Hotspot mutations in the structured ENL YEATS domain link aberrant transcriptional condensates and cancer

Liquid-liquid phase separation in normal hematopoiesis and hematological diseases

Liquid-liquid phase separation (LLPS) is an emerging research field in cellular biology. LLPS-driven biomolecular condensates act as reaction chambers and regulatory hubs for critical processes, including chromatin architecture, gene expression, and metabolism. The dysregulation of these processes frequently impedes the proper execution of physiological functions. Current research indicates that abnormal phase separation plays a significant role in the pathogenesis of diseases and aging. This review briefly overviews the fundamental concepts and research methods related to phase separation. We also summarize studies concerning its physiological functions, particularly emphasizing its role in hematopoiesis. We further discuss how abnormal phase separation can lead to hematological disorders, specifically summarizing its involvement in the pathogenesis of leukemia. Despite recent advancements, elucidating LLPS mechanisms in hematopoiesis remains challenging due to the intricate interplay between biomolecular condensates and cellular function. Future research efforts aiming to reveal the role of LLPS in hematological diseases hold promise for novel therapeutic interventions and a deeper understanding of hematopoietic processes.

Oncogenic fusions converge on shared mechanisms in initiating astroblastoma

Chromosomal rearrangements and gene fusions are the initial events in the development of many cancers. Astroblastoma (ABM), a brain cancer of unknown cellular origin and challenging to treat, is associated with diverse in-frame gene fusions, including MN1-BEND2 and MN1-CXXC5 (refs. 1,2). However, it remains unclear whether these gene fusions contribute to tumorigenesis. Here we show in mice that these two ABM-associated fusions converge on similar molecular activities and initiate malignancy specifically in ventral telencephalon neural progenitors. BEND2 and CXXC5 recognize similar DNA motifs, which indicates a convergence on downstream gene regulation. Expression of MN1-BEND2 in ventral telencephalon neural progenitors results in aberrant cell proliferation, impaired differentiation, a perivascular occupancy pattern of cells reminiscent of ABM and acquisition of an ABM-associated transcriptional signature. By contrast, MN1-BEND2 expression in dorsal telencephalon neural progenitors leads to extensive cell death. This cell-type-specific malignancy depends on OLIG2 expression. Mechanistically, both ABM-associated fusion proteins (MN1-BEND2 and MN1-CXXC5) induce overlapping transcriptional responses, including the activation of a therapeutically targetable PDGFRα pathway. Collectively, our data suggest that distinct ABM-associated fusions upregulate shared transcriptional networks to disrupt the normal development of ventral telencephalon neural progenitors, which leads to oncogenic transformation. These findings uncover new avenues for targeted ABM treatment.

RNA polymerase II partitioning is a shared feature of diverse oncofusion condensates

Condensates regulate transcription by selectively compartmentalizing biomolecules, yet the rules of specificity and their relationship to function remain enigmatic. To identify rules linked to function, we leverage the genetic selection bias of condensate-promoting oncofusions. Focusing on the three most frequent oncofusions driving translocation renal cell carcinoma, we find that they promote the formation of condensates that activate transcription by gain-of-function RNA polymerase II partitioning through a shared signature of elevated π and π-interacting residues and depletion of aliphatic residues. This signature is shared among a broad set of DNA-binding oncofusions associated with diverse cancers. We find that this signature is necessary and sufficient for RNA polymerase II partitioning, gene activation, and cancer cell phenotypes. Our results reveal that dysregulated condensate specificity is a shared molecular mechanism of diverse oncofusions, highlighting the functional role of condensate composition and the power of disease genetics in investigating relationships between condensate specificity and function.

TFE3 fusion oncoprotein condensates drive transcriptional reprogramming and cancer progression in translocation renal cell carcinoma

Translocation renal cell carcinoma (tRCC) presents a significant clinical challenge due to its aggressiveness and limited treatment options. It is primarily driven by fusion oncoproteins (FOs), yet their role in oncogenesis is not fully understood. Here, we investigate TFE3 fusions in tRCC, focusing on NONO::TFE3 and SFPQ::TFE3. We demonstrate that TFE3 FOs form liquid-like condensates with increased transcriptional activity, localizing to TFE3 target genes and promoting cell proliferation and migration. The coiled-coil domains (CCDs) of NONO and SFPQ are essential for condensate formation, prolonging TFE3 FOs' chromatin binding time and enhancing transcription. Compared with wild-type TFE3, TFE3 FOs bind to new chromatin regions, alter chromatin accessibility, and form new enhancers and super-enhancers at pro-growth gene loci. Disruption of condensate formation via CCD modification abolishes these genome-wide changes. Altogether, our integrated analyses underscore the critical functions of TFE3 FO condensates in driving tumor cell growth, providing key insights for future therapeutic strategies.

Deregulated enhancer-promoter communication in cancer through altered nuclear architecture

Enhancers are critical regulators of gene expression. Structural variations in cancer genomes can lead to enhancer hijacking, where oncogenes are activated by mistargeted enhancer activity. Novel enhancer-promoter interactions may also arise through chromosomal rearrangements that create extrachromosomal DNA elements. Additionally, fusion proteins and other mutation-induced alterations in protein properties can lead to the aberrant assembly of proteins into large complexes on the size scale of 0.1-1 μm termed onco-condensates. Transcription factors and co-activators accumulate with cis-regulatory elements in these structures, driving oncogenic programs. Here, we review current evidence of how altered genome architecture and macromolecular assembly result in deregulated enhancer-promoter communication. We discuss emerging strategies to exploit these mechanisms for clinical applications.

Functional specificity in biomolecular condensates revealed by genetic complementation

Biomolecular condensates are thought to create subcellular microenvironments that regulate specific biochemical activities. Extensive in vitro work has helped link condensate formation to a wide range of cellular processes, including gene expression, nuclear transport, signalling and stress responses. However, testing the relationship between condensate formation and function in cells is more challenging. In particular, the extent to which the cellular functions of condensates depend on the nature of the molecular interactions through which the condensates form is a major outstanding question. Here, we review results from recent genetic complementation experiments in cells, and highlight how genetic complementation provides important insights into cellular functions and functional specificity of biomolecular condensates. Combined with observations from human genetic disease, these experiments suggest that diverse condensate-promoting regions within cellular proteins confer different condensate compositions, biophysical properties and functions.

