A complex of platelet glycoproteins Ic and IIa identified by a rat monoclonal antibody

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

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

Integrin and FAK-mediated MAPK activation is required for cyclic strain mitogenic effects in Caco-2 cells

Rhythmic strain stimulates Caco-2 proliferation. We asked whether mitogen-activated protein kinase (MAPK) activation mediates strain mitogenicity and characterized upstream signals regulating MAPK. Caco-2 cells were subjected to strain on collagen I-precoated membranes or antibodies to integrin subunits. Twenty-four hours of cyclic strain increased cell numbers compared with static conditions. MAPK-extracellular signal-regulated kinase (ERK) kinase inhibition (20 microM PD-98059) blocked strain mitogenicity. p38 Inhibition (10 microM SB-202190) did not. Strain rapidly and time-dependently activated focal adhesion kinase (FAK), paxillin, ERK1 and 2, and p38 on collagen. c-Jun NH(2)-terminal kinase (JNK)1 and 2 exhibited delayed activation. Similar activation occurred when Caco-2 cells were subjected to strain on a substrate of functional antibody to the alpha2-, alpha3-, alpha6-, or beta1-integrin subunits but not on a substrate of functional antibody to the alpha5-subunit. FAK inhibition by FAK397 transfection blocked ERK2 and JNK1 activation by in vitro kinase assays, but pharmacological protein kinase C inhibition did not block ERK1 or 2 activation by strain. Strain-induced ERK signals mediate strain's mitogenic effects and may require integrins and FAK activation.

Defects in adhesion and migration, but not in proliferation and differentiation, of embryonic stem cells upon replacement of integrin subunit beta1A by beta1D

Beta1D is a skeletal muscle-specific splice variant of the beta1 integrin subunit, while beta1A integrin subunit has a wide tissue distribution. We have previously shown that replacement of beta1A by beta1D by homologous recombination (knockin) in all mouse tissues was embryonic lethal. Through two successive rounds of homologous recombination, we have now produced embryonic stem (ES) cells expressing beta1D instead of beta1A, and analyzed the ability of beta1D to support ES cell differentiation in vitro and in teratomas in vivo. Beta1D knockin (KI) ES cells grew at a similar rate but as more compact colonies than the beta1A-expressing cells. Increased cell cohesiveness, however, did not appear to involve changes in cadherin activity. Although in both beta1A and beta1D-KI ES cells only one beta1 allele is active; the expression of beta1 integrins in the beta1D-KI ES cells was reduced by 50%, compared with that in the beta1A-expressing cells; this correlated with impaired adhesive and migratory capacities. It appeared that during in vitro cardiac differentiation, in spite of a slight delay in the induction of two cardiac-specific transcripts, the alpha- and beta-myosin heavy chains, contracting cardiomyocytes were detected in similar numbers and at the same time in embryoid bodies (EB) derived from beta1D-KI and from beta1A cells. Furthermore, replacement of beta1A by beta1D in ES cells did not affect neurite differentiation in embryoid bodies in the presence of retinoic acid suggesting that beta1D supports neurogenesis. However, the impaired migration of other cells from the EB, including endodermal cells, prevented the normal outgrowth of neurites in beta1D-KI EB. Finally, injection of beta1D-KI ES cells in the flank of syngeneic mice gave rise to fully developed teratomas containing simple and pluristratified epithelia, muscle, cartilage, blood vessels, and tissues from the neural lineage. These results show that the muscle-specific splice variant beta1D, in spite of its specific cytoplasmic domain, supports the differentiation of many cell types. This further suggests that the embryonic lethality in the beta1D-KI embryos was mainly due to the different ability of beta1 A and beta1D to mediate cell adhesion and migration.

Laminin alpha1-chain shows a restricted distribution in epithelial basement membranes of fetal and adult human tissues

Two novel monoclonal antibodies were raised and used to study the expression of laminin (Ln) alpha1-chain in developing and adult human tissues. In both fetal and adult kidney, a distinct immunoreactivity was seen in basement membranes (BM) of most proximal tubules but not in the distal tubular or glomerular BM or in the basal laminae of blood vessels. Immunoprecipitation of metabolically labeled cultured human renal proximal tubular cells showed an abundant production and deposition of Ln alpha1-chain to the extracellular matrix, suggestive of an epithelial origin of kidney Ln-1. Quantitative cell adhesion experiments with JAR choriocarcinoma cells showed that purified human Ln-1 is a good substrate for cell adhesion that it is differently recognized by integrin receptors when compared to mouse Ln-1. In fetal and adult testes immunoreactivity was solely confined to BM of the seminiferous epithelium. In the airways BM-confined reaction was only seen in fetal budding bronchial tubules (16-19 weeks) at the pseudoglandular stage of development. In the skin a distinct immunoreactivity was confined to BM of developing hair buds but not in epithelial BMs of adult epidermis or of epidermal appendages. In other adult tissues, immunoreactivity was found in BMs of thyroid, salivary, and mammary glands as well as in BMs of endometrium and endocervix, but not of ectocervix or vagina. No immunoreactivity was found in BMs of most of the digestive tract, including the liver and pancreas, except for BMs of esophageal submucosal glands and duodenal Brunner's glands. In fetal specimens, BMs of the bottoms of the intestinal and gastric glands were positive. Basal laminae of blood vessels were generally negative for Ln alpha1 chain with the exception of specimens of both fetal and adult central nervous system in which immunoreactivity for Ln alpha1 chain was prominently confined to capillary walls. The results suggest that outside the central nervous system, Ln alpha1 chain shows a restricted and developmentally regulated expression in BMs of distinct epithelial tissues.

Bidirectional induction of the cognate receptor-ligand α4/VCAM-1 pair defines a novel mechanism of tumor intravasation

Engagement of cell surface adhesion receptors with extracellular constituents and with cellular counter-receptors is crucial for the extravasation of blood-borne neoplastic cells and their seeding at distant sites; however, the early events of tumor dissemination—ie, the intravasation step(s)—have been largely neglected. A role for the 4β7 integrin was hypothesized to explain the high leukemogenicity exhibited by one (NQ22) among several T-cell lymphomas studied. To clarify the mechanisms of early aggressivity, the behavior of highly and poorly leukemogenic cell lines were compared in vitro. Cocultivation of physically separated leukemic cells with resting endothelial cells resulted in the up-regulation of VCAM-1 expression. NQ22 cells expressed mRNA of different cytokines that up-regulate VCAM-1 and at higher levels than cells of a nonaggressive lymphoma, and they migrated more efficiently through an activated endothelial cell layer. With the use of neutralizing antibodies against interferon-γ, granulocyte macrophage colony-stimulating factor, and tumor necrosis factor (TNF)-, it was determined that TNF- is one of the soluble factors released by NQ22 cells involved in the up-regulation of VCAM-1. The finding that vascular cells within the early local growth were strongly positive for VCAM-1 indicated that NQ22 cells could activate endothelial cells also in vivo. Finally, cocultivation of preleukemic 4−NQ22 cells with TNF--activated endothelial cells induced the expression of 4 integrins on the former cells. Reciprocal up-regulation and engagement of 4/VCAM-1 pairs determined the sequential transmigration and intravasation steps, and similar mechanisms might affect the aggressivity of human T lymphoblastic lymphomas.

Bidirectional induction of the cognate receptor-ligand α4/VCAM-1 pair defines a novel mechanism of tumor intravasation

Engagement of cell surface adhesion receptors with extracellular constituents and with cellular counter-receptors is crucial for the extravasation of blood-borne neoplastic cells and their seeding at distant sites; however, the early events of tumor dissemination—ie, the intravasation step(s)—have been largely neglected. A role for the 4β7 integrin was hypothesized to explain the high leukemogenicity exhibited by one (NQ22) among several T-cell lymphomas studied. To clarify the mechanisms of early aggressivity, the behavior of highly and poorly leukemogenic cell lines were compared in vitro. Cocultivation of physically separated leukemic cells with resting endothelial cells resulted in the up-regulation of VCAM-1 expression. NQ22 cells expressed mRNA of different cytokines that up-regulate VCAM-1 and at higher levels than cells of a nonaggressive lymphoma, and they migrated more efficiently through an activated endothelial cell layer. With the use of neutralizing antibodies against interferon-γ, granulocyte macrophage colony-stimulating factor, and tumor necrosis factor (TNF)-, it was determined that TNF- is one of the soluble factors released by NQ22 cells involved in the up-regulation of VCAM-1. The finding that vascular cells within the early local growth were strongly positive for VCAM-1 indicated that NQ22 cells could activate endothelial cells also in vivo. Finally, cocultivation of preleukemic 4−NQ22 cells with TNF--activated endothelial cells induced the expression of 4 integrins on the former cells. Reciprocal up-regulation and engagement of 4/VCAM-1 pairs determined the sequential transmigration and intravasation steps, and similar mechanisms might affect the aggressivity of human T lymphoblastic lymphomas.

