RESUMEN
Oncogenic mutations in KRAS are present in approximately 95% of patients diagnosed with pancreatic ductal adenocarcinoma (PDAC) and are considered the initiating event of pancreatic intraepithelial neoplasia (PanIN) precursor lesions. While it is well established that KRAS mutations drive the activation of oncogenic kinase cascades during pancreatic oncogenesis, the effects of oncogenic KRAS signaling on regulation of phosphatases during this process is not fully appreciated. Protein Phosphatase 2A (PP2A) has been implicated in suppressing KRAS-driven cellular transformation. However, low PP2A activity is observed in PDAC cells compared to non-transformed cells, suggesting that suppression of PP2A activity is an important step in the overall development of PDAC. In the current study, we demonstrate that KRASG12D induces the expression of both an endogenous inhibitor of PP2A activity, Cancerous Inhibitor of PP2A (CIP2A), and the PP2A substrate, c-MYC. Consistent with these findings, KRASG12D sequestered the specific PP2A subunit responsible for c-MYC degradation, B56α, away from the active PP2A holoenzyme in a CIP2A-dependent manner. During PDAC initiation in vivo, knockout of B56α promoted KRASG12D tumorigenesis by accelerating acinar-to-ductal metaplasia (ADM) and the formation of PanIN lesions. The process of ADM was attenuated ex vivo in response to pharmacological re-activation of PP2A utilizing direct small molecule activators of PP2A (SMAPs). Together, our results suggest that suppression of PP2A-B56α through KRAS signaling can promote the MYC-driven initiation of pancreatic tumorigenesis.
RESUMEN
Macrophages elicit immune responses to pathogens through induction of inflammatory genes. Here, we examined the role of three variants of the SWI/SNF nucleosome remodeling complex-cBAF, ncBAF, and PBAF-in the macrophage response to bacterial endotoxin (lipid A). All three SWI/SNF variants were prebound in macrophages and retargeted to genomic sites undergoing changes in chromatin accessibility following stimulation. Cooperative binding of all three variants associated with de novo chromatin opening and latent enhancer activation. Isolated binding of ncBAF and PBAF, in contrast, associated with activation and repression of active enhancers, respectively. Chemical and genetic perturbations of variant-specific subunits revealed pathway-specific regulation in the activation of lipid A response genes, corresponding to requirement for cBAF and ncBAF in inflammatory and interferon-stimulated gene (ISG) activation, respectively, consistent with differential engagement of SWI/SNF variants by signal-responsive transcription factors. Thus, functional diversity among SWI/SNF variants enables increased regulatory control of innate immune transcriptional programs, with potential for specific therapeutic targeting.
Asunto(s)
Ensamble y Desensamble de Cromatina , Proteínas Cromosómicas no Histona , Elementos de Facilitación Genéticos , Inflamación , Macrófagos , Factores de Transcripción , Macrófagos/inmunología , Macrófagos/metabolismo , Animales , Ratones , Factores de Transcripción/metabolismo , Factores de Transcripción/genética , Proteínas Cromosómicas no Histona/metabolismo , Proteínas Cromosómicas no Histona/genética , Inflamación/inmunología , Inflamación/genética , Elementos de Facilitación Genéticos/genética , Cromatina/metabolismo , Regulación de la Expresión Génica , Ratones Endogámicos C57BL , Inmunidad Innata , HumanosRESUMEN
Clinical trials have identified ARID1A mutations as enriched among patients who respond favorably to immune checkpoint blockade (ICB) in several solid tumor types independent of microsatellite instability. We show that ARID1A loss in murine models is sufficient to induce anti-tumor immune phenotypes observed in ARID1A mutant human cancers, including increased CD8+ T cell infiltration and cytolytic activity. ARID1A-deficient cancers upregulated an interferon (IFN) gene expression signature, the ARID1A-IFN signature, associated with increased R-loops and cytosolic single-stranded DNA (ssDNA). Overexpression of the R-loop resolving enzyme, RNASEH2B, or cytosolic DNase, TREX1, in ARID1A-deficient cells prevented cytosolic ssDNA accumulation and ARID1A-IFN gene upregulation. Further, the ARID1A-IFN signature and anti-tumor immunity were driven by STING-dependent type I IFN signaling, which was required for improved responsiveness of ARID1A mutant tumors to ICB treatment. These findings define a molecular mechanism underlying anti-tumor immunity in ARID1A mutant cancers.
