Binding of heparin and heparan sulphate to rat liver cells

Anti-Tumor Effects of Biomimetic Sulfated Glycosaminoglycans on Lung Adenocarcinoma Cells in 2D and 3D In Vitro Models

Lung cancer development relies on cell proliferation and migration, which in turn requires interaction with extracellular matrix (ECM) components such as glycosaminoglycans (GAGs). The mechanisms through which GAGs regulate cancer cell functions are not fully understood but they are, in part, mediated by controlled interactions with cytokines and growth factors (GFs). In order to mechanistically understand the effect of the degree of sulfation (DS) of GAGs on lung adenocarcinoma (LUAD) cells, we synthesized sulfated alginate (AlgSulf) as sulfated GAG mimics with DS = 0.0, 0.8, 2.0, and 2.7. Human (H1792) and mouse (MDA-F471) LUAD cell lines were treated with AlgSulf of various DSs at two concentrations 10 and 100 µg/mL and their anti-tumor properties were assessed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), trypan blue exclusion, and wound healing assays for 2D models and sphere formation assay for the 3D model. The proliferation and number of live MDA-F471 cells at the concentration of 100 µg/mL decreased significantly with the increase in the DS of biomimetic GAGs. In addition, the increase in the DS of biomimetic GAGs decreased cell migration (p < 0.001 for DS = 2.0 and 2.7 compared to control) and decreased the diameter and number of spheres formed (p < 0.001). The increased DS of biomimetic GAGs attenuated the expression of cancer stem cell (CSC)/progenitor markers in the 3D cultures. In conclusion, GAG-mimetic AlgSulf with increased DS exhibit enhanced anti-proliferative and migratory properties while also reducing growth of KRAS-mutant LUAD spheres in vitro. We suggest that these anti-tumor effects by GAG-mimetic AlgSulf are possibly due to differential binding to GFs and consequential decreased cell stemness. AlgSulf may be suitable for applications in cancer therapy after further in vivo validation.

The regulation of basement membrane formation and cell-matrix interactions by defined supramolecular complexes

Several constituents of basement membranes, including type IV collagen, laminin, heparan sulphate proteoglycan and nidogen, form a defined supramolecular complex that is an obligatory intermediate in the formation of this matrix. We have named this defined supramolecular complex the 'basement membrane matrisome'. Matrisome structures composed of other collagens, proteoglycans and glycoproteins may participate in the formation of other extracellular matrices. Cells show specific interactions with components of the extracellular matrix. We discuss studies that indicate that melanoma cells can express receptors for both laminin and fibronectin. However, these receptors are expressed in a reciprocal fashion, depending on the exposure of the cell to these proteins. Binding of either fibronectin or laminin to the cells elicits a distinct phenotype. This represents a mechanism in which cellular activity can be regulated by extracellular matrix factors during development and in repair.

Dermatan carriers for neovascular transport targeting, deep tumor penetration and improved therapy

A new approach to functional tumor imaging and deep interstitial penetration of therapeutic agents is to target the upregulated transport activities of neovascular endothelium. Agents are formulated with the anionic glycosaminoglycan, 435-type dermatan sulfate (DS 435, 22.2 kDa), chemically enriched for oligosaccharide sequences that confer high heparin cofactor II binding and correlate with high tumor uptake. A magnetic resonance (MR) imaging agent is prepared as self-assembling, 5-nm nanoparticles of Fe(+3):deferoxamine (Fe:Df) bound by strong ion pairing to DS, which forms the outer molecular surface (Zeta potential -39 mV). On intravenous (i.v.) injection, Fe:Df-DS rapidly (<7 min) and selectively targets and transports at high capacity across the neovascular endothelium of large (2-cm) Dunning prostate R3327 AT1 rat tumors; releases from the abluminal surface, due to reversible binding of its multivalent, low-affinity (K(d) 10(-4) to 10(-5)) oligosaccharide ligands; and progressively penetrates the interstitium from its initial site of high uptake in the well-perfused outer tumor rim, into the poorly perfused central subregion. By gamma camera imaging of (67)Ga:Df-DS, the agent avoids normal site uptake and clears through the kidneys with a t(1/2) of 18 min. A therapeutic formulation of DS-doxorubicin (DS-dox) is prepared by aqueous high-pressure homogenization of the drug and DS 435, which produces 11-nm nanoparticles of doxorubicin cores coated with DS (Zeta potential -39 mV) that are stable to lyophilization. Microscopic analysis of tumor sections 3 h after i.v. injection shows much higher overall tumor fluorescence and deeper matrix penetration for DS-dox than conventional doxorubicin (dox): >75 vs. <25 microm between the nearest microvessels. DS-dox also results in enhanced tumor-cell internalization and nuclear localization of the drug. Therapeutic efficacies in established (250 +/- 15 mg) MX-1 human breast tumor xenografts at maximum tolerated doses (MTDs) are (control vehicle, dox, dox-DS) (a) median days to 7-fold tumor growth: 8.3, 25.6 (p = 0.0007), 43.2 (p = 0.0001); (b) complete 90-day tumor regressions: 0/10, 0/10, 4/10. These results demonstrate the potential to develop a novel class of carbohydrate-targeted neovascular transport agents for sensitive, high-resolution (100-microm) MR imaging and improved treatment of larger sized human tumor metastases.

Heparin-glutathione III: study with fluorescent probes as indicators of membrane status of bull sperm

Sperm obtained from bull epididymes were used to validate in vitro the effect of heparin and reduced glutathione on sperm membrane status, with the use of sodium dodecyl sulfate (SDS) and Triton X-100 in the presence of propidium iodide (IP) and diacetate fluorescein (FDA). The metabolic activities of treated sperm were qualitatively monitored using an alamar Blue Redox fluorescence indicator. Heparin did not damage the sperm plasma membrane, whereas GSH and SDS at 26 h of incubation dissolved the plasma membrane and the acrosome. On the other hand, at time zero, Triton X-100 showed 75% of sperm stained with IP, indicating plasma membrane damage. Results validated by electron microscopy of thin sections of treated sperm showed complete lack of the membrane, acrosome, and postacrosomal membrane system with 0.01% Triton X-100. Extracellular 15 mM GSH completely disappeared the plasma membrane over the sperm nucleus, leaving the postacrosomal membrane system and nucleus without apparent damage. The metabolic activity was supported over 52 h of incubation in any of the incubation systems tested, including Triton X-100, which showed a spermaticide effect. The authors propose that membrane damage does not mean they are dead, no matter the vital stain employed, and also that FDA-IP staining can be used as a fluorescent marker of sperm plasmatic membrane permeabilization and nuclear swelling.

