Repression of BMI1 in normal and leukemic human CD34+ cells impairs self-renewal and induces apoptosis

Abstract

High expression of BMI1 in acute myeloid leukemia (AML) cells is associated with an unfavorable prognosis. Therefore, the effects of down-modulation of BMI1 in normal and leukemic CD34+AMLcells were studied using a lentiviral RNA interference approach. We demonstrate that downmodulation of BMI1 in cord blood CD34+ cells impaired long-term expansion and progenitor-forming capacity, both in cytokine-driven liquid cultures as well as in bone marrow stromal cocultures. In addition, long-term culture-initiating cell frequencies were dramatically decreased upon knockdown of BMI1, indicating an impaired maintenance of stem and progenitor cells. The reduced progenitor and stem cell frequencies were associated with increased expression of p14ARF and p16INK4A and enhanced apoptosis, which coincided with increased levels of intracellular reactive oxygen species and reduced FOXO3Aexpression. InAMLCD34+ cells, down-modulation of BMI1 impaired long-term expansion, whereby self-renewal capacity was lost, as determined by the loss of replating capacity of the cultures. These phenotypes were also associated with increased expression levels of p14ARF and p16INK4A. Together our data indicate that BMI1 expression is required for maintenance and self-renewal of normal and leukemic stem and progenitor cells, and that expression of BMI1 protects cells against oxidative stress. © 2009 by The American Society of Hematology.