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

---

Query: EC:2.7.7.49 (reverse transcriptase)
31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mechanism for myometrial quiescence during pregnancy is unknown. cGMP plays an integral role in the relaxation of smooth muscle, and nitric oxide (NO) is the most important endogenous activator of soluble guanylate cyclase. The purpose of this study was to determine the effect of gestational age on myometrial cGMP and NO synthase (NOS) activity in the guinea pig. Myometrial cGMP content (measured by RIA) rose slowly until 0.49 (fraction of pregnancy completed) gestation before abruptly increasing to 200 times the non-pregnant control value. It then declined precipitously after 0.87 gestation. Of the known isoenzymes of NOS, the messenger RNAs coding for both endothelial and neuronal NOS could be amplified from the myometrium of pregnant and nonpregnant animals using reverse transcriptase-polymerase chain reaction, but inducible NOS messenger RNA was not found. Myometrial calcium-dependent NOS activity (measured by the conversion of L-[U-14C]arginine to [U-14C]citrulline) declined slowly with advancing gestation (r2 = 0.096; slope = -0.34; P = 0.01), but never differed significantly from the activity in nonpregnant animals [31.1 +/- 11 (term pregnancy) vs. 56.9 +/- 16 (nonpregnant) pmol/min.g; P = NS]. Calcium-independent activity declined shortly after conception, and then rose toward the nonpregnant level (r2 = 0.19; slope = 0.45; P = 0.0009). However, at no time was it significantly different from that in the nonpregnant animal. Pregnancy had no effect on myometrial L-arginine and L-citrulline content. The administration of L-nitro-arginine methyl ester (200 mg/kg) to inhibit NOS dramatically increased blood pressure and reduced fetal renal NOS activity, but had no effect on the myometrial cGMP content. Estradiol (500 micrograms/kg for 5 days) modestly increased cGMP, but in contrast to many tissues in which estradiol increases NOS, it had no effect on myometrial NOS activity. We conclude that pregnancy dramatically increases cGMP by a mechanism independent of NOS. The stimulus remains to be identified. The temporal change in cGMP concentration is consistent with the hypothesis that cGMP mediates myometrial quiescence during pregnancy.
...
PMID:Pregnancy increases guanosine 3',5'-monophosphate in the myometrium independent of nitric oxide synthesis. 798 34

Estradiol treatment for 48 h increases the density of alpha 1B-adrenoceptors in the hypothalamus-preoptic area of ovariectomized female rats by five- to six-fold. Present studies tested the hypothesis that estradiol elevation of hypothalamus-preoptic area alpha 1B-adrenoceptor density is correlated with increased levels of mRNA for this receptor. We developed a semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) protocol for measuring brain alpha 1b-adrenoceptor mRNA. The primers chosen yielded the predicted 409 base pair PCR product when used to amplify authentic alpha 1b-adrenoceptor cDNA. The identity of the RT-PCR products from rat brain was confirmed by restriction digest analysis and sequencing. Moreover, there was a good correlation between the levels of alpha 1b-adrenoceptor mRNA measured by RT-PCR in liver, whole brain and cerebellum with previous measurements using Northern blots and RNAse protection assays. We then performed RT-PCR on total RNA from hypothalamic-preoptic area tissue taken from ovariectomized control rats and from ovariectomized rats injected once or twice with 2 micrograms of estradiol benzoate at 24 or 24 and 48 h before sacrifice. Exposure to estradiol for either 24 or 48 h significantly increased levels of alpha 1b-adrenoceptor mRNA by 86-110% in the hypothalamus-preoptic area of ovariectomized female rats when compared to oil-treated controls. We also examined whether estradiol regulates alpha 1b-adrenoceptor mRNA in the cortex. Cortical alpha 1b-adrenoceptor mRNA levels were reduced to approximately 20% of control levels when measured 24 h after hormone injection. A similar decrease in cortical alpha 1b-adrenoceptor mRNA was observed 48 h after estrogen administration. In summary, estradiol treatment significantly increases the level of alpha 1b-adrenoceptor mRNA in the hypothalamus-preoptic area, a brain region involved in the control of reproductive function. In the cortex, a brain region with relatively few estrogen receptors, the same estrogen treatment reduces alpha 1b-adrenoceptor mRNA levels.
...
PMID:Estradiol regulation of alpha 1b-adrenoceptor mRNA in female rat hypothalamus-preoptic area. 880 75

