Resveratrol inhibits proliferation of primary rat hepatocytes in G0/G1 by inhibiting DNA synthesis

Resveratrol is a phytoalexin that has been shown to inhibit cell proliferation of several cancer cell lines. In some cases this inhibition was specific for the transformed cells when compared with normal cells of the same tissue. To test whether this was the case in rat hepatocytes, we exposed primary rat hepatocytes in culture and transformed rat hepatic cells to this compound and studied its effect on cell proliferation, measuring deoxy-bromouridine incorporation and total DNA. We also studied the effect of resveratrol on the cell cycle of normal and transformed rat hepatocytes. We observed that resveratrol inhibited proliferation in a dose-dependent manner in both cases, with no differential action in the transformed cells compared to the normal ones. This compound arrested the cell cycle in G0/G1 in primary hepatocytes, while it arrested the cell cycle in G2/M in transformed cells. Transformed hepatocytes showed accumulation of cells in the S phase of the cell cycle.

Impact of eugenol and isoeugenol on AhR translocation, target gene expression, and proliferation in human HaCaT keratinocytes

The phenolic derivatives eugenol and isoeugenol, which are naturally found in essential oils of different spices, are commonly used as fragrances. Recently data demonstrated that growth suppression produced by these substances occurs in keratinocytes and that the effects may be mediated via aryl hydrocarbon receptor (AhR) interactions. In this study the effects of eugenol and isoeugenol were determined on intracellular localization of AhR, AhR target gene expression, AhR-dependent cell cycle regulation, and proliferation in HaCaT cells. Both compounds produced a rapid and marked translocation of AhR into the nucleus, induced the expression of the AhR target genes cytochrome P-450 1A1 (CYP1A1) and AhR repressor (AhRR), and inhibited proliferation of HaCaT cells. Among the G(1) phase cell cycle-related proteins, levels of the retinoblastoma protein (RB), which is known to interact with AhR, and levels of the cyclin dependent kinase (CDK) 6 were reduced by eugenol and isoeugenol, whereas steady-state levels of CDK2 and CDK4 remained unaffected. Protein levels of CDK inhibitor (CKI) p27(KIP1), known to be modulated in an AhR-dependent manner, were increased after treatment with both substances. In conclusion, data show that the antiproliferative properties of eugenol and isoeugenol in HaCaT cells are mediated through AhR, and thereby the molecular mechanisms of action in these cells were identified for the first time in this study.

G0/G1 phase arrest and apoptosis induced by manganese chloride on cultured rat astrocytes and protective effects of riluzole

Occupational or environmental exposure to excessive Mn would cause manganism, which is resembled Parkinson disease. However, the mechanism underlying manganism is still unknown. It had been documented that astrocytes play important roles in physiological function in brain. Therefore, in the present study, the cultured astrocytes were exposed to 0, 125, 250, and 500 μM MnCl(2), and cell viability, lactate dehydrogenase (LDH) leakage, morphological change, cell cycle progression, and apoptosis were determined. In addition, 100 μM riluzole (a glutamatergic modulator) was pretreated for 6 h before no MnCl(2) exposure or 500 μM MnCl(2) exposure. The results showed that cell viability inhibited, LDH leakage elevated, morphology injured, G(0)/G(1) phase cell cycle arrested, and apoptosis rate increased in a concentration-dependent manner. Further investigation indicated that riluzole pretreatment reversed cytotoxicity, cell cycle aberration, and apoptosis on astrocytes caused by MnCl(2). These results suggested that MnCl(2) could cause cytotoxicity, cell cycle arrest, and apoptosis concentration-dependently; riluzole might antagonize Mn toxicity on astrocytes.

