A biological guide to glycosaminoglycans: current perspectives and pending questions

Mammalian glycosaminoglycans (GAGs), except hyaluronan (HA), are sulfated polysaccharides that are covalently attached to core proteins to form proteoglycans (PGs). This article summarizes key biological findings for the most widespread GAGs, namely HA, chondroitin sulfate/dermatan sulfate (CS/DS), keratan sulfate (KS), and heparan sulfate (HS). It focuses on the major processes that remain to be deciphered to get a comprehensive view of the mechanisms mediating GAG biological functions. They include the regulation of GAG biosynthesis and postsynthetic modifications in heparin (HP) and HS, the composition, heterogeneity, and function of the tetrasaccharide linkage region and its role in disease, the functional characterization of the new PGs recently identified by glycoproteomics, the selectivity of interactions mediated by GAG chains, the display of GAG chains and PGs at the cell surface and their impact on the availability and activity of soluble ligands, and on their move through the glycocalyx layer to reach their receptors, the human GAG profile in health and disease, the roles of GAGs and particular PGs (syndecans, decorin, and biglycan) involved in cancer, inflammation, and fibrosis, the possible use of GAGs and PGs as disease biomarkers, and the design of inhibitors targeting GAG biosynthetic enzymes and GAG-protein interactions to develop novel therapeutic approaches.

In Vitro Investigation of Hyaluronan/CD44 Network

Hyaluronan is one of the most influential components of the extracellular matrix. It is involved in the regulation of normal tissue function and architecture, while its metabolism is perturbed in a multitude of human diseases like inflammation, cancer, and viral infection. Given the implication of hyaluronan in a vast array of diseases, we describe here assays that can be utilized to study the quantity, size, subcellular localization, and binding capacity of hyaluronan by cells as well as its interactions with its major cellular receptor, CD44. Hopefully, these protocols will provide researchers with useful tools to study the complex hyaluronan biology.

Identification of a Small Molecule Inhibitor of Hyaluronan Synthesis, DDIT, Targeting Breast Cancer Cells

Breast cancer is a common cancer in women. Breast cancer cells synthesize large amounts of hyaluronan to assist their proliferation, survival, migration and invasion. Accumulation of hyaluronan and overexpression of its receptor CD44 and hyaluronidase TMEM2 in breast tumors correlate with tumor progression and reduced overall survival of patients. Currently, the only known small molecule inhibitor of hyaluronan synthesis is 4-methyl-umbelliferone (4-MU). Due to the importance of hyaluronan for breast cancer progression, our aim was to identify new, potent and chemically distinct inhibitors of its synthesis. Here, we report a new small molecule inhibitor of hyaluronan synthesis, the thymidine analog 5'-Deoxy-5'-(1,3-Diphenyl-2-Imidazolidinyl)-Thymidine (DDIT). This compound is more potent than 4-MU and displays significant anti-tumorigenic properties. Specifically, DDIT inhibits breast cancer cell proliferation, migration, invasion and cancer stem cell self-renewal by suppressing HAS-synthesized hyaluronan. DDIT appears as a promising lead compound for the development of inhibitors of hyaluronan synthesis with potential usefulness in breast cancer treatment.

The natural antisense transcript HAS2-AS1 regulates breast cancer cells aggressiveness independently from hyaluronan metabolism

Hyaluronan (HA) is a ubiquitous extracellular matrix component playing a crucial role in the regulation of cell behaviors, including cancer. Aggressive breast cancer cells tend to proliferate, migrate and metastatize. Notably, triple-negative breast cancer cells lacking the expression of estrogen receptor (ER) as well as progesterone receptor and HER2 are more aggressive than ER-positive ones. As currently no targeted therapy is available for triple-negative breast cancer, the identification of novel therapeutic targets has a high clinical priority. In ER-negative cells, tumoral behavior can be reduced by inhibiting HA synthesis or silencing the enzymes involved in its metabolism, such as HA synthase 2 (HAS2). HAS2-AS1 is a long non-coding RNA belonging to the natural antisense transcript family which is known to favor HAS2 gene expression and HA synthesis, thus bolstering malignant progression in brain, ovary, and lung tumors. As the role of HAS2-AS1 has not yet been investigated in breast cancer, in this work we report that ER-positive breast cancers had lower HAS2-AS1 expression compared to ER-negative tumors. Moreover, the survival of patients with ER-negative tumors was higher when the expression of HAS2-AS1 was elevated. Experiments with ER-negative cell lines as MDA-MB-231 and Hs 578T revealed that the overexpression of either the full-length HAS2-AS1 or its exon 2 long or short isoforms alone, strongly reduced cell viability, migration, and invasion, whereas HAS2-AS1 silencing increased cell aggressiveness. Unexpectedly, in these ER-negative cell lines, HAS2-AS1 is involved neither in the regulation of HAS2 nor in HA deposition. Finally, transcriptome analysis revealed that HAS2-AS1 modulation affected several pathways, including apoptosis, proliferation, motility, adhesion, epithelial to mesenchymal transition, and signaling, describing this long non-coding RNA as an important regulator of breast cancer cells aggressiveness.

Involvement of hyaluronan and CD44 in cancer and viral infections

Hyaluronan and its major receptor CD44 are ubiquitously distributed. They have important structural as well as signaling roles, regulating tissue homeostasis, and their expression levels are tightly regulated. In addition to signaling initiated by the interaction of the intracellular domain of CD44 with cytoplasmic signaling molecules, CD44 has important roles as a co-receptor for different types of receptors of growth factors and cytokines. Dysregulation of hyaluronan-CD44 interactions is seen in diseases, such as inflammation and cancer. In the present communication, we discuss the mechanism of hyaluronan-induced signaling via CD44, as well as the involvement of hyaluronan-engaged CD44 in malignancies and in viral infections.

High levels of serum hyaluronan is an early predictor of dengue warning signs and perturbs vascular integrity

BACKGROUND

A main pathological feature of severe dengue virus infection is endothelial hyper-permeability. The dengue virus nonstructural protein 1 (NS1) has been implicated in the vascular leakage that characterizes severe dengue virus infection, however, the molecular mechanisms involved are not known.

METHODS

A cohort of 250 dengue patients has been followed from the onset of symptoms to the recovery phase. Serum hyaluronan levels and several other clinical parameters were recorded. The effect of NS1 treatment of cultured fibroblasts and endothelial cells on the expressions of hyaluronan synthetic and catabolic enzymes and the hyaluronan receptor CD44, were determined, as have the effects on the formation of hyaluronan-rich matrices and endothelial permeability.

FINDINGS

Elevated serum hyaluronan levels (≥70 ng/ml) during early infection was found to be an independent predictor for occurrence of warning signs, and thus severe dengue fever. High circulating levels of the viral protein NS1, indicative of disease severity, correlated with high concentrations of serum hyaluronan. NS1 exposure decreased the expression of CD44 in differentiating endothelial cells impairing the integrity of vessel-like structures, and promoted the synthesis of hyaluronan in dermal fibroblasts and endothelial cells in synergy with dengue-induced pro-inflammatory mediators. Deposited hyaluronan-rich matrices around cells cultured in vitro recruited CD44-expressing macrophage-like cells, suggesting a mechanism for enhancement of inflammation. In cultured endothelial cells, perturbed hyaluronan-CD44 interactions enhanced endothelial permeability through modulation of VE-cadherin and cytoskeleton re-organization, and exacerbated the NS1-induced disruption of endothelial integrity.

INTERPRETATION

Pharmacological targeting of hyaluronan biosynthesis and/or its CD44-mediated signaling may limit the life-threatening vascular leakiness during moderate-to-severe dengue virus infection. FUND: This work was supported in part by grants from the Swedish Cancer Society (2018/337; 2016/445), the Swedish Research Council (2015-02757), the Ludwig Institute for Cancer Research, Uppsala University, the Ministry of Science and Technology, Taiwan (106-2314-B-037-088- and 106-2915-I-037-501-), Kaohsiung Medical University Hospital (KMUH103-3 T05) and Academy of Finland. The funders played no role in the design, interpretation or writing of the manuscript.