Basement membrane laminin-5 is deposited in colorectal adenomas and carcinomas and serves as a ligand for alpha3beta1 integrin

Interplay between laminin-5 (Ln-5) and its integrin (Int) receptors alpha2beta1, alpha3beta1 and alpha6beta4 has been implicated in the progression and invasion of carcinomas. In this study we found abundant immunoreactivity for chains of Ln-5 (alpha3-beta3-gamma2) and Ln-10 (alpha5-beta1-gamma1), as well as for type VII collagen, in basement membranes (BM) of colorectal adenomas. In carcinomas of all differentiation grades, Lns were seen in tumor BMs, whereas type VII collagen was almost absent. Ln-5 appeared to accumulate along the invading edges of carcinomas, while Ln-10 was mostly absent. Immunoreactivity for Ln al chain, a component of Lns-1 and -3, was not seen in adenomas or carcinomas. Immunoreactivity for alpha2, alpha6, beta1 and beta4 Ints was found in all tumors and that for alpha3 Int in all adenomas and most of the carcinomas, often in colocalization with Ln-5. Immunoblotting of carcinoma tissues showed that the gamma2 chain of Ln-5 was present as typical Mr 105000 and 155000 isoforms. Immunoprecipitation experiments showed production of Ln-5 by cultured colon carcinoma cells. In quantitative cell adhesion experiments, function-blocking MAbs to alpha3 and beta1 Int subunits, but not those to Int alpha2 or alpha6 subunits, significantly inhibited the adhesion of cells to Ln-5. Our results suggest that BM composition in colorectal adenomas reflects the properties of surface epithelial BM of colorectal mucosa. In invading carcinomas, trimeric Ln-5, produced by carcinoma cells, is a major BM component and the cells use the alpha3beta1 Int complex for adhesion to Ln-5.

alpha6 integrin is not the obligatory cell receptor for bovine papillomavirus type 4

Recently, alpha6 integrin has been proposed as the epithelial cell receptor for papillomavirus. This study investigated whether alpha6 integrin is the cellular receptor for bovine papillomavirus type 4 (BPV-4), which is strictly epitheliotropic and infects the mucous epithelium of the upper digestive tract. Primary bovine mucosal keratinocytes from the palate of a foetus (PalK) displayed high levels of alpha6 integrin; matched primary fibroblasts from the same biopsy (PalF) expressed almost no alpha6 integrin. However, BPV-4 bound both PalK and PalF to similar, saturable levels. Native BPV-4 virions infected PalK in vitro, as detected by RT-PCR of E7 RNA. Infection could be blocked by excess virus-like particles (VLPs) and by neutralizing antisera against L1-L2 and L1 VLPs or by denaturation of the virions, supporting the view that infection in vitro mimics the process in vivo. alpha6 integrin-negative human keratinocyte cell lines were derived from patients affected by junctional epidermolysis bullosa presenting genetic lesions in their hemidesmosomes. The level of alpha6 integrin expression was determined in these cell lines by in situ immunofluorescence and FACS. Despite the absence of alpha6 integrin expression by BO-SV cells, they were bound by BPV-4 to similar, saturable levels as normal keratinocytes, KH-SV. Furthermore, BO-SV and KH-SV cells were both infected by BPV-4 to apparently the same extent as PalK cells. These results are consistent with the conclusion that alpha6 integrin is not the obligatory receptor for a bovine mucosotropic papillomavirus.

Induction of cell scattering by expression of beta1 integrins in beta1-deficient epithelial cells requires activation of members of the rho family of GTPases and downregulation of cadherin and catenin function

Adhesion receptors, which connect cells to each other and to the surrounding extracellular matrix (ECM), play a crucial role in the control of tissue structure and of morphogenesis. In this work, we have studied how intercellular adhesion molecules and beta1 integrins influence each other using two different beta1-null cell lines, epithelial GE11 and fibroblast-like GD25 cells. Expression of beta1A or the cytoplasmic splice variant beta1D, induced the disruption of intercellular adherens junctions and cell scattering in both GE11 and GD25 cells. In GE11 cells, the morphological change correlated with the redistribution of zonula occluden (ZO)-1 from tight junctions to adherens junctions at high cell confluency. In addition, the expression of beta1 integrins caused a dramatic reorganization of the actin cytoskeleton and of focal contacts. Interaction of beta1 integrins with their respective ligands was required for a complete morphological transition towards the spindle-shaped fibroblast-like phenotype. The expression of an interleukin-2 receptor (IL2R)-beta1A chimera and its incorporation into focal adhesions also induced the disruption of cadherin-based adhesions and the reorganization of ECM-cell contacts, but failed to promote cell migration on fibronectin, in contrast to full-length beta1A. This indicates that the disruption of cell-cell adhesion is not simply the consequence of the stimulated cell migration. Expression of beta1 integrins in GE11 cells resulted in a decrease in cadherin and alpha-catenin protein levels accompanied by their redistribution from the cytoskeleton-associated fraction to the detergent-soluble fraction. Regulation of alpha-catenin protein levels by beta1 integrins is likely to play a role in the morphological transition, since overexpression of alpha-catenin in GE11 cells before beta1 prevented the disruption of intercellular adhesions and cell scattering. In addition, using biochemical activity assays for Rho-like GTPases, we show that the expression of beta1A, beta1D, or IL2R-beta1A in GE11 or GD25 cells triggers activation of both RhoA and Rac1, but not of Cdc42. Moreover, dominant negative Rac1 (N17Rac1) inhibited the disruption of cell-cell adhesions when expressed before beta1. However, all three GTPases might be involved in the morphological transition, since expression of either N19RhoA, N17Rac1, or N17Cdc42 reversed cell scattering and partially restored cadherin-based adhesions in GE11-beta1A cells. Our results indicate that beta1 integrins regulate the polarity and motility of epithelial cells by the induction of intracellular molecular events involving a downregulation of alpha-catenin function and the activation of the Rho-like G proteins Rac1 and RhoA.

Expression of the integrin subunits alpha 5, alpha 6 and beta 1 in the testes of the common marmoset

Integrin subunits alpha 5, alpha 6 and beta 1 were localized in the testis of pre-pubertal or adult non-human primates (Callithrix jacchus) by immunofluorescence staining and in situ hybridization. In animals of all ages subunits alpha 5 and beta 1 were localized in cells of the lamina propria of the seminiferous epithelium. In prepubertal animals, the integrin subunits alpha 5, alpha 6, as well as beta 1, were distributed all over the plasma membrane of Sertoli cells. In adult animals the integrin subunits were confined to those plasma membrane regions of Sertoli cells which are assigned to the basal compartment, including the basement membrane of the seminiferous tubules. Protein expression of integrin subunits alpha 6 and beta 1 was most pronounced in tubular stages in which elongated spermatids were not yet present in the adluminal compartment of the epithelium, suggesting that these integrin subunits are particularly essential at certain developmental stages of spermatogenesis. Non-radioactive in situ hybridization revealed that the mRNA for integrin subunits alpha 5, alpha 6 and beta 1 was expressed by Sertoli cells. In situ hybridization, together with immunofluorescence data, shows that these integrin subunits were exclusively synthesized in Sertoli cells. As to functional aspects, it is concluded that during primate spermatogenesis. Sertoli cell integrins may be involved in both cell matrix as well as cell-cell interactions, particularly during early spermatogenesis.

