Sodium butyrate-induced changes in cultured rabbit articular chondrocyte transmembrane electrical potentials. Relationship between these changes and the proliferative response

Sodium butyrate at 5mM reversibly induced a significant increase of transmembrane potentials (Em) in normal chondrocytes (24 hours after seeding) and arrested their proliferation. This increase in Em levels, which could be temporarily abolished by Tetra-ethyl Ammonium (TEA 5mM), was related to an increase in membrane permeability to K+. This hyperpolarization was correlated with the reversible inhibition of growth in G1 induced by the sodium butyrate.     

Differential effect of D-penicillamine on the cell kinetic parameters of various normal and transformed cellular types

The cell-growth-inhibitory and phase-specific effects of D-penicillamine on cell-cycle progression were investigated using cell-proliferation patterns, quantitative cell-cycle analysis by flow cytometry, and determination of the mitotic index and binucleate cell fraction of normal (rabbit articular chondrocytes, L 809, rabbit fibroblasts) and transformed (HeLa, L 929) cells. D-penicillamine treatment resulted in an inhibition of growth within a dose range of 5 × 10^?4 M to 7.5 × 10^?3 M. Examination of DNA by flow cytometric analysis revealed that rabbit articular chondrocytes were preferentially arrested in the G0/1 phase of the cell cycle, whereas the other cell lines were blocked in the G2 + M phase; the increase in the proportion of cells with G2 + M DNA content was partially due to an enhancement of binucleate cells, resulting in a cytokinesis perturbation for HeLa and L 929 cells. These results showed that D-penicillamine affects cell proliferation through different events according to cell type.     

Long acting cAMP analogues enhance sulfate incorporation into matrix proteoglycans and suppress cell division of fetal rat chondrocytes in monolayer culture.

The relationship between replication and the synthesis of matrix sulfated proteoglycans was investigated with fetal rat chondrocytes grown in monolayer culture. The effect of N6 O2' dibutyryl adenosine 3', 5' cyclic monophosphate (DBcAMP), adenosine 3', 5' cyclic monophosphate (cAMP), 8 Bromo adenosine 3', 5' cyclic monophosphate (8 Br-cAMP), sodium butyrate and hydroxyurea was examined. Between 0.05 and 0.5 mM DBcAMP, a dose related inhibition of cell division and stimulation of [35SO=/4] incorporation into matrix proteoglycans was demonstrated. At the higher concentrations of DBcAMP, cell division was completely inhibited and the enhancement of [35SO=/4] incorporation into matrix proteoglycans ranged between 40 and 120% (P less than 0.01). Utilizing 14C-glucosamine and photometric determination of proteoglycans with Alcian Blue, it was demonstrated that the increase in sulfate incorporation reflected enhanced accumulation of extracellular matrix. The effects of DBcAMP were mimicked by 8 Br-cAMP, suggesting they were mediated by the adenylyl cyclase system. cAMP (0.05-0.5 mM), sodium butyrate (0.1-0.5 mM) and hydroxyurea (0.5-5 mM) partially or fully inhibited cell division, but either failed or only slightly enhanced sulfate incorporation. The enhanced sulfated proteoglycan deposition promoted by DBcAMP began 8 to 12 hours after serum stimulation, its onset occurred prior to thymidine incorporation and the effect persisted for 28 hours. Determination of cell volume demonstrated an increase in size of DBcAMP treated chondrocytes between 8 to 12 hours, coincident with the onset of increased sulfate incorporation. These results are consistent with a model where matrix sulfated proteoglycan deposition by chondrocytes is mediated by intracellular cAMP levels and occurs in the G1 phase of the cell cycle.     

