Degradation of wild-type vasopressin precursor and pathogenic mutants by the proteasome.
Mutations in the gene encoding the antidiuretic hormone arginine vasopressin cause autosomal dominant neurogenic diabetes insipidus. Autoptic data in affected individuals suggest that the neurons expressing mutant vasopressin undergo selective degeneration. Expression studies have shown that the mutants are retained in the endoplasmic reticulum, but how this trafficking defect is linked to neurotoxicity is unknown. One possibility is that unsecreted mutant precursors, or degradation products thereof, are cytotoxic. We therefore investigated the fate of endoplasmic reticulum-retained pathogenic mutants. Our data show that the mutants are retrotranslocated to the cytosol and degraded by the proteasome. In the presence of proteasomal inhibitors, three distinct un- or deglycosylated cytosolic species of vasopressin precursors were stabilized: pre-pro-vasopressin, pro-vasopressin, and an N-terminally truncated form. In addition to the retrotranslocated forms, a fraction of the newly synthesized precursor was not translocated, but was synthesized into the cytosol due to inefficient function of the vasopressin signal peptide. As a result, cytosolic pre-pro-vasopressin and its degradation product were also recovered when wild-type vasopressin was expressed. Cytosolic forms of vasopressin might trigger cytotoxicity in vivo, as has been proposed in the case of prion protein, which also contains an inefficient N-terminal signal peptide.
Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland.
Michael A
MA
Friberg
Martin
M
Spiess
Jonas
J
Rutishauser
D000595:Amino Acid Sequence; D000818:Animals; D001127:Arginine Vasopressin; D019556:COS Cells; D002460:Cell Line; D045744:Cell Line, Tumor; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006031:Glycosylation; D006801:Humans; D008954:Models, Biological; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000378:metabolism*; D009154:Mutation; D009474:Neurons / Q000378:metabolism; D009481:Neurophysins; D010121:Oxytocin; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011480:Protease Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex; D011498:Protein Precursors / Q000378:metabolism / Q000502:physiology*; D021382:Protein Sorting Signals; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D014667:Vasopressins / Q000378:metabolism / Q000502:physiology*
D018076:DNA, Complementary; D009097:Multienzyme Complexes; D009481:Neurophysins; D011480:Protease Inhibitors; D011498:Protein Precursors; D021382:Protein Sorting Signals; D014667:Vasopressins; D001127:Arginine Vasopressin; D010121:Oxytocin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex