Coordinate role for cell surface chondroitin sulfate proteoglycan and alpha 4 beta 1 integrin in mediating melanoma cell adhesion to fibronectin

Cellular recognition and adhesion to the extracellular matrix (ECM) has a complex molecular basis, involving both integrins and cell surface proteoglycans (PG). The current studies have used specific inhibitors of chondroitin sulfate proteoglycan (CSPG) synthesis along with anti-alpha 4 integrin subunit monoclonal antibodies to demonstrate that human melanoma cell adhesion to an A-chain derived, 33-kD carboxyl-terminal heparin binding fragment of human plasma fibronectin (FN) involves both cell surface CSPG and alpha 4 beta 1 integrin. A direct role for cell surface CSPG in mediating melanoma cell adhesion to this FN fragment was demonstrated by the identification of a cationic synthetic peptide, termed FN-C/H-III, within the fragment. FN-C/H-III is located close to the amino terminal end of the fragment, representing residues #1721-1736 of intact FN. FN-C/H-III binds CSPG directly, can inhibit CSPG binding to the fragment, and promotes melanoma cell adhesion by a CSPG-dependent, alpha 4 beta 1 integrin-independent mechanism. A scrambled version of FN-C/H-III does not inhibit CSPG binding or cell adhesion to the fragment or to FN-C/H-III, indicating that the primary sequence of FN-C/H-III is important for its biological properties. Previous studies have identified three other synthetic peptides from within this 33-kD FN fragment that promote cell adhesion by an arginyl-glycyl-aspartic acid (RGD) independent mechanism. Two of these synthetic peptides (FN-C/H-I and FN-C/H-II) bind heparin and promote cell adhesion, implicating cell surface PG in mediating cellular recognition of these two peptides. Additionally, a third synthetic peptide, CS1, is located in close proximity to FN-C/H-I and FN-C/H-II and it promotes cell adhesion by an alpha 4 beta 1 integrin-dependent mechanism. In contrast to FN-C/H-III, cellular recognition of these three peptides involved contributions from both CSPG and alpha 4 integrin subunits. Of particular importance are observations demonstrating that CS1-mediated melanoma cell adhesion could be inhibited by interfering with CSPG synthesis or expression. Since CS1 does not bind CSPG, the results suggest that CSPG may modify the function and/or activity of alpha 4 beta 1 integrin on the surface of human melanoma cells. Together, these results support a model in which the PG and integrin binding sites within the 33-kD fragment may act in concert to focus these two cell adhesion receptors into close proximity on the cell surface, thereby influencing initial cellular recognition events that contribute to melanoma cell adhesion on this fragment.     

Recognition of the A chain carboxy-terminal heparin binding region of fibronectin involves multiple sites: two contiguous sequences act independently to promote neural cell adhesion

Cellular interactions with fibronectin-treated substrata have a complex molecular basis involving multiple domains. A carboxy-terminal cell and heparin binding region of fibronectin (FN) is particularly interesting because it is a strong promoter of neurite outgrowth (Rogers, S.L., J.B. McCarthy, S.L. Palm, L.T. Furcht, and P.C. Letourneau, 1985. J. Neurosci. 5:369-378) and cell attachment (McCarthy, J.B., S.T. Hagen, and L.T. Furcht. 1986. J. Cell Biol. 102:179-188). To further understand the molecular mechanisms of neuronal interactions with this region of FN, we screened two peptides from the 33-kD heparin binding fragment of the FN A chain, FN-C/H II (KNNQKSEPLIGRKKT) and CS1 (Humphries, M.J., A. Komoriya, S.K. Akiyama, K. Olden, and K.M. Yamada. 1987. J. Biol. Chem. 262:6886-6892), for their ability to promote B104 neuroblastoma cell-substratum adhesion and neurite outgrowth. Both FN- C/H II and CS1 promoted B104 cell attachment in a concentration- dependent and saturable manner, with attachment to FN-C/H II exceeding attachment to CS1. In solution, both exogenous FN-C/H II or CS1 partially inhibited cell adhesion to the 33-kD fragment. Similar results were obtained with anti-FN-C/H II antibodies. In contrast, soluble GRGDSP did not affect B104 cell adhesion to FN-C/H II. These results indicate that both FN-C/H II and CS1 represent distinct, RGD- independent, cell adhesion-promoting sites active within the 33-kD fragment, and further define FN-C/H II as a novel neural recognition sequence in FN. B104 adhesion to FN-C/H II and CS1 differs in sensitivity to heparin, yet each peptide inhibited adhesion to the other peptide, suggesting cell adhesion is somehow related at the cellular level. Within the A chain 33-kD fragment, FN-C/H II and CS1 are contiguous, and might represent components of a larger domain with greater neurite-promoting activity since only the 33-kD fragment, and neither individual peptide, was effective at promoting B104 neurite outgrowth. These data further support the hypothesis that cell responses to FN are mediated by multiple sites involving both heparin- sensitive and -insensitive mechanisms.     