Stimulation of DNA synthesis in quiescent rabbit chondrocytes in culture by limited exposure to somatomedin-like growth factors

Cartilage-derived factor (CDF), extracted from fetal bovine cartilage, and multiplication-stimulating activity (MSA) stimulated DNA synthesis in quiescent rabbit costal chondrocytes in culture under serum-free conditions. As described previously, when added in the presence of fibroblast growth factor (FGF) or epidermal growth factor (EGF) a somatomedin-like growth factor, CDF or MSA, synergistically stimulated DNA synthesis in the cultured chondrocytes. The present study showed that exposure of the cells to MSA or CDF for only the initial 5 h was sufficient for transmission of their full stimulatory effect. Furthermore, the limited exposure did not alter the time course of stimulation of DNA synthesis: [3H]thymidine incorporation into DNA began to increase after 16 h and reached a maximum after 24 h. In contrast to the somatomedin-like growth factors, FGF and EGF were required continuously in the culture medium during traverse of the entire G1 phase for stimulation of DNA synthesis, and the mitogenic effects of FGF and EGF in cultured chondrocytes were stronger than those of CDF and MSA. Synergistic stimulation of DNA synthesis by CDF or MSA in the presence of FGF or EGF could be observed as long as FGF or EGF was continuously present, even when CDF or MSA was withdrawn after the first 5 h of culture. These findings suggest that, in contrast to FGF and EGF, somatomedin-like growth factors affect an early distinct stage in the G1 phase of chondrocytes.     

Changes in cell volume and internal sodium concentration in HeLa cells during exponential growth and following lonidamine treatment

Cell volumes decreased in HeLa cells as a function of time after seeding during exponential growth. Cell volume distributions revealed the presence of two cell populations in all stages of growth. When cells approached confluence, the ratio of the two populations abruptly shifted towards that characterised by the smallest volume. Percentages of G1-, S- and G2 + M-phase cells were also measured and it was found that G1 frequency increased as a function of cell density during exponential growth. Intracellular sodium concentration, [Na]i was monitored by 23Na NMR in the presence of 5 mM dysprosium (III) tripolyphosphate. [Na]i increased from 22.8 to 59.0 mM in cells from the second to the seventh day after seeding. Treatment with lonidamine, an antitumoral drug that it is known to slow down cell growth by affecting aerobic glycolysis, produced a complete block of cell progression after a few days of treatment. The progression of cell volume distributions towards smaller volumes and the increase in internal sodium concentration as a function of time after seeding were also affected by the drug. These phenomena were related to the existence of a subpopulation of mitotically inactive G1-phase cells during exponential growth, pointing out that a density-dependent cellular mechanism regulates the cell cycling in HeLa cells.     

Effects of hexavalent chromium on the survival and cell cycle distribution of DNA repair-deficient S. cerevisiae

A broad spectrum of genetic damage results from exposure to hexavalent chromium. These lesions can result in DNA and RNA polymerase arrest, chromosomal aberrations, point mutations and deletions. Because of the complexity of Cr genotoxicity, the repair of Cr(VI)-induced DNA damage is poorly understood. Therefore, our aim was to investigate the sensitivities of DNA repair-deficient Saccharomyces cerevisiae strains to Cr(VI)-induced growth inhibition and lethality. Wild-type, translesion synthesis (rev3) and excision repair (apn1, ntg1, ntg2, rad1) mutants exhibited similar survival following Cr(VI) treatment (0-50mM) and underwent at least one population doubling within 2-4h post-treatment. The simultaneous loss of several excision repair genes (apn1 rad1 ntg1 ntg2) led to slower growth after Cr(VI) exposure (10mM) manifested as an initial delay in S phase progression. Higher concentrations of Cr(VI) (25mM) resulted in a prolonged transit through S phase in every strain tested. A G(2)/M arrest was evident within 1-2h after Cr(VI) treatment (10mM) in all strains and cells subsequently divided after this transient delay. In contrast to all other strains, only recombination-deficient (rad52, rad52 rev3) yeast were markedly hypersensitive towards Cr(VI) lethality. RAD52 mutant strains (rad52, rad52 rev3) also exhibited a significant delay (>6h) in the resumption of replication after Cr(VI) exposure which was related to the immediate and apparently terminal arrest of these yeast in G(2)/M after Cr(VI) treatment. These results, taken together with the recombinogenic effects of Cr(VI) in yeast containing a functional RAD52 gene, suggest that RAD52-mediated recombination is critical for the normal processing of lethal Cr-induced genetic lesions and exit from G(2) arrest. Furthermore, only the combined inactivation of multiple excision repair genes affects cell growth after Cr(VI) treatment.     