High-performance affinity chromatography for the purification of heparin-binding proteins from detergent-solubilized smooth muscle cell membranes

Heparin and heparan sulfates are regulators of cellular events including adhesion, proliferation and migration. In particular, the antiproliferative effect of heparin on smooth muscle cell (SMC) growth is well described. However, its mechanism of action remains unclear. Numerous results suggest an endocytosis mediated by a still unknown heparin receptor on vascular SMCs. In order to identify a putative heparin receptor on SMCs that could be involved in heparin signalling, affinity chromatography supports were developed. In this paper, we describe high-performance liquid affinity chromatography (HPLAC) supports obtained from silica beads coated with dextran polymer substituted by a calculated amount of diethylaminoethyl functions. With a polysaccharide dextran layer, this type of support can be grafted with specific ligands, such as heparin, using conventional coupling methods. In a previous work, we demonstrated, using butanedioldiglycidyl ether, that silica stationary phases coupled to heparin could be used for the fast elution and good peak resolution of heparin-binding proteins. In the present work, an affinity chromatographic fraction of SMC membrane extracts was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and six heparin-binding proteins from dodecyloctaethyleneglycol monoether-solubilized SMCs were observed. Their Mr values were between 40 and 70 kDa, with three major protein bands at 66, 45 and 41 kDa. These results indicate the usefulness of the chromatographic method for purifying heparin binding proteins from SMC membrane.

Heparin-steroid conjugates lacking glucocorticoid or mineralocorticoid activities inhibit the proliferation of vascular endothelial cells

A new class of angiogenesis inhibitors consist of a non-anticoagulating derivative of heparin, which binds to vascular endothelial cells, coupled to a steriod (e.g., cortisol) which suppresses endothelial cell division. We linked heparin to a further 10 steroids in an effort to identify ones which would yield more effective or safer angiogenesis inhibitors. Steroids having a C3 ketone group were linked by reaction with a hydrazide derivative of heparin. Steroids having a C20 ketone group and lacking a C3 ketone could not be prepared by this method, necessitating the development of alternative methods. The most efficient was to convert the steroid into a derivative having a hydrazone group at C20 and then link the steroid hydrazone to heparin. Conjugates prepared from steroids having C3 ketones were at most 6-fold more inhibitory than the free steroids to endothelial cells in tissue culture. In contrast, steroids having a C20 ketone but lacking a C3 ketone (tetrahydrocortisone, tetrahydrocortisol and tetrahydro S) became highly inhibitory to endothelial cells only after conjugation to heparin. They inhibited [3H]thymidine incorporation by 50% at a steroid concentration of 18-30 microM and by 95% at 300 microM. Since tetrahydrocortisone, tetrahydrocortisol and tetrahydro S lack glucocorticoid and mineralocorticoid activity, they may prove safer alternatives to cortisol for prolonged administration, as is likely to be necessary with anti-angiogenic therapies.

Anti-tumor and anti-angiogenic effects in mice of heparin conjugated to angiostatic steroids

Heparin-steroid conjugates have been prepared by linking a non-anti-coagulating derivative of heparin, which binds to endothelial cells, to an angiostatic steroid, which suppresses endothelial cell division. One such conjugate, heparin adipic hydrazide (HAH) linked to cortisol, has previously been shown to inhibit both angiogenesis and the growth of solid tumors in mice. In the present study, heparin hydrazide (HH) was linked to tetrahydro S, tetrahydrocortisone and tetrahydrocortisol, which are devoid of glucocorticoid and mineralocorticoid activity and hence were predicted to have low toxicity to animals. The tetrahydro steroid conjugates were compared with the cortisol conjugate for therapeutic effectiveness against solid Lewis lung carcinoma growing in mice. HAH-cortisol reduced tumor growth by up to 75% whereas a simple mixture of HAH and cortisol was not significantly inhibitory. In contrast to HAH-cortisol, the 3 tetrahydro steroid conjugates did not significantly inhibit tumor growth. The differences in anti-tumor properties of the conjugates correlated with their ability to inhibit angiogenesis in a Matrigel implant model in mice. The tetrahydro steroid conjugates did not significantly inhibit angiogenesis whereas HAH-cortisol inhibited angiogenesis by greater than 90%. Therefore, HAH-cortisol is the most effective heparin-steroid conjugate so far developed.

Sulfated polyanions block Chlamydia trachomatis infection of cervix-derived human epithelia

Using a cell line derived from the human cervix and a rapid fluorescence cytotoxicity assay, we have shown that Chlamydia trachomatis infection can be blocked by certain sulfated polysaccharides (carrageenan, pentosan polysulfate, fucoidan, and dextran sulfate) and glycosaminoglycans (heparin, heparan sulfate, and dermatan sulfate) but not by other glycosaminoglycans (chondroitin sulfate A or C, keratan sulfate, and hyaluronic acid). The most negatively charged molecules are the most effective at blocking infection. Results of infection at 4 degrees C suggest that sulfated polyanions act by preventing the adherence of chlamydiae to target cells. These and additional blocking studies with enzymes suggest that a heparan sulfate-like glycosaminoglycan on the surface of elementary bodies is involved in the adherence of chlamydiae to target cells, probably through a nonspecific charge interaction or possibly a heparin-binding protein. We previously observed that the same sulfated polysaccharides inhibit transmission of human immunodeficiency virus in vitro and suggested that these compounds could be used in a vaginal formulation to inhibit infection by human immunodeficiency virus. The results of the present study suggest that the same type of formulation may inhibit sexual transmission of chlamydia.

Heparin receptors in two murine mammary adenocarcinomas with different metastatic ability: relationship with growth inhibition

Binding of heparin to primary cultured cells of two murine mammary adenocarcinomas with low (M3) and high (MM3) lung, metastatic capacity was determined. Heparin binding was rapid, specific and saturable. MM3 cells grown for 24 h in fetal calf serum (FCS)-free medium exhibited a higher number of binding sites for 3H-heparin [(11 +/- 1) x 10(5) sites per cell than M3 cells [(6.9 +/- 0.6) x 10(5) sites per cell]. However, when M3 cells were grown in the presence of 2% FCS, they showed less heparin binding sites [(3.5 +/- 0.4) x 10(5) sites per cell]. In contrast, dissociation constants were very similar for MM3 and M3 cells grown with or without FCS (Kd = 2-4 x 10(-9) M). Furthermore, heparin inhibited MM3 and M3 cell growth both in the absence or presence of FCS. Competition studies showed that chemically modified heparins lacking antiproliferative effect (O-desulfated; O/N-desulfated N-acetylated and N-desulfated heparins) were not able to inhibit 3H-heparin binding. N-desulfated N-acetylated heparin, which had partial antiproliferative effect, partially inhibited 3H-heparin binding, while heparin with a high antiproliferative activity inhibited more than 90% 3H-heparin binding. The antiproliferative effect of heparin and chemically modified heparins seems to be related to their binding ability to the cell membrane.

