Biomedical subjects

E Engvall

Publications and source records attributed to E Engvall.

At least 91 records · Page 5Linked to original sources

PubMed1988

Merosin, a protein specific for basement membranes of Schwann cells, striated muscle, and trophoblast, is expressed late in nerve and muscle development.

We have identified a tissue-specific basement membrane-associated protein by using monoclonal antibodies prepared against a protein fraction of human placenta. In immunofluorescence, the monoclonal antibodies stained basement membranes of Schwann cells, striated muscle, and trophoblast, whereas no reaction was seen with any other basement membrane or tissue structure. In antibody-affinity chromatography of proteolytic digests of human placenta, a 65-kDa polypeptide was bound by these monoclonal antibodies. Rabbit antisera and monoclonal antibodies raised against the isolated 65-kDa polypeptide stained human and monkey tissues identically to the original monoclonal antibodies and reacted with an 80-kDa polypeptide in tissue extracts prepared without proteolysis. The 65-kDa and 80-kDa polypeptides were shown to be immunologically distinct from laminin, type IV collagen, fibronectin, and major serum proteins. They presumably represent a novel basement membrane-associated protein, which we have named merosin. No merosin immunoreactivity could be detected in cultures of any of 28 established cell lines. In developing mouse tissues, merosin staining first appeared at the newborn stage. The restricted tissue distribution and late developmental appearance of merosin suggest that the protein has a tissue-specific function associated with a high level of differentiation.

Animals↗

PubMed1988

Ultrastructure of type VI collagen in human skin and cartilage suggests an anchoring function for this filamentous network.

An mAb was used in conjunction with immunoelectron microscopy to study the ultrastructure and distribution of the type VI collagen network. Type VI collagen in femoral head and costal cartilage was found distributed throughout the matrix but concentrated in areas surrounding chondrocytes. Three-dimensional information gained from high voltage stereo pair electron microscopy showed that the type VI collagen network in skin was organized into a highly branched, open, filamentous network that encircled interstitial collagen fibers, but did not appear to interact directly with them. Type VI collagen was also found concentrated near basement membranes of nerves, blood vessels, and fat cells although in a less organized state. Labeling was conspicuously reduced close to the epithelial basement membrane in the region of the anchoring fibrils. No labeling of basement membranes was seen. Based on these observations it is suggested that the type VI collagen forms a flexible network that anchors large interstitial structures such as nerves, blood vessels, and collagen fibers into surrounding connective tissues.

Age Factors↗

PubMed1987

Human amnion membrane serves as a substratum for growing axons in vitro and in vivo.

The epithelial cell layer of human amnion membrane can be removed while the basement membrane and stromal surfaces remain morphologically intact. Such a preparation has been used as a substratum for the in vitro culture of dissociated neurons. Embryonic motor neurons from chick ciliary ganglion attached to both surfaces but grew extensive neurites only on the basement membrane. On cross sections of rolled amnion membranes, regenerating axons of cultured neurons were guided along pathways of basement membrane that were immunoreactive with an antibody to laminin. In addition, when rolled amnion membranes were implanted into a lesion cavity between the rat septum and hippocampus, cholinergic neurons extended axons through the longitudinally oriented implant into the hippocampus. Thus, this amnion preparation can serve as a bridge to promote axonal regeneration in vivo in damaged adult brain.

Amnion↗

PubMed1987

Association of laminin with heparan and chondroitin sulfate-bearing proteoglycans in neurite-promoting factor complexes from rat schwannoma cells.

The present studies were undertaken to confirm the presence and identity of a putative proteoglycan associated with laminin in neurite-promoting factor complexes isolated from rat schwannoma cell conditioned medium. Sucrose density gradient centrifugation of the complex resolved two laminin-associated Na2[35S]O4-labeled peaks which were termed Pools A and B. Both pools had nearly all their [35S] cpms associated with glycosaminoglycan, contained heparan sulfate-proteoglycan core protein antigen and displayed a similarly high neurite promoting potency relative to their laminin contents. However, Pool A contained about twice as many [35S] cpms and twice as much proteoglycan core protein per laminin than Pool B. Seventy percent of Pool A cpms was associated with heparan sulfate and 30% with chondroitin sulfate whereas the inverse was true for Pool B. Treatment with heparitinase and/or chondroitinase ABC caused laminin in either pool to elute at lower salt concentrations from DEAE cellulose. In SDS-PAGE the [35S] cpms of both pools ran with the same mobility as laminin but could be separated from laminin under reducing conditions. The Pool A cpms remained at 900 KD and the Pool B cpms spread over the 200-900 KD range. By rotary shadowing electron microscopy, Pool B fractions contained primarily cross-shaped laminin images, often associated with proteoglycan-like images. Pool A fractions contained i) dense, aggregated images including intact laminin from which emanated proteoglycan-like strands, ii) circular images bearing globular domains and less commonly, iii) distorted cross-shaped laminin-like images. These studies support the existence of at least two forms of laminin-proteoglycan complexes which differ in biochemical, immunochemical and ultrastructural characteristics.

