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N S Ross

Publications and source records attributed to N S Ross.

9 recordsLinked to original sources
PubMed1992

Tumor necrosis factor-alpha activates nuclear factor kappa B and induces manganous superoxide dismutase and phosphodiesterase mRNA in human papillary thyroid carcinoma cells.

Human papillary thyroid carcinoma (PTC) has a relatively benign prognosis despite a high frequency of lymphatic metastasis. This suggests that local anticancer factors, generated in lymph nodes, control PTC progression. The cytokine, tumor necrosis factor-alpha (TNF-alpha), may be one such factor. We have previously shown that a human PTC cell line (NP-PTC) has high affinity TNF-alpha receptors. We now report on the action of TNF-alpha in these cells. TNF-alpha decreased [3H]thymidine incorporation as well as cellular DNA content and cell number in a dose-dependent manner. The abundance of phosphodiesterase and manganous superoxide dismutase mRNA species was increased in a time- and dose-dependent manner in the NP-PTC cells after TNF-alpha treatment. TNF-alpha activated NF-kappa B, a nuclear factor thought to mediate multiple actions of TNF-alpha, in these cells with a maximum effect observed after 30 min of treatment. Thus, TNF-alpha has an antiproliferative action on NP-PTC cells, despite its ability to induce the accumulation of mRNA that encodes an enzyme (manganous superoxide dismutase), thought to be cytoprotective. The net antiproliferative effect must therefore be explained by a balance of protective and tumoricidal or static effects that ultimately result in control of tumor spread. These antiproliferative effects may be in part mediated by NF-kappa B and PDE.

Base Sequence↗
PubMed1992

Riboflavin deficiency is associated with selective preservation of critical flavoenzyme-dependent metabolic pathways.

Riboflavin is a water soluble vitamin that serves as a precursor of flavin mononucleotide and flavin adenine dinucleotide. These two compounds are coenzymes in a variety of electron transfer reactions that occur in energy producing, biosynthetic, detoxifying and electron scavenging pathways. When an organism is confronted with inadequate dietary riboflavin, characteristic changes occur in the cellular distribution of the various flavin fractions as well as in the activities of flavin-dependent enzymes. These changes suggest a specific hierarchic response to riboflavin deficiency, e.g. the core electron transfer chain required for ATP synthesis is preserved while the enzymes required for the first step of fatty acid beta-oxidation are diminished. The mechanisms by which the specific changes in enzyme activity are mediated have not been completely identified, but appear to result from a combination of diminished access of normal or near normal levels of apoenzyme to coenzyme and diminished abundance of apoenzyme. The changes in apoenzyme content potentially result from alterations in either protein stability or gene expression. The response to riboflavin deficiency of several key enzyme systems and the pathways affected will be discussed and a hierarchic order by which specific enzyme activities are preserved while others are decreased will be proposed. The current understanding of the molecular mechanisms by which these changes are mediated will be discussed.

Animals↗
PubMed1991

A functional promoter flanks an intronless glutamine synthetase gene.

We recently reported the 5'-flanking nucleotide sequence of a putative glutamine synthetase (GS) gene from 3T3-L1 cells (Bhandari, B., Beckwith, K. D. & Miller, R. E. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 5789-5793). We now find that this gene (GSr) has many, but not all, of the characteristics of a typical retroposon. It lacks introns, it contains a short poly(A) tract at its 3' end; it is flanked by 10-base pair (bp) direct repeats; and it corresponds closely at its 5' end to the transcription start site of the intron-containing GS gene (GSi) (Kuo, C. F. & Darnell, J. E., Jr. (1989) J. Mol. Biol. 208, 45-56). GSr includes a full-length, uninterrupted coding sequence that differs little (less than 5%) from that of the intron-containing gene. By contrast, the 5'-flanking sequence of GSr has no similarity with that of GSi. The first 1,029 bp of the GSr 5'-flanking sequence drives expression of a promoterless bacterial chloramphenical acetyltransferase (CAT) gene in transfected HeLa cells at a level comparable to that of the Rous sarcoma virus promoter. Analysis of variably deleted GSrCAT fusions genes in both HeLa and 3T3-L1 cells indicates that full promoter activity of the 1,029-bp sequence requires greater than 348 bp. Moreover, nuclear extract from 3T3-L1 adipocytes as well as murine liver protects four segments in the GSr 5'-flanking sequence from DNase I digestion. Nevertheless, reverse transcription of RNA from 3T3-L1 adipocytes, mouse adipocytes, or mouse liver followed by primer-directed enzymatic amplification of the reverse transcripts reveals the presence of GSi transcripts but the absence of GSr transcripts. Thus, the 5'-flanking sequence of GSr is an active promoter that drives transcription of GSrCAT fusion genes and includes binding domains for proteins that have the potential to regulate transcription. We conclude that the intronless murine GS gene isolated from 3T3-L1 cells arose as a retroposon that was inserted into the genome downstream of a potentially active promoter.

