Activation of a Tip60/E2F1/ERCC1 network in human lung adenocarcinoma cells exposed to cisplatin

Posttranslational modifications of E2F family members in the physiological state and in cancer: Roles, mechanisms and therapeutic targets

The E2F transcription factor family, whose members are encoded by the E2F1-E2F8 genes, plays pivotal roles in the cell cycle, apoptosis, metabolism, stemness, metastasis, aging, angiogenesis, tumor promotion or suppression, and other biological processes. The activity of E2Fs is regulated at multiple levels, with posttranslational modifications being an important regulatory mechanism. There are numerous types of posttranslational modifications, among which phosphorylation, acetylation, methylation, ubiquitination, SUMOylation, neddylation, and poly(ADP-ribosyl)ation are the most commonly studied in the context of the E2F family. Posttranslational modifications of E2F family proteins regulate their biological activity, stability, localization, and interactions with other biomolecules, affecting cell proliferation, apoptosis, DNA damage, etc., and thereby playing roles in physiological and pathological processes. Notably, these modifications do not always act alone but rather form an interactive regulatory network. Currently, several drugs targeting posttranslational modifications are being studied or clinically applied, in which the proteolysis-targeting chimera and molecular glue can target E2Fs. This review aims to summarize the roles and regulatory mechanisms of different PTMs of E2F family members in the physiological state and in cancer and to briefly discuss their clinical significance and potential therapeutic use.

The E2F family: a ray of dawn in cardiomyopathy

Cardiomyopathies are a group of heterogeneous diseases, characterized by abnormal structure and function of the myocardium. For many years, it has been a hot topic because of its high morbidity and mortality as well as its complicated pathogenesis. The E2Fs, a group of transcription factors found extensively in eukaryotes, play a crucial role in governing cell proliferation, differentiation, and apoptosis, meanwhile their deregulated activity can also cause a variety of diseases. Based on accumulating evidence, E2Fs play important roles in cardiomyopathies. In this review, we describe the structural and functional characteristics of the E2F family and its role in cardiomyocyte processes, with a focus on how E2Fs are associated with the onset and development of cardiomyopathies. Moreover, we discuss the great potential of E2Fs as biomarkers and therapeutic targets, aiming to provide a reference for future research.

The Tudor-knot Domain of KAT5 Regulates Nucleosomal Substrate Acetylation

The lysine acetyltransferase KAT5 is a pivotal enzyme responsible for catalyzing histone H4 acetylation in cells. In addition to its indispensable HAT domain, KAT5 also encompasses a conserved Tudor-knot domain at its N-terminus. However, the function of this domain remains elusive, with conflicting findings regarding its role as a histone reader. In our study, we have employed a CRISPR tiling array approach and unveiled the Tudor-knot motif as an essential domain for cell survival. The Tudor-knot domain does not bind to histone tails and is not required for KAT5's chromatin occupancy. However, its absence leads to a global reduction in histone acetylation, accompanied with genome-wide alterations in gene expression that consequently result in diminished cell viability. Mechanistically, we find that the Tudor-knot domain regulates KAT5's HAT activity on nucleosomes by fine-tuning substrate accessibility. In summary, our study uncovers the Tudor-knot motif as an essential domain for cell survival and reveals its critical role in modulating KAT5's catalytic efficiency on nucleosome and KAT5-dependent transcriptional programs critical for cell viability.

Knockdown of KAT5/KIF11 induces autophagy and promotes apoptosis in anaplastic thyroid cancer cells

K (lysine) acetyltransferase (KAT) 5, which is a member of the KAT family of enzymes, has been found to act as a regulatory factor in various types of cancer. However, the role of KAT5 in anaplastic thyroid carcinoma (ATC) and its underlying mechanism is still elusive. The expression levels of KAT5 and kinesin family member 11 (KIF11) in ATC cells were assessed utilizing reverse transcription-quantitative PCR and western blot analyses. The cell proliferative ability was assessed via Cell Counting Kit-8 assay and using 5-ethynyl-2'-deoxyuridine staining. Flow cytometry and western blot analyses were applied for the assessment of cell apoptosis. Cell autophagy was investigated by employing western blot analysis and immunofluorescence staining. In addition, the enrichment of histone H3 lysine 27 acetylation (H3K27ac) and RNA polymerase II (RNA pol II) was analyzed by chromatin immunoprecipitation assay. It was shown that KAT5 expression was markedly increased in ATC cells. KAT5 depletion suppressed the cell proliferative capability but promoted the induction of apoptosis and autophagy. In addition, the autophagy inhibitor 3-methyladenine reversed the effects of KAT5 deficiency on the proliferative and apoptotic activities of 8505C cells. With regard to the mechanism, it was found that KAT5 inhibited the expression of KIF11 by repressing the enrichment of H3K27ac and RNA pol II. Upregulation of KIF11 expression reversed the effects of KAT5 silencing on the proliferative activity, apoptosis and autophagy of 8505C cells. In conclusion, the results indicated that KAT5 induced autophagy and promoted apoptosis of ATC cells by targeting KIF11, which may provide a promising target for the treatment of ATC.

