Role of topoisomerase IIbeta in the expression of developmentally regulated genes

Mapping catalytically engaged TOP2B in neurons reveals the principles of topoisomerase action within the genome

We trapped catalytically engaged topoisomerase IIβ (TOP2B) in covalent DNA cleavage complexes (TOP2Bccs) and mapped their positions genome-wide in cultured mouse cortical neurons. We report that TOP2Bcc distribution varies with both nucleosome and compartmental chromosome organization. While TOP2Bccs in gene bodies correlate with their level of transcription, highly expressed genes that lack the usually associated chromatin marks, such as H3K36me3, show reduced TOP2Bccs, suggesting that histone posttranslational modifications regulate TOP2B activity. Promoters with high RNA polymerase II occupancy show elevated TOP2B chromatin immunoprecipitation sequencing signals but low TOP2Bccs, indicating that TOP2B catalytic engagement is curtailed at active promoters. Surprisingly, either poisoning or inhibiting TOP2B increases nascent transcription at most genes and enhancers but reduces transcription within long genes. These effects are independent of transcript length and instead correlate with the presence of intragenic enhancers. Together, these results clarify how cells modulate the catalytic engagement of topoisomerases to affect transcription.

The Bisdioxopiperazine ICRF-193 Attenuates LPS-induced IL-1β Secretion by Macrophages

Inhibiting pathological secretion of Interleukin-1β has shown beneficial effects in disease models and in the clinic and thus there is interest in finding inhibitors that can reduce its release from macrophages in response to their activation by foreign pathogens. We used an in vitro human macrophage model to investigate whether ICRF-193, a Topoisomerase II inhibitor could modulate IL1B mRNA expression and IL-1β secretion. These macrophage-like cells readily secrete IL-1β in response to Lipopolysaccharide (LPS). Upon exposure to a non-toxic dose of ICRF-193, IL-1β secretion was diminished by ~ 40%; however, level of transcription of IL1B was unaffected. We show that there was no Topoisomerase 2B (TOP2B) binding to several IL1B gene sites, which may explain why ICRF-193 does not alter IL1B mRNA levels. Hence, we show for the first time that ICRF-193 can reduce IL-1β secretion. Its low cost and the development of water-soluble prodrugs of ICRF-193 warrants its further investigation in the modulation of pathological secretion of this cytokine for the treatment of inflammatory disorders. (165 words).

MeCP2 represses the activity of topoisomerase IIβ in long neuronal genes

A unique signature of neurons is the high expression of the longest genes in the genome. These genes have essential neuronal functions, and disruption of their expression has been implicated in neurological disorders. DNA topoisomerases resolve DNA topological constraints and facilitate neuronal long gene expression. Conversely, the Rett syndrome protein, methyl-CpG-binding protein 2 (MeCP2), can transcriptionally repress long genes. How these factors regulate long genes is not well understood, and whether they interact is not known. Here, we identify and map a functional interaction between MeCP2 and topoisomerase IIβ (TOP2β) in mouse neurons. We profile neuronal TOP2β activity genome wide, detecting enrichment at regulatory regions and gene bodies of long genes, including MeCP2-regulated genes. We show that loss and overexpression of MeCP2 alter TOP2β activity at MeCP2-regulated genes. These findings uncover a mechanism of TOP2β inhibition by MeCP2 in neurons and implicate TOP2β dysregulation in disorders caused by MeCP2 disruption.

Empagliflozin treatment of cardiotoxicity: A comprehensive review of clinical, immunobiological, neuroimmune, and therapeutic implications

Cancer and cardiovascular disorders are known as the two main leading causes of mortality worldwide. Cardiotoxicity is a critical and common adverse effect of cancer-related chemotherapy. Chemotherapy-induced cardiotoxicity has been associated with various cancer treatments, such as anthracyclines, immune checkpoint inhibitors, and kinase inhibitors. Different methods have been reported for the management of chemotherapy-induced cardiotoxicity. In this regard, sodium-glucose cotransporter-2 inhibitors (SGLT2i), a class of antidiabetic agents, have recently been applied to manage heart failure patients. Further, SGLT2i drugs such as EMPA exert protective cardiac and systemic effects. Moreover, it can reduce inflammation through the mediation of major inflammatory components, such as Nucleotide-binding domain-like receptor protein 3 (NLRP3) inflammasomes, Adenosine 5'-monophosphate-activated protein kinase (AMPK), and c-Jun N-terminal kinase (JNK) pathways, Signal transducer and activator of transcription (STAT), and overall decreasing transcription of proinflammatory cytokines. The clinical outcome of EMPA administration is related to improving cardiovascular risk factors, including body weight, lipid profile, blood pressure, and arterial stiffness. Intriguingly, SGLT2 suppressors can regulate microglia-driven hyperinflammation affecting neurological and cardiovascular disorders. In this review, we discuss the protective effects of EMPA in chemotherapy-induced cardiotoxicity from molecular, immunological, and neuroimmunological aspects to preclinical and clinical outcomes.

To Break or Not to Break: The Role of TOP2B in Transcription

Transcription and its regulation pose challenges related to DNA torsion and supercoiling of the DNA template. RNA polymerase tracking the helical groove of the DNA introduces positive helical torsion and supercoiling upstream and negative torsion and supercoiling behind its direction of travel. This can inhibit transcriptional elongation and other processes essential to transcription. In addition, chromatin remodeling associated with gene activation can generate or be hindered by excess DNA torsional stress in gene regulatory regions. These topological challenges are solved by DNA topoisomerases via a strand-passage reaction which involves transiently breaking and re-joining of one (type I topoisomerases) or both (type II topoisomerases) strands of the phosphodiester backbone. This review will focus on one of the two mammalian type II DNA topoisomerase enzymes, DNA topoisomerase II beta (TOP2B), that have been implicated in correct execution of developmental transcriptional programs and in signal-induced transcription, including transcriptional activation by nuclear hormone ligands. Surprisingly, several lines of evidence indicate that TOP2B-mediated protein-free DNA double-strand breaks are involved in signal-induced transcription. We discuss the possible significance and origins of these DSBs along with a network of protein interaction data supporting a variety of roles for TOP2B in transcriptional regulation.

Effects of In Vitro Digestion of Polyphenols from Coffee on Binding Parameters to Human Topoisomerase II α

Type II topoisomerase (TOPII) is an enzyme that influences the topology of DNA. DNA breaks generated by TOPII may result in mutagenic or cytotoxic changes in cancer cells. In this study, we characterized interactions of TOPIIα with coffee extracts and individual chlorogenic acids (CHAs) from the extracts by performing isothermal titration calorimetry (ITC) and molecular docking (MD) simulations. The study showed that the highest affinity to TOPIIα was found in green coffee (ΔG = -38.23 kJ/mol) and monochlorogenic acids fraction of coffee extracts (ΔG = -35.80 kJ/mol), resulting from the high content of polyphenols, such as CHAs, which can bind to the enzyme in the active site. Coffee extracts and their fractions maintained a high affinity for TOPIIα after simulated digestion in the presence of probiotic bacteria. It can be concluded that coffee may be a potential TOPIIα inhibitor considered as a functional food for cancer prevention.

