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PubMed2000

Integrins as receptors for laminins.

Laminins are a family of trimeric glycoproteins present in the extracellular matrix and the major constituents of basement membranes. Integrins are alpha beta transmembrane receptors that play critical roles in both cell-matrix and cell-cell adhesion. Several members of the integrin family, including alpha 1 beta 1, alpha 2 beta 1, alpha 3 beta 1, alpha 6 beta 1, alpha 7 beta 1 and alpha 6 beta 4 heterodimers serve as laminin receptors on a variety of cell types. This review summarizes recent advances in understanding the involvement of individual integrins in cell interactions with laminins and the roles of laminin-binding integrins in adhesion-mediated events in vertebrates, including embryonic development, cell migration and tumor cell invasiveness, cell proliferation and differentiation, as well as basement membrane assembly. We discuss the regulation of integrin function via alternative splicing of cytoplasmic domains of alpha and beta subunits of the integrin receptors for laminins and present examples of functional collaboration between laminin-binding integrins and non-integrin laminin receptors. Advances in our understanding of the laminin-binding integrins continue to demonstrate the essential roles these receptors play in maintaining cell polarity and tissue architecture.

Animals↗

PubMed2001

Activation of beta(1) integrins mediates proliferation and inhibits apoptosis of intestinal CD4-positive lymphocytes.

A characteristic of lamina propria lymphocytes (LPL) is their low proliferative response to stimuli of the CD3 pathway. beta(1) integrins were expressed on LPL; however, their function is unknown. Therefore, we determined whether beta(1) integrins contribute to T cell responses by providing costimulatory signals. Integrins on CD4(+) LPL of controls and patients with inflammatory bowel disease were characterized by flow cytometry. Cells were stimulated by anti-CD3 or anti-CD2 antibodies either alone or in combination with a stimulatory beta(1) integrin antibody (12G10). Proliferation and apoptosis were measured by [(3)H]thymidine pulsing or flow cytometry. Cytokine mRNA and apoptosis-related transcripts were quantified by reverse transcriptase-PCR. We demonstrated that beta(1) integrin costimulation restored CD3-induced proliferation of CD4(+) LPL and reduced activation-induced apoptosis. Activation of beta(1) integrins by addition of 12G10 antibody to CD3-stimulated cells restored their capacity to express proinflammatory cytokine transcripts. Further, expression of the activated form of beta(1) integrins was significantly elevated on LPL from inflamed mucosa. These studies demonstrate that beta(1) integrin costimulation modulates the response of LPL after TCR stimulation. An increased expression of activated beta(1) integrins on LPL in intestinal inflammation may abolish their unresponsiveness to antigens and perpetuate the inflammatory process.

Adult↗

PubMed2001

Focal adhesion kinase regulates beta1 integrin-dependent T cell migration through an HEF1 effector pathway.

Although beta1 integrin-dependent T cell migration is required for immune function, little is known of the signaling pathways regulating this migration. We now show that the cytoplasmic tyrosine kinase, focal adhesion kinase (FAK) plays an essential role in the beta1 integrin-stimulated migration of T cells through regulation of the unique Crk-associated substrate (Cas) family docking protein, human enhancer of filamentation 1 (HEF1) and effects on "outside-in" beta1 integrin signaling. Overexpression of wild-type FAK promoted beta1 integrin-dependent Jurkat T cell migration, whereas FAK mutated in either its autophosphorylation site or proline rich region 1 (PR1)/HEF1 SH3 domain-binding site had a dominant negative effect on migration. In contrast, neither wild-type nor mutant FAK affected Jurkat cell adhesion to fibronectin, a beta1 integrin ligand. The migration of FAK-overexpressing cells directly correlated with the beta1 integrin-inducible tyrosine phosphorylation of endogenous plus wild-type exogenous FAK, and not with phosphorylation of the FAK-related kinase, Pyk2. FAK was also found to regulate both HEF1-promoted migration, and HEF1 tyrosine phosphorylation in beta1 integrin-stimulated cells, in a manner dependent upon the FAK autophosphorylation and PR1 sites, and HEF1 SH3 domain. Together, our results indicate that beta1 integrin-stimulated T cell migration requires a linear beta1 integrin-FAK-HEF1 effector pathway.