The effect of glutamine on A549 cells exposed to moderate hyperoxia

The use of high oxygen concentrations is frequently necessary in the treatment of acute respiratory distress syndrome (ARDS) and bronchopulmonary dysplasia (BPD). High oxygen concentrations, however, are detrimental to cell growth and cell survival. Glutamine (Gln) may be protective to cells during periods of stress and recently has been shown to increase survival in A549 cells exposed to lethal concentrations of oxygen (95% O2). We found that supplemental Gln enhances cell growth in A549 cells exposed to moderate concentrations of oxygen (60% O2). We therefore evaluated the effect of moderate hyperoxia on the cell cycle distribution of A549 cells. At 48 h there was no significant difference in the cell cycle distribution between 2 mM Gln cells in 60% O2 and 2 mM cells in room air. Furthermore, 2 mM Gln cells in 60% O2 had stable protein levels of cyclin B1 consistent with ongoing cell proliferation. In contrast, at 48 h, cells not supplemented with glutamine (Gln-) in 60% O2 had evidence of growth arrest by both flow cytometry (increased percentage of G1 cells) and by decreased protein levels of cyclin B1. G1 growth arrest in the Gln- cells exposed to 60% O2 was not, however, associated with induction of p21 protein. At 72 and 96 h, Gln- cells in 60% O2, began to demonstrate a partial loss of G1 checkpoint regulation and an increase in apoptosis, indicating an increased sensitivity to oxygen toxicity. Glutathione (GSH) concentrations were then measured. 2 mM Gln cells in 60% O2 were found to have higher concentrations of GSH compared to Gln- cells in 60% O2, suggesting that Gln confers protection to the cell during exposure to hyperoxia through up-regulation of GSH. When cells in 60% O2 were given higher concentrations of Gln (5 and 10 mM), cell growth at 96 h was increased compared to cells grown in 2 mM Gln (P<0.04). Clonal survival was also increased in cells exposed 60% O2 and supplemented with higher concentrations of Gln compared to Gln- cells in 60% O2. These studies suggest that supplemental glutamine may improve cell growth and cell viability and therefore may be beneficial to the lung during exposure to moderate concentrations of supplemental oxygen.     

Flow cytometric detection of transforming growth factor-beta expression in rabbit articular chondrocytes (RAC) in culture--association with S-phase traverse.

We have previously shown that TGF-beta 1 decreased the entry of G0/G1-synchronized rabbit articular chondrocytes (RAC) into S-phase, whereas it enhanced the proliferation rate of actively dividing cells (asynchronous or S-phase-synchronized cells). The growth proliferative effect was accompanied by both increased DNA replication rate and G2/M delay. Since TGF-beta mRNA has been detected in chondrocytes, it was of interest to study the expression of the factor in correlation with the cell cycle of RAC. Using cytofluorometric analysis of both DNA content and TGF-beta protein level, we demonstrated that S-phase-synchronized RAC constitutively expressed TGF-beta, whereas G0/G1-synchronized cells only display very low levels of the factor. The data showed that the expression of TGF-beta is correlated with S-phase traverse since it increases with the percentage of cells in S-phase (less than 27% in G0/G1 to 70% in S-phase-synchronized cells). Moreover, exposure of RAC to TGF-beta 1 (1 ng/ml) for 24 h increased the percentage of positive cells, independently of the number of cells in S-phase, indicating that the factor may up-regulate its own expression. All together, these data suggest that TGF-beta could play a role in initiating the proliferation of articular chondrocytes during the early events of osteoarthritis and might take a part in the repair of cartilage matrix.     

