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Monoclonal antibodies against integrin subunits alpha6 and beta1 inhibit migration of gingival epithelium in organ culture.

BACKGROUND: The main problem in the posterior instrumental treatment of periodontitis is the re-epithelization of the periodontal defects, leading to the formation of an unphysiological, long junctional epithelium inhibiting the regeneration of periodontal attachment. A precondition for the re-epithelization is the interaction between epithelial cells and their extracellular matrix mediated by integrins. Integrins are cellular adhesion molecules (CAM), binding to different structures of the extracellular matrix, e.g., collagen, laminin, or fibronectin. METHODS: Biopsy specimens of marginal gingiva, composed of epithelium and subepithelial connective tissue, were cultivated on microporous membranes in tissue culture plates. The culture medium was supplemented with monoclonal antibodies directed against human integrin subunits. The period of cultivation was 6 days and the medium was replaced daily. After cultivation, the tissue development was analyzed by histological and immunohistochemical methods. RESULTS: We found that the combination of antibodies directed against the integrin subunits alpha6 and beta1 inhibited the migration of epithelium completely in 9 out of 10 cultures, whereas control cultures containing none or only irrelevant antibodies demonstrated connective tissues completely covered by epithelium. CONCLUSIONS: Influencing the regeneration of periodontal tissue on a molecular basis by using antibodies directed against integrin subunits may be of future interest in postsurgical treatment of periodontal diseases.

Antibodies, Monoclonal↗

Sperm disintegrins, egg integrins, and other cell adhesion molecules of mammalian gamete plasma membrane interactions.

The cell-cell interactions that occur between sperm and egg involve not only the binding but also the fusion of the gamete plasma membranes. Numerous studies, carried out decades ago and more recently, have implicated several different molecules on both the sperm and egg as being involved in gamete membrane interactions. The sperm proteins that have received the most attention recently have homology to disintegrins, which are proteins in snake venoms that can interact with integrins. These sperm disintegrin-like proteins are members of a molecular family, known as ADAM's (for A Disintegrin and A Metalloprotease) or MDC's (for Metalloprotease, Disintegrin, Cysteine-rich). This review will focus on the molecules that have been implicated in mediating mammalian sperm-egg binding or the fusion of the gamete membranes. The molecules that will be discussed include three members of the ADAM/MDC family on sperm (fertilin alpha, fertilin beta, and cyritestin), integrins on eggs (alpha-6/beta-1 and others), and a number of other egg and sperm molecules, novel and characterized in other systems, that have been implicated in these processes.

ADAM Proteins↗

Dystroglycan and laminins: glycoconjugates involved in branching epithelial morphogenesis.

Branching epithelial morphogenesis is crucial for the development of several organs, such as lung, submandibular gland, mammary gland, tooth, pancreas, and kidney. During early embryogenesis, these organs are composed of a small epithelial rudiment surrounded by mesenchymal cells. Interactions between the two tissue compartments induce growth and branching of the epithelium into the mesenchyme. In each tissue, the epithelial branching has tissue-specific features, but there are many similarities both at the morphological and molecular level. Basement membrane components such as laminin have been implicated in the regulation of epithelial morphogenesis. Here data are reviewed that suggest that interactions between laminin-1 and other basement membrane components and the cell surface are important for epithelial morphogenesis in the kidney, lung, and salivary gland.

Animals↗

Variants of the alpha 6 beta 1 laminin receptor in early murine development: distribution, molecular cloning and chromosomal localization of the mouse integrin alpha 6 subunit.

