Project description:Molecular regulation of stem cell differentiation is exerted through both genetic and epigenetic determinants over distal regulatory or enhancer regions. Understanding the mechanistic action of active or poised enhancers is thus imperative for control of stem cell differentiation. Based on a genome-wide co-occurrence of different epigenetic marks in committed proliferating myoblasts, we have previously generated a 14-state chromatin state model to profile residue-specific histone acetylation in early myoblast differentiation. Here, we use genome-wide chromatin state association to delineate the functional mode of transcription regulators in early myogenic differentiation. We define a role of transcriptional coactivator p300, when recruited by master muscle regulator MyoD, in the establishment and regulation of myogenic loci at the onset of terminal differentiation. In addition, we reveal an enrichment of residue- and loci-specific histone acetylation at p300 associated active or poised enhancers, particularly when enlisted by MyoD. We provide novel molecular insights into the regulation of myogenic enhancers by p300 in concert with MyoD. Our studies present a valuable aptitude for driving stage specific chromatin state or enhancers pharmacologically to treat muscle related diseases and for the identification of additional myogenic targets and molecular interactions for therapeutic development.
Project description:The primary focus of these studies is to define the transcriptional network regulated by ectopic expression of the transcriptional co-activator protein, p300, in order to define its mechanism(s) of action in promoting muscle cell survival. Our laboratory has generated a murine C2-derived myoblast cell line stably expressing an IGF-II cDNA in antisense orientation (C2AS12 cells). These cells proliferate normally in serum-rich growth medium but progressively die in low-serum differentiation medium. Ectopic expression of p300 (a transcriptional co-coactivator with acetyltransferase activity) prevents the progressive cell death induced by serum withdrawal, however, the mechanism of this action is not understood. Further, over-expression of a mutated form of p300, lacking at protein interaction domain (deltaTAZ2), failed to maintain cell viability although it retains catalytic activity. Wild-type and mutant p300 are delivered using recombinant adenoviruses (Ad-p300 and Ad-p300deltaTAZ2) and their expression is regulated by a second recombinant adenovirus encoding the tetracycline transactivator protein (Ad-tTA), affording regulated expression of p300 forms (Tet-off system) and providing a control for viral load. Using these reagents the overall experiment was as follows: Three parallel series of C2AS12 cells were infected with (1) wt p300 + tTA, (2) p300deltaTAZ2 +tTA, (3) wt p300 +tTA +doxycycline. Infected cells were grown to confluence followed by transfer to low-serum differentiation medium (T0). Cell were isolated at this point and following 24 (T24) hours incubation for RNA isolation. Companion dishes of cells were included for analysis by immunocytochemistry to ensure regulated transgene expression and cell viabilities. 6 biological replicates, representing 3 treatment groups, two timepoints and 2 biological outcomes (cell survival with p300wt and apoptotic cell death with p300wt+Dox and p300mut)
Project description:The transcriptional co-activator and acetyltransferase p300 is required for fundamental cellular processes, including differentiation and growth. Here, we report that p300 forms phase separated condensates in the cell nucleus. The phase separation ability of p300 is regulated by autoacetylation and relies on its catalytic core components, including the HAT domain, the autoinhibition loop, and bromodomain. p300 condensates sequester chromatin components, such as histone H3 tail and DNA, and are amplified through binding of p300 to the nucleosome. The catalytic HAT activity of p300 is decreased due to occlusion of the active site in the phase separated droplets, a large portion of which co-localizes with chromatin regions enriched in H3K27me3. Our findings suggest a model in which p300 condensates can act as a storage pool of the protein with reduced HAT activity, allowing p300 to be compartmentalized and concentrated at poised or repressed chromatin regions.
Project description:Deciphering the molecular mechanisms underpinning myoblast differentiation is a critical step in developing the best strategy to promote muscle regeneration in patients suffering from muscle-related diseases. We have previously established that a rexinoid x receptor (RXR)-selective agonist enhances the differentiation and fusion of myoblasts through a direct regulation of MyoD expression, coupled with an augmentation of myogenin protein. Here, we found that RXR signaling modifies the chromatin state distribution of myogenin, promoting the binding preference of myogenin for poised enhancers and a distinct motif. We also found an association of myogenin with rexinoid-responsive gene expression and identified an epigenetic signature related to histone acetyltransferase p300. Moreover, RXR signaling instigates residue-specific histone acetylation at enhancers co-occupied by p300 and myogenin. Thus, genomic distribution of transcriptional regulators is an important designate for identifying novel targets as well as developing therapeutics that modulate epigenetic landscape in a selective manner to promote muscle regeneration.
