Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The ability of a retinoic acid (RA) response element (RARE) in the phosphoenolpyruvate carboxykinase (PEPCK) gene promoter to mediate effects of either RA or thyroid hormone (T3) on gene expression was studied. Fusion gene constructs consisting of PEPCK promoter sequences ligated to the chloramphenicol acetyltransferase (CAT) reporter gene were used for this analysis. While T3 induced CAT expression to a small degree (about twofold) when such constructs were transiently transfected into H4IIE rat hepatoma cells, along with an expression vector encoding the alpha subtype of the T3 receptor (TR), this effect was mediated by promoter sequences distinct from the PEPCK RARE. Although TRs were capable of binding the PEPCK RARE in the form of putative monomers, dimers, and heterodimers with RA receptors (RARs), this element failed to mediate any positive effect of T3 on gene expression. In contrast, the PEPCK RARE mediated six- to eightfold induction of CAT expression by RA. When TRs were coexpressed along with RARs in transfected H4IIE cells, this RA induction was substantially blunted in a T3-independent manner. This inhibitory effect may be due to the binding of nonfunctional TRs or TR-RAR heterodimers to the PEPCK RARE. A model is proposed to explain the previously observed in vivo effects of T3 on PEPCK gene expression.
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PMID:Specificity of a retinoic acid response element in the phosphoenolpyruvate carboxykinase gene promoter: consequences of both retinoic acid and thyroid hormone receptor binding. 194 93

The nuclear genome is the primary locus of activity for thyroid hormone and dexamethasone; however, one well described secondary effect of treatment with these hormones is increased mitochondrial respiratory activity. To examine the mechanism of the increase in respiration, we have treated a rat hepatoma cell line, HTC cells, with thyroid hormone and dexamethasone and measured their effects on the activity of a respiratory chain enzyme and on mitochondrial (mt) RNA and mtDNA levels. Thyroid hormone, but not dexamethasone, increased cytochrome c oxidase activity in HTC cells; the increase in activity was nearly 2-fold over control values. To determine whether this increased activity was the result of coordinate increases in expression of nuclear and cytoplasmic genes for this enzyme, we measured changes in the levels of messenger RNAs for both nuclear and mitochondrially encoded cytochrome oxidase subunits. Treatment of HTC cells with thyroid hormone and/or dexamethasone resulted in 3- to 4-fold increases in the levels of several RNAs encoded in the mt genome, including subunit II of cytochrome c oxidase. In contrast, this treatment had no effect on the messenger RNA encoding a nuclear subunit of this same enzyme. Neither of these hormones had any effect on cell number or on the level of mtDNA. Dose response and time course of thyroid hormone and dexamethasone administration on mtRNA levels were consistent with these hormones acting through their nuclear hormone receptors. Increased expression of the mt genome by alteration of transcription or RNA stability is a likely candidate for a mechanism by which these hormones can regulate mitochondrial activity.
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PMID:Thyroid hormone and dexamethasone increase the levels of a messenger ribonucleic acid for a mitochondrially encoded subunit but not for a nuclear-encoded subunit of cytochrome c oxidase. 169 99

A cDNA clone encoding 55-kDa multifunctional, thyroid hormone binding protein of rabbit skeletal muscle sarcoplasmic reticulum was isolated and sequenced. The cDNA encoded a protein of 509 amino acids, and a comparison of the deduced amino acid sequence with the NH2-terminal amino acid sequence of the purified protein indicates that an 18-residue NH2-terminal signal sequence was removed during synthesis. The deduced amino acid sequence of the rabbit muscle clone suggested that this protein is related to human liver thyroid hormone binding protein, rat liver protein disulfide isomerase, human hepatoma beta-subunit of prolyl 4-hydroxylase and hen oviduct glycosylation site binding protein. The protein contains two repeated sequences Trp-Cys-Gly-His-Cys-Lys proposed to be in the active sites of protein disulfide isomerase. Northern blot analysis showed that the mRNA encoding rabbit skeletal muscle form of the protein is present in liver, kidney, brain, fast- and slow-twitch skeletal muscle, and in the myocardium. In all tissues the cDNA reacts with mRNA of 2.7 kilobases in length. The 55-kDa multifunctional thyroid hormone binding protein was identified in isolated sarcoplasmic reticulum vesicles using a monoclonal antibody specific to the 55-kDa thyroid hormone binding protein from rat liver endoplasmic reticulum. The mature protein of Mr 56,681 contains 95 acidic and 61 basic amino acids. The COOH-terminal amino acid sequence of the protein is highly enriched in acidic residues with 17 of the last 29 amino acids being negatively charged. Analysis of hydropathy of the mature protein suggests that there are no potential transmembrane segments. The COOH-terminal sequence of the protein, Arg-Asp-Glu-Leu (RDEL), is similar to but different from that proposed to be an endoplasmic reticulum retention signal; Lys-Asp-Glu-Leu (KDEL) (Munro, S., and Pelham, H.R.B. (1987) Cell 48, 899-907). This variant of the retention signal may function in a similar manner to the KDEL sequence, to localize the protein to the sarcoplasmic or endoplasmic reticulum. The positively charged amino acids Lys and Arg may thus interchange in this retention signal.
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PMID:Molecular cloning of cDNA encoding a 55-kDa multifunctional thyroid hormone binding protein of skeletal muscle sarcoplasmic reticulum. 169 92

