Wuho/WDR4 deficiency inhibits cell proliferation and induces apoptosis via DNA damage in mouse embryonic fibroblasts

Wuho known as WDR4 encodes a highly conserved WD40-repeat protein, which has known homologues of WDR4 in human and mouse. Wuho-FEN1 interaction may have a critical role in the growth and development, and in the maintenance of genome stability. However, how Wuho gene deletion contributes to cell growth inhibition and apoptosis is still unknown. We utilized CAGGCre-ER transgenic mice have a tamoxifen-inducible cre-mediated recombination cassette to prepare primary mouse embryonic fibroblasts (MEFs) with Wuho deficiency. We have demonstrated that Wuho deficiency would induces γH2AX protein level elevation, heterochromatin relaxation and DNA damage down-stream sequences, including p53 activation, caspase-mediated apoptotic pathway, and p21-mediated G2/M cell cycle arrest.

Ubiquitination of tumor suppressor PML regulates prometastatic and immunosuppressive tumor microenvironment

The tumor microenvironment plays an important role in tumor growth and metastasis. However, the mechanism by which tumor cells regulate the cell and non-cell constituents of surrounding stroma remains incompletely understood. Promyelocytic leukemia (PML) is a pleiotropic tumor suppressor, but its role in tumor microenvironment regulation is poorly characterized. PML is frequently downregulated in many cancer types, including lung cancer. Here, we identify a PML ubiquitination pathway that is mediated by WD repeat 4-containing cullin-RING ubiquitin ligase 4 (CRL4WDR4). Clinically, this PML degradation pathway is hyperactivated in lung cancer and correlates with poor prognosis. The WDR4/PML axis induces a set of cell-surface or secreted factors, including CD73, urokinase-type plasminogen activator receptor (uPAR), and serum amyloid A2 (SAA2), which elicit paracrine effects to stimulate migration, invasion, and metastasis in multiple lung cancer models. In xenograft and genetically engineered mouse models, the WDR4/PML axis elevates intratumoral Tregs and M2-like macrophages and reduces CD8+ T cells to promote lung tumor growth. These immunosuppressive effects were all reversed by CD73 blockade. Our study identifies WDR4 as an oncoprotein that negatively regulates PML via ubiquitination to promote lung cancer progression by fostering an immunosuppressive and prometastatic tumor microenvironment, suggesting the potential of immune-modulatory approaches for treating lung cancer with aberrant PML degradation.

Single-molecule Förster resonance energy transfer (FRET) analysis discloses the dynamics of the DNA-topoisomerase II (Top2) interaction in the presence of TOP2-targeting agents

Topoisomerases play crucial roles in DNA replication, transcription, and recombination. For instance, topoisomerase II (Top2) is critically important for resolving DNA tangles during cell division, and as such, it is a broad anticancer drug target. Top2 regulates DNA topology by transiently breaking one double-stranded DNA molecule (cleavage), allowing a second double strand to pass through the opened DNA gate (opening), and then closing the gate by rejoining the broken ends. Drugs that modulate Top2 catalysis may therefore affect enzymatic activity at several different steps. Previous studies have focused on examining DNA cleavage and ligation; however, the dynamic opening and closing of the DNA gate has been less explored. Here, we used the single-molecule Förster resonance energy transfer (smFRET) method to observe the open and closed state of the DNA gate and to measure dwell times in each state. Our results show that Top2 binds and bends DNA to increase the energy transfer efficiency (E_FRET), and ATP treatment further induces the fluctuation of E_FRET, representing the gate opening and closing. Additionally, our results demonstrate that both types of Top2-targeting anticancer drugs, the catalytic inhibitor dexrazoxane (ICRF187) and mechanistic poison teniposide (VM26), can interfere with DNA gate dynamics and shorten the dwell time in the closed state. Moreover, Top2 bound to the nonhydrolyzable ATP analog 5'-adenylyl-β,γ-imidodiphosphate exhibits altered DNA gate dynamics, but the DNA gate appears to open and close even after N-gate closure. In summary, we have utilized single-molecule detection to unravel Top2 DNA gate dynamics and reveal previously unknown effects of Top2 drugs on these dynamics.

Electron tomographic analysis reveals ultrastructural features of mitochondrial cristae architecture which reflect energetic state and aging

Within mitochondria, the ability to produce energy relies upon the architectural hallmarks of double membranes and cristae invaginations. Herein, we describe novel features of mitochondrial cristae structure, which correspond to the energetic state of the organelle. In concordance with high-energy demand, mitochondria of Drosophila indirect flight muscle exhibited extensive intra-mitochondrial membrane switches between densely packed lamellar cristae that resulted in a spiral-like cristae network and allowed for bidirectional matrix confluency. This highly interconnected architecture is expected to allow rapid equilibration of membrane potential and biomolecules across integrated regions. In addition, mutant flies with mtDNA replication defect and an accelerated aging phenotype accumulated mitochondria that contained subsections of swirling membrane alongside normal cristae. The swirling membrane had impaired energy production capacity as measured by protein composition and function. Furthermore, mitochondrial fusion and fission dynamics were affected in the prematurely aged flies. Interestingly, the normal cristae that remained in the mitochondria with swirling membranes maintained acceptable function that camouflaged them from quality control elimination. Overall, structural features of mitochondrial cristae were described in three-dimension from serial section electron tomographic analysis which reflect energetic state and mtDNA-mediated aging.

Ribosomal Protein S3 Negatively Regulates Unwinding Activity of RecQ-like Helicase 4 through Their Physical Interaction

Human RecQ-like helicase 4 (RECQL4) plays crucial roles in replication initiation and DNA repair; however, the contextual regulation of its unwinding activity is not fully described. Mutations in RECQL4 have been linked to three diseases including Rothmund-Thomson syndrome, which is characterized by osteoskeletal deformities, photosensitivity, and increased osteosarcoma susceptibility. Understanding regulation of RECQL4 helicase activity by interaction partners will allow deciphering its role as an enzyme and a signaling cofactor in different cellular contexts. We became interested in studying the interaction of RECQL4 with ribosomal protein S3 (RPS3) because previous studies have shown that RPS3 activity is sometimes associated with phenotypes mimicking those of mutated RECQL4. RPS3 is a small ribosomal protein that also has extraribosomal functions, including apurnic-apyrimidinic endonuclease-like activity suggested to be important during DNA repair. Here, we report a functional and physical interaction between RPS3 and RECQL4 and show that this interaction may be enhanced during cellular stress. We show that RPS3 inhibits ATPase, DNA binding, and helicase activities of RECQL4 through their direct interaction. Further domain analysis shows that N-terminal 1-320 amino acids of RECQL4 directly interact with the C-terminal 94-244 amino acids of RPS3 (C-RPS3). Biochemical analysis of C-RPS3 revealed that it comprises a standalone apurnic-apyrimidinic endonuclease-like domain. We used U2OS cells to show that oxidative stress and UV exposure could enhance the interaction between nuclear RPS3 and RECQL4. Regulation of RECQL4 biochemical activities by RPS3 along with nuclear interaction during UV and oxidative stress may serve to modulate active DNA repair.

Single-molecule analysis of ϕC31 integrase-mediated site-specific recombination by tethered particle motion

Serine and tyrosine site-specific recombinases (SRs and YRs, respectively) provide templates for understanding the chemical mechanisms and conformational dynamics of strand cleavage/exchange between DNA partners. Current evidence suggests a rather intriguing mechanism for serine recombination, in which one half of the cleaved synaptic complex undergoes a 180° rotation relative to the other. The 'small' and 'large' SRs contain a compact amino-terminal catalytic domain, but differ conspicuously in their carboxyl-terminal domains. So far, only one serine recombinase has been analyzed using single substrate molecules. We now utilized single-molecule tethered particle motion (TPM) to follow step-by-step recombination catalyzed by a large SR, phage ϕC31 integrase. The integrase promotes unidirectional DNA exchange between attB and attP sites to integrate the phage genome into the host chromosome. The recombination directionality factor (RDF; ϕC31 gp3) activates the excision reaction (attL × attR). From integrase-induced changes in TPM in the presence or absence of gp3, we delineated the individual steps of recombination and their kinetic features. The gp3 protein appears to regulate recombination directionality by selectively promoting or excluding active conformations of the synapse formed by specific att site partners. Our results support a 'gated rotation' of the synaptic complex between DNA cleavage and joining.

