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S F Arnold

Publications and source records attributed to S F Arnold.

At least 19 recordsLinked to original sources
PubMed1999

Identification of bone morphogenetic proteins and their receptors in human breast cancer cell lines: importance of BMP2.

The most frequent site of breast cancer metastasis is bone suggesting that some breast cancers express proteins that facilitate this process. We evaluated whether a highly metastatic breast cancer cell line, MDA-MB-231, and a less metastatic breast cancer cell line, MCF-7, contain bone morphogenetic proteins (BMP). Semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) demonstrated that MDA and MCF-7 cells contain mRNAs for BMP receptors IA, IB and II. RT-PCR indicated the presence of mRNAs for BMPs 2 and 3 but not 4 and 7 in breast cells. Using a RT-PCR strategy with molecular beacons, we found that the mRNA for BMP2 in MDA cells was decreased by 75% after a sublethal dose of radiation. An ELISA using an antibody specific for BMP2 demonstrated that BMP2 protein was reduced after radiation of MDA cells. The mRNA for BMP2 was expressed to a lesser extent in MCF-7 cells than MDA cells and was not altered after radiation treatment of MCF-7 cells as demonstrated by molecular beacon RT-PCR. Recombinant human BMP2 decreased the proliferation of MDA cells to a greater extent than MCF-7 cells. These results expand the number of tissues that contain BMPs and demonstrate the effect of this signalling pathway of the growth state of these tissues.

Bone Morphogenetic Protein Receptors↗
PubMed1999

Comparison of short-term estrogenicity tests for identification of hormone-disrupting chemicals.

The aim of this study was to compare results obtained by eight different short-term assays of estrogenlike actions of chemicals conducted in 10 different laboratories in five countries. Twenty chemicals were selected to represent direct-acting estrogens, compounds with estrogenic metabolites, estrogenic antagonists, and a known cytotoxic agent. Also included in the test panel were 17beta++-estradiol as a positive control and ethanol as solvent control. The test compounds were coded before distribution. Test methods included direct binding to the estrogen receptor (ER), proliferation of MCF-7 cells, transient reporter gene expression in MCF-7 cells, reporter gene expression in yeast strains stably transfected with the human ER and an estrogen-responsive reporter gene, and vitellogenin production in juvenile rainbow trout. 17beta-Estradiol, 17alpha-ethynyl estradiol, and diethylstilbestrol induced a strong estrogenic response in all test systems. Colchicine caused cytotoxicity only. Bisphenol A induced an estrogenic response in all assays. The results obtained for the remaining test compounds--tamoxifen, ICI 182.780, testosterone, bisphenol A dimethacrylate, 4-n-octylphenol, 4-n-nonylphenol, nonylphenol dodecylethoxylate, butylbenzylphthalate, dibutylphthalate, methoxychlor, o,p'-DDT, p,p'-DDE, endosulfan, chlomequat chloride, and ethanol--varied among the assays. The results demonstrate that careful standardization is necessary to obtain a reasonable degree of reproducibility. Also, similar methods vary in their sensitivity to estrogenic compounds. Thus, short-term tests are useful for screening purposes, but the methods must be further validated by additional interlaboratory and interassay comparisons to document the reliability of the methods.

DDT↗
PubMed1999

Regulation of transforming growth factor beta1 by radiation in cells of two human breast cancer cell lines.

We have investigated the mechanisms by which radiation inhibits proliferation of human breast cancer cells in culture. Radiation, within the dose range used for treatment of humans, decreased the rate of proliferation of estrogen-independent MDA-MB-231 cells more effectively than it did that of estrogen-dependent MCF-7 cells. The rate of proliferation of MDA-MB-231 cells was also inhibited to a greater extent than that of MCF-7 cells by purified TGFB1. Using an ELISA specific for activated TGFB1, we found that conditioned medium from irradiated MDA-MB-231 or MCF-7 cells contained twofold more TGFB1 than that from nonirradiated cells. Conditioned medium from irradiated breast cancer cells, but not from nonirradiated cells, inhibited the growth of untreated MDA-MB-231 cells. The inhibitory activity was blocked by an anti-TGFB1 neutralizing antibody. An approximately twofold increase in the TGFB1 mRNA in irradiated cells compared to controls was found using semiquantitative reverse-transcriptase PCR. Last, the mRNA for insulin-like growth factor binding protein 3, a reported target of the cell inhibitory activity of TGFB1, was increased threefold upon irradiation. Our results demonstrate that the TGFB1 is increased after irradiation and that the activation of the TGFB1 signaling pathway may sensitize cells to the effects of radiation.

