MOZ and MORF, two large MYSTic HATs in normal and cancer stem cells

Dysregulation of the p300/CBP histone acetyltransferases in human cancer

p300 (E1A binding protein 300) and CBP (CREB-binding protein) are critical regulators of chromatin dynamics and gene expression, playing essential roles in various cellular processes, including proliferation, differentiation, apoptosis, and immune responses. These homologous histone acetyltransferases (HATs) function as transcriptional co-activators by acetylating histones and non-histone proteins. p300/CBP is essential for development, and dysregulation of p300 and CBP has been implicated in several human diseases, particularly cancer. Somatic mutations that inactivate p300/CBP are frequently observed across various cancer types. Additionally, other mutations leading to translocations or truncations of p300/CBP can result in enhanced catalytic activity, potentially representing novel gain-of-function mutations that promote tumor progression. In this review, we discuss the mechanisms underlying the regulation of p300/CBP HAT activity, its dysregulation in cancer, and the development of p300/CBP inhibitors and their potential in cancer therapies.

Targeting KAT6A/B as a New Therapeutic Strategy for Cancer Therapy

The lysine acetyltransferase 6A (KAT6A, MOZ, MYST3) is a member of the MYST family of protein acetyltransferases, which are essential for different biological processes such as craniofacial, embryonic, stem cell development, and hematopoiesis. KAT6A is an oncogene in human acute myeloid leukemia (AML), and KAT6A overexpression in AML is associated with metastases and poor prognoses. Furthermore, KAT6A mutations play an important role in cancer formation and progression and result in therapeutic resistance in both hematopoietic malignancies and solid tumors. In this review, we discuss the structural and biological functions of KAT6A and summarize the influence of KAT6A in the development of various tumors. In addition, the recent KAT6A/B inhibitors, their anticancer activities, challenges, and perspective of developing KAT6A/B inhibitors as anticancer drug candidates were introduced.

Discovery and Characterization of BAY-184: A New Potent and Selective Acylsulfonamide-Benzofuran In Vivo-Active KAT6AB Inhibitor

KAT6A and KAT6B genes are two closely related lysine acetyltransferases that transfer an acetyl group from acetyl coenzyme A (AcCoA) to lysine residues of target histone substrates, hence playing a key role in chromatin regulation. KAT6A and KAT6B genes are frequently amplified in various cancer types. In breast cancer, the 8p11-p12 amplicon occurs in 12-15% of cases, resulting in elevated copy numbers and expression levels of chromatin modifiers like KAT6A. Here, we report the discovery of a new acylsulfonamide-benzofuran series as a novel structural class for KAT6A/B inhibition. These compounds were identified through high-throughput screening and subsequently optimized using molecular modeling and cocrystal structure determination. The final tool compound, BAY-184 (29), was successfully validated in an in vivo proof-of-concept study.

ERα status of invasive ductal breast carcinoma as a result of regulatory interactions between lysine deacetylases KAT6A and KAT6B

Breast cancer (BC) is the leading cause of death among cancer patients worldwide. In 2020, almost 12% of all cancers were diagnosed with BC. Therefore, it is important to search for new potential markers of cancer progression that could be helpful in cancer diagnostics and successful anti-cancer therapies. In this study, we investigated the potential role of the lysine acetyltransferases KAT6A and KAT6B in the outcome of patients with invasive breast carcinoma. The expression profiles of KAT6A/B in 495 cases of IDC and 38 cases of mastopathy (FBD) were examined by immunohistochemistry. KAT6A/B expression was also determined in the breast cancer cell lines MCF-7, BT-474, SK-BR-3, T47D, MDA-MB-231, and MDA-MB-231/BO2, as well as in the human epithelial mammary gland cell line hTERT-HME1 - ME16C, both at the mRNA and protein level. Statistical analysis of the results showed that the nuclear expression of KAT6A/B correlates with the estrogen receptor status: KAT6ANUC vs. ER r = 0.2373 and KAT6BNUC vs. ER r = 0.1496. Statistical analysis clearly showed that KAT6A cytoplasmic and nuclear expression levels were significantly higher in IDC samples than in FBD samples (IRS 5.297 ± 2.884 vs. 2.004 ± 1.072, p < 0.0001; IRS 5.133 ± 4.221 vs. 0.1665 ± 0.4024, p < 0.0001, respectively). Moreover, we noticed strong correlations between ER and PR status and the nuclear expression of KAT6A and KAT6B (nucKAT6A vs. ER, p = 0.0048; nucKAT6A vs. PR p = 0.0416; nucKAT6B vs. ER p = 0.0306; nucKAT6B vs. PR p = 0.0213). Significantly higher KAT6A and KAT6B expression was found in the ER-positive cell lines T-47D and BT-474, whereas significantly lower expression was observed in the triple-negative cell lines MDA-MB-231 and MDA-MB-231/BO2. The outcomes of small interfering RNA (siRNA)-mediated suppression of KAT6A/B genes revealed that within estrogen receptor (ER) positive and negative cell lines, MCF-7 and MDA-MB-231, attenuation of KAT6A led to concurrent attenuation of KAT6A, whereas suppression of KAT6B resulted in simultaneous attenuation of KAT6A. Furthermore, inhibition of KAT6A/B genes resulted in a reduction in estrogen receptor (ER) mRNA and protein expression levels in MCF-7 and MDA-MMB-231 cell lines. Based on our findings, the lysine acetyltransferases KAT6A and KAT6B may be involved in the progression of invasive ductal breast cancer. Further research on other types of cancer may show that KAT6A and KAT6B could serve as diagnostic and prognostic markers for these types of malignancies.

The small inhibitor WM-1119 effectively targets KAT6A-rearranged AML, but not KMT2A-rearranged AML, despite shared KAT6 genetic dependency

BACKGROUND

The epigenetic factors KAT6A (MOZ/MYST3) and KMT2A (MLL/MLL1) interact in normal hematopoiesis to regulate progenitors' self-renewal. Both proteins are recurrently translocated in AML, leading to impairment of critical differentiation pathways in these malignant cells. We evaluated the potential of different KAT6A therapeutic targeting strategies to alter the growth of KAT6A and KMT2A rearranged AMLs.

METHODS

We investigated the action and potential mechanisms of the first-in-class KAT6A inhibitor, WM-1119 in KAT6A and KMT2A rearranged (KAT6Ar and KMT2Ar) AML using cellular (flow cytometry, colony assays, cell growth) and molecular (shRNA knock-down, CRISPR knock-out, bulk and single-cell RNA-seq, ChIP-seq) assays. We also used two novel genetic murine KAT6A models combined with the most common KMT2Ar AML, KMT2A::MLLT3 AML. In these murine models, the catalytic activity of KAT6A, or the whole protein, can be conditionally abrogated or deleted. These models allowed us to compare the effects of specific KAT6A KAT activity inhibition with the complete deletion of the whole protein. Finally, we also tested these therapeutic approaches on human AML cell lines and primary patient AMLs.

RESULTS

We found that WM-1119 completely abrogated the proliferative and clonogenic potential of KAT6Ar cells in vitro. WM-1119 treatment was associated with a dramatic increase in myeloid differentiation program. The treatment also decreased stemness and leukemia pathways at the transcriptome level and led to loss of binding of the fusion protein at critical regulators of these pathways. In contrast, our pharmacologic and genetic results indicate that the catalytic activity of KAT6A plays a more limited role in KMT2Ar leukemogenicity, while targeting the whole KAT6A protein dramatically affects leukemic potential in murine KMT2A::MLLT3 AML.

CONCLUSION

Our study indicates that inhibiting KAT6A KAT activity holds compelling promise for KAT6Ar AML patients. In contrast, targeted degradation of KAT6A, and not just its catalytic activity, may represent a more appropriate therapeutic approach for KMT2Ar AMLs.

