Down-regulation by tumor necrosis factor-alpha of neutrophil cell surface expression of the sialophorin CD43 and the hyaluronate receptor CD44 through a proteolytic mechanism

Resting and activated bovine neutrophils and eosinophils differ in their responses to adrenergic agonists

Polymorphonuclear cells (PMN) provide a rapid response to infection and tissue damage and stress can modify these critical innate immune defences. The study of adrenergic receptor (AR) expression and function in bovine PMNs is limited but both neutrophils and eosinophils express numerous AR genes but differ significantly in their expression of individual AR genes. A flow cytometric technique was developed to differentiate between bovine neutrophils and eosinophils so both neutrophil and eosinophil responses to adrenergic agonists could be analysed. Neutrophils and eosinophils displayed significantly different changes in CD11b, L-selectin, and CD44 expression when activated by bovine serum opsonized zymosan and recombinant bovine interferon gamma. The responses of activated and resting neutrophils and eosinophils were then compared following stimulation with endogenous adrenergic agonists, epinephrine (E) norepinephrine (NE), and synthetic agonists targeting α1-, α2-, or β-ARs. Both resting and activated neutrophils and eosinophils displayed differences in iROS, CD44, and L-selectin expression following stimulation with E and NE. Resting neutrophils displayed pro-inflammatory responses to both E and NE, while resting eosinophils displayed a pro-inflammatory response to only NE. No single synthetic adrenergic agonist fully recapitulated responses observed with either E or NE and responses to adrenergic agonists were dose-dependent. In conclusion, bovine eosinophils and neutrophils responded to multiple adrenergic agonists by altering expression of proteins involved in immune surveillance and pro-inflammatory responses. Significant differences in neutrophil and eosinophil responses to adrenergic agonists are consistent with their differences in AR gene expression. This highlights the importance of analysing separately these two PMN subpopulations when investigating the effects of either endogenous or synthetic AR agonists.

The extracellular sialidase NEU3 primes neutrophils

Some extracellular glycoconjugates have sialic acid as the terminal sugar, and sialidases are enzymes that remove this sugar. Mammals have 4 sialidases and can be elevated in inflammation and fibrosis. In this report, we show that incubation of human neutrophils with the extracellular human sialidase NEU3, but not NEU1, NEU2 or NEU4, induces human male and female neutrophils to change from a round to a more amoeboid morphology, causes the primed human neutrophil markers CD11b, CD18, and CD66a to localize to the cell cortex, and decreases the localization of the unprimed human neutrophil markers CD43 and CD62-L at the cell cortex. NEU3, but not the other 3 sialidases, also causes human male and female neutrophils to increase their F-actin content. Human neutrophils treated with NEU3 show a decrease in cortical levels of Sambucus nigra lectin staining and an increase in cortical levels of peanut agglutinin staining, indicating a NEU3-induced desialylation. The inhibition of NEU3 by the NEU3 inhibitor 2-acetylpyridine attenuated the NEU3 effect on neutrophil morphology, indicating that the effect of NEU3 is dependent on its enzymatic activity. Together, these results indicate that NEU3 can prime human male and female neutrophils, and that NEU3 is a potential regulator of inflammation.

miR205 inhibits stem cell renewal in SUM159PT breast cancer cells

miR205 has a dual activity, as tumor suppressor and as oncogene. Here we analyzed the impact of miR205 ectopic expression in the initial tumorigenic processes of SUM159PT, a triple negative breast cancer cell line with low endogenous levels of miR205. In SUM159PT, miR205 inhibited expression of its targets VEGFA, ErbB3, Zeb1, Fyn and Lyn A/B; it reduced cell proliferation, and Myc/cyclin D1 levels, while increased p27^kip1 expression. miR205 abolished anchorage-independent growth, inhibited migration and invasion, Src-kinases/Stat3 axis activation, and levels of secreted MMP9. miR205 also reduced expression of CD44 and TAZ, E2A.E12, Twist, Snail1 and CK5, associated with epithelial-mesenchymal transition (EMT). Importantly, we show that miR205 inhibited SUM159PT cancer-stem cell renewal, expression in mammospheres of CD44 and ALDH1 stem-cell markers, TAZ, and E2A.E12. All these effects of miR205 were reverted by Anti-miR205 co-expression, demonstrating its specificity. Thus, all these results strongly suggest that ectopic expression of miR205 in SUM159PT affected several parameters associated with initial steps of tumorigenesis.

A bead-assisted flow cytometry method for the semi-quantitative analysis of Extracellular Vesicles

Most experimental approaches commonly employed for the characterization and quantitation of EVs are time consuming, require of specialized instrumentation and often are rather inaccurate. To circumvent the caveats imposed by EV small size, we used general and specific membrane markers in bead assisted flow cytometry, to provide a semi-quantitative measure of EV content in a given sample. EVs were isolated from in vitro cultured cells-conditioned medium and biological fluids by size exclusion chromatography and coupled to latex beads to allow their detection by standard flow cytometers. Our analyses demonstrate a linear correlation between EV concentration and Mean Fluorescence Intensity values in samples cleared of protein contaminants. Comparison with one of the most widespread method such as NTA, suggests a similar linear range and reliable accuracy to detect saturation. However, although detection of the different biomarkers is feasible when tested on ultracentrifugation-enriched samples, protein contamination impairs quantitation of this type of samples by bead-based flow cytometry. Thus, we provide evidence that bead-assisted flow cytometry method is an accurate and reliable method for the semiquantitative bulk analysis of EVs, which could be easily implemented in most laboratories.

Intracellular patterns of sialophorin expression define a new molecular classification of breast cancer and represent new targets for therapy

BACKGROUND

Sialophorin is a transmembrane sialoglycoprotein. Normally, the molecule is only produced by white blood cells where it regulates functions such as intercellular adhesion, intracellular signalling, apoptosis, migration and proliferation.

METHODS

Normal breast tissue and primary breast tumours were analysed by immunohistochemistry for sialophorin expression. The sialophorin-positive breast cancer cell line MCF7 was engineered to stably express either non-targeted or sialophorin-targeted small interfering RNA (siRNA). Assays were then performed in vitro to assess apoptosis, intracellular adhesion, transendothelial migration and cytotoxicity. An orthotopic mouse model assayed ability to produce tumours in vivo.

RESULTS

Normal breast epithelial cells exhibit expression of the N-terminal domain of sialophorin in the cytoplasm but not the nucleus. The majority of these normal cells are also negative for expression of the C-terminal domain. In contrast, malignant breast epithelial cells exhibit N-terminal expression both in the cytoplasm and nucleus and the majority express the C-terminus in the nucleus. Using differential patterns of intracellular expression of the N and C termini of sialophorin, we define six subtypes of breast cancer that are independent of histological and receptor status classification. Targeting sialophorin with siRNA resulted in the MCF7 breast cancer cell line exhibiting increased homotypic adhesion, decreased transendothelial migration, increased susceptibility to apoptosis, increased vulnerability to lysis by natural killer cells and decreased ability to produce tumours in mice.

CONCLUSION

Our results indicate that intracellular patterns of sialophorin expression define a new molecular classification of breast cancer and that sialophorin represents a novel therapeutic target.

Serum amyloid P inhibits granulocyte adhesion

Background

The extravasation of granulocytes (such as neutrophils) at a site of inflammation is a key aspect of the innate immune system. Signals from the site of inflammation upregulate granulocyte adhesion to the endothelium to initiate extravasation, and also enhance granulocyte adhesion to extracellular matrix proteins to facilitate granulocyte movement through the inflamed tissue. During the resolution of inflammation, other signals inhibit granulocyte adhesion to slow and ultimately stop granulocyte influx into the tissue. In a variety of inflammatory diseases such as acute respiratory distress syndrome, an excess infiltration of granulocytes into a tissue causes undesired collateral damage, and being able to reduce granulocyte adhesion and influx could reduce this damage.

Results

We found that serum amyloid P (SAP), a constitutive protein component of the blood, inhibits granulocyte spreading and granulocyte adhesion to extracellular matrix components. This indicates that in addition to granulocyte adhesion inhibitors that are secreted during the resolution of inflammation, a granulocyte adhesion inhibitor is present at all times in the blood. Although SAP affects adhesion, it does not affect the granulocyte adhesion molecules CD11b, CD62L, CD18, or CD44. SAP also has no effect on the production of hydrogen peroxide by resting or stimulated granulocytes, or N-formyl-methionine-leucine-phenylalanine (fMLP)-induced granulocyte migration. In mice treated with intratracheal bleomycin to induce granulocyte accumulation in the lungs, SAP injections reduced the number of granulocytes in the lungs.

