Aurora-A phosphorylates Augmin complex component Hice1 protein at an N-terminal serine/threonine cluster to modulate its microtubule binding activity during spindle assembly

J Biol Chem. 2011 Aug 26;286(34):30097-106. doi: 10.1074/jbc.M111.266767. Epub 2011 Jun 24.

Abstract

Proper assembly of mitotic spindles requires Hice1, a spindle-associated protein. Hice1 possesses direct microtubule binding activity at its N-terminal region and contributes to intraspindle microtubule nucleation as a subunit of the Augmin complex. However, whether microtubule binding activity of Hice1 is modulated by mitotic regulators remains unexplored. Here, we found that Aurora-A kinase, a major mitotic kinase, specifically binds to and phosphorylates Hice1. We identified four serine/threonine clusters on Hice1 that can be phosphorylated by Aurora-A in vitro. Of the four clusters, the Ser/Thr-17-21 cluster was the most critical for bipolar spindle assembly, whereas other phospho-deficient point mutants had a minimal effect on spindle assembly. Immunostaining with a phospho-Ser-19/20 phospho-specific antibody revealed that phosphorylated Hice1 primarily localizes to spindle poles during prophase to metaphase but gradually diminishes after anaphase. Consistently, the phospho-mimic 17-21E mutant reduced microtubule binding activity in vitro and diminished localization to spindles in vivo. Furthermore, expression of the 17-21E mutant led to decreased association of Fam29a, an Augmin component, with spindles. On the other hand, expression of the phospho-deficient 17-21A mutant permitted intraspindle nucleation but delayed the separation of early mitotic spindle poles and the timely mitotic progression. Taken together, these results suggest that Aurora-A modulates the microtubule binding activity of Hice1 in a spatiotemporal manner for proper bipolar spindle assembly.

Publication types

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

MeSH terms

  • Aurora Kinases
  • Cell Line, Tumor
  • Humans
  • Metaphase / physiology*
  • Microtubule-Associated Proteins / genetics
  • Microtubule-Associated Proteins / metabolism*
  • Microtubules / genetics
  • Microtubules / metabolism*
  • Mutation
  • Phosphorylation / physiology
  • Prophase / physiology*
  • Protein Serine-Threonine Kinases / genetics
  • Protein Serine-Threonine Kinases / metabolism*
  • Protein Structure, Tertiary
  • Spindle Apparatus / genetics
  • Spindle Apparatus / metabolism*

Substances

  • HAUS8 protein, human
  • Microtubule-Associated Proteins
  • Aurora Kinases
  • Protein Serine-Threonine Kinases