Cytoplasmic DROSHA and non-canonical mechanisms of MiR-155 biogenesis in FLT3-ITD acute myeloid leukemia

circSLC25A13 acts as a ceRNA to regulate AML progression via miR-616-3p/ADCY2 axis

Circular RNAs (circRNAs), a type of endogenous noncoding RNA (ncRNA), exert vital roles in leukemia progression and are promising prognostic factors. Here, we report a novel circRNA, circSLC25A13 (hsa_circ_0081188), which was increased in acute myeloid leukemia (AML) patients with poor overall survival (OS) comparing to patients with good prognosis. Knockdown of circSLC25A13 in AML cells inhibited proliferation and increased cell apoptosis in vitro and in vivo. Enhanced circSLC25A13 expression promoted the survival of AML cells. Mechanistically, circSLC25A13 played as a microRNA sponge of miR-616-3p, which inhibited the expression of adenylate cyclase 2 (ADCY2). Downregulation of miR-616-3p and overexpression of ADCY2 partially rescued circSLC25A13 deficient induced cell growth arrest. In summary, through competitive absorption of miR-616-3p and thereby upregulating ADCY2 expression, circSLC25A13 promoted AML progression. Moreover, circSLC25A13 may represent a potential novel biomarker for the prognosis of AML and offer a potential therapeutic target for AML treatment.

BMPMDA: Prediction of MiRNA-Disease Associations Using a Space Projection Model Based on Block Matrix

With the high-quality development of bioinformatics technology, miRNA-disease associations (MDAs) are gradually being uncovered. At present, convenient and efficient prediction methods, which solve the problem of resource-consuming in traditional wet experiments, need to be further put forward. In this study, a space projection model based on block matrix is presented for predicting MDAs (BMPMDA). Specifically, two block matrices are first composed of the known association matrix and similarity to increase comprehensiveness. For the integrity of information in the heterogeneous network, matrix completion (MC) is utilized to mine potential MDAs. Considering the neighborhood information of data points, linear neighborhood similarity (LNS) is regarded as a measure of similarity. Next, LNS is projected onto the corresponding completed association matrix to derive the projection score. Finally, the AUC and AUPR values for BMPMDA reach 0.9691 and 0.6231, respectively. Additionally, the majority of novel MDAs in three disease cases are identified in existing databases and literature. It suggests that BMPMDA can serve as a reliable prediction model for biological research.

RNA binding proteins in MLL-rearranged leukemia

RNA binding proteins (RBPs) have recently emerged as important post-transcriptional gene expression regulators in both normal development and disease. RBPs influence the fate of mRNAs through multiple mechanisms of action such as RNA modifications, alternative splicing, and miR-mediated regulation. This complex and, often, combinatorial regulation by RBPs critically impacts the expression of oncogenic transcripts and, thus, the activation of pathways that drive oncogenesis. Here, we focus on the major features of RBPs, their mechanisms of action, and discuss the current progress in investigating the function of important RBPs in MLL-rearranged leukemia.

Venetoclax in combination with nucleoside analogs in acute myelogenous leukemia

PURPOSE OF REVIEW

Venetoclax in combination with nucleoside analogs such as hypomethylating agents (HMA) and low-dose cytarabine (LDAC) has led to unprecedented response and survival outcomes in patients with acute myeloid leukemia (AML). This has spurred the development of regimens combining venetoclax with other nucleoside analogs with distinct mechanisms of action. Here, we review older and newer nucleoside analogs, the rationale for their combination with venetoclax, and clinical evidence for the combination when available.

RECENT FINDINGS

Venetoclax with HMA prolonged survival in a phase 3 study. Additionally, biologic correlates of response and resistance to venetoclax with HMA have been identified. The addition of venetoclax to standard intensive regimens containing higher doses of cytarabine and purine nucleoside analogs are safe and induce very high rates of remission and measurable residual disease negativity (MRD) negativity in newly diagnosed and relapsed/refractory AML. Investigational nucleoside analogs aim to improve upon the safety, bioavailability, or efficacy of approved venetoclax combinations and are currently being evaluated in clinical studies.

SUMMARY

The development of venetoclax with HMA has transformed care for elderly adults with AML and opened the door for novel combinations of venetoclax with other nucleoside analogs. Further clinical studies are needed to see if these novel combinations further improve outcomes in AML particularly for patients with high-risk disease.

MicroRNA networks in FLT3-ITD acute myeloid leukemia

We report on a deregulatory activity on microRNA (miRNA) biogenesis by the FMS-like tyrosine kinase 3 (FLT3)-internal tandem duplication (ITD) in acute myeloid leukemia. FLT3-ITD provides a divergent signal for concurrent and aberrant miR-155 up-regulation and miR-126 down-regulation via a series of miRNA–protein regulatory loops interconnected through SH2-containing inositol phosphatase 1 (SHIP1)/phosphor-protein kinase B (AKT)/Sprouty related EVH1 domain containing 1 (SPRED1) signaling. This divergent input signal eventually converges and amplifies an output signal for leukemic growth.

