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

We studied the effect of a number of amino acids on uptake of L-triiodothyronine (T3) in the human choriocarcinoma cell line, JAR. Tryptophan inhibited saturable T3 uptake by about 57% without any significant effect on the non-saturable uptake. Michaelis constant (Km) for T3 uptake was 1.06 +/- 0.15 microM (n = 15) with the corresponding maximum velocity (Vmax) of 24.2 +/- 3.1 pmol/min/mg cellular protein. For tryptophan uptake the Km was 1.31 +/- 0.26 microM (n = 7) and Vmax was 166.4 +/- 35.7 pmol/min/mg protein. The kinetic parameters for both uptake processes were similar to those reported in normal placenta. Uptake of T3 was inhibited by tryptophan but not phenylalanine, but tryptophan uptake was inhibited both by T3 and phenylalanine. Inhibition of T3 uptake by tryptophan was dose dependent, with an inhibition constant (Ki) of 2.9 +/- 0.5 mM. Similarly, tryptophan uptake was inhibited by T3 and phenylalanine in a dose dependent way with Ki values of 4.9 +/- 0.5 microM and 15.6 +/- 4.8 microM respectively. Km for T3 uptake was significantly increased to 1.86 +/- 0.42 microM (n = 4) in the presence of 3 mM unlabelled tryptophan and, similarly, Km for tryptophan uptake was significantly increased to 9.91 +/- 2.57 microM (n = 3) in the presence of 5 microM unlabelled T3. Efflux of T3 was progressively inhibited by increasing concentrations of both ligands, i.e. was saturable. We conclude that there is mutual competitive inhibition between uptake systems for T3 and tryptophan in JAR cells, but the kinetic parameters of cross-inhibition of uptake by the substrates suggest that the carriers are distinct. T3 may be transported in JAR cells by at least two transport systems with differing substrate specificities. We also demonstrated the presence of a saturable membrane carrier mediating the efflux of T3 from the cells which was subject to trans-inhibition by T3 and tryptophan.
Mol Cell Endocrinol 1994 May
PMID:Interactions between transport of triiodothyronine and tryptophan in JAR cells. 939 54

An alternatively spliced mRNA coding for a variant estrogen receptor (ER) missing exon 4 (ERdelta4) was detected in the breast tumor cell line MCF7 and meningioma tissue by using the reversed transcriptase PCR technique. The trans-activational properties of this mutant ER were assessed in embryo carcinoma P19EC and human choriocarcinoma JEG3 cells by co-transfection of the ERdelta4 expression vector with an oxytocin promoter construct containing an estrogen-responsive element. ERdelta4 did not trans-activate the oxytocin promoter in either a hormone-dependent or -independent manner. Co-transfection of ERdelta4 together with the wtER did not show any interference of ERdelta4 on the stimulation of the oxytocin promoter by the wtER. ERdelta4 was translated in vitro. Its capacity to bind estradiol, and the binding of the variant to a synthetic estrogen-responsive element were compared to those of the wild-type receptor. ERdelta4 did not bind to a synthetic estrogen-responsive element, nor did it bind estradiol. Hence, ERdelta4 appears to be a silent variant and we speculate that it is without any role in tumor progression.
Mol Cell Endocrinol 1994 May
PMID:Functional analysis of an alternatively spliced estrogen receptor lacking exon 4 isolated from MCF-7 breast cancer cells and meningioma tissue. 939 58

