Berberine chloride (dual topoisomerase I and II inhibitor) modulate mitochondrial uncoupling protein (UCP1) in molecular docking and dynamic with in-vitro cytotoxic and mitochondrial ATP production.

Obesity initiates numerous diseases like cardiovascular, metabolic, and type 2 diabetes, and obesity is a vital cause of death worldwide. Plants are necessary to the source of life. Several drug compounds isolated from plants are called phytochemicals which are safe, effective drug moieties to treat several diseases. Berberine chloride is a dual topoisomerase I and II inhibitor, that exhibited potent antitumor activities against several malignancies. However, the effect of Berberine on mitochondria remains unknown. The focus of this study was to determine the role of Berberine on mitochondrial uncoupling protein (UCP1), ATP production, and cytotoxic effect of HEK293T cell at a time and dose-dependent manner analysis by CCK8 assay. The upregulation of mitochondrial UCP1 gene expression reduces adipocyte content by initiating thermogenesis. In this study, berberine chloride significantly up-regulates UCP1 gene expression in brown adipocytes. AT 10 µM concentration of Berberine 48 h treatment demonstrated significant cell death. The decreased level of ATP production leads to mitochondrial uncoupling. Initiate thermogenesis reducing fat droplets in adipocytes. The first time, we used molecular docking and dynamic of Berberine with UCP1 gene in this study and revealed therapeutic potential of Berberine via modulation of mitochondrial UCP1 gene. Further investigation will reveal new insight into mechanisms to treat metabolic-related diseases.Communicated by Ramaswamy H. Sarma.

TOP1 inhibition induces bifurcated JNK/MYC signaling that dictates cancer cell sensitivity.

Rationale: Triple-negative breast cancer (TNBC) does not respond to anti-estrogen and anti-HER2 therapies and is commonly treated by chemotherapy. TNBC has a high recurrence rate, particularly within the first 3 years. Thus, there is an urgent clinical need to develop more effective therapies for TNBC. Topoisomerase I (TOP1) inhibitors cause DNA damage, making these drugs desirable for TNBC treatment since DNA repair machinery is defective in this subtype of breast cancer. Among the main molecular subtypes of breast cancer, the TNBC cell lines exhibited the highest TOP1 inhibition sensitivity. However, clinically used TOP1 inhibitors, such as topotecan and irinotecan, have shown limited clinical applications and the reasons remain unclear. Understanding the mechanism of differential responses to TOP1 blockade and identifying the predictive markers for cancer cell sensitivity will help further TOP1-targeted therapy for TNBC treatment and improve the clinical use of TOP1 inhibitors. Methods: Viability assays were used to evaluate breast cancer cell sensitivity to topotecan and other TOP1 inhibitors as well as TOP2 inhibitors. An in vitro-derived topotecan-resistant TNBC cell model and TNBC xenograft models were employed to confirm cancer cell response to TOP1 blockade. RNA-seq was used to identify potential predictive markers for TNBC cell response to TOP1 blockade. Western blotting and qRT-PCR were performed to measure the protein levels and RNA expression. ATAC-seq and luciferase reporter assays were used to examine MYC transcriptional regulations. The effects of MYC and JNK in cancer cell response to TOP1 inhibition were validated via loss-of-function and gain-of-function experiments. Results: We observed two distinct and diverging cancer cell responses - sensitive versus resistant to TOP1 inhibition, which was confirmed by TNBC xenograft mouse models treated by topotecan. TNBC cells exhibited bifurcated temporal patterns of ATR pathway activation upon TOP1 inhibitor treatment. The sensitive TNBC cells showed an "up then down" dynamic pattern of ATR/Chk1 signaling, while the resistant TNBC cells exhibited a "persistently up" profile. On the contrary, opposite temporal patterns of induced expression of MYC, a key regulator and effector of DNA damage, were found in TNBC cells treated by TOP1 inhibitors. Mechanistically, we showed that TOP1-induced JNK signaling upregulated MYC expression. Furthermore, pharmacological inhibition of ATR reversed TNBC cell resistance to topotecan, whereas MYC knockdown and JNK inhibition reduced cancer cell sensitivity. Conclusions: Dynamic temporal profiles of induced ATR/Chk1 and JNK activation as well as MYC expression, may predict cancer cell response to TOP1 inhibitors. JNK activation-mediated constitutive elevation of MYC expression may represent a novel mechanism governing cancer cell sensitivity to TOP1-targeting therapy. Our results may provide implications for identifying TNBC patients who might benefit from the treatment with TOP1 inhibitors.

