The very late antigen family of heterodimers is part of a superfamily of molecules involved in adhesion and embryogenesis

Dendritic cell expression of ADAM23 governs T cell proliferation and cytokine production through the α(v)β(3) integrin receptor

ADAM23 is a member of the brain macrophage-derived chemokine family. Structural homology of ADAM proteins suggests their function as integrin receptors. Previous studies have linked ADAM23 as a dominant contributor to brain development and cancer metastasis. The present studies now show that ADAM23 expression on DCs partially governs antigen-presentation capacities to responder CD4⁺ T cells. With the use of RNAi approaches, knockdown of ADAM23 in murine BMDCs resulted in impaired T cell activation, proliferation, and cytokine production. Knockdown did not alter the maturation profile of DCs (i.e., costimulatory molecule expression or production of proinflammatory cytokines) but markedly impaired cognate T cell responses. There was a significant decrease in antigen-specific clonal expansion coupled with a global decrease in Th cytokine production. Impaired early activation and proliferation did not alter/skew the balance of Th polarization but significantly depressed total levels of IL-2, IFN-γ, IL-4, and IL-17 cytokine production in CD4⁺ T cells primed by ADAM23 knockdown versus control DCs. Finally, neutralizing antibodies targeting the α(v)β(3) integrin receptors resulted in similar phenotypes of impaired CD4⁺ T cell responses. Taken together, these studies show a novel role of ADAM23 in governing DC antigen presentation to cognate CD4⁺ T cells.

Integrin targeted therapeutics

Integrins are heterodimeric, transmembrane receptors that function as mechanosensors, adhesion molecules and signal transduction platforms in a multitude of biological processes. As such, integrins are central to the etiology and pathology of many disease states. Therefore, pharmacological inhibition of integrins is of great interest for the treatment and prevention of disease. In the last two decades several integrin-targeted drugs have made their way into clinical use, many others are in clinical trials and still more are showing promise as they advance through preclinical development. Herein, this review examines and evaluates the various drugs and compounds targeting integrins and the disease states in which they are implicated.

Identification of integrin alpha3 as a new substrate of the adenovirus E4orf6/E1B 55-kilodalton E3 ubiquitin ligase complex

The human adenovirus E4orf6 and E1B55K proteins promote viral replication by targeting several cellular proteins for degradation. The E4orf6 product has been shown by our group and others to form an E3 ubiquitin ligase complex that contains elongins B and C and cullin family member Cul5. E1B55K associates with this complex, where it is believed to function primarily to introduce bound substrates for degradation via proteasomes. In addition to p53, its first known substrate, the E4orf6/E1B 55-kDa complex (E4orf6/E1B55K) was shown to promote the degradation of Mre11 and DNA ligase IV; however, additional substrates are believed to exist. This notion is strengthened by the fact that none of these substrates seems likely to be associated with additional functions shown to be mediated by the E4orf6-associated E3 ubiquitin ligase complex, including export of late viral mRNAs and blockage of export of the bulk cellular mRNAs from the nucleus. In an attempt to identify new E4orf6/E1B55K substrates, we undertook a proteomic screen using human p53-null, non-small-cell lung carcinoma H1299 cells expressing either E4orf6 protein alone or in combination with E1B55K through infection by appropriate adenovirus vectors. One cellular protein that appeared to be degraded by E1B55K in combination with the E4orf6 protein was a species of molecular mass approximately 130 kDa that was identified as the integrin alpha3 subunit (i.e., very late activation antigen 3 alpha subunit). Preliminary analyses suggested that degradation of alpha3 may play a role in promoting release and spread of progeny virions.

Natalizumab: targeting alpha4-integrins in multiple sclerosis

In 1992, it was shown that monoclonal antibodies blocking alpha(4)-integrins prevent the development of experimental autoimmune encephalomyelitis, an animal model for multiple sclerosis (MS). As alpha(4)beta(1)-integrin was demonstrated to mediate the attachment of immune-competent cells to inflamed brain endothelium in experimental autoimmune encephalomyelitis, the therapeutic effect was attributed to the inhibition of immune cell extravasation and inflammation in the central nervous system. This novel therapeutic approach was rapidly and successfully translated into the clinic. The humanized anti-alpha(4)-integrin antibody natalizumab demonstrated an unequivocal therapeutic effect in preventing relapses and slowing down the pace of neurological deterioration in patients with relapsing-remitting MS in phase II and phase III clinical trials. The occurrence of 3 cases of progressive multifocal leukoencephalopathy in patients treated with natalizumab led to the voluntary withdrawal of the drug from the market. After a thorough safety evaluation of all patients receiving this drug in past and ongoing studies for MS and Crohn's disease, natalizumab again obtained approval in the US and the European Community. A treatment targeting leukocyte trafficking in MS has now re-entered the clinic. Further thorough evaluation is necessary for a better understanding of the risk-benefit balance of this new treatment option for relapsing MS. In this review, we discuss the basic mechanism of action, key clinical results of clinical trials and the emerging indication of natalizumab in MS.

Polymorphisms and haplotypes of integrinalpha1 (ITGA1) are associated with bone mineral density and fracture risk in postmenopausal Koreans

INTRODUCTION

ITGA1 is involved in the early remodeling of osteoarthritic cartilage and plays an essential role in the regulation of mesenchymal stem cell proliferation and cartilage production. We investigated the association between bone parameters and ITGA1 polymorphisms and their haplotype linkage disequilibrium (LD) blocks (BL_hts). Genetic susceptibility to osteoporosis was studied in 946 postmenopausal Korean women.

METHODS

We identified 67 genetic polymorphisms in ITGA1 region by direct sequencing (n = 114). Eight SNPs were genotyped to further investigate their potential involvement in osteoporosis in postmenopausal women (n = 946). Areal BMD of the lumbar spine and proximal femur was measured using dual-energy X-ray absorptiometry.

RESULTS

The SNPs, +73187C>T (exon 3) and +76969T>G (intron 5), and their BL_hts were associated with bone mineral density (BMD) at various femur sites (p = 0.009-0.05). Moreover, +159174A>C (intron 28) and its haplotype BL3_ht1 showed a highly significant association with risk of non-vertebral fracture (p = 0.002-0.005) and the minor allele of +159174A>C showed a protective effect.

CONCLUSIONS

These results are suggestive of the association of ITGA1 with osteoporosis and related risk in postmenopausal women.

Therapeutic anti-integrin (alpha4 and alphaL) monoclonal antibodies: two-edged swords?