Partial rescue of epithelial phenotype in integrin beta4 null mice by a keratin-5 promoter driven human integrin beta4 transgene

Integrin beta4 null mice exhibit extensive epidermal detachment, reminiscent of the human skin blistering disease junctional epidermolysis bullosa associated with pyloric atresia. Hemidesmosomes, the stable adhesion structures of squamous epithelia, are not formed in the absence of alpha6beta4. Null mutant mice die shortly after birth, but apart from their striking epithelial phenotype, no obvious developmental defects have been observed. To elucidate the cause of death in these mice, we generated transgenic mice with a heterologous construct consisting of the squamous epithelial-specific keratin-5 promoter and a human integrin beta4 subunit cDNA. The transgene was not expressed in the presence of endogenous beta4, probably as a result of competition for a limited pool of alpha6 subunits. In a beta4 null background, however, the transgene was expressed, and its expression pattern followed that of squamous epithelial-specific keratins. These rescued pups appeared healthy and ultrastructural analysis revealed that the interspecies heterodimer alpha6(mouse)/beta4(human) was sufficient to trigger the assembly of hemidesmosomes. After a variable period of up to 48 hours after birth these animals began to exhibit haemorrhages at the plantar and palmar areas. We observed the formation of small blisters and found that the transgene was not detectably expressed in this region, which is devoid of hair follicles. The rescued neonates became increasingly cyanotic and died soon after the onset of this phenomenon. We performed a developmental study of the expression of beta4 in the complete respiratory tract, but we found no correlation between the spatiotemporal distribution of beta4 and the onset of the respiratory insufficiency. It became clear, however, that there was a gradual detachment of squamous epithelia in the oral and nasal cavities which led to obstruction of the respiratory tract, suggesting that in beta4 null and rescued mice, neonatal death was a direct consequence of decreased adhesion properties of hairless squamous epithelia, rather than a developmental defect of the lungs.

Integrins mediate a neuronal survival signal for oligodendrocytes

Target-dependent survival of newly differentiated cells is an important part of neural development. In the case of myelin-forming oligodendrocytes, it matches the number of oligodendrocytes to the available axons [1]. In addition to growth factors, an axonal signal regulates this survival: when axons are transected, oligodendrocytes die and, conversely, when the number of axons is increased by genetic manipulation, oligodendrocyte numbers increase [2] [3]. Newly formed oligodendrocytes that fail to contact axons undergo apoptosis, and co-culture experiments that model axon-glial interactions in vitro reveal a neuronal survival effect not present in neuron-conditioned medium [4] [5], suggesting that the signal is non-diffusible and present on the surface of axons. The nature of these neuronal signals is unknown, as are the mechanisms by which they interact with growth-factor-mediated survival signals. As integrins can regulate survival in other cell types [6] [7] [8], we determined whether integrins are involved in the neuronal survival effect. We found that the laminin receptor alpha6beta1 integrin, which is expressed on oligodendrocytes, enhances the sensitivity of oligodendrocytes to the survival effect of growth factors. On the basis of this interaction between integrin and growth-factor-mediated signalling, we propose a simple model by which signals from axons and other cell types might interact to regulate oligodendrocyte cell numbers.

Expression of alpha6 and beta4 integrin subunits throughout the menstrual cycle: no correlation with uterine receptivity

OBJECTIVE

To compare the expression of alpha6 and beta4 integrin subunit levels throughout the menstrual cycle in the endometrium of healthy women and infertile women.

DESIGN

Prospective study.

SETTING

An academic teaching hospital.

PATIENT(S)

Endometrium was collected from 58 women, including healthy subjects (n = 28) and patients undergoing diagnostic testing for infertility (n = 30).

INTERVENTION(S)

Endometrial biopsies were performed throughout the menstrual cycle in healthy women and infertile women.

MAIN OUTCOME MEASURE(S)

Immunohistochemical staining intensity of alpha6 and beta4 using the semiquantitative immunohistochemical score, compared using regression analysis and analysis of variance with Scheffé's correction.

RESULT(S)

There was no correlation between menstrual cycle phase and endometrial integrin subunit alpha6 or beta4 on glandular or luminal epithelium. Even women with identified luteal phase defects had indistinguishable patterns of expression for these integrin subunits during the window of implantation.

CONCLUSION(S)

The integrin subunits alpha6 and beta4 are expressed uniformly throughout the menstrual cycle on glandular and luminal epithelium. These integrins may have a housekeeping role in anchoring endometrial epithelium and do not appear to be useful markers of uterine receptivity.

Blood-group-related carbohydrates are expressed in organotypic cultures of human skin and oral mucosa

Cellular maturation and migration are usually associated with changes in cell-surface carbohydrates, but the relationship between these changes and cell behaviour is at present largely unknown. To investigate whether an organotypic culture system can be used as an in vitro model to study the function of cell-surface carbohydrates, we established organotypic cultures of skin and buccal mucosa. In these cultures, keratinocytes are grown at the air-liquid interface on a supporting matrix consisting of homologous fibroblasts embedded in a collagen type I gel. We examined the expression of blood-group-related carbohydrate structures, including Lewis x, sialylated Lewis x, Lewis y, Lewis a, and Lewis b, on the surface of epithelial cells in the cultures. We compared the results with the expression of more well-established markers, including cytokeratins, integrins, bullous pemphigoid antigen and laminin, in the same cultures. The organotypic skin and oral mucosa cultures showed a histological differentiation pattern analogous to that of normal skin and buccal mucosa, and a tissue-specific expression of carbohydrate structures and cytokeratins. However, both types of organotypic cultures also expressed markers which are normally seen during wound healing, including Lewis y, cytokeratin 16, and cytokeratin 19. We conclude that the organotypic cultures of oral mucosa and skin are suitable models for future studies of the function of cell-surface carbohydrates, although the expression of wound healing markers has to be taken into consideration.

Characterization of a functional relationship between hepatocyte growth factor and mouse bone marrow-derived mast cells

During the early stage (at 4 weeks) of interleukin-3 (IL-3)-induced development, mouse bone marrow-derived mast cells (BMMC) express alpha 4, alpha 5 and alpha 6 integrins, whereas with further maturation beyond 10 weeks, only alpha 5 integrin remains stably expressed. Hepatocyte growth factor (HGF) modulates the growth and movement of diverse cell types upon binding to its receptor, encoded by the proto-oncogene c-met. We report here the expression of c-met by BMMC throughout the course of their development. In addition, HGF stimulated migration of early week-4 BMMC, but not of the later stage week-10 BMMC, on fibronectin and laminin substrates. The developmental stage-dependent effect of HGF on BMMC was due to specific stimulation of the migratory function of alpha 4 and alpha 6, but not alpha 5 integrins. In addition, HGF had no effect on BMMC growth, either alone or in combination with IL-3. While HGF is stimulatory of the migratory function of BMMC, our results show that BMMC in turn can modulate HGF function. Thus, upon activation via the IgE receptors, BMMC released proteases that abolished HGF activities. Analyses of the degradation products by two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blot using antisera prepared against recombinant HGF and the kringle 3 domain of HGF revealed specific degradation of HGF alpha but not beta/beta' subunits. Therefore, our results suggest that: 1) the motogenic effect of HGF on BMMC varies according to the stage of their development, 2) HGF stimulation of BMMC migration is due to selective activation of alpha 4 and alpha 6, but not alpha 5 integrin function, and 3) there exists a two-way relationship between BMMC and HGF such that HGF stimulates the beta 1 integrin-mediated migratory function of BMMC, which can, in turn, modulate HGF function by release of serine proteases.

Expression of laminins 1 and 10 in carcinoma cells and comparison of their roles in cell adhesion

The expression pattern of laminin (Ln) alpha1 chain has been a controversial topic due to discrepancies between mRNA and protein studies. Recently it was reported that the monoclonal antibody 4C7, previously thought to recognize Ln alpha1 chain, actually detects Ln alpha5 chain. This finding makes it necessary to reestimate the role of Ln alpha1 chain and to compare the expression and functions of Ln alpha1 and alpha5 chains. We studied the expression of Ln alpha1 and alpha5 chains and production of Ln-1 and Ln-10 in cultured human carcinoma cells. Ln alpha1 chain mRNA was detected in JAR choriocarcinoma cells and in all four renal cell carcinoma cell lines studied. In contrast, pancreatic, colon, and lung alveolar carcinoma cell lines did not express or produce Ln alpha1 chain, suggesting that Ln-1 (alpha1 beta1 gamma1) is produced only by certain carcinoma cells. Ln alpha5 chain mRNA was expressed in all carcinoma cells, but was not incorporated into extracellular matrix in vitro, as shown with JAR cells. Immunoprecipitation of metabolically labeled cells showed that cells expressing Ln alpha1 mRNA also produced 400-kDa Ln alpha1 chain, whereas all cells produced 380-kDa Ln alpha5 chain. Adhesion to Ln-1 was inhibited by a functionally blocking antibody against alpha6-integrin subunit, whereas adhesion to Ln-10 was inhibited by an antibody against alpha6-integrin in JAR cells and by an antibody against alpha3-integrin in PANC-1 cells. The results suggest that Ln-10 is a ubiquitously expressed Ln isoform in carcinoma cells, and the mechanism of adhesion to Ln-10 is cell-type specific.

