Activation of Toll-like receptor 3 reduces actin polymerization and adhesion molecule expression in endometrial cells, a potential mechanism for viral-induced implantation failure.

STUDY QUESTION: Does activation of endometrial Toll-like receptor 3 (TLR 3) affect cell receptivity to trophoblast adhesion? SUMMARY ANSWER: TLR 3 activation in vitro reduces the attachment of trophoblast cells to endometrial cells by altering the cell cytoskeleton and reducing the expression of adhesion molecules in human endometrial cells. WHAT IS KNOWN ALREADY: It is well documented that the presence of an infection at the time of implantation can lead to implantation failure. The female reproductive tract recognizes invading micro-organisms through the innate pathogen recognition receptors such as the TLRs. STUDY DESIGN, SIZE, DURATION: Poly I:C was used as a TLR 3-specific ligand and endometrial cells were either treated or not with Poly I:C (treated versus control) in vitro. The experiments were performed in three replicates on three separate days. PARTICIPANTS/MATERIALS, SETTING, METHODS: An in vitro assay was developed using RL95-2 (a human endometrial cell line) and JAr (a human trophoblast cell line) cells. Initially, the percentage of attached JAr spheroids to RL95-2 was measured in response to TLR 3 activation. Next, actin polymerization in RL95-2 cells was assessed in response to TLR 2/6, 3 and 5 activation. Phalloidin was used to assess the mean fluorescence intensity of F-actin by flow cytometry or confocal microscopy. Secondly, the influence of TLR 2/6, 3 and 5 activation on the expression of cluster of differentiation 98 (CD98) and ß3 integrin was determined. To further understand through which pathways the TLR 3-induced alterations occur, inhibitors were applied for Toll/interleukin-1 receptor domain-containing adaptor inducing interferon-beta (TRIF), myeloid differentiation primary response 88 (MYD88), mitogen-activated protein kinases (MAPK) and nuclear factor pathways. MAIN RESULTS AND THE ROLE OF CHANCE: We observed that stimulation of TLR 3 in endometrial cells with different concentrations of Poly I:C led to a reduction in the percentage of trophoblasts attached to the endometrial cells in a dose-dependent manner (P < 0.05). This decrease was consistent in the Poly I:C treated group regardless of the co-incubation time (P < 0.05). In addition, our results demonstrated that actin polymerization and CD98 expression significantly decreased only in response to TLR 3 activation (P < 0.05). Activation of endometrial cells with TLR 2/6, 3 and 5 significantly reduced ß3 integrin expression (P < 0.05). These alterations were shown to work via MYD88-MAPK pathways (P < 0.05). LIMITATIONS, REASONS FOR CAUTION: This study has been performed in vitro. Future in vivo studies will be required in order to confirm our data. WIDER IMPLICATIONS OF THE FINDINGS: This is a novel discovery which extends our current knowledge concerning diagnosis and treatment of viral-induced infertility cases. STUDY FUNDING/COMPETING INTERESTS: This research was supported by the COST Action FA1201 (GEMINI) by granting a Short Term Scientific Mission and the Instituto de Salud Carlos III by granting Grant PI11/01645. The authors have no conflict of interest to declare.

Embryonic implantation and leukocyte transendothelial migration: different processes with similar players?

A clear parallelism between the different steps in human embryo-endometrial apposition/adhesion/invasion and leukocyte-endothelium rolling/adhesion/extravasation can be established. During human implantation and leukocyte trafficking, a first wave of soluble mediators regulates the expression and functional activity of adhesion molecules such as L-selectin and integrins, which mediate both processes. Apical surfaces of human endometrial epithelium and endothelium are key elements for the initiation of molecular interactions to capture the blastocyst or leukocyte, respectively. Subsequently, the blastocyst and the leukocyte migrate through the epithelium and endothelium toward their final destination, the endometrial stroma, to initiate placentation or the inflammatory foci as part of the immune response. Similarities between the intermediate molecular mechanisms of these two physiologically unrelated processes are discussed.

Regulatory role of tetraspanin CD9 in tumor-endothelial cell interaction during transendothelial invasion of melanoma cells.

Heterotypic interaction among tumor cells (TCs) and endothelial cells (ECs) may play a critical role during the vascular dissemination of neoplastic cells and during pathologic angiogenesis in tumors. To identify molecules involved in these processes, the distribution of vascular junctional proteins was first studied by immunofluorescence at sites of heterologous intercellular contact using TC-EC mosaic monolayers grown on 2-dimensional collagen. Several members of the tetraspanin superfamily, including CD9, CD81, and CD151, were found to localize at the TC-EC contact area. The localization of tetraspanins to the TC-EC heterologous contact area was also observed during the active transmigration of TCs across EC monolayers grown onto 3-dimensional collagen matrices. Dynamic studies by time-lapse immunofluorescence confocal microscopy showed an active redistribution of endothelial CD9 to points of melanoma insertion. Anti-CD9 monoclonal antibodies were found to specifically inhibit the transendothelial migration of melanoma cells; the inhibitory effect was likely caused by a strengthening of CD9-mediated heterotypic interactions of TCs to the EC monolayer. These data support a novel mechanism of tetraspanin-mediated regulation of TC transcellular migration independent of TC motility and growth during metastasis and a role for these molecules in the formation of TC-EC mosaic monolayers during tumor angiogenesis.

