Single-strand breaks, cell cycle arrest and apoptosis in HL-60 and LLCPK1 cells exposed to 1,2-dibromo-3-chloropropane

We investigated 1,2-dibromo-3-chloropropane (DBCP)-induced DNA damage, cell cycle alterations and cell death in two cell lines, the human leukemia HL-60 and the pig kidney LLCPK₁, both of which are derived from potential target sites for DBCP-induced toxicity. DBCP (30–300 µmol/L) caused a concentration-dependent increase in the levels of DNA single-strand breaks in both cell lines as well as in cultured human renal proximal tubular cells. After extended DBCP exposure in LLCPK₁ cells (100 µmol/L, 30 h), the level of DNA breaks returned almost to control values. Incubation for 48 h showed a clear reduction of growth with DBCP concentrations as low as 10 µmol/L. Flow cytometric analysis showed that DBCP (1–10 µmol/L) exposure for 24 h caused an accumulation of LLCPK₁ cells in the G₂/M-phase. In HL-60 cells the accumulation in G₂/M-phase was less marked, and at higher concentrations the cells accumulated in S-phase. Flow cytometric studies of HL-60 and LLCPK₁ cells exposed to 100–500 µmol/L DBCP showed increased number of apoptotic cells/bodies with a lower DNA content than that of the G₁ cells. Microscopic studies revealed that there were increased numbers of cells with nuclear condensation and fragmentation, indicating that apoptosis was the dominant mode of death in these cell lines, following exposure to DBCP. The characteristic ladder pattern of apoptotic cells was observed when DNA from DBCP-treated HL-60 cells and LLCPK₁ cells was electrophoresed in agarose. The finding that DBCP can cause an accumulation of cells in G₂/M-phase and induce apoptosis in vitro may be of importance for the development of DBCP-induced toxicity in vivo.     

Effects of microwave exposure and Gemcitabine treatment on apoptotic activity in Burkitt’s lymphoma (Raji) cells

Abstract

We investigated the effects of 1.8?MHz Global System for Mobile Communications (GSM)-modulated microwave (MW) radiation on apoptotic level and cell viability of Burkitt’s lymphoma (Raji) cells with or without Gemcitabine, which exhibits cell phase specificity, primarily killing cells undergoing DNA synthesis (S-phase). Raji cells were exposed to 1.8?GHz GSM-modulated MW radiation at a specific absorption rate (SAR) of 0.350?W/kg in a CO₂ incubator. The duration of the exposure was 24?h. The amount of apoptotic cells was analyzed using Annexin V-FITC and propidium iodide (PI) staining with flow cytometer. The apoptotic activity of MW exposed Raji cells was increased significantly. In addition, cell viability of exposed samples was significantly decreased. Combined exposure of MW and Gemcitabine increased the amount of apoptotic cells than MW radiation alone. Moreover, viability of MW?+?Gemcitabine exposed cells was lower than that of cells exposed only to MW. These results demonstrated that MW radiation exposure and Gemcitabine treatment have a synergistic effect on apoptotic activity of Raji cells.     

The phagocytic capacity of macrophages in the S phase of the cell cycle

An inflammatory reaction was induced in the peritoneal cavity of mice. Two days later, the peritoneal macrophages, containing a proportion of S-phase (DNA-synthesizing) cells, were harvested and adhered to glass. Then the S-phase macrophages were labeled with [³H]thymidine (radioautography) and the macrophage monolayers were tested with regard to their ability to phagocytose immunoglobulincoated sheep red blood cells (SRBC). The percentages of S-phase macrophages which had phagocytosed SRBC were a little lower than those found for G-phase (G₁ + G₂) cells. Otherwise, the number of phagocytosed SRBC per macrophage was about equal for macrophages in both phases, and they both responded well by increasing the phagocytosis when the SRBC: macrophage ratio was increased. The S-phase macrophages also phagocytosed latex beads and zymosan particles efficiently.     

