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Biomedical subjects

J F Chiu

Publications and source records attributed to J F Chiu.

At least 91 records · Page 5Linked to original sources
PubMed1984

The enhancement of specific gene transcription in isolated nuclei by added HeLa whole cell extract.

Transcription was carried out in isolated rat liver nuclei by endogenous RNA polymerase with the addition of HeLa whole cell extract (HWCE) in the presence of nucleoside 5'-[gamma-S]triphosphate. The resulting 5'-gamma-thiophosphate on the synthesized RNA allows separation of in vitro initiated RNA from bulk RNA by mercury-agarose chromatography. HWCE not only increased initiation of new RNA chains greater than 3 times but also had no effect on the RNA synthesis by RNA polymerase II. The initiation of transcription of albumin and alpha-fetoprotein genes in an isolated nuclei system was selectively enhanced by HWCE. Using this system, we studied the effect of glucocorticoid on albumin and alpha-fetoprotein gene expression in vitro.

Albumins↗
PubMed1984

Assessment of the anti-tumor potential of glutathione.

This study assesses the effect of reduced glutathione (GSH) on regenerating liver, 3'-methyl-4-dimethylaminoazobenzene (3'-MDAB) hepatocarcinogenesis, and normal and transformed hepatocytes in vitro. GSH administered intragastrically caused only a 30% reduction in thymidine incorporation into liver DNA at 24 h after partial hepatectomy; there was no apparent effect on RNA and protein synthesis. Furthermore, in 3'-MDAB induced hepatocarcinogenesis, all GSH-treated animals developed hepatocyte nodules, and serum alpha-fetoprotein (AFP) levels were not reduced. In vitro, GSH was shown to be cytotoxic to both normal and transformed hepatocytes at serum concentrations under 10%. GSH inhibited [3H]thymidine incorporation slightly in 2 transformed hepatocyte lines, but not in normal hepatocytes.

Animals↗
PubMed1984

Changes in hepatic levels of tyrosine aminotransferase messenger RNA during chemical hepatocarcinogenesis.

The activity of tyrosine aminotransferase (TAT) decreased biphasically in livers of rats fed 3'-methyl-4-dimethylaminoazobenzene (3'-MDAB). TAT activity decreased to an extremely low level at later stages of hepatocarcinogenesis. The activity of TAT is negatively correlated with alpha-fetoprotein (AFP) levels. The level of TAT enzyme activity in precancerous liver and hepatoma is a reflection of the amount of TAT mRNA. Dexamethasone increased the TAT enzyme activity and TAT mRNA concentration in rat livers during chemical carcinogenesis.

Animals↗
PubMed1984

Dexamethasone inhibition of rat hepatoma growth and alpha-fetoprotein synthesis.

The effect of dexamethasone on hepatoma growth and differentiation, as well as the production of alpha-fetoprotein (AFP) and albumin, was investigated. Treatment of rats with dexamethasone strongly reduced (by 83 to 98%) the serum levels of AFP in rats bearing Morris hepatomas 7777, 8994, 7288c , and 9618A2 . Reduced AFP levels were due in part to a large reduction in tumor load in dexamethasone-treated rats. Hepatoma weights, on the average, were reduced by 64 to 90% relative to controls, while a large bowel transplantable tumor was affected only slightly. Lower serum AFP levels in rats with hepatomas 7777, 8994, and 9618A2 also resulted from reduced AFP synthesis, as indicated by lower cytoplasmic AFP levels. Cytoplasmic albumin levels were higher in dexamethasone-treated rats bearing hepatomas 7777, 8994, and 7288c than they were in rats which did not receive dexamethasone. RNA dot hybridization also indicated that dexamethasone reduced the amount of AFP mRNA in hepatoma 7777 while increasing albumin mRNA. Two-dimensional gel electrophoresis of tumor cytosol proteins showed that dexamethasone reduced synthesis of all AFP variants which could be detected by this technique. A number of abundant hepatoma-associated and liver-associated proteins were not significantly affected by dexamethasone.

Animals↗
PubMed1983

Effect of 5-azacytidine on rat liver alpha-fetoprotein gene expression.

Neonatal rats given 5-azacytidine intraperitoneally (30 micrograms/animal/day) on days 1-5 postpartum had 55% lower serum alpha-fetoprotein levels on day 6 compared to saline injected controls. On day 14, alpha-fetoprotein levels were 4-fold lower in 5-azacytidine treated animals. Cytosol alpha-fetoprotein was proportionately reduced. There were no significant changes in liver to body weight ratio, total serum protein, and both serum and cytosol albumin levels. The molecular basis for decreased serum alpha-fetoprotein levels was found to be a reduced concentration of alpha-fetoprotein mRNA in the livers of 5-azacytidine injected animals. These results are discussed with respect to the effects of 5-azacytidine on DNA methylation and cell differentiation.

Aging↗
PubMed1983

The alteration of gene expression in rat liver during chemical carcinogenesis.

The effect of the carcinogen 3'-methyl-4-dimethylaminoazobenzene (3'-MDAB) on the gene expression of rat liver was studied. Hybridization analysis with enriched neoplastic liver specific cDNA demonstrated a noticeable change in gene expression during liver carcinogenesis. The effect of 3'-MDAB on liver specific gene expression was also studied with albumin and alpha-fetoprotein (AFP) genes as models. Serum AFP levels increased dramatically during hepatocarcinogenesis. Amounts of AFP mRNA present in polysomal poly(A)mRNA were determined by translation and hybridization experiments. AFP mRNA increased in carcinogen-treated liver as the serum level of AFP increased. Increase of AFP mRNA in liver cytoplasmic RNAs can be detected as early as 18 days after feeding rats 3'-MDAB and reached peaks at 30-40 and 185 days of treatment. AFP serum level and AFP mRNA in liver cytosol decreased dramatically between these peaks, with a small amount of AFP mRNA and serum AFP detectable in rats treated with 3'-MDAB for 100 days. The increase in amount of AFP mRNA was due to an increase in transcription of the AFP gene in livers of rats treated with carcinogen. Only a slight change in serum albumin concentration and albumin mRNA in livers of rats treated with 3'-MDAB was noticed.

