Effects of selenomethionine on cell growth and on S-adenosylmethionine metabolism in cultured malignant cells.

The effects of selenomethionine (SeMet) on the growth of 17 cultured cell lines were studied. SeMet in the culture medium of three hepatoma cell lines promoted cell growth at subcytotoxic levels (1-20 microM), but the growth of malignant lymphoid and myeloid cells was not stimulated. L-SeMet was cytotoxic to all 17 cell lines when assayed after culture for 3-10 days. A 50% growth inhibition was observed by 30-160 microM-SeMet in a culture medium containing 100 microM-methionine. SeMet cytotoxicity to normal (fibroblasts) and malignant cells was rather similar, excluding specific antineoplastic cytotoxicity. Cytotoxicity was increased by decreasing concentrations of methionine. The DL form of SeMet was less cytotoxic than the L form. L-SeMet was metabolized to a selenium analogue of S-adenosylmethionine approximately as effectively as the natural sulphur analogue methionine in malignant R1.1 lymphoblasts. Concomitantly, S-adenosylmethionine pools were decreased. This occurred early and at cytotoxic SeMet levels. Methionine adenosyltransferase activity was not altered by SeMet treatment. ATP pools were not affected early, and decreases in the synthesis of DNA and protein took place late and were apparently related to cell death. RNA synthesis was slightly stimulated at low cytotoxic SeMet levels by 24 h, but was markedly inhibited after 48 h. The SeMet analogue of S-adenosylmethionine could be effectively utilized in a specific enzymic transmethylation. Neither S-adenosylhomocysteine nor its selenium analogue accumulated in the treated cells. These findings together suggest a direct or indirect involvement of S-adenosylmethionine metabolism in SeMet cytotoxicity, but exclude a gross blockage of transmethylations.     

Influence of selenium on the growth of N-nitrosomethylurea-induced mammary tumor cells in culture

Selenium is an essential dietary trace element which has anticancer properties. Among its effects in rats, selenium has been shown to inhibit the development of carcinogen-induced mammary tumors by interfering with the postinitiation, promotion phase of carcinogenesis. We studied the effects of selenium on the growth of rat mammary tumor cells in primary culture. Our objective was to determine whether selenium had any direct influence on cell growth which might explain its influence on tumor development. Rat mammary tumors were induced by N-nitrosomethylurea. Tumor epithelium was prepared by collagenase dispersion and the cells were separated by Ficoll gradient centrifugation. The tumor epithelium was grown in primary culture using a defined serum-free medium. The addition of low concentrations of sodium selenite, less than 1.0 micrograms/ml, stimulated tumor cell proliferation. Protein synthesis and the production of type IV collagen increased within the first hour of exposure, prior to any measurable increase in DNA synthesis. Concentrations of selenite greater than 1.0 micrograms/ml inhibited cell proliferation, the synthesis of protein, and the replication of DNA in a dose-related manner. These studies demonstrated that selenium has the potential to influence the postinitiation phase of rat mammary tumorigenesis by directly altering the growth of tumor cells, possibly through the regulation of protein synthesis.     

Cellular selenoproteins and the effects of selenite on cell proliferation

The incorporation of radioactive selenium into cellular proteins and the effect of selenite on proliferation were examined in human (HeLa, HT-29, and IMR-90) and mouse (3T3 and CMT-93) cell lines. Proteins incorporating selenium were detected by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Major polypeptide subunits at 60, 23, 21, 19, and 16 kD were detected in the two tumorigenic and one normal human cell lines. The 23 kD polypeptide migrated to the same position on the gel as the major subunit of human erythrocyte glutathione peroxidase. In the mouse cells, the 60 kD polypeptide was almost entirely absent; four other major selenoproteins were detected, with molecular weights similar to those in the human cells. In both mouse and human cells, the same pattern of selenoproteins was observed irrespective of whether the cells were grown in medium containing 10% fetal bovine serum or in defined medium supplemented with 0.1 or 1 microM selenite, or with 1% serum. The effect of selenite on proliferation of HeLa, HT-29, and CMT-93 cells in medium supplemented with 10% fetal bovine serum and in serum-free medium was examined. At concentrations up to about 1 microM, selenite stimulated proliferation of the human cells slightly in serum-free medium but not in serum-supplemented medium. At concentrations of about 5 microM and higher selenite significantly inhibited proliferation of all cells in both types of media. In CMT-93 cells, this inhibition was greater in serum-free medium, but there were no significant differences in this regard in the human cells. These results demonstrate that selenium is stably incorporated into several polypeptides in human and mouse cells, that there are no significant differences in this regard among several cell lines, and slight differences between human and mouse cells. They further confirm that selenium can have a slight stimulatory effect on cell growth, and a much larger inhibitory effect, depending on its concentration.     

