Inhibitory effect of quercetin on the synthesis of a possibly cell-cycle-related 17-kDa protein, in human colon cancer cells

Quercetin modulates signal transductions and targets non-coding RNAs against cancer development

In recent decades, various investigations have indicated that natural compounds have great potential in the prevention and treatment of different chronic disorders including different types of cancer. As a bioactive flavonoid, Quercetin (Qu) is a dietary ingredient enjoying high pharmacological values and health-promoting effects due to its antioxidant and anti-inflammatory characterization. Conclusive in vitro and in vivo evidence has revealed that Qu has great potential in cancer prevention and development. Qu exerts its anticancer influences by altering various cellular processes such as apoptosis, autophagy, angiogenesis, metastasis, cell cycle, and proliferation. In this way, Qu by targeting numerous signaling pathways as well as non-coding RNAs regulates several cellular mechanisms to suppress cancer occurrence and promotion. This review aimed to summarize the impact of Qu on the molecular pathways and non-coding RNAs in modulating various cancer-associated cellular mechanisms.

Application of Quercetin in the Treatment of Gastrointestinal Cancers

Many cellular signaling pathways contribute to the regulation of cell proliferation, division, motility, and apoptosis. Deregulation of these pathways contributes to tumor cell initiation and tumor progression. Lately, significant attention has been focused on the use of natural products as a promising strategy in cancer treatment. Quercetin is a natural flavonol compound widely present in commonly consumed foods. Quercetin has shown significant inhibitory effects on tumor progression via various mechanisms of action. These include stimulating cell cycle arrest or/and apoptosis as well as its antioxidant properties. Herein, we summarize the therapeutic effects of quercetin in gastrointestinal cancers (pancreatic, gastric, colorectal, esophageal, hepatocellular, and oral).

Xanthohumol, a Prenylated Flavonoid from Hops, Induces DNA Damages in Colorectal Cancer Cells and Sensitizes SW480 Cells to the SN38 Chemotherapeutic Agent

In spite of chemotherapy and systematic screening for people at risk, the mortality rate of colorectal cancer (CRC) remains consistently high, with 600,000 deaths per year. This low success rate in the treatment of CRC results from many failures associated with high resistance and the risk of metastasis. Therefore, in response to these therapeutic failures, new strategies have been under development for several years aimed at increasing the effect of anticancer compounds and/or at reducing their secondary effects on normal cells, thus enabling the host to better withstand chemotherapy. This study highlights that xanthohumol (Xn) concentrations under the IC50 values were able to induce apoptosis and to enhance the DNA-damage response (DDR). We demonstrate for the first time that Xn exerts its anticancer activity in models of colon cancer through activation of the ataxia telangiectasia mutated (ATM) pathway. Subsequently, the ability of Xn to restore DNA damage in CRC cells can sensitize them to anticancer agents such as SN38 (7-ethyl-10-hydroxycamptothecin) used in chemotherapy.

Natural flavonoids for the prevention of colon cancer: A comprehensive review of preclinical and clinical studies

Flavonoids comprise a group of natural polyphenols consisting of more than 5,000 subtypes mostly existing in fruits and vegetables. Flavonoids consumption could potentially attenuate the incidence and recurrence risk of colorectal cancers through their antiperoxidative, antioxidant, and anti-inflammatory effects. In addition, these compounds regulate the mitochondrial function, balance the bacterial flora and promote the apoptosis process in cancerous cells. However, some previous data failed to show the effectiveness of flavonoids in reducing the risk of colorectal cancer. In this study, we have reviewed the efficacy of different flavonoids subtypes on the risk of colon cancer and molecular mechanisms involved in this process in both clinical and animal studies. In addition, we tried to elucidate the potential synergy between these compounds and current colorectal cancer treatments.

Flavonoids and Colorectal Cancer Prevention

Colorectal cancer (CRC) is the third most common cancer, but despite advances in treatment, it remains the second most common cause of cancer-related mortality. Prevention may, therefore, be a key strategy in reducing colorectal cancer deaths. Given reports of an inverse association between fruit and vegetable consumption with colorectal cancer risk, there has been significant interest in understanding the metabolism and bioactivity of flavonoids, which are highly abundant in fruits and vegetables and account for their pigmentation. In this review, we discuss host and microbiota-mediated metabolism of flavonoids and the potential mechanisms by which flavonoids can exert protective effects against colon tumorigenesis, including regulation of signaling pathways involved in apoptosis, cellular proliferation, and inflammation and modulation of the gut microbiome.

Antitumoral Potency by Immunomodulation of Chloroform Extract from Leaves of Nitraria retusa, Tunisian Medicinal Plant, via its Major Compounds β-sitosterol and Palmitic Acid in BALB/c Mice Bearing Induced Tumor

This study evaluated the antitumoral effect of Chloroform extract from Nitraria retusa leaves, via its major compounds β-sitosterols and palmitic acid. BALB/c mice were subcutaneously inoculated with B16-F10 cells, then treated intra-peritoneally after 7 days with the chloroform extract for 21 days. They were then euthanized, and the tumors were weighed. Lung parenchyma was analyzed. Lymphocyte and macrophages proliferation, cytotoxic T lymphocyte (CTL) activities were evaluated using the MTT assay. Macrophage phagocytosis was evaluated by measuring the lysosomal activity and nitric oxide production. Antioxidant activity was studied by cellular antioxidant activity on macrophage and splenocytes and by lipid peroxidation inhibitory activity in liver cells, kidney, and serum. β-sitosterols and palmitic acid, major compounds of chloroform extract, impeded remarkably the expansion of the transplantable tumor, protected the lung parenchyma, and increased splenocytes proliferation and both CTL activities in tumor-bearing mice. β-sitosterols and palmitic acid were also seen to have enhanced lysosomal activity of host macrophages and antioxidant cellular activity. Also, they showed an inhibitory effect of lipid peroxidation. Our results suggest that antitumoral effect of β-sitosterols and palmitic acid from chloroform extract is related with its immunomodulatory activity, and opens the way for a nutrition application and coprocessing phytotherapy against cancer.

