Trans-10,cis-12, not cis-9,trans-11, conjugated linoleic acid inhibits G1-S progression in HT-29 human colon cancer cells

Commercial preparations of conjugated linoleic acid (CLA) contain both positional and geometric isomers of octadecadienoic acid, with cis-9,trans-11 CLA (c9t11) and trans-10,cis-12 CLA (t10c12) as the principal isomers. We showed previously that CLA reduced the incidence of colon tumors in rats treated with 1,2-dimethylhydrazine. In addition, our previous in vitro studies showed that t10c12 inhibited the growth of HT-29 and Caco-2 human colon cancer cells, whereas c9t11 had no effect on cell growth. In the present study, to examine the effects of the CLA isomers on cell cycle and cell cycle regulatory proteins, we treated HT-29 cells with various concentrations (0-4 micromol/L) of the individual CLA isomers. A DNA flow cytometric analysis revealed that t10c12 induced a G1 arrest, whereas c9t11 had no effect on the cell cycle. Western blot analysis of total cell lysates revealed no alteration in the protein expression of cyclin A, cyclin D, cyclin E, cyclin-dependent kinase (CDK) 2, or CDK4 due to t10c12 treatment. However, t10c12 substantially increased the protein expression and mRNA accumulation of the CDK inhibitor p21(CIP1/WAF1). The t10c12 isomer increased the association of p21(CIP1/WAF1) with CDK2 and proliferating cell nuclear antigen, but decreased the levels of phosphorylated retinoblastoma protein (Rb), with an increase in the levels of hypophosphorylated Rb protein. An in vitro kinase assay using histone H1 as a substrate showed that the activities of CDK2 were significantly decreased by t10c12. These results indicate that t10c12 exerts its growth inhibitory effects in colon cancer cells through the induction of G1 cell cycle arrest. The induction of p21(CIP1/WAF1) may be one of the mechanisms by which t10c12 inhibits cell cycle progression in HT-29 cells.     

trans-10,cis-12 conjugated linoleic acid inhibits the G1-S cell cycle progression in DU145 human prostate carcinoma cells

Conjugated linoleic acid (CLA) is a group of positional and geometric isomers of linoleic acid, and has evidenced anti-cancer activities in experimental animal cancer models and in vitro studies. The two predominant isomers of CLA are cis-9,trans-11 CLA (c9t11) and trans-10,cis-12 CLA (t10c12). The present study was performed to study the effect of the individual CLA isomers on DU145 cell growth. The cells were incubated in serum-free medium with different concentrations of the fatty acids. Treatment of cells with t10c12 (at 2.5-10 micromol/L) resulted in a dose-dependent reduction in the numbers of viable cells, whereas c9t11 CLA at a concentration of 5 micromol/L slightly increased viable cell numbers at 3 days (P < .05). DNA flow cytometric analysis revealed that the treatment of DU145 cells with t10c12 for 24 hours induced a small but significant increase in the number of cells in the G1 phase, accompanied by a complementary decrease in cells in the S phase. c9t, however, had no effect on cell cycle progression. To determine the molecular mechanisms underlying t10c12-induced G1 arrest, the levels of cell cycle regulatory proteins were estimated by western blot analyses. t10c12 induced a marked increase in p21(CIP1/WAF1) protein levels in a dose-dependent manner. p27(KIP1) was not affected by t10c12. t10c12 moderately decreased cyclin A and cyclin D1 protein levels (P > .05). However, t10c12 did not affect the expression of cyclin-dependent kinase (CDK) 2, CDK4, or cyclin E. t10c12 increased p21(CIP1/WAF1) bound to CDK2 and attenuated CDK2 activity. These results indicate that t10c12-induced p21(CIP1/WAF1) binds to CDK, and inhibits the activity of this enzyme, which results in the observed decrease in the G1-S progression in DU145 cells.     

