Differential expression of activation epitopes of beta1 integrins in psoriasis and normal skin

Mechanotransduction in Skin Inflammation

In the process of mechanotransduction, the cells in the body perceive and interpret mechanical stimuli to maintain tissue homeostasis and respond to the environmental changes. Increasing evidence points towards dysregulated mechanotransduction as a pathologically relevant factor in human diseases, including inflammatory conditions. Skin is the organ that constantly undergoes considerable mechanical stresses, and the ability of mechanical factors to provoke inflammatory processes in the skin has long been known, with the Koebner phenomenon being an example. However, the molecular mechanisms and key factors linking mechanotransduction and cutaneous inflammation remain understudied. In this review, we outline the key players in the tissue's mechanical homeostasis, the available data, and the gaps in our current understanding of their aberrant regulation in chronic cutaneous inflammation. We mainly focus on psoriasis as one of the most studied skin inflammatory diseases; we also discuss mechanotransduction in the context of skin fibrosis as a result of chronic inflammation. Even though the role of mechanotransduction in inflammation of the simple epithelia of internal organs is being actively studied, we conclude that the mechanoregulation in the stratified epidermis of the skin requires more attention in future translational research.

Disproportional increase in psoriasis reports in association with B cell depleting therapies in patients with multiple sclerosis

BACKGROUND

Some pathways involved in the pathogenesis of psoriasis share similarities with processes involved in multiple sclerosis (MS) pathogenesis. However, the association between MS and psoriasis is poorly understood. Since disease-modifying therapies for MS have various targets, it may be possible that the occurrence of psoriasis varies by drug.

OBJECTIVE

To analyze the frequency of psoriasis reports in patients treated with various disease-modifying therapies for MS.

METHODS

Data was collected using the FDA Adverse Event Reporting System (FAERS) and OpenFDA database between January 2009 and June 2020. The study analyzed total reports of psoriasis out of total reports in the "Skin and Subcutaneous Tissue Disorders" category for each drug and explored age, sex distribution, and report source. OpenFDA data was used to perform statistical analyses including reporting odds ratios (ROR) and information components.

RESULTS

The study identified 517 psoriasis reports of 45,547 total skin and subcutaneous tissue disorders (1.13%) in FAERS. The highest proportions of reports in this study were associated with rituximab, ocrelizumab, and interferon beta 1a. The lowest proportion of reports were associated with glatiramer acetate, alemtuzumab, dimethyl fumarate and teriflunomide. Reports of other autoimmune skin disorders were minimal (29 vitiligo, 33 pemphigoid, and 7 pemphigus). Patients primarily drove reports for most DMTs versus healthcare providers. The proportion of reports from female patients were the highest for each DMT except alemtuzumab. OpenFDA query retrieved 302 total reports of psoriasis. Significantly increased reporting odds ratios (RORs, 95% confidence interval) of psoriasis were noted for rituximab (7.14, 3.92-13.00), ocrelizumab (3.79, 2.74-5.23), and fingolimod (1.33, 1.01-1.76). Significantly decreased RORs were noted for natalizumab (0.53, 0.36-0.80), glatiramer acetate (0.58, 0.35-0.96), and dimethyl fumarate (0.71, 0.53-0.94).

CONCLUSION

There are frequent reports of psoriasis in MS patients treated with various DMTs. However, reports and RORs were disproportionally high in association with B cell depleting therapies. Further research is required to determine if certain DMTs may serve as better options for individuals affected by, or at high-risk for developing psoriasis.

Podoplanin suppresses the cell adhesion of epidermal keratinocytes via functional regulation of β1-integrin