Conclusions

We found that SAP, a constitutive component of blood, is a granulocyte adhesion inhibitor. We hypothesize that SAP allows granulocytes to sense whether they are in the blood or in a tissue.

CD43 in the nucleus and cytoplasm of lung cancer is a potential therapeutic target

CD43 is a transmembrane sialoglycoprotein. Normally the molecule is only produced by white blood cells where it regulates functions such as intercellular adhesion, intracellular signaling, apoptosis, migration and proliferation. Two CD43 antibodies were used to interrogate 66 cases of non-small cell lung cancer (NSCLC) and 24 cases of small cell lung cancer (SCLC). In addition, we engineered the CD43-positive lung cancer cell line A549 to stably express either non-targeted or CD43-targeted small-interfering RNA (siRNA). These lines were then subjected to in vitro assays of apoptosis, natural killer (NK) cell cytotoxicity, intercellular adhesion and transendothelial migration. A xenograft mouse model evaluated the ability of the lines to grow primary tumors in vivo. CD43 was found to be expressed in the majority of both SCLC and NSCLC. Inclusive of CD43-negative tumors, differential patterns of nuclear and cytoplasmic expression of CD43 define four molecular subcategories of lung cancer. Targeting CD43 in A549 lung cancer cells, increased homotypic adhesion, decreased heterotypic adhesion and transendothelial migration, increased susceptibility to apoptosis and increased vulnerability to lysis by NK cells. Furthermore, targeting inhibited the growth of primary tumors in nude mice.

Galectin-1 promotes human neutrophil migration

An important step of innate immune response is the recruitment of polymorphonuclear leukocytes (PMN) to injured tissues through chemotactic molecules. Galectins, a family of endogenous lectins, participate in numerous functions such as lymphoid cell migration, homing, cell-cell and cell-matrix interactions. Particularly, galectin-3 (Gal-3) and -9 have been implicated in the modulation of acute and chronic inflammation by inducing the directional migration of monocytes/macrophages and eosinophils, whereas Gal-1 is considered to function as an anti-inflammatory molecule, capable of inhibiting the influx of PMN to the site of injury. In this study, we assessed the effect of Gal-1 on neutrophil recruitment, in the absence of additional inflammatory insults. Contrasting with its capacity to inhibit cell trafficking and modulate the release of mediators described in models of acute inflammation and autoimmunity, we evidenced that Gal-1 has the capacity to induce neutrophil migration both in vitro and in vivo. This effect is not mediated through a G-protein-coupled receptor but potentially through the sialoglycoprotein CD43, via carbohydrate binding and through the p38 mitogen-activated protein kinase pathway. These results suggest a novel biological function for CD43 on neutrophils and highlight that depending on the environment, Gal-1 can act either as chemoattractant or, as a molecule that negatively regulates migration under acute inflammatory conditions, underscoring the potential of Gal-1 as a target for innovative drug development.

The cleavage of neutrophil leukosialin (CD43) by cathepsin G releases its extracellular domain and triggers its intramembrane proteolysis by presenilin/gamma-secretase

The highly negatively charged membrane sialoglycoprotein leukosialin, CD43, is shed during neutrophil activation. This is generally thought to enhance cell adhesion. We here describe two novel consequences of this shedding, during neutrophil activation by phorbol esters or by chemoattractants after TNF-alpha priming. CD43 proteolysis was investigated by Western blotting, using a polyclonal antibody to CD43 intracellular domain. Our data emphasize the importance of a juxtamembranous cleavage of about 50% of membrane CD43 molecules by cathepsin G. Indeed, it is inhibited by alpha1-antichymotrypsin and cathepsin G inhibitor I and is reproduced by exogenous purified cathepsin G. The resulting membrane-anchored C-terminal fragment, CD43-CTF, becomes susceptible to presenilin/gamma-secretase, which releases CD43 intracytoplasmic domain: preincubation with three different gamma-secretase inhibitors, before PMN treatment by agonists or by purified cathepsin G, results in the accumulation of CD43-CTF. Because CD43 binds E-selectin, we also investigated the effect of the soluble extracellular domain CD43s, released by cathepsin G juxtamembranous cleavage, on neutrophil adhesion to endothelial cells. A recombinant CD43s-Fc fusion protein inhibited neutrophil E selectindependent adhesion to endothelial cells under flow conditions, while it had no effect on neutrophil static adhesion. We thus propose that, in addition to its potential pro-adhesive role, CD43 proteolysis results in: (i) the release, by cathepsin G, of CD43 extracellular domain, able to inhibit the adhesion of flowing neutrophils on endothelial cells and thus to participate to the natural control of inflammation; (ii) the release and/or the clearance, by presenilin/gamma-secretase, of CD43 intracellular domain, thereby regulating CD43-mediated signaling.

Distinct Signaling Pathways Are Involved in Leukosialin (CD43) Down-regulation, Membrane Blebbing, and Phospholipid Scrambling during Neutrophil Apoptosis

Although leukosialin (CD43) membrane expression decreases during neutrophil apoptosis, the CD43 molecule, unexpectedly, is neither proteolyzed nor internalized. We thus wondered whether it could be shed on bleb-derived membrane vesicles. Membrane blebbing is a transient event, hardly appreciated during the asynchronous, spontaneous apoptosis of neutrophils. Cell pre-synchronization at 15 degrees C made it possible to observe numerous blebbing neutrophils for a short 1-h period at 37 degrees C. CD43 down-regulation co-occurred with the blebbing stage and phosphatidylserine externalization, shortly after mitochondria depolarization and before nuclear condensation. Blebs detaching from the cell body were observed by time lapse fluorescence microscopy, and the release of bleb-derived vesicles was followed by flow cytometry. Phosphatidylserine externalization required caspases and protein kinase C (PKC) but not the myosin light chain kinase (MLCK). By contrast, bleb formation and release was caspase- and PKC-independent but required an active MLCK, whereas CD43 down-regulation involved caspases but neither PKC nor MLCK. Furthermore, CD43 appeared mostly excluded from membrane blebs by electron microscopy. Thus, CD43 down-regulation does not result from the release of bleb-derived vesicles. Ultracentrifugation of apoptotic cell supernatants made it possible to recover <1 microM microparticles, which contained the entire CD43 molecule. These microparticles expressed neutrophil membrane markers such as CD11b, CD66b, and CD63, together with CD43. In conclusion, we show that the three early membrane events of apoptosis, namely blebbing, phosphatidylserine externalization, and CD43 down-regulation, result from different signaling pathways and can occur independently from one another. CD43 down-regulation results from the shedding of microparticles released during apoptosis but unrelated to the blebbing.

Ligation of intercellular adhesion molecule 3 inhibits GM-CSF production by human eosinophils

BACKGROUND

Intercellular adhesion molecule 3 (ICAM-3) has recently been identified on the surface of eosinophils.

OBJECTIVE

The purpose of this study was to characterize ICAM-3 expression on eosinophils in response to cytokines and to determine whether ligand binding of ICAM-3 modulates inflammatory responses of eosinophils, as it does in other leukocytes.

METHODS

To determine effects of ICAM-3 on eosinophil function, we isolated human eosinophils and used a monoclonal antibody directed against the epitope of ICAM-3 that binds to leukocyte-function antigen-1 to mimic binding of ICAM-3 and this natural ligand. We measured granulocyte-macrophage colony stimulating factor (GM-CSF) production by unstimulated eosinophils and eosinophils stimulated with ionomycin (1 micromol/L), both in the presence and absence of this anti-ICAM-3 antibody.

RESULTS

We found that 99% of eosinophils expressed ICAM-3, regardless of whether allergic symptoms were present or absent. Expression of ICAM-3 was not enhanced by proinflammatory cytokines. Expression of ICAM-3 was reduced in apoptotic cells and in cells incubated with the combination of GM-CSF and tumor necrosis factor-alpha (n = 3). Antibody binding of ICAM-3, which mimics leukocyte-function antigen-1 binding, had no effect on baseline GM-CSF production but reduced by 80% the production of GM-CSF stimulated by ionomycin (control 1969 pg/mL +/- 1259 SD versus anti-ICAM-3 396 pg/mL +/- 207 SD, n = 8) and reduced GM-CSF mRNA content.

