Analysis of DNA content and cyclin protein expression in studies of DNA ploidy, growth fraction, lymphocyte stimulation, and the cell cycle

Lipopolysaccharide treatment arrests the cell cycle of BV-2 microglial cells in G₁ phase and protects them from UV light-induced apoptosis

We previously reported that an optimal dose of lipopolysaccharide (LPS) markedly extends the lifespan of murine primary-cultured microglia by suppressing cell death pathways. In this study, we investigated the effects of LPS pretreatment on UV light-induced apoptosis of cells from the microglial cell line BV-2. More than half of BV-2 cells were apoptotic, and procaspase-3 was cleaved into its active form at 3 h of UV irradiation. In contrast, in BV-2 cells treated with LPS for 24 h, UV irradiation caused neither apoptosis nor procaspase-3 cleavage. LPS treatment arrested the cell cycle in G1 phase and upregulated cyclin-dependent kinase inhibitor p21(Waf1/Cip1) and growth arrest and DNA damage-inducible (GADD) 45α in BV-2 cells. When p21(Waf1/Cip1) and GADD45α were knocked down by small interfering RNA, procaspase-3 was cleaved into its active form to induce apoptosis. Our findings suggest that LPS inhibits UV-induced apoptosis in BV-2 cells through arrest of the cell cycle in G1 phase by upregulation of p21(Waf1/Cip1) and GADD45α. Excessive activation of microglia may play a critical role in the exacerbation of neurodegeneration, therefore, normalizing the precise regulation of apoptosis may be a new strategy to prevent the deterioration caused by neurodegenerative disorders.

Pepsin promotes proliferation of laryngeal and pharyngeal epithelial cells

OBJECTIVE/HYPOTHESIS

Laryngopharyngeal reflux (LPR) is thought to be a significant risk factor for laryngeal squamous cell carcinoma (SCC), but causality has never been proven. It is accepted that chronic reflux into the esophagus can induce metaplastic changes in esophageal mucosa with subsequent increased risk of esophageal adenocarcinoma, but no similar associations have been established for LPR and laryngopharyngeal SCC. The objective of this study was to test the hypothesis that reflux of pepsin into the laryngopharynx can promote carcinogenesis.

STUDY DESIGN

Translational research study.

METHODS

Normal human laryngeal primary epithelial cell cultures and hypopharyngeal FaDu SCC cells were exposed to human pepsin and analyzed by Human Cancer PathwayFinder and miRNA Superarrays, flow cytometry, and Western blot to determine the effect of pepsin on carcinogenesis. Laryngeal biopsy specimens taken from cancer patients and normal control subjects were analyzed for the presence of pepsin by Western blot.

RESULTS

Microarray analysis demonstrated that pepsin significantly altered the expression of 27 genes implicated in carcinogenesis and also affected the expression of 22 microRNAs known to be altered in human head and neck cancers. Pepsin increased proliferation in both FaDu SCC cells and cultured normal laryngeal epithelial primary cells by increasing S phase distribution on flow cytometry analysis in a time- and dose-dependent manner. Furthermore, pepsin was detected in 60% (3/5) human laryngeal cancer biopsies, absent in all (0/5) normal control specimens.

CONCLUSIONS

These data support a role for refluxed pepsin in the promotion of epithelial proliferation and carcinogenesis of the larynx and pharynx.

Phagocytotic competence of differentiated U937 cells for colloidal drug delivery systems in immune cells

Drug delivery into immune cells has high potential for the treatment of all kinds of inflammation, allowing a target-oriented transport of active agents. The advantage of this local drug release is the prevention of negative effects of systemic applications and low-dose application. Thereby, the phagocytotic capability of mature phagocytes is essential. Microparticles can be loaded with immune regulatory substances to control and terminate inflammatory processes. In this study, silica microparticles were co-incubated with monocyte/macrophage-like cells in order to determine phagocytotic particle uptake. The phorbol ester-triggered differentiation was proven by the increased expression of surface markers as phosphatidylserine and CD14 and enhanced lysosomal activity. Particle/cell co-incubation results in cell surface attachment followed by phagocytosis. Phagolysosomal ingestion could be determined by co-localization using fluorescence staining techniques. In contrast, no particle interaction with undifferentiated cells could be found. Under phagolysosomal conditions, multilayer degradation within 22 h could be shown, indicating a valuable carrier basis design for the time-controlled delivery of active agents. Subsequently, it can be assumed that a higher differentiation degree allows phagocytosis of microparticles, providing drug delivery into immuno-active cells.