Transforming growth factor β (TGFβ) induces NUAK kinase expression to fine-tune its signaling output

TGFβ signaling via SMAD proteins and protein kinase pathways up- or down-regulates the expression of many genes and thus affects physiological processes, such as differentiation, migration, cell cycle arrest, and apoptosis, during developmental or adult tissue homeostasis. We here report that NUAK family kinase 1 (NUAK1) and NUAK2 are two TGFβ target genes. NUAK1/2 belong to the AMP-activated protein kinase (AMPK) family, whose members control central and protein metabolism, polarity, and overall cellular homeostasis. We found that TGFβ-mediated transcriptional induction of NUAK1 and NUAK2 requires SMAD family members 2, 3, and 4 (SMAD2/3/4) and mitogen-activated protein kinase (MAPK) activities, which provided immediate and early signals for the transient expression of these two kinases. Genomic mapping identified an enhancer element within the first intron of the NUAK2 gene that can recruit SMAD proteins, which, when cloned, could confer induction by TGFβ. Furthermore, NUAK2 formed protein complexes with SMAD3 and the TGFβ type I receptor. Functionally, NUAK1 suppressed and NUAK2 induced TGFβ signaling. This was evident during TGFβ-induced epithelial cytostasis, mesenchymal differentiation, and myofibroblast contractility, in which NUAK1 or NUAK2 silencing enhanced or inhibited these responses, respectively. In conclusion, we have identified a bifurcating loop during TGFβ signaling, whereby transcriptional induction of NUAK1 serves as a negative checkpoint and NUAK2 induction positively contributes to signaling and terminal differentiation responses to TGFβ activity.

Effects of mutations in the post-translational modification sites on the trafficking of hyaluronan synthase 2 (HAS2)

Vesicular trafficking of hyaluronan synthases (HAS1-3) from endoplasmic reticulum (ER) through Golgi to plasma membrane (PM), and either back to endosomes and lysosomes, or out into extracellular vesicles, is important for their activities. We studied how post-translational modifications affect the trafficking of HAS2 by mutagenesis of the sites of ubiquitination (K190R), phosphorylation (T110A) and O-GlcNAcylation (S221A), using Dendra2- and EGFP-HAS2 transfected into COS1 cells. Confocal microscopy showed HAS2 wild type (wt) and its K190R and S221A mutants in ER, Golgi and extracellular vesicles, while the T110A mutant remained mostly in the ER. HA synthesis was reduced by S221A, while completely blocked by K190R and T110A. Cell-surface biotinylation indicated that T110A was absent from PM, while S221A was close to the level of wt, and K190R was increased in PM. TIRF microscopy analysis gave similar results. Rab10 silencing increased HA secretion by HAS2, likely by inhibiting endocytosis of the enzyme from PM, as reported before for HAS3. Green-to-red photo-conversion of Dendra2-HAS2 constructs suggested slower decay of K190R and S221A than HAS2 wt, while T110A was barely degraded at all. S221D and S221E, the phosphomimetic mutants of this site, decayed faster and blocked hyaluronan synthesis, suggesting alternative O-GlcNAc/-PO₄ substitution to regulate the stability of the enzyme. Probing the role of dynamic O-GlcNAcylation at S221 by adding glucosamine increased the half-life of only HAS2 wt. The Dendra2·HAS2 disappearance from Golgi was slower for K190R. Of the two inactive constructs, K190R co-transfected with HAS2 wt suppressed, whereas T110A had no effect on HA synthesis. Interestingly, the HAS2-stimulated shedding of extracellular vesicles was dependent on HAS residence in PM but independent of HA synthesis. The results indicate that post-translational modifications control the trafficking of HAS2, and that trafficking is an integral part of the post-translational regulation of HAS2 activity.

Regulation of hyaluronan biosynthesis and clinical impact of excessive hyaluronan production

The tightly regulated biosynthesis and catabolism of the glycosaminoglycan hyaluronan, as well as its role in organizing tissues and cell signaling, is crucial for the homeostasis of tissues. Overexpression of hyaluronan plays pivotal roles in inflammation and cancer, and markedly high serum and tissue levels of hyaluronan are noted under such pathological conditions. This review focuses on the complexity of the regulation at transcriptional and posttranslational level of hyaluronan synthetic enzymes, and the outcome of their aberrant expression and accumulation of hyaluronan in clinical conditions, such as systemic B-cell cancers, aggressive breast carcinomas, metabolic diseases and virus infection.

Fluorescence resonance energy transfer (FRET) and proximity ligation assays reveal functionally relevant homo- and heteromeric complexes among hyaluronan synthases HAS1, HAS2, and HAS3

In vertebrates, hyaluronan is produced in the plasma membrane from cytosolic UDP-sugar substrates by hyaluronan synthase 1-3 (HAS1-3) isoenzymes that transfer N-acetylglucosamine (GlcNAc) and glucuronic acid (GlcUA) in alternative positions in the growing polysaccharide chain during its simultaneous extrusion into the extracellular space. It has been shown that HAS2 immunoprecipitates contain functional HAS2 homomers and also heteromers with HAS3 (Karousou, E., Kamiryo, M., Skandalis, S. S., Ruusala, A., Asteriou, T., Passi, A., Yamashita, H., Hellman, U., Heldin, C. H., and Heldin, P. (2010) The activity of hyaluronan synthase 2 is regulated by dimerization and ubiquitination. J. Biol. Chem. 285, 23647-23654). Here we have systematically screened in live cells, potential interactions among the HAS isoenzymes using fluorescence resonance energy transfer (FRET) and flow cytometric quantification. We show that all HAS isoenzymes form homomeric and also heteromeric complexes with each other. The same complexes were detected both in Golgi apparatus and plasma membrane by using FRET microscopy and the acceptor photobleaching method. Proximity ligation assays with HAS antibodies confirmed the presence of HAS1-HAS2, HAS2-HAS2, and HAS2-HAS3 complexes between endogenously expressed HASs. C-terminal deletions revealed that the enzymes interact mainly via uncharacterized N-terminal 86-amino acid domain(s), but additional binding site(s) probably exist in their C-terminal parts. Of all the homomeric complexes HAS1 had the lowest and HAS3 the highest synthetic activity. Interestingly, HAS1 transfection reduced the synthesis of hyaluronan obtained by HAS2 and HAS3, suggesting functional cooperation between the isoenzymes. These data indicate a general tendency of HAS isoenzymes to form both homomeric and heteromeric complexes with potentially important functional consequences on hyaluronan synthesis.

Platelet-derived growth factor β-receptor, transforming growth factor β type I receptor, and CD44 protein modulate each other's signaling and stability

Growth factors, such as platelet-derived growth factor BB (PDGF-BB) and transforming growth factor β (TGFβ), are key regulators of cellular functions, including proliferation, migration, and differentiation. Growth factor signaling is modulated by context-dependent cross-talk between different signaling pathways. We demonstrate in this study that PDGF-BB induces phosphorylation of Smad2, a downstream mediator of the canonical TGFβ pathway, in primary dermal fibroblasts. The PDGF-BB-mediated Smad2 phosphorylation was dependent on the kinase activities of both TGFβ type I receptor (TβRI) and PDGF β-receptor (PDGFRβ), and it was prevented by inhibitory antibodies against TGFβ. Inhibition of the activity of the TβRI kinase greatly reduced the PDGF-BB-dependent migration in dermal fibroblasts. Moreover, we demonstrate that the receptors for PDGF-BB and TGFβ interact physically in primary dermal fibroblasts and that stimulation with PDGF-BB induces internalization not only of PDGFRβ but also of TβRI. In addition, silencing of PDGFRβ by siRNA decreased the stability of TβRI and delayed TGFβ-induced signaling. We further show that the hyaluronan receptor CD44 interacts with both PDGFRβ and TβRI. Depletion of CD44 by siRNA increased signaling via PDGFRβ and TβRI by stabilizing the receptor proteins. Our data suggest that cross-talk between PDGFRβ and TβRI occurs in dermal fibroblasts and that CD44 negatively modulates signaling via these receptors.

