Changes in the concentrations of extracellular Mg++ and Ca++ down-regulate E-cadherin and up-regulate alpha 2 beta 1 integrin function, activating keratinocyte migration on type I collagen

PVP as an Oxygen Vacancy-Inducing Agent in the Development of Black 45S5 Bioactive Glass Fibrous Scaffolds Doped with Zn and Mg Using A-HSBS

Currently, there is an increasing demand for advanced materials that can address the needs of tissue engineering and have the potential for use in treatments targeting tumor cells, such as black bioactive materials in photothermal therapy. Thus, 3D fibrous scaffolds of black 45S5 bioactive glass were produced using the air-heated solution blow spinning (A-HSBS) technique, with polyvinylpyrrolidone (PVP) serving as a spinning aid and an oxygen vacancy-inducing agent. Glass powder with the same composition was synthesized via the sol-gel route for comparison. The samples were characterized using thermogravimetric analysis, X-ray diffraction, FTIR spectroscopy, and scanning electron microscopy, along with in vitro tests using simulated body fluid (SBF), phosphate-buffered saline (PBS), and TRIS solution. The results showed that PVP enhanced oxygen vacancy formation and stabilized the scaffolds at 600 °C. Doping with Zn and Mg ions reduced crystallization while significantly increasing the fiber diameters. Scaffolds doped with Zn exhibited lower degradation rates, delayed apatite formation, and hindered ionic release. Conversely, Mg ions facilitated greater interaction with the medium and rapid apatite formation, completely covering the fibers. The scaffolds showed no cytotoxicity in the MTT assay at concentrations of up to 200 µg/mL for HaCat cells and 0.8 mg/mL for L929 cells. This study demonstrated the effectiveness of using PVP in the production of black bioactive glass scaffolds, highlighting their potential for bone regeneration.

Layer-by-layer assembly of procyanidin and collagen promotes mesenchymal stem cell proliferation and osteogenic differentiation in vitro and in vivo

Collagen, commonly used in tissue engineering, is widespread in various tissues. During bone tissue regeneration, collagen can stimulate the cellular response and determine the fate of cells. In this work, we integrated collagen type II with procyanidin (PC) onto an implant coating by applying a layer-by-layer technique to demonstrate that collagen and PC can participate in the construction of new biomaterials and serve as multifunctional components. The effects of PC/collagen multilayers on the viability of cocultured bone marrow mesenchymal stem cells (BMSCs) were analyzed by cell counting kit-8 analysis and phalloidin staining. The reactive oxygen species level of BMSCs was revealed through immunofluorescent staining and flow cytometry. Osteogenesis-related genes were detected, and in vivo experiment was performed to reveal the effect of newly designed material on the osteogenic differentiation of BMSCs. Our data demonstrated that in BMSCs PC/collagen multilayers accelerated the proliferation and osteogenic differentiation through Wnt/β-catenin signaling pathway and enhanced bone generation around the implant in the bone defect model of rabbit femurs. In summary, combination of collagen and PC provided a new sight for the research and development of implant materials or coatings in the future.

α2β1 integrins spatially restrict Cdc42 activity to stabilise adherens junctions

Background

Keratinocytes form the main protective barrier in the skin to separate the underlying tissue from the external environment. In order to maintain this barrier, keratinocytes form robust junctions between neighbouring cells as well as with the underlying extracellular matrix. Cell–cell adhesions are mediated primarily through cadherin receptors, whereas the integrin family of transmembrane receptors is predominantly associated with assembly of matrix adhesions. Integrins have been shown to also localise to cell–cell adhesions, but their role at these sites remains unclear.

Results

Here we show that α2β1 integrins are enriched at mature keratinocyte cell–cell adhesions, where they play a crucial role in organising cytoskeletal networks to stabilize adherens junctions. Loss of α2β1 integrin has significant functional phenotypes associated with cell–cell adhesion destabilisation, including increased proliferation, reduced migration and impaired barrier function. Mechanistically, we show that α2β1 integrins suppress activity of Src and Shp2 at cell–cell adhesions leading to enhanced Cdc42–GDI interactions and stabilisation of junctions between neighbouring epithelial cells.

Conclusion

Our data reveals a new role for α2β1 integrins in controlling integrity of epithelial cell–cell adhesions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01054-9.

Bioinorganics and Wound Healing

Wound dressings and the healing enhancement (increasing healing speed and quality) are two components of wound care that lead to a proper healing. Wound care today consists mostly of providing an optimal environment by removing waste and necrotic tissues from a wound, preventing infections, and keeping the wounds adequately moist. This is however often not enough to re-establish the healing process in chronic wounds; with the local disruption of vascularization, the local environment is lacking oxygen, nutrients, and has a modified ionic and molecular concentration which limits the healing process. This disruption may affect cellular ionic pumps, energy production, chemotaxis, etc., and will affect the healing process. Biomaterials for wound healing range from simple absorbents to sophisticated bioactive delivery vehicles. Often placing a material in or on a wound can change multiple parameters such as pH, ionic concentration, and osmolarity, and it can be challenging to pinpoint key mechanism of action. This article reviews the literature of several inorganic ions and molecules and their potential effects on the different wound healing phases and their use in new wound dressings.

The Psoriasis Therapeutic Potential of a Novel Short Laminin Peptide C16

Psoriasis is a chronic inflammatory skin disease characterized by excessive growth of keratinocytes and hyperkeratosis in the epidermis. An abnormality of the non-lesional epidermis at an early stage of psoriasis is involved in triggering inflammatory cell infiltration into the dermis. Integrin α5β1 acts as a receptor for fibronectin and has been found to be overexpressed in non-lesional psoriatic epidermis. To investigate whether α5β1 integrin has a potential as a drug target for psoriasis treatment, the α5β1 integrin-binding peptide, C16, was used to obstruct the HaCat keratinocyte cellular responses induced by fibronectin (Fn) in culture and psoriasis-like skin inflammation induced in mice by imiquimod (IMQ). The C16 exhibited antagonistic activity against α5β1 integrin in HaCat cells, with evidence of suppression of the Fn-mediated proliferative, cytoskeletal, and inflammatory responses. Topical treatment with C16 greatly reduced the IMQ-induced epidermal hyperplasia, infiltration of neutrophils/macrophages, and expression of pro-inflammatory mediators in mouse skin. The C16SP (C16-derived short peptide; DITYVRLKF) also exhibited antagonistic activity, suppressing α5β1 integrin activity in culture, and reducing IMQ-induced skin inflammation. Taken together, this study provides the first evidence that α5β1 integrin may be a potential drug target for psoriasis. The synthetic C16 peptide may serve as an agent for psoriasis therapy.

