The neurite-promoting domain of human laminin promotes attachment and induces characteristic morphology in non-neuronal cells

Neural cell-cell and cell-substrate adhesion through N-cadherin, N-CAM and L1

In this study neural (N)-cadherin, neural cell adhesion molecule (N-CAM) and L1 proteins and their antibody equivalents were covalently immobilized on a polyethylene-imine (PEI)-coated glass surface to form neuron-adhesive coatings. Impedance sensing and (supplementary) image analysis were used to monitor the effects of these CAMs. Immobilization of high concentrations of both N-cadherin protein and antibody led to good adhesion of neurons to the modified surface, better than surfaces treated with 30.0 and 100.0 µg ml(-1) N-CAM protein and antibody. L1 antibody and protein coating revealed no significant effect on neuronal cell-substrate adhesion. In a second series of combinatorial experiments, we used the same antibodies and proteins as medium-additives to inhibit cell-cell adhesion between neurons. Adhesion of neurons cultured on N-cadherin protein or antibody-modified surfaces was lowered by the addition of a soluble N-cadherin protein and antibody to the culturing medium, accelerating neuronal aggregation. The presence of a soluble N-CAM antibody or protein had no effect on the adhesion of neuronal cells on a N-cadherin protein-modified surface. On a N-cadherin antibody-coated surface, the addition of a soluble N-CAM protein led to cell death of neurons after 48 h, while a N-CAM antibody had no effect. In the presence of a soluble N-cadherin protein and antibody the aggregation of neurons was inhibited, both on N-CAM protein and N-CAM antibody-modified surfaces. Neurons cultured on immobilized antibodies were less affected by the addition of soluble CAM blockers than neurons cultured on immobilized proteins, indicating that antibody-protein bonds are more stable compared to protein-protein bonds.

Impedance sensing for monitoring neuronal coverage and comparison with microscopy

We investigated the applicability of electric impedance sensing (IS) to monitor the coverage of adhered dissociated neuronal cells on glass substrates with embedded electrodes. IS is a sensitive method for the quantification of changes in cell morphology and cell mobility, making it suitable to study aggregation kinetics. Various sizes of electrodes were compared for the real-time recording of the impedance of adhering cells, at eight frequencies (range: 5 Hz-20 kHz). The real part of the impedance showed to be most sensitive at frequencies of 10 and 20 kHz for the two largest electrodes (7850 and 125,600 μm(2)). Compared to simultaneous microscopic evaluation of cell coverage and cell spreading, IS shows more detail.

Laminin isoforms and their integrin receptors in glioma cell migration and invasiveness: Evidence for a role of alpha5-laminin(s) and alpha3beta1 integrin

Glioma cell infiltration of brain tissue often occurs along the basement membrane (BM) of blood vessels. In the present study we have investigated the role of laminins, major structural components of BMs and strong promoters of cell migration. Immunohistochemical studies of glioma tumor tissue demonstrated expression of alpha2-, alpha3-, alpha4- and alpha5-, but not alpha1-, laminins by the tumor vasculature. In functional assays, alpha3 (Lm-332/laminin-5)- and alpha5 (Lm-511/laminin-10)-laminins strongly promoted migration of all glioma cell lines tested. alpha1-Laminin (Lm-111/laminin-1) displayed lower activity, whereas alpha2 (Lm-211/laminin-2)- and alpha4 (Lm-411/laminin-8)-laminins were practically inactive. Global integrin phenotyping identified alpha3beta1 as the most abundant integrin in all the glioma cell lines, and this laminin-binding integrin exclusively or largely mediate the cell migration. Moreover, pretreatment of U251 glioma cells with blocking antibodies to alpha3beta1 integrin followed by intracerebral injection into nude mice inhibited invasion of the tumor cells into the brain tissue. The cell lines secreted Lm-211, Lm-411 and Lm-511, at different ratios. The results indicate that glioma cells secrete alpha2-, alpha4- and alpha5-laminins and that alpha3- and alpha5-laminins, found in brain vasculature, selectively promote glioma cell migration. They identify alpha3beta1 as the predominant integrin and laminin receptor in glioma cells, and as a brain invasion-mediating integrin.

Immunohistochemical study of extracellular matrix components in epiretinal membranes of vitreoproliferative retinopathy and proliferative diabetic retinopathy

PURPOSE

The migration, proliferation, differentiation, and adhesion of cells and other cellular functions are influenced by the surrounding extracellular matrix in normal and wound healing conditions. The formation of epiretinal membranes, a wound healing process, is a serious complication of retinal diseases, the most important being proliferative diabetic retinopathy (PDR) and proliferative vitreoretinopathy (PVR). In the present study, the authors investigated the expression of various extracellular matrix components and in particular tenascin, fibronectin, laminin, collagen IV, and MMP-3 glycoprotein as well as the expression of glial fibrillary acidic protein in each type of epithelial membrane in order to elucidate the role of these molecules in the formation of these two types of membranes.

METHODS

The authors performed immunohistochemistry in 14 PVR and 14 PDR membranes, using antibodies against the above mentioned extracellular matrix components. Tenascin and fibronectin were observed as major components in the extracellular matrix, while laminin and collagen type IV were detected as minor components in both types of membranes. A higher fibronectin expression in PVR compared with PDR membranes was found (p=0.0035). A positive relationship of its expression with the proliferative activity (p=0.15) and collagen type IV expression (p<0.0001) was also observed.

RESULTS

Tenascin expression was positively correlated with glial fibrillary acidic protein positive cells in PDR membranes (p=0.04). Collagen type IV localized around vessels was observed with high levels in PDR membranes (p=0.0031).

CONCLUSIONS

The results indicated that the extracellular matrix components seem to be involved in PVR and PDR, contributing to tissue remodeling and perhaps by different pathogenetic pathways, which could reflect different stages of development in these two types of membranes.

Preferential locomotion of leukemic cells towards laminin isoforms 8 and 10

To identify the laminin isoforms of the basement membranes that could be implicated in the extravasation process of neoplastic lymphocytes, a number of purified laminins and one native renal laminin complex were comparatively investigated for their ability to promote migration of neoplastic lymphocytes in vitro. The identity/composition of a human placental laminin complex was asserted by combining immunochemical assays, sequence determination of tryptic peptides, and ultrastructural analysis to be composed predominantly of laminin-10 in which the coiled-coil C-terminal regions and the G globular domain of the alpha5 chain were preserved intact despite the enzymatic treatment used for its isolation. Lymphoma and leukemic cell lines failed to migrate towards laminin-4, -9, -11, moved poorly in response to laminin-1, -2/4, -5 and the renal laminin complex, but markedly locomoted towards the subendothelial laminin-8 and -10. The motility-promoting interaction with these latter laminins was interchangeably mediated by the alpha3beta1 and alpha6beta1 integrins. Lymphocyte locomotion on laminins assayed in the presence of cytokines was either reduced or enhanced suggesting that local cytokine milieu could further influence motility response.