Beyond 'speech delay': Expanding the phenotype of BRPF1-related disorder

Pathogenic variants in BRPF1 cause intellectual disability, ptosis and facial dysmorphism. Speech and language deficits have been identified as a manifestation of BRPF1-related disorder but have not been systematically characterized. We provide a comprehensive delineation of speech and language abilities in BRPF1-related disorder and expand the phenotype. Speech and language, and health and medical history were assessed in 15 participants (male = 10, median age = 7 years 4 months) with 14 BRPF1 variants. Language disorders were common (11/12), and most had mild to moderate deficits across receptive, expressive, written, and social-pragmatic domains. Speech disorders were frequent (7/9), including phonological delay (6/9) and disorder (3/9), and childhood apraxia of speech (3/9). All those tested for cognitive abilities had a FSIQ ≥70 (4/4). Participants had vision impairment (13/15), fine (8/15) and gross motor delay (10/15) which often resolved in later childhood, infant feeding impairment (8/15), and infant hypotonia (9/15). We have implicated BRPF1-related disorder as causative for speech and language disorder, including childhood apraxia of speech. Adaptive behavior and cognition were strengths when compared to other monogenic neurodevelopmental chromatin-related disorders. The universal involvement of speech and language impairment is noteable, relative to the high degree of phenotypic variability in BRPF1-related disorder.

Clinical features and underlying mechanisms of KAT6B disease in a Chinese boy

BACKGROUND

Lysine acetyltransferase 6B (KAT6B) encodes a highly conserved histone acetyltransferase that regulates the expression of multiple genes and is essential for human growth and development.

METHODS

We identified a novel frameshift variant c.3185del (p.leu1062Argfs*52) in a 5-year-old Chinese boy and further analyzed KAT6B expression and its interacting complexes and downstream products using real-time quantitative polymerase chain reaction (qPCR). Furthermore, we assessed its three-dimensional protein structure and compared the variant with other reported KAT6B variants.

RESULTS

The deletion changed the leucine at position 1062 into an arginine, resulting in translation termination after base 3340, which may have affected protein stability and protein-protein interactions. KAT6B mRNA expression levels in this case were substantially different from those of the parents and controls in the same age range. There were also significant differences in mRNA expression levels among affected children's parents. RUNX2 and NR5A1, downstream products of the gene, affect the corresponding clinical symptoms. The mRNA expression levels of the two in children were lower than those of their parents and controls in the same age range.

CONCLUSION

This deletion in KAT6B may affect protein function and cause corresponding clinical symptoms through interactions with key complexes and downstream products.

Epigenetic control of cell signalling in cancer stem cells

The self-renewing cancer stem cells (CSCs) represent one of the distinct cell populations occurring in a tumour that can differentiate into multiple lineages. This group of sparsely abundant cells play a vital role in tumour survival and resistance to different treatments during cancer. The lack of exclusive markers associated with CSCs makes diagnosis and prognosis in cancer patients extremely difficult. This calls for the identification of unique regulators and markers for CSCs. Various signalling pathways like the Wnt/β-catenin pathway, Hedgehog pathway, Notch pathway, and TGFβ/BMP play a major role in the regulation and maintenance of CSCs. Epigenetic regulatory mechanisms add another layer of complexity to control these signalling pathways. In this chapter, we discuss about the role of epigenetic mechanisms in regulating the cellular signalling pathways in CSCs. The epigenetic regulatory mechanisms such as DNA methylation, histone modification and microRNAs can modulate the diverse effectors of signalling pathways and consequently the growth, differentiation and tumorigenicity of CSCs. In the end, we briefly discuss the therapeutic potential of targeting these epigenetic regulators and their target genes in CSCs.

The histone acetyltransferase KAT6A is recruited to unmethylated CpG islands via a DNA binding winged helix domain

The lysine acetyltransferase KAT6A (MOZ, MYST3) belongs to the MYST family of chromatin regulators, facilitating histone acetylation. Dysregulation of KAT6A has been implicated in developmental syndromes and the onset of acute myeloid leukemia (AML). Previous work suggests that KAT6A is recruited to its genomic targets by a combinatorial function of histone binding PHD fingers, transcription factors and chromatin binding interaction partners. Here, we demonstrate that a winged helix (WH) domain at the very N-terminus of KAT6A specifically interacts with unmethylated CpG motifs. This DNA binding function leads to the association of KAT6A with unmethylated CpG islands (CGIs) genome-wide. Mutation of the essential amino acids for DNA binding completely abrogates the enrichment of KAT6A at CGIs. In contrast, deletion of a second WH domain or the histone tail binding PHD fingers only subtly influences the binding of KAT6A to CGIs. Overexpression of a KAT6A WH1 mutant has a dominant negative effect on H3K9 histone acetylation, which is comparable to the effects upon overexpression of a KAT6A HAT domain mutant. Taken together, our work revealed a previously unrecognized chromatin recruitment mechanism of KAT6A, offering a new perspective on the role of KAT6A in gene regulation and human diseases.

Role of the MOZ/MLL-mediated transcriptional activation system for self-renewal in normal hematopoiesis and leukemogenesis

Homeostasis in the blood system is maintained by the balance between self-renewing stem cells and nonstem cells. To promote self-renewal, transcriptional regulators maintain epigenetic information during multiple rounds of cell division. Mutations in such transcriptional regulators cause aberrant self-renewal, leading to leukemia. MOZ, a histone acetyltransferase, and MLL, a histone methyltransferase, are transcriptional regulators that promote the self-renewal of hematopoietic stem cells. Gene rearrangements of MOZ and MLL generate chimeric genes encoding fusion proteins that function as constitutively active forms. These MOZ and MLL fusion proteins constitutively activate transcription of their target genes and cause aberrant self-renewal in committed hematopoietic progenitors, which normally do not self-renew. Recent progress in the field suggests that MOZ and MLL are part of a transcriptional activation system that activates the transcription of genes with nonmethylated CpG-rich promoters. The nonmethylated state of CpGs is normally maintained during cell divisions from the mother cell to the daughter cells. Thus, the MOZ/MLL-mediated transcriptional activation system replicates the expression profile of mother cells in daughter cells by activating the transcription of genes previously transcribed in the mother cell. This review summarizes the functions of the components of the MOZ/MLL-mediated transcriptional activation system and their roles in the promotion of self-renewal.

Clinical manifestations and genetic analysis of a newborn with Arboleda−Tham syndrome

Arboleda−Tham syndrome (ARTHS) is a rare disorder first characterized in 2015 and is caused by mutations in lysine (K) acetyltransferase 6A (KAT6A, a.k.a. MOZ, MYST3). Its clinical symptoms have rarely been reported in newborns from birth up to the first few months after birth. In this study, a newborn was diagnosed with ARTHS based on the clinical symptoms and a mutation c.3937G>A (p.Asp1313Asn) in KAT6A. The clinical manifestations, diagnosis, and treatment of the newborn with ARTHS were recorded during follow-up observations. The main symptoms of the proband at birth were asphyxia, involuntary breathing, low muscle tone, early feeding, movement difficulties, weak crying, weakened muscle tone of the limbs, and embrace reflex, and facial features were not obvious at birth. There was obvious developmental delay, as well as hypotonic and oro-intestinal problems in the first few months after birth. Mouse growth factor was used to nourish the brain nerves, and touching, kneading the back, passive movements of the limbs, and audio−visual stimulation were used for rehabilitation. We hope that this study expands the phenotypic spectrum of this syndrome to newborns and the library of KAT6A mutations that lead to ARTHS. Consequently, the data can be used as a basis for genetic counseling and in clinical and prenatal diagnosis for ARTHS prevention.

BRPF1-KAT6A/KAT6B Complex: Molecular Structure, Biological Function and Human Disease

The bromodomain and PHD finger-containing protein1 (BRPF1) is a member of family IV of the bromodomain-containing proteins that participate in the post-translational modification of histones. It functions in the form of a tetrameric complex with a monocytic leukemia zinc finger protein (MOZ or KAT6A), MOZ-related factor (MORF or KAT6B) or HAT bound to ORC1 (HBO1 or KAT7) and two small non-catalytic proteins, the inhibitor of growth 5 (ING5) or the paralog ING4 and MYST/Esa1-associated factor 6 (MEAF6). Mounting studies have demonstrated that all the four core subunits play crucial roles in different biological processes across diverse species, such as embryonic development, forebrain development, skeletal patterning and hematopoiesis. BRPF1, KAT6A and KAT6B mutations were identified as the cause of neurodevelopmental disorders, leukemia, medulloblastoma and other types of cancer, with germline mutations associated with neurodevelopmental disorders displaying intellectual disability, and somatic variants associated with leukemia, medulloblastoma and other cancers. In this paper, we depict the molecular structures and biological functions of the BRPF1-KAT6A/KAT6B complex, summarize the variants of the complex related to neurodevelopmental disorders and cancers and discuss future research directions and therapeutic potentials.

