Abstract OT1-01-02: An open-label, randomized, multi-center phase 2 study evaluating the activity of lasofoxifene relative to fulvestrant for the treatment of postmenopausal women with locally advanced or metastatic ER+/HER2 - breast cancer (MBC) with an ESR1 mutation

Endocrine based therapy is the standard treatment for estrogen receptor positive (ER+) MBC. Agents targeting the ER pathway including aromatase inhibitors (AIs), fulvestrant and tamoxifen along with CDK 4/6 inhibitors are considered standard for first and 2nd line treatment. However, endocrine resistance develops in nearly all patients and the optimal systemic therapy after progression on a CDK 4/6 inhibitor is unknown.

Lasofoxifene is a third generation SERM previously investigated for the treatment of osteoporosis and vulvo-vaginal atrophy (VVA). In a large phase 3 trial evaluating the efficacy of lasofoxifene for the postmenopausal treatment of osteoporosis, lasofoxifene significantly reduced the incidence of ER+ breast cancer. Further unpublished preclinical data have demonstrated significant in vitro and in vivo efficacy in non-clinical breast cancer models including models with and without ESR1 mutants. Moreover, lasofoxifene significantly reduced metastases in ESR1 mutated models. These non-clinical and clinical data provide a strong rationale to pursue a phase 2 clinical trial in women with ER+, ESR1 mutated MBC.

This open-label, multi-center study will compare the efficacy and tolerability of lasofoxifene (5 mg orally daily) to fulvestrant (IM 500 mg D1,15,29 and then q30 D) in a 1:1 randomization. Inclusion criteria include postmenopausal women with ER+ advanced breast cancer; progression on a non-steroidal AI in combination with a CDK 4/6 inhibitor; and a known ESR1 mutation. Approximately 90 patients with measurable or evaluable disease (i.e. bone only) will be recruited to have at least 40 patients per treatment arm. The primary endpoint will be progression free survival (PFS) with secondary endpoints of objective response rate (ORR), clinical benefit rate (CBR), duration of response (DoR) and time to response (TTR). It is assumed that lasofoxifene will double the median PFS compared to fulvestrant in this ESR1 mutation patient population for a hazard ratio 0.5 and a power of 89% to reach a 1-sided p of <0.05.

The study will commence in 4Q2018 and will complete recruitment in 1 year. It is anticipated that 25-30 centers in the US will be participating.

Citation Format: Plourde PV, Schwartzberg LS, Greene GL, Portman DJ, Komm BS, Jenkins SN, Liu P-Y, Portman MD, Goetz MP. An open-label, randomized, multi-center phase 2 study evaluating the activity of lasofoxifene relative to fulvestrant for the treatment of postmenopausal women with locally advanced or metastatic ER+/HER2 - breast cancer (MBC) with an ESR1 mutation [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT1-01-02.

Cardiovascular safety of conjugated estrogens plus bazedoxifene: meta-analysis of the SMART trials

OBJECTIVES

Five randomized, phase-3 trials demonstrated the efficacy and safety of conjugated estrogens/bazedoxifene (CE/BZA) in treating menopausal symptoms and preserving bone. This pooled analysis of these studies describes the cardiovascular safety of CE/BZA.

METHODS

We pooled cardiovascular adjudicated safety data from healthy, non-hysterectomized, postmenopausal women who received ≥ 1 dose of CE 0.45 mg/BZA 20 mg (n = 1585), CE 0.625 mg/BZA 20 mg (n = 1583), any CE/BZA dose (n = 4868), or placebo (n = 1241) for up to 2 years in five trials. Venous thromboembolic events (VTEs), coronary heart disease (CHD), and cerebrovascular events were reviewed by three different independent adjudication committees and summarized using a meta-analytic approach.

RESULTS

The rate of VTEs per 1000 woman-years (95% confidence interval, CI) was 0.3 (0.0-2.0) in women taking CE 0.45 mg/BZA 20 mg, 0 (0.0-1.5) in those taking CE 0.625 mg/BZA 20 mg, 0.7 (0.0-1.5) among women taking any CE/BZA dose, and 0.6 (0.0-2.9) with placebo. The incidence of stroke per 1000 woman-years (95% CI) was 0.4 (0.0-2.4), 0.2 (0.0-1.9), 0.44 (0.0-1.1), and 0.0 (0.0-1.7), respectively. The CHD rate per 1000 woman-years was 2.6 (0.0-5.6), 1.4 (0.0-3.9), 2.4 (1.00-3.7) and 2.0 (0.0-5.2). Compared with placebo, relative risk (95% CI) with any CE/BZA dose was 0.5 (0.1-1.8) for VTE, 0.5 (0.1-2.6) for stroke, and 0.63 (0.23-1.74) for CHD.

CONCLUSIONS

Up to 2 years of CE 0.45 or CE 0.625 mg with BZA 20 mg had an acceptable cardiovascular safety profile, with rates of stroke and CHD comparable to placebo in healthy postmenopausal women. VTE risk was low.

Effects of bazedoxifene/conjugated estrogens on endometrial safety and bone in postmenopausal women

OBJECTIVES

Bazedoxifene/conjugated estrogens (BZA/CE) has demonstrated efficacy in improving vasomotor and vulvar/vaginal atrophy symptoms in postmenopausal women. This study evaluated the endometrial safety of BZA/CE and effects on bone mineral density (BMD) compared with CE/medroxyprogesterone acetate (MPA) and placebo.

METHODS

The Selective estrogens, Menopause, And Response to Therapy (SMART)-4 trial was a 1-year, multicenter, double-blind, randomized, placebo- and active-controlled, phase-3 study in non-hysterectomized, postmenopausal women (n = 1061; aged 40 -< 65 years). Subjects received BZA 20 mg/CE 0.45 or 0.625 mg, CE 0.45 mg/MPA 1.5 mg, or placebo daily. Primary endpoints were the incidence of endometrial hyperplasia and the change in lumbar spine BMD at 1 year. Secondary endpoints included the change in total hip BMD and rates of amenorrhea and breast pain.

RESULTS

At 1 year, no cases of endometrial hyperplasia were identified in the BZA 20-mg/CE 0.45-mg group, while three cases (1.1%) were confirmed for the BZA 20-mg/CE 0.625-mg group (95% one-sided confidence interval upper limit < 4%). Both BZA/CE doses significantly increased lumbar spine and total hip BMD versus placebo (p ≤ 0.001) and showed low incidences of bleeding and breast tenderness, similar to placebo and significantly lower than for CE 0.45 mg/MPA 1.5 mg (p < 0.05). BZA/CE treatment was generally safe and well tolerated.

CONCLUSIONS

BZA 20 mg/CE 0.45 and 0.625 mg significantly improved BMD while maintaining endometrial safety and showed a favorable safety/tolerability profile over 1 year. BZA/CE may be a promising therapy for treating menopausal symptoms and preventing osteoporosis in non-hysterectomized, postmenopausal women.

