Laminin: structure, functions and receptors

The Glycosaminoglycan Side Chains and Modular Core Proteins of Heparan Sulphate Proteoglycans and the Varied Ways They Provide Tissue Protection by Regulating Physiological Processes and Cellular Behaviour

This review examines the roles of HS-proteoglycans (HS-PGs) in general, and, in particular, perlecan and syndecan as representative examples and their interactive ligands, which regulate physiological processes and cellular behavior in health and disease. HS-PGs are essential for the functional properties of tissues both in development and in the extracellular matrix (ECM) remodeling that occurs in response to trauma or disease. HS-PGs interact with a biodiverse range of chemokines, chemokine receptors, protease inhibitors, and growth factors in immune regulation, inflammation, ECM stabilization, and tissue protection. Some cell regulatory proteoglycan receptors are dually modified hybrid HS/CS proteoglycans (betaglycan, CD47). Neurexins provide synaptic stabilization, plasticity, and specificity of interaction, promoting neurotransduction, neurogenesis, and differentiation. Ternary complexes of glypican-1 and Robbo-Slit neuroregulatory proteins direct axonogenesis and neural network formation. Specific neurexin-neuroligin complexes stabilize synaptic interactions and neural activity. Disruption in these interactions leads to neurological deficits in disorders of functional cognitive decline. Interactions with HS-PGs also promote or inhibit tumor development. Thus, HS-PGs have complex and diverse regulatory roles in the physiological processes that regulate cellular behavior and the functional properties of normal and pathological tissues. Specialized HS-PGs, such as the neurexins, pikachurin, and Eyes-shut, provide synaptic stabilization and specificity of neural transduction and also stabilize the axenome primary cilium of phototoreceptors and ribbon synapse interactions with bipolar neurons of retinal neural networks, which are essential in ocular vision. Pikachurin and Eyes-Shut interactions with an α-dystroglycan stabilize the photoreceptor synapse. Novel regulatory roles for HS-PGs controlling cell behavior and tissue function are expected to continue to be uncovered in this fascinating class of proteoglycan.

Nintedanib treatment delays prostate dorsolateral lobe cancer progression in the TRAMP model: contribution to the epithelial-stromal interaction balance

Prostate cancer (PCa) progression mechanism has been linked to epithelial proliferation, tumor invasion ability, and growth factors. Nintedanib (BIBF 1120) has been reported as being FGF and VEGF pathway inhibitors, exhibiting antitumor activity. Thus, the objective herein was to characterize the early Nintedanib treatment effects on the structure and molecules involved in the basal membrane, the extracellular matrix (ECM) maintenance, in addition to the angiogenesis and mitogenic processes at different grades of prostatic tumor development in TRAMP mice. Therefore, 45 male TRAMP mice were divided into control groups: 8-week-old mice (TC8), 12-week-old mice (TC12), and 16-week-old mice (TC16); and treated groups with 10 mg/kg/day Nintedanib dose for 4 weeks. The treated groups were euthanized at 12 (TN12) and 16 (TN16) weeks of age. Samples from the dorsolateral lobe were collected and processed for light microscopy, immunohistochemistry, Western blotting, and microvessel density analysis. The results showed that early Nintedanib treatment led to an increase of healthy epithelium frequency and a reduction of LGPIN and a maximum vascularization density in the TN12 group. Also, treatment led to a well-differentiated adenocarcinoma decrease and an α and β dystroglycan and also laminin 1 increase in the TN16 group. IGFR1 decreased in the TN16 group. To conclude, early Nintedanib treatment led to a reduction in cancer severity, interfering in both ECM compounds and angiogenesis process to then contribute to a balance, not only in the prostatic epithelium and stroma, but also in the epithelial-stromal interaction during PCa progression.

Peripheral nerve reconstruction with collagen tubes filled with denatured autologous muscle tissue in the rat model

Conventional nerve conduits lack cellular and extracellular guidance structures critical for bridging larger defects. In this study, an exogenous matrix for axonal regeneration was provided by pretreated muscle tissue. In 24 rats, 14-mm sciatic nerve segments were resected and surgically reconstructed using one of the following methods: autograft (AG); bovine type I collagen conduit; (MDM) collagen tube filled with modified denatured autologous muscle tissue. For 8 weeks, functional regeneration was evaluated by footprint and video gait analysis. Evaluation was complemented by electrophysiology, as well as qualitative and quantitative structural assessment of nerves and target muscles. Group AG was superior both structurally and functionally, showing higher axon counts, a more normal gait pattern, and less severe muscle atrophy. Fiber quality (fiber size and myelin thickness) was highest in group MDM, possibly related to the myelin-producing effect of muscular laminin. However, axon count was lowest in this group, and ultrastructural analysis of the denatured muscle tissue showed areas of incomplete denaturation that had acted as a mechanical barrier for regenerating axons. In light of these results, the often advocated use of muscular exogenous matrix for peripheral nerve reconstruction is reviewed in the literature, and its clinical application is critically discussed. In conclusion, combined muscle tubes may have a positive influence on nerve fiber maturation. However, muscle pretreatment is not without risks, and denaturation processes need to be further refined.