MOZ and Menin-MLL Complexes Are Complementary Regulators of Chromatin Association and Transcriptional Output in Gastrointestinal Stromal Tumor

Gastrointestinal stromal tumor (GIST) is commonly characterized by activating mutations in the receptor tyrosine kinase KIT. Tyrosine kinase inhibitors are the only approved therapy for GIST, and complementary treatment strategies are urgently needed. As GIST lacks oncogene amplification and relies upon an established network of transcription factors, we hypothesized that unique chromatin-modifying enzymes are essential in orchestrating the GIST epigenome. We identified through genome-scale CRISPR screening that MOZ and Menin-MLL chromatin regulatory complexes are cooperative and unique dependencies in GIST. These complexes were enriched at GIST-relevant genes and regulated their transcription. Inhibition of MOZ and Menin-MLL complexes decreased GIST cell proliferation by disrupting interactions with transcriptional/chromatin regulators, such as DOT1L. MOZ and Menin inhibition caused significant reductions in tumor burden in vivo, with superior effects observed with combined Menin and KIT inhibition. These results define unique chromatin regulatory dependencies in GIST and identify potential therapeutic strategies for clinical application.

SIGNIFICANCE

Although many malignancies rely on oncogene amplification, GIST instead depends upon epigenetic regulation of KIT and other essential genes. Utilizing genome-scale CRISPR dependency screens, we identified complementary chromatin-modifying complexes essential to GIST and characterize the consequences of their disruption, elucidating a novel therapeutic approach to this disease. This article is highlighted in the In This Issue feature, p. 1599.

Stress Responses as Master Keys to Epigenomic Changes in Transcriptome and Metabolome for Cancer Etiology and Therapeutics

From initiation through progression, cancer cells are subjected to a magnitude of endogenous and exogenous stresses, which aid in their neoplastic transformation. Exposure to these classes of stress induces imbalance in cellular homeostasis and, in response, cancer cells employ informative adaptive mechanisms to rebalance biochemical processes that facilitate survival and maintain their existence. Different kinds of stress stimuli trigger epigenetic alterations in cancer cells, which leads to changes in their transcriptome and metabolome, ultimately resulting in suppression of growth inhibition or induction of apoptosis. Whether cancer cells show a protective response to stress or succumb to cell death depends on the type of stress and duration of exposure. A thorough understanding of epigenetic and molecular architecture of cancer cell stress response pathways can unveil a plethora of information required to develop novel anticancer therapeutics. The present view highlights current knowledge about alterations in epigenome and transcriptome of cancer cells as a consequence of exposure to different physicochemical stressful stimuli such as reactive oxygen species (ROS), hypoxia, radiation, hyperthermia, genotoxic agents, and nutrient deprivation. Currently, an anticancer treatment scenario involving the imposition of stress to target cancer cells is gaining traction to augment or even replace conventional therapeutic regimens. Therefore, a comprehensive understanding of stress response pathways is crucial for devising and implementing novel therapeutic strategies.

Role of the Histone Acetyl Transferase MOF and the Histone Deacetylase Sirtuins in Regulation of H4K16ac During DNA Damage Repair and Metabolic Programming: Implications in Cancer and Aging

The accurate repair of genomic damage mediated by ionizing radiation (IR), chemo- or radiomimetic drugs, or other exogenous agents, is necessary for maintenance of genome integrity, preservation of cellular viability and prevention of oncogenic transformation. Eukaryotes have conserved mechanisms designed to perceive and repair the damaged DNA quite efficiently. Among the different types of DNA damage, double strand breaks (DSB) are the most detrimental. The cellular DNA DSB response is a hierarchical signaling network that integrates damage sensing and repair with chromatin structural changes that involve a range of pre-existing and induced covalent modifications. Recent studies have revealed that pre-existing histone modifications are important contributors within this signaling/repair network. This chapter discusses the role of a critical histone acetyl transferase (HAT) known as MOF (males absent on the first) and the histone deacetylases (HDACs) Sirtuins on histone H4K16 acetylation (H4K16ac) and DNA damage repair. We also discuss the role of this important histone modification in light of metabolic rewiring and its role in regulating human pathophysiologic states.

Conserved Structure and Evolution of DPF Domain of PHF10-The Specific Subunit of PBAF Chromatin Remodeling Complex

Transcription activation factors and multisubunit coactivator complexes get recruited at specific chromatin sites via protein domains that recognize histone modifications. Single PHDs (plant homeodomains) interact with differentially modified H3 histone tails. Double PHD finger (DPF) domains possess a unique structure different from PHD and are found in six proteins: histone acetyltransferases MOZ and MORF; chromatin remodeling complex BAF (DPF1–3); and chromatin remodeling complex PBAF (PHF10). Among them, PHF10 stands out due to the DPF sequence, structure, and functions. PHF10 is ubiquitously expressed in developing and adult organisms as four isoforms differing in structure (the presence or absence of DPF) and transcription regulation functions. Despite the importance of the DPF domain of PHF10 for transcription activation, its structure remains undetermined. We performed homology modeling of the human PHF10 DPF domain and determined common and distinct features in structure and histone modifications recognition capabilities, which can affect PBAF complex chromatin recruitment. We also traced the evolution of DPF1–3 and PHF10 genes from unicellular to vertebrate organisms. The data reviewed suggest that the DPF domain of PHF10 plays an important role in SWI/SNF-dependent chromatin remodeling during transcription activation.

The role of MOZ/KAT6A in hematological malignancies and advances in MOZ/KAT6A inhibitors

Hematological malignancies, unlike solid tumors, are a group of malignancies caused by abnormal differentiation of hematopoietic stem cells. Monocytic leukemia zinc finger protein (MOZ), a member of the MYST (MOZ, Ybf2/Sas3, Sas2, Tip60) family, is a histone acetyltransferase. MOZ is involved in various cellular functions: generation and maintenance of hematopoietic stem cells, development of erythroid cells, B-lineage progenitors and myeloid cells, and regulation of cellular senescence. Studies have shown that MOZ is susceptible to translocation in chromosomal rearrangements to form fusion genes, leading to the fusion of MOZ with other cellular regulators to form MOZ fusion proteins. Different MOZ fusion proteins have different roles, such as in the development and progression of hematological malignancies and inhibition of cellular senescence. Thus, MOZ is an attractive target, and targeting MOZ to design small-molecule drugs can help to treat hematological malignancies. This review summarizes recent progress in biology and medicinal chemistry for the histone acetyltransferase MOZ. In the biology section, MOZ and cofactors, structures of MOZ and related HATs, MOZ and fusion proteins, and roles of MOZ in cancer are discussed. In medicinal chemistry, recent developments in MOZ inhibitors are summarized.

Histone Modifications in Stem Cell Development and Their Clinical Implications

Human stem cells bear a great potential for multiple therapeutic applications but at the same time constitute a major threat to human health in the form of cancer stem cells. The molecular processes that govern stem cell maintenance or differentiation have been extensively studied in model organisms or cell culture, but it has been difficult to extrapolate these insights to therapeutic applications. Recent advances in the field suggest that local and global changes in histone modifications that affect chromatin structure could influence the capability of cells to either maintain their stem cell identity or differentiate into specialized cell types. The enzymes that regulate these modifications are therefore among the prime targets for potential drugs that can influence and potentially improve the therapeutic application of stem cells. In this review, we discuss recent findings on the role of histone modifications in stem cell regulation and their potential implications for clinical applications.

