Chromatin loading of E2F-MLL complex by cancer-associated coregulator ANCCA via reading a specific histone mark

Hypoxia-Inducible Factor-Dependent and Independent Mechanisms Underlying Chemoresistance of Hypoxic Cancer Cells

In hypoxic regions of malignant solid tumors, cancer cells acquire resistance to conventional therapies, such as chemotherapy and radiotherapy, causing poor prognosis in patients with cancer. It is widely recognized that some of the key genes behind this are hypoxia-inducible transcription factors, e.g., hypoxia-inducible factor 1 (HIF-1). Since HIF-1 activity is suppressed by two representative 2-oxoglutarate-dependent dioxygenases (2-OGDDs), PHDs (prolyl-4-hydroxylases), and FIH-1 (factor inhibiting hypoxia-inducible factor 1), the inactivation of 2-OGDD has been associated with cancer therapy resistance by the activation of HIF-1. Recent studies have also revealed the importance of hypoxia-responsive mechanisms independent of HIF-1 and its isoforms (collectively, HIFs). In this article, we collate the accumulated knowledge of HIF-1-dependent and independent mechanisms responsible for resistance of hypoxic cancer cells to anticancer drugs and briefly discuss the interplay between hypoxia responses, like EMT and UPR, and chemoresistance. In addition, we introduce a novel HIF-independent mechanism, which is epigenetically mediated by an acetylated histone reader protein, ATAD2, which we recently clarified.

Cancer testis antigens: Emerging therapeutic targets leveraging genomic instability in cancer

Cancer care has witnessed remarkable progress in recent decades, with a wide array of targeted therapies and immune-based interventions being added to the traditional treatment options such as surgery, chemotherapy, and radiotherapy. However, despite these advancements, the challenge of achieving high tumor specificity while minimizing adverse side effects continues to dictate the benefit-risk balance of cancer therapy, guiding clinical decision making. As such, the targeting of cancer testis antigens (CTAs) offers exciting new opportunities for therapeutic intervention of cancer since they display highly tumor specific expression patterns, natural immunogenicity and play pivotal roles in various biological processes that are critical for tumor cellular fitness. In this review, we delve deeper into how CTAs contribute to the regulation and maintenance of genomic integrity in cancer, and how these mechanisms can be exploited to specifically target and eradicate tumor cells. We review the current clinical trials targeting aforementioned CTAs, highlight promising pre-clinical data and discuss current challenges and future perspectives for future development of CTA-based strategies that exploit tumor genomic instability.

Screening Ultra-Large Encoded Compound Libraries Leads to Novel Protein-Ligand Interactions and High Selectivity

The DNA-encoded library (DEL) discovery platform has emerged as a powerful technology for hit identification in recent years. It has become one of the major parallel workstreams for small molecule drug discovery along with other strategies such as HTS and data mining. For many researchers working in the DEL field, it has become increasingly evident that many hits and leads discovered via DEL screening bind to target proteins with unique and unprecedented binding modes. This Perspective is our attempt to analyze reports of DEL screening with the purpose of providing a rigorous and useful account of the binding modes observed for DEL-derived ligands with a focus on binding mode novelty.

Unbiased interrogation of functional lysine residues in human proteome

CRISPR screens have empowered the high-throughput dissection of gene functions; however, more explicit genetic elements, such as codons of amino acids, require thorough interrogation. Here, we establish a CRISPR strategy for unbiasedly probing functional amino acid residues at the genome scale. By coupling adenine base editors and barcoded sgRNAs, we target 215,689 out of 611,267 (35%) lysine codons, involving 85% of the total protein-coding genes. We identify 1,572 lysine codons whose mutations perturb human cell fitness, with many of them implicated in cancer. These codons are then mirrored to gene knockout screen data to provide functional insights into the role of lysine residues in cellular fitness. Mining these data, we uncover a CUL3-centric regulatory network in which lysine residues of CUL3 CRL complex proteins control cell fitness by specifying protein-protein interactions. Our study offers a general strategy for interrogating genetic elements and provides functional insights into the human proteome.

The miR-302/367 cluster: Aging, inflammation, and cancer

MicroRNAs (miRNAs) are a class of noncoding RNAs that occupy a significant role in biological processes as important regulators of intracellular homeostasis. First, we will discuss the biological genesis and functions of the miR-302/367 cluster, including miR-302a, miR-302b, miR-302c, miR-302d, and miR-367, as well as their roles in physiologically healthy tissues. The second section of this study reviews the progress of the miR-302/367 cluster in the treatment of cancer, inflammation, and diseases associated with aging. This cluster's aberrant expression in cells and/or tissues exhibits similar or different effects in various diseases through molecular mechanisms such as proliferation, apoptosis, cycling, drug resistance, and invasion. This article also discusses the upstream and downstream regulatory networks of miR-302/367 clusters and their related mechanisms. Particularly because studies on the upstream regulatory molecules of miR-302/367 clusters, which include age-related macular degeneration, myocardial infarction, and cancer, have become more prevalent in recent years. MiR-302/367 cluster can be an important therapeutic target and the use of miRNAs in combination with other molecular markers may improve diagnostic or therapeutic capabilities, providing unique insights and a more dynamic view of various diseases. It is noted that miRNAs can be an important bio-diagnostic target and offer a promising method for illness diagnosis, prevention, and treatment.

Structure of the human ATAD2 AAA+ histone chaperone reveals mechanism of regulation and inter-subunit communication

ATAD2 is a non-canonical ATP-dependent histone chaperone and a major cancer target. Despite widespread efforts to design drugs targeting the ATAD2 bromodomain, little is known about the overall structural organization and regulation of ATAD2. Here, we present the 3.1 Å cryo-EM structure of human ATAD2 in the ATP state, showing a shallow hexameric spiral that binds a peptide substrate at the central pore. The spiral conformation is locked by an N-terminal linker domain (LD) that wedges between the seam subunits, thus limiting ATP-dependent symmetry breaking of the AAA+ ring. In contrast, structures of the ATAD2-histone H3/H4 complex show the LD undocked from the seam, suggesting that H3/H4 binding unlocks the AAA+ spiral by allosterically releasing the LD. These findings, together with the discovery of an inter-subunit signaling mechanism, reveal a unique regulatory mechanism for ATAD2 and lay the foundation for developing new ATAD2 inhibitors.

ATAD2 is a driver and a therapeutic target in ovarian cancer that functions by upregulating CENPE

Ovarian cancer is a complex disease associated with multiple genetic and epigenetic alterations. The emergence of treatment resistance in most patients causes ovarian cancer to become incurable, and novel therapies remain necessary. We identified epigenetic regulator ATPase family AAA domain-containing 2 (ATAD2) is overexpressed in ovarian cancer and is associated with increased incidences of metastasis and recurrence. Genetic knockdown of ATAD2 or its pharmacological inhibition via ATAD2 inhibitor BAY-850 suppressed ovarian cancer growth and metastasis in both in vitro and in vivo models. Transcriptome-wide mRNA expression profiling of ovarian cancer cells treated with BAY-850 revealed that ATAD2 inhibition predominantly alters the expression of centromere regulatory genes, particularly centromere protein E (CENPE). In ovarian cancer cells, changes in CENPE expression following ATAD2 inhibition resulted in cell-cycle arrest and apoptosis induction, which led to the suppression of ovarian cancer growth. Pharmacological CENPE inhibition phenotypically recapitulated the cellular changes induced by ATAD2 inhibition, and combined pharmacological inhibition of both ATAD2 and CENPE inhibited ovarian cancer cell growth more potently than inhibition of either alone. Thus, our study identified ATAD2 as regulators of ovarian cancer growth and metastasis that can be targeted either alone or in combination with CENPE inhibitors for effective ovarian cancer therapy.