Disease-associated H58Y mutation affects the nuclear dynamics of human DNA topoisomerase IIβ

DNA topoisomerase II (TOP2) is an enzyme that resolves DNA topological problems and plays critical roles in various nuclear processes. Recently, a heterozygous H58Y substitution in the ATPase domain of human TOP2B was identified from patients with autism spectrum disorder, but its biological significance remains unclear. In this study, we analyzed the nuclear dynamics of TOP2B with H58Y (TOP2B H58Y). Although wild-type TOP2B was highly mobile in the nucleus of a living cell, the nuclear mobility of TOP2B H58Y was markedly reduced, suggesting that the impact of H58Y manifests as low protein mobility. We found that TOP2B H58Y is insensitive to ICRF-187, a TOP2 inhibitor that halts TOP2 as a closed clamp on DNA. When the ATPase activity of TOP2B was compromised, the nuclear mobility of TOP2B H58Y was restored to wild-type levels, indicating the contribution of the ATPase activity to the low nuclear mobility. Analysis of genome-edited cells harboring TOP2B H58Y showed that TOP2B H58Y retains sensitivity to the TOP2 poison etoposide, implying that TOP2B H58Y can undergo at least a part of its catalytic reactions. Collectively, TOP2 H58Y represents a unique example of the relationship between a disease-associated mutation and perturbed protein dynamics.

DNA-Stimulated Liquid-Liquid phase separation by eukaryotic topoisomerase ii modulates catalytic function

Type II topoisomerases modulate chromosome supercoiling, condensation, and catenation by moving one double-stranded DNA segment through a transient break in a second duplex. How DNA strands are chosen and selectively passed to yield appropriate topological outcomes - for example, decatenation vs. catenation - is poorly understood. Here, we show that at physiological enzyme concentrations, eukaryotic type IIA topoisomerases (topo IIs) readily coalesce into condensed bodies. DNA stimulates condensation and fluidizes these assemblies to impart liquid-like behavior. Condensation induces both budding yeast and human topo IIs to switch from DNA unlinking to active DNA catenation, and depends on an unstructured C-terminal region, the loss of which leads to high levels of knotting and reduced catenation. Our findings establish that local protein concentration and phase separation can regulate how topo II creates or dissolves DNA links, behaviors that can account for the varied roles of the enzyme in supporting transcription, replication, and chromosome compaction.

Untangling the roles of TOP2A and TOP2B in transcription and cancer

Type II topoisomerases (TOP2) are conserved regulators of chromatin topology that catalyze reversible DNA double-strand breaks (DSBs) and are essential for maintaining genomic integrity in diverse dynamic processes such as transcription, replication, and cell division. While controlled TOP2-mediated DSBs are an elegant solution to topological constraints of DNA, DSBs also contribute to the emergence of chromosomal translocations and mutations that drive cancer. The central importance of TOP2 enzymes as frontline chemotherapeutic targets is well known; however, their precise biological functions and impact in cancer development are still poorly understood. In this review, we provide an updated overview of TOP2A and TOP2B in the regulation of chromatin topology and transcription, and discuss the recent discoveries linking TOP2 activities with cancer pathogenesis.

Anthracycline-induced cardiotoxicity in women without cardiovascular diseases: molecular and genetic predictors

OBJECTIVE

To evaluate role of molecular (endothelin-1, soluble Fas-L, NT-proBNP, TNF-α, interleukin-1β,) and genetic factors (NOS3 (rs1799983), EDNRA (C + 70G, rs5335), NADPH oxidase (C242T, rs4673), p53 protein (polymorphic marker-Arg72Pro exon 4, rs1042522), NOS3 (Glu298Asp, rs1799983), Caspase 8 (CASP8, rs3834129 and rs1045485), interleukin-1β gene (Il-1β, rs1143634), TNF-α gene (rs1800629), SOD2 (rs4880), GPX1 (rs1050450) in development of anthracycline-induced cardiotoxicity (AIC) in women without cardiovascular diseases.

METHODS

A total of 176 women with breast cancer and without cardiovascular diseases who received anthracyclines were enrolled in the study. After the 12 months of chemotherapy (CT), all patients were divided into two groups: group 1 (n = 52) comprised patients with AIC, group 2 (n = 124) comprised those without it.

RESULTS

Based on ROC-analysis, levels of endothelin-1 of ≥9.0 pg/mL (AUC of 0.699), sFas-L of ≥98.3 ng/mL (AUC of 0.990), and NT-proBNP of ≥71.5 pg/mL (AUC of 0.994;) were identified as a cut-off values predicting AIC during 12 months after CT. Whereas, NT-proBNP and sFas-L were more significant predictors than endothelin-1 (p < 0.001). The development of AIC was significantly related to Arg/Arg of p53 protein gene (OR = 2.972; p = 0.001), T/T of NOS3 gene (OR = 3.059, p = 0.018), T/T of NADPH oxidase gene (OR = 2.753, p = 0.008), and C/C of GPX1 (OR = 2.345; p = 0.007).

CONCLUSION

Evaluation of polymorphisms genes of p53 (rs1042522), NOS3 (rs1799983), GPX1 (rs1050450), and NADPH oxidase (rs4673) can be recommended before CT for the risk assessment of AIC development. The serum levels of NT-proBNP and soluble Fas-L after CT may be considered as non-invasive biomarkers for prediction of AIC development during the 12 months.

DNA Topoisomerase II-α Regulated by miR-22-5p Promotes Hepatocellular Carcinoma Invasion and Migration through the Hippo Pathway

DNA topoisomerases (TOPs) are dysregulated in various types of cancer. However, how TOP II-alpha (TOP2A) contributes to hepatocellular carcinoma (HCC) progression remains elusive. Cohort analysis revealed that the increased expression of TOP2A was associated with poor clinical outcomes and TOP2A was significantly upregulated in HCC tissues and cell lines. In vitro, TOP2A expression level is related to cell invasion and migration, which may be due to the alteration of epithelial-mesenchymal transition by the TOP2A. Moreover, we used verteporfin (a Hippo inhibitor) to test how the Hippo pathway promotes the effect of TOP2A on the HCC phenotype and found that TOP2A induces tumor progression through the Hippo pathway. Finally, miR-22-5p inhibited tumor progression by sponging TOP2A.

Mechanisms and Drug Intervention for Doxorubicin-Induced Cardiotoxicity Based on Mitochondrial Bioenergetics

Doxorubicin (DOX) is an anthracycline chemotherapy drug, which is indispensable in antitumor therapy. However, its subsequent induction of cardiovascular disease (CVD) has become the primary cause of mortality in cancer survivors. Accumulating evidence has demonstrated that cardiac mitochondrial bioenergetics changes have become a significant marker for doxorubicin-induced cardiotoxicity (DIC). Here, we mainly summarize the related mechanisms of DOX-induced cardiac mitochondrial bioenergetics disorders reported in recent years, including mitochondrial substrate metabolism, the mitochondrial respiratory chain, myocardial ATP storage and utilization, and other mechanisms affecting mitochondrial bioenergetics. In addition, intervention for DOX-induced cardiac mitochondrial bioenergetics disorders using chemical drugs and traditional herbal medicine is also summarized, which will provide a comprehensive process to study and develop more appropriate therapeutic strategies for DIC.

