Ovulation induction with letrozole and dexamethasone in infertile patients with letrozole-resistant polycystic ovary syndrome.

PURPOSE: To assess efficacy of adjuvant dexamethasone during letrozole cycles for ovulation induction (OI) in women with letrozole-resistant polycystic ovary syndrome (PCOS). METHODS: We retrospectively evaluated 42 cycles of OI from 28 infertile women with letrozole-resistant PCOS between September 2019 and November 2022. Letrozole was initiated on cycle day 3 for 5 days and increased via a stair-step approach to 7.5 mg as indicated. Patients were deemed letrozole-resistant if no dominant follicle was identified on transvaginal ultrasound following this dose. Resistant patients then received 5 additional days of letrozole 7.5 mg with low-dose dexamethasone 0.5 mg for 7 days and had a repeat ultrasound. The primary outcome was ovulation rate determined by the presence of a dominant follicle on ultrasound. Secondary outcomes included endometrial thickness, number of measurable follicles, and pregnancy outcomes among responders. RESULTS: Twenty-two of 28 (79%) letrozole-resistant PCOS patients had evidence of ovulation after the addition of dexamethasone in 35 out of 42 (83%) cycles. Clinical pregnancy occurred in 20% of ovulatory cycles with a cumulative rate of 32%. All clinical pregnancies resulted in a live birth. Patients who responded to adjuvant dexamethasone were more likely to have a shorter duration of infertility; however, there were no differences in other demographics, serum androgens including DHEA-S, or pretreatment glycemic status. CONCLUSION: Adding dexamethasone to letrozole increased ovulation rates in letrozole-resistant PCOS patients undergoing OI with similar pregnancy outcomes to prior studies. The addition of dexamethasone is an effective, inexpensive, and safe option for PCOS patients otherwise at risk for cycle cancelation.

Is there still a role for a cleavage-stage embryo transfer?

OBJECTIVE: To determine whether pregnancy outcomes are poor or futile when an intended day 5 transfer is converted to a cleavage-stage transfer because of poor embryo development or a lower number of embryos. DESIGN: Retrospective cohort study. SETTING: Academic medical center. PATIENTS: Women with a limited number of embryos, defined as ≤6 two pronuclear embryos, after in vitro fertilization. INTERVENTIONS: Patients who had a cleavage-stage transfer were age matched with patients who had a day 5 transfer. MAIN OUTCOME MEASURES: Live birth rate. RESULTS: A total of 146 women were included in the study with 73 women in each group. Cleavage-stage transfer was associated with significantly lower implantation and clinical pregnancy rates compared with those of day 5 transfer. Although the live birth rate of the cleavage-stage transfer group was lower than that of the day 5 transfer group (25% vs. 40%, respectively), the cleavage-stage transfer still resulted in a live birth rate of 25%. A subanalysis comparing women who did and did not achieve live birth after cleavage-stage transfer demonstrated a live birth rate of 27% when at least one grade A embryo was transferred vs. 17% when a lesser quality embryo (grade B or C) was transferred. CONCLUSIONS: As expected, the live birth rate after cleavage-stage transfer was lower than that after day 5 transfer. However, the live birth rate of cleavage-stage transfer still fell into acceptable practice, >5%, for patients who were otherwise at very high risk of having no day 5 embryo transfer. Extended culture may not be necessary for all patients.

Evaluating Markers of Immune Tolerance and Angiogenesis in Maternal Blood for an Association with Risk of Pregnancy Loss.

Pregnancy loss affects approximately 20% of couples. The lack of a clear cause complicates half of all miscarriages. Early evidence indicates the maternal immune system and angiogenesis regulation are both key players in implantation success or failure. Therefore, this prospective study recruited women in the first trimester with known viable intrauterine pregnancy and measured blood levels of immune tolerance proteins galectin-9 (Gal-9) and interleukin (IL)-4, and angiogenesis proteins (vascular endothelial growth factors (VEGF) A, C, and D) between 5 and 9 weeks gestation. Plasma concentrations were compared between groups defined based on (a) pregnancy outcome and (b) maternal history of miscarriage, respectively. In total, 56 women were recruited with 10 experiencing a miscarriage or pregnancy loss in the 2nd or 3rd trimester and 11 having a maternal history or miscarriage. VEGF-C was significantly lower among women with a miscarriage or pregnancy loss. Gal-9 and VEGF-A concentrations were decreased in women with a prior miscarriage. Identification of early changes in maternal immune and angiogenic factors during pregnancy may be a tool to improve patient counseling on pregnancy loss risk and future interventions to reduce miscarriage in a subset of women.

