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PubMed2002

Role of integrins in invasion of endometrial cancer cell lines.

OBJECTIVE: The objective of this study was to determine whether there is a link between integrins and components of the plasminogen system, regarding tumor cell invasion to the artificial extracellular matrix. METHODS: Immunocytochemistry was performed with antibodies directed against integrins alpha2beta1, alpha4beta1, alpha5beta1, alpha6beta1, and alpha(nu)beta3 Cell adhesion was studied by cell attachment to matrix proteins. Integrin-mediated migration of cells into the artificial matrix was studied in an invasion assay. Last, immunoreactivity of the components of the plasminogen system was estimated by ELISA. RESULTS: HEC-1A, Ishikawa, and AN3CA cell lines express the alpha 4 beta 1, alpha 5 beta 1, and alpha 6 beta 1 integrins. Adhesion of cells to fibronectin and laminin was inhibited by monoclonal antibodies directed against appropriate integrin subunits. Migration into the matrigel was partially blocked with mAbs to alpha4beta1 as well as alpha5beta1, alpha6beta1 integrins and their combination. No differences in either uPA or PAI-1 immunoreactivity were found after addition of the mAbs. CONCLUSION: Alpha4beta1, alpha5beta1, and alpha6beta1 heterodimers mediate adhesion as well as migration into the artificial matrix matrigel of endometrial tumor cell lines. A cooperative signaling between these integrins and uPA or its inhibitor in modulation of in vitro cell invasion is rather unprobable.

Antibodies, Monoclonal↗

PubMed2001

Tumor cell adhesion to endothelial cells is increased by endotoxin via an upregulation of beta-1 integrin expression.

BACKGROUND: Recent studies have demonstrated that metastatic disease develops from tumor cells that adhere to endothelial cells and proliferate intravascularly. The beta-1 integrin family and its ligand laminin have been shown to be important in tumor-to-endothelial cell adhesion. Lipopolysaccharide (LPS) has been implicated in the increased metastatic tumor growth that is seen postoperatively. We postulated that LPS increases tumor cell expression of beta-1 integrins and that this leads to increased adhesion. METHODS: The human metastatic colon cancer cell line LS174T was labeled with an enhanced green fluorescent protein (eGFP) using retroviral transfection. Cell cultures were treated with LPS for 1, 2, and 4 h (n = 6 each) and were subsequently cocultured for 30 or 120 min with confluent human umbilical vein endothelial cells (HUVECs), to allow adherence. Adherent tumor cells were counted using fluorescence microscopy. These experiments were carried out in the presence or absence of a functional blocking beta-1 integrin monoclonal antibody (4B4). Expression of beta-1 integrin and laminin on tumor and HUVECs was assessed using flow cytometric analysis. Tumor cell NF-kappaB activation after incubation with LPS was measured. RESULTS: Tumor cell and HUVEC beta-1 integrin expression and HUVEC expression of laminin were significantly (P < 0.05) enhanced after incubation with LPS. Tumor cell adhesion to HUVECs was significantly increased. Addition of the beta-1 integrin blocking antibody reduced tumor cell adhesion to control levels. LPS increased tumor cell NF-kappaB activation. CONCLUSIONS: Exposure to LPS increases tumor cell adhesion to the endothelium through a beta-1 integrin-mediated pathway that is NF-kappaB dependent. This may provide a target for immunotherapy directed at reducing postoperative metastatic tumor growth.

Cell Adhesion↗

PubMed1995

Chimeric integrins expressed in retinal ganglion cells impair process outgrowth in vivo.

Integrin function in retinal ganglion cell (RGC) development was examined in vivo by transfecting genes encoding various dominant forms of the chicken beta 1 integrin subunit into intact eye primordia of Xenopus embryos. RGCs expressing the chimeric chicken/Xenopus integrin receptors exhibited a marked reduction in process outgrowth with only 27% extending an axon and 41% bearing dendrites compared to control levels of 85-88%. None of the integrin constructs impaired the ability of RGC axons to pathfind appropriately or of retinal precursors to migrate to different laminar positions. Chimeric integrin expression also impaired process outgrowth in cells of the inner nuclear layer, although to a lesser extent than RGCs. Transfected diencephalic neurons, by contrast, showed normal levels of process outgrowth. These findings show that beta 1 integrins play an important role in regulating the outgrowth of axons and dendrites from RGCs in the retina but that chimeric integrins do not impair growth cone steering in general.

