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Biomedical subjects

F T Liu

Publications and source records attributed to F T Liu.

At least 19 recordsLinked to original sources
PubMed2001

Apaf-1 protein deficiency confers resistance to cytochrome c-dependent apoptosis in human leukemic cells.

The human leukemia cell lines K562, CEM, CEM/VLB(100), human leukemic blasts, and the bladder cancer J82 cell line have different sensitivities to UV light-induced apoptosis. It is reported that resistance to UV light-induced apoptosis occurs at a point in the apoptotic pathway upstream of caspase-3 but downstream of mitochondrial cytochrome c release. It is demonstrated that the block is due to deficiency of Apaf-1, a critical member of the apoptosome. Sensitivity to apoptosis was independent of caspase-9b or XIAP (inhibitors of apoptosis proteins) expression or levels of procaspase-9. Transfection of Apaf-1 conferred sensitivity to apoptosis in resistant cells. Apaf-1 deficiency may constitute a significant mode of resistance to apoptosis in human leukemia.

Antibodies↗
PubMed2001

Cell cycle regulation by galectin-12, a new member of the galectin superfamily.

Galectins are a family of beta-galactoside-binding animal lectins with conserved carbohydrate recognition domains (CRDs). Here we report the identification and characterization of a new galectin, galectin-12, which contains two domains that are homologous to the galectin CRD. The N-terminal domain contains all of the sequence elements predicted to form the two beta-sheets found in other galectins, as well as conserved carbohydrate-interacting residues. The C-terminal domain shows considerable divergence from the consensus sequence, and many of these conserved residues are not present. Nevertheless, the protein has lactose binding activity, most likely due to the contribution of the N-terminal domain. The mRNA for galectin-12 contains features coding for proteins with growth-regulatory functions. These include start codons in a context that are suboptimal for translation initiation and AU-rich motifs in the 3'-untranslated region, which are known to confer instability to mRNA. Galectin-12 mRNA is sparingly expressed or undetectable in many tissues and cell lines tested, but it is up-regulated in cells synchronized at the G(1) phase or the G(1)/S boundary of the cell cycle. Ectopic expression of galectin-12 in cancer cells causes cell cycle arrest at the G(1) phase and cell growth suppression. We conclude that galectin-12 is a novel regulator of cellular homeostasis.

Amino Acid Sequence↗
PubMed2001

Development of allergic inflammation in a murine model of asthma is dependent on the costimulatory receptor OX40.

Asthma is thought to result from an abnormal expansion of CD4 T cells reactive with airborne allergens, and pathology is controlled by several cytokines of the T helper type 2 (Th2) family. The exact molecules which are involved in generating allergen-reactive T cells are not clear. Studies with blocking reagents or knockout animals have shown that the CD28/B7 interaction partially controls development of allergic asthma in mouse models, but may not be the sole molecule involved. In this report, we have investigated the role of the tumor necrosis factor receptor family member OX40 in allergic inflammation using OX40-deficient mice. OX40 has been shown to participate in regulating clonal expansion and memory development of CD4 T cells and may synergize with CD28. Our studies demonstrate that OX40(-/)- mice, primed with the model allergen ovalbumin and challenged through the airways with aerosolized antigen, are severely impaired in their ability to generate a Th2 response characterized by high levels of interleukin (IL)-5, IL-4, and immunoglobulin E. Moreover, OX40(-/)- mice exhibit diminished lung inflammation, including an 80-90% reduction in eosinophilia and mucus production, less goblet cell hyperplasia, and significantly attenuated airway hyperreactivity. These studies highlight the potential importance of OX40 in development of allergic asthma and suggest that targeting OX40 may prove useful therapeutically.

Allergens↗
PubMed2001

Glycoprotein 90K/MAC-2BP interacts with galectin-1 and mediates galectin-1-induced cell aggregation.

