# Instructive role of MLL fusion proteins in lineage determination and leukemogenesis

> **NIH NIH R01** · UNIVERSITY OF CHICAGO · 2021 · $594,545

## Abstract

The MLL gene at chromosome band 11q23 is frequently rearranged in both acute myeloid and acute
lymphoblastic leukemia. These translocations result in the formation of chimeric fusion proteins containing the
N-terminus of MLL fused to the C-terminus of more than 70 different partner proteins. Although there are
similarities in gene expression among the different MLL fusion proteins, MLL-AF4 (MA4), MLL-AF9 (MA9),
and MLL-ELL (MEL) exhibit distinct gene expression profiles in leukemia cells obtained from patients. Many of
the most common MLL partner proteins, including AF4, AF9, and ELL, are components of a super elongation
complex (SEC) that is critical in transcriptional activation and elongation. Despite the identification that multiple
MLL partner proteins are components of this complex, the basis for the differences in gene expression remains
unclear. Many investigators refer to MLL-rearranged leukemia as a homogenous entity. However, the different
fusions are found in different lineages. MA4 is almost exclusively found in pro-B ALL, MEL only in AML, and
MA9 most commonly in AML but also in pre-B ALL. However, the basis for lineage specification by the different
fusion partners is uncertain. Until now, it has not been possible to perform a direct comparison of the most
common MLL fusions due to the lack of a tractable model of MLL-AF4 leukemia. We have developed a novel
approach to express the MA4 fusion protein and have generated leukemia models using mouse and human
hematopoietic stem and progenitor cells (HSPCs). Importantly, we have generated a faithful model of MA4 pro-
B ALL. Using the unique reagents we have generated, we plan to examine the critical similarities and differences
between these MLL fusion proteins. Each MLL fusion contains a triple FLAG tag that will permit the efficient
purification of protein complexes and facilitate ChIP-seq to identify target genes. Although the partner protein
complexes were identified several years ago, the complexes were immuno-precipitated using the partner proteins
by themselves and not as MLL fusions. In addition, these purifications were performed in cell lines and not in
primary leukemias induced by MLL fusions. In Aim 1, we will define the nature of the oncoprotein complexes
formed in MLL-fusion transformed HSPCs and analyze their contribution to the initiation and maintenance of
these leukemias. In Aim 2, we will identify critical downstream genes regulated by distinct MLL-fusion
complexes in both myeloid and lymphoid cells. We will determine the genomic occupancy of each oncoprotein
by ChIP-Seq. In this way we expect to identify those targets that are common to MLL and unique to each of the
MLL-fusion proteins. In Aim 3, we will determine the cell of origin that is transformed in this MLL-fusion model
system. We will express MA4, MEL, and MA9 in human stem and progenitor cells to determine whether each
oncogene is able to induce leukemia in various progenitor cells and determine how cell of ...

## Key facts

- **NIH application ID:** 10115634
- **Project number:** 5R01CA215504-05
- **Recipient organization:** UNIVERSITY OF CHICAGO
- **Principal Investigator:** JAMES C MULLOY
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $594,545
- **Award type:** 5
- **Project period:** 2017-03-01 → 2023-02-28

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10115634

## Citation

> US National Institutes of Health, RePORTER application 10115634, Instructive role of MLL fusion proteins in lineage determination and leukemogenesis (5R01CA215504-05). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10115634. Licensed CC0.

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