Expression of ENL YEATS domain tumor mutations in nephrogenic or stromal lineage impairs kidney development

Recurrent gain-of-function mutations in the histone reader protein ENL have been identified in Wilms tumor, the most prevalent pediatric kidney cancer. However, their pathological significance in kidney development and tumorigenesis in vivo remains elusive. Here, we generate mouse models mimicking ENL tumor (ENLT) mutations and show that heterozygous mutant expression in Six2+ nephrogenic or Foxd1+ stromal lineages leads to severe, lineage-specific kidney defects, both resulting in neonatal lethality. Six2-ENLT mutant kidneys display compromised cap mesenchyme, scant nephron tubules, and cystic glomeruli, indicative of premature progenitor commitment and blocked differentiation. Bulk and spatial transcriptomic analyses reveal aberrant activation of Hox and Wnt signaling genes in mutant nephrogenic cells. In contrast, Foxd1-ENLT mutant kidneys exhibit expansion in renal capsule and cap mesenchyme, with dysregulated stromal gene expression affecting stroma-epithelium crosstalk. Our findings uncover distinct pathways through which ENL mutations disrupt nephrogenesis, providing a foundation for further investigations into their role in tumorigenesis.

Transcription regulation by biomolecular condensates

Biomolecular condensates regulate transcription by dynamically compartmentalizing the transcription machinery. Classic models of transcription regulation focus on the recruitment and regulation of RNA polymerase II by the formation of complexes at the 1-10 nm length scale, which are driven by structured and stoichiometric interactions. These complexes are further organized into condensates at the 100-1,000 nm length scale, which are driven by dynamic multivalent interactions often involving domain-ligand pairs or intrinsically disordered regions. Regulation through condensate-mediated organization does not supersede the processes occurring at the 1-10 nm scale, but it provides regulatory mechanisms for promoting or preventing these processes in the crowded nuclear environment. Regulation of transcription by transcriptional condensates is involved in cell state transitions during animal and plant development, cell signalling and cellular responses to the environment. These condensate-mediated processes are dysregulated in developmental disorders, cancer and neurodegeneration. In this Review, we discuss the principles underlying the regulation of transcriptional condensates, their roles in physiology and their dysregulation in human diseases.

Converging mechanism of UM171 and KBTBD4 neomorphic cancer mutations

Cancer mutations can create neomorphic protein-protein interactions to drive aberrant function1,2. As a substrate receptor of the CULLIN3-RING E3 ubiquitin ligase complex, KBTBD4 is recurrently mutated in medulloblastoma3, the most common embryonal brain tumour in children4. These mutations impart gain-of-function to KBTBD4 to induce aberrant degradation of the transcriptional corepressor CoREST5. However, their mechanism remains unresolved. Here we establish that KBTBD4 mutations promote CoREST degradation through engaging HDAC1/2 as the direct target of the mutant substrate receptor. Using deep mutational scanning, we chart the mutational landscape of the KBTBD4 cancer hotspot, revealing distinct preferences by which insertions and substitutions can promote gain-of-function and the critical residues involved in the hotspot interaction. Cryo-electron microscopy analysis of two distinct KBTBD4 cancer mutants bound to LSD1-HDAC1-CoREST reveals that a KBTBD4 homodimer asymmetrically engages HDAC1 with two KELCH-repeat β-propeller domains. The interface between HDAC1 and one of the KBTBD4 β-propellers is stabilized by the medulloblastoma mutations, which insert a bulky side chain into the HDAC1 active site pocket. Our structural and mutational analyses inform how this hotspot E3-neosubstrate interface can be chemically modulated. First, we unveil a converging shape-complementarity-based mechanism between gain-of-function E3 mutations and a molecular glue degrader, UM171. Second, we demonstrate that HDAC1/2 inhibitors can block the mutant KBTBD4-HDAC1 interface and proliferation of KBTBD4-mutant medulloblastoma cells. Altogether, our work reveals the structural and mechanistic basis of cancer mutation-driven neomorphic protein-protein interactions.

The phenylalanine-and-glycine repeats of NUP98 oncofusions form condensates that selectively partition transcriptional coactivators

Recurrent cancer-causing fusions of NUP98 produce higher-order assemblies known as condensates. How NUP98 oncofusion-driven condensates activate oncogenes remains poorly understood. Here, we investigate NUP98-PHF23, a leukemogenic chimera of the disordered phenylalanine-and-glycine (FG)-repeat-rich region of NUP98 and the H3K4me3/2-binding plant homeodomain (PHD) finger domain of PHF23. Our integrated analyses using mutagenesis, proteomics, genomics, and condensate reconstitution demonstrate that the PHD domain targets condensate to the H3K4me3/2-demarcated developmental genes, while FG repeats determine the condensate composition and gene activation. FG repeats are necessary to form condensates that partition a specific set of transcriptional regulators, notably the KMT2/MLL H3K4 methyltransferases, histone acetyltransferases, and BRD4. FG repeats are sufficient to partition transcriptional regulators and activate a reporter when tethered to a genomic locus. NUP98-PHF23 assembles the chromatin-bound condensates that partition multiple positive regulators, initiating a feedforward loop of reading-and-writing the active histone modifications. This network of interactions enforces an open chromatin landscape at proto-oncogenes, thereby driving cancerous transcriptional programs.

Nuclear ANLN regulates transcription initiation related Pol II clustering and target gene expression

Anillin (ANLN), a mitotic protein that regulates contractile ring assembly, has been reported as an oncoprotein. However, the function of ANLN in cancer cells, especially in the nucleus, has not been fully understood. Here, we report a role of nuclear ANLN in gene transcriptional regulation. We find that nuclear ANLN directly interacts with the RNA polymerase II (Pol II) large subunit to form transcriptional condensates. ANLN enhances initiated Pol II clustering and promotes Pol II CTD phase separation. Short-term depletion of ANLN alters the chromatin binding and enhancer-mediated transcriptional activity of Pol II. The target genes of ANLN-Pol II axis are involved in oxidoreductase activity, Wnt signaling and cell differentiation. THZ1, a super-enhancer inhibitor, specifically inhibits ANLN-Pol II clustering, target gene expression and esophageal squamous cell carcinoma (ESCC) cell proliferation. Our results reveal the function of nuclear ANLN in transcriptional regulation, providing a theoretical basis for ESCC treatment.