苯丁酸钠对宫颈癌Hela细胞增殖及p21WAF1/CIP1和CDK7表达的影响

目的:探讨苯丁酸钠(SPB)在体外诱导宫颈癌Hela细胞生长抑制和细胞周期阻滞以及对p21WAF1/CIP1和CDK7基因表达的影响。方法:体外培养Hela细胞,应用MTT法检测苯丁酸钠对Hela细胞增殖的影响,流式细胞仪分析细胞周期的变化,半定量RT-PCR法检测细胞p21WAF1/CIP1和CDK7基因表达水平。结果:苯丁酸钠明显抑制Hela细胞增殖,呈时间-剂量依赖性;苯丁酸钠诱导Hela细胞周期阻滞于G0/G1期,使S期细胞数减少;苯丁酸钠促进抑癌基因p21WAF1/CIP1的表达,对CDK7基因的表达有抑制作用。结论:苯丁酸钠在体外抑制宫颈癌Hela细胞的增殖,使之阻滞于G0/G1期,可能与上调p21WAF1/CIP1基因表达、下调CDK7基因表达有关。     

沥青烟致肺损伤细胞凋亡及突变的实验研究

目的探讨沥青烟对肺组织的损伤机制,早期发现沥青烟致肺癌的预警指标。方法建立染毒小鼠模型,进行不同剂量（55、165mg／m^3）和不同时间（30d、60d）染毒,光镜下观察肺组织形态改变;采用免疫组化S-P法,进行p53、p21、eyelin D1染色,观察053、p21^WAF/CIPI和cyclin D1基因蛋白表达;采用流式细胞仪进行小鼠肺组织细胞DNA含量的检测和细胞周期分析。结果随着沥青烟染毒时间和剂量增加,小鼠肺组织表现为不同程度的不典型增生;小鼠肺组织p53基因蛋白在低剂量染毒30d组未见阳性表达,高剂量60d组呈强阳性表达（P〈0．01）。p21^WAF/CIPI基因蛋白表达在低剂量染毒30d组呈阳性表达,高剂量染毒60d组表达明显下调（P〈0．01）。eyclin D1基因蛋白表达同p53基因蛋白表达;小鼠肺组织细胞各周期指数均发生变化,G1期细胞数下降,S期阻滞,进入G2/M期的细胞减少,细胞增殖指数（PI）增加（P〈0．05）,异倍体指数（DI）升高（P〈0．05）,与对照组比较差异均有统计学意义（P〈0．05）。相同染毒时间55mg/m^3剂量组和165mg／m^3剂量组的PI均高于对照组,相同染毒剂量下60d组D1随时间的增加而升高（P〈0．05）。结论沥青烟损伤肺组织影响细胞周期、S期DNA含量增加,细胞增殖能力增强,突变几率提高,可能与p53和cyelin D1基因蛋白表达增高及p21^WAF／CIPI基因蛋白的转录抑制相关。     

Enterolactone Induces G1-phase Cell Cycle Arrest in Nonsmall Cell Lung Cancer Cells by Downregulating Cyclins and Cyclin-dependent Kinases

Flaxseed is a rich source of the plant lignan secoisolariciresinol diglucoside (SDG), which is metabolized into mammalian lignans enterodiol (ED) and enterolactone (EL) in the digestive tract. The anticancer properties of these lignans have been demonstrated for various cancer types, but have not been studied for lung cancer. In this study, we investigated the anticancer effects of EL for several nonsmall cell lung cancer (NSCLC) cell lines of various genetic backgrounds. EL inhibited the growth of A549, H441, and H520 lung cancer cells in concentration- and time-dependent manners. The antiproliferative effects of EL for lung cancer cells were not due to enhanced cell death, but rather due to G₁-phase cell cycle arrest. Molecular studies revealed that EL decreased mRNA or protein expression levels of the G₁-phase promoters cyclin D1, cyclin E, cyclin-dependent kinases (CDK)-2, -4, and -6, and p-cdc25A; decreased phosphorylated retinoblastoma (p-pRb) protein levels; and simultaneously increased levels of p21^WAF1/CIP1, a negative regulator of the G₁ phase. The results suggest that EL inhibits the growth of NSCLC cell lines by downregulating G₁-phase cyclins and CDKs, and upregulating p21^WAF1/CIP1, which leads to G₁-phase cell cycle arrest. Therefore, EL may hold promise as an adjuvant treatment for lung cancer therapy.     

