Integrin receptors and RGD sequences in human keratinocyte migration: unique anti-migratory function of alpha 3 beta 1 epiligrin receptor

Just add water: hydratable, morphologically diverse nanocarrier powders for targeted delivery

Two major obstacles that limit the widespread usage of polymeric nanocarriers include the complexity of formulation methods and their stability during storage. To address both of these issues, here we present morphologically complex nanocarriers in a hydratable powder form, which bypasses the need for expensive, harsh, and/or time-consuming nanocarrier fabrication techniques. The powders are composed of carbohydrates and self-assembling polymer amphiphiles having a low glass transition temperature. Hydration requires less than one minute and only involves the addition of aqueous media (water or saline) to rapidly obtain self-assembled micelles, worm-like micelles (i.e. filomicelles), or polymersomes from poly(ethylene glycol)-b-poly(propylene sulfide) (PEG-b-PPS) polymers. The formulated powders are highly stable, achieving hydration into monodisperse nanocarriers following >6 months of storage. Diverse drug cargoes were efficiently encapsulated during hydration, including hydrophobic small molecules for micellar morphologies, as well as individual and concurrent loading of both hydrophobic and hydrophilic molecules for vesicular morphologies. Hydrated polymersomes are shown to load hydrophilic biological macromolecules, and encapsulated enzymes retain bioactivity. Furthermore, we demonstrate that inclusion of lipid-anchored ligands in powder form permits the surface-display of targeting ligands and enhances target cell uptake, thereby extending this technology to targeted drug delivery applications. Our powder-based formulation strategy was extendable to commercially available polymer amphiphiles, including PEG-b-polystyrene and PEG-b-polycaprolactone. The formulated nanotechnologies described herein are highly modular, require minimal preparation, and remain stable in ambient long-term storage (bypassing cold chain requirements), which will enable their use in medicine (human and veterinary), research, and commercial applications from cosmetics to agriculture.

Engineering the migration and attachment behaviour of primary dermal fibroblasts

The availability of primary cells present in pathological conditions is often very limited due to stringent ethical regulation and patient consent. One such condition is chronic wounds, where dermal fibroblasts show a deficient migration. In vitro models with cellular tools that mimic the in vivo scenario would be advantageous to test new therapies for these challenging wounds. Since the availability of primary dermal fibroblasts present in chronic wounds is restricted and their "shelf-life" limited due to the increased senescence, our aim was to engineer human dermal fibroblasts with impaired migration using synthetic Arg-Gly-Asp (RGD) peptides. We studied fibroblast behaviour on three different two dimensional (2D) surfaces, representative of the dermal extracellular matrix and the materials used in the development of dermal scaffolds, in addition to commercially available, collagen-based 3D dermal scaffolds, demonstrating that the concentration of synthetic RGD peptides necessary to impair migration of dermal fibroblasts should be tailored to the particular surface/material and cell population used. The described technology could be translated to other cell types including established cell lines. A wide range of synthetic peptides exists, which differ in the amino acid sequence, thus increasing the possibilities of this technology.

Bilayered nanofibrous 3D hierarchy as skin rudiment by emulsion electrospinning for burn wound management

Mimicking skin extracellular matrix hierarchy, the present work aims to develop a bilayer skin graft comprising a porous cotton-wool-like 3D layer with membranous structure of PCL-chitosan nanofibers. Emulsion electrospinning with differential stirring periods of PCL-chitosan emulsion results in development of a bilayer 3D structure with varied morphology. The electrospun membrane has fiber diameter ∼274 nm and pore size ∼1.16 μm while fluffy 3D layer has fiber diameter ∼1.62 μm and pore size ∼62 μm. The 3D layer was further coated with collagen I isolated from Cirrhinus cirrhosus fish scales to improve biofunctionality. Surface coating with collagen I resulted in bundling the fibers together, thereby increasing their average diameter to 2.80 μm and decreasing pore size to ∼45 μm. The architecture and composition of the scaffold promotes efficient cellular activity where interconnected porosity with ECM resembling collagen I coating assists cellular adhesion, infiltration, and proliferation from initial days of fibroblast seeding, while keratinocytes migrate on the surface only without infiltrating in the membranous nanofiber layer. Anatomy of the scaffold arising due to variation in pore size distribution at different layers thereby facilitates compartmentalization and prevents initial cellular transmigration. The scaffold also assists in extracellular matrix protein synthesis and keratinocyte stratification in vitro. Further, the scaffold effectively integrates and attaches with third-degree burn wound margins created in rat models and accelerates healing in comparison to standard Tegaderm dressing™. The bilayer scaffold is thus a promising, readily available, cost-effective, off-the-shelf matrix as a skin substitute.

Re-epithelialization of cutaneous wounds in adult zebrafish combines mechanisms of wound closure in embryonic and adult mammals

Re-epithelialization of cutaneous wounds in adult mammals takes days to complete and relies on numerous signalling cues and multiple overlapping cellular processes that take place both within the epidermis and in other participating tissues. Re-epithelialization of partial- or full-thickness skin wounds of adult zebrafish, however, is extremely rapid and largely independent of the other processes of wound healing. Live imaging after treatment with transgene-encoded or chemical inhibitors reveals that re-epithelializing keratinocytes repopulate wounds by TGF-β- and integrin-dependent lamellipodial crawling at the leading edges of the epidermal tongue. In addition, re-epithelialization requires long-range epithelial rearrangements, involving radial intercalations, flattening and directed elongation of cells - processes that are dependent on Rho kinase, JNK and, to some extent, planar cell polarity within the epidermis. These rearrangements lead to a massive recruitment of keratinocytes from the adjacent epidermis and make re-epithelialization independent of keratinocyte proliferation and the mitogenic effect of FGF signalling, which are only required after wound closure, allowing the epidermis outside the wound to re-establish its normal thickness. Together, these results demonstrate that the adult zebrafish is a valuable in vivo model for studying and visualizing the processes involved in cutaneous wound closure, facilitating the dissection of direct from indirect and motogenic from mitogenic effects of genes and molecules affecting wound re-epithelialization.

Integrins are Mechanosensors That Modulate Human Eosinophil Activation

Eosinophil migration to the lung is primarily regulated by the eosinophil-selective family of eotaxin chemokines, which mobilize intracellular calcium (Ca²⁺) and orchestrate myriad changes in cell structure and function. Eosinophil function is also known to be flow-dependent, although the molecular cognate of this mechanical response has yet to be adequately characterized. Using confocal fluorescence microscopy, we determined the effects of fluid shear stress on intracellular calcium concentration ([Ca²⁺]_i) in human peripheral blood eosinophils by perfusing cells in a parallel-plate flow chamber. Our results indicate that fluid perfusion evokes a calcium response that leads to cell flattening, increase in cell area, shape change, and non-directional migration. None of these changes are seen in the absence of a flow stimulus, and all are blocked by chelation of intracellular Ca²⁺ using BAPTA. These changes are enhanced by stimulating the cells with eotaxin-1. The perfusion-induced calcium response (PICR) could be blocked by pre-treating cells with selective (CDP-323) and non-selective (RGD tripeptides) integrin receptor antagonists, suggesting that α₄β₇/α₄β₁ integrins mediate this response. Overall, our study provides the first pharmacological description of a molecular mechanosensor that may collaborate with the eotaxin-1 signaling program in order to control human eosinophil activation.

