A PRC2-Kdm5b axis sustains tumorigenicity of acute myeloid leukemia.

Acute myeloid leukemias (AMLs) with the NUP98-NSD1 or mixed lineage leukemia (MLL) rearrangement (MLL-r) share transcriptomic profiles associated with stemness-related gene signatures and display poor prognosis. The molecular underpinnings of AML aggressiveness and stemness remain far from clear. Studies with EZH2 enzymatic inhibitors show that polycomb repressive complex 2 (PRC2) is crucial for tumorigenicity in NUP98-NSD1+ AML, whereas transcriptomic analysis reveal that Kdm5b, a lysine demethylase gene carrying "bivalent" chromatin domains, is directly repressed by PRC2. While ectopic expression of Kdm5b suppressed AML growth, its depletion not only promoted tumorigenicity but also attenuated anti-AML effects of PRC2 inhibitors, demonstrating a PRC2-|Kdm5b axis for AML oncogenesis. Integrated RNA sequencing (RNA-seq), chromatin immunoprecipitation followed by sequencing (ChIP-seq), and Cleavage Under Targets & Release Using Nuclease (CUT&RUN) profiling also showed that Kdm5b directly binds and represses AML stemness genes. The anti-AML effect of Kdm5b relies on its chromatin association and/or scaffold functions rather than its demethylase activity. Collectively, this study describes a molecular axis that involves histone modifiers (PRC2-|Kdm5b) for sustaining AML oncogenesis.

Mediator subunit MED1 is required for E2A-PBX1-mediated oncogenic transcription and leukemic cell growth.

The chimeric transcription factor E2A-PBX1, containing the N-terminal activation domains of E2A fused to the C-terminal DNA-binding domain of PBX1, results in 5% of pediatric acute lymphoblastic leukemias (ALL). We recently have reported a mechanism for RUNX1-dependent recruitment of E2A-PBX1 to chromatin in pre-B leukemic cells; but the subsequent E2A-PBX1 functions through various coactivators and the general transcriptional machinery remain unclear. The Mediator complex plays a critical role in cell-specific gene activation by serving as a key coactivator for gene-specific transcription factors that facilitates their function through the RNA polymerase II transcriptional machinery, but whether Mediator contributes to aberrant expression of E2A-PBX1 target genes remains largely unexplored. Here we show that Mediator interacts directly with E2A-PBX1 through an interaction of the MED1 subunit with an E2A activation domain. Results of MED1 depletion by CRISPR/Cas9 further indicate that MED1 is specifically required for E2A-PBX1-dependent gene activation and leukemic cell growth. Integrated transcriptome and cistrome analyses identify pre-B cell receptor and cell cycle regulatory genes as direct cotargets of MED1 and E2A-PBX1. Notably, complementary biochemical analyses also demonstrate that recruitment of E2A-PBX1 to a target DNA template involves a direct interaction with DNA-bound RUNX1 that can be further stabilized by EBF1. These findings suggest that E2A-PBX1 interactions with RUNX1 and MED1/Mediator are of functional importance for both gene-specific transcriptional activation and maintenance of E2A-PBX1-driven leukemia. The MED1 dependency for E2A-PBX1-mediated gene activation and leukemogenesis may provide a potential therapeutic opportunity by targeting MED1 in E2A-PBX1+ pre-B leukemia.

E2A-PBX1 functions as a coactivator for RUNX1 in acute lymphoblastic leukemia.