The glycoprotein 90K was originally described as a tumor-secreted antigen and subsequently found to have immunostimulatory activity as well as other possible functions. This protein interacts with an endogenous lectin, galectin-3, and may play a role in tumor metastasis through this interaction. Because 90K is heavily glycosylated, it may also interact with other members of the galectin family, which would contribute to the multifunctionality of 90K. To test this possibility, we studied the recognition of 90K by galectin-1, which, like galectin-3, has been associated with neoplastic transformation. In a solid-phase binding assay, human recombinant galectin-1 bound immobilized human recombinant 90K in a fashion that was inhibitable by lactose. Galectins 1 and 3 appeared to bind to separate sites on 90K because they did not affect the binding of each other. The dissociation constant of galectin-1 to 90K was on the order of 10(-7) M. Galectin-1 also induced aggregation of a human melanoma cell line, A375, in a carbohydrate-dependent manner, and this appeared to be mediated, at least in part, by 90K expressed on A375 cells, since it was inhibitable by a specific anti-90K monoclonal antibody. We conclude that 90K interacts with both galectin-1 and galectin-3 and both interactions contribute to the formation of multicell aggregates. Because both of these galectins as well as 90K are often over-expressed in neoplasm, these interactions may occur in the setting of various carcinomas and contribute to their progression and metastasis.

3T3 Cells↗
PubMed2001

Regulation of mast cell survival by IgE.

Mast cells play critical roles in hypersensitivity and in defense against certain parasites. We provide evidence that mouse mast cell survival and growth are promoted by monomeric IgE binding to its high-affinity receptor, Fc epsilon RI. Monomeric IgE does not promote DNA synthesis but suppresses the apoptosis induced by growth factor deprivation. This antiapoptotic effect occurs in parallel with IgE-induced increases in Fc epsilon RI surface expression but requires the continuous presence of IgE. This process does not involve the FasL/Fas death pathway or several Bcl-2 family proteins and induces a distinctly different signal than Fc epsilon RI cross-linking. The ability of IgE to enhance mast cell survival and Fc epsilon RI expression may contribute to amplified allergic reactions.

Animals↗
PubMed2001

Accelerated diabetic glomerulopathy in galectin-3/AGE receptor 3 knockout mice.

Several molecules were shown to bind advanced glycation end products (AGEs) in vitro, but it is not known whether they all serve as AGE receptors and which functional role they play in vivo. We investigated the role of galectin-3, a multifunctional lectin with (anti)adhesive and growth-regulating properties, as an AGE receptor and its contribution to the development of diabetic glomerular disease, using a knockout mouse model. Galectin-3 knockout mice obtained by gene ablation and the corresponding wild-type mice were rendered diabetic with streptozotocin and killed 4 months later, together with age-matched nondiabetic controls. Despite a comparable degree of metabolic derangement, galectin-3-deficient mice developed accelerated glomerulopathy vs. the wild-type animals, as evidenced by the more pronounced increase in proteinuria, extracellular matrix gene expression, and mesangial expansion. This was associated with a more marked renal/glomerular AGE accumulation, indicating it was attributable to the lack of galectin-3 AGE receptor function. The galectin-3-deficient genotype was associated with reduced expression of receptors implicated in AGE removal (macrophage scavenger receptor A and AGE-R1) and increased expression of those mediating cell activation (RAGE and AGE-R2). These results show that the galectin-3-regulated AGE receptor pathway is operating in vivo and protects toward AGE-induced tissue injury in contrast to that through RAGE.

Animals↗
PubMed2001

Detection of galectin-3 in tear fluid at disease states and immunohistochemical and lectin histochemical analysis in human corneal and conjunctival epithelium.

