Asterless is a Polo-like kinase 4 substrate that both activates and inhibits kinase activity depending on its phosphorylation state

Mol Biol Cell. 2018 Nov 15;29(23):2874-2886. doi: 10.1091/mbc.E18-07-0445. Epub 2018 Sep 26.


Centriole assembly initiates when Polo-like kinase 4 (Plk4) interacts with a centriole "targeting-factor." In Drosophila, Asterless/Asl (Cep152 in humans) fulfills the targeting role. Interestingly, Asl also regulates Plk4 levels. The N-terminus of Asl (Asl-A; amino acids 1-374) binds Plk4 and promotes Plk4 self-destruction, although it is unclear how this is achieved. Moreover, Plk4 phosphorylates the Cep152 N-terminus, but the functional consequence is unknown. Here, we show that Plk4 phosphorylates Asl and mapped 13 phospho-residues in Asl-A. Nonphosphorylatable alanine (13A) and phosphomimetic (13PM) mutants did not alter Asl function, presumably because of the dominant role of the Asl C-terminus in Plk4 stabilization and centriolar targeting. To address how Asl-A phosphorylation specifically affects Plk4 regulation, we generated Asl-A fragment phospho-mutants and expressed them in cultured Drosophila cells. Asl-A-13A stimulated kinase activity by relieving Plk4 autoinhibition. In contrast, Asl-A-13PM inhibited Plk4 activity by a novel mechanism involving autophosphorylation of Plk4's kinase domain. Thus, Asl-A's phosphorylation state determines which of Asl-A's two opposing effects are exerted on Plk4. Initially, nonphosphorylated Asl binds Plk4 and stimulates its kinase activity, but after Asl is phosphorylated, a negative-feedback mechanism suppresses Plk4 activity. This dual regulatory effect by Asl-A may limit Plk4 to bursts of activity that modulate centriole duplication.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cell Cycle / physiology
  • Cell Cycle Proteins / metabolism
  • Cell Line
  • Centrioles / metabolism
  • Drosophila
  • Drosophila Proteins / genetics*
  • Drosophila Proteins / metabolism*
  • Phosphorylation
  • Protein Binding
  • Protein Serine-Threonine Kinases / metabolism*


  • Asl protein, Drosophila
  • Cell Cycle Proteins
  • Drosophila Proteins
  • PLK4 protein, human
  • Protein Serine-Threonine Kinases
  • Sak protein, Drosophila