MicroRNA-497/195 is tumor suppressive and cooperates with CDKN2A/B in pediatric acute lymphoblastic leukemia.

We previously identified an association of rapid engraftment of patient-derived leukemia cells transplanted into NOD/SCID mice with early relapse in B-cell precursor acute lymphoblastic leukemia (BCP-ALL). In a search for the cellular and molecular profiles associated with this phenotype, we investigated the expression of microRNAs (miRNAs) in different engraftment phenotypes and patient outcomes. We found high expression of miR-497 and miR-195 (hereafter miR-497/195) in patient-derived xenograft samples with slow engraftment derived from patients with favorable outcome. In contrast, epigenetic repression and low expression of these miRNAs was observed in rapidly engrafting samples associated with early relapse. Overexpression of miR-497/195 in patient-derived leukemia cells suppressed in vivo growth of leukemia and prolonged recipient survival. Conversely, inhibition of miR-497/195 led to increased leukemia cell growth. Key cell cycle regulators were downregulated upon miR-497/195 overexpression, and we identified cyclin-dependent kinase 4 (CDK4)- and cyclin-D3 (CCND3)-mediated control of G1/S transition as a principal mechanism for the suppression of BCP-ALL progression by miR-497/195. The critical role for miR-497/195-mediated cell cycle regulation was underscored by finding (in an additional independent series of patient samples) that high expression of miR-497/195 together with a full sequence for CDKN2A and CDKN2B (CDKN2A/B) was associated with excellent outcome, whereas deletion of CDKN2A/B together with low expression of miR-497/195 was associated with clearly inferior relapse-free survival. These findings point to the cooperative loss of cell cycle regulators as a new prognostic factor indicating possible therapeutic targets for pediatric BCP-ALL.