title: Parkin mediates the degradation-independent ubiquitination of Hsp70.
abstract: Mutations in the parkin gene cause autosomal recessive, juvenile-onset parkinsonism. Parkin is an E3 ubiquitin ligase that mediates the ubiquitination of protein substrates. Disease-associated mutations cause a loss-of-function of parkin which may compromise the poly-ubiquitination and proteasomal degradation of specific protein substrates, potentially leading to their deleterious accumulation. Here, we identify the molecular chaperones, Hsp70 and Hsc70, as substrates for parkin. Parkin mediates the ubiquitination of Hsp70 both in vitro and in cultured cells. Parkin interacts with Hsp70 via its second RING finger domain and mutations in/near this domain compromise Hsp70 ubiquitination. Ubiquitination of Hsp70 fails to alter its steady-state levels or turnover, nor does it promote its proteasomal degradation. Consistent with this observation, Hsp70 levels remain unaltered in brains from parkin-deficient autosomal recessive, juvenile-onset parkinsonism subjects, whereas alternatively, Hsp70 levels are elevated in the detergent-insoluble fraction of sporadic Parkinson's disease/dementia with Lewy bodies brains. Parkin mediates the multiple mono-ubiquitination of Hsp70/Hsc70 consistent with a degradation-independent role for this ubiquitin modification. Our observations support a novel functional relationship between parkin and Hsc/Hsp70 and support the notion that parkin is a multi-purpose E3 ubiquitin ligase capable of modifying proteins either via attachment of alternatively linked poly-ubiquitin chains or through multiple mono-ubiquitination to achieve alternate biological outcomes.
authors.affiliation: Institute for Cell Engineering, and Department of Neurology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA. djmoore@jhmi.edu
authors.forename: Darren J
authors.initials: DJ
authors.lastname: Moore
authors.forename: Andrew B
authors.initials: AB
authors.lastname: West
authors.forename: Dustin A
authors.initials: DA
authors.lastname: Dikeman
authors.forename: Valina L
authors.initials: VL
authors.lastname: Dawson
authors.forename: Ted M
authors.initials: TM
authors.lastname: Dawson
mesh_terms: D000368:Aged; D001921:Brain / Q000201:enzymology / Q000473:pathology / Q000502:physiology; D002460:Cell Line; D045744:Cell Line, Tumor; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D010300:Parkinson Disease / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000502:physiology*
chemical_list: D018840:HSP70 Heat-Shock Proteins; D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases; C111567:parkin protein