Keratinocyte Migration and a Hypothetical New Role for Extracellular Heat Shock Protein 90 Alpha in Orchestrating Skin Wound Healing

Significance: The treatment and care of patients with skin wounds are a major healthcare expenditure. Burn wounds, iatrogenic surgical wounds, venous stasis dermatitis ulcers, diabetic lower limb ulcers, pressure ulcers, and skin wounds from peripheral neuropathies are largely treated with only supportive care. Despite a great deal of research into using growth factors as therapeutic agents, to date, the field has been disappointing. The only biologic agent that is Federal Drug Administration (FDA) approved for promoting skin wound healing is recombinant platelet-derived growth factor (PDGF-BB), but its modest efficacy and expense limit its use clinically. Recent Advances: Acute hypoxia induced by the clotting of dermal blood vessels during the wounding of skin is a major stress factor that leads to the re-programming of basal keratinocytes to initiate re-epithelialization. The laterally migrating keratinocytes secrete extracellular heat shock protein 90 alpha. Heat shock protein 90 alpha (hsp90α) engages low-density lipoprotein receptor-related protein-1 (LRP-1) cellular receptors and works as an autocrine factor to stimulate keratinocyte migration (re-epithelialization) and as a paracrine factor to stimulate the migration of dermal fibroblasts (fibroplasia) and microvascular endothelial cells (neo-vascularization). Hypoxia-triggered extracellular heat shock protein 90 alpha acts as the master regulator of initial skin wound healing. Critical Issues: It is not yet known how the engagement of hsp90α with the LRP-1 receptor leads to increased motility of keratinocytes, fibroblasts, or microvascular endothelial cells. Understanding the sequence of how an acute skin wound via hypoxic stress leads to cellular events that ultimately induce accelerated wound closure provides numerous targets for new wound-healing therapeutic agents. Future Directions: Developing data for an investigational new drug (IND) application to the FDA for a Phase I study using hsp90α in human skin wounds. Identifying the cellular signaling mechanisms by which hsp90α enhances skin cell migration, leading to accelerated wound closure.

TGFβ loss activates ADAMTS-1-mediated EGF-dependent invasion in a model of esophageal cell invasion

The TGFβ signaling pathway is essential to epithelial homeostasis and is often inhibited during progression of esophageal squamous cell carcinoma. Recently, an important role for TGFβ signaling has been described in the crosstalk between epithelial and stromal cells regulating squamous tumor cell invasion in mouse models of head-and-neck squamous cell carcinoma (HNSCC). Loss of TGFβ signaling, in either compartment, leads to HNSCC however, the mechanisms involved are not well understood. Using organotypic reconstruct cultures (OTC) to model the interaction between epithelial and stromal cells that occur in dysplastic lesions, we show that loss of TGFβ signaling promotes an invasive phenotype in both fibroblast and epithelial compartments. Employing immortalized esophageal keratinocytes established to reproduce common mutations of esophageal squamous cell carcinoma, we show that treatment of OTC with inhibitors of TGFβ signaling (A83-01 or SB431542) enhances invasion of epithelial cells into a fibroblast-embedded Matrigel/collagen I matrix. Invasion induced by A83-01 is independent of proliferation but relies on protease activity and expression of ADAMTS-1 and can be altered by matrix density. This invasion was associated with increased expression of pro-inflammatory cytokines, IL1 and EGFR ligands HB-EGF and TGFα. Altering EGF signaling prevented or induced epithelial cell invasion in this model. Loss of expression of the TGFβ target gene ROBO1 suggested that chemorepulsion may regulate keratinocyte invasion. Taken together, our data show increased invasion through inhibition of TGFβ signaling altered epithelial-fibroblasts interactions, repressing markers of activated fibroblasts, and altering integrin-fibronectin interactions. These results suggest that inhibition of TGFβ signaling modulates an array of pathways that combined promote multiple aspects of tumor invasion.

Human epidermal keratinocyte cell response on integrin-specific artificial extracellular matrix proteins

Cell-matrix interactions play critical roles in regulating cellular behavior in wound repair and regeneration of the human skin. In particular, human skin keratinocytes express several key integrins such as alpha5beta1, alpha3beta1, and alpha2beta1 for binding to the extracellular matrix (ECM) present in the basement membrane in uninjured skin. To mimic these key integrin-ECM interactions, artificial ECM (aECM) proteins containing functional domains derived from laminin 5, type IV collagen, fibronectin, and elastin are prepared. Human skin keratinocyte cell responses on the aECM proteins are specific to the cell-binding domain present in each construct. Keratinocyte attachment to the aECM protein substrates is also mediated by specific integrin-material interactions. In addition, the aECM proteins are able to support the proliferation of keratinocyte stem cells, demonstrating their promise for use in skin tissue engineering.

KSHV attachment and entry are dependent on αVβ3 integrin localized to specific cell surface microdomains and do not correlate with the presence of heparan sulfate

Cellular receptors for KSHV attachment and entry were characterized using tyramide signal amplification (TSA)-enhanced confocal microscopy. Integrins αVβ3, αVβ5 and α3β1 were detected on essentially all the actin-based cell surface microdomains that initially bind KSHV, while the presence of CD98 and heparan sulfate (HS), the putative attachment receptor, was more variable. KSHV bound to the same cell surface microdomains with and without HS indicating that initial attachment of KSHV is not dependent on HS and that receptors other than HS can mediate attachment. A human salivary gland (HSG) epithelial line was identified, which lacks αVβ3 but expresses high levels of HS, α3β1 and other putative KSHV receptors. These cells were resistant to KSHV binding and infection. Reconstitution of cell surface αVβ3 rendered HSG cells highly susceptible to KSHV infection, demonstrating a critical role for αVβ3 in the binding and entry of KSHV that is not shared with other proposed receptors.

Integrin Regulation of Epidermal Functions in Wounds

Significance: Integrins are bidirectional signaling receptors for extracellular matrix that regulate both inside-out signaling that controls keratinocyte-mediated changes to the wound microenvironment and outside-in signaling that controls keratinocyte responses to microenvironmental changes. As such, integrins represent attractive therapeutic targets for treatment of chronic wounds or general promotion of wound healing. Advances in wound management are particularly important as the elderly and diabetic populations within the United States continue to grow. Recent Advances: Although integrins are best known for mediating cell adhesion and migration, integrins in wound epidermis also control cell survival, proliferation, matrix remodeling, and paracrine crosstalk to other cellular compartments of the wound. Importantly, the concept of targeting integrins in the clinic has been established for treatment of certain cancers and other diseases, laying the groundwork for similar exploitation of integrins as targets to treat chronic wounds. Critical Issues: Despite their attractiveness as therapeutic targets, integrins have complex roles in wound healing that are impacted by both their own expression and a highly dynamic wound microenvironment that determines ligand availability. Therefore, identifying relevant integrin ligands in the wound and understanding both distinct and overlapping functions that different integrins play in the epidermis will be critical to determine their precise roles in wound healing. Future Directions: Future research should focus on gaining a thorough understanding of the highly coordinated functions of different integrins in wound epidermis, and on determining which of these functions go awry in pathological wounds. This focus should facilitate development of integrin-targeting therapeutics for treating chronic wounds.