Laminin (A:B1:B2) is a major component of the first basement membrane to appear in the developing mouse embryo. Its effects on morphogenesis and differentiation are mediated by interaction with cell surface receptors that are members of the integrin family. We have studied the expression of the alpha 6 subunit of murine alpha 6 beta 1 and its ligand, laminin, in preimplantation mouse embryos, embryo outgrowths and in embryonic stem (ES) cells and embryonal carcinoma (EC) cells. The alpha 6 subunit is present in the oocyte and throughout preimplantation development. Laminin A chain appears later than alpha 6 and has a more restricted distribution until the late blastocyst stage. alpha 6 beta 1 is strongly expressed in ES and EC cells; the levels of mRNA expression are not altered by differentiation. Molecular cloning of cDNA for the murine integrin alpha 6 subunit from a mammary gland lambda gt11 library showed, as in man, an open reading frame encoding two variants of alpha 6, alpha 6A and alpha 6B. The identity of the alpha 6 amino acid sequence to that in man and chicken is 93% and 73%, respectively. The gene for murine alpha 6 was mapped to chromosome 2. While undifferentiated ES and EC cells express only alpha 6B, alpha 6A is co-expressed in ES cells after differentiation is induced by retinoic acid. alpha 6B is also the only variant expressed in blastocyst stage embryos, but when blastocysts have grown out in culture both alpha 6A and alpha 6B are expressed reflecting the results in the cell lines. We suggest that the deposition of laminin in the embryo is a receptor-mediated process and that the shift in the expression of the variants, as the inner cell mass forms its first differentiated progeny, reflects a change in functional properties.

Amino Acid Sequence↗

Evaluation of integrin molecules involved in substrate adhesion.

Integrins were cross-linked to their extracellular matrix ligands using non-penetrating chemical cross-linkers. This procedure did not disturb the distribution of integrin in the adhesion structure and adhesion plaque integrin staining remained even when the cultures were extracted with ionic detergents. 80-90% of the beta 1 integrin in the cross-linked culture was extracted with RIPA buffer and the remaining 10-20% was recovered following reversal of the cross-linking. This separated two distinct integrin pools, one which can be cross-linked to substrate bound extracellular matrix and one which is not. The specificity of this procedure for cross-linking of integrins involved in substrate adhesion was demonstrated using NIH 3T3 cells which express both alpha 5 beta 1 and alpha 6 beta 1 integrins. alpha 6 was cross-linked only in cells plated on laminin whereas alpha 5 was cross-linked when fibronectin was present. Using antisera directed to the cytoplasmic domains of either alpha 5 or beta 1 integrin, it was demonstrated that these domains can be blocked in the intact cell but the blocking can be removed using ionic detergent extraction after chemical cross-linking. The extracellular matrix associated with the substrate surface but not that associated with the media exposed surface is both cross-linked and retained on the plastic dish following cross-linking.

3T3 Cells↗

Cell localization and redistribution of the 67 kD laminin receptor and alpha 6 beta 1 integrin subunits in response to laminin stimulation: an immunogold electron microscopy study.

The 67 kDa laminin receptor (67LR), one of several cell surface laminin-binding proteins, is involved in the interactions between cancer cells and laminin during tumor invasion and metastasis. A 37 kDa polypeptide (37LRP), previously identified as the 67LR precursor, is abundantly present in the cytoplasm and has been implicated in polysome formation. To better understand the cellular localization of the 67LR and its precursor, transmission electron microscopic studies of human melanoma A2058 cells were carried out using immunogold labeling and a variety of antibodies: (a) affinity purified antibodies directed against 37LRP cDNA-derived synthetic peptides; (b) anti-67LR monoclonal antibodies raised against intact human small cell lung carcinoma cells; and (c) monoclonal antibodies against the subunits of the integrin laminin receptor, alpha 6 beta 1. Double-labeling immunocyto-chemistry revealed that anti-67LR monoclonal antibodies as well as anti-37 LRP antibodies recognized antigens that were localized in the cytoplasm in electron dense structures. As expected, cell membrane labeling was also observed. Surprisingly, alpha 6 and beta 1 integrin subunits were detected in the same cytoplasmic structures positive for the 67LR and the 37LRP. After addition of soluble laminin to A2058 cells in suspension, the number of labeled cytoplasmic structures increased especially in the vicinity of the plasma membrane, and were exported onto the cell surface. Neither fibronectin nor BSA induced such an effect. The data demonstrate that the 67 LR and the 37 LRP antibodies detect colocalized antigens that are in cytoplasmic structures with alpha 6 beta 1 integrin.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Membrane↗

Down-regulation of laminin-binding integrins by 1 alpha,25-dihydroxyvitamin D3 in human melanoma cells in vitro.