Targeting lysine acetylation readers and writers

Lysine acetylation is a major post-translational modification in histones and other proteins that is catalysed by the 'writer' lysine acetyltransferases (KATs) and mediates interactions with bromodomains (BrDs) and other 'reader' proteins. KATs and BrDs play key roles in regulating gene expression, cell growth, chromatin structure, and epigenetics and are often dysregulated in disease states, including cancer. There have been accelerating efforts to identify potent and selective small molecules that can target individual KATs and BrDs with the goal of developing new therapeutics, and some of these agents are in clinical trials. Here, we summarize the different families of KATs and BrDs, discuss their functions and structures, and highlight key advances in the design and development of chemical agents that show promise in blocking the action of these chromatin proteins for disease treatment.

Roles of intrinsically disordered protein regions in transcriptional regulation and genome organization

Eukaryotic transcription is a complex process regulated by transcription factors (TFs), coactivators, and RNA polymerase machineries, many of which contain sizable intrinsically disordered regions (IDRs). Many TFs activate transcription through multivalent IDR-IDR interactions. Optimal levels of such multivalent interactions associated with appropriate IDR concentrations, interaction strengths, or interaction valencies are required for effective transcriptional activation. The interaction selectivity of IDRs is crucial for the precise regulation of transcription, and this selectivity is dependent on the IDR sequences. Furthermore, IDRs modulate gene expression by bringing chromatin sites together to form transcriptionally active chromatin hubs. Mutations in IDRs may cause dysregulation of their multivalent interactions, contributing to diseases, including cancers and neurodegenerative disorders. Understanding the effects of IDR-related mutations on transcription control and genome organization opens new opportunities for developing targeted therapeutic strategies. In this review, we discuss recent reports documenting important functions of IDRs in transcriptional regulation and their implications for human health and disease.

Biomolecular condensates: A new lens on cancer biology

Cells are compartmentalized into different organelles to ensure precise spatial temporal control and efficient operation of cellular processes. Membraneless organelles, also known as biomolecular condensates, are emerging as previously underappreciated ways of organizing cellular functions. Condensates allow local concentration of protein, RNA, or DNA molecules with shared functions, thus facilitating spatiotemporal control of biochemical reactions spanning a range of cellular processes. Studies discussed herein have shown that aberrant formation of condensates is associated with various diseases such as cancers. Here, we summarize how condensates mechanistically contribute to malignancy-related cellular processes, including genomic instability, epigenetic rewiring, oncogenic transcriptional activation, and signaling. An improved understanding of condensate formation and dissolution will enable development of new cancer therapies. Finally, we address the remaining challenges in the field and suggest future efforts to better integrate condensates into cancer research.

Biomolecular condensates in immune cell fate

Fate decisions during immune cell development require temporally precise changes in gene expression. Evidence suggests that the dynamic modulation of these changes is associated with the formation of diverse, membrane-less nucleoprotein assemblies that are termed biomolecular condensates. These condensates are thought to orchestrate fate-determining transcriptional and post-transcriptional processes by locally and transiently concentrating DNA or RNA molecules alongside their regulatory proteins. Findings have established a link between condensate formation and the gene regulatory networks that ensure the proper development of immune cells. Conversely, condensate dysregulation has been linked to impaired immune cell fates, including ageing and malignant transformation. This Review explores the putative mechanistic links between condensate assembly and the gene regulatory frameworks that govern normal and pathological development in the immune system.

ENL mutation and AML: a new model that reveals oncogenic condensate's function in leukemogenesis

Precise regulation of gene expression is essential for proper development and the maintenance of homeostasis in organisms. Studies have shown that some transcriptional regulatory proteins influence gene expression through the formation of dynamic, locally concentrated assemblies known as condensates, while dysregulation of transcriptional condensates was associated with several cancers, such as Ewing sarcoma and AML [Wang Y et al. (2023) Nat Chem Biol 19, 1223-1234; Chandra B et al. (2022) Cancer Discov 12, 1152-1169]. Mutations in the histone acetylation "reader" eleven-nineteen-leukemia (ENL) have been shown to form discrete condensates at endogenous genomic targets, but it remains unclear how ENL mutations drive tumorigenesis and whether it is correlated with their condensate formation property. Liu et al. now show, using a conditional knock-in mouse model, that ENL YEATS domain mutation is a bona fide oncogenic driver for AML. This mutant ENL forms condensates in hematopoietic stem/progenitor cells at the genomic loci of key leukemogenic genes, including Meis1 and Hoxa cluster genes, and disrupting condensate formation via mutagenesis impairs its chromatin and oncogenic function. Furthermore, they show that small-molecule inhibition of the acetyl-binding activity displaces ENL mutant condensates from oncogenic target loci, and this inhibitor significantly impairs the onset and progression of AML driven by mutant ENL in vivo.

Phase-separated chromatin compartments: Orchestrating gene expression through condensation

Eukaryotic genomes are organized into distinct chromatin compartments, some of which exhibit properties of biomolecular condensates. These condensates primarily form due to chromatin-associated proteins/complexes (CAPs). CAPs play a crucial role in gene expression, functioning as either transcriptional repressors or activators. Phase separation, a well-established biophysical phenomenon, is a key driver of chromatin condensate formation by CAPs. Notably, multivalent CAPs with the ability to engage in diverse interactions promote chromatin compaction, leading to the formation of transcriptionally repressed compartments. Conversely, interactions between intrinsically disordered region (IDR)-containing transcriptional regulators, mediated by their multivalent IDRs, lead to the formation of protein-rich, transcriptionally active droplets on decondensed genomic regions. Interestingly, both repressive heterochromatin and activating euchromatin condensates exhibit spontaneous phase separation and selectively enrich components with concordant transcriptional functions. This review delves into the mechanisms by which transcriptionally repressive CAPs orchestrate the formation of repressed chromatin domains. We further explore how a diverse array of transcription-related CAPs or core histone variants, via phase separation, influence gene expression by inducing erroneous transcription events, regulating expression levels, and facilitating the interconversion of transcriptionally repressed and active regions.

