Search

Background Drug addiction is defined as a chronic disease characterized by compulsive drug seeking and episodes of relapse despite prolonged periods of drug abstinence. Neurobiological adaptations, including transcriptional and epigenetic alterations in the nucleus accumbens, are thought to contribute to this life-long disease state. We previously demonstrated that the transcription factor SMAD3 is increased after 7 days of withdrawal from cocaine self-administration. However, it is still unknown which additional factors participate in the process of chromatin remodeling and facilitate the binding of SMAD3 to promoter regions of target genes. Here, we examined the possible interaction of BRG1 — also known as SMARCA4, an adenosine triphosphatase–containing chromatin remodeler — and SMAD3 in response to cocaine exposure. Methods The expression of BRG1, as well as its binding to SMAD3 and target gene promoter regions, was evaluated in the nucleus accumbens and dorsal striatum of rats using western blotting, co-immunoprecipitation, and chromatin immunoprecipitation following abstinence from cocaine self-administration. Rats were assessed for cocaine-seeking behaviors after either intra-accumbal injections of the BRG1 inhibitor PFI3 or viral-mediated overexpression of BRG1. Results After withdrawal from cocaine self-administration, BRG1 expression and complex formation with SMAD3 are increased in the nucleus accumbens, resulting in increased binding of BRG1 to the promoter regions of Ctnnb1 , Mef2d , and Dbn1 . Intra-accumbal infusion of PFI3 attenuated, whereas viral overexpression of Brg1 enhanced, cocaine-reinstatement behavior. Conclusions BRG1 is a key mediator of the SMAD3-dependent regulation of cellular and behavioral plasticity that mediates cocaine seeking after a period of withdrawal. [ABSTRACT FROM AUTHOR]

Brg1, a core subunit of the SWI/SNF chromatin remodeling complex, is essential for development and homeostasis of various organs. However, the functional role of Brg1 in intestinal development and homeostasis, and the underlying molecular mechanism, remain unknown. We found that deletion of Brg1 in the mouse intestine resulted in growth impairment and early death associated with abnormal crypt-villous formation, skewed differentiation into secretory lineage cells, markedly increased apoptosis, and stem cell loss in the duodenum. Furthermore, we found that the Notch signaling pathway was dramatically downregulated in Brg1-deficient duodenum. Remarkably, overexpression of the Notch1 intercellular domain (ICD) partially reversed the prognosis of intestinal Brg1 mutant mice. Notch1 ICD overexpression rescued morphogenesis, prevented over-differentiation into secretory lineage cells, and restored apoptosis to normal levels in Brg1-deficient duodenum, although stem cell loss was not rescued. Our data demonstrate that Brg1 plays an essential role in development and homeostasis, including morphogenesis, stem cell differentiation and cell survival in the duodenum. Mechanistically, the rescue of the intestinal Brg1 mutant phenotype by overexpression of the Notch1 ICD indicates that Notch signaling is a key downstream target that mediates the effects of Brg1. [ABSTRACT FROM AUTHOR]

Aims Dedifferentiated endometrial carcinoma ( DDEC) is defined by the presence of an undifferentiated carcinoma together with an endometrioid carcinoma. Inactivation of SMARCA4 ( BRG1) and inactivation of SMARCB1 ( INI1) were recently described as potential mechanisms underlying the histological dedifferentiation. The aim of this study was to characterize the immunophenotypic features of DDECs, particularly in cases with prototypical histological and molecular features ( BRG1/ INI1 deficiency). Methods and results We evaluated PAX8, oestrogen receptor ( ER) and p53 immunostaining in the endometrioid and the undifferentiated components of 20 BRG1/ INI1-deficient DDECs and 15 BRG1/ INI1-intact DDECs, and compared the results with those of 23 grade 3 endometrioid carcinomas. The differentiated endometrioid component was positive for PAX8 and/or ER in 19 of 20 BRG1/ INI1-deficient DDECs, whereas the corresponding undifferentiated component of all 20 tumours showed a complete absence of PAX8 and ER staining. All except one of the BRG1/ INI1-deficient tumours showed a wild-type p53 staining pattern. PAX8 and ER expression in the undifferentiated component was absent in 67% and 80% of BRG1/ INI1-intact DDECs, respectively, whereas 47% of the BRG1/ INI1-intact DDECs showed a mutated p53 staining pattern. In comparison, absent PAX8 expression and absent ER expression were each observed in the more solid area of 48% and 48% of grade 3 endometrioid carcinomas. Conclusions The consistent absence of PAX8 and ER expression in molecularly defined ( BRG1/ INI1-deficient) DDECs suggests that the loss of PAX8 and ER expression is a fundamental feature of dedifferentiation. The frequent findings of a mutated p53 staining pattern in BRG1/ INI1-intact DDECs indicate that BRG1/ INI1-intact DDECs may be biologically different from BRG1/ INI1-deficient tumours. [ABSTRACT FROM AUTHOR]

Genes encoding angiotensin-converting enzymes (Ace and Ace2) are essential for heart function regulation. Cardiac stress enhances Ace, but suppresses Ace2, expression in the heart, leading to a net production of angiotensin II that promotes cardiac hypertrophy and fibrosis. The regulatory mechanism that underlies the Ace2- to-Ace pathological switch, however, is unknown. Here we report that the Brahma-related gene-1 (Brg1) chromatin remodeler and forkhead box M1 (FoxM1) transcription factor cooperate within cardiac (coronary) endothelial cells of pathologically stressed hearts to trigger the Ace2-to-Ace enzyme switch, angiotensin I-to-II conversion, and cardiac hypertrophy. In mice, cardiac stress activates the expression of Brg1 and FoxM1 in endothelial cells. Once activated, Brg1 and FoxM1 form a protein complex on Ace and Ace2 promoters to concurrently activate Ace and repress Ace2, tipping the balance to Ace2 expression with enhanced angiotensin II production, leading to cardiac hypertrophy and fibrosis. Disruption of endothelial Brg1 or FoxM1 or chemical inhibition of FoxM1 abolishes the stress-induced Ace2-to-Ace switch and protects the heart from pathological hypertrophy. In human hypertrophic hearts, BRG1 and FOXM1 expression is also activated in endothelial cells; their expression levels correlate strongly with the ACE/ACE2 ratio, suggesting a conserved mechanism. Our studies demonstrate a molecular interaction of Brg1 and FoxM1 and an endothelial mechanism of modulating Ace/Ace2 ratio for heart failure therapy. [ABSTRACT FROM AUTHOR]

Eukaryotic gene regulation is associated with changes in chromatin compaction that modulate access to DNA regulatory sequences relevant for transcriptional activation or repression. Although much is known about the mechanism of chromatin remodeling in hormonal gene activation, how repression is accomplished is much less understood. Here we report that in breast cancer cells, ligand-activated progesterone receptor ( PR) is directly recruited to transcriptionally repressed genes involved in cell proliferation along with the kinases ERK1/2 and MSK1. PR recruits BRG1 associated with the HP1γ-LSD1 complex repressor complex, which is further anchored via binding of HP1γ to the H3K9me3 signal deposited by SUV39H2. In contrast to what is observed during gene activation, only BRG1 and not the BAF complex is recruited to repressed promoters, likely due to local enrichment of the pioneer factor FOXA1. BRG1 participates in gene repression by interacting with H1.2, facilitating its deposition and stabilizing nucleosome positioning around the transcription start site. Our results uncover a mechanism of hormone-dependent transcriptional repression and a novel role for BRG1 in progestin regulation of breast cancer cell growth. [ABSTRACT FROM AUTHOR]