Knock-down of CD44 regulates endothelial cell differentiation via NFκB-mediated chemokine production

A striking feature of microvascular endothelial cells is their capacity to fuse and differentiate into tubular structures when grown in three-dimensional (3D) extracellular matrices, in collagen or Matrigel, mimicking the in vivo blood vessel formation. In this study we demonstrate that human telomerase-immortalised foreskin microvascular endothelial (TIME) cells express high levels of the hyaluronan receptor CD44 and the hyaluronidase HYAL2. Knock-down of CD44 or HYAL2 resulted in an inability of TIME cells to form a tubular network, suggesting a key regulatory role of hyaluronan in controlling TIME cell tubulogenesis in 3D matrices. Knock-down of CD44 resulted in an upregulation of mRNA expression of the chemokines CXCL9 and CXCL12, as well as their receptors CXCR3 and CXCR4. This was accompanied by a defect maturation of the tubular structure network and increased phosphorylation of the inhibitor of NFκB kinase (IKK) complex and thus translocation of NFκB into the nucleus and activation of chemokine targed genes. Furthermore, the interaction between CD44 and hyaluronan determines the adhesion of breast cancer cells. In summary, our observations support the notion that the interaction between CD44 and hyaluronan regulates microvascular endothelial cell tubulogenesis by affecting the expression of cytokines and their receptors, as well as breast cancer dissemination.

TGFβ and matrix-regulated epithelial to mesenchymal transition

BACKGROUND

The progression of cancer through stages that guide a benign hyperplastic epithelial tissue towards a fully malignant and metastatic carcinoma, is driven by genetic and microenvironmental factors that remodel the tissue architecture. The concept of epithelial-mesenchymal transition (EMT) has evolved to emphasize the importance of plastic changes in tissue architecture, and the cross-communication of tumor cells with various cells in the stroma and with specific molecules in the extracellular matrix (ECM).

SCOPE OF THE REVIEW

Among the multitude of ECM-embedded cytokines and the regulatory potential of ECM molecules, this article focuses on the cytokine transforming growth factor β (TGFβ) and the glycosaminoglycan hyaluronan, and their roles in cancer biology and EMT. For brevity, we concentrate our effort on breast cancer.

MAJOR CONCLUSIONS

Both normal and abnormal TGFβ signaling can be detected in carcinoma and stromal cells, and TGFβ-induced EMT requires the expression of hyaluronan synthase 2 (HAS2). Correspondingly, hyaluronan is a major constituent of tumor ECM and aberrant levels of both hyaluronan and TGFβ are thought to promote a wounding reaction to the local tissue homeostasis. The link between EMT and metastasis also involves the mesenchymal-epithelial transition (MET). ECM components, signaling networks, regulatory non-coding RNAs and epigenetic mechanisms form the network of regulation during EMT-MET.

GENERAL SIGNIFICANCE

Understanding the mechanism that controls epithelial plasticity in the mammary gland promises the development of valuable biomarkers for the prognosis of breast cancer progression and even provides new ideas for a more integrative therapeutic approach against disease. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

HAS2 and CD44 in breast tumorigenesis

Metastatic spread of breast cancer cells, facilitated by the epithelial-mesenchymal transition (EMT) process, is responsible for the majority of breast cancer mortality. Increased levels of hyaluronan due to deregulation of hyaluronan-synthesizing enzymes, like HAS2, and expression of CD44, the key receptor for hyaluronan, are correlated to poor outcome of patients with basal-like breast cancer. TGFβ induces HAS2 and CD44, both of which are required in the course of efficient TGFβ-induced EMT processes by mammary epithelial cells. Elucidation of the molecular mechanisms underlying tumor-stroma interactions in breast cancer including the regulation of HAS2 and CD44 expression may contribute to the development of better strategies to treat breast cancer patients.

Deregulation of hyaluronan synthesis, degradation and binding promotes breast cancer

Clinical and experimental data indicate that hyaluronan accumulates in breast cancer compared with normal breast epithelium, which correlates to poor prognosis. In this review, we discuss the expression of genes encoding enzymes that synthesize or degrade hyaluronan, i.e. hyaluronan synthases and hyaluronidases or bind hyaluronan, i.e. CD44 and receptor for hyaluronan-mediated motility (RHAMM, also designated as HMMR or CD168), in relation to breast cancer progression. Hyaluronan and hyaluronan receptors have multi-faceted roles in signalling events in breast cancer. A better understanding of the molecular mechanisms underlying these signalling pathways is highly warranted and may lead to improvement of cancer treatment.

Efficient TGFβ-induced epithelial-mesenchymal transition depends on hyaluronan synthase HAS2

Epithelial-mesenchymal transition (EMT) is a developmental program, which can be adopted by cancer cells to increase their migration and ability to form metastases. Transforming growth factor β (TGFβ) is a well-studied inducer of EMT. We demonstrate that TGFβ potently stimulates hyaluronan synthesis via upregulation of hyaluronan synthase 2 (HAS2) in NMuMG mammary epithelial cells. This stimulatory effect requires the kinase active type I TGFβ receptor and is dependent on Smad signaling and activation of the p38 mitogen-activated protein kinase. Knockdown of HAS2 inhibited the TGFβ-induced EMT by about 50%, as determined by the phase contrast microscopy and immunostaining using the EMT marker ZO-1. Furthermore, real-time PCR analysis of the EMT markers fibronectin, Snail1 and Zeb1 revealed decreased expressions upon HAS2 suppression, using specific small interfering RNA (siRNA) for HAS2. Removal of the extracellular hyaluronan by Streptomyces hyaluronidase or inhibiting the binding to its cell surface receptor CD44 by blocking antibodies, did not inhibit TGFβ-induced EMT. Interestingly, HAS2 suppression completely abolished the TGFβ-induced cell migration, whereas CD44 knockdown did not. These observations suggest that TGFβ-dependent HAS2 expression, but not extracellular hyaluronan, has an important regulatory role in TGFβ-induced EMT.

Differential synthesis and binding of hyaluronan by human breast cancer cell lines

In the present study we investigated a panel of human breast cancer cell lines which were sensitive or resistant to the cytotoxic drug doxorubicin, for their abilities to synthesize and bind hyaluronan. We found that MDA-231 and HS-578T cells which express very low amounts of estrogen and progesterone receptors, both synthesized hyaluronan and expressed hyaluronan binding sites on the cell surface as did their doxorubicin-adapted counterparts MDA-231 Dox and HS-578T Dox. The binding was highly specific with a K-d of 0.48x10(-9) M. Most of the hyaluronan binding activity was blocked by mAbs against Hermes-l antigen indicating that the adhesion molecule CD44 is responsible for hyaluronan binding. Only 0.5% of the total amount of labeled hyaluronan added to the cultures was degraded during a period of 16 h. The hormone positive receptor cell lines, MCF-5, Zr-5-1 and Zr-5-1 Dox synthesized only minute amounts of hyaluronan and did not bind hyaluronan or express CD44 receptors. Expression of CD44-related hyaluronan receptors and synthesized hyaluronan may endow hormone receptor negative cells with a highly hydrated environment that facilitates cell motility and invasiveness. The lack of CD44 and thereby the lack of ability to bind hyaluronan in the extracellular matrix may contribute to the non-invasive behavior of hormone positive cell lines.

Hyaluronan synthase 2 (HAS2) promotes breast cancer cell invasion by suppression of tissue metalloproteinase inhibitor 1 (TIMP-1)

Invasion and metastasis are the primary causes of breast cancer mortality, and increased knowledge about the molecular mechanisms involved in these processes is highly desirable. High levels of hyaluronan in breast tumors have been correlated with poor patient survival. The involvement of hyaluronan in the early invasive phase of a clone of breast cancer cell line MDA-MB-231 that forms bone metastases was studied using an in vivo-like basement membrane model. The metastatic to bone tumor cells exhibited a 7-fold higher hyaluronan-synthesizing capacity compared with MDA-MB-231 cells predominately due to an increased expression of hyaluronan synthase 2 (HAS2). We found that knockdown of HAS2 completely suppressed the invasive capability of these cells by the induction of tissue metalloproteinase inhibitor 1 (TIMP-1) and dephosphorylation of focal adhesion kinase. HAS2 knockdown-mediated inhibition of basement membrane remodeling was rescued by HAS2 overexpression, transfection with TIMP-1 siRNA, or addition of TIMP-1-blocking antibodies. Moreover, knockdown of HAS2 suppressed the EGF-mediated induction of the focal adhesion kinase/PI3K/Akt signaling pathway. Thus, this study provides new insights into a possible mechanism whereby HAS2 enhances breast cancer invasion.

