title: The ALS8-associated mutant VAPB(P56S) is resistant to proteolysis in neurons.
abstract: VAMP/synaptobrevin associated proteins A and B (VAPA and VAPB), are type IV membrane proteins enriched on ER and Golgi membranes. Both VAPA and B interact with cytoplasmic lipid transport proteins and cytoskeletal elements to maintain the structure and composition of ER and Golgi membranes. Truncated forms of both proteins are present in some tissues but the functional significance of this is not clear. In rodents processing of VAPA occurs in most tissues, however, truncated forms of VAPB have only been reported in brain tissue. It is demonstrated here that the extent of VAPB processing in rat increases during postnatal development and that it is restricted to neurons. The C-terminal polypeptide generated by this cleavage reaction remains associated with cell membranes, but its subcellular distribution is distinct from the full-length protein. A mutant form of VAPB is associated with a familial form of neurodegenerative disease, amyotrophic lateral sclerosis type 8. The mutant protein, VAPB(P56S) , is resistant to truncation in primary neuronal cultures, although remains sensitive to some form of proteolysis when over-expressed in HEK293 cells. These data suggest that neuronal cells have a particular requirement for VAPB proteolysis and that reduced levels of processed polypeptides may contribute to the neurodegeneration associated with amyotrophic lateral sclerosis type 8.
authors.affiliation: Centre for Integrative Physiology, The University of Edinburgh, Edinburgh, UK.
authors.forename: Christos
authors.initials: C
authors.lastname: Gkogkas
authors.forename: Caroline
authors.initials: C
authors.lastname: Wardrope
authors.forename: Matthew
authors.initials: M
authors.lastname: Hannah
authors.forename: Paul
authors.initials: P
authors.lastname: Skehel
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D000831:Animals, Newborn; D001692:Biological Transport / Q000235:genetics; D016923:Cell Death; D002540:Cerebral Cortex / Q000166:cytology; D004622:Embryo, Mammalian; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism; D005904:Glial Fibrillary Acidic Protein / Q000235:genetics / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics*; D046529:Microscopy, Electron, Transmission / Q000379:methods; D008970:Molecular Weight; D009154:Mutation / Q000235:genetics*; D009457:Neuroglia / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D011392:Proline / Q000235:genetics*; D012333:RNA, Messenger; D051381:Rats; D012694:Serine / Q000235:genetics*; D013347:Subcellular Fractions / Q000378:metabolism; D016708:Synaptophysin / Q000235:genetics / Q000378:metabolism; D014162:Transfection / Q000379:methods; D056811:Unfolded Protein Response / Q000235:genetics
chemical_list: D005904:Glial Fibrillary Acidic Protein; D008565:Membrane Proteins; D012333:RNA, Messenger; D016708:Synaptophysin; C529893:VAPB protein, rat; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D012694:Serine; D011392:Proline