Intrauterine insemination cycles: prediction of success and thresholds for poor prognosis and futile care.

PURPOSE: We aimed to define intrauterine insemination (IUI) cycle characteristics associated with viable birth, identify thresholds below which IUI treatments are consistent with very poor prognosis and futile care, and develop a nomogram for individualized application. METHODS: This retrospective cohort study evaluated couples using fresh partner ejaculate for IUI from January 2005 to September 2017. Variables included female age, semen characteristics, and ovarian stimulation type. Using cycle-level data, we evaluated the association of these characteristics with the probability of viable birth by fitting generalized regression models for a binary outcome with a logit link function, using generalized estimating equation methodology to account for the correlation between cycles involving the same patient. RESULTS: The cohort consisted of 1117 women with 2912 IUI cycles; viable birth was achieved in 275 (9.4%) cycles. Futile care (viable birth rate < 1%) was identified for women age > 43, regardless of stimulation type or inseminate motility (IM). Very poor prognosis (viable birth rate < 5%) was identified for women using oral medications or Clomid plus gonadotropins who were (1) age < 35 with IM < 49%, (2) age 35-37 with IM < 56%, or (3) age ≥ 38, and (4) women age ≥ 38 using gonadotropins only with IM < 60%. A clinical prediction model and nomogram was developed with an optimism-corrected c-statistic of 0.611. CONCLUSIONS: The present study highlights the impact of multiple clinical factors on IUI success, identifies criteria consistent with very poor prognosis and futile care, and provides a nomogram to individualize counseling regarding the probability of a viable birth.

Tubal Ligation and Age at Natural Menopause.

OBJECTIVE: To determine the effect of tubal ligation on age at natural menopause, as a marker of long-term ovarian function. METHODS: Three preexisting population-based cohorts were included in this cross-sectional study. Data from each cohort was analyzed separately. The cohorts were restricted to women who never smoked and had reached natural menopause, without prior hysterectomy or oophorectomy. The following variables were collected: race, age at menarche, age at menopause, history of hysterectomy or oophorectomy, gravidity and parity, tobacco use, and ever use of hormonal contraception. The type of tubal ligation and age at tubal ligation were manually abstracted in cohort 1. For cohorts 2 and 3, history of tubal ligation was obtained from an institutional form, completed by patient report. The primary outcome, age at natural menopause, was compared between the two groups (those with and without a history of tubal ligation). RESULTS: Inclusion criteria was met by 555 women from cohort 1, 1,816 women from cohort 2, and 1,534 women from cohort 3. Baseline characteristics did not differ between cohorts. The percentage with tubal ligation was the same in all cohorts: 26.0%, 25.5%, and 25.0%, respectively. Women with a tubal ligation were more likely to have had at least one pregnancy and to have used hormonal contraception compared with women without a tubal ligation. There was no significant difference in age at natural menopause in women who underwent tubal ligation (50.1, 49.9, 50.0 years, respectively) compared with those who did not (50.7, 49.6, 50.0 years, respectively). The type of tubal ligation (cohort 1 only) had no effect on age at menopause. CONCLUSIONS: Tubal ligation did not affect age at natural menopause in the three large cohorts included in this study.

IGF1R Expression in Ovarian Granulosa Cells Is Essential for Steroidogenesis, Follicle Survival, and Fertility in Female Mice.

Folliculogenesis is a lengthy process that requires the proliferation and differentiation of granulosa cells (GCs) for preovulatory follicle formation. The most crucial endocrine factor involved in this process is follicle-stimulating hormone (FSH). Interestingly, previous in vitro studies indicated that FSH does not stimulate GC proliferation in the absence of the insulinlike growth factor 1 receptor (IGF1R). To determine the role of the IGF1R in vivo, female mice with a conditional knockdown of the IGF1R in the GCs were produced and had undetectable levels of IGF1R mRNA and protein in the GCs. These animals were sterile, and their ovaries were smaller than those of control animals and contained no antral follicles even after gonadotropin stimulation. The lack of antral follicles correlated with a 90% decrease in serum estradiol levels. In addition, under a superovulation protocol no oocytes were found in the oviducts of these animals. Accordingly, the GCs of the mutant females expressed significantly lower levels of preovulatory markers including aromatase, luteinizing hormone receptor, and inhibin α. In contrast, no alterations in FSH receptor expression were observed in GCs lacking IGF1R. Immunohistochemistry studies demonstrated that ovaries lacking IGF1R had higher levels of apoptosis in follicles from the primary to the large secondary stages. Finally, molecular studies determined that protein kinase B activation was significantly impaired in mutant females when compared with controls. These in vivo findings demonstrate that IGF1R has a crucial role in GC function and, consequently, in female fertility.