Transcriptional profiling of human osteoblast differentiation

Osteoblast differentiation is a key aspect of bone formation and remodeling. To further our understanding of the differentiation process, we have developed a collection of conditionally immortalized adult human osteoblast cell lines representing discrete stages of differentiation. To evaluate changes in gene expression associated with differentiation, polyA((+)) RNA from pre-osteoblasts, early and late osteoblasts, and pre-osteocytes was subjected to gene chip analysis using the Affymetrix Hu6800 chip in conjunction with an Affymetrix custom chip enriched in bone and cartilage cDNAs. Overall, the expression of 47 genes was found to change threefold or more on both chips between the pre-osteoblastic and pre-osteocytic stages of differentiation. Many of the observed differences, including down-regulation of collagen type I and collagen-processing enzymes, reflect expected patterns and support the relevance of our results. Other changes have not been reported and offer new insight into the osteoblast differentiation process. Thus, we observed regulation of factors controlling cell cycle and proliferation, reflecting decreased proliferation, and increased apoptosis in pre-osteocytic cells. Elements maintaining the cytoskeleton, extracellular matrix, and cell-cell adhesion also changed with differentiation reflecting profound alterations in cell architecture associated with the differentiation process. We also saw dramatic down-regulation of several components of complement and other immune response factors that may be involved in recruitment and differentiation of osteoclasts. The decrease in this group of genes may provide a mechanism for controlling bone remodeling of newly formed bone. Our screen also identified several signaling proteins that may control osteoblast differentiation. These include an orphan nuclear receptor DAX1 and a small ras-related GTPase associated with diabetes, both of which increased with increasing differentiation, as well as a high mobility group-box transcription factor, SOX4, that was down-regulated during differentiation. In summary, our study provides a comprehensive transcriptional profile of human osteoblast differentiation and identifies several genes of potential importance in controlling differentiation of osteoblasts.

Developing a SERM: stringent preclinical selection criteria leading to an acceptable candidate (WAY-140424) for clinical evaluation

Estrogens are represented by a diverse group of compounds. Within this large family of molecules are tissue-selective estrogens that have been classified as selective estrogen receptor modulators (SERMs). These compounds are characterized by the fact that they exhibit both estrogen agonist and antagonist activity dependent upon the gene promoter and target tissue being examined. SERMs have been intensively studied over the past decade, especially since one, raloxifene, has been approved for the prevention and treatment of postmenopausal osteoporosis. While not a replacement for hormone replacement therapy (HRT), raloxifene can be an alternative to it and other treatments for osteoporosis. The ideal SERM would provide the positive benefits associated with HRT without the uterine and breast stimulation. Raloxifene does achieve some of the benefits of HRT, specifically on the skeleton and lipid metabolism with no apparent uterine effects, and a potential decreased risk of developing breast cancer associated with raloxifene therapy. However, there are a number of parameters that can be improved. A number of SERMs have been evaluated only to fail in development due to, for the most part, uterine safety issues. In order to develop an improved SERM, a stringent screening process was designed to select compounds that did not stimulate the uterus or breast. At the same time, these new compounds would have a positive impact on the skeleton and lipid metabolism with the additional improvement (over raloxifene) of a neutral effect on hot flashes. Under these strict conditions, WAY-140424 was developed and, to date, the preclinical pharmacology data have accurately predicted the clinical response demonstrated in phase I and II trials.

A new antiestrogen, 2-(4-hydroxy-phenyl)-3-methyl-1-[4-(2-piperidin-1-yl-ethoxy)-benzyl]-1H-indol-5-ol hydrochloride (ERA-923), inhibits the growth of tamoxifen-sensitive and -resistant tumors and is devoid of uterotropic effects in mice and rats

PURPOSE

Tamoxifen is an antiestrogen used in women who have estrogen receptor (ER)-alpha-positive breast cancer. Unfortunately, resistance to tamoxifen is common in women with metastatic disease and side effects, including increased risk of endometrial cancer, exist. Here we describe the activity of a new selective ER modulator, ERA-923, in preclinical models focused on these limitations.

EXPERIMENTAL DESIGN

The ability of ERA-923, 4-OH tamoxifen, or raloxifene to inhibit estrogen-stimulated growth was evaluated in cell-based and xenograft assays with tumor cells that are sensitive or resistant to tamoxifen. Uterine effects of selective ER modulators were compared in rodents.

RESULTS

ERA-923 potently inhibits estrogen binding to ER-alpha (IC(50), 14 nM). In ER-alpha-positive human MCF-7 breast carcinoma cells, ERA-923 inhibits estrogen-stimulated growth (IC(50), 0.2 nM) associated with cytostasis. In vitro, a MCF-7 variant with inherent resistance to tamoxifen (10-fold) or 4-OH tamoxifen (>1000-fold) retains complete sensitivity to ERA-923. Partial sensitivity to ERA-923 exists in MCF-7 variants that have acquired profound tamoxifen resistance. In tumor-bearing animals, ERA-923 (10 mg/kg/day given p.o.) inhibits 17beta-estradiol-stimulated growth in human tumors derived from MCF-7, EnCa-101 endometrial, or BG-1 ovarian carcinoma cells, including a MCF-7-variant that is inherently resistant to tamoxifen. Raloxifene is inactive in the MCF-7 xenograft model. Unlike tamoxifen, droloxifene, or raloxifene, ERA-923 is not uterotropic in immature rats or ovariectomized mice. Consistent with this, tamoxifen, but not ERA-923, stimulates the growth of EnCa-101 tumors.

CONCLUSIONS

In preclinical models, ERA-923 has an improved efficacy and safety compared with tamoxifen. Clinical trials with ERA-923 are in progress.

Expression and regulation of Runx2/Cbfa1 and osteoblast phenotypic markers during the growth and differentiation of human osteoblasts

The runt family transcription factor (AML-3/PEBP2alphaA1/Cbfa1/RUNX2) plays a crucial role in formation of the mineralized skeleton during embryogenesis and regulates maturation of the osteoblast phenotype. Because steroid hormones and growth factors significantly influence growth and differentiation properties of osteoblasts, we addressed Cbfa1 as a target gene for regulation by dexamethasone (Dex), 1,25(OH)D(3) (vitamin D(3)), 17beta-estradiol, and transforming growth factor-beta1 (TGF-beta1). The representation of functional protein levels by Western blot analyses and gel mobility shift assays was examined during the growth and mineralization of several conditionally immortalized human osteoblast cell lines HOB 04-T8, 03-CE6, and 03-CE10, each representing different stages of maturation. In situ immunofluorescence demonstrates Cbfa1 is associated with nuclear matrix in punctate domains, some of which are transcriptionally active, colocalizing with phosphorylated RNA polymerase II. Although each of the cell lines exhibited different responses to the steroid hormones and to TGF-beta1, all cell lines showed a similar increase in Cbfa1 protein and DNA binding activity induced only by Dex. On the other hand, Cbfa1 mRNA levels were not altered by Dex treatment. This regulation of Cbfa1 by steroid hormones in human osteoblasts contrasts to modifications in Cbfa1 expression in primary rat calvarial osteoblasts and the mouse MC3T3-E1 osteoblast cell line. Thus, these results reveal multiple levels of regulation of Cbfa1 expression and activity in osteoblasts. Moreover, the data suggest that in committed human osteoblasts, constitutive expression of Cbfa1 may be required to sustain the osteoblast phenotype.

Synthesis and estrogenic activities of novel 7-thiosubstituted estratriene derivatives

A diastereomerically pure series of 7alpha-thioestratrienes was prepared and evaluated for its affinity for both the human estrogen receptor alpha and the more recently discovered estrogen receptor beta. The functional estrogenic activities of the compounds were measured in a MCF-7 ERE-tk-luciferase assay. The activities and selectivities of the compounds were sensitive to the nature of the thioether side chain.