Epidermal stem cells adhere more efficiently to the extracellular matrix (ECM) than the less adhesive differentiating cells due to their high expression of cell adhesion molecules including β1-integrin. Podoplanin is majorly expressed in the markedly proliferative and differentiating basal cells of the wounded and psoriatic epidermis. This study was designed to reveal podoplanin's function in human epidermal keratinocytes (HEK) focusing on its interaction with β1-integrin. We analyzed the adhesion and differentiation of HEK in both podoplanin-overexpressing and -knock-down cells, considering their β1-integrin levels. The basal layer of IL-22-treated hyperproliferative reconstituted epidermis cells (simulating basal hyperproliferative psoriatic epidermal basal cells) expressed higher podoplanin levels than the untreated control cells. The adhesiveness of HaCaT cells, which do not express podoplanin, was reduced after the overexpression of podoplanin. HEK with podoplanin overexpression suppressed the cell adhesion to type I collagen (while downregulating β1-integrin functions) and podoplanin silencing augmented it (by increasing active ECM-bound β1-integrin). The increased cell adhesion to type I collagen induced by podoplanin silencing could be reversed by addition of P5D2, a neutralizing antibody against β1-integrin. In the psoriatic epidermis, podoplanin expression was especially upregulated on the rete ridges of the basal cell layer. This expression pattern was inversely correlated with the total/ECM-bound active β1-integrin-expression, which was stronger at the basal cell layer covering the dermal papillae. Our results indicate that podoplanin inhibits the cell ECM attachment by suppressing β1-integrin and initiating HEK differentiation. Podoplanin is presumably involved in the pathogenesis of psoriasis.

Is the Fractional Laser Still Effective in Assisting Cutaneous Macromolecule Delivery in Barrier-Deficient Skin? Psoriasis and Atopic Dermatitis as the Disease Models

PURPOSE

Most of the investigations into laser-assisted skin permeation have used the intact skin as the permeation barrier. Whether the laser is effective in improving cutaneous delivery via barrier-defective skin is still unclear.

METHODS

In this study, ablative (Er:YAG) and non-ablative (Er:glass) lasers were examined for the penetration of peptide and siRNA upon topical application on in vitro skin with a healthy or disrupted barrier.

RESULTS

An enhanced peptide flux (6.9 fold) was detected after tape stripping of the pig stratum corneum (SC). A further increase of flux to 11.7 fold was obtained after Er:YAG laser irradiation of the SC-stripped skin. However, the application of Er:glass modality did not further raise the flux via the SC-stripped skin. A similar trend was observed in the case of psoriasiform skin. Conversely, the flux was enhanced 3.7 and 2.6 fold after treatment with the Er:YAG and the Er:glass laser on the atopic dermatitis (AD)-like skin. The 3-D skin structure captured by confocal microscopy proved the distribution of peptide and siRNA through the microchannels and into the surrounding tissue.

CONCLUSIONS

The fractional laser was valid for ameliorating macromolecule permeation into barrier-disrupted skin although the enhancement level was lower than that of normal skin.

A novel flow cytometry-based platelet aggregation assay

The main function of platelets is to maintain normal hemostasis. Inefficient platelet production and/or defective platelet function results in bleeding disorders resulting from a wide range of genetic traits and acquired pathologies. Several platelet function tests have been developed for use in the clinic and in experimental animal models. In particular, platelet aggregation is routinely measured in an aggregometer, which requires normal platelet counts and significant blood sample volumes. For this reason, the analysis of thrombocytopenic patients, infants, and animal models is problematic. We have developed a novel flow cytometry test of platelet aggregation, in which 10- to 25-fold lower platelet counts or sample volumes can be used, either of platelet-rich plasma or whole blood from human subjects or mice. This setup can be applied to test in small assay volumes the influence of a variety of stimuli, drugs, and plasma factors, such as antibodies, on platelet aggregation. The presented principle stands as a novel promising tool, which allows analysis of platelet aggregation in thrombocytopenic patients or infants, and facilitates studies in platelets obtained from experimental animal models without the need of special devices but a flow cytometer.

