Epican, a heparan/chondroitin sulfate proteoglycan form of CD44, mediates cell-cell adhesion

The Glycosaminoglycan Side Chains and Modular Core Proteins of Heparan Sulphate Proteoglycans and the Varied Ways They Provide Tissue Protection by Regulating Physiological Processes and Cellular Behaviour

This review examines the roles of HS-proteoglycans (HS-PGs) in general, and, in particular, perlecan and syndecan as representative examples and their interactive ligands, which regulate physiological processes and cellular behavior in health and disease. HS-PGs are essential for the functional properties of tissues both in development and in the extracellular matrix (ECM) remodeling that occurs in response to trauma or disease. HS-PGs interact with a biodiverse range of chemokines, chemokine receptors, protease inhibitors, and growth factors in immune regulation, inflammation, ECM stabilization, and tissue protection. Some cell regulatory proteoglycan receptors are dually modified hybrid HS/CS proteoglycans (betaglycan, CD47). Neurexins provide synaptic stabilization, plasticity, and specificity of interaction, promoting neurotransduction, neurogenesis, and differentiation. Ternary complexes of glypican-1 and Robbo-Slit neuroregulatory proteins direct axonogenesis and neural network formation. Specific neurexin-neuroligin complexes stabilize synaptic interactions and neural activity. Disruption in these interactions leads to neurological deficits in disorders of functional cognitive decline. Interactions with HS-PGs also promote or inhibit tumor development. Thus, HS-PGs have complex and diverse regulatory roles in the physiological processes that regulate cellular behavior and the functional properties of normal and pathological tissues. Specialized HS-PGs, such as the neurexins, pikachurin, and Eyes-shut, provide synaptic stabilization and specificity of neural transduction and also stabilize the axenome primary cilium of phototoreceptors and ribbon synapse interactions with bipolar neurons of retinal neural networks, which are essential in ocular vision. Pikachurin and Eyes-Shut interactions with an α-dystroglycan stabilize the photoreceptor synapse. Novel regulatory roles for HS-PGs controlling cell behavior and tissue function are expected to continue to be uncovered in this fascinating class of proteoglycan.

HS, an Ancient Molecular Recognition and Information Storage Glycosaminoglycan, Equips HS-Proteoglycans with Diverse Matrix and Cell-Interactive Properties Operative in Tissue Development and Tissue Function in Health and Disease

Heparan sulfate is a ubiquitous, variably sulfated interactive glycosaminoglycan that consists of repeating disaccharides of glucuronic acid and glucosamine that are subject to a number of modifications (acetylation, de-acetylation, epimerization, sulfation). Variable heparan sulfate chain lengths and sequences within the heparan sulfate chains provide structural diversity generating interactive oligosaccharide binding motifs with a diverse range of extracellular ligands and cellular receptors providing instructional cues over cellular behaviour and tissue homeostasis through the regulation of essential physiological processes in development, health, and disease. heparan sulfate and heparan sulfate-PGs are integral components of the specialized glycocalyx surrounding cells. Heparan sulfate is the most heterogeneous glycosaminoglycan, in terms of its sequence and biosynthetic modifications making it a difficult molecule to fully characterize, multiple ligands also make an elucidation of heparan sulfate functional properties complicated. Spatio-temporal presentation of heparan sulfate sulfate groups is an important functional determinant in tissue development and in cellular control of wound healing and extracellular remodelling in pathological tissues. The regulatory properties of heparan sulfate are mediated via interactions with chemokines, chemokine receptors, growth factors and morphogens in cell proliferation, differentiation, development, tissue remodelling, wound healing, immune regulation, inflammation, and tumour development. A greater understanding of these HS interactive processes will improve therapeutic procedures and prognoses. Advances in glycosaminoglycan synthesis and sequencing, computational analytical carbohydrate algorithms and advanced software for the evaluation of molecular docking of heparan sulfate with its molecular partners are now available. These advanced analytic techniques and artificial intelligence offer predictive capability in the elucidation of heparan sulfate conformational effects on heparan sulfate-ligand interactions significantly aiding heparan sulfate therapeutics development.

Chondroitin Sulfate-Degrading Enzymes as Tools for the Development of New Pharmaceuticals

Chondroitin sulfates are linear anionic sulfated polysaccharides found in biological tissues, mainly within the extracellular matrix, which are degraded and altered by specific lyases depending on specific time points. These polysaccharides have recently acquired relevance in the pharmaceutical industry due to their interesting therapeutic applications. As a consequence, chondroitin sulfate (CS) lyases have been widely investigated as tools for the development of new pharmaceuticals based on these polysaccharides. This review focuses on the major breakthrough represented by chondroitin sulfate-degrading enzymes and their structures and mechanisms of function in addition to their major applications.

Leishmaniasis and glycosaminoglycans: a future therapeutic strategy?

Leishmania spp. depend on effective macrophage infection to establish and develop in mammalian hosts. Both metacyclic promastigotes and amastigotes are able to infect host cells, and thus they rely on several ligands that, when recognized by macrophage receptors, mediate parasite uptake. During macrophage primary infection with metacyclic forms from the insect vector and during amastigote dissemination via macrophage rupture, both infective stages have to cope with the host extracellular microenvironment, including extracellular matrix molecules. Glycosaminoglycans are abundant in the extracellular matrix and many of these molecules are able to interact with the parasite and the host cell, mediating positive and negative effects for the infection, depending on their structure and/or location. In addition, glycosaminoglycans are present at the surface of macrophages as proteoglycans, playing important roles for parasite recognition and uptake. In this review, we discuss glycosaminoglycans in the context of Leishmania infection as well as the possible applications of the current knowledge regarding these molecules for the development of new therapeutic strategies to control parasite dissemination.