To determine the capacity of the chicken c-erbA (cTR-alpha) gene product in regulating expression of known thyroid hormone-responsive genes, both the cTR-alpha and the viral v-erbA genes were expressed in FAO cells, a rat hepatoma cell line defective for functional thyroid hormone receptors. Upon nuclear expression of the cTR-alpha protein the cells become responsive to thyroid hormone, as detected by expression of a number of genes (malic enzyme, phosphoenolpyruvate carboxykinase, and Na+/K(+)-ATPase) reported to be indirectly induced by the hormone in vivo. In addition, our data show that the c-erbA product directly activates the Moloney murine leukemia virus promoter in a ligand-dependent manner. The data show that the chicken c-erbA-alpha protein can modulate the expression of rat genes under either direct or indirect control by thyroid hormone.
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PMID:The chicken c-erbA alpha-product induces expression of thyroid hormone-responsive genes in 3,5,3'-triiodothyronine receptor-deficient rat hepatoma cells. 215 23

Unesterified long-chain fatty acids strongly inhibited thyroid hormone (T3) binding to nuclear receptors extracted from rat liver, kidney, spleen, brain, testis and heart. Oleic acid was the most potent inhibitor, attaining 50% inhibition at 2.8 microM. Oleic acid similarly inhibited the partially purified receptor and enhanced dissociation of the preformed T3-receptor complex. The fatty acid acted in a soluble form and in a competitive manner for the T3-binding sites, thereby reducing the affinity of the receptor for T3. The affinity of the receptor for oleic acid (Ki) was 1.0 microM. In HTC rat hepatoma cells in culture, fatty acids added to the medium reached the nucleus and inhibited nuclear T3 binding; oleic acid being the most potent. T3 binding of the cells was reversibly restored in fresh medium free of added fatty acids. Oleic acid did not affect all the T3-binding sites in the HTC cells: one form (80%) was inhibited and the other was not and these two forms were commonly present in all rat tissues examined. Thus, fatty acids inhibited the solubilized nuclear receptor as well as a class of nuclear T3-binding sites in cells in culture.
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PMID:Unesterified long-chain fatty acids inhibit thyroid hormone binding to the nuclear receptor. Solubilized receptor and the receptor in cultured cells. 277 51

Alterations in thyroid hormone status and the administration of radiographic contrast agents can markedly influence iodothyronine metabolism and, in particular, the activity of type I 5'-deiodinase (5'DI). In the present studies, the mechanisms responsible for these effects have been reassessed. As previously reported, the addition of iopanoic acid (IOP) to broken cell preparations resulted in a competitive pattern of 5'DI inhibition. However, the in vivo administration to rats of IOP or 3,3',5'-triiodothyronine (rT3) resulted in a noncompetitive pattern of inhibition of 5'DI in the liver, kidney, and thyroid gland, whereby marked decreases in maximal enzyme velocity (V max) were noted, with no change in the value of the Michaelis-Menten constant. In rats rendered hyperthyroid by the injection of 3,5,3'-triiodothyronine (T3), 5'DI activity was significantly increased in the liver and the kidney. The administration of IOP to these thyrotoxic animals resulted in a rapid loss of enzyme activity characterized by an approximate 80% decrease in 5'DI V max values in both tissues. Furthermore, this inhibitory effect persisted for longer than 60 h after a single IOP injection. IOP administration also decreased 5'DI V max levels in the thyroid gland by 52%. In other experiments, treatment of intact Reuber FAO hepatoma cells with IOP or rT3 induced a rapid decrease in 5'DI V max levels. In cells treated with cycloheximide, these agents enhanced the rate of disappearance of enzyme activity by greater than 12-fold, indicating a predominant effect on accelerating the rate of enzyme inactivation and/or degradation. These studies demonstrate that iodothyronines and other iodinated compounds have complex regulatory effects on 5'DI that entail alterations in the rates of both enzyme activation and inactivation. The previously accepted concept that rT3 and IOP impair thyroxine (T4) to T3 conversion in vivo by acting as competitive inhibitors is an oversimplification. Rather, the clinically beneficial effects of administering these agents to patients with hyperthyroidism may result primarily from the rapid and prolonged inactivation of 5'DI which occurs in the thyroid gland and peripheral tissues.
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PMID:Dual mechanisms of regulation of type I iodothyronine 5'-deiodinase in the rat kidney, liver, and thyroid gland. Implications for the treatment of hyperthyroidism with radiographic contrast agents. 283 97

