Positive Allosteric Modulators of AMPA Receptors Reduce Proton-Induced Receptor Desensitization in Rat Hippocampal Neurons

Whole-cell or outside-out patch recordings were used to investigate the effects of protons and positive modulators of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors on the desensitization of glutamate-evoked AMPA receptor currents in isolated hippocampal CA1 neurons. Protons inhibited glutamate-evoked currents (IC50 of 6.2 pH units) but also enhanced the apparent rate and extent of AMPA receptor desensitization. The proton-induced enhancement of desensitization could not be attributed to a reduction in the rate of recovery from desensitization or to a change in the kinetics of deactivation. Non-stationary variance analysis indicated that protons reduced maximum open probability without changing the conductance of AMPA channels. The positive modulators of AMPA receptor desensitization, cyclothiazide and GT-21-005 (an organic nitrate), reduced the proton sensitivity of AMPA receptor desensitization, which suggests that they interact with protons to diminish desensitization. In contrast, the effects of wheat germ agglutinin and aniracetam on AMPA receptor desensitization were independent of pH. These results demonstrate that a reduction in the proton sensitivity of receptor desensitization contributes to the mechanism of action of some positive modulators of AMPA receptors.

[Effects of calcium channel antagonist on gastrin-induced proliferation of HT29 colon carcinoma cells]

OBJECTIVE

This study aimed to assess the effects of nifedipine on gastrin-induced proliferation of HT29 colon carcinoma cells and inquire into the possible mechanisms.

METHODS

Flow cytometry was used to monitor the cytoplasmic free calcium; MTT colorimetry was used to determine the proliferation of HT29 cells.

RESULTS

The results showed that 2.5 x 10(-6) mol/L pentagastrin (PG) induced a quick rise of intracellular free calcium ([Ca2+]i) (P < 0.01). 10(-5) mol/L nifedipine can significantly inhibited the rise of [Ca2+]i induced by pentagastrin (P < 0.01), in parallel, at growth assay we demonstrated that 10(-5)-10(-6) mol/L nifedipine could obviously block the increase in cell number elicited by 2.5 x 10(-6) mol/L PG.

CONCLUSION

These data indicate that nifedipine can stop the influx of Ca2+ and hence inhibit the pentagastrin-induced proliferation.

[Effects of estradiol and isoflavoid on the expression of adhesion molecules on neutrophils]

OBJECTIVE

To elucidate the effects of estradiol and isoflavoid on the expression of adhesion molecules on neutrophils.

METHODS

Neutrophils of healthy subjects and ischemic stroke patients were treated with tumor necrosis factor alpha (TNF alpha), in the presence or absence of different concentrations of isoflavoid (WZ1, WZ2) and estradiol (WZ3, WZ4). Flow cytometry was used to detect the expression of CD18 and CD62L on neutrophil surface.

RESULTS

1. 10 ng/ml TNF alpha could activate neutrophils of healthy subjects; it increased the expression of CD18 by 10% on neutrophil surface and shed CD62L from the surface as shown by a 15% decrease of the fluorescence intensity and a 30% decrease of the percentage of positive cell. 2. Isoflavoid (WZ1, WZ2) had no significant effect on the expression of CD18 and CD62L on neutrophils. 3. Pretreatment of neutrophils with estradiol (WZ3, WZ4) could inhibit the activation of neutrophils by TNF alpha, which decreased the fluorescence intensity of CD18 by 8%, increased the fluorescence intensity of CD62L by 15% and increased the percentage of CD62L positive cell by 20%. 4. TNF alpha could activate the neutrophils of ischemic stroke patients strikingly; it increased the fluorescence intensity of CD18 by 20% and decreased the fluorescence intensity and percentage of positive cell of CD62L by 30%, and there was a significant difference when the patients were compared with the healthy subjects. Estradiol had the same effect on the expression of CD18 and CD62L as on those of healthy subjects.

