BAF180 is a critical regulator of p21 induction and a tumor suppressor mutated in breast cancer

Preclinical evidence in the assembly of mammalian SWI/SNF complexes: Epigenetic insights and clinical perspectives in human lung disease therapy

The SWI/SNF complex, also known as the BRG1/BRM-associated factor (BAF) complex, represents a critical regulator of chromatin remodeling mechanisms in mammals. It is alternatively referred to as mSWI/SNF and has been suggested to be imbalanced in human disease compared with human health. Three types of BAF assemblies associated with it have been described, including (1) canonical BAF (cBAF), (2) polybromo-associated BAF (PBAF), and (3) non-canonical BAF (ncBAF) complexes. Each of these BAF assemblies plays a role, either functional or dysfunctional, in governing gene expression patterns, cellular processes, epigenetic mechanisms, and biological processes. Recent evidence increasingly links the dysregulation of mSWI/SNF complexes to various human non-malignant lung chronic disorders and lung malignant diseases. This review aims to provide a comprehensive general state-of-the-art and a profound examination of the current understanding of mSWI/SNF assembly processes, as well as the structural and functional organization of mSWI/SNF complexes and their subunits. In addition, it explores their intricate functional connections with potentially dysregulated transcription factors, placing particular emphasis on molecular and cellular pathogenic processes in lung diseases. These processes are reflected in human epigenome aberrations that impact clinical and therapeutic levels, suggesting novel perspectives on the diagnosis and molecular therapies for human respiratory diseases.

Cancer-associated polybromo-1 bromodomain 4 missense variants variably impact bromodomain ligand binding and cell growth suppression

The polybromo, brahma-related gene 1-associated factors (PBAF) chromatin remodeling complex subunit polybromo-1 (PBRM1) contains six bromodomains that recognize and bind acetylated lysine residues on histone tails and other nuclear proteins. PBRM1 bromodomains thus provide a link between epigenetic posttranslational modifications and PBAF modulation of chromatin accessibility and transcription. As a putative tumor suppressor in several cancers, PBRM1 protein expression is often abrogated by truncations and deletions. However, ∼33% of PBRM1 mutations in cancer are missense and cluster within its bromodomains. Such mutations may generate full-length PBRM1 variant proteins with undetermined structural and functional characteristics. Here, we employed computational, biophysical, and cellular assays to interrogate the effects of PBRM1 bromodomain missense variants on bromodomain stability and function. Since mutations in the fourth bromodomain of PBRM1 (PBRM1-BD4) comprise nearly 20% of all cancer-associated PBRM1 missense mutations, we focused our analysis on PBRM1-BD4 missense protein variants. Selecting 16 potentially deleterious PBRM1-BD4 missense protein variants for further study based on high residue mutational frequency and/or conservation, we show that cancer-associated PBRM1-BD4 missense variants exhibit varied bromodomain stability and ability to bind acetylated histones. Our results demonstrate the effectiveness of identifying the unique impacts of individual PBRM1-BD4 missense variants on protein structure and function, based on affected residue location within the bromodomain. This knowledge provides a foundation for drawing correlations between specific cancer-associated PBRM1 missense variants and distinct alterations in PBRM1 function, informing future cancer personalized medicine approaches.

Downregulated expression of PBRM1 in sarcomatoid hepatocellular carcinoma

Sarcomatoid hepatocellular carcinoma (SHCC) is a rare and highly lethal subtype of HCC. The present study aimed to explore the unique markers of SHCC using whole gene expression analysis. Subsequently, gene expression analysis was performed using five sarcomatoid and seven carcinomatoid components of seven tissues from patients with SHCC. The results demonstrated a significant downregulation of polybromo 1 (PBRM1) gene expression in the sarcomatoid components. Immunohistochemical staining also indicated a decreased expression of PBRM1 in the sarcomatoid components. Moreover, gene ontology enrichment analysis revealed that most of the 336 differentially expressed genes between the sarcomatoid and carcinomatoid components were involved in functions associated with DNA replication and histone methylation, which was consistent with the loss of function of PBRM1 which encodes Switch/sucrose-non-fermentable chromatin remodeling complex protein. Therefore, the results of the present study suggested that PBRM1 may be a candidate biomarker for the evaluation of SHCC.

Research progress of SWI/SNF complex in breast cancer

In the past decade, numerous epigenetic mechanisms have been discovered to be associated with cancer. The mammalian SWI/SNF complex is an ATP-dependent chromatin remodeling complex whose mutations are associated with various malignancies including breast cancer. As the SWI/SNF complex has become one of the most commonly mutated complexes in cancer, targeting epigenetic mutations acquired during breast cancer progress is a potential means of improving clinical efficacy in treatment strategies. This article reviews the composition of the SWI/SNF complex, its main roles and research progress in breast cancer, and links these findings to the latest discoveries in cancer epigenomics to discuss the potential mechanisms and therapeutic potential of SWI/SNF in breast cancer.

Therapeutic Role of Synthetic Lethality in ARID1A-Deficient Malignancies

AT-rich interaction domain 1A (ARID1A), a mammalian switch/sucrose nonfermenting complex subunit, modulates several cellular processes by regulating chromatin accessibility. It is encoded by ARID1A, an immunosuppressive gene frequently disrupted in a many tumors, affecting the proliferation, migration, and invasion of cancer cells. Targeting molecular pathways and epigenetic regulation associated with ARID1A loss, such as inhibiting the PI3K/AKT pathway or modulating Wnt/β-catenin signaling, may help suppress tumor growth and progression. Developing epigenetic drugs like histone deacetylase or DNA methyltransferase inhibitors could restore normal chromatin structure and function in cells with ARID1A loss. As ARID1A deficiency correlates with enhanced tumor mutability, microsatellite instability, high tumor mutation burden, increased programmed death-ligand 1 expression, and T-lymphocyte infiltration, ARID1A-deficient cells can be a potential therapeutic target for immune checkpoint inhibitors that warrants further exploration. In this review, we discuss the role of ARID1A in carcinogenesis, its crosstalk with other signaling pathways, and strategies to make ARID1A-deficient cells a potential therapeutic target for patients with cancer.

Recent insights into the SWI/SNF complex and the molecular mechanism of hSNF5 deficiency in rhabdoid tumors

Genetic information encoded by DNA is packaged in the nucleus using the chromatin structure. The accessibility of transcriptional elements in DNA is controlled by the dynamic structural changes of chromatin for the appropriate regulation of gene transcription. Chromatin structure is regulated by two general mechanisms, one is histone modification and the other is chromatin remodeling in an ATP-dependent manner. Switch/sucrose nonfermentable (SWI/SNF) complexes utilize the energy from ATP hydrolysis to mobilize nucleosomes and remodel the chromatin structure, contributing to conformational changes in chromatin. Recently, the inactivation of encoding genes for subunits of the SWI/SNF complexes has been documented in a series of human cancers, accounting for up to almost 20% of all human cancers. For example, human SNF5 (hSNF5), the gene that encodes a subunit of the SWI/SNF complexes, is the sole mutation target that drives malignant rhabdoid tumors (MRT). Despite remarkably simple genomes, the MRT has highly malignant characteristics. As a key to understanding MRT tumorigenesis, it is necessary to fully examine the mechanism of chromatin remodeling by the SWI/SNF complexes. Herein, we review the current understanding of chromatin remodeling by focusing on SWI/SNF complexes. In addition, we describe the molecular mechanisms and influences of hSNF5 deficiency in rhabdoid tumors and the prospects for developing new therapeutic targets to overcome the epigenetic drive of cancer that is caused by abnormal chromatin remodeling.

Primary intracranial sarcomas: a clinicopathological investigation

Background

The purpose of this study is to present a series of primary intracranial sarcomas (PIS), a rare type of tumor of the central nervous system, in order to improve our understanding of the disease. These tumors are heterogeneous and prone to recurrence after resection, exhibiting a high mortality rate. As PIS has yet to be understood and studied on a large scale, it is vital for further evaluation and research.

Methods

Our study included 14 cases of PIS. The patients' clinical, pathological, and imaging features were retrospectively analyzed. Additionally, targeted DNA next-generation sequencing (NGS) was applied for the 481-gene panel to detect gene mutations.