CONCLUSIONS

ICAM-3 is highly expressed on the surface of human eosinophils, and downregulation of GM-CSF production by anti-ICAM-3 mAb suggests that ICAM-3 ligation may inhibit eosinophil inflammatory responses and survival.

hnRNP-K and Pur(alpha) act together to repress the transcriptional activity of the CD43 gene promoter

CD43 is an abundant, heavily glycosylated molecule expressed specifically on the surface of leukocytes and platelets. When leukocytes are at rest, CD43 acts to prevent both homotypic and heterotypic interactions. However, during leukocyte activation CD43 expression is repressed, facilitating the intercellular contact required for chemotaxis, phagocytosis, aggregation, adhesion to endothelium, and transendothelial migration. Consequently, CD43 repression plays a vital role both in innate and acquired immunity. Here we report that a dramatic down-regulation of CD43 mRNA levels occurs during activation of the leukocytic cell line K562. This repression coincides with repression of the transcriptional activity of the CD43 gene promoter. We have determined that heterogeneous nuclear ribonucleoprotein K (hnRNP-K) and Pur(alpha) act together to mediate repression of the CD43 promoter during K562 activation. The hnRNP-K molecule and Pur(alpha) bind single-stranded DNA. Therefore, exposure of single-stranded structures within the CD43 promoter probably plays a major role in effecting CD43 repression.

CD44 in cancer

CD44 is a multistructural and multifunctional cell surface molecule involved in cell proliferation, cell differentiation, cell migration, angiogenesis, presentation of cytokines, chemokines, and growth factors to the corresponding receptors, and docking of proteases at the cell membrane, as well as in signaling for cell survival. All these biological properties are essential to the physiological activities of normal cells, but they are also associated with the pathologic activities of cancer cells. Experiments in animals have shown that targeting of CD44 by antibodies, antisense,and CD44-soluble proteins markedly reduces the malignant activities of various neoplasms, stressing the therapeutic potential of anti-CD44 agents. Furthermore, because alternative splicing and posttranslational modifications generate many different CD44 sequences, including, perhaps, tumor-specific sequences, the production of anti-CD44 tumor-specific agents may be a realistic therapeutic approach. However, in many cancers (renal cancer and non-Hodgkin's lymphomas are exceptions), a high level of CD44 expression is not always associated with an unfavorable outcome. On the contrary, in some neoplams CD44 upregulation is associated with a favorable outcome. Even worse, in many cases different research grows analyzing the same neoplastic disease reached contradictory conclusions regarding the correlation between CD44 expression and disease prognosis, possibly due to differences in methodology. These problems must be resolved before applying anti-CD44 therapy to human cancers.

Phenotypic and functional changes on phagocytic cells recruited at the site of Candida albicans infection after chronic varied stress exposure

The transition of Candida albicans from commensalism to pathogenicity is associated with the immune status of the host; resistance to fungus involves macrophages (Mphi) and polymorphonuclear neutrophils (PMN), which act as effector cells. T-cell function is also involved. Previously, we found that in Wistar rats exposed to chronic varied stress (CVS) immediately after C. albicans infection (Ca-S group) some functions of phagocytic cells, such as killer activity and NO production, were strongly modified compared with unstressed, infected animals (Ca group). We examined the phenotypic and functional changes of these effector cells recruited at the site of C. albicans infection. The recruitment of peritoneal cells (PC) was markedly reduced in Ca-S animals and the arrival of Mphi and PMN was selectively diminished after CVS exposure. The integrin CD11b/CD18, implicated in migration and C. albicans phagocytosis, was downregulated in Mphi of Ca-S animals. The activation markers CD54 and MHC-II were upregulated in Mphi after fungal contact. The expression of CD54 was only changed in Ca-S rats. Finally, TNF-alpha production was reduced in PC of Ca-S animals, suggesting an impairment of functional activity. Taken together, the phenotypic and functional changes detected in effector cells may account for the decreased resistance to candidiasis seen in conjunction with CVS. The changes seen also expand our knowledge of the role of Mphi in the control of C. albicans dissemination.

During differentiation of the monocytic cell line U937, Pur alpha mediates induction of the CD11c beta 2 integrin gene promoter

CD11c is a member of the beta(2) integrin family of adhesion molecules that, together with CD18, forms a heterodimeric receptor on the surface of myeloid, NK, dendritic, and certain leukemic, lymphoma, and activated lymphoid cells. Monocytic differentiation is associated with an induction of both CD11c and CD18 gene expression. The resulting CD11c/CD18 receptor mediates firm adhesion to the vascular endothelium, transendothelial migration, chemotaxis, and phagocytosis. Monocytic differentiation can be mimicked in vitro by treatment of the promonocytic cell line U937 with PMA. Recently, we reported that in U937 cells, expression of the CD11c gene is controlled by an unidentified transcription factor that binds ssDNA. This finding suggested that DNA secondary structure plays an important role in controlling the CD11c gene and prompted us to search for additional ssDNA-binding activities with which this gene interacts. In this study, we report that in U937 cells, expression of the CD11c gene is mediated by the ssDNA-binding protein Puralpha. During PMA-induced differentiation, the ability of Puralpha to activate the CD11c promoter in U937 cells increases, as does that of Sp1. Together, these increases in the functional activity of both Puralpha and Sp1 combine to induce CD11c expression.

Down-regulation of CD43 molecule expression on intraperitoneal neutrophils in CAPD patients with peritonitis

To assess the release of proteases from neutrophils infiltrated into the peritoneal cavity in continuous ambulatory peritoneal dialysis (CAPD), we investigated the regulation of CD43, LAM-1 and Mac-1 expression on the neutrophil plasma membrane using FACS analysis in CAPD patients with peritonitis. Five CAPD patients with peritonitis and five CAPD patients without peritonitis were studied. CD43 expression was immunohistochemically determined in both groups of patients using flow cytometry, and comparisons were made between the two groups. Down-regulation of CD43 and LAM-1, and up-regulation of Mac-1 were demonstrated on neutrophils obtained from CAPD dialysate of peritonitis patients after 1-h dwell time. Further up-regulation of Mac-1 developed until a dwell time of 4 h. Immunoblot analysis for neutrophil lysate from dialysate showed the presence of the asialo form of CD43 molecules and their fragments, which may be produced by cleavage of the CD43 molecule at extracellular sites. The intraperitoneal neutrophils in dialysate from CAPD patients with peritonitis are continuously activated during dwell time, and proteases may be released from neutrophils into dialysate after only a short dwell time.

During U937 monocytic differentiation repression of the CD43 gene promoter is mediated by the single-stranded DNA binding protein Pur alpha

Human CD43 is an abundant, heavily glycosylated molecule expressed exclusively on the surface of leucocytes. When leucocytes are at rest, CD43 acts to prevent intercellular interaction but during leucocyte differentiation such cell-cell interaction is facilitated by CD43. This change in the function of CD43 is mediated in part by a reduction in its level of expression. Previous studies have implicated proteolytic cleavage events at the cell surface in causing such reduction. Here, we report that, in an in vitro model of leucocyte differentiation, CD43 mRNA levels were also subject to reduction. Specifically, we demonstrated that within 48 h of the cell line U937 being induced to differentiate along the monocytic pathway, CD43 mRNA levels were reduced by 69%. This decline coincided with a decrease in the activity of the CD43 gene promoter mediated by the single-stranded DNA binding protein Pur alpha. Previously, we have demonstrated that Pur alpha mediates induction of the CD11c beta 2 integrin promoter during U937 differentiation. Consequently, Pur alpha represents a potential means by which the induction of pro-adhesive molecules and the repression of anti-adhesive molecules is co-ordinated during leucocyte differentiation.

