Monocytic leukemia zinc finger (MOZ) interacts with p53 to induce p21 expression and cell-cycle arrest

KAT6A/YAP/TEAD4 pathway modulates osteoclastogenesis by regulating the RANKL/OPG ratio on the compression side during orthodontic tooth movement

BACKGROUND

Orthodontic tooth movement (OTM) is a dynamic equilibrium of bone remodeling, involving the osteogenesis of new bone and the osteoclastogenesis of old bone, which is mediated by mechanical force. Periodontal ligament stem cells (PDLCSs) in the periodontal ligament (PDL) space can transmit mechanical signals and regulate osteoclastogenesis during OTM. KAT6A is a histone acetyltransferase that plays a part in the differentiation of stem cells. However, whether KAT6A is involved in the regulation of osteoclastogenesis by PDLSCs remains unclear.

RESULTS

In this study, we used the force-induced OTM model and observed that KAT6A was increased on the compression side of PDL during OTM, and also increased in PDLSCs under compression force in vitro. Repression of KAT6A by WM1119, a KAT6A inhibitor, markedly decreased the distance of OTM. Knockdown of KAT6A in PDLSCs decreased the RANKL/OPG ratio and osteoclastogenesis of THP-1. Mechanistically, KAT6A promoted osteoclastogenesis by binding and acetylating YAP, simultaneously regulating the YAP/TEAD axis and increasing the RANKL/OPG ratio in PDLSCs. TED-347, a YAP-TEAD4 interaction inhibitor, partly attenuated the elevation of the RANKL/OPG ratio induced by mechanical force.

CONCLUSION

Our study showed that the PDLSCs modulated osteoclastogenesis and increased the RANKL/OPG ratio under mechanical force through the KAT6A/YAP/TEAD4 pathway. KAT6A might be a novel target to accelerate OTM.

Essential gene screening identifies the bromodomain-containing protein BRPF1 as a new actionable target for endocrine therapy-resistant breast cancers

Identifying master epigenetic factors controlling proliferation and survival of cancer cells allows to discover new molecular targets exploitable to overcome resistance to current pharmacological regimens. In breast cancer (BC), resistance to endocrine therapy (ET) arises from aberrant Estrogen Receptor alpha (ERα) signaling caused by genetic and epigenetic events still mainly unknown. Targeting key upstream components of the ERα pathway provides a way to interfere with estrogen signaling in cancer cells independently from any other downstream event. By combining computational analysis of genome-wide 'drop-out' screenings with siRNA-mediated gene knock-down (kd), we identified a set of essential genes in luminal-like, ERα + BC that includes BRPF1, encoding a bromodomain-containing protein belonging to a family of epigenetic readers that act as chromatin remodelers to control gene transcription. To gather mechanistic insights into the role of BRPF1 in BC and ERα signaling, we applied chromatin and transcriptome profiling, gene ablation and targeted pharmacological inhibition coupled to cellular and functional assays. Results indicate that BRPF1 associates with ERα onto BC cell chromatin and its blockade inhibits cell cycle progression, reduces cell proliferation and mediates transcriptome changes through the modulation of chromatin accessibility. This effect is elicited by a widespread inhibition of estrogen signaling, consequent to ERα gene silencing, in antiestrogen (AE) -sensitive and -resistant BC cells and pre-clinical patient-derived models (PDOs). Characterization of the functional interplay of BRPF1 with ERα reveals a new regulator of estrogen-responsive BC cell survival and suggests that this epigenetic factor is a potential new target for treatment of these tumors.

The postbiotic sodium butyrate synergizes the antiproliferative effects of dexamethasone against the AGS gastric adenocarcinoma cells

A growing body of literature underlines the fundamental role of gut microbiota in the occurrence, treatment, and prognosis of cancer. In particular, the activity of gut microbial metabolites (also known as postbiotics) against different cancer types has been recently reported in several studies. However, their in-depth molecular mechanisms of action and potential interactions with standard chemotherapeutic drugs remain to be fully understood. This research investigates the antiproliferative activities of postbiotics- short-chain fatty acid (SCFA) salts, specifically magnesium acetate (MgA), sodium propionate (NaP), and sodium butyrate (NaB), against the AGS gastric adenocarcinoma cells. Furthermore, the potential synergistic interactions between the most active SCFA salt-NaB and the standard drug dexamethasone (Dex) were explored using the combination index model. The molecular mechanisms of the synergy were investigated using reactive oxygen species (ROS), flow cytometry and biochemometric and liquid chromatography-mass spectrometry (LC-MS)-driven proteomics analyses. NaB exhibited the most significant inhibitory effect (p < 0.05) among the tested SCFA salts against the AGS gastric cancer cells. Additionally, Dex and NaB exhibited strong synergy at a 2:8 ratio (40 μg/mL Dex + 2,400 μg/mL NaB) with significantly greater inhibitory activity (p < 0.05) compared to the mono treatments against the AGS gastric cancer cells. MgA and NaP reduced ROS production, while NaB exhibited pro-oxidative properties. Dex displayed antioxidative effects, and the combination of Dex and NaB (2,8) demonstrated a unique pattern, potentially counteracting the pro-oxidative effects of NaB, highlighting an interaction. Dex and NaB individually and in combination (Dex:NaB 40:2400 μg/mL) induced significant changes in cell populations, suggesting a shift toward apoptosis (p < 0.0001). Analysis of dysregulated proteins in the AGS cells treated with the synergistic combination revealed notable downregulation of the oncogene TNS4, suggesting a potential mechanism for the observed antiproliferative effects. These findings propose the potential implementation of NaB as an adjuvant therapy with Dex. Further investigations into additional combination therapies, in-depth studies of the molecular mechanisms, and in vivo research will provide deeper insights into the use of these postbiotics in cancer, particularly in gastric malignancies.

A review of the role of zinc finger proteins on hematopoiesis

The bone marrow is responsible for producing an incredible number of cells daily in order to maintain blood homeostasis through a process called hematopoiesis. Hematopoiesis is a greatly demanding process and one entirely dependent on complex interactions between the hematopoietic stem cell (HSC) and its surrounding microenvironment. Zinc (Zn2+) is considered an important trace element, playing diverse roles in different tissues and cell types, and zinc finger proteins (ZNF) are proteins that use Zn2+ as a structural cofactor. In this way, the ZNF structure is supported by a Zn2+ that coordinates many possible combinations of cysteine and histidine, with the most common ZNF being of the Cys2His2 (C2H2) type, which forms a family of transcriptional activators that play an important role in different cellular processes such as development, differentiation, and suppression, all of these being essential processes for an adequate hematopoiesis. This review aims to shed light on the relationship between ZNF and the regulation of the hematopoietic tissue. We include works with different designs, including both in vitro and in vivo studies, detailing how ZNF might regulate hematopoiesis.