Quercetin: A functional dietary flavonoid with potential chemo-preventive properties in colorectal cancer

Recently, an intense attention has been paid to the application of natural compounds as a novel therapeutic strategy for cancer treatment. Quercetin, a natural flavonol present in many commonly consumed food items, is widely demonstrated to exert inhibitory effects on cancer progression through various mechanisms. Since there is a strong association with diets containing abundant vegetables, fruits, and grains, and significant decline in the risk of colon cancer, accumulation studies have focused on the anticancer potential of quercetin in colorectal cancer. Cell cycle arrest, increase in apoptosis, antioxidant replication, modulation of estrogen receptors, regulation of signaling pathways, inhibition of and metastasis and angiogenesis are among various mechanisms underlying the chemo-preventive effects of quercetin in colorectal cancer. This review covers various therapeutic interactions of Quercetin as to how targets cellular involved in cancer treatment.

Dietary Total Antioxidant Capacity and Colorectal Cancer in the Italian EPIC Cohort

Background

Colorectal cancer is the third most common cancer worldwide. Diet has been hypothesized as involved in colorectal cancer etiology, but few studies on the influence of total dietary antioxidant intake on colorectal cancer risk have been performed.

Methods

We investigated the association between colorectal cancer risk and the total antioxidant capacity (TAC) of the diet, and also of intake of selected antioxidants, in 45,194 persons enrolled in 5 centers (Florence, Naples, Ragusa, Turin and Varese) of the European Prospective Investigation into Cancer and Nutrition (EPIC) Italy study. TAC was estimated by the Trolox equivalent antioxidant capacity (TEAC) assay. Hazard ratios (HRs) for developing colorectal cancer, and colon and rectal cancers separately, adjusted for confounders, were estimated for tertiles of TAC by Cox modeling, stratifying by center.

Results

Four hundred thirty-six colorectal cancers were diagnosed over a mean follow-up of 11.28 years. No significant association between dietary TAC and colorectal cancer incidence was found. However for the highest category of TAC compared to the lowest, risk of developing colon cancer was lower (HR: 0.63; 95% CI: 0.44–0.89, P trend: 0.008). By contrast, increasing TAC intake was associated with significantly increasing risks of rectal cancer (2nd tertile HR: 2.09; 95%CI: 1.19–3.66; 3rd tertile 2.48 95%CI: 1.32–4.66; P trend 0.007). Intakes of vitamin C, vitamin E, and ß-carotene were not significantly associated with colorectal cancer risk.

Conclusions

Further prospective studies are needed to confirm the contrasting effects of high total antioxidant intake on risk of colon and rectal cancers.

Antiproliferative activity of long chain acylated esters of quercetin-3-O-glucoside in hepatocellular carcinoma HepG2 cells

Despite their strong role in human health, poor bioavailability of flavonoids limits their biological effects in vivo. Enzymatically catalyzed acylation of fatty acids to flavonoids is one of the approaches of increasing cellular permeability and hence, biological activities. In this study, six long chain fatty acid esters of quercetin-3-O-glucoside (Q3G) acylated enzymatically and were used for determining their antiproliferative action in hepatocellular carcinoma cells (HepG2) in comparison to precursor compounds and two chemotherapy drugs (Sorafenib and Cisplatin). Fatty acid esters of Q3G showed significant inhibition of HepG2 cell proliferation by 85 to 90% after 6 h and 24 h of treatment, respectively. The cell death due to these novel compounds was associated with cell-cycle arrest in S-phase and apoptosis observed by DNA fragmentation, fluorescent microscopy and elevated caspase-3 activity and strong DNA topoisomerase II inhibition. Interestingly, Q3G esters showed significantly low toxicity to normal liver cells than Sorafenib (P < 0.05), a chemotherapy drug for hepatocellular carcinoma. Among all, oleic acid ester of Q3G displayed the greatest antiproliferation action and a high potential as an anti-cancer therapeutic. Overall, the results of the study suggest strong antiproliferative action of these novel food-derived compounds in treatment of cancer.

Site-specific anticancer effects of dietary flavonoid quercetin

Food-derived flavonoid quercetin, widely distributed in onions, apples, and tea, is able to inhibit growth of various cancer cells indicating that this compound can be considered as a good candidate for anticancer therapy. Although the exact mechanism of this action is not thoroughly understood, behaving as antioxidant and/or prooxidant as well as modulating different intracellular signalling cascades may all play a certain role. Such inhibitory activity of quercetin has been shown to depend first of all on cell lines and cancer types; however, no comprehensive site-specific analysis of this effect has been published. In this review article, cytotoxicity constants of quercetin measured in various human malignant cell lines of different origin were compiled from literature and a clear cancer selective action was demonstrated. The most sensitive malignant sites for quercetin revealed to be cancers of blood, brain, lung, uterine, and salivary gland as well as melanoma whereas cytotoxic activity was higher in more aggressive cells compared to the slowly growing cells showing that the most harmful cells for the organism are probably targeted. More research is needed to overcome the issues of poor water solubility and relatively low bioavailability of quercetin as the major obstacles limiting its clinical use.

Evaluation of a method to quantify quercetin aglycone in onion (Allium cepa) by single- and multi-laboratory validation studies

Official Methods of Analysis of AOAC International (OMA) 2006.07 was originally designed for quantifying flavonol aglycones in ginkgo dietary supplements. To determine whether the method is applicable to the quantification of flavonol aglycones in lyophilized onion samples, single- and multi-laboratory validation studies were performed. Triplicated measurements on 3 different days revealed that the mean quercetin content was 3.48 g/kg dry weight, and the relative repeatability standard deviation (RSD(r)) and the relative intermediate standard deviation (RSD(int)) were 0.8 and 1.8%, respectively. The recovery of quercetin-3-O-glucoside spiked at 3 different amounts (1.56, 3.12, and 6.24 g/kg dry weight of onion) ranged from 98.42 to 100.31%, and the RSD(r) and RSD(int) ranged from 2.2 to 5.9%, and from 3.4 to 5.2%, respectively. A multi-laboratory validation study showed that the mean quercetin contents were 2.80 and 6.61 g/kg dry weight, and that satisfactory inter-laboratory precision (RSD(r) and RSD(R) ranged from 0.41 to 0.92%, and from 6.73 to 7.62%, respectively); all HorRat values were less than 2. These results indicate that OMA 2006.07 is applicable to the determination of the quercetin content of lyophilized onion samples.

