Hyaluronan export by the ABC transporter MRP5 and its modulation by intracellular cGMP

Hyaluronan synthase mediates dye translocation across liposomal membranes

Background

Hyaluronan (HA) is made at the plasma membrane and secreted into the extracellular medium or matrix by phospolipid-dependent hyaluronan synthase (HAS), which is active as a monomer. Since the mechanism by which HA is translocated across membranes is still unresolved, we assessed the presence of an intraprotein pore within HAS by adding purified Streptococcus equisimilis HAS (SeHAS) to liposomes preloaded with the fluorophore Cascade Blue (CB).

Results

CB translocation (efflux) was not observed with mock-purified material from empty vector control E. coli membranes, but was induced by SeHAS, purified from membranes, in a time- and dose-dependent manner. CB efflux was eliminated or greatly reduced when purified SeHAS was first treated under conditions that inhibit enzyme activity: heating, oxidization or cysteine modification with N-ethylmaleimide. Reduced CB efflux also occurred with SeHAS K48E or K48F mutants, in which alteration of K48 within membrane domain 2 causes decreased activity and HA product size. The above results used liposomes containing bovine cardiolipin (BCL). An earlier study testing many synthetic lipids found that the best activating lipid for SeHAS is tetraoleoyl cardiolipin (TO-CL) and that, in contrast, tetramyristoyl cardiolipin (TM-CL) is an inactivating lipid (Weigel et al, J. Biol. Chem. 281, 36542, 2006). Consistent with the effects of these CL species on SeHAS activity, CB efflux was more than 2-fold greater in liposomes made with TO-CL compared to TM-CL.

Conclusions

The results indicate the presence of an intraprotein pore in HAS and support a model in which HA is translocated to the exterior by HAS itself.

Production of glucuronic acid-based polysaccharides by microbial fermentation for biomedical applications

This review provides an overview of the properties, different biosynthetic machineries, and biotechnological production processes of four microbially derived glucuronic acid-based polysaccharides that are of interest for diverse biomedical purposes. In particular, the utilization of hyaluronic acid and heparin sulfate in high-value medical applications is already well established, whereas chondroitin sulfate and alginate show high potential within this ever-growing field. Furthermore, new strategies exploiting genetically engineered microorganisms generated through improving naturally existing pathways or de novo designed ones are described. These new developments result in increased fermentation titers, and thereby, pave the way towards feasible, or at least improved, process economy. Moreover, these strategies also allow for the future possibility of producing tailor-made biopolymers with specified characteristics, even novel molecules.

Inhibitors of hyaluronan export from hops prevent osteoarthritic reactions

SCOPE

An early reaction in osteoarthritic chondrocytes is hyaluronan overproduction followed by proteoglycan loss and collagen degradation. We recently found that hyaluronan is exported by the ATP-binding cassette transporter multidrug resistance associated protein 5 (MRP5) in competition with cGMP and that some phosphodiesterase 5 inhibitors also inhibited hyaluronan export. These inhibitors also prevented osteoarthritic reactions in cartilage. In an effort to identify the improved inhibitors directed primarily toward MRP5, we analyzed the flavonoids.

METHODS AND RESULTS

Prenylflavonoids from hop xanthohumol, isoxanthohumol and 8-prenylnaringenin inhibited MRP5 export at lower concentrations than phosphodiesterase 5 activity. They were analyzed for their effect on IL-induced osteoarthritic reactions in bovine chondrocytes. Xanthohumol was the superior compound to inhibit hyaluronan export, as well as proteoglycan and collagen loss. It also prevented the shedding of metalloproteases into the culture medium. It directly inhibited MRP5, because it reduced the export of the MRP5 substrate fluorescein immediately and did not influence the hyaluronan synthase activity.

CONCLUSIONS

Xanthohumol may be a natural compound to prevent hyaluronan overproduction and subsequent reactions in osteoarthritis.

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.