Adaptor Proteins, Signal Transducing↗

PubMed2003

beta1 integrin-mediated signaling induces intercellular adhesion molecule 1 and Fas on rheumatoid synovial cells and Fas-mediated apoptosis.

OBJECTIVE: Rheumatoid arthritis (RA) synovial cells interact with inflammatory cells, as well as extracellular matrices, through integrins. However, the relevance of beta1 integrin to inflammatory processes in RA remains unclear. We examined the role of beta1 integrin-mediated signaling in RA. METHODS: Expression of cell-surface molecules was assessed by FACScan. Engagement of beta1 integrins was performed by crosslinking using a specific monoclonal antibody (mAb) and ligand matrices such as fibronectin or collagen. To determine the involvement of tyrosine kinases in beta1 integrin-mediated signaling, the cells were pretreated with various inhibitors of intracytoplasmic signaling or were transfected with a wild-type focal adhesion kinase (FAK) or a dominant negative truncation of the FAK expression plasmid via cationic liposome-mediated transfection. Apoptosis of synovial cells was detected by double staining with propidium iodide and annexin V. RESULTS: beta1 integrin was highly expressed on RA synovial cells. Engagement of beta1 integrins by crosslinking as well as by ligand matrices markedly up-regulated expression of intercellular adhesion molecule 1 (ICAM-1) and Fas. Up-regulation of ICAM-1 and Fas induced by beta1 integrin was mediated by the tyrosine kinase signaling pathway, especially involving FAK. Fas-mediated early apoptotic change in the cells was amplified by beta1 crosslinking. CONCLUSION: Our results suggest that interaction of beta1 integrins with extracellular matrix augments expression of ICAM-1 and Fas on RA synovial cells, as well as Fas-mediated apoptosis of synovial cells. This might lead to the spontaneous growth arrest through the Fas/Fas ligand pathway observed in RA synovitis.

Antibodies, Monoclonal↗

PubMed2002

Role for alpha 6 integrin during lens development: Evidence for signaling through IGF-1R and ERK.

We show that alpha 6 integrin function was required for normal lens cell differentiation by using an antisense construct to suppress alpha 6 integrin expression. To elucidate the mechanism by which this integrin functions in the regulation of the lens cell differentiation process, we determined the molecular composition of alpha 6 integrin signaling complexes at distinct stages of differentiation in vivo. Because both alpha 6 integrin and insulin-like growth factor-1 (IGF-1) have been implicated in signaling lens cell differentiation, we examined the possibility that they formed a signaling complex in the embryonic lens. Coprecipitation analysis revealed that alpha 6 integrin/IGF-1 receptor complexes were present and that their association was greatest in the equatorial zone, the region of the embryonic lens in which lens cells proliferate and then initiate their differentiation. These results provide in vivo support for the formation of integrin/growth factor receptor signaling complexes. We also found that extracellular signal-regulated kinase (ERK), a downstream effector of both integrin and growth factor receptor signaling pathways, was associated with the alpha 6 integrin signaling complexes in the embryonic lens. This result was supported by our findings that activated ERK, in addition to its nuclear location, localized to lens cell membranes in specific regions of cell-matrix and cell-cell contact. A connection between integrin ligand engagement and ERK activation was shown in vitro after lens cell attachment to laminin. These results demonstrate that alpha 6 integrin function is required for the early stages of lens cell differentiation most likely through its association with the IGF-1 receptor and the activation of ERK.

Animals↗

PubMed2006

Dominant-negative beta1 integrin mice have region-specific myelin defects accompanied by alterations in MAPK activity.

