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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We previously identified 20 different alternatively spliced estrogen receptor alpha (ERalpha) mRNAs that have deletions in various combinations of exons in breast cancer cell lines using a novel 'Splice Targeted Approach' [J. Steroid Biochem. Mol. Biol. 72 (2000) 249]. In the current study, we compared the frequency of alternatively spliced ERalpha variant expression in 35 reduction mammoplasty and 38 breast cancer tissues with known ERalpha, ERbeta status using this highly specific 'Splice Targeted Approach'. A total of 16 different alternatively spliced variants were identified that have deletions in various combinations of exons in normal, as well as cancer tissues. However, not all 16 variants were present in every tissue. The frequency and type of variants in normal and cancer tissues was significantly different. Majority of normal tissues expressed only single exon deletion variants with the exception of those in combination with exon 2Delta and 7Delta. Tumor tissues, on the other hand, showed increased frequency of multiple exon deletion mRNAs (P<0.019). In addition, cancer tissues also showed an increased frequency of all variants compared with normal tissues (P<0.044). Among the 16 variants, the dominant negative variant, exon 3Delta, showed the most significant increase in cancer tissues (P=0.000032). Specifically, we detected four different mRNAs that have exon 2 deletion-exon 2Delta; 2 and 4Delta; 2 and 5Delta; and 2, 4-5Delta in various combinations in both normal and cancer tissues. A large number of normal tissues expressed two transcripts-exon 2Delta and 2, 4-5Delta. The multiple exon deletion 2, 4-5Delta were predominant in cancer tissues. Only the single exon 3 deletion variant, exon 3Delta, was detected in normal tissues. Cancer tissues showed the presence of a double exon deletion variant, exons 3 and 7Delta, in addition to exon 3Delta. A small fraction of normal tissues showed exons 2-3Delta mRNAs, whereas, cancer tissues showed increased frequency of exons 2-3Delta expression in addition to a triple exon deletion variant, exons 2-3, and 5Delta. The expression of exon 4Delta; or 4 and 7Delta or both was equivalent in normal and cancer tissues. Exon 5Delta transcripts were present at very low levels in both normal and tumor tissues. A small percentage of cancer tissues but not normal tissues showed exon 6Delta mRNA. The presence of single, double, triple and quadruple exon deletion mRNAs, exon 7Delta; 7 and 4Delta; 7, 3-4Delta; 7, 3-5Delta, respectively, were detected in normal as well as cancer tissues. Each normal and cancer tissue had a distinct profile of ERalpha wild type, ERbeta wild type and ERalpha splice variants. Heterogeneity in ER isoform profiles may result in variations in estrogen/anti-estrogen binding and activation/inactivation of estrogen-dependent genes, and, therefore, may have implications in the risk of developing breast cancer, survival with the disease and response to anti-estrogen, as well as other therapies.
J Steroid Biochem Mol Biol 2001 Nov
PMID:Expression of alternatively spliced estrogen receptor alpha mRNAs is increased in breast cancer tissues. 1173 56

Gene activation mediated by nuclear receptors is regulated in a tissue-specific manner and requires interactions between nuclear receptors and their cofactors. Here, we identified and characterized a tissue-specific coactivator, GT198, that interacts with the DNA-binding domains of nuclear receptors. GT198 was originally described as a genomic transcript that mapped to the human breast cancer susceptibility locus 17q12-q21 with unknown function. We show that GT198 exhibits a tissue-specific expression pattern in which its mRNA is elevated in testis, spleen, thymus, pituitary cells, and several cancer cell lines. GT198 is a 217-amino-acid nuclear protein that contains a leucine zipper required for its dimerization. In vitro binding and yeast two-hybrid assays indicated that GT198 interacted with nuclear receptors through their DNA-binding domains. GT198 potently stimulated transcription mediated by estrogen receptor alpha and beta, thyroid hormone receptor beta1, androgen receptor, glucocorticoid receptor, and progesterone receptor. However, the action of GT198 was distinguishable from that of the ligand-binding domain-interacting nuclear receptor coactivators, such as TRBP, CBP, and SRC-1, with respect to basal activation and hormone sensitivity. Furthermore, protein kinase A, protein kinase C, and mitogen-activated protein kinase can phosphorylate GT198 in vitro, and cotransfection of these kinases regulated the transcriptional activity of GT198. These data suggest that GT198 is a tissue-specific, kinase-regulated nuclear receptor coactivator that interacts with the DNA-binding domains of nuclear receptors.
Mol Cell Biol 2002 Jan
PMID:Identification and characterization of a tissue-specific coactivator, GT198, that interacts with the DNA-binding domains of nuclear receptors. 1173 47

