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)

We present pharmacological and genetic evidence that regulation of different genes by glucocorticoid hormones in the rat hepatoma cell line, HTC, occurs in a coordinate manner. We have analyzed the responses of four different glucocorticoid-inducible proteins, tyrosine aminotransferase [L-tyrosine:2-oxoglutarate aminotransferase (EC 2.6.1.5)], glutamine synthetase [L-glutamate:ammonia ligase (EC 6.3.1.2)], a secreted glycoprotein Belt I, and the mouse mammary tumor virus (MMTV)-encoded protein (gp52) in these cells. The concentration of dexamethasone necessary for half-maximal induction of each of these proteins is 10-20 nM, the same concentration necessary to half-saturate glucocorticoid receptors. Furthermore, glucocorticoids of varying potency elicit parallel inductions of these markers. MSN5.3, a glucocorticoid receptor-defective cell line selected for its inability to induce gp52, is also unable to induce the other three cellular gene products. In contrast, another class of variants incapable of gp52 induction retains inducibility of the other three markers. We show here by "superinfection" with MMTV that these cells harbor a defect in the original integrated provirus itself and not in the cellular induction machinery. The results presented here suggest that the induction of glucocorticoid-responsive genes in these cells is mediated by a single glucocorticoid induction pathway.
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PMID:Analysis of glucocorticoid-inducible genes in wild-type and variant rat hepatoma cells. 613 49

alpha 1-acid glycoprotein (alpha 1-AGP), or orosomucoid, is shown to be inducible by glucocorticoids in HTC rat hepatoma cells. Immunoprecipitation of [35S]methionine pulse-labeled proteins from these cells reveals secreted proteins of Mr = 35,000-48,000 (alpha 1-AGP) and Mr greater than 180,000, both of which are greatly enhanced by glucocorticoid treatment. The amount of alpha 1-AGP-specific mRNA in HTC cells is greatly increased (at least 100-fold) in response to glucocorticoids. The new steady-state level of RNA is approached with a t 1/2 of about 8 hr and the RNA consists of a single species of approximately 850 bases. The response is specific for glucocorticoids since: (i) the EC50 for dexamethasone is 30 nM; (ii) the glucocorticoid antagonist, progesterone, inhibits the induction by dexamethasone; and (iii) a glucocorticoid receptor-deficient cell line is incapable of alpha 1-AGP mRNA induction. This is a secondary hormonal response since inhibition of protein synthesis blocks the induction of alpha 1-AGP mRNA by dexamethasone whereas the induction of mouse mammary tumor virus (MMTV) RNA is unaffected.
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PMID:Induction of the acute-phase reactant, alpha 1-acid glycoprotein, by glucocorticoids in rat hepatoma cells. 613 69

We have studied the glucocorticoid-mediated accumulation of alpha 1-acid glycoprotein (AGP) in mRNA in HTC rat hepatoma cells. In contrast to the well-characterized primary response of mouse mammary tumor virus, in vitro transcription assays in isolated nuclei show that the rate of transcription of the AGP gene is high even in the absence of hormone. Despite the constitutive transcription of the AGP gene, no detectable AGP RNA can be found in either the cytoplasm or the nuclei of untreated cells. Previous experiments have shown that the glucocorticoid induction of AGP RNA requires ongoing protein synthesis. In conjunction with the present study, our data suggest that glucocorticoids stimulate accumulation of AGP RNA by inducing an RNA processing factor that allows production of stable transcripts.
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PMID:Glucocorticoid-mediated induction of alpha 1-acid glycoprotein: evidence for hormone-regulated RNA processing. 620 92

We have cloned circular unintegrated mouse mammary tumor virus (MMTV) DNA from infected rat hepatoma cells in bacteriophage lambda. Seven independent clones containing MMTV DNA of homogeneous length of 9 kb (five) or 10 kb (two) were identified. The five 9 kb clones had identical restriction maps consistent with that of 9 kb unintegrated DNA; the other two were aberrant. MMTV DNA inserts were purified, ligated and used for cotransfection of Ltk- cells together with a plasmid containing the thymidine kinase gene of herpes simplex virus. All Tk+ cell clones acquired new MMTV sequences and those transfected with the 9 kb MMTV DNA synthesized normal viral RNA and proteins. Viral gene expression was increased by the addition of dexamethasone.
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PMID:Cloned mouse mammary tumor virus DNA is biologically active in transfected mouse cells and its expression is stimulated by glucocorticoid hormones. 625 99