Evidence that distinct states of the integrin alpha6beta1 interact with laminin and an ADAM

Integrins can exist in different functional states with low or high binding capacity for particular ligands. We previously provided evidence that the integrin alpha6beta1, on mouse eggs and on alpha6-transfected cells, interacted with the disintegrin domain of the sperm surface protein ADAM 2 (fertilin beta). In the present study we tested the hypothesis that different states of alpha6beta1 interact with fertilin and laminin, an extracellular matrix ligand for alpha6beta1. Using alpha6-transfected cells we found that treatments (e.g., with phorbol myristate acetate or MnCl2) that increased adhesion to laminin inhibited sperm binding. Conversely, treatments that inhibited laminin adhesion increased sperm binding. Next, we compared the ability of fluorescent beads coated with either fertilin beta or with the laminin E8 fragment to bind to eggs. In Ca2+-containing media, fertilin beta beads bound to eggs via an interaction mediated by the disintegrin loop of fertilin beta and by the alpha6 integrin subunit. In Ca2+-containing media, laminin E8 beads did not bind to eggs. Treatment of eggs with phorbol myristate acetate or with the actin disrupting agent, latrunculin A, inhibited fertilin bead binding, but did not induce laminin E8 bead binding. Treatment of eggs with Mn2+ dramatically increased laminin E8 bead binding, and inhibited fertilin bead binding. Our results provide the first evidence that different states of an integrin (alpha6beta1) can interact with an extracellular matrix ligand (laminin) or a membrane-anchored cell surface ligand (ADAM 2).

Mediation of sperm-egg fusion: evidence that mouse egg alpha6beta1 integrin is the receptor for sperm fertilinbeta

BACKGROUND

INTRODUCTION

A key step leading to fertilization is the binding of sperm to the egg plasma membrane. When a mammalian sperm reaches the egg plasma membrane, fertilinbeta, an extracellular sperm membrane protein, is believed to bind to an egg plasma membrane receptor triggering fusion. We set out to identify the fertilinbeta binding partner on the egg plasma membrane.

RESULTS

We synthesized an 125-labeled peptide with the consensus Asp-Glu-Cys-Asp (DECD) sequence of fertilinbeta's disintegrin domain. This peptide contains a benzophenone photoaffinity probe and inhibits sperm-egg fusion. Upon photoactivation in the presence of whole mouse eggs, a single polypeptide was covalently labeled. This polypeptide has been identified by immunoprecipitation as an alpha6 integrin complexed with beta1 integrin.

CONCLUSIONS

Our experiments establish that small peptides containing the consensus DECD sequence of sperm fertilinbeta bind specifically to an alpha6beta1 integrin receptor on the egg membrane. We conclude that fertilinbeta binds directly to the alpha6beta1 integrin on the egg surface and this partnership mediates sperm-egg fusion.

Expanded cumuli induce acrosome reaction in boar sperm

The authors investigated acrosomal changes occurring in boar sperm that interact with the expanded cumulus matrix surrounding ovulated pig oocytes. Samples of washed boar sperm obtained from six donors were incubated for 4 hr under capacitating conditions and exposed either to solubilized zonae pellucidae (ZP) or solubilized expanded pig cumuli (SEC) obtained from IVM oocytes. Alternatively, hyaluronic acid, laminin, or fibronectin, components of the extracellular matrix (ECM) were added to capacitated sperm. Acrosomal integrity was evaluated 1 hr later by using FITC-PSA staining. Solubilized cumuli induced acrosome reaction (AR) in a dose-dependent manner with a saturating effect exerted at 2.5 SEC/50 microl. Both 500 nM fibronectin and 500 nM laminin stimulated acrosomal exocytosis, the latter being more effective and inducing saturating levels of AR. By contrast, hyaluronic acid did not affect acrosomal status. Preincubation with anti-laminin antibodies completely prevented the inducing activity of SEC without affecting the activity of solubilized ZP. Consistent with these data, the integrin VLA-6, a receptor with high affinity for laminin, was detected by immunoblotting on the plasma membrane of capacitated boar spermatozoa. In addition, its immunoneutralization, obtained with the preincubation of capacitated sperm with the antibody raised against the alpha chain of VLA-6 integrin, prevented AR upon exposure to laminin or SEC (10.7+/-3.2 and 10.2+/-1.0% respectively), while the samples retained their responsiveness to ZP (29.6+/-1.2%). The results demonstrate that the interaction between laminin, entrapped in the expanded cumuli, and specific integrins present on the sperm membrane can initiate AR, thus taking part in the process of sperm-egg recognition.

The 97 kDa linear IgA bullous dermatosis antigen is not expressed in a patient with generalized atrophic benign epidermolysis bullosa with a novel homozygous G258X mutation in COL17A1

The nature and expression pattern of the 97 kDa linear IgA bullous dermatosis antigen (LAD-1) and its role in epidermolysis bullosa have not been fully elucidated. In this study, we examined the expression of LAD-1 in the skin specimens of 70 patients with the various subtypes of epidermolysis bullosa, including simplex (n = 23), junctional (n = 15), and dystrophic variants (n = 32). For immunolabeling, we used two recently developed monoclonal antibodies to LAD-1 whose epitopes were ultrastructurally localized in the lamina lucida between NC16A and carboxyterminal domains of BPAG2, as well as autoantibodies against LAD-1 from the sera of two patients with linear IgA dermatosis. Among the 70 patients, only one patient with generalized atrophic benign epidermolysis bullosa failed to demonstrate LAD-1 expression. Although other major basement membrane components, including laminin 5, BPAG1, plectin, alpha6 and beta4 integrins, as well as type IV and type VII collagens were normally expressed, BPAG2/type XVII collagen was absent from the skin of this patient. Mutation analysis on COL17A1 using polymerase chain reaction amplification, heteroduplex scanning, and direct nucleotide sequencing revealed that this patient was homozygous for a novel nonsense mutation G258X in exon 11, and her parents were heterozygous carriers for this mutation. This is the first mutation located in the intracellular domain of BPAG2, and resides 817 bp upstream from the N-terminal amino acid sequence of LAD-1. These findings indicate that the absent expression of LAD-1 is observed in a BPAG2-deficient generalized atrophic benign epidermolysis bullosa patient with mutations in both alleles of COL17A1, and not in other epidermolysis bullosa subtypes. These findings also support the notion that LAD-1 is a degradation product of BPAG2.

Compound heterozygosity for a recessive glycine substitution and a splice site mutation in the COL7A1 gene causes an unusually mild form of localized recessive dystrophic epidermolysis bullosa

Type VII collagen is the major component of anchoring fibrils, adhesion structures of stratified epithelia that span the basement membrane region and papillary dermis. Mutations in the gene COL7A1 encoding type VII collagen cause dystrophic epidermolysis bullosa, a clinically heterogeneous autosomal dominant or recessive blistering disorder of the skin and mucous membranes. In this report, we investigate three siblings affected by an unusually mild form of localized recessive dystrophic epidermolysis bullosa who were shown to be compound heterozygotes for novel mutations affecting COL7A1. The maternally inherited mutation is a G-->C transversion that converts a codon for glycine to a codon for arginine (G1347R). The paternal mutation is a neutral G-->A transition at the last base of exon 70(5820G-->A) that alters the correct splicing of COL7A1 pre-mRNA, giving rise to an aberrant mRNA carrying the in-frame skipping of exon 70 in addition to the full-length RNA transcript carrying the G-->A substitution. Consistent with the normal levels of COL7A1 mRNA transcripts detected by northern analysis, immunoblotting and immunofluorescence studies evidenced that the patient keratinocytes synthesize and secrete normal amounts of stable type VII collagen, which is correctly deposited at the dermal-epidermal junction. In addition, mutated type VII collagen molecules assemble to form numerous, normally shaped anchoring fibrils, as shown by electron microscopic examination. The combination of a recessive glycine substitution with a splice site mutation that permits partially correct splicing therefore leads to a normal expression of mutated type VII collagen molecules with marginally altered biologic activity, and to the extremely mild phenotype observed in our patients.

