| Description |
MicroRNA expression is dysregulated in many human cancers, including hematopoietic malignancies. Among hematopoietic malignancies, acute myeloid leukemia (AML) carries a particularly poor prognosis, leading to over 10,000 deaths each year in the US alone. The most common genetic aberration in AML is a gain-of-function mutation in the FMS-like tyrosine kinase 3 (FLT3) receptor. FLT3 internal tandem duplication (ITD) occurs in ~30% of all AML cases, and confers a negative prognosis. MicroRNA expression has been shown to be highly dysregulated in FLT3-ITD+ AML; however, the functional relevance of many of these microRNAs on leukemic phenotypes remains unclear. We performed a genome-wide CRISPR-Cas9 screen to identify which microRNAs, and which of their putative mRNA targets, regulate FLT3-ITD+ AML cell growth. Our screen identified a number of microRNAs that function to suppress or promote FLT3-ITD+ AML cell growth, revealing that microRNAs are extensively integrated into the molecular networks that control tumor cell physiology. We also performed anticorrelation functional profiling to predict relevant microRNA-mRNA target pairs in this context, and identified miR-150 targeting of p53 as a critical relationship governing the growth of these cells. We validated one of our targets, miR-155, as a critical regulator of FLT3-ITD+ AML cell growth in vitro, where miR-155-deficient cells displayed a competitive growth disadvantage compared to cells with miR-155 intact. We extended these findings into an in vivo model of FLT3-ITD-driven myeloid malignancy, where mice containing a FLT3-ITD mutation but lacking miR-155 exhibited decreased myeloid expansion in the bone marrow, spleen, and blood compared to their FLT3-ITD miR-155+/+ counterparts. This phenotype was attributed to miR-155's role in promoting proliferation of the hematopoietic stem cell and myeloid progenitor cell compartments in the bone marrow. Further analysis revealed that miR-155 likely exerts these effects by regulating multiple pathways involved in cellular proliferation, including repressing the interferon response through targeting Cebpb, and activating AKT signaling through targeting of Ship1. These findings correlated with human AML data from The Cancer Genome Atlas dataset, where we found that FLT3-ITD+ AML samples had a decreased interferon signature and lower levels of Cebpb and Ship1 compared to FLT3-WT AML samples. Finally, we treated FLT3-ITD+ AML primary patient samples with a miR-155 inhibitor and observed decreased colony forming potential and increased apoptosis in these cells. These results suggest that miR-155 inhibition could be a novel therapeutic approach in FLT3-ITD+ AML. |
