CHIP Promotes Proteasomal Degradation of Familial ALS-linked Mutant SOD1 by Ubiquitinating Hsp/Hsc70

J Neurochem. 2004 Jul;90(1):231-44. doi: 10.1111/j.1471-4159.2004.02486.x.

Abstract

Over 100 mutants in superoxide dismutase 1 (SOD1) are reported in familial amyotrophic lateral sclerosis (ALS). However, the precise mechanism by which they are degraded through a ubiquitin-proteasomal pathway (UPP) remains unclear. Here, we report that heat-shock protein (Hsp) or heat-shock cognate (Hsc)70, and the carboxyl terminus of the Hsc70-interacting protein (CHIP), are involved in proteasomal degradation of mutant SOD1. Only mutant SOD1 interacted with Hsp/Hsc70 in vivo, and in vitro experiments revealed that Hsp/Hsc70 preferentially interacted with apo-SOD1 or dithiothreitol (DTT)-treated holo-SOD1, compared with metallated or oxidized forms. CHIP, a binding partner of Hsp/Hsc70, interacted only with mutant SOD1 and promoted its degradation. Both Hsp70 and CHIP promoted polyubiquitination of mutant SOD1-associated molecules, but not of mutant SOD1, indicating that mutant SOD1 is not a substrate of CHIP. Moreover, mutant SOD1-associated Hsp/Hsc70, a known substrate of CHIP, was polyubiquitinated in vivo, and polyubiquitinated Hsc70 by CHIP interacted with the S5a subunit of the 26S proteasome in vitro. Furthermore, CHIP was predominantly expressed in spinal neurons, and ubiquitinated inclusions in the spinal motor neurons of hSOD1(G93A) transgenic mice were CHIP-immunoreactive. Taken together, we propose a novel pathway in which ubiquitinated Hsp/Hsc70 might deliver mutant SOD1 to, and facilitate its degradation, at the proteasome.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amyotrophic Lateral Sclerosis / enzymology
  • Amyotrophic Lateral Sclerosis / genetics
  • Amyotrophic Lateral Sclerosis / metabolism*
  • Animals
  • Cells, Cultured
  • Disease Models, Animal
  • HSC70 Heat-Shock Proteins
  • HSP70 Heat-Shock Proteins / genetics
  • HSP70 Heat-Shock Proteins / metabolism*
  • Humans
  • Inclusion Bodies / metabolism
  • Macromolecular Substances
  • Mice
  • Mice, Transgenic
  • Motor Neurons / metabolism
  • Mutation
  • Peptide Hydrolases / metabolism*
  • Proteasome Endopeptidase Complex*
  • Protein Subunits / metabolism
  • Superoxide Dismutase / genetics
  • Superoxide Dismutase / metabolism*
  • Transfection
  • Ubiquitin / metabolism*
  • Ubiquitin-Protein Ligases / genetics
  • Ubiquitin-Protein Ligases / metabolism
  • Ubiquitin-Protein Ligases / physiology*

Substances

  • HSC70 Heat-Shock Proteins
  • HSP70 Heat-Shock Proteins
  • HSPA8 protein, human
  • Hspa8 protein, mouse
  • Macromolecular Substances
  • Protein Subunits
  • Ubiquitin
  • SOD1 G93A protein
  • Superoxide Dismutase
  • STUB1 protein, human
  • Ubiquitin-Protein Ligases
  • Peptide Hydrolases
  • Proteasome Endopeptidase Complex
  • ATP dependent 26S protease