Tamoxifen (TAM) is successfully used for the treatment and prevention of breast cancer. However, many patients that are initially TAM responsive develop tumors that are antiestrogen/TAM resistant (TAM-R). The mechanism behind TAM resistance in estrogen receptor A (ERA)-positive tumors is not understood. The orphan nuclear receptor chicken ovalbumin upstream promoter transcription factor (COUP-TF)-I interacts directly with 4-hydroxytamoxifen (4-OHT)-and estradiol (E 2 )-occupied ERA, corepressors NCoR and SMRT, and inhibit E 2 -induced gene transcription in breast cancer cells. Here we tested the hypothesis that reduced COUP-TFI and COUP-TFII correlate with TAM resistance. We report for the first time that COUP-TFII, but not COUP-TFI, is reduced in three antiestrogen/TAM-R cell lines derived from TAMsensitive (TAM-S) MCF-7 human breast cancer cells and in MDA-MB-231 cells compared with MCF-7. ERA and ERB protein expression was not different between TAM-S and TAM-R cells, but progesterone receptor (PR) was decreased in TAM-R cells. Further, E 2 increased COUP-TFII transcription in MCF-7, but not TAM-R, cells. Importantly, reexpression of COUP-TFII in TAM-S cells to levels comparable to those in MCF-7 was shown to increase 4-OHT-mediated growth inhibition and increased apoptosis. Conversely, knockdown of COUP-TFII in TAM-S MCF-7 cells blocked growth inhibitory activity and increased 4-OHT agonist activity. 4-OHT increased COUP-TFII-ERA interaction f2-fold in MCF-7 cells. COUP-TFII expression in TAM-R cells also inhibited 4-OHT-induced endogenous PR and pS2 mRNA expression. These data indicate that reduced COUP-TFII expression correlates with acquired TAM resistance in human breast cancer cell lines and that COUP-TFII plays a role in regulating the growth inhibitory activity of TAM in breast cancer cells.

Development of the adult male reproductive tract requires proper spatial-temporal expression of the sex hormones testosterone and estrogen during fetal developmental stages and at puberty. Exogenous agents that disrupt the production and/or actions of the testosterone and estrogen and cause aberrant reproductive tract development can be thought of as endocrine disruptors (ED). This review will focus on the impact of ED on testosterone production by Leydig cells during fetal development and in the adult. In particular, the genes encoding the steroidogenic acute regulatory protein (StAR) and cytochrome P450 17 alpha hydroxylase/17,20 lyase (CYP17A1) within the steroid hormone biosynthetic pathway are highlighted as ED targets. We begin with an overview of steroidogenesis and regulation of StAR then summarize the published literature on the effects of diethylstibesterol, phthalate esters, and arsenite on male reproduction with a focus on the expression and function of StAR.

CDB-4022, an indenopryridine, suppresses spermatogenesis and decreases inhibin secretion in adult male rats. In the present study, we investigated the effects of CDB-4022 on Leydig cell function. A single oral dose of CDB-4022 (2.5 mg/kg) resulted in a 2-fold decrease in serum testosterone levels after 7 days that was paralleled by a decrease in Cyp17a1 mRNA and protein levels and 17alpha hydroxylase enzymatic activity compared with vehicle-treated rats. Consistent with the lower serum testosterone levels, pituitary Lhb and Fshb mRNA levels were increased 3.2- and 2.3-fold, respectively, by CDB-4022 treatment. Ultrastructural analysis of pituitary gonadotrophs showed distended endoplasmic reticulum (ER) and fewer secretory granules in CDB-4022-treated rats, characteristic of enhanced secretory activity. Conversely, CDB-4022 increased serum progesterone levels, testicular Star mRNA and protein expression, and the number of Leydig cells per testis. Serum inhibin B levels were undetectable in CDB-4022-treated rats, while serum activin A levels were similar to controls, indicating that the CDB-4022-treated rats have an elevated activin A:inhibin B ratio. In the presence of hCG stimulation, activin A directly suppressed testosterone secretion but enhanced progesterone secretion from rat Leydig cell primary cultures. Likewise, treatment of MA-10 cells with activin A was found to enhance cAMP-stimulated progesterone secretion and STAR expression. Together, our data indicate that CDB-4022 treatment inhibits CYP17A1 and stimulates STAR expression, thereby decreasing testosterone but increasing progesterone production. We propose that unopposed actions of activin A most likely contribute to the steroid profile in rats after CDB-4022 treatment. Our findings establish CDB-4022 as a new model to examine intratesticular control mechanisms that modulate Leydig cell gene expression and function.

Supplementary Figure Legends 1-2 from Decreased Chicken Ovalbumin Upstream Promoter Transcription Factor II Expression in Tamoxifen-Resistant Breast Cancer Cells

Supplementary Figure S2 from Decreased Chicken Ovalbumin Upstream Promoter Transcription Factor II Expression in Tamoxifen-Resistant Breast Cancer Cells