Selective inhibition of estrogen production with aromatase inhibitors has been found to be an effective strategy for breast cancer treatment. Most studies have focused on inhibitor screening and in vitro kinetic analysis of aromatase inhibition using placental microsomes. In order to determine the effects of different inhibitors on aromatase in the whole cell, we have utilized the human choriocarcinoma cell line, JEG-3 in culture to compare and study three classes of aromatase inhibitors, 4-hydroxyandrostenedione, fadrozole (CGS 16949A), and aminoglutethimide. Fadrozole is the most potent competitive inhibitor and aminoglutethimide is the least potent among the three. However, stimulation of aromatase activity was found to occur when JEG-3 cells were preincubated with aminoglutethimide. In contrast, 4-OHA and fadrozole caused sustained inhibition of aromatase activity in both JEG-3 cells and placental microsomes, which was not reversed even after the removal of the inhibitors. 4-OHA bound irreversibly to the active site of aromatase and caused inactivation of the enzyme which followed pseudo-first order kinetics. However, 4-OHA appears to be metabolized rapidly in JEG-3 cells. Sustained inhibition of aromatase induced by fadrozole occurs by a different mechanism. Although fadrozole bound tightly to aromatase at a site distinct from the steroid binding site, the inhibition of aromatase activity by fadrozole does not involve a reactive process. None of the inhibitors stimulated aromatase mRNA synthesis in JEG-3 cells during 8 h treatment. The stimulation of aromatase activity by AG appeared to be due to stabilization of aromatase protein. According to these results, 4-OHA and fadrozole would be expected to be more beneficial in the treatment of breast cancer patients than AG. The increase in aromatase activity by AG may counteract its therapeutic effect and might be partially responsible for relapse of breast cancer patients from this treatment.
J Steroid Biochem Mol Biol
PMID:Mechanisms of the actions of aromatase inhibitors 4-hydroxyandrostenedione, fadrozole, and aminoglutethimide on aromatase in JEG-3 cell culture. 945 98

Differentiation of trophoblast giant cells in the rodent placenta is accompanied by exit from the mitotic cell cycle and onset of endoreduplication. Commitment to giant cell differentiation is under developmental control, involving down-regulation of Id1 and Id2, concomitant with up-regulation of the basic helix-loop-helix factor Hxt and acquisition of increased adhesiveness. Endoreduplication disrupts the alternation of DNA synthesis and mitosis that maintains euploid DNA content during proliferation. To determine how the mammalian endocycle is regulated, we examined the expression of the cyclins and cyclin-dependent kinases during the transition from replication to endoreduplication in the Rcho-1 rat choriocarcinoma cell line. We cultured these cells under conditions that gave relatively synchronous endoreduplication. This allowed us to study the events that occur during the transition from the mitotic cycle to the first endocycle. With giant cell differentiation, the cells switched cyclin D isoform expression from D3 to D1 and altered several checkpoint functions, acquiring a relative insensitivity to DNA-damaging agents and a coincident serum independence. The initiation of S phase during endocycles appeared to involve cycles of synthesis of cyclins E and A, and termination of S was associated with abrupt loss of cyclin A and E. Both cyclins were absent from gap phase cells, suggesting that their degradation may be necessary to allow reinitiation of the endocycle. The arrest of the mitotic cycle at the onset of endoreduplication was associated with a failure to assemble cyclin B/p34(cdk1) complexes during the first endocycle. In subsequent endocycles, cyclin B expression was suppressed. Together these data suggest several points at which cell cycle regulation could be targeted to shift cells from a mitotic to an endoreduplicative cycle.
Mol Biol Cell 1998 Apr
PMID:Reprogramming the cell cycle for endoreduplication in rodent trophoblast cells. 952 78

The hypothalamic hormone CRH is also expressed in the placentas of humans and higher primates and may play an important role in the regulation of labor. In choriocarcinoma cell lines, activation of cAMP-dependent pathways increases human (h)CRH reporter gene expression. A cAMP-responsive region distinct from the cAMP response element at -220 bp, has been identified between -200 and -99 bp, and a candidate transcription factor was identified in nuclear extracts of human, but not rodent, choriocarcinoma cell lines. This region, which does not contain a canonical cAMP response element (CRE), transfers protein kinase A responsiveness to a heterologous promoter. Electromobility shift assays and methylation and uracil interference studies localized factor binding to a 20-bp region from -128 to -109 bp of the hCRH promoter. This 20-bp fragment exhibited a similar shift in nuclear extracts from both human term placenta and from human JEG-3 cells. Base contacts, identified in interference studies, were confirmed as critical for binding, as a mutation of these bases abolished factor binding. Furthermore, a CRH promoter containing this mutation exhibited a diminished response to forskolin. UV cross-linking demonstrated the protein in nuclear extracts from human, but not rodent, choriocarcinoma cell lines and estimated its size as 58 kDa. Although this factor participates in cAMP-regulated gene expression, competition electrophoretic mobility assays demonstrated that the factor does not bind to a CRE. Furthermore, neither anti-CREB nor anti-ATF2 antibodies alter factor binding. These data identify this 58-kDa protein as the human-specific CRH activator previously identified as a candidate factor contributing to the species-specific expression of CRH in human placenta.
Mol Endocrinol 1998 Aug
PMID:Characterization of a human-specific regulator of placental corticotropin-releasing hormone. 971 48