The tetraspanin CD9 modulates epidermal growth factor receptor signaling in cancer cells

CD9 is a member of the tetraspanins, and has been shown to be involved in a variety of cellular activities such as migration, proliferation, and adhesion. In addition, it has been known that CD9 can associate with other proteins. Here we demonstrated the physical and functional association of CD9 with epidermal growth factor receptor (EGFR) on MKN-28 cells. Double-immunofluorescent staining and immunoprecipitation demonstrated the complex formation of CD9-EGFR and CD9-beta(1) integrin, and that both complexes are colocalized on the cell surface especially at the cell-cell contact site. Anti-CD9 monoclonal antibody ALB6 induced a dotted or patch-like aggregation pattern of both CD9-EGFR and CD9-beta(1) integrin. The internalization of EGFR after EGF-stimulation was significantly enhanced by the treatment with ALB6. CD9 can associate with EGFR in hepatocellular carcinoma cells (HepG2/CD9) and Chinese hamster ovary cancer cells (CHO-HER/CD9), which were transfected with pTJ/human EGFR/CD9. Furthermore expression of CD9 specifically attenuated EGFR signaling in CHO-HER/CD9 cells through the down regulation of surface expression of EGFR. These results suggest that CD9 might have an important role that attenuates EGFR signaling. Therefore, CD9 not only associates EGFR but also a new regulator, which may affect EGF-induced signaling in cancer cells.

von Hippel-Lindau Tumor Suppressor Protein Regulates the Assembly of Intercellular Junctions in Renal Cancer Cells through Hypoxia-Inducible Factor–Independent Mechanisms

Inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene is responsible for the development of renal cell cancers (RCC), pheochromocytomas, and tumors in other organs. The best known function of VHL protein (VHL) is to target the hypoxia-inducible factor (HIF) for proteasome degradation. VHL is also required for the establishment of an epithelial-like cell shape in otherwise fibroblastic-like RCC cell lines. However, the underlying mechanisms and whether this is linked to HIF remain undetermined. Because the breakage of intercellular junctions induces a fibroblastic-like phenotype in multiple cancer cell models, we hypothesized that VHL may be required for the assembly of intercellular junctions in RCC cells. Our experiments showed that VHL in RCC cell lines is necessary for the normal organization of adherens and tight intercellular junctions, the maintenance of cell polarity, and control of paracellular permeability. Additionally, 786-O cells reconstituted with wild-type VHL and with a constitutively active form of HIF-2alpha did not reproduce any of the phenotypic alterations of VHL-negative cells. In summary, we show that VHL inactivation in RCC cells disrupts intercellular junctions and cell shape through HIF-independent events, supporting the concept that VHL has additional functions beside its role in the regulation of HIF.

Role of tetraspanins CD9 and CD151 in primary melanocyte motility

Tetraspanins CD9 and CD151 have been implicated in cellular motility and intercellular adhesion in several cellular types. Here, we have studied the subcellular localization and the functional role of these molecules in primary melanocytes. We found that endogenous tetraspanins preferentially clustered in areas of melanocyte homotypic intercellular contacts and at the tips of dendrites. These observations were further confirmed using time-lapse fluorescence confocal microscopy of melanocytes transfected with CD9- and CD151-GFP (green fluorescent protein) constructs, suggesting an involvement of these proteins in cellular contacts and migration. Cell adhesion and migration assays performed using blocking monoclonal antibodies against CD9 and CD151 showed no significant effect on cell-extracellular matrix adhesion, whereas the migration of melanocytes was significantly enhanced. The regulation of the migratory capacity of melanocytes by CD9 and CD151 was further confirmed knocking down the endogenous expression of these tetraspanins with small interference RNA oligonucleotides. Therefore, tetraspanin molecules are localized at motile structures in primary human melanocytes regulating the migratory capacity of these cells.

CDK5 regulates cell-cell and cell-matrix adhesion in human keratinocytes

BACKGROUND

CDK5 is a member of proline-directed serine/threonine kinases. Although its cDNA was originally cloned as a homologue to those for the other members of the cyclin-dependent kinase (CDK) family, CDK5 has been shown to function differently from other CDKs. CDK5 is activated by non-cyclin partners, p35 and p39, and important during brain development by influencing adhesion, migration and differentiation of neurones.

OBJECTIVES

We sought to investigate the expression and functions of CDK5 in human keratinocytes.

METHODS

Expression of CDK5/p35, interaction of CDK5/p35 with adhesion molecules, and its roles in cell-cell and cell-matrix adhesion were studied by reverse transcriptase-polymerase chain reaction, immunoblotting and aggregation/adhesion assays in primary cultured normal human keratinocytes from infant foreskins and a human keratinocyte HaCaT cell line. Localization of CDK5 and p35 in normal human epidermis and psoriatic epidermis was studied by immunohistochemistry.

