Differences in the rate of DNA adduct removal and the efficiency of mutagenesis for two benzo[a]pyrene diol epoxides in CHO cells.

The initiation of carcinogenesis by carcinogens such as 7r,8t-dihydroxy-9,10t-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE-I) is thought to involve the formation of DNA adducts. However, the diastereomeric diol epoxide, 7r,8t-dihydroxy-9,10c-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE-II), also forms DNA adducts but is inactive in standard carcinogenesis models. We have measured the formation and loss of DNA adducts derived from BPDE-II in a DNA-repair-proficient line of Chinese hamster ovary (CHO) cells, AT3-2, and in two derived mutant cell lines, UVL-1 and UVL-10, which are unable to repair bulky DNA adducts. BPDE-II adducts were lost from cellular DNA in AT3-2 cells with a half-life of 13.8 h; this was about twice the rate found for BPDE-I adducts. BPDE-II adducts were also lost from DNA in UVL-1 and UVL-10 cells, but at a much slower rate. When purified DNA was modified in vitro with BPDE-II and then held at 37 degrees C, DNA adducts were removed at a rate identical to that seen in UVL-1 and UVL-10 cells, suggesting that the loss in these cells was not due to enzymatic DNA-repair processes but to chemical lability of the adducts. Mutant frequencies at the APRT and HPRT loci were measured at BPDE-II doses that resulted in greater than 20% survival, and were found to increase linearly with dose. In the DNA-repair-deficient cells, the HPRT locus was moderately hypermutable compared with AT3-2 cells (about 5-fold); the APRT locus was extremely hypermutable, giving about 25-fold higher mutant fractions in UVL-1 and UVL-10 than in AT3-2 cells at equal initial levels of binding. When we compared the mutational efficiency of BPDE-II at both loci in AT3-2 cells (the mutant frequency in mutants/10(6) survivors at a dose that resulted in one adduct per 10(6) base pairs) with our previous studies of BPDE-1, we found that BPDE-II was 4-5 times less efficient as a mutagen than BPDE-I. This difference in mutational efficiency could be explained in part by the increased rate of loss of BPDE-II adducts from the cellular DNA, part of which was due to an increased rate of enzymatic removal of these lesions compared with the removal of BPDE-I adducts.     

Ligand stimulation of transfected and endogenous growth factor receptors enhances cytokine production by mast cells.

IL-3 dependent mast cell lines produce cytokines in response to Fc receptor cross-linkage or to ionomycin. In this study we have observed that cells pre-cultured in IL-3 produce 10-100 times more cytokine after receptor cross-linkage in comparison with IL-4 pre-cultured cells. Although several hematopoietin receptors, including those for IL-3, IL-4 and EPO, do not contain tyrosine kinase domains, their occupancy with ligand causes tyrosine phosphorylation of specific cellular substrates. Therefore, the contribution of tyrosine kinase activation to the ability of an IL-3 dependent mast cell line, CFTL-15, to produce cytokines was analyzed. The CFTL-15 cells were transfected with growth factor receptors containing ligand-inducible tyrosine kinase domains (EGFR and PDGFR, and CSF-IR) or with the EPOR. All of the transfectants were able to proliferate in response to IL-3 or to their respective growth factor and to produce IL-3 in response to IgE receptor cross-linkage. Stimulation of the EGFR and PDGFR transfectants with their respective ligands resulted in the production of IL-3, IL-6, and GM-CSF. Stimulation of the CSF-1R or EPOR transfectants with growth factor alone failed to induce cytokine production. However, in co-stimulation assays each of the growth factors enhanced the amount of cytokine produced in response to Fc epsilon RI cross-linkage. The ability of these stimuli to induce tyrosine phosphorylation in the transfectants was analyzed. Fc epsilon RI cross-linkage in the transfectants routinely induced the tyrosine phosphorylation of 145, 86 and 72 kDa proteins, with occasional phosphorylation of 55, 52, and 40 kDa proteins.(ABSTRACT TRUNCATED AT 250 WORDS)     

Transformation of UV-hypersensitive Chinese hamster ovary cell mutants with UV-irradiated plasmids

Transfection of UV-hypersensitive, DNA repair-deficient Chinese hamster ovary (CHO) cell lines and parental, repair-proficient CHO cells with UV-irradiated pHaprt-1 or pSV2gpt plasmids resulted in different responses by recipient cell lines to UV damage in transfected DNA. Unlike results that have been reported for human cells, UV irradiation of transfecting DNA did not stimulate the genetic transformation of CHO recipient cells. In repair-deficient CHO cells, proportionally fewer transformants were produced with increasing UV damage than in repair-proficient cells in transfections with the UV-irradiated hamster adenine phosphoribosyltransferase (APRT) gene contained in plasmid pHaprt-1. However, transfection of CHO cells with UV-irradiated pSV2gpt resulted in neither decline in transformation frequencies in repair-deficient cell lines relative to repair-proficient cells nor stimulation of genetic transformation by UV damage in the plasmid. Blot hybridization analysis of DNA samples isolated from transformed cells showed no dramatic changes in copy number or arrangement of transfected plasmid DNA with increasing UV dose. We conclude that the responses of recipient cells to UV-damaged transfecting plasmids depend both on the type of recipient cell and the characteristics of the genetic sequence used for transfection.     