Results

The average age for PIS patients was 31.4 years. Headache (7, 50.0%) was the most common symptom leading to the hospital visit. Twelve cases had PIS located in the supratentorial area and two in the cerebellopontine angle region. The maximum tumor diameter ranged from 19.0 mm to 130.0 mm, with an average diameter of 50.3 mm. Pathological types of tumors were heterogeneous, with chondrosarcoma being the most common, followed by fibrosarcoma. Eight of the 10 PIS cases that underwent MRI scanning showed gadolinium enhancement; 7 of these cases were heterogeneous, and 1 of them was garland-like. Targeted sequencing was performed in two cases and identified mutations in genes such as NRAS, PIK3CA, BAP1, KDR, BLM, PBRM1, TOP2A, DUSP2, and CNV deletions of SMARCB1. Additionally, the SH3BP5::RAF1 fusion gene was also detected. Of the 14 patients, 9 underwent a gross total resection (GTR), and 5 chose subtotal resection. Patients who underwent GTR displayed a trend toward superior survival. Among the 11 patients with available follow-up information, one had developed lung metastases, three had died, and eight were alive.

Conclusion

PIS is extremely rare compared to extracranial soft sarcomas. The most common histological type of intracranial sarcoma (IS) is chondrosarcoma. Patients who underwent GTR of these lesions showed improved survival rates. Recent advancements in NGS aided in the identification of diagnostic and therapeutic PIS-relevant targets.

PBRM1-deficient PBAF complexes target aberrant genomic loci to activate the NF-κB pathway in clear cell renal cell carcinoma

PBRM1 encodes an accessory subunit of the PBAF SWI/SNF chromatin remodeller, and the inactivation of PBRM1 is a frequent event in kidney cancer. However, the impact of PBRM1 loss on chromatin remodelling is not well examined. Here we show that, in VHL-deficient renal tumours, PBRM1 deficiency results in ectopic PBAF complexes that localize to de novo genomic loci, activating the pro-tumourigenic NF-κB pathway. PBRM1-deficient PBAF complexes retain the association between SMARCA4 and ARID2, but have loosely tethered BRD7. The PBAF complexes redistribute from promoter proximal regions to distal enhancers containing NF-κB motifs, heightening NF-κB activity in PBRM1-deficient models and clinical samples. The ATPase function of SMARCA4 maintains chromatin occupancy of pre-existing and newly acquired RELA specific to PBRM1 loss, activating downstream target gene expression. Proteasome inhibitor bortezomib abrogates RELA occupancy, suppresses NF-κB activation and delays growth of PBRM1-deficient tumours. In conclusion, PBRM1 safeguards the chromatin by repressing aberrant liberation of pro-tumourigenic NF-κB target genes by residual PBRM1-deficient PBAF complexes.

Advances in the role of SWI/SNF complexes in tumours

Cancer development is a complex process involving both genetic and epigenetic changes. The SWI/SNF (switch/sucrose non-fermentable) chromatin remodelling complex, one of the most studied ATP-dependent complexes, plays an important role in coordinating chromatin structural stability, gene expression and post-translational modifications. The SWI/SNF complex can be classified into BAF, PBAF and GBAF according to their constituent subunits. Cancer genome sequencing studies have shown a high incidence of mutations in genes encoding subunits of the SWI/SNF chromatin remodelling complex, with abnormalities in one or more of these genes present in nearly 25% of all cancers, which indicating that stabilizing normal expression of genes encoding subunits in the SWI/SNF complex may prevent tumorigenesis. In this paper, we will review the relationship between the SWI/SNF complex and some clinical tumours and its mechanism of action. The aim is to provide a theoretical basis to guide the diagnosis and treatment of tumours caused by mutations or inactivation of one or more genes encoding subunits of the SWI/SNF complex in the clinical setting.

PBRM1, SETD2 and BAP1 - the trinity of 3p in clear cell renal cell carcinoma

Biallelic inactivation of the tumour suppressor gene Von Hippel-Lindau (VHL) occurs in the vast majority of clear cell renal cell carcinoma (ccRCC) instances, disrupting cellular oxygen-sensing mechanisms to yield a state of persistent pseudo-hypoxia, defined as a continued hypoxic response despite the presence of adequate oxygen levels. However, loss of VHL alone is often insufficient to drive oncogenesis. Results from genomic studies have shown that co-deletions of VHL with one (or more) of three genes encoding proteins involved in chromatin modification and remodelling, polybromo-1 gene (PBRM1), BRCA1-associated protein 1 (BAP1) and SET domain-containing 2 (SETD2), are common and important co-drivers of tumorigenesis. These genes are all located near VHL on chromosome 3p and are often altered following cytogenetic rearrangements that lead to 3p loss and precede the establishment of ccRCC. These three proteins have multiple roles in the regulation of crucial cancer-related pathways, including protection of genomic stability, antagonism of polycomb group (PcG) complexes to maintain a permissive transcriptional landscape in physiological conditions, and regulation of genes that mediate responses to immune checkpoint inhibitor therapy. An improved understanding of these mechanisms will bring new insights regarding cellular drivers of ccRCC growth and therapy response and, ultimately, will support the development of novel translational therapeutics.

Loss of PBRM1 Alters Promoter Histone Modifications and Activates ALDH1A1 to Drive Renal Cell Carcinoma

Subunits of SWI/SNF chromatin remodeling complexes are frequently mutated in human malignancies. The PBAF complex is composed of multiple subunits, including the tumor-suppressor protein PBRM1 (BAF180), as well as ARID2 (BAF200), that are unique to this SWI/SNF complex. PBRM1 is mutated in various cancers, with a high mutation frequency in clear cell renal cell carcinoma (ccRCC). Here, we integrate RNA-seq, histone modification ChIP-seq, and ATAC-seq data to show that loss of PBRM1 results in de novo gains in H3K4me3 peaks throughout the epigenome, including activation of a retinoic acid biosynthesis and signaling gene signature. We show that one such target gene, ALDH1A1, which regulates a key step in retinoic acid biosynthesis, is consistently upregulated with PBRM1 loss in ccRCC cell lines and primary tumors, as well as non-malignant cells. We further find that ALDH1A1 increases the tumorigenic potential of ccRCC cells. Using biochemical methods, we show that ARID2 remains bound to other PBAF subunits after loss of PBRM1 and is essential for increased ALDH1A1 after loss of PBRM1, whereas other core SWI/SNF components are dispensable, including the ATPase subunit BRG1. In total, this study uses global epigenomic approaches to uncover novel mechanisms of PBRM1 tumor suppression in ccRCC.

IMPLICATIONS

This study implicates the SWI/SNF subunit and tumor-suppressor PBRM1 in the regulation of promoter histone modifications and retinoic acid biosynthesis and signaling pathways in ccRCC and functionally validates one such target gene, the aldehyde dehydrogenase ALDH1A1.

PBAF loss leads to DNA damage-induced inflammatory signaling through defective G2/M checkpoint maintenance

The PBRM1 subunit of the PBAF (SWI/SNF) chromatin remodeling complex is mutated in ∼40% of clear cell renal cancers. PBRM1 loss has been implicated in responses to immunotherapy in renal cancer, but the mechanism is unclear. DNA damage-induced inflammatory signaling is an important factor determining immunotherapy response. This response is kept in check by the G2/M checkpoint, which prevents progression through mitosis with unrepaired damage. We found that in the absence of PBRM1, p53-dependent p21 up-regulation is delayed after DNA damage, leading to defective transcriptional repression by the DREAM complex and premature entry into mitosis. Consequently, DNA damage-induced inflammatory signaling pathways are activated by cytosolic DNA. Notably, p53 is infrequently mutated in renal cancer, so PBRM1 mutational status is critical to G2/M checkpoint maintenance. Moreover, we found that the ability of PBRM1 deficiency to predict response to immunotherapy correlates with expression of the cytosolic DNA-sensing pathway in clinical samples. These findings have implications for therapeutic responses in renal cancer.