Anti-alpha4 and anti-alphaL integrin chain monoclonal antibodies have shown a clear-cut beneficial effect in different animal models of autoimmune and inflammatory disorders as well as in human diseases, including multiple sclerosis, inflammatory bowel disease, and psoriasis. It has been widely assumed that this therapeutic effect is mainly consequence of the blockade of leucocyte adhesion to endothelium, inhibiting thus their extravasation and the inflammatory phenomenon. However, it is evident that both alpha4beta1 (very late antigen-4) and alphaLbeta2 (leucocyte function-associated antigen-1) integrins have additional important roles in other immune phenomena, including the formation of the immune synapse and the differentiation of T helper 1 lymphocytes. Therefore, it is very feasible that the long-term administration of blocking agents directed against these integrins to patients with inflammatory/autoimmune conditions may have undesirable or unexpected effects.

Physiological and Pathological Roles of α3β1 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.

Interaction of Leishmania gp63 with cellular receptors for fibronectin

The most abundant protein on the surface of the promastigote form of the protozoan parasites Leishmania spp. is a 63-kDa molecule, designated gp63 or leishmanolysin. Because gp63 has been shown to possess fibronectin-like properties, we examined the interaction of gp63 with the cellular receptors for fibronectin. We measured the direct binding of Leishmania to human macrophages or to transfected mammalian cells expressing human fibronectin receptors. Leishmania expressing gp63 exhibited modest but reproducible adhesion to human macrophages and to transfected CHO cells expressing alpha4/beta1 fibronectin receptors. In both cases, this interaction depended on gp63 but occurred independently of the SRYD sequence of gp63, because parasites expressing gp63 with a mutated SRYD sequence bound to macrophages and alpha4/beta1 receptor-expressing cells as well as did wild-type parasites. The contribution of gp63 to parasite adhesion was more pronounced when the assays were performed in the presence of complement, suggesting that the receptors for complement and fibronectin may cooperate to mediate the efficient adhesion of parasites to macrophages. The interaction of gp63 with fibronectin receptors may also play an important role in parasite internalization by macrophages. Erythrocytes to which gp63 was cross-linked were efficiently phagocytized by macrophages, whereas control erythrocytes opsonized with complement alone bound to macrophages but remained peripherally attached to the outside of the cell. Similarly, parasites expressing wild-type gp63 were rapidly and efficiently phagocytized by resting macrophages, whereas parasites lacking gp63 were internalized more slowly. This rapid internalization of gp63-expressing parasites was dependent on the beta1 integrins, because pretreatment of macrophages with monoclonal antibodies to the beta1 integrins decreased the internalization of gp63-expressing parasites. These observations indicate that complement receptors are the primary mediators of parasite adhesion; however, maximal parasite adhesion and internalization may require the participation of the beta1 integrins, which recognize fibronectin-like molecules such as gp63 on the surface of the parasite.

Integrin alpha1 localization in murine central and peripheral nervous system

The distribution of neurons expressing integrin alpha1 subunit protein (INTalpha1) was examined in adult mouse tissues of not only the central nervous system, but also the sympathetic ganglia, and the adrenal gland by immunohistochemistry and immunoelectron microscopy. INTalpha1-positive neurons were observed in most tissues examined, and most of them were found to coexpress tyrosine hydroxylase (TH) except for Purkinje cells and hippocampal neurons. Expression of INTalpha1 was also observed in the malpositioned cortical neurons in reeler mutants, and appeared not to be affected by the aberrant cell migration of the reeler cortical neurons. In situ hybridization showed that the expression of INTalpha1 mRNA was correlated with synthesis of the INTalpha1 protein in each case, and this finding indicated that expression of the protein was controlled by transcriptional regulation of the INTalpha1 gene.

Divalent cations and ligands induce conformational changes that are highly divergent among beta1 integrins

Here we show striking differences in conformational regulation among beta1 integrins. Upon manganese stimulation, a beta1 epitope defined by monoclonal antibody (mAb) 9EG7 was induced strongly (on alpha4beta1), moderately (on alpha5beta1), weakly (on alpha2beta1), or was scarcely detectable (on alpha6beta1 and alpha3beta1). Comparable results were seen for the beta1 epitope defined by mAb 15/7. Likewise, soluble ligands caused strong (alpha4beta1), moderate (alpha5beta1), weak (alpha2beta1, alpha6beta1), or minimal (alpha3beta1) induction of the 9EG7 epitope. Exchange or deletion of alpha chain cytoplasmic tails did not alter Mn2+-induced 9EG7 epitope levels. Upon removal of calcium by EGTA or EDTA, the hierarchy of 9EG7 epitope induction was similar (alpha5beta1 > alpha2beta1 > alpha6beta1 > alpha3beta1), except that EGTA reduced rather than induced 9EG7 expression on alpha4beta1. Thus in contrast to other beta1 integrins, calcium uniquely supports constitutive expression of the 9EG7 epitope on alpha4beta1. Likewise, calcium supported vascular cell adhesion molecule-stimulated 9EG7 appearance on alpha4beta1, whereas calcium inhibited ligand-induced 9EG7 epitope on other integrins. Constitutive expression of 9EG7 on alpha4beta1 was eliminated by a D698E mutation in alpha4, suggesting that Asp-698 may play a key role in maintaining atypical alpha4beta1 response to calcium. In conclusion, our results (i) demonstrate that mAb such as 9EG7 and 15/7 have limited diagnostic utility as reporters of ligand or Mn2+ occupancy for beta1 integrins, (ii) indicate pronounced differences in conformational flexibilities (alpha4beta1 > alpha5beta1 > alpha2beta1 > alpha6beta1 > alpha3beta1), (iii) allow us to hypothesize that beta1 integrins may differ markedly in conformation-dependent inside-out signaling, and (iv) have uncovered an atypical alpha4beta1 response to calcium that requires alpha4 Asp-698.

Identification of the integrin alpha 3 beta 1 as a component of a partially purified A-system amino acid transporter from Ehrlich cell plasma membranes