RESULTS

Both CDK5 and p35 were expressed in primary cultured keratinocytes, HaCaT cells and normal human epidermis. Roscovitine, an inhibitor of CDK5, enhanced Ca2+-dependent (cadherin-dependent) aggregation of HaCaT cells whereas it inhibited adhesion of HaCaT cells to fibronectin associated with reduced active states of beta1 integrin. Interestingly, psoriatic skin showed reduced CDK5 and p35 expression in the lower half of the epidermis, which might be associated with decreased amount of activated beta1 integrin in the epidermis of psoriatic skin.

CONCLUSIONS

CDK5/p35 may be involved in cell-cell and cell-matrix adhesion in human keratinocytes by differently regulating cadherins and integrins. Furthermore, reduced expression of CDK5/p35 in the epidermis might be involved in the pathogenesis of psoriasis.

The combination of the Zenon labeling technique and microscopic image analysis to study cell populations in normal and psoriatic epidermis

BACKGROUND

In order to better characterize epidermal cell populations in psoriatic vs. normal skin, fluorescent immunohistochemical techniques were extended with a new labeling technique. The Zenon technique conjugates primary antibodies rapidly and quantitatively after which they are used in the same manner as covalently labeled primary antibodies. Digital microscopic images of epidermal expression of keratin 10 and keratin 6 (differentiation), Ki-67 antigen (proliferation), and keratin 15 and beta-1 integrin (basal layer) were analyzed in a standardized way. Co-expression of different proteins was demonstrated.

METHODS

Sections of normal skin and psoriatic lesions were compared immunohistochemically. Antibodies against keratin 6, 10, and 15 were labeled with the Zenon technique. Antibodies against the Ki-67 antigen and beta-1 integrin were covalently fluorescein isothiocyanate-labeled. Using standardized image analysis, intensity and positive surface area of the different antibodies in the epidermis were measured.

RESULTS

The number of Ki-67-antigen positive cells was significantly increased in lesional psoriatic skin. Intensity and positive surface area of keratin 10 and beta-1 integrin were significantly decreased in comparison to normal epidermis. Differential expression of keratin 6 and keratin 15 was demonstrated.

CONCLUSIONS

Using Zenon technology and image analysis, a description of morphology, co-expression, and quantification of representative markers for epidermal cell populations is possible.

Phenotypical and Functional Differences in Germinative Subpopulations Derived from Normal and Psoriatic Epidermis

A model that explains how maintenance of normal homeostasis in human epidermis is achieved describes a heterogeneous cell population of stem cells (SC) and transit amplifying cells (TAC). There must be a tightly regulated balance between SC self-renewal and the generation of TAC that undergo a limited number of divisions before giving rise to postmitotic, terminally differentiated cells. To investigate whether this balance is disturbed in psoriatic epidermis, we have characterized flow sorted enriched SC and TAC using immunocytochemistry, flow cytometry, and real-time quantitative PCR. Our data demonstrate phenotypical and functional differences in SC (beta(1)-integrin bright) and TAC (beta(1)-integrin dim) enriched fractions between normal and psoriatic keratinocytes. Some of these were expected, such as mRNA levels of keratins 6 and 10 and of the Ki-67 antigen. Most remarkable were differences in phenotype of the psoriatic TAC compared with TAC from normal skin. These subpopulations also displayed striking differences following culture. Downregulation of markers associated with the regenerative phenotype (psoriasin, elafin, psoriasis-associated fatty acid binding protein) in cultured psoriatic dim cells in the absence of hyperproliferation suggests that proliferation and regenerative maturation are coupled. From these results, in combination with our earlier findings, we propose a model for epidermal growth control in which TAC play a crucial role.

Inhibición de la motilidad de células de melanoma con ARN de interferencia de CD9

INTRODUCTION

Although 65 % of the deaths caused by skin cancer are due to melanomas, the possible causes that may explain the aggressiveness of this type of tumor are still unknown. Different approaches have been used to try to find an effective treatment, but they have been unsuccessful. Interference RNA (iRNA) is an essential technique for this research. With this technique, we can selectively "knock down" or silence protein expression. The tetraspanins CD9 and CD151 are molecules involved in cell motility, including melanoma cells.

