Tunicamycin-resistant mutations in mouse FM3A cells

Isolation and characterization of a novel mutant mouse cell line resistant to Newcastle disease virus: constitutive interferon production and enhanced interferon sensitivity

In our attempt to isolate mutant cell lines resistant to Newcastle disease virus (NDV) we developed an improved procedure for enrichment of NDV-resistant cells from mouse FM3A cells and isolated a novel NDV-resistant mutant cell line, Had-2, with characteristics different from Had-1, a previously reported NDV-receptor-deficient mutant strain. Had-2 cells adsorbed NDV normally but the accumulation of viral mRNAs and proteins was inhibited. Had-2 cells had to be grown at higher cell densities in order to be NDV-resistant, and it was revealed that they did not exhibit NDV-resistance when grown at lower cell densities. A conditioned medium prepared from a culture of Had-2 cells grown at high cell density was able to make a low-density culture NDV-resistant. The activity of the conditioned medium to induce NDV-resistance was completely neutralized by addition of both anti interferon (IFN)-alpha and anti IFN-beta antibodies, indicating that Had-2 cells were constitutively releasing IFNs, though their levels were rather low. Had-2 cells were also characterized by an increased sensitivity to IFNs as compared with the parental FM3A cells, since the conditioned medium containing IFNs did not render FM3A cells resistant to NDV.

Aberrant CYP1A1 induction: discrepancy of CYP1A1 mRNA and aryl hydrocarbon hydroxylase activity in mutant cells of mouse hepatoma line, Hepa-1

We have isolated new benzo[a]pyrene-resistant clones, cl-21 and cl-32, of the mouse hepatoma line, Hepa-1. CYP1A1-dependent aryl hydrocarbon hydroxylase activity is not inducible by 2,3,7,8-tetrachlorodibenzo-p-dioxin or 3-methylcholanthrene in these two cell lines. However, mRNA of CYP1A1 is inducible in cl-21 and cl-32 cells, as in the wild-type cells, in spite of an undetectable level of cytosolic Ah receptor. The cl-21 cDNA of Cyp1a-1 was found to have a single mutation leading to an amino acid substitution from Leu (118) to Arg (118). However, the CYP1A1 protein band was not detected on Western immunoblots. The cDNA of cl-32 was found to have a single mutation leading to an amino acid change from Arg (359) to Trp (359). The presence of the mature protein in cl-32 was confirmed by Western blot analysis. Somatic cell hybridization experiments demonstrated that the phenotype of cl-21 and cl-32 is recessive and that these clones belong to the same complementation group. These data suggest that there may be a non-Ah receptor-mediated mechanism of CYP1A1 induction.

Analysis of toxic and mutagenic activities of antiherpesvirus nucleosides against HeLa cells and herpes simplex virus type 1

The toxic and mutagenic activities of five antiherpesvirus agents to HeLa cells and herpes simplex virus type 1 (HSV-1) were investigated. 5-Iodo-2'-deoxyuridine (IDU) and 9-beta-D-arabinofuranosyl-adenine (araA) showed very potent inhibitory effects on cell growth and the cloning efficiency of HeLa cells, whereas 1-beta-D-arabinofuranosyl-E-5-(2-bromovinyl)uracil (BV-araU), E-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) and 9-(2-hydroxyethoxymethyl)guanine (ACV) showed less inhibitory effect. 50% inhibitory doses of BV-araU and BVDU for cell growth were 657 and 253 micrograms/ml, respectively. Although the growth inhibitory activity of BVDU was very weak, as above, the mutagenic activity of this drug to the cells, estimated by induction of colchicine-resistant mutants, was observed to be 4 micrograms/ml, which was a markedly smaller dose than the inhibitory dose for cell growth, and the highest frequency of mutation of the cells was shown at 100 micrograms/ml of BVDU. This activity was more potent than that of IDU. No mutagenic activity of BV-araU, araA and ACV to cells was observed within the concentration range of 1-800 micrograms/ml. IDU showed high mutagenic activity to HSV-1 growing in human embryo lung fibroblasts, and IDU-resistant mutants were induced at a high frequency. BVDU also induced a small amount of BVDU-resistant mutant virus, although this drug induced many mutant cells. No mutagenic activity of BV-araU, araA and ACV to HSV-1 was observed.