Circular RNA Expression Signatures Provide Promising Diagnostic and Therapeutic Biomarkers for Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is a known hematologic malignancy associated with a growing incidence and post-treatment relapse. Hence, finding a reliable diagnostic biomarker for CLL is crucial. Circular RNAs (circRNAs) represent a new class of RNA involved in many biological processes and diseases. This study aimed to define a circRNA-based panel for the early diagnosis of CLL. To this point, the list of the most deregulated circRNAs in CLL cell models was retrieved using bioinformatic algorithms and applied to the verified CLL patients' online datasets as the training cohort (n = 100). The diagnostic performance of potential biomarkers represented in individual and discriminating panels, was then analyzed between CLL Binet stages and validated in individual sample sets I (n = 220) and II (n = 251). We also estimated the 5-year overall survival (OS), introduced the cancer-related signaling pathways regulated by the announced circRNAs, and provided a list of possible therapeutic compounds to control the CLL. These findings show that the detected circRNA biomarkers exhibit better predictive performance compared to current validated clinical risk scales, and are applicable for the early detection and treatment of CLL.

The MOZ-BRPF1 acetyltransferase complex in epigenetic crosstalk linked to gene regulation, development, and human diseases

Acetylation of lysine residues on histone tails is an important post-translational modification (PTM) that regulates chromatin dynamics to allow gene transcription as well as DNA replication and repair. Histone acetyltransferases (HATs) are often found in large multi-subunit complexes and can also modify specific lysine residues in non-histone substrates. Interestingly, the presence of various histone PTM recognizing domains (reader domains) in these complexes ensures their specific localization, enabling the epigenetic crosstalk and context-specific activity. In this review, we will cover the biochemical and functional properties of the MOZ-BRPF1 acetyltransferase complex, underlining its role in normal biological processes as well as in disease progression. We will discuss how epigenetic reader domains within the MOZ-BRPF1 complex affect its chromatin localization and the histone acetyltransferase specificity of the complex. We will also summarize how MOZ-BRPF1 is linked to development via controlling cell stemness and how mutations or changes in expression levels of MOZ/BRPF1 can lead to developmental disorders or cancer. As a last touch, we will review the latest drug candidates for these two proteins and discuss the therapeutic possibilities.

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.

Insights into Regulators of p53 Acetylation

The tumor suppressor p53 is a transcription factor that regulates the expression of dozens of target genes and diverse physiological processes. To precisely regulate the p53 network, p53 undergoes various post-translational modifications and alters the selectivity of target genes. Acetylation plays an essential role in cell fate determination through the activation of p53. Although the acetylation of p53 has been examined, the underlying regulatory mechanisms remain unclear and, thus, have attracted the interest of researchers. We herein discuss the role of acetylation in the p53 pathway, with a focus on p53 acetyltransferases and deacetylases. We also review recent findings on the regulators of these enzymes to understand the mode of p53 acetylation from a broader perspective.

The Four Homeostasis Knights: In Balance upon Post-Translational Modifications

A cancer outcome is a multifactorial event that comes from both exogenous injuries and an endogenous predisposing background. The healthy state is guaranteed by the fine-tuning of genes controlling cell proliferation, differentiation, and development, whose alteration induces cellular behavioral changes finally leading to cancer. The function of proteins in cells and tissues is controlled at both the transcriptional and translational level, and the mechanism allowing them to carry out their functions is not only a matter of level. A major challenge to the cell is to guarantee that proteins are made, folded, assembled and delivered to function properly, like and even more than other proteins when referring to oncogenes and onco-suppressors products. Over genetic, epigenetic, transcriptional, and translational control, protein synthesis depends on additional steps of regulation. Post-translational modifications are reversible and dynamic processes that allow the cell to rapidly modulate protein amounts and function. Among them, ubiquitination and ubiquitin-like modifications modulate the stability and control the activity of most of the proteins that manage cell cycle, immune responses, apoptosis, and senescence. The crosstalk between ubiquitination and ubiquitin-like modifications and post-translational modifications is a keystone to quickly update the activation state of many proteins responsible for the orchestration of cell metabolism. In this light, the correct activity of post-translational machinery is essential to prevent the development of cancer. Here we summarize the main post-translational modifications engaged in controlling the activity of the principal oncogenes and tumor suppressors genes involved in the development of most human cancers.

Herpes Simplex Virus Type 1 Preferentially Enhances Neuro-Inflammation and Senescence in Brainstem of Female Mice

Following acute infection, herpes simplex virus 1 (HSV-1) establishes lifelong latency in neurons. The latency associated transcript (LAT) is the only viral gene abundantly expressed during latency. Wild-type (WT) HSV-1 reactivates more efficiently than LAT mutants because LAT promotes establishment and maintenance of latency. While sensory neurons in trigeminal ganglia (TG) are important sites for latency, brainstem is also a site for latency and reactivation from latency. The principal sensory nucleus of the spinal trigeminal tract (Pr5) likely harbors latent HSV-1 because it receives afferent inputs from TG. The locus coeruleus (LC), an adjacent brainstem region, sends axonal projections to cortical structures and is indirectly linked to Pr5. Senescent cells accumulate in the nervous system during aging and accelerate neurodegenerative processes. Generally senescent cells undergo irreversible cell cycle arrest and produce inflammatory cytokines and chemokines. Based on these observations, we hypothesized HSV-1 influences senescence and inflammation in Pr5 and LC of latently infected mice. This hypothesis was tested using a mouse model of infection. Strikingly, female but not age-matched male mice latently infected with a LAT null mutant (dLAT2903) exhibited significantly higher levels of senescence markers and inflammation in LC, including cell cycle inhibitor p16, NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3), IL-1α, and IL-β. Conversely, Pr5 in female but not male mice latently infected with WT HSV-1 or dLAT2903 exhibited enhanced expression of important inflammatory markers. The predilection of HSV-1 to induce senescence and inflammation in key brainstem regions of female mice infers that enhanced neurodegeneration occurs. IMPORTANCE HSV-1 (herpes simplex virus 1), an important human pathogen, establishes lifelong latency in neurons in trigeminal ganglia and the central nervous system. In contrast to productive infection, the only viral transcript abundantly expressed in latently infected neurons is the latency associated transcript (LAT). The brainstem, including principal sensory nucleus of the spinal trigeminal tract (Pr5) and locus coeruleus (LC), may expedite HSV-1 spread from trigeminal ganglia to the brain. Enhanced senescence and expression of key inflammatory markers were detected in LC of female mice latently infected with a LAT null mutant (dLAT2903) relative to age-matched male or female mice latently infected with wild-type HSV-1. Conversely, wild-type HSV-1 and dLAT2903 induced higher levels of senescence and inflammatory markers in Pr5 of latently infected female mice. In summary, enhanced inflammation and senescence in LC and Pr5 of female mice latently infected with HSV-1 are predicted to accelerate neurodegeneration.

