Diallyl disulfide induces reversible G2/M phase arrest on a p53-independent mechanism in human colon cancer HCT-116 cells

Diallyl disulfide (DADS), a major organosulfur compound of garlic oil, is known to have an anticancer effect on human cancer cells. However, the exact mechanisms of this anticancer activity remain unclear. Here, we investigate the effects of DADS on cell cycle progression in human colon cancer HCT-116 cells by exploring the role played by regulatory molecules such as p53 and cyclin B1. Treatment of HCT-116 cells by DADS induced a marked growth inhibition with a slight reduction in viability and induced transient cell cycle arrest in the G2/M phase. Cyclin B1 is thought to play an important role in this process, as the DADS-induced G2/M phase arrest occurs with the increase of cyclin B1 expression. DADS also significantly induced the expression of p53, which contributes to cell cycle arrest in cancer cells, at a late time-point of 24 h. In addition, knockdown of p53 by siRNA did not affect cell cycle arrest, its reversibility, or the expression of cyclin B1 in the G2/M phase induced by DADS. Based on these results we conclude that, with the dynamic expression of cyclin B1, DADS induces reversible cell cycle arrest in the G2/M phase of HCT-116 cells through a p53-independent mechanism.     

Celecoxib leads to G2/M arrest by induction of p21 and down-regulation of cyclin B1 expression in a p53-independent manner

A unique in vitro system has been developed in our lab that consists of normal enterocytes derived from the rat ileum (IEC-18 cells) and their transformed derivatives with c-K-ras (R1 cells), anti-sense bak (B3 cells) and cyclin D1 (D1 cells). R1 and B3 cells express high level of COX-2 protein and PGE2. IEC 18 and D1 cells express negligible amount of COX-2, and produce very low level of PGE2. A relatively low dose of celecoxib (5-10 microM) induced G2/M arrest, followed by induction of apoptosis in the transformed but not in the normal cells. Down-regulation of cyclin B1 and up-regulation of p21 expressions independent of p53 might have cause this cell cycle block. Growth inhibition was related to COX-2 function with 90-95% reduction in PGE2 production. These findings may be of clinical importance, since low concentration of celecoxib can be achieved in human serum following standard anti-inflammatory (100-200 mg bid) regime.     

Apigenin induces cell cycle arrest and p21/WAF1 expression in a p53-independent pathway

Apigenin, a common dietary flavonoid, has been shown to induce cell growth-inhibition and cell cycle arrest in many cancer cell lines. One important effect of apigenin is to increase the stability of the tumor suppressor p53 in normal cells. Therefore, apigenin is expected to play a large role in cancer prevention by modifying the effects of p53 protein. However, the mechanisms of apigenin's effects on p53-mutant cancer cells have not been revealed yet. We assessed the influence of apigenin on cell growth and the cell cycle in p53-mutant cell lines. Treatment with apigenin resulted in growth-inhibition and G2/M phase arrest in two p53-mutant cancer cell lines, HT-29 and MG63. These effects were associated with a marked increase in the protein expression of p21/WAF1. We have shown that p21/WAF1 mRNA expression was also markedly increased by treatment with apigenin in a dose- and time-dependent manner. However, we could not detect p21/WAF1 promoter activity following treatment with apigenin. Similarly, promoter activity from pG13-Luc, a p53-responsive promoter plasmid, was not activated by treatment with apigenin with or without p53 protein expression. These results suggest that there is a p53-independent pathway for apigenin in p53-mutant cell lines, which induces p21/WAF1 expression and growth-inhibition. Apigenin may be a useful chemopreventive agent not only in wild-type p53 status, but also in cancer with mutant p53.     