Heparan sulfate proteoglycan from the extracellular matrix of human lung fibroblasts. Isolation, purification, and core protein characterization

Confluent cultured human lung fibroblasts were labeled with 35SO4(2-). After 48 h of labeling, the pericellular matrix was prepared by Triton X-100 and deoxycholate extraction of the monolayers. Heparan sulfate proteoglycan (HSPG) accounted for nearly 80% of the total matrix [35S]proteoglycans. After solubilization in 6 M guanidinium HCl and cesium chloride density gradient centrifugation, the majority (78%) of these [35S] HSPG equilibrated at an average buoyant density of 1.35 g/ml. This major HSPG fraction was purified by ion-exchange chromatography on Mono Q and by gel filtration on Sepharose CL-4B, and further characterized by gel electrophoresis and immunoblotting. Intact [35S]HSPG eluted with Kav 0.1 from Sepharose CL-4B, whereas the protein-free [35S]heparan sulfate chains, obtained by alkaline borohydride treatment of the proteoglycan fractions, eluted with Kav 0.45 (Mr approximately 72,000). When analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography, core (protein) preparations, obtained by heparitinase digestion of 125I-labeled HSPG fractions, yielded one major labeled band with apparent molecular mass of approximately 300 kDa. Reduction with beta-mercaptoethanol slightly increased the apparent Mr of the labeled band, suggesting a single polypeptide structure and the presence of intrachain disulfide bonds. Immunoadsorption experiments and immunostaining of electrophoretically separated heparitinase-digested core proteins with monoclonal antibodies raised against matrix and cell surface-associated HSPG suggested that the major matrix-associated HSPG of cultured human lung fibroblasts is distinct from the HSPG that are anchored in the membranes of these cells. Binding studies suggested that this matrix HSPG interacts with several matrix components, both through its glycosaminoglycan chains and through its heparitinase-resistant core. Core (protein) interactions seem to be responsible for the association of the proteoglycan with the extracellular matrix.     

Multiple distinct membrane heparan sulfate proteoglycans in human lung fibroblasts

Heparitinase digestion of the hydrophobic membrane-associated heparan sulfate proteoglycans (HSPG) of fetal human lung fibroblasts yields core proteins of various sizes: i.e. monomeric core proteins of 125, 90, 64, 48, and 35 kDa and a disulfide-linked dimeric core protein composed of approximately 35-kDa subunits. By immunizing BALB/c mice with liposome-incorporated HSPG, we have obtained a total of five anti-HSPG monoclonal antibodies (Mabs, i.e. Mabs S1, 1C7, 2E9, 6G12, and 10H4) with different specificities. Polyacrylamide gel electrophoresis of 125I-labeled membrane HSPG immunoprecipitated with these Mabs revealed that Mabs 1C7 and 2E9 bind only membrane HSPG which yield a 125-kDa core protein after heparitinase digestion, whereas Mab S1-bound HSPG yield a 64-kDa core protein, and Mabs 6G12 and 10H4 retain membrane HSPG with a 48-kDa core protein. Western blotting of the heparitinase-digested proteoglycans and immunostaining with the Mabs confirmed this pattern of reactivity. However, in this assay, Mabs 6G12 and 10H4 also detected a minor approximately 90-kDa core protein in addition to the 48-kDa core protein. Except perhaps for the 10H4 epitope, the epitopes recognized by these Mabs appear to be part of the peptide moieties as they resisted complete deglycosylation of the HSPG with trifluoromethanesulfonic acid. Since these data were inconsistent with a direct relationship between the major core proteins, the 48-, 64-, and 125-kDa core proteins were immunopurified and further compared by peptide mapping with Staphylococcus aureus protease V8, trypsin, and CNBr cleavage. Clearly distinct peptide patterns were obtained for the three different core proteins. These results imply that the 48-, 64-, and the 125-kDa membrane HSPG core proteins of human lung fibroblasts are derived from distinct proteoglycans.     

