Regulation of mitotic spindle assembly factor NuMA by Importin-β

J Cell Biol. 2017 Nov 6;216(11):3453-3462. doi: 10.1083/jcb.201705168. Epub 2017 Sep 22.

Abstract

Ran-guanosine triphosphatase orchestrates mitotic spindle assembly by modulation of the interaction between Importin-α/-β and spindle assembly factors (SAFs). The inhibition of SAFs performed by importins needs to be done without much sequestration from abundant nuclear localization signal (NLS) -containing proteins. However, the molecular mechanisms that determine NLS-binding selectivity and that inhibit activity of Importin-β-regulated SAFs (e.g., nuclear mitotic apparatus protein [NuMA]) remain undefined. Here, we present a crystal structure of the Importin-α-NuMA C terminus complex showing a novel binding pattern that accounts for selective NLS recognition. We demonstrate that, in the presence of Importin-α, Importin-β inhibits the microtubule-binding function of NuMA. Further, we have identified a high-affinity microtubule-binding region that lies carboxyl-terminal to the NLS, which is sterically masked by Importin-β on being bound by Importin-α. Our study provides mechanistic evidence of how Importin-α/-β regulates the NuMA functioning required for assembly of higher-order microtubule structures, further illuminating how Ran-governed transport factors regulate diverse SAFs and accommodate various cell demands.

MeSH terms

  • Animals
  • Antigens, Nuclear / chemistry
  • Antigens, Nuclear / genetics
  • Antigens, Nuclear / metabolism*
  • Cell Cycle Proteins
  • Humans
  • Microtubules / metabolism
  • Models, Molecular
  • Multiprotein Complexes
  • Nuclear Matrix-Associated Proteins / chemistry
  • Nuclear Matrix-Associated Proteins / genetics
  • Nuclear Matrix-Associated Proteins / metabolism*
  • Protein Binding
  • Protein Interaction Domains and Motifs
  • Spindle Apparatus / chemistry
  • Spindle Apparatus / genetics
  • Spindle Apparatus / metabolism*
  • Structure-Activity Relationship
  • Xenopus
  • alpha Karyopherins / metabolism
  • beta Karyopherins / chemistry
  • beta Karyopherins / genetics
  • beta Karyopherins / metabolism*
  • ran GTP-Binding Protein / metabolism

Substances

  • Antigens, Nuclear
  • Cell Cycle Proteins
  • Multiprotein Complexes
  • NUMA1 protein, human
  • Nuclear Matrix-Associated Proteins
  • alpha Karyopherins
  • beta Karyopherins
  • ran GTP-Binding Protein

Associated data

  • PDB/1QGK
  • PDB/1IQ1
  • PDB/5GXW