Background: The Hedgehog (HH) signalling pathway regulates cardiomyogenesis in vivo and in differentiating P19 embryonal carcinoma (EC) cells, a mouse embryonic stem (mES) cell model. To further assess the transcriptional role of HH signalling during cardiomyogenesis in stem cells, we studied the effects of overexpressing GLI2, a primary transducer of the HH signalling pathway, in mES cells. Results: Stable GLI2 overexpression resulted in an enhancement of cardiac progenitor-enriched genes, Mef2c, Nkx2- 5, and Tbx5 during mES cell differentiation. In contrast, pharmacological blockade of the HH pathway in mES cells resulted in lower expression of these genes. Mass spectrometric analysis identified the chromatin remodelling factor BRG1 as a protein which co-immunoprecipitates with GLI2 in differentiating mES cells. We then determined that BRG1 is recruited to a GLI2-specific Mef2c gene element in a HH signalling-dependent manner during cardiomyogenesis in P19 EC cells, a mES cell model. Conclusions: Thus, we propose a mechanism where HH/GLI2 regulates the expression of Mef2c by recruiting BRG1 to the Mef2c gene, most probably via chromatin remodelling, to ultimately regulate in vitro cardiomyogenesis. [ABSTRACT FROM AUTHOR]

Summary An abnormal differentiation state is common in BRCA1-deficient mammary epithelial cells, but the underlying mechanism is unclear. Here, we report a convergence between DNA repair and normal, cultured human mammary epithelial (HME) cell differentiation. Surprisingly, depleting BRCA1 or FANCD2 (Fanconi anemia [FA] proteins) or BRG1, a mSWI/SNF subunit, caused HME cells to undergo spontaneous epithelial-to-mesenchymal transition (EMT) and aberrant differentiation. This also occurred when wild-type HMEs were exposed to chemicals that generate DNA interstrand crosslinks (repaired by FA proteins), but not in response to double-strand breaks. Suppressed expression of ΔNP63 also occurred in each of these settings, an effect that links DNA damage to the aberrant differentiation outcome. Taken together with somatic breast cancer genome data, these results point to a breakdown in a BRCA/FA–mSWI/SNF-ΔNP63-mediated DNA repair and differentiation maintenance process in mammary epithelial cells that may contribute to sporadic breast cancer development. [ABSTRACT FROM AUTHOR]

Our developmental studies provide an insight into the pathogenesis of heart failure in adults. These studies reveal a mechanistic link between fetal cardiomyocytes and pathologically stressed adult cardiomyocytes at the level of chromatin regulation. In embryos, chromatin-regulating factors within the cardiomyocytes respond to developmental signals to program cardiac gene expression to promote cell proliferation and inhibit premature cell differentiation. In the neonatal period, the activity of these developmental chromatin regulators is quickly turned off in cardiomyocytes, coinciding with the cessation of cell proliferation and advance in cell differentiation toward adult maturity. When the mature hearts are pathologically stressed, those chromatin regulators essential for cardiomyocyte development in embryos are reactivated, triggering gene reprogramming to a fetal-like state and pathological cardiac hypertrophy. Furthermore, in the study of chromatin regulation and cardiac gene expression, we identified a long noncoding RNA that interacts with chromatin remodeling factor to regulate the cardiac response to environmental changes. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel. [ABSTRACT FROM AUTHOR]

Chromatin structure is determined by nucleosome positioning, histone modifications, and DNA methylation. How chromatin modifications are coordinately altered under pathological conditions remains elusive. Here we describe a stress-activated mechanism of concerted chromatin modification in the heart. In mice, pathological stress activates cardiomyocytes to express Brg1 (nucleosome-remodeling factor), G9a/Glp (histone methyltransferase), and Dnmt3 (DNA methyltransferase). Once activated, Brg1 recruits G9a and then Dnmt3 to sequentially assemble repressive chromatin—marked by H3K9 and CpG methylation—on a key molecular motor gene ( Myh6 ), thereby silencing Myh6 and impairing cardiac contraction. Disruption of Brg1, G9a or Dnmt3 erases repressive chromatin marks and de-represses Myh6 , reducing stress-induced cardiac dysfunction. In human hypertrophic hearts, BRG1–G9a/GLP–DNMT3 complex is also activated; its level correlates with H3K9/CpG methylation, Myh6 repression, and cardiomyopathy. Our studies demonstrate a new mechanism of chromatin assembly in stressed hearts and novel therapeutic targets for restoring Myh6 and ventricular function. The stress-induced Brg1–G9a–Dnmt3 interactions and sequence of repressive chromatin assembly on Myh6 illustrates a molecular mechanism by which the heart epigenetically responds to environmental signals. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel. [ABSTRACT FROM AUTHOR]

Ocular lensmorphogenesis is a model for investigatingmechanisms of cellular differentiation, spatial and temporal gene expression control, and chromatin regulation. Brg1 (Smarca4) and Snf2h (Smarca5) are catalytic subunits of distinct ATP-dependent chromatin remodeling complexes implicated in transcriptional regulation. Previous studies have shown that Brg1 regulates both lens fiber cell differentiation and organized degradation of their nuclei (denucleation). Here, we employed a conditional Snf2hflox mouse model to probe the cellular and molecular mechanisms of lens formation. Depletion of Snf2h induces premature and expanded differentiation of lens precursor cells forming the lens vesicle, implicating Snf2h as a key regulator of lens vesicle polarity through spatial control of Prox1, Jag1, p27Kip1 (Cdkn1b) and p57Kip2 (Cdkn1c) gene expression. The abnormal Snf2h-/- fiber cells also retain their nuclei. RNA profiling of Snf2h-/- and Brg1-/- eyes revealed differences in multiple transcripts, including prominent downregulation of those encoding Hsf4 and DNase IIβ, which are implicated in the denucleation process. In summary, our data suggest that Snf2h is essential for the establishment of lens vesicle polarity, partitioning of prospective lens epithelial and fiber cell compartments, lens fiber cell differentiation, and lens fiber cell nuclear degradation. [ABSTRACT FROM AUTHOR]