Triterpenoids of Chrysosplenium carnosum

A phytochemical study of the ethanolic extract of Chrysosplenium carnosum Hook. f. et Thoms. led to the isolation of two new oleanane-type triterpenoids, 6β-hydroxy-3-oxoolean-12-en-27-oic acid (1) and 3β, 21α-dihydroxyolean-12-en-27-oic acid (2), along with fourteen known compounds (3-16), all of which were isolated from this plant for the first time. The structures of these compounds were established on the basis of spectroscopic methods. Compounds 1-4 were evaluated for their in vitro anti-tumor activities on B16F10, SP2/0 and Hep-G2 cells lines. Compounds 1, 3 and 4 exhibited strong inhibitory activity against B16F10 and SP2/0 cells' growth, compared with moderate cytotoxic activity against Hep-G2 cells. However, compound 2 showed to be inactive against these tumor cells.

Quercetin enhances tumorigenicity induced by N-ethyl-N'-nitro-N-nitrosoguanidine in the duodenum of mice

Quercetin, a flavonoid, widely distributed in many fruits and vegetables, is well known to have an antitumor effect despite its mutagenicity. In this study, we examined the effect of dietary quercetin on duodenum-tumorigenicity of mice induced by a chemical carcinogen, N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG). Eight-week-old male C57BL/6 mice were divided into 4 groups; ENNG without quercetin (group A), ENNG with 0.2% quercetin (group B), ENNG with 2% quercetin (group C), and 2% quercetin without ENNG (group D). ENNG was given in drinking water for the first 4 weeks, and thereafter quercetin was given in a mixed diet. At week 20, the average number of duodenal tumors per mouse was significantly higher in group C (mean±SE, 7.26±1.75, p<0.05) than in group A (2.32±0.31). The size of the duodenal tumors increased significantly in group B (1.79±0.09 mm, p<0.001) compared with group A (1.43±0.09 mm). In contrast, no duodenal tumor was induced in group D. The present findings suggest that excessive intake of quercetin occasionally is a risk factor for carcinogenesis of some specific organs such as the upper intestine.

Flavonoids: potential Wnt/beta-catenin signaling modulators in cancer

Flavonoids are polyphenolic compounds found throughout the plant kingdom. They occur in every organ but are usually concentrated in leaves and flowers. During the last two decades, in vitro and in vivo studies demonstrated that flavonoids have inhibitory effects on human diseases through targeting of multiple cellular signaling components. Wnt/β-catenin signaling regulates proliferation, differentiation and fate specification in developmental stages and controls tissue homeostasis in adult life. For these reasons, this pathway has received great attention in the last years as potential pathway involved in distinct Human pathologies. In this review we discuss the emerging potential mechanisms for flavonoids on Wnt/β-catenin signaling in cancer and possible investigation strategies to understand flavonoids mode of action on this signaling pathway.

Quantification of quercetin glycosides in 6 onion cultivars and comparisons of hydrolysis-HPLC and spectrophotometric methods in measuring total quercetin concentrations

This study was performed to purify and quantify quercetin glycosides (QG) and aglycone (free) quercetin (Q) in 6 selected onion cultivars and to compare analytical approaches based on high-performance liquid chromatography (HPLC) and spectrophotometry for the quantification of total quercetin (TQ) concentrations. Individual mono- and di-glycoside Q compounds were purified using a semipreparative HPLC and identified by comparing spectral data and by confirming corresponding peaks of QG and Q after incomplete enzyme-hydrolysis. Purified QG were quantified as Q by enzyme-hydrolysis/HPLC. TQ concentrations obtained from 20 onion bulbs with enzyme-hydrolysis/HPLC, no-hydrolysis/HPLC, and a spectrophotometric method without prior hydrolysis were significantly correlated (r(2)= 0.99) and were about 15% higher, identical, or 10% less than those concentrations by a standard acid-hydrolysis/HPLC method, respectively. During enzyme-hydrolysis of onion extracts, progressive reduction of the QG and formation of the corresponding mono-glycosides and Q were monitored using an analytical HPLC. TQ ranged from 83 to 330 microg/g F.W. in 6 selected cultivars of long-day or short-day onions. Q3,4'G and Q4'G were the 2 major compounds and comprised approximately between 94% and 97% of TQ in onions.

Resveratrol and quercetin cooperate to induce senescence-like growth arrest in C6 rat glioma cells

Glioma is the most frequent and malignant primary human brain tumor with dismal prognosis despite multimodal therapy. Resveratrol and quercetin, two structurally related and naturally occurring polyphenols, are proposed to have anticancer effects. We report here that resveratrol and quercetin decreased the cell number in four glioma cell lines but not in rat astrocytes. Low doses of resveratrol (10 microM) or quercetin (25 microM) separately had no effect on apoptosis induction, but had a strong effect on caspase 3/7 activation when administered together. Western blot analyses showed that resveratrol (10 microM) and quercetin (25 microM) caused a reduction in phosphorylation of Akt, but this reduction was not sufficient by itself to mediate the effects of these polyphenols. Most important, resveratrol and quercetin chronically administered presented a strong synergism in inducing senescence-like growth arrest. These results suggest that the combination of polyphenols can potentialize their antitumoral activity, thereby reducing the therapeutic concentration needed for glioma treatment.

Quercetin inhibit human SW480 colon cancer growth in association with inhibition of cyclin D1 and survivin expression through Wnt/beta-catenin signaling pathway

AIM

The Wnt signaling pathway plays a pivotal role in cellular developmental processes and human carcinogenesis. The aim of this study was to investigate the effects of quercetin on the growth of the colon carcinoma cell line and the regulation effect of quercetin on the Wnt/beta-catenin signaling pathway.

METHODS

MTT assay was used to determine the reduction of cell viability of quercetin on SW480 cells and clone 26 cells. The apoptotic rate and cell-cycle analysis after treatment with quercetin was determined by flow cytometry. Effects of quercetin on mRNA expression of cyclin D(1) and survivin were detected by semiquantitative RT-PCR. After treatment with quercetin, the protein expression of cyclin D(1) and survivin in SW480 cells was analyzed by Western blot analysis. We built a Wnt/beta-catenin signaling pathway reporter gene model. The regulation effect of quercetin on the Wnt/beta-catenin signaling transcription was investigated by using this reporter gene model.

RESULTS

Quercetin reduced cell viability in a dose- and time-dependent manner in SW480 and clone 26 cells. The percentages of SW480 cells and clone 26 cells at G(2)/M phase were increased significantly after treatment with 40 approximately 80 micromol/L quercetin for 48 hours. Quercetin induced the apoptosis of SW480 cells in a dose-dependent manner at the concentration of 20, 40, 60, anf 80 micromol/L. However, quercetin only induced the apoptosis of clone 26 cells at the concentration of 80 micromol/L. Quercetin downregulated transcriptional activity of beta-catenin/Tcf in SW480 cells transiently transfected with the TCF-4 reporter gene. Within 24 hours of treatment, a 160-mumol/L concentration of quercetin reduced beta-catenin/Tcf transcriptional activity by about 18-fold. Cyclin D(1) and the survivin gene were downregulated markedly by quercetin in a dose-dependent manner at both the transcription and protein expression levels.

