Sequence and expression of human estrogen receptor complementary DNA

Nur77 is differentially modified in PC12 cells upon membrane depolarization and growth factor treatment

The rat pheochromocytoma cell line PC12 can be induced by growth factors to undergo proliferation and neuronal differentiation. These cells also have excitable membranes that can be depolarized by neurotransmitters or elevated levels of extracellular KCl. Treatment of PC12 cells with growth factors or membrane-depolarizing agents rapidly activates the expression of specific genes whose products are thought to mediate the subsequent biological responses. One such gene, nur77, is a member of the steroid and thyroid hormone receptor gene superfamily. We have identified the Nur77 protein and shown that it is synthesized rapidly and transiently in PC12 cells following stimulation, has a short half-life of 30 to 40 min, and is located in both the nucleus and the cytoplasm. Nur77 is posttranslationally modified, primarily by phosphorylation on serine residues. Phosphopeptide analysis reveals that Nur77 is modified differently upon membrane depolarization than after treatment with growth factors. We hypothesize that the activity of Nur77 is regulated by both differential gene expression and posttranslational modification and that these modes of regulation contribute to distinct downstream responses specific to membrane depolarization and growth factor treatment.

Isolation and characterization of cDNA for an androgen-regulated mRNA in the flank organ of hamsters

Flank organs of hamster are useful for studying androgen-dependent growth of hair follicles and sebaceous glands. To elucidate the mechanism of gene expression regulated by androgen, we constructed a cDNA library from flank organs of male hamsters and screened by a differential hybridization method using cDNA probes from normal and castrated males. We isolated a cDNA clone, termed FAR-17a, whose expression was found to be highly sensitive to androgen. FAR-17a mRNA of 1.8 kb was reduced after castration and reappeared after testosterone treatments. Among several tissues examined, FAR-17a gene was expressed at a high level in flank organ and a low level in testis and earlobe. FAR-17a probe detected a few fragments in genomic DNA of hamster, mouse, suncus, pig, and human, suggesting that this gene is phylogenetically conserved. The sequence of FAR-17a cDNA predicts a protein of 231 amino acids (27,216 daltons) having basic properties. The deduced protein has no significant homologies to proteins previously described.

FTZ-F1, a steroid hormone receptor-like protein implicated in the activation of fushi tarazu

The Drosophila homeobox segmentation gene fushi tarazu (ftz) is expressed in a seven-stripe pattern during early embryogenesis. This characteristic pattern is largely specified by the zebra element located immediately upstream of the ftz transcriptional start site. The FTZ-F1 protein, one of multiple DNA binding factors that interacts with the zebra element, is implicated in the activation of ftz transcription, especially in stripes 1, 2, 3, and 6. An FTZ-F1 complementary DNA has been cloned by recognition site screening of a Drosophila expression library. The identity of the FTZ-F1 complementary DNA clone was confirmed by immunological cross-reaction with antibodies to FTZ-F1 and by sequence analysis of peptides from purified FTZ-F1 protein. The predicted amino acid sequence of FTZ-F1 revealed that the protein is a member of the nuclear hormone receptor superfamily. This finding raises the possibility that a hormonal ligand affects the expression of a homeobox segmentation gene early in embryonic development.

Many peptide fragments of alien antigens are homologous with host proteins, thus canalizing T-cell responses

All proteins of this world are constructed in compliance with the same rule. Accordingly, two totally unrelated proteins, on the average, share 30 identical tripeptides, two tetrapeptides, and one pentapeptide per 500 residues. With this in mind, the 221-residue-long influenza virus hemagglutinin II (IVHA-II), as a representative of alien antigens, was compared with three diverse proteins representing the host: 533-residue-long chicken c-src protein kinase (c-src product of the cellular oncogene of Rous sarcoma virus), 595-residue-long human estrogen receptor, and 585-residue-long human serum albumin. Forty-three tripeptides, two tetrapeptides, and one pentapeptide of IVHA-II were also found in one or the other of the three host proteins. Six regions of IVHA-II (9-22 residues long) in which oligopeptides were clustered that were identical to their host oligopeptides were defined as "host-homologous" regions, and the remaining regions were called "nonself" or "pathogen-specific" regions. Because the total number of host proteins is vastly more than three, host-homologous regions were no doubt underestimated, while only one or two regions of IVHA-II must remain as truly pathogen-specific. Nevertheless, oligopeptide analysis of two known T-cell response-eliciting peptide fragments and one known inert peptide fragment of a virus and a malarial protozoan readily revealed the latter to be a host-homologous region. Of the two known T-cell response-eliciting peptide fragments, one was more nonself than the other. Not surprisingly, the more nonself fragment elicited helper T-cell response from individuals of diverse major histocompatibility complex haplotypes, whereas the less nonself fragment elicited cytotoxic T-cell response only from HLA-A2 human individuals.

Origin of the high constitutive level of progesterone receptor in T47-D breast cancer cells

The T47-D breast cancer cell line constitutively expresses high levels of progesterone receptor (PR). This does not appear to be related to an anomaly in the estrogen receptor (ER) as shown by cloning of the ER cDNA from T47-D cells and its insertion into the expression vector pKSV-10. When transfected into heterologous Cos-7 and L cells this receptor exerts a normal biological activity, stimulating the transcription of a reporter gene only in the presence of estrogen. Moreover, normal estrogen regulation of the transcription of the reporter gene was also observed in situ in T47-D cells. Southern blot experiments showed the presence of four copies of the progesterone receptor gene in T47-D cells. This was related to the existence of four copies of chromosome 11 in these cells. The most likely explanation of the anomalous regulation of progesterone receptor expression in T47-D cells is thus the presence of at least one copy of the PR gene bearing an anomaly in its regulatory region(s).