Sevofluane postconditioning (SPostC) protects heart against ischemia/reperfusion injury. However, SPostC cardioprotection is lost in diabetes whose cardiac heme oxygenase-1 (HO-1) is reduced. Brahma-related gene 1 (Brg1) facilitates nuclear factor-erythroid-2-related factor-2 (Nrf2) to activate HO-1 to increase myocardial antioxidant capacity in response to oxidative stress. However, cardiac Brg1 is reduced in diabetes. We hypothesized that SPostC confers cardioprotection by activating HO-1 through Nrf2/Brg1 and that impaired Nrf2/Brg1/HO-1 in diabetes is responsible for the loss of SPostC. Control and streptozotocin-induced diabetic mice were subjected to 45 min coronary artery occlusion followed by 2 h reperfusion with or without SPostC achieved by exposing the mice to 2% sevoflurane for 15 min at the onset of reperfusion. In in vitro study, H9c2 cells were exposed to normal or high glucose and subjected to 3 h hypoxia followed by 6 h reoxygenation. Diabetic mice displayed larger post-ischemic infarct size, severer cardiomyocytes apoptosis, and increased oxidative stress concomitant with reduced HO-1, nuclear Nrf2 and Brg1 protein expression. These changes were prevented/reversed by SPostC in control but not in diabetic mice, and these beneficial effects of SPostC were abolished by HO-1 inhibition. In H9c2 cells exposed to normal glucose but not high glucose, SPostC significantly attenuated hypoxia/reoxygenation-induced cellular injury and oxidative stress with increased HO-1 and nuclear Nrf2. These SPostC beneficial effects were canceled by HO-1 inhibition. In conclusion, SPostC protects against myocardial ischemia/reperfusion injury through activation of Nrf2/Brg1/HO-1 signaling and impairment of this signaling may be responsible for the loss of SPostC cardioprotection in diabetes. [ABSTRACT FROM AUTHOR]

The Olig2 basic-helix-loop-helix transcription factor promotes oligodendrocyte specification in early neural progenitor cells (NPCs), including radial glial cells, in part by recruiting SWI/SNF chromatin remodeling complexes to the enhancers of genes involved in oligodendrocyte differentiation. How Olig2 expression is regulated during oligodendrogliogenesis is not clear. Here, we find that the Brg1 subunit of SWI/SNF complexes interacts with a proximal Olig2 promoter and represses Olig2 transcription in the mouse cortex at E14, when oligodendrocyte progenitors (OPCs) are not yet found in this location. Brg1 does not interact with the Olig2 promoter in the E14 ganglionic eminence, where NPCs differentiate into Olig2-positive OPCs. Consistent with these findings, Brg1 -null NPCs demonstrate precocious expression of Olig2 in the cortex. However, these cells fail to differentiate into OPCs. We further find that Brg1 is necessary for neuroepithelial-to-radial glial cell transition, but not neuronal differentiation despite a reduction in expression of the pro-neural transcription factor Pax6. Collectively, these and earlier findings support a model whereby Brg1 promotes neurogenic radial glial progenitor cell specification but is dispensable for neuronal differentiation. Concurrently, Brg1 represses Olig2 expression and the specification of OPCs, but is required for OPC differentiation and oligodendrocyte maturation. [ABSTRACT FROM AUTHOR]

Isoflurane postconditioning (IsoPostC) attenuates myocardial ischaemia/reperfusion injury (IRI). Signal transducer and activator of transcription-3 (STAT3) is critical in ischaemic postconditioning cardioprotection, which can be regulated by the Brahma-related gene (Brg1) and nuclear factor-erythroid 2-related factor 2 (Nrf2), although they are both reduced in diabetic hearts. We hypothesized that reduced Brg1/Nrf2 and STAT3 activation may jeopardize IsoPostC-mediated cardioprotection in diabetic hearts. In the present study, Langendorff-perfused, non-diabetic (control) and 8-week-old streptozotocin-induced Type 1 diabetic rat hearts were subjected to 30 min of global ischaemia and 120 min of reperfusion without or with IsoPostC, which was achieved by administering emulsified isoflurane (2.0 %, v/v) in Krebs-Henseleit (KH) solution immediately at the onset of reperfusion for 10 min and switching to KH solution perfusion alone thereafter. Cultured H9C2 cells were exposed to normal glucose (NG, 5.5 mM) or high glucose (HG, 30 mM) and subjected to hypoxia/reoxygenation (HR) in the presence or absence of IsoPostC. Diabetic rats displayed larger post-ischaemic myocardial infarction and more severe haemodynamic dysfunction, associated with increased myocardial oxidative stress and reduced cardiac Brg1, Nrf2 and STAT3 phosphorylation/activation (p-STAT3), compared with controls. These changes were reversed/prevented by IsoPostC in control but not in diabetic rats. In H9C2 cells exposed to NG but not HG, IsoPostC significantly attenuated HR-induced cellular injury and superoxide anion production with increased Brg1, Nrf2 and p-STAT3. These beneficial effects of IsoPostC were abolished by Brg1, Nrf2 or STAT3 gene knockdown. Brg1 or Nrf2 gene knockdown abolished IsoPostC-induced STAT3 activation. N-acetylcysteine restored Brg1, Nrf2 and p-STAT3, and IsoPostC-induced protection in H9C2 cells exposed to HG and HR. In conclusion, IsoPostC confers cardioprotection through Brg1/Nrf2/STAT3 signalling, and impairment of this pathway may be responsible for the loss of IsoPostC cardioprotection in diabetes. [ABSTRACT FROM AUTHOR]

There has been an increasing recognition that mitochondrial perturbations play a central role in human heart failure. Mitochondrial networks, whose function is to maintain the regulation of mitochondrial biogenesis, autophagy (‘mitophagy’) and mitochondrial fusion/fission, are new potential therapeutic targets. Yet our understanding of the molecular underpinning of these processes is just emerging. We recently identified a role of the SWI/SNF ATP-dependent chromatin remodeling complexes in the metabolic homeostasis of the adult cardiomyocyte using cardiomyocyte-specific and inducible deletion of the SWI/SNF ATPases BRG1 and BRM in adult mice (Brg1/Brm double mutant mice). To build upon these observations in early altered metabolism, the present study looks at the subsequent alterations in mitochondrial quality control mechanisms in the impaired adult cardiomyocyte. We identified that Brg1 / Brm double-mutant mice exhibited increased mitochondrial biogenesis, increases in ‘mitophagy’, and alterations in mitochondrial fission and fusion that led to small, fragmented mitochondria. Mechanistically, increases in the autophagy and mitophagy-regulated proteins Beclin1 and Bnip3 were identified, paralleling changes seen in human heart failure. Evidence for perturbed cardiac mitochondrial dynamics included decreased mitochondria size, reduced numbers of mitochondria, and an altered expression of genes regulating fusion (Mfn1, Opa1) and fission (Drp1). We also identified cardiac protein amyloid accumulation (aggregated fibrils) during disease progression along with an increase in pre-amyloid oligomers and an upregulated unfolded protein response including increased GRP78, CHOP, and IRE-1 signaling. Together, these findings described a role for BRG1 and BRM in mitochondrial quality control, by regulating mitochondrial number, mitophagy, and mitochondrial dynamics not previously recognized in the adult cardiomyocyte. As critical to the pathogenesis of heart failure, epigenetic mechanisms like SWI/SNF chromatin remodeling seem more intimately linked to cardiac function and mitochondrial quality control mechanisms than previously realized. [ABSTRACT FROM AUTHOR]