Hormonal Regulation of Cell Elongation in the Hypocotyl of Rootless Soybean: An Evaluation of the Role of DNA Synthesis

A method was developed where soybean seedlings were grown without roots to study the influence of hormones of root origin on shoot growth. Excision of the root resulted in inhibition of apical section growth and DNA synthesis and inhibited elongating section growth. A synthetic cytokinin restored DNA synthesis in the apical section, but did not influence growth in either the apical or elongating sections. Low concentrations of gibberellin with the cytokinin restored growth in the apical section. Gibberellin alone was sufficient to restore growth in the elongating section.An inhibitor of DNA synthesis, 5-fluorodeoxyuridine, inhibited the increase in apical section DNA without inhibiting control or gibberellin-induced growth in the elongating section. Experiments with (14)C-thymidine resulted in no DNA labeling differences in the elongating section under conditions where gibberellin-induced elongation varied from 50% to 73% above controls. It was concluded that gibberellin-induced elongation in soybean hypocotyl occurred in the absence of DNA synthesis. Gibberellin does stimulate DNA synthesis in the apical tissue apart from its effect on cell elongation.Excised soybean hypocotyl elongated maximally at 10(-6)m auxin. At higher auxin concentrations, fresh weight and ethylene production increased, but elongation was reduced. Addition of GA to the higher auxin concentrations resulted in a 50% inhibition in auxin-induced ethylene production and resumption in maximal elongation. Added ethylene inhibited elongation 30% at 2 mul/l. Addition of up to 100 mul/l ethylene did not inhibit elongation with GA present in the incubation medium. Thus GA may counteract ehtylene inhibition of cell elongation in addition to inhibiting ethylene production in auxin-treated tissues.     

Selenium retention and inhibition of cell growth in mouse mammary epithelial cell lines in vitro

The steady state levels of growth inhibitory doses of inorganic selenium were examined in five different mammary epithelial cell lines: MOD, COMMA-D, COMMA-F, COMMA-T, and YN-4. The retention of selenium was monitored using a radioactive isotope,⁷⁵Se. Growth inhibition correlated with high levels of selenium in the cell. Generally, the retention of intracellular selenium was not dependent upon cell density, cell number, net growth rate, or tumorigenicity of the mammary cell lines. One cell line, COMMA-D, exhibited an unique response wherein the amount of selenium retained was low and the growth inhibitory effects of selenium were negligible when the cells were exposed to selenium at low density. However, at high cell densities, the COMMA-D cells responded like the other four cell lines. The growth inhibitory effect of selenium was reversible; upon removal of selenium from the medium, cells start synthesizing DNA within 24h. The retention of selenium was influenced by constituents in the growth medium. In particular, cysteine, but not methionine, purines, or pyrimidines altered selenium retention and counteracted the growth inhibitory effects of selenium. These results indicated that the mammary cell lines, particulary COMMA-D and MOD are good model systems to examine the uptake, retention, localization, and function of inorganic selenium under conditions where it acts as a growth inhibitory agent.     

