Laminin-5 inhibits human keratinocyte migration

p51/p63 Controls Subunit α3 of the Major Epidermis Integrin Anchoring the Stem Cells to the Niche

p51/p63, a member of the tumor suppressor p53 gene family, is crucial for skin development. We describe here identification of ITGA3 encoding integrin alpha(3) as a target of its trans-activating function, proposing that p51/p63 allows epidermal stem cells to express laminin receptor alpha(3)beta(1) for anchorage to the basement membrane. When activated by genotoxic stress or overexpressed ectopically in non-adherent cells, p51/p63 transduced a phenotype to attach to extracellular matrices, which was accompanied by expression of ITGA3. Motifs matching the p53-binding consensus sequence were located in a scattered form in intron 1 of human ITGA3, and served as p51/p63-responsive elements in reporter assays. In addition to the trans-activating ability of the TA isoform, we detected a positive effect of the DeltaN isoform on ITGA3. The high level alpha(3) production in human keratinocyte stem cells diminished upon elimination of p51/p63 by small interfering RNA or by Ca(2+)-induced differentiation. Furthermore, a chromatin immunoprecipitation experiment indicated a physical interaction of p51/p63 with intron 1 of ITGA3. This study provides a molecular basis for the standing hypothesis that p51/p63 is essential for epidermal-mesenchymal interactions.

Signals that Initiate, Augment, and Provide Directionality for Human Keratinocyte Motility

Human keratinocytes (HK) migration plays a critical role in the re-epithelialization of acute skin wounds. Although extracellular matrices (ECM) and growth factors (GF) are the two major pro-motility signals, their functional relationship remains unclear. We investigated how ECM and GF regulate HK motility under defined conditions: (1) in the absence of GF and ECM and (2) with or without GF with cells apposed to a known pro-motility ECM. Our results show that HK migrate on selected ECM even in the total absence of GF. This suggests that certain ECM alone are able to "initiate" HK migration. Unlike ECM, however, GF alone cannot initiate HK migration. HK cannot properly migrate when plated in the presence of GF, regardless of the concentration, without an ECM substratum. The role of GF, instead, is to augment ECM-initiated motility and provide directionality. To gain insights into the mechanism of action by ECM and GF, we compared, side-by-side, the roles of three major mitogen-activated protein kinase cascades, extracellular-signal-regulated kinase (ERK)1/2, p38, and c-Jun N-terminal kinase (JNK). Our data show that ERK1/2 is involved in mediating collagen's initiation signal and GF's augmentation signal. p38 is specific for GF's augmentation signal. JNK is uninvolved in HK motility. Constitutively activated p38 and ERK1/2 alone could not initiate HK migration. Co-expression of both constitutively activated p38 and ERK1/2, however, could partially mimic the pro-motility effects of collagen and GF. This study reveals for the first time the specific functions of ECM and GF in cell motility.

Effectiveness of Adjunctive Low-Dose Doxycycline Therapy on Clinical Parameters and Gingival Crevicular Fluid Laminin-5 γ2 Chain Levels in Chronic Periodontitis

BACKGROUND

Laminin-5 (Ln-5) is involved in the apical migration of epithelial cells during the development of periodontal pockets. Low-dose doxycycline (LDD) can therapeutically modulate the host response with its non-antimicrobial properties. In the present randomized, double-blind, placebo-controlled, parallel arm study, the effectiveness of LDD in combination with non-surgical periodontal therapy on gingival crevicular fluid (GCF) Ln-5 gamma2 chain fragment levels and clinical parameters in patients with chronic periodontitis was examined over a 12-month period.

METHODS

GCF samples were collected and clinical parameters including probing depth (PD), clinical attachment level, gingival index (GI), and plaque index were recorded. Thirty chronic periodontitis patients were randomized either to low-dose doxcycline or placebo groups. LDD group received doxycycline (20 mg, b.i.d.) for 3 months plus scaling and root planing (SRP), while placebo group was given placebo capsules b.i.d. for 3 months plus SRP. The patients were evaluated every 3 months during the 12-month study period. All clinical parameters and GCF sampling were repeated at each visit. GCF Ln-5 gamma2 chain fragment levels were determined by Western immunoblotting using specific antibody and quantitated by computerized image analysis. Friedman test was used for intragroup comparisons followed by Wilcoxon signed rank test to analyze significance of changes over time. The Mann-Whitney test was used to determine differences between both LDD and placebo groups.

RESULTS

Both groups revealed significant improvements in all clinical parameters over the 12-month period (P < 0.0125). LDD group showed a significantly greater reduction in the mean PD scores at 9 and 12 months and in the mean GI scores at all time points than the placebo group (P < 0.05). In the LDD group, GCF Ln-5 gamma2 chain fragment levels were significantly reduced at 3 months (P < 0.0125) and then slightly increased during the rest of the study period. In the placebo group, GCF 45 and 70 kDa Ln-5 gamma2 chain fragments tended to decrease at 3 months compared to baseline, but did not reach significance; these levels continued to increase throughout the remainder of the study period. GCF Ln-5 gamma2 chain fragment levels in LDD group were significantly lower than those of the placebo group during the study period (P < 0.05).

CONCLUSIONS

The present data indicate that LDD therapy in combination with SRP therapy can reduce GCF Ln-5 gamma2 chain fragment levels and improve clinical periodontal parameters in patients with chronic periodontitis. Since matrix metalloproteinases (MMP)-mediated fragmentation of laminin-5 can contribute to pocket formation by stimulating epithelial cell migration, the reduction of Ln-5 gamma2 chain fragment levels could provide a new mechanism by which LDD, adjunctive to SRP, inhibits periodontal disease more effectively than SRP alone. Thus, these results provide extended and additional information about the effectiveness of the LDD therapy as an adjunct to non-surgical periodontal therapy in the long-term management of periodontal disease.

Physiological and Pathological Roles of α3β1 Integrin

Alpha3beta1 integrin has been considered to be a mysterious adhesion molecule due to the pleiotropy in its ligand-binding specificity. However, recent studies have identified laminin isoforms as high-affinity ligands for this integrin, and demonstrated that alpha3beta1 integrin plays a number of essential roles in development and differentiation, mainly by mediating the establishment and maintenance of epithelial tissues. Furthermore, alpha3beta1 integrin is also implicated in many other biological phenomena, including cell growth and apoptosis, angiogenesis and neural functions. This integrin receptor forms complexes with various other membrane proteins, such as the transmembrane-4 superfamily proteins (tetraspanins), cytoskeletal proteins and signaling molecules. Recently, lines of evidence have been reported showing that complex formation regulates integrin functions in cell adhesion and migration, signal transduction across cell membranes, and cytoskeletal organization. In addition to these roles in physiological processes, alpha3beta1 integrin performs crucial functions in various pathological processes, especially in wound healing, tumor invasion and metastasis, and infection by pathogenic microorganisms.

The basement membrane protein laminin-5 acts as a soluble cell motility factor

One of the basement membrane (BM) proteins, laminin-5 (LN5), is known to support efficient cell adhesion and migration through interaction with integrins on the basal plasma membrane. Here, we show that a soluble form of LN5 induced migration of human epithelial cells and carcinoma cells by interacting with integrins on the apical cell surface. Although both LN5 and laminin-10/11 (LN10/11) promoted cell migration when coated onto a plastic surface as insoluble substrata, only LN5 stimulated cell migration in its soluble form on other substrata such as fibronectin (FN), vitronectin (VN) and collagen. Soluble LN5 interacted with integrins alpha3beta1 and alpha6beta1 on the apical cell surface and stimulated cell migration, while the cell morphology was largely dependent on the underlying substratum. Thus, integrin signals from the apical surface and the basal surface synergistically regulated cytoskeletal organization and cell motility. Soluble and insoluble LN5 induced cell motility by activating signal pathways via protein kinase C (PKC), phosphoinositide 3-OH kinase (PI3-K) and MAP kinase. The PKC dependency was more prominent for soluble LN5 than insoluble LN5, and was absent in the stimulation by insoluble LN10/11. In vitro scratch assays with keratinocytes, self-produced soluble LN5 bound to the apical cell surface of migrating cells at the scratched edges, suggesting that soluble LN5 may contribute to cell migration in pathological conditions such as wound healing and tumor invasion.