AdHu5-apoptin induces G2/M arrest and apoptosis in p53-mutated human gastric cancer SGC-7901 cells

The use of anticancer therapeutic agents is limited largely by their severe toxicity to normal tissues. The development of novel agents with tumor-specific cell-killing and effective gene delivery properties is thus very desirable. We used human adenovirus serotype 5 (AdHu5) as a vehicle to deliver the apoptin gene to specifically target gastric cancer in a recombinant gene delivery approach. AdHu5-apoptin is a safe and efficacious agent for the treatment of gastric cancer (GC). Our results show that apoptin protein encoded by the apoptin gene delivered via AdHu5 significantly inhibited the proliferation of SGC-7901 GC cells. Apoptin reduced the clone number by more than 75 % and resulted in cell cycle arrest in the G2/M phase for 48 % of the GC cells. It also induced cleavage of caspase-3, caspase-7, and caspase-9 in the GC cells. Intratumoral and peritumoral in vivo injection of AdHu5-apoptin significantly suppressed tumor growth and induced apoptosis in xenogeneic tumors in mice. The apoptosis induced by AdHu5-apoptin was independent of anti-apoptotic Bcl-2 and Bcl-xL proteins and the p53 pathway. Taken together, our results show that AdHu5-apoptin has great potential as a therapeutic agent for effective treatment of gastric tumors.     

Inactivation of p53 in normal human cells increases G2/M arrest and sensitivity to DNA-damaging agents

p53 mutations are found in about 70% of human cancers. In order to evaluate the role of these mutations in response to chemotherapeutic agents, it is important to distinguish between p53 response to DNA-damaging agents in normal and in tumour cells. Here, using normal human fibroblasts (NHFs), we show that cisplatin and UV radiation induce G₂/M arrest which is temporally linked to p53-protein induction. To study the contribution of p53 to this G₂/M arrest, we inhibited p53 induction in NHFs using p53 anti-sense oligonucleotides. Following exposure of NHFs to UV radiation, the inhibition of p53-protein induction leads to a greater accumulation of cells in the G₂/M phase, but also to a decreased fraction of cells in the G₁ phase. We propose that p53 does not induce G₂/M arrest directly, and that the extent of this arrest may depend on the fraction of cells that do not stop at the G₁ phase following exposure to DNA-damaging agents. Furthermore, inhibition of p53-protein induction leads to increased sensitivity of NHFs to UV radiation. These results suggest that inhibition of p53 protein enhances sensitivity to DNA-damaging agents in normal human cells. Int. J. Cancer 75:432–438, 1998. © 1998 Wiley-Liss, Inc.     

Jaceosidin induces p53-dependent G2/M phase arrest in U87 glioblastoma cells

Flavonoid compounds have been shown to trigger cell cycle arrest at G0/G1, S and G2/M checkpoints, allowing cells to repair DNA damage before entry into mitosis. Jaceosidin, a flavonoid compound, has been reported to induce apoptosis in various cancer cell lines. In our previous study, we established that jaceosidin induces apoptosis in U87 glioblastoma cells through G2/M phase arrest. However the molecular mechanisms oremained unclear. In the present study, mRNA and protein expression levels of major cell cycle regulatory genes were analyzed by semi-quantitative RT-PCR and Western blot studies respectively. The results demonstrated that jaceosidin-induced G2/M phase arrest in U87 cells is associated with DNA fragmentation, up-regulation of p53 and p21 and subsequent down-regulation of cyclin B1 and CDK1 expression at mRNA as well as at protein level. These findings provide insights into jaceosidin-induced G2/M phase arrest in U87 glioblastoma cells.     

Influence of p53 and p21Waf1 expression on G2/M phase arrest of colorectal carcinoma HCT116 cells to proteasome inhibitors

Ubiquitin-mediated protein degradation in vertebrates has been implicated in cell cycle control. In this report we explored the effects of proteasome inhibitors (MG132, lactacystin and ALLN) on cell cycle distribution. Colorectal carcinoma HCT116 cells were treated with proteasome inhibitor MG132. The results showed that MG132 inhibited cell proliferation in a dose-dependent manner. MG132 arrested HCT116 cells at G2/M phase, which was associated with drug-induced blockade of p53 degradation and/or induction of p53-related gene expression along with the accumulation of cyclin B, cyclin A and p21. MG132 treated HCT116 (wild-type) had a similar cell cycle distribution as the MG132 treated HCT116 (p53-/-) and HCT116 (p21-/-) cells, suggesting that p53 and p21 may not be essential for MG132-induced G2/M phase arrest. The release experiments from nocodazole-induced mitotic phase cells indicated that MG132 inhibits the proliferation of HCT116 cells via arrest in the G2 phase. In addition, when HCT116 cells were exposed to combination of sodium butyrate and MG132 enhanced cell growth inhibition and induction of apoptosis were observed.     