Microstructure-modified biodegradable magnesium alloy for promoting cytocompatibility and wound healing in vitro

The microstructure of biomedical magnesium alloys has great influence on anti-corrosion performance and biocompatibility. In practical application and for the purpose of microstructure modification, heat treatments were chosen to provide widely varying microstructures. The aim of the present work was to investigate the influence of the microstructural parameters of an Al-free Mg-Zn-Zr alloy (ZK60), and the corresponding heat-treatment-modified microstructures on the resultant corrosion resistance and biological performance. Significant enhancement in corrosion resistance was obtained in Al-free Mg-Zn-Zr alloy (ZK60) through 400 °C solid-solution heat treatment. It was found that the optimal condition of solid-solution treatment homogenized the matrix and eliminated internal defects; after which, the problem of unfavorable corrosion behavior was improved. Further, it was also found that the Mg ion-release concentration from the modified ZK60 significantly induced the cellular activity of fibroblast cells, revealing in high viability value and migration ability. The experimental evidence suggests that this system can further accelerate wound healing. From the perspective of specific biomedical applications, this research result suggests that the heat treatment should be applied in order to improve the biological performance.

Substrate Stiffness Affects Human Keratinocyte Colony Formation

Restoration of epidermal organization and function in response to a variety of pathophysiological insults is critically dependent on coordinated keratinocyte migration, proliferation, and stratification during the process of wound healing. These processes are mediated by the reconfiguration of both cell-cell (desmosomes, adherens junctions) and cell-matrix (focal adhesions, hemidesmosomes) junctions and the cytoskeletal filament networks that they serve to interconnect. In this study, we investigated the role of substrate elasticity (stiffness) on keratinocyte colony formation in vitro during the process of nascent epithelial sheet formation as triggered by the calcium switch model of keratinocyte culture. Keratinocytes cultured on pepsin digested type I collagen coated soft (nominal E = 1.2 kPa) polyacrylamide gels embedded with fluorescent microspheres exhibited (i) smaller spread contact areas, (ii) increased migration velocities, and (iii) increased rates of colony formation with more cells per colony than did keratinocytes cultured on stiff (nominal E = 24 kPa) polyacrylamide gels. As assessed by tracking of embedded microsphere displacements, keratinocytes cultured on soft substrates generated large local substrate deformations that appeared to recruit adjacent keratinocytes into joining an evolving colony. Together with the observed differences in keratinocyte kinematics and substrate deformations, we developed two ad hoc analyses, termed distance rank (DR) and radius of cooperativity (RC), that help to objectively ascribe what we perceive as increasingly cooperative behavior of keratinocytes cultured on soft versus stiff gels during the process of colony formation. We hypothesize that the differences in keratinocyte colony formation observed in our experiments could be due to cell-cell mechanical signaling generated via local substrate deformations that appear to be correlated with the increased expression of β4 integrin within keratinocytes positioned along the periphery of an evolving cell colony.

The regulation of integrin function by divalent cations

Integrins are a family of α/β heterodimeric adhesion metalloprotein receptors and their functions are highly dependent on and regulated by different divalent cations. Recently advanced studies have revolutionized our perception of integrin metal ion-binding sites and their specific functions. Ligand binding to integrins is bridged by a divalent cation bound at the MIDAS motif on top of either α I domain in I domain-containing integrins or β I domain in α I domain-less integrins. The MIDAS motif in β I domain is flanked by ADMIDAS and SyMBS, the other two crucial metal ion binding sites playing pivotal roles in the regulation of integrin affinity and bidirectional signaling across the plasma membrane. The β-propeller domain of α subunit contains three or four β-hairpin loop-like Ca(2+)-binding motifs that have essential roles in integrin biogenesis. The function of another Ca(2+)-binding motif located at the genu of α subunit remains elusive. Here, we provide an overview of the integrin metal ion-binding sites and discuss their roles in the regulation of integrin functions.

Divalent cations modulate alpha2beta1 integrin-mediated malignancy in a novel 3-dimensional in vitro model of pancreatic cancer

OBJECTIVES

We previously showed that divalent cations regulate alpha2beta1 integrin-mediated pancreatic cancer cell interactions with type I collagen in 2 dimensions (2D), including cell adhesion, migration, and proliferation. Presently, we examined divalent cation-dependent alpha2beta1 integrin-mediated pancreatic cancer cell adhesion and proliferation on type I collagen in a novel 3D in vitro model.

METHODS

Cell attachment, proliferation, and antibody inhibition assays on type I collagen in both 2D and 3D, and microscopy and immunoblotting were used for these studies.

RESULTS

As in 2D, cell attachment on type I collagen in 3D is Mg-dependent and inhibited by Ca. Proliferation in 3D is also Mg-dependent, but maximal when Mg is present at concentrations that promote maximal cell adhesion and Ca is present at concentrations less than Mg. Immunoblotting studies demonstrate that the divalent cation-dependent changes in cell-cell adhesion observed on type I collagen in both 2D and 3D are associated with the changes in E-cadherin and beta-catenin expression. Antibody inhibition assays indicate further that the alpha2beta1 integrin specifically mediates proliferation on type I collagen in 3D under altered divalent cation conditions.

CONCLUSIONS

Divalent cation shifts could activate alpha2beta1 integrin-mediated malignancy in the type I collagen-rich 3D tumor microenvironment of pancreatic cancer.

Development of a calcium-chelating hydrogel for treatment of superficial burns and scalds

Aims: Superficial burns and scalds are usually managed conservatively with traditional dressings. Failure to heal within 3 weeks leads to their management by skin grafting. Our aim was to develop a biomaterial to actively promote keratinocyte migration in superficial burns by modulating local cation concentrations to accelerate keratinocyte migration and deter wounds from contracting, thus potentially reducing the number of such wounds requiring grafting. Materials & methods: We investigated polymeric hydrogels for their Ca2+ chelating properties and enhancement of keratinocyte migration in human tissue-engineered skin models. Results: Dimethylaminoethyl methacrylate:methacrylic acid hydrogel coupled with elevated [Mg2+] reduced media [Ca2+], potentiating keratinocyte migration in tissue-engineered skin models, it also significantly reduced wound model contraction. Conclusion: Dimethylaminoethyl methacrylate:methacrylic acid hydrogels could promote wound healing and reduce wound contraction, a significant complication in burn wound healing.

Divalent cations modulate the integrin-mediated malignant phenotype in pancreatic cancer cells

We have previously demonstrated that pathophysiological shifts in the concentrations of extracellular Mg(2+) and Ca(2+) activate the alpha(2)beta(1) integrin-mediated malignant phenotype on type I collagen in pancreatic cancer cells, as evidenced by increased adhesion, migration and proliferation. In the present study, we examined the integrin and divalent cation specificity of pancreatic cancer cell interactions with other physiologically relevant extracellular matrix proteins, including fibronectin, type IV collagen, laminin and vitronectin. Our results indicate that, like alpha(2)beta(1) integrin-mediated interactions with type I collagen, beta(1) integrin-mediated adhesion to fibronectin, type IV collagen and laminin are promoted by Mg(2+) but not by Ca(2+). On vitronectin, cells attach via alpha(v)beta(5) and beta(1) integrins, and in the presence of either divalent cation. We also demonstrate that, like type I collagen, pancreatic cancer cell migration and proliferation on fibronectin, laminin and type IV collagen is maximal when Mg(2+) is present at concentrations that promote optimal adhesion and Ca(2+) is present at concentrations less than Mg(2+). On vitronectin, Panc-1 cell migration is maximal with decreased Mg(2+) and increased Ca(2+), but the reverse is true for BxPC-3 cells. Both cell lines exhibited maximal proliferation with increased Mg(2+) and decreased Ca(2+), however. Together with evidence indicating that the in vivo local tumor microenvironment contains increased Mg(2+) and decreased Ca(2+), our studies demonstrate that such divalent cation shifts could activate the integrin-mediated malignant phenotype in pancreatic cancer.