JMJD1C forms condensates to facilitate a RUNX1-dependent gene expression program shared by multiple types of AML cells

JMJD1C, a member of the lysine demethylase 3 (KDM3) family, is universally required for the survival of several types of acute myeloid leukemia (AML) cells with different genetic mutations, representing a therapeutic opportunity with broad application. Yet how JMJD1C regulates the leukemic programs of various AML cells is largely unexplored. Here we show that JMJD1C interacts with the master hematopoietic transcription factor RUNX1, which thereby recruits JMJD1C to the genome to facilitate a RUNX1-driven transcriptional program that supports leukemic cell survival. The underlying mechanism hinges on the long N-terminal disordered region of JMJD1C, which harbors two inseparable abilities: condensate formation and direct interaction with RUNX1. This dual capability of JMJD1C may influence enhancer-promoter contacts crucial for the expression of key leukemic genes regulated by RUNX1. Our findings demonstrate a previously unappreciated role for the non-catalytic function of JMJD1C in transcriptional regulation, underlying a mechanism shared by different types of leukemias.

A fine kinetic balance of interactions directs transcription factor hubs to genes

Eukaryotic gene regulation relies on the binding of sequence-specific transcription factors (TFs). TFs bind chromatin transiently yet occupy their target sites by forming high-local concentration microenvironments (hubs and condensates) that increase the frequency of binding. Despite their ubiquity, such microenvironments are difficult to study in endogenous contexts due to technical limitations. Here, we use live embryo light-sheet imaging, single-molecule tracking, and genomics to overcome these limitations and investigate how hubs are localized to target genes to drive TF occupancy and transcription. By examining mutants of a hub-forming TF, Zelda, in Drosophila embryos, we find that hub formation propensity, spatial distributions, and temporal stabilities are differentially regulated by DNA binding and disordered protein domains. We show that hub localization to genomic targets is driven by a finely-tuned kinetic balance of interactions between proteins and chromatin, and hubs can be redirected to new genomic sites when this balance is perturbed.

Engineering Material Properties of Transcription Factor Condensates to Control Gene Expression in Mammalian Cells and Mice

Phase separation of biomolecules into condensates is a key mechanism in the spatiotemporal organization of biochemical processes in cells. However, the impact of the material properties of biomolecular condensates on important processes, such as the control of gene expression, remains largely elusive. Here, the material properties of optogenetically induced transcription factor condensates are systematically tuned, and probed for their impact on the activation of target promoters. It is demonstrated that transcription factors in rather liquid condensates correlate with increased gene expression levels, whereas stiffer transcription factor condensates correlate with the opposite effect, reduced activation of gene expression. The broad nature of these findings is demonstrated in mammalian cells and mice, as well as by using different synthetic and natural transcription factors. These effects are observed for both transgenic and cell-endogenous promoters. The findings provide a novel materials-based layer in the control of gene expression, which opens novel opportunities in optogenetic engineering and synthetic biology.

Biomolecular condensates and disease pathogenesis

Biomolecular condensates or membraneless organelles (MLOs) formed by liquid-liquid phase separation (LLPS) divide intracellular spaces into discrete compartments for specific functions. Dysregulation of LLPS or aberrant phase transition that disturbs the formation or material states of MLOs is closely correlated with neurodegeneration, tumorigenesis, and many other pathological processes. Herein, we summarize the recent progress in development of methods to monitor phase separation and we discuss the biogenesis and function of MLOs formed through phase separation. We then present emerging proof-of-concept examples regarding the disruption of phase separation homeostasis in a diverse array of clinical conditions including neurodegenerative disorders, hearing loss, cancers, and immunological diseases. Finally, we describe the emerging discovery of chemical modulators of phase separation.

Condensate-Promoting ENL Mutation Drives Tumorigenesis In Vivo Through Dynamic Regulation of Histone Modifications and Gene Expression

Gain-of-function mutations in the histone acetylation "reader" eleven-nineteen-leukemia (ENL), found in acute myeloid leukemia (AML) and Wilms tumor, are known to drive condensate formation and gene activation in cellular systems. However, their role in tumorigenesis remains unclear. Using a conditional knock-in mouse model, we show that mutant ENL perturbs normal hematopoiesis, induces aberrant expansion of myeloid progenitors, and triggers rapid onset of aggressive AML. Mutant ENL alters developmental and inflammatory gene programs in part by remodeling histone modifications. Mutant ENL forms condensates in hematopoietic stem/progenitor cells at key leukemogenic genes, and disrupting condensate formation via mutagenesis impairs its chromatin and oncogenic function. Moreover, treatment with an acetyl-binding inhibitor of the mutant ENL displaces these condensates from target loci, inhibits mutant ENL-induced chromatin changes, and delays AML initiation and progression in vivo. Our study elucidates the function of ENL mutations in chromatin regulation and tumorigenesis and demonstrates the potential of targeting pathogenic condensates in cancer treatment. Significance: A direct link between ENL mutations, condensate formation, and tumorigenesis is lacking. This study elucidates the function and mechanism of ENL mutations in leukemogenesis, establishing these mutations as bona fide oncogenic drivers. Our results also support the role of condensate dysregulation in cancer and reveal strategies to target pathogenic condensates.

Single-cell multiomics reveals ENL mutation perturbs kidney developmental trajectory by rewiring gene regulatory landscape

How disruptions to normal cell differentiation link to tumorigenesis remains incompletely understood. Wilms tumor, an embryonal tumor associated with disrupted organogenesis, often harbors mutations in epigenetic regulators, but their role in kidney development remains unexplored. Here, we show at single-cell resolution that a Wilms tumor-associated mutation in the histone acetylation reader ENL disrupts kidney differentiation in mice by rewiring the gene regulatory landscape. Mutant ENL promotes nephron progenitor commitment while restricting their differentiation by dysregulating transcription factors such as Hox clusters. It also induces abnormal progenitors that lose kidney-associated chromatin identity. Furthermore, mutant ENL alters the transcriptome and chromatin accessibility of stromal progenitors, resulting in hyperactivation of Wnt signaling. The impacts of mutant ENL on both nephron and stroma lineages lead to profound kidney developmental defects and postnatal mortality in mice. Notably, a small molecule inhibiting mutant ENL's histone acetylation binding activity largely reverses these defects. This study provides insights into how mutations in epigenetic regulators disrupt kidney development and suggests a potential therapeutic approach.

