# The Role of PHF6 in HSC self-renewal and myeloid expansion

> **NIH NIH R01** · UNIVERSITY OF PENNSYLVANIA · 2021 · $536,436

## Abstract

Abstract / Project Summary
Hematopoietic stem cells (HSCs) require fine-tuned cooperation of transcription factors (TFs) and epigenetic
regulators to maintain normal self-renewal. Precise control of this ability is essential to suppress aberrant
proliferation. Understanding the regulation of self-renewal is therefore crucial for gaining insight into normal
and neoplastic hematopoiesis. PHF6, an enigmatic, leukemia-mutated, chromatin-binding protein specifically
represses HSC self-renewal, providing an attractive model for dissecting the underlying regulatory network.
The goal of this proposal is to illuminate a mechanistic link between normal self-renewal and aberrant
proliferation through dissection of how PHF6 modulates enhancers bound by key hematopoietic TFs.
Our in vivo studies show that Phf6 hematopoietic knockout specifically increases HSC self-renewal while
leaving downstream hematopoiesis largely unperturbed. Pilot experiments indicate that constitutive HOXA9
expression cooperates with Phf6 loss to cause rapid, lethal progenitor expansion. We have thus identified
profoundly contrasting homeostatic and HOXA9-driven phenotypes of Phf6 loss, providing an ideal system to
study how HSC self-renewal is co-opted in aberrant proliferation. Our preliminary data show that PHF6 binds
and represses enhancers co-occupied by the TFs RUNX1, PU.1, IRF8. We have thus identified a mechanistic
basis for PHF6 activity (chromatin co-occupancy with key hematopoietic TFs).
We hypothesize that PHF6 represses HSC self-renewal and aberrant myeloid progenitor expansion through a
common mechanism of modulating enhancers bound by RUNX1, PU.1, and IRF8.
Specific Aim 1: We will determine the role of PHF6 in repressing HSC self-renewal and myeloid progenitor
expansion in vivo by determining whether Phf6 loss accelerates HOXA9-driven myeloid progenitor expansion,
whether R274Q mutation abrogates PHF6 functions in HSCs and myeloid progenitors, and whether Phf6 loss
activates RUNX1/PU.1/IRF8-bound enhancers. The experiments in Aim 1 will advance our understanding of
HSC biology by linking self-renewal to aberrant expansion through a core regulatory circuit downstream of
PHF6.
Specific Aim 2: We will determine the mechanism of PHF6 activity in vitro by determining whether
RUNX1/PU.1/IRF8 recruit PHF6 to chromatin, whether R274Q mutation abrogates PHF6 chromatin binding,
and whether PHF6 recruits additional complexes to repress enhancer activity. The experiments in Aim 2 will
illuminate the sequence of events from recruitment of PHF6 to chromatin by key TFs, to the downstream
effects of PHF6 on enhancer function and consequently on gene expression.
These studies, if successful, will pinpoint a disease-relevant mechanism linking HSC self-renewal to aberrant
progenitor expansion through modulation of enhancers by PHF6 in conjunction with hematopoietic TFs. This
will be an important advance in our understanding of the epigenetic regulation of HSC self-renewal.

## Key facts

- **NIH application ID:** 10095975
- **Project number:** 1R01HL155144-01
- **Recipient organization:** UNIVERSITY OF PENNSYLVANIA
- **Principal Investigator:** Vikram R. Paralkar
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $536,436
- **Award type:** 1
- **Project period:** 2021-01-06 → 2024-12-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10095975

## Citation

> US National Institutes of Health, RePORTER application 10095975, The Role of PHF6 in HSC self-renewal and myeloid expansion (1R01HL155144-01). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10095975. Licensed CC0.

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