Membrane associated proteoglycans in rat testicular peritubular cells

Confluent testicular peritubular cells derived from immature rats were used to study membrane associated proteoglycans (PG). Peripheral material (heparin releasable), membrane and intracellular material (Triton X-100 releasable) were collected, purified by anion exchange chromatography then characterized by gel filtration and by hydrophobic interaction chromatography, followed by enzymatic digestion and chemical treatment. The peripheral material was constituted of two populations of PG (Kav = 0 and 0.10 on Superose 6 column), each containing both heparan sulfate proteoglycans (HSPG) and chondroitin proteoglycans (CSPG) and perhaps a hybrid PG (HSCSPG). These PG being not retained on an octyl Sepharose column, they were devoided of hydrophobic properties. The integral membrane proteoglycans isolated on the basis of their hydrophobic properties represented 20% of the Triton X-100 releasable material, and were exclusively constituted of proteoheparan sulfate. There were no relationships between this membrane HSPG and the peripheral HSPG as evidenced by pulse chase experiments. The mode of intercalation of the hydrophobic HSPG in the cell membrane was studied. The majority of these macromolecules (80%) were sensitive to trypsin and only a minor proportion (20%) were sensitive to phosphatidylinositol specific phospholipase C. Thus, about 80% of the hydrophobic HSPG were intercalated in the cell membrane by a hydrophobic segment of the core protein whereas about 20% were associated with the cell membrane via a phosphatidylinositol residue covalently bound to the core protein of the PG.

Specific binding between human neutrophils and heparin

Heparin binding on polymorphonuclear leucocytes (PMNL) was characterized. Heparin binding was specific, rapid, saturable and reversible. One single class of heparin binding sites was found with a dissociation constant of 1.22 mumol/l and 7.7 x 10(6) sites per PMNL. The binding was independent of the anticoagulant activity of heparin. Heparin affinity chromatography on radio-iodinated cell lysates followed by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulphate revealed a 130 kD heparin binding protein. Heparin binding was inhibited by disodium salt of ethylenediamine tetraacetic acid. Cell surface bound heparin was functionally inactive and did not affect the inactivation of thrombin by antithrombin III. Our study demonstrates that heparin interacts with PMNL by a cell-surface binding protein. These instructions could be consistent with the modifications of some PMNL functional properties in the presence of heparin.

Heparin releasable and nonreleasable forms of heparan sulfate proteoglycan are found on the surfaces of cultured porcine aortic endothelial cells

Evidence suggests that endothelial cell layer heparan sulfate proteoglycans include a variety of different sized molecules which most likely contain different protein cores. In the present report, approximately half of endothelial cell surface associated heparan sulfate proteoglycan is shown to be releasable with soluble heparin. The remaining cell surface heparan sulfate proteoglycan, as well as extracellular matrix heparan sulfate proteoglycan, cannot be removed from the cells with heparin. The heparin nonreleasable cell surface proteoglycan can be released by membrane disrupting agents and is able to intercalate into liposomes. When the heparin releasable and nonreleasable cell surface heparan sulfate proteoglycans are compared, differences in proteoglycan size are also evident. Furthermore, the intact heparin releasable heparan sulfate proteoglycan is closer in size to proteoglycans isolated from the extracellular matrix and from growth medium than to that which is heparin nonreleasable. These data indicate that cultured porcine aortic endothelial cells contain at least two distinct types of cell surface heparan sulfate proteoglycans, one of which appears to be associated with the cells through its glycosaminoglycan chains. The other (which is more tightly associated) is probably linked via a membrane intercalated protein core.

Heparin binds to Leishmania donovani promastigotes and inhibits protein phosphorylation

We show that promastigotes of Leishmania donovani, the causative agent of visceral leishmaniasis (kala-azar), possess heparin receptors on their surface. From a linear Scatchard plot of the binding data obtained using [3H]heparin and viable promastigotes, one derives a binding constant of 4.7 x 10(-7) M and an estimate of 860,000 receptors per parasite. The [3H]heparin bound to parasites could not be displaced by hyaluronic acid or by three other glycosaminoglycans (dermatan sulphate, chondroitin 4-sulphate and chondroitin 6-sulphate). It was demonstrated that exponential phase promastigotes growing in medium 199 supplemented with fetal bovine serum incorporate 35SO4 into a cell-associated macromolecule that has the properties of heparin proteoglycan. Heparin inhibits the activity of the cell-surface histone-protein kinase; incubation of viable promastigotes with [gamma-32P]ATP and MgCl2 (10 mM) in the absence and presence of heparin (0.01-0.5 mg/ml) for 10 min, followed by analysis by SDS/polyacrylamide-gel electrophoresis and autoradiography, revealed that the phosphorylation of 12 or 13 parasite proteins was inhibited by the glycosaminoglycan. These data suggest that heparin may play a role in the host-parasite relationship.

Heparin and heparan sulfate binding sites on B-16 melanoma cells

We have reported previously that the production of a tumor cell factor that stimulates synthesis of fibroblast collagenase is influenced by a fibroblast-deposited matrix component, possibly heparan sulfate-proteoglycan. In this study, binding sites for heparin and heparan sulfate on mouse B-16 melanoma cells have been demonstrated. Binding of 3H-heparin and 35S-heparan sulfate has been shown to occur to whole cells, isolated membranes, and to a component(s) of detergent extracts of the membranes. Scatchard analysis of binding of 3H-heparin yielded a Kd of 2-5 x 10(-8) M and a Bmax of 0.5 x 10(7) heparin molecules bound per cell. Binding of 35S-heparan sulfate was of at least an order of magnitude lower affinity than heparin, but the Bmax was similar to that for heparin. Competition studies showed that 35S-heparan sulfate binding was inhibited totally by heparin and heparan sulfate and partially by dermatan sulfate, but no inhibition was obtained with hyaluronate or chondroitin sulfate. Binding of 3H-heparin was inhibited totally by heparin but to different extents by preparations of heparan sulfate from different tissue sources. The heparin/heparan sulfate binding activity is a protein(s) because it is destroyed by treatment with trypsin. Binding of 3H-heparin to transblots of the detergent extract of the B-16 cell membranes indicated that at least part of the binding activity is a 14,000-dalton protein.

