Proteolytic modification of laminins: functional consequences

Laminin-derived peptide C16 regulates Tks expression and reactive oxygen species generation in human prostate cancer cells

Laminin peptides influence cancer biology. We investigated the role of a laminin-derived peptide C16 regulating invadopodia molecules in human prostate cancer cells (DU145). C16 augmented invadopodia activity of DU145 cells, and stimulated expression Tks4, Tks5, cortactin, and membrane-type matrix metalloproteinase 1. Reactive oxygen species generation is also related to invadopodia formation. This prompted us to address whether C16 would induce reactive oxygen species generation in DU145 cells. Quantitative fluorescence and flow cytometry showed that the peptide C16 increased reactive oxygen species in DU145 cells. Furthermore, significant colocalization between Tks5 and reactive oxygen species was observed in C16-treated cells. Results suggested that the peptide C16 increased Tks5 and reactive oxygen species in prostate cancer cells. The role of C16 increasing Tks and reactive oxygen species are novel findings on invadopodia activity.

Expression and localization of laminin 5, laminin 10, type IV collagen, and amelotin in adult murine gingiva

The biochemical composition of the internal and external basal laminae in the junctional epithelium differs significantly, and the precise cellular origin of their respective molecules remains to be determined. In the present study, the expression and localization of three basement membrane-specific molecules-laminin 5 (γ2 chain), type IV collagen (α1 chain), and laminin 10 (α5 chain)-and one tooth-specific molecule, amelotin, was analyzed in adult murine gingiva by using in situ hybridization and immunohistochemistry. The results showed that the outermost cells in junctional epithelium facing the tooth enamel strongly expressed laminin 5 mRNA, supporting the immunohistochemical staining data. This suggests that laminin 5 is actively synthesized in junctional epithelial cells and that the products are incorporated into the internal basal lamina to maintain firm epithelial adhesion to the tooth enamel throughout life. Conversely, no amelotin mRNA signals were detected in the junctional epithelial cells, suggesting that the molecules localized on the internal basal lamina are mainly derived from maturation-stage ameloblasts. Weak and sporadic expression of type IV collagen in addition to laminin 10 in the gingiva indicates that these molecules undergo turnover less frequently in adult animals.

Immobilization of Cell-Adhesive Laminin Peptides in Degradable PEGDA Hydrogels Influences Endothelial Cell Tubulogenesis

Attachment, spreading, and organization of endothelial cells into tubule networks are mediated by interactions between cells in the extracellular microenvironment. Laminins are key extracellular matrix components and regulators of cell adhesion, migration, and proliferation. In this study, laminin-derived peptides were conjugated to poly(ethylene glycol) (PEG) monoacrylate and covalently incorporated into degradable PEG diacrylate (PEGDA) hydrogels to investigate the influence of these peptides on endothelial cellular adhesion and function in organizing into tubule networks. Degradable PEGDA hydrogels were synthesized by incorporating a matrix metalloproteinase (MMP)–sensitive peptide, GGGPQGIWGQGK (abbreviated PQ), into the polymer backbone. The secretion of MMP-2 and MMP-9 by endothelial cells promotes polymer degradation and consequently cell migration. We demonstrate the formation of extensive networks of tubule-like structures by encapsulated human umbilical vein endothelial cells in hydrogels with immobilized synthetic peptides. The resulting structures were stabilized by pericyte precursor cells (10T1/2s) in vitro. During tubule formation and stabilization, extracellular matrix proteins such as collagen IV and laminin were deposited. Tubules formed in the matrix of metalloproteinase sensitive hydrogels were visualized from 7 days to 4 weeks in response to different combination of peptides. Moreover, hydrogels functionalized with laminin peptides and transplanted in a mouse cornea supported the ingrowth and attachment of endothelial cells to the hydrogel during angiogenesis. Results of this study illustrate the use of laminin-derived peptides as potential candidates for modification of biomaterials to support angiogenesis.

Autocrine transforming growth factor-{beta}1 activation mediated by integrin {alpha}V{beta}3 regulates transcriptional expression of laminin-332 in Madin-Darby canine kidney epithelial cells

Laminin (LM)-332 is an extracellular matrix protein that plays a structural role in normal tissues and is also important in facilitating recovery of epithelia from injury. We have shown that expression of LM-332 is up-regulated during renal epithelial regeneration after ischemic injury, but the molecular signals that control expression are unknown. Here, we demonstrate that in Madin-Darby canine kidney (MDCK) epithelial cells LM-332 expression occurs only in subconfluent cultures and is turned-off after a polarized epithelium has formed. Addition of active transforming growth factor (TGF)-β1 to confluent MDCK monolayers is sufficient to induce transcription of the LM α3 gene and LM-332 protein expression via the TGF-β type I receptor (TβR-I) and the Smad2-Smad4 complex. Significantly, we show that expression of LM-332 in MDCK cells is an autocrine response to endogenous TGF-β1 secretion and activation mediated by integrin αVβ3 because neutralizing antibodies block LM-332 production in subconfluent cells. In confluent cells, latent TGF-β1 is secreted apically, whereas TβR-I and integrin αVβ3 are localized basolaterally. Disruption of the epithelial barrier by mechanical injury activates TGF-β1, leading to LM-332 expression. Together, our data suggest a novel mechanism for triggering the production of LM-332 after epithelial injury.

