O-fucosylation of CCN1 is required for its secretion

•Human CCN1 is O-fucosylated at Thr242.•O-fucosylation-defective mutant of CCN1 decreased the secretion level.•Pofut2-mediated O-fucosylation is required for the secretion of CCN1.•Secretion of CCN1 is regulated by O-fucosylation. The matricellular protein CCN1, also known as Cyr61, is a secreted ligand and has numerous functions. Human CCN1 contains one predicted O-fucosylation site in the thrombospondin type-1 repeat (TSR1) domain at Thr242. In this report, we demonstrated that CCN1 is O-fucosylated at Thr242 using mass spectrometry. Deficiency of O-fucosylation resulted in the decrement of the cell surface localization and the secretion of CCN1. Furthermore, knockdown of protein O-fucosyltransferase 2, which modifies a specific Ser/Thr residue in the TSR1 domain, decreased secreted levels of CCN1. These results demonstrated that O-fucosylation of CCN1 at Thr242 regulates its secretion.