Matrix stiffness-induced upregulation of histone acetyltransferase KAT6A promotes hepatocellular carcinoma progression through regulating SOX2 expression

BACKGROUND

Lysine acetyltransferase 6 A (KAT6A) is a MYST-type histone acetyltransferase (HAT) enzyme, which contributes to histone modification and cancer development. However, its biological functions and molecular mechanisms, which respect to hepatocellular carcinoma (HCC), are still largely unknown.

METHODS

Immunohistochemical, western blot and qRT-PCR analysis of KAT6A were performed. A series of in vitro and in vivo experiments were conducted to reveal the role of KAT6A in the progression of HCC.

RESULTS

We demonstrated that KAT6A expression was upregulated in HCC tissues and cell lines. Clinical analysis showed that increased KAT6A was significantly associated with malignant prognostic features and shorter survival. Gain- and loss-of-function experiments indicated that KAT6A promoted cell viability, proliferation and colony formation of HCC cells in vitro and in vivo. We confirmed that KAT6A acetylates lysine 23 of histone H3 (H3K23), and then enhances the association of the nuclear receptor binding protein TRIM24 and H3K23ac. Consequently, TRIM24 functions as a transcriptional activator to activate SOX2 transcription and expression, leading to HCC tumorigenesis. Restoration of SOX2 at least partially abolished the biological effects of KAT6A on HCC cells. Overexpression of KAT6A acetyltransferase activity-deficient mutants or TRIM24 mutants lacking H3K23ac binding sites did not affect SOX2 expression and HCC biological function. Moreover, matrix stiffness can upregulate the expression of KAT6A in HCC cells.

CONCLUSIONS

Our data support the first evidence that KAT6A plays an oncogenic role in HCC through H3K23ac/TRIM24-SOX2 pathway, and represents a promising therapeutic strategy for HCC patients.

Deciphering the acetylation code of p53 in transcription regulation and tumor suppression

Although it is well established that p53-mediated tumor suppression mainly acts through its ability in transcriptional regulation, the molecular mechanisms of this regulation are not completely understood. Among a number of regulatory modes, acetylation of p53 attracts great interests. p53 was one of the first non-histone proteins found to be functionally regulated by acetylation and deacetylation, and subsequent work has established that reversible acetylation is a general mechanism for regulation of non-histone proteins. Unlike other types of post-translational modifications occurred during stress responses, the role of p53 acetylation has been recently validated in vivo by using the knockin mice with both acetylation-defective and acetylation-mimicking p53 mutants. Here, we review the role of acetylation in p53-mediated activities, with a focus on which specific acetylation sites are critical for p53-dependent transcription regulation during tumor suppression and how acetylation of p53 recruits specific “readers” to execute its promoter-specific regulation of different targets. We also discuss the role of p53 acetylation in differentially regulating its classic activities in cell cycle arrest, senescence and apoptosis as well as newly identified unconventional functions such as cell metabolism and ferroptosis.

Effects of Injury Severity and Brain Temperature on KAT6A Expression after Traumatic Brain Injury in Rats

Background: Traumatic brain injury (TBI) is associated with a range of neural changes. A comprehensive understanding of the injury-induced lysine acetyltransferase 6A (KAT6A) response, particularly the temporal profile of biochemical alterations, is crucial to design effective therapeutic interventions.Methods: Experiments were performed in male Sprague-Dawley rats. The influence of post-traumatic hypothermia (32&#x00B0;C) or hyperthermia (39&#x00B0;C) on the temporal and regional expression profiles of KAT6A was assessed after moderate or severe TBI. qPCR and western blotting were used to determine the expression of KAT6A in different groups.Results: In the ipsilateral and contralateral hemispheres, significantly lower protein and mRNA expression of KAT6A was found after TBI than sham injury. Moreover, two expression minima of KAT6A were observed in the cortex and hippocampus of the ipsilateral hemisphere. A decrease in injury severity was associated with lower levels of KAT6A mRNA at 12 h and protein at 24 h, but KAT6A mRNA at 48 h and protein at 72 h had alterations. Compared with normothermia and hyperthermia, post-traumatic hypothermia intensified the decrease in KAT6A at both the mRNA and protein levels. In contrast, hyperthermia, as compared with normothermia, did not significantly affect the levels of KAT6A mRNA at 12 h and protein at 24 h, but triggered a significant increase in levels of KAT6A mRNA at 24 h and protein at 72 h. Furthermore, an overall upregulation of KAT6A after TBI was associated with greater injury severity in a time-dependent manner.Conclusions: Post-traumatic hypothermia plays a key role in the regulation of KAT6A expression and thus may at least partially explain the phenotype of post-traumatic temperature in secondary injury after TBI.

KAT6A is associated with sorafenib resistance and contributes to progression of hepatocellular carcinoma by targeting YAP

Hepatocellular carcinoma (HCC) is a prevalent solid cancer worldwide and sorafenib is a common treatment. Nevertheless, sorafenib resistance is a severe clinical problem. In the present study, we identified that epigenetic regulator, KAT6A, was overexpressed in clinical HCC tissues and sorafenib-resistant HCC samples. The depletion of KAT6A repressed the cell viability and Edu-positive cell numbers of HCC cells. The IC50 value of sorafenib was increased in sorafenib-resistant HCC cells. In addition, the expression of KAT6A was induced in sorafenib-resistant HCC cells. The depletion of KAT6A suppressed the IC50 of sorafenib. Mechanically, YAP was decreased by the depletion of KAT6A. KAT6A was able to enrich in the promoter of YAP. The silencing of KAT6A reduced the enrichment of histone H3 lysine 23 acetylation (H3K23ac) and RNA polymerase II (RNA pol II) on the promoter of YAP in sorafenib-resistant HCC cells. KAT6A inhibitor WM-1119 repressed the cell proliferation of sorafenib-resistant HCC cells, while overexpression of KAT6A or YAP could reverse the effect in the cells. Meanwhile, the treatment of sorafenib inhibited the viability of sorafenib-resistant HCC cells, while the co-treatment of WM-1119 could improve the effect of sorafenib. Collectively, KAT6A was associated with sorafenib resistance and contributes to progression of HCC by targeting YAP. Targeting KAT6A may be served as a promising therapeutic approach for HCC.

Copy number variations of the KAT6A gene are associated with body measurements of Chinese sheep breeds

Copy number variation (CNV) is one kind of genomic structure variations and presents as gains and losses of genomic fragments. More recently, we have made an atlas of CNV maps for livestock. In the future, it is a primary focus to determine the phenotypic effects of candidate CNVs. Lysine Acetyltransferase 6 A (KAT6A) is a protein coding gene and plays a critical role in many cellular processes. However, the effects of KAT6A CNVs on sheep body measurements remains unknown. In this study, we performed quantitative polymerase chain reaction (qPCR) to detect the presences and distributions of three CNV regions within KAT6A gene in 672 sheep from four Chinese breeds. Association analysis indicated that the three CNVs of KAT6A gene were significantly associated with body measurement(s) in Small-tailed Han sheep (STH) and Hu sheep (HU) (p < 0.05), while no effects on Large-tailed Han sheep (LTH) were observed (p > 0.05) were observed. Additionally, only one CNV was significantly associated with body measurement (body length) in Chaka sheep (CK) (p < 0.05). Our study provided evidence that the CNV(s) of KAT6A gene could be used as candidate marker(s) for molecular breedings of STH, HU, and CK breeds.