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Linfocitos T CD8-positivos , Proteínas de Unión al ADN , Interferón Tipo I , Proteínas de la Membrana , Neoplasias , Transducción de Señal , Factores de Transcripción , Animales , Humanos , Ratones , Linfocitos T CD8-positivos/inmunología , Linfocitos T CD8-positivos/metabolismo , Línea Celular Tumoral , Proteínas de Unión al ADN/metabolismo , Exodesoxirribonucleasas/metabolismo , Inhibidores de Puntos de Control Inmunológico/farmacología , Inhibidores de Puntos de Control Inmunológico/uso terapéutico , Interferón Tipo I/metabolismo , Proteínas de la Membrana/metabolismo , Proteínas de la Membrana/genética , Ratones Endogámicos C57BL , Mutación , Neoplasias/inmunología , Neoplasias/genética , Proteínas Nucleares/metabolismo , Fosfoproteínas/metabolismo , Factores de Transcripción/metabolismo , Masculino , Quimiocinas/genética , Quimiocinas/metabolismoRESUMEN
The polybromo, brahma-related gene 1-associated factors (PBAF) chromatin remodeling complex subunit polybromo-1 (PBRM1) contains six bromodomains that recognize and bind acetylated lysine residues on histone tails and other nuclear proteins. PBRM1 bromodomains thus provide a link between epigenetic posttranslational modifications and PBAF modulation of chromatin accessibility and transcription. As a putative tumor suppressor in several cancers, PBRM1 protein expression is often abrogated by truncations and deletions. However, â¼33% of PBRM1 mutations in cancer are missense and cluster within its bromodomains. Such mutations may generate full-length PBRM1 variant proteins with undetermined structural and functional characteristics. Here, we employed computational, biophysical, and cellular assays to interrogate the effects of PBRM1 bromodomain missense variants on bromodomain stability and function. Since mutations in the fourth bromodomain of PBRM1 (PBRM1-BD4) comprise nearly 20% of all cancer-associated PBRM1 missense mutations, we focused our analysis on PBRM1-BD4 missense protein variants. Selecting 16 potentially deleterious PBRM1-BD4 missense protein variants for further study based on high residue mutational frequency and/or conservation, we show that cancer-associated PBRM1-BD4 missense variants exhibit varied bromodomain stability and ability to bind acetylated histones. Our results demonstrate the effectiveness of identifying the unique impacts of individual PBRM1-BD4 missense variants on protein structure and function, based on affected residue location within the bromodomain. This knowledge provides a foundation for drawing correlations between specific cancer-associated PBRM1 missense variants and distinct alterations in PBRM1 function, informing future cancer personalized medicine approaches.
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Proteínas de Unión al ADN , Mutación Missense , Neoplasias , Dominios Proteicos , Factores de Transcripción , Humanos , Proliferación Celular , Proteínas de Unión al ADN/metabolismo , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/química , Ligandos , Neoplasias/genética , Neoplasias/metabolismo , Neoplasias/patología , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Proteínas Nucleares/química , Unión Proteica , Factores de Transcripción/genética , Factores de Transcripción/metabolismo , Factores de Transcripción/química , Modelos Moleculares , Estructura Terciaria de ProteínaRESUMEN
Bromodomain-containing proteins are readers of acetylated lysine and play important roles in cancer. Bromodomain-containing protein 7 (BRD7) is implicated in multiple malignancies; however, there are no selective chemical probes to study its function in disease. Using crystal structures of BRD7 and BRD9 bromodomains (BDs) bound to BRD9-selective ligands, we identified a binding pocket exclusive to BRD7. We synthesized a series of ligands designed to occupy this binding region and identified two inhibitors with increased selectivity toward BRD7, 1-78 and 2-77, which bind with submicromolar affinity to the BRD7 BD. Our binding mode analyses indicate that these ligands occupy a uniquely accessible binding cleft in BRD7 and maintain key interactions with the asparagine and tyrosine residues critical for acetylated lysine binding. Finally, we validated the utility and selectivity of the compounds in cell-based models of prostate cancer.