N-2-(Phenylamino) Benzamide Derivatives as Dual Inhibitors of COX-2 and Topo I Deter Gastrointestinal Cancers via Targeting Inflammation and Tumor Progression.

Given the close association between inflammation and cancer, combining anti-inflammation therapy is prominent to improve the anticancer effect. Based on I-1, a series of agents targeting COX-2 and Topo I were designed by combining fenamates and phenols. The optimal compound 1H-30 displayed an enhanced inhibitory effect on COX-2 compared to tolfenamic acid and I-1 and showed better inhibition of Topo I than I-1. Importantly, 1H-30 showed potential anticancer effects and suppressed the activation of the NF-κB pathway in cancer cells. 1H-30 inhibited the nuclear translocation of NF-κB and suppressed the production of NO, COX-2, and IL-1ß in RAW264.7. In vivo, 1H-30 showed acceptable pharmacokinetic parameters, decreased the tumor growth without affecting the body weight, down-regulated COX-2 and MMP-9, and induced apoptosis in the CT26.WT tumor-bearing mice. Accordingly, 1H-30 as a potential Topo I/COX-2 inhibitor which possessed anti-inflammatory and anticancer effects, with inhibition of the NF-κB pathway, is promising for gastrointestinal cancer therapy.

Higher detection of JC polyomavirus in colorectal cancerous tissue after pretreatment with topoisomerase I enzyme; colorectal tissue serves as a JCPyV persistence site.

BACKGROUND: The JC polyomavirus has been blamed to contribute in colorectal cancer (CRC), however, the topic is still controversial. Varying detection rate of JCPyV genome has been reported mainly due to technical reasons. Here, we provide summative data on the topic, with emphasize on technical issues. METHODS: Formalin-fixed paraffin-embedded tissue samples from 50 patients with CRC, consisting of tumoral and non-cancerous marginal tissue (totally 100 samples) were included in the study. After DNA extraction, specific JCPyV T-Ag sequences were targeted using Real-time PCR. To unwind the supercoiled JCPyV genome, pretreatment with topoisomerase I, was applied. Immunohistochemical (IHC) staining was performed using an anti-T-Ag monoclonal antibody. RESULTS: In the first attempts, no samples were found to be positive in Real-time PCR assays. However, JCPyV sequences were found in 60% of CRC tissues and 38% of non-cancerous colorectal mucosa after application of pre-treatment step with topoisomerase I enzyme (P = 0.028). T-Ag protein was found in the nuclear compartment of the stained cells in IHC assays. CONCLUSIONS: The presence of JCPyV in CRC tissues, as well as T-Ag localization in the nucleolus, where its oncogenic effect takes place, may provide supporting evidence for JCPyV involvement in CRC development. The study highlights the importance of using topoisomerase I to enhance JCPyV genome detection. Also, colorectal tissue is one of the permissive human tissue for JC resistance after preliminary infection.

Dihydroxylated 2,6-diphenyl-4-chlorophenylpyridines: Topoisomerase I and IIα dual inhibitors with DNA non-intercalative catalytic activity.

With the aim to develop novel antiproliferative agents, a new series of eighteen dihydroxylated 2,6-diphenyl-4-chlorophenylpyridines were systematically designed, prepared, and investigated for their topoisomerase (topo) I and IIα inhibitory properties and antiproliferative effect in three different human cancer cell lines (HCT15, T47D, and HeLa). Compounds 22-30 which possess a meta- or para-phenol on 2-, or 6-position of central pyridine ring showed significant dual topo I and topo IIα inhibitory activities with strong antiproliferative activities against all the tested human cancer cell lines. However, compounds 13-21 which possess an ortho-phenol on 2-, or 6-position of central pyridine ring did not show significant topo I and topo IIα inhibitory activities but displayed moderate antiproliferative activities against all the tested human cancer cell lines. Compound 23 exhibited the highest antiproliferative potency as much as 348.5 and 105 times compared to etoposide and camptothecin, respectively, in T47D cancer cell line. The structure-activity relationship study revealed that the para position of a hydroxyl group at 2-and 6-phenyl ring and chlorine atom at the para position of 4-phenyl ring of the central pyridine exhibited the most significant topo I and topo IIα inhibition, which might indicate introduction of the chlorine atom at the phenyl ring of 4-pyridine have an important role as dual inhibitors of topo I and topo IIα. Compound 30 which showed the most potent dual topo I and topo IIα inhibition with strong antiproliferative activity in T47D cell line was selected to perform further study on the mechanism of action, which revealed that compound 30 functions as a potent DNA non-intercalative catalytic topo I and IIα dual inhibitor.