Animals↗

PubMed1987

Human amnion membrane as a substratum for cultured peripheral and central nervous system neurons.

We report here on the use of human amnion membrane as a substratum for the culture of neuronal cells. Pieces of amnion membrane were bound to nitrocellulose paper as a supporting material, seeded with neurons, and cultured for 1-4 days. Neurons and neurites were visualized after fixation by immunoperoxidase staining using an anti-neurofilament monoclonal antibody. Neurons from embryonic chick ciliary and dorsal root ganglia and fetal rat hippocampus were cultured on either the basement membrane or stromal surface of the amnion membrane. Neurons adhered to both surfaces but extended neurites only on the basement membrane surface. Neurons survived and continued to grow neurites in serum-free medium for at least 4 days. When cultured for 4 days on the basement membrane surface in the presence of 10% fetal calf serum, the ciliary ganglion neurons survived but neurite growth was markedly inhibited, while dorsal root ganglion neurons survived, hypertrophied and grew an extensive network of neurites. Other experiments addressed the question whether the basement membrane surface had an ability to guide growing neurites. Amnion membranes were folded, frozen, cross-sectioned using a cryostat, and placed on the nitrocellulose to give irregular patterns of basement membrane juxtaposed to the collagenous stroma. Ciliary ganglion neurons after 4 days in culture had initiated and extended neurites in patterns which corresponded and were limited to those areas visualized by indirect immunofluorescence staining using anti-laminin antibodies. Thus, in vivo assembled human amnion basement membranes appear to contain signals that both promote and guide neuritic growth from previously axotomized embryonic peripheral and central nervous system neurons. The amnion membrane represents a novel tool for the culture of neuronal cells in vitro and potentially could be used as a neurite-promoting bridging material in vivo for regeneration studies.

Amnion↗

PubMed1986

Interaction of vitronectin with collagen.

Purified human plasma vitronectin was demonstrated to bind to type I collagen immobilized on plastic as measured by enzyme-linked immunosorbent assay and by binding of 125I-radiolabeled vitronectin to a collagen-coated plastic surface. Vitronectin did not bind to immobilized laminin, fibronectin, or albumin in these assays. Vitronectin showed similar interaction with all types of collagen (I, II, III, IV, V, and VI) tested. Collagen unfolded by heat treatment bound vitronectin less efficiently than native collagen. Vitronectin-coated colloidal gold particles bound to type I collagen fibrils as shown by electron microscopy. Salt concentrations higher than physiological interfered with the binding of vitronectin to collagen, suggesting an ionic interaction between the two proteins. Binding studies conducted in the presence of plasma showed that purified vitronectin added to plasma bound to immobilized collagen, whereas the endogenous plasma vitronectin bound to collagen less well. Although fibronectin did not interfere with the binding of vitronectin to native collagen, vitronectin inhibited the binding of fibronectin to collagen. These results show that vitronectin has a collagen-binding site(s) which, unlike that of fibronectin, preferentially recognizes triple-helical collagen and that the binding between vitronectin and collagen has characteristics compatible with the occurrence of such an interaction in vivo.

Blood Proteins↗

PubMed1986

Molecular assembly, secretion, and matrix deposition of type VI collagen.