Tetraspanins and intercellular interactions.

The superfamily of tetraspanins comprises a group of polypeptides with four transmembrane domains that form large supramolecular structures in the plasma membrane through their associations to multiple integral membrane proteins. They are involved in homo- and heterotypic intercellular interactions in different processes such as hematopoiesis, lymphocyte activation, cancer metastasis, and fertilization. Intercellularly located tetraspanins regulate the juxtacrine activity of growth factors, cell fusion, and myelin formation. On the other hand, in motile cells they relocalize from cell-cell junctions to actin-based structures such as filopodia or growth cones and regulate cell motility in wound healing and angiogenesis processes.

The hepatitis B virus X protein (HBx) induces a migratory phenotype in a CD44-dependent manner: possible role of HBx in invasion and metastasis.

The hepatitis B virus X protein (HBx) of the hepatitis B virus (HBV) has been involved in the development of hepatocellular carcinoma (HCC). However, its possible contribution to the metastatic spreading of liver tumors has not been explored so far. We report here the ability of HBx to enhance cell motility, both alone and in synergy with growth factors, and to induce a migratory phenotype in transformed cells. HBx altered the cellular morphology by inducing the formation of pseudopodial protrusions and cytoskeletal rearrangements, which was accompanied by the polarization of cell-surface adhesion molecules, including the hyaluronan (HA) receptor, CD44. Furthermore, HBx induced the redistribution to the pseudopodial tips of F-actin-binding proteins of the ezrin/radixin/moesin (ERM) family in a Rho- and Rac-dependent manner and increased the association of CD44 with moesin. The migration of HBx-bearing cells in response to HA and growth factors was impaired by a blocking anti-CD44 monoclonal antibody (mAb), suggesting that the HBx-induced cell motility is partially mediated by CD44. Interestingly, HBx-bearing cells showed increased HA-interaction efficiency as assessed under laminar flow conditions, which was the result, at least in part, of an enhanced binding affinity of CD44. HBx may therefore contribute to the acquisition of metastatic properties by modifying the migratory behavior of transformed hepatocytes and by increasing their ability to bind HA in the outer margin of the tumors or in secondary target organs.

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

BACKGROUND/AIMS: The hepatitis B virus HBx protein is associated with the development of hepatocellular carcinoma (HCC). However, its possible contribution to tumor spreading has not been explored. The migration of tumor cells through the extracellular matrix (ECM) represents a crucial step in tumor metastasis. Our aim was to study the effect of HBx on the integrin-mediated cell-ECM interaction, and its possible consequences for cell migration. METHODS: Cell-ECM interaction was evaluated by static adhesion experiments, using blocking and stimulating anti-beta1 integrin mAbs. ECM receptor expression was analyzed by flow cytometry. The cellular distribution of the activated beta1 integrin subunit was determined by immunofluorescence analysis, and cell motility was determined by wound-healing assays. RESULTS: HBx-bearing cells showed decreased adhesion to fibronectin, which correlated with a decreased expression of the alpha5 integrin subunit. The activated beta1 subunit was redistributed to the tips of pseudopodial protrusions of HBx-bearing cells, whereas it was evenly localized in the control cells. HBx-induced cell migration was abrogated by irreversible stimulation of beta1 integrins. CONCLUSIONS: These results suggest that HBx might play a role in tumor spreading by modulating the adhesion-deadhesion balance of the cells in the primary tumor site and favoring integrin-mediated cell migration.

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

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

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

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

Involvement of phosphatidylinositol 3-kinase in stromal cell-derived factor-1 alpha-induced lymphocyte polarization and chemotaxis.

The role of phosphatidylinositol 3-kinase (PI3-kinase), an important enzyme involved in signal transduction events, has been studied in the polarization and chemotaxis of lymphocytes induced by the chemokine stromal cell-derived factor-1 alpha (SDF-1 alpha). This chemokine was able to directly activate p85/p110 PI3-kinase in whole human PBL and to induce the association of PI3-kinase to the SDF-1 alpha receptor, CXCR4, in a pertussis toxin-sensitive manner. Two unrelated chemical inhibitors of PI3-kinase, wortmannin and Ly294002, prevented ICAM-3 and ERM protein moesin polarization as well as the chemotaxis of PBL in response to SDF-1 alpha. However, they did not interfere with the reorganization of either tubulin or the actin cytoskeleton. Moreover, the transient expression of a dominant negative form of the PI3-kinase 85-kDa regulatory subunit in the constitutively polarized Peer T cell line inhibited ICAM-3 polarization and markedly reduced SDF-1 alpha-induced chemotaxis. Conversely, overexpression of a constitutively activated mutant of the PI3-kinase 110-kDa catalytic subunit in the round-shaped PM-1 T cell line induced ICAM-3 polarization. These results underline the role of PI3-kinase in the regulation of lymphocyte polarization and motility and indicate that PI3-kinase plays a selective role in the regulation of adhesion and ERM proteins redistribution in the plasma membrane of lymphocytes.

