Binding and internalization of exogenous glycosaminoglycans in weakly and highly metastatic rhabdomyosarcoma cells

Differences in the uptake and nuclear localization of anti-proliferative heparan sulfate between human lung fibroblasts and human lung carcinoma cells

Heparan sulfate inhibits the proliferation of normal human lung fibroblasts (HFL-1) but not of a human lung carcinoma cell-line (A549). In this study we investigated possible mechanisms and structural requirements by which antiproliferative heparan sulfates exerts its effects on binding, uptake and subcellular localisation. Both HFL-1 and A549 cells were incubated with 125I- or rhodamine-labeled L-iduronate-rich antiproliferative heparan sulfate species as well as L-iduronate-poor inactive ones. The antiproliferative heparan sulfate was bound to the cell surface on both HFL-1 and A549 cells, but to a lesser extent and with less affinity to A549 cells. Both cell types bound the antiproliferative heparan sulfate with one high- and with one low affinity site. The L-iduronate-poor heparan sulfate bound to a lesser extent and with less affinity to both cell types compared to the antiproliferative heparan sulfate. The antiproliferative heparan sulfate accumulated in the cytoplasm of HFL-1 cells after 24 h incubation, but after 72 h it was found evenly distributed in the nucleus. The time-scale for antiproliferative activity correlated with nuclear localization. In contrast, in A549 cells it was only found near the nuclear membrane. The inactive heparan sulfate was taken up in considerably smaller amounts compared to the antiproliferative heparan sulfate and could not be detected in the nucleus of either HFL-1 or A549 cells. Our data suggest that the antiproliferative activity of L-iduronate-rich heparan sulfate on normal fibroblasts may be due to direct effects on nuclear processes, such as gene transcription.

Heparan sulfate upregulates platelet-derived growth factor receptors on human lung fibroblasts

Heparan sulfate is a molecule that possesses a large structural variability and which has been shown to inhibit the proliferation of fibroblasts in vitro. The aim of this study was to determine whether the anti-proliferative effects of heparan sulfate were exerted by regulation of the activity of the platelet-derived growth factor and/or of the platelet-derived growth factor receptors. Both l-iduronate-rich, anti-proliferative and the l-iduronate-poor, non-anti-proliferative heparan sulfate species, were incubated with confluent human embryonic lung fibroblasts for 24 h. The mRNA levels for PDGF-AA, PDGF-BB, and their receptors were measured. Binding studies were performed with [125I]-PDGF-BB and [125I]-EGF for 2 h at 4 degreesC in cultures preincubated with both types of heparan sulfate for 24 h. In separate experiments, cultures were incubated together with heparan sulfate and [125I]-PDGF-BB for 2 h at 4 degreesC. Increases of two- to threefold in the mRNA levels for both the alpha- and the beta-receptors of PDGF was obtained after treatment with both types of heparan sulfate, whereas the mRNA levels of both the PDGF-AA and the PDGF-BB were essentially unaffected. A sixfold increase in binding was only noted for [125I]-PDGF-BB in cultures pre-treated with the anti-proliferative heparan sulfate for 24 h, whereas no effect was noted with use of the non-anti-proliferative heparan sulfate. Incubating the [125I]-PDGF-BB and the anti-proliferative heparan sulfate together for 2 h resulted in a smaller, threefold increase in binding. This indicates that the anti-proliferative heparan sulfate both stabilizes and increases expression of the PDGF receptors. To investigate whether the increased number of PDGF receptors could affect cell activity, cells were preincubated with anti-proliferative heparan sulfate and then treated with PDGF-BB. This resulted in an increase in mitogenicity compared to cells treated only with PDGF-BB. Neither an increase in binding for [125I-EGF] nor an increase in the mitogenic response of EGF could be observed in cultures pre-treated with the anti-proliferative heparan sulfate. The results indicate that the extracellular matrix itself may regulate important biological phenomena such as cell proliferation and matrix production through affecting the expression of receptors of PDGF, which initiate both stimulatory and inhibitory signals.

