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Wei Dai

Publications and source records attributed to Wei Dai.

At least 37 records · Page 2Linked to original sources
PubMed2006

Advances in mitotic inhibitors for cancer treatment.

Based on their mechanism of action, anti-tumor drugs that target the cell cycle can be generally divided into three categories, namely, blocking DNA synthesis, causing DNA damage, and disrupting mitotic processes. In terms of mitotic inhibitors, most compounds used in the clinic impair the normal function of mitotic spindles by targeting tubulins, basic building blocks of microtubules. In vivo, these compounds often exhibit significant side effects, thus limiting their efficacy. Mitotic processes are under tight control through surveillance mechanisms commonly termed checkpoints. Defects in the regulation of these checkpoints often result in genomic instability, which predisposes the cell to malignant transformation. As cancer is the consequence of uncontrolled cell division, great efforts have been devoted to discover drugs that target mitosis, thereby halting cell division and inducing mitotic catastrophe with minimal cytotoxicity to non-dividing or normally dividing cells. This review primarily focuses on mitotic proteins that have been explored as new targets for anti-cancer drug development during the past decade.

Antimitotic Agents↗
PubMed2006

BRCA2 in mitotic exit: a new role in regulating genomic stability.

Evaluation of: Daniels MJ, Wang Y, Lee M, Venkitaraman AR: Abnormal cytokinesis in cells deficient in the breast cancer susceptibility protein BRCA2. Science 306, 876-879 (2004). Cytokinesis is the division of the cytoplasm of a parent cell into daughter cells after nuclear division. Cytokinesis failure is often accompanied by the generation of cells with an unstable tetraploidy content, which predisposes the cells to develop aneuploidy and malignancies. A recent study by Venkitaraman's group demonstrates that BRCA2, a breast cancer susceptibility gene product, also functions in mediating normal cytokinesis. Similar to the subcellular localization of Aurora kinase, BRCA2 is present at the cleavage furrow and the midbody during late mitosis. Deficiency in BRCA2 function results in cytokinesis failure, which is associated with abnormal localization of myosin II, a key protein essential for the formation of the cleavage furrow. This study is of significance as it shows for the first time that BRCA2 has a function in controlling mitotic exit, deregulation of which contributes to gross genomic instabilities in daughter cells.

Animals↗
PubMed2006

Phenylhexyl isothiocyanate inhibits histone deacetylases and remodels chromatins to induce growth arrest in human leukemia cells.

Natural isothiocyanates, present in cruciferous vegetables and synthetic phenylhexyl isothiocyanate (PHI) are chemopreventive agents which act by blocking the initiation of carcinogen-induced tumors in rodents. We have demonstrated that isothiocyanates are also growth regulators, inhibiting cell cycle cdk activity and up-regulating inhibitor p21WAF1 (p21) in cancer cells. The up-stream mechanism to modulate cell cycle progression remained to be elucidated. Here, we have demonstrated that exposure of HL-60 leukemia cells to PHI induced G1 arrest and apoptosis. The hypothesis that PHI inhibits cell growth via chromatin remodeling was investigated. PHI mediates the complex cross talk between chromatin and DNA, and it was demonstrated for the first time as an inhibitor of histone deacetylases (HDAC). Thus, the HDAC activity in PHI-exposed HL-60 cells was reduced. Additionally, PHI reduced the expression of HDAC and increased the level of acetyl transferase p300, in favor of accumulation of acetylated histones. Within hours, global acetylation of histones was enhanced. PHI further mediated selective alterations of histone methylation, with a pattern consistent to the marks of transcription competent chromatins. The relationship between acetylated histones and p21 was examined by chromatin immunoprecipitation (ChIP) assay. Chromatins from cells exposed to PHI contained more p21 DNA in the precipitates of hyperacetylated histones, indicating more accessibility of transcription machinery to the p21 promoter after chromatin unfolding. The cell cycle inhibitors were activated as a result. In contrast to the PHI-induced apoptosis in HL-60 cells, which was mediated by caspase-9 up-regulation and bcl-2 reduction, PHI did not induce significant apoptosis in the mononuclear cells from normal peripheral blood and bone marrow. The results revealed a potential selective effect of isothiocyanates to inhibit the growth of malignant cells.

Apoptosis↗
PubMed2006

[Lamivudine administration prevents fulminant hepatic failure in patients with severe chronic hepatitis B].