C7, a novel nucleolar protein, is the mouse homologue of the Drosophila late puff product L82 and an isoform of human OXR1

The C7 gene was identified in a project aimed to characterize differential gene expression upon attachment of cells to extracellular matrix proteins in vitro. C7 is the homologue of Drosophila L82, a late puff gene (Stowers et al. (1999) Dev. Biol. 213, 116-130) and human OXR1, a gene, which protects cells against oxidation (Volkert et al. (2000) Proc. Natl. Acad. Sci. USA 97, 14530-14535). All are transcribed into multiple splice forms with a common 3' domain. Additional members of this novel gene family are found in a number of eukaryotic species. In the mouse, the C7 gene is highly and broadly expressed during development in at least 4 splice forms, 3 of which were sequenced. In the adult, the C7 gene is most highly expressed in brain and testis. Antibodies to recombinant C7 protein localized to nucleoli in a variety of cell types, suggesting that C7 may be involved in the formation or function of this important organelle.

Attachment of A-431 cells on immobilized antibodies to the EGF receptor promotes cell spreading and reorganization of the microfilament system

EGF-like sequences, inherent in a number of extracellular matrix proteins, participate in cell adhesion. It is possible that interactions of these sequences with EGF receptors (EGFR) affect actin filament organization. It was shown previously [Khrebtukova et al., 1991: Exp. Cell Res. 194:48-55] that antibodies specific to EGFR induce capping of these receptors and redistribution of cytoskeletal proteins in A-431 cells. Here we report that A-431 cells attach and spread on solid substrata coated with antibodies to EGFR, even in the absence of serum. Thus, EGFR can act as an adhesion protein and promote microfilament reorganization. Binding of the cells to the EGFR-antibody resulted in the formation of a unique cell shape characterized by numerous, actin-based filopodia radiating from the cell body, but without membrane ruffles. There was also a conspicuous circular belt of actin-containing fibers inside the cell margin, and many irregular actin aggregates in the perinuclear area. The morphologies and actin distributions in A-431 cells spread on fibronectin or laminin 2/4 were very different. On fibronectin, cells had polygonal shapes with numerous stress-fibers and thick actin-containing fibers along the cell edges. On laminin-covered substrata, the cells became fusiform and acquired broad leading lamellae with ruffles. In these cells, there were also a few bundles of filaments running the whole length of the cell body, and shorter bundles extending through the leading lamellae towards the membrane ruffles in the cell edge. These effects and those seen with immobilized EGF suggest that different ligand/receptor complexes induce specific reorganizations of the microfilament system.

Cell adhesion force microscopy

The adhesion forces of cervical carcinoma cells in tissue culture were measured by using the manipulation force microscope, a novel atomic force microscope. The forces were studied as a function of time and temperature for cells cultured on hydrophilic and hydrophobic polystyrene substrates with preadsorbed proteins. The cells attached faster and stronger at 37 degreesC than at 23 degreesC and better on hydrophilic than on hydrophobic substrates, even though proteins adsorb much better to the hydrophobic substrates. Because cell adhesion serves to control several stages in the cell cycle, we anticipate that the manipulation force microscope can help clarify some cell-adhesion related issues.

Kalinin is more efficient than laminin in promoting adhesion of primary keratinocytes and some other epithelial cells and has a different requirement for integrin receptors

Kalinin was purified from squamous cell carcinoma (SCC25) spent culture media using an immunoaffinity column prepared from the mAb BM165. The affinity-purified material was separated by SDS-PAGE into three bands of 165-155, 140, and 105 kD identical to those obtained from normal human keratinocyte cultures and previously identified as kalinin. Kalinin promoted adhesion of a large number of normal cells and established cell lines with an activity similar to other adhesion molecules such as the laminin-nidogen complex, fibronectin, or collagen IV. However, kalinin was a much better substrate than laminin-nidogen complex for adhesion of cells of epithelial origin including primary human keratinocytes. Adhesion to kalinin was followed by cell shape changes ranging from rounded to fully spread cells depending on the cell types. The adhesion-promoting activity of kalinin was conformation dependent and was abolished by heat denaturation. mAb BM165 prevented cell adhesion to kalinin but not to other extracellular matrix substrates. However, either complete or partial inhibition was observed with different cells suggesting the existence of at least two cell-binding sites on the kalinin molecule. Experiments inhibiting cell adhesion with function-blocking anti-integrin subunit antibodies indicated that both alpha 3 beta 1 and alpha 6 beta 1 integrins are involved in the cellular interactions with kalinin, while for cell adhesion to classical mouse Engelbreth-Holm-Swarm laminin only alpha 6 beta 1 integrins, and not alpha 3 beta 1, appeared to be functional. Altogether, these results suggest that kalinin may fulfill additional functions than laminin, particularly for epithelial cells.

Laminin variants: why, where and when?

Laminin is a member of a family of proteins that are composed of three subunits, one heavy chain and two light chains. Five subunits in the laminin family have been cloned and sequenced so far. These include two heavy chains, the laminin A chain and the merosin M chain, and three light chains, B1, B2, and S. These five subunits can form four different laminin variants: A-B1-B2, A-S-B2, M-B1-B2, and M-S-B2, all having the B2 chain in common. Major basement membranes in tissues contain at least one of the four laminin variants. For example, the adult muscle and nerve basement membranes contain M-B1-B2, smooth muscle contains A-B1-B2, the myotendinous junction and the trophoblast basement membrane in the placenta contain M-S-B2, and blood vessels contain A-B1-B2 and/or A-S-B2. In the brain, the merosin M chain is present in association with neuronal fibers. The four members of the laminin family interact with cells in a similar manner. Thus, they promote outgrowth of neurites from neuronal cells and promote attachment and spreading of non-neuronal cells. The interaction of cells with laminins is mediated largely by integrin type receptors, including integrins alpha 1 beta 1, alpha 2 beta 1, alpha 3 beta 1, and alpha 6 beta 1. The expression of the different laminin-like proteins is developmentally regulated. The laminin A chain is the first heavy chain expressed.(ABSTRACT TRUNCATED AT 250 WORDS)

Co-localization and molecular association of dystrophin with laminin at the surface of mouse and human myotubes