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.

KAT6A Acetylation of SMAD3 Regulates Myeloid-Derived Suppressor Cell Recruitment, Metastasis, and Immunotherapy in Triple-Negative Breast Cancer

Aberrant SMAD3 activation has been implicated as a driving event in cancer metastasis, yet the underlying mechanisms are still elusive. Here, SMAD3 is identified as a nonhistone substrate of lysine acetyltransferase 6A (KAT6A). The acetylation of SMAD3 at K20 and K117 by KAT6A promotes SMAD3 association with oncogenic chromatin modifier tripartite motif-containing 24 (TRIM24) and disrupts SMAD3 interaction with tumor suppressor TRIM33. This event in turn promotes KAT6A-acetylated H3K23-mediated recruitment of TRIM24-SMAD3 complex to chromatin and thereby increases SMAD3 activation and immune response-related cytokine expression, leading to enhanced breast cancer stem-like cell stemness, myeloid-derived suppressor cell (MDSC) recruitment, and triple-negative breast cancer (TNBC) metastasis. Inhibiting KAT6A in combination with anti-PD-L1 therapy in treating TNBC xenograft-bearing animals markedly attenuates metastasis and provides a significant survival benefit. Thus, the work presents a KAT6A acetylation-dependent regulatory mechanism governing SMAD3 oncogenic function and provides insight into how targeting an epigenetic factor with immunotherapies enhances the antimetastasis efficacy.

KAT6A, a novel regulator of β-catenin, promotes tumorigenicity and chemoresistance in ovarian cancer by acetylating COP1

Background: Ovarian cancer is a fatal gynecologic malignancy that is found worldwide and exhibits an insidious onset and a lack of early warning symptoms. Despite ongoing studies, the mechanistic basis of the aggressive phenotypes of ovarian cancer remains unclear. Lysine acetyltransferase 6A (KAT6A) is a MYST-type histone acetyltransferase (HAT) enzyme identified as an oncogene in breast cancer, glioblastoma and leukemia. However, the specific functions of KAT6A in ovarian cancer remain unclear. Methods: Immunohistochemistry (IHC) staining and western blotting were performed to characterize KAT6A protein expression in ovarian cancer tissues and cell lines. The biological functions of KAT6A in ovarian cancer were evaluated by cell proliferation, wound healing and transwell invasion assays in vitro. Tumorigenesis and metastasis assays were performed in nude mice to detect the role of KAT6A in vivo. Mass spectrometry and immunoprecipitation assays were performed to detect the KAT6A-COP1 interaction. An in vivo ubiquitination assay was performed to determine the regulation of β-catenin by KAT6A. Results: In the present study, we revealed that KAT6A expression is upregulated in ovarian cancer and is associated with patient overall survival. Downregulation of KAT6A markedly inhibited the proliferation and migration abilities of ovarian cancer cells in vivo and in vitro. Additionally, the inhibition of KAT6A induced apoptosis and enhanced the sensitivity of ovarian cancer cells to cisplatin. Furthermore, KAT6A bound to and acetylated COP1 at K294. The acetylation of COP1 impaired COP1 function as an E3 ubiquitin ligase and led to the accumulation and enhanced activity of β-catenin. Conclusions: Our findings suggest that the KAT6A/COP1/β-catenin signaling axis plays a critical role in ovarian cancer progression and that targeting the KAT6A/COP1/β-catenin signaling axis could be a novel strategy for treating ovarian cancer.

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.

The DPF Domain As a Unique Structural Unit Participating in Transcriptional Activation, Cell Differentiation, and Malignant Transformation

The DPF (double PHD finger) domain consists of two PHD fingers organized in tandem. The two PHD-finger domains within a DPF form a single structure that interacts with the modification of the N-terminal histone fragment in a way different from that for single PHD fingers. Several histone modifications interacting with the DPF domain have already been identified. They include acetylation of H3K14 and H3K9, as well as crotonylation of H3K14. These modifications are found predominantly in transcriptionally active chromatin. Proteins containing DPF belong to two classes of protein complexes, which are the transcriptional coactivators involved in the regulation of the chromatin structure. These are the histone acetyltransferase complex belonging to the MYST family and the SWI/SNF chromatin-remodeling complex. The DPF domain is responsible for the specificity of the interactions between these complexes and chromatin. Proteins containing DPF play a crucial role in the activation of the transcription of a number of genes expressed during the development of an organism. These genes are important in the differentiation and malignant transformation of mammalian cells.

Tumor suppressor p53 cross-talks with TRIM family proteins

p53 is a key tumor suppressor. As a transcription factor, p53 accumulates in cells in response to various stress signals and selectively transcribes its target genes to regulate a wide variety of cellular stress responses to exert its function in tumor suppression. In addition to tumor suppression, p53 is also involved in many other physiological and pathological processes, e.g. anti-infection, immune response, development, reproduction, neurodegeneration and aging. To maintain its proper function, p53 is under tight and delicate regulation through different mechanisms, particularly the posttranslational modifications. The tripartite motif (TRIM) family proteins are a large group of proteins characterized by the RING, B-Box and coiled-coil (RBCC) domains at the N-terminus. TRIM proteins play important roles in regulation of many fundamental biological processes, including cell proliferation and death, DNA repair, transcription, and immune response. Alterations of TRIM proteins have been linked to many diseases including cancer, infectious diseases, developmental disorders, and neurodegeneration. Interestingly, recent studies have revealed that many TRIM proteins are involved in the regulation of p53, and at the same time, many TRIM proteins are also regulated by p53. Here, we review the cross-talk between p53 and TRIM proteins, and its impact upon cellular biological processes as well as cancer and other diseases.