Protein acetylation: a novel modus of obesity regulation

Obesity is a chronic epidemic disease worldwide which has become one of the important public health issues. It is a process that excessive accumulation of adipose tissue caused by long-term energy intake exceeding energy expenditure. So far, the prevention and treatment strategies of obesity on individuals and population have not been successful in the long term. Acetylation is one of the most common ways of protein post-translational modification (PTM). It exists on thousands of non-histone proteins in almost every cell chamber. It has many influences on protein levels and metabolome levels, which is involved in a variety of metabolic reactions, including sugar metabolism, tricarboxylic acid cycle, and fatty acid metabolism, which are closely related to biological activities. Studies have shown that protein acetylation levels are dynamically regulated by lysine acetyltransferases (KATs) and lysine deacetylases (KDACs). Protein acetylation modifies protein-protein and protein-DNA interactions and regulates the activity of enzymes or cytokines which is related to obesity in order to participate in the occurrence and treatment of obesity-related metabolic diseases. Therefore, we speculated that acetylation was likely to become effective means of controlling obesity in the future. In consequence, this review focuses on the mechanisms of protein acetylation controlled obesity, to provide theoretical basis for controlling obesity and curing obesity-related diseases, which is a significance for regulating obesity in the future. This review will focus on the role of protein acetylation in controlling obesity.

In-depth proteomic analysis of proteasome inhibitors bortezomib, carfilzomib and MG132 reveals that mortality factor 4-like 1 (MORF4L1) protein ubiquitylation is negatively impacted

Proteasome inhibitors are an important class of chemotherapeutic drugs. In this study, we performed a large-scale ubiquitylome analysis of the three proteasome inhibitors MG132, bortezomib and carfilzomib. Although carfilzomib is currently being used for the treatment of multiple myeloma, it has not yet been subjected to a global ubiquitylome analysis. In this study, we identified more than 14,000 unique sites of ubiquitylation in more than 4400 protein groups. We introduced stringent criteria to determine the correct ubiquitylation site ratios and used five biological replicates to achieve increased statistical power. With the vast amount of data acquired, we made proteome-wide comparisons between the proteasome inhibitors and indicate candidate proteins that will benefit from further study. We find that in addition to the expected increase in ubiquitylation in the majority of proteins, unexpectedly a select few are specifically and significantly decreased in ubiquitylation at specific sites after treatment with proteasome inhibitors. We chose to follow-up on Mortality factor 4-like 1 (MORF4L1), which was significantly decreased in ubiquitylation at lysine 187 and lysine 104 upon proteasome inhibition, but increased in protein abundance by approximately two-fold. We demonstrate that the endogenous protein level of MORF4L1 is highly regulated by the ubiquitin proteasome system. SIGNIFICANCE: This study provides a highly curated dataset of more than 14,000 unique sites of ubiquitylation in more than 4400 protein groups. For the proper quantification of ubiquitylation sites, we introduced a higher standard by quantifying only those ubiquitylation sites that are not flanked by neighboring ubiquitylation, thereby avoiding the report of incorrect ratios. The sites identified will serve to identify important targets of the ubiquitin proteasome system and aid to better understand the repertoire of proteins that are affected by inhibiting the proteasome with MG132, bortezomib, and carfilzomib. In addition, we investigated the unusual observation that ubiquitylation of the tumor suppressor Mortality factor 4-like (MORF4L1) protein decreases rather than increases upon proteasome inhibition, which may contribute to an additional anti-tumor effect of bortezomib and carfilzomib.

Epigenetics of aging and disease: a brief overview

Aging is an important risk factor for several human diseases such as cancer, cardiovascular disease and neurodegenerative disorders, resulting from a combination of genetic and environmental factors (e.g., diet, smoking, obesity and stress), which, at molecular level, cause changes in gene expression underlying the decline of physiological function. Epigenetics, which include mechanisms regulating gene expression independently of changes to DNA sequence, regulate gene expression by modulating the structure of chromatin or by regulating the binding of transcriptional machinery to DNA. Several studies showed that an impairment of epigenetic mechanisms promotes alteration of gene expression underlying several aging-related diseases. Alteration of these mechanisms is also linked with changes of gene expression that occurs during aging processes of different tissues. In this review, we will outline the potential role of epigenetics in the onset of two age-related pathologies, cancer and cardiovascular diseases.

The Biological Significance of Targeting Acetylation-Mediated Gene Regulation for Designing New Mechanistic Tools and Potential Therapeutics

The molecular interplay between nucleosomal packaging and the chromatin landscape regulates the transcriptional programming and biological outcomes of downstream genes. An array of epigenetic modifications plays a pivotal role in shaping the chromatin architecture, which controls DNA access to the transcriptional machinery. Acetylation of the amino acid lysine is a widespread epigenetic modification that serves as a marker for gene activation, which intertwines the maintenance of cellular homeostasis and the regulation of signaling during stress. The biochemical horizon of acetylation ranges from orchestrating the stability and cellular localization of proteins that engage in the cell cycle to DNA repair and metabolism. Furthermore, lysine acetyltransferases (KATs) modulate the functions of transcription factors that govern cellular response to microbial infections, genotoxic stress, and inflammation. Due to their central role in many biological processes, mutations in KATs cause developmental and intellectual challenges and metabolic disorders. Despite the availability of tools for detecting acetylation, the mechanistic knowledge of acetylation-mediated cellular processes remains limited. This review aims to integrate molecular and structural bases of KAT functions, which would help design highly selective tools for understanding the biology of KATs toward developing new disease treatments.

Zinc Metalloproteins in Epigenetics and Their Crosstalk

More than half a century ago, zinc was established as an essential micronutrient for normal human physiology. In silico data suggest that about 10% of the human proteome potentially binds zinc. Many proteins with zinc-binding domains (ZBDs) are involved in epigenetic modifications such as DNA methylation and histone modifications, which regulate transcription in physiological and pathological conditions. Zinc metalloproteins in epigenetics are mainly zinc metalloenzymes and zinc finger proteins (ZFPs), which are classified into writers, erasers, readers, editors, and feeders. Altogether, these classes of proteins engage in crosstalk that fundamentally maintains the epigenome's modus operandi. Changes in the expression or function of these proteins induced by zinc deficiency or loss of function mutations in their ZBDs may lead to aberrant epigenetic reprogramming, which may worsen the risk of non-communicable chronic diseases. This review attempts to address zinc's role and its proteins in natural epigenetic programming and artificial reprogramming and briefly discusses how the ZBDs in these proteins interact with the chromatin.

Characteristics and outcome of patients with acute myeloid leukaemia and t(8;16)(p11;p13): results from an International Collaborative Study

In acute myeloid leukaemia (AML) t(8;16)(p11;p13)/MYST3-CREBBP is a very rare abnormality. Previous small series suggested poor outcome. We report on 59 patients with t(8;16) within an international, collaborative study. Median age was 52 (range: 16-75) years. AML was de novo in 58%, therapy-related (t-AML) in 37% and secondary after myelodysplastic syndrome (s-AML) in 5%. Cytogenetics revealed a complex karyotype in 43%. Besides MYST3-CREBBP, whole-genome sequencing on a subset of 10 patients revealed recurrent mutations in ASXL1, BRD3, FLT3, MLH1, POLG, TP53, SAMD4B (n = 3, each), EYS, KRTAP9-1 SPTBN5 (n = 4, each), RUNX1 and TET2 (n = 2, each). Complete remission after intensive chemotherapy was achieved in 84%. Median follow-up was 5·48 years; five-year survival rate was 17%. Patients with s-/t-AML (P = 0·01) and those with complex karyotype (P = 0·04) had an inferior prognosis. Allogeneic haematopoietic cell transplantation (allo-HCT) was performed in 21 (36%) patients, including 15 in first complete remission (CR1). Allo-HCT in CR1 significantly improved survival (P = 0·04); multivariable analysis revealed that allo-HCT in CR1 was effective in de novo AML but not in patients with s-AML/t-AML and less in patients exhibiting a complex karyotype. In summary, outcomes of patients with t(8;16) are dismal with chemotherapy, and may be substantially improved with allo-HCT performed in CR1.

