EAPII interacts with ETS1 and modulates its transcriptional function

Mutations in tyrosyl-DNA phosphodiesterase 2 suppress top-2 induced chromosome segregation defects during Caenorhabditis elegans spermatogenesis

Meiosis reduces ploidy through two rounds of chromosome segregation preceded by one round of DNA replication. In meiosis I, homologous chromosomes segregate, while in meiosis II, sister chromatids separate from each other. Topoisomerase II (Topo II) is a conserved enzyme that alters DNA structure by introducing transient double-strand breaks. During mitosis, Topo II relieves topological stress associated with unwinding DNA during replication, recombination, and sister chromatid segregation. Topo II also plays a role in maintaining mitotic chromosome structure. However, the role and regulation of Topo II during meiosis is not well-defined. Previously, we found an allele of Topo II, top-2(it7), disrupts homologous chromosome segregation during meiosis I of Caenorhabditis elegans spermatogenesis. In a genetic screen, we identified different point mutations in 5'-tyrosyl-DNA phosphodiesterase two (Tdp2, C. elegans tdpt-1) that suppress top-2(it7) embryonic lethality. Tdp2 removes trapped Top-2-DNA complexes. The tdpt-1 suppressing mutations rescue embryonic lethality, ameliorate chromosome segregation defects, and restore TOP-2 protein levels of top-2(it7). Here, we show that both TOP-2 and TDPT-1 are expressed in germ line nuclei but occupy different compartments until late meiotic prophase. We also demonstrate that tdpt-1 suppression is due to loss of function of the protein and that the tdpt-1 mutations do not have a phenotype independent of top-2(it7) in meiosis. Lastly, we found that the tdpt-1 suppressing mutations either impair the phosphodiesterase activity, affect the stability of TDPT-1, or disrupt protein interactions. This suggests that the WT TDPT-1 protein is inhibiting chromosome biological functions of an impaired TOP-2 during meiosis.

Characterization of N- and C-terminal endogenously tagged Tyrosyl-DNA phosphodiesterase 2 (TDPT-1) C. elegans strains

We have generated Tyrosyl-DNA phosphodiesterase 2 (TDPT-1) C. elegans strains where CRISPR/Cas9 was used to endogenously tag the protein at either the C- or N-terminus and validated the functionality of the resulting tagged TDPT-1 proteins. We have found that both the N-terminally tagged ( wrmScarlet::tdpt-1) and C-terminally tagged ( tdpt-1::3xflag ) worm TDPT-1 does not affect embryonic viability compared to wild type. Using the N-terminally tagged wrmScarlet::tdpt-1 strain we show, for the first time, that TDPT-1 is expressed in nuclei of the germ line and the soma. Moreover, we validate the expression of TDPT-1 at the protein level using the C-terminally tagged ( tdpt-1::3xflag ) strain.

The repair of topoisomerase 2 cleavage complexes in Arabidopsis

DNA-protein crosslinks (DPCs) and DNA double-stranded breaks (DSBs), including those produced by stalled topoisomerase 2 cleavage complexes (TOP2ccs), must be repaired to ensure genome stability. The basic mechanisms of TOP2cc repair have been characterized in other eukaryotes, but we lack information for plants. Using CRISPR/Cas-induced mutants, we show that Arabidopsis thaliana has two main TOP2cc repair pathways: one is defined by TYROSYL-DNA-PHOSPHODIESTERASE 2 (TDP2), which hydrolyzes TOP2-DNA linkages, the other by the DNA-dependent protease WSS1A (a homolog of human SPARTAN/yeast weak suppressor of smt3 [Wss1]), which also functions in DPC repair. TDP1 and TDP2 function nonredundantly in TOP1cc repair, indicating that they act specifically on their respective stalled cleavage complexes. The nuclease METHYL METHANESULFONATE AND UV-SENSITIVE PROTEIN 81 (MUS81) plays a major role in global DPC repair and a minor role in TOP2cc repair. DSBs arise as intermediates of TOP2cc repair and are repaired by classical and alternative nonhomologous end joining (NHEJ) pathways. Double-mutant analysis indicates that "clean" DNA ends caused by TDP2 hydrolysis are mainly religated by classical NHEJ, which helps avoid mutation. In contrast, the mutagenic alternative NHEJ pathway mainly processes nonligateable DNA ends. Thus, TDP2 promotes maintenance of plant genome integrity by error-free repair of TOP2cc.

Trapped topoisomerase-DNA covalent complexes in the mitochondria and their role in human diseases

Topoisomerases regulate DNA topology, organization of the intracellular DNA, the transmission of genetic materials, and gene expressions. Other than the nuclear genome, mitochondria also harbor the small, circular DNA (mtDNA) that encodes a critical subset of proteins for the production of cellular ATP; however, mitochondria are solely dependent on the nucleus for all the mitochondrial proteins necessary for mtDNA replication, repair, and maintenance. Mitochondrial genome compiles topological stress from bidirectional transcription and replication, therefore imports four nuclear encoded topoisomerases (Top1mt, Top2α, Top2β, and Top3α) in the mitochondria to relax mtDNA supercoiling generated during these processes. Trapping of topoisomerase on DNA results in the formation of protein-linked DNA adducts (PDAs), which are widely exploited by topoisomerase-targeting anticancer drugs. Intriguingly mtDNA is potentially exposed to DNA damage that has been attributed to a variety of human diseases, including neurodegeneration, cancer, and premature aging. In this review, we focus on the role of different topoisomerases in the mitochondria and our current understanding of the mitochondrial DNA damage through trapped protein-DNA complexes, and the progress in the molecular mechanisms of the repair for trapped topoisomerase covalent complexes (Topcc). Finally, we have discussed how the pathological DNA lesions that cause mtDNA damage,trigger mitochondrial fission and mitophagy, which serve as quality control events for clearing damaged mtDNA.

Robustadial A and B from Eucalyptus globulus Labill. and their anticancer activity as selective tyrosyl-DNA phosphodiesterase 2 inhibitors

Tyrosyl-DNA phosphodiesterase 2 (TDP2) is a recently discovered DNA repair enzyme that can repair topoisomerase 2-mediated DNA damage, resulting in cancer cell resistance. In this study, two compounds, robustadial A and B, were isolated from a fraction of the ethyl acetate extract of Eucalyptus globulus Labill. fruits based on TDP2 inhibition screening. The biological experiments indicated that robustadial A and B have TDP2 inhibitory activity with EC₅₀ values of 17 and 42 μM, respectively, but no tyrosyl-DNA phosphodiesterase 1 inhibition at 100 μM. Robustadial A showed significant synergistic effects with the anticancer drug etoposide in four human cancer cell lines, non-small cell lung cancer cell line (A549), prostate cancer cell line (DU145), breast cancer cell line (MCF-7), colorectal adenocarcinoma cell line (HCT-116), and chicken lymphoma cell line (DT40), and chicken lymphoma cell line complementation with human TDP2 (DT40 hTDP2) with combination index values ranging from 0.21 to 0.74. This work will facilitate future efforts for the development of robustadial A-based TDP2 selective inhibitors.

Excision repair of topoisomerase DNA-protein crosslinks (TOP-DPC)

Topoisomerases are essential enzymes solving DNA topological problems such as supercoils, knots and catenanes that arise from replication, transcription, chromatin remodeling and other nucleic acid metabolic processes. They are also the targets of widely used anticancer drugs (e.g. topotecan, irinotecan, enhertu, etoposide, doxorubicin, mitoxantrone) and fluoroquinolone antibiotics (e.g. ciprofloxacin and levofloxacin). Topoisomerases manipulate DNA topology by cleaving one DNA strand (TOP1 and TOP3 enzymes) or both in concert (TOP2 enzymes) through the formation of transient enzyme-DNA cleavage complexes (TOPcc) with phosphotyrosyl linkages between DNA ends and the catalytic tyrosyl residue of the enzymes. Failure in the self-resealing of TOPcc results in persistent TOPcc (which we refer it to as topoisomerase DNA-protein crosslinks (TOP-DPC)) that threaten genome integrity and lead to cancers and neurodegenerative diseases. The cell prevents the accumulation of topoisomerase-mediated DNA damage by excising TOP-DPC and ligating the associated breaks using multiple pathways conserved in eukaryotes. Tyrosyl-DNA phosphodiesterases (TDP1 and TDP2) cleave the tyrosyl-DNA bonds whereas structure-specific endonucleases such as Mre11 and XPF (Rad1) incise the DNA phosphodiester backbone to remove the TOP-DPC along with the adjacent DNA segment. The proteasome and metalloproteases of the WSS1/Spartan family typify proteolytic repair pathways that debulk TOP-DPC to make the peptide-DNA bonds accessible to the TDPs and endonucleases. The purpose of this review is to summarize our current understanding of how the cell excises TOP-DPC and why, when and where the cell recruits one specific mechanism for repairing topoisomerase-mediated DNA damage, acquiring resistance to therapeutic topoisomerase inhibitors and avoiding genomic instability, cancers and neurodegenerative diseases.