In Duchenne muscular dystrophy (DMD), deficiency of the protein dystrophin results in necrosis of muscle myofibres, associated with lesions in the sarcolemma and surrounding basal lamina. Dystrophin has been proposed to be a major component of the sub-sarcolemmal cytoskeleton involved in maintaining the integrity of the myofibre plasma membrane, and is known to associate with a group of sarcolemmal glycoproteins, one of which exhibits high affinity binding to the basal lamina component laminin. However, a direct or indirect transmembrane association of dystrophin in muscle cells with the myofibre basal lamina has not been demonstrated. To address this question we have examined dystrophin immunostaining and immunoprecipitation patterns in cultured mouse and human myotubes in comparison with that of the basal lamina component, laminin. Dual-immunolabelling revealed virtually complete co-localization of dystrophin on the inside surface of the muscle cell sarcolemma with plaques and veined arrays of laminin accumulating on the extracellular face. This pattern of laminin and dystrophin distribution was distinct from that of other cell surface molecules expressed in myotubes such as the neural cell adhesion molecule, NCAM, and the beta 1 integrin receptor, and immunoprecipitation of dystrophin from solubilized myotube extracts resulted in co-purification of laminin B1 chain confirming an association between these two components. The results thus provide the first direct cellular evidence of a transmembrane linkage between dystrophin in the sarcolemmal cytoskeleton with laminin in the overlying basal lamina. While the immunocytochemical distribution of laminin was apparently normal in dystrophin-deficient muscle cells, elevated levels of soluble laminin were present in extracts of mdx compared with normal mouse skeletal muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Recombinant laminin B1 chains exhibit intact short-arm domains but do not form oligomeric molecules

The human laminin B1 chain has been produced in the baculovirus expression system in sufficient amounts for biochemical and functional studies. A full-length cDNA, which was constructed of four partially overlapping clones and verified by in vitro transcription and translation to be functional, was cloned into the transfer vector pVL1392 behind the polyhedrin promoter. The recombinant construct was incorporated by in vivo homologous recombination into the genome of the wild-type baculovirus, Autographa californica nuclear polyhedrosis virus. Infection of Spodoptera frugiperda cells (Sf9) with the recombinant virus resulted in the expression of the recombinant B1 chain (recB1) in these insect cells. The recB1 was found to be synthesized in two forms with apparent molecular masses of 220 kDa and 200 kDa. The 220-kDa form is an N-glycosylated form of recB1, because it was not present in cultures containing tunicamycin, an inhibitor of N-linked glycosylation. The recB1 accumulated inside the cell and only a small portion of it was secreted into the culture medium. Thus purification had to be started from the cell extract in order to obtain reasonable amounts of the protein. About 500 micrograms was obtained from a 500-ml culture with three steps of chromatography, concavalin A, DEAE-Sepharose and Mono Q anion-exchange chromatography. Only the glycosylated form was purified. The recB1 was found to be sensitive to degradation during the purification, because two proteolytic forms of about 180 kDa were present in every preparation. The accumulation of recB1 inside the cell was possibly due to the lack of correct assembly. Electron microscopy studies showed that the short arm part had a native or near-native structure, but the C-terminal heptad repeat domain had not folded correctly and did not exist in an alpha-helical structure, as it does in native laminin. Electron microscopy and cross-linking studies further revealed that recB1 was a monomeric protein. It was also shown to be unable to oligomerize in vitro, suggesting that the B1 chain is not designed to form homo-oligomers. Finally, cell attachment assays were carried out, but the native recB1 appeared to be inactive in these assays.

A synthetic peptide derived from the carboxy terminus of the laminin A chain represents a binding site for the alpha 3 beta 1 integrin

The purpose of this study was to identify the binding site(s) within laminin for the alpha 3 beta 1 integrin receptor. It has been previously shown, using proteolytic fragments and anti-laminin antibodies, that the region in laminin for alpha 3 beta 1 integrin binding is localized to the carboxy-terminal region at the end of the long arm (Gehlsen, K. R., E. Engvall, K. Dickerson, W. S. Argraves, and E. Ruoslahti. 1989. J. Biol. Chem. 264:19034-19038; Tomaselli, K. J., D. E. Hall, L. T. Reichardt, L. A. Flier, K. R. Gehlsen, D. C. Turner, and S. Carbonetto. 1990. Neuron. 5:651-662). Using synthetic peptides, we have identified an amino acid sequence within the carboxy-terminal region of the laminin A chain that is recognized by the alpha 3 beta 1 integrin. The amino acid sequence represented by the synthetic peptide GD-6 (KQNCLSSRASFRGCVRNLRLSR residues numbered 3011 to 3032) of the globular domain of the murine A chain supports cell attachment and inhibits cell adhesion to laminin-coated surfaces. By affinity chromatography, peptide GD-6-Sepharose specifically bound solubilized alpha 3 beta 1 from extracts of surface-iodinated cells in a cation-dependent manner, while it did not bind other integrins. In addition, exogenous peptide GD-6 specifically eluted bound alpha 3 beta 1 from laminin-Sepharose columns but did not elute the alpha 3 beta 1 integrin from a fibronectin-Sepharose column. Using integrin subunit-specific monoclonal antibodies, only those antibodies against the alpha 3 and beta 1 subunits inhibited cell adhesion to peptide GD-6-coated surfaces. Finally, a polyclonal antibody made against peptide GD-6 reacted specifically with both murine and human laminin and significantly inhibited cell adhesion to laminin-coated surfaces but not those coated with other matrix proteins. These results identify the laminin A chain amino acid sequence of peptide GD-6 as representing a binding site in laminin for the alpha 3 beta 1 integrin.

Heterotrimeric configuration is essential to the adhesive function of laminin

Mouse PFHR9 laminin, B1B2-heterodimers, and free B1-chains were separated from one another by gel filtration on Superose 6. The cell attachment promoting activity of these species was measured after immunoprecipitation with monoclonal anti-laminin antibodies coupled to Sepharose 6MB beads. These antibodies, which did not react with the laminin E8 fragment, were directed against epitopes in the NH2-terminus of the laminin B1-chain and in the central region of laminin. After incubation with purified EHS laminin, the immunosorbents revealed efficient adhesion substrates for a rat rhabdomyosarcoma cell line which attached preferentially to the laminin E8 fragment. Although both were immunoprecipitated efficiently, B1B2-heterodimers and B1-chains, unlike PFHR9 laminin, did not support the attachment of RMS cells. On a molar basis B1B2-heterodimers were 24 times less efficient than PFHR9 laminin or EHS laminin in supporting cell attachment. These data suggest that heterotrimeric configuration is essential to the adhesive function of the laminin E8 fragment.

Merosin promotes cell attachment and neurite outgrowth and is a component of the neurite-promoting factor of RN22 schwannoma cells

The laminin-like protein merosin was purified from human placenta in intact form and as pepsin fragments and compared to laminin in heparin affinity chromatography and cell binding assays. Intact merosin and a small fragment of merosin comprising the last two repeats of the heavy chain g domain bind to heparin. Intact merosin and large pepsin fragments of merosin, but not the small C-terminal fragment, mediate the attachment and spreading of several types of cells and promote neurite outgrowth from neuronal cells similar to laminin and its corresponding fragments. Cells with various integrin-type receptors for laminin attached equally well to merosin and laminin, suggesting that several of the known laminin binding receptors also bind to merosin. Antibodies to the beta 1 subunit of integrins inhibited neurite outgrowth on merosin as well as on laminin, confirming the involvement of integrin-mediated interaction of cells with both merosin and laminin. Schwannoma cells, which have previously been shown to produce a laminin-like, neurite-promoting factor, synthesize merosin in vivo and in vitro as shown by protein and mRNA analysis. The results suggest that merosin, which is the more abundant basement membrane protein in the laminin family, has properties very similar to laminin despite differences in the structure of the heavy chain. Furthermore, merosin may be identical to or a component of the neurite-promoting factors previously reported from heart, muscle, and Schwann cells.