The role of MAPK-ERK pathway in 67-kDa laminin receptor-induced FasL expression in human cholangiocarcinoma cells

BACKGROUND AND AIMS

Cancer cells are thought to possess immune evasion properties due to FasL overexpression in many types of human tumors. In the present study, we set out to investigate the role of MAPK-ERK pathway in 67-kDa laminin receptor induced FasL expression and FasL-mediated apoptosis in human cholangiocarcinoma cells.

METHODS

The expression of FasL and its promoter activity in cultured cholangiocarcinoma cells were examined after treatment with laminin or transfection with plasmids containing siRNA targeted to 67-kDa laminin receptor. The effects of MAPK-ERK cascade inhibitor and c-Myc inhibition by siRNA on 67-kDa laminin receptor-induced FasL expression were determined. Apoptosis assay was performed to analyze the apoptosis of lymphocytes cocultured with cholangiocarcinoma cells treated with or without MAPK-ERK cascade inhibitor.

RESULTS

Our results revealed that the specific MAPK-ERK cascade inhibitor, PD98059, significantly attenuated phosphorylation of c-Myc on Ser-62 and FasL upregulation in QBC-939 cells and these cells showed decreased cytotoxicity against Fas-sensitive Jurkat T cells. A luciferase reporter assay revealed that FasL promoter activity was significantly reduced in cells treated with PD98059 or transfected with c-Myc siRNA.

CONCLUSIONS

Based on these results, we conclude that 67LR induces FasL expression and cytotoxicity against Fas-sensitive Jurkat T cells in human cholangiocarcinoma cells through the phosphorylation of c-Myc on Ser-62 and the subsequent activation of the FasL promoter through the ERK pathway.

Expression and function of laminin and integrins on adhesion/migration of primary culture cells derived from rat oral epithelium

BACKGROUND AND OBJECTIVE

It remains controversial whether or not the junctional epithelium cells that are directly attached to teeth migrate on the enamel surface, as those cells are able to adhere firmly to the enamel. The aim of this study was to investigate the expression patterns of laminin gamma(2), integrin beta(4) and integrin alpha(3), and to examine their potential function in cell migration.

MATERIAL AND METHODS

Oral epithelium cells obtained from Sprague-Dawley rats were established in primary culture. We employed a wound-healing assay to characterize the direction of cell extension at the start of cell migration, and observed different localizations of laminin and integrins using immunofluorescence. For functional analyses of integrins, we employed a phosphatidylinositol-3-kinase (PI3K) activator to promote integrin beta(4) function and used P1B5 to inhibit integrin alpha(3) function, and we analyzed the percentage of re-epithelialization as the migration function.

RESULTS

Marked accumulation of laminin gamma(2) was detected in the peripheral cytoplasm of cells adjacent to the wound area, as shown by the results of the migration assay. Integrin beta(4) was detected in the distal cell processes of actively migrating cells, while integrin alpha(3) was found in cell membranes of cells adjacent to the wound area. In the functional analyses, the percentage of re-epithelialization was significantly lower in the PI3K-activator group and in the P1B5-treated group (2.5% and 7.2%, respectively) than in the control group (39.0%) (p < 0.01).

CONCLUSION

The results suggest that laminin gamma(2) is secreted as a foothold for cell migration, that integrin beta(4) participates in cell adhesion and that integrin alpha(3) is involved in cell migration in the primary culture cells.

Regulated laminin-332 expression in human islets of Langerhans

Laminin-332 (LN-332) is a basement membrane component known to exert a beneficial effect on rat pancreatic beta cells in vitro. In this work, we analyzed the expression of LN-332 in human islets, its expression after inflammatory insults by cytokines, and the molecular mechanisms responsible for this effect. By Western blotting and RT-PCR, we showed that LN-332 was expressed in isolated human islets. By immunofluorescence on pancreas sections, we observed that labeling was confined to endocrine cells in islets. Confocal microscopy analysis on isolated islet cells revealed that labeling was granular but did not colocalize with hormone secretory granules. LN-332 was most abundant in cultured islets compared to freshly isolated islets and was found in culture medium, which suggests that it was secreted by islets. When islets were exposed to interleukin (IL)-1beta, expression and secretion of LN-332 increased as compared to control. No effect was observed with tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma. LY294002, an inhibitor of phosphatidylinositol 3-kinase (PI3-K) activity, inhibited culture- and IL-1beta-induced LN-332 expression in islets. These results show that LN-332, known to have some beneficial effect on beta cells in vitro, is produced and secreted by endocrine islet cells and is up-regulated by stressing conditions such as culture and IL-1beta-exposure.

Involvement of laminin and integrins in adhesion and migration of junctional epithelium cells

BACKGROUND AND OBJECTIVE

The junctional epithelium attaches to the enamel surface with hemidesmosomes (of which laminin-5 and integrin-alpha(6)beta(4) are the main components) in the internal basal lamina. Laminin-5 is also involved in cell motility with integrin-alpha(3)beta(1), although their functions have not yet been clarified.The purpose of this study was to determine the functions of those adhesive components between the tooth and the junctional epithelium during cell migration.Because an idea has been proposed that directly attached to tooth cells (DAT cells) may not contribute to cell migration, 5-bromo-2-deoxyuridine staining was performed to confirm cell migration.

