HS2ST1-dependent signaling pathways determine breast cancer cell viability, matrix interactions, and invasive behavior.

Heparan sulfate proteoglycans (HSPGs) act as signaling co-receptors by interaction of their sulfated glycosaminoglycan chains with numerous signaling molecules. In breast cancer, the function of heparan sulfate 2-O-sulfotransferase (HS2ST1), the enzyme mediating 2-O-sulfation of HS, is largely unknown. Hence, a comparative study on the functional consequences of HS2ST1 overexpression and siRNA knockdown was performed in the breast cancer cell lines MCF-7 and MDA-MB-231. HS2ST1 overexpression inhibited Matrigel invasion, while its knockdown reversed the phenotype. Likewise, cell motility and adhesion to fibronectin and laminin were affected by altered HS2ST1 expression. Phosphokinase array screening revealed a general decrease in signaling via multiple pathways. Fluorescent ligand binding studies revealed altered binding of fibroblast growth factor 2 (FGF-2) to HS2ST1-expressing cells compared with control cells. HS2ST1-overexpressing cells showed reduced MAPK signaling responses to FGF-2, and altered expression of epidermal growth factor receptor (EGFR), E-cadherin, Wnt-7a, and Tcf4. The increased viability of HS2ST1-depleted cells was reduced to control levels by pharmacological MAPK pathway inhibition. Moreover, MAPK inhibitors generated a phenocopy of the HS2ST1-dependent delay in scratch wound repair. In conclusion, HS2ST1 modulation of breast cancer cell invasiveness is a compound effect of altered E-cadherin and EGFR expression, leading to altered signaling via MAPK and additional pathways.

Shed proteoglycans in tumor stroma.

Cancer cell behavior is not only governed by tumor cell-autonomous properties but also by the surrounding tumor stroma. Cancer-associated fibroblasts, blood vessels, immune cells and the extracellular matrix of the tumor microenvironment have a profound influence on tumor progression. Proteoglycans control various normal and pathological processes, modulating cell proliferation and motility, cell-matrix interactions, immune cell recruitment and angiogenesis. They are major mediators of cancer cell behavior though a dynamic interplay with extracellular matrix components. During cancer progression, their altered expression can promote the activation of several signaling cascades regulating crucial functional properties of cancer cells. Notably, the function of cell surface proteoglycans can be altered by ectodomain shedding, which converts membrane-bound coreceptors into soluble paracrine effector molecules. In this review, we highlight the importance of proteoglycans and their soluble counterparts in cancer progression and the consequences of their interactions with the adjacent stroma. The dynamic interplay among shed proteoglycans and proteolytic enzymes has a significant impact both on tumor cells and their surrounding stroma, with important implications for the diagnosis of this disease and for novel therapeutic approaches. Graphical Abstract Syndecan shedding. The mechanism of shedding involves the proteolytic cleavage of their ectodomain near the plasma membrane by metzincin enzymes, such as metalloproteinases. N-acetylglucosamine-alpha-L-iduronic acid/beta-D-glucuronic acid (HS) chains can be additionally cleaved by heparanase. Syndecan core protein can be further processed by intramembrane enzymatic cleavage. Syndecans are in a dynamic interplay with the extracellular matrix and several receptor-tyrosine-kinases (RTKs) and various growth factors, for which they act as co-receptors, thus mediating numerous signaling pathways.