P300 Histone Acetyltransferase Activity Research Articles

Near infrared-responsive quinacrine-gold hybrid nanoparticles deregulate HSP-70/P300-mediated H3K14 acetylation in ER/PR+ breast cancer stem cells.

Aim: This study aimed to determine if quinacrine-gold hybrid nanoparticles (QAuNPs)+near-infrared (NIR) deregulate HSP-70/P300 complex-mediated H3K14 acetylation in estrogen receptor/progesterone receptor (ER/PR+) breast cancer stem cells(CSCs). Materials & methods: Various cells and mouse-based systems were used as models. Results: QAuNP+NIR treatment reduced the nuclear translocation of HSP-70, affectedthehistone acetyltransferase activity of P300 and specifically decreased H3K14 acetylation in ER/PR+ breast CSCs. Finally, HSP-70 knockdownshowed a reduction in P300 histone acetyltransferase activity, decreased H3K14 acetylation and inhibited activation of the TGF-β gene. Conclusion: This study revealed that QAuNP+NIR irradiation inhibits oncogenic activation of the TGF-β gene by decreasing H3K14 acetylation mediated through the HSP-70/P300 nuclear complex in ER/PR+ breast CSCs.

Anserine, a Histidine-Containing Dipeptide, Suppresses Pressure Overload-Induced Systolic Dysfunction by Inhibiting Histone Acetyltransferase Activity of p300 in Mice.

Anserine, an imidazole dipeptide, is present in the muscles of birds and fish and has various bioactivities, such as anti-inflammatory and anti-fatigue effects. However, the effect of anserine on the development of heart failure remains unknown. We cultured primary cardiomyocytes with 0.03 mM to 10 mM anserine and stimulated them with phenylephrine for 48 h. Anserine significantly suppressed the phenylephrine-induced increases in cardiomyocyte hypertrophy, ANF and BNP mRNA levels, and histone H3K9 acetylation. An in vitro histone acetyltransferase (HAT) assay showed that anserine directly suppressed p300-HAT activity with an IC50 of 1.87 mM. Subsequently, 8-week-old male C57BL/6J mice were subjected to transverse aortic constriction (TAC) and were randomly assigned to receive daily oral treatment with anserine-containing material, Marine Active® (60 or 200 mg/kg anserine) or vehicle for 8 weeks. Echocardiography revealed that anserine 200 mg/kg significantly prevented the TAC-induced increase in left ventricular posterior wall thickness and the decrease in left ventricular fractional shortening. Moreover, anserine significantly suppressed the TAC-induced acetylation of histone H3K9. These results indicate that anserine suppresses TAC-induced systolic dysfunction, at least in part, by inhibiting p300-HAT activity. Anserine may be used as a pharmacological agent for human heart failure therapy.

Regulation of HDAC11 gene expression in early myogenic differentiation.

Histone acetylation and deacetylation affect the patterns of gene expression in cellular differentiation, playing pivotal roles in tissue development and maintenance. For example, the intrinsic histone acetyltransferase activity of transcriptional coactivator p300 is especially required for the expression of myogenic regulatory factors including Myf5 and MyoD, and consequently for skeletal myogenesis. On the other hand, histone deacetylases (HDACs) remove the acetyl group from histones, which is critical for gene repression in stem cell fate transition. Through integrative omic analyses, we found that while some HDACs were differentially expressed at the early stage of skeletal myoblast differentiation, Hdac11 gene expression was significantly enhanced by nuclear receptor signaling. In addition, p300 and MyoD control Hdac11 expression in milieu of normal and signal-enhanced myoblast differentiation. Thus, HDAC11 may be essential to differential gene expression at the onset of myoblast differentiation.

Molecular features driving condensate formation and gene expression by the BRD4-NUT fusion oncoprotein are overlapping but distinct.