ATPase family AAA domain-containing protein 2 (ATAD2): From an epigenetic modulator to cancer therapeutic target

ATPase family AAA domain-containing protein 2 (ATAD2) has been widely reported to be a new emerging oncogene that is closely associated with epigenetic modifications in human cancers. As a coactivator of transcription factors, ATAD2 can participate in epigenetic modifications and regulate the expression of downstream oncogenes or tumor suppressors, which may be supported by the enhancer of zeste homologue 2. Moreover, the dominant structure (AAA + ATPase and bromine domains) can make ATAD2 a potential therapeutic target in cancer, and some relevant small-molecule inhibitors, such as GSK8814 and AZ13824374, have also been discovered. Thus, in this review, we focus on summarizing the structural features and biological functions of ATAD2 from an epigenetic modulator to a cancer therapeutic target, and further discuss the existing small-molecule inhibitors targeting ATAD2 to improve potential cancer therapy. Together, these inspiring findings would shed new light on ATAD2 as a promising druggable target in cancer and provide a clue on the development of candidate anticancer drugs.

A targetable MYBL2-ATAD2 axis governs cell proliferation in ovarian cancer

The chromatin-modifying enzyme ATAD2 confers oncogenic competence and proliferative advantage in malignances. We previously identified ATAD2 as a marker and driver of cell proliferation in ovarian cancer (OC); however, the mechanisms whereby ATAD2 is regulated and involved in cell proliferation are still unclear. Here, we disclose that ATAD2 displays a classical G2/M gene signature, functioning to facilitate mitotic progression. ATAD2 ablation caused mitotic arrest and decreased the ability of OC cells to pass through nocodazole-arrested mitosis. ChIP-seq data analyses demonstrated that DREAM and MYBL2-MuvB (MMB), two switchable MuvB-based complexes, bind the CHR elements in the ATAD2 promoter, representing a typical feature and principle mechanism of the periodic regulation of G2/M genes. As a downstream target of MYBL2, ATAD2 deletion significantly impaired MYBL2-driven cell proliferation. Intriguingly, ATAD2 silencing also fed back to destabilize the MYBL2 protein. The significant coexpression of MYBL2 and ATAD2 at both the bulk tissue and single-cell levels highlights the existence of the MYBL2-ATAD2 signaling in OC patients. This signaling is activated during tumorigenesis and correlated with TP53 mutation, and its hyperactivation was found especially in high-grade serous and drug-resistant OCs. Disrupting this signaling by CRISPR/Cas9-mediated ATAD2 ablation inhibited the in vivo growth of OC in a subcutaneous tumor xenograft mouse model, while pharmacologically targeting this signaling with an ATAD2 inhibitor demonstrated high therapeutic efficacy in both drug-sensitive and drug-resistant OC cells. Collectively, we identified a novel MYBL2-ATAD2 proliferative signaling axis and highlighted its potential application in developing new therapeutic strategies, especially for high-grade serous and drug-resistant OCs.

Genome-wide survey of D/E repeats in human proteins uncovers their instability and aids in identifying their role in the chromatin regulator ATAD2

D/E repeats are stretches of aspartic and/or glutamic acid residues found in over 150 human proteins. We examined genomic stability of D/E repeats and functional characteristics of D/E repeat-containing proteins vis-à-vis the proteins with poly-Q or poly-A repeats, which are known to undergo pathologic expansions. Mining of tumor sequencing data revealed that D/E repeat-coding regions are similar to those coding poly-Qs and poly-As in increased incidence of trinucleotide insertions/deletions but differ in types and incidence of substitutions. D/E repeat-containing proteins preferentially function in chromatin metabolism and are the more likely to be nuclear and interact with core histones, the longer their repeats are. One of the longest D/E repeats of unknown function is in ATAD2, a bromodomain family ATPase frequently overexpressed in tumors. We demonstrate that D/E repeat deletion in ATAD2 suppresses its binding to nascent and mature chromatin and to the constitutive pericentromeric heterochromatin, where ATAD2 represses satellite transcription.

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Many human proteins contain runs of aspartic/glutamic acid residues (D/E repeats)

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D/E repeats show increased incidence of in-frame insertions/deletions in tumors

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Nuclear and histone-interacting proteins often have long D/E repeats

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D/E repeat of the oncogene ATAD2 controls its binding to pericentric chromatin

ATAD2 Upregulation Promotes Tumor Growth and Angiogenesis in Endometrial Cancer and Is Associated with Its Immune Infiltration

Background

Endometrial cancer is one of the three major gynecologic malignancies, and its incidence continues to rise. ATPase family AAA structural domain-containing protein 2 (ATAD2) is an ATPase protein, which is an independent factor for poor prognosis in endometrial cancer. However, its role in the disease is yet to be determined.

Methods

The Tumor IMmune Estimation Resource (TIMER) database was used to assess ATAD2 expression in pan-cancer, and the relevance of ATAD2 expression in Uterine Corpus Endometrial Carcinoma (UCEC) in clinical settings was obtained using Gene Expression Profiling Interactive Analysis (GEPIA) and UALCAN analysis. In addition, the Human Protein Atlas database was used to assess ATAD2 protein expression in UCEC. Furthermore, in vitro molecular biology and in vivo functional experiments were employed to ascertain the effect of ATAD2 expression on tumor angiogenesis and tumor growth. UALCAN was used to screen for ATAD2 coexpressed genes, and Sangerbox was utilized to perform Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses of these coexpressed genes. Finally, the TIMER, Tumor Immune System Interaction and Drug Bank (TISIDB), and GEPIA databases were used to analyze the relationship between ATAD2 and immune infiltration.

Results

ATAD2 is highly expressed in a variety of tumors, and in UCEC, it plays the role of a protooncogene. Basic experiments revealed that ATAD2 promotes vascular endothelial growth factor expression in endometrial cancer and affects tumor growth and angiogenesis. In addition, GO and KEGG enrichment analyses showed that ATAD2-associated genes were chiefly enriched in certain signaling pathways, such as herpes simplex virus 1 infection and that ATAD2 was associated with immune infiltration in UCEC.

Conclusion

Our findings suggest that ATAD2 promotes tumor growth and angiogenesis in endometrial cancer. Furthermore, ATAD2 is associated with immune infiltration and is a potential diagnostic and therapeutic target.

miR-302 Suppresses the Proliferation, Migration, and Invasion of Breast Cancer Cells by Downregulating ATAD2

Simple Summary

ATPase family AAA domain-containing protein 2 (ATAD2) overexpression is associated with poor survival and disease recurrence in multiple cancers. The current study aimed to investigate the expression and function of ATAD2 in breast cancer. Our results showed that ATAD2 expression was upregulated in human breast cancer tissues and cell lines, while ATAD2 knockdown inhibited the proliferation, migration, and invasion of breast cancer cells. Moreover, we provide evidence suggesting that miR-302 directly targets ATAD2 and thus modulates cancer cell proliferation, migration, and invasion in vitro. Moreover, ATAD2 overexpression rescued the inhibition of tumor growth caused by miR-302 in xenograft mice. These findings indicate that miR-302 plays a crucial role in inhibiting the malignant phenotypes of breast cancer cells by targeting ATAD2.

Abstract

Breast cancer is the most common malignant tumor in women. The ATPase family AAA domain-containing protein 2 (ATAD2) contains an ATPase domain and a bromodomain, and is abnormally expressed in various human cancers, including breast cancer. However, the molecular mechanisms underlying the regulation of ATAD2 expression in breast cancer remain unclear. This study aimed to investigate the expression and function of ATAD2 in breast cancer. We found that ATAD2 was highly expressed in human breast cancer tissues and cell lines. ATAD2 depletion via RNA interference inhibited the proliferation, migration, and invasive ability of the SKBR3 and T47D breast cancer cell lines. Furthermore, Western blot analysis and luciferase assay results revealed that ATAD2 is a putative target of miR-302. Transfection with miR-302 mimics markedly reduced cell migration and invasion. These inhibitory effects of miR-302 were restored by ATAD2 overexpression. Moreover, miR-302 overexpression in SKBR3 and T47D cells suppressed tumor growth in the xenograft mouse model. However, ATAD2 overexpression rescued the decreased tumor growth seen after miR-302 overexpression. Our findings indicate that miR-302 plays a prominent role in inhibiting the cancer cell behavior associated with tumor progression by targeting ATAD2, and could thus be a valuable target for breast cancer therapy.