Basement membrane proteins: structure, assembly, and cellular interactions

Basement membranes are thin layers of a specialized extracellular matrix that form the supporting structure on which epithelial and endothelial cells grow, and that surround muscle and fat cells and the Schwann cells of peripheral nerves. One common denominator is that they are always in close apposition to cells, and it has been well demonstrated that basement membranes do not only provide a mechanical support and divide tissues into compartments, but also influence cellular behavior. The major molecular constituents of basement membranes are collagen IV, laminin-entactin/nidogen complexes, and proteoglycans. Collagen IV provides a scaffold for the other structural macromolecules by forming a network via interactions between specialized N- and C-terminal domains. Laminin-entactin/nidogen complexes self-associate into less-ordered aggregates. These two molecular assemblies appear to be interconnected, presumably via binding sites on the entactin/nidogen molecule. In addition, proteoglycans are anchored into the membrane by an unknown mechanism, providing clusters of negatively charged groups. Specialization of different basement membranes is achieved through the presence of tissue-specific isoforms of laminin and collagen IV and of particular proteoglycan populations, by differences in assembly between different membranes, and by the presence of accessory proteins in some specialized basement membranes. Many cellular responses to basement membrane proteins are mediated by members of the integrin class of transmembrane receptors. On the intracellular side some of these signals are transmitted to the cytoskeleton, and result in an influence on cellular behavior with respect to adhesion, shape, migration, proliferation, and differentiation. Phosphorylation of integrins plays a role in modulating their activity, and they may therefore be a part of a more complex signaling system.

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

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

Elevated 32-kDa LBP and low laminin mRNA expression in developing mouse cerebrum

Several laminin receptors have been identified, originally a high-affinity 67-kDa laminin binding protein ('LBP-67'), and later galactosyltransferase and the low-affinity but functionally potent integrin receptors. Attempts at obtaining cDNA for LBP-67, although unsuccessful, have given rise to a full-length cDNA coding for an interesting 32-kDa protein, tentatively referred to as '32-kDa LBP', whose relationship to LBP-67 is unclear. Since no information is available on the in vivo expression of 32-kDa LBP mRNA nor of the three laminin chains during CNS development, appropriate 35S-antisense and -sense RNA probes were applied to developing mouse cerebral wall at embryonic day (E)10-16, birth and 1-3 weeks after birth. Expression was examined using Northern blot analysis and in situ hybridization. The 32-kDa LBP mRNA was found to be elevated during the embryonic and perinatal period, and then rapidly declined. At the cellular level, 32-kDa LBP mRNA was distributed throughout the embryonic cerebral wall and became concentrated during the perinatal period in the proliferative ventricular zone and in the cortical plate. By comparison, laminin B1, B2, and A chain mRNA expression was relatively low at all times examined, in keeping with the punctate distribution of laminin antigenicity previously observed by others in developing brain parenchyma. Whereas the functional characterization of 32-kDa LBP and the nature of its laminin and proposed nonlaminin ligands is incomplete, the elevated and unique distribution of 32-kDa LBP mRNA raises interesting questions of the role of 32-kDa LBP mRNA in CNS development.

Identification of different laminin binding proteins in basolateral cell membranes of human colorectal carcinomas and normal colonic mucosa

The adhesive properties of tumour cells to laminin, the major glycoprotein of basement membranes, play a crucial part in the complex process of tumour invasion and metastasis. We therefore investigated the expression of laminin binding proteins in isolated basolateral cell membranes of human colorectal carcinomas and the adjacent normal colonic mucosa. Cell membrane binding assays and immunoblotting experiments showed appreciable quantitative and qualitative differences in the expression of these proteins in neoplastic and normal tissue. Epithelial basolateral cell membranes of colorectal carcinomas bound five to eight times more radioactive labelled laminin than basolateral cell membranes of the adjacent normal colonic epithelium. The expression of laminin binding proteins with Mr 66,000-69,000 daltons corresponding to the so called 'Mr 67,000 dalton laminin receptor' was three to four times higher in colorectal carcinomas than in normal colonic epithelium. In addition, laminin binding proteins with higher molecular weights, which may be related to the family of integrins, were also increased in colorectal carcinomas. In particular, laminin binding proteins with Mr 180,000 daltons were exclusively expressed on neoplastic epithelial cells of human colorectal carcinomas. Our data suggest that certain classes of laminin binding proteins may be selectively expressed on colonic tumour cells, leading to an increased capacity for migration, invasion, and metastasis.

Receptor functions for the integrin VLA-3: fibronectin, collagen, and laminin binding are differentially influenced by Arg-Gly-Asp peptide and by divalent cations

The capability of the integrin VLA-3 to function as a receptor for collagen (Coll), laminin (Lm), and fibronectin (Fn) was addressed using both whole cell adhesion assays and ligand affinity columns. Analysis of VLA-3-mediated cell adhesion was facilitated by the use of a small cell lung carcinoma line (NCI-H69), which expresses VLA-3 but few other integrins. While VLA-3 interaction with Fn was often low or undetectable in cells having both VLA-3 and VLA-5, NCI-H69 cells readily attached to Fn in a VLA-3-dependent manner. Both Arg-Gly-Asp (RGD) peptide inhibition studies, and Fn fragment affinity columns suggested that VLA-3, like VLA-5, may bind to the RGD site in human Fn. However, unlike Fn, both Coll and Lm supported VLA-3-mediated adhesion that was not inhibited by RGD peptide, and was totally unaffected by the presence of VLA-5. In addition, VLA-3-mediated binding to Fn was low in the presence of Ca++, but was increased 6.6-fold with Mg++, and 30-fold in the presence of Mn++. In contrast, binding to Coll was increased only 1.2-fold with Mg++, and 1.7-fold in Mn++, as compared to the level seen with Ca++. Together, these experiments indicate that VLA-3 can bind Coll, Lm, and Fn, and also show that (a) VLA-3 can recognize both RGD-dependent and RGD-independent ligands, and (b) different VLA-3 ligands have distinctly dissimilar divalent cation sensitivities.

