Glycosyltransferase ST6Gal-I promotes the epithelial to mesenchymal transition in pancreatic cancer cells

Abstract

ST6Gal-I, an enzyme upregulated in numerous malignancies, adds α2-6-linked sialic acids to select membrane receptors, thereby modulating receptor signaling and cell phenotype. In this study, we investigated ST6Gal-I’s role in epithelial to mesenchymal transition (EMT) using the Suit2 pancreatic cancer cell line, which has low endogenous ST6Gal-I and limited metastatic potential, along with two metastatic Suit2-derived subclones, S2-013 and S2-LM7AA, which have upregulated ST6Gal-I. RNA-Seq results suggested that the metastatic subclones had greater activation of EMT-related gene networks than parental Suit2 cells, and forced overexpression (OE) of ST6Gal-I in the Suit2 line was sufficient to activate EMT pathways. Accordingly, we evaluated expression of EMT markers and cell invasiveness (a key phenotypic feature of EMT) in Suit2 cells with or without ST6Gal-I OE, as well as S2-013 and S2-LM7AA cells with or without ST6Gal-I knockdown (KD). Cells with high ST6Gal-I expression displayed enrichment in mesenchymal markers (N-cadherin, slug, snail, fibronectin) and cell invasiveness, relative to ST6Gal-I-low cells. Contrarily, epithelial markers (E-cadherin, occludin) were suppressed in ST6Gal-I-high cells. To gain mechanistic insight into ST6Gal-I’s role in EMT, we examined the activity of EGFR, a known EMT driver. ST6Gal-I-high cells had greater α2-6 sialylation and activation of EGFR than ST6Gal-I-low cells. The EGFR inhibitor, erlotinib, neutralized ST6Gal-I-dependent differences in EGFR activation, mesenchymal marker expression and invasiveness in Suit2 and S2-LM7AA, but not S2-013, lines. Collectively, these results advance our understanding of ST6Gal-I’s tumor-promoting function by highlighting a role for ST6Gal-I in EMT, which may be mediated, at least in part, by α2-6-sialylated EGFR.

Integrated Systems-Analysis of the Human and Murine Pancreatic Cancer Glycomes Reveal a Tumor Promoting Role for ST6GAL1

“…In line with our sc-RNAseq analysis, staining for ST6GAL1 protein was strongest in epithelial cells, suggesting that ductal or acinar specific expression may significantly contribute to development and/or progression of PDA. Consistent with our observations in patients and the KC mouse model, in vitro cell culture models of pancreatic cancer with ST6GAL1 overexpressed promoted chemo-resistance, cell growth and a stem-cell like phenotype (7,8,(30)(31)(32).…”

“…In ST6KC, we observed significant protection against formation of PanIn lesions, an early step in malignant transformation, and reduction of fibrosis, which is associated with immune suppression and resistance to treatment in PDAC patients (33). This is consistent with the function of ST6GAL1 in cell studies (7,8,(30)(31)(32). Overall, histological assessment of our ST6KC mice demonstrates a clear protective role for genetic deletion of ST6GAL1 in PDA.…”

“…Heterologous expression of human enzymes that can biosynthesize CA-19-9 in a mouse model increased pancreatic inflammation, pointing to a potential role of this epitope in disease initiation (4). Pancreatic cell culture models have also shown a potential role for glycosylation in cell stemness, invasiveness and drug resistance (5)(6)(7)(8).…”

Aberrant Sialylation in Cancer: Biomarker and Potential Target for Therapeutic Intervention?

“…In pancreatic cancer cells, high expression of ST6GAL1 led to increased α-2,6 sialylation and activation of EGFR, as well as upregulation of mesenchymal markers and enhanced cell invasiveness. Interestingly, the EGFR inhibitor erlotinib attenuated the ST6GAL1-dependent differences in EGFR sialylation and activation, EMT marker expression and invasiveness [ 66 ]. In addition, increase of α-2,3 sialylation induced by ST6GAL1 promoted integrin α5β1-dependent adhesion in hepatocarcinoma cells [ 67 ].…”

Role of Glycans on Key Cell Surface Receptors That Regulate Cell Proliferation and Cell Death

“…Sialidase-treated A549 cells were less sensitive to EGF-stimulated cell proliferation than A549 cells without sialidase treatment, and the TKI erlotinib showed no significant effects upon sialidase treatment [ 51 ]. Britain et al [ 52 ] found that high expression levels of α2,6-sialyltransferase ST6Gal I that acts on complex N -glycans of EGFR correlates with EGF-triggered EGFR activation in pancreatic cancer cells [ 52 , 53 ]. The high expression of ST6Gal I also resulted in gefitinib resistance.…”