Differential Transcriptional and Translational Regulations of Calbindm-D9k by Steroid Hormones and Their Receptors in the Uterus of Immature Mice

Dexamethasone Treatment Increases the Intracellular Calcium Level Through TRPV6 in A549 Cells

This study investigated the effect of dexamethasone (DEX) on intracellular calcium levels and the expressions of transient receptor potential cation channel subcomponent V member 6 (TRPV6), sodium-calcium exchanger 1 (NCX1), and plasma membrane calcium ATPase 1 (PMCA1) in A549 cells. The intracellular calcium level, by using the calcium indicator pGP-CMV-GCaMP6f, increased following DEX treatment for 6, 12, and 24 h in A549 cells. In addition, Rhod-4 assay after DEX treatment for 24 h showed that DEX increased the level of intracellular calcium. The expression of the calcium influx TRPV6 gene significantly increased, whereas the expressions of the calcium outflow NCX1 and PMCA1 genes significantly decreased with DEX treatment. The mRNA levels of surfactant protein genes SFTPA1, SFTPB, SFTPC, and SFTPD and the secreted airway mucin genes MUC1 and MUC5AC were investigated by treating cells with DEX. The DEX treatment decreased the mRNA levels of SFTPA1 and SFTPB but increased the mRNA levels of SFTPC and SFTPD. The MUC1 mRNA level was increased by DEX treatment, whereas MUC5AC mRNA was significantly decreased. These results indicate that DEX influences the intracellular calcium level through TRPV6, and affects pulmonary surfactant genes and secreted airway mucin genes in A549 cells.

Inhibition of mucin secretion via glucocorticoid-induced regulation of calcium-related proteins in mouse lung

Calcium is important for physiological functioning in many tissues and is essential in mucus secretion and muscle contraction. Intracellular concentrations of calcium are regulated by calcium-related proteins, such as transient receptor potential cation channel subfamily V member 4 (TRPV 4), TRPV6, Calbindin-D9k (CaBP-9k), sodium-calcium exchanger (NCX1), and plasma membrane Ca2+ ATPase 1 (PMCA1). In this study, the relationship between secretion of pulmonary mucus and calcium regulation was investigated. To confirm the effect of steroid hormones, immature mice were injected with estrogen (E2) or progesterone (P4), and mature mice were injected with dexamethasone (DEX). Subsequently, the location and expression of TRPV4, TRPV6, CaBP-9k, NCX1, and PMCA1 in lung tissue were examined. Periodic acid-Schiff staining was performed to investigate functional aspects of the protein expression. There were no significant differences in calcium-related gene expression in E2- and P4-treated mice, but TRPV4, NCX1, and PMCA1 were increased in DEX-treated mice and were recovered by RU486 treatment. DEX induces the expression of calcium-related proteins through the glucocorticoid receptor-mediated pathway and may involve decreased mucin secretion in the bronchiole. TRPV4, TRPV6, CaBP-9k, NCX1, and PMCA1 were specifically expressed in Clara and alveolar type 2 cells of mouse lung. CC10, a marker of Clara cells, was decreased by DEX. In addition, mucin secretion, which is a functional aspect of this cell, was also decreased by DEX treatment. Control of calcium-related gene expression may affect the control of mucus secretion in the lung. Such a control mechanism can form the basis of studies into diseases such as inflammation attributable to mucus secretion abnormalities, coughing, and respiratory disorders and distress.

Functions and physiological roles of two types of estrogen receptors, ERα and ERβ, identified by estrogen receptor knockout mouse

Estrogens, a class of steroid hormones, regulate the growth, development, and physiology of the human reproductive system. Estrogens also involve in the neuroendocrine, skeletal, adipogenesis, and cardiovascular systems. Estrogen signaling pathways are selectively stimulated or inhibited depending on a balance between the activities of estrogen receptor (ER) α or ERβ in target organs. ERs belong to the steroid hormone superfamily of nuclear receptors, which act as transcription factors after binding to estrogen. The gene expression regulation by ERs is to modulate biological activities, such as reproductive organ development, bone modeling, cardiovascular system functioning, metabolism, and behavior in both females and males. Understanding of the general physiological roles of ERs has been gained when estrogen levels were ablated by ovariectomy and then replenished by treatment with exogenous estrogen. This technique is not sufficient to fully determine the exact function of estrogen signaling in general processes in living tissues. However, a transgenic mouse model has been useful to study gene-specific functions. ERα and ERβ have different biological functions, and knockout and transgenic animal models have distinct phenotypes. Analysis of ERα and ERβ function using knockout mouse models has identified the roles of estrogen signaling in general physiologic processes. Although transgenic mouse models do not always produce consistent results, they are the useful for studying the functions of these genes under specific pathological conditions.