Fisetin inhibits the activities of cyclin-dependent kinases leading to cell cycle arrest in HT-29 human colon cancer cells

Fisetin, a natural flavonol present in edible vegetables, fruits, and wine, was reported to exert anticarcinogenic effects. The objective of the current study was to examine the effect of fisetin on the cell cycle progression of the human colon cancer cell line HT-29. HT-29 cells were cultured in serum-free medium with 0, 20, 40, or 60 micromol/L fisetin. Fisetin dose dependently inhibited both cell growth and DNA synthesis (P < 0.05), with a 79 +/- 1% decrease in cell number observed 72 h after the addition of 60 micromol/L fisetin. Perturbed cell cycle progression from the G(1) to S phase was observed at 8 h with 60 micromol/L fisetin treatment, whereas a G(2)/M phase arrest was observed after 24 h (P < 0.05). The phosphorylation state of the retinoblastoma proteins shifted from hyperphosphorylated to hypophosphorylated in cells treated with 40 micromol/L fisetin. (P < 0.05). Fisetin decreased the activities of cyclin-dependent kinases (CDK)2 and CDK4; these effects were likely attributable to decreases in the levels of cyclin E and D1 and an increase in p21(CIP1/WAF1) levels (P < 0.05). However, fisetin also inhibited CDk4 activity in a cell-free system (P < 0.05), indicating that it may directly inhibit CDk4 activity. The protein levels of cell division cycles (CDC)2 and CDC25C and the activity of CDC2 were also decreased in fisetin-treated cells (P < 0.05). These results indicate that inhibition of cell cycle progression in HT-29 cells after treatment with fisetin can be explained, at least in part, by modification of CDK activities.     

Unique formosan mushroom Antrodia camphorata differentially inhibits androgen-responsive LNCaP and -independent PC-3 prostate cancer cells

Antrodia camphorata (AC), a precious and unique folkloric medicinal mushroom enriched in polyphenolics, isoflavonoids, triterpenoids, and polysaccharides, has been diversely used in Formosa (Taiwan) since the 18th century. In this study, prostate cancer (PCa) cell lines PC-3 (androgen independent) and LNCaP (androgen responsive) were treated with AC crude extract (ACCE) at 50-200 microg/mL, respectively, for 48 h. At the minimum effective dose 150 microg/mL, LNCaP showed a G1/S phase arrest with significant apoptosis. Such dose-dependent behavior of LNCaP cells in response to ACCE was confirmed to proceed as Akt-->p53-->p21-->CDK4/cyclin D1-->G1/S-phase arrest-->apoptosis, which involved inhibiting cyclin D1 activity and preventing pRb phosphorylation. In contrast, being without p53, PC-3 cells showed a G2/M-phase arrest mediated through pathway p21-->cyclin B1/Cdc2-->G2/M-phase arrest, however, with limited degree of apoptosis, implicating that ACCE is able to differentially inhibit the growth of different PCa cells by modulating different cell cycle signaling pathways. We conclude that this unique Formosan mushroom, A. camphorata, due to its nontoxicity, might be used as a good adjuvant anticancer therapy for prostate cancers despite its androgen-responsive behaviors, which has long been a serious drawback often encountered clinically in hormonal refractory cases treated by antihormonal therapies and chemotherapeutics.     

