BackgroundCell surface sialylation is emerging as an important feature of cancer cell metastasis. Sialyltransferase expression has been reported to be altered in tumours and may account for the formation of sialylated tumour antigens. We have focused on the influence of alpha-2,3-sialyltransferase ST3Gal III in key steps of the pancreatic tumorigenic process.Methodology/Principal FindingsST3Gal III overexpressing pancreatic adenocarcinoma cell lines Capan-1 and MDAPanc-28 were generated. They showed an increase of the tumour associated antigen sialyl-Lewisx. The transfectants' E-selectin binding capacity was proportional to cell surface sialyl-Lewisx levels. Cellular migration positively correlated with ST3Gal III and sialyl-Lewisx levels. Moreover, intrasplenic injection of the ST3Gal III transfected cells into athymic nude mice showed a decrease in survival and higher metastasis formation when compared to the mock cells.ConclusionIn summary, the overexpression of ST3Gal III in these pancreatic adenocarcinoma cell lines underlines the role of this enzyme and its product in key steps of tumour progression such as adhesion, migration and metastasis formation.

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In our previous studies we have described that ST3Gal III transfected pancreatic adenocarcinoma Capan-1 and MDAPanc-28 cells show increased membrane expression levels of sialyl-Lewis x (SLex) along with a concomitant decrease in α2,6-sialic acid compared to control cells. Here we have addressed the role of this glycosylation pattern in the functional properties of two glycoproteins involved in the processes of cancer cell invasion and migration, α2β1 integrin, the main receptor for type 1 collagen, and E-cadherin, responsible for cell-cell contacts and whose deregulation determines cell invasive capabilities. Our results demonstrate that ST3Gal III transfectants showed reduced cell-cell aggregation and increased invasive capacities. ST3Gal III transfected Capan-1 cells exhibited higher SLex and lower α2,6-sialic acid content on the glycans of their α2β1 integrin molecules. As a consequence, higher phosphorylation of focal adhesion kinase tyrosine 397, which is recognized as one of the first steps of integrin-derived signaling pathways, was observed in these cells upon adhesion to type 1 collagen. This molecular mechanism underlies the increased migration through collagen of these cells. In addition, the pancreatic adenocarcinoma cell lines as well as human pancreatic tumor tissues showed colocalization of SLex and E-cadherin, which was higher in the ST3Gal III transfectants. In conclusion, changes in the sialylation pattern of α2β1 integrin and E-cadherin appear to influence the functional role of these two glycoproteins supporting the role of these glycans as an underlying mechanism regulating pancreatic cancer cell adhesion and invasion.

Glycosylation is the most common posttranslational modification of proteins and is highly reflective of changes in the environment of a cell. Epigenetic modifications to the genome are stably transmitted to daughter cells without the requirement for genetic sequence alterations. Aberrant regulation of both epigenetic programming and glycosylation patterning are integral aspects of carcinogenesis. The objective of this study was to determine the interplay between these two complex cellular processes. We demonstrate that global DNA methylation changes in ovarian cancer epithelial cells (OVCAR3) resulted in significant alterations in the glycosylation of secreted glycoproteins. These changes included a reduction in core fucosylation, increased branching and increased sialylation. We further show that the change in core fucose levels was mirrored by altered expression of GMDS and FX, key enzymes in fucose biosynthesis. Alterations in the expression of key glycosyltransferase enzymes such as MGAT5 reflect the changes seen in the branching and sialylation of secreted glycans. Overall, our results highlight that modifications to the epigenetic machinery have a profound effect on the glycan structures generated by cells, which may be a key step in understanding metastasis and drug resistance during cancer progression.

This study shows how the intrinsic heterogeneity of cell membrane sialylation regulates the adhesive and migratory potential of pancreatic adenocarcinoma cells.