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Biomedical subjects

J Doehmer

Publications and source records attributed to J Doehmer.

70 records · Page 4Linked to original sources
PubMed1989

Androgen hydroxylation catalysed by a cell line (SD1) that stably expresses rat hepatic cytochrome P-450 PB-4 (IIB1).

Androgen hydroxylation catalysed by Chinese hamster fibroblast SD1 cells, which stably express cytochrome P-450 form PB-4, the rat P450IIB1 gene product, was assessed and compared to that catalysed by purified cytochrome P-450 PB-4 isolated from rat liver. SD1 cell homogenates catalysed the NADPH-dependent hydroxylation of androstenedione and testosterone with a regioselectivity very similar to that purified by P-450 PB-4 (16 beta-hydroxylation/16 alpha-hydroxylation = 6.0-6.8 for androstenedione; 16 beta/16 alpha = 0.9 for testosterone). Homogenates prepared from the parental cell line V79, which does not express detectable levels of P-450 PB-4 or any other cytochrome P-450, exhibited no androgen 16 beta- or 16 alpha-hydroxylase activity. The hydroxylase activities catalysed by the SD1 cell homogenate were selectively and quantitatively inhibited (greater than 90%) by a monoclonal antibody to P-450 PB-4 at a level of antibody (40 pmol of antibody binding sites/mg of SD1 homogenate) that closely corresponds to the P-450 PB-4 content of the cells (48 pmol of PB-4/mg of SD1 homogenate). Fractionation of cell homogenates into cytosol and microsomes revealed that the P-450 PB-4-mediated activities are associated with the membrane fraction. Although the P-450 PB-4-specific content of the SD1 microsomes was 15% of that present in phenobarbital-induced rat liver microsomes, the P-450 PB-4-dependent androstenedione 16 beta-hydroxylase activity of the SD1 membrane fraction was only 2-3% of that present in the liver microsomes. This activity could be stimulated several-fold, however, by supplementation of SD1 microsomes with purified rat NADPH P-450 reductase. These studies establish that a single P-450 gene product (IIB1) can account for the hydroxylation of androgen substrates at multiple sites, and suggest that SD1 cells can be used to assess the catalytic specificity of P-450 PB-4 with other substrates as well.

Androstenedione↗
PubMed1988

Stable expression of rat cytochrome P-450IIB1 cDNA in Chinese hamster cells (V79) and metabolic activation of aflatoxin B1.

V79 Chinese hamster fibroblasts are widely used for mutagenicity testing but have the serious limitation that they do not express cytochromes P-450, which are needed for the activation of many promutagens to mutagenic metabolites. A full-length cDNA clone encoding the monooxygenase cytochrome P-450IIB1 under control of the simian virus 40 early promoter was constructed and cointroduced with the selection marker neomycin phosphotransferase (conferring resistance to G418) into V79 Chinese hamster cells. G418-resistant cells were selected, established as cell lines, and tested for cytochrome P-450IIB1 expression and enzymatic activity. Two cell lines (SD1 and SD3) were found that stably produce cytochrome P-450IIB1. Although purified cytochromes P-450 possess monooxygenase activity only after reconstitution with cytochrome P-450 reductase and phospholipid, the gene product of the construct exhibited this activity. This implies that the gene product is intracellularly localized in a way that allows access to the required components. If compared with V79 cells, the mutation rate for the hypoxanthine phosphoribosyltransferase (HPRT) locus in SD1 cells is markedly increased when exposed to aflatoxin B1, which is activated by this enzyme.

Aflatoxin B1↗
PubMed1983

Enhanced production of hepatitis B surface antigen in NIH 3T3 mouse fibroblasts by using extrachromosomally replicating bovine papillomavirus vector.