Epitope prediction and confirmation for the human androgen receptor: generation of monoclonal antibodies for multi-assay performance following the synthetic peptide strategy

The human androgen receptor (hAR) is an important regulatory protein particularly in male sexual differentiation. The investigation of hAR functionality has been hampered by the lack of AR specific monoclonal antibodies recognizing the functional domains of the receptor. Therefore production of high affinity mono-specific polyclonal (PAbs) and monoclonal antibodies (MAbs) directed to the hAR was initiated following the synthetic peptide (SP) strategy. Five hAR specific peptides were selected on the basis of their predicted antigenic properties avoiding homology with other steroid hormone receptors. Peptide specific polyclonal antisera were obtained following selected immunization protocols. Mono-specific polyclonal antibody responses were elicited to all peptides in mice and rabbits. Crossreactivity of the peptide specific antisera with the native hAR in various biochemical assays was observed with two out of five peptides. Peptide SP61 (hAR residues 301-320) was used for the generation site-directed MAbs specific for the hAR. Specificity for the hAR was established by immunoprecipitation, immune-complex density gradient centrifugation and immunohistochemistry on human prostate tissue sections. The multi-assay performance of the selected high affinity antibodies proved the usefulness of the straight forward peptide approach and opens a wide field of possible biochemical and physiological investigations into questions related to androgen action.

CCAAT-enhancer binding protein: a component of a differentiation switch

The CCAAT-enhancer binding protein (C/EBP) has now been found to promote the terminal differentiation of adipocytes. During the normal course of adipogenesis, C/EBP expression is restricted to a terminal phase wherein proliferative growth is arrested, and specialized cell phenotype is first manifested. A conditional form of C/EBP was developed, making it feasible to test its capacity to regulate the differentiation of cultured adipocytes. Premature expression of C/EBP in adipoblasts caused a direct cessation of mitotic growth. Moreover, when abetted by the effects of three adipogenic hormones, C/EBP promoted terminal cell differentiation. Since C/EBP is expressed in a variety of tissues, it may have a fundamental role in regulating the balance between cell growth and differentiation in higher animals.

Steroid hormone receptors

In the three decades since the original discovery of receptors for steroid hormones, much has been learned about the biochemical processes by which these regulatory agents exert their effects in target tissues. The intracellular receptor proteins are potential transcription factors, needed for optimal gene expression in hormone-dependent cells. They are present in an inactive form until association with the hormone converts them to a functional state that can react with target genes. Transformation of the receptor protein to the nuclear binding form appears to involve the removal of both macromolecular and micromolecular factors that act to keep the receptor form reacting with DNA. Much of the native receptor is present in the nucleus, loosely bound and readily extractable, but for some and possibly all steroid hormones, some receptor is in the cytoplasm, perhaps in equilibrium with a nuclear pool. Methods have been developed for the stabilization, purification, and characterization of receptor proteins, and through cloning and sequencing of their cDNAs, primary structures for these receptors are now known. This has led to the recognition of structural similarities among the family of receptors for the different steroid hormones and to the identification of regions in the protein molecule responsible for the various aspects of their function. Monoclonal antibodies recognizing specific molecular domains are available for most receptors. Despite the knowledge that has been acquired, many important questions remain unsolved. How does association with the steroid remove factors keeping the receptor protein in its native state, and how does binding of the transformed receptor to the response element in the promoter region enhance gene transcription? Once it has converted the receptor to the nuclear binding state, is there a further role for the steroid in modulating transcription? Still not entirely clear is the involvement of phosphorylation and/or dephosphorylation in hormone binding, receptor transformation, and transcriptional activation. Less vital to basic understanding but important in the overall picture is whether the native receptors for gonadal hormones are entirely confined to the nucleus or whether there is an intracellular distribution equilibrium. With the effort now being devoted to this field, and with the application of new experimental techniques, especially those of molecular biology, our understanding of receptor function is progressing rapidly. The precise mechanism of steroid hormone action should soon be completely established.

Steroid hormone receptor gene expression in human breast cancer cells: inverse relationship between oestrogen and glucocorticoid receptor messenger RNA levels

The relative expression in human breast cancer cells of messenger ribonucleic acids (mRNA) encoding different steroid hormone receptors is unknown. Accordingly, mRNA levels in total RNA extracted from 13 human breast cancer cell lines were measured by Northern analysis employing complementary DNA probes for the human oestrogen (ER), progesterone (PR), androgen (AR), vitamin D3 (VDR) and glucocorticoid receptors (GR). The 7 ER+ lines expressed a single 6.4 kilobases (kb) ER mRNA. Interestingly, low concentrations of ER mRNA were detected in the ER- cell lines, MDA-MB-330 and BT 20. PR mRNA, predominantly a 13.5 kb species, was expressed in the 6 lines known to be ER+, PR+ by radioligand binding; however, one ER+ cell line, MDA-MB-134, failed to express PR mRNA. A 10.5 kb AR mRNA was expressed at significantly higher levels in ER+ than ER- cell lines. All cell lines expressed a single 4.6 kb mRNA for VDR and a single 7.4 kb mRNA for GR. ER and PR mRNA levels were positively correlated (p = 0.011) and each was positively correlated with androgen receptor (AR) mRNA levels (p less than or equal to 0.009). ER, PR and AR mRNAs were negatively associated with GR levels (p less than or equal to 0.012), while ER and AR mRNA levels were negatively correlated with mRNA for the epidermal growth factor receptor. In contrast, levels of VDR mRNA were unrelated to the concentration of any other steroid receptor mRNA. Our data demonstrate the coordinate expression of ER, PR and AR genes, and an inverse relationship between sex steroid hormone receptor and GR gene expression in human breast cancer cell lines.