Aberrant formation of biomolecular condensates has been proposed to play a role in several cancers. The oncogenic fusion protein BRD4-NUT forms condensates and drives changes in gene expression in Nut Carcinoma. Here we sought to understand the molecular elements of BRD4-NUT and its associated histone acetyltransferase (HAT), p300, that promote these activities. We determined that a minimal fragment of NUT (MIN) in fusion with BRD4 is necessary and sufficient to bind p300 and form condensates. Furthermore, a BRD4-p300 fusion protein also forms condensates and drives gene expression similarly to BRD4-NUT(MIN), suggesting the p300 fusion may mimic certain features of BRD4-NUT. The intrinsically disordered regions, transcription factor-binding domains, and HAT activity of p300 all collectively contribute to condensate formation by BRD4-p300, suggesting that these elements might contribute to condensate formation by BRD4-NUT. Conversely, only the HAT activity of BRD4-p300 appears necessary to mimic the transcriptional profile of cells expressing BRD4-NUT. Our results suggest a model for condensate formation by the BRD4-NUT:p300 complex involving a combination of positive feedback and phase separation, and show that multiple overlapping, yet distinct, regions of p300 contribute to condensate formation and transcriptional regulation.

6-Shogaol, an Active Component of Ginger, Inhibits p300 Histone Acetyltransferase Activity and Attenuates the Development of Pressure-Overload-Induced Heart Failure.

Hypertrophic stress-induced cardiac remodeling is a compensatory mechanism associated with cardiomyocyte hypertrophy and cardiac fibrosis. Continuation of this response eventually leads to heart failure. The histone acetyltransferase p300 plays an important role in the development of heart failure, and may be a target for heart failure therapy. The phenolic phytochemical 6-shogaol, a pungent component of raw ginger, has various bioactive effects; however, its effect on cardiovascular diseases has not been investigated. One micromolar of 6-shogaol suppressed phenylephrine (PE)-induced increases in cardiomyocyte hypertrophy in rat primary cultured cardiomyocytes. In rat primary cultured cardiac fibroblasts, 6-shogaol suppressed transforming growth factor-beta (TGF-β)-induced increases in L-proline incorporation. It also blocked PE- and TGF-β-induced increases in histone H3K9 acetylation in the same cells and in vitro. An in vitro p300-HAT assay revealed that 6-shogaol suppressed histone acetylation. The mice underwent transverse aortic constriction (TAC) surgery, and were administered 0.2 or 1 mg/kg of 6-shogaol daily for 8 weeks. 6-shogaol prevented TAC-induced systolic dysfunction and cardiac hypertrophy in a dose-dependent manner. Furthermore, it also significantly inhibited TAC-induced increases in histone H3K9 acetylation. These results suggest that 6-shogaol may ameliorate heart failure through a variety of mechanisms, including the inhibition of p300-HAT activity.

Acetylated-PPARγ expression is regulated by different P53 genotypes associated with the adipogenic differentiation of polyploid giant cancer cells with daughter cells.

Polyploid giant cancer cells (PGCCs) with daughter cells express epithelial-mesenchymal transition (EMT)-associated proteins. Highly malignant tumor cells with EMT properties can transdifferentiate into mature tumor cells. In this study, we elucidated the potential for, and underlying mechanism of, adipogenic differentiation of PGCCs with daughter cells (PDCs). Cobalt chloride was used to induce PGCC formation in HEY (wild-type P53) and MDA-MB-231 (mutant P53) cells; these cells were then cultured in adipogenic differentiation medium. Oil red O staining was used to confirm adipogenic differentiation, and the cell cycle was detected with flow cytometry. The expression of adipogenic differentiation-associated proteins and P300 histone acetyltransferase activity were compared before and after adipogenic differentiation. Animal xenograft models were used to confirm the adipogenic differentiation of PDCs. PDCs transdifferentiated into functional adipocytes. Two different cell cycle distributions were observed in PDCs after adipogenic differentiation. The expression levels of PPARγ, Ace-PPARγ, and Ace-P53 were higher in PDCs after adipogenic differentiation than in cells before adipogenic differentiation. Ace-PPARγ and FABP4 expression increased in HEY cells and decreased in MDA-MB-231 PDCs after p53 knockdown. A485 treatment increased Ace-P53, Ace-PPARγ, and FABP4 expression in HEY PDCs by inhibiting SUMOylation of P53. In MDA-MB-231 PDCs, A485 treatment decreased Ace-P53, Ace-PPARγ, and FABP4 expression. Animal experiments also confirmed the adipogenic differentiation of PDCs. Acetylation of P53 and PPARγ plays an important role in the adipogenic differentiation of PDCs.