Conformational studies of antimetastatic laminin-1 derived peptides in different solvent systems, using solution NMR spectroscopy

Due to its critical role in cancer progression, interactions between laminin-1 and the 67 kDa Laminin-Binding Protein (the 67 kDa LBP) have been the focus of a number of structural and biological studies. As laminin-1 is such a large and complex molecule, research interests have turned to the investigation of bioactive peptides derived from binding domains of laminin-1. Two peptides of interest, CDPGYIGSR (peptide 11) and YIGSR, both derived from the beta1 chain of laminin-1, have been shown to block invasion of basement membranes by tumor cells. Substituting the C-terminal arginine to lysine, a conservative substitution, results in a loss of peptide antimetastatic activity. This difference in bioactivity has been attributed, based on numerous modeling studies of free peptide conformations, to structural differences between YIGSR and YIGSK. Yet the nature of the 'active' free peptide backbone conformation has been a matter of debate and controversy. In order to test the validity of the structural modeling claims, we have undertaken detailed conformational studies of the two laminin-1 derived peptides YIGSR and CDPGYIGSR along with the biologically inactive YIGSK analog by two-dimensional solution 1H NMR spectroscopy in three different solvent systems. Herein we report that although both the active (YIGSR, CDPGYIGSR) and the inactive (YIGSK) peptides can adopt several closely related conformations in solution, the two peptides share similar conformational preferences, and there are no significant structural differences between the active and inactive peptides, contrary to previously reported modeling data. We conclude that the basis of the peptide biological activity, in contrast to published models, cannot be attributed to well-defined structural preferences of the free peptides. We infer that the difference in bioactivity observed between YIGSR and YIGSK originates primarily from the chemical nature of the arginine versus lysine sidechain substitution, rather than being due to a structural change in the free peptide conformations.

Nerve growth factor is expressed in rat femoral vein

PURPOSE

Entubulization is a well known method of nerve repair for defects too large to be reconstructed by direct suturing without tension. Vein grafts and alloplastic tubes have been used for entubulization in peripheral and cranial nerves, but the mechanism by which they promote healing is poorly understood. The overall hypothesis of this laboratory is that nerve growth factor (NGF) plays an important role in nerve regeneration after entubulization with a vein graft. The purpose of this pilot study was to localize NGF protein expression in the rat femoral vein.

MATERIALS AND METHODS

Sciatic nerves and femoral veins were harvested from adult male Sprague-Dawley rats. Femoral arteries were also collected and used for comparison and validation of the analysis. All specimens were fixed in paraformaldehyde and embedded in paraffin. Specimens were either stained with hematoxylin and eosin or used for immunohistochemical reaction with anti-NGF antibody.

RESULTS

Sciatic nerve was used as a positive control to identify the monofascicular architecture with hematoxylin and eosin and to document the positive immunohistochemical reaction. NGF immunoreactivity was present in the tunica intima and tunica adventitia of femoral vein and artery but not in the tunica media.

CONCLUSION

The results of this pilot study indicate that NGF is detectable in both the intimal and adventitial layers of the rat femoral vein and artery but not in the smooth muscle wall. These findings suggest that vein grafts could potentially promote nerve regeneration by supplying NGF to the injured nerve.

Evaluation of functional nerve recovery after reconstruction with a poly (DL-lactide-epsilon-caprolactone) nerve guide, filled with modified denatured muscle tissue

The aim of this study was to compare the speed of functional nerve recovery after reconstruction with a biodegradable p(DLLA-epsilon-CL) nerve guide, as filled with either modified denatured muscle tissue (MDMT) or phosphate-buffered saline (PBS). To evaluate both motor and sensory nerve recovery, walking-track analysis and electrostimulation tests were carried out after implantation periods, ranging from 3-15 weeks. Functional nerve recovery after reconstruction of a 15-mm nerve gap, with a biodegradable p(DLLA-epsilon-CL) nerve guide filled with modified denatured muscle tissue, was slightly faster, compared with nerve reconstruction of a 10-mm gap with a biodegradable p(DLLA-epsilon-CL) nerve guide filled with PBS. We conclude that our experiments have demonstrated that the use of MDMT increases the speed of recovery after reconstruction of a nerve gap with a p(DLLA-epsilon-CL) biodegradable nerve guide. Furthermore, the use of MDMT might open perspectives for repair of longer nerve gaps.