Pyloric atresia-junctional epidermolysis bullosa syndrome: mutations in the integrin beta4 gene (ITGB4) in two unrelated patients with mild disease

Junctional epidermolysis bullosa associated with pyloric atresia (EB-PA; OMIM 226730) is a rare autosomal recessively inherited disease in which mucocutaneous fragility is associated with gastrointestinal atresia. This disease is usually fatal within the first few weeks or months of life even following surgical correction of the intestinal obstruction. Recently, mutations in the genes encoding the epithelial integrin alpha6beta4 (ITGA6 and ITGB4) have been identified in several patients with EB-PA. We report two unrelated patients with this disease who have survived into early childhood with mild cutaneous involvement, in whom we have identified pathogenetic mutations in ITGB4. The first patient was a compound heterozygote for a splice site mutation in exon 30 (3793 + 1G-to-A) and a non-sense mutation in exon 36 (W1478X), and the second was a compound heterozygote for a missense mutation in exon 3 (C38R) and a 1 bp deletion in exon 36 (4776delG). Although the non-sense and deletion mutations are predicted to result in markedly reduced beta4 integrin mRNA levels, the presence of the missense or splice site mutation on the second allele may enable the synthesis of some functional, albeit perturbed, beta4 polypeptide. Determination of the molecular mechanisms in these two cases increases our understanding of EB-PA and may enable correlation between genotype and phenotype.

Cre-loxP-mediated inactivation of the alpha6A integrin splice variant in vivo: evidence for a specific functional role of alpha6A in lymphocyte migration but not in heart development

Two splice variants of the alpha6 integrin subunit, alpha6A and alpha6B, with different cytoplasmic domains, have previously been described. While alpha6B is expressed throughout the development of the mouse, the expression of alpha6A begins at 8.5 days post coitum and is initially restricted to the myocardium. Later in ontogeny, alpha6A is found in various epithelia and in certain cells of the immune system. In this study, we have investigated the function of alpha6A in vivo by generating knockout mice deficient for this splice variant. The Cre- loxP system of the bacteriophage P1 was used to specifically remove the exon encoding the cytoplasmic domain of alpha6A in embryonic stem cells, and the deletion resulted in the expression of alpha6B in all tissues that normally express alpha6A. We show that alpha6A-/- mice develop normally and are fertile. The substitution of alpha6A by alpha6B does not impair the development and function of the heart, hemidesmosome formation in the epidermis, or keratinocyte migration. Furthermore, T cells differentiated normally in alpha6A-/- mice. However, the substitution of alpha6A by alpha6B leads to a decrease in the migration of lymphocytes through laminin-coated Transwell filters and to a reduction of the number of T cells isolated from the peripheral and mesenteric lymph nodes. Lymphocyte homing to the lymph nodes, which involves various types of integrin-ligand interactions, was not affected in the alpha6A knockout mice, indicating that the reduced number of lymph node cells could not be directly attributed to defects in lymphocyte trafficking. Nevertheless, the expression of alpha6A might be necessary for optimal lymphocyte migration on laminin in certain pathological conditions.

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

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

Migration of breast epithelial cells on Laminin-5: differential role of integrins in normal and transformed cell types

We examined the role of Laminin-5 (Ln-5) an extracellular matrix component of breast gland basement membrane, in supporting migration of normal (HUMEC), immortalized (MCF-10A), and malignant breast epithelial cells that exhibit different degrees of metastatic potential (MDA-MB-435>MDA-MB-231>MCF-7). HUMEC, MCF-10A, and MCF-7 cells all adhered to purified Ln-5 through the alpha3beta1 integrin receptor in adhesion assays. However, HUMEC and MCF-10A cells remained statically adherent, while MCF-7 cells migrated on Ln-5 in Transwell and colloidal gold displacement assays. Anti-alpha3 integrin antibodies blocked migration of MCF-7 cells on Ln-5. MDA-MB-231 and MDA-MB-435 cells bound and migrated on Ln-5 through a beta1 integrin receptor that is insensitive to antibodies that block the function of alpha1, alpha2, alpha3, alpha4, alpha5, alpha6, and alphaV integrin subunits. Migration of all cell types tested was blocked by CM6, a monoclonal antibody directed to a cell adhesion site on the alpha3 chain of Ln-5. Thus, Ln-5 may play an important role in regulating adhesion and migration in normal and transformed breast epithelium. Our results indicate that the type of integrin utilized by breast cells to interact with Ln-5, as well as its functional state, may determine whether cells will be statically adherent or migratory on Ln-5.

Endothelial cell integrin laminin receptor expression in multiple sclerosis lesions

Laminin, a major glycoprotein component of vessel basement membranes, is recognized by beta1- and beta3-integrins expressed on endothelial cells. To determine how endothelial cell integrins might function in multiple sclerosis (MS) lesions, integrin laminin receptors and laminin were analyzed in central nervous system samples from MS patients and controls by immunohistochemistry. In active MS lesions, endothelial cell VLA-6 and beta1 subunits were decreased compared to controls whereas alpha(v) subunit and VLA-1 were increased. In chronic inactive lesions beta1, VLA-6 and alpha(v) were the same as controls but VLA-1 remained increased. Alpha3 subunit was constant in all samples. By immunoelectron microscopy VLA-1, VLA-6, beta1, and laminin were distributed throughout endothelial cells; alpha(v) was adjacent to and on luminal surfaces; alpha(v) and VLA-1 were on intercellular junctions. These results indicate distinct regulation and functions of these integrins in different lesion stages. In active lesions decreased endothelial cell beta1/VLA-6 could result in their detachment from laminin thereby facilitating leukocyte transvascular migration and blood-brain barrier breakdown. Alpha(v) and VLA-1 on intercellular junctions may participate in re-establishing vessel integrity after leukocyte migration. Luminal surface alpha(v) also likely binds intraluminal ligands and cells. In chronic inactive plaques persistently elevated endothelial cell VLA-1 correlates with long-standing endothelial cell and blood-brain barrier dysfunction.

Hemidesmosome formation is initiated by the beta4 integrin subunit, requires complex formation of beta4 and HD1/plectin, and involves a direct interaction between beta4 and the bullous pemphigoid antigen 180

Hemidesmosomes (HDs) are stable anchoring structures that mediate the link between the intermediate filament cytoskeleton and the cell substratum. We investigated the contribution of various segments of the beta4 integrin cytoplasmic domain in the formation of HDs in transient transfection studies using immortalized keratinocytes derived from an epidermolysis bullosa patient deficient in beta4 expression. We found that the expression of wild-type beta4 restored the ability of the beta4-deficient cells to form HDs and that distinct domains in the NH2- and COOH-terminal regions of the beta4 cytoplasmic domain are required for the localization of HD1/plectin and the bullous pemphigoid antigens 180 (BP180) and 230 (BP230) in these HDs. The tyrosine activation motif located in the connecting segment (CS) of the beta4 cytoplasmic domain was dispensable for HD formation, although it may be involved in the efficient localization of BP180. Using the yeast two-hybrid system, we could demonstrate a direct interaction between beta4 and BP180 which involves sequences within the COOH-terminal part of the CS and the third fibronectin type III (FNIII) repeat. Immunoprecipitation studies using COS-7 cells transfected with cDNAs for alpha6 and beta4 and a mutant BP180 which lacks the collagenous extracellular domain confirmed the interaction of beta4 with BP180. Nevertheless, beta4 mutants which contained the BP180-binding region, but lacked sequences required for the localization of HD1/plectin, failed to localize BP180 in HDs. Additional yeast two- hybrid assays indicated that the 85 COOH-terminal residues of beta4 can interact with the first NH2-terminal pair of FNIII repeats and the CS, suggesting that the cytoplasmic domain of beta4 is folded back upon itself. Unfolding of the cytoplasmic domain may be part of a mechanism by which the interaction of beta4 with other hemidesmosomal components, e.g., BP180, is regulated.

180-kDa bullous pemphigoid antigen defective generalized atrophic benign epidermolysis bullosa: report of four cases with an unusually mild phenotype

Generalized atrophic benign epidermolysis bullosa (GABEB) is a rare variant of non-lethal junctional epidermolysis bullosa characterized by generalized skin blistering healing with atrophy and by atrophic alopecia with onset in childhood. Other features include mild mucosal blistering, dental abnormalities and nail dystrophy. We report four additional cases of GABEB from two families originating from the same isolated village. The patients shared an unusually mild clinical phenotype with cutaneous blisters strictly limited to trauma sites and rare occurrence of oral mucosal lesions. Scalp, eyelash and eyebrow alopecia was present in only two cases. Immunofluorescence studies showed a markedly reduced expression of the 180-kDa bullous pemphigoid antigen (BP180), and northern analysis of cultured keratinocytes indicated that the gene encoding for BP180 is affected in these GABEB patients.