Recent studies have demonstrated the importance of beta1 integrin in oligodendrocyte maturation in vitro. Similar studies in vivo have been difficult due to the embryonic and perinatal lethality of null mutations in integrin subunits. Here, we have generated transgenic mouse models that overexpress full length beta1 integrin or express a dominant-negative beta1 integrin DeltaC (lacking the C-terminal tail) under the control of the proteolipid protein (PLP) promoter. We demonstrate that these transgenes are expressed predominantly in CNS tissues and more specifically in oligodendrocytes. Further analysis reveals that the dominant-negative beta1 integrin DeltaC transgenic mice, but not the full length beta1 integrin mice, have hypomyelinated axons in spinal cords and optic nerves. In addition, there is a significant increase in the number of unmyelinated axons within the spinal cords and optic nerves of the beta1 integrin DeltaC mice. In contrast, the corpus callosum from these mice did not show similar myelin defects. To assess if remyelination would be affected in the corpus callosum, mice were subjected to a cuprizone-induced demyelination. Interestingly, the dominant-negative mice recovered from this insult in a manner similar to the wild type littermates. Axons within the corpus callosum that were remyelinated had normal g-ratios; however, the actual percentage of myelinated axons was significantly reduced compared with wild type mice. We also show that the defects observed in the dominant-negative beta1 integrin DeltaC mice are accompanied by disruption of the MAP-kinase signaling pathway. Our work highlights the importance of beta1 integrin-mediated signaling in CNS myelination in vivo.

Agenesis of Corpus Callosum↗

PubMed2004

The role of fibroblasts in the modulation of integrin-dependent interactions between the gastric cell line HGT-1 and fibronectin.

Fibronectin plays an important role in gastric cancer progression. However, little is known about the microenvironmental factors modulating integrin-dependent interactions between gastric cancer cells and fibronectin. We therefore studied the regulation by fibroblasts of the integrin-dependent adhesion and migration of the gastric cancer cell line HGT-1 onto fibronectin. We first determined, by immunofluorescence, immunoblotting and flow cytometry, that HGT-1 cells expressed alpha3, alpha5, alpha6, alphaV and beta1 integrin chains, and the alphaVbeta3 and alphaVbeta5 dimers. We verified that HGT-1 cells xenografted to the immunosuppressed newborn rat retained the integrin repertoire detected in vitro and were able to induce the formation of tumors rich in fibronectin. By using an in vitro assay in the presence of neutralizing antibodies, we verified that HGT-1 adhesion and migration onto fibronectin involved beta1, alphaV and alpha5 integrin chains; we verified, by using an in situ adhesion test to rat gastric wall frozen sections, that in situ HGT-1 adhesion to fibronectin was integrin dependent. In coculture experiments, we showed that organ-specific fibroblasts from stomach, lung and dermis were able to induce, in a site-specific manner, the expression of beta1, alpha5 and alphaV integrin chains in HGT-1 cells, their integrin-dependent adhesion and migration on fibronectin and their capacity to secrete oncofetal fibronectin. In conclusion, our results show the capacity for tissue-derived fibroblasts to modulate the integrin-dependent interactions between the gastric cell line HGT-1 and fibronectin. They strongly suggest that, in gastric cancer, stromal fibroblasts contribute to promote fibronectin-mediated local invasion by tumor cells.

Animals↗

PubMed2005

COX-2 inhibitors suppress integrin alpha5 expression in human lung carcinoma cells through activation of Erk: involvement of Sp1 and AP-1 sites.