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor with pleiotropic effects in normal physiology or vascular development, xenobiotic metabolism, and cancer. A previous study has reported that BRG1, a component of the SWI/SNF complex, is a coactivator for AHR and is recruited to the promoter region of the CYP1A1 gene in mouse hepatocytes. Recent data suggest that AHR is also expressed in human retinal pigment epithelial cells (ARPE-19), which play a crucial role in retinal physiology and the visual cycle. Multiple studies have shown that the AHR plays an important role in the pathogenesis of retinal diseases including age-related macular degeneration. However, the mechanism of AHR transcriptional activation in retinal pigment cells has not been reported. Here, we demonstrate that the AHR signaling pathway is active in ARPE-19 cells, as in hepatocytes, but with different target gene specificity. We also found that chromatin remodeling by the BRG1-containing SWI/SNF complex is required for the AHR-mediated expression of target genes in ARPE-19 cells. We identified a novel enhancer region (−12 kb) of the CYP1A1 gene in ARPE-19 cells, to which both AHR and BRG1 are recruited in a ligand-dependent manner. BRG1 is associated with the AHR in ARPE-19 cells, and the C-terminal activation domain of the AHR directly interacts with BRG1. Furthermore, depletion of BRG1 caused a reduction in chromatin accessibility at the CYP1A1 enhancer. These results suggest that ARPE-19 cells possess an AHR-mediated transcription pathway with different target gene specificity, and that BRG1 is required for AHR-mediated transcription in ARPE-19 cells. [ABSTRACT FROM AUTHOR]

Background: Inflammatory breast cancer (IBC) is a very aggressive and lethal subtype of breast cancer that accounts for about 4 % of all breast cancers diagnosed in the United States. Despite the efforts of several investigators to identify the molecular factors driving the aggressive phenotype of IBC, a great deal is still unknown about the molecular underpinnings of the disease. In the present study, we investigated the role of interferon-induced transmembrane protein 1 (IFITM1), a well-known interferon-stimulated gene (ISG), in promoting the aggressiveness of SUM149 IBC cells.Methods: Western blot and real-time polymerase chain reaction analyses were performed to assess the protein and messenger RNA (mRNA) levels of IFITM1 and other ISGs in three IBC cell lines: SUM149, MDA-IBC-3, and SUM190. IFITM1 expression and cellular localization were assessed by using immunofluorescence, while the tumorigenic potential was assessed by performing cell migration, invasion, and colony formation assays. Small interfering RNA and short hairpin RNA knockdowns, enzyme-linked immunosorbent assays, and luciferase assays were performed to determine the functional significance of IFITM1 and signal transducers and activators of transcription 1 and 2 (STAT1/2) in SUM149 cells.Results: We found that IFITM1 was constitutively overexpressed at the mRNA and protein levels in triple-negative SUM149 IBC cells, but that it was not expressed in SUM190 and MDA-IBC-3 IBC cells, and that suppression of IFITM1 or blockade of the IFNα signaling pathway significantly reduced the aggressive phenotype of SUM149 cells. Additionally, we found that knockdown of STAT2 abolished IFITM1 expression and IFITM1 promoter activity in SUM149 cells and that loss of STAT2 significantly inhibited the ability of SUM149 cells to proliferate, migrate, invade, and form 2-D colonies. Notably, we found that STAT2-mediated activation of IFITM1 was particularly dependent on the chromatin remodeler brahma-related gene 1 (BRG1), which was significantly elevated in SUM149 cells compared with SUM190 and MDA-IBC-3 cells.Conclusions: These findings indicate that overexpression of IFITM1 enhances the aggressive phenotype of triple-negative SUM149 IBC cells and that this effect is dependent on STAT2/BRG1 interaction. Further studies are necessary to explore the potential of IFITM1 as a novel therapeutic target and prognostic marker for some subtypes of IBCs. [ABSTRACT FROM AUTHOR]

Base Excision Repair (BER) is a conserved, intracellular DNA repair system that recognizes and removes chemically modified bases to insure genomic integrity and prevent mutagenesis. Aberrant BER has been tightly linked with a broad spectrum of human pathologies, such as several types of cancer, neurological degeneration, developmental abnormalities, immune dysfunction and aging. In the cell, BER must recognize and remove DNA lesions from the tightly condensed, protein-coated chromatin. Because chromatin is necessarily refractory to DNA metabolic processes, like transcription and replication, the compaction of the genomic material is also inhibitory to the repair systems necessary for its upkeep. Multiple ATP-dependent chromatin remodelling (ACR) complexes play essential roles in modulating the protein-DNA interactions within chromatin, regulating transcription and promoting activities of some DNA repair systems, including double-strand break repair and nucleotide excision repair. However, it remains unclear how BER operates in the context of chromatin, and if the chromatin remodelling processes that govern transcription and replication also actively regulate the efficiency of BER. In this review we highlight the emerging role of ACR in regulation of BER. [ABSTRACT FROM AUTHOR]

The retinoblastoma (RB) tumor suppressor is known as a master regulator of the cell cycle. RB is mutated or functionally inactivated in the majority of human cancers. This transcriptional regulator exerts its function in cell cycle control through its interaction with the E2F family of transcription factors and with chromatin remodelers and modifiers that contribute to the repression of genes important for cell cycle progression. Over the years, studies have shown that RB participates in multiple processes in addition to cell cycle control. Indeed, RB is known to interact with over 200 different proteins and likely exists in multiple complexes. RB, in some cases, acts through its interaction with E2F1, other members of the pocket protein family (p107 and p130), and/or chromatin remodelers and modifiers. RB is a tumor suppressor with important chromatin regulatory functions that affect genomic stability. These functions include the role of RB in DNA repair, telomere maintenance, chromosome condensation and cohesion, and silencing of repetitive regions. In this review we will discuss recent advances in RB biology related to RB, partner proteins, and their non-transcriptional functions fighting back against genomic instability.

BRG1 is one of two catalytic subunits of the SWI/SNF ATP-dependent chromatin-remodeling complex. In cancer, it has been hypothesized that BRG1 acts as a tumor suppressor. Further study has shown that, under certain circumstances, BRG1 acts as an oncogene. Targeted knockout of BRG1 has proven successful in most cancers in suppressing tumor growth and proliferation. Furthermore, BRG1 effects cancer proliferation in oncogenic KRAS mutated cancers, with varying directionality. Thus, dissecting BRG1's interaction with various cellular pathways can highlight possible intermediates that can facilitate the design of different treatment methods, including BRG1 inhibition. Autophagy and apoptosis are two important cellular responses to stress. BRG1 plays a direct role in autophagy and apoptosis and likely promotes autophagy and suppresses apoptosis, supporting unfettered cancer growth. PRMT5 inhibits transcription by interacting with ATP-dependent chromatin remodeling complexes, such as SWI/SNF. When PRMT5 associates with the SWI/SNF complex, including BRG1, it represses tumor suppressor genes. The Ras/Raf/MAPK/ERK1/2 pathway in cancers is a signal transduction pathway involved in the transcription of genes related to cancer survival. BRG1 has been shown to effect KRAS-driven cancer growth. BRG1 associates with several proteins within the signal transduction pathway. In this review, we analyze BRG1 as a promising target for cancer inhibition and possible synergy with other cancer treatments.

