The hyaluronate receptor is associated with actin filaments

Novel evaluation of the expression patterns CD44 and MMP9 proteins in intracranial meningiomas and their relationship to the overall survival

Background

Meningiomas are common primary brain neoplasms. CD44 is a cell surface glycoprotein receptor that is involved in matrix-mediated cell signaling and cell–matrix adhesion. Matrix metalloproteinase-9 (MMP-9) plays important role in angiogenesis and tumor invasion. The expression of CD44 protein membranous and cytoplasmic (CD44M and CD44C) has been reported in several tumors (such as lobular carcinoma, renal cell carcinoma, sinonasal melanoma, and lymphoma) except CNS tumors.

Methods

This study addressed the expression of CD44M and CD44C and MMP9 proteins in intracranial meningiomas and their relationship to overall survival. The expression patterns of CD44M&C and MMP-9 proteins were examined in 32 cases of benign meningiomas, 12 cases of atypical meningiomas, and 6 cases of anaplastic meningiomas using immunohistochemical staining methods.

Results

There was more evidence of CD44M expression in atypical and anaplastic meningioma (p =  < 0.001). Interestingly, Spearman correlation analyses revealed significant positive correlation between CD44M and MMP9 protein (r = 0.572, p =  < 0.001) in spite of the negative correlation between MMP9 and CD44 score (r = − 0.035 p = 0.405). There was a significant association between Ki67 protein expression and the grade of meningiomas (p < 0.001) and gender (p = 0.026). There was a significant correlation between overall survival (OS) and age, gender, tumor grade, and Ki-67.

Conclusions

Extensive CD44M expression in high-grade meningioma may reflect a tendency toward more invasive power of meningioma cells into surrounding structures (dura, bone, and brain).CD44M/MMP-9 axis presented by this study is open for future investigations.

Hyaluronan Controls the Deposition of Fibronectin and Collagen and Modulates TGF-β1 Induction of Lung Myofibroblasts

The contribution of hyaluronan-dependent pericellular matrix to TGF-β1-driven induction and maintenance of myofibroblasts is not understood. Hyaluronan is an extracellular matrix (ECM) glycosaminoglycan important in cell adhesion, proliferation and migration, and is implicated in myofibroblast formation and maintenance. Reduced turnover of hyaluronan has been linked to differentiation of myofibroblasts and potentiation of lung fibrosis. Fibronectin is a fibril forming adhesive glycoprotein that is also upregulated following induction with TGF-β1. Although they are known to bind each other, the interplay between hyaluronan and fibronectin in the pericellular matrix during myofibroblast induction and matrix assembly is not clear. This study addresses the role of hyaluronan and its interaction with fibrillar matrix components during myofibroblast formation. Hyaluronan and fibronectin were increased and co-localized in the ECM following myofibroblast induction by TGF-β1. Inhibition of hyaluronan synthesis in TGF-β1-induced lung myofibroblasts over a 4day period with 4-methyl umbelliferone (4-MU) further enhanced myofibroblast morphology, caused increased deposition of fibronectin and type I collagen in the ECM, and increased expression of alpha-smooth muscle actin and hyaluronan synthase 2 (HAS2) mRNA. Hyaluronan oligosaccharides or hyaluronidase treatment, which more effectively disrupted the pericellular matrix, had similar effects. CD44 and β1 integrins co-localized in the cell membrane and along some stress fibers. However, CD44 and hyaluronan were specifically excluded from focal adhesions, and associated primarily with cortical actin. Time-lapse imaging of the immediate effects of hyaluronidase digestion showed that hyaluronan matrix primarily mediates attachment of membrane and cortical actin between focal contacts, suggesting that surface adhesion through hyaluronan and CD44 is distinct from focal adhesion through β1 integrins and fibronectin. Fluorescein-labeled hyaluronan bound regularly along fibronectin fibers and co-localized more with β1 integrin and less with CD44. Therefore, the hyaluronan matrix can interfere with the assembly of fibrillar ECM components, and this interplay regulates the degree of myofibroblast formation. These data also suggest that adhesion through hyaluronan matrix impacts cytoskeletal organization, and is potentially part of a clutch mechanism that regulates stick and slip of myofibroblasts by affecting the adhesion to and organization of fibronectin and collagen.

Contribution of the cytoskeleton to the compressive properties and recovery behavior of single cells

The cytoskeleton is known to play an important role in the biomechanical nature and structure of cells, but its particular function in compressive characteristics has not yet been fully examined. This study focused on the contribution of the main three cytoskeletal elements to the bulk compressive stiffness (as measured by the compressive modulus), volumetric or apparent compressibility changes (as further indicated by apparent Poisson's ratio), and recovery behavior of individual chondrocytes. Before mechanical testing, cytochalasin D, acrylamide, or colchicine was used to disrupt actin microfilaments, intermediate filaments, or microtubules, respectively. Cells were subjected to a range of compressive strains and allowed to recover to equilibrium. Analysis of the video recording for each mechanical event yielded relevant compressive properties and recovery characteristics related to the specific cytoskeletal disrupting agent and as a function of applied axial strain. Inhibition of actin microfilaments had the greatest effect on bulk compressive stiffness ( approximately 50% decrease compared to control). Meanwhile, intermediate filaments and microtubules were each found to play an integral role in either the diminution (compressibility) or retention (incompressibility) of original cell volume during compression. In addition, microtubule disruption had the largest effect on the "critical strain threshold" in cellular mechanical behavior (33% decrease compared to control), as well as the characteristic time for recovery ( approximately 100% increase compared to control). Elucidating the role of the cytoskeleton in the compressive biomechanical behavior of single cells is an important step toward understanding the basis of mechanotransduction and the etiology of cellular disease processes.

Attachment of osteocyte cell processes to the bone matrix

In order for osteocytes to perceive mechanical information and regulate bone remodeling accordingly they must be anchored to their extracellular matrix (ECM). To date the nature of this attachment is not understood. Osteocytes are embedded in mineralized bone matrix, but maintain a pericellular space (50-80 nm) to facilitate fluid flow and transport of metabolites. This provides a spatial limit for their attachment to bone matrix. Integrins are cell adhesion proteins that may play a role in osteocyte attachment. However, integrin attachments require proximity between the ECM, cell membrane, and cytoskeleton, which conflicts with the osteocytes requirement for a pericellular fluid space. In this study, we hypothesize that the challenge for osteocytes to attach to surrounding bone matrix, while also maintaining fluid-filled pericellular space, requires different "engineering" solutions than in other tissues that are not similarly constrained. Using novel rapid fixation techniques, to improve cell membrane and matrix protein preservation, and transmission electron microscopy, the attachment of osteocyte processes to their canalicular boundaries are quantified. We report that the canalicular wall is wave-like with periodic conical protrusions extending into the pericellular space. By immunohistochemistry we identify that the integrin alphavbeta3 may play a role in attachment at these complexes; a punctate pattern of staining of beta3 along the canalicular wall was consistent with observations of periodic protrusions extending into the pericellular space. We propose that during osteocyte attachment the pericellular space is periodically interrupted by underlying collagen fibrils that attach directly to the cell process membrane via integrin-attachments.