Evidence for independent metabolism and cell surface localization of cell surface localization of cellular proteoglycans and glycosaminoglycan free chains

The synthesis and turnover of metabolically labeled proteoglycans from medium, cell layer, and substratum-associated compartments were characterized in four cell lines of fibroblastic origin, including a fibrosarcoma line, and in the murine melanoma cell type, B16.F10. Substantial differences were apparent between the various cell types with regard to quantities, hydrodynamic sizes, and compartmentalization of labeled product. Such variations were greater between the different cell lines than between separately labeled cultures of the same cell type. Greater than 85% of cell-associated proteoglycans were accessible to glycosaminoglycan-degrading enzymes added to the medium of monolayer cultures, demonstrating their principal location to be external to the cell membrane. Apparent glycosaminoglycan free chains, determined by a lack of change in hydrodynamic size following alkaline elimination, were among the products from each cell line and were similarly found to be in a principally pericellular location. Results from label-chase studies demonstrated apparent independent kinetics for proteoglycans and glycosaminoglycan free chains, with little conclusive evidence for precursor-product relationships. Also, their processing by the cells was different, since the proteoglycans were shed largely unchanged into the medium for the three cell lines evaluated, whereas the free chains were not recoverable from the medium in significant amounts. The latter observation suggests the internalization of cell surface-associated free chains and their depolymerization at an intracellular site. The results, which indicate that the content, cellular disposition, and turnover of proteoglycans are quite variable between the cell lines studied, may reflect fundamental cell type-specific specialization in the metabolism of these complex substances. Furthermore, the data raise the interesting possibility that glycosaminoglycan free chains may have biological functions at the cellular level, independent of proteoglycans.

Cell surface heparan sulfate proteoglycan and the neoplastic phenotype

Cell surface proteoglycans are strategically positioned to regulate interactions between cells and their surrounding environment. Such interactions play key roles in several biological processes, such as cell recognition, adhesion, migration, and growth. These biological functions are in turn necessary for the maintenance of differentiated phenotype and for normal and neoplastic development. There is ample evidence that a special type of proteoglycan bearing heparan sulfate side chains is localized at the cell surface in a variety of epithelial and mesenchymal cells. This molecule exhibits selective patterns of reactivity with various constituents of the extracellular matrix and plasma membrane, and can act as growth modulator or as a receptor. Certainly, during cell division, membrane constituents undergo profound rearrangement, and proteoglycans may be intimately involved in such processes. The present work will focus on recent advances in our understanding of these complex macromolecules and will attempt to elucidate the biosynthesis, the structural diversity, the modes of cell surface association, and the turnover of heparan sulfate proteoglycans in various cell systems. It will then review the multiple proposed roles of this molecule, with particular emphasis on the binding properties and the interactions with various intracellular and extracellular elements. Finally, it will focus on the alterations associated with the neoplastic phenotype and will discuss the possible consequences that heparan sulfate may have on the growth of normal and transformed cells.

Evidence that Thy-1 and Ly-5 (T-200) antigens interact with sulphated carbohydrates

Recent studies have demonstrated that lymphocytes express an array of cell surface receptors for sulphated polysaccharides (SP). Experiments were undertaken to determine the binding characteristics of these receptors and establish whether any known lymphocyte cell surface antigens interact with sulphated carbohydrates. It was found that murine thymocytes lack receptors for chondroitin-4-sulphate but express saturable, high affinity binding sites for heparin, fucoidan and dextran sulphate, with an apparent affinity constant range of 0.03-2.6 x 10(-9) mol/l. Binding inhibition experiments revealed one class of binding sites on murine thymocytes that is shared by heparin, fucoidan and dextran sulphate and another class of sites that is dextran sulphate-specific. The cell surface receptors for the SP were affinity-purified by applying detergent lysates of 125I-labelled thymocyte membranes to SP-coupled solid supports. It was found that the Thy-1 and Ly-5 (T-200 or leucocyte common antigen) molecules of murine thymocytes bind to sulphated carbohydrates, although the two molecules differed substantially in their reactivity with the four different SP tested. Furthermore, only subpopulations of the Thy-1 and Ly-5 molecules interacted with sulphated sugars. Four additional sulphated carbohydrate-binding molecules were also detected. It is suggested that the SP-binding molecules are involved in the interaction of lymphocytes with glycosaminoglycans on other cells and in the interstitial space.

The cell surface hyaluronate binding sites of invasive human bladder carcinoma cells

High-affinity, cell surface binding sites for hyaluronate were demonstrated on highly invasive human bladder carcinoma cells. These binding sites were shown to be specific for hyaluronate, saturable and exhibit a Km of 0.94 x 10(-9) M and a Bmax of 65 ng hyaluronate/10(6) cells. The binding of [3H]hyaluronate to a fixed cell-affinity column was competed with unlabeled hyaluronate and hyaluronate-hexasaccharide but not with hyaluronate-tetrasaccharide, chondroitin sulfate, heparin or non-sulfated dextran. Pre-treatment of cells with protease destroyed the binding activity whereas pretreatment with Streptomyces hyaluronidase to reveal occupied binding sites had no effect. No hyaluronate-binding activity was observed on normal human fibroblasts.

Proteoglycans synthesized by embryonic chicken retina in culture: composition and compartmentalization

Characteristics of the chondroitin sulfate/dermatan sulfate proteoglycans (CS/DSPGs) and heparan sulfate proteoglycans (HSPGs) from retinas of 14-day chicken embryos were examined following specific lyase digestion of the HSPG and CS/DSPG glycosaminoglycans, respectively. On the basis of gel exclusion chromatography the prevalent CS/DSPGs in the tissue were above Mr 400 X 10(3) with two or three glycosaminoglycan chains of Mr 60-70 X 10(3). The HSPGs existed in two distinct populations in the tissue. Those in the dominant population appeared to be in the range of Mr 250-300 X 10(3) with 9 to 12 glycosaminoglycan chains of Mr 15-25 X 10(3). The other population consisted of free heparan sulfate chains of Mr 15-25 X 10(3). The HSPGs in the medium tended to be intermediate in size. To examine the distribution of proteoglycans, tissues were sequentially homogenized and extracted in saline and reextracted with 4 M guanidine HCl (GdnHCl) and Triton X-100 (TX), or they were washed in heparin solution and dissociated to single cells with trypsin before sequential extraction in saline and GdnHCl with TX. Through comparison of the results of these two extraction methods, CS/DSPGs were found to be almost entirely within the medium or matrix or loosely associated with the cell surface, and most HSPGs were associated with either the basal lamina or the plasma membrane. The single heparan sulfate glycosaminoglycan chains appeared to be intracellular degradation products. These results support reports that CS/DSPGs may be present in the retina interphotoreceptor matrix and that HSPGs may be present in regions of synaptogenesis, associated with cell membranes.

