Inflammatory cytokines can enhance CD44-mediated airway epithelial cell adhesion independently of CD44 expression

In airways, the cell surface molecule CD44 is upregulated on bronchial epithelial cells in areas of damage. We have shown that a blocking standard CD44 (CD44s) antibody caused a 77% (+/- 19%) inhibition of cell migration at 3 h after mechanical damage and decreased epithelial cell repair of cells grown on cell culture filter inserts. With the use of primary human bronchial epithelial cells and the bronchial epithelial cell line 16HBE 14o-, a CD44s antibody inhibited >95% (P < 0.01) of cell binding to hyaluronic acid (HA). The cytokines TNF-alpha, IFN-gamma, IL-1 beta, and IL-4 stimulated a 2- to 3.5-fold increase in CD44-dependent cell binding to HA. IFN-gamma treatment did not increase CD44 expression as assessed by flow cytometry, although phorbol myristate acetate treatment did. This indicates that IFN-gamma-induced cell binding to HA did not require increased CD44 expression. These data indicate that CD44 is important for bronchial epithelial cell binding to HA and that cytokines known to be expressed in inflammation can increase HA binding independently of the level of CD44 expression.     

Functional Hierarchy of Simultaneously Expressed Adhesion Receptors: Integrin α2β1 but Not CD44 Mediates MV3 Melanoma Cell Migration and Matrix Reorganization within Three-dimensional Hyaluronan-containing Collagen Matrices

Haptokinetic cell migration across surfaces is mediated by adhesion receptors including beta1 integrins and CD44 providing adhesion to extracellular matrix (ECM) ligands such as collagen and hyaluronan (HA), respectively. Little is known, however, about how such different receptor systems synergize for cell migration through three-dimensionally (3-D) interconnected ECM ligands. In highly motile human MV3 melanoma cells, both beta1 integrins and CD44 are abundantly expressed, support migration across collagen and HA, respectively, and are deposited upon migration, whereas only beta1 integrins but not CD44 redistribute to focal adhesions. In 3-D collagen lattices in the presence or absence of HA and cross-linking chondroitin sulfate, MV3 cell migration and associated functions such as polarization and matrix reorganization were blocked by anti-beta1 and anti-alpha2 integrin mAbs, whereas mAbs blocking CD44, alpha3, alpha5, alpha6, or alphav integrins showed no effect. With use of highly sensitive time-lapse videomicroscopy and computer-assisted cell tracking techniques, promigratory functions of CD44 were excluded. 1) Addition of HA did not increase the migratory cell population or its migration velocity, 2) blocking of the HA-binding Hermes-1 epitope did not affect migration, and 3) impaired migration after blocking or activation of beta1 integrins was not restored via CD44. Because alpha2beta1-mediated migration was neither synergized nor replaced by CD44-HA interactions, we conclude that the biophysical properties of 3-D multicomponent ECM impose more restricted molecular functions of adhesion receptors, thereby differing from haptokinetic migration across surfaces.     

Effect of sulfated GAGs on the expression and activation of MMP-2 and MMP-9 in corneal and dermal explant cultures

It has been shown previously that hyaluronan (HA) added to fibroblast and keratocyte cell cultures or corneal explant cultures produces an up-regulation of MMP-2 and MMP-9 expression and activation. Here, we examine the effect of sulfated GAG-s, chondroitin 4 and 6 sulfate (CS4, CS6), dermatan sulfate (DS), keratan sulfate (KS) and heparan sulfate (HS) on MMP-2 and 9 expression and activation under the same culture conditions. It appears that CS4 has only minor effects, KS inhibits MMP-2 activation and CS6, DS and HS increase MMP-2 activation in corneal explant cultures. For skin explant cultures, DS, KS and HS strongly increase MMP-9 activation, whereas KS inhibits and DS increases MMP-2 activation. All these effects can be strongly inhibited by the addition of an antibody to CD44, except CS6 and DS. Activation by these two GAGs was only slightly affected, supporting the contention that the effects of HA, CS4, KS and HS are mediated by one of the isoforms of this CD44 receptor. The physio-pathological significance of these results is discussed for cornea and skin ageing, because of the divergent evolution with in vitro ageing of the relative proportions of GAGs synthesised by these two cell types.     

