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L H Graf

Publications and source records attributed to L H Graf.

28 records · Page 2Linked to original sources
PubMed1985

DNA-mediated transfer of human melanoma cell surface glycoprotein gp130: identification of transfectants by erythrocyte rosetting.

DNA sequences encoding a human melanoma membrane-bound sialoglycoprotein of 130,000 molecular weight (gp130) were introduced into a clonal derivative of mouse B-16 melanoma cells with the selectable neomycin resistance gene (aminoglycoside phosphotransferase). Mouse transfectants were identified by a rapid and precise screening method with mouse monoclonal antibodies and erythrocyte rosetting. The frequency of gp130 transfectants was approximately 1 in 2,000 to 5,000 colonies with neo+ cells. Analysis of secondary mouse transfectants has revealed that the transfected gp130 has a molecular weight, isoelectric point, intracellular processing, peptide map, and spatial orientation of surface-exposed epitopes indistinguishable from those seen with gp130 from human melanoma cells. In contrast to primary transfectants, secondary transfectants expressing gp130 lack demonstrable human repetitive sequences.

Animals↗
PubMed1984

Efficient DNA-mediated transfer of selectable genes and unselected sequences into differentiated and undifferentiated mouse melanoma clones.

We have found that three phenotypically dissimilar mouse B16 melanoma subclones are competent recipients for DNA-mediated gene transfer. Two of these approach and a third, amelanotic clone B78H1, surpasses mouse LTK cells in frequencies of transferent colony formation after treatment with either of two codominantly selectable plasmid vectors, pSV2gpt or pGCcos3neo. Melanoma transferents incorporate both selectable plasmid-homologous sequences and substantial amounts of unselected donor DNA into their cellular DNAs. In addition they retain the distinctive states of differentiation characteristic of the untreated clones. Frequencies of pGCcos3neo-mediated transfer of neo gene-encoded antibiotic resistance into B78H1 can reach 10(-2) in response to treatment with as little as 15 ng plasmid/ml coprecipitate/dish. B78H1 cells readily give rise to "secondary" transferents for the neo gene after treatment with DNA from a "primary" B78H1 neo transferent. This gene transfer system has potential applications for study of regulation of melanoma and neural crest differentiation and malignancy.

Animals↗
PubMed1979

Transformation of the gene for hypoxanthine phosphoribosyltransferase.

Purified DNA from wild-type Chinese ovary (CHO) cells has been used to transform three hypoxanthine phosphoribosyltransferase (HPRT) deficient murine cell mutants to the enzyme positive state. Transformants appeared at an overall frequency of 5 x 10(-8) colonies/treated cell and expressed CHO HPRT activity as determined by electrophoresis. One gene recipient, B21, was a newly isolated mutant of LMTK- deficient in both HPRT and thymidine kinase (TK) activities. Transformation of B21 to HPRT+ occurred at 1/5 the frequency of transformation to TK+; the latter was, in turn, an order of magnitude lower than that found in the parental LMTK- cells, 3 x 10(-6). Thus both clonal and marker-specific factors play a role in determining transformability. The specific activity of HPRT in transformant extracts ranged from 0.5 to 5 times the CHO level. The rate of loss of the transformant HPRT+ phenotype, as measured by fluctuation analysis, was 10(-4)/cell/generation. While this value indicates stability compared to many gene transferents, it is much greater than the spontaneous mutation rate at the indigenous locus. The ability to transfer the gene for HPRT into cultured mammalian cells may prove useful for mutational and genetic mapping studies in this well-studied system.

Animals↗
PubMed1978

Heat-stable enterotoxin of Escherichia coli: in vitro effects on guanylate cyclase activity, cyclic GMP concentration, and ion transport in small intestine.

A partially purified preparation of the heat-stable enterotoxin of Escherichia coli caused a rapid and persistent increase in electric potential difference and short-circuit current when added in vitro to the luminal surface of isolated rabbit ileal mucosa. As little as 1 ng/ml produced an easily detectable response. Under short-circuit condition, the enterotoxin abolished net Cl- absorption; this change was half that produced by theophylline, which stimulated net secretion. The enterotoxin did not change cyclic AMP concentration but caused large and persistent increases in cyclic GMP concentration. The electrical and nucleotide responses exhibited similar and unusually broad concentration-dependences and maximal effects could not be demonstrated. Theophylline elevated cyclic GMP concentration 3-fold both in the presence and absense of the enterotoxin, suggesting no effect of the toxin on cyclic GMP phosphodiesterase. Guanylate cyclase [GTP pyrophosphatelyase(cyclizing); EC 4.6.1.2] activity in a crude membrane fraction from intestinal epithelial cells was stimulated 7-fold by the enterotoxin. These results suggest that guanylate cyclase stimulation is the basis for the toxin's diarrheagenic effect.

