Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.7.6 (RNA polymerase)
 34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We demonstrate here that stilbene estrogen (diethylstilbestrol) is converted to nuclear protein binding metabolite(s) both in vitro and in vivo. In vitro reaction of DES with nuclei from hamster liver or kidney in the presence of cumene hydroperoxide or NADPH revealed binding of [3H]DES in nuclear proteins (histones; nonhistones precipitable by 2% TCA, NH2; nonhistones soluble in 2% TCA, NH30). The binding was significantly inhibited by cytochromes P450 inhibitors. In an in vitro system [3H]DES quinone, one of the metabolites of DES, was able to bind to pure nonhistone proteins RNA polymerase and DNA polymerase. The binding of [3H]DES quinone to nonhistones RNA polymerase and DNA polymerase was inhibited by low molecular weight thiols, i.e. glutathione and cysteine, or thiol modifiers, such as n-ethylmaleimide, dithionitrobenzoic acid and hydroxymercuric benzoate. DES and DES metabolites inhibited transcriptional activity. In vivo [3H]DES was able to bind to nuclear proteins of hamster liver, kidneys and testes. The level of in vivo [3H]DES binding to all three types of nuclear proteins (histones, NH2, NH30) in the kidney (target organ) was two or more fold higher than that observed in the liver or testis (nontarget organs). Four nuclear NH30 proteins (mol wts.: 56, 37, 33 and 28 kDa) were irreversibly bound to [3H]DES in vivo. The in vivo binding of [3H]DES to transcriptionally active chromatin NH30 proteins also was observed. The data reported here establish that DES was able to bind to liver or kidney nuclear proteins in vitro, which was catalyzed by nuclear enzymes when fortified with an appropriate cofactor. DES quinone may be one of the protein binding metabolites. DES and DES metabolites inhibited transcriptional activity. The level of in vivo binding of [3H] DES to nuclear proteins of kidney (target organ) was double in comparison with that observed in liver or testis (nontarget organs). In vivo modifications in the chromatin proteins may be a factor in the development of DES-induced renal carcinogenesis is not clear.
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PMID:In vivo binding of diethylstilbestrol to nuclear proteins of kidneys of Syrian hamsters. 773 58

We have previously shown that stilbene estrogen (diethyl-stilbestrol, DES) covalently binds to nonhistone nuclear proteins both in vivo and in vitro. In this study, we demonstrate the differential effects of DES exposure on in organelle transcriptional activity in nuclei isolated from kidney (target organ of cancer) and liver (non target organ) of hamsters. Kidney RNA polymerase (RNA pol) I and III activities were significantly inhibited by 50% at days 8 and 15 of DES exposure compared to that of controls. Liver RNA pol I and III activities were only modestly inhibited (17 and 22%, respectively) by 2 and 8 days of DES exposure, respectively. However, longer exposure of DES to animals did not produce any significant effects on RNA pol I activity. The activity of RNA pol II was affected by DES exposure in both liver and kidney. DES treatment for two days resulted in an increase in RNA pol II activity in kidney. The enhanced enzyme activity was decreased to 50% of that of the control at 15 days of DES treatment. Unlike RNA pol I and III, RNA pol II activity in the liver was inhibited in a time-dependent fashion in response to DES exposure. To understand the mechanism of transcriptional inhibition by DES, we analyzed the effect of DES exposure on the expression of hepatic RNA pol II at both mRNA and protein levels and also phosphorylation of hepatic RNA pol II. The total amount of transcripts or protein contents of hepatic RNA pol II was not altered in response to DES exposure to hamster for 15 days. Total phosphorylation of hepatic RNA pol II was also not affected by 15 days DES exposure. However tyrosine phosphorylation of hepatic RNA pol II was lowered by 2.8-fold compared to that of control enzyme in response to DES exposure for 15 days. An inhibitory effect of DES on the total RNA polymerase activity in both kidney and liver nuclei in the presence of endogenous template was observed in vitro. No inhibitory effect of DES was observed in vitro on transcriptional activity in the presence of exogenously added DNA template. Based on these data it appears that the in vivo inhibition of transcription by DES may be due to alterations in chromatin template or the level of transcription regulating proteins and not due to decreased availability of the chromatin template and/or RNA polymerase. Whether DES related inhibition of transcriptional activity plays a role in the development of kidney cancer is not clear.
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PMID:Organ-specific inhibition of types I, II and III transcriptional activity in hamsters exposed to stilbene estrogen. 776 59

Chronic treatment with the synthetic estrogen diethylstilbestrol induces pituitary tumors in rats and the susceptibility to such tumors is highly strain dependent. The Fischer 344 (F344) strain, which is particularly susceptible, develops pituitary tumors after 30-55 days of estrogen treatment. In contrast, the Sprague-Dawley (SD) strain is relatively resistant to such tumors. DES implants (5 mg) were placed in 21-day-old male rats over a 10-day period and changes in their testes and pituitaries were monitored. Both F344 and SD strains responded similarly by exhibiting a measurable decrease in testes weight to one-third that of controls on day 10. In F344 rats, DNA synthesis in the pituitary increased to 228% as compared with controls after 3 days of DES treatment and remained high on days 7 and 10. In SD rats, DNA synthesis increased to only 150% of that exhibited by controls on day 3 and started to decline on day 7. Surprisingly, total RNA accumulation also responded to DES differentially between these two strains. In F344 rats, the RNA level was 250% as compared with that of controls after 3 days of DES treatment and continued to increase gradually on days 7 and 10. The RNA level in the SD strain increased only slightly from the same DES treatment. A nuclear run-on assay showed elevated pituitary transcription of ribosomal DNA in the F344 rats after 3 days of estrogen administration. The enzymatic activity of pituitary RNA polymerase I, the enzyme responsible for initiating rRNA synthesis, increased twofold in F344 rats when measured after 3 days of estrogen treatment whereas no increase was observed in the SD rats. These results suggest that estrogen-induced changes in the accumulation of rRNA occur at a very early stage in tumorigenesis, prior to any visible tumor growth in the rat pituitary.
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PMID:Estrogen-induced changes in rRNA accumulation and RNA polymerase I activity in the rat pituitary: correlation with pituitary tumor susceptibility. 873 7