MATERIAL AND METHODS

We investigated laminin-gamma(2) (contained only in laminin-5), integrin-beta(4) (involved in cell-extracellular matrix contact) and integrin-alpha(3) (inducing cell migration) in the junctional epithelium, oral gingival epithelium and gingival sulcus epithelium of 6-wk-old ICR mice using laser microdissection, quantitative real-time reverse transcription-polymerase chain reaction, immunofluorescence and 5-bromo-2-deoxyuridine staining.

RESULTS

Laminin and integrins were clearly immuno-localized in the basal lamina of all epithelium. Quantitative analysis of laminin and integrin mRNAs by laser microdissection showed that they were more highly expressed in DAT cells than in basal cells in the oral gingival epithelium. In particular, a 12-fold higher expression of laminin-5 was observed in the junctional epithelium compared with the oral gingival epithelium. 5-Bromo-2-deoxyuridine staining showed rapid coronal migration of DAT cells.

CONCLUSION

These results suggest that the abundant expression of laminin-5 and integrin-alpha(6)beta(4) is involved in the attachment of DAT cells to teeth by hemidesmosomes. Abundant expression of laminin-5 and integrin-alpha(3)beta(1) might assist in DAT cell migration, confirmed by 5-bromo-2-deoxyuridine staining during the turnover of junctional epithelium.

Human laminin-332 degradation by Candida proteinases

BACKGROUND

Human laminin-332 (Lm-332) degradation by 12 Candida strains and effects of synthetic proteinase inhibitors [Ilomastat (ILM), EDTA, chemically modified tetracycline-3(CMT-3), CMT-308, synthetic peptide CTT-2, and Pefabloc] were studied.

MATERIALS AND METHODS

Laminin-332 was incubated with sonicated cell fractions and 10 times concentrated cell-free fractions of reference and clinical strains of C. albicans, C. dubliniensis, C. guilliermondii, C. glabrata, C. krusei, and C. tropicalis. Proteolysis, pH effects, and inhibitors were analyzed by fluorography and zymography.

RESULTS

Cell fractions of all species except C. guilliermondii and cell-free fractions of C. albicans, and C. dubliniensis showed 20-70 kDa gelatinases at pH 5.0 and 6.0. At pH 7.6, C. glabrata, C. krusei, and C. tropicalis cell fractions and C. tropicalis cell-free fractions showed 55-70 kDa gelatinases. CMT-3, CMT-308, and CTT-2 inhibited Candida gelatinases slightly better than Pefabloc, ILM, and EDTA. No Candida fractions degraded Lm-332 at pH 7.6, but at pH 5.0, 100 kDa bands were generated by cell fractions of C. dubliniensis and C. tropicalis; C. albicans and C. glabrata clinical strains; and C. guilliermondii reference strain. C. krusei reference strain yielded three 100-130 kDa bands. C. albicans, C. dubliniensis, and C. tropicalis reference and clinical strain's cell-free fractions generated 100 kDa band.

CONCLUSIONS

Laminin-332 degradation is pH-dependent and differences exist between studied Candida strains. Lm-332 degradation can exert functional disturbances on basement membrane integrity, possibly aiding Candida cell invasion into tissues. Certain synthetic matrix metalloproteinase inhibitors (CMTs, CTT) can inhibit Candida proteinases and may be therapeutically useful in future.

Adhesion and protease activity in cell lines from human salivary gland tumors are regulated by the laminin-derived peptide AG73, syndecan-1 and beta1 integrin

We studied the induction of protease activity by the laminin alpha1-derived peptide AG73 in cells from adenoid cystic carcinoma (CAC2) and myoepithelioma (M1), respectively a malignant and a benign salivary gland tumors. Laminin alpha1 chain and MMP9 were immunolocalized in adenoid cystic carcinoma and myoepithelioma in vivo and in vitro. Cells grown inside AG73-enriched laminin-111 exhibited large spaces in the extracellular matrix, suggestive of remodeling. The broad spectrum MMP inhibitor GM6001 decreased spaces induced by AG73 in CAC2 and M1 cells. This result strongly suggests that AG73-mediated matrix remodeling involves matrix metalloproteinases. CAC2 and M1 cells cultured on AG73 showed a dose-dependent increase of MMP9 secretion, as detected by zymography. Furthermore, siRNA silencing of MMP9 decreased remodeling in 3D cultures. We searched for AG73 receptors regulating MMP9 activity in our cell lines. CAC2 and M1 cells grown on AG73 exhibited colocalization of syndecan-1 and beta1 integrin. siRNA knockdown of syndecan-1 expression in these cells resulted in decreased adhesion to AG73 and reduced protease and remodeling activity. We investigated syndecan-1 co-receptors in both cell lines. Silencing beta1 integrin inhibited adhesion to AG73, matrix remodeling and protease activity. Double-knockdown experiments were carried out to further explore syndecan-1 and beta1 integrin cooperation. CAC2 cells transfected with both syndecan-1 and beta1 integrin siRNA oligos showed significant decrease in adhesion to AG73. Simultaneous silencing of receptors also induced a decrease in protease activity. Our results suggest that syndecan-1 and beta1 integrin signaling downstream of AG73 regulate adhesion and MMP production by CAC2 and M1 cells.

