Staphylococcus aureus alpha-toxin-induced cell death: predominant necrosis despite apoptotic caspase activation.

Recent data suggest that alpha-toxin, the major hemolysin of Staphylococcus aureus, induces cell death via the classical apoptotic pathway. Here we demonstrate, however, that although zVAD-fmk or overexpression of Bcl-2 completely abrogated caspase activation and internucleosomal DNA fragmentation, they did not significantly affect alpha-toxin-induced death of Jurkat T or MCF-7 breast carcinoma cells. Caspase inhibition had also no effect on alpha-toxin-induced lactate dehydrogenase release and ATP depletion. Furthermore, whereas early assessment of apoptosis induction by CD95 resulted solely in the generation of cells positive for active caspases that were, however, not yet permeable for propidium iodide, a substantial proportion of alpha-toxin-treated cells were positive for both active caspases and PI. Finally, electron microscopy demonstrated that even in the presence of active caspases, alpha-toxin-treated cells displayed a necrotic morphology characterized by cell swelling and cytoplasmic vacuolation. Together, our data suggest that alpha-toxin-induced cell death proceeds even in the presence of activated caspases, at least partially, in a caspase-independent, necrotic-like manner.

Limitations of the reverse transcription-polymerase chain reaction method for the detection of carcinoembryonic antigen-positive tumor cells in peripheral blood.

To examine the limitations of reverse transcription (RT)-PCR for the detection of circulating tumor cells in blood, we established a RT-PCR for carcinoembryonic antigen (CEA). Whole blood (10(7) nucleated cells) was mixed with cells from the colon cancer cell line LS174T (concentrations ranging from 0 to 10(6) cells). RT-PCR was performed to detect CEA mRNA in blood under various conditions. Healthy blood donors (n = 24) were examined by the established method for detecting CEA mRNA in blood. We were able to show that there is a detection limit for RT-PCR of 10 tumor cells in total and of 1 tumor cell in 10(5) nucleated cells. To obtain these results, a high number of PCR cycles (first PCR, 30 cycles; nested PCR, 45 cycles) was required. Under these PCR conditions, we found a positive PCR signal in 33% of healthy blood donors (n = 8). To overcome this problem, we reduced the nested PCR to 35 cycles. At that point, none of the controls showed a positive signal for CEA, and there was a subsequent decrease of the detection limit to 1 tumor cell in 10(2)-10(3) nucleated cells, lower than the detection limit of an immunocytological examination (1 tumor cell in 10(4) nucleated cells). When the amplification was performed with the tumor cells only and with no nucleated blood cells present, under exactly the same conditions, there was still a detection limit of 1 tumor cell in 106 nucleated cells. Our data clearly show that there is a severe loss of expected sensitivity of RT-PCR if it is performed in blood or nucleated blood cells. We conclude that PCR for CEA mRNA expression is not more sensitive than immunocytology and is, furthermore, plagued by the problem of a high percentage of false positive results.

Native low-density lipoprotein (LDL) induces the expression of the early growth response gene-1 in human umbilical arterial endothelial cells.

Low-density lipoprotein (LDL) is thought to be involved in the growth of various cell types including human endothelial cells. Nevertheless, little is known about the signal transduction mechanisms underlying the growth-promoting effects of LDL in endothelial cells. Furthermore, the question whether native LDL participates in the described effects remains unanswered. Here, we show that native LDL induces a dose-dependent elevation in free intracellular Ca(2+)-concentration ([Ca2+]i) as well as a rapid and prolonged increase in intracellular pH (pHi) in human umbilical arterial endothelial cells (HUAEC). Native LDL induces a dose-dependent increase of early growth response gene-1 (egr-1) mRNA expression. The effect is maximal 30 min after addition of LDL to the culture medium. Moreover, native LDL causes an increase in DNA-synthesis and cell proliferation. In addition, the effect of acidic fibroblast growth factor (aFGF) on HUAEC proliferation was enhanced by native LDL.

Identification of syntenin and other TNF-inducible genes in human umbilical arterial endothelial cells by suppression subtractive hybridization.

