Leukocyte uropod formation and membrane/cytoskeleton linkage in immune interactions

Cooperative polarization of MCAM/CD146 and ERM family proteins in melanoma

The WRAMP structure is a protein network associated with tail-end actomyosin contractility, membrane retraction, and directional persistence during cell migration. A marker of WRAMP structures is melanoma cell adhesion molecule (MCAM) which dynamically polarizes to the cell rear. However, factors that mediate MCAM polarization are still unknown. In this study, BioID using MCAM as bait identifies the ERM family proteins, moesin, ezrin, and radixin, as WRAMP structure components. We also present a novel image analysis pipeline, Protein Polarity by Percentile ("3P"), which classifies protein polarization using machine learning and facilitates quantitative analysis. Using 3P, we find that depletion of moesin, and to a lesser extent ezrin, decreases the proportion of cells with polarized MCAM. Furthermore, although copolarized MCAM and ERM proteins show high spatial overlap, 3P identifies subpopulations with ERM proteins closer to the cell periphery. Live-cell imaging confirms that MCAM and ERM protein polarization is tightly coordinated, but ERM proteins enrich at the cell edge first. Finally, deletion of a juxtamembrane segment in MCAM previously shown to promote ERM protein interactions impedes MCAM polarization. Our findings highlight the requirement for ERM proteins in recruitment of MCAM to WRAMP structures and an advanced computational tool to characterize protein polarization.

Quantifying Human Natural Killer Cell Migration by Imaging and Image Analysis

Migration is an important function for natural killer cells. Cell motility has implications in development, tissue infiltration, and cytotoxicity, and measuring the properties of natural killer (NK) cell migration using in vitro assays can be highly informative. Many researchers have an interest in studying properties of NK cell migration in the context of genetic mutation, disease, or in specific tissues and microenvironments. Motility assays can also provide information on the localization of proteins during different phases of cell migration. These assays can be performed on different surfaces for migration or coupled with chemoattractants and/or target cells to test functional outcomes or characterize cell migration speeds and phenotypes. NK cells undergo migration during differentiation in tissue, and these conditions can be modeled by culturing NK cells on a confluent bed of stromal cells on glass and imaging cell migration. Alternatively, fibronectin- or ICAM-1-coated surfaces promote NK cell migration and can be used as substrates. Here, we will describe techniques for the experimental setup and analysis of NK cell motility assays by confocal microscopy or in-incubator imaging using commercially available systems. Finally, we describe open-source software for analyzing cell migration using manual tracking or automated approaches and discuss considerations for the implementation of each of these methods.

Lipid raft integrity is required for human leukemia Jurkat T-cell migratory activity

Lipid rafts are membrane microdomains featuring high cholesterol, sphingolipid, and protein content. These microdomains recruit various receptors, ion channels, and signaling molecules for coordination of various cellular functions, including synaptic transmission, immune response, cytoskeletal organization, adhesion, and migration. Many of these processes also depend on Ca²⁺ intake. We have previously shown in Jurkat cells that activity of transient receptor potential vanilloid, type 6 (TRPV6) calcium channel, and TRPV6-mediated Ca²⁺ influx, depend on lipid raft integrity. In this study, using the transwell cell migration assay and time-lapse video microscopy with Jurkat cells, we found that lipid raft destruction was associated with: inhibited cell adhesion and migration; and decreased mean speed, maximum speed, and trajectory length. Using String Server, we constructed a Protein Interaction Network (PIN). The network indicated that TRPV6 proteins interact with the highest probability (0.9) with Src family kinase members (SFKs) involved in processes related to cell migration. Analysis of detergent-resistant membrane fractions and immunoelectron microscopy data confirmed an association in lipid rafts between TRPV6 and Lck kinase, an SFKs member. Destruction of lipid rafts led to uncoupling of TRPV6 clusters with Lck and their departure from the plasma membrane into the cytosol of the cells. Src family kinases are generally associated with their roles in tumor invasion and progression, epithelial-mesenchymal transitions, angiogenesis, and metastatic development. We suggest that a functional interaction between TRPV6 calcium channels and SFKs members in lipid rafts is one of necessary elements of migration and oncogenic signaling in leukemia cells.

Galectin-10, the protein that forms Charcot-Leyden crystals, is not stored in granules but resides in the peripheral cytoplasm of human eosinophils

A predominant protein of human eosinophils is galectin-10 (Gal-10), also known as Charcot-Leyden crystal protein (CLC-P) because of its remarkable ability to form Charcot-Leyden crystals (CLCs), which are frequently found in tissues from patients with eosinophilic disorders. CLC-P/Gal-10 is highly expressed in human eosinophils and considered a biomarker of eosinophil involvement in inflammation. However, the intracellular sites where large pools of CLC-P/Gal-10 constitutively reside are still unclear, and whether this protein is derived or not from eosinophil granules remains to be established. Here, we applied pre-embedding immunonanogold transmission electron microscopy combined with strategies for optimal antigen and cell preservation and quantitative imaging analysis to investigate, for the first time, the intracellular localization of CLC-P/Gal-10 at high resolution in resting and activated human eosinophils. We demonstrated that CLC-P/Gal-10 is mostly stored in the peripheral cytoplasm of human eosinophils, being accumulated within an area of ∼250 nm wide underneath the plasma membrane and not within specific (secretory) granules, a pattern also observed by immunofluorescence. High-resolution analysis of single cells revealed that CLC-P/Gal-10 interacts with the plasma membrane with immunoreactive microdomains of high CLC-P/Gal-10 density being found in ∼60% of the membrane area. Eosinophil stimulation with CCL11 or TNF-α, which are known inducers of eosinophil secretion, did not change the peripheral localization of CLC-P/Gal-10 as observed by both immunofluorescence and immuno-EM (electron microscopy). Thus, in contrast to other preformed eosinophil proteins, CLC-P/Gal-10 neither is stored within secretory granules nor exported through classical degranulation mechanisms (piecemeal degranulation and compound exocytosis).

An insight into the cannibalistic behavior of giant cell granulomas of the jaws

Background:

Cellular cannibalism is defined as a large cell engulfing a smaller one within its cytoplasm. It is predominantly a feature of aggressive malignancies but has recently been demonstrated in giant cell (GC) lesions such as GC tumor of tendon sheath, central GC granuloma (CGCG) and peripheral GC granuloma (PGCG).

Aim:

The aim of the study is to assess the cannibalistic GCs in CGCG and PGCG and correlate with aggressiveness of the lesion.

Settings and Design:

Archival data of histopathologically confirmed cases of CGCG (n = 40) and PGCG (n = 25) were studied in the Department of Oral Pathology, Maulana Azad Institute of Dental Sciences.