Bacterial Toxins↗
PubMed1978

Isolation of nontoxinogenic mutants of Vibrio cholerae in a colorimetric assay for cholera toxin using the S49 mouse lymphosarcoma cell line.

A mouse lymphosarcoma (S49) cell line that is growth-inhibited by agents that elevate intracellular concentrations of adenosine 3':5'-cyclic phosphate was used in a sensitive and convenient colorimetric assay for cholera toxin. S49 cells suspended in Dulbecco's modified Eagle's minimal essential medium containing 10(-5)--10(-6) M RO 20-1724, an analogue of 4-(3,4-demethoxybenzyl)-2-imidazolidinone and a phosphodiesterase inhibitor, were growth-inhibited by subnanogram concentrations of cholera toxin. Effects of toxin were detected by the absence of a yellow pH change (phenol red indicator) which normally accompanies the production of acid metabolites by lymphoma cells. An assay using S49 cells grown in microtiter plates, which is capable of detecting 10 pg of cholera toxin or 0.01 units of cholera antitoxin, was used in screening for nontoxinogenic mutants of Vibrio cholerae strain 569B. The properties of two mutants of the Tox--phenotype, which lacked biologically and immunologically detectable toxin products, are described.

Animals↗
PubMed1976

Increased PRPP synthetase activity in cultured rat hepatoma cells containing mutations in the hypoxanthine-guanine phosphoribosyltransferase gene.

Nine independently derived clones of mutagenized rat hepatoma cells selected for resistance to 6-mercaptopurine (6-MP) or 6-thioguanine (6-ThioG) have been isolated. Each has severely reduced catalytic activity of hypoxanthine-guanine phosphoribosyltransferase (HPRT) and seven of them possess significantly increased activities of phosphoribosylpyrophosphate (PRPP) synthetase. The degrees of elevations of PRPP synthetase activities do not correlate with the degrees of deficiencies of HPRT activities. The cells from one of these clones, 1020/12, posses 40% of the normal HPRT catalytic activity and overproduce purines. We have extensively examined the cells from this clone. Immunotration studies of 1020/12 cells indicate that there is a mutation in the structural gene for HPRT. Although they possess increased specific catalytic activities of the enzyme. PRPP synthetase, the catalytic parameters, heat stability, and isoelectric pH of PRPP synthetase from 1020/12 cells are indistinguishable from those of the enzyme from wild-type cells. The cause of purine overproduction by 1020/12 cells appears to be the elevated PRPP synthetase activity, rather than a PRPP "sparing" effect stemming from reduced HPRT activity. Support for this idea is provided by the observation that the complete loss of HPRT activity in a clone derived from 1020/12 cells does not further enhance the levels of PRPP synthetase or purine overproduction. We propose that the elevated levels of PRPP synthetase activity in these HPRT deficient cells result from a mutational event in the structural gene for HPRT, and that this causes the disruption of a previously undescribed regulatory function of this gene on the expression of the PRPP synthetase gene.

Amidophosphoribosyltransferase↗
PubMed1974

New class of streptomycin-resistant mutants incompatible with supX suppressor mutations in Salmonella typhimurium.

Streptomycin-resistant colonies of Salmonella typhimurium appearing in platings of supX suppressors of strain leu-500 are less variegated in size than are those derived from strain leu-500 counterparts. Several of the streptomycin-resistant leu-500 clones, furthermore, yield suppressors and revertants of the leu-500 auxotrophy at unusually low rates, suggesting that they provide a genetic background inimicable to supX suppression. Two such "suppression-restrictive" leu-500 streptomycin-resistant (str) mutants, designated strains M(1) and M(4), were characterized as to their ability to receive the trp-supX-cysB linkage region by transduction. Coentry of a donor supX deletion mutation with the selected trp(+) marker was not observed even though these sites display more than 10% linkage in control experiments. This was demonstrably the result of nonviability of the combined supX mutant, M(1) or M(4) streptomycin-resistant genotype, rather than the lack of suppression of the leu-500 imparted auxotrophy. Both M(1)- and M(4)-type resistance was accompanied by pleiotropic effects resembling those caused by strB (nonribosomal)- rather than strA (ribosomal)-type resistance, but both restrictive mutants had a high upper limit of resistance corresponding to that of strA-type mutants. Transduction analyses indicated that the str character of neither the M(1) nor the M(4) strain was linked to the strA or the strB gene. These mutations define a previously undescribed locus, which we propose to designate strC, apparently related to streptomycin uptake rather than its intracellular action. Mutation at this locus is evidently incompatible with the inactivation or removal of the supX site, suggesting a functional association between products of the genes.

Chromosome Mapping↗
PubMedDate not supplied

Gene transformation.

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Animals↗