An autoinhibitory switch of the LSD1 disordered region controls enhancer silencing

Transcriptional coregulators and transcription factors (TFs) contain intrinsically disordered regions (IDRs) that are critical for their association and function in gene regulation. More recently, IDRs have been shown to promote multivalent protein-protein interactions between coregulators and TFs to drive their association into condensates. By contrast, here we demonstrate how the IDR of the corepressor LSD1 excludes TF association, acting as a dynamic conformational switch that tunes repression of active cis-regulatory elements. Hydrogen-deuterium exchange shows that the LSD1 IDR interconverts between transient open and closed conformational states, the latter of which inhibits partitioning of the protein's structured domains with TF condensates. This autoinhibitory switch controls leukemic differentiation by modulating repression of active cis-regulatory elements bound by LSD1 and master hematopoietic TFs. Together, these studies unveil alternative mechanisms by which disordered regions and their dynamic crosstalk with structured regions can shape coregulator-TF interactions to control cis-regulatory landscapes and cell fate.

Chromatin and aberrant enhancer activity in KMT2A rearranged acute lymphoblastic leukemia

To make a multicellular organism, genes need to be transcribed at the right developmental stages and in the right tissues. DNA sequences termed 'enhancers' are crucial to achieve this. Despite concerted efforts, the exact mechanisms of enhancer activity remain elusive. Mixed lineage leukemia (MLL or KMT2A) rearrangements (MLLr), commonly observed in cases of acute lymphoblastic leukemia (ALL) and acute myeloid leukemia, produce novel in-frame fusion proteins. Recent work has shown that the MLL-AF4 fusion protein drives aberrant enhancer activity at key oncogenes in ALL, dependent on the continued presence of MLL-AF4 complex components. As well as providing some general insights into enhancer function, these observations may also provide an explanation for transcriptional heterogeneity observed in MLLr patients.

Dysregulation of transcriptional condensates in human disease: mechanisms, biological functions, and open questions

Precise gene expression, crucial for normal development and health, depends on the co-ordinated assembly and function of various factors within the crowded nucleus. Recent evidence suggests that this process is in part regulated by mesoscale compartmentalization and concentration of transcriptional components within condensates, offering a new perspective on gene regulation. Dysregulation of transcriptional condensates is increasingly associated with diseases, indicating a potential role in pathogenesis. In this mini-review, we provide a concise overview of the current understanding of the formation and function of transcriptional condensates, with a specific focus on recent advances in their dysregulation and implications in diseases, notably cancer. We also address limitations in the field and highlight open questions for future research.

Dynamic microenvironments shape nuclear organization and gene expression

Live imaging has revealed that the regulation of gene expression is largely driven by transient interactions. For example, many regulatory proteins bind chromatin for just seconds, and loop-like genomic contacts are rare and last only minutes. These discoveries have been difficult to reconcile with our canonical models that are predicated on stable and hierarchical interactions. Proteomic microenvironments that concentrate nuclear factors may explain how brief interactions can still mediate gene regulation by creating conditions where reactions occur more frequently. Here, we summarize new imaging technologies and recent discoveries implicating microenvironments as a potential driver of nuclear function. Finally, we propose that key properties of proteomic microenvironments, such as their size, enrichment, and lifetimes, are directly linked to regulatory function.

KBTBD4 Cancer Hotspot Mutations Drive Neomorphic Degradation of HDAC1/2 Corepressor Complexes

Cancer mutations can create neomorphic protein-protein interactions to drive aberrant function 1 . As a substrate receptor of the CULLIN3-RBX1 E3 ubiquitin ligase complex, KBTBD4 is recurrently mutated in medulloblastoma (MB) 2 , the most common embryonal brain tumor in children, and pineoblastoma 3 . These mutations impart gain-of-function to KBTBD4 to induce aberrant degradation of the transcriptional corepressor CoREST 4 . However, their mechanism of action remains unresolved. Here, we elucidate the mechanistic basis by which KBTBD4 mutations promote CoREST degradation through engaging HDAC1/2, the direct neomorphic target of the substrate receptor. Using deep mutational scanning, we systematically map the mutational landscape of the KBTBD4 cancer hotspot, revealing distinct preferences by which insertions and substitutions can promote gain-of-function and the critical residues involved in the hotspot interaction. Cryo-electron microscopy (cryo-EM) analysis of two distinct KBTBD4 cancer mutants bound to LSD1-HDAC1-CoREST reveals that a KBTBD4 homodimer asymmetrically engages HDAC1 with two KELCH-repeat propeller domains. The interface between HDAC1 and one of the KBTBD4 propellers is stabilized by the MB mutations, which directly insert a bulky side chain into the active site pocket of HDAC1. Our structural and mutational analyses inform how this hotspot E3-neo-substrate interface can be chemically modulated. First, our results unveil a converging shape complementarity-based mechanism between gain-of-function E3 mutations and a molecular glue degrader, UM171. Second, we demonstrate that HDAC1/2 inhibitors can block the mutant KBTBD4-HDAC1 interface, the aberrant degradation of CoREST, and the growth of KBTBD4-mutant MB models. Altogether, our work reveals the structural and mechanistic basis of cancer mutation-driven neomorphic protein-protein interactions and pharmacological strategies to modulate their action for therapeutic applications.