Kindlin-1 regulates integrin dynamics and adhesion turnover

Loss-of-function mutations in the gene encoding the integrin co-activator kindlin-1 cause Kindler syndrome. We report a novel kindlin-1-deficient keratinocyte cell line derived from a Kindler syndrome patient. Despite the expression of kindlin-2, the patient’s cells display several hallmarks related to reduced function of β1 integrins, including abnormal cell morphology, cell adhesion, cell spreading, focal adhesion assembly, and cell migration. Defective cell adhesion was aggravated by kindlin-2 depletion, indicating that kindlin-2 can compensate to a certain extent for the loss of kindlin-1. Intriguingly, β1 at the cell-surface was aberrantly glycosylated in the patient’s cells, and its expression was considerably reduced, both in cells in vitro and in the patient’s epidermis. Reconstitution with wild-type kindlin-1 but not with a β1-binding defective mutant restored the aberrant β1 expression and glycosylation, and normalized cell morphology, adhesion, spreading, and migration. Furthermore, the expression of wild-type kindlin-1, but not of the integrin-binding-defective mutant, increased the stability of integrin-mediated cell-matrix adhesions and enhanced the redistribution of internalized integrins to the cell surface. Thus, these data uncover a role for kindlin-1 in the regulation of integrin trafficking and adhesion turnover.

Molecular and functional aspects of menstruation in the macaque

Much of our understanding of the molecular control of menstruation arises from laboratory models that experimentally recapitulate some, but not all, aspects of uterine bleeding observed in women. These models include: in vitro culture of endometrial explants or isolated endometrial cells, transplantation of human endometrial tissue into immunodeficient mice and the induction of endometrial breakdown in appropriately pretreated mice. Each of these models has contributed to our understanding of molecular and cellular mechanisms of menstruation, but nonhuman primates, especially macaques, are the animal model of choice for evaluating therapies for menstrual disorders. In this chapter we review some basic aspects of menstruation, with special emphasis on the macaque model and its relevance to the clinical issues of irregular and heavy menstrual bleeding (HMB).

The presence and regulation of connective tissue growth factor in the human endometrium

BACKGROUND

The human endometrium efficiently repairs each month after menstruation. The mechanisms involved in this repair process remain undefined. Aberrations in endometrial repair may lead to the common disorder of heavy menstrual bleeding. We hypothesized that connective tissue growth factor (CTGF) is increased at the time of endometrial repair post-menses and that this increase is regulated by prostaglandins (PGs) and hypoxic conditions present during menstruation.

METHODS AND RESULTS

Examination of 41 endometrial biopsies from 5 stages of the menstrual cycle revealed maximal CTGF mRNA expression (using quantitative RT-PCR) at menstruation and peak protein levels during the proliferative phase. CTGF was immunolocalized to epithelial and stromal cells, with intense staining of occasional stromal cells during the proliferative phase. Dual immunohistochemistry identified these cells as macrophages. Treatment of endometrial epithelial cells with 100 nM PGE(2), PGF(2α) or hypoxia (0.5% O(2)) revealed a significant increase in CTGF mRNA expression (P < 0.01 for all, versus vehicle control). Cells treated simultaneously with PGE(2) and hypoxia revealed a synergistic increase in CTGF expression (P < 0.05 versus PGE(2) or hypoxia alone) and maximal secreted CTGF protein levels (P < 0.05 versus control).

CONCLUSIONS

CTGF is increased in the human endometrium at the time of endometrial repair post-menses. The increase in CTGF may be mediated by PG production and the transient hypoxic episode observed in the endometrium at menstruation.

Epithelial integrins with special reference to oral epithelia

Adhesion of epithelium to the extracellular matrix is crucial for the maintenance of systemic and oral health. In the oral cavity, teeth or artificial dental implants penetrate the soft tissue of the gingiva. In this interface, gingival soft tissue needs to be well attached via the epithelial seal to the tooth or implant surface to maintain health. After injury or wounding, epithelial tissue rapidly migrates to form the initial epithelial cover to restore the barrier against infection. These events are crucially dependent on deposition of extracellular matrix and proper activation and function of integrin receptors in the epithelial cells. Recent experimental evidence suggests that epithelial integrins also participate in the regulation of periodontal inflammation. In this review, we will discuss the structure and function of epithelial integrins and their extracellular ligands and elaborate on their potential role in disease and repair processes in the oral cavity.

Progesterone: a pivotal hormone at menstruation

The human endometrium is exposed to repeated inflammation every month, culminating in tissue breakdown and menstruation. Subsequently, the endometrium has a remarkable capacity for efficient repair and remodeling to enable implantation if fertilization takes place. Endometrial function is known to be governed by the ovarian hormones estradiol and progesterone. This review paper focuses on hormonal control of the cyclical tissue injury and repair that takes place in the local endometrial environment at the time of menstruation. Progesterone levels decline premenstrually as the corpus luteum regresses in the absence of pregnancy, and estradiol levels increase during the postmenstrual phase. The functional impact of these significant changes is discussed, including their immediate and downstream effects. Finally, we examine the contribution of aberrant endometrial function to the presentation of heavy menstrual bleeding and identify potential therapeutic targets for the treatment of this common gynecological problem.

Immobilization of biomolecules on the surface of electrospun polycaprolactone fibrous scaffolds for tissue engineering

To make polycaprolactone (PCL) more suitable for tissue engineering, PCL in the form of electrospun fibrous scaffolds was first modified with 1,6-hexamethylenediamine to introduce amino groups on their surface. Various biomolecules, i.e., collagen, chitosan, and Gly-Arg-Gly-Asp-Ser (GRGDS) peptide, were then immobilized on their surface, with N,N'-disuccinimidylcarbonate being used as the coupling agent. Dynamic water contact angle measurement indicated that the scaffold surface became more hydrophilic after the aminolytic treatment and the subsequent immobilization of the biomolecules. The appropriateness of these PCL fibrous scaffolds for the tissue/cell culture was evaluated in vitro with three different cell lines, e.g., mouse fibroblasts (L929), human epidermal keratinocytes (HEK001), and mouse calvaria-derived preosteoblastic cells (MC3T3-E1). Both the neat and the modified PCL fibrous scaffolds released no substances in the levels that were harmful to these cells. Among the various biomolecule-immobilized PCL fibrous scaffolds, the ones that had been immobilized with type I collagen, a Arg-Gly-Asp-containing protein, showed the greatest ability to support both the attachment and the proliferation of all of the investigated cell types, followed by those that had been immobilized with GRGDS peptide.

