The present study emphasizes the importance of cell surface expression and secretion of
heparanase (
endo-beta-D-glucuronidase) in
tumor angiogenesis and
metastasis. For this purpose, nonmetastatic Eb mouse
lymphoma cells were transfected with the predominantly intracellular human
heparanase or with a readily secreted chimeric construct composed of the human
enzyme and the chicken
heparanase signal peptide. Eb cells overexpressing the secreted
heparanase invaded a reconstituted basement membrane to a much higher extent than cells overexpressing the intracellular
enzyme. Cell invasion was inhibited in the presence of
laminaran sulfate, a potent inhibitor of
heparanase activity and experimental
metastasis. The increased invasiveness in vitro was reflected in vivo by rapid and massive liver colonization and accelerated mortality. In fact, mice inoculated with cells expressing the secreted
enzyme succumb because of liver
metastasis and dysfunction, as early as 10 days after s.c. inoculation of the cells, when their
tumor burden did not exceed 1% of
body weight. Cell surface localization and secretion of
heparanase markedly stimulated
tumor angiogenesis, as demonstrated by a 4-6-fold increase in vessel density and functionality evaluated by MRI of
tumors produced by cells expressing the secreted vs. the nonsecreted
heparanase, consistent with actual counting of blood vessels. Altogether, our results indicate that the potent proangoigenic and prometastatic properties of
heparanase are tightly regulated by its cellular localization and secretion. The increased potency of the secreted
enzyme makes it a promising target for anticancer
drug development.