CONCLUSION

1. TNF alpha is a strong activator of neutrophils; it plays an important role in the occurrence and development of ischemic stroke. 2. Isoflavoid has no obvious effect on the expression of adhesion molecules on neutrophils, so its role in protecting the cardiovascular system may come into play not by the way of affecting adhesion molecules expression. 3. Pretreatment of neutrophils with estradiol could protect them from activation by TNF alpha, thus decreasing the expression of adhesion molecules, the adhesion of neutrophils -endothelial cells, and hence the risk of ischemic stroke. However, in case that the neutrophils have been activated by TNF alpha, estradiol has no effect on the expression of adhesion molecules; this implies that estradiol possibly has no valid anti-adhesion therapeutic effect on ischemic stroke.

[A kinetic study on the relationship between of IL-5, IL-10 and eosinophil apoptosis in asthmatic airway inflammation]

OBJECTIVE

To observe time-course profile of eosinophil apoptosis, in murine asthma models in airway explicate its implication for asthmatic inflammation remission, and investigate the role of IL-5 and IL-10 in modulating cell apoptosis.

METHODS

An animal model of asthma was established by OVA sensitizing-challenging BALB/c mice. Histologic study of lung tissue was made with the use of electronmicroscope. At seven points (0 h, 8 h, 24 h, 48 h, 96 h, Day 7 and Day 14) in the time course after challenge, bronchoalveolar lavage (BAL) was performed obtain BAL cells and recover fluid. Levels of IL-5 and IL-10 were detected by ELISA. Cell apoptosis was assayed by PI stain on a flow cytometer.

RESULTS

After challenge, apoptosis of eosinophils, lymphocytes, endothelial cells could be seen under the electronmicroscope. IL-5 in BALF elevated significantly whereas no significant difference was found between the levels of IL-10 in BALF before and after challenge. Eosinophil apoptosis was identified and a two-phase elevation of apoptosis percentages was observed, although no significant difference was found between average apoptosis in asthmatic group and that in control. Data analyses revealed a negative correlation between apoptosis percentages and the levels of IL-5, and a closer correlation between the percentages and IL-5/IL-10 ratio.

CONCLUSION

IL-5 and IL-10 could up- and down-regulate asthmatic airway inflammation, respectively. EOS underwent apoptosis in situ and this was modulated by IL-5 and IL-10 interaction.

Previous pulmonary diseases and risk of lung cancer in Gansu Province, China

BACKGROUND

Although active smoking is well established as the main cause of lung cancer, there is accumulating evidence that history of prior lung diseases may be an independent risk factor for lung cancer.

METHODS

A population-based case-control study in Gansu Province, China identified 886 lung cancer cases (656 male, 230 female) diagnosed between January 1994 and April 1998. A standardized interview collected information on a variety of potential risk factors including a history of physician-diagnosed non-malignant lung diseases (pulmonary tuberculosis, chronic bronchitis/emphysema, asthma, pneumonia), age and year in which each condition was first diagnosed, and any therapy or hospitalization received.

RESULTS

Pulmonary tuberculosis (odds ratio [OR] = 2.1, 95% CI : 1.4-3.1) and chronic bronchitis/emphysema (OR = 1.4, 95% CI : 1.1-1.8) were associated with increased risk of lung cancer, after adjustment for active smoking and socioeconomic status. The OR for asthma (OR = 1.4, 95% CI : 0.9-2.1) and pneumonia (OR = 1.5, 95% CI : 1.0-2.3) were also elevated. The risk of lung cancer remained significant for pulmonary tuberculosis and chronic bronchitis/emphysema when analysis was limited to the pathologically confirmed cases and self-responders.

CONCLUSIONS

This study provides additional evidence that previous pulmonary tuberculosis and chronic bronchitis/emphysema are causally related to lung cancer, although the precise mechanism is still unclear. The results for asthma and pneumonia, while suggestive of a positive association, did not reach the traditional level of statistical significance and should be interpreted with caution.