Hesperetin induced G1-phase cell cycle arrest in human breast cancer MCF-7 cells: involvement of CDK4 and p21

This study was to investigate the effects of hesperetin on cell proliferation and cell cycle arrest and explored the mechanism for these effects in breast carcinoma MCF-7 cells. Hesperetin significantly inhibited cell proliferation in a dose-dependent manner after treatment for 48 and 72 h and resulted in significant cell cycle arrest in the G1 phase. In the G1-phase related proteins, hesperetin downregulates the cyclin-dependent kinases (CDKs) and cyclins and upregulates p21(Cip1) and p27(Kip1) in cells treated with hesperetin for 48 h and 72 h. After 72 h treatment, these phenomenons were more pronounced. Hesperetin treatment at high concentration for 72 h resulted in a decrease in CDK2 and CDK4 together with cyclin D. In addition, hesperetin increases the binding of CDK4 with p21(Cip1) but not p27(Kip1) or p57(Kip2). Taken together, our data suggest for the first time that the regulation of CDK4 and p21(Cip1)1 may participate in the anticancer activity pathway of hesperetin in MCF-7 cells.     

Extracellular signal-regulated kinase-signaling-dependent G2/M arrest and cell death in murine macrophages by cadmium

Cadmium is a nonessential heavy metal and a well-known persistent environmental pollutant. It causes a variety of toxic effects, including immunotoxicity. The exact mechanism of its cellular effects still is unclear. Cell-cycle regulation is an important factor that modulates cell death; however, cadmium-mediated cell-cycle arrest leading to cell death in murine macrophages has not been investigated. Cadmium at 20 microM induced both apoptotic and necrotic death in murine macrophage (J774A.1) cultures at 24 h. Cadmium at 20 microM triggered re-entry of G0/G1 to the next phase and increased the number of cells in the G2/M phase at 24 h. Phosphorylation of extracellular signal-regulated kinase (ERK) correlated with the cyclin-dependent kinase inhibitor p21WAF1/CIP1 induction. Inhibition of ERK activation by PD98059 resulted in G0/G1 arrest and partially released the cadmium-mediated G2/M arrest. Inhibition of ERK phosphorylation by PD98059 strongly attenuated cadmium-induced necrotic cell death, but did not prevent caspase-3 activation and DNA fragmentation. Necrosis rather than apoptosis was caused by cadmium-induced ERK signaling in J774A.1 cells. A scavenger of reactive oxygen species (ROS), N-acetylcystein, decreased cadmium-induced ERK activation and necrotic cell death, suggesting that cadmium induces the ROS-ERK-p21WAF1/CIP1 signaling pathway, leading to G2/M arrest and cell death. These findings may be important in further understanding the cellular mechanisms of cadmium toxicity to provide information to assess objectively risk for this metal.     

Cyclin D1和CDK4正性调节苯并(a)芘所致人胚肺成纤维细胞周期改变

目的研究苯并(a)芘[B(a)P]对人胚肺成纤维细胞(HELF)的细胞周期分布及细胞周期蛋白D1(cyclin D1)和细胞周期蛋白依赖激酶4(CDK4)蛋白表达的影响,并探讨两种蛋白含量改变与细胞周期效应之间的关系。方法将反义cyclin D1质粒和反义CDK4质粒导入HELF细胞内,建立两种质粒稳定转染的细胞模型。用0.1、0.5、2.5和12.5μmol/L的B(a)P处理HELF细胞24h,用蛋白印迹方法检测cyclin D1和CDK4蛋白表达水平;利用流式细胞技术检测B(a)P处理对HELF细胞及两种稳定转染细胞系细胞周期的影响。结果成功建立了反义cyclin D1和反义CDK4稳定转染的细胞系。不同剂量B(a)P处理可引起cyclin D1蛋白表达的显著增加,但对CDK4蛋白表达无明显影响;2.5μmol/L的B(a)P处理HELF细胞24h后,引起其细胞周期G1期显著下降,S期显著增加;2.5μmol/L的B(a)P处理反义cyclin D1和反义CDK4稳定转染的HELF细胞24h后,对其细胞周期的分布无显著影响。结论Cyclin D1和CDK4基因均参与了B(a)P所致细胞周期改变过程,并发挥正性调节作用。     