Artesunate promotes G2/M cell cycle arrest in MCF7 breast cancer cells through ATM activation

Background

Recent studies have revealed that artesunate (ART) has clear anti-tumor activity, suggesting that it could be a good candidate chemotherapeutic agent. In this study, we researched the inhibitory effect of ART on MCF7 cells and explored the possible mechanisms.

Methods

MTT assay was used to detect the effect of ART on the proliferation of MCF7 cells. Crystal violet staining was used to observe morphological and quantitative changes. Flow cytometry was used to detect the cell cycle of the drug-acting MCF7 cells. In addition, western blotting was used to detect the drug influence on expression of the ATM, phospho-ATM(S1981), H2AX, γH2AX(S139), CHK2 and phospho-CHK2(T68), cdc25C, and phospho-cdc25C(S216).

Results

In the experimental groups, the proliferation of MCF7 cells was inhibited in a dose-dependent manner and the original cell morphology was lost. The number of G2/M phase cells in the experimental groups increased significantly, and the expression of DNA damage response-associated proteins was significantly increased, such as phospho-ATM(S1981), γH2AX(S139), phospho-CHK2(T68), and phospho-cdc25C(S216).

Conclusions

ART can inhibit cell proliferation and promote G2/M arrest in MCF7 cells through ATM activation and the ensuing “ATM-Chk2-Cdc25C” pathway, thus implicating ART as a novel candidate for breast cancer chemotherapy.

     

棕矢车菊素诱导人宫颈癌Hela细胞G2/M期停滞的机制研究

目的:研究棕矢车菊素对宫颈癌（cervical carcinoma,CC）细胞Hela的增殖抑制和周期阻滞能力,探索棕矢车菊素是否具有宫颈癌治疗药物的潜力。方法:MTT比色法检测细胞活力;羧基荧光素二醋酸盐琥珀酰亚胺酯（carboxyfluorescein succinimidyl amino ester,CFSE）法检测细胞增殖水平变化;碘化丙啶（propidium,PI）单染检测细胞周期;免疫印迹法（western blot,WB）检测细胞蛋白表达水平。采用裸鼠成瘤检测棕矢车菊素体外抑制肿瘤效果。结果:棕矢车菊素可以显著抑制Hela细胞活力水平,且具有时间和浓度依赖性;棕矢车菊素抑制Hela细胞增殖,且100 μmol/L棕矢车菊素可显著诱导细胞发生G2/M周期阻滞。分子机制上,研究证明了棕矢车菊素可以通过促进细胞周期检验点激酶（checkpoint kinase 2,CHK2）激活,抑制细胞分裂周期蛋白25同源蛋白C（cell division cyclin 25 homolog C,CDC25C）活力,从而提高无活性的pCDC2水平。棕矢车菊素同时降低了Cyclin B1表达。因此,棕矢车菊素通过抑制G2/M期调控蛋白Cyclin B1/CDC2复合物活性来诱导细胞发生G2/M期阻滞。同时,体外裸鼠成瘤,棕矢车菊素灌胃4周后,小鼠肿瘤体积显著减小。结论:在Hela细胞上,棕矢车菊素具有抑制细胞增殖和诱导G2/M期阻滞的作用,证明了棕矢车菊素具有抗宫颈癌细胞的治疗潜力。     

Cisplatin-induced p53-independent growth arrest and cell death in cancer cells

Classical Kaposi's sarcoma (CKS) is a rare indolent proliferative disease which is particularly prevalent among Jews of Ashkenazi and Mediterranean origin. To define guidelines for its comprehensive management, we conducted a retrospective analysis of 123 patients, focusing mainly on treatment modalities. The CKS-related mortality was 4% (5 patients). Of the 39 patients for whom observation only was the primary approach, 15 (38%) remained progression-free for 1-83 months (median, 4 months). Twenty-nine of the 52 (56%) patients who underwent surgery as the primary approach remained recurrence-free for 1-162 months (median, 15 months). Radiotherapy achieved an objective response in 74 courses (85%), including 50 (58%) complete responses. Symptomatic relief was reported in 95% of the patients. Vinblastine (27 series) achieved an objective response in 73% of series, including 22% complete responses. Multivariate analysis of time to progression with observation alone identified immunosuppression as the only significant independent factor that predicted disease progression. Our study suggests that observation alone may be sufficient for immunocompetent asymptomatic patients; symptomatic resectable lesions are suitable for simple excision; and more advanced disease or unresectable lesions require radiotherapy. If disease is extensive or the other approaches fail, chemotherapy is appropriate. Tailoring the treatment for CKS is an integrative process, requiring good understanding of the role of each available modality in the different clinical disease settings.     