OBJECTIVES: To study the effect of using lamivudine to prevent fulminant hepatic failure (FHF) in patients with chronic hepatitis B. METHODS: 164 patients were randomly put into a conventional supporting treatment control group and a lamivudine treatment group. In the latter, 82 patients were given lamivudine orally at a dose of 100 mg every day besides the support care which was also given to the control group. RESULTS: The rate of deterioration to chronic severe hepatitis in the lamivudine treatment group was significantly lower than that of the control group (23.2% vs. 46.3%, P < 0.01). 52.6% (20/38) with chronic severe hepatitis in the control group died. Only 26.3% (5/19) in the lamivudine treatment group succumbed to terminal liver disease (P < 0.01). There was a significant difference between the two groups in regards to the complication incidence of gastrointestinal bleeding, infections, hepatic coma, and kidney failure (P < 0.05). In addition, the recovery of liver function and liver fibrosis, and the rates of HBeAg loss and seroconversion in the lamivudine treatment group were better than those in the control group. Furthermore, the serum HBV DNA levels decreased more rapidly and continued to be substantially suppressed in the lamivudine treatment group. CONCLUSIONS: Our results suggest that lamivudine administration with improved support care not only is likely to prevent chronic severe hepatitis occurrence in patients with chronic viral hepatitis B of a severe degree, but also shows some efficacy in preventing FHF.

Adult↗
PubMed2005

Solution-phase synthesis and electrochemical hydrogen storage of ultra-long single-crystal selenium submicrotubes.

Ultra-long single-crystalline trigonal selenium submicrotubes were synthesized using a facile one-step solution-phase approach with the assistance of nonionic surfactant Polyoxyethylene(20)sorbitan monolaurate (Tween-20), which turned out to be significant for the formation of ultra-long Se submicrotubes. XRD, Raman, SEM, and TEM were adopted to characterize the morphology, structure and phase composition of the as-prepared Se products. It was found that the length of the obtained Se submicrotubes was over 100 microm. By variation of the experimental parameters, the t-Se spheres, nanowires, and broken microtubes can be prepared. The possible growth mechanism of the ultra-long selenium submicrotubes was explained. In addition, we have also demonstrated that the synthesized ultra-long t-Se submicrotubes using the Tween-20-assisted approach can electrochemically charge and discharge with the high capacity of 265 mAh/g (corresponding to 0.97 wt % hydrogen in SWNTs) under normal atmosphere at room temperature. Cyclic voltammetry was adopted to investigate the adsorption-oxidation behavior of ultra-long selenium submicrotubes. It was observed that the morphology of the synthesized selenium products had a remarkable influence on their capacity of electrochemical hydrogen storage. These differences in hydrogen storage capacity are likely due to the size and density of tubes as well as the microcosmic morphology of different Se samples. The as-obtained ultra-long Se submicrotubes are expected to find wide applications in hydrogen storage, high-energy batteries, and optoelectronic, biologic, and catalytic fields as well as in the studies of structure-property relationships. This simple Tween-assisted approach might be extended to the preparations of one-dimensional nanostructures of tellurium and other anisotropic materials.

Journal Article↗
PubMed2005

Shugoshin, a guardian for sister chromatid segregation.

To ensure sister chromatids to be equally transmitted to daughter cells, it is imperative that physical association of sister chromatids is maintained during S, G2, and early mitosis until the onset of anaphase. Cohesion of sister chromatids in eukaryotes is largely achieved by the cohesin complex. In vertebrates, cohesin molecules are dissociated from chromosome arms but not from centromeres during prophase by the so-called prophase pathway. Although it remains unclear what is the molecular basis by which centromeric cohesin is retained, a flurry of recent studies have shed light on a family of proteins named Shugoshin (Sgo) that are evolutionarily conserved across eukaryotes. Sgo1 functions as a protector of centromeric cohesin during meiosis in yeast and during mitosis in high eukaryotes. Suppression of Sgo1 function results in premature separation of sister chromatids in both meiosis and mitosis. The discovery of members of the Sgo family may help to explain how centromeric cohesin is protected from dissociation from DNA until the onset of anaphase. Given the importance of chromosome cohesion in the maintenance of genomic stability, further characterization of Sgo1 and related molecules may also open up new avenues of research for developing new strategies for cancer intervention.

