ST3GAL5 ‐catalyzed gangliosides inhibit TGF ‐β‐induced epithelial‐mesenchymal transition via TβRI degradation

Abstract

Epithelial‐mesenchymal transition (EMT) is pivotal in the initiation and development of cancer cell metastasis. We observed that the abundance of glycosphingolipids (GSLs), especially ganglioside subtypes, decreased significantly during TGF‐β‐induced EMT in NMuMG mouse mammary epithelial cells and A549 human lung adenocarcinoma cells. Transcriptional profiling showed that TGF‐β/SMAD response genes and EMT signatures were strongly enriched in NMuMG cells, along with depletion of UDP‐glucose ceramide glucosyltransferase (UGCG), the enzyme that catalyzes the initial step in GSL biosynthesis. Consistent with this finding, genetic or pharmacological inhibition of UGCG promoted TGF‐β signaling and TGF‐β‐induced EMT. UGCG inhibition promoted A549 cell migration, extravasation in the zebrafish xenograft model, and metastasis in mice. Mechanistically, GSLs inhibited TGF‐β signaling by promoting lipid raft localization of the TGF‐β type I receptor (TβRI) and by increasing TβRI ubiquitination and degradation. Importantly, we identified ST3GAL5‐synthesized a ‐series gangliosides as the main GSL subtype involved in inhibition of TGF‐β signaling and TGF‐β‐induced EMT in A549 cells. Notably, ST3GAL5 is weakly expressed in lung cancer tissues compared to adjacent nonmalignant tissues, and its expression correlates with good prognosis. image How is dynamic epithelial‐mesenchymal transition (EMT) of cancer cells controlled upstream? This study identifies plasma membrane glycosphingolipid (GSL) composition and related biosynthesis enzymes as key suppressors of dynamic EMT and malignant transformation in human epithelia. Quantitative mass spectrometry determines EMT‐induced alterations of GSLs. A‐series ganglioside expression is strongly decreased upon TGF‐β stimulation of normal breast and lung cancer cells undergoing EMT. GSL biosynthesis enzymes UGCG and ST3GAL5 inhibit TGF‐β‐induced EMT, invasion and metastasis in vitro and in vivo . Depletion of UGCG or ST3GAL5 favors TβRI localization in lipid rafts, triggering its ubiquitination and subsequent degradation. ST3GAL5 expression is reduced in aggressive human lung cancer and correlates with better prognosis.