Antibody-induced shedding of CD44 from adherent cells is linked to the assembly of the cytoskeleton

CD44 is a widely expressed integral membrane glycoprotein that serves as a specific adhesion receptor for the extracellular matrix glycosaminoglycan hyaluronan. CD44 participates in a variety of physiological and pathological processes through its role in cell adhesion. Under appropriate conditions, the ectodomain of CD44 is proteolytically removed from the cell surface. In this study we show that excessive CD44 shedding can be induced in mouse fibroblasts and monocytes upon exposure of these cells to a CD44-specific Ab immobilized on plastic, whereas treatment with phorbol ester induces significantly enhanced CD44 release from the monocytes only. CD44 shedding proceeds normally in fibroblasts and monocytes deficient in TNF-alpha converting enzyme (TACE), a sheddase involved in the processing of several substrates. Conversely, activation of the CD44 protease has no effect on the release of TNF-alpha from TACE-expressing cells, although the same metalloprotease inhibitor effectively blocks both TACE and the CD44 sheddase. Concomitant with anti-CD44 Ab- or phorbol ester-induced CD44 shedding, dramatic changes are observed in cell morphology and the structure of the actin cytoskeleton. Disruption of actin assembly with cytochalasin reduces CD44 shedding, but not the release of TNF-alpha. Moreover, pharmacological activation of Rho family GTPases Rac1 and Cdc42, which regulate actin filament assembly into distinct cytoskeletal structures, has a profound effect on CD44 release. We conclude that the CD44 sheddase and TACE are distinct enzymes, and that Ab- and phorbol ester-enhanced cleavage of CD44 is controlled in a cell type-dependent fashion by Rho GTPases through the cytoskeleton.

Different proteolytic mechanisms involved in Fc gamma RIIIb shedding from human neutrophils

The Fc gamma receptor type IIIb (CD16) is highly expressed on human neutrophils and is found in a soluble form in plasma and in other body fluids. Upon activation of neutrophils in vitro, Fc gamma RIIIb is shed from the cell surface by proteolytic cleavage. We have now investigated the effect of metalloproteinase inhibitors and a serine proteinase inhibitor on the shedding of Fc gamma RIIIb induced by phorbol 12-myristate 13-acetate (PMA) or cytochalasin B (cyto B) + N-formyl-methionyl-leucyl-phenylalanine (fMLP). Metalloproteinase inhibitors blocked to a large extent PMA-induced, but not cyto B + fMLP-induced shedding of Fc gamma RIIIb. Inhibition of members of the ADAM (a disintegrin and metalloproteinase) family appeared most efficient. In contrast, the serine protease inhibitor N-methoxysuccinyl-alanine-alanine-proline-valine-chloromethylketone (MeOsuc-AAPV-CMK) largely blocked cyto B + fMLP-induced, but not PMA-induced shedding of Fc gamma RIIIb. Metalloproteinase inhibitors in combination with the serine proteinase inhibitor resulted in full inhibition of Fc gamma RIIIb shedding induced by either PMA or cyto B + fMLP. The shedding of Fc gamma RIIIb that accompanied apoptosis was inhibited by 60% in the presence of inhibitors of metalloproteinases but was insensitive to inhibition of serine proteinases. These results show that distinct types of proteolytic enzyme are involved in the stimulus-induced shedding of Fc gamma RIIIb from human neutrophils and suggest that these proteinases may become differentially activated under various physiological or pathological conditions.

Reduced CD43 expression on the neutrophils of MDS patients correlates with an activated phenotype of these cells

CD43 (also known as leukosialin and sialophorin) is a surface sialoglycoprotein expressed at high levels on most leukocytes implicated in adhesion, antiadhesion, and activation/proliferation mechanisms. We studied the expression of this molecule on the leukocytes of patients with myelodysplastic syndromes (MDSs) in an effort to detect acquired deficiencies of this molecule. We used immunofluorescence flow cytometry in analyzing whole blood and isolated neutrophils from 49 MDS patients, 33 men and 16 women aged 33 to 85 years (median, 75 years), and 18 healthy individuals aged 35 to 80 years (median, 72 years). According to French-American-British classification criteria, 13 patients had refractory anemia, 18 had refractory anemia with ringed sideroblasts, 9 had refractory anemia with excess of blasts, 4 had refractory anemia with excess of blasts in transformation to acute leukemia, and 5 had chronic myelomonocytic leukemia. We found decreased expression of CD43 on the neutrophils of these patients, and we correlated this finding with the activation status of these cells as it is defined by their phenotypes. We studied the expression of CD11b, CD18, CD35, CD67, CD69, CD44, and CD53 molecules known to be changed in the activated form of neutrophils. CD43 expression correlated positively with CD53 and CD44 expression and negatively with CD11b, CD18, CD35, CD67, and CD69 expression. Additionally, increased levels of soluble vascular cell adhesion molecules were detected in these patients, suggesting endothelial cell activation. In conclusion, we believe that the decreased expression of CD43 on the neutrophils of MDS patients is associated with activation of these cells and is probably due to cleavage of the molecule from the cell surface and that the same mechanism is possibly responsible for the parallel down-regulation of CD44 and CD53.

Myoepithelial-specific CD44 shedding is mediated by a putative chymotrypsin-like sheddase

Our previous studies have demonstrated that myoepithelial cells, which surround incipient carcinomas in situ of the breast and other organs, exert antiinvasive and antiangiogenic effects in vitro through the elaboration of a number of different suppressor molecules among which include the shed membrane CD44. The present study addresses the mechanism of this myoepithelial CD44 shedding. This CD44 shedding is enhanced by PMA pretreatment, is specific for myoepithelial CD44, and inhibited by chymotrypsin-like inhibitors (chymostatin, alpha(1)-antichymotrypsin, TPCK, and SCCA-2) but not by trypsin-like inhibitors (TLCK), nor papain-like inhibitors (SCCA-1) nor hydroxamate-based or general metalloproteinase inhibitors (BB2516 (marimastat), 1,10-phenanthroline, and TIMP-1). The effect of PMA can be mimicked by exogenous chymotrypsin but not by other proteases. The CD44 shedding activity cannot be transferred by conditioned media, cell-cell contact, peripheral membrane, or integral membrane fractions. However, cell-free purified integral plasma membrane fractions obtained from myoepithelial cells pretreated with PMA also exhibit CD44 shedding which is inhibited by chymotrypsin-like inhibitors. These findings support the presence and activation of a putative chymotrypsin-like sheddase as the mechanism of CD44 shedding in myoepithelial cells.

Identification of polymorphonuclear leukocyte and HL-60 cell receptors for adhesins of Streptococcus gordonii and Actinomyces naeslundii

Interactions of oral streptococci and actinomyces with polymorphonuclear leukocytes (PMNs), mediated by sialic acid- and Gal/GalNAc-reactive adhesins, respectively, result in activation of the PMNs and thereby may contribute to the initiation of oral inflammation. Sialidase treatment of PMNs or HL-60 cells abolished adhesion of Streptococcus gordonii but was required for adhesion of Actinomyces naeslundii. The same effects of sialidase were noted for adhesion of these bacteria to a major 150-kDa surface glycoprotein of either PMNs or undifferentiated HL-60 cells and to a 130-kDa surface glycoprotein of differentiated HL-60 cells. These glycoproteins were both identified as leukosialin (CD43) by immunoprecipitation with a specific monoclonal antibody (MAb). Adhesion of streptococci and actinomyces to a 200-kDa minor PMN surface glycoprotein was also detected by bacterial overlay of untreated and sialidase-treated nitrocellulose transfers, respectively. This glycoprotein was identified as leukocyte common antigen (CD45) by immunoprecipitation with a specific MAb. CD43 and CD45 both possess extracellular mucinlike domains in addition to intracellular domains that are implicated in signal transduction. Consequently, the interactions of streptococci and actinomyces with the mucinlike domains of these mammalian cell surface glycoproteins result not only in adhesion but, in addition, may represent the initial step in PMN activation by these bacteria.

CD43 gene expression is mediated by a nuclear factor which binds pyrimidine-rich single-stranded DNA

CD43 is a leukocyte-specific surface molecule which plays an important role both in adhesion and signal transduction. We have identified a site spanning nucleotides +18 to +39 within the human CD43 gene promoter which in vitro is hypersensitive to cleavage by nuclease S1. Repeats of this region are sufficient to activate expression of a heterologous promoter in CD43-positive cell lines. Two nuclear factors, PyRo1 and PyRo2, interact with the hypersensitive site. PyRo1 is a single-stranded DNA-binding protein which binds the pyrimidine-rich sense strand. Mutation analysis demonstrates that the motif TCCCCT is critical for PyRo1 interaction. Replacement of this motif with the sequence CATATA abolishes PyRo1 binding and reduces expression of the CD43 promoter by 35% in Jurkat T lymphocytic cells and by 52% in the pre-erythroid/pre-megakaryocytic cell line K562. However, this same replacement failed to affect expression in U937 monocytic cells or in CEM T lymphocytic cells. PyRo1, therefore, exhibits cell-specific differences in its functional activity. Further analysis demonstrated that PyRo1 not only interacts with the CD43 gene promoter but also motifs present within the promoters of the CD11a, CD11b, CD11c and CD11d genes. These genes encode the alpha subunits of the beta2 integrin family of leukocyte adhesion receptors. Deletion of the PyRo1 binding site within the CD11c gene reduced promoter activity in T lymphocytic cells by 47%. However, consistent with our analysis of the CD43 gene, the effect of this same deletion within U937 monocytic cells was less severe. That PyRo1 binds preferentially to single-stranded DNA and sequences within the CD43 and CD11 gene promoters suggests that expression of these genes is influenced by DNA secondary structure.