Integrin alpha3beta1 inhibits directional migration and wound re-epithelialization in the skin

Re-epithelialization after skin wounding requires both migration and hyperproliferation of keratinocytes. Laminin-332 is deposited during migration over the provisional matrix. To investigate the function of the laminin-332 binding integrin alpha3beta1 in wound re-epithelialization, we generated Itga3flox/flox; K14-Cre mice lacking the alpha3 subunit specifically in the basal layer of the epidermis. These mice are viable but display several skin defects, including local inflammation, hair loss, basement membrane duplication and microblistering at the dermal-epidermal junction, whereas hemidesmosome assembly and keratinocyte differentiation are not impaired. Wound healing is slightly faster in the absence of integrin alpha3beta1, whereas proliferation, the distribution of other integrins and the deposition of basement membrane proteins in the wound bed are unaltered. In vitro, cell spreading is rescued by increased surface expression of alpha6beta1 integrin in the absence of integrin alpha3. The alpha3-deficient keratinocytes migrate with an increased velocity and persistence, whereas proliferation, growth factor signaling, hemidesmosome assembly, and laminin-332 deposition appeared to be normal. We suggest that integrin alpha3beta1 delays keratinocyte migration during wound re-epithelialization, by binding to the laminin-332 that is newly deposited on the wound bed.

alpha3beta1 integrin-controlled Smad7 regulates reepithelialization during wound healing in mice

Effective reepithelialization after injury is essential for correct wound healing. The upregulation of keratinocyte alpha3beta1 integrin during reepithelialization suggests that this adhesion molecule is involved in wound healing; however, its precise role in this process is unknown. We have shown here that retarded reepithelialization in Itga3(-/-) mouse skin wounds is due predominantly to repressed TGF-beta1-mediated responses. Specifically, expression of the inhibitor of TGF-beta1-signaling Smad7 was elevated in Itga3(-/-) keratinocytes. Indeed, in vivo blockade of Smad7 increased the rate of reepithelialization in Itga3(-/-) and WT wounds to similar levels. Our data therefore indicate that the function of alpha3beta1 integrin as a mediator of keratinocyte migration is not essential for reepithelialization but suggest instead that alpha3beta1 integrin has a major new in vivo role as an inhibitor of Smad7 during wound healing. Moreover, our study may identify a previously undocumented function for Smad7 as a regulator of reepithelialization in vivo and implicates Smad7 as a potential novel target for the treatment of cutaneous wounds.

Integrin alphaVbeta3 Binds to the RGD motif of glycoprotein B of Kaposi's sarcoma-associated herpesvirus and functions as an RGD-dependent entry receptor

Kaposi's sarcoma-associated herpesvirus (KSHV) envelope-associated glycoprotein B (gB) is involved in the initial steps of binding to host cells during KSHV infection. gB contains an RGD motif reported to bind the integrin alpha(3)beta(1) during virus entry. Although the ligand specificity of alpha(3)beta(1) has been controversial, current literature indicates that alpha(3)beta(1) ligand recognition is independent of RGD. We compared alpha(3)beta(1) to the RGD-binding integrin, alpha(V)beta(3), for binding to envelope-associated gB and a gB(RGD) peptide. Adhesion assays demonstrated that beta(3)-CHO cells overexpressing alpha(V)beta(3) specifically bound gB(RGD), whereas alpha(3)-CHO cells overexpressing alpha(3)beta(1) did not. Function-blocking antibodies to alpha(V)beta(3) inhibited the adhesion of HT1080 fibrosarcoma cells to gB(RGD), while antibodies to alpha(3)beta(1) did not. Using affinity-purified integrins and confocal microscopy, alpha(V)beta(3) bound to gB(RGD) and KSHV virions, demonstrating direct receptor-ligand interactions. Specific alpha(V)beta(3) antagonists, including cyclic and dicyclic RGD peptides and alpha(V)beta(3) function-blocking antibodies, inhibited KSHV infection by 70 to 80%. Keratinocytes from alpha(3)-null mice lacking alpha(3)beta(1) were fully competent for infection by KSHV, and reconstitution of alpha(3)beta(1) function by transfection with alpha(3) cDNA reduced KSHV infectivity from 74% to 55%. Additional inhibitory effects of alpha(3)beta(1) on the cell surface expression of alpha(V)beta(3) and on alpha(V)beta(3)-mediated adhesion of alpha(3)-CHO cells overexpressing alpha(3)beta(1) were detected, consistent with previous reports of transdominant inhibition of alpha(V)beta(3) function by alpha(3)beta(1). These observations may explain previous reports of an inhibition of KSHV infection by soluble alpha(3)beta(1). Our studies demonstrate that alpha(V)beta(3) is a cellular receptor mediating both the cell adhesion and entry of KSHV into target cells through binding the virion-associated gB(RGD).

Hypoxia induces epidermal keratinocyte matrix metalloproteinase-9 secretion via the protein kinase C pathway

Hypoxia promotes keratinocyte migration on wound bed connective tissues and is a profound biological signal that transforms a basal keratinocyte, destined to differentiate, into a motile cell that is essential for re-epithelialization. In this study, we examined the effect of hypoxia on keratinocyte-derived collagenases associated with keratinocyte migration. Cells plated on various connective tissue matrices under normoxic and hypoxic conditions, demonstrated a two-fold increase in the 92 kDa, type IV collagenase (MMP-9) when examined by quantitative zymography and ELISA. Western blotting and ELISA demonstrated a two-fold increase in tissue inhibitor of metalloproteinase (TIMP-1), an enzyme that binds to MMP-9 and inhibits its activity. The hypoxia-induced increase in cell motility could be inhibited by a neutralizing antibody to MMP-9. Northern blotting demonstrated that MMP-9 and TIMP-1 mRNA increased 2.5- to 4-fold, 2-12 h after the cells were made hypoxic. The hypoxia-induced changes in MMP-9 and TIMP-1 were inhibited by staurosporine and bisindolylmaleimide, inhibitors of protein kinase C (PKC), but not by inhibitors of tyrosine phosphorylation and the mitogen-activated protein kinase pathway. Inhibition of PKC also inhibited hypoxia-induced keratinocyte migration on type I collagen. These data provide evidence that hypoxia-induced keratinocyte migration is mediated by increased cellular secretion of MMP-9 via the PKC pathway.

The effect of self-designed bifunctional RGD-containing fusion protein on the behavior of human keratinocytes and dermal fibroblasts

In this study, self-designed bifunctional RGD-containing fusion protein (BFP) was grafted on the petri dish to evaluate its cytotoxicity and attachment efficiency on primary cultured keratinocytes and dermal fibroblasts. Two lengths of the GRGDS sequences were separately fused to the N-terminus and C-terminus of the Trichoderma koningii cellobiohydrolase I gene cellulose-binding domain, to serve as linking molecule between the cell and the substrate. The grafting procedure was no more labor-intensive and could be done just in aqueous condition itself. The epidermal keratinocytes and dermal fibroblasts, harvested and separated from human foreskin, were cultured in serum-free keratinocyte culture medium and DMEM, respectively. The BFP was dissolved in double-deionized water, and was prepared at different concentrations. The BFP solution was subsequently added into the petri dish for grafting. MTT assay, total DNA measurement, and lactate dehydrogenase analysis were used to evaluate the cell viability, cell proliferation, and cytotoxicity. The immunochemical stain and SEM examination were chosen to make sure that the cultured cells still kept in phenotype. The results showed that the self-designed BFP was successfully coated on the petri dish to improve the cells' adhesion. The whole coating procedure was just done in aqueous solution without any organic solvent being involved. This method was much simpler than the traditional one, and there was no possibility to damage the immobilized biomolecules. From the results of the study, BFP could enhance attachment of keratinocytes and dermal fibroblasts without losing normal cell morphology and keep keratinocytes on the desired differentiation pathway. We believe that coating BFP on petri dish not only enhanced the keratinocyte attachment but also promoted keratinocytes proliferation. We suggest that the self-designed BFP has a great potential to apply on surface modification for the tissue-engineering scaffolds in the future.