Tumor cell expression of COX-2 has been implicated in the progression of murine and human lung cancer. Inhibition of COX-2 by nonsteroidal antiinflammatory drugs reduces the risk of cancer development in humans and suppresses tumor growth in animal models. However, the underlying mechanisms for this beneficial effect are not fully understood. Here we explore the potential link between the anticancer effects of COX-2 inhibitors and the expression of the integrin alpha5beta1. Expression of this integrin in carcinoma cells is associated with invasiveness and malignant progression. This, together with our studies showing that fibronectin, the ligand of alpha5beta1, stimulates the growth of human lung carcinoma cells, and that this effect is mediated through alpha5beta1-dependent signals, has prompted us to examine the effects of COX-2 inhibitors on alpha5beta1 expression in human non small cell lung carcinoma (NSCLC) cells. We found that the selective COX-2 inhibitors NS398 and Nimesulide decreased mRNA expression and protein production of the integrin alpha5 subunit. This effect was associated with inhibition of NSCLC cell adhesion to fibronectin. The COX-2 inhibitors triggered the phosphorylation of extracellular signal-regulated kinase (Erk) in a time-dependent manner, and the inhibitor of Mek-1/Erk PD98095 prevented their inhibitory effects on integrin alpha5 expression. Transient transfection assays showed that the COX-2 inhibitors affected integrin alpha5 gene transcription by acting between -92 to -41 bp of the human integrin alpha5 gene promoter. Gel mobility shift assays showed that the COX-2 inhibitors increased Sp1 DNA binding, but decreased that of AP-1. These effects were accompanied by an increase in Sp1 protein and a decrease in c-Jun protein expression, as well as inhibition of SAPK/JNK phosphorylation. The Sp1 inhibitor, Mithramycin A, also blocked the inhibitory effect of the COX-2 inhibitors on alpha5 expression and promoter activity. Overall, these findings suggest that COX-2 inhibitors suppress alpha5beta1 integrin expression in NSCLC through effects on integrin alpha5 gene transcription mediated by Erk activation, increased Sp1, decreased AP-1 DNA binding and inactivation of SAPK/JNK signals. Our observations unveil a new mechanism of action against NSCLC for COX-2 inhibitors that relates to regulation of integrin alpha5 gene expression and, consequently, recognition of extracellular matrices (i.e., fibronectin) by tumor cells. (c) 2005 Wiley-Liss, Inc.

Carcinoma, Non-Small-Cell Lung↗

PubMed2002

Overexpression of integrin alphav promotes human osteosarcoma cell populated collagen lattice contraction and cell migration.

Cells attach and interact with the extracellular matrix (ECM) through heterodimeric alphabeta integrin receptors. Specifically, the promiscuous alphavbeta3 integrin and the alpha2beta1 integrin receptors engage numerous matrix components to influence cell adhesion, cell motility, and matrix organization. However, the role of alphav integrin mediating cell-collagen interactions is not clear. In the in vitro cell populated collagen lattice (PCL), a model of cell-matrix interaction, integrin receptors play a role in lattice contraction. To elucidate alphav integrins' effects on cell-collagen interactions, human osteosarcoma (HOS) cells were transfected with alphav integrin (alphav-pcDNA 3.1+). Control HOS cells were transfected with pcDNA 3.1+ vector alone. HOS-alphav cell PCLs contracted to a greater degree than control HOS cell PCLs (P < or = 0.0001). RT-PCR revealed that HOS-alphav cells express both beta1 and beta3 integrins, indicating that alphav has the potential to form a partnership with either beta1 or beta3 integrin. The alphavbeta3 specific inhibitory antibody LM609 significantly retarded HOS-alphav cell PCL contraction (P < or = 0.001), suggesting that alphavbeta3 promotes enhanced HOS-alphav cell PCL contraction. When plated on plastic, control HOS cells show greater elongation compared to HOS-alphav cells. In addition, HOS-alphav cells migrated faster and to a greater degree than control HOS cells (P < or = 0.0001). The possibility that enhanced HOS-alphav cell migration and HOS-alphav cell PCL contraction was caused by increased myosin ATPase activity was examined. HOS-alphav cells showed less myosin ATPase activity than control HOS cells, by an ATP cell contraction bioassay. The enhancement of HOS-alphav cell migration and lattice contraction appears unrelated to increased myosin ATPase activity.