The RBPJ/DAPK3/UBE3A signaling axis induces PBRM1 degradation to modulate the sensitivity of renal cell carcinoma to CDK4/6 inhibitors

Renal cell carcinoma (RCC) is a kind of malignant tumor originating from the renal tubular epithelium. Approximately 30% of patients with renal cancer are found to have metastasis when first diagnosed. Exploring other effective treatment methods in addition to surgery is an urgent need in the research field of renal cell carcinoma. Polybromo 1 (PBRM1) is the second most mutated gene in RCC, with a mutation rate of ~40%. Notably, the posttranscriptional modification of PBRM1 in RCC is unclear. In this study, we performed unbiased mass spectrometry of PBRM1 and identified ubiquitin-protein ligase E3A (UBE3A), an extensively studied E3 ligase that can bind with PBRM1 and regulate the stability of PBRM1 in renal cancer cells. We further found that RBPJ/DAPK3 modulated the E3 ligase activity of UBE3A by interfering with the PKA phosphorylation of UBE3A. Finally, we demonstrated that the RBPJ/DAPK3/UBE3A/PBRM1/p21 axis contributed to the sensitivity of renal cancer cells to CDK4/6 inhibitors. In addition, in combination with RBPJ inhibitors, CDK4/6 inhibitors showed synergistically enhanced effects on renal cancer cells. In summary, we not only revealed a novel RBPJ/DAPK3/UBE3A/PBRM1/p21 signaling axis but also identified a combination strategy for overcoming the resistance of renal cancer cells to CDK4/6 inhibitors.

Emerging Molecular Dependencies of Mutant EGFR-Driven Non-Small Cell Lung Cancer

Epidermal growth factor receptor (EGFR) mutations are the molecular driver of a subset of non-small cell lung cancers (NSCLC); tumors that harbor these mutations are often dependent on sustained oncogene signaling for survival, a concept known as “oncogene addiction”. Inhibiting EGFR with tyrosine kinase inhibitors has improved clinical outcomes for patients; however, successive generations of inhibitors have failed to prevent the eventual emergence of resistance to targeted agents. Although these tumors have a well-established dependency on EGFR signaling, there remain questions about the underlying genetic mechanisms necessary for EGFR-driven oncogenesis and the factors that allow tumor cells to escape EGFR dependence. In this review, we highlight the latest findings on mutant EGFR dependencies, co-operative drivers, and molecular mechanisms that underlie sensitivity to EGFR inhibitors. Additionally, we offer perspective on how these discoveries may inform novel combination therapies tailored to EGFR mutant NSCLC.

Mutational Analysis of PBRM1 and Significance of PBRM1 Mutation in Anti-PD-1 Immunotherapy of Clear Cell Renal Cell Carcinoma

Renal cell carcinoma is a common solid tumor. PBRM1 is one of the most mutation-prone genes in clear cell renal cell carcinoma (ccRCC) with the occurrence of mutation in 40% of ccRCC patients. Mutations in PBRM1 have been correlated with the efficacy of immunotherapy. However, the mutation types of PBRM1 are not well characterized. The effects of PBRM1 expression levels in the tumor microenvironment are not well studied. In addition, the mechanism and effect of anti-PD-1 immunotherapy in ccRCC tumor microenvironments are not well clarified. In this study, using bioinformatics methods we analyzed the alternation frequency and expression levels of PBRM1 in various tumors. Next, we experimentally validated their expression levels in ccRCC tissues from human and mouse models. We attempted to clarify the mechanisms of anti-PD-1 immunotherapy in ccRCC with various PBRM1 expression levels. Our results showed that deficiency of PBRM1 protein is correlated with CD4 T cell reduction in human and mouse ccRCC tissues. We also showed that anti-PD-1 Immunotherapy can increase the infiltration of T cells in both PBRM1 high and PBRM1 low tumors but to different degrees. Our study indicates that the reduction of CD4 cells in tumor tissues with low expression of PBRM1 may explain the compromised efficacy of anti-PD-1 immunotherapy in patients with PBRM1 mutated ccRCC. Our study sheds light on the potential of PBRM1 as a therapeutic target in ccRCC.

The Bromodomains of the mammalian SWI/SNF (mSWI/SNF) ATPases Brahma (BRM) and Brahma Related Gene 1 (BRG1) promote chromatin interaction and are critical for skeletal muscle differentiation

Skeletal muscle regeneration is mediated by myoblasts that undergo epigenomic changes to establish the gene expression program of differentiated myofibers. mSWI/SNF chromatin remodeling enzymes coordinate with lineage-determining transcription factors to establish the epigenome of differentiated myofibers. Bromodomains bind to acetylated lysines on histone N-terminal tails and other proteins. The mutually exclusive ATPases of mSWI/SNF complexes, BRG1 and BRM, contain bromodomains with undefined functional importance in skeletal muscle differentiation. Pharmacological inhibition of mSWI/SNF bromodomain function using the small molecule PFI-3 reduced differentiation in cell culture and in vivo through decreased myogenic gene expression, while increasing cell cycle-related gene expression and the number of cells remaining in the cell cycle. Comparative gene expression analysis with data from myoblasts depleted of BRG1 or BRM showed that bromodomain function was required for a subset of BRG1- and BRM-dependent gene expression. Reduced binding of BRG1 and BRM after PFI-3 treatment showed that the bromodomain is required for stable chromatin binding at target gene promoters to alter gene expression. Our findings demonstrate that mSWI/SNF ATPase bromodomains permit stable binding of the mSWI/SNF ATPases to promoters required for cell cycle exit and establishment of muscle-specific gene expression.

The Role of ARID1A in Tumors: Tumor Initiation or Tumor Suppression?

Genes encoding subunits of SWItch/Sucrose Non-Fermenting (SWI/SNF) chromatin remodeling complexes are collectively mutated in 20% of all human cancers, among which the AT-rich interacting domain-containing protein 1A (ARID1A, also known as BAF250a, B120, C1orf4, Osa1) that encodes protein ARID1A is the most frequently mutated, and mutations in ARID1A have been found in various types of cancer. ARID1A is thought to play a significant role both in tumor initiation and in tumor suppression, which is highly dependent upon context. Recent molecular mechanistic research has revealed that ARID1A participates in tumor progression through its effects on control of cell cycle, modulation of cellular functions such as EMT, and regulation of various signaling pathways. In this review, we synthesize a mechanistic understanding of the role of ARID1A in human tumor initiation as well as in tumor suppression and further discuss the implications of these new discoveries for potential cancer intervention. We also highlight the mechanisms by which mutations affecting the subunits in SWI/SNF complexes promote cancer.

Beyond the coding genome: non-coding mutations and cancer

Latest advancements in genomics involving individuals from different races and geographical locations has led to the identification of thousands of common as well as rare genetic variants and copy number variations (CNVs). These studies have surprisingly revealed that the majority of genetic variation is not present within the coding region but rather in the non-coding region of the genome, which is also termed as "Medical Genome". This short review describes how mutations/variations within; regulatory sequences, architectural proteins and transcriptional regulators give rise to the aberrant gene expression profiles that drives cellular transformations and malignancies.

Prognostic and Predictive Value of PBRM1 in Clear Cell Renal Cell Carcinoma

Renal cell carcinoma (RCC) is the most frequent kidney solid tumor, the clear cell RCC (ccRCC) being the major histological subtype. The probability of recurrence and the clinical behavior of ccRCC will greatly depend on the different clinical and histopathological features, already incorporated to different scoring systems, and on the genomic landscape of the tumor. In this sense, ccRCC has for a long time been known to be associated to the biallelic inactivation of Von Hippel-Lindau (VHL) gene which causes aberrant hypoxia inducible factor (HIF) accumulation. Recently, next generation-sequencing technologies have provided the bases for an in-depth molecular characterization of ccRCC, identifying additional recurrently mutated genes, such as PBRM1 (≈40-50%), SETD2 (≈12%), or BAP1 (≈10%). PBRM1, the second most common mutated gene in ccRCC after VHL, is a component of the SWI/SNF chromatin remodeling complex. Different studies have investigated the biological consequences and the potential role of PBRM1 alterations in RCC prognosis and as a drug response modulator, although some results are contradictory. In the present article, we review the current evidence on PBRM1 as potential prognostic and predictive marker in both localized and metastatic RCC.