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.

Laminin 5 deposition regulates keratinocyte polarization and persistent migration

Repair of wounded epidermis requires both keratinocyte migration and deposition of laminin 5 over exposed dermal collagen. To understand the coupling between leading cell migration and laminin 5 deposition, we developed a novel migration assay using time-lapse microscopy. We demonstrate that in migrating, human keratinocytes the deposition of laminin 5 promoted 'processive migration', characterized by stable cell polarization that was tightly coupled to persistent, linear migration in the absence of a chemotactic gradient. Processive migration required deposition of laminin 5, which was restricted to the rear of the polar cell. Integrin alpha 3 beta 1 interacted with these laminin 5 deposits at contact sites that did not require actin-dependent cross-linking. Further, we show that the migrating cells switched adhesion by integrin alpha 2 beta 1 on collagen at the front of the cell to integrin alpha 3 beta 1 on exogenous laminin 5 at the rear of the cell. Along with this switch of integrin usage was the removal of collagen from sites under the cell that precisely correlated with deposition of laminin 5. Processive migration was blocked with suppressors of microtubule dynamics (nocodazole and taxol) or rottlerin, a PKC-delta inhibitor. These drugs were also shown to block deposition of laminin 5 but, surprisingly, constitutive secretion was unimpaired, suggesting deposition was a regulated event. Thus, at the front of the cell, the leading lamellipodium was stabilized through integrin interactions in focal complexes with the exogenous substratum. However, at the rear of the cell, stable cell polarization and linear migration was promoted by laminin 5 deposits and integrin alpha 3 beta 1.

Thymosin beta 4 stimulates laminin-5 production independent of TGF-beta

Thymosin beta 4 (Tbeta(4)) stimulates epithelial cell migration and promotes laminin-5 (LM-5) expression. Using gene expression analysis with human corneal epithelial cells treated with Tbeta(4), we find that both LM-5 gamma2 chain and transforming growth factor beta 1 (TGFbeta-1) are increased by more than 2-fold over untreated cells. These findings were confirmed by RT-PCR and at the protein level. Although TGFbeta-1 increases LM-5 synthesis in a dose-dependent manner, it does not appear to be the mechanism by which Tbeta(4) acts on LM-5 gamma2 chain synthesis based on three independent experiments. In a time-course analysis, Tbeta(4) increases LM-5 gamma2 chain expression at 2 h and peaks at 6 h, while TGFbeta-1 increases LM-5 gamma2 chain expression only at 4 h and peaks at 8 h. When Tbeta(4)-induced LM-5 gamma2 chain expression is blocked with neutralizing antibodies to TGFbeta-1, LM-5 gamma2 chain expression is increased. Finally, in TGFbeta-1 knock-out mice, Tbeta(4) increases LM-5 gamma2 chain expression to levels higher than that observed in wild-type mice treated with Tbeta(4). These findings demonstrate that Tbeta(4) induces both TGFbeta-1 and LM-5 gamma2 chain expression in corneal epithelial cells. Tbeta(4) and TGFbeta-1 increase LM-5 gamma2 chain expression by independent pathways. Suppression of TGFbeta-1 further increases LM-5 gamma2 chain expression.

Normal human keratinocytes bind to the alpha3LG4/5 domain of unprocessed laminin-5 through the receptor syndecan-1

Basal keratinocytes of the epidermis adhere to their underlying basement membrane through a specific interaction with laminin-5, which is composed by the association of alpha3, beta3, and gamma2 chains. Laminin-5 has the ability to induce either stable cell adhesion or migration depending on specific processing of different parts of the molecule. One event results in the cleavage of the carboxyl-terminal globular domains 4 and 5 (LG4/5) of the alpha3 chain. In this study, we recombinantly expressed the human alpha3LG4/5 fragment in mammalian cells, and we show that this fragment induces adhesion of normal human keratinocytes and fibrosarcoma-derived HT1080 cells in a heparan- and chondroitin sulfate-dependent manner. Immunoprecipitation experiments with Na2 35SO4-labeled keratinocyte and HT1080 cell lysates as well as immunoblotting experiments revealed that the major proteoglycan receptor for the alpha3LG4/5 fragment is syndecan-1. Syndecan-4 from keratinocytes also bound to alpha3LG4/5. Furthermore we could show for the first time that unprocessed laminin-5 specifically binds syndecan-1, while processed laminin-5 does not. These results demonstrate that the LG4/5 modules within unprocessed laminin-5 permit its cell binding activity through heparan and chondroitin sulfate chains of syndecan-1 and reinforce previous data suggesting specific properties for the precursor molecule.

Co-expression of p16(INK4A) and laminin 5 gamma2 by microinvasive and superficial squamous cell carcinomas in vivo and by migrating wound and senescent keratinocytes in culture

The high frequency of mutation, deletion, and promoter silencing of the gene encoding p16(INK4A) (p16) in premalignant dysplasias and squamous cell carcinomas (SCC) of epidermis and oral epithelium classifies p16 as a tumor suppressor. However, the point during neoplastic progression at which this protein is expressed and presumably impedes formation of an SCC is unknown. Induction of p16 has been found to be responsible for the senescence arrest of normal human keratinocytes in culture, suggesting the possibility that excessive or spatially abnormal cell growth in vivo triggers p16 expression. We examined 73 skin and oral mucosal biopsy specimens immunohistochemically to test this hypothesis. p16 was not detectable in benign hyperplastic lesions, but instead was expressed heterogeneously in some dysplastic and carcinoma in situ lesions and consistently at areas of microinvasion and at superficial margins of advanced SCCs. p16-positive cells in these regions coexpressed the gamma2 chain of laminin 5, identified previously as a marker of invasion in some carcinomas. Normal keratinocytes undergoing senescence arrest in culture proved to coordinately express p16 and gamma2 and this was frequently associated with increased directional motility. Keratinocytes at the edges of wounds made in confluent early passage cultures also coexpressed p16 and gamma2, accompanying migration to fill the wound. These results have identified the point during neoplastic progression in stratified squamous epithelial at which the tumor suppressor p16 is expressed and suggest that normal epithelia may use the same mechanism to generate non-dividing, motile cells for wound repair.

Inflammatory mediators in wound healing

This article provides much evidence that the inflammatory process has direct effects on normal and abnormal wound healing. As better understanding develops for the mechanism for these outcomes, targeted proinflammatory and anti-inflammatory interventions are likely to be successful. When inflammation is maintained as a regulated and orchestrated response, effective and normal wound healing is likely to result.

Wound bed preparation: a systematic approach to wound management

The healing process in acute wounds has been extensively studied and the knowledge derived from these studies has often been extrapolated to the care of chronic wounds, on the assumption that nonhealing chronic wounds were simply aberrations of the normal tissue repair process. However, this approach is less than satisfactory, as the chronic wound healing process differs in many important respects from that seen in acute wounds. In chronic wounds, the orderly sequence of events seen in acute wounds becomes disrupted or "stuck" at one or more of the different stages of wound healing. For the normal repair process to resume, the barrier to healing must be identified and removed through application of the correct techniques. It is important, therefore, to understand the molecular events that are involved in the wound healing process in order to select the most appropriate intervention. Wound bed preparation is the management of a wound in order to accelerate endogenous healing or to facilitate the effectiveness of other therapeutic measures. Experts in wound management consider that wound bed preparation is an important concept with significant potential as an educational tool in wound management. This article was developed after a meeting of wound healing experts in June 2002 and is intended to provide an overview of the current status, role, and key elements of wound bed preparation. Readers will be able to examine the following issues; the current status of wound bed preparation; an analysis of the acute and chronic wound environments; how wound healing can take place in these environments; the role of wound bed preparation in the clinic; the clinical and cellular components of the wound bed preparation concept; a detailed analysis of the components of wound bed preparation.