Single-Cell multiomics reveals ENL mutation perturbs kidney developmental trajectory by rewiring gene regulatory landscape

Cell differentiation during organogenesis relies on precise epigenetic and transcriptional control. Disruptions to this regulation can result in developmental abnormalities and malignancies, yet the underlying mechanisms are not well understood. Wilms tumors, a type of embryonal tumor closely linked to disrupted organogenesis, harbor mutations in epigenetic regulators in 30-50% of cases. However, the role of these regulators in kidney development and pathogenesis remains unexplored. By integrating mouse modeling, histological characterizations, and single-cell transcriptomics and chromatin accessibility profiling, we show that a Wilms tumor-associated mutation in the chromatin reader protein ENL disrupts kidney development trajectory by rewiring the gene regulatory landscape. Specifically, the mutant ENL promotes the commitment of nephron progenitors while simultaneously restricting their differentiation by dysregulating key transcription factor regulons, particularly the HOX clusters. It also induces the emergence of abnormal progenitor cells that lose their chromatin identity associated with kidney specification. Furthermore, the mutant ENL might modulate stroma-nephron interactions via paracrine Wnt signaling. These multifaceted effects caused by the mutation result in severe developmental defects in the kidney and early postnatal mortality in mice. Notably, transient inhibition of the histone acetylation binding activity of mutant ENL with a small molecule displaces transcriptional condensates formed by mutant ENL from target genes, abolishes its gene activation function, and restores developmental defects in mice. This work provides new insights into how mutations in epigenetic regulators can alter the gene regulatory landscape to disrupt kidney developmental programs at single-cell resolution in vivo . It also offers a proof-of-concept for the use of epigenetics-targeted agents to rectify developmental defects.

Targeting the Epigenetic Reader ENL Inhibits Super-Enhancer-Driven Oncogenic Transcription and Synergizes with BET Inhibition to Suppress Tumor Progression

Epigenetic alterations at cis-regulatory elements (CRE) fine-tune transcriptional output. Epigenetic readers interact with CREs and can cooperate with other chromatin regulators to drive oncogene transcription. Here, we found that the YEATS domain-containing histone acetylation reader ENL (eleven-nineteen leukemia) acts as a key regulator of super-enhancers (SE), which are highly active distal CREs, across cancer types. ENL occupied the majority of SEs with substantially higher preference over typical enhancers, and the enrichment of ENL at SEs depended on its ability to bind acetylated histones. Rapid depletion of ENL by auxin-inducible degron tagging severely repressed the transcription of SE-controlled oncogenes, such as MYC, by inducing the decommissioning of their SEs, and restoring ENL protein expression largely reversed these effects. Additionally, ENL was indispensable for the rapid activation of SE-regulated immediate early genes in response to growth factor stimulation. Furthermore, ENL interacted with the histone chaperone FACT complex and was required for the deposition of FACT over CREs, which mediates nucleosome reorganization required for transcription initiation and elongation. Proper control of transcription by ENL and ENL-associated FACT was regulated by the histone reader BRD4. ENL was overexpressed in colorectal cancer and functionally contributed to colorectal cancer growth and metastasis. ENL degradation or inhibition synergized with BET inhibitors that target BRD4 in restraining colorectal cancer progression. These findings establish the essential role of epigenetic reader ENL in governing SE-driven oncogenic transcription and uncover the potential of ENL intervention to increase sensitivity to BET inhibition.

SIGNIFICANCE

ENL plays a key role in decoding epigenetic marks at highly active oncogenic super-enhancers and can be targeted in combination with BET inhibition as a promising synergistic strategy for optimizing cancer treatment.

Lead Optimization of Small Molecule ENL YEATS Inhibitors to Enable In Vivo Studies: Discovery of TDI-11055

Eleven-nineteen leukemia (ENL) is an epigenetic reader protein that drives oncogenic transcriptional programs in acute myeloid leukemia (AML). AML is one of the deadliest hematopoietic malignancies, with an overall 5-year survival rate of 27%. The epigenetic reader activity of ENL is mediated by its YEATS domain that binds to acetyl and crotonyl marks on histone tails and colocalizes with promoters of actively transcribed genes that are essential for leukemia. Prior to the discovery of TDI-11055, existing inhibitors of ENL YEATS showed in vitro potency, but had not shown efficacy in in vivo animal models. During the course of the medicinal chemistry campaign described here, we identified ENL YEATS inhibitor TDI-11055 that has an improved pharmacokinetic profile and is appropriate for in vivo evaluation of the ENL YEATS inhibition mechanism in AML.

Transcriptional condensates: a blessing or a curse for gene regulation?

Whether phase-separation is involved in the organization of the transcriptional machinery and if it aids or inhibits the transcriptional process is a matter of intense debate. In this Mini Review, we will cover the current knowledge regarding the role of transcriptional condensates on gene expression regulation. We will summarize the latest discoveries on the relationship between condensate formation, genome organization, and transcriptional activity, focusing on the strengths and weaknesses of the experimental approaches used to interrogate these aspects of transcription in living cells. Finally, we will discuss the challenges for future research.

The intrinsically disordered transcriptional activation domain of CIITA is functionally tuneable by single substitutions: An exception or a new paradigm?

During protein evolution, some amino acid substitutions modulate protein function ("tuneability"). In most proteins, the tuneable range is wide and can be sampled by a set of protein variants that each contains multiple amino acid substitutions. In other proteins, the full tuneable range can be accessed by a set of variants that each contains a single substitution. Indeed, in some globular proteins, the full tuneable range can be accessed by the set of site-saturating substitutions at an individual "rheostat" position. However, in proteins with intrinsically disordered regions (IDRs), most functional studies-which would also detect tuneability-used multiple substitutions or small deletions. In disordered transcriptional activation domains (ADs), studies with multiple substitutions led to the "acidic exposure" model, which does not anticipate the existence of rheostat positions. In the few studies that did assess effects of single substitutions on AD function, results were mixed: the ADs of two full-length transcription factors did not show tuneability, whereas a fragment of a third AD was tuneable by single substitutions. In this study, we tested tuneability in the AD of full-length human class II transactivator (CIITA). Sequence analyses and experiments showed that CIITA's AD is an IDR. Functional assays of singly-substituted AD variants showed that CIITA's function was highly tuneable, with outcomes not predicted by the acidic exposure model. Four tested positions showed rheostat behavior for transcriptional activation. Thus, tuneability of different IDRs can vary widely. Future studies are needed to illuminate the biophysical features that govern whether an IDR is tuneable by single substitutions.