RNA topoisomerase is prevalent in all domains of life and associates with polyribosomes in animals

DNA Topoisomerases are essential to resolve topological problems during DNA metabolism in all species. However, the prevalence and function of RNA topoisomerases remain uncertain. Here, we show that RNA topoisomerase activity is prevalent in Type IA topoisomerases from bacteria, archaea, and eukarya. Moreover, this activity always requires the conserved Type IA core domains and the same catalytic residue used in DNA topoisomerase reaction; however, it does not absolutely require the non-conserved carboxyl-terminal domain (CTD), which is necessary for relaxation reactions of supercoiled DNA. The RNA topoisomerase activity of human Top3β differs from that of Escherichia coli topoisomerase I in that the former but not the latter requires the CTD, indicating that topoisomerases have developed distinct mechanisms during evolution to catalyze RNA topoisomerase reactions. Notably, Top3β proteins from several animals associate with polyribosomes, which are units of mRNA translation, whereas the Top3 homologs from E. coli and yeast lack the association. The Top3β-polyribosome association requires TDRD3, which directly interacts with Top3β and is present in animals but not bacteria or yeast. We propose that RNA topoisomerases arose in the early RNA world, and that they are retained through all domains of DNA-based life, where they mediate mRNA translation as part of polyribosomes in animals.

The C-terminal 20 Amino Acids of Drosophila Topoisomerase 2 Are Required for Binding to a BRCA1 C Terminus (BRCT) Domain-containing Protein, Mus101, and Fidelity of DNA Segregation

Eukaryotic topoisomerase 2 (Top2) and one of its interacting partners, topoisomerase IIβ binding protein 1 (TopBP1) are two proteins performing essential cellular functions. We mapped the interacting domains of these two proteins using co-immunoprecipitation and pulldown experiments with truncated or mutant Drosophila Top2 with various Ser-to-Ala substitutions. We discovered that the last 20 amino acids of Top2 represent the key region for binding with Mus101 (the Drosophila homolog of TopBP1) and that phosphorylation of Ser-1428 and Ser-1443 is important for Top2 to interact with the N terminus of Mus101, which contains the BRCT1/2 domains. The interaction between Mus101 and the Top2 C-terminal regulatory domain is phosphorylation-dependent because treatment with phosphatase abolishes their association in pulldown assays. The binding affinity of N-terminal Mus101 with a synthetic phosphorylated peptide spanning the last 25 amino acids of Top2 (with Ser(P)-1428 and Ser(P)-1443) was determined by surface plasmon resonance with a Kd of 0.57 μm In an in vitro decatenation assay, Mus101 can specifically reduce the decatenation activity of Top2, and dephosphorylation of Top2 attenuates this response. Next, we endeavored to establish a cellular system for testing the biological function of Top2-Mus101 interaction. Top2-silenced S2 cells rescued by Top2Δ20, Top2 with 20 amino acids truncated from the C terminus, developed abnormally high chromosome numbers, which implies that Top2-Mus101 interaction is important for maintaining the fidelity of chromosome segregation during mitosis.

Drosophila mitochondrial topoisomerase III alpha affects the aging process via maintenance of mitochondrial function and genome integrity

BACKGROUND

Mitochondria play important roles in providing metabolic energy and key metabolites for synthesis of cellular building blocks. Mitochondria have additional functions in other cellular processes, including programmed cell death and aging. A previous study revealed Drosophila mitochondrial topoisomerase III alpha (Top3α) contributes to the maintenance of the mitochondrial genome and male germ-line stem cells. However, the involvement of mitochondrial Top3α in the mitochondrion-mediated aging process remains unclear. In this study, the M1L flies, in which Top3α protein lacks the mitochondrial import sequence and is thus present in cell nuclei but not in mitochondria, is used as a model system to examine the role of mitochondrial Top3α in the aging of fruit flies.

RESULTS

Here, we reported that M1L flies exhibit mitochondrial defects which affect the aging process. First, we observed that M1L flies have a shorter life span, which was correlated with a significant reduction in the mitochondrial DNA copy number, the mitochondrial membrane potential, and ATP content compared with those of both wildtype and transgene-rescued flies of the same age. Second, we performed a mobility assay and electron microscopic analysis to demonstrate that the locomotion defect and mitophagy of M1L flies were enhanced with age, as compared with the controls. Finally, we showed that the correlation between the mtDNA deletion level and aging in M1L flies resembles what was reported in mammalian systems.

CONCLUSIONS

The results reported here demonstrate that mitochondrial Top3α ablation results in mitochondrial genome instability and its dysfunction, thereby accelerating the aging process.

Probing conformational changes in human DNA topoisomerase IIα by pulsed alkylation mass spectrometry

Type II topoisomerases are essential enzymes for solving DNA topological problems by passing one segment of DNA duplex through a transient double-strand break in a second segment. The reaction requires the enzyme to precisely control DNA cleavage and gate opening coupled with ATP hydrolysis. Using pulsed alkylation mass spectrometry, we were able to monitor the solvent accessibilities around 13 cysteines distributed throughout human topoisomerase IIα by measuring the thiol reactivities with monobromobimane. Most of the measured reactivities are in accordance with the predicted ones based on a homology structural model generated from available crystal structures. However, these results reveal new information for both the residues not covered in the structural model and potential differences between the modeled and solution holoenzyme structures. Furthermore, on the basis of the reactivity changes of several cysteines located at the N-gate and DNA gate, we could monitor the movement of topoisomerase II in the presence of cofactors and detect differences in the DNA gate between two closed clamp enzyme conformations locked by either 5'-adenylyl β,γ-imidodiphosphate or the anticancer drug ICRF-193.

Dietary isothiocyanate-induced apoptosis via thiol modification of DNA topoisomerase IIα

Studies in animal models have indicated that dietary isothiocyanates (ITCs) exhibit cancer preventive activities through carcinogen detoxification-dependent and -independent mechanisms. The carcinogen detoxification-independent mechanism of cancer prevention by ITCs has been attributed at least in part to their ability to induce apoptosis of transformed (initiated) cells (e.g. through suppression of IκB kinase and nuclear factor κB as well as other proposed mechanisms). In the current studies we show that ITC-induced apoptosis of oncogene-transformed cells involves thiol modification of DNA topoisomerase II (Top2) based on the following observations. 1) siRNA-mediated knockdown of Top2α in both SV40-transformed MEFs and Ras-transformed human mammary epithelial MCF-10A cells resulted in reduced ITC sensitivity. 2) ITCs, like some anticancer drugs and cancer-preventive dietary components, were shown to induce reversible Top2α cleavage complexes in vitro. 3) ITC-induced Top2α cleavage complexes were abolished by co-incubation with excess glutathione. In addition, proteomic analysis revealed that several cysteine residues on human Top2α were covalently modified by benzyl-ITC, suggesting that ITC-induced Top2α cleavage complexes may involve cysteine modification. Interestingly, consistent with the thiol modification mechanism for Top2α cleavage complex induction, the thiol-reactive selenocysteine, but not the non-thiol-reactive selenomethionine, was shown to induce Top2α cleavage complexes. In the aggregate, our results suggest that thiol modification of Top2α may contribute to apoptosis induction in transformed cells by ITCs.

Separate and combined biochemical activities of the subunits of a naturally split reverse gyrase

Reverse gyrase reanneals denatured DNA and induces positive supercoils in DNA, an activity that is critical for life at very high temperatures. Positive supercoiling occurs by a poorly understood mechanism involving the coordination of a topoisomerase domain and a helicase-like domain. In the parasitic archaeon Nanoarchaeum equitans, these domains occur as separate subunits. We express the subunits, and characterize them both in isolation and as a heterodimer. Each subunit tightly associates and interacts with the other. The topoisomerase subunit enhances the catalytic specificity of the DNA-dependent ATPase activity of the helicase-like subunit, and the helicase-like subunit inhibits the relaxation activity of the topoisomerase subunit while promoting positive supercoiling. DNA binding preference for both single- and double-stranded DNA is partitioned between the subunits. Based on a sensitive topological shift assay, the binding preference of helicase-like subunit for underwound DNA is modulated by its binding with ATP cofactor. These results provide new insight into the mechanism of positive supercoil induction by reverse gyrase.

RecQ4: the second replicative helicase?

