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CHIP deletion reveals functional redundancy of E3 ligases in promoting degradation of both signaling proteins and expanded glutamine proteins.

Abstract
CHIP (carboxy terminus of Hsc70-interacting protein) an E3 ubiquitin ligase that binds to Hsp70 and Hsp90, promotes degradation of several Hsp90-regulated signaling proteins and disease-causing proteins containing expanded glutamine tracts. In polyglutamine disease models, CHIP has been considered a primary protection factor by promoting degradation of these misfolded proteins. Here, we show that two CHIP substrates, the glucocorticoid receptor (GR), a classic Hsp90-regulated signaling protein, and the expanded glutamine androgen receptor (AR112Q), are degraded at the same rate in CHIP(-/-) and CHIP(+/+) mouse embryonic fibroblasts after treatment with the Hsp90 inhibitor geldanamycin. CHIP(-/-) cytosol has the same ability as CHIP(+/+) cytosol to ubiquitinate purified neuronal nitric oxide synthase (nNOS), another established CHIP substrate. To determine whether other E3 ubiquitin ligases that bind to Hsp70 (Parkin) or Hsp90 (Mdm2) act on CHIP substrates, each E3 ligase was co-expressed with the GR, nNOS, AR112Q or Q78 ataxin-3. CHIP lowered the levels of all four proteins, Parkin acted on nNOS and Q78 ataxin-3 but not on the steroid receptors, and Mdm2 did not affect any of the co-expressed proteins. Moreover, both CHIP and Parkin co-localized to aggregates of the expanded glutamine AR formed in cell culture and in a knock-in mouse model of spinal and bulbar muscular atrophy. These observations establish that CHIP does not play an exclusive role in regulating the turnover of Hsp90 client signaling proteins or expanded glutamine tract proteins, and show that the Hsp70-dependent E3 ligase Parkin acts redundantly to CHIP on some substrates.
AuthorsYoshihiro Morishima, Adrienne M Wang, Zhigang Yu, William B Pratt, Yoichi Osawa, Andrew P Lieberman
JournalHuman molecular genetics (Hum Mol Genet) Vol. 17 Issue 24 Pg. 3942-52 (Dec 15 2008) ISSN: 1460-2083 [Electronic] England
PMID18784277 (Publication Type: Comparative Study, Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
Chemical References
  • Intercellular Signaling Peptides and Proteins
  • Glutamine
  • STUB1 protein, human
  • Stub1 protein, mouse
  • Ubiquitin-Protein Ligases
Topics
  • Animals
  • Cells, Cultured
  • Gene Deletion
  • Glutamine (genetics, metabolism)
  • HeLa Cells
  • Humans
  • Intercellular Signaling Peptides and Proteins (genetics, metabolism, physiology)
  • Mice
  • Mice, Knockout
  • Signal Transduction (genetics)
  • Ubiquitin-Protein Ligases (deficiency, genetics, physiology)

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