Animals↗
PubMed2005

[Infection of Helicobacter pylori strains with multiple vacA m-region subtypes and/or iceA mixed genotype among the Bai, Naxi, and Han populations in Yunnan province].

OBJECTIVE: To study the epidemiology and pathogenicity of mixed infection of Helicobacter pylori (H. pylori) strains with multiple vacA m-region subtypes and/or iceA mixed genotype among the Bai, Naxi, and Han populations in Yunnan province. METHODS: Gastric mucous membrane were obtained by gastroscopy from 444 patients with digestive ulcer or chronic gastritis, 165 of Han nationality, 117 of Bai nationality, and 162 of Naxi nationality. H. pylori was isolated from 109 patients and cultured. RT-PCR was used to detect the Helicobacter pylori strains vacA gene subtype and iceA genes. RESULTS: The overall rates of vacA gene s1 type and vacA gene s2 type were 98.2% (107/109) and 1.8% (2/109) respectively. The overall rates of vacA gene m2 type, vacA gene m1a type, vacA gene m1b type, and mixed types were 45.9% (50/109), 0.9% (1.109), 23.9% (26/109), and 11% (12/109) respectively; and m region was not identified in 18.3% (20/109) of the strains. The overall rates of iceA1 and iceA2 genes were 67.0% (73/109) and 41.3% (45/109) respectively. In the specimens from the patients of Bai nationality, as regards the s region, only s1 type was identified in all specimens; the rates of vacA gene m2 type, vacA gene m1a type, vacA gene m1b type, and mixed type were 45.2% (14/31), 3.2% (1/31), 12.9% (4/31), and 16.2% (5/31) respectively, and m region was not identified in 22.6% of the strains; and the rates of iceA1 and iceA2 were 87.1% (27/31) and 61.3% (19/31) respectively. In the specimens from the patients of Naxi nationally, The rates of vacA gene s1 type and s2 type were 95.6% (43/45) and 4.4% (2/45), the rates of vacA gene m2 type, vacA gene m1b type, and mixed m-type were 33.3% (15/45), 37.8% (17/45), and 6.7% (3/45) respectively, no m1a type was found, and m region was not identified in 22.2% of the strains; the rates of iceA1 and iceA2 were 48.9% (22/45) and 31.1% (14/45) respectively. In the specimens of the patients of Han nationality, as regards the s region, all specimens were s1 type; the rates of vacA gene m2 type, vacA gene m1b type, and mixed type were 63.6% (21/33), 15.2% (5/33), and 12.1% (4/33) respectively, and m region was not identified in 9.1% (3/33) of the strains; the rates of iceA1 and iceA2 were 72.7% (24/33) and 36.4% (12/33) respectively. 34 of the 109 patients (31.2%) suffered from mixed infection of vacA gene m mixed subtype and/or iceA mixed genotype, 64.7% of which (22/34) suffering iceA1 + iceA2 infection, 23.5% of which (8/34) being iceA + vacA mixed infection, and 11.8% of which (4/34) being vacA subtype mixed infection, with the former incidence of the former group significantly higher than those of the 2 latter groups (both P < 0.001). The mixed infection rate of the Bai nationality (67.7%, 21/31) was significantly higher than those of the Naxi nationality (20.0%, 9/45, P < 0.001) and Han nationality (12.1%, 4/33, P > 0.001) without a significant difference between the Naxi and Han nationalities (P > 0.05). The mixed infection rate of iceA1 + iceA2 of the Bai nationality (61.3%, 19/31) was significantly higher than those of the Naxi nationality (17.8%, 8/45, P < 0.001) and Han nationality (9.1%, 3/33, P < 0.001) without a significant difference between the Naxi and Han nationalities (P > 0.05). The mixed rate of the patients with digestive ulcer was 30.2% (16/53), not significantly different from that of the patients with chronic gastritis (32.1%, 18/56, P > 0.05). 16 of the 34 cases of mixed infection were patients of digestive ulcer; and 8 of the 34 cases were patients with chronic gastritis. 8 of the 34 cases (23.5%) of mixed infection were cases of infection of vacA gene m mixed subtypes and iceA mixed genotype; among which 7 were patients with digestive ulcer and 1 case was patient of chronic gastritis. Thus the rate of vacA gene m mixed subtypes and iceA mixed genotype was 43.8% (7/16) in the patients with digestive ulcer, significantly higher than in the patient with chronic gastritis (5.6%, 1/18, P = 0.014). 22 of the 34 cases of mixed infection (64.7%) suffered from infection of iceA mixed gene subtypes. Among these 22 cases 15 were patients with chronic gastritis and 7 were patients with digestive ulcer. Thus the rate of iceA mixed subtypes infection was 43.8% (7/16) in the patients with digestive ulcer, significantly lower than in the patient with chronic gastritis (83.3%, 15/18, P = 0.016). In the 21 mixed infection patients of Bai nationality, the rate of vacA gene mixed sybtype + iceA gene mixed subtypes infection was 100% in the patients with digestive ulcer (100%, 5/5), significantly higher than that of single vacA gene subtype + iceA gene mixed subtypes (37.5%, 6/16, P = 0.0258). The mixed infection rate of H. pylori strains was 32.1%. CONCLUSION: The mixed infection rate of the Bai nationality is higher than those of the Han and Naxi nationalities. Detection of mixed infection by vacA genotypes is more sensitive in Han populations. Detection of multiple infections by iceA gene mixed subtypes is more sensitive in Bai and Naxi populations.