Mutagenicity of various chemicals including nickel and cobalt compounds in cultured mouse FM3A cells

Employing a suspension culture of FM3A cells, we examined the cytotoxic and mutagenic effects of various chemical compounds. Mutagenicity of various types of mutagens (MNNG, ENNG, sterigmatocystin, mitomycin C, Trp-P-1, and X-rays) was sensitively detected by this assay. Mutagenicity of Trp-P-2 was detected in the presence of an activating enzyme system. Nickel(II) and cobalt(II) compounds (NiCl2, Ni(CH3COO)2, nickel complex [(C2H5)4N]2 [NiCl4], CoCl2, and a cobalt complex [(C2H5)4N]2-[CoCl4]) were cytotoxic to FM3A cells at concentrations of over 1 X 10(-4) M, and produced 2-6-fold increases of the control in the average number of 6-thioguanine-resistant (6TGr) colonies over a very narrow concentration range of 2-4 X 10(-4) M. Comparison of the mutagenicity of various chemical compounds suggested that some of the nickel(II) and cobalt(II) compounds were very weak mutagens.

An FM3A mutant, G258, with a mutation that affects both cell growth and oligosaccharide-lipid synthesis

I have previously isolated a temperature-sensitive FM3A mutant (G258) defective in asparagine-linked glycosylation. G258 shows not only the temperature sensitivity for cell growth, but also temperature sensitivity for synthesis of oligosaccharide-lipid (Nishikawa, Y. (1984) J. Cell. Physiol. 119, 260-266). In the present study, I isolated revertants for cell growth from G258 cells. All three growth revertants also showed reversion on the synthesis of oligosaccharide-lipid. These results imply that the temperature sensitivity for oligosaccharide-lipid synthesis of G258 couples with the temperature sensitivity for cell growth of the mutant. A possible mechanism of the coupling between impaired oligosaccharide-lipid synthesis and growth arrest of G258 cells at 39 degrees C is discussed.

High level of aphidicolin resistance with multiple mutations in mouse FM3A cell mutants

Spontaneous mutants of mouse FM3A cells (AC1, AC2, and AC3), highly resistant to aphidicolin (3000-, 2500-, and 300-fold increase in resistance, respectively), were isolated by multistep selection. The DNA synthesizing activity in permeabilized cells of all three mutants was substantially resistant to aphidicolin, like that in intact cells. The DNA polymerase activity in nuclear extracts in AC1 and AC3, but not AC2, was resistant to aphidicolin. Partially purified DNA polymerase alpha from AC3, but not from AC1 or AC2, showed resistance to aphidicolin. The apparent Ki value for aphidicolin of AC3 polymerase alpha was three to four times that of the enzyme from the parent cells, but the apparent Km values of the enzyme for dCTP and dTTP were normal. All the mutants showed cross-resistance to both arabinofuranosyladenine and arabinofuranosylcytosine. The AC3 mutant had expanded deoxyribonucleoside triphosphate pools. On two-dimensional polyacrylamide gel electrophoresis, AC1 gave a new protein (mol wt 40 kDa). The aphidicolin-resistance trait was reversible in AC2, unlike in AC1 and AC3. These results show that in mammalian cells there are at least two mechanisms of aphidicolin-resistance that involve an altered DNA polymerase alpha that is resistant to aphidicolin and simultaneous expansion of the four DNA-precursor pools.