The interaction of hyaluronate with the cell surface: the hyaluronate receptor and the core protein

Two distinct mechanisms are discussed by which hyaluronate interacts with the surfaces of cells: first, through a receptor which binds to hyaluronate with high affinity; and second, through a hydrophobic protein which is covalently linked to hyaluronate. The hyaluronate receptor is a transmembrane glycoprotein of Mr 85,000 which appears to interact with actin filaments of the cytoskeleton. It recognizes a sequence of six sugar residues of hyaluronate and also binds to chondroitin sulphate with a lower affinity. On the cell surface the receptors bind hyaluronate in cooperative fashion whereby two or more receptors can bind to the same molecule of hyaluronate, resulting in a high affinity. Immunohistochemical staining with a monoclonal antibody to the receptor indicates that it is present on epithelia, macrophages and other mononuclear phagocytes as well as some type of neurons. In epithelia the receptors presumably help to mediate cell attachment to the basement membrane which is often rich in hyaluronate. The receptor also appears to be preferentially expressed on proliferating epithelial cells and may serve as a marker for some types of carcinomas. Macrophages and related cells also have large amounts of the receptor, where it may serve in cell migration and/or in the homing of the cells to certain types of tissues. Recent studies have suggested that cell surface hyaluronate is covalently attached to a membrane-associated core protein. First, if cultured rat fibrosarcoma cells are fixed with glutaraldehyde the cell surface hyaluronate remains associated with the cells even under conditions expected to break non-covalent bonds. Second, when cell surface hyaluronate is partitioned with Triton X-114 a significant fraction is recovered in the hydrophobic phase, suggesting attachment to a hydrophobic protein. And finally, the binding of cell surface hyaluronate to nitrocellulose appears to be mediated through a covalent linkage to a protein.

The role of a cell-associated hyaluronan-binding protein in fibroblast behaviour

In a model culture system hyaluronan has been shown to promote cell ruffling and random cell locomotion. At the same time it promotes both protein tyrosine phosphorylation and phospholipid breakdown. These results indicate that this glycosaminoglycan, in addition to its previously described role as a regulator of adhesion and cytoskeletal organization, may also influence cell behaviour via second messenger formation. A cell-associated hyaluronan-binding protein (cell-HABP) has been isolated from locomoting fibroblasts that may represent one binding site that transduces these effects of hyaluronan. This protein is concentrated in the lamellae and ruffles of migrating fibroblasts but is lost from the cell surface as cell locomotion slows. It is a large (molecular mass estimated at 1-2 x 10(6) daltons) complex of proteins that includes a hyaluronan-binding site and a protein kinase. The protein kinase is responsive to hyaluronan and is related, antigenically, to the pp60src protein kinase. The function of cell-HABP has not been characterized but its location, regulated distribution and enzyme characteristics suggest that it may be involved in hyaluronan-regulated cell locomotion.

Hyaluronate-cell interactions and growth factor regulation of hyaluronate synthesis during limb development

Hyaluronate is a major component of the intercellular matrix surrounding proliferating and migrating cells in embryonic tissues. When placed in culture, mesodermal cells from the early, proliferative stages of limb development produce high levels of hyaluronate and exhibit prominent hyaluronate-dependent pericellular coats. Cells from the subsequent stages of mesodermal condensation that precede differentiation to cartilage and muscle produce less hyaluronate and do not exhibit these coats. Also at this time, binding sites specific for hyaluronate appear on the surface of the mesodermal cells. These binding sites may participate in the mechanism of condensation by mediating cell aggregation and the endocytosis of hyaluronate. Further changes in hyaluronate-cell interaction occur during differentiation of the condensed mesoderm to cartilage and muscle. Hyaluronate synthesis and pericellular coat formation in the mesoderm are stimulated by a factor, related to transforming growth factor-beta, that is produced by the surrounding ectoderm. The early limb also contains high levels of basic fibroblast growth factor. Its concentration is highest at the earliest stages, when cell proliferation and hyaluronate synthesis are prominent activities, and this factor has been shown to stimulate both these activities in cultures of limb mesodermal cells. Thus fibroblast growth factor and transforming growth factor-beta may be important in the regulation of early growth and morphogenesis of the limb.

PKC-induced stiffening of hyaluronan/CD44 linkage; local force measurements on glioma cells

Interaction of cells with hyaluronan (HA) rich extracellular matrix involves the membrane receptor CD44. HA-CD44 interactions are particularly important in the development of glioma pathogenesis for its implication in tumor cells spreading. Highly motile states rely on the spaciotemporal regulation of HA-CD44 interactions occurring in specific cytoskeletal-supported membrane organization such as microvilli or the leading edge observed in migrating cell. We used AFM-based force measurement to probe the HA-CD44 interaction at localized regions at the surface of living glioma cells expressing high level of the CD44 standard isoform. We show that unstimulated cells interact with HA over their entire surfaces and are highly deformable when force is exerted on individual HA molecules bound to membrane CD44 receptors. Conversely, in PKC-activated cells the probed interactions are concentrated at the leading edge of the cells with reduced membrane deformability. Taken together, our results show that PKC-enhanced motility in glioma cells is associated with a redistribution of CD44 receptors at the leading edges concomitant with a stiffer anchoring of CD44 to the cell surface involving the actin cytoskeleton.

Bench-to-bedside review: the role of glycosaminoglycans in respiratory disease

The extracellular matrix (ECM) plays a significant role in the mechanical behaviour of the lung parenchyma. The ECM is composed of a three-dimensional fibre mesh that is filled with various macromolecules, among which are the glycosaminoglycans (GAGs). GAGs are long, linear and highly charged heterogeneous polysaccharides that are composed of a variable number of repeating disaccharide units. There are two main types of GAGs: nonsulphated GAG (hyaluronic acid) and sulphated GAGs (heparan sulphate and heparin, chondroitin sulphate, dermatan sulphate, and keratan sulphate). With the exception of hyaluronic acid, GAGs are usually covalently attached to a protein core, forming an overall structure that is referred to as proteoglycan. In the lungs, GAGs are distributed in the interstitium, in the sub-epithelial tissue and bronchial walls, and in airway secretions. GAGs have important functions in lung ECM: they regulate hydration and water homeostasis; they maintain structure and function; they modulate the inflammatory response; and they influence tissue repair and remodelling. Given the great diversity of GAG structures and the evidence that GAGs may have a protective effect against injury in various respiratory diseases, an understanding of changes in GAG expression that occur in disease may lead to opportunities to develop innovative and selective therapies in the future.

Expression of proteins associated with cell-matrix adhesion in proliferative vitreoretinopathy designed by Dispase model

PURPOSE

During recent years, the interaction of cell surface molecule, extracellular matrix proteins, and cytoskeletal elements has been a topic for research for the purpose of understanding the mechanisms of pathologic conditions. This study aims to evaluate the expression of CD44, as a cell surface adhesion molecule; fibronectin (FN), as an extracellular and a cell surface protein; vinculin and actin/á-smooth muscle actin (alfa-SMA), as cytoskeletal elements; and the interactions of these proteins in the microenvironment of proliferative vitreoretinopathy (PVR).

METHODS

This experimental study was designed by the intravitreal Dispase model in rabbits and proteins' expression were evaluated via immunohistochemical staining.

RESULTS

As a cell surface protein, CD44 expression was determined in only four eyes focally and weakly, but in a small number of cells. Among the cytoskeletal proteins, vinculin expression was the most extensive and the strongest in intensity in epi- and subretinal membranes. Alpha-SMA expression was mostly present within small foci of cells. Fibronectin expression was determined in some of the eyes only faintly.

CONCLUSIONS

Vinculin seems to be involved in PVR pathogenesis. Variability in co-distribution of the expression of vinculin, FN, and alfa-SMA reflects the dynamic interactions evolving between cell and extracellular matrix during the epi- and subretinal membrane formations. The results of this study were determined not to be in support of the assumption that CD44 has a functional role in the pathogenesis of PVR.

CD44 in cancer progression: adhesion, migration and growth regulation

It is well established that the large array of functions that a tumour cell has to fulfil to settle as a metastasis in a distant organ requires cooperative activities between the tumour and the surrounding tissue and that several classes of molecules are involved, such as cell-cell and cell-matrix adhesion molecules and matrix degrading enzymes, to name only a few. Furthermore, metastasis formation requires concerted activities between tumour cells and surrounding cells as well as matrix elements and possibly concerted activities between individual molecules of the tumour cell itself. Adhesion molecules have originally been thought to be essential for the formation of multicellular organisms and to tether cells to the extracellular matrix or to neighbouring cells. CD44 transmembrane glycoproteins belong to the families of adhesion molecules and have originally been described to mediate lymphocyte homing to peripheral lymphoid tissues. It was soon recognized that the molecules, under selective conditions, may suffice to initiate metastatic spread of tumour cells. The question remained as to how a single adhesion molecule can fulfil that task. This review outlines that adhesion is by no means a passive task. Rather, ligand binding, as exemplified for CD44 and other similar adhesion molecules, initiates a cascade of events that can be started by adherence to the extracellular matrix. This leads to activation of the molecule itself, binding to additional ligands, such as growth factors and matrix degrading enzymes, complex formation with additional transmembrane molecules and association with cytoskeletal elements and signal transducing molecules. Thus, through the interplay of CD44 with its ligands and associating molecules CD44 modulates adhesiveness, motility, matrix degradation, proliferation and cell survival, features that together may well allow a tumour cell to proceed through all steps of the metastatic cascade.

