Brg1 Overexpression Research Articles

BRG1 mediates epigenetic regulation of TNFα-induced CCL2 expression in oral tongue squamous cell carcinoma cells.

Strong evidence has indicated that upregulation of chemokine (CC motif) ligand-2 (CCL2) expression and the presence of an inflammatory tumor microenvironment significantly contribute to the migratory and invasive properties of oral squamous cell carcinoma, specifically oral tongue squamous cell carcinoma (OTSCC). However, the precise epigenetic mechanism responsible for enhanced CCL2 expression in response to the inflammatory mediator tumor necrosis factor alpha (TNF-α) in OTSCC remains inadequately elucidated. We have demonstrated that the production of CCL2 can be induced by TNF-α, and this induction is mediated by the chromatin remodel protein BRG1. Through the use of a chromatin immunoprecipitation (ChIP) assay, we have found that BRG1 was involved in the recruitment of acetylated histones H3 and H4 at the CCL2 promoter, thereby activating TNF-α-induced CCL2 transcription. Furthermore, we have observed that recruitment of NF-κB p65 to the CCL2 promoter was increased following BRG1 overexpression and decreased after BRG1 knockdown in OTSCC cells. Our Re-ChIP assay has shown that BRG1 knockdown completely inhibits the recruitment of both acetylated histone H3 or H4 and NF-κB to the CCL2 promoter. In summary, the findings of our study demonstrate that BRG1 plays a significant role in mediating the production of CCL2 in OTSCC cells in response to TNF-α stimulation. This process involves the cooperative action of acetylated histone and NF-κB recruitment to the CCL2 promoter site. Our data suggest that BRG1 serves as a critical epigenetic mediator in the regulation of TNF-α-induced CCL2 transcription in OTSCC cells.

Examining the effects of BRG1 over-expression on Candida albicans strains growing as pseudohyphae.

The pathogen Candida albicans is pleiomorphic and grows in yeast and filamentous forms but the relationship between the regulation of different filamentous forms is unclear. BRG1 encodes a DNA binding protein which is an important regulator of morphology. Mutants lacking BRG1 grow as yeast under all conditions tested and over-expressing BRG1 drives hyphal growth even in the absence of inducing signals. A number of genetic mutants in repressors of filamentation form pseudohyphae under yeast conditions and some of these mutants can form hyphae under hypha-inducing conditions. This study examines the position of BRG1 in the regulatory networks that govern filamentation by examining the effect of over-expressing BRG1 in pseudohyphal mutants.

Chromatin-Remodeling Factor BRG1 Is a Negative Modulator of L. donovani in IFNγ Stimulated and Infected THP-1 Cells.

Intracellular pathogens manipulate the host cell for their own survival by contributing to modifications of host epigenome, and thus, altering expression of genes involved in the pathogenesis. Both ATP-dependent chromatin remodeling complex and histone modifications has been shown to be involved in the activation of IFNγ responsive genes. Leishmania donovani is an intracellular pathogen that causes visceral leishmaniasis. The strategies employed by Leishmania donovani to modulate the host epigenome in order to overcome the host defense for their persistence has been worked out in this study. We show that L. donovani negatively affects BRG1, a catalytic subunit of mammalian SWI/SNF chromatin remodeling complex, to alter IFNγ induced host responses. We observed that L. donovani infection downregulates BRG1 expression both at transcript and protein levels in cells stimulated with IFNγ. We also observed a significant decrease in IFNγ responsive gene, Class II transactivator (CIITA), as well as its downstream genes, MHC-II (HLA-DR and HLA-DM). Also, the occupancy of BRG1 at CIITA promoters I and IV was disrupted. A reversal in CIITA expression and decreased parasite load was observed with BRG1 overexpression, thus, suggesting BRG1 is a potential negative regulator for the survival of intracellular parasites in an early phase of infection. We also observed a decrease in H3 acetylation at the promoters of CIITA, post parasite infection. Silencing of HDAC1, resulted in increased CIITA expression, and further decreased parasite load. Taken together, we suggest that intracellular parasites in an early phase of infection negatively regulates BRG1 by using host HDAC1 for its survival inside the host.

Activation of Akt-dependent Nrf2/ARE pathway by restoration of Brg-1 remits high glucose-induced oxidative stress and ECM accumulation in podocytes.