Extracellular matrix heparan sulfate proteoglycans modulate the mitogenic capacity of acidic fibroblast growth factor

Confluent cultures of human endothelial cells deposit into extracellular matrix (ECM) distinct heparan sulfate proteoglycans (HSPG) which modulate acidic fibroblast growth factor's (aFGF) ability to stimulate human endothelial cell mitogenic capacity. Extracellular matrix 35S-HSPG were isolated from cultures metabolically labelled with Na235SO4 by DEAE-Sepharose, Sepharose CL-4B, and aFGF-Affi-Gel 15 column chromatography and identified by resistance to chondroitinase ABC and sensitivity to nitrous acid. Fifty to sixty percent of the 35S-HSPG deposited into ECM do not bind aFGF. The bound 35S-HSGP (40-50% of the total counts applied) eluted from the aFGF-Affi-Gel column after the addition of buffer containing 2 M NaCl. aFGF-binding and aFGF-nonbinding 35S-HSPG were individually pooled and further purified by Sepharose CL-4B column chromatography. 35S-HSPG which bind aFGF, designated HSPGP, were 100-fold superior to heparin in augmenting the mitogenic efficacy of aFGF in sparse proliferating cultures. In contrast, however, 35S-HSPG, which did not bind aFGF, designated HSPG1, inhibited aFGF-stimulated proliferation in both sparse and subconfluent endothelial cell cultures. The majority of the biological activity of both aFGF-potentiating HSPGP and aFGF-inhibitory HSPG1 was contained in the glycosaminoglycan chains released by alkaline borohydride treatment of intact HSPGP or HSPG1, respectively. 3H-Core protein derived from HSPGP or HSPG1 contained only minor biological activity. The ability of heparitinase or heparinase (Flavobacterium heparinum) to abolish biological activity differed, depending upon the HSPG tested, also suggested that these are two distinct HSPGs.     

RGD-independent cell adhesion to the carboxy-terminal heparin-binding fragment of fibronectin involves heparin-dependent and -independent activities

Cell adhesion to extracellular matrix components such as fibronectin has a complex basis, involving multiple determinants on the molecule that react with discrete cell surface macromolecules. Our previous results have demonstrated that normal and transformed cells adhere and spread on a 33-kD heparin binding fragment that originates from the carboxy-terminal end of particular isoforms (A-chains) of human fibronectin. This fragment promotes melanoma adhesion and spreading in an arginyl-glycyl-aspartyl-serine (RGDS) independent manner, suggesting that cell adhesion to this region of fibronectin is independent of the typical RGD/integrin-mediated binding. Two synthetic peptides from this region of fibronectin were recently identified that bound [3H]heparin in a solid-phase assay and promoted the adhesion and spreading of melanoma cells (McCarthy, J. B., M. K. Chelberg, D. J. Mickelson, and L. T. Furcht. 1988. Biochemistry. 27:1380-1388). The current studies further define the cell adhesion and heparin binding properties of one of these synthetic peptides. This peptide, termed peptide I, has the sequence YEKPGSP-PREVVPRPRPGV and represents residues 1906-1924 of human plasma fibronectin. In addition to promoting RGD-independent melanoma adhesion and spreading in a concentration-dependent manner, this peptide significantly inhibited cell adhesion to the 33-kD fragment or intact fibronectin. Polyclonal antibodies generated against peptide I also significantly inhibited cell adhesion to the peptide, to the 33-kD fragment, but had minimal effect on melanoma adhesion to fibronectin. Anti-peptide I antibodies also partially inhibited [3H]heparin binding to fibronectin, suggesting that peptide I represents a major heparin binding domain on the intact molecule. The cell adhesion activity of another peptide from the 33-kD fragment, termed CS1 (Humphries, M. J., A. Komoriya, S. K. Akiyama, K. Olden, and K. M. Yamada. 1987. J. Biol. Chem., 262:6886-6892) was contrasted with peptide I. Whereas both peptides promoted RGD-independent cell adhesion, peptide CS1 failed to bind heparin, and exogenous peptide CS1 failed to inhibit peptide I-mediated cell adhesion. The results demonstrate a role for distinct heparin-dependent and -independent cell adhesion determinants on the 33-kD fragment, neither of which are related to the RGD-dependent integrin interaction with fibronectin.     

Partial characterization of proteoglycans synthesized by human glomerular epithelial cells in culture