Influence of layer-by-layer (LbL) assembled CaCO(3)-carriers on macrophage signaling cascades

Numerous drawbacks in the current medical treatment of chronic inflammations still require the design of sensitive and gentle methods without side effects. Layer-by-layer (LbL) coated microcarriers loaded with a cocktail of anti-inflammatory substances are supposed to be a new challenge for the medical treatment of immunoreactive cells such as macrophages and polymorphonuclear leukocytes (PMN). Nevertheless, microcarrier application requires biocompatibility of the system itself. Therefore, the aim of this study was to investigate microcarrier CaCO(3) systems LbL coated with biopolymers and a lipid bilayer, respectively, regarding the maintenance of the release of pro-inflammatory cytokines as TNFα and IL1β at normal levels. Only marginal increases after microcarrier interaction were allowed. The required microcarrier optimization results in the maximum use of a carrier/cell ratio of 1:1 for biopolymer-coated carriers and a carrier/cell ratio up to 5:1 for lipid-bilayer-coated carriers during the coincubation with macrophage-like cells. Low formation of reactive oxygen species (ROS) could not be maintained by either reduced carrier/cell ratios or by a surface lipid bilayer.

Cytogenetic characterization and H-ras associated transformation of immortalized human mammary epithelial cells

INTRODUCTION

Immortalization is a key step in malignant transformation, but immortalization alone is insufficient for transformation. Human mammary epithelial cell (HMEC) transformation is a complex process that requires additional genetic changes beyond immortalization and can be accomplished in vitro by accumulation of genetic changes and expression of H-ras.

METHODS

HMEC were immortalized by serial passaging and transduction with the catalytic subunit of the human telomerase gene (hTERT). The immortalized cells were passaged in vitro and studied by a combination of G-banding and Spectral Karyotyping (SKY). H-ras transduced, hTERT immortalized cells were cloned in soft agar and injected into nude mice. Extensive analysis was performed on the tumors that developed in nude mice, including immunohistochemistry and western blotting.

RESULTS

Immortal HMEC alone were not tumorigenic in gamma-irradiated nude mice and could not grow in soft agar. Late passage hTERT immortalized HMEC from a donor transduced with a retroviral vector containing the mutant, autoactive, human H-ras61L gene acquired anchorage independent growth properties and the capacity for tumorigenic growth in vivo. The tumors that developed in the nude mice were poorly differentiated epithelial carcinomas that continued to overexpress ras. These cells were resistant to doxorubicin mediated G1/S phase arrest but were sensitive to treatment with a farnesyltransferase inhibitor.

CONCLUSION

Some of the cytogenetic changes are similar to what is observed in premalignant and malignant breast lesions. Despite these changes, late passage immortal HMEC are not tumorigenic and could only be transformed with overexpression of a mutant H-ras oncogene.

Cytotoxic and apoptogenic effect of tea (Camellia sinensis var. assamica) root extract (TRE) and two of its steroidal saponins TS1 and TS2 on human leukemic cell lines K562 and U937 and on cells of CML and ALL patients

The anticancer activity of di- and tri-terpenes and other polyphenolic compounds present in tea is already reported. We evaluated the cytotoxic and apoptogenic effect of tea root extract (TRE) and two of its steroidal saponins named as TS1 and TS2, on human cell lines and on cells from leukemic patients. It was found that TRE, TS1 and TS2 significantly decreased cell count and that TRE caused apoptosis, as confirmed morphologically by confocal microscopy and by flow-cytometric analysis using Annexin-V FITC and propidium iodide (PI). Cell count and MTT assay in normal white blood cells (WBC) of healthy volunteers revealed that TRE produced insignificant reduction in cell count and cytotoxicity.