TDP2 negatively regulates axon regeneration by inducing SUMOylation of an Ets transcription factor

In Caenorhabditis elegans, the JNK MAP kinase (MAPK) pathway is important for axon regeneration. The JNK pathway is activated by a signaling cascade consisting of the growth factor SVH-1 and its receptor tyrosine kinase SVH-2. Expression of the svh-2 gene is induced by axonal injury in a process involving the transcription factors ETS-4 and CEBP-1. Here, we find that svh-14/mxl-1, a gene encoding a Max-like transcription factor, is required for activation of svh-2 expression in response to axonal injury. We show that MXL-1 binds to and inhibits the function of TDPT-1, a C. elegans homolog of mammalian tyrosyl-DNA phosphodiesterase 2 [TDP2; also called Ets1-associated protein II (EAPII)]. Deletion of tdpt-1 suppresses the mxl-1 defect, but not the ets-4 defect, in axon regeneration. TDPT-1 induces SUMOylation of ETS-4, which inhibits ETS-4 transcriptional activity, and MXL-1 counteracts this effect. Thus, TDPT-1 interacts with two different transcription factors in axon regeneration.

Mammalian Tyrosyl-DNA Phosphodiesterases in the Context of Mitochondrial DNA Repair

Mammalian mitochondria contain four topoisomerases encoded in the nuclear genome: TOP1MT, TOP2α, TOP2β, and TOP3α. They also contain the two known tyrosyl-DNA phosphodiesterases (TDPs): TDP1 and TDP2, including a specific TDP2^S isoform. Both TDP1 and TDP2 excise abortive topoisomerase cleavage complexes (TOPccs), yet their molecular structures and mechanisms are different. TDP1 is present across eukaryotes, from yeasts to humans and belongs to the phospholipase D family. It functions without a metal cofactor and has a broad activity range, as it also serves to cleanse blocking 3′-DNA ends bearing phosphoglycolate, deoxyribose phosphate, nucleoside, nucleoside analogs (zidovudine), abasic moieties, and with a lower efficiency, TOP2ccs. Found in higher vertebrates, TDP2 is absent in yeast where TDP1 appears to perform its functions. TDP2 belongs to the exonuclease/endonuclease/phosphodiesterase family and requires magnesium as a cofactor to excise TOP2ccs, and it also excises TOP1ccs, albeit with a lower efficiency. Here, we review TDP1 and TDP2 in the context of mitochondrial DNA repair and discuss potential new research areas centered on the mitochondrial TDPs.

Effect of TDP2 on the Level of TOP2-DNA Complexes and SUMOylated TOP2-DNA Complexes

DNA topoisomerase II (TOP2) activity involves a normally transient double-strand break intermediate in which the enzyme is coupled to DNA via a 5′-phosphotyrosyl bond. However, etoposide and other topoisomerase drugs poison the enzyme by stabilising this enzyme-bridged break, resulting in the accumulation of TOP2-DNA covalent complexes with cytotoxic consequences. The phosphotyrosyl diesterase TDP2 appears to be required for efficient repair of this unusual type of DNA damage and can remove 5′-tyrosine adducts from a double-stranded oligonucleotide substrate. Here, we adapt the trapped in agarose DNA immunostaining (TARDIS) assay to investigate the role of TDP2 in the removal of TOP2-DNA complexes in vitro and in cells. We report that TDP2 alone does not remove TOP2-DNA complexes from genomic DNA in vitro and that depletion of TDP2 in cells does not slow the removal of TOP2-DNA complexes. Thus, if TDP2 is involved in repairing TOP2 adducts, there must be one or more prior steps in which the protein-DNA complex is processed before TDP2 removes the remaining 5′ tyrosine DNA adducts. While this is partly achieved through the degradation of TOP2 adducts by the proteasome, a proteasome-independent mechanism has also been described involving the SUMOylation of TOP2 by the ZATT E3 SUMO ligase. The TARDIS assay was also adapted to measure the effect of TDP2 knockdown on levels of SUMOylated TOP2-DNA complexes, which together with levels of double strand breaks were unaffected in K562 cells following etoposide exposure and proteasomal inhibition.

New fluorescence-based high-throughput screening assay for small molecule inhibitors of tyrosyl-DNA phosphodiesterase 2 (TDP2)

Tyrosyl-DNA phosphodiesterase 2 (TDP2) repairs topoisomerase II (TOP2) mediated DNA damages and causes resistance to TOP2-targeted cancer therapy. Inhibiting TDP2 could sensitize cancer cells toward TOP2 inhibitors. However, potent TDP2 inhibitors with favorable physicochemical properties are not yet reported. Therefore, there is a need to search for novel molecular scaffolds capable of inhibiting TDP2. We report herein a new simple, robust, homogenous mix-and-read fluorescence biochemical assay based using humanized zebrafish TDP2 (14M_zTDP2), which provides biochemical and molecular structure basis for TDP2 inhibitor discovery. The assay was validated by screening a preselected library of 1600 compounds (Z' ≥ 0.72) in a 384-well format, and by running in parallel gel-based assays with fluorescent DNA substrates. This library was curated via virtual high throughput screening (vHTS) of 460,000 compounds from Chembridge Library, using the crystal structure of the novel surrogate protein 14M_zTDP2. From this primary screening, we selected the best 32 compounds (2% of the library) to further assess their TDP2 inhibition potential, leading to the IC₅₀ determination of 10 compounds. Based on the dose-response curve profile, pan-assay interference compounds (PAINS) structure identification, physicochemical properties and efficiency parameters, two hit compounds, 11a and 19a, were tested using a novel secondary fluorescence gel-based assay. Preliminary structure-activity relationship (SAR) studies identified guanidine derivative 12a as an improved hit with a 6.4-fold increase in potency over the original HTS hit 11a. This study highlights the importance of the development of combination approaches (biochemistry, crystallography and high throughput screening) for the discovery of TDP2 inhibitors.

ERK3 regulates TDP2-mediated DNA damage response and chemoresistance in lung cancer cells

Posttranslational modifications (PTMs), such as phosphorylation and ubiquitination, play critical regulatory roles in the assembly of DNA damage response proteins on the DNA damage site and their activities in DNA damage repair. Tyrosyl DNA phosphodiesterase 2 (TDP2) repairs Topoisomerase 2 (Top2)-linked DNA damage, thereby protecting cancer cells against Top2 inhibitors-induced growth inhibition and cell death. The regulation of TDP2 activity by post-translational modifications in DNA repair, however, remains unclear. In the current study, we have found that ERK3, an atypical MAPK, phosphorylates TDP2 at S60 and regulates TDP2's phosphodiesterase activity, thereby cooperatively protecting lung cancer cells against Top2 inhibitors-induced DNA damage and growth inhibition. As such, our study revealed a post-translational regulation of TDP2 activity and discovered a new role of ERK3 in increasing cancer cells’ DNA damage response and chemoresistance to Top2 inhibitors.

