N
-Methyladenosine (m
A) on mRNAs mediates different biological processes and its dysregulation contributes to tumorigenesis. How m
A dictates its diverse molecular and cellular effects in leukemias ...remains unknown. We found that YTHDC1 is the essential m
A reader in myeloid leukemia from a genome-wide CRISPR screen and that m
A is required for YTHDC1 to undergo liquid-liquid phase separation and form nuclear YTHDC1-m
A condensates (nYACs). The number of nYACs increases in acute myeloid leukemia (AML) cells compared with normal hematopoietic stem and progenitor cells. AML cells require the nYACs to maintain cell survival and the undifferentiated state that is critical for leukemia maintenance. Furthermore, nYACs enable YTHDC1 to protect m
A-mRNAs from the PAXT complex and exosome-associated RNA degradation. Collectively, m
A is required for the formation of a nuclear body mediated by phase separation that maintains mRNA stability and control cancer cell survival and differentiation.
N6-Methyladenosine (m6A) on mRNAs mediates different biological processes and its dysregulation contributes to tumorigenesis. How m6A dictates its diverse molecular and cellular effects in leukemias ...remains unknown. We found that YTHDC1 is the essential m6A reader in myeloid leukemia from a genome-wide CRISPR screen and that m6A is required for YTHDC1 to undergo liquid-liquid phase separation and form nuclear YTHDC1-m6A condensates (nYACs). The number of nYACs increases in acute myeloid leukemia (AML) cells compared with normal hematopoietic stem and progenitor cells. AML cells require the nYACs to maintain cell survival and the undifferentiated state that is critical for leukemia maintenance. Furthermore, nYACs enable YTHDC1 to protect m6A-mRNAs from the PAXT complex and exosome-associated RNA degradation. Collectively, m6A is required for the formation of a nuclear body mediated by phase separation that maintains mRNA stability and control cancer cell survival and differentiation.
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•YTHDC1 is required for AML cell survival, differentiation state, and leukemogenesis•YTHDC1 binds to m6A and forms nuclear condensates (nYACs) mediated by LLPS•nYACs are more abundant in AML cells compared with normal blood cells•nYACs protect mRNAs (i.e., MYC and others) from degradation by the PAXT complex
Using AML cell lines and patient samples Cheng et al. identify a requirement for YTHDC1 in myeloid leukemogenesis. YTHDC1 undergoes liquid-liquid phase separation by binding to m6A to form dynamic nuclear condensates. These nuclear bodies are increased in myeloid leukemia cells and protect mRNAs from the PAXT-exosome complex.
Clinical trials investigating histone deacetylase inhibitors (HDACi) to reverse HIV-1 latency aim to expose reservoirs in antiretroviral (ARV)-treated individuals to clearance by immune effectors, ...yet have not driven measurable reductions in the frequencies of infected cells. We therefore investigated the effects of the class I-selective HDACi nanatinostat and romidepsin on various blocks to latency reversal and elimination, including viral splicing, antigen presentation, and CD8
T cell function. In
CD4
T cells from ARV-suppressed individuals, both HDACi significantly induced viral transcription, but not splicing nor supernatant HIV-1 RNA. In an HIV-1 latency model using autologous CD8
T cell clones as biosensors of antigen presentation, neither HDACi-treated CD4
T cell condition induced clone degranulation. Both HDACi also impaired the function of primary CD8
T cells in viral inhibition assays, with nanatinostat causing less impairment. These findings suggest that spliced or cell-free HIV-1 RNAs are more indicative of antigen expression than unspliced HIV-RNAs and may help to explain the limited abilities of HDACi to generate CD8
T cell targets
Antiretroviral (ARV) drug regimens suppress HIV-1 replication but are unable to cure infection. This leaves people living with HIV-1 burdened by a lifelong commitment to expensive daily medication. Furthermore, it has become clear that ARV therapy does not fully restore health, leaving individuals at elevated risk for cardiovascular disease, certain types of cancers, and neurocognitive disorders, as well as leaving them exposed to stigma. Efforts are therefore under way to develop therapies capable of curing infection. A key focus of these efforts has been on a class of drugs called histone deacetylase inhibitors (HDACi), which have the potential of exposing hidden reservoirs of HIV-1 to elimination by the immune system. Unfortunately, clinical trial results with HDACi have thus far been disappointing. In the current study, we integrate a number of experimental approaches to build a model that provides insights into the limited activity of HDACi in clinical trials and offers direction for future approaches.
