Mannose-dependent endoplasmic reticulum (ER)-Golgi intermediate compartment-53-mediated ER to Golgi trafficking of coagulation factors V and VIII

The endoplasmic reticulum-Golgi intermediate compartment (ERGIC) is the sit e of segregation of secretory proteins for anterograde transport, via packa ging into COPII-coated transport vesicles, ERGIC-53 is a homohexameric tran smembrane lectin localized to the ERGIC that exhibits mannose-selective pro perties in vitro. Null mutations in ERGIC-53 were recently shown to be resp onsible for the autosomal recessive bleeding disorder, combined deficiency of coagulation factors V and VIII, We have studied the effect of defective ER to Golgi cycling by ERGIC-53 on the secretion of factors V and VIII, The secretion efficiency of factor V and factor VIII was studied in a tetracyc line-inducible HeLa cell line overexpressing a wild-type ERGIC-53 or a cyto solic tail mutant of ERGIC-53 (KKAA) that is unable to exit the ER due to m utation of two COOH-terminal phenylalanine residues to alanines, The result s show that efficient trafficking of factors V and VIII requires a function al ERGIC-53 cycling pathway and that this trafficking is dependent on post- translational modification of a specific cluster of asparagine (N)-linked o ligosaccharides to a fully glucose-trimmed, mannose9 structure.