Activation of the alpha2beta1 integrin-mediated malignant phenotype on type I collagen in pancreatic cancer cells by shifts in the concentrations of extracellular Mg2+ and Ca2+

The authors have previously demonstrated that alpha(2)beta(1) integrin-mediated pancreatic cancer cell adhesion to Type I collagen is Mg(2+)-dependent, inhibited by Ca(2+), and that this integrin, purified from cell lysates using Type I-collagen-sepharose in Mg(2+), can be eluted with Ca(2+). In the present study, the authors examined the divalent cation-dependency of alpha(2)beta(1) integrin-mediated pancreatic cancer cell adhesion, migration and proliferation on Type I collagen, an extracellular matrix protein shown to be highly up-regulated, and to promote the malignant phenotype in vitro and in vivo. The results indicate that cells attach to Type I collagen maximally when Mg(2+) is greater than 1 mM, and that addition of increasing concentrations of Ca(2+) reduces this adhesion. These effects are reversible, in that previous cell attachment in Mg(2+) can be reversed by adding Ca(2+), and vice versa. They also demonstrate that pancreatic cancer cells migrate and proliferate on Type I collagen in Mg(2+) alone, but maximally when Mg(2+) is present at concentrations that promote maximal cell adhesion and Ca(2+) is present at concentrations less than Mg(2+). Cell adhesion and proliferation assays, as well as affinity chromatography on Type I collagen using anti-integrin function-blocking monoclonal antibodies indicate that the effects of these divalent cation shifts are mediated specifically by the alpha(2)beta(1) integrin. As pancreatic juice contains over 1,200-fold more Mg(2+) than Ca(2+) and solid tumors are characterized by increased magnesium load, these data indicate that such pathophysiological divalent cation shifts could be involved in the activation of the alpha(2)beta(1) integrin-mediated malignant phenotype on Type I collagen in the pancreatic cancer.

The integrin-extracellular matrix axis in pancreatic cancer

Pancreatic cancer is the fifth leading cause of adult cancer death in the United States, with 5-year survival rates of only 1% to 4%. Current therapeutic strategies generally result in only a few months of extended life. Recent evidence from several independent laboratories in vitro and in vivo indicate that integrin-mediated cell attachment to the extracellular matrix (ECM), components of which are highly up-regulated in pancreatic cancer, evokes phenotypes and signaling pathways that regulate tumor cell growth and migration. In this review, we will discuss our current understanding of the role of the ECM in directing pancreatic cancer growth, progression, and metastasis. Topics covered include a survey of the existing literature regarding the in vivo and in vitro expression of the ECM and its cell surface receptors, the integrins, in pancreatic cancer; mechanisms involved in the integrin-ECM-mediated malignant phenotype; and future directions for the study of the integrin-ECM axis and its role in pancreatic cancer progression, including potential therapeutic strategies.

Determination of the ligand-binding specificities of the alpha2beta1 and alpha1beta1 integrins in a novel 3-dimensional in vitro model of pancreatic cancer

OBJECTIVES

Pancreatic cancer cells express 2 known collagen-binding integrins, alpha2beta1 and alpha1beta1. The ligand-binding specificity of alpha1beta1 and the integrin/s responsible for mediating the malignant phenotype on type I collagen in the 3-dimensional (3D) tumor microenvironment have not been determined in pancreatic cancer. The aim of the present study was to determine the ligand-binding specificities of the alpha2beta1 and alpha1beta1 integrins using a novel 3D in vitro model of pancreatic cancer.

METHODS

We used 3D type I collagen-glycosaminoglycan scaffolds in adhesion and proliferation assays with pancreatic cancer cell lines, as well as affinity chromatography and inhibition of adhesion assays.

RESULTS

We demonstrate for the first time that CFPAC, BxPC-3, Colo-357, FG, and Panc-1 cells attach to 3D type I collagen scaffolds in an alpha2beta1-specific manner and that this integrin-specific adhesion is required for subsequent cell proliferation. MiaPaCa-2 cells, which do not express the alpha2beta1 or alpha1beta1 integrins, do not attach or proliferate on 3D type I collagen scaffolds. We also demonstrate the novel finding that the alpha1beta1 integrin is a type IV collagen receptor in pancreatic cancer cells.

CONCLUSIONS

These data indicate that targeting alpha2beta1 integrin-specific type I collagen adhesion may have therapeutic value in the treatment of pancreatic cancer.

Integrin α2β1 Is Required for Regulation of Murine Wound Angiogenesis but Is Dispensable for Reepithelialization

The alpha2beta1 integrin functions as the major receptor for collagen type I on a large number of different cell types, including keratinocytes, fibroblasts, endothelial cells, and a variety of inflammatory cells. Recently, we demonstrated that adhesion of keratinocytes to collagen critically depends on alpha2beta1, whereas fibroblasts can partly compensate for loss of alpha2beta1 in simple adhesion to collagen. However, in three-dimensional collagen matrices, alpha2beta1-null fibroblasts are hampered in generating mechanical forces. These data suggested a pivotal role for alpha2beta1 during wound healing in vivo. Unexpectedly, reepithelialization of excisional wounds of alpha2beta1-null mice was not impaired, indicating that keratinocytes do not require adhesion to or migration on collagen for wound closure. Whereas wound contraction and myofibroblast differentiation were similar, wound tensile strain was reduced in alpha2beta1-null mice, suggesting subtle changes in organization of the extracellular matrix. In addition, we observed reduced influx of mast cells into the granulation tissue, whereas infiltration of other inflammatory cells was not impaired. Interestingly, ablation of alpha2beta1 resulted in strong enhancement of neovascularization of granulation tissue and sponge implants. Both ultrastructurally and functionally, these new blood vessels appeared intact. In conclusion, our data show unique and overlapping functions of alpha2beta1 integrin during murine cutaneous wound healing.

