit human cell adhesion to collagen (P1H5), fibronectin (P1F8 or P1D6), and collagen and fibronectin (P1B5) that react with a family of structurally similar glycoproteins referred to as extracellular matrix receptors (ECMRs) II, VI, and I, respectively. Each member of this family contains a unique alpha subunit, recognized by the antibodies, and a common beta subunit, each of approximately 140 kD. We show here that ECMR VI is identical to the fibronectin receptor (FNR), very late antigen (VLA) 5, and platelet glycoproteins Ic-IIa and shall be referred to as FNR. Monoclonal antibodies to FNR inhibit lymphocyte, fibroblast, and platelet adhesion to fibronectin-coated surfaces. ECMRs I, II, and FNR were differentially expressed in platelets, resting or activated lymphocytes, and myeloid, epithelial, endothelial, and fibroblast cell populations, suggesting a functional role for the receptors in vascular emigration and selective tissue localization. Tissue staining of human fetal skin localized ECMRs I and II to the basal epidermis primarily, while monoclonal antibodies to the FNR stained both the dermis and epidermis. Experiments carried out to investigate the functional roles of these receptors in mediating cell adhesion to complex extracellular matrix (ECM) produced by cells in culture revealed that complete inhibition of cell adhesion to ECM required antibodies to both the FNR and ECMR II, the collagen adhesion receptor. These results show that multiple ECMRs function in combination to mediate cell adhesion to complex EMC templates and predicts that variation in ECM composition and ECMR expression may direct cell localization to specific tissue domains.

Extracellular matrix receptors, ECMRII and ECMRI, for collagen and fibronectin correspond to VLA-2 and VLA-3 in the VLA family of heterodimers

The Very Late Activation Antigen (VLA) proteins are a family of five related heterodimers, which also are part of the integrin superfamily of cell adhesion molecules. Except for the identification of VLA-5 as a fibronectin receptor structure, the functions of the VLA proteins have remained unclarified. In this paper, immunoprecipitation experiments with both anti-alpha and anti-beta subunit antibodies showed that the previously identified cell adhesion receptor for collagen, extracellular matrix receptor II (ECMRII), is equivalent to VLA-2. At the same time a previously described multispecific cell adhesion receptor for collagen, fibronectin, and laminin (ECMRI) has been shown to be identical to VLA-3. Although the mAb 12F1 and P1H5 both recognized VLA-2 (ECMRII), they appeared to define distinct epitopes on the alpha 2 subunit. On the other hand, the mAb P1B5 and J143 recognized the alpha 3 subunit of VLA-3 (ECMRI) at or near the same site. Consistent with the collagen receptor functions of VLA-2 (ECMRII) and VLA-3 (ECMRI), anti-VLA beta antiserum blocked cell attachment to collagen.

The human fibroblast class II extracellular matrix receptor mediates platelet adhesion to collagen and is identical to the platelet glycoprotein Ia-IIa complex

A monoclonal antibody, P1H5, to the human fibroblast class II extracellular matrix receptor (ECMR II) specifically inhibits human fibroblast adhesion to collagen and immunoprecipitates a cell surface receptor containing an alpha and beta subunit of approximately 140 kilodaltons each (Wayner, E. A., and Carter, W. G. (1987) J. Cell Biol. 105, 1873-1884). We report here that P1H5 also specifically inhibits adhesion of unactivated human platelets to type I and III collagens, but not to fibronectin. Immunoprecipitation of the class II ECMR from Triton X-100 detergent lysates of platelets, after cell surface iodination, identified the platelet collagen receptor. Peptide mapping confirmed that the II alpha and II beta subunits immunoprecipitated from platelets are structurally homologous with those derived from fibroblasts. The platelet ECMR II alpha and -beta subunits comigrate with platelet membrane glycoproteins Ia and IIa, respectively, on two-dimensional nonreduced-reduced sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels. These results indicate that platelet and fibroblast adhesion to collagen are both mediated by a similar receptor and that the alpha and beta subunits of this receptor are identical to platelet membrane glycoproteins Ia and IIa, respectively. Although glycoprotein Ia has been previously implicated as a collagen binding protein, our results are the first direct evidence that platelet glycoprotein Ia is associated with glycoprotein IIa in a heterodimer complex and that this complex, by mediating platelet attachment, is an actual receptor for platelet adhesion to collagen.

Characterization of the class III collagen receptor, a phosphorylated, transmembrane glycoprotein expressed in nucleated human cells

We previously identified a 90-kDa cell surface glycoprotein, termed the class III collagen receptor (CRIII), that bound to collagen in affinity chromatography experiments (Wayner, E. A., and Carter, W. G. (1987) J. Cell Biol. 105, 1873-1884). Here, we utilize monoclonal antibodies to define three domains of the CRIII, hydrophobic transmembrane, phosphorylated cytoplasmic, and glycosylated extracellular. The domain designations are based on the following characteristics. (i) Differential extraction, phase partitioning with Triton X-114, and incorporation into liposomes all indicate that the CRIII is an intrinsic membrane receptor with a hydrophobic domain. After incorporation into liposomes the CRIII binds collagen. (ii) Immunofluorescence microscopy reveals that most nucleated cells express the CRIII and that after extraction with Triton X-100, the Triton-insoluble CRIII distributes in a fibrillar pattern at the cell periphery and in closed loops that partially co-distributed with vimentin. The CRIII contains phosphoserine residues which are located on a cytoplasmic domain that may interact with the cytoskeleton. (iii) The CRIII contains 25% carbohydrate in 8-10 asparagine-linked carbohydrate chains of 2800 daltons each bound to a 65-kDa core peptide in the extracellular domain. Peptide mapping with trypsin defined a glycosylated 27-kDa extracellular fragment and a phosphorylated and glycosylated 35-kDa transmembrane fragment. These data suggest a model for the CRIII that links the cytoskeleton with the extracellular matrix.