Targeting Histone Epigenetic Modifications and DNA Damage Responses in Synthetic Lethality Strategies in Cancer?

Synthetic lethality strategies are likely to be integrated in effective and specific cancer treatments. These strategies combine different specific targets, either in similar or cooperating pathways. Chromatin remodeling underlies, directly or indirectly, all processes of tumor biology. In this context, the combined targeting of proteins associated with different aspects of chromatin remodeling can be exploited to find new alternative targets or to improve treatment for specific individual tumors or patients. There are two major types of proteins, epigenetic modifiers of histones and nuclear or chromatin kinases, all of which are druggable targets. Among epigenetic enzymes, there are four major families: histones acetylases, deacetylases, methylases and demethylases. All these enzymes are druggable. Among chromatin kinases are those associated with DNA damage responses, such as Aurora A/B, Haspin, ATM, ATR, DNA-PK and VRK1-a nucleosomal histone kinase. All these proteins converge on the dynamic regulation chromatin organization, and its functions condition the tumor cell viability. Therefore, the combined targeting of these epigenetic enzymes, in synthetic lethality strategies, can sensitize tumor cells to toxic DNA-damage-based treatments, reducing their toxicity and the selective pressure for tumor resistance and increasing their immunogenicity, which will lead to an improvement in disease-free survival and quality of life.

The Acetyltransferase KAT5 Inhibitor NU 9056 Promotes Apoptosis and Inhibits JAK2/STAT3 Pathway in Extranodal NK/T Cell Lymphoma

BACKGROUND

Extranodal natural killer/T cell lymphoma (ENKTL) is an aggressive malignant non-Hodgkin's lymphoma (NHL) with a poor prognosis. Therefore, novel therapeutic biomarkers and agents must be identified for the same. KAT5 inhibitor, NU 9056, is a small molecule that can inhibit cellular proliferation; however, its role in ENKTL has not been studied.

OBJECTIVE

The present study investigated the effect of NU 9056 in ENKTL cells and explored the possible molecular mechanism for its antitumour effect.

METHODS

The role of NU 9056 in ENKTL cells was investigated through the Cell Counting Kit-8 assay, flow cytometry, Western blot, and real-time quantitative polymerase chain reaction assay.

RESULTS

NU 9056 inhibited ENKTL cell proliferation and induced G2/M phase arrest. NU 9056 also induced apoptosis by upregulating DR4, DR5, and caspase 8 expressions. Additionally, NU 9056 increased the expression of Bax, Bid, and cytochrome C and decreased the expression of Bcl-2, Mcl-1, and XIAP. Furthermore, NU 9056 activated endoplasmic reticulum (ER) stress and inhibited the JAK2/STAT3 signalling pathway. The p38 mitogen-activated protein kinase (MAPK) signalling pathway was also activated by NU 9056, and the ERK signalling pathway was suppressed in natural killer/T cell lymphoma cells.

CONCLUSION

NU 9056 inhibited cell proliferation, arrested cell cycle in the G2/M phase, and induced apoptosis through the stimulation of ER stress, thus inhibiting the JAK2/STAT3 signalling pathway and regulating MAPK pathways in ENKTL cells.

TRPS1 drives heterochromatic origin refiring and cancer genome evolution

Exploitation of naturally occurring genetic mutations could empower the discovery of novel aspects of established cancer genes. We report here that TRPS1, a gene linked to the tricho-rhino-phalangeal syndrome (TRPS) and recently identified as a potential breast cancer driver, promotes breast carcinogenesis through regulating replication. Epigenomic decomposition of TRPS1 landscape reveals nearly half of H3K9me3-marked heterochromatic origins are occupied by TRPS1, where it encourages the chromatin loading of APC/C, resulting in uncontrolled origin refiring. TRPS1 binds to the genome through its atypical H3K9me3 reading via GATA and IKAROS domains, while TRPS-related mutations affect its chromatin binding, replication boosting, and tumorigenicity. Concordantly, overexpression of wild-type but not TRPS-associated mutants of TRPS1 is sufficient to drive cancer genome amplifications, which experience an extrachromosomal route and dynamically evolve to confer therapeutic resistance. Together, these results uncover a critical function of TRPS1 in driving heterochromatin origin firing and breast cancer genome evolution.

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.

