Alterations in membrane lipid dynamics of leukemic cells undergoing growth arrest and differentiation: dependency on the inducing agent

Fresh Garlic Extract Induces Growth Arrest and Morphological Differentiation of MCF7 Breast Cancer Cells

Consumption of diets rich in fruits and vegetables is often associated with a reduced risk of developing cancer, particularly breast cancer. Considering that 1 in 8 women in the United States will develop breast cancer in the course of her lifetime, dietary manipulation could have a major impact on the incidence of breast cancer. We report here that fresh extracts of garlic (not boiled) arrested the growth and altered the morphology of MCF7 breast cancer cells. Deregulated levels of E-cadherin, cytokeratin8/18, and β-catenin correlated with the altered phenotype. We propose that early down-regulation of cyclin D1, reduced phosphorylation of ERK1, and increased phosphorylation of eIF2-α triggered the phenotypical changes. Reduced expression of hsp27 and sam68 and elevated levels of Rb and p21 further contributed to the sustained growth reduction. These findings provide a better understanding of the cellular responses to dietary supplements and provide potential options to treat breast cancer.

Knockdown of hTERT alters biophysical properties of K562 cells resulting in decreased migration rate in vitro

It has been shown that 90% of tumors, including hematological malignant tumors and leukemia, have much higher levels of telomerase expression than normal cells. To investigate the effect of telomerase on leukemia cells, we transfected K562, a human erythroleukemia cell line with an antisense-hTERT (human telomerase reverse transcriptase) cDNA vector, and examined the biological and biophysical properties of the stably transfected cells (referred to as KAT). Un-transfected cells (K562) and cells transfected with the empty vector (referred to as KC) were used as controls. Cell growth curve and (3)H-TdR test showed that the growth rate and DNA synthesis of KAT decreased compared with those of K562 and KC cells. Apoptosis and cell cycle distribution in KAT cells under normal culture condition were similar to those of K562 and KC cells, but changed after serum deprivation. KAT cells had significantly different biophysical characteristics from K562 and KC in terms of cell electrophoresis, membrane fluidity, membrane fluidity, and viscoelasticity. Furthermore, the transendothelial migration rate of KAT was much lower than those of K562 and KC cells. Confocal microscopy showed that KAT cells had higher F-actin content, suggesting the reorganization of cytoskeleton. Flow cytometry analysis revealed a lowered intracellular calcium concentration and CD71 expression, explaining the high F-actin content in KAT cells. In conclusion, we found that the knockdown of hTERT in K562 cells changed their cytoskeleton and biophysical features, and reduced the cell migration.

The interferon-inducible protein viperin inhibits influenza virus release by perturbing lipid rafts

Interferons initiate the host antiviral response by inducing a number of genes, most with no defined antiviral function. Here we show that the interferon-induced protein viperin inhibits influenza A virus release from the plasma membrane of infected cells. Viperin expression altered plasma membrane fluidity by affecting the formation of lipid rafts, which are detergent-resistant membrane microdomains known to be the sites of influenza virus budding. Intracellular interaction of viperin with farnesyl diphosphate synthase (FPPS), an enzyme essential for isoprenoid biosynthesis, decreased the activity of the enzyme. Overexpression of FPPS reversed viperin-mediated inhibition of virus production and restored normal membrane fluidity, and reduction of FPPS levels by siRNA inhibited virus release and replication, indicating that the FPPS interaction underlies viperin's effects. These findings suggest that targeting the release stage of the life cycle may affect the replication of many enveloped viruses. Furthermore, FPPS may be an attractive target for antiviral therapy.

Tumor-derived factors impaired motility and immune functions of dendritic cells through derangement of biophysical characteristics and reorganization of cytoskeleton

The generation and progress of tumors are accompanied with a marked suppression of human immune system. To explore the mechanisms by which tumors escape from immune recognition, we studied the influences of tumor microenvironment on differentiation of dendritic cells (DCs), which play an important role in tumor immunology, by biophysical and immunological methods. It was found that the cytokines derived from tumors caused an increase in osmotic fragility and a decrease in membrane fluidity of DCs, disordering and elevated expression levels of cytoskeleton, and changes of the gene transcriptional levels and energy status of the cells. Moreover, IL-12 production and the expression levels of some surface-marker molecules were also suppressed. These changes led to impaired capabilities of antigen uptake, cell motility and naïve T cell activation; the abnormal biophysical characteristics of DCs may be one aspect of the immune escape mechanism of tumor. These results provide insights into the importance of the reconstruction of tumor microenvironment for immunotherapy based on the anti-cancer activities of DCs.

Gallium-Inducible Transferrin-Independent Iron Acquisition Is a Property of Many Cell Types: Possible Role of Alterations in the Plasma Membrane

BACKGROUND

We have previously shown that human myeloid cell types can acquire large amounts of iron (Fe)3+ from low-molecular-weight chelates by a process that is independent of adenosine triphosphate and dramatically increased by gallium (Ga) and other multivalent cationic metals.