Site-directed polyclonal antibodies inhibit binding of activated estrogen receptor to DNA

We have generated three polyclonal antisera to the DNA-binding domain of the human estrogen receptor (hER). Antiserum AT2A was generated against a peptide spanning amino acids 231-245 of hER, while antisera AT3A and AT3B were generated against a peptide spanning amino acids 247-261 of hER. The interaction of these three antisera with ER has been characterized by sucrose density gradient analysis. The antisera bound to the unactivated (8S), salt-activated (4S), and heat transformed (5S) ER complex. All the antisera appeared to be site-specific since binding of salt-activated ER to the antisera was blocked by the presence of excess free synthetic peptides. Antisera AT3A and AT3B inhibited the binding to DNA of the KCl-activated 4S ER and the heat-transformed 5S ER. Although antiserum AT2A bound to ER, it did not inhibit DNA binding of activated ER complexes. The ability of antisera AT3A and AT3B to inhibit ER binding to DNA was concentration dependent. Once bound to the DNA, ER complexes were not significantly affected by incubation with the antisera, suggesting that binding of DNA to ER inhibits antibody ER interaction and renders that domain inaccessible to the antibodies. These results demonstrate that site-directed antibodies to ER inhibit binding of activated ER complexes to DNA in vitro.

Phosphorylation of the estradiol receptor in MCF-7 human breast cancer cells in culture

Double labelling and Western blot techniques were used to demonstrate phosphorylation of estradiol receptor. Cells in monolayer culture were incubated with [32P]orthophosphate for 18 h followed by covalent whole cell labelling of the estradiol receptor with tritiated tamoxifen aziridine [( 3H]TA). Labelled receptor was precipitated with the monoclonal antibodies H222 or JS 34/32, coupled to protein A-Sepharose, and purified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), or transferred to nitrocellulose paper. Receptor protein was detected on the Western blot with the monoclonal antibody H222 and rabbit anti-rat peroxidase conjugate. Phosphorylated receptor was visualized by autoradiography. Tritium and 32P activities were monitored in the gels. Two phosphorylated forms of the receptor (molecular weights 67 and 50 kDa) have been detected in MCF-7 cells. Estradiol treatment of the cells was found to increase phosphorylation of the receptor. In estradiol-treated cells both phosphorylated receptor forms were present mainly in the nuclear extract. Both forms bound [3H]TA as evidence by SDS-PAGE. [3H]TA binding was abolished by excess non-radioactive estradiol. In addition two phosphorylated proteins of approximately 120 and 90 kDa were regularly coprecipitated with receptor in cytosol. These proteins did not bind [3H]TA. The 90 kDa phosphorylated protein was identified as a heat shock protein (hsp-90).

Hormonal dependency of cerebral meningiomas. Part 1: Female sex steroid receptors and their significance as specific markers for adjuvant medical therapy

Female sex steroid receptors were examined in 50 human cerebral meningiomas. For estrogen receptors, high-affinity binding sites (dissociation constant (Kd): 0.05 to 0.2 nM) were found in the cytosolic fraction with a capacity of less than 4 fmol/mg protein in 10 meningiomas using a dextran-coated charcoal (DCC) assay. In the same cytosolic fraction, the solid-phase enzyme immunoassay revealed only one cytosol with a positive colorimetric reaction equal to 5 fmol/mg protein. However, in the nuclear compartment, none of the tumors stained positively for estrogen receptors with immunohistochemical techniques. In addition, the most convincing evidence for the absence of estrogen receptors was obtained by in situ hybridization using an oligonucleotide probe complementary to a fraction of the human receptor messenger ribonucleic acid (mRNA). In none of the 50 meningiomas was the expression of estrogen mRNA coding for the estrogen receptor detected. For progesterone receptors, high-affinity binding sites (Kd: 0.3 to 2.6 nM) were found in 49 of the 50 tumors using a DCC assay. In the same cytosols, solid-phase enzyme immunoassay revealed that each tumor was positive for progesterone receptors. However, in the nuclear compartment, only five tumors had partially positive staining for progesterone receptors with immunohistochemical techniques. Within the confines of this study, it is concluded that: 1) the estrogen receptor is generally absent in meningioma tissue, and 2) the progesterone receptor is mainly absent in the nuclear compartment, leading to the conclusion that the cytosolic progesterone receptor may be an inactive form. This study suggests that female sex steroid receptors are not primarily involved in the proliferative rate of cerebral meningiomas and that they are of no current significance as markers for adjuvant medical therapy of most meningiomas.

Antibodies against synthetic peptides recognize the human and rat androgen receptor

Antibodies against two synthetic peptides (aa 299-311 and aa 544-559) selected in different immunogenic domains of the human AR, were induced in rabbits. Antiserum reactivity against the native receptor was investigated by gel permeation chromatography and sucrose density gradient centrifugation using [3H]mibolerone-labeled rat prostate cytosol and [3H]5 alpha-dihydrotestosterone-labeled T-47D cytosol as a source of AR. The absence of cross-reactivity of the antisera with estrogen, progesterone and glucocorticoid receptor was confirmed by density gradient centrifugation of rat uterus cytosol labeled with [3H]E2 or [3H]ORG 2058 and rat liver cytosol labeled with [3H]dexamethasone. After partial proteolytic breakdown of rat prostate AR by endogenous proteases the steroid-labeled receptor was recognized only by the second peptide (aa 544-559) antibody. This proteolytic breakdown could be prevented to a large degree by addition of a high concentration of soybean trypsin inhibitor. The specific AR antibodies provide new tools for the functional analysis of AR, since they interact selectively with specific domains of the receptor.

