Role Of Chromatin Remodeling Research Articles

Differential Roles of SWI/SNF Complexes in Metal Regulation

SWI/SNF complexes play a major role in chromatin remodeling in mammalian cells. Mammalian DNA is compacted into chromatin by nucleosomes and other factors. The level of compaction is regulated largely by SWI/SNF complexes. These complexes remodel nucleosomes by displacing or evicting them, or by exchanging histones. By controlling which areas of the chromatin are available for transcription, SWI/SNF complexes have a large impact on gene expression. There are three main classes of SWI/SNF complexes: Brg/Brm‐associated factor (BAF), polybromo‐associated BAF (PBAF), and non‐canonical BAF (ncBAF). We hypothesized that these distinct classes of SWI/SNF complexes may have different roles, and respond to environmental and cellular signals in a specific manner. Preliminary data from our lab showed that the PBAF, and potentially the BAF complexes, may play a role in stress, homeostasis, and metal regulation in proliferating and differentiating myoblasts. We used cultured C2C12 myoblasts partially depleted of a representative subunit of each SWI/SNF complex, as these cells have an intrinsic high demand for transition metals for proper growth, differentiation, and function. Knock‐down myoblasts were treated with sublethal concentrations of different metals, and we analyzed the correlation of each SWI/SNF complex with the expression of the metal protective transcription factor (Mtf1) and metal responsive metallothionein‐1 (Mt1) genes. Our work provides the first mechanistic evidence of the contribution of specific chromatin remodelers to the expression of the main metal protective transcription factor and effector genes necessary for surviving metal toxicity.

Histone acetyltransferase GCN5-mediated lysine acetylation modulates salt stress aadaption of Trichoderma.

Trichoderma viride has a wide range of applications in plant growth promotion, biological control, cellulase production, and biomass utilization. Salinity is a major limitation to Trichoderma strains in the natural environment and fermentation environment, and to improve the adaptability of Trichoderma to salt stress is of great significance to its applications in industry and agriculture. Histone acetylation plays important roles in the regulation of physiological and biochemical processes including various stress responses. GCN5 is the most representative histone acetylase, which plays vital roles in chromatin remodeling of promoters to facilitate the transcription activation. In this paper, we identified a GCN5-encoding gene TvGCN5 in T. viride Tv-1511, and characterized the function and regulating mechanism of TvGCN5-mediated acetylation of histone H3 in the salt adoption of Tv-1511, by constructions of the deletion mutants (Tv-1511-△GCN5) and overexpression mutants (Tv-1511-GCN5-OE) of TvGCN5. Results showed that compared with wild-type Tv-1511, the over-expression of TvGCN5 resulted in the longer mycelia diameter and more biomass under salt stress. Furthermore, Tv-1511-△GCN5 strains obtained the improved sodium (Na+) compartmentation and antioxidant capacity by upregulating the transcriptional levels of genes encoding PM H+-ATPase, vacuolar H+-ATPase, and antioxidant enzymes. Notably, the changes in the transcriptional expressions of these genes are tightly modulated by the TvGCN5-mediated acetylated level of histone H3 in their promoter regions. In all, these results reveal that TvGCN5 plays an important role in stress tolerance of T. viride Tv-1511, and provides potential insight to facilitate the application of epigenetic modulation in the expanding utilization of Trichoderma. KEY POINTS: • Overexpresison of TvGCN5 improves the adoption of T. viride Tv-1511 to salt stress by increasing acetylation level of histone H3 on the promoter regions of sodium-transport and antioxidant-related genes, at H3K9ac, H3K14ac, H3K23ac, and H3K27ac. • Overexprsison of TvGCN5 enhances the ion transport and compartmentation capacity by upregulating the expressions and activities of PM and vacuolar H+-ATPase to tolerate salt stress. • Overexprsison of TvGCN5 promotes the antioxidant capacity by increasing the expressions and activities of antioxidant enzymes in response to salt stress.

