Electrical coupling between olfactory glomeruli

In the Drosophila antennal lobe, excitation can spread between glomerular processing channels. In this study, we investigated the mechanism of lateral excitation. Dual recordings from excitatory local neurons (eLNs) and projection neurons (PNs) showed that eLN-to-PN synapses transmit both hyperpolarization and depolarization, are not diminished by blocking chemical neurotransmission, and are abolished by a gap-junction mutation. This mutation eliminates odor-evoked lateral excitation in PNs and diminishes some PN odor responses. This implies that lateral excitation is mediated by electrical synapses from eLNs onto PNs. In addition, eLNs form synapses onto inhibitory LNs. Eliminating these synapses boosts some PN odor responses and reduces the disinhibitory effect of GABA receptor antagonists on PNs. Thus, eLNs have two opposing effects on PNs, driving both direct excitation and indirect inhibition. We propose that when stimuli are weak, lateral excitation promotes sensitivity, whereas when stimuli are strong, lateral excitation helps recruit inhibitory gain control.

Effects of cadmium on absorption, excretion, and distribution of nickel in rats

The effects of cadmium (Cd (II)) on absorption, excretion, and distribution of nickel (Ni (II)) were studied in rats using (63)Ni-NiCl(2) as radiotracer in the presence and absence of CdCl(2), through intraperitoneal injection (i.p.). The time-concentration curves in the blood were fitted with a two-compartment model. The peak time (t ((peak))) is 0.31 h in the absence of Cd (II), and it is 5.5 h in the presence of Cd (II). The levels of nickels were higher at 3 h and lower (close to zero) at 24 h in all organs of interest, except kidneys, in the absence of Cd (II). There still residue Ni (II) at 72 h post-injection in the presence of Cd (II). The Cd (II) did effect the total Ni (II) excretion 24 h post-injection. Our study showed that cadmium has a competitive effect on the absorption of nickel and an inhibitory effect on the elimination of it, so cadmium may induce the bioaccumulation of nickel in the body.

Changes in the peritubular tissue of rat testis after cadmium treatment

The present study demonstrates histological and immunohistochemical changes in the peritubular testicular tissue of rat testis after application of cadmium chloride. After 5-day cadmium exposure, advanced deterioration of the boundary testicular tissue, mainly oedema, disarrangement of collagen fibres and peritubular cells, dilatation and thrombosis of blood vessels were observed. Changes in the boundary tissue were accompanied with desquamation of the germinal epithelium. Immunohistochemically, positive reaction for alpha-smooth muscle actin and desmin in tunica media of large testicular blood vessels basically was not affected. No reaction for vimentin was seen in endothelial cells of blood capillaries, whereas positive reaction presented only these cells in large blood vessels. The myofibroblasts positively reacting for desmin and alpha-smooth muscle actin form a single incomplete layer in the lamina propria of seminiferous tubules. Vimentin reactivity in the myofibroblasts and in the supporting Sertoli cells as well as Leydig cells in damaged testicular tissue was not observed. An increase in fibroblasts and free inflammatory cells positive for vimentin in the peritubular space on the peripheric area of the testis was observed.

Influence of metal ions on the interaction between gatifloxacin and calf thymus DNA

To study the interaction between gatifloxacin (GT), metal ions (Cu(2+), Cd(2+), Co(2+), Mg(2+)) and calf thymus DNA under condition of physiology pH, UV absorption and fluorescence methods were adopted. Result shows that metal ions and DNA are able to react with GT in ground state. In further research, by studying the influence of metal ions on binding of GT with DNA in metal ions-GT-DNA ternary system, we found that influential mechanism of Mg(2+) on the binding of GT with DNA may be different from the other three. Mg(2+) can act as a bridge in the binding of GT's carboxyl/carbonyl with DNA phosphate in certain concentration range; while Cu(2+), Cd(2+), Co(2+) can combine directly with GT by reaction between GT carboxyl/carbonyl and DNA base, and enhance the binding ability of GT with DNA. The influence extent and type depend not only on the binding site of DNA with metal ions (phosphate or base), but also the binding ability of which. The stronger the binding ability of metal ions with DNA base is, the larger their promotion to binding of GT with DNA is. The order of metal ions' influential ability on the binding of GT-DNA is identical to the binding ability order of metal ions with DNA base, that is: Cu(2+)>Cd(2+)>Co(2+)>Mg(2+).

