Tumor promotion or suppression: Revisiting the role of EXT1 and Heparan sulfate.

Heparan sulfate (HS), a linear sulfated polysaccharide attached to proteoglycans, modulates the availability and activity of growth factors and cytokines to regulate cell signaling, adhesion, and migration. Exostosin-1 (EXT1), a key glycosyltransferase for HS chain elongation, is increasingly implicated in cancer development and progression. Although originally identified as a tumor suppressor in hereditary multiple exostoses, EXT1 exhibits a complex, context-dependent role in cancer. The effects of EXT1 in cancer differ by cell and tumor type, exerting both tumor-suppressing and tumor-promoting effects. Notably, EXT1 also alters the tumor microenvironment via its expression in stromal fibroblasts and endothelial cells, further influencing tumor behavior. This review discusses the functions of HS and EXT1, emphasizing the roles of EXT1 in cancer and its microenvironment. A deeper understanding of these mechanisms may offer novel therapies targeting the HS biosynthetic pathway.