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Lisina , Neoplasias de la Próstata , Humanos , Masculino , Proteínas Cromosómicas no Histona/antagonistas & inhibidores , Ligandos , Lisina/química , Neoplasias de la Próstata/tratamiento farmacológico , Factores de TranscripciónRESUMEN
PBRM1 is a subunit of the PBAF chromatin remodeling complex, which is mutated in 40-50% of clear cell renal cell carcinoma patients. It is thought to largely function as a chromatin binding subunit of the PBAF complex, but the molecular mechanism underlying this activity is not fully known. PBRM1 contains six tandem bromodomains which are known to cooperate in binding of nucleosomes acetylated at histone H3 lysine 14 (H3K14ac). Here, we demonstrate that the second and fourth bromodomains from PBRM1 also bind nucleic acids, selectively associating with double stranded RNA elements. Disruption of the RNA binding pocket is found to compromise PBRM1 chromatin binding and inhibit PBRM1-mediated cellular growth effects.
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Cromatina , Neoplasias Renales , Humanos , Cromatina/genética , ARN/genética , Proteínas Nucleares/metabolismo , Histonas/metabolismo , Neoplasias Renales/genética , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Factores de Transcripción/metabolismoRESUMEN
Signal-dependent RNA Polymerase II (Pol2) productive elongation is an integral component of gene transcription, including those of immediate early genes (IEGs) induced by neuronal activity. However, it remains unclear how productively elongating Pol2 overcome nucleosomal barriers. Using RNAi, three degraders, and several small molecule inhibitors, we show that the mammalian SWI/SNF complex of neurons (neuronal BAF, or nBAF) is required for activity-induced transcription of neuronal IEGs, including Arc . The nBAF complex facilitates promoter-proximal Pol2 pausing, signal-dependent Pol2 recruitment (loading), and importantly, mediates productive elongation in the gene body via interaction with the elongation complex and elongation-competent Pol2. Mechanistically, Pol2 elongation is mediated by activity-induced nBAF assembly (especially, ARID1A recruitment) and its ATPase activity. Together, our data demonstrate that the nBAF complex regulates several aspects of Pol2 transcription and reveal mechanisms underlying activity-induced Pol2 elongation. These findings may offer insights into human maladies etiologically associated with mutational interdiction of BAF functions.
RESUMEN
PBRM1 is a subunit of the PBAF chromatin remodeling complex that uniquely contains six bromodomains. PBRM1 can operate as a tumor suppressor or tumor promoter. PBRM1 is a tumor promoter in prostate cancer, contributing to migratory and immunosuppressive phenotypes. Selective chemical probes targeting PBRM1 bromodomains are desired to elucidate the association between aberrant PBRM1 chromatin binding and cancer pathogenesis and the contributions of PBRM1 to immunotherapy. Previous PBRM1 inhibitors unselectively bind SMARCA2 and SMARCA4 bromodomains with nanomolar potency. We used our protein-detected NMR screening pipeline to screen 1968 fragments against the second PBRM1 bromodomain, identifying 17 hits with Kd values from 45 µM to >2 mM. Structure-activity relationship studies on the tightest-binding hit resulted in nanomolar inhibitors with selectivity for PBRM1 over SMARCA2 and SMARCA4. These chemical probes inhibit the association of full-length PBRM1 to acetylated histone peptides and selectively inhibit growth of a PBRM1-dependent prostate cancer cell line.
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Histonas , Neoplasias de la Próstata , Masculino , Humanos , Histonas/metabolismo , Dominios Proteicos , Cromatina , Neoplasias de la Próstata/tratamiento farmacológico , Carcinógenos , ADN Helicasas/metabolismo , Proteínas Nucleares/metabolismo , Factores de Transcripción/metabolismo , Proteínas de Unión al ADN/metabolismoRESUMEN
ARID2 is the most recurrently mutated SWI/SNF complex member in melanoma; however, its tumor-suppressive mechanisms in the context of the chromatin landscape remain to be elucidated. Here, we model ARID2 deficiency in melanoma cells, which results in defective PBAF complex assembly with a concomitant genomic redistribution of the BAF complex. Upon ARID2 depletion, a subset of PBAF and shared BAF-PBAF-occupied regions displays diminished chromatin accessibility and associated gene expression, while BAF-occupied enhancers gain chromatin accessibility and expression of genes linked to the process of invasion. As a function of altered accessibility, the genomic occupancy of melanoma-relevant transcription factors is affected and significantly correlates with the observed transcriptional changes. We further demonstrate that ARID2-deficient cells acquire the ability to colonize distal organs in multiple animal models. Taken together, our results reveal a role for ARID2 in mediating BAF and PBAF subcomplex chromatin dynamics with consequences for melanoma metastasis.