Xenobiotic, bile acid, and cholesterol transporters: function and regulation

Transporters influence the disposition of chemicals within the body by participating in absorption, distribution, and elimination. Transporters of the solute carrier family (SLC) comprise a variety of proteins, including organic cation transporters (OCT) 1 to 3, organic cation/carnitine transporters (OCTN) 1 to 3, organic anion transporters (OAT) 1 to 7, various organic anion transporting polypeptide isoforms, sodium taurocholate cotransporting polypeptide, apical sodium-dependent bile acid transporter, peptide transporters (PEPT) 1 and 2, concentrative nucleoside transporters (CNT) 1 to 3, equilibrative nucleoside transporter (ENT) 1 to 3, and multidrug and toxin extrusion transporters (MATE) 1 and 2, which mediate the uptake (except MATEs) of organic anions and cations as well as peptides and nucleosides. Efflux transporters of the ATP-binding cassette superfamily, such as ATP-binding cassette transporter A1 (ABCA1), multidrug resistance proteins (MDR) 1 and 2, bile salt export pump, multidrug resistance-associated proteins (MRP) 1 to 9, breast cancer resistance protein, and ATP-binding cassette subfamily G members 5 and 8, are responsible for the unidirectional export of endogenous and exogenous substances. Other efflux transporters [ATPase copper-transporting beta polypeptide (ATP7B) and ATPase class I type 8B member 1 (ATP8B1) as well as organic solute transporters (OST) alpha and beta] also play major roles in the transport of some endogenous chemicals across biological membranes. This review article provides a comprehensive overview of these transporters (both rodent and human) with regard to tissue distribution, subcellular localization, and substrate preferences. Because uptake and efflux transporters are expressed in multiple cell types, the roles of transporters in a variety of tissues, including the liver, kidneys, intestine, brain, heart, placenta, mammary glands, immune cells, and testes are discussed. Attention is also placed upon a variety of regulatory factors that influence transporter expression and function, including transcriptional activation and post-translational modifications as well as subcellular trafficking. Sex differences, ontogeny, and pharmacological and toxicological regulation of transporters are also addressed. Transporters are important transmembrane proteins that mediate the cellular entry and exit of a wide range of substrates throughout the body and thereby play important roles in human physiology, pharmacology, pathology, and toxicology.

Targeting CD44 in mast cell regulation

IMPORTANCE OF THE FIELD

Accumulating evidence suggests that mast cells are involved in a wide variety of immune responses including chronic inflammation, immune tolerance and tumor immunity. Mast cells originate from hematopoietic stem cells and undergo terminal differentiation in the tissues, in which they are ultimately resident. Heterogeneity of tissue mast cells is, therefore, one of the key concepts for a better understanding of various immune responses.

AREAS COVERED IN THIS REVIEW

This review describes the candidate genes involved in regulation of cutaneous mast cell differentiation, with a particular attention to CD44, which is the primary receptor for hyaluronan.

WHAT THE READER WILL GAIN

CD44 is involved in various aspects of cutaneous inflammation. Regarding mast cells, CD44 is upregulated upon differentiation and maturation of mast cells, and plays a critical role in regulation of cutaneous mast cell number. Since both degradation and decrease of hyaluronan are often observed upon chronic inflammation, CD44 might be involved in modulation of local immune responses through regulation of cutaneous mast cell functions.

TAKE HOME MESSAGE

Understanding of cutaneous immune responses should require clarification of local mast cell functions, a part of which is regulated by extracellular matrix components and their membrane receptors.

ABC transporters do not contribute to extracellular translocation of hyaluronan in human breast cancer in vitro

Extracellular translocation of the polysaccharide, hyaluronan (HA) has been thought to be mediated via its transmembrane synthetic enzyme, hyaluronan synthase (HAS) but recent studies have indicated that the ATP-Binding-Cassette (ABC) transporter, MRP5 contributes to this process. Liberated and cell-associated HA contributes to breast cancer initiation and progression, and therefore the inhibition of ABC transporters and consequently HA transport could provide therapeutic benefit in the treatment of breast cancer. Quantitation of ABC transporter genes, MRP1-5, BCRP and MDR1 were determined in six breast cancer cell lines selected for their differential HA synthetic rates. Low endogenous expression of transporters was detected but no significant correlation existed between ABC transporter and HAS gene expression or HA production. A dose titration of up to ten times the IC(50) of ten small molecule ABC transporter inhibitors did not significantly inhibit HA export in four breast cancer cell lines. Unlike the changes observed after inhibition of HA synthesis by the characterised inhibitor 4-MU, inhibition of ABC transporters did not alter the cell morphology, HA glycocalyx or the intracellular quantity or localisation of HA. Collectively these data indicate that ABC transporters do not contribute to the extracellular transport of HA in breast cancer, supporting a role for the hyaluronan synthase in translocation.