We have previously reported [McCormick and Johnstone (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 7877-7881] the partial purification of the Na(+)-dependent A-system amino acid transporter from Ehrlich cell plasma membranes and have suggested that a 120-130 kDa peptide, a major component of the purified fraction [octyl glucoside (OG) extract], is involved in Na(+)-dependent amino acid transport. In the present study, N-terminal sequence analysis of the 120-130 kDa peptide revealed a sequence similar to that of the alpha 3 subunit of the integrin alpha 3 beta 1. The presence of alpha 3 beta 1 was confirmed by Western blots of the OG extract probed with anti-alpha 3 or -beta 1 antibodies. Western blots also showed that an antibody originally raised against the 120-130 kDa peptide crossreacts with both the alpha 3 and beta 1 integrin subunits. Co-purification of alpha 3 beta 1 and Na(+)-dependent transport activity suggested that the two activities might be associated. Evidence that alpha 3 plays a role in transport is shown by the fact that an antibody against human alpha 3, but not beta 1, removed transport activity (approximately 25% loss) from cholate-solubilized Ehrlich membranes. Further purification of OG extracts using concanavalin A and wheat-germ lectin columns resulted in the separation of transport activity from the bulk (but not all) of alpha 3 beta 1 integrin without loss of the transport activity. These results indicate that the integrin itself is not essential for amino acid transport. Reconstitution of a purified alpha 3 beta 1-depleted protein fraction showed high levels of Na(+)-dependent, alpha-methylaminoisobutyric-acid-inhibitable amino acid transport in proteoliposomes, whereas reconstituted integrin alone showed little transport activity. However, in the integrin-depleted fractions, high amino acid uptake occurred in K+ which compromised the accurate measurement of the Na(+)-dependent component of uptake. The data suggest that alpha 3 may be associated with the A-system transporter and may modulate the activity of this carrier. Moreover, transfection of K562 and RD cells with human alpha 3 and alpha 2 cDNA showed that the former but not the latter increased A-system transport, thus providing more direct evidence that alpha 3 may modulate A-system transport activity.

Identification of an 80kD protein associated with the alpha 3 beta 1 integrin as a proteolytic fragment of the alpha 3 subunit: studies with human keratinocytes

We have characterised a protein of approximately 80kD previously observed to co-immunoprecipitate with the alpha 3 beta 1 integrin in lysates of surface labelled human epidermalkeratinocytes. The 80kD protein only appeared when keratinocytes were harvested with trypsin/EDTA prior to lysis and a protein of similar molecular mass could be immunoprecipitated from human dermal fibroblasts following treatment of the cells with trypsin/EDTA. N terminal sequencing established that the 80kD protein had homology with the alpha 3 integrin subunit. Peptide-mass fingerprinting was used to confirm that the protein comprised the amino terminus of alpha 3 and established that the site of cleavage was after amino acid 629. The 80kD fragment could be coimmunoprecipitated with alpha 3 beta 1 using an antibody to the cytoplasmic domain of the alpha 3 subunit, showing that the fragment remained complexed with intact alpha 3 beta 1. When antibodies to the cytoplasmic and extracellular domains of alpha 3 were used to label human epidermis by immunofluorescence, the staining patterns were indistinguishable and there is therefore no evidence that proteolysis of alpha 3 plays a role in keratinocyte detachment from the basement membrane during terminal differentiation. Whether the 80kD fragment has any effects, positive or negative, on alpha 3 beta 1-mediated adhesion remains to be determined.

Expression of wild-type and mutated rabbit osteopontin in Escherichia coli, and their effects on adhesion and migration of P388D1 cells

Recombinant wild-type rabbit osteopontin (rOP) and the protein with an aspartate-to-glutamate transposition induced by a point mutation in the rabbit OP cDNA within the Gly-Arg-Gly-Asp-Ser (GRGDS) sequence were expressed in Escherichia coli and purified to homogeneity. P388D1 cells bound rOP in a saturable manner. rOP induced adhesion and haptotaxis of P388D1 cells, whereas mutated rabbit OP (rOPmut) did not. Anti-rOP IgG F(ab')2 and synthetic GRGDS peptide inhibited rOP-mediated adhesion and haptotaxis of P388D1 cells. Fibronectin (FN)-mediated adhesion of P388D1 cells was markedly inhibited in the presence of fluid-phase rOP. Adhesion of P388D1 cells to rOP was significantly inhibited by anti-[alpha-subunits of VLA4 (alpha 4) and VLA5 (alpha 5)] monoclonal antibodies (mAbs), but not by anti-[alpha-subunit of vitronectin (VN) receptor (alpha V) or Mac-1 (alpha M)] mAb. Adhesion of P388D1 cells to FN and VN was significantly inhibited by anti-alpha V mAb but not anti-alpha 4, -alpha 5 or -alpha M mAb. Haptotaxis of P388D1 cells to rOP was significantly inhibited by anti-alpha V mAb, but not by anti-alpha 4, -alpha 5 and alpha M mAbs, whereas that to FN showed no inhibition with all three mAbs. Haptotaxis of P388D1 cells to VN was significantly inhibited by anti-alpha 5 and -alpha V mAbs but not by anti-alpha 4 and -alpha M mAbs. Similar features of inhibition of adhesion and haptotaxis of P388D1 cells to human OP were observed by mAbs. rOP had no chemotactic effect on P388D1 cells. Significant polymorphonuclear leucocyte migration was observed 3-12 h after intradermal injection of rOP into rabbits.

PUVA suppresses the expression of cell adhesion molecules of lymphocytes

To determine the therapeutic mechanism of PUVA in psoriasis vulgaris, the effects of PUVA on activated T lymphocytes were investigated in vitro. Peripheral blood mononuclear cells (PBMC) obtained from healthy volunteers were activated with Con A stimulation (Con A blasts). Both untreated PBMC and Con A blasts were irradiated with UVA light in the presence of 8-methoxypsoralen (8-MOP). The expressions of CD4, CD8, VLA-4 and LFA-1 of PBMC and Con A blasts were stained with each monoclonal antibody and the intensity of fluorescence was analyzed by FACScan. PUVA-treated PBMC showed decreased response to both Con A and PHA stimulation. PUVA treatment also suppressed the IL-2 production of Con A blasts and IL-2 response of PBMC with increasing UVA fluence. The expressions of LFA-1, VLA-4, CD4, CD8 and CD25 (IL-2R) molecules were decreased in PUVA-treated Con A blasts. Con A blasts were more sensitive than untreated PBMC to PUVA treatment. These results suggest that the therapeutic effects of PUVA on psoriasis vulgaris can be induced by suppression of the expression of cell surface molecules of activated T lymphocytes.

Quantitative switch in integrin expression accompanies differentiation of F9 cells treated with retinoic acid