SMARCA4/BRG1 is a catalytic subunit of the SWItch/sucrose non-fermentable (SWI/SNF) complex and its inactivation is known to drive a variety of cancers across different organs. SMARCA4/BRG1-deficient carcinoma is a relatively new entity in the sinonasal region, and a comprehensive molecular investigation of the underlying genetic abnormalities is largely lacking. In this study, we report two new cases of SMARCA4/BRG1-deficient sinonasal carcinoma with targeted next-generation sequencing analysis, both of which revealed activating mutation of CTNNB1 in addition to somatic loss-of-function mutation of SMARCA4, providing further insights into its tumorigenesis and theoretical basis for the potential future targeted therapy. Activating CTNNB1 mutations in our cases may provide further evidence that SMARCA4-deficient sinonasal carcinoma, sinonasal teratocarcinosarcoma, and olfactory carcinoma are genetically closely related lesions, as recently proposed in the literature., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Long non-coding RNAs (lncRNAs) can act as regulatory RNAs which, by altering the expression of target genes, impact on the cellular phenotype and cardiovascular disease development. Endothelial lncRNAs and their vascular functions are largely undefined. Deep RNA-Seq and FANTOM5 CAGE analysis revealed the lncRNA LINC00607 to be highly enriched in human endothelial cells. LINC00607 was induced in response to hypoxia, arteriosclerosis regression in non-human primates, post-atherosclerotic cultured endothelial cells from patients and also in response to propranolol used to induce regression of human arteriovenous malformations. siRNA knockdown or CRISPR/Cas9 knockout of LINC00607 attenuated VEGF-A-induced angiogenic sprouting. LINC00607 knockout in endothelial cells also integrated less into newly formed vascular networks in an in vivo assay in SCID mice. Overexpression of LINC00607 in CRISPR knockout cells restored normal endothelial function. RNA- and ATAC-Seq after LINC00607 knockout revealed changes in the transcription of endothelial gene sets linked to the endothelial phenotype and in chromatin accessibility around ERG-binding sites. Mechanistically, LINC00607 interacted with the SWI/SNF chromatin remodeling protein BRG1. CRISPR/Cas9-mediated knockout of BRG1 in HUVEC followed by CUT&RUN revealed that BRG1 is required to secure a stable chromatin state, mainly on ERG-binding sites. In conclusion, LINC00607 is an endothelial-enriched lncRNA that maintains ERG target gene transcription by interacting with the chromatin remodeler BRG1 to ultimately mediate angiogenesis., (© 2023. The Author(s).)

In recent years, it has been shown that Z-DNA formation in DNA plays functionally significant roles in nucleic acid metabolism, such as gene expression, chromosome recombination, and epigenetic regulation. The reason for the identification of these effects is mainly due to the advancement of Z-DNA detection methods in target genome regions in living cells.The heme oxygenase-1 (HO-1) gene encodes an enzyme that degrades an essential prosthetic heme, and environmental stimuli, including oxidative stress, lead to robust induction of the HO-1 gene. Many DNA elements and transcription factors are involved in the induction of the HO-1 gene, and Z-DNA formation in the thymine-guanine (TG) repetitive sequence in the human HO-1 gene promoter region is required for maximum gene induction.Here, we describe a detailed protocol for Z-DNA detection in the human HO-1 gene promoter region based on chromatin immunoprecipitation with quantitative PCR. We also provide some control experiments to consider in routine lab procedures., (© 2023. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Chronic alcohol consumption causes liver steatosis, cell death, and inflammation. Melatonin (MLT) is reported to alleviate alcoholic liver disease (ALD)-induced injury. However, its direct regulating targets in hepatocytes are not fully understood. In the current study, a cell-based screening model and a chronic ethanol-fed mice ALD model were used to test the protective mechanisms of MLT. MLT ameliorated ethanol-induced hepatocyte injury in both cell and animal models (optimal doses of 10 μmol/L and 5 mg/kg, respectively), including lowered liver steatosis, cell death, and inflammation. RNA-seq analysis and loss-of-function studies in AML-12 cells revealed that telomerase reverse transcriptase (TERT) was a key downstream effector of MLT. Biophysical assay found that epidermal growth factor receptor (EGFR) on the hepatocyte surface was a direct binding and regulating target of MLT. Liver specific knock-down of Tert or Egfr in the ALD mice model impaired MLT-mediated liver protection, partly through the regulation of nuclear brahma-related gene-1 ( BRG1 ). Long-term administration (90 days) of MLT in healthy mice did not cause evident adverse effect. In conclusion, MLT is an efficacious and safe agent for ALD alleviation. Its direct regulating target in hepatocytes is EGFR and downstream BRG1-TERT axis. MLT might be used as a complimentary agent for alcoholics., Competing Interests: The authors declare no conflicts of interest., (© 2022 Chinese Pharmaceutical Association and Institute of Materia Medica, Chinese Academy of Medical Sciences. Production and hosting by Elsevier B.V.)

Background: The Brg1 (Brahma-related gene 1) is an important chromatin remodeling factor protein. The Brg1 protein can promote the transcriptional activation or inhibit target genes through regulating ATP hydrolysis which rearranges the nucleosomes position and the histone DNA interaction. In this study, we explored the role of Brg1 in house dust mite (HDM) stimulated airway inflammation., Methods: The wild-type C57BL/6 mice (wild-type, WT) and alveolar epithelial cells specifically knockout Brg1 mice (Brg1 fl/fl ) were selected as the experimental subjects. HDM was used to stimulate human bronchial epithelial cells (16HBE) to construct an model of airway inflammation in vitro. The asthma group was established with HDM, and the control group was treated with normal saline. Wright's staining for the detection of differential counts of inflammatory cells in bronchoalveolar lavage fluid (BALF). Invasive lung function was used to assess the airway compliance. Hematoxylin and eosin (HE) staining and periodic acid-schiff (PAS) staining were used to detect mucus secretion. Immunohistochemistry was used to measure mucin glycoprotein 5AC (MUC5AC) protein expression in airway epithelium. Western blotting was used to detect the MUC5AC and JAK1/2-STAT6 proteins in mouse lung tissues and 16HBE cells. Co-immunoprecipitation (Co-IP) and Chromatin Immunoprecipitation (CHIP) were used to detect whether Brg1 could regulate the JAK1/2-STAT6 signaling pathway., Results: The airway inflammation, pulmonary ventilation resistance, airway mucus secretion, MUC5AC and IL-13 in BALF and MUC5AC protein expression in lung tissue of Brg1 knockout mice stimulated by HDM were lower than those of wild-type mice. The expression of MUC5AC protein in HDM stimulated Brg1 knockdown 16HBE cells was significantly lower than that in the control group. In vivo and in vitro, it was found that the activation of JAK1/2-STAT6 signal pathway in mouse lung tissue or 16HBE cells was inhibited after knockdown of Brg1 gene. The Co-IP and CHIP results showed that Brg1 could bind to the JAK1/2 promoter region and regulate the expression of JAK1/2 gene., Conclusion: The Brg1 may promote the secretion of airway mucus stimulated by HDM through regulating the JAK1/2-STAT6 pathway. Knockdown of Brg1 reduced mucus secretion in HDM stimulated airway inflammation., Competing Interests: Competing interests The authors declare that they have no competing interests., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Background: An intricate gene regulatory network drives neural crest migration and differentiation. How epigenetic regulators contribute to this process is just starting to be understood. Results: We found that mutation of med14 or brg1 in zebrafish embryos resulted in a cluster of neural crest cell-related defects. In med14 or brg1 mutants, neural crest cells that form the jaw skeleton were specified normally and migrated to target sites. However, defects in their subsequent terminal differentiation were evident. Transplantation experiments demonstrated that med14 and brg1 are required directly in neural crest cells. Analysis of med14; brg1 double mutant embryos suggested the existence of a strong genetic interaction between members of the Mediator and BAF complexes. Conclusions: These results suggest a critical role for Mediator and BAF complex function in neural crest development, and may also clarify the nature of defects in some craniofacial abnormalities. [ABSTRACT FROM AUTHOR]

