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R W Erbe

Publications and source records attributed to R W Erbe.

At least 37 records · Page 2Linked to original sources
PubMed1981

Decreased rates of methionine synthesis by methylene tetrahydrofolate reductase-deficient fibroblasts and lymphoblasts.

Methionine synthesis from homocysteine was measured in intact human fibroblasts and lymphoblasts using a [14C]formate label. Seven fibroblast lines and two lymphoblast lines derived from patients with 5,10-methylene tetrahydrofolate reductase deficiency had rates of methionine synthesis that were from 4 to 43% of normal. When the patients were divided by clinical status into mildly (two patients), moderately (two patients), and severely (three patients) affected, methionine biosynthesis expressed as a percent of control values was 43 and 33%, 11 and 10%, and 7, 6, and 4%, respectively, in fibroblasts. Similar data for the two lymphoblast lines were 36 and 26% for a mildly and moderately affected patient, respectively. These data are to be contrasted with the measurement of residual enzyme activity in cell extracts which agrees less precisely with the clinical status of the patients. In the presence of normal methionine synthetase activity, the rate of synthesis of methionine from homocysteine is a function of the activity of the enzyme 5,10-methylene tetrahydrofolate reductase, and measurement of the methionine biosynthetic capacity of cells deficient in this enzyme accurately reflects the clinical status of the patient from whom the cells were derived.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1980

Expression of the human argininosuccinate synthetase gene in hamster transferents.

The structural gene for human argininosuccinate synthetase [L-citrulline:L-aspartate ligase (AMP-forming), EC 6.3.4.5] was transferred to argininosuccinate synthetase-deficient Chinese hamster cells via metaphase chromosomes isolated from human lymphoblast line MGL8D1, a constitutive overproducer of argininosuccinate synthetase, and from its repressible parent, MGL8B2. Argininosuccinate synthetase expression was selected for in citrulline-containing medium, and the human origin of the argininosuccinate synthetase expressed by seven transferents was identified by isoelectric focusing. Stable transferents expressing MGL8D1 argininosuccinate synthetase fell into two classes: (i) those whose argininosuccinate synthetase activity was reduced to 10-50% by arginine, similar to the repression of argininosuccinate synthetase synthesis observed in normal human lymphoblasts, and (ii) those that constitutively expressed argininosuccinate synthetase when grown in the presence of arginine or citrulline. Two transferents from the MGL8B2 donor constitutively expressed human arginonosuccinate synthetase. Three hamster revertants were isolated that constitutively expressed hamster argininosuccinate synthetase. Transferents and revertants exhibited growth-dependent changes in argininosuccinate synthetase activity, in contrast to the constant synthetase activity levels in donor lymphoblasts during growth. The isolation of stable transferents that constitutively or repressibly express argininosuccinate synthetase makes possible the analysis of regulatory signals influencing expression of the argininosuccinate synthetase gene.

Animals↗
PubMed1980

Regulation of methionine adenosyltransferase in normal diploid and simian virus 40-transformed human fibroblasts.

Methionine adenosyltransferase activity in normal diploid and simian virus 40 (SV40)-transformed human fibroblasts increased severalfold when cell monolayers were cultured in medium deficient in L-methionine. This increase in methionine adenosyltransferase activity required RNA and protein syntheses and probably represented a derepression of the enzyme's biosynthesis. Furthermore, studies with RNA synthesis inhibitors suggested that the regulation of this enzyme activity in human fibroblasts involved posttranscriptional mechanisms. The inclusion of homocysteine thiolactone, a metabolic precursor of methionine, in the methionine-deficient medium inhibited the derepression in normal human fibroblasts but augmented the derepression in fully transformed fibroblasts. These differences in derepression patterns thus appeared related to altered metabolism of homocysteine and/or methionine in SV40-transformed human fibroblasts and as such may serve as a transformation marker in SV40-transformed cells.

Cell Line↗
PubMed1979

Reversion to methionine independence in simian virus 40-transformed human and malignant rat fibroblasts is associated with altered ploidy and altered properties of transformation.

Many transformed and malignant cells, unlike normal cells, do not grow when methionine in the growth medium is replaced by its immediate precursor homocysteine [Chello, P. & Bertino, J. (1973) Cancer Res. 33, 1898-1904 and Hoffman, R. & Erbe, R. (1976) Proc. Natl. Acad. Sci. USA 73, 1523-1527]. Rare cells from those populations revert to methionine independence [Hoffman, R., Jacobsen, S. & Erbe, R. (1978) Biochem. Biophys. Res. Commun. 82, 228-234]. We report here that methionine-independent revertants of both human fibroblasts transformed by simian virus 40 and malignant rat fibroblasts concomitantly revert for some of the properties associated with the transformed state. Of the 13 methionine-independent revertants described here, 5 showed increased anchorage dependence as reflected by reduced cloning efficiences in methylcellulose; 8 showed an increased serum requirement for optimal growth; 8 showed decreased cell density in medium containing high serum; and 3 altered their cell morphology significantly. Eight of the 13 have increased chromosome numbers. All lines tested contained immunologically identifiable tumor antigen of simian virus 40. Thus by selecting for methionine independence it is possible to select for heterogeneous transformation revertants, indicating further a relationship between altered methionine metabolism and oncogenic transformation. Therefore a positive metabolic method to select for transformation revertants has been developed, and its use has resulted in selection of human transformation revertants.

Animals↗
PubMed1979

Transfer of tumor cells between cell aggregates as a model for adhesive changes in metastasis.

A model for cell detachment which may influence metastasis in vivo is described involving the transfer of hamster melanoma cells from aggregates of those tumor cells to hamster fibroblast aggregates. The aggregates were made by the spontaneous association of cultured cells. Tumor and fibroblast aggregates were then incubated together but separated by a nylon net that allowed only single cells to pass. Melanoma cells rapidly separated from the tumor aggregates, crossed the net, and attached to the fibroblast aggregates, but fibroblast cells did not. This model of metastasis reflects the postulated role of cell-to-cell adhesion in metastasis and will allow further study of the role of cell attachments in metastasis.

Animals↗
PubMed1976

High in vivo rates of methionine biosynthesis in transformed human and malignant rat cells auxotrophic for methionine.

Unlike normal cells, malignant rat and two simian virus 40-transformed human cell lines can neither grow nor survive in B12-and folate-supplemented media in which methionine is replaced by homocysteine. Yet three lines of evidence indicate that the malignant and transformed cells synthesize large amounts of methionine endogenously through the reaction catalyzed by 5-methyltetrahydropteroyl-L-glutamate; L-homocysteine S-methyltransferase (EC 2.1.1.13). (1) The activities of this methyltransferase were comparable in extracts of malignant and normal cells. (2) The uptake of radioactive label from [5-14C]methyltetrahydropteroyl-L-glutamic acid (5-Me-H4PteGlu) was at least as great in the malignant cells as in the normals and was nearly totally dependent on the addition of homocysteine, the methyl acceptor; furthermore, 59-84% of the label incorporated by cells was recovered as methionine.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