Keratinocyte motility induced by TGF-beta1 is accompanied by dramatic changes in cellular interactions with laminin 5

Transforming growth factor-beta1 (TGF-beta1) has the ability to induce epithelial cell migration while stopping proliferation. In this study, we show that, concomitant to promoting migration of normal human keratinocytes in vitro, TGF-beta1 induced a marked decrease in their adhesion capacity to processed alpha3-containing laminin 5-coated surfaces. Indeed, the expression levels of alpha3 and alpha6 integrin subunit mRNA and protein, as well as the cell surface alpha3beta1 and alpha6beta4 integrins, were down-regulated. Recent studies showed that keratinocytes over express and deposit laminin 5 during migration and we have shown that laminin 5 found in the matrix of TGF-beta1 induced migrating keratinocytes is present in its unprocessed form [Décline and Rousselle, 2001: J. Cell Sci. 114:811-823]. We show here that TGF-beta1 treatment of the cells promoted a significant increase in their adhesion to the alpha3 chain carboxy-terminal LG4/5 subdomain and that this interaction is likely to be mediated by a heparan sulfate proteoglycan type of receptor. Our results indicate that alpha6beta4 and alpha3beta1 integrin interactions with laminin 5 are diminished during migration while a specific interaction occurs between an additional cellular receptor and the alpha3 LG4/5 module present on unprocessed laminin 5.

Induction of a laminin isoform and alpha(3)beta(1)-integrin in renal ischemic injury and repair in vivo

Ischemic injury to the kidney, a major cause of acute renal failure, leads to the detachment and loss of numerous tubular epithelial cells. Integrin-laminin interactions may promote regeneration of the damaged epithelium by influencing kidney epithelial cell adhesion and differentiation. Laminins are major structural components of basement membranes. Of the various laminin isoforms, laminin-5 is of particular interest because of its proposed role in the healing of skin wounds. In this study, we investigate the expression of laminin-5 in rat kidney after unilateral ischemia. Using a polyclonal antibody generated against laminin-5, we find that immunostaining is confined to the basement membranes of collecting ducts in the papilla and the major and minor calyces in normal kidney. With injury and regeneration, however, immunostaining becomes much more intense and widespread in basement membranes along the nephron. Immunoblotting of ischemic kidney extracts reveals significantly increased expression of a polypeptide of approximately 220 kDa, possibly corresponding to a precursor of one of the three laminin-5 chains. Immunoblotting and immunostaining also demonstrate significantly increased expression and altered localization of the alpha(3)-integrin subunit, a receptor for laminin-5. These results indicate that there is induction of a laminin isoform, possibly laminin-5, and alpha(3)beta(1)-integrin in the ischemic kidney and may implicate this receptor-ligand combination in the pathogenesis of acute renal failure and/or repair of the injured kidney epithelium.

Transmembrane collagen XVII, an epithelial adhesion protein, is shed from the cell surface by ADAMs

Collagen XVII, a type II transmembrane protein and epithelial adhesion molecule, can be proteolytically shed from the cell surface to generate a soluble collagen. Here we investigated the release of the ectodomain and identified the enzymes involved. After surface biotinylation of keratinocytes, the ectodomain was detectable in the medium within minutes and remained stable for >48 h. Shedding was enhanced by phorbol esters and inhibited by metalloprotease inhibitors, including hydroxamates and TIMP-3, but not by inhibitors of other protease classes or by TIMP-2. This profile implicated MMPs or ADAMs as candidate sheddases. MMP-2, MMP-9 and MT1-MMP were excluded, but TACE, ADAM-10 and ADAM-9 were shown to be expressed in keratinocytes and to be actively involved. Transfection with cDNAs for the three ADAMs resulted in increased shedding and, vice versa, in TACE-deficient cells shedding was significantly reduced, indicating that transmembrane collagen XVII represents a novel class of substrates for ADAMs. Functionally, release of the ectodomain of collagen XVII from the cell surface was associated with altered keratinocyte motility in vitro.

Decreased expression of alpha3 and beta1 integrin subunits is responsible for differentiation-associated changes in cells behavior in terminally differentiated human oral keratinocytes

Primary normal human oral keratinocytes (NHOKs) terminally differentiate in serial subculture. To investigate whether this subculture-induced differentiation of NHOKs affects integrin expression and cell-matrix interaction, we studied the expression levels of integrin subunits and cellular response to the extracellular matrix (ECM) proteins in NHOKs at different population doublings. The phosphorylation statuses of focal adhesion kinase (FAK), extracellular signal regulated kinase (ERK), p38, and c-Jun amino-terminal kinase (JNK) were also determined in NHOK cells cultured on ECM proteins, to evaluate the functions of integrins with respect to cellular responses to ECM proteins. The expression levels of alpha3 and beta1 integrin subunits progressively decreased in NHOKs undergoing terminal differentiation. The ability of NHOKs to spread upon laminin and type I collagen significantly decreased in terminally differentiated oral keratinocytes. Keratinocyte migration was significantly increased on type I collagen for terminally differentiated NHOKs. Similar results were seen following preincubation of rapidly proliferating NHOKs with function-blocking antibodies to alpha3 or beta1 integrin subunit. In contrast, fibronectin had no effect on cellular responses in NHOKs, which were almost negligible in the expression levels of alpha5 integrin subunits. The extent of FAK phosphorylation in terminally differentiated NHOKs was notably lower than that of rapidly proliferating cells, but was enhanced in terminally differentiated cells that were cultured on type I collagen. Our results indicate that decreased expression of alpha3 and beta1 integrin subunits is responsible for differentiation-associated changes in cells behavior in terminally differentiated oral keratinocytes. Our data also show that the abrogation of the alpha5beta1 integrin function caused by omitting alpha5 subunit is linked to the loss of a cell-fibronectin interaction in human oral keratinocytes.

Expression of eotaxin, an eosinophil-selective chemokine, parallels eosinophil accumulation in the vesiculobullous stage of incontinentia pigmenti

Incontinentia pigmenti (IP) is an X-linked dominant genodermatosis primarily affecting female children. The initial vesiculobullous stage of IP is characterized clinically by inflammatory papules, blisters, and pustules, and histopathologically by acanthosis, keratinocyte necrosis, epidermal spongiosis and massive epidermal eosinophil infiltration. The cause of this multisystem disease is attributed to the mutations of an X-linked regulatory gene, termed nuclear factor-kappaB essential modulator (NEMO). The exact mechanism of epidermal eosinophil accumulation has not yet been determined. We explored the possible role of an eosinophil-selective, nuclear factor-kappaB-activated chemokine, eotaxin, in the accumulation of eosinophils in the initial stage of the disease. Monoclonal antibody (6H9) specific for human eotaxin strongly labelled the suprabasal epidermis of IP skin, paralleling the upper epidermal accumulation of eosinophils, but did not label the epidermis of normal skin or lesional skin from patients with other inflammatory skin diseases not characterized by prominent eosinophil accumulation, namely dermatitis herpetiformis and selected cases of atopic dermatitis lacking significant numbers of eosinophils. In addition, endothelial cells in lesional skin of IP also exhibited strong expression of eotaxin, which correlated with perivascular and intravascular eosinophil infiltration. We also examined the in vitro effects on epidermally derived eotaxin of several cytokines that were nuclear factor-kappaB-activated and/or known to induce eotaxin expression. In normal human keratinocytes, proinflammatory cytokines either independently (IL-1alpha) or synergistically (tumour necrosis factor-alpha (TNF-alpha)/ interferon-gamma (IFN-gamma) and TNF-alpha/IL-4) up-regulated eotaxin expression. These studies suggest that release of cytokines during the initial inflammatory stage of IP induces epidermal expression of eotaxin, which may play a role in the epidermal accumulation of eosinophils.