The transcriptional regulation of pathological cardiac hypertrophy involves the interplay of transcription factors and chromatin remodeling enzymes. The Microphthalmia-Associated Transcription Factor (MITF) is highly expressed in cardiomyocytes and is required for cardiac hypertrophy. However, the transcriptional mechanisms by which MITF promotes cardiac hypertrophy have not been elucidated. In this study, we tested the hypothesis that MITF promotes cardiac hypertrophy by activating transcription of pro-hypertrophy genes through interactions with the SWI/SNF chromatin remodeling complex. In an in vivo model of cardiac hypertrophy, expression of MITF and the BRG1 subunit of the SWI/SNF complex increased coordinately in response to pressure overload. Expression of MITF and BRG1 also increased in vitro when cardiomyocytes were stimulated with angiotensin II or a β-adrenergic agonist. Both MITF and BRG1 were required to increase cardiomyocyte size and activate expression of hypertrophy markers in response to β-adrenergic stimulation. We detected physical interactions between MITF and BRG1 in cardiomyocytes and found that they cooperate to regulate expression of a pro-hypertrophic transcription factor, GATA4. Our data show that MITF binds to the E box element in the GATA4 promoter and facilitates recruitment of BRG1. This is associated with enhanced expression of the GATA4 gene as evidenced by increased Histone3 lysine4 tri-methylation (H3K4me3) on the GATA4 promoter. Thus, in hypertrophic cardiomyoctes, MITF is a key transcriptional activator of a pro-hypertrophic gene, GATA4, and this regulation is dependent upon the BRG1 component of the SWI/SNF complex. [ABSTRACT FROM AUTHOR]

The formation of intricately organized aortic and pulmonic valves from primitive endocardial cushions of the outflow tract is a remarkable accomplishment of embryonic development. While not always initially pathologic, developmental semilunar valve (SLV) defects, including bicuspid aortic valve, frequently progress to a disease state in adults requiring valve replacement surgery. Disrupted embryonic growth, differentiation, and patterning events that “trigger” SLV disease are coordinated by gene expression changes in endocardial, myocardial, and cushion mesenchymal cells. We explored roles of chromatin regulation in valve gene regulatory networks by conditional inactivation of the Brg1-associated factor (BAF) chromatin remodeling complex in the endocardial lineage. Endocardial Brg1-deficient mouse embryos develop thickened and disorganized SLV cusps that frequently become bicuspid and myxomatous, including in surviving adults. These SLV disease-like phenotypes originate from deficient endocardial-to-mesenchymal transformation (EMT) in the proximal outflow tract (pOFT) cushions. The missing cells are replaced by compensating neural crest or other non-EMT-derived mesenchyme. However, these cells are incompetent to fully pattern the valve interstitium into distinct regions with specialized extracellular matrices. Transcriptomics reveal genes that may promote growth and patterning of SLVs and/or serve as disease-state biomarkers. Mechanistic studies of SLV disease genes should distinguish between disease origins and progression; the latter may reflect secondary responses to a disrupted developmental system. [ABSTRACT FROM AUTHOR]

Changes in chromatin structure (chromatin remodeling) are essential regulatory processes for neuronal development, but the molecular mechanisms are unclear. The aim of the present study was to assess the effects of conditional knockout (Ko) of the Brahma-related gene-1 ( Brg1 ) in the mouse central nervous system (CNS) on postnatal development. Brg1 was deleted in the CNS by crossing mice carrying the Brg1 conditional allele with a transgenic line expressing Cre under the control of the Nex 1 promoter. Brg1, PSD-95, NR2A and NR2B protein expressions were assessed using western blotting. Immunofluorescence, Nissl and TUNEL staining were used to assess cortical neuron viability. Hippocampal neurons were extracted from mouse embryos to observe the effects of neuronal degeneration associated with oxidative stress using Paraquat dichloride x-hydrate or 80% oxygen. Brg1 fx/fx ;NEX-Cre mice were significantly smaller in both body size and brain size after P35 conditional Ko of Brg1 in mouse cortical progenitors. The amount of neurons and their dendritic branches were significantly reduced in Brg1 Ko cortexes during early postnatal development. Absence of Brg1 may result in increased number of astrocytes. Loss of Brg1 increased damaged and dying neurons associated with oxidative stress. Furthermore, loss of NR2A in the Brg1 Ko cortex during early postnatal development, and delayed the NR2B–NR2A switch. Therefore, Brg1 may play a critical role in neuronal growth by regulating the NR2B–NR2A switch. Our findings provide an insight in chromatin remodeling regulation in postnatal neuronal development. [ABSTRACT FROM AUTHOR]

Mammalian SWI/SNF chromatin-remodeling complexes utilize either BRG1 or Brm as alternative catalytic subunits to alter the position of nucleosomes and regulate gene expression. Genetic studies have demonstrated that SWI/SNF complexes are required during cardiac development and also protect against cardiovascular disease and cancer. However, Brm constitutive null mutants do not exhibit a cardiomyocyte phenotype and inducible Brg1 conditional mutations in cardiomyocyte do not demonstrate differences until stressed with transverse aortic constriction, where they exhibit a reduction in cardiac hypertrophy. We recently demonstrated the overlapping functions of Brm and Brg1 in vascular endothelial cells and sought here to test if this overlapping function occurred in cardiomyocytes. Brg1/Brm double mutants died within 21 days of severe cardiac dysfunction associated with glycogen accumulation and mitochondrial defects based on histological and ultrastructural analyses. To determine the underlying defects, we performed nontargeted metabolomics analysis of cardiac tissue by GC/MS from a line of Brg1/Brm double-mutant mice, which lack both Brg1 and Brm in cardiomyocytes in an inducible manner, and two groups of controls. Metabolites contributing most significantly to the differences between Brg1/Brm double-mutant and control-group hearts were then determined using the variable importance in projection analysis. Increased cardiac linoleic acid and oleic acid suggest alterations in fatty acid utilization or intake are perturbed in Brg1/Brm double mutants. Conversely, decreased glucose-6-phosphate, fructose-6-phosphate, and myoinositol suggest that glycolysis and glycogen formation are impaired. These novel metabolomics findings provide insight into SWI/SNF-regulated metabolic pathways and will guide mechanistic studies evaluating the role of SWI/SNF complexes in homeostasis and cardiovascular disease prevention. [ABSTRACT FROM AUTHOR]

