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A new prototype of nanoconjugate, Polycefin, was synthesized for targeted delivery of antisense oligonucleotides and monoclonal antibodies to brain tumors. The macromolecular carrier contains: 1. biodegradable, nonimmunogenic, nontoxic β-poly(l-malic acid) of microbial origin; 2. Morpholino antisense oligonucleotides targeting laminin α4 and β1 chains of laminin-8, which is specifically overexpressed in glial brain tumors; 3. monoclonal anti-transferrin receptor antibody for specific tissue targeting; 4. oligonucleotide releasing disulfide units; 5. l-valine containing, pH-sensitive membrane disrupting unit(s), 6. protective poly(ethylene glycol); 7. a fluorescent dye (optional). Highly purified modules were conjugated directly with N-hydroxysuccinimidyl ester-activated β-poly-(l-malic acid) at pendant carboxyl groups or at thiol containing spacers via thioether and disulfide bonds. Products were chemically validated by physical, chemical, and functional tests. In vitro experiments using two human glioma cell lines U87MG and T98G demonstrated that Polycefin was delivered into the tumor cells by a receptor-mediated endocytosis mechanism and was able to inhibit the synthesis of laminin-8 α4 and β1 chains at the same time. Inhibition of laminin-8 expression was in agreement with the designed endosomal membrane disruption and drug releasing activity. In vivo imaging showed the accumulation of intravenously injected Polycefin in brain tumor tissue via the antibody-targeted transferrin receptor-mediated endosomal pathway in addition to a less efficient mechanism known for high molecular mass biopolymers as enhanced permeability and retention effect. Polycefin was nontoxic to normal and tumor astrocytes in a wide range of concentrations, accumulated in brain tumor, and could be used for specific targeting of several biomarkers simultaneously.

A new prototype of polymer-derived drug delivery system, the nanoconjugate Polycefin, was tested for its ability to accumulate in tumors based on enhanced permeability and retention (EPR) effect and receptor mediated endocytosis. Polycefin was synthesized for targeted delivery of Morpholino antisense oligonucleotides into certain tumors. It consists of units that are covalently conjugated with poly(β-L-malic acid) (Mw 50,000, Mw/Mn 1.3) highly purified from cultures of myxomycete Physarum polycephalum. The units are active in endosomal uptake, disruption of endosomal membranes, oligonucleotide release in the cytoplasm, and protection against enzymatic degradation in the vascular system. The polymer is biodegradable, non-immunogenic and non-toxic. Polycefin was also coupled with AlexaFluor 680 C2-maleimide dye for in vivo detection.

Nude mice received subcutaneous injections of MDA-MB 468 human breast cancer cells into the left posterior mid-dorsum or intracranial injections of human glioma cell line U87MG. Polycefin at concentration of 2.5 mg/kg was injected via the tail vein. In vivo fluorescence tumor imaging was performed at different time points, 0–180 min up to 24 h after the drug injection. The custom-made macro-illumination imaging MISTI system was used to examine the in vivo drug accumulation in animals bearing human breast and brain tumors. In breast tumors the fluorescence signal in large blood vessels and in the tumor increased rapidly until 60 min and remained in the tumor at a level 6 times higher than in non-tumor tissue (180 min) (p < 0.003). In brain tumors drug accumulated selectively in 24 h without any detectable signal in non-tumor areas. The results of live imaging were corroborated histologically by fluorescence microscopic examination of various organs. In addition to tumors, only kidney and liver showed some fluorescent signal. © 2007 Elsevier Ireland Ltd. All rights reserved.

Tumor-specific targeting using achievements of nanotechnology is a mainstay of increasing efficacy of anti-tumor drugs. To improve drug targeting we covalently conjugated for the first time two different monoclonal antibodies, an anti-mouse transferrin receptor antibody and a mouse autoimmune anti-nucleosome antibody 2C5, onto the drug delivery nanoplatform, poly(β-L-malic acid). The active anti-tumor drug components attached to the same carrier molecule were antisense oligonucleotides to vascular protein laminin-8. The resulting drug, a new Polycefin variant, was administered intravenously into glioma-bearing xenogeneic animals. The drug delivery system was targeted across mouse endothelial system by the anti-mouse transferring receptor antibody and to the tumor cell surface by the anti-nucleosome antibody 2C5. The targeting efficacies of the Polycefin variants bearing either two antibodies or each single antibody were compared in vitro and in vivo. ELISA confirmed the co-existence of two antibodies on the same nanoplatform molecule and their functional activities. Fluorescence imaging analysis after 24 h of intravenous injection demonstrated significantly higher tumor accumulation of Polycefin variants with the tandem configuration of antibodies than with single antibodies. The results suggest improved efficacy for tandem configuration of antibodies than for single configurations carried by a drug delivery vehicle.

