Acute myeloid leukemias (AML) are clonal disorders of hematopoietic progenitor cells which are characterized by relevant heterogeneity in terms of phenotypic, genotypic, and clinical features. Among the genetic aberrations that control disease development there are microRNAs (miRNAs). miRNAs are small non-coding RNAs that regulate, at post-transcriptional level, translation and stability of mRNAs. It is now established that deregulated miRNA expression is a prominent feature in AML. Functional studies have shown that miRNAs play an important role in AML pathogenesis and miRNA expression signatures are associated with chemotherapy response and clinical outcome. In this review we summarized miRNA signature in AML with different cytogenetic, molecular and clinical characteristics. Moreover, we reviewed the miRNA regulatory network in AML pathogenesis and we discussed the potential use of cellular and circulating miRNAs as biomarkers for diagnosis and prognosis and as therapeutic targets.

Pluripotency confers Embryonic Stem Cells (ESCs) the ability to differentiate in ectoderm, endoderm, and mesoderm derivatives, producing the majority of cell types. Although the majority of ESCs divide without losing pluripotency, it has become evident that ESCs culture consists of multiple cell populations with different degrees of potency that are spontaneously induced in regular ESC culture conditions. Zscan4, a key pluripotency factor, marks ESC subpopulation that is referred to as high-level of pluripotency metastate. Here, we report that in ESC cultures treated with retinoic acid (RA), Zscan4 ESCs metastate is strongly enhanced. In particular, we found that induction of Zscan4 metastate is mediated via RA receptors (RAR-alpha, RAR-beta, and RAR-gamma), and it is dependent on phosphoinositide-3-kinase (PI3K) signaling. Remarkably, Zscan4 metastate induced by RA lacks canonical pluripotency genes Oct3/4 and Nanog but retained both self-renewal and pluripotency capabilities. Finally we demonstrated that the conditional ablation of Zscan4 subpopulation is dispensable for both endoderm and mesoderm but is required for ectoderm lineage. In conclusion, our research provides new insights about the role of RA signaling during ESCs high pluripotency metastate fluctuation.

Embryonic stem cells (ESCs) are derived from inner cell mass (ICM) of the blastocyst. In serum/LIF culture condition, they show variable expression of pluripotency genes that mark cell fluctuation between pluripotency and differentiation metastate. The ESCs subpopulation marked by zygotic genome activation gene (ZGA) signature, including Zscan4, retains a wider differentiation potency than epiblast-derived ESCs. We have recently shown that retinoic acid (RA) significantly enhances Zscan4 cell population. However, it remains unexplored how RA initiates the ESCs to 2-cell like reprogramming. Here we found that RA is decisive for ESCs to 2C-like cell transition, and reconstructed the gene network surrounding Zscan4. We revealed that RA regulates 2C-like population co-activating Dux and Duxbl1. We provided novel evidence that RA dependent ESCs to 2C-like cell transition is regulated by Dux, and antagonized by Duxbl1. Our suggested mechanism could shed light on the role of RA on ESC reprogramming.

Lin28A is a highly conserved RNA-binding protein that concurs to control the balance between stemness and differentiation in several tissue lineages. Here, we report the role of miR-128a/Lin28A axis in blocking cell differentiation in acute myeloid leukemia (AML), a genetically heterogeneous disease characterized by abnormally controlled proliferation of myeloid progenitor cells accompanied by partial or total inability to undergo terminal differentiation. First, we found Lin28A underexpressed in blast cells from AML patients and AML cell lines as compared with CD34+ normal precursors. In vitro transfection of Lin28A in NPM1-mutated OCI-AML3 cell line significantly triggered cell-cycle arrest and myeloid differentiation, with increased expression of macrophage associate genes (EGR2, ZFP36 and ANXA1). Furthermore, miR-128a, a negative regulator of Lin28A, was found overexpressed in AML cells compared with normal precursors, especially in acute promyelocytic leukemia (APL) and in ‘AML with maturation’ (according to 2016 WHO classification of myeloid neoplasms and acute leukemia). Its forced overexpression by lentiviral infection in OCI-AML3 downregulated Lin28A with ensuing repression of macrophage-oriented differentiation. Finally, knockdown of miR-128a in OCI-AML3 and in APL/AML leukemic cells (by transfection and lentiviral infection, respectively) induced myeloid cell differentiation and increased expression of Lin28A, EGR2, ZFP36 and ANXA1, reverting myeloid differentiation blockage. In conclusion, our findings revealed a new mechanism for AML differentiation blockage, suggesting new strategies for AML therapy based upon miR-128a inhibition.

Embryonic stem cells (ESCs) fluctuate among different levels of pluripotency defined as metastates. Sporadically, metastable cellular populations convert to a highly pluripotent metastate that resembles the preimplantation two-cell embryos stage (defined as 2C stage) in terms of transcriptome, DNA methylation, and chromatin structure. Recently, we found that the retinoic acid (RA) signaling leads to a robust increase of cells specifically expressing 2C genes, such as members of the Prame family. Here, we show that Gm12794c, one of the most highly upregulated Prame members, and previously identified as a key player for the maintenance of pluripotency, has a functional role in conferring ESCs resistance to RA signaling. In particular, RA-dependent expression of Gm12794c induces a ground state-like metastate, as evaluated by activation of 2C-specific genes, global DNA hypomethylation and rearrangement of chromatin similar to that observed in naive totipotent preimplantation epiblast cells and 2C-like cells. Mechanistically, we demonstrated that Gm12794c inhibits Cdkn1A gene expression through the polycomb repressive complex 2 (PRC2) histone methyltransferase activity. Collectively, our data highlight a molecular mechanism employed by ESCs to counteract retinoic acid differentiation stimuli and contribute to shed light on the molecular mechanisms at grounds of ESCs naive pluripotency-state maintenance.