CSF-1 activates MAPK-dependent and p53-independent pathways to induce growth arrest of hormone-dependent human breast cancer cells

The CSF-1 receptor (CSF-1R) is expressed in >50% of human breast cancers. To investigate the consequence of CSF-1R expression, hormone-dependent human breast cancer cell lines, MCF-7 and T-47D, were transfected with CSF-1R. Unexpectedly, CSF-1 substantially inhibited estradiol (E2) and insulin-dependent proliferation of MCF-7 transfectants (MCF-7fms) and prevented cyclin E/cdk2 and cyclin A/cdk2 activation, consistent with a G1 arrest. In contrast, CSF-1 increased DNA synthesis in T-47D transfectants (T-47Dfms) alone and with E2 or insulin. In response to CSF-1, there was a marked and sustained upregulation of the cyclin-dependent kinase inhibitor, p21Waf1/Cip1, in MCF-7fms but not T-47Dfms. CSF-1 also markedly upregulated cyclin D1 in MCF-7fms. The coordinate increase in cyclin D1 and p21 had the effect of decreasing the specific but not absolute activity of cyclin D1/cdk4. p53 was not involved since CSF-1 induction of p21 was unaffected by dominant-negative p53 expression. ERK activation by CSF-1 was robust and sustained in MCF-7fms and to a much lesser extent in T-47Dfms. Using pharmacological and transient transfection approaches, we showed that ERK activation was necessary and sufficient for p21 induction in MCF-7fms. Moreover, activated MEK inhibited E2-stimulated cdk2 activity. Our findings indicate that the consequence of CSF-1R-mediated signals in human breast cancer cells is dependent on the genetic background of the particular tumor.     

Adriamycin induced G2/M cell cycle arrest in transitional cell cancer cells with wt p53 and p21(WAF1/CIP1) genes

Adriamycin (ADM), widely used for systemic and local treatment of bladder tumors, triggers apoptosis in bladder cancer cells. Here we investigated the effect of ADM on cell cycle progression and expression of cell cycle regulating proteins in bladder cancer cell lines with various p53 and p21(WAF1/CIP1) status. Flowcytometric analysis was used to estimate the cell cycle distribution of T24, HT-1376, RT4, and SCaBER bladder cancer cell lines. Cell cycle regulating proteins were analyzed by Immunoblot. Treatment of RT4 cells, bearing wild type p53 and p21(WAF1/CIP1), with ADM induced expression of both proteins and cell cycle arrest, not in G1, as was anticipated, but in the G2 phase. Simultaneously, Retinoblastoma (Rb) protein expression was decreased. Expression of PCNA, which is a target gene of E2F, was not changed. The results suggest that even if the tumor cells bear wild type (wt) p53 and wt p21(WAF1/CIP1) and both proteins accumulate due to genotoxic stimuli, the cell cycle arrest might happen not in the G1 but in the G2 phase.     

Curcumin induces G2/M cell cycle arrest in a p53-dependent manner and upregulates ING4 expression in human glioma