Brahma-related gene 1 (Brg-1) is perceived as a cytoprotective protein due to its role in alleviating oxidative stress and apoptosis. Our study aimed to explore the role and mechanism of Brg-1 in high glucose (HG)-stimulated podocytes. The HG exposure downregulated Brg-1 and inactivated the protein kinase B (Akt) pathway in podocytes. Restoration of Brg-1 inhibited HG-induced viability reduction of podocytes. The HG-induced increase of reactive oxygen species and malondialdehyde levels and decrease of superoxide dismutase activity in podocytes were reversed by the Brg-1 overexpression. The Brg-1 overexpression terminated the HG-induced production of fibronectin, collagen IV, transforming growth factor-β1, and connective tissue growth factor. In addition, the Brg-1 overexpression activated Akt-dependent nuclear factor E2-related factor 2 (Nrf2)/antioxidant response element (ARE) signaling in HG-stimulated podocytes. However, inhibition of the Akt pathway or Nrf2 silencing counteracted the protective effects of Brg-1 in HG-stimulated podocytes. In conclusion, the Brg-1 overexpression suppressed HG-induced oxidative stress and extracellular matrix accumulation by activation of Akt-dependent Nrf2/ARE signaling in podocytes.

T3 Critically Affects the Mhrt/Brg1 Axis to Regulate the Cardiac MHC Switch: Role of an Epigenetic Cross-Talk.

The LncRNA my-heart (Mhrt) and the chromatin remodeler Brg1 inhibit each other to respectively prevent or favor the maladaptive α-myosin-heavy-chain (Myh6) to β-myosin-heavy-chain (Myh7) switch, so their balance crucially guides the outcome of cardiac remodeling under stress conditions. Even though triiodothyronine (T3) has long been recognized as a critical regulator of the cardiac Myh isoform composition, its role as a modulator of the Mhrt/Brg1 axis is still unexplored. Here the effect of T3 on the Mhrt/Brg1 regulatory circuit has been analyzed in relation with chromatin remodeling and previously identified T3-dependent miRNAs. The expression levels of Mhrt, Brg1 and Myh6/Myh7 have been assessed in rat models of hyperthyroidism or acute myocardial ischemia/reperfusion (IR) treated with T3 replacement therapy. To gain mechanistic insights, in silico analyses and site-directed mutagenesis have been adopted in combination with gene reporter assays and loss or gain of function strategies in cultured cardiomyocytes. Our results indicate a pivotal role of Mhrt over-expression in the T3-dependent regulation of Myh switch. Mechanistically, T3 activates the Mhrt promoter at two putative thyroid hormone responsive elements (TRE) located in a crucial region that is necessary for both Mhrt activation and Brg1-dependent Mhrt repression. This newly identified T3 mode of action requires DNA chromatinization and is critically involved in mitigating the repressive function of the Brg1 protein on Mhrt promoter. In addition, T3 is also able to prevent the Brg1 over-expression observed in the post-IR setting through a pathway that might entail the T3-mediated up-regulation of miR-208a. Taken together, our data evidence a novel T3-responsive network of cross-talking epigenetic factors that dictates the cardiac Myh composition and could be of great translational relevance.

Upregulation of heme oxygenase-1 by Brahma-related gene 1 through Nrf2 signaling confers protective effect against high glucose-induced oxidative damage of retinal ganglion cells

High glucose (HG)-induced oxidative damage of retinal ganglion cells (RGCs) contributes to the pathogenesis of diabetic retinopathy, a severe complication of diabetes mellitus. Brahma-related gene 1 (Brg1) has currently emerged as a cytoprotective protein that alleviates oxidative damage induced by various stress. However, whether Brg1 is involved in the regulation of HG-induced oxidative damage of RGCs remains unknown. In this study, we aimed to investigate the potential role and underlying mechanism of Brg1 in regulating HG-induced damage of RGCs. We found that Brg1 expression was significantly downregulated in RGCs in response to HG treatment. Functional experiments showed that Brg1 knockdown enhanced HG-induced apoptosis and production of reactive oxygen species, while Brg1 overexpression suppressed HG-induced apoptosis and reactive oxygen species production, showing a protective effect. Moreover, Brg1 overexpression resulted in an increase in nuclear expression of nuclear factor-erythroid-2-related factor-2 (Nrf2) and the expression of heme oxygenase-1 (HO-1) in RGCs. Notably, inhibition of Nrf2 or HO-1 significantly blocked Brg1-mediated protection against HG-induced damage. Overall, these findings demonstrate that Brg1 protects RGCs from HG-induced oxidative damage through promotion of Nrf2/HO-1 signaling, indicating a potential role of Brg1 in the pathogenesis of diabetic retinopathy.

