Biomedical subjects

C D Takemoto

Publications and source records attributed to C D Takemoto.

6 recordsLinked to original sources

PubMed1991

Specific decrease in liver insulin-like growth factor-I and brain insulin-like growth factor-II gene expression in energy-restricted rats.

Four-week-old male rats were maintained for 10 d on a series of diets containing a constant high level of dietary protein and total energy at 100, 70, 60 or 50% of the ad libitum intake rate. Under these conditions, growth rate varied as a function of dietary energy. Serum insulin-like growth factor (IGF)-I was decreased in the energy-restricted animals. Total hepatic IGF-I mRNA was decreased by approximately the same factor as circulating IGF-I protein. In contrast to previous results obtained with protein-restricted animals, serum albumin mRNA was not decreased in the energy-restricted animals. Brain IGF-II mRNA was slightly decreased in animals fed the 70 and 60% energy diets and was decreased by 50% in animals fed the 50% energy diet. Insulin-like growth factor binding protein-2 (IGFBP-2) gene expression was increased in the liver but not in the brain of the energy-restricted animals, indicating that dietary energy regulates IGFBP-2 gene expression differently in liver and brain. The results demonstrate specific changes in liver IGF-I and IGFBP-2 gene expression and brain IGF-II gene expression in animals that are growth-retarded because of a restriction of dietary energy.

Animals↗

PubMed1990

Effect of dietary protein deprivation on insulin-like growth factor (IGF)-I and -II, IGF binding protein-2, and serum albumin gene expression in rat.

Circulating levels of insulin-like growth factor I (IGF-I) and serum albumin are decreased under conditions of chronic dietary protein limitation. To investigate the biochemical mechanism(s) involved in the regulation of IGF-I and serum albumin synthesis by dietary protein, we studied the effects of protein limitation on IGF-I and serum albumin gene expression in young growing rats maintained on isocaloric diets containing 20%, 12%, 8%, or 4% protein. Animals maintained on the 12%, 8%, or 4% protein diets exhibited slight, moderate, or severe growth deficiency, respectively, and a decreased abundance of hepatic IGF-I messenger RNA (mRNA). The decrease in IGF-I mRNA was most pronounced for the largest [7.7 kilobase (kb)] species, which was decreased by 87% in animals maintained on the 4% protein diet compared with animals on the 20% protein diet. The 0.9 kb species of IGF-I mRNA exhibited a smaller (46%) reduction in abundance in animals maintained on the 4% protein diet. The differential regulation of the 7.7 kb IGF-I mRNA species compared with the shorter IGF-I mRNA species suggests that a sequence or sequences within the long 3'-untranslated region of this mRNA species may play a role in regulating its abundance under conditions of protein limitation. Serum albumin mRNA was also decreased (by 62%) in the animals maintained on the 4% protein diet. The level of serum albumin gene transcription was not decreased in animals on the low protein diets, suggesting that nutrition regulates albumin mRNA at a posttranscriptional step. There was considerable animal-to-animal variability in the level of IGF-I gene transcription within each dietary group. The mean level of IGF-I gene transcription was decreased by 46% in the animals on the 4% protein diet compared with animals on the 20% protein diet, although this decrease was not statistically significant because of the animal-to-animal variability in IGF-I gene transcription within the dietary groups. Additional studies of brain RNA from animals on the four diets indicated that brain IGF-II mRNA was decreased by 57% in animals on the 4% protein diet. It has been demonstrated recently that expression of the gene for IGF binding protein-2 (IGFBP-2) is strongly induced in the liver of fasting animals. To investigate the possible regulation of the IGFBP-2 gene in the protein-limited animals, the abundance of liver and brain IGFBP-2 mRNA was analyzed in animals on the four diets.(ABSTRACT TRUNCATED AT 400 WORDS)

Actins↗

PubMed1990

Effect of fasting on insulin-like growth factor-I (IGF-I) and growth hormone receptor mRNA levels and IGF-I gene transcription in rat liver.

Previous studies have indicated that the concentration of circulating insulin-like growth factor-I (IGF-I) declines in young growing rats that have been fasted or maintained on a protein-deficient diet. To investigate the molecular mechanism(s) by which IGF-I levels are regulated by nutrition, we measured the levels of IGF-I mRNA in 6-week-old male control rats fed ad libitum, rats fasted for 24, 48, or 72 h, and rats fasted for 48 or 72 h and then refed for 24 h. The abundance of several IGF-I mRNA species (8.0, 4.0, 1.7, and 1.0 kilobases) decreased in the fasting animals and rebounded after 24 h of refeeding, although not to the initial control levels. The 1 kilobase IGF-I mRNA species exhibited a 43% decrease after 24 h of fasting, a 76% decrease after 48 h of fasting, and an 82% decrease after 72 h of fasting. Hepatic GH receptor mRNA also decreased in fasting rats. This indicates that the GH receptor down-regulation that occurs in fasting is accompanied by and probably at least partly caused by a decline in GH receptor mRNA. The magnitude and kinetics of the decline in GH receptor mRNA were similar to the magnitude and kinetics of the decline in IGF-I mRNA, suggesting that the two mRNAs may be regulated by a similar mechanism. There was no significant change in the levels of liver beta-actin or serum albumin mRNA under the same conditions, indicating that the regulation of IGF-I and GH receptor mRNA was specific. In addition, the levels of brain IGF-II, beta-actin, and alpha-tubulin mRNAs were not significantly changed by fasting. To further elucidate the molecular mechanism for regulation of hepatic IGF-I mRNA, nuclear transcription elongation assays were performed using nuclei isolated from the liver of control rats, rats fasted for 72 h, and fasted-refed rats. There was considerable animal-to-animal variability in IGF-I gene transcription within each group. The mean level of IGF-I gene transcription was lower in the fasting animals than in the fed controls. However, this decrease was not statistically significant, and the magnitude of the decrease did not account for the 79% decrease in total IGF-I mRNA. These results suggest that IGF-I mRNA is regulated at least partly at the posttranscriptional level.