Triple negative breast cancer: approved treatment options and their mechanisms of action

PURPOSE

Breast cancer, the most prevalent cancer worldwide, consists of 4 main subtypes, namely, Luminal A, Luminal B, HER2-positive, and Triple-negative breast cancer (TNBC). Triple-negative breast tumors, which do not express estrogen, progesterone, and HER2 receptors, account for approximately 15-20% of breast cancer cases. The lack of traditional receptor targets contributes to the heterogenous, aggressive, and refractory nature of these tumors, resulting in limited therapeutic strategies.

METHODS

Chemotherapeutics such as taxanes and anthracyclines have been the traditional go to treatment regimens for TNBC patients. Paclitaxel, docetaxel, doxorubicin, and epirubicin have been longstanding, Food and Drug Administration (FDA)-approved therapies against TNBC. Additionally, the FDA approved PARP inhibitors such as olaparib and atezolizumab to be used in combination with chemotherapies, primarily to improve their efficiency and reduce adverse patient outcomes. The immunotherapeutic Keytruda was the latest addition to the FDA-approved list of drugs used to treat TNBC.

RESULTS

The following review aims to elucidate current FDA-approved therapeutics and their mechanisms of action, shedding a light on the various strategies currently used to circumvent the treatment-resistant nature of TNBC cases.

CONCLUSION

The recent approval and use of therapies such as Trodelvy, olaparib and Keytruda has its roots in the development of an understanding of signaling pathways that drive tumour growth. In the future, the emergence of novel drug delivery methods may help increase the efficiency of these therapies whiel also reducing adverse side effects.

Topoisomerase 2β and DNA topology during B cell development

Topoisomerase 2β (TOP2B) introduces transient double strand breaks in the DNA helix to remove supercoiling structures and unwind entangled DNA strains. Advances in genomic technologies have enabled the discovery of novel functions for TOP2B in processes such as releasing of the paused RNA polymerase II and maintaining the genome organization through DNA loop domains. Thus, TOP2B can regulate transcription directly by acting on transcription elongation and indirectly by controlling interactions between enhancer and promoter regions through genome folding. The identification of TOP2B mutations in humans unexpectedly revealed a unique role of TOP2B in B-cell progenitors. Here we discuss the functions of TOP2B and the mechanisms leading to the B-cell development defect in patients with TOP2B deficiency.

Mitotherapy in doxorubicin induced cardiotoxicity: A promising strategy to reduce the complications of treatment

AIMS

Doxorubicin is a potent and broad-spectrum antineoplastic medication prescribed for both solid and hematological malignancies. Despite its value, the clinical use of doxorubicin is limited due to cardio-oncologic complication and cardiotoxic adverse effect. Among the mechanisms proposed for its toxicity, mitochondrial dysfunction has gained more attention. Therefore, if damaged mitochondria are replaced by normal efficient mitochondria, cardiac toxicity is expected to be reduced or improved. In this way, we have studied the efficiency of transplantation of freshly isolated rat liver mitochondria in neonatal rat cardiomyocytes that have been damaged by doxorubicin.

MATERIALS AND METHODS

For this purpose, isolated mitochondria were characterized using mitochondrial complex II, membrane potential and swelling evaluations, and also fluorescence and electron microscopy. Afterward, the effect of mitotherapy on the damaged cardiomyocytes was investigated by using annexin V/PI staining, MTT, ROS, MMP, lipid peroxidation, GSH and ATP evaluations.

KEY FINDINGS AND SIGNIFICANCE

Transplanted mitochondria could remarkably enter the neonatal rat cardiomyocytes. Addition of mitochondria to the damaged cardiomyocytes, significantly increased cell viability by reducing the level of reactive oxygen species and lipid peroxidation, increasing of ∆Ψ, ATP and GSH contents and decreasing of apoptotic and necrotic cell death. Our results showed that mitotherapy has a significant restorative effect on cardiotoxicity induced by doxorubicin, which promises a better future to reduce the complications of cancer treatment.

Evolutionary History of TOPIIA Topoisomerases in Animals

TOPIIA topoisomerases are required for the regulation of DNA topology by DNA cleavage and re-ligation and are important targets of antibiotic and anticancer agents. Humans possess two TOPIIA paralogue genes (TOP2A and TOP2B) with high sequence and structural similarity but distinct cellular functions. Despite their functional and clinical relevance, the evolutionary history of TOPIIA is still poorly understood. Here we show that TOPIIA is highly conserved in Metazoa. We also found that TOPIIA paralogues from jawed and jawless vertebrates had different origins related with tetraploidization events. After duplication, TOP2B evolved under a stronger purifying selection than TOP2A, perhaps promoted by the more specialized role of TOP2B in postmitotic cells. We also detected genetic signatures of positive selection in the highly variable C-terminal domain (CTD), possibly associated with adaptation to cellular interactions. By comparing TOPIIA from modern and archaic humans, we found two amino acid substitutions in the TOP2A CTD, suggesting that TOP2A may have contributed to the evolution of present-day humans, as proposed for other cell cycle-related genes. Finally, we identified six residues conferring resistance to chemotherapy differing between TOP2A and TOP2B. These six residues could be targets for the development of TOP2A-specific inhibitors that would avoid the side effects caused by inhibiting TOP2B. Altogether, our findings clarify the origin, diversification and selection pressures governing the evolution of animal TOPIIA.

In situ gel implant for postsurgical wound management and extended chemoimmunotherapy against breast cancer recurrence