Functional assessment of sciatic nerve reconstruction: biodegradable poly (DLLA-epsilon-CL) nerve guides versus autologous nerve grafts

The aim of this study was to compare functional nerve recovery after reconstruction with a biodegradable p(DLLA-epsilon-CL) nerve guide filled with modified denatured muscle tissue (MDMT), or an autologous nerve graft. We evaluated nerve recovery using walking track analysis (measurement of the sciatic function index [SFI]) and electrostimulation tests. Functional nerve recovery after reconstruction with a biodegradable p(DLLA-epsilon-CL) nerve guide filled with MDMT was faster when compared with nerve reconstruction using an autologous nerve graft. We conclude that in case of a short nerve gap in the rat, reconstruction can best be carried out using a p(DLLA-epsilon-CL) biodegradable nerve guide filled with MDMT.

Phosphorylcholine-containing polyurethanes for the control of protein adsorption and cell attachment via photoimmobilized laminin oligopeptides

In this study, we synthesized a biomaterial whose surface inhibits non-specific protein and cell attachment. The polymer was designed to mimic the external cell plasma membrane properties through the introduction of particular chemical constituents of the cell membrane: phospholipid polar headgroups. This was done by copolymerizing phosphorylcholine (PC) groups into a polyurethane polymer backbone (PCPUR). Peptides known to induce specific cell attachment were subsequently bound to the surface of this copolymer in a photoadressible manner to obtain surfaces that allowed the attachment of cells in a specific pattern. Two polymers with different phosphorylcholine concentrations were synthesized and their bulk and surface properties were characterized through differential scanning calorimetry, wettability measurements, angle-resolved X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. Protein and lipid adsorption investigation using optical waveguide light mode spectroscopy showed that the irreversible adsorption of both proteins and lipids is drastically reduced as a result of simultaneous contributions of the PC groups, molecular mobility and strong hydrophilicity of the polymers. Consequently, this leads to a marked reduction in the cellular attachment response, which further decreases with increasing PC concentration. Finally, when the polymer surface was photo-derivatized, attachment of the neural NG108-15 cell line occurred only on the areas of the PCPUR where the laminin CDPGYIGSR peptide sequence was photoimmobilized. Cell attachment was nevertheless found to be non-specific with respect to the peptide sequence used and reasons for such results are therefore discussed.

Changes in the expression and distribution of fibronectin, laminin and tenascin by cultured fibroblasts from skin lesions of patients with tuberous sclerosis

Fibronectin, laminin and tenascin play an important part in the assembly of the extracellular matrix and the interaction of cells with it. In this study, changes in their expression and distribution associated with tuberous sclerosis are reported. Fibroblasts from three different tuberous sclerosis skin lesions (forehead plaque, neck fibroma and ungual fibroma) secreted more fibronectin and tenascin into their culture medium than did normal skin fibroblasts. Immunohistochemistry and flow cytometry showed that cells from an ungual fibroma which secreted most of each of these glycoproteins also retained more of them, associated mainly with the cell surface and a perinuclear area. Laminin was also produced by all fibroblasts but only in those from the neck fibroma was more both secreted and retained. The proportions of fibronectin/laminin/tenascin secreted by the skin lesion fibroblasts were markedly different from normal. The results suggest that the characteristic tissue hardening of skin lesions in tuberous sclerosis may result, at least in part, from differences in the expression and distribution of these critical components of the extracellular matrix and its consequent abnormal assembly.

Lectins inhibit periodontal ligament fibroblast attachment, spreading and migration on laminin substrates

The ways in which carbohydrate signals from the extracellular matrix influence the responses of periodontal ligament (PDL) fibroblasts are essentially unknown. The purpose of this study, using video digital image analysis, was to examine the effects of lectins on the attachment, spreading and migrational responses of rat periodontal ligament fibroblasts on the highly glycosylated glycoprotein laminin (LN) in vitro. PDL fibroblasts were isolated from rat molar teeth and grown in culture. Bound LN and control substrates (bovine serum albumin and untreated plastic) were incubated with solutions of either wheatgerm agglutinin (WGA), specific for N-acetylglucosamine, or concanavalin A (ConA), specific for mannose, in 96-well plates. Unbound lectin was rinsed away and 10.0 x 10(3) cells were seeded per well and allowed to attach for 1.5 h. Incubation of LN substrates with WGA, prior to the addition of any cells, inhibited PDL fibroblast binding more than 5-fold. ConA, however, had no effect on cell binding but inhibited mean individual cell spreading nearly 3-fold under similar assay conditions. The effects could be prevented by adding each lectin's respective specific sugar. The lectins had no effects on the control substrates. In a 24-h cell migration assay WGA and ConA both significantly inhibited migration of PDL fibroblasts. It is likely that WGA inhibited cell attachment and cell migration, by binding to oligosaccharides and blocking access to adjacent polypeptide cell recognition sequences on LN. The results from the ConA experiments, where binding was allowed but spreading was severely inhibited, suggest a possible informational role for the carbohydrates present on LN.