E2A, a basic helix-loop-helix transcription factor, plays a crucial role in determining tissue-specific cell fate, including differentiation of B-cell lineages. In 5% of childhood acute lymphoblastic leukemia (ALL), the t(1,19) chromosomal translocation specifically targets the E2A gene and produces an oncogenic E2A-PBX1 fusion protein. Although previous studies have shown the oncogenic functions of E2A-PBX1 in cell and animal models, the E2A-PBX1-enforced cistrome, the E2A-PBX1 interactome, and related mechanisms underlying leukemogenesis remain unclear. Here, by unbiased genomic profiling approaches, we identify the direct target sites of E2A-PBX1 in t(1,19)-positive pre-B ALL cells and show that, compared with normal E2A, E2A-PBX1 preferentially binds to a subset of gene loci cobound by RUNX1 and gene-activating machineries (p300, MED1, and H3K27 acetylation). Using biochemical analyses, we further document a direct interaction of E2A-PBX1, through a region spanning the PBX1 homeodomain, with RUNX1. Our results also show that E2A-PBX1 binding to gene enhancers is dependent on the RUNX1 interaction but not the DNA-binding activity harbored within the PBX1 homeodomain of E2A-PBX1. Transcriptome analyses and cell transformation assays further establish a significant RUNX1 requirement for E2A-PBX1-mediated target gene activation and leukemogenesis. Notably, the RUNX1 locus itself is also directly activated by E2A-PBX1, indicating a multilayered interplay between E2A-PBX1 and RUNX1. Collectively, our study provides the first unbiased profiling of the E2A-PBX1 cistrome in pre-B ALL cells and reveals a previously unappreciated pathway in which E2A-PBX1 acts in concert with RUNX1 to enforce transcriptome alterations for the development of pre-B ALL.

Karyopherin Kap114p-mediated trans-repression controls ribosomal gene expression under saline stress.

Nuclear accessibility of transcription factors controls gene expression, co-regulated by Ran-dependent nuclear localization and a competitive regulatory network. Here, we reveal that nuclear import factor-facilitated transcriptional repression attenuates ribosome biogenesis under chronic salt stress. Kap114p, one of the karyopherin-ßs (Kap-ßs) that mediates nuclear import of yeast TATA-binding protein (yTBP), exhibits a yTBP-binding affinity four orders of magnitude greater than its counterparts and suppresses binding of yTBP with DNA. Our crystal structure of Kap114p reveals an extensively negatively charged concave surface, accounting for high-affinity basic-protein binding. KAP114 knockout in yeast leads to a high-salt growth defect, with transcriptomic analyses revealing that Kap114p modulates expression of genes associated with ribosomal biogenesis by suppressing yTBP binding to target promoters, a trans-repression mechanism we attribute to reduced nuclear Ran levels under salinity stress. Our findings reveal that Ran integrates the nuclear transport pathway and transcription regulatory network, allowing yeast to respond to environmental stresses.

Andrographolide and its fluorescent derivative inhibit the main proteases of 2019-nCoV and SARS-CoV through covalent linkage.

The coronavirus disease 2019 (COVID-19) pandemic caused by 2019 novel coronavirus (2019-nCoV) has been a crisis of global health, whereas the effective vaccines against 2019-nCoV are still under development. Alternatively, utilization of old drugs or available medicine that can suppress the viral activity or replication may provide an urgent solution to suppress the rapid spread of 2019-nCoV. Andrographolide is a highly abundant natural product of the medicinal plant, Andrographis paniculata, which has been clinically used for inflammatory diseases and anti-viral therapy. We herein demonstrate that both andrographolide and its fluorescent derivative, the nitrobenzoxadiazole-conjugated andrographolide (Andro- NBD), suppressed the main protease (Mpro) activities of 2019-nCoV and severe acute respiratory syndrome coronavirus (SARS-CoV). Moreover, Andro-NBD was shown to covalently link its fluorescence to these proteases. Further mass spectrometry (MS) analysis suggests that andrographolide formed a covalent bond with the active site Cys145 of either 2019-nCoV Mpro or SARS-CoV Mpro. Consistently, molecular modeling analysis supported the docking of andrographolide within the catalytic pockets of both viral Mpros. Considering that andrographolide is used in clinical practice with acceptable safety and its diverse pharmacological activities that could be beneficial for attenuating COVID-19 symptoms, extensive investigation of andrographolide on the suppression of 2019-nCoV as well as its application in COVID-19 therapy is suggested.

TAF2, within the TFIID complex, regulates the expression of a subset of protein-coding genes.