Hyaluronan-CD44 interactions as potential targets for cancer therapy

It is becoming increasingly clear that signals generated in tumor microenvironments are crucial to tumor cell behavior, such as survival, progression and metastasis. The establishment of these malignant behaviors requires that tumor cells acquire novel adhesion and migration properties to detach from their original sites and to localize to distant organs. CD44, an adhesion/homing molecule, is a major receptor for the glycosaminoglycan hyaluronan, which is one of the major components of the tumor extracellular matrix. CD44, a multistructural and multifunctional molecule, detects changes in extracellular matrix components, and thus is well positioned to provide appropriate responses to changes in the microenvironment, i.e. engagement in cell-cell and cell-extracellular matrix interactions, cell trafficking, lymph node homing and the presentation of growth factors/cytokines/chemokines to co-ordinate signaling events that enable the cell responses that change in the tissue environment. The potential involvement of CD44 variants (CD44v), especially CD44v4-v7 and CD44v6-v9, in tumor progression has been confirmed for many tumor types in numerous clinical studies. The downregulation of the standard CD44 isoform (CD44s) in colon cancer is postulated to result in increased tumorigenicity. CD44v-specific functions could be caused by their higher binding affinity than CD44s for hyaluronan. Alternatively, CD44v-specific functions could be caused by differences in associating molecules, which may bind selectively to the CD44v exon. This minireview summarizes how the interaction between hyaluronan and CD44v can serve as a potential target for cancer therapy, in particular how silencing CD44v can target multiple metastatic tumors.

Hyaluronan synthesis is inhibited by adenosine monophosphate-activated protein kinase through the regulation of HAS2 activity in human aortic smooth muscle cells

Hyaluronan (HA) is an extracellular matrix glycosaminoglycan (GAG) involved in cell motility, proliferation, tissue remodeling, development, differentiation, inflammation, tumor progression, and invasion and controls vessel thickening in cardiovascular diseases. Therefore, the control of HA synthesis could permit the fine-tuning of cell behavior, but the mechanisms that regulate HA synthesis are largely unknown. Recent studies suggest that the availability of the nucleotide-sugar precursors has a critical role. Because the formation of UDP-sugars is a highly energetically demanding process, we have analyzed whether the energy status of the cell could control GAG production. AMP-activated protein kinase (AMPK) is the main ATP/AMP sensor of mammalian cells, and we mimicked an energy stress by treating human aortic smooth muscle cells (AoSMCs) with the AMPK activators 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside and metformin. Under these conditions, HA synthesis, but not that of the other GAGs, was greatly reduced. We confirmed the inhibitory effect of AMPK using a specific inhibitor and knock-out cell lines. We found that AMPK phosphorylated Thr-110 of human HAS2, which inhibits its enzymatic activity. In contrast, the other two HAS isoenzymes (HAS1 and HAS3) were not modified by the kinase. The reduction of HA decreased the ability of AoSMCs to proliferate, migrate, and recruit immune cells, thereby reducing the pro-atherosclerotic AoSMC phenotype. Interestingly, such effects were not recovered by treatment with exogenous HA, suggesting that AMPK can block the pro-atherosclerotic signals driven by HA by interaction with its receptors.

The activity of hyaluronan synthase 2 is regulated by dimerization and ubiquitination

Hyaluronan is a component of the extracellular matrix, which affects tissue homeostasis. In this study, we investigated the regulatory mechanisms of one of the hyaluronan-synthesizing enzymes, HAS2. Ectopic expression of Flag- and 6myc-HAS2 in COS-1 cells followed by immunoprecipitation and immunoblotting revealed homodimers; after co-transfection with Flag-HAS3, also heterodimers were seen. Furthermore, the expressed HAS2 was ubiquitinated. We identified one acceptor site for ubiquitin on lysine residue 190. Mutation of this residue led to inactivation of the enzymatic activity of HAS2. Interestingly, K190R-mutated HAS2 formed dimers with wt HAS2 and quenched the activity of wt HAS2, thus demonstrating a functional role of the dimeric configuration.

Importance of hyaluronan-CD44 interactions in inflammation and tumorigenesis

Hyaluronan is an apparently simple polysaccharide that is responsible for tissue hydration but also stimulates cell proliferation, migration, and differentiation via binding to cell surface receptors, such as CD44. The amounts of hyaluronan increase during inflammation and tumorigenesis through the action of chemokines and growth factors. This review discusses some of the evidence that hyaluronan-CD44 complexes trigger signaling cascades that modulate inflammation and tumor progression.

Hyaluronan production regulation from porcine hyalocyte cell line by cytokines

The objective of this study were to establish a cell line derived from porcine hyalocytes and to investigate the regulation of hyaluronan (HA) synthesis in response to cytokines. After 50 passages of the cells derived from porcine vitreous tissue, a cell line was generated. The immortalized cells showed fibroblastic morphology. The cell doubling time was 56.9h. In the mRNA level, the cells expressed plate-derived growth factor (PDGF) alpha receptor, PDGF beta receptor, transforming growth factor-beta (TGF-beta) type I receptor, TGF-beta type II receptor, CD44, collagen type I, collagen type II, glial fibrillary acidic protein (GFAP), hyaluronan synthase (HAS) 2, HAS 3 and beta-actin. In the protein level, GFAP was expressed in this cell line. S-100 protein and cytokeratin were not detected. Stimulation with TGF-beta1 and/or PDGF-BB induced a marked increase in the expression level of HAS2 mRNA, and induced HA production. TGF-beta1 stimulated HAS2 expression through the signal transduction pathway including Smad 2,3,4. In summary, this report constitutes the first successful immortalization of porcine hyalocyte cells. The production of HA was induced from the generated porcine hyalocyte cell line under the stimulation of TGF-beta1 and/or PDGF-BB, which may be related to the pathogenesis of proliferative membrane formation in proliferative vitreo-retinal diseases.

Silencing of hyaluronan synthase 2 suppresses the malignant phenotype of invasive breast cancer cells

Accumulation of hyaluronan has been demonstrated in the peritumoral breast cancer stroma and nests of tumor cells. In this study, we have quantified the production of hyaluronan and the expression of mRNAs encoding hyaluronan synthesizing (HAS) and hyaluronan degrading (HYAL) enzymes in a panel of breast cancer cell lines. The analysis revealed that highly invasive breast cancer cells produce high amounts of hyaluronan and express preferentially HAS2 mRNA, whereas less invasive breast cancer cells produce low amount of hyaluronan and express HAS1 and HYAL1 mRNAs. We explored the importance of HAS2 expression for breast cancer tumorigenicity, by specifically silencing the HAS2 gene using RNA interference (RNAi)-mediated suppression in the invasive breast cancer cell line Hs578T. This led to a less aggressive phenotype of the breast tumor cells, as assessed by cell growth, both in anchorage-dependent and anchorage-independent cultures. siRNA-mediated knock down of HAS2 in Hs578T breast tumor cells led to an up-regulation of HAS1, HAS3 and HYAL1 mRNAs, resulting in only a 50% decrease in the net hyaluronan production; however, the synthesized hyaluronan was of lower size and more polydisparse compared to control siRNA-treated cells. Interestingly, Hs578T cells deprived of HAS2 migrated only half as efficiently as HAS2 expressing cells through cell-free areas in a culture wounding assay and through Transwell polycarbonate membrane as well as invaded a Matrigel layer. These results imply that alterations in HAS2 expression and endogenously synthesized hyaluronan affect the malignant phenotype of Hs578T breast cancer cells.