Calcium and magnesium competitively influence the growth of a PMR1 deficientSaccharomyces cerevisiaestrain

PMR1, the Ca2+/Mn2+ ATPase of the secretory pathway in Saccharomyces cerevisiae was the first member of the secretory pathway Ca2+ ATPases (SPCA) to be characterized. In the past few years, pmr1Delta yeast have received more attention due to the recognition that the human homologue of this protein, hSPCA1 is defective in chronic benign pemphigus or Hailey-Hailey disease (HHD). Recent publications have described pmr1Delta S. cerevisiae as a useful model organism for studying the molecular pathology of HHD. Some observations indicated that the high Ca2+ sensitive phenotype of PMR1 defective yeast strains may be the most relevant in this respect. Here we show that the total cellular calcium response of a pmr1Delta S. cerevisiae upon extracellular Ca2+ challenge is decreased compared to the wild type strain similarly as observed in keratinocytes. Additionally, the novel magnesium sensitivity of PMR1 defective yeast is revealed, which appears to be a result of competition for uptake between Ca2+ and Mg2+ at the plasma membrane level. Our findings indicate that extracellular Ca2+ and Mg2+ competitively influence the intracellular Ca2+ homeostasis of S. cerevisiae. These observations may further our understanding of HHD.

GSK3 and PKB/Akt are associated with integrin-mediated regulation of PTHrP, IL-6 and IL-8 expression in FG pancreatic cancer cells

We have demonstrated recently that PTHrP is upregulated in pancreatic adenocarcinoma and that the ECM exerts regulatory control, at least in part, over PTHrP expression. In our present study, we examined the potential signaling interactions between these 2 pathways. Our results demonstrate that, under serum-free conditions, adhesion of FG pancreatic adenocarcinoma cells on Fn is mediated by the alpha5beta1 integrin, whereas adhesion to Type I collagen is mediated by the alpha2beta1 integrin. alpha5beta1 integrin-mediated adhesion to Fn results in a phenotype that includes a reduction in cell proliferation, increased E-cadherin localization in cell-cell contacts, increased beta-catenin localization throughout the cell, inhibition of haptokinetic cell migration, and increased expression of PTHrP, IL-6 and IL-8 relative to alpha2beta1 integrin-mediated adhesion on Type I collagen. A phosphoprotein immunoblotting screen of FG pancreatic cancer cells grown on either Fn or Type I collagen indicates that GSK3 and PKB/Akt are differentially phosphorylated on these 2 substrates. These results implicate GSK3 and PKB/Akt in the integrin-mediated regulation of PTHrP, IL-6 and IL-8 in pancreatic cancer.

Bathing in a magnesium-rich Dead Sea salt solution improves skin barrier function, enhances skin hydration, and reduces inflammation in atopic dry skin

Magnesium salts, the prevalent minerals in Dead Sea water, are known to exhibit favorable effects in inflammatory diseases. We examined the efficacy of bathing atopic subjects in a salt rich in magnesium chloride from deep layers of the Dead Sea (Mavena(R) Dermaline Mg(46) Dead Sea salt, Mavena AG, Belp, Switzerland). Volunteers with atopic dry skin submerged one forearm for 15 min in a bath solution containing 5% Dead Sea salt. The second arm was submerged in tap water as control. Before the study and at weeks 1-6, transepidermal water loss (TEWL), skin hydration, skin roughness, and skin redness were determined. We found one subgroup with a normal and one subgroup with an elevated TEWL before the study. Bathing in the Dead Sea salt solution significantly improved skin barrier function compared with the tap water-treated control forearm in the subgroup with elevated basal TEWL. Skin hydration was enhanced on the forearm treated with the Dead Sea salt in each group, which means the treatment moisturized the skin. Skin roughness and redness of the skin as a marker for inflammation were significantly reduced after bathing in the salt solution. This demonstrates that bathing in the salt solution was well tolerated, improved skin barrier function, enhanced stratum corneum hydration, and reduced skin roughness and inflammation. We suggest that the favorable effects of bathing in the Dead Sea salt solution are most likely related to the high magnesium content. Magnesium salts are known to bind water, influence epidermal proliferation and differentiation, and enhance permeability barrier repair.

The extracellular matrix differentially regulates the expression of PTHrP and the PTH/PTHrP receptor in FG pancreatic cancer cells

OBJECTIVES

Previous studies by our laboratory have demonstrated that parathyroid hormone-related protein (PTHrP) and its receptor (PTH/PTHrP receptor) are commonly expressed in pancreatic cancer and suggest their participation in the progression of this devastating disease. It has also been demonstrated that one of the major hallmarks of pancreatic adenocarcinoma is an increased production of the extracellular matrix (ECM), a critical regulator of diverse cellular processes such as differentiation, proliferation, and angiogenesis. The present study focused on the relationship between the PTHrP and ECM axes in the pathobiology of pancreatic cancer.

METHOD AND RESULTS

Using the FG pancreatic adenocarcinoma cell line, we demonstrate a significant inverse correlation between FG cell proliferation and PTHrP expression that depended on the ECM protein on which the cells were cultured (P < 0.05). Generally, ECM proteins that promoted the strongest proliferation, including type I collagen, type IV collagen, and laminin, resulted in decreased expression of PTHrP. Conversely, ECM proteins that promoted the weakest proliferation, including fibronectin, vitronectin, and BSA, resulted in increased expression of PTHrP. A similar trend was found between FG cell proliferation and the PTH/PTHrP receptor expression, with Pearson correlation coefficients of 0.480 (mRNA) and -0.591 (protein).

CONCLUSION

These observations demonstrate a unique functional relationship between the ECM and PTHrP axes and have important implications for our understanding of the complex mechanisms responsible for the progression of pancreatic cancer and its metastases.

Novispirin G10-induced lung toxicity in a Klebsiella pneumoniae infection model

Mammalian cathelicidins are a class of innate antimicrobial peptides isolated from leukocytes and epithelial cells that aid host defense against bacterial infections. Synthetic analogs of cathelicidins offer the promise of potent broad-spectrum antimicrobial efficacy. We developed a combined lung infection and ex vivo whole-blood assay model to characterize the toxicity and efficacy of synthetic cathelicidin-derived peptides. Male C57BL/6 mice were administered saline or Klebsiella pneumoniae by intratracheal instillation. Five hours later, the Klebsiella-infected mice were instilled with saline, tobramycin (1 mg/kg of body weight or 10 mg/kg), novispirin G10 (0.4 mg/kg), or a combination of tobramycin (1 mg/kg) and G10 (0.4 mg/kg). At 24 h, bronchoalveolar lavage fluid (BAL) was collected for analysis of culturable bacteria and for markers of inflammation and lung toxicity. Blood samples were analyzed for circulating cytokines. Recovery of Klebsiella from the lung, recruitment of neutrophils, and production of interleukin-6 (IL-6) in BAL samples were highly correlated (r=0.68 and 0.84, respectively; P<0.01). Animals treated with G10 or G10 plus tobramycin had increased hemoglobin (P<0.001) and protein (P<0.001) levels compared to those for Klebsiella-infected or tobramycin-alone-treated animals. The levels of circulating IL-6 in mice infected with Klebsiella were 1000- to 10,000-fold higher than in the noninfected controls. The highest levels of IL-6 were measured in mice given G10 alone or in combination with tobramycin. These studies demonstrated that G10 was relatively nontoxic in saline-treated mice but was highly toxic in mice infected with Klebsiella. This finding establishes the importance of investigating candidate antimicrobial agents in an in vivo infection model.