Immunotherapy of tumors with xenogeneic endothelial cells as a vaccine

The breaking of immune tolerance against autologous angiogenic endothelial cells should be a useful approach for cancer therapy. Here we show that immunotherapy of tumors using fixed xenogeneic whole endothelial cells as a vaccine was effective in affording protection from tumor growth, inducing regression of established tumors and prolonging survival of tumor-bearing mice. Furthermore, autoreactive immunity targeting to microvessels in solid tumors was induced and was probably responsible for the anti-tumor activity. These observations may provide a new vaccine strategy for cancer therapy through the induction of an autoimmune response against the tumor endothelium in a cross-reaction.

Activation of vanadium nitrogenase expression in Azotobacter vinelandii DJ54 revertant in the presence of molybdenum

Azotobacter vinelandii carries three different and genetically distinct nitrogenase systems on its chromosome. Expression of all three nitrogenases is repressed by high concentrations of fixed nitrogen. Expression of individual nitrogenase systems is under the control of specific metal availability. We have isolated a novel type of A. vinelandii DJ54 revertant, designated A. vinelandii BG54, which carries a defined deletion in the nifH gene and is capable of diazotrophic growth in the presence of molybdenum. Inactivation of nifDK has no effect on growth of this mutant strain in nitrogen-free medium suggesting that products of the nif system are not involved in supporting diazotrophic growth of A. vinelandii BG54. Similar to the wild type, A. vinelandii BG54 is also sensitive to 1 mM tungsten. Tn5-B21 mutagenesis to inactivate the genes specific to individual systems revealed that the structural genes for vnf nitrogenase are required for diazotrophic growth of A. vinelandii BG54. Analysis of promoter activity of different nif systems revealed that the vnf promoter is activated in A. vinelandii BG54 in the presence of molybdenum. Based on these data we conclude that A. vinelandii BG54 strain utilizes vnf nitrogenase proteins to support its diazotrophic growth.

Kinetic study of eosinophil apoptosis and its relationship to Th2 cytokines in asthmatic murine model

OBJECTIVE

To investigate the significance and regulatory mechanism of eosinophil apoptosis in asthmatic airway inflammation using an animal models, as well as its relationship to IL-5 and IL-10.

METHODS

An animal model of asthma was established by ovalbumin (OVA) sensitizing-challenging BALB/C mice. At seven points in the time course after challenge, bronchoalveolar lavage (BAL) was performed to obtain BAL cells. Levels of two Th2 cytokines, IL-5 and IL-10 were detected by ELISA. A double label technique combining CD15 with CD49d was used to distinguish eosinophils from other cell types. Cell apoptosis was assayed by PI stain using a flow cytometer.

RESULTS

Eosinophil apoptosis was identified and a two-phase elevation of apoptosis percentages was observed, although no significant difference was found between average apoptosis in the asthmatic group and that in the control. Analysis of kinetic changes of eosinophil apoptosis and cytokine levels revealed a negative correlation between apoptosis percentages and levels of IL-5, and a closer correlation between apoptosis percentages and the IL-5/IL-10 ratio. Dexamethasone pretreatment markedly reduced IL-5 levels in BAL, elevated eosinophil apoptosis percentages, but had no effect on IL-10 levels.

CONCLUSION

Eosinophils underwent apoptosis in asthmatic airways. Equilibrium between IL-5 and IL-10 not only regulated eosinophil infiltration, but also modulated cell apoptosis.

[Effect of temperature on energy budget of Taiwanese red tilapia hybrid (Oreochromis niloticus x O. mossambicus)]

The energy budget of Taiwanese red tilapia hybrid (Oreochromis niloticus x O. massambicus) with a body weight of 25.33-26.23 g was measured at salinity 14 and at water temperature 22, 28 and 34 degrees C in July-August 1996. The results showed that its specific growth rate, conversion efficiency and maximum food consumption were significantly affected by temperature, and reached peaks of 1.79, 60.01% and 2.59% B.W.d-1 at 28 degrees C. The effect of temperature on the absorption efficiency was not significant, with an average absorption efficiency 64.58%. The effect of temperature on the proportions of food energy allocated to each component of the energy budget was significant. The ratio of growth energy was the highest(26.4%) at temperature 28 degrees C, and that of metabolism energy was 37.23%.