Inactivation of mirk/dyrk1b kinase targets quiescent pancreatic cancer cells

A major problem in the treatment of cancer arises from quiescent cancer cells that are relatively insensitive to most chemotherapeutic drugs and radiation. Such residual cancer cells can cause tumor regrowth or recurrence when they reenter the cell cycle. Earlier studies showed that levels of the serine/theronine kinase Mirk/dyrk1B are elevated up to 10-fold in quiescent G(0) tumor cells. Mirk uses several mechanisms to block cell cycling, and Mirk increases expression of antioxidant genes that decrease reactive oxygen species (ROS) levels and increase quiescent cell viability. We now show that a novel small molecule Mirk kinase inhibitor blocked tumor cells from undergoing reversible arrest in a quiescent G(0) state and enabled some cells to exit quiescence. The inhibitor increased cycling in Panc1, AsPc1, and SW620 cells that expressed Mirk, but not in HCT116 cells that did not. Mirk kinase inhibition elevated ROS levels and DNA damage detected by increased phosphorylation of the histone protein H2AX and by S-phase checkpoints. The Mirk kinase inhibitor increased cleavage of the apoptotic proteins PARP and caspase 3, and increased tumor cell kill several-fold by gemcitabine and cisplatin. A phenocopy of these effects occurred following Mirk depletion, showing drug specificity. In previous studies Mirk knockout or depletion had no detectable effect on normal tissue, suggesting that the Mirk kinase inhibitor could have a selective effect on cancer cells expressing elevated levels of Mirk kinase.

[Resistance of leukemia KG1a cells with positive N-cadherin in phase G(0) against killing activity of VP16]

Drug resistance is an important character of leukemic stem cells. To explore the mechanism of the chemotherapy resistance of N-cadherin positive leukemia cells, the quiescent state of N-cadherin positive leukemia cells was determined by flow cytometry and the relationship of G(0) phase cell ratio with the chemotherapy resistance was analyzed. After KG1a cells were induced to enter cell cycle, the G(0) phase cell ratio and the sensitivity of cells to VP16 were determined. Finally the quiescent state and drug resistance properties of KG1a cells were determined after inhibiting N-cadherin-mediated cell-cell interaction by EGTA treatment. The results showed that the G(0) phase cell ratio in N-cadherin positive KG1a cells was higher than that in N-cadherin negative KG1a cells. After KG1a cells were induced to enter cell cycle, the G(0) phase cell ratio was decreased significantly and the sensitivity of KG1a cells to VP16 increased. Following EGTA treatment for 24 hours, the G(0) phase cell ratio decreased and the drug-sensitivity was enhanced significantly. It is concluded that N-cadherin-mediated adhesion keeps N-cadherin positive leukemia cells in quiescent state of G(0) phase, thus protect these leukemia cells against VP16 chemotherapy.

Effects of acute and chronic hypoxia on the radiosensitivity of gastric and esophageal cancer cells

AIM

The aim of this study was to examine the effects of hypoxia on radiosensitivity and to analyze the mechanisms responsible for radiation resistance in gastric and esophageal cancer.

MATERIALS AND METHODS

A gastric cancer cell line, OCUM-12, and an esophageal cancer cell line, TE-6, were used. The effects of hypoxia with irradiation on the growth-activity, cell cycle distribution, and gene expression were examined.

RESULTS

Both acute and chronic hypoxia decreased radiosensitivity of cancer cells. The radiosensitivity of chronic hypoxic cells was significantly enhanced by reoxygenation. Acute and chronic all hypoxia reduced the percentage of cells in the G(2)/M and S phases, respectively. In acute hypoxia, the mRNA expression of BRCA1 and BRCA2 was reduced in cancer cells. Reoxygenation increased the expression of BRCA1 and BRCA2.

CONCLUSION

Hypoxia is associated with radiation resistance. Therefore, reoxygenation may enhance the radiosensitivity of hypoxic cells. BRCA1 and BRCA2 may be associated with factors for radiation resistance by regulation of cell cycle progression.

The mechanism of neogambogic acid-induced apoptosis in human MCF-7 cells

Neogambogic acid (NGA), an active ingredient in garcinia, can inhibit the growth of some solid tumors and result in an anticancer effect. We hypothesize that NGA may be responsible for the inhibition of proliferation of human breast cancer cell line MCF-7 cells. To investigate its anticancer mechanism in vitro, MCF-7 cells were treated with various concentrations of NGA. Results of MTT (methyl thiazolyl tetrazolum) assay showed that treatment with NGA significantly reduced the proliferation of MCF-7 cells in a dose-dependent manner. NGA could increase the expression of the apoptosis-related proteins FasL, caspase-3, caspase-8, caspase-9, and Bax and decrease the expression of anti-apoptotic protein Bcl-2 accompanied by the mitochondrial transmembrane damage. The antiproliferative effect of NGA on MCF-7 cells is due to the G(0)/G(1) arrest, increased apoptosis and activation of Fas/FasL and cytochrome C pathway. These results provide an important insight into the cellular and molecular mechanisms through which NGA impairs the proliferation of breast cancer cells.