Interaction of cortactin and Arp2/3 complex is required for sphingosine-1-phosphate-induced endothelial cell remodeling

Sphingosine-1-phosphate (S1P) induces capillary formation of endothelial cells on Matrigel in accompany with actin assembly and accumulation of cortactin and Arp2/3 complex at the cell-leading edge. Suppression of cortactin expression with a cortactin antisense oligo significantly impaired S1P-induced capillary formation, migration of endothelial cells, and actin assembly at the cell periphery. Overexpression of wild-type cortactin tagged by green fluorescent protein (GFP) increased the S1P-induced tube formation and cell motility, whereas the cells overexpressing the mutant formed poorly capillary network and became less motile in response to S1P. Analysis of distribution in Triton X-100 insoluble fractions demonstrated that the cortactin mutant inhibited the association of wild-type cortactin and Arp2/3 complex with the actin-enriched complex. Furthermore, actin polymerization at and distribution of Arp2/3 complex as well as endogenous cortactin into the cell-leading edge mediated by S1P was disturbed. These data suggest that the interaction between cortactin and Arp2/3 complex plays an important role in S1P-mediated remodeling of endothelial cells.

Effects of Hyaluronic Acid on the Polymorphonuclear Leukocyte (PMN) Release of Active Oxygen and Protection of Bovine Corneal Endothelial Cells from Activated PMNs

The goal of this study was to evaluate the function of hyaluronic acid (HA) on the active oxygen release from polymorphonuclear leukocytes (PMNs) and the protective effect of bovine corneal endothelial cells (BCEC) from activated PMNs. We used HA with three different molecular weights (MW 700,000, 2,000,000, and 4,000,000) and five different concentrations (0, 0.1, 1, 2, and 3 mg/ml). We evaluated the amount of released superoxide from activated PMNs by using dismutase-inhibitable ferricytochrome C reduction. To compare the property and protective effect of HA with those of other viscoelastic substances, we used the same concentration of methylcellulose. HA suppressed superoxide release from PMNs and protected BCEC from activated PMNs in a dose-dependent, rather than a molecular weight-dependent, manner. The effect of HA reached almost a plateau at concentration above 2 mg/ml. However, methylcellulose, another viscoelastic substance, showed a similar effect. Therefore, it seems that the suppression of superoxide released from PMNs is not a property that is unique to HA, but is a general property of viscoelastic substances. Our results indicate that the action mechanism of HA proceeds not only through cell surface HA-receptor. We think that HA also acts as a physical barrier and/or a scavenger of superoxide.

Regulation of proximal tubular epithelial cell CD44-mediated binding and internalisation of hyaluronan

BACKGROUND

Increased expression of the connective tissue polysaccharide hyaluronan (HA) in the renal corticointerstitium is associated with progressive renal fibrosis. Numerous studies have demonstrated involvement proximal tubular epithelial cells in the fibrotic process and in the current study we have characterised their expression of the HA receptor, CD44, and examined changes in CD44 expression and function in response to either IL-1beta or glucose.

METHODS

Characterisation of CD44 splice variant expression was carried out in primary cultures of human proximal tubular cells (PTC) and HK2 cells. Binding and internalisation HA was examined by addition of exogenous of fluorescein-HA (fl-HA), and expression of CD44 examined by immunoblot analysis and flow cytometry. Alteration in "functional" CD44 was determined by immunoprecipitation of CD44 following stimulation in the presence of fl-HA.

RESULTS

PTC, both primary culture and the PTC cell line, HK2, express at least 5 CD44 splice variants, the expression of which are not altered by addition of either IL-1beta or 25mM D-glucose. Addition of either stimulus increased cell surface binding and internalisation of fl-HA and increased expression of functionally active CD44. Increased binding and internalisation of fl-HA, was blocked by anti-CD44 antibody, and by the inhibition of O-glycosylation.

CONCLUSIONS

The data demonstrate that stimuli inducing PTC HA synthesis also regulate PTC-HA interactions. Furthermore increased HA binding and internalisation is the result of post-translational modification of CD44 by O-glycosylation, rather than by alteration in expression of CD44 at the cell surface, or by alternate use of CD44 splice variants.

The role of the CD44/ezrin complex in cancer metastasis

CD44 is a cell adhesion molecule that was traditionally known as 'homing receptor'. This molecule is known to interact with the ezrin family (ERM family) members and form a complex that plays diverse roles within both normal and abnormal cells, particularly cancer cells. CD44 and ezrin and their respective complex have properties suggesting that they may be important in the process of tumour-endothelium interactions, cell migrations, cell adhesion, tumour progression and metastasis. This article reviews the role of CD44, ezrin family and the CD44/ezrin complex in cancer cells and their clinical impact in patients with cancer.

E-cadherin negatively regulates CD44-hyaluronan interaction and CD44-mediated tumor invasion and branching morphogenesis

CD44 is a principal cell-surface receptor for hyaluronan (HA). Up-regulation of CD44 is often associated with morphogenesis and tumor invasion. On the contrary, reduction of cell-cell adhesion due to down-regulation of E-cadherin is associated with the invasive and metastatic phenotype of carcinomas. In our current study, we investigated the functional relationship between CD44 and E-cadherin. We established an inverse correlation between CD44 and E-cadherin indicating that the cells expressing higher levels of E-cadherin display weaker binding affinity between CD44 and HA. By using TA3 murine mammary carcinoma (TA3) cells, which display CD44-dependent HA binding, branching morphogenesis, and invasion, we demonstrated an inverse functional relationship between CD44 and E-cadherin by transfecting exogenous E-cadherin into the cells. Our results showed that increased expression of E-cadherin in TA3 cells, but not ICAM-1, weakens the binding between CD44 and HA and blocks spreading of the cells on HA substratum and CD44-mediated branching morphogenesis and tumor cell invasion. The results reported here demonstrated for the first time that E-cadherin negatively regulated CD44-HA interaction and CD44 function and suggested that balanced function of CD44 and E-cadherin may be essential for normal epithelial cell functions, and imbalanced up-regulation of CD44 function and/or down-regulation of E-cadherin function likely contributes to tumor progression.

Contribution of F-actin to barrier properties of the blood-joint pathway

OBJECTIVES

Because fibroblast filamentous actin (F-actin) influences cutaneous interstitial matrix swelling pressure (5), we investigated whether F-actin in fibroblast-derived synoviocytes influences the hydraulic permeability of the trans-synovial interstitial pathway. The study also tested whether F-actin in fenestrated synovial endothelium contributes to the blood-joint barrier in vivo.

METHODS

The clearance of Evans blue-albumin (EVA) from plasma into the knee joint cavity was determined in joint infused with F-actin disrupting cytochalasin D (1-200 microM), latrunculin B (100 microM) or vehicle in anesthetized rabbits. The hydraulic permeability of the lining was determined as the slope relating net trans-synovial flow Q(s) to intra-articular pressure P(j). Synovium was examined histologically after i.v. Monastral blue to assess endothelial leakiness.

