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Patients with acute myeloid leukemia (AML) carrying high-risk genetic lesions or high residual disease levels after therapy are particularly exposed to the risk of relapse. Here, we identified the long non-coding RNA CDK6-AS1 able to cluster an AML subgroup with peculiar gene signatures linked to hematopoietic cell differentiation and mitochondrial dynamics. CDK6-AS1 silencing triggered hematopoietic commitment in healthy CD34+ cells, whereas in AML cells the pathological undifferentiated state was rescued. This latter phenomenon derived from RUNX1 transcriptional control, responsible for the stemness of hematopoietic precursors and for the block of differentiation in AML. By CDK6-AS1 silencing in vitro, AML mitochondrial mass decreased with augmented pharmacological sensitivity to mitochondria-targeting drugs. In vivo, the combination of tigecycline and cytarabine reduced leukemia progression in the AML-PDX model with high CDK6-AS1 levels, supporting the concept of a mitochondrial vulnerability. Together, these findings uncover CDK6-AS1 as crucial in myeloid differentiation and mitochondrial mass regulation.

BackgroundLong non-coding RNAs (lncRNAs) play a variety of cellular roles, including regulation of transcription and translation, leading to alterations in gene expression. Some lncRNAs modulate the expression of chromosomally adjacent genes. Here, we assess the roles of the lncRNA CASC15 in regulation of a chromosomally nearby gene, SOX4, and its function in RUNX1/AML translocated leukemia.ResultsCASC15 is a conserved lncRNA that was upregulated in pediatric B-acute lymphoblastic leukemia (B-ALL) with t (12; 21) as well as pediatric acute myeloid leukemia (AML) with t (8; 21), both of which are associated with relatively better prognosis. Enforced expression of CASC15 led to a myeloid bias in development, and overall, decreased engraftment and colony formation. At the cellular level, CASC15 regulated cellular survival, proliferation, and the expression of its chromosomally adjacent gene, SOX4. Differentially regulated genes following CASC15 knockdown were enriched for predicted transcriptional targets of the Yin and Yang-1 (YY1) transcription factor. Interestingly, we found that CASC15 enhances YY1-mediated regulation of the SOX4 promoter.ConclusionsOur findings represent the first characterization of this CASC15 in RUNX1-translocated leukemia, and point towards a mechanistic basis for its action.

Posttranscriptional control of gene expression is important for defining both normal and pathological cellular phenotypes. In vitro, RNA-binding proteins (RBPs) have recently been shown to play important roles in posttranscriptional regulation; however, the contribution of RBPs to cell specification is not well understood. Here, we determined that the RBP insulin-like growth factor 2 mRNA-binding protein 3 (IGF2BP3) is specifically overexpressed in mixed lineage leukemia-rearranged (MLL-rearranged) B-acute lymphoblastic leukemia (B-ALL), which constitutes a subtype of this malignancy associated with poor prognosis and high risk of relapse. IGF2BP3 was required for the survival of B-ALL cell lines, as knockdown led to decreased proliferation and increased apoptosis. Enforced expression of IGF2BP3 provided murine BM cells with a strong survival advantage, led to proliferation of hematopoietic stem and progenitor cells, and skewed hematopoietic development to the B cell/myeloid lineage. Cross-link immunoprecipitation and high throughput sequencing uncovered the IGF2BP3-regulated transcriptome, which includes oncogenes MYC and CDK6 as direct targets. IGF2BP3 regulated transcripts via targeting elements within 3' untranslated regions (3'UTR), and enforced IGF2BP3 expression in mice resulted in enhanced expression of Myc and Cdk6 in BM. Together, our data suggest that IGF2BP3-mediated targeting of oncogenic transcripts may represent a critical pathogenetic mechanism in MLL-rearranged B-ALL and support IGF2BP3 and its cognate RNA-binding partners as potential therapeutic targets in this disease.

UnlabelledLong noncoding RNAs (lncRNA) have been found to play a role in gene regulation with dysregulated expression in various cancers. The precise role that lncRNA expression plays in the pathogenesis of B-acute lymphoblastic leukemia (B-ALL) is unknown. Therefore, unbiased microarray profiling was performed on human B-ALL specimens, and it was determined that lncRNA expression correlates with cytogenetic abnormalities, which was confirmed by qRT-PCR in a large set of B-ALL cases. Importantly, high expression of BALR-2 correlated with poor overall survival and diminished response to prednisone treatment. In line with a function for this lncRNA in regulating cell survival, BALR-2 knockdown led to reduced proliferation, increased apoptosis, and increased sensitivity to prednisolone treatment. Conversely, overexpression of BALR-2 led to increased cell growth and resistance to prednisone treatment. Interestingly, BALR-2 expression was repressed by prednisolone treatment and its knockdown led to upregulation of the glucocorticoid response pathway in both human and mouse B cells. Together, these findings indicate that BALR-2 plays a functional role in the pathogenesis and/or clinical responsiveness of B-ALL, and that altering the levels of particular lncRNAs may provide a future direction for therapeutic development.ImplicationslncRNA expression has the potential to segregate the common subtypes of B-ALL, predict the cytogenetic subtype, and indicate prognosis.

In the development of novel immunotherapeutic approaches, the step of target identification is a challenging process, because it aims at identifying robust tumor‐associated antigens (TAAs) specific for the pathological population and causing no off‐target effects. Here we propose CD72 as a novel and robust TAA for pediatric acute leukemias. We provided an outline of CD72 expression assessed by flow cytometry on a variety of cancer cell lines and primary samples, including normal bone marrow (BM) samples and hematopoietic stem and progenitor cells. We analyzed CD 72 expression on a cohort of 495 pathological pediatric BM aspirates, including: 215 B‐cell precursor acute lymphoblastic leukemias (BCP‐ALL), 156 acute myeloid leukemias (AMLs), 88 T‐lineage ALLs or lymphoblastic lymphomas with BM infiltration, 13 B‐lineage lymphoblastic lymphomas with BM infiltration, 9 myelodysplastic syndromes with increased blasts (5%–9% blasts on BM: MDS‐IB1) and 14 non‐hematopoietic solid tumors infiltrating BM. Results showed that CD72 is highly expressed in almost all BCP‐ALL and the majority of AML at diagnosis, including BCP‐ALL cases characterized by CD19 loss. These findings support a potential role for advanced diagnostics and novel immunotherapy approaches, providing a pan‐ALL and AML target. [ABSTRACT FROM AUTHOR]