Diagnosis of Arboleda-Tham syndrome by whole genome sequencing in an Asian boy with severe developmental delay

Diagnosis of a 9-month-old boy brought to our genetics clinic with chief complaints of developmental delay (DD), failure to thrive, microcephaly, trunk hypotonia and hypertonia of the extremities. Multiple congenital defects but no significant syndromes or diseases were impressed. The chromosomal analysis and array comparative genomic hybridization (aCGH) revealed no significant pathogenic changes. Whole Genome Sequencing (WGS) identified a p.Glu1139fs de novo mutation of the KAT6A gene. The patient's phenotype was consistent clinically with Arboleda-Tham syndrome (ARTHS). Reviewing the literature showed that this is the first patient in Taiwan detected by WGS and that it involves a novel mutation. Comparing the highly variable clinical presentations of this syndrome with our patient, this boy's features and severe developmental defects seem to be due to a late-truncating mutation at the carboxyl end of the KAT6A protein. Our study demonstrates the power of WGS to confirm a diagnosis within 4 weeks for this rare condition.

The key roles of the lysine acetyltransferases KAT6A and KAT6B in physiology and pathology

Histone modifications and more specifically ε-lysine acylations are key epigenetic regulators that control chromatin structure and gene transcription, thereby impacting on various important cellular processes and phenotypes. Furthermore, lysine acetylation of many non-histone proteins is involved in key cellular processes including transcription, DNA damage repair, metabolism, cellular proliferation, mitosis, signal transduction, protein folding, and autophagy. Acetylation affects protein functions through multiple mechanisms including regulation of protein stability, enzymatic activity, subcellular localization, crosstalk with other post-translational modifications as well as regulation of protein-protein and protein-DNA interactions. The paralogous lysine acetyltransferases KAT6A and KAT6B which belong to the MYST family of acetyltransferases, were first discovered approximately 25 years ago. KAT6 acetyltransferases acylate both histone H3 and non-histone proteins. In this respect, KAT6 acetyltransferases play key roles in regulation of transcription, various developmental processes, maintenance of hematopoietic and neural stem cells, regulation of hematopoietic cell differentiation, cell cycle progression as well as mitosis. In the current review, we discuss the physiological functions of the acetyltransferases KAT6A and KAT6B as well as their functions under pathological conditions of aberrant expression, leading to several developmental syndromes and cancer. Importantly, both upregulation and downregulation of KAT6 proteins was shown to play a role in cancer formation, progression, and therapy resistance, suggesting that they can act as oncogenes or tumor suppressors. We also describe reciprocal regulation of expression between KAT6 proteins and several microRNAs as well as their involvement in cancer formation, progression and resistance to therapy.

Role of histone acetyltransferase inhibitors in cancer therapy

The development of cancer is a complex phenomenon driven by various extrinsic as well as intrinsic risk factors including epigenetic modifications. These post-translational modifications are encountered in diverse cancer cells and appear for a relatively short span of time. These changes can significantly affect various oncogenic genes and proteins involved in cancer initiation and progression. Histone lysine acetylation and deacetylation processes are controlled by two opposing classes of enzymes that modulate gene regulation either by adding an acetyl moiety on a histone lysine residue by histone lysine acetyltransferases (KATs) or via removing it by histone deacetylases (KDACs). Deregulated KAT activity has been implicated in the development of several diseases including cancer and can be targeted for the development of anti-neoplastic drugs. Here, we describe the predominant epigenetic changes that can affect key KAT superfamily members during carcinogenesis and briefly highlight the pharmacological potential of employing lysine acetyltransferase inhibitors (KATi) for cancer therapy.

Patent spotlight: small-molecule lysine acetyltransferase inhibitors (KATi)

Lysine (or histone) acetyltransferases plays a key role in genome maintenance and gene regulation and dysregulation of acetylation is a recognized feature of many diseases, including several cancers. Here, the patent landscape surrounding lysine acetyltransferase inhibitors (KATi or HATi), with a focus on small-molecule compounds, is outlined and assessed. Overall, the 36 KATi-specific patents found were categorized into two distinct groups: specific small-molecule inhibitors (compounds and molecules) and patents applying KATi for targeted disease treatment. These patents recognize the emergent potential of KATi to significantly impact on the management of many diseases (including multiple cancer types, neurological disorders and immunological syndromes), improving the range of treatments (and drug classes) available for personalized medicine.

Insights Into the Function of the NuA4 Complex in Plants

Chromatin remodeling plays a key role in the establishment and maintenance of gene expression patterns essential for plant development and responses to environmental factors. Post-translational modification of histones, including acetylation, is one of the most relevant chromatin remodeling mechanisms that operate in eukaryotic cells. Histone acetylation is an evolutionarily conserved chromatin signature commonly associated with transcriptional activation. Histone acetylation levels are tightly regulated through the antagonistic activity of histone acetyltransferases (HATs) and histone deacetylases (HDACs). In plants, different families of HATs are present, including the MYST family, which comprises homologs of the catalytic subunit of the Nucleosome Acetyltransferase of H4 (NuA4) complex in yeast. This complex mediates acetylation of histones H4, H2A, and H2A.Z, and is involved in transcriptional regulation, heterochromatin silencing, cell cycle progression, and DNA repair in yeast. In Arabidopsis and, other plant species, homologs for most of the yeast NuA4 subunits are present and although the existence of this complex has not been demonstrated yet, compelling evidence supports the notion that this type of HAT complex functions from mosses to angiosperms. Recent proteomic studies show that several Arabidopsis homologs of NuA4 components, including the assembly platform proteins and the catalytic subunit, are associated in vivo with additional members of this complex suggesting that a NuA4-like HAT complex is present in plants. Furthermore, the functional characterization of some Arabidopsis NuA4 subunits has uncovered the involvement of these proteins in the regulation of different plant biological processes. Interestingly, for most of the mutant plants deficient in subunits of this complex characterized so far, conspicuous defects in flowering time are observed, suggesting a role for NuA4 in the control of this plant developmental program. Moreover, the participation of Arabidopsis NuA4 homologs in other developmental processes, such as gametophyte development, as well as in cell proliferation and stress and hormone responses, has also been reported. In this review, we summarize the current state of knowledge on plant putative NuA4 subunits and discuss the latest progress concerning the function of this chromatin modifying complex.

Metabolism and epigenetics of pancreatic cancer stem cells

Pancreatic Cancer (PDA) is an aggressive malignancy characterized by early spread and a high mortality. Current studies suggest that a subpopulation of cells exist within tumors, cancer stem cell (CSC), which are capable of self-renewal and give rise to unique progeny which form the major neoplastic cellular component of tumors. While CSCs constitute a small cellular subpopulation within the tumor, their resistance to chemotherapy and radiation make them an important therapeutic target for eradication. Along with distinctive phenotypic properties, CSCs possess a unique metabolic plasticity allowing them to rapidly respond and adapt to environmental changes. These cells and their progeny also display a significantly altered epigenetic state with distinctive patterns of DNA methylation. Several mechanisms of cross-talk between epigenetic and metabolic pathways in PDA exist which ultimately contribute to the observed cellular plasticity and enhanced tumorigenesis. In this review we discuss various examples of this metabolic-epigenetic interplay and how it may constitute a new avenue for therapy specifically targeting CSCs in PDA.

Brpf1 Haploinsufficiency Impairs Dendritic Arborization and Spine Formation, Leading to Cognitive Deficits

Haploinsufficiency of the bromodomain and PHD finger-containing protein 1 (BRPF1) gene causes intellectual disability (ID), which is characterized by impaired intellectual and cognitive function; however, the neurological basis for ID and the neurological function of BRPF1 dosage in the brain remain unclear. Here, by crossing Emx1-cre mice with Brpf1^fl/fl mice, we generated Brpf1 heterozygous mice to model BRPF1-related ID. Brpf1 heterozygotes showed reduced dendritic complexity in both hippocampal granule cells and cortical pyramidal neurons, accompanied by reduced spine density and altered spine and synapse morphology. An in vitro study of Brpf1 haploinsufficiency also demonstrated decreased frequency and amplitude of miniature EPSCs that may subsequently contribute to abnormal behaviors, including decreased anxiety levels and defective learning and memory. Our results demonstrate a critical role for Brpf1 dosage in neuron dendrite arborization, spine morphogenesis and behavior and provide insight into the pathogenesis of BRPF1-related ID.

