Understanding Heparan Sulfate Biosynthesis and Functional Implications of Heparanase

Heparan sulfate (HS) proteoglycans are present on the plasma membrane of all animal cells studied so far and are a major component of extracellular matrices. Heparanase is an endo-ß-glucuronidase that cleaves HS chains at internally located ß-glucuronidic linkages1. Except its conventional enzymatic function, non-enzyme function and its function in the nucleus have been demonstrated recently. Regulation of HS biosynthesis has long been a myth. By generating HEK293 cells that overexpress different doses of C5-epimerase and a mutant without catalytic activity we created tools to analyze HS chain structure. We show that HS chain length increases in a dose dependent manner, dependent on the enzymatic activity of C5-epimerase, which can be reversed by co-overexpresssing with 2-O-sulfotransferase. Lipoprotein lipase (LpL) is a HS-bound enzyme that processes the triglycerides of lipoproteins from both exogenous and endogenous sources. Underdeveloped adipose tissue was revealed in heparanase transgenic mice, due to compromised LpL activity. Mechanistically, a likely possibility was demonstrated due to HS shedding related to overexpressed heparanase. The finding that breast cancer T47D cells which overexpress heparanase adopt a higher rate of aerobic glycolysis fueling cell proliferation and cell survival added up to the diverse functions of heparanase. Transcriptomic analysis after knockdown of heparanase in melanoma cells confirmed involvement in inflammatory responses as studied previously, and regulation of cell adhesion, ECM components, apoptosis and nucleosome assembly emerged as novel functional and mechanistic indications of heparanase. Supported by experimental evidence, heparanase’s effect in cell adhesion and apoptosis validated its role in cancer progression. Moreover, regulation of nucleosome assembly prompts further investigation into its action mode in the nucleus. Taken together, the present study adds to the elucidation of HS biosynthesis and depicts novel roles of heparanase, highlighting its multifaceted roles in cancer and providing exciting notions for future studies