Monoclonal antibodies reactive with the tissue form of type VI collagen were used to isolate the type VI collagen polypeptides from cultured fibroblasts and muscle cells. Two [35S]methionine-labeled polypeptides of 260 and 140 kD were found intracellularly, in the medium, and in the extracellular matrix of metabolically labeled cells. These polypeptides were disulfide cross-linked into very large complexes. The 260- and 140-kD polypeptides were intimately associated and could not be separated from each other by reduction without denaturation. In the absence of ascorbic acid, both polypeptides accumulated inside the cell, and their amounts in the medium and in the matrix were decreased. These results suggest that both the 260- and the 140-kD polypeptides are integral parts of the type VI collagen molecule. Examination of type VI collagen isolated from the intracellular pool by electron microscopy after rotary shadowing revealed structures corresponding to different stages of assembly of type VI collagen. Based on these images, a sequence for the intracellular assembly of type VI collagen could be discerned. Type VI collagen monomers are approximately 125 nm long and are composed of two globules separated by a thin strand. The monomers assemble into dimers and tetramers by lateral association. Only tetramers were present in culture media, whereas both tetramers and multimers were found in extracellular matrix extracts. The multimers appeared to have assembled from tetramers by end-to-end association into filaments that had prominent knobs and a periodicity of approximately 110 nm. These results show that, unlike other collagens, type VI collagen is assembled into tetramers before it is secreted from the cells, and they also suggest an extracellular aggregation mechanism that appears to be unique to this collagen.

Animals↗

PubMed1986

Type VI collagen in extracellular, 100-nm periodic filaments and fibrils: identification by immunoelectron microscopy.

Filaments and fibrils that exhibit a 100-nm axial periodicity and occur in the medium and in the deposited extracellular matrix of chicken embryo and human fibroblast cultures have been tentatively identified with type VI collagen on the basis of their similar structural characteristics (Bruns, R. R., 1984, J. Ultrastruct. Res., 89:136-145). Using indirect immunoelectron microscopy and specific monoclonal and polyclonal antibodies, we now report their positive identification with collagen VI and their distribution in fibroblast cultures and in tendon. Primary human foreskin fibroblast cultures, labeled with anti-type VI antibody and studied by fluorescence microscopy, showed a progressive increase in labeling and changes in distribution with time up to 8 d in culture. With immunoelectron microscopy and monoclonal antibodies to human type VI collagen followed by goat anti-mouse IgG coupled to colloidal gold, they showed in thin sections specific 100-nm periodic labeling on extracellular filaments and fibrils: one monoclonal antibody (3C4) attached to the band region and another (4B10) to the interband region of the filaments and fibrils. Rabbit antiserum to type VI collagen also localized on the band region, but the staining was less well defined. Control experiments with antibodies to fibronectin and to procollagen types I and III labeled other filaments and fibrils, but not those with a 100-nm period. Heavy metal-stained fibrils with the same periodic and structural characteristics also have been found in both adult rat tail tendon and embryonic chicken tendon subjected to prolonged incubation in culture medium or treatment with adenosine 5'-triphosphate at pH 4.6. We conclude that the 100-nm periodic filaments and fibrils represent the native aggregate form of type VI collagen. It is likely that banded fibrils of the same periodicity and appearance, reported by many observers over the years in a wide range of normal and pathological tissues, are at least in part, type VI collagen.

Adenosine Triphosphate↗

PubMed1986

C3d fragment of complement interacts with laminin and binds to basement membranes of glomerulus and trophoblast.

Two mouse monoclonal antibodies generated against human placental homogenate were found to react specifically with human complement component C3. In immunofluorescence of human tissues, these antibodies gave a bright linear staining outlining the glomerular basement membrane of the adult kidney and the trophoblast basement membrane of placenta. An identical staining pattern was observed with a rabbit C3d antiserum which also prevented binding of the monoclonal antibodies to tissue sections. Only negligible basement membrane staining was observed in the same tissues with antisera to human C3c, C5, IgG, IgA, or IgM. When interactions of C3 with basement membrane proteins were tested in enzyme immunoassays and column chromatography, C3(H2O) was found to bind efficiently to solid-phase laminin. Native C3 from fresh plasma did not bind to laminin but C3 from plasma treated with methylamine bound efficiently. When C3 was cleaved with trypsin, C3b and C3d but not C3c bound to laminin-Sepharose. The interaction of C3 and laminin was inhibited by soluble laminin and by high ionic strength. The results indicate that C3d, a biologically active breakdown product of C3, can be found in glomerular and placental basement membranes in the absence of signs for ongoing local complement activation or immune complex deposition. It is possible that binding affinities between C3 and basement membrane molecules, especially laminin, are involved in the retention of C3d at these sites. Such interactions between C3 and components of the glomerular basement membrane could play important roles in complement-related pathological processes of the glomerulus.

Antibodies, Monoclonal↗

PubMed1986

Mapping of domains in human laminin using monoclonal antibodies: localization of the neurite-promoting site.