Tumor-Promoting ATAD2 and Its Preclinical Challenges

ATAD2 has received extensive attention in recent years as one prospective oncogene with tumor-promoting features in many malignancies. ATAD2 is a highly conserved bromodomain family protein that exerts its biological functions by mainly AAA ATPase and bromodomain. ATAD2 acts as an epigenetic decoder and transcription factor or co-activator, which is engaged in cellular activities, such as transcriptional regulation, DNA replication, and protein modification. ATAD2 has been reported to be highly expressed in a variety of human malignancies, including gastrointestinal malignancies, reproductive malignancies, urological malignancies, lung cancer, and other types of malignancies. ATAD2 is involved in the activation of multiple oncogenic signaling pathways and is closely associated with tumorigenesis, progression, chemoresistance, and poor prognosis, but the oncogenic mechanisms vary in different cancer types. Moreover, the direct targeting of ATAD2’s bromodomain may be a very challenging task. In this review, we summarized the role of ATAD2 in various types of malignancies and pointed out the pharmacological direction.

Proteolysis of a histone acetyl reader, ATAD2, induces chemoresistance of cancer cells under severe hypoxia by inhibiting cell cycle progression in S phase

Cancer cells acquire chemoresistance in hypoxic regions of solid tumors, which is suggested to be at least partly due to reduction of their proliferative activity. However, molecular mechanisms behind it have not been fully elucidated. Here, we revealed the importance of active proteolysis of a histone acetylation reader, ATPase family AAA domain containing 2 (ATAD2), under hypoxia. We found that inactivation of an O₂/Fe²⁺/α-ketoglutarate-dependent dioxygenase triggered ATAD2 proteolysis by the proteasome system upon severe hypoxia in a hypoxia-inducible factors (HIFs)-independent manner. Consistently, ATAD2 expression levels were markedly lower in perinecrotic hypoxic regions in both xenografted and clinical tumor tissues. The ATAD2 proteolysis was accompanied by a decrease in the amount of acetylated histone H3 lysine 27 and inhibited cell cycle progression from the early to late S phase under severe hypoxia. The retardation of S phase progression induced chemoresistance, which was blocked by overexpression of ATAD2. Together, these results indicate that ATAD2 proteolysis upon severe hypoxia induces chemoresistance of cancer cells through heterochromatinization and the subsequent retardation of S phase progression; therefore, inhibition of ATAD2 proteolysis is expected to be a strategy to overcome chemoresistance of hypoxic tumor cells.

ATAD2 drives colorectal cancer progression by regulating TRIM25 expression via a positive feedback loop with E2F transcriptional factors

ATPase family AAA domain-containing protein 2 (ATAD2) is highly expressed in a variety of cancer types, and acts as a co-activator of androgen and estrogen receptors, as well as MYC and E2F transcription factors, to promote tumor cell proliferation. However, the regulation of ATAD2 and its related mechanisms are still elusive. Here, we show that ATAD2 protein was stabilized during DNA damage response in colorectal cancer (CRC) cells. TRIM25, an oncogenic ubiquitin E3 ligase, can interact with ATAD2 and stabilize ATAD2 upon genotoxic insult. We further demonstrated that ATAD2 played a tumor promoting role in CRC and acted as a transcriptional co-activator of E2Fs to promote the expression of TRIM25. Thus, our results revealed an unknown ATAD2-E2Fs-TRIM25 positive feedback loop that drove CRC progression.

RAD21 is a driver of chromosome 8 gain in Ewing sarcoma to mitigate replication stress

In this study, Su et al. investigate why ∼50% of Ewing sarcomas, driven by the EWS-FLI1 fusion oncogene, harbor chromosome 8 gains. Using an evolution approach, they show that trisomy 8 mitigates EWS-FLI1-induced replication stress through gain of a copy of RAD21, and deleting one copy of RAD21 in trisomy 8 cells largely neutralizes the fitness benefit of chromosome 8 gain and reduces tumorgenicity of a Ewing sarcoma cancer cell line in soft agar assays.

Aneuploidy, defined as whole-chromosome gain or loss, causes cellular stress but, paradoxically, is a frequent occurrence in cancers. Here, we investigate why ∼50% of Ewing sarcomas, driven by the EWS-FLI1 fusion oncogene, harbor chromosome 8 gains. Expression of the EWS-FLI1 fusion in primary cells causes replication stress that can result in cellular senescence. Using an evolution approach, we show that trisomy 8 mitigates EWS-FLI1-induced replication stress through gain of a copy of RAD21. Low-level ectopic expression of RAD21 is sufficient to dampen replication stress and improve proliferation in EWS-FLI1-expressing cells. Conversely, deleting one copy in trisomy 8 cells largely neutralizes the fitness benefit of chromosome 8 gain and reduces tumorgenicity of a Ewing sarcoma cancer cell line in soft agar assays. We propose that RAD21 promotes tumorigenesis through single gene copy gain. Such genes may explain some recurrent aneuploidies in cancer.

ATAD2 interacts with C/EBPβ to promote esophageal squamous cell carcinoma metastasis via TGF-β1/Smad3 signaling

Background

Distant metastasis is the leading cause of death for esophageal squamous cell carcinoma (ESCC) with limited treatment options and unsatisfactory effectiveness. Bromodomain (BRD) containing proteins are emerging targets for cancer therapy with promising effects. As a unique member of BRD family, the function and molecular mechanism of ATAD2 in cancer development is seldomly investigated.

Methods

The clinical impact of ATAD2 was assessed both at RNA and protein level in 75 and 112 ESCC patients separately. The biological function of ATAD2 was investigated in vitro and in vivo. Signaling pathway and downstream effectors of ATAD2 were identified by RNA sequencing, luciferase reporter, co-immunoprecipitation, chromatin immunoprecipitation, immunofluorescence and western blot assay.

Results

We found that elevated ATAD2 expression was significantly associated with lymph node metastasis, advanced clinical stage as well as poor survival of ESCC patients. Silencing ATAD2 significantly suppressed ESCC cell migration and invasion in vitro, and inhibited tumor growth and lung metastasis in vivo. Mechanically, we identified a new cofactor, C/EBPβ. ATAD2 directly interacted with C/EBPβ and promoted its nuclear translocation, which directly bound to the promoter region of TGF-β1 and activated its expression. Further, we demonstrated that TGF-β1 activated its downstream effectors in a Smad3 dependent manner. In addition, we further found that ATAD2 promoted ESCC metastasis through TGF-β signaling induced Snail expression and the subsequent epithelial-mesenchymal transition.

Conclusion

Our findings demonstrated the pro-metastatic function of ATAD2 and uncovered the new molecular mechanism by regulating C/EBPβ/TGF-β1/Smad3/Snail signaling pathway, thus providing a potential target for the treatment of ESCC metastasis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-01905-x.