Nanoconjugates are emerging as promising drug-delivery vehicles because of their multimodular structure enabling them to actively target discrete cells, pass through biological barriers and simultaneously carry multiple drugs of various chemical nature. Nanoconjugates have matured from simple devices to multifunctional, biodegradable, nontoxic and nonimmunogenic constructs, capable of delivering synergistically functioning drugs in vivo. This review mainly concerns the Polycefin family of natural-derived polymeric drug-delivery devices as an example. This type of vehicle is built by hierarchic conjugation of functional groups onto the backbone of poly(malic acid), an aliphatic polyester obtained from the microorganism Physarum polycephalum. Particular Polycefin variants target human brain and breast tumors implanted into animals specifically and actively and could be detected easily by noninvasive imaging analysis. Delivery of antisense oligonucleotides to a tumor-specific angiogenic marker using Polycefin resulted in significant inhibition of tumor angiogenesis and increase of animal survival.

Laminins are the major constituents of blood vessel basement membranes (BMs). Each laminin is a trimer consisting of three assembled polypeptide chains, α, β and γ. More than 15 laminin isoforms are known to date and the expression of specific isoforms may change in certain pathological conditions. Here we show that during progression of glial tumors laminin-9 (α4β2γ1) is switched to laminin-8 (α4β1γ1), which is dramatically increased in glial brain tumors. Laminin-8 overproduction by glial tumor cells facilitates spread of glioma. Brain tumors with laminin-8 overexpression recur faster after standard treatment and patients have shorter survival time. Laminin-8 may be thus used as a predictor of tumor recurrence, patient survival and as a potential molecular target for glioma therapy.

Introduction

Laminins are the major components of vascular and parenchymal basement membranes. We previously documented a switch in the expression of vascular laminins containing the α4 chain from predominantly laminin-9 (α4β2γ1) to predominantly laminin-8 (α4β1γ1) during progression of human brain gliomas to high-grade glioblastoma multiforme. Here, differential expression of laminins was studied in blood vessels and ductal epithelium of the breast.

Method

In the present study the expressions of laminin isoforms α1–α5, β1–β3, γ1, and γ2 were examined during progression of breast cancer. Forty-five clinical samples of breast tissues including normal breast, ductal carcinomas in situ, invasive ductal carcinomas, and their metastases to the brain were compared using Western blot analysis and immunohistochemistry for various chains of laminin, in particular laminin-8 and laminin-9.

Results

Laminin α4 chain was observed in vascular basement membranes of most studied tissues, with the highest expression in metastases. At the same time, the expression of laminin β2 chain (a constituent of laminin-9) was mostly seen in normal breast and carcinomas in situ but not in invasive carcinomas or metastases. In contrast, laminin β1 chain (a constituent of laminin-8) was typically found in vessel walls of carcinomas and their metastases but not in those of normal breast. The expression of laminin-8 increased in a progression-dependent manner. A similar change was observed from laminin-11 (α5β2γ1) to laminin-10 (α5β1γ1) during breast tumor progression. Additionally, laminin-2 (α2β1γ1) appeared in vascular basement membranes of invasive carcinomas and metastases. Chains of laminin-5 (α3β3γ2) were expressed in the ductal epithelium basement membranes of the breast and diminished with tumor progression.

Conclusion

These results suggest that laminin-2, laminin-8, and laminin-10 are important components of tumor microvessels and may associate with breast tumor progression. Angiogenic switch from laminin-9 and laminin-11 to laminin-8 and laminin-10 first occurs in carcinomas in situ and becomes more pronounced with progression of carcinomas to the invasive stage. Similar to high-grade brain gliomas, the expression of laminin-8 (and laminin-10) in breast cancer tissue may be a predictive factor for tumor neovascularization and invasion.