Confluent adult and fetal human glomerular epithelial cells were incubated for 24 h in the presence of [3H]-amino acids and [35S]sulfate. Two heparan-35SO4 proteoglycans were released into the culture medium. These 35S-labeled proteoglycans eluted as a single peak from anion exchange chromatographic columns, but were separable by gel filtration on Sepharose CL-6B columns. The larger heparan-35SO4 proteoglycan eluted with the column void volume and at a Kav of 0.26 from Sepharose CL-4B columns. The most abundant medium heparan-35SO4 proteoglycan was a high buoyant density proteoglycan similar in hydrodynamic size (Sepharose CL-6B Kav 0.23) to those previously described in glomerular basement membranes and isolated glomeruli. Heparan-35SO4 chains from both proteoglycans were 36 kDa. A smaller proportion of Sepharose CL-6B excluded dermatan-35SO4 proteoglycan was also synthesized by these cells. The predominant protein cores of both medium heparan-35SO4 proteoglycans were approximately 230 and 180 kDa. A hybrid chondroitin/dermatan-heparan-35SO4 proteoglycan with an 80-kDa protein core copurified with the smaller medium heparan-35SO4 proteoglycan. This 35S-labeled proteoglycan appeared as a diffuse, chondroitinase ABC sensitive 155-kDa fluorographic band in sodium dodecyl sulfate-polyacrylamide gels after the Sepharose CL-6B Kav 0.23 35S-labeled proteoglycan fraction was digested with heparitinase. The heparitinase generated heparan sulfate proteoglycan protein cores and the 155-kDa hybrid proteoglycan fragment had molecular weights similar to those previously identified in rat glomerular basement membrane and glomeruli using antibodies against a basement membrane tumor proteoglycan precursor (Klein et al. J. Cell Biol. 106, 963-970, 1988). Thus, human glomerular epithelial cells in culture are capable of synthesizing, processing, and releasing heparan sulfate proteoglycans which are similar to those synthesized in vivo and found in the glomerular basement membrane. These proteoglycans may belong to a family of related basement membrane proteoglycans.     

Interaction of heparin with a synthetic pentadecapeptide from the C-terminal heparin-binding domain of fibronectin

The synthetic pentadecapeptide FN-C/H II (KNNQKSEPLIGRKKT-NH(2)) has the sequence of the carboxy-terminal heparin-binding domain of module III(14) of fibronectin. Interaction of FN-C/H II with bovine lung heparin has been studied by (1)H and (23)Na NMR spectroscopy and by heparin affinity chromatography. FN-C/H II binds to heparin from pD <2 up to pD approximately 10; at higher pD, the binding decreases as the lysine side-chain ammonium groups are titrated. Na(+) counterions are displaced from the counterion condensation volume that surrounds sodium heparinate by FN-C/H II, which provides direct evidence that the binding involves electrostatic interactions. The pK(A) values for each of the five ammonium groups of FN-C/H II increase upon binding to heparin which, together with chemical shift data, indicates that the binding involves both delocalized and direct electrostatic interactions between ammonium groups of FN-C/H II and carboxylate and/or sulfate groups of heparin. NMR data also provide evidence for the direct interaction of the guanidinium group of the arginine side chain with anionic sites on heparin. The affinity of heparin for FN-C/H II and for 13 analogue peptides in which lysine and arginine residues were systematically substituted with alanine increases as the number of basic residues increases. The relative contribution of each lysine and arginine to the affinity of heparin for FN-C/H II is R(12) > K(13) > K(14) > K(1) > K(5). Nuclear Overhauser enhancement (NOE) data indicate that, while FN-C/H II is largely unstructured in aqueous solution, the bound peptide interconverts among overlapping, turn-like conformations over the L(9) - T(15) segment of the peptide. NOE data for the interaction of FN-C/H II with a heparin-derived hexasaccharide, together with the number of Na(+) ions displaced from heparin by FN-C/H II as determined by (23)Na NMR, indicates that the peptide binds to a hexasaccharide segment of heparin. Identical NMR and heparin affinity chromatography results were obtained for the interaction of FN-C/H II and its D-amino acid analogue peptide with heparin, which is of interest for the potential use of peptides as therapeutic agents for diseases in which cell adhesion plays a critical role.     

硫酸乙酰肝素蛋白聚糖对培养人脐静脉内皮细胞合成蛋白聚糖的影响

以[35S」-Na2SO4为示踪物,观察人正常主动脉中的硫酸乙酸肝素蛋白聚糖（HSPG）对培养的第一代人脐静脉内皮细胞（hUVEC）合成蛋白聚糖（PG）的影响．用解聚提取法及离子交换柱层析分离人主动脉HSPG．35S-PGs的混合物用离子交换及凝胶过滤柱层析法分离35S-HSPG,35S-硫酸软骨素-硫酸皮肤素PG（35S-CSDSPG）及35S-硫酸皮肤素PG（35S-DSPG）．结果发现实验组（加HSPG）与对照组（未加HSPG）相比,hU-VEC的35S-PGs总量（培养液+细胞层）无差别,但实验组培养液中35S-PGs总量升高、35S-DSPG、35S-CSDSPG及其相对百分含量均升高,而35S-HSPG及其百分含量降低．细胞层的35S-PGs,35S-HSPG及其相对百分含量降低,35S-DSPG及其相对百分含量升高,而CSDSPG未见差别．     

Heparan sulfate proteoglycans of human lung fibroblasts. Structural heterogeneity of the core proteins of the hydrophobic cell-associated forms