Gallic acid induces G₀/G₁ phase arrest and apoptosis in human leukemia HL-60 cells through inhibiting cyclin D and E, and activating mitochondria-dependent pathway

Gallic acid (GA) induces apoptosis in different types of cancer cell lines. In this study, we investigate the apoptotic effects induced by GA in human promyelocytic leukemia HL-60 cells, and clarify the underlying mechanism. Our results showed that GA reduced the viability of HL-60 cells in a dose- and time-dependent manner. GA led to G(0)/G(1) phase arrest in HL-60 cells through promoting p21 and p27 and inhibiting the levels of cyclin D and cyclin E. GA caused DNA damage and fragmentation in HL-60 cells as assayed using DAPI staining and Comet assay. Flow cytometric analysis revealed that GA increased Ca(2+) levels and reduced the mitochondrial membrane potential (ΔΨ(m)) in HL-60 cells. Apoptotic protein expressions were determined by Western blotting. The results indicated that GA-mediated apoptosis of HL-60 cells mainly depended on mitochondrial pathway, by promoting the release of cytochrome c, apoptosis-inducing factor (AIF) and endonuclease G (Endo G) and by up-regulating the protein expression of Bcl-2-associated X protein (BAX), caspase-4, caspase-9 and caspase-3. In addition, GA also activated the death receptor-dependent pathway by enhancing the protein expressions of fatty acid synthase (FAS), FAS ligand (FASL), caspase-8 and BCL-2 interacting domain (BID). We determined the mRNA expression of the gene levels of these proteins by real-time PCR. The results showed that GA-mediated apoptosis of HL-60 cells mainly depended on up-regulation of the mRNA of caspase-8, caspase-9, caspase-3, AIF and Endo G. In conclusion, GA-induced apoptosis occurs through the death receptor and mitochondria-mediated pathways. The evaluation of GA as a potential therapeutic agent for treatment of leukemia seems warranted.

GADD45α and annexin A1 are involved in the apoptosis of HL-60 induced by resveratrol

Resveratrol (3,4',5-trihydroxy-trans-stilbene), one of secondary metabolites of low molecular weight present in plant, has various important biological effects. It can induce apoptosis in human leukemia cell types in vitro, although the mechanism is not fully understood. In the present study, we demonstrated reduced viability and DNA synthesis, as well as increased proportion of the subdiploid cell population, in HL-60 cells as determined by cell cycle analysis with resveratrol. Resveratrol treatment resulted in a gradual time-dependent decrease in the expression of anti-apoptotic Bcl-2 and increase in that of Bax, annexin A1, growth arrest- and DNA damage-induced gene 45α (GADD45α), and cleaved caspase-3. In addition, resveratrol markedly increased caspase-3 activity in cells. Our results suggest that resveratrol could inhibit the proliferation and induce apoptosis of HL-60 cells through a GADD45α and annexin A1/caspase-3 pathway.

Combined valproic acid and celecoxib treatment induced synergistic cytotoxicity and apoptosis in neuroblastoma cells

BACKGROUND

The effects of combined valproic acid (VPA) and celecoxib treatment on cancer cells have not been reported. In this study, we examined the effects of VPA and celecoxib, alone and combined, on human SH-SY5Y neuroblastoma cells.

MATERIALS AND METHODS

The cytotoxicity effects of VPA, celecoxib, and combined VPA and celecoxib treatment on neuroblastoma cells were studied. The apoptotic fraction and the cell cycle distribution of neuroblastoma cells were analyzed by flow-activated cell sorter analysis. Western blot analysis was used to investigate the expression of cyclooxygenase-2, p53, 14-3-3σ, p21, p27, Bcl-2 and Bax in neuroblastoma cells treated with various regimens.

RESULTS

Combined VPA and celecoxib treatment caused more cytotoxicity and apoptosis in neuroblastoma cells than individual drug treatment (p<0.05). In addition, combination treatment caused more neuroblastoma cells to accumulate in the G0/G1 phase of the cell cycle (p<0.04) and induced higher p21 and p27 expression than individual drug treatment or control.

CONCLUSION

Combined VPA and celecoxib treatment induced more cytotoxicity and apoptosis in neuroblastoma cells than individual drug treatment. The effects were probably related to the increased p21 and p27 expression, and G0/G1 accumulation of neuroblastoma cells.

