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1.
Transformed rat thyroid cells fail to express thyroglobulin. Cells transformed with a Kirsten murine sarcoma virus carrying a temperature-sensitive ras allele lose their transformation phenotype when shifted to the nonpermissive (39 degrees C) temperature. The thyroglobulin promoter, however, remains inactive. Similarly, transfection of these cells with a thyroglobulin promoter fused to a neomycin resistance reporter gene does not produce clones resistant to G418. Treatment of the transfected cells with the DNA demethylating agent 5-azacytidine reactivates the thyroglobulin promoter and yields stable G418-resistant clones. We show that thyroglobulin promoter activity is correlated with the presence of a thyroid-specific nuclear factor, TgTF1. TgTF1 cannot be detected in transformed cells but reappears after treatment with 5-azacytidine at 39 degrees C. Restoration of Ras activity at 33 degrees C leads to the rapid loss of TgTF1 and G418 resistance.  相似文献   

2.
Ts-694 is a temperature sensitive mutant of hamster cells which is blocked in the G1 phase of the cell cycle at the restrictive temperature of 39 degrees. A comparison of the Lys-tRNA isoacceptors by RPC-5 chromatography showed a decrease in tRNA5Lys and an increase in tRNA4Lys at 39 degrees. This was identical to the changes seen in confluent cultures at the permissive temperature of 33 degrees. These Lys-tRNA changes were not seen in ts-694 cells blocked in G1 by isoleucine deficiency, nor in two other G1 ts mutants at the restrictive temperature. Cells trapped in S phase by a thymidine block also contained decreased levels of tRNA4Lys when raised to 39 degrees. Both tRNA4Lys levels and cell division increased when the cells were returned to the permissive temperature. An in vitro assay was established for the modification of tRNA5Lys to tRNA4Lys with tRNA6Lys and tRNA2Lys as intermediates. The first reaction is the synthesis of tRNA6Lys which involves the introduction of a modified uridine at the third position of the anticodon. Extracts of 694 cells grown at 33 degrees were able to modify rat liver [3H] tRNA5Lys to tRNA6Lys and tRNA4Lys in vitro when assayed at 25 degrees but not at 39 degrees. Extracts of Balb/c 3T3 cells, however, were more active at 39 degrees than at 25 degrees showing that the normal enzyme is not temperature sensitive. Ts-694 cell tRNA, isolated from cells grown at 33 degrees was aminoacylated at both 25 degrees and 39 degrees with rat liver synthetases. tRNA4Lys was present at both temperatures indicating that ts-694 cells do not contain a temperature sensitive tRNA4Lys.  相似文献   

3.
The effects of antifebriles and anticancer drug on human vascular endothelial cells (HVE) and several cultured human cells were investigated. The HVE were isolated from umbilical cord veins by enzyme treatment and cultured successively in aerated synthetic medium, RPMI-1640, with 20% preclostrum new born calf serum. The presence of factor VIII antigen in the HVE was determined by enzyme-labeled antibody method. Cell count and protein amount were examined at regular intervals. At 3 hour-expose, sulpyrine was more toxic to the cultured cells than aspirin at 37 degrees C. The cytotoxicity of sulpyrine was markedly enhanced at 40 degrees C than at 37 degrees C. However, there was no enhancement in the cytotoxicity of aspirin at 40 degrees C. Cultured HVE and normal human fetal lung (HAIN-55) cells at 37 degrees C were sensitive to sulpyrine, and their sensitivity of the cells to the drug were markedly enhanced when they were incubated at 41 degrees C. In contrast, sensitivity of malignant human cells (HeLa cells) to sulpyrine was not found at 37 degrees C, however sensitivity of the cells to the drug was manifested at 41 degrees C of incubation. There was no effect of 5-fluorouracil (FU) on the growth of HVE and HAIN-55 cells at 41 degrees C, while HeLa cells showed high susceptibility to FU at the same temperature. The results showed the possibility that normal human cells may be sensitive to antifebrile drugs but not to anticancer drug at ordinary and high temperature, whereas malignant human cell may be susceptible to both antifebrile drugs and anticancer drug at high temperature.  相似文献   