Novel TDP2-ubiquitin interactions and their importance for the repair of topoisomerase II-mediated DNA damage

Tyrosyl DNA phosphodiesterase 2 (TDP2) is a multifunctional protein implicated in DNA repair, signal transduction and transcriptional regulation. In its DNA repair role, TDP2 safeguards genome integrity by hydrolyzing 5′-tyrosyl DNA adducts formed by abortive topoisomerase II (Top2) cleavage complexes to allow error-free repair of DNA double-strand breaks, thereby conferring cellular resistance against Top2 poisons. TDP2 consists of a C-terminal catalytic domain responsible for its phosphodiesterase activity, and a functionally uncharacterized N-terminal region. Here, we demonstrate that this N-terminal region contains a ubiquitin (Ub)-associated (UBA) domain capable of binding multiple forms of Ub with distinct modes of interactions and preference for either K48- or K63-linked polyUbs over monoUb. The structure of TDP2 UBA bound to monoUb shows a canonical mode of UBA-Ub interaction. However, the absence of the highly conserved MGF motif and the presence of a fourth α-helix make TDP2 UBA distinct from other known UBAs. Mutations in the TDP2 UBA-Ub binding interface do not affect nuclear import of TDP2, but severely compromise its ability to repair Top2-mediated DNA damage, thus establishing the importance of the TDP2 UBA–Ub interaction in DNA repair. The differential binding to multiple Ub forms could be important for responding to DNA damage signals under different contexts or to support the multi-functionality of TDP2.

Deazaflavin Inhibitors of Tyrosyl-DNA Phosphodiesterase 2 (TDP2) Specific for the Human Enzyme and Active against Cellular TDP2

Tyrosyl-DNA phosphodiesterase 2 repairs irreversible topoisomerase II-mediated cleavage complexes generated by anticancer topoisomerase-targeted drugs and processes replication intermediates for picornaviruses (VPg unlinkase) and hepatitis B virus. There is currently no TDP2 inhibitor in clinical development. Here, we report a series of deazaflavin derivatives that selectively inhibit the human TDP2 enzyme in a competitive manner both with recombinant and native TDP2. We show that mouse, fish, and C. elegans TDP2 enzymes are highly resistant to the drugs and that key protein residues are responsible for drug resistance. Among them, human residues L313 and T296 confer high resistance when mutated to their mouse counterparts. Moreover, deazaflavin derivatives show potent synergy in combination with the topoisomerase II inhibitor etoposide in human prostate cancer DU145 cells and TDP2-dependent synergy in TK6 human lymphoblast and avian DT40 cells. Deazaflavin derivatives represent the first suitable platform for the development of potent and selective TDP2 inhibitors.

Mode of action of DNA-competitive small molecule inhibitors of tyrosyl DNA phosphodiesterase 2

Tyrosyl-DNA phosphodiesterase 2 (TDP2) is a 5'-tyrosyl DNA phosphodiesterase important for the repair of DNA adducts generated by non-productive (abortive) activity of topoisomerase II (TOP2). TDP2 facilitates therapeutic resistance to topoisomerase poisons, which are widely used in the treatment of a range of cancer types. Consequently, TDP2 is an interesting target for the development of small molecule inhibitors that could restore sensitivity to topoisomerase-directed therapies. Previous studies identified a class of deazaflavin-based molecules that showed inhibitory activity against TDP2 at therapeutically useful concentrations, but their mode of action was uncertain. We have confirmed that the deazaflavin series inhibits TDP2 enzyme activity in a fluorescence-based assay, suitable for high-throughput screen (HTS)-screening. We have gone on to determine crystal structures of these compounds bound to a 'humanized' form of murine TDP2. The structures reveal their novel mode of action as competitive ligands for the binding site of an incoming DNA substrate, and point the way to generating novel and potent inhibitors of TDP2.

Divergent Requirement for a DNA Repair Enzyme during Enterovirus Infections

Viruses of the Enterovirus genus of picornaviruses, including poliovirus, coxsackievirus B3 (CVB3), and human rhinovirus, commandeer the functions of host cell proteins to aid in the replication of their small viral genomic RNAs during infection. One of these host proteins is a cellular DNA repair enzyme known as 5' tyrosyl-DNA phosphodiesterase 2 (TDP2). TDP2 was previously demonstrated to mediate the cleavage of a unique covalent linkage between a viral protein (VPg) and the 5' end of picornavirus RNAs. Although VPg is absent from actively translating poliovirus mRNAs, the removal of VPg is not required for the in vitro translation and replication of the RNA. However, TDP2 appears to be excluded from replication and encapsidation sites during peak times of poliovirus infection of HeLa cells, suggesting a role for TDP2 during the viral replication cycle. Using a mouse embryonic fibroblast cell line lacking TDP2, we found that TDP2 is differentially required among enteroviruses. Our single-cycle viral growth analysis shows that CVB3 replication has a greater dependency on TDP2 than does poliovirus or human rhinovirus replication. During infection, CVB3 protein accumulation is undetectable (by Western blot analysis) in the absence of TDP2, whereas poliovirus protein accumulation is reduced but still detectable. Using an infectious CVB3 RNA with a reporter, CVB3 RNA could still be replicated in the absence of TDP2 following transfection, albeit at reduced levels. Overall, these results indicate that TDP2 potentiates viral replication during enterovirus infections of cultured cells, making TDP2 a potential target for antiviral development for picornavirus infections.

IMPORTANCE

Picornaviruses are one of the most prevalent groups of viruses that infect humans and livestock worldwide. These viruses include the human pathogens belonging to the Enterovirus genus, such as poliovirus, coxsackievirus B3 (CVB3), and human rhinovirus. Diseases caused by enteroviruses pose a major problem for public health and have significant economic impact. Poliovirus can cause paralytic poliomyelitis. CVB3 can cause hand, foot, and mouth disease and myocarditis. Human rhinovirus is the causative agent of the common cold, which has a severe economic impact due to lost productivity and severe health consequences in individuals with respiratory dysfunction, such as asthma. By gaining a better understanding of the enterovirus replication cycle, antiviral drugs against enteroviruses may be developed. Here, we report that the absence of the cellular enzyme TDP2 can significantly decrease viral yields of poliovirus, CVB3, and human rhinovirus, making TDP2 a potential target for an antiviral against enterovirus infections.

PAR2-SMAD3 in microvascular endothelial cells is indispensable for vascular stability via tissue factor signaling

Tissue factor (TF) signaling regulates gene expression and protein synthesis leading to the modulation of cell function. Recently, we have demonstrated in microvascular endothelial cells (mECs) that TF signaling induces activation of ETS1 transcription factor. Because combinatorial control is a characteristic property of ETS family members, involving the interaction between ETS1 and other transcription factors, here we investigate whether additional transcription factors are involved in TF-induced angiogenesis. We show by in vitro and in vivo experiments that in addition to ETS1, SMAD3 contributes to tube-like stabilization induced by TF in mECs. Whereas the ability of TF-overexpressing cells to induce gene expression through ETS1 is dependent on AKT signaling, SMAD3 induces ETS1 by an alternative AKT-independent pathway. Moreover, while TF-AKT-ETS1 pathway to induce CCL2 is PAR2-independent, PAR2 is required for TF-SMAD3-induced CCL2 expression. PAR2-dependent activation of SMAD3 is mediated by PKC phosphorylation. In addition, disruption of SMAD3 expression in mECs reduces ERK1/2 phosphorylation and decreases target gene promoter activity. In conclusion, in mECs TF-induced angiogenesis seems to be the result of two signaling pathways: TF-induced microvessel formation is regulated through β1 integrin-AKT-ETS1; and TF-induced microvessel stabilization is regulated via PAR2-SMAD3 that is indispensable for the maintenance of vascular integrity.

The role of the transcription factor Ets1 in carcinoma

Ets1 belongs to the large family of the ETS domain family of transcription factors and is involved in cancer progression. In most carcinomas, Ets1 expression is linked to poor survival. In breast cancer, Ets1 is primarily expressed in the triple-negative subtype, which is associated with unfavorable prognosis. Ets1 contributes to the acquisition of cancer cell invasiveness, to EMT (epithelial-to-mesenchymal transition), to the development of drug resistance and neo-angiogenesis. The aim of this review is to summarize the current knowledge on the functions of Ets1 in carcinoma progression and on the mechanisms that regulate Ets1 activity in cancer.