Cyelin D1和CDK4正性调节苯并(a)芘所致人胚肺成纤维细胞周期改变

目的 研究苯并(a)芘[B(a)P]对人胚肺成纤维细胞(HELF)的细胞周期分布及细胞周期蛋白D1(cyclin D1)和细胞周期蛋白依赖激酶4(CDK4)蛋白表达的影响,并探讨两种蛋白含量改变与细胞周期效应之间的关系.方法 将反义cychn D1质粒和反义CDK4质粒导入HELF细胞内.建立两种质粒稳定转染的细胞模型.用0.1、0.5、2.5和12.5μmol/L的B(a)P处理HELF细胞24h.用蛋白印迹方法检测cvclin D1和CDK4蛋白表达水平;利用流式细胞技术检测B(a)P处理对HELF细胞及两种稳定转染细胞系细胞周期的影响.结果 成功建立了反义cyelin D1和反义CDK4稳定转染的细胞系.不同剂量B(a)P处理可引起cvclin D1蛋白表达的显著增加,但对CDK4蛋白表达无明显影响;2.5/μmol/L的B(a)P处理HELF细胞24h后,引起其细胞周期G1期显著下降,S期显著增加;2.5μmol/L的B(a)P处理反义cyclin D1和反义CDK4稳定转染的HELF细胞24h后,对其细胞周期的分布无显著影响.结论 Cyelin D1和CDK4基因均参与了B(a)P所致细胞周期改变过程,并发挥正性调节作用.     

植酸对人肝癌细胞株HepG_2细胞周期及相关蛋白表达的影响

目的研究肌醇六磷酸(IP6)对人肝癌细胞株HepG2细胞周期的影响并探讨其作用机制。方法以体外培养人肝癌细胞株HepG2为研究对象,应用流式细胞仪检测不同浓度IP6作用24h后对HepG2周期的影响;以免疫细胞化学法检测IP6对细胞周期相关蛋白cyclinD1、Rb、P27表达的影响;RT-PCR法检测IP6对HepG2细胞cyclinD1、CDK4 mRNA表达的影响。结果经IP6作用处理的HepG2细胞的细胞周期发生G1期阻滞。免疫细胞化学结果显示:与对照组比,各IP6浓度组均能抑制cyclinD1蛋白的表达(F=225.02,q=15.20-25.35,P<0.05),上调Rb(F=63.31,q=2.77-13.06,P<0.05)、P27蛋白的表达(F=254.75,q=4.71-25.71,P<0.05);RT-PCR结果显示,与对照组相比,各IP6浓度组均能抑制cyclinD1(F=672.34,q=16.41-41.99,P<0.05)和CDK4 mRNA(F=108.35,q=5.32-16.27,P<0.05)的表达。结论 IP6对HepG2细胞生长具有明显的抑制作用。其机制可能是IP6降低cyclinD1、CDK4水平,上调Rb、P27蛋白的水平而作用于G1-S限制点,使HepG2细胞周期发生G1期阻滞,从而起到抑制细胞增殖的作用。     

Kaempferol induced the apoptosis via cell cycle arrest in human breast cancer MDA-MB-453 cells

