A synthetic oestrogen antagonist, tamoxifen, inhibits oestrogen-induced transcriptional, but not post-transcriptional, regulation of gene expression

Ovarian mRNA Expression and Regulation of Matrix Metalloproteinase 16 in the Domestic Hen

In mammals, membrane-bound matrix metalloproteinases (MT-MMPs) are thought to play an important role in ovarian remodeling. However, the role and regulation of these proteases in the ovary of birds remain largely unknown. One of MT-MMPs, i. e., MMP-16, has been found in the hen ovary; therefore, this study was undertaken to examine whether the transcript level of MMP-16 changes during follicle development and whether gonadotropins and estrogen are involved in the regulation of this enzyme expression. The relative expression of MMP-16 mRNA in the ovarian follicles (white, yellowish, small yellow, and the granulosa and theca layers of three of the largest yellow preovulatory [F3-F1]) was examined 22 h and 3 h before F1 follicle ovulation as well as following equine chorionic gonadotropin (eCG) or tamoxifen (estrogen receptor modulator, TMX) treatments by quantitative real-time polymerase chain reaction (qRT-PCR). MMP-16 transcripts were detected in all examined ovarian tissues of control and treated hens. The relative expression of MMP-16 depended on follicular size/maturation and the layer of the follicular wall. A relatively higher expression of MMP-16 mRNA in the granulosa layer at 3 h compared to 22 h before ovulation of F1 was found. The injections of eCG decreased transcript abundance of MMP-16 in white and small yellow follicles, as well as in the theca layer of F3-F2 and the granulosa layer of the F1 follicle. In turn, TMX caused an increase in mRNA expression of MMP-16 in the theca layer of the largest preovulatory follicles and a decrease in the granulosa layer of the F1 follicle. Our results provide the first mRNA expression analysis of MMP-16 in the hen ovary under different physiological states. In addition, results indicate a possible role of gonadotropins and estrogen in regulating the transcription of MMP-16 in the chicken ovary.

MiR-34a-5p promotes autophagy and apoptosis of ovarian granulosa cells via the Hippo-YAP signaling pathway by targeting LEF1 in chicken

Follicular atresia is a natural physiological phenomenon in poultry reproduction. It is well known that follicular atresia is caused by both autophagy and apoptosis of granulosa cells. In current experiment, we evaluated the function of miR-34a-5p on autophagy and apoptosis in chicken follicular atresia. First, the follicular atresia model of chicken was successfully constructed by subcutaneous injection of tamoxifen (TMX), and found the expression of miR-34a-5p in the atresia follicles obviously increased. Then, we confirmed that miR-34a-5p accelerates autophagy and apoptosis of chicken granulose cells in vitro, and miR-34a-5p could induce apoptosis by mediating autophagy. Mechanistically, lymphoid enhancer binding factor 1 (LEF1) was deemed as a target gene for miR-34a-5p. On the contrary, LEF1 overexpression attenuated the autophagy and apoptosis of chicken granular cells. In addition, it was confirmed that the miR-34a-5p/LEF1 axis plays a regulatory role in chicken granulosa cells by mediating the Hippo-YAP signaling pathway. Taken together, this study demonstrated that miR-34a-5p contributes to autophagy and apoptosis of chicken follicular granulosa cells by targeting LEF1 to mediate the Hippo-YAP signaling pathway.

Tamoxifen-induced alterations in the expression of selected matrix metalloproteinases (MMP-2, -9, -10, and -13) and their tissue inhibitors (TIMP-2 and -3) in the chicken ovary