AT-rich interactive domain 1A (ARID1A) cannot be considered a morphological marker for prostate cancer progression: A pilot study

Prostate cancer (PCa) is one of the most common cancers worldwide but it presents many subtypes and patient heterogeneity. It is necessary to discriminate localised not aggressive PCa and metastatic cancer in order to better define the personalised treatment. The identification of an appropriate biomarker to combine with Gleason grading system, that is one of the most important prognostic factors in prostate cancer outcome, remains a major clinical issue. We have tested AT-rich interactive domain 1A (ARID1A) in prostate tissue is order to verify its possible role as morphological marker for prostate cancer progression. ARID1A is a tumour suppressor protein playing a pivotal role in chromatin remodelling during transcriptional regulation. It was decreased in many cancers correlating with tumour aggressiveness. Our data shown that ARID1A had a nuclear staining and that it is significantly decreased in prostate cancers suggesting that it can be involved in this neoplasm but it is not able to discriminate prostate cancer progression.

PP2A is activated by cytochrome c upon formation of a diffuse encounter complex with SET/TAF-Iβ

Intrinsic protein flexibility is of overwhelming relevance for intermolecular recognition and adaptability of highly dynamic ensemble of complexes, and the phenomenon is essential for the understanding of numerous biological processes. These conformational ensembles—encounter complexes—lack a unique organization, which prevents the determination of well-defined high resolution structures. This is the case for complexes involving the oncoprotein SET/template-activating factor-Iβ (SET/TAF-Iβ), a histone chaperone whose functions and interactions are significantly affected by its intrinsic structural plasticity. Besides its role in chromatin remodeling, SET/TAF-Iβ is an inhibitor of protein phosphatase 2A (PP2A), which is a key phosphatase counteracting transcription and signaling events controlling the activity of DNA damage response (DDR) mediators. During DDR, SET/TAF-Iβ is sequestered by cytochrome c (Cc) upon migration of the hemeprotein from mitochondria to the cell nucleus. Here, we report that the nuclear SET/TAF-Iβ:Cc polyconformational ensemble is able to activate PP2A. In particular, the N-end folded, globular region of SET/TAF-Iβ (a.k.a. SET/TAF-Iβ ΔC)—which exhibits an unexpected, intrinsically highly dynamic behavior—is sufficient to be recognized by Cc in a diffuse encounter manner. Cc-mediated blocking of PP2A inhibition is deciphered using an integrated structural and computational approach, combining small-angle X-ray scattering, electron paramagnetic resonance, nuclear magnetic resonance, calorimetry and molecular dynamics simulations.

SATB1 enhances gastric cancer progression and metastasis via upregulation of CLIP4/DZIP1/ PRICKLE2 axis in gastric cancer patients

SATB1 (Special AT-rich sequence binding protein 1) plays key role in chromatin remodeling and geneexpression. SATB1 has been shown to promote invasion, migration and metastasis. However, the underlying molecular mechanisms, function and clinicopathological features of SATB1 in gastric cancer (GC) remains poorly understood. Here, we show that SATB1 plays critical role in GC progression. SATB1 upregulates in GC patients’ samples and shows co-apmlification with a subset of oncogenic proteins (PRICKLE2, ZEB1, CBWX7, WWTR1, ENAH, DZIP1, IGSF11, ZSCAN18, GFRA2, GFRA1, FGFR1, HDAC4, GHR, TIMP3, CLIP4, TAGLN and ILK) in different subtypes of GC. SATB1 shows positive correlation with GC promoting oncogenes and enhances the expression of metastasis associated genes in GC samples to potentiate GC progression. SATB1 enhances WNT/NOTCH signaling axis in GC samples. In contrast, STAB1 suppresses a network of tumor suppressor genes in GC samples. Moreover, SATB1 expression negatively correlates with GC patient’s survival. Importantly, we found that SATB1 co-amplified genes CLIP4, DZIP1 and PRICKLE2 independently involve in GC progression. Overexpression of CLIP4, DZIP1 and PRICKLE2 show poor survival rates in GC patients. DZIP1 empowers AKT3/FGF2/FGFR1 and CXCR3/CXCR6 in GC patients. PRICKLE2 enhances GC progression by targeting FGFR1/NOTCH3/WNT4 signaling. Taken together, these results identified novel roles of SATB1, CLIP4, DZIP1 and PRICKLE2 in the GC invasion, migration and metastasis using cancer bioinformatics approach. These results highlights clinical significance of SATB1, CLIP4, DZIP1 and PRICKLE2 in GC patients and furthermore, these proteins may serve as prognostic markers in GC. These results also provide SATB1, CLIP4, DZIP1 and PRICKLE2 as potential chemotherapeutic targets in treatment of gastric cancer patients.

