Role of CD44 cytoplasmic domain in hyaluronan binding

The hyaluronan (HA) binding activity of mutant CD44 constructs expressed in AKR1 T-lymphoma cells was evaluated by flow cytometry using fluoresceinconjugated HA (Fl-HA). Previous studies showed that wild-type hematopoietic CD44 bound Fl-HA when expressed in AKR1, but that truncated “tailless” CD44, lacking all but six amino acids of the cytoplasmic domain, did not bind. Here, we show that a disulfide-bonded dimer of CD44, formed by substituting the transmembrane region of CD3ζ chain for that of CD44, binds Fl-HA, even when the cytoplasmic domain of the CD44 dimer is absent. We conclude that dimerization of CD44 abrogates the requirement for the cytoplasmic domain, suggesting that the cytoplasmic domain of CD44 may contribute to HA binding by promoting CD44 clustering. These results suggest that changes in the distribution of CD44 on the cell surface, induced by molecular interactions either from within the cell or from outside, may regulate its role as a receptor. Further studies sought to localize the region of the CD44 cytoplasmic domain contributing to HA binding by the construction of a series of cytoplasmic domain truncation mutants and internal deletion mutants. All of the mutant CD44 molecules bound Fl-HA similarly to wild-type CD44. Thus, it was not possible to assign the function mediating HA binding to a specific region of the cytoplasmic domain, suggesting either that multiple regions of the cytoplasmic domain can promote enhancement of HA binding, or that the role of the cytoplasmic domain in mediating this function does not require a specific amino acid sequence.     

Chimeric CD4/CD44 molecules associate with CD44 via the transmembrane region and reduce hyaluronan binding in T cell lines

Cells of the immune system tightly regulate the binding ability of cell adhesion molecules. The binding of the extracellular matrix component hyaluronan to CD44 is no exception, yet the mechanisms that regulate its binding are poorly understood. In this study a chimeric CD4/CD44 molecule, containing the extracellular domain of CD4 and the transmembrane and cytoplasmic domains of CD44, was expressed in two CD44⁺ mouse T lymphoma cell lines, BW5147 and T28. This resulted in the reduced ability of endogenous CD44 to constitutively bind hyaluronan. Immunoprecipitation of the chimeric protein in 1 % Brij-96 indicated an association between the chimera and endogenous CD44. Using various chimeric CD4/CD44 molecules, the transmembrane region of CD44 was found to mediate this association. In addition, the association of chimeric CD4/CD44 molecules with endogenous CD44 correlated with reduced hyaluronan binding. Thus, the transmembrane region of CD44 is required for the association with CD44 molecules in the cell membrane and we propose that the self-association of CD44 molecules occurs on the T cell surface to promote hyaluronan binding. Cellular events altering the interactions of the transmembrane region of CD44 thus have the potential to regulate the hyaluronan binding ability of CD44.     

Hyaluronan binding by CD44 is regulated by a phosphorylation-independent mechanism

CD44 is an adhesion receptor for which the major characterized ligand is the extracellular matrix glycosaminoglycan, hyaluronan. This interaction underlies CD44-mediated cell attachment, cell migration, and matrix remodelling during development and wound healing. Truncation of the CD44 cytoplasmic domain does not prevent cell surface expression of this hyaluronan receptor but it dramatically impairs ligand binding. In this study we have examined the role of phosphorylation in regulating this function by mutating the target serine residues to either neutral amino acids with the aim of creating a phosphorylation-incompetent molecule, or to acidic residues to mimic a fully phosphorylated CD44. In transfected AKR1 cells the behavior of both the neutral and acidic mutants was indistinguishable from wild-type CD44, indicating that there is a phosphorylation-independent mechanism involved in regulating hyaluronan binding.     

Hyaluronan‐binding by CD44 reduces the memory potential of activated murine CD8 T cells

Expansion and death of effector CD8 T cells are regulated to limit immunopathology and cells that escape contraction go on to generate immunological memory. CD44, a receptor for the extracellular matrix component hyaluronan, is a marker of activated and memory T cells. Here, we show with a murine model that the increase in CD44 expression and hyaluronan binding induced upon CD8 T cell activation was proportional to the strength of TCR engagement, thereby identifying the most strongly activated T cells. When CD44^?/? and CD44^+/+ OT‐I CD8 T cells were adoptively transferred into mice challenged with Listeria‐OVA, there was a slight increase in the percentage of CD44^+/+ cells at the effector site. However, CD44^+/+ cells were out‐competed by CD44^?/? cells after the contraction phase in the lymphoid tissues, and the CD44^?/? cells preferentially formed more memory cells. The hyaluronan‐binding CD44^+/+ CD8 effector T cells showed increased pAkt expression, higher glucose uptake, and were more susceptible to cell death during the contraction phase compared to non‐binding CD44^+/+ and CD44^?/? OT‐I CD8 T cells, suggesting that CD44 and its engagement with hyaluronan skews CD8 T cells toward a terminal effector differentiation state that reduces their ability to form memory cells.     