MATERIAL AND METHODS

A375 melanoma cell line, anti-CD9 and anti-CD151 monoclonal antibodies, and iRNA against CD9 and CD151. Immunofluorescence techniques, flow cytometry, cell transfection, cell selection with magnetic beads and evaluation of cell migration in a wound-healing model.

RESULTS

The A375 cells express CD9 and CD151. By using iRNA against CD9 and CD151, we managed to inhibit the expression of these proteins. The cells transfected with iRNA against CD9 showed significant inhibition of their motility.

DISCUSSION

We managed to silence the expression of CD9 and CD151 using iRNA techniques in the A375 melanoma cell line. The reduction in CD9 caused the inhibition of cell motility, while the interference with CD151 expression had a more moderate effect. This data indicates that the knockdown of tetraspanins may be a future target for the treatment of melanoma.

DNA Repair Capacity of Lymphoblastoid Cell Lines From Sisters Discordant for Breast Cancer

BACKGROUND

Interindividual differences in DNA repair capacity may influence cancer risk. We tested whether the nucleotide excision repair pathway was deficient in breast cancer case patients by analyzing sister pairs.

METHODS

Cell lines derived from sisters discordant for breast cancer (137 families containing 158 case patients and 154 control sisters) were obtained from the Metropolitan New York Registry of Breast Cancer Families. Lymphoblastoid cells were treated with benzo[a]pyrene diolepoxide (BPDE) for 30 minutes and were either harvested immediately or were washed and cultured in complete medium for 4 hours to allow DNA repair. Immunofluorescence using a polyclonal anti-BPDE-DNA primary antibody was used to quantify BPDE-DNA adducts. Percent DNA repair capacity was calculated from the difference between staining immediately after treatment minus that after 4 hours of repair, divided by the initial damage and was categorized into quartiles based on control values. Odds ratios and 95% confidence intervals (CIs) were calculated using conditional logistic regression models adjusted for age at blood donation, body mass index, and smoking. Statistical tests were two-sided.

RESULTS

Mean percent DNA repair capacity was lower in breast cancer case patients than in control subjects (difference = 8.6, 95% CI = 4.3 to 13.8, P = .001). Using the quartile with the highest percent DNA repair capacity as the referent group, adjusted odds ratios of breast cancer increased from 1.23 (95% CI = 0.57 to 2.65) to 2.38 (95% CI = 1.17 to 4.86) to 2.99 (95% CI = 1.45 to 6.17) (P(trend) = .002) as DNA repair capacity decreased.

CONCLUSIONS

Deficient DNA repair capacity is associated with increased breast cancer risk.

Effects of angiotensin II receptor signaling during skin wound healing

The tissue angiotensin (Ang) system, which acts independently of the circulating renin Ang system, is supposed to play an important role in tissue repair in the heart and kidney. In the skin, the role of the system for wound healing has remained to be ascertained. Our study demonstrated that oral administration of selective AngII type-1 receptor (AT(1)) blocker suppressed keratinocyte re-epithelization and angiogenesis during skin wound healing in rats. Immunoprecipitation and Western blot analysis indicated the existence of AT(1) and AngII type-2 receptor (AT(2)) in cultured keratinocytes and myofibroblasts. In a bromodeoxyuridine incorporation study, induction of AT(1) signaling enhanced the incorporation into keratinocytes and myofibroblasts. Wound healing migration assays revealed that induction of AT(1) signaling accelerated keratinocyte re-epithelization and myofibroblasts recovering. In these experiments, induction of AT(2) signaling acted vice versa. Taken together, our study suggests that skin wound healing is regulated by balance of opposing signals between AT(1) and AT(2).

