To investigate the mechanism(s) underlying the expression of primate-specific microRNAs (miRs), we sought DNA regulatory elements and proteins mediating expression of the primate-specific hsa-miR-608 ...(miR-608), which is located in the SEMA4G gene and facilitates the cholinergic blockade of inflammation by targeting acetylcholinesterase mRNA. ‘Humanized’ mice carrying pre-miR-608 flanked by 250 bases of endogenous sequences inserted into the murine Sema4g gene successfully expressed miR-608. Moreover, by flanking miR-608 by shortened fragments of its human genome region we identified an active independent promoter within the 150 nucleotides 5′ to pre-miR-608, which elevated mature miR-608 levels by 100-fold in transfected mouse- and human-originated cells. This highlighted a regulatory role of the 5′ flank as enabling miR-608 expression. Moreover, pull-down of the 150-base 5′ sequence revealed its interaction with ribosomal protein L24 (RPL24), implicating an additional mechanism controlling miR-608 levels. Furthermore, RPL24 knockdown altered the expression of multiple miRs, and RPL24 immunoprecipitation indicated that up- or down-regulation of the mature miRs depended on whether their precursors bind RPL24 directly. Finally, further tests showed that RPL24 interacts directly with DDX5, a component of the large microprocessor complex, to inhibit miR processing. Our findings reveal that RPL24, which has previously been shown to play a role in miR processing in
Arabidopsis thaliana
, has a similar evolutionarily conserved function in miR biogenesis in mammals. We thus characterize a novel extra-ribosomal role of RPL24 in primate miR regulation.
Graphical abstract
Clonal hematopoiesis (CH) is an aging-associated condition characterized by the clonal outgrowth of pre-leukemic cells that acquire specific mutations. Although individuals with CH are healthy, they ...are at an increased risk of developing myeloid malignancies, suggesting that additional alterations are needed for the transition from a pre-leukemia stage to frank leukemia. To identify signaling states that cooperate with pre-leukemic cells, we used an in vivo RNAi screening approach. One of the most prominent genes identified was the ubiquitin ligase TRAF6. Loss of TRAF6 in pre-leukemic cells results in overt myeloid leukemia and is associated with MYC-dependent stem cell signatures. TRAF6 is repressed in a subset of patients with myeloid malignancies, suggesting that subversion of TRAF6 signaling can lead to acute leukemia. Mechanistically, TRAF6 ubiquitinates MYC, an event that does not affect its protein stability but rather represses its functional activity by antagonizing an acetylation modification.
Display omitted
•Loss of TRAF6 results in progression of clonal hematopoiesis to AML/MPN•Loss of TRAF6 results in increased MYC activation•TRAF6 ubiquitinates MYC and represses its transcriptional activity•TLR-induced TRAF6 activation suppresses MYC function in AML
Individuals with clonal hematopoiesis have an increased risk of developing hematopoietic malignancies. Starczynowski and colleagues demonstrate that loss of TRAF6 signaling contributes to the development of AML/MPN in the context of clonal hematopoiesis by activating MYC. TRAF6 functions as a tumor suppressor by ubiquitinating MYC and repressing its transcriptional activity.
BH3 mimetics are used as an efficient strategy to induce cell death in several blood malignancies, including acute myeloid leukemia (AML). Venetoclax, a potent BCL-2 antagonist, is used clinically in ...combination with hypomethylating agents for the treatment of AML. Moreover, MCL1 or dual BCL-2/BCL-xL antagonists are under investigation. Yet, resistance to single or combinatorial BH3-mimetic therapies eventually ensues. Integration of multiple genome-wide CRISPR/Cas9 screens revealed that loss of mitophagy modulators sensitizes AML cells to various BH3 mimetics targeting different BCL-2 family members. One such regulator is MFN2, whose protein levels positively correlate with drug resistance in patients with AML. MFN2 overexpression is sufficient to drive resistance to BH3 mimetics in AML. Insensitivity to BH3 mimetics is accompanied by enhanced mitochondria-endoplasmic reticulum interactions and augmented mitophagy flux, which acts as a prosurvival mechanism to eliminate mitochondrial damage. Genetic or pharmacologic MFN2 targeting synergizes with BH3 mimetics by impairing mitochondrial clearance and enhancing apoptosis in AML.
AML remains one of the most difficult-to-treat blood cancers. BH3 mimetics represent a promising therapeutic approach to eliminate AML blasts by activating the apoptotic pathway. Enhanced mitochondrial clearance drives resistance to BH3 mimetics and predicts poor prognosis. Reverting excessive mitophagy can halt BH3-mimetic resistance in AML. This article is highlighted in the In This Issue feature, p. 1501.
Acute myeloid leukemia (AML) is a hematopoietic malignancy with poor prognosis and limited treatment options. Here we provide a comprehensive census of the bone marrow immune microenvironment in ...adult and pediatric patients with AML. We characterize unique inflammation signatures in a subset of AML patients, associated with inferior outcomes. We identify atypical B cells, a dysfunctional B-cell subtype enriched in patients with high-inflammation AML, as well as an increase in CD8
GZMK
and regulatory T cells, accompanied by a reduction in T-cell clonal expansion. We derive an inflammation-associated gene score (iScore) that associates with poor survival outcomes in patients with AML. Addition of the iScore refines current risk stratifications for patients with AML and may enable identification of patients in need of more aggressive treatment. This work provides a framework for classifying patients with AML based on their immune microenvironment and a rationale for consideration of the inflammatory state in clinical settings.
Abstract
Acute myeloid leukemia (AML) is a hematopoietic malignancy with poor prognosis and limited treatment options. Here we provide a comprehensive single cell RNA-Sequencing census of the bone ...marrow immune microenvironment in adult and pediatric AML patients. We characterize unique inflammation signatures in a subset of AML patients, associated with inferior outcomes. We identify atypical B cells, a dysfunctional B cell subtype enriched in high-inflammation AML patients, as well as an increase in CD8+ GZMK+ and regulatory T cells, accompanied by a reduction in T cell clonal expansion. We derive an inflammation-associated gene score (iScore) that associates with poor survival outcomes in AML patients. Addition of the iScore refines current risk stratifications for AML patients and may enable identification of patients in need of more aggressive treatment. This work provides a first framework for classifying AML patients based on their immune microenvironment and a rationale for consideration of the inflammatory state in clinical settings.
Citation Format: Audrey Lasry, Bettina Nadorp, Maarten Fornerod, Deedra Nicolet, Huiyun Wu, Christopher J Walker, Zhengxi Sun, Matthew T Witkowski, Anastasia N Tikhonova, Maria Guillamot, Geraldine Cayanan, Anna Yeaton, Tanja A Gruber, Ann-Kathrin Eisfeld, Iannis Aifantis. Inflammation remodels the immune microenvironment in acute myeloid leukemia abstract. In: Proceedings of the AACR Special Conference: Acute Myeloid Leukemia and Myelodysplastic Syndrome; 2023 Jan 23-25; Austin, TX. Philadelphia (PA): AACR; Blood Cancer Discov 2023;4(3_Suppl):Abstract nr A20.