RESULTS

EVA permeation in vivo was increased up to 25-fold by cytochalasin (p = 0.0002, ANOVA), with an EC(50) of 23 microM (95% confidence limits 13-43 microM). Washout quickly reversed the increase. Latrunculin had a similar effect. F-actin disruption switched Q(s) from drainage (control) to filtration into the cavity at low P(j) in vivo and raised the conductance Q(s)/dP(j) by 2.13 (p = 0.001, ANOVA). Circulatory arrest abolished these effects. Monastral blue revealed numerous endothelial leaks.

CONCLUSIONS

F-actin is crucial to the barrier function of fenestrated endothelium in situ. No significant effect of synoviocyte F-actin on matrix permeability was detected.

Influence of actin cytoskeleton on intra-articular and interstitial fluid pressures in synovial joints

Fibroblast microfilamentous actin (F-actin) influences interstitial fluid pressure via linkages to collagen in rat skin (Berg et al., 2001). The present aims were to determine whether the actin cytoskeleton of synovial endothelium, fibroblasts, and synoviocytes influences in vivo (i) fluid exchange between a joint cavity and synovial microcirculation and (ii) extracellular fluid pressures in joints. Rabbit knee joints were treated intra-articularly with the F-actin disrupting drugs cytochalasin D and latrunculin B while joint fluid pressure P(j) was recorded. In joints injected with small volumes of control solution, P(j) fell with time (-0.05 +/- 0.01 cm H2O x min(-1), mean +/- SEM, n = 9, equivalent drainage rate 3.9 microl x min(-1)). Cytochalasin or latrunculin reversed this in approximately 4 min in vivo; P(j) increased with time, e.g., +0.12 +/- 0.04 cm H2O x min(-1) at 200 microM cytochalasin (equivalent filtration rate into joint 6.6-12.5 microl x min(-1), n = 4), with a cytochalasin EC50 of 45 microM. Plasma gamma-globulin clearance into the joint cavity was also increased. Post mortem, cytochalasin did not reverse dP(j)/dt and had no more effect on P(j) than did control solution. Also, when synovial interstitial fluid pressures were measured by servonull micropipette post mortem (control -0.95 +/- 0.37 cmH2O, n = 18) cytochalasin had no significant effect on interstitial pressure over 60 min, even at 1 mM. It was concluded that synovial endothelial F-actin has an important role in the normal synovial microvascular resistance to fluid filtration and plasma gamma-globulin permeation and is thus a potential link between pro-inflammatory mediators and arthritic joint effusions. The results provided no support for the hypothesis that synoviocyte F-actin influences the swelling tendency of synovial matrix and hence extracellular fluid pressures, in contrast to the findings of Berg et al. (2001) in rat dermis.

Anti-Fas-induced apoptosis in chondrocytes reduced by hyaluronan: evidence for CD44 and CD54 (intercellular adhesion molecule 1) invovement

OBJECTIVE

To investigate the in vitro effect of therapeutic hyaluronan (HA) of 500-730 kd on anti-Fas-induced apoptosis of chondrocytes from osteoarthritis (OA) patients, and to assess its mechanism of action by analyzing the role of the 2 HA receptors, CD44 and CD54 (intercellular adhesion molecule 1 [ICAM-1]).

METHODS

Chondrocytes isolated from human OA knee cartilage were cultured and the effect of HA on both spontaneous and anti-Fas-induced apoptosis was evaluated. Apoptosis was analyzed by JAM test (for quantitative analysis of fragmented DNA), cell death detection immunoassay (for quantitative analysis of oligonucleosome), TUNEL assay, and electron microscopy. Blocking experiments with anti-CD44 and anti-CD54 alone or in combination were performed to investigate the HA mechanism of action.

RESULTS

Both quantitative tests demonstrated that anti-Fas significantly induced apoptosis of isolated OA chondrocytes. HA at 1,000 microg/ml significantly reduced the anti-Fas-induced apoptosis of chondrocytes but did not affect spontaneous chondrocyte apoptosis. These data were also confirmed by TUNEL staining and by electron microscopy morphologic evaluation. The antiapoptotic effects of HA on anti-FAS-induced chondrocyte apoptosis were significantly decreased by both anti-CD44 (mean +/- SD 57 +/- 12% inhibition) and anti-ICAM-1 (31 +/- 22% inhibition). The mixture of the 2 antibodies had an additive effect, since the rate of inhibition increased to 87 +/- 13%.

CONCLUSION

These data demonstrate that 500-730-kd HA exerts an antiapoptotic effect on anti-FAS-induced chondrocyte apoptosis by binding its specific receptors (CD44 and ICAM-1). Furthermore, this HA fraction may be able to slow down chondrocyte apoptosis in OA by regulating the processes of cartilage matrix degradation.

Anti-Fas-induced apoptosis in chondrocytes reduced by hyaluronan: evidence for CD44 and CD54 (intercellular adhesion molecule 1) invovement

OBJECTIVE

To investigate the in vitro effect of therapeutic hyaluronan (HA) of 500-730 kd on anti-Fas-induced apoptosis of chondrocytes from osteoarthritis (OA) patients, and to assess its mechanism of action by analyzing the role of the 2 HA receptors, CD44 and CD54 (intercellular adhesion molecule 1 [ICAM-1]).

METHODS

Chondrocytes isolated from human OA knee cartilage were cultured and the effect of HA on both spontaneous and anti-Fas-induced apoptosis was evaluated. Apoptosis was analyzed by JAM test (for quantitative analysis of fragmented DNA), cell death detection immunoassay (for quantitative analysis of oligonucleosome), TUNEL assay, and electron microscopy. Blocking experiments with anti-CD44 and anti-CD54 alone or in combination were performed to investigate the HA mechanism of action.

RESULTS

Both quantitative tests demonstrated that anti-Fas significantly induced apoptosis of isolated OA chondrocytes. HA at 1,000 microg/ml significantly reduced the anti-Fas-induced apoptosis of chondrocytes but did not affect spontaneous chondrocyte apoptosis. These data were also confirmed by TUNEL staining and by electron microscopy morphologic evaluation. The antiapoptotic effects of HA on anti-FAS-induced chondrocyte apoptosis were significantly decreased by both anti-CD44 (mean +/- SD 57 +/- 12% inhibition) and anti-ICAM-1 (31 +/- 22% inhibition). The mixture of the 2 antibodies had an additive effect, since the rate of inhibition increased to 87 +/- 13%.

CONCLUSION

These data demonstrate that 500-730-kd HA exerts an antiapoptotic effect on anti-FAS-induced chondrocyte apoptosis by binding its specific receptors (CD44 and ICAM-1). Furthermore, this HA fraction may be able to slow down chondrocyte apoptosis in OA by regulating the processes of cartilage matrix degradation.

Homing-associated cell adhesion molecule (H-CAM/CD44) on human CD34+ hematopoietic progenitor cells

Human CD34+ hematopoietic progenitor cells (HPCs) express CD44 and can directly adhere to hyaluronate (HA) via CD44. Furthermore, CD44 may also be involved in the regulation of CD34+ HPC proliferation and development. The expression of CD44 molecules on CD34+ hematopoietic progenitor cells is significantly lower on bone marrow (BM) CD34+ cells compared with circulating CD34+ cells in cord blood and peripheral blood. Myeloid and erythroid progenitor cells are found predominantly in CD34+ CD44+ cell fractions. More interestingly, CD34+ CD44- cells expressing B-lymphocyte-associated CD10 and CD19 would represent unique B-lymphocyte committed precursors in the BM, which might undergo apoptotic cell death in the early steps of B-cell differentiation.

Disruption of intracerebral progression of C6 rat glioblastoma by in vivo treatment with anti-CD44 monoclonal antibody

OBJECT

Glioblastoma multiforme (GBM) invasiveness is a complex process that involves recognition and attachment of GBM cells to particular extracellular matrix (ECM) molecules before migrating into proteolytically modified matrix and inducing angiogenesis. The CD44 molecule, which is a transmembrane adhesion molecule found on a wide variety of cells including GBM, has been suggested as the principal mediator of migration and invasion. The aim of the present study was to demonstrate whether an antibody specific to the standard form of CD44 (CD44s, 85-90 kD) might prevent invasion and thus disrupt progression of C6 GBM in vivo.