Recent work has greatly contributed to the understanding of the biology and biochemistry of RecQ4. It plays an essential non-enzymatic role in the formation of the CMG complex, and thus replication initiation, by means of its Sld2 homologous domain. The helicase domain of RecQ4 has now been demonstrated to possess 3'-5' DNA helicase activity, like the other members of the RecQ family. The biological purpose of this activity is still unclear, but helicase-dead mutants are unable to restore viability in the absence of wildtype RecQ4. This indicates that RecQ4 performs a second role, which requires helicase activity and is implicated in replication and DNA repair. Thus, it is clear that two helicases, RecQ4 and Mcm2-7, are integral to replication. The nature of the simultaneous involvement of these two helicases remains to be determined, and possible models will be proposed.

The phosphoCTD-interacting domain of Topoisomerase I

The N-terminal domain (NTD) of Drosophila melanogaster (Dm) Topoisomerase I has been shown to bind to RNA polymerase II, but the domain of RNAPII with which it interacts is not known. Using bacterially-expressed fusion proteins carrying all or half of the NTDs of Dm and human (Homo sapiens, Hs) Topo I, we demonstrate that the N-terminal half of each NTD binds directly to the hyperphosphorylated C-terminal repeat domain (phosphoCTD) of the largest RNAPII subunit, Rpb1. Thus, the amino terminal segment of metazoan Topo I (1-157 for Dm and 1-114 for Hs) contains a novel phosphoCTD-interacting domain that we designate the Topo I-Rpb1 interacting (TRI) domain. The long-known in vivo association of Topo I with active genes presumably can be attributed, wholly or in part, to the TRI domain-mediated binding of Topo I to the phosphoCTD of transcribing RNAPII.

Analysis of the eukaryotic topoisomerase II DNA gate: a single-molecule FRET and structural perspective

Type II DNA topoisomerases (topos) are essential and ubiquitous enzymes that perform important intracellular roles in chromosome condensation and segregation, and in regulating DNA supercoiling. Eukaryotic topo II, a type II topoisomerase, is a homodimeric enzyme that solves topological entanglement problems by using the energy from ATP hydrolysis to pass one segment of DNA through another by way of a reversible, enzyme-bridged double-stranded break. This DNA break is linked to the protein by a phosphodiester bond between the active site tyrosine of each subunit and backbone phosphate of DNA. The opening and closing of the DNA gate, a critical step for strand passage during the catalytic cycle, is coupled to this enzymatic cleavage/religation of the backbone. This reversible DNA cleavage reaction is the target of a number of anticancer drugs, which can elicit DNA damage by affecting the cleavage/religation equilibrium. Because of its clinical importance, many studies have sought to determine the manner in which topo II interacts with DNA. Here we highlight recent single-molecule fluorescence resonance energy transfer and crystallographic studies that have provided new insight into the dynamics and structure of the topo II DNA gate.

ISG15 as a novel tumor biomarker for drug sensitivity

Tumor cells are known to exhibit highly varied sensitivity to camptothecins (CPT; e.g., irinotecan and topotecan). However, the factors that determine CPT sensitivity/resistance are largely unknown. Recent studies have shown that the ubiquitin-like protein, IFN-stimulated gene 15 (ISG15), which is highly elevated in many human cancers and tumor cell lines, antagonizes the ubiquitin/proteasome pathway. In the present study, we show that ISG15 is a determinant for CPT sensitivity/resistance possibly through its effect on proteasome-mediated repair of topoisomerase I (TOP1)-DNA covalent complexes. First, short hairpin RNA-mediated knockdown of either ISG15 or UbcH8 (major E2 for ISG15) in breast cancer ZR-75-1 cells decreased CPT sensitivity, suggesting that ISG15 overexpression in tumors could be a factor affecting intrinsic CPT sensitivity in tumor cells. Second, the level of ISG15 was found to be significantly reduced in several tumor cells selected for resistance to CPT, suggesting that altered ISG15 regulation could be a significant determinant for acquired CPT resistance. Parallel to reduced CPT sensitivity, short hairpin RNA-mediated knockdown of either ISG15 or UbcH8 in ZR-75-1 cells resulted in increased proteasomal degradation of CPT-induced TOP1-DNA covalent complexes. Taken together, these results suggest that ISG15, which interferes with proteasome-mediated repair of TOP1-DNA covalent complexes, is a potential tumor biomarker for CPT sensitivity.

Single-molecule measurements of the opening and closing of the DNA gate by eukaryotic topoisomerase II

Type II DNA topoisomerases are essential and ubiquitous enzymes that perform important functions in chromosome condensation and segregation and in regulating intracellular DNA supercoiling. Topoisomerases carry out these DNA transactions by passing one segment of DNA through the other by using a reversible, enzyme-bridged double strand break. The transient enzyme/DNA adduct is mediated by a phosphodiester bond between the active-site tyrosine and a backbone phosphate of DNA. The opening and closing of the DNA gate, a critical step for strand passage during the catalytic cycle, is coupled to this cleavage/religation. We designed a unique oligonucleotide substrate with a pair of fluorophores straddling the topoisomerase II cleavage site, allowing the use of FRET to monitor the opening of the DNA gate. The DNA substrate undergoes an enzyme-mediated transition between a closed and open state in the presence of ATP, similar to the overall topoisomerase II catalyzed reaction. Single-molecule fluorescence microscopy measurements demonstrate that the transition has comparable rate constants for both the opening and closing reaction during steady-state ATP hydrolysis, with an apparent equilibrium constant near unity. In the presence of AMPPNP, a reduction in FRET occurs, suggesting an opening or partial opening of the DNA gate. However, the single-molecule experiments indicate that the open and closed states do not interconvert at a measurable rate.

Preparation of membrane proteins from Drosophila embryos

INTRODUCTIONDrosophila embryos provide a unique system for the study of membrane proteins because of an extensive database in both genetics and biochemistry. Drosophila early embryos have an extraordinary peak in membrane biogenesis with a 23-fold increase in membrane area over ~45 minutes. This protocol describes purification of Drosophila membranes using equilibrium sedimentation in a sucrose density step gradient (0.5 M, 2.0 M, 2.5 M). It also includes two methods to determine the membrane association of a protein of interest: (1) alkaline wash and (2) Triton X-114 phase separation.

A novel, topologically constrained DNA molecule containing a double Holliday junction: design, synthesis, and initial biochemical characterization

The double Holliday junction (dHJ) is a central intermediate to homologous recombination, but biochemical analysis of the metabolism of this structure has been hindered by the lack of a substrate that adequately replicates the endogenous structure. We have synthesized a novel dHJ substrate that consists of two small, double stranded DNA circles conjoined by two Holliday junctions (HJs). Its biochemical synthesis is based on the production of two pairs of single stranded circles from phagemids, followed by their sequential annealing with reverse gyrase. The sequence between the two HJs is identical on both strands, allowing the HJs to migrate without the generation of unpaired regions of DNA, whereas the distance between the HJs is on the order of gene conversion tracts thus far measured in Drosophila and mouse model systems. The structure of this substrate also provides similar topological constraint as would occur in an endogenous dHJ. Digestion of the dHJ substrate by T7 endonuclease I resolves the substrate into crossover and non-crossover products, as predicted by the Szostak model of double strand break repair. This substrate will greatly facilitate the examination of the mechanism of resolution of double Holliday junctions.

Drosophila melanogaster topoisomerase IIIalpha preferentially relaxes a positively or negatively supercoiled bubble substrate and is essential during development

Eukaryotic type IA topoisomerases are important for the normal function of the cell, and in some cases essential for the organism, although their role in DNA metabolism remains to be elucidated. In this study, we cloned Drosophila melanogaster topoisomerase (topo) IIIalpha from an embryonic cDNA library and expressed and purified the protein to >95% homogeneity. This enzyme partially relaxes a hypernegatively supercoiled plasmid substrate consistent with other purified topo IIIs. A novel, covalently closed bubble substrate was prepared for this study, which topo IIIalpha fully relaxed, regardless of the handedness of the supercoils. Experiments with the bubble substrate demonstrate that topo IIIalpha has much different reaction preferences from those obtained by plasmid substrate-based assays. This is presumably due to the fact that solution conditions can affect the structure of plasmid based substrates and therefore their suitability as a substrate. A mutant allele of the Top3alpha gene, Top3alpha191, was isolated through imprecise excision mutagenesis of an existing P-element inserted in the first intron of the gene. Top3alpha191 is recessive lethal, with most of the homozygous individuals surviving to pupation but never emerging to adulthood. Whereas this mutation can be rescued by a Top3alpha transgene, ubiquitous overexpression of D. melanogaster topo IIIbeta cannot rescue this allele.