Polarization and interaction of adhesion molecules P-selectin glycoprotein ligand 1 and intercellular adhesion molecule 3 with moesin and ezrin in myeloid cells

In response to the chemoattractants interleukin 8, C5a,N-formyl-methionyl-leucyl-phenylalanine, and interleukin 15, adhesion molecules P-selectin glycoprotein ligand 1 (PSGL-1), intercellular adhesion molecule 3 (ICAM-3), CD43, and CD44 are redistributed to a newly formed uropod in human neutrophils. The adhesion molecules PSGL-1 and ICAM-3 were found to colocalize with the cytoskeletal protein moesin in the uropod of stimulated neutrophils. Interaction of PSGL-1 with moesin was shown in HL-60 cell lysates by isolating a complex with glutathione S-transferase fusions of the cytoplasmic domain of PSGL-1. Bands of 78- and 81-kd were identified as moesin and ezrin by Western blot analysis. ICAM-3 and moesin also coeluted from neutrophil lysates with an anti-ICAM-3 immunoaffinity assay. Direct interaction of the cytoplasmic domains of ICAM-3 and PSGL-1 with the amino-terminal domain of recombinant moesin was demonstrated by protein-protein binding assays. These results suggest that the redistribution of PSGL-1 and its association with intracellular molecules, including the ezrin-radixin-moesin actin-binding proteins, regulate functions mediated by PSGL-1 in leukocytes stimulated by chemoattractants.

Polarization and interaction of adhesion molecules P-selectin glycoprotein ligand 1 and intercellular adhesion molecule 3 with moesin and ezrin in myeloid cells

In response to the chemoattractants interleukin 8, C5a,N-formyl-methionyl-leucyl-phenylalanine, and interleukin 15, adhesion molecules P-selectin glycoprotein ligand 1 (PSGL-1), intercellular adhesion molecule 3 (ICAM-3), CD43, and CD44 are redistributed to a newly formed uropod in human neutrophils. The adhesion molecules PSGL-1 and ICAM-3 were found to colocalize with the cytoskeletal protein moesin in the uropod of stimulated neutrophils. Interaction of PSGL-1 with moesin was shown in HL-60 cell lysates by isolating a complex with glutathione S-transferase fusions of the cytoplasmic domain of PSGL-1. Bands of 78- and 81-kd were identified as moesin and ezrin by Western blot analysis. ICAM-3 and moesin also coeluted from neutrophil lysates with an anti-ICAM-3 immunoaffinity assay. Direct interaction of the cytoplasmic domains of ICAM-3 and PSGL-1 with the amino-terminal domain of recombinant moesin was demonstrated by protein-protein binding assays. These results suggest that the redistribution of PSGL-1 and its association with intracellular molecules, including the ezrin-radixin-moesin actin-binding proteins, regulate functions mediated by PSGL-1 in leukocytes stimulated by chemoattractants.

Human mast cells express the hyaluronic-acid-binding isoform of CD44 and adhere to hyaluronic acid

CD44 is expressed in various isoforms on multiple cell lineages including those of hematopoietic origin and is believed in part to mediate cell adhesion to hyaluronic acid. Elevated levels of soluble CD44 (sCD44) have been identified in the serum of some patients with specific neoplasms. We thus sought to determine whether human mast cells express functional CD44 and whether sCD44 might be associated with systemic mast cell disease. Using a standard assay, CD34(+)-derived cultured human mast cells were first demonstrated to adhere to hyaluronic-acid-coated surfaces. Human mast cells were then found by flow cytometry to express CD44S, but not the v5, v6, v7, and v8 isoforms, and to shed CD44S following activation induced by PMA or aggregation of FcvarepsilonRI. However, CD44S was not found to be consistently elevated in serum obtained from patients with mastocytosis or individuals experiencing anaphylaxis. Thus, human cultured mast cells express and shed CD44S, which appears to mediate the attachment of these cells to hyaluronic acid.

Identification and characterization of CD44RC, a novel alternatively spliced soluble CD44 isoform that can potentiate the hyaluronan binding activity of cell surface CD44

Soluble CD44 proteins generated by proteolytic cleavage or aberrant intron retention have been shown to antagonize the ligand binding activity of the corresponding cell surface receptor, inducing apoptosis and inhibiting tumor growth. Interestingly, such findings appear to contradict recent studies demonstrating a correlation between the presence of high levels of soluble CD44 in the serum of cancer patients and poor prognosis. In the present study, we report the cloning of a novel, naturally occurring, differentially expressed, soluble CD44 isoform, designated CD44RC, which, in contrast to previously described soluble CD44 proteins, can dramatically enhance the hyaluronan binding activity of cell surface CD44. Sequence analysis suggests that CD44RC is generated by an alternative splicing event in which the 3' end of CD44 exon 2 is spliced into an internal splice acceptor site present within exon 18, altering reading frame and giving rise to a soluble protein with a unique COOH terminus. Functional studies suggest that CD44RC enhances hyaluronan binding by adhering to chondroitin sulfate side-chains attached to cell surface CD44, generating a multivalent complex with increased avidity for hyaluronan.

Signaling Through CD43 Induces Natural Killer Cell Activation, Chemokine Release, and PYK-2 Activation

Natural killer (NK) cell activation is the result of a balance between positive and negative signals triggered by specific membrane receptors. We report here the activation of NK cells induced through the transmembrane glycoprotein CD43 (leukosialin, sialophorin). Engagement of CD43 by specific antibodies stimulated the secretion of the chemokines RANTES, macrophage inflammatory protein (MIP)-1, and MIP-1β, which was prevented by treatment of cells with the specific tyrosine kinase inhibitor genistein. Furthermore, signaling through CD43 increased the cytotoxic activity of NK cells and stimulated an increase in the tyrosine kinase activity in antiphosphotyrosine immune complexes of NK cell lysates. PYK-2 was identified among the tyrosine kinase proteins that become activated. Hence, PYK-2 activation was observed after 20 minutes of CD43 stimulation, reached a maximum after 45 to 60 minutes, and decreased to almost basal levels after 120 minutes of treatment. Together, these results demonstrate the role of CD43 as an activation molecule able to transduce positive activation signals in NK cells, including the regulation of chemokine synthesis, killing activity, and tyrosine kinase activation.

TNFalpha and IL-4 regulation of hyaluronan binding to monocyte CD44 involves posttranslational modification of CD44

Our previous studies have identified TNFalpha as a positive regulator and IL-4 as a negative regulator of human monocyte CD44-HA binding. In order to determine the mechanisms of IL-4- and TNFalpha-mediated regulation of monocyte HA binding, we measured HA binding and CD44 expression on peripheral blood monocytes following monocyte treatment with TNFalpha or IL-4, as well as following monocyte treatment with inhibitors of protein synthesis, N- and O-linked glycosylation, and chondroitin sulfation. IL-4 decreased CD44-HA binding on monocytes initially treated with TNFalpha. Similarly, pretreatment of monocytes with IL-4 prevented subsequent TNFalpha-mediated HA binding. Cycloheximide (protein synthesis inhibitor), tunicamycin (N-linked glycosylation inhibitor), and beta-d-xyloside (chondroitin sulfation inhibitor) all inhibited IL-4-mediated downregulation of TNFalpha-induced monocyte HA binding. Western blot analysis of CD44 from TNFalpha-treated monocytes revealed a 5-10 Mr decrease in the standard isoform of CD44. In contrast, IL-4 treatment of monocytes inhibited CD44-HA binding and reversed the 5- to 10-kDa decrease in monocyte CD44 Mr. Finally, studies with F10.44.2, a CD44 mab that enhances CD44-HA binding, indicated that IL-4 treatment of monocytes not only diminished constitutive HA binding, but also diminished CD44 mab-induced HA binding. Taken together, these data suggested that IL-4-mediated inhibition of TNFalpha-induced monocyte HA binding was dependent not only on protein synthesis, but also on N-linked glycosylation and chondroitin-sulfate modification of either CD44 or, alternatively, another monocyte protein(s) that may regulate the ability of CD44 to bind HA.