Small cell carcinoma of the ovary, hypercalcemic type is a very rare aggressive neoplasm of unknown histogenesis, affecting mainly girls and young women. Recently, inactivating mutations in SMARCA4 ( BRG1 ), a member of the switch/sucrose nonfermenting chromatin remodeling complex, has been identified as driver events in most cases. We herein describe 3 cases in 34, 34, and 37-year-old women. Symptoms were mainly abdominal pain and mass. One patient was normocalcemic, and the other 2 had no preoperative serum calcium values available. All patients received radical hysterectomy with salpingo-oophorectomy, lymphadenectomy, and variable multimodality therapy. Two developed abdominal recurrences/metastases and died of disease at 4 and 12 months. One patient was alive without disease 17 months after surgery and radiochemotherapy. Histologic examination showed undifferentiated neoplasms composed of diffuse sheets, nests and cords of noncohesive monomorphic small blue/basaloid cells (classic variant, 1 case), and large undifferentiated/rhabdoid cells with abundant cytoplasm (large cell/rhabdoid variant, 2 case) admixed with minor small cell areas. One case contained rare isolated goblet cells, but true glandular component was absent. All tumors expressed vimentin and variably pancytokeratin and WT1. Nuclear SMARCB1 was intact in all cases (1 case showed small foci with mosaic loss). All tumors showed complete loss of SMARCA4. In conclusion, SMARCA4 immunohistochemistry represents a highly valuable emerging tool in identifying small cell carcinoma of the ovary, hypercalcemic type in routine practice. Distinguishing this aggressive neoplasm from juvenile granulosa cell tumor and other undifferentiated ovarian cancers is mandatory in selecting appropriate chemotherapeutic regimens and would allow better characterization of this entity, for which targeted molecular therapy still remains to be established. [ABSTRACT FROM AUTHOR]

Genes encoding subunits of the two SWI/SNF chromatin remodelling complexes (BAF and PBAF) are mutated in almost 20% of all human cancers. In addition to a role in regulating transcription, recent work from our laboratory and others identified roles for both complexes in DNA damage responses and the maintenance of sister chromatid cohesion, which may have profound impacts on genome stability and contribute to its role as a tumour suppressor. Here, we review some of the transcription-independent functions of the SWI/SNF chromatin remodelling complex and discuss these in light of their potential relevance to tumourigenesis. [ABSTRACT FROM AUTHOR]

Transcription-regulating long non-coding RNAs (lncRNAs) have the potential to control the site-specific expression of thousands of target genes. Previously, we showed that Evf2, the first described ultraconserved lncRNA, increases the association of transcriptional activators (DLX homeodomain proteins) with key DNA enhancers but represses gene expression. In this report, mass spectrometry shows that the Evf2-DLX1 ribonucleoprotein (RNP) contains the SWI/SNFrelated chromatin remodelers Brahma-related gene 1 (BRG1, SMARCA4) and Brahma-associated factor (BAF170, SMARCC2) in the developing mouse forebrain. Evf2 RNA colocalizes with BRG1 in nuclear clouds and increases BRG1 association with key DNA regulatory enhancers in the developing forebrain. While BRG1 directly interacts with DLX1 and Evf2 through distinct binding sites, Evf2 directly inhibits BRG1 ATPase and chromatin remodeling activities. In vitro studies show that both RNA-BRG1 binding and RNA inhibition of BRG1 ATPase/remodeling activity are promiscuous, suggesting that context is a crucial factor in RNA-dependent chromatin remodeling inhibition. Together, these experiments support a model in which RNAs convert an active enhancer to a repressed enhancer by directly inhibiting chromatin remodeling activity, and address the apparent paradox of RNA-mediated stabilization of transcriptional activators at enhancers with a repressive outcome. The importance of BRG1/RNA and BRG1/homeodomain interactions in neurodevelopmental disorders is underscored by the finding that mutations in Coffin-Siris syndrome, a human intellectual disability disorder, localize to the BRG1 RNA-binding and DLX1-binding domains. [ABSTRACT FROM AUTHOR]

Pancreatic ductal adenocarcinoma (PDA) develops predominantly through pancreatic intraepithelial neoplasia (PanIN) and intraductal papillary mucinous neoplasm (IPMN) precursor lesions. Pancreatic acinar cells are reprogrammed to a "ductal-like" state during PanIN-PDA formation. Here, we demonstrate a parallel mechanism operative in mature duct cells during which functional cells undergo "ductal retrogression" to form IPMN-PDA. We further identify critical antagonistic roles for Brahma-related gene 1 (Brg1), a catalytic subunit of the SWI/SNF complexes, during IPMN-PDA development. In mature duct cells, Brg1 inhibits the dedifferentiation that precedes neoplastic transformation, thus attenuating tumor initiation. In contrast, Brg1 promotes tumorigenesis in full-blown PDA by supporting a mesenchymal-like transcriptional landscape. We further show that JQ1, a drug that is currently being tested in clinical trials for hematological malignancies, impairs PDA tumorigenesis by both mimicking some and inhibiting other Brg1-mediated functions. In summary, our study demonstrates the context-dependent roles of Brg1 and points to potential therapeutic treatment options based on epigenetic regulation in PDA. [ABSTRACT FROM AUTHOR]

Background/Aims: Cardiac remodeling is a common pathophysiological change along with chronic hypertension and myocardial infarction. Recent evidence indicated that cardiac tissue expressed peroxisome proliferator-activated receptor γ (PPARγ). However, the functional role of PPARγ in cardiac remodeling remained unclear. The present study was designed to investigate the relationship between PPARγ activation and pressure overload-induced cardiac remodeling. Methods: Cardiac remodeling model was successfully established by abdominal aorta ligation. Cardiac fibrosis and cardiomyocyte hypertrophy were simulated by 100 nM angiotensin II (Ang II) in vitro. Haemodynamic parameters, the expressions of Brg1, α-MHC, β-MHC, transforming growth factor beta 1 (TGF-β1), collagen-I, collagen-III and NF-κB were examined. Results: Morphological and haemodynamic measurements showed that the activation of PPARγ improved the impaired cardiac function and decreased interstitial fibrosis in cardiac remodeling rats. Further results also showed that the activation of PPARγ inhibited the expressions of Brg1 and TGF-β1 in the cardiac remodeling hearts. The activation of PPARγ also inhibited the proliferation and collagen production of cardiac fibroblasts, and down-regulated the activity of Brg1 and the expression of TGF-β1 induced by Ang II in cultured neonatal rat cardiomyocytes and cardiac fibroblasts, respectively, through NF-κB pathway. Conclusions: These results suggested that PPARγ activation effectively inhibited cardiac remodeling processes by suppression of Brg1 and TGF-β1 expressions through NF-κB pathway in the pressure-overloaded hearts induced by abdominal aorta ligation in rats. © 2015 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

DNA double-strand breaks (DSBs) are a type of lethal DNA damage. The repair of DSBs requires tight coordination between the factors modulating chromatin structure and the DNA repair machinery. BRG1, the ATPase subunitof the chromatin remodelling complex Switch/Sucrose non-fermentable (SWI/SNF), is often linked to tumorigenesis and genome instability, and its role in DSB repair remains largely unclear. In the present study, we show that BRG1 is recruited to DSB sites and enhances DSB repair. Using DR-GFP and EJ5-GFP reporter systems, we demonstrate that BRG1 facilitates homologous recombination repair rather than nonhomologous end-joining (NHEJ) repair. Moreover, the BRG1-RAD52 complex mediates the replacement of RPA with RAD51 on single-stranded DNA (ssDNA) to initiate DNA strand invasion. Loss of BRG1 results in a failure of RAD51 loading onto ssDNA, abnormal homologous recombination repair and enhanced DSB-induced lethality. Our present study provides a mechanistic insight into how BRG1, which is known to be involved in chromatin remodelling, plays a substantial role in the homologous recombination repair pathway in mammalian cells. [ABSTRACT FROM AUTHOR]