BACKGROUND/AIM: Components of the tear fluid contribute to the biochemical defence system of the eye. To reveal whether the immune mediator and lipopolysaccharide binding galectin-3 is present in tears, tear samples were collected from eyes in healthy and pathological states. Investigation of expression of galectin-3 and galectin-3 reactive glycoligands in normal human conjunctival and corneal epithelia was also initiated as a step to understand the role of galectin-3 in ocular surface pathology. METHODS: Immunoblot analysis using either a rabbit polyclonal or a mouse monoclonal antibody against galectin-3 was employed to detect galectin-3 in tear fluid. Galectin-3 expression in tissue specimens was detected by immunocytochemistry employing A1D6 mouse monoclonal antibody, and galectin-3 reactive glycoligands were visualised by lectin histochemistry using labelled galectin-3. RESULTS: Galectin-3 was found only in tears from patients with ocular surface disorders. It was expressed in normal corneal and conjunctival epithelia but not in lacrimal glands. Inflammatory leucocytes and goblet cells found in galectin-3 containing tear fluid also expressed galectin-3. Galectin-3 binding sites were detected on the surface of conjunctival and corneal epithelial cells co-localising with desmoglein. CONCLUSIONS: This study revealed expression of galectin-3 in tear fluid obtained from patients with eye diseases. The role of this endogenous lectin (produced by inflammatory as well as epithelial cells) in antimicrobial action and inflammation modulation could be expected.

Antigens, Differentiation↗
PubMed2001

Inhibition of IgE-mediated mast cell activation by the paired Ig-like receptor PIR-B.

The potential of the paired Ig-like receptors of activating (PIR-A) and inhibitory (PIR-B) types for modifying an IgE antibody-mediated allergic response was evaluated in mouse bone marrow-derived mast cells. Although mast cells produced both PIR-A and PIR-B, PIR-B was found to be preferentially expressed on the cell surface, where it was constitutively tyrosine phosphorylated and associated with intracellular SHP-1 protein tyrosine phosphatase. PIR-B coligation with the IgE receptor (FcepsilonRI) inhibited IgE-mediated mast cell activation and release of serotonin. Surprisingly, the inhibitory activity of PIR-B was unimpaired in SHP-1-deficient mast cells. A third functional tyrosine-based inhibitory motif, one that fails to bind the SHP-1, SHP-2, and SHIP phosphatases, was identified in parallel studies of FcepsilonRI-bearing rat basophilic leukemia (RBL) cells transfected with constructs having mutations in the PIR-B cytoplasmic region. These results define the preferential expression of the PIR-B molecules on mast cells and an inhibitory potential that can be mediated via a SHP-1-independent pathway.

Animals↗
PubMed2001

Expression of galectin-3-reactive ligands in squamous cancer and normal epithelial cells as a marker of differentiation.

The definition of biological markers for oropharynx and larynx cancer is essential to predict their clinical behavior. Since cellular glycans play an important role in biological information transfer, we have employed an endogenous lectin, galectin-3, to examine in primary squamous carcinomas, lymph node metastases, and physiological squamous epithelia whether glycans recognized by this lectin are altered in relation to the state of differentiation. The expression of galectin-3 was concomitantly evaluated by immunohistochemistry using the A1D6 monoclonal antibody. In addition, other antibodies were used for the detection of cytokeratins and desmosomal proteins (desmoplakin-1 and desmoglein). The results show the expression of galectin-3-reactive ligands in moderately/highly differentiated carcinomas only in areas exhibiting a high level of keratinization. Except for one patient out of 14, metastatic cells in lymph nodes expressed no accessible binding sites for galectin-3. No galectin-3-reactivity was detected in the basal cell layer of all studied normal epithelia (which contains the proliferating cells). The suprabasal layers were positive in epidermis and epithelium of tongue and cornea and negative in epithelium of palatine tonsil. The tumor cells expressed galectin-3 with an intensity positively correlated with tumor differentiation. The position of galectin-3-reactive sites colocalized with the two tested desmosomal proteins. However, presence of these proteins was also detected in areas of tumor and suprabasal layers of tonsil epithelium where no binding reactivity for galectin-3 was found. The present study showed that expression of galectin-3-reactive glycoligands is differentiation-dependent in normal as well as malignant squamous cells. Colocalization of galectin-3-reactive sites with desmosomal proteins (desmoplakin-1 and desmoglein) suggests an association of the galectin-3 ligand(s) with the cell surface, pointing to a potential participation of galectin-3 in mediation of intercellular contacts in these tumor types.

Antigens, Differentiation↗
PubMed2000

Human galectin-3 is a novel chemoattractant for monocytes and macrophages.

