A distinct set of long non-coding RNAs in childhood MLL-rearranged acute lymphoblastic leukemia: biology and epigenetic target.

Long non-coding RNAs (lncRNAs) have been recently found to be pervasively transcribed in human genome and link to diverse human diseases. However, the expression patterns and regulatory roles of lncRNAs in hematopoietic malignancies have not been reported. Here, we carried out a genome-wide lncRNA expression study in MLL-rearranged acute lymphoblastic leukemia (MLL-r ALL) and established lncRNA/messenger RNA coexpression networks to gain insight into the biological roles of these dysregulated lncRNAs. We detected a number of lncRNAs that were differentially expressed in MLL-r ALL samples compared with MLL-r wild-type and identified unique lncRNA expression patterns between MLL-r subtypes with different translocations as well as between infant MLL-r ALL with other MLL-r ALL patients, suggesting that they might be served as novel biomarkers for the disease. Importantly, several lncRNAs that correspond with membrane protein genes, including a lysosome-associated membrane protein, were identified. No such link between the membrane proteins and MLL-r leukemia has been reported previously. Impressively, the functional analysis showed that several lncRNAs corresponded to the expression of MLL-fusion protein target genes, including HOXA9, MEIS1, etc., while some other associated with histone-related functions or membrane proteins. Further experiments characterize the effect of some lncRNAs on MLL-r leukemia apoptosis and proliferation as the function of the coexpressed HOXA gene cluster. Finally, a set of lncRNAs epigenetically regulated by H3K79 methylation were also discovered. These findings may provide novel insights into the mechanisms of lncRNAs involved in the initiation of MLL-r leukemia. This is the first study linking lncRNAs to leukemogenesis.

A set of miRNAs that involve in the pathways of drug resistance and leukemic stem-cell differentiation is associated with the risk of relapse and glucocorticoid response in childhood ALL.

Relapse is a major challenge in the successful treatment of childhood acute lymphoblastic leukemia (ALL). Despite intensive research efforts, the mechanisms of ALL relapse are still not fully understood. An understanding of the molecular mechanisms underlying treatment outcome, therapy response and the biology of relapse is required. In this study, we carried out a genome-wide microRNA (miRNA) microarray analysis to determine the miRNA expression profiles and relapse-associated miRNA patterns in a panel of matched diagnosis-relapse or diagnosis-complete remission (CR) childhood ALL samples. A set of miRNAs differentially expressed either in relapsed patients or at diagnosis compared with CR was further validated by quantitative real-time polymerase chain reaction in an independent sample set. Analysis of the predicted functions of target genes based on gene ontology 'biological process' categories revealed that the abnormally expressed miRNAs are associated with oncogenesis, classical multidrug resistance pathways and leukemic stem cell self-renewal and differentiation pathways. Several targets of the miRNAs associated with ALL relapse were experimentally validated, including FOXO3, BMI1 and E2F1. We further investigated the association of these dysregulated miRNAs with clinical outcome and confirmed significant associations for miR-708, miR-223 and miR-27a with individual relapse-free survival. Notably, miR-708 was also found to be associated with the in vivo glucocorticoid therapy response and with disease risk stratification. These miRNAs and their targets might be used to optimize anti-leukemic therapy, and serve as novel targets for development of new countermeasures of leukemia. This fundamental study may also contribute to establish the mechanisms of relapse in other cancers.

Camptothecin induces apoptosis in cancer cells via microRNA-125b-mediated mitochondrial pathways.

Camptothecin (CPT) is an effective chemotherapeutic agent for treatment of patients with cancer. The mechanisms underlying CPT-mediated responses in cancer cells are not fully understood. MicroRNA (miRNA) play important roles in tumorigenesis and drug sensitivity. However, the interaction between camptothecin and miRNA has not been previously explored. In this study, we verified that miR-125b was down-regulated in CPT-induced apoptosis in cancer cells and that ectopic expression of miR-125b partially restored cell viability and inhibited cell apoptosis that was induced by CPT. In addition, we demonstrated that CPT induced apoptosis in cancer cells by miR-125b-mediated mitochondrial pathways via targeting to the 3'-untranslated (UTR) regions of Bak1, Mcl1, and p53. A significant increase in Bak1, Mcl1, and p53 protein levels was detected in response to the treatments of CPT. It is noteworthy that the expression levels of Bak1, Mcl1, and p53 increased in a time-dependent manner and negatively correlated with miR-125b expression. It is noteworthy that we revealed that miR-125b directly targeted the 3'UTR regions of multiple genes in a CPT-induced mitochondrial pathway. In addition, most targets of miR-125b were proapoptotic genes, whereas some of the targets were antiapoptotic genes. We hypothesized that miR-125b may mediate the activity of chemotherapeutic agents to induce apoptosis by regulating multiple targets. This is the first report to show that camptothecin induces cancer cell apoptosis via miRNA-mediated mitochondrial pathways. The results suggest that suppression of miR-125b may be a novel approach for the treatment of cancer.

miR-125b, a target of CDX2, regulates cell differentiation through repression of the core binding factor in hematopoietic malignancies.

