Cell Cycle Arrest

During the last decade, there has been clear progress in using threshold in risk assessment but its acceptance by scientists is still under debate. Contrary to indirect DNA-damaging agents, DNA-reactive agents have been assumed to have a non-threshold mode of action, as they directly induce DNA lesions that potentially can be converted into mutations. However, in recent years there is a growing number of data establishing threshold doses even for these DNA-reactive compounds. Indeed, there are several defence and repair mechanisms that provide protection and that may be responsible for genotoxic thresholds. In this context, we recently showed that DNA-oxidizing agents exhibit a thresholded dose-response in vitro with respect to chromosomal alterations. We have hypothesized the involvement of different cellular responses whose nature and efficiency depend on the stress level. The aim of this study was to develop a more complete understanding of these underlying mechanisms. We investi...

Cellular stress and DNA damage up-regulate and activate p53, fundamental for cell cycle control, senescence, DNA repair and apoptosis. The specific mechanism(s) that determine whether p53-dependent cell cycle arrest or p53-dependent apoptosis prevails in response to specific DNA damage are poorly understood. In this study, we investigated two types of DNA damage, chromium treatment and gamma irradiation (IR) that induced similar levels of p53, but that mediated two distinct p53-dependent cell fates. Chromium exposure induced a robust DNA-dependent protein kinase (DNA-PK)-mediated apoptotic response that was accompanied by the rapid loss of the cyclin-dependent kinase inhibitor 1A (p21) protein, whereas IR treatment-induced cell cycle arrests that was supported by the rapid induction of p21. Inhibition of DNA-PK effectively blocked chromium-, but not IR-induced p53 stabilization and activation. In contrast, inhibition of ATM and ATR by caffeine had the inverse effect of blocking IR-, but not chromium-induced p53 stabilization and activation. Chromium exposure ablated p21 transcription but PUMA and Bax transcription was significantly enhanced compared to non-damaged cells. In contrast, IR treatment triggered significant p21 mRNA synthesis in addition to PUMA and Bax mRNA production. While chromium treatment enhanced the binding of p53 and RNA polymerase II (RNA Pol II) to both the p21 and PUMA promoters, RNA Pol II elongation was only observed along the PUMA gene and not the p21 gene. In contrast, following IR treatment, RNA Pol II elongation was observed on both p21 and PUMA. Chromium-induced apoptosis therefore involves DNA-PK-mediated p53 activation followed by preferential transcription of pro-apoptotic PUMA over anti-apoptotic p21 genes.

Colorectal cancer (CRC) is the second most fatal and the third most diagnosed type of cancer worldwide. Despite having multifactorial causes, most CRC cases are mainly determined by dietary factors. In recent years, a large number of studies have attributed a protective effect to polyphenols and foods containing these compounds (fruits and vegetables) against CRC. Indeed, polyphenols have been reported

This article reviews the mechanisms by which glucosinolate breakdown products are thought to inhibit carcinogenesis. It describes how isothiocyanates, thiocyanates, nitriles, cyano-epithioalkanes and indoles are produced from glucosinolates through the actions of myrosinase, epithiospecifier protein and epithiospecifier modifier protein released from cruciferous vegetables during injury to the plant. The various biological activities displayed by these phytochemicals are described. In particular, their abilities to induce cytoprotective genes, mediated by the Nrf2 (NF-E2 related factor 2) and AhR (arylhydrocarbon receptor) transcription factors, and their abilities to repress NF-κB (nuclear factor-κB) activity, inhibit histone deacetylase, and inhibit cytochrome P450 are outlined. Isothiocyanates appear to alter gene expression through modification of critical thiols in regulatory proteins such as Keap1 (Kelch-like ECH-associated protein 1) or IKK (IκB kinase), causing activation of Nrf2 and inactivation of NF-κB, respectively. Certain indoles act as ligands for AhR. Isothiocyanates and indoles are also capable of affecting cell cycle arrest and stimulating apoptosis. The mechanisms responsible for these anti-proliferative responses are discussed.

Context: Moringa plant (Moringa oleifera) is one of the medicinal plants used as traditional medicine for the treatment of the variety of diseases including cancer. Recently, extensive research has been conducted on leaf extracts of M. oleifera to evaluate their potential cytotoxic effects. Several studies have reported anti proliferative activity of water and alcoholic extracts of leaf, bark and seed of M. oleifera on some cancer cell line, including HepG2 liver cancer cell, A549 lung cancer cell, Caco-2 colon cancer cell, MCF7 and MDA-MB-231 breast cancer cells.

