# Mechanisms underlying USP1-mediated bypass of EWS-FLI1 oncogene-induced replication stress in Ewing sarcoma

> **NIH NIH R01** · UNIVERSITY OF NEBRASKA MEDICAL CENTER · 2022 · $351,131

## Abstract

PROJECT SUMMARY
 Replication stress leading to genome instability is an early driver of tumorigenesis and has been
associated with overexpression of oncogenes. In normal cells, activation of the DNA damage response (DDR)
pathway serves as a barrier to tumorigenesis leading to cell cycle arrest inducing cellular senescence or cell
death in response to high burden of genome instability. However, in cancer cells upon oncogene-induced
replication stress the protective barrier of DDR, cell death and senescence is bypassed leading to uncontrolled
cell proliferation. Therefore, deciphering the mechanisms that bypass oncogene-induced replication stress and
senescence will help understand the basic science underlying disease progression and will identify new targets
for therapy.
 Ewing sarcoma (EWS) is driven by a chromosomal translocation and in-frame gene fusion between
EWSR1 and ETS family of transcription factors. In majority of the EWS cases, the chromosomal translocation
results in the generation of EWS-FLI1 oncogene. EWS-FLI1 functions as an aberrant transcription factor that
drives the development and progression of EWS. Expression of EWS-FLI1 oncogene leads to oncogene-induced
replication stress and genome instability. However, the molecular mechanism underlying bypass of EWS-FLI1
oncogene-induced replication stress response pathways is largely unknown. Our preliminary data shows that
USP1 deubiquitinase is overexpressed in EWS cell lines and tumors. USP1 regulates DDR and is required for
genome stability and stem cell maintenance. We find that USP1 expression is regulated by EWS-FLI1 in EWS.
Importantly, inhibition of USP1 activity using small molecule USP1 inhibitors resulted in growth arrest of EWS
cell lines indicating that USP1 expression and activity is important for EWS cell proliferation and progression.
Notably, USP1 depletion led to a decrease in the levels of HELLS chromatin remodeling protein. The function of
USP1 or HELLS in EWS pathogenesis has not been investigated. In this study, we will examine the regulation
of HELLS by USP1 deubiquitinase (Aim 1), determine the mechanism by which USP1 promotes EWS cell
proliferation (Aim 2), and determine the effect of USP1 knockdown on EWS tumor formation in vivo and the
efficacy of USP1 inhibition in combination with chemotherapeutic drugs at suppressing EWS cell proliferation
(Aim 3).
 Successful completion of this study will unravel novel mechanistic insights into USP1 mediated bypass
of EWS-FLI1 oncogene-induced replication stress and help evaluate USP1 targeted treatment strategies for
EWS.

## Key facts

- **NIH application ID:** 10446807
- **Project number:** 1R01CA263504-01A1
- **Recipient organization:** UNIVERSITY OF NEBRASKA MEDICAL CENTER
- **Principal Investigator:** GARGI GHOSAL
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $351,131
- **Award type:** 1
- **Project period:** 2022-08-05 → 2027-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10446807

## Citation

> US National Institutes of Health, RePORTER application 10446807, Mechanisms underlying USP1-mediated bypass of EWS-FLI1 oncogene-induced replication stress in Ewing sarcoma (1R01CA263504-01A1). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10446807. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*