Approaches to characterize chromatin subcompartment organization in the cell nucleus

The mechanism of self-organization of chromatin subcompartments on the 0.1-1 μm scale and their impact on genome-associated activities has long been a key aspect of research on nuclear organization. Understanding the underlying structure-function relationship, however, remains challenging due to the complex hierarchical structure of chromatin and the polymorphic organization of subcompartments that assemble around it. Towards this goal, approaches to measure local properties and compositional dynamics of chromatin in its endogenous cellular environment are instrumental. Here, we discuss recent advancements in studying these features and their functional implications in protein and RNA enrichment and genome accessibility.

Small-molecule tools for YEATS domain proteins

Chromatin reader domains are protein folds that bind to post-translational modifications of histones and other chromatin-associated proteins. Compared to other families of reader domains, the discovery that YEATS domains bind to acylated lysines is relatively recent. Four human proteins harbor a YEATS domain, and each is present in protein complexes that regulate chromatin and transcription (ENL, AF9, YEATS2, and YEATS4). Without chemical tools to enable temporally resolved perturbations, it is often unclear how reader domains contribute to protein function. Here, we will discuss recent progress in developing small-molecule tools for YEATS domains and highlight their usefulness for making biological discoveries.

Transcriptional condensates and phase separation: condensing information across scales and mechanisms

Transcription is the fundamental process of gene expression, which in eukaryotes occurs within the complex physicochemical environment of the nucleus. Decades of research have provided extreme detail in the molecular and functional mechanisms of transcription, but the spatial and genomic organization of transcription remains mysterious. Recent discoveries show that transcriptional components can undergo phase separation and create distinct compartments inside the nucleus, providing new models through which to view the transcription process in eukaryotes. In this review, we focus on transcriptional condensates and their phase separation-like behaviors. We suggest differentiation between physical descriptions of phase separation and the complex and dynamic biomolecular assemblies required for productive gene expression, and we discuss how transcriptional condensates are central to organizing the three-dimensional genome across spatial and temporal scales. Finally, we map approaches for therapeutic manipulation of transcriptional condensates and ask what technical advances are needed to understand transcriptional condensates more completely.

Liquid-Liquid Phase Separation Sheds New Light upon Cardiovascular Diseases

Liquid-liquid phase separation (LLPS) is a biophysical process that mediates the precise and complex spatiotemporal coordination of cellular processes. Proteins and nucleic acids are compartmentalized into micron-scale membrane-less droplets via LLPS. These droplets, termed biomolecular condensates, are highly dynamic, have concentrated components, and perform specific functions. Biomolecular condensates have been observed to organize diverse key biological processes, including gene transcription, signal transduction, DNA damage repair, chromatin organization, and autophagy. The dysregulation of these biological activities owing to aberrant LLPS is important in cardiovascular diseases. This review provides a detailed overview of the regulation and functions of biomolecular condensates, provides a comprehensive depiction of LLPS in several common cardiovascular diseases, and discusses the revolutionary therapeutic perspective of modulating LLPS in cardiovascular diseases and new treatment strategies relevant to LLPS.

Onco-condensates: formation, multi-component organization, and biological functions

Numerous cellular processes occur in the context of condensates, a type of large, membrane-less biomolecular assembly generated through phase separation. These condensates function as a hub of diversified cellular events by concentrating the required components. Cancer frequently coopts biomolecular condensation mechanisms to promote survival and/or proliferation. Onco-condensates, which refer to those that have causal roles or are critically involved in tumorigenicity, operate to abnormally elevate biological output of a proliferative process, or to suppress a tumor-suppressive pathway, thereby promoting oncogenesis. Here, we summarize advances regarding how multi-component onco-condensates are established and organized to promote oncogenesis, with those related to chromatin and transcription deregulation used as showcases. A better understanding should enable development of new means of targeting onco-condensates as potential therapeutics.

Liquid‒liquid phase separation: roles and implications in future cancer treatment

Liquid‒liquid phase separation (LLPS) is a phenomenon driven by weak interactions between biomolecules, such as proteins and nucleic acids, that leads to the formation of distinct liquid-like condensates. Through LLPS, membraneless condensates are formed, selectively concentrating specific proteins while excluding other molecules to maintain normal cellular functions. Emerging evidence shows that cancer-related mutations cause aberrant condensate assembly, resulting in disrupted signal transduction, impaired DNA repair, and abnormal chromatin organization and eventually contributing to tumorigenesis. The objective of this review is to summarize recent advancements in understanding the potential implications of LLPS in the contexts of cancer progression and therapeutic interventions. By interfering with LLPS, it may be possible to restore normal cellular processes and inhibit tumor progression. The underlying mechanisms and potential drug targets associated with LLPS in cancer are discussed, shedding light on promising opportunities for novel therapeutic interventions.

The YEATS domain epigenetic reader proteins ENL and AF9 and their therapeutic value in leukemia

Recent studies have uncovered similarities and differences between 2 highly homologous epigenetic reading proteins, namely, ENL (MLLT1) and AF9 (MLLT3) with therapeutic implications. The importance of these proteins has traditionally been exemplified by their involvement in chromosomal translocations with the mixed-lineage leukemia gene (MLL; aka KMT2a). MLL rearrangements occur in a subset of acute leukemias and generate potent oncogenic MLL-fusion proteins that impact epigenetic and transcriptional regulation. Leukemic patients with MLL rearrangements display intermediate-to-poor prognoses, necessitating further mechanistic research. Several protein complexes involved in regulating RNA polymerase II transcription and the epigenetic landscape are hijacked in MLL-r leukemia, which include ENL and AF9. Recent biochemical studies have defined a highly homologous YEATS domain in ENL and AF9 that binds acylated histones, which aids in the localization and retention of these proteins to transcriptional targets. In addition, detailed characterization of the homologous ANC-1 homology domain (AHD) on ENL and AF9 revealed differential association with transcriptional activating and repressing complexes. Importantly, CRISPR knockout screens have demonstrated a unique role for wild-type ENL in leukemic stem cell function, whereas AF9 appears important for normal hematopoietic stem cells. In this perspective, we examine the ENL and AF9 proteins with attention to recent work characterizing the epigenetic reading YEATS domains and AHD on both wild-type proteins and when fused to MLL. We summarized the drug development efforts and their therapeutic potential and assess ongoing research that has refined our understanding of how these proteins function, which continues to reveal new therapeutic avenues.