The potential involvement of membrane estrogen binding sites in the induction of ERE-dependent transcriptional activity as well as in the regulation of intracellular estrogen receptor alpha (ER-alpha) level under estradiol (E2) stimulation was investigated. Our approach relied upon the use of two DCC-treated E2-BSA (bovine serum albumin) solutions (E2-6-BSA and E2-17-BSA). The absence of detectable free E2 in these solutions was established. Both E2-BSA conjugates led to a transient dose-dependent stimulation of the expression of ERE-luciferase (LUC) reporter gene in MVLN cells (MCF-7 cells stably transfected with a pVit-tk-LUC reporter plasmid), a property not recorded with free E2, which maintained enhanced transcriptional activity during the whole experiment. A very low concentration of E2 (10 pM) synergistically acted with E2-BSA conjugates. Hence, ERE-dependent transcriptional activity induced by these conjugates appeared to result from their known interactions with membrane estrogen binding sites. Anti-estrogens (AEs: 4-OH-TAM and RU 58,668), which antagonize genomic ER responses, abrogated the luciferase activity induced by E2-BSA conjugates, confirming a potential relationship between membrane-related signals and intracellular ER. Moreover, induction of luciferase was recorded when the cells were exposed to IBMX (3-isobutyl-1-methylxanthine) and cyclic nucleotides (cAMP/cGMP), suggesting the implication of the latter in the signal transduction pathway leading to the expression of the reporter gene. Growth factors (IGF-I, EGF and TGF-alpha) also slightly stimulated luciferase and synergistically acted with 10 pM E2, or 1 microM E2-BSA conjugates, in agreement with the concept of a cross-talk between steroids and peptides acting on the cell membrane. Remarkably, E2-BSA conjugates, IBMX and all investigated growth factors failed to down-regulate intracellular ER in MCF-7 cells, indicating the need for a direct intracellular interaction of the ligand with the receptor to regulate its level. ER elimination was, however, found in the presence of conditioned media (CMs) prepared from cells pre-exposed to E2-BSA conjugates, suggesting that they may produce (a) modulator(s) that may enhance receptor down-regulation when released within the medium.
J Steroid Biochem Mol Biol 2002 Jan
PMID:Evaluation of potential implication of membrane estrogen binding sites on ERE-dependent transcriptional activity and intracellular estrogen receptor-alpha regulation in MCF-7 breast cancer cells. 1186 70

Chromatin is the physiological template for many nuclear processes in eukaryotes, including transcription by RNA polymerase II. In vivo, chromatin is assembled from genomic DNA, core histones, linker histones such as histone H1, and nonhistone chromatin-associated proteins. Histone H1 is thought to act as a general repressor of transcription by promoting the compaction of chromatin into higher-order structures. We have used a biochemical approach, including an in vitro chromatin assembly and transcription system, to examine the effects of histone H1 on estrogen receptor alpha (ER alpha)-mediated transcription with chromatin templates. We show that histone H1 acts as a potent repressor of ligand- and coactivator-regulated transcription by ER alpha. Histone H1 exerts its repressive effect without inhibiting the sequence-specific binding of ER alpha to chromatin or the overall extent of targeted acetylation of nucleosomal histones by the coactivator p300. Instead, histone H1 acts by blocking a specific step in the ER alpha-dependent transcription process, namely, transcription initiation, without affecting transcription reinitiation. Together, our data indicate that histone H1 acts selectively to reduce the overall level of productive transcription initiation by restricting promoter accessibility and preventing the ER alpha-dependent formation of a stable transcription pre-initiation complex.
Mol Cell Biol 2002 Apr
PMID:Histone H1 represses estrogen receptor alpha transcriptional activity by selectively inhibiting receptor-mediated transcription initiation. 1190 41