Role of Matrix Metalloproteinase-9 Dimers in Cell Migration: DESIGN OF INHIBITORY PEPTIDES*

Non-proteolytic activities of matrix metalloproteinases (MMPs) have recently been shown to impact cell migration, but the precise mechanism remains to be understood. We previously demonstrated that the hemopexin (PEX) domain of MMP-9 is a prerequisite for enhanced cell migration. Using a biochemical approach, we now report that dimerization of MMP-9 through the PEX domain appears necessary for MMP-9-enhanced cell migration. Following a series of substitution mutations within the MMP-9 PEX domain, blade IV was shown to be critical for homodimerization, whereas blade I was required for heterodimerization with CD44. Blade I and IV mutants showed diminished enhancement of cell migration compared with wild type MMP-9-transfected cells. Peptides mimicking motifs in the outermost strands of the first and fourth blades of the MMP-9 PEX domain were designed. These peptides efficiently blocked MMP-9 dimer formation and inhibited motility of COS-1 cells overexpressing MMP-9, HT-1080, and MDA-MB-435 cells. Using a shRNA approach, CD44 was found to be a critical molecule in MMP-9-mediated cell migration. Furthermore, an axis involving a MMP-9-CD44-EGFR signaling pathway in cell migration was identified using antibody array and specific receptor tyrosine kinase inhibitors. In conclusion, we dissected the mechanism of pro-MMP-9-enhanced cell migration and developed structure-based inhibitory peptides targeting MMP-9-mediated cell migration.     

Role for autocrine TGF-β1 in regulating differentiation of a human leukemic cell line toward osteoclast-like cells

Increasing evidence suggests that transforming growth factor-β (TGF-β) is involved in bone formation during remodeling. Using a recently cloned human leukemic cell line (FLG 29.1 cells) we demonstrate that these cells synthesize and secrete TGF-β1 and that exogenous or autocrine TGF-β1 can induce the same features of osteoclastic-like cells, exerting its effects through the binding to TGF-β specific receptors. Scatchard analysis of ¹²⁵I-labeled TGF-β1 to FLG 29.1 cells revealed the presence of a single high affinity binding site with a Kd value of ～25 pM and a binding capacity of ～900 sites/cell. Affinity labeling experiments showed that FLG 29.1 cells express type I and type II TGF-β receptors. Stimulation of FLG 29.1 cells with low TGF-β1 doses reduced cell proliferation and increased cell adhesion and tartrate resistant acid phosphatase (TRAcP) activity. Pretreatment of FLG 29.1 cells with TGF-β1 caused a significant and dose-dependent response to calcitonin. Northern blot of total mRNA and analysis of the conditioned media (CM) showed that TGF-β1 was synthesized by FLG 29.1 cells. TPA treatment, which induces partial differentiation of these cells, markedly increased TGF-β1 mRNA expression and growth factor release. The majority of TGF-β1 secreted by TPA-treated cells was in its latent form. However, anti-TGF-β antibodies inhibited TGF-β1 and TPA-induced growth inhibition, calcitonin responsiveness, and TRAcP activity, suggesting that the TPA effect is mediated in part by autocrine TGF-β1 and indicating that the cells can activate and respond to the TGF-β that they secrete. These findings support a potential autocrine role for TGF-β1 in osteoclast differentiation. © 1994 Wiley-Liss, Inc.     

A Novel CD44-binding Peptide from the Pro-Matrix Metalloproteinase-9 Hemopexin Domain Impairs Adhesion and Migration of Chronic Lymphocytic Leukemia (CLL) Cells

(pro)MMP-9 binds to CLL cells through the PEX9 domain and contributes to CLL progression. To biochemically characterize this interaction and identify potential therapeutic targets, we prepared GST-PEX9 forms containing structural blades B1B2 or B3B4. We recently described a sequence in blade B4 (P3 sequence) that bound α4β1 integrin and partially impaired cell adhesion and migration. We have now studied the possible contribution of the B1B2 region to cell interaction with PEX9. CLL cells bound to GST-B1B2 and CD44 was the primary receptor. GST-B1B2 inhibited CLL cell migration as effectively as GST-B3B4. Overlapping synthetic peptides spanning the B1B2 region identified the sequence FDAIAEIGNQLYLFKDGKYW, present in B1 and contained in peptide P6, as the most effective site. P6 inhibited cell adhesion to PEX9 in a dose-dependent manner and with an IC₅₀ value of 90 μm. P6 also inhibited cell adhesion to hyaluronan but had no effect on adhesion to VCAM-1 (α4β1 integrin ligand), confirming its specific interaction with CD44. Spatial localization analyses mapped P6 to the central cavity of PEX9, in close proximity to the previously identified P3 sequence. Both P6 and P3 equally impaired cell adhesion to (pro)MMP-9. Moreover, P6 synergistically cooperated with P3, resulting in complete inhibition of CLL cell binding to PEX9, chemotaxis, and transendothelial migration. Thus, P6 is a novel sequence in PEX9 involved in cell-PEX9/(pro)MMP-9 binding by interacting with CD44. Targeting both sites, P6 and P3, should efficiently prevent (pro)MMP-9 binding to CLL cells and its pathological consequences.     