This study examined the effects of endogenous overexpression of laminin-8 on angiogenesis and wound healing in primary human dermal microvascular endothelial cells (HDMECs). HDMECs expressed laminin-8 and laminin-10, but no other laminins, as determined by radioimmunoprecipitation assay using a panel of antibodies to individual laminin chains. To study laminin-8 function, full-length human laminin α4 cDNA was retrovirally transferred to HDMEC, and specific overexpression of laminin-8 was verified by Western blot. Laminin-8 overexpression promoted endothelial cell spreading and migration in scratch assays and accelerated angiogenic tubule formation in collagen gel overlay assays. Strong inhibitory effect of β1 integrin and weak inhibition by αvβ3 integrin antibodies were observed in laminin-8-stimulated cell migration, but only β1 integrin antibodies affected tubule formation. These studies suggest that laminin-8 overexpression may prove to be a useful method to engineer HDMECs to promote angiogenesis and wound repair.

Biodegradable nanopolymers are believed to offer great potential in cancer therapy. Here, we report the characterization of a novel, targeted, nanobiopolymeric conjugate based on biodegradable, nontoxic, and nonimmunogenic PMLA [poly(β-l-malic acid)]. The PMLA nanoplatform was synthesized for repetitive systemic treatments of HER2/neu-positive human breast tumors in a xenogeneic mouse model. Various moieties were covalently attached to PMLA, including a combination of morpholino antisense oligonucleotides (AON) directed against HER2/neu mRNA, to block new HER2/neu receptor synthesis; anti-HER2/neu antibody trastuzumab (Herceptin), to target breast cancer cells and inhibit receptor activity simultaneously; and transferrin receptor antibody, to target the tumor vasculature and mediate delivery of the nanobiopolymer through the host endothelial system. The results of the study showed that the lead drug tested significantly inhibited the growth of HER2/neu-positive breast cancer cells in vitro and in vivo by enhanced apoptosis and inhibition of HER2/neu receptor signaling with suppression of Akt phosphorylation. In vivo imaging analysis and confocal microscopy demonstrated selective accumulation of the nanodrug in tumor cells via an active delivery mechanism. Systemic treatment of human breast tumor-bearing nude mice resulted in more than 90% inhibition of tumor growth and tumor regression, as compared with partial (50%) tumor growth inhibition in mice treated with trastuzumab or AON, either free or attached to PMLA. Our findings offer a preclinical proof of concept for use of the PMLA nanoplatform for combination cancer therapy.

Laminins are major constituents of basement membranes and are essential for tissue homeostasis. Laminin-511 is highly expressed in the intestine and its absence causes severe malformation of the intestine and embryonic lethality. To understand the mechanistic role of laminin-511 in tissue homeostasis, we used RNA profiling of embryonic intestinal tissue of lama5 knockout mice and identified a lama5 specific gene expression signature. By combining cell culture experiments with mediated knockdown approaches, we provide a mechanistic link between laminin α5 gene deficiency and the physiological phenotype. We show that laminin α5 plays a crucial role in both epithelial and mesenchymal cell behavior by inhibiting Wnt and activating PI3K signaling. We conclude that conflicting signals are elicited in the absence of lama5, which alter cell adhesion, migration as well as epithelial and muscle differentiation. Conversely, adhesion to laminin-511 may serve as a potent regulator of known interconnected PI3K/Akt and Wnt signaling pathways. Thus deregulated adhesion to laminin-511 may be instrumental in diseases such as human pathologies of the gut where laminin-511 is abnormally expressed as it is shown here.

The expression of the constituent alpha 1 chain of laminin-1, a major component of basement membranes, is markedly regulated during development and differentiation. We have designed an antisense RNA strategy to analyze the direct involvement of the alpha 1 chain in laminin assembly, basement membrane formation, and cell differentiation. We report that the absence of alpha 1-chain expression, resulting from the stable transfection of the human colonic cancer Caco2 cells with an eukaryotic expression vector comprising a cDNA fragment of the alpha 1 chain inserted in an antisense orientation, led to (a) an incorrect secretion of the two other constituent chains of laminin-1, the beta 1/gamma 1 chains, (b) the lack of basement membrane assembly when Caco2-deficient cells were cultured on top of fibroblasts, assessed by the absence of collagen IV and nidogen deposition, and (c) changes in the structural polarity of cells accompanied by the inhibition of an apical digestive enzyme, sucrase-isomaltase. The results demonstrate that the alpha 1 chain is required for secretion of laminin-1 and for the assembly of basement membrane network. Furthermore, expression of the laminin alpha 1-chain gene may be a regulatory element in determining cell differentiation.