The long noncoding RNA THRIL knockdown protects hypoxia-induced injuries of H9C2 cells through regulating miR-99a.

Myocardial infarction (MI) is a leading cause of disease with high morbidity and mortality worldwide. Recent studies have revealed that long non-coding RNAs (lncRNAs) are involved in heart disease pathogenesis. This study aimed to investigate the effect and the molecular basis of THRIL on hypoxia-injured H9C2 cells. THRIL, miR-99a and Brahma-related gene 1 (Brg1) expressions in H9C2 cells were altered by transient transfections. The cells were subjected to hypoxia for 4 h, and then the levels of THRIL, miR-99a and Brg1 were investigated. Cell viability, migration and invasion, and apoptotic cells were respectively measured by trypan blue exclusion assay, transwell migration assay and flow cytometry assay. Dual luciferase reporter assay was conducted to verify the interaction between miR-99a and THRIL. Furthermore, levels of apoptosis-, PI3K/AKT and mTOR pathways-related factors were measured by western blotting. Hypoxia induced an increase of THRIL but a reduction of miR-99a and Brg1. THRIL inhibition significantly attenuated hypoxia-induced cell injuries, as increased cell viability, migration and invasion, and decreased cell apoptosis. THRIL negatively regulated miR-99a expression through sponging with miR-99a binding site, and miR-99a inhibition abolished the protective effects of THRIL knockdown against hypoxia-induced injury in H9C2 cells. Furthermore, miR-99a positively regulated the expression of Brg1. Brg1 inhibition promoted hypoxia-induced cell injuries, while Brg1 overexpression alleviated hypoxia-induced cell injuries. Moreover, Brg1 overexpression activated PI3K/AKT and mTOR pathways. This study demonstrated that THRIL inhibition represented a protective effect against hypoxia-induced injuries in H9C2 cells by up-regulating miR-99a expression.

Abstract 578: Brg1 Protects Cardiomyocytes Against Oxidative Damage Through Activation of the Nrf2 Signaling Pathway in Acute Myocardial Infarction

Background: Brahma-related gene 1 (Brg1), the core ATPase subunit of a large chromatin remodeling complex, plays critical role in the regulation of gene expression during cardiac growth, differentiation. In adults, Brg1 is turned off in cardiomyocytes and reactivated by cardiac stress. How Brg1 in myocardial infarction (MI) is poorly understood. The Keap1-Nrf2-ARE pathway plays an important role in the development of MI. However, by which Nrf2 activation is mediated in MI still remains to be determined. Methods and results: In vivo, adult male C57BL/6 mice were subjected to ligation of the left anterior descending coronary artery for MI model. Our data demonstrated that in peri-infarct zone, the protein of Brg1 was significantly increased 7 days after MI compared with the sham group, accompanied by Nrf2 nuclear translocation, and upregulation of the expressions of NQO1, GSTP1, HO1. We further revealed that with adenoviral intramyocardial injection, the Brg1 overexpression reduced the percentage myocardial infarct, improved cardiac dysfunction, decreased the relative fluorescence intensity of ROS with fluorescent probe DHE in MI mice. Conversely, shRNA-mediated knockdown of Brg1 enlarged the percentage myocardial infarct, exacerbated cardiac dysfunction, increased the relative fluorescence intensity of ROS. More importantly, the Brg1 overexpression significantly induced Nrf2 translocation from cytoplasm to nuclear and upregulated NQO1, GSTP1 and HO1 expressions. Whereas Brg1 knockdown decreased the level of Nrf2 protein in the nucleus, suppressed NQO1,GSTP1 and HO1 expressions. In vitro, Oxygen-Glucose deprivation(OGD) on neonatal cardiomyocytes was established. The effects of Brg1 on OGD and Nrf2 activation were observed with gain- and loss-of-function approaches to regulate Brg1 expression. The results were consistent with in vivo study. Moreover, the down-regulation of Nrf2 by brusatol inhibited the increase of these antioxidative genes induced by Brg1 overexpression. Conclusions: This study indicated that Brg1-induced cardiac protection was partially mediated through transcription activator Nrf2. The Brg1-Nrf2-ARE pathway may represent a novel therapeutic target for preventing cardiac dysfunction in patients with MI.

Propofol alleviates oxidative stress via upregulating lncRNA-TUG1/Brg1 pathway in hypoxia/reoxygenation hepatic cells.