Oestradiol (E2) is one of the most important factors supporting the growth and evolution of breast cancer; consequently, to block this hormone has been one of the main targets in recent years. The evaluation of oestrogens (oestrone, oestradiol and their sulphates) in the breast tissue of post-menopausal patients with breast cancer indicates high levels, particularly of oestrone sulphate (E1S) which is 15-25 times higher than in the plasma. Two main pathways are involved in the formation of oestrogens the sulphatase pathway which transforms E1,S into oestrone (E1), and the aromatase pathway which converts androgens into oestrogens. Comparative studies in breast cancer tissues show that the sulphatase pathway is 50-300 times more important than that of the aromatase pathway. Using intact cells and physiological concentrations of E1S (5 x 10(9)M) the conversion to oestradiol was very intense with the hormone-dependent (T-171). MCF-7) breast cancer cells, but very little or no E2 was obtained with the hormone-independent (MDA-MB-231, MDA-MB-436) cells. However, when the latter cells were homogenized, the oestrone sulphatase became very intense. This contradiction in the comparison of the sulphatase activity of the intact cell and the homogenate of the hormone-independent cells can be explained by the presence of inhibitory factors or the absence of positive factor(s) involved in the enzyme activity, which could be related to the evolution of the cancer to hormone-independence. Testing different substances, it was proven that promegestone (R-5020), and danazol, as well as decapeptyl in the presence of heparin, are very active in inhibiting sulphatase activity in hormone-dependent breast cancer cells. Using reverse transcriptase-PCR it was possible to detect the presence of oestrone sulphatase mRNA in different mammary cancer cells. The expression of this mRNA is significantly higher in T-471) and MDA-MB-231 than in the other cell lines. A correlation of this mRNA with the enzymatic activities of oestrone sulphate was observed. The progestagen, R-5020, can significantly decrease the sulphatase mRNA in MCF-7 and T-471) cells. As this progestagen can also inhibit the enzyme itself, it is suggested that the decrease in sulphatase activity by antisulphatase agents in breast cancer cells is a complex mechanism involving not only the effect on the enzyme but also the transcriptional factor(s). It is concluded that in addition to the control of aromatase, specific inhibition of oestrone sulphatase with antisulphatase agents can open new possibilities in breast cancer treatment.
...
PMID:Control and expression of oestrone sulphatase activities in human breast cancer. 894 93

Estradiol accelerates oviductal embryo transport in the rat through changes of genomic expression in oviductal cells. However, the genes involved are unknown. We used a differential display by reverse transcription-polymerase chain reaction to detect estradiol (E2)-dependent genes in the rat oviduct. Rats on day 2 of pregnancy were untreated or treated with 10 micrograms of E2 and the oviducts were extracted at 30, 180 and 360 min later and used to isolate RNA. Products of reverse transcriptase-PCR, made with pairs of arbitrary and oligo-deoxythymidine primers, were separated on denaturing polyacrylamide gels and candidate bands were excised and reamplified. Truly positive cDNA fragments determined by a single strand conformation polymorphism assay were cloned and sequenced. A ribonuclease protection assay confirmed that clone 25 is up-regulated by E2 in the oviduct at 30, 180 and 360 min. This clone exhibited no homology with known genes and in situ hybridization showed it is only expressed in the epithelial cells of the isthmic segment. Clone 25 is likely to represent a new gene, which is up-regulated by E2 in the epithelium of the isthmic segment of the rat oviduct. Its time frame of response is compatible with a mediator of the effect of E2 on oviductal embryo transport.
...
PMID:A segment and epithelium specific messenger ribonucleic acid fragment up-regulated by estradiol in the rat oviduct. 1147 19

Transgenic mice were generated in which a 2.2-kb segment of the 5'-flanking sequence of the mouse oviduct-specific glycoprotein (OGP) gene was used to drive expression of the simian virus 40 large T antigen (Tag). These mice spontaneously developed tumors in the female reproductive tract. Analysis using reverse transcriptase-polymerase chain reaction showed that the 2.2-kb OGP 5'-flanking region drove Tag mRNA expression in the oviduct, uterus, vagina, and ovary, but not in other tissues. Histological and immunohistochemical analyses revealed that the tumor cells were distributed in the oviduct, endometrium, myometrium, and vagina; and had atypical features, abnormal mitosis, and Tag expression. Ovariectomy suppressed Tag expression, and thereby, blocked tumorigenesis in the transgenic mice. Estradiol administration to ovariectomized transgenic mice led to dramatic hyperplasia of the reproductive tract tissues in association with enhanced Tag expression, both in intensity and distribution. These results demonstrated that a 2.2-kb fragment of the 5'-flanking sequence of the mouse OGP gene was capable of directing the expression of Tag and inducing tumorigenesis in female reproductive tract tissues in an estrogen-dependent manner. Estrogen response elements present in the promoter region were functional in vivo. These transgenic mice represent a unique model, since they develop tumors in the oviducts as well as in other tissues derived from the Mullerian duct.
...
PMID:Mouse transgenic for murine oviduct-specific glycoprotein promoter-driven simian virus 40 large T-antigen: tumor formation and its hormonal regulation. 1220 26