Apoptosis- and endoplasmic reticulum stress-related genes were regulated by estrogen and progesterone in the uteri of calbindin-D(9k) and -D(28k) knockout mice

Calcium (Ca(2+)) is an important regulator of apoptotic signaling. Calbindin-D(9k) (CaBP-9k) and -D(28k) (CaBP-28k) have a high affinity for Ca(2+) ions. Uterine calbindins appear to be involved in the regulation of myometrial activity by intracellular Ca(2+). In addition, uterine calbindins are expressed in the mouse endometrium and are regulated by steroid hormones during implantation and development. The aim of the present study was to evaluate the regulation of apoptosis in the uteri of CaBP-9k, CaBP-28k, and CaBP-9k/28k knockout (KO) mice. Our findings indicated that Bax protein was enhanced in the uteri of CaBP-28k and CaBP-9k/28k KO mice compared to wild-type (WT) and CaBP-9k KO mice, but no difference was observed in Bcl-2 protein expression. The expressions of caspase 3, 6, and 7 proteins were higher in both CaBP-28k and CaBP-9k/28k KO mice than in WT and CaBP-9k KO mice. These results suggest that the absence of CaBP-28k increases apoptotic signaling. We also investigated the expression of endoplasmic reticulum (ER) stress genes by Western blot analysis in calbindin KO mice. C/EBP homologous protein and immunoglobulin heavy chain-binding protein protein levels were elevated in CaBP-28k KO mice compared to WT mice. When immature mice were treated with 17β-estradiol (E2) or progesterone (P4) for 3 days, we found that the expressions of Bax and caspase 3 protein were increased by E2 treatment in WT and CaBP-9k KO mice, and by P4 treatment in CaBP-28k KO mice. These results indicate that CaBP-28k blocks the up-regulation of apoptosis-related genes and ER stress genes, implying that CaBP-28k may decrease the expression of genes involved in apoptosis and ER stress in murine uterine tissue.

Estrogen receptor α is involved in the induction of Calbindin-D(9k) and progesterone receptor by parabens in GH3 cells: a biomarker gene for screening xenoestrogens

The effects of paraben, a xenoestrogen with known endocrine disrupting bioactivity were evaluated. We used the induction of an estrogenic biomarker gene - Calbindin-D(9k) (CaBP-9k) to investigate the xenoestrogenic activity of a panel of parabens (methyl-, ethyl-, propyl-, isopropyl-, butyl-, and isobutylparabens) in GH3 rat pituitary cancer cell line. Following 24-h treatment, a significant increase in CaBP-9k expression of transcript and protein was dependent on the concentration-treated as well as the linear length of the alkyl chain from methyl- to isobutylparabens. Interestingly, co-treatment with fulvestrant, a pure antiestrogen largely reversed the paraben-dependent induction of CaBP-9k mRNA and protein in GH3 cell line. To better understand the mechanism of CaBP-9k induction by these endocrine disrupting compounds, we measured the levels of estrogen receptor (ERα) and progesterone receptor (PR) expression following parabens exposure. Also, we monitored the transiently transfected with plasmids containing of estrogen response element (ERE) sequence into GH3. In the GH3 cells, a large increase in PR mRNA and protein was observed in a concentration-dependent manner after parabens treatment that was effectively blocked in the presence of antagonist of 17β-estradiol (fulvestrant). And, luciferase activity was expressed from the putative ERE and expression was stimulated by parabens. To confirm that ERα signaling is involved in parabens induction of CaBP-9k and PR mRNA and protein, we treated GH3 cells with an antiestrogen, fulvestrant, which blocked the paraben-induced upregulation of CaBP-9k and PR. Taken together, these results indicate that CaBP-9k and PR is induced by parabens via the ER pathway in GH3 cell line.

Implantation-related expression of epidermal growth factor family molecules and their regulation by progesterone in the pregnant rat

The uterine expressions of epidermal growth factor(EGF) family are examined to elucidate their exact role(s) in rat pregnancy. EGF and its receptors' (EGF-R) mRNA levels increased significantly at implantation after which their expression gradually decreased. Heparin-binding EGF (HB-EGF) and transforming growth factor-alpha (TGF-alpha) showed a modest expression at gestation day (GD), GD4 and GD3, respectively, but were much strongly expressed at mid-pregnancy.Amphiregulin (Areg) was strongly expressed around implantation (GD4) and at mid-pregnancy (GD12).Treatment of pregnant rats with RU486 at GD5 or GD8 blocked the expression of all the genes, and administration of immature rats with progesterone (P4) induced the uterine expression of all the genes except HB-EGF. In addition, HB-EGF,TGF-alpha, and Areg proteins in the uterine and glandular epitheliums may participate in mid-pregnancy. Taken together, all of these activities are likely to be controlled by P4 in the uterus of pregnant rats.