Tracking the Dynamic Histone Methylation of H3K27 in Live Cancer Cells.

Histone methylations play a crucial role in chromatin remodeling and genome regulations. However, there is a lack of tools to visualize these histone modifications with high spatiotemporal resolutions in live cells. We have developed a biosensor based on fluorescence resonance energy transfer (FRET) and incorporated it into nucleosomes, capable of monitoring the trimethylation of H3K27 (H3K27me3) in live cells. We also revealed that the performance of the FRET biosensor can be significantly improved by adjusting the linkers within the biosensor. An improved biosensor enables the live-cell imaging of different histone methylation status, induced by the suppressive H3.3K27M or existing in breast cancer cells with varying genetic backgrounds. We have further applied the biosensor to reveal the dynamic coupling between H3K27me3 changes and caspase activity representing the initiation of apoptosis in cancer cells by imaging both H3K27me3 and caspase activity simultaneously in the same live cells. Thus, this new FRET biosensor can provide a powerful tool to visualize the epigenetic regulation in live cells with high spatial temporal resolutions.

Chromatin Content Capture Reveals Acute Leukaemia Oncogenic Vulnerability Point in Human B Cell Development

Human B cell development in adult human bone marrow (BM) is tightly regulated through well-defined stages to produce adaptive immune cells with assembled and functional B cell antigen receptor (BCR)(Martin et al., 2016). To produce mature B cells with functional immunoglobulin receptors, B cell progenitors must undergo multiple stages of highly regulated chromatin remodelling and transcriptional reprogramming which correspond to unique patterns of surface protein expression (Nutt and Kee, 2007). This complex process is frequently dysregulated in B cell neoplasia such as B cell Acute Lymphoblastic Leukemia (B-ALL). B-ALL is highly heterogenous in its phenotypic and clinical presentation, as well as in its underlying molecular features such as DNA methylation patterns and genetic aberrations (Cobaleda and Sánchez‐García, 2009). The lack of general mechanism of leukemogenesis has made it difficult to identify when and where adult and pediatric B-ALL blasts diverge from normal B cell development. Here we show that across 5 B-ALL patients and 3 cell lines with diverse phenotypic and clinical presentations, blasts are epigenetically arrested at a conserved point within healthy human B cell development.First, we sought to establish a trajectory of normal B cell development to delineate the phenotypic and concomitant epigenetic changes occurring in BM progenitors as they differentiate into naïve B cells. To capture phenotype, function, and epigenetic state via single cell chromatin content (chromotype) of developing B cells in BM, we developed a multiplexed, high throughput, single cell proteomic method (chromotyping) to simultaneously measure cell surface markers, intracellular regulators such as transcription factors and chromatin structure regulators such as histone post-translational modifications (i.e. H3K4me3, H3K27me3, H2AK119ubi) and chromatin re-modelers (i.e. CTCF, DNMT1, MLL1). Using these surrogates for single cell, global chromatin content, we notably identified 3 coordinated epigenetic inflection or switch (S) points in healthy B cell development corresponding to previously characterized phenotypic landmarks of STAT5 signalling and active re-arrangement of IgH loci (S1), CD24 expression-linked high translation and proliferation (S2), and IgM and CD20 expression-linked BCR assembly completion (S3) (Bendall et al., 2014).To determine how these coordinated chromotypes translated to chromatin accessibility and primed gene regulation networks, we isolated BM B cell population from these chromatin content transition points and analysed them with our modified ATAC-seq protocol, InTAC-seq (Baskar et al., 2021). Strikingly, the chromatin accessibility landscape revealed putative oncogenic priming with high activity of leukemic TFs such as PAX5, TCF3, ZEB1 and ID4 predominantly at S2 and some at S3 switch points. By integrating our InTAC-seq data with publicly available single cell ATAC and RNA seq data on BM, we located this oncogenic primed state as existing from S2 to before S3 (IgH rearranged, late pro- / Pre-B cell stage) in healthy B cell development. This integration further associated this state with high activity of ASCL1 (role in chromatin remodelling) and high expression of STMN1 (Leukaemia-associated phosphoprotein 18).Finally we showed that across B-ALL patients (n=5) and cell lines (REH, NALM6, SUBP15), chromatin accessibility of neoplastic B cells indeed continue to occupy this point of oncogenic vulnerability in the B cell developmental space from S2 to right before S3 in our integrated scATAC map, despite variable immunophenotypes. This corresponds to a coordinated minima in our chromotyping map (lowest, coordinated abundance of chromatin structure regulators across trajectory). Further analysis of B-ALL patients reinforced the divergence between immunophenotypic and epigenetic heterogeneity within and between samples. Taken together, our findings identify key epigenetic switch points in B cell development and their underlying chromatin accessibility and gene expression patterns. Consequently, we reveal a point of epigenetic vulnerability in healthy B cell development that could be predisposed to leukemic transformation. This work opens up the possibility for new diagnostic strategies for B-ALL utilizing chromatin content and could pave the way for epigenetic modulation-based treatments beyond DNA methylation inhibition. DisclosuresDavis: Novartis Pharmaceuticals: Honoraria; Jazz Pharmaceuticals: Research Funding.

BAZ1B the Protean Protein.

The bromodomain adjacent to the zinc finger domain 1B (BAZ1B) or Williams syndrome transcription factor (WSTF) are just two of the names referring the same protein that is encoded by the WBSCR9 gene and is among the 26–28 genes that are lost from one copy of 7q11.23 in Williams syndrome (WS: OMIM 194050). Patients afflicted by this contiguous gene deletion disorder present with a range of symptoms including cardiovascular complications, developmental defects as well as a characteristic cognitive and behavioral profile. Studies in patients with atypical deletions and mouse models support BAZ1B hemizygosity as a contributing factor to some of the phenotypes. Focused analysis on BAZ1B has revealed this to be a versatile nuclear protein with a central role in chromatin remodeling through two distinct complexes as well as being involved in the replication and repair of DNA, transcriptional processes involving RNA Polymerases I, II, and III as well as possessing kinase activity. Here, we provide a comprehensive review to summarize the many aspects of BAZ1B function including its recent link to cancer.

The budding yeast protein Chl1p is required for delaying progression through G1/S phase after DNA damage