Sexual dimorphism characterizes baboon myocardial androgen receptors but not myocardial estrogen and progesterone receptors

Using biochemical methods we established that estrogen receptor content and distribution and progesterone receptor content in female and male baboon myocardium did not differ between sexes. In contrast, myocardial androgen receptor distribution between cytosolic and nuclear compartments was sexually dimorphic. Female baboon myocardial androgen receptors were restricted to the cytosolic compartment, whereas male myocardial androgen receptors were distributed between the cytosolic and nuclear compartments. Using human estrogen receptor cDNA we showed that baboon aorta, myocardium and uterus contain a 6.3 kb estrogen receptor transcript. Analyses performed with human progesterone receptor cDNA established that baboon aorta and uterus contain an 8 kb progesterone receptor transcript; however, progesterone receptor transcripts were not demonstrable in baboon myocardial RNA preparations. Because relative hybridization signal intensity reflected known uterine and aortic progesterone receptor content, failure to detect progesterone receptor transcripts in myocardial preparations may reflect sensitivity limitations and the fact that aortic progesterone receptor content is 5-fold greater than that of myocardium. Immunocytochemical analyses demonstrated that baboon myocardial progesterone receptors were present in greater than 25% of myocytes and generally absent from other myocardial cells. Our studies establish that: (1) gonadal steroid hormone receptor gene transcription occurs in cells of the baboon cardiovasculature, (2) these steroid hormone receptors may be physiologically functional, and (3) gonadal steroid hormone receptors may be restricted to specialized cells of the cardiovasculature.

Osteoclasts isolated from membranous bone in children exhibit nuclear estrogen and progesterone receptors

Osteoclasts were isolated from membranous bone from four children without metabolic bone disease who were undergoing craniotomy for either tumor or trauma. Both freshly isolated osteoclasts and those cultured for 4-7 days exhibited the following characteristics: production of tartrate-resistant acid phosphatase (9.5-14.8 units), contraction in response to application of 100 mg/ml of human calcitonin, and formation of resorption lacunae on devitalized bone wafers. Nuclear estrogen and progesterone receptors were demonstrated by immunohistochemical techniques and quantitated in two of the patients by radioimmunoassay (estrogen receptor RIA, 23.6 and 23.8 cpm/micrograms protein; progesterone receptor RIA, 36.7 and 74.2 cpm/micrograms protein). The demonstration of sex steroid hormone receptors in the nucleus of osteoclasts derived from children with normal membranous bone has established a potential mechanism whereby direct modulation of bone resorption by the sex steroid estrogen and progesterone may occur.

A steroid/thyroid hormone receptor superfamily member in Drosophila melanogaster that shares extensive sequence similarity with a mammalian homologue

A gene in Drosophila melanogaster that maps cytologically to 2C1-3 on the distal portion of the X-chromosome encodes a member of the steroid/thyroid hormone receptor superfamily. The gene was isolated from an embryonic cDNA library using an oligonucleotide probe that specifies the consensus amino acid sequence in the DNA-binding domain of several human receptors. The conceptual amino acid sequence of 2C reveals at least four regions of homology that are shared with all identified vertebrate receptors. Region I includes the two cysteine-cysteine zinc fingers that comprise a DNA-binding domain which typifies all members of the superfamily. In addition, three regions (Regions II-IV) in the carboxy-terminal portion of the protein that encode the putative hormone-binding domain of the 2C gene product resemble similar sequences in vertebrate steroid/thyroid hormone receptors. The similarity suggests that this Drosophila receptor possesses many of the regulatory functions attributed to these regions in vertebrate counterparts. A portion of Region II also resembles part of the human c-jun oncoprotein's leucine zipper, which in turn, has been demonstrated to be the heterodimerization site between the jun and fos oncoproteins. The 2C receptor-like protein most resembles the mouse H2RII binding protein, a member of the superfamily which has been implicated in the regulation of major histocompatibility complex (MHC) class I gene expression. These two gene products are 83% identical in the DNA-binding domain and 50% identical in the putative hormone-binding domain, although no ligand has been identified for either protein. The high degree of similarity in the hormone-binding domain between the 2C protein and the H2RII binding protein outside regions II-IV suggests specific functional roles which are not shared by other members of the superfamily.

Proteins that bind to Drosophila chorion cis-regulatory elements: a new C2H2 zinc finger protein and a C2C2 steroid receptor-like component

Gel mobility-shift assays have been used to identify proteins that bind specifically to the promoter region of the Drosophila s15 chorion gene. These proteins are present in nuclear extracts of ovarian follicles, the tissue where s15 is expressed during development, and bind to specific elements of the promoter that have been shown by transformation analysis to be important for in vivo expression. The DNA binding specificity has been used for molecular cloning of two components from expression cDNA libraries and for their tentative identification with specific DNA-binding proteins of the nuclear extracts. The mRNAs for both of these components, CF1 and CF2, are differentially enriched in the follicles. DNA sequence analysis suggests that both CF1 and CF2 are novel Drosophila transcription factors. CF2 is a member of the C2H2 family of zinc finger proteins, whereas CF1 is a member of the family of steroid hormone receptors. The putative DNA-binding domain of CF1 is highly similar to the corresponding domains of certain vertebrate hormone receptors and recognizes a region of DNA with similar, hyphenated palindromic sequences. The nature of CF1 raises the possibility of hormonal control of choriogenesis in Drosophila.