Phenotype of a calbindin-D9k gene knockout is compensated for by the induction of other calcium transporter genes in a mouse model

CaBP-9k may be involved in the active calcium absorption and embryo implantation. Although we generated CaBP-9k KO mice to explore its function, no distinct phenotypes were observed in these KO mice. It can be hypothesized that TRPV5 and 6 and plasma membrane calcium ATPase 1b may play a role in the regulation of calcium transport to compensate CaBP-9k deficiency in its KO model.

INTRODUCTION

Active calcium transport in the duodenum and kidney is carried in three steps: calcium entry through epithelial Ca2+ channels (TRPV5 and TRPV6), buffering and/or transport by calbindin-D9k (CaBP-9k) and -D28k (CaBP-28k), and extrusion through the plasma membrane calcium ATPase 1b (PMCA1b) and sodium/calcium exchanger 1. Although the molecular mechanism of calcium absorption has been studied using knockouts (KOs) of the vitamin D receptor and CaBP-28k in animals, the process is not fully understood.

MATERIALS AND METHODS

We generated CaBP-9k KO mice and assessed the phenotypic characterization and the molecular regulation of active calcium transporting genes when the mice were fed different calcium diets during growth.

RESULTS

General phenotypes showed no distinct abnormalities. Thus, the active calcium transport of CaBP-9k-null mice proceeded normally in this study. Therefore, the compensatory molecular regulation of this mechanism was elucidated. Duodenal TRPV6 and CaBP-9k mRNA of wildtype (WT) mice increased gradually during preweaning. CaBP-9k is supposed to be an important factor in active calcium transport, but its role is probably compensated for by other calcium transporter genes (i.e., intestinal TRPV6 and PMCA1b) during preweaning and renal calcium transporters in adult mice.

CONCLUSIONS

Depletion of the CaBP-9k gene in a KO mouse model had little phenotypic effect, suggesting that its depletion may be compensated for by calcium transporter genes in the intestine of young mice and in the kidney of adult mice.

Uterine TRPV6 expression during the estrous cycle and pregnancy in a mouse model

Maintenance of uterine calcium balance is crucial for physiological functioning, including smooth muscle contraction and embryo implantation. Although calbindins were previously thought to act as important uterine calcium-processing genes for female reproductive function, they were not enough to attest the roles of calcium ions in the reproductive organs. Previously, we reported that rat transient receptor potential cation channel, subfamily V, member 6 (TRPV6) was expressed and regulated by hormones in the uterus. In the present study, we observed uterine TRPV6 expression in a mouse model to clarify the mutual roles of these two calcium-processing genes in female reproductive organs. We investigated uterine TRPV6 mRNA expression during the estrous cycle and pregnancy, as well as its regulation by the steroid hormones estrogen (E2) and progesterone (P4) in mice. Uterine TRPV6 mRNA levels increased at estrus and fluctuated in the uterus, placenta, and fetal membrane during pregnancy. Uterine TRPV6 mRNA increased in mid- and late pregnancy, and its expression was strongly induced in midpregnancy in the labyrinth and spongy zones of the placenta, and in the fetal membrane. E2 (17beta-estradiol) was found to regulate uterine TRPV6 expression in the luminal and glandular epitheliums. In addition, we determined that ERalpha tightly regulated uterine TRPV6 transcription. Together, these results suggest that for uterine function in normal pregnancy, TRPV6 is regulated by E2 via an ERalpha-dependent pathway.

Calbindin D9k is not required for 1,25-dihydroxyvitamin D3-mediated Ca2+ absorption in small intestine

The exact role of calbindin D9k in vitamin D-mediated calcium absorption has been debated but remains unsettled. In 129/OlaHsd mice, calbindin D9k was found highest in duodenum (36-50%) and kidney (24-34%) followed by stomach, lung and uterus. Age does not affect the relative distribution of calbindin D9k but it does decline with age in duodenum of both male and female 129/Ola mice. Recently, we produced a null calbindin D9k mutant 129/OlaHsd mouse; this mouse proved to be indistinguishable from the wild-type in phenotype and in a serum calcium level regardless of age or gender. We have now examined directly whether the mutant mouse can absorb calcium from the intestine in response to the active form of vitamin D. The calbindin D9k null mutant mouse is fully able to absorb calcium from the intestine in response to 1,25-dihydroxyvitamin D3. It is, therefore, clear that calbindin D9k is not required for vitamin D-induced intestinal calcium absorption.