Preadipocyte screening by laminin in porcine stromal vascular cell cultures

OBJECTIVE

To determine if subpopulations of cells in stromal vascular (S-V) cultures could be segregated and separated based on affinity for laminin substratum.

RESEARCH METHODS AND PROCEDURES

S-V cells were seeded and allowed to attach for various times; 4 hours was found to be optimal for cell attachment. Cultures were rinsed after 4 hours of seeding, and S-V cells were divided into three subpopulations based on affinity for laminin: (1) cells that did not attach to laminin; (2) cells that had a low affinity for laminin; and (3) cells that had a high affinity for laminin. After 24 hours, cultures were either stained for the AD-3 antigen (a marker for preadipocytes), C/EBP-alpha (a terminal differentiation marker), or C/EBP-delta (an early preadipocyte marker). Companion cultures were treated with various media for 9 days and stained with oil red-O.

RESULTS

Cells with a high affinity for laminin had the highest proportion of AD-3 and C/EBP-alpha positive cells and the highest proportion of fat cells after treatment with insulin +/- dexamethasone. Cells with a low affinity for laminin had the highest proportion of C/EBP-delta cells and the highest proportion of fat cells after treatment with fetal bovine serum+dexamethasone, followed by insulin.

DISCUSSION

These results indicate that differentiating preadipocytes adhere to laminin to a much greater degree than do non-preadipocytes. Therefore, laminin-coated dishes can be used to screen S-V cells to produce preadipocyte or fibroblast-enriched S-V cultures.

Involvement of the YIGSR sequence of laminin in protein tyrosine phosphorylation

We have examined the mechanism of signaling by the 67 kDa YIGSR binding protein of laminin and its properties in neuroblastoma cells. Ligand displacement analysis showed that the interaction with the C(YIGSR)3-NH2 peptide amide is of intermediate affinity (1.5 x 10[-7] M). Cross-linking experiments with sulfo-MBS detected an additional protein with a molecular mass of 116 kDa that binds the YIGSR sequence. Incubation of neuroblastoma cells with C(YIGSR)3-NH2 peptide amide or antibody directed against the 67 kDa laminin binding protein induces tyrosine phosphorylation of proteins with a molecular mass ranging from 115 to 130 kDa and another heterogeneous protein group of 32 kDa.

Peripheral nerve regeneration: comparison of laminin and acidic fibroblast growth factor

PURPOSE

In an effort to show the differences between neurotrophic factors, laminin and acidic fibroblast growth factor (aFGF) were compared in terms of their abilities to regenerate axons in vivo over an extended distance.

MATERIALS AND METHODS

The sciatic nerve was transected in 15 Sprague-Dawley rats. A 15-mm Silastic tube (Dow Corning, Midland, MI) was placed between the ends of the cut nerve and filled with either laminin, aFGF, or buffer applied to collagen sponges.

RESULTS

Ten weeks postimplantation, mean axon counts showed that both laminin (2432) and aFGF (1612) produced significantly higher numbers of axons than controls (1009) (P < .05) and that laminin showed significantly more nerve regeneration than aFGF (P < .05).

CONCLUSION

These results indicate that laminin and aFGF enhance peripheral nerve regeneration across a large gap, presumably through their neurotrophic effects and mitogenic properties on supporting cells. Furthermore, it is concluded that the transient nature of aFGF's effect on the regenerative environment limits its effectiveness at regenerating axons over a prolonged period of time.

Migration of gingival fibroblasts on fibronectin and laminin

The migrational behavior of fibroblasts is critical for the maintenance and healing of the periodontium. The purpose of this study was to determine, in vitro, the differences found in gingival fibroblast migration on the following substrates: fibronectin, laminin, bovine serum albumin (BSA), or plastic. Filter paper strips soaked in solutions of the test molecules were placed in 35 mm culture dishes. Equimolar amounts of the various proteins were allowed to dry onto the plastic in a discrete band. The bands were masked and 5.0 x 10(4) cells seeded. Rat gingival fibroblasts were allowed to attach for 1.5 hours and the protein bands uncovered and incubation continued for 24 hours under standard conditions. Cells were fixed, stained and cell images captured, computer digitized and migrational areas and cell numbers and areas quantified after converting pixels to microm. Cell migration was enhanced on fibronectin substrates. Statistically significant differences (P < 0.01) were found for total area covered (fibronectin, mean = 110.8 mm2 vs. controls: plastic, mean = 28.2 mm2; BSA, mean = 18.2 mm2) and the number of cells migrating as compared to controls (fibronectin, mean = 1184 vs. controls: plastic, mean = 304, BSA, mean = 230). No significant differences in area covered or numbers of cells migrating were found between controls and cells exposed to other substrates. Mean spread area per cell was not statistically significantly different for any of the conditions. Numbers of cells migrating on substrates other than fibronectin were reduced even more when protein synthesis was inhibited using cycloheximide. In this system fibronectin serves as a cue to recruit significantly greater numbers of fibroblasts to migrate for greater distances than the other molecules tested.

