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.

Bovine aortic and corneal endothelial cells synthesize a growth factor that remains mostly cell-associated but can also be extracted from the subendothelial extracellular matrix (ECM) deposited by these cells. The endothelial cellderived growth factors extracted from cell lysates and from the extracellular matrix appear to be structurally related to basic fibroblast growth factor by the criteria that they (i) bind to heparin-Sepharose and are eluted at 1.4-1.6 M NaCl, (ii) have a molecular weight of about 18,400, (iii) cross-react with anti-basic fibroblast growth factor antibodies when analyzed by electrophoretic blotting and immunoprecipitation, and (iv) are potent mitogens for bovine aortic and capillary endothelial cells. It is suggested that endothelium can store growth factors capable of autocrine growth promotion in two ways: by sequestering growth factor within the cell and by incorporating it into the underlying extracellular matrix.

Extracellular matrix (ECM) and basement membranes (BMs) present a physical barrier that requires enzymatic degradation during endothelial cell (EC) sprouting at early stages of angiogenesis. These multimolecular structures also serve as a storage depot for heparin-binding angiogenic factors. Heparan sulfate proteoglycans (HSPGs) are responsible for the self-assembly and integrity of the ECM and BM structure, as well as for sequestration of growth and differentiation factors. Recently, we reported the cloning of heparanase, an endo-β-Dglucuronidase degrading heparan sulfate (HS), and provided direct evidence for its role in tumor metastasis. We now demonstrate that heparanase is intimately involved in angiogenesis and elucidate its mode of action. Apart from its direct involvement in ECM degradation and EC migration (vascular sprouting), heparanase releases active basic fibroblast growth factor (bFGF) from the subendothelial ECM, as well as bFGF-stimulating HS degradation fragments from the EC surface. Interestingly, ECM-derived HS fragments induced little or no potentiation of the growth-promoting activity of bFGF. The angiogenic effect of heparanase was demonstrated in vivo (via the Matrigel plug assay) by showing a three-to fourfold increase in neovascularization induced by murine T-lymphoma cells after stable transfection with the heparanase gene. Increased tissue vascularity was also observed in a mouse wound-healing model in response to topical administration of recombinant heparanase. Immunohistochemical staining of human colon carcinoma tissue revealed a high expression of the heparanase protein in the endothelium of sprouting capillaries and small vessels, but not of mature quiescent blood vessels. The ability of heparanase to promote tumor angiogenesis and its involvement in tumor metastasis make it a promising target for cancer therapy.Key words: heparan sulfate proteoglycans • extracellular matrix • endothelial cells • basic fibroblast growth factor • wound healing eparan sulfate proteoglycans (HSPGs) are most abundant in cell surfaces, extracellular matrix (ECM), and basement membranes (BMs) (1, 2). BMs represent specialized ECM structures that underlie endothelial cells (ECs) in the blood vessel wall, as well as epithelial cells in various tissues and organs. HSPGs, the major polysaccharide-containing component of BMs, play a key role in the self-assembly and integrity of the BM multimolecular architecture. This function is clearly ascribed to the heparan sulfate (HS) carbohydrate side chains (1, 2), interacting through specific attachment sites with the main protein components of H the ECM and BM, such as collagen IV, laminin, and fibronectin. HSPGs are also actively involved in orchestrating cellular responses in both normal and pathological conditions (1, 2), ranging from pregnancy and development to neovascularization and metastatic spread of malignant tumors.The importance of HS and especially its enzymatic degradation during angiogenesis and metastasis has attracted growing attention during the...

Ulcerative colitis (UC) is a chronic inflammatory bowel disease that is closely associated with colon cancer. Expression of the enzyme heparanase is clearly linked to colon carcinoma progression, but its role in UC is unknown. Here we demonstrate for what we believe to be the first time the importance of heparanase in sustaining the immune-epithelial crosstalk underlying colitis-associated tumorigenesis. Using histological specimens from UC patients and a mouse model of dextran sodium sulfate-induced colitis, we found that heparanase was constantly overexpressed and activated throughout the disease. We demonstrate, using heparanase-overexpressing transgenic mice, that heparanase overexpression markedly increased the incidence and severity of colitis-associated colonic tumors. We found that highly coordinated interactions between the epithelial compartment (contributing heparanase) and mucosal macrophages preserved chronic inflammatory conditions and created a tumor-promoting microenvironment characterized by enhanced NF-κB signaling and induction of STAT3. Our results indicate that heparanase generates a vicious cycle that powers colitis and the associated tumorigenesis: heparanase, acting synergistically with the intestinal flora, stimulates macrophage activation, while macrophages induce production (via TNF-α-dependent mechanisms) and activation (via secretion of cathepsin L) of heparanase contributed by the colon epithelium. Thus, disruption of the heparanase-driven chronic inflammatory circuit is highly relevant to the design of therapeutic interventions in colitis and the associated cancer.

Incubation of platelets, neutrophils, and lymphoma cells with Descemet's membranes of bovine corneas and with the extracellular matrix (ECM) produced by cultured corneal endothelial cells resulted in release of basic fibroblast growth factor (bFGF), which stimulated the proliferation of 3T3 fibroblasts and vascular endothelial cells. Similar requirements were observed for release of endogenous bFGF stored in Descemet's membrane and of exogenous bFGF sequestered by the subendothelial ECM. Release of ECM-resident bFGF by platelets, neutrophils, and lymphoma cells was inhibited by carrageenan lambda, but not by protease inhibitors, in correlation with the inhibition of heparanase activity expressed by these cells. Degradation of the ECM-heparan sulfate side chains by this endo-beta-D-glucuronidase is thought to play an important role in cell invasion, particularly in the extravasation of blood-borne tumor cells and activated cells of the immune system. We propose that both heparanase and ECM-resident bFGF may modulate the cell response to contact with its local environment. Heparanase-mediated release of active bFGF from storage in basement membranes provides a novel mechanism for a localized induction of neovascularization in various normal and pathological processes, such as wound healing, inflammation, and tumor development.