Animals↗

PubMed2000

Adhesive events in retinal development and function: the role of integrin receptors.

Cells in the developing retina contact a vast array of molecular cues in their microenvironment that are thought to guide their development. Many of these cues are embedded in the surface of neighboring cells or deposited within the extracellular matrix (ECM). Evidence has accumulated that cell-cell and cell-ECM interactions are essential in many phases of neural development, including neuroblast migration, determination of cell fate, axon outgrowth and synapse formation. In this chapter, we examine the developmental and functional roles fulfilled by integrins, a family of receptors for ECM molecules and cell adhesion molecules (CAMs). We have approached this problem by addressing a series of three questions: (1) which integrins are expressed in developing retina? (2) when and where are they expressed? and, (3) what functions do they carry out? Integrins have previously been implicated in axon extension, but new evidence suggests that they are also involved in earlier developmental events in preaxonal neuroblasts. High levels of expression of at least eight integrin subunits have been documented in these young retinal cells, and integrins containing the beta 1 subunit have been implicated in migration of adolescent retinal ganglion cells. Integrin expression persists through adulthood, both in the retina and in the neighboring layer of the retinal pigment epithelium (RPE). The integrin alpha v beta 5 has been shown to reside on the apical surface of the RPE and has been implicated in the phagocytosis of shed photoreceptor outer segments.

Animals↗

PubMed1995

Fibronectin and integrins in invasion and metastasis.

The adhesive glycoprotein fibronectin and integrin receptors appear to play important roles in the progression of metastatic disease. Fibronectin is a multifunctional extracellular glycoprotein that has at lest two independent cell adhesion regions with different receptor specificities. The cell adhesive region in the central portion of fibronectin is comprised of at least two minimal amino acid sequences--an Arg-Gly-Asp (RGD) sequence and a Pro-His-Ser-Arg-Asn (PHSRN) sequence--which function in synergy. Another cell adhesive region is located near the carboxy-terminus in the alternatively spliced IIICS module. The critical minimal sequences for this region Leu-Asp-Val (LDV) and Arg-Glu-Asp-Val (REDV) which function in an additive rather than synergistic fashion. Integrins are heterodimeric, transmembrane cell adhesion receptors for fibronectin and other extracellular matrix molecules. Several different integrins bind to fibronectin. The alpha 5 beta 1 fibronectin-specific integrin binds to the central RGD/PHSRN site. The alpha 4 beta 1 integrin binds to the IIICS site. Fibronectin-integrin interactions are important in tumor cell migration, invasion, and metastasis. In addition to promoting cell adhesion to the extracellular matrix, these proteins may also function in chemotaxis and control of proliferation. Peptide and antibody inhibitors of fibronectin and integrin functions have been shown to be effective inhibitors of metastasis, and are potentially important reagents for the study and control of cancer.

Amino Acid Sequence↗

PubMed1995

Integrin expression in non-small cell carcinoma of the lung.

Alteration of integrin expression in a number of different malignant diseases has been recognized, with a trend of downregulation of collagen-laminin binding integrin expression in epithelial tumor types noted. This study evaluated the expression of a panel of integrin subunits that included subunits that form receptors that bind to collagen and laminin (alpha 2, alpha 3, alpha 6 beta 4) and subunits that form receptors that bind to fibronectin and fibrinogen (alpha 5, alpha V, beta 3, beta 6) in 51 specimens of non-small cell carcinoma (NSCCA) of the lung by use of immunohistochemistry. Integrin expression was then correlated with histologic type (squamous vs. adenocarcinoma), absence or presence of hilar or mediastinal nodal metastasis at resection, and cellular differentiation (well or poorly differentiated). In general, downregulation of the collagen-laminin binding subunits was noted in tumor cells of the NSCCA specimens when compared to the progenitor normal bronchial epithelium. No differences were noted in integrin expression between squamous cell and adenocarcinoma or between node-positive or node-negative tumors. However, downregulation of the integrin subunit alpha 3 was noted to be significantly more common in poorly differentiated tumors (p = 0.02) and several of the other collagen-laminin binding subunits also appeared to be more downregulated in poorly differentiated tumors. No upregulation was seen in the alpha 5 subunit of the fibronectin receptor or the beta 3 subunit of the vitronectin receptor, however, approximately 50% of tumors showed upregulation of the beta 6 subunit, the great majority of these being well-differentiated, node-negative tumors. Downregulation of the collagen-laminin integrins may thus be associated with differentiation of NSCCA, but not metastasis, and may serve as an adjunctive prognostic marker of disease. The beta 6 subunit appears to be associated with malignant transformation, but may serve as a positive prognostic factor.