Differential response of antioxidant enzymes to cadmium stress in tolerant and sensitive cell line of cucumber (Cucumis sativus L.)

Previously, a stable cell suspension of cucumber tolerant to 100 microM CdCl(2) was obtained (Gzyl & Gwóźdź, 2005, Plant Cell Tissue Organ Cult 80: 59-67). In this study, the relationship between the activity of antioxidant enzymes and cadmium tolerance of cucumber cells was analyzed. A cadmium-sensitive and the cadmium-tolerant cell lines were exposed to 100 microM and 200 microM CdCl(2) and the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APOX) and guaiacol peroxidase (POX) were determined. In the sensitive cell line, a decrease of total activity of SOD and POX was observed, whereas the activity of CAT and APOX significantly increased in metal-supplemented medium. By contrast, in the tolerant cells, the total activity of antioxidant enzymes decreased (SOD, CAT) or was maintained at approximately the same level (APOX, POX). Moreover, a different pattern of isoenzyme activity was observed in the tolerant and sensitive cells. These results suggest that an enhanced activity of antioxidant enzymes is not directly involved in the increased tolerance to cadmium of the selected cucumber cell line.

Peroxisome dynamics in Arabidopsis plants under oxidative stress induced by cadmium

Peroxisomes are organelles with an essentially oxidative metabolism that are involved in various metabolic pathways such as fatty acid beta-oxidation, photorespiration, and metabolism of reactive oxygen species (ROS) and reactive nitrogen species. These organelles are highly dynamic but there is little information about the regulation of, and the effects of environment on, peroxisome movement. In this work a stable Arabidopsis line expressing the GFP-SKL peptide targeted to peroxisomes was characterized. Peroxisome-associated fluorescence was observed in all tissues, including leaves (mesophyll and epidermal cells, trichomes, and stomata) and roots. The dynamics of peroxisomes in epidermal cells was examined by confocal laser microscope, and various types of movement were observed. The speed of movement differed depending on the plant age. Treatment of plants with CdCl(2) (100 microM) produced a significant increase in speed, which was dependent on endogenous ROS and Ca(2+), but was not related to actin cytoskeleton modifications. In light of the results obtained, it is proposed that the increase in peroxisomal motility observed in Arabidopsis plants could be a cellular mechanism of protection against the Cd-imposed oxidative stress. Other possible roles for the enhanced peroxisome movement in plant cell physiology are discussed.

Cloning and expression analysis of 14 lipid transfer protein genes from Tamarix hispida responding to different abiotic stresses

Plant lipid transfer proteins (LTPs) are ubiquitous lipid-binding proteins that are involved in various stress responses. In this study, we cloned 14 unique LTP genes (ThLTP 1-14) from Tamarix hispida Willd. (Tamaricaceae) to investigate their roles under various abiotic stress conditions. The expression profiles of the 14 ThLTPs in response to NaCl, polyethylene glycol (PEG), NaHCO(3), CdCl(2) and abscisic acid (ABA) exposure in root, stem and leaf tissues were investigated using real-time RT-PCR. The results showed that all 14 ThLTPs were expressed in root, stem and leaf tissues under normal growth conditions. However, under normal growth conditions, ThLTP abundance varied in each organ, with expression differences of 9000-fold in leaves, 540-fold in stems and 3700-fold in roots. These results indicated that activity and/or physiological importance of these ThLTPs are quite different. Differential expression of the 14 ThLTPs was observed (> 2-fold) for NaCl, PEG, NaHCO(3) and CdCl(2) in at least one tissue indicating that they were all involved in abiotic stress responses. All ThLTP genes were highly induced (> 2-fold) under ABA treatment in roots, stems and/or leaves, and particularly in roots, suggesting that ABA-dependent signaling pathways regulated ThLTPs. We hypothesize that ThLTP expression constitutes an adaptive response to abiotic stresses in T. hispida and plays an important role in abiotic stress tolerance.

