The most described biological program involved in cancer cell dissemination and growth at metastatic sites is Epithelial-to-Mesenchymal (EMT) and its reverse process Mesenchymal-to-Epithelial transition (MET), respectively. This usually confers to epithelial cancer cells being orchestrated by a series of well-described EMT proteins leading to mesenchymal cell features. However, the possible involvement of glycosphingolipids (GSL), cellular components of the cell surface membrane consisting of a ceramide and glycan compartment, has not been investigated in detail.
Here we accessed large ovarian cancer transcriptomic data sets and show that the expression profile of specific genes encoding glycosyltransferases (e.g. A4GALT for globosides or ST3GAL5 for gangliosides) involved in GSL synthesis differs during EMT/MET, coinciding with changes of classical EMT marker (e.g. CDH1 or VIM). Next, we homozygously deleted the globoside glycosyltransferase A4GALT (elevated in ovarian cancer cells with epithelial features) using the CRISPR-Cas9 system. The depletion of globosides was confirmed by LC-ESI-MS/MS and flow cytometry. We further observed an acquisition of mesenchymal traits as evidenced by in vitro as well as in vivo assays (anoikis-resistance, enhanced cell motility and dissemination in zebrafish) and enhanced doxorubicin resistance in A4GALT knockout cells. Most intriguingly, we provide evidence that E-cadherin-mediated cell-cell adhesion is strictly dependent on enzymatically active A4GALT (experimental setup comprising wildtype, knockout, rescue wildtype, and rescue mutant of A4GALT) and hence on the abundance of globosides. This indicates that specific GSLs exert a pivotal role upstream of E-cadherin. Vice versa, mesenchymal cancer cells acquire epithelial traits upon genomic deletion of ganglioside-encoding genes, e.g. gain of E-cadherin.
Taken together, our data shed new light into a yet underestimated class of biomolecules during EMT/MET in an ovarian cancer model and propose a pivotal role of GSL during the reversible transition of cancer cells form epithelial to mesenchymal types.