Intrinsic Disorder of the BAF Complex: Roles in Chromatin Remodeling and Disease Development

The two-meter-long DNA is compressed into chromatin in the nucleus of every cell, which serves as a significant barrier to transcription. Therefore, for processes such as replication and transcription to occur, the highly compacted chromatin must be relaxed, and the processes required for chromatin reorganization for the aim of replication or transcription are controlled by ATP-dependent nucleosome remodelers. One of the most highly studied remodelers of this kind is the BRG1- or BRM-associated factor complex (BAF complex, also known as SWItch/sucrose non-fermentable (SWI/SNF) complex), which is crucial for the regulation of gene expression and differentiation in eukaryotes. Chromatin remodeling complex BAF is characterized by a highly polymorphic structure, containing from four to 17 subunits encoded by 29 genes. The aim of this paper is to provide an overview of the role of BAF complex in chromatin remodeling and also to use literature mining and a set of computational and bioinformatics tools to analyze structural properties, intrinsic disorder predisposition, and functionalities of its subunits, along with the description of the relations of different BAF complex subunits to the pathogenesis of various human diseases.

Novel Interactions between the Human T-Cell Leukemia Virus Type 1 Antisense Protein HBZ and the SWI/SNF Chromatin Remodeling Family: Implications for Viral Life Cycle

The human T-cell leukemia virus type 1 (HTLV-1) regulatory proteins Tax and HBZ play indispensable roles in regulating viral and cellular gene expression. BRG1, the ATPase subunit of the SWI/SNF chromatin remodeling complex, has been demonstrated to be essential not only for Tax transactivation but also for viral replication. We sought to investigate the physical interaction between HBZ and BRG1 and to determine the effect of these interactions on Tax-mediated long terminal repeat (LTR) activation. We reveal that HTLV-1 cell lines and adult T-cell leukemia (ATL) cells harbor high levels of BRG1. Using glutathione S-transferase (GST) pulldown and coimmunoprecipitation assays, we have demonstrated physical interactions between BRG1 and HBZ and characterized the protein domains involved. Moreover, we have identified the PBAF signature subunits BAF200 and BAF180 as novel interaction partners of HBZ, suggesting that the PBAF complex may be required for HTLV-1 transcriptional repression by HBZ. Additionally, we found that BRG1 expression translocates HBZ into distinct nuclear foci. We show that HBZ substantially represses HTLV-1 LTR activation by Tax/BRG1. Interestingly, we found that Tax stabilizes the expression of exogenous and endogenous BRG1 and that HBZ reverses this effect. Finally, using a chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR) assay, we illustrate that HBZ facilitates the downregulation of HTLV-1 transcription by deregulating the recruitment of SWI/SNF complexes to the promoter. Overall, we conclude that SWI/SNF complexes, in addition to other cellular transcription factors, are involved in HBZ-mediated suppression of HTLV-1 viral gene expression.IMPORTANCE The pathogenic potential of HTLV-1 is linked to the indispensable multifaceted functions of the viral regulatory proteins Tax and HBZ, encoded by the sense and antisense viral transcripts, respectively. The interaction between Tax and the SWI/SNF family of chromatin remodeling complexes has been associated with HTLV-1 transcriptional activation. To date, the relationship between the SWI/SNF chromatin remodeling family and HBZ, the only viral protein that is consistently expressed in infected cells and ATL cells, has not been elucidated. Here, we have characterized the biological significance of the SWI/SNF family in regard to viral transcriptional repression by HBZ. This is important because it provides a better understanding of the function and role of HBZ in downregulating viral transcription and, hence, its contribution to viral latency and persistence in vivo, a process that may ultimately lead to the development of ATL.

New Insights into the Role of Polybromo-1 in Prostate Cancer

The human protein Polybromo-1 (PBMR1/BAF180) is a component of the SWI/SNF chromatin-remodeling complex that has been reported to be deregulated in tumors. However, its role in prostate cancer (PCa) is largely unknown. In this study, we described the PBRM1 transcriptional levels and the protein expression/localization in tissues of PCa patients and in prostatic cell lines. Increased PBRM1 mRNA levels were found in PCa samples, when compared to benign disease, and were correlated with higher Gleason score. We also verified that only the nuclear localization of PBRM1 protein is correlated with a more aggressive disease and high Prostate-Specific Antigen (PSA) levels in tissue microarrays. Intriguing expression patterns of mRNA and protein were identified in the cell lines. Although PBRM1 protein was restricted to the nuclei, in tumor cell lines in non-neoplastic cells, it was also present in vesicular-like structures that were dispersed within the cytoplasm. We knocked-down PBRM1 in the castration-resistant PCa (CRPC) cell line PC-3 and we verified that PBRM1 promotes the expression of several markers of aggressiveness, including EpCAM, TGF-β, and N-Cadherin. Therefore, our data supported the hypothesis that PBRM1 displays a pivotal role in the promotion and maintenance of the malignant behavior of PCa, especially in CRPC.

PBRM1 Regulates Stress Response in Epithelial Cells

Polybromo1 (PBRM1) is a chromatin remodeler subunit highly mutated in cancer, particularly clear cell renal carcinoma. PBRM1 is a member of the SWI/SNF subcomplex, PBAF (PBRM1-Brg1/Brm-associated factors), and is characterized by six tandem bromodomains. Here we establish a role for PBRM1 in epithelial cell maintenance through the expression of genes involved in cell adhesion, metabolism, stress response, and apoptosis. In support of a general role for PBRM1 in stress response and apoptosis, we observe that loss of PBRM1 results in an increase in reactive oxygen species generation and a decrease in cellular viability under stress conditions. We find that loss of PBRM1 promotes cell growth under favorable conditions but is required for cell survival under conditions of cellular stress.

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PBRM1 facilitates the expression of stress response genes in epithelial cells

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Deletion of PBRM1 promotes growth under low-stress conditions

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PBRM1 restrains ROS generation and induces apoptosis under high-stress conditions

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Under H₂O₂ stress, PBRM1 cooperates with cJun and NRF2 to induce gene expression

Inhibition of Triple-Negative Breast Cancer Cell Aggressiveness by Cathepsin D Blockage: Role of Annexin A1

Triple-negative breast cancers (TNBCs) are more aggressive than other breast cancer (BC) subtypes and lack effective therapeutic options. Unraveling marker events of TNBCs may provide new directions for development of strategies for targeted TNBC therapy. Herein, we reported that Annexin A1 (AnxA1) and Cathepsin D (CatD) are highly expressed in MDA-MB-231 (TNBC lineage), compared to MCF-10A and MCF-7. Since the proposed concept was that CatD has protumorigenic activity associated with its ability to cleave AnxA1 (generating a 35.5 KDa fragment), we investigated this mechanism more deeply using the inhibitor of CatD, Pepstatin A (PepA). Fourier Transform Infrared (FTIR) spectroscopy demonstrated that PepA inhibits CatD activity by occupying its active site; the OH bond from PepA interacts with a CO bond from carboxylic acids of CatD catalytic aspartate dyad, favoring the deprotonation of Asp³³ and consequently inhibiting CatD. Treatment of MDA-MB-231 cells with PepA induced apoptosis and autophagy processes while reducing the proliferation, invasion, and migration. Finally, in silico molecular docking demonstrated that the catalytic inhibition comprises Asp²³¹ protonated and Asp³³ deprotonated, proving all functional results obtained. Our findings elucidated critical CatD activity in TNBC cell trough AnxA1 cleavage, indicating the inhibition of CatD as a possible strategy for TNBC treatment.

Mutations in renal cell carcinoma

Renal cell carcinoma (RCC) is a commonly diagnosed and histologically diverse urologic malignancy. Clear cell RCC (ccRCC) is by far the most common, followed by the papillary and chromophobe subtypes. Sarcomatoid differentiation is a morphologic change that can be seen in all subtypes that typically portends a poor prognosis. In the past, treatment options for RCC were limited to cytokine-based therapy with a high-toxicity profile and low response rate. An increased understanding of the molecular basis of RCC has led to substantial improvement in treatment options in the form of targeted therapy and immunotherapy. A significant early discovery in RCC was frequent inactivation of the Von Hippel Lindau gene in ccRCC, which ultimately led to the development of vascular endothelial growth factor and mammalian target of rapamycin inhibitors. Further genomic sequencing of ccRCC tumors has identified other common mutations including BAP-1, PBRM1, SETD2, and PIK3CA. Many recent studies have explored how these mutations can affect prognosis and response to treatment. Likewise, papillary RCC has also been studied at the molecular level, which has shown a high level of mutations in the MET gene; early clinical data suggest the utility of MET targeted therapy. Finally, regarding the rarer sarcomatoid tumors, mutations in TP53 and NF2 may be important to their development. As we continue to learn more about what drives RCC at the molecular level, treatment options for RCC patients are diversifying.

