Hyaluronan: from extracellular glue to pericellular cue

Increased mesangial cell hyaluronan expression in lupus nephritis is mediated by anti-DNA antibody-induced IL-1beta

The mechanism by which anti-DNA antibodies contribute to the pathogenesis of lupus nephritis (LN) remains to be fully elucidated. Hyaluronan (HA) is an important extracellular matrix constituent that accumulates during tissue injury, and participates in lymphocyte recruitment to sites of inflammation. The role of HA in the pathogenesis of LN has not been defined. We investigated the expression of HA in renal biopsies and circulating HA levels in patients with diffuse proliferative LN, and the effect of human anti-DNA antibodies on HA synthesis in cultured human mesangial cells (HMC). HA expression was increased in the mesangium, and in the periglomerular and tubular distribution in LN kidney biopsies. LN patients showed increased levels of circulating HA, especially during active disease, which correlated with anti-DNA antibody titers (r=0.35, P=0.0234). Anti-DNA antibodies isolated during active LN but not remission increased de novo synthesis of (3)H-labeled HA, which was accompanied by induction of HA synthase (HAS) II transcription, and enhanced IL-1beta, IL-6, and tumor necrosis factor-alpha secretion in HMC (P<0.001 for all). Only anti-DNA antibody induction of IL-1beta enhanced HA synthesis, which was abrogated by inhibitors of de novo mRNA or protein synthesis. Our findings demonstrate that HA expression is significantly increased within the mesangium in diffuse proliferative LN mediated through anti-DNA antibody-induced IL-1beta. Given that HA plays a pivotal role during inflammatory responses, influences cellular behavior and assists in the recruitment of lymphocytes to sites of injury, it is likely that HA contributes to the pathogenesis of LN.

XHas2 activity is required during somitogenesis and precursor cell migration in Xenopus development

In vertebrates, hyaluronan biosynthesis is regulated by three transmembrane catalytic enzymes denoted Has1, Has2 and Has3. We have previously cloned the Xenopus orthologues of the corresponding genes and defined their spatiotemporal distribution during development. During mammalian embryogenesis, Has2 activity is known to be crucial, as its abrogation in mice leads to early embryonic lethality. Here, we show that, in Xenopus,morpholino-mediated loss-of-function of XHas2 alters somitogenesis by causing a disruption of the metameric somitic pattern and leads to a defective myogenesis. In the absence of XHas2, early myoblasts underwent apoptosis, failing to complete their muscle differentiation programme. XHas2 activity is also required for migration of hypaxial muscle cells and trunk neural crest cells (NCC). To approach the mechanism whereby loss of HA,following XHas2 knockdown, could influence somitogenesis and precursor cell migration, we cloned the orthologue of the primary HA signalling receptor CD44 and addressed its function through an analogous knockdown approach. Loss of XCD44 did not disturb somitogenesis, but strongly impaired hypaxial muscle precursor cell migration and the subsequent formation of the ventral body wall musculature. In contrast to XHas2,loss of function of XCD44 did not seem to be essential for trunk NCC migration, suggesting that the HA dependence of NCC movement was rather associated with an altered macromolecular composition of the ECM structuring the cells' migratory pathways. The presented results, extend our knowledge on Has2 function and, for the first time, demonstrate a developmental role for CD44 in vertebrates. On the whole, these data underlie and confirm the emerging importance of cell-ECM interactions and modulation during embryonic development.

An introductory review of cell mechanobiology

Mechanical loads induce changes in the structure, composition, and function of living tissues. Cells in tissues are responsible for these changes, which cause physiological or pathological alterations in the extracellular matrix (ECM). This article provides an introductory review of the mechanobiology of load-sensitive cells in vivo, which include fibroblasts, chondrocytes, osteoblasts, endothelial cells, and smooth muscle cells. Many studies have shown that mechanical loads affect diverse cellular functions, such as cell proliferation, ECM gene and protein expression, and the production of soluble factors. Major cellular components involved in the mechanotransduction mechanisms include the cytoskeleton, integrins, G proteins, receptor tyrosine kinases, mitogen-activated protein kinases, and stretch-activated ion channels. Future research in the area of cell mechanobiology will require novel experimental and theoretical methodologies to determine the type and magnitude of the forces experienced at the cellular and sub-cellular levels and to identify the force sensors/receptors that initiate the cascade of cellular and molecular events.

Magnetic resonance imaging visualization of hyaluronidase in ovarian carcinoma

Hyaluronan, a high molecular weight, negatively charged polysaccharide, is a major constituent of the extracellular matrix. High molecular weight hyaluronan is antiangiogenic, but its degradation by hyaluronidase generates proangiogenic breakdown products. Thus, by expression of hyaluronidase, cancer cells can tilt the angiogenic balance of their microenvironment. Indeed, hyaluronidase-mediated breakdown of hyaluronan correlates with aggressiveness and invasiveness of ovarian cancer metastasis and with tumor angiogenesis. The goal of this work was to develop a novel smart contrast material for detection of hyaluronidase activity by magnetic resonance imaging (MRI). Gadolinium-diethylenetriaminepentaacetic acid (GdDTPA) covalently linked to hyaluronan on the surface of agarose beads showed attenuated relaxivity. Hyaluronidase, either purified from bovine testes or secreted by ES-2 and OVCAR-3 human epithelial ovarian carcinoma cells, activated the hyaluronan-GdDTPA-beads by rapidly altering the R1 and R2 relaxation rates. The change in relaxation rates was consistent with the different levels of biologically active hyaluronidase secreted by those cells. Hyaluronan-GdDTPA-beads were further used for demonstration of MRI detection of hyaluronidase activity in the proximity of s.c. ES-2 ovarian carcinoma tumors in nude mice. Thus, hyaluronan-GdDTPA-beads could allow noninvasive molecular imaging of hyaluronidase-mediated tilt of the peritumor angiogenic balance.