Epidermal growth factor and insulin-like growth factor-1 preserve cell viability in the absence of protein synthesis

Summary Prolonged exposure of cells to the potent protein synthesis inhibitor cycloheximide (CHX) terminates in cell death. In the present study we investigated the effect of epidermal growth factor (EGF), insulin-like growth factor-1 (IGF-1), and insulin on cell death induced by CHX in the human cancerous cell lines MDA-231 and MCF-7 (breast), KB (oral epidermoid), HEP-2 (larynx epidermoid), and SW-480 (colon), and correlated this effect to the inhibition rate of protein synthesis. Cell death was evaluated by measuring either dead cells by trypan blue dye exclusion test or by the release of lactic dehydrogenase into the culture medium. CHX was shown to induce cell death in a concentration (1 to 60 μg/ml) and time (24 to 72 h)-dependent manner in each of the five cell lines. EGF at physiologic concentrations (2 to 40 ng/ml) reduced cell death close to control level (without CHX) in the cell lines HEP-2, KB, MDA-231, and SW-480, but had almost no effect on cell death in the MCF-7 cells. IGF-1 at physiologic concentrations (2 to 40 ng/ml) reduced cell death nearly to control level in the MCF-7 cells, but had only a partial effect in the other four cell lines. Insulin at supraphysiologic concentration (10 000 ng/ml) mimicked the effect of IGF-1 in each of the cell lines. CHX at concentrations that induced about 60% cell death, inhibited about 90% of protein synthesis as measured by [³H]leucine incorporation. Protein synthesis remained inhibited although cell viability was preserved by EGF or IGF-1. These results indicated that the mechanism by which EGF or IGF-1 preserve cell viability does not require new protein synthesis and may be mediated via a posttranslational modification effect.     

DHEA inhibits cell growth and induces apoptosis in BV-2 cells and the effects are inversely associated with glucose concentration in the medium

Dehydroepiandrosterone (DHEA), a major steroid secreted by the adrenal gland which decreases with age after adolescence, is available as a nutritional supplement. DHEA is known to have antiproliferative effects but the mechanism is unclear. In this study using BV-2 cells, a murine microglial cell line, we investigated the effect of DHEA on cell viability and the interaction between DHEA and glucose concentrations in the medium. We showed that DHEA inhibited cell viability and G6PD activity in a dose-dependent manner and that the effect of DHEA on cell viability was inversely associated with glucose concentrations in the medium, i.e. lowered glucose strongly enhanced the inhibition of cell viability by DHEA. DHEA inhibited cell growth by causing cell cycle arrest primarily in the G0--G1 phase, and the effect was more pronounced at zero glucose (no glucose added, G0) than high glucose (4.5 mg/ml of the medium, G4.5). Glucose deprivation also enhanced apoptosis induced by DHEA. At G4.5, DHEA did not induce formation of DNA ladder until it reached 200 microM. However, at G0, 100 microM DHEA was able to induce apoptosis, as evidenced by the formation of DNA ladder, elevation of histone-associated DNA fragmentation and increase in cells positively stained with annexin V-FITC and annexin V-FITC/propidium iodide. The interactions between DHEA and glucose support the contention that DHEA exerts its antiproliferative effects through alteration of glucose metabolism, possibly by inhibition of G6PD activity leading to decreased supply of ribose-5-phosphate for synthesis of DNA and RNA. Although DHEA is only antiproliferative at pharmacological levels, our results indicate that its antiproliferative effect can be enhanced by limiting the supply of glucose such as by energy restriction. In addition, the present study shows that glucose concentration is an important factor to consider when studying the antiproliferative and toxicological effects of DHEA.     

The effect of various seleno-compounds on ehrlich ascites tumor cells

The effect of various concentrations and forms of selenium on in vitro viability of Ehrlich Ascites Tumor Cells (EATC) was investigated. Sodium selenite, selenium dioxide, seleno-dl-cystine, and seleno-dl-methionine, dramatically decreased EATC viability as measured by dye exclusion. Sodium selenate only marginally decreased EATC viability. Cell viabilities decreased with increasing selenium in the incubation media and as a function of time. Viabilities determined by dye exclusion did not correlate with the inhibition of tumor growth observed after treatment with selenium. Intraperitoneal injections of selenite in mice previously inoculated with EATC significantly inhibited tumor development. Delaying intraperitoneal injections of selenite to 5 and 7 days after inoculation of mice with EATC reduced the effectiveness of this nutrient on the inhibition of EATC growth. Incubation of EATC in vitro with supplemental selenium prior to injection of mice completely inhibited EATC development in vivo before any appreciable alteration in cell viability was observed.     