The C-terminus of the gamma 2 chain but not of the beta 3 chain of laminin-332 is indirectly but indispensably necessary for integrin-mediated cell reactions

Using a recombinant mini-laminin-332, we showed that truncation of the three C-terminal amino acids of the gamma 2 chain, but not of the C-terminal amino acid of the beta 3 chain, completely abolished alpha 3 beta 1 integrin binding and its cellular functions, such as attachment and spreading. However, a synthetic peptide mimicking the gamma 2 chain C-terminus did not interfere with alpha 3 beta 1 integrin binding or cell adhesion and spreading on laminin-332 as measured by protein interaction assays and electric cell-substrate impedance sensing. Nor was the soluble peptide able to restore the loss of integrin-mediated cell adhesiveness to mini-laminin-332 after deletion of the gamma 2 chain C-terminus. These findings spoke against the hypothesis that the gamma 2 chain C-terminus of laminin-332 is a part of the alpha 3 beta 1 integrin interaction site. In addition, structural studies with electron microscopy showed that truncation of the gamma 2 chain C-terminus opened up the compact supradomain structure of LG1-3 domains. Thus, by inducing or stabilizing an integrin binding-competent conformation or array of the LG1-3 domains, the gamma 2 chain C-terminus plays an indirect but essential role in laminin-332 recognition by alpha 3 beta 1 integrin and, hence, its cellular functions.

SIKVAV, a laminin alpha1-derived peptide, interacts with integrins and increases protease activity of a human salivary gland adenoid cystic carcinoma cell line through the ERK 1/2 signaling pathway

Adenoid cystic carcinoma is a frequently occurring malignant salivary gland neoplasm. We studied the induction of protease activity by the laminin-derived peptide, SIKVAV, in cells (CAC2) derived from this neoplasm. Laminin alpha1 and matrix metalloproteinases (MMPs) 2 and 9 were immunolocalized in adenoid cystic carcinoma cells in vivo and in vitro. CAC2 cells cultured on SIKVAV showed a dose-dependent increase of MMP9 as detected by zymography and colocalization of alpha3 and alpha6 integrins. Small interfering RNA (siRNA) knockdown of integrin expression in CAC2 cells resulted in decreased adhesion to the peptide. SIKVAV affinity chromatography and immunoblot analysis showed that alpha3, alpha6, and beta1 integrins were eluted from the SIKVAV column, which was confirmed by mass spectrometry and a solid-phase binding assay. Small interfering RNA experiments also showed that these integrins, through extracellular signal-regulated kinase (ERK) 1/2 signaling, regulate MMP secretion induced by SIKVAV in CAC2 cells. We propose that SIKVAV increases protease activity of a human salivary gland adenoid cystic carcinoma cell line through alpha3beta1 and alpha6beta1 integrins and the ERK 1/2 signaling pathway.

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.

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.

Regulated synthesis and functions of laminin 5 in polarized madin-darby canine kidney epithelial cells

Renal tubular epithelial cells synthesize laminin (LN)5 during regeneration of the epithelium after ischemic injury. LN5 is a truncated laminin isoform of particular importance in the epidermis, but it is also constitutively expressed in a number of other epithelia. To investigate the role of LN5 in morphogenesis of a simple renal epithelium, we examined the synthesis and function of LN5 in the spreading, proliferation, wound-edge migration, and apical-basal polarization of Madin-Darby canine kidney (MDCK) cells. MDCK cells synthesize LN5 only when subconfluent, and they degrade the existing LN5 matrix when confluent. Through the use of small-interfering RNA to knockdown the LN5 alpha3 subunit, we were able to demonstrate that LN5 is necessary for cell proliferation and efficient wound-edge migration, but not apical-basal polarization. Surprisingly, suppression of LN5 production caused cells to spread much more extensively than normal on uncoated surfaces, and exogenous keratinocyte LN5 was unable to rescue this phenotype. MDCK cells also synthesized laminin alpha5, a component of LN10, that independent studies suggest may form an assembled basal lamina important for polarization. Overall, our findings indicate that LN5 is likely to play an important role in regulating cell spreading, migration, and proliferation during reconstitution of a continuous epithelium.

Laminin 5 regulates polycystic kidney cell proliferation and cyst formation

Renal cyst formation is the hallmark of autosomal dominant polycystic kidney disease (ADPKD). ADPKD cyst-lining cells have an increased proliferation rate and are surrounded by an abnormal extracellular matrix (ECM). We have previously shown that Laminin 5 (Ln-5, a alpha(3)beta(3)gamma(2) trimer) is aberrantly expressed in the pericystic ECM of ADPKD kidneys. We report that ADPKD cells in primary cultures produce and secrete Ln-5 that is incorporated to the pericystic ECM in an in vitro model of cystogenesis. In monolayers, purified Ln-5 induces ERK activation and proliferation of ADPKD cells, whereas upon epidermal growth factor stimulation blocking endogenously produced Ln-5 with anti-gamma(2) chain antibody reduces the sustained ERK activation and inhibits proliferation. In three-dimensional gel culture, addition of purified Ln-5 stimulates cell proliferation and cyst formation, whereas blocking endogenous Ln-5 strongly inhibits cyst formation. Ligation of alpha(6)beta(4) integrin, a major Ln-5 receptor aberrantly expressed by ADPKD cells, induces beta(4) integrin phosphorylation, ERK activation, cell proliferation, and cyst formation. These findings indicate that Ln-5 is an important regulator of ADPKD cell proliferation and cystogenesis and suggest that Ln-5 gamma(2) chain and Ln-5-alpha(6)beta(4) integrin interaction both contribute to these phenotypic changes.