Dynamic study of the transition from hyaluronan- to integrin-mediated adhesion in chondrocytes

Membrane-bound hyaluronan mediates the initial adhesive interactions between many cell types and external surfaces. In RCJ-P chondrocytes, such early contacts are mediated through a thick hyaluronidase-sensitive coat. The early adhesion is followed by integrin-mediated interactions and the formation of stable focal adhesions. During this process, the distance between the cell membrane and the surface is reduced from micrometers to few tens of nanometers. The transition from hyaluronan- to integrin-mediated adhesion was studied on glass surfaces by total internal reflection fluorescence microscopy. Hyaluronan-mediated adhesion precedes focal adhesions formation by 2-10 min. After these initial interactions, the pericellular hyaluronan remains sequestered into discrete pockets between the cell and the surface, which are a few hundreds nanometers thick and a few micrometers wide, and are flanked by focal adhesions. The hyaluronan coat facilitates the nucleation of small paxillin-rich contacts, which later mature into focal adhesions. These dynamic studies demonstrate that pericellular hyaluronan mediates initial cell-surface adhesion, and regulates the formation of focal adhesions.

Expression of hyaluronan in human tumor progression

Background

The development and progression of human tumors is accompanied by various cellular, biochemical and genetic alterations. These events include tumor cells interaction with extracellular matrix molecules including hyaluronan (HA). Hyaluronan is a large polysaccharide associated with pericellular matrix of proliferating, migrating cells. Its implication in malignant transformation, tumor progression and with the degree of differentiation in various invasive tumors has well accepted. It has been well known the role HA receptors in tumor growth and metastasis in various cancer tissues. Previously we have observed the unified over expression of Hyaluronic Acid Binding Protein (HABP), H11B2C2 antigen by the tumor cells in various types progressing tumor tissues with different grades. However, the poor understanding of relation between HA and HA-binding protein expression on tumor cells during tumor progression as well as the asymmetric observations of the role of HA expression in tumor progression prompted us to examine the degree of HA expression on tumor cells vs. stroma in various types of human tumors with different grades.

Methods

In the present study clinically diagnosed tumor tissue samples of different grades were used to screen the histopathological expression of hyaluronan by using b-PG (biotinylated proteoglycan) as a probe and we compared the relative HA expression on tumor cells vs. stroma in well differentiated and poorly differentiated tumors. Specificity of the reaction was confirmed either by pre-digesting the tissue sections with hyaluronidase enzyme or by staining the sections with pre-absorbed complex of the probe and HA-oligomers.

Results

We show here the down regulation of HA expression in tumor cells is associated with progression of tumor from well differentiated through poorly differentiated stage, despite the constant HA expression in the tumor associated stroma.

Conclusion

The present finding enlighten the relative roles of HA expression on tumor vs. stroma during the progression of tumors.

Glycosaminoglycans and their proteoglycans: host‐associated molecular patterns for initiation and modulation of inflammation

Glycosaminoglycans, linear carbohydrates such as heparan sulfate and hyaluronan, participate in a variety of biological processes including cell-matrix interactions and activation of chemokines, enzymes and growth factors. This review will discuss progress in immunology and the science of wound repair that has revealed the importance of glycosaminoglycans, and their proteoglycans, in the inflammatory process. Heparan sulfate enables growth factor function and modifies enzyme/inhibitor functions, such as antithrombin III and heparin cofactor II. Heparan sulfate also interacts with cytokines/chemokines and participates in leukocyte selectin binding to promote the recruitment of leukocytes. Chondroitin sulfate/dermatan sulfate regulates growth factor activity and is an alternate modulator of heparin cofactor II. In addition, dermatan sulfate induces ICAM-1 expression on endothelial cells and also recruits leukocytes via selectin interactions. Hyaluronan alternatively participates in leukocyte recruitment via interaction with CD44, while activating various inflammatory cells, such as macrophages, through CD44-dependent signaling. Hyaluronan also signals through Toll-like receptor 4 to induce dendritic cell maturation and promote cytokine release by dendritic cells and endothelial cells. Taken together, the field of glycosaminoglycan biology provides new clues and explanations of the process of inflammation and suggests new therapeutic approaches to human disease.

Tumor cells enhance their own CD44 cleavage and motility by generating hyaluronan fragments

Hyaluronan (HA) is an extracellular matrix glycosaminoglycan that interacts with cell-surface receptors, including CD44. Although HA usually exists as a high molecular mass polymer, HA of a much lower molecular mass that shows a variety of biological activities can be detected under certain pathological conditions, particularly in tumors. We previously reported that low molecular weight HAs (LMW-HAs) of a certain size range induce the proteolytic cleavage of CD44 from the surface of tumor cells and promote tumor cell migration in a CD44-dependent manner. Here, we show that MIA PaCa-2, a human pancreatic carcinoma cell line, secreted hyaluronidases abundantly and generated readily detectable levels of LMW-HAs ranging from approximately 10- to 40-mers. This occurred in the absence of any exogenous stimulation. The tumor-derived HA oligosaccharides were able to enhance CD44 cleavage and tumor cell motility. Inhibition of the CD44-HA interaction resulted in the complete abrogation of these cellular events. These results are consistent with the concept that tumor cells generate HA oligosaccha-rides that bind to tumor cell CD44 through the expression of their own constitutive hyaluronidases. This enhances their own CD44 cleavage and cell motility, which would subsequently promote tumor progression. Such an autocrine/paracrine-like process may represent a novel activation mechanism that would facilitate and promote the malignant potential of tumor cells.