Antibodies, Monoclonal↗

PubMed1996

Covisualization by computational optical-sectioning microscopy of integrin and associated proteins at the cell membrane of living onion protoplasts.

Using higher-resolution wide-field computational optical-sectioning fluorescence microscopy, the distribution of antigens recognized by antibodies against animal beta 1 integrin, fibronectin, and vitronectin has been visualized at the outer surface of enzymatically protoplasted onion epidermis cells and in depectinated cell wall fragments. On the protoplast all three antigens are colocalized in an array of small spots, as seen in raw images, in Gaussian filtered images, and in images restored by two different algorithms. Fibronectin and vitronectin but not beta 1 integrin antigenicities colocalize as puncta in comparably prepared and processed images of the wall fragments. Several control visualizations suggest considerable specifity of antibody recognition. Affinity purification of onion cell extract with the same anti-integrin used for visualization has yielded protein that separates in SDS-PAGE into two bands of about 105-110 and 115-125 kDa. These bands are again recognized by the visualization antibody, which was raised against the extracellular domain of chicken beta 1 integrin, and are also recognized by an antibody against the intracellular domain of chicken beta 1 integrin. Because beta 1 integrin is a key protein in numerous animal adhesion sites, it appears that the punctate distribution of this protein in the cell membranes of onion epidermis represents the adhesion sites long known to occur in cells of this tissue. Because vitronectin and fibronection are matrix proteins that bind to integrin in animals, the punctate occurrence of antigenically similar proteins both in the wall (matrix) and on enzymatically prepared protoplasts reinforces the concept that onion cells have adhesion sites with some similarity to certain kinds of adhesion sites in animals.

Binding Sites, Antibody↗

PubMed2004

Physiological and pathological roles of alpha3beta1 integrin.

Alpha3beta1 integrin has been considered to be a mysterious adhesion molecule due to the pleiotropy in its ligand-binding specificity. However, recent studies have identified laminin isoforms as high-affinity ligands for this integrin, and demonstrated that alpha3beta1 integrin plays a number of essential roles in development and differentiation, mainly by mediating the establishment and maintenance of epithelial tissues. Furthermore, alpha3beta1 integrin is also implicated in many other biological phenomena, including cell growth and apoptosis, angiogenesis and neural functions. This integrin receptor forms complexes with various other membrane proteins, such as the transmembrane-4 superfamily proteins (tetraspanins), cytoskeletal proteins and signaling molecules. Recently, lines of evidence have been reported showing that complex formation regulates integrin functions in cell adhesion and migration, signal transduction across cell membranes, and cytoskeletal organization. In addition to these roles in physiological processes, alpha3beta1 integrin performs crucial functions in various pathological processes, especially in wound healing, tumor invasion and metastasis, and infection by pathogenic microorganisms.

Animals↗

PubMed2006

Expression of the cytoplasmic domain of beta1 integrin induces apoptosis in adult rat ventricular myocytes (ARVM) via the involvement of caspase-8 and mitochondrial death pathway.

Stimulation of beta-adrenergic receptor (beta-AR) induces cardiac myocyte apoptosis. Integrins, a family of cell-surface receptors, play an important role in the regulation of cardiac myocyte apoptosis and ventricular remodeling. Cleavage of extracellular domain of beta1 integrin, also called integrin shedding, is observed during cardiac hypertrophy and progression to early heart failure. Here we show that stimulation of beta-AR induces beta1 integrin fragmentation in mouse heart. To examine the role of intracellular domain of beta1 integrin in cardiac myocyte apoptosis, a chimeric receptor consisting of the cytoplasmic tail domain of beta(1A) integrin and the extracellular/transmembrane domain of the interleukin-2 receptor (TAC-beta1) was expressed in adult rat ventricular myocytes (ARVM) using adenoviruses. TAC-beta1 increased the percentage of apoptotic ARVM as measured by TUNEL-staining assay. TAC-beta1-induced apoptosis was found to be associated with increased cytosolic cytochrome c and decreased mitochondrial membrane potential. TAC-beta1 increased caspase-8 activity. Z-IETD-FMK, a specific caspase-8 inhibitor, significantly inhibited TAC-beta1-induced apoptosis. TAC-beta1 expression also increased cleavage of Bid, a pro-apoptotic Bcl-2 family protein. These data suggest that shedding of beta1 integrin may be a mechanism of induction of apoptosis during beta-AR-stimulated cardiac remodeling.

