Transcriptional Repression of the Neurofibromatosis-1 Tumor Suppressor by the t(8;21) Fusion Protein

Abstract

Von Recklinghausen's disease is a relatively common familial genetic disorder characterized by inactivating mutations of the Neurofibromatosis-1 (NF1) gene that predisposes these patients to malignancies, including an increased risk for juvenile myelomonocytic leukemia. However, NF1 mutations are not common in acute myeloid leukemia (AML). Given that the RUNX1 transcription factor is the most common target for chromosomal translocations in acute leukemia, we asked if NF1 might be regulated by RUNX1. In reporter assays, RUNX1 activated the NF1 promoter and cooperated with C/EBPα and ETS2 to activate the NF1 promoter over 80-fold. Moreover, the t(8;21) fusion protein RUNX1-MTG8 (R/M), which represses RUNX1-regulated genes, actively repressed the NF1 promoter. R/M associated with the NF1 promoter in vivo and repressed endogenous NF1 gene expression. In addition, similar to loss of NF1, R/M expression enhanced the sensitivity of primary myeloid progenitor cells to granulocyte-macrophage colony-stimulating factor. Our results indicate that the NF1 tumor suppressor gene is a direct transcriptional target of RUNX1 and the t(8;21) fusion protein, suggesting that suppression of NF1 expression contributes to the molecular pathogenesis of AML.

ACKNOWLEDGMENTS

We thank the members of the Hiebert lab for helpful discussions and encouragement, K. Scott Luce for expert technical assistance, and the Vanderbilt-Ingram Cancer Center sequencing facility for support. We offer special thanks to Nancy Ratner for the NF1 antisera.

This work was supported by National Institutes of Health grants RO1-CA87549, RO1-CA64140, RO1-CA77274, and RO1-CA74177; a center grant from the National Cancer Institute (CA68485); and the Vanderbilt-Ingram Cancer Center.