Role of laminin in the morphogenetic cascade during coculture of Sertoli cells with peritubular cells

Observations summarized in this article demonstrate an essential role of laminin during the restructuring processes that occur during coculture of Sertoli cells with testicular peritubular cells. The data presented indicate that laminin becomes detectable on the free surfaces of Sertoli cells only after reaggregation of Sertoli cells begins, coincident with the initiation of repolarization at a specific stage of the morphogenetic cascade. We infer that laminin deposited at this time serves as a cohesion molecule that permits peritubular cells to come into close contact with Sertoli cells and subsequently to spread along the free surfaces of Sertoli cells. These conclusions and inferences are based on the following experiments. Cycloheximide-treated peritubular cells in culture in MEM containing cycloheximide readily attach to laminin-coated polystyrene surfaces. By contrast, added peritubular cells do not attach onto monolayers of Sertoli cells in monoculture or onto Sertoli cells plated on top of peritubular cells and maintained in coculture for periods of up to 48 h. In cocultures maintained for 6 days, however, labeled peritubular cells readily adhere to the free surfaces of reaggregated Sertoli cells. Laminin, but not fibronectin, appears on the free surfaces of the reaggregated Sertoli cells at this time, coinciding with the period of initial mound formation. The addition of antilaminin IgG, but not antifibronectin IgG, blocks the attachment of cycloheximide-treated peritubular cells to laminin-coated plates and also blocks the subsequent migration of peritubular cells required to form a monolayer. Similarly, anti-laminin IgG inhibits the attachment and spreading of labeled peritubular cells seeded on the free surfaces of reaggregated Sertoli cells in mounds generated during the morphogenetic cascade. We interpret the combined data to indicate that the appearance of laminin on the free surfaces of Sertoli cells is required to permit peritubular cells to adhere and subsequently to migrate on Sertoli cell surfaces, resulting in the formation of a tubule-like structure.

Laminin receptor expression in rat intestine and liver during development and differentiation

BACKGROUND/AIMS

Studies have identified a 67-kilodalton high-affinity laminin receptor (LR) whose expression has also been related to development, differentiation, and neoplastic transformation. The relationship of the 67-kilodalton LR to hepatic and enterocyte development and to enterocyte differentiation was investigated.

METHODS

LR messenger RNA (mRNA) was identified using a complementary DNA isolated from a rat crypt cell library. LR and integrin (alpha 6, beta 1, and beta 4) expression by rat intestinal crypt cells was compared with that of the more differentiated villus cells using Northern blotting. Developmental differences in LR expression were studied in fetal and neonatal rats. The pattern of LR expression in fetal and adult rat intestines was examined further by in situ hybridization.

RESULTS

LR mRNA levels were highest in fetal liver and intestine and adult rat crypt cells. LR mRNA levels were 9-10 times greater in crypt than in villus cells. Integrin subunit expression differed little between crypt and villus cells. Nascent transcription studies showed that the proportion of newly transcribed LR mRNA per total RNA synthesized was similar for crypt and villus cells, suggesting posttranscriptional control of LR mRNA levels in villus cells.

CONCLUSIONS

Increased LR mRNA expression is a feature of the fetal intestine and of the undifferentiated, mitotically active crypt cells.

Laminin SIKVAV peptide-induced angiogenesis in vivo is potentiated by neutrophils

Angiogenesis has been investigated in vivo using subcutaneously injected reconstituted basement membrane (Matrigel) supplemented with angiogenic factors. Previously we found that the laminin-derived synthetic peptide containing SIKVAV (ser-ile-lys-val-ala-val) promoted angiogenesis in vivo. In parallel studies, it was observed that new vessel formation in response to this peptide occurred several days after basic fibroblast growth factor-induced angiogenesis. Since this delay suggested that SIKVAV-induced angiogenesis may be secondary to other events, we investigated here earlier time points to determine if both indirect and direct mechanisms of angiogenesis are involved. We found that neutrophils are continuously recruited to the SIKVAV-containing plugs between 4 hours to 3 days following the initial injection. By day 7, columns of endothelial cells begin to migrate into the plug and form small blood vessels. In contrast, neutropenic mice had a 62% reduction in SIKVAV-induced angiogenesis when compared to control mice. Freshly isolated neutrophils also degraded laminin, the major component of the basement membrane Matrigel. These cells also produced factors in response to SIKVAV peptide which induced proliferation of human umbilical vein endothelial cells relative to a control peptide. In vitro experiments utilizing human neutrophils demonstrated that these cells migrate to the SIKVAV peptide and possess a specific cell surface SIKVAV binding protein of approximately 56 kD. These data suggest that neutrophils are induced to migrate to the Matrigel plugs, at least in part, by SIKVAV peptide, where they may release their own angiogenic factors and degrade the matrix, thus physically facilitating cell migration and liberating additional angiogenic matrix fragments and/or cytokines.