The time course of incorporation of [14C]arachidonic acid and [3H]docosahexaenoic acid into various lipid fractions in placental choriocarcinoma (BeWo) cells was investigated. BeWo cells were found to rapidly incorporate exogenous [14C]arachidonic acid and [3H] docosahexaenoic acid into the total cellular lipid pool. The extent of docosahexaenoic acid esterification was more rapid than for arachidonic acid, although this difference abated with time to leave only a small percentage of the fatty acids in their unesterified form. Furthermore, uptake was found to be saturable. In the cellular lipids these fatty acids were mainly esterified into the phospholipid (PL) and the triacyglycerol (TAG) fractions. Smaller amounts were also detected in the diacylglycerol and cholesterol ester fractions. Almost 60% of the total amount of [3H]Docosahexaenoic acid taken up by the cells was esterified into TAG whereas 37% was in PL fractions. For arachidonic acid the reverse was true, 60% of the total uptake was incorporated into PL fractions whereas less than 35% was in TAG. Marked differences were also found in the distribution of the fatty acids into individual phospholipid classes. The higher incorporation of docosahexaenoic acid and arachidonic acid was found in PC and PE, respectively. The greater cellular uptake of docosahexaenoic acid and its preferential incorporation in TAG suggests that both uptake and transport modes of this fatty acid by the placenta to fetus is different from that of arachidonic acid.
Mol Cell Biochem 1998 Aug
PMID:Differential distribution and metabolism of arachidonic acid and docosahexaenoic acid by human placental choriocarcinoma (BeWo) cells. 974 26

Two types of endocrine therapy that have been successfully applied to patients with hormone-dependent breast cancer are the non-steroidal antiestrogen tamoxifen, and inhibitors of aromatase, the enzyme that synthesizes estrogens. The major drawback with tamoxifen is that it acts as a partial estrogen-agonist and this is believed to mediate, at least in part, acquired tumor resistance to the drug as well as endometrial hyperplasia and carcinoma in some patients. The newer and more potent antiestrogen ICI 182,780 is a steroidal molecule that is devoid of estrogenic activity. We now report that ICI 182,780 is also an inhibitor of aromatase activity in fibroblasts isolated from the normal human breast as well as other carcinoma cell lines that express aromatase (MCF-7Ca breast cancer and JEG-3 choriocarcinoma). ICI 182,780 (1 microM) did not affect aromatase activity levels in human placental microsomes and only inhibited aromatase activity in each of the cell lines following a prolonged incubation period. In the fibroblasts, inhibition of aromatase activity by ICI 182,780 was shown to be time and dose-dependent. In contrast, tamoxifen and 17beta-estradiol were shown to have no effect on aromatase activity levels. ICI 182,780 inhibited aromatase activity levels with IC50 values of 16.80 nM in MCF-7Ca cells, 125.50 nM in JEG-3 cells and 386.1 nM in breast fibroblasts. These values were compared to those for known aromatase inhibitors, and in each of the cell lines the order of potency was letrozole>4-OHA>anastrozole>ICI 182,780. The inhibition of aromatase activity by ICI 182,780 was sustained even after the antiestrogen was removed from the cells indicating that ICI 182,780 may be remaining bound to the enzyme. Although ICI 182,780 had no effect on the proliferation of the fibroblasts, or JEG-3 cells, it significantly inhibited the growth of MCF-7Ca cells. This growth inhibition appeared to be due to the antiestrogenic activity of ICI 182,780 and not to its aromatase inhibiting effects. ICI 182,780 did not inhibit aromatase activity by down-regulating levels of the aromatase transcript. These results show that in addition to being a potent antiestrogen, ICI 182,780 is also an inhibitor of cellular aromatase activity, and suggest that by interfering with the actions of estrogen by two distinct mechanisms, ICI 182,780 may be a suitable drug for treating patients with hormone-dependent breast cancer.
J Steroid Biochem Mol Biol 1998 Nov
PMID:The steroidal antiestrogen ICI 182,780 is an inhibitor of cellular aromatase activity. 988 86