Postsurgical recurrence of breast cancer is closely related to the inflammatory tumor microenvironment evoked by surgical wounds. Toll-like receptor 4 (TLR4) signaling contributes to NF-κB activation thus secreting various inflammatory cytokines. Herein, we developed an in situ photo-crosslinked hydrogel (D/T gel) concurrently loaded with doxorubicin (DOX) and a TLR4 antagonist, resatorvid (TAK-242). Its therapeutic effect against breast cancer postsurgical relapse was accomplished through remodeling the proinflammatory tumor microenvironment. The obtained gel network exhibited ideal biodegradability and biocompatibility, which motivated dermal wound healing in the full thickness wound model in mice. Despite the initial burst release of DOX, D/T gels exhibited extended-release of both DOX and TAK-242 for up to 21 days in vitro. TAK-242 was demonstrated to inhibit the lipopolysaccharide-induced NF-κB activation and downregulate TLR4 levels in both RAW264.7 and 4T1 cells. In a 4T1-Luc tumor postsurgical recurrence model, D/T gel significantly suppressed recurrent tumor growth by elevating the concentrations of DOX and TAK-242 at the tumor sites and remodeling the TLR4 activation-induced proinflammatory microenvironment. Overall, the D/T gel platform technology is proven to deliver therapeutics directly to the surgical wound bed, attenuating the dual inflammatory responses induced by DOX and surgical wounding thus greatly potentiating its efficacy in preventing postsurgical tumor recurrence. STATEMENT OF SIGNIFICANCE: Postsurgical recurrence of breast cancer is closely related to the inflammatory tumor microenvironment (TME) evoked by surgical wounds. Although chemotherapeutics lead to extensive residual tumor cell necrosis, multiple inflammatory cytokines are secreted simultaneously, which are conducive to tumor recurrence. In this work, a TLR4 antagonist, TAK-242, was combined with DOX to reverse the dual inflammatory TME induced by surgical wounding and chemotherapy. To elevate the concentration of therapeutics at the tumor site, a photocrosslinked hydrogel (D/T gel) implant coloaded with TAK-242 and DOX was developed and applied on the postsurgical bed. Consequently, D/T gel attenuated the dual inflammatory responses and greatly potentiated its efficacy in preventing postsurgical tumor recurrence.

TOP2B's contributions to transcription

Transcription is regulated and mediated by multiprotein complexes in a chromatin context. Transcription causes changes in DNA topology which is modulated by DNA topoisomerases, enzymes that catalyse changes in DNA topology via transient breaking and re-joining of one or both strands of the phosphodiester backbone. Mammals have six DNA topoisomerases, this review focuses on one, DNA topoisomerase II beta (TOP2B). In the absence of TOP2B transcription of many developmentally regulated genes is altered. Long genes seem particularly susceptible to the lack of TOP2B. Biochemical studies of the role of TOP2B in transcription regulated by ligands such as nuclear hormones, growth factors and insulin has revealed PARP1 associated with TOP2B and also PRKDC, XRCC5 and XRCC6. Analysis of publicly available databases of protein interactions confirms these interactions and illustrates interactions with other key transcriptional regulators including TRIM28. TOP2B has been shown to interact with proteins involved in chromosome organisation including CTCF and RAD21. Comparison of publicly available Chip-seq datasets reveals the location at which these proteins interact with genes. The availability of resources such as large datasets of protein-protein interactions, e.g. BioGrid and IntAct and protein-DNA interactions such as Chip-seq in GEO enables scientists to extend models and propose new hypotheses.

The Prevailing Role of Topoisomerase 2 Beta and its Associated Genes in Neurons

Topoisomerase 2 beta (TOP2β) is an enzyme that alters the topological states of DNA by making a transient double-strand break during the transcription process. The direct interaction of TOP2β with DNA strand results in transcriptional regulation of certain genes and some studies have suggested that a particular set of genes are regulated by TOP2β, which have a prominent role in various stages of neuron from development to degeneration. In this review, we discuss the role of TOP2β in various phases of the neuron's life. Based on the existing reports, we have compiled the list of genes, which are directly regulated by the enzyme, from different studies and performed their functional classification. We discuss the role of these genes in neurogenesis, neuron migration, fate determination, differentiation and maturation, generation of neural circuits, and senescence.

Association of Cardiotoxicity With Doxorubicin and Trastuzumab: A Double-Edged Sword in Chemotherapy

Anticancer drugs play an important role in reducing mortality rates and increasing life expectancy in cancer patients. Treatments include monotherapy and/or a combination of radiation therapy, chemotherapy, hormone therapy, or immunotherapy. Despite great advances in drug development, some of these treatments have been shown to induce cardiotoxicity directly affecting heart function and structure, as well as accelerating the development of cardiovascular disease. Such side effects restrict treatment options and can negatively affect disease management. Consequently, when managing cancer patients, it is vital to understand the mechanisms causing cardiotoxicity to better monitor heart function, develop preventative measures against cardiotoxicity, and treat heart failure when it occurs in this patient population. This review discusses the role and mechanism of major chemotherapy agents with principal cardiovascular complications in cancer patients.

Empagliflozin Significantly Prevents the Doxorubicin-induced Acute Cardiotoxicity via Non-antioxidant Pathways

Empagliflozin (EMPA) is a SGLT-2 inhibitor that has positive effects on cardiovascular outcomes. In this study, we aim to evaluate the possible protective effects of EMPA against doxorubicin (DOX)-induced acute cardiotoxicity. Non-diabetic Sprague-Dawley rats were randomized into four groups. The control group received serum physiologic (1 ml), the EMPA group received EMPA, the DOX group was administered cumulatively 18 mg/kg body weight DOX. The DOX+EMPA group was administered DOX and EMPA. In the DOX group, LVDED (P < 0.05) and LVSED (P < 0.01), QTc interval (P < 0.001), the ratio of karyolysis and karyorrhexis (P < 0.001) and infiltrative cell proliferation (P < 0.001) were found to be higher than; EF, FS and normal cell morphology were lower than the control group (P < 0.001). In the DOX+EMPA group, LVEDD (P < 0.05) and LVESD (P < 0.01) values, QTc interval (P < 0.001), karyolysis and karyorrhexis ratios (P < 0.001) and infiltrative cell proliferation were lower (P < 0.01); normal cell morphology and EF were higher compared to the DOX group (P < 0.001). Our results showed that empagliflozin significantly ameliorated DOX-induced acute cardiotoxicity.

Chemotherapeutic drugs: Cell death- and resistance-related signaling pathways. Are they really as smart as the tumor cells?

Chemotherapeutic drugs kill cancer cells or control their progression all over the patient's body, while radiation- and surgery-based treatments perform in a particular site. Based on their mechanisms of action, they are classified into different groups, including alkylating substrates, antimetabolite agents, anti-tumor antibiotics, inhibitors of topoisomerase I and II, mitotic inhibitors, and finally, corticosteroids. Although chemotherapeutic drugs have brought about more life expectancy, two major and severe complications during chemotherapy are chemoresistance and tumor relapse. Therefore, we aimed to review the underlying intracellular signaling pathways involved in cell death and resistance in different chemotherapeutic drug families to clarify the shortcomings in the conventional single chemotherapy applications. Moreover, we have summarized the current combination chemotherapy applications, including numerous combined-, and encapsulated-combined-chemotherapeutic drugs. We further discussed the possibilities and applications of precision medicine, machine learning, next-generation sequencing (NGS), and whole-exome sequencing (WES) in promoting cancer immunotherapies. Finally, some of the recent clinical trials concerning the application of immunotherapies and combination chemotherapies were included as well, in order to provide a practical perspective toward the future of therapies in cancer cases.