METHODS

Immunostaining demonstrated homogeneous expression of CD44s on the surface of C6 GBM cells and tumors. Flow cytometric analysis demonstrated binding saturation of anti-CD44s monoclonal antibody (mAb) to the receptor at 1 microg/5 x 10(5) cells. Blocking of CD44s in vitro resulted in a dose-dependent progressive (up to 94+/-2.7%; mean +/- standard deviation [SD]) detachment of C6 cells from ECM-coated culture. Blocking of CD44s in vivo resulted in significantly reduced C6 brain tumors (3.6+/-0.4% [SD])--measured as the quotient: tumor surface (mm2)/brain surface (mm2) x 100--compared with untreated (19.9+/-0.9%) or sham-treated (19.2+/-1.1 to 19.3+/-2.5% [SD]) rats. Disruption of C6 GBM progression correlated with an improved food intake; treated rats were significantly less cachectic (166.6+/-16.4 g [SD]) than those that were untreated (83+/-2.7 g [SD]) or sham-treated (83.4+/-1.1 to 83+/-2.2 g [SD]) rats.

CONCLUSIONS

The authors conclude that CD44s-targeted treatment with specific mAb may represent an effective means for preventing progression of highly invasive GBMs.

Signal transduction via CD44: role of plasma membrane microdomains

CD44 is the principal cell surface receptor for extracellular matrix glycosaminoglycan hyaluronan. CD44-hyaluronan mediated cell adhesion is important in several pathophysiological processes such as inflammation and metastatic spread of cancer cells. It has been recently recognized that CD44 also functions as a signaling receptor in a variety of cell types. Cell stimulation by monoclonal anti-CD44 antibody or natural CD44 ligands activate several signaling pathways that culminate in cell proliferation, cytokine secretion, chemokine gene expression and cytolytic effector functions. One of the earliest signaling events following stimulation via CD44 is tyrosine phosphorylation of intracellular proteins substrates, and CD44 mediated cellular activation could be abolished by protein tyrosine kinase (PTK) inhibitors. The Src-family non-receptor PTKs such as Lck, Fyn, Lyn and Hck were shown to be coupled to CD44 via sphingolipid-rich microdomains (lipid rafts) of the plasma membrane. Studies on T cell receptor and IgE receptor mediated signaling in lymphocytes and mast cells have consolidated the notion that microdomains consist of signaling platforms where components of multiple signaling pathways are assembled. Co-isolation of CD44 with microdomains strongly suggests that CD44 generates cellular activation signals utilizing the signaling machinery of the plasma membrane microdomains.

Analysis of CD44-containing lipid rafts: Recruitment of annexin II and stabilization by the actin cytoskeleton

CD44, the major cell surface receptor for hyaluronic acid (HA), was shown to localize to detergent-resistant cholesterol-rich microdomains, called lipid rafts, in fibroblasts and blood cells. Here, we have investigated the molecular environment of CD44 within the plane of the basolateral membrane of polarized mammary epithelial cells. We show that CD44 partitions into lipid rafts that contain annexin II at their cytoplasmic face. Both CD44 and annexin II were released from these lipid rafts by sequestration of plasma membrane cholesterol. Partition of annexin II and CD44 to the same type of lipid rafts was demonstrated by cross-linking experiments in living cells. First, when CD44 was clustered at the cell surface by anti-CD44 antibodies, annexin II was recruited into the cytoplasmic leaflet of CD44 clusters. Second, the formation of intracellular, submembranous annexin II-p11 aggregates caused by expression of a trans-dominant mutant of annexin II resulted in coclustering of CD44. Moreover, a frequent redirection of actin bundles to these clusters was observed. These basolateral CD44/annexin II-lipid raft complexes were stabilized by addition of GTPgammaS or phalloidin in a semipermeabilized and cholesterol-depleted cell system. The low lateral mobility of CD44 in the plasma membrane, as assessed with fluorescent recovery after photobleaching (FRAP), was dependent on the presence of plasma membrane cholesterol and an intact actin cytoskeleton. Disruption of the actin cytoskeleton dramatically increased the fraction of CD44 which could be recovered from the light detergent-insoluble membrane fraction. Taken together, our data indicate that in mammary epithelial cells the vast majority of CD44 interacts with annexin II in lipid rafts in a cholesterol-dependent manner. These CD44-containing lipid microdomains interact with the underlying actin cytoskeleton.

CD44s-targeted treatment with monoclonal antibody blocks intracerebral invasion and growth of 9L gliosarcoma

Glioma invasiveness is a complex process involving recognition and attachment of tumor cells to particular extracellular matrix (ECM) molecules prior to migrating into proteolytically modified matrix and inducing angiogenesis. CD44 is a group of transmembrane adhesion molecules found on a wide variety of cells including gliomas that has been suggested as the principal mediator of migration/invasion. The aim of the present study was to demonstrate whether antibody specific for the standard form of CD44 (CD44s, 85-90 kDa) might prevent invasion, thus blocking growth of the 9L gliosarcoma in vivo. High expression of CD44s on the surface of 9L cells and brain tumors was demonstrated by immunochemistry. Fluorescence-activated cell sorting (FACS) demonstrated binding saturation of anti-CD44s monoclonal antibody (mAb) to the receptor at 1 microg/5 x 10(5) cells. Blocking of CD44s in vitro resulted in a dose-dependent progressive, up to 95%+/-2.5% detachment of 9L cells from ECM-coated culture surfaces. Blocking of CD44s in vivo resulted in significantly reduced 9L brain tumors (2.5%+/-0.4%)--measured as the quotient: tumor surface (mm2)/brain surface (mm2) x 100--as compared to untreated (16.1%+/-2.2%) or sham-treated rats (16%+/-3.7% to 16.1%+/-3%). We conclude that CD44s-targeted treatment with specific mAb may be an effective means for preventing glioma progression.

Heparan sulfate-modified CD44 promotes hepatocyte growth factor/scatter factor-induced signal transduction through the receptor tyrosine kinase c-Met

CD44 has been implicated in tumor progression and metastasis, but the mechanism(s) involved is as yet poorly understood. Recent studies have shown that CD44 isoforms containing the alternatively spliced exon v3 carry heparan sulfate side chains and are able to bind heparin-binding growth factors. In the present study, we have explored the possibility of a physical and functional interaction between CD44 and hepatocyte growth factor/scatter factor (HGF/SF), the ligand of the receptor tyrosine kinase c-Met. The HGF/SF-c-Met pathway mediates cell growth and motility and has been implicated in tumor invasion and metastasis. We demonstrate that a CD44v3 splice variant efficiently binds HGF/SF via its heparan sulfate side chain. To address the functional relevance of this interaction, Namalwa Burkitt's lymphoma cells were stably co-transfected with c-Met and either CD44v3 or the isoform CD44s, which lacks heparan sulfate. We show that, as compared with CD44s, CD44v3 promotes: (i) HGF/SF-induced phosphorylation of c-Met, (ii) phosphorylation of several downstream proteins, and (iii) activation of the MAP kinases ERK1 and -2. By heparitinase treatment and the use of a mutant HGF/SF with greatly decreased affinity for heparan sulfate, we show that the enhancement of c-Met signal transduction induced by CD44v3 was critically dependent on heparan sulfate moieties. Our results identify heparan sulfate-modified CD44 (CD44-HS) as a functional co-receptor for HGF/SF which promotes signaling through the receptor tyrosine kinase c-Met, presumably by concentrating and presenting HGF/SF. As both CD44-HS and c-Met are overexpressed on several types of tumors, we propose that the observed functional collaboration might be instrumental in promoting tumor growth and metastasis.