Identification of alterations in the nucleotide sequence of the chromatin remodeling gene PBRM1 in clear cell renal cell carcinoma patients

Kidney cancer is a heterogeneous group of malignant tumors, the vast majority of which are renal cell carcinomas (RCC) of various morphological types, of which the most common is the clear cell renal cell carcinoma (ccRCC). Particular attention in the carcinogenesis of the ccRCC is given to a number of tumor suppressor genes located on the short arm of the third chromosome. One of these genes, which are inactivated in the case of ccRCC is the PBRM1 gene encoding the PBAF SWI/SNF subunit of the chromatin remodeling complex, BAF180. The PBRM1 gene is located on the short arm of the third chromosome in the 3p21 region near the von Hippel-Lindau gene (VHL), the mutation in which is the main event in the occurrence of ccRCC. The aim of our investigation is identification of changes in the nucleotide sequence of the PBRM1 tumor suppressor gene in patients with ccRCC. 210 pairs of DNA samples isolated from ccRCC tissue were studied. Analysis of changes in the nucleotide sequence of DNA was carried out by HRM analysis and direct sequencing. In the PBRM1 gene, two somatic mutations were found (c.233G>A (p.D45N) in exon 2, c.1675-1676delTC in exon 15) which were not described previously, and one known polymorphic variant rs17264436 (in exon 23). The frequency of detected mutations was 0.95 % of cases. Analysis of the allelic association for the polymorphic locus rs17264436 showed a statistically significant increase in the risk of developing advanced kidney cancer in carriers of allele rs17264436*A, which can be used in the development of prognostic marker panels. Perhaps the low frequency of mutations in the samples we studied is due to the fact that the inactivation of the PBRM1 gene takes place in other ways, and may also be due to the ethno-specificity of the studied group of patients.

Heterologous expression of the human polybromo-1 protein in the methylotrophic yeast Pichia pastoris

The human polybromo-1 protein (BAF180) is a known driver mutation in clear cell renal cell carcinoma, where it is mutated in approximately 40% of cases. BAF180 is the chromatin-targeting subunit of the PBAF complex. BAF180 has six bromodomains, two BAH domains, and one HMG box. Bromodomains are known to recognize acetylated-lysines on histones and play a role in nucleosome recognition. BAH domains are required for ubiquitination of PCNA, a key regulator of DNA damage. The putative HMG box, if functional, may be involved in DNA-binding. While the binding specificities of individual bromodomains have been studied by our lab and others, the results have failed to reach a consensus. The acetyl-histone binding features of the full-length protein is unknown and is the motivation for this work. The hypothetical HMG and BAH domains have not been studied and the actual function of these regions is currently unknown. Thus, the precise interactions of this large and complex protein are not well-studied. Advances in understanding this large protein have been hindered by the inability to express and purify recombinant full-length BAF180 protein. Currently, only phenomenological studies using BAF180 expressed in mammalian cells have been conducted. Here, we report the successful expression, purification of full-length biologically active BAF180 protein using the GAP promoter in the heterologous host Pichia pastoris. The ability to express full-length and mutated BAF180 will allow for biophysical binding studies. Knowledge of the binding interactions is critical for us to understand the role of BAF180 in cancer development and its progression.

Genetic characterization of Polish ccRCC patients: somatic mutation analysis of PBRM1, BAP1 and KDMC5, genomic SNP array analysis in tumor biopsy and preliminary results of chromosome aberrations analysis in plasma cell free DNA

BACKGROUND

Mutation analysis and cytogenetic testing in clear cell renal cell carcinoma (ccRCC) is not yet implemented in a routine diagnostics of ccRCC.

MATERIAL AND METHODS

We characterized the chromosomal alterations in 83 ccRCC tumors from Polish patients using whole genome SNP genotyping assay. Moreover, the utility of next generation sequencing of cell free DNA (cfDNA) in patients plasma as a potential tool for non-invasive cytogenetic analysis was tested. Additionally, tumor specific somatic mutations in PBRM1, BAP1 and KDM5C were determined.

RESULTS

We confirmed a correlation between deletions at 9p and higher tumor size, and deletion of chromosome 20 and the survival time. In Fuhrman grade 1, only aberrations of 3p and 8p deletion, gain of 5q and 13q and gains of chromosome 7 and 16 were present. The number of aberrations increased with Fuhrman grade, all chromosomes displayed cytogenetic changes in G3 and G4. ccRCC specific chromosome aberrations were observed in cfDNA, although discrepancies were found between cfDNA and tumor samples. In total 12 common and 94 rare variants were detected in PBRM1, BAP1 and KDM5C, with four potentially pathogenic variants. We observed markedly lower mutation load in PBRM1.

CONCLUSIONS

Cytogenetic analysis of cfDNA may allow more accurate diagnosis of tumor aberrations and therefore the correlation between the chromosome aberrations in cfDNA and clinical outcome should be studied in larger cohorts. The functional studies on in BAP1, KDM5C, PBRM1 mutations in large, independent sample set would be necessary for the assessment of their prognostic and diagnostic potential.

Chromatin regulation and immune escape

Deficiency in a chromatin remodeling complex enhances tumor immunotherapy

BAFfling pathologies: Alterations of BAF complexes in cancer

To activate or repress specific genes, chromatin is constantly modified by chromatin-remodeling complexes. Among these complexes, the SWItch/Sucrose Non-Fermenting (SWI/SNF) complex, also referred to as BRG1-Associated Factor (BAF) complex, moves the nucleosome along chromatin using energy provided by ATP hydrolysis. In mammalian organisms, the SWI/SNF complex is composed of 10-15 subunits, depending on cell type, and a defect in one of these subunits can have dramatic consequences. In this review we will focus on the alterations identified in the SWI/SNF (BAF) complex subunits that lead to cancerous pathologies. While SMARCB1 was the first mutated subunit to be reported in a majority of malignant rhabdoid tumors, the advent of next-generation sequencing allowed the discovery of mutations in various SWI/SNF subunits within a broad spectrum of cancers. In most cases, the mutation leads to a loss of expression or to a truncated subunit unable to perform its function. Even though it is now commonly acknowledged that approximately 20% of all cancers present a mutation in a SWI/SNF subunit, some cancers are associated to a specific alteration of a SWI/SNF subunit, which acts either as tumor suppressor genes or as oncogenes, and therefore constitute diagnostic or prognostic biomarkers. Consistently, therapeutic strategies targeting SWI/SNF subunits or the genes affected downstream have been revealed to treat cancers.

The epigenetic modifier PBRM1 restricts the basal activity of the innate immune system by repressing retinoic acid-inducible gene-I-like receptor signalling and is a potential prognostic biomarker for colon cancer

It has long been known that patients suffering from inflammatory bowel disease (IBD) have an increased risk of developing colorectal cancer (CRC). The innate immune system of host cells provides a first-line defence against pathogenic infection, whereas an uncontrolled inflammatory response under homeostatic conditions usually leads to pathological consequences, as exemplified by the chronic inflammation of IBD. The key molecules and pathways keeping innate immunity in check are still poorly defined. Here, we report that the chromatin remodeller polybromo-1 (PBRM1) is a repressor of innate immune signalling mediated by retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs). Knockdown of PBRM1 in colon cancer cells increased the expression of two receptor genes (RIG-I and MDA5) and upregulated interferon (IFN)-related and inflammation-related gene signatures. The innate immune signal stimulated by a double-stranded RNA viral mimic was exaggerated by PBRM1 suppression. PBRM1 cooperated with polycomb protein EZH2 to directly bind the cis-regulatory elements of RIG-I and MDA5, thereby suppressing their transcription. Moreover, upregulation of RIG-I and MDA5 is required for IFN response activation induced by PBRM1 silencing. TRIM25, a protein stimulated by the RLR pathway and IFN production, physically interacted with PBRM1 and induced PBRM1 protein destabilization by promoting its ubiquitination. These findings reveal a PBRM1-RLR regulatory circuit that can keep innate immune activity at a minimal level in resting cells, and also ensure a robust inflammatory response in the case of pathogen invasion. PBRM1 was found to be downregulated in primary tissues from patients with CRC or IBD, and its expression correlated negatively with that of RLR genes and interferon-stimulated genes in CRC samples. Lower PBRM1 expression was associated with advanced pathological grade and poorer survival of CRC patients, indicating that PBRM1 could serve as a potential prognostic biomarker for CRC. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