Autoradiography↗
PubMed1990

Riboflavin deficiency in cultured rat hepatoma cells: a model for studying the hepatic effects of riboflavin deficiency.

The acyl-CoA dehydrogenases are a family of mitochondrial flavoenzymes required for fatty acid beta-oxidation and branched-chain amino acid degradation. The hepatic activity of these enzymes, particularly the short-chain acyl-coenzyme A (CoA) dehydrogenase, is markedly decreased in riboflavin deficient rats. We now report that the in vivo effects of riboflavin deficiency on the beta-oxidation enzymes of this group are reproduced in FAO rat hepatoma cells cultured in riboflavin-deficient medium. Although it has been long known that hepatic short-chain acyl-CoA dehydrogenase activity is the most severely affected of the straight-chain specific enzymes in riboflavin deficiency, the mechanism by which its activity is decreased has not been reported. We have used this new cell culture system to characterize further this mechanism. Whole cell extracts from riboflavin-deficient and control cells were subjected to analysis by denaturing polyacrylamide gel electrophoresis. The contents of the gels were then electroblotted onto nitrocellulose filters and probed with short-chain acyl-CoA dehydrogenase-specific antiserum. The relative abundance of enzyme antigen was estimated autoradiographically. Our findings indicate that short-chain acyl-CoA dehydrogenase activity changes in parallel with its antigen, suggesting that riboflavin deprivation does not affect the activity of individual enzyme molecules. Further, no evidence of extramitochondrial enzyme precursor was found on the blots, making unlikely a significant block in the mitochondrial uptake process. These findings suggest that changes in short-chain acyl-CoA dehydrogenase activity in riboflavin deficiency result from either increased synthesis or decreased degradation of the enzyme.

Acyl-CoA Dehydrogenase↗
PubMed1987

Acyl-CoA dehydrogenase activity in the riboflavin-deficient rat. Effects of starvation.

Riboflavin deficiency in weanling rats causes a metabolic disorder characterized by failure to oxidize fatty acids. The disorder is similar to that seen in several human diseases, some of which are responsive to pharmacological doses of riboflavin. Previous analysis of the riboflavin-deficient rat has shown that the failure of fatty acid oxidation is due to a decrease in the activity of the acyl-CoA dehydrogenases of beta-oxidation. The activity of these flavoenzymes in liver rapidly decreases when a riboflavin-deficient diet is initiated. The objectives of these experiments were to analyse the effects of starvation on liver mitochondria isolated from the riboflavin-deficient rat. Our studies show that the decreased mitochondrial fatty acid oxidation induced by riboflavin deficiency is partially reversed by starvation. The extent of this reversal is proportional to the duration of starvation. The starvation-associated increase in fatty acid oxidation is mediated by an increase in the mitochondrial short-chain acyl-CoA dehydrogenase activity. The activity of this enzyme is increased such that the ratio of short-chain acyl-CoA dehydrogenase apoenzyme to holoenzyme does not change. We conclude that short-chain acyl-CoA dehydrogenase activity is limiting for fatty acid oxidation when its activity falls below a critical point. The increased mitochondrial specific activity of short-chain acyl-CoA dehydrogenase during starvation may result from an increased availability of flavin coenzyme or an increase in enzyme catalytic efficiency.

Acyl-CoA Dehydrogenase↗
PubMed1987

Partial muscle carnitine palmitoyltransferase-A deficiency. Rhabdomyolysis associated with transiently decreased muscle carnitine content after ibuprofen therapy.

After initiation of ibuprofen therapy, a 45-year-old woman developed muscle weakness and tenderness with rhabdomyolysis, culminating in respiratory failure. A muscle biopsy specimen showed a vacuolar myopathy, and markedly decreased muscle carnitine content and carnitine palmitoyltransferase activity. Following recovery, muscle carnitine content was normal but carnitine palmitoyltransferase activity was still abnormally low. The ratio of palmitoyl-coenzyme A plus carnitine to palmitoylcarnitine oxidation by muscle mitochondria isolated from the patient was markedly decreased. We conclude that transiently decreased muscle carnitine content interacted with partial deficiency of carnitine palmitoyltransferase-A to produce rhabdomyolysis and respiratory failure and that ibuprofen may have precipitated the clinical event.

Acyltransferases↗