Emerging oncogene ATAD2: Signaling cascades and therapeutic initiatives

ATAD2 is a promising oncoprotein with tumor-promoting functions in many cancers. It is a valid cancer drug-target and a potential cancer-biomarker for multiple malignancies. As a cancer/testis antigen (CTA), ATAD2 could also be a probable candidate for immunotherapy. It is a unique CTA that belongs to both AAA+ ATPase and bromodomain family proteins. Since 2007, several research groups have been reported on the pleiotropic oncogenic functions of ATAD2 in diverse signaling pathways, including Rb/E2F-cMyc pathway, steroid hormone signaling pathway, p53 and p38-MAPK-mediated apoptotic pathway, AKT pathway, hedgehog signaling pathway, HIF1α signaling pathway, and Epithelial to Mesenchymal Transition (EMT) pathway in various cancers. In all these pathways, ATAD2 participates in chromatin dynamics, DNA replication, and gene transcription, demonstrating its role as an epigenetic reader and transcription factor or coactivator to promote tumorigenesis. However, despite the progress, an overall mechanism of ATAD2-mediated oncogenesis in diverse origin is elusive. In this review, we summarize the accumulated evidence to envision the overall ATAD2 signaling networks during carcinogenesis and highlight the area where missing links await further research. Besides, the structure-function aspect of ATAD2 is also discussed. Since the efforts have already been initiated to explore targeted drug molecules and RNA-based therapeutic alternatives against ATAD2, their potency and prospects have been elucidated. Together, we believe this is a well-rounded review on ATAD2, facilitating a new drift in ATAD2 research, essential for its clinical implication as a biomarker and/or cancer drug-target.

Roles and mechanisms of BAP1 deubiquitinase in tumor suppression

The BAP1 gene has emerged as a major tumor suppressor mutated with various frequencies in numerous human malignancies, including uveal melanoma, malignant pleural mesothelioma, clear cell renal cell carcinoma, intrahepatic cholangiocarcinoma, hepatocellular carcinoma, and thymic epithelial tumors. BAP1 mutations are also observed at low frequency in other malignancies including breast, colorectal, pancreatic, and bladder cancers. BAP1 germline mutations are associated with high incidence of mesothelioma, uveal melanoma, and other cancers, defining the "BAP1 cancer syndrome." Interestingly, germline BAP1 mutations constitute an important paradigm for gene-environment interactions, as loss of BAP1 predisposes to carcinogen-induced tumorigenesis. Inactivating mutations of BAP1 are also identified in sporadic cancers, denoting the importance of this gene for normal tissue homeostasis and tumor suppression, although some oncogenic properties have also been attributed to BAP1. BAP1 belongs to the deubiquitinase superfamily of enzymes, which are responsible for the maturation and turnover of ubiquitin as well as the reversal of substrate ubiquitination, thus regulating ubiquitin signaling. BAP1 is predominantly nuclear and interacts with several chromatin-associated factors, assembling multi-protein complexes with mutually exclusive partners. BAP1 exerts its function through highly regulated deubiquitination of its substrates. As such, BAP1 orchestrates chromatin-associated processes including gene expression, DNA replication, and DNA repair. BAP1 also exerts cytoplasmic functions, notably in regulating Ca²⁺ signaling at the endoplasmic reticulum. This DUB is also subjected to multiple post-translational modifications, notably phosphorylation and ubiquitination, indicating that several signaling pathways tightly regulate its function. Recent progress indicated that BAP1 plays essential roles in multiple cellular processes including cell proliferation and differentiation, cell metabolism, as well as cell survival and death. In this review, we summarize the biological and molecular functions of BAP1 and explain how the inactivation of this DUB might cause human cancers. We also highlight some of the unresolved questions and suggest potential new directions.

Discovery of novel ATAD2 bromodomain inhibitors that trigger apoptosis and autophagy in breast cells by structure-based virtual screening

ATAD2 has been reported to play an important role in the processes of numerous cancers and validated to be a potential therapeutic target. This work is to discover potent ATAD2 inhibitors and elucidate the underlying mechanisms in breast cancer. A novel ATAD2 bromodomain inhibitor (AM879) was discovered by combining structure-based virtual screening with biochemical analyses. AM879 presents potent inhibitory activity towards ATAD2 bromodomain (IC₅₀ = 3565 nM), presenting no inhibitory activity against BRD2-4. Moreover, AM879 inhibited MDA-MB-231 cells proliferation with IC₅₀ value of 2.43 µM, suppressed the expression of c-Myc, and induced significant apoptosis. Additionally, AM978 could induce autophagy via PI3K-AKT-mTOR signalling in MDA-MB-231 cells. This study demonstrates the development of potent ATAD2 inhibitors with novel scaffolds for breast cancer therapy.

The Global Phosphorylation Landscape of SARS-CoV-2 Infection

The causative agent of the coronavirus disease 2019 (COVID-19) pandemic, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has infected millions and killed hundreds of thousands of people worldwide, highlighting an urgent need to develop antiviral therapies. Here we present a quantitative mass spectrometry-based phosphoproteomics survey of SARS-CoV-2 infection in Vero E6 cells, revealing dramatic rewiring of phosphorylation on host and viral proteins. SARS-CoV-2 infection promoted casein kinase II (CK2) and p38 MAPK activation, production of diverse cytokines, and shutdown of mitotic kinases, resulting in cell cycle arrest. Infection also stimulated a marked induction of CK2-containing filopodial protrusions possessing budding viral particles. Eighty-seven drugs and compounds were identified by mapping global phosphorylation profiles to dysregulated kinases and pathways. We found pharmacologic inhibition of the p38, CK2, CDK, AXL, and PIKFYVE kinases to possess antiviral efficacy, representing potential COVID-19 therapies.

METTL3 plays multiple functions in biological processes

N⁶-methyladenosine (m⁶A) is the most common internal modification of mRNAs in higher eukaryotic. This process is performed by methyltransferase. Methyltransferase-like 3 (METTL3) is the best known m⁶A methyltransferase that functions in the reversible epi-transcriptome modulation of m⁶A modification. Besides acting as a m⁶A methyltransferase, METTL3 also regulates mRNA translation and other biological processes. In recent years, studies have identified numerous roles and molecular mechanisms associated with METTL3 in multiple biological processes. However, these findings have not been summarized. In this review, we have systematically summarized the most recent important roles of METTL3 in various biological processes, including cell cycle progression, cell proliferation, cell apoptosis, cell migration and invasion, cell differentiation and inflammatory response. In addition, we discuss the prospect of using a METTL3 as a new diagnostic biomarker and therapeutic target for human cancers.

Integrated Bioinformatics Analysis of the Clinical Value and Biological Function of ATAD2 in Hepatocellular Carcinoma

ATPase family AAA domain-containing protein 2 (ATAD2), a chromatin regulator and an oncogenic transcription cofactor, is frequently overexpressed in many cancers, particularly in hepatocellular carcinoma (HCC). By integrating open-access online mRNA datasets and our institutional tissue data on HCC, the clinical role and functions of ATAD2 were analyzed by bioinformatic algorithms. We systematically examined ATAD2 expression in HCC based on a large sample population, integrating data from our institution and the GEO, Oncomine, and TCGA datasets. Aberrant ATAD2 expression related to pathways was identified by bioinformatic algorithms. The effects of ATAD2 downregulation on the cycle cell were also determined. A pooled analysis from 28 datasets indicated that ATAD2 overexpression was found in HCC (SMD = 8.88, 95% CI: 5.96–11.81, P < 0.001) and was correlated with poor survival. Subgroup analysis of Asian patients with a serum alpha-fetoprotein (AFP) concentration < 200 ng/ml in stage I + II showed that the ATAD2-high group had a more unfavorable overall survival (OS) rate than the ATAD2-low group. The receiver operating characteristic curve indicated that the efficiency of ATAD2 for HCC diagnosis was considerable (area under the curve = 0.89, 95% CI: 0.86–0.91). Functional analysis based on bioinformatic algorithms demonstrated that ATAD2 participates in cell division, mitotic nuclear division, DNA replication, repair, and cell cycle processes. ATAD2 knockout in HCC cells downregulated cyclin C and cyclin D1 protein levels and resulted in G1/S phase arrest in vitro. The kinesin family member C1 (KIFC1), shugoshin 1 (SGO1), GINS complex subunit 1 (GINS1), and TPX2 microtubule nucleation factor (TPX2) genes were closely related to ATAD2 upregulation. ATAD2 may interact with TTK protein kinase (TTK) to accelerate HCC carcinogenesis. ATAD2 plays a vital role in HCC carcinogenesis by disturbing the interaction between chromatin proteins and DNA. Targeting ATAD2 represents a promising method for the development of therapeutic treatments for cancer.