F9 embryonal carcinoma cells resemble epithelial cells when in monolayer culture. After treatment with retinoic acid these cells differentiate into fibroblastic-like cells in a sequence that has been modeled as the mammalian equivalent of the differentiation from stem cells of the inner cell mass to parietal endoderm. This study examined the changes in integrin subtypes that accompany retinoic acid-induced differentiation of F9 cells. Although several integrins were found to be present on the surface of F9 cells and retinoic acid-induced (RA) cells, the two dominant integrins were alpha 3 beta 1 and alpha 5 beta 1. Differentiation of F9 cells resulted in about 10- to 25-fold increase in the amount of alpha 3 beta 1 integrin protein as measured by immunoprecipitation of cell surface labeled material. There was a corresponding several-fold reduction of alpha 5 beta 1 protein. The concentration of alpha 3 mRNA was about the same in F9 and RA cells while the concentration of alpha 5 mRNA dropped several-fold after retinoic acid treatment. Thus alpha 3 regulation appeared to be largely posttranscriptional while the drop in alpha 5 protein may have been a result of transcriptional down-regulation. Quantitative measurement of adhesion suggested that most of the F9 and RA cell-substrate adhesion to fibronectin or laminin is mediated by these integrins. They are the dominant integrins present, and antibodies to either these integrins or to the substrate blocked the adhesion. Despite the large switch in integrin subtype protein expression there was little difference between the two cell types in initial cell interactions when adhesive affinities were measured quantitatively. Also there was no difference between the two phenotypes in rate of initial adhesive strengthening. The phenotypic difference was first observed with later events in the attachment and spreading of the RA-treated cells to the substrate. These results show that retinoic acid treatment alters the amounts of alpha 5 and alpha 3 integrin subunits during the F9 to RA phenotypic switch. The data show that these integrins are important in the cell-substrate adhesion to fibronectin and laminin. They show, however, that the phenotypic changes observed with differentiation are not associated with the initial preferential adhesions to the substrate, but rather with consequences that alter the cytoskeletal architecture of the cell.

Cell-type related and spatial variation in the expression of integrins in cutaneous tumors

Integrins constitute a group of transmembrane proteins which mediate cell-cell and cell-matrix interactions. Previous studies have shown both increased and decreased expression of integrins in relation to malignancy and invasion. In the present study, we investigated integrin distribution in cutaneous tumors by using monoclonal antibodies on frozen tissue sections. Antibodies to integrin subunits alpha v, alpha 3, alpha 4, alpha 5, alpha 6, beta 1 and beta 3 were used. The study was designed to explore (i) the association between integrin expression and the tumor type, and (ii) the effect on the integrin expression of the location of the tumor, i.e. whether it grows intraepidermally or within various compartments of the dermis (papillary or reticular). Beta 1, beta 3 and alpha 3 were strongly or moderately expressed in the epithelial and stromal cells of basal cell carcinomas (BCC), seborrheic keratoses, solar keratoses, dermatofibromas (DF), and showed a variable expression in the nevic cells of benign and dysplastic nevocellular nevi. alpha v and in alpha 5 appeared strongly expressed in the stromal cells of BCC and DF, while only a focal, often weak staining was seen in nevic cells and in the epithelial cells of BCCs. In some nevocellular nevi, they were only expressed, together with alpha 4, in the deep-seated nevic cells in the reticular dermis. alpha 6 was expressed by tumor cells of BCCs and nevocellular nevi only within the dermo-epidermal junction. In seborrheic keratosis and solar keratosis a basement membrane-associated staining pattern for alpha 6 was seen in the basal cell layer, with focal discontinuities in solar keratosis.(ABSTRACT TRUNCATED AT 250 WORDS)

A role of VLA-6 laminin receptor in invasion of breast carcinoma

The integrin VLA-6 as a laminin receptor and laminin as a ligand for laminin receptor were detected immunohistochemically in normal, benign tumor and carcinoma tissues of the breast. Epithelial cells of both normal breast and benign tumor were in almost all cases strongly immunoreactive for VLA-6 in the plasma membrane. Carcinoma cells in 34 of 70 cases (49%) with an invasive component were not immunoreactive for VLA-6, and no carcinoma cells showed strong positivity. Although carcinoma cells in only four of 51 cases (8%) with intraductal components were negative for VLA-6, 37 cases (72%) showed weak expression of VLA-6 and 10 cases (20%) showed strong expression of VLA-6. A concordant expression of VLA-6 on carcinoma cells and laminin around carcinoma cell nests with an invasive component was observed, and VLA-6 expression in carcinoma cells was correlated to tubular formation in carcinoma cell nests as an indicator of differentiation. These findings suggest that loss of VLA-6 plays a role in the invasion of breast carcinoma, and that VLA-6 laminin receptor and laminin may contribute to tubular differentiation of breast carcinoma cells.

Adhesion molecules and their role in cancer metastasis

This article describes various adhesion molecules and reviews evidence to support a mechanistic role for adhesion molecules in the process of cancer metastasis. A variety of evidence supports the involvement of specific adhesion molecules in metastasis. 1. For example, some cancer cells metastasize to specific organs, irrespective of the first organ encountered by the circulating cancer cells. This ability to colonize a specific organ has been correlated with the preferential adhesion of the cancer cells to endothelial cells derived from the target organ. This suggests that cancer cell/endothelial cell adhesion is involved in cancer cell metastasis and that adhesion molecules are expressed on the endothelium in an organ-specific manner. 2. Further, inclusion of peptides that inhibit cell adhesion, such as the YIGSR- or RGD-containing peptides, is capable of inhibiting experimental metastasis. 3. Metastasis can be enhanced by acute or chronic inflammation of target vessels, or by treatment of animals with inflammatory cytokines, such as interleukin-1. In vitro, cancer cell/endothelial cell adhesion can be enhanced by pretreating the endothelial cell monolayer with cytokines, such as interleukin-1 or tumor necrosis factor-alpha. This suggests that, in addition to organ-specific adhesion molecules, a population of inducible endothelial adhesion molecules is involved and is relevant to metastasis. 4. Further support for this model is found in the comparison to leukocyte/endothelial adhesion during leukocyte trafficking. Convincing evidence exists, both in vivo and in vitro, to demonstrate an absolute requirement for leukocyte/endothelial adhesion before leukocyte extravasation can occur. The relevance of this comparison to metastasis is reinforced by the observation that some of the adhesion molecules involved in leukocyte/endothelial adhesion are also implicated in cancer cell/endothelial adhesion. The involvement of adhesion molecules suggests a potential therapy for metastasis based on interrupting adhesive interactions that would augment other treatments for primary tumors.

Regulation of fibronectin and laminin binding activity in cultured human lymphoblastic cell lines

The current study shows that a clonal derivative of the Jurkat cell line up-regulates both the avidity and density of the alpha 6/beta 1 receptor in response to phorbol 12-myristate 13-acetate (PMA). This derivative attaches to fibronectin and, to a lesser degree, laminin constitutively. Adhesion and spreading are dramatically up-regulated following treatment with PMA. The response on fibronectin peaks within 4 hours, is insensitive to cyclohexamide, can be blocked by monoclonal antibodies (Mabs) to the beta 1 and alpha 5 subunits of the beta 1 family of integrins, and is not associated with increased expression of the alpha 5 or beta 1 epitopes at the cell surface. In contrast, the response on laminin is biphasic. The early phase parallels the response on fibronectin. The second phase peaks after 48-72 hours of treatment with PMA, is sensitive to cycloheximide, can be blocked by Mabs to the beta 1 and alpha 6 subunits, and is associated with increased expression of the alpha 6 epitope. Both the density independent and dependent responses to PMA in Jurkat cells are blocked by the protein kinase inhibitor staurosporine. The HSB-2, CEM, Molt-4, and HPB-ALL T-lymphoblastic cell lines also up-regulate attachment to fibronectin and laminin following treatment with PMA. All four lines constitutively attach to fibronectin and show rapid up-regulation of attachment following treatment with PMA. None of the lines attach to laminin prior to PMA treatment; however, specific adhesion developed after 4-120 hours of treatment. The most mature lines (Jurkat and HPB-ALL) up-regulated adhesion on laminin more rapidly than the less phenotypically mature lines (CEM, Molt-4, and HSB-2). In summary, clonal derivatives of the Jurkat cell line up-regulated attachment to laminin through protein kinase dependent increases in alpha 6/beta 1 receptor avidity and density. In addition, the expression of functional receptors for laminin is linked to developmental maturity in a series of T-lymphoblastic cell lines.