Hyaluronan oligosaccharides induce matrix metalloproteinase 13 via transcriptional activation of NFkappaB and p38 MAP kinase in articular chondrocytes

Hyaluronan exerts a variety of biological effects on cells including changes in cell migration, proliferation, and matrix metabolism. However, the signaling pathways associated with the action of hyaluronan on cells have not been clearly defined. In some cells, signaling is induced by the loss of cell-hyaluronan interactions. The goal of this study was to use hyaluronan oligosaccharides as a molecular tool to explore the effects of changes in cell-hyaluronan interactions and determine the underlying molecular events that become activated. In this study, hyaluronan oligosaccharides induced the loss of extracellular matrix proteoglycan and collagen from cultured slices of normal adult human articular cartilage. This loss was coincident with an increased expression of matrix metalloproteinase (MMP)-13. MMP-13 expression was also induced in articular chondrocytes by hyaluronan (HA) hexasaccharides but not by HA tetrasaccharides nor high molecular weight hyaluronan. MMP-13 promoter-reporter constructs in CD44-null COS-7 cells revealed that both CD44-dependent and CD44-independent events mediate the induction of MMP-13 by hyaluronan oligosaccharides. Electromobility gel shift assays demonstrated the activation of chondrocyte NFkappaB by hyaluronan oligosaccharides. NFkappaB activation was also documented in C-28/I2 immortalized human chondrocytes by luciferase promoter assays and phosphorylation of IKK-alpha/beta. The link between activation of NFkappaB and MMP-13 induction by HA oligosaccharides was further confirmed through the use of the NFkappaB inhibitor helenalin. Inhibition of MAP kinases also demonstrated the involvement of p38 MAP kinase in the hyaluronan oligosaccharide induction of MMP-13. Our findings suggest that hyaluronan-CD44 interactions affect matrix metabolism via activation of NFkappaB and p38 MAP kinase.     

Homophilic interactions of Tetraspanin CD151 up-regulate motility and matrix metalloproteinase-9 expression of human melanoma cells through adhesion-dependent c-Jun activation signaling pathways

The tetraspanin membrane protein CD151 has been suggested to regulate cancer invasion and metastasis by initiating signaling events. The CD151-mediated signaling pathways involved in this regulation remain to be revealed. In this study, we found that stable transfection of CD151 into MelJuSo human melanoma cells lacking CD151 expression significantly increased cell motility, matrix metalloproteinase-9 (MMP-9) expression, and invasiveness. The enhancement of cell motility and MMP-9 expression by CD151 overexpression was abrogated by inhibitors and small interfering RNAs targeted to focal adhesion kinase (FAK), Src, p38 MAPK, and JNK, suggesting an essential role of these signaling components in CD151 signaling pathways. Also, CD151-induced MMP-9 expression was shown to be mediated by c-Jun binding to AP-1 sites in the MMP-9 gene promoter, indicating AP-1 activation by CD151 signaling pathways. Meanwhile, CD151 was found to be associated with alpha(3)beta(1) and alpha(6)beta(1) integrins in MelJuSo cells, and activation of associated integrins was a prerequisite for CD151-stimulated MMP-9 expression and activation of FAK, Src, p38 MAPK, JNK, and c-Jun. Furthermore, CD151 on one cell was shown to bind to neighboring cells expressing CD151, suggesting that CD151 is a homophilic interacting protein. The homophilic interactions of CD151 increased motility and MMP-9 expression of CD151-transfected MelJuSo cells, along with FAK-, Src-, p38 MAPK-, and JNK-mediated activation of c-Jun in an adhesion-dependent manner. Furthermore, C8161 melanoma cells with endogenous CD151 were also shown to respond to homophilic CD151 interactions for the induction of adhesion-dependent activation of FAK, Src, and c-Jun. These results suggest that homophilic interactions of CD151 stimulate integrin-dependent signaling to c-Jun through FAK-Src-MAPKs pathways in human melanoma cells, leading to enhanced cell motility and MMP-9 expression.     