Interactions of Sertoli cells with laminin are essential to maintain integrity of the cytoskeleton and barrier functions of cells in culture in the two-chambered assembly

The addition of anti-laminin IgG to the basal surfaces of rat Sertoli cells in culture in a two-chambered assembly results in a perturbation of F-actin arrangements, including disruption of the pericellular circumferal rings, impairments of the Sertoli cell permeability barrier, and subsequently focal defoliation, followed by cell reaggregation. The pentapeptide YIGSR, which competes with the laminin receptor for laminin (Kleinman and Weeks: Curr. Oph. Cell Biol., 1:964-967, 1989; Graf et al.: Biochemistry, 26:6896-6900, 1987) also elicited focal defoliation of Sertoli cells from the extracellular matrix-coated filter in the two-chambered assembly. Addition of YIGSR to Sertoli cell cultures resulted in cell detachment within 2 to 3 h. In contrast, the irrelevant peptide YIGSE had no detectable effects. The anti-laminin IgG was effective only when added to the chamber in which access was readily available to the basal surfaces of Sertoli cells, but YIGSR was effective when added either to the outer chamber or to the inner chamber. These data were interpreted to indicate that the Sertoli cell barrier generated in the two-chambered assembly allowed a relatively rapid diffusion of YIGSR between chambers, but prevented the rapid equilibration of anti-laminin IgG between compartments. Addition of anti-laminin IgG to the basal, but not to the apical surfaces of Sertoli cells, resulted in more rapid rates of equilibration of [3H]-methoxyinulin and [86Rb]Cl across the Sertoli cell monolayer. This evidence of impairment to the integrity of the barrier was detected prior to the disruption of stress fibers and focal defoliation, but after evidence of dissolution of the circumferal F-actin ring, which occurred within 1 h after addition of anti-laminin IgG. We consider the possibility that a transmembrane link exists between extracellular laminin and cytoskeletal elements which modulates the circumferal F-actin ring. We further postulate that this linkage can influence the nature of tight junctional complexes, and thereby the integrity of the Sertoli cell barrier.

Dystrophin-glycoprotein complex and laminin colocalize to the sarcolemma and transverse tubules of cardiac muscle

The expression and subcellular distribution of the dystrophin-glycoprotein complex and laminin were examined in cardiac muscle by immunoblot and immunofluorescence analysis of rabbit and sheep papillary muscle. The five dystrophin-associated proteins (DAPs), 156-DAG, 59-DAP, 50-DAG, 43-DAG, and 35-DAG, were identified in rabbit ventricular muscle and found to codistribute with dystrophin in both papillary myofibers and Purkinje fibers. The DAPs and dystrophin codistributed not only in the free surface sarcolemma but also in interior regions of the myofibers where T tubules are present. Neither the DAPs nor dystrophin were detected in intercalated discs, a specialized region of cardiac sarcolemma where neighboring myocardial cells are physically joined by cell-cell junctions. Similarly, in bundles of Purkinje fibers, which lack T tubules, DAPs and dystrophin were also found to codistribute at the free surface sarcolemma but were not detected either in the region of surface sarcolemma closely apposed to a neighboring Purkinje fiber or in interior regions of these myofibers. Comparison between the distribution of the dystrophin-glycoprotein complex and laminin showed that laminin codistributes with the components of this complex in both papillary myofibers and Purkinje fibers. These results are consistent with previous findings demonstrating that the extracellularly exposed 156-DAG (dystroglycan) of the skeletal muscle dystrophin-glycoprotein complex binds laminin, a component of the basement membrane. Although we demonstrate that DAPs, dystrophin, and laminin colocalize to the sarcolemma in rabbit and sheep papillary myofibers as they do in skeletal myofibers, the most striking difference between the subcellular distribution of these proteins in cardiac and skeletal muscle is that the dystrophin-glycoprotein complex and laminin also localize to regions of the fibers where T tubules are distributed in cardiac but not in skeletal muscle. These results imply that the protein composition and thus possibly some functions of T tubules in cardiac muscle are distinct from those of skeletal muscle.