Thalidomide derivatives and the immune system. I. Changes in the pattern of integrin receptors and other surface markers on T lymphocyte subpopulations of marmoset blood

Treatment of marmosets (Callithrix jacchus) with thalidomide (Thd) or its derivative EM12 (which is also teratogenic, but more stable to hydrolysis) resulted in the lack of reaction of adhesion surface receptors (integrins) on T lymphocytes in venous blood. Lymphocyte subsets appeared, for example CD4+CD2-, which are not found under normal conditions. (a) There was no clear effect of the treatments on the total number of leukocytes or lymphocytes or on the total number of CD4+ or CD8+ T lymphocytes. (b) A decrease in the percentage of the cytotoxic T cells carrying the CDw29 marker (CD8+CD56+CDw29+) at a dose as low as 5 mg EM12/kg bw, and an increase in the percentage of suppressor cells carrying the CDw29 marker (CD8+CD56-CDw29+) at 10 mg EM12/kg bw were found. Similar effects were induced by Thd at somewhat higher doses, while supidimide (Sup) was less active even at the very high dose of 100 mg/kg bw. Especially at the lower doses these effects occurred with a lag phase and persisted after discontinuation of the dosing. Alterations induced in helper T cell subpopulations by Thd or EM12 were less impressive (no significant effect was observed with 5 mg EM12/kg bw). Some changes were observed at higher dose levels in the CD4+CD45RA+CDw29+ cells and the CD4+CD45RACDw29+ cells. (c) The most significant effect, reduction in the reactivity of CD2+, was detectable subsequent to daily oral doses as low as 10 mg Thd/kg or 1 mg EM12/kg bw. Peak plasma concentrations to be expected under these experimental conditions are less than 1 micrograms/ml. (d) The surface receptors found to be affected include among others: CD2 (LFA-2) and CD11a (LFA-1 alpha) and CD18 (LFA-1 beta). Clearly, CD4+ cells were found to be more susceptible to the loss of the integrin receptors than CD8+ cells. (e) The effect persisted for several weeks subsequent to the discontinuation of the dosing. (f) A rough estimate of the relative potency to reduce the CD2 receptor in the marmoset suggests EM12 to be five to ten times more potent than Thd. Sup, a Thd derivative reported to exhibit no or a low teratogenic potency, was found to be at least five times less potent than Thd. (g) The alterations of surface adhesion receptors by the substances studied in this investigation were not confined to T lymphocytes. We also observed similar effects on B lymphocytes, monocytes, and neutrophils, and many other cell types carrying such receptors might be affected.(ABSTRACT TRUNCATED AT 400 WORDS)

Synovial fluid cells in juvenile arthritis: evidence of selective T cell migration to inflamed tissue

The perpetuation of chronic synovitis in juvenile arthritis (JA) is a complex interaction of local and systemic regulatory mechanism. We examined the cell surface phenotype of synovial fluid cells and peripheral blood lymphocytes from 15 patients with JA to better understand the mechanism of local inflammation. Synovial fluid and peripheral blood mononuclear cells were analysed for cell surface expression of CD2, CD3, CD4, CD8, CD19, CD25, CD29, CD45R and Ia using flow cytometry. We found a very low percentage of B cells with a concomitant increase of T cells in synovial fluid as compared with peripheral blood. A large percentage of the synovial fluid T cells were HLA-DR+, or activated T cells, and there was a relative decrease in CD4+ cells in synovial fluid as compared with peripheral blood. There was only a minimal increase in CD25+ synovial fluid cells. The synovial fluid CD4+ cells were mainly of the CD2high, CD29+, CD45RO phenotype. This CD4 phenotype found on synovial fluid cells from patients with JA and in particular the CD29 cell surface marker, which recognizes a common beta-chain of adhesion molecules, is associated with binding to extracellular matrix proteins and is also associated with 'primed' T cells. Our results demonstrated the presence of T cells which either selectively migrate to synovium and synovial fluid or are activated in situ in the joint.

A point mutation of integrin beta 1 subunit blocks binding of alpha 5 beta 1 to fibronectin and invasin but not recruitment to adhesion plaques

A point mutation in a highly conserved region of the beta 1 subunit, Asp130 to Ala (D130A) substitution, abrogates the Arg-Gly-Asp (RGD)-dependent binding of alpha 5 beta 1 to fibronectin (FN) without disrupting gross structure or heterodimer assembly. The D130A mutation also interferes with binding to invasin, a ligand that lacks RGD sequence. In spite of the lack of detectable FN binding by alpha 5 beta 1(D130A), it was recruited to adhesion plaques formed on FN by endogenous hamster receptors. Thus, intact ligand binding function is not required for recruitment of alpha 5 beta 1 to adhesion plaques. Overexpression of beta 1(D130A) partially interfered with endogenous alpha 5 beta 1 function, thus defining a dominant negative beta 1 integrin mutation.

Fibroblast-mediated collagen gel contraction does not require fibronectin-alpha 5 beta 1 integrin interaction

Fibroblasts cultured within free-floating collagen gels can bind to and reorganize the surrounding collagen fibrils into a more dense and compact arrangement. Collagen gel contraction provides an in vitro model for studying fibroblast-collagen interactions important in wound healing, fibrosis, scar contraction, and connective tissue morphogenesis. We have assessed the role of fibronectin and its interaction with the alpha 5 beta 1 "high affinity" fibronectin-specific integrin receptor in collagen gel contraction. A variety of agents, which specifically inhibit fibronectin-alpha 5 beta 1 interactions, were tested for their abilities to inhibit fibroblast-mediated collagen gel contraction. These included anti-alpha 5 beta 1 monoclonal antibodies, the synthetic peptide GRGDSP, the cell adhesive fragment of fibronectin, and an antibody against the cell adhesive region of fibronectin. None of these agents inhibited collagen gel contraction. Therefore, it is concluded that fibronectin-alpha 5 beta 1 interactions are not necessary for collagen gel contraction. However, collagen gel contraction is dependent on a member or members of the beta 1 subfamily of integrin matrix receptors. A polyclonal antiserum and a monoclonal antibody, both directed against the beta 1 subunit of integrin matrix receptors, inhibited the spreading of fibroblasts in the collagen gel and inhibited collagen gel contraction. This study demonstrates that fibroblast-mediated collagen gel contraction is independent of fibronectin-alpha 5 beta 1 interactions but dependent on an interaction of beta 1 integrin matrix receptors with collagen fibers.