Materials and Methods:

Quantification of cannibalistic cells was performed using H&E stain on microscopic sections. One hundred GCs were examined in each slide, and the number of cannibalistic cells was expressed in percentage.

Results:

GC cannibalism was observed in all cases. The mean number of cannibalistic GCs in CGCG was 44.67 which was significantly higher (P = 0.028) than PGCG (mean 28.04). In aggressive (n = 18) CGCG, the mean number of cannibalistic GCs was 51.27 which was significantly higher (P = 0.019) than cannibalistic GCs in nonaggressive (n = 22) CGCG (mean 39.27). No significant difference was observed between the number of cannibalistic cells in recurrent (mean = 52.9) and nonrecurrent (mean = 49.2) cases of CGCG (P > 0.05). Two of the nine cases treated initially by steroid showed fewer and smaller cannibalistic GCs with vesicular nuclei.

Conclusion:

There was a clear distinction in the mean cannibalistic count between aggressive and nonaggressive CGCG. Hence, the aggressiveness of the lesion could be assessed following which appropriate treatment modality can be constituted.

CD4+ T Cell Fate Decisions Are Stochastic, Precede Cell Division, Depend on GITR Co-Stimulation, and Are Associated With Uropodium Development

During an immune response, naïve CD4⁺ T cells proliferate and generate a range of effector, memory, and regulatory T cell subsets, but how these processes are co-ordinated remains unclear. A traditional model suggests that memory cells use mitochondrial respiration and are survivors from a pool of previously proliferating and glycolytic, but short-lived effector cells. A more recent model proposes a binary commitment to either a memory or effector cell lineage during a first, asymmetric cell division, with each lineage able to undergo subsequent proliferation and differentiation. We used improved fixation and staining methods with imaging flow cytometry in an optimized in vitro system that indicates a third model. We found that cell fates result from stochastic decisions that depend on GITR co-stimulation and which take place before any cell division. Effector cell commitment is associated with mTORC2 signaling leading to uropodium development, while developing memory cells lose mitochondria, have a nuclear localization of NFκB and depend on TGFβ for their survival. Induced, T helper subsets and foxp3⁺ regulatory T cells were found in both the effector and memory cell lineages. This in vitro model of T cell differentiation is well suited to testing how manipulation of cytokine, nutrient, and other components of the microenvironment might be exploited for therapeutic purposes.

Role of the Cytoskeleton in Myeloid Cell Function

During an innate immune response, myeloid cells undergo complex morphological adaptations in response to inflammatory cues, which allow them to exit the vasculature, enter the tissues, and destroy invading pathogens. The actin and microtubule cytoskeletons are central to many of the most essential cellular functions including cell division, cell morphology, migration, intracellular trafficking, and signaling. Cytoskeletal structure and regulation are crucial for many myeloid cell functions, which require rapid and dynamic responses to extracellular signals. In this chapter, we review the roles of the actin and microtubule cytoskeletons in myeloid cells, focusing primarily on their roles in chemotaxis and phagocytosis. The role of myeloid cell cytoskeletal defects in hematological disorders is highlighted throughout.

Lis1 Regulates Germinal Center B Cell Antigen Acquisition and Affinity Maturation

The germinal center (GC) is the site where activated B cells undergo rapid expansions, somatic hypermutation, and affinity maturation. Affinity maturation is a process of Ag-driven selection. The amount of Ag acquired and displayed by GC B cells determines whether it can be positively selected, and therefore Ag acquisition has to be tightly regulated to ensure the efficient affinity maturation. Cell expansion provides sufficient quantity of GC B cells and Abs, whereas affinity maturation improves the quality of Abs. In this study, we found that Lis1 is a cell-intrinsic regulator of Ag acquisition capability of GC B cells. Lack of Lis1 resulted in redistribution of polymerized actin and accumulation of F-actin at uropod; larger amounts of Ags were acquired and displayed by GC B cells, which presumably reduced the selection stringency. Affinity maturation was thus compromised in Lis1-deficient mice. Consistently, overexpression of Lis1 in GC B cells led to less Ag acquisition and display. Additionally, Lis1 is required for GC B cell expansion, and Lis1 deficiency blocked the cell cycle at the mitotic phase and GC B cells were prone to apoptosis. Overall, we suggest that Lis1 is required for GC B cell expansion, affinity maturation, and maintaining functional intact GC response, thus ensuring both the quantity and quality of Ab response.

Hydrogen Peroxide Triggers a Dual Signaling Axis To Selectively Suppress Activated Human T Lymphocyte Migration

H₂O₂ is an early danger cue required for innate immune cell recruitment to wounds. To date, little is known about whether H₂O₂ is required for the migration of human adaptive immune cells to sites of inflammation. However, oxidative stress is known to impair T cell activity, induce actin stiffness, and inhibit cell polarization. In this study, we show that low oxidative concentrations of H₂O₂ also impede chemokinesis and chemotaxis of previously activated human T cells to CXCL11, but not CXCL10 or CXCL12. We show that this deficiency in migration is due to a reduction in inflammatory chemokine receptor CXCR3 surface expression and cellular activation of lipid phosphatase SHIP-1. We demonstrate that H₂O₂ acts through an Src kinase to activate a negative regulator of PI3K signaling, SHIP-1 via phosphorylation, providing a molecular mechanism for H₂O₂-induced chemotaxis deficiency. We hypothesize that although H₂O₂ serves as an early recruitment trigger for innate immune cells, it appears to operate as an inhibitor of T lymphocyte immune adaptive responses that are not required until later in the repair process.

Tunneling nanotubes mediate the transfer of stem cell marker CD133 between hematopoietic progenitor cells

Deciphering all mechanisms of intercellular communication used by hematopoietic progenitors is important, not only for basic stem cell research, but also in view of their therapeutic relevance. Here, we investigated whether these cells can produce the thin F-actin-based plasma membrane protrusions referred to as tunneling nanotubes (TNTs), which are known to bridge cells over long distances without contact with the substratum and transfer cargo molecules along them in various biological processes. We found that human primary CD34⁺ hematopoietic progenitors and leukemic KG1a cells develop such structures upon culture on primary mesenchymal stromal cells or specific extracellular-matrix-based substrata. Time-lapse video microscopy revealed that cell dislodgement is the primary mechanism responsible for TNT biogenesis. Surprisingly, we found that, among various cluster of differentiation (CD) markers, only the stem cell antigen CD133 is transferred between cells. It is selectively and directionally transported along the surface of TNTs in small clusters, such as cytoplasmic phospho-myosin light chain 2, suggesting that the latter actin motor protein might be implicated in this process. Our data provide new insights into the biology of hematopoietic progenitors that can contribute to our understanding of all facets of intercellular communication in the bone marrow microenvironment under healthy or cancerous conditions.