Lipid-soluble ginseng extract induces apoptosis and G0/G1 cell cycle arrest in NCI-H460 human lung cancer cells

This study was performed to elucidate the anticancer mechanism of a lipid-soluble ginseng extract (LSGE) by analyzing induction of apoptosis and arrest of cell cycle progression using the NCI-H460 human lung cancer cell line. Proliferation of NCI-H460 cells was potently inhibited by LSGE in a dose-dependent manner. The cell cycle arrest at the G0/G1 phase in NCI-H460 cells was induced by LSGE. The percentage of G0/G1 phase cells significantly increased, while that of S phase cells decreased after treatment with LSGE. The expression levels of cyclin-dependent kinase2 (CDK2), CDK4, CDK6, cyclin D3 and cyclin E related to G0/G1 cells progression were also altered by LSGE. In addition, LSGE-induced cell death occurred through apoptosis, which was accompanied by increasing the activity of caspases including caspase-8, caspase-9 and caspase-3. Consistent with enhancement of caspase activity, LSGE increased protein levels of cleaved caspase-3, caspase-8, caspase-9, and poly-ADP-ribose polymerase (PARP). These apoptotic effects of LSGE were inhibited by the pan-caspase inhibitor Z-VAD-fmk. These findings indicate that LSGE inhibits NCI-H460 human lung cancer cell growth by cell cycle arrest at the G0/G1 phase and induction of caspase-mediated apoptosis.

3-Oxoolean-12-en-27-oic acid inhibits the proliferation of non-small cell lung carcinoma cells by inducing cell-cycle arrest at G0/G1 phase

BACKGROUND

Inhibition of cell-cycle progression is a target for the treatment of cancer. 3-Oxoolean-12-en-27-oic acid (3-OOLA) has shown significant anticancer activity towards diverse cancer cells, but has not been investigated for non-small cell lung carcinoma (NSCLC) cells. In this study, we investigated the antiproliferative effect of 3-OOLA in NSCLC cell lines and its underlying mechanism.

MATERIALS AND METHODS

The MTT assay, bromodeoxyuridine (BrdU) incorporation assay, and flow cytometry were used for cell proliferation studies, and annexin V staining for apoptotic effects. Western blot analysis was used to evaluate expression of cell-cycle regulatory proteins, such as cyclins and cyclin-dependent kinases (CDKs).

RESULTS

3-OOLA caused G0/G1 phase cell-cycle arrest without inducing apoptosis in NSCLC cells, and Western blot analyses demonstrated down-regulation of cyclin D1, cyclin E and phosphorylated Rb.

CONCLUSION

3-OOLA inhibits cell proliferation of NSCLC cells by inducing cell-cycle arrest at G0/G1 through down-regulation of cyclin D1 and cyclin E.

AP-1 is a component of the transcriptional network regulated by GSK-3 in quiescent cells

BACKGROUND

The protein kinase GSK-3 is constitutively active in quiescent cells in the absence of growth factor signaling. Previously, we identified a set of genes that required GSK-3 to maintain their repression during quiescence. Computational analysis of the upstream sequences of these genes predicted transcription factor binding sites for CREB, NFκB and AP-1. In our previous work, contributions of CREB and NFκB were examined. In the current study, the AP-1 component of the signaling network in quiescent cells was explored.

METHODOLOGY/PRINCIPAL FINDINGS

Using chromatin immunoprecipitation analysis, two AP-1 family members, c-Jun and JunD, bound to predicted upstream regulatory sequences in 8 of the 12 GSK-3-regulated genes. c-Jun was phosphorylated on threonine 239 by GSK-3 in quiescent cells, consistent with previous studies demonstrating inhibition of c-Jun by GSK-3. Inhibition of GSK-3 attenuated this phosphorylation, resulting in the stabilization of c-Jun. The association of c-Jun with its target sequences was increased by growth factor stimulation as well as by direct GSK-3 inhibition. The physiological role for c-Jun was also confirmed by siRNA inhibition of gene induction.

CONCLUSIONS/SIGNIFICANCE

These results indicate that inhibition of c-Jun by GSK-3 contributes to the repression of growth factor-inducible genes in quiescent cells. Together, AP-1, CREB and NFκB form an integrated transcriptional network that is largely responsible for maintaining repression of target genes downstream of GSK-3 signaling.