Evidence that conditionally immortalized human osteoblasts express an osteocalcin receptor

Osteocalcin (OC) is an abundant noncollagenous bone matrix protein, yet its function is largely unknown. However, targeted ablation of two OC genes in mice lead to increased bone formation (Ducy et al. Nature 382:448-452; 1996). This implied that OC inhibits osteoblast activity, and that these cells express an OC receptor. In order to characterize the putative OC receptor, we used the Cytosensor microphysiometer to measure responses of a proliferative-stage, conditionally immortalized human osteoblast cell line (HOB-03-C5) to purified bovine OC (bOC). The Cytosensor measures a change in the extracellular acidification rate, which is primarily a measurement of metabolic activity. Treatment of the HOB cells for 5-60 sec with 0.17 micromol/L bOC generated a time-dependent, transient increase in the acidification rate that became optimal after 25 sec. Likewise, treatment of the cells for 25 sec with 0.021 to 1.9 micromol/L bOC caused a dose-dependent 70% increase in the acidification rate. Pre-treatment of the cells for 2 h with inhibitors of adenylyl cyclase, phospholipase C, and intracellular calcium release inhibited the response of the cells to bOC by 50%-100%, which suggested that the putative OC receptor was coupled to a G-protein. These observations from the Cytosensor were confirmed by measuring intracellular cyclic-adenosine monophosphate (cAMP) concentrations in response to bOC. Treatment of the cells for 10 min with bOC decreased basal cAMP levels by 65% in a dose-dependent manner with an IC50 of 0.22 microM. However, cotreatment of the cells with forskolin, which activates adenylyl cyclase, blunted this suppression. Moreover, pretreatment of the cells with pertussis toxin for 48 h, which inhibits G(alpha)i proteins, reversed the suppressive effects of bOC on cAMP production. Treatment of the HOB cells for 48 h with 0.19 to 1.5 micromol/L bOC caused a dose-dependent 40% decrease in alkaline phosphatase activity with an IC50 of 0.21 micromol/L, which suggested that OC may inhibit HOB activity. Finally, although the maturation stage, conditionally immortalized HOB-02-C1 cells also responded to bOC as measured by the Cytosensor, two osteosarcoma cell lines, SaOS-2 and ROS 17/2.8, exhibited a 5- to 10-fold lower response to the bone matrix protein, suggesting that the putative OC receptor was downregulated in these cells. However, all of these bone cell lines responded to parathyroid hormone treatment. In conclusion, these results provide evidence that the HOB cells express an OC receptor, and that this receptor appears to be coupled to a G(alpha)-protein.

Suppression of ligand-dependent estrogen receptor activity by bone-resorbing cytokines in human osteoblasts

Estrogens are important for bone homeostasis and are classified as antiresorptive agents. One of the mechanisms for this effect is the inhibition of cytokine-induced bone resorption, which is mediated in part through an interaction between the estrogen receptor (ER) and nuclear factor (NF)-kappaB in osteoblasts. We present evidence that bone-resorbing cytokines that activate NF-kappaB conversely inhibit ligand-dependent ER activity in the conditionally immortalized human osteoblast cell line, HOB-03-CE6. Treatment of HOB-03-CE6 cells with 17beta-estradiol (17beta-E2) up-regulated reporter gene activity [ERE-thymidine kinase (tk)-luciferase] 3- to 5-fold in a dose-dependent manner (EC50 = 1.0 pM). However, cotreatment of the cells with 17beta-E2 and increasing concentrations of either tumor necrosis factor-alpha (TNF alpha), interleukin-1alpha (IL-1alpha), or IL-1beta completely suppressed ERE-tk-luciferase activity in a dose-dependent manner (IC50 = 0.05-5.0 pM). On the other hand, treatment of the cells with growth factors either up-regulated or had no effect on ERE-tk-luciferase expression. Neither TNF alpha, IL-1alpha, nor IL-1beta treatment affected basal reporter gene activity in the cells, and the TNF alpha effect was reversed by a neutralizing antibody to the cytokine. TNF alpha treatment also suppressed ligand-dependent ER activity in MCF-7 human breast cancer cells, but not in Chinese hamster ovary cells that overexpressed human ER alpha, even though both cell lines responded to the cytokine as measured by the up-regulation of NFkappaB-tk-luciferase activity. TNF alpha treatment did not affect the steady state levels of either ER alpha or ER beta messenger RNA expression by the HOB-03-CE6 cells, nor did it reduce [125I]17beta-E2 binding. Moreover, TNF alpha treatment only weakly inhibited ligand-dependent glucocorticoid receptor activity in the HOB-03-CE6 cells. Bone-resorbing cytokines, which do not signal through the NF-kappaB pathway, did not suppress ERE-tk-luciferase activity in HOB-03-CE6 cells. Treatment of the cells with 17beta-E2 partially suppressed the activation of NF-kappaB by TNF alpha, but did not block cytokine-induced IL-6 secretion. Finally, cotreatment of HOB-03-CE6 cells with an antisense oligonucleotide to NF-kappaB p50 partially reversed the suppression of ERE-tk-luciferase activity by TNF alpha. In summary, these data provide evidence for a potent feedback inhibition of estrogen action in human osteoblasts that is at least partly mediated by the activation of NF-kappaB.

A novel human estrogen receptor beta: identification and functional analysis of additional N-terminal amino acids

A novel human estrogen receptor beta (hERbeta) was cloned from human testis mRNA, ovary and thymus cDNA utilizing PCR and 5' RACE methods. The 5' end of hERbeta contained an additional open reading frame, in-frame and upstream of the published clones. hERbeta encodes a protein of 530 amino acids with an approximate molecular weight of 63 kDa and is larger than the previously reported rat, mouse and human protein. To determine the functional role of additional N-terminal amino acids, we compared the transcription functions of receptor lacking (hERbetaT) and receptor containing (hERbetaL) this N-terminal extension. hERbetaL is more active than hERbetaT in transactivating ERE-based reporter genes. hERbetaL, but not hERbetaT, attenuated cytokine mediated NFkappaB activation. Taken together, the additional N-terminal amino acids appear to play a role in modulating estrogen responsive gene expression in vitro.

Estrogen Receptor-α Is Developmentally Regulated during Osteoblast Differentiation and Contributes to Selective Responsiveness of Gene Expression

Estrogen responsiveness of bone is a fundamental regulatory mechanism operative in skeletal homeostasis. We examined the expression of estrogen receptor-alpha (ER) messenger RNA (mRNA) in cultured rat calvarial-derived osteoblasts during progressive development of the osteoblast phenotype. Levels of ER message were compared with the expression of traditional osteoblastic markers that have been mapped throughout the differentiation process of these cells. ER transcripts, measured using semiquantitative RT-PCR analysis, were expressed at low levels in early stage proliferating osteoblasts and increased at confluence upon initial expression of bone cell phenotypic genes. A 23-fold up-regulation of ER mRNA expression coincided with the initiation of alkaline phosphatase activity (day 8). ER mRNA levels progressively increased 70-fold, reaching a maximum level on days 22-25 in fully differentiated osteoblasts when osteocalcin expression peaked, but declined precipitously by day 32 in osteocytic cells. Analysis of RNA isolated directly from rat calvaria confirmed these in vitro results and demonstrated that ER message levels become more abundant postnatally as bone becomes more mineralized. We also examined the responsiveness of osteoblasts to 17beta-estradiol (17beta-E2) at two periods of maturation: the nodule-forming stage (day 14) and the late mineralization stage (day 30). Estradiol suppressed the levels of alkaline phosphatase, osteocalcin, osteonectin, and ER mRNAs on day 14, but up-regulated these messages on day 30. In contrast, 17beta-E2 treatment regulated the steady state levels of transforming growth factor-beta1 and type I procollagen mRNAs only in the late mineralization stage, whereas histone H4 message was unaffected by the steroid at either stage of differentiation. Thus, the observed developmental expression of ER mRNA correlates with progressive osteoblast differentiation and may be a contributing factor to differential regulation of bone cell gene expression by 17beta-E2.