Binding of heparin to human endothelial cell monolayer and extracellular matrix in culture

Endothelial binding of heparin contributes to its local antithrombotic action and catabolism. However, it is uncertain whether heparin may be bound to a damaged or even de-endothelialized vessel surface. Therefore, the binding of 3H-heparin to cultured endothelial cell monolayer and extracellular matrix was studied. The binding reached equilibrium after 4 h. 3H-heparin bound to endothelium could be displaced by unlabelled heparin which competed for about 80% of binding. The binding became saturable when the concentration of heparin exceeded 30-times the therapeutical value. Approximately 6 X 10(11) binding sites for heparin per cm2 of endothelium were calculated. Heparin was bound not only to endothelial cells but also to extracellular matrix, even when it was exposed in the absence of cells. About 40% of binding sites were localized in the extracellular matrix fraction. A similar affinity of binding of 3H-heparin to complete endothelium, endothelial cells and extracellular matrix was estimated /Kd of almost 1 microM/. The binding of heparin to extracellular matrix should be considered in the interpretation of heparin interaction with endothelium.

Glycosaminoglycans as probes to monitor differences in fertility of bulls

Recently high molecular weight polysaccharides termed glycosaminoglycans have been successfully used to capacitate bull sperm in vitro. Heparin, one class of glycosaminoglycan, binds to sperm in a manner typical of receptor-ligand interaction. Bulls with above average nonreturn rates produce sperm that exhibit a higher frequency of acrosome reactions when exposed to glycosaminoglycans in vitro. In addition, the binding affinity that sperm possess for heparin is related to nonreturn rates of bulls, and binding affinity decreases in semen samples with a high frequency of abnormal sperm. Glycosaminoglycans may be useful probes to evaluate in vitro cellular changes that sperm complete prior to fertilization and serve as markers of sperm membrane defects, which ultimately affect fertility of a bull.

A role for sulfated polysaccharide recognition in sponge cell aggregation

Molecules binding sulfated polysaccharides were detected as lectins in cholate lysates of cells from twelve sponge species. Each species exhibited a unique binding profile. The pattern of binding indicated that the specificity was most probably determined by the orientation of the sulfate groups on the polysaccharide chains. Cells from each of the three species examined in more detail were found to express sulfated polysaccharide-binding molecules at their surface and at least one of the polysaccharides recognized was found to inhibit the reaggregation of cells from each species. Moreover, in all but one instance, lectins for the inhibitory polysaccharide were both detected in cell lysates and shown to be expressed at the cell surface. Sulfated polysaccharides, therefore, appeared to be involved in cell interaction events in the Porifera. This conclusion was confirmed by the isolation via ion exchange chromatography of an endogenous polysaccharide from an O. tenuis cell extract. This molecule contained uronic acid and hexose units in a ratio of 2:1, 11.9% sulfur and less than 0.5% protein. It inhibited the aggregation of O. tenuis cells and the agglutination of dextran-sulfate- and polyvinyl-sulfate-coupled erythrocytes by O. tenuis cell lysates. O. tenuis cell aggregation was also inhibited by polyvinyl sulfate and dextran sulfate and molecules binding these compounds were expressed on the surface of O. tenuis cells. Thus, is was probable that the cell surface receptor for polyvinyl sulfate and dextran sulfate and isolated sponge sulfated polysaccharide are one and the same. Finally, using a dextran sulfate affinity procedure, a 35 kD dextran-sulfate-binding protein was isolated from the surface of O. tenuis cells. The possibility that the polysaccharide isolated from O. tenuis cell extracts in the absence of calcium is the monomeric form of a cell aggregation-enhancing factor is discussed.

Binding of chondroitin sulfate, dermatan sulfate and fat-storing cell-derived proteoglycans to rat hepatocytes

1. The interaction of isolated rat hepatocytes with exogenous 3H-labeled chondroitin-4-sulfate and dermatan sulfate and with biosynthetically 35S-labeled proteoglycans secreted by cultured rat liver fat-storing cells has been studied. 2. All ligands are bound by hepatocytes in a concentration-dependent manner. Scatchard-plot analysis of the data revealed the existence of high- and low-affinity binding modes. 3. The cell-bound exogenous [3H]glycosaminoglycans could be displaced by each unlabeled ligand and by heparin, whereas displacement of the endogenous material was less effective. 4. Binding of all ligands to hepatocytes increased with time. For the exogenous glycosaminoglycans the two- to threefold amount was retained at 37 degrees C as compared to 4 degrees C; it was markedly reduced by pretreatment of the cells with trypsin. 5. Degradation of the exogenous ligands could be detected neither for the cell-bound fraction nor for the free glycosaminoglycans in the culture medium. 6. The binding of the ligands to hepatocytes is viewed as a cell-matrix interaction. Its possible pathobiochemical relevance in liver fibrosis or neoplasia is discussed.

Purification and characterization of a human pituitary growth factor

A growth factor has been purified to homogeneity from human pituitary glands. The pituitary growth factor (PGF) is trypsin-sensitive and acid- and heat-labile and has a molecular weight of 18,000 and an isoelectric point of 7.5. PGF was purified by heparin and copper affinity chromatography followed by carboxymethylcellulose 52. The amino-terminal amino acid sequence of PGF was established as PALPEXGGXGA and is identical with that of basic fibroblast growth factor at the identified amino acid residues. PGF was mitogenic for rabbit fetal chondrocytes and bovine corneal endothelial cells in the range of 0.015-15 ng mL-1. Heparin alone at low concentrations (0.5 microgram mL-1) was found to be weakly mitogenic for rabbit fetal chondrocytes. In combination with PGF a marked increase in cell growth was observed, which was inhibited by protamine sulfate. These data demonstrate the presence of a potent mitogen in human pituitaries that is structurally related to basic fibroblast growth factor and synergizes with heparin to promote cell growth.

Heparin-induced aggregation of lymphoid cells

The effects of different carbohydrates on cell-to-cell adhesion were examined in an aggregation assay, which consisted of swirling a suspension of cells and monitoring the loss of single cells with a Coulter Counter. Of the carbohydrates tested, only heparin and dextran sulfate induced cell aggregation. This effect occurred in freshly isolated mouse splenocytes and in cultured cells of lymphoid origin (P388, YAA-CI) but not in cell lines of fibroblastic origins (3T3, SV-3T3, BHK, and PY-BHK). Using the YAA-CI cell line for further study, we found that aggregation could be induced by relatively small amounts of heparin (less than 10 micrograms/ml). Binding experiments with 3H-heparin showed that under normal physiological conditions each YAA-CI cell bound approximately 2 X 10(6) molecules of heparin at saturation with a Kd of 3.5 X 10(-7) M. This binding was blocked by both unlabelled heparin and dextran sulfate but not by other carbohydrates. When the pH of the medium was decreased, the heparin-induced aggregation was inhibited, and the Kd of the 3H-heparin binding was increased. In a similar fashion, when the ionic strength of the medium was increased, heparin-induced aggregation was inhibited and the Kd of the interaction was increased. These results suggest that the aggregation is inversely related to the Kd of the interaction and that the binding of heparin to the cell surface is primarily of an ionic nature.