Integrin α6β1-laminin interactions regulate early myotome formation in the mouse embryo

We addressed the potential role of cell-laminin interactions during epaxial myotome formation in the mouse embryo. Assembly of the myotomal laminin matrix occurs as epaxial myogenic precursor cells enter the myotome. Most Myf5-positive and myogenin-negative myogenic precursor cells localise near assembled laminin, while myogenin-expressing cells are located either away from this matrix or in areas where it is being assembled. In Myf5nlacZ/nlacZ (Myf5-null) embryos, laminin,collagen type IV and perlecan are present extracellularly near myogenic precursor cells, but do not form a basement membrane and cells are not contained in the myotomal compartment. Unlike wild-type myogenic precursor cells, Myf5-null cells do not express the α6β1 integrin, a laminin receptor, suggesting that integrin α6β1-laminin interactions are required for myotomal laminin matrix assembly. Blockingα6β1-laminin binding in cultured wild-type mouse embryo explants resulted in dispersion of Myf5-positive cells, a phenotype also seen in Myf5nlacZ/nlacZ embryos. Furthermore, inhibition ofα6β1 resulted in an increase in Myf5 protein and ectopic myogenin expression in dermomyotomal cells, suggesting that α6β1-laminin interactions normally repress myogenesis in the dermomyotome. We conclude that Myf5 is required for maintaining α6β1 expression on myogenic precursor cells, and that α6β1 is necessary for myotomal laminin matrix assembly and cell guidance into the myotome. Engagement of laminin byα6β1 also plays a role in maintaining the undifferentiated state of cells in the dermomyotome prior to their entry into the myotome.

Proteolytic processing of the laminin alpha3 G domain mediates assembly of hemidesmosomes but has no role on keratinocyte migration

Laminin-5 (Lm5), the major adhesion ligand of basal epithelial cells, undergoes complex extracellular proteolytic processing that influences cell adhesion and migration. In tumor cell lines, the proteolytic truncation of the C-terminal G domain of the Lm alpha3 chain induces assembly of hemidesmosomes and downregulates cell migration. To define the biological functions of the alpha3 G domain processing in physiological conditions, we have expressed a series of mutant alpha3 complementary DNA in human primary alpha3-null keratinocytes immortalized by human papillomavirus E6E7 (HKalpha3 cells). Using monolayer and organotypic cell cultures we show that: (1) the hinge region between subdomains G3 and G4 carries the proteolytic cleavage sites; (2) nucleation of the hemidesmosomal proteins is independent of the proteolytic maturation of the alpha3 G domain, whereas formation of mature hemidesmosomes relies on proteolytic cleavage of alpha3; and (3) the proteolytic processing plays no role in cell migration, which suggests that nucleation of hemidesmosomal structures in culture does not reflect the migratory potential of the epithelial cells. Our results also demonstrate that HKalpha3 cells are a unique model system, which will be useful to dissect the functions and molecular interactions of Lm5.

Membrane type 1 matrix metalloprotease cleaves laminin-10 and promotes prostate cancer cell migration

Disruption of the extracellular matrix by proteases is crucial for tumor invasion. Laminin-10 (Ln-10) has previously been identified as a substrate for cell migration and cell adhesion, and is present in the basal lamina (BL) of both normal prostate and prostate cancer. Here, we investigate a role for membrane type 1 matrix metalloprotease (MT1-MMP) in modifying this Ln-10-rich BL. MT1-MMP is a transmembrane member of the MMP family that has been demonstrated to be upregulated as prostate cancer progresses from normal to prostate intraepithelial neoplasia to invasive cancer, suggesting a role for MT1-MMP in the invasion of prostate cancer. We show that MT1-MMP cleaves the alpha5 chain of purified human Ln-10 from its 350-kDa form into 310-, 190-, 160-, and 45-kDa fragments. This cleavage causes a decrease in DU-145 prostate cancer cell adhesion to purified Ln-10, and an increase in transmigration of DU-145 cells through cleaved Ln-10. We also show that prostate cancer cells expressing membrane-bound MT1-MMP cleave the alpha5 chain of Ln-10. Ln alpha5-chain cleavage is also observed in human prostate cancer tissues. These findings suggest that prostate cancer cells expressing high levels of MT1-MMP have increased invasive potential through their ability to degrade and invade Ln-10 barriers.

Uncoordinated production of Laminin-5 chains in airways epithelium of allergic asthmatics

BACKGROUND

Laminins are a group of proteins largely responsible for the anchorage of cells to basement membranes. We hypothesized that altered Laminin chain production in the bronchial mucosa might explain the phenomenon of epithelial cell shedding in asthma. The aim was to characterize the presence of Laminin chains in the SEBM and epithelium in allergic and non-allergic asthmatics.