CONCLUSION

The results indicate that the molecular mechanism underlying the antitumor effect of quercetin in SW480 colon cancer cells is related to the inhibition of expression of cyclin D(1) and survivin as well as the Wnt/beta-catenin signaling pathway. Therefore, the Wnt/beta-catenin signaling pathway could be qualified as one of the promising targets for innovative treatment strategies of colorectal cancer.

Effect of pectin enhancement on plasma quercetin and fecal flora in rutin-supplemented mice

Few reports have considered the effects of dietary fiber on plasma quercetin and the intestinal flora. We investigated the effects of pectin on the plasma and fecal flora of mice fed a diet supplemented with the quercetin glycoside rutin. Male mice were randomly divided into 2 groups, which were fed a pectin-rutin (PR) or cellulose-rutin (CR) diet for 14 d. Plasma quercetin and isorhamnetin metabolites were measured by high-performance liquid chromatography. Feces were immediately processed with bacteriological procedures. The fecal flora was investigated. Plasma quercetin and isorhamnetin concentrations were significantly higher in the PR diet group, as was the plasma isorhamnetin/quercetin ratio. The composition of the intestinal flora differed between the 2 dietary groups. The total number of fecal bacteria was significantly larger in the PR group, in which most types of bacteria were more abundant, with the exceptions of bifidobacteria, fusiform-shaped bacteria, and staphylococci. The lower gut seemed to be the major absorption site for rutin. Pectin might thus enhance the bioavailability of quercetin from rutin by altering the metabolic activity of the intestinal flora and/or gut physiological function.

Colorectal cancer prevention in inflammatory bowel disease and the role of 5-aminosalicylic acid: a clinical review and update

A roundtable consensus meeting was held to consolidate current knowledge on the etiology of colorectal cancer in patients with inflammatory bowel disease and to review current strategies, both diagnostic and preventive, specifically addressing the role of 5-aminosalicylic acid. Specific topics that were addressed included: the epidemiology of colorectal cancer, including an assessment of risk factors and the impact of colonoscopy on colorectal cancer incidence and mortality; the origin and evolution of dysplasia nomenclature and the natural history of dysplasia; review of the experience of St. Mark's Hospital (London) as gleaned from its surveillance database; mechanisms by which 5-aminosalicylic acid is thought to exert a chemopreventive effect; the potential future role of 5-aminosalicylic acid in chemopreventive strategies; chemoprevention in familial adenomatous polyposis; and other future research directions. This article provides a comprehensive overview of the issues discussed and should act as a guide to shaping the design of future studies in this area.

Antioxidant properties and free radical-scavenging reactivity of a family of hydroxynaphthalenones and dihydroxyanthracenones

This study was undertaken to investigate the free radical-scavenging and antioxidant activities of various structurally related hydroquinones including hydroxynaphthalenones and dihydroxyanthracenones. Electron spin resonance spectroscopy and spin trapping techniques were used to evaluate the ability of hydroquinones to scavenge hydroxyl, diphenylpicrylhydrazyl, and galvinoxyl radicals. In addition, the oxygen radical absorbing capacity assay using fluorescein (ORAC-FL) was used to obtain the relative antioxidant capacity of these radicals. The rate constants of the first H atom abstraction by 2,2-diphenyl-2-picrylhydrazyl (k(2)), were obtained under pseudo-first-order conditions. The free radical-scavenging activities and k(2) values discriminate well between hydroxynaphthalenones and dihydroxyanthracenones, showing that the latter have better antioxidant properties. The aforementioned experimental data agree with quantum-chemical results demonstrating the relevance of intramolecular H bonding to radical-scavenging activities.

Modification of membranes by quercetin, a naturally occurring flavonoid, via its incorporation in the polar head group

Quercetin is a naturally occurring flavonoid that has a lot of beneficial properties to human health. In this report, using the spin label technique, the influence of quercetin on the fluidity of multilamellar DPPC liposomes was studied. The polarity of the environment preferred by quercetin was also examined by determining the dependence of the position of electronic absorption maxima on dielectric properties of different environments. Autofluorescence of quercetin was also used to examine its distribution in cells. An additional aim of the study was to find how quercetin presence affects human skin fibroblasts. The results showed that incorporation of quercetin at physiological pH into DPPC liposomes caused changes in the partition coefficient of the Tempo spin label between water and polar head group phases. By determining the electronic absorption maxima, we observed that the chromophore of quercetin is localized in the polar head region. Fluorescence microscopy of HSF cells showed quercetin presence in the membrane, cytoplasm and inside the nucleus. Ultrastructural observation revealed some changes, especially in membranous structures, after flavonol treatment. From the results we have concluded that quercetin present in the membrane and other structures can cause changes within cells crucial for its pharmacological activity.

NAG-1 up-regulation mediated by EGR-1 and p53 is critical for quercetin-induced apoptosis in HCT116 colon carcinoma cells

Quercetin, a flavonoid molecule ubiquitously present in nature, has multiple effects on cancer cells, including the inhibition of cell proliferation and migration. However, the responsible molecular mechanisms are not fully understood. We found that quercetin induces the expression of NAG-1 (Non-steroidal anti-inflammatory drug activated gene-1), a TGF-beta superfamily protein, during quercetin-induced apoptosis of HCT116 human colon carcinoma cells. Reporter assays using the luciferase constructs containing NAG-1 promoter region demonstrate that early growth response-1 (EGR-1) and p53 are required for quercetin-mediated activation of the NAG-1 promoter. Overexpression of NAG-1 enhanced the apoptotic effect of quercetin, but suppression of quercetin-induced NAG-1 expression by NAG-1 siRNA attenuated quercetin-induced apoptosis in HCT116 cells. Taken together, the present study demonstrates for the first time that quercetin induces apoptosis via NAG-1, providing a mechanistic basis for the apoptotic effect of quercetin in colon carcinoma cells.