Matrix metalloproteinases (MMPs) are a family of peptidases that disintegrate extracellular matrix (ECM) molecules associated with tissue remodeling, including reproductive tissues. Their actions are largely controlled by specific tissue inhibitors of MMPs (TIMPs). The role and regulation of MMPs in the chicken ovary is largely unknown. The aim of the present study was to examine the effect of tamoxifen (TMX; estrogen receptor modulator) treatment on the expression of selected members of the MMP system in the laying hen ovary. The activity of MMP-2 and -9 was also examined. Real-time polymerase chain reaction and western blot analyses revealed changes in mRNA and/or protein expression of MMP-2, -9, -10, -13, TIMP-2, and TIMP-3 in the following ovarian follicles after TMX treatment: white (WF), yellowish (YF), small yellow (SYF), and the largest yellow preovulatory (F3-F1). The response to TMX depended on the stage of follicle development and the layer of follicular wall. Moreover, ovarian regression following TMX treatment was accompanied by both an increase in total activity of MMP-2 in the theca layer of F3-F2 and granulosa layer of F2, and a decrease in total activity of MMP-2 in the WF, YF, and SYF, and MMP-9 in theca of F3-F1. In conclusion, the TMX-induced changes in MMP-2, -9, -10, and -13, and TIMP-2 and -3 mRNA expression, as well as MMP-2 and -9 activity, were dependent on tissue and the stage of follicular maturation. Our findings strongly suggests a role for estrogen in regulating the transcription, translation, and/or posttranslational activity of members of the MMP system. Further, these components may be involved in the orchestration of ECM turnover and cellular functions during ovary regression, which occur under conditions of reduced estrogenic activity.

Tamoxifen activates hypothalamic l-dopa synthesis to stimulate ovarian estrogen production in chicken

Estrogen is the primary sex hormone responsible for the development and modulation of the female reproductive system in all vertebrates including avian species. The actions of estrogen are mediated by the estrogen receptor, which could be modulated by the selective estrogen receptor modulator tamoxifen (TAM). In this study, we administered TAM into the actively laying chicken to investigate the ovarian and hypothalamic responses to the estrogen action blockage. The laying was disrupted and the development of the pre-ovulatory hierarchical follicles was arrested. However, the TAM treatment caused an increase of estrogen level in both serum and ovary. Among the main estrogen targeted tissues, the hypothalamus showed specific dopaminergic activation as indicated by gene expression analysis. In the ovary, l-dopa, the precursor of dopamine, could stimulate the estrogen synthesis in undifferentiated follicles but not in the differentiated pre-ovulatory follicles. Thus, we established a feedback loop links ovarian estrogen production with hypothalamic l-dopa synthesis and we propose that the dopamine is involved in estrogen action to regulate the ovarian follicle development and ovulation.

Alterations in apoptotic markers and egg-specific protein gene expression in the chicken oviduct during pause in laying induced by tamoxifen

The aim of this study was to examine the cell apoptosis, gene expression and activity of caspases 2, 3, 8 and 9, and the mRNA expression of selected egg-specific proteins in the chicken oviduct during pause in egg laying induced by tamoxifen (TMX) treatment. The experiment was carried out on Hy-Line Brown laying hens. The control birds were treated subcutaneously with vehicle (ethanol) and the experimental ones with TMX at a dose of 6 mg/kg of body weight. Hens were treated daily until a pause in egg laying occurred and sacrificed on Day 7 of the experiment. Within the oviductal wall, the highest number of apoptotic cells (TUNEL-positive) was found in the luminal epithelium and the lowest in the stroma. The administration of TMX increased the percentage of apoptotic cells in the magnum, isthmus, and shell gland as well as immunoreactivity for caspases 3 and 9. Real-time PCR analysis revealed the segment-dependent mRNA expression of caspases 2, 3, 8 and 9. Treatment of hens with TMX elevated the level of caspase-2 transcript in the infundibulum, caspases 2, 3 and 8 in the isthmus, and caspase-9 in the shell gland (P < 0.05 - P < 0.001). As shown by fluorometric method TMX caused an increase in the activity of caspases 3 and 8 in the magnum, isthmus and shell gland, and the activity of caspases 2 and 9 in the isthmus and shell gland (P < 0.05 - P < 0.01). The expression of ovalbumin, avidin and ovocleidin-116 mRNAs was decreased (P < 0.05 - P < 0.001), ovocalyxin-36 mRNA level tended to increase, and ovocalyxin-32 expression was not affected by TMX. The results obtained indicate that caspases are involved in the chicken oviduct regression during a pause in laying induced by TMX, and estrogen is involved in the regulation of examined caspase expression and activity. The changes in mRNA transcript levels of some examined egg-specific proteins after TMX treatment suggest that there is a relationship between estrogen action and the expression of these genes.

