A simplified laminin nomenclature

Alpha4 chain laminins are widely expressed in renal cell carcinomas and have a de-adhesive function

Laminin (Lm) alpha4 chain, a constituent of Lm-411 and Lm-421, is mainly localized to mesenchyme-derived tissues, and is suggested to have a role in formation and function of endothelium, transmigration of inflammatory cells through endothelium, and invasion of certain tumors. In this study, we evaluated the distribution of alpha4 chain Lms in 33 conventional (clear cell) renal cell carcinomas (RCCs) (31 primary tumors, two metastases), two papillary RCCs, and two oncocytomas by immunohistochemistry. In all tumors, immunoreactivity for Lm alpha4 chain was found in vasculature and stroma. Basement membranes were detected around tumor cell islets in 34/37 tumors. They showed immunoreactivity for Lm alpha4 chain in 28/34 cases. Northern blotting, inhibition of protein secretion with monensin, and immunoprecipitation combined with Western blotting showed that Caki-2, ACHN, and Caki-1 renal carcinoma cell lines produce alpha4 chain Lms. In cell adhesion assay, recombinant human Lm-411 did not promote adhesion of renal carcinoma cells but inhibited adhesion to fibronectin (Fn). In cell migration assay, the cells migrated more on Lm-411 than on Fn. The results suggest that alpha4 chain Lms have a de-adhesive function and could thus play a role in detachment, migration and invasion of renal carcinoma cells in vivo.

Reduced migration, altered matrix and enhanced TGFbeta1 signaling are signatures of mouse keratinocytes lacking Sdc1

We have reported previously that syndecan-1 (Sdc1)-null mice show delayed re-epithelialization after skin and corneal wounding. Here, we show that primary keratinocytes obtained from Sdc1-null mice and grown for 3-5 days in culture are more proliferative, more adherent and migrate more slowly than wt keratinocytes. However, the migration rates of Sdc1-null keratinocytes can be restored to wild-type levels by replating Sdc1-null keratinocytes onto tissue culture plates coated with fibronectin and collagen I, laminin (LN)-332 or onto the matrices produced by wild-type cells. Migration rates can also be restored by treating Sdc1-null keratinocytes with antibodies that block alpha6 or alphav integrin function, or with TGFbeta1. Antagonizing either beta1 integrin function using a function-blocking antibody or TGFbeta1 using a neutralizing antibody reduced wild-type keratinocyte migration more than Sdc1-null keratinocyte migration. Cultures of Sdc1-null keratinocytes accumulated less collagen than wild-type cultures but their matrices contained the same amount of LN-332. The Sdc1-null keratinocytes expressed similar total amounts of eight different integrin subunits but showed increased surface expression of alphavbeta6, alphavbeta8, and alpha6beta4 integrins compared with wild-type keratinocytes. Whereas wild-type keratinocytes increased their surface expression of alpha2beta1, alphavbeta6, alphavbeta8, and alpha6beta4 after treatment with TGFbeta1, Sdc1-null keratinocytes did not. Additional data from a dual-reporter assay and quantification of phosphorylated Smad2 show that TGFbeta1 signaling is constitutively elevated in Sdc1-null keratinocytes. Thus, our results identify TGFbeta1 signaling and Sdc1 expression as important factors regulating integrin surface expression, activity and migration in keratinocyte and provide new insight into the functions regulated by Sdc1.

The Laminin 511/521-binding site on the Lutheran blood group glycoprotein is located at the flexible junction of Ig domains 2 and 3

The Lutheran blood group glycoprotein, first discovered on erythrocytes, is widely expressed in human tissues. It is a ligand for the alpha5 subunit of Laminin 511/521, an extracellular matrix protein. This interaction may contribute to vaso-occlusive events that are an important cause of morbidity in sickle cell disease. Using x-ray crystallography, small-angle x-ray scattering, and site-directed mutagenesis, we show that the extracellular region of Lutheran forms an extended structure with a distinctive bend between the second and third immunoglobulin-like domains. The linker between domains 2 and 3 appears to be flexible and is a critical determinant in maintaining an overall conformation for Lutheran that is capable of binding to Laminin. Mutagenesis studies indicate that Asp312 of Lutheran and the surrounding cluster of negatively charged residues in this linker region form the Laminin-binding site. Unusually, receptor binding is therefore not a function of the domains expected to be furthermost from the plasma membrane. These studies imply that structural flexibility of Lutheran may be essential for its interaction with Laminin and present a novel opportunity for the development of therapeutics for sickle cell disease.

Role of Laminin Terminal Globular Domains in Basement Membrane Assembly

Laminins contribute to basement membrane assembly through interactions of their N- and C-terminal globular domains. To further analyze this process, recombinant laminin-111 heterotrimers with deletions and point mutations were generated by recombinant expression and evaluated for their ability to self-assemble, interact with nidogen-1 and type IV collagen, and form extracellular matrices on cultured Schwann cells by immunofluorescence and electron microscopy. Wild-type laminin and laminin without LG domains polymerized in contrast to laminins with deleted alpha1-, beta1-, or gamma1-LN domains or with duplicated beta1- or alpha1-LN domains. Laminins with a full complement of LN and LG domains accumulated on cell surfaces substantially above those lacking either LN or LG domains and formed a lamina densa. Accumulation of type IV collagen onto the cell surface was found to require laminin with separate contributions arising from the presence of laminin LN domains, nidogen-1, and the nidogen-binding site in laminin. Collectively, the data support the hypothesis that basement membrane assembly depends on laminin self-assembly through formation of alpha-, beta-, and gamma-LN domain complexes and LG-mediated cell surface anchorage. Furthermore, type IV collagen recruitment into the laminin extracellular matrices appears to be mediated through a nidogen bridge with a lesser contribution arising from a direct interaction with laminin.

Binding of netrin-4 to laminin short arms regulates basement membrane assembly

Netrins were first identified as neural guidance molecules, acting through receptors that are members of the DCC and UNC-5 family. All netrins share structural homology to the laminin N-terminal domains and the laminin epidermal growth factor-like domains of laminin short arms. Laminins use these domains to self-assemble into complex networks. Here we demonstrate that netrin-4 is a component of basement membranes and is integrated into the laminin polymer via interactions with the laminin gamma1 andgamma3 short arms. The binding is mediated through the laminin N-terminal domain of netrin-4. In contrast to netrin-4, other members of the netrin family do not bind to these laminin short arms. Moreover, a truncated form of netrin-4 completely inhibits laminin-111 self-assembly in vitro, and full-length netrin-4 can partially disrupt laminin self-interactions. When added to explant cultures, netrin-4 retards salivary gland branching morphogenesis.

Distinct roles of integrins alpha6 and alpha4 in homing of fetal liver hematopoietic stem and progenitor cells

Homing of hematopoietic stem cells (HSCs) into the bone marrow (BM) is a prerequisite for establishment of hematopoiesis during development and following transplantation. However, the molecular interactions that control homing of HSCs, in particular, of fetal HSCs, are not well understood. Herein, we studied the role of the alpha6 and alpha4 integrin receptors for homing and engraftment of fetal liver (FL) HSCs and hematopoietic progenitor cells (HPCs) to adult BM by using integrin alpha6 gene-deleted mice and function-blocking antibodies. Both integrins were ubiquitously expressed in FL Lin(-)Sca-1(+)Kit(+) (LSK) cells. Deletion of integrin alpha6 receptor or inhibition by a function-blocking antibody inhibited FL LSK cell adhesion to its extracellular ligands, laminins-411 and -511 in vitro, and significantly reduced homing of HPCs to BM. In contrast, the anti-integrin alpha6 antibody did not inhibit BM homing of HSCs. In agreement with this, integrin alpha6 gene-deleted FL HSCs did not display any homing or engraftment defect compared with wild-type littermates. In contrast, inhibition of integrin alpha4 receptor by a function-blocking antibody virtually abrogated homing of both FL HSCs and HPCs to BM, indicating distinct functions for integrin alpha6 and alpha4 receptors during homing of fetal HSCs and HPCs.

Dystroglycan: a possible mediator for reducing congenital muscular dystrophy?