Biodiversity of CS–proteoglycan sulphation motifs: chemical messenger recognition modules with roles in information transfer, control of cellular behaviour and tissue morphogenesis

Chondroitin sulphate (CS) glycosaminoglycan chains on cell and extracellular matrix proteoglycans (PGs) can no longer be regarded as merely hydrodynamic space fillers. Overwhelming evidence over recent years indicates that sulphation motif sequences within the CS chain structure are a source of significant biological information to cells and their surrounding environment. CS sulphation motifs have been shown to interact with a wide variety of bioactive molecules, e.g. cytokines, growth factors, chemokines, morphogenetic proteins, enzymes and enzyme inhibitors, as well as structural components within the extracellular milieu. They are therefore capable of modulating a panoply of signalling pathways, thus controlling diverse cellular behaviours including proliferation, differentiation, migration and matrix synthesis. Consequently, through these motifs, CS PGs play significant roles in the maintenance of tissue homeostasis, morphogenesis, development, growth and disease. Here, we review (i) the biodiversity of CS PGs and their sulphation motif sequences and (ii) the current understanding of the signalling roles they play in regulating cellular behaviour during tissue development, growth, disease and repair.

Collective invasion in ductal and lobular breast cancer associates with distant metastasis

Breast cancer undergoes collective tissue invasion and, in experimental models, can collectively metastasize. The prevalence of collective invasion and its contribution to distant metastasis in clinical disease, however, remains poorly defined. We here scored the adipose tissue invasion of primary invasive ductal carcinoma (IDC), expressing E-cadherin, and E-cadherin negative invasive lobular carcinoma (ILC) and identified predominantly collective invasion patterns (86/86 samples) in both carcinoma types. Whereas collective invasion in IDC lesions retained adherens junctions, multicellular clusters and “Indian files” in ILC, despite the absence of adherens junctions (AJ) proteins E-cadherin and β-catenin, retained CD44 at cell–cell contacts. By histomorphological scoring and semi-automated image analysis, we show that the extent of collective invasion into the adipose tissue correlated with decreased distant metastasis-free survival (5-year follow-up; hazard ratio: 2.32 and 2.29, respectively). Thus, collective invasion represents the predominant invasion mode in breast cancer, develops distinct junctional subtypes in IDC and ILC, and associates with distant metastasis, suggesting a critical role in systemic dissemination.

Isolation of All CD44 Transcripts in Human Epidermis and Regulation of Their Expression by Various Agents

CD44, a cell surface proteoglycan, is involved in many biological events. CD44 transcripts undergo complex alternative splicing, resulting in many functionally distinct isoforms. To date, however, the nature of these isoforms in human epidermis has not been adequately determined. In this study, we isolated all CD44 transcripts from normal human epidermis, and studied how their expressions are regulated. By RT-PCR, we found that a number of different CD44 transcripts were expressed in human epidermis, and we obtained all these transcripts from DNA bands in agarose and acrylamide gels by cloning. Detailed sequence analysis revealed 18 CD44 transcripts, 3 of which were novel. Next, we examined effects of 10 different agents on the expression of CD44 transcripts in cultured human keratinocytes, and found that several agents, particularly epidermal growth factor, hydrogen peroxide, phorbol 12-myristate 13-acetate, retinoic acid, calcium and fetal calf serum differently regulated their expressions in various patterns. Furthermore, normal and malignant keratinocytes were found to produce different CD44 transcripts upon serum stimulation and subsequent starvation, suggesting that specific CD44 isoforms are involved in tumorigenesis via different CD44-mediated biological pathways.

Proteoglycans in Normal and Healing Skin

Significance: Proteoglycans have a distinct spatial localization in normal skin and are essential for the correct structural development, organization, hydration, and functional properties of this tissue. The extracellular matrix (ECM) is no longer considered to be just an inert supportive material but is a source of directive, spatial and temporal, contextual information to the cells via components such as the proteoglycans. There is a pressing need to improve our understanding of how these important molecules functionally interact with other matrix structures, cells and cellular mediators in normal skin and during wound healing. Recent Advances: New antibodies to glycosaminoglycan side chain components of skin proteoglycans have facilitated the elucidation of detailed localization patterns within skin. Other studies have revealed important proliferative activities of proteinase-generated fragments of proteoglycans and other ECM components (matricryptins). Knockout mice have further established the functional importance of skin proteoglycans in the assembly and homeostasis of the normal skin ECM. Critical Issues: Our comprehension of the molecular and structural complexity of skin as a complex, dynamic, constantly renewing, layered connective tissue is incomplete. The impact of changes in proteoglycans on skin pathology and the wound healing process is recognized as an important area of pathobiology and is an area of intense investigation. Future Directions: Advanced technology is allowing the development of new artificial skins. Recent knowledge on skin proteoglycans can be used to incorporate these molecules into useful adjunct therapies for wound healing and for maintenance of optimal tissue homeostasis in aging skin.

The biology of CD44 and HCELL in hematopoiesis: the 'step 2-bypass pathway' and other emerging perspectives

PURPOSE OF REVIEW

The homing and egress of hematopoietic stem and progenitor cells (HSPCs) to and from marrow, respectively, and the proliferation and differentiation of HSPCs within marrow are complex processes critically regulated by the ordered expression and function of adhesion molecules that direct key cell-cell and cell-matrix interactions. The integral membrane molecule CD44, known primarily for its role in binding hyaluronic acid, is characteristically expressed on HSPCs. Conspicuously, human HSPCs uniquely display a specialized glycoform of CD44 known as hematopoietic cell E-/L-selectin ligand (HCELL), which is the most potent ligand for both E-selectin and L-selectin expressed on human cells. This review focuses on recent advances in our understanding of the biology of CD44 and HCELL in hematopoiesis.