Lack of effect of butyrate on S phase DNA synthesis despite presence of histone hyperacetylation

The effects of sodium butyrate on [³H]thymidine incorporation and cell growth characteristics in randomly growing and synchronized HeLa S₃ cells have been examined in an attempt to determine what effects, if any, butyrate has on S phase cells. Whereas 5 mM sodium butyrate rapidly inhibits [⁵H]thymidine incorporation in a randomly growing cell populations, it has no effect on incorporation during the S phase in cells synchronized by double thymidine block techniques. This lack of effect does not result from an impaired ability of the S phase cells to take up butyrate, since butyrate administration during this period leads to histone hyperacetylation that is identical with that seen with butyrate treatment of randomly growing cells. Furthermore, the ability to induce such hyperacetylation with butyrate during an apparently normal progression through S phase indicates that histone hyperacetylation probably has no effect on the overall process of DNA replication. Temporal patterns of [³H]thymidine incorporation and cell growth following release from a 24-h exposure to butyrate confirm blockage of cell growth in the G1 phase of the cell cycle. Thus, the inhibition by butyrate of [³H]thymidine incorporation in randomly growing HeLa S₃ cell populations can be accounted for solely on the basis of a G1 phase block, with no inhibitory effects on cells already engaged in DNA synthesis or cells beyond the G1 phase block at the time of butyrate administration.     

Periodate-Modified Gangliosides Enhance Surface Binding of Tetanus Toxin to PC 12 Pheochromocytoma Cells

The interaction of 125I-labeled tetanus toxin with PC12 pheochromocytoma cells in monolayer cultures has been examined. Under regular growth conditions, the PC12 cells bind 125I-tetanus toxin to a limited degree compared with dissociated cerebral neuron cultures. After exposure to nerve growth factor for 2 days in low serum-containing media with growth factor supplements, binding of toxin increases over twofold compared with untreated PC12 cells. Binding can also be enhanced (greater than 2.5-fold) after treatment of cells with 2 mM sodium metaperiodate for 20 min. Dissociated cerebral neurons but not fibroblasts in cell culture bind more toxin after periodate treatment. The effect of periodate can be abolished by 5 mM sodium borohydride. A ganglioside isolated from periodate-treated PC12 cells and tentatively identified as GT1b [(N-acetylneuraminyl)galactosyl-N-acetylgalactosaminyl(N- acetylneuraminyl-N-acetylneuraminyl)-galactosyl-glucosylceramide] binds 125I-tetanus toxin on silica gel chromatoplates and on nitrocellulose paper. There are no indications to suggest binding to a polypeptide from treated cells after polyacrylamide gel electrophoresis. Cells artificially supplemented with GT1b and subsequently treated with periodate effectively bind the toxin. The data suggest that modified sialyl groups linked to gangliosides, and not to proteins, are preferential targets for tetanus toxin.     

Effect of sodium butyrate on cell proliferation and cell cycle in porcine intestinal epithelial (IPEC-J2) cells

Conflicting results have been reported that butyrate in normal piglets leads either to an increase or to a decrease of jejunal villus length, implying a possible effect on the proliferation of enterocytes. No definitive study was found for the biological effects of butyrate in porcine jejunal epithelial cells. The present study used IPEC-J2 cells, a non-transformed jejunal epithelial line to evaluate the direct effects of sodium butyrate on cell proliferation, cell cycle regulation, and apoptosis. Low concentrations (0.5 and 1 mM) of butyrate had no effect on cell proliferation. However, at 5 and 10 mM, sodium butyrate significantly decreased cell viability, accompanied by reduced levels of p-mTOR and PCNA protein. Sodium butyrate, in a dose-dependent manner, induced cell cycle arrest in G0/G1 phase and reduced the numbers of cells in S phase. In addition, relative expression of p21, p27, and pro-apoptosis bak genes, and protein levels of p21Waf1/Cip1, p27Kip1, cyclinD3, CDK4, and Cleave-caspase3 were increased by higher concentrations of sodium butyrate (1, 5, 10 mM), and the levels of cyclinD1 and CDK6 were reduced by 5 and 10 mM butyrate. Butyrate increased the phosphorylated form of the signaling molecule p38 and phosphorylated JNK. In conclusion, the present in vitro study indicated that sodium butyrate inhibited the proliferation of IPEC-J2 cells by inducing cell cycle arrest in the G0/G1 phase of cell cycles and by increasing apoptosis at high concentrations.     

