Changes In Human Cells Research Articles

Toxicogenomics of drug delivery systems: Exploiting delivery system-induced changes in target gene expression to enhance siRNA activity

Synthetic siRNAs are typically formulated with drug delivery systems (DDS) that improve cellular uptake for optimal gene silencing activity. Here, we show that two PAMAM dendrimer DDS, differing only in their structural architecture, elicit many different gene expression changes in human cells including opposing effects on the expression of epidermal growth factor receptor (EGFR), a gene targeted for silencing by siRNA. Despite providing similar improvements in siRNA uptake, these two formulations led to a ∼10-fold variation in anti-EGFR siRNA activity. These data show that gene expression changes induced by DDS, separate from their ability to enhance cell uptake, determine ‘apparent’ siRNA potency and thus offer the possibility of tailoring delivery system-siRNA combinations for additive or synergistic effects on gene silencing.

Specific Cell Behavior of Human Fibroblast onto Carbohydrate Surface Detected by Glycoblotting Films

We synthesized an aminooxyl polymer that is reactive with the reduced end of carbohydrates using our sugar-displaying approach. The carbohydrates were easily immobilized on the polymer film (glycoblotting film) by simple immersion in a in sugar solution through stable oxime bond. The in vitro behaviors of human fibroblasts on the carbohydrate-coated surface were investigated. The adhesion of human fibroblasts on the cellobiose- and cellotriose-coated surfaces was much greater than on the other coated surfaces and the noncoated surface. This result indicated that simple structural differences in carbohydrates induced biological changes in human cells, especially cell adhesion. Our approach provides a high-throughput assay system for carbohydrate-related cell adhesion and proliferation.

Gene expression changes in human cells after exposure to mobile phone microwaves

Possible biological effects of mobile phone microwaves were investigated in vitro. In this study, which was part of the 5FP EU project REFLEX (Risk Evaluation of Potential Environmental Hazards From Low-Energy Electromagnetic Field Exposure Using Sensitive in vitro Methods), six human cell types, immortalized cell lines and primary cells, were exposed to 900 and 1800 MHz. RNA was isolated from exposed and sham-exposed cells and labeled for transcriptome analysis on whole-genome cDNA arrays. The results were evaluated statistically using bioinformatics techniques and examined for biological relevance with the help of different databases. NB69 neuroblastoma cells, T lymphocytes, and CHME5 microglial cells did not show significant changes in gene expression. In EA.hy926 endothelial cells, U937 lymphoblastoma cells, and HL-60 leukemia cells we found between 12 and 34 up- or down-regulated genes. Analysis of the affected gene families does not point towards a stress response. However, following microwave exposure, some but not all human cells might react with an increase in expression of genes encoding ribosomal proteins and therefore up-regulating the cellular metabolism.

Zidovudine induces S-phase arrest and cell cycle gene expression changes in human cells

Antiretroviral therapy for the human immunodeficiency virus-1 (HIV-1) typically includes two nucleoside reverse transcriptase inhibitors (NRTIs). 3'-Azido-3'-deoxythymidine (AZT, Zidovudine) plus 2'-deoxy-3'-thiacytidine (3TC, Lamivudine) is a combination that is used frequently. The NRTIs are mutagenic nucleoside analogs that become incorporated into DNA and terminate replication. We therefore hypothesized that exposure to this class of drug may alter cell cycle parameters. We used flow cytometry to examine the cell cycle in human epithelioid carcinoma (HeLa) cells exposed to AZT and 3TC alone, as well as a series of AZT/3TC dose combinations: (A) 125.0 microM AZT/12.5 microM 3TC; (B) 250.0 microM AZT/25.0 microM 3TC; and (C) 500 microM AZT/50 microM 3TC. At 24 h, at all doses, there was a good cell viability (>/=68%), and incorporation of AZT into nuclear DNA. Using flow cytometry, a dose-related increase in the percentage of cells in S phase, from 9.5% with no drug, to 36.0% with dose C, was observed in cells exposed for 24 h (P = 0.001, ANOVA). A concomitant decrease in the percentage of cells in G(1) phase, from 82.6% with no drug to 58.5% with dose C, was observed in cells exposed for 24 h (P = 0.017, ANOVA). A similar S phase arrest was seen in cells exposed to 125, 250 and 500 microM AZT alone, but there was no S phase alteration with 50 microM 3TC alone, suggesting that AZT is responsible for the accumulation of cells in S phase. To elucidate the accumulation of cells in S phase and explore the cell cycle gene expression changes induced by AZT and 3TC, we used c-DNA microarray, Cell Cycle Super Array and real-time PCR. There was a strong upregulation of the DNA damage-inducible transcript 3 (DDIT3 or GADD153) in NRTI-exposed cells. In addition, AZT induced an upregulation of cyclin D1 accompanied by a downregulation of the cyclin D1-associated inhibitors P18 and P57, and the G(1)-S check point gene P21, the net effect of which would be to foster a cell progression into S phase. Cyclin A2 was down-regulated in cells exposed to AZT, suggesting a block in S-G(2)-M progression that would also be consistent with the accumulation of cells in S phase. Overall, the study demonstrates that AZT, but not 3TC, causes an arrest of cells in S phase with a consistent alteration in the expression of several cell cycle genes.