PATIENTS AND METHODS

Biopsies were taken from the bronchi of 11 patients with allergic and 9 patients with non-allergic asthma and from 7 controls and stained with antibodies against the Laminin (ln) chains alpha1-alpha5, beta1-beta2 and gamma1-gamma2.

RESULTS

Lns-2,-5 and -10 were the main Laminins of SEBM. The layer of ln-10 was thicker in the two asthmatic groups while an increased thickness of lns-2 and -5 was only seen in allergic asthmatics. The ln gamma2-chain, which is only found in ln 5, was exclusively expressed in epithelial cells in association with epithelial injury and in the columnar epithelium of allergic asthmatics.

CONCLUSION

The uncoordinated production of chains of ln-5 in allergic asthma could have a bearing on the poor epithelial cell anchorage in these patients.

Epithelial cell motility on laminin-5: regulation by matrix assembly, proteolysis, integrins and erbB receptors

Cell migration plays a central role in a wide variety of biological events, including embryogenesis, inflammatory immune response, wound healing, or cancer invasion. Tight regulation of cell motility is a prerequisite for normal development and maintenance of an organism, and to avoid metastatic spread of tumor cells. An important determinant of migratory efficiency is the substrate over which a cell migrates. Laminin-5 (Ln-5) is an extracellular matrix component prominent in basement membranes and as such it is a substrate in direct contact with epithelial cells. Interestingly, Ln-5 has been shown to both stimulate and downregulate epithelial cell migration. In this article, we plan to give an overview on the different mechanisms cells employ to regulate their migratory behavior on Ln-5. We will discuss how proteolytic processing of Ln-5 acts as posttranslational modification that plays a major role in the regulation of cell migration. The different proteolytic Ln-5 species may bind to distinct cell surface receptors called integrins, which translate substrate binding into a specific cellular response that triggers cell motility. Furthermore, interaction between Ln-5-binding integrins and other transmembrane and cytoplasmic proteins increases complexity and may allow fine-tuning of cell migration in response to the cellular environment.

Recombinant human laminin-5 domains. Effects of heterotrimerization, proteolytic processing, and N-glycosylation on alpha3beta1 integrin binding

Human laminin-5 fragments, comprising the heterotrimeric C-terminal part of the coiled-coil (CC) domain and the globular (G) domain with defined numbers of LG subdomains, were produced recombinantly. The alpha3' chain with all five LG subdomains was processed proteolytically in a manner similar to the wild-type alpha3 chain. Conditions were established under which the proteolytic cleavage was either inhibited in cell culture or was brought to completion in vitro. The shorter chains of the laminin-5CCG molecule, beta3'and gamma2', produced in a bacterial expression system associated into heterodimers, which then combined spontaneously with the alpha3' chains in vitro to form heterotrimeric laminin-5CCG molecules. Only heterotrimeric laminin-5CCG with at least subdomains LG1-3, but not the single chains, supported binding of soluble alpha3beta1 integrin, proving the coiled-coil domain of laminin-5 to be essential for its interaction with alpha3beta1 integrin. The N-glycosylation sites in wild-type alpha3 chain were mapped by mass spectrometry. Their location in a structural model of the LG domain suggested that large regions on both faces of the LG1 and LG2 domains are inaccessible by other proteins. However, neither heterotrimerization nor alpha3beta1 integrin binding was affected by the loss of N-linked glycoconjugates. After the proteolytic cleavage between the subdomains LG3 and LG4, the LG4-5 tandem domain dissociated from the rest of the G domain. Further, the laminin-5CCG molecule with the alpha3'LG1-3 chain showed an increased binding affinity for alpha3beta1 integrin, indicating that proteolytic processing of laminin-5 influences its interaction with alpha3beta1 integrin.

The basement membrane matrix in malignancy

Cancer is the second most common cause of death among Americans, although for several age groups it ranks first. Most of these deaths are not due to the primary tumour but rather to tumour cell metastases to distant organs. There are many steps that lead to metastasis, all of which are being studied with the goal of preventing these fatalities. Normally, cells attach to the extracellular matrix to maintain tissue integrity. During cancer progression, cells become more motile and acquire invasive qualities. Tumour cells move along blood and lymph vessels or invade into them to travel to distant sites. Then, the tumour cells must attach to the vessel wall, extravasate from the vessel, invade the new tissue, proliferate, and form a secondary tumour. Angiogenesis, the formation of new blood vessels, is critical to survival of these cells at the new site and is also important for primary tumour growth and spread. Tumour cell metastasis is a complex cascade of sequential steps, each of which is not yet fully understood. Progress has been made in identifying several key activators, one of which is the extracellular matrix. A major tumour promoter is the glycoprotein laminin, which is predominantly found in the extracellular matrix produced by endothelial and epithelial cells. This review will follow the metastatic process with particular attention to the effect of laminin on tumour cells.