Human NK cell development requires CD56-mediated motility and formation of the developmental synapse

While distinct stages of natural killer (NK) cell development have been defined, the molecular interactions that shape human NK cell maturation are poorly understood. Here we define intercellular interactions between developing NK cells and stromal cells which, through contact-dependent mechanisms, promote the generation of mature, functional human NK cells from CD34⁺ precursors. We show that developing NK cells undergo unique, developmental stage-specific sustained and transient interactions with developmentally supportive stromal cells, and that the relative motility of NK cells increases as they move through development in vitro and ex vivo. These interactions include the formation of a synapse between developing NK cells and stromal cells, which we term the developmental synapse. Finally, we identify a role for CD56 in developmental synapse structure, NK cell motility and NK cell development. Thus, we define the developmental synapse leading to human NK cell functional maturation.

CD56, a splicing variant of NCAM, marks human NK cell differentiation stages. Here the authors show that developing human NK cells form CD56-enriched synapses with stromal cells, and CD56 is critical to promote motility of NK cells that increases with their maturation.

Molecular Mechanisms of HTLV-1 Cell-to-Cell Transmission

The tumorvirus human T-cell lymphotropic virus type 1 (HTLV-1), a member of the delta-retrovirus family, is transmitted via cell-containing body fluids such as blood products, semen, and breast milk. In vivo, HTLV-1 preferentially infects CD4⁺ T-cells, and to a lesser extent, CD8⁺ T-cells, dendritic cells, and monocytes. Efficient infection of CD4⁺ T-cells requires cell-cell contacts while cell-free virus transmission is inefficient. Two types of cell-cell contacts have been described to be critical for HTLV-1 transmission, tight junctions and cellular conduits. Further, two non-exclusive mechanisms of virus transmission at cell-cell contacts have been proposed: (1) polarized budding of HTLV-1 into synaptic clefts; and (2) cell surface transfer of viral biofilms at virological synapses. In contrast to CD4⁺ T-cells, dendritic cells can be infected cell-free and, to a greater extent, via viral biofilms in vitro. Cell-to-cell transmission of HTLV-1 requires a coordinated action of steps in the virus infectious cycle with events in the cell-cell adhesion process; therefore, virus propagation from cell-to-cell depends on specific interactions between cellular and viral proteins. Here, we review the molecular mechanisms of HTLV-1 transmission with a focus on the HTLV-1-encoded proteins Tax and p8, their impact on host cell factors mediating cell-cell contacts, cytoskeletal remodeling, and thus, virus propagation.

Plasma membrane-associated superstructure: Have we overlooked a new type of organelle in eukaryotic cells?

A variety of intriguing plasma membrane-associated regions, including focal adhesions, adherens junctions, tight junctions, immunological synapses, neuromuscular junctions and the primary cilia, among many others, have been described in eukaryotic cells. Emphasizing their importance, alteration in their molecular structures induces or correlates with different pathologies. These regions display surface proteins connected to intracellular molecules, including cytoskeletal component, which maintain their cytoarchitecture, and signalling proteins, which regulate their organization and functions. Based on the molecular similarities and other common features observed, we suggest that, despite differences in external appearances, all these regions are just the same superstructure that appears in different locations and cells. We hypothesize that this superstructure represents an overlooked new type of organelle that we call plasma membrane-associated superstructure (PMAS). Therefore, we suggest that eukaryotic cells include classical organelles (e.g. mitochondria, Golgi and others) and also PMAS. We speculate that this new type of organelle might be an innovation associated to the emergence of eukaryotes. Finally we discuss the implications of the hypothesis proposed.

Anti-inflammatory peptides from cardiac progenitors ameliorate dysfunction after myocardial infarction

Background

Cardiac cell therapy has been proposed as one of the new strategies against myocardial infarction. Although several reports showed improvement of the function of ischemic heart, the effects of cell therapy vary among the studies and the mechanisms of the beneficial effects are still unknown. Previously, we reported that clonal stem cell antigen‐1–positive cardiac progenitor cells exerted a therapeutic effect when transplanted into the ischemic heart. Our aims were to identify the cardiac progenitor‐specific paracrine factor and to elucidate the mechanism of its beneficial effect.

Methods and Results

By using an antibody array, we found that soluble junctional adhesion molecule‐A (JAM‐A) was abundantly secreted from cardiac progenitor cells. Pretreatment of neutrophils with conditioned medium from cultured cardiac progenitor cells or soluble JAM‐A inhibited transendothelial migration and reduced motility of neutrophils. These inhibitory effects were attenuated by anti–JAM‐A neutralizing antibody. Injection of cardiac progenitor cells into infarct heart attenuated neutrophil infiltration and expression of inflammatory cytokines. Injection of soluble JAM‐A–expressing, but not of JAM‐A siRNA–expressing, cardiac progenitor cells into the infarct heart prevented cardiac remodeling and reduced fibrosis area.

Conclusions

Soluble JAM‐A secreted from cardiac progenitor cells reduces infiltration of neutrophils after myocardial infarction and ameliorates tissue damage through prevention of excess inflammation. Our finding may lead to a new therapy for cardiovascular disease by using the anti‐inflammatory effect of JAM‐A.

Malarial pigment hemozoin impairs chemotactic motility and transendothelial migration of monocytes via 4-hydroxynonenal

Natural hemozoin, nHZ, is avidly phagocytosed in vivo and in vitro by human monocytes. The persistence of the undigested β-hematin core of nHZ in the phagocyte lysosome for long periods of time modifies several cellular immune functions. Here we show that nHZ phagocytosis by human primary monocytes severely impaired their chemotactic motility toward MCP-1, TNF, and FMLP, by approximately 80% each, and their diapedesis across a confluent human umbilical vein endothelial cell layer toward MCP-1 by 45±5%. No inhibition was observed with latex-fed or unfed monocytes. Microscopic inspection revealed polarization defects in nHZ-fed monocytes due to irregular actin polymerization. Phagocytosed nHZ catalyzes the peroxidation of polyunsaturated fatty acids and generation of the highly reactive derivative 4-hydroxynonenal (4-HNE). Similar to nHZ phagocytosis, the exposure of monocytes to in vivo-compatible 4-HNE concentrations inhibited cell motility in both the presence and the absence of chemotactic stimuli, suggesting severe impairment of cytoskeleton dynamics. Consequently, 4-HNE conjugates with the cytoskeleton proteins β-actin and coronin-1A were immunochemically identified in nHZ-fed monocytes and mass spectrometrically localized in domains of protein-protein interactions involved in cytoskeleton reorganization and cell motility. The molecular and functional modifications of actin and coronin by nHZ/4-HNE may also explain impaired phagocytosis, another motility-dependent process previously described in nHZ-fed monocytes. Further studies will show whether impaired monocyte motility may contribute to the immunodepression and the frequent occurrence of secondary infections observed in malaria patients.

