A distinct glucocorticoid hormone response regulates phosphoprotein maturation in rat hepatoma cells

1986 ◽  
Vol 6 (2) ◽  
pp. 574-585
Author(s):  
K Karlsen ◽  
A K Vallerga ◽  
J Hone ◽  
G L Firestone
Keyword(s):  
Receptor Binding ◽  
De Novo ◽  
Hepatoma Cell ◽  
Hepatoma Cell Line ◽  
Hormone Response ◽  
Absolute Level ◽  
Chase Period ◽  
Glucocorticoid Hormone ◽  
Tumor Virus ◽  
Rat Hepatoma

Glucocorticoid hormone-dependent maturation of the mouse mammary tumor virus (MMTV) phosphorylated polyprotein (Pr74) allows experimental access to certain posttranslational regulatory circuits under steroid control in M1.54 cells, an MMTV-infected rat hepatoma cell line. Pulse-chase experiments revealed that [35S]methionine-labeled Pr74 synthesized in uninduced cells could be converted posttranslationally into p24, a stable phosphorylated maturation product, only after 4 h of exposure to 1 microM dexamethasone, a synthetic glucocorticoid. This regulated processing could be prevented by prior exposure, during the chase period, to inhibitors of RNA (actinomycin D) or protein (cycloheximide or puromycin) synthesis. Moreover, half-maximal production of p24 occurred at 10 nM dexamethasone, a concentration that approximated half-maximal receptor binding and stimulation of MMTV transcript synthesis. Kinetic, hormonal, and genetic evidence suggest that p24 expression did not require or result from the overall glucocorticoid-dependent increase in polyprotein concentration. First, 20 h after dexamethasone withdrawal, Pr74 maturation was completely deinduced, whereas the absolute level of this MMTV precursor remained 10-fold over its basal level. Second, progesterone, which competes with dexamethasone for receptor binding, facilitated the regulated production of p24 but prevented the steroid-mediated accumulation of functional MMTV mRNA. Lastly, certain glucocorticoid-responsive variants, derived from M1.54 cells by resistance to complement cytolysis, expressed p24 in the presence or absence of glucocorticoid-induced levels of Pr74. Taken together, our results suggest that the glucocorticoid-regulated maturation of MMTV phosphopolyproteins resulted from an independent hormone response that required normal receptor function and de novo RNA and protein synthesis.

scholarly journals A distinct glucocorticoid hormone response regulates phosphoprotein maturation in rat hepatoma cells.

1986 ◽  
Vol 6 (2) ◽  
pp. 574-585 ◽  
Author(s):  
K Karlsen ◽  
A K Vallerga ◽  
J Hone ◽  
G L Firestone
Keyword(s):  
Receptor Binding ◽  
De Novo ◽  
Hepatoma Cell ◽  
Hepatoma Cell Line ◽  
Hormone Response ◽  
Absolute Level ◽  
Chase Period ◽  
Glucocorticoid Hormone ◽  
Tumor Virus ◽  
Rat Hepatoma

Glucocorticoid hormone-dependent maturation of the mouse mammary tumor virus (MMTV) phosphorylated polyprotein (Pr74) allows experimental access to certain posttranslational regulatory circuits under steroid control in M1.54 cells, an MMTV-infected rat hepatoma cell line. Pulse-chase experiments revealed that [35S]methionine-labeled Pr74 synthesized in uninduced cells could be converted posttranslationally into p24, a stable phosphorylated maturation product, only after 4 h of exposure to 1 microM dexamethasone, a synthetic glucocorticoid. This regulated processing could be prevented by prior exposure, during the chase period, to inhibitors of RNA (actinomycin D) or protein (cycloheximide or puromycin) synthesis. Moreover, half-maximal production of p24 occurred at 10 nM dexamethasone, a concentration that approximated half-maximal receptor binding and stimulation of MMTV transcript synthesis. Kinetic, hormonal, and genetic evidence suggest that p24 expression did not require or result from the overall glucocorticoid-dependent increase in polyprotein concentration. First, 20 h after dexamethasone withdrawal, Pr74 maturation was completely deinduced, whereas the absolute level of this MMTV precursor remained 10-fold over its basal level. Second, progesterone, which competes with dexamethasone for receptor binding, facilitated the regulated production of p24 but prevented the steroid-mediated accumulation of functional MMTV mRNA. Lastly, certain glucocorticoid-responsive variants, derived from M1.54 cells by resistance to complement cytolysis, expressed p24 in the presence or absence of glucocorticoid-induced levels of Pr74. Taken together, our results suggest that the glucocorticoid-regulated maturation of MMTV phosphopolyproteins resulted from an independent hormone response that required normal receptor function and de novo RNA and protein synthesis.

scholarly journals A domain of methylation change at the albumin locus in rat hepatoma cell variants.