4.
We have shown that heat shock does not induce the synthesis of hsp70 in FM3A cells maintained at a low culture temperature of 33 degrees C although it does so in cells maintained at 37 degrees C [T. Hatayama et al. (1991) Biochem. Int. 24, 467-474]. In this paper, we show that FM3A cells maintained at 37 degrees C produced hsp70 mRNA during continuous heating at 42 degrees C or during postincubation at either 37 or 33 degrees C after being heated at 45 degrees C for 15 min, whereas cells maintained at 33 degrees C did not produce hsp70 mRNA during continuous heating at 37, 39, 42, or 45 degrees C, or during postincubation after being heated at any temperature. Thus the lack of hsp70 synthesis in cells maintained at 33 degrees C seemed to be due to the absence of hsp70 mRNA induction. Also, hsp70 was accumulated in cells maintained at 37 degrees C during continuous heating at 42 degrees C and during postincubation at 37 degrees C after heat shock at 45 degrees C, but not during postincubation at 33 degrees C. The cellular level of the constitutive hsp73 as well as the mRNA level were both similar in cells maintained at 33 and 37 degrees C. On the other hand, the cellular level of the constitutive hsp105 in cells maintained at 33 degrees C was only half of that in cells maintained at 37 degrees C. These hsp105 levels increased significantly in both types of cells after continuous heating at 39 degrees C. These findings indicate that the culture temperature affects not only the induction of hsp70 mRNA but also the accumulation of hsp70 and hsp105 in the cells.  相似文献   

5.
The transport of [3H]deoxyuridine by the active nucleoside transport system into the isolated rabbit choroid plexus was measured in vitro under various conditions. Choroid plexuses were incubated in artificial CSF containing 1 microM [3H]deoxyuridine and 1 microM nitrobenzylthioinosine for 5 min under 95% O2-5% CO2 at 37 degrees C and the accumulation of [3H]deoxyuridine measured. Nitrobenzylthioinosine was added to the artificial CSF at a concentration (1 microM) that did not inhibit the active nucleoside transport system but did inhibit the separate, saturable nucleoside efflux system. The active transport of deoxyuridine into the choroid plexus depended on Na+ in the medium, as ouabain, substitution of Li+ and choline for Na+, and poly-L-lysine all inhibited deoxyuridine transport. Thiocyanate in place of chloride and penetrating sulfhydryl reagents also inhibited the active transport of deoxyuridine into choroid plexus. The active transport of deoxyuridine into choroid plexus, which is inhibited by naturally occurring ribo- and deoxyribonucleosides (IC50 = 7-21 microM), was not inhibited (IC50 much greater than 150 microM) by nucleosides with certain alterations on the 2', 3', or 5' positions in D-ribose or 2-deoxy-D-ribose (e.g., adenine arabinoside, 3'-deoxyadenosine, xylosyladenosine); or the pyrimidine or purine rings (e.g., 6-azauridine, xanthosine, 7-methylinosine, or 8-bromoadenosine). Other analogues were effective (IC50 = 8-26 microM; e.g., 5-substituted pyrimidine nucleosides, 7-deazaadenosine, 6-mercaptoguanosine) or less effective (IC50 = 46-145 microM; e.g., 5-azacytidine, 3-deazauridine) inhibitors of deoxyuridine transport into the isolated choroid plexus.  相似文献   

6.
Temperature-sensitive mutants of Japanese encephalitis virus.   总被引:2,自引:2,他引:0       下载免费PDF全文
Ten stable temperature-sensitive mutants of Japanese encephalitis virus were isolated after mutagenesis by growth of cloned wild-type virus in the presence of the nucleic acid precursor analogs 5-fluorouracil and 5-azacytidine. Mutants were selected which grew at least 100-fold better at 33 degrees C than at 41 degrees C. The 5-fluorouracil was found to be more effective at inducing temperature-sensitive mutations than was 5-azacytidine. Analysis of the virus-specific RNA and proteins synthesized by each mutant at the nonpermissive temperature was used to determine biochemical phenotypes. The mutants were analyzed for abilities to complement in mixed infections. Although inefficient and sometimes nonreciprocal, complementation occurred at higher levels than previously reported for flavivirus mutants. Interference between mutants in some mixed infections was also observed. Seven complementation groups were defined. Three groups contained mutants incapable of synthesizing virus-specific RNA at the nonpermissive temperature, whereas the remaining complementation groups displayed an RNA+ phenotype. Levels of protein synthesis comparable to that of wild type were observed at the nonpermissive temperature in three groups. Two other groups were represented by mutants which synthesized only low levels of virus-specific proteins at the higher temperature. Mutants in the remaining two groups did not produce detectable levels of proteins under nonpermissive conditions.  相似文献   