Mechanisms of wound reepithelialization: hints from a tissue-engineered reconstructed skin to long-standing questions

Wound closure of epithelial tissues must occur efficiently to restore rapidly their barrier function. We have developed a tissue-engineered wound-healing model composed of human skin keratinocytes and fibroblasts to better understand the mechanisms of reepithelialization. It allowed us to quantify the reepithelialization rate, which was significantly accelerated in the presence of fibrin or platelet-rich plasma. The reepithelialization of these 6 mm excisional wounds required the contribution of keratinocyte proliferation, migration, stratification, and differentiation. The epidermis regenerated progressively from the surrounding wound margins. After 3 days, the neoepidermis showed a complete spectrum of changes. Near the wound margin, the differentiation of the neoepidermis (keratins 1/10, filaggrin, and loricrin) and regeneration of the dermoepidermal junction (laminin 5 and collagen IV) were more advanced than toward the wound center, where the proliferative index was significantly increased. The spatial distribution of keratinocytes distinguished by particular features suggests two complementary mechanisms of reepithelialization: 1) the passive displacement of the superficial layers near the wound margin that would rapidly regenerate a barrier function and 2) the crawling of keratinocytes over each other at the tip of the progressing neoepidermis. Therefore, this study brings a new perspective to long-standing questions concerning wound reepithelialization.

Extracellular matrix and keratinocyte migration

We are just beginning to understand some of the cellular mechanisms involved in human keratinocyte migration on extracellular matrix. Extracellular matrix components have differing effects on keratinocyte motility. Signalling through integrin receptors and secretion of collagenase are both components of this process. An understanding of the effect of extracellular matrix on keratinocyte migration has direct relevance to the problem of wound re-epithelialization and will assist in the development of therapeutic efforts to enhance wound healing artificially.

The short arm of the laminin gamma2 chain plays a pivotal role in the incorporation of laminin 5 into the extracellular matrix and in cell adhesion

Laminin 5 is a basement membrane component that actively promotes adhesion and migration of epithelial cells. Laminin 5 undergoes extracellular proteolysis of the γ2 chain that removes the NH₂-terminal short arm of the polypeptide and reduces the size of laminin 5 from 440 to 400 kD. The functional consequence of this event remains obscure, although lines of evidence indicate that cleavage of the γ2 chain potently stimulated scattering and migration of keratinocytes and cancer cells. To define the biological role of the γ2 chain short arm, we expressed mutated γ2 cDNAs into immortalized γ2-null keratinocytes. By immunofluorescence and immunohistochemical studies, cell detachment, and adhesion assays, we found that the γ2 short arm drives deposition of laminin 5 into the extracellular matrix (ECM) and sustains cell adhesion. Our results demonstrate that the unprocessed 440-kD form of laminin 5 is a biologically active adhesion ligand, and that the γ2 globular domain IV is involved in intermolecular interactions that mediate integration of laminin 5 in the ECM and cell attachment.

Reduced expression of the epithelial adhesion ligand laminin 5 in the skin causes intradermal tissue separation

Laminin 5, the major keratinocyte adhesion ligand, is found in the lamina lucida subregion of the epidermal basement membrane of the skin, where it colocalizes with the anchoring filaments. Mutations in the genes encoding laminin 5 cause junctional epidermolysis bullosa, an inherited skin blistering disease characterized by abnormal hemidesmosomes and cleavage of the lamina lucida leading to epidermal detachment. In this work we describe the genetic basis of a new subtype of lethal inherited epidermolysis bullosa associated with reduced skin reactivity to laminin 5, presence of mature hemidesmosomes, and intradermal cleavage of the skin. The epidermolysis bullosa patients were heterozygous for a nonsense mutation (Q896X) and a splice site mutation (764-10T-->G) in the gene (LAMC2) for the gamma2 chain of laminin 5. The nonsense mutation causes accelerated decay of the corresponding mRNA, while the splice site mutation results in maturation of a cryptic wild-type gamma2 mRNA leading to reduced expression of wild-type laminin 5. In vitro studies using the probands' keratinocytes showed that secretion of reduced amounts of functional laminin 5 in the patient, although permitting formation of hemidesmosomes, fail to restore efficient cell adhesion. Our results provide the first evidence that laminin 5 contributes to the firm adhesion of the epithelial basement membrane to the underlying stroma. They also show that a low expression level of laminin 5 induces assembly of mature hemidesmosomes in vivo but fails to assure a stable cohesion of the dermal-epidermal junction.

Inhibitory role of alpha 6 beta 4-associated erbB-2 and phosphoinositide 3-kinase in keratinocyte haptotactic migration dependent on alpha 3 beta 1 integrin

Keratinocytes and other epithelial cells express two receptors for the basement membrane (BM) extracellular matrix component laminin-5 (Ln-5), integrins alpha 3 beta 1 and alpha 6 beta 4. While alpha 3 beta 1 mediates adhesion, spreading, and migration (Kreidberg, J.A. 2000. Curr. Opin. Cell Biol. 12:548--553), alpha 6 beta 4 is involved in BM anchorage via hemidesmosomes (Borradori, L., and A. Sonnenberg. 1999. J. Invest. Dermatol. 112:411--418). We investigated a possible regulatory interplay between alpha 3 beta 1 and alpha 6 beta 4 in cell motility using HaCaT keratinocytes as a model. We found that alpha 6 beta 4 antibodies inhibit alpha 3 beta 1-mediated migration on Ln-5, but only when migration is haptotactic (i.e., spontaneous or stimulated by alpha 3 beta 1 activation), and not when chemotactic (i.e., triggered by epidermal growth factor receptor). Inhibition of migration by alpha 6 beta 4 depends upon phosphoinositide 3-kinase (PI3-K) since it is abolished by PI3-K blockers and by dominant-negative PI3-K, and constitutively active PI3-K prevents haptotaxis. In HaCaT cells incubated with anti-alpha 6 beta 4 antibodies, activation of PI3-K is mediated by alpha 6 beta 4-associated erbB-2, as indicated by erbB-2 autophosphorylation and erbB-2/p85 PI3-K coprecipitation. Furthermore, dominant-negative erbB-2 abolishes inhibition of haptotaxis by anti-alpha 6 beta 4 antibodies. These results support a model whereby (a) haptotactic cell migration on Ln-5 is regulated by concerted action of alpha 3beta 1 and alpha 6 beta 4 integrins, (b) alpha 6 beta 4-associated erbB-2 and PI3-K negatively affect haptotaxis, and (c) chemotaxis on Ln-5 is not affected by alpha 6 beta 4 antibodies and may require PI3-K activity. This model could be of general relevance to motility of epithelial cells in contact with BM.

Loss of alpha3beta1 integrin function results in an altered differentiation program in the mouse submandibular gland

Mammalian submandibular gland (SMG) development leads to the establishment of highly organized secretory acinar and nonsecretory ductal epithelial cells. The ability of maturing salivary epithelial cells to attain their differentiated state has been shown to depend, in part, on interactions between extracellular matrix (ECM) proteins and their integrin receptors. In a search for key regulators of salivary cell lineage, we have studied alpha3beta1 integrin, a receptor for the basement membrane protein laminin, by characterizing embryonic day 18 (E18) SMGs isolated from mice carrying a targeted mutation in the alpha3 integrin gene. Transmission electron microscopy studies showed that the mutant SMGs exhibited an aberrant differentiation phenotype with defects in the apical-basal polarity axis and in the basement membrane. Based on immunohistochemistry and Western blot analyses, the alpha3beta1-deficient SMGs had altered expression and/or localization of several ECM and adhesive molecules, including laminin beta1, fibronectin, alpha5 integrin, and E-cadherin. These changes correlated with alterations in the activation state of Ras-extracellular signal-regulated kinase (ERK), as well as the expression and/or localization of Cdc42 and RhoA, two Rho GTPases that regulate the organization of the actin cytoskeleton. We conclude that alpha3beta1 is required for normal salivary cell differentiation and that its absence affects multiple components of adhesive complexes and their associated signalling pathways.