The inhibition effect of 2,3,7,8-tetrachlorinated dibenzo-p-dioxin-induced aryl hydrocarbon receptor activation in human hepatoma cells with the treatment of cadmium chloride

Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), considered as endocrine disruptors, tend to accumulate in fatty tissues. Dioxin-responsive element chemical activated luciferase gene expression assay (DRE-luciferase assay) has been recognized as a semi-quantitative method for screening dioxins for its fast and low-cost as compared with HRGC/HRMS. However, some problems with the bioassay, including specificity, detection variation resulted from different cleanup strategies, and uncertainty of false-negative or false-positive results, remain to be overcome. Cadmium is a prevalent environmental contaminant around the world. This study was aimed to examine the effects of cadmium on the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced activation of aryl hydrocarbon receptor (AhR)-mediated gene expression in human hepatoma cells (Huh7-DRE-Luc cells and Huh7 cells). Ethoxyresorufin-O-deethylase (EROD) and DRE-luciferase assay were employed to determine the enzyme activity of cytochrome P450 1A1 (CYP1A1) and activation of AhR, respectively. The results showed that Cd(2+) levels significantly inhibited the induction of TCDD-induced CYP1A1 and DRE luciferase activation in hepatoma cells. The 50% inhibited concentrations (IC(50)) of CdCl(2) were 0.414 microM (95% confidence interval (C.I.): 0.230-0.602 microM) in Huh7-DRE-Luc cells and 23.2 microM (95% C.I.: 21.7-25.4 microM) in Huh7 cells. Accordingly, prevention of interference with non-dioxin-like compounds in a DRE-luciferase assay is of great importance in an extensive cleanup procedure.

Comparison of chemical binding to recombinant fathead minnow and human estrogen receptors alpha in whole cell and cell-free binding assays

Mammalian receptors and assay systems are generally used for in vitro screening of endocrine-disrupting chemicals with the assumption that minor differences in amino acid sequences among species do not translate into significant differences in receptor function. Objectives of the present study were to evaluate the performance of two different in vitro assay systems (a whole cell and a cell-free competitive binding assay) in assessing whether binding of chemicals differs significantly between full-length recombinant estrogen receptors from fathead minnows (fhERalpha) and those from humans (hERalpha). It was confirmed that 17beta-estradiol displays a reduction in binding to fhERalpha at an elevated temperature (37 degrees C), as has been reported with other piscine estrogen receptors. Several of the chemicals (17beta-estradiol, ethinylestradiol, alpha-zearalanol, fulvestrant, dibutyl phthalate, benzyl butyl phthalate, and cadmium chloride) displayed higher affinity for fhERalpha than for hERalpha in the whole cell assay, while only dibutyl phthalate had a higher affinity for fhERalpha than for hERalpha in the cell-free assay. Both assays were effective in identifying strong binders, weak binders, and nonbinders to the two receptors. However, the cell-free assay provided a less complicated and more efficient binding platform and is, therefore, recommended over the whole cell binding assay. In conclusion, no strong evidence showed species-specific binding among the chemicals tested.

INCREASED CALCIUM INFLUX THROUGH ACETYLCHOLINE RECEPTORS IN DUNCE NEURONS

Calcium homeostasis was studied in dunce, a Drosophila mutant that is defective in learning and memory. Fura 2-AM fluorescence photometry was used to measure the intracellular calcium concentration in wild type and dunce cleavage-arrested neurons under resting conditions and in response to neurotransmitters. After acetylcholine application, the peak [Ca2+]i was greater in dunce (693 +/- 125 nM) than in wild type neurons (464 +/- 154 nM), but half decay time was shorter in dunce (66 +/- 15 s) than in wild type neurons (104 +/- 40 s). In contrast, the application of glutamate, NMDA, dopamine, and serotonin had no effect on [Ca2+]i. These results indicate that calcium influx through acetylcholine receptors is increased in dunce, compared to wild type neurons. The results also suggest that calcium extrusion to the outside and/or calcium buffering are enhanced in dunce, compared to wild type neurons. This disturbance in the homeostasis of cytosolic calcium concentration in dunce may be implicated in defective associative learning in Drosophila, and may play a role in acute and chronic neurodegenerative disorders in the mammalian brain.

