 
         
         Summary
         
         Protein C (PC) deficiency and plasmin inhibitor (PI) deficiency are inherited thrombotic
            and haemorrhagic disorders. We investigated the intracellular degradation of mutant
            proteins, using naturally occurring PC and PI mutants that lead to congenital deficiencies.
            To examine the necessity of N-linked glycosylation for the proteasomal degradation
            of PC and PI, PC178 and PC331 mutants treated with tunicamycin and N-glycosylation-lacking
            mutants, PC92Stop and PI-America were pulse chased. The analysis revealed that the
            speed of degradation of the tunicamycin-treated PC mutants, PC92Stop and PI-America
            lacking glycosylation, was slower than that of N-glycosylated mutants. Immunoprecipitation
            and immunoblot analysis showed that PC178 and PC331 mutants were associated with molecular
            chaperones, Bip, GRP94, and calreticulin. PI-America was associated with only Bip.
            Although degradation of mutants was mediated by proteasomes, no association with ubiquitin
            was detected. Co-transfection of endoplasmic reticulum (ER) degradation enhancing
            α-mannosidase-like protein (EDEM) accelerated the degradation of N-glycosylated PC.
            In the absence of autophagy using Atg5-deficient cell lines, the degradation of the
            PC331 mutant was mildly accelerated but that of PC178, PI-America and PI-Okinawa mutants
            was not influenced. While the degradation of the PC and PI mutants was facilitated
            by N-glycosylation moieties, they were ubiquitin-independently degraded by proteasomes,
            irrespective of the presence or absence of N-glycosylation. Molecular chaperone binding
            was influenced by the presence of N-glycosylation moieties. When the misfolded or
            truncated mutant proteins are functionally active, proteasome inhibitors such as bortezomib
            may have therapeutic potential for treatment of protein deficiencies.
         
         Keywords
Endoplasmic reticulum-associated degradation - N-linked glycosylation - protein C
            - plasmin inhibitor - proteasome inhibitor