The autoantigen DNA topoisomerase I interacts with chemokine receptor 7 and exerts cytokine-like effects on dermal fibroblasts.

OBJECTIVE: Previous studies have demonstrated that, once released into the extracellular environment, the systemic sclerosis (SSc)-associated autoantigen DNA topoisomerase I (topo I) binds specifically to the surface of fibroblasts via an unknown receptor. We extended these results by identifying topo I-mediated cellular effects and characterizing the specific target of topo I on fibroblast surfaces. METHODS: Purified topo I was used to investigate intracellular signaling pathway activation and tested for cell migration. To demonstrate the expression of specific chemokine receptors on fibroblasts, we performed immunoblotting and flow cytometry. To evaluate the direct interaction between chemokine receptor and topo I, a protein-protein based enzyme-linked immunosorbent assay (ELISA) was used. Finally, topo I coupled to the fluorochrome phycoerythrin (PE) was used to investigate competition of topo I specific binding on fibroblast surfaces with chemokine ligand. RESULTS: Topo I stimulated the phosphorylation of phospholipase Cγ1, c-Raf, ERK-1/2, and p38 MAPK, intracellular signaling pathways that stimulated fibroblast migration via a G(αi) protein-coupled receptor. CCR7 was found to interact directly with topo I. Furthermore, its ligand, CCL21, competed in vitro for this interaction and in vivo with the binding of PE-coupled topo I to fibroblast surfaces. CONCLUSION: These new roles of topo I in fibroblast physiology and the identification of its target on the cell surface demonstrate that topo I is a bifunctional autoantigen and open up new perspectives of study in the field of SSc-associated anti-topo I autoantibodies.

Practical strategies for suppressing hypoxia-inducible factor activity in cancer therapy.

The utility of anti-angiogenic strategies for cancer control is strongly compromised by hypoxia-driven phenotypic changes in cancer cells, which make cancer cells more invasive and more prone to give rise to metastases. A key mediator of this phenotypic shift is the transcription factor hypoxia-inducible factor-1 (HIF-1), which acts directly and indirectly to promote the epidermal-mesenchymal transition, boost cancer invasiveness, increase production of angiogenic factors, and induce chemoresistance. In some cancers, HIF-1 activity is constitutively elevated even in aerobic environments, making the cancer harder to treat and control. Practical strategies for suppressing HIF-1 activation may include the following: inhibiting NF-kappaB activation with salicylic acid and/or silibinin, which should decrease transcription of the HIF-1alpha gene; suppressing translation of HIF-1alpha mRNA with drugs that inhibit mTOR or topoisomerase I; supporting the effective activity of prolyl hydroxylases - which promote proteasomal degradation of HIF-1alpha under aerobic conditions - with antioxidant measures, alpha-ketoglutarate, and possibly dichloroacetate; promoting the O(2)-independent proteasomal degradation of HIF-1alpha with agents that inhibit the chaperone protein Hsp90; and blocking HIF-1 binding to its DNA response elements with anthracyclines. The utility of various combinations of these strategies should be tested in cancer cell cultures and rodent xenograft models; initial efforts in this regard have yielded encouraging results. Comprehensive strategies for suppressing HIF-1 activity can be expected to complement the efficacy of cancer chemotherapy and of effective anti-angiogenic regimens.

Mechanism of hydrolysis of a novel indolocarbazole topoisomerase I inhibitor.