Expression of meltrin-alpha mRNA is not restricted to fusagenic cells

Meltrin-alpha is a myoblast gene product reported to be required for cell fusion [Yagami-Hiromasa et al. (1995): Nature 377:652-656]. Because Northern blots revealed expression only in muscle and bone, the suggestion was made that meltrin-alpha is expressed exclusively by fusagenic cells in these tissues (myoblast and osteoclast). We studied expression of meltrin-alpha mRNA in a panel of tissues and cell lines using the polymerase chain reaction and found it widely expressed. Meltrin-alpha mRNA was readily detected in the osteoblast, the most abundant cell type in bone. In situ hybridization analysis on sections of neonatal mice revealed high levels of expression in the trabecular meshwork of long bones, the basal regions of the dermis and its underlying mesenchyme. We conclude that expression of meltrin-alpha mRNA is not restricted to fusagenic cells and that, in bone, the osteoblast is the major source.

Functional properties of a conditionally phenotypic, estrogen-responsive, human osteoblast cell line

Osteoblasts are established targets of estrogen action in bone. We screened 66 conditionally immortalized clonal human osteoblast cell lines for estrogen receptors (ERs) using reverse transcriptase-polymerase chain reaction (RT-PCR) analysis for ER alpha mRNA and transactivation of adenovirus-estrogen response element (ERE)-tk-luciferase by 17 beta-estradiol (17 beta-E2) for functional ER protein. One of these cell lines, termed HOB-03-CE6, was chosen for further characterization. The cells, which were conditionally immortalized with a temperature-sensitive SV40 large T antigen, proliferated at the permissive temperature (34 degrees C) but stopped dividing at the nonpermissive temperature (> or = 39 degrees C). Alkaline phosphatase activity and osteocalcin secretion were upregulated by 1 alpha, 25-dihydroxyvitamin D3 in a dose-dependent manner. The cells also expressed type I collagen and other bone matrix proteins, secreted a variety of growth factors and cytokines, formed mineralized nodules based on alizarin red-S and von Kossa histochemical staining, and responded to dexamethasone, all-trans retinoic acid, and transforming growth factor-beta 1. This cell line expressed 42-fold less ER message than MCF-7 human breast cancer cells, as determined by quantitative RT-PCR. However, adenovirus-ERE-tk-luciferase activity was upregulated three- to fivefold in these cells by 17 beta-E2 with an EC50 of 64 pM. Furthermore, this upregulation was suppressed by co-treatment with the anti-estrogen ICI-182, 780. Cytosolic extracts of these cells specifically bound [125I]-17 beta-E2 in a concentration-dependent manner with a Bmax of 2.7 fmoles/mg protein (approximately 1,200 ERs/cell) and a Kd of 0.2 nM. DNA gel-shift analysis using a [32P]-ERE demonstrated the presence of ERs in nuclear extracts of these cells. Moreover, binding of the extracts to this ERE was blocked by a monoclonal antibody to the human ER DNA-binding domain. We evaluated these cells for 14 of 20 reported endogenous responses to 17 beta-E2 in osteoblasts. Although most of these responses appeared to be unaffected by the steroid, 17 beta-E2 suppressed parathyroid hormone-induced cAMP production, as well as basal interleukin-6 mRNA expression; conversely, the steroid upregulated the steady-state expression of alkaline phosphatase message in these cells. In summary, we have identified a clonal, conditionally phenotypic, human osteoblast cell line that expresses functional ERs and exhibits endogenous responses to 17 beta-E2. This cell line will be a valuable in vitro model for exploring some of the molecular mechanisms of estrogen action in bone.

Establishment and hormonal regulation of a conditionally transformed preosteocytic cell line from adult human bone

Osteocytes are differentiated forms of osteoblasts that arise upon entrapment within the bone matrix. In this report, we describe the establishment and hormonal regulation of the first conditionally transformed human preosteocytic cell line. Primary adult bone cells were obtained from protease cell line. Primary adult bone cells were obtained from protease digestion of cancellous chips. The cells were infected with adenovirus-ori- SV40 tsA 209, which encodes for a temperature-sensitive large T-antigen. After immortalization, we isolated a clone designated HOB-01-C1. This cell line expressed the mutant T-antigen and proliferated at the permissive temperature (34 C) but stopped dividing at the nonpermissive temperature (39-40 C). Electron microscopy of cells incubated at 39 C demonstrated the presence of preosteocytic cellular processes, some of which appeared to form gap junctions or were rich in microfilaments. The clone expressed alpha 1 type (I) procollagen messenger RNA (mRNA) and secreted type I procollagen C peptide at both temperatures, and this expression was elevated 1.6-fold to 1.8-fold at 40 degrees C. The cells expressed very low basal levels of alkaline phosphatase activity (approximately 0.02 nmol/min.mg), which was increased 2- to 5-fold in a dose-dependent manner by 0.1-100 nM 1 alpha,25-dihydroxyvitamin D3 (vitamin D3) at both temperatures. Vitamin D3 also increased osteocalcin secretion in a dose-dependent manner when the clone was maintained at 34 C (approximately 6-fold), and this stimulation was enhanced > 5 fold at 40 C. In contrast to the low expression of alkaline phosphatase, the cells secreted high amounts of osteocalcin in response to vitamin D3 (approximately 15 ng/mg cell protein); this biochemical profile also resembled that of preosteocytes. Alizarin red-S histochemical staining demonstrated that these cells rapidly produced mineralized nodules at both temperatures. PTH (10 and 100 nM) had no effect on the intracellular accumulation of cAMP at 34 C but stimulated a 14- to 18-fold increase in the production of this second messenger at 40 C. In contrast, 100 nM prostaglandin E2 and 1 microM forskolin stimulated cAMP synthesis better at 34 C. Western blot analysis indicated that the cells expressed CD44, a putative osteocytic marker, at both temperatures. Finally, interleukin-1 beta and tumor necrosis factor-alpha (1-1000 pM) stimulated dose-dependent increases in the secretion of interleukin-6 and monocyte chemoattractant protein-1 at 34 C and 40C. We conclude that the HOB-01-C1 cell line has a preosteocytic phenotype. Moreover, these cells respond to calcitropic hormones and bone resorbing cytokines.