The CD44 Receptor of Lymphoma Cells: Structure-Function Relationships and Mechanism of Activation

Migration of some tumor cells, and their lodgment in target organs, is dependent on the activation of cell surface CD44 receptor, usually detected by its ability to bind hyaluronic acid (HA) or other ligands. In an attempt to reveal the mechanism of tumor cell CD44 activation, we compared the physical and chemical properties of CD44 in nonactivated LB cell lymphoma with those in phorbol 12-myristate 13-acetate (PMA)-activated LB cells and of an LB cell subline (designated HA9) expressing constitutively-active CD44. In contrast to nonactivated LB cells, PMA-activated LB cells and HA9 cells displayed a CD44-dependent ability to bind HA. The ability of activated cell CD44 to bind HA was not dependent on microfilament or microtubule integrity or on changes in CD44 mobility on the membrane plane, indicating that the CD44 activation status is not associated with cytoskeleton function. Aside from the increased expression of CD44 on the surface of PMA-activated LB cells and HA9 cells, qualitative differences between the CD44 of nonactivated and activated LB cells were also detected: the CD44 of the activated lymphoma was (i) larger in molecular size, (ii) displayed a broader CD44 isoform repertoire, including a CD44 variant that binds HA, and (iii) its glycoprotein contained less sialic acid. Indeed, after removal of sialic acid from their cell surface by neuraminidase, LB cells acquired the ability to bind HA. However, a reduced dose of neuraminidase did not confer HA binding on LB cells, unless they were also activated by a low concentration of PMA, which by itself was ineffective. Similarly, under suboptimal conditions, a synergistic effect was obtained with tunicamycin and PMA: each one alone was ineffective but in combination they induced the acquisition of HA binding by the lymphoma cells, while their CD44 expression was not enhanced. Unveiling of the activation mechanism of CD44, by exposing the cells to PMA stimulation or to deglycosylation, is not only academically important, but it also has practical implications, as activated CD44 may be involved in the support of tumor progression.     

The CD44 receptor of lymphoma cells: structure-function relationships and mechanism of activation

Migration of some tumor cells, and their lodgment in target organs, is dependent on the activation of cell surface CD44 receptor, usually detected by its ability to bind hyaluronic acid (HA) or other ligands. In an attempt to reveal the mechanism of tumor cell CD44 activation, we compared the physical and chemical properties of CD44 in nonactivated LB cell lymphoma with those in phorbol 12-myristate 13-acetate (PMA)-activated LB cells and of an LB cell subline (designated HA9) expressing constitutively-active CD44. In contrast to nonactivated LB cells, PMA-activated LB cells and HA9 cells displayed a CD44-dependent ability to bind HA. The ability of activated cell CD44 to bind HA was not dependent on microfilament or microtubule integrity or on changes in CD44 mobility on the membrane plane, indicating that the CD44 activation status is not associated with cytoskeleton function. Aside from the increased expression of CD44 on the surface of PMA-activated LB cells and HA9 cells, qualitative differences between the CD44 of nonactivated and activated LB cells were also detected: the CD44 of the activated lymphoma was (i) larger in molecular size, (ii) displayed a broader CD44 isoform repertoire, including a CD44 variant that binds HA, and (iii) its glycoprotein contained less sialic acid. Indeed, after removal of sialic acid from their cell surface by neuraminidase, LB cells acquired the ability to bind HA. However, a reduced dose of neuraminidase did not confer HA binding on LB cells, unless they were also activated by a low concentration of PMA, which by itself was ineffective. Similarly, under suboptimal conditions, a synergistic effect was obtained with tunicamycin and PMA: each one alone was ineffective but in combination they induced the acquisition of HA binding by the lymphoma cells, while their CD44 expression was not enhanced. Unveiling of the activation mechanism of CD44, by exposing the cells to PMA stimulation or to deglycosylation, is not only academically important, but it also has practical implications, as activated CD44 may be involved in the support of tumor progression.     