Runx1 and RORγt Cooperate to Upregulate IL-22 Expression in Th Cells through Its Distal Enhancer

IL-22 is a cytokine that plays a pivotal role in regulating tissue homeostasis at barrier surfaces and is produced by activated CD4+ Th cells. Currently, the molecular mechanisms regulating Il22 gene expression are still unclear. In this study, we have identified a crucial cis-regulatory element located 32 kb upstream of the mouse Il22 promoter, termed conserved noncoding sequence (CNS)-32. We demonstrated that CNS-32 acts as an enhancer in reporter assays and contains binding motifs for Runt-related transcription factor (Runx)1 and retinoic acid-related orphan receptor γt (RORγt). Mutation of these motifs significantly abrogated the reporter activity, suggesting a role for both factors in the control of enhancer-mediated Il22 expression. Runx1 and RORγt occupancy and elevated histone H4 acetylation at CNS-32 were evident, as naive T cells differentiated into IL-22-producing Th22 cells. Overexpression of Runx1 promoted IL-22 production by inducing RORγt and IL-23 receptor, all critical to Th22 cell induction. Although Runx1 alone enhanced IL-22 production in Th22 cells, it was further enhanced in the presence of RORγt. Conversely, short hairpin RNA-mediated knockdown of core-binding factor β, a cofactor essential for Runx1 activity, was effective in limiting IL-22 production. Collectively, our results suggest that IL-22 production is controlled by a regulatory circuit in which Runx1 induces RORγt and then partners with RORγt to direct Il22 expression through their targeting of the Il22 enhancer.

Say-Barber-Biesecker-Young-Simpson syndrome and Genitopatellar syndrome: Lumping or splitting?

The Say-Barber-Biesecker-Young-Simpson variant of Ohdo syndrome (SBBYSS) and Genitopatellar syndrome (GTPTS) are 2 rare but clinically well-described diseases caused by de novo heterozygous sequence variants in the KAT6B gene. Both phenotypes are characterized by significant global developmental delay/intellectual disability, hypotonia, genital abnormalities, and patellar hypoplasia/agenesis. In addition, congenital heart defects, dental abnormalities, hearing loss, and thyroid anomalies are common to both phenotypes. This broad clinical overlap led some authors to propose the concept of KAT6B spectrum disorders. On the other hand, some clinical features could help to differentiate the 2 disorders. Furthermore, it is possible to establish a genotype-phenotype correlation when considering the position of the sequence variant along the gene, supporting the notion of the 2 disorders as really distinct entities.

Emerging Role of Histone Acetyltransferase in Stem Cells and Cancer

Protein acetylation is one of the most important posttranslational modifications catalyzed by acetyltransferases and deacetylases, through the addition and removal of acetyl groups to lysine residues. Lysine acetylation can affect protein-nucleic acid or protein-protein interactions and protein localization, transport, stability, and activity. It regulates the function of a large variety of proteins, including histones, oncoproteins, tumor suppressors, and transcription factors, thus representing a crucial regulator of several biological processes with particular prominent roles in transcription and metabolism. Thus, it is unsurprising that alteration of protein acetylation is involved in human disease, including metabolic disorders and cancers. In this context, different hematological and solid tumors are characterized by deregulation of the protein acetylation pattern as a result of genetic or epigenetic changes. The imbalance between acetylation and deacetylation of histone or nonhistone proteins is also involved in the modulation of the self-renewal and differentiation ability of stem cells, including cancer stem cells. Here, we summarize a combination of in vitro and in vivo studies, undertaken on a set of acetyltransferases, and discuss the physiological and pathological roles of this class of enzymes. We also review the available data on the involvement of acetyltransferases in the regulation of stem cell renewal and differentiation in both normal and cancer cell population.

Cancer stem cells and tumorigenesis

Cancer is one of the most serious diseases all over the world, and the cancer stem cell (CSC) model accounts for tumor initiation, metastasis, drug resistance, and relapse. The CSCs within tumor bulk have the capacity to self-renew, differentiate, and give rise to a new tumor. The self-renewal of CSCs is precisely regulated by various modulators, including Wnt/β-catenin signaling, Notch signaling, Hedgehog signaling, transcription factors, chromatin remodeling complexes, and non-coding RNAs. CSCs reside in their niches that are also involved in the self-renewal maintenance of CSCs and protection of CSCs from chemotherapy, radiotherapy, and even endogenous damages. Moreover, CSCs can also remodel their niches to initiate tumorigenesis. The mutual interactions between CSCs and their niches play a critical role in the regulation of CSC self-renewal and tumorigenesis as well. Many surface markers of CSCs have been identified, and these markers become first choices for CSC targeting. Due to heterogeneity and plasticity, targeting CSCs is still a big challenge for tumor elimination. In this review, we summarize recent progresses on the biological features of CSCs and targeting strategies against CSCs.

Identifying Small-Molecule Binding Sites for Epigenetic Proteins at Domain-Domain Interfaces

Epigenetics is a rapidly growing field in drug discovery. Of particular interest is the role of post-translational modifications to histones and the proteins that read, write, and erase such modifications. The development of inhibitors for reader domains has focused on single domains. One of the major difficulties of designing inhibitors for reader domains is that, with the notable exception of bromodomains, they tend not to possess a well-enclosed binding site amenable to small-molecule inhibition. As many of the proteins in epigenetic regulation have multiple domains, there are opportunities for designing inhibitors that bind at a domain-domain interface which provide a more suitable interaction pocket. Examination of X-ray structures of multiple domains involved in recognising and modifying post-translational histone marks using the SiteMap algorithm identified potential binding sites at domain-domain interfaces. For the tandem plant homeodomain-bromodomain of SP100C, a potential inter-domain site identified computationally was validated experimentally by the discovery of ligands by X-ray crystallographic fragment screening.

Acetylation of the Cd8 Locus by KAT6A Determines Memory T Cell Diversity

How functionally diverse populations of pathogen-specific killer T cells are generated during an immune response remains unclear. Here, we propose that fine-tuning of CD8αβ co-receptor levels via histone acetylation plays a role in lineage fate. We show that lysine acetyltransferase 6A (KAT6A) is responsible for maintaining permissive Cd8 gene transcription and enabling robust effector responses during infection. KAT6A-deficient CD8(+) T cells downregulated surface CD8 co-receptor expression during clonal expansion, a finding linked to reduced Cd8α transcripts and histone-H3 lysine 9 acetylation of the Cd8 locus. Loss of CD8 expression in KAT6A-deficient T cells correlated with reduced TCR signaling intensity and accelerated contraction of the effector-like memory compartment, whereas the long-lived memory compartment appeared unaffected, a result phenocopied by the removal of the Cd8 E8I enhancer element. These findings suggest a direct role of CD8αβ co-receptor expression and histone acetylation in shaping functional diversity within the cytotoxic T cell pool.

The multifaceted role of lysine acetylation in cancer: prognostic biomarker and therapeutic target

Lysine acetylation is a post-translational modification that regulates gene transcription by targeting histones as well as a variety of transcription factors in the nucleus. Recently, several reports have demonstrated that numerous cytosolic proteins are also acetylated and that this modification, affecting protein activity, localization and stability has profound consequences on their cellular functions. Interestingly, most non-histone proteins targeted by acetylation are relevant for tumorigenesis. In this review, we will analyze the functional implications of lysine acetylation in different cellular compartments, and will examine our current understanding of lysine acetyltransferases family, highlighting the biological role and prognostic value of these enzymes and their substrates in cancer. The latter part of the article will address challenges and current status of molecules targeting lysine acetyltransferase enzymes in cancer therapy.

Bivalent complexes of PRC1 with orthologs of BRD4 and MOZ/MORF target developmental genes in Drosophila

Kang et al. confirm PRC1–Br140 and PRC1–Fs(1)h interactions and identify their genomic binding sites. PRC1–Br140 bind developmental genes in fly embryos, with analogous co-occupancy of PRC1 and BRD1 at bivalent loci in human ES cells.