Galectin-3 is a beta-galactoside-binding protein implicated in diverse biological processes. We found that galectin-3 induced human monocyte migration in vitro in a dose-dependent manner, and it was chemotactic at high concentrations (1.0 microM) but chemokinetic at low concentrations (10-100 nM). Galectin-3-induced monocyte migration was inhibited by its specific mAb and was blocked by lactose and a C-terminal domain fragment of the protein, indicating that both the N-terminal and C-terminal domains of galectin-3 are involved in this activity. Pertussis toxin (PTX) almost completely blocked monocyte migration induced by high concentrations of galectin-3. Galectin-3 caused a Ca2+ influx in monocytes at high, but not low, concentrations, and both lactose and PTX inhibited this response. There was no cross-desensitization between galectin-3 and any of the monocyte-reactive chemokines examined, including monocyte chemotactic protein-1, macrophage inflammatory protein-1alpha, and stromal cell-derived factor-1alpha. Cultured human macrophages and alveolar macrophages also migrated toward galectin-3, but not monocyte chemotactic protein-1. Finally, galectin-3 was found to cause monocyte accumulation in vivo in mouse air pouches. These results indicate that galectin-3 is a novel chemoattractant for monocytes and macrophages and suggest that the effect is mediated at least in part through a PTX-sensitive (G protein-coupled) pathway.

Animals↗
PubMed2000

Alteration of the cytoplasmic/nuclear expression pattern of galectin-3 correlates with prostate carcinoma progression.

Galectin-3, a member of the beta-galactoside-binding lectin family, is involved in a variety of biological events including interactions with galactose-containing glycoconjugates, cell proliferation, differentiation and apoptosis. Galectin-3 appears to intervene during tumor progression and altered expression patterns have been reported in a variety of malignancies. In our study, we have examined the expression of galectin-3 in a population of 145 prostate carcinoma samples using immunohistochemistry. We found that most of the non-tumoral prostatic glands exhibited moderate immunostaining for galectin-3 localized in both nucleus and cytoplasm. In prostatic cancer cells, galectin-3 was usually not expressed or decreased compared with the normal glands. Interestingly, when galectin-3 was detected in the cancer cells, it was consistently excluded from the nucleus and only present in the cytoplasmic compartment. The latter observation was also made for prostatic intraepithelial neoplasia (PIN) cells. Furthermore, we found that the levels of galectin-3 expression in the cancer cells were significantly associated with prostate-specific antigen (PSA) relapse in univariate analysis (p = 0.044). Cytoplasmic expression of galectin-3 in the carcinoma cells was an independent predictor of disease progression in multivariate analysis, after the pathological stage and the Gleason score. Our data demonstrate that galectin-3 is generally down-regulated in human prostate carcinoma cells, and consistently excluded from the nucleus. Interestingly, specific cytoplasmic expression of galectin-3 in a subset of lesions is associated with disease progression. These results suggest that galectin-3 might play anti-tumor activities when present in the nucleus, whereas it could favor tumor progression when expressed in the cytoplasm. Further studies should determine the exact role and mechanisms by which galectin-3 differentially affects cell behavior in the different locations where it is expressed.

Aged↗
PubMed2000

Requirement of divalent galactoside-binding activity of ecalectin/galectin-9 for eosinophil chemoattraction.

We have previously isolated and cloned a novel eosinophil chemoattractant (ECA) from a human T-cell-derived expression library. This ECA, termed ecalectin, is a variant of human galectin-9, a member of a beta-galactoside binding animal lectin family, which contains two conserved carbohydrate recognition domains (CRDs). In the present study, we addressed whether carbohydrate binding activity is required for the ECA activity of ecalectin and whether both CRDs are essential for this activity. Recombinant full-length wild-type ecalectin (ecalectin-WT) and N-terminal and C-terminal CRD (ecalectin-NT and -CT, respectively) were generated. All of these recombinant proteins exhibited affinity for lactose, a property shared by galectins, but ecalectin-WT exhibited substantially higher hemagglutination activities than ecalectin-NT and -CT. Furthermore, ecalectin-WT showed over 100-fold higher ECA activity than ecalectin-NT and -CT; combination of recombinant domain fragments did not reconstitute the ECA and hemagglutination activities of the full-length protein. ECA activity of ecalectin-WT was inhibited by lactose in a dose-dependent manner. Site-directed mutation of positions Arg(65) of ecalectin-NT and Arg(239) of ecalectin-CT to an aspartic acid residue resulted in the loss of both lactose-binding and ECA activities. We conclude that divalent galactoside-binding activity is required for eosinophil chemoattraction by ecalectin.