Preferential cleavage of plasmid-based R-loops and D-loops by Drosophila topoisomerase IIIbeta

The topoisomerase (topo) III enzymes are found in organisms ranging from bacteria to humans, yet the precise cellular function of these enzymes remains to be determined. We previously found that Drosophila topo IIIbeta can relax plasmid DNA only if the DNA is first hypernegatively supercoiled. To investigate the possibility that topo IIIbeta requires a single-stranded region for its relaxation activity, we formed R-loops and D-loops in plasmids. In addition to containing a single-stranded region, these R-loops and D-loops have the advantage of being covalently closed and supercoiled, thus allowing us to assay for supercoil relaxation. We found that topo IIIbeta preferentially cleaves, rather than relaxes, these substrates. The cleavage of the R-loops and D-loops, which is primarily in the form of nicking, occurs to a greater extent at a temperature that is lower than the optimal temperature for relaxation of hypernegatively supercoiled plasmid. In addition, the cleavage can be readily reversed by high salt or high temperature, and the products fail to enter the gel in the absence of proteinase K treatment and are not observed with an active-site Y332F mutant of topo IIIbeta, indicating that the cleavage is mediated by a topoisomerase. We mapped the cleavage to the unpaired strand within the loop region and found that the cleavage occurs along the length of the unpaired strand. These studies suggest that the topo III enzyme behaves as a structure-specific endonuclease in vivo, providing a reversible DNA cleavage activity that is specific for unpaired regions in the DNA.

Induction of topoisomerase II activity after ErbB2 activation is associated with a differential response to breast cancer chemotherapy

ErbB2 (HER-2) gene amplification and overexpression have been shown to predict a better outcome with doxorubicin-based chemotherapy as opposed to alkylator-based chemotherapy in early stage breast cancer. To understand the mechanism of differential response to these two regimens, we have evaluated the effect of signaling through the ErbB2 receptor on downstream enzymes that may affect drug response, using two different models. The first system employs breast cancer cells that have high levels of endogenous ErbB2 by gene amplification (BT-474 and SKBR3 cells). The second system allows us to isolate the effect of ErbB2 receptor-mediated intracellular signaling using an epidermal growth factor receptor-ErbB2 chimeric receptor activated by epidermal growth factor. Our experiments show that the cytotoxicity of doxorubicin is inhibited in ErbB2+ breast cancer cells by the anti-ErbB2 antibody, Herceptin. This is accompanied by a decrease in topoisomerase (topo) IIalpha protein and activity, suggesting that this is the mechanism of change in doxorubicin response. In addition, a 10-100-fold (1-2 log) decrease in the LD(50) of doxorubicin is seen after ErbB2 activation using the chimeric receptor model. Furthermore, we see a 100-fold decrease in the LD(50) of etoposide, another topo II inhibitor. This increase in doxorubicin sensitivity is associated with a 4.5-fold increase in the amount of topo IIalpha protein and an increase in topo II activity as measured by DNA decatenating and unknotting activities, as well as cleavable complex formation. In contradistinction to doxorubicin, we have observed an increased resistance to cyclophosphamide chemotherapy after chimeric receptor activation. We propose that the differential benefit seen with doxorubicin- versus alkylator-based chemotherapy in ErbB2+ breast cancer is due, in some cases, to ErbB2-mediated topo IIalpha activation. These data also suggest hypotheses for the optimal sequencing of Herceptin and chemotherapy agents in ErbB2+ breast cancer.

Atp-bound topoisomerase ii as a target for antitumor drugs

Topoisomerase II (TOP2) poisons interfere with the breakage/reunion reaction of TOP2 resulting in DNA cleavage. In the current studies, we show that two different classes (ATP-sensitive and -insensitive) of TOP2 poisons can be identified based on their differential sensitivity to the ATP-bound conformation of TOP2. First, in the presence of 1 mm ATP or the nonhydrolyzable analog adenosine 5'-(beta,gamma-imino)triphosphate, TOP2-mediated DNA cleavage induced by ATP-sensitive TOP2 poisons (e.g. doxorubicin, etoposide, mitoxantrone, and 4'-(9-acridinylamino)methanesulfon-m-anisidide) was 30-100-fold stimulated, whereas DNA cleavage induced by ATP-insensitive TOP2 poisons (e.g. amonafide, batracylin, and menadione) was only slightly (less than 3-fold) affected. In addition, ADP was shown to strongly antagonize TOP2-mediated DNA cleavage induced by ATP-sensitive but not ATP-insensitive TOP2 poisons. Second, C427A mutant human TOP2alpha, which exhibits reduced ATPase activity, was shown to exhibit cross-resistance to all ATP-sensitive but not ATP-insensitive TOP2 poisons. Third, using ciprofloxacin competition assay, TOP2-mediated DNA cleavage induced by ATP-sensitive but not ATP-insensitive poisons was shown to be antagonized by ciprofloxacin. These results suggest that ATP-bound TOP2 may be the specific target of ATP-sensitive TOP2 poisons. Using Lac repressor-operator complexes as roadblocks, we show that ATP-bound TOP2 acts as a circular clamp capable of entering DNA ends and sliding on unobstructed duplex DNA.

Essential functions of DNA topoisomerase I in Drosophila melanogaster

DNA topoisomerase I (topo I) is an essential enzyme involved in replication, transcription, and recombination. To probe the functions of topo I during Drosophila development, we used top1-deficient flies with heat-shock-inducible top1 transgenes and were able to observe both zygotic and maternal functions of top1. A critical period for the zygotic function is in the late larval and early pupal stages. Topo I is required for larval growth and cell proliferation in imaginal disc tissues. The maternal functions consist of two aspects: oogenesis and early embryogenesis. During oogenesis, topo I is detected in the nuclei of early germ-line cells and follicle cells. The mutant ovary exhibits abnormal proliferation and defective nuclear morphology in these cells. There are extranumeral germ-line cells in individual egg chambers, while the follicle cells are underreplicated. Topo I is also stored maternally in early embryos. It localizes to the nuclei during interphase and prophase, but disperses into the cytoplasm at metaphase. Embryos from the mutant mother frequently show disrupted nuclear divisions with defects in chromosome condensation and segregation. The cytological and genetic analysis of the top1 mutant demonstrates that in Drosophila, topo I plays critical roles in many developmental stages active in cell proliferation.

Discontinuous actin hexagon, a protein essential for cortical furrow formation in Drosophila, is membrane associated and hyperphosphorylated

discontinuous actin hexagon (dah) is a maternal-effect gene essential for the formation of cortical furrows during Drosophila embryogenesis, and DAH protein colocalizes with actin in these furrows. Biochemical fractionation experiments presented here demonstrate that DAH is highly enriched in the membrane fraction and that its membrane association is resistant to high-salt and alkaline washes. Furthermore, it partitions into the detergent phase of the Triton X-114 solution, indicating its tight binding to the membranes. DAH can also interact with the actin cytoskeleton, because a fraction of DAH remains insoluble to nonionic detergent along with actin. These biochemical characterizations suggest that DAH may play a role in the linkage of the actin cytoskeleton to membranes. Using phosphatase inhibitors, we detected multiple phosphorylated forms of DAH in embryonic extracts. The DAH phosphorylation peaks during cellularization, a stage at which DAH function is critical. A kinase activity is coimmunoprecipitated with the DAH complex and hyperphosphorylates DAH in vitro. Purified casein kinase I can also hyperphosphorylate DAH in the immune complex. Both DAH localization and phosphorylation are disrupted in another maternal-effect mutant, nuclear-fallout. It is possible that nuclear-fallout collaborates with dah and directs DAH protein localization to the cortical furrows.

The Drosophila centrosomal protein Nuf is required for recruiting Dah, a membrane associated protein, to furrows in the early embryo

During mitosis of the Drosophila cortical syncytial divisions, actin-based membrane furrows separate adjacent spindles. Our genetic analysis indicates that the centrosomal protein Nuf is specifically required for recruitment of components to the furrows and the membrane-associated protein Dah is primarily required for the inward invagination of the furrow membrane. Recruitment of actin, anillin and peanut to the furrows occurs normally in dah-derived embryos. However, subsequent invagination of the furrows fails in dah-derived embryos and the septins become dispersed throughout the cytoplasm. This indicates that stable septin localization requires Dah-mediated furrow invagination. Close examination of actin and Dah localization in wild-type embryos reveals that they associate in adjacent particles during interphase and co-localize in the invaginating furrows during prophase and metaphase. We show that the Nuf centrosomal protein is required for recruiting the membrane-associated protein Dah to the furrows. In nuf-mutant embryos, much of the Dah does not reach the furrows and remains in a punctate distribution. This suggests that Dah is recruited to the furrows in vesicles and that the recruiting step is disrupted in nuf mutants. These studies lead to a model in which the centrosomes play an important role in the transport of membrane-associated proteins and other components to the developing furrows.