BAF180 regulates cellular senescence and hematopoietic stem cell homeostasis through p21

BAF180 (also called PBRM1), a subunit of the SWI/SNF complex, plays critical roles in the regulation of chromatin remodeling and gene transcription, and is frequently mutated in several human cancers. However, the role of mammalian BAF180 in tumor suppression and tissue maintenance in vivo remains largely unknown. Here, using a conditional somatic knockout approach, we explored the cellular and organismal functions of BAF180 in mouse. BAF180 deletion in primary mouse embryonic fibroblasts (MEFs) triggers profound cell cycle arrest, premature cellular senescence, without affecting DNA damage response or chromosomal integrity. While somatic deletion of BAF180 in adult mice does not provoke tumor development, BAF180 deficient mice exhibit defects in hematopoietic system characterized by progressive reduction of hematopoietic stem cells (HSCs), defective long-term repopulating potential, and hematopoietic lineage developmental aberrations. BAF180 deletion results in elevated p21 expression in both MEFs and HSCs. Mechanistically, we showed that BAF180 binds to p21 promoter, and BAF180 deletion enhances the binding of modified histones associated with transcriptional activation on p21 promoter. Deletion of p21 rescues cell cycle arrest and premature senescence in BAF180 deficient MEFs, and partially rescues hematopoietic defects in BAF180 deficient mice. Together, our study identifies BAF180 as a critical regulator of cellular senescence and HSC homeostasis, which is at least partially regulated through BAF180-mediated suppression of p21 expression. Our results also suggest that senescence triggered by BAF180 inactivation may serve as a failsafe mechanism to restrain BAF180 deficiency-associated tumor development, providing a conceptual framework to further understand BAF180 function in tumor biology.

The SWI/SNF Protein PBRM1 Restrains VHL-Loss-Driven Clear Cell Renal Cell Carcinoma

PBRM1 is the second most commonly mutated gene after VHL in clear cell renal cell carcinoma (ccRCC). However, the biological consequences of PBRM1 mutations for kidney tumorigenesis are unknown. Here, we find that kidney-specific deletion of Vhl and Pbrm1, but not either gene alone, results in bilateral, multifocal, transplantable clear cell kidney cancers. PBRM1 loss amplified the transcriptional outputs of HIF1 and STAT3 incurred by Vhl deficiency. Analysis of mouse and human ccRCC revealed convergence on mTOR activation, representing the third driver event after genetic inactivation of VHL and PBRM1. Our study reports a physiological preclinical ccRCC mouse model that recapitulates somatic mutations in human ccRCC and provides mechanistic and therapeutic insights into PBRM1 mutated subtypes of human ccRCC.

BAF180: Its Roles in DNA Repair and Consequences in Cancer

In 2011, Varela et al. reported that the PBRM1 gene is mutated in approximately 40% of clear cell renal cell carcinoma cases. Since then, the number of studies relating PBRM1 mutations to cancers has substantially increased. BAF180 has now been linked to more than 30 types of cancers, including ccRCC, cholangiocarcinomas, esophageal squamous cell carcinoma, bladder cancer, and breast cancer. The mutations associated with BAF180 are most often truncations, which result in a loss of protein expression. This loss has been shown to adversely affect the expression of genes, likely because BAF180 is the chromatin recognition subunit of PBAF. In addition, BAF180 functions in numerous DNA repair mechanisms. Its roles in mediating DNA repair are likely the mechanism by which BAF180 acts a tumor suppressor protein. As research on this protein gains more interest, scientists will begin to piece together the complicated puzzle of the BAF180 protein and why its loss often results in cancer.

PBRM1 regulates proliferation and the cell cycle in renal cell carcinoma through a chemokine/chemokine receptor interaction pathway

PBRM1 is a novel tumor suppressor gene that can inhibit cancer cell proliferation and predict the outcome of renal cell carcinoma (RCC), but its biological role needs further elucidation. We examined expression of the PBRM1 gene in RCC cell lines and the effect of PBRM1 on cell proliferation and cell cycle in RCC ACHN cells. Microarray processing and analysis was used to explore novel pathways involved in tumorigenesis related to PBRM1 knockdown. PBRM1 was expressed at high levels in RCC ACHN cells and lentivirus-mediated PBRM1 knockdown in these cells caused an increase in the proportion of cells in S phase of the cell cycle and promoted in vitro proliferation and migration. In vivo experiments showed that downregulation of PBRM1 promoted tumorigenesis in nude mice. In pathway gene chip analysis, the chemokine/chemokine receptor interaction pathway showed the greatest difference in gene expression upon PBRM1 knockdown. Protein levels of IL6ST and CCL2 were increased, whereas levels of interleukin (IL)-8, IL-6, and CXCL2 were decreased, in knockdown cells. Re-expression of IL-8 in PBRM1 knockdown ACHN cells could significantly decrease cell proliferation/migration and induced cell arrest in the G2/M phase. These findings indicate that PBRM1 alters cell cycle progression and inhibits proliferation and migration of ACHN cells through the chemokine/chemokine receptor pathway.

Stability of the PHF10 subunit of PBAF signature module is regulated by phosphorylation: role of β-TrCP

The PBAF chromatin-remodeling complexes are multi-protein machines, regulating expression of genes involved in proliferation and differentiation. PHF10 is a subunit of the PBAF essential for its association with chromatin. Mammalian PHF10 is expressed as four ubiquitous isoforms, which are alternatively incorporated in the complex and differ by their influence on transcription of target genes. PHF10 have different domain structure and two of them (PHF10-S isoforms) lack C-terminal PHD domains, which enables their phosphorylation by CK-1. Here we have found that PBAF subunits have low turnover rate, except for PHF10 which has much lower half-life, and is degraded by β-TrCP. The β-TrCP knockdown stabilizes PBAF core subunits - BRG1 and BAF155 and specific subunits - PHF10, BAF200, BAF180 and BRD7. PHF10 isoforms contain two non-canonical β-TrCP degrons and are degraded by β-TrCP in a phospho-dependent manner. But phosphorylation of PHF10-S degrons by CK-1, contrary to previously described degrons, prevents their degradation. Targeted molecular docking demonstrated that phosphorylated forms of PHF10 bind to β-TrCP with much lower affinity than non-phosphorylated ones, contrary to previously described degrons. This unorthodox mechanism proposes that phosphorylation of β-TrCP degrons by CK-1 could not only degrade a set of proteins, but also stabilize a different set of targets.

Functional role of SETD2, BAP1, PARP-3 and PBRM1 candidate genes on the regulation of hTERT gene expression

Narrowing the search for the critical hTERT repressor sequence(s) has identified three regions on chromosome 3p (3p12-p21.1, 3p21.2 and 3p21.3-p22). However, the precise location and identity of the sequence(s) responsible for hTERT transcriptional repression remains elusive. In order to identify critical hTERT repressor sequences located within human chromosome 3p12-p22, we investigated hTERT transcriptional activity within 21NT microcell hybrid clones containing chromosome 3 fragments. Mapping of chromosome 3 structure in a single hTERT-repressed 21NT-#3fragment hybrid clone, revealed a 490kb region of deletion localised to 3p21.3 and encompassing the histone H3, lysine 36 (H3K36) trimethyltransferase enzyme SETD2; a putative tumour suppressor gene in breast cancer. Three additional genes, BAP1, PARP-3 and PBRM1, were also selected for further investigation based on their location within the 3p21.1-p21.3 region, together with their documented role in the epigenetic regulation of target gene expression or hTERT regulation. All four genes (SETD2, BAP1, PARP-3 and PBRM1) were found to be expressed at low levels in 21NT. Gene copy number variation (CNV) analysis of SETD2, BAP1, PARP-3 and PBRM1 within a panel of nine breast cancer cell lines demonstrated single copy number loss of all candidate genes within five (56%) cell lines (including 21NT cells). Stable, forced overexpression of BAP1, but not PARP2, SETD2 or PBRM1, within 21NT cells was associated with a significant reduction in hTERT expression levels relative to wild-type controls. We propose that at least two sequences exist on human chromosome 3p, that function to regulate hTERT transcription within human breast cancer cells.