Alpha 6 beta 4 integrin regulates keratinocyte chemotaxis through differential GTPase activation and antagonism of alpha 3 beta 1 integrin

Growth factor-induced cell migration and proliferation are essential for epithelial wound repair. Cell migration during wound repair also depends upon expression of laminin-5, a ligand for alpha 6 beta 4 integrin. We investigated the role of alpha 6 beta 4 integrin in laminin-5-dependent keratinocyte migration by re-expressing normal or attachment-defective beta 4 integrin in beta 4 integrin null keratinocytes. We found that expression of beta 4 integrin in either a ligand bound or ligand unbound state was necessary and sufficient for EGF-induced cell migration. In a ligand bound state, beta 4 integrin supported EGF-induced cell migration though sustained activation of Rac1. In the absence of alpha 6 beta 4 integrin ligation, Rac1 activation became tempered and EGF chemotaxis proceeded through an alternate mechanism that depended upon alpha 3 beta 1 integrin and was characterized by cell scattering. alpha 3 beta 1 integrin also relocalated from cell-cell contacts to sites of basal clustering where it displayed increased conformational activation. The aberrant distribution and activation of alpha 3 beta 1 integrin in attachment-defective beta 4 cells could be reversed by the activation of Rac1. Conversely, in WT beta 4 cells the normal cell-cell localization of alpha 3 beta 1 integrin became aberrant after the inhibition of Rac1. These studies indicate that the extracellular domain of beta 4 integrin, through its ability to bind ligand, functions to integrate the divergent effects of growth factors on the cytoskeleton and adhesion receptors so that coordinated keratinocyte migration can be achieved.

Immunofluorescent surface labelling, flow sorting and culturing of putative epidermal stem cells derived from small skin punch biopsies

Basal keratinocytes of human epidermis strongly express the cell surface glycoprotein beta(1)-integrin, and putatively harbour epidermal stem cells. Selective sorting and culturing of keratinocyte stem cells forms the basis for studies on the role of these cells as targets for therapeutic intervention and gene therapy. Here we have studied variables which affect cell surface labelling for beta(1)-integrin, flow sorting and subsequent culturing of beta(1)-integrin-positive and beta(1)-integrin-negative keratinocytes. Keratinocytes were derived from small human skin punch biopsies (3 or 4 mm in diameter), and we tested a number of variables such as choice of proteolytic enzyme for cell isolation, cell concentration, fixation, storage of fixed cell suspensions and labelling conditions. In contrast to thermolysin treatment for cell isolation, trypsin treatment left most cell surface beta(1)-integrin molecules intact. Ethanol and paraformaldehyde fixation interfered with beta(1)-integrin detection, and unfixed cells gave the best results. Optimisation of all the individual steps resulted in a labelling protocol for reproducible staining and sorting of the cells. Sorted cells were seeded in 96-well plates (300 cells/well) and colonies were obtained in more than 50% of the wells with beta(1)-integrin-positive keratinocytes. In plates with beta(1)-integrin-negative cells, only 10% of the wells contained keratinocyte colonies. Flow sorted keratinocytes obtained by trypsin formed numerous colonies in cell culture experiments. In cell suspensions obtained with thermolysin, only sparse colonies were formed. We conclude that our methodology permits the use of small human tissue samples for cell labelling and sorting, while preserving the clonogenic potential.

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.

Basal keratinocytes from uninvolved psoriatic skin exhibit accelerated spreading and focal adhesion kinase responsiveness to fibronectin

We previously proposed that the keratinocyte hyperproliferative state in psoriatic skin results from a combination of T cell cytokine interaction with basal keratinocytes that exist in a primed state. We now provide evidence that basal keratinocytes from psoriatic uninvolved skin are in a preactivated state with regard to their interaction with fibronectin. Freshly isolated basal keratinocytes (K(1)/K(10)(-)) from non-lesional psoriatic skin demonstrated a significantly higher percentage of spreading cells 1 h after plating on fibronectin-coated plates than keratinocytes isolated from normal skin (p =0.0002). No differences were observed on collagen-laminin-coated plates, however. The keratinocyte spreading on fibronectin-coated plates involved alpha 5 beta 1 and alpha V beta 1 integrins. To address the potential signaling cascades that may respond to integrin changes in psoriatic keratinocytes, focal adhesion kinase changes were assessed. The percentage of keratinocytes from psoriatic uninvolved skin that exhibit positive focal adhesion kinase staining was significantly greater than the percentage from healthy volunteers after 1 h incubation on fibronectin (p =0.006). Additionally, focal adhesion kinase isolated from uninvolved psoriatic keratinocytes had a greater degree of tyrosine phosphorylation. Thus, the proliferative effect of fibronectin in combination with T cell lymphokines on psoriatic uninvolved basal keratinocyte progenitors may be due to abnormal in vivo integrin-driven focal adhesion kinase activity and downstream signaling.