Induction of Apoptosis and Antiproliferative Activity of Naringenin in Human Epidermoid Carcinoma Cell through ROS Generation and Cell Cycle Arrest

A natural predominant flavanone naringenin, especially abundant in citrus fruits, has a wide range of pharmacological activities. The search for antiproliferative agents that reduce skin carcinoma is a task of great importance. The objective of this study was to analyze the anti-proliferative and apoptotic mechanism of naringenin using MTT assay, DNA fragmentation, nuclear condensation, change in mitochondrial membrane potential, cell cycle kinetics and caspase-3 as biomarkers and to investigate the ability to induce reactive oxygen species (ROS) initiating apoptotic cascade in human epidermoid carcinoma A431 cells. Results showed that naringenin exposure significantly reduced the cell viability of A431 cells (p<0.01) with a concomitant increase in nuclear condensation and DNA fragmentation in a dose dependent manner. The intracellular ROS generation assay showed statistically significant (p<0.001) dose-related increment in ROS production for naringenin. It also caused naringenin-mediated epidermoid carcinoma apoptosis by inducing mitochondrial depolarization. Cell cycle study showed that naringenin induced cell cycle arrest in G₀/G₁ phase of cell cycle and caspase-3 analysis revealed a dose dependent increment in caspase-3 activity which led to cell apoptosis. This study confirms the efficacy of naringenin that lead to cell death in epidermoid carcinoma cells via inducing ROS generation, mitochondrial depolarization, nuclear condensation, DNA fragmentation, cell cycle arrest in G₀/G₁ phase and caspase-3 activation.     

Investigation of the Effects of 2.1 GHz Microwave Radiation on Mitochondrial Membrane Potential (ΔΨ m), Apoptotic Activity and Cell Viability in Human Breast Fibroblast Cells

In the present study we aimed to investigate the effects of 2.1 GHz Wideband Code Division Multiple Access (W-CDMA) modulated Microwave (MW) Radiation on cell survival and apoptotic activity of human breast fibroblast cells. The cell cultures were exposed to W-CDMA modulated MW at 2.1 GHz at a SAR level of 0.607 W/kg for 4 and 24 h. The cell viability was assessed by MTT [3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] method. The percentage of apoptotic cells was analyzed by Annexin V-FITC and PI staining. 5,5′,6,6′-Tetrachloro-1,1′,3,3′- tetraethylbenzimidazolcarbocyanine iodide (JC-1) was used to measure Mitochondrial Membrane Potential (ΔΨ _m). sFasL and Fas/APO-1 protein levels were determined by ELISA method. 2.1 GHz MW radiation was shown to be able to inhibit cell proliferation and induce apoptosis in human breast fibroblast cells. The cell viability of MW-exposed cells was decreased significantly. The percentages of Annexin V-FITC positive cells were higher in MW groups. ΔΨ _m was decreased significantly due to MW radiation exposure. However, neither sFas nor FasL level was significantly changed in MW-exposed fibroblast cells. The results of this study showed that 2.1 GHz W-CDMA modulated MW radiation-induced apoptotic cell death via the mitochondrial pathway.     

Apoptosis induced by ardipusilloside III through BAD dephosphorylation and cleavage in human glioblastoma U251MG cells

Ardipusilloside III is a saponin newly isolated from Ardisia pusilla A.DC. Since saponins have exhibited broad anti-cancer and pro-apoptotic activity, we investigated the ability of ardipusilloside III to induce apoptosis in human glioblastoma U251MG cells, as well as the involvement of apoptotic signaling pathways. Ardipusilloside III markedly suppressed proliferation of U251MG cells in a time- and dose-dependent manner (P < 0.05, IC₅₀ = 8.2 μg/ml), but did not affect the growth of primary cultures of human astrocytes. Ardipusilloside III-treated U251MG cells underwent typical apoptotic changes. Exposure to a low dose of ardipusilloside III provoked G₂/M-phase cell cycle arrest, which preceded apoptosis characterized by the appearance of cells with sub-G₁ DNA content. However, a higher dose of ardipusilloside III induced apoptosis without first causing cell cycle arrest. In addition, ardipusilloside III exposure resulted in time-dependent BAD dephosphorylation and cleavage as well as activation of caspase-8 and caspase-3. Therefore, both the intrinsic pathway of apoptosis, mediated by BAD dephosphorylation and cleavage, and the extrinisic pathway of apoptosis, mediated by caspase-8 and caspase-3 activation, were involved in ardipusilloside III-induced apoptosis. These data suggest that ardipusilloside III is a reliable candidate for chemotherapeutic treatment of human glioblastomas, and should be investigated further. Hong Lin, Xiang Zhang, Guang Cheng, and Hai-Feng Tang contributed equally to the work.     