BackgroundThe budding yeast protein Chl1p is a nuclear protein required for sister-chromatid cohesion, transcriptional silencing, rDNA recombination, ageing and plays an instrumental role in chromatin remodeling. This helicase is known to preserve genome integrity and spindle length in S-phase. Here we show additional roles of Chl1p at G1/S phase of the cell cycle following DNA damage.ResultsG1 arrested cells when exposed to DNA damage are more sensitive and show bud emergence with faster kinetics in chl1 mutants compared to wild-type cells. Also, more damage to DNA is observed in chl1 cells. The viability falls synergistically in rad24chl1 cells. The regulation of Chl1p on budding kinetics in G1 phase falls in line with Rad9p/Chk1p and shows a synergistic effect with Rad24p/Rad53p. rad9chl1 and chk1chl1 shows similar bud emergence as the single mutants chl1, rad9 and chk1. Whereas rad24chl1 and rad53chl1 shows faster bud emergence compared to the single mutants rad24, rad53 and chl1. In presence of MMS induced damage, synergistic with Rad24p indicates Chl1p’s role as a checkpoint at G1/S acting parallel to damage checkpoint pathway. The faster movement of DNA content through G1/S phase and difference in phosphorylation profile of Rad53p in wild type and chl1 cells confirms the checkpoint defect in chl1 mutant cells. Further, we have also confirmed that the checkpoint defect functions in parallel to the damage checkpoint pathway of Rad24p.ConclusionChl1p shows Rad53p independent bud emergence and Rad53p dependent checkpoint activity in presence of damage. This confirms its requirement in two different pathways to maintain the G1/S arrest when cells are exposed to damaging agents. The bud emergence kinetics and DNA segregation were similar to wild type when given the same damage in nocodazole treated chl1 cells which establishes the absence of any role of Chl1p at the G2/M phase. The novelty of this paper lies in revealing the versatile role of Chl1p in checkpoints as well as repair towards regulating G1/S transition. Chl1p thus regulates the G1/S phase by affecting the G1 replication checkpoint pathway and shows an additive effect with Rad24p for Rad53p activation when damaging agents perturb the DNA. Apart from checkpoint activation, it also regulates the budding kinetics as a repair gene.

Multiple roles for PARP1 in ALC1-dependent nucleosome remodeling

The SNF2 family ATPase Amplified in Liver Cancer 1 (ALC1) is the only chromatin remodeling enzyme with a poly(ADP-ribose) (PAR) binding macrodomain. ALC1 functions together with poly(ADP-ribose) polymerase PARP1 to remodel nucleosomes. Activation of ALC1 cryptic ATPase activity and the subsequent nucleosome remodeling requires binding of its macrodomain to PAR chains synthesized by PARP1 and NAD+ A key question is whether PARP1 has a role(s) in ALC1-dependent nucleosome remodeling beyond simply synthesizing the PAR chains needed to activate the ALC1 ATPase. Here, we identify PARP1 separation-of-function mutants that activate ALC1 ATPase but do not support nucleosome remodeling by ALC1. Investigation of these mutants has revealed multiple functions for PARP1 in ALC1-dependent nucleosome remodeling and provides insights into its multifaceted role in chromatin remodeling.

Multiple Sclerosis: Enzymatic Cross Site-Specific Hydrolysis of H1 Histone by IgGs against H1, H2A, H2B, H3, H4 Histones, and Myelin Basic Protein.

Histones play a key role in chromatin remodeling and gene transcription. Further, free histones in the blood act as damage-associated molecules. Administration of histones to animals results in systemic inflammatory and toxic effects. Myelin basic protein is the principal constituent element of the myelin-proteolipid sheath of axons. Abzymes (antibodies with catalytic activities) are the original features of some autoimmune diseases. In this study, electrophoretically homogeneous IgGs against H1, H2A, H2B, H3, and H4 histones and myelin basic protein (MBP) were isolated from the blood sera of multiple sclerosis (MS) patients by several affinity chromatographies. Using MALDI mass spectrometry, the sites of H1 histone cleavage by IgGs against H1, H2A, H2B, H3, H4, and MBP were determined. It was shown that IgGs against H1 split H1 at 12 sites, while the number of cleavage sites by abzymes against other histones was lower: H2A (9), H2B (7), H3 (3), and H4 (3). The minimum rate of H1 hydrolysis was observed for antibodies against H3 and H4. A high rate of hydrolysis and the maximum number of H1 hydrolysis sites (17) were found for antibodies against MBP. Only a few sites of H1 hydrolysis by anti-H1 antibodies coincided with those for IgGs against H2A, H2B, H3, H4, and MBP. Thus, the polyreactivity of complexation and the enzymatic cross-activity of antibodies against H1, four other histones, and MBP have first been shown. Since histones act as damage molecules, abzymes against histones and MBP can play a negative role in the pathogenesis of MS and probably other different diseases as well.