Murine leukemia virus Gag localizes to the uropod of migrating primary lymphocytes

B and CD4(+) T lymphocytes are natural targets of murine leukemia virus (MLV). Migrating lymphocytes adopt a polarized morphology with a trailing edge designated the uropod. Here, we demonstrate that MLV Gag localizes to the uropod in polarized B cells and CD4(+) T cells. The uropod localization of MLV Gag was dependent on plasma membrane (PM) association and multimerization of Gag but independent of the viral glycoprotein Env. Basic residues in MA that are required for MLV Gag recruitment to virological synapses between HEK293 and XC cells were dispensable for uropod localization in migrating B cells. Ultrastructural studies indicated that both wild-type and basic-residue mutant Gag localized to the outer surface of the PM at the uropod. Late-domain mutant virus particles were seen at the uropod in form of budding-arrested intermediates. Finally, uropods mediated contact between MLV-infected B cells and uninfected T cells to form virological synapses. Our results suggest that MLV, not unlike HIV, accumulates at the uropod of primary lymphocytes to facilitate viral spreading through the formation of uropod-mediated cell-cell contacts.

IMPORTANCE

Viruses have evolved mechanisms to coordinate their assembly and budding with cell polarity to facilitate their spreading. In this study, we demonstrated that the viral determinants for MLV Gag to localize to the uropod in polarized B cells are distinct from the requirements to localize to virological synapses in transformed cell lines. Basic residues in MA that are required for the Gag localization to virological synapses between HEK293 and XC cells are dispensable for Gag localization to the uropod in primary B cells. Rather, plasma membrane association and capsid-driven multimerization of Gag are sufficient to drive MLV Gag to the uropod. MLV-laden uropods also mediate contacts between MLV-infected B cells and uninfected T cells to form virological synapses. Our results indicate that MLV accumulates at the uropod of primary lymphocytes to facilitate viral spreading through the formation of uropod-mediated cell-cell contacts.

Rho GTPases at the crossroad of signaling networks in mammals: impact of Rho-GTPases on microtubule organization and dynamics

Microtubule (MT) organization and dynamics downstream of external cues is crucial for maintaining cellular architecture and the generation of cell asymmetries. In interphase cells RhoA, Rac, and Cdc42, conspicuous members of the family of small Rho GTPases, have major roles in modulating MT stability, and hence polarized cell behaviors. However, MTs are not mere targets of Rho GTPases, but also serve as signaling platforms coupling MT dynamics to Rho GTPase activation in a variety of cellular conditions. In this article, we review some of the key studies describing the reciprocal relationship between small Rho-GTPases and MTs during migration and polarization.

Flotillins in receptor tyrosine kinase signaling and cancer

Flotillins are highly conserved proteins that localize into specific cholesterol rich microdomains in cellular membranes. They have been shown to be associated with, for example, various signaling pathways, cell adhesion, membrane trafficking and axonal growth. Recent findings have revealed that flotillins are frequently overexpressed in various types of human cancers. We here review the suggested functions of flotillins during receptor tyrosine kinase signaling and in cancer. Although flotillins have been implicated as putative cancer therapy targets, we here show that great caution is required since flotillin ablation may result in effects that increase instead of decrease the activity of specific signaling pathways. On the other hand, as flotillin overexpression appears to be related with metastasis formation in certain cancers, we also discuss the implications of these findings for future therapy aspects.

Studies of macrophage cellular response to the extracellular hydrogen peroxide by tilapia model

Reactive oxygen species (ROS) may act as signaling molecules in the physiology responses and the present study aims to investigate the effect of extracellular hydrogen peroxide on macrophages cellular response. The results obtained in the present study showed that the extracellular hydrogen peroxide affectively alter the membrane potential of the cell membrane and ion exchange channels in the cell membrane through intracellular NAD turnover that may lead to an intracellular calcium ion concentration alteration and subsequently induce the downstream signal activation.

P-glycoprotein binds to ezrin at amino acid residues 149-242 in the FERM domain and plays a key role in the multidrug resistance of human osteosarcoma

Overexpression of the mdr1 gene encoding P-glycoprotein (Pgp) exerts a major role in reducing the effectiveness of cytotoxic therapy in osteosarcoma. The interaction between actin and Pgp has been shown to be instrumental in the establishment of multidrug resistance (MDR) in human tumor cells. The cytoskeleton linker ezrin exerts a pivotal role in maintaining the functional connection between actin and Pgp. We investigated the role of ezrin in a human multidrug-resistant osteosarcoma cell line overexpressing Pgp and compared it to its counterpart that overexpresses an ezrin deletion mutant. The results showed that Pgp binds at amino acid residues 149-242 of the N-terminal domain of ezrin. The interaction between ezrin and Pgp occurs in the plasma membrane of MDR cells, where they also co-localize with the ganglioside G(M1) located in lipid rafts. The overexpression of the ezrin deletion mutant entirely restored drug susceptibility of osteosarcoma cells, consistent with Pgp dislocation to cytoplasmic compartments and abrogation of G(M1) /Pgp co-localization at the plasma membrane. Our study provides evidence that ezrin exerts a key role in MDR of human osteosarcoma cells through a Pgp-ezrin-actin connection that is instrumental for the permanence of Pgp into plasma membrane lipid rafts. We also show for the first time that Pgp-binding site is localized to amino acid residues 149-242 of the ezrin Band 4.1, Ezrin/Radixin/Moesin (FERM) domain, thus proposing a specific target for future molecular therapy aimed at counteracting MDR in osteosarcoma patients.

Cell cannibalism and cancer

Cellular cannibalism, defined as a large cell enclosing a slightly smaller one within its cytoplasm. In this review, we discussed the morphology, possible mechanism, and the cytological significance of cannibalism in relation to malignancy. Cannibalism is a completely different entity than phagocytosis, entosis, and emeriopoliosis. It is an important morphologic feature to distinguish benign from malignant lesions. Cannibalism has been described in various cancers such as, bladder cancer, breast cancer, lung cancer, etc, and this is related with the aggressiveness of the malignancy.