Glucocorticoids regulate the rate of transcription of integrated murine mammary tumor virus (MTV) genes in most clones of MTV-infected rat hepatoma tissue culture (HTC) cells. To determine whether hormonal regulation is mediated from flanking cellular sequences or rather from within the viral DNA, we analyzed the relative rates of transcription of MTV and adjacent HTC sequences in two lines of infected HTC cells, J2.15 and J2.17, each of which contains a single insertion of MTV DNA. In addition, we measured in uninfected HTC cells the transcriptional rates of the corresponding "preinsertion fragments," which may be viewed as the equivalent sequences bearing deletions of MTV DNA; the two genomic segments into which integration occurred in the two lines are unrelated. Previous work showed that glucocorticoids induce the accumulation of MTV RNA in J2.17, whereas viral transcripts are not detected in J2.15, RNA pulse-labeling experiments indicate that glucocorticoids stimulate that rate of MTV gene transcription in J2.17 but not in J2.15; in contrast, no labeled RNA hybridizing to flanking sequences was detected either in the uninfected or in the infected cells. We conclude that the host site of integration cells. We conclude that the host site of integration of MTV need not be transcriptionally active or hormonally responsive to permit viral gene expression. Furthermore, these rate measurements indicate that glucocorticoid-stimulated MTV RNA synthesis in J2.17 does not reflect readthrough transcription from a regulated cellular promoter. This notion is independently supported by transcript mapping experiments showing that the 5' terminus of nuclear MTV RNA is at a site on MTV DNA approximately 1.2 kb downstream from the host-viral junction. Thus our data are consistent with the presence of a hormone-responsive element within the provirus.
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PMID:Mammary tumor virus DNA contains sequences required for its hormone-regulated transcription. 627 99

Glucocorticoid hormones selectively stimulate the rate of transcription of integrated mammary tumor virus (MTV) sequences in infected rat hepatoma cells. Using two independent assays, we find that purified rat liver glucocorticoid receptor protein binds specifically to at least four widely separated regions on pure MTV proviral DNA. One of these specific binding domains, which itself contains at least two distinct receptor binding sites, resides within a fragment of viral DNA that maps 110-449 bp upstream of the promoter for MTV RNA synthesis. Three other binding domains lie downstream of the promoter and within the MTV primary transcription unit. Restriction fragments bearing separate binding domains have been introduced into cultured cells; transformants have been recovered in which the introduced fragments are expressed under glucocorticoid control. Thus, it appears that this assay will be useful for assessing the biological significance of the receptor binding sites detected in vitro.
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PMID:Multiple specific binding sites for purified glucocorticoid receptors on mammary tumor virus DNA. 629 68

Adenosine 5'-O-(2-thiotriphosphate) (ATP beta S) and guanosine 5'-O-(2-thiotriphosphate) (GTP beta S) were used to demonstrate initiation of mouse mammary tumor virus (MMTV) RNA in preparations of whole nuclei from control and glucocorticoid-treated MMTV-infected rat hepatoma tissue culture cells. RNA chains initiated in the cell-free reaction retain a thiol group at the 5' end and can be separated from thiol-free RNA chains by chromatography on mercury-Sepharose. The abundance of MMTV sequences was determined by nucleic acid hybridization with filter-bound DNA representing four different regions of the MMTV genome. About six times more MMTV RNA is initiated with GTP beta S than with ATP beta S. Most of the cell-free initiation of MMTV RNA occurs within or very near a 380-nucleotide section of the proviral long terminal repeat that is the presumptive site of transcription initiation in vivo. The sensitivity of MMTV RNA initiation and synthesis to alpha-amanitin and actinomycin D are characteristic of DNA-directed transcription by RNA polymerase II. Nuclei from glucocorticoid-treated cells initiate approximately 10 times more MMTV RNA than nuclei from control cells.
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PMID:Region-specific initiation of mouse mammary tumor virus RNA synthesis by endogenous RNA polymerase II in preparations of cell nuclei. 629 6