Cholesterol is essential for mitosis progression and its deficiency induces polyploid cell formation

As an essential component of mammalian cell membranes, cells require cholesterol for proliferation, which is either obtained from plasma lipoproteins or synthesized intracellularly from acetyl-CoA. In addition to cholesterol, other non-sterol mevalonate derivatives are necessary for DNA synthesis, such as the phosphorylated forms of isopentane, farnesol, geranylgeraniol, and dolichol. The aim of the present study was to elucidate the role of cholesterol in mitosis. For this, human leukemia cells (HL-60) were incubated in a cholesterol-free medium and treated with SKF 104976, which inhibits cholesterol biosynthesis by blocking sterol 14alpha-demethylase, and the expression of relevant cyclins in the different phases of the cell cycle was analyzed by flow cytometry. Prolonged cholesterol starvation induced the inhibition of cytokinesis and the formation of polyploid cells, which were multinucleated and had mitotic aberrations. Supplementing the medium with cholesterol completely abolished these effects, demonstrating they were specifically due to cholesterol deficiency. This is the first evidence that cholesterol is essential for mitosis completion and that, in the absence of cholesterol, the cells fail to undergo cytokinesis, entered G1 phase at higher DNA ploidy (tetraploidy), and then progressed through S (rereplication) into G2, generating polyploid cells.

Inhibition of acute myeloid leukemia cell growth by mono-specific and bi-specific anti-CD33 × anti-CD64 antibodies

Bi-specific anti-CD33 x anti-CD64 antibodies (BsAb) mediated more potent and longer-lasting inhibition of proliferation of human leukemia cell lines and primary acute myeloid leukemia (AML) samples compared to mono-specific anti-CD33 mAb. There were no differences between these two antibodies in cellular internalization over time. The inhibitory effect of BsAb was mimicked by a mouse IgG2a subclass mono-specific anti-CD33 mAb. These findings indicate that enhanced inhibition of proliferation was caused by simultaneous ligation of both CD33 and CD64 molecules. We conclude that inhibition of leukemia cell growth initiated by BsAb during prolonged exposure may have therapeutic value for the treatment of AML.

The inhibitory effect of anti-CD33 monoclonal antibodies on AML cell growth correlates with Syk and/or ZAP-70 expression

OBJECTIVES

Acute myeloid leukemia (AML) cells express the cell surface antigen CD33 that can function as a downregulator of cell growth, mediating growth arrest and apoptosis. The protein kinase Syk is an essential element in several cascades coupling certain antigen receptors to cell responses. Recently we reported that CD33 recruits Syk for its signaling in AML cell lines. In this study, we further investigated the mechanism(s) of Syk engagement in CD33 signaling in primary AML samples.

METHODS

We investigated 25 primary AML samples for their proliferative response (3H-thymidine incorporation) and biochemical changes (Western blot analysis) to anti-CD33 mAb treatment.

RESULTS

Proliferation studies demonstrated that 14 (56%) of AML samples were responsive (R) while 11 (44%) were nonresponsive (n-R) to inhibitory antibody activity. Seven of 25 AML samples (28%) expressed undetectable levels of Syk. However, cells from two of these patients expressed the ZAP-70 protein kinase. In Syk/ZAP-70(+) samples, CD33 ligation inhibited proliferation in 70% of cases, while none of the Syk/ZAP-70(-) samples was responsive. There were significant biochemical differences between responder and nonresponder AML populations. In responder samples, CD33 ligation induced phosphorylation of CD33 andSyk and formation of the CD33/Syk complex. In nonresponder samples, CD33 was not phosphorylated, and Syk was in complex with the SHP-1 protein phosphatase constitutively.

CONCLUSIONS

Syk is an important component in the regulation of proliferation in AML cells. The differential response of AML cells to CD33 ligation is associated with the level of the Syk expression.

Identification of 6-methylsulfinylhexyl isothiocyanate as an apoptosis-inducing component in wasabi

The ethanol extract from Japanese horseradish wasabi was found to inhibit cell proliferation in human monoblastic leukemia U937 cells by inducing apoptotic cell death. Separation by methods including silica gel chromatography and preparative HPLC gave an active compound, which was identified as 6-methylsulfinylhexyl isothiocyanate (6-HITC). Several lines of evidence indicated that 6-HITC induced apoptosis in U937 cells and human stomach cancer MKN45 cells. Thus, 6-HITC is potentially useful as a natural anti-cancer agent.