PS-BPB02-8: CURCUMIN, AN INHIBITOR OF P300-HAT ACTIVITY, PREVENTS HYPERTENSION-INDUCED CARDIAC HYPERTROPHY WITH PRESERVED SYSTOLIC FUNCTION IN DAHL RATS

Background: Hypertension causes left ventricular hypertrophy (LVH) with a preserved systolic function. While LVH might be a compensatory process, its presence of LVH is associated with an increased incidence of cardiovascular events and heart failure. Recently, we found that curcumin, a major curcuminoid isolated from Curcuma longa, inhibits the histone acetyltransferase (HAT) activity of p300 as well as the p300-induced acetylation of histones and a hypertrophy-responsive transcription factor, GATA-4, in cultured cardiomyocytes. Furthermore, curcumin prevents deterioration of the systolic function in rat heart failure models in vivo. However, whether curcumin prevents the development of hypertension-induced LVH at an early stage of hypertension is unclear. Objective: To solve this problem, we have utilized a salt-sensitive Dahl rat (DS) model of hypertension. Methods: We randomized 6-week-old DS (n = 19) and control salt-resistant Dahl rats (DR, n = 10) to curcumin or the vehicle group. Then, these rats were given a high-salt diet and subjected to daily oral treatment with 50 mg/kg/day of curcumin or its vehicle (1% Gum arabic) for 6 weeks. Results: There were no differences between curcumin and vehicle in any data examined before treatment (6 weeks of age). The high-salt diet-induced a similar degree of hypertension in these two groups of DS compared with DR. At 12 weeks of age, transthoracic echocardiography in the vehicle group showed that the LV wall thickness, LV mass, and LV fractional shortening were significantly higher in DS compared with DR, and the LV systolic and diastolic dimensions were significantly smaller in DS than DR. Curcumin treatment significantly (p < 0.01) decreased the LV wall thickness in DS but not DR. Curcumin also significantly (p < 0.01) decreased the LV mass in DS, but not in DR. However, LV fractional shortening in DS was similar between the two groups. Curcumin also prevented the increases in hypertension-induced myocardial cell hypertrophy and perivascular fibrosis. Furthermore, curcumin significantly attenuated the up-regulation of hypertrophy-response gene transcriptions as well as acetylation of GATA4 but not phosphorylation of ERK1/2 and GATA4 in the heart. Conclusions: The natural compound, curcumin, inhibits the development of hypertension-induced concentric LVH without affecting the systolic function through inhibition of GATA4-acetylation. Thus, this compound might be applicable to patients with early-stages hypertensive heart diseases.

Abstract 10318: Polyunsaturated Fatty Acids, EPA and DHA Possess a Potent P300-hat Inhibitor and Prevent Mi-Induced Development of Heart Failure in Rats