Laminins are major constituents of basement membranes. At least 16 isoforms have now been described, each with distinct spatio-temporal expression patterns and functions. The laminin-511 heterotrimer (α5β1γ1) is one of the more recent isoforms to be identified and a potent adhesive and pro-migratory substrate for a variety of normal and tumor cell lines in vitro. As our understanding of its precise function in normal tissues and in pathologies is rapidly unraveling, current evidence suggests an important regulatory role in cancer. This review describes published data on laminin-511 expression in several malignancies and experimental evidence from both in vitro and in vivo studies supporting its functional role during tumor progression. A particular emphasis is put on more recent studies from our laboratory and that of others indicating that laminin-511 contributes to tumor dissemination and metastasis in advanced breast carcinomas and other tumor types. Collectively, the experimental evidence suggests that high expression of laminin-511 has prognostic significance and that targeting tumor-laminin-511 interactions may have therapeutic potential in advanced cancer patients.

In multicellular organisms cell growth and differentiation are influenced by soluble factors, cell-cell interactions and cell-extracellular matrix interactions. We have used the rat mammary gland as a model system to study the role of extracellular matrix components in the regulation of milk protein gene expression. Since mammary epithelial cells differentiate on a basement membrane in vivo, we investigated the effects of basement membrane components on the expression of the milk protein genes, alpha-casein, alpha-lactalbumin, and transferrin. We have demonstrated that a basement membrane gel, as well as its major basement membrane component, laminin, induced alpha-casein and alpha-lactalbumin expression as much as 160-fold compared to tissue culture plastic. We demonstrate that laminin affects mRNA stability as well as having an effect on protein stability and secretion. Laminin interacts with mammary epithelial cells via an 68 kD cell surface receptor which is capable of interacting with the cellular cytoskeleton. In order to provide evidence that laminin affects on mammary differentiation are mediated through this receptor via the cytoskeleton, we examined the effects of cytoskeletal disrupting agents on milk protein gene expression. We demonstrate that cytochalasin D or colchicine selectively block laminin-mediated milk protein gene expression by affecting mRNA stability. Based on these experiments, we propose a model in which laminin affects mammary gene expression through interaction with cell surface receptors which interact with the cytoskeleton resulting in stabilization of mRNAs for milk protein genes.

Images

Treatment options for triple negative breast cancer (TNBC) are generally limited to cytotoxic chemotherapy. Recently, anti-epidermal growth factor receptor (EGFR) therapy has been introduced for TNBC patients. We engineered a novel nanobioconjugate based on a poly(β-L-malic acid) (PMLA) nanoplatform for TNBC treatment. The nanobioconjugate carries anti-tumor nucleosome-specific monoclonal antibody (mAb) 2C5 to target breast cancer cells, anti-mouse transferrin receptor (TfR) antibody for drug delivery through the host endothelial system, and Morpholino antisense oligonucleotide (AON) to inhibit EGFR synthesis. The nanobioconjugates variants were: (1) P (BioPolymer) with AON, 2C5 and anti-TfR for tumor endothelial and cancer cell targeting, and EGFR suppression (P/AON/2C5/TfR), and (2) P with AON and 2C5 (P/AON/2C5). Controls included (3) P with 2C5 but without AON (P/2C5), (4) PBS, and (5) P with PEG and leucine ester (LOEt) for endosomal escape (P/mPEG/LOEt). Drugs were injected intravenously to MDA-MB-468 TNBC bearing mice. Tissue accumulation of injected nanobioconjugates labeled with Alexa Fluor 680 was examined by Xenogen IVIS 200 (live imaging) and confocal microscopy of tissue sections. Levels of EGFR, phosphorylated and total Akt in tumor samples were detected by western blotting.

In vitro western blot showed that the leading nanobioconjugate P/AON/2C5/TfR inhibited EGFR synthesis significantly better than naked AON. In vivo imaging revealed that 2C5 increased drug-tumor accumulation. Significant tumor growth inhibition was observed in mice treated with the lead nanobioconjugate (1) [P = 0.03 vs. controls; P<0.05 vs. nanobioconjugate variant (2)]. Lead nanobioconjugate (1) also showed stronger inhibition of EGFR expression and Akt phosphorylation than other treatments. Treatment of TNBC with the new nanobioconjugate results in tumor growth arrest by inhibiting EGFR and its downstream signaling intermediate, phosphorylated Akt. The nanobioconjugate represents a new generation of nanodrugs for treatment of TNBC.

