Sequence and expression of human estrogen receptor complementary DNA

A fourth type of rabbit protein kinase C

Three rabbit cDNA clones coding for three types of protein kinase C (PKC alpha, beta, and gamma) have recently been identified and the structures determined [Ohno, S., Kawasaki, H., Imajoh, S., Suzuki, K., Inagaki, M., Yokokura, H., Sakoh, T., & Hidaka, H. (1987) Nature (London) 325, 161-166]. By use of these cloned cDNAs as hybridization probes, a fourth type (delta) of cDNA clone, which encodes a protein highly homologous to PKC alpha, beta, and gamma, was identified. PKC delta is composed of 697 amino acid residues and contains several peptide sequences determined at the protein level with the brain PKC preparation. This indicates that this molecular type (PKC delta) is, along with PKC alpha, beta, and gamma, a constituent of the brain PKC preparation. Sequence comparison among the four PKC types revealed that PKC delta is somewhat distinct from the other PKC types. PKC delta shows 99% amino acid sequence identity with rat PKC type I [Knopf, J. L., Lee, M.-H., Sultzman, L. A., Kriz, R. W., Loomis, C. R., Hewick, R. M., & Bell, R. M. (1986) Cell (Cambridge, Mass.) 46, 491-502], indicating relationship of these PKC types. The mRNA for PKC delta is exclusively concentrated in the brain.

Steroid receptor-mediated inhibition of rat prolactin gene expression does not require the receptor DNA-binding domain

Prolactin gene expression is negatively regulated by glucocorticoids, and by estrogens when positive estrogen regulatory elements in the prolactin gene are removed. Mutational analysis of estrogen receptor confirms that inhibition is a function of receptor, and that transcriptional activation and inhibition require distinct, separable structural elements. Inhibition is dependent on a 63 amino acid region (amino acids 251-314) distinct from the DNA-binding and steroid-binding domains. The comparable region of glucocorticoid receptor confers inhibitory actions on a hybrid receptor. Multiple, nonoverlapping sequences in the rat prolactin 5'-flanking genomic region that confer inhibition by both steroid hormones contain related cis-active elements that bind a common, tissue-specific positive transcription factor, called Pit-1. Experimental results indicate that positive and negative transcriptional effects of estrogen receptor are mediated by separate functional domains, and suggest the protein-protein interactions between steroid hormone receptors and other transcription factor(s) mediate inhibition.

The avian erythroblastosis virus erbA oncogene encodes a DNA-binding protein exhibiting distinct nuclear and cytoplasmic subcellular localizations

The protein product of the v-erbA oncogene of avian erythroblastosis virus was analyzed by use of site-specific antisera. The v-erbA protein was found to exist in distinct nuclear and cytoplasmic forms. Both nuclear and cytoplasmic species of the v-erbA protein were capable of binding to DNA, a property predicted based on the structural relatedness the v-erbA polypeptide shares with the thyroid and steroid hormone receptors. A mutation within the v-erbA coding region which inhibited DNA binding and nuclear localization also inhibited the ability of the v-erbA protein to potentiate erythroid transformation, consistent with a model of the v-erbA protein as a transcriptional regulator.

Rat antibodies as probes for the characterization of progesterone receptor A and B proteins from laying hen oviduct cytosol

The chicken oviduct contains two different hormone binding forms of the progesterone receptor, A and B. We have prepared rat antisera against both forms of the receptor partially purified from laying hen oviduct. The anti-progesterone receptor A antiserum reacts with both receptor forms on Western blots, while the anti-progesterone receptor B antiserum reacts mainly with the B form. Both antisera also react with the native progesterone receptor proteins as shown by sedimentation analysis of the antibody-receptor complexes. Receptors A and B are recognized on Western blots of total protein from dissolved tissue, indicating that both forms are likely to be physiological components. Epitope mapping experiments show that immunogenicity of both receptor molecules is restricted to structurally related protein domains of 28 kDa in receptor A and of 52 kDa in receptor B.