A MYST family histone acetyltransferase, MoSAS3, is required for development and pathogenicity in the rice blast fungus

Histone acetylation has been established as a principal epigenetic regulatory mechanism in eukaryotes. Sas3, a histone acetyltransferase belonging to the largest family of acetyltransferase, MYST, is the catalytic subunit of a conserved histone acetyltransferase complex. To date, the functions of Sas3 and its orthologues have been extensively studied in yeast, humans and flies in relation to global acetylation and transcriptional regulation. However, its precise impact on development and pathogenicity in fungal plant pathogens has yet to be elucidated. Considering the importance of Sas3 in H3K14 acetylation, here we investigate the roles of its orthologue in the rice blast fungus, Magnaporthe oryzae (Pyricularia oryzae). Unlike a previously reported Sas3 deletion in yeast, which led to no remarkable phenotypic changes, we found that MoSAS3 deletion alone had a profound effect on fungal growth and development, including asexual reproduction, germination and appressorium formation in M. oryzae. Such defects in pre-penetration development resulted in complete loss of pathogenicity in the deletion mutant. Furthermore, genetic analysis of MoSAS3 and MoGCN5 encoding a Gcn5-related N-acetyltransferase family histone acetyltransferase suggested that two conserved components of histone acetylation are integrated differently into epigenetic regulatory mechanisms in the yeast and a filamentous fungus. RNA-seq analysis of ΔMosas3 showed two general trends: many DNA repair and DNA damage response genes are up-regulated, while carbon and nitrogen metabolism genes are down-regulated in ΔMosas3. Our work demonstrates the importance of MYST family histone acetyltransferase as a developmental regulator and illuminates a degree of functional variation in conserved catalytic subunits among different fungal species.

The Role of the Cyclin Dependent Kinase Inhibitor p21cip1/waf1 in Targeting Cancer: Molecular Mechanisms and Novel Therapeutics

p21^cip1/waf1 mediates various biological activities by sensing and responding to multiple stimuli, via p53-dependent and independent pathways. p21 is known to act as a tumor suppressor mainly by inhibiting cell cycle progression and allowing DNA repair. Significant advances have been made in elucidating the potential role of p21 in promoting tumorigenesis. Here, we discuss the involvement of p21 in multiple signaling pathways, its dual role in cancer, and the importance of understanding its paradoxical functions for effectively designing therapeutic strategies that could selectively inhibit its oncogenic activities, override resistance to therapy and yet preserve its tumor suppressive functions.

p53 activation by Cr(VI): a transcriptionally limited response induced by ATR kinase in S-phase

Cellular reduction of carcinogenic chromium(VI) causes several forms of Cr-DNA damage with different genotoxic properties. Chromate-treated cultured cells have shown a strong proapoptotic activity of the DNA damage-sensitive transcription factor p53. However, induction of p53 transcriptional targets by Cr(VI) in rodent lungs was weak or undetectable. We examined Cr(VI) effects on the p53 pathway in human cells with restored levels of ascorbate that acts as a principal reducer of Cr(VI) in vivo but is nearly absent in standard cell cultures. Ascorbate-restored H460 and primary human cells treated with Cr(VI) contained higher levels of p53 and its Ser15 phosphorylation, which were induced by ATR kinase. Cr(VI)-stimulated p53 phosphorylation occurred in S-phase by a diffusible pool of ATR that was separate from the chromatin-bound pool targeting DNA repair substrates at the sites of toxic mismatch repair of Cr-DNA adducts. Even when more abundantly present than after exposure to the radiomimetic bleomycin, Cr(VI)-stabilized p53 showed a much more limited activation of its target genes in two types of primary human cells. No increases in mRNA were found for nucleotide excision repair factors and a majority of proapoptotic genes. A weak transcription activity of Cr(VI)-upregulated p53 was associated with its low lysine acetylation in the regulatory C-terminal domain, resulting from the inability of Cr(VI) to activate ATM in ascorbate-restored cells. Thus, p53 activation by ascorbate-metabolized Cr(VI) represents a limited genome-protective response that is defective in upregulation of DNA repair genes and proapoptotic transcripts for elimination of damaged cells.

p53 modifications: exquisite decorations of the powerful guardian

The last 40 years have witnessed how p53 rose from a viral binding protein to a central factor in both stress responses and tumor suppression. The exquisite regulation of p53 functions is of vital importance for cell fate decisions. Among the multiple layers of mechanisms controlling p53 function, posttranslational modifications (PTMs) represent an efficient and precise way. Major p53 PTMs include phosphorylation, ubiquitination, acetylation, and methylation. Meanwhile, other PTMs like sumoylation, neddylation, O-GlcNAcylation, adenosine diphosphate (ADP)-ribosylation, hydroxylation, and β-hydroxybutyrylation are also shown to play various roles in p53 regulation. By independent action or interaction, PTMs affect p53 stability, conformation, localization, and binding partners. Deregulation of the PTM-related pathway is among the major causes of p53-associated developmental disorders or diseases, especially in cancers. This review focuses on the roles of different p53 modification types and shows how these modifications are orchestrated to produce various outcomes by modulating p53 activities or targeted to treat different diseases caused by p53 dysregulation.

Mutant TP53 modulates metastasis of triple negative breast cancer through adenosine A2b receptor signaling

Purpose

The identification of genes with synthetic lethality in the context of mutant TP53 is a promising strategy for the treatment of basal-like triple negative breast cancer (TNBC). This study investigated regulators of mutant TP53 (R248Q) in basal-like TNBC and their impact on tumorigenesis.

Experimental Design

TNBC cells were analyzed by RNA-seq, and synthetic-lethal shRNA knock-down screening, to identify genes related to the expression of mutant TP53. A tissue microarray of 232 breast cancer samples, that included 66 TNBC cases, was used to assess clinicopathological correlates of tumor protein expression. Functional assays were performed in vitro and in vivo to assess the role of ADORA2B in TNBC.

Results

Transcriptome profiling identified ADORA2B as up-regulated in basal-like TNBC cell lines with R248Q-mutated TP53, with shRNA-screening suggesting the potential for a synthetic-lethal interaction between these genes. In clinical samples, ADORA2B was highly expressed in 39.4% (26/66) of TNBC patients. ADORA2B-expression was significantly correlated with ER (P < 0.01), PgR (P = 0.027), EGFR (P < 0.01), and tumor size (P = 0.037), and was an independent prognostic factor for outcome (P = 0.036). In line with this, ADORA2B-transduced TNBC cells showed increased tumorigenesis, and ADORA2B knockdown, along with mutant p53 knockdown, decreased metastasis both in vitro and in vivo. Notably, the cytotoxic cyclic peptide SA-I suppressed ADORA2B expression and tumorigenesis in TNBC cell lines.

Conclusions

ADORA2B expression increases the oncogenic potential of basal-like TNBC and is an independent factor for poor outcome. These data suggest that ADORA2B could serve as a prognostic biomarker and a potential therapeutic target for basal-like TNBC.

Lycorine: A prospective natural lead for anticancer drug discovery

•

Outline of the anticancer properties and associated molecular mechanism mediated by lycorine.

•

Comprehensive analysis of the structure activity relationship associated with anticancer activity of lycorine.

•

Summary of the pharmacological aspects and implications for future directions with this compound.