Identification of a second site compensatory mutation in the Fe-protein that allows diazotrophic growth of Azotobacter vinelandii UW97

Azotobacter vinelandii UW97 is defective in nitrogen fixation due to a replacement of serine at position 44 by phenylalanine in the Fe-protein [Pulakat, L., Hausman, B.S., Lei, S. and Gavini, N. (1996) J. Biol. Chem. 271, 1884-1889]. Serine residue 44 is located in a conserved domain that links the nucleotide binding site and the MoFe-protein docking surface of the Fe-protein. Therefore, it is possible that the loss of function by A. vinelandii UW97-Fe-protein may be caused by global conformational disruption or disruption of the conformational change upon MgATP binding. To determine whether it is possible to generate a functional nitrogenase complex via a compensating second site mutation(s) in the Fe-protein, we have attempted to isolate genetic revertants of A. vinelandii UW97 that can grow on nitrogen-free medium. One such revertant, designated A vinelandii BG9, encoded a Fe-protein that retained the Ser44Phe mutation and also had a second mutation that caused the replacement of a lysine at position 170 by glutamic acid. Lysine 170 is highly conserved and is located in a conserved region of the Fe-protein. This region is implicated in stabilizing the MgATP-induced conformation of the Fe-protein and in docking to the MoFe-protein. Further complementation analysis showed that the Fe-protein mutant that retained serine 44 but contained the substitution of lysine at position 170 by glutamic acid was also non-functional. Thus, neither Ser44Phe nor Lys170Glu mutants of Fe-protein were functional; however, the Fe-protein in A. vinelandii BG9 that contained both substitutions could support diazotrophic growth on the strain.

[Quantification analysis of vascular endothelial cells in human solid tumor]

Angiogenesis is essential for the growth and metastasis of solid tumors. Intratumoral microvessel count, which represents a measure of tumor angiogenesis, has been associated with prognosis of patients with a variety of malignancies. But till now, it is still a problem to quantitate the angiogenesis of tumors exactly. In this study, the endothelial cells in 20 solid tumors were conjugated with anti-CD34 monoclonal antibodies labelled with red-fluorescent substances, and were observed by fluorescence microscopy and quantitated by flow cytometry. The results of flow cytometry were analysed by t-test. The correlation was analysed between percentage of flow cytometry and vessel counts (light microscopy, x 200) in each tumor which was stained with anti-CD34 monoclonal antibodies and anti-VIII factor related antigen polyclonal antibodies by using immunohistochemistry. The results showed there was significant difference between the treatment group and control group in flow cytometry, and a significant correlation between the endothelial cells percentage by flow cytometry and the vessel counts by immunohistochemistry was observed, although the average vessel counts were approximately three times with CD34 staining as much as with VIII factor related antigen staining. These data indicate that flow cytometry as a novel method can quantitate angiogenesis of tumors exactly and quickly.

[The relationship of cellular DNA content with clinical stage and biological features of colorectal cancer]

The purpose of this study was to explore the relationship of cellular DNA content with clinical stage and biological features of cancer. Flow cytometry was performed on fresh specimens from 86 patients from 1997 to 1998. Forty-five (53.3%) specimens were found to contain cells with abnormal DNA (DNA nondiploidy). Although none of the sex, age, site, differentiation variables correlated with flow cytometric DNA ploidy, nondiploidy was associated with Dukes' stage and lymph node metastasis. Duke's A stage tumors were more frequently diploid than were more advanced tumors, but no difference between Duke's B, C and D stages were observed. These findings suggest that ploidy is associated with some pathological factors.