We have constructed a recombinant pBR322 plasmid composed of a subgenomic transforming fragment of bovine papillomavirus DNA and the hepatitis B surface antigen gene from cloned hepatitis B virus DNA and used it for transfection of NIH 3T3 mouse fibroblasts. The transformed cells retain the plasmids in extrachromosomal form with a copy number of about 50 to 100 per cell. Expression of the hepatitis B surface antigen gene linked to bovine papillomavirus DNA is independent of its orientation relative to the bovine papillomavirus vector. Cell lines continuously secreting high amounts of hepatitis B surface antigen into the medium could be established. The antigen is released into the culture medium as 22-nm particles, having the same physical properties and constituent polypeptides as those found in the serum of hepatitis B virus-infected patients.

Animals↗
PubMed1982

Recombinant retroviral DNA yielding high expression of hepatitis B surface antigen.

A genomic fragment of hepatitis B virus encoding the surface antigen (HBsAg) was inserted into the proviral genome of Moloney mouse sarcoma virus (MSV), obtained from the mouse cell line G8 -124. The recombinant DNA was introduced into NIH 3T3 mouse fibroblasts. Cells, morphologically transformed by the oncogene of MSV (v-mosM) were selected, established as cell lines and tested for expression of HBsAg. An expression level of up to 4.5 micrograms/10(7) cells/day was detected.

Animals↗
PubMed1982

Introduction of rat growth hormone gene into mouse fibroblasts via a retroviral DNA vector: expression and regulation.

We have introduced the rat growth hormone gene into mouse fibroblasts via a retroviral DNA vector. The ability of the viral DNA to induce foci in the recipient cells was used as a dominant selection marker. Several copies of rat growth hormone DNA were integrated in the mouse cells. The transformed mouse cells expressed rat growth hormone-specific mRNA and secreted mature rat growth hormone. In rat cells, the expression of this gene is regulated by glucocorticoids. We demonstrate that hormone-dependent regulation transfers with the clone and thus appears to be an intrinsic property of the gene or its RNA products.

Animals↗
PubMed1980

Assignment of the gene for cytoplasmic glutamate-oxaloacetate transaminase to mouse chromosome 19 using chinese hamster x mouse somatic cell hybrids.

Chinese hamster and mouse cytoplasmic glutamate-oxaloacetate transaminase (GOT-1, EC 2.6.1.1) were separated by isoelectric focusing of cell extracts on thin-layer polyacrylamide plates. The expression of mouse GOT-1 was correlated with the retention of mouse chromosomes and the expression of 16 marker isozymes in 77 Chinese hamster x mouse somatic cell hybrids. Mouse GOT-1 expression was discordant to the expression of isozyme genes assigned to mouse chromosomes 1, 2, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 16, 17, 18, and X. Furthermore it showed no concordant expression with mouse chromosomes 3, 13, and 15. The expression of mouse GOT-1 was highly concordant to mouse chromosome 19 in 21 hybrid clones analyzed karyotypically. Our data confirm by means of somatic cell genetics the chromosomal assignment of the mouse GOT-1 gene based on Mendelian genetics by Eicher, Reynolds, and Southard (3). The appearance of a heteropolymeric band in hybrid cells expressing mouse GOT-1 suggests that this enzyme molecule is probably composed of two subunits.

Animals↗
PubMed1979

Genetic transmission of Moloney leukemia virus: mapping of the chromosomal integration site.

Mice genetically transmitting the exogenous Moloney leukemia virus (Balb/Mo) have been previously derived. These animals carried one copy of Moloney virus DNA (M-MuLV) in their germ line and transmitted the virus as a single Mendelian gene to the next generation. Homozygous BALB/Mo mice were used to genetically map the M-MuLV locus. Embryo fibroblasts were fused to established Chinese hamster cells and somatic cell hybrids were selected. Segregation of mouse chromosomal markers in the hybrids was correlated to the loss of M-MuLV-specific sequences as detected by molecular hybridization. Of 15 isozymes located on different mouse chromosomes only triosephosphate isomerase segregated syntenic with the M-MuLV gene, suggesting that the virus was integrated on chromosome No. 6. This was confirmed by sexual genetic experiments analyzing segregation of Moloney viremia and two markers on chromosome 6 and 15, respectively. The results show that M-MuLV expression is linked to wa-1 on chromosome 6 at a distance of about 30 map units. These data define a new genetic locus, Mov-1, representing the structural gene of M-MuLV in BALB/Mo mice.