Alpha-dystroglycan is a highly glycosylated peripheral protein forming a complex with the membrane-spanning beta-dystroglycan and establishing a connection between the extracellular matrix and the cytoskeleton. In skeletal muscle, as part of the larger dystrophin-glycoprotein complex, dystroglycan is believed to be essential for maintaining the structural and functional stability of muscle fibers. Recent work highlights the role of abnormal dystroglycan glycosylation at the basis of glycosyltransferase-deficient congenital muscular dystrophies. Notably, modulation of glycosyltransferase activity can restore alpha-dystroglycan receptor function in these disorders. Moreover, transgenic approaches favoring the interaction between dystroglycan and the extracellular matrix molecules also represent an innovative way to restore skeletal muscle structure. These pioneering approaches might comprise an important first step towards the design of gene-transfer-based strategies for the rescue of congenital muscular dystrophies involving dystroglycan.

Functional integrin subunits regulating cell-matrix interactions in the intervertebral disc

Cellular interactions with the extracellular matrix are key factors regulating cell survival, differentiation, and response to environmental stimuli in cartilagenous tissues. Much is known about the extracellular matrix proteins in the intervertebral disc (IVD) and their variations with region, age, or degenerative state of the tissue. In contrast, little is known of the integrin cell surface receptors that directly bind to and interact with these matrix proteins in the IVD. In almost all tissues, these integrin-mediated cell-matrix interactions are important for transducing environmental cues arising from mechanical stimuli, matrix degradation fragments, and cytokines into intracellular signals. In this study, cells from the nucleus pulposus and anulus fibrosus regions of porcine IVDs were analyzed via flow cytometry to quantify integrin expression levels upon isolation and after monolayer culture. Assays of cell attachment to collagens, fibronectin, and laminin were performed after functional blocking of select integrin subunits to evaluate the role of specific integrins in cell attachment. In situ distribution and co-localization of integrins and laminin were also characterized. Results identify integrin receptors critical for IVD cell interactions with collagens (alpha1beta1) and fibronectin (alpha5beta1). Additionally, dramatic differences in cell-laminin interactions were observed between cells of the nucleus and anulus regions, including differences in alpha6 integrin expression, cell adhesion to laminin, and in situ pericellular environments. These findings suggest laminin-cell interactions may be important and unique to the nucleus pulposus region of the IVD. The results of this study provide new information on functional cell-matrix interactions in tissues of the IVD.

Linker molecules between laminins and dystroglycan ameliorate laminin-alpha2-deficient muscular dystrophy at all disease stages

Mutations in laminin-α2 cause a severe congenital muscular dystrophy, called MDC1A. The two main receptors that interact with laminin-α2 are dystroglycan and α7β1 integrin. We have previously shown in mouse models for MDC1A that muscle-specific overexpression of a miniaturized form of agrin (mini-agrin), which binds to dystroglycan but not to α7β1 integrin, substantially ameliorates the disease (Moll, J., P. Barzaghi, S. Lin, G. Bezakova, H. Lochmuller, E. Engvall, U. Muller, and M.A. Ruegg. 2001. Nature. 413:302–307; Bentzinger, C.F., P. Barzaghi, S. Lin, and M.A. Ruegg. 2005. Matrix Biol. 24:326–332.). Now we show that late-onset expression of mini-agrin still prolongs life span and improves overall health, although not to the same extent as early expression. Furthermore, a chimeric protein containing the dystroglycan-binding domain of perlecan has the same activities as mini-agrin in ameliorating the disease. Finally, expression of full-length agrin also slows down the disease. These experiments are conceptual proof that linking the basement membrane to dystroglycan by specifically designed molecules or by endogenous ligands, could be a means to counteract MDC1A at a progressed stage of the disease, and thus opens new possibilities for the development of treatment options for this muscular dystrophy.

Laminins in normal, keratoconus, bullous keratopathy and scarred human corneas

The laminin composition (LMalpha1-alpha5, beta1-beta3, gamma1 and gamma2 chains) of normal corneas and corneal buttons from keratoconus, bullous keratopathy (BKP), Fuchs' dystrophy + BKP, Fuchs' dystrophy without BKP and scar after deep lamellar keratoplasty (DLKP) was investigated with immunohistochemistry. The epithelial basement membranes (BMs) of both normal and diseased corneas contained LMalpha3, alpha5, beta1, beta3, gamma1 and gamma2 chains. The epithelial BM morphology was altered in the different diseases. Scarring was associated with irregular BM and ectopic stromal localization of different laminin chains. The Descemet's membrane (DM) contained LMalpha5, beta1 and gamma1 chains in all cases and additionally LMbeta3 and gamma2 chains in the majority of keratoconus corneas. The interface in the DLKP cornea had patches of LMalpha3, alpha4, alpha5, beta1 and beta2 chains, and an extra BM-like structure under the Bowman's membrane. These results suggest that laminin chains participate in the process of corneal scarring and in the pathogenesis of some corneal diseases. The novel finding of LMalpha3, beta3 and gamma2 in the DM of keratoconus buttons indicates that this membrane is also involved in the disease and that some cases of keratoconus may have a congenital origin, without normal downregulation of the LMbeta3 chain.

The short arm of laminin gamma2 chain of laminin-5 (laminin-332) binds syndecan-1 and regulates cellular adhesion and migration by suppressing phosphorylation of integrin beta4 chain

The proteolytic processing of laminin-5 at the short arm of the gamma2 chain (gamma2sa) is known to convert this laminin from a cell adhesion type to a motility type. Here, we studied this mechanism by analyzing the functions of gamma2sa. In some immortalized or tumorigenic human cell lines, a recombinant gamma2sa, in either soluble or insoluble (coated) form, promoted the adhesion of these cells to the processed laminin-5 (Pr-LN5), and it suppressed their migration stimulated by serum or epidermal growth factor (EGF). Gamma2sa also suppressed EGF-induced tyrosine phosphorylation of integrin beta4 and resultant disruption of hemidesmosome-like structures in keratinocytes. Gamma2sa bound to syndecan-1, and this binding, as well as its cell adhesion activity, was blocked by heparin. By analyzing the activities of three different gamma2sa fragments, the active site of gamma2sa was localized to the NH(2)-terminal EGF-like sequence (domain V or LEa). Suppression of syndecan-1 expression by the RNA interference effectively blocked the activities of domain V capable of promoting cell adhesion and inhibiting the integrin beta4 phosphorylation. These results demonstrate that domain V of the gamma2 chain negatively regulates the integrin beta4 phosphorylation, probably through a syndecan-1-mediated signaling, leading to enhanced cell adhesion and suppressed cell motility.

Basement membrane protein distribution in LYVE-1-immunoreactive lymphatic vessels of normal tissues and ovarian carcinomas

The endothelial cells of blood vessels assemble basement membranes that play a role in vessel formation, maintenance and function, and in the migration of inflammatory cells. However, little is known about the distribution of basement membrane constituents in lymphatic vessels. We studied the distribution of basement membrane proteins in lymphatic vessels of normal human skin, digestive tract, ovary and, as an example of tumours with abundant lymphatics, ovarian carcinomas. Basement membrane proteins were localized by immunohistochemistry with monoclonal antibodies, whereas lymphatic capillaries were detected with antibodies to the lymphatic vessel endothelial hyaluronan receptor-1, LYVE-1. In skin and ovary, fibrillar immunoreactivity for the laminin alpha4, beta1, beta2 and gamma1 chains, type IV and XVIII collagens and nidogen-1 was found in the basement membrane region of the lymphatic endothelium, whereas also heterogeneous reactivity for the laminin alpha5 chain was detected in the digestive tract. Among ovarian carcinomas, intratumoural lymphatic vessels were found especially in endometrioid carcinomas. In addition to the laminin alpha4, beta1, beta2 and gamma1 chains, type IV and XVIII collagens and nidogen-1, carcinoma lymphatics showed immunoreactivity for the laminin alpha5 chain and Lutheran glycoprotein, a receptor for the laminin alpha5 chain. In normal lymphatic capillaries, the presence of primarily alpha4 chain laminins may therefore compromise the formation of endothelial basement membrane, as these truncated laminins lack one of the three arms required for efficient network assembly. The localization of basement membrane proteins adjacent to lymphatic endothelia suggests a role for these proteins in lymphatic vessels. The distribution of the laminin alpha5 chain and Lutheran glycoprotein proposes a difference between normal and carcinoma lymphatic capillaries.