Base Sequence↗
PubMed1997

Evaluation of clinical and environmental anti-estrogens with human estrogen receptor expressed in Saccharomyces cerevisiae: a novel role for ABC-cassette transporters in mediating anti-estrogenic activity.

The effectiveness of anti-estrogens in treating estrogen-dependent diseases is limited by the acquired resistance of some diseases to anti-estrogens. This effect could occur by the export of anti-estrogens by cell membrane transport proteins. To study this phenomenon we have expressed human estrogen receptor (hER) and an estrogen-sensitive reporter in wild-type yeast and two transport-defective strains. In the wild-type strain, the most effective anti-estrogen was nafoxidine. 4-Hydroxy tamoxifen and clomiphene were inactive whereas tamoxifen had significant inhibitory activity in the wild-type strain. Using a strain missing the ABC-cassette transporter Snq2, clomiphene had anti-estrogenic activity. 4-Hydroxy tamoxifen had anti-estrogenic activity only in yeast lacking the transporter Pdr5. Whole cell binding assays indicated that 4-hydroxy tamoxifen is exported by Pdr5. Environmental chemicals such as polychlorinated biphenyls function as partial estrogens and anti-estrogens in yeast. In the absence of Pdr5 or Snq2, the estrogenic activity of 4-hydroxy, 2',4',6'-trichloro biphenyl (3-PCB) was substantially reduced in comparison to its activity in the wild-type strain. Interestingly, the antiestrogenic activity of 3-PCB was equivalent in the wild-type and transporter-defective strains. Our results suggest a novel role for ABC-cassette transporters in regulating the activity of clinical and environmental anti-estrogens.

ATP-Binding Cassette Transporters↗
PubMed1997

Synergistic responses of steroidal estrogens in vitro (yeast) and in vivo (turtles).

Many environmental agents exert estrogenic activity. Previous studies from our laboratories demonstrated that certain combinations of environmental estrogens (i) reverse the sex of male turtle embryos in a synergistic manner (Bergeron et al., (1994) Environ. Hlth Perspect. 102, 780-782), and (ii) synergistically transactivate the human estrogen receptor (hER) in yeast and mammalian cells (Arnold et al., (1996) Science 272, 1489-1492). Because our findings with synthetic estrogens suggested that combinations of naturally-occurring steroidal estrogens might also produce synergistic activity of the ER, we used the same model systems to measure the activity of combinations of steroidal estrogens. The activity of combinations of estrone, estradiol-17beta or estradiol-17alpha in yeast strains expressing hER was synergistic at submaximal concentrations of both estrogenic compounds. However, synergy was not observed with mixtures of estrogens when the concentration of one of the estrogens alone was maximally active in yeast. Ligand-binding assays in yeast performed with various radiolabeled estrogens suggested that multiple estrogens may interact with the receptor. The estrogen-dependent process of sex-reversal of turtle embryos incubated at a male-producing temperature was used to determine whether steroidal estrogens also had synergistic activity in vivo. In this instance, a combination of estriol and estradiol-17beta was effective in reversing the gonadal sex of turtle embryos from males to females in a synergistic manner. Our results suggest that the synergy of some combinations of estrogens, synthetic or steroidal, may play a role in the estrogen-dependent process of sexual development in certain species.

Animals↗
PubMed1997

Transcriptional activation of the human estrogen receptor by DDT isomers and metabolites in yeast and MCF-7 cells.