Serum CD44 in non-Hodgkin's lymphoma

CD44 molecule is a cell surface glycoprotein involved in several cell-cell and cell-matrix interactions. It has been linked to the growth and spread of malignancies. The majority of non-Hodgkin's lymphomas (NHL) express CD44 reflecting the CD44 expression of the normal lymphocytic counterparts. Cell surface CD44 has been suggested to be involved in hematogenous distribution of NHL, and elevated levels of serum CD44 (s-CD44) have been detected in various malignant diseases. Circulating s-CD44 has been found to be functionally active according to several functional studies. In patients with NHL increased s-CD44 levels have been detected at the time of diagnosis and at progression of the disease and s-CD44 levels change in parallel with response to therapy. Moreover, a high s-CD44 level at diagnosis is associated with a high tumor burden, poor response to treatment and unfavorable outcome in NHL.

CD43, a molecule with multiple functions

To initiate a specific immune response, lymphoid cells integrate a variety of signals generated through the orchestrated interaction of multiple cell surface molecules with their counter-receptors. As a result of the specific recognition of the antigen through antigen-specific receptors, and of the monitoring of their particular environment through the so-called coreceptor molecules, lymphoid cells go through elaborate processes of maturation and activation, contributing to the plasticity and sensitivity of immune response. CD43 is the major sialic acid rich protein on the surface of lymphocytes. However, the specific roles of this protein in different lymphoid cells under normal physiological conditions remain largely unknown. In this review we will mainly focus on the recent advances concerning the functions of this molecule as a coreceptor of different lymphoid cells as well as on the participation of this molecule in different pathologies.

Changes in neutrophil surface phenotype during hemodialysis

The initiation of hemodialysis using cuprophane membranes is followed by a rapid fall in the circulating neutrophil count. This neutropenia is caused by a transient sequestration of neutrophils in the lung due to homotypic aggregation, largely in response to generation of C5a by contact of plasma with the dialyzer. The transient nature of hemodialysis neutropenia is due to desensitization of neutrophils to stimulation by C5a, thus demonstrating desensitization in vivo. To examine the in vivo effects on surface phenotype of continuous exposure of neutrophils to C5a over 3 h, the surface expression of 22 antigens was examined by flow cytometry in patients undergoing dialysis. Neutropenia was prominent at 15 min and absent at 60 and 180 min of dialysis. CD10, CD11b, CD11c, CD13, CD18, CD35, CD45, CD66acde, and CD66b were upregulated at 15 min and remained upregulated at 180 min. CD61 and CD63 increased slightly at 15 min and returned to baseline by 180 min. CD16 and CD62L were down regulated at 15 min and normalized by 180 min. CD15s, CDw17, CD32, and CD44 were slightly down regulated at 15 min and then returned to baseline by 180 min. CD11a, CD15, CD24, CD31, and CDw65 did not change during dialysis. This study demonstrates the changes in surface phenotype of neutrophils during prolonged in vivo exposure to C5a over 3 h, during which time neutrophils become desensitized to subsequent stimulation by similar concentrations of C5a but maintain responsiveness to other chemotactic stimuli.

The glycosylphosphatidylinositol-anchored form and the transmembrane form of CD58 are released from the cell surface upon antibody binding

The adhesion molecule CD58 is expressed on the cell surface in both a transmembrane form and a glycosylphosphatidylinositol (GPI)-anchored form. Here we report that CD58 is released from JY cells following cross-linking by immobilized anti-CD58 monoclonal antibodies. Antibodies to other cell surface proteins, as well as PMA and LPS, did not trigger CD58 release. The release resulted from membrane cleavage, since biotin-labeled CD58 was released from biotinylated cells, and down-modulation of CD58 surface expression accompanied accumulation of soluble CD58 IN culture media. We have previously reported the isolation of JY variant cells, which lack expression of GPI anchored proteins and thus express only the transmembrane form of CD58. Here we show that these variant cells release CD58 upon crosslinking, indicating that the transmembrane isoform is released, probably by proteolysis. Antibodies directed to the cytoplasmic domain of CD58, in contrast to antibodies against an extracellular epitope of CD58, did not react with released CD58, supporting a membrane cleavage mechanism. It is also shown that CD58, released from [3H]ethanolamine-labeled JY cells, contained ethanolamine. This result demonstrated that the GPI-anchored CD58 can be released in parallel to the transmembrane isoform and that this release does not result from proteolytic cleavage, since cleavage by a protease would have removed the ethanolamine. The present data suggest that the two isoforms of CD58 are released upon antibody binding and that their release is mediated by distinct mechanisms.

Pentoxifylline Inhibits Adhesion and Activation of Human T Lymphocytes

We have herein studied the effect of pentoxifylline (PTX) on the adhesion and activation of human T lymphocytes. We found that PTX inhibited the adhesion of T cells to the β1 and β2 integrin ligands VCAM-1 and ICAM-1; this inhibitory activity was dose dependent, with a maximal effect from 12 to 24 h. We also found that PTX was able to interfere with the activation of β1 integrins induced by intracellular signals; however, the conformational change of β1 integrins induced by extracellular stimuli (e.g., activating mAbs, or Mn2+) was not significantly affected by this drug. In addition, the homotypic aggregation of T cells induced by anti-β1 and -β2 integrin chain mAbs was also inhibited by PTX. PTX had a significant inhibitory effect on the T lymphocyte expression of the activation Ags CD25 (IL-2Rα-chain), CD69 (activation-inducer molecule), and CD98 (4F2) induced by PHA. Accordingly, PTX also interfered with early cell activation events such as the rise in intracellular Ca2+ and the activation of the Na+/H+ antiporter induced by PHA and phorbol esters, respectively. Furthermore, this drug inhibited both the cell cycle progression and cell proliferation of T cells induced through the CD3/TCR complex. However, this drug did not show any effect on the cell activation/proliferation induced by PMA plus ionomycin. Our results indicate that PTX interferes efficiently with the activation and cell adhesion of human T lymphocytes. These effects may be of relevance for the clinical uses of this drug.

CD43 Interacts With Moesin and Ezrin and Regulates Its Redistribution to the Uropods of T Lymphocytes at the Cell-Cell Contacts

Chemokines as well as the signaling through the adhesion molecules intercellular adhesion molecule (ICAM)-3 and CD43 are able to induce in T lymphocytes their switching from a spherical to a polarized motile morphology, with the formation of a uropod at the rear of the cell. We investigated here the role of CD43 in the regulation of T-cell polarity, CD43-cytoskeletal interactions, and lymphocyte aggregation. Pro-activatory anti-CD43 monoclonal antibody (MoAb) induced polarization of T lymphocytes with redistribution of CD43 to the uropod and the CCR2 chemokine receptor to the leading edge of the cell. Immunofluorescence analysis showed that all three ezrin-radixin-moesin (ERM) actin-binding proteins localized in the uropod of both human T lymphoblasts stimulated with anti-CD43 MoAb and tumor-infiltrating T lymphocytes. Radixin localized at the uropod neck, whereas ezrin and moesin colocalized with CD43 in the uropod. Biochemical analyses showed that ezrin and moesin coimmunoprecipitated with CD43 in T lymphoblasts. Furthermore, in these cells, the CD43-associated moesin increased after stimulation through CD43. The interaction of moesin and ezrin with CD43 was specifically mediated by the cytoplasmic domain of CD43, as shown by precipitation of both ERM proteins with a GST-fusion protein containing the CD43 cytoplasmic tail. Videomicroscopy analysis of homotypic cell aggregation induced through CD43 showed that cellular uropods mediate cell-cell contacts and lymphocyte recruitment. Immunofluorescence microscopy performed in parallel showed that uropods enriched in CD43 and moesin localized at the cell-cell contact areas of cell aggregates. The polarization and homotypic cell aggregation induced through CD43 was prevented by butanedione monoxime, indicating the involvement of myosin cytoskeleton in these phenomena. Altogether, these data indicate that CD43 plays an important regulatory role in remodeling T-cell morphology, likely through its interaction with actin-binding proteins ezrin and moesin. In addition, the redistribution of CD43 to the uropod region of migrating lymphocytes and during the formation of cell aggregates together with the enhancing effect of anti-CD43 antibodies on lymphocyte cell recruitment suggest that CD43 plays a key role in the regulation of cell-cell interactions during lymphocyte traffic.