Actin polymerization modulates CD44 surface expression, MMP-9 activation, and osteoclast function

CD44 and MMP-9 are implicated in cell migration. In the current study, we tested the hypothesis that actin polymerization is critical for CD44 surface expression and MMP-9 activity on the cell surface. To understand the underlying molecular mechanisms involved in CD44 surface expression and MMP-9 activity on the cell surface, osteoclasts were treated with bisphosphonate (BP) alendronate, cytochalasin D (Cyt D), and a broad-spectrum MMP inhibitor (GM6001). BP has been reported to block the mevalonate pathway, thereby preventing prenylation of small GTPase signaling required for actin cytoskeleton modulation. We show in this study that osteoclasts secrete CD44 and MMP-9 into the resorption bay during migration and bone resorption. Results indicate that actin polymerization is critical for CD44 surface expression and osteoclast function. In particular, the surface expression of CD44 and the membrane activity of MMP-9 are reduced in osteoclasts treated with alendronate and Cyt D despite the membrane levels of MMP-9 being unaffected. Although GM6001 blocked MMP-9 activity, osteoclast migration, and bone resorption, the surface levels of CD44 were unaffected. We suggest that the surface expression of CD44 requires actin polymerization. Disruption of podosome and actin ring structures by Cyt D and alendronate not only resulted in reduced localization of MMP-9 in these structures but also in osteoclast migration and bone resorption. These results suggest that inhibition of actin polymerization by alendronate and Cyt D is effective in blocking CD44/MMP-9 complex formation on the cell surface, secretion of active form of MMP-9, and osteoclast migration. CD44/MMP-9 complex formation may signify a unique motility-enhancing signal in osteoclast function.     

Fibroblast growth factor‐2 stimulates directed migration of periodontal ligament cells via PI3K/AKT signaling and CD44/hyaluronan interaction

Fibroblast growth factor‐2 (FGF‐2) regulates a variety of functions of the periodontal ligament (PDL) cell, which is a key player during tissue regeneration following periodontal tissue breakdown by periodontal disease. In this study, we investigated the effects of FGF‐2 on the cell migration and related signaling pathways of MPDL22, a mouse PDL cell clone. FGF‐2 activated the migration of MPDL22 cells and phosphorylation of phosphatidylinositol 3‐kinase (PI3K) and akt. The P13K inhibitors, Wortmannin and LY294002, suppressed both cell migration and akt activation in MPDL22, suggesting that the PI3K/akt pathway is involved in FGF‐2‐stimulated migration of MPDL22 cells. Moreover, in response to FGF‐2, MPDL22 showed increased CD44 expression, avidity to hyaluronan (HA) partly via CD44, HA production and mRNA expression of HA synthase (Has)‐1, 2, and 3. However, the distribution of HA molecular mass produced by MPDL22 was not altered by FGF‐2 stimulation. Treatment of transwell membrane with HA facilitated the migration of MPDL22 cells and an anti‐CD44 neutralizing antibody inhibited it. Interestingly, the expression of CD44 was colocalized with HA on the migrating cells when stimulated with FGF‐2. Furthermore, an anti‐CD44 antibody and small interfering RNA for CD44 significantly decreased the FGF‐2‐induced migration of MPDL22 cells. Taken together, PI3K/akt and CD44/HA signaling pathways are responsible for FGF‐2‐mediated cell motility of PDL cells, suggesting that FGF‐2 accelerates periodontal regeneration by regulating the cellular functions including migration, proliferation and modulation of extracellular matrix production. J. Cell. Physiol. 226: 809–821, 2011. © 2010 Wiley‐Liss, Inc.     