RECENT FINDINGS

New data indicate that CD44-mediated events in hematopoiesis are more complex than previously imagined. Ex-vivo glycan engineering has established that HCELL serves as a 'bone marrow homing receptor'. Moreover, biochemical studies now show that CD44 forms bimolecular complexes with a variety of membrane proteins, one of which is VLA-4. Engagement of CD44 or of HCELL directly induces VLA-4 activation via G-protein-dependent signaling, triggering a 'step 2-bypass pathway' of cell migration, and extravascular lodgment, in absence of chemokine receptor engagement.

SUMMARY

Recent studies have further clarified the roles of CD44 and its glycoform HCELL in hematopoietic processes, providing key insights on how targeting these molecules may be beneficial in promoting hematopoiesis and in treating hematologic malignancies.

Heparan sulfate proteoglycans in healthy and diseased systems

Heparin and heparan sulfate (HS) are glycosaminoglycans (GAGs) that are synthesized in the tissues and organs of mammals. They are synthesized and attached to a core protein as proteoglycans through serine-glycine concensus motifs along the core protein. These GAGs are linear polysaccharides composed of repeating disaccharide saccharide units that are variously modified along their length. As a consequence of these modifications naturally occurring heparin and HS are extremely heterogeneous in their structures. A diverse range of proteins bind heparin and HS. The types of proteins that bind are dictated by the structure of the HS or heparin chains with which they are interacting. Heparan sulfates play major roles in tissue development and in maintaining homeostasis within healthy individuals. Recent genetic studies illustrate that alterations in their structural organization can have important consequences often giving rise to, or directly causing, a disease situation. A greater understanding of the repertoire of proteins with which heparin and HS interact and the diseases that can be caused by perturbations in the structures of heparin and HS proteoglycan may provide insights into possible therapeutic interventions. These issues are discussed with a focus on musculoskeletal phenotypes and diseases.

Cancer cells in transit: the vascular interactions of tumor cells

Metastasis is a highly regulated, multistep process in which cancerous cells shed from the primary tumor and enter the circulatory system, where they interact extensively with host cells before they lodge and colonize the target organ. The adhesive interactions of circulating tumor cells with platelets, leukocytes, and endothelial cells facilitate their survival and extravasation from the vasculature, thus representing critical kick-off events for the colonization of distant organs. This review presents our current mechanistic knowledge on vascular interactions of tumor cells, and it discusses biochemical and cell and molecular biology techniques used for the identification of novel receptor-ligand pairs mediating these interactions. This review brings together diverse observations about the contributions of key molecular constituents, including selectins, fibrin(ogen), and CD44, in one mechanistic interpretation. Understanding the molecular underpinnings of adhesive interactions between tumor cells and host cells may provide guidelines for developing promising antimetastatic therapies when initiated early in the course of disease progression.

Reduced production of sulfated glycosaminoglycans occurs in Zambian children with kwashiorkor but not marasmus

BACKGROUND

Kwashiorkor, a form of severe malnutrition with high mortality, is characterized by edema and systemic abnormalities. Although extremely common, its pathophysiology remains poorly understood, and its characteristic physical signs are unexplained.

OBJECTIVE

Because kwashiorkor can develop in protein-losing enteropathy, which is caused by a loss of enterocyte heparan sulfate proteoglycan (HSPG), and previous observations suggest abnormal sulfated glycosaminoglycan (GAG) metabolism, we examined whether intestinal GAG and HSPG are abnormal in children with kwashiorkor.

DESIGN

Duodenal biopsy samples collected from Zambian children with marasmus (n = 18), marasmic kwashiorkor (n = 8), and kwashiorkor (n = 15) were examined for expression of HSPG, GAGs, and immunologic markers and compared against reference samples from healthy UK control children. GAG and HSPG expression density and inflammatory cell populations were quantitated by computerized analysis.

RESULTS

The kwashiorkor group was less wasted and had a lower HIV incidence than did the other groups. All duodenal biopsy samples showed inflammation compared with the histologically uninflamed control samples. Biopsy samples from marasmic children had greater inflammation and greater CD3+ and HLA-DR (human leukocyte antigen DR)-positive cell densities than did samples from children with kwashiorkor. Expression of both HSPG and GAGs was similar between marasmic and well-nourished UK children but was markedly lower in children with kwashiorkor in both the epithelium and lamina propria. Although underglycosylated and undersulfated, epithelial syndecan-1 protein was normally expressed in kwashiorkor, which confirmed that abnormalities arise after core protein synthesis.

CONCLUSIONS

Intestinal HSPG loss occurs in kwashiorkor, which may precipitate protein-losing enteropathy to cause edema. If occurring systemically, impaired HSPG expression could cause several previously unexplained features of kwashiorkor. We speculate that a genetic predisposition to reduced HSPG biosynthesis may offer a contrasting selective advantage, by both diminishing protein catabolism during transient undernutrition and protecting against specific infectious diseases.

Heparan sulfate proteoglycans: a GAGgle of skeletal-hematopoietic regulators

This review summarizes our current understanding of the presence and function of heparan sulfate proteoglycans (HSPGs) in skeletal development and hematopoiesis. Although proteoglycans (PGs) comprise a large and diverse group of cell surface and matrix molecules, we chose to focus on HSPGs owing to their many proposed functions in skeletogenesis and hematopoiesis. Specifically, we discuss how HSPGs play predominant roles in establishing and regulating niches during skeleto-hematopoietic development by participating in distinct developmental processes such as patterning, compartmentalization, growth, differentiation, and maintenance of tissues. Special emphasis is placed on our novel hypothesis that mechanistically links endochondral skeletogenesis to the establishment of the hematopoietic stem cell (HSC) niche in the marrow. HSPGs may contribute to these developmental processes through their unique abilities to establish and mediate morphogen, growth factor, and cytokine gradients; facilitate signaling; provide structural stability to tissues; and act as molecular filters and barriers.