Heparan sulfate proteoglycans (HSPG) were solubilized from human lung fibroblast monolayers with detergent. Presumptive membrane-associated forms displaying hydrophobic properties were purified by gel filtration on Sepharose CL-4B, by ion-exchange chromatography on Mono Q and by incorporation in lipid vesicles. The HSPG preparations were 125I-iodinated and treated with heparitinase before sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Five radiolabeled proteins with apparent molecular weights of 125,000, 90,000, 64,000, 48,000, and 35,000 were visualized by autoradiography. A sixth protein, identified in nonreduced 125I-HSPG preparations, appeared as a non-HS chain-bearing Mr 35,000 peptide which was disulfide-linked to an HS chain-bearing peptide of similar size. This multiplicity of core proteins did not seem to result from proteolysis during the heparitinase treatment itself, since some of the core proteins migrated independently during gel filtration before heparitinase digestion. Moreover, heparitinase digestion of 125I-HSPG purified by affinity chromatography on an immobilized monoclonal antibody yielded only the Mr 64,000 protein. Alternative depolymerizations of the HS chains by heparinase or HNO2 also yielded multiple protein bands. These results imply that heterogeneity of the core protein moiety may be a genuine property of the hydrophobic HSPG of human lung fibroblasts. The occurrence of multiple integral membrane HSPG forms may be relevant for the multiple functions that have been ascribed to cell-surface HSPG.     

Purification and analysis of the core protein of the protease-resistant intracellular chondroitin sulfate E proteoglycan from the interleukin 3-dependent mouse mast cell

Chondroitin sulfate E proteoglycan was extracted in the presence of protease inhibitors from 6 X 10(9) mouse bone marrow-derived, interleukin 3-dependent mast cells, of which 3 X 10(7) had been biosynthetically labeled with [35S]sulfate or [3H]glycine. Chondroitin sulfate E proteoglycan was purified to apparent homogeneity by density-gradient centrifugation, differential molecular weight dialysis, DEAE-52 ion exchange chromatography, and Sepharose CL-4B gel filtration chromatography. Chondroitin sulfate E proteoglycan, radiolabeled with [3H]glycine or [35S]sulfate, filtered as a single peak of radioactivity on Sepharose CL-4B with a Kav of 0.41. When purified [3H]glycine-labeled proteoglycan was digested with chondroitinase ABC and subjected to gel filtration, all of the radioactivity was shifted to a lower molecular weight. As assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis the Mr of the peptide core obtained by chondroitinase ABC treatment was approximately 10,000. The purified proteoglycan was resistant to degradation by collagenase, clostripain, trypsin, chymotrypsin, elastase, chymopapain, V8 protease, proteinase K, and Pronase, as assessed by gel filtration chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Analysis of the core peptide of the intact proteoglycan revealed that glycine, serine, and glutamic acid/glutamine accounted for 70% of the total amino acids and were present in a molar ratio of 4.3/1.6/1.0. When analyzed for neutral hexose content by gas-liquid chromatography, the proteoglycan contained approximately 2% of its weight as mannose, fucose, galactose, and other sugars, indicating that oligosaccharides were linked to the peptide core. The mouse bone marrow-derived mast cell chondroitin sulfate E proteoglycan, like the rat serosal mast cell heparin proteoglycan, is markedly protease resistant, has highly sulfated glycosaminoglycans, and contains a peptide core that is rich in serine and glycine. These characteristics of the mast cell class of intracellular proteoglycans may contribute to their function in stimulus-induced granule secretion as well as in mediator storage, including retention of cationic neutral proteases.     

A cell surface chondroitin sulfate proteoglycan, immunologically related to CD44, is involved in type I collagen-mediated melanoma cell motility and invasion

The metastatic spread of tumor cells occurs through a complex series of events, one of which involves the adhesion of tumor cells to extracellular matrix (ECM) components. Multiple interactions between cell surface receptors of an adherent tumor cell and the surrounding ECM contribute to cell motility and invasion. The current studies evaluate the role of a cell surface chondroitin sulfate proteoglycan (CSPG) in the adhesion, motility, and invasive behavior of a highly metastatic mouse melanoma cell line (K1735 M4) on type I collagen matrices. By blocking mouse melanoma cell production of CSPG with p-nitrophenyl beta-D-xylopyranoside (beta-D-xyloside), a compound that uncouples chondroitin sulfate from CSPG core protein synthesis, we observed a corresponding decrease in melanoma cell motility on type I collagen and invasive behavior into type I collagen gels. Melanoma cell motility on type I collagen could also be inhibited by removing cell surface chondroitin sulfate with chondroitinase. In contrast, type I collagen-mediated melanoma cell adhesion and spreading were not affected by either beta-D-xyloside or chondroitinase treatments. These results suggest that mouse melanoma CSPG is not a primary cell adhesion receptor, but may play a role in melanoma cell motility and invasion at the level of cellular translocation. Furthermore, purified mouse melanoma cell surface CSPG was shown, by affinity chromatography and in solid phase binding assays, to bind to type I collagen and this interaction was shown to be mediated, at least in part, by chondroitin sulfate. Additionally we have determined that mouse melanoma CSPG is composed of a 110-kD core protein that is recognized by anti-CD44 antibodies on Western blots. Collectively, our data suggests that interactions between a cell surface CD44-related CSPG and type I collagen in the ECM may play an important role in mouse melanoma cell motility and invasion, and that the chondroitin sulfate portion of the proteoglycan seems to be a critical component in mediating this effect.     