Reducing oxidative stress is an effective method to prevent hepatic ischaemia/reperfusion injury (HIRI). This study focuses on the role of propofol on the oxidative stress of hepatic cells and the involved lncRNA-TUG1/Brahma-related gene 1 (Brg1) pathway in HIRI mice. The mouse HIRI model was established and was intraperitoneally injected with propofol postconditioning. Hepatic injury indexes were used to evaluate HIRI. The oxidative stress was indicated by increasing 8-isoprostane concentration. Mouse hepatic cell line AML12 was treated with hypoxia and subsequent reoxygenation (H/R). The targeted regulation of lncRNA-TUG1 on Brg1 was proved by RNA pull-down, RIP (RNA-binding protein immunoprecipitation) and the expression level of Brg1 responds to silencing or overexpression of lncRNA-TUG1. Propofol alleviates HIRI and induces the upregulation of lncRNA-TUG1 in the mouse HIRI model. Propofol increases cell viability and lncRNA-TUG1 expression level in H/R-treated hepatic cells. In H/R plus propofol-treated hepatic cells, lncRNA-TUG1 silencing reduces cell viability and increased oxidative stress. LncRNA-TUG1 interacts with Brg1 protein and keeps its level via inhibiting its degradation. Brg1 overexpression reverses lncRNA-TUG1 induced the reduction of cell viability and the increase in oxidative stress. LncRNA-TUG1 silencing abrogates the protective role of propofol against HIRI in the mouse HIRI model. LncRNA-TUG1 has a targeted regulation of Brg1, and thereby affects the oxidative stress induced by HIRI. This pathway mediates the protective effect of propofol against HIRI of hepatic cell.

The chromatin remodeling protein BRG1 links ELOVL3 trans-activation to prostate cancer metastasis

Prostate cancer malignancies are intimately correlated with deregulated fatty acid metabolism. The underlying epigenetic mechanism is not fully understood. In the present study we investigated the mechanism whereby the chromatin remodeling protein BRG1 regulates the transcription of long-chain fatty acid elongase 3 (Elovl3) in prostate cancer cells. We report that in response to pro-metastatic cues (androgen and TGF-β) BRG1 expression was up-regulated along with Elvol3 in prostate cancer cells. BRG1 over-expression potentiated whereas BRG1 knockdown attenuated prostate cancer cell migration and invasion. Coincidently, Elovl3 was up-regulated following BRG1 over-expression and down-regulated after BRG1 knockdown in prostate cancer cells. Further analysis revealed that BRG1 interacted with and was recruited by retinoic acid receptor-related orphan receptor (RORγ) to the Elovl3 promoter to activate transcription. Chromatin immunoprecipitation (ChIP) profiling demonstrated that BRG1 interacted with histone acetyltransferase p300 to activate Elovl3 transcription. Depletion of p300 by siRNA or inhibition of p300 by curcumin attenuated Elovl3 trans-activation in prostate cancer cells. Together, our data identify a novel epigenetic pathway that links Elovl3 transcription to prostate cancer cell migration and invasion.

Overexpression of Brg1 alleviates high glucose-induced retinal ganglion cell apoptosis though regulating Notch/Hes1 signaling

High glucose (HG)-caused damage of retinal ganglion cells (RGCs) plays an important role in the pathogenesis of diabetic retinopathy, a common and severe complication of diabetes mellitus. Accumulating evidence has reported that brahma-related gene 1 (Brg1) exerts a cytoprotective role in protection of cells from various injuries. In this study, we investigated the role of Brg1 in regulating HG-induced injury of RGCs. We found that RGCs treated with HG exhibited a low expression level of Brg1 compared with untreated RGCs. Gain-of-function experiments showed that Brg1 overexpression significantly improved the viability and reduced the apoptosis of RGCs exposed to HG. Notably, our data revealed that Brg1 overexpression increased the expression of Notch ligands, including Jagged 1, Jagged 2, Delta-like 1, and Delta-like 4. Moreover, Brg1 overexpression upregulated the expression of Notch1 intracellular domain (NICD) and Hes1, which resulted in activation of Notch signaling. Blockade of Notch signaling partially reversed Brg1-mediated protection effect in HG-treated RGCs, while overexpression of NICD significantly attenuated the promotion effect of Brg1 silencing on HG-induced injury in RGCs. Taken together, these results suggest that Brg1 protects RGCs against HG-induced injury through enhancing the activation of Notch signaling, suggesting a potential target for preserving RGCs in diabetic retinopathy.

