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Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of hormones and cytokines on angiotensinogen production were studied in primary cultured rat hepatocytes. The basal secretion of angiotensinogen decreased during culture. The addition of dexamethasone and (Bu)2cAMP completely prevented this decrease. Angiotensinogen secretion by freshly plated hepatocytes was slightly increased in response to dexamethasone, but after 24 h in culture, hepatocytes no longer responded to dexamethasone alone. When hepatocytes were treated with (Bu)2cAMP, glucagon, or forskolin, angiotensinogen secretion increased in response to dexamethasone in a concentration-dependent manner. 17 beta-Estradiol and T3 failed to stimulate angiotensinogen secretion in either the presence or absence of (Bu)2cAMP. Interleukin-6 (IL-6) exhibited a stimulatory activity on angiotensinogen secretion, which was dependent on the presence of dexamethasone, whereas IL-1 and tumor necrosis factor had no effect in either the presence or absence of dexamethasone and/or (Bu)2cAMP. Unlike primary cultured hepatocytes, angiotensinogen secretion by rat hepatoma H4IIEC3 cells increased in response to dexamethasone alone. This increase was not enhanced by (Bu)2cAMP, but was enhanced by IL-6. Thus, in primary cultures of rat hepatocytes, neither glucocorticoid, cAMP, nor IL-6 alone stimulated angiotensinogen production, but a combination of glucocorticoid and cAMP or of glucocorticoid and IL-6 exhibited a stimulatory activity on angiotensinogen production. These results suggest that angiotensinogen production in the liver is synergistically regulated by these factors, whereas the hepatoma cell line H4IIEC3 lacks the regulatory mechanism of cAMP on glucocorticoid-induced angiotensinogen production.
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PMID:Stimulation of angiotensinogen production in primary cultures of rat hepatocytes by glucocorticoid, cyclic adenosine 3',5'-monophosphate, and interleukin-6. 131 Dec 38

Glucocorticoids are well known inducers of transcription of the liver angiotensinogen (AOG) gene. However, the doses and the conditions under which they exert this effect in vivo are not known. To investigate this question, we have implanted rats with wax pellets containing 80% corticosterone (B). These pellets increased plasma B and induced clear signs of hypercorticism. However, they did not stimulate plasma AOG, whereas acute injections of dexamethasone (DEX) had a robust effect. In additional experiments, we have determined that: 1) chronic exposure to DEX was less effective than acute DEX in stimulating the production of liver AOG in rats and AOG secretion by rat hepatoma cells; 2) at maximally effective doses, B stimulated the production of AOG by hepatoma cells less effectively than DEX; and 3) DEX had less effect on AOG secretion than on AOG messenger RNA concentration, both in vivo and in vitro. All three mechanisms may have contributed concomitantly to the absence of response of plasma AOG to mild and chronic elevations of plasma B. These results suggest that glucocorticoids are unlikely to be primary regulators of liver AOG.
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PMID:The stimulation of liver angiotensinogen by glucocorticoids depends on the type of steroid and its mode of administration. 142 36

A reverse haemolytic plaque assay (RHPA) for angiotensinogen was developed in rat hepatoma H4 cells and applied to investigate the possible secretion of angiotensinogen from rat pituitary cells in primary culture. Over a 24-hour incubation period in Cunningham chambers plaques with a mean area of 2,800 +/- 430 and 590 +/- 220 microns2/plaque (SD, n = 6) formed around all viable H4 cells and 2.8 +/- 0.59% of viable pituitary cells respectively. As a positive control PRL secretion from lactotrophs was routinely checked by the RHPA and shown to form plaques with a mean area of 4,050 +/- 1,850 microns2/plaque after a 4-hour incubation. By comparing plaque size in H4 cells with angiotensinogen release in cell culture, as quantified by radioimmunoassay, the secretion rate of angiotensinogen from pituitary cells was calculated as 22 +/- 8 ng/10(6) cells/24 h. Plaque-forming cells consisted of two morphologically distinct populations; 78% being small cells (less than 6 microns diameter) containing little cytoplasm and 22% were large (greater than 9 microns diameter) cells with an abundant cytoplasm. Immunocytochemical staining of pituitary cells after formation of plaques with anti-angiotensinogen, anti-LH and anti-PRL antiserum showed that the large plaque-forming cells were gonadotrophs and none were lactotrophs. All plaque-forming cells stained for angiotensinogen but only 44% of the viable cells which stained for angiotensinogen actually formed plaques. The possibility that cellular angiotensinogen was imported from extracellular sources was investigated by incubation of pituitary cells with pure 125I-angiotensinogen for periods up to 24 h. No uptake of the radiolabelled protein was found.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Angiotensinogen secretion by single rat pituitary cells: detection by a reverse haemolytic plaque assay and cell identification by immunocytochemistry. 150 59