Space flight affects motility and cytoskeletal structures in human monocyte cell line J-111

Certain functions of immune cells in returning astronauts are known to be altered. A dramatic depression of the mitogenic in vitro activation of human lymphocytes was observed in low gravity. T-cell activation requires the interaction of different type of immune cells as T-lymphocytes and monocytes. Cell motility based on a continuous rearrangement of the cytoskeletal network within the cell is essential for cell-cell contacts. In this investigation on the International Space Station we studied the influence of low gravity on different cytoskeletal structures in adherent monocytes and their ability to migrate. J-111 monocytes were incubated on a colloid gold substrate attached to a cover slide. Migrating cells removed the colloid gold, leaving a track recording cell motility. A severe reduction of the motility of J-111 cells was found in low gravity compared to 1g in-flight and ground controls. Cell shape appeared more contracted, whereas the control cells showed the typical morphology of migrating monocytes, i.e., elongated and with pseudopodia. A qualitative and quantitative analysis of the structures of F-actin, β-tubulin and vinculin revealed that exposure of J-111 cells to low gravity affected the distribution of the different filaments and significantly reduced the fluorescence intensity of F-actin fibers. Cell motility relies on an intact structure of different cytoskeletal elements. The highly reduced motility of monocytes in low gravity must be attributed to the observed severe disruption of the cytoskeletal structures and may be one of the reasons for the dramatic depression of the in vitro activation of human lymphocytes.

Behavioral and structural differences in migrating peripheral neutrophils from patients with chronic obstructive pulmonary disease

RATIONALE

There are increased neutrophils in the lungs of patients with chronic obstructive pulmonary disease (COPD), but it is unclear if this is due to increased inflammatory signal or related to the inherent behavior of the neutrophils. This is critical, because inaccurate or excessive neutrophil chemotaxis could drive pathological accumulation and tissue damage.

OBJECTIVES

To assess migratory dynamics of neutrophils isolated from patients with COPD compared with healthy smoking and nonsmoking control subjects and patients with α(1)-antitryspin deficiency.

METHODS

Migratory dynamics and structure were assessed in circulating neutrophils, using phase and differential interference contrast microscopy and time-lapse photography. The effect of COPD severity was studied. Surface expression of receptors was measured using flow cytometry. The in vitro effects of a phosphoinositide 3-kinase inhibitor (LY294002) were studied.

MEASUREMENTS AND MAIN RESULTS

COPD neutrophils moved with greater speed than cells from either control group but with reduced migratory accuracy, in the presence of IL-8, growth-related oncogene α, formyl-methionyl-leucyl-phenylalanine, and sputum. This was present across all stages of COPD. Structurally, COPD neutrophils formed fewer pseudopods during migration. There were no differences in surface expression of the receptors CXCR1, CXCR2, or FPR1. LY294002 reduced COPD neutrophil migratory speed while increasing chemotactic accuracy, returning values to normal. The inhibitor did not have these effects in healthy control subjects or patients with a similar degree of lung disease.

CONCLUSIONS

COPD neutrophils are intrinsically different than cells from other studied populations in their chemotactic behavior and migratory structure. Differences are not due to surface expression of chemoattractant receptors but instead appear to be due to differences in cell signaling.

Differential effects of ceramide and sphingosine 1-phosphate on ERM phosphorylation: probing sphingolipid signaling at the outer plasma membrane

ERM proteins are regulated by phosphorylation of the most C-terminal threonine residue, switching them from an activated to an inactivated form. However, little is known about the control of this regulation. Previous work in our group demonstrated that secretion of acid sphingomyelinase acts upstream of ERM dephosphorylation, suggesting the involvement of sphingomyelin (SM) hydrolysis in ERM regulation. To define the role of specific lipids, we employed recombinant bacterial sphingomyelinase (bSMase) as a direct probe of SM metabolism at the plasma membrane. bSMase induced a rapid dose- and time-dependent decrease in ERM dephosphorylation. ERM dephosphorylation was driven by ceramide generation and not by sphingomyelin depletion, as shown using recombinant sphingomyelinase D. The generation of ceramide at the plasma membrane was sufficient for ERM regulation, and no intracellular SM hydrolysis was required, as was visualized using Venus-tagged lysenin probe, which specifically binds SM. Interestingly, hydrolysis of plasma membrane bSMase-induced ceramide using bacterial ceramidase caused ERM hyperphosphorylation and formation of cell surface protrusions. The effects of plasma membrane ceramide hydrolysis were due to sphingosine 1-phosphate formation, as ERM phosphorylation was blocked by an inhibitor of sphingosine kinase and induced by sphingosine 1-phosphate. Taken together, these results demonstrate a new regulatory mechanism of ERM phosphorylation by sphingolipids with opposing actions of ceramide and sphingosine 1-phosphate. The approach also defines a tool kit to probe sphingolipid signaling at the plasma membrane.

Modifications in host cell cytoskeleton structure and function mediated by intracellular HIV-1 Tat protein are greatly dependent on the second coding exon

The human immunodeficiency virus type 1 (HIV-1) regulator Tat is essential for viral replication because it achieves complete elongation of viral transcripts. Tat can be released to the extracellular space and taken up by adjacent cells, exerting profound cytoskeleton rearrangements that lead to apoptosis. In contrast, intracellular Tat has been described as protector from apoptosis. Tat gene is composed by two coding exons that yield a protein of 101 amino acids (aa). First exon (1–72aa) is sufficient for viral transcript elongation and second exon (73–101 aa) appears to contribute to non-transcriptional functions. We observed that Jurkat cells stably expressing intracellular Tat101 showed gene expression deregulation 4-fold higher than cells expressing Tat72. Functional experiments were performed to evaluate the effect of this deregulation. First, NF-κB-, NF-AT- and Sp1-dependent transcriptional activities were greatly enhanced in Jurkat-Tat101, whereas Tat72 induced milder but efficient activation. Second, cytoskeleton-related functions as cell morphology, proliferation, chemotaxis, polarization and actin polymerization were deeply altered in Jurkat-Tat101, but not in Jurkat-Tat72. Finally, expression of several cell surface receptors was dramatically impaired by intracellular Tat101 but not by Tat72. Consequently, these modifications were greatly dependent on Tat second exon and they could be related to the anergy observed in HIV-1-infected T cells.

The Janus-faced role of ezrin in "linking" cells to either normal or metastatic phenotype

In the majority of eukaryotic cells, the ezrin, radixin and moesin (ERM) proteins are involved in many physiologic functions including regulation of actin cytoskeleton, control of cell shape, adhesion, motility and modulation of signal transduction pathways. In a previous study, we used a dominant negative ezrin-mutant to address ezrin involvement in remodeling of actin cytoskeleton and subsequently we depicted ezrin key role in melanoma cell migration and progression. Herein, we highlight recent advances on ezrin involvement in the metastatic phenomenon, including also some more neglected ezrin-related functions. Novel molecular processes driven by ezrin activation include: phagocytosis, acquisition of resistance to chemotherapeutics and triggering of programmed cell death signals. Recent data support an integrated role of ezrin also in development of tumor malignancy. On one hand, ezrin may be responsible of deranged execution of specific known functions such as adhesion and motility and on the other, it may also participate to unique metastatic determinants, through the establishment of aberrant linkages with tumor-related proteins. For instance, ezrin misslocalization, absence or deranged activity has started to be correlated with tumor progression in many tumors of different species, including humans. Concomitantly, ezrin may act simultaneously as a regulatory or deregulatory chaperon in both normal and tumor cells. It is still to be established whether this Janus-faced feature of ezrin is due to some unknown transforming Zelig-like property or to the fact that a tumor-associated molecule preferentially links to ezrin thus distracting it from its normal connections. However, the contribution of ezrin functional deregulation to the acquisition of the metastatic phenotype appears clear and ezrin or ezrin aberrant associations may represent good candidates for future anti-tumor therapies.