Bacterial Proteins↗
PubMed2005

Efficient inhibition of hepatitis B virus replication by hammerhead ribozymes delivered by hepatitis delta virus.

Although it has been suggested that hepatitis delta virus (HDV) can be used as a vector to deliver biologically active RNAs into hepatocytes, modified HDV as a specific transporting and replicating vector in anti-viral research has not been investigated. In this study, we focused on the development of HDV as a replicative vector to deliver hammerhead ribozyme into hepatocytes and the study of the roles of delivered hammerhead ribozyme on the replication of hepatitis B virus (HBV). To investigate the effects of ribozyme delivered by HDV on HBV replication, we designed two hammerhead ribozymes that specifically target the hepatitis B virus genome. These two ribozymes were then inserted into the genome of hepatitis delta virus. Results showed that transfection of cells with tandem modified HDV cDNA resulted in the production of monomer form of sense and anti-sense genomic RNA indicating the recombinant HDV-ribozyme could replicate effectively. Our data also indicated that ribozymes delivered by the modified HDV had higher level of inhibition activity against HBV replication than that of ribozyme alone. This system provides a new approach for the study of mechanisms of HBV replication as well as for the potential treatment of HBV infection.

Cell Line↗
PubMed2005

VEGF-mediated survivin expression in neuroblastoma cells.

BACKGROUND: Vascular endothelial growth factor (VEGF) up-regulates a number of cellular survival signals in endothelial cells. We hypothesize that VEGF will up-regulate survivin, a member of the IAP family of anti-apoptotic proteins, via the PI3K/Akt cell signaling pathway in human neuroblastoma cells. MATERIALS AND METHODS: IMR-32 human neuroblastoma cells are cultured with VEGF at varying times and in escalating doses. A specific inhibitor of PI3-kinase, LY294002, is used to block Akt phosphorylation. Immunoblot is used to measure protein expression, and Hoechst staining is used to detect apoptosis. RESULTS: Stimulation of IMR-32 neuroblastoma cells with VEGF results in an increase in survivin protein expression in both a dose- and a time-dependent fashion. Akt phosphorylation is also increased after stimulation with exogenous VEGF. Blockade of Akt phosphorylation with LY294002 abrogates the effects of VEGF upon survivin and phosphorylated Akt protein expression. CONCLUSIONS: VEGF has been shown to up-regulate a number of survival signals in endothelial cells. We have found that exposure of human neuroblastoma cells to exogenous VEGF results in an increased expression of survivin protein and phosphorylated Akt, and inhibition of PI3-kinase abrogates those effects. It appears that VEGF is important for promotion of neuroblastoma cellular survival through the up-regulation of survival proteins, and not only through its angiogenic properties.

Apoptosis↗
PubMed2005

Enforced adhesion of hematopoietic cells to culture dish induces endomitosis and polyploidy.