The integrin-binding domain of invasin is sufficient to allow bacterial entry into mammalian cells

Yersinia pseudotuberculosis is able to enter normally nonphagocytic host cells by multiple pathways, the most efficient of which is mediated by invasin, a 986-amino-acid bacterial outer membrane protein. It has previously been shown that the C-terminal 192 amino acids of invasin are sufficient to bind mammalian cells. To determine if additional regions of the invasin protein are necessary to promote entry, we developed a novel assay that tests the ability of various invasin derivatives to confer on Staphylococcus aureus the ability to enter animal cells. We determined that the 192-amino-acid cell-binding region of invasin, when used to coat the bacterial cell surface, was also sufficient to promote cellular penetration. These results suggest that the simple binding of invasin to its receptors is sufficient to mediate entry and that the bacterium plays a largely passive role in the entry process.

Leukocyte integrins: structure, function and regulation of their activity

Adhesion is a crucial requirement for the correct regulation of immune and inflammatory responses. In the immune system, leukocytes can interact with each other and with vascular endothelium as well as with extracellular matrix components, changing rapidly and transiently from circulating non-adherent to adherent states. Most of these interactions are mediated by integrins. This review will focus mainly on the structure and function of integrins expressed by leukocytes. The mechanisms for regulating the functional activity of these adhesion receptors, as well as the intracellular signals transduced through integrins, are described.

Integrin receptors and RGD sequences in human keratinocyte migration: unique anti-migratory function of alpha 3 beta 1 epiligrin receptor

The migration of keratinocytes over the wound bed plays an important role in the re-epithelialization of cutaneous wounds. However, the mechanisms by which keratinocytes migrate over extracellular matrix components are unknown. In this study, we sought to determine if the RGD sequences in matrix molecules and recognition of these sequences by keratinocytes played a role in the locomotion of keratinocytes. After allowing the cells to attach to the matrix, RGD-containing peptides or control peptides were added to a keratinocyte migration assay. The addition of RGD-containing peptide dramatically inhibited keratinocyte locomotion on a matrix of fibronectin but not on collagen matrices. Therefore, RGD recognition is a critical step for fibronectin-mediated migration but not for collagen-mediated migration. Because the RGD sequences are recognized by cell-surface integrin receptors in a number of cell types, we next examined the roles of integrin receptors in human keratinocyte migration. Using monospecific antibodies that recognize integrin subunits, we found that blocking the beta 1 subunit inhibited the migration of keratinocytes on matrices of fibronectin, interstitial collagen, and basement membrane collagen. Blocking the alpha 5 beta 1 receptor significantly inhibited migration on fibronectin but not on collagen matrices. Conversely, blocking the alpha 2 beta 1 receptor inhibited migration on collagen matrices but not on fibronectin. Blocking the alpha 3 beta 1 receptor uniquely enhanced migration on fibronectin and collagen matrices. In contrast to cells apposed to matrices without the receptor blocked, the enhanced migration in the presence of anti-alpha 3 beta 1 antibody occurred at the later time points of the migration assay. The enhancement of migration by blocking the alpha 3 beta 1 integrin receptor suggests that the interaction of the alpha 3 beta 1 receptor with matrices is associated with immobility.

Synergistic effects of nerve growth factor and phorbol 12-myristate 13-acetate on rapid motility and process formation in PC12 cells: the role of laminin

A126-1B2 cells, a PKA (cAMP-dependent protein kinase)-deficient variant of PC12 cells, but not parental PC12 cells, form processes within 15-30 min of exposure to both nerve growth factor (NGF) and activators of protein kinase C when grown on tissue culture plastic (Glowacka and Wagner, J Neurosci Res 25: 453-462, 1990). Time-lapse microscopy has demonstrated that these processes are formed by a novel mechanism, i.e., rapid movement of the cell body away from a point of attachment, which morphologically resembles a growth cone. These "fast" neurites are attached to the substratum at a number of points, which display membrane activity in the form of active ruffling and the extension of filopodia and membrane pleats. Thus, these processes are formed by a mechanism distinct from that used by PC12 and other neuronal cells to form processes in culture. Wild-type PC12 cells also migrate and form fast neurites in response to a combination of NGF and phorbol 12-myristate 13-acetate (PMA), when they are grown in conditioned media or plates, suggesting that a secreted factor that can bind to the substratum is essential for the rapid formation of these neurites. Similarly, wild-type PC12 cells grown on a laminin-coated substratum also migrate and form "fast neurites" in response to a combination of NGF and PMA. This rapid migration is attenuated by an anti-alpha 1, beta 1-integrin antisera, implicating a laminin-integrin interaction; and it is inhibited by alpha-lactalbumin, suggesting an involvement of a beta 1,4 galactosyltransferase in the response. The formation of fast neurites is not dependent on concurrent protein synthesis, but it is inhibited by lithium, cytochalasin D, and methylthioadenosine or pretreatment of cells with NGF. Thus PC12 cells grown on the appropriate substrate have the ability to migrate rapidly and thereby form neuron-like processes within minutes of exposure to NGF and PMA. This morphological response to a combination of agents may provide an alternative means by which nerve cells form connections. Alternatively, it may reflect a mechanism that facilitates cellular migration during developmental processes.