Laminins and other strange proteins

Laminins are large multidomain proteins of the extracellular matrix (ECM) with important functions in the development and maintenance of cellular organization and supramolecular structure, in particular in basement membranes. Each molecule is composed of three polypeptide chains, A (300-400 kDa) and B1 and B2 (180-200 kDa), which together form the characteristic cross-shaped laminin structure with three short arms and one long arm. Many different domains have been identified in laminin by sequence analysis, structural investigations, and functional studies. Each short arm is formed by homologous N-terminal portions of one of the three chains. Structurally, each short arm contains two or three globular domains which are connected by rows of manyfold-repeated Cys-rich "EGF-like" domains. In all three chains this region is followed by a long heptad repeat region similar to those found in many alpha-helical coiled-coil proteins. These parts of the three laminin chains constitute a triple-stranded coiled-coil domain, which forms the extended rodlike structure of the long arm. This is the only domain in the protein which is made up of more than one chain and consequently serves the function of chain assembly. The two B chains are terminated by the coiled-coil domain, but the A chain contains an additional C-terminal segment which accounts for five globular domains located at the tip of the long arm. Several important functions of laminin have been assigned to individual domains in either the short arms or terminal regions of the long arm.(ABSTRACT TRUNCATED AT 250 WORDS)

Competition between cell-substratum interactions and cell-cell interactions

Clusterin, a glycoprotein which elicits the aggregation of a wide variety of cells (Fritz, I. B., and Burdy, K.:J. Cell Physiol., 140:18-28, 1989), has been utilized to investigate some of the factors modulating the competition between cell-substratum interactions and cell-cell interactions. We compared the responses to clusterin by anchorage-independent cells (erythrocytes) with those by anchorage-dependent TM4 cells (a cell line derived from neonatal mouse testis cells). Cells were maintained in culture in the presence of various substrata chosen to enhance cell-substratum interactions (laminin-coated wells), or to diminish cell-substratum interactions (agarose-coated wells). Results obtained showed that the aggregation of erythrocytes elicited by clusterin was independent of the nature of the substratum. In contrast, clusterin addition resulted in aggregation of anchorage-dependent TM4 cells only when TM4 cell-substratum interactions were weak. Thus, clusterin did not aggregate TM4 cells plated upon a laminin substratum, but readily aggregated TM4 cells plated upon an agarose-coated substratum, independent of the sequence of addition of cells and clusterin to the culture dish. We utilized YIGSR, a peptide which competes with laminin for laminin receptors, to determine the possible role of laminin receptors on TM4 cells in the competition between cell-substratum interactions and cell-cell interactions. The presence of YIGSR did not alter responses of erythrocytes to clusterin under all conditions examined. In contrast, the responses of TM4 cells to clusterin were greatly changed. YIGSR addition resulted in the inhibition of aggregation of TM4 cells otherwise elicited by clusterin. YIGSR also prevented attachment of TM4 cells to a laminin-coated surface, but this was reversed by the presence of clusterin. We discuss the possible roles of clusterin and laminin in altering the balance in the competition between cell to cell interactions and cell to substratum interactions.

Quantitative and qualitative analysis of the extracellular matrix protein, laminin, in Hirschsprung's disease

Previous immunohistochemical studies have shown an abnormal distribution of extracellular matrix (ECM) proteins, including laminin, in the smooth muscle layer of muscularis externa in Hirschsprung's disease (HD) bowel. These findings supported the hypothesis that an abnormal ECM microenvironment may be responsible for the failure of migration and/or development of the neural crest cells in the gut in HD. In order to determine the cause of the abnormality in laminin distribution, solid-phase enzyme-linked immunosorbent assays and immunoblots were used to quantitate the ECM protein laminin and characterize its subunits, respectively, in extracts of the dissected smooth muscle layer of the muscularis externa. In the aganglionic bowel, laminin (median concentration, 32.4 ng/mg of tissue) was found to be present in significantly greater quantity than in both the normoganglionic bowel of the same specimen (median, 17.2 ng/mg, P less than or equal to .05) and the normal bowel of age-matched controls (median, 9.7 ng/mg, P less than or equal to .05). Laminin concentration was also found to be significantly higher in normoganglionic HD bowel (median, 17.2 ng/mg) than in age-matched control specimens (median, 10.8 ng/mg, P less than or equal to .05). No difference was observed in the subunit composition of laminin in HD and control extracts analysed by immunoblot after polyacrylamide gel electrophoresis. This study demonstrates a quantitative abnormality of laminin in the bowel in HD, supporting the hypothesis that "abnormal microenvironment" may have a role in the pathogenesis of HD.

Laminin enhances binding of Toxoplasma gondii tachyzoites to J774 murine macrophage cells

We investigated the effects of the extracellular matrix proteins laminin and fibronectin on the attachment of tachyzoites of Toxoplasma gondii to the murine macrophage cell line J774. Laminin but not fibronectin increased parasite attachment to J774 cells in a dose-dependent fashion. Cyclic YIGSR, a laminin-derived peptide which inhibits laminin binding to the 32/67-kDa laminin-binding protein on host cells, blocked the laminin-mediated enhancement of parasite attachment. An antiserum to the 32/67-kDa laminin-binding protein also inhibited binding of parasites to J774 cells. These results, in conjunction with our previous observations (G. C. Furtado, F. L. Collins, and K. A. Joiner, submitted for publication), demonstrate that tachyzoites bearing surface laminin bind to multiple laminin receptors in attaching to different target cells.