IL-6-induced acetylation of E2F1 aggravates oxidative damage of retinal pigment epithelial cell line

Oxidative damage in retinal pigment epithelial cells (RPE) is considered to be a crucial pathogenesis of age-related macular degeneration (AMD). Although dysregulation of the DNA repair system has been found in RPE cells of AMD patients, the detailed molecular mechanisms of this dysregulation and their relationship with the intraocular microenvironment of AMD patients remain unclear. Here, we established an RPE model of H₂O₂-induced oxidative stress and found that Sirtuin 1 (Sirt1)-mediated deacetylation of E2F transcription factor 1 (E2F1) was required for oxidation resistance in RPE cells. Moreover, E2F1 induced the expression of the chromatin-binding protein, high mobility group AT-Hook 1 (HMGA1), which promoted the transcription of glucose 6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of the pentose phosphate pathway, to increase NADPH level for antioxidant defense. Interrupting the E2F1/HMGA1/G6PD regulatory axis increased reactive oxygen species (ROS) levels, DNA damage, and apoptosis in RPE cells under oxidative stress. Notably, interleukin 6 (IL-6), an inflammatory cytokine that is known to be upregulated in the intraocular fluid of AMD patients, induced phosphorylation (S47) of Sirt1 by activating PI3K/AKT/mTOR signaling, thereby inhibiting Sirt1 activity and increasing the acetylation of E2F1. Specific inhibitors of PI3K/AKT/mTOR signaling decreased DNA damage and ROS while increasing NADPH in RPE cells. Collectively, our findings demonstrate that IL-6-induced acetylation of E2F1 impairs the antioxidant capacity of RPE cells by disturbing the pentose phosphate pathway, which elucidates a relationship between the intraocular microenvironment and RPE oxidative damage in AMD and provides a possible therapeutic target for AMD.

The E2F1 transcription factor and RB tumor suppressor moonlight as DNA repair factors

The E2F1 transcription factor and RB tumor suppressor are best known for their roles in regulating the expression of genes important for cell cycle progression but, they also have transcription-independent functions that facilitate DNA repair at sites of damage. Depending on the type of DNA damage, E2F1 can recruit either the GCN5 or p300/CBP histone acetyltransferases to deposit different histone acetylation marks in flanking chromatin. At DNA double-strand breaks, E2F1 also recruits RB and the BRG1 ATPase to remodel chromatin and promote loading of the MRE11-RAD50-NBS1 complex. Knock-in mouse models demonstrate important roles for E2F1 post-translational modifications in regulating DNA repair and physiological responses to DNA damage. This review highlights how E2F1 moonlights in DNA repair, thus revealing E2F1 as a versatile protein that recruits many of the same chromatin-modifying enzymes to sites of DNA damage to promote repair that it recruits to gene promoters to regulate transcription.

Lysine Acetyltransferase Inhibitors From Natural Sources

Acetylation of histone and non-histone protein lysine residues has been widely described as a critical modulator of several cell functions in humans. Lysine acetyltransferases (KATs) catalyse the transfer of acetyl groups on substrate proteins and are involved in multiple physiological processes such as cell signalling, metabolism, gene regulation, and apoptosis. Given the pivotal role of acetylation, the alteration of KATs enzymatic activity has been clearly linked to various cellular dysfunctions leading to several inflammatory, metabolic, neurological, and cancer diseases. Hence, the use KAT inhibitors (KATi) has been suggested as a potentially successful strategy to reverse or prevent these conditions. To date, only a few KATi have proven to be potential drug candidates, and there is still a keen interest in designing molecules showing drug-like properties from both pharmacodynamics and pharmacokinetics point of view. Increasing literature evidence has been highlighting natural compounds as a wide source of molecular scaffolds for developing therapeutic agents, including KATi. In fact, several polyphenols, catechins, quinones, and peptides obtained from natural sources (including nuts, oils, root extracts, and fungi metabolites) have been described as promising KATi. Here we summarize the features of this class of compounds, describing their modes of action, structure-activity relationships and (semi)-synthetic derivatives, with the aim of assisting the development of novel more potent, isoform selective and drug-like KATi.

E2F1 acetylation directs p300/CBP-mediated histone acetylation at DNA double-strand breaks to facilitate repair

E2F1 and retinoblastoma (RB) tumor-suppressor protein not only regulate the periodic expression of genes important for cell proliferation, but also localize to DNA double-strand breaks (DSBs) to promote repair. E2F1 is acetylated in response to DNA damage but the role this plays in DNA repair is unknown. Here we demonstrate that E2F1 acetylation creates a binding motif for the bromodomains of the p300/KAT3B and CBP/KAT3A acetyltransferases and that this interaction is required for the recruitment of p300 and CBP to DSBs and the induction of histone acetylation at sites of damage. A knock-in mutation that blocks E2F1 acetylation abolishes the recruitment of p300 and CBP to DSBs and also the accumulation of other chromatin modifying activities and repair factors, including Tip60, BRG1 and NBS1, and renders mice hypersensitive to ionizing radiation (IR). These findings reveal an important role for E2F1 acetylation in orchestrating the remodeling of chromatin structure at DSBs to facilitate repair.