Monoclonal antibodies were made against a truncated form of human laminin isolated from placenta. 12 antibodies were isolated and characterized. All antibodies stained basement membranes in placenta and immunoprecipitated laminin from media of cultured choriocarcinoma cells. Three antibodies, 3E5, 4C7, and 4E10, partially blocked the neurite-promoting activity of laminin. Addition of a second antibody, goat anti-mouse IgG, caused more complete blocking of the activity. Two of the blocking antibodies, 4C7 and 4E10, reacted with epitopes within the globular domain at the end of the long arm of laminin, and the third one, 3E5, reacted at the end of the rod-like portion of the long arm adjacent to the globular domain, as shown by electron microscopy after rotary shadowing. Five nonblocking antibodies used in the same test reacted with epitopes in other domains of the molecule. Blocking antibodies 3E5 and 4E10 could be used in immunoblotting and both antibodies reacted with the same polypeptides in pepsin fragments of human laminin, the predominant polypeptides being approximately 400 kD. When a crude extract of human amnion was used as a source of intact laminin, the 4E10 antibody detected a single polypeptide of approximately 400 kD. A nonblocking antibody, 2E8, which reacted at the center of the laminin cross, reacted predominantly with a 200-kD polypeptide in human laminin fragments and exclusively with a 200-kD polypeptide in amnion extract and in rat laminin. Our results with human laminin match the results by Edgar, D., R. Timpl, and H. Thoenen, 1984, EMBO (Eur. Mol. Biol. Organ.) J., 3:1463-1468, in which the neurite-promoting activity of mouse laminin resides at the end of the long arm, which is also the site for heparin binding. However, since the active fragments of human laminin did not bind to heparin, the neurite-promoting site should be different from the heparin-binding site. Our results further suggest that the neurite-promoting site may be contained in or close to the 400-kD component of laminin.

Animals↗

PubMed1986

Fibrillin, a new 350-kD glycoprotein, is a component of extracellular microfibrils.

A new connective tissue protein, which we call fibrillin, has been isolated from the medium of human fibroblast cell cultures. Electrophoresis of the disulfide bond-reduced protein gave a single band with an estimated molecular mass of 350,000 D. This 350-kD protein appeared to possess intrachain disulfide bonds. It could be stained with periodic acid-Schiff reagent, and after metabolic labeling, it contained [3H]glucosamine. It could not be labeled with [35S]sulfate. It was resistant to digestion by bacterial collagenase. Using mAbs specific for fibrillin, we demonstrated its widespread distribution in the connective tissue matrices of skin, lung, kidney, vasculature, cartilage, tendon, muscle, cornea, and ciliary zonule. Electron microscopic immunolocalization with colloidal gold conjugates specified its location to a class of extracellular structural elements described as microfibrils. These microfibrils possessed a characteristic appearance and averaged 10 nm in diameter. Microfibrils around the amorphous cores of the elastic fiber system as well as bundles of microfibrils without elastin cores were labeled equally well with antibody. Immunolocalization suggested that fibrillin is arrayed periodically along the individual microfibril and that individual microfibrils may be aligned within bundles. The periodicity of the epitope appeared to match the interstitial collagen band periodicity. In contrast, type VI collagen, which has been proposed as a possible microfibrillar component, was immunolocalized with a specific mAb to small diameter microfilaments that interweave among the large, banded collagen fibers; it was not associated with the system of microfibrils identified by the presence of fibrillin.

Actin Cytoskeleton↗

PubMed1986

Heterogeneity of basement membranes of the human genitourinary tract revealed by sequential immunofluorescence staining with monoclonal antibodies to laminin.

We used monoclonal antibodies specific for human laminin to analyze immunohistochemically the heterogeneity of the basement membranes in various parts of the genitourinary tract. By indirect immunofluorescence microscopy we show that antibody 3H11 reacts with all epithelial basement membranes in the kidneys, testes, epididymis, prostate, uterus, oviduct, and ovary, as well as the smooth muscle cells, blood vessels, and nerves. Antibody 4E10 reacted with most epithelial basement membranes in these organs but was unreactive with the basement membranes of peripheral glomerular capillary loops and the basement membranes of the oviductal mucosa, seminiferous tubules, straight tubules, and rete testis. Hilar seminiferous tubules were reactive with 4E10. In contrast to 3H11, which reacted with all vascular, subendothelial, and muscular basement membranes, 4E10 reacted only with the subendothelial basement membrane of capillaries and veins. The difference in the distribution of epitopes could be demonstrated in tissue sections sequentially reacted with two monoclonal antibodies, but only if the antibody of restricted reactivity (4E10) was used first. These data show that the heterogeneous expression of distinct epitopes of laminin in basement membranes can be demonstrated in the same tissue section by sequential staining. This heterogeneity of basement membranes most likely reflects conformational differences in the expression of epitopes on the laminin molecule in various anatomic structures.