Effect of the hepatitis B virus HBx protein on integrin-mediated adhesion to and migration on extracellular matrix

BACKGROUND/AIMS

The hepatitis B virus HBx protein is associated with the development of hepatocellular carcinoma (HCC). However, its possible contribution to tumor spreading has not been explored. The migration of tumor cells through the extracellular matrix (ECM) represents a crucial step in tumor metastasis. Our aim was to study the effect of HBx on the integrin-mediated cell-ECM interaction, and its possible consequences for cell migration.

METHODS

Cell-ECM interaction was evaluated by static adhesion experiments, using blocking and stimulating anti-beta1 integrin mAbs. ECM receptor expression was analyzed by flow cytometry. The cellular distribution of the activated beta1 integrin subunit was determined by immunofluorescence analysis, and cell motility was determined by wound-healing assays.

RESULTS

HBx-bearing cells showed decreased adhesion to fibronectin, which correlated with a decreased expression of the alpha5 integrin subunit. The activated beta1 subunit was redistributed to the tips of pseudopodial protrusions of HBx-bearing cells, whereas it was evenly localized in the control cells. HBx-induced cell migration was abrogated by irreversible stimulation of beta1 integrins.

CONCLUSIONS

These results suggest that HBx might play a role in tumor spreading by modulating the adhesion-deadhesion balance of the cells in the primary tumor site and favoring integrin-mediated cell migration.

Tetraspanins in intercellular adhesion of polarized epithelial cells: spatial and functional relationship to integrins and cadherins

The subcellular distribution of tetraspanin molecules and their functional relationship with integrins in cell-cell adhesion was studied in detail in different polarized epithelial cell models. CD9, CD81 and CD151 tetraspanins were localized at lateral cell-cell contact sites in a similar distribution to E-cadherin. Interestingly, CD9 was partially localized at the apical microvillae of Madin-Darby canine kidney cells forming multimolecular complexes distinct from those found on the basolateral membrane, suggesting the coexistence of differential tetraspanin webs with different subcellular localization. We found that tetraspanin-associated beta1 integrins at cell-to-cell contacts were in a low-affinity conformational state, and that their localization at intercellular contacts was independent of cadherin expression and adhesion. Furthermore, integrin-tetraspanin complexes were functionally relevant in cell-cell adhesion in a cadherin-independent manner, without requiring a conformational change of the integrin moiety. Nevertheless, the integrin alpha3beta1 was ligand-binding competent and this binding did not disrupt association to tetraspanins. Moreover, Chinese hamster ovary cells treated with anti-tetraspanin mAbs or activatory anti-beta1 integrin mAbs were able to develop tubule-like structures. Together, these data support tetraspanin association as a new regulatory mechanism of integrin function and suggest a role for tetraspanins-integrin complexes in providing the cell with the spatial cues necessary for their proper polarization.

Tetraspanins are localized at motility-related structures and involved in normal human keratinocyte wound healing migration

We have described previously that beta1 integrins, which mediate keratinocyte cell adhesion and migration, are in ligand-occupied conformation at the basal surface but not at the lateral and apical surfaces of keratinocytes. This led us to study the cellular localization and function of tetraspanin molecules, which have been postulated to modulate integrin activity. We found that CD9 and CD81 are highly expressed by keratinocytes clearly delineating filopodia at lateral and apical surfaces. CD63 and CD151 are largely expressed in the intracellular compartment, although some membrane expression is observed. We found accumulation of CD9, CD81, and CD151 together with alpha3 and beta1 integrins at intercellular junctions. In low calcium medium, this intercellular space is crossed by a zipper of filopodia enriched in alpha3beta1 and tetraspanin proteins. Interestingly, the expression of CD9, CD81, and beta1 and alpha3 integrins was detected in the footprints and rippings of motile keratinocytes, suggesting their role in both adhesion to extracellular matrix and keratinocyte motility. beta1 integrins were only partially activated in the rips, whereas cytoskeleton-linking proteins such as talin were completely absent. On the other hand, antitetraspanin antibodies did not stain focal adhesions, which contain talin. The involvement of tetraspanins in keratinocyte motility was assessed in a wound healing migration assay. Inhibition of cell migration was observed with antibodies to CD9, CD81, beta1, and alpha3, and, to a lesser extent, to CD151. Together these results indicate that tetraspanin-integrin complexes might be involved in transient adhesion and integrin recycling during keratinocyte migration, as well as in intercellular recognition.

