CD99 Promotes Self-renewal in Hematopoietic Stem Cells and Leukemia Stem Cells by Regulating Protein Synthesis

Blood production is sustained by hematopoietic stem cells (HSCs), which are typically the only blood cells capable of long-term self-renewal. HSCs exhibit and depend on low levels of protein synthesis to self-renew. However, the mechanisms by which HSCs regulate protein synthesis to maintain their self-renewal capacity during proliferative stress and leukemogenesis remain unknown. Here we show CD99, a protein upregulated in leukemia stem cells (LSCs) in acute myeloid leukemia (AML), is required for the self-renewal of proliferating HSCs and LSCs. We found that loss of CD99 in HSCs and LSCs leads to increased protein synthesis and that their self-renewal capacity can be restored by translation inhibition. These data demonstrate a functional role for CD99 in constraining protein synthesis, which may promote the clonal expansion of HSCs and LSCs that leads to AML. Furthermore, these studies demonstrate that similar to HSCs, LSCs depend on maintenance of tightly regulated protein synthesis rates. Overall design: To investigate the molecular consequences of loss of CD99 in hematopoietic stem and progenitor cells, hematopoietic stem cells (HSCs) and granulocyte macrophage progenitors (GMPs) were purified from the bone marrow of 10-12 week old CD99 KO mice for RNA-sequencing.