Development and characterization of a conditionally transformed adult human osteoblastic cell line

Many osteoblastic cell lines are currently in use, but these have limitations either in terms of their relevance to adult human biology and disease or in terms of their suitability for biochemical and molecular analyses. Consequently, we undertook the development of conditionally transformed adult human osteoblastic cell lines. Osteoblasts were obtained from a normal explant cancellous bone chip culture. These cells were infected with adenovirus-ori-SV40 tsA 209, which encodes a temperature-sensitive large T-antigen mutant. Cells immortalized with this virus express a transformed phenotype at the permissive temperature of 34 degrees C but revert to a normal phenotype at the nonpermissive temperature of 40 degrees C. Using this approach, we have isolated several cell clones and describe the characterization of one that was designated HOB-02-C1. Immunocytochemistry revealed that > 95% of the cells express the large T-antigen at both temperatures. These cells exponentially proliferate at 34 degrees C with a doubling time of approximately 2 days but irreversibly stop dividing at 40 degrees C. However, cell volume increases > 2-fold when the cells are maintained for 6 days at the higher temperature. This clone expresses alpha 1 type (I) procollagen mRNA and secretes type I procollagen C-peptide at both temperatures, although the levels were slightly elevated at 40 degrees C. The cell line expresses alkaline phosphatase activity at 34 degrees C, and the basal level of this enzyme increases 2- to 6-fold at 40 degrees C. Alkaline phosphatase activity is induced 4- to 8-fold by 1 alpha,25-dihydroxyvitamin D3 (vitamin D3) at both temperatures, but transforming growth factor-beta 1 (TGF-beta 1) suppresses enzyme expression > 90% at 40 degrees C. Vitamin D3 also induces a 10-fold increase in osteocalcin secretion when the clone is maintained at 34 degrees C, and this induction is enhanced > 8-fold at 40 degrees C. Parathyroid hormone and forskolin stimulate a 4- to 6-fold increase in the production of intracellular cyclic AMP (cAMP) by the cells at 34 degrees C, and this stimulation is enhanced 2- to 4-fold at 40 degrees C. In contrast, prostaglandin E2 stimulates a 7- to 8-fold increase in cAMP only when the cells are maintained at 34 degrees C. This cell line secretes TGF-beta 1 and interleukin-6 (IL-6) at 34 degrees C, but only the basal secretion of IL-6 increases 70% at 40 degrees C. Finally, alizarin red-S histochemical staining demonstrates that these cells produce mineralized nodules at both temperatures. In summary, the results of this study indicate that the HOB-02-C1 cells have a mature osteoblastic phenotype. Consequently, this new cell line and others obtained in a similar fashion should be valuable in vitro tools for cellular, biochemical, and molecular studies of adult human osteoblast biology.

1,25(OH)2D3-dependent regulation of calbindin-D28k mRNA requires ongoing protein synthesis in chick duodenal organ culture

Organ culture of 19-day-old chick embryo duodena was utilized to evaluate the mechanism of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3)-dependent calbindin-D28k (CaBP) expression. Duodenal CaBP and 1,25(OH)2D3 receptor (VDR) expression were assessed by Western blot analysis, while CaBP and VDR mRNA levels were determined by Northern blot analysis. In untreated duodena, both VDR protein and mRNA were present, while CaBP protein and mRNA were undetectable. Treatment of cultured duodena with 25 nM 1,25(OH)2D3 resulted in detectable CaBP mRNA after 4 h which continued to increase during a 24 h time period. Under these conditions, localization of [3H-1 beta]1 alpha,25(OH)2D3 in duodenal chromatin is rapid (< or = 30 min). Thus, the delayed accumulation of detectable CaBP mRNA cannot be explained by slow nuclear binding of 1,25(OH)2D3. The inclusion of 1.6 microM actinomycin D in the organ culture partially inhibited the 1,25(OH)2D3-regulated increase in CaBP mRNA, which implies that there is a transcriptional component involved in the increased CaBP mRNA levels. Similarly, quantitative polymerase chain reaction studies allowed the detection of CaBP pre-mRNA and mRNA sequences 1 h after hormone treatment, suggesting that CaBP gene transcription is initiated rapidly. Treatment of cultures with 36 microM cycloheximide 1 h prior to 1,25(OH)2D3 addition resulted in superinduction of VDR mRNA levels but sharply reduced CaBP steady-state mRNA levels. This dramatic reduction in CaBP mRNA reveals that 1,25(OH)2D3-mediated CaBP expression is dependent on ongoing protein synthesis. Thus, we propose that a labile auxiliary protein or other cofactor, which may or may not be 1,25(OH)2D3-dependent, is necessary for 1,25(OH)2D3-mediated CaBP gene transcription in chick duodena.

Stable expression of the calbindin-D28K complementary DNA interferes with the apoptotic pathway in lymphocytes

The WEHI7.2 thymoma cell line undergoes apoptotic cell death when exposed to glucocorticoids and agents that increase intracellular cAMP. Several lines of evidence indicate that calcium may play an important role in events culminating in lymphocyte apoptosis. In these studies, calbindin-D28K was stably overexpressed in WEHI7.2 cells to determine if increasing the Ca(2+)-binding capacity of the cell interferes with the apoptotic pathway. Indeed, stable expression of calbindin-D28K decreased the apoptotic effects of dexamethasone and forskolin, and the level of resistance to these agents correlated with the relative amount of calbindin expressed in each line. Overexpression of calbindin also increased cell survival in the presence of the calcium ionophore A23187. The stably expressed calcium-binding protein appeared to exert its protective effect subsequent to transcriptional activation, since glucocorticoid- and cAMP-induced gene expression were not affected. These data support the proposal that calcium fluxes are involved in apoptosis and suggest that high level expression of proteins that buffer calcium fluxes can effectively suppress death in apoptosis-susceptible cells.

Evaluation of a putative vitamin D response element in the avian calcium binding protein gene

A primary response of the avian intestine to 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] is increased synthesis of a 28-kD calcium-binding protein, calbindin-D28k (CaBP). This study examined whether 1,25-(OH)2D3 regulates CaBP gene transcription by an interaction of the vitamin D receptor (VDR) with a vitamin D-responsive element (VDRE) in the CaBP promoter. A genomic clone of CaBP containing about 1 kb of 5'-flanking DNA and 13 kb of the structural gene was isolated. 5'-Flanking DNA from -320 to -306 had considerable sequence similarity to VDREs identified in other genes. Indeed, a portion of the CaBP gene containing this region (-743 to +47) linked to a growth hormone reporter construct elicited a 1,25-(OH)2D3-dependent, VDR-dependent increase in reporter expression in transiently transfected chicken embryo fibroblasts. However, deletion analysis demonstrated that the sequences responsible for this induction reside 3' to -133 and the putative VDRE at -320 to -306 was not involved in the response. Furthermore, transfection of heterologous promoter constructs consisting of a Ban I fragment (-354 to -252) linked to the Herpes simplex thymidine kinase promoter revealed no effect of this region on reporter expression. Gel mobility shift analysis confirmed that this putative VDRE in the CaBP promoter was not a high-affinity binding site for VDR. Consequently, functional significance with respect to the primary induction of CaBP by 1,25-(OH)2D3 cannot be ascribed to this region of the CaBP promoter.