An occludin-focal adhesion kinase protein complex at the blood-testis barrier: a study using the cadmium model

Several integral membrane proteins that constitute the blood-testis barrier (BTB) in mammalian testes, in particular rodents, are known to date. These include tight junction (TJ) proteins (e.g. occludin, junctional adhesion molecule-A, claudins), basal ectoplasmic specialization proteins (e.g. N-cadherin), and gap junction proteins (e.g. connexin43). However, the regulators (e.g. protein kinases and phosphatases) that affect these proteins, such as their interaction with the cytoskeletal actin, which in turn confer cell adhesion at the TJ, remain largely unknown. We report herein that focal adhesion kinase (FAK) is a putative interacting partner of occludin, but not claudin-11 or junctional adhesion molecule-A. Immunohistochemistry and fluorescence microscopy studies illustrated that the expression of FAK in the seminiferous epithelium of adult rat testes was stage specific. FAK colocalized with occludin at the BTB in virtually all stages of the seminiferous epithelial cycle but considerably diminished in stages VIII-IX, at the time of BTB restructuring to facilitate the transit of primary leptotene spermatocytes. Using Sertoli cells cultured in vitro with established TJ-permeability barrier and ultrastructures of TJ, basal ectoplasmic specialization and desmosome-like junction that mimicked the BTB in vivo, FAK was shown to colocalize with occludin and zonula occludens-1 (ZO-1) at the Sertoli-Sertoli cell interface. When these Sertoli cell cultures were treated with CdCl(2) to perturb the TJ-barrier function, occludin underwent endocytic-mediated internalization in parallel with FAK and ZO-1. Thus, these findings demonstrate that FAK is an integrated regulatory component of the occludin-ZO-1 protein complex, suggesting that functional studies can be performed to study the role of FAK in BTB dynamics.

[Protection of radiosensitive human cells against the action of heavy metals by antimutagens and adapting factors: association with genetic and protein polymorphisms]

Cells of a diploid line obtained from embryos with the Down's syndrome, known to be unable to repair gamma-induced DNA damage, were treated with natural (garlic extract, retinol) and synthetic (crown compound) antimutagens and with adapting factors (heat shock, low CdCl2 concentrations, 10(-8) M). The protective effect was evaluated by registering DNA breaks and cell survival, and the protection coefficients were calculated. The most effective results were obtained with the use of the garlic extract and retinol. No protection of the DNA structure was observed when cells were treated with low concentrations of cadmium chloride and then with high concentrations, i. e., no adaptive response (AR) was formed under these conditions. The spectrum of proteins in treated and control cells as well as detoxication genes (GSTM1, GSTT1 , CYPIA1) were determined.

A pseudo-phytochelatin synthase in the ciliated protozoan Tetrahymena thermophila

Phytochelatins (PCs) and metallothioneins (MTs) are the two major heavy metal chelating peptides in eukaryotes. We report here on the identification of a biosynthetically inactive pseudo-phytochelatin synthase enzyme (TtpsiPCS) in the ciliate Tetrahymena thermophila, the first of this kind (pseudo-PCS) to be described in eukaryotes. TtpsiPCS which resembles a true PCS at the N-terminal region, while it is most divergent in its Cys-poor C-terminal region, was found to be up-regulated under cadmium stress conditions. However, only glutathione (GSH) hydrolysis products, but not PCs, could be detected in extracts from Cd-treated cells. The latter feature is reminiscent of pseudo-PCS enzymes recently identified in cyanobacteria, which are also biosynthetically inactive, but capable to hydrolyze GSH.

Tissue-specific cadmium accumulation and its effects on nitrogen metabolism in tobacco (Nicotiana tabaccum, Bureley v. Fb9)

Tobacco (Nicotiana Tabaccum, Bureley v. Fb9) seedlings were grown for 30 days on control medium, and then treated for seven days with different concentrations (0, 10, 20, 50 and 100 muM) of CdCl(2). Cadmium (Cd) was mostly accumulated in the leaves. However, nitrate reductase and nitrite reductase activities (NR, EC 1.6.1.6 and NiR, EC 1.7.7.1) were more inhibited by Cd stress in the roots than in leaves. Glutamine synthetase activity (GS, EC 6.3.1.2) was inhibited by Cd treatment in roots and leaves. In both organs, aminating activity of glutamate dehydrogenase (GDH, EC 1.4.1.2) and protease activity were significantly stimulated in the leaves and roots of stressed plants. The lesser extents of Cd stress effects on leaves, despite their high Cd accumulation, suggest that: (i) tobacco leaves may evolve adaptive process to partially inactivate Cd ions; and (ii) tobacco is useful for phytoremediation.

