Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Complementary DNA (cDNA) clones encoding human-androgen receptors (haR) were isolated using synthetic oligonucleotides homologous to the human glucocorticoid, estradiol, progesterone, and aldosterone receptors as probes to screen a human testis lambda gt11 cDNA library. One of the receptor proteins (hARa) produced in vitro bound the [3H]dehydrotestosterone ([3H]DHT) with high affinity and selectivity similar to the human androgen receptor present in target tissues and cells. A second cDNA clone (hARb) encoding an identical amino terminal and DNA binding domains, but differing by four amino acids at the hormone binding domain, did not bind [3H]DHT with high affinity when incubated with protein expressed by in vitro transcription-translation. Cotransfection of hARa in an expression vector with mouse mammary tumor virus (MMTV)-bacterial chloramphenicol acetyltransferase chimeric plasmids, followed a hormone-dependent trans-activation, defining the binding affinity of hARa between 5 x 10(-10) and 1 x 10(-9) M for [3H]DHT. A similar cotransfection experiment with hARb indicated a KD of hARb for [3H]DHT to be above approximately 10(-8) M. The deduced primary structures of hARa and hARb contain the viral erbA homologous region found in other steroid, thyroid, and vitamin receptors and is identical to the hAR sequences reported by others. The amino acid sequence differs at the Gly stretch (16 Gly instead of 27, 24 or 23) of the N-terminal domain and in hARb, the sequence reads I.F.F.F.F.L.L (816-822) instead of K.F.F.D.E-L (816-821) in the hARa and other reported hAR sequences. The difference of four amino acids in the steroid binding domain of hARb is associated with altered DHT binding and thus a lack of trans-activation by way of AR responsive elements in MMTV-long terminal repeat. The interaction of hARa and hARb with synthetic responsive elements by gel-retardation assay and their responsiveness in trans-activation by calcium phosphate coprecipitation demonstrates that hARb can inhibit trans-activation by hARa in this system.
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PMID:Specific region in hormone binding domain is essential for hormone binding and trans-activation by human androgen receptor. 234 76

Androgens have significant beneficial effects on the skeleton. However, studies on the effects of androgens on osteoblasts are limited due to the absence of appropriate model systems that combine completeness of the osteoblastic phenotype, rapid proliferation rate, and stable expression of the androgen receptor (AR). Thus, we stably transfected the conditionally immortalized human fetal osteoblastic cell line (hFOB) with the human wild-type AR (hAR) cDNA. Compared to nontransfected hFOB cells, constitutive hAR mRNA expression in three independent hAR-transfected hFOB clones (hFOB/AR) was 15-fold higher in hFOB/AR-16, 62-fold higher in hFOB/AR-2, and 72-fold higher in hFOB/AR-6 cells, respectively, as assessed by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Detectable constitutive levels of hAR mRNA by Northern blot analysis were present in hFOB/AR-2 and hFOB/AR-6 cells, but not in hFOB/AR-16 or hFOB cells, respectively. Treatment with 5 alpha-dihydrotestosterone (5 alpha-DHT) (10(-8) M) for 24 h did not alter hAR mRNA steady state levels in the hFOB/AR cell lines. Nuclear binding studies demonstrated 152 +/- 73 (mean +/- SEM) functional hARs/nucleus in non-transfected hFOB cells, 3,940 +/- 395 functional hARs/nucleus in hFOB/AR-2 cells, and 3,987 +/- 823 hARs/nucleus in hFOB/AR-6 cells, respectively. Treatment with 5 alpha-DHT increased the expression of a transiently transfected androgen response element-chloramphenicol acetyltransferase (ARE-CAT) reporter construct in hFOB/AR-6 cells in a dose- and time-dependent manner; no such effect was observed in transiently transfected hFOB cells lacking exogenously transfected hARs. Moreover, 5 alpha-DHT-induced ARE-CAT expression was inhibited by the selective androgen receptor antagonist, hydroxyflutamide. In summary, we have developed and characterized androgen-responsive osteoblastic cell lines derived from normal human fetal bone that express physiological levels of functional hARs. These cell lines should provide a suitable model for further studies on the effects of androgens on osteoblast function, including the identification of potential androgen-regulated growth factors and cytokines.
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PMID:Development and characterization of a conditionally immortalized human osteoblastic cell line stably transfected with the human androgen receptor gene. 928 32