Correlation between cell substrate attachment in vitro and cell surface heparan sulfate affinity for fibronectin and collagen

Heparan sulfate glycosaminoglycan, isolated from the cell surface of nonadhering murine myeloma cells (P3X63-Ag8653), does not bind to plasma fibronectin, but binds partially to collagen type I, as assayed by affinity chromatography with proteins immobilized on cyanogen bromide-activated Sepharose 4B. Identical results were obtained when myeloma heparan sulfate was cochromatographed, on the same fibronectin and collagen columns, with cell surface heparan sulfates collagen columns, with cell surface heparan sulfates from adhering Swiss mouse 3T3 and SV3T3 cells. These latter heparan sulfates do, however, bind to both fibronectin and collagen, as reported earlier (Stamatoglou, S.C., and J.M. Keller, 1981, Biochim. Biophys. Acta., 719:90-97). Cell adhesion assays established that hydrated collagen substrata can support myeloma cell attachment, but fibronectin cannot. Saturation of the heparan sulfate binding sites on the collagen substrata with heparan sulfate or heparin, prior to cell inoculation, abolished the ability to support cell adhesion, whereas chondroitin 4 sulfate, chondroitin 6 sulfate, and hyaluronic acid had no effect.     

A peptide derived from tenascin-C induces beta1 integrin activation through syndecan-4

Tenascin-C (TN-C) is unique for its cell adhesion modulatory function. We have shown that TNIIIA2, a synthetic 22-mer peptide derived from TN-C, stimulated beta1 integrin-mediated cell adhesion of nonadherent and adherent cell types, by inducing activation of beta1 integrin. The active site of TNIIIA2 appeared cryptic in the TN-C molecule but was exposed by MMP-2 processing of TN-C. The following results suggest that cell surface heparan sulfate (HS) proteoglycan (HSPG), including syndecan-4, participated in TNIIIA2-induced beta1 integrin activation: 1) TNIIIA2 bound to cell surface HSPG via its HS chains, as examined by photoaffinity labeling; 2) heparitinase I treatment of cells abrogated beta1 integrin activation induced by TNIIIA2; 3) syndecan-4 was isolated by affinity chromatography using TNIIIA2-immobilized beads; 4) small interfering RNA-based down-regulation of syndecan-4 expression reduced TNIIIA2-induced beta1 integrin activation, and consequent cell adhesion to fibronectin; 5) overexpression of syndecan-4 core protein enhanced TNIIIA2-induced activation of beta1 integrin. However, treatments that targeted the cytoplasmic region of syndecan-4, including ectopic expression of its mutant truncated with the cytoplasmic domains and treatment with protein kinase Calpha inhibitor G?6976, did not influence the TNIIIA2 activity. These results suggest that a TNIIIA2-related matricryptic site of the TN-C molecule, exposed by MMP-2 processing, may have bound to syndecan-4 via its HS chains and then induced conformational change in beta1 integrin necessary for its functional activation. A lateral interaction of beta1 integrin with the extracellular region of the syndecan-4 molecule may be involved in this conformation change.     

Identification of an alternatively spliced site in human plasma fibronectin that mediates cell type-specific adhesion