In the present investigation the effect of 1 alpha,25(OH)2D3 on the expression of the integrin laminin receptor on the melanoma cell line SK-MEL-28 has been examined. The SK-MEL-28 cells were shown to contain high-affinity receptors for 1 alpha,25(OH)2D3 and cell proliferation was found to be inhibited in a dose-dependent manner in response to the hormone. Using monoclonal antibodies against the alpha 6-sub-unit of the integrin laminin receptor, immunocytochemistry demonstrated that exposure of cells to 1 alpha,25(OH)2D3 for 5 days caused a reduced staining intensity. This observation was further confirmed by dot blot analysis, where a dose-dependent decline of alpha 6 expression was obtained after treatment of the cells with 1 alpha,25(OH)2D3 for 6 days. FACS-analysis was performed in order to quantify this decline, and it was found that the level of alpha 6-subunits on the cell surface was reduced by more than 40%. Additional investigations including Northern blot analyses of poly(A)+RNA extracts also showed a dose-dependent reduction of alpha 6 mRNA. Interestingly, the decrease of alpha 6 expression on the surface of SK-MEL-28 melanoma cells was accompanied by a reduced ability of the cells to adhere to an artificial basement membrane. In conclusion, the present investigation shows that besides having an antiproliferative effect on the SK-MEL-28 melanoma cells, 1 alpha,25(OH)2D3 is also able to inhibit the surface expression of the alpha 6-subunit of the integrin laminin receptor. Moreover, the results strongly indicate that 1 alpha,25(OH)2D3 exerts its regulatory effect on the alpha 6-subunit at the transcriptional level rather than at the protein level.

Antigens, CD↗

Chemokines fail to up-regulate beta 1 integrin-dependent adhesion in human Th2 T lymphocytes.

Th1 and Th2 cells are functionally distinct subsets of CD4+ T lymphocytes whose tissue-specific homing to sites of inflammation is regulated in part by the differential expression of P- and E-selectin ligands and selected chemokine receptors. Here we investigated the expression and function of beta 1 integrins in Th1 and Th2 cells polarized in vitro. Th1 lymphocytes adhere transiently to the extracellular matrix ligands laminin 1 and fibronectin in response to chemokines such as RANTES and stromal cell-derived factor-1, and this process is paralleled by the activation of the Rac1 GTPase and by a rapid burst of actin polymerization. Selective inhibitors of phosphoinositide-3 kinase prevent efficiently all of the above processes, whereas the protein kinase C inhibitor bisindolylmaleimide prevents chemokine-induced adhesion without affecting Rac1 activation and actin polymerization. Notably, chemokine-induced adhesion to beta 1 integrin ligands is markedly reduced in Th2 cells. Such a defect cannot be explained by a reduced sensitivity to chemokine stimulation in this T cell subset, nor by a defective activation of the signaling cascade involving phosphoinositide-3 kinase, Rac1, and actin turnover, as all these processes are activated at comparable levels by chemokines in the two subsets. We propose that reduced beta 1 integrin-mediated adhesion in Th2 cells may restrain their ability to invade and/or reside in sites of chronic inflammation, which are characterized by thickening of basement membranes and extensive fibrosis, requiring efficient interaction with organized extracellular matrices.

Actins↗

Monocytic cells synthesize, adhere to, and migrate on laminin-8 (alpha 4 beta 1 gamma 1).

Laminins, a growing family of large heterotrimeric proteins with cell adhesive and signaling properties, are major components of vascular and other basement membranes. Expression, recognition, and use of laminin isoforms by leukocytes are poorly understood. In monoblastic THP-1 cells, transcripts for laminin gamma(1)-, beta(1)-, and alpha(4)-chains were detected by RT-PCR. Following immunoaffinity purification on a laminin beta(1) Ab-Sepharose column, laminin beta(1)- (220 kDa), gamma(1)- (200 kDa), and alpha(4)- (180/200 kDa) chains were detected by Western blotting in THP-1 cells and in two other monoblastic cell lines, U-937 and Mono Mac 6. After cell permeabilization, a mAb to laminin gamma(1)-chain reacted with practically all blood monocytes by immunofluorescence flow cytometry, and laminin-8 (alpha(4)beta(1)gamma(1)) could be isolated also from these cells. Monoblastic JOSK-I cells adhered constitutively to immobilized recombinant laminin-8, less than to laminin-10/11 (alpha(5)beta(1)gamma(1)/alpha(5)beta(2)gamma(1)) but to a higher level than to laminin-1 (alpha(1)beta(1)gamma(1)). Compared with the other laminin isoforms, adhesion to laminin-8 was preferentially mediated by alpha(6)beta(1) and beta(2) integrins. Laminin-8 and, to a lower extent, laminin-1 promoted spontaneous and chemokine-induced migration of blood monocytes, whereas laminin-10/11 was inhibitory. Altogether, the results indicate that leukocytes, as other cell types, are able to synthesize complete laminin molecules. Expression, recognition, and use of laminin-8 by leukocytes suggest a major role of this laminin isoform in leukocyte physiology.