Mammalian Antioxidant Defenses Are Not Inducible by H2O2

As an approach to understanding how mammals regulate H(2)O(2) toxicity, intracellular concentration to prevent its we analyzed the genome-wide mRNA profile changes of human cells after treatment with a non-toxic H(2)O(2) concentration. We identified a large and essentially late H(2)O(2) response of induced and repressed genes that unexpectedly comprise few or no antioxidants but mostly apoptosis and cell cycle control activities. The requirement of the p53 regulator for regulating about a third of this H(2)O(2) stimulon and the lack of an associated enhancement of total cellular H(2)O(2) scavenging activity further suggest that H(2)O(2) elicits a stress antiproliferative/repair response that does not increase antioxidant defenses. We conclude that mammalian antioxidant defenses are constitutive, a finding that contrasts with the oxidant-inducibility of such defenses in microorganisms. This finding might be important in understanding the role of H(2)O(2) as a key signaling molecule in mammals.

Mismatch repair-dependent transcriptome changes in human cells treated with the methylating agent N-methyl-n'-nitro-N-nitrosoguanidine.

DNA mismatch repair (MMR) plays a key role in the cytotoxic response of human cells to methylating agents, however, the cascade of events leading to cell cycle arrest and cell death has yet to be characterized. We studied the role of MMR in the transcriptional response to DNA methylation damage in two human cellular models: (a). the lymphoblastoid cell line TK6 and its derivative MT1, which is mutated in the MMR gene hMSH6; and (b). the epithelial cell line 293T Lalpha in which the expression of the MMR gene hMLH1 can be tightly regulated and p53 is inactivated. Upon N-methyl-N'-nitro-N-nitrosoguanidine treatment, only cells with functional MMR were killed, but the type of cytotoxic response differed. In TK6 cells, S-phase arrest and apoptosis were accompanied by a dramatic change in gene expression, notably, an up-regulation of several genes encoding growth inhibitors and proapoptotic factors both p53 dependent and independent. In contrast, the MMR-dependent transcriptional response in 293T Lalpha cells was substantially less pronounced than in TK6 cells, despite an efficient induction of a G(2)-M checkpoint and nonapoptotic cell death. Thus, we demonstrate that in human cells of different origin, MMR-mediated killing by methylating agents occurs through different pathways and regardless of the p53 status. Moreover, once DNA methylation damage has been processed by the MMR system, tumor cells might be committed to die, although one or more of their signaling pathways are impaired.

Effect of hypoxia on gene expression by human hepatocytes (HepG2).