Elevated expression of hyaluronan and its CD44 receptor in the duodenal mucosa of coeliac patients

AIMS: Since hyaluronan (HA) metabolism is disturbed in some malignant tumours and in inflammatory diseases, we analysed HA and its receptor CD44 as well as the expression of the Ki67 nuclear protein, a marker of cell proliferation, in histological sections of duodenal biopsies of coeliac disease patients and controls. METHODS AND RESULTS: The study group consisted of 52 patients with coeliac disease in remission, 40 patients with newly diagnosed disease and 10 healthy control subjects. HA was detected with a specific biotinylated probe prepared from cartilage aggrecan and link protein, and CD44 with an antibody recognizing all forms of CD44 and another specific for its v6 variant. For the expression of the nuclear protein, monoclonal antibody MIB-1 was used. The percentage of HA-positive cells in surface epithelium was higher in newly diagnosed patients (13%) compared with patients in remission (11%) and controls (2%). In addition, HA intensity in the lamina propria was decreased in the newly diagnosed patients. In patients with active disease, 22-26% of the surface epithelium was CD44+, whereas the corresponding figure in patients in remission was 5%, and that of controls 1%. The more intensive MIB-1 labelling in the duodenal epithelium of coeliac patients without treatment was normalized after gluten-free diet. CONCLUSIONS: The HA-positive coat on surface epithelium seen even in patients in remission suggests persistent or even permanent changes in the epithelial permeability barrier in coeliac disease.     

Mouse B cell activation is inhibited by CD44 cross-linking

Lymphocyte activation and trafficking are indispensable to the immune system. CD44 is an adhesion molecule with known importance in T cell activation, lymphocyte trafficking, and tumor metastasis. Although CD44 has been shown to participate in the activation, rolling and adhesion, and homing of T cells, the role of CD44 on B cells is relatively unknown. The effects of CD44 cross-linking on murine B cell activation via CD40L was explored using the anti-CD44 mAbs RK3G9 and IM7. When immobilized on a plate, both RK3G9 and IM7 were found to strongly inhibit B cell proliferation and Ig production, especially at lower cell input concentrations. IgE inhibition was especially prominent. In contrast, soluble RK3G9 added to the B cell cultures had no effect. The inhibitory effect of anti-CD44 on B cell activation was not influenced by the addition of the anti-FcγRII, indicating that Fc cross-linking did not play a role in this inhibition. As Ig production requires several days for both B cell proliferation and differentiation to occur, the effects of delayed addition of immobilized anti-CD44 mAbs were studied, and the results indicated no inhibition after 96 hrs of culture. Finally, B cells were activated by either LPS or anti-IgM F(ab')₂. While LPS-induced B cell activation was inhibited by immobilized anti-CD44 mAbs, anti-IgM activation was refractory. Interestingly, addition of both anti-IgM and CD40L or LPS resulted in some modulation of the inhibitory activity. These results suggest that CD44 cross-linking could control polyclonal B cell activation by CD40L, but allow sIgM/CD40L activation to continue.     

人CD44的结构与功能

CD44是属于黏附因子家族的跨膜糖蛋白。它广泛表达于多种内皮细胞、间充质细胞、造血干细胞及中胚层来源的细胞和组织。其最初作用被描述为介导淋巴细胞归巢到外周淋巴组织;后来发现CD44蛋白在多种生理和病理过程中起到重要作用,如造血、免疫反应(淋巴细胞活化和归巢)、发育、创伤愈合、炎症和肿瘤等。本文旨在分析CD44结构与功能的关系,探讨其与癌症的相关性。     

A CD44 monoclonal antibody differentially regulates CD11a/CD18 binding to intercellular adhesion molecules CD54, CD102 and CD50

We have made a monoclonal anti-CD44 antibody which is able to activate the leukocyte integrin CD11a/CD18. Activated T cells strongly aggregated, and the aggregation was shown to be intercellular adhesion molecule (ICAM)-1 (CD54) and ICAM-2 (CD102) dependent. Using purified ICAM coated on plastic, only binding to ICAM-1 was increased by the CD44 antibody, whereas activation by phorbol ester increased binding to both ICAM-1 and ICAM-3. The binding to ICAM-2 was not affected by either treatment. These findings show that the CD11a/CD18 integrin can be activated in a ligand-specific manner by engagement of CD44.     

