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At least 217 records · Page 12Linked to original sources
PubMed2005

Curcumin selectively induces apoptosis in deregulated cyclin D1-expressed cells at G2 phase of cell cycle in a p53-dependent manner.

Curcumin (diferuloylmethane) is known to induce apoptosis in tumor cells. In asynchronous cultures, with time-lapse video-micrography in combination with quantitative fluorescence microscopy, we have demonstrated that curcumin induces apoptosis at G(2) phase of cell cycle in deregulated cyclin D1-expressed mammary epithelial carcinoma cells, leaving its normal counterpart unaffected. In our search toward delineating the molecular mechanisms behind such differential activities of curcumin, we found that it selectively increases p53 expression at G(2) phase of carcinoma cells and releases cytochrome c from mitochondria, which is an essential requirement for apoptosis. Further experiments using p53-null as well as dominant-negative and wild-type p53-transfected cells have established that curcumin induces apoptosis in carcinoma cells via a p53-dependent pathway. On the other hand, curcumin reversibly inhibits normal mammary epithelial cell cycle progression by down-regulating cyclin D1 expression and blocking its association with Cdk4/Cdk6 as well as by inhibiting phosphorylation and inactivation of retinoblastoma protein. In addition, curcumin significantly up-regulates cell cycle inhibitory protein (p21Waf-1) in normal cells and arrests them in G(0) phase of cell cycle. Therefore, these cells escape from curcumin-induced apoptosis at G(2) phase. Interestingly, these processes remain unaffected by curcumin in carcinoma cells where cyclin D1 expression is high. Similarly, in ectopically overexpressed system, curcumin cannot down-regulate cyclin D1 and thus block cell cycle progression. Hence, these cells progress into G(2) phase and undergo apoptosis. These observations together suggest that curcumin may have a possible therapeutic potential in breast cancer patients.

Animals↗
PubMed2000

The G2-phase DNA-damage checkpoint.

DNA damage causes cell-cycle delay before S phase, during replication and before mitosis. This involves a number of highly conserved proteins that sense DNA damage and signal the cell-cycle machinery. Kinases that were initially discovered in yeast model systems have recently been shown to regulate the regulators of cyclin-dependent kinases and to control the stability of p53. This shows the importance of checkpoint proteins for maintaining genome stability. Here, we discuss recent data from yeast and metazoans that suggest a remarkable conservation of the organization of the G2 DNA-damage checkpoint pathway.

Animals↗
PubMed2006

Mitogen-activated protein kinase kinase 1-dependent Golgi unlinking occurs in G2 phase and promotes the G2/M cell cycle transition.

Two controversies have emerged regarding the signaling pathways that regulate Golgi disassembly at the G(2)/M cell cycle transition. The first controversy concerns the role of mitogen-activated protein kinase activator mitogen-activated protein kinase kinase (MEK)1, and the second controversy concerns the participation of Golgi structure in a novel cell cycle "checkpoint." A potential simultaneous resolution is suggested by the hypothesis that MEK1 triggers Golgi unlinking in late G(2) to control G(2)/M kinetics. Here, we show that inhibition of MEK1 by RNA interference or by using the MEK1/2-specific inhibitor U0126 delayed the passage of synchronized HeLa cells into M phase. The MEK1 requirement for normal mitotic entry was abrogated if Golgi proteins were dispersed before M phase by treatment of cells with brefeldin A or if GRASP65, which links Golgi stacks into a ribbon network, was depleted. Imaging revealed that unlinking of the Golgi apparatus begins before M phase, is independent of cyclin-dependent kinase 1 activation, and requires MEK signaling. Furthermore, expression of the GRASP family member GRASP55 after alanine substitution of its MEK1-dependent mitotic phosphorylation sites inhibited both late G(2) Golgi unlinking and the G(2)/M transition. Thus, MEK1 plays an in vivo role in Golgi reorganization, which regulates cell cycle progression.

Cell Division↗
PubMed2001

Chemopreventive agent resveratrol, a natural product derived from grapes, reversibly inhibits progression through S and G2 phases of the cell cycle in U937 cells.