A Novel Role of Fibrin in Epidermal Healing: Plasminogen-Mediated Migration and Selective Detachment of Differentiated Keratinocytes

Recent studies have shown that fibrin promotes epidermal regeneration in vitro and maintains the stem cell population after transplantation of keratinocytes in vivo. As epidermal keratinocytes do not express integrin alpha(v)beta3, the receptor for fibrin and fibrinogen, the mechanism through which fibrin affects epidermal cells remains elusive. To investigate the role of fibrin in epidermal wound healing, we developed an in vitro model in which fibrin was added to the top of wounded keratinocyte monolayers grown on collagen. With this matrix topology, keratinocytes migrate between the collagen on their basal side and fibrin on their apical side mimicking migration of the epidermis in vivo. Using this model, we found that fibrin promoted keratinocyte migration in low and high calcium concentrations by exposing the cells to plasminogen. The migration rate depended strongly on the concentration of fibrinogen and the rate of plasmin-mediated fibrin degradation. Surprisingly, fibrin and fibrinogen caused significant detachment of keratinocytes which was prevented by the addition of calcium. Further examination using flow cytometry revealed that the detached cells were larger, more granular, and had very low levels of beta1 integrin, which are all signs of differentiated keratinocytes. Our results suggest a novel dual role of fibrin in epidermal healing. First, fibrin promotes keratinocyte migration indirectly by exposing plasminogen to migrating cells, and second, fibrin selectively disrupts adhesion of differentiated keratinocytes. Our data are novel and may have important implications in understanding wound healing and in the use of fibrin as a biomaterial for protein and gene delivery.

Human dermal fibroblasts do not exhibit directional migration on collagen I in direct-current electric fields of physiological strength

Endogenous electric fields are generated lateral to skin wounds, with the cathodal pole of the field residing in the center of the wound. These fields are thought to be an important mechanism in guiding the migration of keratinocytes and other cells into wounds to effect healing. In this work, human dermal fibroblasts were exposed to direct current electric fields of physiological strength, and their migrational behavior was quantitated. Only random migration of human dermal fibroblasts was observed in direct-current electric fields under conditions that support the directional migration of human epidermal keratinocytes. Additionally, neither the presence of serum nor serum plus additional Mg++ in the experimental medium supported directional migration. Migratory rates of fibroblasts varied depending on the experimental medium used: in serum-containing medium the average velocity was as low as 0.23 micro m/min, while in serum-free keratinocyte medium the average velocity was as high as 0.36 micro m/min. These studies suggest that dermal fibroblasts do not respond to the endogenous electric field of a wound, and use other migratory cues to direct their movement into the wound bed.

Partial characterization of cell-type X collagen interactions

Type X collagen is a short-chain non-fibrillar collagen that is deposited exclusively at sites of new bone formation. Although this collagen has been implicated in chondrocyte hypertrophy and endochondral ossification, its precise function remains unclear. One possible function could be to regulate the processes of chondrocyte hypertrophy through direct cell-type X collagen interactions. Adhesions of embryonic chick chondrocytes, and cell lines with known expression of collagen-binding integrins (MG63 and HOS), were assayed on chick type X collagen substrates, including the native, heat-denatured and pepsin-digested collagen, and the isolated C-terminal non-collagenous (NC1) domain. Type X collagen supported the greatest level of adhesion for all cell types tested. The involvement of the alpha2beta1 integrin in type X collagen-cell interaction was demonstrated by adhesion studies in the presence of Mg(2+) and Ca(2+) ions and integrin-function-blocking antibodies. Cells expressing alpha2beta1 integrin (chick chondrocytes and MG63 cells) also adhered to heat-denatured type X collagen and the isolated NC1 domain; however, removal of the non-collagenous domains by limited pepsinization of type X collagen resulted in very low levels of adhesion. Both focal contacts and actin stress-fibre formation were apparent in cells plated on type X collagen. The presence of alpha2 and beta1 integrin subunits in isolated chondrocytes and epiphyseal cartilage was also confirmed by immunolocalization. Our results demonstrate, for the first time, that type X collagen is capable of interacting directly with chondrocytes and other cells, primarily via alpha2beta1 integrin. These findings are atypical from the fibrillar collagen-cell interactions via collagen binding integrins in that: (1) the triple-helical conformation is not strictly required for cell adhesion; (2) the NC1 domain is also involved in the adhesion of alpha2beta1-expressing cells. These data form the basis for further studies into the mechanism and biological significance of type X collagen deposition in the growth plate.

Modulation in vitro of keratinocyte integrins by interferon-alpha and interferon-gamma

BACKGROUND

Interferon-alpha and -gamma are glycoproteins with antiviral and immunoregulatory properties. In vitro studies have shown a role for these cytokines in the regulation of epidermal keratinocyte growth and differentiation. In the same way, integrins are adhesion molecules which regulate keratinocyte proliferation and differentiation.

AIM

To determine whether the regulatory activity of interferons on keratinocyte proliferation and differentiation is related to a modulation of keratinocyte integrins.

METHODS

Two different methods were used: monolayers and reconstituted skin, incubated either with 1,200 U/mL interferon-alpha or 500 U/mL interferon-gamma or control medium for 48 h. The integrin expression was assessed by flow cytometry and immunohistochemistry.

RESULTS

In monolayers, only the alpha3 subunit was significantly inhibited by interferon-gamma. In reconstituted skin, where keratinocytes are differentiated, both interferons had an inductive effect on beta1 expression and interferon-alpha had an inhibitory effect on alpha6 expression.

CONCLUSION

Interferon-alpha and -gamma induce a modulatory effect on alpha3, alpha6 and beta1 which appears to be related to the state of differentiation. Moreover, the decreased expression of alpha6 and alpha3 could be one of the mechanisms involved in the formation of bullous lesions during long-term interferon therapy.

Collagen-binding I domain integrins--what do they do?

Collagens are the most abundant proteins in the mammalian body and it is well recognized that collagens fulfill an important structural role in the extracellular matrix in a number of tissues. Inactivation of the collagen alpha 1(I) gene in mice results in embryonic lethality and collagen mutations in humans cause defects leading to disease. Integrins constitute a major group of receptors for extracellular matrix components, including collagens. Currently four collagen-binding I domain-containing integrins are known, namely alpha 1 beta 1, alpha 2 beta 1, alpha 10 beta 1 and alpha 11 beta 1. Unlike the undisputed role of collagens as structural elements, the biological importance of integrin mediated cell-collagen interactions is far from clear. This is in part due to the limited information available on the most recent additions of the integrin family, alpha 10 beta 1 and alpha 11 beta 1. Future studies using gene inactivation of individual and multiple integrin genes will allow testing of the hypothesis that collagen-binding integrins have redundant functions but will also shed light on their importance in pathological conditions. In this review we will describe what is currently known about the collagen-binding integrins and discuss their biological functions.