PFKFB4 is critical for the survival of acute monocytic leukemia cells

Acute myeloid leukemia (AML), which is characterized by an overproliferation of blood cells, is divided into several subtypes in adults and children. Of those subtypes, acute monocytic leukemia (M4/M5, AMoL) is reported to be associated with abnormal gene fusions that result in monocytic cell differentiation being blocked. However, few studies have shown a relationship between cellular metabolism and the initiation of AMoL. Here, we use the open-access database TCGA to analyze the expression of enzymes in the metabolic cycle and find that PFKFB4 is highly expressed in AMoL. Subsequently, knocking down PFKFB4 in THP-1 and U937 cells significantly inhibits cell growth and increases the sensitivity of cells to chemical drug-induced apoptosis. In line with the gene-editing alterations, treatment with a PFKFB4 inhibitor exhibits similar effects on THP-1 and U937 proliferation and apoptosis. In addition, we find that PFKFB4 functions as a reliable target of the epigenetic regulator MLL, which is a well-known modulator in AMoL. Mechanistically, MLL promotes PFKFB4 expression at the transcriptional level through the putative E2F6 binding site in the promoter of the pfkfb4 gene. Taken together, our results suggest PFKFB4 serves as a downstream target of MLL and functions as a potent therapeutic target in AMoL.

The ATAD2/ANCCA homolog Yta7 cooperates with Scm3HJURP to deposit Cse4CENP-A at the centromere in yeast

The AAA⁺ ATPase and bromodomain factor ATAD2/ANCCA is overexpressed in many types of cancer, but how it contributes to tumorigenesis is not understood. Here, we report that the Saccharomyces cerevisiae homolog Yta7^ATAD2 is a deposition factor for the centromeric histone H3 variant Cse4^CENP-A at the centromere in yeast. Yta7^ATAD2 regulates the levels of centromeric Cse4^CENP-A in that yta7∆ causes reduced Cse4^CENP-A deposition, whereas YTA7 overexpression causes increased Cse4^CENP-A deposition. Yta7^ATAD2 coimmunoprecipitates with Cse4^CENP-A and is associated with the centromere, arguing for a direct role of Yta7^ATAD2 in Cse4^CENP-A deposition. Furthermore, increasing centromeric Cse4^CENP-A levels by YTA7 overexpression requires the activity of Scm3^HJURP, the centromeric nucleosome assembly factor. Importantly, Yta7^ATAD2 interacts in vivo with Scm3^HJURP, indicating that Yta7^ATAD2 is a cochaperone for Scm3^HJURP The absence of Yta7 causes defects in growth and chromosome segregation with mutations in components of the inner kinetochore (CTF19/CCAN, Mif2^CENP-C, Cbf1). Since Yta7^ATAD2 is an AAA⁺ ATPase and potential hexameric unfoldase, our results suggest that it may unfold the Cse4^CENP-A histone and hand it over to Scm3^HJURP for subsequent deposition in the centromeric nucleosome. Furthermore, our findings suggest that ATAD2 overexpression may enhance malignant transformation in humans by misregulating centromeric CENP-A levels, thus leading to defects in kinetochore assembly and chromosome segregation.

Silencing METTL3 inhibits the proliferation and invasion of osteosarcoma by regulating ATAD2

BACKGROUND

Osteosarcoma is the most common primary malignant bone tumor in children and young adults. RNA N⁶-methyladenosine (m⁶A) is the most abundant internal modification in mammalian mRNA, which is involved in tumorigenesis and tumor progression. It has been reported that methyltransferase-like 3 (METTL3), the first reported m6A "writer", plays critical roles in cancer progression. However, its role and molecular mechanism in osteosarcoma is poor studied. In this study, we aimed to investigate the functional role and underlying mechanism of METTL3 in the progression of osteosarcoma.

METHODS

We detected the mRNA expression of METTL3 in osteosarcoma cell lines, and immunofluorescence assay was performed to observe the location of METTL3. Cell lines with METTL3 gene overexpression or knockdown were established by pcDNA3.1-METTL3 or siRNA interferences in order to determine the function of METTL3 in osteosarcoma in vitro. Transcriptomic RNA sequencing (RNA-seq) were used to screen the target genes of METTL3 in osteosarcoma.

RESULTS

We found that METTL3 localized in cytoplasm and nucleus of osteosarcoma cells. Silencing METTL3 in SAOS-2 and MG63 cells significantly inhibited the m⁶A methylation level, proliferation, migration, and invasion abilities, as well as promoted cell apoptosis. However, up-regulation of METTL3 had no significant effect on the biological behaviors of U2OS cells. Further mechanism analysis suggested that METTL3 knockdown inhibited the expression of ATPase family AAA domain containing 2 (ATAD2). Moreover, ATAD2 knockdown inhibited the proliferation and invasion of SAOS-2 and MG63 cells, while its overexpression showed a significant increase in cell proliferation and invasion. Furthermore, METTL3 knockdown abrogated the promoting effects of ATAD2 overexpression on osteosarcoma cells proliferation and invasion.

CONCLUSION

Overall, our study revealed that METTL3 functions as an oncogene in the growth and invasion of osteosarcoma by regulating ATAD2, suggesting a potential therapeutic target for osteosarcoma treatment.

Therapeutic Targeting of MDR1 Expression by RORγ Antagonists Resensitizes Cross-Resistant CRPC to Taxane via Coordinated Induction of Cell Death Programs

Overexpression of ATP-binding cassette subfamily B member 1 (ABCB1)-encoded multidrug resistance protein 1 (MDR1) constitutes a major mechanism of cancer drug resistance including docetaxel (DTX) and cabazitaxel (CTX) resistance in castration-resistant prostate cancer (CRPC). However, no therapeutics that targets MDR1 is available at clinic for taxane sensitization. We report here that retinoic acid receptor-related orphan receptor γ (RORγ), a nuclear receptor family member, unexpectedly mediates MDR1/ABCB1 overexpression. RORγ plays an important role in controlling the functions of subsets of immune cells and has been an attractive target for autoimmune diseases. We found that its small-molecule antagonists are efficacious in resensitizing DTX and CTX cross-resistant CRPC cells and tumors to taxanes in both androgen receptor-positive and -negative models. Our mechanistic analyses revealed that combined treatment with RORγ antagonists and taxane elicited a robust synergy in killing the resistant cells, which involves a coordinated alteration of p53, Myc, and E2F-controlled programs critical for both intrinsic and extrinsic apoptosis, survival, and cell growth. Our results suggest that targeting RORγ with small-molecule inhibitors is a novel strategy for chemotherapy resensitization in tumors with MDR1 overexpression.

Small Molecules Targeting the Specific Domains of Histone-Mark Readers in Cancer Therapy

Epigenetic modifications (or epigenetic tags) on DNA and histones not only alter the chromatin structure, but also provide a recognition platform for subsequent protein recruitment and enable them to acquire executive instructions to carry out specific intracellular biological processes. In cells, different epigenetic-tags on DNA and histones are often recognized by the specific domains in proteins (readers), such as bromodomain (BRD), chromodomain (CHD), plant homeodomain (PHD), Tudor domain, Pro-Trp-Trp-Pro (PWWP) domain and malignant brain tumor (MBT) domain. Recent accumulating data reveal that abnormal intracellular histone modifications (histone marks) caused by tumors can be modulated by small molecule-mediated changes in the activity of the above domains, suggesting that small molecules targeting histone-mark reader domains may be the trend of new anticancer drug development. Here, we summarize the protein domains involved in histone-mark recognition, and introduce recent research findings about small molecules targeting histone-mark readers in cancer therapy.

