Defining the Epitranscriptomic Mechanisms of Leukemia Stem Cell Generation
Acute myeloid leukemia (AML) is an aggressive hematological malignancy that presents at a median age of 60. AML is one of the most common and most rapidly lethal hematological malignancies in adults (https://seer.cancer.gov/statfacts/html/amyl.html). AML has a primary (de novo) and secondary form. Secondary AML (sAML) may evolve from antecedent bone marrow stem cell disorders such as myelodysplastic syndrome (MDS), characterized by ineffective blood formation and cytopenias. Approximately 30-40% of patients with MDS transform to sAML, which is associated with a dismal one-year survival of only 30%. The high mortality rate is related, at least in part, to generation of therapy resistant acute myeloid leukemia stem cells (LSC) from pre-leukemic MDS hematopoietic stem and progenitor cells (HSPC) that acquire the capacity to transit the cell cycle, survive and self-renew in a deregulated manner. Thus, elucidation of molecular mechanisms driving LSC generation from pre-leukemic MDS HSPC is critical for developing effective targeted therapies.
Although DNA mutations fuel cancer heterogeneity and enable therapeutic resistance, there is an emerging role for epitranscriptomics i.e. post-transcriptional RNA changes. These RNA modifications play pivotal roles in gene expression regulation and RNA fate with regard to editing, splicing, stability, and translation. A family of adenosine deaminase associated with RNA (ADAR) editases, including ADAR1 and ADAR2, mediate RNA mutagenesis by converting adenosine-to-inosine (A-to-I). ADAR1 is a double-stranded RNA binding protein that is a focal point for this rapidly expanding field of RNA modifications in protein-coding and non-coding RNAs. We and other groups discovered that ADAR1-mediated A-to-I editing contributes to therapeutic resistance and cancer stem cell generation in a broad array of malignancies. ADAR1 induces malignant reprogramming of pre-malignant progenitors into self-renewing cancer stem cells by deregulating production of coding and non-coding stem cell regulatory transcripts. Our overall goal is to define the role of ADAR1 in the oncogenic transformation of pre-leukemic progenitors in MDS into self-renewing leukemia stem cells (LSCs).
Role of the Bone Marrow Niche in Aged and Myelodysplastic Syndrome Hematopoietic Stem and Progenitor Cell Dysfunction
As the U.S. population ages, increased prevalence of age-related bone marrow degenerative disorders, such as bone marrow failure syndromes and hematologic malignancies, have placed a significant burden on health care resources. During aging, impaired hematopoietic stem and progenitor cell (HSPC) maintenance induced by clonal DNA mutations as well as the bone marrow niche-driven RNA processing deregulation can set the stage for myelodysplastic syndrome (MDS) initiation. Our lab and others have shown that increased adenosine deaminase associated with RNA1 (ADAR1)-mediated adenosine-to-inosine (A-to-I) editing contributes to therapeutic resistance in a broad array of malignancies. We discovered that lentivirally enforced ADAR1 expression in HSPCs enhanced myeloid differentiation commensurate with the up-regulation of the transcription factor PU.1 and reduced dormancy. Whole transcriptome RNA sequencing (RNA-seq) analysis demonstrated that inflammatory cytokine pathways and RNA editing increased during normal aged HSPC evolution to MDS. We hypothesize that niche dependent activation of RNA editing by ADAR1 provides a competitive advantage for MDS over normal HSPCs. The majority of ADAR1-meditated RNA editing events in humans occur within double-stranded RNA loops created by primate-specific Alu sequences, which comprise 10% of the human genome, thereby underscoring important ADAR1 functional differences exist between human HSPCs compared with their murine counterparts. However, the limited research effort aimed at deciphering the role of ADAR1-mediated RNA editing in HSPC maintenance has been primarily performed in mouse models rather than highly purified human HSPCs. Because ADAR1 is activated by inflammatory cytokines that accelerate aging and MDS initiation, our main goal is to define the niche-dependent role of RNA editing on human HSPC cell fate and cell cycle regulation during aging and MDS initiation. To do this we are performing whole transcriptome and single cell RNA-sequencing (RNA-Seq) on young versus aged healthy donor HPSCs as well as HPSCs from MDS patients. To determine the functional role of ADAR1 in HSPC aging and MDS initiation we are examining stromal co-cultures with or without the addition of inflammatory cytokines and humanized aged HPSCs and MDS immunocompromised mouse models. Our overarching goal is to determine the biological, diagnostic and prognostic significance of ADAR1-mediated RNA editing in HSPC aging compared with MDS initiation.
Pre-Cancer Evolution Atlas
Myeloproliferative neoplasms (MPNs) are hematological malignancies involving proliferation of one or more of the blood producing lineages such as red blood cells, platelets, or white cells. MPNs include polycythemia vera (PV), essential thrombocytopenia (ET), primary myelofibrosis (PMF), and chronic myeloid leukemia (CML). MPNs typically present with age, the biggest risk factor. Dr. Jamieson and her team have embarked on a comprehensive research initiative to establish an atlas of MPNs to determine biomarkers of progression; conceptualize, create and assess the viability of predictive tests; initiate novel drug development; and develop molecular predictors of therapeutic response for MPNs. To compile the MPN atlas, whole genome and transcriptome sequencing has been performed on saliva and blood stem and progenitor cells from patients with different stages of MPNs. In addition, healthy young and aged individuals have been included in the analysis. To date, greater than 100 individuals have been analyzed and the sequencing has generated an incredible amount of genetic data (>10 terabytes). Our approach takes into account individual differences in each person's genes, environments, and lifestyles to tailor specific therapies.