Gliomas are the most common and lethal primary tumors of the central nervous system (CNS). Despite current rigorous treatment protocols, effect of chemotherapy has failed to improve patient outcome significantly. Curcumin is a potent antioxidant that possesses both anti-inflammatory and anti-tumor activities, can suppress the initiation, promotion, and metastasis of different tumors. Its anti-tumor properties in various cancer models and negligible toxicity in normal cells make it a promising chemotherapeutic candidate. But the effect and the molecular mechanism of curcumin on gliomas are still recognized limitedly. The goal of the study is to elucidate the inhibitory effect and possible mechanisms of curcumin on glioma. After the treatment of curcumin, glioma cells U251 growth in vitro were significantly inhibited in a dose-dependent manner, and the low dose of curcumin induced G2/M cell cycle arrest. The high dose of curcumin not only enhanced G2/M cell cycle arrest, but also induced S phase of cell cycle arrest. But no obvious pre-G1 peak was observed at the different doses of curcumin. Genome DNA electrophoresis further confirmed that no DNA ladder was formed after the treatment of curcumin in U251 cells. Results of Western blot analysis demonstrated that ING4 expression was almost undetectable in U251 cells, but significantly up-regulated during cell cycle arrest induced by curcumin, and p53 expression was up-regulated followed by induction of p21^{WAF−1/CIP−1} and ING4. The results demonstrate that curcumin exerts inhibitory action on glioma cell growth and proliferation via induction of cell cycle arrest instead of induction of apoptosis in a p53-dependent manner, and ING4 possibly is in part involved in the signal pathways.     

EGFR inhibition in glioblastoma cells induces G2/M arrest and is independent of p53

Mutations involving the TP53 gene are frequently identified in up to 50% of all human tumors, including glioblastomas. Analysis of expression patterns of TP53 in glioblastomas shows that it is mainly mutated in secondary glioblastomas and is less common in primary GBMs. However, the prognostic significance of TP53 loss of function in astrocytomas has always been controversial. In contrast, EGFR/erbB2 complexes have been implicated in the poor prognosis of several cancers, including glioblastomas. Our previous work showed that transforming phenotypes could be inhibited by interfering with active EGFR/erbB2 complex using mutant erbB2 proteins in wild-type p53 GBM cells. To assess the dependence of EGFR inhibited phenotype on p53, we used three mutant p53 glioblastoma cell lines in the present study and showed that mutant erbB2 can be exploited to inhibit EGFR-mediated oncogenic transformation irrespective of p53 status. Ectopic expression of a mutant erbB2 receptor (T691S) in mutant p53 GBM cells resulted in slower growth rate than empty vector controls. T691S-expressing clones exhibited a more flattened and nontransformed morphology. Consistently, T691S inhibited transformation in soft agar assays and tumor formation in nude mice independent of p53 status. Biochemical analysis showed reduced Akt and GSK-3 alpha/beta, but not p42/44MAPK phosphorylation, in T691S-expressing cells, when compared to parental controls, suggesting the P13-K pathway may be more relevant than MAPK for glial cell transformation. Cell cycle analysis showed reduced cyclin D1 and CDK6 and increased phospho-Cdc-2 (Tyr15) and p15INK4B in erbB2-inhibited cells, suggesting that nonfunctional EGFR/erbB2 complexes exert their inhibitory effects at various stages of the cell cycle to block the progression of cells through G2/M via Akt/GSK-3/Cdc2 pathway. Collectively, these observations provide a basis for receptor-based therapies that disable erbB receptors and inhibit proliferative signals in erbB-expressing human cancers including glioblastomas, regardless of their TP53 status.     

Oestrogen causes G2/M arrest and apoptosis in breast cancer cells MDA-MB-231

Flavonoids have been shown to exert many biological activities within cancer cells, and oestrogen is known to be structurally related to flavonoids. We investigated the effects of oestrogen in cancer cells to determine if its activities would be similar to those of flavonoids. When 50 microM 17 beta-oestradiol (oestradiol) was added to the oestrogen receptor (ER) alpha-negative breast cancer cell line MDA-MB-231, growth arrest was apparent, similar to that observed with genistein and daidzein. Oestradiol exhibited a dose response curve for the growth arrest similar to those of genistein and daidzein. Apoptosis occurred in the breast cancer cells after treatment with 50 microM oestradiol, genistein, or daidzein, with similar profiles. Flow cytometry analysis revealed that oestradiol treatment caused G2/M arrest and apoptosis. Cell-cycle arrest at G2/M began at 6 h after treatment, and apoptosis began within 24 h. Because MDA-MB-231 cells are ER alpha negative, these results suggest that oestradiol induces cell-cycle arrest and apoptosis through an ER alpha-independent pathway.     