HYAL1 hyaluronidase in prostate cancer: a tumor promoter and suppressor

Hyaluronidases degrade hyaluronic acid, which promotes metastasis. HYAL1 type hyaluronidase is an independent prognostic indicator of prostate cancer progression and a biomarker for bladder cancer. However, it is controversial whether hyaluronidase (e.g., HYAL1) functions as a tumor promoter or as a suppressor. We stably transfected prostate cancer cells, DU145 and PC-3 ML, with HYAL1-sense (HYAL1-S), HYAL1-antisense (HYAL1-AS), or vector DNA. HYAL1-AS transfectants were not generated for PC-3 ML because it expresses little HYAL1. HYAL1-S transfectants produced < or = 42 milliunits (moderate overproducers) or > or = 80 milliunits hyaluronidase activity (high producers). HYAL1-AS transfectants produced <10% hyaluronidase activity when compared with vector transfectants (18-24 milliunits). Both blocking HYAL1 expression and high HYAL1 production resulted in a 4- to 5-fold decrease in prostate cancer cell proliferation. HYAL1-AS transfectants had a G2-M block due to decreased cyclin B1, cdc25c, and cdc2/p34 expression and cdc2/p34 kinase activity. High HYAL1 producers had a 3-fold increase in apoptotic activity and mitochondrial depolarization when compared with vector transfectants and expressed activated proapoptotic protein WOX1. Blocking HYAL1 expression inhibited tumor growth by 4- to 7-fold, whereas high HYAL1 producing transfectants either did not form tumors (DU145) or grew 3.5-fold slower (PC-3 ML). Whereas vector and moderate HYAL1 producers generated muscle and blood vessel infiltrating tumors, HYAL1-AS tumors were benign and contained smaller capillaries. Specimens of high HYAL1 producers were 99% free of tumor cells. This study shows that, depending on the concentration, HYAL1 functions as a tumor promoter and as a suppressor and provides a basis for anti-hyaluronidase and high-hyaluronidase treatments for cancer.

Adenovirus-mediated gene transfer of mutated IkappaB kinase and IkappaBalpha reveal NF-kappaB-dependent as well as NF-kappaB-independent pathways of HAS1 activation

It has become increasingly clear that hyaluronan is more than the simple matrix molecule it was once thought to be but instead takes part in a multitude of biological functions. Three genes encode for hyaluronan synthases (HAS). We demonstrated earlier that HAS2 and HAS3 are constitutively activated in type-B synoviocytes (fibroblast-like synoviocytes) and, furthermore, that the only gene that readily responds to stimulation with a series of proinflammatory cytokines is HAS1. Here we probe the involvement of the transcription factor NF-kappaB in induced and noninduced HAS activation. Transforming growth factor (TGF) beta1 as well as interleukin (IL)-1beta are both strong inducers of HAS1 transcription. Stimulation of fibroblast-like synoviocytes with IL-1beta resulted in rapid degradation of IkappaBalpha, an event that was preceded by IkappaBalpha phosphorylation. Interestingly, TGFbeta1 neither affected IkappaBalpha levels, nor did it cause phosphorylation of IkappaBalpha. In addition, TGFbeta1 had no effect on IkappaBbeta and IkappaBepsilon levels. Electrophorectic mobility shift assays demonstrate that IL-1beta is a potent inducer of NF-kappaB translocation; however, TGFbeta1 treatment did not result in shifting bands. Two adenovirus constructs were used to further clarify differences in TGFbeta1- and IL-1beta-induced HAS1 activation. Overexpressing IkappaBalpha completely abolished the IL-1beta effect on HAS1 but did not interfere with TGFbeta1-induced HAS1 mRNA accumulation. Identical results were obtained when a dominant negative IKK was overexpressed. Interestingly, neither overexpression of IkappaBalpha nor of IKK had any effect on HAS2 and HAS3 mRNA levels. Taken together, HAS1 can be activated by distinct pathways; IL-1beta utilizes NF-kappaB, and TGFbeta1 does not. Furthermore, HAS2 and HAS3 are activated without the involvement of NF-kappaB.

