Higher-order Oligomerization Promotes Localization of SPOP to Liquid Nuclear Speckles

EMBO J. 2016 Jun 15;35(12):1254-75. doi: 10.15252/embj.201593169. Epub 2016 May 23.

Abstract

Membrane-less organelles in cells are large, dynamic protein/protein or protein/RNA assemblies that have been reported in some cases to have liquid droplet properties. However, the molecular interactions underlying the recruitment of components are not well understood. Herein, we study how the ability to form higher-order assemblies influences the recruitment of the speckle-type POZ protein (SPOP) to nuclear speckles. SPOP, a cullin-3-RING ubiquitin ligase (CRL3) substrate adaptor, self-associates into higher-order oligomers; that is, the number of monomers in an oligomer is broadly distributed and can be large. While wild-type SPOP localizes to liquid nuclear speckles, self-association-deficient SPOP mutants have a diffuse distribution in the nucleus. SPOP oligomerizes through its BTB and BACK domains. We show that BTB-mediated SPOP dimers form linear oligomers via BACK domain dimerization, and we determine the concentration-dependent populations of the resulting oligomeric species. Higher-order oligomerization of SPOP stimulates CRL3(SPOP) ubiquitination efficiency for its physiological substrate Gli3, suggesting that nuclear speckles are hotspots of ubiquitination. Dynamic, higher-order protein self-association may be a general mechanism to concentrate functional components in membrane-less cellular bodies.

Keywords: isodesmic self‐association; membrane‐less organelle; prostate cancer; speckle‐type POZ protein; ubiquitin ligase.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Nucleus / metabolism*
  • Humans
  • Kruppel-Like Transcription Factors / metabolism
  • Macromolecular Substances / metabolism*
  • Nerve Tissue Proteins / metabolism
  • Nuclear Proteins / metabolism*
  • Protein Binding
  • Protein Domains
  • Protein Multimerization*
  • Repressor Proteins / metabolism*
  • Ubiquitination
  • Zinc Finger Protein Gli3

Substances

  • GLI3 protein, human
  • Kruppel-Like Transcription Factors
  • Macromolecular Substances
  • Nerve Tissue Proteins
  • Nuclear Proteins
  • Repressor Proteins
  • SPOP protein, human
  • Zinc Finger Protein Gli3