Actins↗

PubMed1988

Amino acid limitation negatively regulates insulin-like growth factor-II mRNA levels and E-domain peptide secretion at a post-transcriptional step in BRL-3A rat liver cells.

Deprivation of cultured BRL-3A rat liver cells for a single essential amino acid (leucine, methionine, tryptophan, or phenylalanine) under conditions in which the cells remain highly viable causes a decreased secretion of insulin-like growth factor-II (IGF-II) E-domain peptide into the culture medium. This decrease is observed within 8 h after shifting the cells into amino acid-deficient medium. The magnitude of this decrease is greatest in tryptophan-deprived cultures, in which there is a 66% decrease in IGF-II E-domain peptide secretion over a 24-h incubation as compared with E-domain peptide secretion in control cultures incubated in complete medium. Northern blot analysis has indicated that the decrease in IGF-II E-domain peptide secretion observed in amino acid-deprived cells is correlated with a decreased abundance of the major 3.6-kilobase (kb) species of IGF-II mRNA, as well as several minor species. In contrast, the level of a 1-kb species of IGF-II mRNA is not decreased in amino acid-limited cells. In addition, one other specific mRNA, that encoded by the alpha-tubulin gene, also is not significantly decreased in the leucine, phenylalanine, or tryptophan-limited cells. These results indicate that amino acid limitation specifically decreases the level of certain IGF-II mRNA species. The 3.6- and 1-kb IGF-II mRNA species differ only in the length of the 3'-untranslated region, suggesting the existence of a specific regulatory sequence in the long 3'-untranslated region of the 3.6-kb mRNA species that regulates levels of this mRNA species under conditions of amino acid limitation. IGF-II gene transcription is not decreased in the amino acid-limited cells. This indicates that the decrease in IGF-II mRNA and E-domain peptide secretion observed in the amino acid-deprived cells is caused primarily by a post-transcriptional regulatory mechanism.

Amino Acids, Essential↗

PubMed1988

Regulation of albumin mRNA in H4 rat hepatoma cells by the availability of essential amino acids.

Deprivation of cultured H4 rat hepatoma cells for an essential amino acid (leucine, methionine, tryptophan or phenylalanine) under conditions in which the cells remain highly viable leads to a decrease in cytoplasmic albumin mRNA. The magnitude of this decrease is greatest in tryptophan-deprived and phenylalanine-deprived cells. In the tryptophan-deprived cells there is approximately a 15-17-fold decrease in albumin mRNA relative to total cytoplasmic RNA, and a 7-8-fold specific decrease in albumin mRNA relative to alpha-tubulin mRNA. Deprivation of the H4 cells for leucine or tryptophan causes approximately a 40-45% decrease in albumin gene transcription; however, this effect does not account for the 15-17-fold decrease in albumin mRNA abundancy caused by tryptophan limitation, or the greater effect of tryptophan limitation as compared to leucine limitation on albumin mRNA. Therefore, the decrease in albumin mRNA caused by tryptophan limitation is caused primarily by a post-transcriptional regulatory mechanism.

Amino Acids, Essential↗

PubMed1987

Insulin negatively regulates albumin mRNA at the transcriptional and post-transcriptional level in rat hepatoma cells.

Treatment of cultured H4-II-E rat hepatoma cells with insulin causes a large decrease in cytoplasmic serum albumin mRNA. This effect is observed at low doses of insulin (ED50 = 2 pM), consistent with the effect being mediated by interaction of insulin with high affinity insulin receptors. The reduction in cytoplasmic albumin mRNA is first observed 8-12 h following insulin addition, and albumin mRNA continues to decrease up to 28 h following hormone addition. Northern blot analysis of purified poly(A)+ RNA has indicated that insulin causes a decrease in albumin mRNA relative to total cytoplasmic poly(A)+ RNA. In addition, one other specific mRNA, that encoded by the alpha-tubulin gene, is not decreased following insulin treatment. These results indicate that insulin induces a specific decrease in albumin mRNA. This effect is largely reversed if essential amino acids are added along with the insulin, suggesting that the insulin effect is related to limitation of the cells for essential amino acids. Insulin reduces transcription of the albumin gene 4.7-fold, as measured by nuclear transcription assays. However, this inhibition of albumin gene transcription does not fully account for the 57-fold decrease in albumin mRNA, indicating that insulin also exerts a negative effect on albumin mRNA at a post-transcriptional step.

Animals↗