CD44 and adhesion of normal and leukemic CD34+ cells to bone marrow stroma

CD44 has long been implicated in the interaction between hematopoietic progenitors and bone marrow stroma. More recently it has become apparent that CD44 antibodies cannot only inhibit CD44 mediated adhesion to hyaluronic acid and cellular ligands but can stimulate adhesion to these ligands. The mechanism involved in CD44 antibody stimulated adhesion to cellular layers is still not known. While adhesion of T cells to keratinocytes is integrin mediated it appears that adhesion of hematopoietic progenitors to bone marrow stromal layers is the result of an antibody induced conformational change in the CD44 molecule similar to that seem for the augmentation of hyaluronic acid binding by some CD44 antibodies. The ligand for CD44 involved in this binding has not been identified but it does not appear to be hyaluronic acid.

Expression of CD44 in Apc and Tcf mutant mice implies regulation by the WNT pathway

Overexpression of cell surface glycoproteins of the CD44 family is an early event in the colorectal adenoma-carcinoma sequence. This suggests a link with disruption of APC tumor suppressor protein-mediated regulation of beta-catenin/Tcf-4 signaling, which is crucial in initiating tumorigenesis. To explore this hypothesis, we analyzed CD44 expression in the intestinal mucosa of mice and humans with genetic defects in either APC or Tcf-4, leading to constitutive activation or blockade of the beta-catenin/Tcf-4 pathway, respectively. We show that CD44 expression in the non-neoplastic intestinal mucosa of Apc mutant mice is confined to the crypt epithelium but that CD44 is strongly overexpressed in adenomas as well as in invasive carcinomas. This overexpression includes the standard part of the CD44 (CD44s) as well as variant exons (CD44v). Interestingly, deregulated CD44 expression is already present in aberrant crypt foci with dysplasia (ACFs), the earliest detectable lesions of colorectal neoplasia. Like ACFs of Apc-mutant mice, ACFs of familial adenomatous polyposis (FAP) patients also overexpress CD44. In sharp contrast, Tcf-4 mutant mice show a complete absence of CD44 in the epithelium of the small intestine. This loss of CD44 concurs with loss of stem cell characteristics, shared with adenoma cells. Our results indicate that CD44 expression is part of a genetic program controlled by the beta-catenin/Tcf-4 signaling pathway and suggest a role for CD44 in the generation and turnover of epithelial cells.

CD44 expression in sinonasal melanomas: is loss of isoform expression associated with advanced tumour stage?

The expression of the adhesion molecule CD44 was examined in 14 primary sinonasal melanomas (SMs), aggressive neoplasms with short survival times, as CD44 overexpression has been linked to poor survival in human cancers. Immunohistochemistry was performed on formalin-fixed, paraffin-embedded sections with CD44 isoform-specific monoclonal antibodies to the CD44 standard (s) and variant isoforms (v) v5 and v6. CD44s, v5, and v6 were strongly expressed in a membranous pattern in SM in situ, early invasive SM, and in uninvolved respiratory/squamous epithelium. In invasive SM, membranous CD44s expression was identified in a large proportion of melanoma cells. Membranous staining of CD44v5 and v6 was lost in invasive SM, independently of the histological subtype. Diffuse cytoplasmic staining was observed focally in invasive SM and loss of cytoplasmic expression of CD44v6 and v5 was associated with advanced tumour stage in the linear-by-linear association test (p = 0.042 and 0.066, respectively). CD44s may not be important for malignant transformation, as it is expressed in both benign and malignant melanocytes. Loss of membranous CD44 isoform expression in widely invasive SM suggests that loss of cellular adhesion facilitates matrix and vascular infiltration and dissemination of sinonasal melanoma cells.

A Directly Spliced Exon 10–Containing CD44 Variant Promotes the Metastasis and Homotypic Aggregation of Aggressive Non-Hodgkin's Lymphoma

Variants of the CD44 cell-surface adhesion molecule include additional sequences encoded by combinations of exons from the membrane proximal domain (exons 6–14). Preliminary studies suggest that these additional variable membrane proximal sequences may alter the ligand specificity, glycosylation, and biologic function of CD44. In earlier studies, we found that primary extranodal and widely disseminated aggressive non-Hodgkin's lymphomas (NHLs) and normal activated B cells expressed a directly spliced exon 10–containing variant (CD44ex10), whereas normal resting B cells expressed larger exon 10–containing variants (CD44ex10-14 and CD44ex7-14). To obtain additional information regarding the function of exon 10–containing CD44 variants in aggressive NHL, we generated aggressive NHL transfectants that expressed CD44ex10, CD44ex10-14, CD44ex7-14, the standard CD44 isoform (CD44H), or vector alone, and evaluated the local tumorogenicity, aggregation, and metastatic potential of these transfectants. CD44ex10 aggressive NHL transfectants were more likely to cause local tumor formation in nude mice than transfectants expressing the larger exon 10–containing variants, CD44H, or vector alone. In addition, cell suspensions derived from CD44ex10 local tumors exhibited far greater homotypic aggregation than those obtained from other CD44 or vector-only local tumors. In nude mice that received CD44ex10 transfectants, distant metastases were also significantly more likely to develop than in animals that were given either the CD44ex10-14, CD44ex7-14, CD44H, or vector-only transfectants. These data provide the first evidence that the directly spliced exon 10–containing CD44 variant (CD44ex10) has a unique biologic function in aggressive NHL.

A Directly Spliced Exon 10–Containing CD44 Variant Promotes the Metastasis and Homotypic Aggregation of Aggressive Non-Hodgkin's Lymphoma

Variants of the CD44 cell-surface adhesion molecule include additional sequences encoded by combinations of exons from the membrane proximal domain (exons 6–14). Preliminary studies suggest that these additional variable membrane proximal sequences may alter the ligand specificity, glycosylation, and biologic function of CD44. In earlier studies, we found that primary extranodal and widely disseminated aggressive non-Hodgkin's lymphomas (NHLs) and normal activated B cells expressed a directly spliced exon 10–containing variant (CD44ex10), whereas normal resting B cells expressed larger exon 10–containing variants (CD44ex10-14 and CD44ex7-14). To obtain additional information regarding the function of exon 10–containing CD44 variants in aggressive NHL, we generated aggressive NHL transfectants that expressed CD44ex10, CD44ex10-14, CD44ex7-14, the standard CD44 isoform (CD44H), or vector alone, and evaluated the local tumorogenicity, aggregation, and metastatic potential of these transfectants. CD44ex10 aggressive NHL transfectants were more likely to cause local tumor formation in nude mice than transfectants expressing the larger exon 10–containing variants, CD44H, or vector alone. In addition, cell suspensions derived from CD44ex10 local tumors exhibited far greater homotypic aggregation than those obtained from other CD44 or vector-only local tumors. In nude mice that received CD44ex10 transfectants, distant metastases were also significantly more likely to develop than in animals that were given either the CD44ex10-14, CD44ex7-14, CD44H, or vector-only transfectants. These data provide the first evidence that the directly spliced exon 10–containing CD44 variant (CD44ex10) has a unique biologic function in aggressive NHL.

Engagement of variant CD44 confers resistance to anti-integrin antibody-mediated apoptosis in a colon carcinoma cell line

The LIM 1863 colon carcinoma cell line grows as structured organoids around a central lumen, and we have previously demonstrated that the three-dimensional arrangement protects the individual cells from apoptosis induced by an anti-alpha v integrin antibody, 23C6 (Bates et al., 1994). Here we show that the intercellular forces which drive spheroid formation can be overcome by exposure of the cells to a collagen substrate, or more specifically through ligation of the CD44 receptor by a monoclonal antibody. Binding to immobilized anti-CD44 antibody induced a monolayer morphology which is accompanied by fibronectin production and secretion, and expression of the integrin alpha v beta 6. Significantly, the cells of the monolayer acquired resistance to 23C6 antibody-mediated apoptosis over time and this property was sustained even after removal from the monolayer. We provide data to show that this resistance is not dependent on monolayer morphology, constant engagement of the CD44 receptor, loss of the 23C6 antigen, or elevation of Bcl-2 or Bcl-XL protein. The CD44 expressed by LIM 1863 is shown to be the metastatic variant of the molecule therefore these results provide a possible explanation for the selective advantages conferred by expression of this variant for metastasizing colon cancer cells. Overall, the findings of this study support a model for the development of malignancy through the production of specific survival and growth signals as a direct consequence of a signaling event induced by stimulation of an epithelial variant of CD44.