Introduction: The histone acetyltransferase (HAT) activity of p300 has a crucial role in the development of heart failure. Although many studies have shown a cardioprotective effect of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), omega-3 unsaturated fatty acids, little is known about the effects of these acids on cardiomyocyte hypertrophy. In this study, we investigated the effects of these acids on cardiomyocyte hypertrophy and the development of heart failure in rats with myocardial infarction (MI). Methods and Results: In cardiomyocytes, EPA and DHA (10 μM) significantly suppressed equally PE-induced cardiomyocyte hypertrophy, hypertrophy-response gene transcriptions, and acetylation of histone-H3K9. Furthermore, p300-induced hypertrophic responses were also suppressed by EPA and DHA. The result of an in vitro p300-HAT assay revealed that EPA and DHA directly inhibited p300-HAT activity (IC50: 37.8 μM, 30.6 μM) and induced allosteric inhibition of histones and competitive inhibition of acetyl-CoA in vitro . In addition, palmitic acid and stearic acid could not inhibit them. MI-operated rats (FS<40%) were randomly assigned to 3 groups; vehicle (saline), EPA, and DHA (1g/kg). One week after the operation, oral administrations were repeated for 6 weeks. The echocardiographic analysis demonstrated that both EPA and DHA treatments prevented MI-induced left ventricular remodeling with preserved FS. Furthermore, EPA and DHA significantly suppressed the MI-induced increase in myocardial cell diameter, perivascular fibrosis, mRNA levels of hypertrophic and fibrotic markers, and acetylation of histone H3K9. In the left ventricle, EPA contents were lower than those of the other fatty acids, and no difference in each group. The EPA group exhibited higher docosapentaenoic acid (DPA) and DHA content than the vehicle group. The DHA group increased DHA content but not DPA and EPA contents. Conclusion: These results suggested that both EPA and DHA suppressed MI-induced development of heart failure through the inhibition of p300-HAT activity. The cardioprotective effect of EPA on MI might be attributed to the conversion of DHA or EPA metabolites.

Methods to Evaluate the Effects of HAT/KAT Inhibition on SIAH2-Driven Reactive Oxygen Species Generation in Helicobacter pylori-Infected Gastric Epithelial Cells.

Helicobacter pylori infection is one of the leading factors that promotes, among other diseases, gastric cancer (GC). Infection of gastric epithelial cells (GECs) by H. pylori enhances the expression as well as acetylation of the E3 ubiquitin ligase SIAH2 which promotes GC progression. The histone acetyltransferase (HAT) activity of p300 catalyzes SIAH2 acetylation following H. pylori infection. Since reactive oxygen species (ROS) generation in H. pylori-infected GECs accelerates GC progression, acetylation-mediated SIAH2 regulation might be a crucial modifier of ROS generation in the infected GECs. Here, we describe a compendium of methods to evaluate the effects of HAT/lysine acetyl transferase (KAT) inhibitors (HAT/KATi) on SIAH2-mediated ROS regulation in H. pylori-infected GECs.

P300 promotes tumor recurrence by regulating radiation-induced conversion of glioma stem cells to vascular-like cells

Glioma stem cells (GSC) exhibit plasticity in response to environmental and therapeutic stress leading to tumor recurrence, but the underlying mechanisms remain largely unknown. Here, we employ single-cell and whole transcriptomic analyses to uncover that radiation induces a dynamic shift in functional states of glioma cells allowing for acquisition of vascular endothelial-like and pericyte-like cell phenotypes. These vascular-like cells provide trophic support to promote proliferation of tumor cells, and their selective depletion results in reduced tumor growth post-treatment in vivo. Mechanistically, the acquisition of vascular-like phenotype is driven by increased chromatin accessibility and H3K27 acetylation in specific vascular genes allowing for their increased expression post-treatment. Blocking P300 histone acetyltransferase activity reverses the epigenetic changes induced by radiation and inhibits the adaptive conversion of GSC into vascular-like cells and tumor growth. Our findings highlight a role for P300 in radiation-induced stress response, suggesting a therapeutic approach to prevent glioma recurrence.

SIK2 protects against renal tubular injury and the progression of diabetic kidney disease

Despite optimal medical therapy, many patients with diabetic kidney disease (DKD) progress to end-stage renal disease. The identification of new biomarkers and drug targets for DKD is required for the development of more effective therapies. The apoptosis of renal tubular epithelial cells is a key feature of the pathogenicity associated with DKD. SIK2, a salt-inducible kinase, regulates important biological processes, such as energy metabolism, cell cycle progression and cellular apoptosis. In our current study, a notable decrease in the expression of SIK2 was detected in the renal tubules of DKD patients and murine models. Functional experiments demonstrated that deficiency or inactivity of SIK2 aggravates tubular injury and interstitial fibrosis in diabetic mice. Based on transcriptome sequencing, molecular mechanism exploration revealed that SIK2 overexpression reduces endoplasmic reticulum (ER) stress-mediated tubular epithelial apoptosis by inhibiting the histone acetyltransferase activity of p300 to activate HSF1/Hsp70. Furthermore, the specific restoration of SIK2 in tubules blunts tubular and interstitial impairments in diabetic and vancomycin-induced kidney disease mice. Together, these findings indicate that SIK2 protects against renal tubular injury and the progression of kidney disease, and make a compelling case for targeting SIK2 for therapy in DKD.

