Regulation of mRNA levels of rat liver carbamoylphosphate synthetase by glucocorticosteroids and cyclic AMP as estimated with a specific cDNA

Groot, C. J. De; Zonneveld, Anton Jan van; Mooren, P.G.; Zonneveld, D.; Dool, Annemieke van den; Bogaert, Annelies; Lamers, W. H.; Moorman, Antoon F.M.; Charles, R.

doi:10.1016/0006-291x(84)91040-4

Cited by 37 publications

(15 citation statements)

References 22 publications

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“…Nuclear Run-off Assays-Nuclei were prepared from rat livers as described previously (36). Briefly, fresh liver tissues were homogenized in homogenization buffer (15 mM Hepes, 60 mM KCl, 3 mM MgCl 2 , 1 mM EDTA, 0.15 mM spermine, 0.5 mM spermidine, 5 mM DTT) containing 0.3 M sucrose.…”

Section: Methodsmentioning

confidence: 99%

Molecular Sites of Regulation of Expression of the Rat Cationic Amino Acid Transporter Gene

Aulak

Liu

et al. 1996

Journal of Biological Chemistry

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Cat-1 is a protein with a dual function, a high affinity, low capacity cationic amino acid transporter of the y ؉ system and the receptor for the ecotropic retrovirus. We have suggested that Cat-1 is required in the regenerating liver for the transport of cationic amino acids and polyamines in the late G 1 phase, a process that is essential for liver cells to enter mitosis. In our earlier studies we had shown that the cat-1 gene is silent in the quiescent liver but is induced in response to hormones, insulin, and glucocorticoids, and partial hepatectomy. Here we demonstrate that cat-1 is a classic delayed early growth response gene in the regenerating liver, since induction of its expression is sensitive to cycloheximide, indicating that protein synthesis is required. The peak of accumulation of the cat-1 mRNA (9-fold) by 3 h was not associated with increased transcriptional activity of the cat-1 gene in the regenerating liver, indicating posttranscriptional regulation of expression of this gene. Induction of the cat-1 gene results in the accumulation of two mRNA species (7.9 and 3.4 kilobase pairs (kb)). Both mRNAs hybridize with the previously described rat cat-1/2.9-kb cDNA clone. However, the 3 end of a longer rat cat-1 cDNA (rat cat-1/6.5-kb) hybridizes only to the 7.9-kb mRNA transcript. Sequence analysis of this clone indicated that the two mRNA species result from the use of alternative polyadenylation signals. The 6.5-kb clone contains a number of AT-rich mRNA destabilizing sequences which is reflected in the half-life of the cat-1 mRNAs (90 min for 7.9-kb mRNA and 250 min for 3.4-kb mRNA). Treatment of rats with cycloheximide superinduces the level of the 7.9-kb cat-1 mRNA in the kidney, spleen, and brain, but not in the liver, suggesting that cell type-specific labile factors are involved in its regulation. We conclude that the need for protein synthesis for induction of the cat-1 mRNA, the short lived nature of the mRNAs, and the multiple sites for regulation of gene expression indicate a tight control of expression of the cat-1 gene within the regenerating liver and suggest that y ؉ cationic amino acid transport in liver cells is regulated at the molecular level.

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Section: Methodsmentioning

confidence: 99%

Molecular Sites of Regulation of Expression of the Rat Cationic Amino Acid Transporter Gene

Aulak

Liu

et al. 1996

Journal of Biological Chemistry

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“…It is accepted that the changes in enzyme activity are brought about by changes in amounts of the enzyme proteins (Schimke, 1964;Nicoletti, 1977;Tsuda et al 1979;Saheki et al 1980;Mori et al 1981;de Groot et al 1984). There seems to be no evidence for allosteric effectors, except for N-AG, nor of activity being controlled by phosphorylationadephosphorylation, as with the branched-chain amino acid dehydrogenases (Randle, 1984;Harris et al 1986).…”

Section: The Biochemical Evidencementioning

confidence: 99%

“…The fact that four of the ®ve genes are on separate chromosomes (Jackson et al 1986) makes this coordination all the more remarkable. The suggestion that it is all brought about by glucocorticoids and glucagon working through cyclic AMP seems rather simplistic (de Groot et al 1984).…”

Section: The Biochemical Evidencementioning

confidence: 99%

The mysteries of nitrogen balance

Waterlow¹

1999

Nutr. Res. Rev.