Quercetin mediates preferential degradation of oncogenic Ras and causes autophagy in Ha-RAS-transformed human colon cells

Several food polyphenols act as chemopreventers by reducing the incidence of many types of cancer, especially in colon epithelia. In this study, we have investigated whether the flavonoid quercetin can modulate cell proliferation and survival by targeting key molecules and/or biological processes responsible for tumor cell properties. The effect of quercetin on the expression of Ras oncoproteins was specifically studied using systems of either constitutive or conditional expression of oncogenic RAS in human epithelial cells. Our findings suggest that quercetin inhibits cell viability as well as cancer cell properties like anchorage-independent growth. These findings were further supported at the molecular level, since quercetin treatment resulted in a preferential reduction of Ras protein levels in cell lines expressing oncogenic Ras proteins. Notably, in cells that only express wild-type Ras or in those where the oncogenic Ras allele was knocked out, quercetin had no evident effects upon Ras levels. We have shown that quercetin drastically reduces half-life of oncogenic Ras but has no effect when the cells are treated with a proteasome inhibitor. Moreover, in Ha-RAS-transformed cells, quercetin induces autophagic processes. Since quercetin downregulates the levels of oncogenic Ras in cancer cells, we propose that this flavonoid could act as a chemopreventive agent for cancers with frequent mutations of RAS genes.

Apple flavonoids inhibit growth of HT29 human colon cancer cells and modulate expression of genes involved in the biotransformation of xenobiotics

Flavonoids from fruits and vegetables probably reduce risks of diseases associated with oxidative stress, including cancer. Apples contain significant amounts of flavonoids with antioxidative potential. The objectives of this study were to investigate such compounds for properties associated with reduction of cancer risks. We report herein that apple flavonoids from an apple extract (AE) inhibit colon cancer cell growth and significantly modulate expression of genes related to xenobiotic metabolism. HT29 cells were treated with AE at concentrations delivering 5-50 microM of one of the major ingredients, phloridzin ("phloridzin-equivalents," Ph.E), to the cell culture medium, with a synthetic flavonoid mixture mimicking the composition of the AE or with 5-100 microM individual flavonoids. HT29 cell growth was inhibited by the complex extract and by the mixture. HT29 cells were treated with nontoxic doses of the AE (30 microM, Ph.E) and after 24 h total RNA was isolated to elucidate patterns of gene expression using a human cDNA-microarray (SuperArray) spotted with 96 genes of drug metabolism. Treatment with AE resulted in an upregulation of several genes (GSTP1, GSSTT2, MGST2, CYCP4F3, CHST5, CHST6, and CHST7) and downregulation of EPHX1, in comparison to the medium controls. The enhanced transcriptional activity of GSTP1 and GSTT2 genes was confirmed with real-time qRT-PCR. On the basis of the pattern of differential gene expression found here, we conclude that apple flavonoids modulate toxicological defense against colon cancer risk factors. In addition to the inhibition of tumor cell proliferation, this could be a mechanism of cancer risk reduction.

Effects of 9,10-dihydroxy-4,4-dimethyl-5,8-dihydro-1(4H)-anthracenone derivatives on tumor cell respiration

A series of tricyclic hydroquinones, incorporating a carbonyl group in the ortho position relative to the phenol function, were tested as inhibitors of oxygen uptake against the TA3 mouse carcinoma cell line and its multidrug-resistant variant TA3-MTX-R. The title compound, which proved to be the most active one, also exhibited low micromolar dose-dependent growth inhibition of the human tumor U937 cell line (human monocytic leukemia). A tentative structure-activity relationship is proposed for these substances. A comparison between the cytotoxicities of the title compound and 4,4-dimethyl-5,8-dihydroxynaphthalene-1-one, with their activities as inhibitors of oxygen uptake by the TA3-MTX-R cell line, is presented. Also, the inhibition of oxygen uptake by 6-(4-methylpent-3-enyl)-1,4-naphthoquinone was determined and compared with its reported cytotoxicity toward P-388 (murine lymphocytic leukemia), A-549 (human lung carcinoma), HT-29 (human colon carcinoma), and MEL-28 (human melanoma) cells. The inhibition of oxygen uptake by TA3-MTX-R cells is useful as a quick test for preliminary screening of possible anticancer activity.

Quercetin arrests G2/M phase and induces caspase-dependent cell death in U937 cells

Quercetin, a natural product derived from grapes, has been shown to prevent carcinogenesis in murine models. We report here that quercetin induces anti-proliferation and arrests G2/M phase in U937 cells. The G2/M phase accumulation was accompanied by an increase in the level of the cyclin B. In contrast, the level of the cyclin D, cyclin E, E2F1, and E2F2 was marked decreased in quercetin-treated U937 cells. Removal of quercetin from the culture medium stimulates U937 cells to synchronously re-enter the cell cycle, decrease expression level of cyclin B, and increased the expression level of cyclin D and cyclin E. These data demonstrate that quercetin causes reversible G2/M phase arrest, which was related with dramatic changes in the level of cyclin B, cyclin D, and cyclin E. Quercetin-induced down-regulation of cyclin D and cyclin E was associated with suppression of transcriptional levels but not protein stability. In addition, quercetin-treated U937 cells showed DNA fragmentation, increased sub-G1 population, and generated a 60kDa cleavage product of PLC-gamma1 in a dose-dependent manner, which were significantly inhibited by z-VAD-fmk. These data clearly indicate that quercetin-induced apoptosis is associated with caspase activation. In summary, the growth inhibition of the quercetin is highly related to cell cycle arrest at the G2/M phase and induction of caspase-dependent apoptosis in human promonocytic U937 cells.

Quercetin Induces Necrosis and Apoptosis in SCC-9 Oral Cancer Cells

Evidence has accumulated that dietary polyphenols, in particular, flavonoids, have protective effects against oral cancer. In this study, we have examined the effects of quercetin, a major dietary flavonoid, on cell growth and necrosis/apoptosis and cell cycle regulation in human oral squamous carcinoma SCC-9 cells. Quercetin induced dose- and time-dependent, irreversible inhibition of cell growth and cellular DNA synthesis. Light microscopy and lactate dehydrogenase measurements showed modifications in the morphology and membrane integrity of these cells after quercetin treatment. Propidium iodide/annexin V staining showed that quercetin induced necrosis at 24 h and 48 h, whereas at 72 h cells underwent apoptosis, correlating with caspase-3 activation. Flow cytometry studies of the cell cycle distribution showed that quercetin induced mainly S-phase arrest. Thymidylate synthase (TS), a key S-phase enzyme, was inhibited in a time- and dose-dependent fashion by quercetin at the protein level. A lack of effect on TS mRNA suggested that TS down-regulation occurred at the translational level. In conclusion, our data support a view that quercetin initially induces a stress response, resulting in necrosis of these oral epithelial cells. Prolonged exposure of the surviving cells to quercetin causes apoptosis, presumably mediated by inhibition of TS protein.