CD18 Antigens↗

Altered expression of beta 1 integrins in renal carcinoma cell lines exposed to vinblastine.

BACKGROUND: Cellular expression of P-glycoprotein (P-gp) which mediates a well characterized mechanism of multidrug resistance (MDR) has been reported previously to be associated with an enhanced tumor dissemination. Since adhesion receptors of the beta 1 integrin family play a substantial role in tumor spread, we studied expression of VLA-1 to -6 in a total of four renal carcinoma cell (RCC) lines prior to and after induction of MDR via exposure to vinblastine. MATERIAL AND METHODS: Surface expression of P-gp and VLA-1 to -6 was determined immunocytochemically in untreated pre-established renal carcinoma cell lines (Caki-1, Caki-2, A498) and a cell line derived from a RCC patient who had received a vinblastine-containing therapy regimen prior to the resection of a local relapse of the tumor (EH). Resistant sublines were cultivated in the presence of 1 ng/ml and 10 ng/ml of vinblastine sulfate, respectively. RESULTS: In all cell lines examined, an increased number of P-gp expressing cells was observed upon exposure to vinblastine. Significant changes of beta 1 integrin expression were observed in three of four RCC cell lines. A de novo expression of VLA-1, VLA-2, and VLA-4 as detected by immunocytochemistry occurred in resistant Caki-1 cells. A498 cells showed an increasing number of VLA-2 positive cells in drug resistant sublines. In contrast, a decrease of VLA-2 and VLA-5 expression was found in EH cells, the only cell line exhibiting P-gp expression prior to vinblastine exposure. Caki-2 cells showed no significant changes of surface integrin expression upon treatment with vinblastine. CONCLUSIONS: Our results demonstrate that induction of drug resistance can be associated with substantial changes of the integrin phenotype in renal carcinoma cell lines. In our experiments, among all VLAs studied, VLA-2 was most frequently altered in expression by RCC cell lines. The significance of these observations for aberrant metastatic properties of multidrug resistant tumor cells will be the subject of further studies.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

Upregulation of integrin alpha6/beta1 and chemokine receptor CCR1 by interleukin-12 promotes the migration of human type 1 helper T cells.

CD4(+) T helper 1 (Th1) cells and Th2 cells are distinguished based on the pattern of cytokines they are able to produce. Selectin ligands and chemokine receptors are differentially expressed in Th1 and Th2 cells, providing a basis for tissue-specific recruitment of helper T-cell subsets. However, the modes and mechanisms regulating tissue-specific localization of Th1 and Th2 cells are still largely unknown. Here, we show the preferential expression on Th1 cells of the integrin alpha6/beta1, which is distinctly regulated by the Th1-inducing cytokines interleukin-12 (IL-12) and interferon-alfa (IFN-alpha). The pattern of integrin alpha6/beta1 regulation closely mirrors that of the chemokine receptor CCR1. Analysis of signal transducer and activator of transcription 4 (Stat4) activation by IL-12 and IFN-alpha shows distinct signaling kinetics by these cytokines, correlating with the pattern of CCR1 and integrin alpha6/beta1 expression. Unlike IFN-alpha, the ability of IL-12 to generate prolonged intracellular signals appears to be critical for inducing integrin alpha6/beta1 upregulation in Th1 cells. The expression and upregulation of CCR1 and alpha6/beta1 integrin promotes the migration of Th1 cells. These findings suggest that the exquisite regulation of integrin alpha6/beta1 and CCR1 may play an important role in tissue-specific localization of Th1 cells.