7.
To identify specific cellular factors which could be required during the synthesis of retroviral DNA, we have studied the replication of murine leukemia virus in mouse cells temperature sensitive for cell DNA synthesis (M. L. Slater and H. L. Ozer, Cell 7:289-295, 1976) and in several of their revertants. This mutation has previously been mapped on the X chromosome. We found that a short incubation of mutant cells at a nonpermissive temperature (39 degrees C) during the early part of the virus cycle (between 0- to 20-h postinfection) greatly inhibited virus production. This effect was not observed in revertant or wild-type cells. Molecular studies by the Southern transfer procedure of the unintegrated viral DNA synthesized in these cells at a permissive (33 degrees C) or nonpermissive temperature revealed that the levels of linear double-stranded viral DNA (8.8 kilobase pairs) were nearly identical in mutant or revertant cells incubated at 33 or 39 degrees C. However, the levels of two species of supercoiled viral DNA (with one or two long terminal repeats) were significantly lower in mutant cells incubated at 39 degrees C than in mutant cells incubated at 33 degrees C or in revertant cells incubated at 39 degrees C. Pulse-chase experiments showed that linear viral DNA made at 39 degrees C could not be converted into supercoiled viral DNA in mutant cells after a shift down to 33 degrees C. In contrast, such conversion was observed in revertant cells. Restriction endonuclease analysis did not detect differences in the structure of linear viral DNA made at 39 degrees C in mutant cells as compared to linear viral DNA isolated from the same cells at 33 degrees C. However, linear viral DNA made at 39 degrees C in mutant cells was poorly infectious in transfection assays. Taken together, these results strongly suggest that this X-linked gene, affecting mouse cell DNA synthesis, is operating in the early phase of murine leukemia virus replication. It seems to affect the level of production of unintegrated linear viral DNA only slightly while greatly reducing the infectivity of these molecules. In contrast, the accumulation of supercoiled viral DNA and subsequent progeny virus production are greatly reduced. Our pulse-chase experiments suggest that the apparent, but not yet identified, defect in linear viral DNA molecules might be responsible for their subsequent impaired circularization.  相似文献   

8.
The induction of thermotolerance was studied in a temperature sensitive mouse cell line, ts85, and results were compared with those for the wild-type FM3A cells. At the nonpermissive temperature of 39 degrees C, ts85 cells are defective in the degradation of short-lived abnormal proteins, apparently because of loss of activity of a ubiquitin-activating enzyme. The failure of the ts85 cells to develop thermotolerance to 41-43 degrees C after incubation at the nonpermissive temperature of 39 degrees C correlated with the failure of the cells to degrade short-lived abnormal proteins at 39 degrees C. However, the failure of the ts85 cells to develop thermotolerance to 43 degrees C during incubation at 33 degrees C after either arsenite treatment or heating at 45.5 degrees C for 6 or 10 min did not correlate with protein degradation rates. Although the rate of degrading abnormal protein was reduced after heating at 45.5 degrees C for 10 min, the rates were normal after arsenite treatment or heating at 45.5 degrees C for 6 min. In addition, when protein synthesis was inhibited with cycloheximide both during incubation at 33 degrees C or 39 degrees C and during heating at 41-43 degrees C, resistance to heating was observed, but protein degradation rates at 39 degrees C or 43 degrees C were not altered by the cycloheximide treatment. Therefore, there is apparently no consistent relationship between rates of degrading abnormal proteins and the ability of cells to develop thermotolerance and resistance to heating in the presence of cycloheximide.  相似文献   