Enhanced transglutaminase activity in transformed human lung fibroblast cells after exposure to sodium butyrate

The low level of transglutaminase activity in virus-transformed human embryonic lung fibroblasts (WI-38 VA13A) increased markedly when cells were exposed to sodium butyrate. The effect of sodium butyrate was time- and concentration-dependent and fully reversible. Transformed cells exposed for 5 days to 1 mM sodium butyrate had fewer cells, showed an 8–10-fold higher transglutaminase activity, and stained more abundantly for transglutaminase and pericellular fibronectin than control cells when examined by indirect immunofluorescence. Non-transformed cells (WI-38) showed only a 2–4-fold increase in transglutaminase activity when treated in a similar manner. Studies with metabolic inhibitors revealed the increase in activity was the result of synthesis of new protein. Kinetic studies showed the affinity of putrescine for the enzyme was essentially unchanged but the number of active sites increased 9-fold following exposure to sodium butyrate. Enhanced transglutaminase activity returned to control levels within 7 days after subculture and sodium butyrate removal. These findings suggest that sodium butyrate offers a potential model system to understand better the role of transglutaminase in cells in culture; particularly growth control in transformed cells.     

Variation of Ap4A and other dinucleoside polyphosphates in stressed Drosophila cells

The unusual bis(5'-nucleosidyl)oligophosphates: Ap4A, Ap4G, Ap3A, and Ap3G, have been measured in cultures of Drosophila cells. Exponentially growing cells contain concentrations of 0.25, 0.31, 0.87, and 2.25 microM, respectively. These nucleotides have been followed after stressing the cells either by CdCl2 addition or by heat-shock treatment. Their concentrations are not affected by exposure to 500 microM CdCl2 during 6 h. Beyond this threshold of cadmium concentration, the nucleotides increase. With 5 mM CdCl2, an enhancement by 2 orders of magnitude of all the dinucleoside tri- and tetra-phosphates is observed. Upon heat-shock from 19 to 37 degrees C, Ap4A, Ap3A, and Ap3G increase up to 2.2, 3, and 3.3 times their initial levels, respectively. The increase is achieved within 1 h.     

Differential effects of transforming growth factor-beta and epidermal growth factor on the cell cycle of cultured rabbit articular chondrocytes

We examined the effect of transforming growth factor (TGF-beta) on the proliferative rate and cell cycle of cultured rabbit articular chondrocytes using cell counting, cytofluorometry, and [3H]-thymidine incorporation. In the presence of 2% or 10% FCS (fetal calf serum), TGF-beta at 0.01, 0.1, 1, and 10 ng/ml had an inhibitory effect on cell proliferation after 24 h exposure with a dose dependence only for 2% FCS. Flow cytometric analysis of cell DNA content at that time showed that a high proportion of cells were arrested in late S-phase (SQ or G2Q) in either 2% or 10% FCS-containing medium. In both cases, a disappearance of the cell blockage occurred between 24 and 48 h after TGF-beta addition. However, whereas a stimulation of cell proliferation rate was observed at that time in cultures containing 10% FCS, a dose-dependence inhibition of cell growth was detected, in contrast, for 2% FCS-treated cells. Presence of TGF-beta during the last 24 h was not necessary to release the arrested cells. Furthermore, platelet-poor plasma at 10% produced the same effects as FCS, suggesting that platelet-derived factors, such as platelet-derived growth factor (PDGF), could not be responsible for the release of blocked cells in this case. We compared the effect of TGF-beta to that of epidermal growth factor (EGF), used at an optimal concentration (10 ng/ml). In both slowly growing (2% FCS) and proliferating chondrocytes (10% FCS), EGF caused a significant increase of cell proliferation as early as 24 h. No arrest in late S-phase but an augmentation of the percentage of cells in S- and G2M-phases were observed. When combined, TGF-beta and EGF did not induce synergistic effect on the chondrocyte proliferation, as estimated by cell counting. [3H]-thymidine labeling showed that the factors induced identical maxima of incorporation but the peak occurred earlier for TGF-beta than for EGF (approximately 6 h versus 12 h, respectively). Although both factors induce similar cell-number increases at 48 h in 10% FCS-containing medium, these proliferative effects were due to different actions on the cell cycle. The present study indicates that TGF-beta induces first a recruitment of chondrocytes in noncycling SQ- or G2Q-blocked cells. The, the release of these cells may produce either apparent stimulation of cell proliferation if sufficient levels of an unknown serum factor are present (10% FCS) or an inhibition of growth rate when only reduced amounts of this factor are available (2% FCS).(ABSTRACT TRUNCATED AT 400 WORDS)     