Genome-wide interactions between FSH and insulin-like growth factors in the regulation of human granulosa cell differentiation.

Study question: Is the genome-wide response of human cumulus cells to FSH and insulin-like growth factors (IGFs) comparable to the response observed in undifferentiated granulosa cells (GCs)? Summary answer: FSH actions in human cumulus cells mimic those observed in preantral undifferentiated GCs from laboratory animals, and approximately half of the regulated genes are dependent on the simultaneous activation of the IGF1 receptor (IGF1R). What is known already: Animal studies have shown that FSH and the IGFs system are required for follicle growth and maturation. In humans, IGF levels in the follicular fluid correlate with patients' responses to IVF protocols. The main targets of FSH and IGFs in the ovary are the GCs; however, the genomic mechanisms involved in the response of GCs to these hormones are unknown. Study design, size, duration: Human cumulus cells isolated from IVF patients were cultured for 48 h in serum-free media in the presence of vehicle, FSH, IGF1R inhibitor or their combination. Participants/materials, setting, methods: Discarded cumulus cells were donated to research by reproductive-aged women undergoing IVF due to non-ovarian etiologies of infertility at a university-affiliated clinic. The effect of FSH and/or IGF1R inhibition on cumulus cell function was evaluated using Affymetrix microarrays, quantitative PCR, western blot, promoter assays and hormone level measurements. Main results and the role of chance: The findings demonstrate that human cumulus cells from IVF patients respond to FSH with the expression of genes known to be markers of the preantral to preovulatory differentiation of GCs. These results also demonstrate that ~50% of FSH-regulated genes require IGF1R activity and suggest that several aspects of follicle growth are coordinately regulated by FSH and IGFs in humans. This novel approach will allow for future mechanistic and molecular studies on the regulation of human follicle maturation. Large scale data: Data set can be accessed at Gene Expression Omnibus number GSE86427. Limitations, reasons for caution: Experiments were performed using primary human cumulus cells. This may not represent the response of intact follicles. Wider implications of the findings: Understanding the mechanisms involved in the regulation of GC differentiation by FSH and IGF in humans will contribute to improving treatments for infertility. Study funding/competing interest(s): The project was financed by the National Instituted of Health grant number R56HD086054 and R01HD057110 (C.S.). The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript. We have no competing interests to declare.

GATA4 and GATA6 Knockdown During Luteinization Inhibits Progesterone Production and Gonadotropin Responsiveness in the Corpus Luteum of Female Mice.

The surge of luteinizing hormone triggers the genomic reprogramming, cell differentiation, and tissue remodeling of the ovulated follicle, leading to the formation of the corpus luteum. During this process, called luteinization, follicular granulosa cells begin expressing a new set of genes that allow the resulting luteal cells to survive in a vastly different hormonal environment and to produce the extremely high amounts of progesterone (P4) needed to sustain pregnancy. To better understand the molecular mechanisms involved in the regulation of luteal P4 production in vivo, the transcription factors GATA4 and GATA6 were knocked down in the corpus luteum by crossing mice carrying Gata4 and Gata6 floxed genes with mice carrying Cre recombinase fused to the progesterone receptor. This receptor is expressed exclusively in granulosa cells after the luteinizing hormone surge, leading to recombination of floxed genes during follicle luteinization. The findings demonstrated that GATA4 and GATA6 are essential for female fertility, whereas targeting either factor alone causes subfertility. When compared to control mice, serum P4 levels and luteal expression of key steroidogenic genes were significantly lower in conditional knockdown mice. The results also showed that GATA4 and GATA6 are required for the expression of the receptors for prolactin and luteinizing hormone, the main luteotropic hormones in mice. The findings demonstrate that GATA4 and GATA6 are crucial regulators of luteal steroidogenesis and are required for the normal response of luteal cells to luteotropins.

FSH Regulates IGF-2 Expression in Human Granulosa Cells in an AKT-Dependent Manner.