1985 ◽  
Vol 5 (1) ◽  
pp. 214-225 ◽  
Author(s):  
A Orlofsky ◽  
L A Chasin
Keyword(s):  
De Novo ◽  
Hepatoma Cell ◽  
Northern Blotting ◽  
Cell Protein ◽  
Hepatoma Cell Line ◽  
Mrna Levels ◽  
Albumin Production ◽  
Albumin Mrna ◽  
Rat Hepatoma ◽  
De Novo Methylation

A well-differentiated rat hepatoma cell line, Fu5-5, yields variant clones whose rate of secretion of serum albumin ranges from 40 to less than 0.08 micrograms of albumin/mg of cell protein per 48 h. Clones were classified as high producers (10 to 40 micrograms/mg per 48 h), intermediate producers (1 to 10 micrograms/mg per 48 h), low producers (0.1 to 1.0 micrograms/mg per 48 h), and null variants (less than 0.1 micrograms/mg per 48 h). Albumin synthetic rates are proportional to secretion rates and range from 0.9 to less than 0.002% of total protein synthesis as measured by pulse-labeling. Steady-state albumin mRNA levels were measured by filter hybridization of fragmented, end-labeled mRNA and by Northern blotting. Message levels are proportional to albumin synthetic rates except for a high producer in which albumin mRNA is less elevated than the synthetic rate. The extent of methylation was quantitated at each of 24 CpG-containing sites or site clusters at the albumin locus. These sites span a region that contains the albumin gene as well as 10 kilobases of the 5' flank and 1 kilobase of the 3' flank. An 8-kilobase region is described, with boundaries in the 5' flank and in the middle of the gene, within which all 11 sites examined showed a correlation of undermethylation with the high-producer phenotype. In contrast, 12 of 13 sites outside of this region showed no phenotype correlation. Null variants derived from a high producer underwent de novo methylation of this domain. Six independent hybrid clones derived from the cross of a high producer with a null variant showed extinction of albumin production and hypermethylation of the domain. Apparently these cells retain the capacity for the de novo methylation of these specific sites.

A domain of methylation change at the albumin locus in rat hepatoma cell variants

1985 ◽  
Vol 5 (1) ◽  
pp. 214-225
Author(s):  
A Orlofsky ◽  
L A Chasin
Keyword(s):  
De Novo ◽  
Hepatoma Cell ◽  
Northern Blotting ◽  
Cell Protein ◽  
Hepatoma Cell Line ◽  
Mrna Levels ◽  
Albumin Production ◽  
Albumin Mrna ◽  
Rat Hepatoma ◽  
De Novo Methylation

A well-differentiated rat hepatoma cell line, Fu5-5, yields variant clones whose rate of secretion of serum albumin ranges from 40 to less than 0.08 micrograms of albumin/mg of cell protein per 48 h. Clones were classified as high producers (10 to 40 micrograms/mg per 48 h), intermediate producers (1 to 10 micrograms/mg per 48 h), low producers (0.1 to 1.0 micrograms/mg per 48 h), and null variants (less than 0.1 micrograms/mg per 48 h). Albumin synthetic rates are proportional to secretion rates and range from 0.9 to less than 0.002% of total protein synthesis as measured by pulse-labeling. Steady-state albumin mRNA levels were measured by filter hybridization of fragmented, end-labeled mRNA and by Northern blotting. Message levels are proportional to albumin synthetic rates except for a high producer in which albumin mRNA is less elevated than the synthetic rate. The extent of methylation was quantitated at each of 24 CpG-containing sites or site clusters at the albumin locus. These sites span a region that contains the albumin gene as well as 10 kilobases of the 5' flank and 1 kilobase of the 3' flank. An 8-kilobase region is described, with boundaries in the 5' flank and in the middle of the gene, within which all 11 sites examined showed a correlation of undermethylation with the high-producer phenotype. In contrast, 12 of 13 sites outside of this region showed no phenotype correlation. Null variants derived from a high producer underwent de novo methylation of this domain. Six independent hybrid clones derived from the cross of a high producer with a null variant showed extinction of albumin production and hypermethylation of the domain. Apparently these cells retain the capacity for the de novo methylation of these specific sites.