Expression and localization of matrix metalloproteinases (MMP-2, -7, -9) and their tissue inhibitors (TIMP-2, -3) in the chicken oviduct during pause in laying induced by tamoxifen

Induced pause in egg laying simulates natural molting events in which the hen's reproductive organs regress and rejuvenate. Such processes require extracellular matrix remodeling that is maintained, at least in part, by the action of proteolytic enzymes known as matrix metalloproteinases (MMPs). Nevertheless, information concerning the expression and hormonal regulation of MMP system members in chickens is scarce. Therefore, MMP-2, -7, and -9 and their tissue inhibitors (TIMP-2, -3) expression and localization were investigated in all segments of the domestic hen oviduct (infundibulum, magnum, isthmus, shell gland, vagina) during a pause in egg laying induced by tamoxifen (TMX)-an estrogen receptor modulator. Hy-Line Brown hens were treated daily with TMX (n = 6) at a dose of 6 mg/kg of body weight or a vehicle (n = 6) until complete cessation of egg laying (for 7 days). Chickens were decapitated on Day 7 of the experiment. Real-time polymerase chain reaction and Western blotting revealed section-dependent expression of MMP-2, -7, -9 and TIMP-2 and -3. Immunohistochemistry found tissue and cell-dependent localization of examined proteins in the wall of the oviduct. The MMP-2, TIMP-2, and TIMP-3 were localized mainly in the luminal epithelium, MMP-7 in the luminal and glandular epithelium, whereas MMP-9 was detected only in the connective tissue. Treatment of chickens with TMX markedly elevated the relative expression of MMP-7 and MMP-9 mRNA in the oviduct, but did not affect MMP-2, TIMP-2, and TIMP-3 mRNA levels. However, TMX increased the MMP-2 protein level in the infundibulum, shell gland, and vagina as well as activity of MMP-2 evaluated by gelatin zymography. The results obtained indicate that MMP-2, MMP-7, and MMP-9 are involved in chicken oviduct regression. Moreover, changes in the expression and activity of chosen MMPs after TMX treatment may indicate a contribution of estrogen in the regulation of transcription, translation, and/or the activity of selected elements of the MMP system.

Effect of tamoxifen on sex steroid concentrations in chicken ovarian follicles

The aim of the present investigation was to study the effect of tamoxifen (TAM), an oestrogen receptor antagonist, on the concentrations of sex hormones in chicken ovarian follicles. The experiment was carried out on Hy-line hens which were randomly divided into two groups (control and experimental). TAM was given at a dose of 4 mg/hen (per os) at first once a day for 7 consecutive days, and subsequently four times a day for the next 6 days. Control hens received placebo. Birds were killed on the day after the last TAM treatment. From the dissected ovaries the following compartments were isolated: stroma with follicles < 1 mm, white non-hierarchical (1-4 mm and 4-8 mm) and yellow hierarchical follicles (F6-F1; 18-35 mm). The concentrations of the sex steroids progesterone (P4), testosterone (T) and oestradiol (E2) in the ovarian follicles were determined by radioimmunoassay. In the TAM-treated group, a gradual decrease in egg-laying rate was observed from the 4th day of the experiment. Eventually, egg laying stopped entirely on the 12th day of the experiment. TAM significantly decreased the weight of the ovary and affected the sex hormone concentrations in the ovarian follicles. Following TAM treatment (1) a significant increase in E2 and T concentrations in the stroma, white follicles and the F4 and F1 follicles, (2) a significant decrease in E2 and T concentrations in the F2 follicle, and (3) a significant decline of P4 in the F4 to F1 follicles were observed. The results indicate that the blockade of oestrogen receptors by TAM significantly modulates the process of chicken ovarian steroidogenesis.

Regulation of the estrogen-inducible gene expression profile by the breast cancer susceptibility gene BRCA1

The tumor suppressor gene BRCA1 functions in part as a caretaker in preserving the integrity of the genome, but also exhibits tissue-specific function by inhibiting estrogen receptor activity. Because estrogen (E2) induces a wide range of gene expression changes (by nongenomic and several transcriptional pathways), we sought to determine how comprehensive is the BRCA1-mediated inhibition of E2-induced gene expression alterations. Using cDNA-spotted microarrays, we identified a relatively large number of gene expression alterations (both increased and decreased expression) in MCF-7 cells caused by E2, some of which have been reported in previous studies. However, in the presence of exogenous wild-type BRCA1 (wtBRCA1), the response to E2 was severely blunted, with only about 10% the number of gene expression changes as that found in the absence of wtBRCA1. Examples of these findings were confirmed by semiquantitative and quantitative RT-PCR assays. In contrast to wtBRCA1, the induction by E2 of several E2-responsive genes was not inhibited by a full-length tumor-associated mutant BRCA1 protein [T300G (or (61)Cys-->Gly)]. For three E2-responsive genes whose induction by E2 was inhibited by wtBRCA1, wtBRCA1 had little or no effect on the mRNA half-life in the presence of E2. Consistent with these findings, wtBRCA1 inhibited E2-stimulated proliferation of MCF-7 cells, but wtBRCA1 failed to inhibit the proliferation of MCF-7 cells stimulated by IGF-I. Our findings suggest that BRCA1 globally inhibits the response to estrogen in a dose- and time-dependent fashion. The implications of these findings for understanding how BRCA1 may act to restrain E2 action in vivo are considered.