Hyaluronan synthesis is required for IL-2-mediated T cell proliferation

Hyaluronan (HA) is a glycosaminoglycan composed of N-acetylglucosamine and glucuronic acid subunits. Previous studies have suggested that CD44 expressed by T cells bind exogenous HA for their proliferation. However, HA endogenously synthesized by T cells may participate in their autocrine proliferation. In this study, we examined the role of endogenous HA in T cell proliferation using the highly specific HA synthase inhibitor, 4-methylumbelliferone (4-MU). We found that 4-MU inhibited the mitogen-induced synthesis of HA by T cells. Moreover, 4-MU inhibited T cell proliferation in a dose-dependent manner when cells were cultured with different stimuli, including Con A, PMA/ionomycin, and allogeneic spleen cells. Furthermore, 4-MU inhibited mitogen-stimulated IL-2 secretion, suggesting that HA may play a role in the production of this cytokine. Addition of IL-2 to T cells treated with 4-MU and Con A reversed the block in cell proliferation, showing that impaired IL-2 production is a likely mechanism for the inhibited division of T cells. Surprisingly, an anti-CD44 Ab antagonistic for HA binding did not reduce IL-2 secretion or T cell proliferation. Importantly, 4-MU did not alter the surface expression of CD44 or the ability of CD44 to bind to HA. Thus, HA-mediated IL-2 production and T cell proliferation are CD44 independent. Our results strongly suggest that HA synthesized by T cells themselves is critical for their IL-2-mediated proliferation and have revealed a previously unrecognized role for endogenous HA in T cell biology.     

Hyaluronan-CD44 interaction stimulates Rac1 signaling and PKN gamma kinase activation leading to cytoskeleton function and cell migration in astrocytes

Both hyaluronan [HA, the major glycosaminoglycans in the extracellular matrix (ECM)] and CD44 (a primary HA receptor) are associated with astrocyte activation and tissue repair following central nervous system (CNS) injury. In this study we investigated the question of whether HA-CD44 interaction influences astrocyte signaling and migration. Our data indicated that HA binding to the cultured astrocytes stimulated Rac1 signaling and cytoskeleton-mediated migration. To determine the cellular and molecular basis of these events, we focused on PKN gamma, a Rac1-activated serine/threonine kinase in astrocytes. We determined that HA binding to astrocytes stimulated Rac1-dependent PKN gamma kinase activity which, in turn, up-regulated the phosphorylation of the cytoskeletal protein, cortactin, and attenuated the ability of cortactin to cross-link F-actin. Further analyses indicated that the N-terminal antiparallel coiled-coil (ACC) domains of PKN gamma interacted with Rac1, and transfection of astrocytes with PKN gamma-ACCcDNA inhibited PKN gamma activity. Over-expression of the PKN gamma-ACC domain also functions as a dominant-negative mutant to block HA/CD44-mediated PKN gamma activation of cortactin and astrocyte migration. Taken together, these findings strongly suggest that hyaluronan/CD44 interaction with Rac1-PKN gamma plays a pivotal role in cytoskeleton activation and astrocyte migration. These newly discovered HA/CD44-induced astrocyte function may provide important insight into novel therapeutic treatments for tissue repair following CNS injury.     

Rapid expression and activation of MMP-2 and MMP-9 upon exposure of human breast cancer cells (MCF-7) to fibronectin in serum free medium

Interactions between tumour cells and the extracellular matrix (ECM) strongly influence tumour development, affecting cell survival, proliferation and migration. Many of these interactions are mediated through a family of cell surface receptors named integrins. Fibronectin and its integrin receptors play important roles in tumour development. The alpha5beta 1 integrin interacts with the central cell adhesive region of fibronectin and requires both the RGD and synergy sites for maximal binding. Matrix metalloproteinases (MMPs) are a family of zinc dependent endopeptidases. They are capable of digesting the different components of the ECM and basement membrane. The ECM gives structural support to cells and plays a central role in cell adhesion, differentiation, proliferation and migration. Binding of ECM to integrins modulates expression and activity of the different MMPs. Our experimental findings demonstrate that cultivation of human breast cancer cells, MCF-7, in serum free medium in the presence of fibronectin upregulates the activity of MMP-2 and MMP-9. Blocking of alpha5beta 1 integrin with anti-alpha5 monoclonal antibody inhibits the fibronectin-induced MMP activation response appreciably. This strongly indicates alpha5beta 1 mediated signalling events in activation of MMP-2 and MMP-9. Phosphorylation of FAK and PI-3 kinase and the nuclear translocation of ERK and NF-kappaB upon fibronectin binding demonstrate possible participation of the FAK/PI-3K/ERK signalling pathways in the regulation of MMP-2 activity.     