Structural and functional characterization of a novel molluskan ortholog of TRAF and TNF receptor-associated protein from disk abalone (Haliotis discus discus)

Immune signaling cascades have an indispensable role in the host defense of almost all the organisms. Tumor necrosis factor (TNF) signaling is considered as a prominent signaling pathway in vertebrate as well as invertebrate species. Within the signaling cascade, TNF receptor-associated factor (TRAF) and TNF receptor-associated protein (TTRAP) has been shown to have a crucial role in the modulation of immune signaling in animals. Here, we attempted to characterize a novel molluskan ortholog of TTRAP (AbTTRAP) from disk abalone (Haliotis discus discus) and analyzed its expression levels under pathogenic stress. The complete coding sequence of AbTTRAP consisted of 1071 nucleotides, coding for a 357 amino acid peptide, with a predicted molecular mass of 40 kDa. According to our in-silico analysis, AbTTRAP resembled the typical TTRAP domain architecture, including a 5'-tyrosyl DNA phosphodiesterase domain. Moreover, phylogenetic analysis revealed its common ancestral invertebrate origin, where AbTTRAP was clustered with molluskan counterparts. Quantitative real time PCR showed universally distributed expression of AbTTRAP in selected tissues of abalone, from which more prominent expression was detected in hemocytes. Upon stimulation with two pathogen-derived mitogens, lipopolysaccharide (LPS) and polyinosinic:polycytidylic acid (poly I:C), transcript levels of AbTTRAP in hemocytes and gill tissues were differentially modulated with time. In addition, the recombinant protein of AbTTRAP exhibited prominent endonuclease activity against abalone genomic DNA, which was enhanced by the presence of Mg(2+) in the medium. Collectively, these results reinforce the existence of the TNF signaling cascade in mollusks like disk abalone, further implicating the putative regulatory behavior of TTRAP in invertebrate host pathology.

Tyrosyl-DNA-phosphodiesterases (TDP1 and TDP2)

TDP1 and TDP2 were discovered and named based on the fact they process 3'- and 5'-DNA ends by excising irreversible protein tyrosyl-DNA complexes involving topoisomerases I and II, respectively. Yet, both enzymes have an extended spectrum of activities. TDP1 not only excises trapped topoisomerases I (Top1 in the nucleus and Top1mt in mitochondria), but also repairs oxidative damage-induced 3'-phosphoglycolates and alkylation damage-induced DNA breaks, and excises chain terminating anticancer and antiviral nucleosides in the nucleus and mitochondria. The repair function of TDP2 is devoted to the excision of topoisomerase II- and potentially topoisomerases III-DNA adducts. TDP2 is also essential for the life cycle of picornaviruses (important human and bovine pathogens) as it unlinks VPg proteins from the 5'-end of the viral RNA genome. Moreover, TDP2 has been involved in signal transduction (under the former names of TTRAP or EAPII). The DNA repair partners of TDP1 include PARP1, XRCC1, ligase III and PNKP from the base excision repair (BER) pathway. By contrast, TDP2 repair functions are coordinated with Ku and ligase IV in the non-homologous end joining pathway (NHEJ). This article summarizes and compares the biochemistry, functions, and post-translational regulation of TDP1 and TDP2, as well as the relevance of TDP1 and TDP2 as determinants of response to anticancer agents. We discuss the rationale for developing TDP inhibitors for combinations with topoisomerase inhibitors (topotecan, irinotecan, doxorubicin, etoposide, mitoxantrone) and DNA damaging agents (temozolomide, bleomycin, cytarabine, and ionizing radiation), and as novel antiviral agents.

Understanding the role of ETS-mediated gene regulation in complex biological processes

Ets factors are members of one of the largest families of evolutionarily conserved transcription factors, regulating critical functions in normal cell homeostasis, which when perturbed contribute to tumor progression. The well-documented alterations in ETS factor expression and function during cancer progression result in pleiotropic effects manifested by the downstream effect on their target genes. Multiple ETS factors bind to the same regulatory sites present on target genes, suggesting redundant or competitive functions. The anti- and prometastatic signatures obtained by examining specific ETS regulatory networks will significantly improve our ability to accurately predict tumor progression and advance our understanding of gene regulation in cancer. Coordination of multiple ETS gene functions also mediates interactions between tumor and stromal cells and thus contributes to the cancer phenotype. As such, these new insights may provide a novel view of the ETS gene family as well as a focal point for studying the complex biological control involved in tumor progression. One of the goals of molecular biology is to elucidate the mechanisms that contribute to the development and progression of cancer. Such an understanding of the molecular basis of cancer will provide new possibilities for: (1) earlier detection, as well as better diagnosis and staging of disease; (2) detection of minimal residual disease recurrences and evaluation of response to therapy; (3) prevention; and (4) novel treatment strategies. Increased understanding of ETS-regulated biological pathways will directly impact these areas.

Overexpression of TTRAP inhibits cell growth and induces apoptosis in osteosarcoma cells

TTRAP is a multi-functional protein that is involved in multiple aspects of cellular functions including cell proliferation, apoptosis and the repair of DNA damage. Here, we demonstrated that the lentivirus-mediated overexpression of TTRAP significantly inhibited cell growth and induced apoptosis in osteosarcoma cells. The ectopic TTRAP suppressed the growth and colony formation capacity of two osteosarcoma cell lines, U2OS and Saos-2. Cell apoptosis was induced in U2OS cells and the cell cycle was arrested at G2/M phase in Saos-2 cells. Exogenous expression of TTRAP in serum-starved U2OS and Saos-2 cells induced an increase in caspase-3/-7 activity and a decrease in cyclin B1 expression. In comparison with wild-type TTRAP, mutations in the 5'-tyrosyl-DNA phosphodiesterase activity of TTRAP, in particular TTRAP^E152A, showed decreased inhibitory activity on cell growth. These results may aid in clarifying the physiological functions of TTRAP, especially its roles in the regulation of cell growth and tumorigenesis. [BMB Reports 2013; 46(2): 113-118]

TDP2-dependent non-homologous end-joining protects against topoisomerase II-induced DNA breaks and genome instability in cells and in vivo

Anticancer topoisomerase "poisons" exploit the break-and-rejoining mechanism of topoisomerase II (TOP2) to generate TOP2-linked DNA double-strand breaks (DSBs). This characteristic underlies the clinical efficacy of TOP2 poisons, but is also implicated in chromosomal translocations and genome instability associated with secondary, treatment-related, haematological malignancy. Despite this relevance for cancer therapy, the mechanistic aspects governing repair of TOP2-induced DSBs and the physiological consequences that absent or aberrant repair can have are still poorly understood. To address these deficits, we employed cells and mice lacking tyrosyl DNA phosphodiesterase 2 (TDP2), an enzyme that hydrolyses 5'-phosphotyrosyl bonds at TOP2-associated DSBs, and studied their response to TOP2 poisons. Our results demonstrate that TDP2 functions in non-homologous end-joining (NHEJ) and liberates DSB termini that are competent for ligation. Moreover, we show that the absence of TDP2 in cells impairs not only the capacity to repair TOP2-induced DSBs but also the accuracy of the process, thus compromising genome integrity. Most importantly, we find this TDP2-dependent NHEJ mechanism to be physiologically relevant, as Tdp2-deleted mice are sensitive to TOP2-induced damage, displaying marked lymphoid toxicity, severe intestinal damage, and increased genome instability in the bone marrow. Collectively, our data reveal TDP2-mediated error-free NHEJ as an efficient and accurate mechanism to repair TOP2-induced DSBs. Given the widespread use of TOP2 poisons in cancer chemotherapy, this raises the possibility of TDP2 being an important etiological factor in the response of tumours to this type of agent and in the development of treatment-related malignancy.

Structural basis for recognition of 5'-phosphotyrosine adducts by Tdp2

The DNA-repair enzyme Tdp2 resolves 5'-phosphotyrosyl DNA adducts and mediates resistance to anticancer drugs that target covalent topoisomerase-DNA complexes. Tdp2 also participates in key signaling pathways during development and tumorigenesis and cleaves a protein-RNA linkage during picornavirus replication. The crystal structure of zebrafish Tdp2 bound to DNA reveals a deep, narrow basic groove that selectively accommodates the 5' end of single-stranded DNA in a stretched conformation. The crystal structure of the full-length Caenorhabditis elegans Tdp2 shows that this groove can also accommodate an acidic peptide stretch in vitro, with glutamate and aspartate side chains occupying the DNA backbone phosphate-binding sites. This extensive molecular mimicry suggests a potential mechanism for autoregulation and interaction of Tdp2 with phosphorylated proteins in signaling. Our study provides a framework to interrogate functions of Tdp2 and develop inhibitors for chemotherapeutic and antiviral applications.