Endothelial cells play an important regulatory role in inflammatory responses by upregulating various proinflammatory gene products including cytokines and adhesion molecules. A highly potent mediator of this process is tumor necrosis factor-alpha (TNF). In the present study, the suppression subtractive hybridization (SSH) method was employed to identify rarely transcribed TNF-inducible genes in human umbilical arterial endothelial cells. Following mRNA isolation of non-stimulated and TNF-stimulated cells, cDNAs of both populations were prepared and subtracted by suppression PCR. Sequencing of the enriched cDNAs identified 12 genes differentially expressed including vascular cell adhesion molecule-1, monocyte chemoattractant protein-1, interleukin-8 and IkappaBalpha, an inhibitor of the transcription factor nuclear factor-kappaB. Interestingly, also syntenin, a PDZ motif-containing protein which binds to the cytoplasmic domain of syndecans, was identified by SSH. Time course studies using RT-PCR analysis confirmed that all genes were differentially expressed and rapidly induced by TNF. Our data reveal that SSH is a powerful technique of high sensitivity for the detection of differential gene expression in primary arterial endothelial cells.

Effects of antithrombin III on tumor necrosis factor-alpha and interleukin-1beta synthesis in vascular smooth muscle cells.

In the course of sepsis, severe coagulopathy and disseminated intravascular coagulation (DIC) are common events. Therefore, substances known to interfere with the coagulation cascade have been studied in animal models of sepsis. Among them, antithrombin III (AT III) was reported to be a promising therapeutic tool because it exhibited anti-inflammatory properties in addition to its anticoagulative effects. In our studies using vascular smooth muscle cells (VSMC) as a monoculture model, contradictory effects of AT III on the release of the proinflammatory agonists tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) were found. Whereas AT III inhibited the lipopolysaccharide (LPS)-induced production of these cytokines on both the transcriptional and the translational levels when given at higher concentrations (5 or 10 U/ml), lower amounts of AT III did not show this suppressive effect. In contrast, 0.5, 1, and 5 U/ml AT III led to an enhancement of TNF-alpha synthesis when combined with LPS. To date, we cannot provide a mechanism to explain the AT III-promoted modulation of TNF-alpha and IL-1beta generation in VSMC. However, with respect to its potential therapeutic benefit in systemic inflammatory conditions, AT III should not be regarded strictly as an anti-inflammatory modulator.

Action of dihydropyridine calcium antagonists on early growth response gene expression and cell growth in vascular smooth muscle cells.

OBJECTIVE: Evidence suggests that calcium antagonists may suppress vascular smooth muscle cell (VSMC) growth and proliferation, which may be a crucial step in the pathogenesis of hypertension and atherosclerosis. DESIGN: The effects of the dihydropyridine calcium antagonists nifedipine, nitrendipine, nisoldipine, nimodipine and isradipine on cell growth induced by platelet-derived growth factor (PDGF)-AB and angiotensin II (Ang II), and expression of the transcription factors c-fos and early-growth response gene 1 (egr-1) were investigated. METHODS: Proliferation of VSMC in culture was measured by [3H]-thymidine incorporation into cell DNA and by cell count. Expression of c-fos and egr-1 messenger RNA (mRNA) was determined by the Northern blot technique. RESULTS: All of the calcium antagonists blunted the PDGF-induced rise in VSMC DNA synthesis. The inhibitory potency of isradipine on PDGF-stimulated DNA synthesis was approximately 10-fold that of the other calcium antagonists used, isradipine having a half-maximal inhibitory concentration (IC50) of (4.2 +/- 0.16) x 10(-7) mol/l. The calcium antagonists investigated also inhibited Ang II-induced DNA synthesis. Isradipine (10(-6) mol/l) completely abolished the PDGF-induced cell proliferation. Both PDGF (50 ng/ml) and Ang II (10(-7) mol/l) induced c-fos and egr-1 mRNA expression, having maximum effect after 30 min. In the case of c-fos, pre-incubation with 5 x 10(-6) mol/l isradipine led to a decrease in both Ang II- and PDGF-induced expression of this immediate-early gene. The expression of egr-1 was not affected by pre-incubation with 5 x 10(-6) mol/l isradipine. CONCLUSIONS: All calcium antagonists investigated in the present study inhibited cell growth. Isradipine was more potent in blocking growth factor-induced cell growth than the other calcium antagonists studied. The inhibitory effect of the dihydropyridine calcium antagonists appears to be dependent on the expression of c-fos.