The full extent to which hypoxia produces gene expression changes in human cells is unknown. We used late-generation oligonucleotide arrays to catalog hypoxia-induced changes in gene expression in HepG2 cells. Five paired sets of cultures were subjected to either control (room air-5% CO(2)) or hypoxic (1% O(2)-5% CO(2)) conditions for 24 h, and RNA was analyzed on an Affymetrix cDNA array containing approximately 12,600 sequences. A statistically significant change in expression was shown by 2,908 sequences (1,255 increased and 1,653 decreased). The observed changes were highly concordant with published literature on hypoxic stress but showed relatively little overlap (12-22%) with changes in gene expression that have been reported to occur after heat stress in other systems. Of note, of these 2,908 sequences, only 387 (213 increased and 174 decreased) both exhibited changes in expression of twofold or greater and were highly expressed in at least three of the five experiments. We conclude that the effect of hypoxia on gene expression by HepG2 cells is broad, has a significant component of downregulation, and includes a relatively small number of genes whose response is truly independent of cell and stress type.

Nanosecond pulsed electric field (nsPEF) effects on cells and tissues: apoptosis induction and tumor growth inhibition

Pulse power technology using high intensity (up to 300 kV/cm) nanosecond pulsed electric fields (nsPEF) has been applied for decontamination and amelioration of biofouling, but until now effects on human cells have not been investigated. To analyze structural and functional changes in human cells and solid tumors following exposure to nsPEF, we utilized flow cytometry and immunofluorescence microscopy. We provide further support for the hypothesis that as the pulse duration is decreased, there is a lower incidence of electric field interactions at the plasma membrane and a higher incidence of interactions with intracellular structures. The nsPEF effects are pulse duration/electric field intensity-dependent and energy density- or temperature-independent. We also show that nsPEF induces programmed cell. death (apoptosis) in cultured cells as indicated by cell shrinkage, Annexin-V-FITC binding to phosphatidylserine on intact cells, and caspase activation. Mouse fibrosarcoma tumors exposed to nsPEF exhibit fragmented DNA and reduced tumor growth in a mouse model. These studies show that nsPEF effects are distinctly different than electroporation pulses and provide the first evidence for the potential application of nsPEF to induce apoptosis and inhibit tumor growth.

Modulation of expression of monocyte/macrophage plasminogen activator activity and its implications for attenuation of vasculopathy.

The binding of urokinase-type plasminogen activator (uPA) to its receptor (uPAR) on cell surfaces has the potential to influence degradation of extracellular matrix (ECM). Thus, uPA bound to monocyte/macrophages and its interactions with plasminogen activator inhibitors types 1 and 2 (PAI-1 and PAI-2) may modify atherogenesis by altering cell-associated proteolytic activity, degradation of ECM, and neointimal formation at sites of vascular injury. To determine whether the expression of proteins on the surface of cells involved in fibrinolysis changes in human cells in response to mediators implicated in atherogenesis, we exposed U937 cells (an immortal human monocyte-like cell line) to transforming growth factor-beta (TGF-beta) and to thrombin. Induction of uPAR mRNA occurred with TGF-beta (5 ng/mL) in a time-dependent fashion (P = .05; n = 4). Thrombin (5 National Institutes of Health [NIH] U/mL) increased uPAR mRNA by 2.8-fold above control (n = 4) without altering PAI-1 mRNA or protein synthesis (n = 4). The increase in uPAR gene expression in cells exposed to either TGF-beta or thrombin translated into a functional increase in cell-surface proteolytic activity. Under control conditions, U937 cells expressed PAI-2 but not PAI-1 mRNA. PAI-2 mRNA expression increased (P < .05; n = 4) with thrombin (5 NIH U/mL) but was suppressed by TGF-beta (5 ng/mL). TGF-beta induced PAI-1 mRNA within 6 hours accompanied by a 9-fold increase in PAI-1 protein from 6 hours (2.9 +/- 1.9 ng/mL) to 24 hours (20.0 +/- 9.6 ng/mL, P = .005; n = 3) paralleled by increased synthesis as shown in metabolic labeling experiments with 35S-methionine and immunoprecipitation of labeled PAI-1. PAI-1 mRNA and protein expression were seen in human coronary artery atherectomy specimens as well and were localized to analogous monocyte/macrophages and to smooth muscle cells as judged from results of in situ hybridization and immunocytochemistry studies. The results indicate that there is induction of PAI-1 and uPAR in U937 cells exposed to TGF-beta and thrombin. In atheroma, analogous processes may modulate early migration of luminal monocytes into the subintimal space and proteolysis of ECM. Thus, cell surface, monocyte-directed fibrinolysis may influence atherosclerosis, restenosis, or both.