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Proteínas Cromosómicas no Histona , Melanoma , Factores de Transcripción , Animales , Cromatina , Ensamble y Desensamble de Cromatina , Regulación de la Expresión Génica , Humanos , Melanoma/genética , Factores de Transcripción/genética , Factores de Transcripción/metabolismoRESUMEN
Polycomb repressive complexes (PRCs) are a heterogenous collection of dozens, if not hundreds, of protein complexes composed of various combinations of subunits. PRCs are transcriptional repressors important for cell-type specificity during development, and as such, are commonly mis-regulated in cancer. PRCs are broadly characterized as PRC1 with histone ubiquitin ligase activity, or PRC2 with histone methyltransferase activity; however, the mechanism by which individual PRCs, particularly the highly diverse set of PRC1s, alter gene expression has not always been clear. Here we review the current understanding of how PRCs act, both individually and together, to establish and maintain gene repression, the biochemical contribution of individual PRC subunits, the mis-regulation of PRC function in different cancers, and the current strategies for modulating PRC activity. Increased mechanistic understanding of PRC function, as well as cancer-specific roles for individual PRC subunits, will uncover better targets and strategies for cancer therapies.
RESUMEN
MicroRNAs (miRNAs, miRs) regulate cell fate decisions by post-transcriptionally tuning networks of mRNA targets. We used miRNA-directed pathway discovery to reveal a regulatory circuit that influences Ig class switch recombination (CSR). We developed a system to deplete mature, activated B cells of miRNAs, and performed a rescue screen that identified the miR-221/222 family as a positive regulator of CSR. Endogenous miR-221/222 regulated B cell CSR to IgE and IgG1 in vitro, and miR-221/222-deficient mice exhibited defective IgE production in allergic airway challenge and polyclonal B cell activation models in vivo. We combined comparative Ago2-HITS-CLIP and gene expression analyses to identify mRNAs bound and regulated by miR-221/222 in primary B cells. Interrogation of these putative direct targets uncovered functionally relevant downstream genes. Genetic depletion or pharmacological inhibition of Foxp1 and Arid1a confirmed their roles as key modulators of CSR to IgE and IgG1.
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Cambio de Clase de Inmunoglobulina/genética , MicroARNs/genética , Recombinación Genética/genética , Animales , Linfocitos B/inmunología , Femenino , Expresión Génica/genética , Expresión Génica/inmunología , Redes Reguladoras de Genes/genética , Hipersensibilidad/genética , Hipersensibilidad/inmunología , Cambio de Clase de Inmunoglobulina/inmunología , Inmunoglobulina E/genética , Inmunoglobulina G/genética , Masculino , Ratones , MicroARNs/inmunología , Recombinación Genética/inmunologíaRESUMEN
Methyllysine reader proteins bind to methylated lysine residues and alter gene transcription by changing either the compaction state of chromatin or by the recruitment of other multiprotein complexes. The polycomb paralog family of methyllysine readers bind to trimethylated lysine on the tail of histone 3 (H3) via a highly conserved aromatic cage located in their chromodomains. Each of the polycomb paralogs are implicated in several disease states. CBX6 and CBX8 are members of the polycomb paralog family with two structurally similar chromodomains. By exploring the structure-activity relationships of a previously reported CBX6 inhibitor we have discovered more potent and cell permeable analogs. Our current report includes potent, dual-selective inhibitors of CBX6 and CBX8. We have shown that the -2 position in our scaffold is an important residue for selectivity amongst the polycomb paralogs. Preliminary cell-based studies show that the new inhibitors impact cell proliferation in a rhabdoid tumor cell line.