Cells of epithelial or endothelial lineage when forced to grow in suspension undergo the detachment-induced death termed "anoikis". In the present study we explored the reverse situation namely the effect of enforcement of hematopoietic lineage cells that are normally maintained in suspension to grow attached. Towards this end murine L1210 or human HL-60 and Jurkat leukemia cells were cultured in slide chambers coated with poly-L- or poly-D- lysine, or with compound 48/80, the polycations attracting them electrostatically. Within minutes after the transfer L1210 cells strongly adhered to bottom surface of the dish and shortly thereafter binuclear-, and later on, polynuclear-cells become apparent. The frequency of nuclei per cell was increasing with time and polykaryons with up to 16 nuclei and high DNA ploidy (DI = 16.0) were apparent after 48 h. After 4 days the size (volume) of some polykaryons exceeded by over 340-fold the volume of mononuclear cells. The presence of mitotic figures and abnormal mitotic spindles in adhering polykaryons provided evidence of the impeded cytokinesis that led to endomitosis. Most polykaryons excluded trypan blue, had balanced growth (unchanged protein/DNA ratio compared to monokaryons), and showed no evidence of apoptosis. Individual nuclei within each polykaryon replicated DNA in synchrony. The strong cell attachment and aborted cytokinesis were cell line specific since no significant endomitosis was observed in Jurkat- or HL-60- cells which did not strongly attach to polycation-coated surfaces. Defective cytokinesis and induction of polyploidy by this mechanism, if occurs in vivo (e.g., mediated by integrins), may lead to aneuploidy and therefore have tumorigenic consequences. The phenomenon offers novel experimental model for induction of polyploidy and provides alternative to cytocholasin B to prevent cytokinesis in the mutagenicity cytokinesis-blocked micronucleus (CBMN) assay.

Animals↗
PubMed2005

Ultraviolet irradiation-induced K(+) channel activity involving p53 activation in corneal epithelial cells.

Recent studies from our lab found that ultraviolet (UV) irradiation induces a voltage-gated potassium (Kv) channel activation and subsequently activates JNK signaling pathway resulting in apoptosis. The present study in rabbit corneal epithelial (RCE) cells is to investigate mechanisms of UV irradiation-induced Kv channel activity involving p53 activation in parallel to DNA damage-induced signaling pathway. UV irradiation-induced signaling events were characterized by measurements of JNK activation and further downstream p53 phosphorylation. UV irradiation elicited an early response in the cell membrane through activation of Kv channels to activate the JNK signaling pathway and p53 phosphorylation. Exposure of RCE cells to UV irradiation within a few min resulted in JNK and p53 activations that were markedly inhibited by suppression of Kv channel activity. However, suppression of Kv channel activity failed to prevent p53 activation induced by extended DNA damages through prolonging UV exposure time (more than 15 min). In addition, caffeine inhibited UV-induced activation of SEK, an upstream MAPK kinase of JNK, resulting in suppression of both Kv channel-involved and DNA damage-induced p53 activation. Our results indicate in these cells that UV irradiation induces earlier and later intracellular events that link to activation of JNK and p53. The early event in response to UV irradiation is initiated by activating Kv channels in the cell membrane, and the later event is predominated by UV irradiation-caused DNA damage.

Animals↗
PubMed2005

Further characterization of human DNA polymerase delta interacting protein 38.

Polymerase delta interacting protein 38 (PDIP38) was identified as a human DNA polymerase (pol) delta interacting protein through a direct interaction with p50, the small subunit of human pol delta. PDIP38 was also found to interact with proliferating cell nuclear antigen, which suggested that it might play a role in vivo in the processes of DNA replication and DNA repair in the nucleus. In order to characterize further this novel protein, we have examined its subcellular localization by the use of immunochemical and cellular fractionation techniques. These studies show that PDIP38 is a novel mitochondrial protein and is localized mainly to the mitochondria. PDIP38 was shown to possess a functional mitochondrial targeting sequence that is located within the first 35 N-terminal amino acid residues. The mature PDIP38 protein is about 50 amino acid residues smaller than the full-length precursor PDIP38 protein, consistent with it being processed by cleavage of the mitochondrial targeting sequence during entry into the mitochondria. His-tagged mature PDIP38 inhibited pol delta activity in vitro and interacted with human papillomavirus 16 E7 oncoprotein, suggesting that PDIP38 might play a role in the pol delta-mediated viral DNA replication. Although the localization of PDIP38 to the mitochondria suggests that it serves functions within the mitochondria, we cannot eliminate the possibility that it may be involved in pol delta-mediated DNA replication or DNA repair under certain conditions such as viral infection.

Cell Line↗
PubMed2005

Insulin-activated, K+-channel-sensitive Akt pathway is primary mediator of ML-1 cell proliferation.