Aim: To evaluate the cytotoxic effect of n-hexane fraction of M. oleifera (hMO) leaves on T47D breast cancer cells.

Methods: The M. oleifera leaves were extracted using ethanol, then fractionated with n-hexane. The cytotoxic activity was determined using MTT assay. Apoptosis and cell cycle arrest were analyzed using flow-cytometry and expression of Bcl-2 and cyclin D1 were analyzed using immunocytochemistry.

Results: Based on preliminary MTT assay, T47D treated with hMO demonstrated a medium cytotoxic effect and inhibited cell proliferation with an IC50 value of 235.58 µg/mL. Detection of apoptosis showed that hMO induced apoptosis mediated cell death in slow manner. In addition, hMO was also induce cell cycle arrest on G0-G1 and G2-M phase. Immunocytochemistry assay showed that the hMO decreased expression of anti-apoptosis protein, Bcl-2, and cell cycle regulator protein, cyclin D1, in concentration dependent manner.

Conclusions: hMO has properties to induce apoptosis and cell cycle arrest on T47D cells. hMO has a potential compound to be explored and developed as a chemo preventive agent for breast cancer. These results provide evidence for anticancer activity of M. oleifera leaves extract since it cause growth inhibition, induced apoptosis and cell cycle arrest.

Extract of Boesenbergia pandurata (Kaempferia pandurata) (Zingiberaceae) has been used as a replacement for K. rotunda, the main ingredient of a popular traditional tonic called “jamu” especially for women in Indonesia. From our previous study, ethanolic extract of B. pandurata showed strong inhibitory effects on the growth of cancer cells, similar to ethanolic extract of Curcuma longa. C. longa and its bioactive compound, curcumin, have shown potential anticancer activity in in vitro and in vivo studies and have undergone clinical trials. Panduratin A, a chalcone derivative isolated from B. pandurata, was found to inhibit the growth of MCF-7 human breast cancer and HT-29 human colon adenocarcinoma cells with an IC50 of 3.75 and 6.56 µg/ml, respectively. Panduratin A arrested cancer cells labelled with Annexin-V and propidium iodide in the G0/G1 phase and induced apoptosis in a dose-dependent manner. In an animal model study, male Sprague–Dawley rats were fed with AIN diet containing ethanolic extracts prepared from the equivalent of 4% by weight of dried rhizomes of B. pandurata and C. longa. Aberrant crypt foci (ACFs) were induced by two subcutaneous doses (15 mg/kg body weight) of azoxymethane (AOM) 1 week apart. The rats were killed 10 weeks later, and the ACFs were assessed in the colon. At the dose given to rats, it appeared that the extracts were not toxic. Total ACFs were slightly reduced by B. pandurata extract compared to control group but not significantly different. Extract of B. pandurata may have a protective effect against colon cancer but additional studies using different models, such as a breast cancer model, need to be carried out.

JNK and ERK MAP kinases regulate cellular responses to genotoxic stress in a cell type and cell context-dependent manner. However, the factors that determine and execute JNK- and ERK-controlled stress responses are only partly known. In this study, we investigate the roles of the AP-1 components ATF3 and Fra1 in JNK- and ERK-dependent cell cycle arrest and apoptosis. We show that the anti-cancer drug cisplatin or UV light activates both JNK and ERK in human glioblastoma cells lacking functional p53. Inhibition experiments of JNK or ERK activities revealed that the ERK pathway strongly promotes cisplatin- and UV-induced apoptosis in these glioblastoma cells. Furthermore, JNK but not ERK is required for ATF3 induction, and both ERK and JNK are necessary for post-transcriptional induction of Fra1 in response to cisplatin or UV. Knock-down of ATF3 and Fra1 results in increased and decreased cisplatin-induced apoptosis, respectively, indicating that ATF3 is an anti-apoptotic JNK effector and Fra1 is a pro-apoptotic ERK/JNK effector. Knock-down experiments also revealed that ATF3 and Fra1, respectively, enhance and reduce S-phase arrest through differential modulation of the Chk1–Cdk2 pathway. Thus, we identify novel reciprocal functions of ATF3 and Fra1 in JNK- and ERK-dependent DNA damage responses.