Separation of important new platelet glycoproteins (GPIa, GPIc, GPIc*, GPIIa and GMP-140) by f.p.l.c. Characterization by monoclonal antibodies and gas-phase sequencing

A large number of membrane glycoproteins (around 40) are present on the surface of human blood platelets. Some of these glycoproteins are expressed in relatively small amounts, and their functions, as well as their structure, remain to be elucidated. The aim of the present study was to separate rapidly, under non-denaturing conditions, and characterize minor glycoproteins such as Very Late Antigens (VLA) (GPIa, GPIc, GPIc* and GPIIa) and GMP-140 (also known as PADGEM). VLAs and GMP-140 are respectively members of the integrin and selectin families. Platelet membrane glycoproteins were separated by wheat-germ agglutinin lectin affinity and Mono Q anion-exchange f.p.l.c. Peaks bearing isolated glycoproteins were electrophoresed on one- or two-dimensional SDS/polyacrylamide gels, Western blotted on to Immobilon poly(vinylidene difluoride) membranes and gas-phase-sequenced. The identity of isolated glycoproteins was also obtained by the use of monoclonal or polyclonal antibodies and tryptic peptide maps. Five minor [GPIa, GPIc, GPIc*, GPIIa and GMP 140 (PADGEM)], as well as a major (GPIIIb) glycoprotein, were eluted at low salt concentrations. GPIIb-IIIa and GPIb were eluted at high salt concentrations. The N-terminal sequence of platelet GPIa was identical with that obtained by Takada & Hemler [(1989) J. Cell Biol. 109, 397-407]. However, the N-terminal sequence of platelet GPIc + Ic* and GPIIa were found to differ from those deduced from cDNA sequences isolated from human placenta or umbilical-vein endothelial-cell cDNA libraries. The combined use of f.p.l.c. and gas-phase sequencing techniques provides a very powerful tool to separate and characterize rapidly platelet or other cellular proteins for structural, immunological and functional studies.

Laminin-binding integrin alpha 7 beta 1: functional characterization and expression in normal and malignant melanocytes

A novel integrin, alpha 7 beta 1, that specifically binds with high affinity to laminin has been identified on melanoma cells. This complex was purified from both human and murine melanoma cells by laminin-affinity chromatography, and the alpha 7 subunit was recovered after gel electrophoresis. N-terminal amino acid sequence analysis of the alpha 7 subunit from both human and mouse cells verifies that this integrin is distinct from other alpha chains in the beta 1 family, although strikingly similar to the alpha 6 subunit. By using specific proteolytically derived fragments of laminin, it was determined that the alpha 7 beta 1 complex binds selectively to the E8 region, which represents part of the long arm of laminin. In contrast, the receptor failed to bind to the P1 fragment, which contains the intersection of the short arms of laminin. Although the alpha 7 beta 1 complex was commonly expressed in melanoma cells, this integrin was not detected in normal melanocytes, suggesting that alpha 7 expression may be associated with malignant transformation. These results establish the existence of a novel integrin that binds to the E8 domain of laminin and appears to mediate cell adhesion to this ligand.

Molecular cloning and expression of the cDNA for alpha 3 subunit of human alpha 3 beta 1 (VLA-3), an integrin receptor for fibronectin, laminin, and collagen

alpha 3 beta 1 (VLA-3), a member of the integrin family of cell adhesion receptors, may function as a receptor for fibronectin, laminin, and collagen. A partial cDNA clone (2.4 kb) for the human alpha 3 subunit was selected from an endothelial cell lambda gt11 cDNA library by specific antibody screening. Several overlapping cDNA clones were subsequently obtained, of a total length of 4.6 kb from various cDNA libraries. The reconstructed alpha 3 cDNA was expressed on the surface of chinese hamster ovary cells as detected by an alpha 3-specific mAb after transfection, suggesting that the cDNA is authentic. Within this sequence was an open reading frame, encoding for 1,051 amino acids, including a signal peptide of 32 residues, a long extracellular domain (959 residues), a transmembrane domain (28 residues), and a short cytoplasmic segment (32 residues). Overall, the alpha 3 amino acid sequence was 25-37% similar to the other integrin alpha subunits that are cleaved, with most similarity to the alpha 6 sequence (37%), and less similarity to those alpha subunits that have I domains (15-20%, excluding the I domain sequence itself). Features most like those in other alpha subunits are (a) the positions of 18/19 cysteine residues, (b) three potential metal binding domains of the general structure DX(D/N)X(D/N)GXXD, and (c) the predicted transmembrane domain. The mass of alpha 3 calculated from its amino acid sequence is 113,505. The human alpha 3 sequence was 89% identical to hamster galactoprotein b3, and 70% similar to the chicken CSAT antigen band 2 protein partial sequence, suggesting that these two polypeptides are homologues of human alpha 3.

Characterization of a type IV collagen major cell binding site with affinity to the alpha 1 beta 1 and the alpha 2 beta 1 integrins

The aim of this investigation was to identify the domains of type IV collagen participating in cell binding and the cell surface receptor involved. A major cell binding site was found in the trimeric cyanogen bromide-derived fragment CB3, located 100 nm away from the NH2 terminus of the molecule, in which the triple-helical conformation is stabilized by interchain disulfide bridges. Cell attachment assays with type IV collagen and CB3 revealed comparable cell binding activities. Antibodies against CB3 inhibited attachment on fragment CB3 completely and on type IV collagen to 80%. The ability to bind cells was strictly conformation dependent. Four trypsin derived fragments of CB3 allowed a closer investigation of the binding site. The smallest, fully active triple-helical fragment was (150)3-amino acid residues long. It contained segments of 27 and 37 residues, respectively, at the NH2 and COOH terminus, which proved to be essential for cell binding. By affinity chromatography on Sepharose-immobilized CB3, two receptor molecules of the integrin family, alpha 1 beta 1 and alpha 2 beta 1, were isolated. Their subunits were identified by sequencing the NH2 termini or by immunoblotting. The availability of fragment CB3 will allow for a more in-depth study of the molecular interaction of a short, well defined triple-helical ligand with collagen receptors alpha 1 beta 1 and alpha 2 beta 1.

Distribution of beta 1, alpha 1, alpha 2 and alpha 3 integrin chains in basal cell carcinomas

The integrins are alpha beta heterodimeric transmembrane proteins mediating cell-substratum as well as cell-cell interactions. Changes in their expression and/or function seem to occur in a number of malignant epithelial neoplasms and may in part explain their abnormal patterns of growth and differentiation. Using monoclonal antibodies to the beta 1 (DH12), alpha 1 (TS2/7), alpha 2 (B1.515), and alpha 3 (E1.56) integrin chains, the alpha 1 beta 1 (VLA-1), alpha 2 beta 1 (VLA-2), and alpha 3 beta 1 (VLA-3) integrin receptors were studied on cryostat sections of 22 basal cell carcinomas (BCCs) and adjacent normal tissues by a standard peroxidase-antiperoxidase technique. In non-neoplastic skin, VLA-2 and VLA-3 were found in the basal layer, eccrine glands, and cells of the outer root sheath in which VLA-1 was detected. In BCCs, there was a considerably higher expression of VLA-2 and VLA-3 compared with epidermal basal cells but similar to that seen in hair bulb and outer root sheath. In two cases of nodular BCC showing evidence of regression, both VLA-2 and VLA-3 were completely negative, in contrast to non-regressing foci which were strongly positive. The high level of expression of two adhesion molecules (VLA-2 and VLA-3) involved in cell-substratum as well as cell-cell interactions may account for the more indolent pattern of growth characteristic of BCC and perhaps reflect its high degree of differentiation towards the hair follicle.