Gonadotropin releasing hormone-I (GnRH-I), a decapeptide serves as a key regulator of reproduction. Recently, several groups have identified in the mammalian brain a second form of GnRH, of unknown function, designated GnRH-II. The human neuronal medulloblastoma cells (TE-671) were recently demonstrated to express the two forms of GnRH (GnRH-I and GnRH-II). We used this cell line, as a model system, to investigate the regulation of human GnRH-I and GnRH-II genes by estrogen. Estrogen is one of the principal regulators of GnRH-I in hypothalamic neurons, acting as a classic homeostatic feedback molecule between the gonads and the brain. In this study, we investigated the regulation of the two GnRH forms by estrogen, in the human neuronal cell line TE-671. We demonstrate, for the first time, that the hGnRH-II and hGnRH-I genes are differentially regulated by estrogen. Using reverse transcriptase-polymerase chain reaction (RT-PCR) and Southern hybridization, we found that estrogen increases endogenous hGnRH-II mRNA levels and decreases endogenous hGnRH-I mRNA levels. Furthermore, we found these effects to be promoter-mediated. We cloned the hGnRH-I and hGnRH-II promoter constructs upstream to a luciferase reporter plasmid, and cotransfected these constructs with an estrogen receptor alpha into the TE-671 neuronal cells. Luciferase activity of GnRH promoter constructs treated with estrogen demonstrates that the differential regulation of the GnRH genes by estrogen is mediated at the transcription level.
J Mol Neurosci
PMID:The transcription of the hGnRH-I and hGnRH-II genes in human neuronal cells is differentially regulated by estrogen. 1193 51

Nuclear receptors (NRs) regulate transcription in a ligand-dependent way through two types of coactivator complexes: the p160/CBP histone acetyl transferase (HAT) complex and the DRIP/TRAP/SMCC complex without HAT activity. Here we identified a large human (h) coactivator complex necessary for the estrogen receptor alpha (ERalpha) transactivation. This complex contains the GCN5 HAT, the c-Myc interacting protein TRRAP/PAF400, TAF(II)30, and other subunits. Similarly to known TFTC (TBP-free TAF(II)-containing)-type HAT complexes (hTFTC, hPCAF, and hSTAGA), TRRP directly interacted with liganded ER alpha, or other NRs. ER alpha transactivation was enhanced by the purified complex in vitro. Antisense TRRAP RNA inhibited estrogen-dependent cell growth of breast cancer cells. Thus, the isolated TFTC-type HAT complex acts as a third class of coactivator complex for NR function.
Mol Cell 2002 Mar
PMID:Nuclear receptor function requires a TFTC-type histone acetyl transferase complex. 2493 68

The pS2 promoter is complex with binding sites for a number of protein factors that may participate in modulating its activity. The pS2 gene was transcriptionally activated by estrogens in HepG2 cells transformed (HepER3) to express the estrogen receptor alpha (ERalpha). The phorbol ester phorbol 12-myristate 13-acetate (PMA) stimulated pS2 expression in both HepER3 and the parental, non-ER-expressing HepG2 cells, although its activity was substantially less in HepG2 cells. The use of selective protein kinase inhibitors suggested that the MAPK pathway contributes substantially to estrogen stimulation of the pS2 promoter. The activator protein 1 (AP1) site at -332 to -338 in the pS2 promoter had a dominant role in the response to both estrogens and PMA, although the estrogen response element at -393 to -405 was essential to mediate the response to estrogen. The potentiation of pS2 promoter activity by the AP1 motif in response to estrogen was dependent on the ligand binding domain of ERalpha. Furthermore, the presence of an intact AP1 element in the pS2 promoter sustained suppression of pS2 promoter activity by an LXXLL peptide. In summary, the data suggest that the effect of estrogen is mediated through a cross-talk between the estrogen-responsive element and the AP1 response element and that ERalpha plays a crucial role in mediating the effect of both estrogen and PMA.
Mol Pharmacol 2002 Jun
PMID:pS2 Gene expression in HepG2 cells: complex regulation through crosstalk between the estrogen receptor alpha, an estrogen-responsive element, and the activator protein 1 response element. 1202 87