Benzene metabolite, 1,2,4-benzenetriol, induces micronuclei and oxidative DNA damage in human lymphocytes and HL60 cells.

The triphenolic metabolite of benzene, 1,2,4-benzenetriol (BT), is readily oxidized to its corresponding quinone via a semiquinone radical. During this process, active oxygen species are formed that may damage DNA and other cellular macromolecules. The ability of BT to induce micronuclei (MN) and oxidative DNA damage has been investigated in both human lymphocytes and HL60 cells. An antikinetochore antibody based micronucleus assay was used to distinguish MN containing kinetochores and potentially entire chromosomes (kinetochore-positive, K+) from those containing acentric chromosome fragments (kinetochore-negative, K-). BT increased the frequency of MN formation twofold in lymphocytes and eightfold in HL60 cells with the MN being 62% and 82% K+, respectively. A linear dose-related increase in total MN, mainly in K(+)-MN, was observed in both HL60 cells and lymphocytes. Addition of copper ions (Cu2+) potentiated the effect of BT on MN induction threefold in HL60 cells and altered the pattern of MN formation from predominantly K+ to K-. BT also increased the level of 8-hydroxy-2'-deoxyguanosine (8-OH-dG), a marker of active oxygen-induced DNA damage. Cu2+ again enhanced this effect. Thus, BT has the potential to cause both numerical and structural chromosomal changes in human cells. Further, it may cause point mutations indirectly by generating oxygen radicals. BT may therefore play an important role in benzene-induced leukemia.

Pyruvate kinase deficiency in dog and human erythrocytes: effects of energy depletion on cation composition and cellular hydration.

Pyruvate kinase-(PK) deficient human reticulocytes incubated 4 hr under conditions where mitochondrial oxidative phosphorylation is inhibited become ATP-depleted. Concomitantly, these energy-depleted red blood cells (RBC) lose massive amounts of potassium and water. PK-deficient reticulocyte-rich RBC from a Basenji dog, incubated under the same conditions, also manifest ATP-depletion and K-loss. In contrast to the cation changes in human cells, however, K-loss in PK-deficient dog reticulocyte-rich RBC is balanced by an equivalent Na gain, and consequently these canine erythrocytes do not undergo any change in cellular hydration. Potassium depletion and dehydration, which may be related to membrane injury in human RBC, do not appear to be involved in the hemolysis of PK-deficient dog erythrocytes.

Ultrastructural Changes in Human Cells Associated with Herpesvirus Latency and Reactivation in Vitro

Establishment and maintenance of virus latency is one of the most intriguing and challenging questions in virology. Significant gaps in our understanding of the manner in which herpes simplex virus (HSV) is maintained in the latent state and subsequently reactivated remain unanswered. O'Neill et al. developed an in vitro latency system1 in which HSV type 2 (HSV-2)-infected human embryonic lung (HEL) cells treated with cytosine arabinoside (ara-C) do not produce infectious virus for several days after drug removal. The period during which HSV-2 is inapparent can be extended by incubating infected cells at 39.5°C after drug removal. The advantage of this in vitro system is that it eliminates many complex factors associated with in vivo models and provides a simple reproducible method to examine latent HSV-2 infection.

Cell-cycle inhibition by misonidazole of human cells cultivated in vitro under aerobic conditions.

By means of flow cytometric recording of DNA histograms and counting of cells in synchronized populations, we have found that misonidazole (MIS) in clinically relevant concentrations induces cell-kinetic changes in human cells (NHIK 3025) cultivated in vitro under aerobic conditions. The effect seems to be a general lengthening of the cell cycle, affecting all phases. However, induction of this effect is phase-dependent, since only cells exposed to MIS during mitosis and/or early G1 will suffer significant cell-cycle prolongation. In exponentially growing populations this effect of MIS leads to a transient increase in the fraction of G1 cells and a corresponding decrease in the fraction of S cells. The possible significance of this effect for the clinical use of MIS is discussed.