Sex hormone-binding globulin (SHBG) production in humans has been thought to be stimulated by estrogens and thyroid hormone and inhibited by androgens. However, recent data indicate that SHBG production in vitro is stimulated by both androgens and estrogens. This study was designed to determine what other hormonal factors regulate SHBG production. Since hyperinsulinemia and hyperprolactinemia both occur in disease states in which low serum SHBG levels are found, the effects of insulin and PRL were compared to and/or studied in combination with estradiol (E2), T4, and testosterone (T) in a human hepatoma cell line (Hep G2). Hep G2 cells were grown to near confluence in medium including 10% fetal calf serum, and then 72-h experimental incubations were carried out which used only fetal calf serum-free medium. Compared to control incubations, both insulin (10(-8) mol/L) and PRL (10(-8) mol/L) decreased SHBG production from 65.0 +/- 0.6 (+/- SE) to 46.8 +/- 1.1 and 46.8 +/- 1.2 nmol/10(6) cells, respectively (P less than 0.01). Insulin also inhibited both E2 and T4-stimulated SHBG production. T stimulated SHBG production to the same degree as E2. Finally, both E2 and insulin significantly increased cell number, an important consideration when expressing the effect of a hormone on SHBG production in cultured cells. We conclude that insulin and PRL inhibit SHBG production and confirm that T4, T, and E2 stimulate SHBG production in vitro. These findings suggest that insulin and PRL may be important factors in the regulation of SHBG production in vivo.
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PMID:Inhibition of sex hormone-binding globulin production in the human hepatoma (Hep G2) cell line by insulin and prolactin. 284 59

The significance of thyroxine (T4) uptake from serum in the assessment of thyroid status was evaluated, using human hepatoma (Hep G2) cells, in 30 euthyroid subjects, 6 hypothyroid and 19 hyperthyroid patients, and in 23 athyreotic cancer patients under T4 suppressive therapy. Cellular thyroxine (CT4) was determined according to Sarne and Refetoff, J. Clin. Endocrinol. Metab. 61: 1046, 1985. CT4 averaged 9.9 +/- 2.8 pg/well (mean +/- SD, range 5.7-15.3) in euthyroid subjects, 1.5 +/- 1.0 pg/well (range 0.05-4.2) in hypothyroid patients, 40.5 +/- 18.8 pg/well (range 18.3 +/- 104.7) in hyperthyroid patients, and 23.7 +/- 7.2 pg/well (range 14.2-40.2) in T4-treated patients. In eu-, hypo- and hyperthyroid patients, a significant correlation was observed between CT4 and free T4 index (FT4I), free T4 (FT4) or Sex Hormone Binding Globulin (SHBG) values. In T4-treated patients, CT4 values were correlated with FT4I values, but not with FT4 or SHBG levels. All T4-treated patients with elevated SHBG levels had elevated FT4, FT4I and CT4 values. In contrast, of the 16 T4-treated subjects with normal serum SHBG concentrations, all but one had normal FT3, 3 (19%) had elevated FT4, 10 (62%) elevated FT4I and 13 (81%) elevated CT4, but all (100%) had undetectable TSH levels. Thus, considering serum SHBG concentrations as a parameter of hepatic tissue response to thyroid hormone, CT4 values, at least in T4-treated patients, do not accurately reflect the liver responsiveness to thyroid hormone action.
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PMID:Thyroxine uptake by human hepatoma cells from serum of patients submitted to long-term thyroxine suppressive therapy. 285 21