Migration of keratinocytes is impaired on glycated collagen I

Advanced glycation end products are the chemical modification of proteins induced by sugars in a hyperglycemic condition. Extracellular matrix proteins are prominent targets of nonenzymatic glycation because of their slow turnover rates. The aim of this study was to investigate the influence of nonenzymatic glycation of type I collagen on the migration of keratinocytes. The migration of keratinocytes was dramatically promoted on native type I collagen-coated dishes compared with that on uncoated dishes. When type I collagen was glycated with glycolaldehyde, large amounts of advanced glycation end products were produced; the glycated collagen I-coated dishes did not promote the migration of keratinocytes. Glycated collagen I did not affect the proliferative capacity of keratinocytes. However, the adhesion of keratinocytes to glycated collagen I was profoundly diminished in a glycation intensity-dependent manner. alpha2beta1 integrin is responsible for the migration and adhesion of keratinocytes to type I collagen. Pretreatment with glycated collagen I did not affect the expression level or functional activity of alpha2beta1 integrin on keratinocytes. These findings suggest that in the presence of glycated collagen I, keratinocytes lose their adhesive and migratory abilities. As the glycation did not modify the alpha2beta1 integrin on keratinocytes, it is suggested that glycation may diminish the binding capacity of type I collagen.

Poly(ethylene glycol) enhances cell motility on protein-based poly(ethylene glycol)-polycarbonate substrates: a mechanism for cell-guided ligand remodeling

The regulation of cell motility on ligand-adsorbed poly(ethylene glycol) (PEG)-based polymeric biomaterials is governed by variables that are not well characterized. In this report, we examined keratinocyte migratory responsiveness to PEG-variant tyrosine-derived polycarbonates adsorbed with equivalent levels of the cell adhesion ligand, fibronectin. The equivalently adsorbed ligand adopted differential distributions, confirmed via atomic force microscopy, and the total number of exposed cell-binding domains (CBD), quantified through immunosorbent fluorometry, varied as a function of PEG concentration. Specifically, the CBD exposure was maximized at 4 mol % PEG and diminished at 8 mol % PEG, suggesting, based on our previous work (Tziampazis et al., Biomaterials 2000;21:511-520), that activation of cell adhesion and motility could be potentially promoted through increased CBD exposure at intermediate levels of PEG. This was confirmed through cell migration studies wherein cell speed values increased from 11 to 22 microm/h as the PEG concentration was increased from 0 to 4 mol %. Unexpectedly, however, high cell motility rates were sustained at 8 mol % PEG despite diminished levels of initial CBD exposure beyond 4 mol % PEG, suggesting that factors other than the initial CBD exposure may additionally have a role in activating cell migration at higher levels of PEG. Through studies of direct ligand mobility, cell-ligand-polymer interactions via atomic force microscopy, and CBD variation and integrin receptor roles in ligand remodeling, we offer evidence that cell motility is enhanced by a new mechanism for the regimen of higher PEG concentration: upon cell attachment and spreading, the ligand exhibits greater "slippage" at the polymer interface, and undergoes cell-engendered remodeling, which further activates cell motility, likely through enhanced exposure of hitherto encrypted sites for cell binding and signaling.

Retroviral gene transfer to human epidermal keratinocytes correlates with integrin expression and is significantly enhanced on fibronectin

Human epidermal keratinocytes are an important target for gene therapy because they can be easily expanded in culture and used to generate skin substitutes for the treatment of wounds, genetic diseases of the skin, and for delivery of proteins to the systemic circulation. Although retroviral transduction results in permanent genetic modification, differentiation and loss of transduced cells from the epidermis results in temporary transgene expression. To ensure permanent genetic modification, epidermal stem cells must be transduced with high efficiency. We evaluated gene transfer on two different substrates and found that the efficiency of gene transfer is substantially higher on a substrate of recombinant fibronectin (FN), when compared to tissue culture plastic (TCP). The rate of retroviral transduction on FN is four times faster than transduction on tissue culture plates and is independent of polybrene (PB). The transduction efficiency correlates with the levels of expression of integrin subunits alpha5, alpha2, and beta1, which have been shown to correlate with stem cell phenotype. Notably, cells that adhere rapidly to FN are transduced more efficiently than slowly adherent cells. In addition, integrin-blocking antibodies decrease the efficiency of gene transfer in a dose-dependent manner. Our results suggest that FN may enhance retroviral gene transfer to the least differentiated cells, thereby increasing the potential of genetically modified keratinocytes to treat short- and long-term disease states.

Ligation of integrin alpha 3beta 1 by laminin 5 at the wound edge activates Rho-dependent adhesion of leading keratinocytes on collagen

Wounding of the epidermis signals the transition of keratinocytes from quiescent anchorage on endogenous basement membrane laminin 5 to migration on exposed dermal collagen. In this study, we attempt to characterize activation signals that transform quiescent keratinocytes into migratory leading cells at the wound edge. Previously, we reported that adhesion and spreading on collagen via integrin alpha(2)beta(1) by cultured human foreskin keratinocytes (HFKs) requires RhoGTP, a regulator of actin stress fibers. In contrast, adhesion and spreading on laminin 5 requires integrins alpha(3)beta(1) and alpha(6)beta(4) and is dependent on phosphoinositide 3-hydroxykinase (Nguyen, B. P., Gil, S. G., and Carter, W. G. (2000) J. Biol. Chem. 275, 31896-31907). Here, we report that quiescent HFKs do not adhere to collagen but adhere and spread on laminin 5. By using collagen adhesion as one criterion for conversion to a "leading wound cell," we found that activation of collagen adhesion requires elevation of RhoGTP. Adhesion of quiescent HFKs to laminin 5 via integrin alpha(3)beta(1) and alpha(6)beta(4) is sufficient to increase levels of RhoGTP required for adhesion and spreading on collagen. Consistently, adhesion of quiescent HFKs to laminin 5, but not collagen, also promotes expression of the precursor form of laminin 5, a characteristic of leading keratinocytes in the epidermal outgrowth. We suggest that wounding of quiescent epidermis initiates adhesion and spreading of keratinocytes at the wound edge on endogenous basement membrane laminin 5 via alpha(3)beta(1) and alpha(6)beta(4) in a Rho-independent mechanism. Spreading on endogenous laminin 5 via alpha(3)beta(1) is necessary but not sufficient to elevate expression of precursor laminin 5 and RhoGTP, allowing for subsequent collagen adhesion via alpha(2)beta(1), all characteristics of leading keratinocytes in the epidermal outgrowth.

RhoA-dependent switch between alpha2beta1 and alpha3beta1 integrins is induced by laminin-5 during early stage of HT-29 cell differentiation

Integrin-mediated interactions between the basement membrane and epithelial cells control the differentiation of epithelia. We characterized the modulation of adhesive behaviors to basement membrane proteins and of integrin function in the human colon adenocarcinoma HT-29 cell line, which differentiates into enterocytes after the substitution of galactose for glucose in the medium. We demonstrate an increased capability of these cells to adhere to collagen type IV during the early stage of differentiation. This effect occurs without any changes in integrin cell surface expression but rather results from an alpha2beta1/alpha3beta1 integrin switch, alpha3beta1 integrin becoming the major collagen receptor. The increase in laminin-5 secretion and deposit on the matrix is a key factor in the mechanism regulating cell adhesion, because it is responsible for the activation of alpha3beta1 integrin. Furthermore, down-regulation of RhoA GTPase activity occurs during HT-29 cell differentiation and correlates with the activation of the integrin alpha3beta1. Indeed, C3 transferase, a RhoA GTPase inhibitor, induces a similar alpha2beta1/alpha3beta1 switch in undifferentiated HT-29 cells. These results indicate that the decrease in RhoA activation is the biochemical mechanism underlying this integrin switch observed during cell differentiation. The physiological relevance of such modulation of integrin activity in the functioning of the crypt-villus axis is discussed.