We have isolated mutant derivatives of M1.54 (a mammary tumor virus [MTV]-infected rat hepatoma [HTC] cell line containing multiple integrated proviruses) that fail to express hormone-inducible cell surface viral glycoproteins. In wild-type M1.54, the synthetic glucocorticoid dexamethasone selectively stimulates the rate of synthesis of MTV RNA. In addition, dexamethasone is essential for posttranslational maturation of three of the four cell surface viral glycoproteins processed from the MTV glycosylated precursor polyprotein; the fourth mature species is produced constitutively. Two mutant phenotypes are described; each contains glucocorticoid receptors that are indistinguishable from the wild-type receptor with respect to hormone affinity, intracellular concentration, nuclear translocation efficiency, DNA-cellulose chromatography, and sedimentation rate. In one class, represented by the mutant line CR1, dexamethasone fails to stimulate the low basal rate of MTV gene transcription; surprisingly, hormonal regulation of tyrosine aminotransferase activity is also defective in CR1, whereas several other cellular responses to dexamethasone are normal. In the second class of mutants, represented by CR4, dexamethasone stimulates synthesis of MTV transcripts indistinguishable from those produced in M1.54, but only the constitutive cell surface viral glycoprotein is expressed. Thus, these mutants define two distinct and novel aspects of glucocorticoid regulated gene expression in HTC cells: CR4 contains a defect in a hormone inducible protein maturation pathway that acts on specific viral (and presumably cellular) precursor polypeptides, whereas the lesion in CR1 appears to affect the expression of a subset of the gene products normally under glucocorticoid control in M1.54.
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PMID:Two classes of mutant mammary tumor virus-infected HTC cell with defects in glucocorticoid-regulated gene expression. 630 Jun 55

The relationship of protein glycosylation to compartmentalization and processing of mouse mammary tumor virus (MTV) glycoproteins has been examined in M1.54, a cloned line of MTV-infected rat hepatoma tissue culture cells. Previous work established that full maturation of MTV glycoproteins in this cell line requires dexamethasone, a synthetic glucocorticoid (Firestone, G. L., Payvar, F., and Yamamoto, K. R. (1982) Nature (Lond.) 300, 221-225). The ability to regulate production of the full complement of five mature membrane-associated and secreted viral glycoproteins from one initially synthesized precursor has been used to advantage in the present work. At concentrations of tunicamycin that specifically inhibit N-linked protein glycosylation, incorporation of [35S]methionine into total cellular and secreted protein is not detectably affected, MTV-specific mRNAs are produced normally, and the nonglycosylated form of the glycosylated viral precursor polyprotein accumulates within the cells. However, tunicamycin inhibits the site-specific cleavage of the glycosylated polyprotein and distribution of MTV polypeptides to the cell surface and extracellular fractions. Thus, when tunicamycin-treated cultures of M1.54 are exposed to dexamethasone and [35S]methionine, no labeled viral antigens are detected in the culture medium. Similarly, tunicamycin prevents the appearance of membrane-associated viral antigens that can be labeled externally by lactoperoxidase-mediated iodination and it protects the cells against the cytolytic effects of MTV-specific antiserum and complement. Taken together, these results are consistent with the view that while glycosylation of some proteins may be unessential for their compartmentalization and processing, it does appear to be correlated with proper maturation of others. The hormone-dependent maturation of MTV glycoproteins in M1.54 may be particularly useful for study of this latter class since glycosylation is stringently associated with their compartmentalization and cleavage.
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PMID:The role of protein glycosylation in the compartmentalization and processing of mouse mammary tumor virus glycoproteins in mouse mammary tumor virus-infected rat hepatoma cells. 630 28

The rate of transcription of murine mammary tumor virus (MTV) sequences in MTV-infected rat hepatoma tissue culture cells is strongly affected by both glucocorticoid hormones and the chromosomal position of provirus integration. We have characterized MTV RNAs produced in J2.17 and M1.54, independent isolates containing, respectively, 1 and 10 proviruses integrated at distinct chromosomal loci. M1.54, but not J2.17, synthesized MTV RNA in the absence of glucocorticoids; the rate of hormone-stimulated viral gene transcription in M1.54 was 50- to 100-fold higher than in J2.17. In each case in which MTV genes were expressed (J2.17 induced, M1.54 basal and induced), the viral RNAs produced were indistinguishable. RNA blotting revealed accumulation of two transcripts, 7.8 and 3.8 kilobases; the latter was likely produced from the former by RNA splicing. Sites used for transcription initiation, polyadenylation, and splicing have been identified from the sizes of end-labeled hybridization probes protected from digestion with mung bean nuclease; the unique initiation and polyadenylation sites were both encoded within the MTV long-terminal-repeat sequence. The efficiencies of splicing and of utilization of the polyadenylation signal did not appear to vary as functions of chromosomal position or hormonal stimulation. Differences in rates of viral gene transcription were reflected in the differential accumulation of the 5'-terminal 136 nucleotides of MTV RNA. Thus, glucocorticoids and chromosomal position appeared to affect solely the efficiency of utilization of the MTV promoter, leaving unchanged the sites of initiation, splicing, and polyadenylation, as well as the efficiencies of the latter two processes.
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PMID:Glucocorticoids and chromosomal position modulate murine mammary tumor virus transcription by affecting efficiency of promoter utilization. 630 97


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