Identification of licocoumarone as an apoptosis-inducing component in licorice

The 70% methanol soluble fraction from a licorice acetone extract was found to inhibit cell proliferation in human monoblastic leukemia U937 cells by inducing apoptosis. Separation by the methods including preparative HPLC provided us with an active compound, which was identified as licocoumarone. Several lines of evidence indicated that licocoumarone induced apoptosis in U937 cells. Thus, licocoumarone is suggested to be potentially useful as a natural anti-cancer agent.

Apoptosis induction by lectin isolated from the mushroom Boletopsis leucomelas in U937 cells

A 15-kDa lectin was isolated from the edible mushroom Kurokawa by affinity chromatography using N,N'-diacetylchitobiose-Sepharose 4B. The results of microsequencing analysis indicated that the lectin has a partial amino acid sequence similar to the mushroom lectin, Agaricus bisporus agglutinin (ABA). We found that the Kurokawa lectin inhibited proliferation of human monoblastic leukemia U937 cells dose-dependently. Several lines of evidence indicated that this inhibition was due to its apoptosis induction. We observed that the lectin induced apoptotic bodies formation, chromatin condensation, and DNA ladder formation, features of apoptosis. The DNA ladder formation was inhibited by a general inhibitor of caspases, which are known to play essential roles in apoptosis. In contrast, ABA did not have cell growth-inhibiting or apoptosis-inducing activities. Thus, the Kurokawa lectin is the first mushroom lectin with apoptosis-inducing activity.

NS1- and minute virus of mice-induced cell cycle arrest: involvement of p53 and p21(cip1)

The nonstructural protein NS1 of the autonomous parvovirus minute virus of mice (MVMp) is cytolytic when expressed in transformed cells. Before causing extensive cell lysis, NS1 induces a multistep cell cycle arrest in G(1), S, and G(2), well reproducing the arrest in S and G(2) observed upon MVMp infection. In this work we investigated the molecular mechanisms of growth inhibition mediated by NS1 and MVMp. We show that NS1-mediated cell cycle arrest correlates with the accumulation of the cyclin-dependent kinase (Cdk) inhibitor p21(cip1) associated with both the cyclin A/Cdk and cyclin E/Cdk2 complexes but in the absence of accumulation of p53, a potent transcriptional activator of p21(cip1). By comparison, MVMp infection induced the accumulation of both p53 and p21(cip1). We demonstrate that p53 plays an essential role in the MVMp-induced cell cycle arrest in both S and G(2) by using p53 wild-type (+/+) and null (-/-) cells. Furthermore, only the G(2) arrest was abrogated in p21(cip1) null (-/-) cells. Together these results show that the MVMp-induced cell cycle arrest in S is p53 dependent but p21(cip1) independent, whereas the arrest in G(2) depends on both p53 and its downstream effector p21(cip1). They also suggest that induction of p21(cip1) by the viral protein NS1 arrests cells in G(2) through inhibition of cyclin A-dependent kinase activity.

Blockade of the extracellular signal-regulated kinase pathway induces marked G1 cell cycle arrest and apoptosis in tumor cells in which the pathway is constitutively activated: up-regulation of p27(Kip1)

Constitutive activation of the ERK pathway is associated with the neoplastic phenotype of a relatively large number of human tumor cells. Blockade of the ERK pathway by treatment with PD98059, a specific inhibitor of mitogen-activated protein (MAP) kinase/ERK kinase (MEK), completely suppressed the growth of tumor cells in which the pathway is constitutively activated (RPMI-SE and HT1080 cells). Consistent with its prominent antiproliferative effect, PD98059 induced a remarkable G(1) cell cycle arrest, followed by a modest apoptotic response, in these tumor cells. Selective up-regulation of p27(Kip1) was observed after PD98059 treatment of RPMI-SE and HT1080 cells. Overexpression in RPMI-SE cells of either a kinase-negative form of MEK1 or wild-type MAP kinase phosphatase-3 also induced up-regulation of p27(Kip1). The up-regulation of p27(Kip1) correlated with increased association of p27(Kip1) with cyclin E-cyclin-dependent kinase (CDK) 2 complexes, a concomitant inhibition of cyclin E-CDK2 kinase activity, and a consequent decrease in the phosphorylation state of retinoblastoma protein, which would culminate in the marked G(1) cell cycle arrest observed in these tumor cells. These results suggest that the complete growth suppression that follows specific blockade of the ERK pathway in tumor cells in which the pathway is constitutively activated is mediated by up-regulation of p27(Kip1).