Angiotensin type-1 (AT1) receptor gene expression in primarily cultured human arterial umbilical endothelial cells.

The aim of this study was to investigate the interaction of angiotensin II (Ang II) and human umbilical arterial endothelial cells (HUAEC). Specific binding of 125I-ANG II to primarily cultured HUAEC showed a K(D) of 1.98 +/- 0.53 x 10(-9) M (n = 5) with a maximum binding site of 2.84 +/- 1.07 x 10(-13) mol/mg protein (n = 5). In later passages (third and fifth subculture), this binding site was no longer detectable. Gene expression analysis revealed a strong expression of the angiotensin type-I receptor (AT1-R) in the primarily cultured HUAEC, with a decrease in additional passages. In primarily cultured HUAEC, Ang II (10(-10)-10(-6) M) induced a concentration-dependent increase in intracellular free calcium ([Ca2+]i) that could be blocked by a preincubation with candesartan (TCV-112) but not by PD123319. These data show the expression of the AT1-R in primary cultures of HUAEC. The Ang II-induced increase in [Ca2+]i seems to be mediated by this receptor.

Different patterns of inducible nitric oxide synthase gene expression in ovarian carcinoma cell lines.

BACKGROUND: Stimulation of inducible nitric oxide synthase (iNOS) and release of nitric oxide by tumor cells may play a critical role in cancer development, either by exhibiting tumoricidal effects or by promoting tumor progression. MATERIALS AND METHODS: In the present study, we investigated four ovarian carcinoma cell lines with respect to their iNOS expressing characteristics. RESULTS: Following incubation with interferon-gamma, tumor necrosis factor-alpha and interleukin-1 beta, a marked stimulation of iNOS gene expression was found in SKOV-6 and OVCAR-3 cells, while only minor iNOS synthesis was detectable in HOC-7. Time-dependent accumulation of nitrite/nitrate in the culture supernatant indicated that the three cell lines were stimulated to produce and release nitric oxide. In contrast, no NO generation was observed in the fourth cell line under investigation, 2774. CONCLUSION: Due to the growth regulatory functions attributed to NO, variations in NO production may be of importance e.g. following interferon-gamma therapy in patients with ovarian cancer.

Competitive reverse transcription/polymerase chain reaction for the quantification of p53 and mdm2 mRNA expression.

Wild-type p53 (wtp53) is a tumour suppressor gene involved in cell cycle regulation. The mdm2 protein can complex with the p53 protein and influence its function as a regulator of cell growth. To detect and quantify wtp53 and mdm2 mRNA expression, we established the competitive reverse transcription/polymerase chain reaction for these genes and for the housekeeping gene glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The target RNA differed from the competitor cRNA by having 183 bp, 205 bp and 173 bp deletions for p53, mdm2 and GAPDH, respectively. Target RNA and known concentrations of competitor cRNA were co-reverse transcribed and co-amplified with the same primers. Target cDNA and the corresponding competitor cDNA were amplified at the same efficiency.

Reverse transcriptase-polymerase chain reaction (RT-PCR): a sensitive method to examine basic fibroblast growth factor-induced expression of the early growth response gene-1 (egr-1) in human umbilical arterial endothelial cells.

Immediate-early genes are expressed upon growth and differentiation in a large variety of cells and species. In the present study we investigated the effect of basic fibroblast growth factor (bFGF) on early growth response gene-1 (egr-1)-mRNA expression in human umbilical arterial endothelial cells (HUAEC). The detection of this gene in HUAEC was performed by Northern blotting and by reverse transcriptase-polymerase chain reaction (RT-PCR). For RT-PCR specific primers for egr-1 and glyceraldehyde-3-phosphate-dehydrogenase (GAPDH) were constructed and PCR conditions were optimized. bFGF induced a time- and concentration-dependent increase of egr-1 expression. Maximal expression occurred within 30 min of stimulation with bFGF at a concentration of 50-100 ng ml-1. RT-PCR gave highly reproducible and specific results. The comparison of both methods showed comparable results but a higher sensitivity for RT-PCR in detecting the egr-1 mRNA. RT-PCR is an excellent method for detecting the expression of egr-1 mRNA in HUAEC.