Anti-progestogenic effect of flutamide on uterine expression of calbindin-D9k mRNA and protein in immature mice

A calcium binding protein, calbindin-D9k (CaBP-9k), is a cytosolic protein and regulated by steroid hormones in the reproductive tissues. Mouse CaBP-9k gene was predominantly regulated by progesterone (P4), whereas rat CaBP-9k was mainly regulated by 17beta-estradiol (E2) in the uterus. The induction of CaBP-9k can be employed as a biomarker for steroidal substrates as endocrine disruptors (EDs). Flutamide (FLU) is a non-steroidal anti-androgen or pro-drug that is rapidly metabolized to hydroxyflutamide, which may have both an anti-androgenic and anti-progestogenic activities. Thus, in the present study, we employed immature mice (14-day-old) subcutaneously injected with P4 (20 mg/kg/day) and/or FLU (5 mg/kg/day) for 3 consecutive days in the presence or absence of RU486, a pure PR antagonist (30 mg/kg/day), to analyze uterine CaBP-9k expression in this model. When immature mice were treated with P4, the expression levels of CaBP-9k mRNA and protein were significantly increased by P4. P4-induced expression levels of CaBP-9k mRNA and protein were abolished by FLU, in part, suggesting that FLU is a partial antagonist of P4 in the regulation of uterine CaBP-9k in immature mice. In addition, P4-induced CaBP-9k expression was completely reversed by RU486. Increased expression levels of CaBP-9k mRNA and protein were maintained for 24h after final injection with P4 in a time-dependent manner. However, CaBP-9k mRNA rapidly disappeared after 48 h and its protein level is similar with its mRNA. Treatment with FLU suppressed partially P4-induced CaBP-9k mRNA and protein until 24 h. Taken together, these results indicate that FLU has an anti-progestogenic activity and plays a role as a partial antagonist of P4 in the regulation of uterine CaBP-9k in immature mouse model.

Biology and physiology of Calbindin-D9k in female reproductive tissues: involvement of steroids and endocrine disruptors

Although Calbindin-D9k (CaBP-9k), a cytosolic calcium binding protein which has calcium binding sites, is expressed in various tissues, i.e., intestine, uterus, and placenta, potential roles of this gene and its protein are not clearly understood. Uterine CaBP-9k may be involved in controlling myometrial activity related with intracellular calcium level and is not under the control of vitamin D despite the presence of vitamin D receptors. But, it is under the control of the sex steroid hormones, estrogen (E2) and progesterone (P4), in female reproductive systems including the uterus and placenta. Thus, in this review, we summarize recent research literature in regards to the expression and regulation of CaBP-9k in mammals and introduce the research data of recent studies by us and others.

Gene expression changes induced in the testis by transplacental exposure to high and low doses of 17{alpha}-ethynyl estradiol, genistein, or bisphenol A

The purpose of this study was to determine (1) the transcriptional program elicited by exposure to three estrogen receptor (ER) agonists: 17 alpha-ethynyl estradiol (EE), genistein (Ges), and bisphenol A (BPA) during fetal development of the rat testis and epididymis; and (2) whether very low dosages of estrogens (evaluated over five orders of magnitude of dosage) produce unexpected changes in gene expression (i.e., a non-monotonic dose-response curve). In three independently conducted experiments, Sprague-Dawley rats were dosed (sc) with 0.001-10 microg EE/kg/day, 0.001-100 mg Ges/kg/day, or 0.002-400 mg BPA/kg/day. While morphological changes in the developing reproductive system were not observed, the gene expression profile of target tissues were modified in a dose-responsive manner. Independent dose-response analyses of the three studies identified 59 genes that are significantly modified by EE, 23 genes by Ges, and 15 genes by BPA (out of 8740), by at least 1.5 fold (up- or down-regulated). Even more genes were observed to be significantly changed when only the high dose is compared with all lower doses: 141, 46, and 67 genes, respectively. Global analyses aimed at detecting genes consistently modified by all of the chemicals identified 50 genes whose expression changed in the same direction across the three chemicals. The dose-response curve for gene expression changes was monotonic for each chemical, with both the number of genes significantly changed and the magnitude of change, for each gene, decreasing with decreasing dose. Using the available annotation of the gene expression changes induced by ER-agonist, our data suggest that a variety of cellular pathways are affected by estrogen exposure. These results indicate that gene expression data are diagnostic of mode of action and, if they are evaluated in the context of traditional toxicological end-points, can be used to elucidate dose-response characteristics.