Direct interaction between E47 and p21 controls LT-HSC proliferation and functional longevity (P4471)

Abstract

Abstract Long-term hematopoietic stem cells (LT-HSCs) are important multipotent cells that replenish all immune cells lost due to natural turnover, infection or injury. LT-HSC proliferation is controlled by cell cycle regulators and upstream transcription factors but direct links between the two have not been established. Here, we demonstrate a mechanistic link between the transcription factor E47 and the major cell cycle regulator p21 in controlling LT-HSC proliferation, self-renewal, and functional competence. Gain-of-function and loss-of-function studies show that E47 directly regulates p21 transcription in HSCs. Using E47/p21 compound heterozygotes, a powerful approach for analyzing HSC activity in vivo, we show a 2-fold increase in BrdU+ LT-HSCs compared to WT or single HET controls in both steady state conditions and under transplantation stress. E47HETp21HET HSCs are also more sensitive to mitotoxic challenge with 5-FU resulting in a 45% decrease in HSC numbers compared to treated controls. In serial adoptive transfer assays, a rigorous challenge to HSC self-renewal, E47HETp21HET HSCs were decreased by 40% and 60% in secondary and tertiary recipients, respectively. In addition to hyperproliferation and poor self-renewal, E47HETp21HET adoptive transfer recipients had selective myeloid bias indicating HSC skewing. Together, these data suggest a developmental stage-specific, cell-intrinsic collaboration between E47 and p21 in the regulation of LT- HSC competence in vivo.