The degradation kinetics and reaction product profile of the antitumor agent 1 in aqueous solution was studied. Hydrolysis of the pendant imide ring of 1 is the primary mode of thermal degradation in aqueous solution, and the pH rate profile of 1 has a V-shape indicating that hydrolysis of the imide ring can be catalyzed by either acid or base. Hydrolysis of 1 to the anhydride derivative 3 or the dicarboxylic acid derivative 4 is stepwise and the intermediates 2a and 2b formed by initial hydrolytic attack have been observed under alkaline conditions. An overall mechanism for the hydrolysis of 1 in aqueous solution has been proposed. Extrapolating Arrhenius behavior to the hydrolysis reaction of 1 in aqueous solution maintained at a pH value of 4 suggests an aqueous buffered formulation has sufficient thermal stability to be considered a robust room temperature drug product.

90-kDa heat shock protein inhibition abrogates the topoisomerase I poison-induced G2/M checkpoint in p53-null tumor cells by depleting Chk1 and Wee1.

The G(2)/M cell cycle checkpoint is regulated by a multitude of signaling pathways after genotoxic stress. Herein, we report that treatment with the 90-kDa heat shock protein (Hsp90) molecular chaperone inhibitor 17-allylamino-17-demethoxygeldanamycin (17AAG) selectively abrogates the G(2)/M checkpoint induced by 7-ethyl-10-hydroxycamptothecin (SN-38), an active metabolite of irinotecan, in p53-null compared with p53-intact HCT116 colon cancer cells. The basis for this selectivity can be explained in part by the lack of p21 induction in p53-null cells. In accord with published results, we could show that treatment with 17AAG resulted in depletion of Chk1, a known Hsp90 client protein. In addition, we observed a time- and dose-dependent decrease in Wee1 kinase level, a negative regulator of mitosis, after 17AAG treatment in gastrointestinal cancer cells. Depletion of Wee1 protein preceded mitotic entry induced by 17AAG, and this decrease could be partially rescued by cotreatment with a proteasome inhibitor. Coimmunoprecipitation experiments showed that Hsp90 and Wee1 interacted in whole cells, and 17AAG treatment decreased the degradative half-life of Wee1, indicating that Wee1 is another Hsp90 client in mammalian cells. Knockdown of Chk1 and Wee1 by short interfering RNA each resulted in abrogation of the G(2)/M checkpoint induced by SN-38. The combination of SN-38 and 17AAG was shown to be synergistic in p53-null but not in parental HCT116 cells by median effect/combination index analysis. Taken together, 17AAG specifically inhibits the G(2)/M checkpoint in p53-defective cells by down-regulation of two critical checkpoint kinases, Chk1 and Wee1.

Effects of the Cdc2-like kinase-family and DNA topoisomerase I on the alternative splicing of eNOS in TNF-alpha-stimulated human endothelial cells.

Nitric oxide (NO) is synthesized by endothelial nitric oxide synthase (eNOS) and plays an important role in vascular homeostasis and cardiovascular diseases. It has recently been shown that increased expression of alternatively spliced eNOS isoforms eNOS 13A, B and C and heterodimerization with 'full-length' eNOS is associated with a decreased eNOS activity. The regulatory pathways enabling this phenomenon are completely unknown. This study examined the effect of Cdc2-like kinases and DNA topoisomerase I on eNOS splicing in TNF-alpha-induced human umbilical vein endothelial cells (HUVECs). We found that inhibition of DNA topoisomerase I, but not Cdc2-like kinases, prevents the TNF-alpha-induced increase in eNOS isoform expression and NO reduction in HUVEC. Moreover, we show that the inhibition of DNA topoisomerase I or the Cdc2-like kinases differently modulates the phosphorylation of the serine/arginine-rich proteins SRp75 and SRp55. Our results demonstrate, for the first time, that DNA topoisomerase I but not Cdc2-like kinases serves as an important regulator of the differential eNOS isoform expression in endothelial cells, thereby modulating the TNF-alpha-induced eNOS activity switch.

p21CDKN1A allows the repair of replication-mediated DNA double-strand breaks induced by topoisomerase I and is inactivated by the checkpoint kinase inhibitor 7-hydroxystaurosporine.