Regulatory decisions in Drosophila require Polycomb group (PcG) proteins to maintain the silent state and Trithorax group (TrxG) proteins to oppose silencing. Since PcG and TrxG are ubiquitous and lack apparent sequence specificity, a long-standing model is that targeting occurs via protein interactions; for instance, between repressors and PcG proteins. Instead, we found that Pc-repressive complex 1 (PRC1) purifies with coactivators Fs(1)h [female sterile (1) homeotic] and Enok/Br140 during embryogenesis. Fs(1)h is a TrxG member and the ortholog of BRD4, a bromodomain protein that binds to acetylated histones and is a key transcriptional coactivator in mammals. Enok and Br140, another bromodomain protein, are orthologous to subunits of a mammalian MOZ/MORF acetyltransferase complex. Here we confirm PRC1–Br140 and PRC1–Fs(1)h interactions and identify their genomic binding sites. PRC1–Br140 bind developmental genes in fly embryos, with analogous co-occupancy of PRC1 and a Br140 ortholog, BRD1, at bivalent loci in human embryonic stem (ES) cells. We propose that identification of PRC1–Br140 “bivalent complexes” in fly embryos supports and extends the bivalency model posited in mammalian cells, in which the coexistence of H3K4me3 and H3K27me3 at developmental promoters represents a poised transcriptional state. We further speculate that local competition between acetylation and deacetylation may play a critical role in the resolution of bivalent protein complexes during development.

Acetylation and deacetylation in cancer stem-like cells

Cancer stem-like cell (CSC) model has been established to investigate the underlying mechanisms of tumor initiation and progression. The imbalance between acetylation and deacetylation of histone or non-histone proteins, one of the important epigenetic modification processes, is closely associated with a wide variety of diseases including cancer. Acetylation and deacetylation are involved in various stemness-related signal pathways and drive the regulation of self-renewal and differentiation in normal developmental processes. Therefore, it is critical to explore their role in the maintenance of cancer stem-like cell traits. Here, we will review the extensive dysregulations of acetylation found in cancers and summarize their functional roles in sustaining CSC-like properties. Additionally, the use of deacetyltransferase inhibitors as an effective therapeutic strategy against CSCs is also discussed.

De Novo Mutation of KAT6B Gene Causing Atypical Say-Barber-Biesecker-Young-Simpson Syndrome or Genitopatellar Syndrome

Mutations in KAT6B gene are responsible for Say-Barber-Biesecker-Young-Simpson syndrome (SBBYSS) and genitopatellar syndrome (GPS), with most mutations occurring in exon 18. A 4-year-old Chinese boy presented with short stature but no other clinical features of SBBYSS or GPS had a de novo novel nonsense pathogenic mutation in exon 14 of the KAT6B gene at position c.2636T>A (p.Leu879X). The correlation analysis of genotype-phenotype indicated distinctive clinical features (short stature, growth hormone deficiency, and delayed bone age) compared with the classical mutations of KAT6B gene. To the best of our knowledge, this is the first report of KAT6B gene mutation in any Chinese individual. This work expands the mutant phenotypic spectrum of the KAT6B gene.

Exploitation of EP300 and CREBBP Lysine Acetyltransferases by Cancer

p300 and CREB-binding protein (CBP), two homologous lysine acetyltransferases in metazoans, have a myriad of cellular functions. They exert their influence mainly through their roles as transcriptional regulators but also via nontranscriptional effects inside and outside of the nucleus on processes such as DNA replication and metabolism. The versatility of p300/CBP as molecular tools has led to their exploitation by viral oncogenes for cellular transformation and by cancer cells to achieve and maintain an oncogenic phenotype. How cancer cells use p300/CBP in their favor varies depending on the cellular context and is evident by the growing list of loss- and gain-of-function genetic alterations in p300 and CBP in solid tumors and hematological malignancies. Here, we discuss the biological functions of p300/CBP and how disruption of these functions by mutations and alterations in expression or subcellular localization contributes to the cancer phenotype.

Histone Acetyltransferase Activity of MOF Is Required for MLL-AF9 Leukemogenesis

Chromatin-based mechanisms offer therapeutic targets in acute myeloid leukemia (AML) that are of great current interest. In this study, we conducted an RNAi-based screen to identify druggable chromatin regulator-based targets in leukemias marked by oncogenic rearrangements of the MLL gene. In this manner, we discovered the H4K16 histone acetyltransferase (HAT) MOF to be important for leukemia cell growth. Conditional deletion of Mof in a mouse model of MLL-AF9-driven leukemogenesis reduced tumor burden and prolonged host survival. RNA sequencing showed an expected downregulation of genes within DNA damage repair pathways that are controlled by MOF, as correlated with a significant increase in yH2AX nuclear foci in Mof-deficient MLL-AF9 tumor cells. In parallel, Mof loss also impaired global H4K16 acetylation in the tumor cell genome. Rescue experiments with catalytically inactive mutants of MOF showed that its enzymatic activity was required to maintain cancer pathogenicity. In support of the role of MOF in sustaining H4K16 acetylation, a small-molecule inhibitor of the HAT component MYST blocked the growth of both murine and human MLL-AF9 leukemia cell lines. Furthermore, Mof inactivation suppressed leukemia development in an NUP98-HOXA9-driven AML model. Taken together, our results establish that the HAT activity of MOF is required to sustain MLL-AF9 leukemia and may be important for multiple AML subtypes. Blocking this activity is sufficient to stimulate DNA damage, offering a rationale to pursue MOF inhibitors as a targeted approach to treat MLL-rearranged leukemias. Cancer Res; 77(7); 1753-62. ©2017 AACR.

Identification of MYST3 as a novel epigenetic activator of ERα frequently amplified in breast cancer

Estrogen receptor α (ERα) is a master driver of a vast majority of breast cancers. Breast cancer cells often develop resistance to endocrine therapy via restoration of the ERα activity through survival pathways. Thus identifying the epigenetic activator of ERα that can be targeted to block ERα gene expression is a critical topic of endocrine therapy. Here, integrative genomic analysis identified MYST3 as a potential oncogene target that is frequently amplified in breast cancer. MYST3 is involved in histone acetylation via its histone acetyltransferase domain (HAT) and, as a result, activates gene expression by altering chromatin structure. We found that MYST3 was amplified in 11% and/or overexpressed in 15% of breast tumors, and overexpression of MYST3 correlated with worse clinical outcome in estrogen receptor+ (ER+) breast cancers. Interestingly, MYST3 depletion drastically inhibited proliferation in MYST3-high, ER+ breast cancer cells, but not in benign breast epithelial cells or in MYST3-low breast cancer cells. Importantly, we discovered that knocking down MYST3 resulted in profound reduction of ERα expression, while ectopic expression of MYST3 had the reversed effect. Chromatin immunoprecipitation revealed that MYST3 binds to the proximal promoter region of ERα gene, and inactivating mutations in its HAT domain abolished its ability to regulate ERα, suggesting MYST3 functioning as a histone acetyltransferase that activates ERα promoter. Furthermore, MYST3 inhibition with inducible MYST3 shRNAs potently attenuated breast tumor growth in mice. Together, this study identifies the first histone acetyltransferase that activates ERα expression which may be potentially targeted to block ERα at transcriptional level.

Histone acetyltransferase activity of MOF is required for adult but not early fetal hematopoiesis in mice

K(lysine) acetyltransferase 8 (KAT8, also known as MOF) mediates the acetylation of histone H4 at lysine 16 (H4K16ac) and is crucial for murine embryogenesis. Lysine acetyltransferases have been shown to regulate various stages of normal hematopoiesis. However, the function of MOF in hematopoietic stem cell (HSC) development has not yet been elucidated. We set out to study the role of MOF in general hematopoiesis by using a Vav1-cre-induced conditional murine Mof knockout system and found that MOF is critical for hematopoietic cell maintenance and HSC engraftment capacity in adult hematopoiesis. Rescue experiments with a MOF histone acetyltransferase domain mutant illustrated the requirement for MOF acetyltransferase activity in the clonogenic capacity of HSCs and progenitors. In stark contrast, fetal steady-state hematopoiesis at embryonic day (E) 14.5 was not affected by homozygous Mof deletion despite dramatic loss of global H4K16ac. Hematopoietic defects start manifesting in late gestation at E17.5. The discovery that MOF and its H4K16ac activity are required for adult but not early and midgestational hematopoiesis supports the notion that multiple chromatin regulators may be crucial for hematopoiesis at varying stages of development. MOF is therefore a developmental-stage-specific chromatin regulator found to be essential for adult but not early fetal hematopoiesis.