Chemotaxis towards hyaluronan is dependent on CD44 expression and modulated by cell type variation in CD44-hyaluronan binding

The accumulation of the extracellular matrix glycosaminoglycan hyaluronan by tumours and tumour-associated stroma promotes cancer cell invasion and metastasis. Using the Dunn chamber chemotaxis assay, we demonstrate for the first time that high molecular mass hyaluronan acts as a soluble chemoattractant promoting the directional migration of MDA-MB-468 and MDA-MB-231 breast cancer cells. Moreover, chemotaxis towards hyaluronan, but not foetal bovine serum, can be abrogated following treatment of the cells with siRNA oligonucleotides to downregulate CD44 expression. These data indicate that CD44 is the principal receptor mediating this response and that CD44 expression is not a general requirement for cell migration and gradient sensing, rather it elicits a ligand-specific response. However, expression of CD44 alone is not sufficient to drive chemotaxis towards hyaluronan, as NIH-3T3 fibroblasts were unable to respond to a hyaluronan gradient even when transfected with high levels of human CD44. For NIH-3T3 cells to bind exogenous hyaluronan, it was necessary to both increase the level of receptor expression and remove a hyaluronan pericellular matrix. Together, these studies reveal a direct mechanism for promoting cell invasion into the hyaluronan-rich matrix and predict that in the complex multicellular environment in vivo, multiple mechanisms exist to regulate the ability of a cell to respond to a chemotactic hyaluronan gradient.

Regulation of protein function by glycosaminoglycans--as exemplified by chemokines

Immune modulators such as cytokines and growth factors exert their biological activity through high-affinity interactions with cell-surface receptors, thereby activating specific signaling pathways. However, many of these molecules also participate in low-affinity interactions with another class of molecules, referred to as proteoglycans. Proteoglycans consist of a protein core to which glycosaminoglycan (GAG) chains are attached. The GAGs are long, linear, sulfated, and highly charged heterogeneous polysaccharides that are expressed throughout the body in different forms, depending on the developmental or pathological state of the organ/organism. They participate in many biological functions, including organogenesis and growth control, cell adhesion, signaling, inflammation, tumorigenesis, and interactions with pathogens. Recently, it was demonstrated that certain chemokines require interactions with GAGs for their in vivo function. The GAG interaction is thought to provide a mechanism for retaining chemokines on cell surfaces, facilitating the formation of chemokine gradients. These gradients serve as directional cues to guide the migration of the appropriate cells in the context of their inflammatory, developmental, and homeostatic functions. In this review, we discuss GAGs and their interaction with proteins, with a special emphasis on the chemokine system.

Hyaluronan: a critical component of epithelial-mesenchymal and epithelial-carcinoma transitions

Hyaluronan plays a central role in the transition of epithelia to mesenchyme in the embryo and in the acquisition of transformed properties in carcinoma cells. In some cases, hyaluronan is both essential and sufficient for induction of epithelial-mesenchymal transitions (EMTs). Underlying its role are the effects of hyaluronan on receptor kinase activities, cell survival pathways, and multidrug transporters. A more complete understanding of the mechanisms whereby hyaluronan exerts its influences on cell behavior will enhance our understanding of normal and pathological EMTs and may lead to improved therapies for cancer patients.

Regulation of hyaluronan synthase-2 expression in human intestinal mesenchymal cells: mechanisms of interleukin-1beta-mediated induction

Elevated levels of hyaluronan are associated with numerous inflammatory diseases including inflammatory bowel disease. The purpose of this study was to determine whether a cause and effect relationship might exist among proinflammatory cytokines, IL-1beta, TNF-alpha, IFN-gamma, or transforming growth factor-beta (TGF-beta) and hyaluronan expression in human JDMC and, if so, to identify possible mechanisms involved in the induction of hyaluronan expression. TGF-beta, TNF-alpha, and IFN-gamma had little or no effect on hyaluronan production by these cells. Treatment with IL-1beta induced an approximate 30-fold increase in the levels of hyaluronan in the medium of human jejunum-derived mesenchymal cells. Ribonuclease protection analysis revealed that steady-state transcript levels for hyaluronan synthase (HAS)2 were present at very low levels in untreated cells but increased as much as 18-fold in the presence of IL-1beta. HAS3 transcript levels were also increased slightly by exposure of these cells to IL-1beta. Expression of HAS1 transcripts was not detected under any condition in these cells. IL-1beta induction of hyaluronan expression was inhibited in cells transfected with short interfering RNA corresponding to HAS2 transcripts. Inhibitors of the p38 and ERK1/2 mitogen-activated pathways but not JNK/SAPK blocked the IL-1beta-mediated induction of hyaluronan expression and the increase in HAS2 transcript expression. These results suggest that IL-1beta induction of HAS2 expression involves multiple signaling pathways that act in concert, thus leading to an increase in expression of hyaluronan by jejunum-derived mesenchymal cells.

Hyaluronan metabolism: a major paradox in cancer biology

Paradoxically, both hyaluronan (HA) and hyaluronidases, the enzymes that eliminate HA, can correlate with cancer progression. Levels of HA on the surface of tumor cells are indicators of poor outcome. Certain hyaluronidases, products of tumor suppressor genes eliminated in the course of tumor spread, are used clinically in anti-cancer chemotherapy regimens. Such information would indicate that cancer progression is inhibited by hyaluronidase. Yet progression of certain cancers correlates with levels of hyaluronidase activity. An attempt is made here to understand such apparent contradictions by examining details of HA metabolism. Anabolic and catabolic pathways are comprised of the HA synthases and hyaluronidases, respectively. There are several enzymes that synthesize HA, each under a different control mechanism, generating products of differing polymer size. The hyaluronidases degrade HA in step-wise fashion, the polymer decreasing in size in quantum steps, each size-specific polymer having a different biological activity. Superimposed on these are the potent hyaluronidase inhibitors, about which very little is known. These components of HA metabolism are reviewed here for possible roles in supporting or suppressing malignant transformation, growth, invasion and metastatic spread of tumors. Such a systematic approach may reveal mechanisms used in the course of cancer progression, resolve some of the apparent disparities, render new prognostic markers, and provide new targets for therapeutic intervention.