Pyrin and ASC co-localize to cellular sites that are rich in polymerizing actin

Familial Mediterranean fever (FMF) is an autoinflammatory disease caused by mutations in the MEFV locus, which encodes the protein pyrin. While it is known that pyrin is expressed in myeloid cells and several fibroblastic cell types, the exact function of pyrin in these cells and the mechanism underlying the pathological effect of pyrin mutations have yet to be revealed. Here, we document that in migrating human monocytes, pyrin protein is dramatically polarized at the leading edge, where it co-localizes with polymerizing actin. ASC (Apoptosis-associated Speck protein with CARD domain), a known pyrin-interacting protein and a critical component of the inflamma-some, is also located at the leading edge in migrating monocytes. Similarly, both pyrin and ASC concentrate in dynamically polymerizing actin-rich tails generated by Listeria monocytogenes. Pyrin's B-box and coiled-coil region is required for its association with Listeria tails. Pyrin also binds, with low affinity and via the same domains, to actin, VASP, and Arp3. Though disease-causing mutations in pyrin do not appear to alter its localization to the leading edge or to Listeria rocket tails, they could potentially have important functional consequences in the context of processes such as migration and cell synapse formation. The co-localization of pyrin and ASC together at such sites may provide an important link between cytoskeletal signaling and inflammasome function.

Elevated protein tyrosine phosphatase activity provokes Eph/ephrin-facilitated adhesion of pre-B leukemia cells

Signaling by Eph receptors and cell-surface ephrin ligands modulates adhesive cell properties and thereby coordinates cell movement and positioning in normal and oncogenic development. While cell contact–dependent Eph activation frequently leads to cell-cell repulsion, also the diametrically opposite response, cell-cell adhesion, is a probable outcome. However, the molecular principles regulating such disparate functions have remained controversial. We have examined cell-biologic mechanisms underlying this switch by analyzing ephrin-A5–induced cell-morphologic changes of EphA3-positive LK63 pre-B acute lymphoblastic leukemia cells. Their exposure to ephrin-A5 surfaces leads to a rapid conversion from a suspended/nonpolarized to an adherent/polarized cell type, a transition that relies on EphA3 functions operating in the absence of Eph-kinase signaling. Cell morphology change and adhesion of LK63 cells are effectively attenuated by endogenous protein tyrosine phosphatase (PTP) activity, whereby PTP inhibition and productive EphA3-phosphotyrosine signaling reverse the phenotype to nonadherent cells with a condensed cytoskeleton. Our findings suggest that Eph-associated PTP activities not only control receptor phosphorylation levels, but as a result switch the response to ephrin contact from repulsion to adhesion, which may play a role in the pathology of hematopoietic tumors.

Single exposure of human fibroblasts (WI-38) to a sub-cytotoxic dose of UVB induces premature senescence

In this work, we present a new model of stress-induced premature senescence obtained by exposing human fibroblasts (WI-38) at early passages (passages 2-4) to a single sub-cytotoxic dose of UVB (200 mJ/cm(2)). We show that this treatment leads to the appearance of several biomarkers of senescence such as enlarged and flattened cell morphology, the presence of nuclear heterochromatic foci and beta-galactosidase activity. Furthermore, we demonstrate that a mild ROS production and p53 activation are upstream events required for the induction of premature senescence. Our method represents an alternative in vitro model in photoaging research and could be used to test potential anti-photoaging compounds.

Involvement of Fyn kinase in Kit and integrin-mediated Rac activation, cytoskeletal reorganization, and chemotaxis of mast cells

Kit receptor and its ligand stem cell factor (SCF) are critical regulators of mast cell production, proliferation, degranulation, and chemotaxis. In this study, we investigated how Fyn kinase regulates chemotaxis of mast cells toward SCF. On beta1-integrin engagement, Fyn-deficient (fyn(-/-)) mast cells displayed a striking defect in cell spreading and lamellipodia formation compared to wild-type mast cells. The hematopoietic-specific Src family kinases (Lyn/Fgr/Hck) were not required for initial SCF-induced cell spreading. Reduced SCF-induced activation of Rac1 and Rac2 GTPases, p38 mitogen-activated protein kinase, and filamentous actin polymerization was observed in fyn(-/-) mast cells compared to wild-type mast cells. Retroviral-mediated expression of Fyn, constitutively active forms of Rac2 or phosphatidylinositol 3-kinase (PI3K) in fyn(-/-) mast cells rescued defects in SCF-induced cell polarization and chemotaxis of Fyn-deficient mast cells. Thus, we conclude that Fyn kinase plays a unique role upstream of PI3K and Rac GTPases to promote the reorganization of the cytoskeleton during mast cell spreading and chemotaxis.

Potential Role for IL-7 in Fas-Mediated T Cell Apoptosis During HIV Infection

IL-7 promotes survival of resting T lymphocytes and induces T cell proliferation in lymphopenic conditions. As elevated IL-7 levels occur in HIV-infected individuals in addition to high Fas expression on T cells and increased sensitivity to Fas-induced apoptosis, we analyzed whether IL-7 has a regulatory role in Fas-mediated T cell apoptosis. We show that IL-7 up-regulates Fas expression on naive and memory T cells through a mechanism that involves translocation of Fas molecules from intracellular compartments to the cell membrane. IL-7 induced the association of Fas with the cytoskeletal component ezrin and a polarized Fas expression on the cell surface. The potential role of IL-7 in Fas up-regulation in vivo was verified in IL-7-treated macaques and in HIV-infected or chemotherapy treated patients by the correlation between serum IL-7 levels and Fas expression on T cells. IL-7 treatment primed T cells for Fas-induced apoptosis in vitro and serum IL-7 levels correlated with the sensitivity of T cells to Fas-induced apoptosis in HIV-infected individuals. Our data suggest an important role for IL-7 in Fas-mediated regulation of T cell homeostasis. Elevated IL-7 levels associated with lymphopenic conditions, including HIV-infection, might participate in the increased sensitivity of T cells for activation-induced apoptosis.