CONTEXT: IGF-2 is highly expressed in the granulosa cells of human dominant ovarian follicles; however, little is known about the regulation of the IGF-2 gene or the interaction of IGF-2 and FSH during follicle development. OBJECTIVE: To examine the mechanisms involved in the regulation of the IGF-2 gene by FSH and the interplay between FSH and IGF-2 during granulosa cell differentiation. Design, Setting, Patients, and Interventions: Cumulus granulosa cells were separated from cumulus-oocyte complexes isolated from the follicular aspirates of in vitro fertilization patients and cultured for in vitro studies. MAIN OUTCOME: Protein and mRNA levels of IGF-2 and CYP19A1 (aromatase) were quantified using Western blot and quantitative real-time PCR. IGF-2 promoter-specific activation was determined by the amplification of alternative exons by PCR. Cell proliferation was assessed after treatment with FSH and/or IGF-2. RESULTS: FSH significantly enhanced IGF-2 expression after 8 hours of treatment and at low doses (1 ng/mL). Reciprocally, IGF-2 synergized with FSH to increase cell proliferation and the expression of CYP19A1. When IGF-2 activity was blocked, FSH was no longer able to stimulate CYP19A1 expression. Determination of IGF-2 promoter usage in human cumulus cells showed that the IGF-2 gene is driven by promoters P3 and P4. However, FSH exclusively increased P3 promoter-derived transcripts. Moreover, the FSH-induced stimulation of P3-driven IGF-2 transcripts was blocked by cotreatment with inhibitors of AKT or IGF-1 receptor (IGF-1R). The inhibitory effect of the IGF-1R inhibitor on FSH-induced IGF-2 mRNA accumulation was reversed by overexpression of a constitutively active AKT construct. CONCLUSIONS: FSH is a potent enhancer of IGF-2 expression in human granulosa cells. In return, IGF-2 activation of the IGF-1R and AKT is required for FSH to stimulate CYP19A1 expression and proliferation of granulosa cells. These findings suggest a positive loop interaction between FSH and IGF-2 that is critical for human granulosa cell proliferation and differentiation.

IGF1R signaling is necessary for FSH-induced activation of AKT and differentiation of human Cumulus granulosa cells.

CONTEXT: FSH is routinely administered to in vitro fertilization patients to induce follicle maturation. During this process, granulosa cells differentiate and acquire specific functional characteristics that are required to coordinate ovulation and oocyte maturation. OBJECTIVE: The objective of the study was to gain insight into the molecular mechanisms regulating human granulosa cell differentiation. Design, Setting, Patients, and Interventions: Cumulus and mural granulosa cells were isolated from the follicular aspirates of in vitro fertilization patients and analyzed immediately or cultured in serum-free media in the presence of FSH, IGFs, or an inhibitor of type I IGF receptor (IGF1R) activity. MAIN OUTCOME: We quantified the mRNA and protein levels of steroidogenic enzymes, components of the IGF system, and gonadotropin receptors; measured 17ß-estradiol levels; and examined the activation of intracellular signaling pathways to assess the granulosa cell differentiation as well as the FSH and IGF actions in both cumulus and mural cells. RESULTS: In freshly isolated cells, LH receptor (Lhr) and steroidogenic acute regulator (Star) were expressed at lower levels in cumulus than mural cells, whereas FSH receptor (Fshr) and anti-Müllerian hormone (Amh) were expressed at higher levels in cumulus than mural cells. In vitro, the expression of Igf2, the differentiation markers Lhr, Star, and Cyp19a1 (aromatase) as well as 17ß-estradiol production remained low in untreated cumulus cells but increased significantly after FSH treatment. Strikingly, this stimulatory effect of FSH was abolished by the inhibition of IGF1R activity. FSH-induced activation of v-akt murine thymoma viral oncogene homolog 3 (AKT) required IGF1R activity, and overexpression of constitutively active AKT rescued the induction of differentiation markers and 17ß-estradiol production by FSH in the presence of the IGF1R inhibitor. CONCLUSIONS: The cumulus cell response to FSH resembles the differentiation of preantral to preovulatory granulosa cells. This differentiation program requires IGF1R activity and subsequent AKT activation.

GATA4 and GATA6 silencing in ovarian granulosa cells affects levels of mRNAs involved in steroidogenesis, extracellular structure organization, IGF-I activity, and apoptosis.

