# E2F family transcription factors are directly regulated by TRIM28 to promote castration-resistance in prostate cancer

> **NIH NIH R03** · UNIVERSITY OF KENTUCKY · 2022 · $76,500

## Abstract

Prostate cancer (PCa) is the second-leading cause of cancer-related death in American men.
Androgen deprivation therapies that target the androgen receptor (AR) are the mainstay treatment
for metastatic PCa. New generation anti-androgen enzalutamide (Enz) significantly increases
PCa patient survival. However resistance to Enz develops rapidly. Importantly, castration-
resistant prostate cancer (CRPC) is driven primarily by aberrant activation of the AR in the milieu
of low androgen. The AR exerts its tumorigenic roles mainly through genomic regulation of target
gene expression. This genomic action is tightly regulated by a number of cofactors, and one of
which is TRIM24. We recently reported that TRIM28 is an upstream regulator of TRIM24 protein
stability in CRPC, where both TRIM24 and TRIM28 expression is highly elevated. Mechanistically,
TRIM28 stabilizes TRIM24 by preventing TRIM24 from SPOP-driven ubiquitination and
degradation, and thereby TRIM24 is able to reactivate AR signaling in CRPC. To explore the
TRIM28-mediated downstream signaling, genome-wide transcriptome analysis revealed that
TRIM28 engaged in various oncogenic pathway including cell cycle and DNA replication. By
interrogating cell cycle signature genes, we showed that TRIM28 induces E2F1, E2F2 and E2F3
gene expression in PCa. In addition, TRIM28 ChIP-seq revealed that TRIM28 directly binds to
promoter region of transcription factor E2F1-E2F3, which play a pivotal role in activating
transcription of the genes required for cell cycle progression. Further, deregulated expression or
activity of the E2F family has often been detected in many human cancers, which leads to
uncontrolled cell proliferation. In this proposal, we hypothesize that E2F transcription factor is a
critical downstream target of TRIM28 and clinically-available E2F small molecules inhibitor
LY101-4B may suppress CRPC progression. To test this hypothesis, three specific aims are
proposed. In Aim1 we will first validate the direct regulation of E2F1-E2F3 gene expression by
TRIM28 with the use of genomic approaches. Aim2 will examine clinical expression of E2F and
evaluate the efficacy of E2F inhibitor in CRPC cell lines and xenografts.

## Key facts

- **NIH application ID:** 10445046
- **Project number:** 5R03CA256230-02
- **Recipient organization:** UNIVERSITY OF KENTUCKY
- **Principal Investigator:** Ka-wing Fong
- **Activity code:** R03 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $76,500
- **Award type:** 5
- **Project period:** 2021-07-05 → 2024-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10445046

## Citation

> US National Institutes of Health, RePORTER application 10445046, E2F family transcription factors are directly regulated by TRIM28 to promote castration-resistance in prostate cancer (5R03CA256230-02). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10445046. Licensed CC0.

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