We have examined the human androgen receptor (hAR) for its ability to activate AR-dependent transcription of a transgene in a ligand-independent manner. The transcriptional activity was determined by analysis of chloramphenicol acetyltransferase (CAT) activity in T47D cells cotransfected with a plasmid expressing the hAR and a natural AR-regulated promoter (the MVDP androgen-dependent enhancer) ligated to the reporter CAT gene. In this study, the effects of the protein kinase C (PKC) activator 12-O-tetradecanoyphorbol-13 acetate (TPA) on AR activity were tested. We demonstrated that in the absence of androgen, TPA enhanced AR-mediated transactivation by 10-12-fold. This effect was specific of the PKC pathway since stimulation to the PKA pathway did not activate the unliganded AR. This ligand-independent pathway can function through another androgen-regulated promoter as shown by the use of the mouse mammary tumor virus MMTV-CAT reporter. The human glucocorticoid receptor (hGR) and the rabbit progesterone receptor (rPR) could not be activated by TPA, indicating that the effects are not universal for steroid receptors. A reporter plasmid containing the MVDP androgen response element (ARE) in front of the thymidine kinase promoter ligated to the CAT gene was activated by DHT but not by TPA, indicating that the context of the natural promoter is critical for ligand-independent activation of the AR. Exogenous c-jun enhanced transcriptional activation by the AR in a ligand-dependent manner, but had no effect in the absence of DHT. Base pair substitutions in both AR-binding (5'-TGTTCT-3' to 5'-TTTTTT-3') and NF1-binding (5'-GTGGCTG-3' to 5'-GTTTTTG-3') sites resulted in a loss of TPA responsiveness. Our results suggest that ligand-independent activation of the AR by TPA results from interaction of unliganded AR with other proteins in the transcription machinery.
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PMID:Phorbol ester causes ligand-independent activation of the androgen receptor. 978 Feb 30

For many years it has been recognized that sex steroids have profound effects on bone metabolism. The current perception is that estrogen decreases bone resorption and androgen increases bone deposition. To investigate the potential for androgens to directly modulate bone resorption, we have examined avian osteoclast and human and mouse osteoclast-like cells for androgen responsiveness. There was a dose-dependent decrease in resorption activity in response to alpha-dihydrotestosterone (alpha-DHT), beta-DHT, testosterone, or the synthetic androgen RU1881. This decrease was blocked by cotreatment with the specific androgen antagonist hydroxyflutamide. Further examination of avian osteoclasts revealed that the cells exhibited specific and saturable nuclear binding of tritiated RU1881 and that alpha-DHT stimulated the activity of the androgen response element as measured by using a chloramphenicol acetyltransferase reporter plasmid. In addition, avian osteoclasts responded to androgen treatment with elevated production and secretion of transforming growth factor beta, a well documented response to androgen exposure in other cell systems. Treatment with either alpha-DHT or beta-DHT for 24 hours resulted in a significant dose-dependent decrease in secretion of cathepsin B and tartrate-resistant acid phosphatase. This response to beta-DHT, a stereoisomer of alpha-DHT that is inactive in other androgen receptor-dependent systems, supports the hypothesis that the osteoclast androgen receptor has unusual ligand-binding properties. Taken together, these results confirm the presence of functional androgen receptors in these cells and support the conclusion that osteoclasts are able to respond directly to androgens in vitro and thus are potential androgen target cells in vivo.
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PMID:Androgens regulate bone resorption activity of isolated osteoclasts in vitro. 989 63