E2F1, which localises to DNA double-strand breaks (DSBs) to promote repair, is acetylated in response to DNA damage but the role this plays in DNA repair is unknown. Here the authors show that E2F1 acetylation creates a binding motif for the bromodomains of the p300/KAT3B and CBP/KAT3A acetyltransferases, which is required for recruitment of p300 and CBP to DSBs, to facilate repair.

Long noncoding RNA FBXL19-AS1 induces tumor growth and metastasis by sponging miR-203a-3p in lung adenocarcinoma

The pivotal roles of long noncoding RNAs have been reported in various cancers. Recently, FBXL19-AS1 was proposed to be involved in tumor progression. However, its role in lung adenocarcinoma (LUAD) remains elusive. In this study, we observed that FBXL19-AS1 was significantly upregulated in LUAD tissues and high FBXL19-AS1 expression in LUAD was associated with a poor prognosis. Nevertheless, miR-203-3p showed the opposite effect. Moreover, cell viability and apoptosis analysis revealed that FBXL19-AS1 knockdown could arrest LUAD cells in G0/G1 phase and inhibit cell proliferation, migration and invasion in vitro and inhibited LUAD tumor progress in vivo. Mechanistically, we identified FBXL19-AS1 could act as a miR-203a-3p sponge using dual-luciferase reporter assay. In addition, we demonstrated that downregulation of miR-203a-3p reversed growth inhibition of LUAD cells caused by FBXL19-AS1 knockdown. Finally, FBXL19-AS1/miR-203a-3p axis was found to associate with baculoviral IAP repeat-containing protein 5.1-A-like (survivin), distal-less homeobox 5, E2F transcription factor 1, and zinc finger E-box binding homeobox 2 to regulate metastasis in LUAD cells. This study reveals a significance and mechanism of FBXL19-AS1 in LUAD proliferation and metastasis and offers a potential prognostic marker and a therapeutic target for patients with LUAD.

The broken cycle: E2F dysfunction in cancer

The cyclin-dependent kinase (CDK)-RB-E2F axis forms the core transcriptional machinery driving cell cycle progression, dictating the timing and fidelity of genome replication and ensuring genetic material is accurately passed through each cell division cycle. The ultimate effectors of this axis are members of a family of eight distinct E2F genes encoding transcriptional activators and repressors. E2F transcriptional activity is tightly regulated throughout the cell cycle via transcriptional and translational regulation, post-translational modifications, protein degradation, binding to cofactors and subcellular localization. Alterations in one or more key components of this axis (CDKs, cyclins, CDK inhibitors and the RB family of proteins) occur in virtually all cancers and result in heightened oncogenic E2F activity, leading to uncontrolled proliferation. In this Review, we discuss the activities of E2F proteins with an emphasis on the newest atypical E2F family members, the specific and redundant functions of E2F proteins, how misexpression of E2F transcriptional targets promotes cancer and both current and developing therapeutic strategies being used to target this oncogenic pathway.

Myc and the Tip60 chromatin remodeling complex control neuroblast maintenance and polarity in Drosophila

Stem cells establish cortical polarity and divide asymmetrically to simultaneously maintain themselves and generate differentiating offspring cells. Several chromatin modifiers have been identified as stemness factors in mammalian pluripotent stem cells, but whether these factors control stem cell polarity and asymmetric division has not been investigated so far. We addressed this question in Drosophila neural stem cells called neuroblasts. We identified the Tip60 chromatin remodeling complex and its interaction partner Myc as regulators of genes required for neuroblast maintenance. Knockdown of Tip60 complex members results in loss of cortical polarity, symmetric neuroblast division, and premature differentiation through nuclear entry of the transcription factor Prospero. We found that aPKC is the key target gene of Myc and the Tip60 complex subunit Domino in regulating neuroblast polarity. Our transcriptome analysis further showed that Domino regulates the expression of mitotic spindle genes previously identified as direct Myc targets. Our findings reveal an evolutionarily conserved functional link between Myc, the Tip60 complex, and the molecular network controlling cell polarity and asymmetric cell division.

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.