Abrogating drug resistance in malignant peripheral nerve sheath tumors by disrupting hyaluronan-CD44 interactions with small hyaluronan oligosaccharides

Malignant peripheral nerve sheath tumors (MPNST) develop in approximately 10% of neurofibromatosis type-1 patients and are a major contributing factor to neurofibromatosis-1 patient mortality and morbidity. MPNSTs are multidrug resistant, and thus long-term patient survival rates are poor after standard doxorubicin or multiagent chemotherapies. We show that the hyaluronan receptor CD44 forms complexes with multidrug transporters, BCRP (ABCG2) and P-glycoprotein (ABCB1), in the plasma membrane of human MPNST cells. Small hyaluronan oligosaccharides antagonize hyaluronan-CD44-mediated processes and inhibit hyaluronan production. Treatment of MPNST cells with the hyaluronan oligomers causes disassembly of CD44-transporter complexes and induces internalization of CD44, BCRP, and P-glycoprotein. Consequently, the oligomers suppress drug transporter activity and increase sensitivity to doxorubicin treatment in culture. In vivo, systemic administration of hyaluronan oligomers inhibits growth of MPNST xenografts. Moreover, the oligomers and doxorubicin act synergistically in vivo, in that combined suboptimal doses induce tumor regression to a greater extent than the additive effects of each agent alone. These findings indicate that constitutive hyaluronan-CD44 interactions contribute to drug transporter localization and function at the plasma membrane, and that attenuating hyaluronan-CD44 interactions sensitizes MPNSTs to doxorubicin in vitro and in vivo. These results also show the potential efficacy of hyaluronan oligomers, which are nontoxic and nonimmunogenic, as an adjuvant for chemotherapy in MPNST patients.

Hyaluronan substratum induces multidrug resistance in human mesenchymal stem cells via CD44 signaling

Little information is available concerning multidrug resistance (MDR) in mesenchymal stem cells, although several studies have reported that MDR is associated with hyaluronan in neoplastic cells. We have evaluated whether a hyaluronan-coated surface modulates MDR in placenta-derived human mesenchymal stem cells (PDMSCs). We have found that PDMSCs cultured on a tissue-culture polystyrene surface coated with 30 microg/cm(2) hyaluronan are more resistant than control PDMSCs to doxorubicin. Inhibiting PI3K/Akt signaling has shown that the PI3K/Akt pathway modulates both P-glycoprotein activity and doxorubicin resistance. In addition, 10 microM verapamil dramatically suppresses the doxorubicin resistance induced by the hyaluronan-coated surface, indicating that P-glycoprotein activity is necessary for MDR. We have further found that PDMSCs treated with CD44 small interfering RNA (siRNA) and grown on a polystyrene surface coated with 30 microg/cm(2) hyaluronan have fewer P-glycoprotein(+) cells and lower CD44 expression levels (less than 60% in both cases) than PDMSCs not treated with CD44 siRNA and grown on the hyaluronan-coated surface. Moreover, treatment with CD44 siRNA suppresses the hyaluronan-substratum-induced doxorubicin resistance. We conclude that a hyaluronan substratum induces MDR in PDMSCs through CD44 signaling.