Cell-cycle arrest in G0/G1 phase of growth factor-induced endothelial cell proliferation by various calcium channel blockers.

Calcium channel blockers cause antiproliferative effects on various cells in culture. Since angioneogenesis is a crucial step in the development of tumor growth, we examined the influence of different calcium channel blockers on human umbilical arterial endothelial cell (HUAEC) growth. Cell growth was measured by cell count, by [3H]thymidine incorporation, and by a 5-bromo-2-deoxyuridine (BrdU-incorporation immunofluorescence assay. Cell-cycle analysis was performed by flow cytometric analysis. Nifedipine, isradipine, diltiazem, and verapamil dose-dependently inhibited the basic fibroblast growth factor (bFGF)-induced [3H]thymidine incorporation. Fifty micromolars of nifedipine, isradipine, diltiazem, and verapamil completely inhibited bFGF-induced proliferation of HUAEC. Ten micromolars of each calcium channel blocker abolished the bFGF-induced increase in cell count. Five micromolars of isradipine completely blocked the bFGF-induced BrdU incorporation. Stimulation of HUAEC with bFGF (50 ng/ml) for 24 h caused a 2-fold increase in cells that entered S and G2+M phase in comparison with control cells. Five micromolars of isradipine abolished this effect completely. We conclude that calcium channel blockers are able to inhibit cell proliferation by a cell-cycle arrest in G0/G1 phase.

Effect of vitamin E and vitamin C on the DNA synthesis of human umbilical arterial endothelial cells.

BACKGROUND: Endothelial cell growth and reendothealization after vascular injury protect the vessel wall against endothelial dysfunction which is believed to play a major role in the pathogenesis of atherosclerosis. AIM: of the study To investigate a possible protective role of antioxidant vitamins in the present study, the effect of vitamin E (alpha-tocopherol) alone and in combination with vitamin C on the DNA synthesis of human umbilical arterial endothelial cells (HUAEC) was examined. Furthermore, because oxidized low-density lipoprotein (ox-LDL) is thought to be involved in atherogenesis, the combined effect of vitamin E and vitamin C with ox-LDL and the influence of vitamin-pretreated LDL on HUAEC proliferation were investigated. METHODS: DNA-synthesis was determined by measurement of [3H]thymidine incorporation into the cell DNA. RESULTS: Vitamin E alone and in combination with vitamin C resulted in an increase in [3H]thymidine incorporation into cell DNA, especially in the presence of basic fibroblast growth factor (bFGF). All vitamin-pretreated LDL samples and ox-LDL led to a nearly complete inhibition of endothelial DNA-synthesis. The ox-LDL-induced effect could not be prevented by vitamin E alone nor in combination with vitamin C. CONCLUSIONS: It seems that once LDL oxidation is in process, vitamin E alone and in combination with vitamin C is ineffective to exert its antioxidative capacity under the conditions used. Thus, vitamin E alone and combined with vitamin C may act as antiatherogens by inducing endothelial cell growth.

Antithrombin III enhances inducible nitric oxide synthase gene expression in vascular smooth muscle cells.

Evidence suggests that antithrombin III (ATIII) exerts anti-inflammatory properties in addition to its anti-coagulative mechanisms. In animal models of sepsis, ATIII affected cytokine plasma concentrations with a decrease of pro-inflammatory cytokines. In addition to cytokines, excessive production of nitric oxide (NO) derived from inducible nitric oxide synthase (iNOS) might represent another important mediator of the cytotoxic events during sepsis. Regarding ATIII as a potential anti-inflammatory modulator, one may speculate that ATIII inhibits the synthesis of iNOS-derived NO. However, our data demonstrate that ATIII further stimulates iNOS gene expression when applied together with either interleukin-1 beta or the combination of lipopolysaccharide plus interferon-gamma. The most prominent synergistic effects on NO synthesis were found when ATIII was given at higher concentrations (1, 5, and 10 U/ml). Although the mechanisms of ATIII signal transduction remain to be established, intensification of interleukin-1 beta or interferon-gamma/lipopolysaccharide-induced NO synthesis by ATIII does not attribute to the anti-inflammatory properties of ATIII.