Stability of A+U-Rich Element Binding Factor 1 (AUF1)-Binding Messenger Ribonucleic Acid Correlates with the Subcellular Relocalization of AUF1 in the Rat Uterus upon Estrogen Treatment

The nucleocytoplasmic shuttling protein, A+U-rich element binding factor 1 (AUF1), is one of the RNA-binding proteins that specifically bind adenylate-uridylate rich elements (AREs) in mRNA 3'-untranslated regions (UTRs), and acts as a regulator of ARE-mediated mRNA degradation in the cytoplasm. We previously reported that in the female rat uterus, the levels of specific AUF1 isoform mRNAs (p40/p45) were increased by 17 beta-estradiol (E2) treatment. Therefore, we examined the role of AUF1 in the regulation of E2-mediated mRNA turnover in the rat uterus. We identified ABIN2 and Ier2/pip92 mRNAs as candidate targets of AUF1 in the rat uterus. We found that AUF1-binding elements were present in the 3'-UTR of both mRNAs and that the 3'-UTRs functioned as mRNA turnover regulatory elements. In the ovariectomized rat uterus, the nucleocytoplasmic localization of AUF1p40/p37 isoform proteins was regulated by E2. We also found that cytoplasmic AUF1-bound mRNA levels changed coincidentally with the cytoplasmic levels of AUF1p40/p37. Finally, we confirmed that the subcellular localization of AUF1p40 controlled the stability of target mRNAs in vitro, such that cytoplasmically localized AUF1p40 led to marked mRNA stabilization, whereas nuclear-localized AUF1p40 stabilized target mRNA only slightly. These results suggested that E2-inducible ARE-containing gene transcripts are regulated, at least in part, via mRNA stabilization through the nucleocytoplasmic relocalization of AUF1.

The biology of breast carcinoma

The biology of breast carcinoma is complex, with multiple factors contributing to its development and progression. The current review focuses on the role of several critical genes including estrogen receptor, progesterone receptor, retinoic acid receptor-beta, epidermal growth factor receptor family members, p53, BRCA1, and BRCA2 as risk factors for the development of disease, predictors of prognosis and response to therapy, and as therapeutic targets. Studies of the biology of these and other genes that contribute to the development and progression of breast carcinoma have had and will continue to have great impact on all aspects of disease management.

A+U-rich-element RNA-binding factor 1/heterogeneous nuclear ribonucleoprotein D gene expression is regulated by oestrogen in the rat uterus

Oestrogen-mediated gene expression is regulated at both the transcriptional and post-transcriptional levels. The molecular mechanism of transcriptional regulation has been well characterized. On the other hand, there is little understanding of the mechanism of post-transcriptional regulation. To clarify the mechanism of oestrogen-mediated post-transcriptional regulation, we focused on A+U-rich-element RNA-binding factor 1/heterogeneous nuclear ribonucleoprotein D (AUF1/hnRNP D), which is known as a regulator of cytosolic mRNA degradation and nuclear pre-mRNA maturation. However, little is known about the expression levels and the regulation of AUF1/hnRNP D mRNA in tissues. We further investigated the expression levels of AUF1/hnRNP D isoform mRNAs to determine whether AUF1/hnRNP D gene expression is regulated by oestrogen in the ovariectomized adult female rat uterus. Uterine AUF1/hnRNP D mRNA was induced by a single subcutaneous injection (1 microg/kg) of 17beta-oestradiol (E2), reaching a peak level within 6 h. Furthermore, we observed that the E2-induced AUF1/hnRNP D isoform mRNAs are p45 and p40 transcripts, and that E2-mediated induction is suppressed by the oestrogen receptor antagonist ICI 182,780. Finally, using the transcriptional inhibitor actinomycin D, we confirmed that the E2-mediated increase in AUF1/hnRNP D mRNA is caused by E2-dependent AUF1/hnRNP D mRNA stabilization.