Hyaluronan, CD44 and Emmprin: partners in cancer cell chemoresistance

Hyaluronan not only is an important structural component of extracellular matrices but also interacts with cells during dynamic cell processes such as those occurring in cancer. Consequently, interactions of hyaluronan with tumor cells play important cooperative roles in various aspects of malignancy. Hyaluronan binds to several cell surface receptors, including CD44, thus leading to co-regulation of signaling pathways that are important in regulation of multidrug resistance to anticancer drugs, in particular anti-apoptotic pathways induced by activation of receptor tyrosine kinases. Emmprin, a cell surface glycoprotein of the Ig superfamily, stimulates hyaluronan production and downstream signaling consequences. Emmprin and CD44 also interact with various multidrug transporters of the ABC family and monocarboxylate transporters associated with resistance to cancer therapies. Moreover, hyaluronan-CD44 interactions are critical to these properties in the highly malignant, chemotherapy-resistant cancer stem-like cells. Perturbations of the hyaluronan-CD44 interaction at the plasma membrane by various antagonists result in attenuation of receptor tyrosine kinase and transporter activities and inhibition of tumor progression in vivo. These antagonists, especially small hyaluronan oligomers, may be useful in therapeutic strategies aimed at preventing tumor refractoriness or recurrence due to drug-resistant sub-populations within malignant cancers.

Hyaluronan: a constitutive regulator of chemoresistance and malignancy in cancer cells

Hyaluronan not only is an important structural component of extracellular matrices but also interacts instructively with cells during embryonic development, healing processes, inflammation, and cancer. It binds to several different types of cell surface receptors, including CD44, thus leading to co-regulation of important signaling pathways, notably those induced by activation of receptor tyrosine kinases. Consequently, interactions of both stromal and tumor cell-derived hyaluronan with tumor cells play important cooperative roles in several aspects of malignancy. This review focuses on cell autonomous hyaluronan-tumor cell interactions that lead to activation of receptor tyrosine kinases and enhanced drug resistance. Particular emphasis is placed on the role of hyaluronan-CD44 interactions in drug transporter expression and activity, especially in cancer stem-like cells that are highly malignant and resistant to chemotherapy. Antagonists of hyaluronan-CD44 interaction, especially small hyaluronan oligomers, may be useful in therapeutic strategies aimed at preventing tumor recurrence from these therapy-resistant sub-populations within malignant cancers.

Inhibition of hyaluronan export reduces collagen degradation in interleukin-1 treated cartilage

Background

Osteoarthrosis is characterized by cartilage erosion, proteolysis of aggrecan and collagen, and disturbed rates of synthesis of aggrecan and hyaluronan by chondrocytes, with hyaluronan over-production being an early reaction. We considered that inhibition of hyaluronan export might prevent subsequent proteoglycan loss and collagen degradation.

Methods

To test this hypothesis, we studied a tissue culture model using bovine cartilages explants activated with IL-1α to induce osteoarthritic reactions using the phosphodiesterase-5 inhibitors tadalafil, zaprinast and vardenafil.

Results

These drugs inhibited hyaluronan export, but they did not inhibit hyaluronan synthase activity. Simultaneously, they inhibited proteoglycan loss and collagen degradation, but not their synthesis. They also reduced the release of gelatinases into the culture media and diffusion of the indicator protein horseradish peroxidase through the cartilage explants. The mechanism of action of these compounds may be through inhibition of hyaluronan exporter multidrug resistance-associated protein 5 (MRP5), because the effective drug concentrations were much higher than required for phosphodiesterase-5 inhibition and intracellular cGMP accumulation.

Conclusion

Inhibition of hyaluronan over-production may be an appropriate target to attenuate IL-1-induced reactions in osteoarthritic cartilage.

A 'GAG' reflex prevents repair of the damaged CNS

The extracellular matrix of the central nervous system (CNS) serves as both a supporting structure for cells and a rich source of signaling molecules that can influence cell proliferation, survival, migration and differentiation. A large proportion of this matrix is composed of proteoglycans--proteins with long chains of polysaccharides, called glycosaminoglycans (GAGs), covalently attached. Although many of the activities of proteoglycans depend on their core proteins, GAGs themselves can influence cell signaling. Here we review accumulating evidence that two GAGs, chondroitin sulfate and hyaluronan, play essential roles during nervous system development but also accumulate in chronic CNS lesions and inhibit axonal regeneration and remyelination, making them significant hindrances to CNS repair. We propose that the balance between the synthesis and degradation of these molecules dictates, in part, how regeneration and recovery from CNS damage occurs.