Specific blockade of the ERK pathway inhibits the invasiveness of tumor cells: down-regulation of matrix metalloproteinase-3/-9/-14 and CD44

Elevated expression of matrix metalloproteinases (MMPs) is associated with increased metastatic potential in many tumor cells. As activation of the ERK pathway has been linked to the expression of MMP-9, we examined a possible correlation between ERK activation, MMP-9 expression, and invasive phenotype in human tumor cells. Activation state of the ERK pathway in tumor cells was well correlated with the invasive phenotype, which was determined by the ability of cells to invade through reconstituted extracellular matrix. Elevated expression of MMP-9 as well as of MMP-3, MMP-14, and CD44 was observed in tumor cells in which constitutive activation of the ERK pathway is detected. Blockade of the ERK pathway by treatment with PD184352, a specific and powerful inhibitor of mitogen-activated protein (MAP) kinase/ERK kinase (MEK), suppressed the expression of MMP-3, MMP-9, MMP-14, and CD44, and inhibited markedly the invasiveness of tumor cells. These results imply that, in addition to anti-proliferative effects, specific blockade of the ERK pathway is expected to result in anti-metastatic effects in tumor cells.     

Hyaluronan promotes signaling interaction between CD44 and the transforming growth factor beta receptor I in metastatic breast tumor cells

In this study we have examined the interaction between CD44 (a hyaluronan (HA) receptor) and the transforming growth factor beta (TGF-beta) receptors (a family of serine/threonine kinase membrane receptors) in human metastatic breast tumor cells (MDA-MB-231 cell line). Immunological data indicate that both CD44 and TGF-beta receptors are expressed in MDA-MB-231 cells and that CD44 is physically linked to the TGF-beta receptor I (TGF-betaRI) (and to a lesser extent to the TGF-beta receptor II (TGF-betaRII)) as a complex in vivo. Scatchard plot analyses and in vitro binding experiments show that the cytoplasmic domain of CD44 binds to TGF-betaRI at a single site with high affinity (an apparent dissociation constant (K(d)) of approximately 1.78 nm). These findings indicate that TGF-betaRI contains a CD44-binding site. Furthermore, we have found that the binding of HA to CD44 in MDA-MB-231 cells stimulates TGF-betaRI serine/threonine kinase activity which, in turn, increases Smad2/Smad3 phosphorylation and parathyroid hormone-related protein (PTH-rP) production (well known downstream effector functions of TGF-beta signaling). Most importantly, TGF-betaRI kinase activated by HA phosphorylates CD44, which enhances its binding interaction with the cytoskeletal protein, ankyrin, leading to HA-mediated breast tumor cell migration. Overexpression of TGF-betaRI by transfection of MDA-MB-231 cells with TGF-betaRIcDNA stimulates formation of the CD44.TGF-betaRI complex, the association of ankyrin with membranes, and HA-dependent/CD44-specific breast tumor migration. Taken together, these findings strongly suggest that CD44 interaction with the TGF-betaRI kinase promotes activation of multiple signaling pathways required for ankyrin-membrane interaction, tumor cell migration, and important oncogenic events (e.g. Smad2/Smad3 phosphorylation and PTH-rP production) during HA and TGF-beta-mediated metastatic breast tumor progression.     

Induction of CD44 and MMP expression by hyaluronidase treatment of articular chondrocytes

In this study, the effects of fragmentation of the glycosoaminoglycans of the cell-associated matrix by hyaluronidase (HAase) on the expression of CD44 receptor and matrix metalloproteinase (MMP) mRNAs in cultured articular chondrocytes were examined. Chondrocytes, isolated from rabbit and bovine articular cartilage, were treated with bovine testicular HAase (0-200 units/ml) in the presence or absence of an antibody for CD44. The mRNA levels of CD44, CD44 variant (CD44v), MMPs (MMP-1, -3 and -9), and tissue inhibitors of metalloproteinases (TIMP-1 and TIMP-2) were determined by RT-PCR. The treatment of cultured chondrocytes with HAase resulted in the production of low molecular weight fragments of hyaluronan (HA). The expression of CD44, CD44v and MMP (MMP-1, -3 and -9) mRNAs, but not TIMP-1 or TIMP-2 mRNA, was up-regulated in the cultures treated with HAase, whereas this expression was not affected by treatment with purified HA of 1.0 x 10(5) Da. Furthermore, the induction of CD44 and MMPs on treatment with HAase was suppressed by an anti-CD44 antibody. The results suggest that the fragmentation of HA may lead to cartilage destruction in terms of the enhanced expression of MMPs as well as the upregulation of CD44.