Calcium: a potential central regulator in wound healing in the skin

Calcium has an established role in the normal homeostasis of mammalian skin and serves as a modulator in keratinocyte proliferation and differentiation. Gradients of calcium concentration increasing from 0.5 mM in the basal layer to > 1.4 mM in the stratum granulosum are consistent with migration patterns in response to minor abrasion (normal wear). Dermal fibroblasts require calcium but are approximately 100 times less sensitive than keratinocytes. Normal calcium metabolism in the skin is dependent on cell membrane and cytosolic calcium binding proteins (calmodulin, cadherins, etc.), but their modulation through parathyroid hormone, vitamin D or growth factors in normal or damaged tissue is not well documented. In wound repair, calcium is predominantly involved as Factor IV in the hemostatic phase, but it is expected to be required in epidermal cell migration and regeneration patterns in later stages of healing. Calcium alginate dressings are designed to liberate calcium early in the acute phase to promote hemostasis, but it is presently unclear whether the supplementary calcium influences the intracellular environment at later stages of wound repair, notably during the remodeling phase. Although experimental studies suggest that control of calcium is obligatory in wound management, we know very little as to how calcium in the wound bed is modulated through hormones, vitamin D, or various growth factors. Also, there is limited information as to how calcium released either from dressings, platelets, or from the circulation through the action of parathyroid hormone, growth factors or other modulators influences cell migration and remodeling in skin wounds, although experimental models suggest that management of calcium is essential in wound management.

Activity of novispirin G10 against Pseudomonas aeruginosa in vitro and in infected burns

The emergence of multidrug-resistant microbes has serious implications for managing infection and sepsis and has stimulated efforts to develop alternative treatments, such as antimicrobial peptides. The objective of this study was to test a designer peptide, novispirin G10, against multidrug-resistant microorganisms. By two-stage radial diffusion assays, its activity against such organisms compared favorably with that of standard antibiotics and other antimicrobial peptides. It killed bacteria very rapidly, was nonhemolytic, and was relatively noncytotoxic. The peptide induced an immediate, massive efflux of potassium from Pseudomonas aeruginosa, suggesting that it altered the permeability of its inner membrane. The presence of human serum reduced but did not eliminate its activity. We tested the in vivo activity of novispirin G10 in rats with an infected, partial-thickness burn that covered 20% of their total body surface area. The burned area was seeded with 10(6) CFU of a Silvadene-resistant P. aeruginosa strain, and 24 h later a single treatment with 0, 1, 3, or 6 mg of synthetic novispirin G10 (n = 16 at each concentration) per kg was given intradermally. Significant bacterial killing (P < 0.0001) was evident within 4 h in each peptide group compared to controls receiving vehicle. Antimicrobial peptides such as novispirin G10 may provide a useful alternative or adjunct to standard antibiotic agents in treating burns or other wound infections.

Fibrinogen and fibrin are anti-adhesive for keratinocytes: a mechanism for fibrin eschar slough during wound repair

During cutaneous wound repair the epidermis avoids the fibrin-rich clot; rather it migrates down the collagen-rich dermal wound margin and over fibronectin-rich granulation tissue. The mechanism(s) underlying keratinocyte movement in this precise pathway has not been previously addressed. Here we demonstrate that cultured human keratinocytes do not express functional fibrinogen/fibrin receptors, specifically alpha v beta 3. Biologic modifiers known to induce integrin expression or activation did not induce adhesion to fibrin, fibrinogen, or its fragments. Epidermal explant outgrowth and single epidermal cell migration failed to occur on either fibrin or fibrinogen. Surprisingly, fibrin and fibrinogen mixed at physiologic molar ratios with fibronectin abrogated keratinocyte attachment to fibronectin. Keratinocytes transduced with the beta 3 integrin subunit cDNA, expressed alpha v beta 3 on their surface and attached to and spread on fibrinogen and fibrin. beta-gal cDNA-transduced keratinocytes did not demonstrate this activity. Furthermore, beta 3 cDNA-transduced keratinocyte adhesion to fibrin was inhibited by LM609 monoclonal antibody to alpha v beta 3 in a concentration-dependent fashion. From these data, we conclude that normal human keratinocytes cannot interact with fibrinogen and its derivatives due to the lack of alpha v beta 3. Thus, fibrinogen and fibrin are authentic anti-adhesive for keratinocytes. This may be a fundamental reason why the migrating epidermis dissects the fibrin eschar from wounds.

E-cadherin expression in wound healing of mouse skin

BACKGROUND

E-cadherin has been studied extensively in other systems but little attention has been paid to its role in wound healing. We investigated E-cadherin expression in epithelial wound healing in vivo by focusing on the migrating cells in the epithelial tongue and the mitotic cells in the non-injured side apart from the original wound edge.

METHODS

Round full-thickness excisional wounds (6 mm in diameter) and full-thickness incisional wounds were prepared dorsally in mice. On various days after the operation, E-cadherin expression was examined by immunohistochemical staining using a monoclonal antibody specific for E-cadherin.

RESULTS

In both models, the level of E-cadherin expression did not decrease on the 1st postoperative (P.O.) day. After the 2nd P.O. day, E-cadherin expression decreased in cells at a site 500 microm apart from the original wound edge. After the 3rd P.O. day, decreased expression was also observed in cells at the top and in the basal layer of the epithelial tongue. This decreased expression continued for 1 or 2 days after the meeting of the epithelial tongue. There was no significant difference in the expression of E-cadherin between two models.

CONCLUSIONS

The results suggested that E-cadherin expression decreases in epithelial cells. This decrease may depend on the activity of migration and mitosis. In addition, the change was similar in both the excisional and incisional wounds.

Elastin peptides induce migration and terminal differentiation of cultured keratinocytes via 67 kDa elastin receptor in vitro: 67 kDa elastin receptor is expressed in the keratinocytes eliminating elastic materials in elastosis perforans serpiginosa

To delineate the molecular mechanism of transepidermal elimination of dermal elastic materials in elastosis perforans serpiginosa, the interaction between elastin and cultured keratinocytes was studied in vitro. Synthetic elastin peptide VGVAPG elicited chemotactic responses to the cultured keratinocytes at the dose of 10-9 M. Treatment of keratinocytes with 10-6 or 10-5 M elastin peptides resulted in the suppression of cell growth and the increased expression of involucrin and transglutaminase-1, markers of terminal differentiation. When cultured keratinocytes were treated with the elastin peptides, the expression of 67 kDa elastin receptor was increased. The induction of terminal differentiation by elastin peptides was attenuated by the treatment with the combination of anti-67 kDa elastin receptor antibody. The results indicate that elastin is a potent inducer of migration and terminal differentiation of cultured keratinocytes, which is mediated by the 67 kDa elastin receptor. In the lesional skins of patients with elastosis perforans serpiginosa, the 67 kDa elastin receptor was specifically expressed in the epidermis immediately surrounding the elastic materials that were being eliminated. The elastin receptor may be involved in the interaction between keratinocytes and elastin in elastosis perforans serpiginosa.