Adult↗

PubMed1985

Origin of laminin in the extracellular matrix of human tumor xenografts in nude mice.

Monoclonal antibodies reacting exclusively with laminin of human origin and a polyclonal antibody reacting with both murine and human laminin were used to immunohistochemically study the extracellular matrix of four human tumors grown as xenografts in nude mice: a lung carcinoma and a yolk sac carcinoma because they produced cell associated laminin in vitro; and two hepatocellular carcinomas which did not produce cell associated laminin in vitro. The extracellular matrix of the xenografts of the lung carcinoma and the yolk sac carcinoma contained laminin of both human and murine origin. Xenografts of liver carcinoma contained only laminin of mouse origin. This shows that the malignant cells capable of laminin production in vitro contribute this glycoprotein to the extracellular matrix of the solid tumor formed by them in vivo.

Animals↗

PubMed1985

Isolation and characterization of rat schwannoma neurite-promoting factor: evidence that the factor contains laminin.

Rat RN22 schwannoma cells in vitro release into their growth medium a macromolecular factor that, when bound to polyornithine-coated culture substrata, will stimulate neuritic regeneration from axotomized peripheral and central neurons. During the purification of this factor, the neurite-promoting activity co-purifies with laminin immunoreactivity as measured by an enzyme-linked immunoadsorbent assay. The purified factor has an immunoreactivity per milligram of protein similar to that of purified rat yolk sac tumor laminin. After sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing conditions, the purified factor exhibits a major band at 200 kilodaltons (kD) and two minor ones at about 130 and 35 kD. The 200-kD band comigrates with the 200-kD band of purified rat laminin. After SDS-PAGE under non-reducing conditions, the rat schwannoma factor and rat laminin both exhibit a band in the 900-kD range with the schwannoma factor band migrating slightly faster than the laminin one. The 200-kD (reducing conditions) and 900-kD (non-reducing conditions) bands of both the schwannoma factor and laminin are stained by immunoblotting with antisera raised against rat and human laminin and against a partially purified preparation of the schwannoma factor. On immunoblots the 400-kD band of laminin (a band not seen in the schwannoma factor preparation) also stains with all three antisera. When the antibodies from each of the three antisera are immobilized on protein A-agarose beads, the beads will completely remove from solution the neurite-promoting activities of both the schwannoma factor and laminin. Antibodies raised against rat laminin fail to block the neurite-promoting activity of the purified schwannoma factor but totally block that of rat laminin. In contrast, antibodies raised against the schwannoma factor will block the neurite-promoting activities of both the schwannoma factor and laminin. By rotary shadowing electron microscopy the schwannoma factor preparation exhibits cross-shaped images similar but not identical to those previously reported for rat and mouse laminin. In addition, the schwannoma factor preparation contains images resembling proteoglycans.

Animals↗

PubMed1984

Neurite-promoting factors and extracellular matrix components accumulating in vivo within nerve regeneration chambers.

The outgrowth of neurites from cultured neurons can be induced by the extracellular matrix glycoproteins, fibronectin and laminin, and by polyornithine-binding neurite-promoting factors (NPFs) derived from culture media conditioned by Schwann, or other cultured cells. We have examined the occurrence of fibronectin, laminin and NPFs during peripheral nerve regeneration in vivo. A previously established model of peripheral nerve regeneration was used in which a transected rat sciatic nerve regenerates through a silicone chamber bridging a 10 mm interstump gap. The distribution of fibronectin and laminin during regeneration was assessed by indirect immunofluorescence. Seven days after nerve transection the regenerating structure within the chamber consisted primarily of a fibrous matrix which stained with anti-fibronectin but not anti-laminin. At 14 days, cellular outgrowths from the proximal and distal stumps (along which neurites grow) had entered the fibronectin-containing matrix, consistent with a role of fibronectin in promoting cell migration. Within these outgrowths non-vascular as well as vascular cells stained with anti-fibronectin and anti-laminin. Within the degenerated distal nerve segment, cell characteristic of Bungner bands (rows of Schwann cells along which regenerating neurites extend) stained with anti-fibronectin and laminin. The fluid surrounding the regenerating nerve was found to contain NPF activity for cultured ciliary ganglia neurons which markedly increased during the period of neurite growth into the chamber. In previous studies using this particular neurite-promoting assay, laminin but to a much lesser extent fibronectin also promoted neurite outgrowth.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1984

Type VI collagen. Studies on its localization, structure, and biosynthetic form with monoclonal antibodies.