The SWI/SNF chromatin remodeling factor DPF3 regulates metastasis of ccRCC by modulating TGF-β signaling

DPF3, a component of the SWI/SNF chromatin remodeling complex, has been associated with clear cell renal cell carcinoma (ccRCC) in a genome-wide association study. However, the functional role of DPF3 in ccRCC development and progression remains unknown. In this study, we demonstrate that DPF3a, the short isoform of DPF3, promotes kidney cancer cell migration both in vitro and in vivo, consistent with the clinical observation that DPF3a is significantly upregulated in ccRCC patients with metastases. Mechanistically, DPF3a specifically interacts with SNIP1, via which it forms a complex with SMAD4 and p300 histone acetyltransferase (HAT), the major transcriptional regulators of TGF-β signaling pathway. Moreover, the binding of DPF3a releases the repressive effect of SNIP1 on p300 HAT activity, leading to the increase in local histone acetylation and the activation of cell movement related genes. Overall, our findings reveal a metastasis-promoting function of DPF3, and further establish the link between SWI/SNF components and ccRCC.

750 Minocycline suppresses lipogenesis via inhibition of p300 histone acetyltransferase activity in human SZ95 sebocytes

Minocycline is a second-generation tetracycline drug that is widely used to treat a variety of infectious and inflammatory diseases such as acne vulgaris. The effects of minocycline on acne vulgaris have been primarily attributed to its anti-inflammatory effect; however, the relevance between its sebum-regulating effect and epigenetic regulation in human sebaceous glands remains unexplored. Here, we identified a potential underlying epigenetic mechanism of the sebum inhibitory effect of minocycline in human SZ95 sebocytes.

Abstract B011: P300 histone acetyltransferase mediates glioma stem cell adaptive response to therapeutic stress

Abstract Glioma stem-like and tumor cells exhibit phenotypic plasticity in response to environmental and therapeutic stress leading to tumor recurrence, but the underlying mechanisms remain largely unknown. In this study, we employed single-cell and whole transcriptomic analyses to uncover that radiation-stress induces a dynamic shift in functional states of glioma cells allowing for acquisition of vascular endothelial-like and pericyte-like cell phenotypes. These vascular-like cells provide trophic support to promote proliferation of tumor cells, and their selective depletion results in reduced tumor growth post-treatment in vivo. Mechanistically, the acquisition of vascular-like phenotype is driven by increased chromatin accessibility and H3K27 acetylation in specific vascular gene regions allowing for their increased expression post-treatment. Blocking P300 histone acetyltransferase activity using a small molecule inhibitor C646 or gene knockdown reverses the epigenetic changes induced by radiation, inhibits the adaptive conversion of GSC into vascular-like cells, reduces tumor growth and enhances animal survival. Our findings highlight an important role for P300 in mediating adaptive response of glioma stem cells to therapeutic-stress, and opens a new therapeutic avenue for preventing glioma recurrence. Citation Format: Sree Deepthi Muthukrishnan, Riki Kawaguchi, Pooja Nair, Alvaro Alvarado, Harley Kornblum. P300 histone acetyltransferase mediates glioma stem cell adaptive response to therapeutic stress [abstract]. In: Proceedings of the AACR Special Conference on the Evolutionary Dynamics in Carcinogenesis and Response to Therapy; 2022 Mar 14-17. Philadelphia (PA): AACR; Cancer Res 2022;82(10 Suppl):Abstract nr B011.