Topoisomerase IIα represses transcription by enforcing promoter-proximal pausing

Accumulation of topological stress in the form of DNA supercoiling is inherent to the advance of RNA polymerase II (Pol II) and needs to be resolved by DNA topoisomerases to sustain productive transcriptional elongation. Topoisomerases are therefore considered positive facilitators of transcription. Here, we show that, in contrast to this general assumption, human topoisomerase IIα (TOP2A) activity at promoters represses transcription of immediate early genes such as c-FOS, maintaining them under basal repressed conditions. Thus, TOP2A inhibition creates a particular topological context that results in rapid release from promoter-proximal pausing and transcriptional upregulation, which mimics the typical bursting behavior of these genes in response to physiological stimulus. We therefore describe the control of promoter-proximal pausing by TOP2A as a layer for the regulation of gene expression, which can act as a molecular switch to rapidly activate transcription, possibly by regulating the accumulation of DNA supercoiling at promoter regions.

Topoisomerase IIβ immunoreactivity (IR) co-localizes with neuronal marker-IR but not glial fibrillary acidic protein-IR in GLI3-positive medulloblastomas: an immunohistochemical analysis of 124 medulloblastomas from the Japan Children's Cancer Group

We previously reported observing GLI3 in medulloblastomas expressing neuronal markers (NM) and/or glial fibrillary acidic protein (GFAP). Furthermore, patients with medulloblastomas expressing NM or GFAP tended to show favorable or poor prognosis, respectively. In the present study, we focused on the role of topoisomerase IIβ (TOP2β) as a possible regulator for neuronal differentiation in medulloblastomas and examined the pathological roles of GLI3, NM, GFAP, and TOP2β expressions in a larger population. We divided 124 medulloblastomas into three groups (NM-/GFAP-, NM +/GFAP-, and GFAP +) based on their immunoreactivity (IR) against NM and GFAP. The relationship among GLI3, NM, GFAP, and TOP2β was evaluated using fluorescent immunostaining and a publicly available single-cell RNA sequencing dataset. In total, 87, 30, and 7 medulloblastomas were classified as NM-/GFAP-, NM + /GFAP-, and GFAP +, and showed intermediate, good, and poor prognoses, respectively. GLI3-IR was frequently observed in NM +/GFAP-  and GFAP + , and TOP2β-IR was frequently observed only in NM +/GFAP-  medulloblastomas. In fluorescent immunostaining, TOP2β-IR was mostly co-localized with NeuN-IR but not with GFAP-IR. In single-cell RNA sequencing, TOP2β expression was elevated in CMAS/DCX-positive, but not in GFAP-positive, cells. NM-IR and GFAP-IR are important for estimating the prognosis of patients with medulloblastoma; hence they should be assessed in clinical practice.

Down regulation of DNA topoisomerase IIβ exerts neurodegeneration like effect through Rho GTPases in cellular model of Parkinson's disease by Down regulating tyrosine hydroxylase

Initiating the transcriptional activation of neuronal genes, DNA topoisomerase IIβ (topo IIβ) has a crucial role in neural differentiation and brain development. Inhibition of topo IIβ activity causes shorter axons and deteriorated neuronal connections common in neurodegenerative diseases. We previously reported that topo IIβ silencing could give rise to neurodegeneration through dysregulation of Rho GTPases and may contribute to pathogenesis of neurodegenerative diseases. Although there are several studies available proposing a link between Parkinson's Disease (PD) and Rho GTPases, there have been no reports analyzing the topo IIβ-dependent association of PD and Rho GTPases. Here, for the first time, we identified that topo IIβ has a regulatory role on Rho GTPases contributing to PD-like pathology. We analyzed the association between topo IIβ and PD by comparing topo IIβ expression levels of Retinoic Acid (RA) and Brain-derived neutrophic factor (BDNF) induced and MPP+-intoxicated SH-SY5Y cells used as an in vitro PD model. While both mRNA and protein levels of topo IIβ increase in neural differentiated cells, a significant decrease is detected in the PD model. Additionally, silencing of topo IIβ by specific siRNAs caused phenotypic alterations like deteriorated neural connections and transcriptional regulations such as upregulation of RhoA and downregulation of Cdc42, Rac1, and tyrosine hydroxylase gene expressions. Our results suggest that topo IIβ downregulation may cause neurodegeneration through dysregulation of Rho-GTPases leading to PD-like pathology.

Diversity and Functions of Type II Topoisomerases

The DNA double helix provides a simple and elegant way to store and copy genetic information. However, the processes requiring the DNA helix strands separation, such as transcription and replication, induce a topological side-effect - supercoiling of the molecule. Topoisomerases comprise a specific group of enzymes that disentangle the topological challenges associated with DNA supercoiling. They relax DNA supercoils and resolve catenanes and knots. Here, we review the catalytic cycles, evolution, diversity, and functional roles of type II topoisomerases in organisms from all domains of life, as well as viruses and other mobile genetic elements.

DNA Double-Strand Breaks Are a Critical Regulator of Fear Memory Reconsolidation

Numerous studies have shown that following retrieval, a previously consolidated memory requires increased transcriptional regulation in order to be reconsolidated. Previously, it was reported that histone H3 lysine-4 trimethylation (H3K4me3), a marker of active transcription, is increased in the hippocampus after the retrieval of contextual fear memory. However, it is currently unknown how this epigenetic mark is regulated during the reconsolidation process. Furthermore, though recent evidence suggests that neuronal activity triggers DNA double-strand breaks (DSBs) in some early-response genes, it is currently unknown if DSBs contribute to the reconsolidation of a memory following retrieval. Here, using chromatin immunoprecipitation (ChIP) analyses, we report a significant overlap between DSBs and H3K4me3 in area CA1 of the hippocampus during the reconsolidation process. We found an increase in phosphorylation of histone H2A.X at serine 139 (H2A.XpS139), a marker of DSB, in the Npas4, but not c-fos, promoter region 5 min after retrieval, which correlated with increased H3K4me3 levels, suggesting that the two epigenetic marks may work in concert during the reconsolidation process. Consistent with this, in vivo siRNA-mediated knockdown of topoisomerase II β, the enzyme responsible for DSB, prior to retrieval, reduced Npas4 promoter-specific H2A.XpS139 and H3K4me3 levels and impaired long-term memory, indicating an indispensable role of DSBs in the memory reconsolidation process. Collectively, our data propose a novel mechanism for memory reconsolidation through increases in epigenetic-mediated transcriptional control via DNA double-strand breaks.

Topoisomerase IIβ targets DNA crossovers formed between distant homologous sites to induce chromatin opening

Type II DNA topoisomerases (topo II) flip the spatial positions of two DNA duplexes, called G- and T- segments, by a cleavage-passage-resealing mechanism. In living cells, these DNA segments can be derived from distant sites on the same chromosome. Due to lack of proper methodology, however, no direct evidence has been described so far. The beta isoform of topo II (topo IIβ) is essential for transcriptional regulation of genes expressed in the final stage of neuronal differentiation. Here we devise a genome-wide mapping technique (eTIP-seq) for topo IIβ target sites that can measure the genomic distance between G- and T-segments. It revealed that the enzyme operates in two distinctive modes, termed proximal strand passage (PSP) and distal strand passage (DSP). PSP sites are concentrated around transcription start sites, whereas DSP sites are heavily clustered in small number of hotspots. While PSP represent the conventional topo II targets that remove local torsional stresses, DSP sites have not been described previously. Most remarkably, DSP is driven by the pairing between homologous sequences or repeats located in a large distance. A model-building approach suggested that topo IIβ acts on crossovers to unknot the intertwined DSP sites, leading to chromatin decondensation.