Propofol post‐conditioning alleviates hepatic ischaemia reperfusion injury via BRG1‐mediated Nrf2/HO‐1 transcriptional activation in human and mice

To explore the effects of propofol post‐conditioning (PPC) on hepatic ischaemia/reperfusion injury (HIRI) and the potential mechanisms that might be involved in the interaction of Brahma‐related gene1(BRG1) and Nuclear‐related factor 2(Nrf2). Patients were randomized into PPC(n = 16) and non‐PPC(NPC)( n = 21) groups. Propofol(2 mg/kg) was infused within 10 min. of the onset of liver reperfusion during liver transplantation in the PPC group. Liver function tests, as well as Brg1, Nrf2, Heme oxygenase‐1(HO‐1) and NADPH:quinone oxidoreductase1(NQO1) expression levels were evaluated. CMV‐Brg1 mice were designed to investigate the role of Brg1 overexpression during HIRI. Brg1 and Nrf2 siRNA were used to examine the relationship between Brg1 and Nrf2/HO‐1 pathways in propofol‐mediated effects in a human hepatocyte(L02) hypoxia/reoxygenation(H/R) model. In patients, PPC attenuated both donor liver pathological and function injury, and reducing oxidative stress markers, compared to the NPC group, 24 hrs after surgery. PPC increased liver Brg1, Nrf2, HO‐1 and NQO1 expression. In mice, PPC reduced HIRI by decreasing liver oxidative stress and activating Nrf2/HO‐1 pathway, accompanied by up‐regulation of BRG1 expression. BRG1 overexpression activated Nrf2/HO‐1 transcription in CMV‐BRG1 mice during HIRI. In vitro, PPC significantly elevated expression of Nrf2, HO‐1 and NQO1, resulting in a reduction of cell DCFH‐DA and 8‐isoprostane levels and decreased lactate dehydrogenase levels, leading to an overall increase in cell viability. Moreover, the protective effects of propofol were partially abrogated in Nrf2‐knock‐down or BRG1‐knock‐down hepatocytes. Nrf2‐knock‐down drastically reduced protein expression of HO‐1 and NQO1, while Brg1‐knock‐down decreased HO‐1 expression. Propofol post‐conditioning alleviates HIRI through BRG1‐mediated Nrf2/HO‐1 transcriptional activation.

Abstract 450: Brg1 Attenuates Cardiac Dysfunction by Activating Sonic Hedgehog Pathway in Acute Myocardial Infarction

Background: Brahma-related gene 1 (Brg1), the core ATPase subunit of a large chromatin remodeling complex, plays critical role in the regulation of gene expression during cardiac growth, differentiation. In adults, Brg1 is turned off in cardiomyocytes and reactivated by cardiac stress. How Brg1 in myocardial infarction (MI) is poorly understood. The sonic hedgehog (Shh) pathway was activated to protect the injured cardiomyocytes during the development of MI. However, by which Shh activation is mediated in MI still remains to be determined. Methods and results: Adult male C57BL/6 mice were subjected to ligation of the left anterior descending coronary artery for MI model. We investigated Brg1 activation and how it regulated the gene expressions of Shh pathway in peri-infarct zone in MI mice. Our data demonstrated that in peri-infarct zone, the protein of Brg1 was significantly increased 7 days after MI compared with the sham group in control mice, accompanied by upregulation of shh, patched-1 (Ptch1), and glioma-associated oncogene-1(Gli1). We further revealed that with adenoviral intramyocardial injection, the Brg1 overexpression reduced the percentage myocardial infarct, improved cardiac dysfunction, decreased the number of apoptotic cells and upregulated the ratio of Bcl-2/Bax in MI mice. Conversely, shRNA-mediated knockdown of Brg1 enlarged the percentage myocardial infarct, exacerbated cardiac dysfunction, increased the apoptotic cells and downregulated the ratio of Bcl-2/Bax. More importantly, the Brg1 overexpression increased Shh, Ptch1 and Gli1 expressions, whereas Brg1 knockdown suppressed Shh, Ptch1 and Gli1 expressions. Chromatin immunoprecipitation confirmed that Brg1 were recruited to the regulatory elements of Shh, Ptch1 and Gli1. This recruitment was associated with transcriptional upregulation of these three genes. Conclusions: This study indicated that in MI mice, the myocardial Brg1 is upregulated and that the upregulated Brg1 contributes to protection of cardiac function and activation of Shh pathway. Strategies that are aimed at augment the Brg1-Shh pathway may offer useful means for preventing and treating cardiac dysfunction in patients with MI. Key words: Acute myocardial infarction, Brg1, Shh pathway