Isolation and characterization of mouse FM3A cell mutants which are devoid of Newcastle disease virus receptors

A method was developed to select host cell mutants which did not permit the replication of Newcastle disease virus (NDV), and 14 isolates of NDV-nonpermissive mutants of mouse FM3A cells were obtained. All these isolates were judged to be deficient in NDV receptors, since their ability to adsorb 3H-labeled NDV virions was markedly decreased. They were tested for genetic complementation in pairs by cell fusion and shown to fall into a single recessive complementation group, which was designated as Had-1. Vesicular stomatitis virus was able to replicate in this mutant to produce infectious progeny, but the glycoprotein of the released virion was abnormal in size, suggesting a defective processing of the asparagine-linked carbohydrate chains in the mutant cell. The Had-1 mutant was resistant to wheat germ agglutinin, but sensitive to a Griffonia simplicifolia lectin, GS-II, which recognizes terminal N-acetylglucosamine residues. The altered sensitivity to these plant lectins compared with that of the parental FM3A cells indicates that sialylated sugar chains on the cell surface are almost absent from the Had-1 cells, thereby rendering the cells NDV receptor deficient.

Purification and characterization of adenine phosphoribosyltransferase from mouse mammary carcinoma FM3A cells in culture

Adenine phosphoribosyltransferase has been purified to apparent homogeneity from mouse mammary tumor FM3A cells. The purified enzyme, with a specific activity of 20.6 X 10(6) units/g protein at 30 degrees C, was homogeneous as judged by polyacrylamide gel electrophoresis and Ouchterlony double immunodiffusion analysis. The native enzyme had a molecular weight of 44,000 and a subunit composition of 23,000. Apparent Km values for adenine and 5-phosphoribosyl-1-pyrophosphate (PRib-PP) were 6.6 microM and 1.2 microM, respectively. Free Mg2+ was an essential activator with a half-maximal effect at 0.4 mM. AMP was an inhibitor, competitive with PRib-PP, and the Ki value was estimated to be 24 microM. The enzyme activity was not significantly affected by 2,6-diaminopurine, 4-carbamoylimidazolium 5-olate, 8-azaadenine, and 2-fluoro-6-aminopurine. An antibody against the purified mouse adenine phosphoribosyltransferase was raised in a rabbit. The enzyme derived from either mouse, Chinese hamster, or human cells was completely neutralized and precipitated by this antibody, indicating that these enzymes share a common antigenic determinant.

Isolation and analysis of a mammalian temperature-sensitive mutant defective in G2 functions

A temperature-sensitive (ts) mutant, designated tsFT210, was isolated from a mouse mammary carcinoma cell line, FM3A. The tsFT210 cells grew normally at 33 degrees C (permissive temperature), but more than 80% of the cells were arrested at the G2 phase at 39 degrees C (non-permissive temperature) as revealed by flow-microfluorimetric analysis. DNA replication and synthesis of other macromolecules by this mutant seemed to be normal at 39 degrees C for at least 10 h. However, in this mutant, hyperphosphorylation of H1 histone from the G2 to M phase, which occurs in the normal cell cycle, could not be detected at the non-permissive temperature. This suggests that a gene product which is temperature-sensitive in tsFT210 cells is necessary for hyperphosphorylation of H1 histone and that this gene product may be related to chromosome condensation.

Selective expression of adult beta-globin but not embryonic y-globin genes in hybrids of mouse yolk-sac and erythroleukemia cells

Hybrid cells from mouse erythroleukemia and yolk-sac cells from 12-day-old mouse embryos were formed, and the expression of adult beta-globin and embryonic y-globin genes was examined. In these hybrid cells, hemoglobin synthesis could be induced by the addition of dimethylsulfoxide. The adult beta-globin genes from both parental chromosomes were expressed, but embryonic y-globin genes were not. These results suggest that the expression of adult genes dominates that of embryonic genes.