Identification of redundant angiogenic sites in laminin alpha1 and gamma1 chains

The degradation of the extracellular matrix is one of the first steps involved in angiogenesis, the formation of new vessels from preexisting ones. Laminin, a large extracellular matrix protein, has many biological activities, including the promotion of angiogenesis. Screening of the laminin-1 chains identified 20 angiogenic peptides, of which, A13 and C16, from the alpha1 and gamma1 chains, respectively, were the most active. We recently identified the receptors for C16 as the integrins alpha5beta1 and alphavbeta3. Here, we show unexpectedly that A13 is a redundant active site to C16 present in the N-terminal globular domain of the alpha1 chain. The peptides are located in homologous sites present in the last globular domains of their respective chains, and their amino acids are 66% conserved, as compared to the inactive homologous site in the beta1 chain, B19 to B20, which is only 18%-23% conserved. Cell attachment studies demonstrated that both A13 and C16 reciprocally inhibited their adhesion activity, whereas the corresponding laminin beta1 chain peptides were inactive. Chorioallantoic membrane assays showed that the in vivo angiogenic activity of A13 is blocked by a C16 antagonist, C16S, which also binds to the same integrin receptors. A13 affinity chromatography and immunoprecipitation analysis showed that the alphavbeta3 and alpha5beta1 integrin receptors bind to this sequence. We have therefore identified redundant activity on two laminin chains. These highly conserved functional sites are likely important mediators of the biological responses of laminins because either one or both of these chains (active sites) are present in almost all laminin isoforms identified to date.

Laminin chain expression suggests that laminin-10 is a major isoform in the mouse hippocampus and is degraded by the tissue plasminogen activator/plasmin protease cascade during excitotoxic injury

Laminins are important components of the extracellular matrix, and participate in neuronal development, survival and regeneration. The tissue plasminogen activator/plasmin extracellular protease cascade and downstream laminin degradation are implicated in excitotoxin-induced neuronal degeneration. To determine which specific laminin chains are involved, we investigated the expression of laminins in the hippocampus, and the cell types expressing them. Reverse transcription-PCR demonstrated that the messenger RNAs for all laminin chains could be detected in the hippocampus. To determine the localization of laminin chain expression, immunostaining was used. This method showed that alpha5, beta1 and gamma1 are most highly expressed in the neuronal cell layers. Immunoblotting confirmed the hippocampal expression of the chains alpha5, beta1 and gamma1, and RNA in situ hybridization showed a neuronal expression pattern of alpha5, beta1 and gamma1. At early time points following intrahippocampal injection of kainate, alpha5, beta1 and gamma1 chain immunoreactivities were lost. In addition, tissue plasminogen activator-deficient mice, which are resistant to kainate-induced neuronal death, show no significant change in laminins alpha5, beta1 and gamma1 after intrahippocampal kainate injection. Taken together, these results suggest that laminin-10 (alpha5-beta1-gamma1) comprises a major neuronal laminin in the mouse hippocampus, and is degraded before neuronal death during excitotoxic injury by the tissue plasminogen activator/plasmin protease cascade. By identifying a neuronal laminin (laminin-10) that participates in neuronal degeneration after excitotoxic injury, this study clarifies the molecular definition of the extracellular matrix in the hippocampus and further defines a pathway for mechanisms of neuronal death.

Laminin modulates morphogenic properties of the collagen XVIII endostatin domain

We have shown previously that the oligomeric endostatin domain of collagen XVIII (NC1) functioned as a motility-inducing factor regulating the extracellular matrix-dependent morphogenesis of endothelial cells. This motogenic activity gave rise to structures resembling filipodia and lamellipodia and was dependent on Rac, Cdc42, and mitogen-activated protein kinase. Here, we demonstrate that these properties of endostatin are primarily mediated by laminin in the basement membrane and heparan sulfates on the cell surface. The sites of interaction between laminin and oligomeric endostain include the N-terminal regions of all three laminin chains (amino acids 204-1243 of the alpha chain, 932-1161 of the beta chain, and 150-965 of the gamma chain). A monoclonal antibody that blocks the interactions between endostatin and laminin was utilized to inhibit the motogenic activity of endostatin. In parallel, we have engineered selective point mutations and produced recombinant forms that lack binding to heparan sulfates on the cell surface. Our data are consistent with a model of endostatin with two binding sites: one mainly to laminin in the basement membrane and the other to heparan sulfates on the cell surface. The two binding domains on endostatin appear to be separate with the possibility of some overlap between the two sites.

Function of laminins and laminin-binding integrins in gingival epithelial cell adhesion

BACKGROUND

In human gingiva, epithelial cells attach to their adjacent tissues by means of specialized molecular adhesion complexes and a basement membrane. Little is known about the synthesis of adhesion proteins by gingival keratinocytes; we, therefore, studied how cultured immortalized gingival epithelial cells produce laminins and express laminin-binding integrins. We presumed that different laminins and integrins would be involved in the adhesion of gingival epithelial cells.

METHODS

We cultured gingival keratinocytes and studied their production of laminins and expression of integrins using immunofluorescence microscopy, immunoprecipitation, and immunoblotting methods and by quantitative cell adhesion experiments. We also studied how gingival tissue expresses these adhesion proteins in vivo by using immunofluorescence microscopy.