Dynamics of lipid raft components during lymphocyte apoptosis: The paradigmatic role of GD3

Several investigations have been carried out since many years in order to precisely address the function of lipid rafts in cell life and death. On the basis of the biochemical nature of lipid rafts, composed by sphingolipids, including gangliosides, sphingomyelin, cholesterol and signaling proteins, a plethora of possible interactions with various subcellular structures has been suggested. Their structural and functional role at the plasma membrane as well as in cell organelles such as endoplasmic reticulum and Golgi apparatus has been analyzed in detail in several studies. In particular, a specific activity of lipid rafts has been hypothesized to contribute to cell death by apoptosis. Although detected in various cell types, the role of lipid rafts in apoptosis has however been mostly studied in lymphocytes where the physiological apoptotic program occurs after CD95/Fas triggering. In this review, the possible contribution of lipid rafts to the cascade of events leading to T cell apoptosis after CD95/Fas ligation are summarized. Particular attention has been given to the mitochondrial raft-like microdomains, which may represent preferential sites where some key reactions can take place and can be catalyzed, leading to either survival or death of T cells.

Cytoskeleton changes and impaired motility of monocytes at modelled low gravity

Investigations performed in space have shown that gravity changes affect important cellular mechanisms like proliferation, differentiation, genetic expression, cytoskeletal architecture, and motility in lymphocytes, monocytes, and other mammalian cells. In particular, a dramatic depression of the mitogenic in vitro activation of human peripheral blood lymphocytes was observed at low gravity. The hypothesis of the present work is that a reduced interaction between T lymphocytes and monocytes, essential for the second signalling pathway, might be one of the reasons for the observed depression of the in vitro activation of human lymphocytes. Cell motility and with it a continuous rearrangement of the cytoskeletal network within the cell is essential for cell-to-cell contacts. Whereas nonactivated lymphocytes in suspension are highly motile at low gravity, no data are available so far on the motility of adherent monocytes. It thus can be argued that impaired monocyte locomotion and cytoskeletal changes could be responsible for a reduced interaction of monocytes with T lymphocytes. In this study, the locomotion ability of J-111 cells, an adherent monocyte cell line, attached to colloidal gold particles on coverslips and exposed to modelled low gravity in the random positioning machine was found to be severely reduced compared with that of controls and the structures of actin, tubulin, and vinculin were affected.

The role of FAS to ezrin association in FAS-mediated apoptosis

The acquisition of a cell polarity is a crucial requirement for a number of cellular functions, including apoptosis. Cell polarization is an actin cytoskeleton-driven process, through a connection between actin and an increasing number of membrane proteins. The major actors in this connection are ezrin, radixin and moesin, a family of proteins with a high level of homology. Their structure includes an epitope that links to membrane proteins and the other that binds to the actin molecule. In this review we discuss recent data showing that the Fas linkage to the actin cytoskeleton is ezrin mediated and it is an essential requirement for susceptibility to the Fas-mediated apoptosis. The ezrin region responsible of Fas binding consists of 18 aminoacids mapped on the median lobe of the ezrin FERM domain. This binding is specific and of key importance in the control of cell homeostasis. Moreover, Fas-ezrin co-localization, ezrin phosphorylation and early acquisition of susceptibility to Fas-mediated apoptosis, may have a role in some human diseases in which programmed cell death seems to be a central pathogenetic mechanism, such as AIDS.

A role for the neuronal protein collapsin response mediator protein 2 in T lymphocyte polarization and migration

The semaphorin-signaling transducer collapsin response mediator protein 2 (CRMP2) has been identified in the nervous system where it mediates Sema3A-induced growth cone navigation. In the present study, we provide first evidence that CRMP2 is present in the immune system and plays a critical role in T lymphocyte function. CRMP2 redistribution at the uropod in polarized T cells, a structural support of lymphocyte motility, suggests that it may regulate T cell migration. This was evidenced in primary T cells by small-interfering RNA-mediated CRMP2 gene silencing and blocking Ab, as well as CRMP2 overexpression in Jurkat T cells tested in a chemokine- and semaphorin-mediated transmigration assay. Expression analysis in PBMC from healthy donors showed that CRMP2 is enhanced in cell subsets bearing the activation markers CD69+ and HLA-DR+. Heightened expression in T lymphocytes of patients suffering from neuroinflammatory disease with enhanced T cell-transmigrating activity points to a role for CRMP2 in pathogenesis. The elucidation of the signals and mechanisms that control this pathway will lead to a better understanding of T cell trafficking in physiological and pathological situations.

Ezrin Immunoreactivity Reveals Specific Astrocyte Activation in Cerebral HIV

The actin-binding protein ezrin is associated with cellular shape changes, motility, tumor invasion, and lymphocyte activation. We have earlier shown that ezrin immunoreactivity (IR) is faintly present in normal astrocytes but increased in malignant human astrogliomas. We studied the role of ezrin in astrocyte activation, applying immunostaining on serial paraffin sections from human autopsied brain tissues (51 cases). Cerebral HIV infection was chosen as a model displaying consistent exemplary astrocyte activation. Semiquantitative ezrin-IR was compared with the common glial markers GFAP, ferritin, and HLA-DR in relation to clinical and morphologic criteria of HIV encephalopathy. In all cases with HIV infection, GFAP-, HLA-DR-, and ferritin-IR were elevated in comparison to normal brain tissues. In contrast, high ezrin-IR in HIV infection strictly correlated with additional HIV encephalopathy. HIV encephalopathy with particularly high ezrin-IR was correlated with neuronal apoptosis (TUNEL). Combined ezrin-IR and GFAP-IR thus reveals 2 distinct states of astrocytic activation. Normal ezrin-IR, when paralleled by upregulated GFAP, reflects astroglial activation not associated with neuronal apoptosis. High ezrin-IR indicates specific astrocyte stressors related to cellular damage within the central nervous system. Ezrin-IR might also provide a diagnostic tool for the classification of HIV encephalopathy.

Cell migration in 3D matrix

The ability of cells to migrate within the extracellular matrix and to remodel it depends as much on the physical and biochemical characteristics of a particular matrix as on cellular properties. Analyzing the different modes of migration of cells in matrices, and how cells switch between these modes, is vital for understanding a variety of physiological and pathological processes. Recent work provides new insights, but also raises some debates about the mechanisms and regulation of cell migration in three-dimensional matrices.