CD43 Interacts With Moesin and Ezrin and Regulates Its Redistribution to the Uropods of T Lymphocytes at the Cell-Cell Contacts

Chemokines as well as the signaling through the adhesion molecules intercellular adhesion molecule (ICAM)-3 and CD43 are able to induce in T lymphocytes their switching from a spherical to a polarized motile morphology, with the formation of a uropod at the rear of the cell. We investigated here the role of CD43 in the regulation of T-cell polarity, CD43-cytoskeletal interactions, and lymphocyte aggregation. Pro-activatory anti-CD43 monoclonal antibody (MoAb) induced polarization of T lymphocytes with redistribution of CD43 to the uropod and the CCR2 chemokine receptor to the leading edge of the cell. Immunofluorescence analysis showed that all three ezrin-radixin-moesin (ERM) actin-binding proteins localized in the uropod of both human T lymphoblasts stimulated with anti-CD43 MoAb and tumor-infiltrating T lymphocytes. Radixin localized at the uropod neck, whereas ezrin and moesin colocalized with CD43 in the uropod. Biochemical analyses showed that ezrin and moesin coimmunoprecipitated with CD43 in T lymphoblasts. Furthermore, in these cells, the CD43-associated moesin increased after stimulation through CD43. The interaction of moesin and ezrin with CD43 was specifically mediated by the cytoplasmic domain of CD43, as shown by precipitation of both ERM proteins with a GST-fusion protein containing the CD43 cytoplasmic tail. Videomicroscopy analysis of homotypic cell aggregation induced through CD43 showed that cellular uropods mediate cell-cell contacts and lymphocyte recruitment. Immunofluorescence microscopy performed in parallel showed that uropods enriched in CD43 and moesin localized at the cell-cell contact areas of cell aggregates. The polarization and homotypic cell aggregation induced through CD43 was prevented by butanedione monoxime, indicating the involvement of myosin cytoskeleton in these phenomena. Altogether, these data indicate that CD43 plays an important regulatory role in remodeling T-cell morphology, likely through its interaction with actin-binding proteins ezrin and moesin. In addition, the redistribution of CD43 to the uropod region of migrating lymphocytes and during the formation of cell aggregates together with the enhancing effect of anti-CD43 antibodies on lymphocyte cell recruitment suggest that CD43 plays a key role in the regulation of cell-cell interactions during lymphocyte traffic.

Role of two conserved glycine residues in the beta-propeller domain of the integrin alpha4 subunit in VLA-4 conformation and function

The N-terminal region of the alpha integrin subunits is predicted to fold into a beta-propeller domain. Using K562 alpha4 transfectants we show that mutations at alpha4 subunit residues Gly130 and Gly190 affect the conformation of this domain causing a reduction in the recognition of alpha4 by anti-alpha4 antibodies which map to the beta-propeller. The improper alpha4 conformation also led to an altered association with the beta1 subunit, and to a lack of alpha4beta1 adhesion to VCAM-1 and CS-1/fibronectin, as well as an abolishment of anti-alpha4- and anti-beta1-dependent homotypic aggregation. The total conservation of Gly130 and Gly190 among integrin alpha subunits suggests their importance in the correct folding of their respective beta-propeller domains, and thus, in the adhesive activity of the integrins.

CD44 and CD69 represent different types of cell-surface activation markers for human eosinophils

Eosinophils (EOS) purified from peripheral blood or late-phase bronchoalveolar lavage (BAL) were analyzed with 473 monoclonal antibodies (mAbs) from the Fifth International Workshop on Human Leukocyte Antigens in an attempt to identify markers of EOS activation. Two strategies were used: (1) to look for surface markers absent on fresh EOS but present after in vivo activation (e. g., in late-phase BAL fluid [BALF]) or after in vitro culture for up to 72 h with cytokines (<= 10 ng/ml of interleukin-3 [IL-3], IL-5, or granulocyte-macrophage colony-stimulating factor [GM-CSF]); and (2) to look for markers constitutively expressed on fresh EOS that were increased after activation in vivo or after culture in vitro. With indirect immunofluorescence and flow cytometry, the first approach revealed that among approximately 350 mAbs tested, only those recognizing CD69 became bound to late-phase BALF EOS or cytokine-cultured EOS, but not to fresh EOS. Using the second approach, we observed statistically significant concentration- and time-dependent increases in CD44 expression in EOS cultured with IL-3, IL-5, or GM-CSF (approximately 2-fold increase in fluorescence intensity, P < 0.05), but not with interferon-gamma (IFN-gamma) (up to 100 ng/ml), whereas levels of 15 other constitutively expressed markers were unchanged. Despite increased expression, neither fresh nor cytokine-cultured EOS adhered to immobilized hyaluronate, a ligand for CD44. Additionally, simultaneous comparison of hypodense (specific gravity < 1.085 g/liter) and normodense (specific gravity > 1.085 g/liter) EOS from allergic donors consistently revealed higher levels of CD44 expression (approximately 3- to 8-fold) but not CD69 expression on hypodense EOS. We conclude that CD69 and CD44 represent different types of activation markers for human EOS. These findings may be useful in assessing the state of EOS activation in vitro and in vivo.

A splice variant of CD44 expressed in the apical ectodermal ridge presents fibroblast growth factors to limb mesenchyme and is required for limb outgrowth

Signals from the apical ectodermal ridge (AER) of the developing vertebrate limb, including fibroblast growth factor-8 (FGF-8), can maintain limb mesenchymal cells in a proliferative state. We report here that a specific CD44 splice variant is crucial for the proliferation of these mesenchymal cells. Epitopes carried by this variant colocalize temporally and spatially with FGF-8 in the AER throughout early limb development. A splice variant containing the same sequences expressed on model cells binds both FGF-4 and FGF-8 and stimulates mesenchymal cells in vitro. When applied to the AER, an antibody against a specific CD44 epitope blocks FGF presentation and inhibits limb outgrowth. Therefore, CD44 is necessary for limb development and functions in a novel growth factor presentation mechanism likely relevant in other physiological and pathological situations where a cell surface protein presents a signaling molecule to a neighboring cell.

CD43 (sialophorin, leukosialin) shedding is an initial event during neutrophil migration, which could be closely related to the spreading of adherent cells

Leukosialin is a negatively-charged mucin-like membrane protein of leukocytes. This anti-adhesive molecule prevents uncontrolled cellular interactions and is proteolytically cleaved during neutrophil activation. CD43 is shed in vivo during neutrophil migration to the inflammatory site. We have analysed the decrease in CD43 expression during in vitro adherence of TNF-alpha activated PMN. CD43 was quantitated by flow cytometry on TNF-alpha-activated PMN either maintained in suspension or allowed to adhere then detached with EDTA. Although TNF did not induce significant modification of CD43 expression on suspended cells, we showed that 40% of membrane CD43 is released during neutrophil TNF-induced adhesion to serum-coated plates or endothelial cells, and that migration through the endothelial monolayer did not result in further shedding. Adhesion-blocking anti-beta 2 integrin mAbs prevented CD43 shedding. beta 2 integrin "activation" by anti-CD 18 mAbs or Mn ions did not decrease CD43 expression if adhesion was prevented by stirring. Inhibitors of signal transduction or of cytoskeleton association, which allowed cells to adhere but not to spread, inhibited the shedding of CD43 during adhesion. We conclude that CD43 shedding is not promoted by beta 2 integrins engagement or adhesion but is concomitant with spreading of adherent cells.