Irregular expression of hyaluronan and its CD44 receptor is associated with metastatic phenotype in laryngeal squamous cell carcinoma

 The distributions of hyaluronan (HA) and its CD44 receptor were studied in 24 normal, 27 dysplastic samples of laryngeal epithelium and in 172 squamous cell carcinomas (LSCC), using a specific probe prepared from cartilage proteoglycan (bHABC, biotinylated hyaluronan binding complex) and a monoclonal antibody (Hermes 3). HA and CD44 were expressed similarly in all normal and about 90% of dysplastic and neoplastic laryngeal epithelia. In the normal epithelium HA and CD44 were homogeneously distributed throughout the epithelium, whereas the most superficial layers were negative. This was in contrast to the picture in dysplastic epithelium and well-differentiated invasive carcinomas, which were entirely HA and CD44 positive. Local areas with a low signal for HA and CD44 were present in 11% and 22% of the samples with dysplasia, and in 27% and 28% of those with carcinoma, respectively. The presence of this staining irregularity was associated with poor differentiation of the carcinoma, a significantly elevated mitotic index and a high frequency of nodal spreading and metastases. Furthermore, the irregular staining showed a trend towards poor disease-free survival, suggesting that an altered metabolism of HA is a common feature in LSCC and is associated with an aggressive growth pattern. Received: 9 June 1998 / Accepted: 28 September 1998     

Tyrosine kinase-dependent activation of human NK cell functions upon triggering through CD44 receptor

We recently showed evidence of CD44-mediated enhancement of natural killer (NK) cell cytotoxic activity and induction of intracellular Ca²⁺ flux. In this study, we evaluated whether CD44 plays a stimulatory role in NK cell functions, such as cytokine production and activation antigen expression. Our results indicate that ligation of the CD44 receptor results in the induction of expression of the CD69 surface activation antigen as well as in the enhancement of phorbol ester-induced TNF-α secretion. We report also evidence for the coupling of CD44 receptor to a protein tyrosine kinase(s) pathway. CD44 engagement rapidly stimulates the tyrosine phosphorylation of several cellular substrates. Pretreatment of NK cells with the tyrosine kinase inhibitor herbimycin A resulted in marked decrease of CD44-stimulated phosphorylation, indicating that it activates tyrosine kinase(s). Furthermore, the drug also prevents CD44-mediated TNF-α production and CD69 expression. These findings indicate that protein tyrosine phosphorylation is an early and critical event in CD44-mediated activation of NK cell functions.     

CD44与乳腺癌的研究进展

CD44基因蛋白是一种细胞表面跨膜糖蛋白,属于黏附分子家族。CD44基因外显子根据表达方式可分为标准型CD44(CD44s)和变异型CD44(CD44v)两种类型。大量研究发现,CD44蛋白参与细胞-细胞、细胞-胞外基质之间的特异性粘附,CD44及其亚型在乳腺癌的异常表达可能与癌症的发生、发展和转移密切相关。此外,乳腺癌干细胞表面高度表达CD44分子,针对CD44分子与乳腺癌干细胞关系的研究,将会为临床上对乳腺癌的诊断、治疗选择以及预后预测提供更充分的理论依据。     

Expression of CD 44 s, CD 44 v 3 and CD 44 v 6 in benign and malignant breast lesions: correlation and colocalization with hyaluronan