Brg1-mediated Nrf2/HO-1 pathway activation alleviates hepatic ischemia\u2013reperfusion injury

Cytoprotective gene heme oxygenase 1 (HO-1) could be induced by nuclear factor E2-related factor 2 (Nrf2) nuclear translocation. The purpose of this study was to determine the role of Brahma-related gene 1 (Brg1), a catalytic subunit of SWI2/SNF2-like chromatin remodeling complexes, in Nrf2/HO-1 pathway activation during hepatic ischemia–reperfusion (HIR). Our results showed that hepatic Brg1 was inhibited during early HIR while Brg1 overexpression reduced oxidative injury in CMV-Brg1 mice subjected to HIR. Moreover, promoter-driven luciferase assay showed that overexpression of Brg1 by adenovirus transfection in AML12 cells selectively enhanced HO-1 gene expression after hypoxia/reoxygenation (H/R) treatment but did not affect the other Nrf2 target gene NQO1. Furthermore, inhibition of HO-1 by the selective HO-1 inhibitor zinc protoporphyria could partly reverse the hepatic protective effects of Brg1 overexpression while HO-1-Adv attenuated AML12 cells H/R damage. Further, chromatin immunoprecipitation analysis revealed that Brg1 overexpression, which could significantly increase the recruitment of Brg1 protein to HO-1 but not NQO1 promoter, was recruited by Nrf2 to the HO-1 regulatory regions in AML12 hepatocytes subjected to H/R. In conclusion, our results demonstrated that restoration of Brg1 during reperfusion could enhance Nrf2-mediated inducible expression of HO-1 during HIR to effectively increase antioxidant ability to combat against hepatocytes damage.

Overexpression of Brg1 Alleviates Hepatic Ischemia/Reperfusion-Induced Acute Lung Injury through Antioxidative Stress Effects.

Aim To investigate whether overexpression of Brahma-related gene-1 (Brg1) can alleviate lung injury induced by hepatic ischemia/reperfusion (HIR) and its precise mechanism. Methods Cytomegalovirus-transgenic Brg1-overexpressing (CMV-Brg1) mice and wild-type (WT) C57BL/6 mice underwent HIR. Lung histology, oxidative injury markers, and antioxidant enzyme concentrations in the lung were assessed. The protein expression levels of Brg1, nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), and NAD(P)H:quinone oxidoreductase 1 (NQO1) in the lung were analyzed by Western blotting. Results In the WT group, histopathological analysis revealed that lung damage peaked at 6 h after HIR. Meanwhile, the lung reactive oxygen species (ROS) and 8-isoprostane levels were significantly increased. The protein expression of Brg1 in lung tissue decreased to a minimum at 6 h. Overexpression of Brg1 alleviated lung injury and decreased the amounts of oxidative products, including the levels of 8-isoprostane and ROS, as well as the percentage of positive cells for 4-hydroxynonenal (4-HNE) and 8-oxo-2′-deoxyguanosine (8-OHdG). Brg1 overexpression increased the expression and nuclear translocation of Nrf2 as well as activated the antioxidases. In addition, it decreased the expression of inflammatory factors. Conclusion Overexpression of Brg1 alleviates oxidative lung injury induced by HIR, likely through the Nrf2 pathway.

DNA demethylation induces SALL4 gene re-expression in subgroups of hepatocellular carcinoma associated with Hepatitis B or C virus infection.