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.

Phosphorylation of focal adhesion kinase (pp125(FAK)) is increased in human keratinocytes induced to migrate by extracellular matrices

During the healing process of skin wounds, human keratinocytes migrate across a provisional matrix of the wound bed. The mechanisms by which keratinocytes migrate on connective tissue are not known. In this study, we examined the role of focal adhesion kinase (FAK), an 125 kDa protein that co-localizes with focal adhesions in cells plated on extracellular matrix. We induced human keratinocytes into various states of migration by plating them on extracellular matrices that minimally, moderately, or strongly induce cellular migration, and then examined the expression of FAK at the protein level and its degree of tyrosine phosphorylation using Western immunoblotting and immunoprecipitation. In highly migratory human keratinocytes, we found that three proteins were predominantly tyrosine phosphorylated, one of them being FAK. Tyrosine phosphorylation of FAK tightly correlated with the level of cellular motility but not cell attachment to the matrix. Time course experiments demonstrated that in highly motile keratinocytes, tyrosine phosphorylation of FAK peaked at 12 h, the time when maximal migration on the matrix ensues. In contrast to FAK, the beta1 integrin subunit of human keratinocytes that configures with the alpha2, alpha3, and alpha5 integrin subunits to form integrin receptors for matrix, did not display tyrosine phosphorylation linked to motility. Using anti-sense oligonucleotides to FAK, we demonstrate that FAK is required for human keratinocyte migration, but not for focal adhesion formation.

alpha v beta 6 Integrin upregulates matrix metalloproteinase 9 and promotes migration of normal oral keratinocytes

The integrin alpha v beta 6 is a fibronectin receptor that is undetectable on normal keratinocytes in situ, but is increased significantly in wound healing and in culture-established keratinocytes, suggesting that it may promote changes associated with cell motility. Using normal human oral keratinocytes we have shown that cultured cells express relatively high levels of alpha v beta 6 and this integrin has a functional role in both cell adhesion and migration towards fibronectin. We provide experimental evidence that the increased expression of alpha v beta 6 by normal human oral keratinocytes results in coordinate changes, which promote a more migratory phenotype. Thus increased expression of alpha v beta 6 results in a fibronectin-dependent increase in pro-matrix metalloproteinase 9, matrix metalloproteinase 9 activity increases normal human oral keratinocyte migration, and this may be further dependent on plasmin activation. The results suggest a key role for alpha v beta 6 in these processes and indicate a coordinated link between alpha v beta 6 expression and upregulation of matrix metalloproteinase 9. It appears that alpha v beta 6 may function in normal human oral keratinocyte migration through matrix-metalloproteinase-9-dependent and -independent mechanisms.

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.

Mouse keratinocytes immortalized with large T antigen acquire alpha3beta1 integrin-dependent secretion of MMP-9/gelatinase B

Remodeling of the extracellular matrix during tissue development, wound repair and tumor cell invasion depends on the coordinated regulation of cell adhesion receptors, matrix proteins and enzymes that proteolyse the extracellular matrix. Integrin alpha3beta1 is a major receptor on epidermal keratinocytes for laminin-5 in the cutaneous basement membrane and is required for normal basement membrane organization during skin development. alpha3beta1 is also expressed at high levels in the majority of adherent transformed cells and in most tumors, and it could have similar roles in extracellular matrix remodeling during tumorigenesis and cell invasion. In the present study, we show that alpha3beta1 expression is required in immortalized mouse keratinocytes (MK) for the production of the matrix metalloproteinase MMP-9/gelatinase B, an MMP that is coexpressed with alpha3beta1 in epithelial cell carcinomas and during wound healing, and contributes to the invasive potential of some tumor cells. MMP-9 was expressed in MK cells derived from wild-type mice, but not in MK cells derived from alpha3-null mice. Reconstitution of alpha3beta1 expression in alpha3-null MK cells through transfection with the alpha3 subunit restored MMP-9 secretion, indicating an alpha3beta1-dependent pathway for MMP-9 production. alpha3beta1-dependent expression of MMP-9 was associated with the immortalized phenotype, since nonimmortalized, primary keratinocytes required soluble growth factors, but not alpha3beta1, for efficient expression of MMP-9. Our results suggest that an alpha3beta1-independent pathway(s) for MMP-9 production is suppressed in keratinocytes immortalized with large T antigen, and that an alpha3beta1-dependent pathway is required for sustained production of MMP-9 in the absence of other pathways.

The PHSRN sequence induces extracellular matrix invasion and accelerates wound healing in obese diabetic mice

The PHSRN sequence of the plasma fibronectin (pFn) cell-binding domain induces human keratinocytes and fibroblasts to invade the naturally serum-free extracellular matrices of sea urchin embryos. The potency of acetylated, amidated PHSRN (Ac-PHSRN-NH(2)) is significantly increased, making it more active on a molar basis than the 120-kDa cell-binding domain of pFn. Arginine is important to this activity because PHSAN and PHSEN are inactive, as is a randomized sequence peptide, Ac-HSPNR-NH(2). One treatment with Ac-PHSRN-NH(2) stimulates reepithelialization and contraction of dermal wounds in healing-impaired, obese diabetic C57BL6/KsJ db/db mice. Wound closure is equally rapid in treated db/db and db/+ mice and may be more rapid than in untreated nondiabetic db/+ littermates. In contrast, treatment with either Ac-HSPNR-NH(2) or normal saline (NS) has no effect. Analysis of sectioned db/db wounds shows that, in contrast to treatment with Ac-HSPNR-NH(2) or NS, a single Ac-PHSRN-NH(2) treatment stimulates keratinocyte and fibroblast migration into wounds, enhances fibroplasia and vascularization in the provisional matrix, and stimulates the formation of prominent fibers that may be associated with wound contraction.

Substrate-adsorbed collagen and cell secreted fibronectin concertedly induce cell migration on poly(lactide-glycolide) substrates

Limited epithelial cell migration on synthetic polymeric biomaterials, such as polyesters, presents a serious challenge to their use as scaffolds for artificial skin analogs. The mechanisms by which a physiologic matrix interface on such polymers may regulate and promote cell migration under 'activated conditions' were the focus of this study. We have quantified the migration behavior of epidermal growth factor (EGF) stimulated epidermal keratinocytes on 50:50 poly-D,L(lactide-glycolide) (PLGA) substrates, following exogenous and cell-derived substrate conditioning based on the model matrix proteins, collagen and fibronectin. We report that 'non-conditioned' PLGA substrates elicited poor levels of keratinocyte migration. However, keratinocyte migration was significantly enhanced upon the adsorption of type I collagen, and was only weakly enhanced with fibronectin adsorption. Molecular analysis of the mechanism of enhanced migration on collagen-PLGA substrates showed that keratinocyte migration was sensitive to cell-derived fibronectin conditioning, but not to cell-secreted collagen conditioning. Fibronectin control of cell migration on collagen-PLGA was found to be both stoichiometric and biologically specific, mediated via adhesion involving keratinocyte alpha v integrin receptors. Based on our results, we propose a unique paradigm for induction of cell migration on a non-physiologic synthetic polymer using concerted interactions between primary, polymer-instructed matrix remodeling and secondary, cell-derived matrix remodeling.