Deoxyribonucleoside triphosphate pools and differential thymidine sensitivities of cultured mouse lymphoma and myeloma cells

The effects of various concentrations of thymidine on DNA synthesis and deoxyribonucleoside triphosphate contents of a highly thymidine-sensitive cultured mouse lymphoma cell line (WEHI-7) and a relatively resistant mouse myeloma cell line (HPC-108) have been studied by 32P-labelling techniques. DNA synthesis in the myeloma cells was inhibited by thymidine at concentrations of 10(-3) M or greater, while DNA synthesis in the lymphoma cells was inhibited by concentrations 30-fold lower, consistent with the 25-fold difference between the two cell lines in sensitivity to growth inhibition by thymidine. Thymidine caused marked elevation of the dTTP and dGTP pools, slight elevation or no change in the dATP pool and a marked decrease in the dCTP pool in cells of both lines. The greater resistance of HPC-108 cells to thymidine inhibition was related to the finding that they normally contained a much higher concentration of dCTP than did the WEHI-7 cells. Pool size measurements on thymidine-treated (10(-4) M) cells of an additional seven sensitive lymphoma and six relatively resistant myeloma cell lines indicated that in all 15 lines studied, with one exception, a critical concentration of dCTP of about 32 nmol per ml of cell volume was required for the maintenance of normal rates of DNA synthesis. The dCTP content found normally in the lymphoma cells was only a little above this concentration. Amongst the myeloma lines, three contained similarly low levels of dCTP, but were more resistant to thymidine inhibition probably because of their inefficient production of dTTP from thymidine. Cells of the other four myeloma lines (including HPC-108) normally contained much higher dCTP concentrations. The mechanism of thymidine action was explained by reference to the known allosteric properties of ribonucleotide reductase.     

Inhibition by 2-deoxy-D-ribose of DNA synthesis and growth in Raji cells

When Raji cells were cultured for 3 days in serum-free medium, addition of 2-deoxy-D-ribose at the start of culture inhibited incorporation of [3H]thymidine and cell division. At deoxyribose concentrations between 1 and 5 mM, viability was 80% or greater after 3 days of culture even though 5 mM deoxyribose inhibited thymidine incorporation 95-99%. Inhibition by deoxyribose could be completely reversed if the culture medium was replaced with fresh medium up to 8 hr after the start of culture. The inhibition was specific for deoxyribose since other monosaccharides had no effect. Inhibition of DNA synthesis did not appear to be due to depletion of essential nutrients in the medium since the percentage inhibition of thymidine incorporation by cells cultured either in suboptimal serum-free media or in media supplemented with 0.025-5% human AB serum was similar. When DNA repair synthesis was measured as hydroxyurea-resistant thymidine incorporation, addition of deoxyribose to Raji cultures caused increased thymidine incorporation. These results, together with data from others, suggest that deoxyribose damages DNA.     

Effect of selenium compounds and thiols on human mammary tumor cells

The effect on cell viability and growth rate of sodium selenite, selenocystine, sodium selenate, and selenomethionine at selenium concentrations of 6.25 and 12.5 uM was studied in vitro on cells of the human mammary tumor cell line HTB123/DU4475. Selenite and selenocystine affected both cell viability and growth rate of the tumor cells at these selenium concentrations. Selenite and selenocystine decreased intracellular glutathione concentrations, but did not affect tumor cell glutathione peroxidase activity. After six days of exposure to either selenate or selenomethionine, the viability of tumor cells remained stable, but cell growth, as measured by numbers of cells, was retarded. Neither selenate nor selenomethionine produced changes in concentrations of intracellular glutathione. The toxic effect of selenite on tumor cells was enhanced by addition of 0.25 mM glutathione to the growth medium. Preincubation of the tumor cells with 62.5 uM buthionine sulfoximine decreased cellular glutathione to 15% of controls at 24 h and enhanced the toxicity of selenite toward the tumor cells. Glutathione, 2-mercaptoethanol, and L-cysteine were all toxic to the tumor cells in a dose-dependent manner.     