The expression of aromatase, the enzyme that transforms testosterone into estradiol, was analyzed by reverse transcriptase polymerase chain reaction in the inferior olive of adult male rats. The expression of this messenger in the inferior olive suggests that this brain area may be able to synthesize estradiol. The neuroprotective role of estradiol in the inferior olive was then assessed in a model of cerebellar ataxia, achieved by the ip administration of 3-acetylpyridine (3-AP). In a first experiment, male Wistar rats were orchidectomized to diminish the plasmatic levels of testosterone, the direct precursor of estradiol. Immediately after castration, animals were implanted with a silicone tube that was either empty or filled with estradiol. One week later, animals were injected with 3-AP. Estradiol treatment resulted in a significant reduction in neuronal death in the olive. In a second experiment, animals were treated with fadrozole, an aromatase inhibitor, to assess the role of endogenous estradiol formation in neuroprotection. The results show that the inhibition of aromatase activity, and therefore the decrease in endogenous estrogen formation, increases the death in inferior olive. In conclusion, this study indicates that the inferior olive is a steroidogenic tissue and that olivary neurons are protected by exogenous and endogenous estradiol.
...
PMID:Endogenous estrogen formation is neuroprotective in model of cerebellar ataxia. 1277 2

The brains of mammals have at least three estradiol-binding proteins: estradiol receptor-alpha (ERalpha), ERbeta, and sex hormone-binding globulin (SHBG). In this study we compare the effects of estradiol treatment on the expression of mRNA for these three estradiol-binding proteins in two reproductively important brain areas, the medial preoptic area-anterior hypothalamus (MPOA-AH) and medial hypothalamus (MH) as well as in the hippocampus in ovariectomized rats, using the reverse transcriptase-polymerase chain reaction (RT-PCR). We also used surface-enhanced laser desorption ionization time of flight (SELDI-TOF) mass spectrometry (MS) to analyze the effects of estradiol in ovariectomized rats on SHBG levels in the MPOA-MH as well as the neurohypophysis. In vivo estradiol treatment in ovariectomized rats eliminated or significantly reduced expression of all three estradiol-binding proteins in both the MPOA-AH and MH. This change in ERalpha, ERbeta, and SHBG expression did not occur in the hippocampus. Both Northern blot and DNA sequence analysis confirmed the results of the RT-PCR for SHBG. SELDI-TOF MS analysis demonstrated that in vivo estradiol treatments resulted in dramatically decreased levels of SHBG in the hypothalamus and that a reduction in SHBG mRNA by estradiol treatment also resulted in a reduction in SHBG protein levels. Estradiol treatment also eliminated detectable SHBG from the neurohypophysis, suggesting that estradiol controls SHBG levels in this release site. That in vivo estradiol treatments had the same inhibitory effects on mRNA levels for SHBG and both ERs suggests similar translational control mechanisms for all three steroid-binding proteins in the brain. That estradiol treatments also reduced pituitary SHBG suggests that such treatment releases SHBG from the neurohypophysis.
...
PMID:Estradiol control of expression and levels of estradiol-binding proteins in the medial preoptic area, medial hypothalamus and pituitary. 1291 58

Telomerase, a ribonucleoprotein enzyme that functions as a reverse transcriptase, is detected exclusively in immortal cells such as germ cells, stem cells and cancer cells. Telomerase activity is present in almost all human cancers. Telomerase activation is considered to be essential to maintain the integrity of the replicating tumor cell and to establish immortality. Based on this concept antiestrogen should initially regulate estrogen-stimulated telomerase but the enzyme would be expected to be constitutive in tamoxifen-resistant tumor cells. We have studied the estrogen regulation of telomerase in T47D:A18 breast cancer cells with a TRAPEZE Telomerase detection kit. Estradiol significantly increased telomerase activity after a 2-day treatment. Telomerase activity induced by estradiol was up to 10-fold higher within 4 days. Antiestrogens 4-hydroxytamoxifen (4-OHT) and ICI 182,780 were inactive alone and significantly blocked estradiol-stimulated increase in telomerase. These effects were correlated with changes in cell replications and changes in the cell cycle. In contrast, 4-OHT resistant T47D:A18 cells (T47D:A18/4-OHT, cultured in 1 microM 4-OHT for 6 months) grew spontaneously and had no changes in the cell cycle with estrogen treatment. The estrogen receptor (ERalpha) was present and still regulated at an estrogen responsive luciferase reporter gene with estrogen despite the fact that progesterone receptor was not increased in response to estradiol in T47D:A18/4-OHT cells. However, telomerase activity was increased about 40-fold in T47D:A18/4-OHT cells and this was not regulated by ICI 182,780. We conclude that the differential regulation of telomerase gene might be an important transition for tamoxifen resistance in T47D:A18 breast cancer cells.
...
PMID:Deregulation of estrogen induced telomerase activity in tamoxifen-resistant breast cancer cells. 1621 Dec 43

