# Role of Nuclear Actin Polymerization in Double-Strand Break Mobility and Repair

> **NIH NIH F30** · COLUMBIA UNIVERSITY HEALTH SCIENCES · 2020 · $31,540

## Abstract

Project Summary:
 Double-strand breaks (DSBs) are DNA lesions that yield loss of genetic material when unrepaired and
chromosome rearrangements when mis-repaired. Abrogating the repair of DSBs generated by chemotherapy
and ionizing radiation remains a major goal in the development of more effective cancer treatments. In
mammalian cells and yeast, DSBs migrate into clusters, which is postulated to concentrate repair factors in
centers to favor more efficient repair7,8,16. In particular, homology-directed repair (HDR) is associated with
increased chromosomal mobility and clustering5,6,9,. The molecular basis for DSB movement however, remains
enigmatic. The machinery that drives actin polymerization is found in the nucleus23,30,31,32. Notably, the Arp2/3
complex, an actin nucleation promoting factor, as well as its activator WASP, a Wiskott-Aldrich syndrome
family member, are known to generate propulsive forces by nucleating a highly-branched network of actin
filaments15. Recently, genotoxic agents were shown to trigger actin polymerization in the nucleoplasm of
mammalian cells11. However, the role of actin filaments in DSB repair is not characterized. Recently, we
performed a proteomic screen using liquid chromatography mass spectrometry to identify novel proteins
recruited to damaged chromatin in Xenopus laevis cell-free extracts. Surprisingly, we observe enrichment of
the Arp2/3 complex, β-actin, and actin filament capping proteins in DSB-containing chromatin relative to
undamaged controls. In mammalian cells, we find that the Arp2/3 complex co-localizes with WASP at DSBs
destined for repair by HDR. Following genome-wide generation of DSBs, we observe clustering of DSB foci,
particularly in S and G2 when HDR predominates. Notably, we show that inhibition of actin polymerization by
small molecule inactivation of WASP or Arp2/3 reduces DSB clustering and repair by homology-directed
mechanisms. We propose, therefore, that the Arp2/3 complex is poised to play a critical role in the
polymerization of actin polymers that cluster DSBs for HDR.
 The overarching goal of this study is to understand the role actin polymerization plays in DSB mobility
and investigate whether Arp2/3 inhibitors synergize with DNA damaging chemotherapies. Given that WASP
and the Arp2/3 complex are enriched in damaged chromatin, I hypothesize that nuclear actin polymerization
drives DSB clustering for DSB repair. I will investigate this hypothesis in the following three aims:
Aim 1: Characterize the spatiotemporal dynamics of nuclear actin polymerization during DSB repair
Aim 2: Investigate actin-driven chromosomal motion during DSB repair and translocation formation
Aim 3: Assess whether Arp2/3 inhibitors chemosensitize tumor cells to DNA damaging therapies

## Key facts

- **NIH application ID:** 9856423
- **Project number:** 5F30CA217049-03
- **Recipient organization:** COLUMBIA UNIVERSITY HEALTH SCIENCES
- **Principal Investigator:** Benjamin R Schrank
- **Activity code:** F30 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $31,540
- **Award type:** 5
- **Project period:** 2018-03-01 → 2020-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9856423

## Citation

> US National Institutes of Health, RePORTER application 9856423, Role of Nuclear Actin Polymerization in Double-Strand Break Mobility and Repair (5F30CA217049-03). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/9856423. Licensed CC0.

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