In vitro modulation of inducible nitric oxide synthase gene expression and nitric oxide synthesis by procalcitonin.

OBJECTIVE: Serum procalcitonin (PCT) concentration was recently introduced as valuable diagnostic marker for systemic bacterial infection and sepsis. At present, the cellular sources and biological properties of PCT are unclear. During sepsis and septic shock, inducible nitric oxide synthase (iNOS) gene expression is stimulated followed by the release of large amounts of nitric oxide (NO). We investigated the possible association between PCT and iNOS gene expression in an in vitro cell culture model. DESIGN: Prospective, controlled in vitro cell culture study. SETTING: University research laboratories. INTERVENTIONS: Confluent rat vascular smooth muscle cells (VSMC) were incubated for 24 hrs and 48 hrs with PCT (1 ng/mL, 10 ng/mL, 100 ng/mL, 1,000 ng/mL, 5,000 ng/mL) alone or with the combination of tumor necrosis factor-alpha (TNF-alpha, 500 U/mL) plus interferon-gamma (IFN-gamma, 100 U/mL). iNOS gene expression was measured by qualitative as well as quantitative polymerase chain reaction analysis, NO release was estimated by the modified Griess method. MEASUREMENTS AND MAIN RESULTS: PCT in increasing concentrations had no effect on iNOS gene expression and nitrite/nitrate release for 24 hrs and 48 hrs, respectively. However, PCT ameliorated TNF-alpha/IFN-gamma-induced iNOS gene expression in a dose-dependent manner (maximal inhibition at PCT 100 ng/mL by -66% for 24 hrs and -80% for 48 hrs). This was accompanied by a significantly reduced release of nitrite/nitrate into the cell culture supernatant (maximal reduction at PCT 100 ng/mL by -56% and -45% for 24 hrs and 48 hrs, respectively). CONCLUSIONS: We conclude that recombinant PCT inhibits the iNOS-inducing effects of the proinflammatory cytokines TNF-alpha/ IFN-gamma in a dose-dependent manner. This might be a counter-regulatory mechanism directed against the large production of NO and the concomitant systemic hypotension in severe sepsis and septic shock.

Cytokine-inducible growth factor gene expression in human umbilical endothelial cells.

Endothelial cells are known to be involved in different growth promoting processes like angioneogenesis, atherosclerosis or haematopoiesis. A great number of polypeptide growth factors crucial in this context have been isolated and they may be expressed in endothelial cells in either a constitutional or an inducible manner. The aim of the study was to examine the cytokine-inducibility of growth factor gene expression in endothelial cells. As uniform stimulators interleukin 1-alpha (IL-1alpha) and tumour necrosis factor (TNF)-alpha were chosen. Human umbilical arterial endothelial cells (HUAEC) were treated with either IL-1alpha or TNF-alpha and the gene expression of various growth factors was detected by reverse transcription-polymerase chain reaction (RT-PCR). We could demonstrate in HUAEC that stimulation with IL-1alpha- and TNF-alpha led to the mRNA expression of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) which are crucial in the process of angioneogenesis and atherosclerosis as well as of the granulocyte-colony stimulating factor (G-CSF), granulocyte macrophage-colony stimulating factor (GM-CSF) and stem cell factor (SCF) which are main growth factors in haematopoiesis. The demonstration of the inducibility of a wide range of various growth factor genes in endothelial cells is of major interest regarding the growth regulatory role of the endothelium.

Tumour necrosis factor-alpha gene expression and production in human umbilical arterial endothelial cells.