An RNA virus hijacks an incognito function of a DNA repair enzyme

A previously described mammalian cell activity, called VPg unlinkase, specifically cleaves a unique protein-RNA covalent linkage generated during the viral genomic RNA replication steps of a picornavirus infection. For over three decades, the identity of this cellular activity and its normal role in the uninfected cell had remained elusive. Here we report the purification and identification of VPg unlinkase as the DNA repair enzyme, 5'-tyrosyl-DNA phosphodiesterase-2 (TDP2). Our data show that VPg unlinkase activity in different mammalian cell lines correlates with their differential expression of TDP2. Furthermore, we show that recombinant TDP2 can cleave the protein-RNA linkage generated by different picornaviruses without impairing the integrity of viral RNA. Our results reveal a unique RNA repair-like function for TDP2 and suggest an unusual role in host-pathogen interactions for this cellular enzyme. On the basis of the identification of TDP2 as a potential antiviral target, our findings may lead to the development of universal therapeutics to treat the millions of individuals afflicted annually with diseases caused by picornaviruses, including myocarditis, aseptic meningitis, encephalitis, hepatitis, and the common cold.

Biochemical characterization of human tyrosyl-DNA phosphodiesterase 2 (TDP2/TTRAP): a Mg(2+)/Mn(2+)-dependent phosphodiesterase specific for the repair of topoisomerase cleavage complexes

TDP2 is a multifunctional enzyme previously known for its role in signal transduction as TRAF and TNF receptor-associated protein (TTRAP) and ETS1-associated protein 2 (EAPII). The gene has recently been renamed TDP2 because it plays a critical role for the repair of topoisomerase II cleavage complexes (Top2cc) and encodes an enzyme that hydrolyzes 5'-tyrosine-DNA adducts that mimic abortive Top2cc. Here we further elucidate the DNA-processing activities of human recombinant TDP2 and its biochemical characteristics. The preferred substrate for TDP2 is single-stranded DNA or duplex DNA with a four-base pair overhang, which is consistent with the known structure of Top2cc or Top3cc. The k(cat)/K(m) of TDP1 and TDP2 was determined. It was found to be 4 × 10(5) s(-1)M(-1) for TDP2 using single-stranded 5'-tyrosyl-DNA. The processing of substrates as short as five nucleotides long suggests that TDP2 can directly bind DNA ends. 5'-Phosphodiesterase activity requires a phosphotyrosyl linkage and tolerates an extended group attached to the tyrosine. TDP2 requires Mg(2+) or Mn(2+) for efficient catalysis but is weakly active with Ca(2+) or Zn(2+). Titration with Ca(2+) demonstrates a two-metal binding site in TDP2. Sequence alignment suggests that TDP2 contains four conserved catalytic motifs shared by Mg(2+)-dependent endonucleases, such as APE1. Substitutions at each of the four catalytic motifs identified key residues Asn-120, Glu-152, Asp-262, and His-351, whose mutation to alanine significantly reduced or completely abolished enzymatic activity. Our study characterizes the substrate specificity and kinetic parameters of TDP2. In addition, a two-metal catalytic mechanism is proposed.

Mutant p53 cooperates with ETS2 to promote etoposide resistance

Mutant p53 (mtp53) promotes chemotherapy resistance through multiple mechanisms, including disabling proapoptotic proteins and regulating gene expression. Comparison of genome wide analysis of mtp53 binding revealed that the ETS-binding site motif (EBS) is prevalent within predicted mtp53-binding sites. We demonstrate that mtp53 regulates gene expression through EBS in promoters and that ETS2 mediates the interaction with this motif. Importantly, we identified TDP2, a 5'-tyrosyl DNA phosphodiesterase involved in the repair of DNA damage caused by etoposide, as a transcriptional target of mtp53. We demonstrate that suppression of TDP2 sensitizes mtp53-expressing cells to etoposide and that mtp53 and TDP2 are frequently overexpressed in human lung cancer; thus, our analysis identifies a potentially "druggable" component of mtp53's gain-of-function activity.

Ets-1 is essential for connective tissue growth factor (CTGF/CCN2) induction by TGF-β1 in osteoblasts

Background

Ets-1 controls osteoblast differentiation and bone development; however, its downstream mechanism of action in osteoblasts remains largely undetermined. CCN2 acts as an anabolic growth factor to regulate osteoblast differentiation and function. CCN2 is induced by TGF-β1 and acts as a mediator of TGF-β1 induced matrix production in osteoblasts; however, the molecular mechanisms that control CCN2 induction are poorly understood. In this study, we investigated the role of Ets-1 for CCN2 induction by TGF-β1 in primary osteoblasts.

Results

We demonstrated that Ets-1 is expressed and induced by TGF-β1 treatment in osteoblasts, and that Ets-1 over-expression induces CCN2 protein expression and promoter activity at a level similar to TGF-β1 treatment alone. Additionally, we found that simultaneous Ets-1 over-expression and TGF-β1 treatment synergize to enhance CCN2 induction, and that CCN2 induction by TGF-β1 treatment was impaired using Ets-1 siRNA, demonstrating the requirement of Ets-1 for CCN2 induction by TGF-β1. Site-directed mutagenesis of eight putative Ets-1 motifs (EBE) in the CCN2 promoter demonstrated that specific EBE sites are required for CCN2 induction, and that mutation of EBE sites in closer proximity to TRE or SBE (two sites previously shown to regulate CCN2 induction by TGF-β1) had a greater effect on CCN2 induction, suggesting potential synergetic interaction among these sites for CCN2 induction. In addition, mutation of EBE sites prevented protein complex binding, and this protein complex formation was also inhibited by addition of Ets-1 antibody or Smad 3 antibody, demonstrating that protein binding to EBE motifs as a result of TGF-β1 treatment require synergy between Ets-1 and Smad 3.

Conclusions

This study demonstrates that Ets-1 is an essential downstream signaling component for CCN2 induction by TGF-β1 in osteoblasts, and that specific EBE sites in the CCN2 promoter are required for CCN2 promoter transactivation in osteoblasts.

Parkinson's disease DJ-1 L166P alters rRNA biogenesis by exclusion of TTRAP from the nucleolus and sequestration into cytoplasmic aggregates via TRAF6

Mutations in PARK7/DJ-1 gene are associated to autosomal recessive early onset forms of Parkinson's disease (PD). Although large gene deletions have been linked to a loss-of-function phenotype, the pathogenic mechanism of missense mutations is less clear. The L166P mutation causes misfolding of DJ-1 protein and its degradation. L166P protein may also accumulate into insoluble cytoplasmic aggregates with a mechanism facilitated by the E3 ligase TNF receptor associated factor 6 (TRAF6). Upon proteasome impairment L166P activates the JNK/p38 MAPK apoptotic pathway by its interaction with TRAF and TNF Receptor Associated Protein (TTRAP). When proteasome activity is blocked in the presence of wild-type DJ-1, TTRAP forms aggregates that are localized to the cytoplasm or associated to nucleolar cavities, where it is required for a correct rRNA biogenesis. In this study we show that in post-mortem brains of sporadic PD patients TTRAP is associated to the nucleolus and to Lewy Bodies, cytoplasmic aggregates considered the hallmark of the disease. In SH-SY5Y neuroblastoma cells, misfolded mutant DJ-1 L166P alters rRNA biogenesis inhibiting TTRAP localization to the nucleolus and enhancing its recruitment into cytoplasmic aggregates with a mechanism that depends in part on TRAF6 activity. This work suggests that TTRAP plays a role in the molecular mechanisms of both sporadic and familial PD. Furthermore, it unveils the existence of an interplay between cytoplasmic and nucleolar aggregates that impacts rRNA biogenesis and involves TRAF6.