Association of beta 1 integrin with protein kinase activity in large detergent resistant complexes

Integrins play a critical role in cell adhesion and mediate cell signaling. This report identifies the association of serine protein kinase activity with the beta 1 integrin by immunoprecipitation and phosphoamino acid analysis techniques. Reprecipitation techniques suggested that the serine kinase activity was not a member of the protein kinase C family. By gel filtration, most of the protein kinase activity associated with beta 1 integrin as well as most of the cell-surface beta 1 integrin was present in large detergent resistant complexes. These results suggest that serine protein kinase activity associated with the beta 1 integrin may play a role in signaling via the beta 1 integrin.

Role of the bullous pemphigoid antigen 180 (BP180) in the assembly of hemidesmosomes and cell adhesion--reexpression of BP180 in generalized atrophic benign epidermolysis bullosa keratinocytes

Bullous pemphigoid antigen 180 (BP180) is a transmembrane component of hemidesmosomes (HD), cell-substrate attachment complexes in stratified and complex epithelia. To determine the role of BP180 in the assembly of HD and cell adhesion, using SV40 virions we have immortalized BP180-deficient keratinocytes derived from a patient with the inherited skin blistering disorder generalized atrophic benign epidermolysis bullosa (GABEB). The GABEB keratinocytes form HD-like structures, which contain alpha 6 beta 4 integrin and HD1/plectin, but not the bullous pemphigoid antigen 230 (BP230). The expression of integrin subunits by GABEB keratinocytes was comparable to that of an immortalized normal human keratinocyte cell line (NHK), except for alpha 6 and beta 4, which were less strongly expressed in GABEB cells. In short-term adhesion assays, both GABEB keratinocytes and NHK bound strongly and to a similar extent to laminin-1, laminin-5, fibronectin, and type IV and V collagens, which suggests that BP180 is not involved in promoting the initial adhesion to these ligands. Transfection of GABEB keratinocytes with cDNAs for wild-type or a mutant of BP180 lacking the collagenous extracellular domain resulted in the expression of recombinant BP180 proteins that were correctly polarized at the basal cell surface together with alpha 6 beta 4. In addition, restored synthesis of BP180 affected the subcellular localization of BP230, which was no longer diffusely distributed in the cytoplasm, but was found in HD-like structures. In contrast, a BP180 mutant with a 36-amino-acid deletion from the amino terminus of the cytoplasmic domain failed to localize to HD-like structures. These results demonstrate that a region within the cytoplasmic domain of BP180 is essential for its localization into HD and that BP180 may play a critical role in coordinating the subcellular distribution of BP230.

Glomerular extracellular matrix components and integrins

It has become apparent that extracellular matrix components and their cellular receptors, the integrins, are important regulators of glomerular development and function. In this rapidly evolving field we studied the production of extracellular matrix components and integrins by rat glomerular visceral epithelial and mesangial cells, using molecular probes and antibodies that have recently become available. Special attention was paid to laminin isoforms and to splice variants of the integrin subunits alpha 3 and alpha 6. Results were compared to the in vivo expression in human fetal, newborn and adult kidneys. The mesangial cells were found to produce laminin-1, nidogen and two as yet unidentified laminin isoforms with putative alpha chains of about 395 (alpha x) and of 375 kDa (alpha y), tentatively described before as bovine kidney laminin. Furthermore, they expressed the integrins alpha 1 beta 1, alpha 2 beta 1, alpha 3A beta 1, alpha 5 beta 1, alpha v beta 3, alpha v beta 5, and small amounts of alpha 6A beta 1 and alpha 6B beta 1. The glomerular visceral epithelial cells produced the two new laminin isoforms mentioned above, laminin-5, but no laminin-1 or nidogen. The integrins alpha 2 beta 1, alpha 3A beta 1, alpha 6A beta 4, alpha 6B beta 4 and the integrin subunit alpha v were found to be expressed. We show that during nephrogenesis, the laminin alpha 1 chain disappears and is replaced by another alpha chain, possibly one of the two as yet unidentified alpha chains mentioned above. The laminin beta 1 chain is replaced by the beta 2 chain somewhat later in glomerular development. In general, the integrins found to be expressed in glomeruli of adult kidney were consistent with those found in cultured glomerular visceral epithelial and mesangial cells. No splice variant switch of the integrin alpha 3 or alpha 6 subunits could be demonstrated during nephrogenesis. Our results suggest an important role for the mesangial cell in providing nidogen as a crucial component of the supramolecular structure of the glomerular basement membrane. Furthermore our results indicate that laminin alpha x beta 2 gamma 1 and alpha y beta 2 gamma 1 isoforms are important in the glomerulus of adult kidney and that the integrin alpha 3A beta 1 is the main integrin receptor for laminin isoforms on glomerular visceral epithelial and mesangial cells, both in vitro and in vivo.

Compound heterozygosity for an out-of-frame deletion and a splice site mutation in the LAMB3 gene causes nonlethal junctional epidermolysis bullosa

Laminin-5 is the major adhesion ligand of epithelial cells. Mutations in the genes encoding laminin-5 cause junctional epidermolysis bullosa (JEB), a clinically and genetically heterogeneous group of recessively inherited blistering disease of skin and mucous membranes. In this report, we describe a patient with a non-lethal variant of JEB who is a compound heterozygous for mutations affecting the LAMB3 gene. The paternally inherited mutation is a deletion of a single base (T) leading to a frameshift and premature termination codon. It results in mRNA decay. The maternally inherited mutation is a G-->A transition at the last base of exon 7 (628G-->A) which converts a codon for glutamic acid in a codon for lysine (E210K). The mutation 628G-->A alters the correct splicing of LAMB3 pre-mRNA giving rise to two aberrant mRNA, in addition to the RNA transcript carrying the G-->A substitution. This result is compatible with the reduced expression of mutated laminin 5 molecules with altered biological activity, and the mild JEB phenotype observed in the patient.

Neoexpression of the epithelial adhesion complex antigens in thyroid tumours is associated with proliferation and squamous differentiation markers

Integrin dimer alpha 6 beta 4 is a transmembrane component of an epithelial cell adhesion complex that consists of hemidesmosomes (HDs), basement membrane (BM)-associated laminin-5 (Ln-5), and anchoring filaments/type VII collagen, all of which are absent from normal thyroid follicular epithelium. In the present study, the expression of epithelial cell adhesion complex antigens in thyroid tumours was investigated using immunohistochemistry. In addition to integrin subunits alpha 6 and beta 4, immunoreactivity was found for all chains of Ln-5, alpha 3, beta 3 and gamma 2, type VII collagen and hemidesmosomal antigen, HD1, in most thyroid carcinomas associated with tumour anaplasia and papillary growth pattern and located at the border of parenchymal cells and connective tissue or blood vessel walls. In addition, a more restricted expression of bullous pemphigoid antigens 180 and 230 (BP180 and BP230), constituents of HDs, was found in some papillary and anaplastic carcinomas and atypical adenomas. Adhesion complex antigens were located to regions of cells which were immunoreactive for cytokeratin (ck)-5 and proliferating cell nuclear antigen Ki-67. The results suggest that in thyroid carcinomas, the emergence of adhesion complex antigens is associated with squamous differentiation and high proliferative activity.

The integrin alpha6beta4 functions in carcinoma cell migration on laminin-1 by mediating the formation and stabilization of actin-containing motility structures

Functional studies on the alpha6beta4 integrin have focused primarily on its role in the organization of hemidesmosomes, stable adhesive structures that associate with the intermediate filament cytoskeleton. In this study, we examined the function of the alpha6beta4 integrin in clone A cells, a colon carcinoma cell line that expresses alpha6beta4 but no alpha6beta1 integrin and exhibits dynamic adhesion and motility on laminin-1. Time-lapse videomicroscopy of clone A cells on laminin-1 revealed that their migration is characterized by filopodial extension and stabilization followed by lamellae that extend in the direction of stabilized filopodia. A function-blocking mAb specific for the alpha6beta4 integrin inhibited clone A migration on laminin-1. This mAb also inhibited filopodial formation and stabilization and lamella formation. Indirect immunofluorescence microscopy revealed that the alpha6beta4 integrin is localized as discrete clusters in filopodia, lamellae, and retraction fibers. Although beta1 integrins were also localized in the same structures, a spatial separation of these two integrin populations was evident. In filopodia and lamellae, a striking colocalization of the alpha6beta4 integrin and F-actin was seen. An association between alpha6beta4 and F-actin is supported by the fact that alpha6beta4 integrin and actin were released from clone A cells by treatment with the F-actin- severing protein gelsolin and that alpha6beta4 immunostaining at the marginal edges of clone A cells on laminin-1 was resistant to solubilization with Triton X-100. Cytokeratins were not observed in filopodia and lamellipodia. Moreover, alpha6beta4 was extracted from these marginal edges with a Tween-40/deoxycholate buffer that solubilizes the actin cytoskeleton but not cytokeratins. Three other carcinoma cell lines (MIP-101, CCL-228, and MDA-MB-231) exhibited alpha6beta4 colocalized with actin in filopodia and lamellae. Formation of lamellae in these cells was inhibited with an alpha6-specific antibody. Together, these results indicate that the alpha6beta4 integrin functions in carcinoma migration on laminin-1 through its ability to promote the formation and stabilization of actin-containing motility structures.