The angiotensinogen gene encodes the precursor protein for the potent vasoconstrictor angiotensin II. Although the gene is expressed in several tissues, the liver is the major source of circulating protein. In previous in-vivo studies we have found that a mini-gene containing 750 bp of 5'-flanking sequence is transcribed in a manner which largely parallels the expression of the endogenous gene. In this report, we characterized conserved elements in the promoter region, in order to determine their role in the transcription of the angiotensinogen gene. Constructs fused to the chloramphenicol acetyl transferase (CAT) reporter gene were transfected into hepatocarcinoma Hep G2 cells as well as into nonhepatic cell lines. We found that 5'-deletion mutant constructs, containing sequences from +25 to -90 bp and -321 to -750 bp, were each able to activate transcription. These constructs contain the TATA box and core promoter sequences, including an Sp1-binding site, and two glucocorticoid responsive elements respectively. In the non-hepatic cell lines, HeLa and Jeg-3, we found that the constructs were transcribed at a much lower rate when compared with the expression of a plasmid containing the Rous sarcoma virus long terminal repeat fused to the CAT gene. Constructs which included sequence 5' to -244 were oestrogen inducible. An element which is conserved between rodent and human angiotensinogen promoters is contained within a sequence which is oestrogen responsive, while another binds the liver-enriched transcriptional activator hepatocyte nuclear factor 1. However, the role of this transactivator in the transcription of angiotensinogen remains uncertain.
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PMID:The function of conserved elements in the promoter of the mouse angiotensinogen gene. 151 23

We examined the effect of chronic hypo- and hyper- thyroidism on angiotensinogen (AOG) gene expression in rat liver and brain. Chronic hypothyroidism resulted in approximately a 50% decrease in plasma AOG and AOG messenger RNA (mRNA) concentrations in liver, diencephalon, and brain stem. In contrast, plasma AOG and liver AOG mRNA concentrations were elevated by about 75% during hyperthyroidism, but no change was seen in diencephalon and brain stem. In vitro, the effect of T3 on AOG secretion by rat hepatoma cell lines H35 and H4IIEC-3 depended on the type of cell line used and on the growth status of the cells. At confluency, H35 cells were more responsive to T3 than H4IIEC-3 cells. In addition, subconfluent H35 cells were less responsive to T3 than confluent ones, although no difference was observed in the number of nuclear T3 binding sites or in the responsiveness to dexamethasone. T3 also increased AOG mRNA concentration in confluent H35 cells. Finally, AOG secretion by primary cultures of rat astrocytes increased approximately 1.8-fold following exposure to T3. The fact that T3 increased the production of AOG by these various types of cell culture in vitro suggests that it acted directly upon these cells, and that the effect of thyroid hormone was not dependent on the prior stimulation of another hormone. However, the difference in responsiveness between confluent and subconfluent H35 cells indicates that the action of thyroid hormones may be dependent on the induction of secondary genes within these cells.
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PMID:Effects of thyroid hormones on angiotensinogen gene expression in rat liver, brain, and cultured cells. 153 89

Angiotensinogen is the precursor molecule of one of the most potent vasoactive substances, angiotensin-II. Angiotensinogen is normally synthesized in the liver and secreted into the plasma where it is converted into angiotensin-II by the combined proteolytic action of renin and angiotensin converting enzyme. Angiotensinogen levels in the plasma are modulated by a number of pathological and physiological factors. In order to understand the regulation of angiotensinogen gene expression, we have constructed an expression vector in which 688 bp of the 5'-flanking region of the rat angiotensinogen gene were attached to the chloramphenicol acetyl transferase (CAT) coding sequence. We have also obtained 5'-sequential deletion mutants from the rat angiotensinogen promoter attached to the CAT gene, and have identified multiple cis-acting DNA sequences involved in the regulation of angiotensinogen gene expression by transient transfection of these recombinant DNA molecules in human hepatoma cell lines, Hep3B, and HepG2.
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PMID:Identification of cis-acting DNA elements involved in the regulation of angiotensinogen gene expression. 155 46

The regulation of angiotensinogen gene expression by steroid hormones in the rat liver has been examined. In the intact animal, dexamethasone (7 mg/kg ip) and estradiol (7 mg/kg sc) caused an increase in plasma angiotensinogen, which became first apparent after 5 or 9 h, respectively, and resulted in plasma concentrations 4.6- and 1.9-fold higher than in controls at 24 h. These changes were preceded by comparable increases in hepatic angiotensinogen messenger RNA (mRNA). In contrast, dihydrotestosterone (10 mg/kg sc) failed to alter plasma angiotensinogen, although hepatic angiotensinogen mRNA and total RNA were slightly elevated. In isolated hepatocytes exposed to either dexamethasone or estradiol (10 microM each) angiotensinogen mRNA started to increase within less than 1 or 3 h, respectively, followed, with a further time lag of about 2 h, by an increase in secretion rate of angiotensinogen. Dihydrotestosterone (10 and 100 microM) induced a rapid increase in total hepatocyte RNA (1.3-fold) and angiotensinogen mRNA (2-fold) with a peak at 2 h. Surprisingly, angiotensinogen secretion remained either unaltered (10 microM dihydrotestosterone) or even decreased (100 microM dihydrotestosterone). In a hepatoma cell line (FT02B) and a subclone (Fe 33) stably transfected with the human estrogen receptor, dexamethasone and estradiol induced an increase in angiotensinogen mRNA and secretion with the same characteristics as in hepatocytes. In conclusion, in this study a direct effect of estradiol on angiotensinogen mRNA and secretion in hepatocytes could be established, which differs from that of dexamethasone by a delayed onset of action. The observation, both in vivo and in vitro, that dihydrotestosterone induced an increase in total RNA and angiotensinogen mRNA, which is not accompanied by an increased angiotensinogen secretion, cannot be explained at present. This study also demonstrates the usefulness of a hepatoma cell line stably transfected with the estrogen receptor gene for the investigation of estrogen-dependent effects in vitro.
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PMID:Regulation of hepatic angiotensinogen synthesis and secretion by steroid hormones. 159 63