Similarity between the estrogen receptor and the DNA-binding domain of the tetracycline repressor

The amino-terminus region of tetracycline (tet) repressors contains a helix-turn-helix structure that binds to DNA. A computer-based comparison of a residues 18-61 of the tet repressor, which contains this DNA-binding domain, with a residues 304-347 of the human estrogen receptor (ER) yields a score that is 6.7 standard deviations higher than that obtained with 2,500 comparisons of randomized sequences of these segments. The probability of getting this score by chance is less than 10(-11). This part of the ER could be important in nuclear actions of ER in target tissues.

Identification of a new class of steroid hormone receptors

The gonads and adrenal glands produce steroids classified into five major groups which include the oestrogens, progestins, androgens, glucocorticoids and mineralocorticoids. Gonadal steroids control the differentiation and growth of the reproductive system, induce and maintain sexual characteristics and modulate reproductive behaviour. Adrenal steroids also influence differentiation as well as being metabolic regulators. The effects of each steroid depend primarily on its specific receptors, the nature of which could therefore provide a basis for classification of steroid hormone action. The successful cloning, sequencing and expression of the human glucocorticoid (hGR) (ref. 1), oestrogen (hER), progesterone (hPR), and mineralocorticoid (hMR) receptors, complementary DNA, plus homologues from various species, provides the first opportunity to study receptor structure and its influence on gene expression. Sequence comparison and mutational analysis show structural features common to all groups of steroid hormone receptors. The receptors share a highly conserved cysteine-rich region which functions as the DNA-binding domain. This common segment allows the genome to be scanned for related gene products: hMR cDNA for example, was isolated using an hGR hybridization probe. In this study, using the DNA-binding domain of the human oestrogen receptor cDNA as a hybridization probe, we have isolated two cDNA clones encoding polypeptides with structural features suggestive of cryptic steroid hormone receptors which could participate in a new hormone response system.

In situ photolabelling of the human androgen receptor

In situ photoaffinity labelling of the human androgen receptor has been performed in the LNCaP (Lymph Node Carcinoma of the Prostate) cell line. The covalently labelled receptors were identified by SDS-PAGE. Intact LNCaP cells, incubated with [3H]-R1881 and subsequently irradiated with u.v. light and directly solubilized in SDS-buffer, revealed two photolabelled protein bands at 110 and 50 kDa. Irradiation of intact cells and subsequent isolation of nuclei followed by extraction with 0.5 M NaCl resulted in one major photolabelled protein band at 110 kDa. The labelling of this band could be completely suppressed by a 100-fold molar excess of non-radioactive R1881. Photolabelling of androgen receptors in a cytosolic preparation of LNCaP cells after anion exchange chromatography resulted in a much lower labelling efficiency compared with the in situ labelling procedure, although the androgen receptor was purified 100-fold. The steroid binding domain of the human androgen receptor has been partially mapped with chymotrypsin and S. aureus V8 protease digestion. Proteolytic digestion with chymotrypsin of purified photoaffinity-labelled 110 kDa human androgen receptor resulted in the generation of a 15 kDa peptide which still contains the covalently linked hormone. It is concluded that the in situ photoaffinity labelling technique can be applied successfully for characterization of the steroid binding domain of androgen receptors in prostate cancer cells and in other androgen target cells. Furthermore, it was demonstrated that the human androgen receptor is a monomer with a molecular mass of 110 kDa, of which the steroid binding site is confined to a 15 kDa domain.

Nuclear estrogen receptor molecular heterogeneity in the mouse uterus

Holomeric estrogen receptor (ER) prepared from ovariectomized mouse uteri displays heterogeneous electrophoretic mobility when analyzed by NaDodSO4/PAGE. ER derived from nuclei (ERn) appears as a closely spaced doublet having apparent molecular masses of 66.4 and 65 kDa, while ER from the cytosolic compartment (ERc) has a single band of 65 kDa. Both partially purified ERc and the 8S form of unactivated ERc show only the 65-kDa band. The appearance of the ERn doublet is hormonally inducible, and the relative proportions of the two doublet bands are influenced by the type of hormone treatment, with weakly estrogenic compounds yielding the lower band as predominant while potent estrogens increase the proportion of the upper band. Steroid binding of the ERn doublet was determined by [3H]tamoxifen aziridine affinity labeling of both the 66.4- and the 65-kDa peptides; binding to the 65-kDa peptide was predominant. The ERn doublet displays a time dependency after estrogen administration with maximal amounts occurring in a bimodal fashion at 1 and 8 hr.