In this study, we determined whether the DDT isomers p,p'-DDT [1,1,1,-trichloro-2,2-bis(p-chlorophenyl)ethane], o,p'-DDT [1,1,1-trichloro-2(p-chlorophenyl)-2-(o-chlorophenyl)ethane], and their metabolites p,p'-DDD [1,1-dichloro-2,2-bis(p-chlorophenyl)ethane], o,p'-DDD [1,1-dichloro-2-(p-chlorophenyl)-2-(o-chlorophenyl)ethane], p,p'-DDE [1,1,-dichloro-2,2-bis(p-chlorophenyl)ethylene], o,p'-DDE [1,1-dichloro-2-(p-chlorophenyl)-2-(o-chlorophenyl)ethylene], and p,p'-DDA [2,2-bis(p-chlorophenyl)acetic acid], could bind to and transcriptionally activate the human estrogen receptor (hER). Novel results from competitive binding assays showed that o,p'-DDD, o,p'-DDE, and p,p'-DDT, as well as the established environmental estrogen o,p'-DDT, were able to bind specifically to the hER with approximately 1000-fold weaker affinities for the hER than that of estradiol. In contrast, only o,p'-DDT, but not p,p'-DDT, bound to the rat estrogen receptor. Moreover, two yeast expression-reporter systems, constructed to test if the DDT isomers and metabolites could transcriptionally activate the hER, demonstrated that an o,p'-DDT metabolite could transactivate the hER or LexA-hER fusion protein with just a 140- to 300-fold weaker potency than that of estradiol. The DDT isomers and metabolites that bound the hER in vitro triggered estrogen receptor-mediated transcription of the lacZ reporter gene in the yeast systems. Furthermore, the DDT isomers and metabolites that transactivated the hER elicited an additive response when given together or with estradiol. The DDT isomers and metabolites that triggered transcription of the yeast expression-reporter systems also stimulated two estrogenic endpoints in estrogen-responsive MCF-7 cells: the induction of the progesterone receptor and the down-regulation of the hER. Thus, in MCF-7 cells and in yeast expression-reporter systems, certain DDT isomers and metabolites act directly as agonists and transactivate the hER at concentrations found in human tissues.

Animals↗
PubMed1997

o,p'-DDT and its metabolites inhibit progesterone-dependent responses in yeast and human cells.

Using a combination of in vitro assays we have evaluated whether DDT metabolites can interact with the progesterone receptor pathway in yeast expressing human progesterone receptor (hPR) and in T47D human breast cancer cells which express endogenous hPR. In transactivation assays using both yeast and T47D cells, o,p'-DDT and the metabolites p,p'-DDT, o,p'-DDD, p,p'-DDD, o,p'-DDE, p,p'-DDE, p,p'-DDA, and DDOH inhibited progesterone-induced reporter gene activity in a dose-dependent manner. None of the DDT metabolites functioned as hPR agonists. Whole cell competition binding assays using T47D cells indicated that the inhibitory effects of DDT metabolites on progesterone-dependent activites may occur through both hPR-dependent and hPR-independent pathways. Our results and previous reports of DDT metabolites interacting with estrogen and androgen receptors suggests that this class of environmental chemicals may interact with numerous hormone receptor signaling pathways.

Binding, Competitive↗
PubMed1997

Several synthetic chemicals inhibit progesterone receptor-mediated transactivation in yeast.

The human progesterone receptor (hPR) B-form and a progesterone-sensitive reporter were expressed in yeast and used to screen a library of synthetic chemicals for their ability to function as agonists or antagonists of hPR. The transcriptional activity of hPR was not increased in the presence of over 40 individual chemicals. Seven chemicals decreased progesterone-dependent activity in yeast. The most effective chemicals were 6-hydroxychrysene, 1-hydroxypyrene, 4-hydroxy, 2',4',6'-trichloro biphenyl, and 4-hydroxy, 2',3',4',5'-tetrachloro biphenyl. The decrease of progesterone-mediated transactivation strongly correlated with their displacement of [3H]progesterone from hPR. The absence of the hydroxyl group on the above chemicals completely abolished their inhibitory activity. The other chemicals which decreased progesterone activity were endosulfan II, endosulfan sulfate, and lindane. These chemicals did not inhibit [3H]progesterone binding, suggesting that they inhibit progesterone action by interacting with a region of hPR distinct from binding [3H]progesterone or by a mechanism independent of hPR. These results highlight the utility of yeast for screening hormonally-active chemicals. In addition, hydroxylation appears to be essential for the interaction of some chemicals with hPR.