Removal of glycosaminoglycans from bovine granulosa cells contributes to increased binding of hydrogen-3 heparin

Granulosa cells from small or large bovine follicles were pretreated with enzymes that hydrolyze various glycosaminoglycans, and binding of [3H]-heparin to the granulosa was measured. Binding of [3H] heparin increased significantly after enzymatic pretreatments with chondroitinase ABC and fungal hyaluronidase, and similar results were obtained with granulosa from small and large follicles. No changes in binding of [3H] heparin were detected after hydrolyses with chondroitinase AC and heparinase in either follicle size. Heparitinase, which hydrolyzes heparan sulfate, led to a significant 50% increase in binding of [3H] heparin to granulosa from large follicles but was without effect in small follicles. These results suggest that the lower binding of [3H] heparin, which has been reported with follicular enlargement, may be due to heparan sulfate occupying or obstructing binding sites for heparin on granulosa from large follicles.

Specific binding of [3H]heparin to bovine granulosa cell membranes

Bovine granulosa cell membranes from small (SFM) and large (LFM) antral follicles were incubated with [3H]heparin, a commercial radioactively labeled glycosaminoglycan (GAG). Binding was specific, reversible, saturable, and dependent on time, pH, ionic strength and divalent cations. SFM exhibited different [3H]heparin binding characteristics compared to LFM. The addition of a physiological concentration of calcium (2 mM) yielded significant differences (P less than 0.02) in [3H]heparin binding for SFM (87 590 +/- 4206 dpm/10(6) cells) compared to LFM (55 230 +/- 2816 dpm/10(6) cells). SFM and LFM showed maximum [3H]heparin binding at pH 6.5 and pH 5.5, respectively. Increasing the ionic strength by addition of 0.07-2.0 M NaCl interfered with binding. Addition of unlabeled heparin (0.1-100 micrograms/ml) displaced [3H]heparin bound to SFM and LFM in a dose-dependent manner, as did dextran sulfate, a non-GAG sulfated branched polysaccharide. Commercial chondroitin sulfate ABC displaced the bound [3H]heparin only at doses between 50 and 500 mg/ml. GAGs purified from FF suppressed binding 39% at a concentration of 5.9 mg/ml. Photomicrographs of fluorescein-labeled heparin bound to granulosa cells showed localized areas of heparin binding to the cell surface. These experiments demonstrated that the GAG heparin specifically bound to bovine granulosa cell membranes, and that significant differences existed between the binding characteristics of SFM and LFM.

Relationship of nonreturn rates of dairy bulls to binding affinity of heparin to sperm

The binding of the glycosaminoglycan [3H] heparin to bull spermatozoa was compared with nonreturn rates of dairy bulls. Semen samples from five bulls above and five below an average 71% nonreturn rate were used. Samples consisted of first and second ejaculates on a single day collected 1 d/wk for up to 5 consecutive wk. Saturation binding assays using [3H] heparin were performed to quantitate the binding characteristics of each sample. Scatchard plot analyses indicated a significant difference in the binding affinity for [3H] heparin between bulls of high and low fertility. Dissociation constants were 69.0 and 119.3 pmol for bulls of high and low fertility, respectively. In contrast, the number of binding sites for [3H] heparin did not differ significantly among bulls. Differences in binding affinity of [3H] heparin to bull sperm might be used to predict relative fertility of dairy bulls.

Binding and endocytosis of heparin by human endothelial cells in culture

Binding of heparin and low molecular weight heparin fragments (CY 222, Mr range 1500-8000) to human vascular endothelial cells was studied. Primary culture of human umbilical vein endothelial cells and either 125I or 3H-labeled heparin or [125I]CY 222 were used. Slow, saturable and specific binding was found. No other tested glycosaminoglycan, excepting a highly sulfated heparan fraction, was able to compete for heparin binding. Two groups of binding sites for [3H]heparin could be distinguished: one with high affinity (Kd = 0.12 microM) and another with lower affinity (Kd = 1.37 microM) and a relative large capacity of binding (1.16 X 10(7) molecules/cell) was calculated. The Kd for unlabeled heparin, as calculated from competition experiments, was 0.23 microM. Much lower affinity was calculated for unlabeled low molecular weight heparin fragments CY 222 (Kd = 4.3 microM) from competition experiments with [125I]CY 222. The binding reversibility was only partial for unfractionated heparin. Even by chasing with unlabeled compound, a fraction of 25-30% was not dissociable from endothelial cells. This fraction was much lower if incubation was carried out at 4 degrees C. The addition of basic proteins (histones) to the incubation medium greatly enhanced the undissociable binding at 37 degrees C, but not at 4 degrees C. The undissociable fraction of heparin was not available to degradation by purified microbial heparinase. These results suggest that a fraction of bound heparin is internalized by the vascular endothelium.

Lymphocytes express a diverse array of specific receptors for sulfated polysaccharides

Lymphocyte receptors for sulfated polysaccharides were detected in two ways, namely, by the ability of lymphocytes to form rosettes with sheep red blood cells (SRBC) coupled with one of fourteen different sulfated polysaccharides, and by the ability of cholate extracts of lymphocytes to hemagglutinate the same sulfated polysaccharide-coupled SRBC. It was found that murine lymphocytes lacked receptors for a number of glycosaminoglycans, such as hyaluronic acid, chondroitin-4-sulfate, chondroitin-6-sulfate, and dermatan sulfate, but reacted strongly with heparin, arteparon, and a number of sulfated polysaccharides of plant and bacterial origin. In each case receptor activity was demonstrated by rosetting and by the ability of lymphocyte lysates to strongly agglutinate sulfated polysaccharide-coupled SRBC. The receptors exhibited a high degree of diversity as evidenced by (a) only subpopulations of lymphocytes, particularly splenic B cells, expressing receptors for some of the sulfated polysaccharides and (b) hemagglutination-inhibition analyses revealing numerous subsets of receptors with different binding specificities. Receptor diversity was further highlighted by a 48% difference in the hemagglutination-inhibiton results between thymus and spleen. It is proposed that these receptors are involved in cell-cell communication and lymphocyte homing and recirculation. The likely target structures for the receptors in vivo are the heparan sulfates, a ubiquitous and structurally diverse family of sulfated glycosaminoglycans.

Chemically induced renal papillary necrosis and upper urothelial carcinoma. Part 1

In the past, renal papillary necrosis (RPN) has been commonly associated with long-term abusive analgesic intake, but over recent years a wide variety of industrially and therapeutically used chemicals have been shown to induce this lesion experimentally or in man. Destruction of the renal papilla may result in: (1) secondary degenerative cortical changes which precede chronic renal failure or (2) a rapidly metastasizing upper urothelial carcinoma, which has a very poor prognosis. This article will briefly review the published data on the morphology, function, and biochemistry of the normal renal medulla and the pathology associated with RPN, together with the secondary changes which give rise to cortical degeneration or epithelial carcinoma. It will then examine in detail those chemicals which have been reported to cause RPN in an attempt to delineate structure-activity relationships. Finally, the many different theories that have been proposed to explain the pathophysiology of RPN will be examined and an hypothesis will be put forward to explain the primary pathogenesis of the lesion and its secondary consequences.

