Congenital diseases caused by defective O -glycosylation of Notch receptors.

The Notch signaling pathway is highly conserved and essential for animal development. It is required for cell differentiation, survival, and proliferation. Regulation of Notch signaling is a crucial process for human health. Ligands initiate a signal cascade by binding to Notch receptors expressed on a neighboring cell. Notch receptors interact with ligands through their epidermal growth factor-like repeats (EGF repeats). Most EGF repeats are modified by O -glycosylation with residues such as O -linked N -acetylglucosamine ( O -GlcNAc), O -fucose, and O -glucose. These O -glycan modifications are important for Notch function. Defects in O -glycosylation affect Notch-ligand interaction, trafficking of Notch receptors, and Notch stability on the cell surface. Although the roles of each modification are not fully understood, O -fucose is essential for binding of Notch receptors to their ligands. We reported an EGF domain-specific O -GlcNAc transferase (EOGT) localized in the endoplasmic reticulum. Mutations in genes encoding EOGT or NOTCH1 cause Adams-Oliver syndrome. Dysregulation of Notch signaling because of defects or mutations in Notch receptors or Notch signal-regulating proteins, such as glycosyltransferases, induce a variety of congenital disorders. In this review, we discuss O -glycosylation of Notch receptors and congenital human diseases caused by defects in O -glycans on Notch receptors.