# Novel roles for p27 as transcriptional co-regulator of cJun in stem cells and development

> **NIH NIH R01** · GEORGETOWN UNIVERSITY · 2023 · $584,586

## Abstract

Project Summary
p27 is a CDK inhibitor that limits normal cell proliferation. We showed p27 C-terminal phosphorylation at T157
and T198 by AKT increases in mid G1 and p27pT157pT198 (p27pTpT) facilitates interaction with novel protein
partners. We recently showed C-terminal p27pTpT phosphorylation promotes its association with cJun.
Genomic profiling showed p27 is co-recruited with cJun to over half of cJun chromatin binding sites to either
activate or repress target genes. p27/cJun activated targets include TGFB2, and are associated with EMT, and
programs that upregulate stem cells and alter cell adhesion and migration. Profiles of target genes repressed
by p27/cJun suggest that p27pTpT opposes tissue differentiation. A subset of p27/cJun target genes bind to a
STAT3 consensus motif and p27, cJun and STAT3 all appear to bind and co-regulate cMYC. Notably,
p27pTpT is a driver of stem cell potency: cellular p27pTpT upregulates spheres, SOX2, NANOG and cMYC
and tumor initiating cells in vivo. Our TG-p27CK-DD mice transgenic for a p27 phosphomimetic mutant that
fails to bind cyclin/CDKs, show multi-organ overgrowth and increased size, suggesting that p27CK-DD
abrogates WTp27 actions to restrain normal stem and progenitor expansion. This grant investigates the role of
p27 as a transcriptional regulator in normal cells and development. Our data support the hypothesis that
WTp27 plays important transcriptional roles during differentiation, to limit stem and progenitor cell expansion in
various tissues. In contrast, upon C-terminal phosphorylation, p27 interacts with cJun, STAT3 and other factors
to expand or maintain tissue stem or progenitor cells and oppose differentiation. We will compare p27WT,
p27CDK and p27CK-DD MEFS in AIM1 to evaluate how p27 interacts with cJun and STAT3 on chromatin to
govern gene expression across the cell cycle from G0, to mid-G1 and the G1/S phase transition. We will
investigate if increased C-terminal p27 phosphorylation alters co-regulator and target gene selection and
abrogates the co-repressive functions of p27 in quiescent cells. In AIM2, we will separate actively transcribed
euchromatin from transcriptionally inactive heterochromatin and carry out ChIP-seq and ChIP-Mass Spec to
identify the chromatin associated p27 interactome involved in transactivator versus repressor complexes. AIM3
will study mouse development, tissue differentiation, and adult stem and progenitor populations in TG-p27CK-
DD and TG-p27CK- mice. We will test if p27CK-DD confers stronger reprogramming potential on MEFs and
disrupts differentiation of iPSC into embryoid bodies. This work will elucidate a novel function of p27 as a
phosphorylation-dependent transcriptional regulator with implications for tissue stem cell control and potential
applications in regenerative medicine. Controlled modulation of p27, or of p27 target genes identified herein,
might offer potential to expand or regenerate hematologic and other tissues. Understanding how p27/cJ...

## Key facts

- **NIH application ID:** 10703218
- **Project number:** 5R01CA253111-04
- **Recipient organization:** GEORGETOWN UNIVERSITY
- **Principal Investigator:** JOYCE MARIE SLINGERLAND
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2023
- **Award amount:** $584,586
- **Award type:** 5
- **Project period:** 2020-09-01 → 2025-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10703218

## Citation

> US National Institutes of Health, RePORTER application 10703218, Novel roles for p27 as transcriptional co-regulator of cJun in stem cells and development (5R01CA253111-04). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10703218. Licensed CC0.

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