9.
The nucleoside analogs 5-azacytidine (azacitidine) and 5-aza-2′-deoxycytidine (decitabine) are active against acute myeloid leukemia and myelodysplastic syndromes. Cellular transport across membranes is crucial for uptake of these highly polar hydrophilic molecules. We assessed the ability of azacitidine, decitabine, and, for comparison, gemcitabine, to interact with human nucleoside transporters (hNTs) in Saccharomyces cerevisiae cells (hENT1/2, hCNT1/2/3) or Xenopus laevis oocytes (hENT3/4). All three drugs inhibited hCNT1/3 potently (K i values, 3–26 μM), hENT1/2 and hCNT2 weakly (K i values, 0.5–3.1 mM), and hENT3/4 poorly if at all. Rates of transport of [3H]gemcitabine, [14C]azacitidine, and [3H]decitabine observed in Xenopus oocytes expressing individual recombinant hNTs differed substantially. Cytotoxicity of azacitidine and decitabine was assessed in hNT-expressing or hNT-deficient cultured human cell lines in the absence or presence of transport inhibitors where available. The rank order of cytotoxic sensitivities (IC 50 values, μM) conferred by hNTs were hCNT1 (0.1) > hENT1 (0.3) ? hCNT2 (8.3), hENT2 (9.0) for azacitidine and hENT1 (0.3) > hCNT1 (0.8) ? hENT2, hCNT2 (>100) for decitabine. Protection against cytotoxicity was observed for both drugs in the presence of inhibitors of nucleoside transport, thus suggesting the importance of hNTs in manifestation of toxicity. In summary, all seven hNTs transported azacitidine, with hCNT3 showing the highest rates, whereas hENT1 and hENT2 showed modest transport and hCNT1 and hCNT3 poor transport of decitabine. Our results show for the first time that azacitidine and decitabine exhibit different human nucleoside transportability profiles and their cytotoxicities are dependent on the presence of hNTs, which could serve as potential biomarkers of clinical response.  相似文献   

10.
S49 mouse leukemia cells exhibit both equilibrative and Na(+)-dependent, concentrative formycin B transport. The latter represents only a minor nucleoside transport component and is detectable only when equilibrative nucleoside transport is inhibited by dipyridamole or another transport inhibitor. Thus in uncontaminated S49 cells formycin B accumulated only to slightly above the intracellular-extracellular equilibrium level. In contrast, in suspensions of S49 cells contaminated with mycoplasma, formycin B accumulated in the intracellular water space in unmodified form to 40-50-times the extracellular concentration in a dipyridamole-independent manner during 90 min of incubation at 37 degrees C. The mycoplasma active formycin B transport system was inhibited by all nucleosides tested, including thymidine and deoxycytidine, which are not substrates for the concentrative nucleoside transporter of S49 cells. Mycoplasma contamination was detected by the presence of cell-associated adenosine phosphorylase activity.  相似文献   

11.
The initial rate of [14C]uridine transport by guinea pig erythrocytes was investigated at different temperatures. At 37, 22, and 10 degrees C the concentration dependence of uridine zero-trans influx and equilibrium exchange influx was resolved into two components; (a) a saturable component which followed simple Michaelis-Menten kinetics and which was inhibited by nitrobenzylthioinosine, and (b) a linear component of low magnitude and insensitive to nitrobenzylthioinosine inhibition. The maximum velocity, Vmax, of zero-trans uridine influx for the saturable transport system was 70-fold higher at 37 than 10 degrees C (1.24, 0.20, and 0.018 mmol/L of cells per hour at 37, 22, and 10 degrees C, respectively). Similarly, the apparent affinity, Km, for zero-trans influx decreased as the temperature was lowered (0.27, 0.066, and 0.038 mM at 37, 22, and 10 degrees C, respectively). In contrast, uridine equilibrium exchange influx was less temperature dependent (Vmax, 2.80, 0.89, and 0.14 mmol/L of cells per hour; apparent Km 0.61, 0.36, and 0.24 mM at 37, 22, and 10 degrees C, respectively). These results demonstrate that the mobility of the empty carrier is impaired to a greater extent than the mobility of the loaded carrier temperature decreased. However, the kinetic constants for zero-trans uridine influx and efflux at 37 degrees C were similar, indicating that the nucleoside transporter exhibited directional symmetry at 37 degrees C. Arrhenius plots of the maximum velocity for equilibrium exchange and zero-trans uridine influx were discontinuous above 25 degrees C, but between 20 and 5 degrees C the plots were linear (Ea = 22 and 30 kcal/mol for equilibrium exchange and zero-trans influx, respectively.  相似文献   

