title: Proteasome inhibition promotes Parkin-Ubc13 interaction and lysine 63-linked ubiquitination.
abstract: Disruption of the ubiquitin-proteasome system, which normally identifies and degrades unwanted intracellular proteins, is thought to underlie neurodegeneration. Supporting this, mutations of Parkin, a ubiquitin ligase, are associated with autosomal recessive parkinsonism. Remarkably, Parkin can protect neurons against a wide spectrum of stress, including those that promote proteasome dysfunction. Although the mechanism underlying the preservation of proteasome function by Parkin is hitherto unclear, we have previously proposed that Parkin-mediated K63-linked ubiquitination (which is usually uncoupled from the proteasome) may serve to mitigate proteasomal stress by diverting the substrate load away from the machinery. By means of linkage-specific antibodies, we demonstrated here that proteasome inhibition indeed promotes K63-linked ubiquitination of proteins especially in Parkin-expressing cells. Importantly, we further demonstrated that the recruitment of Ubc13 (an E2 that mediates K63-linked polyubiquitin chain formation exclusively) by Parkin is selectively enhanced under conditions of proteasomal stress, thus identifying a mechanism by which Parkin could promote K63-linked ubiquitin modification in cells undergoing proteolytic stress. This mode of ubiquitination appears to facilitate the subsequent clearance of Parkin substrates via autophagy. Consistent with the proposed protective role of K63-linked ubiquitination in times of proteolytic stress, we found that Ubc13-deficient cells are significantly more susceptible to cell death induced by proteasome inhibitors compared to their wild type counterparts. Taken together, our study suggests a role for Parkin-mediated K63 ubiquitination in maintaining cellular protein homeostasis, especially during periods when the proteasome is burdened or impaired.
authors.affiliation: Department of Physiology, National University of Singapore, Singapore, Singapore ; Neurodegeneration Research Laboratory, National Neuroscience Institute, Singapore, Singapore.
authors.forename: Grace G Y
authors.initials: GG
authors.lastname: Lim
authors.forename: Katherine C M
authors.initials: KC
authors.lastname: Chew
authors.forename: Xiao-Hui
authors.initials: XH
authors.lastname: Ng
authors.forename: Adeline
authors.initials: A
authors.lastname: Henry-Basil
authors.forename: Roy W X
authors.initials: RW
authors.lastname: Sim
authors.forename: Jeanne M M
authors.initials: JM
authors.lastname: Tan
authors.forename: Chou
authors.initials: C
authors.lastname: Chai
authors.forename: Kah-Leong
authors.initials: KL
authors.lastname: Lim
mesh_terms: D001343:Autophagy / Q000187:drug effects; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D008239:Lysine / Q000378:metabolism*; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors / Q000494:pharmacology*; D011485:Protein Binding / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D059748:Proteolysis / Q000187:drug effects; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination / Q000187:drug effects*
chemical_list: D002352:Carrier Proteins; D009419:Nerve Tissue Proteins; D061988:Proteasome Inhibitors; C118958:SNCAIP protein, human; C471607:UBE2N protein, human; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; C111567:parkin protein; D046988:Proteasome Endopeptidase Complex; D008239:Lysine
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