Development and characterization of monoclonal antibodies to a specific domain of human estrogen receptor

We have synthesized three peptides with amino acid sequences identical to those spanning amino acids 201-215, 231-245, and 247-261 of the human estrogen receptor (hER). These peptides were conjugated to keyhole limpet hemocyanin and used as immunogens to develop monoclonal antibodies (MoAbs) to hER. Antibody responses were only elicited by the peptide with amino acid sequence 247-261. Splenocytes from immunized mice were used for hybridoma production. Of the seven MoAbs that recognized the native (functional) form of the ER, four (MoAbs 16, 33, 114, and 213) recognized the ER with high affinity, as demonstrated by the increased sedimentation coefficient of the antibody-complexed ER in sucrose density gradients. Antibodies 318, 35, and 36 bound to ER with low affinity since they immunoprecipitated ER, but the ER-antibody complex appeared to dissociate on sucrose density gradients. The high-affinity MoAbs appear to be site-specific since the peptide competed effectively for binding of the receptor by the antibody. The fact that they reacted with ER from human breast cancer and calf, rat, and mouse uterine tissues suggests that this epitope of the receptor is conserved in these species. Although the DNA-binding region appears to be conserved among the various steroid receptors, these MoAbs did not recognize the native forms of progesterone, androgen, or glucocorticoid receptors. These MoAbs bound to the KCl-activated 4S ER and heat-transformed 5S ER, suggesting that the antibody-binding site is accessible in the monomeric and dimeric forms of ER. The antibodies did not recognize the untransformed 8S ER in the presence of molybdate and without KCl, suggesting that the antibody-binding site in the oligomeric form of ER is inaccessible. The fact that the antibodies did bind to the unoccupied 4S ER was demonstrated by the data obtained with sucrose density gradient analysis followed by postlabeling of ER with [3H]estradiol. The antibodies bound to ERs with high affinity (KD = 0.4 to 1.8 nM). At a fixed concentration of antibody, ERs ranging from 20 to 1,000 fmol were detectable. These MoAbs did not inhibit nuclear or DNA binding of ER in vitro. This can be attributed to the dissociation of the antibodies from ER when the latter interacts with its acceptor site. These results demonstrate the development of site-specific MoAbs to the native form of the hER using synthetic peptides as immunogens.

A family of positive regulators related to the Pseudomonas putida TOL plasmid XylS and the Escherichia coli AraC activators

The XylS family consists of a least 8 different transcriptional regulators. Six of these proteins are positive regulators for the catabolism of carbon sources (benzoate and sugars) in Escherichia coli, Pseudomonas putida and Erwinia carotovora, and two of them are involved in pathogenesis in Escherichia coli and Yersinia enterocolitica. Based on protein alignments, the members of this family exhibit a long stretch of homology at the C-terminal end. The regulators involved in the catabolism of carbon sources stimulate transcription from their respectively regulated promoters only in the presence of effectors. In two of the regulators, mutations at the non-homologous N-terminus alter affinity and specificity for effectors while mutations at the conserved C-terminus part decrease activation of transcription from their corresponding regulated promoters. It is thus probable that the variable N-terminus end in this family of regulators contains the motif involved in effector recognition, while the C-terminal end is involved in DNA-binding. These proteins seem to be related by common ancestry and may act through similar mechanisms of positive regulation effected through similar folding patterns.

Estrogen induction of hepatocellular carcinomas in Armenian hamsters

Liver tumors were found in most Armenian hamsters (Cricetulus migratorius) injected with on 15-mg pellet of diethylstilbestrol. The tumors were detectable as early as 1 1/2 mo after diethylstilbestrol administration and were usually present as multiple nodules that progressively increased in size. Histologically, the multicentric neoplasms were all hepatocellular carcinomas of varied degrees of differentiation and frequently (42.8%) contained Mallory bodies; preneoplastic lesions were not observed. This hepatocellular carcinoma hamster model is unique because estrogen alone without any other known mutagen is responsible for induction of hepatocellular carcinoma.

Receptor interconversion model of hormone action. 2. Requirement of both kinase and phosphatase activities for conferring estrogen binding activity to the estrogen receptor

Three interconvertible forms of the estrogen receptor have been identified in the oviduct of estrogen-stimulated chicks. The non-estradiol binding form (Rnb) can be converted to the lower affinity binding form (Ry, Kd = 0.8 nM) by a process requiring the gamma-phosphoryl moiety of ATP. The enzymatic activity (Fy) essential for this "receptor potentiation" has been isolated from oviduct cytosol using ammonium sulfate fractionation, DEAE chromatography, and HPLC size-exclusion chromatography. The potentiation appears to require both kinase and phosphatase activities. The Fy kinase characteristically phosphorylates casein, histones, and glycogen synthase. Comparison of the kinase with casein kinase II, which also phosphorylates casein and glycogen synthase, indicates that Fy represents a distinct protein kinase since its activity is not stimulated by spermine or inhibited by heparin. Fy-mediated conversion of Rnb to Ry is blocked by the phosphatase inhibitors vanadate, fluoride, and pyrophosphate. The substrate specificity of the Fy phosphatase activity is distinct from that of the two well-characterized protein phosphatases 1 and 2A. Moreover, the requirement for Fy phosphatase activity in converting Rnb to Ry could not be mimicked by its substitution with purified protein phosphatases 1 or 2A. The unique substrate specificity of the oviduct protein phosphatase and protein kinase, which are apparently necessary to confer estradiol binding characteristics to the receptor, implies that these enzymes play a key role in the control of the estrogen receptor in its function as a transcription factor.