Role of macrophage glycosaminoglycans in the cellular catabolism of oxidized LDL by macrophages

Macrophage binding sites for oxidized LDL (Ox-LDL) include class A scavenger receptors (SR-As), the CD-36 molecule, and an additional but hitherto unidentified binding site. Because cell-surface glycosaminoglycans (GAGs) were previously shown to be involved in the cellular uptake of native LDL and lipoprotein(a), several strategies to assess the participation of heparan sulfate (HS) and chondroitin sulfate (CS) in macrophage catabolism of Ox-LDL were used. First, incubation of J-774 A.1 macrophage-like cells with either heparinase or chondroitinase, or with both enzymes together, reduced the binding, uptake, and degradation of 125I-Ox-LDL by 20% to 45%, in comparison with control nontreated cells, while catabolism of 125I-labeled acetylated LDL (Ac-LDL) and native LDL were unaffected. Second, the proteoglycan (PG) cellular content was increased by cell enrichment with exogenous GAGs or by using human monocyte-derived macrophages from two patients with Sanfilippo mucopolysaccharidosis, which are characterized by cellular HS accumulation. In these macrophages, cellular uptake of 125I-Ox-LDL increased, while catabolism of 125I-Ac-LDL and native LDL were unaffected. Experiments using conditioned media from control, heparinase-digested, or chondroitinase-digested macrophages indicated that neither secreted GAGs nor released digestion products played any role in Ox-LDL catabolism. To evaluate potential interactions between cell-surface GAGs and known receptors for Ox-LDL, we used excess unlabeled Ac-LDL to block SR-As or anti-CD-36 antibodies to block CD-36, and then examined the catabolism of 125I-Ox-LDL by GAG-enriched or -depleted macrophages. Both excess unlabeled Ac-LDL and anti-CD-36 antibodies reduced 125I-Ox-LDL catabolism, but only excess unlabeled Ac-LDL completely abolished the increase in 125I-Ox-LDL catabolism on GAG enrichment of the cells, indicating a cooperation between exogenous GAGs and cell-surface SR-As in the catabolism of OX-LDL. Moreover, the addition of GAGases to macrophages that were preincubated with anti-CD-36 antibodies and excess Ac-LDL further reduced macrophage degradation of Ox-LDL in comparison with cells that were pretreated only with anti-CD-36 antibodies and Ac-LDL, indicating a more complex role for endogenous GAGs. Overall, these studies demonstrate a substantial contribution of macrophage-associated GAGs in the catabolism of Ox-LDL, which is mediated in part by a cooperation between GAGs and cell-surface SR-As.

Binding, internalization, and degradation of antiproliferative heparan sulfate by human embryonic lung fibroblasts

Binding, internalization, and degradation of 125I-labeled, antiproliferative, or nonantiproliferative heparan sulfate by human embryonic lung fibroblasts was investigated. Both L-iduronate-rich, antiproliferative heparan sulfate species as well as L-iduronate-poor, inactive ones were bound to trypsin-releasable, cell-surface sites. Both heparan sulfate types were bound with approximately the same affinity to one high-affinity site (Kd approximately 10(-8) M) and to one low-affinity site (Kd approximately 10(-6) M), respectively. Results of Hill-plot analysis suggested that the two sites are independent. Competition experiments with unlabeled glycosaminoglycans indicated that the binding sites had a selective specificity for sulfated, L-iduronate-rich heparan sulfate. Dermatan sulfate, which is also antiproliferative, was weakly bound to the cells. The antiproliferative effects of heparan and dermatan sulfate appeared to be additive. Hence, the two glycosaminoglycans probably exert their effect through different mechanisms. At concentrations above 5 micrograms/ml (approximately 10(-7) M), heparan sulfate was taken up by human embryonic lung fibroblasts, suggesting that the low-affinity site represents an endocytosis receptor. The antiproliferative effect of L-iduronate-rich heparan sulfate species was also exerted at the same concentrations. The antiproliferative species was taken up to a greater degree than the inactive one, suggesting a requirement for internalization. However, competition experiments with dextran sulfate suggested that both the high-affinity and the low-affinity sites are involved in mediating the antiproliferative effect. Structural analysis of the inactive and active heparan sulphate preparations indicated that although sulphated L-iduronate appears essential for antiproliferative activity, it is not absolutely required for binding to the cells. Degradation of internalized heparan sulfate was analyzed by polyacrylamide gel electrophoresis using a sensitive detection technique. The inactive species was partially degraded, whereas the antiproliferative one was only marginally affected.