Project description:Here, we identified a novel lncRNA named lncMREF as a specific positive regulator of muscle regeneration in mice, pigs and humans. Functional studies demonstrated that lncMREF is significantly upregulated in activated skeletal muscle satellite cells and promotes myogenic differentiation and muscle regeneration. Mechanistically, lncMREF interacts with Smarca5 to promote chromatin remodeling and accessibility when muscle satellite cells are activated, thereby facilitating genomic binding of p300/H3K27 to upregulate the expression of myogenic regulators, such as MyoD and cell differentiation. Our results unravel a new temporal-specific epigenetic regulation during muscle regeneration and reveal that lncMREF/Smarca5-mediated epigenetic programming is responsible for muscle satellite cell differentiation, which provides new insights into the regulatory mechanism of muscle regeneration in adult animals.
Project description:The coactivator p300/CBP regulates genes by facilitating the assembly of transcriptional machinery and by acetylating histones and other factors. However, it remains mostly unclear how both functions of p300 are dynamically coordinated during gene control. Here, we showed that p300 appears to orchestrate two functions through the formation of dynamic co-condensates with certain transcription factors (TFs), which is mediated by the interactions between the TF’s trans-activation domain (TAD) and the intrinsically disordered regions (IDRs) of p300. Co-condensation enables spatially defined, all-or-none activation of p300’s catalytic activity, priming the recruitment of other coactivators including Brd4. We further revealed that co-condensation modulates transcriptional initiation rate and burst duration of target genes, underlying nonlinear and cooperative gene regulatory functions. Intriguingly, such modulation is consistent with how p300 shapes transcriptional bursting kinetics globally. Together, complementary lines of evidence suggest a new p300-mediated gene control mechanism, where TF and p300 co-condensation contributes to transcriptional bursting regulation and cooperative gene control.
Project description:Dysregulated gene expression is one of the most prevalent features in human cancers. Here, we show that most subtypes of acute myeloid leukemia (AML) depend on the aberrant assembly of the MYB transcriptional co-activator complex. By rapid and selective peptidomimetic interference with the binding of CBP/P300 to MYB, but not CREB or MLL1, we find that the leukemic functions of MYB are mediated by CBP/P300-mediated co-activation of a distinct set of transcriptional factor complexes that are aberrantly assembled with MYB in AML cells. This therapeutic remodeling is accompanied by dynamic redistribution of CBP/P300 complexes to genes that control cellular differentiation and growth. Thus, aberrantly organized transcription factor complexes control convergent gene expression programs in AML cells. These findings establish a compelling strategy for pharmacologic reprogramming of oncogenic gene expression that supports its targeting for leukemias and other human cancers caused by dysregulated gene control.
Project description:Long noncoding RNAs play important roles in the spatial and temporal regulation of muscle development and regeneration. Nevertheless, the determination of their biological functions and mechanisms underlying muscle satellite cell differentiation remains challenging. Here, we identified a novel lncRNA named lncMREF as a specific positive regulator of muscle regeneration in mice, pigs and humans. Functional studies demonstrated that lncMREF is significantly upregulated in activated skeletal muscle satellite cells and promotes myogenic differentiation and muscle regeneration. Mechanistically, lncMREF interacts with Smarca5 to promote chromatin remodeling and accessibility when muscle satellite cells are activated, thereby facilitating genomic binding of p300/H3K27 to upregulate the expression of myogenic regulators, such as MyoD and cell differentiation. Our results unravel a new temporal-specific epigenetic regulation during muscle regeneration and reveal that lncMREF/Smarca5-mediated epigenetic programming is responsible for muscle satellite cell differentiation, which provides new insights into the regulatory mechanism of muscle regeneration in adult animals.
Project description:Long noncoding RNAs play important roles in the spatial and temporal regulation of muscle development and regeneration. Nevertheless, the determination of their biological functions and mechanisms underlying muscle satellite cell differentiation remains challenging. Here, we identified a novel lncRNA named lncMREF as a specific positive regulator of muscle regeneration in mice, pigs and humans. Functional studies demonstrated that lncMREF is significantly upregulated in activated skeletal muscle satellite cells and promotes myogenic differentiation and muscle regeneration. Mechanistically, lncMREF interacts with Smarca5 to promote chromatin remodeling and accessibility when muscle satellite cells are activated, thereby facilitating genomic binding of p300/H3K27 to upregulate the expression of myogenic regulators, such as MyoD and cell differentiation. Our results unravel a new temporal-specific epigenetic regulation during muscle regeneration and reveal that lncMREF/Smarca5-mediated epigenetic programming is responsible for muscle satellite cell differentiation, which provides new insights into the regulatory mechanism of muscle regeneration in adult animals.