Prognostic value of ATPase family, AAA+ domain containing 2 expression in human cancers: A systematic review and meta-analysis

BACKGROUND

ATPase family, AAA+ domain containing 2 (ATAD2) is also known as AAA+ nuclear coregulator cancer-associated protein or PRO2000. ATAD2 has been reported as a prognostic factor in different cancer types, but the association between ATAD2 high expression and survival is still unclear. Thereby, this meta-analysis was performed to evaluate the prognostic value of ATAD2 high expression in human cancers.

METHODS

All of the studies included were retrieved from PubMed, EMBASE, and Cochrane Library electronic databases. The clinical outcomes were evaluated by calculating hazard ratio (HR) with their 95% confidence interval (CI).

RESULTS

Thirteen studies including 2689 patients were eligible for this analysis. The pooled results showed that ATAD2 over-expression was significantly associated with shorter overall survival (OS) (HR = 2.32, 95% CI = 1.77-3.02), as well as shorter recurrence-free survival (RFS), disease-free survival (DFS), and disease-specific survival (DSS) (HR = 1.83, 95% CI = 1.51-2.23) among human cancers. Subgroup analyses for OS were implemented in terms of region, tumor type, and sample size and the results were coincident with overall pooled results. Begg funnel plot and Egger test showed the presence of publication bias for OS. Sensitivity analysis indicated that both results were not affected for removing any study.

CONCLUSION

ATAD2 would be likely to act as a prognostic biomarker for the patients of different cancer types and provide a guide on clinical treatment. Prospective clinical studies are needed to support these findings.

A Qualified Success: Discovery of a New Series of ATAD2 Bromodomain Inhibitors with a Novel Binding Mode Using High-Throughput Screening and Hit Qualification

The bromodomain of ATAD2 has proved to be one of the least-tractable proteins within this target class. Here, we describe the discovery of a new class of inhibitors by high-throughput screening and show how the difficulties encountered in establishing a screening triage capable of finding progressible hits were overcome by data-driven optimization. Despite the prevalence of nonspecific hits and an exceptionally low progressible hit rate (0.001%), our optimized hit qualification strategy employing orthogonal biophysical methods enabled us to identify a single active series. The compounds have a novel ATAD2 binding mode with noncanonical features including the displacement of all conserved water molecules within the active site and a halogen-bonding interaction. In addition to reporting this new series and preliminary structure-activity relationship, we demonstrate the value of diversity screening to complement the knowledge-based approach used in our previous ATAD2 work. We also exemplify tactics that can increase the chance of success when seeking new chemical starting points for novel and less-tractable targets.

Landscape of the Plasmodium Interactome Reveals Both Conserved and Species-Specific Functionality

Malaria represents a major global health issue, and the identification of new intervention targets remains an urgent priority. This search is hampered by more than one-third of the genes of malaria-causing Plasmodium parasites being uncharacterized. We report a large-scale protein interaction network in Plasmodium schizonts, generated by combining blue native-polyacrylamide electrophoresis with quantitative mass spectrometry and machine learning. This integrative approach, spanning 3 species, identifies >20,000 putative protein interactions, organized into 600 protein clusters. We validate selected interactions, assigning functions in chromatin regulation to previously unannotated proteins and suggesting a role for an EELM2 domain-containing protein and a putative microrchidia protein as mechanistic links between AP2-domain transcription factors and epigenetic regulation. Our interactome represents a high-confidence map of the native organization of core cellular processes in Plasmodium parasites. The network reveals putative functions for uncharacterized proteins, provides mechanistic and structural insight, and uncovers potential alternative therapeutic targets.

A framework for identifying dysregulated chromatin regulators as master regulators in human cancer

MOTIVATION

Chromatin regulators (CRs) are frequently dysregulated to reprogram the epigenetic landscape of the cancer genome. However, the underpinnings of the dysregulation of CRs and their downstream effectors remain to be elucidated.

RESULTS

Here, we designed an integrated framework based on multi-omics data to identify candidate master regulatory CRs affected by genomic alterations across eight cancer types in The Cancer Genome Atlas. Most of them showed consistent activated or repressed (i.e. oncogenic or tumor-suppressive) roles in cancer initiation and progression. In order to further explore the insight mechanism of the dysregulated CRs, we developed an R package ModReg based on differential connectivity to identify CRs as modulators of transcription factors (TFs) involved in tumorigenesis. Our analysis revealed that the connectivity between TFs and their target genes (TGs) tended to be disrupted in the patients who had a high expression of oncogenic CRs or low-expression of tumor-suppressive CRs. As a proof-of-principle study, 14 (82.4%) of the top-ranked 17 driver CRs in liver cancer were able to be validated by literature mining or experiments including shRNA knockdown and dCas9-based epigenetic editing. Moreover, we confirmed that CR SIRT7 physically interacted with TF NFE2L2, and positively modulated the transcriptional program of NFE2L2 by affecting ∼64% of its TGs.

AVAILABILITY AND IMPLEMENTATION

ModReg is freely accessible at http://cis.hku.hk/software/ModReg.tar.gz.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

ATAD2 is associated with malignant characteristics of pancreatic cancer cells

Pancreatic cancer is one of the most aggressive human cancers and is associated with a poor prognosis. To develop a novel strategy for pancreatic cancer treatment, it is essential to elucidate the molecular mechanisms underlying the invasion and proliferation of cancer cells. ATPase family AAA domain containing protein 2 (ATAD2) is a highly conserved protein with an AAA+ domain and a bromodomain. Accumulating studies have demonstrated that ATAD2 is associated with the progression of multiple cancers. The present study demonstrated that ATAD2 depletion suppressed cell invasion and migration. In addition, ATAD2 knockdown suppressed anchorage-independent growth of pancreatic cancer cells. Finally, ATAD2 depletion was demonstrated to sensitize pancreatic cancer cells to gemcitabine. The results of the present study indicate that ATAD2 is involved in the malignant characteristics of pancreatic cancer.

Disulfide bridge formation influences ligand recognition by the ATAD2 bromodomain

The ATPase family, AAA domain-containing protein 2 (ATAD2) has a C-terminal bromodomain, which functions as a chromatin reader domain recognizing acetylated lysine on the histone tails within the nucleosome. ATAD2 is overexpressed in many cancers and its expression is correlated with poor patient outcomes, making it an attractive therapeutic target and potential biomarker. We solved the crystal structure of the ATAD2 bromodomain and found that it contains a disulfide bridge near the base of the acetyllysine binding pocket (Cys1057-Cys1079). Site-directed mutagenesis revealed that removal of a free C-terminal cysteine (C1101) residue greatly improved the solubility of the ATAD2 bromodomain in vitro. Isothermal titration calorimetry experiments in combination with the Ellman's assay demonstrated that formation of an intramolecular disulfide bridge negatively impacts the ligand binding affinities and alters the thermodynamic parameters of the ATAD2 bromodomain interaction with a histone H4K5ac peptide as well as a small molecule bromodomain ligand. Molecular dynamics simulations indicate that the formation of the disulfide bridge in the ATAD2 bromodomain does not alter the structure of the folded state or flexibility of the acetyllysine binding pocket. However, consideration of this unique structural feature should be taken into account when examining ligand-binding affinity, or in the design of new bromodomain inhibitor compounds that interact with this acetyllysine reader module.

