The role of the histone chaperone Chaf1b in sustaining the Hoxa9-driven AML differentiation block

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Project Summary/Abstract I received my undergraduate degree from Cornell University, my PhD in molecular biology from Princeton University, and am currently a postdoctoral researcher and Special Fellow of the Leukemia and Lymphoma Society at Harvard Medical School and Boston Children's Hospital. After studying the molecular basis of breast cancer metastasis in graduate school, I transitioned to the field of epigenetics in the laboratory of Yang Shi for my postdoc. I have received extensive experimental and scholarly training in my postdoc. I learned the rigors of basic chromatin biochemistry in my first postdoctoral project, and recently published a co-first author paper based on this work. This study was featured as the cover article in the journal Cell and reported the identification of a novel metazoan epigenetic DNA modification, N6-methyladenine (6mA). My scholarly training has involved extensive scientific writing and has enabled me to write three successful postdoc fellowship applications (from the NIH, ACS, and LLS), two successful grants for Dr. Shi based on my work (from the Samuel Waxman Cancer Research Foundation and the Harvard Epigenetics Initiative), and one recently published review paper as a co-author in the journal Nature Reviews Molecular Biology. My current postdoctoral research merges my background in cancer biology with my recent training in chromatin biochemistry and focuses on the epigenetic basis of the differentiation block that characterizes acute myeloid leukemia (AML). AML is the most lethal hematological malignancy and is the cause of more than 10,000 annual US death. AML is typically treated by chemotherapy, though patients often relapse and have limited therapeutic options. The promyelocytic subtype of AML can be cured by “differentiation therapy” – induction of differentiation and inhibition of proliferation with retinoic acid – but this approach has been ineffective in other AML subtypes. Recent work has suggested that this block to non-APL AML differentiation is epigenetic in nature. Stable – yet reversible – chromatin alterations are thought to disable myeloid differentiation gene expression programs in these cells. I have recently established a robust genetic screening approach to uncover epigenetic regulators of non-APL AML differentiation programs. These screens have identified the Chaf1b subunit of the Caf-1 histone remodeling complex as a critical regulator of the Hoxa9- driven AML differentiation block. The overall goal of the work proposed in this application is to determine the molecular, chromatin-based mechanisms by which Chaf1b functions to regulate AML cell differentiation. The goal of my first Aim in this proposal is to use biochemical approaches to identify the proteins and long non- coding RNAs (lncRNAs) that associate with Chaf1b and the greater Caf-1 complex in AML cells. I will then focus on determining which of these interacting proteins and RNAs are most critical in recruiting Chaf1b to its target genomic loci and help sustain its activity as a differentiation-blocking protein. In Aim 2 I will use extensive epigenomic profiling approaches to identify the chromatin remodeling and transcriptomic processes that are altered as cells differentiate in response to inhibition of Chaf1b. I will then compare these epigenomic data to those obtained from my recent profiling of the normal, physiological myeloid differentiation program to determine whether loss of Chaf1b induces differentiation through typical or atypical mechanisms. Finally, in Aim 3 I will determine the potential of Chaf1b as a candidate therapeutic target by testing whether its inhibition induces differentiation and reduces disease burden or affects normal hematopoiesis in mouse AML models. While I am currently a postdoc, the proposed research is to be carried out as an independent investigator, which is my immediate career goal. The initial phase of preparing for this transition has been very promising. I have recently had interviews for tenure-track faculty positions at the University of Pennsylvania, Princeton University, and the Mount Sinai School of Medicine. Mt. Sinai has recently invited me for a second visit and I am awaiting responses from UPenn and Princeton. To help facilitate this transition, I will have collaborative and consultative support of field leaders in hematopoiesis (Dr. David Scadden), AML (Dr. Kimberly Stegmaier), and lncRNA/computational biology (Dr. John Rinn). These scientists are committed to guiding me through the transition process and helping me start my independent career in the strongest possible position. Once independent, my research will focus on epigenetic regulation of AML cell differentiation. However, my long term vision is to bring the concept of targeting cell fate decisions from blood lineage cancers to selected solid tumors of interest. “Differentiation therapy” has been underexplored in solid tumors, but the importance of stemness and de-differentiation programs has been clearly implicated in certain malignancies such as brain cancer. Therefore, toward the end of the proposed funding period, I will aim to establish differentiation-based screening methodology for selected brain cancers and will work on characterizing the molecular mechanisms of screen hits using a combination of genetic, biochemical, epigenomic, and animal models. I believe that this direction will lead to conceptual and therapeutic advances and will have direct clinical relevance.