This study provides evidence for the importance of p21(CDKN1A) for the repair of replication-mediated DNA double-strand breaks (DSBs) induced by topoisomerase I. We report that defects of p21(CDKN1A) and p53 enhance camptothecin-induced histone H2AX phosphorylation (gammaH2AX), a marker for DNA DSBs. In human colon carcinoma HCT116 cells with wild-type (wt) p53, gammaH2AX reverses after camptothecin removal. By contrast, gammaH2AX increases after camptothecin removal in HCT116 cells deficient for p53 (p53-/-) or p21(CDKN1A) (p21-/-) as the cells reach the late-S and G2 phases. Since p21-/- cells exhibit similar S-phase arrest as wt cells in response to camptothecin and aphidicolin does not abrogate the enhanced gammaH2AX formation in p21-/- cells, we conclude that enhanced gammaH2AX formation in p21-/- cells is not due to re-replication. The cell cycle checkpoint abrogator and Chk1/Chk2 inhibitor 7-hydroxystaurosporine (UCN-01) also increases camptothecin-induced gammaH2AX formation and inhibits camptothecin-induced p21(CDKN1A) upregulation in HCT116 wt cells. TUNEL (terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling) assays demonstrate that gammaH2AX formation in late S and G2 cells following CPT treatment corresponds to DNA breaks. However, these breaks are not related to apoptotic DNA fragmentation. We propose that p21(CDKN1A) prevents the collapse of replication forks damaged by stabilized topoisomerase I cleavage complexes.

Assessment of antioxidant / anticarcinogenic activity of plant extracts by a combination of molecular methods.

Cancer chemoprevention is considered to be a promising approach for cancer control, as it has been identified by both epidemiological and molecular studies that environmental factors are the major causes of cancer. Chemoprevention can be defined as the use of agents to prevent, inhibit or reverse the process of carcinogenesis. Several epidemiological studies have shown that fruits, vegetables and common beverages, as well as herbs and plants, are rich sources of chemopreventive compounds. In the present report, a battery of in vitro methods for the identification of chemopreventive agents are presented. These methods include: i) inhibition of bleomycin-induced mutations in Salmonella typhimurium TA102 cells, ii) inhibition of bleomycin-induced sister chromatid exchanges (SCEs) in human peripheral blood lymphocytes, iii) protection from mitomycin C-induced DNA strand breakage and iv) inhibition of topoisomerase I DNA relaxation. The first three methods are also used for the identification of agents which prevent reactive oxygen species (ROS)-mediated DNA damage.

Phase I/II trial of simultaneous whole-brain irradiation and dose-escalating topotecan for brain metastases.

BACKGROUND AND PURPOSE: Topotecan penetrates the blood-brain barrier and sensitizes tumor cells against radiation. A phase I/II dose-escalating trial of repetitive daily i. v. topotecan application simultaneously with whole-brain irradiation (WBRT) was conducted to estimate toxicity, maximum tolerated dose and survival in patients with inoperable brain metastases. PATIENTS AND METHODS: In 47 patients suffering from previously untreated brain metastases, topotecan was applied on a daily i. v. schedule simultaneously with WBRT (36 Gy/3-Gy fractions). The infusion schedule started at the beginning of WBRT and was discontinued during weekends. Each infusion was completed within 1-2 h before irradiation. In a dose-finding study, topotecan was escalated from 5 x 0.5 mg/m(2), 8 x 0.5 mg/m(2), 12 x 0.5 mg/m(2) to 12 x 0.6 mg/m(2). RESULTS: Altogether, 38/47 patients (81%) completed the prescribed schedule. Leukopenia and thrombocytopenia were dose-limiting. Grade 3/4 hematologic toxicity occurred in 5/32 chemonaïve patients (16%) and 7/15 patients (47%) with previous chemotherapy. At 12 x 0.6 mg/m(2), 2/4 patients experienced grade 4 leukopenia/thrombopenia. Nonhematologic toxicities were generally mild to moderate and unrelated to topotecan. Response evaluation was possible in 26/47 patients, overall response rate was 58% (CR [complete remission] 5/26, PR [partial remission] 10/26, NC [no change] 8/26). Median survival amounted to 5.1 months. In 15/42 patients (36%), brain metastases were the dominant cause of death. CONCLUSION: For a daily topotecan schedule simultaneous to WBRT, the maximum tolerated dose is 12 x 0.5 mg/m(2) in chemonaïve patients. For chemo-pretreated patients, daily doses should be reduced to 0.4 mg/m(2). A phase III trial has now been started to find out whether WBRT + topotecan increases survival compared to WBRT alone.