Antibodies, Monoclonal↗

PubMed1990

Distribution of integrins and their ligands in the trunk of Xenopus laevis during neural crest cell migration.

We have examined the distribution in Xenopus embryos of beta 1 subunits of integrin, as recognized by cross-reactive antibodies against the avian integrin beta 1 subunit. These antibodies recognize a doublet of bands of approximately 120 kD in Xenopus embryos. The distribution pattern of these integrin cell surface receptors was compared with that of two possible ligands, fibronectin and laminin, in the extracellular matrix during the time of neural crest cell migration. Integrin immunoreactivity in the early neurula was observed lightly outlining somite and epidermal cells and the notochord. The integrin immunostaining increased with developmental age and was observed on most cell types in the embryo but was particularly notable in the intersomitic clefts through which motoraxons grow. The immunoreactivity in this region was not, however, wholly on the axon surfaces, since intersomitic integrin remained detectable in embryos in which the neural tube had been ablated. Fibronectin and laminin were more extensively distributed than integrin at all stages examined. Immunoreactivity for both was observed around the neural tube, notochord, somites, epidermis, dorsal mesentery, and lateral plate mesoderm. The distribution of laminin and fibronectin around the somites was particularly interesting since it was non-uniform and similar to that of integrin. Strongest staining was observed in the intersomitic clefts, and weakest staining was observed on the medial surface of the somites, which faces the neural tube and notochord. The major differences in distribution pattern between the fibronectin and laminin immunoreactivities were that only fibronectin was detected in the mesenchyme of the dorsal fin. Our results demonstrate that a molecule homologous to avian integrin is present in Xenopus embryos during neural crest cell migration and motoraxon outgrowth. Its presence in the intersomitic clefts and on the surface of many embryonic cell types together with the abundant distribution of its ligands are consistent with a potentially important developmental function in neurite outgrowth and/or muscle development.

Animals↗

PubMed2005

The cytoplasmic tail of the alpha3 integrin subunit promotes neurite outgrowth in PC12 cells.

Binding of integrins to proteins of the extracellular matrix (ECM) provides structural and signaling information for biological processes such as cell proliferation, migration, neurite outgrowth, and differentiation. Integrins represent a family of heterodimeric transmembrane cell surface receptors. Besides connecting the ECM with the cytoskeleton, integrins also induce various signaling pathways in response to ligand binding. Integrin ligation leads to cytoplasmic protein-protein interactions requiring both integrin cytoplasmic tails. These sequences are initiation points for focal adhesion formation and subsequent signal transduction cascades. In this study, we addressed the question of whether the short cytoplasmic tail of the alpha(3) integrin subunit of alpha(3)beta(1) integrin is required for alpha(3)beta(1) integrin-dependent processes. For this purpose, cDNA representing the extracellular and transmembrane domain of the interleukin 2 receptor (IL2R) alpha subunit and the cytoplasmic sequence of the alpha(3) integrin subunit was transfected into PC12 cells. Autonomous expression of the cytoplasmic alpha(3) tail does not affect attachment but leads to inhibition of neuronal differentiation on laminin 5. This indicates that the cytoplasmic alpha(3) sequence is not required for cell attachment but is necessary for long-term adhesion and for the reorganization of the cytoskeleton that precedes neuronal differentiation. Inhibition of neurite outgrowth by chimeric IL2R-alpha(3) can be rescued by treatment of transfected cells with the pharmacological inhibitor Y27632, which inhibits the RhoA downstream effector Rho kinase alpha.

Animals↗

PubMed1994

Identification of integrin receptors on cultured human bone cells.