KAT-Independent Gene Regulation by Tip60 Promotes ESC Self-Renewal but Not Pluripotency

Although histone-modifying enzymes are generally assumed to function in a manner dependent on their enzymatic activities, this assumption remains untested for many factors. Here, we show that the Tip60 (Kat5) lysine acetyltransferase (KAT), which is essential for embryonic stem cell (ESC) self-renewal and pre-implantation development, performs these functions independently of its KAT activity. Unlike ESCs depleted of Tip60, KAT-deficient ESCs exhibited minimal alterations in gene expression, chromatin accessibility at Tip60 binding sites, and self-renewal, thus demonstrating a critical KAT-independent role of Tip60 in ESC maintenance. In contrast, KAT-deficient ESCs exhibited impaired differentiation into mesoderm and endoderm, demonstrating a KAT-dependent function in differentiation. Consistent with this phenotype, KAT-deficient mouse embryos exhibited post-implantation developmental defects. These findings establish separable KAT-dependent and KAT-independent functions of Tip60 in ESCs and during differentiation, revealing a complex repertoire of regulatory functions for this essential chromatin remodeling complex.

Targeting cancer using KAT inhibitors to mimic lethal knockouts

Two opposing enzyme classes regulate fundamental elements of genome maintenance, gene regulation and metabolism, either through addition of an acetyl moiety by histone acetyltransferases (HATs) or its removal by histone de-acetyltransferases (HDAC), and are exciting targets for drug development. Importantly, dysfunctional acetylation has been implicated in numerous diseases, including cancer. Within the HAT superfamily the MYST family holds particular interest, as its members are directly involved in the DNA damage response and repair pathways and crucially, several members have been shown to be down-regulated in common cancers (such as breast and prostate). In the present study we focus on the development of lysine (K) acetyltransferase inhibitors (KATi) targeting the MYST family member Tip60 (Kat5), an essential protein, designed or discovered through screening libraries. Importantly, Tip60 has been demonstrated to be significantly down-regulated in many cancers which urgently require new treatment options. We highlight current and future efforts employing these KATi as cancer treatments and their ability to synergize and enhance current cancer treatments. We investigate the different methods of KATi production or discovery, their mechanisms and their validation models. Importantly, the utility of KATi is based on a key concept: using KATi to abrogate the activity of an already down-regulated essential protein (effectively creating a lethal knockout) provides another innovative mechanism for targeting cancer cells, while significantly minimizing any off-target effects to normal cells. This approach, combined with the rapidly developing interest in KATi, suggests that KATi have a bright future for providing truly personalized therapies.

Chronic treatment with cisplatin induces chemoresistance through the TIP60-mediated Fanconi anemia and homologous recombination repair pathways

The Fanconi anemia pathway in coordination with homologous recombination is essential to repair interstrand crosslinks (ICLs) caused by cisplatin. TIP60 belongs to the MYST family of acetyltransferases and is involved in DNA repair and regulation of gene transcription. Although the physical interaction between the TIP60 and FANCD2 proteins has been identified that is critical for ICL repair, it is still elusive whether TIP60 regulates the expression of FA and HR genes. In this study, we found that the chemoresistant nasopharyngeal carcinoma cells, derived from chronic treatment of cisplatin, show elevated expression of TIP60. Furthermore, TIP60 binds to the promoters of FANCD2 and BRCA1 by using the chromatin immunoprecipitation experiments and promote the expression of FANCD2 and BRCA1. Importantly, the depletion of TIP60 significantly reduces sister chromatid exchange, a measurement of HR efficiency. The similar results were also shown in the FNACD2-, and BRCA1-deficient cells. Additionally, these TIP60-deficient cells encounter more frequent stalled forks, as well as more DNA double-strand breaks resulting from the collapse of stalled forks. Taken together, our results suggest that TIP60 promotes the expression of FA and HR genes that are important for ICL repair and the chemoresistant phenotype under chronic treatment with cisplatin.

Mutations of Chromatin Structure Regulating Genes in Human Malignancies

Chromatin structure regulating processes mediated by the adenosine triphosphate (ATP) –dependent chromatin remodeling complex and the covalent histone-modifying complexes are critical to gene transcriptional control and normal cellular processes, including cell stemness, differentiation, and proliferation. Gene mutations, structural abnormalities, and epigenetic modifications that lead to aberrant expression of chromatin structure regulating members have been observed in most of human malignancies. Advances in next-generation sequencing (NGS) technologies in recent years have allowed in-depth study of somatic mutations in human cancer samples. The Cancer Genome Atlas (TCGA) is the largest effort to date to characterize cancer genome using NGS technology. In this review, we summarize somatic mutations of chromatin-structure regulating genes from TCGA publications and other cancer genome studies, providing an overview of genomic alterations of chromatin regulating genes in human malignancies.