We have compared the molecular specificities of the adhesive interactions of melanoma and fibroblastic cells with fibronectin. Several striking differences were found in the sensitivity of the two cell types to inhibition by a series of synthetic peptides modeled on the Arg-Gly-Asp-Ser (RGDS) tetrapeptide adhesion signal. Further evidence for differences between the melanoma and fibroblastic cell adhesion systems was obtained by examining adhesion to proteolytic fragments of fibronectin. Fibroblastic BHK cells spread readily on fl3, a 75-kD fragment representing the RGDS-containing, "cell-binding" domain of fibronectin, but B16-F10 melanoma cells could not. The melanoma cells were able to spread instead on f9, a 113-kD fragment derived from the large subunit of fibronectin that contains at least part of the type III connecting segment difference region (or "V" region); f7, a fragment from the small fibronectin subunit that lacks this alternatively spliced polypeptide was inactive. Monoclonal antibody and fl3 inhibition experiments confirmed the inability of the melanoma cells to use the RGDS sequence; neither molecule affected melanoma cell spreading, but both completely abrogated fibroblast adhesion. By systematic analysis of a series of six overlapping synthetic peptides spanning the entire type III connecting segment, a novel attachment site was identified in a peptide near the COOH- terminus of this region. The tetrapeptide sequence Arg-Glu-Asp-Val (REDV), which is somewhat related to RGDS, was present in this peptide in a highly hydrophilic region of the type III connecting segment. REDV appeared to be functionally important, since this synthetic tetrapeptide was inhibitory for melanoma cell adhesion to fibronectin but was inactive for fibroblastic cell adhesion. REDV therefore represents a novel adhesive recognition signal in fibronectin that possesses cell type specificity. These results suggest that, for some cell types, regulation of the adhesion-promoting activity of fibronectin may occur by alternative mRNA splicing.     

Aggregated proteoglycan synthesis in organ cultures of human nucleus pulposus.

Proteoglycans isolated under associative conditions in the presence of protease inhibitors from human nucleus pulposus contained 17% aggregate and 83% non-aggregating monomer (Kav = 0.5 on Sepharose CL-2B). Isolated aggregate after reduction and alkylation was resolved into two components (Kav = 0.15 and 0.43) on Sepharose CL-2B. Labeled proteoglycans isolated from parallel samples pulsed with [35S]sulfate and chased for up to 18 h were present largely as aggregated material (up to 78%). Reduction and alkylation of the labeled samples gave a labeled proteoglycan monomer with Kav = 0.15. Both the labeled and unlabeled chondroitin sulfate chains had the same distribution on Sepharose CL-6B and equivalent molecular weights (Mr = 2.0 x 10(3)). After chondroitinase ABC digestion, the unlabeled keratan sulfate-protein core was polydisperse with a Kav = 0.38 on Sepharose CL-4B while the labeled keratan sulfate-protein core had a Kav = 0.05. This indicates that the newly synthesized proteoglycan had a large core protein and suggests that the proteoglycans present in nucleus pulposus are originally synthesized as large molecular weight, aggregating proteoglycans.     

Ovarian carcinoma cells synthesize both chondroitin sulfate and heparan sulfate cell surface proteoglycans that mediate cell adhesion to interstitial matrix

Metastatic ovarian carcinoma metastasizes by intra-peritoneal, non-hematogenous dissemination. The adhesion of the ovarian carcinoma cells to extracellular matrix components, such as types I and III collagen and cellular fibronectin, is essential for intra-peritoneal dissemination. The purpose of this study was to determine whether cell surface proteoglycans (a class of matrix receptors) are produced by ovarian carcinoma cells, and whether these proteoglycans have a role in the adhesion of ovarian carcinoma cells to types I and III collagen and fibronectin. Proteoglycans were metabolically labeled for biochemical studies. Both phosphatidylinositol-anchored and integral membrane-type cell surface proteoglycans were found to be present on the SK-OV-3 and NIH:OVCAR-3 cell lines. Three proteoglycan populations of differing hydrodynamic size were detected in both SK-OV-3 and NIH:OVCAR-3 cells. Digestions with heparitinase and chondroitinase ABC showed that cell surface proteoglycans of SK-OV-3 cells had higher proportion of chondroitin sulfate proteoglycans (75:25 of chondroitin sulfate:heparan sulfate ratio), while NIH:OVCAR-3 cells had higher proportion of heparan sulfate proteoglycans (10:90 of chondroitin sulfate:heparan sulfate ratio). RT-PCR indicated the synthesis of a unique assortment of syndecans, glypicans, and CD44 by the two cell lines. In adhesion assays performed on matrix-coated titer plates both cell lines adhered to types I and III collagen and cellular fibronectin, and cell adhesion was inhibited by preincubation of the matrix with heparin, heparan sulfate, chondroitin sulfate, dermatan sulfate, or chondroitin glycosaminoglycans. Treatment of the cells with heparitinase, chondroitinase ABC, or methylumbelliferyl xyloside also interfered with adhesion confirming the role of both heparan sulfate and chondroitin sulfate cell surface proteoglycans as matrix receptors on ovarian carcinoma cells.     