Hyaluronan accumulates in demyelinated lesions and inhibits oligodendrocyte progenitor maturation

Demyelination is the hallmark of numerous neurodegenerative conditions, including multiple sclerosis. Oligodendrocyte progenitors (OPCs), which normally mature into myelin-forming oligodendrocytes, are typically present around demyelinated lesions but do not remyelinate affected axons. Here, we find that the glycosaminoglycan hyaluronan accumulates in demyelinated lesions from individuals with multiple sclerosis and in mice with experimental autoimmune encephalomyelitis. A high molecular weight (HMW) form of hyaluronan synthesized by astrocytes accumulates in chronic demyelinated lesions. This form of hyaluronan inhibits remyelination after lysolecithin-induced white matter demyelination. OPCs accrue and do not mature into myelin-forming cells in demyelinating lesions where HMW hyaluronan is present. Furthermore, the addition of HMW hyaluronan to OPC cultures reversibly inhibits progenitor-cell maturation, whereas degrading hyaluronan in astrocyte-OPC cocultures promotes oligodendrocyte maturation. HMW hyaluronan may therefore contribute substantially to remyelination failure by preventing the maturation of OPCs that are recruited to demyelinating lesions.

The sweet and sour of cancer: glycans as novel therapeutic targets

A growing body of evidence supports crucial roles for glycans at various pathophysiological steps of tumour progression. Glycans regulate tumour proliferation, invasion, haematogenous metastasis and angiogenesis, and increased understanding of these roles sets the stage for developing pharmaceutical agents that target these molecules. Such novel agents might be used alone or in combination with operative and/or chemoradiation strategies for treating cancer.

The interstitial distribution of macromolecules in rat tumours is influenced by the negatively charged matrix components

Knowledge of macromolecular distribution volumes is essential in understanding fluid transport within normal and pathological tissues. In this study in vivo we determined the distribution volumes of several macromolecules, including one monoclonal antibody, in tumours and tested whether charges associated with the tumour extracellular matrix influence their available volumes. Steady state levels of the monoclonal antibody trastuzumab (Herceptin) (pI = 9.2), IgG (pI = 7.6) as well as native (pI = 5.0) and cationized albumin (pI = 7.6) were established in rats bearing dimethylbenzanthracene (DMBA)-induced mammary tumours by continuous infusion using osmotic minipumps. After a 5-7 day infusion period, the rats were nephrectomized and the extracellular volume was determined with 51Cr-labelled EDTA. Plasma volumes were measured with 125I-labelled human serum albumin or rat IgM in a separate series. Steady state concentrations of probes were determined in the interstitial fluid that was isolated by centrifugation from tumours or by post mortem wick implantation in the back skin. Calculations were made for interstitial fluid volume (Vi), along with the available (Va/Vi) and excluded (Ve/Vi) relative interstitial volume fractions. The Ve/Vi for the positively charged trastuzumab in tumours averaged 0.29 +/- 0.03 (n = 16), a value which was significantly lower than the corresponding one for IgG of 0.36 +/- 0.02 (n = 16). Native albumin was excluded from 38% of the tumour interstitial fluid, whereas cationization of albumin reduced the excluded volume by approximately 50%. Our experiments suggest that the tumour interstitium acts as a negatively charged matrix and is an important factor in determining the macromolecular distribution volume.

Gammadelta T cell-induced hyaluronan production by epithelial cells regulates inflammation

Nonhealing wounds are a major complication of diseases such as diabetes and rheumatoid arthritis. For efficient tissue repair, inflammatory cells must infiltrate into the damaged tissue to orchestrate wound closure. Hyaluronan is involved in the inflammation associated with wound repair and binds the surface of leukocytes infiltrating damaged sites. Skin gammadelta T cells play specialized roles in keratinocyte proliferation during wound repair. Here, we show that gammadelta T cells are required for hyaluronan deposition in the extracellular matrix (ECM) and subsequent macrophage infiltration into wound sites. We describe a novel mechanism of control in which gammadelta T cell-derived keratinocyte growth factors induce epithelial cell production of hyaluronan. In turn, hyaluronan recruits macrophages to the site of damage. These results demonstrate a novel function for skin gammadelta T cells in inflammation and provide a new perspective on T cell regulation of ECM molecules.

Rho GTPase-dependent signaling is required for macrophage migration inhibitory factor-mediated expression of cyclin D1

Our previous studies demonstrated that the proinflammatory peptide, macrophage migration inhibitory factor (MIF), functions as an autocrine mediator of both growth factor- and integrin-dependent sustained ERK MAPK activation, cyclin D1 expression, and cell cycle progression. We now report that MIF promotes the activation of the canonical ERK MAPK cascade and cyclin D1 expression by stimulating the activity of the Rho GTPase and downstream signaling to stress fiber formation. Rho-dependent stress fiber accumulation promotes the sustained activation of ERK and subsequent cyclin D1 expression during G(1)-S phase cell cycle progression. This pathway is reported to be dependent upon myosin light chain (MLC) kinase, integrin clustering, and subsequent activation of focal adhesion kinase, leading to sustained MAPK activity. Our studies reveal that recombinant MIF induces cyclin D1 expression in a Rho-, Rho kinase-, MLC kinase-, and ERK-dependent manner in asynchronous NIH 3T3 fibroblasts. Moreover, MIF(-/-) murine embryonic fibroblasts display aberrant cyclin D1 expression that is linked to defective Rho activity, stress fiber formation, and MLC phosphorylation. These results suggest that MIF is an integral autocrine mediator of Rho GTPase-dependent signaling events and provide mechanistic insight into how MIF regulates proliferative, migratory, and oncogenic processes.