Effects of lead and/or cadmium on the expression of metallothionein in the kidney of rats

Lead acetate (300 mg/L) and/or cadmium chloride (50 mg/L) were administered as drinking water of Sprague-Dawley rats for 8 weeks to investigate the possible combined effect of these metals on the expression of metallothionein (MT) in kidneys. Immunohistochemical staining and real-time quantitative polymerase chain reaction analyses were performed on kidney samples to identify the distribution of MT and to quantify the relative expression levels of MT-1 and MT-2 gene, respectively. There is no significant difference in distribution of the intensity, amount of MT immunostaining, and expression level of MT-1 and MT-2 gene in the kidneys between the lead group and control group (P > 0.05), whereas those in the cadmium group and (Pb + Cd) group were significantly higher than that in the control group (P < 0.01). Compared to the (Pb + Cd) group with the lead or cadmium group, the expression level of MT-1 and MT-2 gene increased significantly (P < 0.01). In summary, there was an obvious synergistic effect of lead combined with cadmium on the expression of metallothionein in the kidney of rats.

Detection of ubiquitination in 2DE

Ubiquitination involves the tagging of proteins with one (mono-) or more (poly-) ubiquitin molecules. Primarily the role of ubiquitination involves mainly short-lived and regulatory proteins being tagged with a poly-ubiquitin tail, thus introducing a hydrophobic patch that allows the protein to be identified and degraded by the 26S proteasome. Transfer of ubiquitin to the lysine residue of a target protein is a multi-step ATP-dependent process. The functions of ubiquitination have been extended in recent years to all areas of biology, many of them proteasome independent. As a small fraction of any protein may potentially be ubiquitinated, this may explain the wide range and large number of proteins that have been identified as being tagged with ubiquitin in the literature. This chapter outlines a general method for an indication of ubiquitination levels and identification of ubiquitinated proteins by two-dimensional electrophoresis in combination with immunoblotting.

[CdCl2-induced morphogenetic variation of Triticum aestivum cultivars]

The effect cadmium chloride on released local cultivars of soft spring wheat (Triticum aestivum) has been studied under laboratory and field conditions in order to widen the variation spectrum of this plant. It has been found that treatment of grains with a 0.01% aqueous solution of CdCl2 induces the appearance of tall, strong plants with productive bushiness in the M1 generation that are characterized by various morphological changes: elongated ears, scales, and grains; increased number of grains per ear and mass of 1000 grains; anthocyan pigmentation of the stem and leaf axil; etc. Study of meiosis showed chromosome aggregation, displacement of the mitotic spindle of the metaphase plate, and empty (sterile) cells in anaphases (AI and AII). The altered characters of M1 plants are preserved in the M2-M4 generations.

Oxygen flux as an indicator of physiological stress in fathead minnow (Pimephales promelas) embryos: a real-time biomonitoring system of water quality

The detection of harmful chemicals and biological agents in real time is a critical need for protecting freshwater ecosystems. We studied the real-time effects of five environmental contaminants with differing modes of action (atrazine, cadmium chloride, pentachlorophenol, malathion, and potassium cyanide) on respiratory oxygen consumption in 2-day postfertilization fathead minnow (Pimephales promelas) eggs. Our objective was to assess the sensitivity of fathead minnow eggs using the self-referencing micro-optrode technique to detect instantaneous changes in oxygen consumption after brief exposures to low concentrations of contaminants. Oxygen consumption data indicated that the technique is indeed sensitive enough to reliably detect physiological alterations induced by four of the five contaminants. After 2 h of exposure, we identified significant increases in oxygen consumption upon exposure to pentachlorophenol (100 and 1000 microg/L), cadmium chloride (0.0002 and 0.002 microg/L), and atrazine (150 microg/L). In contrast, we observed a significant decrease in oxygen flux after exposuresto potassium cyanide (44 and 66 microg/L) and atrazine (1500 microg/L). No effects were detected after exposures to malathion (200 and 340 microg/L). Our work is the first step in development of a new technique for physiologically coupled biomonitoring as a sensitive and reliable tool for the detection of environmental toxicants.