Keratinocyte migration requires alpha2beta1 integrin-mediated interaction with the laminin 5 gamma2 chain

Keratinocyte migration is an absolute requirement for correct epithelialization during the process of wound healing. This process requires changes in extracellular matrix ligand expression as well as changes in ligand-binding affinity of the corresponding cellular integrins. In this study, we attempt to understand the role of laminin 5 in migration by investigating the integrin-mediated interactions of migrating keratinocytes with their newly synthesized laminin 5. We chose to induce migration of freshly isolated NHK in vitro by exposing them to TGF-beta1 which, in addition to promoting epithelial cell migration, is also known to prevent cell proliferation. This important feature allowed the study to be focused on cell migration without interfering with cell proliferation. We confirm that keratinocyte migration on plastic, fibronectin or collagen IV substrates requires endogenous laminin 5 deposition, which is predominantly detected under its unprocessed form. Despite a crucial role for laminin 5 in migration, we show that this process is accompanied by a significant decrease in adhesion to purified laminin 5. Moreover, we provide evidence that the alpha2beta1 integrin interaction with newly synthesized laminin 5 renders the cells more adherent and retards migration. Conversely, we provide evidence that the alpha2beta1 integrin-laminin 5 interaction is absolutely required for keratinocyte migration and that the alpha2beta1 integrin is responsible for cell spreading on laminin 5. Finally, we demonstrate that the alpha2beta1 integrin binding to laminin 5 occurs within the short arm of the gamma2 subunit.

Laminin synthesis and the adhesion characteristics of immortalized human corneal epithelial cells to laminin isoforms

We have studied the synthesis of laminins (Ln) and determined the specific integrins mediating the adhesion of immortalized human corneal epithelial cells to mouse Ln-1, and human Lns-5 and -10. Immunofluorescence microscopy of the cells demonstrated integrin alpha(2), alpha(3), alpha(6), beta(1)and beta(4)subunits, integrins alpha(6)and beta(4)being found in a typical 'leopard-skin' like manner. Immunoprecipitation studies showed that the cells produced alpha 3, beta 3 and gamma 2 chains of Ln-5, but not Lns-1 or -10. In culture Ln-5 was found as small plaques beneath the adhering cells within 1 hr, while in 4 hr widely spread Ln-5 plaques were observed in colocalization with beta(4)integrin subunit. By using a quantitative cell adhesion assay and function-blocking monoclonal antibodies we showed that integrin beta(1)subunit plays a role in mediating corneal epithelial cell adhesion to mouse Ln-1. However, none of the available function-blocking antibodies to integrin alpha-subunits inhibited the adhesion. Integrin alpha(3)beta(1)complex mediated the adhesion of corneal epithelial cells to human Lns-5 and -10. Integrin complex alpha(3)beta(1), as well as laminin alpha(3)chain, was also shown to mediate cell adhesion to newly produced endogenous Ln-5. The present results show that integrin alpha(3)beta(1)complex mediates the adhesion of corneal epithelial cells to Lns-5 and -10, while a yet unknown integrin alpha subunit appears to play a role in the adhesion to Ln-1. The results also show that among corneal basement membrane laminins, Ln-5 is synthetized by epithelial cells while Ln-10 may be a product of keratocytes.

Tumor cell budding and laminin-5 expression in colorectal carcinoma can be modulated by the tissue micro-environment

Expression of laminin-5 alpha3, beta3 and gamma2 protein subunits was investigated in colorectal adenocarcinomas using immunostaining and confocal microscopy. The laminin-5 heterotrimer was found in basement membranes and as extracellular deposits in tumor stroma. In contrast to the alpha3 subunit, which was under-expressed, the gamma2 and beta3 subunits were detected in the cytoplasm of carcinoma cells dissociating (budding) from neoplastic tubules, suggestive of focal alterations in laminin-5 assembly and secretion. Laminin-5 gamma2 or beta3 subunit-reactive budding carcinoma cells expressed cytokeratins but not vimentin; they did not proliferate and were not apoptotic. Furthermore, expression of laminin-5 gamma2 and beta3 subunits in budding cells was associated with focal under-expression of the E-cadherin-beta-catenin complex. Results from xenograft experiments showed that budding activity in colorectal adenocarcinomas could be suppressed when these tumors grew at ectopic s.c. sites in nude mice. In vitro, cultured colon carcinoma cells, but not adenoma-derived tumor cells, shared the laminin-5 phenotype expressed by carcinoma cells in vivo. Using colon carcinoma cell lines implanted orthotopically and invading the cecum of nude mice, the laminin-5-associated budding was restored, indicating that this phenotype is not only determined by tumor cell properties but also dependent on the tissue micro-environment. Our results indicate that both laminin-5 alpha3 subunit expression and cell-cell cohesiveness are altered in budding carcinoma cells, which we consider to be actively invading. We propose that the local tissue micro-environment contributes to these events.

Stromelysin-2 is upregulated during normal wound repair and is induced by cytokines

Stromelysin-2 is a matrix metalloproteinase that degrades in vitro several protein components relevant to wound repair such as collagens III and IV, gelatin, nidogen, laminin-1, proteoglycans, and elastin. Furthermore, it can activate other matrix metalloproteinases, such as collagenase-1 (matrix metalloproteinase-1) and collagenase-2 (matrix metalloproteinase-8), as well as 92 kDa gelatinase. The aim of this study was to determine in a large variety of wounds (normally healing dermal and mucosal wounds, suction blisters, ex vivo cultures, diabetic, decubitus, rheumatic, and venous ulcers) and keratinocyte cultures, which factors contribute to stromelysin-2 expression and how it is induced in relation to other matrix metalloproteinases. Our results show that stromelysin-2 mRNA and protein are upregulated later (at 3 d) than matrix metalloproteinase-1 in normally healing wounds and ex vivo explants, in which stromelysin-2 is invariably expressed by keratinocytes migrating over dermal matrix. The number of keratinocytes expressing stromelysin-2 was greatest in chronic inflamed diabetic and venous ulcers compared with rheumatoid and decubitus ulcers, six of which had no signal. In keratinocyte cultures, tumor necrosis factor-alpha, epidermal growth factor, and transforming growth factor-beta1 induced stromelysin-2 expression as measured by quantitative reverse transcriptase-polymerase chain reaction, whereas different matrices did not upregulate the mRNA. Immunostaining demonstrated stromal transforming growth factor-beta1 in contact with the stromelysin-2-positive keratinocytes. Our results suggest that stromelysin-2 expression is important for the normal repair process and is upregulated by cytokines rather than cell-matrix interactions. Stromelysin-2 is most likely to participate in the remodeling of the newly formed basement membrane, and is not overexpressed in retarded wound healing.

Deposition of laminin 5 in epidermal wounds regulates integrin signaling and adhesion

Adhesion of keratinocytes in a wound outgrowth to laminin 5 in the basement membrane via integrins alpha6beta4 and alpha3beta1 is distinct from adhesion to dermal collagen via alpha2beta1 or to fibronectin via alpha5beta1. Leading cells in the outgrowth are distinguished from following keratinocytes by deposition of laminin 5, failure to communicate via gap junctions and sensitivity to toxin B, an inhibitor of RhoGTPase. Laminin 5 deposited by leading keratinocytes onto dermal collagen dominates over dermal ligands and changes the cell signals required for adhesion from collagen-dependent to laminin-5-dependent. Thus, deposition of laminin 5 can instruct keratinocytes to switch from an activated phenotype to a quiescent and integrated epithelial phenotype.