Animals↗
PubMed1979

Germ line integration of Moloney leukemia virus: identification of the chromosomal integration site.

The chromosomal integration site of the structural gene of Moloney murine leukemia virus (M-MuLV) in the genome of BALB/Mo mice was mapped genetically. These mice transmit the exogenous M-MuLV as an endogenous virus at a single Mendelian locus. Two independent experimental approaches were used: (i) Non-virus-producing fibroblasts prepared from homozygous BALB/Mo embryos were fused to Chinese hamster Wg3-h-o cells. In an analysis of 30 independent mouse-Chinese hamster cell hybrid clones, the segregation of the viral genome measured by molecular hybridization and enzymes assigned to 16 different mouse chromosomes were compared. We found a highly concordant segregation of M-MuLV sequences and the mouse enzyme triosephosphate isomerase (TPI, EC 5.3.1.1), whose gene has been assigned to chromosome 6. A further karyotype analysis of 9 clones, in which the chromosomes were identified cytochemically, supported this result. (ii) The segregation of the viral genome was studied in backcrosses of BALB/Mo with ABP/J mice. In the backcross ABP/Jx(ABP/JxBALB/Mo) a linkage of the M-MuLV genome to the morphological marker wa-1 on mouse chromosome 6 was found. This confirmed the conclusion that the M-MuLV genome is integrated in mouse chromosome 6. These experiments define the genetic locus Mov-1, denoting the genetically transmitted structural gene of M-MuLV in BALB/Mo mice.

Animals↗
PubMedDate not supplied

Applications of stable V79-derived cell lines expressing rat cytochromes P4501A1, 1A2, and 2B1.

1. Chinese hamster V79-derived cell lines, stably expressing cytochromes P4501A1, 1A2, and 2B1 activities, were constructed by genetic engineering in continuation of our work to establish a battery of V79 derived cell lines designed to study the metabolism of xenobiotics. 2. Cell lines XEM1 and XEM2, expressing cytochrome P4501A1, were capable of the O-dealkylation of 7-ethoxycoumarin and the hydroxylation of benzo[a]pyrene. 3. Cell lines XEMd.MZ and XEMd.NH, expressing P4501A2, were shown to hydroxylate 17 beta-estradiol and 2-aminofluorene. 4. Cell line SD1, expressing cytochrome P4502B1, was able to hydroxylate testosterone stereo- and regio-specifically at the 16 alpha and 16 beta positions. 5. Cell lines were validated in mutagenicity, cytotoxicity, and metabolism studies employing benzo[a]pyrene, trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene, cyclophosphamide, ifosfamide, and picene. 6. Construction of metabolically-competent V79-derived cell lines be recombinant DNA technology will be a fundamental improvement for the evaluation of the cytotoxic, genotoxic and pharmacological properties of a chemical.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMedDate not supplied

Cloning of CYP11B1 and CYP11B2 from normal human adrenal and their functional expression in COS-7 and V79 Chinese hamster cells.

The cDNAs of human 11 beta hydroxylase (CYP11B1) and aldosterone synthase (CYP11B2) were cloned from surgically removed normal human adrenal using polymerase chain reaction. The cloned cDNAs were transfected into COS-7 cells and steroid hydroxylase activity of the two cytochromes P450 expressed was determined in order to elucidate their the functional characteristics. Stable expression of human CYP11B1 or CYP11B2 was performed in V79 hamster cells and confirmed by Southern blotting, Northern blotting, and enzymatic activity. Interestingly, recombinant V79 cells were able to support CYP11B1 and CYP11B2 dependent steroid conversion without additional heterologous expression of the corresponding electron donor system.

Adrenal Glands↗
PubMedDate not supplied

Increase in proto-oncogene raf expression precedes differentiation induction in different clonal rhabdomyosarcoma subpopulations.