Endogenous muscle lectin inhibits myoblast adhesion to laminin

L-14, a dimeric lactose-binding lectin with subunits of 14 kD, is expressed in a wide range of vertebrate tissues. Several functions have been postulated for this lectin, but definitive evidence for a specific biological role has been elusive. In muscle, L-14 is secreted during differentiation and accumulates with laminin in basement membrane surrounding each myofiber. Here we present evidence that laminin is a major glycoprotein ligand for L-14 in differentiating mouse C2C12 muscle cells and that binding of secreted L-14 to polylactosamine oligosaccharides of substrate laminin induces loss of cell-substratum adhesion. These results suggest that one function of L-14 is to regulate myoblast detachment from laminin during differentiation and fusion into tubular myofibers.

Expression of a neurally related laminin binding protein by neural crest-derived cells that colonize the gut: relationship to the formation of enteric ganglia

In order to give rise to the enteric nervous system (ENS), cells migrating from the neural crest must find the bowel and cease migrating at appropriate locations within the gut. Previous studies of the development of the ENS in a mutant mouse have led to the hypothesis that laminin in the enteric mesenchyme may act as a signal to crest-derived cells to cease migrating and extend neurites (or glial processes). Implied in this hypothesis is the idea that crest-derived cells, as a prelude to their participation in ganglion formation, acquire a neurally related laminin receptor, which they do not express at pre-enteric stages of migration. As a partial test of this hypothesis, single and double label immunocytochemistry at light and electron microscopic (EM) levels were used to study the expression of cell surface laminin binding proteins by crest-derived cells in the process of migrating to or within the developing chick gut. Two antibodies (called 3070 and alpha-110) raised against neuronal cell surface laminin binding proteins were employed for this purpose. Laminin binding protein immunoreactivity was found to be expressed within the bowel and ganglion of Remak by a subset of crest-derived cells (identified immunocytochemically with NC-1/HNK-1 antibodies) and by all of those developing as neurons (identified immunocytochemically with antibodies to neurofilament-associated proteins). Laminin binding protein immunoreactivity was also found to be expressed in fixed neural structures elsewhere in the embryos, including cranial and spinal roots, nerves, and ganglia. In contrast, laminin binding protein immunoreactivity was not expressed by migrating crest-derived cells in the vicinity of the vagal or sacral regions of the neuraxis (from which the precursors of the ENS take origin); nor was it expressed by juxta-pharyngeal vagal crest-derived cells migrating to the foregut through the caudal branchial arches or by the caudal stream of sacral crest-derived cells approaching the hindgut. EM immunocytochemistry confirmed that laminin binding protein immunoreactivity in the bowel was located on the surfaces of crest-derived cells, and was exhibited both by those cells that could only be distinguished from their neighbors by their NC-1/HNK-1 immunoreactivity and by cells developing as neurons or glia. EM immunocytochemistry also revealed that the surfaces of crest-derived cells migrating through the enteric mesenchyme were contacted by many small osmiophilic "puffs" of laminin-immunoreactive extracellular material. These puffs coincided in location with membrane sites that expressed the immunoreactivity of the laminin binding protein. These observations are consistent with the hypothesis that laminin plays a role in the formation of enteric ganglia.

Identification and partial characterization of laminin binding proteins in immature rat Sertoli cells

Laminin, a major component of basement membrane extracellular matrices, promotes differentiation in a number of cell types, including Sertoli cells. We have identified and characterized Sertoli cells. We have identified and characterized Sertoli cell surface molecules which interact with laminin. Using laminin-Sepharose affinity chromatography and [125I]laminin binding to Sertoli cell plasma membranes, binding proteins have been identified with the Mr 110,000, 67,000, 55,000, 45,000, 36,000, and 25,000. In addition, the Mr 110,000 and 67,000 laminin binding proteins were phosphorylated. The 67,000, 45,000, and 36,000 react with antibodies to the previously characterized laminin receptor and these antibodies stain the basolateral surface of Sertoli cells in vivo. Cultured Sertoli cells stain for laminin receptor both on the cell surface and within the cells. Antiserum to the 32,000 and 67,000 laminin binding proteins partially inhibited spreading of Sertoli cells on a laminin-coated culture dish, suggesting a functional importance of those proteins in Sertoli cell differentiation. The 25,000 and 45,000 laminin binding proteins reacted with integrin antibodies, but no high-molecular-weight forms could be detected. Integrin was localized to the cell surface and intracellularly but antibodies did not block Sertoli cell spreading on laminin. This work represents the first identification and characterization of extracellular matrix binding proteins in an endocrine organ and suggests an important role for the nonintegrin 32/67 laminin binding proteins.