Chemically induced renal papillary necrosis and upper urothelial carcinoma. Part 2

In the past, renal papillary necrosis (RPN) has been commonly associated with long-term abusive analgesic intake, but over recent years a wide variety of industrially and therapeutically used chemicals have been shown to induce this lesion experimentally or in man. Destruction of the renal papilla may result in: (1) secondary degenerative cortical changes which precede chronic renal failure or (2) a rapidly metastasizing upper urothelial carcinoma, which has a very poor prognosis. This article will briefly review the published data on the morphology, function, and biochemistry of the normal renal medulla and the pathology associated with RPN, together with the secondary changes which give rise to cortical degeneration or epithelial carcinoma. It will then examine in detail those chemicals which have been reported to cause RPN in an attempt to delineate structure-activity relationships. Finally, the many different theories that have been proposed to explain the pathophysiology of RPN will be examined and an hypothesis will be put forward to explain the primary pathogenesis of the lesion and its secondary consequences.

Evidence for diabetes-induced alterations in the sulfation of heparin sulfate intestinal epithelial cells

35S-heparan sulfate (HS) metabolism by intestinal epithelial cells isolated from streptozotocin-diabetic and control rats was studied. In diabetic cells, a greater amount of 35S-radioactivity was incorporated into HS, however specific radioactivity of this polysaccharide was decreased. Studies into the distribution of sulfate residues in HS after selective deamination of the glucosamine units within the glycosaminoglycan (GAG)-chain, demonstrated that O-sulfate groups are preferentially located in relatively small deamination products: tetrasaccharides and disaccharides. A lower amount of radioactivity related to N-sulfate groups was found in HS from diabetic cells compared to that of control cells demonstrating that, in diabetes, less glucosamine residues within HS chains are subjected to N-sulfation. An increase in the percentage of 35-sulfate and in the percentage amount of uronic acid in tetrasaccharides of HS of diabetic cells indicated that a greater number of tetrasaccharides were generated by deaminative degradation of this HS. Since a decrease in the specific activity of uronic acid in disaccharides as in tetrasaccharides from HS of diabetic cells was observed, it is clear that the degree of O-sulfation of this HS is reduced. It is suggested, that "in vivo" changes in HS metabolism in diabetic intestinal epithelial cells lie in a disturbance in the degree of N- and O-sulfation of disaccharide units within the HS macromolecule.

Isolation of the major chondroitin sulfate/dermatan sulfate and heparan sulfate proteoglycans from embryonic chicken retina

A technique is presented for the preparation of three major proteoglycans from 14-day embryonic chicken retinas following their culture overnight with [35S]sulfate and either [3H]glucosamine or [3H]serine. Homogenization of the tissue in saline permitted extraction of heterogeneous soluble proteoglycans separately from most of the heparan sulfate proteoglycans. The latter were extracted from the 140,000g pellet with 0.5% Triton X-100 in 8 M urea. The medium plus the saline and urea-detergent extracts were separated from low-molecular-weight contaminants, and fractionated into two peaks of radioactivity on Sephacryl S-300 in saline with 3 M urea and 0.5% Triton X-100. The proteoglycans were isolated directly from these fractions on DEAE-Sephacel, and subjected to ultrafiltration concentration and then further purification on cesium chloride density gradient centrifugation in 4 M guanidine hydrochloride. A further step involving cetylpyridinium chloride precipitation was examined, but it resulted in essentially no further purification. The fractionations separated a large chondroitin sulfate/dermatan sulfate proteoglycan from the culture medium that was excluded from S-300 and of low buoyant density; a large heparan sulfate proteoglycan from the urea-detergent extract that was also excluded from S-300 and of low buoyant density; and two smaller and possibly related heparan sulfate proteoglycans. One was found in the medium and showed low to intermediate buoyant density; the other was isolated from the urea-detergent extract and showed a significantly higher buoyant density, associated with a lower protein content. The saline extract contained both of the two larger proteoglycans and only minor amounts of the smaller molecules.

Binding sites and endocytosis of heparin and polylysine are changed when the two molecules are given as a complex to Chinese hamster ovary cells

This paper characterizes the complex formed in vitro between polylysine and heparin in the presence of heparin excess, and investigates the interaction of this complex with the surface of Chinese hamster ovary cells. It examines the kinetics of surface binding and cellular uptake of the complex and shows that both processes can be distinguished from those of free heparin and free polylysine. The view that these three ligands bind to different surface sites is further supported by the fact that their interaction with cells is influenced differently by cell detachment with trypsin, detachment with EGTA or exposure to acid pH. Membrane transport of the complex is a saturable process suggestive of receptor-mediated endocytosis. It is, however, less effective than would be expected on the basis of the binding kinetics. Only 40% of the complex bound at 0 degrees C is internalized during a 2 h reincubation period at 37 degrees C, suggesting some degree of uncoupling between binding and endocytosis. These data confirm prior results obtained with methotrexate-polylysine conjugates. We had shown that the addition of heparin to a medium containing a methotrexate-polylysine conjugate leads unexpectedly to a marked cellular uptake of drug conjugate, which is capable of killing cells that are otherwise resistant to free methotrexate (Shen, W.-C. and Ryser, H.J.-P. (1981) Proc. Natl. Acad. Sci. USA 78, 7589-7593). The polylysine X heparin complex is therefore of interest as a potential carrier for intracellular drug delivery through endocytosis.

Adhesion of human amnion epithelial cells to extracellular matrix. Evidence for multiple mechanisms

Human amnion epithelial cells attach and flatten slowly (approximately 65 min) onto plastic in the presence of serum but much more rapidly (20-30 min) onto subcellular matrix (SCM) deposited by the same cells. This matrix contains both fibronectin and laminin, but neither molecule on its own can reproduce its adhesive properties. Cells attach on surfaces containing fibronectin and laminin and extend filopodial and lamellipodial areas of cytoplasm without extensive flattening in the perinuclear region. Matrix deposited onto plastic by amnion epithelial cells has trypsin-sensitive and trypsin-resistant, papain-sensitive adhesion-promoting components. Cell spreading triggered by the latter but not the former can be inhibited by pretreating the adhering cells with heparin. Other GAGs are without effect. The results are discussed in terms of multiple interactions between epithelial cells and basal laminae.