Mutations of human topoisomerase II alpha affecting multidrug resistance and sensitivity

Two mutations, R450Q and P803S, in the coding region of the human topoisomerase II alpha gene have been identified in the atypical multidrug resistant (at-MDR) cell line, CEM/VM-1, which exhibits resistance to many structurally diverse topoisomerase II-targeting antitumor drugs such as VM-26, doxorubicin, m-AMSA, and mitoxantrone. The R450Q mutation mapped in the ATP utilization domain, while the P803S mutation mapped in the vicinity of the active site tyrosine of human topoisomerase II alpha. However, the roles of these two mutations in conferring multidrug resistance are unclear. To study the roles of these two mutations in conferring multidrug resistance, we have characterized the recombinant human DNA topoisomerase II alpha containing either single or double mutations. We show that both R450Q and P803S mutations confer resistance in the absence of ATP. However, in the presence of ATP, the R450Q, but not the P803S, mutation can confer multidrug resistance. The R450Q enzyme was shown to exhibit impaired ATP utilization both for enzyme catalysis and for its ability to form the circular protein clamp. Interestingly, an unrelated mutation, G437E, which is also located in the same domain as the R450Q mutation, exhibited multidrug hypersensitivity in the absence of ATP. However, in the presence of ATP, the G437E enzyme is only minimally hypersensitive to various topoisomerase II drugs. In contrast to the R450Q enzyme, the G437E enzyme exhibited enhanced ATP utilization for enzyme catalysis. In the aggregate, these results support the notion that the multidrug resistance and sensitivity of these mutant enzymes are due to a specific defect in ATP utilization during enzyme catalysis.

The hydrophilic, protease-sensitive terminal domains of eucaryotic DNA topoisomerases have essential intracellular functions

The amino-terminus of eucaryotic DNA topoisomerase I and the carboxy-terminus of eucaryotic DNA topoisomerase II contain sequences that are enriched in charged amino acid residues, hyper-sensitive to protease digestion, not required for the in vitro topoisomerase activities, able to tolerate insertion and deletion mutations, and thus may have a disordered structure. In an interesting contrast to the catalytically essential core domain, the sequences in these terminal hydrophilic domains are not conserved among the topoisomerases from different species. However, many lines of evidence, including those presented here, demonstrate that the topoisomerase tail domains have critical intracellular functions. The biological functions of the amino-terminus of topoisomerase I include the nuclear import and targeting to the transcriptionally active loci. The carboxy-terminus of topoisomerase II also contains the sequences necessary for nuclear localization and possibly sequences necessary for other critical functions.

Penile cancer in Taiwan--20 years' experience at National Taiwan University Hospital

To analyze the characteristics and prognostic factors of penile cancer in Taiwanese, we retrospectively reviewed the clinical data of patients with a diagnosis of penile cancer treated during a 20-year period (1977-1996) at National Taiwan University Hospital (NTUH). Of 71 patients treated for penile cancer during the study period, 17 were referred from other hospitals or clinics. Our analyses focused on the 54 previously untreated patients. Growth on the penis was the main symptom in all cases. Palpable inguinal lymph nodes were found only in 14 patients. All 54 patients with primary tumors were treated surgically. Pathologic examination showed squamous cell carcinoma (SCC) in 43 cases, extra-mammary Paget's disease in three, verrucous carcinoma in three, Bowen's disease in two, cutaneous lymphoma in two and basal cell carcinoma in one. Twenty-six (48%) patients had stage I penile cancer, 13 (24%) had stage II, seven (13%) had stage III, and eight (15%) had stage IV cancer. The five-year survival rate was 78% among patients with SCC and 84% among those with nonsquamous malignancies (p = 0.80). The five-year cumulative survival rates according to Jackson's cancer stage were 100% for patients with stage I, 88.9% for those with stage II, 66.7% for those with stage III, and 0% for those with stage IV (p < 0.001). Tumor staging (p = 0.027) and adjuvant chemotherapy (p = 0.042) were found to be the most significant prognostic factors. Penile cancer accounted for 0.254% of all malignancies among male patients at the NTUH during the study period. Our findings indicate that penile cancer is uncommon in Taiwanese and its prognosis is closely related to tumor staging and management. Early diagnosis and appropriate treatment may lead to prolonged survival.

Analysis of a core domain in Drosophila DNA topoisomerase II. Targeting of an antitumor agent ICRF-159

To investigate the biochemical properties of individual domains of eukaryotic topoisomerase (topo) II, two truncation mutants of Drosophila topo II were generated, ND406 and core domain. Both mutants lack the ATPase domain, corresponding to the N-terminal 406 amino acid residues in Drosophila protein. The core domain also lacks 240 amino acid residues of the hydrophilic C-terminal region. The mutant proteins have lost DNA strand passage activity while retaining the ability to cleave the DNA and the sequence preference in protein/DNA interaction. The cleavage experiments carried out in the presence of several topo II poisons suggest that the core domain is the key target for these drugs. We have used glass-fiber filter binding assay and CsCl density gradient ultracentrifugation to monitor the formation of a salt-stable, protein-clamp complex. Both truncation mutant proteins can form a clamp complex in the presence of an antitumor agent, ICRF-159, suggesting that the drug targets the core domain of the enzyme and promotes the intradimeric closure at the N-terminal interface of the core domain. Furthermore, the salt stability of the closed protein clamp induced by ICRF-159 depends on the presence and closure of the N-terminal ATPase domain.

Targeting to transcriptionally active loci by the hydrophilic N-terminal domain of Drosophila DNA topoisomerase I

DNA topoisomerase I (topo I) from Drosophila melanogaster contains a nonconserved, hydrophilic N-terminal domain of about 430 residues upstream of the conserved core domains. Deletion of this N terminus did not affect the catalytic activity of topo I, while further removal of sequences into the conserved regions inactivated its enzymatic activity. We have investigated the cellular function of the Drosophila topo I N-terminal domain with top1-lacZ transgenes. There was at least one putative nuclear localization signal within the first 315 residues of the N-terminal domain that allows efficient import of the large chimeric proteins into Drosophila nuclei. The top1-lacZ fusion proteins colocalized with RNA polymerase II (pol II) at developmental puffs on the polytene chromosomes. Either topo I or the top1-lacZ fusion protein was colocalized with RNA pol II in some but not all of the nonpuff, interband loci. However, the fusion proteins as well as RNA pol II were recruited to heat shock puffs during heat treatment, and they returned to the developmental puffs after recovery from heat shock. By immunoprecipitation, we showed that two of the largest subunits of RNA pol II coprecipitated with the N-terminal 315-residue fusion protein by using antibodies against beta-galactosidase. These data suggest that the topo I fusion protein can be localized to the transcriptional complex on chromatin and that the N-terminal 315 residues were sufficient to respond to cellular processes, especially during the reprogramming of gene expression.

Complex response of breast epithelial cell lines to topoisomerase inhibitors

The topoisomerase inhibitors, camptothecin and etoposide target the activity of topoisomerase I and II respectively. These agents, or their analogues, are undergoing clinical trials for the treatment of metastatic breast cancer. In this study, we examined the response of eight breast epithelial cell lines, including six lines derived from breast cancers and two immortalized normal epithelial lines to camptothecin and etoposide. The lines varied by 700 fold in their sensitivity to the growth inhibiting effects of camptothecin and 30 fold in their response to etoposide. The BT474 line was the most resistant to both agents. The other cell lines did not have uniform sensitivity to both drugs, i.e., some lines were sensitive to one drug but relatively resistant to the other. A variety of parameters in these lines were analyzed to elucidate mechanisms of resistance including S phase, doubling time, expression and activity of topoisomerase I and II, expression of mdr-1, p53 status, cell cycle arrest, level of apoptosis, and expression of the apoptotic proteins Bcl-2 and Bax. We found that low levels of the topo I protein and its enzymatic activity were associated with increased resistance to camptothecin. This was not true for topo II activity and etoposide. Increased apoptotic responses were generally observed in cell lines that were sensitive to etoposide and this correlated with low ratios of Bcl-2/Bax protein. No single parameter was entirely predictive of response. However, the BT474 line displayed a series of characteristics including slow growth, the presence of mutant p53, low topo I activity, and a high Bcl-2/Bax ratio which together likely contributed to the resistance of this line to both etoposide and camptothecin.