Dietary restriction of calcium, phosphorus, and vitamin D elicits differential regulation of the mRNAs for avian intestinal calbindin-D28k and the 1,25-dihydroxyvitamin D3 receptor

We investigated the regulation of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]-induced calbindin-D28k (CaBP) and of the vitamin D receptor (VDR) by evaluating CaBP protein, CaBP mRNA, and VDR mRNA under conditions of altered intake of vitamin D, calcium, or phosphorus. Chickens were maintained for 10 days on one of four diets: vitamin D-deficient, normal (1.0% Ca and 1.1% P), low calcium (0.1% Ca and 1.2% P), and low phosphorus (1.1% Ca and 0.3% P). CaBP was undetectable in D-deficient duodena and was elevated above normal values by low-calcium (3.1-fold) and low-phosphorus (2.3-fold) intake. Contradictory to published data, we observed a correlation between CaBP protein and mRNA levels in that the CaBP mRNA was absent in D-deficient intestine and augmented threefold and twofold in low-calcium and low-phosphate duodena, respectively. In contrast, VDR mRNA concentrations were identical in vitamin D-deficient and normal duodena, implying that intestinal VDR is not dependent upon 1,25-(OH)2D3 for basal expression. Chickens fed a low-phosphorus diet displayed a twofold increase in VDR mRNA, but those fed a low-calcium diet exhibited a dramatic decrease in VDR mRNA. These data show that CaBP mRNA and protein levels are modulated in a tightly coupled fashion, and they are consistent with previous conclusions that augmented circulating 1,25-(OH)2D3 stimulates CaBP expression when dietary calcium or phosphorus is limiting. However, a more complex regulation of VDR expression occurs in that low-phosphorus restriction enhances VDR mRNA levels, possibly via increased circulating 1,25-(OH)2D3. Conversely, reduced dietary calcium diminishes VDR mRNA despite increased circulating 1,25-(OH)2D3, indicating that another factor, such as parathyroid hormone, is a predominant downregulator of VDR.

Evidence for early induction of calmodulin gene expression in lymphocytes undergoing glucocorticoid-mediated apoptosis

Glucocorticoid treatment of certain lymphoma cell lines and thymocytes activates a self-destructive pathway of programmed cell death referred to as apoptosis. Calcium and calmodulin (CaM) may be important signals in the apoptotic cascade because an early event is a sustained elevation in cytosolic Ca2+ and CaM inhibitors interfere with the death pathway. In the present study, expression of the CaM gene was examined during glucocorticoid-induced apoptosis in WEHI7.2 lymphocytes. Steady state levels of CaM mRNA were increased up to 10-fold following a 4-6-h exposure of WEHI7.2 cells to 10(-6) M dexamethasone. This increase was mediated through the glucocorticoid receptor since the response was not observed in WEHI7.418, a variant line which does not express active glucocorticoid receptor. Induction of CaM mRNA was dose-dependent and highly specific for glucocorticoids, as other steroids were unable to elicit the response. A stringent cell specificity was also observed. Pretreatment of WEHI7.2 lymphocytes with cycloheximide did not interfere with dexamethasone-dependent increases in CaM mRNA levels, and studies with actinomycin D demonstrated that the stability of the transcript was not altered by hormone, Finally, a calmodulin inhibitor elicited a protective effect on WEHI7.2 cells following glucocorticoid exposure. These results indicate that CaM mRNA levels were hormonally controlled in WEHI7.2 lymphocytes and support the putative involvement of CaM in glucocorticoid-induced apoptosis.

Estrogen binding and estrogenic responses in normal human osteoblast-like cells

A finite human cell line was established from trabecular bone explants obtained from a 48-year-old woman. These cells, designated BG688, were characterized as osteoblast-like in phenotype using the following independent criteria: (1) the presence of histochemically detectable alkaline phosphatase (AP) activity; (2) response to the calciotropic hormone 1,25-(OH)2D3 as assessed by increased AP activity; (3) synthesis and secretion of the osteoblast-specific marker bone gla protein; and (4) expression of alpha 1(I)-procollagen and alpha 1(III)-procollagen mRNAs in a pattern similar to that of other osteoblast-like cell lines. In addition to these classic osteoblast markers, BG688 cells also possess approximately 2400 high-affinity (Kd = 0.45 nM) 17 beta-estradiol (E2) binding sites per cell. The binding of E2 to these sites is specific, and of the steroid hormone agonists tested, E2 and diethylstilbestrol elicited the greatest amount of competition with radiolabeled E2. BG688 cells were also shown to respond to a physiologic concentration (10 nM) of E2. In vitro translation products of poly(A)+ RNA obtained from control and hormone-treated cells revealed a pleiotropic influence of E2 on the relative abundance of several mRNAs as assessed by two-dimensional gel electrophoretic analysis of their corresponding peptides. E2 also elicits a twofold increase in the steady-state concentration of alpha 1(I)-procollagen mRNA as demonstrated by northern blot hybridization. Thus, we here extend our previous data obtained in osteoblast-like osteosarcoma cells to indicate that a normal osteoblastic cell line is a target for the action of estrogen.(ABSTRACT TRUNCATED AT 250 WORDS)

High-affinity androgen binding and androgenic regulation of alpha 1(I)-procollagen and transforming growth factor-beta steady state messenger ribonucleic acid levels in human osteoblast-like osteosarcoma cells

Clinical observations have demonstrated a positive effect of estrogens and androgens on the maintenance of structural bone integrity. This study examines the direct effects of androgenic hormones on the osteoblast-like human osteosarcoma cell line, HOS TE85. Employing radiolabeled dihydrotestosterone (DHT), 2800 saturable, high-affinity (dissociation constant = 0.66 nM) androgen binding sites were detected per HOS TE85 cell. Androgen binding was specific in that DHT and testosterone (T) displayed significantly greater competition than the progestins, progesterone and medroxyprogesterone. The expression of androgen receptors in HOS TE85 cells was further substantiated by Northern analysis. A human androgen receptor complementary DNA probe revealed a 9.5 kilobase transcript which corresponds to the predominant human androgen receptor transcript detected in human male reproductive tissues. Androgens were also found to elicit biological responses in HOS TE85 cells. Physiological concentrations of DHT and T decreased HOS TE85 cell proliferation as assessed by cell count. This finding suggests that DHT may also play a role in osteoblast differentiation. In support of this hypothesis, treatment with T (24 h, 10 nM) enhanced the abundance of both alpha 1(I)-procollagen messenger RNA (mRNA) (5-fold) and transforming growth factor-beta mRNA (2.2 fold). The nonaromatizable androgen DHT (24 h, 10 nM) elicited an increase in the steady state concentration of alpha 1(I)-procollagen mRNA similar to the increase observed with T treatment. Thus, in addition to the recent discovery of estradiol receptors and estrogenic regulation of HOS TE85 cells, it is now evident that these osteoblast-like osteosarcoma cells also express high affinity androgen binding sites and can respond biologically to androgens.

The vitamin D-responsive element in the rat bone Gla protein gene is an imperfect direct repeat that cooperates with other cis-elements in 1,25-dihydroxyvitamin D3- mediated transcriptional activation

The gene for rat bone gla protein (BGP) was isolated and 1250 basepairs (bp), including 1100 bp of 5' flanking DNA, were placed up-stream of the human GH reporter gene. After transient transfection into the osteoblast-like rat osteosarcoma cell line ROS 17/2.8, the BGP promoter demonstrated a low level of basal activity that was increased approximately 10-fold by the addition of 10(-8) M 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. A single 250-bp fragment (-523 to -274) was sufficient to confer hormone inducibility upon both heterologous and homologous promoters. Deletion studies, complemented by evaluation with synthetic oligomers, enabled localization of the 1,25-(OH)2D3 response element to within 19 bp (-456 to -438), containing an element with an imperfect direct repeat [GGTGA(N4)GGACA] and homology to other steroid-responsive elements. Gel retardation assays demonstrated that partially purified chick intestinal 1,25-(OH)2D3 receptor bound specifically and with high affinity to a DNA fragment containing the putative 1,25-(OH)2D3 response element, and this binding was perturbed by monoclonal antibodies to the 1,25-(OH)2D3 receptor. Surprisingly, the 250-bp fragment, when linked in an antisense orientation with respect to the BGP promoter, blocked basal and hormone-dependent gene expression. However, a 246-bp fragment 5' to the 250-bp element (-1100 to -855) restored 20-fold inducibility when linked to the first fragment in the same orientation, suggesting cooperativity between at least two elements to achieve the hormonal regulation observed in this gene.