EPA诱导人肝癌细胞SMMC-7721凋亡及端粒酶活性调控机制研究

目的:探究二十碳五烯酸(Eicosa Pentaenoic Acid.EPA)对SMMC-7721人肝癌细胞的凋亡、端粒逆转录酶h TERT的调控作用及端粒酶表达活性的影响。方法:体外培养SMMC-7721人肝癌细胞,用不同浓度的EPA(0μM、25μM、50μM、100μM、200μM)作用于SMMC-7721肝癌细胞(24 h、48 h、72 h)后,显微镜下观察其形态学变化;应用MTT法检测SMMC-7721肝癌细胞细胞增殖变化情况;Western-blot法检测h TERT、Bax、Bcl-2蛋白表达水平变化;Real Time-PCR检测h TERTm RNA的表达变化;ELISA法检测SMMC-7721肝癌细胞端粒酶活性的表达水平。结果:EPA可诱导肝癌细胞SMMC-7721发生细胞凋亡,具有明显的时间计量依赖关系。在此过程中Bcl-2蛋白表达的降低和Bax蛋白表达上调,同时端粒酶逆转录酶h TERT蛋白及其m RNA的表达水平和端粒酶活性均明显降低。结论:抑制端粒酶逆转录酶基因(h TERTm RNA)表达而抑制端粒酶的活性、诱导癌细胞凋亡,可能是EPA的抗癌作用机制之一。     

Arrest of the cell cycle reduces susceptibility of target cells to perforin-mediated lysis

Cytotoxic T lymphocytes secrete a pore-forming cytolysin, perforin, that damages membranes of target cells. They also ligate Fas receptors on target cells and provoke apoptotic death. A20 (B lymphoma) and P815 (mastocytoma) cell lines were examined for their susceptibility to perforin-mediated lysis and to Fas-induced apoptosis after blockade of the cell cycle at the G₁/S interface. Cells were arrested at the G₁/S interface by inhibition of DNA synthesis with thymidine or aphidicolin. Subsequently, the treated cells were incubated either with CTL cytotoxic granules or the Fas-specific monoclonal antibody Jo-2. We show that arrest of the cell cycle at the G₁/S interface markedly reduced the susceptibility of target cells to perforin-mediated lysis. In contrast, growth arrest with thymidine or aphidicolin increased susceptibility of A20 and P815 cells to Fas-mediated apoptosis. Susceptibility to lysis by intact CTLs was not affected significantly by blockade of target cells with aphidicolin or thymidine. When cells surviving exposure to perforin-containing granules were isolated on Ficoll density gradients and cell-cycle profiles were examined by flow cytometry, the ratio of G₁ to G₂cells increased among the survivors exposed to granules in contrast to controls incubated with buffer alone. The data suggest that cells in G₁ phase of the cell cycle are less susceptible to the perforin pathway than cells in G₂and S phases but are more susceptible to the Fas pathway. J. Cell. Biochem. 69:425–435, 1998. © 1998 Wiley-Liss, Inc.     

The Protein Kinase C�� Catalytic Fragment Is Critical for Maintenance of the G2/M DNA Damage Checkpoint

Protein kinase Cδ (PKCδ) is an essential component of the intrinsic apoptotic program. Following DNA damage, such as exposure to UV radiation, PKCδ is cleaved in a caspase-dependent manner, generating a constitutively active catalytic fragment (PKCδ-cat), which is necessary and sufficient for keratinocyte apoptosis. We found that in addition to inducing apoptosis, expression of PKCδ-cat caused a pronounced G₂/M cell cycle arrest in both primary human keratinocytes and immortalized HaCaT cells. Consistent with a G₂/M arrest, PKCδ-cat induced phosphorylation of Cdk1 (Tyr¹⁵), a critical event in the G₂/M checkpoint. Treatment with the ATM/ATR inhibitor caffeine was unable to prevent PKCδ-cat-induced G₂/M arrest, suggesting that PKCδ-cat is functioning downstream of ATM/ATR in the G₂/M checkpoint. To better understand the role of PKCδ and PKCδ-cat in the cell cycle response to DNA damage, we exposed wild-type and PKCδ null mouse embryonic fibroblasts (MEFs) to UV radiation. Wild-type MEFs underwent a pronounced G₂/M arrest, Cdk1 phosphorylation, and induction of apoptosis following UV exposure, whereas PKCδ null MEFs were resistant to these effects. Expression of PKCδ-green fluorescent protein, but not caspase-resistant or kinase-inactive PKCδ, was able to restore G₂/M checkpoint integrity in PKCδ null MEFs. The function of PKCδ in the DNA damage-induced G₂/M cell cycle checkpoint may be a critical component of its tumor suppressor function.     