Mitotic cycle and production of chromosome structural changes in human cells

Mitotic cycle and production of chromosome structural changes in human cells

Surface changes of human cells productively infected with human adenoviruses

Productive infection of human embryonic kidney (HEK) cells with a group C adenovirus (type 2) resulted in surface changes that were detected as increased agglutination in the presence of concanavalin A (Con A). Agglutination increased as the infection progressed, with maximum response to Con A occurring by 48 hr. Treatment with cytosine arabinoside either for the entire infection or beginning 8 hr after infection prevented the surface alterations. In contrast to the agglutination produced by adenovirus 2, infection with a group A adenovirus (type 12) did not cause a changed response to Con A. However, infection with two cytocidal mutants derived from adenovirus 12 resulted in membrane changes detectable by Con A. These findings demonstrate that specific viral gene functions are required for the surface changes occurring during productive infection of adenoviruses. Since the cytocidal mutants are nononcogenic, the ability to produce surface changes during productive infection seems to be unrelated to the oncogenicity of the virus.

Chromosome changes in human cells induced by herpes simplex, types 1 and 2.

HERPES simplex virus (HSV) is of interest both as a common infectious agent and because of its putative role (type 2 virus) in carcinoma of the cervix1,2. The type 1 virus induces chromosome damage in both established and primary cell cultures of the Chinese hamster3–5, in cultured Syrian hamster cells6 and in cultured monkey kidney cells7. In human leucocytes Aya et al.8 have described HSV induced breaks, while Stich et al.5 described more extreme effects, including fragmentation, in human embryonic lung cells. But neither damage by HSV type 2 nor the full range of effects in human cells induced by either types 1 or 2 has been described. Here we describe various chromosome abnormalities produced by both forms of HSV, and point out similarities between some of these abnormalities and those which occur in human cancers, in permanent human leucocyte cell lines, and in human fibroblasts transformed by SV40.

Leucocyte alloantigens as markers on cultured human cells

R ECENT studies have shown that tissue culture cell lines are frequently contaminated with cells from a species other than that from which the cell line was thought to be derived [l, 5, 7, 8, lo]. The most commonly detected contamination is of animal cell lines by human cells, but it is also possible that one human cell line may be contaminated by cells from another human cell line. This contamination could not, of course, be detected using species specific antisera. In order to detect such contamination, and as a necessary prerequisite for the study of antigen synthesis and of genetic change in human cells, a search for alloantigens2 on cultured human cells has been initiated. Chalmers ef al. [3] observed that leucocyte alloantibodies can be shown (by the mixed antiglobulin reaction), to react with HeLa cells and it has now been found that, with certain sera, mixed agglutination between cultured human cells and human leucocytes can be produced (Fig. 1). The mixed agglutination reaction requires the presence of the same antigen on both tissue culture cell and on the indicator cell (leucocytes) which are linked together by suitable antibody and is therefore better suited to the analysis of the antigens of cultured human cells than systems like the mixed antiglobulin reaction [3] which detect only the combination of antibody with tissue cell. This report describes preliminary investigations on several human cell lines, the characteristics of which are given in Table I. The results of mixed agglutination tests on these cell lines using human leucocytes obtained from blood group 0 persons and fixed with formalin are shown in Table I. The antiserum used in the experiments summarized in this Table was obtained from a multiparous woman, and contains alloantibodies of many different specificities, as yet unanalysed. The techniques of preparing the indicator leucocytes and of performing the mixed agglutination reaction have been described elsewhere [3, 51. From Table II it may be seen that there is considerable antigenic diversity between cell lines, and that different HeLa cell lines show different patterns of cross reactions with indicator leucocytes. This serum does not react with a continuous rhesus monkey line (EMK IO I), with either primary or continuous vervet cell cultures or with a primary culture of puppy kidney cells, although there is some reaction with a primary rhesus monkey cell culture. These results suggest that leucocyte alloantigens may be used in the identification of human cell lines, and in distinguishing between different human cell lines, but further antigenic analysis of the sera used is obviously needed before any conclusions may be drawn about the relationships between different cell lines,