MORC2 Interactome: Its Involvement in Metabolism and Cancer.

Microrchidia 2 (MORC2) is an emerging chromatin modifier with a role in chromatin remodeling and epigenetic regulation. MORC2 is found to be upregulated in most cancers, playing a significant role in tumorigenesis and tumor metastasis. Recent studies have demonstrated that MORC2 is a scaffolding protein, which interacts with the proteins involved in DNA repair, chromatin remodeling, lipogenesis, and glucose metabolism. In this review, we discuss the domain architecture and cellular and subcellular localization of MORC2. Further, we highlight MORC2-specific interacting partners involved in metabolic reprogramming and other pathological functions such as cancer progression and metastasis.

ARID1 proteins: from transcriptional and post-translational regulation to carcinogenesis and potential therapeutics.

The ARID1 proteins are mutually exclusive subunits of the BRG1/BRM-associated factor (BAF) complexes that play an important role in chromatin remodeling and regulate many fundamental cell functions. The role of ARID1s is well defined as a tumor-suppressive. Thecancer cellsevolve different mechanisms to downregulate ARID1s and inactivate their functions. ARID1s are frequently mutated in human cancer. The recent findings of ARID1A/B downregulation at transcriptional and translational levels along with their low levels in human cancers indicate the significance of regulatory mechanisms of ARID1s in cancers. In this review, we present the current knowledge on the regulation and alterations of ARID1 protein expression in human cancers and indicate the importance of regulators of ARID1s as a prognostic marker and in potential therapeutic strategies.

Selective Targeting of Epigenetic Readers and Histone Deacetylases in Autoimmune and Inflammatory Diseases: Recent Advances and Future Perspectives.

Histone deacetylases (HDACs) and bromodomain-containing proteins (BCPs) play a key role in chromatin remodeling. Based on their ability to regulate inducible gene expression in the context of inflammation and cancer, HDACs and BCPs have been the focus of drug discovery efforts, and numerous small-molecule inhibitors have been developed. However, dose-limiting toxicities of the first generation of inhibitors, which typically target multiple HDACs or BCPs, have limited translation to the clinic. Over the last decade, an increasing effort has been dedicated to designing class-, isoform-, or domain-specific HDAC or BCP inhibitors, as well as developing strategies for cell-specific targeted drug delivery. Selective inhibition of the epigenetic modulators is helping to elucidate the functions of individual epigenetic proteins and has the potential to yield better and safer therapeutic strategies. In accordance with this idea, several in vitro and in vivo studies have reported the ability of more selective HDAC/BCP inhibitors to recapitulate the beneficial effects of pan-inhibitors with less unwanted adverse events. In this review, we summarize the most recent advances with these strategies, discussing advantages and limitations of these approaches as well as some therapeutic perspectives, focusing on autoimmune and inflammatory diseases.

LncRNA transcription induces meiotic recombination through chromatin remodelling in fission yeast

Noncoding RNAs (ncRNAs) are involved in various biological processes, including gene expression, development, and disease. Here, we identify a novel consensus sequence of a cis-element involved in long ncRNA (lncRNA) transcription and demonstrate that lncRNA transcription from this cis-element activates meiotic recombination via chromatin remodeling. In the fission yeast fbp1 gene, glucose starvation induces a series of promoter-associated lncRNAs, referred to as metabolic-stress-induced lncRNAs (mlonRNAs), which contribute to chromatin remodeling and fbp1 activation. Translocation of the cis-element required for mlonRNA into a well-characterized meiotic recombination hotspot, ade6-M26, further stimulates transcription and meiotic recombination via local chromatin remodeling. The consensus sequence of this cis-element (mlon-box) overlaps with meiotic recombination sites in the fission yeast genome. At one such site, the SPBC24C6.09c upstream region, meiotic double-strand break (DSB) formation is induced in an mlon-box-dependent manner. Therefore, mlonRNA transcription plays a universal role in chromatin remodeling and the regulation of transcription and recombination.