The interactions of bone cells with their surrounding extracellular microenvironment may be mediated by integrins, a family of heterodimeric glycoproteins consisting of alpha and beta subunits that noncovalently interact to form cell-substratum adhesion receptors. We previously described the integrins on calvarial bone cells in rats with use of polyclonal antibodies against some integrin subunits. In the present study, we expanded this initial characterization by employing a more complete panel of monoclonal antibodies to identify integrins on human bone cells. Minced fragments of trabecular bone obtained during total knee arthroplasty were grown in culture until bone cells became confluent. The cells then were dissociated, plated again, grown to confluence, and assayed for alkaline phosphatase activity, response of cyclic adenosine monophosphate to stimulation with parathyroid hormone, and osteocalcin content. The percentage of the cells that adhered to various substrates was measured; 60-70% adhered to type-I collagen, fibronectin, vitronectin, and poly-D-lysine; 40-50% adhered to type-IV collagen, laminin, and gelatin; and only 10% adhered to fibrinogen. Flow cytometric analysis with anti-integrin monoclonal antibodies and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of immunoprecipitates of the human bone cells revealed high levels of alpha 1 beta 1, alpha 3 beta 1, alpha 5, beta 1 and alpha v beta 5 integrins and much lower levels of alpha 2 beta 1, alpha 4 beta 1, alpha v beta 1, and alpha v beta 3 integrins. This description of the integrin repertoire of cultured human bone cells represents the first step toward an understanding of the role played by integrins in the growth, maintenance, and repair of bone.

Aged↗

PubMed1999

The beta1-integrin cytosolic domain optimizes phospholipase A2-mediated arachidonic acid release required for NIH-3T3 cell spreading.

Inhibition of PLA2 activity and rescue by addition of exogenous AA was used to demonstrate that AA production is essential for integrin-mediated NIH-3T3 murine cell spreading. Both AA release and cell spreading after attachment to a FN substrate were inhibited by the PLA2 inhibitor mepacrine. AA release was essential for signaling spreading since the inhibition of spreading induced by mepacrine was overcome by exogenous AA. Cells ectopically expressing full-length chicken beta1-integrins both released AA and spread fully on a substrate of anti-chicken beta1-integrin monoclonal antibody, and inhibition of PLA2 by mepacrine suppressed both spreading and AA release. Exogenous AA also reversed this mepacrine-induced inhibition of spreading. The role of the beta1-integrin cytosolic domain in AA release was examined by comparing responses of cells expressing full-length chicken beta1-integrins versus cells expressing a deletion mutant chicken beta1-integrin with a truncated cytosolic domain. Cells expressing a truncated chicken beta1-integrin released significantly less AA and failed to spread on the anti-chicken beta1-integrin antibody substrate. Furthermore, clustering full-length receptors with soluble antibody stimulated greater AA release than clustering of receptors having truncated cytosolic domains. These data suggest the beta1-integrin cytosolic domain is required for optimal PLA2 activation to produce AA necessary for cell spreading.

3T3 Cells↗

PubMed1993

Alpha 5 integrin is a critical component of adhesion plaques in myogenesis.

We investigated the distribution and expression of alpha 5 beta 1 and alpha 3 beta 1 integrin in differentiating myogenic cells in culture. The myogenic cells expressed both alpha 5 and alpha 3 integrin subunits with the same molecular sizes as those expressed by chicken embryo fibroblasts (CEF). However, the ratio of total alpha 5 to alpha 3 was threefold higher in the muscle cultures than that in CEF cultures. A new method is described whereby adhesion plaque-associated integrin was cross-linked to its extracellular matrix ligand on the substrate using a nonpenetrating cross-linker, BS3, and integrin not involved in substrate adhesion as well as cytoskeletal proteins were removed with a zwitterionic detergent. alpha 5 and beta 1 integrin, but not alpha 3 could be cross-linked to fibronectin at adhesion plaques throughout myogenesis in culture. Alpha 5 beta 1 integrin was found only at the edge of myoblasts 4 hr after plating but became distributed under their entire surface by 1 day in culture. When the muscle cells became elongated, a morphology they express after the initiation of terminal differentiation, and as they began to fuse, alpha 5 was found redistributed in small adhesion plaques along the lateral edges of the postmitotic myocytes and early myotubes. In mature myotubes, which are large multinucleated branched structures, alpha 5 beta 1 integrin was localized to parallel streaks underneath their entire substrate surface. Throughout the different stages of myogenesis, vinculin colocalized with alpha 5 beta 1 integrin in adhesion plaques, but alpha-actinin only colocalized to the adhesion plaques in myoblasts, not in myotubes. These studies suggest that alpha 5 beta 1 integrin through its dynamic interaction with both fibronectin and the cytoskeleton is important for both the signals which initiate the differentiation process and for subsequent morphological and structural changes during the differentiation process.