Voltage-gated K(+) channel activities are involved in regulating growth factor-stimulated cell proliferation in a variety of cell types. Here we report that suppression of a voltage-gated K(+) channel with 4-aminopyridine (4-AP), barium, and tetraethylammonium inhibited both EGF- and insulin-stimulated myeloblastic leukemia ML-1 cell proliferation in a concentration-dependent manner. Both MAPK/ERK and Akt pathways are known to mediate cell proliferative signals of a variety of growth factors including insulin. In serum-starved ML-1 cells, insulin rapidly stimulated phosphorylation of ERK1/2 and Akt, and the phosphorylation levels peaked approximately 30 min after treatment. Pretreatment of ML-1 cells with 4-AP potently and dose-dependently prevented phosphorylation of ERK1/2 and Akt. However, insulin-induced activation of the Akt pathway also played a role in promoting ML-1 cell proliferation. Flow cytometry analysis revealed that although ML-1 cells were primarily arrested at G(1) phase by serum starvation for 36 h, they reentered the cell cycle after treatment with serum or insulin for 24 h. However, concomitant 4-AP treatment was able to attenuate cell cycle progression in synchronized ML-1 cells stimulated with growth factors. Our results strongly suggest that a 4-AP-sensitive K(+) channel activity plays an important role in controlling proliferation of ML-1 cells by affecting the activation of multiple signal transduction processes induced by insulin.

4-Aminopyridine↗
PubMed2005

Colonic tumorigenesis in BubR1+/-ApcMin/+ compound mutant mice is linked to premature separation of sister chromatids and enhanced genomic instability.

Faithful chromosome segregation is essential for the maintenance of genetic stability during cell division and it is at least partly monitored by the spindle checkpoint, a surveillance mechanism preventing the cell from prematurely entering anaphase. The adenomatous polyposis coli (Apc) gene also plays an important role in regulating genomic stability, as mutations of Apc cause aneuploidy. Here we show that whereas Apc(Min)(/+) mice developed many adenomatous polyps, mostly in the small intestine, by 3 mo of age; BubR1(+/-)Apc(Min)(/+) compound mutant mice developed 10 times more colonic tumors than Apc(Min)(/+) mice. The colonic tumors in BubR1(+/-)Apc(Min)(/+) mice were in higher grades than those observed in Apc(Min)(/+) mice. Consistently, BubR1(+/-)Apc(Min)(/+) murine embryonic fibroblasts (MEFs) contained more beta-catenin and proliferated at a faster rate than WT or BubR1(+/-) MEFs. Moreover, BubR1(+/-)Apc(Min)(/+) MEFs slipped through mitosis in the presence of nocodazole and exhibited a higher rate of genomic instability than that of WT or BubR1(+/-) or Apc(Min)(/+) MEFs, accompanied by premature separation of sister chromatids. Together, our studies suggest that BubR1 and Apc functionally interact in regulating metaphase-anaphase transition, deregulation of which may play a key role in genomic instability and development and progression of colorectal cancer.

Animals↗
PubMed2005

Histone H2AX phosphorylation after cell irradiation with UV-B: relationship to cell cycle phase and induction of apoptosis.

Damage to DNA that engenders double-strand breaks (DSBs) triggers phosphorylation of histone H2AX on Ser-139. Expression of phosphorylated H2AX (gammaH2AX) can be revealed immunocytochemically; the intensity of gammaH2AX immunofluorescence (IF) measured by cytometry was reported to correlate with the frequency of DSBs induced by X-ray radiation or by DNA damaging antitumor drugs. The aim of the present study was to measure expression of gammaH2AX following exposure of HeLa and HL-60 cells to a wide range of doses of UV-B light (6.1 J/m(2)-3.45 kJ/m(2)) and using multiparameter flow and laser scanning cytometry (LSC) to correlate DNA damage with cell cycle phase and induction of apoptosis. In both cell lines, the highest degree of H2AX phosphorylation induced by UV was seen in S-phase cells, particularly during early portion of S. In cells that did not replicate DNA (G(1), G(2) and M) the degree of H2AX phosphorylation was markedly lower than that in S-phase cells, and was strongly UV dose-dependent. Furthermore, the level of UV-induced gammaH2AX in G(1), G(2) and M was much higher in HeLa- than in HL-60- cells. Apoptotic cells become apparent >2h after exposure to UV and exhibited nearly an order of magnitude higher intensity of gammaH2AX IF than that initially induced by UV; predominantly S-phase cells underwent apoptosis. While the suppression of DNA replication, by aphidicolin prevented the induction of H2AX phosphorylation by UV in most S phase cells, it had no effect on a small cohort of cells that appeared to be entering S-phase, that expressed very high levels of gammaH2AX. Furthermore, aphidicolin itself induced gammaH2AX in early-S phase cells. The induction of gammaH2AX by UV was inhibited, but the incidence of apoptosis increased, by 5 mM caffeine, a known inhibitor of PI-3-related kinases. The data are consistent with the notion that H2AX phosphorylation observed throughout S phase reflects formation of DSBs due to the collision of replication forks with the UV-induced primary DNA lesions. Induction of gammaH2AX in G(1), G(2) and M is likely a response to the primary DSBs generated during UV exposure and/or DNA repair. It is unclear why the latter process was more pronounced in HeLa than in HL-60 cells.

