Development and characterization of a cell line that stably expresses an estrogen-responsive luciferase reporter for the detection of estrogen receptor agonist and antagonists.

Recently several advisory committees (EDSTAC, ICCVAM) have recommended that stable estrogen-dependent gene expression assays be developed for screening chemicals for estrogenic activity because of the high degree of specificity of the response and potential for use in a high-throughput mode. In this paper we describe a specific, sensitive assay developed for screening chemicals for estrogenic and antiestrogenic activities. T47D human breast cancer cells, which naturally express estrogen receptor (ER) alpha and beta, were stably transfected with a triplet ERE (estrogen-responsive elements)-promoter-luciferase reporter gene construct. The transformed cells were named T47D-KBluc. These cells are sensitive to the potent estrogens, 17beta-estradiol, ethynyl estradiol, and diethylstibesterol, and well-characterized weaker environmental estrogens like genistein, HPTE (an estrogenic pesticide metabolite), and 4-nonylphenol. The EC50 for estradiol was about 0.01 nM, reaching maximal induction at 0.1 nM. The antiestrogen, ICI 182,780, was able to completely inhibit the induction of luciferase expression by 0.1 nM estradiol at 10 nM, with an IC50 of 1 nM. In addition, we were able to replicate, in this in vitro assay, the observation that low concentrations of cadmium were able to induce estrogen-dependent gene expression, an effect that was completely inhibited by the potent antiestrogen ICI 182,780. The potent glucocorticoid receptor agonist, dexamethasone, was without effect as an ER agonist at concentrations up to 10 nM, whereas the potent androgen, dihydrotestosterone (DHT), showed no induction at concentration of 50 microM, but was a partial agonist at high concentrations of 0.2 mM and above. In summary, we have developed a specific, sensitive estrogen-responsive gene expression assay in a stable cell line that could possibly be adapted for high throughput screening of large numbers of chemicals for estrogenic and antiestrogenic activity. In addition, herein we also provide key protocol recommendations necessary to identify and eliminate common problems encountered in in vitro screening for estrogenicity.

A novel cell line, MDA-kb2, that stably expresses an androgen- and glucocorticoid-responsive reporter for the detection of hormone receptor agonists and antagonists.

The U.S. Environmental Protection Agency has proposed that in vitro assays for estrogen receptor (ER)- and androgen receptor (AR)-mediated actions be included in a Tier-I screening battery to detect hormonally active chemicals. Herein we describe the development of a novel stable cell line, MDA-kb2, for screening of androgen agonist and antagonists and to characterize its specificity and sensitivity to endocrine-disrupting chemicals. The breast cancer cell line, MDA-MB-453, was stably transformed with the MMTV.luciferase.neo reporter gene construct. Since both GR and AR are present in the MDA-MB-453 cells, and both receptors can act through the MMTV promoter, compounds that act through either AR or GR activate the MMTV luciferase reporter. As expected, AR agonists such as dihydrotestosterone (DHT), and GR agonists such as dexamethasone (DEX), corticosterone, and aldosterone induce luciferase expression at appropriate concentrations. DHT consistently produced 3-9-fold induction at concentrations from 0.1 to 10 nM. At 1 to 1000 nM, DEX induced luciferase activity 1.3-19.5-fold. To distinguish AR- from GR-mediated ligands, chemicals were assayed concurrently with the antiandrogen, hydroxyflutamide (OHF), which blocks AR- but not GR-mediated responses. In addition, known AR antagonists, including hydroxyflutamide, vinclozolin, vinclozolin metabolites M1 and M2, p,p'-DDE, and linuron inhibited DHT-induced luciferase gene expression at appropriate concentrations in this system. We have found that these cells are relatively easy to culture and maintain. Responsiveness was monitored over time and was stable for more than 80 passages. Some advantages of this assay are that it is relatively rapid (2 days), eliminates the need for transfection, can be conducted in a 96-well plate format, and produces consistent reproducible results. In summary, we have developed a cell line that can be used to screen chemicals, not just for AR- but for GR-mediated activities as well.