Hematopoietic Progenitor Cells and Cellular Microenvironment: Behavioral and Molecular Changes upon Interaction

Cell-cell contact between stem cells and cellular determinants of the microenvironment plays an essential role in controlling cell division. Using human hematopoietic progenitor cells (CD34+/CD38-) and a stroma cell line (AFT024) as a model, we have studied the initial behavioral and molecular sequel of this interaction. Time-lapse microscopy showed that CD34+/CD38- cells actively migrated toward and sought contact with stroma cells and 30% of them adhered firmly to AFT024 stroma through the uropod. CD44 and CD34 are colocalized at the site of contact. Gene expression profiles of CD34+/CD38- cells upon cultivation with or without stroma for 16, 20, 48, or 72 hours were analyzed using our human genome cDNA microarray. Chk1, egr1, and cxcl2 were among the first genes upregulated within 16 hours. Genes with the highest upregulation throughout the time course included tubulin genes, ezrin, c1qr1, fos, pcna, mcm6, ung, and dnmt1, genes that play an essential role in reorganization of the cytoskeleton system, stabilization of DNA, and methylation patterns. Our results demonstrate directed migration of CD34+/CD38- cells toward AFT024 and adhesion through the uropod and that upon interaction with supportive stroma, reorganization of the cytoskeleton system, regulation of cell division, and maintenance of genetic stability represent the most essential steps.

Human immunodeficiency virus (HIV)-1 proteins and cytoskeleton: partners in viral life and host cell death

Cytoskeletal components play a major role in the human immunodeficiency virus-1 (HIV-1) infection. A wide variety of molecules belonging to the microfilament system, including actin filaments and actin binding proteins, as well as microtubules have a key role in regulating both cell life and death. Cell shape maintenance, cell polarity and cell movements as well as cytoplasmic trafficking of molecules determining cell fate, including apoptosis, are in fact instructed by the cytoskeleton components. HIV infection and viral particle production seem to be controlled by cytoskeleton as well. Furthermore, HIV-associated apoptosis failure can also be regulated by the actin network function. In fact, HIV protein gp120 is able to induce cytoskeleton-driven polarization, thus sensitizing T cells to CD95/Fas-mediated apoptosis. The microfilament system seems thus to be a sort of cytoplasmic supervisor of the viral particle, the host cell and the bystander cell's very fate.

CD95 capping is ROCK-dependent and dispensable for apoptosis

Upon engagement, the CD95 receptor is rapidly clustered into cellular 'caps'. This receptor capping is one of the first events to take place following activation and it has been proposed to be important for the initiation of apoptotic signaling. As the biological roles of CD95 capping are still elusive, we explored in detail the role of capping in induction of apoptosis in lymphocytes. CD95 capping was shown to be uncoupled from apoptosis, as apoptosis could occur in the absence of CD95 capping and, vice versa, capping could occur without inducing apoptosis. CD95 capping occurred concomitantly with reorganization of the actin cytoskeleton and aggregation of lipid rafts. While inhibition of actin polymerization and caspase-8 activity had cell type-specific effects on capping in type I and type II cells, the rapid CD95-mediated cellular polarization, as visualized by the orchestrated reorganization of CD95, F-actin and lipid rafts, was shown to be dependent on signaling by Rho kinase (ROCK) in both cell types, however, by distinct activation mechanisms in the respective cell type. CD95 activated RhoA exclusively in the type II cell, whereas ROCK activation was caspase-dependent in the type I cell. Taken together, our results imply that CD95 capping and the subsequent cellular polarization is a ROCK signaling-regulated process that does not correlate with the induction of apoptosis, but is more likely to be involved in the emerging non-apoptotic functions of CD95.

Integrin-dependent interaction of lipid rafts with the actin cytoskeleton in activated human platelets

Dynamic connections between actin filaments and the plasma membrane are crucial for the regulation of blood platelet functions. Protein complexes associated with αIIbβ3 integrin-based cytoskeleton structures are known to play a role in these processes. However, mechanisms involving lateral organizations of the plasma membrane remain to be investigated. Here, we demonstrate that a large fraction of platelet lipid rafts specifically associates with the actin cytoskeleton upon activation. This association was inhibited by antagonists of fibrinogen-αIIbβ3 binding and did not occur in type I Glanzman's thrombasthenic platelets. The raft-cytoskeleton interaction is a reversible process correlating with the intensity and stability of platelet aggregation. Although only a minor fraction of αIIbβ3 was recovered in rafts upon activation, this integrin specifically upregulated the level of PtdIns(4,5)P2 in membrane microdomains and induced the recruitment of several actin-modulating proteins known to directly or indirectly interact with this lipid. Controlled disruption of rafts did not affect αIIbβ3-mediated platelet aggregation in response to high concentrations of thrombin but significantly inhibited fibrin clot retraction. We propose that rafts participate in the organization of membrane-cytoskeleton interactions where αIIbβ3-mediated tension forces apply during the late phase of platelet activation.

Translocation of Fas by LPA prevents ovarian cancer cells from anti-Fas-induced apoptosis

OBJECTIVES

Alterations in the expression of Fas have been demonstrated in various cancers as a mechanism for tumor cells to escape from immune surveillance. In this study, we observed the effect of lysophosphatidic acid (LPA) on Fas expression and function in ovarian cancer cells.

METHODS

Ovarian cancer cell lines were incubated with or without LPA and Fas cell surface presentations were detected by flow cytometry. Anti-Fas IgM was added for induction and analysis of apoptosis by flow cytometry. Cell lysis and subcellular fractions were probed for protein expression by Western blot. Cells were also stained with human anti-Fas Ab, followed with Rhodamine red-X-conjugated goat anti-mouse IgG, and immunofluorescence images were acquired on a Nikon digital camera.

RESULTS

Following treatment with LPA, ovarian cancer cells showed significant rapid reduction of Fas presentation on the cell surface. LPA protected ovarian cancer cells from anti-Fas-induced apoptosis. Cell lysis and subcellular fractionations proved that LPA treatment induced a translocation of Fas receptors, along with phosphorylated ezrin, from the membrane anchored to the actin cytoskeleton, to the cytosol. Translocation of the Fas receptor reduced Fas concentration in the membrane and may inhibit its clustering and internalization during early apoptosis induced by anti-Fas. DISC staining proved that LPA inhibited Fas receptor aggregation and caspase-8 activation at the membrane, which further inhibited caspase-3 and 7 activation in the cytosol.

CONCLUSIONS

Our studies suggest that LPA induces translocation of Fas from the cell membrane to the cytosol, which may provide a mechanism by which ovarian cancer cells evade FasL-bearing immune cells.

Trichomoniasis

Trichomoniasis is perhaps the most common curable sexually transmitted disease worldwide, yet few resources are devoted to its control. It is associated with potentially serious complications such as preterm birth and human immunodeficiency virus acquisition and transmission. The immunology of a related organism, Tritrichomonas foetus, which causes disease in cattle, has been investigated to some extent, but more work is needed for the human strain, Trichomonas vaginalis. In addition, although trichomoniasis is easily treated with oral metronidazole, there is concern that the number of strains resistant to this antibiotic are increasing, and currently no alternative is licensed in the United States. As more is appreciated concerning the important public health implications of this common infection, more work will need to be done in understanding the diagnosis, treatment, and immunology of this organism.