Nature is the most abundant source for novel drug discovery. Lycorine is a natural alkaloid with immense therapeutic potential. Lycorine is active in a very low concentration and with high specificity against a number of cancers both in vivo and in vitro and against various drug-resistant cancer cells. This review summarized the therapeutic effect and the anticancer mechanisms of lycorine. At the same time, we have discussed the pharmacology and comparative structure-activity relationship for the anticancer activity of this compound. The researches outlined in this paper serve as a foundation to explain lycorine as an important lead compound for new generation anticancer drug design and provide the principle for the development of biological strategies to utilize lycorine in the treatment of cancers.

STXBP4 regulates APC/C-mediated p63 turnover and drives squamous cell carcinogenesis

Levels of the N-terminally truncated isoform of p63 (ΔN p63), well documented to play a pivotal role in basal epidermal gene expression and epithelial maintenance, need to be strictly regulated. We demonstrate here that the anaphase-promoting complex/cyclosome (APC/C) complex plays an essential role in the ubiquitin-mediated turnover of ΔNp63α through the M-G1 phase. In addition, syntaxin-binding protein 4 (Stxbp4), which we previously discovered to bind to ΔNp63, can suppress the APC/C-mediated proteolysis of ΔNp63. Supporting the physiological relevance, of these interactions, both Stxbp4 and an APC/C-resistant version of ΔNp63α (RL7-ΔNp63α) inhibit the terminal differentiation process in 3D organotypic cultures. In line with this, both the stable RL7-ΔNp63α variant and Stxbp4 have oncogenic activity in soft agar and xenograft tumor assays. Notably as well, higher levels of Stxbp4 expression are correlated with the accumulation of ΔNp63 in human squamous cell carcinoma (SCC). Our study reveals that Stxbp4 drives the oncogenic potential of ΔNp63α and may provide a relevant therapeutic target for SCC.

Investigation of the changes in the expression levels of MOZ gene in colorectal cancer tissues

Background

MOZ is one of the most important histone acetyltransferases (HATs) that has an effective role in gene expression. It is an important partner in chromosomal rearrangement that usually occurs in hematological malignancies such as leukemia. Besides these malignancies, its role in solid tumors has been reported. In the present study, we aimed to quantify of MOZ messenger RNA (mRNA) expression in colorectal cancer (CRC) tissues from a northwest population of Iran and consequently to assess the effect of MOZ in CRC.

Methods

Tumorous and adjacent non-tumorous tissues recruited from 26 patients with CRC. mRNA extraction and complementary DNA (cDNA) synthesis were performed from these tissues, at the next step quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR) was carried out. Finally, expression levels were statistically analyzed using IBM SPSS Statistics 24.0 software and independent t-test. Statistical significance was considered as P≤0.05.

Results

The results showed significantly higher expression of MOZ in the majority of CRC tissues compared to normal colorectal tissues (P=0.048). There were no significant correlations between expression levels of MOZ and clinical parameters of patients (P>0.05).

Conclusions

Our data showed that dysregulation of MOZ is potentially involved in the pathogenesis of CRC and we could suggest that there is a straight relationship between tumor formation and MOZ expression. These results showed possible role of MOZ as a prognostic factor in the said population.

CITED2 affects leukemic cell survival by interfering with p53 activation

CITED2 (CBP/p300-interacting-transactivator-with-an-ED-rich-tail 2) is a regulator of the acetyltransferase CBP/p300 and elevated CITED2 levels are shown in a number of acute myeloid leukemia (AML). To study the in vivo role of CITED2 in AML maintenance, AML cells were transduced with a lentiviral construct for RNAi-mediated knockdown of CITED2. Mice transplanted with CITED2-knockdown AML cells (n=4) had a significantly longer survival compared to mice transplanted with control AML cells (P<0.02). In vitro, the reduction of CITED2 resulted in increased p53-mediated apoptosis and CDKN1A expression, whereas BCL2 levels were reduced. The activation of p53 upon CITED2 knockdown is not a direct consequence of increased CBP/p300-activity towards p53, since no increased formation of CBP/p300/p53 complexes was demonstrated and inhibition of CBP/p300-activity could not rescue the phenotype of CITED2-deficient cells. Instead, loss of CITED2 had an inhibitory effect on the AKT-signaling pathway, which was indicated by decreased levels of phosphorylated AKT and altered expression of the AKT-pathway regulators PHLDA3 and SOX4. Notably, simultaneous upregulation of BCL2 or downregulation of the p53-target gene PHLDA3 rescued the apoptotic phenotype in CITED2-knockdown cells. Furthermore, knockdown of CITED2 led to a decreased interaction of p53 with its inhibitor MDM2, which results in increased amounts of total p53 protein. In summary, our data indicate that CITED2 functions in pathways regulating p53 activity and therefore represents an interesting target for AML therapy, since de novo AML cases are characterized by an inactivation of the p53 pathway or deregulation of apoptosis-related genes.

Histone Acetyltransferase KAT6A Upregulates PI3K/AKT Signaling through TRIM24 Binding

Lysine acetyltransferase KAT6A is a chromatin regulator that contributes to histone modification and cancer, but the basis of its actions are not well understood. Here, we identify a KAT6A signaling pathway that facilitates glioblastoma (GBM), where it is upregulated. KAT6A expression was associated with GBM patient survival. KAT6A silencing suppressed cell proliferation, cell migration, colony formation, and tumor development in an orthotopic mouse xenograft model system. Mechanistic investigations demonstrated that KAT6A acetylates lysine 23 of histone H3 (H3K23), which recruits the nuclear receptor binding protein TRIM24 to activate PIK3CA transcription, thereby enhancing PI3K/AKT signaling and tumorigenesis. Overexpressing activated AKT or PIK3CA rescued the growth inhibition due to KAT6A silencing. Conversely, the pan-PI3K inhibitor LY294002 abrogated the growth-promoting effect of KAT6A. Overexpression of KAT6A or TRIM24, but not KAT6A acetyltransferase activity-deficient mutants or TRIM24 mutants lacking H3K23ac-binding sites, promoted PIK3CA expression, AKT phosphorylation, and cell proliferation. Taken together, our results define an essential role of KAT6A in glioma formation, rationalizing its candidacy as a therapeutic target for GBM treatment. Cancer Res; 77(22); 6190-201. ©2017 AACR.

Dysfunctional diversity of p53 proteins in adult acute myeloid leukemia: projections on diagnostic workup and therapy

The heterogeneous nature of acute myeloid leukemia (AML) and its poor prognosis necessitate therapeutic improvement. Current advances in AML research yield important insights regarding AML genetic, epigenetic, evolutional, and clinical diversity, all in which dysfunctional p53 plays a key role. As p53 is central to hematopoietic stem cell functions, its aberrations affect AML evolution, biology, and therapy response and usually predict poor prognosis. While in human solid tumors TP53 is mutated in more than half of cases, TP53 mutations occur in less than one tenth of de novo AML cases. Nevertheless, wild-type (wt) p53 dysfunction due to nonmutational p53 abnormalities appears to be rather frequent in various AML entities, bearing, presumably, a greater impact than is currently appreciated. Hereby, we advocate assessment of adult AML with respect to coexisting p53 alterations. Accordingly, we focus not only on the effects of mutant p53 oncogenic gain of function but also on the mechanisms underlying nonmutational wtp53 inactivation, which might be of therapeutic relevance. Patient-specific TP53 genotyping with functional evaluation of p53 protein may contribute significantly to the precise assessment of p53 status in AML, thus leading to the tailoring of a rationalized and precision p53-based therapy. The resolution of the mechanisms underlying p53 dysfunction will better address the p53-targeted therapies that are currently considered for AML. Additionally, a suggested novel algorithm for p53-based diagnostic workup in AML is presented, aiming at facilitating the p53-based therapeutic choices.

