ABSTRACT
BACKGROUND: Acute myeloid leukemia (AML) represents a heterogeneous disorder with recurrent chromosomal alterations and molecular abnormalities. Among AML with normal karyotype (NK-AML) FLT3 activating mutation, internal tandem duplication (FLT3-ITD), is present in about 30% of patients, conferring unfavorable outcome. Our previous data demonstrated specific up-regulation of miR-155 in FLT3-ITD+ AML. miR-155 is known to be directly implicated in normal hematopoiesis and in some pathologies such as myeloid hyperplasia and acute lymphoblastic leukemia. METHODS AND RESULTS: To investigate about the potential influence of miR-155 de-regulation in FLT3-mutated AML we generated a transcription factors regulatory network and combined this with data from multiple sources that predict miR-155 interactions. From these analyses, we derived a sub-network, called "miR-155 module" that describes functional relationship among miR-155 and transcription factors in FLT3-mutated AML. We found that "miR-155 module" is characterized by the presence of six transcription factors as central hubs: four miR-155 regulators (JUN, RUNX1, FOSb, JUNB) and two targets of miR-155 (SPI1, CEBPB) all known to be "master" genes of myelopoiesis. We found, in FLT3-mutated AML, a significant down-regulation of miR-155 target genes CEBPB and SPI1 and up-regulation of miR-155 regulator genes JUN and RUNX1. We also showed that PKC412-related FLT3 inhibition, in MV4-11 cell line, causes down-regulation of miR-155 and increased level of mRNA and protein of miR-155 target SPI1. We showed in experiments of miR-155 mimic in K562 cell line, a high increase of miR-155 and an inverse correlation with the mRNA levels of its targets SPI1 and CEBPB. Moreover silencing of miR-155 in primary AMLs causes mRNA up-regulation of its target SPI1 and CEBPB. CONCLUSION: Our results suggest that activating mutation of FLT3 in AML can lead, through the induction of JUN, to an increased expression of miR-155, which then causes down-regulation of SPI1 and CEBPB and consequently may causes block of myeloid differentiation.
Subject(s)
Gene Regulatory Networks/physiology , Leukemia, Myeloid, Acute/genetics , MicroRNAs/physiology , Mutation , fms-Like Tyrosine Kinase 3/genetics , Adult , Aged , Aged, 80 and over , Female , Gene Expression Profiling , Gene Expression Regulation, Leukemic , Humans , K562 Cells , Male , Middle Aged , Young AdultABSTRACT
This study evaluated the loss and expression level of miRNAs 14q32 clusters in acute lymphoblastic leukemia (ALL) patients with cryptic deletions at 14q32 chromosomal band to investigate their involvement in this disease. We demonstrate that a subset of ALL cases bearing 14q32 LOH showed a down-regulation of miRNA 14q32 clusters, which is directly linked to the submicroscopic chromosomal deletion. As a consequence of miRNAs deregulation we reported an inverse correlation with the expression of their target BCL11a, a transcription factor involved in lymphoid differentiation. These results suggest that 14q32/miRNA clusters LOH may be another mechanism involved in lymphoid B cell transformation and differentiation and therefore, could be used as a diagnostic marker and therapeutic target in subsets of ALL.
Subject(s)
Carrier Proteins/biosynthesis , Chromosomes, Human, Pair 14/genetics , Gene Expression Regulation, Leukemic/genetics , Loss of Heterozygosity , MicroRNAs/genetics , Neoplasm Proteins/biosynthesis , Nuclear Proteins/biosynthesis , Precursor Cell Lymphoblastic Leukemia-Lymphoma/genetics , RNA, Neoplasm/genetics , Sequence Deletion , Adolescent , Adult , Aged , Carrier Proteins/genetics , Cell Differentiation/genetics , Cell Transformation, Neoplastic/genetics , Child , Chromosomes, Human, Pair 14/ultrastructure , Female , Humans , Male , MicroRNAs/biosynthesis , Middle Aged , Neoplasm Proteins/genetics , Nuclear Proteins/genetics , RNA, Neoplasm/biosynthesis , Repressor Proteins , Up-Regulation , Young AdultABSTRACT
Acute myeloid leukemia (AML) the most common acute leukemia in adults is characterized by various cytogenetic and molecular abnormalities. However, the genetic etiology of the disease is not yet fully understood. MicroRNAs (miRNA) are small noncoding RNAs which regulate the expression of target mRNAs both at transcriptional and translational level. In recent years, miRNAs have been identified as a novel mechanism in gene regulation, which show variable expression during myeloid differentiation. We studied miRNA expression of leukemic blasts of 29 cases of newly diagnosed and genetically defined AML using quantitative reverse transcription polymerase chain reaction (RT-PCR) for 365 human miRNA. We showed that miRNA expression profiling reveals distinctive miRNA signatures that correlate with cytogenetic and molecular subtypes of AML. Specific miRNAs with consolidated role on cell proliferation and differentiation such as miR-155, miR-221, let-7, miR-126 and miR-196b appear to be associated with particular subtypes. We observed a significant differentially expressed miRNA profile that characterizes two subgroups of AML with different mechanism of leukemogenesis: core binding factor (CBF) and cytogenetically normal AML with mutations in the genes of NPM1 and FLT3-ITD. We demonstrated, for the first time, the inverse correlation of expression levels between miRNA and their targets in specific AML genetic groups. We suggest that miRNA deregulation may act as complementary hit in the multisteps mechanism of leukemogenesis offering new therapeutic strategies.