Aberrant lysine acetylation in tumorigenesis: Implications in the development of therapeutics

The 'language' of covalent histone modifications translates environmental and cellular cues into gene expression. This vast array of post-translational modifications on histones are more than just covalent moieties added onto a protein, as they also form a platform on which crucial cellular signals are relayed. The reversible lysine acetylation has emerged as an important post-translational modification of both histone and non-histone proteins, dictating numerous epigenetic programs within a cell. Thus, understanding the complex biology of lysine acetylation and its regulators is essential for the development of epigenetic therapeutics. In this review, we will attempt to address the complexities of lysine acetylation in the context of tumorigenesis, their role in cancer progression and emphasize on the modalities developed to target lysine acetyltransferases towards cancer treatment.

KAT5 (Tip60) is a potential therapeutic target in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a rare aggressive cancer of the pleura. Asbestos exposure (through inhalation) is the most well established risk factor for mesothelioma. The current standard of care for patients suffering from MPM is a combination of cisplatin and pemetrexed (or alternatively cisplatin and raltitrexed). Most patients, however, die within 24 months of diagnosis. New therapies are therefore urgently required for this disease. Lysine acetyltransferases (KATs) including KAT5 have been linked with the development of cisplatin resistance. This gene may therefore be altered in MPM and could represent a novel candidate target for intervention. Using RT-PCR screening the expression of all known KAT5 variants was found to be markedly increased in malignant tumors compared to benign pleura. When separated according to histological subtype, KAT5 was significantly overexpressed in both the sarcomatoid and biphasic subgroups for all transcript variants. A panel of MPM cell lines including the normal pleural cells LP9 and Met5A was screened for expression of KAT5 variants. Treatment of cells with a small molecule inhibitor of KAT5 (MG-149) caused significant inhibition of cellular proliferation (p<0.0001), induction of apoptosis and was accompanied by significant induction of pro-inflammatory cytokines/chemokines.

A bivalent role of TIP60 histone acetyl transferase in human cancer

Acetylation is a major modification that is required for gene regulation, genome maintenance and metabolism. A dysfunctional acetylation plays an important role in several diseases, including cancer. A group of enzymes-lysine acetyltransferases are responsible for this modification and act in regulation of transcription as cofactors and by acetylation of histones and other proteins. Tip60, a member of MYST family, is expressed ubiquitously and is the acetyltransferase catalytic subunit of human NuA4 complex. This HAT has a well-characterized involvement in many processes, such as cellular signaling, DNA damage repair, transcriptional and cellular cycle. Aberrant lysine acetyltransferase functions promote or suppress tumorigenesis in different cancers such as colon, breast and prostate tumors. Therefore, Tip60 might be a potential and important therapeutic target in the cancer treatment; new histone acetyl transferase inhibitors were identified and are more selective inhibitors of Tip60.

A novel assay revealed that ribonucleotide reductase is functionally important for interstrand DNA crosslink repair

Cells have evolved complex biochemical pathways for DNA interstrand crosslink (ICL) removal. Despite the chemotherapeutic importance of ICL repair, there have been few attempts to identify which mechanistic DNA repair inhibitor actually inhibits ICL repair. To identify such compounds, a new and robust ICL repair assay was developed using a novel plasmid that contains synthetic ICLs between a CMV promoter region that drives transcription and a luciferase reporter gene, and an SV40 origin of replication and the large T antigen (LgT) gene that enables self-replication in mammalian cells. In a screen against compounds that are classified as inhibitors of DNA repair or synthesis, the reporter generation was exquisitely sensitive to ribonucleotide reductase (RNR) inhibitors such as gemcitabine and clofarabine, but not to inhibitors of PARP, ATR, ATM, Chk1, and others. The effect was observed also by siRNA downregulation of RNR. Moreover, the reporter generation was also particularly sensitive to 3-AP, a non-nucleoside RNR inhibitor, but not significantly sensitive to DNA replication stressors, suggesting that the involvement of RNR in ICL repair is independent of incorporation of a nucleotide RNR inhibitor into DNA to induce replication stress. The reporter generation from a modified version of the plasmid that lacks the LgT-SV40ori motif was also adversely affected by RNR inhibitors, further indicating a role for RNR in ICL repair that is independent of DNA replication. Intriguingly, unhooking of cisplatin-ICL from nuclear DNA was significantly inhibited by low doses of gemcitabine, suggesting an unidentified functional role for RNR in the process of ICL unhooking. The assay approach could identify other molecules essential for ICLR in quantitative and flexible manner.

