Exostosin glycosyltransferase 1 (EXT1) is a glycosyltransferase involved in the elongation of the saccharide chain of heparan sulfate proteoglycans (HSPGs). HSPGs, also known as Heparanosome, are important components of the extracellular matrix (ECM) and the cell surface. The ECM profile has been extensively studied in high-grade serous ovarian cancer (HGSOC), but data on the involvement of HPSGs in platinum resistance are still incomplete.

HGSOC patients from the TCGA dataset (73 resistant and 107 sensitive) were stratified in terms of their response to platinum-based therapy. The copy number alterations (CNAs) that occurred in the TCGA patients, leading to altered mRNA expression, were analyzed using the PathScore algorithm. The biosynthesis of HSPGs was significantly (p <0.05) enriched in the resistant patients with a high percentage of amplifications of the Ext1 gene. EXT1 protein expression was analyzed by immunohistochemistry on a microarray of 25 resistant and 25 sensitive patients. EXT1 protein levels were elevated in 60% of resistant patients compared to 24% of sensitive patients (p < 0.05). Ovarian cancer cells were transfected with an Ext1-expressing vector (COV318 and MDAH2774) and/or interfered by shRNAs targeting the Ext1 gene (shEXT1 OVCAR-5 and OVCAR-429) to investigate the deposition and distribution of HPSGs and to determine how they affect the signal transduction, cell motility and invasion, and drug sensitivity of cancer cells.

EXT1-overexpressing cells synthesized an increased amount of HSPGs and showed reduced sensitivity to platinum-based drugs, which could be restored by heparinase treatment. In contrast, cells which experienced EXT1 knockdown showed increased sensitivity to platinum-based drugs. Through the transcriptomics analysis of EXT1 knockdown cells, we detected significantly reduced expressions of the Lcn2, Cacna2d1, Edn1, and Tagln genes. In addition, the GO analysis of shExt1 knockdown cells revealed a lower enrichment of the EMT category, as reflected by reduced cell motility in vitro, which was analyzed by time lapse microscopy. These effects could be partly explained by the lower accumulation of INFg and TNFa in cells lacking EXT1. Our preliminary results suggest that Heparanosome architecture can alter the behavior of cancer cells and their response to external stimuli. These phenomena may play an important role in the development of recurrence in patients resistant to platinum-based drugs.