A 46-kDa antigen associated with estrogen receptor in human breast cancer

A 65-kDa estrogen receptor (ER) protein has been demonstrated both by sucrose gradient analysis and by immunoblot, using anti-ER monoclonal antibodies (MAbs). Since the ER is denatured in many experimental situations, such as formaldehyde fixing of samples for histochemistry and electroimmunoblotting studies, in this work we used a denatured 60-70-kDa ER-rich protein preparation as antigen for mice immunization in order to raise anti-ER MAbs. That material was obtained by affinity purification on an allyl-estradiol matrix of the MCF-7 cytosolic ER, followed by further isolation and enrichment by PAGE. NS-1 myeloma cells and spleen lymphocytes from the immunized mice were fused, and resultant hybridoma colonies were screened by [125I]-estradiol-labelled nuclear ER immunoprecipitation. The isolated MAb, E476, shows a moderate ability to precipitate ER and reacts strongly with a 46-kDa antigen in Western blot assay. The 46-kDa antigen was not detectable in native cytosol but became reactive after 50% ammonium sulfate precipitation of cytosolic proteins. The 46-kDa antigen appeared concentrated in the NaSCN plus estradiol eluate of the affinity column used for cytosolic ER purification. Freshly prepared 60-70-kDa material from the preparative gel electrophoresis did not show any E476 reactivity. However, when the 60-70-kDa proteins were frozen, thawed and speed vacuum concentrated, the 46-kDa antigen became detectable. Storage increased the reactivity of the 60-70-kDa material with the E476 MAb. The 46-kDa antigen was present only in the ER positive cell lines, and was absent in all negative cell lines tested. The 46-kDa protein is also present in the ER positive human breast cancer specimens. We conclude that the 46-kDa protein identified with the E476 MAb in human breast cancer is probably a naturally occurring ER fragment.

Isolation of cDNA encoding transcription factor Sp1 and functional analysis of the DNA binding domain

Transcription factor Sp1 is a protein present in mammalian cells that binds to GC box promoter elements and selectively activates mRNA synthesis from genes that contain functional recognition sites. We have isolated a cDNA that encodes the 696 C-terminal amino acid residues of human Sp1. By expression of truncated fragments of Sp1 in E. coli, we have localized the DNA binding activity to the C-terminal 168 amino acid residues. In this region, Sp1 has three contiguous Zn(II) finger motifs, which are believed to be metalloprotein structures that interact with DNA. We have found that purified Sp1 requires Zn(II) for sequence-specific binding to DNA. Thus, it is likely that Sp1 interacts with DNA by binding of the Zn(II) fingers. To facilitate the identification of mutant variants of Sp1 that are defective in DNA binding, we have also devised a bacterial colony assay for detection of Sp1 binding to DNA.

Structure of the chromosomal chicken progesterone receptor gene

We have isolated cosmid clones containing the chromosomal chicken progesterone receptor gene. The gene consists of eight exons and is approximately 38 kilobases long. Individual exons correlate well with conserved functional domains of the receptor molecule. Alternative polyadenylylation in the second intron results in a putative non-hormone-binding protein. The cap site of the gene is heterogeneous over at least 14 base pairs and lies in a very G + C-rich region. The promoter lacks "TATA" and "CAAT" boxes, but CCGCCC motifs exist in the surrounding region.

RNA polymerase II transcription factors H4TF-1 and H4TF-2 require metal to bind specific DNA sequences

Specific DNA-binding and in vitro transcription activities of H4TF-1 and H4TF-2 are inactivated by chelating agents. Binding activity is restored by addition of Zn2+, and H4TF-2 is also reactivated by Fe2+. In contrast, preformed factor-DNA complexes are resistant to chelators. Therefore, metal ions are a required component of the H4TF-1 and H4TF-2 DNA-binding domains.