Krüppel-like factor 4 mediates anti-proliferative effects of progesterone with G₀/G₁ arrest in human endometrial epithelial cells

Activation of the progesterone receptor (PR) inhibits cell proliferation in various reproductive tissues. However, the molecular mechanisms underlying the regulation of cell proliferation by PR remain poorly understood. It is well established that Krüppel-like factor 4 (KLF4), a family of zinc fingercontaining transcription factors, induces cell cycle arrest in epithelial cells. In this study, we investigated whether KLF4 served as a target of PR activation during cell proliferation using human endometrial epithelial cells. PR agonists, progesterone and dienogest, were found to produce a lasting increase in the expression of KLF4 mRNA, followed by a decrease in cyclin D1 mRNA, and inhibit cell proliferation with G₀/G₁ arrest. KLF4 knockdown using KLF4 small interferingRNA abrogated the inhibition of cell proliferation by PR agonists. In addition, forced expression of KLF4 inhibited cyclin D1 promoter transactivation. These results suggest that PR agonists induce KLF4 expression and then inhibit cyclin D1 expression, and consequently inhibit cell proliferation in human endometrial epithelial cells. In terms of human reproductive tissue, KLF4 may be a factor concerning cell cycle, directly responsive to PR activation.

The antimicrobial peptide cecropin A induces caspase-independent cell death in human promyelocytic leukemia cells

Most antimicrobial peptides have been shown to have antitumoral activity. Cecropin A, a linear 37-residue antimicrobial polypeptide produced by the cecropia moth, has exhibited cytotoxicity in various human cancer cell lines and inhibitory effects on tumor growth. In this study, we investigated the apoptosis induced by cecropin A in the promyelocytic cell line HL-60. Treatment of cells with cecropin A was characterized by loss of viability in a dose-dependent manner, lactate dehydrogenase (LDH) leakage, and modest attenuation of lysosomal integrity measured by neutral red assay. An increase of reactive oxygen species (ROS) generation, DNA fragmentation, and phosphatidylserine externalization were quantified following cecropin A exposure at a concentration of 30 microM, whereas cecropin A-induced apoptosis was independent of caspase family members, because the activity of caspase-8 and -9 were irrelevant. Nevertheless, caspase-3 activity showed a significant increase at concentrations of 20-40 microM, but a considerable reduction at 50 microM. Flow cytometry analysis revealed a dissipation of the mitochondrial transmembrane potential (Deltapsi(m)), and the accumulation of cells at sub-G1 phase measured by FACS analysis of propidium iodide (PI) stained nuclei suggested induction of apoptosis. Morphological changes measured by Hoechst 33342 or acridine orange/ethidium bromide staining showed nuclear condensation, corroborating the apoptotic action of cecropin A. Overall, these data indicate that cecropin A is able to induce apoptosis in HL-60 cells through a signaling mechanism mediated by ROS, but independently of caspase activation.

L-arginine attenuates high glucose-accelerated senescence in human umbilical vein endothelial cells

OBJECTIVE

Endothelial dysfunction is a key event in the onset and progression of atherosclerosis associated with diabetes. Increasing cell senescence may lead to endothelial dysfunction and contribute to vascular complications. Therefore, we aimed to elucidate the possible role and mechanism of L-arginine in preventing cell senescence induced by high glucose.

METHODS

HUVECs were respectively cultured under normal control glucose (5.5mM), high glucose (33mM), co-incubation with L-arginine (800microM)and high glucose, and senescence was identified by beta-galactosidase staining, change of cell cycle and telomerase activity. Akt and eNOS activity was analyzed by western blot.

RESULTS

High glucose significantly increased number of beta-galactosidase-positive stained cells, inhibited telomerase activity, increased proportion of cells in the G(0)/G(1) phase and reduced proportion in the S phase, and decreased NO synthesis. L-arginine significantly attenuated these senescent alterations. Furthermore, high glucose induced a decrease in Akt and eNOS activity, and L-arginine prevented the decrease in activity. The PI3K inhibitor LY294002 or eNOS inhibitor L-NAME attenuated anti-senescence effect of L-arginine.

CONCLUSION

L-arginine may have an anti-senescence effect via the PI3K/Akt pathway in HUVECs exposed to high glucose and it might be a therapeutic agent for diabetic vascular complications.