Resveratrol, a natural product derived from grapes, has been shown to prevent carcinogenesis in murine models. We report here that resveratrol induces antiproliferation and arrests the S phase in human histiocytic lymphoma U937 cells. Resveratrol induces arrest in the S phase at low concentrations (30-60 microM), but high concentrations do not induce S phase accumulation in U937 cells. Removal of resveratrol from the culture medium stimulates U937 cells to reenter the cell cycle synchronously, as judged by the expression patterns of cyclin E, A and by fluorescent activated cell sorting analysis. These data demonstrate that resveratrol causes S phase arrest and reversible cell cycle arrest. Thus, resveratrol provides an important new cell cycle blocker as well as a cancer chemopreventive agent.

Antineoplastic Agents, Phytogenic↗
PubMed1998

S- and G2-phase cell cycle arrests and apoptosis induced by ganciclovir in murine melanoma cells transduced with herpes simplex virus thymidine kinase.

Mechanism of cell killing by transfer of Herpes simplex virus type-1 thymidine kinase (HSVtk) and subsequent ganciclovir (GCV) treatment was examined in B16F10 murine melanoma model. While parental B16F10 melanoma cells were resistant to GCV at 100 microM or higher, HSVtk-transduced B16F10 melanoma cell clones became susceptible to GCV with IC50 of 0.1 to 0.3 microM. By means of various parameters including characteristic morphological changes, in situ DNA end-labeling, DNA ladder pattern, flow cytometric detection of sub-G1 DNA content, and annexin V binding of inverted cell surface phosphatidylserine, apoptosis was shown to be associated with the cell killing of ganciclovir on HSVtk-transduced melanoma B16F10 cells. Kinetic analysis showed that the signs of apoptosis were observed not until 60 h of continued GCV treatment and preceded first by a rise in p53 protein level in 12 h and then by S-phase/G2-phase cell cycle arrest associated with corresponding increases in the level of cyclin B1 protein but no apparent change in protein level of Bax or Cdc2. These results suggest that apoptosis occurred as a result of ganciclovir-induced cell cycle arrests rather than direct chemical effect on HSVtk-transduced B16F10 melanoma cells.

Animals↗
PubMed1994

Heterogeneity of chromosome damage in beta-thalassaemia traits. An evaluation of spontaneous and gamma-ray-induced micronuclei and chromosome aberrations in lymphocytes in vitro after G0 and G2 phase irradiation.

This study is an attempt to evaluate the chromosomal radiosensitivity of beta-thalassaemia traits compared with healthy individuals from the general population, necessitated by the fact that beta-thalassaemia trait is present in 1-17% of different population groups in India and the chances of encountering them in radiation and chemical related industries do exist. Spontaneous chromosome aberration frequencies in peripheral blood lymphocytes from beta-thalassaemia traits were found to be in the normal range, whereas significantly higher frequencies of micronuclei (MN) were observed in thalassaemia traits. Based on MN frequency at 2 Gy, beta-thalassaemia traits fall into two distinct categories. A hypersensitive group with significant increase in radiation-induced MN over the control group, and a second group with MN frequency slightly above normal individuals. Even when compared with the fitted data at 2 Gy obtained from the pooled results of extensive dose-response investigations from 0.5-5 Gy gamma-rays with normal donors for MN, dicentrics and total aberrations, the difference between the means of MN frequencies in beta-thalassaemia traits and normals is significant. MN have a higher control level, a higher value for the alpha component, and much lower value for the beta component, when compared with total aberrations. Both in 2-Gy irradiated G0 lymphocytes as well as 0.5 and 1-Gy irradiated G2 lymphocytes, there is a certain degree of hypersensitivity when the results are meaned over a number of individuals, but some individuals overlap within the normal range. In G0 irradiated lymphocytes from beta-thalassaemia traits, the dicentric chromosome is the only aberration category in which the yield is seen to rise. The heterogeneity in chromosomal radiosensitivity observed in beta-thalassaemia traits is discussed in terms of the oxidative damage consequent to the genetic and biochemical features peculiar to the beta-thalassaemia trait cell. The data presented herein may have wider implications in radiation protection.