A novel thyroid hormone receptor encoded by a cDNA clone from a human testis library

The c-erbA gene belongs to a multigene family that encodes transcriptional regulatory proteins including the v-erbA oncogene product, steroid hormone receptors, and the vitamin D3 receptor. A v-erbA DNA probe encoding the DNA-binding region of the v-erbA protein was used to screen a human complementary DNA testis library. One of the clones isolated, erbA-T-1, was found to encode a 490-amino acid protein (erbA-T). The erbA-T polypeptide shows high homology with the proteins encoded by both the chicken c-erbA and the human c-erbA-beta genes but is most closely related to the chicken gene. The chicken c-erbA and the human c-erbA-beta genes encode high-affinity receptors for thyroid hormone, and here it is shown that the erbA-T protein binds specifically to 3,5,3'-triiodo-L-thyronine with a dissociation constant of 3.8 +/- 0.2 x 10(-10) M. These data imply that more than one thyroid hormone receptor exists in humans and that these receptors might have different tissue- and gene-activating specificities.

Analysis of the 4-hydroxytamoxifen (4-OHTAM) bound nuclear estrogen receptor from MCF-7 cells by limited proteolysis

The assumption that a different conformational form was induced in the nuclear estrogen receptor following binding by antiestrogens compared to estrogens was studied by analysing the proteolytic fragments of the receptor following limited digestion with chymotrypsin and trypsin. Nuclei were isolated from MCF-7 cells previously exposed to [3H] 4-OHTAM. The proteolytic digestion was performed either on the micrococcal nuclease hydrolysate or on intact nuclei. The molecular weights (Mr) were calculated from the sedimentation coefficients (S) determined on a sucrose gradient and from the Stokes radii (Rs) estimated by gel filtration. Digestion of the nuclei with micrococcal nuclease solubilized a receptor form of Mr = 155,000. This receptor form was degraded by chymotrypsin to a receptor of Mr = 63,000 which could not be further dissociated by 0.4 M KCl and 3 M urea. A similar receptor molecule was released by chymotrypsin from intact nuclei. Digestion of the micrococcal nuclease hydrolysate with trypsin degraded the receptor to a form of a Mr = 67,000 which could not be further dissociated by 0.4 M KCl and 3 M urea. Digestion of intact nuclei with trypsin followed by micrococcal nuclease, solubilized a receptor form of Mr = 80,000 which could be further dissociated with 0.4 M KCl and 3 M urea to a receptor form of Mr = 67,000. This trypsin degraded receptor form seems to be similar in Mr to the chymotrypsin degraded form. On the other hand different receptor fragments of Mr = 33,000 and Mr = 60,000 were excised by chymotrypsin and trypsin respectively from the estradiol ligated estrogen receptor. (Geier et al., J. steroid Biochem. 26 [1987] 35-40.) These results support the assumption of a different conformational form for the antiestrogen ligated receptor, compared to the estrogen ligated receptor since they were differentially susceptible to proteolytic degradation by chymotrypsin.

Localization of the human progesterone receptor gene to chromosome 11q22-q23

The human progesterone receptor gene was mapped by in situ hybridization using two cDNA probes corresponding to the 5' and 3' part of the coding sequence. This gene was localized to 11q22-q23.

The chicken c-erbA proto-oncogene is preferentially expressed in erythrocytic cells during late stages of differentiation

We analyzed the expression of the c-erbA proto-oncogene in different tissues of chicken embryos. c-erbA transcripts were found at low levels in the lung, kidney, liver, and heart and in high amounts in embryonic blood cells. Nuclease mapping assays proved that these transcripts were true c-erbA transcripts. In situ hybridization on fractionated embryonic blood cells showed that c-erbA transcripts were predominantly found in erythroblasts, particularly during the final step of differentiation. Life span analysis of c-erbA mRNAs revealed their relative instability, demonstrating that the high level of c-erbA transcripts in embryonic erythroblasts was not the result of passive accumulation. These results suggest that the c-erbA genes play some role in erythrocyte differentiation.