Effect of Molecular Weight on the Exponential Growth and Morphology of Hyaluronan/Chitosan Multilayers: A Surface Plasmon Resonance Spectroscopy and Atomic Force Microscopy Investigation

The layer-by-layer growth of multilayer assemblies of two polysaccharides, the polyanion hyaluronan (HA) and the polycation chitosan (CH), was investigated using atomic force microscopy (AFM) and surface plasmon resonance (SPR) spectroscopy, with primary emphasis on the effect of the polysaccharide molecular weights on the film thickness and surface morphology. The HA/CH multilayers exhibit an exponential increase of the optical film thickness with the number of deposited bilayers. We show that the multilayer thickness at a given stage depends on the size of both CH, the diffusing polyelectrolyte, and HA, the non-diffusing species. Assemblies (12 bilayers) of high molecular weight polysaccharides (HA, 360,000; CH, 160,000) were twice as thick (approximately 900 nm vs approximately 450 nm) as those obtained with low molecular weight polymers (HA, 30,000; CH, 31,000), as assessed by AFM scratch tests. The exponential growth rate is the same for the high and low molecular weight pairs; the larger film thicknesses observed by SPR and by AFM arising from an earlier onset of the steep exponential growth phase in the case of the high molecular weight pair. In all cases, isolated islets form during the deposition of the first CH layer onto the underlying HA. Upon further film growth, individual islets coalesce into larger vermiculate features. The transition from distinct islands to vermiculate structures depends on the molecular weights of the polysaccharides and the lower molecular weight construct presents larger worm-like surface domains than the high molecular weight pair.

Towards a Structure for a TSG-6·Hyaluronan Complex by Modeling and NMR Spectroscopy

The Link module from human TSG-6, a hyaladherin with roles in ovulation and inflammation, has a hyaluronan (HA)-binding groove containing two adjacent tyrosine residues that are likely to form CH-pi stacking interactions with sequential rings in the sugar. We have used this observation to construct a model of a protein.HA complex, which was then tested against existing experimental information and by acquisition of new NMR data sets of [(13)C, (15)N]HA (8-mer) complexed with unlabeled protein. A major finding of this analysis was that acetamido side chains of two GlcNAc rings fit into hydrophobic pockets on either side of the adjacent tyrosines, providing a selectivity mechanism of HA over other polysaccharides. Furthermore, two basic residues have a separation that matches that of glucuronic acids in the sugar, consistent with the formation of salt bridges; NMR experiments at a range of pH values identified protein groups that titrate due to their proximity to a free carboxylate in HA. Sequence alignment and construction of homology models for all human Link modules in their HA-bound states revealed that many of these features are conserved across the superfamily, thus allowing the prediction of functionally important residues. In the case of cartilage link protein, its two Link modules were docked together (using bound HA as a guide), identifying hydrophobic residues likely to form an intra-Link module interface as well as amino acids that could be involved in supporting intermolecular interactions between link proteins and chondroitin sulfate proteoglycans. Here, we propose a mechanism for ternary complex formation that generates higher order helical structures, as may exist in cartilage aggregates.

Characterization of complexes formed between TSG-6 and inter-alpha-inhibitor that act as intermediates in the covalent transfer of heavy chains onto hyaluronan

The high molecular mass glycosaminoglycan hyaluronan (HA) can become modified by the covalent attachment of heavy chains (HCs) derived from the serum protein inter-alpha-inhibitor (IalphaI), which is composed of three subunits (HC1, HC2 and bikunin) linked together via a chondroitin sulfate moiety. The formation of HC.HA is likely to play an important role in the stabilization of HA-rich extracellular matrices in the context of inflammatory disease (e.g. arthritis) and ovulation. Here, we have characterized the complexes formed in vitro between purified human IalphaI and recombinant human TSG-6 (an inflammation-associated protein implicated previously in this process) and show that these complexes (i.e. TSG-6 x HC1 and TSG-6 x HC2) act as intermediates in the formation of HC x HA. This is likely to involve two transesterification reactions in which an ester bond linking an HC to chondroitin sulfate in intact IalphaI is transferred first onto TSG-6 and then onto HA. The formation of TSG-6 x HC1 and TSG-6 x C2 complexes was accompanied by the production of bikunin x HC2 and bikunin x HC1 by-products, respectively, which were observed to break down, releasing free bikunin and HCs. Both TSG-6 x HC formation and the subsequent HC transfer are metal ion-dependent processes; these reactions have a requirement for either Mg2+ or Mn2+ and are inhibited by Co2+. TSG-6, which is released upon the transfer of HCs from TSG-6 onto HA, was shown to combine with IalphaI to form new TSG-6 x HC complexes and thus be recycled. The finding that TSG-6 acts as cofactor and catalyst in the production of HC x HA complexes has important implications for our understanding of inflammatory and inflammation-like processes.