The functions of exogenous and endogenous laminin-5 on corneal epithelial cells

Recent evidence suggests that the basement membrane not only separates basal cells from Bowman's layer, but also has a crucial role in the proliferation, differentiation and migration of corneal epithelial cells. The basement membrane is composed of a mixture of matrix components including collagens, laminins and heparan sulfate proteoglycans. In these extracellular matrixes, laminin is a major component of the basement membrane. Of 11 laminin isoformes, laminin-5 is a variant, composed of three nonidentical subunits alpha3, beta3, gamma2 and is a major component of the corneal basement membrane. However, little is known about the interactions of laminin-5 with corneal epithelial cells. In this study, we investigated the functions of laminin-5 on SV-40 transfected human corneal epithelial cells (HCE cells). We also revealed different functions between exogenous and endogenous laminin-5 on HCE cells. Laminin-5 is synthesized initially as a 490 kDa molecule that undergoes specific processing to cleavaged isoforms after being secreted. The alpha3 subunit is processed from 200-190 kDa to 160 kDa/145 kDa. The gamma2 subunit is processed from 150 kDa to 105 kDa/80 kDa. The beta3 subunit (140 kDa) is not processed. Exogenously added laminin-5 (soluble form) in this study was purified from a serum-free, conditioned medium of a human gastric carcinoma cell line STKM-I. This soluble laminin is a processed isoform containing alpha3 (160 kDa), beta3 (140 kDa) and gamma2 (105 kDa) chains. On the other hand, immunocytochemical analysis showed that HCE cells themselves secreted laminin-5 endogenously. Western blotting analysis revealed that HCE cells initially produced unprocessed isoform containing 190 kDa alpha3, 140 kDa beta3 and 150 kDa gamma2 chains and that after being secreted, the alpha3 chain was processed to 160 kDa/145 kDa and the gamma2 chain was processed to 105 kDa. Initially we investigated the functions of exogenous (processed) laminin-5 on HCE cells. Exogenously added laminin-5 strongly promoted cell adhesion via alpha3beta1 integrin, cell spreading, assembly of hemidesmosomes and mildly inhibited cell migration. Next we estimated the effect of endogenous (unprocessed) laminin-5 on HCE cells. Using an anti laminin-5 monoclonal antibody (mAb) or anti integrin alpha3beta1 mAbs, the blocking of the interaction between endogenously secreted laminin-5 and HCE cells caused strong inhibition of cell migration. Integrin alpha3beta1 and alpha6beta4 were expressed in HCE cells. These integrins are receptors of laminin-5. But, anti integrin alpha6beta4 mAbs did not have any blocking ability against cell migration. These results indicated that endogenous (unprocessed) laminin-5 has a crucial role in cell migration on HCE cells via alpha3beta1 integrin. In conclusion, structural differences between exogenous (processed) and endogenous (unprocessed) laminin-5 regulated their functions on HCE cells. Exogenously added laminin-5 strongly promoted cell adhesion, cell spreading and assembly of hemidesmosomes. Endogenously secreted laminin-5 had a crucial role in cell migration. In the future, processed soluble laminin-5 could be a useful drug for the prevention of recurrent corneal erosion, and unprocessed soluble laminin-5 could be applied for the treatment of prolonged corneal epithelial defects.

Epithelial cell-specific laminin 5 is required for survival of early thymocytes

The gene LamC2 encoding the gamma2 chain of laminin 5, an epithelial cell-specific extracellular matrix protein, was identified in a PCR-based subtracted cDNA library from mouse thymic stromal cells. The mRNA existed in two alternative forms (5.1 and 2.4 kb). The full-length message was highly expressed in SCID thymus and in a nurse cell line, but not in other thymic epithelial cell lines, while the short form was more widely expressed. In situ hybridization and immunohistochemical staining revealed laminin 5 expression mostly in the subcapsular region of the adult thymus. Addition to fetal thymic organ cultures of a cell adhesion-blocking mAb to the alpha3 chain of laminin 5 interrupted T cell development. There was a 40% reduction in the total yield of thymocytes, and the most profound decrease (75-90%) was seen in the CD25+CD44+ and CD25+CD44-subsets of the CD4-CD8- double negative fraction. Most of the surviving double negative thymocytes expressed Sca-1, and there were significant increases in the number of cells with CD69 expression and in the fraction of annexin V-stained cells. None of these changes were observed with a nonblocking anti-laminin alpha3 chain mAb. These results suggest that the interaction between double negative thymoctyes and laminin 5 made by subcapsular epithelial cells is required for the survival and differentiation of mouse thymocytes.

Re-epithelialization rate and protein expression in the suction-induced wound model: comparison between intact blisters, open wounds and calcipotriol-pretreated open wounds

We have investigated re-epithelialization following induction of suction blisters in humans in intact blisters, open wounds, i.e. blister roofs removed immediately after blister induction, and calcipotriol-pretreated open wounds. Intact blisters simulate blister healing in bullous disease, while open wounds simulate re-epithelialization during wound healing. Re-epithelialization was clearly faster in open wounds than in intact blisters, and was not affected by calcipotriol pretreatment. Bullous pemphigoid antigen 2 (BP180), bullous pemphigoid antigen 1 (BP230), plectin/hemidesmosomal 1 protein (HD1), laminin 5, laminin alpha5, laminin beta1, type VII collagen, tenascin-C, beta4, alphavbeta5, alpha5 and alpha9 integrins were studied in intact blisters and open wounds by immunohistochemistry. Hemidesmosomal plaque proteins BP230 and plectin/HD1, which connect the keratin cytoskeleton to the hemidesmosome, appeared earlier at the leading edge in intact blisters than in open wounds. Band-like immunostaining in the basement membrane for laminin 5, alpha5 and beta1 chains was continuous in blister bases, but partially discontinuous in open wound bases. The other antigens studied showed similar expression in intact blisters and open wounds. BP180, BP230, plectin/HD1, beta4 integrin, laminin 5 and tenascin-C expression were further studied in calcipotriol-pretreated open wounds. Calcipotriol did not affect the expression of these antigens. The immunohistochemical results suggest that the keratin cytoskeleton is linked to the basal plasma membrane of migrating basal cells via BP230 and plectin/HD1 earlier in the more slowly re-epithelializing blisters than in open wounds. An intact laminin sheath may inhibit keratinocyte migration in intact blisters.

Fab fragments directed against laminin 5 induce subepidermal blisters in neonatal mice

Patients with one form of cicatricial pemphigoid have IgG autoantibodies directed against laminin 5 (alpha3beta3gamma2), an adhesion protein in epidermal basement membrane. Anti-laminin 5 autoantibodies are not found in patients with other skin or mucosal diseases and hence serve as a specific marker for this autoimmune blistering disorder. The demonstration that experimental and patient anti-laminin 5 IgG are pathogenic in animal models indicated that such autoantibodies are central to disease pathophysiology. To investigate further the role of antibody valence and complement in triggering lesion formation in vivo, rabbit anti-laminin 5 (or normal, control) Fab fragments were passively transferred to neonatal BALB/c mice. Mice receiving anti-laminin 5 Fab fragments developed, in a dose-related fashion, circulating anti-basement membrane antibodies, deposits of immunoreactive rabbit IgG (but not murine C3) in epidermal basement membranes, and subepithelial blisters of skin and mucous membranes. Such alterations were not observed in mice treated with equivalent concentrations of normal rabbit Fab fragments. These studies demonstrated that neither complement activation nor cross-linking of laminin 5 in epidermal basement membranes was required for induction of subepidermal blister formation in this animal model of a human autoimmune bullous disease.

Molecular cloning of canine bullous pemphigoid antigen 2 cDNA and immunomapping of NC16A domain by canine bullous pemphigoid autoantibodies

The autoantibody-mediated subepidermal blistering skin disease bullous pemphigoid affects both humans and dogs. We previously demonstrated that canine bullous pemphigoid patient's autoantibodies targeted skin basement membrane component and a 180-kDa keratinocyte protein. We extend our works to partially isolate the cDNA encoding canine bullous pemphigoid antigen 2 (BPAg2, BP180). Total RNA extracted from a papillomavirus-immortalized canine keratinocyte cell line and a cultured canine squamous carcinoma cell line SCC 2/88 were used to isolate fragments of cDNA encoding BPAg2 by reverse transcription-PCR and 5'-rapid amplification of cDNA end. The isolated sequence included the 5'-untranslated region, the entire intracellular, transmembranous, and extracellular NC16A autoantigenic domains, plus a small segment of the collagenous domain. Sequence analyses of the isolated cDNA showed 87 and 85% identities between canine and human at the nucleotide sequence and at the deduced amino acid sequence levels, respectively. The canine BPAg2 sequence was confirmed by a rabbit antibody raised against a 18-amino acid peptide deduced from the canine NC16A nucleotide sequence. Autoantibodies from canine bullous pemphigoid patients' sera recognized epitopes within the human NC16A domain. The cloning of the cDNA encoding this disease-associated protein may allow us to develop a canine model in dissecting the immunopathologic mechanism underlying bullous pemphigoid.

