Heparanase induces VEGF C and facilitates tumor lymphangiogenesis

Heparanase is an endoglycosidase that specifically cleaves heparan sulfate side chains, a class of glycosaminoglycans abundantly present in the extracellular matrix and on the cell surface. Heparanase activity is strongly implicated in tumor angiogenesis and metastasis attributed to remodeling of the subepithelial and subendothelial basement membranes. We hypothesized that similar to its proangiogenic capacity, heparanase is also engaged in lymphangiogenesis and utilized the D2-40 monoclonal antibody to study lymphangiogenesis in tumor specimens obtained from 65 head and neck carcinoma patients. Lymphatic density was analyzed for association with clinical parameters and heparanase staining. We provide evidence that lymphatic vessel density (LVD) correlates with head and neck lymph node metastasis (N-stage, p = 0.007) and inversely correlates with tumor cell differentiation (p = 0.007). Notably, heparanase staining correlated with LVD (p = 0.04) and, moreover, with VEGF C levels (p = 0.01). We further demonstrate that heparanase overexpression by epidermoid, breast, melanoma and prostate carcinoma cells induces a 3- to 5-fold elevation in VEGF C expression in vitro and facilitates tumor xenograft lymphangiogenesis in vivo, whereas heparanase gene silencing was associated with decreased VEGF C levels. These findings suggest that heparanase plays a unique dual role in tumor metastasis, facilitating tumor cell invasiveness and inducing VEGF C expression, thereby increasing the density of lymphatic vessels that mobilize metastatic cells.