Growth factor regulation of hyaluronan synthesis and degradation in human dermal fibroblasts: importance of hyaluronan for the mitogenic response of PDGF-BB

The glycosaminoglycan hyaluronan is important in many tissuerepair processes. We have investigated the synthesis of hyaluronan in a panel of cell lines of fibroblastic and epithelial origin in response to PDGF (platelet-derived growth factor)-BB and other growth factors. Human dermal fibroblasts exhibited the highest hyaluronan-synthesizing activity in response to PDGF-BB. Analysis of HAS (hyaluronan synthase) and HYAL (hyaluronidase) mRNA expression showed that PDGF-BB treatment induced a 3-fold increase in the already high level of HAS2 mRNA, and increases in HAS1 and HYAL1 mRNA, whereas the levels of HAS3 and HYAL2 mRNA were not affected. Furthermore, PDGF-BB also increased the amount and activity of HAS2 protein, but not of HYAL1 and HYAL2 proteins. Using inhibitors for MEK1/2 [MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase 1/2] (U0126) and for PI3K (phosphoinositide 3-kinase) (LY294002), as well as the SN50 inhibitor, which prevents translocation of the active NF-kappaB (nuclear factor kappaB) to the nucleus, we observed a complete inhibition of both HAS2 transcriptional activity and hyaluronan synthesis, whereas inhibitors of other signalling pathways were without any significant effect. TGF-beta1 (transforming growth factor-beta1) did not increase the activity of hyaluronan synthesis in dermal fibroblasts, but increased the activity of HYALs. Importantly, inhibition of hyaluronan binding to its receptor CD44 by the monoclonal antibody Hermes-1, inhibited PDGF-BB-stimulated [3H]thymidine incorporation of dermal fibroblasts. We conclude that the ERK MAPK and PI3K signalling pathways are necessary for the regulation of hyaluronan synthesis by PDGF-BB, and that prevention of its binding to CD44 inhibits PDGF-BB-induced cell growth.

Hyaluronan accumulation in thyroid tissue: evidence for contributions from epithelial cells and fibroblasts

Graves' disease (GD) and Hashimoto's thyroiditis (HT) are autoimmune processes often associated with hyperthyroidism and hypothyroidism, respectively. Despite their diverging clinical presentations, immune activation drives both diseases and results in connective tissue accumulation of the nonsulfated glycosaminoglycan, hyaluronan. The hydrophilic property of hyaluronan contributes to the pathogenesis of thyroid-associated ophthalmopathy, dermopathy and hypothyroid myxedema. Whether hyaluronan accumulates in the thyroid and plays a role in goiter formation in GD and HT remains unknown. We report here that levels of hyaluronan are increased in thyroid tissue from individuals with both diseases compared with glands uninvolved with autoimmune disorders. The transcript encoding hyaluronan synthase (HAS)-3, one of three mammalian HAS isoforms, was detected in thyroid tissue. Isolated thyrocytes in primary culture express all three HAS isoforms when treated with IL-1beta. Thyrocytes and thyroid fibroblasts produce hyaluronan under basal culture conditions and IL-1beta enhances levels of this molecule in both cell types. On a per-cell basis, fibroblasts produce more hyaluronan than do thyrocytes under basal conditions and after cytokine treatment. Synthesis in thyrocytes can also be altered by increasing serum concentration in the medium and by modifying culture density. Our findings suggest that hyaluronan accumulation in thyroid tissue might derive from thyrocytes and fibroblasts. Moreover, this glycosaminoglycan becomes more abundant as a consequence of autoimmune disease. It may therefore contribute to increased thyroid volume in GD and HT. Coupled with the newly identified influence exerted by hyaluronan on immunocompetent cells, our findings represent potentially important insights into the pathogenesis of autoimmune thyroid diseases.

Inhibition of platelet-derived growth factor-BB-induced receptor activation and fibroblast migration by hyaluronan activation of CD44

The extracellular matrix molecule hyaluronan was found to suppress platelet-derived growth factor (PDGF) beta-receptor activation and PDGF-BB-induced migration of primary human dermal fibroblasts. The suppressive effect of hyaluronan was neutralized by a monoclonal antibody that specifically inhibits hyaluronan binding to its receptor CD44. Moreover, co-immunoprecipitation experiments showed that the PDGF beta-receptor and CD44 can form a complex. Interestingly, the inhibitory effect of hyaluronan on PDGF beta-receptor activation was not seen in the presence of the tyrosine phosphatase inhibitor pervanadate. Our observations suggest that hyaluronan suppresses PDGF beta-receptor activation by recruiting a CD44-associated tyrosine phosphatase to the receptor.

Hyaluronan and its binding proteins in the epithelium and intraluminal fluid of the bovine oviduct

Hyaluronan (HA) is involved in several important steps of sperm storage and of fertilization. This study investigates the presence and concentration of HA in oviductal fluid (ODF), together with the localization of HA and the presence of hyaluronan-binding proteins (HABPs) in the oviductal epithelium of normally cycling dairy heifers and cows. The concentration and amount of HA in ODF, collected over the course of several oestrous cycles via catheters placed in the isthmic and ampullar tubal segments, were measured using an ELISA. The concentration and amount of HA in ODF did not vary significantly between these anatomical regions, nor between the stages of the oestrous cycle (p>0.05), although the amount of HA seemed to peak during oestrous. The most HA per day (2.9±0.64μg, least square mean±SEM) was produced on the day of ovulation, whereas the lowest amount (1.25±0.68μg) was produced 4 days before ovulation. To investigate the localization of HA, tissue samples were retrieved at well-defined stages of the oestrous cycle and from corresponding regions of the oviduct. Sections and protein extracts from the tissue samples were studied histochemically using biotinylated HABP and immunoblotted with fluorescein isothiocyanate (FITC)-HA, respectively. Presence of HA labelling in the oviductal epithelium was restricted to the sperm reservoir, a localization that seemed to be cycle-independent. The immunoblotting of samples from the lining epithelium revealed seven bands of HABPs. We confirm that the bovine oviduct produces HA and its binding proteins, and that HA is mainly localized to the epithelium of the sperm reservoir.

Antisense-Mediated Suppression of Hyaluronan Synthase 2 Inhibits the Tumorigenesis and Progression of Breast Cancer

The progression of several cancers is correlated with the increased synthesis of the glycosaminoglycan, hyaluronan. Hyaluronan is synthesized at the plasma membrane by various isoforms of hyaluronan synthases (HAS). The importance of HAS2 expression in highly invasive breast cancer was characterized by the antisense inhibition of HAS2 (ASHAS2). The effect of HAS2 inhibition on cell proliferation, migration, hyaluronan metabolism, and receptor status was characterized in vitro, whereas the effect on tumorigenicity and metastasis was established in vivo. HAS2 inhibition resulted in a 24-hour lag in proliferation that was concomitant to transient arrest of 79% of the cell population in G0-G1. Inhibition of HAS2 did not alter the expression of the other HAS isoforms, whereas hyaluronidase (HYAL2) and the hyaluronan receptor, CD44, were significantly down-regulated. ASHAS2 cells accumulated greater amounts of high molecular weight hyaluronan (>10,000 kDa) in the culture medium, whereas mock and parental cells liberated less hyaluronan of three distinct molecular weights (100, 400, and 3,000 kDa). The inhibition of HAS2 in the highly invasive MDA-MB-231 breast cancer cell line inhibited the initiation and progression of primary and secondary tumor formation following s.c. and intracardiac inoculation into nude mice, whereas controls readily established both primary and secondary tumors. The lack of primary and secondary tumor formation was manifested by increased survival times where ASHAS2 animals survived 172% longer than the control animals. Collectively, these unique results strongly implicate the central role of HAS2 in the initiation and progression of breast cancer, potentially highlighting the co-dependency between HAS2, CD44, and HYAL2 expression.

