# Identifying/Targeting Mechanisms of Lymphomagenesis Driven by CREBBP Inactivation

> **NIH NIH R01** · UNIVERSITY OF TX MD ANDERSON CAN CTR · 2024 · $348,019

## Abstract

ABSTRACT
Follicular lymphoma (FL) is an indolent but incurable malignancy of germinal center B (GCB)-cells, and is the
second most common form of non-Hodgkin lymphoma (NHL). Mutations of CREBBP, which encodes a lysine
acetyltransferase (KAT) protein, occur in ~60% of FL and arise early during disease evolution. We found that
conditional knock-out (KO) of Crebbp in murine models and can cooperate with Bcl2 over-expression to drive B-
cell lymphoma, but that these tumors had key differences to FL. Furthermore, FL tumors have a predominance
of missense mutations within the CREBBP KAT domain and infrequently harbor nonsense/frameshift mutations
that are modeled by KO. We therefore modeled the most frequent CREBBP KAT domain mutation, R1446C,
using CRISPR editing of a CREBBP wild-type (WT) lymphoma cell line and found that CREBBP-R1446C
mutation has a more profound epigenetic effect than biallelic knock-out (KO). Regions with reduced H3K27Ac
were enriched for loci that are normally bound by both CREBBP and BCL6 in germinal center B-cells, suggesting
that the loss H3K27Ac may be linked to failure of CREBBP to oppose BCL6-dependent HDAC3 activity. Notably,
BCL6 also recruits EZH2 and loss of H3K27Ac in CREBBP-R1446C cells was accompanied by a gain of the
EZH2-catalyzed H3K27me3 mark, suggesting that enhancer inactivation via loss of H3K27Ac is followed by
enhancer decommissioning through addition of H3K27me3. Furthermore, the CREBBP mutation phenotype
could be partially rescued by either HDAC3 or EZH2 inhibition, and was further enhanced by combination of
HDAC3 and EZH2 inhibitors. These results suggest that CREBBP KAT domain mutations suppress histone
acetylation through a dominant repressive mechanism, and that epigenetic crosstalk between CREBBP and
EZH2 may play a prominent role in regulating the epigenetic landscape of B-cell lymphoma. We have extended
upon these observations by performing biochemical and structural analysis of major CREBBP mutational
hotspots and observed key differences between the R1446C/H alleles and the next most common hotspots at
Y1482 and Y1503. These amino acids all reside within the catalytic pocket of CREBBP, but R1446 mediates
interaction with the CoA portion of the acetyl donor, acetyl-CoA, while Y1482 and Y1503 mediate interaction with
the acetyl group. While R1446 mutations maintain some catalytic activity, the Y1482 and Y1503 mutations are
catalytically dead. Therefore, these mutations are likely to have different functional consequences. In this
proposal, we aim to (i) characterize the mechanism of dominant epigenetic repression by CREBBP KAT domain
mutations and differences in function between KAT domain hotspot mutations, and (ii) define the role of
epigenetic crosstalk between CREBBP and EZH2 in B-cell lymphoma, and the consequences for response to
targeted agents.

## Key facts

- **NIH application ID:** 10814232
- **Project number:** 5R01CA201380-08
- **Recipient organization:** UNIVERSITY OF TX MD ANDERSON CAN CTR
- **Principal Investigator:** Michael Richard Green
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $348,019
- **Award type:** 5
- **Project period:** 2016-08-04 → 2027-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10814232

## Citation

> US National Institutes of Health, RePORTER application 10814232, Identifying/Targeting Mechanisms of Lymphomagenesis Driven by CREBBP Inactivation (5R01CA201380-08). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10814232. Licensed CC0.

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