Quercetin, a potent inhibitor against beta-catenin/Tcf signaling in SW480 colon cancer cells

Dysregulation of Wnt/beta-catenin pathway plays a central role in early events in colorectal carcinogenesis. We examined the effect of quercetin, a famous anti-tumor agent, against beta-catenin/Tcf signaling in SW480 cells. Quercetin inhibited the transcriptional activity of beta-catenin/Tcf in SW480 and also in HEK293 cells transiently transfected with constitutively active mutant beta-catenin gene, whose product is not induced to be degraded by APC-Axin-GSK3beta complex, so we concluded that its inhibitory mechanism was related to beta-catenin itself or downstream components. To investigate the precise inhibitory mechanism, we performed EMSA showing that binding of the Tcf complexes to its specific DNA-binding sites was strongly suppressed by quercetin. Immunoprecipitation analysis also showed that the binding of beta-catenin to Tcf-4 was also disrupted by quercetin. Western blot analysis proved these decreased bindings resulted from decreased level of beta-catenin and Tcf-4 product in nucleus caused by quercetin. Together, we suggest that quercetin is an excellent inhibitor of beta-catenin/Tcf signaling in SW480 cell lines, and the reduced beta-catenin/Tcf transcriptional activity is due to the decreased nuclear beta-catenin and Tcf-4 proteins.

Vitamins, Phytochemicals, Diets, and Their Implementation in Cancer Chemoprevention

With progressive "Westernization" of the dietary pattern in Asian countries, such as Korea and Japan, unhealthy signs, such as increases in obesity and incidence rate of cancers, are starting to appear in recent statistics. These results support the hypothesis that a dietary pattern of low fats and high antioxidants based on plant foods will reduce the risk of cancer Recently, antioxidative vitamins and phenolic phytochemicals derived from our daily diet have received much attention because of their potential chemopreventive activities. Their chemopreventive mechanisms have been suggested mainly due to their protective effects against oxidative DNA damage. However. several studies have shown that dietary antioxidant supplements, such as vitamins and phenolic phytochemicals, are not beneficial; they may rather, cause DNA damage. These results suggest that a metabolomics approach might demonstrate that antioxidant rich whole diets play a more important role, rather than individual antioxidants in cancer prevention. On the other hand, the chemopreventive mechanisms of dietary vitamins and phenolic phytochemicals may be associated with the inhibition of other carcinogenic processes, particularly tumor promotion, rather than that of tumor initiation. In this article, possible cancer-preventive mechanisms of dietary vitamins and phenolic phytochemicals, are reviewed.

Dietary flavonoids and cancer risk in the Zutphen Elderly Study

Flavonoids are polyphenolic antioxidants naturally present in vegetable foods. Some flavonoids, such as quercetin, inhibit carcinogenesis in rodents, but their effect in humans is unknown. We measured the flavonoids quercetin, kaempferol, myricetin, apigenin, and luteolin in foods and assessed flavonoid intake in 1985 by dietary history in 738 men aged 65-84 years without a history of cancer, who were then followed for five years. Mean flavonoid intake was 25.9 mg/day. The major sources of flavonoid intake were tea at 61% and vegetables and fruits (mainly onions, kale, endive, and apples) at 38%. Between 1985 and 1990, 75 men developed cancer (all sites) and 34 men died from cancer. Flavonoid intake in 1985 was not associated with incidence of all-cause cancer (p for trend = 0.54) or with mortality from all-cause cancer (p for trend = 0.51). Flavonoid intake was also not associated with risk of cancers of the alimentary and respiratory tract (p for trend = 0.92). Adjustment for age, body mass index, smoking, physical activity, and vitamin C, vitamin E, beta-carotene, and dietary fiber intake did not change the relative risks. A high intake of flavonoids from vegetables and fruits only was inversely associated with risk of cancer of the alimentary and respiratory tract (relative risk of highest vs. lowest tertile = 0.51, 95% confidence interval 0.25-1.05); these results suggest the presence of other nonvitamin components with anticarcinogenic potential in these foods. We conclude that intake of flavonoids, mainly from tea, apples, and onions, does not predict a reduced risk of all-cause cancer or of cancer of the alimentary and respiratory tract in elderly men. The effect of flavonoids on risk of cancer at specific sites needs further investigation in prospective cohort studies.

Suppression of intestinal crypt cell proliferation and aberrant crypt foci by dietary quercetin in rats

Quercetin inhibits proliferation of human gastric and colonic cancer cells in vitro by suppressing mitosis and increasing apoptosis. Quercetin might therefore act as an anticarcinogen in the alimentary tract, but previous findings have been inconsistent. We fed rats quercetin at dietary concentrations of 1, 5, 20, and 50 g/kg. At < or = 20 g/kg, we observed a statistically significant reduction in the frequency of crypt cell mitosis in proximal, mid, and distal small intestine and in distal colon, amounting to approximately 40% of control at 1 g/kg. There was no effect on apoptosis. Quercetin metabolites, but not quercetin aglycone, were detected in plasma of rats fed quercetin at 20 and 50 g/kg. In a second experiment, rats were fed quercetin at 1 g/kg after treatment with 1,2-dimethylhydrazine to induce aberrant crypt foci. In dimethylhydrazine-treated and control rats, crypt cell mitosis was suppressed at 48 h and 42 days after injection, and there was a statistically significant reduction in the number of aberrant crypts and larger aberrant crypt foci (> 4 crypts/focus) in the distal colon of treated animals. These findings demonstrate that quercetin can inhibit intestinal crypt cell proliferation in vivo, but the effect diminishes as the level of dietary exposure increases. At low concentrations, dietary quercetin inhibits induction of aberrant crypts by a mechanism that does not involve increased crypt cell apoptosis.