METHODS

To provide further insight into the mechanism responsible and its relevance to other cellular systems, we investigated Fe acquisition from nitrilotriacetic acid (NTA) by several myeloid and nonmyeloid cell lines in the presence and absence of Ga.

RESULTS

Most nonmyeloid cells examined exhibited similar ability to acquire Fe from NTA. Ga increased the apparent maximum velocity (Vmax), with minimal changes in apparent Michaelis constant (Km), of all cell lines. Both erythrocytes and erythrocyte ghosts acquired Fe from NTA, which increased with Ga exposure, analogous to nucleated cells. However, liposomes made from phospholipids did not exhibit Ga-inducible Fe association. Enzymes that modify surface proteins and carbohydrates did not alter HL-60 cell Fe acquisition. Modifying HL-60 membrane fatty acid content had only a minimal effect. Ga exposure did not change membrane potential or fluidity. However, electron microscopy suggested that Ga alters plasma membrane physical properties.

CONCLUSION

Multivalent cations appear to induce changes in cell membranes that may alter their interaction with Fe3+ and probably other multivalent cations.

Effect of tumor necrosis factor-alpha and interferon-gamma on intestinal P-glycoprotein expression, activity, and localization in Caco-2 cells

The P-glycoprotein (Pgp), a drug efflux pump, is expressed in intestinal epithelial cells, where it constitutes a barrier against xenobiotics. In inflammatory bowel disease, a dysregulation in the production of tumor necrosis factor (TNF)alpha and interferon (IFN)gamma, and an alteration of Pgp expression and activity have been reported. The aim of this study was to investigate the effects of TNF alpha and IFN gamma on intestinal Pgp expression, activity, and localization in Caco-2 cells grown on filters. TNF alpha induced both a strong time-dependent diminution (-56%) of MDR1 mRNA (semiquantitative reverse transcription polymerase chain reaction) and a significant decrease of unidirectional transport of rhodamine 123 after 48 h of exposure at 10 ng/mL. By confocal laser scanning microscopy, the Pgp was mainly localized to the apical plasma membrane of both control and TNF alpha-treated cells. By contrast, IFN gamma induced up-regulation of both mRNA MDR1 and Pgp protein expression without incidence on Pgp activity. Interestingly, a colocalization of Pgp with lateral F-actin was observed. Associated with TNF alpha, IFN gamma produced neither an antagonist nor synergistic effect on Pgp activity. In conclusion, our results demonstrate an inhibitory effect of TNF alpha and no effect of IFN gamma on Pgp transport activity using rhodamine 123 as a substrate. Mechanisms of action of these cytokines remain to be studied.

Wild type p53 gene causes reorganization of cytoskeleton and, therefore, the impaired deformability and difficult migration of murine erythroleukemia cells

We studied the role of p53 gene in the biophysics and biology in murine erythroleukemia cell line (MEL), with the goal of understanding the influence of this tumor suppressor gene on the deformability and metastasis of tumor cells. Experiments were performed on MEL and p53-transfected MEL (MEL-M with mutant p53 gene and MEL-W with wild-type p53 gene). The cell growth curves indicated that the over-expression of wild-type p53 gene significantly suppressed the growth of MEL, with G(0)-G(1) arrest and apoptosis shown by flow cytometric assays. Confocal laser scanning microscopy revealed that the MEL-W had a more compact organization of the F-Actin cytoskeleton than MEL and MEL-M. Fluorescence polarization measurement indicated a higher membrane fluidity of MEL-W than the other two groups. Fourier transform infrared spectroscopy (FT-IR) showed changes in the composition and/or structure of membrane lipids in MEL-W, with decreases in secondary structures of proteins such as alpha-helix, turns and bends and random coil, in comparison to MEL and MEL-M. The osmotic fragility curves indicated that MEL-W was more fragile and micropipette experiments showed that they had increased elasticity and reduced deformability in comparison to MEL and MEL-M. The adhesion assay with the use of the flow chamber revealed a lower adhesion rate of MEL-W to endothelial cells at high shear stress. The present study on the molecular biology with biophysics of MEL cells contributes to our knowledge on the tumor suppressor gene p53.

Increased circulating monocyte activation in patients with unstable coronary syndromes

OBJECTIVES

The primary objective of this research was to assess the activation level of circulating monocytes in patients with unstable angina.

BACKGROUND

Markers of systemic inflammatory responses are increased in patients with unstable coronary syndromes, but the activation state and invasive capacity of circulating monocytes have not been directly assessed.

METHODS

Peripheral blood mononuclear cell (MC) activation in blood samples isolated from patients with stable and unstable coronary artery disease was measured in two studies. In study 1, a modified Boyden chamber assay was used to assess spontaneous cellular migration rates. In study 2, optical analysis of MC membrane fluidity was correlated with soluble CD14 (sCD14), a cellular activation marker.