Laminin-5-deficient human keratinocytes: defective adhesion results in a saltatory and inefficient mode of migration

Laminin-5 is a major adhesion protein of the skin basement membrane and crucially involved in integrin-mediated cell substrate attachment of keratinocytes, which is important for hemidesmosomal anchorage as well as for keratinocyte migration during epidermal wound healing. To investigate its role in keratinocyte migration, we analyzed laminin-5-deficient cells of patients with a lethal variant of junctional epidermolysis bullosa. Normal migrating keratinocytes adopted monopolar morphology with a distinct front lamella and employed a continuous mode of translocation. In contrast, laminin-5-deficient cells assumed a stretched bipolar shape with two lamella regions and migrated in a discontinuous, saltatory manner characterized by significantly decreased directional persistence and reduced migration velocity. The distinct morphology as well as the migratory phenotype apparently resulted from a defect in the formation of cell substrate adhesions that were completely missing in the cell body and less stable in the lamella regions. Accordingly in normal keratinocytes, a bipolar shape and a saltatory migration mode were inducible by blocking laminin-5-mediated substrate adhesion. Our findings clearly point to an essential role of laminin-5 in forming dynamic cell substrate adhesion during migration of epidermal keratinocytes and provide an explanation for the cellular mechanisms that underlie the lethal form of junctional epidermolysis bullosa.

The coiled-coil structure potential of the laminin LCC domain is very fragmented and does not differentiate between natural and non-detected isoforms

There are 15 known laminins, which differ in the isoforms of the three chains that assemble into the cross-shape molecules that are observed by electron microscopy. The amino acid sequences of the rod-like portion of the long arm have long been recognized as having a potential for coiled-coil structure formation; however, an experimental determination of its structure is hampered by the complexity of laminin, a multidomain, heterotrimeric, and glycosilated 800 kDa molecule. Here, we have investigated the coiled-coil structure potential of laminin to evaluate its distribution along the long arm, the presence of conserved patterns, and differences between natural and non-natural isoforms. With these aims, we have analysed the sequences of each laminin chain in the context of the three-chain assemblies to yield an overall score of coiled-coil potential for the 15 natural laminins and for the other 30 possible but non-detected ones. The potential has been calculated with two different existing methods to exclude algorithm specific biases and with different chain alignments to evaluate the dependency of the results on uncertainties in the specific alignment along the domain. The analysis shows that the distribution of the potential is discontinuous, highly fragmented along the arm, without a common pattern except for a higher potential at the C-terminus, and that natural and non-natural laminins cannot be distinguished based on their coiled-coil potential, indicating that other factors are responsible for the selection of chain assembly.

Crystal structure and cell surface anchorage sites of laminin alpha1LG4-5

The laminin G-like (LG) domains of laminin-111, a glycoprotein widely expressed during embryogenesis, provide cell anchoring and receptor binding sites that are involved in basement membrane assembly and cell signaling. We now report the crystal structure of the laminin alpha1LG4-5 domains and provide a mutational analysis of heparin, alpha-dystroglycan, and galactosylsulfatide binding. The two domains of alpha1LG4-5 are arranged in a V-shaped fashion similar to that observed with laminin alpha2 LG4-5 but with a substantially different interdomain angle. Recombinant alpha1LG4-5 binding to heparin, alpha-dystroglycan, and sulfatides was dependent upon both shared and unique contributions from basic residues distributed in several clusters on the surface of LG4. For heparin, the greatest contribution was detected from two clusters, 2719RKR and 2791KRK. Binding to alpha-dystroglycan was particularly dependent on basic residues within 2719RKR, 2831RAR, and 2858KDR. Binding to galactosylsulfatide was most affected by mutations in 2831RAR and 2766KGRTK but not in 2719RKR. The combined analysis of structure and activities reveal differences in LG domain interactions that should enable dissection of biological roles of different laminin ligands.

Laminin isoforms in development and disease

The members of the laminin family of heterotrimers are major constituents of all basement membranes, sheet-like extracellular structures, present in almost all organs. The laminins bind to cell surface receptors and thereby tightly connect the basement membrane to the adjacent cell layer. This provides for the specific basement membrane functions to stabilize cellular structures, to serve as effective physical barriers, and furthermore, to govern cell fate by inducing intracellular signalling cascades. Many different types of diseases involve basement membranes and laminins. Metastasizing solid tumors must pass through basement membranes to reach the vascular system, and various microbes and viruses enter the cells through direct interaction with laminins. Furthermore, whereas mutations in one specific laminin chain lead to a muscular disorder, mutations of other laminin chains cause skin blistering and kidney defects, respectively. This review summarizes recent progress concerning the molecular mechanisms of laminins in development and disease. The current knowledge may lead to clinical treatment of lamininopathies and may include stem-cell approaches as well as gene therapy.

Def-6, a guanine nucleotide exchange factor for Rac1, interacts with the skeletal muscle integrin chain alpha7A and influences myoblast differentiation

Integrin alpha7beta1 is the major laminin binding integrin receptor of muscle cells. The alpha7 chain occurs in several splice isoforms, of which alpha7A and alpha7B differ in their intracellular domains only. The fact that the expression of alpha7A and alpha7B is tightly regulated during skeletal muscle development suggests different and distinct roles for both isoforms. However, so far, functional properties and interacting proteins were described for the alpha7B chain only. Using a yeast two-hybrid screen, we have found that Def-6, a guanine nucleotide exchange factor for Rac1, binds to the intracellular domain of the alpha7A subunit. The specificity of the Def-6-alpha7A interaction has been shown by direct yeast two-hybrid binding assays and coprecipitation experiments. This is the first description of an alpha7A-specific and -exclusive interaction, because Def-6 did not bind to any other tested integrin cytoplasmic domain. Interestingly, the binding of Def-6 to alpha7A was abolished, when cells were cotransfected with an Src-related kinase, which is known to phosphorylate Def-6 and stimulate its exchange activity. We found expression of Def-6 was not only restricted to T-lymphocytes as described thus far but in a more widespread manner, including different muscle tissues. In cells, Def-6 is seen in newly forming cell protrusions and focal adhesions, and its localization partially overlaps with the alpha7A integrin receptor. C2C12 myoblasts overexpressing Def-6 show a delay of Rac1 inactivation during myogenic differentiation and abnormal myotube formation. Thus, our data suggest a role for Def-6 in the fine regulation of Rac1 during myogenesis with the integrin alpha7A chain guiding this regulation in a spatio-temporal manner.

Attachment to laminin-111 facilitates transforming growth factor beta-induced expression of matrix metalloproteinase-3 in synovial fibroblasts

BACKGROUND

In the synovial membrane of patients with rheumatoid arthritis (RA), a strong expression of laminins and matrix degrading proteases was reported.

AIM

To investigate the regulation of matrix metalloproteinases (MMPs) in synovial fibroblasts (SFs) of patients with osteoarthritis (OA) and RA by attachment to laminin-1 (LM-111) and in the presence or absence of costimulatory signals provided by transforming growth factor beta (TGFbeta).

METHODS

SFs were seeded in laminin-coated flasks and activated by addition of TGFbeta. The expression of genes was investigated by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR), immunocytochemistry and ELISA, and intracellular signalling pathways by immunoblotting, and by poisoning p38MAPK by SB203580, MEK-ERK by PD98059 and SMAD2 by A-83-01.

RESULTS

Attachment of SF to LM-111 did not activate the expression of MMPs, but addition of TGFbeta induced a fivefold higher expression of MMP-3. Incubation of SF on LM-111 in the presence of TGFbeta induced a significant 12-fold higher expression of MMP-3 mRNA, and secretion of MMP-3 was elevated 20-fold above controls. Functional blocking of LM-111-integrin interaction reduced the laminin-activated MMP-3 expression significantly. Stimulation of SF by LM-111 and TGFbeta activated the p38MAPK, ERK and SMAD2 pathways, and inhibition of these pathways by using SB203580, PD98059 or A-83-01 confirmed the involvement of these pathways in the regulation of MMP-3.