The aim of present study was to investigate the effects of kaempferol on cellular proliferation and cell cycle arrest and explore the mechanism for these effects in human breast carcinoma MDA-MB-453 cells. Cells were treated with kaempferol at various concentrations (ranging from 1 to 200 µM) for 24 and 48 hrs. Kaempferol significantly inhibited cancer cell growth in cells exposed to 50 and 10 µM of kaempferol and incubated for 24 and 48 hrs, respectively. Exposure to kaempferol resulted in cell cycle arrest at the G2/M phase. Of the G2/M-phase related proteins, kaempferol down-regulated CDK1 and cyclin A and B in cells exposed to kaempferol. In addition, small DNA fragments at the sub-G0 phase were increased by up to 23.12 and 31.90% at 10 and 50 µM incubated for 24 and 48 hrs, respectively. The kaempferol-induced apoptosis was associated with the up-regulation of p53. In addition, the phosphorylation of p53 at the Ser-15 residue was observed with kaempferol. Kaempferol inhibits cell proliferation by disrupting the cell cycle, which is strongly associated with the induction of arrest at G2/M phase and may induce apoptosis via p53 phosphorylation in human breast carcinoma MDA-MB-453 cells.     

苯并(a)芘对不同时相人胚肺成纤维细胞阻滞作用

目的 研究低遗传损伤浓度苯并(a)芘(BaP)对人胚肺成纤维细胞(HELF)的细胞周期调控的影响.方法 0.5%血清饥饿法及10%血清再刺激方法获得处于各细胞周期时相的HELF;分别以二甲基亚砜(DMSO)、2,10和50μmol/L BaP于血清再刺激后10~12,16~18和22~24 h作用HELF2 h;采用流式细胞术分析细胞周期分布;采用蛋白印迹法分析细胞周期调控蛋白Cyclin D、Cyclin E、Cyclin A、Cyclin B、P53、P21和P16表达.结果 BaP针对血清再刺激后10~12,16~18和22~24 h作用均引起明显的S期细胞比例的下降;血清再刺激后10~12 h作用引起G0/G1期细胞比例增加,BaP低、中、高浓度组分别为36.79%,42.73%,43.28%,伴随Cyclin D表达明显下降;血清再刺激后16~18 h作用引起G2/M期细胞比例增加,BaP低、中、高浓度组分别为18.46%,23.55%,28.44%,伴随P53和P21表达增强;血清再刺激后22~24 h作用引起G0/G1期细胞比例增加,BaP低、中、高浓度组分别为38.92%,54.08%,51.69%,伴随P53和P21表达增强.结论 BaP针对不同时相的HELF作用顺序激活了G1和G2 2种周期关卡监控机制,并产生相应的周期阻滞效应.     

茶多酚和茶色素对肝癌细胞株HepG2细胞周期的影响

为探讨茶对肝癌细胞周期的影响 ,体外培养人肝癌细胞株HepG2 ,加入终浓度为 50mg L和 1 0 0mg L茶多酚和茶色素作用 48h后 ,流式细胞仪分析DNA含量 ,Westernblot观察对细胞周期蛋白P2 1 WAF1 CIP1 和细胞周期素D1 (cyclinD1 ) ,RT PCR检测细胞周期素依赖激酶 4 (Cdk4)在mRNA水平上的表达情况。结果表明 ,茶多酚和茶色素引起了细胞周期G1 期阻滞 (G1 arrest) ,抑制了cyclinD1蛋白的表达 ,诱导了P2 1 WAF1 CIP1 蛋白的表达增加 ,并且显著抑制了Cdk4在mRNA水平上的表达。因此 ,诱导细胞周期阻滞可能是茶预防肿瘤的一个重要机制     

Aqueous Extracts of Toona sinensis Leaves Inhibit Renal Carcinoma Cell Growth and Migration Through JAK2/stat3, Akt,MEK/ERK,and mTOR/HIF-2α Pathways