The emerging role of PI3K/AKT-mediated epigenetic regulation in cancer

The PI3-kinase/AKT pathway integrates signals from external cellular stimuli to regulate essential cellular functions, and is frequently aberrantly activated in human cancers. Recent research demonstrates that tight regulation of the epigenome is critical in preserving and restricting transcriptional activation, which can impact cellular growth and proliferation. In this review we examine mechanisms by which the PI3K/AKT pathway regulates the epigenome to promote oncogenesis, and highlight how connections between PI3K/AKT and the epigenome may impact the future therapeutic treatment of cancers featuring a hyperactivated PI3K/AKT pathway.

STXBP4 Drives Tumor Growth and Is Associated with Poor Prognosis through PDGF Receptor Signaling in Lung Squamous Cell Carcinoma

Purpose: Expression of the ΔN isoform of p63 (ΔNp63) is a diagnostic marker highly specific for lung squamous cell carcinoma (SCC). We previously found that Syntaxin Binding Protein 4 (STXBP4) regulates ΔNp63 ubiquitination, suggesting that STXBP4 may also be an SCC biomarker. To address this issue, we investigated the role of STXBP4 expression in SCC biology and the impact of STXBP4 expression on SCC prognosis.Experimental Design: We carried out a clinicopathologic analysis of STXBP4 expression in 87 lung SCC patients. Whole transcriptome analysis using RNA-seq was performed in STXBP4-positive and STXBP4-negative tumors of lung SCC. Soft-agar assay and xenograft assay were performed using overexpressing or knockdown SCC cells.Results: Significantly higher levels of STXBP4 expression were correlated with accumulations of ΔNp63 in clinical lung SCC specimens (Spearman rank correlation ρ = 0.219). Notably, STXBP4-positive tumors correlated with three important clinical parameters: T factor (P < 0.001), disease stage (P = 0.030), and pleural involvement (P = 0.028). Whole transcriptome sequencing followed by pathway analysis indicated that STXBP4 is involved in functional gene networks that regulate cell growth, proliferation, cell death, and survival in cancer. Platelet-derived growth factor receptor alpha (PDGFRα) was a key downstream mediator of STXBP4 function. In line with this, shRNA mediated STXBP4 and PDGFRA knockdown suppressed tumor growth in soft-agar and xenograft assays.Conclusions: STXBP4 plays a crucial role in driving SCC growth and is an independent prognostic factor for predicting worse outcome in lung SCC. These data suggest that STXBP4 is a relevant therapeutic target for patients with lung SCC. Clin Cancer Res; 23(13); 3442-52. ©2017 AACR.

Driver gene classification reveals a substantial overrepresentation of tumor suppressors among very large chromatin-regulating proteins

Compiling a comprehensive list of cancer driver genes is imperative for oncology diagnostics and drug development. While driver genes are typically discovered by analysis of tumor genomes, infrequently mutated driver genes often evade detection due to limited sample sizes. Here, we address sample size limitations by integrating tumor genomics data with a wide spectrum of gene-specific properties to search for rare drivers, functionally classify them, and detect features characteristic of driver genes. We show that our approach, CAnceR geNe similarity-based Annotator and Finder (CARNAF), enables detection of potentially novel drivers that eluded over a dozen pan-cancer/multi-tumor type studies. In particular, feature analysis reveals a highly concentrated pool of known and putative tumor suppressors among the <1% of genes that encode very large, chromatin-regulating proteins. Thus, our study highlights the need for deeper characterization of very large, epigenetic regulators in the context of cancer causality.

Histone H3 Lysine 9 Acetylation Obstructs ATM Activation and Promotes Ionizing Radiation Sensitivity in Normal Stem Cells

Dynamic spatiotemporal modification of chromatin around DNA damage is vital for efficient DNA repair. Normal stem cells exhibit an attenuated DNA damage response (DDR), inefficient DNA repair, and high radiosensitivity. The impact of unique chromatin characteristics of stem cells in DDR regulation is not yet recognized. We demonstrate that murine embryonic stem cells (ES) display constitutively elevated acetylation of histone H3 lysine 9 (H3K9ac) and low H3K9 tri-methylation (H3K9me3). DNA damage-induced local deacetylation of H3K9 was abrogated in ES along with the subsequent H3K9me3. Depletion of H3K9ac in ES by suppression of monocytic leukemia zinc finger protein (MOZ) acetyltransferase improved ATM activation, DNA repair, diminished irradiation-induced apoptosis, and enhanced clonogenic survival. Simultaneous suppression of the H3K9 methyltransferase Suv39h1 abrogated the radioprotective effect of MOZ inhibition, suggesting that high H3K9ac promoted by MOZ in ES cells obstructs local upregulation of H3K9me3 and contributes to muted DDR and increased radiosensitivity.

CBP/p300 acetyltransferase activity in hematologic malignancies

CREB binding protein (CBP) and p300 are critical regulators of hematopoiesis through both their transcriptional coactivator and acetyltransferase activities. Loss or mutation of CBP/p300 results in hematologic deficiencies in proliferation and differentiation as well as disruption of hematopoietic stem cell renewal and the microenvironment. Aberrant lysine acetylation mediated by CBP/p300 has recently been implicated in the genesis of multiple hematologic cancers. Understanding the effects of disrupting the acetyltransferase activity of CBP/p300 could pave the way for new therapeutic approaches to treat patients with these diseases.

Regulation of KAT6 Acetyltransferases and Their Roles in Cell Cycle Progression, Stem Cell Maintenance, and Human Disease

The lysine acetyltransferase 6 (KAT6) histone acetyltransferase (HAT) complexes are highly conserved from yeast to higher organisms. They acetylate histone H3 and other nonhistone substrates and are involved in cell cycle regulation and stem cell maintenance. In addition, the human KAT6 HATs are recurrently mutated in leukemia and solid tumors. Therefore, it is important to understand the mechanisms underlying the regulation of KAT6 HATs and their roles in cell cycle progression. In this minireview, we summarize the identification and analysis of the KAT6 complexes and discuss the regulatory mechanisms governing their enzymatic activities and substrate specificities. We further focus on the roles of KAT6 HATs in regulating cell proliferation and stem cell maintenance and review recent insights that aid in understanding their involvement in human diseases.