Expression of hepaCAM is downregulated in cancers and induces senescence-like growth arrest via a p53/p21-dependent pathway in human breast cancer cells

Previously, we reported the identification of a novel immunoglobulin-like cell adhesion molecule hepaCAM that is frequently downregulated and inhibits cell growth in hepatocellular carcinoma. In this study, we show that the expression of hepaCAM is suppressed in diverse human cancers. Aiming to evaluate the biological role of hepaCAM in breast cancer, we stably transfected the MCF7 cell line with either wild-type hepaCAM or its mutant hCAM-tailless that lacked the cytoplasmic domain. We found that hepaCAM inhibited colony formation and cell proliferation and arrested cells in the G(2)/M phase. Intriguingly, hepaCAM was capable of inducing cellular senescence as defined by the enlarged cell morphology and increased beta-galactosidase activity. Furthermore, hepaCAM elevated the expression levels of senescence-associated proteins including p53, p21 and p27. In contrast, cell growth inhibition and senescence were less apparent in cells overexpressing hCAM-tailless mutant. To determine if the p53-mediated pathway was involved in hepaCAM-induced senescence, we used the small-interfering RNA system to knock down endogenous p53 expression. In the presence of hepaCAM, downregulation of p53 resulted in a clear reduction of p21, insignificant change in p27 and alleviated senescence. Together, the results suggest that the expression of hepaCAM in MCF7 cells not only inhibits cell growth but also induces cellular senescence through the p53/21 pathway.     

Phenethyl isothiocyanate (PEITC) promotes G2/M phase arrest via p53 expression and induces apoptosis through caspase- and mitochondria-dependent signaling pathways in human prostate cancer DU 145 cells

Phenethyl isothiocyanate (PEITC), one of many compounds found in cruciferous vegetables, has been reported as a potential anticancer agent. In earlier studies, PEITC was shown to inhibit cell growth and induction of apoptosis in many cancer cell lines. However, no report has shown whether PEITC can induce apoptosis in human prostate cancer cells. Herein, we aimed to determine whether PEITC has anticancer activity in DU 145 human prostate cancer cells. As a result, we found that PEITC induced a dose-dependent decrease in cell viability through induction of cell apoptosis and cell cycle arrest in the G(2)/M phase of DU 145 cells. PEITC induced morphological changes and DNA damage in DU 145 cells. The induction of G(2)/M phase arrest was mediated by the increase of p53 and WEE1 and it reduced the level of CDC25C protein. The induction of apoptosis was mediated by the activation of caspase-8-, caspase-9- and caspase-3-depedent pathways. Results also showed that PEITC caused mitochondrial dysfunction, increasing the release of cytochrome c and Endo G from mitochondria, and led cell apoptosis through a mitochondria-dependent signaling pathway. This study showed that PEITC might exhibit anticancer activity and become a potent agent for human prostate cancer cells in the future.     

p53 effects both the duration of G2/M arrest and the fate of temozolomide-treated human glioblastoma cells

Temozolomide (TMZ) is a DNA-methylating agent that has recently been introduced into Phase II and III trials for the treatment of gliomas. TMZ produces O6-methylguanine in DNA, which mispairs with thymine during the next cycle of DNA replication. Subsequent futile cycles of DNA mismatch repair can lead to a p53-associated apoptotic cell death, although this mechanism has been described mostly in hematopoietic neoplasms. We studied the action of TMZ in gliomas and the role p53 might play by using U87 glioma cells that were either p53-wild-type or p53-deficient (by virtue of expression of the viral oncoprotein E6). LN-Z308 cells, in which p53 gene is deleted, were also used. p53-proficient U87 MG cells underwent a prolonged, p53- and p21(Waf1/Cip1)-associated G2-M arrest beginning 2 days after TMZ treatment. Although very few of these cells underwent apoptosis, most underwent senescence over a 10-day period. p53-deficient (E6-transfected U87 and LN-Z308) cells similarly underwent G2-M arrest in response to TMZ, but this arrest was accompanied by only minor changes in p53 or p21(Waf1/Cip1) and was reversed within 7 days of TMZ treatment in association with the appearance of cells with either 8n or subG1 DNA content. These results suggest that glioma cells respond to TMZ by undergoing G2-M arrest. p53 is not necessary for this G2-M arrest to occur but is important in the duration of G2-M arrest and in the ultimate fate of TMZ-treated cells. Therefore, the integrity of the G2-M cell cycle checkpoint may be important in the cytotoxicity of TMZ in glioma cells.