MicroRNA-125b (miR-125b), a small noncoding RNA molecule, has been found to be deregulated and functions as an oncogene in many cancers including hematopoietic malignancies. However, the mechanisms accounting for miR-125b dysregulation remain to be elucidated. The present study aims to identify the factors that might contribute to up-regulation of miR-125b in human hematopoietic malignancies and its downstream targets for lineage-specific differentiation. We at first reported that CDX2, a homeobox transcription factor, binds to promoter regions of the miR-125b gene and activates transcriptional regulation of miR-125b in malignant myeloid cells. We further revealed that increasing levels of CDX2 in malignant myeloid cells activate miR-125b expression, which in turn inhibits core binding factor ß (CBFß) translation, thereby counteracting myeloid cell differentiation, at least for granulocytic lineage, and promoting leukemogenesis. Interestingly, we found that this novel pathway including CDX2, miR-125b, and CBFß was mediated by undergoing all-trans-retinoic acid induction. Once differentiation ensues with all-trans-retinoic acid treatment, CDX2 activity decreases, leading to a reduction in miR-125b transcription and up-regulation of CBFß in myeloid cells and in patients. The study provides a new mechanism that contributes to hematopoietic malignancies, which could involve deregulation of miR-125b and its up- and downstream factors. As altered expression of miRNAs has been reported in a wide range of malignancies, delineating the underlying molecular mechanisms of aberrant miRNA expression and characterizing the upstream and downstream factors will help to understand important steps in the pathogenesis of these afflictions.

[Research Advances in the Mechanisms of BRD4 and Its Inhibitors in Hematologic Malignancies--Review].

Bromodomain-containing protein 4 (BRD4) is one of the most important members in the bromodomain and extra terminal domain(BET) family, it plays an important role in cellular physiology in human body, such as cell cycles, cell proliferation, and immune response. Recent studies have shown that BRD4 is associated with occurrence and development of acute myeloblastic leukemia, multiple myeloma and lymphoma. The mechanisms of BRD4 in hematologic malignancies including the regulation of c-Myc expression, and participation of the composition of super-enhancer, etc. At present, many kinds of inhibitors have been developed to target inhibit BRD4 for therapy in hematologic malignancies, and some of BRD4 inhibitors have entered phase Ⅱ clinical trials, which suggested that BRD4 inhibitors are expected to become new therapeutic agents for hematologic malignancies. In this review, the research advance of BRD4 and BRD4 inhibitors in hematologic malignancies was summarized briefly.

MIR125B1 represses the degradation of the PML-RARA oncoprotein by an autophagy-lysosomal pathway in acute promyelocytic leukemia.

Acute promyelocytic leukemia (APL) is characterized by the t(15;17)-associated PML-RARA fusion gene. We have previously found that MIR125B1 is highly expressed in patients with APL and may be associated with disease pathogenesis; however, the mechanism by which MIR125B1 exerts its oncogenic potential has not been fully elucidated. Here, we demonstrated that MIR125B1 abundance correlates with the PML-RARA status. MIR125B1 overexpression enhanced PML-RARA expression and inhibited the ATRA-induced degradation of the PML-RARA oncoprotein. RNA-seq analysis revealed a direct link between the PML-RARA degradation pathway and MIR125B1-arrested differentiation. We further demonstrated that the MIR125B1-mediated blockade of PML-RARA proteolysis was regulated via an autophagy-lysosomal pathway, contributing to the inhibition of APL differentiation. Furthermore, we identified DRAM2 (DNA-damage regulated autophagy modulator 2), a critical regulator of autophagy, as a novel target that was at least partly responsible for the function of MIR125B1 involved in autophagy. Importantly, the knockdown phenotypes for DRAM2 are similar to the effects of overexpressing MIR125B1 as impairment of PML-RARA degradation, inhibition of autophagy, and myeloid cell differentiation arrest. These effects of MIR125B1 and its target DRAM2 were further confirmed in an APL mouse model. Thus, MIR125B1 dysregulation may interfere with the effectiveness of ATRA-mediated differentiation through an autophagy-dependent pathway, representing a novel potential APL therapeutic target.