Untangling trapped topoisomerases with tyrosyl-DNA phosphodiesterases

DNA topoisomerases alleviate the torsional stress that is generated by processes that are central to genome metabolism such as transcription and DNA replication. To do so, these enzymes generate an enzyme intermediate known as the cleavage complex in which the topoisomerase is covalently linked to the termini of a DNA single- or double-strand break. Whilst cleavage complexes are normally transient they can occasionally become abortive, creating protein-linked DNA breaks that threaten genome stability and cell survival; a process promoted and exploited in the cancer clinic by the use of topoisomerase 'poisons'. Here, we review the consequences to genome stability and human health of abortive topoisomerase-induced DNA breakage and the cellular pathways that cells have adopted to mitigate them, with particular focus on an important class of enzymes known as tyrosyl-DNA phosphodiesterases.

DNA binding activity of the proximal C-terminal domain of rat DNA topoisomerase IIβ is involved in ICRF-193-induced closed-clamp formation

DNA topoisomerase II (topo II) is an essential enzyme that regulates DNA topology by DNA cleavage and re-ligation. In vertebrates, there are two isozymes, α and β. The C-terminal domain (CTD) of the isozymes, which shows a low degree of sequence homology between α and β, is involved in each isozyme-specific intracellular behavior. The CTD of topo IIβ is supposedly involved in topo II regulation. Topo IIβ is maintained in an inactive state in the nucleoli by the binding of RNA to the 50-residue region termed C-terminal regulatory domain (CRD) present in the CTD. Although in vitro biochemical analysis indicates that the CTD of topo IIβ has DNA binding activity, it is unclear whether CTD influences catalytic reaction in the nucleoplasm. Here, we show that the proximal CTD (hereafter referred to as pCTD) of rat topo IIβ, including the CRD, is involved in the catalytic reaction in the nucleoplasm. We identified the pCTD as a domain with DNA binding activity by in vitro catenation assay and electrophoretic mobility shift assay. Fluorescence recovery after photo-bleaching (FRAP) analysis of pCTD-lacking mutant (ΔpCTD) showed higher mobility in nucleoplasm than that of the wild-type enzyme, indicating that the pCTD also affected the nuclear dynamics of topo IIβ. ICRF-193, one of the topo II catalytic inhibitors, induces the formation of closed-clamp intermediates of topo II. Treatment of ΔpCTD with ICRF-193 significantly decreased the efficiency of closed-clamp formation. Altogether, our data indicate that the binding of topo IIβ to DNA through the pCTD is required for the catalytic reaction in the nucleoplasm.

Mechanisms of Anthracycline-Induced Cardiotoxicity: Is Mitochondrial Dysfunction the Answer?

Cardiac side effects are a major drawback of anticancer therapies, often requiring the use of low and less effective doses or even discontinuation of the drug. Among all the drugs known to cause severe cardiotoxicity are anthracyclines that, though being the oldest chemotherapeutic drugs, are still a mainstay in the treatment of solid and hematological tumors. The recent expansion of the field of Cardio-Oncology, a branch of cardiology dealing with prevention or treatment of heart complications due to cancer treatment, has greatly improved our knowledge of the molecular mechanisms behind anthracycline-induced cardiotoxicity (AIC). Despite excessive generation of reactive oxygen species was originally believed to be the main cause of AIC, recent evidence points to the involvement of a plethora of different mechanisms that, interestingly, mainly converge on deregulation of mitochondrial function. In this review, we will describe how anthracyclines affect cardiac mitochondria and how these organelles contribute to AIC. Furthermore, we will discuss how drugs specifically targeting mitochondrial dysfunction and/or mitochondria-targeted drugs could be therapeutically exploited to treat AIC.

Transcriptional supercoiling boosts topoisomerase II-mediated knotting of intracellular DNA

Recent studies have revealed that the DNA cross-inversion mechanism of topoisomerase II (topo II) not only removes DNA supercoils and DNA replication intertwines, but also produces small amounts of DNA knots within the clusters of nucleosomes that conform to eukaryotic chromatin. Here, we examine how transcriptional supercoiling of intracellular DNA affects the occurrence of these knots. We show that although (−) supercoiling does not change the basal DNA knotting probability, (+) supercoiling of DNA generated in front of the transcribing complexes increases DNA knot formation over 25-fold. The increase of topo II-mediated DNA knotting occurs both upon accumulation of (+) supercoiling in topoisomerase-deficient cells and during normal transcriptional supercoiling of DNA in TOP1 TOP2 cells. We also show that the high knotting probability (P^kn ≥ 0.5) of (+) supercoiled DNA reflects a 5-fold volume compaction of the nucleosomal fibers in vivo. Our findings indicate that topo II-mediated DNA knotting could be inherent to transcriptional supercoiling of DNA and other chromatin condensation processes and establish, therefore, a new crucial role of topoisomerase II in resetting the knotting–unknotting homeostasis of DNA during chromatin dynamics.

Analysis of apoptosis related genes in nurses exposed to anti-neoplastic drugs

BACKGROUND

Anti-neoplastic agents are widely used in the treatment of cancer and some non-neoplastic diseases. These drugs have been proved to be carcinogens, teratogens, and mutagens. Concern exists regarding the possible dangers of the staff handling anti-cancer drugs. The long-term exposure of nurses to anti-neoplastic drugs is still a controversial issue. The purpose of this study was to monitor cellular toxicity parameters and gene expression in nurses who work in chemotherapy wards and compare them to nurses who work in other wards.

METHODS

To analyze the apoptosis-related genes overexpression and cytotoxicity effects, peripheral blood lymphocytes obtained from oncology nurses and the control group.

THE RESULTS

Significant alterations in four analyzed apoptosis-related genes were observed in oncology nurses. In most individual samples being excavated, Bcl-2 overexpression is superior to that of Bax. Prominent P53 and Hif-1α up-regulation were observed in oncology nurses. Moreover, all cytotoxicity parameters (cell viability, ROS formation, MMP collapse, Lysosomal membrane damage, Lipid peroxidation, Caspase 3 activity and Apoptosis phenotype) in exposed oncology nurses were significantly (p < 0.001) higher than those of unexposed control nurses. Up-regulation of three analyzed apoptosis-related genes were observed in nurses occupationally exposed to anti-cancer drugs.

CONCLUSION

Our data show that oxidative stress and mitochondrial toxicity induced by anti-neoplastic drugs lead to overexpression of apoptosis-related genes in oncology nurses.