Effects of adenine arabinoside on lymphocytes infected with Epstein-Barr virus.

Low concentrations of adenine arabinoside inhibited growth of two Epstein-Barr virus producer cell lines in culture, while not significantly affecting a nonproducer cell line and a B-cell-negative line. These observations were extended to include freshly infected cells. Mitogen-stimulated human umbilical cord blood lymphocytes were unaffected by the drug at concentration levels that inhibited [3H]thymidine incorporation into the DNA of Epstein-Barr virus-stimulated cells. DNA synthesis in Epstein-Barr virus-superinfected Raji cells was also adversely affected by adenine arabinoside. However, these same low concentrations of adenine arabinoside in the triphosphate form produced less effect on DNA synthesis in nuclear systems and DNA polymerase assays than on growth or DNA synthesis in whole cells. Therefore the effects reported here of low concentrations of the drug on whole cells may be only in part related to DNA polymerase inhibition. The work reported here suggests that adenine arabinoside has multiple sites of action in infected cells.     

Proteoglycans in human malignant mesothelioma. Stimulation of their synthesis induced by epidermal, insulin and platelet-derived growth factors involves receptors with tyrosine kinase activity.

Identification of proteoglycans in two human malignant mesothelioma cell lines, one with epithelial differentiation and the other with fibroblast-like phenotype, and the effects of epidermal (EGF), insulin-like (IGF-I) and platelet-derived (PDGF-BB) growth factors on the synthesis of hyaluronan (HA) and proteoglycans (PGs) were studied. Both cell lines synthesize HA and PGs: these last were recovered both as secreted and cell-associated compounds. Chondroitin sulfate (CS) containing PGs are mainly organized as versican in the extracellular medium and as thrombomodulin and syndecan in the cell membrane. Heparan sulfate (HS) containing PGs are mainly in the form of perlecan in the culture medium, whereas cell-associated HSPGs were recovered mainly as syndecan-1, -2 and -4. Receptors for EGF, IGF-I and PDGF-BB were identified in both cell lines. In addition to cell proliferation, these growth factors stimulated the synthesis of HA and PGs, the pattern of stimulation being unique for each of them and depending on the cell phenotype. EGF increased the synthesis of HA and PGs. IGF-I showed similar stimulatory effects on the synthesis of CSPGs, whereas higher amounts were needed to influence the synthesis of HA and HSPGs, the latter only being stimulated in the epithelial cell line. PDGF-BB stimulated the synthesis of HA, HSPGs and CSPGs at low concentrations, while the stimulatory effect was abolished at higher levels. Incubation with genistein inhibited the HA and PG synthesis induced by growth factors in a mode depending on both growth factor and genistein concentrations. The results clearly suggest that the stimulatory effects of EGF, IGF-I and PDGF-BB on matrix synthesis, expressed as proteoglycan synthesis, are mediated via receptor-growth factor complexes and the protein tyrosine kinase intracellular pathway.     

Growth and morphological changes induced by lithium chloride treatment of HL-60 cells

HL-60 cells were grown in culture and their proliferative behaviour and response to lithium were studied. Treatment of cells with lithium concentrations of up to 5 mM enhanced cell proliferation, however above 5 mM lithium, cell growth was inhibited. Cell viability remained above 90% with concentrations of lithium below 10 mM. With increasing concentrations of lithium cell death increased rapidly to about 70% after 3 days at 50 mM. DNA synthesis was also strongly inhibited by concentrations of lithium above 5 mM. At 50 mM lithium, [3H]-thymidine incorporation was 1%. Electron microscopy seems to indicate that the plasma membrane is the main target for lithium cytotoxicity, whilst lithium uptake studies suggest that cytotoxicity might be related to the accumulation of lithium within the cells.     