Cyclic GMP-dependent feedback inhibition of AMPA receptors is independent of PKG

In central neurons, the second messenger cGMP is believed to induce long-term changes in efficacy at glutamatergic synapses through activation of protein kinase G (PKG). Stimulating nitric oxide synthase, activating soluble guanylyl cyclase or elevating concentrations of intracellular cGMP depressed excitatory synaptic transmission in CA1 hippocampal neurons. Unexpectedly, intracellular cGMP depressed responses of AMPA receptors and inhibited excitatory postsynaptic currents in hippocampal neurons independently of phosphorylation. Our findings demonstrate that cGMP's modulation of excitatory transmission may involve a coupling of AMPA channel activity to levels of cGMP.

[The relations of cellular DNA content to lymph node metastasis in gastric carcinoma]

The objectives of this study were to evaluate the relations of cellular DNA content, S-phase fraction (SPF) and G2/M-phase(G2/MPF) to lymph node metastasis in gastric carcinoma by using flow cytometry. The results showed that the incidence of lymph node metastasis and SPF were significantly higher in aneuploid carcinoma than in diploid carcinoma(P < 0.05). But the G2/MPF values did not correlate with lymph node metastasis. These findings suggest that correlations between cellular DNA content, SPF and the extent of lymph node metastasis are present.

Proteasome inhibition circumvents solid tumor resistance to topoisomerase II-directed drugs

Physiological cell conditions, such as glucose deprivation and hypoxia, play a role in developing drug resistance in solid tumors. These tumor-specific conditions cause decreased expression of DNA topoisomerase IIalpha (topo IIalpha), rendering cells resistant to topo II-targeted drugs, such as etoposide and doxorubicin. We show here that inhibition of proteasome attenuated drug resistance by inhibiting topo IIalpha depletion induced by glucose starvation and hypoxia. topo IIalpha restoration was seen only at the protein levels, indicating that the topo IIalpha protein depletion occurred through a proteasome-mediated degradation mechanism. The stress-induced etoposide resistance was effectively prevented in vitro by the proteasome inhibitor lactacystin in both intrinsically resistant and sensitive tumor cells (colon cancer HT-29 and ovarian cancer A2780 cells, respectively). Furthermore, lactacystin effectively enhanced the antitumor activity of etoposide in the refractory HT-29 xenograft. These results indicate that lactacystin could serve as a new therapeutic agent to circumvent resistance to topo II-targeted chemotherapy in solid tumors.

Neuronal nicotinic receptors in non-neuronal cells: new mediators of tobacco toxicity?

The nicotinic acetylcholine receptors are prototypic ionotropic receptors that mediate fast synaptic transmission. However, also non-excitable cells, and particularly the tegumental cells that line external and internal body surfaces, express acetylcholine receptors of neuronal type sensitive to nicotine. Bronchial epithelial cells, endothelial cells of blood vessels and skin keratinocytes express neuronal nicotinic receptors composed of alpha(3), alpha(5), beta(2) and beta(4) subunits, similar to those expressed in sympathetic ganglia, and neuronal nicotinic receptors composed of alpha(7) subunits. Neuronal nicotinic receptors in tegumental cells are involved in modulating cell shape and motility, and therefore in maintaining the integrity of the surfaces lined by those cells. Neuronal nicotinic receptors in non-neuronal tissues may modulate other functions, including cell proliferation and differentiation. Acetylcholine is synthesized, secreted and degraded by a variety of cells, including the tegumental cells that express neuronal nicotinic receptors. Thus, acetylcholine may function as a local "hormone" that is able to modulate cell functions that require fast adaptation to new conditions. The presence of neuronal nicotinic receptors sensitive to nicotine in tissues known to be involved in tobacco toxicity, like bronchi and blood vessels, raises the possibility that they mediate some of the toxic effects of smoking.

[Cell cycle analysis and pathological changes of malignant tumors treated with electrochemical therapy]

To investigate the mechanism and to observe the effectiveness of electrochemical therapy(ECT), 33 patients of late stage cancers which treated by ECT were included in this study. Flow cytometry (FCM) and pathology were used to observe the changes of tumor cells before and after ECT. Tumor cells of G1, G2/M, S phases and aneuploid cells were found to be killed almostly and the ratio of apoptosis was elevated greatly after ECT. Also, pathological evidence proved the death of tumor cells and some characters of apoptosis. So, ECT can non-selectively kill tumor cells and induce the apoptosis of them, and FCM was a way to evaluate the effectiveness of ECT.