Laminin and s-laminin are produced and released by astrocytes, Schwann cells, and schwannomas in culture

Components of the extracellular matrix (ECM) have been implicated in the regulation of neuronal migration, axonal growth, and synaptogenesis. We have examined cultures of glial cells, Schwann cells, and schwannomas for the expression of two components of the ECM, laminin and s-laminin, using immunohistochemical and Western blot techniques. Laminin is a potent promotor of neurite outgrowth in cultures of both central and peripheral neurons, and is present in all ECMs. In contrast, s-laminin (for synaptic laminin), a recently described homolog of laminin, is highly localized at the neuromuscular synaptic cleft (Sanes and Chiu, Cold Spring Harbor Symp. Quant. Biol. 1983;48:667-678; Chiu and Sanes, Dev. Biol. 1984;103:456-467) and shows selective adhesivity for motor neurons (Hunter et al. Cell 1989;59:905-913). While the distribution of these ECM components have been well documented in situ, the sources of these extracellular molecules are unclear. We report that astrocytes cultured in serum-free medium maintain an organized ECM that only bears laminin immunoreactivity; s-laminin appears to be sequestered intracellularly. However, both molecules are found in the astrocyte conditioned medium. Thus, under these growth conditions, astrocytes produce and release laminin and s-laminin, but only incorporate the former into an ECM. In contrast, neither molecule is present in comparable cultures of oligodendrocytes. Although no established ECM is seen in cultures of Schwann cells or schwannomas, laminin and s-laminin immunoreactivity are present within cells and in the conditioned media. These results indicate that certain populations of non-neuronal support cells and cell lines can produce and release both synaptic and extrasynaptic components of the ECM. The assembly of these different molecules into an organized basal lamina may require the presence of additional factors or interaction with neurons.

Multiple ligand binding functions for VLA-2 (alpha 2 beta 1) and VLA-3 (alpha 3 beta 1) in the integrin family

In our studies of VLA-3 we have shown (i) that a single integrin (VLA-3) can bind to multiple ligands by different mechanisms, involving RGD and non-RGD sites, which are regulated differently by divalent cations. Also we showed from the primary sequence of VLA-3 that it is only distantly related to the other cleaved alpha subunits. In our studies of VLA-2 we have shown that a single integrin may have at least three functional forms, depending on the cell type where expressed. In addition, we have expressed functional VLA-2 in RD cells, resulting in both Coll and Lm binding functions in vitro, and increased tumor cell metastasis in vivo in nude mice.

Molecular heterogeneity of basal laminae: isoforms of laminin and collagen IV at the neuromuscular junction and elsewhere

Laminin and collagen IV are components of most basal laminae (BLs). Recently, both have been shown to be products of multigene families. The A, B1, and B2 subunits of the laminin trimer are products of related genes, and the BL components merosin M and s-laminin are homologues of the A and B1 subunits, respectively. Similarly, five related collagen IV chains, alpha 1(IV)-alpha 5(IV), have been described. Here, we used a panel of subunit-specific antibodies to determine the distribution of the laminin and collagen IV isoforms in adult BLs. First, we compared synaptic and extrasynaptic portions of muscle fiber BL, in light of evidence that axonal and muscle membranes interact selectively with synaptic BL during neuromuscular regeneration. S-laminin, laminin A, and collagens alpha 3(IV) and alpha 4(IV) are greatly concentrated in synaptic BL; laminin B1 is apparently absent from synaptic BL; collagens alpha 1(IV) and alpha 2(IV) are less abundant in synaptic than extrasynaptic BL; and laminin B2 and merosin M are present at similar levels synaptically and extrasynaptically. These results reveal widespread differences between synaptic and extrasynaptic BL, and implicate several novel polypeptides as candidate mediators of neuromuscular interactions. Second, we widened our inquiry to assess the composition of several other BLs: endoneurial and perineurial BLs in intramuscular nerves, BLs associated with intramuscular vasculature, and glomerular and tubular BLs in kidney. Of eight BLs studied, at least seven have distinct compositions, and of the nine BL components tested, at least seven have distinct distributions. These results demonstrate a hitherto undescribed degree of heterogeneity among BLs.

Recognition of the laminin E8 cell-binding site by an integrin possessing the alpha 6 subunit is essential for epithelial polarization in developing kidney tubules

It has been previously shown that A-chain and domain(E8)-specific antibodies to laminin that inhibit cell adhesion also interfere with the establishment of epithelial cell polarity during kidney tubule development (Klein, G., M. Langegger, R. Timpl, and P. Ekblom. 1988. Cell. 55:331-341). A monoclonal antibody specific for the integrin alpha 6 subunit, which selectively blocks cell binding to E8, was used to study the receptors involved. Immunofluorescence staining of embryonic kidneys and of organ cultures of metanephric mesenchyme demonstrated coappearance of the integrin alpha 6 subunit and the laminin A-chain in regions where nonpolarized mesenchymal cells convert into polarized epithelial cells. Both epitopes showed marked colocalization in basal areas of tubules, while an exclusive immunostaining for alpha 6 was observed in lateral and apical cell surfaces of the tubular epithelial cells. Organ culture studies demonstrated a consistent inhibition of kidney epithelium development by antibodies against the alpha 6 subunit. The data suggest that the recognition of E8 cell-binding site of laminin by a specific integrin is crucial for the formation of kidney tubule epithelium from undifferentiated mesenchymal stem cells. In some other cell types (endothelium, some ureter cells) an exclusive expression of alpha 6 with no apparent colocalization of laminin A-chain in the corresponding basement membrane was seen. Thus, in these cells, integrins possessing the alpha 6 subunit may bind to laminin isoforms that differ from those synthesized by developing tubules.

Spreading of B16 F1 cells on laminin and its proteolytic fragments P1 and E8: involvement of laminin carbohydrate chains

The properties of EHS laminin and its proteolytic fragments E8 and P1 to promote spreading of B16 F1 murine melanoma cells were studied in short-term adhesion assays. The cells exhibited similar attachment rates but distinct spread morphologies on laminin, P1, and E8 fragments. The extent of spreading and the shape of the cells were quantitatively defined by two geometrical parameters: the surface and the form factor. These parameters were computed with an automatic image analyzer. Wheat germ agglutinin (WGA), applied to laminin-coated substrates, totally blocked cell spreading, but did not modify attachment percentages. Under similar conditions, WGA partially inhibited cell spreading on the E8 fragment and had no effect on the P1 fragment. In Western blot analysis, P1 fragment, contrary to laminin and E8, did not bind WGA. Laminin galactosylation and cell treatment with alpha-lactalbumin, which should prevent cell galactosyltransferase (GalTase) from binding to N-acetylglucosamine (GlcNAc) residues of the substrate, had no effect on the spreading ability of B16 F1 cells. The role of laminin N-linked carbohydrate chains in the induction of B16 F1 cell spreading was studied further after endoglycosidase F (Endo F) treatment of the substrates. The loss of carbohydrate chains was estimated by the reduction of iodinated lectin binding and by SDS-PAGE. Endo F treatment of laminin (85% of WGA binding inhibition) and E8 (40-50%) had no effect on cell spreading. In contrast, Endo F treatment of P1 fragment (85% of Con A binding inhibition) reduced both cell surface and form factor of B16 F1 cells. These results suggest that: (i) other spreading systems may act in concert with or in place of GalTase/GlcNAc interactions, (ii) the N-linked sugar chains of P1, which are not recognized by WGA, are involved in the spreading process of B16 F1 cells on this fragment, (iii) the epitopes of E8 fragment and E8 domain in laminin which are responsible for spreading are differently masked by WGA, (iv) the binding of WGA to laminin may impair cell spreading by steric hindrance.

