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Dephosphorylation enables the recruitment of 53BP1 to double-strand DNA breaks

Dong-Hyun Lee1, Sanket S Acharya2, Mijung Kwon3

  • 1Department of Radiation Oncology, Dana-Farber Cancer Institute, Boston, MA 02115, USA; Department of Biological Sciences, College of Science, Chonnam National University, Gwangju 500-757, Republic of Korea.

Molecular Cell
|April 8, 2014
PubMed

Insights

Mitotic exclusion of 53BP1, a key DNA repair protein, is regulated by phosphorylation at T1609/S1618. This prevents its chromatin binding during mitosis, ensuring proper cell division and restoring DNA damage response in G1.

Area of Science:

  • Cellular biology
  • Molecular biology
  • Genetics

Background:

  • 53BP1 exclusion from chromatin is crucial for attenuating the DNA damage response (DDR) during mitosis.
  • The precise mechanisms and physiological relevance of this mitotic exclusion remain incompletely understood.

Purpose of the Study:

  • To elucidate the molecular regulation of 53BP1 exclusion during mitosis.
  • To identify the functional consequences of aberrant 53BP1 chromatin binding during cell division.
  • To uncover the phosphatase responsible for reversing 53BP1 inhibition in interphase.

Main Methods:

  • Phosphorylation site mapping of 53BP1 during mitosis.
  • Biochemical assays to assess 53BP1-nucleosome interactions.
  • Mitotic progression analysis in cells with altered 53BP1 phosphorylation.
  • Investigation of PP4C/R3β phosphatase activity on 53BP1.

Main Results:

  • 53BP1 is phosphorylated at T1609 and S1618 within its ubiquitination-dependent recruitment (UDR) motif during mitosis.
  • Phosphorylation of T1609/S1618 inhibits 53BP1 binding to ubiquitinated histone H2A and mitotic chromatin.
  • Mutant 53BP1 (T1609A/S1618A) ectopic recruitment causes mitotic defects, reversible by inhibiting nonhomologous end-joining (NHEJ).
  • The PP4C/R3β phosphatase complex dephosphorylates T1609/S1618, enabling 53BP1 chromatin recruitment in G1 phase.

Conclusions:

  • Identifies critical 53BP1 phosphorylation sites (T1609, S1618) regulating its mitotic chromatin exclusion.
  • Reveals PP4C/R3β as the phosphatase counteracting 53BP1 phosphorylation, restoring DNA damage response potential during interphase.
  • Establishes the physiological importance of regulated 53BP1 chromatin binding for accurate cell division and DNA repair.

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