Chromosome Aberrations↗
PubMed2000

Reprimo, a new candidate mediator of the p53-mediated cell cycle arrest at the G2 phase.

A novel gene, Reprimo, in which induction in cells exposed to X-irradiation is dependent on p53 expression, has been isolated. Ectopic p53 expression results in the induction of its mRNA. Reprimo is a highly glycosylated protein and, when ectopically expressed, it is localized in the cytoplasm and induces G(2) arrest of the cell cycle. In the arrested cells, both Cdc2 activity and nuclear translocation of cyclin B1 are inhibited, suggesting the involvement of Reprimo in the Cdc2.cyclin B1 regulation pathway. Thus, Reprimo may be a new member involved in the regulation of p53-dependent G(2) arrest of the cell cycle.

Amino Acid Sequence↗
PubMed2005

The importance of abrogation of G2-phase arrest in combined effect of TRAIL and ionizing radiation.

BACKGROUND: In this work we studied the relationship between the enhanced expression of DR5 receptor and the effect of combination of TRAIL and ionizing radiation on cell cycle arrest and apoptosis induction in human leukemia cell line HL-60. MATERIAL AND METHODS: DR5, APO2.7 and cell cycle were analyzed by flow cytometry. Proteins Bid and Mcl-1 were analyzed by Western-blotting. For clonogenic survival, colony assay on methylcellulose was used. RESULTS: Ionizing radiation caused significantly enhanced positivity of DR5 receptors 24 h after irradiation with high doses (6 and 8 Gy). An increase of DR5 receptor positivity after a dose of 2 Gy was not statistically significant and application of TRAIL 48 h after irradiation did not increase the apoptosis induction. However, a decrease of radiation-induced G(2) phase arrest and an increase of apoptosis were observed when TRAIL was applied 16 h before irradiation with the dose of 2 Gy. Incubation with 6 microg/l TRAIL for 16 h reduced D(0) value from 2.9 Gy to 1.5 Gy. The induction of apoptosis by TRAIL was accompanied by Bid cleavage and a decrease of antiapoptotic Mcl-1 16 h after incubation with TRAIL. CONCLUSION: TRAIL in concentration of 6 microg/l applied 16 h before irradiation by the dose of 1.5 Gy caused the death of 63% of clonogenic tumor cells, similarly as the dose of 2.9 Gy alone, which is in good correlation with the enhanced apoptosis induction.

Apoptosis Regulatory Proteins↗
PubMed2003

DNA damage in HeLa cells induced arrest at a discrete point in G2 phase as defined by CENP-F localization.

G(2) is defined as the time in the cell cycle after DNA synthesis is complete but before the initiation of mitosis. However, as the molecular events of the cell cycle are described, G(2) can be seen to be a sequence of events rather than a static phase. For example, CENP-F increases in amount in early G(2), after DNA synthesis is complete, but localizes to the nuclear rim and then to the kinetochores before mitosis commences. After DNA damage cells may arrest in G(2) through TP53-dependent and independent mechanisms, raising the question of the precise position of the arrest within G(2). HeLa cells lack functional TP53; this allowed us to examine the TP53-independent mechanism of G(2) arrest. Here we showed that the DNA damage-induced G(2) arrest in HeLa cells is positioned in early G(2), before redistribution of CENP-F to the nuclear envelope and kinetochores, and before chromosome condensation commences.

Chromosomal Proteins, Non-Histone↗
PubMed1992

The Saccharomyces cerevisiae NPS1 gene, a novel CDC gene which encodes a 160 kDa nuclear protein involved in G2 phase control.