Endothelial cells act as an interface between the blood and tissues, and are known to be involved in inflammatory processes. These cells are responsive to and produce different cytokines. Tumour necrosis factor-alpha (TNF-alpha) not only is one of the most important inflammatory peptides, but also can be induced by lipopolysaccharide (LPS). The focus of the present study was on TNF-alpha gene expression and production in human umbilical arterial endothelial cells (HUAEC), including the kinetics of this process. Interleukin-1alpha (IL-1alpha), LPS and TNF-alpha, which are all known to be elevated in septic shock, were used as stimulators at concentrations commonly found in patients with sepsis. Through the use of reverse transcriptase/PCR, immunohistochemical reactions and ELISA techniques, we showed that, in HUAEC, all three stimuli were able to induce gene expression and production of TNF-alpha. Furthermore, this induction by IL-1alpha, LPS and TNF-alpha occurred in a time- and concentration-dependent manner in these cells. TNF-alpha expression and production was induced by all three agents at concentrations commonly found in patients with sepsis. TNF-alpha mRNA was observed within 30 min regardless of the stimulus used, but the levels peaked at different times. Since it is well established that TNF-alpha is able to induce the synthesis of IL-1alpha in endothelial cells and, as shown in the present study, TNF-alpha and IL-1alpha are themselves able to induce the synthesis of TNF-alpha in endothelial cells, an autocrine potentiation of cytokine release in sepsis can be proposed. This situation could lead to a locally acting 'vicious cycle' which, when considered in addition to the known ability of TNF-alpha to induce apoptosis, could mean that various organs will be damaged, a condition associated with sepsis. Thus these results provide further evidence for the important role played by the endothelium in inflammation.

High percentage of false-positive results of cytokeratin 19 RT-PCR in blood: a model for the analysis of illegitimate gene expression.

Cytokeratin 19 (CK19) RT-PCR is widely used in order to detect circulating tumor cells in peripheral blood and bone marrow. However, increasing amounts of information support the fact that it is also associated with a high percentage of false-positive results. In our study, we not only managed to demonstrate the significant limitations of this method, but were also able to clarify the reasons behind these limitations. We developed a completely novel RT-PCR for CK19 and sequenced an intron at nucleotide (nt) 980 of the CK19 mRNA to exclude DNA contamination. Tumor dilution experiments were performed in order to analyze the specificity and sensitivity of the method. Control experiments using the blood of healthy donors were performed. Tumor cell dilution experiments gave a detection limit of one tumor cell. If tumor cells were mixed with an equal volume of pure mononuclear cells, the detection limit was 1 tumor cell in 10(5) mononuclear cells. RT-PCR of mononuclear cells from healthy blood donors gave false-positive results in 29% of the cases. We conclude that a significant decrease in the sensitivity of CK19 RT-PCR occurs if it is performed in blood cells and that the illegitimate CK19 gene expression in normal cells can lead to false-positive results. These limitations have to be taken into account if RT-PCR is to be used for the detection of tumor cells either in blood or in bone marrow in clinical practice.

A method for the rapid construction of cRNA standard curves in quantitative real-time reverse transcription polymerase chain reaction.

Quantification of nucleic acids, especially of mRNA, is increasingly important in biomedical research. The recently developed quantitative real-time polymerase chain reaction (PCR) - a highly sensitive technology for the rapid, accurate and reproducible quantification of gene expression - offers major advantages over conventional quantitative PCR. Transcript quantification is performed in the exponential phase of the PCR reaction through extrapolation of fluorescence signals from a standard calibration curve which represents the initial copy number for a given fluorescence signal. We have developed a method for gene transcript quantification which is based on a LightCycler - assisted real-time PCR in combination with a simple and rapid approach for the construction of external cRNA standards with identical gene sequences as the target gene. Synthesis of cRNAs was performed by in vitro transcription with T7 RNA polymerase followed by reverse transcription and real-time PCR. We applied this approach for transcript quantification of eukaryotic initiation factor 3 p110 (EIF3S8) mRNA in normal testicular tissue. We also present a rapid and simple strategy for the construction of cRNA standards for use in real-time PCR.