The CD9 molecule is expressed on human extravillous trophoblasts, which invade the endometrium during implantation and placentation. To elucidate the role of CD9 in trophoblastic function, we investigated the expression of CD9 protein and mRNA in BeWo cells, a human trophoblast-like choriocarcinoma cell line, using immunohistochemistry, Western blotting and reverse transcription-polymerase chain reaction (RT-PCR). When BeWo cells were cultured with anti-CD9 monoclonal antibodies (mAb), their invasion through the extracellular matrices was significantly enhanced in a dose-dependent manner. Cell proliferation and human chorionic gonadotrophin production were unaffected. On the other hand, culture in the presence of mAb against integrins alpha3, alpha5 and beta1, which partially block the interaction with the extracellular matrices, inhibited BeWo cell invasion. Anti-CD9 monoclonal antibody had a stimulatory effect on BeWo cell invasion in the presence of anti-integrin alpha3 antibody. In contrast, it had no effect in the presence of mAb against integrins alpha5 and beta1, which were also highly expressed on BeWo cells. These findings suggest that CD9 has a function connected with the invasive properties of BeWo cells, which is partially mediated by integrin alpha5beta1. This may relate to the involvement of CD9 in trophoblastic invasion.
Mol Hum Reprod 1999 Feb
PMID:CD9 is involved in invasion of human trophoblast-like choriocarcinoma cell line, BeWo cells. 1006 73

Although the regulatory mechanisms controlling alpha and beta human chorionic gonadotrophin (HCG) expression have been investigated in choriocarcinoma cell model systems, little is known about the regulation of HCG subunit synthesis in non-tumourigenic trophoblasts. We therefore investigated alphaHCG mRNA transcription in villous cytotrophoblasts isolated from term placentae and have shown for the first time that the proximal alphaHCG gene promoter is functional in these cells. By establishing conditions which allow efficient transient transfection of immunopurified cells, we have demonstrated that a 363 bp sequence in the proximal 5' flanking region of the alphaHCG gene is sufficient to direct trophoblast-specific expression of a luciferase reporter. After 12-60 h cultivation, an increase in endogenous alphaHCG mRNA expression could be detected, indicating that aggregated villous trophoblasts undergo biochemical differentiation. Concomitantly, we observed induction of alphaHCG promoter-driven luciferase activity, suggesting that the 363 bp sequence of the proximal 5' flanking region is sufficient to direct differentiation-dependent increase of alphaHCG mRNA. Continuous luciferase expression required functional cAMP-response elements (CREs), since deletion of both recognition sequences eliminated differentiation-dependent transcription of the reporter. Elevation of cAMP values increased transcription of the wild-type construct; however, it did not affect promoter activity of the mutant plasmid. Moreover, we have demonstrated that during in-vitro differentiation, CREs interacted with increasing amounts of phosphorylated activating transcription factor/cyclic AMP response element-binding protein (ATF-1/CREB-1) suggesting that these cAMP-dependent DNA-binding factors are major determinants in regulating alphaHCG gene expression in villous trophoblasts.
Mol Hum Reprod 1999 Jun
PMID:Cyclic AMP- and differentiation-dependent regulation of the proximal alphaHCG gene promoter in term villous trophoblasts. 1034 Oct 6

Maintenance of telomeres, commonly through expression of telomerase activity, is necessary but may not be sufficient for human cells to escape from the cellular senescence program and become immortal. We report here that human tumor cells could undergo cellular senescence in the presence of telomerase activity when a specific normal human chromosome was introduced via microcell-mediated chromosome transfer. The cell models studied include SiHa (uterine cervical carcinoma cells expressing E6 and E7 oncoproteins of human papillomavirus type 16) with a transferred chromosome 2, CC1 (choriocarcinoma cells expressing an amino-terminally truncated p53 protein) with a transferred chromosome 7, and JTC-32 (bladder carcinoma cells) with a transferred chromosome 11. The microcell hybrids with the indicated chromosomes ceased to divide after five to 10 population doublings and showed senescence-associated beta-galactosidase activity but still expressed the genes encoding three components of human telomerase, consistent with the retention of telomerase activity. These results are evidence for barriers to human cell immortalization, which involve activation of unidentified senescence-inducing genes that function independently of inactivation of telomerase.
Mol Carcinog 1999 Aug
PMID:Telomerase-independent senescence of human immortal cells induced by microcell-mediated chromosome transfer. 1044 31


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