Recent developments in flow cytometry

Flow cytometry has experienced considerable expansion of available parameters during the last years. Various new techniques that allow the direct analysis of antigen-specific lymphocytes by direct labeling with antigen or according to functional parameters following in vitro antigen stimulation will have enormous impact on immunological research, diagnosis, and therapy. This article concentrates on the basic principles and applications of these important technological developments in flow cytometry and focuses on the analysis of specific lymphocytes.

Role of caspases and NF-kappaB signaling in hydrogen peroxide- and superoxide-induced hepatocyte apoptosis

Reactive oxygen intermediates (ROI) have been implicated as mediators of hepatocyte death resulting from a variety of forms of liver injury. To delineate the mechanisms that underlie ROI-induced apoptosis, the roles of caspase activation and nuclear factor-kappaB (NF-kappaB) signaling were determined in the rat hepatocyte cell line RALA255-10G after treatment with H(2)O(2) or the superoxide generator menadione. By 8 h, H(2)O(2) and menadione caused 26% and 33% cell death, respectively. Death from both ROI occurred by apoptosis as indicated by morphology under fluorescence microscopy, the induction of caspase activation and DNA fragmentation, and the cleavage of poly(ADP-ribose) polymerase. Despite the presence of caspase activation in both forms of apoptosis, caspase inhibition blocked H(2)O(2)- but not menadione-induced apoptosis. In contrast, inhibition of NF-kappaB activation decreased cell death from both ROI. Different ROI, therefore, induce distinct apoptotic pathways in RALA hepatocytes that are both caspase dependent and independent. In contrast to the known protective effect of NF-kappaB activation in tumor necrosis factor-alpha-induced hepatocyte apoptosis, NF-kappaB promotes hepatocellular death from ROI in these cells.

Cytokine response gene 6 induces p21 and regulates both cell growth and arrest

Cytokine response gene #6 (CR6), cloned from interleukin 2-stimulated T lymphocytes, is homologous to GADD45 and MyD118, genes which promote cell cycle arrest and apoptosis. To determine how this gene family could possibly mediate both cell survival/proliferation and cell cycle arrest/death, transfectants were generated so that the genes could be expressed ectopically, independently from their normal inducing agents. In cycling retinoblastoma protein-negative (pRb-) cells, ectopic CR6 expression blocked G2/M transition, but did not prevent G1/S transition so that endoreduplication resulted. By comparison, when CR6, GADD45, and MyD118 genes were expressed ectopically in proliferating pRb+ cells, either G1/S or G2/M transition was effectively blocked, so that there was no endoreduplication. Consistent with these findings, in proliferating pRb-cells, ectopic expression of CR6 promoted the expression of both G1 and G2/M cyclins. By comparison, in pRb+ cells, the expression of G1 cyclins was increased, while expression of the mitotic cyclins was decreased. However, in pRb+ cells, cyclin-dependent kinase activities associated with both G1 and G2/M cyclins were decreased. Moreover, ectopic expression of all three genes resulted in the expression of the CKI, p21, both in pRb- and pRb+ cells. The physiologic induction of CR6 expression by IL2 in quiescent normal human T cells occurs transiently in the first half of G1, coordinately with the expression of p21. Therefore, this gene family regulates G1 and G2, and promotes either cell growth or arrest by a common mechanism.

Ceramide induces caspase-independent apoptosis in rat hepatocytes sensitized by inhibition of RNA synthesis