We studied the effects of 17beta-estradiol, progesterone, and dihydrotestosterone on in vitro growth of human metastatic melanoma. Each sex hormone inhibited the growth of melanoma receptor-dependently; 17beta-estradiol inhibited 3H-thymidine uptake of estrogen receptor-positive WM266-4 and NM26, but not that of the receptor-negative HS15. Progesterone inhibited 3H-thymidine uptake of progesterone receptor-positive WM266-4 and HS15, but not that of the receptor-negative NM26. Dihydrotestosterone inhibited 3H-thymidine uptake of androgen receptor-positive HS15 and NM26, but not that of the receptor-negative WM266-4. The growth inhibition by each hormone was counteracted by the respective hormone receptor antagonist. The combination of more than two hormones neither gave additive nor synergistic growth inhibition. The growth inhibition by each sex hormone was counteracted by interleukin-8 but not by the other growth factors. Each sex hormone reduced the constitutive interleukin-8 secretion and mRNA levels in the respective receptor-positive melanoma but not in the receptor-negative melanoma. Transient transfection showed that each sex hormone inhibited the constitutive chloramphenicol acetyltransferase expression driven by interleukin-8 promoter in the respective receptor-positive melanoma but not in the receptor-negative melanoma. Transfection with a series of 5'-deleted interleukin-8 promoter/chloramphenicol acetyltransferase reporter constructs demonstrated that the sequences between -98 and -63 bp on interleukin-8 promoter may be involved in the transcriptional repression. These data suggest that 17beta-estradiol, progesterone, and dihydrotestosterone suppress the growth of melanoma by inhibiting interleukin-8 production in a receptor-dependent manner.
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PMID:17beta-estradiol, progesterone, and dihydrotestosterone suppress the growth of human melanoma by inhibiting interleukin-8 production. 1151 5

Serum apolipoprotein AI (apoAI) levels correlate with the risk of developing atherosclerosis. Previous studies have suggested that dehydroepiandrosterone (DHEA) lowers high-density lipoprotein (HDL)-cholesterol levels. We investigated whether or not DHEA may lower HDL-cholesterol levels by suppressing apoAI gene transcription in hepatocytes. ApoAI mRNA levels, assessed by Northern blotting, were suppressed in HepG2 cells treated with DHEA (34%) (10 microg/mL) or testosterone (36%) (T, 1 microg/mL). Estradiol alone (E2, 1 microg/mL) had relatively little effect on apoAI mRNA levels, while E2 in combination with DHEA prevented a decrease in apoAI mRNA levels compared to DHEA alone. To determine whether these effects were due to changes in apoAI gene transcription, HepG2 cells were transfected with a plasmid carrying the full-length promoter of the rat apoAI gene ligated into a chloramphenicol acetyltransferase (CAT) reporter construct. The plasmid pCMV.SPORT-beta-gal was included in each transfection to normalize the data to transfection efficiency. Cells were then cultured in the presence or absence of DHEA (10 microg/mL), T (1 microg/mL), 17alpha-methyltestosterone (MTT, 1 microg/mL), 5alpha-dihydrotestosterone (DHT, 1 microg/mL), E2 (1 microg/mL), or a combination of DHEA plus E2, T plus E2, MTT plus E2, and DHT plus E2, for 24 hours. CAT activity, relative to beta-galactosidase activity, was reduced by 19.6%, 57.6%, 38.6%, and 54.6% with DHEA, T, DHT, and MTT addition, respectively. E2 increased CAT activity by 43.8%. When the androgens (ie, DHEA, T, DHT, or MTT) were combined with E2, apoAI promoter activity was suppressed. We conclude, therefore, that androgens downregulate apoAI promoter activity in the presence or absence of E2. However, the changes in mRNA levels do not always reflect changes in promoter activity, suggesting that these steroids may have additional post-transcriptional effects on steady-state apoAI mRNA levels. It remains to be established if the transcriptional effects we observed are mediated through an androgen response element.
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PMID:Effects of dehydroepiandrosterone on rat apolipoprotein AI gene expression in the human hepatoma cell line, HepG2. 1188 77

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