Toona sinensis (TS) is a type of deciduous tree, which is distributed widely in Asia and used as a traditional herb medicine. Previously, we demonstrated that aqueous extracts of TS leaves (TSL-1) induce apoptosis in two clear types of human renal carcinoma cells (ccRCC) via mitochondria-dependent pathway. In this study, we further investigated the more detailed mechanism of TSL-1-induced antitumor effects on ccRCCs. TSL-1 treatment arrested ccRCC cells in G0/G1 phase through the decrease of cyclin D1, cyclin-dependent kinase (CDK)2, and CDK4 as well as induction of p53 and FOXO3a protein expressions. On the other hand, the inhibitory effects of TSL-1 on migration were also observed in 786-O and A-498 cells. Mechanically, we presented that TSL-1 could suppress cell cycle progression and motility via inhibiting the phosphorylation of JAK2/stat3, Akt, MEK/ERK, and mTOR in a concentration- and time-dependent manner. Moreover, we found that TSL-1 inhibited p21, HIF-2α, c-Myc, VEGF, and MMP9 protein expressions in both cell lines. In conclusion, these findings suggested that TS-induced apoptosis and its antimigration activity in ccRCC cells were accompanied by inactivation of several oncogenic pathways.     

Unique Formosan Mushroom Antrodia camphorata Differentially Inhibits Androgen-Responsive LNCaP and -Independent PC-3 Prostate Cancer Cells

Antrodia camphorata (AC), a precious and unique folkloric medicinal mushroom enriched in polyphenolics, isoflavonoids, triterpenoids, and polysaccharides, has been diversely used in Formosa (Taiwan) since the 18th century. In this study, prostate cancer (PCa) cell lines PC-3 (androgen independent) and LNCaP (androgen responsive) were treated with AC crude extract (ACCE) at 50–200 μ g/mL, respectively, for 48 h. At the minimum effective dose 150 μ g/mL, LNCaP showed a G ₁ /S phase arrest with significant apoptosis. Such dose-dependent behavior of LNCaP cells in response to ACCE was confirmed to proceed as Akt → p53→ p21→ CDK4/cyclin D1→ G ₁ /S-phase arrest→ apoptosis, which involved inhibiting cyclin D1 activity and preventing pRb phosphorylation. In contrast, being without p53, PC-3 cells showed a G ₂ /M-phase arrest mediated through pathway p21→ cyclin B1/Cdc2→ G ₂ /M-phase arrest, however, with limited degree of apoptosis, implicating that ACCE is able to differentially inhibit the growth of different PCa cells by modulating different cell cycle signaling pathways. We conclude that this unique Formosan mushroom, A. camphorata, due to its nontoxicity, might be used as a good adjuvant anticancer therapy for prostate cancers despite its androgen-responsive behaviors, which has long been a serious drawback often encountered clinically in hormonal refractory cases treated by antihormonal therapies and chemotherapeutics.     

Estrogen receptor-β mediates the inhibition of DLD-1 human colon adenocarcinoma cells by soy isoflavones

To understand the relationship between the role of soy isoflavones and estrogen receptor (ER)-β in colon tumorigenesis, we investigated the cellular effects of soy isoflavones (composed of genistein, daidzein, and glycitein) in DLD-1 human colon adenocarcinoma cells with or without ER-β gene silencing by RNA interference (RNAi). Soy isoflavones decreased the expression of proliferating cell nuclear antigen (PCNA), extracellular signal-regulated kinase (ERK)-1/2, AKT, and nuclear factor (NF)-κB. Soy isoflavones dose-dependently caused G2/M cell cycle arrest and downregulated the expression of cyclin A. This was associated with inhibition of cyclin dependent kinase (CDK)-4 and up-regulation of its inhibitor p21(cip1) expressions. ER-β gene silencing lowered soy isoflavone-mediated suppression of cell viability and proliferation. ERK-1/2 and AKT expressions were unaltered and NF-κB was modestly upregulated by soy isoflavones after transient knockdown of ER-β expression. Soy isoflavone-mediated arrest of cells at G2/M phase and upregulation of p21(cip1) expression were not observed when ER-β gene was silenced. These findings suggest that maintaining the expression of ER-β is crucial in mediating the growth-suppressive effects of soy isoflavones against colon tumors. Thus upregulation of ER-β status by specific food-borne ER-ligands such as soy isoflavones could potentially be a dietary prevention or therapeutic strategy for colon cancer.