Melatonin inhibits the proliferation of estrogen receptor alpha (ERalpha)-positive (MCF-7), but not ERalpha-negative (MDA-MB-231) breast cancer cells. Here, we assessed the effect of MT(1) melatonin receptor stable overexpression in MCF-7 and MDA-MB-231 breast cancer cells on the growth-suppressive effects of melatonin. Parental and vector-transfected MCF-7 cells demonstrated a modest, but significant, growth-suppressive response to melatonin; however, melatonin treatment of MT(1)-transfected MCF-7 cells resulted in significantly enhanced growth-suppression. This response was blocked by an MT1/MT2 melatonin receptor antagonist. Interestingly, MT(1)-overexpression did not induce a melatonin-sensitive phenotype in melatonin-insensitive MDA-MB-231 cells. Finally, Northern blot analysis demonstrated an enhanced inhibition of ERalpha mRNA expression and an enhanced induction of pancreatic spasmolytic polypeptide (pS2) by melatonin in MT(1)-transfected MCF-7 cells relative to vector-transfected MCF-7 cells. These data suggest the involvement of the MT(1) melatonin receptor in mediation of melatonin effects on growth-suppression and gene-modulation in breast cancer cells.
Mol Cell Endocrinol 2002 Jun 28
PMID:MT(1) melatonin receptor overexpression enhances the growth suppressive effect of melatonin in human breast cancer cells. 1208 76

Estrogen (E) and progesterone exert profound influence on development and reproduction. In vitro, steroid receptor coactivators (SRCs) are nuclear proteins that interact with DNA-bound steroid receptors to potentiate their transcriptional efficiency. We examined the effects of antisense oligonucleotides to SRC-1, SRC-2, and SRC-3 on female sexual behavior and steroid receptor-mediated transcription. Rat (r) SRC-1, rSRC-2, and rSRC-3 genes were cloned. Our results reveal a significant inhibitory effect by antisense (AS) to SRC-1 and SRC-2, but not SRC-3, on hormone-induced reproductive behavior. Importantly, sexual behavior was attenuated through estrogen receptor alpha (ERalpha)-dependent, rather than progesterone receptor (PR)-dependent, transcription, as E failed to induce the synthesis of PR content in the medial basal hypothalamus, and immunoreactive PR in the ventromedial nucleus were depleted in tissue from rSRC-1-AS- and rSRC-2-AS-treated, but not rSRC-3-AS-treated, rats primed with E. Consistent with interruption of ERalpha-induced transcription, high dose of E and epidermal growth factor alone failed to induce sexual behavior in females treated with either rSRC-1-AS or SRC-2-AS. Immunoreactive SRC-1 and SRC-2, but not SRC-3, proteins were abundant in the ventromedial nucleus, thus demonstrating that the biological activities of hypothalamic steroid receptors are selectively regulated by regional distribution of specific SRCs. As SRC-1 knockout mice have only a slight loss in reproductive function, the possibility that genetic adaptation occurs during development was tested. Mouse (m) SRC-1-AS suppressed lordosis in wild-type, but not SRC-1, knockout mice, whereas mSRC-2-AS suppressed behavior in both genotypes. mSRC-3-AS had no effect in either genotype, and SRC-3 knockout mice exhibited full receptivity. Collectively, the findings clearly implicate dual regulation of ERalpha-dependent function by SRC-1 and SRC-2 in the intact female brain. In the genetic, but not acute, absence of SRC-1, up-regulation of SRC-2 serves as a critical adaptive mechanism during female development.
Mol Endocrinol 2002 Jul
PMID:Acute disruption of select steroid receptor coactivators prevents reproductive behavior in rats and unmasks genetic adaptation in knockout mice. 1208 47

Gender-related differences in the unstimulated and estrogen-induced activation of the mitogen-activated protein kinases (MAPKs) ERK1 and ERK2, cell proliferation, and cell death were examined using rat cortical astrocytes in culture. Females have higher unstimulated levels of phosphorylated ERK1 and ERK2 than males. 17beta-Estradiol (E(2)) decreases activation of ERK1 and ERK2, with females showing a greater response than males. Further, E(2) results in more inhibition of DNA synthesis and greater increase in cell death in females than in males. The inhibitory effects of E(2) on DNA synthesis are mimicked and enhanced by a specific MAPK kinase (MEK) inhibitor, PD98059. Finally, the inhibitory effects of E(2) are blocked by the estrogen receptor antagonist tamoxifen in astrocytes from females but not males, with ER-alpha (estrogen receptor alpha) present in the former but not the latter. Taken together, these results suggest that the sex differences in unstimulated and estrogen-modulated activation of MAPKs may result in differential regulation of cell proliferation and death in astrocytes and possibly contribute to sexual dimorphisms in brain development.
Brain Res Mol Brain Res 2002 Jun 30
PMID:Sex-related differences in MAPKs activation in rat astrocytes: effects of estrogen on cell death. 1210 87


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