The polyunsaturated fatty acids, EPA and DHA, ameliorate myocardial infarction-induced heart failure by inhibiting p300-HAT activity in rats

While the cardioprotective functions of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and omega-3 unsaturated fatty acids have been previously demonstrated, little is known about their effects on cardiomyocyte hypertrophy. In this study, we compared the effects of EPA and DHA on hypertrophic responses in cardiomyocytes and development of heart failure in rats with myocardial infarction (MI). Both EPA and DHA significantly suppressed phenylephrine- and p300-induced cardiomyocyte hypertrophy, transcription of hypertrophy response genes, and acetylation of histone H3K9 in cardiomyocytes. EPA and DHA directly inhibited p300-histone acetyltransferase activity (IC50: 37.8 and 30.6 μM, respectively). Further, EPA- and DHA-induced allosteric inhibition of histones and competitive inhibition of acetyl-CoA, and significantly prevented p300-induced hypertrophic responses. Rats with moderate MI (left ventricular fractional shortening [FS] <40%) were randomly assigned to three groups, namely, vehicle (saline), EPA (1 g/kg), and DHA (1 g/kg). One week after the operation, rats were orally administrated with test agents for 6 weeks. Echocardiographic analysis demonstrated that both EPA and DHA treatments preserved FS and prevented MI-induced left ventricular remodeling. Furthermore, EPA and DHA significantly suppressed the MI-induced increase in myocardial cell diameter, perivascular fibrosis, mRNA levels of hypertrophic markers, fibrosis, and acetylation of histone H3K9. The effects on hypertrophic responses and the development of heart failure were not different between EPA and DHA groups. Both EPA and DHA suppressed hypertrophic responses and the development of heart failure to the same extent through the inhibition of p300-HAT activity.

Minocycline suppresses lipogenesis via inhibition of p300 histone acetyltransferase activity in human SZ95 sebocytes.

Minocycline is a second-generation tetracycline drug, which is widely used to treat diverse infectious and inflammatory diseases such as acne vulgaris. The effects of minocycline on acne vulgaris have been mainly attributed to its anti-inflammatory effect; however, its sebum-regulating effect and the relevance to epigenetic regulation in human sebaceous glands remain uninvestigated. To identify the potential underlying epigenetic mechanism of sebum-inhibitory effects of minocycline in human SZ95 sebocytes. The quantity of lipid droplets and the expression of key lipogenic genes were analysed in minocycline-treated SZ95 sebocytes. To examine whether the sebum-inhibitory effects of minocycline are relevant to histone acetylation, we analysed the effects of minocycline on p300 HAT and total HDAC activity. To elucidate the functional implication of p300 HAT inhibition by minocycline in sebocytes, we assessed the effect of p300 knockdown, inhibition and overexpression on lipid accumulation in SZ95 sebocytes. Minocycline suppressed the insulin and liver X receptor agonist-induced lipid accumulation and the expression of the key lipogenic transcription factor sterol regulatory element-binding protein 1 (SREBP1) and its downstream genes, fatty acid synthase (FAS) and acetyl-CoA carboxylase α (ACCα). Minocycline inhibited p300 HAT activity in a concentration-dependent manner, but demonstrated no effect on global HDAC activity, resulting in a significant decrease in histone acetylation. Downregulation of p300 by knockdown or inhibition significantly suppressed SREBP1 expression, histone acetylation and lipid accumulation, whereas p300 overexpression enhanced these effects. Moreover, p300 overexpression rescued minocycline-inhibited SREBP1 expression and lipid synthesis. Our findings revealed a novel sebum-regulating effect of minocycline. Moreover, as p300 HAT is a key epigenetic regulator of sebaceous lipogenesis, its inhibitors could be used for the treatment of acne vulgaris.

