Heparanase modulates Shh and Wnt3a signaling in human medulloblastoma cells

the pathogenesis of medulloblastoma (MB), the most common and aggressive brain tumor in children, is poorly understood. MB tumors respond to factors secreted by cerebellar purkinje neurons, such as Sonic hedgehog (Shh) and Wingless-type MMTV integration site family member 3a (Wnt3a). Understanding the modulation of Shh/Wnt signaling is critical for the development of new MB treatments. Shh and Wnt3a induce MB cell proliferation and bind heparan sulfate glycosaminoglycan chains (HS-GAGs). HS-GAGs are components of syndecans, cell surface HS proteoglycans (HSPGs) which act as co-receptors for extracellular matrix-based ligands, and are targets of heparanase (HPSE). We hypothesized that extracellular HPSE activity modulates MB intracellular signaling of Shh/Wnt3a, involving syndecan-1 and -4 carboxy terminal-associated proteins and downstream targets. We compared the regulation of Shh/Wnt3a signaling subsequent to treatment with exogenous human active HPSE in MB lines possessing increased invasive abilities. We identified guanine nucleotide exchange factor-H1 (GEF-H1), a small GTpase guanine nucleotide exchange factor, as a new component of a syndecan signaling complex. Secondly, we demonstrated that HPSE modulated Shh/Wnt3-dependent expression and the intracellular distribution of GEF-H1, β-catenin and N-Myc. Thirdly, HPSE modulated Shh/Wnt3a-dependent gene expression of heparan sulfate proteoglycan (HSPG) and Gli transcription factors. Fourthly, pre-treatment with HPSE, alone or prior to Shh/Wnt3a exposure, altered small GTPase (Racl/RhoA) activities differentially and promoted RhoA activation. Finally, the differential regulation of Racl/RhoA activities by HPSE affected MB cell proliferation and invasion. Our results indicate that the HPSE/HSPG axis is implicated in critical MB cell signaling pathways with potential relevance for MB treatment.