CONCLUSION

Attachment of SF to LM-111 by itself has only minor effects on the expression of MMP-1 or MMP-3, but it facilitates the TGFbeta-induced expression of MMP-3 significantly. This mode of MMP-3 induction may therefore contribute to inflammatory joint destruction in RA independent of the proinflammatory cytokines interleukin (IL)1beta or tumour necrosis factor (TNF)alpha.

Mesenchymal cells contribute to the synthesis and deposition of the laminin-5 gamma2 chain in the invasive front of oral squamous cell carcinoma

Tumour progression in oral squamous cell carcinoma (OSCC) is associated with a reorganisation of extracellular matrix. Laminin-5 (Ln-5) plays an important role for tumour migration and shows an increased expression in areas of direct tumour/stroma interactions. We have previously shown stromal spot like Ln-5/gamma2 chain deposits distant from the basement membrane region. In this study we have analysed which cell type is responsible for Ln-5/gamma2 chain synthesis in situ. Furthermore, we studied its spatial relation to TGF-beta1 as well as the Ln-5 modulating enzymes matrix metalloproteinase (MMP) 2, membrane type-1 (MT1-) MMP and bone morphogenetic protein (BMP-) 1 by different techniques including triple immunofluorescence labelling and in situ hybridisation in OSCC. We found that the stromal spot-like Ln-5 deposits occurred in the invasive front in the vicinity of mesenchymal cells and vessel structures. In particular, not only carcinoma cells but also mesenchymal cells were shown to express the Ln-5/gamma2 chain mRNA. Moreover, stromal Ln-5 deposits showed a spatial association with TGF-beta1 as well as with MT1-MMP and BMP-1. Based on these findings we suggest that mesenchymal cells contribute to the promotion of tumour cell migration as well as vessel formation in OSCC by providing and organising promigratory Ln-5 fragments.

A quantitative co-localization analysis of large unspliced tenascin-C(L) and laminin-5/gamma2-chain in basement membranes of oral squamous cell carcinoma by confocal laser scanning microscopy

BACKGROUND

A structural interaction of the oncofetal large tenascin-C splice variants (Tn-C(L)) and the gamma2-chain of laminin-5 (Ln-5/gamma2) was recently demonstrated in oral squamous cell carcinoma (OSCC). In situ different patterns of co-localization and co-deposition of both proteins could be detected. Especially the co-localization in re-established basement membrane (BM) structures seemed to be biologically meaningful within the process of tumour progression.

METHODS

The amount of Tn-C(L) incorporated in reorganized OSCC BM structures at the tumour margins was investigated by a laser scanning microscopy-based quantitative co-localization analysis.

RESULTS

In the BM of normal oral mucosa no Tn-C(L) could be detected. In dysplastic and neoplastic oral mucosa a distinct co-localization of Tn-C(L) and Ln-5/gamma2 in the BM region could be observed. The extent of Tn-C(L) arrangement into reorganized BM structures correlated with malignancy grade.

CONCLUSIONS

The results suggest at first, a modulation of carcinomatous BM structures by the inclusion of oncofetal matrix proteins during tumour progression and secondly, the BM incorporation of the adhesion-modulating molecule Tn-C(L) as a pre-invasive structural phenomenon in OSCC.

Lack of Nidogen-1 and -2 Prevents Basement Membrane Assembly in Skin-Organotypic Coculture

Nidogens are considered as classical linkers joining laminin and collagen IV networks in basement membranes (BMs); however, recent genetic approaches have suggested that nidogens function in a tissue-specific and developmental context. Thus, in mice lacking both nidogen-1 and -2 heart and lung were severely affected, causing neonatal death. Furthermore, in various locations, extravasation of erythrocytes was observed implying microvascular defects. Mice expressing solely either isoform, had a functional BM, although nidogen-2 binds with lower affinity to the laminin gamma1 chain. Having previously blocked BM formation by interfering with nidogen-1 binding to laminin in skin-organotypic cocultures, here we investigated the roles of nidogen-1 and -2 in this model. For that purpose, human HaCaT cells were grown in three-dimensional cocultures on collagen matrices containing murine fibroblasts of varying nidogen deficiency. As with our experiments blocking laminin-nidogen interaction, lack of both nidogens completely prevented BM deposition and ultrastructural assembly of BM and hemidesmosomes, although other BM proteins remained detectable at comparable levels with no signs of degradation. Supplementation by recombinant nidogen-1 or -2 restored these structures, as shown by immunofluorescence and electron microscopy, confirming that in this system nidogen-2 is equivalent to nidogen-1, and both can promote the development of a functional BM zone.

Caspase proteolysis of the integrin beta4 subunit disrupts hemidesmosome assembly, promotes apoptosis, and inhibits cell migration

Caspases are a conserved family of cell death proteases that cleave intracellular substrates at Asp residues to modify their function and promote apoptosis. In this report we identify the integrin beta4 subunit as a novel caspase substrate using an expression cloning strategy. Together with its alpha6 partner, alpha6beta4 integrin anchors epithelial cells to the basement membrane at specialized adhesive structures known as hemidesmosomes and plays a critical role in diverse epithelial cell functions including cell survival and migration. We show that integrin beta4 is cleaved by caspase-3 and -7 at a conserved Asp residue (Asp(1109)) in vitro and in epithelial cells undergoing apoptosis, resulting in the removal of most of its cytoplasmic tail. Caspase cleavage of integrin beta4 produces two products, 1) a carboxyl-terminal product that is unstable and rapidly degraded by the proteasome and 2) an amino-terminal cleavage product (amino acids 1-1109) that is unable to assemble into mature hemidesmosomes. We also demonstrate that caspase cleavage of integrin beta4 sensitizes epithelial cells to apoptosis and inhibits cell migration. Taken together, we have identified a previously unrecognized proteolytic truncation of integrin beta4 generated by caspases that disrupts key structural and functional properties of epithelial cells and promotes apoptosis.

The requirement of the glutamic acid residue at the third position from the carboxyl termini of the laminin gamma chains in integrin binding by laminins

Laminins are the major cell-adhesive proteins in the basement membrane, consisting of three subunits termed alpha, beta, and gamma. The putative binding site for integrins has been mapped to the G domain of the alpha chain, although trimerization with beta and gamma chains is necessary for the G domain to exert its integrin binding activity. The mechanism underlying the requirement of beta and gamma chains in integrin binding by laminins remains poorly understood. Here, we show that the C-terminal region of the gamma chain is involved in modulation of the integrin binding activity of laminins. We found that deletion of the C-terminal three but not two amino acids within the gamma1 chain completely abrogated the integrin binding activity of laminin-511. Furthermore, substitution of Gln for Glu-1607, the amino acid residue at the third position from the C terminus of the gamma1 chain, also abolished the integrin binding activity, underscoring the role of Glu-1607 in integrin binding by the laminin. We also found that the conserved Glu residue of the gamma2 chain is necessary for integrin binding by laminin-332, suggesting that the same mechanism operates in the modulation of the integrin binding activity of laminins containing either gamma1 or gamma2 chains. However, the peptide segment modeled after the C-terminal region of gamma1 chain was incapable of either binding to integrin or inhibiting integrin binding by laminin-511, making it unlikely that the Glu residue is directly recognized by integrin. These results, together, indicate a novel mechanism operating in ligand recognition by laminin binding integrins.

Malignancy-related 67kDa laminin receptor in adenoid cystic carcinoma. Effect on migration and beta-catenin expression

Adenoid cystic carcinoma is a malignant salivary gland neoplasm with recurrence and metastasis. We studied the expression of a malignancy-related non-integrin laminin receptor, the 67LR, in this neoplasm. Immunohistochemistry showed 67LR in adenoid cystic carcinoma. This receptor binds a sequence of laminin beta1 chain, the YIGSR peptide. We studied the effect of 67LR and YIGSR in cells (CAC2) from adenoid cystic carcinoma. Three-dimensional cultures of cells embedded into either laminin-111 gel (controls) or YIGSR-enriched laminin-111 (treated) were prepared and studied by light microscopy. CAC2 cells treated with YIGSR appeared fibroblast-like, while control cells were epithelioid. Blockage of 67LR by antibody abolished YIGSR effect in three-dimensional cultures. We analysed the relevance of 67LR and YIGSR on beta-catenin expression in CAC2 cells. Immunofluorescence and immunoblot showed that YIGSR decreased beta-catenin, while blockage of 67LR restored the presence of this molecule. The 67LR and YIGSR induced fibroblast-like morphology in CAC2 cells, with disruption of cell-cell contacts and decrease of beta-catenin. These features resemble epithelial-mesenchymal transition (EMT). EMT also increases cell migration. In monolayer assays YIGSR increased migration of CAC2 cells. We conclude that 67LR and YIGSR are involved in epithelial-mesenchymal transition, modulation of beta-catenin expression, and migratory activity of CAC2 cells.

