Submitted March 9, 2009
Accepted June 18, 2009
Repression of BMI1 in normal and leukemic human CD34+ cells impairs self-renewal and induces apoptosis
Aleksandra Rizo, Sandra Olthof, Lina Han, Edo Vellenga, Gerald de Haan, and Jan Jacob Schuringa*
Department of Cell Biology, Section Stem Cell Biology, University of Groningen, University Medical Center Groningen, Groningen, Netherlands
Department of Hematology, University of Groningen, University Medical Center Groningen, Groningen, Netherlands
* Corresponding author; email: j.schuringa{at}int.umcg.nl.
High expression of BMI1 in acute myeloid leukemia (AML) cells is associated with an unfavorable prognosis. Therefore, the effects of downmodulation of BMI1 in normal and leukemic CD34+ AML cells were studied using a lentiviral RNAi 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 (LTC-IC) frequencies were dramatically decreased upon knock-down 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 (ROS) and reduced FOXO3A expression. In AML CD34+ cells downmodulation 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.
