title: Increased polyubiquitination and proteasomal degradation of a Munc18-1 disease-linked mutant causes temperature-sensitive defect in exocytosis.
abstract: Munc18-1 is a critical component of the core machinery controlling neuroexocytosis. Recently, mutations in Munc18-1 leading to the development of early infantile epileptic encephalopathy have been discovered. However, which degradative pathway controls Munc18-1 levels and how it impacts on neuroexocytosis in this pathology is unknown. Using neurosecretory cells deficient in Munc18, we show that a disease-linked mutation, C180Y, renders the protein unstable at 37°C. Although the mutated protein retains its function as t-SNARE chaperone, neuroexocytosis is impaired, a defect that can be rescued at a lower permissive temperature. We reveal that Munc18-1 undergoes K48-linked polyubiquitination, which is highly increased by the mutation, leading to proteasomal, but not lysosomal, degradation. Our data demonstrate that functional Munc18-1 levels are controlled through polyubiquitination and proteasomal degradation. The C180Y disease-causing mutation greatly potentiates this degradative pathway, rendering Munc18-1 unable to facilitate neuroexocytosis, a phenotype that is reversed at a permissive temperature.
authors.affiliation: Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia. Electronic address: s.martin@uq.edu.au.
authors.forename: Sally
authors.initials: S
authors.lastname: Martin
authors.affiliation: Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia.
authors.forename: Andreas
authors.initials: A
authors.lastname: Papadopulos
authors.affiliation: Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia.
authors.forename: Vanesa M
authors.initials: VM
authors.lastname: Tomatis
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD 4072, Australia.
authors.forename: Emma
authors.initials: E
authors.lastname: Sierecki
authors.affiliation: Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia.
authors.forename: Nancy T
authors.initials: NT
authors.lastname: Malintan
authors.affiliation: Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia.
authors.forename: Rachel S
authors.initials: RS
authors.lastname: Gormal
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD 4072, Australia.
authors.forename: Nichole
authors.initials: N
authors.lastname: Giles
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD 4072, Australia.
authors.forename: Wayne A
authors.initials: WA
authors.lastname: Johnston
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD 4072, Australia.
authors.forename: Kirill
authors.initials: K
authors.lastname: Alexandrov
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD 4072, Australia.
authors.forename: Yann
authors.initials: Y
authors.lastname: Gambin
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD 4072, Australia.
authors.forename: Brett M
authors.initials: BM
authors.lastname: Collins
authors.affiliation: Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia. Electronic address: f.meunier@uq.edu.au.
authors.forename: Frederic A
authors.initials: FA
authors.lastname: Meunier
mesh_terms: D000818:Animals; D005089:Exocytosis / Q000502:physiology; D006801:Humans; D008958:Models, Molecular; D051938:Munc18 Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D017354:Point Mutation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D051381:Rats; D050600:SNARE Proteins / Q000378:metabolism; D054875:Ubiquitination
chemical_list: D051938:Munc18 Proteins; D050600:SNARE Proteins; D046988:Proteasome Endopeptidase Complex