Ras-transfection up-regulated HaCaT cell migration: inhibition by Marimastat

Cell migration is an essential process in physiological and pathological conditions such as wound healing and tumor invasion. This phenomenon involves cell adhesion on the extracellular matrix mediated by integrins, and cell detachment promoted in part by metalloproteinases (MMPs). In the present study, the migration of two HaCaT-ras clones (metastatic or not), was compared with HaCaT cells, and normal human primary cultured keratinocytes. Using colloidal gold migration assay, the migration index on type I and type IV collagen was similar for primary cultured keratinocytes and HaCaT, whereas it was markedly higher for the HaCaT-ras clones. High motility of ras-transfected cells was confirmed from an in vitro wound healing assay. It was not correlated with changes in integrin expression or related to a different adhesion on extracellular matrix. The Marismastat (BB-2516), a MMP inhibitor, inhibited in a dose-dependent effect the migration in both assays, demonstrating the important role of MMPs in the migration process. Under our experimental conditions, MMP-1 activity was not detected in HaCaT and MMP-9 activity was secreted by these cells only after their stimulation by EGF. Here, MMP-2 was the major gelatinolytic activity secreted by all the cells and its secretion was markedly higher for HaCaT-nis clones compared with HaCaT. In addition, Western blotting results confirmed a higher expression of MMP-2 associated with a lower expression of TIMP-2 in HaCaT-ras compared with HaCaT. These results suggest that Ha-ras oncogene could be a stimulating factor of migration and might modified the balance between MMP-2 and TIMP-2 in keratinocyte cell lines.

Chemotaxis of Amoeba proteus in the developing pH gradient within a pocket-like chamber studied with the computer assisted method

A new "U" shaped, pocket-like chamber was used to observe the chemotactic responses of individual cells. This method permits monitoring of both the development of the concentration gradient of a tested substance and cell locomotion. We investigated the chemotactic responses of Amoeba proteus and observed that the amoebae moved in positively and negatively developing [H+] gradients towards the solution of lower pH in a pH range 5.75-7.75. The chemotactic response of amoebae to [H+] gradients required the presence of extracellular calcium ions. It was blocked and random locomotion was restored by the replacement of calcium with magnesium in the cell medium. Time-lapse video recording and data processing were accomplished with computer-assisted methods. This made it possible to compare selected methods of data presentation and analysis for cells locomoting in isotropic and anisotropic conditions. The cell trajectories were determined and displayed in circular diagrams, lengths of cell tracks and final cell displacements were estimated and a few parameters characterizing cell locomotion were computed.

Mouse proximal tubular cell-cell adhesion inhibits apoptosis by a cadherin-dependent mechanism

Adhesion of epithelial cells to matrix is known to inhibit apoptosis. However, the role of cell-cell adhesion in mediating cell survival remains uncertain. Primary cultures of mouse proximal tubular (MPT) cells were used to examine the role of cell-cell adhesion in promoting survival. When MPT cells were deprived of both cell-matrix and cell-cell adhesion, they died by apoptosis. However, when incubated in agarose-coated culture dishes (to prevent cell-matrix adhesion) and at high cell density (to allow cell-cell interactions), MPT cells adhered to one another and remained viable. Expression of E-cadherin among suspended, aggregating cells increased with time. A His-Ala-Val (HAV)-containing peptide that inhibits homophilic E-cadherin binding prevented cell-cell aggregation and promoted apoptosis of MPT cells in suspension. By contrast, inhibition of potential beta(1)-integrin-mediated interactions between cells in suspension did not prevent either aggregation or survival of suspended cells. Aggregation of cells in suspension activated phosphatidylinositol 3-kinase (PI3K), an event that was markedly reduced by the presence of the HAV peptide. LY-294002, an inhibitor of PI3K, also inhibited survival of suspended cells. In summary, we provide novel evidence that MPT cells, when deprived of normal cell-matrix interactions, can adhere to one another in a cadherin-dependent fashion and remain viable. Survival of aggregated cells depends on activation of PI3K.

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.

Migration of human keratinocytes in electric fields requires growth factors and extracellular calcium

Currents that leak out of wounds generate electric fields lateral to the wound. These fields induce directional locomotion of human keratinocytes in vitro and may promote wound healing in vivo. We have examined the effects of growth factors and calcium, normally present in culture medium and the wound fluid, on the directional migration of human keratinocytes in culture. In electric fields of physiologic strength (100 mV per mm), keratinocytes migrated directionally towards the cathode at a rate of about 1 microm per min. This directional migration requires several growth factors. In the absence of these growth factors, the cell migration rate decreased but directionality was maintained. Epidermal growth factor alone restored cell migration rates at concentrations as low as 0.2 ng per ml. Insulin at 5-100 microg per ml or bovine pituitary extract at 0.2%-2% vol/vol also stimulated keratinocyte motility but was not sufficient to fully restore the migration rate. Keratinocyte migration in electric fields requires extracellular calcium. Changes in calcium concentrations from 3 microM to 3.3 mM did not significantly change keratinocyte migration rate nor directionality in electric fields; however, addition of the chelator ethyleneglycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid to migration medium reduced, and eventually abolished, keratinocyte motility. Our results show that (i) growth factors and extracellular calcium are required for electric field-induced directional migration of human keratinocytes, and (ii) keratinocytes migrate equally well in low and high calcium media.

Directed expression of keratin 16 to the progenitor basal cells of transgenic mouse skin delays skin maturation

We previously hypothesized that the type I keratin 16 (K16) plays a role in the process of keratinocyte activation that occurs in response to skin injury (Paladini, R.D., K. Takahashi, N.S. Bravo, and P.A. Coulombe. 1996. J. Cell Biol. 132:381-397). To further examine its properties in vivo, the human K16 cDNA was constitutively expressed in the progenitor basal layer of transgenic mouse skin using the K14 gene promoter. Mice that express approximately as much K16 protein as endogenous K14 display a dramatic postnatal phenotype that consists of skin that is hyperkeratotic, scaly, and essentially devoid of fur. Histologically, the epidermis is thickened because of hyperproliferation of transgenic basal cells, whereas the hair follicles are decreased in number, poorly developed, and hypoproliferative. Microscopically, the transgenic keratinocytes are hypertrophic and feature an altered keratin filament network and decreased cell-cell adhesion. The phenotype normalizes at approximately 5 wk after birth. In contrast, control mice expressing a K16-K14 chimeric protein to comparable levels are normal. The character and temporal evolution of the phenotype in the K16 transgenic mice are reminiscent of the activated EGF receptor- mediated signaling pathway in skin. In fact, tyrosine phosphorylation of the EGF receptor is increased in the newborn skin of K16 transgenic mice. We conclude that expression of K16 can significantly alter the response of skin keratinocytes to signaling cues, a distinctive property likely resulting from its unique COOH-terminal tail domain.