Haloacid induced alterations in fertility and the sperm biomarker SP22 in the rat are additive: validation of an ELISA.

Dibromoacetic acid (DBA) and bromochloroacetic acid (BCA) are prevalent disinfection by-products of drinking water that produce defects in spermatogenesis and fertility in adult rats. Previously we demonstrated that BCA compromises the fertility of cauda epididymal rat sperm and SP22, a sperm membrane protein that is highly correlated with the fertility of these sperm. Herein, we administered DBA and BCA, individually and in combination, to determine whether fertility and levels of SP22 on sperm were diminished in an additive fashion. Moreover, we wished to validate an immunoassay for quantitation of SP22. In a dose finding study, animals were exposed by oral gavage daily for 14 days to: BCA alone at 1.6, 4, and 8 mg/kg; DBA at equimolar levels of 2, 5, and 10 mg/kg; and two binary mixtures of 1.6 mg/kg BCA + 2 mg/kg DBA and 4 mg/kg BCA + 5 mg/kg DBA. The ED(50)s for the decrease in SP22 quantified by two-dimensional SDS-PAGE were 7.2 and 4.6 mg/kg for DBA and BCA. The ED(50)s for the decrease in SP22 quantified by ELISA were 8.1 and 5.9 mg/kg for DBA and BCA. The definitive study consisted of 2 and 4 mg/kg DBA, 1.6 and 3.2 mg/kg BCA, and a 2 mg/kg DBA + 1.6 mg/kg BCA mixture. The ED(50)s for decreases in fertility assessed by intrauterine insemination were 3.5 mg/kg and 2.7 mg/kg for DBA and BCA. Immunolocalization of SP22 in spermatocytes and spermatids, as well as on the cytoplasmic droplet and the equatorial segment of luminal sperm, was decreased by the DBA + BCA mixture. The decrease in SP22 in testicular parenchyma was comparable to that observed for sperm extracts. Based on 2D SDS-PAGE, ELISA, or fertility the haloacid-induced decreases in SP22 or fertility were additive or synergistic. The correlation between SP22 levels by ELISA and fertility was r(2) = 0.72 compared to 0.82 for SP22 levels by 2D SDS-PAGE and fertility, validating SP22 quantitation by ELISA.

Localization of the sperm protein SP22 and inhibition of fertility in vivo and in vitro.

We previously established that levels of the sperm membrane protein, SP22, are highly correlated with the fertility of sperm from the cauda epididymidis of rats exposed to both epididymal and testicular toxicants, and that a testis-specific SP22 transcript is expressed in postmeiotic germ cells. In this study, polyclonal and monoclonal antibodies were generated to study the expression of SP22 in the testis and epididymis, and to determine whether SP22 plays a coincidental or causal role in fertility. Polyclonal antiserum was raised in sheep against full-length recombinant rat SP22 (rSP22). Hybridoma clones were generated from mice immunized with rSP22 and boosted with native SP22; positive clones were used for ascites production. Immunoblots indicated that affinity-purified anti-rSP22 immunoglobulin (Ig) and ascites Ig recognized denatured and native SP22, respectively. Linear epitope mapping of the 189-amino acid SP22 sequence revealed 3 distinct peptide sequences recognized by anti-rSP22 Ig, and 1 sequence recognized by ascites Ig. Cytoplasm of round spermatids and heads of elongating/elongated spermatids immunostained with both anti-rSP22 and ascites antibodies. Isolated rete testis sperm revealed discrete staining over the cytoplasmic droplet, whereas staining was apparent over the equatorial segment of the head by the time sperm reached the caput epididymidis. Clear cells were, interestingly, immunostained along the length of the epididymis. Ascites Ig and anti-SP22 Ig each recognized the equatorial segment of sperm heads from rat, hamster, bull, rabbit, and human. Ascites Ig and affinity-purified anti-rSP22 Ig each significantly inhibited the fertility of cauda epididymal sperm from the rat in vivo, as well as the fertilization rates of cauda epididymal sperm in vitro. Moreover, affinity-purified anti-rSP22 significantly inhibited in vitro fertilization of both zona-intact and zona-free hamster oocytes, suggesting that SP22 may play a role in both the zona penetration and membrane fusion steps of fertilization.

