Golgi stress response by proteoglycans

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Glycosaminoglycans (GAGs) are components of proteoglycans (PGs), which are abundant on the surfaces of most cells and in extracellular matrices. PGs are known to function as cofactors in a variety of biological processes. Most biological activities of PGs are attributed to the GAG side chains that interact with diverse protein ligands via specific saccharide sequences. EXTL2, a member of the EXT family of tumor suppressors, functions to suppress any GAG biosynthesis that is enhanced by a xylose kinase, and thus lack of EXTL2 causes GAG overproduction and structural changes to GAGs. These poor-quality GAGs have effects on the cell signaling such as HGF-mediated and BMP-mediated signaling, and consequently disturb liver regeneration and blood vessel remodeling. Therefore, the EXTL2-dependent mechanism that regulates GAG biosynthesis might be a "quality control system" for PGs and GAGs produced in the absence of EXTL2 can be closely associated with diseases.