Regulation of MDR1 expression and drug resistance by a positive feedback loop involving hyaluronan, phosphoinositide 3-kinase, and ErbB2

Multidrug resistance is a potent barrier to effective, long term therapy in cancer patients. It is frequently attributed to enhanced expression of multidrug transporters or to the action of receptor kinases, such as ErbB2, and downstream anti-apoptotic signaling pathways, such as the phosphoinositide 3-kinase/Akt pathway. However, very few connections have been made between receptor kinases or anti-apoptotic pathways and multidrug transporter expression or function. Data presented herein show that constitutive interaction of the pericellular polysaccharide, hyaluronan, with its receptor, CD44, regulates assembly and activation of an ErbB2-containing signaling complex, which in turn stimulates phosphoinositide 3-kinase activity in multidrug-resistant MCF-7/Adr human breast carcinoma cells. Phosphoinositide 3-kinase activates Akt and downstream anti-apoptotic events, which contribute to drug resistance. However, hyaluronan and phosphoinositide 3-kinase stimulate expression of the multidrug transporter, MDR1 (P-glycoprotein), in an interdependent, but Akt-independent, manner. Furthermore, constitutively active phosphoinositide 3-kinase, but not Akt, stimulates hyaluronan production. These Akt-independent effects are dominant over the effects of Akt on doxorubicin resistance in MCF-7/Adr cells. Thus hyaluronan, phosphoinositide 3-kinase, and ErbB2 form a positive feedback loop that strongly amplifies MDR1 expression and regulates drug resistance in these cells. This pathway may also be important in progression of other malignant characteristics. These results illustrate the potential importance of hyaluronan as a therapeutic target in multidrug-resistant carcinomas.

Tumour regulation of fibroblast hyaluronan expression: a mechanism to facilitate tumour growth and invasion

Hyaluronan, a high molecular weight glycosaminoglycan is associated with cellular proliferation and migration. In a number of different tumour types, there is a close correlation between tumour progression and hyaluronan production, either by the tumour cells or the surrounding stromal cells. We have examined the ability of an aggressive melanoma cell line (C8161) to stimulate the synthesis of fibroblast hyaluronan, and the association of cell-surface CD44 receptors and hyaluronan with invasion. Melanoma cell-conditioned medium (CM) prepared in low glucose medium (1 mg/ml) stimulated the synthesis of fibroblast glycosaminoglycan as measured by [3H] glucosamine incorporation, and the synthesis of hyaluronan as measured using a specific hyaluronan-binding plate assay, while tumour cell-CM prepared in high glucose medium (4.5 mg/ml) inhibited the synthesis of fibroblast glycosaminoglycan. High glucose tumour cell-CM contained large amounts of lactate that appeared to inhibit the tumour-derived factor stimulation of fibroblast glycosaminoglycan synthesis, as removal of the lactate restored the stimulating activity. Melanoma cells seeded on contracted collagen lattices and incubated at the air/liquid interface rapidly formed a multilayered cell mass on the surface, with significant invasion of the gel. Hyaluronan staining was apparent within the collagen gel, and strong staining was seen around the invading tumour cells, but not around those cell layers near the surface. CD44 expression on the tumour cells was confined to those invading cells and corresponded to cellular hyaluronan staining. Hyaluronan staining was also apparent around and between tumour cells invading fibroblast-free collagen lattices. Monolayer cultures of C8161 cells stained strongly for CD44, but few cells stained for hyaluronan, while no detectable hyaluronan was released into the medium. In summary, the C8161 melanoma cells stimulated the synthesis of fibroblast hyaluronan, and in collagen lattices, only the invasive tumour cells expressed CD44 and hyaluronan, either in the presence or absence of fibroblasts.

Biosynthesis of Hyaluronan

Hyaluronan (HA), a functionally essential glycosaminoglycan in vertebrate tissues and a putative virulence factor in certain pathogenic bacteria, is an extended linear polymer composed of alternating units of glucuronic acid (GlcUA) and N-acetylglucosamine (GlcNAc). Uncertainty regarding the mechanism of HA biosynthesis has included the directionality of chain elongation, i.e. whether addition of monosaccharide units occurs at the reducing or non-reducing terminus of nascent chains. We have investigated this problem using yeast-derived recombinant HA synthases from Xenopus laevis (xlHAS1) and from Streptococcus pyogenes (spHAS). The enzymes were incubated with UDP-[3H]GlcUA and UDP-[14C]GlcNAc, under experimental conditions designed to yield HA chains with differentially labeled reducing-terminal and non-reducing terminal domains. Digestion of the products with a mixture of beta-glucuronidase and beta-N-acetylglucosaminidase exoenzymes resulted in truncation of the HA chain strictly from the non-reducing end and release of labeled monosaccharides. The change in 3H/14C ratio of the monosaccharide fraction, during the course of exoglycosidase digestion, was interpreted to indicate whether sugar units had been added at the reducing or non-reducing end. The results demonstrate that the vertebrate xlHAS1 and the bacterial spHAS extend HA in opposite directions. Chain elongation catalyzed by xlHAS1 occurs at the non-reducing end of the HA chain, whereas elongation catalyzed by spHAS occurs at the reducing end. The spHAS is the first glycosyltransferase that has been unanimously demonstrated to function at the reducing end of a growing glycosaminoglycan chain.