Heparin reverses Rhodamine 123 extrusion by multidrug resistant cells

The effect of heparin as a reversing agent of multidrug resistance (MDR) was tested on normal mononuclear cells from 24 healthy volunteers and leukaemic cells from 12 acute myeloid leukaemia, five chronic myeloid leukaemia, five acute lymphoid leukaemia and three chronic lymphoid leukaemia patients. Two cell lines were used as controls, the human erythroleukaemia K562 and its vincristine-resistant derivative K562-Lucena 1. Heparin was not cytotoxic by itself as determined using a MTT assay and cell counts. MDR modulation was assessed by Rhodamine 123 extrusion using flow-cytometry. Modulation of the resistant cell line was produced by the classical reversing agent verapamil and also by heparin, the same being observed in normal and leukaemic cells and being independent of the type of leukaemia. Our work suggests that heparin may be considered a potential MDR modulator.

Cell surface expression of HIP, a novel heparin/heparan sulfate binding protein, of human uterine epithelial cells and cell lines

Previous studies established that uterine epithelial cells and cell lines express cell surface heparin/heparan sulfate (HP/HS)-binding proteins (Wilson, O., Jacobs, A. L., Stewart, S., and Carson, D. D. (1990) J. Cell. Physiol. 143, 60-67; Raboudi, N., Julian, J., Rohde, L. H., and Carson, D. D. (1992) J. Biol. Chem. 267, 11930-11939). The accompanying paper (Liu, S., Smith, S. E., Julian, J., Rohde, L. H., Karin, N. J., and Carson, D. D. (1996) J. Biol. Chem. 271, 11817-11823) describes the cloning of a full-length cDNA corresponding to a candidate cell surface HP/HS interacting protein, HIP, expressed by a variety of human epithelia. A synthetic peptide was synthesized corresponding to an amino acid sequence predicted from the cDNA sequence and used to prepare a rabbit polyclonal antibody. This antibody reacted with a protein with an apparent Mr of 24,000 by SDS-polyacrylamide gel electrophoresis that was highly enriched in the 100,000 x g particulate fraction of RL95 cells. This molecular weight is similar to that of the protein expressed by 3T3 cells transfected with HIP cDNA. HIP was solubilized from this particulate fraction with NaCl concentrations > or = 0.8 M demonstrating a peripheral association consistent with the lack of a membrane spanning domain in the predicted cDNA sequence. HIP was not released by heparinase digestion suggesting that the association is not via membrane-bound HS proteoglycans. NaCl-solubilized HIP bound to heparin-agarose in physiological saline and eluted with NaCl concentrations of 0.75 M and above. Furthermore, incubation of 125I-HP with transblots of the NaCl-solubilized HIP preparations separated by two-dimensional gel electrophoresis demonstrated direct binding of HP to HIP. Indirect immunofluorescence studies demonstrated that HIP is expressed on the surfaces of intact RL95 cells. Binding of HIP antibodies to RL95 cell surfaces at 4 degrees C was saturable and blocked by preincubation with the peptide antigen. Single cell suspensions of RL95 cells formed large aggregates when incubated with antibodies directed against HIP but not irrelevant antibodies. Finally, indirect immunofluorescence studies demonstrate that HIP is expressed in both lumenal and glandular epithelium of normal human endometrium throughout the menstrual cycle. In addition, HIP expression increases in the predecidual cells of post-ovulatory day 13-15 stroma. Collectively, these data indicate that HIP is a membrane-associated HP-binding protein expressed on the surface of normal human uterine epithelia and uterine epithelial cell lines.