Adjuvants, Immunologic↗

Laminin isoforms 8 and 10 are primary components of the subendothelial basement membrane promoting interaction with neoplastic lymphocytes.

To determine whether subendothelial laminins (LNs) could be implicated in the extravasation of neoplastic lymphocytes, we have examined the distribution of a number of LN isoforms in human vascular structures of adult individuals and have assayed the ability of the isolated LN molecules to promote adhesion of lymphoma and leukemic cells in vitro using a novel cell adhesion assay, CAFCA, Centrifugal Assay for Fluorescence-based Cell Adhesion (E. Giacomello et al., Biotechniques, 26: 758-762, 1999; P. Spessotto et al., Methods Mol. Biol., 139: 321-343, 2000). The use of previously characterized LN chain-specific antibodies showed that the vast majority of the smaller vascular compartments, known to correspond to sites of lymphocyte transmigration, expressed the subunits involved in the structuring of 9 of the 12 LN isoforms known to date. Eight LN isoforms (i.e., LN-1, -2, -4, -5, -8, -9, -10, and -11) and four naturally occurring LN complexes were isolated from various tissues and cultured cells by combined gel filtration, ion exchange, and immunoaffinity chromatographies, and the identity/composition of the isolated LNs/LN complexes was asserted by immunochemical means and amino-acid sequencing. Notwithstanding the widespread colocalization of LN isoforms, a panel of neoplastic B- and T-cell lines and lymphocytes isolated from patients affected by chronic lymphocytic B-cell leukemia attached preferentially and with high avidity to purified LN-8, purified LN-10, and LN-10-containing protein complexes, whereas lymphocytes derived from patients diagnosed with acute lymphocytic leukemia failed to bind to these LNs. All of the tested neoplastic lymphocytes failed to adhere to the isolated LN-1, LN-4, LN-9, and LN-11 and attached moderately well to purified LN-2 and LN-5. The interaction of transformed lymphocytes with LNs was cation-dependent and interchangeably mediated by the alpha3beta1 and alpha6beta1 integrins. The degree of engagement of the two LN receptors was dependent upon their relative levels of cell surface expression, whereas, irrespective of the phenotype, lymphocytes deprived of either of these receptors were incapable of LN binding. The findings suggest that LN-8 and LN-10 may act in an independent or complementary fashion as primary components of the endothelial basement membrane favoring the interaction of extravasating neoplastic lymphocytes. Thus, our results would demonstrate that different LN isoforms may evoke diverse cellular responses in different cell types and that this divergence may be the basis for the redundancy of LN distribution in a number of vascular structures.

Animals↗

The metastatic odyssey: the integrin connection.

This article explores the mechanistic basis of carcinoma progression by focusing on the contribution of integrins. Integrins are essential for progression because of their ability to mediate physical interactions with extracellular matrices and their ability to regulate signaling pathways that control actin dynamics and cell movement, and for growth and survival. This article centers on a6 integrins (a6B1 and a6B4), which are receptors for the laminin family of basement membrane components. Numerous studies have implicated these integrins in cancer progression and have provided a rationale for studying the mechanistic basis of their contribution to aggressive disease.

Actins↗

Clonal expansion of hepatic stem/progenitor cells following flow cytometric cell sorting.

Although hepatic stem cells are believed to exist and play a critical role in developing and regenerating liver, little is known about their cell surface specificity or differentiation capabilities. To make prospective studies of hepatic stem cells possible, we established an in vitro culture system for identification and characterization of hepatic stem/progenitor cells. By combining this culture system with fluorescence activated cell sorting (FACS), a population of cells that were capable of forming large colonies and providing their descendants for relative longer period was isolated from fetal mouse livers. These data suggest that hepatic stem/progenitor cells with high proliferative potential are existent in the developing mouse liver, and that they are enriched by using flow cytometry.

Animals↗

[Mechanism of enhanced invasiveness of human hepatocellular carcinoma by integrin alpha 6 beta 1].

