# Investigation into the function of RNA polymerase II promoter proximal pausing during terminal erythroid maturation

> **NIH NIH R01** · UNIVERSITY OF ROCHESTER · 2024 · $347,565

## Abstract

Erythropoiesis is a finely orchestrated process that involves generating a ~2.5 million red blood cells per
second to maintain homeostasis and prevent anemia. RNA Polymerase II (RNAPII) pausing is a highly regulated
and fundamental mechanism of transcriptional regulation, whereby transcription is initiated, but pauses 30-60
bp downstream of the transcription start site. Release of paused RNAPII into active elongation requires
phosphorylation of RNAPII and associated inhibitory factors by positive transcription elongation factor beta
(pTEFb). Our group has shown that regulation of RNAPII activity is an essential determinant of erythroid cell
function, with central roles in the regulation of gene expression and cell cycle progression. HEXIM1 is a key
regulator of pTEFb activity that can enforce pausing or facilitate pause release, depending on genomic context.
HEXIM1 is essential for erythropoiesis, and promotes erythroid proliferation and the expression of GATA1-target
genes. Despite its importance, fundamental questions remain regarding the mechanisms by which HEXIM1
regulates RNAPII activity and promotes erythroid gene expression. HEXIM1 is classically thought of as a
transcriptional repressor, which enforces RNAPII pausing by sequestering pTEFb in the 7SK complex. Data from
our group and others suggests the HEXIM1-pTEFb-7sk complex can be targeted to specific genes, where it is
available for “onsite” release of pTEFb, facilitating pause release. In Aim 1, we will address the hypothesis
that delivery of pTEFb to specific genes by HEXIM1 and the 7SK Complex is essential for both steady
state and stress erythropoiesis. RNAPII pausing is regulated by cell type- and maturation stage-specific
transcription factors and signaling pathways. Early erythropoiesis is comprised of the differentiation of multipotent
progenitors to erythroid progenitors, while terminal maturation consists of the maturation of proerythroblasts
through several intermediates into orthochromatic erythroblasts that ultimately enucleate. In contrast to terminally
maturing cells, erythroid progenitors have the ability to undergo self-renewal divisions, and to expand in response
to anemic stress. HEXIM1 is expressed in erythroid progenitors and upregulated in terminally maturing cells.
Other key regulators of pTEFb, including Bromodomain Protein 4 (BRD4), and the Mediator Complex are highly
expressed in erythroid progenitors and down regulated during terminal maturation. Erythroid progenitors also
have higher levels of RNAPII than terminally maturing cells. These data suggest that the transcriptional
environment of erythroid progenitors is distinct from that of terminally maturing cells. In Aim2, we will address
the hypothesis that RNAPII activity is regulated in a maturation stage-specific manner. The proposed
studies will provide novel insights into the mechanisms that govern normal and perturbed erythropoiesis, and
have the potential to identify novel therapeutic targets for inher...

## Key facts

- **NIH application ID:** 10997022
- **Project number:** 2R01DK124777-05
- **Recipient organization:** UNIVERSITY OF ROCHESTER
- **Principal Investigator:** LAURIE A. STEINER
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $347,565
- **Award type:** 2
- **Project period:** 2020-04-01 → 2028-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10997022

## Citation

> US National Institutes of Health, RePORTER application 10997022, Investigation into the function of RNA polymerase II promoter proximal pausing during terminal erythroid maturation (2R01DK124777-05). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10997022. Licensed CC0.

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