Cell adhesion, spreading and neurite stimulation by laminin fragment E8 depends on maintenance of secondary and tertiary structure in its rod and globular domain

The cell adhesion, spreading and neurite-promoting properties of mouse tumor laminin fragment E8, which contains major site(s) responsible for laminin-cell interactions, were probed by proteolytic degradation, denaturation, synthetic peptides and antibody inhibition. Removal of more than half of the N-terminal portion contributing to the rod-like domain did not effect cell attachment or spreading although neurite-promoting activity was reduced. More extensive degradation of the rod or of the globular domains of E8, or separation of the globule from the rod, also resulted in loss of cell spreading activity although weak attachment was found to an A chain subfragment comprising the globular domain and a short piece of the rod. Exposure of E8 to increasing concentrations of dissociating agents produce an apparently reversible denaturation but an irreversible loss of both attachment and neurite-promoting activities, as did reduction and alkylation of disulfide bonds in the globular domain. Although cell adhesion and spreading were blocked by antibodies to an alpha 6 integrin subunit, neurite outgrowth was unaffected, indicating two distinct receptors for these two activities. Furthermore, a synthetic peptide, the sequence of which is found in the vicinity of adhesion and neurite-promoting sites and previously implicated in neurite growth and cell attachment activities, was found to be inactive. These results indicate that the major cell attachment and neurite-promoting sites of laminin are distinct although both require the native conformation of parts of the rod and the terminal globular domain of the long arm of laminin.

Identification and characterization of a 43-kilodalton laminin fragment from the "A" chain (long arm) with high-affinity heparin binding and mammary epithelial cell adhesion-spreading activities

A recently described procedure of reduction and carboxymethylation followed by heparin-Sepharose chromatography [Arumugham et al. (1988) Connect. Tissue Res. 18, 135-147] was used to characterize high-affinity heparin binding fragments of the laminin "A" chain. Two laminin fragments of Mr 53K and 43K selectively bound to the heparin-Sepharose column from the chymotrypsin digest of laminin, indicating that these fragments originate from the "A" chain. Without reduction and carboxymethylation but in the presence of 2.0 M urea, the heparin-Sepharose-bound material from the chymotrypsin laminin digest contains all the attachment-promoting activity for normal mouse mammary epithelial cells. The reduced 200-kDa intact three short arm fragment, fragments of Mr 70K-160K obtained either from laminin or from the reduced 200-kDa three short arm fragment, and the 53-kDa heparin binding fragment were all inactive in promoting the adhesion of mouse mammary epithelial cells. The mammary epithelial cell adhesion and spreading properties of laminin are associated with the high-affinity heparin binding 43-kDa fragment. The mammary epithelial cells attach to the 43-kDa fragment substrate and synthesize laminin, collagen type IV, and desmoplankins I and II as are the cells attached to laminin substrate and to the cells grown on tissue culture dishes. The biologically active 43-kDa fragment is generated from laminin, but not from the three short arm fragment. These results suggest that normal mouse mammary epithelial cells interact with laminin through a single site which is present in the 43-kDa heparin binding fragment located on the long arm of the "A" chain.

The alpha 1/beta 1 and alpha 6/beta 1 integrin heterodimers mediate cell attachment to distinct sites on laminin

This study was undertaken to determine the roles of individual alpha/beta 1 integrin heterodimers in promoting cellular interactions with the different attachment-promoting domains of laminin (LN). To do this, antibodies to the integrin beta 1 subunit or to specific integrin alpha subunits were tested for effects on cell attachment to LN, to elastase fragments E1-4 and E1, derived from the short arms and core of LN's cruciform structure, and to fragment E8 derived from the long arm of this structure. The human JAR choriocarcinoma cells used in this study attached to LN and to fragments E1 and E8. Attachment to E1-4 required a much higher substrate coating concentration, suggesting that it is a poor substrate for JAR cell attachment. The ability of cells to attach to different LN domains suggested the presence of more than one LN receptor. These multiple LN receptors were shown to be beta 1 integrin heterodimers because antibodies to the integrin beta 1 subunit inhibited attachment of JAR cells to LN and its three fragments. To identify the individual integrin alpha/beta 1 heterodimers that mediate interactions with these LN domains, mAbs specific for individual beta 1 heterodimers in human cells were used to study JAR cell interactions with LN and its fragments. An anti-alpha 6/beta 1-specific mAb, GoH3, virtually eliminated cell attachment to E8 and partially inhibited attachment to E1 and intact LN. Thus the major alpha 6/beta 1 attachment domain is present in fragment E8. An alpha 1/beta 1-specific mAb (S2G3) strongly inhibited cell attachment to collagen IV and partially inhibited JAR attachment to LN fragment E1. Thus, the alpha 1/beta 1 heterodimer is a dual receptor for collagen IV and LN, interacting with LN at a site in fragment E1. In combination, the anti-alpha 1- and anti-alpha 6-specific antibodies completely inhibited JAR cell attachment to LN and fragment E1. Thus, the alpha 1/beta 1 and alpha 6/beta 1 integrin heterodimers each function as LN receptors and act together to mediate the interactions of human JAR choriocarcinoma cells with LN.

Merosin, a tissue-specific basement membrane protein, is a laminin-like protein

Merosin is a basement membrane-associated protein found in placenta, striated muscle, and peripheral nerve. A 3.6-kilobase merosin cDNA clone was isolated from a placental cDNA expression library. The clone contained a 3.4-kilobase open reading frame, the 3' portion of which includes protein sequences of proteolytic fragments of merosin. The deduced amino acid sequence of the merosin polypeptide was similar to that of the COOH-terminal region of the 400-kDa A chain of laminin. This part of laminin forms the large globule at the end of the long arm of the laminin cross and is thought to contain the neurite-promoting site and the major cell binding site(s) in laminin. The sequence identity between merosin and the laminin A chain in this region is nearly 40%. An antiserum against a synthetic peptide from the middle of the merosin cDNA sequence identified a 300-kDa polypeptide in placental extracts, indicating that the merosin polypeptide is similar in size to the laminin A chain. Intact merosin was isolated from placental extracts and shown to be covalently associated with the laminin B chains and to have a cross-like structure similar to that of laminin. The similarities between merosin and laminin show that both proteins are members of the same family of basement membrane proteins.