Animals↗

PubMed1996

Inhibition of cranial neural crest adhesion in vitro and migration in vivo using integrin antisense oligonucleotides.

Although it is well-established that beta1 integrins play a functional role in the migration of cranial neural crest cells, little is known about the number or importance of their associated alpha subunits. Here, we have utilized antisense oligonucleotides (aONs) against various mammalian integrin alpha subunits to functionally "knock out" integrins in vitro and in vivo. First, we examined the attachment in vitro of cranial neural crest cells to fibronectin and laminin in the presence of antisense or reversed-sense oligonucleotides using a quantitative adhesion assay. We found three alpha integrin aONs that blocked attachment to fibronectin substrates only, one that blocked attachment to laminin substrates only, and one that blocked attachment to both fibronectin and laminin. As expected, an aON to chick beta1 integrin reduced attachment to both fibronectin and laminin substrates. These results suggest that there are three or more functionally distinct integrin heterodimers on avian cranial neural crest cells. Second, we examined the ability of aONs against various alpha integrin subunits to perturb cranial neural crest migration in vivo by injecting the oligonucleotides into the cranial mesenchyme through which neural crest cells migrate. Those alpha aONs that inhibited cell attachment in vitro also caused neural crest and/or neural tube abnormalities after injection in vivo. In addition, two aONs that had no effect in vitro did affect emigration of neural crest cells in vivo. Immunoprecipitations revealed that some integrin subunits were depleted after treatment with antisense but not reversed-sense oligonucleotides both in vivo and in vitro. The results suggest that integrin alpha subunits are required for cranial neural crest cell attachment and emigration.

Animals↗

PubMed1994

Laminin isoforms promote attachment of hepatocytes via different integrins.

Three isoforms of laminin were compared for the ability to promote adhesion of primary rat hepatocytes. In tests of initial attachment to these substrates, kidney laminin (alpha k, beta 1, gamma 1, and alpha k, beta 2, gamma 1) was shown to be a more efficient substrate than Engelbreth Holm Swarm (EHS) (alpha 1, beta 1, gamma 1) or heart laminin (alpha 2, beta 1, gamma 1, and alpha 2, beta 2, gamma 1). Hepatocyte attachment to EHS laminin and heart laminin was completely inhibited by antibodies specific for the integrin subunit beta 1, while a combination of beta 1 integrin antibodies and GRGDS peptide was needed for total inhibition of hepatocyte attachment to kidney laminin. Antiserum directed to the integrin subunit beta 3 could not substitute for the GRGDS peptide in this inhibition. Antibodies against the integrin subunit alpha 1 efficiently blocked adhesion of hepatocytes to collagen type I and to the P1 domain of EHS laminin. However, this antibody had essentially no effect on the attachment to kidney laminin and had only a minor inhibitory effect on attachment to heart laminin, to intact EHS laminin, or to the isolated fragment E8 of EHS laminin. Combining the alpha 1 integrin antibody with GRGDS peptide gave no further inhibition on these substrates. These results show that a recently described isoform of laminin from bovine kidney is an efficient substrate for initial attachment of hepatocytes, interacting with at least one beta 1-containing integrin and an RGD-dependent integrin not containing beta 1 or beta 3 subunits. Native EHS laminin uses integrin alpha 1 beta 1 for hepatocyte binding to the center of the cross (fragment P1) and other beta 1 integrin(s) in addition to alpha 1 beta 1 as receptors for the distal part of the long arm (fragment E8).