[The effect of vasectomy on spermatogenesis and proliferation of rat spermatogenic cell]

In order to explore the effect of vasectomy on spermatogenesis and proliferation of rat spermatogenic cell, we detected the DNA content of rat spermatogenic cells by flow cytometry at 4 weeks and 8 weeks after vasectomy. The results showed that the percentages of 1C cell group (spermatid and sperm) in the two experimental groups were apparently lower than that of the two control groups respectively (P < 0.05), but the percentage of 2C cell group (spermatogonium and spermotocyte) in the two experiment groups were much higher than those of the two control groups respectively (P < 0.05); The proliferation index (PI) of experimental groups was significantly lower than that of control groups (P < 0.05) and most of the cells in the experimental groups were on G0/G phase. The percentage of S-phase cell in the 8 weeks experimental group was obviously lower than that of the 4 weeks experimental group. These findings suggest that vasectomy in rat may affect many stages in spermatogenesis and delay the proliferation of spermatogenic cell.

[Flow cytometry for testing chemosensitivity of malignant bone tumors]

OBJECTIVE

To study chemosensitivity and multidrug resistance of malignant bone tumors and to make an individual protocol of chemotherapy with sensitive antitumor agents.

METHODS

Apoptosis induced by MTX, ADM, MMC, VP-16, VCR and CTX, and chemosensitivity in 32 fresh specimens of malignant bone tumors were analyzed by flow cytometry (FCM) and quantitative immunofluorescence. The expression of P-glycoprotein (P170) in the specimen and the relation between P170, multidrug resistance, and chemosensitivity were detected.

RESULTS

The rate of apoptosis was significantly different in malignant bone tumor cells treated with different drugs: MTX (30.50 +/- 10.22)%, ADM (26.28 +/- 9.35)%, MMC (23.11 +/- 7.38)%, VP-16 (18.17 +/- 6.14)%, VCR (4.44 +/- 2.55)%, and CTX (1.22 +/- 0.59)%. The individual variation of cell apoptosis was prominent in the specimens of same pathological type treated with same agent. There was lower chemosensitivity in the malignant bone tumors with a high expression of P170.

CONCLUSIONS

Chemosensitivity testing by flow cytometry is a simple, quick and sensitive assay. Quantitative analysis of expression of P170 could be used to predict multidrug resistance and its chemosensitivity of malignant bone tumors.

[Changes of F-actin in neutrophils under fluid shear stress]

Neutrophils are the main defender in the body, and their physiological characters are associated with functions. Because the environments of neutrophils maturation and storage are different from their function environment, they have to adapt thess changes. Filamentous actin (F-actin), as one of the important cytoskeleton components of neutrophils, has different quantity and distribution under different physiological conditions. Previous researches are all focused on static activation of neutrophils using various stimulants such as formyl-methionyl-leucyl-phenylalanine (f-MLP) and tumor necrosis factor(TNF). In our study, Low-Shear 30 and NXE-1 rheometers were used to provide steady or sinusoidaloscillatory fluid shear stress on separated neutrophils. Fluorescent agent Tritc-Phalloidin was added to label F-actin and the mean fluorescent intensity tested by flow cytometry was used as the indication of F-actin quantity and confocal laser scan microscope was used to detect the distribution of F-actin in neutrophils. We found that F-actin polymerization was significantly decreased under both steady and sinusoidal-oscillatory shear stress when the shear stress was below certain level. The density of the cortex F-actin near cell membrane in cells sheared became thinner than in that without shear stress. f-MLP and TNF both could increase actin polymerization in neutophils due to activation. When neutorphils were activated with f-MLP or TNF under shear stress, the quantity of F-actin in the cells was also decreased, but it was still higher than that in the cells absent of f-MLP or TNF. We concluded that neutrophils had different mechanical properties in different fluid environments. F-actin content and distribution would change according to the shear stress values to play their determinant role in neutrophils mechanical adaptation. The mechanism of actin polymerization in neutrophils for mechanical action is probably different from that for chemoattractants and cytokine activation.