Knockdown of the transcription factors GATA4 and GATA6 in granulosa cells (GCs) impairs folliculogenesis and induces infertility. To investigate the pathways and genes regulated by these factors, we performed microarray analyses on wild-type GCs or GCs lacking GATA4, GATA6, or GATA4/6 (G4(gcko), G6(gcko), and G4/6(gcko)) after in vivo treatment with equine chorionic gonadotropin. GATA4 deletion affected a greater number of genes than GATA6, which correlates with the subfertility observed in G4(gcko) mice and the normal reproductive function found in G6(gcko) animals. An even greater number of genes were affected by the deletion of both factors. Moreover, the expression of FSH receptor, LH receptor, inhibin α and ß, versican, pregnancy-associated plasma protein A, and the regulatory unit 2b of protein kinase A, which are known to be crucial for ovarian function, was greatly affected in double GATA4 and GATA6 knockouts when compared with single GATA-deficient animals. This suggests that GATA4 and GATA6 functionally compensate for each other in the regulation of key ovarian genes. Functional enrichment revealed that ovulation, growth, intracellular signaling, extracellular structure organization, gonadotropin and growth factor actions, and steroidogenesis were significantly regulated in G4/6(gcko) mice. The results of this analysis were confirmed using quantitative polymerase chain reaction, immunohistochemical, and biological assays. Treatment of GCs with cAMP/IGF-I, to bypass FSH and IGF-I signaling defects, revealed that most of the affected genes are direct targets of GATA4/6. The diversity of pathways affected by the knockdown of GATA underscores the important role of these factors in the regulation of GC function.

Testosterone-dependent interaction between androgen receptor and aryl hydrocarbon receptor induces liver receptor homolog 1 expression in rat granulosa cells.

Androgens play a major role in the regulation of normal ovarian function; however, they are also involved in the development of ovarian pathologies. These contrasting effects may involve a differential response of granulosa cells to the androgens testosterone (T) and dihydrotestosterone (DHT). To determine the molecular pathways that mediate the distinct effects of T and DHT, we studied the expression of the liver receptor homolog 1 (LRH-1) gene, which is differentially regulated by these steroids. We found that although both T and DHT stimulate androgen receptor (AR) binding to the LRH-1 promoter, DHT prevents T-mediated stimulation of LRH-1 expression. T stimulated the expression of aryl hydrocarbon receptor (AHR) and its interaction with the AR. T also promoted the recruitment of the AR/AHR complex to the LRH-1 promoter. These effects were not mimicked by DHT. We also observed that the activation of extracellular regulated kinases by T is required for AR and AHR interaction. In summary, T, but not DHT, stimulates AHR expression and the interaction between AHR and AR, leading to the stimulation of LRH-1 expression. These findings could explain the distinct response of granulosa cells to T and DHT and provide a molecular mechanism by which DHT negatively affects ovarian function.

IGF-I signaling is essential for FSH stimulation of AKT and steroidogenic genes in granulosa cells.

FSH and IGF-I synergistically stimulate gonadal steroid production; conversely, silencing the FSH or the IGF-I genes leads to infertility and hypogonadism. To determine the molecular link between these hormones, we examined the signaling cross talk downstream of their receptors. In human and rodent granulosa cells (GCs), IGF-I potentiated the stimulatory effects of FSH and cAMP on the expression of steroidogenic genes. In contrast, inhibition of IGF-I receptor (IGF-IR) activity or expression using pharmacological, genetic, or biochemical approaches prevented the FSH- and cAMP-induced expression of steroidogenic genes and estradiol production. In vivo experiments demonstrated that IGF-IR inactivation reduces the stimulation of steroidogenic genes and follicle growth by gonadotropins. FSH or IGF-I alone stimulated protein kinase B (PKB), which is also known as AKT and in combination synergistically increased AKT phosphorylation. Remarkably, blocking IGF-IR expression or activity decreased AKT basal activity and abolished AKT activation by FSH. In GCs lacking IGF-IR activity, FSH stimulation of Cyp19 expression was rescued by overexpression of constitutively active AKT. Our findings demonstrate, for the first time, that in human, mouse, and rat GCs, the well-known stimulatory effect of FSH on Cyp19 and AKT depends on IGF-I and on the expression and activation of the IGF-IR.

Minireview: Inflammation: an instigator of more aggressive estrogen receptor (ER) positive breast cancers.