A Src-H3 acetylation signaling axis integrates macrophage mechanosensation with inflammatory response

Macrophages are mechanosensitive cells that can exquisitely fine-tune their function in response to their microenvironment. While macrophage polarization results in concomitant changes in cell morphology and epigenetic reprogramming, how biophysically-induced signaling cascades contribute to gene regulatory programs that drive polarization remains unknown. We reveal a cytoskeleton-dependent Src-H3 acetylation (H3Ac) axis responsible for inflammation-associated histone hyperacetylation. Inflammatory stimuli caused increases in traction forces, Src activity and H3Ac marks in macrophages, accompanied by reduced cell elongation and motility. These effects were curtailed following disruption of H3Ac-signaling through either micropattern-induced cell elongation or inhibition of H3Ac readers (BRD proteins) directly. Src activation relieves the suppression of p300 histone acetyltransferase (HAT) activity by PKCδ. Furthermore, while inhibition of Src reduced p300 HAT activity and H3Ac marks globally, local H3Ac levels within the Src promoter were increased, suggesting H3Ac regulates Src levels through feedback. Together, our study reveals an adhesome-to-epigenome regulatory nexus underlying macrophage mechanosensation, where Src modulates H3Ac-associated epigenetic signaling as a means of tuning inflammatory gene activity and macrophage fate decisions in response to microenvironmental cues.

Nuclear condensates of p300 formed though the structured catalytic core can act as a storage pool of p300 with reduced HAT activity

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 histone acetyltransferase (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.

OMRT-5. Therapy-induced reprogramming drives glioma vascular transdifferentiation and recurrence

Therapy-resistant glioma cells elicit remarkable phenotypic plasticity leading to aggressive tumor recurrence. Here, we used single-cell and whole transcriptomic sequencing to uncover that radiation treatment induces a dynamic shift in functional states of glioma cells allowing for acquisition of either stem-like, mesenchymal-like or vascular-like phenotypes. The predominant phenotype switch induced by radiation in surviving tumor cells is the vascular-like cell state, resulting in transdifferentiation to endothelial-like and pericyte-like cells in distinct cell clusters. The transdifferentiated endothelial-like and pericyte-like cells secrete trophic factors to support proliferation of tumor cells, and their selective ablation results in reduced tumor growth and recurrence post-treatment. Mechanistically, the acquisition of vascular-like phenotype is driven by increased acetylation and chromatin accessibility in vascular genes and in regions for binding of vascular specification transcription factors. Blocking histone acetylation using a small molecule inhibitor targeting P300 histone acetyltransferase activity prior to radiation treatment inhibits the vascular-like transdifferentiation of glioma cells and tumor growth. Our findings indicate that radiation therapy-induces rewiring of glioma cells that promotes vascular cell-like transdifferentiation, tumor growth and recurrence.

Carnosol Is a Novel Inhibitor of p300 Acetyltransferase in Breast Cancer.

Carnosol, a natural polyphenol abundant in edible plants such as sage, rosemary, and oregano, has shown promising anticancer activity against various types of cancers. Nonetheless, very little is known about its molecular mechanism of action or its downstream target(s). We have previously shown that carnosol inhibits cellular proliferation, migration, invasion, and metastasis as well as triggers autophagy and apoptosis in the highly invasive MDA-MB-231 breast cancer cells. Here, we report that carnosol induces histone hypoacetylation in MDA-MB-231 and Hs578T breast cancer cells. We show that, while carnosol does not affect HDACs, it promotes a ROS-dependent proteasome degradation of p300 and PCAF histone acetyl transferases (HATs) without affecting other HATs such as GCN5 and hMOF. Carnosol-induced histone hypoacetylation remains persistent even when p300 and PCAF protein levels were rescued from degradation by (i) the inhibition of the proteasome activity by the proteasome inhibitors MG-132 and bortezomib, and (ii) the inhibition of ROS accumulation by the ROS scavenger, N-acetylcysteine. In addition, we report that, in a cell-free system, carnosol efficiently inhibits histone acetyltransferase activity of recombinant p300 but not that of PCAF or GCN5. Molecular docking studies reveal that carnosol inhibits p300 HAT activity by blocking the entry of the acetyl-CoA binding pocket of the catalytic domain. The superimposition of the docked conformation of the p300 HAT domain in complex with carnosol shows a similar orientation as the p300 structure with acetyl-CoA. Carnosol occupies the region where the pantetheine arm of the acetyl-CoA is bound. This study further confirms carnosol as a promising anti-breast cancer therapeutic compound and identifies it as a novel natural p300 inhibitor that could be added to the existing panel of inhibitors.