Progesterone regulation of estradiol-induced rat uterine secretory protein, complement C3

Previously, using DNA sequencing, Northern and Southern analysis, and immunohistochemical data, we identified an estrogen-stimulated secretory protein as the third component of complement (C3). In this study, we demonstrate that progesterone modulated the estradiol regulation of C3 in immature rats as well as during the normal reproductive cycle. C3 was most abundant during estrus and reached its lowest concentration in diestrus. Immunoprecipitations reveal that progesterone prevented the estradiol-stimulated increase in radiolabeled C3 both in the media and tissue. The mechanism for the progesterone inhibition of estrogen-stimulated C3 appeared to be at the level of transcription or possibly mRNA stability since progesterone blocked the estradiol-stimulated increase in C3 mRNA.

The stimulation of uterine complement component C3 gene expression by antiestrogens

We have previously demonstrated that complement component C3 is regulated by estradiol in the rat uterus. The antiestrogens tamoxifen, LY117018, and LY156758 exert both agonist and antagonist effects on the immature rat uterus. In this study, these three antiestrogens also stimulated an increase in the synthesis and secretion of C3. The combination of LY117018 and estradiol did not increase C3 to a greater extent than LY117018 alone, which suggests a similar mechanism of regulation. The regulation may be transcriptional since both estradiol and tamoxifen increase the concentration of C3 mRNA. Results of in situ hybridization revealed that the increase in C3 mRNA occurred in the luminal epithelial cells. Although the induction by estradiol and the antiestrogens was similar in most aspects, the time course for tamoxifen-stimulated synthesis differed from estradiol in that the time required to achieve maximal concentrations of C3 was delayed by 12 h with tamoxifen. This pattern did not appear to be related to the time it took to convert tamoxifen to 4-hydroxytamoxifen since the C3 response for these antiestrogens were identical. The antiestrogen-stimulated increase in C3 synthesis and mRNA concentration was prevented by the co-administration of progesterone lending support to the hypothesis that the antiestrogens regulate C3 synthesis via a mechanism similar to estrogen.

Estrogen regulation of tissue-specific expression of complement C3

The administration of estradiol to immature rats results in the increased synthesis and secretion of a 180-kDa protein, composed of 115- and 65-kDa subunits, by the uterine luminal epithelial cells. A monoclonal antibody against the 180-kDa protein was utilized to isolate the corresponding cDNA (LE-1) from a rat uterine luminal epithelial cell cDNA lambda gt11 expression library. This LE-1 cDNA was sequenced and shown to be homologous to complement component C3. The sequence was approximately 81 and 90% homologous to human and mouse C3, respectively. The LE-1 cDNA sequence was homologous with the 3' portion of the C3 mRNA containing the alpha subunit (115 kDa). Uterine mRNA isolated from immature rats treated with 1 microgram of estradiol for 24 h demonstrated a 25-fold increase in the concentration of a 6.0-kilobase mRNA by Northern hybridization with either LE-1 or authentic human C3 cDNA probes. To further examine the possibility that the estradiol-regulated secretory protein was C3, an aliquot of radiolabeled media protein from control and estradiol-stimulated rat uteri was incubated with goat anti-rat C3 antibody. The immunoprecipitated radiolabeled protein from estradiol-treated animals was increased significantly (p less than 0.01) compared to media from control animals. Analysis of the immunoprecipitated proteins on nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a single protein of 180 kDa from estradiol-stimulated uterine media, whereas no detectable proteins were immunoprecipitated from media obtained from control uteri. Also, when the immunoprecipitated protein was reduced (20 mM dithiothreitol) it dissociated into two subunits of 115 and 65 kDa. Immunohistochemical studies demonstrated the presence of C3 only in the epithelial cells of estrogen-stimulated rat uteri. In addition, the estradiol-stimulated mRNA was only detectable in uterine epithelial cell RNA. Analysis of liver RNA demonstrated a 6.0-kilobase mRNA, as in the uterus, when hybridized with LE-1. However, unlike the uterus, its concentration was not influenced by estrogen administration with up to three daily injections of 100 micrograms of diethylstilbestrol. Based on biophysical, DNA sequence, and antibody data we conclude that rat uterine epithelial cells produce C3 in response to estradiol whereas the expression in the liver was not modulated by estrogens.

Estrogen binding, receptor mRNA, and biologic response in osteoblast-like osteosarcoma cells

High specific activity estradiol labeled with iodine-125 was used to detect approximately 200 saturable, high-affinity (dissociation constant approximately equal to 1.0 nM) nuclear binding sites in rat (ROS 17/2.8) and human (HOS TE85) clonal osteoblast-like osteosarcoma cells. Of the steroids tested, only testosterone exhibited significant cross-reactivity with estrogen binding. RNA blot analysis with a complementary DNA probe to the human estrogen receptor revealed putative receptor transcripts of 6 to 6.2 kilobases in both rat and human osteosarcoma cells. Type I procollagen and transforming growth factor-beta messenger RNA levels were enhanced in cultured human osteoblast-like cells treated with 1 nM estradiol. Thus, estrogen can act directly on osteoblasts by a receptor-mediated mechanism and thereby modulate the extracellular matrix and other proteins involved in the maintenance of skeletal mineralization and remodeling.

Cloning of estrogen-regulated messenger ribonucleic acids from rat uterus

A cDNA library prepared from the mRNA of uteri of estrogen-stimulated immature female rats was constructed in lambda gt10. Differential screening of the hybrid phages was performed using control and stimulated cDNAs as probes. Selected clones were then characterized by Northern and Southern blot hybridizations. In all, eight unique clones corresponding to estrogen-stimulated messages in rat uterus were identified. These clones hybridized to uterine mRNAs varying in size from 1.4-8.4 kilobases. Three of the clones were characterized as coding for three different types of collagen, and one as coding for smooth muscle actin. These are described in more detail elsewhere. The kinetics of increase in estrogen-regulated messages was examined. After a single injection of estradiol, five clones, including the three collagen mRNAs, showed two peaks of accumulation, at 4 and 24 h. Messages of two other clones were maximal at 12 h. The actin clone hybridized to mRNAs with peaks at 4 h for cytoskeletal actins and 8-12 h for smooth muscle actins. Sequential 24-h injections of the hormone produced multiple peaks of mRNA accumulation with a timing consistent with the kinetics found after a single injection of hormone. The multiple injections, however, did not result in enhanced mRNA accumulation for any of these clones. In fact, several messages showed suppressed accumulation with continued estradiol administration. Accumulated inhibitory factors in uterine cells may be responsible for this refractory condition. Except for the actin mRNA, the estradiol-stimulated mRNAs were expressed mainly in uterus and ovary. These clones may be useful in studies on the mechanism of action of estrogenic hormones and their tissue-specific regulation of gene expression.

