Purpose: To elucidate new molecular mechanisms able to down-regulated the mRNA levels of key oncogenes, such as B-Myb and E2F1, in a therapeutic perspective. Experimental Design: B-Myb and E2F1 mRNA levels were evaluated in primary B chronic lymphocytic leukemia (B-CLL, n=10), acute myeloid leukemia (AML, n=5) patient cells, in a variety of p53wild-type and p53mutated/deleted leukemic cell lines, as well as in primary endothelial cells and fibroblasts. Knock-down experiments with siRNA for p53 and E2F1 and overexpression experiments with miR34a were performed to elucidate the role of these pathways in promoting B-Myb down-regulation. Results: In vitro exposure to Nutlin-3, a non-genotoxic activator of p53, variably down-regulated the expression of B-Myb in primary leukemic cells, in p53wild-type myeloid (OCI, MOLM) and lymphoblastoid (SKW6.4, EHEB) but not in p53mutated (NB4, BJAB, MAVER) or p53deleted (HL-60) leukemic cell lines. The transcriptional repression of B-Myb was observed also in primary normal endothelial cells and fibroblasts. B-Myb down-regulation played a critical role in the cell cycle block in G1 phase induced by Nutlin-3, as demonstrated by transfection experiments with specific siRNA. Moreover, we have provided experimental evidence suggesting that miR-34a is a central mediator in the repression of B-Myb both directly and through E2F1. Conclusions: Due to the role of B-Myb and E2F1 transcription factors in controlling cell cycle progression of leukemic cells, the down-regulation of these oncogenes by miR-34a suggests the usefulness of therapeutic approaches aimed to modulate the levels of miR-34a.
- Received December 6, 2010.
- Revision received February 16, 2011.
- Accepted February 20, 2011.
- Copyright © 2011, American Association for Cancer Research.