Effects of acronycine on nucleic acid synthesis and population growth in mammalian tumor cell cultures

Acronycine — an alkaloid with antineoplastic activity against a wide range of experimental tumors — at concentrations of 0.5-12 μg/ml rapidly inhibits RNA synthesis in L5178Y mouse lymphoma and IRC rat monocytic leukemia cultures. Culture growth is arrested only at acronycine concentrations which markedly inhibit RNA synthesis. DNA synthesis is inhibited at rather higher concentrations but this is not a prerequisite of the arrest of growth. It is suggested that the arrest of growth may be a consequence of the inhibition of RNA synthesis. In both cultures arrest of growth coincides with the appearance of many cells with two apparently normal nuclei. Cells are not arrested in mitosis. It is shown these binucleated cells very probably arise from an inhibition of cell cleavage. Studies with synchronized cultures show that at low drug concentrations, more than one cell cycle may elapse before growth is arrested and binucleated cells appear, indicating the effect on cytokinesis is not immediate. The results suggest that the arrest of growth may be a result of a slow depletion of a component essential for cell cleavage. The disturbance at division is a major factor in arresting growth at low drug concentrations. At higher acronycine concentrations, when RNA synthesis may be inhibited by 80–90%, the cytotoxic effects appear earlier and are less specifically directed at cytokinesis; DNA synthesis is then also rapidly and markedly inhibited.     

Products of lipopolysaccharide-activated macrophages (tumor necrosis factor-alpha, transforming growth factor-beta) but not lipopolysaccharide modify DNA synthesis by rat trophoblast cells exhibiting the 80-kDa lipopolysaccharide-binding protein

Pregnancy losses from gram negative bacterial infections could be caused by direct effects of LPS on placental cells, or indirectly via LPS activation of macrophages in the uteroplacental unit. To evaluate those alternatives, LPS, LPS-activated peritoneal cells, conditioned medium from LPS-activated peritoneal cells, and some purified and recombinant molecules known to be secreted by activated macrophages were tested for their abilities to modify DNA synthesis by rat trophoblast cells. Three trophoblast cell lines derived from midgestation placentas of outbred and inbred rats were used for the experiments. Although the 80-kDa LPS-binding protein was demonstrated on trophoblast cells, LPS alone had no effect on the ability of trophoblast cells to synthesize DNA. In cocultures, trophoblast cell DNA synthesis was slightly enhanced by low concentrations of both unstimulated and LPS-activated peritoneal cells. At higher concentrations, LPS-activated cells caused significant inhibition of DNA synthesis by trophoblast cells. Conditioned media from LPS-activated peritoneal cells were highly inhibitory to trophoblast cell DNA synthesis. When specific molecules likely to be components of those media were tested, IL-1 was found to have a modest but reproducible stimulatory effect and PGE2 did not change trophoblast cell incorporation of [3H]TdR. In contrast, trophoblast cell DNA synthesis was markedly inhibited in a dose-dependent manner by both TNF-alpha and TGF-beta 1. No differences in the sensitivity of trophoblast cells from outbred and inbred rats were observed. Given the limitations of the experimental model system, the results suggest that in cases of infection by gram-negative bacteria LPS may have an adverse effect on pregnancy by stimulating resident macrophages to generate and release molecules that are inhibitory to trophoblast cell DNA synthesis.     

Supra-physiological folic acid concentrations induce aberrant DNA methylation in normal human cells in vitro

The micronutrients folate and selenium may modulate DNA methylation patterns by affecting intracellular levels of the methyl donor S-adenosylmethionine (SAM) and/or the product of methylation reactions S-adenosylhomocysteine (SAH). WI-38 fibroblasts and FHC colon epithelial cells were cultured in the presence of two forms of folate or four forms of selenium at physiologically-relevant doses, and their effects on LINE-1 methylation, gene-specific CpG island (CGI) methylation and intracellular SAM:SAH were determined. At physiologically-relevant doses the forms of folate or selenium had no effect on LINE-1 or CGI methylation, nor on intracellular SAM:SAH. However the commercial cell culture media used for the selenium studies, containing supra-physiological concentrations of folic acid, induced LINE-1 hypomethylation, CGI hypermethylation and decreased intracellular SAM:SAH in both cell lines. We conclude that the exposure of normal human cells to supra-physiological folic acid concentrations present in commercial cell culture media perturbs the intracellular SAM:SAH ratio and induces aberrant DNA methylation.     