Signal transduction by steroid hormones: nuclear localization is differentially regulated in estrogen and glucocorticoid receptors

The glucocorticoid receptor accumulates in nuclei only in the presence of bound hormone, whereas the estrogen receptor has been reported to be constitutively nuclear. To investigate this distinction, we compared the nuclear localization domains of the two receptors and the capacity of their respective hormone-binding regions to regulate nuclear localization activity. As with the glucocorticoid receptor, we showed that the human estrogen receptor contained a nuclear localization signal between the DNA-binding and hormone-binding regions (amino acids 256-303); however, in contrast to the glucocorticoid receptor, the estrogen receptor lacked a second nuclear localization domain within the hormone-binding region. Moreover, the hormone-binding domain of the unliganded estrogen receptor failed to regulate nuclear localization signals, although it efficiently regulated other receptor functions. We conclude that the two receptors employ a common mechanism for signal transduction involving a novel "inactivation" function, but that they differ in their control of nuclear localization. Thus, despite the strong relatedness of the estrogen and glucocorticoid receptors in structure and activity, certain differences in their properties could have important functional implications.

The E75 ecdysone-inducible gene responsible for the 75B early puff in Drosophila encodes two new members of the steroid receptor superfamily

A pulse of the steroid hormone ecdysone at the end of Drosophila larval development triggers coordinate changes in both larval and imaginal tissues that result in metamorphosis to the adult fly. In larval salivary glands, this pulse activates a genetic regulatory hierarchy manifested by the induction of two kinds of transcription puffs in the polytene chromosomes: a small set of "early" puffs representing a primary response to the hormone, and a complex set of "late" puffs whose delayed appearance is dependent on proteins synthesized during the primary response. We isolated a 50-kb ecdysone-inducible gene, E75, that occupies the early puff locus at 75B. E75 contains two overlapping transcription units. The E75 A unit is a coextensive with the E75 gene and contains six exons: two 5'-proximal exons, A0 and A1, which are specific to this unit, and exons 2-5, which are common to both units. The E75 B unit is 20 kb long and contains five exons, a 5'-terminal exon, B1, located within the second intron of E75 A, and the common exons 2-5. Large open reading frames start within the first exon of each unit and continue into the last exon and therefore encode two different proteins. Both proteins exhibit sequence similarity to the conserved DNA-binding and hormone-binding domains of proteins in the steroid receptor superfamily. The two putative zinc fingers that characterize the DNA-binding domain are encoded by exon A1 and exon 2, so that the E75 A protein contains both fingers, whereas the E75 B protein contains only the second. Both proteins contain the same putative hormone-binding domain encoded by exon 4.

The Drosophila seven-up gene, a member of the steroid receptor gene superfamily, controls photoreceptor cell fates

The Drosophila seven-up (svp) gene was isolated as a lethal insertion in an "enhancer trap" screen. It is expressed and required in photoreceptor cell precursors R1, R3, R4, and R6 during eye development. The absence of svp+ function causes a transformation of these cells toward an R7 cell fate, as judged by morphology and expression of an R7-specific marker. This transformation depends in part on the sevenless gene product. Our results show that svp is involved in control of cell fate during the generation of neuronal diversity. Molecular analysis of svp reveals that it is a member of the steroid receptor gene superfamily and is likely to be a Drosophila homolog of the human transcription factor COUP.

Inverse relationship between estrogen receptor and epidermal growth factor receptor mRNA levels in human breast cancer cell lines

Epidermal growth factor receptors (EGF-R) are present in a number of human breast cancer cell lines and tumor biopsies. Furthermore, it has been suggested that EGF-R levels are higher in estrogen receptor negative (ER-) than in ER+ human breast tumors and that EGF-R status may be a prognostic indicator in breast cancer. The present study was undertaken to establish whether there is a quantitative relationship between EGF-R and ER mRNA concentrations in a series of 10 well-characterized human breast cancer cell lines. All cell lines expressed detectable quantities of EGF-R mRNA by Northern analysis but the relative abundance of EGF-R mRNA varied more than 50-fold. Two transcripts corresponding to the 10.5- and 5.8-kb mRNAs described in other cell types were present but in different relative proportions in different cell lines. When these lines were divided into an ER+ and an ER- group based on their ability to bind estradiol, ER- cell lines were shown to express significantly higher concentrations of EGF-R mRNA than did ER+ cell lines (p less than 0.005). Furthermore, linear-regression analysis revealed a significant inverse relationship between ER and EGF-R mRNA concentrations both within the group of 10 human breast cancer cell lines as a whole (r = 0.66) and within the 6 functionally ER + lines (r = 0.77). This demonstration of a significant (p less than 0.005) inverse relationship between the concentrations of ER and EGF-R mRNAs in ER + cell lines raises the possibility of reciprocal regulation of the expression of these genes in human breast cancer.

Molecular cloning of new human TR2 receptors: a class of steroid receptor with multiple ligand-binding domains

Previously we isolated a new group of cDNA clones from human testis cDNA libraries which might code for new steroid receptors. The cDNA and predicted amino acid sequences of two of these receptors, named TR2-5 and TR2-7 receptors, were determined. We report here the nucleotide and deduced amino acid structures of two other receptors that we named TR2-9 and TR2-11 receptors. The calculated MW of TR2-5 receptor, TR2-7 receptor, TR2-9 receptor and TR2-11 receptor are 52,982, 20,528, 50,849 and 67,223 respectively, which match well with the apparent MW of in vitro translated products. The 26 amino acids involved in the formation of "Zn-fingers" are conserved. The ligand-binding domain of TR2-9 receptor is 16 amino acids shorter and has 3 different amino acids compared with TR2-5 receptor. The TR2-11 receptor has a ligand-binding domain which is longer and quite different compared with the other TR2 receptors. The multiple ligand-binding domains of TR2 receptor could be the products of different genes or may be due to RNA splicing errors. So far, we have failed to find binding activity with any known steroid hormone; this promotes the possibility that an unidentified steroid hormone may be involved.

