# Potential role of heterochromatin protein 1γ  in the control of FOXP3 stability and expression in induced CD4+ regulatory T cells

> **NIH NIH R21** · BETH ISRAEL DEACONESS MEDICAL CENTER · 2020 · $262,500

## Abstract

PROJECT SUMMARY
This proposal focuses on histone code reader Cbx3/HP1γ potential ability to regulate the stability/expression of
FOXP3 (X chromosome-encoded transcription factor forkhead box P3), and whether its regulatory function can
be commandeered to treat autoimmune disorders, graft-versus-host disease (GVHD) and/or prevent graft
rejection.
 CD4+ regulatory T (Treg) cells represent a unique lineage of CD4+ T cells whose crucial function is to
maintain self-tolerance and control autoimmunity. Thus, Treg cells are being exploited to treat GVHD and
some autoimmune disorders. Due to its low numbers, naturally occurring Treg cells are difficult to isolate. For
this reason, induced Treg (iTreg) cells are being used in the clinic. However, the instability of FOXP3
expression in Treg cells poses a serious potential limitation. Therefore, the challenge is to identify novel means
to stabilize FOXP3 expression.
 FOXP3 stability/expression is regulated in part by three conserved noncoding sequence (CNS1/2/3)
elements found in the first intron of Foxp3. Of these, CNS2 controls the stability of FOXP3 expression through
CNS2 DNA modification (methylation or demethylation) status. DNA methylation is controlled by a balance
between DNA methyltransferases (DNMTs) and DNA demethylases that act in concert with transcription
factors and accessory proteins to regulate gene expression. Genetic deletion of Dnmt1 leads to enhanced
FOXP3 expression suggesting that DNMT1 limits FOXP3 expression. How DNMT1 activity is regulated in Treg
cells is still unknown. An attractive target is Cbx3/HP1γ shown to interact with methyl groups of histones H3 at
lysine 9 (H3K9Me3) and DNMT1. Our preliminary results demonstrate that Cbx3/HP1γ-deficient iTreg cells
express more FOXP3, both protein and transcripts.
 We propose that in normal CD4+ Treg cells, Cbx3/HP1γ restrains FOXP3 expression. Mechanistically,
Cbx3/HP1γ occupies the Foxp3 locus via its ability to interact with histones H3K9m3 as well as DNMT1 to
maintain a fully methylated and repressed Foxp3 locus. In the absence or decreased level of Cbx3/HP1γ,
methylation of Foxp3 is lost or reduced resulting in FOXP3 sustained and stable expression. Thus, Cbx3/HP1γ-
deficient iTreg cells would be more stable and could be used to treat immune disorders and/or GVHD.
 If successful, our proposal will reveal that the histone code reader Cbx3/HP1γ regulates Foxp3
stability/expression. Our findings will contribute to understanding the complex epigenetic regulation of Foxp3
stability/expression and Treg development. Our results will provide novel means to manipulate the epigenome
of CD4+ T cells to generate stable iTregs with sustained Foxp3 expression to treat autoimmune disorders,
GVHD and/or prevent chronic graft rejection in humans.

## Key facts

- **NIH application ID:** 9822956
- **Project number:** 5R21AI137751-02
- **Recipient organization:** BETH ISRAEL DEACONESS MEDICAL CENTER
- **Principal Investigator:** To-Ha Thai
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $262,500
- **Award type:** 5
- **Project period:** 2018-12-01 → 2021-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9822956

## Citation

> US National Institutes of Health, RePORTER application 9822956, Potential role of heterochromatin protein 1γ  in the control of FOXP3 stability and expression in induced CD4+ regulatory T cells (5R21AI137751-02). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/9822956. Licensed CC0.

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