Monoclonal antibodies were prepared by immunization with whole tissue and were selected for their reactivity with extracellular matrices in tissue immunofluorescence. Two such antibodies were used to isolate the corresponding antigen from pepsin extracts of human placental tissue by immunochromatography. In each case, polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate showed that the isolated material was composed of four polypeptides of Mr between 57,000 and 85,000 that were disulfide-bonded into a high molecular weight aggregate. Amino acid analyses showed that the isolated material was partly collagenous. The material was shown to be antigenically related to previously isolated peptic fragments of type VI collagen and it shared their unique structure as revealed by electron microscopy. Based on these findings, it was concluded that the isolated material was a form of type VI collagen. In immunofluorescence, the monoclonal antibodies localized type VI collagen throughout the connective tissue and in the extracellular matrix of cultured fibroblasts. Polypeptides presumably comprising the intact form of this collagen were isolated from cultures of metabolically radiolabeled fibroblast cell cultures using the two monoclonal antibodies. The isolated material consisted of two polypeptides of Mr 240,000 and 140,000 that were extensively disulfide cross-linked. Four additional monoclonal antibodies bound the same radioactive polypeptides from fibroblast cultures, but only one of them reacted with the fragments isolated from pepsin-digested placenta. Since all six antibodies were originally selected based on tissue immunofluorescence, and therefore react with the tissue form of the protein, the tissue form appears to be more similar to the polypeptides detected in fibroblast cultures than to the pepsin-resistant fragments. Since these monoclonal antibodies apparently recognize different parts of the molecule, they will be useful for further study of the structure and function of the intact form of type VI collagen.

Amino Acids↗

PubMed1984

Clonal tumorigenic endodermal cell lines producing basement membrane components.

Tumors were developed from the mouse teratocarcinoma-derived endodermal cell line PF HR-9 by subcutaneous injections in syngeneic mice of large numbers of cells previously cultured for several years at high cell density. Cell cultures were established from the tumors and the cells were cloned. The cloned sublines were highly malignant in vivo and tumor metastases were occasionally observed. The tumors contained abundant extracellular material, which was distinctly laminated and contained type IV collagen, laminin, and heparan sulfate proteoglycan. The tumorigenic sublines were also shown to have retained markers of the original cells, such as the cytoskeletal proteins Endo A and B. These cell lines should be useful for biosynthetic studies on basement membrane and cytoskeletal components and the tumors for isolation of these macromolecules and their mRNAs.

Animals↗

PubMed1984

Adhesion of platelets to laminin in the absence of activation.

The binding of platelets to components in the subendothelial matrix is an initial event in hemostasis and thrombosis. The glycoprotein components of the matrix are considered important in this interaction. Of these, collagen binds and activates platelets and induces their aggregation. In this study we demonstrate that substrate-bound laminin causes time- and concentration-dependent adherence of human platelets to the substrate. The binding of platelets to laminin was found to be similar in some respects, but different in others, to their binding to surfaces coated with fibronectin or collagen. The binding of platelets to laminin or fibronectin was not associated with their activation under conditions in which type I collagen activates the platelets as measured by [14C]serotonin secretion. Platelets bound to laminin and fibronectin differed in their appearance; they remained rounded on laminin whereas they flattened completely on fibronectin. Binding of platelets to fibronectin, but not laminin, is inhibited by a recently described peptide (Pierschbacher, M., and E. Ruoslahti, 1984, Nature (Lond.), 309:30-33) containing the cell-attachment tetrapeptide sequence of fibronectin, which suggests that separate receptors exist for laminin and fibronectin. These studies establish laminin as a platelet-binding protein and suggest that laminin can contribute to the adhesiveness of exposed tissue matrices to platelets. Since laminin and fibronectin do not activate platelets, whereas collagen does, and laminin differs from fibronectin in that it does not induce spreading of the attached platelets, all three proteins appear to confer different signals to the platelets. Some of these may be related to platelet functions other than those necessary for the formation of a hemostatic plug.

Blood Platelets↗