Approximately 75% of breast tumors express the estrogen receptor (ER), and women with these tumors will receive endocrine therapy. Unfortunately, up to 50% of these patients will fail ER-targeted therapies due to either de novo or acquired resistance. ER-positive tumors can be classified based on gene expression profiles into Luminal A- and Luminal B-intrinsic subtypes, with distinctly different responses to endocrine therapy and overall patient outcome. However, the underlying biology causing this tumor heterogeneity has yet to become clear. This review will explore the role of inflammation as a risk factor in breast cancer as well as a player in the development of more aggressive, therapy-resistant ER-positive breast cancers. First, breast cancer risk factors, such as obesity and mammary gland involution after pregnancy, which can foster an inflammatory microenvironment within the breast, will be described. Second, inflammatory components of the tumor microenvironment, including tumor-associated macrophages and proinflammatory cytokines, which can act on nearby breast cancer cells and modulate tumor phenotype, will be explored. Finally, activation of the nuclear factor κB (NF-κB) pathway and its cross talk with ER in the regulation of key genes in the promotion of more aggressive breast cancers will be reviewed. From these multiple lines of evidence, we propose that inflammation may promote more aggressive ER-positive tumors and that combination therapy targeting both inflammation and estrogen production or actions could benefit a significant portion of women whose ER-positive breast tumors fail to respond to endocrine therapy.

CBP mediates NF-κB-dependent histone acetylation and estrogen receptor recruitment to an estrogen response element in the BIRC3 promoter.

Estrogen receptor (ER) and NF-κB are transcription factors with profound effects on breast cancer cell proliferation and survival. While many studies demonstrate that ER and NF-κB can repress each other, we previously identified a gene signature that is synergistically upregulated by these two factors in more aggressive luminal B breast tumors. Herein, we examine a novel mechanism of cross talk between ER and NF-κB that results in the upregulation of the antiapoptotic gene BIRC3 (also known as cIAP2). We demonstrate that NF-κB, acting through two response elements, is required for ER recruitment to an adjacent estrogen response element (ERE) in the BIRC3 promoter. This effect is accompanied by a major increase in NF-κB-dependent histone acetylation around the ERE. Interestingly, CBP, a histone acetyltransferase previously implicated in repressive interactions between ER and NF-κB, plays a permissive role by promoting histone acetylation and ER recruitment, as well as enhanced expression of BIRC3. These findings suggest a new gene regulatory mechanism by which inflammation and NF-κB activation can influence ER recruitment to inherently inactive ER binding sites. This fine-tuning mechanism may explain how two factors that generally repress each other's activity may work together on certain genes to promote breast cancer cell survival and tumor progression.

Proinflammatory cytokines enhance estrogen-dependent expression of the multidrug transporter gene ABCG2 through estrogen receptor and NF{kappa}B cooperativity at adjacent response elements.

Constitutive activation of NFκB in estrogen receptor (ER)-positive breast cancer is associated with tumor recurrence and development of anti-estrogen resistance. Furthermore, a gene expression signature containing common targets for ER and NFκB has been identified and found to be associated with the more aggressive luminal B intrinsic subtype of ER-positive breast tumors. Here, we describe a novel mechanism by which ER and NFκB cooperate to up-regulate expression of one important gene from this signature, ABCG2, which encodes a transporter protein associated with the development of drug-resistant breast cancer. We and others have confirmed that this gene is regulated primarily by estrogen in an ER- and estrogen response element (ERE)-dependent manner. We found that whereas proinflammatory cytokines have little effect on this gene in the absence of 17ß-estradiol, they can potentiate ER activity in an NFκB-dependent manner. ER allows the NFκB family member p65 to access a latent NFκB response element located near the ERE in the gene promoter. NFκB recruitment to the gene is, in turn, required to stabilize ER occupancy at the functional ERE. The result of this cooperative binding of ER and p65 at adjacent response elements leads to a major increase in both ABCG2 mRNA and protein expression. These findings indicate that estrogen and inflammatory factors can modify each other's activity through modulation of transcription factor accessibility and/or occupancy at adjacent response elements. This novel transcriptional mechanism could have important implications in breast cancer, where both inflammation and estrogen can promote cancer progression.

Structure of flexible filamentous plant viruses.

Flexible filamentous viruses make up a large fraction of the known plant viruses, but in comparison with those of other viruses, very little is known about their structures. We have used fiber diffraction, cryo-electron microscopy, and scanning transmission electron microscopy to determine the symmetry of a potyvirus, soybean mosaic virus; to confirm the symmetry of a potexvirus, potato virus X; and to determine the low-resolution structures of both viruses. We conclude that these viruses and, by implication, most or all flexible filamentous plant viruses share a common coat protein fold and helical symmetry, with slightly less than 9 subunits per helical turn.