Animals↗

PubMed2004

A preliminary optical and electron microscopic study of the beta(1) integrin distribution pattern of human osteosarcoma-derived cells.

Immunogold labelling was used to study the organisation of the beta(1) integrins on osteosarcoma-derived osteoblasts (Saos-2 and MG-63). Monolayers of cells were prepared in multiwell culture plates on both uncovered and collagen-covered coverslips, and beta(1) integrins were primarily labelled using mouse monoclonal antibodies to beta(1) integrins. Indirect immunofluorescence labels using an anti-mouse fluorescein-conjugated goat antibody showed an even distribution of the beta(1) integrins on the cell membranes of all cell types used. A concentration of 2 microg/ml of the primary antibodies and a 1:100 dilution of the secondary antibodies were determined as the optimal concentration for labelling to use with indirect localisation of the primary antibodies gold conjugated to goat anti-mouse antibodies and viewed under an electron microscope. Ten nanometre gold particles were used for transmission electron microscopy (TEM) and 40 nm gold particles for scanning electron microscopy. TEM showed that beta(1) integrins were mainly clustered on the cell membrane processes with less labelling on the cell membranes themselves. The distribution of beta(1) integrins on osteosarcoma cells supports the concept that integrins may function by forming focal adhesions at the site of the cytoplasmic membrane processes.

Bone Neoplasms↗

PubMed2005

Integrin stimulation induces calcium signalling in rat cardiomyocytes by a NO-dependent mechanism.

The myocardial stretch-induced increase in intracellular [Ca(2+)] ([Ca(2+)](i)) is considered to be caused by integrin stimulation. Myocardial stretch is also associated with increased nitric oxide (NO) formation. We hypothesised that NO is implicated in calcium signalling following integrin stimulation. Integrins of neonatal rat cardiomyocytes were stimulated with a pentapeptide containing the Arg-Gly-Asp (RGD) sequence. [Ca(2+)](i) was measured with Fura2, [NO](i) was measured with DAF2 and phosphorylation of focal adhesion kinase (FAK) was monitored with immunofluorescence techniques. Integrin stimulation increased both [NO](i) and [Ca(2+)](i), the latter response being inhibited by ryanodine receptor-2 (RyR2) blockers and by N(G)-monomethyl-L-arginine (L-NMMA), an inhibitor of NOS, but resistant to GdCl(3), diltiazem and wortmannin. Integrin-induced intracellular Ca(2+) release thus appears to be independent of the influx of extracellular Ca(2+) and phosphatidylinositol-3 kinase activity. In addition, integrin stimulation induced phosphorylation of FAK. Our results provide evidence for an integrin-induced Ca(2+) release from RyR2 which is mediated by NO formation, probably via FAK-induced NOS activation.

Animals↗

PubMed2006

Positive expression of E-cadherin suppresses cell adhesion to fibronectin via reduction of alpha5beta1 integrin in human breast carcinoma cells.

E-cadherin mainly mediated the epithelial cell-cell adhesion, and integrin signaling can modulate the signaling pathway of E-cadherin in the different levels. Up to now, however, it is still unclear that whether E-cadherin could interfere with cell-matrix interaction, a typical adhesion through integrins. In this study we investigated the effects of E-cadherin on cell-matrix adhesion and alpha5beta1 integrin expression in human breast carcinoma cells. It was found that either mRNA or protein level of alpha5 and beta1 subunits of integrin decreased in E-cad-231 compared with Mock-231. Furthermore, the promoter activity of alpha5 gene was inhibited in E-cad-231 compared with Mock-231. Consistently, phosphorylated focal adhesion kinase, a closer key downstream protein kinase of integrin signaling, were also down-regulated in E-cad-231. Furthermore, distribution of beta-catenin was observed and data showed beta-catenin was accumulated in the nucleus in Mock-231, while disappeared from the nucleus and mainly accumulated near the cell surface membrane in E-cad-231. LiCl, a molecule that can inhibit the GSK-3beta activity and down-regulate beta-catenin degradation, could inversely stimulate expression of alpha5 and beta1 integrin. Taken together, these results indicated that positive expression of E-cadherin inhibits the cell adhesion to extracellular matrix mediated by alpha5beta1 integrin signaling.

Breast Neoplasms↗

PubMed2005

Expression and localisation of alphav integrins in human odontoblasts.

