MicroRNA Expression Contributes to Hypoxia-Inducible Factor-1a-Induced Differentiation of Myeloid Leukemic Cells.

Abstract 1007

Poster Board I-29

In our previous study, we showed that the hypoxia or hypoxia-mimetic agents induces differentiation of myeloid leukemic cells. During this event, hypoxia-inducible factor-1a (HIF-1a) exerts a critical role in its transcriptional activity-independent manner. MicroRNAs (miRNAs) regulate the expression of 30% of the transcripts of human genome on a posttranscriptional level. Recent work on miRNA has shed light on the possible involvement of miRNA genes in biological processes such as cell proliferation, differentiation and hematopoiesis. To reveal the miRNA expression profile and related roles in HIF-1a-induced differentiation of myeloid leukemic cells, miRNA expression profiling was analyzed by microarray in HIF-1a-expressing U937T cells (U937T^clone) and HIF-1a-absent cells (U937T^empty) in 0 day, 2 days and 4 days after tetracycline removal. The differentially expressed miRNAs, as verified by quantitative real-time RT-PCR and Northern blot, were subjected to gene ontology (GO) analysis and pathway analysis. The upregulated and downregulated miRNAs in U937T^clone cells in three time points after tetracycline removal were 11 miRNAs and 7 miRNAs, respectively. The differential expression of miR-26a, -107, -19b, -20a, -17, -92a, -92b and -106a was validated. On the basis of bioinformatic analysis, we focused on the changed components of miRNA 17-92 cluster and miRNA 106a-92 cluster, mostly considered as oncomirs, which have the similar downregulated expression profile. The results showed that miR-17 was significantly depressed by 40% and 70% in 2 and 4 days after tetracycline removal in U937T^clone. And miR-20a was significantly depressed by 60% and 80%, respectively. High-enrichment GOs containing differentiation-related targeted genes and miRNA-gene networks revealed STAT3 as one of the highest degree of target genes, which was targeted by the three changed components of miR-17 family (miR-17, -20a and -106a). STAT3 protein was validated to be upregulated in U937T^clone after tetracycline removal by Western blot, and no fluctuation in STAT3 mRNA levels was observed, which may uncover the critical role of miR-17 family in the cell differentiation induced by HIF-1a. In summary, significantly different miRNA profiles were seen in U937T^clone cells as compared to U937T^emptycells. The downregulation of the components of miRNA 17-92 and 106a-92 cluster may contribute to HIF-1a-induced myeloid leukemic cell differentiation by targeting STAT3 or other signaling pathways. Further functional study of these miRNAs will be carried out by overexpression and knockdown experiments. These data would shed new insights for understanding mechanisms underlying leukemogenesis and designing the new therapeutic strategy for differentiation induction of acute myelogenous leukemia.