In vitro binding of 67Ga to Ehrlich ascites tumor cells

The binding of 67Ga to Ehrlich ascites tumor cells (ETC) was studied in vitro. Acid mucopolysaccharide (AMPS) present at the cell surface of ETC was identified as heparan sulfate (HS). The extent of 67Ga binding to ETC reached a plateau (ca. 10% of the added dose) at 1-2 h after the start of incubation. The binding was higher under neutral or alkaline conditions than under acidic conditions. Heparin and heparitinase treatment both significantly decreased the extent of 67Ga binding to ETC. Mild treatment with protease, including trypsin or papain, also decreased the binding. On the contrary, the treatment with trypsin under severe conditions markedly increased the extent of 67Ga binding to ETC. These results support the hypothesis that HS plays an important role as a 67Ga receptor in the mechanism of gallium binding to ETC.

Structure and properties of an under-sulfated heparan sulfate proteoglycan synthesized by a rat hepatoma cell line

A rat hepatoma cell line was shown to synthesize heparan sulfate and chondroitin sulfate proteoglycans. Unlike cultured hepatocytes, the hepatoma cells did not deposit these proteoglycans into an extracellular matrix, and most of the newly synthesized heparan sulfate proteoglycans were secreted into the culture medium. Heparan sulfate proteoglycans were also found associated with the cell surface. These proteoglycans could be solubilized by mild trypsin or detergent treatment of the cells but could not be displaced from the cells by incubation with heparin. The detergent-solubilized heparan sulfate proteoglycan had a hydrophobic segment that enabled it to bind to octyl-Sepharose. This segment could conceivably anchor the molecule in the lipid interior of the plasma membrane. The size of the hepatoma heparan sulfate proteoglycans was similar to that of proteoglycans isolated from rat liver microsomes or from primary cultures of rat hepatocytes. Ion-exchange chromatography on DEAE-Sephacel indicated that the hepatoma heparan sulfate proteoglycans had a lower average charge density than the rat liver heparan sulfate proteoglycans. The lower charge density of the hepatoma heparan sulfate can be largely attributed to a reduced number of N-sulfated glucosamine units in the polysaccharide chain compared with that of rat liver heparan sulfate. Hepatoma heparan sulfate proteoglycans purified from the culture medium had a considerably lower affinity for fibronectin-Sepharose compared with that of rat liver heparan sulfate proteoglycans. Furthermore, the hepatoma proteoglycan did not bind to the neoplastic cells, whereas heparan sulfate from normal rat liver bound to the hepatoma cells in a time-dependent reaction. The possible consequences of the reduced sulfation of the heparan sulfate proteoglycan produced by the hepatoma cells are discussed in terms of the postulated roles of heparan sulfate in the regulation of cell growth and extracellular matrix formation.

Substrate adhesion of rat hepatocytes: on the mechanism of attachment to fibronectin

We examined the mechanisms of cell attachment to fibronectin-coated substrates. Inhibition of cell attachment was obtained by species-specific antifibronectin antibodies, which presumably recognize a distinct antigenic structure in the protein located at, or in the immediate vicinity of, the cell-binding site. The inhibiting antibodies could be adsorbed on a column of Sepharose substituted with plasma fibronectin. The initial phase of cell attachment was also inhibited by addition of soluble fibronectin to the incubation medium in a reaction that exhibited specificity and concentration dependence. These data suggest that cell-binding sites are available in an active form on the surface of soluble fibronectin. However, the inhibitory effect of fibronectin was greatly enhanced by adding the protein together with heparin, heparan sulfate, collagen, or a fibronectin-binding collagen peptide (CB-7), which is consistent with an "activation" of fibronectin on binding to these matrix components. A similar activation of fibronectin was obtained by cleaving the protein with trypsin. We discuss these findings in relation to conformational rearrangements in the fibronectin molecule. Data is presented supporting a mechanism of cell attachment to fibronectin involving multiple weak interactions between cellular receptors and substrate molecules, although some steps in the attachment process appear to disobey the requirements for such a mechanism.

Specific binding of the glycosaminoglycan 3H-heparin to bull, monkey, and rabbit spermatozoa in vitro

In Vitro binding and some binding parameters of the glycosaminoglycan heparin to viable epididymal or ejaculated bull spermatozoa, ejaculated rabbit spermatozoa, and frozen-thawed rhesus monkey spermatozoa were investigated. Nonspecific binding was affected only by the concentration of 3H-heparin, whereas specific binding was saturable, reversible, and dependent on the pH, temperature, and calcium concentration of the incubation medium. Magnesium concentration dependence was observed in the presence of calcium but could not be detected in the absence of calcium. Bound 3H-heparin was displaced by several orders of magnitude greater concentrations of chondroitin sulfate. Scatchard plot analysis suggested multiple binding affinities for 3H-heparin to spermatozoa. 3H-heparin was shown to bind to sperm heads and flagella. Fluorescein-labeled heparin bound to acrosomal, postacrosomal, and flagellar membranes. It was concluded that the specific binding of heparin involved a proteinaceous component on, or intercalated with, spermatozoal membranes. Thus, glycosaminoglycans present in the female reproductive tract may contribute to sperm capacitation and enhance the likelihood of successful fertilization in mammals.

Proteoglycans and cell adhesion. Their putative role during tumorigenesis

In this review, evidence that proteoglycans are involved in cell adhesion and related behavior is considered, together with their putative role(s) during tumorigenesis. Proteoglycans are large, carboxylated and/or sulfated structures that interact with specific binding sites on cell surfaces. Their distribution and synthesis in tissues alter with the onset of tumorigenesis so that hyaluronic acid is generally increased and heparan sulfate decreased in the developing tumor and surrounding tissue. However, the precise role of proteoglycans during the tumorigenic process is far from clarified. Data suggest any putative roles will be related to the adhesive properties that these molecules confer to cells. Hyaluronic acid and chondroitin sulfate appear to be weakly adhesive molecules that may promote 'transformed' characteristics when they occur on cells in large amounts. These characteristics include reduced cell spreading, increased cell motility, as well as reduced contact inhibition. Consistent with such properties, neither hyaluronic acid nor chondroitin sulfate are localized in specialized adhesion sites such as focal or close contacts. In contrast, heparan sulfate is associated with increased cell-substratum adhesion and is involved in the spreading of cells onto fibronectin and other substrata. Its presence is generally associated with reduced motility and with a well-spread morphology. Unlike hyaluronate and chondroitin sulfate, heparan sulfate is found in specialized contacts. These adhesive properties of proteoglycans predict an instructive role in tumor development, and recent experiments have defined an involvement of these molecules in metastatic arrest. Additional studies utilizing invasive and metastatic tumor variants including tumor cells that employ different mechanisms to invade are required to clarify the role of proteoglycans in tumor progression.