Cell Cycle-Dependent Control and Roles of DNA Topoisomerase II

Type II topoisomerases are ubiquitous enzymes in all branches of life that can alter DNA superhelicity and unlink double-stranded DNA segments during processes such as replication and transcription. In cells, type II topoisomerases are particularly useful for their ability to disentangle newly-replicated sister chromosomes. Growing lines of evidence indicate that eukaryotic topoisomerase II (topo II) activity is monitored and regulated throughout the cell cycle. Here, we discuss the various roles of topo II throughout the cell cycle, as well as mechanisms that have been found to govern and/or respond to topo II function and dysfunction. Knowledge of how topo II activity is controlled during cell cycle progression is important for understanding how its misregulation can contribute to genetic instability and how modulatory pathways may be exploited to advance chemotherapeutic development.

Mutations in topoisomerase IIβ result in a B cell immunodeficiency

B cell development is a highly regulated process involving multiple differentiation steps, yet many details regarding this pathway remain unknown. Sequencing of patients with B cell-restricted immunodeficiency reveals autosomal dominant mutations in TOP2B. TOP2B encodes a type II topoisomerase, an essential gene required to alleviate topological stress during DNA replication and gene transcription, with no previously known role in B cell development. We use Saccharomyces cerevisiae, and knockin and knockout murine models, to demonstrate that patient mutations in TOP2B have a dominant negative effect on enzyme function, resulting in defective proliferation, survival of B-2 cells, causing a block in B cell development, and impair humoral function in response to immunization.

Topoisomerases are required to release topological stress on DNA during replication and transcription. Here, Broderick et al. report genetic variants in TOP2B that cause a syndromic B cell immunodeficiency associated with reduced TOP2B function, defects in B cell development and B cell activation.

A new Thiocyanoacetamide protects rat sperm cells from Doxorubicin-triggered cytotoxicity whereas Selenium shows low efficacy: In vitro approach

Doxorubicin (DOX) exhibits a wide-ranging spectrum of antitumor activities which maintain its clinical use despite its devastating impact on highly proliferating cells. The present work was designed to develop a new approach which aims to protect male germ cells from DOX cytotoxicity. Thus, an assessment of the protective potential of a new thioamide analog (thiocyanoacetamide; TA) compared to selenium (Se) was performed in rat sperms exposed to DOX in vitro. Oxygen consumption rate (OCR) was measured after exposure to three different doses (0.5, 1, 1.5 and 2 μM) of DOX, Se or TA, and the suitable concentrations were selected for further studies afterwards. Motility, OCR in a time-dependent manner, glucose extracellular concentration and lipid peroxidation (LPO) were measured. Fatty acid (FA) content was assessed by gas chromatography (GC-FID). Cell death, superoxide anion (O₂^-), mitochondrial membrane potential (MMP), and DNA damage were evaluated by flow cytometry. TA association with DOX increased OCR and glucose uptake, improved cell survival and decreased DNA damage. The co-administration of DOX with Se increased OCR, significantly prevented O₂^- overproduction, and decreased LPO. Collected data brought new insights regarding this transformed TA, which showed better efficiency than Se in reducing DOX cytotoxic stress in sperms.

Anthracyclines as Topoisomerase II Poisons: From Early Studies to New Perspectives

Mammalian DNA topoisomerases II are targets of anticancer anthracyclines that act by stabilizing enzyme-DNA complexes wherein DNA strands are cut and covalently linked to the protein. This molecular mechanism is the molecular basis of anthracycline anticancer activity as well as the toxic effects such as cardiomyopathy and induction of secondary cancers. Even though anthracyclines have been used in the clinic for more than 50 years for solid and blood cancers, the search of breakthrough analogs has substantially failed. The recent developments of personalized medicine, availability of individual genomic information, and immune therapy are expected to change significantly human cancer therapy. Here, we discuss the knowledge of anthracyclines as Topoisomerase II poisons, their molecular and cellular effects and toxicity along with current efforts to improve the therapeutic index. Then, we discuss the contribution of the immune system in the anticancer activity of anthracyclines, and the need to increase our knowledge of molecular mechanisms connecting the drug targets to the immune stimulatory pathways in cancer cells. We propose that the complete definition of the molecular interaction of anthracyclines with the immune system may open up more effective and safer ways to treat patients with these drugs.

Increasing the distance between two monomers of topoisomerase IIβ under the action of antitumor agent 4β-sulfur-(benzimidazole) 4'-demethylepipodophyllotoxin

Topoisomerases II (Top2s) are a group of essential enzymes involved in replication, transcription, chromosome condensation, and segregation via altering DNA topology. The mechanism of the Top2s poisons such as etoposide (VP-16) was reported as stabilizing the Top2-DNA complex and engendering permanent DNA breakage. As the structurally similar compound of VP-16, a novel 4β-sulfur-substituted 4′-demethylepipodophyllotoxin (DMEP) derivative (compound C-Bi) with superior antitumor activity was developed in our previous study. To understand the structural basis of the compound action, the crystal structure (2.54 Å) of human Top2 β-isoform (hTop2β) cleavage complexes stabilized by compound C-Bi was determined. However, compound C-Bi was not visible in the crystal structure. Through the comparison of the structures of hTop2β-DNA-etoposide ternary complex and hTop2β-DNA binary complex, it could be observed that the distance between drug-binding sites Arg503 of the two monomers was 26.62 Å in hTop2β-DNA-etoposide ternary complex and 34.54 Å in hTop2β-DNA binary complex, respectively. Significant twist were observed in the DNA chains of binary complex. It suggested that compound C-Bi played antitumor roles through increasing spacing of hTop2β monomers. The changes in hTop2β structure further caused double changes in the torsional direction and migration distance of the DNA chains, resulting in impeding religation of DNA.

The role of E2F1-topoIIβ signaling in regulation of cell cycle exit and neuronal differentiation of human SH-SY5Y cells

This study aims to test the role of E2F1-topoIIβ signaling in neuronal differentiation of SH-SY5Y cells. With retinoic acid (RA) induction, a high percentage of cells were found to be arrested at the G₀/G₁ phase, with decreased levels of cyclinD1, CDK4, phosphorylation status of pRb and E2F1, in addition to an elevated level of p27. The cells were shown to differentiate into neuronal phenotypes characterized by highly expressed neuronal markers, MAP2 and enriched topoIIβ, and remarkable neurite outgrowth. Exogenously forced E2F1 expression with a specific E2F1 plasmid led to suppression of topoIIβ expression and disruption of the neuronal differentiation of SH-SY5Y cells. On further examination using the ChIP assay, we found that E2F1 bound directly to the promoter region of topoIIβ, and its binding ability was inversely correlated with topoIIβ expression in response to RA induction. Thus, our findings suggest that E2F1-topoIIβ signaling may play a role in regulation of cell cycle exit and neuronal differentiation.

Investigating DNA supercoiling in eukaryotic genomes

Supercoiling is a fundamental property of DNA, generated by polymerases and other DNA-binding proteins as a consequence of separating/bending the DNA double helix. DNA supercoiling plays a key role in gene expression and genome organization, but has proved difficult to study in eukaryotes because of the large, complex and chromatinized genomes. Key approaches to study DNA supercoiling in eukaryotes are (1) centrifugation-based or electrophoresis-based techniques in which supercoiled plasmids extracted from eukaryotic cells form a compacted writhed structure that migrates at a rate proportional to the level of DNA supercoiling; (2) in vivo approaches based on the preferential intercalation of psoralen molecules into under-wound DNA. Here, we outline the principles behind these techniques and discuss key discoveries, which have confirmed the presence and functional potential of unconstrained DNA supercoiling in eukaryotic genomes.