BRM promoter insertion polymorphisms increase the risk of cancer: A meta-analysis

INTRODUCTION

Many studies have suggested that the BRM promoter insertion polymorphisms might be associated with susceptibility to many different types of cancer. However, previous studies reported contradictory results. This current meta-analysis was performed to address this issue.

EVIDENCE ACQUISITION

A comprehensive search was conducted in multiple databases, including PubMed, Embase and China National Knowledge Infrastructure (CNKI). We collected relevant articles to explore the association between the BRM insertion polymorphisms and susceptibility of cancers.

EVIDENCE SYNTHESIS

For the BRM-741 polymorphism, a total of 2901 cases and 3667 controls from 6 studies were included. For the BRM-1321 polymorphism, a total of 2899 cases and 3769 controls from 6 studies were included. Overall, a significant difference was observed in BRM-741 (OR 0.81; 95%CI 0.68, 0.96; P=0.02) and BRM-1321 (OR 0.76; 95%CI 0.66, 0.88; P<0.01) for allele frequency (D versus I). In the subgroup analysis, for the BRM-741, a significant difference was observed in Asian (OR 0.88; 95%CI 0.78, 0.99; P=0.03) for D versus I. Similarly, for the BRM-1321, a significant difference was observed in Asian (OR 0.43; 95%CI 0.32, 0.58; P<0.001) and Caucasian (OR 0.74; 95%CI 0.62, 0.88; P<0.001) for DD versus II.

CONCLUSIONS

BRM-741 and BRM-1321 insertion polymorphisms are associated with susceptibility to cancer. Further studies are warranted to verify the clinical utility of BRM promoter insertion polymorphisms in human tumors.

A genetic interaction analysis identifies cancer drivers that modify EGFR dependency

In this study, Liao et al. comprehensively investigated how cancer drivers genetically interact. They searched for modifiers of EGFR dependency by performing CRISPR, shRNA, and expression screens in a NSCLC model, and their data provide strong support for the hypothesis that many cancer drivers can substitute for each other in certain contexts.

A large number of cancer drivers have been identified through tumor sequencing efforts, but how they interact and the degree to which they can substitute for each other have not been systematically explored. To comprehensively investigate how cancer drivers genetically interact, we searched for modifiers of epidermal growth factor receptor (EGFR) dependency by performing CRISPR, shRNA, and expression screens in a non-small cell lung cancer (NSCLC) model. We elucidated a broad spectrum of tumor suppressor genes (TSGs) and oncogenes (OGs) that can genetically modify proliferation and survival of cancer cells when EGFR signaling is altered. These include genes already known to mediate EGFR inhibitor resistance as well as many TSGs not previously connected to EGFR and whose biological functions in tumorigenesis are not well understood. We show that mutation of PBRM1, a subunit of the SWI/SNF complex, attenuates the effects of EGFR inhibition in part by sustaining AKT signaling. We also show that mutation of Capicua (CIC), a transcriptional repressor, suppresses the effects of EGFR inhibition by partially restoring the EGFR-promoted gene expression program, including the sustained expression of Ets transcription factors such as ETV1. Together, our data provide strong support for the hypothesis that many cancer drivers can substitute for each other in certain contexts and broaden our understanding of EGFR regulation.

Transcriptional Regulation by Wild-Type and Cancer-Related Mutant Forms of p53

TP53 missense mutations produce a mutant p53 protein that cannot activate the p53 tumor suppressive transcriptional response, which is the primary selective pressure for TP53 mutation. Specific codons of TP53, termed hotspot mutants, are mutated at elevated frequency. Hotspot forms of mutant p53 possess oncogenic properties in addition to being deficient in tumor suppression. Such p53 mutants accumulate to high levels in the cells they inhabit, causing transcriptional alterations that produce pro-oncogenic activities, such as increased pro-growth signaling, invasiveness, and metastases. These forms of mutant p53 very likely use features of wild-type p53, such as interactions with the transcriptional machinery, to produce oncogenic effects. In this review, we discuss commonalities between wild-type and mutant p53 proteins with an emphasis on transcriptional processes.

Context-dependent role for chromatin remodeling component PBRM1/BAF180 in clear cell renal cell carcinoma

A subset of clear cell renal cell carcinoma (ccRCC) tumors exhibit a HIF1A gene mutation, yielding two ccRCC tumor types, H1H2 type expressing both HIF1α and HIF2α, and H2 type expressing HIF2α, but not functional HIF1α protein. However, it is unclear how the H1H2 type ccRCC tumors escape HIF1's tumor-suppressive activity. The polybromo-1 (PBRM1) gene coding for the BAF180 protein, a component of the SWItch/Sucrose Non-Fermentable (SWI/SNF) chromatin remodeling complex, is inactivated in 40% ccRCCs, the function and mechanism of BAF180 mutation is unknown. Our previous study indicates that BAF180-containing SWI/SNF chromatin remodeling complex is a co-activator for transcription factor HIF to induce HIF target genes. Thus, our questions are if BAF180 is involved in HIF-mediated hypoxia response and if PBRM1/BAF180 mutation has any association with the HIF1A retention in H1H2 type ccRCC. We report here that BAF180 is mutated in H1H2 ccRCC cell lines and tumors, and BAF180 re-expression in H1H2 ccRCC cell lines reduced cell proliferation/survival, indicating that BAF180 has tumor-suppressive role in these cells. However, BAF180 is expressed in HIF1-deficient H2 ccRCC cell lines and tumors, and BAF180 knockdown in H2 type ccRCC cell lines reduced cell proliferation/survival, indicating that BAF180 has tumor-promoting activity in these cells. In addition, our data show that BAF180 functions as co-activator for HIF1- and HIF2-mediated transcriptional response, and BAF180's tumor-suppressive and -promoting activity in ccRCC cell lines depends on co-expression of HIF1 and HIF2, respectively. Thus, our studies reveal that BAF180 function in ccRCC is context dependent, and that mutation of PBRM1/BAF180 serves as an alternative strategy for ccRCC tumors to reduce HIF1 tumor-suppressive activity in H1H2 ccRCC tumors. Our studies define distinct functional subgroups of ccRCCs based on expression of BAF180, and suggest that BAF180 inhibition may be a novel therapeutic target for patients with H2, but not H1H2, ccRCC tumors.

The epigenetic landscape of renal cancer

The majority of kidney cancers are associated with mutations in the von Hippel-Lindau gene and a small proportion are associated with infrequent mutations in other well characterized tumour-suppressor genes. In the past 15 years, efforts to uncover other key genes involved in renal cancer have identified many genes that are dysregulated or silenced via epigenetic mechanisms, mainly through methylation of promoter CpG islands or dysregulation of specific microRNAs. In addition, the advent of next-generation sequencing has led to the identification of several novel genes that are mutated in renal cancer, such as PBRM1, BAP1 and SETD2, which are all involved in histone modification and nucleosome and chromatin remodelling. In this Review, we discuss how altered DNA methylation, microRNA dysregulation and mutations in histone-modifying enzymes disrupt cellular pathways in renal cancers.

Discovery and Optimization of a Selective Ligand for the Switch/Sucrose Nonfermenting-Related Bromodomains of Polybromo Protein-1 by the Use of Virtual Screening and Hydration Analysis

Bromodomains (BRDs) are epigenetic interaction domains currently recognized as emerging drug targets for development of anticancer or anti-inflammatory agents. In this study, development of a selective ligand of the fifth BRD of polybromo protein-1 (PB1(5)) related to switch/sucrose nonfermenting (SWI/SNF) chromatin remodeling complexes is presented. A compound collection was evaluated by consensus virtual screening and a hit was identified. The biophysical study of protein-ligand interactions was performed using X-ray crystallography and isothermal titration calorimetry. Collective data supported the hypothesis that affinity improvement could be achieved by enhancing interactions of the complex with the solvent. The derived SAR along with free energy calculations and a consensus hydration analysis using WaterMap and SZmap algorithms guided rational design of a set of novel analogues. The most potent analogue demonstrated high affinity of 3.3 μM and an excellent selectivity profile, thus comprising a promising lead for the development of chemical probes targeting PB1(5).

