Heparanase Augments Epidermal Growth Factor Receptor Phosphorylation: Correlation with Head and Neck Tumor Progression

Abstract

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 metastasis attributed to remodeling of the subepithelial and subendothelial basement membranes, resulting in dissemination of metastatic cancer cells. Moreover, heparanase up-regulation was noted in an increasing number of primary human tumors, correlating with tumors larger in size, increased microvessel density, and reduced postoperative survival rate, implying that heparanase function is not limited to tumor metastasis. This notion is supported by recent findings revealing induction of signaling molecules (i.e., Akt, p38) and gene transcription [i.e., tissue factor, vascular endothelial growth factor (VEGF)] by enzymatically-inactive heparanase. Here, we provide evidence that active and inactive heparanase proteins enhance epidermal growth factor receptor (EGFR) phosphorylation. Enhanced EGFR phosphorylation was associated with increased cell migration, cell proliferation, and colony formation, which were attenuated by Src inhibitors. Similarly, heparanase gene silencing by means of siRNA was associated with reduced Src and EGFR phosphorylation levels and decreased cell proliferation. Moreover, heparanase expression correlated with increased phospho-EGFR levels and progression of head and neck carcinoma, providing a strong clinical support for EGFR modulation by heparanase. Thus, heparanase seems to modulate two critical systems involved in tumor progression, namely VEGF expression and EGFR activation. Neutralizing heparanase enzymatic and nonenzymatic functions is therefore expected to profoundly affect tumor growth, angiogenesis, and metastasis.