A cutting-edge approach unravels a novel role for CDK6 in leukemic progenitor cells

CDK6 induces a complex transcriptional program to block p53 in hematopoietic cells. CDK6 binds to the promoters of genes including p53-antagonists. Cells lacking CDK6 kinase function are required to mutate p53 to achieve a fully transformed immortalized state. Overall design: Studies of molecular mechanisms of hematopoiesis and leukemogenesis are hampered by the unavailability of progenitor cell lines that accurately mimic the situation in vivo. We now report a robust method to generate and maintain LSK (lin-, Sca-1+, c-Kit+) cells which closely resemble MPP1 cells. HPCLSK reconstitute hematopoiesis in lethally irradiated recipient mice over more than eight months. Upon transformation with different oncogenes including BCR/ABL, FLT3-ITD or MLL-AF9 their leukemic counterparts maintain stem cell properties in vitro and recapitulate leukemia formation in vivo. The method to generate HPCLSK can be applied to transgenic mice and we illustrate it for CDK6-deficient animals. Upon BCR/ABLp210 transformation, Cdk6-/- HPCLSKs induce disease with a significantly enhanced latency and reduced incidence, showing the importance of CDK6 in leukemia formation. Studies of the CDK6 transcriptome in murine HPCLSK and human BCR/ABL+ cells have verified that certain pathways depend on CDK6 and have uncovered a novel CDK6-dependent signature, suggesting a role for CDK6 in leukemic progenitor cell homing. Loss of CDK6 may thus lead to a defect in homing. The HPCLSK system represents a unique tool for combined in vitro and in vivo studies and enables the production of large quantities of genetically modifiable hematopoietic or leukemic stem/progenitor cells.