Constraints imposed by supercoiling on in vitro amplification of polyomavirus DNA.

Previous attempts to identify oncogenic polyomaviruses in human cancers have yielded conflicting results, even with the application of PCR technology. Here, it was considered whether the topological features of the polyomavirus genome interfere with efficient PCR amplification. Plasmid and SV40 DNAs were used as a model system for comparing the amplification efficiency of supercoiled, circular relaxed and linear templates. It was found that detection of circular templates required 10 times more molecules than detection of identical but linear templates. Supercoiling hindered the in vitro amplification of SV40 circles by a factor of 10, and erratic amplification of supercoiled SV40 occurred with subpicogram amounts of template. Accordingly, topoisomerase I treatment of DNA improved the PCR detection of supercoiled SV40, significantly decreasing the number of false-negative samples. Previously described, yet controversial, polyomavirus presence in human tissues should be reconsidered and topoisomerase I-sensitive polyomavirus amplification might help to detect polyomavirus genomes in mammalian tissues.

Combined topoisomerase I inhibition for the treatment of metastatic colon cancer.

The objective of this study was to define the maximally tolerated dose (MTD) and response rate of a combination of two topoisomerase I inhibitors, topotecan and irinotecan, in patients with metastatic colon cancer. Eleven patients, the majority with previously progressive disease on 5-fluorouracil-based regimens, were enrolled onto a phase I/II dose escalation trial utilizing continuous infusion topotecan for 2 weeks and weekly irinotecan x 3 with cycles repeated every 28 days. Dosages of topotecan utilized included 0.2 and 0.25mg/m2/day. Irinotecan was administered at a dose of 62 mg/m2 by i.v. bolus. Patients were followed for toxicity and response. The MTD of the combination of agents was found to be 0.25mg/m2/day for topotecan and 62 mg/m2 for irinotecan. The most common serious toxicities were diarrhea and nausea/vomiting. Only one patient experienced grade III neutropenia. There were no complete or partial responses. However, four patients had prolonged disease stabilization (SD) of up to 324 days and this group remained on protocol therapy for an average of 227 days (p=0.0005 versus patients not achieving SD). We concluded that the MTD for this combination of topoisomerase I inhibitors, given on this particular schedule, has been defined. This combination cannot be recommended as a first- or second-line therapy for patients with metastatic colon cancer based on the responses observed. However, approximately one-third of patients achieved prolonged disease stabilization. Topotecan with irinotecan may be useful as a palliative regimen for a subgroup of colon cancer patients.

The expressions of p21 and pRB may be good indicators for the sensitivity of esophageal squamous cell cancers to CPT-11: Cell proliferation activity correlates with the effect of CPT-11.

Previously, we demonstrated that CPT-11 is an effective agent against esophageal squamous cell cancers (ESCC), and that the protein level of DNA topoisomerase I can be a predictor for sensitivity to CPT-11 (Jpn J Cancer Res 2001; 92: 1335-41). Here, we describe our search for additional predictors of sensitivity to CPT-11, mainly among cell cycle-regulating proteins, because the cytotoxicity of CPT-11 is significantly correlated with the percentage of ESCC cells in S-phase. To this end, we selected and examined the expressions of 5 proteins involved in G1-S transition, i.e., p53, cyclin D1, p21, p27, and pRB, in 14 ESCC cell lines by western blot analysis. Among these proteins, the expression levels of p21 and pRB showed significant differences that were associated with the IC50 values for CPT-11 (P = 0.0339 and P = 0.0109, respectively). Namely, the expression of p21 or pRB independently could be a good indicator of CPT-11 efficacy in ESCC. In addition, the cell proliferation activities examined by enzyme-linked immunosorbent assay (ELISA) using 5-bromo-2'-deoxyuridine (BrdU) showed a significant correlation with the percentage of total S-phase cells (correlation coefficient = 0.568, P = 0.0324), and an inverse correlation with the IC50 values for CPT-11 (correlation coefficient =-0.601, P = 0.0213). Because, as in the case of DNA topoisomerase I, the cell proliferation activity determined using BrdU shows a close relationship with the MIB-1 labeling index, immunohistochemical studies of p21, pRB, and MIB-1 in resected ESCC specimens and/or biopsy samples could make it possible to predict more precisely the sensitivity of ESCC patients to CPT-11 prior to treatment.