Signal transduction via CD43 (leukosialin, sialophorin) and associated biological effects in human mast cell line (HMC-1)

CD43 has been shown to be involved in the regulation of cellular adhesion and activation of leukocytes, but its functional significance for mast cell biology has been poorly defined. We demonstrate here that mAb engagement of surface CD43 on human leukemic (HMC-1) mast cells initiates a signaling cascade which involves protein kinase C, while tyrosine kinases appear to play a minor role, as evidenced by effects of different kinase inhibitors on homotypic aggregation induced via CD43. Furthermore, administration of an activating anti-CD43 mAb is shown to induce and promote TNF-alpha- and to enhance IL-8-secretion from HMC-1 cells, but it does not initiate histamine, tryptase, or LTC4 release, suggesting that the intracellular pathways leading to aggregation and release of certain mast cell mediators are differentially regulated. Additionally, engagement of CD43 on HMC-1 cells leads to down-regulation of CD43 surface expression, implying that CD43 may be potentially involved in its own regulation.

A novel region of the alpha4 integrin subunit with a modulatory role in VLA-4-mediated cell adhesion to fibronectin

The integrin VLA-4 (alpha4 beta1) is a receptor for fibronectin and vascular cell-adhesion molecule 1 (VCAM-1). Four functionally different epitopes, designated A, B1, B2 and C, have previously been defined on the alpha4 subunit. Using K562 alpha4 mutant transfectants we found that alpha4 amino acids Tyr151, Gln152, Asp153, Tyr154 and Val155 are important for the structure of the epitope B2. Mutations at alpha4 Gln152 substantially impaired the transfectant adhesion to a CS-1-containing fragment of fibronectin (FN-H89), whereas this adhesion was not affected on the other alpha4 mutant transfectants. None of the alpha4 mutations significantly altered the adhesion of the different alpha4 transfectants to VCAM-1. In addition, we have identified residues Gln152, Asp153 and Tyr154 as part of the alpha4 epitope B2 involved in homotypic cell aggregation. The decrease in adhesion to FN-H89 shown by Gln152 alpha4 mutant transfectants was the result of an inefficient binding of FN-H89 by VLA-4 mutated at this residue. Also, mutant VLA-4 displayed an altered reactivity with HUTS-21, an anti-beta1 monoclonal antibody that reacts with functionally active VLA integrins. Adhesion to FN-H89 was not restored unless stimuli that increase the ligand-binding affinity of VLA heterodimers were added, suggesting that cell adhesion was affected in the initial phases. These results indicate that alpha4 Gln152 modulates cell adhesion to FN-H89 by playing important roles in the maintenance and/or the acquisition of an active state of VLA-4, an integrin that is normally expressed on the cell surface in a range of multiple activation states. The location of the alpha4 Gln152 residue on a loop of the upper surface of the proposed beta-propeller structure suggests a close association with potential ligand-binding sites.

Moesin interacts with the cytoplasmic region of intercellular adhesion molecule-3 and is redistributed to the uropod of T lymphocytes during cell polarization

During activation, T lymphocytes become motile cells, switching from a spherical to a polarized shape. Chemokines and other chemotactic cytokines induce lymphocyte polarization with the formation of a uropod in the rear pole, where the adhesion receptors intercellular adhesion molecule-1 (ICAM-1), ICAM-3, and CD44 redistribute. We have investigated membrane-cytoskeleton interactions that play a key role in the redistribution of adhesion receptors to the uropod. Immunofluorescence analysis showed that the ERM proteins radixin and moesin localized to the uropod of human T lymphoblasts treated with the chemokine RANTES (regulated on activation, normal T cell expressed, and secreted), a polarization-inducing agent; radixin colocalized with arrays of myosin II at the neck of the uropods, whereas moesin decorated the most distal part of the uropod and colocalized with ICAM-1, ICAM-3, and CD44 molecules. Two other cytoskeletal proteins, beta-actin and alpha-tubulin, clustered at the cell leading edge and uropod, respectively, of polarized lymphocytes. Biochemical analysis showed that moesin coimmunoprecipitates with ICAM-3 in T lymphoblasts stimulated with either RANTES or the polarization- inducing anti-ICAM-3 HP2/19 mAb, as well as in the constitutively polarized T cell line HSB-2. In addition, moesin is associated with CD44, but not with ICAM-1, in polarized T lymphocytes. A correlation between the degree of moesin-ICAM-3 interaction and cell polarization was found as determined by immunofluorescence and immunoprecipitation analysis done in parallel. The moesin-ICAM-3 interaction was specifically mediated by the cytoplasmic domain of ICAM-3 as revealed by precipitation of moesin with a GST fusion protein containing the ICAM-3 cytoplasmic tail from metabolically labeled Jurkat T cell lysates. The interaction of moesin with ICAM-3 was greatly diminished when RANTES-stimulated T lymphoblasts were pretreated with the myosin-disrupting drug butanedione monoxime, which prevents lymphocyte polarization. Altogether, these data indicate that moesin interacts with ICAM-3 and CD44 adhesion molecules in uropods of polarized T cells; these data also suggest that these interactions participate in the formation of links between membrane receptors and the cytoskeleton, thereby regulating morphological changes during cell locomotion.

Expression of mouse CD43 in the B cell lineage of transgenic mice causes impaired immune responses to T-independent antigens

CD43 (leukosialin), a sialylated glycoprotein expressed on the surface of most hematopoietic cells, has been implicated in cell adhesion and signaling. However, its precise physiological function remains unclear. We used mouse CD43 (mCD43)-immunoglobulin enhancer-transgenic (TG) mice to study the role of mCD43 in vivo. Previous work revealed that mCD43 expression on mature B cells in these mice resulted in immunodeficiency to T-dependent (TD) antigens (Ag), possibly by impairing B-T cell interactions. In the present study we have immunized the TG mice with the T-independent (TI) Ag fluorescein-(Fl) lipopolysaccharide (LPS) (TI type 1 Ag) and Fl-Ficoll (TI type 2 Ag). Surprisingly, the mCD43-Ig enhancer expressing mice were impaired in their ability to mount humoral responses to both Fl-LPS and Fl-Ficoll, and had decreased numbers of cells responding to Ag in vivo. Flow cytometric analysis was performed on peritoneal B-1 cells, a population which often plays a major role in humoral responses to TI Ag such as bacterial Ag. This analysis revealed similar B220, IgM and CD5 expression patterns for the TG and nontransgenic (NTG) B-1 cells. In addition, purified peritoneal B-1 cells from TG and NTG mice were able to respond to LPS. Stimulation of splenic B cells in vitro with Fl-LPS and Fl-Ficoll revealed that, in contrast to NTG B cell responses, TG B cell responses could not be enhanced by co-culture with T cells. However, soluble T cell factor enhancement of the TG B cell responses was normal. These data suggest that the mCD43 expression on B cells may inhibit cell interactions that are important for enhanced TI Ag responses. The anti-adhesive forces of mucins in general may thus be critical in regulating both TD and TI humoral responses.

Leukosialin (CD43) is proteolytically cleaved from stimulated HMC-1 cells

Leukosialin (CD43), the major sialoprotein on circulating leukocytes, has been previously described to be down-regulated on neutrophils following activation with phorbol myristate acetate (PMA). The other single cells previously examined, blood lymphocytes, do not down-regulate CD43 when stimulated by PMA. Recently, we have characterized leukosialin on the human mast cell line HMC-1 and observed that leukosialin is down-regulated after stimulation with PMA. In the present study, we have investigated the mechanism of PMA-mediated down-regulation of CD43 on HMC-1 cells (subclone 5C6). PMA caused the release of soluble leukosialin (123 kD) during HMC-1 cell activation. The molecular weight of soluble leukosialin was nearly identical to that of the cell-membrane bound molecule, suggesting a cleavage proximal from the cell membrane. Inhibitors of serine proteases, like phenylmethylsulphonyl fluoride (PMSF), benzamidine and 3, 4-dichloroisocoumarin, blocked the PMA-mediated cleavage of CD43. In all experiments, the inhibition of CD43-down-regulation was dependent on the concentration of protease inhibitors. Treatment of HMC-1 cells with various proteases (trypsin, alpha-chymotrypsin, elastase, papain, nagarse) substantially decreased anti-CD43 binding capacity and caused the release of soluble leukosialin (116 kD) or its fragments into the supernatant. Pretreatment of HMC-1 cells with neuraminidases from Vibrio cholerae or Arthrobacter ureafaciens resulted in an increased sensitivity of CD43 against proteases, whereas the effects of PMA were not influenced. In conclusion, proteolytic cleavage of CD43 is described for the first time in a cell other than neutrophils, namely HMC-1 cells. Our results suggest that serine proteases are involved in the PMA-mediated down-regulation of leukosialin on HMC-1 cells.