KBH-A42, a histone deacetylase inhibitor, inhibits the growth of doxorubicin-resistant leukemia cells expressing P-glycoprotein

Multidrug resistance mediated by the drug efflux protein, P-glycoprotein (P-gp), is one of the principal mechanisms by which tumor cells escape the cell death induced by chemotherapeutic agents. In our previous study, we demonstrated that KBH-A42 [N-hydroxy-3-(2-oxo-1-(3-phenylpropyl)-1,2,5,6-tetrahydropyridin-3-yl)propanamide], a synthetic histone deacetylase inhibitor, effectively inhibited the growth of several human cancer cell lines. In this study, we attempted to determine whether KBH-A42 was also capable of inhibiting the growth of multidrug-resistant cells. Doxorubicin dose-dependently inhibited the growth of P-gp-negative K562 human leukemia cells, but did not show substantial inhibition on the growth of P-gp-positive K562/ADR cells even at 10 microM, the highest concentration of KBH-A42 used, which increased the acetylation of histones in these leukemia cells, dose-dependently and effectively inhibited the cell growth, regardless of the presence of P-gp in the cells. KBH-A42 mediated G0/G1 cell cycle arrest, probably as the result of the down-regulation of CDK2, CDK4 and CDK6 and the up-regulation of p21WAF1. When the expression of p21WAF1 was ablated by a specific siRNA, the inhibition of cell growth by KBH-A42 was partly reduced in both cell lines. In addition to the cell cycle arrest, KBH-A42 also induced apoptosis in these cells, which was accompanied by the activation of caspases, including caspase-9, caspase-8 and caspase-3. The pan-caspase inhibitor, Z-VAD-fmk, partially blocked the cell death induced by KBH-A42. These results indicate that KBH-A42 induces cell cycle arrest and apoptosis via the up-regulation of p21WAF1 and caspase activation, respectively, regardless of the presence of P-gp in the leukemia cells.

Polyphenol-rich extract from mulberry leaf inhibits vascular smooth muscle cell proliferation involving upregulation of p53 and inhibition of cyclin-dependent kinase

This study was carried out to investigate the impact of polyphenol-rich extract from mulberry leaf on the proliferation of vascular smooth muscle cell (VSMC) and verify its mechanism in vitro. VSMC proliferation is an important pathophysiological process in the development of atherosclerosis, which is the major cause of coronary artery disease (CAD). Polyphenol-rich foods, such as mulberry leaf, have been reported to reduce the risk of CAD. The effect of mulberry leaf extract (MLE) on cell growth was measured by a growth curve assay, on distribution of cells in the cell cycle by flow cytometry, and on cyclin-dependent kinase (CDK) activity and cell-cycle regulatory proteins by Western blot, immunoblotting, and immunoprecipitation analyses. The results showed that MLE induced phosphorylation of p53, promoted expression of p21 and p27, decreased CDK2/4 activity, inhibited phosphorylation of Rb, and thereby blocked the G1 to S transition in the cell cycle.

Effects of cold stress, corticosterone and catecholamines on phagocytosis in mice: differences between resting and activated macrophages

OBJECTIVE

We subjected mice to acute cold stress and studied the effect on phagocytosis by peritoneal macrophages mediated by 3 types of phagocytic receptors: Fcgamma, complement receptors 3 (CR3) and mannose and beta-glucan receptors.

METHODS

Mice were subjected to a cold stress condition (4 degrees C for 4 h), and then peritoneal macrophages were harvested and phagocytosis assays performed in vitro.

RESULTS

We found a striking difference between resting and lipopolysaccharide (LPS)-activated macrophages (by intraperitoneal injection of LPS 4 days before the stress experiment): for resting macrophages cold stress caused a decrease in phagocytosis mediated by Fcgamma or mannose receptors, while for activated macrophages we observed an increase in phagocytosis by the 3 types of receptors. These effects were associated with an increase in plasma concentrations of corticosterone and catecholamines following the cold stress. In order to verify whether these hormone changes could account for the observed effects on phagocytosis, we performed in vitro assays by incubating macrophages harvested from nonstressed animals with these hormones for 4 h at 37 degrees C and measuring their phagocytic capacity. The following experiments were done: (a) with resting (nonactivated) macrophages; (b) with macrophages previously activated in vitro by incubation with LPS; (c) with macrophages previously activated in vivo by intraperitoneal injection of mice with LPS, 4 days before harvesting the cells. We found that for resting macrophages, corticosterone decreased phagocytosis mediated by Fcgamma and mannose and beta-glucan receptors, but catecholamines had no effect. For macrophages activated either in vivo or in vitro, catecholamines caused an increase in phagocytosis (excluding mannose receptors) while corticosterone had no effect.

CONCLUSION

The above findings suggest that stress can regulate phagocytosis in different ways, depending on the kind of phagocytic receptor involved, the level of stress hormones and the physiological state of the macrophages.