Undifferentiated/dedifferentiated endometrial carcinomas (UDEC and DDEC) are rare, aggressive uterine neoplasms, with no specific line of differentiation. A significant proportion of these cases feature mutations of SWI/SNF chromatin remodeling complex members, including ARID1A, SMARCA4, and SMARCB1 genes. To study these entities more comprehensively, we identified 10 UDECs and 10 DDECs from our pathology archives, obtained clinicopathologic findings and follow-up data, and performed immunohistochemical studies for ARID1A, BRG1 (SMARCA4), and INI1 (SMARCB1) proteins. In addition, we successfully conducted targeted next-generation sequencing for 23 samples, including 7 UDECs, and 7 undifferentiated and 9 well/moderately-differentiated components of DDECs. Cases consisted of 18 hysterectomies and 2 curettage/biopsy specimens. Patient age ranged from 47 to 77 years (median, 59 years), with a median tumor size of 8.0 cm (range, 2.5-13.0 cm). All cases demonstrated lymphovascular invasion and the majority (13/20) were FIGO stage III-IV. By immunohistochemistry, ARID1A loss was observed in 15 cases, BRG1 loss in 4, and all cases had intact INI1 expression. A trend for enrichment of the undifferentiated component of DDECs for ARID1A loss was seen, although not statistically significant. Sequencing revealed frequent pathogenic mutations in PTEN, PIK3CA, ARID1A, CTNNB1, and RNF43, a recurrent MAX pathogenic mutation, and MYC and 12p copy number gains. In DDECs, the undifferentiated component featured a higher tumor mutational burden compared to the well/moderately-differentiated component; however, the mutational landscape largely overlapped. Overall, our study provides deep insights into the mutational landscape of UDEC/DDEC, SWI/SNF chromatin remodeling complex member status, and their potential relationships with tumor features., (Copyright © 2022 Elsevier Inc. All rights reserved.)

The SWI/SNF chromatin remodeling complex plays a role in the repair of UV-induced DNA damage. It was proposed that chromatin remodeling activities are utilized to increase the accessibility of NER machinery and checkpoint factors to the damaged DNA. It was shown recently that BRCA1 contributes to UV damage response by promoting photoproduct excision, triggering post-UV checkpoint activation and post replicative repair. In this study, we show that BRCA1 rapidly binds to UV damage sites when cells are undergoing DNA synthesis. In contrast, two phosphorylated forms of BRCA1 do not accumulate at sites of UV damage. Depletion of BRG1, a core subunit of the human SWI/SNF-BAF complex, impairs the recruitment of BRCA1 to the damage sites and attenuates DNA damage induced BRCA1 phosphorylation. At UV lesions-stalled replication forks, BRG1 promotes RPA phosphorylation in response to UV irradiation, since UV-induced phosphorylation of chromatin bound RPA drops significantly when BRG1 is depleted in human cells. Importantly, activation of the ATM/ATR kinases is attenuated when BRG1 is depleted. We propose that BRG1 modulates BRCA1 response to UV irradiation by regulating ATM/ATR activation.

Objective(s): Epigenetic regulation of gene expression can be carried out through chromatin remodeling enzymes such as SWI/SNF. Brg1 also known as SMARCA4 is a catalytic subunit of SWI/SNF, which is necessary for MMPs expression. Matrix metalloproteinases (MMPs) are known as important player enzymes during tumor progression and metastasis. Aberrant epigenetic modification of chromatin should be precisely clarified to reveal probable unknown pathways in ESCC progression. Probable role of Brg1 in ESCC tumorigenesis and metastasis was studied through the assessment of Brg1 mRNA expression in KYSE30, and further evaluation about the biology of Brg1 was performed through the Brg1 silencing. Materials and Methods: Level of Brg1 mRNA expression in KYSE30 was compared to normal tissues using the real time polymerase chain reaction (PCR). Moreover, KYSE30 cells were transfected with Brg1-siRNA to silence the Brg1. Results: Our results showed for the first time that Brg1 mRNA expression was increased in KYSE30 cell line (ESCC cell line) compared with normal esophageal tissue of ESCC patients. Rate of transfection in KYSE30 was also between 40 to 50%, using the pSilencer-Brg1shRNA (1:1 ratio). Conclusion: Our data indicated that chromatin remodeling machinery is a novel aspect in tumor biology of ESCC, and overexpression of Brg1 as an important member of SWI/SNF might be involved in the migration and invasion of ESCC tumoral cells. [ABSTRACT FROM AUTHOR]

Myogenesis involves the stable commitment of progenitor cells followed by the execution of myogenic differentiation, processes that are coordinated by myogenic regulatory factors, microRNAs and BAF chromatin remodeling complexes. BAF60a, BAF60b and BAF60c are structural subunits of the BAF complex that bind to the core ATPase Brg1 to provide functional specificity. BAF60c is essential for myogenesis; however, the mechanisms regulating the subunit composition of BAF/Brg1 complexes, in particular the incorporation of different BAF60 variants, are not understood. Here we reveal their dynamic expression during embryo myogenesis and uncover the concerted negative regulation of BAF60a and BAF60b by the muscle-specific microRNAs (myomiRs) miR-133 and miR-1/ 206 during somite differentiation. MicroRNA inhibition in chick embryos leads to increased BAF60a or BAF60b levels, a concomitant switch in BAF/Brg1 subunit composition and delayed myogenesis. The phenotypes are mimicked by sustained BAF60a or BAF60b expression and are rescued by morpholino knockdown of BAF60a or BAF60b. This suggests that myomiRs contribute to select BAF60c for incorporation into the Brg1 complex by specifically targeting the alternative variants BAF60a and BAF60b during embryo myogenesis, and reveals that interactions between tissue-specific non-coding RNAs and chromatin remodeling factors confer robustness to mesodermal lineage determination. [ABSTRACT FROM AUTHOR]

Gemcitabine is a standard chemotherapeutic agent for locally advanced and metastatic pancreatic cancer. However, the chemoresistance of pancreatic cancer is the major barrier to efficient chemotherapy. Here, we reported that BRG1, a chromatin modulator, was exclusively overexpressed in human pancreatic ductal adenocarcinoma tissues. BRG1 knockdown inhibited PANC-1 and MIA PaCa-2 cell growth in vitro and in vivo, reduced the phosphorylation/activation of Akt and p21cip/waf, enhanced intrinsic and gemcitabine induced apoptosis and attenuated gemcitabine-induced downregulation of E-cadherin. Moreover, by establishing acquired chemoresistance of MIA PaCa-2 cells in vitro, we found that BRG1 knockdown effectively reversed the chemoresistance to gemcitabine. Surprisingly, inhibiting Akt phosphorylation resulted in BRG1 suppression in pancreatic cancer cells, indicating BRG1 as a new downstream target of Akt signalling. Taken together, our findings suggest that BRG1 promotes both intrinsic and acquired chemoresistance of pancreatic cancer cells, and BRG1 crosstalks with Akt signalling to form a positive feedback loop to promote pancreatic cancer development. [ABSTRACT FROM AUTHOR]