PMID: 29402915

 

    Legend: Sugar

Title : Amnionless-mediated glycosylation is crucial for cell surface targeting of cubilin in renal and intestinal cells

Abstract :

1. Mutations in either cubilin ( CUBN ) or amnionless ( AMN ) genes cause Imerslund-Gräsbeck syndrome (IGS), a hereditary disease characterised by anaemia attributed to selective intestinal malabsorption of cobalamin and low-molecular weight proteinuria
2. Although cubilin protein does not have a transmembrane segment, it functions as a multi-ligand receptor by binding to the transmembrane protein , amnionless
3. We established a system to quantitatively analyse membrane targeting of the protein complex in cultured renal and intestinal cells and analysed the pathogenic mechanisms of mutations found in IGS patients
4. A novel CUBN mutation, several previously reported CUBN missense mutations and all previously reported AMN missense mutations resulted in endoplasmic reticulum (ER) retention and completely inhibited amnionless-dependent plasma membrane expression of cubilin
5. The ER retention of cubilin and amnionless was confirmed in renal proximal tubular cells of a patient with IGS
6. Notably, the interaction between cubilin and amnionless was not sufficient, but amnionless-mediated glycosylation of cubilin was necessary for their surface expression
7. Quantitative mass spectrometry and mutagenesis demonstrated that N-linked glycosylation of at least 4 residues of cubilin protein was required for its surface targeting
8. These results delineated the molecular mechanisms of membrane trafficking of cubilin in renal and intestinal cells