First person – Srinivas Animireddy

ABSTRACT First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Srinivas Animireddy is first author on ‘Aberrant cytoplasmic localization of ARID1B activates ERK signaling and promotes oncogenesis’, published in JCS. Srinivas conducted the research described in this article while a PhD student in Dr Murali Dharan Bashyam's lab at the Centre for DNA Fingerprinting and Diagnostics (CDFD), Hyderabad, India. He is now a postdoc in the lab of Dr Blaine Bartholomew at the MD Anderson Cancer Center, Smithville, TX, investigating the role of chromatin remodelers in development and diseases.

Nucleoporin 210 Serves a Key Scaffold for SMARCB1 in Liver Cancer.

The roles of chromatin remodelers and their underlying mechanisms of action in cancer remain unclear. In this study, SMARCB1, known initially as a bona fide tumor suppressor gene, was investigated in liver cancer. SMARCB1 was highly upregulated in patients with liver cancer and was associated with poor prognosis. Loss- and gain-of-function studies in liver cells revealed that SMARCB1 loss led to reduced cell proliferation, wound healing capacity, and tumor growth in vivo. Although upregulated SMARCB1 appeared to contribute to switch/sucrose nonfermentable (SWI/SNF) complex stability and integrity, it did not act using its known pathways antagonism with EZH2 or association between TP53 or AMPK. SMARCB1 knockdown induced a mild reduction in global H3K27 acetylation, and chromatin immunoprecipitation sequencing of SMARCB1 and acetylated histone H3K27 antibodies before and after SMARCB1 loss identified Nucleoporin210 (NUP210) as a critical target of SMARCB1, which bound its enhancer and changed H3K27Ac enrichment and downstream gene expression, particularly cholesterol homeostasis and xenobiotic metabolism. Notably, NUP210 was not only a putative tumor supporter involved in liver cancer but also acted as a key scaffold for SMARCB1 and P300 to chromatin. Furthermore, SMARCB1 deficiency conferred sensitivity to doxorubicin and P300 inhibitor in liver cancer cells. These findings provide insights into mechanisms underlying dysregulation of chromatin remodelers and show novel associations between nucleoporins and chromatin remodelers in cancer. SIGNIFICANCE: This study reveals a novel protumorigenic role for SMARCB1 and describes valuable links between nucleoporins and chromatin remodelers in cancer by identifying NUP210 as a critical coregulator of SMARCB1 chromatin remodeling activity.

Abstract 17084: Nuclear Smooth Muscle α-actin Participates in Chromatin Remodeling at Smooth Muscle Contractile Gene Promoters

