TMEM260 is a protein-specific O-mannosyltransferase

Mutations in the TMEM260 gene cause structural heart defects and renal anomalies syndrome (SHDRA), but the function of the encoded protein remains unknown. We report that TMEM260 is an ER-located protein O-mannosyltransferase that selectively glycosylates defined extracellular immunoglobulin, plexin, transcription factor (IPT) domains of the hepatocyte growth factor receptor (cMET), macrophage-stimulating protein receptor (RON), and plexin receptors. We demonstrate that disease-causing TMEM260 mutations impair O-mannosylation of IPT domains and that TMEM260 knock out in cells results in receptor maturation defects and abnormal growth of 3D cell models. Thus, our study identifies a new, receptor-specific O-mannosylation pathway that serves critical functions during e.g. epithelial morphogenesis.