Asunto(s)
Antineoplásicos/farmacología , Péptidos/farmacología , Complejo Represivo Polycomb 1/antagonistas & inhibidores , Proteínas del Grupo Polycomb/antagonistas & inhibidores , Antineoplásicos/química , Línea Celular , Proliferación Celular/efectos de los fármacos , Relación Dosis-Respuesta a Droga , Ensayos de Selección de Medicamentos Antitumorales , Humanos , Ligandos , Estructura Molecular , Péptidos/química , Complejo Represivo Polycomb 1/metabolismo , Proteínas del Grupo Polycomb/metabolismo , Relación Estructura-ActividadRESUMEN
Polycomb group (PcG) proteins are epigenetic regulators that facilitate both embryonic development and cancer progression. PcG proteins form Polycomb repressive complexes 1 and 2 (PRC1 and PRC2). PRC2 trimethylates histone H3 lysine 27 (H3K27me3), a histone mark recognized by the N-terminal chromodomain (ChD) of the CBX subunit of canonical PRC1. There are five PcG CBX paralogs in humans. CBX2 in particular is upregulated in a variety of cancers, particularly in advanced prostate cancers. Using CBX2 inhibitors to understand and target CBX2 in prostate cancer is highly desirable; however, high structural similarity among the CBX ChDs has been challenging for developing selective CBX ChD inhibitors. Here, we utilize selections of focused DNA encoded libraries (DELs) for the discovery of a selective CBX2 chromodomain probe, SW2_152F. SW2_152F binds to CBX2 ChD with a Kd of 80â nM and displays 24-1000-fold selectivity for CBX2 ChD over other CBX paralogs inâ vitro. SW2_152F is cell permeable, selectively inhibits CBX2 chromatin binding in cells, and blocks neuroendocrine differentiation of prostate cancer cell lines in response to androgen deprivation.
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Carcinoma Neuroendocrino/metabolismo , Regulación Neoplásica de la Expresión Génica/genética , Complejo Represivo Polycomb 1/química , Proteínas del Grupo Polycomb/metabolismo , Neoplasias de la Próstata/metabolismo , Bibliotecas de Moléculas Pequeñas/química , Secuencia de Aminoácidos , Antagonistas de Andrógenos/metabolismo , Diferenciación Celular , Línea Celular Tumoral , Permeabilidad de la Membrana Celular , Histonas/metabolismo , Humanos , Ligandos , Masculino , Complejo Represivo Polycomb 1/genética , Unión Proteica , Bibliotecas de Moléculas Pequeñas/metabolismoRESUMEN
In higher order organisms, the genome is assembled into a protein-dense structure called chromatin. Chromatin is spatially organized in the nucleus through hierarchical folding, which is tightly regulated both in cycling cells and quiescent cells. Assembly and folding are not one-time events in a cell's lifetime; rather, they are subject to dynamic shifts to allow changes in transcription, DNA replication, or DNA damage repair. Chromatin is regulated at many levels, and recent tools have permitted the elucidation of specific factors involved in the maintenance and regulation of the three-dimensional (3D) genome organization. In this review/perspective, we aim to cover the potential, but relatively unelucidated, crosstalk between 3D genome architecture and the ATP-dependent chromatin remodelers with a specific focus on how the architectural proteins CTCF and cohesin are regulated by chromatin remodeling.
RESUMEN
Switch/sucrose-nonfermentable (SWI/SNF) chromatin-remodeling complexes are critical regulators of chromatin dynamics during transcription, DNA replication, and DNA repair. A recently identified SWI/SNF subcomplex termed GLTSCR1/1L-BAF (GBAF; or "noncanonical BAF", ncBAF) uniquely contains bromodomain-containing protein BRD9 and glioma tumor suppressor candidate region 1 (GLTSCR1) or its paralog GLTSCR1-like (GLTSCR1L). Recent studies have identified a unique dependency on GBAF (ncBAF) complexes in synovial sarcoma and malignant rhabdoid tumors, both of which possess aberrations in canonical BAF (cBAF) and Polybromo-BAF (PBAF) complexes. Dependencies on GBAF in malignancies without SWI/SNF aberrations, however, are less defined. Here, we show that GBAF, particularly its BRD9 subunit, is required for the viability of prostate cancer cell lines in vitro and for optimal xenograft tumor growth in vivo. BRD9 interacts with androgen receptor (AR) and CCCTC-binding factor (CTCF), and modulates AR-dependent gene expression. The GBAF complex exhibits overlapping genome localization and transcriptional targets as bromodomain and extraterminal domain-containing (BET) proteins, which are established AR coregulators. Our results demonstrate that GBAF is critical for coordinating SWI/SNF-BET cooperation and uncover a new druggable target for AR-positive prostate cancers, including those resistant to androgen deprivation or antiandrogen therapies. SIGNIFICANCE: Advanced prostate cancers resistant to androgen receptor antagonists are still susceptible to nontoxic BRD9 inhibitors, making them a promising alternative for halting AR signaling in progressed disease.