RESULTS

In immunofluorescence microscopy, the cells were seen to organize chains of laminin-5 (alpha3beta03gamma2) to extracellular patches, whereas the alpha5 chain of laminin-10 (alpha5betalgamma1) could only be seen intracellularly. Of the laminin-binding integrin subunits, integrin a6 subunit was organized to dotted arrays, typical of prehemidesmosomal adhesions, whereas integrin alpha3 subunit was located at cell-cell junctions, in prehemidesmosomal structures, and at some locations also in small focal-contact like patches. Integrin beta1 subunit was found at cell-cell junctions and in focal contacts. Immunoprecipitation experiments showed that the cells synthesize and secrete chains of laminin-5 and laminin-10. In quantitative cell adhesion experiments, the cells adhered efficiently to these laminins by using cooperatively integrin alpha3beta1 and alpha6beta1 integrin complexes. None of the other known laminin-binding integrin subunits appeared to be significantly involved in cell adhesion to these laminin isoforms.

CONCLUSIONS

Our results provide new information on gingival epithelial cell adhesion and extracellular matrix production and may thus aid in the understanding of periodontal physiology.

The junctional epithelium around murine teeth differs from gingival epithelium in its basement membrane composition

It is not known whether epithelial differentiation patterns are reflected in the composition of gingival basement membranes (BMs). We have investigated the expression of laminin isoforms and associated BM components in the murine dento-epithelial junction by using immunofluorescence microscopy. Our results show that chains of laminins 5/6/7/10/11 are expressed in the BM of outer gingival epithelium. The external BM between junctional epithelium (JE) and connective tissue differs from gingival BM by lacking laminin-7 and -11 chains. The internal basal lamina (IBL) between JE and tooth contains only laminin-5. Collagen chains alpha1,2(IV) and nidogen-1 are present in other BMs except the IBL. The dento-epithelial junction thus has a unique BM composition, suggesting that epithelial cells are able to secrete two extracellular matrices in a polarized manner. The exclusive expression of the non-self-polymerizing laminin-5 indicates that the IBL is not a BM by definition, but rather a simple extracellular matrix lacking network structure.

Overexpression of laminin alpha1 chain in colonic cancer cells induces an increase in tumor growth

Laminins represent a growing family of glycoproteins constituting the basement membrane. They are known to direct many biological processes. With respect to carcinogenesis, laminins play an important role in cell adhesion, mitogenesis, differentiation and even metastasis. To further study the biological significance of laminin-1 (composed of alpha1, beta1 and gamma1 chains) in intestinal cell differentiation or tumorigenesis, an alpha1-laminin expression vector was introduced into the HT29 colonic cancer cells, in which laminin alpha1 chain is not expressed. Upon transfection of the alpha1 chain, the alpha1beta1gamma1 trimer was found secreted in the media along with free alpha1 chain as assessed by immunoprecipitation. The presence of the laminin alpha1 chain did not significantly modify the levels of the other laminin chains nor the integrins expressed by the HT29 cells. In spite of similar growth properties with the control cells in vitro (plastic dish, soft agar), the laminin alpha1 transfectants showed a significantly increased tumor growth when injected in nude mice. Histologic and immunohistochemic examination of the laminin alpha1-expressing tumors points to an increased recruitment of the host stromal and vascular cells, without modification in the differentiation profile and invasion potential. In parallel, a clear accumulation of laminin-10 (alpha5beta1gamma1) at the carcinoma/stromal interface and a segregation of the integrin beta4 subunit at the basal pole of the cancer cells occurred, compared to control tumors. Overall, our observations emphasize the importance of laminin-1 as a chemoattractant of both stromal and vascular cells and in epithelial/stromal cell interactions for the organization of the basement membrane and segregation of integrins leading to an epithelial cell growth signal. Such a sequence of events is reminiscent of what occurs during development.

A comparative quantitative analysis of laminin-5 in the basement membrane of normal, hyperplastic, and malignant oral mucosa by confocal immunofluorescence imaging

Laminin-5 (Ln-5) is a heterotrimeric basement membrane (BM) molecule (alpha3beta3gamma2). It is a principal protein constituent of the anchoring filaments, which connect the BM with the hemidesmosomes of the basal keratinocytes and possess a crucial function in keratinocyte adhesion. Confocal immunofluorescence imaging is introduced for a quantitative evaluation of the Ln-5 content in the BM of oral squamous epithelium. The BM of normal oral mucosa was used as a reference (100%) for comparative analysis and showed a nearly uniform Ln-5 immunofluorescence intensity (99-100%). In all hyperplastic lesions of oral mucosa, the Ln-5 immunofluorescence intensity was increased (107-141%). The increased Ln-5 content in the BM of hyperplastic lesions suggests an increased keratinocyte-BM adhesion, possibly resulting in a higher stability of the oral mucosa. In contrast, in the oral squamous cell carcinoma (OSCC) invasive front, the remaining BM segments were characterized by a decrease in Ln-5 immunofluorescence intensity (35-74%). A stronger decrease of Ln-5-linked kerationocyte-BM adhesion correlates with a higher tumor grade. Because in central areas of carcinoma BM segments with a normal Ln-5 content could be demonstrated, the fundamental Ln-5 diminution in BM segments of the invasive front should be considered as an invasion-associated phenomenon.