Endothelial cell heparanase modulation of lipoprotein lipase activity. Evidence that heparan sulfate oligosaccharide is an extracellular chaperone

Mammalian heparanase: gene cloning, expression and function in tumor progression and metastasis

Heparan sulfate proteoglycans interact with many extracellular matrix constituents, growth factors and enzymes. Degradation of heparan sulfate by endoglycosidic heparanase cleavage affects a variety of biological processes. We have purified a 50-kDa heparanase from human hepatoma and placenta, and now report cloning of the cDNA and gene encoding this enzyme. Expression of the cloned cDNA in insect and mammalian cells yielded 65-kDa and 50-kDa recombinant heparanase proteins. The 50-kDa enzyme represents an N-terminally processed enzyme, at least 100-fold more active than the 65-kDa form. The heparanase mRNA and protein are preferentially expressed in metastatic cell lines and specimens of human breast, colon and liver carcinomas. Low metastatic murine T-lymphoma and melanoma cells transfected with the heparanase cDNA acquired a highly metastatic phenotype in vivo, reflected by a massive liver and lung colonization. This represents the first cloned mammalian heparanase, to our knowledge, and provides direct evidence for its role in tumor metastasis. Cloning of the heparanase gene enables the development of specific molecular probes for early detection and treatment of cancer metastasis and autoimmune disorders.

Apolipoprotein E containing high density lipoprotein stimulates endothelial production of heparan sulfate rich in biologically active heparin-like domains. A potential mechanism for the anti-atherogenic actions of vascular apolipoprotein e

Reduced heparin and heparan sulfate (HS) proteoglycans (PG) have been observed in both inflammation and atherosclerosis. Methods to increase endogenous heparin and heparan sulfate are not known. We found that incubation of endothelial cells with 500-1,000 micrograms/ml high density lipoprotein (HDL) increased 35SO4 incorporation into PG by 1.5-2.5-fold. A major portion of this increase was in HS and was the result of increased synthesis. Total PG core proteins were not altered by HDL; however, the ratio of 35SO4 to [3H]glucosamine was increased by HDL, suggesting increased sulfation of glycosaminoglycans. In addition, HDL increased the amount of highly sulfated heparin-like HS in the subendothelial matrix. HS from HDL-treated cells bound 40 +/- 5% more 125I-antithrombin III (requires 3-O sulfated HS) and 49 +/- 3% fewer monocytes. Moreover, the HS isolated from HDL-treated cells inhibited smooth muscle cell proliferation (by 83 +/- 5%) better than control HS (56 +/- 6%) and heparin (42 +/- 6%). HDL isolated from apolipoprotein E (apoE)-null mice did not stimulate HS production unless apoE was added. ApoE also stimulated HS production in the absence of HDL. ApoE did not increase 35SO4 incorporation in macrophages and fibroblasts, suggesting that this is an endothelial cell-specific process. Receptor-associated protein inhibited apoE-mediated stimulation of HS only at higher (20 micrograms/ml) doses, suggesting the involvement of a receptor-associated protein-sensitive pathway in mediating apoE actions. In summary, our data identify a novel mechanism by which apoE and apoE-containing HDL can be anti-atherogenic. Identification of specific apoE peptides that stimulate endothelial heparin/HS production may have important therapeutic applications.

Partial purification of heparanase activities in Chinese hamster ovary cells: evidence for multiple intracellular heparanases

