Extracellular sulfatases (SULF1 and SULF2) selectively remove 6-O-sulfate groups from heparan sulfate proteoglycans (HSPGs) and by this process control important interactions of HSPGs with extracellular factors including morphogens, growth factors, and extracellular matrix components. The expression of SULF1 and SULF2 is dynamically regulated during development and is altered in pathological states such as glioblastoma (GBM), a highly malignant and highly invasive brain cancer. SULF2 protein is increased in an important subset of human GBM and it helps regulate receptor tyrosine kinase signaling and tumor growth in a murine model of the disease. By altering ligand binding to HSPGs, SULF2 has the potential to modify the extracellular availability of factors important in a number of cell processes including proliferation, chemotaxis, and migration. Diffuse invasion of malignant tumor cells into surrounding healthy brain is a characteristic feature of GBM that makes therapy challenging. Here, we describe methods to assess SULF2 expression in human tumor tissue and cell lines and how to relate this to tumor cell invasion.

Alterations in glycosylation are common in cancer and are thought to contribute to disease. Lung cancer and primary malignant brain cancer, most commonly glioblastoma, are genetically heterogeneous diseases with extremely poor prognoses. In this review, we summarize the data demonstrating that glycosylation is altered in lung and brain cancer. We then use specific examples to highlight the diverse roles of glycosylation in these two deadly diseases and illustrate shared mechanisms of oncogenesis. In addition to alterations in glycoconjugate biosynthesis, we also discuss mechanisms of postsynthetic glycan modification in cancer. We suggest that alterations in glycosylation in lung and brain cancer provide novel tumor biomarkers and therapeutic targets.

Glioblastoma (GBM) is the most common primary malignant brain tumor of adults and confers a poor prognosis due, in part, to diffuse invasion of tumor cells. Heparan sulfate (HS) glycosaminoglycans, present on the cell surface and in the extracellular matrix, regulate cell signaling pathways and cell-microenvironment interactions. In GBM, the expression of HS glycosaminoglycans and the enzymes that regulate their function are altered, but the actual HS content and structure are unknown. However, inhibition of HS glycosaminoglycan function is emerging as a promising therapeutic strategy for some cancers. In this study, we use liquid chromatography-mass spectrometry analysis to demonstrate differences in HS disaccharide content and structure across four patient-derived tumorsphere lines (GBM1, 5, 6, 43) and between two murine tumorsphere lines derived from murine GBM with enrichment of mesenchymal and proneural gene expression (mMES and mPN, respectively) markers. In GBM, the heterogeneous HS content and structure across patient-derived tumorsphere lines suggested diverse functions in the GBM tumor microenvironment. In GBM5 and mPN, elevated expression of sulfatase 2 (SULF2), an extracellular enzyme that alters ligand binding to HS, was associated with low trisulfated HS disaccharides, a substrate of SULF2. In contrast, other primary tumorsphere lines had elevated expression of the HS-modifying enzyme heparanase (HPSE). Using gene editing strategies to inhibit HPSE, a role for HPSE in promoting tumor cell adhesion and invasion was identified. These studies characterize the heterogeneity in HS glycosaminoglycan content and structure across GBM and reveal their role in tumor cell invasion.Implications: HS-interacting factors promote GBM invasion and are potential therapeutic targets. Mol Cancer Res; 15(11); 1623-33. ©2017 AACR.

Signaling from multiple receptor tyrosine kinases (RTK) contributes to therapeutic resistance in glioblastoma (GBM). Heparan sulfate (HS), present on cell surfaces and in the extracellular matrix, regulates cell signaling via several mechanisms. To investigate the role for HS in promoting RTK signaling in GBM, we generated neural progenitor cells deficient for HS by knockout of the essential HS-biosynthetic enzyme Ext1, and studied tumor initiation and progression. HS-null cells had decreased proliferation, invasion, and reduced activation of multiple RTKs compared with control. In vivo tumor establishment was significantly decreased, and rate of tumor growth reduced with HS-deficient cells implanted in an HS-poor microenvironment. To investigate if HS regulates RTK activation through platelet-derived growth factor receptor α (PDGFRα) signaling, we removed cell surface HS in patient-derived GBM lines and identified reduced cell surface PDGF-BB ligand. Reduced ligand levels were associated with decreased phosphorylation of PDGFRα, suggesting HS promotes ligand-receptor interaction. Using human GBM tumorspheres and a murine GBM model, we show that ligand-mediated signaling can partially rescue cells from targeted RTK inhibition and that this effect is regulated by HS. Indeed, tumor cells deficient for HS had increased sensitivity to EGFR inhibition in vitro and in vivo. IMPLICATIONS: Our study shows that HS expressed on tumor cells and in the tumor microenvironment regulates ligand-mediated signaling, promoting tumor cell proliferation and invasion, and these factors contribute to decreased tumor cell response to targeted RTK inhibition.