Induction of keratinocyte IL-8 expression and secretion by IgG autoantibodies as a novel mechanism of epidermal neutrophil recruitment in a pemphigus variant

A subset of pemphigus herpetiformis, a rare pemphigus variant, is characterized histopathologically by subcorneal acantholysis and neutrophilic infiltration. The mechanism of neutrophil infiltration is unknown, but chemokines such as IL-8 may play a role. We investigated the possible role of IL-8 in two such cases. Direct and indirect immunofluorescence studies demonstrated in vivo-bound and circulating IgG epithelial cell surface-binding autoantibodies, both predominated by IgG4 subclass. ELISA and immunoblotting studies revealed that the patients' IgG autoantibodies recognized recombinant desmoglein 1 but not desmoglein 3. Preadsorption of the patients' sera with recombinant desmoglein 1 completely removed the epidermal cell surface immunostaining. Significantly, immunohistochemistry demonstrated intense expression of IL-8, co-localized with in vivo-bound IgG, in the upper epidermis, where the acantholysis took place. Affinity-purified sera IgG from these two patients, a normal individual, and a pemphigus vulgaris patient containing desmoglein 1 autoantibodies, were incubated with normal human keratinocytes in vitro. Cells treated with these patients' IgG secreted a seven-to-nine-fold increase of IL-8 (30-37 pg/ml) compared with the controls (2-4 pg/ml) and expressed a higher intensity of cytoplasmic IL-8 staining. These data demonstrate a novel functional role for IL-8 in the pathogenesis of the neutrophil-dominant subset of pemphigus herpetiformis. The autoantibody-induced epidermal cell IL-8 expression may represent a novel mechanism of epidermal neutrophil recruitment.

Distribution of laminin and fibronectin isoforms in oral mucosa and oral squamous cell carcinoma

The expression of laminin and fibronectin isoforms varies with cellular maturation and differentiation and these differences may well influence cellular processes such as adhesion and motility. The basement membrane (BM) of fetal oral squamous epithelium contains the laminin chains, alpha2, alpha3, alpha5, beta1, beta2, beta3, gamma1 and gamma2. The BM of adult normal oral squamous epithelium comprises the laminin chains, alpha3, alpha5, beta1, beta3, gamma1 and gamma2. A re-expression of the laminin alpha2 and beta2 chains could be shown in adult hyperproliferative, dysplastic and carcinomatous lesions. In dysplasia and oral squamous cell carcinoma (OSCC), multifocal breaks of the BM are present as indicated by laminin chain antibodies. These breaks correlate to malignancy grade in their extent. Moreover, in the invasion front the alpha3 and gamma2 chain of laminin-5 can immunohistochemically be found outside the BM within the cytoplasm of budding carcinoma cells and in the adjacent stroma. The correlation between the morphological pattern of invasive tumour clusters and a laminin-5 immunostaining in the adjacent stroma may suggest, first, that a laminin-5 deposition outside the BM is an immunohistochemical marker for invasion and second, that OSCC invasion is guided by the laminin-5 matrix. Expression of oncofetal fibronectins (IIICS de novo glycosylated fibronectin and ED-B fibronectin) could be demonstrated throughout the stromal compartment. However, the ED-B fibronectin synthesizing cells (RNA/RNA in situ hybridization) are confined to small stroma areas and to single stroma and inflammatory cells in the invasion front. A correlation of the number of ED-B fibronectin synthesizing cells to malignancy grade could not be seen. ED-B fibronectin mRNA-positive cells seem to be concentrated in areas of fibrous stroma recruitment with a linear alignment of stromal fibro-/myofibroblasts (desmoplasia). Double staining experiments (ED-B fibronectin in situ hybridization and alpha-smooth muscle actin immunohistochemistry) indicated that the stroma myofibroblasts are a preferential source of ED-B fibronectin. In conclusion, in OSCC, a fetal extracellular matrix conversion is demonstrable. Tumour cells (laminin alpha2 and beta2 chain) and recruited stromal myofibroblasts (oncofetal ED-B fibronectin) contribute to the fetal extracellular matrix milieu.

Expression of laminin-5 in ameloblastomas and human fetal teeth

Extracellular matrix proteins have been shown to play important roles in the cell migration and differentiation in both normal and pathological conditions. In the present study, we used immunohistochemistry and in situ hybridization to determine the distribution of laminin-5 in ameloblastomas and developing human teeth. In ameloblastomas, the immunoreaction for the laminin-5 gamma2 chain was confined to the tumor cells of the peripheral area. The staining reaction was variable, being mostly weak and fragmented in the basement membrane structures surrounding the neoplastic islands. Some peripheral epithelial cells and some invading small ameloblastoma cell islands showed intense intracellular staining for the gamma2 chain. Tumor cells in the proliferating areas of ameloblastomas expressed gamma2 chain mRNA. The laminin-5 gamma2 chain was located beneath the dental lamina and in the outer, but not in the inner, enamel epithelium of the developing teeth. During the early hard tissue apposition stage, intense staining for the gamma2 chain was confined to ameloblasts, which also gave a strong signal for gamma2 chain mRNA. These results suggest that laminin-5 may contribute to the infiltrative and progressive growing potential of ameloblastomas. During human tooth development, however, laminin-5 may participate in the terminal differentiation of ameloblasts and in enamel matrix formation.

Quantifying lamella dynamics of cultured cells by SACED, a new computer-assisted motion analysis

Formation of lamellipodia and the retraction of ruffles are essential activities during motility and migration of eukaryotic cells. We have developed a computer-assisted stroboscopic method for the continuous observation of cell dynamics (stroboscopic analysis of cell dynamics, SACED) that allows one to analyze changes in lamellipodia protrusion and ruffle retraction with high resolution in space and time. To demonstrate the potential of this method we analyzed keratinocytes in culture, unstimulated or stimulated with epidermal growth factor (EGF), which is known to induce cell motility and migration. Keratinocytes stimulated with EGF exhibited a 2.6-fold increase in their migration velocity, which coincided with enhanced ruffle retraction velocity (144%) and increased ruffle frequency (135%) compared to control cells. We also recorded an enhanced frequency of lamellipodia (135%), whereas the velocity of lamellipodia protrusion remained unchanged. These results on ruffle and lamellipodia dynamics in epidermal cells show that SACED is at least equal to established methods in terms of accuracy. SACED is, however, advantageous concerning resolution in time and therefore allows one to analyze the activity of lamellipodia and ruffles in as yet unknown detail. Moreover, SACED offers two opportunities that render this technique superior to established methods: First, several parameters relevant to cell motility can be analyzed simultaneously. Second, a large number of cells can conveniently be examined, which facilitates the compilation of statistically significant data.

The alpha3 laminin subunit, alpha6beta4 and alpha3beta1 integrin coordinately regulate wound healing in cultured epithelial cells and in the skin

Previously, we demonstrated that proteolytic processing within the globular domain of the alpha3 subunit of laminin-5 (LN5) converts LN5 from a cell motility-inducing factor to a protein complex that can trigger the formation of hemidesmosomes, certain cell-matrix attachment sites found in epithelial cells. We have prepared a monoclonal antibody (12C4) whose epitope is located toward the carboxy terminus of the globular domain of the alpha3 laminin subunit. This epitope is lost from the alpha3 subunit as a consequence of proteolytic processing. Antibody 12C4 stains throughout the matrix of cells that fail to process the alpha3 laminin subunit, but does not recognize the matrix of confluent cultures of MCF-10A cells, which efficiently process their alpha3 laminin chain. In subconfluent populations of MCF-10A cells, 12C4 only stains matrix deposited at the outer edges of cell colonies. In these cells, integrin alpha3beta1 occasionally colocalizes with the staining generated by the 12C4 antibody but alpha6beta4 integrin does not. In wounded MCF-10A cell cultures, the 12C4 antibody stains the extracellular matrix beneath those cells at the very edge of the cellular sheet that moves to cover the wound site. A similar phenomenon is observed in human skin wounds, since we also detect expression of the unprocessed alpha3 laminin subunit at the leading tip of the sheet of epidermal cells that epithelializes skin wounds in vivo. In addition, using alpha3 laminin subunit and integrin function-inhibiting antibodies, we provide evidence that LN5 and its two integrin receptors (alpha6beta4 and alpha3beta1) appear necessary for wound healing to occur in MCF-10A cell culture wounds. We propose a model for healing of wounded epithelial tissues based on these results.