OBJECTIVE: To study the mechanism of enhanced invasiveness of human hepatocellular carcinoma (HCC) by laminin (LN) receptor integrin alpha 6 beta 1. METHODS: A stable transfectant of HCC Bel 7402 cell line, the alpha 6 beta 1 receptors of which were replaced by non-functional LN receptor alpha 6 beta 4-TR using dominant negative strategy, was used. Motility of the non-transfected, mock transfected and transfected tumor cells was assessed by the number of cells migrated to an area scratched out of cells on tumor cell monolayer. Tumor cell invasion was examined by cell penetration through a Matrigel layer in Boyden chamber. Matrix metalloproteinases (MMPs) secretion was detected by gelatin zymography. RESULTS: The migration of HCC Bel 7402 cells expressing dominant negative alpha 6 beta 1 was significantly decreased. Their invasive capability was decreased by 46.7%. The secretion of MMP-9 was almost totally inhibited and the activated MMP-2 was decreased by 43.9%. CONCLUSION: The decrease in cell motility, invasiveness and MMPs secretion of HCC cells expressing dominant negative alpha 6 beta 4 TR implies that LN-integrin interaction plays important role in HCC progression.

Carcinoma, Hepatocellular↗

Megakaryocytic cells synthesize and platelets secrete alpha5-laminins, and the endothelial laminin isoform laminin 10 (alpha5beta1gamma1) strongly promotes adhesion but not activation of platelets.

Following vascular injury, basement membrane (BM) components of the blood vessels are exposed to circulating cells and may contribute to hemostasis and/or thrombosis. Laminins 8 (LN-8) (alpha4beta1gamma1) and 10 (LN-10) (alpha5beta1gamma1) are major laminin isoforms of the endothelial BM, and LN-8 is also secreted by activated platelets. In the present study, we demonstrate synthesis of alpha5-laminins LN-10 and LN-11 (alpha5beta2gamma1) by megakaryocytic cells, and intracellular expression of these laminin isoforms in blood platelets. In contrast to platelet LN alpha4 chain that had an apparent molecular weight of 180 kDa and associated mostly to LNbeta1 chain, platelet LNalpha5 consisted of 300/350 kDa polypeptides and associated mainly to LNbeta2. Both alpha4- and alpha5-laminins were secreted by platelets following stimulation. When compared to recombinant human (rh) LN-8, rhLN-10 was much more adhesive to platelets, though adhesion to both proteins was largely mediated via alpha6beta1 integrin. In spite of their adhesive properties, rhLN-8 and rhLN-10 induced neither P-selectin expression nor cell aggregation, two signs of platelet activation. This study demonstrates synthesis/expression of heterotrimeric alpha5-laminins in hematopoietic/blood cells, and provides evidence for the adhesive, but not activating, role of endothelial laminin isoforms in platelet biology.

Blood Platelets↗

Differential expression of integrins on human thymocyte subpopulations.

Integrins represent a candidate group of cell surface receptors that may control the homing and population of the thymus by T-cell precursors and the subsequent migration of developing thymocytes through the thymic architecture. We have used multiparameter flow cytometric methods to characterize the expression of several members of the integrin family (alpha 3 beta 1, alpha 4 beta 1, alpha 5 beta 1, alpha 6 beta 1, and alpha L beta 2) on thymocyte subpopulations and have correlated integrin expression with other well-defined thymocyte differentiation markers. alpha 4 beta 1 was expressed by all thymocytes, but expression was highest on CD4-CD8- double-negative (DN) cells, high on CD+CD8+ double-positive (DP) cells, and lowest on mature single-positive (SP) cells, alpha 3 beta 1, alpha 5 beta 1, and alpha 6 beta 1 were present on 13%, 63%, and 26% of thymocytes, respectively, with maximal levels of expression on DN and SP cells, and low levels of expression on DP cells. Simultaneous analysis of alpha 4 beta 1, alpha 5 beta 1, and CD3 expression suggested a pathway of T-cell differentiation in the thymus in which the majority of the DN cells were alpha 4 beta 1hi alpha 5 beta 1hi, the DP cells alpha 4 beta 1hi alpha 5 beta 1lo/-, and the most mature SP cells were alpha 4 beta 1int. The stage-specific expression of integrins strongly implies their functional involvement during T-cell maturation in the thymus.

Cell Differentiation↗