Plasticity of integrin expression by nerve-derived connective tissue cells. Human Schwann cells, perineurial cells, and fibroblasts express markedly different patterns of beta 1 integrins during nerve development, neoplasia, and in vitro

Strikingly selective expression patterns of beta 1, alpha 2, alpha 3, and alpha 5 integrin subunits were revealed in endoneurium, perineurium, and epineurium of fetal and adult human peripheral nerve by immunostaining with specific antibodies. The alpha 2 subunit was expressed only on Schwann cells both in fetal and adult nerve, whereas the alpha 3 epitopes were expressed exclusively in the adult tissue and were primarily present on perineurial cells. The alpha 5 epitopes were expressed only on the innermost cell layer of perineurium of fetal and adult nerve. The tumor cells within schwannomas and cutaneous neurofibromas expressed both alpha 2 and alpha 3 subunits, indicating that Schwann cells have the potential to express also the alpha 3 subunit in vivo. Cell cultures established from human fetal nerve and neurofibromas revealed expression of the alpha 2 and alpha 5 epitopes on Schwann cells, perineurial cells, and fibroblasts, whereas only Schwann cells contained the alpha 3 epitopes which were occasionally concentrated on the adjacent Schwann cells at cell-cell contacts. Our findings emphasize that nerve connective tissue cells change their profiles for expression of extracellular matrix receptors under conditions which have different regulatory control signals exerted by, for example, axons, humoral factors, or the extracellular matrix of the peripheral nerve. This plasticity may play an important role during nerve development and in neoplastic processes affecting the connective tissue compartments of peripheral nerve.

Expression of collagen binding integrins during cardiac development and hypertrophy

The interaction between components of the extracellular matrix and the cell surface of cardiac myocytes appears to be regulated in part by receptors belonging to the integrin superfamily. The expression of the integrins was investigated at different stages of development of the heart as well as during cardiac hypertrophy. The characterization of the membrane proteins showed that a beta 1-integrin and associated alpha-chains were responsible for the interaction with collagen, laminin, and fibronectin. Immunoprecipitation data indicated that the presence of specific alpha-chains varied with development. These data were correlated with the ability of the isolated myocytes to attach to specific components of the extracellular matrix. The expression of the alpha 1-chain was prominently associated with the recognition of interstitial collagens. The presence of the alpha 1-chain was also associated with stages when collagen synthesis was increased, especially during fetal and neonatal growth and cardiac hypertrophy. Immunohistochemical localization with the antiserum against beta 1-integrin demonstrated its specific localization near the Z lines of cardiac myocytes. The localization both in vitro and in vivo indicated that the beta 1-integrin may play a role in myofibrillogenesis during development. The present immunohistochemical, cell adhesion, and biochemical data clearly indicate that integrins play a major role in the regulation of the interaction between cardiac myocytes and the extracellular matrix during development and disease.

Expression and role of integrins in adhesion of human colonic carcinoma cells to extracellular matrix components

We have examined integrin expression and function in the human colon carcinoma cell line HT29, and in clonal sublines derived from the HT29 line. These cells express several different integrin subunits including beta 1, alpha 2, 3, 6 and alpha v, but do not express the classic alpha 5/beta 1 fibronectin receptor. Clonal variation in the pattern of integrin expression was quite limited. The profile of integrin expression correlates well with the adhesive behavior of HT29 cells. Thus the cells adhere well to vitronectin, laminin and type IV collagen, but not at all to fibronectin. Adhesion to collagen was completely blocked by an anti-beta 1 monoclonal antibody, indicating that beta 1 integrins mediate this process. Adhesion to laminin was strongly blocked by anti-beta 1 monoclonal or anti-beta 6 monoclonal, suggesting that the alpha 6/beta 1 complex functions in attachment to laminin; this was somewhat surprising since immunoprecipitation experiments indicate that most of the alpha 6 subunit seems to be associated with the beta 4 subunit. Despite their strong adherence to laminin, collagen and vitronectin, HT29 cells are not very motile and, in response to gradients of these proteins, do not migrate nearly as well as CHO cells tested under similar conditions. Since HT29 cells can undergo an enterocyte-like differentiation in glucose-free medium, we compared integrin expression in HT29 and its subclones during the process of differentiation. There was no correlation between the state of differentiation, as assessed by expression of brush-border hydrolases, and the level of expression of any of the integrin subunits measured. Thus the pattern of integrin expression in these colonic tumor cells seems to be a characteristic of the cell line, and is not readily modified by changes in cell growth or differentiation.

The RGD containing site of the mouse laminin A chain is active for cell attachment, spreading, migration and neurite outgrowth

The laminin A chain has been sequenced by cDNA cloning and was found to contain an RGD sequence. Synthetic peptides containing the RGD sequence and flanking amino acids were active in mediating cell adhesion, spreading, migration, and neurite outgrowth. Furthermore, endothelial cell attachment to a laminin substrate was inhibited by an RGD-containing synthetic peptide. Antisera against the integrin (fibronectin) receptor, and monoclonal antibody to the integrin, VLA-6, inhibited cell interaction with laminin, as well as with peptides containing an RGD sequence. These results suggest that the RGD containing site of laminin is active and interacts with the integrin family of receptors in certain cells.

Expression and functions of very late antigen 1 in inflammatory joint diseases

In the human immune system, very late antigen 1 (VLA-1), a putative collagen receptor, is expressed on the surface of T lymphocytes that have undergone mitogenic or antigenic stimulation. A new VLA-1-specific monoclonal antibody, 1B3.1, was used to probe the expression and function of VLA-1 on T lymphocytes in patients with arthritis. Synovial mononuclear cells from the joints of patients with rheumatoid arthritis or other joint diseases contained 32.9 +/- 13.8% 1B3.1-positive cells (42.8 +/- 10.4% in patients with rheumatoid arthritis and 28 +/- 12.6% in non rheumatoid patients). In the peripheral blood, patients with active rheumatoid arthritis expressed VLA-1 on 11.7 +/- 6.0% of their mononuclear cells, compared to 1.9 +/- 1.5% in controls (P less than 0.001). Using dual fluorescence analysis, virtually all the 1B3.1-positive synovial cells were CD3+ T lymphocytes and included both CD4+ and CD8+ T cells. When 1B3.1-expressing synovial mononuclear cells or in vitro activated T lymphocytes were triggered with anti-CD3 antibodies, marked augmentation of their proliferation occurred if they were simultaneously cross-linked with mab 1B3.1. Collagen type IV, a putative ligand of VLA-1, also augmented T-cell proliferation to anti-CD3. The data suggest that the VLA-1 molecule could play an important role in the pathophysiology of arthritis by modulating T-cell activation in these diseases.