Nucleosome Positioning by an Evolutionarily Conserved Chromatin Remodeler Prevents Aberrant DNA Methylation in Neurospora

In the filamentous fungus Neurospora crassa, constitutive heterochromatin is marked by tri-methylation of histone H3 lysine 9 (H3K9me3) and DNA methylation. We identified mutations in the Neurospora defective in methylation-1 (dim-1) gene that cause defects in cytosine methylation and implicate a putative AAA-ATPase chromatin remodeler. Although it was well-established that chromatin remodelers can affect transcription by influencing DNA accessibility with nucleosomes, little was known about the role of remodelers on chromatin that is normally not transcribed, including regions of constitutive heterochromatin. We found that dim-1 mutants display both reduced DNA methylation in heterochromatic regions as well as increased DNA methylation and H3K9me3 in some intergenic regions associated with highly expressed genes. Deletion of dim-1 leads to atypically spaced nucleosomes throughout the genome and numerous changes in gene expression. DIM-1 localizes to both heterochromatin and intergenic regions that become hyper-methylated in dim-1 strains. Our findings indicate that DIM-1 normally positions nucleosomes in both heterochromatin and euchromatin and that the standard arrangement and density of nucleosomes is required for the proper function of heterochromatin machinery.

Aiming to Miss a Moving Target: Bromo and Extra Terminal Domain (BET) Selectivity in Constrained ATAD2 Inhibitors

ATAD2 is a cancer-associated protein whose bromodomain has been described as among the least druggable of its class. In our recent disclosure of the first chemical probe against this bromodomain, GSK8814 (6), we described the use of a conformationally constrained methoxy piperidine to gain selectivity over the BET bromodomains. Here we describe an orthogonal conformational restriction strategy of the piperidine ring to give potent and selective tropane inhibitors and show structural insights into why this was more challenging than expected. Greater understanding of why different rational approaches succeeded or failed should help in the future design of selectivity in the bromodomain family.

Epigenetic tools (The Writers, The Readers and The Erasers) and their implications in cancer therapy

Addition of chemical tags on the DNA and modification of histone proteins impart a distinct feature on chromatin architecture. With the advancement in scientific research, the key players underlying these changes have been identified as epigenetic modifiers of the chromatin. Indeed, the plethora of enzymes catalyzing these modifications, portray the diversity of epigenetic space and the intricacy in regulating gene expression. These epigenetic players are categorized as writers: that introduce various chemical modifications on DNA and histones, readers: the specialized domain containing proteins that identify and interpret those modifications and erasers: the dedicated group of enzymes proficient in removing these chemical tags. Research over the past few decades has established that these epigenetic tools are associated with numerous disease conditions especially cancer. Besides, with the involvement of epigenetics in cancer, these enzymes and protein domains provide new targets for cancer drug development. This is certain from the volume of epigenetic research conducted in universities and R&D sector of pharmaceutical industry. Here we have highlighted the different types of epigenetic enzymes and protein domains with an emphasis on methylation and acetylation. This review also deals with the recent developments in small molecule inhibitors as potential anti-cancer drugs targeting the epigenetic space.

TRRAP is a central regulator of human multiciliated cell formation

Multiciliated cells (MCCs) function to promote directional fluid flow across epithelial tissues. Wang et al. show that TRRAP, a component of multiple histone acetyltransferase complexes, is required for airway MCC formation and regulates a network of genes involved in MCC differentiation and function.

The multiciliated cell (MCC) is an evolutionarily conserved cell type, which in vertebrates functions to promote directional fluid flow across epithelial tissues. In the conducting airway, MCCs are generated by basal stem/progenitor cells and act in concert with secretory cells to perform mucociliary clearance to expel pathogens from the lung. Studies in multiple systems, including Xenopus laevis epidermis, murine trachea, and zebrafish kidney, have uncovered a transcriptional network that regulates multiple steps of multiciliogenesis, ultimately leading to an MCC with hundreds of motile cilia extended from their apical surface, which beat in a coordinated fashion. Here, we used a pool-based short hairpin RNA screening approach and identified TRRAP, an essential component of multiple histone acetyltransferase complexes, as a central regulator of MCC formation. Using a combination of immunofluorescence, signaling pathway modulation, and genomic approaches, we show that (a) TRRAP acts downstream of the Notch2-mediated basal progenitor cell fate decision and upstream of Multicilin to control MCC differentiation; and (b) TRRAP binds to the promoters and regulates the expression of a network of genes involved in MCC differentiation and function, including several genes associated with human ciliopathies.

Modes of Interaction of KMT2 Histone H3 Lysine 4 Methyltransferase/COMPASS Complexes with Chromatin

Regulation of gene expression is achieved by sequence-specific transcriptional regulators, which convey the information that is contained in the sequence of DNA into RNA polymerase activity. This is achieved by the recruitment of transcriptional co-factors. One of the consequences of co-factor recruitment is the control of specific properties of nucleosomes, the basic units of chromatin, and their protein components, the core histones. The main principles are to regulate the position and the characteristics of nucleosomes. The latter includes modulating the composition of core histones and their variants that are integrated into nucleosomes, and the post-translational modification of these histones referred to as histone marks. One of these marks is the methylation of lysine 4 of the core histone H3 (H3K4). While mono-methylation of H3K4 (H3K4me1) is located preferentially at active enhancers, tri-methylation (H3K4me3) is a mark found at open and potentially active promoters. Thus, H3K4 methylation is typically associated with gene transcription. The class 2 lysine methyltransferases (KMTs) are the main enzymes that methylate H3K4. KMT2 enzymes function in complexes that contain a necessary core complex composed of WDR5, RBBP5, ASH2L, and DPY30, the so-called WRAD complex. Here we discuss recent findings that try to elucidate the important question of how KMT2 complexes are recruited to specific sites on chromatin. This is embedded into short overviews of the biological functions of KMT2 complexes and the consequences of H3K4 methylation.

ATAD2 is an epigenetic reader of newly synthesized histone marks during DNA replication

ATAD2 (ATPase family AAA domain-containing protein 2) is a chromatin regulator harboring an AAA+ ATPase domain and a bromodomain, previously proposed to function as an oncogenic transcription co-factor. Here we suggest that ATAD2 is also required for DNA replication. ATAD2 is co-expressed with genes involved in DNA replication in various cancer types and predominantly expressed in S phase cells where it localized on nascent chromatin (replication sites). Our extensive biochemical and cellular analyses revealed that ATAD2 is recruited to replication sites through a direct interaction with di-acetylated histone H4 at K5 and K12, indicative of newly synthesized histones during replication-coupled chromatin reassembly. Similar to ATAD2-depletion, ectopic expression of ATAD2 mutants that are deficient in binding to these di-acetylation marks resulted in reduced DNA replication and impaired loading of PCNA onto chromatin, suggesting relevance of ATAD2 in DNA replication. Taken together, our data show a novel function of ATAD2 in cancer and for the first time identify a reader of newly synthesized histone di-acetylation-marks during replication.

ATAD2 in cancer: a pharmacologically challenging but tractable target

INTRODUCTION

ATAD2 protein is an emerging oncogene that has strongly been linked to the etiology of multiple advanced human cancers. Therapeutically, despite the fact that genetic suppression/knockdown studies have validated it as a compelling drug target for future therapeutic development, recent druggability assessment data suggest that direct targeting of ATAD2's bromodomain (BRD) may be a very challenging task. ATAD2's BRD has been predicted as a 'difficult to drug' or 'least druggable' target due to the concern that its binding pocket, and the areas around it, seem to be unfeasible for ligand binding. Areas covered: In this review, after shedding light on the multifaceted roles of ATAD2 in normal physiology as well as in cancer-etiology, we discuss technical challenges rendered by ATAD2's BRD active site and the recent drug discovery efforts to find small molecule inhibitors against it. Expert opinion: The identification of a novel low-nanomolar semi-permeable chemical probe against ATAD2's BRD by recent drug discovery campaign has demonstrated it to be a pharmacologically tractable target. Nevertheless, the development of high quality bioavailable inhibitors against ATAD2 is still a pending task. Moreover, ATAD2 may also potentially be utilized as a promising target for future development of RNAi-based therapy to treat cancers.