We have cloned the gene NPS1 (nuclear protein of Saccharomyces) which encodes a nuclear protein of mol. wt 156 735 Daltons (1359 amino acids) essential for cell growth. NPS1 contains a 2 kb sequence that is highly homologous to the S. cerevisiae SNF2/GAM1 gene known as a transcriptional regulator for multiple genes. However, the NPS1 gene was found to have a distinct function from SNF2/GAM1. The growth of the cells carrying a nps1 delta :: URA3 deletion allele and galactose-inducible NPS1 on a plasmid was arrested under NPS1-repressed conditions with a cell cycle arrest phenotype, being arrested at the large-bud stage with a single nucleus that had a DNA content of G2/M phase. When the arrested cells were further incubated under NPS1-repressed conditions, re-replication of DNA occurred in some of the arrested cells without passage through mitosis. In the predicted amino acid sequence of NPS1, sequences homologous to the catalytic domain of protein kinases were found. We constructed a mutation which results in the substitution of a highly conserved lysine residue (Lys792) in the presumed ATP-binding site of this kinase-like domain with a glutamic acid codon. The mutant gene failed to rescue the growth defect caused by NPS1 disruption, suggesting that Lys792 is essential for the function of NPS1.

Amino Acid Sequence↗
PubMed2004

HSP90 and checkpoint-dependent lengthening of the G2 phase observed in plant cells under hypoxia and cold.

Proliferating cells of Allium cepa L. roots became adapted to hypoxia (5% oxygen) and cold (10 degrees C) by acquiring new steady-state kinetics of growth. The cell cycle time increased from the 17.6 h in control meristems up to 29.7 and 69.0 h under hypoxia and cold conditions, respectively. Acclimation of the proliferating cells was stress specific. No acclimation took place after 24 h of heat treatment (40 degrees C). Under cold treatment, all cycle phases enlarged uniformly. However, under hypoxia, while the G(1) and S cycle phases roughly doubled in their timing, the expected checkpoint-dependent lengthening of G(2) did not take place. This failure in lengthening G(2) in response to hypoxia correlated with a failure in the overinduction of a single peptide with a molecular mass of about 134 kDa which is among those recognised by an HSP90 antibody. Moreover, the presence of this large peptide of the HSP90 family proved to be a marker for cell proliferation. It was always absent from the contiguous differentiated cells of the root. Lastly, the mitochondrial chaperonin recognized by an HSP60 antibody in these roots not involved in photosynthesis was always higher in the proliferating than in the nonproliferating cells.

Cell Hypoxia↗
PubMed1990

Analysis of chromatid damage in G2 phase induced by heavy ions and X-rays.

The induction of chromatid aberrations was examined in Golden hamster embryo (GHE) cells 2 h after exposure to X-rays or heavy ions. Compared with X-rays the frequencies of gaps and deletions were almost one-half in the case of He ions, and much lower in cells irradiated with N ions. The induction of exchanges by He ions and N ions was also less than that by X-rays. The relative number of gaps, deletions and exchanges were 0.4, 0.5 and 0.4 for He ions, and 0.2, 0.2 and 0.4 for N ions. The mitotic indices were almost the same in X-irradiated and heavy-ion-exposed cells. Chromatid aberrations induced by heavy ions tended to persist longer than those induced by X-rays during successive culture passages after exposure. The present results suggest a difference in the quality of chromatid damage induced by X-rays and heavy ions.

Animals↗
PubMed2003

Permanent cell cycle exit in G2 phase after DNA damage in normal human fibroblasts.

Although the Cdk inhibitor p21(Waf1/Cip1), one of the transcriptional targets of p53, has been implicated in the maintenance of G(2) arrest after DNA damage, its function at this stage of the cell cycle is not really understood. Here, we show that the exposure of normal human fibroblasts (NHFs) to genotoxic agents provokes permanent cell cycle exit in G(2) phase, whereas mouse embryo fibroblasts and transformed human cells progress through mitosis and arrest in G(1) without intervening cytokinesis. p21(Waf1/Cip1) exerts a key role in driving this G(2) exit both by inhibiting cyclin B1-Cdk1 and cyclin A-Cdk1/2 complexes, which control G(2)/M progression, and by blocking the phosphorylation of pRb family proteins. NHFs with compromised pRb proteins could still efficiently arrest in G(2) but were unable to exit the cell cycle, resulting in cell death. Our experiments show that, when under continuous genotoxic stress, normal cells can reverse their commitment to mitotic progression due to passage through the restriction point and that mechanisms involving p21(Waf1/Cip1) and pocket proteins can induce exit in G(2) and G(1).