Papilloma development is delayed in osteopontin-null mice: implicating an antiapoptosis role for osteopontin

Osteopontin is a secreted, adhesive glycoprotein, whose expression is markedly elevated in several types of cancer and premalignant lesions, implicating its association with carcinogenesis. To test the hypothesis that induced osteopontin is involved in tumor promotion in vivo, osteopontin-null and wild-type (WT) mice were subjected to a two-stage skin chemical carcinogenesis protocol. Mice were initiated with 7,12-dimethylbenz(a)anthracene (DMBA) applied on to the dorsal skin followed by twice weekly application of 12-O-tetradecanoylphorbol-13-acetate (TPA) for 27 weeks. Osteopontin-null mice showed a marked decrease both in tumor/papilloma incidence and multiplicity compared with WT mice. Osteopontin is minimally expressed in normal epidermis, but on treatment with TPA its expression is highly induced. To determine the possible mechanism(s) by which osteopontin regulates tumor development, we examined cell proliferation and cell survival. Epidermis from osteopontin-null and WT mice treated with TPA thrice or with DMBA followed by TPA for 11 weeks showed a similar increase in epidermal hyperplasia, suggesting that osteopontin does not mediate TPA-induced cell proliferation. Bromodeoxyuridine staining of papillomas and adjacent epidermis showed no difference in cell proliferation between groups. However, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling analyses indicated a greater number of apoptotic cells in DMBA-treated skin and papillomas from osteopontin-null versus WT mice. These studies are the first to show that induction of the matricellular protein osteopontin facilitates DMBA/TPA-induced cutaneous carcinogenesis most likely through prevention of apoptosis.

Fibroblast invasive migration into fibronectin/fibrin gels requires a previously uncharacterized dermatan sulfate-CD44 proteoglycan

After tissue injury, fibroblast migration from the peri-wound collagenous stroma into the fibrin-laden wound is critical for granulation tissue formation and subsequent healing. Recently we found that fibroblast transmigration from a collagen matrix into a fibrin matrix required the presence of fibronectin. Several integrins-alpha 4 beta 1, alpha 5 beta 1, and alpha v beta 3-with known fibronectin binding affinity were necessary for this invasive migration. Here we examined another family of cell surface receptors: the proteoglycans. We found that dermatan sulfate was required for fibroblast migration into a fibronectin/fibrin gel. This conclusion was based on beta-xyloside inhibition of glycanation and specific glycosaminoglycan degradation. CD44, a cell surface receptor known to bind hyaluronan, not infrequently exists as a proteoglycan, decorated with various glycosaminoglycan chains including heparan sulfate and chondroitin sulfate, and as such can bind fibronectin. We found that CD44H, the non-spliced isoform of CD44, was necessary for fibroblast invasion into fibronectin/fibrin gels. Resting fibroblasts expressed mostly nonglycanated CD44H core protein, which became glycanated with chondroitin sulfate and dermatan sulfate, but not heparan sulfate, after a 24 h incubation with platelet-derived growth factor, the stimulus used in the migration assay. These results demonstrate that dermatan sulfate-CD44H proteoglycan is essential for fibroblast migration into fibrin clots and that platelet-derived growth factor, the stimulus for migration, induces the production of chondroitin-sulfate- and dermatan-sulfate-glycanated CD44H.

Hyaluronan and CD44: strategic players for cell-matrix interactions during chondrogenesis and matrix assembly

Embryonic induction, soluble and insoluble factors, receptors, and signal transduction are orchestrated for the morphogenesis of the cartilage elements. The interaction of cells with the extracellular matrix (ECM) may lead to altered cellular response to morphogens based on the formation of new adhesive contacts, or the uncoupling of cell-matrix interactions. Hyaluronan's influence on cell behavior, and its intimate association with cells are accomplished by a wide variety of specific binding proteins for hyaluronan. The temporal expression of the hyaluronan receptor CD44 (which is expressed as several alternatively spliced variants) may be strategic to many of these cell-matrix interactions during chondrogenesis. CD44 expression is temporally coincident with the reduction of intercellular spaces at the regions of future cartilage deposition. The spatial organization of CD44 at the cell surface may function to establish or regulate the structure of the pericellular matrix dependent on a hyaluronan scaffold. As the ECM is modified during embryogenesis, the cellular response to inductive signals may be altered. An uncoupling of chondrocyte-hyaluronan interaction leads to chondrocytic chondrolysis. Thus, consideration of cell-matrix interactions during chondrogenesis, in the light of our current understanding of the temporal and spatial expression of signaling morphogens, should become a promising focus of future research endeavors.

Hyaluronan, CD44 and versican in epidermal keratinocyte tumours

BACKGROUND

The high molecular weight polysaccharide hyaluronan is a major component of the extracellular matrix between the vital cells of human skin epidermis. The levels of hyaluronan, and those of the hyaluronan receptor CD44 and the hyaluronan binding proteoglycan versican, correlate with the aggressiveness of different human carcinomas of epithelial origin.

OBJECTIVES

To study skin keratinocyte tumours for the expression of hyaluronan, the hyaluronan receptor CD44 and the hyaluronan binding proteoglycan versican.

METHODS

Paraffin-embedded sections of 114 basal cell carcinomas (BCC), 31 in situ carcinomas (ISC) and 35 squamous cell carcinomas (SCC) were stained with a hyaluronan specific probe, biotinylated hyaluronan binding complex, and with monoclonal antibodies against CD44 and versican.