Humans↗
PubMed1997

Identification and characterization of estrogen and progesterone receptors from the oviduct of the American alligator (Alligator mississippiensis).

A protein extract prepared from the egg shell fiber-secreting region of the oviduct of Alligator mississippiensis was assayed for the presence of receptors for estrogen and progesterone. In the presence of [3H]-estradiol-17 beta, the extract contained an estrogen-binding activity which reached equilibrium at 25 degrees C in 1 h. Scatchard analysis demonstrated that a single estrogen-binding activity was present in the extract with a Kd of 0.5 nM for [3H]estradiol-17 beta. A steroid specificity competition assay showed the estrogen binding activity strongly recognized estradiol-17 beta and diethylstilbestrol (DES) and weakly interacted with estrone, estriol, estradiol-17 alpha, and dihydrotestosterone (DHT). The estrogen binding activity did not recognize testosterone, dexamethasone or progesterone. The extract exhibited a DNA-binding activity that recognized an estrogen response element in a gel mobility shift assay. We have also identified a high affinity binding activity in the extract that specifically recognized the synthetic progestin R5020 with a Kd of 0.9 nM. This binding activity recognized 17 alpha-estradiol, dexamethasone, testosterone, and estriol. This activity did not recognize DHT, DES, or estradiol-17 beta. These data suggest the presence of estrogen and progesterone receptors in the oviduct of the alligator.

Alligators and Crocodiles↗
PubMed1997

Inhibition of 17 beta-estradiol and progesterone activity in human breast and endometrial cancer cells by carbamate insecticides.

Using a combination of in vitro assays we have examined the capacities of contemporary-exposure chemicals to modulate human estrogen and human progesterone receptor (hER and hPR) activity in human breast and endometrial cancer cells. The carbamate insecticides aldicarb, Baygon (propoxur), bendiocarb, carbaryl, methomyl, and oxamyl were used in this study. The carbamates alone weakly activated estrogen- or progesterone-responsive reporter genes in breast and endometrial cancer cells. All of the carbamates decreased estradiol- or progesterone-induced reporter gene activity in the breast and endometrial cancer cells. In whole cell competition binding assays, the carbamates demonstrated a limited capacity to displace radiolabeled estrogen or progesterone from ER or PR. Based on the results presented here, the carbamate insecticides may represent a class of chemicals which function through a mechanism separate from ligand-binding and, therefore, may act as general endocrine modulators in mammalian cells.

Binding, Competitive↗
PubMed1997

The estrogenic and antiestrogenic activities of phytochemicals with the human estrogen receptor expressed in yeast.

We have used the expression of the human estrogen receptor (hER) and two estrogen response elements linked to the lacZ gene in yeast (YES) to study the estrogenic and antiestrogenic activities of various phytochemicals. Coumestrol, alpha-zearalenol, or genistein could produce beta-galactosidase activity comparable to estradiol, but these required concentrations 100 to 1000-fold greater than estradiol. These compounds did not possess antiestrogenic activity. Narigenin, kaempferide, phloretin, biochanin A, flavone, or chrysin only partially induced beta-galactosidase activity in the YES at any concentration tested. When narigenin, kaempferide, or phloretin was given concurrently with estradiol, the estradiol-dependent beta-galactosidase activity was not inhibited by more than 50%. However, biochanin A, flavone, or chrysin could inhibit the activity of estradiol in a dose-response manner with IC50 values of 500 nM, 2 microM, and 10 microM, respectively. Combinations of biochanin A, chrysin, and flavone decreased estradiol-dependent beta-galactosidase activity in an additive fashion. Similar to the antiestrogens tamoxifen or ICI 182, 780, the antiestrogenic activity of these compounds with the exception of chrystin involved the disruption of hER dimerization, as demonstrated in the yeast two-hybrid system. Biochanin A, chrysin, or flavone were less effective in inhibiting the activity of an estrogenic polychlorinated biphenyl than they were inhibiting the activity of estradiol. Interestingly, this latter group of antiestrogenic phytocompounds did not inhibit the estrogenic activity of such phytochemicals as coumestrol or genistein. These results suggest that the antiestrogenic activity of biochanin A and flavone occurs by a mechanism similar to tamoxifen or ICI 182,780. Moreover, it seems that phytochemicals functioning as antiestrogens do not inhibit the activity of all estrogenic chemicals to the same extent. This suggests that conformational changes induced by different estrogens bound to the hER may regulate the antiestrogenic activity of a compound.