Disposition of the flavonoid quercetin in rats after single intravenous and oral doses

The pharmacokinetic and mean time tissue distribution parameters, after a single 50-mg/kg dose of quercetin administered as intravenous bolus, oral solution, and oral suspension, were determined using rat as an animal model. Following intravenous administration, the elimination rate constant and the elimination half-life were found to be 0.0062 min(-1) and 111 min, respectively. Examining the mean time tissue distribution parameters reflected a strong binding affinity of the drug molecules to both plasma and tissue proteins. In addition, the low permeability rate of drug molecules in the peripheral system was demonstrated. Following the oral administration of the drug, the extent of absorption was greater from solution than from suspension. Moreover, the solution showed a shorter Tmax and a higher Cmax than suspension. The absolute bioavailability for the solution was 0.275 and that for suspension was 0.162. The mean residence time (MRT) and the mean absorption time (MAT) were higher for suspension, reflecting the need for dissolving the drug in order to be absorbed. The mean (in-vivo) dissolution time (MDT(in-vivo)) was 34.5 min. Thus, an oral quercetin formulation that can readily form a drug solution in the gastrointestinal tract may enhance the absorption of the drug.

Flavonoids and gene expression in mammalian cells

Flavonoids appear to regulate the expression of many genes. As expected, when multiple flavonoids were compared in one study, structure-specificity was always observed. Unfortunately, little information is available regarding the proportion of contribution of various structural elements. Also, we have very limited information on their molecular mechanisms of action. The affinity of flavonoids for ER could explain the stimulatory effect on genes with ERE but other modes of action apparently also exist and need to be further explored. Physiological relevance is always a concern when investigating the regulation of gene expression by environmental chemicals such as flavonoids. One factor of concern is the in vivo concentration of flavonoids. Besides intestinal cells, liver cells and skin cells, other tissues obtain flavonoids through blood circulation. Thus, plasma concentrations of flavonoids are normally discussed. Steady state plasma concentrations of flavonoids are usually not much higher than 1 microM even in populations that consume large amounts of plant material. This concentration is relatively low compared to the concentrations of flavonoids that were commonly used in cell culture systems to demonstrate their effectiveness. Nevertheless, we have evidence that some flavonoids may accumulate in the cell. The effect of quercetin on metallothionein expression in Caco-2 cells persisted for at least 24 hours after its removal from the culture medium (Kuo et al., 1998). Also, long-term treatment of cultured cells with quercetin at low concentrations led to a similar effect on metallothionein expression as one high concentration treatment (Kuo et al., 2001). If intracellular accumulation of certain flavonoids is a shared characteristic for various cell types, it implies that routine ingestion of flavonoids could lead to biological effects at the concentration lower than predicted from a single treatment. Experiments to address possible cell/tissue accumulation of flavonoids are greatly needed.

The biochemistry and medical significance of the flavonoids

Flavonoids are plant pigments that are synthesised from phenylalanine, generally display marvelous colors known from flower petals, mostly emit brilliant fluorescence when they are excited by UV light, and are ubiquitous to green plant cells. The flavonoids are used by botanists for taxonomical classification. They regulate plant growth by inhibition of the exocytosis of the auxin indolyl acetic acid, as well as by induction of gene expression, and they influence other biological cells in numerous ways. Flavonoids inhibit or kill many bacterial strains, inhibit important viral enzymes, such as reverse transcriptase and protease, and destroy some pathogenic protozoans. Yet, their toxicity to animal cells is low. Flavonoids are major functional components of many herbal and insect preparations for medical use, e.g., propolis (bee's glue) and honey, which have been used since ancient times. The daily intake of flavonoids with normal food, especially fruit and vegetables, is 1-2 g. Modern authorised physicians are increasing their use of pure flavonoids to treat many important common diseases, due to their proven ability to inhibit specific enzymes, to simulate some hormones and neurotransmitters, and to scavenge free radicals.

Isoflavones for prevention of cancer, cardiovascular diseases, gynecological problems and possible immune potentiation

Japanese women show low incidence of and mortality from breast cancer, cardiovascular disease and climacteric symptoms compared to Caucasians. High soy bean intake is considered to attribute to that, but it is not clear whether soy protein itself or isoflavones (IFs) mixed in the soy protein has such effects. Presence of IFs in soy beans was varied by site, so we made IF-rich tablets from daidzein-rich soy germ (hypocotyl) for intervention studies. Our intervention study on young women by using the IF-rich tablet (20 and 40 mg/day) showed slight elongation of the menstrual cycle, but no adverse effects occurred. Intervention study on climacteric women showed improvement of bone density, hypertension and climacteric symptoms. Health effects of IFs on cancer occurrence, cardiovascular diseases, gynecological problems and possible immune potentiation are reviewed from functional aspects.

A comparison of the anticarcinogenic properties of four red wine polyphenols

BACKGROUND

There has been growing interest in the analysis of certain polyphenols in wine, especially flavonoids, trihydroxystilbenes and phenolic acids, stimulated by intense research into their potential benefits to human health. One of their main properties in this regard is their antioxidant activity, which enables them to attenuate the development of atherosclerosis, inflammatory diseases, and cancer.

METHODS

A two stage CD-1 mouse skin cancer model using 9,10-dimethyl-1,2-benzanthracene (DMBA) as initiator and phorbol 12-myristate 13-acetate (TPA) as promoter was employed to compare the antitumorigenic activities of one polyphenol from each of four different classes: flavanols [(+)-catechin], stilbenes (trans-resveratrol), flavonols (quercetin) and hydroxybenzoic acids (gallic acid). Animals were treated with specific polyphenols at doses ranging from 0 to 25 micromoles (dissolved in 200 microL acetone), twice a week for eighteen weeks. The solution was applied topically to the shaved dorsal region of each animal. The relative potencies of the polyphenols were compared by evaluating the percentage inhibition of tumor formation in individual mice and the number of mice developing one or more tumors with the different dose schedules.

RESULTS

Probit analysis revealed that quercetin was the most (ED(50)<1 micromole) and gallic acid the least effective (ED(50) 5-10 micromoles). (+)-Catechin and trans-resveratrol were intermediate, with ED(50) values of 5 and 6 micromoles, respectively.

CONCLUSION

We have shown recently that trans-resveratrol is absorbed much more efficiently than (+)-catechin and quercetin in humans after oral consumption. Taking this and the relative concentrations in red wine into account, together with the present results, we conclude that trans-resveratrol may be the most effective anticancer polyphenol present in red wine as consumed po by healthy human subjects.