RESULTS

Compared with normal epidermis, ISC and well differentiated SCCs showed an enhanced hyaluronan signal on carcinoma cells while CD44 expression level resembled that of normal skin. Less differentiated SCCs showed reduced and irregular expression of both hyaluronan and CD44 on carcinoma cells. In BCCs, hyaluronan and CD44 signals were absent or very low on the surface of carcinoma cells. However, hyaluronan was frequently present on BCC cell nuclei, a feature completely absent in ISC, SCC and normal epidermis. An accumulation of hyaluronan in the connective tissue stroma around the tumour was more frequent in SCCs than BCCs. Versican staining was positive around hair follicles and dermal blood vessels of normal skin. Peritumoral versican signal was present in a part of the BCCs but not in other tumours.

CONCLUSIONS

The completely different hyaluronan and CD44 expression patterns in BCC and SCC probably reflect the different origins of the tumours, with BCC an undifferentiated keratinocyte and SCC a keratinocyte at an early stage in the differentiation pathway. The difference in hyaluronan and CD44 expression between these tumours may also contribute to the difference in their capacity to metastasize.

Role of sulfation in CD44-mediated hyaluronan binding induced by inflammatory mediators in human CD14(+) peripheral blood monocytes

Activation of T cells by Ag or stimulation of monocytes with inflammatory cytokines induces CD44 to bind to hyaluronan (HA), an adhesion event implicated in leukocyte-leukocyte, leukocyte-endothelial cell, and leukocyte-stromal cell interactions. We have previously shown that TNF-alpha induces CD44 sulfation in a leukemic cell line, which correlated with the induction of HA binding and CD44-mediated adhesion. In this study, we establish that TNF-alpha and IFN-gamma induce HA binding and the sulfation of CD44 in CD14(+) PBMC, whereas no induced HA binding or CD44 sulfation was observed in CD14(-) PBMC stimulated with TNF-alpha. Treatment of cells with NaClO(3), an inhibitor of sulfation, prevented HA binding in a significant percentage of CD14(+) PBMC induced by TNF-alpha, LPS, IL-1beta, or IFN-gamma. Furthermore, stimulation with TNF-alpha or IFN-gamma in the presence of NaClO(3) reduced the ability of isolated CD44H to bind HA, demonstrating a direct effect of CD44H sulfation on HA binding. In contrast, the transient induction of HA binding in T cells by PHA was not affected by NaClO(3), suggesting that activated T cells do not use sulfation as a mechanism to regulate HA binding. Overall, these results demonstrate that inducible sulfation of CD44H is one mechanism used by CD14(+) peripheral blood monocytes to induce HA binding in response to inflammatory agents such as TNF-alpha and IFN-gamma.

Hyaluronidase can modulate expression of CD44

CD44 is a family of transmembrane glycoproteins with multiple isoforms generated by alternative exon splicing of a single gene. CD44 and its variants are expressed on a wide variety of cells including cancer cells. The mechanisms by which splice variant exons are selected are unknown. The presence of hyaluronan in the environment of the cell appears to influence that selection process. The expression of particular splice variants of CD44 as well as the simultaneous presence of hyaluronan is important for motility, invasion, and the metastatic spread of some tumors. The influence of hyaluronidase digestion on the expression of CD44 in human cancer cell lines was examined. CD44 isoforms containing alternatively spliced exons were sensitive to hyaluronidase digestion in all lines examined, but differences between cell lines were observed. Expression of CD44s, the standard form, was resistant to digestion in two of three cell lines. A tentative model was formulated proposing that CD44 isoforms containing splice variants are unstable, requiring the continuous presence of ligand for expression. CD44s is relatively more stable, not requiring the continuous presence of hyaluronan. Additionally, a number of new CD44 variant isoforms, not previously observed, were identified.

Reduced level of CD44 and hyaluronan associated with unfavorable prognosis in clinical stage I cutaneous melanoma

The cell surface glycoprotein CD44 and its ligand, hyaluronan (HA), enhance growth and metastatic capacity of melanoma cells in vitro, but their clinical significance in primary cutaneous melanoma is still unclear. Therefore, we studied whether the levels of CD44 and HA associate with disease progression and survival of cutaneous melanoma. A series of 292 clinical stage I cutaneous melanomas was analyzed by immunohistochemistry using an anti-CD44H antibody (clone 2C5). HA was demonstrated histochemically using a biotinylated HA-specific affinity probe (bHABC). The reduced staining levels of CD44 and HA were associated with each other and indicators of progressive disease. Reduced CD44 and HA level, high tumor thickness, high pT category, high Clark's level, bleeding, and male gender predicted short univariate recurrence free survival (RFS) and overall survival (OS). In Cox's multivariate analysis (N: = 251), the decreased level of CD44, high tumor thickness, and bleeding predicted independently short RFS. High tumor thickness and bleeding were associated with short OS. We conclude that the reduced cell surface CD44 and HA levels associate with poor prognosis in clinical stage I cutaneous melanoma. The notion that the decreased level of CD44 independently predicts short RFS suggests that reduced cell surface CD44 enhances the spreading potential in localized cutaneous melanoma and that quantification of CD44 offers a prognostic tool for its clinical evaluation.