Actin genes encode for cytoskeletal proteins that polymerize to function in cellular motility, adhesion, and contraction. In mammalian cells, ubiquitously expressed β-actin also moves into the nucleus and associates with chromatin remodeling complexes, however a nuclear function of muscle-specific α-actins has not been previously assessed. We hypothesized that smooth muscle α-actin (SMA) plays a role in chromatin remodeling during the differentiation of smooth muscle cells (SMCs) to enable cell fate specification of SMCs. In explanted SMCs from human and mouse ascending aortas, cell fractionation and 2D gel electrophoresis identify both SMA and β-actin in the nuclear lysates. Nuclear SMA but not β-actin accumulates with SMC differentiation driven by serum starvation and transforming growth factor-β1 treatment. SMA accumulates into the nucleus early in the differentiation of SMCs from neural crest progenitor cells, prior to cytosolic accumulation. Immunoprecipitation studies show that SMA binds specifically to the INO80 and the SWI/SNF chromatin remodeling complexes, and this binding increases with SMC differentiation. Chromatin immunoprecipitation reveals that SMA is bound to the promoters of SMC-specific genes, including Acta2 , Cnn1, and Myh11 and that SMA is enriched over β-actin at these promoters with SMC differentiation. Finally, overexpression of SMA tagged with a nuclear localization sequence (NLS) in multiple cell types increases expression of SMC markers, whereas NLS-tagged β-actin localizes to the nucleus to the same extent but does not increase SMC marker expression in any cell type. Finally, we assessed whether skeletal muscle α-actin (SKA) and cardiac muscle α-actin (CMA) may play a similar role in skeletal and cardiac muscle cells. Both SKA and CMA translocate into the nucleus. CMA accumulates into the nucleus early in the differentiation of cardiomyocytes from pluripotent stem cells. Immunoprecipitation reveals that SKA binds to the SWI/SNF complex in differentiated C2C12 myotube cell cultures. These data support that nuclear SMA enriches with and participates in SMC differentiation, and suggest a potential nuclear role for other muscle specific α-actins in developing muscle cells.

Abstract PO-036: Defining the role of chromatin remodelers in pancreatic cancer

Abstract Pancreatic ductal adenocarcinoma (PDAC) is a disease characterized by aggressive metastasis and resistance to therapy, making clinical management a significant challenge. We have focused on understanding how pancreatic cancer may be influenced by developmental and stem cell signals as they are often aberrantly re-activated during cancer progression. Given the central role for epigenetic regulation in development, we hypothesized that epigenetic factors may be required to sustain the self-renewal and aggressive nature of pancreatic cancer cells. To this end, we carried out a functional screen and identified Smarcd3, a component of the SWI/SNF (Baf) nucleosome remodeling complex, as a novel functional dependency in PDAC. SWI/SNF coordinates context-specific gene regulation in development and is frequently dysregulated in cancer. However, Smarcd3 has not been linked to functions in PDAC and represents a new epigenetic mediator of tumorigenesis. We found that Smarcd3 was uniquely up-regulated in PDAC stem cells and was required for the in vivo propagation of mouse and patient-derived tumors. Further using integrated RNA-seq, ChIP-seq, and network analysis we found that Smarcd3 regulates global SWI/SNF binding and histone acetylation, driving the epigenetic regulation of core cell fate and metabolic programs. Specifically, we found that Smarcd3 regulated genes converging on the mevalonate pathway and ultimately cholesterol biosynthesis, which has been directly implicated in stem signaling in PDAC. Collectively, these data identify Smarcd3 as a critical novel dependency and epigenetic regulator of pancreatic cancer metabolism. Citation Format: Lesley Paige Ferguson, Jovylyn Gatchalian, Nikki Lytle, Nirakar Rajbhandari, Matthew McDermott, Kendall Chambers, Sara Brin Rosenthal, Christian Schuerch, Inti Zlobec, Marten Wartenberg, Eva Diamantis, José A. Galván, Sonia Albini, Lorenzo Puri, Benoit Bruneau, Andrew M. Lowy, Diana Hargreaves, Tannishtha Reya. Defining the role of chromatin remodelers in pancreatic cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PO-036.

Recent Development of Novel HDAC6 Isoform-selective Inhibitors.

As an important post-transcription modification, histone deacetylation plays significant roles in chromatin remodeling and gene expression. The aberrant modification of histone deacetylation leads to various diseases. As a critical member of histone deacetylase (HDAC), HDAC6 serves as a key modulator in many physiological processes. Abnormal expression of HDAC6 gives rise to cancer, neurodegeneration and other diseases. Here, we have reviewed recent advances in physiological, protein structure and development of HDAC6 selective inhibitors.