Sal-like protein 4 (SALL4), an embryonic stem cell transcriptional regulator, is re-expressed by an unknown mechanism in poor prognosis hepatocellular carcinoma (HCC), often associated with chronic hepatitis B virus (HBV) infection. Herein, we investigated the mechanism of SALL4 re-expression in HBV-related HCCs. We performed bisulfite sequencing PCR of genomic DNA isolated from HBV-related HCCs and HBV replicating cells, and examined DNA methylation of a CpG island located downstream from SALL4 transcriptional start site (TSS). HBV-related HCCs expressing increased SALL4 exhibited demethylation of specific CpG sites downstream of SALL4 TSS. Similarly, SALL4 re-expression and demethylation of these CpGs was observed in HBV replicating cells. SALL4 is also re-expressed in poor prognosis HCCs of other etiologies. Indeed, increased SALL4 expression in hepatitis C virus-related HCCs correlated with demethylation of these CpG sites. To understand how CpG demethylation downstream of SALL4 TSS regulates SALL4 transcription, we quantified by chromatin immunoprecipitation (ChIP) assays RNA polymerase II occupancy of SALL4 gene, as a function of HBV replication. In absence of HBV replication, RNA polymerase II associated with SALL4 exon1. By contrast, in HBV replicating cells RNA polymerase II occupancy of all SALL4 exons increased, suggesting CpG demethylation downstream from SALL4 TSS influences SALL4 transcriptional elongation. Intriguingly, demethylated CpGs downstream from SALL4 TSS are within binding sites of octamer-binding transcription factor 4 (OCT4) and signal transducer and activator of transcription3 (STAT3). ChIP assays confirmed occupancy of these sites by OCT4 and STAT3 in HBV replicating cells, and sequential ChIP assays demonstrated co-occupancy with chromatin remodeling BRG1/Brahma-associated factors. BRG1 knockdown reduced SALL4 expression, whereas BRG1 overexpression increased SALL4 transcription in HBV replicating cells. We conclude demethylation of CpGs located within OCT4 and STAT3 cis-acting elements, downstream of SALL4 TSS, enables OCT4 and STAT3 binding, recruitment of BRG1, and enhanced RNA polymerase II elongation and SALL4 transcription.

BRG1 Expression in Diffuse Large B Cell Lymphoma (DLBCL) Is Associated with Advanced Disease Stage

Background: BRG1 is a component of the highly conserved multisubunit, 2.0-MDa mammalian transcriptional coactivator complex SWI/SNF. This chromatin-remodeling complex is critical for the regulation of gene transcription, thereby controlling diverse cellular processes including differentiation, proliferation, tumorigenesis and DNA repair. BRG1 gene is frequently down regulated or conversely, in some cases, up regulated in cancer cell lines and tumors, implicating that BRG1 may regulate cancer proliferation and progression. BRG1 is currently considered a potential selective therapeutic target. BRG1 expression level has been related to cancer cell migration and invasion and studies have suggested that BRG1 may serve as a prognostic marker in certain cancers. Few studies exist on expression of BRG1 in lymphoproliferative disorders and diffuse large B cell lymphoma (DLBCL) in particular. Our study was aimed at determining the immunohistochemical expression of the BRG1 protein in DLBCL and its potential association with clinicopathologic variables.Design: Formalin-fixed, paraffin embedded sections from 49 Diffuse Large B-cell Lymphomas (DLBCL), were immunostained by a manual method (DAKO LSAB+ System-HRP) using rabbit monoclonal BRG1 (Abcam, Cambridge, MA) antibody. Nuclear and cytoplasmic immunoreactivity was semiquantitatively assessed in all cases. Scoring was based on staining intensity (weak, moderate, intense) and percentage of positive tumor cells (focal <= 10%, regional 11-50%, diffuse >50%). Results were correlated with clinicopathologic variables.Results: BRG1 immunoreactivity was predominately nuclear. Intense diffuse nuclear BRG1 overexpression was observed in 22/49 (45%) cases and correlated with tumor stage [73% stage 4 vs 63% stage 3 vs 40% stage 2 vs 13% stage 1, (p=0.005)]. There were no other correlations that reached statistical significance.Conclusion: BRG1 nuclear expression is increased in DLBCL and is associated with advanced tumor stage. This association with an important adverse prognostic indicator warrants further study of BRG1 expression and its potential as a selective therapeutic target in DLBCL. DisclosuresNo relevant conflicts of interest to declare.

BRG1 Is Required for Formation of Senescence-Associated Heterochromatin Foci Induced by Oncogenic RAS or BRCA1 Loss

Cellular senescence is an important tumor suppression mechanism. We have previously reported that both oncogene-induced dissociation of BRCA1 from chromatin and BRCA1 knockdown itself drive senescence by promoting formation of senescence-associated heterochromatin foci (SAHF). However, the molecular mechanism by which BRCA1 regulates SAHF formation and senescence is unclear. BRG1 is a chromatin-remodeling factor that interacts with BRCA1 and pRB. Here we show that BRG1 is required for SAHF formation and senescence induced by oncogenic RAS or BRCA1 loss. The interaction between BRG1 and BRCA1 is disrupted during senescence. This correlates with an increased level of chromatin-associated BRG1 in senescent cells. BRG1 knockdown suppresses the formation of SAHF and senescence, while it has no effect on BRCA1 chromatin dissociation induced by oncogenic RAS, indicating that BRG1 functions downstream of BRCA1 chromatin dissociation. Furthermore, BRG1 knockdown inhibits SAHF formation and senescence induced by BRCA1 knockdown. Conversely, BRG1 overexpression drives SAHF formation and senescence in a DNA damage-independent manner. This effect depends upon BRG1's chromatin-remodeling activity as well as the interaction between BRG1 and pRB. Indeed, the interaction between BRG1 and pRB is enhanced during senescence. Chromatin immunoprecipitation analysis revealed that BRG1's association with the human CDKN2A and CDKN1A gene promoters was enhanced during senescence induced by oncogenic RAS or BRCA1 knockdown. Consistently, knockdown of pRB, p21(CIP1), and p16(INK4a), but not p53, suppressed SAHF formation induced by BRG1. Together, these studies reveal the molecular underpinning by which BRG1 acts downstream of BRCA1 to promote SAHF formation and senescence.

