Abstract 2694: Histone acetyltransferase activity of MOF is required for MLL-AF9 leukemogenesis
Authors: Valerio Daria G. , Xu Haiming , Chen Chun-Wei , Hoshii Takayuki , Eisold Meghan , Delaney Christopher , Cusan Monica , Deshpande Aniruddha J. , Huang Chun-Hao , Lujambio Amaia , Zheng George , Pandita Tej K. , Lowe Scott W. , Armstrong Scott A. 
Published: July 2016

Chromosomal rearrangements of the Mixed-Lineage Leukemia (MLL) gene are found in 5-10% of all patients with acute leukemia and associated with a poor prognosis. MLL-rearrangements are more frequently present in pediatric and infant patients where AF9 is one of the most common fusion partners.

In order to identify novel druggable targets in MLL-AF9 rearranged leukemia, we conducted a chromatin regulator focused RNAi screen in murine MLL-AF9 leukemia cells and found hairpins targeting (K)Lysine Acetyltransferase 8 (Kat8, also known as Mof) and the previously identified target Bromodomain Containing 4 (Brd4), to be the most potent suppressors of cell growth. MOF is a histone 4 lysine 16 (H4K16) acetyltransferase and member of the MYST family of histone acetyltransferases (HATs). MOF has been shown to be crucial for murine embryogenesis and is a cell-type dependent regulator of chromatin state and various cellular processes such as T-cell differentiation, DNA damage response and cell cycle progression.

Using a conditional murine Mof knockout system, we studied the role of MOF in MLL-AF9 leukemogenesis in detail. In vitro inactivation of Mof in MLL-AF9 transformed mouse hematopoietic stem and progenitor cells led to impaired colony-forming capacity. The specificity of this phenotype was shown by expression of exogenous full-length Mof, which fully rescued transformed cells from the dramatic phenotype. Inactivation of Mof in vivo, lead to reduced tumor burden and prolonged survival of mice bearing MLL-AF9 leukemia cells. RNA sequencing data comparing MLL-AF9 cells with homozygous Mof loss to a wild type control, showed a significant enrichment of genes within the apoptosis (NES 1.98, FDR-q &lt;0.0001) and p53 (NES 2.23, FDR-q &lt;0.0001) pathway. These gene expression data suggest that the importance of MOF in MLL-AF9 leukemogenesis may be through interaction with p53, inducing proliferation and suppressing apoptosis. In addition, we found a reduction of actively cycling cells and a loss of global H4K16 acetylation (H4K16ac) upon Mof knockout. In line with this finding of H4K16ac loss, rescue experiments with HAT domain mutated MOF illustrated that the HAT activity of MOF is indispensable for MLL-AF9 leukemia maintenance. Finally, experiments with the selective MYST protein HAT inhibitor MG149, showed a strong anti-proliferative effect on murine, as well as human MLL-AF9 leukemia cell lines, and MG149 inhibition induced global H4K16ac loss in these cells.

These results indicate that MOF HAT activity is required for MLL-AF9 leukemia maintenance. Our data further suggest that MOF HAT activity may be a good target for new small molecule inhibitor development for the treatment of patients with MLL-AF9 rearranged leukemia.

Citation Format: Daria G. Valerio, Haiming Xu, Chun-Wei Chen, Takayuki Hoshii, Meghan Eisold, Christopher Delaney, Monica Cusan, Aniruddha J. Deshpande, Chun-Hao Huang, Amaia Lujambio, George Zheng, Tej K. Pandita, Scott W. Lowe, Scott A. Armstrong. Histone acetyltransferase activity of MOF is required for MLL-AF9 leukemogenesis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2694.