Interactions of pentosan polysulfate with cartilage matrix proteins and synovial fibroblasts derived from patients with osteoarthritis

Pentosan polysulfate (PPS) has been shown to improve symptoms of patients with osteoarthritis (OA) when studied under double-blinded conditions. Laboratory studies indicated that this drug exhibits multiple actions, including the preservation of articular cartilage (AC) proteoglycans in animal models of OA and the stimulation of hyaluronan synthesis by synovial fibroblasts in vitro and in vivo. As PPS is strongly anionic and has a molecular weight of approximately 5700 Da its ability to enter connective tissues rich in proteoglycans and interact with the resident cells has been questioned. In the present studies, experiments were undertaken to isolate and characterize proteins in human AC which have the potential to bind PPS. Thrombospondin was identified in 4.0 M GuHCl extracts of human AC as a PPS-binding protein. Furthermore, synovial fibroblasts derived from OA joints were shown to secrete thrombospondin and also bind PPS. Using bovine erythrocytes conjugated with PPS a rosetting of the synovial fibroblast could be demonstrated. The level of rosetting was not affected by pre-incubating cultures with thrombospondin antibody suggesting that PPS was interacting directly with the cells. Kinetic studies of 3H-PPS uptake by synovial fibroblasts showed saturation of binding sites within 30 min when cells were maintained at 4 degrees C but preservation of drug uptake for up to 120 min when cells were cultured at 37 degrees C. These data, together with the finding that cells labeled with drug at 37 degrees C showed higher incorporation, than at 4 degrees C after trypsin digestion suggests that PPS first binds to the cell membrane when at 37 degrees C is internalized, possibly by pinocytosis.

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.

Endocytosis, partial degradation and release of heparan sulfate by elicited mouse peritoneal macrophages

Interactions between glycosaminoglycans (GAGs) and low density lipoprotein (LDL) are thought to influence the progression of atherogenesis. In an effort to gauge whether macrophages mediate GAG-LDL interaction by GAG modification, we have investigated the endocytosis, degradation and retro-endocytosis of the GAG heparan sulfate (HS) by mouse peritoneal macrophages. Radiolabelled HS was produced by derivatization with sulfosuccinimidyl-3-(4-hydroxyphenyl) propionate and radio-iodination by the chloramine T method. The amount of 125I-HS internalized by cultures of thioglycollate-elicited macrophages rose over a 24 h time period in proportion to the amount of tracer added to the wells (2-2500 ng ml-1). Analysis of GAG molecular weight was performed using gel filtration chromatography and polyacrylamide gel electrophoresis. After a 24 h pulse period, the 125I-HS in the intracellular fraction of the cultured cells was of smaller molecular weight than for control material. During a 24 h cold chase, fragments of 125I-HS were released into the medium. These fragments had lower affinity for Polybrene-Sepharose but did not appear significantly N-desulfated as determined by low pH nitrous acid treatment. The NADPH oxidase inhibitor diphenylene iodonium, although minimizing basal and phorbol ester-triggered radical output, did not inhibit 125I-HS depolymerization. These data indicate that elicited macrophages can interact with and reduce the polymer length of HS without extensively desulfating the molecule. They are consistent with a mechanism by which the macrophage internalizes and partially degrades HS by endoglucuronidase activity rather than NADPH oxidase-generated free radicals, followed by release of the products into the extracellular milieu.

Accumulation of heparan sulfate in the culture of human melanoma cells with different metastatic ability

Glycosaminoglycans were metabolically labeled in subconfluent cultures of highly metastatic 7Gp122 and poorly metastatic IC8 variants and of the low metastatic parental M4Be human melanoma cell line. Proteoglycans were separated by DEAE Trisacryl chromatography from the culture medium, from the heparin extract of the cell layer and from the heparin-extracted cell residue lyzed with detergents. Glycosaminoglycans were released from the proteoglycans by reductive alkaline hydrolysis and heparan sulfate (HS) was detected by deaminative cleavage with nitrous acid. Expressed on cell protein basis, the labeled HS content in the medium and in the cell layer decreased with increasing metastatic ability. The extraction of HS with heparin from the 7Gp122 cells indicated that this variant was enriched in (polypeptide bound) HS non inserted into the plasma membrane, compared with the low metastatic IC8 and M4Be cells. The HS fraction in heparin extract and in the heparin-extracted cell residue exhibited molecular mass heterogeneity on gel permeation chromatography and it contained HS fragments. Scission with nitrous acid followed by molecular sieve chromatography of the degradation products indicated that the tetra- and disaccharide repeats separated by the N-sulfated glucosamine residue were present in about equal amounts and constituted 60% of the HS chains in the IC8 and M4Be cells. HS from 7Gp122, IC8 and M4Be cells did not bind antithrombin III with high affinity but it was capable of binding bFGF in in vitro assay.