AIMS: To examine the expression of CD 44 s, CD 44 v 3 and CD 44 v 6 in breast lesions, and to correlate it with the expression of hyaluronan (HA). Methods and results: CD 44 expression was studied in 75 breast tissue samples, consisting of benign, premalignant and malignant breast lesions, using immunohistochemistry. CD 44 s, but not CD 44 v 3 or CD 44 v 6, was found in the stromal cells, and it was similar in benign and malignant tumours. In benign lesions CD 4 v 6 was detected in 20-30% of the ductal epithelial cells, while C 44 v 3 and CD 44 s were not expressed. CD 44 s, CD 44 v 3 and CD 44 v 6 were all up-regulated in the in situ carcinomas and invasive carcinomas. The level of CD 44 expression in carcinoma cells did not correlate with the type or differentiation of the tumours. CD 44 and HA expression levels were not closely linked in the benign or malignant breast lesions, because HA was overexpressed later in breast cancer progression than CD 44. However, in breast carcinomas CD 44 and HA positivity was often found in the same areas of the sections, and the dual staining confirmed actual colocalization of CD 44 s and HA in the same cells. Conclusions: CD 44 s, CD 44 v 3 and CD 44 v 6 are up-regulated earlier than HA in breast carcinoma progression, and in later stages they often colocalize with cell surface HA.     

Hyaluronan,CD44, and Cyclooxygenase-2 in Colon Cancer

Carcinomas arising from colon epithelia develop or progress in a stromal microenvironment that is elevated in hyaluronan; interactions between elevated hyaluronan and the CD44 receptors on epithelial tumor cells activate an HA-receptor tyrosine kinase-mediated cell survival pathway. In this review we provide evidence that the hyaluronan-ErbB2-PI3kinase/AKT-ß-catenin-COX-2 signaling axis leads to intestinal epithelial and colon tumor cell division and proliferation. This review includes a summary of the authors work over the past years as well as citations of specific reviews related to role of hyaluronan in the pathogenesis of colon cancer.     

Mouse B Cell Activation is Inhibited by CD44 Cross-Linking

Lymphocyte activation and trafficking are indispensable to the immune system. CD44 is an adhesion molecule with known importance in T cell activation, lymphocyte trafficking, and tumor metastasis. Although CD44 has been shown to participate in the activation, rolling and adhesion, and homing of T cells, the role of CD44 on B cells is relatively unknown. The effects of CD44 cross-linking on murine B cell activation via CD40L was explored using the anti-CD44 mAbs RK3G9 and IM7. When immobilized on a plate, both RK3G9 and IM7 were found to strongly inhibit B cell proliferation and Ig production, especially at lower cell input concentrations. IgE inhibition was especially prominent. In contrast, soluble RK3G9 added to the B cell cultures had no effect. The inhibitory effect of anti-CD44 on B cell activation was not influenced by the addition of the anti-FcγRII, indicating that Fc cross-linking did not play a role in this inhibition. As Ig production requires several days for both B cell proliferation and differentiation to occur, the effects of delayed addition of immobilized anti-CD44 mAbs were studied, and the results indicated no inhibition after 96 hrs of culture. Finally, B cells were activated by either LPS or anti-IgM F(ab′)₂. While LPS-induced B cell activation was inhibited by immobilized anti-CD44 mAbs, anti-IgM activation was refractory. Interestingly, addition of both anti-IgM and CD40L or LPS resulted in some modulation of the inhibitory activity. These results suggest that CD44 cross-linking could control polyclonal B cell activation by CD40L, but allow sIgM/CD40L activation to continue.     

Multivalent dendrimers presenting spatially controlled clusters of binding epitopes in thermoresponsive hyaluronan hydrogels

The controlled presentation of biofunctionality is of key importance for hydrogel applications in cell-based regenerative medicine. Here, a versatile approach was demonstrated to present clustered binding epitopes in an injectable, thermoresponsive hydrogel. Well-defined multivalent dendrimers bearing four integrin binding sequences and an azido moiety were covalently grafted to propargylamine-derived hyaluronic acid (Hyal-pa) using copper-catalyzed alkyne–azide cycloaddition (CuAAC), and then combined with pN-modified hyaluronan (Hyal-pN). The dendrimers were prepared by synthesizing a bifunctional diethylenetriamine pentaacetic acid core with azido and NHBoc oligo(ethylene glycol) aminoethyl branches, then further conjugated with solid-phase synthesized RGDS and DGRS peptides. Azido terminated pN was synthesized by reversible addition-fragmentation chain transfer polymerization and reacted to Hyal-pa via CuAAC. Nuclear magnetic resonance (NMR), high performance liquid chromatography, size exclusion chromatography and mass spectroscopy proved that the dendrimers had well-defined size and were disubstituted. NMR and atomic absorption analysis confirmed the hyaluronan was affixed with dendrimers or pN. Rheological measurements demonstrated that dendrimers do not influence the elastic or viscous moduli of thermoresponsive hyaluronan compositions at a relevant biological concentration. Finally, human mesenchymal stromal cells were encapsulated in the biomaterial and cultured for 21 days, demonstrating the faculty of this dendrimer-modified hydrogel as a molecular toolbox for tailoring the biofunctionality of thermoresponsive hyaluronan carriers for biomedical applications.     