Aphidicolin↗
PubMed2005

Novel assay utilizing fluorochrome-tagged physostigmine (Ph-F) to in situ detect active acetylcholinesterase (AChE) induced during apoptosis.

It was recently reported that acetylcholinesterase (AChE) is expressed in cells undergoing apoptosis and that its presence is essential for assembly of the apoptosome and subsequent caspase-9 activation. To obtain a marker of active AChE that could assay this enzyme in live intact cells and be applicable to fluorescence microscopy and cytometry, the fluorescein-tagged physostigmine (Ph-F), high affinity ligand (inhibitor) reactive with the active center of AChE, was constructed and tested for its ability to in situ label AChE and measure its induction during apoptosis. Ph-F inhibited cholinesterase activity in vitro (IC50 = 10(-6) and 5 x 10(-6) M for equine butyrylcholinesterase and human erythrocyte AChE, respectively) and was a selective marker of cells and structures that were AChE-positive. Thus, exposure of mouse bone marrow cells to Ph-F resulted in the exclusive labeling of megakaryocytes, and of the diaphragm muscle, preferential labeling of the nerve-muscle junctions (end-plates). During apoptosis of carcinoma HeLa cells and leukemic HL-60 or Jurkat cells triggered either by the DNA topoisomerase 1 inhibitor topotecan (TPT) or by oxidative stress (H2O2), the cells become reactive with Ph-F. Their Ph-F derived fluorescence was measured by flow and laser scanning cytometry. The appearance of Ph-F binding sites during apoptosis was preceded by the loss of mitochondrial potential, was concurrent with the presence of activated caspases, and was followed by loss of membrane integrity. At a very early stage of apoptosis, when nucleolar segregation was apparent, the Ph-F binding sites were distinctly localized within the nucleolus and at later stages of apoptosis in the cytoplasm. During apoptosis triggered by TPT, Ph-F binding was preferentially induced in S-phase cells. Our data on megakaryocytes and end-plates indicate that Ph-F reacts with active sites of AChE, and can be used to reveal the presence of this enzyme in live cells and possibly to study its expression in disorders of the neurological cholinergic system. The findings are also compatible with the reports that AChE may be induced during apoptosis. In fact, the simple and rapid Ph-F binding assay may serve as a convenient marker of apoptotic cells. However, the proposed role of active AChE as an essential factor for assembly of the apoptosome and caspase activation is in question because the AChE inhibitors Ph, Ph-F and BW284c51 did not protect the cells from apoptosis induced by TPT or H2O2. Further studies are thus needed to ascertain the induction and role of AChE in apoptosis.

Acetylcholinesterase↗
PubMed2005

Regulation of cell cycle checkpoints by polo-like kinases.

Protein kinases play a pivotal role in execution of cell division. Polo and Polo-like kinases have emerged as major regulators for various cell cycle checkpoints. Early genetic studies have demonstrated that CDC5, a budding yeast counterpart of vertebrate Plks, is essential for successful mitotic progression. Mammalian Plks localize primarily to the centrosome during interphase and the mitotic apparatus during mitosis. Many key cell cycle regulators such as p53, Cdc25C, cyclin B, components of the anaphase-promoting complex, and mitotic motor proteins are directly targeted by Plks. Although the exact mechanism of action of these protein kinases in vivo remains to be elucidated, Plks are important mediators for various cell cycle checkpoints that monitor centrosome duplication, DNA replication, formation of bipolar mitotic spindle, segregation of chromosomes, and mitotic exit, thus protecting cells against genetic instability during cell division.

Animals↗