Malignant transformation and abnormal expression of eukaryotic initiation factor in bronchial epithelial cells induced by cadmium chloride

OBJECTIVE

To analyze the relationship between malignant transformation and abnormal expression of eukaryotic initiation factor 3 (eIF3 p36) in human bronchial epithelial (16HBE) cells induced by cadmium chloride (CdCl2).

METHODS

16HBE cells were treated several times with different concentrations of CdCl2. Tumorigenic potential of transformed cells was identified by assays for anchorage-independent growth in soft agar and for tumorigenicity in nude mice after the 35th passage. Total RNA was isolated from 16HBE cells induced by CdCl2, including non-transformed, Cd-transformed, and Cd-tumorigenic cell lines. Special primers for eIF3 p36 were designed and the expression of eIF3 mRNA in different cell lines was detected with fluorescent quantitative-polymerase chain reaction technique (FQ-PCR).

RESULTS

The 35th passage of 16HBE cells transformed by CdCl2 exhibited overlapping growth. Compared with the non-transformed cells, colonies of transformed cell lines in soft agar showed statistically significant increases and dose-dependent effects (P<0.01). All Cd-induced transformed cell lines formed tumors in nude mice within 2 weeks of inoculation, but none of the mice injected with non-transformed cells showed tumors even after 3 weeks. All tumors were pathologically identified as poorly differentiated squamous cell carcinoma. The eIF3 p36 genes in different stages of 16HBE cells transformed by CdCl2 were elevated as compared with the non-transformed control (P<0.01), and the eIF3 expression increased with the degree of cell malignancy.

CONCLUSION

CdCl2 is capable of inducing morphological transformation in 16HBE cells and transformed cells are potentially tumorigenic. Over-expression of eIF3 p36 is positively correlated with malignant transformation of 16HBE cells induced by CdCl2 and may be one of the molecular mechanisms potentially responsible for carcinogenesis due to Cd.

[Cloning and expression of a novel metallothionein gene LbMT2 from Limonium bicolor]

The full length cDNA of a novel metallothionein (LbMT2) gene was cloned from a cDNA library of Limonium bicolor. The LbMT2 gene cloned is 518 bp in length, which includes a 64 bp of 5' untranslated region (UTR) and a 205 bp of 3' untranslated region. This gene has an open reading frame (ORF) of 249 bp in length, encoding a protein of 82 amino acid residues with the molecular mass of 8.1 kDa and theoretical pI of 4.71. The expression of LbMT2 gene in L. bicolor in response to CuSO4, CdCl2, NaCl, cold, and PEG was further investigated using real time quantitative PCR. In both leaf and root of L. bicolor, the expression of LbMT2 was induced by CuSO4, CdCl2, NaCl, and cold, but inhibited by PEG stress. LbMT2 gene was inserted into a prokaryotic expression vector (pGEX-4T-2) to produce the recombinant expression vector pGEX-LbMT2. The expression of LbMT2 in E. coli BL21 was induced with IPTG, which produced a protein band with expected size of 35 kDa on SDS-PAGE.

[Influence of cadmium on structure and functions of mitochondria in hepatic cells]

OBJECTIVE

To study the effects of cadmium on the structure and functions of mitochondria in hepatocytes.

METHODS

Mitochondria were isolated from cultured human hepatocytes of the line WRL-68 and co-cultured with cadmium chloride (CdCl2) of the concentration of 1, 5, and 10 micromol/L, and WRL-68 cells not treated with CdCl2 (0 micromol/L) was used as control group. Cyclosporin A (CsA) was added into the culture medium. Mitochondrial permeability transition pore (MPTP) opening degree was tested by spectrophotometer. Morphologic changes of mitochondria were observed under transmission electron microscope. The activities of Na+ -K+ -ATPase, Ca2+ -Mg2+ -ATPase, LDH, superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and the contents of malondialdehyde (MDA) were measured Mitochondria membrane potential (MMP) was monitored by spectrofluorimeter with fluorescence dye Rh-123.