The basement membrane is a highly intricate and organized portion of the extracellular matrix that interfaces with a variety of cell types including epithelial, endothelial, muscle, nerve, and fat cells. The laminin family of glycoproteins is a major constituent of the basement membrane. The sixteen known laminin isoforms are formed from combinations of α, β, and γ chains, with each chain containing specific domains capable of interacting with cellular receptors such as integrins and other extracellular ligands. In addition to its role in the assembly and architectural integrity of the basement membrane, laminins interact with cells to influence proliferation, differentiation, adhesion, and migration, processes activated in normal and pathologic states. In vitro these functions are regulated by the posttranslational modifications of the individual laminin chains. In vivo laminin knock-out mouse studies have been particularly instructive in defining the function of specific laminins in mammalian development and have also highlighted its role as a key component of the basement membrane. In this review, we will define how laminin structure complements function and explore its role in both normal and pathologic processes.

Background

Laminins represent major components of basement membranes and play various roles in embryonic and adult tissues. The functional laminin molecule consists of three chains, alpha, beta and gamma, encoded by separate genes. There are twelve different laminin genes identified in mammals to date that are highly homologous in their sequence but different in their tissue distribution. The laminin alpha -1 gene was shown to have the most restricted expression pattern with strong expression in ocular structures, particularly in the developing and mature lens.

Results

We identified the zebrafish lama1 gene encoding a 3075-amino acid protein (lama1) that possesses strong identity with the human LAMA1. Zebrafish lama1 transcripts were detected at all stages of embryo development with the highest levels of expression in the developing lens, somites, nervous and urogenital systems. Translation of the lama1 gene was inhibited using two non-overlapping morpholino oligomers that were complementary to sequences surrounding translation initiation. Morphant embryos exhibited an arrest in lens development and abnormalities in the body axis length and curvature.

Conclusion

These results underline the importance of the laminin alpha 1 for normal ocular development and provide a basis for further analysis of its developmental roles.

Various invasive pathogens attach to host tissues via the extracellular matrix component laminin, the major glycoprotein found within basement membranes. Previous investigations identified the laminin-binding adhesin Tp0751 within the spirochete bacterium Treponema pallidum. In the current study, Tp0751 was shown to attach to a variety of laminin isoforms that are widely distributed throughout the host, including laminins 1, 2, 4, 8, and 10. Such universal attachment is conducive for an adhesin present within a highly invasive pathogen that encounters a variety of tissue sites during the course of infection. Additional studies systematically identified the amino acid residues within Tp0751 that contribute to laminin binding using synthetic peptides designed from the mature protein sequence. The minimum laminin-binding region of the adhesin was localized to 10 amino acids; peptides containing these residues inhibited attachment of Tp0751 and T. pallidum to laminin. Further, Tp0751-specific antibodies inhibited attachment of T. pallidum to laminin. This study furthers our knowledge of the interaction of T. pallidum with laminin, an association that is proposed to facilitate bacterial traversal of basement membranes and subsequent entry into the circulation and tissue invasion. As such, these investigations will reveal new targets for possible prevention of bacterial dissemination and establishment of chronic infection.

Contact of cultured mammary epithelial cells with the basement membrane protein laminin induces multiple responses, including cell shape changes, growth arrest, and, in the presence of prolactin, transcription of the milk protein β-casein. We sought to identify the specific laminin receptor(s) mediating the multiple cell responses to laminin. Using assays with clonal mammary epithelial cells, we reveal distinct functions for the α6β4 integrin, β1 integrins, and an E3 laminin receptor. Signals from laminin for β-casein expression were inhibited in the presence of function-blocking antibodies against both the α6 and β1 integrin subunits and by the laminin E3 fragment. The α6-blocking antibody perturbed signals mediated by the α6β4 integrin, and the β1-blocking antibody perturbed signals mediated by another integrin, the α subunit(s) of which remains to be determined. Neither α6- nor β1-blocking antibodies perturbed the cell shape changes resulting from cell exposure to laminin. However, the E3 laminin fragment and heparin both inhibited cell shape changes induced by laminin, thereby implicating an E3 laminin receptor in this function. These results elucidate the multiplicity of cell-extracellular matrix interactions required to integrate cell structure and signaling and ultimately permit normal cell function.