Spatial and temporal control of laminin-332 (5) and -511 (10) expression during induction of anagen hair growth

Basement membrane plays important roles in hair growth. We characterized changes in laminin isoform expression during hair cycling. At the mRNA level, laminin-511 (10) expression underwent a steady increase during anagen stages. In contrast, laminin-332 (5) expression was initially upregulated in outer root sheath (ORS) keratinocytes at anagen II and then transiently downregulated. Laminin-332 significantly increased coincident with the signal in inner root sheath and hair matrix cells after anagen IV. Levels of laminin-332 proteins were also upregulated at late anagen I-III but dropped after anagen IV. This decrease coincided with increased levels of mRNA encoding the two proteases, membrane type 1 metalloproteinase and bone morphogenetic protein 1, involved in laminin-332 processing. Immunohistochemistry demonstrated that laminin-332 and alpha6 beta4 integrin were well colocalized, but their signals were remarkably decreased in the lower half of follicles after anagen VI. Consistent with these data, ultrastructurally mature hemidesmosomes were seen in ORS keratinocytes at anagen II, whereas at anagen VI, only fragmental hemidesmosomes were present. In hair follicle culture, laminin-511 (10)/521 (11)-rich human placental laminin enhanced hair growth, whereas recombinant laminin-332 antagonized hair growth induced by laminin-511. Our results indicate a positive role for laminin-511 and a negative role for laminin-332 on hair growth.

Visions for novel biophysical elucidations of extracellular matrix networks

The extracellular matrix consists of multifunctional molecules, which are composed of a large numbers of different domains. Clearly these domains and even the entire molecules do not function independently as isolated species, but interact with each other in large networks. In many cases specific regions of the networks may be considered as molecular machines in which the different molecules are arranged in highly defined spatial structures and act in a dynamic, concerted fashion. At present most structural information is limited to single molecules, and dynamics have been measured mainly for pairs of interacting partners in solution. Work needs to be extended to large integrated systems and the functions of molecular machines need to be explored. Electron tomography, fluorescence resonance energy transfer, and other biophysical techniques are very promising.

The β3 chain short arm of laminin-332 (laminin-5) induces matrix assembly and cell adhesion activity of laminin-511 (laminin-10)

The basement membrane (BM) protein laminin-332 (Lm332) (laminin-5) has unique activity and structure as compared with other laminins: it strongly promotes cellular adhesion and migration, and its alpha3, beta3, and gamma2 chains are all truncated in their N-terminal regions (short arms). In the present study, we investigated the biological function of the laminin beta3 chain. When the beta3 chain short arm (beta3SA) was overexpressed in HEK293 cells (beta3SA-HEK), they deposited a large amount of beta3SA and a small amount of laminin-511 (Lm511) (laminin-10) on culture plates. Control HEK293 cells secreted Lm511 but failed to deposit it. The extracellular matrix (ECM) deposited by beta3SA-HEK cells strongly promoted cell attachment and spreading. The beta3SA-HEK ECM did not directly bind Lm511, but it stimulated control HEK293 cells to deposit Lm511 on the culture plates. Although purified beta3SA did not support cell adhesion by itself, it enhanced the cell adhesion activity of Lm511. Experiments with anti-integrin antibodies also suggested that the strong cell adhesion activity of the beta3SA-HEK ECM was derived from the synergistic action of beta3SA and Lm511. It has previously been found that beta3SA binds an unknown cell surface receptor. Taken together, the present study suggests that the short arm of the laminin beta3 chain enhances the matrix assembly of Lm511 and its cell adhesion activity by interacting with its receptor.

Examination of basement membrane components associated with the bovine seminiferous tubule basal lamina

Immunohistology has been used to examine the distribution of certain components of the basement membrane (BM) associated with bovine spermatogonial germ cells that are located within the seminiferous tubules. Histology was performed on testis tissue from Brahman cattle (Bos indicus) of three different age groups: pre-pubescent (4–6 months), juvenile (8–10 months) and adult (18–24 months) animals. There were no major changes in the BM composition apparent between these three age groups, except for certain lectin staining. These data suggest that the predominant collagen type IV component may have an α3 and α4 composition, although other chains, including the α5 and α6 chains, were also present. Possibly the main laminin type present was laminin 121 (α1β2γ1), although other variants were also present. Both nidogen-1 and perlecan, which are normal BM components, were also found as part of the seminiferous tubule BM. Interstitial collagens, such as type I, III and VI collagens, were found in the peritubular space, but were not part of the BM itself, although type VI collagen was most visible in the peritubular zone adjacent to the tubules. Examination of the BM with a range of lectins gave strong staining for (glcNAc)2 entities, weak positive staining for α-l-fuc, but little or no staining for α-galNAc and (glcNAc)3 at all ages, whereas staining for α-gal, β-gal(1→3)galNAc and α-man showed developmental changes.

What mouse mutants teach us about extracellular matrix function

For many years the extracellular matrix was viewed as a benign scaffold for arranging cells within connective tissues, but it is now being redefined as a dynamic, mobile, and flexible key player in defining cellular behavior. Gene targeting, transgene expression, and spontaneous mutations of extracellular matrix proteins in mice have greatly accelerated our mechanistic view of the structural and instructive functions of the extracellular matrix in developmental and regenerative processes. This review summarizes the phenotypes of genetic mouse models carrying mutations in extracellular matrix proteins, with specific emphasis on recent advances. The application of reverse genetics has demonstrated the multifunctionality of matrix proteins in a biological context and, in addition, has brought a novel perspective to the understanding of human pathologies.

Molecular and diagnostic aspects of genetic skin fragility

Genetic syndromes with skin fragility represent a heterogeneous group of very rare disorders caused by mutations in genes encoding proteins or protein subunits important for the mechanical resistance of keratinocytes and for cell-cell or cell-extracellular matrix adhesion. The common symptoms are skin blistering or peeling, with various degrees of severity and distribution, ranging from localized to generalized forms. Associated features include involvement of skin annexes, mucous membranes, teeth, muscles or the digestive tract. Morphological investigation of skin samples provides evidence for the tissue level of blister formation, while immunostainings may reveal defective proteins, providing clues concerning the genetic origin of the disease. Extensive mutation analysis and subsequent identification of new gene defects provide accurate diagnostics, and lead to better understanding of the functions of the respective proteins, with the potential for new therapeutic strategies.

Matrilysin 1 influences colon carcinoma cell migration by cleavage of the laminin-5 beta3 chain

Matrilysin 1 [matrix metalloproteinase 7 (MMP7)] is one of the most important metalloproteinases expressed in human tissues. This enzyme is generally not expressed by normal differentiated epithelial colon cells, but has been shown to be up-regulated in human colon adenomas and adenocarcinomas. Little is known about the role of MMP7 in cell invasion and its involvement in proteolytic processes. By searching the ligands of MMP7 in the colonic carcinoma cells HT29, we identified laminin-5/laminin-332 (LN5) as a specific target for MMP7 enzymatic activity. LN5, composed of alpha3, beta3, and gamma2 chains, is an important component of epithelial basement membranes where it induces firm adhesion and hemidesmosome formation. In this study, we show that LN5 and MMP7 are coexpressed in HT29 cells as well as in HT29 xenograft tumors and human colorectal adenocarcinomas. We provide evidence that human LN5 is a ligand for MMP7 and that a specific cleavage occurs in its beta3 chain, giving rise to a carboxyl-terminal beta3 chain fragment of 90 kDa. We have identified the MMP7 cleavage site at position Ala(515)-Ile(516) in the beta3 chain. Videomicroscopic analysis of HT29 cells plated on LN5 substrates reveals that the MMP7-processed LN5 significantly enhances cell motility. Moreover, the delayed migration of HT29 cells obtained after specific inhibition of MMP7 reinforces the hypothesis supporting its involvement in cell migration. Altogether, our results show that MMP7 is likely to play a crucial role in the regulation of carcinoma cell migration by targeting specific proteolytic processing of the LN5 beta3 chain.