Epidermal growth factor induces tumour marker AKR1B10 expression through activator protein-1 signalling in hepatocellular carcinoma cells

AKR1B10 (aldo-keto reductase 1B10) is overexpressed in liver and lung cancer, and plays a critical role in tumour development and progression through promoting lipogenesis and eliminating cytotoxic carbonyls. AKR1B10 is a secretory protein and potential tumour marker; however, little is known about the regulatory mechanism of AKR1B10 expression. The present study showed that AKR1B10 is induced by mitogen EGF (epidermal growth factor) and insulin through the AP-1 (activator protein-1) signalling pathway. In human HCC (hepatocellular carcinoma) cells (HepG2 and Hep3B), EGF (50 ng/ml) and insulin (10 nM) stimulated endogenous AKR1B10 expression and promoter activity. In the AKR1B10 promoter, a putative AP-1 element was found at bp -222 to -212. Deletion or mutation of this AP-1 element abrogated the basal promoter activity and response to EGF and AP-1 proteins. This AP-1 element bound to nuclear proteins extracted from HepG2 cells, and this binding was stimulated by EGF and insulin in a dose-dependent manner. Chromatin immunoprecipitation showed that the AP-1 proteins c-Fos and c-Jun were the predominant factors bound to the AP-1 consensus sequence, followed by JunD and then JunB. The same order was followed in the stimulation of endogenous AKR1B10 expression by AP-1 proteins. Furthermore, c-Fos shRNA (short hairpin RNA) and AP-1 inhibitors/antagonists (U0126 and Tanshinone IIA) inhibited endogenous AKR1B10 expression and promoter activity in HepG2 cells cultured in vitro or inoculated subcutaneously in nude mice. U0126 also inhibited AKR1B10 expression induced by EGF. Taken together, these results suggest that AKR1B10 is up-regulated by EGF and insulin through AP-1 mitogenic signalling and may be implicated in hepatocarcinogenesis.

Few Smad proteins and many Smad-interacting proteins yield multiple functions and action modes in TGFβ/BMP signaling in vivo

Signaling by the many ligands of the TGFβ family strongly converges towards only five receptor-activated, intracellular Smad proteins, which fall into two classes i.e. Smad2/3 and Smad1/5/8, respectively. These Smads bind to a surprisingly high number of Smad-interacting proteins (SIPs), many of which are transcription factors (TFs) that co-operate in Smad-controlled target gene transcription in a cell type and context specific manner. A combination of functional analyses in vivo as well as in cell cultures and biochemical studies has revealed the enormous versatility of the Smad proteins. Smads and their SIPs regulate diverse molecular and cellular processes and are also directly relevant to development and disease. In this survey, we selected appropriate examples on the BMP-Smads, with emphasis on Smad1 and Smad5, and on a number of SIPs, i.e. the CPSF subunit Smicl, Ttrap (Tdp2) and Sip1 (Zeb2, Zfhx1b) from our own research carried out in three different vertebrate models.

Altered levels of Ets-1 transcription factor and matrix metalloproteinases in melanocytes from patients with vitiligo

BACKGROUND

Vitiligo is characterized by the loss of functional melanocytes from the epidermis. Repigmentation in vitiligo is initiated by activation, proliferation and migration of melanoblasts from the outer root sheath of hair follicles, or melanocytes from the border area of vitiligo lesions, into the depigmented epidermis. Cell migration plays a crucial role during repigmentation in vitiligo.

OBJECTIVES

To investigate the role of matrix metalloproteinases (MMPs) and their transcription factor Ets-1 in vitiligo.

METHODS

Skin biopsies were taken from 15 patients with vitiligo and six controls to culture melanocytes from clinically active perilesional and normal skin. Expression of MMP-1, MMP-2, MMP-9 and Ets-1 was examined by reverse transcriptase-polymerase chain reaction analysis. Expression of Ets-1 was also confirmed with Western blot analysis. Activity of MMP-2 and MMP-9 was assessed using gelatin zymography.

RESULTS

The activity of MMP-2 and MMP-9 was significantly lower in patients with vitiligo compared with the controls. The expression of MMP-2 and MMP-9 was also significantly lower in patients with vitiligo. There was no expression of Ets-1 transcription factor at either the transcriptional or translational level in melanocytes cultured from patients with vitiligo.

CONCLUSION

The absence of a basal level of expression of Ets-1 significantly decreases the expression and activity of MMP-2 and MMP-9. Significant decreases in MMP-2 and MMP-9 activity could possibly reduce the migration of melanocyte precursors (melanoblasts) from the outer root sheath of hair follicles or migration of melanocytes from the border of vitiligo lesions into clinically depigmented epidermis which is crucial to the repigmentation of vitiliginous skin.

Pleiotropic functions of EAPII/TTRAP/TDP2: cancer development, chemoresistance and beyond

EAPII (also called TTRAP, TDP2), a protein identified a decade ago, has recently been shown to function as an oncogenic factor. This protein was also proven to be the first 5'- tyrosyl-DNA phosphodiesterase. EAPII has been demonstrated to have promiscuous protein associations, broad responsiveness to various extracellular signals, and pleiotropic functions in the development of human diseases including cancer and neurodegenerative disease. Emerging data suggest that EAPII is a multi-functional protein: EAPII repairs enzyme (topoisomerase)-mediated DNA damage by removing phosphotyrosine from DNA adducts; EAPII is involved in multiple signal transduction pathways such as TNF-TNFR, TGFβ and MAPK, and EAPII is responsive to immune defense, inflammatory response, virus infection and DNA toxins (chemo or radiation therapy). This review focuses on the current understanding of EAPII biology and its potential relations to many aspects of cancer development, including chromosome instability, tumorigenesis, tumor metastasis and chemoresistance, suggesting it as a potential target for intervention in cancer and other human diseases.

TTRAP is a novel component of the non-canonical TRAF6-TAK1 TGF-β signaling pathway

Transforming growth factor-β (TGF-β) principally relays its effects through the Smad pathway however, accumulating evidence indicate that alternative signaling routes are also employed by this pleiotropic cytokine. For instance recently, we have demonstrated that ligand occupied TGF-β receptors can directly trigger the TRAF6-TAK1 signaling module, resulting in MAP kinase activation. Here we report identification of the adaptor molecule TTRAP as a novel component of this non-canonical TGF-β pathway. We show that the protein associates with TGF-β receptors and components of the TRAF6-TAK1 signaling module, resulting in differential regulation of TGF-β activated p38 and NF-κB responses. Modulation of cellular TTRAP level affects cell viability in the presence of TGF-β, suggesting that the protein is an important component of the TGF-β induced apoptotic process.

The PML nuclear bodies-associated protein TTRAP regulates ribosome biogenesis in nucleolar cavities upon proteasome inhibition

TRAF and TNF receptor-associated protein (TTRAP) is a multifunctional protein that can act in the nucleus as a 5'-tyrosyl DNA phosphodiesterase and in the cytoplasm as a regulator of cell signaling. In this paper we show that in response to proteasome inhibition TTRAP accumulates in nucleolar cavities in a promyelocytic leukemia protein-dependent manner. In the nucleolus, TTRAP contributes to control levels of ribosomal RNA precursor and processing intermediates, and this phenotype is independent from its 5'-tyrosyl DNA phosphodiesterase activity. Our findings suggest a previously unidentified function for TTRAP and nucleolar cavities in ribosome biogenesis under stress.

Oncogenic role of EAPII in lung cancer development and its activation of the MAPK-ERK pathway

Cancer progression involves multiple complex and interdependent steps, including progressive proliferation, angiogenesis and metastases. The complexity of these processes requires a comprehensive elucidation of the integrated signaling networks for better understanding. EAPII interacts with multiple cancer-related proteins, but its biological significance in cancer development remains unknown. In this report we identified the elevated level of EAPII protein in non-small-cell lung carcinoma (NSCLC) patients and NSCLC cell lines in culture. The oncogenic role of EAPII in lung cancer development was demonstrated using NSCLC cells with genetic manipulations that influence EAPII expression: EAPII overexpression increases proliferation of NSCLC cells with an accelerated transition of cell cycle and facilitates xenograft tumor growth in vivo; EAPII knockdown results in apoptosis of NSCLC cells and reduces xenograft tumor formation. To further explore the mechanism of EAPII's oncogenic role in lung cancer development and to elucidate the potential signaling pathway(s) that EAPII may impact, we employed antibody array to investigate the alternation of the major signaling pathways in NSCLC cells with altered EAPII level. We found that EAPII overexpression significantly activated Raf1 and ERK1/2, but not c-Jun N-terminal kinase and p38 pathways. Consistently, the protein and mRNA levels of MYC and cyclin D1, which are targets of the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK-ERK) pathway, are significantly increased by EAPII overexpression. Taken together, we demonstrated that EAPII is an oncogenic factor and the activation of MAPK-ERK signaling pathway by EAPII may contribute to lung cancer development.