Phase I and pharmacokinetic evaluation of intravenous hyaluronic acid in combination with doxorubicin or 5-fluorouracil

BACKGROUND

Pre-clinically, hyaluronan (HA) has been demonstrated to systemically target chemotherapeutic drugs to tumours while ameliorating treatment toxicities. This study is a preliminary clinical investigation to determine if HA could be safely used in combination with 5-fluorouracil (5-FU) and doxorubicin (DOX).

METHODS

Thirty patients with metastatic cancer were intravenously administered 500 mg/m2 HA in combination with escalating doses of DOX (30-60 mg/m2) or 5-FU (cumulative dose of 1,350-2,250 mg/m2 per cycle). The effect of pre-administration of 20 mg/m2 of folinic acid on HA/5-FU chemotherapy was also investigated. Patients were randomized to receive either HA/chemotherapy or chemotherapy alone in their first treatment cycle and vice versa for the second cycle. Patients received HA and chemotherapy in all subsequent cycles.

RESULTS

Treatment was well tolerated, tumour responses were observed and the co-administration of HA did not alter the pharmacokinetics of clinically relevant doses of 5-FU or DOX.

CONCLUSION

High doses of intravenous high-molecular-weight HA can be safely co-administered with clinical doses of chemotherapy without significantly altering the toxicity or pharmacokinetics of the drugs or HA.

Hyaluronan fragments induce endothelial cell differentiation in a CD44- and CXCL1/GRO1-dependent manner

Hyaluronan is a glycosaminoglycan of the extracellular matrix. In tumors and during chronic inflammatory diseases, hyaluronan is degraded to smaller fragments, which are known to stimulate endothelial cell differentiation. In this study, we have compared the molecular mechanisms through which hyaluronan dodecasaccharides (HA12), and the known angiogenic factor, fibroblast growth factor 2 (FGF-2), induce capillary endothelial cell sprouting in a three-dimensional collagen gel. The gene expression profiles of unstimulated and HA12- or FGF-2-stimulated endothelial cells were compared using a microarray analysis approach. The data revealed that both FGF-2 and HA12 promoted endothelial cell morphogenesis in a process depending on the expression of ornithine decarboxylase (Odc) and ornithine decarboxylase antizyme inhibitor (Oazi) genes. Among the genes selectively up-regulated in response to HA12 was the chemokine CXCL1/GRO1 gene. The notion that the induction of CXCL1/GRO1 is of importance for HA12-induced endothelial cell sprouting was supported by the fact that morphogenesis was inhibited by antibodies specifically neutralizing the CXCL1/GRO1 protein product. HA12-stimulated endothelial cell differentiation was exerted via binding to CD44 since it was inhibited by antibodies blocking CD44 function. Our data show that hyaluronan fragments and FGF-2 affect endothelial cell morphogenesis by the induction of overlapping but also by distinct sets of genes.

Expression of hyaluronan synthase-3 in porcine oviducal epithelium during oestrus

Hyaluronan (HA) has been related to fertilization and embryo development in the pig. Furthermore, HA is present in pig oviduct fluid and the lining epithelium, particularly of the pre-ovulatory sperm reservoir. Because the mechanisms that regulate HA synthesis have not yet been clarified, semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) was conducted to assess the expression of mRNAs of two HA-synthesizing enzymes (has2 and has3) in the oviduct epithelium (uterotubal junction, isthmus, ampullary-isthmic junction and ampulla segments) of non-inseminated (control) and inseminated (treatment) sows at pre-, peri- and post-ovulatory oestrus. Only has3 mRNA was detected; it was present in all tubal segments of both control and treatment samples. The level of has3 expression did not vary significantly between non-inseminated and inseminated specimens, but there was a tendency (NS) for increased mean values during the peri- and post-ovulatory stages compared with pre-ovulation. It is concluded that has3 is expressed by the porcine endosalpinx epithelium and the levels of expression do not vary during the critical periods of sperm transport and fertilization, despite fluctuating levels of HA in the tubal fluid at corresponding periods.

Renal hyaluronan accumulation and hyaluronan synthase expression after ischaemia-reperfusion injury in the rat

BACKGROUND

Hyaluronan (HA) is a connective tissue component with unique water binding and pro-inflammatory properties. It has been suggested that HA is involved in normal renal water handling but also in several pathological conditions such as organ rejection and ischaemia-reperfusion (IR) injury.

METHODS

In anaesthetized normal rats we investigated if renal cortical HA accumulation and the intrarenal distribution and expression of HA synthases (Has 1, 2 and 3) correlate with renal dysfunction after renal IR injury. After 20, 30 or 45 min of unilateral renal ischaemia and 72 h of reperfusion, renal function and cortical HA content were measured. Has 1, 2 and 3 mRNA were determined in control and IR kidneys subjected to 45 min ischaemia and 72 h reperfusion.

RESULTS

IR kidneys had reduced urine concentrating ability, potassium excretion, glomerular filtration rate (GFR) and renal blood flow. On average, IR kidneys had more than 10 times higher amounts of cortical HA than the contralateral control kidney and their water content was elevated while medullary HA was largely unaffected. Has 2 expression in the cortex was heavily up-regulated in IR kidneys while Has 3 remained at control levels. Has 1 could never be detected. There was a direct correlation between the amount of cortical HA and the time period of ischaemia and also between the cortical amount of HA and depression of functional parameters.

CONCLUSIONS

IR injury depresses parameters of renal function, which coincides with an elevated cortical HA content and Has 2 expression. The enhanced Has 2 expression indicates that the cortical HA accumulation is primarily dependent on increased HA synthesis and not impaired degradation/elimination. The water binding and pro-inflammatory properties of HA may contribute to renal dysfunction after IR.

Expression of hyaluronan synthase in intraocular proliferative diseases: regulation of expression in human vascular endothelial cells by transforming growth factor-beta

PURPOSE

To investigate the role of hyaluronan (HA) and elucidate the mechanisms that regulate the expression of hyaluronan-synthesizing enzymes in vascular endothelial cells (VECs) in intraocular proliferative diseases.

METHODS

Cultured VECs were used. Hyaluronan synthase (HAS) expression was determined on the mRNA products obtained by reverse transcription polymerase chain reaction (RT-PCR). The effect of transforming growth factor-beta(1)(TGF-beta(1)) and/or platelet-derived growth factor-BB (PDGF-BB) on HAS expression was examined by quantitative RT-PCR and Western blot analysis. HAS expression in intraocular proliferative membranes was observed by immunohistochemistry.

RESULTS

Cultured VECs expressed the three HAS isoforms. Stimulation of VECs with TGF-beta(1) induced a marked increase in the expression level of HAS2 mRNA and protein. The stimulatory effect of PDGF-BB was less potent. A synergistic or additive effect between TGF-beta(1) and PDGF-BB-induced HA synthesis was not observed. Furthermore, HAS1 and HAS2 exhibited differential expression in VECs and non-VECs populating intraocular proliferative membranes.

CONCLUSIONS

The expression of each HAS isoform is regulated differently by growth factors and cytokines in VECs. Importantly, HA-synthesizing enzymes were expressed in cells populating proliferative membranes obtained from eyes of patients with proliferative vitreoretinal diseases, and thus may be key molecules in the events that control progression of the proliferative diseases.

Importance of hyaluronan biosynthesis and degradation in cell differentiation and tumor formation

Hyaluronan is an important connective tissue glycosaminoglycan. Elevated hyaluronan biosynthesis is a common feature during tissue remodeling under both physiological and pathological conditions. Through its interactions with hyaladherins, hyaluronan affects several cellular functions such as cell migration and differentiation. The activities of hyaluronan-synthesizing and -degrading enzymes have been shown to be regulated in response to growth factors. During tumor progression hyaluronan stimulates tumor cell growth and invasiveness. Thus, elucidation of the molecular mechanisms which regulate the activities of hyaluronan-synthesizing and -degrading enzymes during tumor progression is highly desired.

