Faster synthesis and slower degradation of liver protein during developmental growth

Conde, Rubén D.; Scornik, Oscar A.

doi:10.1042/bj1660115

Cited by 53 publications

(23 citation statements)

References 20 publications

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“…Others have reported lower rates of protein degradation in postnatal developing brain than in adult brain using estimations derived from the decay of radioactivity in proteins labeled by injection of NaH['4C]03 into 5-day-old rats (Dahl and Weibel, 1979). The reason(s) for this discrepancy are not apparent, since KD derived by subtracting K , from K s and by measurement after pulse labeling was reduced with both methods in developing versus adult liver (Conde and Scornik, 1977).…”

Section: Discussionmentioning

confidence: 95%

Protein Turnover in Brain of the Rat Fetus

Johnson

1985

Journal of Neurochemistry

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Protein synthesis in vivo was studied in whole brain of rat fetuses using continuous intravenous infusion of L-[U-14C]tyrosine into unrestrained pregnant rats at 19 and 21 days gestation. Protein degradation (KD) was calculated by subtracting fractional growth rate of brain protein (KG) from the fractional synthesis rate (KS). KS was high at both gestational ages (0.42 +/- 0.03 days-1 at day 19, 0.47 +/- 0.029 days-1 at 21 days), comparable to values previously reported for newborn rat cerebral hemispheres, and threefold higher than is seen in adult animals. KD was similar at both 19 and 21 days gestation (0.19-0.24) and lower than that reported in neonatal rat brain using similar techniques. Protein accretion during the most rapid phase of brain growth (fetus) is accomplished by similar rates of protein synthesis, but decreased rates of degradation when compared with a slower growth phase (newborn). KD in the brain of the rapidly growing fetus is slightly higher than in adult cerebral hemispheres.

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Section: Discussionmentioning

confidence: 95%

Protein Turnover in Brain of the Rat Fetus

Johnson

1985

Journal of Neurochemistry

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“…Previous investigations have shown that the initially rapid growth of the liver not only results from a high rate of protein synthesis, but also from a low rate of protein degradation during the suckling period (23). Intrahepatic protein synthesis and degradation are known to be controlled by amino acids, insulin, and glucagon (cf Refs.…”

Section: Discussionmentioning

confidence: 99%

Changes in Hepatic Nitrogen Balance in Plasma Concentrations of Amino Acids and Hormones and in Cell Volume after Overnight Fasting in Perinatal and Adult Rat

et al. 1995

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ARSTRImportant regulatory factors of intrahepatic protein synthesis and proteolysis are amino acids, glucagon, insulin, and cell volume. We have investigated the changes in these factors with development and after an overnight fast and evaluated their contribution to changes in the hepatic nitrogen balance in vivo. In the fed state, glucagon levels were highest in suckling animals and gradually declined in older rats, whereas the concentration of insulin increased during development. The amino acid concentrations in liver and plasma declined during the suckling period to levels that in vitro are highly permissive for induction of autophagic proteolysis. In all age groups investigated, fasting was associated with a drop in hepatic protein content, together with a marked decrease in hepatocellular volume and insulin concentrations. On the other hand, glucagon concentrations and the concentration of many amino acids in plasma and liver responded to fasting with a pronounced decrease in perinatal and suckling animals, but this response had become blunted at weaning and had disappeared in adult animals. These findings suggest that insulin and/or hepatocellular volume are more likely candidates as short-term physiologic regulators of the hepatic nitrogen balance than are glucagon or amino acids. In glucosesupplemented fetuses, high levels of insulin could not compensate for a decreased hepatocellular volume in averting a catabolic state, suggesting that cell volume is the more important factor. Although our study cannot discriminate between the effects of fasting on protein synthesis and degradation, our findings show unequivocally that, for a rapid growth of the liver, suckling animals have to be fed around-the-clock. (Pediatr Res 38: 1018-1025, 1995)The cellular protein content is regulated by modulation of the rates of synthesis and/or degradation. The nutritional and hormonal status have been shown to be of paramount importance as modulators of the rate of synthesis and degradation of proteins in the liver (1-7). In vivo studies in which the effect of refeeding after prolonged periods of starvation (2-5 d) was studied (8-10) and in vitro studies with perfused livers (cf. Ref. I), freshly isolated (6,7,11,12) or cultured hepatocytes (13-15) have identified amino acids and the hormones insulin and glucagon as major determinants of hepatic lysosomal proteolysis and protein synthesis. High ambient concentrations of amino acids and insulin suppress intrahepatic proteolysis (1, 6, 7) and stimulate protein synthesis (16-19), whereas glucagon exerts the opposite effect (1,13,14,20). More recently, it was proposed that lysosomal proteolysis in rat liver is also regulated by changes in the volume of the hepatocyte, an increase in cell volume being inhibitory (21, 22). As indicated, most of these findings were obtained from in vitro studies, involving strong manipulation of the nutritional and hormonal environment of the hepatocytes. In this respect, we had previously observed in cultured hepatocytes that intrahepatic lysoso...

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“…A comparative study of adult and neonatal mouse livers found that rates of protein turnover, rather than protein synthesis, accounted for the greatest difference between growing and non-growing organs (Conde and Scornik, 1977). Conditions that stimulate tissue growth, such as partial hepatectomy, refeeding following starvation, and growth factor addition, have been shown to cause a reduction in the basal rate of autophagy (Muller et al, 1987;Pfeifer, 1979;Pfeifer and Bertling, 1977), whereas growth-suppressive signals such as contact inhibition and substrate detachment can induce autophagy (Otsuka and Moskowitz, 1978;Papadopoulos and Pfeifer, 1987).…”

Section: Autophagymentioning

confidence: 99%

Body building: regulation of shape and size by PI3K/TOR signaling during development

Neufeld

2003

Mechanisms of Development

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Growth of organisms and their constituent parts responds to both intrinsic and extrinsic cues during development: organisms of a given species generally grow at a predictable rate and to a specific body size, but individuals can modify this program during development in response to environmental conditions. Recent experiments, using gene knockouts and targeted overexpression, have revealed the central role of a signaling network controlled by the PI3K and TOR kinases in this regulation. These signaling molecules control growth by coordinately regulating a large number of cell biological processes. This review focuses on the cellular activities regulated by PI3K and TOR during development, and discusses how changes in different aspects of cellular metabolism may interact to regulate growth.

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Faster synthesis and slower degradation of liver protein during developmental growth

Cited by 53 publications

References 20 publications

Protein Turnover in Brain of the Rat Fetus

Protein Turnover in Brain of the Rat Fetus

Changes in Hepatic Nitrogen Balance in Plasma Concentrations of Amino Acids and Hormones and in Cell Volume after Overnight Fasting in Perinatal and Adult Rat

Body building: regulation of shape and size by PI3K/TOR signaling during development

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