Bleomycin↗
PubMed2001

Genetic analysis of the DNA-dependent protein kinase reveals an inhibitory role of Ku in late S-G2 phase DNA double-strand break repair.

Two major complementary double-strand break (DSB) repair pathways exist in vertebrates, homologous recombination (HR), which involves Rad54, and non-homologous end-joining, which requires the DNA-dependent protein kinase (DNA-PK). DNA-PK comprises a catalytic subunit (DNA-PKcs) and a DNA-binding Ku70 and Ku80 heterodimer. To define the activities of individual DNA-PK components in DSB repair, we targeted the DNA-PKcs gene in chicken DT40 cells. DNA-PKcs deficiency caused a DSB repair defect that was, unexpectedly, suppressed by KU70 disruption. We have shown previously that genetic ablation of Ku70 confers RAD54-dependent radioresistance on S-G(2) phase cells, when sister chromatids are available for HR repair. To test whether direct interference by Ku70 with HR might explain the Ku70(-/-)/DNA-PKcs(-/-/-) radioresistance, we monitored HR activities directly in Ku- and DNA-PKcs-deficient cells. The frequency of intrachromosomal HR induced by the I-SceI restriction enzyme was increased in the absence of Ku but not of DNA-PKcs. Significantly, abrogation of HR activity by targeting RAD54 in Ku70(-/-) or DNA-PKcs(-/-/-) cells caused extreme radiosensitivity, suggesting that the relative radioresistance seen with loss of Ku70 was because of HR-dependent repair pathways. Our findings suggest that Ku can interfere with HR-mediated DSB repair, perhaps competing with HR for DSB recognition.

Animals↗
PubMed2003

The G2-phase decatenation checkpoint is defective in Werner syndrome cells.

It has been proposed that cells monitor chromatid catenation status after DNA replication and inhibit progression into mitosis until chromatids are correctly decatenated by topoisomerase II (TopoII). Studies in yeast have suggested that TopoII may interact with RecQ helicases during this process. Using ICRF187, a TopoII catalytic inhibitor that prevents chromatid decatenation without producing DNA strand breaks, we demonstrated that cells deficient of WRN, a human RecQ helicase, displayed a defect in decatenation checkpoint activation, which was corrected by ectopic expression of wild-type WRN. We also provide evidence that BRCA1 is phosphorylated in an ATR-dependent manner in response to decatenation checkpoint activation and that this phosphorylation is not detectable in Werner syndrome cells. Furthermore, ICRF187 treatment resulted in coimmunoprecipitation of WRN and TopoII. Finally, we demonstrated that override of the decatenation checkpoint resulted in enhanced chromosomal damage and apoptosis only in the absence of WRN, but not in normal cells. Our findings suggest that WRN plays a role in the activation of G(2) decatenation checkpoint and that the abortive function of this pathway itself does not appear to be sufficient to cause genomic instability but rather predisposes to genomic instability and apoptotic cell death in the absence of other "caretaker" genes, such as WRN.

Apoptosis↗
PubMed2000

Influence of the sampling time on chromosomal aberrations at G2 phase in Syrian hamster embryonic cells irradiated with different types of radiation.

PURPOSE: To investigate the time-course of chromosomal aberrations following radiations of differing LET. MATERIALS AND METHODS: Syrian hamster embryonic cells were irradiated with nitrogen ions (LET(infinity) = 530 keV/microm) and helium-ions (LET(infinity) = 36 and 77 keV/microm), also 137Cs gamma-rays as a reference radiation. The frequency of chromatid-type aberrations was determined after 0-6 h incubation in a 5% CO2 incubator at 37 degrees C. RESULTS: The amount of chromosomal damage per cell for nitrogen ions detected immediately after irradiation was lower than induced by 137Cs gamma-rays. In contrast, helium ions were more effective than gamma rays in inducing chromatid type damage. The RBE values for the nitrogen-ion beams were 0.45 for gaps, 0.43 for deletions and 0.20 for exchanges. For helium-ion beams, the RBE values for the 36 keV/microm beams and the 77 keV/microm beams were 1.2 and 1.5 for gaps, 1.3 and 2.1 for deletions, and 1.5 and 1.9 for exchanges, respectively. The frequency of cells with chromosomal damage following exposure to gamma-rays and helium-ion beams showed a downward trend with increasing incubation period. In contrast, in the case of nitrogen-ion beams, there was an increase with the incubation period. CONCLUSIONS: The results show that it is possible to underestimate chromosomal damage for different types of radiation by scoring aberrations at a single fixed sampling time.