CD44-regulated intracellular proliferation of Listeria monocytogenes

CD44 has been implicated in immune and inflammatory processes. We have analyzed the role of CD44 in the outcome of Listeria monocytogenes infection in murine bone marrow-derived macrophages (BMM). Surprisingly, a dramatically decreased intracellular survival of L. monocytogenes was observed in CD44(-/-) BMM. CD44(-/-) heart or lung fibroblast cultures also showed reduced bacterial levels. Moreover, livers from CD44(-/-)-infected mice showed diminished levels of L. monocytogenes. In contrast, intracellular growth of Salmonella enterica serovar Typhimurium was the same in CD44(-/-) and control BMM. The CD44-mediated increased bacterial proliferation was not linked to altered BMM differentiation or to secretion of soluble factors. CD44 did not mediate listerial uptake, and it played no role in bacterial escape from the primary phagosome or formation of actin tails. Furthermore, CD44-enhanced listerial proliferation occurred in the absence of intracellular bacterial spreading. Interestingly, coincubation of BMM with hyaluronidase or anti-CD44 antibodies that selectively inhibit hyaluronan binding increased intracellular listerial proliferation. Treatment of cells with hyaluronan, in contrast, diminished listerial growth and induced proinflammatory transcript levels. We suggest that L. monocytogenes takes advantage of the CD44-mediated signaling to proliferate intracellularly, although binding of CD44 to certain ligands will inhibit such response.

Hyaluronan content in experimental carcinoma is not correlated to interstitial fluid pressure

Mechanism(s) for generation of the high tumor interstitial fluid pressure (TIFP) that is characteristic of carcinoma is not known. We investigated the role of hyaluronan, the major water-binding polysaccharide of the extracellular matrix, for the generation of a high TIFP. A human anaplastic thyroid carcinoma (KAT-4) xenografted to athymic mice and a syngeneic rat colon carcinoma (PROb) were used. Neither KAT-4 nor PROb cells produced hyaluronan (HA) in culture, however, both cell lines produced factors that stimulated HA-synthesis by cultured fibroblasts. Modulating hyaluronan levels by transfection of PROb carcinoma cells with hyaluronan synthase-2 revealed no correlation between hyaluronan content and TIFP. Furthermore, lowering of TIFP by treating KAT-4 tumors with a specific inhibitor of TGF-beta 1 and -beta 3 did not change the concentration of hyaluronan in the tumors. In summary, our results suggest that a modulation of hyaluronan content is not a major pathogenetic mechanism for the generation of the characteristically high TIFP in malignant carcinomas.

Hyaluronan synthase in trabecular meshwork cells

BACKGROUND/AIMS

Hyaluronan is present in the trabecular meshwork where it is involved in the pathophysiology of aqueous outflow environment. In this study, the expression and regulation of hyaluronan synthase (HAS), which is the enzyme synthesising hyaluronan, in trabecular meshwork cells were investigated.

METHODS

Cultured bovine trabecular meshwork cells (BTMCs) were used. HAS expression in BTMCs was examined by RT-PCR. The effects of transforming growth factor beta (TGF-beta) and platelet derived growth factor BB (PDGF-BB) on HAS expression in BTMCs were examined by quantitative RT-PCR. The HAS2 expression by TGF-beta and PDGF-BB at the protein level was also confirmed immunohistochemically. The production of hyaluronan from BTMCs was detected by high performance liquid chromatography (HPLC).

RESULTS

Three HAS isoforms were expressed in BTMCs at the mRNA level. Among HAS isoforms, only the expression of HAS2 mRNA was increased by the administration of TGF-beta or PDGF-BB. HAS2 upregulation by these growth factors was also confirmed at the protein level. Further, hyaluronan production from BTMCs was stimulated by TGF-beta or PDGF-BB.

CONCLUSION

Expression of HAS in trabecular meshwork may maintain the hyaluronan content in the aqueous outflow pathway. Its production is regulated by TGF-beta and PDGF-BB. The regulation of the expression of HAS in trabecular meshwork might be useful for modulating the aqueous outflow environment.

Immunohistochemical localization and expression of the hyaluronan receptor CD44 in the epithelium of the pig oviduct during oestrus

Hyaluronan is related to essential reproductive processes in pigs. Hyaluronan produced by cumulus cells builds, via specific cell surface receptors, an extracellular matrix responsible for cumulus cell cloud expansion during final oocyte maturation, a preparatory event for ovulation and fertilization. In addition, hyaluronan that has been localized in the pig oviduct both in the intraluminal fluid and on the surface of the lining epithelium of the preovulatory sperm reservoir, has proven beneficial during in vitro fertilization and embryo culture, thus indicating that it has a role in vivo. This study monitored the immunolocalization, protein determination and gene expression of the major cell surface hyaluronan receptor CD44 in the epithelial lining of the pig oviduct during selected stages of standing oestrus, in relation to spontaneous ovulation. The CD44 immunostaining in the lining epithelium was localized to the surface membrane and the supranuclear domain of mainly the secretory cells, particularly in the sperm reservoir of both treatment (inseminated) and control (non-inseminated) specimens. Up to four hyaluronan-binding protein (HABP) bands (60, 90, 100 and 200 kDa) were detected in the tubal epithelium, and the 200 kDa band was determined as CD44 by immunoblotting. The expression of CD44 mRNA was higher before than after ovulation (P < 0.05), most conspicuously in the uterotubal junction (UTJ). In addition, CD44 expression in the preovulatory UTJ and the ampullary-isthmic junction (AIJ) of control animals was higher than in those that were inseminated (P < 0.05 and P < 0.01 for UTJ and AIJ, respectively). The results demonstrate for the first time that the specific hyaluronan receptor CD44 is expressed by the oviduct epithelial cells during spontaneous oestrus, and is particularly abundant in the sperm reservoir before ovulation. Presence of spermatozoa in this segment seemed to downregulate the receptor. The variation in the expression of CD44 in relation to spontaneous ovulation and the presence of spermatozoa indicate that the hyaluronan CD44-signalling pathway may play a role in oviduct function during sperm storage and fertilization in pigs.

Immunohistochemical localization and expression of the hyaluronan receptor CD44 in the epithelium of the pig oviduct during oestrus

Hyaluronan is related to essential reproductive processes in pigs. Hyaluronan produced by cumulus cells builds, via specific cell surface receptors, an extracellular matrix responsible for cumulus cell cloud expansion during final oocyte maturation, a preparatory event for ovulation and fertilization. In addition, hyaluronan that has been localized in the pig oviduct both in the intraluminal fluid and on the surface of the lining epithelium of the preovulatory sperm reservoir, has proven beneficial during in vitro fertilization and embryo culture, thus indicating that it has a role in vivo. This study monitored the immunolocalization, protein determination and gene expression of the major cell surface hyaluronan receptor CD44 in the epithelial lining of the pig oviduct during selected stages of standing oestrus, in relation to spontaneous ovulation. The CD44 immunostaining in the lining epithelium was localized to the surface membrane and the supranuclear domain of mainly the secretory cells, particularly in the sperm reservoir of both treatment (inseminated) and control (non-inseminated) specimens. Up to four hyaluronan-binding protein (HABP) bands (60, 90, 100 and 200 kDa) were detected in the tubal epithelium, and the 200 kDa band was determined as CD44 by immunoblotting. The expression of CD44 mRNA was higher before than after ovulation (P < 0.05), most conspicuously in the uterotubal junction (UTJ). In addition, CD44 expression in the preovulatory UTJ and the ampullary-isthmic junction (AIJ) of control animals was higher than in those that were inseminated (P < 0.05 and P < 0.01 for UTJ and AIJ, respectively). The results demonstrate for the first time that the specific hyaluronan receptor CD44 is expressed by the oviduct epithelial cells during spontaneous oestrus, and is particularly abundant in the sperm reservoir before ovulation. Presence of spermatozoa in this segment seemed to downregulate the receptor. The variation in the expression of CD44 in relation to spontaneous ovulation and the presence of spermatozoa indicate that the hyaluronan CD44-signalling pathway may play a role in oviduct function during sperm storage and fertilization in pigs.