Involvement of CD44 exon v10 in B-cell activation

Abstract: The family of CD44 glycoproteins has been suggested to be involved in lymphocyte homing, maturation and activation. Using in vitro blocking studies with a monoclonal antibody, we here addressed the question of functional activity of CD44 variant exon v10 (CD44v10) in B-cell activation. We became interested in this question by the observation that CD44v10 was transiently expressed on activated T cells, B cells and mono-cytes as well as on a subpopulation of bone marrow cells. A potential ligand, as revealed by staining with a CD44v10 receptor globulin, was only detected on monocytes. Anti-CD44v10 had no major impact on T-cell activation and no influence on primed B cells, but interfered with the mounting of a primary B-cell response to T-independent and T-dependent antigens. Addition of anri-CD44v10 at different stages during the activation process revealed that CD44v10 was not engaged in B-cell-T-cell interactions. The antibody exerted some effect on monocyte activation as defined by a slight decrease in IL-1 production, but most efficiently inhibited antigen-specific as well as mitogen-induced B-cell activation when present during the co-culture of virgin B cells with monocytes. These findings, together with the observation that a CD44v10 ligand was only detected on monocytes but not on lymphocytes, point towards a requirement for CD44v10 in a B-cell-monocyte interaction. Furthermore, since activation of B cells by engagement both of the B-cell receptor and of mitogen receptors was inhibited by anti-CD44v10, the data suggest that a costimulatory function of CD44v10 proceeds independent of the B-cell receptor.     

The CD44/integrins interplay and the significance of receptor binding and re-presentation in the uptake of RGD-functionalized hyaluronic acid

We have studied the interplay between two endocytic receptors for a carrier structure bearing two complementary ligands. Hyaluronic acid (HA; three different molecular weights) was functionalized with an RGD-containing peptide; this ancillary ligand allows the macromolecule to bind to α_v integrins in addition to the classical HA internalization receptor (CD44). The uptake of HA-RGD and of native HA was assessed in a phagocytic cell model (J774.2 murine macrophages), studying the kinetics of internalization and its mechanistic details. Indications of a synergic binding to integrins and CD44 emerged for HA-RGD; possibly, a first binding to integrins allows for a pre-concentration of the macromolecule on the cell surface, which is then followed by its binding to CD44. The endocytic mechanism and kinetics appeared then dominated by CD44, which has a much slower turnover than integrins. In this study we have demonstrated that the knowledge of the rate-determining steps of the internalization of a carrier is necessary for assessing its performance. In this case, the presence of multiple ligands on a carrier was beneficial in some respect (e.g. in improved binding/targeting), but may not be sufficient to overcome penetration barriers that arise from slow receptor re-presentation.     

CD44介导的透明质酸对单核细胞黏附和迁移的作用

目的研究透明质酸（HA）在单核细胞中的分布,HA受体CD44和细胞问黏附分子-1（ICAM-1）在单核细胞中的表达以及HA及其受体对单核细胞黏附和迁移的影响.方法用Percoll非连续密度梯度离心法分离狗外周血单核细胞,然后用免疫荧光染色法标记单核细胞的HA、CD44和ICAM-1.通过用透明质酸酶（HAase）消化细胞表面的HA、在培养皿底面和细胞培养池膜上涂布HA和在培养液中添加HA,观察细胞表面的HA、底物HA和游离HA对细胞黏附和迁移的影响.以抗体阻断剂抑制CD44或ICAM-1,研究HA受体的介导作用.结果单核细胞表面和细胞内存在HA,并表达CD44和ICAM-1.消化细胞表面HA后,黏附和迁移的单核细胞数减少.在培养皿底面和细胞培养池膜上铺HA,黏附和迁移的细胞数增加.培养液中加入HA,黏附和迁移的细胞数减少.阻断CD44后,HA底物上黏附和迁移的细胞数减少,而阻断ICAM-1后黏附和迁移的单核细胞数无明显变化.结论单核细胞内外分布有HA.单核细胞表面的HA和底物HA促进细胞的黏附和迁移,但游离HA阻碍单核细胞的黏附和迁移.CD44介导HA对单核细胞黏附和迁移的作用.