O-glycans on death receptors in cells modulate their sensitivity to TRAIL-induced apoptosis through affecting on their stability and oligomerization.

The TNF-related apoptosis-inducing ligand (TRAIL) triggers apoptosis in cells by signaling through the O-glycosylated death receptors (DR4 and DR5), but the sensitivity to TRAIL-induced apoptosis of cells varies, and the attributes of this phenomenon are complex. Human carcinoma cells often express truncated O-glycans, Tn (GalNAcα1-Ser/Thr), and Sialyl-Tn (Siaα2-6GalNAcα1-Ser/Thr, STn) on their surface glycoproteins, yet molecular mechanisms in terms of advantages for tumor cells to have these truncated O-glycans remain elusive. Normal extended O-glycan biosynthesis is regulated by a specific molecular chaperone Cosmc through assisting of the correct folding of Core 1 β3 Galactosyltransferase (T-synthase). Here, we use tumor cell lines harboring mutations in Cosmc, and therefore expressing Tn and STn antigens to study the role of O-glycans in TRAIL-induced apoptosis. Expression of Tn and STn in tumor cells attenuates their sensitivity to TRAIL treatment; when transfected with wild-type Cosmc, these tumor cells thus express normal extended O-glycans and become more sensitive to TRAIL treatment. Mechanistically, Tn/STn antigens impair homo-oligomerization and stability of DR4 and DR5. These results represent the first mechanistic insight into how O-glycan structures on cell surface modulate their sensitivity to apoptotic stimuli, suggesting expression of Tn/STn may offer tumor cell survival advantages through altering DR4 and/or DR5 activity.