Inhibition of proliferation of a hepatoma cell line by fucoxanthin in relation to cell cycle arrest and enhanced gap junctional intercellular communication

Fucoxanthin is one of the most abundant carotenoids found in Undaria pinnatifida and has been shown to inhibit tumor proliferation in vitro. However, the mechanisms underlying the anti-cancer effects of fucoxanthin are unclear. In this study, we hypothesized that fucoxanthin may cause cell cycle arrest and enhance gap junctional intercellular communication (GJIC) in SK-Hep-1 human hepatoma cells. Data revealed that fucoxanthin (1-20microM) strongly and concentration-dependently inhibited the proliferation of SK-Hep-1 cells at 24h of incubation, whereas fucoxanthin facilitated the growth of a murine embryonic hepatic (BNL CL.2) cells at 24h of incubation and only slightly slowed the cell proliferation at 48h. In SK-Hep-1 cells, fucoxanthin caused cell cycle arrest at G0/G1 phase and induced cell apoptosis, as evidenced by increased subG1 cells and induction of DNA strand breaks. Using scrape loading-dye-transfer assay, fucoxanthin was found to significantly enhance GJIC of SK-Hep-1 cells without affecting that of BNL CL.2 cells. In addition, fucoxanthin significantly increased protein and mRNA expressions of connexin 43 (Cx43) and connexin 32 (Cx32) in SK-Hep-1 cells. Moreover, fucoxanthin markedly increased the concentration of intracellular calcium levels in SK-Hep-1 cells. Thus, fucoxanthin is specifically antiproliferative against SK-Hep-1 cells, and the effect is associated with upregulation of Cx32 and Cx43, which enhances GJIC of SK-Hep-1 cells. The enhanced GJIC may be responsible for the increase of the intracellular calcium level, which then causes cell cycle arrest and apoptosis.

Doxorubicin-mediated apoptosis in glioma cells requires NFAT3

Nuclear factor of activated T cells (NFAT), a family of transcription factors, has been implicated in many cellular processes, including some cancers. Here, we characterize, for the first time, the role of NFAT3 in doxorubicin (DOX)-mediated apoptosis, migration, and invasion in SNB19 and U87 glioma cells. This study demonstrates that the specific knockdown of NFAT3 results in a dramatic inhibition of the apoptotic effect induced by DOX and favors cell survival. Inhibition of NFAT3 activation by shNFAT3 (shNF3) significantly downregulated tumor necrosis factor (TNF)-alpha induction, its receptor TNFR1, caspase 10, caspase 3, and poly (ADP-ribose) polymerase, abrogating DOX-mediated apoptosis in glioma cells. DOX treatment resulted in NFAT3 translocation to the nucleus. Similarly, shNF3 treatment in SNB19 and U87 cells reversed DOX-induced inhibition of cell migration and invasion, as determined by wound healing and matrigel invasion assays. Taken together, these results indicate that NFAT3 is a prerequisite for the induction of DOX-mediated apoptosis in glioma cells.

Apoptotic effect of cyclosporin a and dexamethasone in malignant cells of patients with B-chronic lymphocytic leukemia

B-chronic lymphocytic leukemia (B-CLL) is a malignant disorder characterized by the accumulation of the leukemic cells in the G0-G1 phase of the cell cycle and expressing high levels of the anti-apoptotic protein Bcl-2. Since we observed that the treatment of autoimmune complications with Cyclosporine A (CsA) determined in some CLL patients an improvement not only of the autoimmune phenomena, but also of the leukemic process, we evaluated the in vitro cytotoxicity of CsA as compared to Dexamethasone (Dex) on leukemic cells. Leukemic cells obtained from 32 B-CLL patients showed a heterogeneous pattern of spontaneous apoptosis at 24 h interval and this pattern permitted to identify: Group 1 (14/32) with high (>20%) apoptotic rate and Group 2 (18/32) with low cell death. CsA and Dex increased cell death in both groups with a different timing by an apoptotic mechanism that does not involve Bcl-2. Furthermore, in Group 2, CsA-induced apoptosis was significant higher than that observed with Dex both at 4 and 24 h. We suggest that, in B-CLL, CsA has a significant pro-apoptotic activity manifested also in patients with low spontaneous apoptosis. Our observations might be taken into account to consider new therapeutic strategies in B-CLL.