Isoform-Selective ATAD2 Chemical Probe with Novel Chemical Structure and Unusual Mode of Action

ATAD2 (ANCCA) is an epigenetic regulator and transcriptional cofactor, whose overexpression has been linked to the progress of various cancer types. Here, we report a DNA-encoded library screen leading to the discovery of BAY-850, a potent and isoform selective inhibitor that specifically induces ATAD2 bromodomain dimerization and prevents interactions with acetylated histones in vitro, as well as with chromatin in cells. These features qualify BAY-850 as a chemical probe to explore ATAD2 biology.

KDM4A Coactivates E2F1 to Regulate the PDK-Dependent Metabolic Switch between Mitochondrial Oxidation and Glycolysis

The histone lysine demethylase KDM4A/JMJD2A has been implicated in prostate carcinogenesis through its role in transcriptional regulation. Here, we describe KDM4A as a E2F1 coactivator and demonstrate a functional role for the E2F1-KDM4A complex in the control of tumor metabolism. KDM4A associates with E2F1 on target gene promoters and enhances E2F1 chromatin binding and transcriptional activity, thereby modulating the transcriptional profile essential for cancer cell proliferation and survival. The pyruvate dehydrogenase kinases (PDKs) PDK1 and PDK3 are direct targets of KDM4A and E2F1 and modulate the switch between glycolytic metabolism and mitochondrial oxidation. Downregulation of KDM4A leads to elevated activity of pyruvate dehydrogenase and mitochondrial oxidation, resulting in excessive accumulation of reactive oxygen species. The altered metabolic phenotypes can be partially rescued by ectopic expression of PDK1 and PDK3, indicating a KDM4A-dependent tumor metabolic regulation via PDK. Our results suggest that KDM4A is a key regulator of tumor metabolism and a potential therapeutic target for prostate cancer.

Protein dynamics and structural waters in bromodomains

Bromodomains are epigenetic readers of acetylated lysines that are integral parts of histone tails. The 61 bromodomains in humans are structurally highly conserved but specifically bind to widely varying recognition motifs, suggesting that dynamic rather than static factors are responsible for recognition selectivity. To test this hypothesis, the dynamics of the binding sites and structural water molecules of four bromodomains (ATAD2, BAZ2B, BRD2(1) and CREBBP) representing four different subtypes is studied with 1 μs MD simulations using the RSFF2 force field. The different dynamics of the ZA-loops and BC-loops between the four bromodomains leads to distinct patterns for the opening and closing of the binding pocket. This in turn determines the structural and energetic properties of the structural waters in the binding pocket, suggesting that these waters are not only important for the recognition itself, as has been proposed previously, but also contribute to the selectivity of different bromodomains.

Patent Highlights June-July 2017

A snapshot of noteworthy recent developments in the patent literature of relevance to pharmaceutical and medical research and development.

The ATAD2 bromodomain binds different acetylation marks on the histone H4 in similar fuzzy complexes

Bromodomains are protein modules adopting conserved helix bundle folds. Some bromodomain-containing proteins, such as ATPase family AAA domain-containing protein 2 (ATAD2), isoform A, have attracted much interest because they are overexpressed in many types of cancer. Bromodomains bind to acetylated lysine residues on histone tails and thereby facilitate the reading of the histone code. Epigenetic regulators in general have been implicated as indicators, mediators, or causes of a large number of diseases and disorders. To interfere with or modulate these processes, it is therefore of fundamental interest to understand the molecular mechanisms by which epigenetic regulation occurs. Here, we present results from molecular dynamics simulations of a doubly acetylated histone H4 peptide bound to the bromodomain of ATAD2 (hereafter referred to as ATAD2A). These simulations revealed how the flexibility of ATAD2A's major loop, the so-called ZA loop, creates an adaptable interface that preserves the disorder of both peptide and loop in the bound state. We further demonstrate that the binding involves an almost identical average pattern of interactions irrespective of which acetyl mark is inserted into the pocket. In conjunction with a likely mechanism of electrostatically driven recruitment, our simulation results highlight how the bromodomain is built toward promiscuous binding with low specificity. In conclusion, the simulations indicate that disorder and electrostatic steering function jointly to recruit ATAD2A to the histone core and that these fuzzy interactions may promote cooperativity between nearby epigenetic marks.

Biological function and histone recognition of family IV bromodomain-containing proteins

Bromodomain proteins function as epigenetic readers that recognize acetylated histone tails to facilitate the transcription of target genes. There are approximately 60 known human bromodomains, which are divided into eight sub-families based on structural conservation. The bromodomain-containing proteins in family IV include seven members (BRPF1, BRPF2, BRPF3, BRD7, BRD9, ATAD2, and ATAD2b). The bromodomains of each of these proteins recognize and bind acetyllysine residues on histone tails protruding from the nucleosome. However, the histone marks recognized by each bromodomain protein can be very different. The BRPF1 subunit of the MOZ histone acetyltransferase (HAT) recognizes acetylated histones H2AK5ac, H4K12ac, H3K14ac, H4K8ac, and H4K5ac. While the bromodomain of BRD7, a member of the SWI/SNF complex, was shown to preferentially recognize acetylated histones H3K9ac, H3K14ac, H4K8ac, H4K12ac, and H4K16ac. The bromodomains of BRPF2 and BRPF3 have similar sequences, and function as part of the HBO1 HAT complex, but there is limited data on which histone ligands they bind. Similarly, there is little known about the histone targets of the BRD9 and ATAD2b bromodomain proteins. Interestingly, the ATAD2 bromodomain was recently shown to preferentially bind to the di-acetylated H4K5acK12ac mark found in newly synthesized histones following DNA replication. However, despite the physiological importance of the family IV bromodomains, little is known about how they function at the molecular or atomic level. In this review, we summarize our understanding of how family IV bromodomains recognize and select for acetyllysine marks and discuss the importance of acetylated histone recognition for their biological functions.

Functions of bromodomain-containing proteins and their roles in homeostasis and cancer

Bromodomains (BRDs) are evolutionarily conserved protein-protein interaction modules that are found in a wide range of proteins with diverse catalytic and scaffolding functions and are present in most tissues. BRDs selectively recognize and bind to acetylated Lys residues - particularly in histones - and thereby have important roles in the regulation of gene expression. BRD-containing proteins are frequently dysregulated in cancer, they participate in gene fusions that generate diverse, frequently oncogenic proteins, and many cancer-causing mutations have been mapped to the BRDs themselves. Importantly, BRDs can be targeted by small-molecule inhibitors, which has stimulated many translational research projects that seek to attenuate the aberrant functions of BRD-containing proteins in disease.

Acetylation Reader Proteins: Linking Acetylation Signaling to Genome Maintenance and Cancer

Chromatin-based DNA damage response (DDR) pathways are fundamental for preventing genome and epigenome instability, which are prevalent in cancer. Histone acetyltransferases (HATs) and histone deacetylases (HDACs) catalyze the addition and removal of acetyl groups on lysine residues, a post-translational modification important for the DDR. Acetylation can alter chromatin structure as well as function by providing binding signals for reader proteins containing acetyl-lysine recognition domains, including the bromodomain (BRD). Acetylation dynamics occur upon DNA damage in part to regulate chromatin and BRD protein interactions that mediate key DDR activities. In cancer, DDR and acetylation pathways are often mutated or abnormally expressed. DNA damaging agents and drugs targeting epigenetic regulators, including HATs, HDACs, and BRD proteins, are used or are being developed to treat cancer. Here, we discuss how histone acetylation pathways, with a focus on acetylation reader proteins, promote genome stability and the DDR. We analyze how acetylation signaling impacts the DDR in the context of cancer and its treatments. Understanding the relationship between epigenetic regulators, the DDR, and chromatin is integral for obtaining a mechanistic understanding of genome and epigenome maintenance pathways, information that can be leveraged for targeting acetylation signaling, and/or the DDR to treat diseases, including cancer.