Antigens, Differentiation↗
PubMed2000

Role for IgE in airway secretions: IgE immune complexes are more potent inducers than antigen alone of airway inflammation in a murine model.

IgE is present in airway secretions from human patients with allergic rhinitis and bronchial asthma. However, the contribution of IgE present locally to the overall airway inflammation is not well understood. We hypothesize that Ag-specific IgE can capture airborne Ags and form immune complexes. These immune complexes may function as potent inducers of immune responses in the lung, contributing to the perpetuation of airway inflammation. BALB/c mice were first sensitized with OVA in alum systemically and then challenged with nebulized OVA. Bronchoalveolar lavage (BAL) fluid from these mice contained significant amounts of IgE, of which >50% was Ag specific. The IgE levels in airway secretions remained elevated for more than 15 days after the termination of Ag exposure. Significant amounts of IgE-OVA immune complexes were detected in BAL fluid from the OVA-challenged mice. For comparison of IgE immune complexes vs Ag alone, we treated OVA-immunized mice with intranasal administration of trinitrophenyl-OVA or trinitrophenyl-OVA-anti-DNP IgE. Those treated with the immune complexes showed significantly higher levels of IL-4 and more pronounced eosinophilia in BAL fluid than did those receiving the Ag alone. The IgE immune complexes did not augment the inflammatory response in high affinity IgE receptor (FcepsilonRI)-deficient mice. We conclude that IgE present in the airways can capture the Ag and that the immune complexes thus formed may augment allergic airway response in an FcepsilonRI-dependent manner. Thus, IgE present in airway secretions may facilitate Ag-mediated allergic airway inflammation.

Aerosols↗
PubMed2000

Galectin-3 overexpression protects from apoptosis by improving cell adhesion properties.

Galectin-3 is a carbohydrate-binding protein endowed with affinity for beta-galactosides. It plays a role in cell-cell and cell-matrix interactions. Furthermore, it has been hypothesized to be involved in tumor progression and metastasis. To address the role of galectin-3 in the invasive and metastatic processes, we stably overexpressed galectin-3 in human breast carcinoma cell lines, and we evaluated the influence of elevated galectin-3 expression on several cell features, including cellular homotypic and heterotypic interactions and cell survival. No differences in various parameters related with cell growth features and proliferation were detected. By contrast, we found that galectin-3 overexpressing cells, with respect to low galectin-3 expressing cells, exerted: (1) a significantly enhanced adhesion to laminin, fibronectin and vitronectin exerted both directly or via increased expression of specific integrins, e.g., alpha-4 and beta-7; (2) a remodeling of those cytoskeletal elements associated with cell spreading, i.e., microfilaments; (3) an enhanced survival upon exposure to different apoptotic stimuli, such as cytokine and radiation. Collectively, our results indicate that overexpression of galectin-3 may play a role in tumor cell invasion and metastasis by specifically influencing cell adhesion to the extracellular matrix. This may confer selective survival advantage and resistance to the particular homeless-induced apoptosis called anoikia.

Antigens, Differentiation↗
PubMed2000

Targeted disruption of the galectin-3 gene results in attenuated peritoneal inflammatory responses.

