DYRKIA kinase-substrate interactions in normal and malignant hematopoiesis

The dual specificity tyrosine-regulated kinase 1A (DYRK1A), encoded on human chromosome 21, is thought to play causative roles in several Down syndrome (DS)-associated pathologies due to increased gene dosage. These include neurological phenotypes and DS-acute megakaryocytic leukemia, a disease in which we have previously shown a tumor-promoting role for DYRK1A. Numerous proteins with diverse biological functions can be phosphorylated by DYRK1A, yet the kinase-substrate interactions that are relevant to hematopoiesis remain largely unknown, and several that are known appear to be cell-type specific. For example, we recently found that DYRK1A is essential for cell cycle exit and survival during lymphoid, but not myeloid, development. Other hematopoietic cell types, such as hematopoietic stem cells and granulocytes, are also affected by the loss of DYRK1A, but our preliminary data suggest that the mechanisms underlying these changes are distinct from those in lymphoid cells. To gain a more complete understanding of DYRK1A function in hematopoiesis, we will first utilize a conditional knockout mouse model to study DYRK1A loss-of-function in hematopoietic stem cells and myeloid cells. Second, to identify relevant kinase-substrate interactions in these and other hematopoietic cell types, we will use an unbiased screening method to find cell type-specific DYRK1A targets. This approach utilizes a point mutation in DYRK1A that confers the ability to use bulky ATP-analogs to phosphorylate substrate proteins. This method allows for proteome-wide labeling of direct DYRK1A targets, which can subsequently be identified by mass spectrometry. Finally, we will extend our previous findings that a DYRK1A inhibitor can induce apoptosis in acute lymphoblastic leukemia (ALL) cell lines and primary patient samples. This will include analysis of leukemia-initiating/stem cell activity in mouse models of B- and T-ALL, in which we can use the conditional DYRK1A allele to manipulate its expression level in each disease. Furthermore, we will establish xenografts of primary human leukemia samples in immunodeficient mice to evaluate the potential therapeutic benefit of DYRK1A inhibition. Collectively, these experiments will expand our knowledge of important DYRK1A substrates in hematopoietic cells, and will provide a pre-clinical basis for therapeutic targeting of DYRK1A in leukemia.