Integrin alphabeta heterodimers mediate adhesion to the extracellular matrix and at cell-cell contacts and initiate intracellular signalling cascades in response to a variety of inductive factors. Apart from the expression of alphavbeta3 that we have previously reported, little is known about the expression of integrins in odontoblasts. Here, we investigated the expression of alphav-binding beta integrin subunits in healthy human dental pulp in vivo and in odontoblasts differentiated in vitro. Reverse transcription/polymerase chain reaction analysis revealed the expression of alphav, beta1, beta5 and beta8 integrin mRNA, but not beta6, in whole pulp cells. Flow cytometry showed that the alphav and beta1 subunits were the most intensely expressed. Immunohistochemistry demonstrated that the beta1 subunit was localised in newly differentiated odontoblasts in the root and in mature odontoblasts in the crown, including their intradentinal cell processes. The alphav chain was predominantly expressed by mature odontoblasts and alphavbeta5 was only observed in mature odontoblasts. In vitro differentiated odontoblasts expressed genes for alphav, beta1 and beta5, but not for beta6 and beta8. A comparison of integrin profiles between cultured pulp cells and in vitro differentiated odontoblasts revealed that odontoblast maturation was characterised by a significant increase in the expression of alphav and beta1 subunits and alphavbeta5 integrin. The beta8 subunit was detected in nerve cells only. Histological analysis of teeth from alphav knockout mice showed no obvious structural modification in the odontoblast layer. Thus, human mature odontoblasts express alphavbeta3, alphavbeta5 and perhaps alphavbeta1 integrins, with the possible presence of alpha-beta1 pairs. The roles that these molecules play in the exchange of information throughout the odontoblast layer remain to be determined.

Adolescent↗

PubMed1997

Distribution of alpha-integrin subunits in fetal polycystic kidney diseases.

An alteration in cell/matrix interactions is one of the suggested mechanisms leading to cyst formation in polycystic kidney diseases. Most of these interactions are mediated by beta 1-integrins, a subfamily of integrin receptors, formed by the association of the beta 1-chain with different alpha-subunits. To date, no study on alpha-integrin subunit distribution during the early stages of cyst development has been reported. Using immunofluorescence, we analyzed the distribution of alpha-integrin subunits (alpha 1, alpha 2, alpha 3, alpha 5, and alpha 6) and basement membrane proteins in kidneys of fetuses with autosomal dominant (ADPKD) or autosomal recessive polycystic kidney disease (ARPKD). The distribution was compared with that observed in normal fetal and post-natal kidneys, and in fetal cystic dysplasia and Meckel syndrome. Marked increase in alpha 1-integrin staining was observed in normal and cystic collecting duct cells of both polycystic diseases (PKD), compared with normal and cystic controls. The distribution of integrin subunits alpha 2, alpha 3, and alpha 6 was irregular in cyst epithelial cells of PKD and cystic controls. The increased expression of the alpha 1-subunit specifically observed in PKD collecting duct cells may be an early consequence of the genetic defect in ARPKD. In ADPKD it parallels the reported expression of polycystin, the protein product of PKD1. The irregular expression of alpha 2, alpha 3, and alpha 6 integrin subunits observed in all types of cysts suggests that cell/matrix interactions are altered early and may participate in the development of cysts, perhaps by contributing to the deregulation of cell survival in cystic diseases.

Antibodies, Monoclonal↗

PubMed2005

Role of the beta1-integrin subunit in the adhesion, extravasation and migration of T24 human bladder carcinoma cells.

The abilities of tumor cells to extravasate from the blood vessel system and to migrate through the connective tissue are prerequisites in metastasis formation. Both processes are chiefly mediated by integrins, which mediate both cell-cell and cell-matrix interactions. We investigated the role of integrin subunits in the adhesion, extravasation and migration of the highly invasive human bladder carcinoma cell line T24. Here we show that inhibition of the beta(1)-integrin subunit using the specific beta(1)-integrin blocking antibody 4B4 significantly reduces the adhesion to HUVEC and transmigratory activity of T24 cells. The blockade of the beta(1)-integrin subunit also resulted in a significantly reduced locomotory activity of T24 cells. A detailed cell migration analysis on a single cell level revealed that blockade of the beta(1)-integrin subunit leads to an altered migration pattern of single cells but does not influence migration per se. Migration parameters such as time active, velocity and distance migrated were significantly reduced as compared to untreated control cells. Our observations strongly suggest a central role for the beta(1)-integrin subunit in forming the cell-cell and cell-matrix bonds necessary for adhesion, extravasation and migration.