Ceramide has been implicated as a second messenger in intracellular signaling pathways leading to apoptosis in nonhepatic cells. To determine whether ceramide can mediate hepatocyte apoptosis, the cytotoxicity of ceramide was determined in rat hepatocytes. The rat hepatocyte cell line, RALA255-10G, and primary rat hepatocytes were completely resistant to toxicity from 10 to 100 micromol/L C2 ceramide. Resistance was not the result of a failure to take up ceramide, because ceramide treatment did cause nuclear factor-kappaB (NF-kappaB) activation. Because ceramide may mediate cell death from tumor necrosis factor alpha (TNF-alpha), the ability of RNA synthesis inhibition and NF-kappaB inactivation to sensitize hepatocytes to ceramide toxicity was examined. RALA hepatocytes were sensitized to ceramide toxicity by coadministration of actinomycin D (ActD). Cell death occurred by apoptosis as determined by the presence of morphological evidence of apoptosis, caspase activation, poly(ADP-ribose) polymerase (PARP) degradation, and DNA hypoploidy. Despite the induction of apoptosis associated with caspase activation, cell death from ActD/ceramide was not blocked by caspase inhibition. Inhibition of NF-kappaB activation also sensitized RALA hepatocytes to ceramide toxicity, but to a lesser extent than for TNF-alpha. Thus, unlike many nonhepatic cell types, rat hepatocytes are resistant to cell death from ceramide because of the transcriptionally dependent up-regulation of a protective gene(s). The ability of ActD and NF-kappaB inactivation to sensitize RALA hepatocytes to ceramide toxicity suggests that ceramide may act as a downstream mediator of TNF-alpha toxicity.

Involvement of p21 in the PKC-induced regulation of the G2/M cell cycle transition

Activation of protein kinase C (PKC) inhibits cell cycle progression at the G1/S and G2/M transitions. We found that phorbol 12-myristate 13-acetate (PMA) induced upregulation of p21, not only in MCF-7 cells arrested in the G1 phase as previously shown, but also in cells delayed in the G2 phase. This increase in p21 in cells accumulated in the G1 and G2/M phases of the cell cycle after PMA treatment was inhibited by the PKC inhibitor GF109203X. This indicates that PKC activity is required for PMA-induced p21 upregulation and cell cycle arrest in the G1 and G2/M phases of the cell cycle. To further assess the role of p21 in the PKC-induced G2/M cell cycle arrest independently of its G1 arrest, we used aphidicolin-synchronised MCF-7 cells. Our results show that, in parallel with the inhibition of cdc2 activity, PMA addition enhanced the associations between p21 and either cyclin B or cdc2. Furthermore, we found that after PMA treatment p21 was able to associate with the active Tyr-15 dephosphorylated form of cdc2, but this complex was devoid of kinase activity indicating that p21 may play a role in inhibition of cdc2 induced by PMA. Taken together, these observations provide evidence that p21 is involved in integrating the PKC signaling pathway to the cell cycle machinery at the G2/M cell cycle checkpoint.

Phosphorylation of retinoblastoma susceptibility gene protein assayed in individual lymphocytes during their mitogenic stimulation

Phosphorylation of the protein encoded by retinoblastoma susceptibility gene (pRb) is the key event of the cell cycle committing the cell to enter S phase and also required for progression through S and G2. We describe a new methodology to monitor pRb phosphorylation in individual cells and correlate it with the cell cycle position. Specifically, pRb phosphorylation in human lymphocytes was assayed immunocytochemically using mAb which recognizes underphosphorylated pRb (pRbP-) conjugated with a fluorochrome of one color combined with mAb which reacts with pRb regardless of its phosphorylation (total pRb; pRbT) tagged with another color fluorochrome. DNA was stained with still another color fluorochrome and cell fluorescence was measured by multiparameter flow cytometry. Specificity of anti-pRbP- mAb was confirmed by preincubation of the permeabilized cells with phosphatase. Analysis of pRbP- or a ratio of pRbP-/pRbT revealed that pRb was underphosphorylated in over 98% of the nonstimulated lymphocytes. The proportion of cells with underphosphorylated pRb dropped to 20% between 3 and 8 h after addition of the mitogen phytohemagglutinin (PHA). Phosphorylation of pRb within a cell was rapid and complete since reactivity of individual lymphocytes with anti-pRbP-mAb was lost abruptly rather than step-wise during stimulation. Phosphorylation of pRb coincided with the appearance of cyclin D3, which was induced 3 h and peaked 12 h after addition of PHA. The nonspecific protein kinase inhibitor staurosporine at a concentration known to arrest lymphocytes in G1 but not to interfere with the induction of cyclin D3 (20 nM) prevented pRb phosphorylation. The present assay can be applied for screening antitumor drugs targeting CDKs and be useful for monitoring pRb phosphorylation in human tumors, the feature of a possible prognostic value in oncology.