Characterization of the Ah receptor for 2,3,7,8-tetrachlorodibenzo-p-dioxin: use of chemical crosslinking and a monoclonal antibody directed against a 59-kDa protein associated with steroid receptors

The Ah receptor regulates induction of cytochrome P450IA1 (aryl hydrocarbon hydroxylase) by "3-methylcholanthrene-type" compounds and mediates the toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin and related halogenated aromatic hydrocarbons. Hepatic Ah receptor from untreated rodents is localized in the cytosol and has an apparent molecular mass of 250 to 300 kDa. This large form can be dissociated into a smaller ligand-binding subunit upon exposure to high ionic strength. The Ah receptor displays many structural similarities to the receptors for steroid hormones. Two non-ligand-binding proteins have been identified to be associated with the cytosolic forms of the steroid hormone receptors. The first is a 90-kDa heat shock protein (hsp 90); the second is a 59-kDa protein (p59) of unknown function. The cytosolic Ah receptor ligand-binding subunit previously has been shown to be associated with hsp 90. In the present study, we used a monoclonal antibody, KN 382/EC1, generated against the 59-kDa protein which is associated with rabbit steroid receptors to determine if p59 also is a component of the large cytosolic Ah receptor complex. Cytosolic forms of rabbit progesterone receptor, glucocorticoid receptor, and Ah receptor were analyzed by velocity sedimentation on sucrose gradients under low-ionic-strength conditions and in the presence of molybdate. Progesterone receptor from rabbit uterine cytosol and glucocorticoid receptor from rabbit liver each had a sedimentation coefficient of approximately 9 S. In the presence of KN 382/EC1 antibody the progesterone receptor and the glucocorticoid receptor both underwent a shift in sedimentation to a value of approximately 11 S. The increase in sedimentation velocity is an indication that the receptor-protein complexes are interacting with the antibody. Under low-ionic-strength conditions the Ah receptors from rabbit uterine cytosol and liver cytosol had a sedimentation coefficient of approximately 9 S. However, in contrast to the steroid receptors, the Ah receptor showed no change in its sedimentation properties in either tissue in the presence of KN 382/EC1, indicating that the antibody is not interacting with the Ah receptor. Multimeric Ah receptor complexes that were chemically crosslinked still did not show any interaction with KN 382/EC1. These data indicate that the 59-kDa protein either is not associated with the Ah receptor or is present in an altered form which the antibody cannot recognize.

A member of the steroid hormone receptor gene family is expressed in the 20-OH-ecdysone inducible puff 75B in Drosophila melanogaster

Drosophila melanogaster DNA has been cloned which encompasses a major part of the 20-OH-ecdysone inducible puff 75B. One 20-OH-ecdysone responsive transcription unit was detected which is expressed into two transcripts which accumulate upon the incubation of salivary glands of 3rd instar larvae with 20-OH-ecdysone. This accumulation is correlated with the 20-OH-ecdysone induced activity of puff 75B. 75B cDNA analysis indicates that the activity of puff 75B leads to the synthesis of a protein which belongs to the steroid and thyroid hormone receptor superfamily. The highest similarity of the derived 75B protein sequence was found to the DNA and ligand binding domains of human retinoic acid receptor. A study of the tissue distribution in larvae revealed that 75B mRNA is present in most, if not all 20-OH-ecdysone target tissues. It is proposed that 75B protein is a DNA-binding protein playing a key role in mediating the regulation of the larval molt by 20-OH-ecdysone.

Characterization and partial purification of an estrogen type II binding site in chick oviduct cytosol

An estrogen binding site of moderate affinity (Kd approximately 10 nM) and high capacity (approximately 25-70 pmol/g of tissue) was measured in DES-stimulated chick oviduct cytosol. Saturation analysis by [3H]estradiol exchange demonstrated that this binding site displayed sigmoidal binding characteristics suggesting a cooperative binding mechanism. Competition analysis with a number of compounds demonstrated that the bioflavonoid luteolin was a better competitor for binding to type II sites in chick than either estradiol or DES. Steroid specificity was demonstrated by the inability of 17 alpha-estradiol, progesterone, testosterone, corticosterone, and the triphenylethylene antiestrogen nafoxidine (U-1100A) to compete for [3H]-17 beta-estradiol binding to chick oviduct cytosol preparations. In addition, the binding site appeared to be sensitive to sulfhydryl reducing reagents as evidenced by a 75% reduction in binding activity in the presence of dithiothreitol. Both prelabeling and postlabeling procedures used in conjunction with Sephacryl S-300 chromatography resulted in a single major peak of type II binding activity representing a molecular weight in the 40,000 range. Type II binding activity was recoverable after precipitation with ammonium sulfate, and this material was subjected to a variety of column chromatography procedures in order to achieve further purification of the type II site. Significant purification of the site was achieved with a bioflavonoid-Sepharose (quercetin-Sepharose) affinity matrix. The purified type II sites eluted from quercetin-Sepharose displayed the same sigmoidal binding curves characteristic of native cytosol.

Modulation of estrogen receptor and epidermal growth factor receptor mRNAs by phorbol ester in MCF 7 breast cancer cells

Previous studies have demonstrated an inverse relationship between estrogen receptor (ER) and epidermal growth factor receptor (EGF-R) gene expression in human breast cancer cells. This relationship was further investigated in MCF 7 cells treated with 12-O-tetradecanoylphorbol-13-acetate (TPA). Exposure to 10 nM TPA resulted in a time-dependent increase in EGF-R mRNA, first apparent at 3 h and maximal between 9 and 24 h. There was a concomitant fall in ER mRNA with a maximum decline to 15-20% of control between 12 and 24 h. Although EGF-R mRNA levels declined between 24 and 72 h, both EGF-R mRNA and EGF-R binding remained above control levels and this was accompanied by a sustained depression of ER mRNA. These data support the view that ER and EGR-R gene expression is inversely regulated in human breast cancer and describe for the first time an inhibitory effect of a phorbol ester on steroid hormone receptor gene expression.