Platelet-derived growth factor receptor-induced feed-forward inhibition of excitatory transmission between hippocampal pyramidal neurons

Growth factor receptors provide a major mechanism for the activation of the nonreceptor tyrosine kinase c-Src, and this kinase in turn up-regulates the activity of N-methyl-D-aspartate (NMDA) receptors in CA1 hippocampal neurons (1). Unexpectedly, applications of platelet-derived growth factor (PDGF)-BB to cultured and isolated CA1 hippocampal neurons depressed NMDA-evoked currents. The PDGF-induced depression was blocked by a PDGF-selective tyrosine kinase inhibitor, by a selective inhibitor of phospholipase C-gamma, and by blocking the intracellular release of Ca(2+). Inhibitors of cAMP-dependent protein kinase (PKA) also eliminated the PDGF-induced depression, whereas a phosphodiesterase inhibitor enhanced it. The NMDA receptor-mediated component of excitatory synaptic currents was also inhibited by PDGF, and this inhibition was prevented by co-application of a PKA inhibitor. Src inhibitors also prevented this depression. In recordings from inside-out patches, the catalytic fragment of PKA did not itself alter NMDA single channel activity, but it blocked the up-regulation of these channels by a Src activator peptide. Thus, PDGF receptors depress NMDA channels through a Ca(2+)- and PKA-dependent inhibition of their modulation by c-Src.

Regulated expression of the nifM of Azotobacter vinelandii in response to molybdenum and vanadium supplements in Burk's nitrogen-free growth medium

Azotobacter is a diazotrophic bacterium that harbors three genetically distinct nitrogenases referred to as nif, vnf, and anf systems. The nifM is an accessory gene located in the nif gene cluster and is transcriptionally regulated by the NifA. However, Azotobacter mutants that lack NifA are known to synthesize functional NifM and this accessory protein is known to be needed for the activity of nitrogenase-2 and nitrogenase-3. To determine how the transcription of nifM is regulated when Azotobacter is grown under conditions in which nitrogenase-2 or nitrogenase-3 is expressed, we generated an Azotobacter vinelandii strain that carries a nifM:lacZ-kanamycin resistance gene cassette in its chromosome. In this strain the nifM open reading frame was disrupted by the presence of a lacZ-kanamycin resistance gene cassette so that it could not produce active NifM. Moreover, the lacZ gene was placed under the transcriptional control elements of the nifM gene so that the lacZ expression could be used as a marker to determine the extent of expression of the nifM gene under different growth conditions. Our results show that this strain was unable to grow in Burk's nitrogen-free medium supplemented with either molybdenum or vanadium or lacking both metals suggesting that in the absence of functional NifM none of the nitrogenases were active. It was also found that the nifM expression was differentially regulated when the A. vinelandii cells were grown under conditions that activate nitrogenase-2 and nitrogenase-3, as determined by liquid beta-galactosidase activity measurements. These results suggest that the transcriptional activators, VnfA and AnfA, may regulate the nifM expression.

Genetic analysis of nif regulatory genes by utilizing the yeast two-hybrid system detected formation of a NifL-NifA complex that is implicated in regulated expression of nif genes