TFIID, one of the general transcription factor (GTF), regulates transcriptional initiation of protein-coding genes through direct binding to promoter elements and subsequent recruitment of other GTFs and RNA polymerase II. Although generally required for most protein-coding genes, accumulated studies have also demonstrated promoter-specific functions for several TFIID subunits in gene activation. Here, we report that TBP-associated factor 2 (TAF2) specifically regulates TFIID binding to a small subset of protein-coding genes and is essential for cell growth of multiple cancer lines. Co-immunoprecipitation assays revealed that TAF2 may be sub-stoichiometrically associated with the TFIID complex, thus indicating a minor fraction of TAF2-containing TFIID in cells. Consistently, integrated genome-wide profiles show that TAF2 binds to and regulates only a small subset of protein-coding genes. Furthermore, through the use of an inducible TAF2 degradation system, our results reveal a reduction of TBP/TFIID binding to several ribosomal genes upon selective ablation of TAF2. In addition, depletion of TAF2, as well as the TAF2-regulated ribosomal protein genes RPL30 and RPL39, decreases ribosome assembly and global protein translation. Collectively, this study suggests that TAF2 within the TFIID complex is of functional importance for TBP/TFIID binding to and expression of a small subset of protein-coding genes, thus establishing a previously unappreciated promoter-selective function for TAF2.

Structural convergence endows nuclear transport receptor Kap114p with a transcriptional repressor function toward TATA-binding protein.

The transcription factor TATA-box binding protein (TBP) modulates gene expression in nuclei. This process requires the involvement of nuclear transport receptors, collectively termed karyopherin-ß (Kap-ß) in yeast, and various regulatory factors. In previous studies we showed that Kap114p, a Kap-ß that mediates nuclear import of yeast TBP (yTBP), modulates yTBP-dependent transcription. However, how Kap114p associates with yTBP to exert its multifaceted functions has remained elusive. Here, we employ single-particle cryo-electron microscopy to determine the structure of Kap114p in complex with the core domain of yTBP (yTBPC). Remarkably, Kap114p wraps around the yTBPC N-terminal lobe, revealing a structure resembling transcriptional regulators in complex with TBP, suggesting convergent evolution of the two protein groups for a common function. We further demonstrate that Kap114p sequesters yTBP away from promoters, preventing a collapse of yTBP dynamics required for yeast responses to environmental stress. Hence, we demonstrate that nuclear transport receptors represent critical elements of the transcriptional regulatory network.

EZH2 noncanonically binds cMyc and p300 through a cryptic transactivation domain to mediate gene activation and promote oncogenesis.

Canonically, EZH2 serves as the catalytic subunit of PRC2, which mediates H3K27me3 deposition and transcriptional repression. Here, we report that in acute leukaemias, EZH2 has additional noncanonical functions by binding cMyc at non-PRC2 targets and uses a hidden transactivation domain (TAD) for (co)activator recruitment and gene activation. Both canonical (EZH2-PRC2) and noncanonical (EZH2-TAD-cMyc-coactivators) activities of EZH2 promote oncogenesis, which explains the slow and ineffective antitumour effect of inhibitors of the catalytic function of EZH2. To suppress the multifaceted activities of EZH2, we used proteolysis-targeting chimera (PROTAC) to develop a degrader, MS177, which achieved effective, on-target depletion of EZH2 and interacting partners (that is, both canonical EZH2-PRC2 and noncanonical EZH2-cMyc complexes). Compared with inhibitors of the enzymatic function of EZH2, MS177 is fast-acting and more potent in suppressing cancer growth. This study reveals noncanonical oncogenic roles of EZH2, reports a PROTAC for targeting the multifaceted tumorigenic functions of EZH2 and presents an attractive strategy for treating EZH2-dependent cancers.

BAHCC1 binds H3K27me3 via a conserved BAH module to mediate gene silencing and oncogenesis.