Topoisomerase I and ATP activate cDNA synthesis of human immunodeficiency virus type 1.

Replication of human immunodeficiency virus type 1 (HIV-1) is regulated at reverse transcription. Cellular topoisomerase I has been reported to be carried into HIV-1 virions and enhance cDNA synthesis in vitro, suggesting that topoisomerase I expressed in virus producer cells regulates reverse transcription. Here, by employing both indicator cell assay and endogenous reverse transcription (ERT) assay, we show that topoisomerase I and adenosine triphosphate (ATP) enhanced cDNA synthesis of HIV-1. In addition, topoisomerase I mutants, R488A and K532A, lacking enzymatic activity, attenuated the efficiency of cDNA synthesis and resulted in inhibition of the infectivity of HIV-1, suggesting that the activity of topoisomerase I lacking in these mutants is indispensable for the cDNA synthesis in the HIV-1 replication process. Furthermore, ATP could dissociate topoisomerase I from the topoisomerase I-RNA complex and enhance cDNA synthesis in vitro. These findings suggest that cellular topoisomerase I and ATP play a pivotal role in the synthesis of cDNA of HIV-1.

Resolution of a Holliday junction by vaccinia topoisomerase requires a spacer DNA segment 3' of the CCCTT/ cleavage sites.

Vaccinia virus DNA topoisomerase catalyzes resolution of synthetic Holliday junctions in vitro. The mechanism entails concerted transesterifications at two recognition sites, 5'-CCCTT/, that are opposed within a partially mobile four-way junction. Efficient resolution occurs on a junction with a 10 bp segment of branch mobility (5'-GCCCTTATCG) that extends 4 bp 3' of the scissile phosphate. Here we report that resolution is decreased when branch mobility is limited to an 8 bp segment extending 2 bp 3' of the cleavage site and then eliminated when branch mobility is confined to the 6 bp GCCCTT sequence 5' of the scissile phosphate. We surmise that a spacer region 3' of CCCTT is needed for simultaneous cleavage at two opposing sites at the junction. Branch mobility is not required for reaction chemistry at a junction, because topoisomerase cleaves a single CCCTT site in a non-mobile four-way junction where the scissile phosphate is at the crossover point. The junction resolvase activity of topo-isomerase may be involved in forming the hairpin telomeres of the vaccinia genome.

Poisoning of human DNA topoisomerase I by ecteinascidin 743, an anticancer drug that selectively alkylates DNA in the minor groove.

Ecteinascidin 743 (Et743, National Service Center 648766) is a potent antitumor agent from the Caribbean tunicate Ecteinascidia turbinata. Although Et743 is presently in clinical trials for human cancers, the mechanisms of antitumor activity of Et743 have not been elucidated. Et743 can alkylate selectively guanine N2 from the DNA minor groove, and this alkylation is reversed by DNA denaturation. Thus, Et743 differs from other DNA alkylating agents presently in the clinic (by both its biochemical activities and its profile of antitumor activity in preclinical models). In this study, we investigated cellular proteins that can bind to DNA alkylated by Et743. By using an oligonucleotide containing high-affinity Et743 binding sites and nuclear extracts from human leukemia CEM cells, we purified a 100-kDa protein as a cellular target of Et743 and identified it as topoisomerase I (top1). Purified top1 was then tested and found to produce cleavage complexes in the presence of Et743, whereas topoisomerase II had no effect. DNA alkylation was essential for the formation of top1-mediated cleavage complexes by Et743, and the distribution of the drug-induced top1 sites was different for Et743 and camptothecin. top1-DNA complexes were also detected in Et743-treated CEM cells by using cesium chloride gradient centrifugation followed by top1 immunoblotting. These data indicate that DNA minor groove alkylation by Et743 induces top1-mediated protein-linked DNA breaks and that top1 is a target for Et743 in vitro and in vivo.