Expression of hyaluronan synthase 2 or hyaluronidase 1 differentially affect the growth rate of transplantable colon carcinoma cell tumors

Advanced colorectal cancers are often associated with elevated amounts of hyaluronan. To investigate the importance of hyaluronan in colon carcinoma tumor progression, we have expressed by stable transfection hyaluronan synthase 2 (Has2) and hyaluronidase 1 (Hyal1) in the rat colon carcinoma cell line, PROb. We found that hyaluronan overproduction led to a higher growth rate of tumor cells in vitro, and to a faster development of transplantable tumors in syngeneic rats, compared to the mock-transfectants. Has2 transfected PROb cells gave rise to tumors that were significantly less vascularized, but had a significantly larger viable tumor fraction compared to tumors generated from mock-transfectants. In contrast, Hyal1 overexpression suppressed the growth rate of tumor cells both in vitro and in vivo. Moreover, tumors derived from Hyal1-transfected cells had a significantly larger necrotic area than tumors derived from mock- and Has2-transfectants. Our study demonstrates that Has2 overproduction promotes tumorigenicity, whereas Hyal1 overexpression suppresses tumorigenicity in an experimental model for colon carcinoma.

Improvement of rat liver graft function after storage in University of Wisconsin solution containing testicular hyaluronidase

Hyaluronan accumulates at sites of inflammation, which affects the organization of matrix and thereby the proliferation, migration, and adherence of cells. In this study we investigated possible beneficial effects of the hyaluronan-degrading enzyme hyaluronidase on rat liver graft viability. Orthotopic rat liver transplantation was performed using a cuff technique in Wistar AL Bacharach Glaxo (WAG) rats grafted with WAG livers, which had been stored in the University of Wisconsin (UW) solution or in UW solution enriched with testicular hyaluronidase. Liver tissue architecture, as well as tissue and serum hyaluronan levels, were determined using immunohistochemistry and biochemical assays. Addition of testicular hyaluronidase (0.4 mg/mL) to livers preserved for 24 hours in cold UW solution followed by brief exposure to Ringer's lactate both prolonged the function of the grafted livers and improved their viability (4 of 10 grafts survived, compared with 0 of 10 in the control group). Hyaluronidase treatment did not damage the liver tissue architecture, and a reduced edema was observed in the survivors. Furthermore, 10 minutes after restoration of circulation, higher serum hyaluronan levels were observed in nonsuccessful compared with successful transplantations, whereas no differences in the levels of other serum viability markers were detected. We conclude that addition of testicular hyaluronidase to storage UW solution limits liver cell damage and considerably improves graft function. Furthermore, our data suggest that serum hyaluronan level is a better marker than other serum markers for early evaluation of postoperative graft function.

Testicular hyaluronidase induces tubular structures of endothelial cells grown in three-dimensional collagen gel through a CD44-mediated mechanism

Cultured brain capillary endothelial cells grown in a 3-dimensional collagen gel can form tubular structures after stimulation by angiogenic factors. We found that treatment of such cultures with testicular hyaluronidase led to formation of tubular structures and cell survival. Anion-exchange chromatography of the enzyme preparation on a MonoQ column revealed the presence of the angiogenic factor basic fibroblast growth factor (bFGF) in the flow-through fraction, as determined by immunoblotting; part of the effect on endothelial cell morphogenesis could thus be ascribed to bFGF. However, adsorbed fractions eluted with increasing concentrations of NaCl, which exhibited hyaluronan-degrading activity at neutral pH, did not contain bFGF but were still able to induce tube-like structures of the endothelial cells. Streptomyces hyaluronidase failed to evoke the same effect. Interestingly, blocking of hyaluronan binding to CD44 receptors by the monoclonal antibody KM114 inhibited the effect of hyaluronidase, but not of bFGF, on endothelial cell tube formation. Our data suggest a CD44-mediated specific role for certain populations of testicular hyaluronidase in the induction of angiogenesis.

Hyaluronan production increases the malignant properties of mesothelioma cells

Malignant pleural mesotheliomas is in most cases associated with elevated amounts of hyaluronan. To investigate the importance of hyaluronan for the malignant properties of mesotheliomas, we have expressed murine hyaluronan synthase 2 (HAS2) in the non-hyaluronan producing mesothelioma cell line, Mero-25. We found that upon hyaluronan overproduction the mesothelioma cells changed their epitheloid character to a fibroblastic phenotype and were surrounded by pericellular matrices, the size of which correlated to the amount of synthesized hyaluronan. HAS2-transfected cells with the ability to synthesize about 520 ng hyaluronan/5 x 10(4)cells/24 h exhibited about a 2-fold increase in the expression of the cell surface hyaluronan receptor CD44 and their locomotion increased compared to that of mock-transfected Mero-25 cells. Furthermore, the malignant properties of mesothelioma cell clones as determined by the ability to grow in a soft agar assay correlated to their hyaluronan production. These results provide evidence for an important role of hyaluronan in the aggressive spread of mesotheliomas in adjacent non-cancerous stromal tissues.

HGF/SF induces mesothelial cell migration and proliferation by autocrine and paracrine pathways

Mesothelial repair differs from that of other epithelial-like surfaces as healing does not occur solely by centripetal in-growth of cells as a sheet from the wound margins. Mesothelial cells lose their cell-cell junctions, divide, and adopt a fibroblast-like morphology while scattering across and covering the wound surface. These features are consistent with a cellular response to hepatocyte growth factor/scatter factor (HGF/SF). In this study, we examined the ability of mesothelial cells to secrete HGF/SF and investigated its possible role as an autocrine regulator of mesothelial cell motility and proliferation. We found that human primary mesothelial cells expressed HGF/SF mRNA and secreted active HGF/SF into conditioned medium as determined by ELISA and in a scattering bioassay. These cells also expressed the HGF/SF receptor, Met, as shown by RT-PCR and by Western blot analysis and immunofluorescence. Incubation of mesothelial cells with neutralizing antibodies to HGF/SF decreased cell migration to 25% of controls, whereas addition of HGF/SF disrupted cell-cell junctions and induced scattering and enhanced mesothelial cell migration. Furthermore, HGF/SF showed a small but significant mitogenic effect on all mesothelial cell lines examined. In conclusion, HGF/SF is produced by mesothelial cells and induces both motility and proliferation of these cells. These data are consistent with HGF/SF playing an autocrine role in mesothelial healing.

Expression regulation of hyaluronan synthase in corneal endothelial cells

PURPOSE

Our previous study showed that hyaluronan synthase (HAS), the enzyme protein of hyaluronan (HA) biosynthesis, is expressed in ocular tissues including the corneal endothelium. In the current study, the mechanism that regulates HAS expression in bovine corneal endothelial cells (BCECs) was investigated.

METHODS

Cultured BCECs were used. HAS expression in BCECs at the mRNA level was detected by reverse transcription-polymerase chain reaction (RT-PCR) and Northern blot analysis. The effects of transforming growth factor (TGF)-beta and platelet-derived growth factor (PDGF)-BB on HAS expression were examined by quantitative RT-PCR. The involvement of the Smad family (intracellular signal transducer of TGF-beta) was also investigated. The expression of HAS in BCECs at the protein level was confirmed by immunocytochemistry and Western blot analysis.

RESULTS

Three HAS isoforms in BCECs were expressed at the mRNA level. The transcriptional sizes of each HAS in BCECs were 4.9 kb for HAS1, 2.8 kb for HAS2, and 1.6 kb for HAS3. The expression of HAS2 at the mRNA level was stimulated by TGF-beta1 and/or PDGF-BB treatment. In contrast, HAS1 and HAS3 expression was not affected by these growth factors. The additive effects of TGF-beta1 and PDGF-BB were observed in the stimulation of the expression levels of HAS2. HAS2 upregulation by these growth factors was also detected by Western blot analysis. The stimulation of the expression of HAS2 at the mRNA level by TGF-beta was accelerated by the overexpression of Smad2, Smad3, and Smad4 and inhibited by that of Smad7, all of which were confirmed to be involved in the signal transduction from TGF-beta through HAS expression.

CONCLUSIONS

Although three HAS isoforms were expressed in the corneal endothelial cells, the expression of HAS2 was upregulated by TGF-beta1 and/or PDGF-BB. HAS2 expression was regulated by TGF-beta through Smad family members.