Structure of the Drosophila DNA topoisomerase I gene and expression of messages with different lengths in the 3' untranslated region

The nucleotide sequence of the Drosophila DNA topoisomerase I gene (top1) has been determined. Structurally, top1 consists of eight exons and seven introns. The top1 coding region contains a new class of opa repeats, encoding clusters of serine residues instead of glutamine repeats usually seen in Drosophila genes of the neurogenic loci. A unique feature of top1 is the developmental switch of its transcripts: a heterogeneous population of transcripts ranging from 3.8 to 4.2kb seen maximally at 0-2h of embryogenesis and a 5.2-kb transcript maximal at 6-12h of embryonic development. The transcripts expressed in the 0-2-h embryo have been shown as maternal storage products specific to ovarian tissues. RACE analysis shows that whereas the 6-12-h transcripts have a single site for polyadenylation, there are at least 12 different sites for poly(A) addition to the 0-2-h transcripts. An additional intron specific for the maternal storage transcripts appears in some of the 0-2-h transcripts. No significant heterogeneity at the 5' end of the top1 transcripts is seen. Sequence searches have revealed a number of regulatory sequences for potential translational control in the 3' untranslated region.

Combined cytotoxic effects of tamoxifen and chemotherapeutic agents on bladder cancer cells: a potential use in intravesical chemotherapy

OBJECTIVE

To evaluate whether tamoxifen enhances the cytotoxicity of chemotherapeutic agents on bladder cancer cells, and the possible mechanism(s) of action.

MATERIALS AND METHODS

The in vitro inhibition of cell growth was examined in a model simulating intravesical chemotherapy using two bladder cancer cell lines (TSGH-8301, HTB9) and three commonly used intravesical cytotoxic agents (doxorubicin, mitomycin C, and thiotepa) in the presence or absence of tamoxifen or verapamil as modulators. The expression of the multi-drug resistance-related gene mdr-1 was evaluated by reverse-transcription polymerase chain reaction and Southern blotting (RT-PCR-SB) to determine its transcript level, by flow cytometric analysis of the P-glycoprotein (P-gp) product level with C-219 monoclonal antibody and by the rhodamine-123 retention and efflux assay for P-gp activity. Transforming growth factor beta-1 (TGF beta-1) levels in tamoxifen-conditioned culture medium were determined with enzyme-linked immunosorbant assay (ELISA).

RESULTS

Tamoxifen at concentrations > or = 30 microM significantly enhanced the cytotoxicity of the three chemotherapeutic agents to both cell lines, as shown by a marked reduction in the drug concentration which inhibited growth by 50% (IC50). The enhancement of cytotoxicity was significantly dependent on the concentration of tamoxifen. However, tamoxifen alone caused significant toxic effects to TSGH-8301 at > or = 40 microM and to HTB9 at > or = 30 microM. Median-effect analysis showed additive or less-than-additive combination effects between tamoxifen and chemotherapeutic agents and only a minimal synergism in a narrow range of maximal cytotoxicity (fraction affected > 0.9). Thus, the reduction of IC50s by tamoxifen was mostly because it was cytotoxic to the bladder cancer cells used. No enhancement of cytotoxicity was observed in verapamil-modulated cells. Transcripts of mdr-1 could not be detected by RT-PCR-SB, nor was P-gp detected by flow cytometric analysis in the two cell lines. Furthermore, no active P-gp function was detected by the rhodamine-123 retention and efflux study, indicating that the primary chemoresistance mechanisms of the two cell lines were not mediated by mdr-1, nor could tamoxifen or verapamil act through modulation of the mdr-1 pathway in the two cell lines. Tamoxifen at 3 and 10 microM down-regulated the secretion of TGF beta-1 from TSGH-8301 in a concentration-dependent manner, in contrast to the findings that tamoxifen was cytotoxic to the bladder cancer cells used and that tamoxifen up-regulated TGF beta-1 in a breast cancer model, suggesting that there may be a different mechanism of response to TGF beta-1 in these bladder cancer cells.

CONCLUSION

Tamoxifen enhanced the cytotoxicity of chemotherapeutic agents largely through its toxic effects on the bladder cancer cells. The mode of action of tamoxifen was not through the regulation of TGF beta-1 or the function of mdr-1. Although cytotoxic levels of tamoxifen (> 50 microM) can be achieved easily in the intravesical model, further study is necessary before tamoxifen can be used clinically in intravesical chemotherapy.

Tamoxifen enhances the chemosensitivity of bladder carcinoma cells

PURPOSE

Chemosensitizers, which enhance cellular chemosensitivity and reduce chemoresistance, are expected to substantially improve response rates of systemic chemotherapy for patients with metastatic bladder cancer. Tamoxifen is a nonsteroidal antiestrogen that has been shown to reverse drug resistance in vitro in some cancer models through pathways not related to its antiestrogenic effect. In this study we tried to evaluate its possible effect on chemosensitization of bladder cancer cells.

MATERIALS AND METHODS

In vitro chemosensitivity tests were done with 3 bladder cancer cell lines and 4 cytotoxic agents (methotrexate, vinblastine, doxorubicin and cisplatin) in the presence or absence of graded concentrations of tamoxifen. Verapamil was used in parallel experiments to compare the degrees of chemosensitization. The transcript and protein product [P-glycoprotein, (P-gp)] levels of the mdr-1 gene were also examined in the 3 cell lines by reverse-transcription polymerase chain reaction (RT-PCR) and flow cytometric assay, respectively.

RESULTS

Tamoxifen at 5 and especially 10 microM. concentrations, which were minimally toxic to the 3 bladder cancer cell lines used, enhanced the chemosensitivity of bladder cancer cells in most drug combinations in a dose-dependent manner. In some combinations 10 microM. tamoxifen did better than 5 microM. in chemosensitization. The effect of chemosensitization was more evident in cells treated with 10 microM. tamoxifen plus methotrexate and vinblastine in which 12.9 to 95.4-fold and 12.4 to 21.3-fold IC50 reduction was observed, respectively. A less prominent, but still significant, effect could be seen in doxorubicin- and cisplatin-treated cells. Verapamil, although used at concentrations up to 10 microM. which are higher than systemically tolerable, was not able to enhance chemosensitivity of the 3 bladder cancer cell lines. By flow cytometric analysis of the P-gp level and by RT-PCR assay of the mdr-1 gene transcript level, it was shown that little if any mdr-1 gene expression could be detected in the 3 cell lines. This implies that the mdr-1 gene function may play a minimal role in drug resistance mechanisms of bladder cancer cells and that tamoxifen exerts its chemosensitization effect through pathways other than mdr-1 gene function modulation.

CONCLUSIONS

Tamoxifen was shown to be a good chemosensitizer in a bladder cancer cell model and may well be tried in combination with systemic chemotherapy for metastatic human bladder cancers in the clinical setting.

Expressions of E-cadherin and exon v6-containing isoforms of CD44 and their prognostic values in human transitional cell carcinoma

Cell surface adhesion molecules, E-cadherin and exon v6 containing CD44 isoforms (CD44v6), were readily found in well-to-moderately differentiated urothelial cell lines but were down-regulated in poorly differentiated cell lines. One hundred and fifteen tumors of transitional cell carcinoma (TCC) were examined with E-cadherin and CD44v6 specific antibodies. Sixty-five (56.5%) tumors exhibited a preserved type while 50 (43.5%) showed a reduced type for CD44v6. Sixty-seven (58.3%) tumors were classified as the preserved type, and 48 (41.7%) were classified as the reduced type for E-cadherin. The staining pattern of E-cadherin was the same as that of CD44v6 in 87.0% (100 of 115) of tumors. The frequency of the reduced type was higher in poorly differentiated carcinomas (32 of 52 for CD44v6, p = 0.001; 27 of 52 for E-cadherin, p = 0.112) and tumors with an invasive growth pattern (22 of 27 for CD44v6, p < 0.001; 20 of 27 for E-cadherin, p < 0.001) than it was in well-differentiated carcinomas and tumors with expansile growth. However, the association with lymph node involvement or distant metastasis did not reach statistical significance. There was no difference in survival in reference to the expression patterns of CD44v6 and E-cadherin. Furthermore, neither marker was a significant prognostic factor for tumor recurrence and survival according to Cox's multiple variant regression analysis.

