Identification of Converging Pathways in the pathogenesis of NPM-RARA Variant Acute Promyelocytic Leukemia

Acute Promyelocytic Leukemia is a subset of Acute Myeloid Leukemias, and is commonly associated with the presence of chromosomal translocations leading to the expression of the PML-RARA fusion protein. Less frequent cases of APL have been identified that express rare variant RARA fusion proteins, such as NPM-RARA. The presence of these fusions results in deregulated RARA signaling and response to the RARA ligand, ATRA. However, studies have indicated that loss of retinoid signaling alone is not sufficient to result in the leukemia. The goals of this thesis were to determine genes and pathways deregulated in variant APL that can serve as cooperating events in APL, through candidate pathway analysis and high-throughput gene expression profiling. Using a cell line model expressing variant fusion proteins associated with APL, we identified the deregulation of the NF-kappaB signaling pathway in APL, and describe the functional analysis of this pathway in our in vitro model. We next assessed whether promotion of survival signals could serve as a contributing factor in the accumulation of leukemic blasts in APL patient bone marrow. Our results indicated that PML-RARA and NPM-RARA expressing cells showed increased survival in the presence of TNFalpha, compared to wild type control cells. These data suggested a greater ability on the part of NPM-RARA cells to survive in the presence of TNFalpha. We also report for the first time the gene expression profiles of, and transcriptional effects of ATRA on, cells expressing the variant fusion proteins. Finally, we determined that the partner protein Nucleophosmin (NPM) has increased cytoplasmic localization in cells expressing the APL fusion proteins, and interacts within complexes comprising of RARA and RXRA. We further determined that the fusion can interfere with NPM function and cellular localization. Taken together, these studies provide evidence for the involvement of secondary hits in APL biology.Ph