Cocaine induces alterations in mitochondrial membrane potential and dual cell cycle arrest in rat c6 astroglioma cells

Investigations with astroglial cells carry more prominence in drug abuse studies. However, due to earlier perception that astroglial cells were only passive bystanders in neural signal transmission, not many investigations were conducted on the toxicity of various abused drugs, like cocaine. The present study was aimed to discern the effect of cocaine on rat astroglioma cells and analyzed qualitatively for morphological features as well as vacuolation by phase contrast microscope, quantitatively for cytotoxicity, mitochondrial membrane potential by rhodamine- 123 fluorometric assay, and cell cycle analysis by flow cytometry. Based on population cell doubling time studies, glial cells were grown in 10% FBS in RPMI 1640 medium and treated with cocaine for 24 or 48 h. Microscopic assessments clearly demonstrated massive vacuolation and significant disruption at general architecture of glial cell morphology with cocaine. Chronic cocaine treatment (24 or 48 h) caused significant loss of cell viability. The sublethal dose of cocaine was found to be 4.307 and 3.794 mM at 24 and 48 h, respectively. Cocaine reduced the mitochondrial membrane potential in a dose dependent manner with ED(50) of 4 mM after 24 h. Cell cycle analysis suggested dual inhibition at G0/G1 and G2/M phases after 24 and 48 h, respectively. In summary, our findings suggest that cocaine toxicity was due to loss of mitochondrial membrane potential, vacuolation, and dual inhibition of cell cycle phases. These results may shed light in understanding the onset of some early key events in cocaine-induced toxicity in glial cells.

Overexpression of catalase delays G0/G1- to S-phase transition during cell cycle progression in mouse aortic endothelial cells

Although it is understood that hydrogen peroxide (H(2)O(2)) promotes cellular proliferation, little is known about its role in endothelial cell cycle progression. To assess the regulatory role of endogenously produced H(2)O(2) in cell cycle progression, we studied the cell cycle progression in mouse aortic endothelial cells (MAECs) obtained from mice overexpressing a human catalase transgene (hCatTg), which destroys H(2)O(2). The hCatTg MAECs displayed a prolonged doubling time compared to wild-type controls (44.0 +/- 4.7 h versus 28.6 +/- 0.8 h, p<0.05), consistent with a diminished growth rate and H(2)O(2) release. Incubation with aminotriazole, a catalase inhibitor, prevented the observed diminished growth rate in hCatTg MAECs. Inhibition of catalase activity with aminotriazole abrogated catalase overexpression-induced antiproliferative action. Flow cytometry analysis indicated that the prolonged doubling time was principally due to an extended G(0)/G(1) phase in hCatTg MAECs compared to the wild-type cells (25.0 +/- 0.9 h versus 15.9 +/- 1.4 h, p< 0.05). The hCatTg MAECs also exhibited decreased activities of the cyclin-dependent kinase (Cdk) complexes responsible for G(0)/G(1)- to S-phase transition in the cell cycle, including the cyclin D-Cdk4 and cyclin E-Cdk2 complexes. Moreover, the reduction in cyclin-Cdk activities in hCatTg MAECs was accompanied by increased protein levels of two Cdk inhibitors, p21 and p27, which inhibit the Cdk activity required for the G(0)/G(1)- to S-phase transition. Knockdown of p21 and/or p27 attenuated the antiproliferative effect of catalase overexpression in MAECs. These results, together with the fact that catalase is an H(2)O(2) scavenger, suggest that endogenously produced H(2)O(2) mediates MAEC proliferation by fostering the transition from G(0)/G(1) to S phase.

The centrosome protein NEDD1 as a potential pharmacological target to induce cell cycle arrest

BACKGROUND

NEDD1 is a protein that binds to the gamma-tubulin ring complex, a multiprotein complex at the centrosome and at the mitotic spindle that mediates the nucleation of microtubules.

RESULTS

We show that NEDD1 is expressed at comparable levels in a variety of tumor-derived cell lines and untransformed cells. We demonstrate that silencing of NEDD1 expression by treatment with siRNA has differential effects on cells, depending on their status of p53 expression: p53-positive cells arrest in G1, whereas p53-negative cells arrest in mitosis with predominantly aberrant monopolar spindles. However, both p53-positive and -negative cells arrest in mitosis if treated with low doses of siRNA against NEDD1 combined with low doses of the inhibitor BI2536 against the mitotic kinase Plk1. Simultaneous reduction of NEDD1 levels and inhibition of Plk1 act in a synergistic manner, by potentiating the anti-mitotic activity of each treatment.

CONCLUSION

We propose that NEDD1 may be a promising target for controlling cell proliferation, in particular if targeted in combination with Plk1 inhibitors.