The extracellular matrix as an adhesion checkpoint for mammary epithelial function

The development of the mammary gland is spatially regulated by the interaction of the mammary epithelium with the extracellular matrix (ECM). Cells receive cues from the ECM through a family of adhesion receptors called integrins, consisting of alpha- and beta-chain dimers. Integrins assist cells in sensing their appropriate developmental context in response to both hormones and growth factors. Here we argue that cell adhesion to the ECM plays a key role in specific developmental checkpoints, particularly in alveolar survival, morphogenesis and function. Specific ablation of alphabeta1-integrins in the luminal epithelium of the mammary gland shows that this sub-type of receptors is required for proliferation, accurate morphological organisation, as well as milk secretion. Downstream, small Rho GTPases mediate cellular polarisation and differentiation. Current challenges in studying the integration of signals in checkpoints of mammary gland development are discussed.

Integrin beta4 regulates migratory behavior of keratinocytes by determining laminin-332 organization

Whether alpha6beta4 integrin regulates migration remains controversial. beta4 integrin-deficient (JEB) keratinocytes display aberrant migration in that they move in circles, a behavior that mirrors the circular arrays of laminin (LM)-332 in their matrix. In contrast, wild-type keratinocytes and JEB keratinocytes, induced to express beta4 integrin, assemble laminin-332 in linear tracks over which they migrate. Moreover, laminin-332-dependent migration of JEB keratinocytes along linear tracks is restored when cells are plated on wild-type keratinocyte matrix, whereas wild-type keratinocytes show rotation over circular arrays of laminn-332 in JEB keratinocyte matrix. The activities of Rac1 and the actin cytoskeleton-severing protein cofilin are low in JEB keratinocytes compared with wild-type cells but are rescued following expression of wild-type beta4 integrin in JEB cells. Additionally, in wild-type keratinocytes Rac1 is complexed with alpha6beta4 integrin. Moreover, Rac1 or cofilin inactivation induces wild-type keratinocytes to move in circles over rings of laminin-332 in their matrix. Together these data indicate that laminin-332 matrix organization is determined by the alpha6beta4 integrin/actin cytoskeleton via Rac1/cofilin signaling. Furthermore, our results imply that the organizational state of laminin-332 is a key determinant of the motility behavior of keratinocytes, an essential element of skin wound healing and the successful invasion of epidermal-derived tumor cells.

Regulation of proliferation and chondrogenic differentiation of human mesenchymal stem cells by laminin-5 (laminin-332)

Laminin-5 (laminin-332) is an important basement membrane protein that regulates cell attachment and motility. Recent studies have shown that laminin-5 is expressed in human mesenchymal stem cells (MSCs) in culture and that the laminin gamma2 chain is transiently expressed in chondrocytes during development. These studies suggest that laminin-5 may be involved in the regulation of chondrogenic differentiation of MSCs. In this study, we examined a possible role of laminin-5 in the proliferation and differentiation of human MSCs. When MSCs were incubated in the presence of a coated or soluble form of laminin-5 in a growth medium, they proliferated more rapidly than nontreated cells, keeping their differentiation potential. On the other hand, laminin-5 potently suppressed the chondrogenic differentiation of MSCs. These activities were mediated mainly by integrin alpha3beta1. However, laminin-5 had no effect on the osteogenic differentiation of MSCs. These results suggest that laminin-5 may contribute to the development of bone tissues by promoting the proliferation and by suppressing the chondrogenic differentiation of MSCs.

The Sp family of transcription factors regulates the human laminin alpha1 gene in JAR choriocarcinoma cells

Laminin-111 (alpha1beta1gamma1) is the major component of the embryonic and extra-embryonic basement membrane. The laminin alpha1 chain shows a restricted and developmentally regulated expression in basement membranes of distinct epithelial tissues while beta1 and gamma1 chains have a wide tissue distribution. To understand how human laminin alpha1 chain expression is controlled, we cloned and characterized the 5'-flanking region of the human laminin alpha1 (LAMA1) gene. Transfection studies using serially deleted promoter constructs and JAR choriocarcinoma cells revealed that the minimal promoter fragment resided in the +31 to -206 region, which contains a number of GC- and GT/A-rich motifs for the binding of the Sp family of transcription factors. Electrophoretic mobility shift assays and mutational analyses revealed that Sp1 and Sp3 bound specifically to these elements and are important for the promoter activity. Furthermore, we showed that Krüppel-like factors KLF4 and KLF6 also activate transcription of the human LAMA1 gene. Chromatin immunoprecipitation analysis demonstrated recruitment of these transcription factors to the promoter region. These results indicate that transcription of the human LAMA1 gene is controlled by a combination of the actions of Sp1/Sp3 and Krüppel-like factors, KLF4 and KLF6.

Salivary gland branching morphogenesis

Salivary gland branching morphogenesis involves coordinated cell growth, proliferation, differentiation, migration, apoptosis, and interaction of epithelial, mesenchymal, endothelial, and neuronal cells. The ex vivo analysis of embryonic mouse submandibular glands, which branch so reproducibly and beautifully in culture, is a powerful tool to investigate the molecular mechanisms regulating epithelium-mesenchyme interactions during development. The more recent analysis of genetically modified mice provides insight into the genetic regulation of branching morphogenesis. The review begins, as did the field historically, focusing on the role of the extracellular matrix (ECM), and its components such as glycosaminoglycans, collagens, and laminins. Following sections describe the modification of the ECM by proteases and the role of cell-matrix and cell-cell receptors. The review then focuses on two major families of growth factors implicated in salivary gland development, the fibroblast growth factors (FGFs) and the epidermal growth factors (EGFs). The salivary gland phenotypes in mice with genetic modification of FGFs and their receptors highlight the central role of FGFs during salivary gland branching morphogenesis. A broader section mentions other molecules implicated from analysis of the phenotypes of genetically modified mice or organ culture experiments. The review concludes with speculation on some future areas of research.

Dystroglycan loss disrupts polarity and beta-casein induction in mammary epithelial cells by perturbing laminin anchoring

Precise contact between epithelial cells and their underlying basement membrane is crucial to the maintenance of tissue architecture and function. To understand the role that the laminin receptor dystroglycan (DG) plays in these processes, we assayed cell responses to laminin-111 following conditional ablation of DG gene (Dag1) expression in cultured mammary epithelial cells. Strikingly, DG loss disrupted laminin-111-induced polarity and beta-casein production, and abolished laminin assembly at the step of laminin binding to the cell surface. Dystroglycan re-expression restored these deficiencies. Investigations of the mechanism revealed that DG cytoplasmic sequences were not necessary for laminin assembly and signaling, and only when the entire mucin domain of extracellular DG was deleted did laminin assembly not occur. These results demonstrate that DG is essential as a laminin-111 co-receptor in mammary epithelial cells that functions by mediating laminin anchoring to the cell surface, a process that allows laminin polymerization, tissue polarity and beta-casein induction. The observed loss of laminin-111 assembly and signaling in Dag1(-/-) mammary epithelial cells provides insights into the signaling changes occurring in breast carcinomas and other cancers, where the binding function of DG to laminin is frequently defective.

Proteinuria precedes podocyte abnormalities inLamb2-/- mice, implicating the glomerular basement membrane as an albumin barrier

Primary defects in either podocytes or the glomerular basement membrane (GBM) cause proteinuria, a fact that complicates defining the barrier to albumin. Laminin beta2 (LAMB2) is a GBM component required for proper functioning of the glomerular filtration barrier. To investigate the GBM's role in glomerular filtration, we characterized GBM and overlying podocyte architecture in relation to development and progression of proteinuria in Lamb2-/- mice, which model Pierson syndrome, a rare congenital nephrotic syndrome. We found ectopic deposition of several laminins and mislocalization of anionic sites in the GBM, which together suggest that the Lamb2-/- GBM is severely disorganized, although it is ultrastructurally intact. Importantly, albuminuria was detectable shortly after birth and preceded podocyte foot process effacement and loss of slit diaphragms by at least 7 days. Expression and localization of slit diaphragm and foot process-associated proteins appeared normal at early stages. GBM permeability to the electron-dense tracer ferritin was dramatically elevated in Lamb2-/- mice, even before widespread foot process effacement. Increased ferritin permeability was not observed in nephrotic CD2-associated protein-null (Cd2ap-/-) mice, which have a primary podocyte defect. Together these data show that the GBM serves as a barrier to protein in vivo and that the glomerular slit diaphragm alone is not sufficient to prevent the passage of albumin into the urinary space.

