A Prevalent Cancer Associated Glycan, Globo H Ceramide, Induces Immunosuppression by Reducing Notch1 Signaling

Abstract

Globo H, a hexasaccharide initially identified as a ceramide-linked glycolipid from human breast cancer cell line MCF-7, is over-expressed on the surface of many common cancers, but its function is unknown. Here we demonstrated the uptake of globo H ceramide (GHCer) by human peripheral blood mononuclear cells (PBMC) upon co-culture with MCF-7 cells. Significantly, the expression of globo H on tumor-infiltrating lymphocytes was observed in 61% of globo H positive breast cancer tissues. Addition of synthetic GHCer to human PBMC, mouse splenocytes or purified CD4+ T cells inhibited their proliferative response to anti-CD3/CD28 to 60 1%, 50 7% and 62 5% of control, respectively, and reduced the secretion of IL-2, IFN- and IL-4. GHCer also significantly suppressed the proliferation of splenocytes or purified CD19+ B cells to 45 10% and 26 3% of control in response to LPS or LPS + IL4 +CD40 ligand and their IgM production to 12 5%, 8 3%, and IgG to 34 9%, 35 5%, respectively, with neglible induction of plasma cells. Ceramide displayed no such inhibitory effects. On the other hand, GHCer failed to raise the number of regulatory T cells, or their expression of FOXP3/CTLA4, nor did it increase apoptosis. Notably, GHCer significantly suppressed the Notch1 signaling during activation of human PBMC and murine T and B cells. Furthermore, GHCer upregulated the expression of id3 and itch by 2.10.2 and 4.7 0.4 folds, respectively, leading to ID3-dependent downregulation of Notch1 and Itch-mediated Notch1 degradation. These results provide the first evidence for GHCer to facilitate the escape of cancer cells from immune surveillance.