An essential role for the interaction between hyaluronan and hyaluronan binding proteins during joint development

We studied the expression of hyaluronan binding proteins (HABPs) during the development of embryonic chick joints, using immunocytochemistry and biotinylated HA. The expression of actin capping proteins and of actin itself was also studied because the cytoskeleton is important in controlling HA-HABP interactions. Three cell surface HABPs were localized in the epiphyseal cartilage, articular fibrocartilage, and interzone that comprise the developing joint. Of these three HABPs, CD44 was associated with the articular fibrocartilages and interzone, whereas RHAMM and the IVd4 epitope were associated with all three tissues. Biotinylated HA was localized to interzone and articular fibrocartilages before cavity formation and within epiphyseal chondrocytes post cavitation. Actin filament bundles were observed at the developing joint line, as was the expression of the actin capping protein moesin. Manipulation of joint cavity development, using oligosaccharides of HA, disrupted joint formation and was associated with decreases in CD44 and actin filament expression as well as decreased hyaluronan synthetic capability. These results suggest that HA is actively bound by CD44 at the developing joint line and that HA-HABP interactions play a major role in the initial separation events occurring during joint formation.

Ultrastructural analysis of human epidermal CD44 reveals preferential distribution on plasma membrane domains facing the hyaluronan-rich matrix pouches

We used immunogold staining and stereology to examine the ultrastructural localization and to estimate the relative content of CD44 in different strata and cell types of normal human epidermis. We found that CD44 existed almost exclusively on the plasma membranes; only rare labeling occurred on vesicular structures within the cytoplasm. Quantitation of the immunogold particles indicated that the labeling density of melanocytes corresponded to that of basal keratinocytes, and Langerhans cells displayed a labeling density of approximately 10% that of the surrounding spinous cells. Among keratinocyte strata, the highest labeling density occurred on spinous cells, suggesting upregulation of CD44 after detachment from the basement membrane. The plasma membrane distribution of CD44 was compartmentalized, with little signal on cell-cell and cell-substratum contact sites such as desmosomes, the plasma membrane domain facing the basement membrane, and the close apposition of terminally differentiating granular cells. In contrast, CD44 was abundant on plasma membrane domains facing an open intercellular space, rich in hyaluronan. This distribution is in line with a role of CD44 as a hyaluronan receptor, important in the maintenance of the intercellular space for nutritional and cell motility functions in stratified epithelia.

Immunolocalization of CD44 and the ezrin-radixin-moesin (ERM) family in the stratum intermedium and papillary layer of the mouse enamel organ

We studied the immunohistochemical localization of CD44 and the ezrin-radixin-moesin (ERM) family of actin binding proteins in mouse enamel organ, using confocal laser scanning microscopy and transmission electron microscopy to clarify their role in cytoskeletal organization. At the differentiation stage of ameloblasts, immunoreactivity to CD44 was detected on the plasma membrane of the inner enamel epithelium, the stellate reticulum, the stratum intermedium, and the external enamel epithelium. In accordance with the differentiation of preameloblasts into secretory ameloblasts, immunoreactivity increased in the stratum intermedium cells. At the maturation stage, intense immunoreactivity was observed on the papillary layer cells. For the ERM family, the stratum intermedium and the papillary layer cells were stained with anti-ezrin and -radixin monoclonal antibodies but not with the anti-moesin antibody. Electron microscopic observations revealed that CD44, ezrin, and radixin were localized in the region at which preameloblasts came into contact with the stratum intermedium at the differentiation stage. At the secretory and maturation stages, they were concentrated in the microvilli of the stratum intermedium and the papillary layer cells. These findings suggest that the CD44-ezrin-radixin-actin filament system is involved in cell-cell interaction between preameloblasts and the stratum intermedium, and in the cytoskeletal organization of the cells in the stratum intermedium and the papillary layer.

Influence of hyaluronic acid or phorbol 12-myristate 13-acetate on the migration capacity of a murine lymphoma cell line (Eb) and its metastatic variant (ESb)

The in vitro migration of two murine T cell lymphoma cell lines (Eb and ESb) was studied employing a three-dimensional collagen matrix and time-lapse video recording. In the highly metastatic cell line ESb, which had a low spontaneous locomoting activity, migration could clearly be stimulated by hyaluronic acid (HA) whereas only a small increase was found after incubation with phorbol myristate acetate (PMA). The observed stimulation could be attributed to an increase in recruitment of locomoting cells and not to changes in migration parameters of motile individual cells such as percentage of time locomoting, velocity or distance migrated. Incubation of the low metastatic cell line Eb with HA led to a decrease in migration but blocking of CD44, the principle ligand for HA, by preincubation with an anti-CD44 mAb (KM114), followed by HA exposure increased the locomoting activity significantly. The effect was based on both an increase in recruitment as well as in all migration parameters regarding motile individual Eb cells.

Hyaluronic acid-specific regulation of cytokines by human uterine fibroblasts

The physiological inflammatory response can provide an effective mechanism for delivering the baby at the time of parturition. We characterized the mechanisms by which hyaluronic acid (HA) regulates interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), and interleukin-8 (IL-8) production in human uterine fibroblasts. A dose-dependent increase in cytokine release was observed over an HA concentration range of 10 microg/ml to 1 mg/ml. The action of HA on the cytokine production is mediated by CD44. Under serum-free conditions, HA-induced cytokine generation was significantly less compared with production in the presence of serum, suggesting involvement of serum proteins. Addition of inter-alpha-trypsin inhibitor (ITI) under serum-free conditions enhanced the HA-induced synthesis of TNF-alpha, which stimulated the temporary release of IL-8. In addition, HA and IL-1beta stimulated the release of hyaluronidase by the fibroblasts. These results indicate that cytokine production in human uterine fibroblasts is regulated in a CD44-HA-ITI-specific fashion. HA may be involved in the regulation of delivery in part through the selective release of cytokines that contribute to uterine cervical ripening.

Interaction between Entamoeba histolytica and intestinal epithelial cells involves a CD44 cross-reactive protein expressed on the parasite surface

This study shows that Entamoeba histolytica binds hyaluronic acid. The binding molecule was identified as an 80-kDa membrane protein and was recognized by anti-CD44 monoclonal antibodies. These data indicate that a CD44 cross-reacting adherence molecule is expressed on E. histolytica.