Carcinoma↗

PubMedDate not supplied

Near-infrared fluorescence imaging of tumor integrin alpha v beta 3 expression with Cy7-labeled RGD multimers.

PURPOSE: Cell adhesion molecule integrin alpha v beta 3 is an excellent target for tumor interventions because of its unique expression on the surface of several types of solid tumor cells and on almost all sprouting tumor vasculatures. Here, we describe the development of near-infrared (NIR) fluorochrome Cy7-labeled RGD peptides for tumor integrin targeting. PROCEDURES: Mono-, di-, and tetrameric RGD peptides were synthesized and conjugated with Cy7. The integrin specificity of these fluorescent probes was tested in vitro for receptor binding assay and fluorescence microscopy and in vivo for subcutaneous U87MG tumor targeting. RESULTS: The tetrameric RGD peptide probe with the highest integrin affinity showed the highest tumor activity accumulation and strongest tumor-to-normal tissue contrast. This uptake is integrin-specific as the signal accumulated in the tumor can be effectively blocked by unconjugated RGD peptide antagonist of integrin alpha v beta 3. CONCLUSIONS: Noninvasive NIR fluorescence imaging is able to detect and semiquantify tumor integrin expression based upon the highly potent tetrameric RGD peptide probe.

Animals↗

PubMed1991

Multiple integrins share the ability to induce elevation of intracellular pH.

Previous work has shown that adhesion of anchorage-dependent cells to fibronectin via integrin alpha 5 beta 1 leads to activation of the Na-H antiporter and a rise in intracellular pH (pHi). We now show that adhesion of bovine capillary endothelial cells (BCE) to fibrinogen; collagens type III, IV, and V; laminin; and vitronectin; ligands that bind other members of the integrin family, resulted in significant elevations in pHi. Other ligands (basic fibroblast growth factor, concanavalin A, and thrombin), which bind cells when immobilized on plastic, but that do not bind integrins and do not support cell growth, do not elevate pHi. Adhesion to an antibody against integrin alpha v beta 3 also elevates pHi. Adhesion of peripheral human T lymphocytes to an antibody against the integrin LFA-1 induced a rise in pHi. Antibodies to CD2 or ICAM-2 had only slight effects on pHi, whereas an antibody to the T cell receptor complex that strongly activates T cells induced a large increase in pHi. We conclude that elevation of pHi by integrins is specific and is a property shared by many members of the integrin family.

Animals↗

PubMed1991

Isolation of alpha 6 beta 1 integrins from platelets and adherent cells by affinity chromatography on mouse laminin fragment E8 and human laminin pepsin fragment.

Ligand affinity chromatography was used to identify receptors on platelets and two adherent cell lines, OV-CAR-4 and HBL-100, for the E8 fragment of murine laminin. A complex of two polypeptides (140 and 110 kDa nonreduced) was bound by the E8 affinity columns from all three cell types and was eluted with EDTA. This heterodimeric complex was identified as the alpha 6 beta 1 integrin by immunoprecipitation with specific antibodies against either the alpha 6 or the beta 1 subunit. The alpha 6 beta 1 integrin did not bind to an affinity column containing fragment P1 originating from a different part of murine laminin which, however, bound the alpha IIb beta 3 integrin from platelets. Furthermore, in immunofluorescence staining, the alpha 6 beta 1 integrin localizes in focal contacts of OVCAR-4 cells attached to laminin and E8 but not to fibronectin substrates. These results, combined with previous antibody inhibition studies, unequivocally identify the alpha 6 beta 1 integrin as a specific receptor for fragment E8. Affinity chromatography of OVCAR-4 and HBL-100 cells on a large pepsin fragment of laminin from human placenta yielded integrin alpha 3 beta 1. When alpha 3 beta 1 was removed from lysates of OVCAR-4 cells by preclearing with an alpha 3-specific monoclonal antibody, alpha 6 beta 1 was able to bind to human laminin as well. Integrin alpha 6 beta 1 on platelets which do not express alpha 3 beta 1 binds directly to human laminin. These results indicate that both alpha 3 beta 1 and alpha 6 beta 1 can act as receptors for human laminin and may interfere by steric hindrance. The alpha 6 beta 4 complex, which is strongly expressed on HBL-100 cells, did not bind to either mouse laminin fragment E8 or human laminin affinity columns.

Amino Acid Sequence↗