Although placental development and implantation depend on the coordination of trophoblast proliferation, differentiation and invasion, little is known about the cell cycle regulators that govern the control of these events. The hypothesis that the coordinated expression of cell cycle progression and inhibition factors will determine whether cytotrophoblasts proliferate or undergo cell cycle arrest or cell cycle exit allowing subsequent differentiation was tested. The cell cycle promotors cyclin A, cyclin B1, PCNA, Ki67 and the cell cycle inhibitors p21, p27 and p57 were immunolocalized in tissue sections of first trimester pregnancies (weeks 6 and 9–12). Double staining with cytokeratin 7 allowed unambiguous identification of extravillous cytotrophoblast (EVT) in the decidua. Villous cytotrophoblasts were immunolabelled for Ki67 and cyclin A but only few were stained with anti-cyclin B1. The syncytiotrophoblast was devoid of immunoreactivity for any of the cell cycle progression factors. It expressed especially p21, whereas p27 and p57 were predominantly found in villous cytotrophoblasts. PCNA, Ki67, cyclin A and cyclin B1 were immunolocalized in proximal and distal EVTs of anchoring villi and in EVT which had invaded the upper decidual segments. All EVTs strongly expressed p27 and p57, but not p21. These data clearly suggest different functions for p21, p27 and p57 in placental development with distinct roles for p21 and p57 in syncytiotrophoblast and EVT differentiation, respectively. p27 appears to be involved in both the processes. The results may also challenge the concept of differential mitotic activity in the proximal and distal parts of the first trimester cytotrophoblast cell column, but more functional studies are clearly needed. The presence of p27 and p57 in EVT cells, which invade the deciduas deeply, may account for the loss of mitogenic potential of these cells.

Purpose In previous research, we found that 10-methoxy-9-nitrocamptothecin (MONCPT) possessed potent anti-tumor activity in A549 cells in vitro and in vivo. In this paper, our purpose is to investigate the mechanism of MONCPT-induced cell cycle arrest in A549 cells. Methods Cell cycle distribution was measured using flow cytometry (FCM). Protein expression and RNA expression were analyzed by western blotting and real-time PCR, respectively. SiRNA technology was introduced to silence the expression of p53 and p38. Results FCM showed that MONCPT induced cell cycle G2/M arrest in time- and dose-dependent manner. The levels of feedback loop proteins PLK-1, Cdc25C, and cyclinB1 were obviously increased from 12 to 24 h, and then reduced from 36 to 48 h by MONCPT (100.0 nM). Moreover, down-regulation of p-AKT in A549 cells was seen after treated with 100.0 nM MONCPT for 12–48 h. Over-expression of p53 and p21 in A549 cells treated with MONCPT was observed in time-dependent manner. When wild type p53 expression was specifically inhibited by RNA-interference, A549 cells treated with MONCPT delayed the onset of G2/M arrest; meanwhile p-ERK and Cdc2 were up-regulated while p21 and CDK7 were down-regulated in A549 cells treated with MONCPT and p53 SiRNA transfection in contrast to cells treated with 100.0 nM MONCPT alone. In addition, our results exhibited that MONCPT obviously down-regulated p-ERK, JNK, p-JNK, and p-p38. Treatment with p38 mitogen-activated protein kinase (MAPK) SiRNA obviously inhibited p38 MAPK and delayed the G2/M arrest induced by 50.0 nM MONCPT after 48 h. Conclusion Cell cycle regulators, AKT, p53, and MAPK, as therapeutic targets for MONCPT to induce cell cycle G2/M arrest in the context of anticancer therapy.

In spite of the global consumption of mushrooms, only two epidemiological studies demonstrated an inverse correlation between mushroom intake and the risk of cancer. Therefore, in the present study we evaluated whether extracts from edible mushrooms Agaricus bisporus (portabella), Flammulina velutipes (enoki), Lentinula edodes (shiitake) and Pleurotus ostreatus (oyster) affect the growth of breast and colon cancer cells. Here, we identified as the most potent, P. ostreatus (oyster mushroom) which suppressed proliferation of breast cancer (MCF-7, MDA-MB-231) and colon cancer (HT-29, HCT-116) cells, without affecting proliferation of epithelial mammary MCF-10A and normal colon FHC cells. Flow cytometry revealed that the inhibition of cell proliferation by P. ostreatus was associated with the cell cycle arrest at G0/G1 phase in MCF-7 and HT-29 cells. Moreover, P. ostreatus induced the expression of the tumor suppressor p53 and cyclin-dependent kinase inhibitor p21(CIP1/WAF1), whereas i...