Laminins are large heterotrimeric, multidomain proteins that play a central role in organising and establishing all basement membranes. Despite a total of 45 potential heterotrimeric chain combinations formed through the coiled-coil domain of the 11 identified laminin chains (α1–5, β1–3, γ1–3), to date only 15 different laminin isoforms have been reported. This observation raises the question whether laminin assembly is regulated by differential gene expression or specific chain recognition. To address this issue, we here perform a complete analysis of laminin chain assembly and specificity. Using biochemical and biophysical techniques, all possible heterotrimeric combinations from recombinant C-terminal coiled-coil fragments of all chains were analysed. Apart from laminin 323 (α3, β2, γ3), for which no biochemical evidence of its existence in vivo is available, these experiments confirmed all other known laminin isoforms and identified two novel potential chain combinations, laminins 312 (α3, β1, γ2) and 422 (α4, β2, γ4). Our findings contribute to the understanding of basement membrane structure, function and diversity.

Laminin is a key component of the basement membrane and is involved in the structural scaffold and in cell proliferation and differentiation. Research has identified 19 laminin isoforms, which are assemblies of α, β, and γ chains (eg, the α1, β1, and γ1 chains form the laminin 111 isoform). Although laminin is known to be present in the anterior pituitary, the specific laminin isoforms have not been identified. This study used molecular biological and histochemical techniques—namely, RT-PCR, immunohistochemistry, and in situ hybridization—to identify the laminin isoforms and laminin-producing cells in rat anterior pituitary. RT-PCR showed that laminin α1, α3, and α4 genes were expressed in anterior pituitary. Immunohistochemistry revealed laminin α1 in gonadotrophs and laminin α4 in almost all vascular endothelial cells. Laminin α3 was seen in a subset of vascular endothelial cells. We then performed in situ hybridization to localize β and γ chains in these cells and found that laminin β1, β2, and γ1 were expressed in gonadotrophs and that laminin β1 and γ1 were expressed in endothelial cells. In conclusion, we identified gonadotroph-type (laminin 111 and 121) and vascular-type (laminin 411 and 311) laminin isoforms in rat anterior pituitary.

The laminin α4 chain, a component of laminin-8 and -9, is expressed in basement membranes, such as those beneath endothelia, the perineurium of peripheral nerves, and around developing muscle fibers. Laminin α4-null mice presented with hemorrhages during the embryonic and neonatal period and had extensive bleeding and deterioration of microvessel growth in experimental angiogenesis, as well as mild locomotion defects. Histological examination of newborn mice revealed delayed deposition of type IV collagen and nidogen into capillary basement membranes, and electron microscopy showed discontinuities in the lamina densa. The results demonstrate a central role for the laminin α4 chain in microvessel growth and, in the absence of other laminin α chains, in the composition of endothelial basement membranes.

Laminins have dramatic and varied actions on neurons in vitro. However, their in vivo function in brain development is not clear. Here we show that knockout of laminin γ1 in the cerebral cortex leads to defects in neuritogenesis and neuronal migration. In the mutant mice, cortical layer structures were disrupted, and axonal pathfinding was impaired. During development, loss of laminin expression impaired phosphorylation of FAK and paxillin, indicating defects in integrin signaling pathways. Moreover, both phosphorylation and protein levels of GSK-3β were significantly decreased, but only phosphorylation of AKT was affected in the mutant cortex. Knockout of laminin γ1 expression in vitro, dramatically inhibited neurite growth. These results indicate that laminin regulates neurite growth and neuronal migration via integrin signaling through the AKT/GSK-3β pathway, and thus reveal a novel mechanism of laminin function in brain development.

Directional migration of MDCK cells is regulated by the ratio of the deposited basement membrane proteins laminin-511 and laminin-332. Knockdown of laminin-511 or its receptor integrin α3 inhibits directional migration and destabilizes cell–cell contacts, disturbing the polarization machinery.

