In the hematopoietic system, the interplay of particular transcription factors instructs normal hematopoietic stem cells (HSC) to function in a precise manner. While it is known that expression deregulation of specific factors in these transcriptional networks disrupts normal HSC function and leads to the formation of leukemia initiating cells (LIC), superordinate gene expression regulation by epigenetic mechanisms, is still poorly understood. We and others have identified a particular chromatin remodeling factor, special AT-rich sequence-binding protein 1 (SATB1) as an important epigenetic factor governing gene expression in normal T-cell and myeloid differentiation, and in leukemia. Our preliminary data show: SATB1 is required for self-renewal function of HSC, sequence alterations within the SATB1-binding site of an upstream regulatory element of the myeloid master regulator PU.1 act as disease modifiers in AML, and while SATB1 is highly expressed in normal hematopoietic stem and progenitor cells, its expression is impaired in AML patient-derived LIC. We hypothesize that this chromatin remodeling protein regulates the function of normal HSC and malignant stem cells. Since epigenetic alterations do not change the DNA sequences and are pharmacologically reversible, they have been regarded as promising targets for therapy. We propose to investigate epigenetic gene regulation by the chromatin-remodeling protein SATB1 in HSC and LIC. The function of SATB1-dependent gene expression regulation in HSC and LIC will be characterized using in vivo models, such as stem cell transplantation assays. Additionally, these functional studies will be accompanied with integrated epigenomic analyses investigating the mechanism of SATB1-dependent HSC and LIC regulation. We will utilize global chromatin immunoprecipitation analysis (ChIP-seq) in combination with gene expression and DNA methylation pattern analysis. Given our observation that SATB1 is down- regulated in LIC of AML patients, binding of SATB1 to low affinity binding sites may be abrogated and cause expression changes of genes involved in the formation or maintenance of LIC. We will restore SATB1 expression in AML patient-derived LIC and evaluate whether this has an anti-leukemic effect. We will characterize SATB1 binding patterns in AML LIC with low and restored SATB1 expression by ChIP-seq combined with gene expression profiling. Genes differentially occupied and expressed will be further functionally analyzed to determine their potential use as therapeutic targets. Our preliminary data make SATB1 a potential paradigm for epigenetic regulation of tumor suppressor genes in leukemia stem cells. Our study will contribute to elucidating novel molecular pathways that can be targeted for the development of LIC-directed epigenetic therapeutic approaches.
Project Narrative Our study will investigate the function of special AT-rich sequence-binding protein 1 (SATB1), a DNA- organizing ('epi-genetic') factor we have found in normal blood stem cells and cells that initiate acute myeloid leukemia (AML). Our preliminary data show that the presence of SATB1 is required to ensure normal blood stem cell function and our observations further suggest that SATB1 critically contributes not only to the function of normal blood stem cells, but also cells that initiate leukemia. The results of our study will add to our current understanding of normal blood cell production and will also identify fundamentally novel pathways and targets for specific, leukemia initiating cell-directed therapies.