Immunoselection of cDNAs to avian intestinal calcium binding protein 28K and a novel calmodulin-like protein: assessment of mRNA regulation by the vitamin D hormone

Calcium's role in a variety of cellular processes has been well documented. The storage, distribution, and delivery of calcium are regulated by a family of binding proteins including troponin C, calmodulin, parvalbumin, and vitamin D dependent calcium binding protein (CaBP-28), all of which have evolved from a common ancestral gene. To evaluate vitamin D regulation of gene transcription, a CaBP-28 cDNA (767 base pairs) was isolated from a chicken intestine lambda gt11 library utilizing a polyvalent CaBP-28 antibody as a probe. Coincident with the identification of the CaBP-28 cDNA, a group of cDNAs also was isolated (with the anti-CaBP-28 antibody) that demonstrated 84% nucleotide homology and 99% deduced amino acid homology with chicken brain calmodulin (CaM). This new CaM-like cDNA was named neoCaM. There is little nucleotide homology between the CaBP-28 cDNA and neoCaM. The CaBP-28 cDNA hybridizes with three transcripts of 2000, 2900, and 3300 bases which are dramatically induced by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], while the neoCaM cDNA recognizes three distinct (from CaBP-28) transcripts. Two of these mRNAs are 1400 and 1800 bases as described for brain CaM, but another larger 4000-base transcript is detected with neoCaM. Neither the CaM nor the neoCaM transcript reveals any modulation by 1,25(OH)2D3. Herein, we discuss the possible significance of not only the isolation of both cDNAs with a single antibody but also the relation of neoCaM to other well-characterized CaM cDNAs.

Estrogen regulation of alpha 1(I)-procollagen messenger ribonucleic acid in the rat uterus

A cDNA library, prepared from mRNA isolated from the uteri of 3-day estradiol-stimulated immature rats, was constructed in pBR322. From this library an estrogen-regulated clone, pERU3, was isolated. This clone contained sequences complementary to uterine mRNA that migrated during gel electrophoresis as a double band of about 5.0 and 5.8 kilobases. Little of this mRNA was seen in several other tissues examined. An increase in the amount of this RNA in uterus was seen 2 h after estradiol treatment, with maximum hybridization occurring, in different experiments, between 18 and 36 h, followed by a decline. Hybridization of the cDNA insert of the pERU3 plasmid with known probes indicated that it coded for alpha 1(I)-procollagen. This conclusion was supported by in vitro translation experiments in which the hybrid-selected mRNA complementary to pERU3 DNA was shown to code for a collagenase-sensitive protein with a size corresponding to that of alpha 1(I)-procollagen. This system, therefore, provides an additional tool for the study of the estrogen regulation of gene expression in the uterus.

Estrogen regulation of protein synthesis in the immature rat uterus: the effects of progesterone on proteins released into the medium during in vitro incubations

We have previously identified two major medium proteins secreted from the rat uterus during in vitro incubations that appear to be estrogen regulated. In this study, immature rats were treated with estradiol (E2) progestins, and actinomycin D. Medium proteins were analyzed after incubation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. E2 (1 microgram) increased the synthesis of proteins with mol wt of 115,000 and 65,000. Progesterone inhibited this increase when given in doses of 500 and 250 micrograms and when given within 8 h of estradiol. Lower doses of progesterone were not completely inhibitory. When actinomycin D was given within 6 h of E2, it also inhibited the E2 stimulated increase. This system may provide a useful marker for monitoring hormonal action in the luminal epithelium and may help in understanding hormonal regulation of gene expression.

Hormonal regulation of rat uterine secretory protein synthesis

Treatment of the rat uterus with estradiol results in many morphological and biochemical changes. In order to examine the biochemical mechanisms of these changes, we are interested in finding a protein which can be used as an end-point indicator or marker. Estradiol administration results in the increased synthesis and release of a 115,000 and 65,000 dalton protein into the incubation media. In this paper, we demonstrate that these proteins are actually subunits of a larger protein having a molecular weight of 180,000 daltons. This protein appears to be specific to the uterus and may be produced mainly or solely by the epithelial cells. In the normal estrous cycle, maximal production is seen at estrus with essentially no production at diestrus. In the immature rat, synthesis of the 180K dalton protein is blocked by the interaction of progesterone and estradiol. However, unlike some uterine responses, the 180K protein is increased by treatment with several antiestrogens. This protein is also present in sufficient quantities to allow for the production of monoclonal antibodies. Thus this protein has many attributes of an excellent "marker protein" and will be of value in future studies aimed at elucidating the molecular mechanism(s) of steroid hormone action in the uterus.

Estrogen regulation of protein synthesis in the immature rat uterus: the analysis of proteins released into the medium during in vitro incubation

Immature rats were treated with estradiol (E2) or other steroids before their uteri were removed and incubated under in vitro conditions in the presence of [35S]methionine. The analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the radiolabeled proteins synthesized and released into the incubation medium demonstrate that E2 regulates the appearance of two proteins. These two proteins have mol wt of 115,000 and 65,000. The concentration of proteins in the medium increases linearly with time, suggesting that they may be secreted. These two proteins were not produced by several other tissues in response to E2 and appear to be specific to the uterus. They also appear to be increased only by estrogens (E2 greater than estrone greater than estriol) and not by other steroids tested. They are increased in response to a single injection within 6 h, and the maximal concentration of proteins occurs approximately 24 h after E2 administration. The protein concentrations have essentially returned to control values by 72 h after hormone injection. The kinetics of the induction is the same for both proteins, suggesting that their increase may be coordinated. Based on the tissue and hormone specificity of the increase in the 115,000- and the 65,000-dalton proteins, they may serve as reliable markers for the study of the uterine response to E2.

Comparison of media proteins from ovariectomized rat uteri following estrogen treatment

Ovariectomized rats were treated with estradiol for 3 days after which their uteri were incubated in vitro and radioactive media proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Media were also chromatographed on G-25 Sephadex Blue Sepharose columns to isolate subsets of proteins. The results demonstrate that two proteins are consistently increased following estrogen treatment. These proteins have molecular weights of 104,000 and 65,000. Neither protein binds to Blue Sepharose to a great extent. The use of the protein synthesis inhibitors, emetine and actinomycin D, demonstrates that the proteins are synthesized de novo. These two proteins may serve as markers for genomic response to estradiol in the rat uterus.

Steroidal regulation of rat uterine in vitro mRNA translation products

Total rat uterine mRNA was isolated following 1,2 or 3 days of estradiol, 3 days of progesterone, or 3 days of progesterone and estradiol treatment of immature animals. The mRNA translation products were analyzed by 2-dimensional electrophoresis. The results demonstrate that a number of mRNA products were affected by varying the hormonal conditions. Estradiol consistently caused an increase in mRNA in vitro translation products corresponding to polypeptides with mol. wt of 40,000 Daltons (p40), 59,000 Daltons (p59). A polypeptide with a mol. wt of 37,000 Daltons (p37) consistently decreases in concentration following estradiol administration. Progesterone, alone, caused a decrease in p37, p59, and a slight increase in p40. When progesterone was combined with estradiol we detected translation product levels similar to those seen following 1 day of estradiol treatment. Thus, the change in mRNA populations as a response of the immature rat uterus to estradiol and progesterone can be utilized to characterize the tissue's response to these hormones. This type of study also provides a method for detecting gene products which may possibly be utilized as potential markers to investigate estrogen and progesterone action.