1-[4-(2-Dimethylaminoethoxy)-phenyl]-1,2-diphenylbut-1-(Z)-ene (tamoxifen, TAM) is a nonsteroidal antiestrogen that has been commonly used for the prevention and treatment of estrogen receptor-positive breast cancer. TAM is extensively metabolized into several primary active metabolites including 4-hydroxy-TAM (4-OH-TAM) and endoxifen. Glucuronidation is the major phase II metabolic pathway important in their excretion. Whereas high antiestrogenic activity has been reported for both 4-OH-TAM and endoxifen, studies examining the effect of glucuronide conjugation of these metabolites have not previously been performed. In the present study, the antiestrogenic activities of glucuronidated TAM metabolites were determined by examining their effect on the induction of the estrogen-responsive progesterone receptor (PGR) gene. 17beta-Estradiol (E(2))-mediated PGR gene expression in MCF-7 cells was determined by real-time reverse transcriptase-polymerase chain reaction for each TAM metabolite isomer. E(2) (1 x 10(-10) M) induction of PGR mRNA was 6-fold after a 12-h incubation; only unconjugated TAM metabolites inhibited this effect. A virtually identical dose-dependent inhibition of E(2)-induced PGR gene expression was found for both the trans- and cis-isomers of 4-OH-TAM and endoxifen, with maximal inhibition attained at 1 x 10(-6) M of TAM metabolite. The glucuronide conjugates of all 4-OH-TAM and endoxifen isomers exhibited no effect on E(2)-mediated induction of PGR expression at all concentrations of TAM metabolite examined in this study. These data indicate that isomers of both 4-OH-TAM and endoxifen exhibit roughly equipotent antiestrogenic effects on E(2)-induced gene expression and that glucuronide conjugates of the same metabolites effectively negate this activity. This result may have important implications in terms of both whole-body and target tissue-specific glucuronidation pathways and individual responses to TAM therapy and cancer prevention.
...
PMID:Elimination of antiestrogenic effects of active tamoxifen metabolites by glucuronidation. 1762 Mar 45

Angiotensin-converting enzyme (ACE) and ACE2 and the AT1 and AT2 receptors are pivotal points of regulation in the renin-angiotensin system. ACE and ACE2 are key enzymes in the formation and degradation of angiotensin II (Ang II) and angiotensin-(1-7)(Ang-(1-7)). Ang II acts at either the AT1 or the AT2 receptor to mediate opposing actions of vasoconstriction or vasodilatation respectively. While it is known that oestrogen acts to downregulate ACE and the AT(1) receptor, its regulation of ACE2 and the AT2 receptor and the involvement of a specific oestrogen receptor subtype are unknown. To investigate the role of oestrogen receptor-alpha (ERalpha) in the regulation by oestrogen of ACE/ACE2 and AT1/AT2 mRNAs in lung and kidney, ovariectomized female mice lacking apolipoprotein E (ee) with the ERalpha (AAee) or without the ERalpha (alphaalphaee) were treated with 17beta-oestradiol (6 microg day(-1)) or placebo for 3 months. ACE, ACE2, AT1 receptor and AT2 receptor mRNAs were measured using reverse transcriptase, real-time polymerase chain reaction. In the kidney, 17beta-oestradiol showed 1.7-fold downregulation of ACE mRNA in AAee mice, with 2.1-fold upregulation of ACE mRNA in alphaalphaee mice. 17beta-Oestradiol showed 1.5- and 1.8-fold downregulation of ACE2 and AT1 receptor mRNA in AAee mice; this regulation was lost in alphaalphaee mice. 17beta-Oestradiol showed marked (81-fold) upregulation of the AT(2) receptor mRNA in AAee mice. In the lung, 17beta-oestradiol treatment had no effect on AT1 receptor mRNA in AAee mice, but resulted in a 1.5-fold decreased regulation of AT1 mRNA in alphaalphaee mice. There was no significant interaction of oestrogen with ERalpha in the lung for ACE, ACE2 and AT2 receptor genes. These studies reveal tissue-specific regulation by 17beta-oestradiol of ACE/ACE2 and AT1/AT2 receptor genes, with the ERalpha receptor being primarily responsible for the regulation of kidney ACE2, AT1 receptor and AT2 receptor genes.
...
PMID:Tissue-specific regulation of ACE/ACE2 and AT1/AT2 receptor gene expression by oestrogen in apolipoprotein E/oestrogen receptor-alpha knock-out mice. 1819 35


1 2 Next >>

---