Transcription of the Tollip gene is elevated in intestinal epithelial cells through impaired O-GlcNAcylation-dependent nuclear translocation of the negative regulator Elf-1

Intestinal epithelial cells (IECs) must be tolerant of the large number of commensal bacteria inhabiting the intestinal tract to avoid excessive inflammatory reactions. Toll-interacting protein (Tollip), a negative regulator of Toll-like receptor signaling, is known to be expressed at high levels in IECs, and to thereby contribute to the hyporesponsiveness of IECs to commensals. In this study, we analyzed the underlying mechanisms for elevated transcription of the Tollip gene in IECs using a human IEC line, Caco-2, and a human monocyte line, THP-1, as a control. Elf-1 was identified as a transcription factor that negatively regulates Tollip gene expression. The transcription factor Elf-1 was localized in the nucleus by O-linked N-acetylglucosamine (O-GlcNAc) modification, whereas the unmodified form was detected only in the cytoplasm. Comparison of Caco-2 and THP-1 cells revealed that O-GlcNAc modification of Elf-1 was significantly lower in IECs than in monocytes. Collectively, the results indicate that insufficient O-GlcNAc modification prevents Elf-1-mediated transcriptional repression and thereby upregulates Tollip gene expression in IECs.

TDP2/TTRAP is the major 5'-tyrosyl DNA phosphodiesterase activity in vertebrate cells and is critical for cellular resistance to topoisomerase II-induced DNA damage

Topoisomerase II (Top2) activity involves an intermediate in which the topoisomerase is covalently bound to a DNA double-strand break via a 5′-phosphotyrosyl bond. Although these intermediates are normally transient, they can be stabilized by antitumor agents that act as Top2 “poisons,” resulting in the induction of cytotoxic double-strand breaks, and they are implicated in the formation of site-specific translocations that are commonly associated with cancer. Recently, we revealed that TRAF and TNF receptor-associated protein (TTRAP) is a 5′-tyrosyl DNA phosphodiesterase (5′-TDP) that can cleave 5′-phosphotyrosyl bonds, and we denoted this protein tyrosyl DNA phosphodiesterase-2 (TDP2). Here, we have generated TDP2-deleted DT40 cells, and we show that TDP2 is the major if not the only 5′-TDP activity present in vertebrate cells. We also show that TDP2-deleted DT40 cells are highly sensitive to the anticancer Top2 poison, etoposide, but are not hypersensitive to the Top1 poison camptothecin or the DNA-alkyating agent methyl methanesulfonate. These data identify an important mechanism for resistance to Top2-induced chromosome breakage and raise the possibility that TDP2 is a significant factor in cancer development and treatment.

Methylation matters: binding of Ets-1 to the demethylated Foxp3 gene contributes to the stabilization of Foxp3 expression in regulatory T cells

The forkhead-box protein P3 (Foxp3) is a key transcription factor for the development and suppressive activity of regulatory T cells (Tregs), a T cell subset critically involved in the maintenance of self-tolerance and prevention of over-shooting immune responses. However, the transcriptional regulation of Foxp3 expression remains incompletely understood. We have previously shown that epigenetic modifications in the CpG-rich Treg-specific demethylated region (TSDR) in the Foxp3 locus are associated with stable Foxp3 expression. We now demonstrate that the methylation state of the CpG motifs within the TSDR controls its transcriptional activity rather than a Treg-specific transcription factor network. By systematically mutating every CpG motif within the TSDR, we could identify four CpG motifs, which are critically determining the transcriptional activity of the TSDR and which serve as binding sites for essential transcription factors, such as CREB/ATF and NF-κB, which have previously been shown to bind to this element. The transcription factor Ets-1 was here identified as an additional molecular player that specifically binds to the TSDR in a demethylation-dependent manner in vitro. Disruption of the Ets-1 binding sites within the TSDR drastically reduced its transcriptional enhancer activity. In addition, we found Ets-1 bound to the demethylated TSDR in ex vivo isolated Tregs, but not to the methylated TSDR in conventional CD4(+) T cells. We therefore propose that Ets-1 is part of a larger protein complex, which binds to the TSDR only in its demethylated state, thereby restricting stable Foxp3 expression to the Treg lineage.

Src is a major signaling component for CTGF induction by TGF-beta1 in osteoblasts

Connective tissue growth factor (CTGF/CCN2) is induced by transforming growth factor beta1 (TGF-beta1) where it acts as a downstream mediator of TGF-beta1 induced matrix production in osteoblasts. We have shown the requirement of Src, Erk, and Smad signaling for CTGF induction by TGF-beta1 in osteoblasts; however, the potential interaction among these signaling pathways remains undetermined. In this study we demonstrate that TGF-beta1 activates Src kinase in ROS17/2.8 cells and that treatment with the Src family kinase inhibitor PP2 prevents Src activation and CTGF induction by TGF-beta1. Additionally, inhibiting Src activation prevented Erk activation, Smads 2 and 3 activation and nuclear translocation by TGF-beta1, demonstrating that Src is an essential upstream signaling partner of both Erk and Smads in osteoblasts. MAPKs such as Erk can modulate the Smad pathway directly by mediating the phosphorylation of Smads or indirectly through activation/inactivation of required nuclear co-activators that mediate Smad DNA binding. When we treated cells with the Erk inhibitor, PD98059, it inhibited TGF-beta1-induced CTGF protein expression but had no effect on Src activation, Smad activation or Smad nuclear translocation. However PD98059 impaired transcriptional complex formation on the Smad binding element (SBE) of the CTGF promoter, demonstrating that Erk activation was required for SBE transactivation. These data demonstrate that Src is an essential upstream signaling transducer of Erk and Smad signaling with respect to TGF-beta1 in osteoblasts and that Smads and Erk function independently but are both essential for forming a transcriptionally active complex on the CTGF promoter in osteoblasts.

A human 5'-tyrosyl DNA phosphodiesterase that repairs topoisomerase-mediated DNA damage

Topoisomerases regulate DNA topology and are fundamental to many aspects of chromosome metabolism. Their activity involves the transient cleavage of DNA, which, if it occurs near sites of endogenous DNA damage or in the presence of topoisomerase poisons, can result in abortive topoisomerase-induced DNA strand breaks. These breaks feature covalent linkage of the enzyme to the DNA termini by a 3'- or 5'-phosphotyrosyl bond and are implicated in hereditary human disease, chromosomal instability and cancer, and underlie the clinical efficacy of an important class of anti-tumour poisons. The importance of liberating DNA termini from trapped topoisomerase is illustrated by the progressive neurodegenerative disease observed in individuals containing a mutation in tyrosyl-DNA phosphodiesterase 1 (TDP1), an enzyme that cleaves 3'-phosphotyrosyl bonds. However, a complementary human enzyme that cleaves 5'-phosphotyrosyl bonds has not been reported, despite the effect of DNA double-strand breaks containing such termini on chromosome instability and cancer. Here we identify such an enzyme in human cells and show that this activity efficiently restores 5'-phosphate termini at DNA double-strand breaks in preparation for DNA ligation. This enzyme, TTRAP, is a member of the Mg(2+)/Mn(2+)-dependent family of phosphodiesterases. Cellular depletion of TTRAP results in increased susceptibility and sensitivity to topoisomerase-II-induced DNA double-strand breaks. TTRAP is, to our knowledge, the first human 5'-tyrosyl DNA phosphodiesterase to be identified, and we suggest that this enzyme is denoted tyrosyl DNA phosphodiesterase-2 (TDP2).

PhiC31 integrase interacts with TTRAP and inhibits NFkappaB activation

Phage PhiC31 integrase-mediated gene delivery is believed to be safer than using retroviral vectors since the protein confines its insertion of the target gene to a limited number of sites in mammalian genomes. To evaluate its safety in human cells, it is important to understand the interactions between this integrase and cellular proteins. Here we show that PhiC31 integrase interacts with TTRAP as presented by yeast two-hybrid and co-immunoprecipitation assays. Reducing the expression of endogenous TTRAP can increase the efficiency of PhiC31 integrase-mediated integration. A possible effect of interaction between PhiC31 integrase and TTRAP was highlighted by the fact that PhiC31 integrase inhibited the NFkappaB activation mediated by IL-1 in a dose-dependent manner. Because low dose of PhiC31 integrase can mediate considerable recombination events, we suggest that low dose of PhiC31 integrase be used when this integrase is applied in human cells.