Dynamic behavior of DNA topoisomerase IIβ in response to DNA double-strand breaks

DNA topoisomerase II (Topo II) is crucial for resolving topological problems of DNA and plays important roles in various cellular processes, such as replication, transcription, and chromosome segregation. Although DNA topology problems may also occur during DNA repair, the possible involvement of Topo II in this process remains to be fully investigated. Here, we show the dynamic behavior of human Topo IIβ in response to DNA double-strand breaks (DSBs), which is the most harmful form of DNA damage. Live cell imaging coupled with site-directed DSB induction by laser microirradiation demonstrated rapid recruitment of EGFP-tagged Topo IIβ to the DSB site. Detergent extraction followed by immunofluorescence showed the tight association of endogenous Topo IIβ with DSB sites. Photobleaching analysis revealed that Topo IIβ is highly mobile in the nucleus. The Topo II catalytic inhibitors ICRF-187 and ICRF-193 reduced the Topo IIβ mobility and thereby prevented Topo IIβ recruitment to DSBs. Furthermore, Topo IIβ knockout cells exhibited increased sensitivity to bleomycin and decreased DSB repair mediated by homologous recombination (HR), implicating the role of Topo IIβ in HR-mediated DSB repair. Taken together, these results highlight a novel aspect of Topo IIβ functions in the cellular response to DSBs.

The Roles of DNA Topoisomerase IIβ in Transcription

Type IIA topoisomerases allow DNA double helical strands to pass through each other by generating transient DNA double strand breaks βDSBs), and in so doing, resolve torsional strain that accumulates during transcription, DNA replication, chromosome condensation, chromosome segregation and recombination. Whereas most eukaryotes possess a single type IIA enzyme, vertebrates possess two distinct type IIA topoisomerases, Topo IIα and Topo IIβ. Although the roles of Topo IIα, especially in the context of chromosome condensation and segregation, have been well-studied, the roles of Topo IIβ are only beginning to be illuminated. This review begins with a summary of the initial studies surrounding the discovery and characterization of Topo IIβ and then focuses on the insights gained from more recent studies that have elaborated important functions for Topo IIβ in transcriptional regulation.

Post-translational modifications in DNA topoisomerase 2α highlight the role of a eukaryote-specific residue in the ATPase domain

Type 2 DNA topoisomerases (Top2) are critical components of key protein complexes involved in DNA replication, chromosome condensation and segregation, as well as gene transcription. The Top2 were found to be the main targets of anticancer agents, leading to intensive efforts to understand their functional and physiological role as well as their molecular structure. Post-translational modifications have been reported to influence Top2 enzyme activities in particular those of the mammalian Top2α isoform. In this study, we identified phosphorylation, and for the first time, acetylation sites in the human Top2α isoform produced in eukaryotic expression systems. Structural analysis revealed that acetylation sites are clustered on the catalytic domains of the homodimer while phosphorylation sites are located in the C-terminal domain responsible for nuclear localization. Biochemical analysis of the eukaryotic-specific K168 residue in the ATPase domain shows that acetylation affects a key position regulating ATP hydrolysis through the modulation of dimerization. Our findings suggest that acetylation of specific sites involved in the allosteric regulation of human Top2 may provide a mechanism for modulation of its catalytic activity.

The Novel C-terminal Truncated 90-kDa Isoform of Topoisomerase IIα (TOP2α/90) Is a Determinant of Etoposide Resistance in K562 Leukemia Cells via Heterodimerization with the TOP2α/170 Isoform

DNA topoisomerase IIα (170 kDa, TOP2α/170) is essential in proliferating cells by resolving DNA topological entanglements during chromosome condensation, replication, and segregation. We previously characterized a C-terminally truncated isoform (TOP2α/90), detectable in human leukemia K562 cells but more abundantly expressed in a clonal subline, K/VP.5, with acquired resistance to the anticancer agent etoposide. TOP2α/90 (786 aa) is the translation product of a TOP2α mRNA that retains a processed intron 19. TOP2α/90 lacks the active-site tyrosine-805 required to generate double-strand DNA breaks as well as nuclear localization signals present in the TOP2α/170 isoform (1531 aa). Here, we found that TOP2α/90, like TOP2α/170, was detectable in the nucleus and cytoplasm of K562 and K/VP.5 cells. Coimmunoprecipitation of endogenous TOP2α/90 and TOP2α/170 demonstrated heterodimerization of these isoforms. Forced expression of TOP2α/90 in K562 cells suppressed, whereas siRNA-mediated knockdown of TOP2α/90 in K/VP.5 cells enhanced, etoposide-mediated DNA strand breaks compared with similarly treated cells transfected with empty vector or control siRNAs, respectively. In addition, forced expression of TOP2α/90 in K562 cells inhibited etoposide cytotoxicity assessed by clonogenic assays. qPCR and immunoassays demonstrated TOP2α/90 mRNA and protein expression in normal human tissues/cells and in leukemia cells from patients. Together, results strongly suggest that TOP2α/90 expression decreases drug-induced TOP2α-DNA covalent complexes and is a determinant of chemoresistance through a dominant-negative effect related to heterodimerization with TOP2α/170. Alternative processing of TOP2α pre-mRNA, and subsequent synthesis of TOP2α/90, may be an important mechanism regulating the formation and/or stability of cytotoxic TOP2α/170-DNA covalent complexes in response to TOP2α-targeting agents.

Topoisomerases as anticancer targets

Many cancer type-specific anticancer agents have been developed and significant advances have been made toward precision medicine in cancer treatment. However, traditional or nonspecific anticancer drugs are still important for the treatment of many cancer patients whose cancers either do not respond to or have developed resistance to cancer-specific anticancer agents. DNA topoisomerases, especially type IIA topoisomerases, are proved therapeutic targets of anticancer and antibacterial drugs. Clinically successful topoisomerase-targeting anticancer drugs act through topoisomerase poisoning, which leads to replication fork arrest and double-strand break formation. Unfortunately, this unique mode of action is associated with the development of secondary cancers and cardiotoxicity. Structures of topoisomerase-drug-DNA ternary complexes have revealed the exact binding sites and mechanisms of topoisomerase poisons. Recent advances in the field have suggested a possibility of designing isoform-specific human topoisomerase II poisons, which may be developed as safer anticancer drugs. It may also be possible to design catalytic inhibitors of topoisomerases by targeting certain inactive conformations of these enzymes. Furthermore, identification of various new bacterial topoisomerase inhibitors and regulatory proteins may inspire the discovery of novel human topoisomerase inhibitors. Thus, topoisomerases remain as important therapeutic targets of anticancer agents.