Animals↗

PubMed1995

Functional role of cell surface integrins on human trophoblast cell migration: regulation by TGF-beta, IGF-II, and IGFBP-1.

Trophoblast invasion of the human uterus is stringently controlled by the microenvironment. Invasive extravillous trophoblast cells in situ as well as in culture express a selective repertoire of cell surface integrins. Since migration is a necessary step in the invasion cascade, we tested whether certain integrins or invasion-regulating molecules, i.e., TGF-beta, IGF-II, and IGFBP-1 produced at the fetomaternal interface had a functional role on trophoblast migration. Flow cytometric analysis of integrin expression and the use of an in vitro cell migration assay revealed that exogenous TGF-beta upregulates integrin expression and reduces migratory ability to the invasive trophoblast, whereas IGF-II has no effect on integrin expression but stimulates migration. Trophoblast migration was inhibited in the presence of alpha 5 and beta 1 integrin blocking antibodies, indicating its dependence on the expression of these subunits. Furthermore, IGFBP-1, which contains an RGD sequence recognizing certain integrins, stimulated migration, an effect that was blocked by pretreatment with anti-alpha 5 or -beta 1 blocking Abs. These studies demonstrate that the migration of first trimester invasive trophoblast in vitro (1) requires the expression of alpha 5 and beta 1 integrin subunits, (2) is inhibited by TGF-beta, possibly due to increased cell adhesiveness to the extracellular matrix, (3) is stimulated by IGF-II by an as yet undetermined mechanism, and (4) is stimulated by IGFBP-1, likely by interaction with the RGD binding site of the alpha 5 beta 1 integrin. The invasion-regulating effects of TGF-beta, IGF-II, and IGFBP-1 may thus, at least in part, be due to their migration-regulating effects on the invasive trophoblast.

Antibodies↗

PubMed1995

Chondrocyte and chondrosarcoma cell integrins with affinity for collagen type II and their response to mechanical stress.

Mechanical stress is an important regulator of chondrocyte functions but the mechanisms by which chondrocytes sense mechanical signals are unknown. Receptors for matrix molecules are likely involved in the mechanical signaling. In the first part of this study we identified integrins with affinity for the cartilage-specific collagen type II. We report that the collagen-binding integrins alpha 1 beta 1 and alpha 2 beta 1 isolated from bovine chondrocytes or human chondrosarcoma cells bound collagen type II as judged from affinity chromatography. The integrins alpha 3 beta 1 or alpha 9 beta 1 did not bind collagen type II-Sepharose. In the second part of the study we investigated the effect of mechanical stress on expression of matrix molecules and integrin subunits. Chondrocytes and chondrosarcoma cells, cultured on uncoated flexible silicone membranes in the presence of serum, were exposed to mechanical stress by the Flexercell system. Dynamic stimulation of chondrocytes for 3 h increased the mRNA expression of collagen type II and aggrecan as judged by Northern blotting, while the beta 1-integrin subunit was not changed. When chondrosarcoma cells were exposed to mechanical stimulation under the same conditions, mRNA expression of alpha 5 was found to increase while beta 1, alpha 2, and alpha v did not increase to significant levels. In another study the effect of mechanical stress on integrins was investigated when the cells were cultured on collagen type II-coated flex-dishes. Three hours of dynamic stress increased the mRNA expression of alpha 2-integrin subunit while the level of mRNA for integrin subunits beta 1, alpha 1, alpha 5, and alpha v showed no or small changes, indicating that matrix components may modulate the expression of integrins during mechanical stress.

Aggrecans↗