Zona fasciculata-like cells determine the response of plasma aldosterone to metoclopramide and aldosterone synthase messenger ribonucleic acid level in aldosterone-producing adenoma

The different responses of plasma aldosterone to ACTH and angiotensin II in aldosterone-producing adenoma (APA) is thought to be due to the various cellular compositions of the tumors. To investigate whether the dopaminergic regulation of aldosterone in APA is also dependent on the cellular types, we studied the effects of metoclopramide on plasma aldosterone in six patients with APA. The messenger RNA (mRNA) levels of aldosterone synthase (P450aldo), 11 beta-hydroxylase (P450(11) beta), and 17 alpha-hydroxylase (P450(17) alpha) of APA and normal adrenal glands were determined by competitive polymerase chain reaction. After administration of metoclopramide (an antagonist of dopamine-2 receptor), the increment of plasma aldosterone correlated inversely with the percentage of zona fasciculata cells of APA. The mRNA level of P450aldo in the tumorous portion was much higher, whereas the levels of P450(11) beta and P450(17) alpha mRNAs were lower, than those of the nontumorous portion and normal adrenals. There was a correlation of the percentage of zona fasciculata cells in APA with the levels of P450aldo and P450(11) beta mRNAs, but not with P450(17) alpha mRNA. These results suggest that differential responsiveness of plasma aldosterone to metoclopramide may be due to various proportions of different cell types in APA that may have different expression of dopamine-2 receptor. In addition, this histologically dependent expression was present at the transcriptional level of the gene responsible for aldosterone biosynthesis.

Ileal neobladder reconstruction after radical cystoprostatectomy

To improve the outcome and patient acceptance of bladder substitution, five male patients underwent O-shaped ileal neobladder reconstruction, after radical cystoprostatectomy for invasive bladder cancer, with a mean follow-up of 11 months. With only 40 cm of ileal segment, an O-shaped neobladder was constructed after complete detubularization. Bilateral ureters were implanted using the Le Duc-Camey method. Six months after operation, all patients were totally continent during the day time, and one patient suffered from mild incontinence at night, which could be overcome by waking to void once or twice. The satisfactory continence levels are in agreement with a urodynamic study of the neobladder which showed a low pressure, high-capacity (mean, 456 mL) reservoir in the cystometric tracings. The mean maximal flow rate was 22.2 mL/sec, the mean residual urine was minimal (10 to 20 mL), the mean maximal urethral closing pressure was 74.4 cm H2O and the mean functional profile length was 2.9 cm. All renal units do not have neovesico-ureteral reflux. Two patients showed unilateral hydronephrosis which subsided later, one patient sustained bilateral hydronephrosis and died of jejunal perforation five months postoperatively. There were few perioperative complications and no patient expressed regret at having undergone the procedure. We consider bladder substitution to be the treatment of choice in male patients requiring radical cystoprostatectomy.

Role of urinary cytology and urinary deoxyribonucleic acid flow cytometry in the diagnosis of bladder cancer

In order to determine the diagnostic efficiencies of urinary cytology and urinary deoxyribonucleic acid (DNA) flow cytometry (FCM) in the detection of bladder cancer, 92 patients were studied from March 1991 to the end of July 1992. Thirty cases had previously undergone operation for bladder cancer and 62 cases were suspected as bladder cancer. One to three fresh voided urine samples from the same patient were sent for conventional urinary cytology and urinary DNA FCM analysis. Each patient underwent cystoscopic examination or surgical histopathologic examination to verify the presence of bladder tumor. From December 1991 to the end of July 1992, 52 cases were analyzed and reported separately due to improved FCM techniques. Urinary DNA FCM showed a higher sensitivity than cytology in both the total (p < 0.05) and the second half time period (p < 0.01). Cytology showed a statistically superior specificity against FCM in the total period (p < 0.05) but not in the second half time period (p > 0.1). Combining sensitivity and specificity, FCM's overall accuracy rate was better than cytology in the second half time period (p < 0.05). To clarify the specific features of bladder tumors in which FCM showed superior sensitivity than cytology, we analysed the detection rates for various features of bladder tumor in the second half time period. FCM was better than cytology in detecting multiple tumors, small tumors and papillary tumors. No statistical differences were obtained if tumors were single, larger than 3 cm or flat in outer surface. To our knowledge, no previous similar analysis has been reported in the literature.(ABSTRACT TRUNCATED AT 250 WORDS)

Linker insertion mutagenesis of Drosophila topoisomerase II. Probing the structure of eukaryotic topoisomerase II

The sequences of all type II DNA topoisomerases, and possibly some of their key structural features, are conserved. The N-terminal and middle regions of the eukaryotic DNA topoisomerase II are homologous to the bacterial gyrase subunits B and A, respectively, and the hydrophilic C-terminal region is more divergent among these enzymes. To gain further insights into the structure of eukaryotic topoisomerase II, we constructed 23 linker insertion mutants of Drosophila DNA topoisomerase II. These mutant proteins were expressed in a heterologous yeast system, in which we have previously demonstrated that Drosophila DNA topoisomerase II could be functionally expressed and complement yeast top2 mutations. The linker insertion mutants were characterized genetically by testing for complementation of yeast top2ts mutation at the non-permissive temperature and complementation of yeast top2 null mutation using a color sector assay. We also partially purified the mutant proteins and examined their enzymatic activity by unknotting the P4 knotted DNA. There appears to be a good correlation between the in vivo and in vitro activities. There are nine fully active, six partially active, and eight negative linker insertion mutants. All five linker insertion mutants in the C-terminal region are active and two linker insertion mutants located in the junction of the two regions homologous to gyrB/gyrA subunits are also active. In addition, we also mapped the trypsin-sensitive sites in Drosophila DNA topoisomerase II. The C-terminal region is extremely sensitive to trypsin digestion. Another major trypsin-sensitive site is located between Lys406 and Thr407, which is near the protease sites also observed in the bacterial gyrB subunit and yeast topoisomerase II. We discuss the possible structural and functional implications of these results.

DNA topoisomerase I is essential in Drosophila melanogaster

Both biochemical and genetic experiments suggest that the type I DNA topoisomerase may participate in DNA replication, recombination, transcription, and other aspects of DNA metabolism. Despite its apparent importance, genetic studies in unicellular organisms including eubacteria and yeasts indicate that topoisomerase I is not essential for viability. We have previously isolated the cDNA clone encoding DNA topoisomerase I from Drosophila melanogaster. We report here the cytogenetic mapping of top1 to the X chromosome at 13C1 and isolation of top1 genomic DNA. Using P-element mutagenesis, we have isolated a mutant deficient in Drosophila topoisomerase I functions. Genetic studies of this mutant show that topoisomerase I is essential for the growth and development of the fruit fly, a multicellular organism. The biological functions of topoisomerase I are inferred from our analysis of the regulation of topoisomerase I expression during Drosophila development.

The glutathione S-transferase D genes. A divergently organized, intronless gene family in Drosophila melanogaster

We have characterized a cluster of glutathione S-transferase genes located at 87B on the Drosophila polytene chromosome near the heat shock genes, hsp70. These genes, designated gst Ds in the glutathione S-transferase gene superfamily, are closely linked within a approximately 60-kilobase DNA segment. The gene family has a minimum of eight intronless genes organized in divergent orientations. Two of the genes are probably GST pseudogenes in that their open reading frames are shorter than functional GSTs, and no RNAs from them have been detected thus far. The amino acid sequence identity among the functional genes ranges from 53 to 75% in pairwise comparisons. The intergenic regions are much more AT rich (63-73%) than the coding regions (41-52%), consistent with being promoter/regulatory sequences in Drosophila melanogaster. The mRNA size for each gene suggests that these genes are probably expressed individually from separate promoters. This is the first documentation of definitive physical linkage of a functional glutathione S-transferase multigene family. The genes are divergently organized, and a gradation of sequence similarity exists among the encoded GST isozymes. The patterns of sequence similarity in pairwise comparisons of the family members suggest that gene conversion may have played a role in the evolution of this GST multigene family. We propose that the Drosophila gst D genes provide a unique system for studying GST gene regulation, in vivo physiological functions, and evolution of substrate specificities with a global perspective. The gst D genes in other organisms should be intronless and can be isolated directly from genomic DNAs for functional analyses at the gene and protein levels.