Nuclear accumulation of cyclin D1 following long-term fractionated exposures to low-dose ionizing radiation in normal human diploid cells

Cyclin D1 is a mitogenic sensor that responds to growth signals from the extracellular environment and regulates the G₁-to-S cell cycle transition. When cells are acutely irradiated with a single dose of 10 Gy, cyclin D1 is degraded, causing cell cycle arrest at the G₁/S checkpoint. In contrast, cyclin D1 accumulates in human tumor cells that are exposed to long-term fractionated radiation (0.5 Gy/fraction of X-rays). In this study we investigated the effect of fractionated low-dose radiation exposure on cyclin D1 localization in 3 strains of normal human fibroblasts. To specifically examine the nuclear accumulation of cyclin D1, cells were treated with a hypotonic buffer containing detergent to remove cytoplasmic cyclin D1. Proliferating cell nuclear antigen (PCNA) immunofluorescence was used to identify cells in S phase. With this approach, we observed S-phase nuclear retention of cyclin D1 following low-dose fractionated exposures, and found that cyclin D1 nuclear retention increased with exposure time. Cells that retained nuclear cyclin D1 were more likely to have micronuclei than non-retaining cells, indicating that the accumulation of nuclear cyclin D1 was associated with genomic instability. Moreover, inhibition of the v-akt murine thymoma viral oncogene homolog (AKT) pathway facilitated cyclin D1 degradation and eliminated cyclin D1 nuclear retention in cells exposed to fractionated radiation. Thus, cyclin D1 may represent a useful marker for monitoring long-term effects associated with exposure to low levels of radiation.     

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 (_H2AX) can be revealed immunocytochemically; the intensity of ?H2AX 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 ?H2AX following exposure of HeLa and HL-60 cells to a wide range of doses of UV-B light (6.1 J/m²-3.45 kJ/m²) 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 (G₁, G₂ 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 &gamma;H2AX in G₁, G₂ 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 &gamma;H2AX IF than that initially induced by UV; predominantly S-phase cells underwent apoptosis. While the suppression of DNA replication 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 &gamma;H2AX. Furthermore, aphidicolin itself induced &gamma;H2AX in early-S phase cells. The induction of &gamma;H2AX 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 &gamma;H2AX in GG₁, GG₂ 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.     

Growth inhibitory effect of quercetin on SW 872 human liposarcoma cells

Adipocytic tumors represent the largest single group of soft tissue tumors. In the present study, we investigated the antiproliferative potential of quercetin in SW 872 human liposarcoma cells. Cell viability was significantly influenced by quercetin treatment in a time- and dose-dependent manner. Flow cytometric analyses of SW 872 human liposarcoma cells exposed to quercetin showed that the increase of apoptotic cells was time- and dose-dependent. The percentages of normal cells were decreased and apoptotic cells (including early apoptotic and late apoptotic) were increased with increasing concentrations of quercetin. Quercetin-induced apoptosis in SW 872 human liposarcoma cells was associated with the loss of mitochondrial membrane potential (DeltaPsi(m)). The apoptosis in SW 872 human liposarcoma cells induced by quercetin was mediated through the activation of caspase-3, Bax, and Bak and then cleavage of PARP and downregulation of Bcl-2. These results demonstrate that quercetin may prevent atypical lipomatous tumors/well-differentiated liposarcomas from mature adipocytic proliferation, which may contribute to its antiproliferative function.     

Caffeine induces a second wave of apoptosis after low dose-rate gamma radiation of HL-60 cells

Most cell lines that lack functional p53 protein are arrested in the G₂ phase of the cell cycle due to DNA damage. It was previously found that the human promyelocyte leukemia cells HL-60 (TP53 negative) that had been exposed to ionizing radiation at doses up to 10 Gy were arrested in the G₂ phase for a period of 24 h. The radioresistance of HL-60 cells that were exposed to low dose-rate gamma irradiation of 3.9 mGy/min, which resulted in a pronounced accumulation of the cells in the G₂ phase during the exposure period, increased compared with the radioresistance of cells that were exposed to a high dose-rate gamma irradiation of 0.6 Gy/min. The D₀ value (i.e. the radiation dose leading to 37% cell survival) for low dose-rate radiation was 3.7 Gy and for high dose-rate radiation 2.2 Gy. In this study, prevention of G₂ phase arrest by caffeine (2 mM) and irradiation of cells with low dose-rate irradiation in all phases of the cell cycle proved to cause radiosensitization (D₀=2.2 Gy). The irradiation in the presence of caffeine resulted in a second wave of apoptosis on days 5–7post-irradiation. Caffeine-induced apoptosis occurring later than day 7 post-irradiation is postulated to be a result of unscheduled DNA replication and cell cycle progress.     