Differences in sensitivity but not selectivity of xenoestrogen binding to alligator versus human estrogen receptor alpha.

Reproductive abnormalities in alligators exposed to contaminants in Lake Apopka, Florida, USA represent a clear example of endocrine disruption in wildlife. Several of these contaminants that are not able to bind to mammalian estrogen receptors (such as atrazine and cyanazine) have previously been reported to bind to the alligator estrogen receptor from oviductal tissue. Binding of known Lake Apopka contaminants to full length estrogen receptors alpha from human (hERalpha) and alligator (aERalpha) was assessed in a side-by-side comparison within the same assay system. Baculovirus-expressed recombinant hERalpha and aERalpha were used in a competitive binding assay. Atrazine and cyanazine were not able to bind to either receptor. p,p'-Dicofol was able to bind to aERalpha with a concentration inhibiting 50% of binding (IC50) of 4 microM, while only partially displacing 17beta-estradiol (E2) from hERalpha and yielding a projected IC50 of 45 microM. Chemicals that only partially displaced E2 from either receptor, including some dichlorodiphenyltrichloroethane (DDT) metabolites and trans-nonachlor, appeared to have higher affinity for aERalpha than hERalpha. p,p'-Dicofol-mediated transcriptional activation through aERalpha and hERalpha was assessed to further explore the preferential binding of p,p'-dicofol to aERalpha over hERalpha. p,p'-Dicofol was able to stimulate transcriptional activation in a similar manner with both receptors. However, the in vitro results obtained with p,p'-dicofol were not reflected in an in vivo mammalian model, where Kelthane (mixed o,p'- and p,p'-dicofol isomers) did not elicit estrogenic effects. In conclusion, although there was no evidence of exclusively species-specific estrogen receptor binders, some xenoestrogens, especially p,p'-dicofol, had a higher affinity for aERalpha than for hERalpha.

Identification of estrogenic compounds emitted from the combustion of computer printed circuit boards in electronic waste.

Rapid changes in technology have brought about a surge in demand for electronic equipment. Many of these products contain brominated flame-retardants (BFRs) as additives to decrease the rate of combustion, raising concerns about their toxicological risk. In our study, emissions from the combustion of computer-printed circuit boards were evaluated in the T47D-KBluc estrogen-responsive cell line at a series of concentrations. There was significant activity from the emission extract when compared to the positive control, 0.1 nM estradiol. After HPLC fractionation, GC/MS identified ten chemicals which included bisphenol A; the brominated derivates mono-, di-, and tribisphenol, triphenyl phosphate, triphenyl phosphine oxide, 4'-bromo-[1,1'-biphenyl]-4-ol,3,5-dibromo-4-hydroxybiphenyl,3,5-dibromo-2-hydroxybiphenyl, and the oxygenated polyaromatic hydrocarbon benzanthrone. Commercially available samples of these ten compounds were tested. The compound 4'-bromo-[1,1'-biphenyl]-4-ol resulted in dose-dependent significant increases for luciferase activity at concentrations ranging from 0.1 to 10 microM in the T47D-KBluc assay. The chemical also demonstrated an affinity for binding to the estrogen receptor (ER) with an IC50 of 2 x 10(-7) M. To determine the uterotrophic activity, three doses (50, 100, and 200 mg/kg/day) of 4'-bromo-[1,1'-biphenyl]-4-ol were administered to adult ovariectomized Long-Evans rats for 3 days. Treatment of the animals with 200 mg/ kg/day showed an increase in uterine weight Hence one new chemical, released by burning of electrical wastes, was identified which displays estrogenic activity both in vitro and in vivo. However, it was about 1000-fold less potent than ethynyl estradiol.