Cooperation of isoforms of laminin-332 and tenascin-CL during early adhesion and spreading of immortalized human corneal epithelial cells

The repair of corneal wounds requires both epithelial cell adhesion and migration. We have studied the early adhesion process of immortalized human corneal epithelial (HCE) cells and show by field emission scanning electron microscopy (FESEM) that the cells first adhere via foot-like process to the growth substratum and later present lamellar spreading. During early adhesion indirect immunofluorescence showed that the cells codeposited laminin (Lm) -332 and the large subunit of tenascin-C (Tn-CL) as a demarcated plaque beneath the cells. Instead, unprocessed Lm-332 (alpha 3'32) was found in a wider area in cells showing lamellar spreading and was also prominently expressed in the cytoplasm of the migrating marginal cells in the in vitro wounded HCE cultures. Confocal laser scanning microscopy (CLSM) showed that the Golgi apparatus was located to the vicinity of the Lm-332/Tn-CL-containing adhesion plaque and accordingly treatment of the cells with demecolcine, dispersing the Golgi apparatus, prevented the formation of plaques. This suggests that formation of the adhesion plaque depends on a direct vectorial secretion of Lm-332 and Tn-CL to the culture substratum. Instead, cytochalasin B treatment disrupted microfilaments and arborized the cells but did not affect the deposition of Tn-CL/Lm-332 as a plaque beneath the cells. The suggestion was supported by immunoprecipitation experiments which showed that Tn-CL and Lm alpha 3' chain were found in cell-free matrices on the culture substratum of spreading cells but not at all (Tn-CL) or much less (Lm-332) in the culture medium. Quantitative cell adhesion experiments showed that HCE cells did not adhere to plain Tn-C coat and that integrin (Int) alpha(3)beta(1) mediated the adhesion of HCE cells to purified Lm-332 and to Lm-332/Tn-C while Int beta4 did not mediate adhesion to these proteins. Taken together, our data suggest that Lm-332 and Tn-CL cooperate in early adhesion process of HCE cells. Furthermore, the results show that Lm-3'32 isoform functions in the spreading of the cells beyond the early adhesion stage and appears to emerge into HCE cells starting to migrate in experimental wounds.

Abnormal development of glomerular endothelial and mesangial cells in mice with targeted disruption of the lama3 gene

Mice with targeted disruption of the lama3 gene, which encodes the alpha3 chain of laminin-5 (alpha3beta3gamma2, 332), develop a blistering skin disease similar to junctional epidermolysis bullosa in humans. These animals also develop abnormalities in glomerulogenesis. In both wild-type and mutant animals (lama3(-/-)), podocytes secrete glomerular basement membrane and develop foot processes. Endothelial cells migrate into this scaffolding and secrete a layer of basement membrane that fuses with the one formed by the podocyte. In lama3(-/-) animals, glomerular maturation arrests at this stage. Endothelial cells do not attenuate, develop fenestrae, or form typical lumens, and mesangial cells (MCs) were not identified. LN alpha3 subunit (LAMA3) protein was identified in the basement membrane adjacent to glomerular endothelial cells (GEnCs) in normal rats and mice. In developing rat glomeruli, the LAMA3 subunit was first detectable in the early capillary loop stage, which corresponds to the stage at which maturation arrest was observed in the mutant mice. Lama3 mRNA and protein were identified in isolated rat and mouse glomeruli and cultured rat GEnCs, but not MC. These data document expression of LAMA3 in glomeruli and support a critical role for it in GEnC differentiation. Furthermore, LAMA3 chain expression and/or another product of endothelial cells are required for MC migration into the developing glomerulus.

Laminin alpha1 chain LG4 module promotes cell attachment through syndecans and cell spreading through integrin alpha2beta1

The laminin alpha1 chain is a subunit of laminin-1, a heterotrimeric basement membrane protein. The LG4-5 module at the C terminus of laminin alpha1 contains major binding sites for heparin, sulfatide, and alpha-dystroglycan and plays a critical role in early embryonic development. We previously identified active synthetic peptides AG73 and EF-1 from the sequence of laminin alpha1 LG4 for binding to syndecan and integrin alpha2beta1, respectively. However, their activity and functional relationship within the laminin-1 and LG4 as well as the functional relation between these sites and alpha-dystroglycan binding sites in LG4 are not clear. To address these questions, we created mutant recombinant LG4 proteins containing alanine substitutions within the AG73 (M1), EF-1 (M2, M3), and alpha-dystroglycan binding sites (M4, M5) and analyzed their activities. We found that recombinant proteins rec-M1 and rec-M5, containing mutations within M1 and M5, respectively, did not bind heparin or lymphoid cell lines expressing syndecans. These results suggest that LG4 binds to heparin and syndecans through M1 and M5. Rec-M1 and rec-M5 reduced fibroblast attachment, whereas mutant rec-M2 and rec-M3 retained cell attachment activity but did not promote cell spreading. Fibroblast attachment to rec-LG4 was inhibited by heparin but not by integrin antibodies. Spreading of fibroblasts on rec-LG4 was inhibited by anti-integrin alpha2 and beta1 but not by anti-integrin alpha1 and alpha6. These results suggest that the M1 and M5 sites are necessary for cell attachment on LG4 through syndecans and that the EF-1 site is for cell spreading activity through integrin alpha2beta1. In contrast, laminin-1-mediated fibroblast attachment and spreading were not inhibited by heparin or anti-integrin alpha2. Our findings indicate that LG4 has a unique function distinct from laminin-1 and suggest that laminin alpha1 LG4-5 may also be produced by a proteolytic cleavage in certain tissues where it exerts its activity.

Laminin alpha1 chain improves laminin alpha2 chain deficient peripheral neuropathy

Absence of laminin alpha2 chain leads to a severe form of congenital muscular dystrophy (MDC1A) associated with peripheral neuropathy. Hence, future therapies should be aimed at alleviating both muscle and neurological dysfunctions. Pre-clinical studies in animal models have mainly focused on ameliorating the muscle phenotype. Here we show that transgenic expression of laminin alpha1 chain in muscles and the peripheral nervous system of laminin alpha2 chain deficient mice reduced muscular dystrophy and largely corrected the peripheral nerve defects. The presence of laminin alpha1 chain in the peripheral nervous system resulted in near-normal myelination, restored Schwann cell basement membranes and improved rotarod performance. In summary, we postulate that laminin alpha1 chain is an excellent substitute for laminin alpha2 chain in multiple tissues and suggest that treatment with laminin alpha1 chain may be beneficial for MDC1A in humans.

Laminin-332 alters connexin profile, dye coupling and intercellular Ca2+ waves in ciliated tracheal epithelial cells

BACKGROUND

Tracheal epithelial cells are anchored to a dynamic basement membrane that contains a variety of extracellular matrix proteins including collagens and laminins. During development, wound repair and disease of the airway epithelium, significant changes in extracellular matrix proteins may directly affect cell migration, differentiation and events mediated by intercellular communication. We hypothesized that alterations in cell matrix, specifically type I collagen and laminin alpha3beta3gamma2 (LM-332) proteins within the matrix, directly affect intercellular communication in ciliated rabbit tracheal epithelial cells (RTEC).

METHODS

Functional coupling of RTEC was monitored by microinjection of the negatively charged fluorescent dyes, Lucifer Yellow and Alexa 350, into ciliated RTEC grown on either a LM-332/collagen or collagen matrix. Coupling of physiologically significant molecules was evaluated by the mechanism and extent of propagated intercellular Ca2+ waves. Expression of connexin (Cx) mRNA and proteins were assayed by reverse transcriptase - polymerase chain reaction and immunocytochemistry, respectively.