Activation of peripheral blood T cells by interaction and migration through endothelium: role of lymphocyte function antigen-1/intercellular adhesion molecule-1 and interleukin-15.

Cell adhesion molecules have a key role in the migration of T cells to inflammatory foci. However, the effect of the endothelial-lymphocyte interaction on the activation of the latter cells remains unresolved. We have studied the effect of resting and stimulated endothelial cells (ECs) on the activation of peripheral blood T cells (PBTLs), as assessed by the expression of CD69 and CD25 activation antigens. The incubation of PBTLs with tumor necrosis factor-alpha-activated EC monolayers, either alive or fixed, induced the expression of CD69 but not CD25, preferentially in the CD8(+) CD45RO+ cell subset. Furthermore, it induced the production of cytokines such as IFN-gamma, but not that of interleukin-2 (IL-2) and IL-4. EC treated with other stimuli such as IL-1beta, IFN-gamma, or lipopolysaccharide also showed the same proactivatory effect on T cells. Lymphocyte activation was almost completely inhibited by blocking anti-CD18 and anti-intercellular adhesion molecule-1 (anti-ICAM-1) monoclonal antibodies (MoAbs), but only slightly affected by MoAbs against CD49d, vascular cell adhesion molecule-1, and anti-IL-15. In addition, the interaction of PBTL with immobilized ICAM-1 induced CD69 expression in the same memory T-cell subset. IL-15 induced T-cell activation with expression of CD69 and CD25, and production of IFN-gamma, and its effect was additive with that triggered by cell adhesion to either EC or immobilized ICAM-1. The transmigration of PBTLs through either confluent EC monolayers or ICAM-1-coated membranes also induced efficiently the expression of CD69. When IL-15 was used as chemoattractant in these assays, a further enhancement in CD69 expression was observed in migrated cells. Together these results indicate that stimulated endothelium may have an important role in T-cell activation, through the lymphocyte function antigen-1/ICAM-1 pathway, and that IL-15 efficiently cooperates in this phenomenon. These observations could account for the abundance of CD69(+) cells in the lymphocytic infiltrates of several chronic inflammatory diseases.

Regulation of endothelial cell motility by complexes of tetraspan molecules CD81/TAPA-1 and CD151/PETA-3 with alpha3 beta1 integrin localized at endothelial lateral junctions.

Cell-to-cell junction structures play a key role in cell growth rate control and cell polarization. In endothelial cells (EC), these structures are also involved in regulation of vascular permeability and leukocyte extravasation. To identify novel components in EC intercellular junctions, mAbs against these cells were produced and selected using a morphological screening by immunofluorescence microscopy. Two novel mAbs, LIA1/1 and VJ1/16, specifically recognized a 25-kD protein that was selectively localized at cell-cell junctions of EC, both in the primary formation of cell monolayers and when EC reorganized in the process of wound healing. This antigen corresponded to the recently cloned platelet-endothelial tetraspan antigen CD151/PETA-3 (platelet-endothelial tetraspan antigen-3), and was consistently detected at EC cell-cell contact sites. In addition to CD151/PETA-3, two other members of the tetraspan superfamily, CD9 and CD81/ TAPA-1 (target of antiproliferative antibody-1), localized at endothelial cell-to-cell junctions. Biochemical analysis demonstrated molecular associations among tetraspan molecules themselves and those of CD151/ PETA-3 and CD9 with alpha3 beta1 integrin. Interestingly, mAbs directed to both CD151/PETA-3 and CD81/ TAPA-1 as well as mAb specific for alpha3 integrin, were able to inhibit the migration of ECs in the process of wound healing. The engagement of CD151/PETA-3 and CD81/TAPA-1 inhibited the movement of individual ECs, as determined by quantitative time-lapse video microscopy studies. Furthermore, mAbs against the CD151/PETA-3 molecule diminished the rate of EC invasion into collagen gels. In addition, these mAbs were able to increase the adhesion of EC to extracellular matrix proteins. Together these results indicate that CD81/TAPA-1 and CD151/PETA-3 tetraspan molecules are components of the endothelial lateral junctions implicated in the regulation of cell motility, either directly or by modulation of the function of the associated integrin heterodimers.