scholarly journals Glucocorticoid-regulated localization of cell surface glycoproteins in rat hepatoma cells is mediated within the Golgi complex.

1988 ◽  
Vol 106 (5) ◽  
pp. 1463-1474 ◽  
Author(s):  
O K Haffar ◽  
G W Aponte ◽  
D A Bravo ◽  
N J John ◽  
R T Hess ◽  
...  
Keyword(s):  
Cell Surface ◽  
Hepatoma Cell ◽  
Acquired Resistance ◽  
Hepatoma Cell Line ◽  
Oligosaccharide Processing ◽  
Viral Glycoproteins ◽  
Tumor Virus ◽  
Organelle Morphology ◽  
Rat Hepatoma ◽  
Endoglycosidase H

Glucocorticoid hormones regulate the post-translational maturation and sorting of cell surface and extracellular mouse mammary tumor virus (MMTV) glycoproteins in M1.54 cells, a stably infected rat hepatoma cell line. Exposure to monensin significantly reduced the proteolytic maturation and externalization of viral glycoproteins resulting in a stable cellular accumulation of a single 70,000-Mr glycosylated polyprotein (designated gp70). Cell surface- and intracellular-specific immunoprecipitations of monensin-treated cells revealed that gp70 can be localized to the cell surface only in the presence of 1 microM dexamethasone, while in uninduced cells gp70 is irreversibly sequestered in an intracellular compartment. Analysis of oligosaccharide processing kinetics demonstrated that gp70 acquired resistance to endoglycosidase H with a half-time of 65 min in the presence or absence of hormone. In contrast, gp70 was inefficiently galactosylated after a 60-min lag in uninduced cells while rapidly acquiring this carbohydrate modification in the presence of dexamethasone. Furthermore, in the absence or presence of monensin, MMTV glycoproteins failed to be galactosylated in hormone-induced CR4 cells, a complement-selected sorting variant defective in the glucocorticoid-regulated compartmentalization of viral glycoproteins to the cell surface. Since dexamethasone had no apparent global effects on organelle morphology or production of total cell surface-galactosylated species, we conclude that glucocorticoids induce the localization of cell surface MMTV glycoproteins by regulating a highly selective step within the Golgi apparatus after the acquisition of endoglycosidase H-resistant oligosaccharide side chains but before or at the site of galactose attachment.

scholarly journals Stimulation of de novo glutathione synthesis by nitrofurantoin for enhanced resilience of hepatocytes

2021 ◽  
Author(s):  
Lukas S. Wijaya ◽  
Carina Rau ◽  
Theresa S. Braun ◽  
Serif Marangoz ◽  
Vincent Spegg ◽  
...  
Keyword(s):  
De Novo ◽  
Hepatoma Cell ◽  
Proteasome Inhibitors ◽  
Essential Element ◽  
Hepatoma Cell Line ◽  
Related Factor ◽  
Human Hepatoma Cell ◽  
Intact Cells ◽  
Intracellular Glutathione ◽  
Endogenous Antioxidant