12.
Synthesis of mature 28-S ribosomal RNA and 60-S ribosomal subunits is inhibited in baby hamster kidney (BHK) cell line ts 422E at non-permissive temperature (39 degrees C). This leads to a 66% decrease of total ribosomes per cell, a marked imbalance between the large and small ribosomal subunits in the cytoplasm and a decrease of cells per dish after prolonged culture at 30 degrees C. However, inhibition of ribosome synthesis does not affect progression of cells through the G1 period of the cell division cycle, the length of the pre-replicative period, and the rate of entry of cells into S phase. In contrast to culture at non-permissive temperature, culture of BHK ts 422E cells in the presence of 0.04 micrograms/ml actinomycin D at 33 degrees C inhibits markedly the entry into S period. It is concluded that low doses of actinomycin D exert their inhibitory effect on cell growth by preventing maturation and transport of mRNA rather than by interfering with ribosome synthesis. Microfluorometric analysis revealed only slight differences in the distribution of BHK ts 422E cells in G1, S and G2 phases of the cycle either when cultured at 33 degrees C or at 39 degrees C. When too few ribosomes per cell are produced in BHK ts 422E cells at 39 degrees C, cells do not seem to be arrested reversibly at a specific point of the cell cycle but rather to die at random.  相似文献   

13.
A heat-sensitive (hs, arrested at 39.5 degrees C, multiplying at 33 degrees C) and a cold-sensitive (cs, arrested at 33 degrees C, multiplying at 39.5 degrees C) cell cycle variant were isolated from an undifferentiated P-815 murine mastocytoma line. At the respective nonpermissive temperature, both the hs and the cs variant cells were reversibly arrested with a DNA content, typical of G1 phase. The cells of two cs variant subclones, when exposed to the nonpermissive temperature of 33 degrees C, formed metachromatically staining granules with an ultrastructure resembling that of mature mast cells. In addition, the cellular 5-hydroxytryptamine content underwent a marked increase, and the cells responded to compound 48/80 by degranulation as described for normal mast cells. On the other hand, in cells of two hs variant subclones, essentially no mast cell granules were detectable at either 33 or 39.5 degrees C. As previously reported, the cs cell cycle variant phenotype is expressed dominantly in heterokaryons obtained by fusing cs with wild-type cells, whereas hs cell cycle variant cells, similar to other hs mutants, were found to behave recessively under these conditions. Thus the state of proliferative quiescence induced in the cs cells at 33 degrees C is qualitatively different from the state of cell cycle arrest observed in hs cells at 39.5 degrees C and may represent a model for proliferative quiescence of differentiated cells in the intact organism.  相似文献   

14.
Red blood cells from the Pacific hagfish (Eptatretus stouti) were found to possess a facilitated diffusion nucleoside transport system insensitive to inhibition by the nucleoside transport inhibitor nitrobenzylthioinosine (NBMPR). Uridine uptake by this route was saturable (apparent Km 0.14 mM; Vmax 2 mmol/l cells per h at 10 degrees C), inhibited by inosine and adenosine, and blocked both by the vasodilator dipyridamole and by the thiol-reactive agent p-chloromercuriphenylsulphonate. The properties of this carrier resemble closely those of NBMPR-insensitive nucleoside transport systems in some mammalian neoplastic cell lines and in rat red cells. The presence of this type of carrier in a primitive vertebrate suggests that such transporters have a broad biological distribution and that they pre-date or arose at an early stage of vertebrate evolution.  相似文献   