BRG1 and NRG1 form a novel feedback circuit regulating Candida albicans hypha formation and virulence

In the opportunistic fungal pathogen Candida albicans both cellular morphology and the capacity to cause disease are regulated by the transcriptional repressor Nrg1p. One of the genes repressed by Nrg1p is BRG1, which encodes a putative GATA family transcription factor. Deletion of both copies of this gene prevents hypha formation. We discovered that BRG1 overexpression is sufficient to overcome Nrg1p-mediated repression and drive the morphogenetic shift from yeast to hyphae even in the absence of environmental stimuli. We further observed that expression of BRG1 influences the stability of the NRG1 transcript, thus controlling filamentation through a feedback loop. Analysis of this phenomenon revealed that BRG1 expression is required for the induction of an antisense NRG1 transcript. This is the first demonstration of a role for mRNA stability in regulating the key C. albicans virulence trait: the ability to form hyphae.

Abstract 3956: BRCA1 chromatin dissociation induced by oncogene activation promotes formation of senescence-associated heterochromatin foci and senescence via chromatin remodeling factor BRG1

Abstract Background: Cellular senescence is a state of irreversible cell growth arrest that is an important tumor suppression mechanism in vivo. Activation of oncogenes such as Ras in primary mammalian cells typically triggers senescence and formation of senescence-associated heterochromatin foci (SAHF) that contributes to senescence-associated cell cycle exit. We have previously showed that dissociation of BRCA1 from chromatin induced by oncogenic Ras plays a key role in promoting cellular senescence by driving SAHF formation. However, the mechanism by which BRCA1 chromatin dissociation promotes SAHF formation and senescence remains to be determined. BRG1 is an ATP dependent SWI/SNF chromatin-remodeling factor that interacts with BRCA1. Components of SWI/SNF complex including BRG1 are often deregulated in human cancer. Here we examined the role of BRG1 in regulating formation of SAHF trigged by BRCA1 chromatin dissociation induced by oncogenic Ras. Results: We discovered that the interaction between BRG1 and BRCA1 is disrupted during oncogenic RAS induced senescence. Interestingly, BRG1 accumulates in chromatin fraction while BRCA1 becomes dissociated from chromatin. Notably, BRG1 knockdown suppresses formation of SAHF and senescence, while has no effects on BRCA1 chromatin dissociation in Ras-infected cells, suggesting that BRG1 functions downstream of BRCA1 chromatin dissociation in promoting SAHF formation and senescence. Indeed, BRG1 knockdown is sufficient to inhibit SAHF formation and senescence induced by BRCA1 knockdown. Conversely, BRG1 overexpression drives SAHF formation and senescence. Notably, senescence induced by BRG1 overexpression is independent of DNA damage response, further supporting the idea that BRG1 functions downstream of BRCA1 chromatin dissociation during Ras induced senescence. Mechanistically, chromatin immunoprecipitation analysis revealed that, in Ras-expressing or BRCA1 knockdown cells, there is an increased association of BRG1 with the promoters of p16INK4a and p21CIP, both of which are key regulators of SAHF formation and senescence. Significance: These studies revealed the molecular underpinning by which BRCA1 chromatin dissociation promotes SAHF formation and senescence. They also imply that BRG1 inactivation contributes to cancer development by suppressing cellular senescence. (R.Z. is an Ovarian Cancer Research Fund (OCRF) Liz Tilberis Scholar. This work was supported in part by a NCI FCCC-UPenn ovarian cancer SPORE (P50 CA083638) pilot project and SPORE career development award, a DOD ovarian cancer academy award (OC093420), and an OCRF program project.) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3956. doi:1538-7445.AM2012-3956