Dietary antioxidants during cancer chemotherapy: impact on chemotherapeutic effectiveness and development of side effects

Several studies suggest that dietary supplementation with antioxidants can influence the response to chemotherapy as well as the development of adverse side effects that results from treatment with antineoplastic agents. Administration of antineoplastic agents results in oxidative stress, i.e., the production of free radicals and other reactive oxygen species (ROS). Oxidative stress reduces the rate of cell proliferation, and that occurring during chemotherapy may interfere with the cytotoxic effects of antineoplastic drugs, which depend on rapid proliferation of cancer cells for optimal activity. Antioxidants detoxify ROS and may enhance the anticancer effects of chemotherapy. For some supplements, activities beyond their antioxidant properties, such as inhibition of topoisomerase II or protein tyrosine kinases, may also contribute. ROS cause or contribute to certain side effects that are common to many anticancer drugs, such as gastrointestinal toxicity and mutagenesis. ROS also contribute to side effects that occur only with individual agents, such as doxorubicin-induced cardiotoxicity, cisplatin-induced nephrotoxicity, and bleomycin-induced pulmonary fibrosis. Antioxidants can reduce or prevent many of these side effects, and for some supplements the protective effect results from activities other than their antioxidant properties. Certain side effects, however, such as alopecia and myelosuppression, are not prevented by antioxidants, and agents that interfere with these side effects may also interfere with the anticancer effects of chemotherapy.

Identification of quercetin 3-O-beta-D-glucuronide as an antioxidative metabolite in rat plasma after oral administration of quercetin

The potential beneficial effect of dietary quercetin (3,3',4',5,7-pentahydroxyflavone) has attracted much attention in relation to the prevention of cardiovascular disease. It is generally recognized that dietary quercetin is subject to metabolic conversion resulting in conjugated forms during absorption and circulation. However, no quercetin conjugates have yet been identified from biological fluids or tissues. In the present study, we isolated and characterized two quercetin conjugates from the plasma of quercetin-administered rats. The blood plasma was collected from 26 rats 30 min after oral administration of quercetin (250 mg/kg body weight), concentrated, dissolved in 2% acetic acid aqueous solution (pH 2.65), and extracted with ethyl acetate. Two compounds (P2, P3) were obtained from the extract by repeated reversed-phase HPLC. On the other hand, two quercetin glucuronides were synthesized chemically and identified as quercetin 3-O-beta-D-glucuronide (Q3GA) and quercetin 4'-O-beta-D-glucuronide (Q4'GA), as determined from FABMS, 1H- and 13C-NMR, and HMBC data. The retention times of P2 and P3 in the HPLC chromatogram corresponded to those of Q3GA and Q4'GA, respectively. FABMS data demonstrated that P2 and P3 are quercetin monoglucuronides. 1H-NMR data for P2 were completely in agreement with those for Q3GA. P2 was therefore identified as Q3GA. This is, to our knowledge, the first evidence that Q3GA accumulates in vivo after oral administration of quercetin. Q3GA is likely to act as an effective antioxidant in blood plasma low-density lipoprotein, because this conjugated metabolite was found to possess a substantial antioxidant effect on copper ion-induced oxidation of human plasma low-density lipoprotein as well as 1,1-diphenyl-2-picrylhydrazyl radical-scavenging activity.

Dietary agents in cancer prevention: flavonoids and isoflavonoids

Flavones and isoflavones may play a prominent role in cancer prevention since these compounds are found in numerous plants that are associated with reduced cancer rates. This article reviews recent epidemiological and animal data on isoflavones and flavones and their role in cancer prevention. It covers aspects of the bioavailability of these dietary constituents and explores their mechanism of action. Human epidemiology data comes primarily from studies in which foods rich in isoflavones or flavones are associated with cancer rates. This approach has been particularly useful with isoflavones because of their abundance in specific foods, including soy foods. The bioavailability of flavones and isoflavones has been shown to be influenced by their chemical form in foods (generally glycoside conjugates), their hydrophobicity, susceptibility to degradation, the microbial flora of the consumer, and the food matrix. Some information is available on how these factors influence isoflavone bioavailability, but the information on flavones is more limited. Many mechanisms of action have been identified for isoflavone/flavone prevention of cancer, including estrogenic/antiestrogenic activity, antiproliferation, induction of cell-cycle arrest and apoptosis, prevention of oxidation, induction of detoxification enzymes, regulation of the host immune system, and changes in cellular signaling. It is expected that some combination of these mechanisms will be found to be responsible for cancer prevention by these compounds. Compelling data suggest that flavones and isoflavones contribute to cancer prevention; however, further investigations will be required to clarify the nature of the impact and interactions between these bioactive constituents and other dietary components.

Human cyclophilin 40 is a heat shock protein that exhibits altered intracellular localization following heat shock

The unactivated steroid receptors are chaperoned into a conformation that is optimal for binding hormone by a number of heat shock proteins, including Hsp90, Hsp70, Hsp40, and the immunophilin, FKBP52 (Hsp56). Together with its partner cochaperones, cyclophilin 40 (CyP40) and FKBP51, FKBP52 belongs to a distinct group of structurally related immunophilins that modulate steroid receptor function through their association with Hsp90. Due to the structural similarity between the component immunophilins, FKBP52 and cyclophilin 40, we decided to investigate whether CyP40 is also a heat shock protein. Exposure of MCF-7 breast cancer cells to elevated temperatures (42 degrees C for 3 hours) resulted in a 75-fold increase in CyP40 mRNA levels, but no corresponding increase in CyP40 protein expression, even after 7 hours of heat stress. The use of cycloheximide to inhibit protein synthesis revealed that in comparison to MCF-7 cells cultured at 37 degrees C, those exposed to heat stress (42 degrees C for 3 hours) displayed an elevated rate of degradation of both CyP40 and FKBP52 proteins. Concomitantly, the half-life of the CyP40 protein was reduced from more than 24 hours to just over 8 hours following heat shock. As no alteration in CyP40 protein levels occurred in cells exposed to heat shock, an elevated rate of degradation would imply that CyP40 protein was synthesized at an increased rate, hence the designation of human CyP40 as a heat shock protein. Application of heat stress elicited a marked redistribution of CyP40 protein in MCF-7 cells from a predominantly nucleolar localization, with some nuclear and cytoplasmic staining, to a pattern characterized by a pronounced nuclear accumulation of CyP40, with no distinguishable nucleolar staining. This increase in nuclear CyP40 possibly resulted from a redistribution of cytoplasmic and nucleolar CyP40, as no net increase in CyP40 expression levels occurred in response to stress. Exposure of MCF-7 cells to actinomycin D for 4 hours resulted in the translocation of the nucleolar marker protein, B23, from the nucleolus, with only a small reduction in nucleolar CyP40 levels. Under normal growth conditions, MCF-7 cells exhibited an apparent colocalization of CyP40 and FKBP52 within the nucleolus.