Curing HIV infection will require the elimination of a reservoir of infected CD4+ T cells that persists despite HIV-specific cytotoxic T cell (CTL) responses. Although viral latency is a critical ...factor in this persistence, recent evidence also suggests a role for intrinsic resistance of reservoir-harboring cells to CTL killing. This resistance may have contributed to negative outcomes of clinical trials, where pharmacologic latency reversal has thus far failed to drive reductions in HIV reservoirs. Through transcriptional profiling, we herein identified overexpression of the prosurvival factor B cell lymphoma 2 (BCL-2) as a distinguishing feature of CD4+ T cells that survived CTL killing. We show that the inducible HIV reservoir was disproportionately present in BCL-2hi subsets in ex vivo CD4+ T cells. Treatment with the BCL-2 antagonist ABT-199 was not sufficient to drive reductions in ex vivo viral reservoirs when tested either alone or with a latency-reversing agent (LRA). However, the triple combination of strong LRAs, HIV-specific T cells, and a BCL-2 antagonist uniquely enabled the depletion of ex vivo viral reservoirs. Our results provide rationale for novel therapeutic approaches targeting HIV cure and, more generally, suggest consideration of BCL-2 antagonism as a means of enhancing CTL immunotherapy in other settings, such as cancer.
HIV persists, despite immune responses and antiretroviral therapy, in viral reservoirs that seed rebound viremia if therapy is interrupted. Previously, we showed that the BCL-2 protein contributes to ...HIV persistence by conferring a survival advantage to reservoir-harboring cells. Here, we demonstrate that many of the BCL-2 family members are overexpressed in HIV-infected CD4
T cells, indicating increased tension between proapoptotic and prosurvival family members-and suggesting that inhibition of prosurvival members may disproportionately affect the survival of HIV-infected cells. Based on these results, we chose to study BCL-X
due to its consistent overexpression and the availability of selective antagonists. Infection of primary CD4
T cells with HIV resulted in increased BCL-X
protein expression, and treatment with two selective BCL-X
antagonists, A-1155463 and A-1551852, led to selective death of productively infected CD4
T cells. In a primary cell model of latency, both BCL-X
antagonists drove reductions in HIV DNA and in infectious cell frequencies both alone and in combination with the latency reversing agent bryostatin-1, with little off-target cytotoxicity. However, these antagonists, with or without bryostatin-1 or in combination with the highly potent latency reversing agent combination phorbol myristate acetate (PMA) + ionomycin, failed to reduce total HIV DNA and infectious reservoirs in
CD4
T cells from antiretroviral therapy (ART)-suppressed donors. Our results add to growing evidence that bona fide reservoir-harboring cells are resistant to multiple "kick and kill" modalities-relative to latency models. We also interpret our results as encouraging further exploration of BCL-X
antagonists for cure, where combination approaches, including with immune effectors, may unlock the ability to eliminate
reservoirs.
Although antiretroviral therapy (ART) has transformed HIV infection into a manageable chronic condition, there is no safe or scalable cure. HIV persists in "reservoirs" of infected cells that reinitiate disease progression if ART is interrupted. Whereas most efforts to eliminate this reservoir have focused on exposing these cells to immune-mediated clearance by reversing viral latency, recent work shows that these cells also resist being killed. Here, we identify a "prosurvival" factor, BCL-X
, that is overexpressed in HIV-infected cells, and demonstrate selective toxicity to these cells by BCL-X
antagonists. These antagonists also reduced reservoirs in a primary-cell latency model but were insufficient to reduce "natural" reservoirs in
CD4
T cells-adding to growing evidence that the latter are resilient in a way that is not reflected in models. We nonetheless suggest that the selective toxicity of BCL-X
antagonists to HIV-infected cells supports their prioritization for testing in combinations aimed at reducing
reservoirs.