Butyrate blocks the accumulation of CDC2 mRNA in late G1 phase but inhibits both the early and late G1 progression in chemically transformed mouse fibroblasts BP-A31

Sodium butyrate (6 mM) blocks the resumption of the cell division cycle in serum-deprived chemically transformed Balb/c-3T3 mouse fibroblasts (BP-A31). The inhibition of G1 progression by sodium butyrate is not restricted to a specific mitogenic signaling pathway and is equally effective when tetradecanoyl phorbol acetate (TPA), insulin, or fetal calf serum (FCS) is used as inducer. The inhibitor acts in early as well as late G1 phase as indicated by experiments in which inhibitor was added and withdrawn at different times after restimulation of quiescent cells by FCS. At the gene expression level, sodium butyrate does not affect the inducibility of early cell cycle-related genes (c-myc, c-jun) while blocking the induction of cdc 2 mRNA, a late G1 marker. We conclude that sodium butyrate does not interfere with the growth factor signaling pathways regulating the (early) cell cycle-related gene expression. However, the presence of sodium butyrate early in G1 phase inhibits the cascade of events leading eventually to the expression of late G1-characteristic genes such as cdc2. The antimitogenic activity of sodium butyrate may be related to its interference with an (unknown) process involved in the "mitogenic" cascade.     

Culture at a Higher Temperature Mildly Inhibits Cancer Cell Growth but Enhances Chemotherapeutic Effects by Inhibiting Cell-Cell Collaboration

Acute febrile infections have historically been used to treat cancer. To explore the underlying mechanism, we studied chronic effects of fever on cancer cell growth and chemotherapeutic efficacy in cell culture. We found that culturing cancer cells at 39°C mildly inhibited cell growth by arresting the cells at the G1 phase of the cell cycle. When cells were seeded in culture dishes at a lower density, e.g. about 1000–2000 cells per 35-mm dish, the growth inhibition was much greater, manifested as many fewer cell colonies in the 39°C dishes, compared with the results at a higher density seeding, e.g. 20,000 cells per dish, suggesting that cell-cell collaboration as the Allee effect in cell culture is inhibited at 39°C. Withdrawal of cells from serum enhanced the G1 arrest at 39°C and, for some cell lines such as A549 lung cancer cells, serum replenishment failed to quickly drive the cells from the G1 into the S and G2-M phases. Therapeutic effects of several chemotherapeutic agents, including clove bud extracts, on several cancer cell lines were more potent at 39°C than at 37°C, especially when the cells were seeded at a low density. For some cell lines and some agents, this enhancement is long-lasting, i.e. continuing after the cessation of the treatment. Collectively these results suggest that hyperthermia may inhibit cancer cell growth by G1 arrest and by inhibition of cell-cell collaboration, and may enhance the efficacy of several chemotherapeutic agents, an effect which may persist beyond the termination of chemotherapy.     