15.
D A Averill  C Su 《Radiation research》1999,151(6):694-702
Development of multidrug resistance to anticancer agents is a major limitation for the success of cancer chemotherapy. The chemosensitizer verapamil increases intracellular accumulation of drugs such as adriamycin in certain multidrug-resistant cell lines. When combined with verapamil, hyperthermia should be able to alter membrane permeability to adriamycin and to enhance the cytotoxicity of the drug. Verapamil increased the cytotoxicity of adriamycin in multidrug-resistant Chinese hamster ovary cells (CH(R)C5) but not in drug-sensitive cells (AuxB1). Hyperthermia (42 degrees C) alone clearly increased the cytotoxicity of adriamycin in AuxB1 cells. There was also a small increase in CH(R)C5 cells at 42 and 43 degrees C. In drug-resistant cells, the cytotoxicity of adriamycin increased considerably when verapamil was combined with heat. This effect was dependent on temperature and increased with time of incubation. At 37 degrees C, verapamil increased the uptake of adriamycin in CH(R)C5 cells, while drug efflux decreased. When verapamil was combined with hyperthermia, drug efflux decreased even further. These results led to an overall increase in intracellular accumulation of the drug. In drug-sensitive cells, hyperthermia increased both the uptake and efflux of adriamycin, but verapamil had no effect. Verapamil plus heat increased the cytotoxicity of adriamycin in drug-resistant cells, and this was accompanied by altered permeability of the membrane to the drug. Hyperthermia combined with verapamil could be beneficial by increasing the effectiveness of adriamycin in the elimination of multidrug-resistant cells in a localized target region.  相似文献   

16.
In this study we have investigated the acquisition of thermotolerance in a Xenopus laevis kidney A6 epithelial cell line at both the level of cell survival and translation. In cell survival studies, A6 cells were incubated at temperatures ranging from 22 to 35 degrees degrees C for 2 h followed by a thermal challenge at 39 degrees degrees C for 2 h and a recovery period at 22 degrees C for 24 h. Optimal acquisition of thermotolerance occurred at 33 degrees degrees C. For example, exposure of A6 cells to 39 degrees degrees C for 2 h resulted in only 3.4% survival of the cells whereas prior exposure to 33 degrees C for 2 h enhanced the survival rate to 69%. This state of thermotolerance in A6 cells was detectable after 1 h at 33 degrees C and was maintained even after 18 h of incubation. Cycloheximide inhibited the acquisition of thermotolerance at 33 degrees C suggesting the requirement for ongoing protein synthesis. The optimal temperature for the acquisition of translational thermotolerance also occurred at 33 degrees C. Treatment of A6 cells at 39 degrees C for 2 h resulted in an inhibition of labeled amino acid incorporation into protein which recovered to approximately 14% of control after 19 h at 22 degrees C whereas cells treated at 33 degrees C for 2 h prior to the thermal challenge recovered to 58% of control levels. These translationally thermotolerant cells displayed relatively high levels of the heat shock proteins hsp30, hsp70, and hsp90 compared to pretreatment at 22, 28, 30, or 35 degrees C. These studies demonstrate that Xenopus A6 cells can acquire a state of thermotolerance and that it is correlated with the synthesis of heat shock proteins.  相似文献   

17.
A temperature-sensitive mutant, designated tsFT101, was isolated from a mouse mammary carcinoma cell line, FM3A, and given an initial characterization. In this cell line, cytokinesis was blocked at a non-permissive temperature (39 degrees C), but DNA synthesis and nuclear division proceeded normally for at least 24 h at 39 degrees C as detected respectively by autoradiography and cytofluorometric analysis. As a result, multinucleate cells accumulated at 39 degrees C (more than 95% in 36 h). When the culture was returned to a permissive temperature (33 degrees C) after 24 h of arrest at 39 degrees C, cytokinesis was resumed and there was a rapid decrease in the number of multinucleate cells. At 39 degrees C, tsFT101 cells had less F-actin than cells at 33 degrees C, indicative of the existence of an abnormality in actin polymerization in this mutant.  相似文献   

18.
We have isolated a mutant clone from mouse FM3A cells with temperature-sensitive defects both in cytokinesis and in thymidine kinase enzyme activity. The clone, designated tsCl.B59, was isolated after mutagenesis at 33 degrees C followed by exposure to cytosine arabinoside at 39 degrees C. It was derived from a thymidine kinase deficient, 5-bromodeoxyuridine-resistant clone (S-BUCl.42) which was originally derived from wild-type clone H-5 of FM3A cells. The temperature-sensitive mutant clone grows normally at 33 degrees C, but not at 39 degrees C, where it exhibits an increased frequency of multinucleate cells due to defective cytokinesis. Unlike the parental S-BUCl.42 cells, which have negligible thymidine kinase activity and are unable to incorporate 3H-thymidine, the mutant in corporates substantial amounts of 3H-thymidine at 33 degrees C, although its thymidine kinase activity remains lower than that of wild-type H-5 cells. When cultures of tsCl.B59 cells are transferred to 39 degrees C, incorporation of 3H-thymidine decreases markedly. The decrease has been shown to be due to thermolability of the thymidine kinase in tsCl.B59 cells.  相似文献   