Transient and locally restricted expression of laminin A chain mRNA by developing epithelial cells during kidney organogenesis

Three polypeptide chains, A, B1, and B2, have been described for mouse laminin, a basement membrane protein. We studied expression of laminin A, B1, and B2 mRNA in the developing mouse kidney. Induction of kidney mesenchyme differentiation in vitro led to an increased expression of B1 and B2 chain mRNA on day 1 of development. In contrast, expression of A chain mRNA increased on day 2, when epithelial cell polarization begins. Laminin A mRNA and polypeptide were expressed only by epithelia during in vivo development as well. Some polarized cell types producing basement membrane (endothelium, some adult epithelia) lacked the A chain mRNA and polypeptide, although they did express B chains. Laminin with the 400 kd A chain is therefore a transient form appearing at specific sites of kidney morphogenesis, whereas isoforms with a different A chain or without it have a more widespread distribution.

Identification of laminin binding proteins in cell membranes of a human colon adenocarcinoma cell line

The invasion of malignant cells through the basement membrane is a critical step in local infiltration and metastasis. Adhesion and invasion of malignant cells may be modulated by their receptor mediated binding to the basement membrane glycoprotein laminin. We studied the specific adhesion of human colon adenocarcinoma derived HT 29 cells to laminin and its proteolytic fragments. The major cell adhesion domain of laminin was localised in the central part of the cross shaped molecule. Immunoblotting experiments on separated HT 29 cell membranes using specific antibodies or radiolabelled laminin fragments revealed two major laminin-binding cell surface components with Mr of 67,000 and 69,000 D similar to the putative laminin receptor described for other tissues. Using a nitrocellulose filter disk assay, the specific interaction between cell surface binding proteins and proteolytic fragments originating from the central core of the laminin molecule could be further corroborated. In contrast, interaction of HT 29 cell membranes with the pentapeptide YIGSR (tyr-ile-gly-ser-arg), a sequence domain of the B1-chain of the laminin molecule, thought to be responsible for cell adhesion, was significantly weaker.

Selective immunoreactivities of kidney basement membranes to monoclonal antibodies against laminin: localization of the end of the long arm and the short arms to discrete microdomains

To examine the ultrastructural distribution of laminin within kidney basement membranes, we prepared rat anti-mouse laminin mAbs to use in immunolocalization experiments. Epitope domains for these mAbs were established by immunoprecipitation, immunoblotting, affinity chromatography, and rotary shadow EM. One mAb bound to the laminin A and B chains on blots and was located to a site approximately 15 nm from the long arm-terminal globular domain as shown by rotary shadowing. Conjugates of this long arm-specific mAb were coupled to horseradish peroxidase (HRP) and intravenously injected into mice. Kidney cortices were fixed for microscopy 3 h after injection. HRP reaction product was localized irregularly within the renal glomerular basement membrane (GBM) and throughout mesangial matrices. In addition, this mAb bound in linear patterns specifically to the laminae rarae of basement membranes of Bowman's capsule and proximal tubule. This indicates the presence of the long arm immediately beneath epithelial cells in these sites. The laminae densae of these basement membranes were negative by this protocol. In contrast, the lamina rara and densa of distal tubular basement membranes (TBM) were both heavily labeled with this mAb. A different ultrastructural binding pattern was seen with eight other mAbs, including two that mapped to different sites on the short arms by rotary shadowing and five that blotted to a large pepsin-resistant laminin fragment (P1). These latter mAbs bound weakly or not at all to GBM but all bound throughout mesangial matrices. In contrast, discrete spots of HRP reaction product were seen across all layers of Bowman's capsule BM and proximal TBM. These same mAbs, however, bound densely across the full width of distal TBM. Our findings therefore show that separate strata of different basement membranes are variably immunoreactive to these laminin mAbs. The molecular orientation or integration of laminin into the three dimensional BM meshwork therefore varies with location. Alternatively, there may be a family of distinct laminin-like molecules distributed within basement membranes.

Primary sequence of a motor neuron-selective adhesive site in the synaptic basal lamina protein S-laminin

S-laminin, a novel homolog of laminin, is concentrated in a subset of basal laminae including the basal lamina that passes between motor nerve terminals and muscle fibers at the neuromuscular junction. Here we used recombinant fragments to localize a neuronal attachment site to the C-terminal 10% of s-laminin. We then used synthetic peptides spanning the active fragment to identify the primary sequence of the adhesive site as Leu-Arg-Glu (LRE): neurons attach to an immobilized LRE-containing peptide, and soluble LRE blocks attachment of neurons to the s-laminin fragment. Whereas ciliary ganglion neurons (which normally innervate muscle fibers) adhered well both to laminin and to an s-laminin fragment, sensory and central neurons and several neuronal cell lines all adhered well to laminin but poorly to the s-laminin fragment. Together, these results define a motor neuron-selective attachment site on s-laminin.

Endothelial cells use alpha 2 beta 1 integrin as a laminin receptor

Human umbilical vein endothelial cells attach and spread on laminin-coated substrates. Affinity chromatography was used to identify the attachment receptor. Fractionation of extracts from surface-iodinated endothelial cells on human laminin-Sepharose yielded a heterodimeric complex, the subunits of which migrated with molecular sizes corresponding to 160/120 kD and 160/140 kD under nonreducing and reducing conditions, respectively. The purified receptor bound to laminin and slightly less to fibronectin and type IV collagen in a radioreceptor assay. This endothelial cell laminin receptor was classified as an alpha 2 beta 1 integrin because monoclonal and polyclonal antibodies directed against the alpha 2 and bet 1 subunits immunoprecipitated the receptor. Cytofluorometric analysis and immunoprecipitation showed that the alpha 2 subunit is an abundant integrin alpha subunit in the endothelial cells and that the alpha subunits associated with laminin binding in other types of cells are expressed in these cells only at low levels. The alpha 2 beta 1 integrin appears to be a major receptor for laminin in the endothelial cells, because an anti-alpha 2 monoclonal antibody inhibited the attachment of the endothelial cells to human laminin. These results define a new role for the alpha 2 subunit in laminin binding and suggest that the ligand specificity of the alpha 2 beta 1 integrin, which is known as a collagen receptor in other types of cells, can be modulated by cell type-specific factors to include laminin binding.

Molecular mechanisms of avian neural crest cell migration on fibronectin and laminin