Overexpression of the oncofetal Fn variant containing the EDA splice-in segment in the dermal-epidermal junction of psoriatic uninvolved skin

The extracellular matrix protein, Fn, has critical functions in cell attachment, migration, differentiation, and proliferation. We have previously shown that fibronectin (Fn) is abnormally expressed and potentiates entry into the cell cycle of basal keratinocytes in uninvolved psoriatic skin, in combination with T cell lymphokines. It is not known what type of Fn is present in psoriatic skin, however, and how this Fn may regulate signaling. Embryonic forms of cellular Fn containing extra domains, designated EDA and EDB, are generated by alternative splicing and are seen in proliferating, developing tissue and in wound healing. Because the EDA segment enhances the integrin binding sequence Arg, Gly, Asp (RGD), which, when present, has been shown to be critical in integrin-extracellular matrix signaling, we were particularly interested in determining whether or not EDA-containing Fn (EDA+Fn) represented the aberrantly expressed Fn in psoriasis. Increased EDA+ Fn protein was demonstrated by immunostaining at the dermal-epidermal junction in clinically uninvolved skin from six of six patients with psoriasis, but not in skin from control subjects. Using reverse transcription polymerase chain reaction an increased ratio of EDA+ Fn versus EDA- Fn mRNA was present in epidermal samples from psoriatic but not control individuals. Interestingly, the EDA+Fn in the psoriatic epidermis had the IIICS region spliced out (EDA+, FDB-, IIICS-, III9+), which was shared with normal epidermis (EDA-, EDB-, IIICS-, III9+). These results suggest a selective predominance of the EDA+ Fn isoform at the dermal-epidermal junction of psoriatic skin. The consistent aberrant localization of EDA+ Fn at the dermal-epidermal junction in uninvolved skin of psoriatics may confer the hyperresponsiveness of psoriatic uninvolved basal keratinocytes for rapid cellular proliferation in response to T cell signals. Key words: immunohistochemistry/integrin/keratinocyte/RT-PCR.

Expression of integrin alpha9 subunit and tenascin in oral leukoplakia, lichen planus, and squamous cell carcinoma

OBJECTIVES

Integrin alpha9 subunit is a member of beta1 integrin family and binds tenascin (TN). It is expressed by stratified squamous epithelium and may be associated with cell differentiation and growth. We studied if the expression of alpha9 integrin and TN is altered in leukoplakia, lichen planus, and squamous cell carcinoma (SCC).

METHODS

Frozen sections of tissue samples obtained from normal human keratinized (16 subjects) and non-keratinized (three subjects) oral mucosa, oral leukopakias with dysplasia (19 subjects), reticular type lichen planus (nine subjects), or oral mucosal SCC (23 subjects) were stained immunohistochemically with antibodies against alpha9 integrin and TN.

RESULTS

In contrast to its most prominent localization at the cell membranes of the basal epithelial cells in the normal mucosa, alpha9 integrin was localized in a more diffuse pattern with focal loss of expression at the epithelial cell membranes in leukoplakic dysplasia, lichen planus, and SCC. In some areas of SCC, alpha9 integrin localized throughout all cell layers of the tumor epithelium. In most areas, alpha9 integrin colocalized with TN but in heavily inflamed areas there was focal loss of TN and alpha9 integrin at the basement membrane zone.

CONCLUSIONS

The findings show that alpha9 integrin expression is altered in leukoplakic dysplasia, lichen planus, and SCC.