In diazotrophic organisms, nitrogenase synthesis and activity are tightly regulated. Two genes, nifL and nifA, are implicated as playing a major role in this regulation. NifA is a transcriptional activator, and its activity is inhibited by NifL in response to availability of excess fixed nitrogen and high O(2) tension. It was postulated that NifL binds to NifA to inhibit NifA-mediated transcriptional activation of nif genes. Mutational analysis combined with transcriptional activation studies clearly is in agreement with the proposal that NifL interacts with NifA. However, several attempts to identify NifA-NifL interactions by using methods such as coimmunoprecipitations and chemical cross-linking experiments failed to detect direct interactions between these proteins. Here we have taken a genetic approach, the use of a yeast two-hybrid protein-protein interaction assay system, to investigate NifL interaction with NifA. A DNA fragment corresponding to the kinase-like domain of nifL was PCR amplified and was used to generate translation fusions with the DNA binding domain and the DNA activation domain of the yeast transcriptional activator GAL4 in yeast two-hybrid vectors. Similarly, a DNA fragment corresponding to the catalytic domain of nifA was PCR amplified and used to generate translation fusions with the DNA-binding domain and the DNA-activation domain of GAL4 in yeast two-hybrid vectors. After introducing appropriate plasmid combinations in yeast cells, the existance of direct interaction between NifA and NifL was analyzed with the MATCHMAKER yeast two-hybrid system by testing for the expression of lacZ and his3 genes. These analyses showed that the kinase-like domain of NifL directly interacts with the catalytic domain of NifA.

[Effect of immunologic treatment on lymphocyte subsets in patients with myasthenia gravis]

OBJECTIVE

To study the abnormalities of cellular immunity of myasthenia gravis (MG) and the effects of glucocorticoid (GC) therapy and thymectomy on lymphocyte subsets in patients with myasthenia gravis.

METHODS

Phenotypic analysis of peripheral blood lymphocyte in 39 patients with MG and 18 healthy controls were completed using flow cytometry and immunofluorescence double-staining methods; changes of lymphocyte subsets were studied in 15 of the MG patients after GC therapy and 7 of the MG patients after thymectomy.

RESULTS

(1) The percentage of pan-T (CD(+)(5)), pan-B (CD(+)(19)), traditional B cell, CD(+)(4)T cell in patients with MG did not significantly differ from that in healthy controls. An increase in CD(+)(8) cell was observed in MG patients as compared with normal controls. Among the CD(+)(4) T lymphocyte subsets, there was significant decrease of the percentage of CD(+)(4) CD(45)RA(+) (suppressor-inducer) and increase of the percentage of CD(+)(4) CD(45)RA(-) (helper-inducer) subsets in MG patients than controls; the percentage of CD(+)(5) B cell was significantly increased in MG patients as compared with that in healthy controls. (2) After GC therapy, the percentages of pan-T (CD(+)(5)), pan-B (CD(+)(19)), traditional B cell, CD(+)(4) T cell, CD(+)(8) T cell, CD(+)(4) CD(45)RA(-), CD(+)(5) B cell decreased. (3) After thymectomy, the proportions of T, B lymphocyte subsets did not change significantly.

CONCLUSION

Not only changes of T cell subsets (CD(+)(4) and CD(+)(8) T lymphocyte subsets) were shown, but also there were abnormal changes of functional CD(+)(4) T lymphocyte subsets and CD(+)(5) B lymphocyte which may play an important role in the pathogenesis of MG. There is comprehensive inhibiting action of GC on cellular immunity in MG patients, while there is no such effect with thymectomy on the lymphocyte subsets in MG patients.

[An analysis of DNA content in 405 cases of human tumor by flow cytometry]

This study was intended to evaluate the relationship between the DNA content of cell cycle and the histology in human tumors. We detected the DNA content in 405 cases of fresh human tumor tissue by means of flow cytometry and observed the histology of tumor with light microscopy. The occurrences of aneuploidy in 22 cases of benign tumor and 383 cases of malignant tumor were 27% and 52% respectively. There were differences in aneuploidy in different histologic types of tumor. The aneuploidy in adenocarcinoma was about 50%, that in sarcoma was more than 37%, and that in squamous carcinoma less than 17%. S > or = 10, G2/m > or = 10 or S > or = 20, G2/m > or = 5 were present in malignant tumors, but were not found in benign tumors. The results suggest that there is obvious difference in the occurrences of aneuploidy in benign and malignant tumors and in different histologic type of tumor(P < 0.05). Benign and malignant tumor may be distinguished when SPF and G2/m reach a higher level (P < 0.01).