In vitro modulation of keratinocyte wound healing integrins by zinc, copper and manganese

Although the trace elements zinc, copper and manganese are used in vivo for their healing properties, their mechanism of action is still only partially known. Some integrins expressed by basal layer keratinocytes play an essential part in healing, notably alpha2beta1, alpha3beta1, alpha6beta4 and alphaVbeta5, whose expression and distribution in epidermis are modified during the re-epithelialization phase. This study demonstrates how the expression of these integrins are modulated in vitro by trace elements. Integrin expression was studied in proliferating keratinocytes in monolayer cultures and in reconstituted skin that included a differentiation state. After 48 h incubation with zinc gluconate (0.9, 1.8 and 3.6 microg/mL), copper gluconate (1, 2 and 4 microg/mL), manganese gluconate (0.5, 1 and 2 microg/mL) and control medium, integrin expression was evaluated by FACScan and immunohistochemistry. Induction of alpha2, alpha3, alphaV and alpha6 was produced by zinc gluconate 1.8 microg/mL in monolayers, of alpha2, alpha6 and beta1 by copper gluconate 2 and 4 microg/mL and of all the integrins studied except alpha3 by manganese gluconate 1 microg/mL. Thus, alpha6 expression was induced by all three trace elements. The inductive effect of zinc was particularly notable on integrins affecting cellular mobility in the proliferation phase of wound healing (alpha3, alpha6, alphaV) and that of copper on integrins expressed by suprabasally differentiated keratinocytes during the final healing phase (alpha2, beta1 and alpha6), while manganese had a mixed effect.

Integrins and the kidney: biology and pathobiology

Integrins represent a superfamily of cell surface molecules that are important mediators of cell-extracellular matrix interactions. Of the many known integrin subunit combinations, only a few (alpha 1 beta 1, alpha 2 beta 1, alpha 3 beta 1, alpha 6 beta 1, alpha 8 beta 1 and alpha v beta 3) appear to play significant roles in renal development and function. The current understanding of these roles is reviewed. Potential therapeutic benefits from the alteration of integrin function by arginine-glycine-aspartic acid peptides in renal ischemic injury have been suggested. Reduced tubular obstruction is a potential mechanism, however other mechanisms remain to be explored. Finally, recent studies suggest a mechanism whereby abnormal interactions between integrins and non-specifically glycosylated glomerular basement membrane components could be involved in the pathogenesis of diabetic nephropathy. The elucidation of other potential pathophysiological roles for integrins in renal disease has just begun.

Lack of intrinsic polarity in the ligand-binding ability of keratinocyte beta1 integrins

Within the basal layer of the epidermis the beta1 integrins have a pericellular distribution. Two monoclonal antibodies, 15/7 and 12G10, that detect a conformation of the beta1 integrin subunit that is induced following cation or ligand occupancy selectively recognized beta1 integrins at the basement membrane zone in vivo and in focal adhesions of cultured keratinocytes; they did not recognize integrins on the apical and upper lateral membranes of basal keratinocytes nor integrins on the suprabasal keratinocytes of hyperproliferative epidermis. Inhibition of intercellular adhesion did not induce the 15/7 epitope on the lateral and apical membrane domains. The surface distribution of the epitopes was consistent with the antibodies acting as reporters of ligand-binding; in addition, the 15/7 epitope was exposed on unglycosylated, immature beta1 integrins. Although the apical membrane of basal keratinocytes is not normally in contact with extracellular matrix proteins, we found that it was capable of binding fibronectin-coated beads and that the 15/7 epitope was exposed on plasma membrane in contact with the beads. When a chimeric molecule consisting of the extracellular domain of CD8 and the cytoplasmic domain of the beta1 integrin subunit, used to mimic a constitutively active beta1 heterodimer, was introduced into keratinocytes it localized to the basal, lateral and apical membrane domains. We conclude that although the conformation of the keratinocyte beta1 integrins differs between the basal and the lateral/apical membrane domains there is no intrinsic polarity in the ligand binding potential of the receptors.

Novel roles for alpha3beta1 integrin as a regulator of cytoskeletal assembly and as a trans-dominant inhibitor of integrin receptor function in mouse keratinocytes

Previously we found that alpha3beta1 integrin-deficient neonatal mice develop micro-blisters at the epidermal-dermal junction. These micro-blisters were associated with poor basement membrane organization. In the present study we have investigated the effect of alpha3beta1-deficiency on other keratinocyte integrins, actin-associated proteins and F-actin organization. We show that the absence of alpha3beta1 results in an increase in stress fiber formation in keratinocytes grown in culture and at the basal face of the basal keratinocytes of alpha3-null epidermis. Moreover, we see a higher concentration of actin-associated proteins such as vinculin, talin, and alpha-actinin at focal contact sites in the alpha3-deficient keratinocytes. These changes in focal contact composition were not due to a change in steady-state levels of these proteins, but rather to reorganization due to alpha3beta1 deficiency. Apart from the loss of alpha3beta1 there is no change in expression of the other integrins expressed by the alpha3-null keratinocytes. However, in functional assays, alpha3beta1 deficiency allows an increase in fibronectin and collagen type IV receptor activities. Thus, our findings provide evidence for a role of alpha3beta1 in regulating stress fiber formation and as a trans-dominant inhibitor of the functions of the other integrins in mouse keratinocytes. These results have potential implications for the regulation of keratinocyte adhesion and migration during wound healing.

Initiation of skin basement membrane formation at the epidermo-dermal interface involves assembly of laminins through binding to cell membrane receptors

To study the mechanism of basement membrane formation, we determined by immunochemistry temporal and spatial expression of laminin-5 (Ln-5), laminin-1 (Ln-1) and their integrin receptors during early skin morphogenesis. A 3-dimensional skin culture was used that allows the study of the sequential molecular events of basement membrane formation at the epidermodermal interface. During early anchorage of keratinocytes to the extracellular matrix there is expression of Ln-5, BP-230 antigen and alpha3, beta1 integrin subunits. During epidermal stratification and prior to the formation of the lamina densa there is assembly of Ln-5, Ln-1, collagen IV and nidogen accompanied by keratinocyte basal clustering of alpha2, alpha3, alpha6, beta1, and beta4+ integrin subunits. The assembly pattern of Ln-1 and Ln-5 can be disturbed with functional antibodies against the beta1 (AIIB2) and alpha6 (GoH3) integrin subunits. Ln-1 assembly can also be disturbed with antibodies against its E8 domain and by competitive inhibition with a synthetic peptide (AG-73) derived from its G-4 domain. Quantitative RT-PCR showed that the dermis contributes about 80% of the laminin gamma)1 chain mRNA while 20% is produced by the epidermis which emphasizes its dual tissue origin and the major contribution of the mesenchyma in laminin production. The laminin gamma2 chain mRNA, present in Ln-5, was mostly of epidermal origin. This study presents evidence that during the initiation of basement membrane formation, laminins bind to keratinocyte plasma membrane receptors and thus may serve as nucleation sites for further polymerization of these compounds by a self-assembly process.