19.
We established adrenal medullary cell lines from transgenic mice expressing an oncogene, the temperature-sensitive simian virus 40 large T-antigen, under the control of the tyrosine hydroxylase promoter. A clonal cell line, named tsAM5D, conditionally grew at a permissive temperature of 33 degrees C and exhibited the dopaminergic chromaffin cell phenotype as exemplified by the expression pattern of mRNA for catecholamine-synthesizing enzymes and secretory vesicle-associated proteins. tsAM5D cells proliferated at the permissive temperature in response to basic fibroblast growth factor (bFGF) and ciliary neurotrophic factor (CNTF). At a non-permissive temperature of 39 degrees C, bFGF and CNTF acted synergistically to differentiate tsAM5D cells into neuron-like cells. In addition, tsAM5D cells caused to differentiate by bFGF plus CNTF at 39 degrees C became dependent solely on nerve growth factor for their survival and showed markedly enhanced neurite outgrowth. In the presence of bFGF and CNTF, the morphological change induced by the temperature shift was associated with up-regulated expression of neuronal marker genes including neuron-specific enolase, growth-associated protein-43, microtubule-associated protein 2, neurofilament, and p75 neurotrophin receptor, indicating that the cells underwent neuronal differentiation. Thus, we demonstrated that tsAM5D cells could proliferate at permissive 33 degrees C, and also had the capacity to terminally differentiate into neuron-like cells in response to bFGF and CNTF when the oncogene was inactivated by shifting the temperature to non-permissive 39 degrees C. These results suggest that tsAM5D cells should be a good tool to allow a detailed study of mechanisms regulating neuronal differentiation.  相似文献   

20.
We examined the mos-specific intracellular RNA species in 6m2 cells, an NRK cell line nonproductively infected with the ts110 mutant of Moloney murine sarcoma virus. These cells present a normal phenotype at 39 degrees C and a transformed phenotype at 28 or 33 degrees C, expressing two viral proteins, termed P85gag-mos and P58gag, at 28 to 33 degrees C, whereas only P58gag is expressed at 39 degrees C. It has been previously shown that 6m2 cells contain two virus-specific RNA species, a 4.0-kilobase (kb) RNA coding for P58gag and a 3.5-kb RNA coding for P85gag-mos. Using both Northern blot and S1 nuclease analyses, we show here that the 3.5-kb RNA is the predominant viral RNA species in 6m2 cells grown at 28 degrees C, whereas only the 4.0-kb RNA is detected at 39 degrees C. During temperature shift experiments, the 3.5-kb RNA species disappears after a shift from 28 to 39 degrees C and is detected again after a shift back from 39 to 28 degrees C. By Southern blot analysis, we have detected only one ts110 proviral DNA in the 6m2 genome. This observation, as well as previously published heteroduplex and S1 nuclease analyses which showed that the 3.5-kb RNA species lacks about 430 bases found at the gag gene-mos gene junction in the 4.0-kb RNA, suggests that the 3.5-kb RNA is a splicing product of the 4.0-kb RNA. The absence of the 3.5-kb RNA when 6m2 cells are grown at 39 degrees C indicates that the splicing reaction is thermosensitive. The splicing defect of the ts110 Moloney murine sarcoma virus viral RNA in 6m2 cells cannot be complemented by acute Moloney murine leukemia virus superinfection, since no 3.5-kb ts110 RNA was detected in acutely superinfected 6m2 cells maintained at 39 degrees C. The spliced Moloney murine leukemia virus env mRNA, however, is found in acutely infected cells maintained at 39 degrees C, suggesting that the lack of ts110 viral RNA splicing at 39 degrees C is not due to an obvious host defect. In sharp contrast, however, 6m2 cells chronically superinfected with Moloney murine leukemia virus produce a 3.5-kb RNA species at 39 degrees C as well as at 28 degrees C and contain proviral DNAs corresponding to the two viral RNA species.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   

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