Isolation and characterization of mutator mutants from cultured mouse FM3A cells

A method to select mutator mutants was developed and 3 mutants were isolated from cultured mouse FM3A cells. Fluctuation analyses revealed that these mutator mutants have increased rates of spontaneous mutation at 3 genetic loci tested (resistance to ouabain, blasticidin S and tunicamycin). None of the 3 mutator mutants showed altered sensitivity to aphidicolin or arabinofuranosylcytosine, and so they differed from the mammalian mutator mutants reported previously. Also, all the mutator mutants had the same sensitivity as wild-type to UV or other DNA-damaging agents. Thus, these mutator mutants do not seem to have any deficiency in the DNA-repair process. To determine whether the mutator activity was due to the intracellular dNTP pool imbalance, 4 dNTPs in these mutator mutants were determined by high-pressure liquid chromatography and compared to that of the wild-type cells. The results show that there is no large dNTP pool imbalance in these mutator mutants. Since the mutator activity is not associated with the dNTP pool imbalance, these mutants may have altered protein(s) directly involved in DNA replication.

Isolation of a temperature-sensitive FM3A mutant deficient in asparagine-linked glycosylation by selecting for resistance to tritiated mannose suicide

Protein glycosylation mutants in the mouse mammary carcinoma cell line FM3A were selected for ability to withstand exposure to [2-3H]mannose at 39 degrees C. G258 , one of the mutant cells isolated, has been characterized. G258 cells were temperature-sensitive for cell growth. Moreover, G258 cells showed temperature sensitivity for [3H]mannose incorporation into the TCA-insoluble fraction. To study the biochemical basis of the defect in glycoprotein biosynthesis, the formation of lipid-linked saccharides was examined. The results showed that the formation of lipid-linked oligosaccharides was severely inhibited in G258 cells at 39 degrees C. At 33 degrees C, G258 cells synthesized Glc3Man9GlcNAc2-PP-Dol, the fully assembled lipid-linked oligosaccharides, but at 39 degrees C, G258 cells were able to synthesize merely the smaller lipid-linked oligosaccharides (approximately up to Man3GlcNAc2 -PP-Dol), but were unable to synthesize the larger lipid-linked oligosaccharides.

Genetic and biochemical studies on the activation and cytotoxic mechanism of bredinin, a potent inhibitor of purine biosynthesis in mammalian cells

To study the activation and cytotoxic mechanism of bredinin (4-carbamoyl-1-beta-D-ribofuranosylimidazolium-5-olate), a novel nucleoside antibiotic with potent cytotoxic and immunosuppressive effects, we isolated in a single-step manner five mutants resistant to 10 microM bredinin from cultured mouse mammary carcinoma FM3A cells mutagenized with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Such resistant (Brdr) mutants were 15- to 19-fold less sensitive to the antibiotic than wild-type cells and maintained stably their resistant phenotypes in the absence of bredinin for more than 3 months. They were cross-resistant to tubercidin, an adenosine analog. Like wild-type cells, Brdr mutants were capable of incorporating radioactivity from ring-labeled adenosine into the acid-insoluble macromolecular fraction. However, hypoxanthine-guanine phosphoribosyltransferase-deficient (HGPRT-) mutants derived from the Brdr cells did not incorporate the radioactivity at all or at a markedly reduced rate, indicating that blockade of the pathway via adenosine deaminase present in the Brdr cells resulted in loss of their ability to utilize adenosine. Enzyme assays using cell-free extracts revealed that all the Brdr mutants had less than 3% of the adenosine kinase (AK) activity found in wild-type cells. These results demonstrate that the bredinin resistance is attributed to a defective AK activity and, therefore, that bredinin is metabolized by AK, which may phosphorylate it to a toxic nucleotide, bredinin 5'-monophosphate (Brd-MP), in sensitive cells. Among exogenously added purine bases, guanine was able to reverse the cytotoxic effect of bredinin on both wild-type cells and F5 cells carrying the vector pSV2-Escherichia coli xanthine-guanine phosphoribosyltransferase (XGPRT) gene, while xanthine was able to do so only in F5 cells because the base was metabolized to XMP by the cells. These results support the mechanism of bredinin cytotoxicity, that Brd-MP formed in sensitive cells exposed to the antibiotic blocks the conversion of IMP to XMP by inhibiting IMP dehydrogenase.