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Neoplasias de la Próstata/patología , Receptores Androgénicos/metabolismo , Factores de Transcripción/fisiología , Antagonistas de Receptores Androgénicos/farmacología , Animales , Línea Celular Tumoral , Proliferación Celular/genética , Supervivencia Celular/efectos de los fármacos , Supervivencia Celular/genética , Progresión de la Enfermedad , Regulación Neoplásica de la Expresión Génica/efectos de los fármacos , Células HEK293 , Humanos , Masculino , Ratones , Ratones Desnudos , Células PC-3 , Neoplasias de la Próstata/genética , Neoplasias de la Próstata/metabolismo , ARN Interferente Pequeño/farmacología , Receptores Androgénicos/genética , Transducción de Señal/efectos de los fármacos , Transducción de Señal/genética , Factores de Transcripción/antagonistas & inhibidores , Factores de Transcripción/genética , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
SWI/SNF (BAF) complexes are a diverse family of ATP-dependent chromatin remodelers produced by combinatorial assembly that are mutated in and thought to contribute to 20% of human cancers and a large number of neurologic diseases. The gene-activating functions of BAF complexes are essential for viability of many cell types, limiting the development of small molecule inhibitors. To circumvent the potential toxicity of SWI/SNF inhibition, we identified small molecules that inhibit the specific repressive function of these complexes but are relatively nontoxic and importantly synergize with ATR inhibitors in killing cancer cells. Our studies suggest an avenue for therapeutic enhancement of ATR/ATM inhibition and provide evidence for chemical synthetic lethality of BAF complexes as a therapeutic strategy in cancer.
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Proteínas de la Ataxia Telangiectasia Mutada/antagonistas & inhibidores , Ensamble y Desensamble de Cromatina/efectos de los fármacos , Neoplasias/patología , Factores de Transcripción/metabolismo , Ciclo Celular/efectos de los fármacos , Células HCT116 , Humanos , Inhibidores de Proteínas Quinasas/farmacologíaRESUMEN
Polycomb repressive complex 1 (PRC1) is critical for mediating gene expression during development. Five chromobox (CBX) homolog proteins, CBX2, CBX4, CBX6, CBX7, and CBX8, are incorporated into PRC1 complexes, where they mediate targeting to trimethylated lysine 27 of histone H3 (H3K27me3) via the N-terminal chromodomain (ChD). Individual CBX paralogs have been implicated as drug targets in cancer; however, high similarities in sequence and structure among the CBX ChDs provide a major obstacle in developing selective CBX ChD inhibitors. Here we report the selection of small, focused, DNA-encoded libraries (DELs) against multiple homologous ChDs to identify modifications to a parental ligand that confer both selectivity and potency for the ChD of CBX8. This on-DNA, medicinal chemistry approach enabled the development of SW2_110A, a selective, cell-permeable inhibitor of the CBX8 ChD. SW2_110A binds CBX8 ChD with a Kd of 800 nM, with minimal 5-fold selectivity for CBX8 ChD over all other CBX paralogs in vitro. SW2_110A specifically inhibits the association of CBX8 with chromatin in cells and inhibits the proliferation of THP1 leukemia cells driven by the MLL-AF9 translocation. In THP1 cells, SW2_110A treatment results in a significant decrease in the expression of MLL-AF9 target genes, including HOXA9, validating the previously established role for CBX8 in MLL-AF9 transcriptional activation, and defining the ChD as necessary for this function. The success of SW2_110A provides great promise for the development of highly selective and cell-permeable probes for the full CBX family. In addition, the approach taken provides a proof-of-principle demonstration of how DELs can be used iteratively for optimization of both ligand potency and selectivity.