The cloned human oestrogen receptor contains a mutation which alters its hormone binding properties

We demonstrate here that the human oestrogen receptor (hER) cDNA clone pOR8 obtained from MCF-7 cells contains an artefactual point mutation which results in the substitution of a valine for a glycine at amino acid position 400 (Gly-400----Val-400). This mutation in the hormone binding domain of the cloned hER destabilizes its structure and decreases its apparent affinity for oestradiol at 25 degrees C, but not at 4 degrees C, when compared with the wild-type hER with a Gly-400.

Mechanisms of nuclear localization of the progesterone receptor: evidence for interaction between monomers

Deletion mutants of the rabbit progesterone receptor were used to identify two major mechanisms of its nuclear localization. A putative signal sequence, homologous to that of the SV40 large T antigen, was localized around amino acids 638-642 and shown to be constitutively active. When amino acids 638-642 were deleted, the receptor became cytoplasmic but could be shifted into the nucleus by the addition of hormone (or anti-hormone); it was almost fully active. The second mechanism consisted of the activation of the DNA binding domain. By deleting epitopes recognized by monoclonal antibodies, it was possible to follow different receptor mutants inside the same cells. In the absence of ligand, the receptor was transferred into the nucleus as a monomer. After administration of hormone (or anti-hormone) a "cytoplasmic" monomer was transferred into the nucleus through interaction with a "nuclear" monomer. These interactions occurred through the steroid binding domains of both monomers.

Adipsin and complement factor D activity: an immune-related defect in obesity

Adipsin is a serine protease that is secreted by adipocytes into the bloodstream; it is deficient in several animal models of obesity, representing a striking example of defective gene expression in this disorder. Recombinant mouse adipsin was purified and its biochemical and enzymatic properties were studied in order to elucidate the function of this protein. Activated adipsin has little or no proteolytic activity toward most substrates but has the same activity as human complement factor D, cleaving complement factor B when it is complexed with activated complement component C3. Like authentic factor D, adipsin can activate the alternative pathway of complement, resulting in red blood cell lysis. Decreased (58 to 80 percent) complement factor D activity, relative to lean controls, was observed as a common feature of several experimental models of obesity, including the ob/ob, db/db, and monosodium glutamate (MSG)-injected mouse and the fa/fa rat. These results suggest that adipsin and the alternative pathway of complement may play an unexpected but important role in the regulation of systemic energy balance in vivo.

A novel member of the thyroid/steroid hormone receptor family is encoded by the opposite strand of the rat c-erbA alpha transcriptional unit

A cDNA encoding a novel member of the thyroid/steroid hormone receptor superfamily, called Rev-ErbA alpha, has been isolated from a rat GH3 cell library. Rev-ErbA alpha is an approximately 56-kilodalton protein most similar in structure to the thyroid hormone receptor (c-erbA) and the retinoic acid receptor, but it does not bind either thyroid hormone or retinoic acid. The mRNA encoding Rev-ErbA alpha is present in many tissues and is particularly abundant in skeletal muscle and brown fat. A genomic DNA fragment containing the entire Rev-ErbA alpha cDNA sequence was isolated and characterized. Remarkably, this DNA fragment also contained a portion of the c-erbA alpha gene. r-erbA alpha-1 and r-erbA alpha-2 are alternative splice products of the c-erbA alpha gene and are members of the receptor superfamily. The genes encoding Rev-ErbA alpha and r-erbA alpha-2 overlap, with their coding strands oriented opposite one another. A 269-base-pair segment of the bidirectionally transcribed region is exonic in both the Rev-ErbA alpha and r-erbA alpha-2 genes, resulting in complementary mRNAs. Thus, through alternative splicing and opposite-strand transcription, a single genomic locus codes for three different members of the thyroid/steroid hormone receptor superfamily. Potential implications of this unusual genomic arrangement are discussed.

Mapping on the calf estrogen receptor of the binding domain for an antibody interfering with receptor activation

The localization on the calf estrogen receptor of the binding domain for B36 (an IgM antibody which prevents and reverses the effects of receptor activation) has been studied by means of controlled proteolysis of the receptor-estradiol complex using trypsin, chymotrypsin, and papain. We successively determined for intact and proteolyzed receptor-estradiol complex (i) the abilities of estradiol-binding species to aggregate in low salt medium, to bind to nonspecific DNA absorbed onto cellulose, and to interact with B36 antibody in sucrose gradients; (ii) the hydrodynamic properties of estradiol-binding species, by gel permeation chromatography and sucrose gradient centrifugation in high salt media and (iii) the molecular weights of B36-reactive species, by immunoblot analysis. Three tryptic receptor fragments of Mr 36,000, 34,000, and 33,000 and two chymotryptic fragments of Mr 36,000 and 33,000 included both the hormone- and B36-binding domains but did not interact with DNA, whereas at least two receptor fragments resulting from the action of chymotrypsin and papain bound estradiol with high affinity but interacted neither with DNA nor with B36. Taking into account these results and assuming that structure of the calf estrogen receptor is similar to those of sequenced estrogen receptors (which show a highly conserved organization with considerable homologies in the functional domains), we propose that the B36-binding domain is located either between the DNA- and hormone-binding domains (model I) or at the C-terminal end of the estrogen receptor (model II). The regions that include the main proteolytic cleavage sites of the receptor are also specified, and the abilities of the two models of the calf estrogen receptor to account for the effect of B36 on receptor activation are discussed.