Aggresome-forming TTRAP mediates pro-apoptotic properties of Parkinson's disease-associated DJ-1 missense mutations

Mutations in PARK7 DJ-1 have been associated with autosomal-recessive early-onset Parkinson's disease (PD). This gene encodes for an atypical peroxiredoxin-like peroxidase that may act as a regulator of transcription and a redox-dependent chaperone. Although large gene deletions have been associated with a loss-of-function phenotype, the pathogenic mechanism of several missense mutations is less clear. By performing a yeast two-hybrid screening from a human fetal brain library, we identified TRAF and TNF receptor-associated protein (TTRAP), an ubiquitin-binding domain-containing protein, as a novel DJ-1 interactor, which was able to bind the PD-associated mutations M26I and L166P more strongly than wild type. TTRAP protected neuroblastoma cells from apoptosis induced by proteasome impairment. In these conditions, endogenous TTRAP relocalized to a detergent-insoluble fraction and formed cytoplasmic aggresome-like structures. Interestingly, both DJ-1 mutants blocked the TTRAP protective activity unmasking a c-jun N-terminal kinase (JNK)- and p38-MAPK (mitogen-activated protein kinase)-mediated apoptosis. These results suggest an active role of DJ-1 missense mutants in the control of cell death and position TTRAP as a new player in the arena of neurodegeneration.

TTRAP is a novel PML nuclear bodies-associated protein

PML nuclear body (PML NB) is an important macromolecular nuclear structure that is involved in many essential aspects of cellular function. Tens of proteins have been found in PML NBs, and promyelocytic leukemia protein (PML) has been proven to be essential for the formation of this structure. Here, we showed that TRAF and TNF receptor-associated protein (TTRAP) was a novel PML NBs-associated protein. TTRAP colocalized with three important PML NBs-associated proteins, PML, DAXX and Sp100 in the typical fashion of PML NBs. By yeast mating assay, TTRAP was identified to interact with these PML NBs-associated proteins. The transcription and expression of TTRAP could be induced by IFN-gamma, representing another common feature of PML NBs-associated proteins. These results would not only be important for understanding PML NBs but also be helpful in studying the TTRAP function in the future.

Thirty-kilodalton Tat-interacting protein suppresses tumor metastasis by inhibition of osteopontin transcription in human hepatocellular carcinoma

It has been previously demonstrated that the 30-kDa Tat-interacting protein (TIP30) plays an important role in the suppression of hepatocarcinogenesis by acting as a tumor suppressor. Here we report that TIP30 suppresses metastasis of hepatocellular carcinoma (HCC) through inhibiting the transcription of osteopontin (OPN), a key molecule in the development of tumor metastasis. The expression of TIP30 messenger RNA was reverse to that of OPN messenger RNA in HCC cell lines. Ectopic expression of TIP30 greatly suppressed OPN expression, inhibited invasion of HCC cells through extracellular matrix (ECM) and adhesion with fibronectin in vitro, whereas down-regulation of TIP30 by RNA-mediated interference enhanced OPN expression and promoted metastatic abilities of HCC cells in vitro. Moreover, overexpression of TIP30 significantly inhibited the growth and lung metastases of HCC cells in nude mice. In contrast, down-regulation of TIP30 greatly promoted tumor cell growth and metastases in vivo. TIP30 repressed OPN transcription through interaction with Ets-1 and suppressed the transcriptional activity of Ets-1 and synergistic actions of Ets-1 and alkaline phosphatase-1. Thus, TIP30 may act as an Ets-1 modulator and inhibit tumor metastasis through abrogating Ets-1-dependent transcription. Moreover, expression of TIP30 was inversely associated with OPN expression in HCC tissue samples as detected by immunohistochemistry assay.

CONCLUSION

Our results reveal a novel pathway by which OPN and possibly other Ets-1 target genes involved in tumor metastasis are regulated by TIP30 and elucidate a mechanism for metastasis promoted by TIP30 deficiency.

Efficient system for biotinylated recombinant Ets-1 production in Escherichia coli: a useful tool for studying interactions between Ets-1 and its partners

Identification of Ets-1 interaction partners is critical for understanding its properties. Ets-1 DNA-binding is governed by an intramolecular mechanism called autoinhibition. Ets-1 increases its DNA-binding affinity by counteracting autoinhibition through binding either to a particular organization of Ets binding sites (EBS) in palindrome, as in the Stromelysin-1 promoter, or to EBS adjacent to DNA-binding sites of its partners by combinatorial interactions, as in the Collagenase-1 promoter. Identification of new Ets-1 interaction partners should allow the identification of new functions for this transcription factor. To this end, we fused a biotin tag to Ets-1 protein in order to copurify it and its partners by affinity. For the first time, we cloned, produced in Escherichia coli and purified a biotinylated recombinant Ets-1 protein using the T7-Impact system (New England Biolabs), adapted to induce biotinylation. Nearly 100% biotinylation was attained without altering Ets-1 properties. Biotinylated Ets-1 bound to and transactivated the Stromelysin-1 promoter the same way as native Ets-1 did. It also conserved interactions with known Ets-1 partners such as c-Jun, Erk-2 and Runx-1. In addition, streptavidin pull-down and surface plasmon resonance assays demonstrated that biotinylated Ets-1 is a useful tool for qualitative and quantitative studies of Ets-1 interaction with its partners.

Ttrap is an essential modulator of Smad3-dependent Nodal signaling during zebrafish gastrulation and left-right axis determination

During vertebrate development, signaling by the TGFbeta ligand Nodal is critical for mesoderm formation, correct positioning of the anterior-posterior axis, normal anterior and midline patterning, and left-right asymmetric development of the heart and viscera. Stimulation of Alk4/EGF-CFC receptor complexes by Nodal activates Smad2/3, leading to left-sided expression of target genes that promote asymmetric placement of certain internal organs. We identified Ttrap as a novel Alk4- and Smad3-interacting protein that controls gastrulation movements and left-right axis determination in zebrafish. Morpholino-mediated Ttrap knockdown increases Smad3 activity, leading to ectopic expression of snail1a and apparent repression of e-cadherin, thereby perturbing cell movements during convergent extension, epiboly and node formation. Thus, although the role of Smad proteins in mediating Nodal signaling is well-documented, the functional characterization of Ttrap provides insight into a novel Smad partner that plays an essential role in the fine-tuning of this signal transduction cascade.

Transcription factor ETS1 is critical for human uterine decidualization

The aim of this study was to examine whether the transcription factor ETS1 plays a critical role in the regulation of human decidualization. Decidual fibroblast cells were decidualized in vitro by treatment with medroxyprogesterone, estradiol (E(2)) and dibutyryl cyclic AMP or prostaglandin E(2) in the absence or presence of an ETS1 antisense oligonucleotide (oligo) that blocks the translation of ETS1 mRNA. Control experiments were performed using a control oligo that did not affect ETS1 expression and the induction of specific marker genes for decidualization. The ETS1 antisense oligo markedly inhibited ETS1 protein expression and significantly inhibited downstream targets of ETS1 action. On day 6 of culture, the decidualized fibroblast cells that had been exposed to the ETS1 antisense oligo contained 40-90% less mRNAs for prolactin, insulin growth factor binding protein 1 (IGFBP-1) and other decidualization-specific markers (laminin, tissue inhibitor of metalloproteinase-3 [TIMP3], endometrial bleeding associated factor [EBAF] and decorin) than those of control cells that had not been exposed to the ETS1 antisense oligo. GAPDH mRNA levels, which do not change during decidualization, were unaffected by either the ETS1 antisense or the control oligo. The cells decidualized in the presence of the ETS1 antisense oligo also released significantly less prolactin, EBAF and IGFBP-1 protein, determined by western blot analyses, than the control cells. Taken together, these findings strongly suggest that ETS1 plays a critical role in the induction of human decidualization.