Expression of the laminin gamma2 chain in different histological types of lung carcinoma. A study by immunohistochemistry and in situ hybridization

Sixty-four malignant lung tumours and 12 of their regional lymph node metastases were analysed for expression of the laminin gamma2 chain by immunohistochemistry and in situ hybridization. Expression of the laminin gamma2 chain was strongest in squamous cell carcinomas, followed by adenocarcinomas and large cell carcinomas. Positive cells, except for large cell carcinomas, were located at the epithelial-stromal interface of tumour clusters. An important exception was small cell lung carcinoma, with only a low level of laminin gamma2 chain expression. Apart from tumour type, this may reflect the relatively scanty fibrous stroma in these tumours and supports previous observations that small cell lung carcinoma cells, contrary to other types, lack surface expression of alpha(6)beta(4) integrin, the specific laminin-5 binding receptor. In frozen sections, immunohistochemistry showed linear basement membranes around tumour clusters in squamous cell carcinomas and adenocarcinomas. This shows that carcinoma cells are capable of heavy deposition of the laminin gamma2 chain around tumour clusters and suggests that a laminin gamma2 chain-containing substrate may be of significance for the spread and growth of malignant tumours.

The SFL activity secreted by metastatic carcinoma cells is related to laminin 5 and mediates cell scattering in an integrin-independent manner

We have previously reported that an in vivo-selected metastatic variant of NBT-II rat carcinoma cells, M-NBT-II, produces and secretes a factor with cell-scattering activity, SFL, that is potentially involved in tumor progression. This biological activity was purified and characterized as a laminin 5 (LN5) -related protein. This SFL/LN5 protein consists of the (alpha)3, (beta)3 and (gamma)2 chains of expected sizes. Laminin 5 is a multifunctional secreted glycoprotein thought to be involved in cell adhesion and migration, mainly via its interaction with (alpha)3(beta)1 and (alpha)6(beta)4 integrins. SFL/LN5, and purified human laminin 5, induced the scattering and motility of MDCK cells and the formation of actin stress fibers and focal contacts in A549 cells. These events were dependent on activation of the small GTP-binding protein Rho. (Alpha)v colocalized with vinculin in the focal contacts of activated cells whereas (alpha)3 and (alpha)6 integrins did not. Blocking antibodies directed against (alpha)3 and (alpha)6 integrins or the laminin 5 integrin-binding site did not abolish SFL/LN5 biological activity, which, in contrast, was completely inhibited by heparin. Thus, SFL/LN5 activity in epithelial cell scattering and cytoskeletal reorganization is probably independent of integrin receptors.

Structure and function of hemidesmosomes: more than simple adhesion complexes

The attachment of cells to the extracellular matrix is of crucial importance in the maintenance of tissue structure and integrity. In stratified epithelia such as in skin as well as in other complex epithelia multiprotein complexes called hemidesmosomes are involved in promoting the adhesion of epithelial cells to the underlying basement membrane. In the past few years our understanding of the role of hemidesmosomes has improved considerably. Their importance has become apparent in clinical conditions, in which absence or defects of hemidesmosomal proteins result in devastating blistering diseases of the skin. Molecular genetic studies have increased our knowledge of the function of the various components of hemidesmosomes and enabled the characterization of protein-protein interactions involved in their assembly. It has become clear that the alpha6beta4 integrin, a major component of hemidesmosomes, is able to transduce signals from the extracellular matrix to the interior of the cell, that critically modulate the organization of the cytoskeleton, proliferation, apoptosis, and differentiation. Nevertheless, our knowledge of the mechanisms regulating the functional state of hemidesmosomes and, hence, the dynamics of cell adhesion, a process of crucial importance in development, wound healing or tumor invasion, remains limited. The aims of this review are to highlight the recent progresses of our knowledge on the organization and assembly of hemidesmosomes, their involvement in signaling pathways as well as their participation in clinical pathologic conditions.

Biology and function of hemidesmosomes

Hemidesmosomes are cell-substratum adhesion sites that connect the extracellular matrix to the keratin cytoskeleton. Our knowledge of the function of these structures has greatly increased as a result of studies on patients with aberrant expression of hemidesmosome components and studies using targeted inactivation of mouse genes encoding these components. Insight into the formation of hemidesmosomes, as well as into protein-protein interactions that occur in these junctional complexes, has recently been gained by in vitro cell transfections, blot overlay and yeast two-hybrid assays. In addition, recent results indicate that the alpha6 beta4 integrin is involved in the transduction of signals that are induced by the extracellular matrix and which modulate processes as diverse as cell proliferation, differentiation, apoptosis, migration and tissue morphogenesis. Thus it seems that hemidesmosomes do not merely maintain dermo-epidermal adhesion and tissue integrity, but that they are also implicated in intracellular signaling. Here we discuss recently published data on the biology and function of hemidesmosomes.

Structure and assembly of hemidesmosomes

The hemidesmosome is a complex junction containing many proteins. The keratin cytoskeleton attaches to its cytoplasmic plaque, while its transmembrane elements interact with components of the extracellular matrix. Hemidesmosome assembly involves recruitment of alpha 6 beta 4 integrin heterodimers, as well as cytoskeletal elements and cytoskeleton-associated proteins to the cell surface. In our cell culture models, these phenomena appear to be triggered by laminin-5 in the extracellular matrix. Cell interaction with laminin-5 apparently induces both phosphorylation and dephosphorylation of subunits of alpha 6 beta 4 integrin. There is emerging evidence that such events are necessary for subsequent cytoskeleton anchorage to the hemidesmosome cytoplasmic plaque. Once assembled, the hemidesmosome plays an essential role in maintaining firm epithelial adhesion to the basement membrane, with hemidesmosome disruption being a hallmark of certain devastating blistering diseases. However, the hemidesmosome is more than just a stable anchor, as it may also be the site of signal transduction, mediated by its alpha 6 beta 4 integrin component. This review discusses our current knowledge of the structure and assembly of the hemidesmosome.

The role of laminin-5 in TGF alpha/EGF-mediated corneal epithelial cell motility

Transforming growth factor alpha (TGF alpha) and epidermal growth factor (EGF) stimulate corneal epithelial cell wound closure. However, the role of these growth factors in regulating corneal epithelial cell motility on basement membrane proteins such as laminin has not been elucidated. In the present study we demonstrate that in an in vitro model of corneal wound healing, TGF alpha has no deleterious effects on the deposition of the laminin-5 isoform into the extracellular matrix structure underlying epithelial cells resurfacing bare collagenous stroma. In primary culture, a population of corneal epithelial cells are stimulated by TGF alpha or EGF to become highly motile. These cells are associated with an endogenously secreted, and extracellularly deposited, 'trail' of laminin-5. The laminin-5 trail is specifically associated with motile cells, as non-motile corneal epithelium exhibiting numerous cell-cell contacts does not display a similar laminin-5 localization pattern. In contrast to these observations, a preparation of laminin-5 known to promote cell spreading, adhesion, and formation of hemidesmosomes, when presented exogenously to cultured corneal epithelial cells, does not stimulate motility. However, a commercially available preparation of laminin derived from human placenta which does not contain laminin-5 does significantly promote the migration of TGF alpha- or EGF-stimulated corneal epithelial cells. From these results, it is hypothesized that endogenously secreted laminin-5 functions to promote migration in corneal epithelial cells which have been treated with TGF alpha or EGF. Exogenously presented laminin-5 does not function similarly, but functions to promote corneal epithelial cell adhesion.