Heparanases are mammalian endoglycosidases that cleave heparan sulphate glycosaminoglycans from proteoglycan core proteins and degrade them into shorter chains. The enzymes have been proposed to act in a variety of cellular processes, including proteoglycan catabolism, remodelling of basement membranes and release of heparan sulphate-binding ligands from their extracellular storage sites. Additional functions for heparanases may be to generate short heparan sulphate chains that stabilize or activate other proteins. While heparanase activities have been described in a number of tissues and cell lines, it is not known how many different enzymes are responsible for these activities. Our recent studies characterizing the short glycosaminoglycans produced in Chinese hamster ovary (CHO) cells suggested that multiple heparanases are necessary for the formation of the short heparan sulphate chains [Bame and Robson (1997) J. Biol. Chem. 272, 2245-2251]. We examined whether this is the case by purifying heparanase activity from CHO cell homogenates. Based on their ability to bind ion-exchange resins and their elution from gel-filtration columns, four separate heparanase activities were partially purified. All four activities cleave free glycosaminoglycans over a broad pH range of 3.5-6.0 or 6. 5, suggesting that they act in the endosomal/lysosomal pathway. The sizes of the short heparan sulphate chains generated by the partially purified heparanases ranged from 6 to 9 kDa, and for two of the activities the product size is pH-dependent. Three of the four activities degrade proteoglycans as well as the free glycosaminoglycan chain. Interestingly, all four enzymes generate short glycosaminoglycans with a sulphate-rich, modified domain at the non-reducing end of the newly formed chain. Since our previous studies showed that in CHO cells there is also a population of short heparan sulphates with a modified domain at the reducing end of the chain, this suggests that there may be another heparanase in CHO cells that was not purified. Alternatively, our findings suggest that the formation of short heparan sulphate glycosaminoglycans inside CHO cells may be a result of the concerted action of multiple heparanases, and may depend on the proportions of the different enzymes and the environment in which the chains are degraded.

Oligosaccharide sequence of human breast cancer cell heparan sulfate with high affinity for laminin

Laminin-1 is a basement membrane glycoprotein implicated in tumor-host adhesion, which involves the cell-binding domain(s) of laminin-1 and tumor cell surface heparan sulfate (HS). The specific tumor cell surface HS oligosaccharide sequences that are necessary for binding to laminin-1 have not been characterized. To identify this laminin-binding oligosaccharide sequence, GlcNSO4-rich oligosaccharides terminating with [3H]2,5-anhydromannitol (AManR) residues were isolated from human breast cancer cell (MCF-7)-derived HS through hydrazinolysis/high pH (4.0) nitrous acid treatment/[3H]NaBH4 reduction. These oligosaccharides were chromatographed on a laminin-1 affinity column. A high affinity dodecasaccharide was isolated and characterized. Disaccharide analysis yielded IdoA(2-SO4) --> AManR(6-SO4) as the only disaccharide upon treatment of this dodecasaccharide with nitrous acid at low pH (1.5). The sequence of laminin-binding high affinity oligosaccharide is therefore [IdoA(2-SO4) --> GlcNSO4(6-SO4)]5[IdoA(2-SO4) --> AManR(6-SO4)]. Low affinity dodecasaccharides composed of [IdoA(2-SO4) --> GlcNSO4(6-SO4)]5, [IdoA(2-SO4) --> GlcNSO4] were also isolated by laminin-1 affinity chromatography. Molecular modeling studies indicate that a heparin-binding peptide sequence corresponding to amino acid residues 3010-3031 (KQNCLSSRASFRGCVRNLRLSR) in the G domain of laminin-1, modeled as a right-handed alpha-helix, carries an array of basic residues well placed to bind to clusters of sulfate groups on the high affinity dodecasaccharide.

Substrate specificity of heparanases from human hepatoma and platelets

Heparan sulfate proteoglycans, attached to cell surfaces or in the extracellular matrix, interact with a multitude of proteins via their heparan sulfate side chains. Degradation of these chains by limited (endoglycosidic) heparanase cleavage is believed to affect a variety of biological processes. Although the occurrence of heparanase activity in mammalian tissues has been recognized for many years, the molecular characteristics and substrate recognition properties of the enzyme(s) have remained elusive. In the present study, the substrate specificity and cleavage site of heparanase from human hepatoma and platelets were investigated. Both enzyme preparations were found to cleave the single beta-D-glucuronidic linkage of a heparin octasaccharide. A capsular polysaccharide from Escherichia coli K5, with the same (-GlcUAbeta1,4-GlcNAcalpha1,4-)n structure as the unmodified backbone of heparan sulfate, resisted heparanase degradation in its native state as well as after chemical N-deacetylation/N-sulfation or partial enzymatic C-5 epimerization of beta-D-GlcUA to alpha-L-IdceA. By contrast, a chemically O-sulfated (but still N-acetylated) K5 derivative was susceptible to heparanase cleavage. O-Sulfate groups, but not N-sulfate or IdceA residues, thus are essential for substrate recognition by the heparanase(s). In particular, selective O-desulfation of the heparin octasaccharide implicated a 2-O-sulfate group on a hexuronic acid residue located two monosaccharide units from the cleavage site, toward the reducing end.