Isolation and characterization of a gene encoding DNA topoisomerase I in Drosophila melanogaster

We synthesized a DNA probe specific for the gene encoding eucaryotic DNA topoisomerase I by the polymerase chain reaction. The sequences of the primers for this reaction were deduced from the regions with extensive homology among the enzymes from the fission and budding yeasts, and the human. From the clones isolated by screening a Drosophila cDNA library with this DNA probe, two cDNA clones of 3.8 and 5.2 kb were characterized and completely sequenced. Both cDNA sequences contain an identical open reading frame for 972 amino acid residues. The 3.8 kb messenger RNA is likely generated by using a polyadenylation site 5' upstream to that used in generating the 5.2 kb mRNA. The predicted amino acid sequence shows that a segment of 420 amino acid residues at the amino terminus is hydrophilic, similar to the amino terminal 200 residues in the yeast and human enzymes. Furthermore, the Drosophila enzyme is unique in that the amino terminal 200 residues are enriched in serine and histidine residues; most of them are present in clusters. The rest of the Drosophila sequence is highly homologous to those from yeast and human enzymes. The evolutionarily conserved residues are identified and are likely the critical elements for the structure and function of this enzyme. A plasmid vector containing the cloned cDNA was constructed for the expression of Drosophila protein in Escherichia coli. The enzymatic and immunochemical analysis of the polypeptide produced in this heterologous expression system demonstrated that the expressed protein shares similar enzymatic properties and antigenic epitopes with DNA topoisomerase I purified from Drosophila embryos or tissue culture cells, thus establishing the bacterial expression system being useful for the future structure/function analysis of the Drosophila enzyme.

[Clinical analysis of urolithiasis in Poh Ai Hospital of I-Lan, Taiwan, R.O.C.--a comparative study with urolithiasis in Japan]

Between August 1987 and December 1990, 546 patients were admitted to the department of Urology at the Poh Ai Hospital of I-Lan, Taiwan, R.O.C. for the treatment of urinary stones. These urinary stone cases accounted for 50 to 60% of all urology patients admitted. The incidence of urolithiasis in I-Lan was estimated at 147/100,000 population in 1990. There were 402 male patients and 144 female patients, The male to female ratio was 2.8: 1. There were 450 upper urinary tract stones (kidney, ureter) in 314 males and 136 females, and 79 lower urinary tract stones (bladder, urethra) in 72 males and 7 females. The ratio of upper to lower urinary tract stones was 6:1. Endourological treatments such as percutaneous nephrolithotripsy and transurethral ureterolithotripsy have increased rapidly in recent years. A summary of the present analysis for composition of 365 stones follows. The most frequent type was calcium-containing stone (92.3%), followed by infection stone (4.7%), then uric acid (UA) stone (3.0%). There were no UA stones found in the female patients. According to urinalysis criteria of more than 10 WBC/HPF (x 400), pyuria was found in 67 cases of 334 metabolic stones (20.1%), and 11 cases of 17 infection stones (67.7%). There were neither pediatric case of stone formation nor cystine stones.

DNA topoisomerases

DNA topoisomerases play an important role in regulating DNA structure, thus affecting many aspects of chromosome function inside cells. Recent progress in this field raises exciting questions regarding the distinct and critical functions of multiple topoisomerases, and the roles of DNA topoisomerases in the processes of chromosome condensation, decondensation, and segregation.

Characterization of a newly established human bladder carcinoma cell line, NTUB1

A new human bladder cancer cell line, NTUB1, has been derived from the surgical specimen of a 70-year-old female patient diagnosed with poorly differentiated transitional cell carcinoma. It has been successfully propagated in vitro for over 24 months without evidence of reaching senescence. Population doubling time was about 21 hours at the 32nd passage. It was tumorigenic in nude mice, and the histologic findings of the heterotransplanted tumor resembled the original tumor. Expression of keratin proteins confirmed its epithelial origin. Cytogenetic analysis showed multiple chromosome changes. Anticancer drugs, including thiotepa and adriamycin, were tested in vitro, and the cytotoxicity did not exceed 50% of the control value; likewise, in this patient chemotherapy was not effective. On the other hand, a combination of recombinant tumor necrosis factor and interferon tau in vitro was more effective against this tumor.

The Drosophila glutathione S-transferase 1-1 is encoded by an intronless gene at 87B

The Drosophila glutathione S-transferase 1-1 is a dimer of a 209 amino acid subunit, designated DmGST1. DmGST1 is encoded by a member of a multigene family. Sequence analysis of a genomic clone for GST1 revealed that it is encoded by an intronless gene. We designate this gene and its other family members the GST D genes in the glutathione S-transferase gene superfamily. The Drosophila GST D genes are mapped by in situ hybridization to chromosome 3R at 87B of the polytene chromosome, which is flanked by the two clusters of hsp70 genes at 87A7 and 87C1. Cytogenetic data in the literature indicated that a puff occurred in this region under heat shock. We report that the glutathione S-transferase activity in Kco cells as determined by conjugation with 1-chloro-2,4-dinitrobenzene is elevated slightly to two-fold under heat shock. The implication of this finding is discussed.

Serum level of immunosuppressive acidic protein in patients with urological malignancies

Immunosuppressive acidic protein (IAP) is a non-specific immunoreactive protein arising from inflammatory or malignant conditions in the human body. We determined the IAP levels in 65 cases with urological malignancies and in 31 cases with benign diseases as a control group during a 9-month period. There were significantly higher serum levels of IAP in cases of bladder transitional cell carcinoma (p = 0.025), prostate adenocarcinoma (p less than 0.00001) and upper urinary tract urothelial cancer (kidney and/or ureter, p = 0.013) as compared with those of the control group. Significant differences in IAP between different tumor stages were found in the bladder cancer group with high stage cases having higher IAP levels (p less than 0.0005). However, no significant differences were found between different tumor gradings. Most of the prostate cancer patients had extremely high IAP values (1,029 +/- 490 micrograms/ml) in this study. Renal cell carcinoma and testicular tumors showed no statistical differences from the control group (p = 0.89 and 0.37, respectively). No differences could be found in the different age groups (by decades) or sexes. The serum IAP level can be a good non-specific tumor marker for bladder cancer staging and probably a good follow-up tool for most urological malignancy patients.

Drosophila topoisomerase II-DNA interactions are affected by DNA structure

The binding of purified Drosophila topoisomerase II to the highly bent DNA segments from the SV40 terminus of replication and C. fasciculata kinetoplast minicircle DNA (kDNA) was examined using electron microscopy (EM). The probability of finding topoisomerase II positioned at or near the bent SV40 terminus and Crithidia fasciculata kDNA was two- and threefold higher, respectively, than along the unbent pBR325 DNA into which the elements had been cloned. Closer examination demonstrated that the enzyme bound preferentially to the junction between the bent and non-bent sequences. Using gel electrophoresis, a cluster of strong sodium dodecyl sulfate-induced topoisomerase II cleavage sites was mapped to the SV40 terminus DNA, and two weak cleavage sites to the C. fasciculata kDNA. As determined by EM, Drosophila topoisomerase II foreshortened the apparent length of DNA by only 15 base-pairs when bound, arguing that it does not wrap DNA around itself. When bound to pBR325 containing the C. fasciculata kDNA and the SV40 terminus, topoisomerase II often produced DNA loops. The size distribution was that predicted from the known probability of any two points along linear DNA colliding. In vitro mapping of topoisomerase II on DNA whose ends were blocked by avidin protein revealed that binding is enhanced at sites located near a blocked end as compared to a free end. These observations may contribute towards establishing a framework for understanding topoisomerase II-DNA interactions.

Drosophila glutathione S-transferase 1-1 shares a region of sequence homology with the maize glutathione S-transferase III

We have characterized a Drosophila glutathione S-transferase (RX:glutathione R-transferase, EC 2.5.1.18) cDNA encoding a protein of 209 amino acids. The cDNA was expressed in Escherichia coli harboring the expression plasmid construct pGTDml-KK. The active enzyme, designated as Drosophila glutathione S-transferase 1-1, had a specific activity toward 1-chloro-2,4-dinitrobenzene comparable to that for the mammalian glutathione S-transferases but did not have as broad a substrate specificity pattern. There is a region of 44 amino acids in this enzyme that shares 66% identity with an analogous region of maize glutathione S-transferase III. Drosophila glutathione S-transferase 1-1 had no obvious homology to any mammalian or parasitic glutathione S-transferases. The gene was found to be a member of a multigene family.