Gamma irradiation induced apoptotic changes in the chromatin structure of human erythroleukemia K562 cells

Exponentially growing human erythroleukemia K562 cells were synchronized by centrifugal elutriation prior to and after Co⁶⁰ γ-irradiation (4 Gy). Forward scatter flow cytometry used for size analysis revealed the increase of an early apoptotic cell population ranging from lower (0.05 C-value) to higher DNA content (∼1 C) as the cells progressed through the S phase. The increase in cellular DNA content expressed in C-values correlated with apoptotic chromatin changes manifested as many small apoptotic bodies in early S phase and larger but less numerous disintegrated apoptotic bodies in late S phase. Most significant changes after exposure to γ-irradiation took place in early S phase resulting in an increase of nuclear size by more than 50%. Cell fractions containing irradiated cells showed enhanced growth arrest at 2.4 C-value, which was accompanied by apoptosis. Apoptotic cell cycle arrest near to the G₁/G₀ checkpoint and apoptotic changes indicate that the radiation resistance of K562 cells is related to the bypass of the early stage of the p53 apoptotic pathway. Apoptotic changes in chromatin structure induced by γ-irradiation indicate that these injury-specific changes can be identified and distinguished from chromatin changes induced by UV radiation or heavy metals.     

Regulation of Survivin and Bcl‐2 in HepG2 Cell Apoptosis Induced by Quercetin

Quercetin, a widely distributed bioflavonoid, has been shown to induce growth inhibition in a variety of human cancer cells. However, the regulation of survivin and Bcl‐2 on the quercetin‐induced cell‐growth inhibition and apoptosis in cancer cells remains unclear. In the present study, we report that quercetin can inhibit proliferation and induce apoptosis in HepG2 cells in dose‐ and time‐dependent manner. Hoechst 33258 and acridine orange/ethidium bromide (AO/EB) staining showed that HepG2 cells underwent the typical morphologic changes of apoptosis characterized by nuclear shrinkage, chromatin condensation, or fragmentation after exposure to quercetin. Cell‐cycle analysis reveals a significant increase of the proportion of cells in G₀/G₁ phase. We also demonstrate that the levels of survivin and Bcl‐2 protein expression in HepG2 cells decreased concurrently, and the levels of p53 protein increased significantly after treatment with quercetin by immunocytochemistry analysis. Relative activity of caspase‐3 and caspase‐9 increased significantly. These data clearly indicate that quercetin‐induced apoptosis is associated with caspase activation, and the levels of survivin and Bcl‐2. Our results indicate that the expression of survivin may be associated with Bcl‐2 expression, and the inhibition expression of survivin, in conjunction with Bcl‐2, might cause more pronounced apoptotic effects. Together, concurrent down‐regulated survivin and Bcl‐2 play an important role in HepG2 cell apoptosis induced by quercetin.     

Preferential Fas-mediated apoptotic execution at G1 phase: the resistance of mitotic cells to the cell death

Apoptosis is induced by various stresses generated from the extracellular and intracellular environments. The fidelity of the cell cycle is monitored by surveillance mechanisms that arrest its further progression if any crucial process has not been completed or damages are sustained, and then the cells with problems undergo apoptosis. Although the molecular mechanisms involved in the regulation of the cell cycle and that of apoptosis have been elucidated, the links between them are not clear, especially that between cell cycle and death receptor-mediated apoptosis. By using the HeLa.S-Fucci (fluorescent ubiquitination-based cell cycle indicator) cells, we investigated the relationship between the cell cycle progression and apoptotic execution. To monitor apoptotic execution during cell cycle progression, we observed the cells after induction of apoptosis with time-lapse fluorescent microscopy. About 70% of Fas-mediated apoptotic cells were present at G₁ phase and about 20% of cells died immediately after cytokinesis, whereas more than 60% of etoposide-induced apoptotic cells were at S/G₂ phases in random culture of the cells. These results were confirmed by using synchronized culture of the cells. Furthermore, mitotic cells showed the resistance to Fas-mediated apoptosis. In conclusion, these findings suggest that apoptotic execution is dependent on cell cycle phase and Fas-mediated apoptosis preferentially occurs at G₁ phase.