Epigenetic factor EPC1 is a master regulator of DNA damage response by interacting with E2F1 to silence death and activate metastasis-related gene signatures

Transcription factor E2F1 is a key regulator of cell proliferation and apoptosis. Recently, it has been shown that aberrant E2F1 expression often detectable in advanced cancers contributes essentially to cancer cell propagation and characterizes the aggressive potential of a tumor. Conceptually, this requires a subset of malignant cells capable of evading apoptotic death through anticancer drugs. The molecular mechanism by which the pro-apoptotic activity of E2F1 is antagonized is widely unclear. Here we report a novel function for EPC1 (enhancer of polycomb homolog 1) in DNA damage protection. Depletion of EPC1 potentiates E2F1-mediated apoptosis in response to genotoxic treatment and abolishes tumor cell motility. We found that E2F1 directly binds to the EPC1 promoter and EPC1 vice versa physically interacts with bifunctional E2F1 to modulate its transcriptional activity in a target gene-specific manner. Remarkably, nuclear-colocalized EPC1 activates E2F1 to upregulate the expression of anti-apoptotic survival genes such as BCL-2 or Survivin/BIRC5 and inhibits death-inducing targets. The uncovered cooperativity between EPC1 and E2F1 triggers a metastasis-related gene signature in advanced cancers that predicts poor patient survival. These findings unveil a novel oncogenic function of EPC1 for inducing the switch into tumor progression-relevant gene expression that may help to set novel therapies.

KATs in cancer: functions and therapies

Post-translational acetylation of lysines is most extensively studied in histones, but this modification is also found in many other proteins and is implicated in a wide range of biological processes in both the cell nucleus and the cytoplasm. Like phosphorylation, acetylation patterns and levels are often altered in cancer, therefore small molecule inhibition of enzymes that regulate acetylation and deacetylation offers much potential for inhibiting cancer cell growth, as does disruption of interactions between acetylated residues and ‘reader’ proteins. For more than a decade now, histone deacetylase (HDAC) inhibitors have been investigated for their ability to increase acetylation and promote expression of tumor suppressor genes. However, emerging evidence suggests that acetylation can also promote cancer, in part by enhancing the functions of oncogenic transcription factors. In this review we focus on how acetylation of both histone and non-histone proteins may drive cancer, and we will discuss the implications of such changes on how patients are assigned to therapeutic agents. Finally, we will explore what the future holds in the design of small molecule inhibitors for modulation of levels or functions of acetylation states.

Expression of ERCC1, TYMS, RRM1, TUBB3, non-muscle myosin II, myoglobin and MyoD1 in lung adenocarcinoma pleural effusions predicts survival in patients receiving platinum-based chemotherapy

The association between the expression of excision repair cross‑complementing gene 1 (ERCC1), thymidylate synthase (TYMS), ribonuleotide reductase M1 (RRM1), βIII‑tubulin (TUBB3), non‑muscle myosin II, myoglobin and MyoD1 in metastatic lung adenocarcinoma, and clinical outcomes with platinum‑based chemotherapy treatment is not well‑established. Recently, increasing attention has been focused on the involvement of ERCC1, TYMS, RRM1 and TUBB3 in the development of drug resistance. There has been less research into the role of muscle myosin II, myoglobin and MyoD1 in the pathogenesis of lung cancer, although these genes are known to have important functions within tumor cells. In the current study, malignant pleural effusion from 116 patients with untreated lung adenocarcinoma diagnosed between 2011 and 2012, were collected. The protein expression levels of ERCC1, TYMS, RRM1 and TUBB3 were evaluated with immunocytochemistry and western blot analysis. The expression levels of non‑muscle myosin II, myoglobin and MyoD1 were measured in a subset of 50 patients, treated with platinum‑based chemotherapy. The association of each of these seven factors with one another, as well as with patient survival were analyzed. Immunohistochemistry demonstrated that the percentage of pleural fluid samples from patients with lung adenocarcinoma expressing ERCC1, TYMS, RRM1 and TUBB3 was 37, 36.2, 82.7 and 69.8%, respectively. In the subset of 50 patients in whom the remaining factors were analyzed, the percentage expressing non‑muscle myosin II was 48%, for myoglobin the figure was 40% and for MyoD1 it was 38%. There was a positive correlation between each pair of the above seven molecules with the exception of TYMS and RRM1. Expression of ERCC1, TYMS, TUBB3, non‑muscle myosin II, myoglobin and MyoD1 genes was associated with decreased survival in patients with metastatic lung adenocarcinoma. Expression of ERCC1, TYMS, TUBB3, non‑muscle myosin II, myoglobin and MyoD1 was also associated with decreased survival rates of patients with lung adenocarcinoma treated with platinum‑based chemotherapy. These factors may be used as clinical biomarkers to predict the biological behavior and chemoresistance of tumor cells, and the survival of patients with lung carcinoma.

Transcription addiction: can we garner the Yin and Yang functions of E2F1 for cancer therapy?