Negative cooperativity between alpha 3 beta 1 and alpha 2 beta 1 integrins in human mammary carcinoma MDA MB 231 cells

The alpha 3 beta 1 integrin has been implicated as a receptor for several matrix components, including collagen, fibronectin, and laminins. The function of alpha 3 beta 1 seems to be very versatile involving cell adhesion to or migration on ECM, establishment of cell-cell contacts in aggregates, as well as linkage to intracellular tyrosine phosphorylation cascades. Here we report a strong induction of attachment of alpha 3 beta 1 integrin expressing human breast carcinoma cell line MDA MB 231 to matrix proteins by two alpha 3 integrin subunit function-blocking monoclonal antibodies (P1B5 and ASC-1). In contrast, stimulation of adhesion to ECM by inhibitory alpha 3 integrin-specific antibodies was not observed in the alpha 3 beta 1 integrin-expressing nonmalignant human mammary epithelial cell line MCF-10A or the human breast carcinoma cell line MDA MB 468 that expressed relatively low amounts of alpha 3 beta 1 integrin at the cell surface. This increase was specific for collagens and not observed on fibronectin or laminin. Physiological concentrations of bivalent cations were not required. MAb P1B5 did not induce homotypic aggregation of MDA MB 231 cells. The P1B5-induced increase in cell attachment to collagens could be prevented but not reduced below control levels by blocking mAb to the alpha 2 integrin subunit. Function blocking anti-alpha 5 integrin subunit mAb was without effect while anti-beta 1-mAb completely abolished adhesion. Our data indicate that negative cooperativity between integrins results in transdominant inhibition of alpha 2 beta 1 function by alpha 3 beta 1 in human MDA MB 231 but not MDA MB 468 tumor cells or nonmalignant MCF-10A cells.

Hypoxia increases human keratinocyte motility on connective tissue

Re-epithelialization of skin wounds depends upon the migration of keratinocytes from the cut margins of the wound and is enhanced when human keratinocytes are covered with occlusive dressings that induce hypoxia. In this study, two independent migration assays were used to compare cellular motility on connective tissue components under normoxic or hypoxic conditions. Human keratinocytes apposed to collagens or fibronectin exhibited increased motility when subjected to hypoxic (0.2 or 2% oxygen) conditions compared with normoxic (9 or 20% oxygen) conditions. When compared with normoxic cells, hypoxic keratinocytes exhibited increased expression and redistribution of the lamellipodia-associated proteins (ezrin, radixin, and moesin). Furthermore, hypoxic keratinocytes demonstrated decreased secretion of laminin-5, a laminin isoform known to inhibit keratinocyte motility. Hypoxia did not alter the number of integrin receptors on the cell surface, but did induce enhanced secretion of the 92-kD type IV collagenase. These data demonstrate that hypoxia promotes human keratinocyte motility on connective tissue. Hypoxia-driven motility is associated with increased expression of lamellipodia proteins, increased expression of collagenase and decreased expression of laminin-5, the locomotion brake for keratinocytes.

Laminin-5 inhibits human keratinocyte migration

Laminin-5 (previously known as kalinin, epiligrin, and nicein) is an adhesive protein localized to the anchoring filaments within the lamina lucida space of the basement membrane zone lying between the epidermis and dermis of human skin. Anchoring filaments are structures within the lamina lucida and lie immediately beneath the hemidesmosomes of the overlying basal keratinocytes apposed to the basement membrane zone. Human keratinocytes synthesize and deposit laminin-5. Laminin-5 is present at the wound edge during reepithelialization. In this study, we demonstrate that laminin-5, a powerful matrix attachment factor for keratinocytes, inhibits human keratinocyte migration. We found that the inhibitory effect of laminin-5 on keratinocyte motility can be reversed by blocking the alpha3 integrin receptor. Laminin-5 inhibits keratinocyte motility driven by a collagen matrix in a concentration-dependent fashion. Using antisense oligonucleotides to the alpha3 chain of laminin-5 and an antibody that inhibits the cell binding function of secreted laminin-5, we demonstrated that the endogenous laminin-5 secreted by the keratinocyte also inhibits the keratinocyte's own migration on matrix. These findings explain the hypermotility that characterizes keratinocytes from patients who have forms of junctional epidermolysis bullosa associated with defects in one of the genes encoding for laminin-5 chains, resulting in low expression and/or functional inadequacy of laminin-5 in these patients. These studies also suggest that during reepithelialization of human skin wounds, the secreted laminin-5 stabilizes the migrating keratinocyte to establish the new basement membrane zone.

Integrin and basement membrane normalization in mouse grafts of human keratinocytes--implications for epidermal homeostasis

Integrin patterns and formation of basement membrane (BM) were investigated in correlation to epidermal growth and differentiation during skin regeneration in human keratinocyte transplants on nude mice. Immuno-fluorescence and transmission electron microscopy (TEM) showed that different stages of tissue reconstruction were characterized by a sequence of coordinated events. Features of the initial tissue activation, with rapid keratinocyte proliferation around day 4, including cells in a suprabasal position, were: (1) a marked increase in and extended distribution of the integrin chains alpha 2, alpha 3, beta 1 and alpha 6, while beta 4 already showed a preferential basal location; (2) de novo expression of alpha 5 and alpha v; and (3) marked deposition of laminin-5 and nidogen but low levels of other BM components. Tissue normalization during the 2nd week, initiated by a drastic decrease in the number of proliferating cells after day 4, now strictly in basal position, was signified: by (1) orthotopic staining for basal-type keratins (K5, K14) together with a regular pericellular alpha 2 beta 1 and alpha 3 beta 1 distribution, (2) linear, balanced deposition of BM components (e.g. laminin-1, type IV collagen) and (3) colocalization of integrin alpha 6 beta 4 and bullous pemphigoid antigen. Simultaneously at 7 days hemidesmosomes and a defined BM had developed (TEM), becoming continuous at 14 days. This coincided with the regular distribution of suprabasal keratins (K1, K10) as well as intermediate (involucrin) and late differentiation markers (filaggrin, loricrin). Type-VII collagen deposition, still irregular at 14 days, became continuous at 22 days together with developing BM-anchoring fibrils indicating final tissue consolidation. This model mimics principal stages of epidermal wound healing in human skin and implies a linkage between BM assembly, integrin distribution and the compartment of proliferation competent cells, which in turn determines the onset of differentiation. Thus, apart from the balance of diffusible growth regulators, this positional control of keratinocytes, largely accomplished by integrin-matrix interactions, seems to be prerequisite to establishment and maintenance of tissue homeostasis.

Laminins: a family of diverse multifunctional molecules of basement membranes

Laminins represent a growing family of disulfide-linked heterotrimers constituted by the association of three genetically different polypeptides, the alpha, beta, and gamma chains. Laminins are endowed with structural and biological functions. They play a direct critical role in the control of cellular behavior by providing cells with specific information through interactions with cell surface receptors. Because of their structural properties, they represent crucial building blocks for tissue assembly, architecture, and stability. The expression of laminin chain variants is spatio-temporally regulated, which suggests that laminin isoforms might have different functions responsible for the biological and morphological polymorphism of basement membranes. The different cells present in the skin express several laminin chains, which lead to the deposition of various laminin isoforms, whose mechanical and biological functions are likely to be adapted to the properties of the dermo-epidermal junction. Recently, defective laminin isoforms have been shown to be associated with several inborn and acquired diseases, illustrating a major structural function for laminins in skin integrity.