MicroRNA-708 is a novel regulator of the Hoxa9 program in myeloid cells.

MicroRNAs (miRNAs) are commonly deregulated in acute myeloid leukemia (AML), affecting critical genes not only through direct targeting, but also through modulation of downstream effectors. Homeobox (Hox) genes balance self-renewal, proliferation, cell death, and differentiation in many tissues and aberrant Hox gene expression can create a predisposition to leukemogenesis in hematopoietic cells. However, possible linkages between the regulatory pathways of Hox genes and miRNAs are not yet fully resolved. We identified miR-708 to be upregulated in Hoxa9/Meis1 AML inducing cell lines as well as in AML patients. We further showed Meis1 directly targeting miR-708 and modulating its expression through epigenetic transcriptional regulation. CRISPR/Cas9 mediated knockout of miR-708 in Hoxa9/Meis1 cells delayed disease onset in vivo, demonstrating for the first time a pro-leukemic contribution of miR-708 in this context. Overexpression of miR-708 however strongly impeded Hoxa9 mediated transformation and homing capacity in vivo through modulation of adhesion factors and induction of myeloid differentiation. Taken together, we reveal miR-708, a putative tumor suppressor miRNA and direct target of Meis1, as a potent antagonist of the Hoxa9 phenotype but an effector of transformation in Hoxa9/Meis1. This unexpected finding highlights the yet unexplored role of miRNAs as indirect regulators of the Hox program during normal and aberrant hematopoiesis.

Endogenous Tumor Suppressor microRNA-193b: Therapeutic and Prognostic Value in Acute Myeloid Leukemia.

Purpose Dysregulated microRNAs are implicated in the pathogenesis and aggressiveness of acute myeloid leukemia (AML). We describe the effect of the hematopoietic stem-cell self-renewal regulating miR-193b on progression and prognosis of AML. Methods We profiled miR-193b-5p/3p expression in cytogenetically and clinically characterized de novo pediatric AML (n = 161) via quantitative real-time polymerase chain reaction and validated our findings in an independent cohort of 187 adult patients. We investigated the tumor suppressive function of miR-193b in human AML blasts, patient-derived xenografts, and miR-193b knockout mice in vitro and in vivo. Results miR-193b exerted important, endogenous, tumor-suppressive functions on the hematopoietic system. miR-193b-3p was downregulated in several cytogenetically defined subgroups of pediatric and adult AML, and low expression served as an independent indicator for poor prognosis in pediatric AML (risk ratio ± standard error, -0.56 ± 0.23; P = .016). miR-193b-3p expression improved the prognostic value of the European LeukemiaNet risk-group stratification or a 17-gene leukemic stemness score. In knockout mice, loss of miR-193b cooperated with Hoxa9/Meis1 during leukemogenesis, whereas restoring miR-193b expression impaired leukemic engraftment. Similarly, expression of miR-193b in AML blasts from patients diminished leukemic growth in vitro and in mouse xenografts. Mechanistically, miR-193b induced apoptosis and a G1/S-phase block in various human AML subgroups by targeting multiple factors of the KIT-RAS-RAF-MEK-ERK (MAPK) signaling cascade and the downstream cell cycle regulator CCND1. Conclusion The tumor-suppressive function is independent of patient age or genetics; therefore, restoring miR-193b would assure high antileukemic efficacy by blocking the entire MAPK signaling cascade while preventing the emergence of resistance mechanisms.

Micro-ribonucleic acid-155 is a direct target of Meis1, but not a driver in acute myeloid leukemia.

Micro-ribonucleic acid-155 (miR-155) is one of the first described oncogenic miRNAs. Although multiple direct targets of miR-155 have been identified, it is not clear how it contributes to the pathogenesis of acute myeloid leukemia. We found miR-155 to be a direct target of Meis1 in murine Hoxa9/Meis1 induced acute myeloid leukemia. The additional overexpression of miR-155 accelerated the formation of acute myeloid leukemia in Hoxa9 as well as in Hoxa9/Meis1 cells in vivo However, in the absence or following the removal of miR-155, leukemia onset and progression were unaffected. Although miR-155 accelerated growth and homing in addition to impairing differentiation, our data underscore the pathophysiological relevance of miR-155 as an accelerator rather than a driver of leukemogenesis. This further highlights the complexity of the oncogenic program of Meis1 to compensate for the loss of a potent oncogene such as miR-155. These findings are highly relevant to current and developing approaches for targeting miR-155 in acute myeloid leukemia.

MicroRNA-155 is upregulated in MLL-rearranged AML but its absence does not affect leukemia development.

MicroRNA-155 (miR-155) is an oncogenic miRNA upregulated in various tumor types and leukemias and has been suggested as a potential drug target. Based on our previous work detecting high miR-155 levels in response to Meis1 overexpression in a murine Hox leukemia model, we show here the relationship among HOXA9, MEIS1, and miR-155 levels in MLL-translocated acute myeloid leukemia (AML) patients. Using mouse bone marrow cells transformed by MLL-fusion genes expressing graduated levels of Meis1, we show a positive correlation between miR-155 and Meis1. However, using a miR-155-knockout mouse model, we show that the absence and the depletion of miR-155 have no effect on leukemia formation or progression. We also show for the first time that miR-155 levels are correlated with MLL translocations, but that miR-155 expression is dispensable for the formation of AML and has no effect on leukemia progression.

The pathologic effect of a novel neomorphic Fgf9(Y162C) allele is restricted to decreased vision and retarded lens growth.

Fibroblast growth factor (Fgf) signalling plays a crucial role in many developmental processes. Among the Fgf pathway ligands, Fgf9 (UniProt: P54130) has been demonstrated to participate in maturation of various organs and tissues including skeleton, testes, lung, heart, and eye. Here we establish a novel Fgf9 allele, discovered in a dominant N-ethyl-N-nitrosourea (ENU) screen for eye-size abnormalities using the optical low coherence interferometry technique. The underlying mouse mutant line Aca12 was originally identified because of its significantly reduced lens thickness. Linkage studies located Aca12 to chromosome 14 within a 3.6 Mb spanning interval containing the positional candidate genes Fgf9 (MGI: 104723), Gja3 (MGI: 95714), and Ift88 (MGI: 98715). While no sequence differences were found in Gja3 and Ift88, we identified an A→G missense mutation at cDNA position 770 of the Fgf9 gene leading to an Y162C amino acid exchange. In contrast to previously described Fgf9 mutants, Fgf9(Y162C) carriers were fully viable and did not reveal reduced body-size, male-to-female sexual reversal or skeletal malformations. The histological analysis of the retina as well as its basic functional characterization by electroretinography (ERG) did not show any abnormality. However, the analysis of head-tracking response of the Fgf9(Y162C) mutants in a virtual drum indicated a gene-dosage dependent vision loss of almost 50%. The smaller lenses in Fgf9(Y162C) suggested a role of Fgf9 during lens development. Histological investigations showed that lens growth retardation starts during embryogenesis and continues after birth. Young Fgf9(Y162C) lenses remained transparent but developed age-related cataracts. Taken together, Fgf9(Y162C) is a novel neomorphic allele that initiates microphakia and reduced vision without effects on organs and tissues outside the eye. Our data point to a role of Fgf9 signalling in primary and secondary lens fiber cell growth. The results underline the importance of allelic series to fully understand multiple functions of a gene.