Topography of dolichyl phosphate synthesis in rat liver microsomes. Transbilayer arrangement of dolichol kinase and long-chain prenyltransferase

The topography of the dolichyl phosphate biosynthetic enzymes within the plane of rat liver microsomes was investigated by the use of two impermeant inhibitors of enzyme activity: trypsin and mercury-dextran. Mercury-dextran was found to inactivate over 50% of the activities of the CTP-dependent dolichol kinase and the long-chain prenyltransferase. Trypsin caused over 90% inactivation of the long-chain prenyltransferase and 60% inactivation of the dolichol kinase. In addition, the CTP-dependent dolichol kinase was inhibited over 90% by CDP applied externally to sealed microsomes. Inactivation of the dolichyl phosphate biosynthetic enzymes by the impermeant probes occurred under conditions where the mannose-6-phosphatase activity was highly latent. It was concluded that the active sites of these two enzymes are located on the external surface of the microsomal membranes and that dolichyl phosphate biosynthesis occurs asymmetrically on the cytoplasmic surface of the endoplasmic reticulum.     

Resistance of Pseudomonas to Quaternary Ammonium Compounds: II. Cross-Resistance Characteristics of a Mutant of Pseudomonas aeruginosa

Tube dilution experiments showed that benzalkonium chloride (BC)-resistant mutants of Pseudomonas aeruginosa grown in the presence of 1,000 mug of BC per ml were at least 20 times more sensitive to polymyxin B and colistin sulfate than the BC-sensitive (BCS) parent strain. BCS cells selected for resistance to 500 mug of polymyxin B per ml remained sensitive to BC. There was little difference in the amount of carbenicillin, gentamicin sulfate, or rifampin needed to prevent growth of either the BCS or BC-resistant (BCR) strains. Growth of BCR cells was inhibited by ethylenediaminetetraacetate at a concentration of 400 mug/ml or less, whereas the BCS strain grew at ethylenediaminetetraacetate levels of 10,000 mug/ml. Phenylmercuric acetate and thimerosal inhibited growth of BCR and BCS cells at concentrations of 10 mug/ml or less. BCR cells were cross-resistant to >1,000 mug/ml concentrations of five other quaternary ammonium compounds, including three with C(16) alkyls and two with alkyl groups of shorter length. The BCS strain was also resistant to >1,000 mug/ml concentrations of the three quaternary ammonium compounds with C(16) alkyl groups but, in addition to BC, was inhibited by 200 mug/ml levels or less of the two quaternary ammonium compounds containing alkyl groups of less than 16 carbon atoms.     

Superinduction of the murine B cell Fc epsilon RII by T helper cell clones. Role of IL-4

Th cell clones are known to induce an IL-4 dependent polyclonal IgE synthesis. Because IL-4 can induce the expression of the low affinity FcR for IgE (Fc epsilon RII) the ability of Th cell clones to induce Fc epsilon RII on purified splenic B cells was analyzed. It was found that a TH2 clone could cause a 50- to 100-fold superinduction of Fc epsilon RII after 2 days in culture; after 3 days, the Fc epsilon RII levels had almost returned to base line. The superinduction was inhibited by an anti-IL-4 antibody, 11B11, indicating its dependence on IL-4. A TH1 clone could cause a modest (four fold) induction of Fc epsilon RII, and this induction was not influenced by 11B11. A similar Fc epsilon RII induction was seen when using the supernatant from activated TH1 cells. The component(s) causing this relatively low level Fc epsilon RII induction is not known; a variety of known lymphokines were tested, and only IL-4 demonstrated any capacity for Fc epsilon RII induction on LPS-activated B cells. Addition of rIL-4 at concentrations of 400 U/ml or greater to the TH1 culture was sufficient to cause a Fc epsilon RII superinduction similar to that seen with the TH2 clone, while 40 U/ml was not. In order to determine a potential role for the Fc epsilon RII or its soluble fragment on the IgE synthesis mediated by TH2, a monoclonal anti-Fc epsilon RII, B3B4, was added to the culture. The addition of B3B4 did not have an influence on IgE levels in this system.