Heparan sulfate proteoglycans as extracellular docking molecules for matrilysin (matrix metalloproteinase 7)

Many matrix metalloproteinases (MMPs) are tightly bound to tissues; matrilysin (MMP-7), although the smallest of the MMPs, is one of the most tightly bound. The most likely docking molecules for MMP-7 are heparan sulfate proteoglycans on or around epithelial cells and in the underlying basement membrane. This is established by extraction experiments and confocal microscopy. The enzyme is extracted from homogenates of postpartum rat uterus by heparin/heparan sulfate and by heparinase III treatment. The enzyme is colocalized with heparan sulfate in the apical region of uterine glandular epithelial cells and can be released by heparinase digestion. Heparan sulfate and MMP-7 are expressed at similar stages of the rat estrous cycle. The strength of heparin binding by recombinant rat proMMP-7 was examined by affinity chromatography, affinity coelectrophoresis, and homogeneous enzyme-based binding assay; the K(D) is 5-10 nM. Zymographic measurement of MMP-7 activity is greatly enhanced by heparin. Two putative heparin-binding peptides have been identified near the C- and N-terminal regions of proMMP-7; however, molecular modeling suggests a more extensive binding track or cradle crossing multiple peptide strands. Evidence is also found for the binding of MMP-2, -9, and -13. Binding of MMP-7 and other MMPs to heparan sulfate in the extracellular space could prevent loss of secreted enzyme, provide a reservoir of latent enzyme, and facilitate cellular sensing and regulation of enzyme levels. Binding to the cell surface could position the enzyme for directed proteolytic attack, for activation of or by other MMPs and for regulation of other cell surface proteins. Dislodging MMPs by treatment with compounds such as heparin might be beneficial in attenuating excessive tissue breakdown such as occurs in cancer metastasis, arthritis, and angiogenesis.

Prognostic importance of the expression of CD44 splice variants in oral squamous cell carcinomas

Considering squamous cell carcinomas (SCCs) of the oral cavity and oropharynx the molecular mechanisms underlying the infiltration and destruction of adjacent tissue as well as the metastatic spread are largely unknown. In this context, the detection of defective expression of cellular adhesion molecules in the tumour cells, e.g. CD44, might be important and correlated with prognosis. Paraffin-embedded tumour-tissue from 99 patients with primary oral and oropharyngeal SCC, additionally including corresponding lymph-node metastases in nine cases, was analysed for expression of the CD44 splice variants v4, v5, v6, v7, and v9 by means of immunohistochemistry. A diminution of at least one of the examined CD44 isoforms compared to the normal oral epithelium was observed in 39.4% of the squamous cell carcinomas. No correlations could be found between CD44 expression and pT- or pN-stage. However, decreased expression of v9 was correlated with higher histological grade (p < 0.001). Moreover, reduced CD44 expression was a statistically significant independent predictor for shorter survival time (p = 0.002) as well as shorter recurrence-free interval (p = 0.004) in addition to pT- and pN-stage. The separate analysis showed that particularly the decreased v7 (p = 0.04) and v9 (p < 0.02) expression in the tumour cells was associated negatively with survival.

Type IV pili of pathogenic Neisseriae elicit cortical plaque formation in epithelial cells

The pathogenic Neisseriae Neisseria meningitidis and Neisseria gonorrhoeae, initiate colonization by attaching to host cells using type IV pili. Subsequent adhesive interactions are mediated through the binding of other bacterial adhesins, in particular the Opa family of outer membrane proteins. Here, we have shown that pilus-mediated adhesion to host cells by either meningococci or gonococci triggers the rapid, localized formation of dramatic cortical plaques in host epithelial cells. Cortical plaques are enriched in both components of the cortical cytoskeleton and a subset of integral membrane proteins. These include: CD44v3, a heparan sulphate proteoglycan that may serve as an Opa receptor; EGFR, a receptor tyrosine kinase; CD44 and ICAM-1, adhesion molecules known to mediate inflammatory responses; f-actin; and ezrin, a component that tethers membrane components to the actin cytoskeleton. Genetic analyses reveal that cortical plaque formation is highly adhesin specific. Both pilE and pilC null mutants fail to induce cortical plaques, indicating that neisserial type IV pili are required for cortical plaque induction. Mutations in pilT, a gene required for pilus-mediated twitching motility, confer a partial defect in cortical plaque formation. In contrast to type IV pili, many other neisserial surface structures are not involved in cortical plaque induction, including Opa, Opc, glycolipid GgO4-binding adhesins, polysialic acid capsule or a particular lipooligosaccharide variant. Furthermore, it is shown that type IV pili allow gonococci to overcome the inhibitory effect of heparin, a soluble receptor analogue, on gonococcal invasion of Chang and A431 epithelial cells. These and other observations strongly suggest that type IV pili play an active role in initiating neisserial infection of the mucosal surface in vivo. The functions of type IV pili and other neisserial adhesins are discussed in the specific context of the mucosal microenvironment, and a multistep model for neisserial colonization of mucosal epithelia is proposed.

Growth and differentiation regulate CD44 expression on human keratinocytes

Several members of the CD44 family of hyaluronan receptors are expressed on keratinocytes. To identify factors that might be important in regulating CD44 expression, we studied CD44 expression on keratinocytes growing in vitro under a variety of conditions and on cells isolated directly from epidermis. Using Western immunoblots and metabolic labeling, we showed that the pattern of CD44 proteins expressed by keratinocytes was strongly influenced by growth and differentiation. Many protein forms of CD44 are expressed on proliferating keratinocytes in preconfluent cultures, whereas only a few forms are expressed on differentiated cells and in confluent cultures. In preconfluent monolayers, at least four splice variants were identified, including epican, CD44H, CD44E, and a 180-kDa variant. In differentiated cells or in confluent cultures, by contrast, only epican and the 180-kDa protein variant were found. Synthesis of all variants is strongly downregulated when keratinocytes become confluent or when they differentiate. Epican is the predominant form of CD44 on keratinocytes under all conditions and is expressed as a heparan, chondroitin, or keratan sulfate proteoglycan. Preconfluent basal keratinocytes, but not confluent or differentiated keratinocytes, also express chondroitin sulfate proteoglycan forms of CD44E and of the 180-kDa core protein. The modal size of the epican expressed on differentiated keratinocytes is smaller than the size of the epican expressed on basal keratinocytes. Thus, cell confluence and differentiation regulate several aspects of CD44 expression on keratinocytes, suggesting nuances in function for the different protein forms.