Abnormal phase separation of biomacromolecules in human diseases

Membrane-less organelles (MLOs) formed through liquid-liquid phase separation (LLPS) are associated with numerous important biological functions, but the abnormal phase separation will also dysregulate the physiological processes. Emerging evidence points to the importance of LLPS in human health and diseases. Nevertheless, despite recent advancements, our knowledge of the molecular relationship between LLPS and diseases is frequently incomplete. In this review, we outline our current understanding about how aberrant LLPS affects developmental disorders, tandem repeat disorders, cancers and viral infection. We also examine disease mechanisms driven by aberrant condensates, and highlight potential treatment approaches. This study seeks to expand our understanding of LLPS by providing a valuable new paradigm for understanding phase separation and human disorders, as well as to further translate our current knowledge regarding LLPS into therapeutic discoveries.

Phase-separated DropCRISPRa platform for efficient gene activation in mammalian cells and mice

Liquid-liquid phase separation (LLPS) plays a critical role in regulating gene transcription via the formation of transcriptional condensates. However, LLPS has not been reported to be engineered as a tool to activate endogenous gene expression in mammalian cells or in vivo. Here, we developed a droplet-forming CRISPR (clustered regularly interspaced short palindromic repeats) gene activation system (DropCRISPRa) to activate transcription with high efficiency via combining the CRISPR-SunTag system with FETIDR-AD fusion proteins, which contain an N-terminal intrinsically disordered region (IDR) of a FET protein (FUS or TAF15) and a transcription activation domain (AD, VP64/P65/VPR). In this system, the FETIDR-AD fusion protein formed phase separation condensates at the target sites, which could recruit endogenous BRD4 and RNA polymerase II with an S2 phosphorylated C-terminal domain (CTD) to enhance transcription elongation. IDR-FUS9Y>S and IDR-FUSG156E, two mutants with deficient and aberrant phase separation respectively, confirmed that appropriate phase separation was required for efficient gene activation. Further, the DropCRISPRa system was compatible with a broad set of CRISPR-associated (Cas) proteins and ADs, including dLbCas12a, dAsCas12a, dSpCas9 and the miniature dUnCas12f1, and VP64, P65 and VPR. Finally, the DropCRISPRa system could activate target genes in mice. Therefore, this study provides a robust tool to activate gene expression for foundational research and potential therapeutics.

Phase separation in gene transcription control

Phase separation provides a general mechanism for the formation of biomolecular condensates, and it plays a vital role in regulating diverse cellular processes, including gene expression. Although the role of transcription factors and coactivators in regulating transcription has long been understood, how phase separation is involved in this process is just beginning to be explored. In this review, we highlight recent advance in elucidating the molecular mechanisms and functions of transcriptional condensates in gene expression control. We discuss the different condensates formed at each stage of the transcription cycle and how they are dynamically regulated in response to diverse cellular and extracellular cues that cause rapid changes in gene expression. Furthermore, we present new findings regarding the dysregulation of transcription condensates and their implications in human diseases.

Phase Separation in Biology and Disease; Current Perspectives and Open Questions

In the past almost 15 years, we witnessed the birth of a new scientific field focused on the existence, formation, biological functions, and disease associations of membraneless bodies in cells, now referred to as biomolecular condensates. Pioneering studies from several laboratories [reviewed in1-3] supported a model wherein biomolecular condensates associated with diverse biological processes form through the process of phase separation. These and other findings that followed have revolutionized our understanding of how biomolecules are organized in space and time within cells to perform myriad biological functions, including cell fate determination, signal transduction, endocytosis, regulation of gene expression and protein translation, and regulation of RNA metabolism. Further, condensates formed through aberrant phase transitions have been associated with numerous human diseases, prominently including neurodegeneration and cancer. While in some cases, rigorous evidence supports links between formation of biomolecular condensates through phase separation and biological functions, in many others such links are less robustly supported, which has led to rightful scrutiny of the generality of the roles of phase separation in biology and disease.4-7 During a week-long workshop in March 2022 at the Telluride Science Research Center (TSRC) in Telluride, Colorado, ∼25 scientists addressed key questions surrounding the biomolecular condensates field. Herein, we present insights gained through these discussions, addressing topics including, roles of condensates in diverse biological processes and systems, and normal and disease cell states, their applications to synthetic biology, and the potential for therapeutically targeting biomolecular condensates.

Conformational and Thermodynamic Differences Underlying Wild-Type and Mutant Eleven-Nineteen-Leukemia YEATS Domain Specificity for Epigenetic Marks

Histone post-translational modifications (PTMs) are interpreted by multiple reader domains and proteins to regulate gene expression. The eleven-nineteen-leukemia (ENL) YEATS domain is a prototypical PTM reader that recognizes multiple lysine acetylation marks on the histone H3 tails as a way of recruiting chromatin remodellers. Two ENL YEATS mutations have been identified which have been linked with leukemia, Wilms tumor, and other forms of cancer and result in either an insertion or deletion of residues in the loop connecting beta sheets distant from the protein active site. In vitro experiments have shown that these mutations modulate the selectivities of YEATS domains for various lysine acetylation marks, although different experiments have provided contrasting views on the abilities of the insertion and deletion mutants to discern specific PTMs. Here, we have performed multiple molecular dynamics simulations of wild-type and insertion and deletion mutant YEATS domains free from and in complex with two PTM peptides: one that is acetylated at K9 of H3 and the other that is acetylated at residue K27 of H3. Results show that these two peptides have distinct flexibilities and binding energetics when bound to YEATS domains and that these properties are affected by interactions with residues within and outside of the peptide consensus motif. Furthermore, these properties are modulated by the YEATS insertion and deletion mutants, which results in disparate binding effects in these systems. Together, these results suggest that only the partial exposure of histone tails is sufficient in the context of nucleosomes for YEATS-mediated recognition of acetylation marks on histone tails. They also caution against the overinterpretation of results obtained from experiments on reader domain-histone peptide binding in isolation and not in the full-length nucleosome context.