Cell surface heparan sulfate released by heparanase promotes melanoma cell migration and angiogenesis

Heparan sulfate (HS) proteoglycans are essential components of the cell-surface and extracellular matrix (ECM) which provide structural integrity and act as storage depots for growth factors and chemokines, through their HS side chains. Heparanase (HPSE) is the only mammalian endoglycosidase known that cleaves HS, thus contributing to matrix degradation and cell invasion. The enzyme acts as an endo-beta-D-glucuronidase resulting in HS fragments of discrete molecular weight size. Cell-surface HS is known to inhibit or stimulate tumorigenesis depending upon size and composition. We hypothesized that HPSE contributes to melanoma metastasis by generating bioactive HS from the cell-surface to facilitate biological activities of tumor cells as well as tumor microenvironment. We removed cell-surface HS from melanoma (B16B15b) by HPSE treatment and resulting fragments were isolated. Purified cell-surface HS stimulated in vitro B16B15b cell migration but not proliferation, and importantly, enhanced in vivo angiogenesis. Furthermore, melanoma cell-surface HS did not affect in vitro endothelioma cell (b.End3) migration. Our results provide direct evidence that, in addition to remodeling ECM and releasing growth factors and chemokines, HPSE contributes to aggressive phenotype of melanoma by releasing bioactive cell-surface HS fragments which can stimulate melanoma cell migration in vitro and angiogenesis in vivo.