AbstractToxicity is not only a function of damage mechanisms, but is also determined by cellular resilience factors. Glutathione has been reported as essential element to counteract negative influences. The present work hence pursued the question how intracellular glutathione can be elevated transiently to render cells more resistant toward harmful conditions. The antibiotic nitrofurantoin (NFT) was identified to stimulate de novo synthesis of glutathione in the human hepatoma cell line, HepG2, and in primary human hepatocytes. In intact cells, activation of NFT yielded a radical anion, which subsequently initiated nuclear-factor-erythroid 2-related-factor-2 (Nrf2)-dependent induction of glutamate cysteine ligase (GCL). Application of siRNA-based intervention approaches confirmed the involvement of the Nrf2-GCL axis in the observed elevation of intracellular glutathione levels. Quantitative activation of Nrf2 by NFT, and the subsequent rise in glutathione, were similar as observed with the potent experimental Nrf2 activator diethyl maleate. The elevation of glutathione levels, observed even 48 h after withdrawal of NFT, rendered cells resistant to different stressors such as the mitochondrial inhibitor rotenone, the redox cycler paraquat, the proteasome inhibitors MG-132 or bortezomib, or high concentrations of NFT. Repurpose of the antibiotic NFT as activator of Nrf2 could thus be a promising strategy for a transient and targeted activation of the endogenous antioxidant machinery.

Activation of the silent endogenous cholesterol-7-alpha-hydroxylase gene in rat hepatoma cells: a new complementation group having resistance to 25-hydroxycholesterol

1991 ◽  
Vol 11 (4) ◽  
pp. 2049-2056
Author(s):  
J K Leighton ◽  
S Dueland ◽  
M S Straka ◽  
J Trawick ◽  
R A Davis
Keyword(s):  
Cell Line ◽  
Cholesterol Biosynthesis ◽  
Hepatoma Cell ◽  
Regulatory Elements ◽  
Hepatoma Cells ◽  
Complementation Group ◽  
Hepatoma Cell Line ◽  
Cytotoxic Action ◽  
Hydroxylase Activity ◽  
Rat Hepatoma

The oxysterol 25-hydroxycholesterol acts both as a regulatory sterol determining the expression of genes governed by sterol regulatory elements and as a substrate for 7-alpha-hydroxylase, the first and rate-limiting enzyme in the bile acid synthetic pathway. Most wild-type nonhepatic cells are killed by the cytotoxic action of 25-hydroxycholesterol. In contrast, liver cells, which express 7-alpha-hydroxylase activity, are resistant to killing by 25-hydroxycholesterol. We examined the possibility that selection for resistance to 25-hydroxycholesterol might lead to the derivation of a cell line expressing 7-alpha-hydroxylase. A rat hepatoma cell line (7-alpha-hydroxylase minus) was transfected with human DNA and screened for resistance to 25-hydroxycholesterol. Although parental hepatoma cells were all killed within a week, a 25-hydroxycholesterol-resistant cell line (L35 cells) which showed stable expression of 7-alpha-hydroxylase activity and mRNA was obtained. These cells exhibited normal inhibition of cholesterol biosynthesis by 25-hydroxycholesterol. Blocking 7-alpha-hydroxylase activity with ketoconazole also blocked the resistance of L35 cells to 25-hydroxycholesterol. Isolation of microsomes from these cells showed levels of 7-alpha-hydroxylase activity (22.9 pmol/min/mg of protein) that were comparable to the activity (33.2 pmol/min/mg) of microsomes isolated from the livers of rats killed during the high point of the diurnal cycle. Parental cells had no detectable activity. These data show a new complementation group for 25-hydroxycholesterol resistance: expression of 7-alpha-hydroxylase. Dexamethasone increased both the activity and the cellular content of mRNA coding for 7-alpha-hydroxylase. Since dactinomycin blocked the ability of dexamethasone to induce mRNA, active transcription is required. Southern analysis of genomic DNA showed that L35 cells contain the rat (endogenous) gene but not the human gene. Furthermore, the RNA expressed by L35 cells is similar in size to rat RNA and is distinct from the human form of 7-alpha-hydroxylase. The combined data indicate that L35 cells are resistant to 25-hydroxycholesterol because they express 7-alpha-hydroxylase. The mechanism responsible involves activation of the endogenous (silent) gene of the parental rat hepatoma cell.

Specific modulation by ethanol of the protein synthesis pattern in the C2 rat hepatoma cell line

1988 ◽  
Vol 6 (1) ◽  
pp. 85-93 ◽  
Author(s):  
M.N. Chobert ◽  
P. Vincens ◽  
G. Guellaën ◽  
R. Barouki ◽  
Y. Laperche ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Cell Line ◽  
Hepatoma Cell ◽  
Hepatoma Cell Line ◽  
Rat Hepatoma Cell Line ◽  
Rat Hepatoma
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