Gene expression profiling of epigenetic chromatin modification enzymes and histone marks by cigarette smoke: implications for COPD and lung cancer

Chromatin-modifying enzymes mediate DNA methylation and histone modifications on recruitment to specific target gene loci in response to various stimuli. The key enzymes that regulate chromatin accessibility for maintenance of modifications in DNA and histones, and for modulation of gene expression patterns in response to cigarette smoke (CS), are not known. We hypothesize that CS exposure alters the gene expression patterns of chromatin-modifying enzymes, which then affects multiple downstream pathways involved in the response to CS. We have, therefore, analyzed chromatin-modifying enzyme profiles and validated by quantitative real-time PCR (qPCR). We also performed immunoblot analysis of targeted histone marks in C57BL/6J mice exposed to acute and subchronic CS, and of lungs from nonsmokers, smokers, and patients with chronic obstructive pulmonary disease (COPD). We found a significant increase in expression of several chromatin modification enzymes, including DNA methyltransferases, histone acetyltransferases, histone methyltransferases, and SET domain proteins, histone kinases, and ubiquitinases. Our qPCR validation data revealed a significant downregulation of Dnmt1, Dnmt3a, Dnmt3b, Hdac2, Hdac4, Hat1, Prmt1, and Aurkb We identified targeted chromatin histone marks (H3K56ac and H4K12ac), which are induced by CS. Thus CS-induced genotoxic stress differentially affects the expression of epigenetic modulators that regulate transcription of target genes via DNA methylation and site-specific histone modifications. This may have implications in devising epigenetic-based therapies for COPD and lung cancer.

BRPF1 is essential for development of fetal hematopoietic stem cells

Hematopoietic stem cells (HSCs) serve as a life-long reservoir for all blood cell types and are clinically useful for a variety of HSC transplantation-based therapies. Understanding the role of chromatin organization and regulation in HSC homeostasis may provide important insights into HSC development. Bromodomain- and PHD finger-containing protein 1 (BRPF1) is a multivalent chromatin regulator that possesses 4 nucleosome-binding domains and activates 3 lysine acetyltransferases (KAT6A, KAT6B, and KAT7), suggesting that this protein has the potential to stimulate crosstalk between different chromatin modifications. Here, we investigated the function of BRPF1 in hematopoiesis by selectively deleting its gene in murine blood cells. Brpf1-deficient pups experienced early lethality due to acute bone marrow failure and aplastic anemia. The mutant bone marrow and fetal liver exhibited severe deficiency in HSCs and hematopoietic progenitors, along with elevated reactive oxygen species, senescence, and apoptosis. BRPF1 deficiency also reduced the expression of multipotency genes, including Slamf1, Mecom, Hoxa9, Hlf, Gfi1, Egr, and Gata3. Furthermore, BRPF1 was required for acetylation of histone H3 at lysine 23, a highly abundant but not well-characterized epigenetic mark. These results identify an essential role of the multivalent chromatin regulator BRPF1 in definitive hematopoiesis and illuminate a potentially new avenue for studying epigenetic networks that govern HSC ontogeny.

Bioinformatic analysis reveals the expression of unique transcriptomic signatures in Zika virus infected human neural stem cells

BACKGROUND

The single-stranded RNA Flavivirus, Zika virus (ZIKV), has recently re-emerged and spread rapidly across the western hemisphere's equatorial countries, primarily through Aedes mosquito transmission. While symptoms in adult infections appear to be self-limiting and mild, severe birth defects, such as microcephaly, have been linked to infection during early pregnancy. Recently, Tang et al. (Cell Stem Cell 2016, doi: 10.1016/j.stem.2016.02.016) demonstrated that ZIKV efficiently infects induced pluripotent stem cell (iPSC) derived human neural progenitor cells (hNPCs), resulting in cell cycle abnormalities and apoptosis. Consequently, hNPCs are a suggested ZIKV target.

METHODS

We analyzed the transcriptomic sequencing (RNA-seq) data (GEO: GSE78711) of ZIKV (Strain: MR766) infected hNPCs. For comparison to the ZIKV-infected hNPCs, the expression data from hNPCs infected with human cytomegalovirus (CMV) (Strain: AD169) was used (GEO: GSE35295). Utilizing a combination of Gene Ontology, database of human diseases, and pathway analysis, we generated a putative systemic model of infection supported by known molecular pathways of other highly related viruses.

RESULTS

We analyzed RNA-sequencing data for transcript expression alterations in ZIKV-infected hNPCs, and then compared them to expression patterns of iPSC-derived hNPCs infected with CMV, a virus that can also induce severe congenital neurological defects in developing fetuses. We demonstrate for the first time that many of cellular pathways correlate with clinical pathologies following ZIKV infection such as microcephaly, congenital nervous system disorders and epilepsy. Furthermore, ZIKV activates several inflammatory signals within infected hNPCs that are implicated in innate and acquired immune responses, while CMV-infected hNPCs showed limited representation of these pathways. Moreover, several genes related to pathogen responses are significantly upregulated upon ZIKV infection, but not perturbed in CMV-infected hNPCs.

CONCLUSION

The presented study is the first to report enrichment of numerous pro-inflammatory pathways in ZIKV-infected hNPCs, indicating that hNPCs are capable of signaling through canonical pro-inflammatory pathways following viral infection. By defining gene expression profiles, new factors in the pathogenesis of ZIKV were identified which could help develop new therapeutic strategies.

The BRPF2/BRD1-MOZ complex is involved in retinoic acid-induced differentiation of embryonic stem cells

The scaffold protein BRPF2 (also called BRD1), a key component of histone acetyltransferase complexes, plays an important role in embryonic development, but its function in the differentiation of embryonic stem cells (ESCs) remains unknown. In the present study, we investigated whether BRPF2 is involved in mouse ESC differentiation. BRPF2 depletion resulted in abnormal formation of embryoid bodies, downregulation of differentiation-associated genes, and persistent maintenance of alkaline phosphatase activity even after retinoic acid-induced differentiation, indicating impaired differentiation of BRPF2-depleted ESCs. We also found reduced global acetylation of histone H3 lysine 14 (H3K14) in BRPF2-depleted ESCs, irrespective of differentiation status. Further, co-immunoprecipitation analysis revealed a physical association between BRPF2 and the histone acetyltransferase MOZ in differentiated ESCs, suggesting the role of BRPF2-MOZ complexes in ESC differentiation. Together, these results suggest that BRPF2-MOZ complexes play an important role in the differentiation of ESCs via H3K14 acetylation.

The Enok acetyltransferase complex interacts with Elg1 and negatively regulates PCNA unloading to promote the G1/S transition

KAT6 histone acetyltransferases (HATs) are highly conserved in eukaryotes and are involved in cell cycle regulation. However, information regarding their roles in regulating cell cycle progression is limited. Here, we report the identification of subunits of the Drosophila Enok complex and demonstrate that all subunits are important for its HAT activity. We further report a novel interaction between the Enok complex and the Elg1 proliferating cell nuclear antigen (PCNA)-unloader complex. Depletion of Enok in S2 cells resulted in a G1/S cell cycle block, and this block can be partially relieved by depleting Elg1. Furthermore, depletion of Enok reduced the chromatin-bound levels of PCNA in both S2 cells and early embryos, suggesting that the Enok complex may interact with the Elg1 complex and down-regulate its PCNA-unloading function to promote the G1/S transition. Supporting this hypothesis, depletion of Enok also partially rescued the endoreplication defects in Elg1-depleted nurse cells. Taken together, our study provides novel insights into the roles of KAT6 HATs in cell cycle regulation through modulating PCNA levels on chromatin.