We investigated the 5'-flanking region of the rat angiotensinogen gene to define the DNA elements conferring inducibility by glucocorticoids and estrogens. Two putative glucocorticoid-responsive elements (GREs) based on sequence comparison were identified. Here we report the functional importance of these sequences. We constructed several deletion mutants of the 5'-region in front of the bacterial reporter gene for chloramphenicol acetyltransferase (CAT). The angiotensinogen-CAT-reporter plasmids (pRagCAT) were transiently transfected into the rat hepatoma cells FTO 2B and Fe 33. All pRagCAT constructs in which the 5'-region contained at least one of the two GRE consensus sequences were stimulated by dexamethasone. On the other hand, deletion mutants containing no GRE sequences were not inducible with dexamethasone. In additional experiments, the transcriptional functions of the two putative GREs were assessed by cloning synthetic oligonucleotides encompassing the GRE sequences directly in front of the heterologous herpes simplex virus thymidine-kinase promoter. Our results showed that each synthetic GRE was capable of stimulating the heterologous TK promoter after administration of dexamethasone and that both GREs together act synergistically. We also investigated the transcriptional control of angiotensinogen by estrogen. Although no estrogen-responsive element consensus sequences were detectable by sequence comparison, we did identify sequences between -60 to -92 which conferred estrogen inducibility to the rat angiotensinogen gene. In this region, a so-called half-palindromic estrogen-responsive element is localized at nucleotides -87 to -91.
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PMID:Glucocorticoid- and estrogen-responsive elements in the 5'-flanking region of the rat angiotensinogen gene. 166 57

We have isolated the human angiotensinogen gene from a genomic library and determined the exon-intron junction sequences. The gene is 12 kilobases long and consists of five exons interrupted by four introns, as a single copy in the human genome. Of particular interest are the positions of the introns in the human angiotensinogen gene which are identical to those in the highly homologous human alpha 1-antitrypsin and alpha 1-antichymotrypsin genes, as well as rat and mouse angiotensinogen genes. Northern blot analysis showed that human hepatoma cells (HepG2) produce a large amount of angiotensinogen mRNA but not human glioma cells (T98G). To assay the promoter activity, the 1.3-kilobase genomic fragment containing the 5'-flanking region, first exon, and a part of first intron at positions -1222 to +44 was fused upstream to the chloramphenicol acetyltransferase gene, then transfected into HepG2 and T98G cells. The gene sequence was active only in HepG2 cells, suggesting the presence of a functional promoter. Analysis of deletion mutants demonstrated that the 76-base pairs region from -32 to +44 containing the TATA box and first exon is the minimal promoter, whose activity is as high as that of the SV40 enhancer-promoter. Since the basal expression of the human angiotensinogen gene is much higher in HepG2 than T98G cells, these results may reflect cell-specific differences in the gene transcription.
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PMID:Structure and expression of the human angiotensinogen gene. Identification of a unique and highly active promoter. 169 23

Angiotensinogen mRNA is found in many extrahepatic tissues, where it may participate in local angiotensin-generating systems. In this study we explore the feasibility of using anti-sense RNA to decrease angiotensinogen production in rat H4IIEC3 hepatoma cells. An amplifiable shuttle vector was modified to allow the production of high levels of stable anti-sense RNA from two regions of the mouse angiotensinogen gene under the control of the inducible sheep metallothionein promoter. Stably transformed, clonal cell lines expressing anti-sense RNA for angiotensinogen were isolated after selection with the aminoglycoside G418. Subsequently, the number of chromosomally integrated copies of the angiotensinogen anti-sense constructs was coamplified by methotrexate selection for dihydrofolate reductase activity carried on the shuttle vector. With a 20- to 30-fold induction of the anti-sense RNAs, the target angiotensinogen mRNA level was reduced to 25-30% of control values. The specificity of this effect was confirmed by showing no decrease in either beta-tubulin or neomycin phosphotransferase mRNA levels. Using tissue-specific promoters, it should be possible to direct these effects to specific organs in transgenic mice. However, in agreement with results from other groups, our findings suggest that it will not be possible to eradicate completely the target gene product using the anti-sense RNA strategy.
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PMID:Inducible anti-sense RNA for angiotensinogen in stably transformed hepatoma cell lines. 169 79


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