RESULTS

Increased rates of spontaneous monocyte migration (p < 0.01) were detected in patients with unstable angina (UA) (Canadian Cardiovascular Society [CCS] angina class IV) on comparison to patients with acute myocardial infarction (MI), stable angina (CCS angina classes I to III) or normal donors. No significant increase in lymphocyte migration was detected in any patient category. Baseline MC membrane fluidity measurements and sCD14 levels in patients with CCS class IV angina were significantly increased on comparison with MCs from normal volunteers (p < 0.001). A concomitant reduction in the MC response to activation was detected (p < 0.05).

CONCLUSIONS

Using two complementary assays, activated monocytes with increased invasive capacity were detected in the circulation of patients with unstable angina. This is the first demonstration of increased monocyte invasive potential in unstable patients, raising the issue that systemic inflammation may both reflect and potentially drive plaque instability.

Induction of disabled-2 gene during megakaryocyte differentiation of k562 cells

Megakaryocyte differentiation is often accompanied by the changes of gene expression pattern. Here we reported that the expression of DAB2, a putative adaptor protein in cell signaling, was induced at the protein and mRNA levels upon 12-O-tetradecanoylphorbol-13-acetate-mediated megakaryocyte differentiation of human chronic myeloid leukemic K562 cells. On the other hand, the differentiation agents DMSO and retinoic acid had no effect on DAB2 expression. Analysis of promoter activity with the human DAB2 luciferase reporter constructs suggested that the regulation is partially at the transcriptional level. The responsive sequences located within an 80-bp DAB2 promoter region. To determine the involvement of MEK1-p42/p44 MAPK pathway in mediating DAB2 gene expression, we have performed the following experiments and found that (i) there was sustained activation of p42/p44 MAPK, but not p38 MAPK, upon K562 cells differentiation; (ii) application of MEK1 inhibitor U0126 reduced the expression of DAB2 protein, mRNA and promoter activity, as well as cell differentiation; (iii) constitutively active MEK1 increased DAB2 promoter activity; and (iv) dominant negative ERK2 abolished constitutively active MEK1-induced DAB2 promoter activity. Taken together, our results indicate that DAB2 gene is induced upon megakaryocyte differentiation by the MEK1-p42/p44 MAPK pathway and may define a new role of DAB2 in hematopoietic cell differentiation.

1,25-Dihydroxycholecalciferol enhances butyrate-induced p21(Waf1/Cip1) expression

Butyrate, a short-chain fatty acid produced in the colon, as well as its prodrug tributyrin, reduce proliferation and increase differentiation of colon cancer cells. p21(Waf1/Cip1) and p27(Kip1) are negative regulators of cell cycle and are thought to have a key function in the differentiation of various cell lines. We studied the effects of butyrate on differentiation, VDR expression, as well as on p21(Waf1/Cip1) and p27(Kip1) expression in human colon cancer cells (Caco-2). Butyrate induced cell differentiation, which was further enhanced after addition of 1,25-dihydroxycholecalciferol. Synergistic effect of butyrate and dihydroxycholecalciferol in Caco-2 cells was due to butyrate-induced overexpression of VDR. While butyrate as well as dihydroxycholecalciferol increased p21(Waf1/Cip1) and p27(Kip1) expression, in contrast combined exposure of butyrate and dihydroxycholecalciferol resulted in a synergistic amplification of p21(Waf1/Cip1), but not of p27(Kip1) expression. These data imply that butyrate selectively increases p21(Waf1/Cip1) expression via upregulation of VDR in Caco-2 cells.

Morphological and molecular evidence of differentiation during etoposide-induced apoptosis in human lymphoblastoid cells

The relationship between apoptosis and cell differentiation has been a subject for continuous debate, with evidence showing leukaemic cell differentiation and drug-induced apoptosis have reciprocal, interdependent and a highly schedule-dependent relationship. We have addressed this relationship in terms of a widely-used model for apoptosis induced by cytotoxic drugs: namely the effect of etoposide on CEM cells. In respect of commitment toward differentiation, we assessed changes in expression of marker genes and the level of CD3 antigenicity. Changes in these parameters following exposure of CEM cells to etoposide was similar to that observed following treatment of the same cells with phorbol 12-myristate 13-acetate (PMA), though this latter treatment did not cause cell death. Similarities in response to etoposide and PMA also included generation of 50 kilobase fragmentation of DNA and convolution of nuclei as assessed by transmission electron microscopy. However, condensation of chromatin and externalization of phosphatidylserine were only recorded in response to the cytotoxic drug and not in response to PMA. The data are consistent with apoptosis in these lymphoblastoid cells being accompanied by activation of specific markers of T-cell differentiation, but ultimately involving processes unequivocally associated with cell death.