Three clonal rat rhabdomyosarcoma subpopulations (A, B, C) with a block of differentiation at different levels of rhabdomyogenesis were exposed to the differentiation inducers retinoic acid (RA), N-methylformamide (NMF) and sodium butyrate (NaBut). Since an increased expression of c-raf and c-fos had recently been demonstrated for subpopulation C after exposure to RA and NMF (1), the mRNA expression of c-raf, c-fos and retinoic acid receptor (RAR) alpha, beta and gamma was compared in all three subpopulations. After exposure to RA, NMF or NaBut, subpopulation C exhibited a significant (p = 0.0001) increase in creatine kinase (CK) activity and in morphological differentiation. In subpopulation B, the response was confined to a significant (p = 0.0001) increase in creatine kinase activity, whereas subpopulation A proved to be differentiation-refractory. On the molecular level, a uniform increase in c-raf expression became evident in all three subpopulations after 6 to 12 hours, persisting at an elevated level throughout the observation period of 120 hours. In contrast, the pattern of c-fos expression observed after exposure to RA, NMF or NaBut was heterogeneous. Expression of RAR alpha and gamma was detected in all subpopulations, whereas RAR beta mRNA was not expressed. Summarizing our results, the uniform pattern of c-raf expression might suggest a participation of c-raf in differentiation signal transduction. Since the three subpopulations differ markedly in their degree of differentiation, the block of differentiation characteristic for each subpopulation supposedly becomes effective only after the action of the c-raf gene product.

Animals↗
PubMedDate not supplied

Search for cell culture systems with diverse xenobiotic-metabolizing activities and their use in toxicological studies.

Many toxic effects are not caused by the administered compound itself, but are due to metabolites. All cell types express some xenobiotic-metabolizing enzymes, but levels and patterns are very variable. Critical metabolic steps may occur within the target cell and/or at other sites. This complex situation is difficult to mimic in vitro. The further problem is that cells that are taken into culture tend to rapidly cease the expression of important xenobiotic-metabolizing enzymes. Part of the problem may be solved by the addition of exogenous metabolizing systems, for example, in the form of freshly isolated hepatocytes, crude subcellular preparations, or purified enzymes. In these systems, the plasma membrane of the target cell may act as a barrier for the active metabolite and thereby lead to false negative results. The alternative is the use of metabolically active target cells. We therefore screened 18 cell lines for monooxygenase, cytochrome P-450 reductase, epoxide hydrolase, glutathione transferase, and UDP-glucuronosyl transferase activities. In further studies, IEC-17, IEC-18, and HuFoe-15 cells showed their capabilities of activating a broad spectrum of structurally heterogenous promutagens, as indicated by the induction of micronuclei. These cells, however, were not suited for the study of a more relevant genetic end point, the induction of hereditary functional changes (gene mutations), implying that a compromise had to be made on the level of the toxicodynamics. In the second approach, cDNAs encoding the rat cytochromes P-450IA1 and P-450IIB1, set under the control of a constitutive promoter, were transfected into V79 Chinese hamster cells, which do not express cytochromes P-450 but are ideal target cells for gene mutation assays. The resulting substrains (XEM1, XEM2, XEM3; SD1) stably expressed cytochromes P-450IA1 and P-450IIB1, respectively, and showed the corresponding monooxygenase activities. Aflatoxin B1, cyclophosphamide, dibutylnitrosamine, and benzo[a]pyrene mutated SD1 and/or XEM1 and XEM2 cells, but were inactive in parental V79 cells. The mutagenicity of benzo[a]pyrene 7,8-trans-dihydrodiol was about 1000 times more potent in XEM1 and XEM2 cells than in SD1 and V79 cells. Other promutagens were inactive in V79 as well as in the genetically engineered daughter lines. This system therefore is not yet optimal in general screening for the detection of new mutagens, but appears ideal in the identification of critical xenobiotic-metabolizing enzymes for a given mutagen.

Animals↗