ABSTRACT
MicroRNAs are key regulators of many biological processes, including cell differentiation. These small RNAs exert their function assembled in the RNA-induced silencing complexes (RISCs), where members of Argonaute (Ago) family of proteins provide a unique platform for target recognition and gene silencing. Here, by using myeloid cell lines and primary blasts, we show that Ago2 has a key role in human monocytic cell fate determination and in LPS-induced inflammatory response of 1,25-dihydroxyvitamin D3 (D3)-treated myeloid cells. The silencing of Ago2 impairs the D3-dependent miR-17-5p/20a/106a, miR-125b and miR-155 downregulation, the accumulation of their translational targets AML1, VDR and C/EBPß and monocytic cell differentiation. Moreover, we show that Ago2 is recruited on miR-155 host gene promoter and on the upstream region of an overlapping antisense lncRNA, determining their epigenetic silencing, and miR-155 downregulation. These findings highlight Ago2 as a new factor in myeloid cell fate determination in acute myeloid leukemia cells.
Subject(s)
Argonaute Proteins/metabolism , Leukemia, Myeloid, Acute/metabolism , Argonaute Proteins/genetics , Blotting, Western , CCAAT-Enhancer-Binding Proteins/genetics , CCAAT-Enhancer-Binding Proteins/metabolism , Calcitriol/pharmacology , Cell Differentiation/drug effects , Cell Differentiation/physiology , Cell Line, Tumor , Core Binding Factor Alpha 2 Subunit/genetics , Core Binding Factor Alpha 2 Subunit/metabolism , HL-60 Cells , Humans , Leukemia, Myeloid, Acute/genetics , MicroRNAs/genetics , Receptors, Calcitriol/genetics , Receptors, Calcitriol/metabolismABSTRACT
Blocks in genetic programs required for terminal myeloid differentiation and aberrant proliferation characterize acute myeloid leukemia (AML) cells. 1,25-Dihydroxy-vitamin D3 (VitD3) arrests proliferation of AML cells and induces their differentiation into mature monocytes. In a previous study, we showed that miR-26a was induced upon VitD3-mediated monocytic differentiation. Here, we identify E2F7 as a novel target of miR-26a. We show that E2F7 significantly promotes cell cycle progression and inhibits monocytic differentiation of AML cells. We also demonstrate that E2F7 binds the cyclin-dependent kinase inhibitor p21(CIP1/WAF1) (cyclin-dependent kinase inhibitor 1A) promoter repressing its expression. Moreover, interfering with E2F7 expression results in inhibition of c-Myc (v-myc myelocytomatosis viral oncogene homolog) transcriptional activity. This leads to the downregulation of c-Myc transcriptional target miR-17-92 cluster, whose expression has a well-defined role in contributing to block monocytic differentiation and sustain AML cell proliferation. Finally, we show that the expression of E2F7 is upregulated in primary blasts from AML patients. Thus, these findings indicate that the newly identified miR-26a target E2F7 might have an important role in monocytic differentiation and leukemogenesis.
Subject(s)
Cell Differentiation , Cell Proliferation , E2F7 Transcription Factor/genetics , Leukemia, Myeloid, Acute/genetics , Leukemia, Myeloid, Acute/physiopathology , MicroRNAs/genetics , Monocytes/cytology , Cell Cycle , Cells, Cultured , Cyclin-Dependent Kinase Inhibitor p21/genetics , Cyclin-Dependent Kinase Inhibitor p21/metabolism , E2F7 Transcription Factor/metabolism , HL-60 Cells , Humans , Leukemia, Myeloid, Acute/metabolism , MicroRNAs/metabolism , Monocytes/metabolism , U937 CellsABSTRACT
In the acute promyelocytic leukemia (APL) bearing the t(15;17), all-trans-retinoic acid (ATRA) treatment induces granulocytic maturation and complete remission of leukemia. We identified miR-342 as one of the microRNAs (miRNAs) upregulated by ATRA during APL differentiation. This miRNA emerged as a direct transcriptional target of the critical hematopoietic transcription factors PU.1 and interferon regulatory factor (IRF)-1 and IRF-9. IRF-1 maintains miR-342 at low levels, whereas the binding of PU.1 and IRF-9 in the promoter region following retinoic ATRA-mediated differentiation, upregulates miR-342 expression. Moreover, we showed that enforced expression of miR-342 in APL cells stimulated ATRA-induced differentiation. These data identified miR-342 as a new player in the granulocytic differentiation program activated by ATRA in APL.