HIV persists, despite immune responses and antiretroviral therapy, in viral reservoirs that seed rebound viremia if therapy is interrupted. Previously, we showed that the BCL-2 protein contributes to ...HIV persistence by conferring a survival advantage to reservoir-harboring cells. Here, we demonstrate that many of the BCL-2 family members are overexpressed in HIV-infected CD4+ T cells, indicating increased tension between proapoptotic and prosurvival family members—and suggesting that inhibition of prosurvival members may disproportionately affect the survival of HIV-infected cells. Based on these results, we chose to study BCL-XL due to its consistent overexpression and the availability of selective antagonists. Infection of primary CD4+ T cells with HIV resulted in increased BCL-XL protein expression, and treatment with two selective BCL-XL antagonists, A-1155463 and A-1551852, led to selective death of productively infected CD4+ T cells. In a primary cell model of latency, both BCL-XL antagonists drove reductions in HIV DNA and in infectious cell frequencies both alone and in combination with the latency reversing agent bryostatin-1, with little off-target cytotoxicity. However, these antagonists, with or without bryostatin-1 or in combination with the highly potent latency reversing agent combination phorbol myristate acetate (PMA) + ionomycin, failed to reduce total HIV DNA and infectious reservoirs in ex vivo CD4+ T cells from antiretroviral therapy (ART)-suppressed donors. Our results add to growing evidence that bona fide reservoir-harboring cells are resistant to multiple “kick and kill” modalities—relative to latency models. We also interpret our results as encouraging further exploration of BCL-XL antagonists for cure, where combination approaches, including with immune effectors, may unlock the ability to eliminate ex vivo reservoirs. IMPORTANCE Although antiretroviral therapy (ART) has transformed HIV infection into a manageable chronic condition, there is no safe or scalable cure. HIV persists in “reservoirs” of infected cells that reinitiate disease progression if ART is interrupted. Whereas most efforts to eliminate this reservoir have focused on exposing these cells to immune-mediated clearance by reversing viral latency, recent work shows that these cells also resist being killed. Here, we identify a “prosurvival” factor, BCL-XL, that is overexpressed in HIV-infected cells, and demonstrate selective toxicity to these cells by BCL-XL antagonists. These antagonists also reduced reservoirs in a primary-cell latency model but were insufficient to reduce “natural” reservoirs in ex vivo CD4+ T cells—adding to growing evidence that the latter are resilient in a way that is not reflected in models. We nonetheless suggest that the selective toxicity of BCL-XL antagonists to HIV-infected cells supports their prioritization for testing in combinations aimed at reducing ex vivo reservoirs.
RNA binding proteins (RBPs) are key arbiters of post-transcriptional regulation and are found to be found dysregulated in hematological malignancies. Here, we identify the RBP RBMX and its retrogene ...RBMXL1 to be required for murine and human myeloid leukemogenesis. RBMX/L1 are overexpressed in acute myeloid leukemia (AML) primary patients compared to healthy individuals, and RBMX/L1 loss delayed leukemia development. RBMX/L1 loss lead to significant changes in chromatin accessibility, as well as chromosomal breaks and gaps. We found that RBMX/L1 directly bind to mRNAs, affect transcription of multiple loci, including
(HP1α), and control the nascent transcription of the
locus. Forced CBX5 expression rescued the RBMX/L1 depletion effects on cell growth and apoptosis. Overall, we determine that RBMX/L1 control leukemia cell survival by regulating chromatin state through their downstream target
. These findings identify a mechanism for RBPs directly promoting transcription and suggest RBMX/L1, as well as CBX5, as potential therapeutic targets in myeloid malignancies.
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