FUT4 (fucosyltransferase 4) is an alpha-3-fucosyltransferase that catalyzes synthesis of fucosylated oligosaccharides, particularly Lewis Y antigens, on glycoproteins and glycolipids 1. The enzyme is localized to the Golgi apparatus and trans-Golgi network, where it adds fucose residues to carbohydrate moieties during glycoprotein biosynthesis 2. FUT4 is expressed early during human embryogenesis in developing tissues 3 and shows cell-type-specific regulation via distinct promoter elements in different tissues 2. FUT4 expression is transcriptionally regulated by multiple factors: HSF1 and Sp1 promote expression in breast cancer cells through ERK1/2 MAPK and PI3K/Akt signaling 1, while androgen receptor activation upregulates FUT4 in melanoma 4. Conversely, MyoD1 suppresses FUT4 transcription in gastric cancer 5, and miR-493-5p downregulates FUT4 expression in breast cancer 6. Clinically, elevated FUT4 expression correlates with cancer progression and metastasis across multiple malignancies. In breast cancer, FUT4 promotes cell proliferation and invasiveness 1. In melanoma, FUT4 mediates androgen-driven invasiveness by fucosylating L1CAM and disrupting adherens junctions 4. In gastric cancer and osteosarcoma, FUT4 suppression reduces migration, invasion, and promotes apoptosis 5, 7. Additionally, FUT4-mediated fucosylation of haptoglobin amplifies inflammatory responses in sepsis through Mincle-dependent signaling 8, suggesting FUT4 contributes to pathological inflammation.