We have examined the molecular interactions of avian neural crest cells with fibronectin and laminin in vitro during their initial migration from the neural tube. A 105-kDa proteolytic fragment of fibronectin encompassing the defined cell-binding domain (65 kDa) promoted migration of neural crest cells to the same extent as the intact molecule. Neural crest cell migration on both intact fibronectin and the 105-kDa fragment was reversibly inhibited by RGD-containing peptides. The 11.5-kDa fragment containing the RGDS cell attachment site was also able to support migration, whereas a 50-kDa fragment corresponding to the adjacent N-terminal portion of the defined cell-binding domain was unfavorable for neural crest cell movement. In addition to the putative "cell-binding domain," neural crest cells were able to migrate on a 31-kDa fragment corresponding to the C-terminal heparin-binding (II) region of fibronectin, and were inhibited in their migration by exogenous heparin, but not by RGDS peptides. Heparin potentiated the inhibitory effect of RGDS peptides on intact fibronectin, but not on the 105-kDa fragment. On substrates of purified laminin, the extent of avian neural crest cell migration was maximal at relatively low substrate concentrations and was reduced at higher concentrations. The efficiency of laminin as a migratory substrate was enhanced when the glycoprotein occurred complexed with nidogen. Moreover, coupling of the laminin-nidogen complex to collagen type IV or the low density heparan sulfate proteoglycan further increased cell dispersion, whereas isolated nidogen or the proteoglycan alone were unable to stimulate migration and collagen type IV was a significantly less efficient migratory substrate than laminin-nidogen. Neural crest cell migration on laminin-nidogen was not affected by RGDS nor by YIGSR-containing peptides, but was reduced by 35% after addition of heparin. The predominant motility-promoting activity of laminin was localized to the E8 domain, possessing heparin-binding activity distinct from that of the N-terminal E3 domain. Migration on the E8 fragment was reduced by greater than 70% after addition of heparin. The E1' fragment supported a minimal degree of migration that was RGD-sensitive and heparin-insensitive, whereas the primary heparin-binding E3 fragment and the cell-adhesive P1 fragment were entirely nonpermissive for cell movement.(ABSTRACT TRUNCATED AT 400 WORDS)

Rat mesangial cell-matrix interactions in culture

The glomerular mesangium contains fibronectin (FN), laminin, and collagen IV, but it remains unclear whether these matrix proteins affect mesangial cellular functions. The present experiments were designed to test whether cell-matrix interactions could affect some functions of mesangial cells. Cultured rat mesangial cells synthesized a cellular form of FN that was both secreted and incorporated into an extensive, fibrillar pericellular matrix. This FN matrix was increased in high-density cultures and was more developed in human mesangial cells. Rat mesangial cells in vitro displayed a marked capacity to incorporate exogenous FN into a pericellular matrix, demonstrating that accumulations of FN in the mesangial matrix could result from endogenous and/or exogenous sources. Rat mesangial cells also expressed RGD-sensitive integrin receptors for FN, laminin, and collagens I and IV that promoted cell adhesion and that directed differential changes in morphology. Indirect evidence suggested the existence of other mesangial binding sites for extracellular matrix proteins. FN and collagen IV also stimulated modest increases in [3H]thymidine uptake and cell number by quiescent cells. Taken together, these results suggest that cultured mesangial cells present a model system for studying the regulation of cell-matrix interactions in the mesangium.

A laminin-pepsin fragment with cell attachment and neurite outgrowth activity at distinct sites

Laminin is a large basement membrane glycoprotein which influences the behavior and morphology of a variety of cells. We have found that laminin and a pepsin fragment of laminin (P-lam) contain distinct sites for HT-1080 human fibrosarcoma cell attachment and for neurite outgrowth activity of PC12 and NG108-15 cell lines. Reduction and alkylation of laminin and P-lam fragment disulfide bonds, in the absence of denaturing agents, markedly reduced the cell attachment activity without reducing the neurite outgrowth response. The P-lam fragment (approximately 375 kDa) was found to contain part of the cross region of laminin and a portion of the long arm, on the basis of recognition by antisera against laminin synthetic peptides and fusion proteins. Modification of arginine residues by cyclohexanedione also had no effect on neurite outgrowth but reduced HT-1080 cell adhesion. Modification of lysine residues by succinic and citraconic anhydride, however, abolished laminin neurite outgrowth but not cell attachment activity. Neurite outgrowth activity was recovered by reversing the lysine modification. These data support the existence on laminin of separate sites for cell attachment and for neurite outgrowth.

The E8 subfragment of laminin promotes locomotion of myoblasts over extracellular matrix

The locomotion of murine myoblasts over the extracellular matrix components laminin and fibronectin was analyzed using quantitative videomicroscopy, and the organization of the cytoskeleton was observed in parallel immunofluorescence studies. Cells plated on the laminin-nidogen complex locomoted twice as fast as on laminin alone. The main form of translocation on laminin was a jerky cycle of prolonged lamellipod extension followed by rapid (approximately 200- less than 500 microh h-1) movement of the cell body into the extended lamellipod. The locomotion-stimulating activity of laminin resides in the elastase digestion fragment E8, part of the laminin long arm, while the E1-4 fragment containing the three short arms is inactive. Myoblasts moved poorly over fibronectin irrespective of whether high, intermediate, or low coating concentrations were used (approximately 5,000- approximately 10 fmol cm-2). In contrast, the locomotory responses both to laminin and to E8 peaked sharply at coating concentrations approximately 20-50 fmol cm-2 and decreased at higher concentrations. This response corresponds to that expected for a haptotactic stimulant. When cells locomoted over a mixed substrate of laminin and fibronectin, the fibronectin effects appeared to predominate. The cytoskeleton has been implicated in many cellular motile processes. Within 6 h on fibronectin many cells expressed vinculin-containing focal contacts, elaborated stress fibers and had periodically organized alpha actinin, whereas on laminin, most cells showed diffuse vinculin and alpha actinin and a fine meshlike actin cytoskeleton. We conclude that the poor locomotion of cells over fibronectin is because of the cytoskeletal stabilization it induces.

Laminin A chain synthetic peptide which supports neurite outgrowth

Neurons from peripheral and central nervous tissue as well as from established cell lines respond to low concentrations of laminin with rapid extension of axon-like processes. Two sites on laminin have been identified which stimulate neurite outgrowth, the major site residing at the end of the long arm of laminin. Recently laminin has been cloned and sequenced allowing for synthetic peptides to be prepared and tested for biological activity. We report here that antisera against synthetic peptides corresponding to A and to B1 chain sequences at the end of the long arm can partially inhibit laminin-mediated neurite outgrowth. Further, we show that a 19 amino acid synthetic peptide (CSRARKQAASIKVAVSADR) from the long arm of the laminin A chain is capable of stimulating neuronal-like process formation to almost the same extent as laminin and competes with laminin for stimulation of neurite outgrowth.

Neuronal laminin receptors

The ability of the extracellular matrix protein laminin to regulate the survival and differentiation of neurons has led to the search for a neuronal laminin receptor. This article reviews the evidence for the existence of laminin receptors, and then goes on to discuss the difficulties in making the jump from a pharmacological demonstration of the receptor to its molecular identification.

Structure and biological activity of basement membrane proteins

Collagen type IV, laminin, heparan sulfate proteoglycans, nidogen (entactin) and BM-40 (osteonectin, SPARC) represent major structural proteins of basement membranes. They are well-characterized in their domain structures, amino acid sequences and potentials for molecular interactions. Such interactions include self-assembly processes and heterotypic binding between individual constituents, as well as binding of calcium (laminin, BM-40) and are likely to be used for basement membrane assembly. Laminin, collagen IV and nidogen also possess several cell-binding sites which interact with distinct cellular receptors. Some evidence exists that those interactions are involved in the control of cell behaviour. These observations have provided a more defined understanding of basement membrane function and the definition of new research goals in the future.