PI3 Kinase Inactivation in Myelodysplastic Syndrome

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Myelodysplastic Syndrome (MDS) affects at least 10,000 people each year in the U.S., and is particularly prevalent in the aging population. MDS is a clonal disorder arising in hematopoietic stem cells (HSCs), characterized by impaired myeloid and erythroid differentiation and genomic instability. There are currently few therapeutic approaches available to improve cytopenias in MDS patients. Mutations in RNA splicing factors are observed in 50% of MDS cases, and are important contributors to MDS initiation and progression. Most hematopoietic growth factors and cytokines signal through the PI3 kinase (PI3K)/AKT pathway. We have found that compound deletion of the three PI3K isoforms P110a, b, and d in mouse hematopoietic cells leads to a phenotype resembling MDS, with cytopenias, impaired HSC differentiation and genomic instability. Interestingly, we observed enrichment of our TKO HSC expression signature in an MDS patient gene expression dataset. Furthermore, a subset of MDS samples have elevated expression levels of the negative regulator PTEN, suggesting functional inactivation of PI3K in these MDS patients. Our preliminary data reveals that HSCs in PI3K triple knockout (TKO) mice have a defect in autophagy, an intracellular recycling mechanism that is important for the maintenance of HSC differentiation. We found that pharmacologic induction of autophagy can improve differentiation of TKO HSCs. We also observed widespread alterations in mRNA splicing in TKO HSCs. Therefore, PI3K TKO mice are a valuable new model system to study the mechanisms of MDS initiation and progression. We hypothesize that maintenance of PI3K signaling in HSCs is required to maintain HSC differentiation and to protect HSCs from DNA damage. We propose to (1) determine whether induction of autophagy can improve myeloid and erythroid differentiation in MDS patient samples, (2) delineate the mechanism by which PI3K and its downstream kinase AKT control mRNA splicing in HSCs and in MDS, and (3) determine whether MDS cells with splicing factor mutations are more sensitive to inhibition of PI3K/AKT signaling. These approaches will further our understanding of how growth factor and cytokine signaling regulates autophagy and mRNA splicing through PI3K/AKT in MDS initiation. We also plan to test several therapeutic approaches to improve differentiation in MDS, including induction of autophagy and inhibition of PI3K/AKT in MDS with splicing factor mutations.