113

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The ®rst part of this review is concerned with the balance between N input and output as urinary urea. I start with some observations on classical biochemical studies of the operation of the urea cycle. According to Krebs, the cycle is instantaneous and automatic, as a result of the irreversibility of the ®rst enzyme, carbamoyl-phosphate synthetase 1 (EC 6.3.5.5; CPS-I), and it should be able to handle many times the normal input to the cycle. It is now generally agreed that acetyl glutamate is a necessary co-factor for CPS-1, but not a regulator. There is abundant evidence that changes in dietary protein supply induce coordinated changes in the amounts of all ®ve urea-cycle enzymes. How this coordination is achieved, and why it should be necessary in view of the properties of the cycle mentioned above, is unknown. At the physiological level it is not clear how a change in protein intake is translated into a change of urea cycle activity. It is very unlikely that the signal is an alteration in the plasma concentration either of total amino-N or of any single amino acid. The immediate substrates of the urea cycle are NH 3 and aspartate, but there have been no measurements of their concentration in the liver in relation to urea production. Measurements of urea kinetics have shown that in many cases urea production exceeds N intake, and it is only through transfer of some of the urea produced to the colon, where it is hydrolysed to NH 3 , that it is possible to achieve N balance. It is beginning to look as if this process is regulated, possibly through the operation of recently discovered urea transporters in the kidney and colon. The second part of the review deals with the synthesis and breakdown of protein. The evidence on whole-body protein turnover under a variety of conditions strongly suggests that the components of turnover, including amino acid oxidation, are in¯uenced and perhaps regulated by amino acid supply or amino acid concentration, with insulin playing an important but secondary role. Molecular biology has provided a great deal of information about the complex processes of protein synthesis and breakdown, but so far has nothing to say about how they are coordinated so that in the steady state they are equal. A simple hypothesis is proposed to ®ll this gap, based on the self-evident fact that for two processes to be coordinated they must have some factor in common. This common factor is the amino acid pool, which provides the substrates for synthesis and represents the products of breakdown. The review concludes that although the achievement and maintenance of N balance is a fact of life that we tend to take for granted, there are many features of it that are not understood, principally the control of urea production and excretion to match the intake, and the coordination of protein synthesis and breakdown to maintain a relatively constant lean body mass.

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“…(iii) PEPCK: a 1.1kb Pst I fragment from the 3' end of the cDNA for the phosphoenolpyruvate carboxykinase gene (PEPCK) (Beale et al, 1985). (iv) albumin: a 1.0kb DNA insert from the pALB cDNA (Groot et al, 1984). (v) TAT: the cDNA for the tyrosine aminotransferase gene (Ganns et al, 1994).…”

Section: Plasmids and Dna Hybridization Probesmentioning

confidence: 99%

Control of expression of the gene for the arginine transporter Cat-1 in rat liver cells by glucocorticoids and insulin

Liu

Hatzoglou

1998

Amino Acids

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Hepatic arginine and lysine uptake is partly regulated by changes in the transport activity of a group of cell surface proteins exhibiting properties of the transport system y+. The Cat-1 gene encodes a sodium-independent high-affinity cationic amino acid transporter of the y+ system which is nearly undetectable in the quiescent liver. In this paper we investigate the regulation of expression of Cat-1 in the quiescent rat liver by glucocorticoids and insulin, two hormones which play a critical role in amino acid dependent pathways of hepatic metabolism. Injection of insulin and glucocorticoids resulted in a rapid (15-30 min, 4-5 fold) increase in transcription which returned to basal levels within 4 hours. In contrast to the rapid single peak of transcriptional induction of the Cat-1 gene, the accumulation of the Cat-1 mRNAs occurred transiently with two peaks, the first at 30 minutes and the second at 2-4 hours following hormone treatment. These data indicate that expression of the Cat-1 gene in the quiescent liver can be transiently induced by both transcriptional and post-transcriptional mechanisms. In FTO2B rat hepatoma cells, expression of the gene is constitutive and accumulation of Cat-1 mRNAs in response to dexamethasone and insulin was dependent on transcription and protein synthesis. Furthermore, the accumulation of the basal level of the Cat-1 mRNAs was reduced by 70%, upon treatment of cells with inhibitors of protein synthesis for 6 h, when the transcription rate of the gene did not decrease significantly. We conclude the following: (i) under normal physiologic conditions, expression of the Cat-1 gene in the quiescent liver is negligible, probably to prevent unnecessary transport and metabolism of arginine by the hepatic arginase in the hepatocytes. (ii) in the cases when hepatic cationic amino acid transport is needed, such as following feeding, cellular growth and illness, glucocorticoids and insulin induce expression of the Cat-1 gene in liver cells through induction of transcription and stabilization of the mRNA. (iii) constitutive Cat-1 mRNA accumulation in rat hepatoma cells depends on protein synthesis through a labile regulated factor. Overall, constitutive expression of Cat-1 is associated with hepatic cellular growth and transformation.

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Regulation of mRNA levels of rat liver carbamoylphosphate synthetase by glucocorticosteroids and cyclic AMP as estimated with a specific cDNA

Cited by 37 publications

References 22 publications

Molecular Sites of Regulation of Expression of the Rat Cationic Amino Acid Transporter Gene

Molecular Sites of Regulation of Expression of the Rat Cationic Amino Acid Transporter Gene

The mysteries of nitrogen balance

Control of expression of the gene for the arginine transporter Cat-1 in rat liver cells by glucocorticoids and insulin

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