The expression of integrin subunits alpha 6 and beta 4 by corneal epithelial cells on modified hydrogel surfaces

Our goal was to quantitate the expression and localization of integrin subunits alpha 6 and beta 4 by corneal epithelial cells on defined synthetic substrates. Previously we demonstrated that the cytoplasmic pH and translocation of the alpha 6 integrin subunit to the cell membrane was modified by ionic interactions. These results suggest that changes in the ionic interactions at the cell-substrate interface not only alter the intracellular milieu but ultimately affect the expression of adhesion proteins. To test this hypothesis, hydroxyethylmethacrylate (hema) hydrogels were modified by the addition of amines (N,N-dimethylaminoethylmethacrylate) or carboxyl moieties (methacrylic acid). Changes in the distribution of mRNA and protein were monitored using confocal laser scanning microscopy. The steady state level of integrin mRNA was evaluated, and the results indicate that while the plating efficiency was identical on all surfaces, the expression and localization of integrin subunits was surface dependent. Alpha 6 and beta 4 proteins were localized along the basal surface of nonpermeabilized cells cultured on laminin, on surfaces with amine moieties, and on those with amine and carboxyl moieties. The level of diffuse cytoplasmic staining increased with the presence of carboxyl moieties. Alpha 6 and beta 4 integrin subunits were negligible when the surfaces contained carboxyl moieties alone. The expression of alpha 6 and beta 4 mRNA was higher on surfaces containing amine moieties than on surfaces containing only carboxyl moieties. These results indicate that the characteristics of the substrate and the resulting cell-matrix interaction alter protein and mRNA expression of integrin subunits.

Integrins mediate adhesion to agrin and modulate agrin signaling

Agrin, a basal lamina-associated proteoglycan, is a crucial nerve-derived organizer of postsynaptic differentiation at the skeletal neuromuscular junction. Because integrins serve as cellular receptors for many basal lamina components, we asked whether agrin interacts with integrins. Agrin-induced aggregation of acetylcholine receptors on cultured myotubes was completely blocked by antibodies to the beta1 integrin subunit and partially blocked by antibodies to the alpha(v) integrin subunit. Agrin-induced clustering was also inhibited by antisense oligonucleotides to alpha(v) and a peptide that blocks the alpha(v) binding site. Non-muscle cells that expressed alpha(v) and beta1 integrin subunits adhered to immobilized agrin, and this adhesion was blocked by anti-alpha(v) and anti-beta1 antibodies. Integrin alpha(v)-negative cells that did not adhere to agrin were rendered adherent by introduction of alpha(v). Together, these results implicate integrins, including alpha(v)beta1, as components or modulators of agrin's signal transduction pathway.

Immunolocalization of integrins in the normal lung and in pulmonary carcinomas

Cryosections of normal adult lung (n = 7) and pulmonary epithelial tumors, including squamous (n = 8), adeno (n = 8), bronchioloalveolar (n = 5), and large cell (n = 4) carcinomas (SCC, ACC, BAC, LCC), carcinoids (Cd, n = 7), and neuroendocrine carcinomas (NEC) of variable grades (n = 14) were immunostained by the avidin-biotin peroxidase (ABC) method with monoclonal antibodies to the alpha1-6 and alpha(v) and the beta1-4 integrin subunits. Normal adult alveolar septae showed variably intense immunoreactivity for alpha1,3,6 and beta1, whereas reactions for alpha5 and alpha(v) were weaker and uneven; the remaining integrin subunits were not detected. Bronchial and bronchiolar epithelium showed variably intense staining for alpha2.3,6,v and beta1,4. Reactions were often, though not invariably, basally polarized. SCC, ADC, and LCC showed variably intense reactions for alpha2.3,6,v and beta1,4. BAC were strongly and uniformly stained for alpha1.3 and beta1. In Cd, alpha1,2,3,v and beta1 reactions were noted, whereas in NEC, weak alpha1,3 and beta1 staining was detected with only traces of alpha6 and alpha(v). We conclude that alveolar epithelial cells do not express the hemidesmosome-associated, laminin-binding integrin alpha6beta4 of the bronchial epithelium but rather the alpha1beta1 and alpha3beta1, collagen IV, and laminin receptors, respectively. SCC, ADC, and sampled LCC express an integrin repertory qualitatively similar to that of the bronchial epithelium. Distinct from the latter, the integrin repertory of BAC parallels that of the alveolar epithelium by its strong expression of the multipotential alpha1beta1 and alpha3beta1 integrins. NEC tumors do not display the laminin receptors alpha6beta4 and alpha6beta1 shown by SCC and ADC but express instead alpha1beta1, a collagen IV-laminin receptor rarely found in epithelial neoplasms except for BAC. In NEC tumors, integrins, especially alpha2, decrease with dedifferentiation. Notably distinct from epithelial mesotheliomas, the major fibronectin-binding integrin alpha5beta1 was not found in any type of lung carcinoma.

A homozygous in-frame deletion in the collagenous domain of bullous pemphigoid antigen BP180 (type XVII collagen) causes generalized atrophic benign epidermolysis bullosa

We report a missplicing event affecting the expression of bullous pemphigoid antigen BP180 (type XVII collagen) in a patient with generalized atrophic benign epidermolysis bullosa (GABEB). The segregation of the mutated allele in the family is consistent with the pathogenic role of the mutation. The homozygous mutation 2441-2A --> G disrupts a splice-site sequence in gene (BPAG2) for BP180 and results in an in-frame exon skipping within the collagenous ectodomain of the protein. The consequent deletion of 9 amino acids in the mutant BP180 is predicted to alter the structure of the homotrimer and is expected to exert a deleterious effect on stability of the protein that would account for the complete absence of immunoreactivity of the proband's skin to antibodies directed against BP180. These findings underscore the importance of structural integrity of the extracellular domain of BP180 for the stability of the protein.

Neuronal differentiation in SH-SY5Y human neuroblastoma cells induces synthesis and secretion of tenascin and upregulation of alpha(v) integrin receptors

Human SH-SY5Y neuroblastoma cells were induced to neuronal differentiation by using 12-0-tetradecanoylphorbol-13-acetate (TPA) and retinoic acid (RA). Both treatments rapidly induced long neurites and increased the content of neurofilaments as shown by immunocytochemistry and immunoblotting. Immunoprecipitation and immunoblotting of the culture medium with monoclonal antibodies demonstrated a rapid onset of synthesis and secretion of Mr 280,000 tenascin (Tn) polypeptide with TPA and both Mr 280,000 and 190,000 Tn polypeptides with RA and an increased secretion of extradomain A cellular fibronectin (EDA-Fn) upon both treatments. Upon RA treatment both Tn polypeptides were also found in extracellular matrix preparations of the differentiated cells. A diffuse extracellular Tn immunoreactivity and a distinct cytoplasmic reaction were seen in differentiated cells especially after exposure to monensin to inhibit cellular secretion. Instead, immunoprecipitation experiments suggested that laminin was synthesized by the cells but was not upregulated upon differentiation. Experiments with purified Tn, used to coat the culture substratum, demonstrated that the undifferentiated cells were unable to adhere or spread on Tn but rapidly acquired the spreading capacity upon differentiation with the inducing agents. In immunofluorescence and immunoblotting the undifferentiated cells presented only a faint heterogenous reaction for beta1 integrin (Int) subunit, whereas cells exposed to RA presented a strong reaction for the Int alpha1 and beta1 subunits, hence suggestive of Int alpha1beta1, and for Int alpha(v) subunit. Cells exposed to TPA showed an enhanced immunoreaction for Int alpha2 and beta1 subunits, suggestive of Int alpha2beta1, and for Int alpha(v) subunit. Immunoreactivity for Int alpha(v) located to distinct punctate plaques in the differentiated cells after both inducing agents. The results suggest that Tn is produced by cultured neuronally differentiating cells, and it is accompanied by the acquitance of an adhesion receptor for Tn.

