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Akt switches TopBP1 function from checkpoint activation to transcriptional regulation through phosphoserine

Kang Liu1, Joshua D Graves, Jessica D Scott

  • 1Section of Hematology/Oncology, Departments of Medicine and Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas, USA.

Molecular and Cellular Biology
|October 2, 2013
PubMed

Insights

Akt-induced phosphorylation of TopBP1 protein causes it to oligomerize, which switches its function from activating cell checkpoints to regulating transcription. This mechanism is therapeutically relevant for cancer treatment.

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Cancer Research

Background:

  • Akt phosphorylates TopBP1 protein, inducing oligomerization required for E2F1 activity repression.
  • The precise mechanism linking Akt-mediated phosphorylation to TopBP1 oligomerization was previously undetermined.

Purpose of the Study:

  • To elucidate the mechanism of Akt-induced TopBP1 oligomerization.
  • To investigate the functional consequences of TopBP1 oligomerization on cellular processes and its clinical relevance.

Main Methods:

  • Site-directed mutagenesis of TopBP1 BRCT domains.
  • In vitro size exclusion chromatography.
  • Analysis of protein recruitment to chromatin and protein binding interactions.

Main Results:

  • Phosphorylated Ser-1159 on TopBP1 binds to its 7th and 8th BRCT domains, mediating oligomerization.
  • Mutations disrupting this interaction abolish TopBP1 oligomerization and E2F1 repression.
  • TopBP1 oligomerization prevents chromatin recruitment and ATR binding during replicative stress, inhibiting checkpoint activation.
  • Akt inhibition in PTEN-mutated cancer cells reverses TopBP1 oligomerization, restoring checkpoint activation.

Conclusions:

  • Akt regulates TopBP1 quaternary structure, switching its function from checkpoint activation to transcriptional regulation.
  • Targeting Akt with inhibitors can disrupt TopBP1 oligomerization in cancer cells, reverting its function to promote cell survival via checkpoint activation.

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