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.

Expression of the MOZ-TIF2 oncoprotein in mice represses senescence

The MOZ-TIF2 translocation, which fuses monocytic leukemia zinc finger protein (MOZ) histone acetyltransferase (HAT) with the nuclear co-activator TIF2, is associated with the development of acute myeloid leukemia. We recently found that in the absence of MOZ HAT activity, p16(INK4a) transcriptional levels are significantly increased, triggering an early entrance into replicative senescence. Because oncogenic fusion proteins must bypass cellular safeguard mechanisms, such as senescence and apoptosis, to induce leukemia, we hypothesized that this repressive activity of MOZ over p16(INK4a) transcription could be preserved, or even reinforced, in MOZ leukemogenic fusion proteins, such as MOZ-TIF2. We describe here that, indeed, MOZ-TIF2 silences expression of the CDKN2A locus (p16(INK4a) and p19(ARF)), inhibits the triggering of senescence and enhances proliferation, providing conditions favorable to the development of leukemia. Furthermore, we describe that abolishing the MOZ HAT activity of the fusion protein leads to a significant increase in expression of the CDKN2A locus and the number of hematopoietic progenitors undergoing senescence. Finally, we report that inhibition of senescence by MOZ-TIF2 is associated with increased apoptosis, suggesting a role for the fusion protein in p53 apoptosis-versus-senescence balance. Our results underscore the importance of the HAT activity of MOZ, preserved in the fusion protein, for repression of the CDKN2A locus transcription and the subsequent block of senescence, a necessary step for the survival of leukemic cells.

Bivalent interaction of the PZP domain of BRPF1 with the nucleosome impacts chromatin dynamics and acetylation

BRPF1 (bromodomain PHD finger 1) is a core subunit of the MOZ histone acetyltransferase (HAT) complex, critical for normal developmental programs and implicated in acute leukemias. BRPF1 contains a unique assembly of zinc fingers, termed a PZP domain, the physiological role of which remains unclear. Here, we elucidate the structure-function relationship of this novel epigenetic reader and detail the biological and mechanistic consequences of its interaction with nucleosomes. PZP has a globular architecture and forms a 2:1 stoichiometry complex with the nucleosome, bivalently interacting with histone H3 and DNA. This binding impacts the nucleosome dynamics, shifting the DNA unwrapping/rewrapping equilibrium toward the unwrapped state and increasing DNA accessibility. We demonstrate that the DNA-binding function of the BRPF1 PZP domain is required for the MOZ-BRPF1-ING5-hEaf6 HAT complex to be recruited to chromatin and to acetylate nucleosomal histones. Our findings reveal a novel link between chromatin dynamics and MOZ-mediated acetylation.

The Role of Histone Acetyltransferases in Normal and Malignant Hematopoiesis

Histone, and non-histone, protein acetylation plays an important role in a variety of cellular events, including the normal and abnormal development of blood cells, by changing the epigenetic status of chromatin and regulating non-histone protein function. Histone acetyltransferases (HATs), which are the enzymes responsible for histone and non-histone protein acetylation, contain p300/CBP, MYST, and GNAT family members. HATs are not only protein modifiers and epigenetic factors but also critical regulators of cell development and carcinogenesis. Here, we will review the function of HATs such as p300/CBP, Tip60, MOZ/MORF, and GCN5/PCAF in normal hematopoiesis and the pathogenesis of hematological malignancies. The inhibitors that have been developed to target HATs will also be reviewed here. Understanding the roles of HATs in normal/malignant hematopoiesis will provide the potential therapeutic targets for the hematological malignancies.

De novo nonsense mutations in KAT6A, a lysine acetyl-transferase gene, cause a syndrome including microcephaly and global developmental delay

Chromatin remodeling through histone acetyltransferase (HAT) and histone deactylase (HDAC) enzymes affects fundamental cellular processes including the cell-cycle, cell differentiation, metabolism, and apoptosis. Nonsense mutations in genes that are involved in histone acetylation and deacetylation result in multiple congenital anomalies with most individuals displaying significant developmental delay, microcephaly and dysmorphism. Here, we report a syndrome caused by de novo heterozygous nonsense mutations in KAT6A (a.k.a., MOZ, MYST3) identified by clinical exome sequencing (CES) in four independent families. The same de novo nonsense mutation (c.3385C>T [p.Arg1129∗]) was observed in three individuals, and the fourth individual had a nearby de novo nonsense mutation (c.3070C>T [p.Arg1024∗]). Neither of these variants was present in 1,815 in-house exomes or in public databases. Common features among all four probands include primary microcephaly, global developmental delay including profound speech delay, and craniofacial dysmorphism, as well as more varied features such as feeding difficulties, cardiac defects, and ocular anomalies. We further demonstrate that KAT6A mutations result in dysregulation of H3K9 and H3K18 acetylation and altered P53 signaling. Through histone and non-histone acetylation, KAT6A affects multiple cellular processes and illustrates the complex role of acetylation in regulating development and disease.

p53 Acetylation: Regulation and Consequences

Post-translational modifications of p53 are critical in modulating its tumor suppressive functions. Ubiquitylation, for example, plays a major role in dictating p53 stability, subcellular localization and transcriptional vs. non-transcriptional activities. Less is known about p53 acetylation. It has been shown to govern p53 transcriptional activity, selection of growth inhibitory vs. apoptotic gene targets, and biological outcomes in response to diverse cellular insults. Yet recent in vivo evidence from mouse models questions the importance of p53 acetylation (at least at certain sites) as well as canonical p53 functions (cell cycle arrest, senescence and apoptosis) to tumor suppression. This review discusses the cumulative findings regarding p53 acetylation, with a focus on the acetyltransferases that modify p53 and the mechanisms regulating their activity. We also evaluate what is known regarding the influence of other post-translational modifications of p53 on its acetylation, and conclude with the current outlook on how p53 acetylation affects tumor suppression. Due to redundancies in p53 control and growing understanding that individual modifications largely fine-tune p53 activity rather than switch it on or off, many questions still remain about the physiological importance of p53 acetylation to its role in preventing cancer.

Histone target selection within chromatin: an exemplary case of teamwork

Histone modifiers like acetyltransferases, methyltransferases, and demethylases are critical regulators of most DNA-based nuclear processes, de facto controlling cell cycle progression and cell fate. These enzymes perform very precise post-translational modifications on specific histone residues, which in turn are recognized by different effector modules/proteins. We now have a better understanding of how these enzymes exhibit such specificity. As they often reside in multisubunit complexes, they use associated factors to target their substrates within chromatin structure and select specific histone mark-bearing nucleosomes. In this review, we cover the current understanding of how histone modifiers select their histone targets. We also explain how different experimental approaches can lead to conflicting results about the histone specificity and function of these enzymes.