Differential expression of integrins and laminin-5 in normal oral epithelia

beta 1 and beta 4 integrins are receptors on epithelial cells mediating cell-extracellular matrix adhesion. Furthermore, alpha 2 beta 1 and alpha 3 beta 1 contribute to cell-cell adhesion. Laminin-5 in epithelial basement membranes (BMs) is a ligand for alpha 6 beta 4 and alpha 3 beta 1. Expression of different integrins and laminin-5 was studied in oral epithelium to characterize regional variations in these adhesion molecules. Monoclonal antibodies directed against alpha 2-alpha 6 beta 1/alpha 6 beta 4 and laminin-5 were examined in cryopreserved biopsies of normal mucosa by immunohistochemistry. Laminin-5 was expressed as a line along the BMs. The junctional epithelium showed a unique phenotype: Laminin-5 was detected in the internal BM at the tooth surface and in the external BM, where excessive laminin-5 was seen in the stroma. alpha 6 beta 4 was expressed in all cells of the junctional epithelium. Integrins alpha 4 beta 1 and alpha 5 beta 1 were not detected in the epithelia, whereas alpha 2 beta 1 and alpha 3 beta 1 showed differential expression. Epithelia with well-developed rete pegs and connective tissue papillae showed polarized alpha 3 beta 1 expression along the BM in the rete pegs, in contrast to negative expression at the tips of the connective tissue papillae. A variation in the suprabasal distribution of alpha 2 beta 1 and alpha 3 beta 1 was observed between epithelia from different regions. alpha 2 beta 1 and alpha 3 beta 1 were detected in basal/parabasal cells in keratinized epithelia, whereas there was increased suprabasal expression in nonkeratinized mucosa. These results indicate inhomogeneity in the basal cell population of oral squamous epithelia and differential expression of integrins, which may reflect differences in the underlying stroma. Laminin-5 deposits in the stroma underneath the junctional epithelium may indicate subclinical gingival inflammation.

Laminin-5 inhibits human keratinocyte migration

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

alpha3beta1 Integrin is required for normal development of the epidermal basement membrane

Integrins alpha3beta1 and alpha6beta4 are abundant receptors on keratinocytes for laminin-5, a major component of the basement membrane between the epidermis and the dermis in skin. These integrins are recruited to distinct adhesion structures within keratinocytes; alpha6beta4 is present in hemidesmosomes, while alpha3beta1 is recruited into focal contacts in cultured cells. To determine whether differences in localization reflect distinct functions of these integrins in the epidermis, we studied skin development in alpha3beta1-deficient mice. Examination of extracellular matrix by immunofluorescence microscopy and electron microscopy revealed regions of disorganized basement membrane in alpha3beta1-deficient skin. Disorganized matrix was first detected by day 15.5 of embryonic development and became progressively more extensive as development proceeded. In neonatal skin, matrix disorganization was frequently accompanied by blistering at the dermal-epidermal junction. Laminin-5 and other matrix proteins remained associated with both the dermal and epidermal sides of blisters, suggesting rupture of the basement membrane itself, rather than detachment of the epidermis from the basement membrane as occurs in some blistering disorders such as epidermolysis bullosa. Consistent with this notion, primary keratinocytes from alpha3beta1-deficient skin adhered to laminin-5 through alpha6 integrins. However, alpha3beta1-deficient keratinocytes spread poorly compared with wild-type cells on laminin-5, demonstrating a postattachment requirement for alpha3beta1 and indicating distinct roles for alpha3beta1 and alpha6beta4. Our findings support a novel role for alpha3beta1 in establishment and/or maintenance of basement membrane integrity, while alpha6beta4 is required for stable adhesion of the epidermis to the basement membrane through hemidesmosomes.

Epidermal growth factor system is a physiological regulator of development of the mouse fetal submandibular gland and regulates expression of the alpha6-integrin subunit

Epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) regulate branching morphogenesis of fetal mouse submandibular gland (SMG) rudiments in vitro. The EGF system (EGF, TGF-alpha, and their shared receptor, EGFR) also regulates expression of integrins and their ligands in the extracellular matrix. We show here that inhibition of EGFR tyrosine-kinase activity by a tyrphostin retards in vitro development of SMGs. Using total RNA isolated from pooled SMGs taken from intact mouse fetuses, mRNA transcripts for EGF, TGF-alpha, and EGFR were detected by reverse transcription-polymerase chain reaction (RT-PCR), and age-dependent variations in the levels of these mRNA were quantitatively determined by nuclease protection assays. These findings suggest that the EGF system is operative in the in vivo development of this gland. alpha6-Integrin subunit was localized by immunofluorescence at the basal surface of epithelial cells. Branching morphogenesis of cultured SMG rudiments was inhibited by anti-alpha6 antibodies. Synthesis of alpha6-subunit in cultured SMGs, detected by metabolic labeling and immunoprecipitation, was increased by EGF and drastically reduced by tyrphostin. RT-PCR revealed that mRNAs for alpha6- and beta1- and beta4-integrin subunits are expressed at all ages between embryonic day 13 and postnatal day 7. These findings suggest that 1) the EGF system is a physiologic regulator of development of fetal mouse SMG, and 2) one mechanism by which it acts may be by regulating expression of integrins, which in turn control interaction of epithelial cells with the extracellular matrix.

The subcellular distribution of the high molecular mass protein, HD1, is determined by the cytoplasmic domain of the integrin beta 4 subunit

The high molecular mass protein, HD1, is a structural protein present in hemidesmosomes as well as in distinct adhesion structures termed type II hemidesmosomes. We have studied the distribution and expression of HD1 in the GD25 cells, derived from murine embryonal stem cells deficient for the beta 1 integrin subunit. We report here that these cells possess HD1 but not BP230 or BP180; two other hemidesmosomal constituents, and express only traces of the alpha 6 beta 4 integrin. By immunofluorescence and interference reflection microscopy HD1 was found together with vinculin at the end of actin filaments in focal contacts. In OVCAR-4 cells, derived from a human ovarian carcinoma which, like GD25 cells, only weakly express alpha 6 beta 4, HD1 was also localized in focal contacts. Upon transfection of both GD25 and OVCAR-4 cells with cDNA for the human beta 4 subunit the subcellular distribution of HD1 changed significantly. HD1 is then no longer present in focal contacts but in other structures at cell-substrate contacts, colocalized with alpha 6 beta 4. These junctional complexes are probably the equivalent of the type II hemidesmosomes. Transfection of GD25 cells with beta 1 cDNA did not affect the distribution of HD1, which indicates that the localization of HD1 in focal contacts was not due to the absence of beta 1. Moreover, in GD25 cells transfected with cDNA encoding a beta 4/beta 1 chimera, in which the cytoplasmic domain of beta 4 was replaced by that of beta 1, the distribution of HD1 was unaffected. Our findings indicate that the cytoplasmic domain of beta 4 determines the subcellular distribution of HD1 and emphasize the important role of alpha 6 beta 4 in the assembly of hemidesmosomes and other junctional adhesive complexes containing HD1.

Pleural mesotheliomas have an integrin profile distinct from visceral carcinomas

Cryosections of epithelial, sarcomatoid, and biphasic malignant mesotheliomas (EMM, n = 11; SMM, n = 5; BMM, n = 6) of the pleura were immunostained with monoclonal antibodies to integrin subunits alpha 1-6 and v, and beta 1-4. Localization patterns were compared with those known to occur in pulmonary and other adenocarcinomas (PADC, ADC). EMM and the epithelial component of BMM (ecBMM) expressed alpha 1,3,5,6, and v and beta 1 and 4. SMM and the sarcomatoid elements of BMM (scBMM) reacted variably for alpha 1,3,5,6 and v, and beta1. Reactions for alpha3, found in all tumors, were strongest in EMM, ecBMM, and PADC. Our findings indicate that EMM and ecBMM parallel PADC and most ADC in their expression of alpha6 beta4, underscoring that this laminin integrin receptor is intimately associated with these neoplastic epithelial phenotypes. Also, our observations on alpha3 beta1 suggest that this cell-cell adhesion-mediating integrin is related to the epithelial phenotype. Notably, all malignant mesotheliomas (MM), including those with distinct glandular structures, expressed the alpha5 beta1 fibronectin receptor, thus paralleling most sarcomas and differing from PADC and most other ADC. We conclude that irrespective of architectural and cytologic variants, transformed mesothelial cells possess an integrin repertory that differs significantly from that of most ADC, including those of the lung. These findings set mesothelium apart from epithelia and may prove helpful as adjunct tools for the differential diagnosis between EMM and AD.