Growth regulation of ovarian cancer cells by epidermal growth factor and tranforming growth factors α and β1

Regulation of ovarian cancer growth is poorly understood. In this study, the effects of EGT, TGFα and TGFβ1 on two ovarian cancer cell lines (OVCAR-3 and CAOV-3) were investigated. The results showed that EGF/TGFα stimulated cell growth and DNA synthesis in OVCAR-3 cell, but inhibited cell proliferation and DNA synthesis in CAOV-3 cells. TGFβ1 invariably inhibited cell proliferation and DNA synthesis in both cell lines. These efefects on growth factors are dose dependent. The interaction of TGFβ1 and EGF/TGFα was antagonistic in OVCAR-3 cells. In contrast, EGF/TGFα and TGFβ1 had an additive inhibitory effect on CAOV-3 cells. Our results demonstrated that mature and functional EGF receptors are present in both cell lines and that they are capable of ligand binding, internalization, processing and ligand-enhanced autophosphorylation. Both high- and low-affinity binding are present in these cell lines, with CAOV-3 cells having about 2–3 fold higher total receptors than OVCAR-3 cells. These results together with those from our previous studies show that these cells express TGFα, TGFβ1 and EGF receptors and that cell growth may be modulated by these growth factors in an autocrine can paracrine manner. This report presents evidence supporting the important roles of growth factors in ovarian cancer growth and provides a foundation for futher study into the mechanism of growth regulation by growth factors in these cell lines.     

Some Effects of Pentamidine Di-isethionate on Crithidia fasciculata

SYNOPSIS. Growth-inhibitory concentrations of pentamidine inhibit to a similar extent net synthesis of DNA, RNA, protein and phospholipid by washed cell suspensions of Crithidia fasciculata. The incorporation of ³H-thymidine into DNA, ¹⁴C-adenine into DNA and RNA and ¹⁴C-lysine into protein is similarly inhibited. The same concentrations of drug have little or no effect on viability, motility, 1-C metabolism, respiration or K⁺ content of organisms, altho they do cause increased amounts of intracellular ATP. Lysine uptake (in the absence of arginine) is, however, inhibited. At higher concentrations of drug respiration is inhibited and organisms lose K⁺. The mode of action of pentamidine is considered in the light of these observations and a mechanism of uptake of pentamidine into organisms is suggested.     

Cu2+对拟南芥根的局部毒性及诱导DNA损伤和细胞死亡

该文探讨了不同浓度的Cu²⁺胁迫对拟南芥(Arabidopsis thaliana)根生长、活性氧(ROS)积累、抗氧化酶活性、质膜完整性和细胞活性的影响, 通过分根实验初步分析了Cu²⁺毒性效应的影响范围。结果表明, Cu²⁺胁迫可显著抑制拟南芥主根伸长, 诱导ROS积累及DNA损伤, 促发抗氧化酶活性升高, 破坏质膜完整性, 且Cu²⁺浓度越高, 毒性效应越明显, 在高浓度Cu²⁺胁迫下细胞活性显著降低。分析各参数之间的关系, 表明ROS的积累与超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)及抗坏血酸过氧化物酶(APX)的活性呈显著正相关; ROS积累与DNA损伤、质膜完整性、细胞活性之间具有显著的近线性关系。分根实验结果表明, 只有在添加重金属Cu²⁺(75 μmol·L^–1)一侧培养基中的根生长受抑制, 并出现ROS积累、细胞死亡, 暗示Cu²⁺对拟南芥根系的局部毒性效应可能是由于ROS的局部性积累导致受胁迫根系一侧的细胞死亡所引起的。