Hyaluronan bound to CD44 on keratinocytes is displaced by hyaluronan decasaccharides and not hexasaccharides

Abundant hyaluronan is present between epidermal keratinocytes. However, virtually nothing is known regarding its organization in the limited extracellular space between these cells. We have used metabolic labeling with [3H]glucosamine and [35S]sulfate and a hyaluronan-specific biotinylated probe to study the metabolism of hyaluronan and its localization in monolayer cultures of a rat epidermal keratinocyte cell line. Hyaluronan (approximately 20 fg/cell) was present on the apical and lateral surfaces of the cells in two nearly equal pools, either in patches (approximately 160/cell) or diffusely spread. The hyaluronan in the patches is bound to CD44 as indicated by co-localization with an antibody to CD44, and by displacement with hyaluronan decasaccharides as well as with an antibody that blocks hyaluronan binding to CD44. The inability of hyaluronan oligomers shorter than 10 monosaccharides to displace hyaluronan suggests that CD44 dimerization or cooperative interactions are required for tight binding. The diffuse hyaluronan pool is likely bound to hyaluronan synthase during its biosynthesis.

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.

CD44 substituted with heparan sulfate and endo-beta-galactosidase-sensitive oligosaccharides: a major proteoglycan in adult human epidermis

CD44 is a group of cell surface glycoproteins that is generated from a single gene by mRNA splice variation. Its functions in matrix adhesion and tumor invasion are strongly influenced by glycosylation. We studied the glycosylated tissue forms of CD44 from extracts of normal adult human epidermis by using western blotting and immunoprecipitation from short-term skin organ cultures. An antibody for CD44 (Hermes 3) precipitated 7-17% of all 35SO4-labeled proteoglycans (PGs) synthesized in epidermis. Immunoprecipitates digested with heparitinase lost 40-68% of incorporated 35SO4 and 24-40% of [3H]glucosamine, indicating that heparan sulfate was the predominant glycosaminoglycan in epidermal CD44. Chondroitinase ABC released 10-25% and 6-12% of 35SO4 and [3H]glucosamine, respectively. Less than 5% of both isotopes were susceptible to keratanase. Five to 33% of 35SO4 and 26-37% of [3H]glucosamine, however, was released by endo-beta-galactosidase, implying marked substitution by oligosaccharides with N-acetyllactosamine repeats. Heparitinase pretreatment retarded, whereas endo-beta-galactosidase enhanced the mobility of the > or = 180-kDa polydisperse CD44 on agarose gel electrophoresis. On SDS-polyacrylamide gel electrophoresis, however, western blotting and fluorographs of 35SO4-labeled immunoprecipitates showed the main CD44 isoform at > or = 250 kDa and a shift to 180-200 kDa after heparitinase treatment. Keratanase, keratanase II, and chondroitinase ABC had minor effects. A less abundant form of CD44, with a core of 100 kDa, partly substituted with chondroitinase ABC- and endo-beta-galactosidase-sensitive chains, was also present. Therefore, the large heparan sulfate-substituted CD44 forms a significant part of all proteoglycans in normal human epidermis. Both the large and the 100-kDa variant of epidermal CD44 contain endo-beta-galactosidase-sensitive oligosaccharides not previously noted in other cells or tissues.

CD44 isoforms with exon v6 and metastasis of primary N0M0 breast carcinomas

New isoforms of CD44 with alternatively spliced exons have recently been described. Expression of exon v6 seems to be of particular interest. It has indeed been associated with poorer outcome of breast cancer patients with node invasion at diagnosis. However, no data were available for patients N0M0 (with neither metastasis nor node invasion at diagnosis). Moreover, previous statistical analyses were realized using immunohistochemical methods to detect CD44v6 expression although several variants with exon v6 have been described. We investigated expression of isoforms containing CD44v6 using an RT-PCR approach and a panel of 25 normal breast specimens, 10 mammary fibroadenomas, 8 cystic samples and 52 primary breast tumors (38 invasive N0M0). Normal breasts, fibroadenomas, and cysts all express the same variant, A (with exon v6 only), while several transcripts are amplified in tumors. Expression of variants other than A correlates with acquisition of a malignant phenotype. Invasive cancers also express additional variants in comparison with in situ carcinomas. Metastasis capacities seem to be associated with transcription of variants other than A but also with no transcription of some of them, variants D (with exons v6 and v10) and L (with exons v6 to v10). Expression of variants D and L correlates with higher percentages of disease-free survival and better outcome. Expression of CD44 splice variants with exon v6, as detected by RT-PCR, might be a useful prognostic factor for breast cancer. However, since the series size is small, our results need to be confirmed by later studies on a larger number of patients.