Animals↗
PubMed2004

Arrest of human lung fibroblasts in G2 phase after irradiation is regulated by converging phosphatidylinositol-3 kinase and beta1-integrin signaling in vitro.

PURPOSE: Cell-matrix interactions might confer cellular radioresistance in vitro. As a function of radiation, the impact of fibronectin (FN) and phosphatidylinositol-3 kinase (PI3K)-related signaling on survival, the cell cycle, and the beta1-integrin signaling kinases integrin-linked kinase (ILK), protein kinase Balpha/Akt (PKBalpha/Akt), and glycogen synthase kinase-3beta (GSK-3beta) was examined in normal lung fibroblasts in vitro. METHODS AND MATERIALS: Normal human CCD32 lung fibroblasts grown on polystyrene, FN, or poly-L-lysine were irradiated with 0-8 Gy. Colony forming assays, flow cytometric DNA analysis, immunoblotting (Chk1, Chk2, Cdc25C, Cdk1, 14-3-3, p53, p21), and protein kinase assays (ILK, PKBalpha/Akt, GSK-3beta) were performed with or without PI3K inhibition using LY294002 or wortmannin. RESULTS: FN significantly elevated clonogenic survival of CCD32 cells after irradiation compared with polystyrene or poly-L-lysine. FN improved accumulation of irradiated cells in G(2)/M (60%) compared with polystyrene (43%). LY294002 prevented radiation-dependent G(2) blockage on polystyrene; on FN, G(2) arrest was only slightly reduced. Radiation- and PI3K inhibition-related changes in expression and phosphorylation of the various cell cycle proteins tested correlated with the cell cycle data acquired. The kinase activities of ILK, PKBalpha/Akt, and GSK-3beta were strongly induced by irradiation on polystyrene, but not on FN, which was a result of a FN-mediated increase of basal kinase activities. In contrast to polystyrene, FN enabled radiation-dependent induction of ILK and GSK-3beta in a PI3K-independent manner. CONCLUSION: The data indicate a tight convergence of cell-matrix and cell-growth factor interactions that seem to optimize the cellular responsiveness to ionizing radiation in terms of survival and G(2) arrest. ILK, PKBalpha/Akt, and GSK-3beta involved in integrin signaling were uncovered as new molecular factors within the cellular radiation response. Our findings might also provide insight into normal tissue effects and cellular radioresistance.

Androstadienes↗
PubMed1990

Effects of irradiation on nuclear protein synthesis in G2 phase of the cell cycle.

A method was developed to determine the synthesis of nuclear proteins throughout the cell cycle which was resolved into six compartments on the basis of DNA and nuclear protein content (i.e., early and late G1, early and late S, etc). Using this technique cell-cycle-specific synthesis of certain nuclear proteins was observed. Of particular interest was a 170-kDa protein(s) whose synthesis was initiated in early S phase and reached a maximum rate in late G2. Following irradiation with 6.8 Gy of 137Cs gamma rays the synthesis of the 170-kDa protein(s) declined in the G2 population with near total inhibition seen by 24 h. Synthesis of the 170-kDa protein(s) appeared to be slightly enhanced, and the postirradiation inhibition of its synthesis was reversed, in the presence of 3 mM caffeine. Also, the synthesis of 55-kDa nuclear protein(s) was stimulated throughout the cell cycle in the presence of 3 mM caffeine. These observations suggest new possibilities regarding the mechanism of the X-ray-induced G2 block and its reversal by caffeine. However, the exact role of these nuclear proteins in cellular events remains to be ascertained.

Caffeine↗