An AML1-ETO/miR-29b-1 regulatory circuit modulates phenotypic properties of acute myeloid leukemia cells.

Sayyed K Zaidi,Andrew W Perez,Gary S Stein,Elizabeth S White,Jane B Lian,Janet L Stein

doi:10.18632/oncotarget.18127

Abstract

Acute myeloid leukemia (AML) is characterized by an aggressive clinical course and frequent cytogenetic abnormalities that include specific chromosomal translocations. The 8;21 chromosomal rearrangement disrupts the key hematopoietic RUNX1 transcription factor, and contributes to leukemia through recruitment of co-repressor complexes to RUNX1 target genes, altered subnuclear localization, and deregulation of the myeloid gene regulatory program. However, a role of non-coding microRNAs (miRs) in t(8;21)-mediated leukemogenesis is minimally understood. We present evidence of an interplay between the tumor suppressor miR-29b-1 and the AML1-ETO (also designated RUNX1-RUNX1T1) oncogene that is encoded by the t(8;21). We find that AML1-ETO and corepressor NCoR co-occupy the miR-29a/b-1 locus and downregulate its expression in leukemia cells. Conversely, re-introduction of miR-29b-1 in leukemia cells expressing AML1-ETO causes significant downregulation at the protein level through direct targeting of the 3’ untranslated region of the chimeric transcript. Restoration of miR-29b-1 expression in leukemia cells results in decreased cell growth and increased apoptosis. The AML1-ETO-dependent differentiation block and transcriptional program are partially reversed by miR-29b-1. Our findings establish a novel regulatory circuit between the tumor-suppressive miR-29b-1 and the oncogenic AML1-ETO that controls the leukemic phenotype in t(8;21)-carrying acute myeloid leukemia.

Highlights

Acute Myeloid Leukemia (AML) is an aggressive neoplasm with frequent cytogenetic abnormalities, a recurrent clinical course and a limited number of drug treatment options [1]
We find that the locus is co-occupied by both AML1-ETO and N-CoR, suggesting that miR29b-1 is a key component of leukemia signature
We experimentally verified these findings using ChIP-qPCR in Kasumi-1 cells; antibodies specific for AML1-ETO and RUNX1 were used for immunoprecipitation and an isotype-matched normal IgG was used as control

Summary

Introduction

Acute Myeloid Leukemia (AML) is an aggressive neoplasm with frequent cytogenetic abnormalities, a recurrent clinical course and a limited number of drug treatment options [1]. RUNX1 protein transcriptionally regulates genes essential for myeloid differentiation by interacting with promoter regulatory regions in a sequence specific manner via the amino-terminal DNA binding domain and recruiting coregulatory proteins for transcriptional activation or suppression via carboxy terminus [2], [5]. AML1-ETO protein retains the DNA binding domain of RUNX1, but the ETO moiety replaces the carboxy terminus that contains protein interaction domains necessary for normal functional activity, as well as the subnuclear targeting signal responsible for the punctate nuclear localization of RUNX1 regulatory complexes [10]-[12]. The chimeric transcript encoding the AML1-ETO oncogene carries the 3’UTR of the ETO gene that is distinct from that of the wild type Runx RNA [14]. Because the ETO gene is not normally expressed in hematopoietic cells, specific targeting of its 3’UTR has potential therapeutic value in AML

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Conclusion