MiR-126 and miR-155 are key microRNAs (miRNAs) that regulate, respectively, hematopoietic cell quiescence and proliferation. Herein we showed that in acute myeloid leukemia (AML), the biogenesis of these two miRNAs is interconnected through a network of regulatory loops driven by the FMS-like tyrosine kinase 3-internal tandem duplication (FLT3-ITD). In fact, FLT3-ITD induces the expression of miR-155 through a noncanonical mechanism of miRNA biogenesis that implicates cytoplasmic Drosha ribonuclease III (DROSHA). In turn, miR-155 down-regulates SH2-containing inositol phosphatase 1 (SHIP1), thereby increasing phosphor-protein kinase B (AKT) that in turn serine-phosphorylates, stabilizes, and activates Sprouty related EVH1 domain containing 1 (SPRED1). Activated SPRED1 inhibits the RAN/XPO5 complex and blocks the nucleus-to-cytoplasm transport of pre-miR-126, which cannot then complete the last steps of biogenesis. The net result is aberrantly low levels of mature miR-126 that allow quiescent leukemia blasts to be recruited into the cell cycle and proliferate. Thus, miR-126 down-regulation in proliferating AML blasts is downstream of FLT3-ITD–dependent miR-155 expression that initiates a complex circuit of concatenated regulatory feedback (i.e., miR-126/SPRED1, miR-155/human dead-box protein 3 [DDX3X]) and feed-forward (i.e., miR-155/SHIP1/AKT/miR-126) regulatory loops that eventually converge into an output signal for leukemic growth.

Spred1 deficit promotes treatment resistance and transformation of chronic phase CML

Spred1 is highly expressed in normal hematopoietic stem cells (HSCs). Lack of Spred1 function has been associated with aberrant hematopoiesis and acute leukemias. In chronic myelogenous leukemia (CML), Spred1 is reduced in patients with accelerated phase (AP) or blast crisis (BC) CML, thereby suggesting that deficit of this protein may contribute to disease transformation. In fact, Spred1 knockout (KO) in SCLtTA/BCR-ABL CML mice either globally, or restricted to hematopoietic cells (i.e., HSCs) or to endothelial cells (ECs), led to transformation of chronic phase (CP) CML into AP/BC CML. Upon BCR-ABL induction, all three Spred1 KO CML models showed AP/BC features. However, compared with global Spred1 KO, the AP/BC phenotypes of HSC-Spred1 KO and EC-Spred1 KO CML models were attenuated, suggesting a concurrent contribution of Spred1 deficit in multiple compartments of the leukemic bone marrow niche to the CML transformation. Spred1 KO, regardless if occurred in HSCs or in ECs, increased miR-126 in LSKs (Lin-Sca-1+c-Kit+), a population enriched in leukemic stem cells (LSCs), resulting in expansion of LSCs, likely through hyperactivation of the MAPK/ERK pathway that augmented Bcl-2 expression and stability. This ultimately led to enhancement of Bcl-2-dependent oxidative phosphorylation that supported homeostasis, survival and activity of LSCs and drove AP/BC transformation.

Targeting miR-126 in inv(16) acute myeloid leukemia inhibits leukemia development and leukemia stem cell maintenance

Acute myeloid leukemia (AML) harboring inv(16)(p13q22) expresses high levels of miR-126. Here we show that the CBFB-MYH11 (CM) fusion gene upregulates miR-126 expression through aberrant miR-126 transcription and perturbed miR-126 biogenesis via the HDAC8/RAN-XPO5-RCC1 axis. Aberrant miR-126 upregulation promotes survival of leukemia-initiating progenitors and is critical for initiating and maintaining CM-driven AML. We show that miR-126 enhances MYC activity through the SPRED1/PLK2-ERK-MYC axis. Notably, genetic deletion of miR-126 significantly reduces AML rate and extends survival in CM knock-in mice. Therapeutic depletion of miR-126 with an anti-miR-126 (miRisten) inhibits AML cell survival, reduces leukemia burden and leukemia stem cell (LSC) activity in inv(16) AML murine and xenograft models. The combination of miRisten with chemotherapy further enhances the anti-leukemia and anti-LSC activity. Overall, this study provides molecular insights for the mechanism and impact of miR-126 dysregulation in leukemogenesis and highlights the potential of miR-126 depletion as a therapeutic approach for inv(16) AML.

miR-126 is highly expressed in inv(16) Acute myeloid leukemia (AML) but its role is unclear. Here, the authors show that the aberrant expression of miR-126 in inv(16) AML is directly due to the CBFB-MYH11 fusion gene and that it can promote AML development and leukemia stem cell maintenance, highlighting miR-126 as a therapeutic target for inv(16) AML patients

Splice and Dice: Intronic microRNAs, Splicing and Cancer

Introns span only a quarter of the human genome, yet they host around 60% of all known microRNAs. Emerging evidence indicates the adaptive advantage of microRNAs residing within introns is attributed to their complex co-regulation with transcription and alternative splicing of their host genes. Intronic microRNAs are often co-expressed with their host genes, thereby providing functional synergism or antagonism that is exploited or decoupled in cancer. Additionally, intronic microRNA biogenesis and the alternative splicing of host transcript are co-regulated and intertwined. The importance of intronic microRNAs is under-recognized in relation to the pathogenesis of cancer.