CD44: structure, function, and association with the malignant process

CD44 is a ubiquitous multistructural and multifunctional cells surface adhesion molecule involved in cell-cell and cell-matrix interactions. Twenty exons are involved in the genomic organization of this molecule. The first five and the last 5 exons are constant, whereas the 10 exons located between these regions are subjected to alternative splicing, resulting in the generation of a variable region. Differential utilization of the 10 variable region exons, as well as variations in N-glycosylation, O-glycosylation, and glycosaminoglycanation (by heparan sulfate or chondroitin sulfate), generate multiple isoforms (at least 20 are known) of different molecular sizes (85-230 kDa). The smallest CD44 molecule (85-95 kDa), which lacks the entire variable region, is standard CD44 (CD44s). As it is expressed mainly on cells of lymphohematopoietic origin, CD44s is also known as hematopoietic CD44 (CD44H). CD44s is a single-chain molecule composed of a distal extracellular domain (containing, the ligand-binding sites), a membrane-proximal region, a transmembrane-spanning domain, and a cytoplasmic tail. The molecular sequence (with the exception of the membrane-proximal region) displays high interspecies homology. After immunological activation, T lymphocytes and other leukocytes transiently upregulate CD44 isoforms expressing variant exons (designated CD44v). A CD44 isform containing the last 3 exon products of the variable region (CD44V8-10, also known as epithelial CD44 or CD44E), is preferentially expressed on epithelial cells. The longest CD44 isoform expressing in tandem eight exons of the variable region (CD44V3-10) was detected in keratinocytes. Hyaluronic acid (HA), an important component of the extracellular matrix (ECM), is the principal, but by no means the only, ligand of CD44. Other CD44 ligands include the ECM components collagen, fibronectin, laminin, and chondroitin sulfate. Mucosal addressin, serglycin, osteopontin, and the class II invariant chain (Ii) are additional, ECM-unrelated, ligands of the molecule. In many, but not in all cases, CD44 does not bind HA unless it is stimulated by phorbol esters, activated by agonistic anti-CD44 antibody, or deglycosylated (e.g., by tunicamycin). CD44 is a multifunctional receptor involved in cell-cell and cell-ECM interactions, cell traffic, lymph node homing, presentation of chemokines and growth factors to traveling cells, and transmission of growth signals. CD44 also participates in the uptake and intracellular degradation of HA, as well as in transmission of signals mediating hematopoiesis and apoptosis. Many cancer cell types as well as their metastases express high levels of CD44. Whereas some tumors, such as gliomas, exclusively express standard CD44, other neoplasms, including gastrointestinal cancer, bladder cancer, uterine cervical cancer, breast cancer and non-Hodgkin's lymphomas, also express CD44 variants. Hence CD44, particularly its variants, may be used as diagnostic or prognostic markers of at least some human malignant diseases. Furthermore, it has been shown in animal models that injection of reagents interfering with CD44-ligand interaction (e.g., CD44s- or CD44v-specific antibodies) inhibit local tumor growth and metastatic spread. These findings suggest that CD44 may confer a growth advantage on some neoplastic cells and, therefore, could be used as a target for cancer therapy. It is hoped that identification of CD44 variants expressed on cancer but not on normal cells will lead to the development of anti-CD44 reagents restricted to the neoplastic growth.

Immunolocalization of CD44 and the ERM family in bone cells of mouse tibiae

We studied the immunohistochemical localization of CD44, hyaluronate receptor, and the ezrin-radixin-moesin (ERM) family, actin binding proteins, in bone cells using confocal laser scanning microscopy and transmission electron microscopy to clarify the mechanism of the organization of their cytoskeletons. In osteoclasts, intense immunoreactivity to CD44 could be detected on their basolateral plasma membranes. There was less reactivity observed in the area of the plasma membrane in direct contact with the bone surface. The immunogold electron-microscopical method revealed that CD44 was mainly localized on the microvilli of the basolateral plasma membrane. The plasma membrane of the clear zone and the ruffled border were not immunolabeled with CD44. As for the ERM family, the basolateral plasma membrane of osteoclasts was stained with antimoesin monoclonal antibody, but not with ezrin or radixin. In osteoblasts attached to the bone surface, immunoreactivity to CD44 was restricted to their cytoplasmic processes. They showed immunoreactivities to radixin and moesin on the cytoplasmic side of their plasma membrane when in contact with each other. However, although osteocytes in the bone matrix demonstrate an intense immunolabeling with CD44 on their plasma membrane, they scarcely show immunoreactivity to the ERM family. These findings suggest that: (1) the CD44-moesin-actin filament system is involved in the organization of cytoskeletons in the basolateral plasma membrane of osteoclasts; and (2) other mechanisms, rather than the CD44 and the ERM family, may be involved in the cells of osteoblast lineage.

Expression of multiple CD44 isoforms in the apical ectodermal ridge of the embryonic mouse limb

Previous immunohistochemical studies have shown that CD44 is highly enriched within the apical ectodermal ridge of the developing limb (Wheatley et al. [1993] Development 119: 295-306), but the particular isoforms of CD44 were not identified. We show here that CD44s (standard or "hemopoietic" isoform) and several CD44 variants, especially V3-V10, V4-V10, and V6-V10, are concentrated in the apical ectodermal ridge in the early mouse limb. Since CD44s is a major cell surface receptor for hyaluronan, we compared its localization with that of hyaluronan. In the early limb bud, hyaluronan is distributed throughout the mesoderm but is absent from all regions of the ectoderm. Hyaluronan is especially enriched in the basement membrane separating ectoderm and mesoderm, except beneath the apical ectodermal ridge where it is absent. Since CD44s is a known endocytic receptor for hyaluronan, its presence in ridge ectoderm could lead to degradation of hyaluronan destined for the neighboring region of basement membrane, thus facilitating interaction of the ridge with underlying mesoderm. The CD44 (V3-V10) isoform found in the ridge is expressed elsewhere as a proteoglycan with heparan sulfate chains that bind fibroblast growth factors. Since fibroblast growth factors are present in the ridge and are essential for limb morphogenesis, CD44 (V3-V10) is likely to act as a cofactor or modulator in the growth-promoting action or maintenance of the ridge.

Analysis of human articular chondrocyte CD44 isoform expression and function in health and disease

Interactions between articular chondrocytes and components of the extracellular matrix are of potential importance in the normal function of cartilage and in the pathophysiology of arthritis. Little is known of the basis of these interactions, but cell adhesive molecules such as CD44 are likely to be involved. Immunohistology using six well-characterized anti-CD44 monoclonal antibodies demonstrated standard CD44 isoform (CD44H) expression by all chondrocytes in normal and osteoarthrotic (OA) cartilage but absence of the CD44E variant. Polymerase chain reaction (PCR) of reverse transcribed mRNA from monolayer cultures of normal and OA chondrocytes using primer sequences which span the region containing variably spliced exons produced a predominant band representing the standard form of CD44, which lacks the variable exons 6-15 (v1-v10). No product was seen at the expected size of the epithelial variant of CD44 (CD44v8-10). Use of exon-specific primers, however, showed expression of variant exons resulting in multiple minor isoforms. Standard CD44 was also shown to be the predominantly expressed isoform identified by immunoprecipitation, but human articular chondrocytes did not adhere to hyaluronan in vitro. Chondrocyte CD44 may function as an adhesion receptor for other matrix molecules such as fibronectin or collagen.

CD44-related chondroitin sulfate proteoglycan, a cell surface receptor implicated with tumor cell invasion, mediates endothelial cell migration on fibrinogen and invasion into a fibrin matrix

Microvascular endothelial cell invasion into the fibrin provisional matrix is an integral component of angiogenesis during wound repair. Cell surface receptors which interact with extracellular matrix proteins participate in cell migration and invasion. Malignant cells use CD44-related chondroitin sulfate proteoglycan (CSPG) as a matrix receptor to mediate migration and invasion. In this study, we examine whether cell surface CSPG can mediate similar events in nonmalignant wound microvascular endothelial cells or whether use of CSPG for migration and invasion is a property largely restricted to malignant cells. After inhibiting CSPG synthesis with p-nitrophenyl beta-d xylopyranoside (beta-d xyloside), wound microvascular endothelial cells were capable of attaching and spreading on the surface of a fibrin gel; however, their ability to invade the fibrin matrix was virtually eliminated. To begin to examine the mechanism by which endothelial cells use CSPG to invade fibrin matrices, cell adhesion and migration on fibrinogen was examined. Endothelial cell adhesion and migration on fibrinogen were inhibited by both beta-d xyloside and after cleavage of chondroitin sulfate from the core protein by chondroitinase ABC. We have determined that wound microvascular endothelial cells express the majority of their proteoglycan as CSPG and that the CSPG core protein is immunologically related to CD44. PCR studies show that these cells express both the "standard" (CD44H) isoform and an isoform containing the variably spliced exon V3. In addition, anti-CD44 antibody blocks endothelial cell migration on fibrinogen. Affinity chromatography studies reveal that partially purified microvascular endothelial cell CSPG binds fibrinogen. These findings suggest that CD44-related CSPG, a molecule implicated in the invasive behavior of tumor cells, is capable of binding fibrinogen/fibrin, thereby mediating endothelial cell migration and invasion into the fibrin provisional matrix during wound repair.