RESULTS

CdCl2 reduced the absorbance of mitochondria, signifying the opening of MPTP, concentration-dependently. The absorbance of mitochondria co-cultured with CsA and CdCl2 10 micromol/L was higher than that of the. CdCl2, 10 micromol/L group. Mild swelling was seen in the mitochondria treated with CdCl2. The MMP values of the CdCl2 5 and 10 micromol/L groups were significantly lower than that of the control group (P < 0.05, P < 0.01). The activity levels of ATPase, LDH, SOD, and GSH-Px in mitochondria decreased in the CdCl2 groups (all P < 0.05), and the contents of MDA increased in the CdCl2 groups compared with the control group.

CONCLUSION

CdCl2 causes destruction of mitochondria structure, opening of MPTP, decrease of MMP, and changes of vitality of mitochondria enzymes that all play important roles in apoptosis of hepatocytes.

[Proteolytic enzymes and trypsin inhibitors of higher plants under stress conditions]

The response of the components of a protease-inhibitor system of legume and cereal crops to stress factors was studied. It was found that salinization, heavy metal ions, and phytopathogenic flora inhibit the activity of neutral, acidic, and alkaline proteases at early stages of seed germination, the degree of the inhibition of the endoprotease activity being dependent on the index of tolerance of legume and cereal crops. It was shown that, in response to unfavorable conditions, accumulation of trypsin inhibitors occurs, which is accompanied by the appearance of new protein components, as indicated by electrophoresis. The results confirm the presumption that serine protease inhibitors are involved in the response of plants to stress factors.

MTT2, a copper-inducible metallothionein gene from Tetrahymena thermophila

Metallothioneins (MTs) are ubiquitous, cysteine-rich, metal-binding proteins whose transcriptional activation is induced by a variety of stimuli, in particular heavy metals such as cadmium, copper and zinc. Here we describe the sequence and organization of a novel copper-inducible metallothionein gene (MTT2) from Tetrahymena thermophila. Based on its deduced sequence, the gene encodes a protein 108 amino acids, containing 29 cysteine residues (30%) arranged in motifs characteristic of vertebrate and invertebrate MTs. We demonstrate that the 5'-region of the MTT2 gene can act as an efficient promoter to drive the expression of heterologous genes in the Tetrahymena system. In the latter case, a gene for a candidate vaccine antigen against Ichthyophthirius multifiliis, a ubiquitous parasite of freshwater fish, was expressed at high levels in transformed T. thermophila cell lines. Moreover, the protein was properly folded and targeted to the plasma membrane in its correct three-dimensional conformation. This new copper-inducible MT promoter may be an attractive alternative to the cadmium-inducible MTT1 promoter for driving ectopic gene expression in Tetrahymena and could have a great impact on biotechnological perspectives.

Catalytic inactive heme oxygenase-1 protein regulates its own expression in oxidative stress

Heme oxygenase-1 (HO-1) catalyzes the degradation of heme and forms antioxidant bile pigments as well as the signaling molecule carbon monoxide. HO-1 is inducible in response to a variety of chemical and physical stress conditions to function as a cytoprotective molecule. Therefore, it is important to maintain the basal level of HO-1 expression even when substrate availability is limited. We hypothesized that the HO-1 protein itself could regulate its own expression in a positive feedback manner, and that this positive feedback was important in the HO-1 gene induction in response to oxidative stress. In cultured NIH 3T3 cells, transfection of HO-1 cDNA or intracellular delivery of pure HO-1 protein resulted in activation of a 15-kb HO-1 promoter upstream of luciferase as visualized by bioluminescent technology and increased HO-1 mRNA and protein levels. These effects were independent of HO activity because an enzymatically inactive mutant form of HO-1 similarly activated the HO-1 promoter and incubation with HO inhibitor metalloporphyrin SnPP did not affect the promoter activation. In addition, HO-1-specific siRNA significantly reduced hemin and cadmium chloride-mediated HO-1 induction. Furthermore, deletion analyses demonstrated that the E1 and E2 distal enhancers of the HO-1 promoter are required for this HO-1 autoregulation. These experiments document feed-forward autoregulation of HO-1 in oxidative stress and suggest that HO-1 protein has a role in the induction process. We speculate that this mechanism may be useful for maintaining HO-1 expression when substrate is limited and may also serve to up-regulate other genes to promote cytoprotection and to modulate cell proliferation.