Cellular uptake of T3 was examined using rat H4 hepatoma cells. Uptake of [125I]T3 (10(-11) M) from serum-free medium was measured as the cell-associated counts retained by washed cells (2 X 10(6) per well). Displaceable uptake was 84% of total uptake at 2 min (2.9% of total counts). T4, tetraiodothyroacetic acid, triiodothyroacetic acid, rT3, and D-T3 were 2-5% as effective as T3 in displacing uptake. Nonequilibrium kinetics indicated a half-maximal uptake at 680 nM T3 with approximately 7 million sites per cell. Displaceable uptake was time and temperature dependent and was 73% inhibited by 2 mM KCN and 52% by 10 mM bacitracin but not by 2 mM ouabain or 10 microM cytochalasin B. Phloretin, 100 microM, inhibited uptake by 66%. T3 uptake was directly related to the free T3 concentration over the range of albumin concentrations, 0-10 g/liter. The nonbile acid cholephil compounds, bromosulfophthalein, iopanoic acid, and indocyanine green (all 100 microM) inhibited T3 uptake to 62%, 17%, and 5% of control, respectively. Taurocholate, methylaminoisobutyric acid, and oleic acid were noninhibitory. The half-inhibitory concentrations of reactive nonsteroidal antiinflammatory drugs were: meclofenamic acid (25 microM), mefenamic acid (45 microM), fenclofenac (69 microM), flufenamic acid (100 microM), and diclofenac (230 microM). Aspirin, ibuprofen, oxyphenbutazone, and phenylbutazone (all 100 microM) were noninhibitory. Diphenylhydantoin inhibited uptake to 50% at 75 microM. These findings suggest that T3 uptake by cultured rat hepatocytes is by an energy-dependent, saturable, stereo-selective mechanism that is dependent on cell membrane proteins. This mechanism appears to be shared by a number of other ligands, including nonbile acid cholephils and several nonsteroidal antiinflammatory drugs of the anthranilic and phenylacetic acid classes, as well as diphenylhydantoin. The bile acid taurocholate, oleic acid, and a probe for type A amino acid uptake were inactive. The extent to which these effects may modify expression of thyroid hormone action remains to be established.
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PMID:Uptake of 3,5,3'-triiodothyronine by cultured rat hepatoma cells is inhibitable by nonbile acid cholephils, diphenylhydantoin, and nonsteroidal antiinflammatory drugs. 291 9

The nuclear thyroid hormone receptors isolated from cultured human hepatoma cells (Hep G2) were characterized and compared with those from cultured human fibroblasts and rat liver. The Hep G2 nuclear thyroid hormone receptors had an affinity constant (Ka) of 2.1 X 10(10) M-1 and maximal binding capacity (MBC) of 21.0 fmol/100 micrograms DNA for T3 in assays performed on isolated nuclei. 16% of nuclear receptors were released into the media during incubation and had the same Ka. Salt-extracted receptors had a Ka of 1.8 X 10(10) M-1 and MBC of 0.1 pmol/mg protein for T3. Density gradient sedimentation and gel filtration chromatography revealed a sedimentation coefficient of 3.4 S and Stokes radius of 34 A. From these values, a molecular weight of 49,000 and total frictional ratio (f/f0) of 1.4 were calculated, suggesting an asymmetrical shape of the receptor molecule. Heat inactivation occurred with t1/2 of 28.1, 18.0, and 7.9 min at 38, 43, 45 degrees C, respectively. Isoelectric focusing (IEF) of Hep G2 nuclear receptors demonstrated T3 binding proteins at pH 5.3-5.5, 5.7, and 5.9. Evidence that these are nuclear thyroid hormone receptors includes the following: Triiodothyroacetic acid was the most potent competitor of [125I]T3 binding to these proteins followed by L-T3, and L-T4. Cytosolic protein, human serum, and fetal calf serum failed to show the same T3 binding proteins. Ka of these proteins measured by T3 displacement was 1.1-3.2 X 10(9) M-1. Human fibroblast nuclear extract showed similar T3 binding pattern in IEF, except for a slight difference in pI of an acidic band.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Thyroid hormone receptors in a human hepatoma cell line: multiple receptor forms on isoelectric focusing. 303 21


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