Sustained directional migration of epithelial cells is essential for regeneration of injured epithelia. Front–rear polarity of migrating cells is determined by local activation of a signaling network involving Cdc42 and other factors in response to spatial cues from the environment, the nature of which are obscure. We examined the roles of laminin (LM)-511 and LM-332, two structurally different laminin isoforms, in the migration of Madin–Darby canine kidney cells by suppressing expression of their α subunits using RNA interference. We determined that knockdown of LM-511 inhibits directional migration and destabilizes cell–cell contacts, in part by disturbing the localization and activity of the polarization machinery. Suppression of integrin α3, a laminin receptor subunit, in cells synthesizing normal amounts of both laminins has a similar effect as knockdown of LM-511. Surprisingly, simultaneous suppression of both laminin α5 and laminin α3 restores directional migration and cell–cell contact stability, suggesting that cells recognize a haptotactic gradient formed by a combination of laminins.

Laminins are large heterotrimeric cross-shaped extracellular matrix glycoproteins with terminal globular domains and a coiled-coil region through which the three chains are assembled and covalently linked. Laminins are key components of basement membranes, and they serve as attachment sites for cell adhesion, migration and proliferation. In this work, we produced a recombinant fragment comprising the entire laminin coiled-coil of the α1-, β1-, and γ1-chains that assemble into a stable heterotrimeric coiled-coil structure independently of the rest of the molecule. This domain was biologically active and not only failed to serve as a substrate for cell attachment, spreading and focal adhesion formation but also inhibited cell adhesion to laminin when added to cells in a soluble form at the time of seeding. Furthermore, gene array expression profiling in cells cultured in the presence of the laminin coiled-coil domain revealed up-regulation of genes involved in cell motility and invasion. These findings were confirmed by real-time quantitative PCR and zymography assays. In conclusion, this study shows for the first time that the laminin coiled-coil domain displays anti-adhesive functions and has potential implications for cell migration during matrix remodeling.

Laminin is a major glycoprotein of the basement membrane. Although its precise localization and orientation within this structure is unknown, it is presumably anchored to other macromolecules such as type IV collagen or proteoheparan sulfate. In vitro, laminin has the ability to self-assemble and to bind to type IV collagen molecules at distinct sites. To identify more precisely the domains of the complex, cross- shaped laminin molecule that are involved in these interactions, images of laminin-laminin dimers and laminin-type IV collagen complexes obtained by the rotary shadowing method were analyzed. We observed that the complex domain at the end of the long arm of laminin is predominantly involved in these interactions. By using Fab fragments of antibodies specific for a peptide fragment derived from this complex domain, it is shown that laminin self-assembly is inhibited in their presence, as measured by turbidity and by electron microscopy. In addition, these antibodies inhibit the specific interaction of laminin with type IV collagen. These data suggest that the complex domain at the end of the long arm of laminin contains binding sites of potential importance for the assembly of basement membranes.

Laminin-332 is a heterotrimeric basement membrane component comprised of the α3, ß3, and γ2 laminin chains. Laminin-332 modulates epithelial cell processes, such as adhesion, migration, and differentiation and is prominent in many embryonic and adult tissues. In skin, laminin-332 is secreted by keratinocytes and is a key component of hemidesmosomes connecting the keratinocytes to the underlying dermis. In mice, lack of expression of any of the three Laminin-332 chains result in impaired anchorage and detachment of the epidermis, similar to that seen in human junctional epidermolysis bullosa, and death occurs within a few days after birth. To bypass the early lethality of laminin-332 deficiency caused by the knockout of the mouse laminin γ2 chain, we expressed a dox-controllable human laminin γ2 transgene under a keratinocyte-specific promoter on the laminin γ2 (Lamc2) knockout background. These mice appear similar to their wild-type littermates, do not develop skin blisters, are fertile, and survive >1.5 years. Immunofluorescence analyses of the skin showed that human laminin γ2 colocalized with mouse laminin α3 and ß3 in the basement membrane zone underlying the epidermis. Furthermore, the presence of “humanized” laminin-332 in the epidermal basement membrane zone rescued the alterations in the deposition of hemidesmosomal components, such as plectin, collagen type XVII/BP180, and integrin α6 and ß4 chains, seen in conventional Lamc2 knockout mice, leading to restored formation of hemidesmosomes. These mice will be a valuable tool for studies of organs deficient in laminin-332 and the role of laminin-332 in skin, including wound healing.