Heparan sulfate synthesis is a central component of the EMT program

Cancer cells exploit the epithelial-mesenchymal transition (EMT) program to gain aggressive phenotypes, including cell-cell junction release and enhanced migratory capabilities. Heparan sulfate (HS) is a linear polysaccharide composed of sulfated sugars, mainly present on the cell surface and extra-cellular matrix, which act as coreceptor to stimulate EMT-associated signaling pathways. However, the mechanisms that govern HS production during the EMT are not fully understood. By analyzing gene expression datasets, we identified a significant correlation between the expression of the HS chain elongation enzyme, exostosin glycosyltransferase 1 (EXT1), and EMT markers in both cancer cell lines and patient data. We found that manipulating EXT1 expression and activity results in a significant effect on the cell state. Specifically, EXT1 knockout (KO) in mesenchymal-like breast cancer cell line (MDA-MB-231) resulted in an epithelial-like phenotype that abolished theirs in vitro aggressive features, including migration, invasion, stemness and in vivo characteristics such as tumor growth kinetics, and metastasis. Additionally, EXT1 overexpression in epithelial-like breast cancer cells enhanced HS expression levels and exhibited a mesenchymal-like phenotype in vitro and in vivo. Next, we decoded the molecular mechanism underlying this phenomenon and found that in MDA-MB-231 EXT1 loss and subsequent reduction in HS levels, inhibited the IL6/JAK/STAT3 signaling pathway. Together, we identified the metabolic enzyme EXT1 as a major regulator of the EMT program through its role in HS synthesis.