Epigenomic Consequences of Coding and Noncoding Driver Mutations

Chromatin alterations are integral to the pathogenic process of cancer, as demonstrated by recent discoveries of frequent mutations in chromatin-modifier genes and aberrant DNA methylation states in different cancer types. Progress is being made on elucidating how chromatin alterations, and how proteins catalyzing these alterations, mechanistically contribute to tissue-specific tumorigenesis. In parallel, technologies enabling the genome-wide profiling of histone modifications have revealed the existence of noncoding driver genetic alterations in cancer. In this review, we survey the current knowledge of coding and noncoding cancer drivers, and discuss their impact on the chromatin landscape. Translational implications of these findings for novel cancer therapies are also presented.

An integrative genomics approach for identifying novel functional consequences of PBRM1 truncated mutations in clear cell renal cell carcinoma (ccRCC)

BACKGROUND

Clear cell renal cell carcinoma (ccRCC) is the most common type of kidney cancer. Recent large-scale next-generation sequencing analyses reveal that PBRM1 is the second most frequently mutated gene harboring many truncated mutations and has a suspected tumor suppressor role in ccRCC. However, the biological consequences of PBRM1 somatic mutations (e.g., truncated mutations) that drive tumor progression in ccRCC remain unclear.

METHODS

In this study, we proposed an integrative genomics approach to explore the functional consequences of PBRM1 truncated mutations in ccRCC by incorporating somatic mutations, mRNA expression, DNA methylation, and microRNA (miRNA) expression profiles from The Cancer Genome Atlas (TCGA). We performed a systematic analysis to detect the differential molecular features in a total of 11 ccRCC samples harboring PBRM1 truncated mutations from the 33 "pan-negative" ccRCC samples. We excluded the samples that had any of the five high-confidence driver genes (VHL, BAP1, SETD2, PTEN and KDM5C) reported in ccRCC to avoid their possible influence in our results.

RESULTS

We identified 613 differentially expressed genes (128 up-regulated and 485 down-regulated genes using cutoff |log2FC| > 1 and p < 0.05) in PBRM1 mutated group versus "pan-negative" group. The gene function enrichment analysis revealed that down-regulated genes were significantly enriched in extracellular matrix organization (adjusted p = 2.05 × 10(-7)), cell adhesion (adjusted p = 2.85 × 10(-7)), and ion transport (adjusted p = 9.97 × 10(-6)). Surprisingly, 26 transcriptional factors (TFs) genes including HOXB9, PAX6 and FOXC1 were found to be significantly differentially expressed (23 over expressed TFs and three lower expressed TFs) in PBRM1 mutated group compared with "pan-negative" group. In addition, we identified 1405 differentially methylated CpG sites (targeting 1308 genes, ||log2FC| > 1, p < 0.01) and 185 significantly altered microRNAs (|log2FC| > 1, p < 0.05) associated with truncated PBRM1 mutations. Our integrative analysis suggested that methylation and miRNA alterations were likely the downstream events associated with PBRM1 truncation mutations.

CONCLUSIONS

In summary, this study provided some important insights into the understanding of tumorigenesis driven by PBRM1 truncated mutations in ccRCC. The approach may be applied to many driver genes in various cancers.

The developmental and pathogenic roles of BAF57, a special subunit of the BAF chromatin-remodeling complex

Mammalian SWI/SNF or BAF chromatin-remodeling complexes are polymorphic assemblies of homologous subunit families that remodel nucleosomes. BAF57 is a subunit of the BAF complexes; it is encoded only in higher eukaryotes and is present in all mammalian assemblies. Its main structural feature is a high-mobility group domain, the DNA-binding properties of which suggest that BAF57 may play topological roles as the BAF complex enters or exits the nucleosome. BAF57 displays specific interactions with a number of proteins outside the BAF complex. Through these interactions, it can accomplish specific functions. In the embryo, BAF57 is responsible for the silencing of the CD4 gene during T-cell differentiation, and during the repression of neuronal genes in non-neuronal cells, BAF57 interacts with the transcriptional corepressor, Co-REST, and facilitates repression. Extensive work has demonstrated a specific role of BAF57 in regulating the interactions between BAF and nuclear hormone receptors. Despite its involvement in oncogenic pathways, new generation sequencing studies do not support a prominent role for BAF57 in the initiation of cancer. On the other hand, evidence has emerged to support a role for BAF57 as a metastasis factor, a prognosis marker and a therapeutic target. In humans, BAF57 is associated with disease, as mutations in this gene predispose to important congenital disorders, including menigioma disease or the Coffin-Siris syndrome. In this article, we present an exhaustive analysis of the BAF57 molecular and biochemical properties, cellular functions, loss-of-function phenotypes in living organisms and pathological manifestations in cases of human mutations.

PBRM1 suppresses bladder cancer by cyclin B1 induced cell cycle arrest

Growing evidence indicates that dys-regulation of PBRM1 contributes to tumorigenesis. However, little is known about the biological function of PBRM1 in the development or progression of bladder cancer. In this study, we aimed to elucidate the pathophysiological role of PBRM1 in bladder cancer. We assessed the expression of PBRM1 in 64 bladder cancer tissue samples with matching normal tissues. We explored the biological functions of PBRM1 both in vitro and in vivo. Mutational status of PBRM1 was analyzed. Effect of PBRM1 on cell cycle was evaluated. qRT-PCR and Western blot were carried out to evaluate the expression of cyclins affected by PBRM1. Our results showed that PBRM1 expression was significantly reduced in bladder cancer cells and tissues compared to their normal counterparts. The reduced expression of PBRM1 was associated with advanced tumor stage, low differentiation grade and worse patient outcome. Further functional analysis demonstrated that PBRM1 suppressed bladder cancer cell proliferation, migration, colony formation in vitro and tumorigenicity in vivo. Genetic alteration analysis showed no amino-acid sequence altering mutations. We found that PBRM1 could block the G2/M transition by repressing cyclin B1. Our data indicated that PBRM1 functions as a tumor suppressor in bladder cancer by repressing cyclin B1 expression.

PBRM1 Regulates the Expression of Genes Involved in Metabolism and Cell Adhesion in Renal Clear Cell Carcinoma

Polybromo-1 (PBRM1) is a component of the PBAF (Polybromo-associated-BRG1- or BRM-associated factors) chromatin remodeling complex and is the second most frequently mutated gene in clear-cell renal cell Carcinoma (ccRCC). Mutation of PBRM1 is believed to be an early event in carcinogenesis, however its function as a tumor suppressor is not understood. In this study, we have employed Next Generation Sequencing to profile the differentially expressed genes upon PBRM1 re-expression in a cellular model of ccRCC. PBRM1 re-expression led to upregulation of genes involved in cellular adhesion, carbohydrate metabolism, apoptotic process and response to hypoxia, and a downregulation of genes involved in different stages of cell division. The decrease in cellular proliferation upon PBRM1 re-expression was confirmed, validating the functional role of PBRM1 as a tumor suppressor in a cell-based model. In addition, we identified a role for PBRM1 in regulating metabolic pathways known to be important for driving ccRCC, including the regulation of hypoxia response genes, PI3K signaling, glucose uptake, and cholesterol homeostasis. Of particular novelty is the identification of cell adhesion as a major downstream process uniquely regulated by PBRM1 expression. Cytoskeletal reorganization was induced upon PBRM1 reexpression as evidenced from the increase in the number of cells displaying cortical actin, a hallmark of epithelial cells. Genes involved in cell adhesion featured prominently in our transcriptional dataset and overlapped with genes uniquely regulated by PBRM1 in clinical specimens of ccRCC. Genes involved in cell adhesion serve as tumor suppressor and maybe involved in inhibiting cell migration. Here we report for the first time genes linked to cell adhesion serve as downstream targets of PBRM1, and hope to lay the foundation of future studies focusing on the role of chromatin remodelers in bringing about these alterations during malignancies.