Galectin-3 is a member of a growing family of beta-galactoside-binding animal lectins. Previous studies have demonstrated a variety of biological activities for this protein in vitro, including activation of cells, modulation of cell adhesion, induction of pre-mRNA splicing, and regulation of apoptosis. To assist in fully elucidating the physiological and pathological functions of this protein, we have generated galectin-3-deficient (gal3(-/-)) mice by targeted interruption of the galectin-3 gene. Gal3(-/-) mice consistently developed fewer inflammatory cell infiltrations in the peritoneal cavities than the wild-type (gal3(+/+)) mice in response to thioglycollate broth treatment, mainly due to lower numbers of macrophages. Also, when compared to cells from gal3(+/+) mice, thioglycollate-elicited inflammatory cells from gal3(-/-) mice exhibited significantly lower levels of NF-kappaB response. In addition, dramatically different cell-spreading phenotypes were observed in cultured macrophages from the two genotypes. Whereas macrophages from gal3(+/+) mice exhibited well spread out morphology, those from gal3(-/-) mice were often spindle-shaped. Finally, we found that peritoneal macrophages from gal3(-/-) mice were more prone to undergo apoptosis than those from gal3(+/+) mice when treated with apoptotic stimuli, suggesting that expression of galectin-3 in inflammatory cells may lead to longer cell survival, thus prolonging inflammation. These results strongly support galectin-3 as a positive regulator of inflammatory responses in the peritoneal cavity.

Animals↗
PubMed2000

Role of galectin-3 as a receptor for advanced glycosylation end products.

The advanced glycosylation end product (AGE)-binding proteins identified so far include the components of the AGE-receptor complex p60, p90 and galectin-3, receptor for advanced glycosylation end products (RAGE), and the macrophage scavenger receptor types I and II. Galectin-3 interacts with beta-galactoside residues of several cell surface and matrix glycoproteins through the carbohydrate recognition domain and is also capable of peptide-peptide associations mediated by its N-terminus domain. These structural properties enable galectin-3 to exert multiple functions, including the modulation of cell adhesion, the control of cell cycle, and the mRNA splicing activity. Moreover, in macrophages, astrocytes, and endothelial cells, galectin-3 has been shown to exhibit a high-affinity binding for AGEs; the lack of a transmembrane anchor sequence or signal peptide suggests that it associates with other AGE-receptor components rather than playing an independent role as AGE-receptor. In tissues that are targets of diabetic vascular complications, such as the mesangium and the endothelium, galectin-3 is not expressed or only weakly expressed under basal conditions, at variance with p90 and p60 but becomes detectable with aging and is induced or up-regulated by the diabetic milieu, which only slightly affects the expression of p90 or p60. This (over)expression of galectin-3 may in turn modulate AGE-receptor-mediated events by modifying the function of the AGE-receptor complex, which could play a role in the pathogenesis of target tissue injury. Up-regulated galectin-3 expression may also exert direct effects on tissue remodeling, independently of AGE ligands, by virtue of its adhesive and growth regulating properties.

Animals↗
PubMed2000

Interaction between galectin-3 and FcgammaRII induces down-regulation of IL-5 gene: implication of the promoter sequence IL-5REIII.

Our previous work demonstrated the capacity of galectin-3 (a beta-galactoside binding animal lectin) to inhibit IL-5 gene expression in different cell types, but the interaction of lectin with the cells and the pathways for the inhibition process are unknown. One of the purposes of this work was to study the cellular ligand for galectin-3. We have demonstrated that galectin-3 can bind to the low affinity IgG receptor (FcgammaRII or CD32) by using different experimental approaches, such as flow cytometry, fusion protein GST technology, and with a model of FcgammaRII-deficient mice. To further analyze the interaction between FcgammaRII and galectin-3, and its implication in IL-5 gene down-regulation we used FcgammaRII-deficient mice. When PBMC from these mice were incubated with galectin-3, the expression of the IL-5 gene was unchanged. However, when PBMC from wild type mice and FcgammaRIII-deficient mice were incubated with galectin-3, IL-5 gene expression was down-regulated. Finally, we studied the implication of the negative regulatory sequence in the IL-5 gene promoter. In the presence of galectin-3, a DNA-protein complex was formed with the IL-5REIII region. This complex was not observed when unrelated oligonucleotide was used. So, galectin-3 induces a pathway, which activates a transcription factor that binds to IL-5REIII. This interaction is capable of inhibiting IL-5 gene transcription.

Animals↗