Asunto(s)
Antineoplásicos/química , Inhibidores Enzimáticos/química , Biblioteca de Genes , Ligandos , Complejo Represivo Polycomb 1/metabolismo , Proteínas Recombinantes de Fusión/metabolismo , Secuencia de Aminoácidos , Línea Celular Tumoral , Permeabilidad de la Membrana Celular , Proliferación Celular/efectos de los fármacos , Cromatina/metabolismo , Clonación Molecular , ADN/metabolismo , Desarrollo de Medicamentos , Expresión Génica , Histonas/química , Humanos , Ligasas/metabolismo , Lisina/química , Complejo Represivo Polycomb 1/antagonistas & inhibidores , Complejo Represivo Polycomb 1/genética , Unión Proteica , Proteínas Recombinantes de Fusión/genética , Relación Estructura-Actividad , Especificidad por Sustrato , Translocación GenéticaRESUMEN
We report the selection of DNA-encoded small molecule libraries against protein targets within the cytosol and on the surface of live cells. The approach relies on generation of a covalent linkage of the DNA to protein targets by affinity labeling. This cross-linking event enables subsequent copurification by a tag on the recombinant protein. To access targets within cells, a cyclic cell-penetrating peptide is appended to DNA-encoded libraries for delivery across the cell membrane. As this approach assesses binding of DELs to targets in live cells, it provides a strategy for selection of DELs against challenging targets that cannot be expressed and purified as active.
Asunto(s)
Péptidos de Penetración Celular/química , Proteínas/genética , Proteínas/metabolismo , Bibliotecas de Moléculas Pequeñas/farmacología , Péptidos de Penetración Celular/metabolismo , Reactivos de Enlaces Cruzados/química , Citosol/efectos de los fármacos , Citosol/metabolismo , ADN/química , Fluoresceínas/química , Células HEK293 , Humanos , Lípidos , Péptidos Cíclicos/química , Reacción en Cadena de la Polimerasa , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismo , Bibliotecas de Moléculas Pequeñas/química , Tetrahidrofolato Deshidrogenasa/genética , Transfección , Trimetoprim/farmacologíaRESUMEN
Polybromo1 (PBRM1) is a chromatin remodeler subunit highly mutated in cancer, particularly clear cell renal carcinoma. PBRM1 is a member of the SWI/SNF subcomplex, PBAF (PBRM1-Brg1/Brm-associated factors), and is characterized by six tandem bromodomains. Here we establish a role for PBRM1 in epithelial cell maintenance through the expression of genes involved in cell adhesion, metabolism, stress response, and apoptosis. In support of a general role for PBRM1 in stress response and apoptosis, we observe that loss of PBRM1 results in an increase in reactive oxygen species generation and a decrease in cellular viability under stress conditions. We find that loss of PBRM1 promotes cell growth under favorable conditions but is required for cell survival under conditions of cellular stress.
RESUMEN
SANT domains are found in a number of chromatin regulators. They contain approximately 50 amino acids and have high similarity to the DNA binding domain of Myb related proteins. Though some SANT domains associate with DNA others have been found to bind unmodified histone tails. There are two SANT domains in Enhancer of Zeste 2 (EZH2), the catalytic subunit of the Polycomb Repressive Complex 2 (PRC2), of unknown function. Here we show that the first SANT domain (SANT1) of EZH2 is a histone binding domain with specificity for the histone H4 N-terminal tail. Using NMR spectroscopy, mutagenesis, and molecular modeling we structurally characterize the SANT1 domain and determine the molecular mechanism of binding to the H4 tail. Though not important for histone binding, we find that the adjacent stimulation response motif (SRM) stabilizes SANT1 and transiently samples its active form in solution. Acetylation of H4K16 (H4K16ac) or acetylation or methylation of H4K20 (H4K20ac and H4K20me3) are seen to abrogate binding of SANT1 to H4, which is consistent with these modifications being anti-correlated with H3K27me3 in-vivo. Our results provide significant insight into this important regulatory region of EZH2 and the first characterization of the molecular mechanism of SANT domain histone binding.