CD44 and the adhesion of neoplastic cells

CD44 is a family of transmembrane glycoproteins that act mainly as a receptor for hyaluronan. It can also bind some other extracellular matrix ligands (chondroitin sulphate, heparan sulphate, fibronectin, serglycin, osteopontin) with lower affinity. CD44 is encoded by a single gene containing 20 exons, 10 of which (v1-v10) are variant exons inserted by alternative splicing. The standard, ubiquitously expressed isoform of CD44, does not contain sequences encoded by these variant exons. Numerous variant isoforms of CD44 containing different combinations of exons v1-v10 inserted into the extracellular domain can be expressed in proliferating epithelial cells and activated lymphocytes. CD44 plays a significant role in lymphocyte homing. Both alternative splicing and glycosylation influence receptor function of the molecule, usually reducing its affinity to hyaluronan. The cytoplasmic domain of CD44 communicates with the cytoskeleton via ankyrin and proteins belonging to the ezrin-moesin-radixin family. Relatively little is known about the intracellular events following interactions of CD44 with its ligands. Some variant isoforms, especially those containing sequences encoded by v6-v10, are overexpressed in both human and animal neoplasms. In a rat pancreatic adenocarcinoma model one of the variant CD44 isoforms was proved to be determinant in the metastatic process. For some human neoplasms (carcinomas of the digestive tract, non-Hodgkin's lymphomas, thyroid carcinomas, and others) correlations have been made between the particular pattern of CD44 variants produced by neoplastic cells and clinicopathological parameters of tumours, such as grade, stage, presence of metastases, and survival. In vitro studies indicate that modifications of CD44 expression result in different ligand recognition and influence cell motility, invasive properties, and metastatic potential of experimental tumours. Investigation of CD44 neoexpression can be useful both in early cancer diagnosis and in predicting tumour behaviour. It can also contribute to better understanding of molecular mechanisms leading to neoplastic transformation.

A deficit of chondroitin sulfate proteoglycans on the bladder uroepithelium in interstitial cystitis

OBJECTIVES

To investigate the abundance of chondroitin sulfate proteoglycans at the bladder lumenal and subepithelial surfaces in bladder biopsies derived from patients with interstitial cystitis (IC) and controls.

METHODS

Tissue sections derived from biopsies from 31 IC patients and 24 pathologically normal control sections were labeled for proteoglycans using the 2B6 anti-"stub" antibody and detected by immunohistochemistry.

RESULTS

On the lumenal surface, 5 of 31 (19%) IC sections were positive for proteoglycans versus 14 of 24 (58%) control sections (P = 0.00011). At the basal surface, 5 of 19 IC patients were positive versus 7 of 12 controls (P = 0.032).

CONCLUSIONS

A deficit of bladder lumenal and basal proteoglycans is associated with IC. The deficit in basal layer proteoglycans suggests an altered urothelial differentiation program. The lumenal deficit suggests that the charge-dependent exclusion of ions from the bladder surface is compromised in IC.

CD44 expression on epidermal melanocytes

We examined CD44 expression on melanocytes to begin to understand what role CD44 might have in the normal behavior of melanocytes and to provide a basis for comparing CD44 expression in melanoma cells. CD44 was expressed on the entire surface of melanocytes and accentuated at the tips of dendritic processes. Two predominant forms of CD44 are expressed on cultured human foreskin melanocytes. One form has the covalent addition of chondroitin sulfate, whereas the other form has no chondroitin sulfate. Both use the hematopoietic, or CD44H, core protein. Using polymerase chain reaction primers that span the site where alternative splicing of CD44 occurs, we found only the cDNA coding CD44H. 12-O-Tetradecanoylphorbol 13-acetate increases the size of the chondroitin sulfate chain(s) attached to CD44 but not the proportion of CD44 molecules that carry chondroitin sulfate. Ninety percent of proteoglycans on melanocytes are chondroitin sulfate proteoglycans, and the CD44 chondroitin sulfate proteoglycan represented 10% of that total. These data show that CD44H is expressed as a "part-time" chondroitin sulfate proteoglycan on normal cultured melanocytes.

A di-hydrophobic Leu-Val motif regulates the basolateral localization of CD44 in polarized Madin-Darby canine kidney epithelial cells

Both in vivo and in vitro the distribution of the resident plasma membrane adhesion protein, CD44, is restricted to the basolateral domain of polarized epithelial cells, suggesting a role in interepithelial interactions. To determine how this localization might be regulated a range of CD44 cytoplasmic domain mutations were generated and a minimal 5 amino acid sequence, His330-Leu-Val-Asn-Lys334, was identified which when deleted results in expression of CD44 on the apical microvillal membrane. Further mutagenesis throughout this regions pinpointed a critical di-hydrophobic motif, Leu331/Val332. The ability of wild type but not mutant CD44 cytoplasmic domains to redirect an apically targeted protein, placental alkaline phosphatase, to the basolateral plasma membrane demonstrates that this sequence can function as a dominant localization signal. This His330-Lys334 sequence is spatially separate from other CD44 regulatory elements and as discussed here, a comparison with known basolateral sorting sequences identified in other transmembrane proteins suggests that a distinct mechanism operates to retain resident plasma membrane proteins in their correct plasma membrane subdomains.

CD44 is the major peanut lectin-binding glycoprotein of human epidermal keratinocytes and plays a role in intercellular adhesion

Although binding of peanut agglutinin (PNA) to keratinocytes is often used as a marker of terminal differentiation, the identity of the PNA-binding glycoproteins has been unclear. We now show that an antiserum raised against the glycoproteins recognises isoforms of CD44, the most abundant of which could be labelled with [35S]sulphate, indicating the presence of glycosaminoglycan side chains. RT-PCR analysis showed that keratinocytes expressed at least 5 forms of CD44 containing different numbers of exons from the variable region of the extracellular domain and also expressed the standard ‘haemopoietic’ form of CD44 which lacks the variable exons. Standard and variant isoforms of CD44 were expressed both by proliferating keratinocytes and cells undergoing terminal differentiation, although the level of CD44 mRNAs decreased when keratinocytes were placed in suspension to induce differentiation. The role of CD44 in intercellular adhesion was investigated by plating keratinocytes onto a rat pancreatic carcinoma line transfected with different CD44 isoforms. Keratinocyte adhesion to transfectants expressing variant exons 4–7 was greater than to cells expressing standard CD44 and could be inhibited with hyaluronan or digestion with hyaluronidase. These observations confirm earlier predictions that the PNA-binding glycoproteins of keratinocytes play a role in intercellular adhesion.