Ubiquitin-dependent and ubiquitin-independent control of subunit stoichiometry in the SWI/SNF complex

J Biol Chem. 2010 Nov 12;285(46):35665-74. doi: 10.1074/jbc.M110.173997. Epub 2010 Sep 9.

Abstract

The mammalian SWI/SNF chromatin remodeling complex is a key player in multiple chromatin transactions. Core subunits of this complex, including the ATPase, Brg-1, and various Brg-1-associated factors (BAFs), work in concert to maintain a functional remodeling complex. This intra-complex regulation is supervised by protein-protein interactions, as stoichiometric levels of BAF proteins are maintained by proteasomal degradation. We show that the mechanism of BAF155-mediated stabilization of BAF57 involves blocking its ubiquitination by preventing interaction with TRIP12, an E3 ubiquitin ligase. Consequently, as opposed to complexed BAF57, whose principal lysines are unavailable for ubiquitination, uncomplexed BAF57 can be freely ubiquitinated and degraded by the proteasome. Additionally, a BAF57 mutant, which contains no lysine residues, was found to retain its ability to be stabilized by interaction with BAF155, suggesting that in addition to the ubiquitin-dependent mechanism of BAF57 degradation, there exists a ubiquitin-independent mechanism that may involve the direct interaction of BAF57 with the proteasome. We propose that this regulatory mechanism exists to ensure functional fidelity of the complex and prevent the accumulation of uncomplexed proteins, which may disrupt the normal activity of the complex.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, N.I.H., Intramural

MeSH terms

  • Amino Acid Substitution
  • Blotting, Western
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism
  • Cell Line, Tumor
  • Chromosomal Proteins, Non-Histone / genetics
  • Chromosomal Proteins, Non-Histone / metabolism*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism
  • Humans
  • Immunoprecipitation
  • Mutation
  • Proteasome Endopeptidase Complex / metabolism*
  • Protein Binding
  • Protein Subunits / genetics
  • Protein Subunits / metabolism
  • RNA Interference
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*
  • Transfection
  • Ubiquitin / metabolism*
  • Ubiquitin-Protein Ligases / genetics
  • Ubiquitin-Protein Ligases / metabolism
  • Ubiquitination

Substances

  • Carrier Proteins
  • Chromosomal Proteins, Non-Histone
  • DNA-Binding Proteins
  • Protein Subunits
  • SMARCC1 protein, human
  • SMARCE1 protein, human
  • SWI-SNF-B chromatin-remodeling complex
  • Transcription Factors
  • Ubiquitin
  • TRIP12 protein, human
  • Ubiquitin-Protein Ligases
  • Proteasome Endopeptidase Complex