Anticarcinogenic Agents↗
PubMed1997

Estradiol-binding mechanism and binding capacity of the human estrogen receptor is regulated by tyrosine phosphorylation.

We have investigated the effects of tyrosine phosphorylation on the estradiol-binding mechanism and binding capacity of the human estrogen receptor (hER). The wild type hER and a point mutant form of the hER, in which tyrosine 537 was mutated to phenylalanine (Y537F hER), were expressed in Sf9 insect cells. The wild type hER, but not the Y537F hER, reacted with a anti-phosphotyrosine monoclonal antibody, indicating that tyrosine 537 was the only tyrosine phosphorylated on the hER. Scatchard and Hill analyses of the the binding interaction of [3H]estradiol with the wild type hER indicated that the addition of millimolar phosphotyrosine, but not tyrosine, phosphate, or phosphoserine, abolished the cooperative binding mechanism of the hER. These observations are consistent with the idea that phosphotyrosine blocks dimerization and site-site interactions between the hER monomers. The wild type hER bound 10-fold more [3H]estradiol than the Y537F hER. Treatment of the purified wild type hER with a tyrosine phosphatase decreased the binding capacity of the hER by approximately 90%, whereas, a serine/threonine phosphatase had no effect. The estrogen-binding capacity of the tyrosine-dephosphorylated hER was completely restored by rephosphorylation of tyrosine 537 with p60c-src, a tyrosine kinase. These results indicate that p60c-src can restore estrogen binding to the tyrosine-dephosphorylated hER and that dimerization and cooperative site-site interaction of the hER occur via a phosphotyrosine-binding interaction.

Dimerization↗
PubMed1997

In vitro synergistic interaction of alligator and human estrogen receptors with combinations of environmental chemicals.

The effect of mixtures of environmental chemicals with hormonal activity has not been well studied. To investigate this phenomenon, the estrogen receptor (ER) from the American alligator (aER) or human (hER) was incubated with [3H]17beta-estradiol in the presence of selected environmental chemicals individually or in combination. The environmental chemicals included the insecticide chlordane, which has no estrogenic activity, and the pesticides dieldrin and toxaphene, which have very weak estrogenic activity. Chlordane, dieldrin, and toxaphene individually demonstrated no appreciable displacement of [3H]17beta-estradiol from aER and hER at the concentration tested. A combination of these chemicals inhibited the binding of [3H]17beta-estradiol by 20 to 40%. Alachlor, a chemical recently discovered to have weak estrogenic activity, also displaced [3H]17beta-estradiol more effectively in combination with dieldrin than alone. These results indicate that combinations of some environmental chemicals inhibit [3H]17beta-estradiol binding in a synergistic manner. This suggests that the ER may contain more than one site for binding environmental chemicals. The possibility that the ER binds multiple environmental chemicals adds another level of complexity to the interaction between the environment and the endocrine system.

Acetamides↗
PubMed1996

Inhibition of progesterone receptor activity in yeast by synthetic chemicals.