Classically, as a transcription factor family, the E2Fs are known to regulate the expression of various genes whose products are involved in a multitude of biological functions, many of which are deregulated in diseases including cancers. E2F is deregulated and hyperactive in most human cancers with context dependent, dichotomous and contradictory roles in almost all cancers. Cancer cells have an insatiable demand for transcription to ensure that gene products are available to sustain various biological processes that support their rapid growth and survival. In this context, cutting-off hyperactivity of transcription factors that support transcription dependence could be a valuable therapeutic strategy. However, one of the greatest challenges of targeting a transcription factor is the global effects on non-cancerous cells given that they control cellular functions in general. Recently, there is growing realization regarding the possibility to target the oncogenic activation of transcription factors to modulate transcription addiction without affecting the normal activity required for cell functions. In this review, we used E2F1 as a prototype transcription factor to address transcription factor activity in cancer cell functions. We focused on melanoma considering that E2F1 executes critical functions in response to UV, an etiological factor of cutaneous melanoma and lies immediately downstream of the CDKN2A/pRb axis, which is frequently deregulated in melanoma. Further, activation of E2F1 in melanomas can also occur independent of loss of CDKN2A. Given its activated status and the ability to transcriptionally control a plethora of genes involved in regulating melanoma development and progression, we review the current literature on its differential role in controlling signaling pathways involved in melanoma as well as therapeutic resistance, and discuss the practical value of weaning melanoma cells from E2F1-mediated transcription dependence for melanoma management.

The diversity of histone versus nonhistone sirtuin substrates

The members of the Sir2 family, or sirtuins, are major regulators of the response to different types of stress. The members of the family have adapted to increasing complexities throughout evolution and have become diversified by increasing their number, specificity, and localization and acquiring novel functions. Sirtuins have been consistently implicated in the cross-talk between the genomic information and environment from the prokaryotes onward. Evidence suggests that in the transition to eukaryotes, histones became one of the basic and most conserved targets of the family, to the extent that in yeast and mammals, sirtuins were originally described as NAD(+)-dependent histone deacetylases and classified as class III histone deacetylases. A growing number of studies have determined that sirtuins also target a wide range of nonhistone proteins. Many of these targets are also directly or indirectly related to chromatin regulation. The number of targets has grown considerably in the last decade but has provoked an ill-founded discussion that neglects the importance of histones as sirtuin targets. In this review, we summarize our knowledge regarding the range of sirtuin targets described to date and discuss the different functional implications of histone and nonhistone targets throughout evolution.

Connecting chromatin modifying factors to DNA damage response

Cells are constantly damaged by factors that can induce DNA damage. Eukaryotic cells must rapidly load DNA repair proteins onto damaged chromatin during the DNA damage response (DDR). Chromatin-remodeling complexes use the energy from ATP hydrolysis to remodel nucleosomes and have well-established functions in transcription. Emerging lines of evidence indicate that chromatin-remodeling complexes are important and may remodel nucleosomes during DNA damage repair. New studies also reveal that ATP-dependent chromatin remodeling is involved in cell cycle progression, signal transduction pathways, and interaction and modification of DDR-related proteins that are specifically and intimately connected with the process of DNA damage. This article summarizes the recent advances in our understanding of the interplay between chromatin remodeling and DNA damage response.

Clinical significance of E2F1 protein expression in non-small cell lung cancer

BACKGROUND

The transcription factor E2F1 has been implicated in cell cycle control and DNA damage response. Paradoxically, E2F1 can promote apoptosis and function as tumor suppressor. In non-small cell lung cancer (NSCLC), there are conflicting data for clinical significance of E2F1 expression. In this study, we investigated the protein expression of E2F1 in patients with stage I-III NSCLC, and its correlation with clinical outcome.

RESULTS

56 paired adjacent non-tumor/tumor matched samples were prospectively obtained from patients undergoing surgery for stage I-III NSCLC at Taipei Veterans General Hospital. The protein expression of E2F1 was determined by Western blot analysis. The levels of E2F1 protein were significantly higher in tumor samples than in non-tumor lung specimens (P = 0.008). Overexpression of E2F1 was defined as a more than 2-fold expression in the tumorous sample compared with the corresponding nontumorous one, and was noted in 21 patients (37.5%). There was no significant difference in overall survival (P = 0.44) or probability of freedom from recurrence (P = 0.378) between patients with E2F1 overexpression vs. non-overexpressors. Additionally, there was no significant association between E2F1 overexpression and any clinicopathologic parameter such as histological type, stage, or angiolymphatic invasion of tumor.

CONCLUSION

E2F1 protein is frequently overexpressed in NSCLC. There is no correlation between E2F1 protein expression and clinical outcome such as survival and freedom from progression.