Cell migration and MMP-9 secretion are increased by epidermal growth factor in HaCaT-ras transfected cells

Mutated RAS oncoproteins and epidermal growth factor (EGF) are thought to contribute to the proliferative, invasive and metastatic properties of transformed cells. In the present study, we investigated the role of EGF in two H-ras transfected clones and compared it to that in the parental cell line, HaCaT and primary cultured keratinocytes. Our findings show that the motility on type I collagen, measured by the migration index, was similar for both the HaCaT cell line and normal human keratinocytes, whereas it was higher for the HaCaT-ras clones. These results suggest an involvement of the ras oncogene in the stimulation of cell migration. EGF in cell pretreatment or during the migration assay also caused an increase in migration of all the cells, but preserved the difference between HaCaT and HaCaT-ras. However, no significant difference in EGF-R expression was detected between normal cultured keratinocytes, HaCaT and HaCaT-ras cell lines with or without EGF pretreatment. Moreover, when the cells were stimulated with EGF, the MMP-9 activity was greatly increased in a dose-dependent manner in all the cells, and EGF stimulation particularly highlights the increased amount of MMP-9 in HaCaT-ras cells compared to HaCaT cells. In conclusion, EGF is able to enhance motility and to up-regulate MMP-9 activity in all cells, but with a higher impact in HaCaT-ras cells without an overexpression of EGF-R. As EGF acts in synergy with the H-ras mutation, they could be implicated in the local invasion by the HaCaT-ras clones.

Adhesion of cultured human kidney mesangial cells to native entactin: role of integrin receptors

Entactin is an extracellular matrix glycoprotein which binds to laminin and is found in most renal basement membranes and in the glomerular mesangial matrix. In the present study, we have characterized specific integrin receptors on cultured human mesangial cells (CHMC) responsible for adhesion to native entactin. The integrin receptors alpha 2 beta 1, alpha 3 beta 1, alpha 5 beta 1, alpha v beta 3, alpha v beta 5, and alpha 6 complexed with either beta 1 or beta 4 could be immune precipitated from detergent extracts of metabolically labeled CHMC. Adhesion assays with inhibitory anti integrin monoclonal antibodies (mab) demonstrated that CHMC use both alpha v beta 3 and a beta 1-containing integrin to bind surfaces coated with native entactin. Optimal binding of CHMC to native entactin required the participation of cations. Using wild type and mutant recombinant entactin fragments, the binding site for the alpha v beta 3 receptor was localized to the RGD sequence on the rod or E domain of entactin. CHMC adhesion to mutant full length recombinant entactin ligands lacking the E domain RGD sequence confirmed the presence of ligand binding site(s) for beta 1 integrin receptor(s). Differences in CHMC binding characteristics to recombinant and full length entactin compared to native bovine basement membrane entactin were observed. This suggests that tertiary molecular structure may contribute to entactin ligand binding properties. Primary amino acid residue sequences and tertiary structure of entactin may play roles in forming functional cell attachment sites in native basement membrane entactin.

Enhancement of cell interactions with collagen/glycosaminoglycan matrices by RGD derivatization

The interaction of three cell types important to the wound repair process with collagen/glycosaminoglycan (GAG) dermal regeneration matrices covalently modified with an Arg-Gly-Asp (RGD)-containing peptide was characterized. Function-blocking monoclonal antibodies directed against various integrin subunits were used to demonstrate that human fibroblasts attached to the unmodified matrix through the integrin, alpha2beta1. Human endothelial cells and human keratinocytes, however, attached minimally to the unmodified matrix. After modification of the collagen/GAG matrix with RGD-containing peptide, endothelial cells and keratinocytes attached and spread well on the matrix. This attachment was RGD dependent as evidenced by essentially complete inhibition with competing soluble peptide. In terms of overall cell number, fibroblast cell attachment remained unchanged on the RGD peptide-modified matrix compared to the unmodified material. Antibody and peptide inhibition studies demonstrate, however, that attachment to the modified matrix was mediated by both alpha2beta1 and RGD-binding integrins. We have successfully introduced a specific RGD receptor-mediated attachment site on collagen/GAG dermal regeneration matrices, resulting in enhanced cell interaction of important wound healing cell types. This modification could have important implications for the performance of these matrices in promoting dermal regeneration.

Integrin activation: the link between ligand binding and signal transduction

A major function of the integrin family of receptors is to provide a physical connection between extracellular adhesion proteins and intracellular cytoskeletal/signalling molecules. These linkages are dynamic and are influenced in a bidirectional manner by changes in the microenvironment of the plasma membrane that occur both inside and outside of cells. The mechanisms employed by integrins to transduce information are complex, but a series of recent studies has clarified their molecular basis. In particular, explanations for the interdependence of ligand binding, occupancy by divalent cations and receptor conformation have been obtained, and some of the key sites responsible for each property have been localized within the integrin heterodimer. These insights now permit a better visualization of the intricate molecular switch that controls the adhesive phenotype.

Restricted expression and function of laminin 1-binding integrins in normal and malignant oral mucosal keratinocytes

Squamous cell carcinoma of the oral cavity spreads by initial invasion of the laminin-rich basement membrane. We examined the adhesion and motility of human oral SCC cells and normal mucosal keratinocytes and found that the SCC cells readily attached and migrated on laminin 1 substrates but migrated poorly on collagen type I and fibronectin. The normal keratinocytes, however, adhered poorly to and were non-motile on laminin 1 yet readily and preferentially attached and migrated on fibronectin and collagen type I. Analysis with blocking anti-integrin antibodies showed that the SCC cells used the alpha 6 beta 1 complex to attach and migrate on laminin 1 and that this activity was confined to the E8 long arm fragment of laminin. Affinity chromatography on laminin-Sepharose columns revealed that the SCC cells, but not normal keratinocytes, expressed high levels of the alpha 6 beta 1 laminin 1 receptor. Metabolic pulse-chase analysis indicated that in contrast to the SCC cells, keratinocytes did not have a stable pool of beta 1 subunit precursor. Preferential pairing of alpha 6 with beta 4 and the deficiency in pre-beta 1 levels appear to account for the failure of keratinocytes to form significant alpha 6 beta 1 complex. Additionally, the presence of laminin 1 in co-coating experiments blocked keratinocyte adhesion to other immobilized ligands, such as collagen type I or fibronectin. This anti-adhesive effect seemed to reflect a general paralysis of cell adhesive function, since laminin 1 also diminished the adhesion of keratinocytes to substrates coated with immobilized anti-integrin subunit antibody. The inhibitory activity of laminin 1 resided in the E1' and E8 fragments, and not in the E3, E4 or G domains. Collectively, our results indicate that laminin 1 is a restrictive ligand for normal keratinocytes, apparently because of their failure to assemble and express the alpha 6 beta 1 complex or other functional laminin receptors and their sensitivity to the anti-adhesive activity of laminin itself. The elevated expression of alpha 6 beta 1 following malignant conversion of muscosal keratinocytes promotes their migration on laminin, a process important during invasion and metastasis.