Numerous synthetic chemicals have estrogenic activity by interacting with the estrogen receptor. In this report, we test the hypothesis that some estrogenic chemicals may also modulate the human progesterone receptor (hPR) signaling pathway. This was evaluated by examining synthetic chemicals for their ability to modulate the activity of hPR expressed in yeast. The transcriptional activity of hPR was not increased in the presence of several synthetic chemicals. However, the estrogenic chemicals p-nonylphenol and 4-tert-octyphenol, and pentachlorophenol, effectively inhibited the activity of the hPR in yeast. Competition binding studies indicated these chemicals effectively competed with radiolabeled R5020, a synthetic progestin, for binding to the hPR in yeast. These results indicate that some synthetic chemicals directly inhibit the activity of hPR in yeast. The observations that some estrogenic chemicals can also inhibit hPR activity suggest a potential mechanism for the reported potent estrogenic activities of these chemicals.

Binding, Competitive↗
PubMed1996

The anti-estrogenic activity of selected polynuclear aromatic hydrocarbons in yeast expressing human estrogen receptor.

Polynuclear aromatic hydrocarbons (PAH) represent a large class of chemicals present in environment. We have used yeast strain ER(wt) expressing human estrogen receptor (hER) and an estrogen-sensitive reporter to characterize the estrogenic or anti-estrogenic activities of 21 PAHs. The PAHs did not exhibit estrogenic activity in yeast strain ER(wt). Four of the PAHs, dibenz[a,h]anthracene, 6-hydroxy-chrysene, 2,3-benzofluorene, and benzo(a)pyrene, inhibited estradiol-dependent reporter activity in strain ER(wt). A mutant hER lacking the amino terminus expressed in yeast was inhibited by the four PAHs to a lesser extent than the full-length hER. 6-hydroxy-chrysene, 2,3-benzofluorene, and benzo(a)pyrene, but not dibenz[a,h]anthracene, weakly displaced [3H]estradiol from the hER in a competition binding assay. A strong correlation between the inhibition of [3H]estradiol-binding from the hER and the reduction of hER-mediated transactivation in yeast was not observed. These observations suggest that the PAHs dibenz[a,h]-anthracene, 6-hydroxy-chrysene, 2,3-benzofluorene, and benzo(a)pyrene may antagonize activity in yeast by binding to an anti-estrogen binding site on the hER or by mechanisms independent of the hER.

Binding, Competitive↗
PubMed1996

The inhibition of estrogen receptor-mediated responses by chloro-S-triazine-derived compounds is dependent on estradiol concentration in yeast.

The chloro-S-triazine derived compounds atrazine, atrazine desisopropyl, cyanazine, and simazine are commonly used herbicides. These compounds do not have estrogenic activity in yeast expressing human estrogen receptor (hER) and an estrogen-sensitive reporter. In the presence of a concentration of estradiol (20 nM) that induced maximal reporter activity in yeast, the triazines did not inhibit reporter activity. However, the triazines decreased reporter activity in a dose dependent manner in the presence of a submaximal concentration of estradiol (0.5 nM). The estradiol-dependent activity of a mutant hER lacking the amino terminus was not inhibited by the triazines in yeast. Competition binding assays demonstrated that the triazines displaced radiolabeled estradiol from recombinant hER. These results suggest that the ability of the triazines to inhibit estrogen receptor-mediated responses in yeast occur through their interaction with hER and is dependent on the concentration of estradiol.

Atrazine↗
PubMed1996

Synergistic activation of estrogen receptor with combinations of environmental chemicals.

Certain chemicals in the environment are estrogenic. The low potencies of these compounds, when studied singly, suggest that they may have little effect on biological systems. The estrogenic potencies of combinations of such chemicals were screened in a simple yeast estrogen system (YES) containing human estrogen receptor (hER). Combinations of two weak environmental estrogens, such as dieldrin, endosulfan, or toxaphene, were 1000 times as potent in hER-mediated transactivation as any chemical alone. Hydroxylated polychlorinated biphenyls shown previously to synergistically alter sexual development in turtles also synergized in the YES. The synergistic interaction of chemical mixtures with the estrogen receptor may have profound environmental implications. These results may represent a previously uncharacterized level of regulation of estrogen-associated responses.

Binding, Competitive↗