RESULTS

When compared to RTEC grown on collagen alone, RTEC grown on LM-332/collagen displayed a significant increase in dye transfer. Although mechanical stimulation of RTEC grown on either LM-332/collagen or collagen alone resulted in intercellular Ca2+ waves, the mechanism of transfer was dependent on matrix: RTEC grown on LM-332/collagen propagated Ca2+waves via extracellular purinergic signaling whereas RTEC grown on collagen used gap junctions. Comparison of RTEC grown on collagen or LM-332/collagen matrices revealed a reorganization of Cx26, Cx43 and Cx46 proteins.

CONCLUSION

Alterations in airway basement membrane proteins such as LM-332 can induce connexin reorganizations and result in altered cellular communication mechanisms that could contribute to airway tissue function.

Extracellular matrix of the human cyclic corpus luteum

Extracellular matrix regulates many cellular processes likely to be important for development and regression of corpora lutea. Therefore, we identified the types and components of the extracellular matrix of the human corpus luteum at different stages of the menstrual cycle. Two different types of extracellular matrix were identified by electron microscopy; subendothelial basal laminas and an interstitial matrix located as aggregates at irregular intervals between the non-vascular cells. No basal laminas were associated with luteal cells. At all stages, collagen type IV alpha1 and laminins alpha5, beta2 and gamma1 were localized by immunohistochemistry to subendothelial basal laminas, and collagen type IV alpha1 and laminins alpha2, alpha5, beta1 and beta2 localized in the interstitial matrix. Laminin alpha4 and beta1 chains occurred in the subendothelial basal lamina from mid-luteal stage to regression; at earlier stages, a punctate pattern of staining was observed. Therefore, human luteal subendothelial basal laminas potentially contain laminin 11 during early luteal development and, additionally, laminins 8, 9 and 10 at the mid-luteal phase. Laminin alpha1 and alpha3 chains were not detected in corpora lutea. Versican localized to the connective tissue extremities of the corpus luteum. Thus, during the formation of the human corpus luteum, remodelling of extracellular matrix does not result in basal laminas as present in the adrenal cortex or ovarian follicle. Instead, novel aggregates of interstitial matrix of collagen and laminin are deposited within the luteal parenchyma, and it remains to be seen whether this matrix is important for maintaining the luteal cell phenotype.

Snail-dependent and -independent Epithelial-Mesenchymal Transition in Oral Squamous Carcinoma Cells

Disappearance of E-cadherin is a milestone for epithelial-mesenchymal transition (EMT), found both in carcinomas and in some fibrotic diseases. We have studied the mechanisms of EMT in oral squamous cell carcinoma (SCC) cells isolated from primary tumor (43A) and its recurrent tumor (43B). Whereas the cells from primary carcinoma displayed a typical phenotype of squamous epithelial cells including E-cadherin and laminin-332 (laminin-5), cells from recurrent tumor expressed characteristics of dedifferentiated, EMT-experienced tumors. 43B cells expressed E-cadherin repressors ZEB-1/δEF1 and especially ZEB-2/SIP1, which therefore appear as candidates for endogenous EMT in these cells. Differences between endogenous and exogenous EMT were assessed by transfecting 43A cells with SNAIL cDNA. SNAIL-transfected cells showed complete EMT phenotype with fibroblastoid appearance, vimentin filaments, E-cadherin/N-cadherin switch, lack of hemidesmosomes and, as a new feature of EMT, lack of laminin-332 synthesis. Upregulation of ZEB-1 and ZEB-2 was evident in these cells, suggesting that SNAIL can regulate these E-cadherin repressors. New monoclonal antibodies against SNAIL showed nuclear immunoreactivity not only in the SNAIL-transfected cells but also in carcinoma cells lacking production of Lm-332 and showing signs of EMT. These results suggest that changes in the epithelial cell differentiation program and EMT in SCC cells can result from the interplay among several E-cadherin repressors; however, SNAIL alone is able to accomplish a complete EMT. (J Histochem Cytochem 54:1263-1275, 2006)

Current insights into the formation and breakdown of hemidesmosomes

Hemidesmosomes are multiprotein adhesion complexes that promote epithelial stromal attachment in stratified and complex epithelia. Modulation of their function is of crucial importance in a variety of biological processes, such as differentiation and migration of keratinocytes during wound healing and carcinoma invasion, in which cells become detached from the substrate and acquire a motile phenotype. Although much is known about the signaling potential of the alpha6beta4 integrin in carcinoma cells, the events that coordinate the disassembly of hemidesmosomes during differentiation and wound healing remain unclear. The binding of alpha6beta4 to plectin has a central role in hemidesmosome assembly and it is becoming clear that disrupting this interaction is a crucial event in hemidesmosome disassembly. In addition, further insight into the functional interplay between alpha3beta1 and alpha6beta4 has contributed to our understanding of hemidesmosome disassembly and cell migration.

A hypomorphic mutation in the mouse laminin alpha5 gene causes polycystic kidney disease

Extracellular matrix abnormalities have been found in both human and animal models of polycystic kidney disease (PKD). A new mouse PKD model has been produced through insertion of a PGKneo cassette in an intron of the gene that encodes laminin alpha5 (Lama5), a major tubular and glomerular basement membrane component that is important for glomerulogenesis and ureteric bud branching. Lama5neo represents a hypomorphic allele as a result of aberrant splicing. Lama5neo/neo mice exhibit PKD, proteinuria, and death from renal failure by 4 wk of age. This contrasts with mice that totally lack Lama5, which die in utero with multiple developmental defects. At 2 d of age, Lama5neo/neo mice exhibited mild proteinuria and microscopic cystic transformation. By 2 wk, cysts were grossly apparent in cortex and medulla, involving both nephron and collecting duct segments. Tubular basement membranes seemed to form normally, and early cyst basement membranes showed normal ultrastructure but developed marked thickening as cysts enlarged. Overall, Lama5 protein levels were severely reduced as a result of mRNA frameshift caused by exon skipping. This was accompanied by aberrant accumulation of laminin-332 (alpha3beta3gamma2; formerly called laminin-5) in some cysts, as also observed in human PKD. This constitutes the first evidence that a primary defect in an extracellular matrix component can cause PKD.

Laminin isoforms and lung development: All isoforms are not equal

Laminins are a major component of basement membranes. Each laminin molecule is a heterotrimeric glycoprotein composed of one alpha, one beta, and one gamma chain. Fifteen laminin isoforms exist, assembled from various combinations of 5alpha, 3beta, and 3gamma chains. The embryonic lung has abundant laminin isoforms. Increasing evidence suggests that different laminin isoforms have unique functions in lung development. Studies of embryonic lung explants and organotypic co-cultures show that laminin alpha1 and laminin 111 are important for epithelial branching morphogenesis and that laminin alpha2 and laminin 211 have a role in smooth muscle cell differentiation. In vivo studies of laminin alpha5-deficient mice indicate that this laminin chain, found in laminins 511 and 521, is essential for normal lobar septation in early lung development and normal alveolization and distal epithelial cell differentiation and maturation in late lung development. However, not all of the laminin chains present in the developing lung appear to be necessary for normal lung development since laminin alpha4 null mice do not have obvious lung abnormalities and laminin gamma2 null mice have only minimal changes in lung development. The mechanisms responsible for the lung phenotypes in mice with laminin mutations are unknown, but it is clear that multiple laminin isoforms are crucial for lung development and that different laminin isoforms exhibit specific, non-overlapping functions.

Aspects of extracellular matrix remodeling in development and disease

The extracellular matrix is the major constituent of organic matter in both plants and animals, where it provides the interface between individual cells. In most tissues, with some notable exceptions such as bone marrow, the volume of extracellular matrix equals or exceeds the volume of intracellular space and organelles, making matrix an abundant constituent through which cells exert their functions and receive cues. The matrix may therefore be considered the basic structural entity that supports the function of an organ, and in connective tissues the matrix is the organ itself to which function is tied throughout the life of its resident cells. In this review, a select number of proteinases involved in some of the more conspicuous matrix remodeling events of the mammalian organism are explored. Evidence from both animal models and human diseases is discussed in relation to normal physiological processes, including instances in which aberrant matrix remodeling leads to disease states.