Animals↗
PubMed1983

Enzyme-linked immunosorbent assay for use with nuclear protein-DNA complex antigens.

An enzyme-linked immunosorbent assay (ELISA) was developed for identification and quantification of nuclear antigens (nonhistone protein-DNA complexes from chromatin). Until now, the complement fixation assay has been the only immunoassay routinely applied to nonhistone protein-DNA complexes. The ELISA is considerably more sensitive than the micro-complement fixation test for assaying the immunospecificity of nuclear protein-DNA complexes. Dilutions of rabbit antisera as great as 1:6400 could be used to detect nanogram quantities of antigen, chicken reticulocyte chromatin or dehistonized rat liver chromatin.

Animals↗
PubMed1981

Hormonal modulation of alpha-fetoprotein gene expression in newborn rat livers.

Suppression of serum alpha-fetoprotein (AFP) levels in glucocorticoid treated newborn rats was investigated. Daily intraperitoneal injection of 2 micrograms/g body weight of dexamethasone into newborn rats greatly reduced the concentration of AFP in the serum and liver cytosol. In contrast, this treatment stimulated liver ornithine decarboxylase activity. The reduction in AFP levels is not due to a change of distribution of AFP molecular variants, inhibition of secretion of synthesized AFP by the liver or disruption of liver polysomes. Glucocorticoids decrease the AFP levels in hormone-treated rats by supressing the synthesis of AFP. The size of AFP polysomes isolated from the livers of dexamethasone-treated rats were as large as those from normal rats. However, the amount of AFP-producing polysomes in hormone-treated rat liver is only 14% of the controls. By hybridization assays, it was found that dexamethasone treated livers contained decreased amounts of AFP mRNA sequences in liver cytoplasmic and nuclear RNAs. The decreased amounts of AFP mRNA sequences in hormone-treated liver are caused by both a decrease in the rate of AFP mRNA transcription and in AFP mRNA stability.

Animals↗
PubMed1981

Vitamin B6 metabolism in Morris hepatomas.

The enzymes involved in the metabolism of vitamin B6 were measured in Morris hepatomas and livers of female Buffalo rats fed pyridoxine-sufficient and deficient diets. Pyridoxal phosphate levels in plasmas hepatomas, and livers were also determined. Nontumor-bearing animals were maintained as controls. Regardless of the B6 nutritional status, the concentration of pyridoxal phosphate was lower in the hepatomas than in the livers of the host animals. The apoenzyme levels of ornithine decarboxylase, a pyridoxal phosphate-dependent enzyme, were higher in the hepatomas from animals fed the B6-deficient diet. Liver pyridoxine kinase activity was higher in B6-sufficient animals. In contrast, tumor pyridoxine kinase activity was influenced by B6 intake and was significantly lower than that in host liver. Liver pyridoxine phosphate oxidase activity was not significantly affected by B6 intake or by the presence of tumor. In contrast, hepatomas had little or no pyridoxine phosphate oxidase activity. Pyridoxine phosphate phosphatase activity was elevated in tumors relative to livers. These data indicate that the metabolism of vitamin B6 is markedly different in the hepatomas than in host or control livers and suggest that the tumor is apparently incapable of the complete synthesis of co-enzymatically active pyridoxal phosphate from inactive precursor forms such as pyridoxine.

Animals↗
PubMed1981

Changes in tumor-specific nuclear antigen activity in carcinogen-treated colon by tumor promoter and carcinogen inhibitors.

Changes in the immunospecificity of the nuclear antigens were demonstrated in the colon chromatin of rats treated with 1,2-dimethylhydrazine. Tumor-specific nuclear antigen appeared in the early stages of chemically induced colon carcinogenesis. Sodium barbiturate, in conjunction with the carcinogen, induced a higher level of nuclear antigen activity than that obtained with carcinogen alone. The rise of immunoactivity in carcinogen-treated colon chromatin can be abolished by simultaneous treatment with disulfiram or butylated hydroxytoluene.

Animals↗
PubMed1980

Immunologically specific complexes of chromosomal nonhistone proteins with deoxyribonucleic acid in chicken erythroid nuclei.

Erythroid cell-specific antisera capable of detecting chromosomal nonhistone protein-DNA complexes were obtained by injecting rabbits with dehistonized chicken reticulocyte chromatin. The specific antigenic nonhistone protein-DNA complexes were relatively inaccessible to the antiserum in isolated erythrocyte chromatin. However, isolation of chromatin from cells at earlier stages of erythropoiesis or treatment of isolated erythrocyte chromatin with polyanions or phenylhydrazine provided materials with significantly increased immunological reactivity. The altered activity was caused by changes in conformation occurring at two levels: a specific one, determined by chromosomal nonhistone proteins, and a more general one, determined by histones. Immunological examination of fractionated products obtained from limited nuclease digestion revealed the localization of the antigenic complexes in the nuclease-resistant, large fragments of erythroid chromatin. The nuclease-resistant DNA isolated from the immunologically reactive fragments migrated in gel electrophoresis as a diffuse band of between 1000 and 2000 base pairs. No preferential accumulation of globin-specifying DNA sequences could be found in this nuclease-resistant DNA. The protein fraction containing the immunologically cell-specific complexes in chicken erythrocyte chromatin was glycosylated and moderately acidic (by amino acid anaysis) with an electrophoretically determined Mr of approximately 90000.

Animals↗