Membrane-associated chondroitin sulfate proteoglycans of human lung fibroblasts

Cultured human fetal lung fibroblasts produce some chondroitin sulfate proteoglycans that are extracted as an aggregate in chaotropic buffers containing 4 M guanidinium chloride. The aggregated proteoglycans are excluded from Sepharose CL4B and 2B, but become included, eluting with a Kav value of 0.53 from Sepharose CL4B, when Triton X-100 is included in the buffer. Conversely, some of the detergent-extractable chondroitin sulfate proteoglycans can be incorporated into liposomes, suggesting the existence of a hydrophobic membrane-intercalated chondroitin sulfate proteoglycan fraction. Purified preparations of hydrophobic chondroitin sulfate proteoglycans contain two major core protein forms of 90 and 52 kD. A monoclonal antibody (F58-7D8) obtained from the fusion of myeloma cells with spleen cells of BALB/c mice that were immunized with hydrophobic proteoglycans recognized the 90- but not the 52-kD core protein. The epitope that is recognized by the antibody is exposed at the surface of cultured human lung fibroblasts and at the surface of several stromal cells in vivo, but also at the surface of Kupffer cells and of epidermal cells. The core proteins of these small membrane-associated chondroitin sulfate proteoglycans are probably distinct from those previously identified in human fibroblasts by biochemical, immunological, and molecular biological approaches.     

Human fibronectin contains distinct adhesion- and motility-promoting domains for metastatic melanoma cells

The active migration of tumor cells through extracellular matrices has been proposed to play a role in certain aspects of metastasis. Metastatic tumor cells migrate in vitro in response to substratum-bound adhesive glycoproteins such as fibronectin. The present studies use affinity-purified proteolytic fragments of fibronectin to determine the nature of adhesion- and/or motility-promoting domains within the protein. Two distinct fragments were identified with cell adhesion-promoting activities. By a number of criteria, the adhesive activity promoted by these two fragments was distinct. One fragment, a 75-kD tryptic fragment purified by monoclonal antibody chromatography, promoted the adhesion, spreading, and haptotactic motility of melanoma cells. Experiments using a synthetic cell attachment peptide in solution indicated that at least part of the attachment activity exhibited by the 75-kD fragment is mediated by the sequence arg-gly-asp-ser. It was not possible to demonstrate migration-stimulating activity using a small (11.5 kD) peptic fragment containing this sequence (Pierschbacher, M.D., E. G. Hayman, and E. Ruoslahti, 1981, Cell, 26:259-267) suggesting that another cell-binding activity within the 75 kD fragment distinct from arg-gly-asp-ser might be required for motility. The second fragment that stimulated melanoma adhesion was a 33-kD tryptic/catheptic carboxyl-terminal heparin-binding fragment, which is localized to the A chain of fibronectin. This fragment promotes adhesion and spreading but not the motility of these cells. Melanoma adhesion to this heparin-binding fragment was sensitive to the effects of cycloheximide, which contrasted adhesion to the haptotaxis-promoting fragment. Importantly, these studies illustrate that haptotaxis in response to fibronectin is not due to simple adhesion gradients of this protein. The results are discussed in light of a model for multiple distinct cell surface constituents mediating cell adhesion and motility on fibronectin.     

Human basement membrane heparan sulfate proteoglycan core protein: a 467-kD protein containing multiple domains resembling elements of the low density lipoprotein receptor, laminin, neural cell adhesion molecules, and epidermal growth factor

The primary structure of the large human basement membrane heparan sulfate proteoglycan (HSPG) core protein was determined from cDNA clones. The cDNA sequence codes for a 467-kD protein with a 21-residue signal peptide. Analysis of the amino acid sequence showed that the protein consists of five domains. The amino-terminal domain I contains three putative heparan sulfate attachment sites; domain II has four LDL receptor-like repeats; domain III contains repeats similar to those in the short arms of laminin; domain IV has lg-like repeats resembling those in neural cell adhesion molecules; and domain V contains sequences resembling repeats in the G domain of the laminin A chain and repeats in the EGF. The domain structure of the human basement membrane HSPG core protein suggests that this mosaic protein has evolved through shuffling of at least four different functional elements previously identified in other proteins and through duplication of these elements to form the functional domains. Comparison of the human amino acid sequence with a partial amino acid sequence from the corresponding mouse protein (Noonan, D. M., E. A. Horigan, S. R. Ledbetter, G. Vogeli, M. Sasaki, Y. Yamada, and J. R. Hassell. 1988. J. Biol. Chem. 263:16379-16387) shows a major difference between the species in domain IV, which contains the Ig repeats: seven additional repeats are found in the human protein inserted in the middle of the second repeat in the mouse sequence. This suggests either alternative splicing or a very recent duplication event in evolution. The multidomain structure of the basement membrane HSPG implies a versatile role for this protein. The heparan sulfate chains presumably participate in the selective permeability of basement membranes and, additionally, the core protein may be involved in a number of biological functions such as cell binding, LDL-metabolism, basement membrane assembly, calcium binding, and growth- and neurite-promoting activities.