Galactosyltransferase activity and cell growth: uridine diphosphate (UDP)galactose inhibition of murine leukemic L1210 cells

UDPgalactose inhibits the growth of mouse leukemic L1210 cells. In calf serum supplemented Dulbecco's medium (CS-DMEM), 1.2 mM UDPgalactose (UDPgal) inhibited cell growth by 50% (IC50), and 5 mM UDPgalactose inhibited cell growth by 92%. Other nucleotide sugars as well as galactose, glucose, and galactose-1-phosphate had little or no effect on cell growth. Uridine nucleotides, which inhibit galactosyltransferase activity, protected L1210 cells from the growth inhibitory effect of UDPgalactose when both were added simultaneously to culture media. Unlike mouse 3T12 cells, in which no inhibition of cell growth was observed with heat-inactivated calf serum (HICS)-DMEM, 5 mM UDPgalactose inhibited L1210 cell growth in HICS-DMEM to the same degree as that observed in CS-DMEM. In contrast to 3T12 cells, L1210 cells secrete significant galactosyltransferase activity into the media. Complete inhibition of 3T12 cell growth by UDPgal was observed if HICS-DMEM medium was first conditioned by L1210 cells for 48 hours. No difference in cell growth or [3H]thymidine uptake was detected after 6 hours of exposure to UDPgalactose, but both were significantly decreased at 24 and 48 hours. Flow cytometric analysis of UDPgalactose effects on L1210 cells revealed no differences in the distribution of cells in G1, S, or G2-M of the cell cycle after 6 hours of incubation, but after 16 hours of UDPgalactose treatment, L1210 cells were arrested in early S phase. These cells were completely viable and morphologically similar to control L1210 cells. Normal growth was resumed when UDPgal was removed. The data suggest that UDPgalactose inhibition of cell growth requires extracellular galactosyltransferase activity and that the effect is mediated via the cell membrane.     

Biochemical and morphological characteristics of selenite-induced apoptosis in human hepatoma hep G2 cells

Selenium is a cellular growth inhibitor in many mammary tumor cells. To comprehend the mechanism for the selenium-induced cell death, we examined the effects of sodium selenite, which has been one of the most extensively investigated selenium compounds, in human hepatoma Hep G2 cells. Cell viability gradually decreased after treatment with sodium selenite within the concentration range of 10–50 μM. Low (10 μM) selenite has shown a high-percentage laddering pattern compared to the high (25 μM) cytotoxic selenium concentration in agarose gel electrophoresis. G₂M-phase enrichment was also concentration dependent. The most consistent transmission electron microscopic finding was the existence of large lysosomes. Based on these data, we hypothesize that sodium selenite predominantly shows its apoptotic effect over hydrogen selenite accumulation.     

二氧化硫衍生物对蚕豆幼苗生长和细胞周期的影响

研究SO₂体内衍生物NaHSO₃与Na₂SO₃(1:3,mmol/L)对蚕豆幼苗生长和细胞分裂的影响。结果表明:SO₂衍生物(浓度在0~30mmol/L)对幼苗生长的抑制作用具有剂量效应和时间效应关系,短时间处理效应不明显,处理48h后蚕豆幼根生长抑制,168h后幼苗根上部分长度(芽长)表现生长抑制,根长和芽长与处理浓度间呈负线性相关。SO₂衍生物处理12~36h,导致根尖细胞分裂指数下降,根尖中前期细胞减少,间期、后期和末期细胞增多,表明SO₂衍生物能够阻止细胞进入分裂态,延长分裂过程,这可能是SO₂衍生物处理组根尖细胞分裂指数降低,幼苗生长抑制的主要原因。     

Butyrate-synchronized cloned T cells retain their dependence on interleukin-2 for growth induction : A model system for growth regulation

Treatment of ST2/K9 cells, a cloned mouse T-cell line, with 1 mM sodium butyrate for 24 h leads to complete growth arrest in G1. This block is completely reversible and restimulation of cellular growth is entirely dependent on the presence of interleukin-2 (Il-2) in the culture medium. Additional as yet undefined serum factors are necessary for maintenance of further proliferation. After release from butyrate-induced growth arrest, Il-2 is required only during the induction phase of DNA replication. At the onset of thymidine incorporation, the growth factor can be removed, after which DNA replication occurs and the cells are able to complete only one cycle of duplication. The data presented here show that synchronization with sodium butyrate promotes cellular accumulation in the lymphokine-sensitive phase of the cell cycle. On the basis of the parameters established for restimulation of these cells, the detailed characterization of the molecular events involved in Il-2-mediated growth is possible.