Experimental (tamoxifen-induced) manipulation of female reproduction in zebra finches (Taeniopygia guttata)

Experimental manipulation of reproductive phenotype is a potentially powerful approach for understanding the fitness relationships of traits such as egg size, egg composition, and egg number. In this study, I investigated the effect of the antiestrogen tamoxifen on multiple, estrogen-dependent reproductive traits in female zebra finches (Taeniopygia guttata). Short-term tamoxifen treatment of egg-laying females (two daily injections before laying) had no effect on the timing or the pattern of egg laying compared to sham controls. However, tamoxifen treatment caused (1) a marked, but transient, decrease in egg size; (2) increased within-clutch egg-size variation; (3) a reduction in plasma vitellogenin (VTG) levels; and (4) lower dry yolk and yolk protein content of tamoxifen-treated females. Plasma levels of the second yolk precursor, very low density lipoprotein (VLDL), were not affected by tamoxifen, and tamoxifen appeared to have no effect on oviduct function in egg-laying females. These results are consistent with tamoxifen blocking estrogen receptors in the liver, suppressing VTG production, and decreasing the plasma pool of yolk precursors below a level required to maintain yolk formation at the normal rate. Tamoxifen treatment can therefore be used successfully to manipulate several components of the female reproductive phenotype (egg composition, intraclutch egg-size variation) to further explore the fitness consequences of these traits.

A nuclear matrix-associated factor, SAF-B, interacts with specific isoforms of AUF1/hnRNP D

One class of heterogeneous nuclear ribonucleoproteins (hnRNPs), AUF1/hnRNP D, consists of four isoform proteins (p45, p42, p40, and p37) which are generated by alternative splicing. The present study was therefore undertaken to clarify any isoform-specific differences in terms of their functions and nucleocytoplasmic localization. All isoforms primarily localized in the nucleus. However, heterokaryon analysis and a study using RNA polymerase II inhibitor revealed that p40/p37 exhibited a continuous shuttling between the nucleus and cytoplasm. Constant nuclear retention activity was mapped to the p45/p42-specific sequence at the C-terminal region, which is retained by alternative splicing. Using this domain as a probe, we performed a yeast two-hybrid screening and we found that scaffold attachment factor B (SAF-B), a nuclear matrix-associated protein, exhibits protein-protein interaction to this region. Colocalization of p45/p42 and SAF-B was observed as a speckle in the nucleus. Interestingly, p45/p42 isoforms appeared to act as a negative regulator in gene expression by forming a complex with SAF-B. Thus, the present study revealed that the isoform-specific functions of AUF1/hnRNP D are defined by intracellular shuttling capacity.

Interaction of thyroxine and estrogen on the expression of estrogen receptor alpha, cholecystokinin, and preproenkephalin messenger ribonucleic acid in the limbic-hypothalamic circuit

To study thyroid hormone and estrogen interactions in the central nervous system (CNS), the expression of estrogen sensitive genes was examined within the limbic-hypothalamic circuit. Estrogen up-regulates the expression of reproductively relevant neuropeptide messenger RNAs (mRNAs) encoding cholecystokinin (CCK) and enkephalin, peptides that stimulate lordosis. Estrogen down-regulates the expression of the estrogen receptor alpha (ER alpha) mRNA in the nuclei of the circuit. We examined the possibility that thyroid hormone treatment would block the estrogen modulation of these messages. Estradiol benzoate (EB), EB + thyroxine (T4), T4, or oil were administered to ovariectomized, adult female rats for 10 days. Isotopic in situ hybridization histochemistry revealed that within the limbic-hypothalamic nuclei, levels of CCK and preproenkephalin (PPE) mRNA levels were significantly higher in EB and EB + T4-treated animals compared with T4 or oil-treated animals. ER alpha mRNA levels were low in EB treated animals, elevated in T4 or oil-treated animals and further elevated in EB + T4-treated animals. In summary, T4 treatment had neither an independent nor an antagonistic effect on estrogen induced expression of CCK or PPE mRNA in the circuit. However, T4 did prevent the normal estrogenic decrease of ER alpha mRNA levels in the nuclei of the limbic-hypothalamic circuit.