Trimethylated histone H3 lysine 27 (H3K27me3) regulates gene repression, cell-fate determination and differentiation. We report that a conserved bromo-adjacent homology (BAH) module of BAHCC1 (BAHCC1BAH) 'recognizes' H3K27me3 specifically and enforces silencing of H3K27me3-demarcated genes in mammalian cells. Biochemical, structural and integrated chromatin immunoprecipitation-sequencing-based analyses demonstrate that direct readout of H3K27me3 by BAHCC1 is achieved through a hydrophobic trimethyl-L-lysine-binding 'cage' formed by BAHCC1BAH, mediating colocalization of BAHCC1 and H3K27me3-marked genes. BAHCC1 is highly expressed in human acute leukemia and interacts with transcriptional corepressors. In leukemia, depletion of BAHCC1, or disruption of the BAHCC1BAH-H3K27me3 interaction, causes derepression of H3K27me3-targeted genes that are involved in tumor suppression and cell differentiation, leading to suppression of oncogenesis. In mice, introduction of a germline mutation at Bahcc1 to disrupt its H3K27me3 engagement causes partial postnatal lethality, supporting a role in development. This study identifies an H3K27me3-directed transduction pathway in mammals that relies on a conserved BAH 'reader'.

Heterogeneous Nuclear Ribonucleoproteins A1 and A2 Function in Telomerase-Dependent Maintenance of Telomeres.

The A/B subfamily of heterogeneous nuclear ribonucleoproteins (hnRNPs A/B), which includes hnRNP A1, A2/B1, and A3, plays an important role in cell proliferation. The simultaneous suppression of hnRNP A1/A2, but not the suppression of hnRNP A1 or A2 alone, has been shown to inhibit cell proliferation and induce apoptosis in cancer cells, but not in mortal normal cells. However, the molecular basis for such a differential inhibition of cell proliferation remains unknown. Here, we show that the simultaneous suppression of hnRNP A1 and hnRNP A2 resulted in dysfunctional telomeres and induced DNA damage responses in cancer cells. The inhibition of apoptosis did not alleviate the inhibition of cell proliferation nor the formation of dysfunctional telomeres in cancer cells depleted of hnRNP A1/A2. Moreover, while proliferation of mortal normal fibroblasts was not sensitive to the depletion of hnRNP A1/A2, the ectopic expression of hTERT in normal fibroblasts rendered these cells sensitive to proliferation inhibition, which was associated with the production of dysfunctional telomeres. Our study demonstrates that hnRNP A1 and A2 function to maintain telomeres in telomerase-expressing cells only, suggesting that the maintenance of functional telomeres in telomerase-expressing cancer cells employs factors that differ from those used in the telomerase-negative normal cells.

Heterogeneous nuclear ribonucleoproteins A1 and A2 modulate expression of Tid1 isoforms and EGFR signaling in non-small cell lung cancer.

The Tid1 protein is a DnaJ co-chaperone that has two alternative splicing isoforms: Tid1 long form (Tid1-L) and Tid1 short form (Tid1-S). Recent studies have shown that Tid1-L functions as a tumor suppressor by decreasing EGFR signaling in various cancers, including head and neck cancer and non-small cell lung cancer (NSCLC). However, the molecular mechanism responsible for regulating the alternative splicing of Tid1 is not yet known. Two splicing factors, heterogeneous nuclear ribonucleoproteins (hnRNP) A1 and A2, participate in alternative splicing and are known to be overexpressed in lung cancers. In this work, we examined if hnRNP A1 and A2 could regulate the alternative splicing of Tid1 to modulate tumorigenesis in NSCLC. We report that RNAi-mediated depletion of both hnRNP A1/A2 (but not single depletion of either) increased Tid1-L expression, inhibited cell proliferation and attenuated EGFR signaling. Analyses of the expression levels of hnRNP A1, hnRNP A2, EGFR and Tid1-L in NSCLC tissues revealed that hnRNP A1 and A2 are positively correlated with EGFR, but negatively correlated with Tid1-L. NSCLC patients with high-level expression of hnRNP A1, hnRNP A2 and EGFR combined with low-level expression of Tid1-L were associated with poor overall survival. Taken together, our results suggest that hnRNP A1 or A2 are both capable of facilitating the alternative splicing of exon 11 in the Tid1 pre-mRNA, thereby suppressing the expression of Tid1-L and allowing EGFR-related signaling to facilitate NSCLC tumorigenesis.