Hyaluronan Constitutively Regulates ErbB2 Phosphorylation and Signaling Complex Formation in Carcinoma Cells

Hyaluronan is enriched in many types of human cancers, and manipulations of hyaluronan expression or interactions have a major influence on tumor progression in animal models. Increased ErbB2 activity is characteristic of several cancers and is responsible for many aspects of malignant cell behavior in these cancers. In this study we show that constitutively high levels of active, i.e. autophosphorylated, ErbB2 in HCT116 colon carcinoma cells and TA3/St mammary carcinoma cells are dependent on endogenous hyaluronan-CD44 interaction. Dependence on hyaluronan-CD44 interaction was demonstrated by the administration of hyaluronan oligomers, experimentally induced expression of soluble CD44, and small interfering RNA knockdown of CD44 expression. On the other hand, increasing hyaluronan production by overexpression of hyaluronan synthase 2 or emmprin causes elevated ErbB2 phosphorylation in MCF-7 mammary carcinoma cells, which normally exhibit low levels of ErbB2 activity. Furthermore, in HCT116 and TA3/St cells, inhibition of endogenous hyaluronan-CD44 interaction causes disassembly of a constitutive, lipid raft-associated, signaling complex containing phosphorylated ErbB2, CD44, ezrin, phosphoinositide 3-kinase, and the chaperone molecules, Hsp90 and cdc37. Stimulation of hyaluronan production in MCF-7 cells induces assembly of this complex. We conclude that hyaluronan regulates ErbB2 activity and its interactions with other signaling factors in carcinoma cells.

Composition of perineuronal nets in the adult rat cerebellum and the cellular origin of their components

The decrease in plasticity that occurs in the central nervous system during postnatal development is accompanied by the appearance of perineuronal nets (PNNs) around the cell body and dendrites of many classes of neuron. These structures are composed of extracellular matrix molecules, such as chondroitin sulfate proteoglycans (CSPGs), hyaluronan (HA), tenascin-R, and link proteins. To elucidate the role played by neurons and glial cells in constructing PNNs, we studied the expression of PNN components in the adult rat cerebellum by immunohistochemistry and in situ hybridization. In the deep cerebellar nuclei, only large excitatory neurons were surrounded by nets, which contained the CSPGs aggrecan, neurocan, brevican, versican, and phosphacan, along with tenascin-R and HA. Whereas both net-bearing neurons and glial cells were the sources of CSPGs and tenascin-R, only the neurons expressed the mRNA for HA synthases (HASs), cartilage link protein, and link protein Bral2. In the cerebellar cortex, Golgi neurons possessed PNNs and also synthesized HASs, cartilage link protein, and Bral2 mRNAs. To see whether HA might link PNNs to the neuronal cell surface by binding to a receptor, we investigated the expression of the HA receptors CD44, RHAMM, and LYVE-1. No immunolabelling for HA receptors on the membrane of net-bearing neurons was found. We therefore propose that HASs, which can retain HA on the cell surface, may act as a link between PNNs and neurons. Thus, HAS and link proteins might be key molecules for PNN formation and stability.

CD44 modulates Smad1 activation in the BMP-7 signaling pathway

Bone morphogenetic protein 7 (BMP-7) regulates cellular metabolism in embryonic and adult tissues. Signal transduction occurs through the activation of intracellular Smad proteins. In this paper, using a yeast two-hybrid screen, Smad1 was found to interact with the cytoplasmic domain of CD44, a receptor for the extracellular matrix macromolecule hyaluronan. Coimmunoprecipitation experiments confirmed the interaction of Smad1 with full-length CD44—interactions that did not occur when CD44 receptors truncated within the cytoplasmic domain were tested. Chondrocytes overexpressing a truncated CD44 on a background of endogenous full-length CD44 no longer exhibited Smad1 nuclear translocation upon BMP-7 stimulation. Further, pretreatment of chondrocytes with Streptomyces hyaluronidase to disrupt extracellular hyaluronan–cell interactions inhibited BMP-7–mediated Smad1 phosphorylation, nuclear translocation of Smad1 or Smad4, and SBE4–luciferase reporter activation. These results support a functional link between the BMP signaling cascade and CD44. Thus, changes in hyaluronan–cell interactions may serve as a means to modulate cellular responsiveness to BMP.

Preparation and application of biologically active fluorescent hyaluronan oligosaccharides

We report the production of biologically active hyaluronan (HA) oligosaccharides labeled with the fluorophore 2-aminobenzoic acid (2AA). Oligosaccharides from 4 to 40 residues in length were purified to homogeneity by ion exchange chromatography using a logarithmic gradient. Molecular weight and purity characterization of HA oligosaccharides is facilitated by 2AA derivatization because it enhances signals in MALDI-TOF MS and improves FACE (fluorophore-assisted carbohydrate electrophoresis) analysis by avoiding the inverted parabolic migration characteristic of 2-aminoacridone (AMAC)-labeled sugars. The small size and shape of the fluorophore maintains the biological activity of the derivatized oligosaccharides, as demonstrated by their ability to compete for polymeric HA binding to the G1-domain of human recombinant versican (VG1). An electrophoretic mobility shift assay was used to study VG1 binding to labeled HA 8-, 10-, 20-, 30-, and 40-mers, and although no stable VG1 binding was observed to labeled 8-mers, the equilibrium dissociation constant (100 nM) for VG1 with HA(10) was estimated from densitometry analysis of the free oligosaccharide. Interactions involving HA 20-, 30-, and 40-mers (proposed to be multivalent) could also be studied using this protocol. Oligosaccharides labeled with 2AA therefore show excellent potential as probes in fluorescence-based assays that investigate protein-carbohydrate interactions.