Detection of estrogen receptor mRNA in human uterus

We transcribed a cDNA clone of the human estrogen receptor (ER) with T7 RNA polymerase. The 32P-cRNA transcript complementary to ER mRNA was hybridized to poly(A)+ RNA from human uterus and revealed a single band of approximately 4.2 kilobases. No hybridization was seen with the cRNA probe of the opposite orientation. Hybridization of total RNA from calf and rat uterus yielded a single band at approximately 3.8 kilobases for both species. Total RNA from rat spleen did not hybridize. A 35S-labeled cRNA probe was prepared for in situ hybridization of ER mRNA in human uterus and spleen. Autoradiographic signal was present over endometrial epithelium, stromal cells of the lamina propria, and smooth muscle cells of the myometrium but was absent from sections of spleen. The ER mRNA hybridization label was located over cytoplasm and nuclei of uterine target cells.

Amplification of the neu (c-erbB-2) oncogene in human mammmary tumors is relatively frequent and is often accompanied by amplification of the linked c-erbA oncogene

We investigated alterations in the structure and expression of oncogenes in mammary tumors and mammary tumor-derived cell lines. In 16 of 95 samples, we detected amplification of the human neu oncogene, also known as c-erB-2, accompanied by overexpression in the tumors from which intact RNA could be isolated. In 10 of these DNAs, the linked oncogene c-erbA was also amplified, whereas another gene on human chromosome 17, p53, was present in normal copy numbers. Overexpression of c-erbA could not be detected in the tumors analyzed. The relatively high frequency of neu amplification points to a functional role in human breast cancer. Coamplification of the c-erbA oncogene could contribute to this disease as well but is most likely fortuitous.

Cloning of human mineralocorticoid receptor complementary DNA: structural and functional kinship with the glucocorticoid receptor

Low-stringency hybridization with human glucocorticoid receptor (hGR) complementary DNA was used to isolate a new gene encoding a predicted 107-kilodalton polypeptide. Expression studies demonstrate its ability to bind aldosterone with high affinity and to activate gene transcription in response to aldosterone, thus establishing its identity as the human mineralocorticoid receptor (hMR). This molecule also shows high affinity for glucocorticoids and stimulates a glucocorticoid-responsive promoter. Together the hMR and hGR provide unexpected functional diversity in which hormone-binding properties, target gene interactions, and patterns of tissue-specific expression may be used in a combinatorial fashion to achieve complex physiologic control.

Non-histone chromatin proteins that recognize specific sequences of DNA

Numerous chromatographic procedures have recently been developed to purify to near homogeneity various eukaryotic non-histone chromatin proteins that recognize and bind to specific sequences of DNA. In this brief review we have discussed a number of these different methods that we feel are important and probably represent the starting points for much of the future research work in this area. We view this coverage as being only an introduction, however, and strongly recommend that the reader consult the original papers for details of methods and protocols. We, nevertheless, hope that the information presented here will be of some assistance to those researchers and students who wish to become acquainted with the latest developments in this rapidly advancing field of chromatography. Although it is evident from what has been presented that the purification of each DNA sequence-specific non-histone chromatin protein initially starts with common or classical isolation and fractionation procedures, the final (and often crucial) steps of enrichment and purification often involve distinctive or unique procedures for each individual protein of interest. In many cases these final steps involve new techniques such as DNA sequence-specific bioaffinity and photoaffinity chromatography which not only ensure the isolation of specific protein species from complex mixtures but also result in a tremendous enrichment for nuclear proteins that are often present in the nucleus in extremely low concentrations. Furthermore, the entire process of protein purification has been remarkedly facilitated with the advent of high-performance liquid chromatographic and fast protein liquid chromatographic techniques which now allow for the very rapid separation and purification of proteins in a matter of minutes from mixtures that in the recent past would have required hours or days to purify. Thus, separation and purification techniques are now available that set the stage for the rapid isolation of rare, DNA sequence-specific, NHC nuclear proteins from almost any cellular source. It is therefore reasonable to anticipate that in the near future there will be major advances made in our understanding of the specific nuclear proteins that regulate gene expression in eukaryotic cells.

Nucleotide sequence of the chicken proto-oncogene c-erbA corresponding to domain 1 of v-erbA

The nucleotide sequence of the chicken proto-oncogene c-erbA, the cellular counterpart of the viral oncogene v-erbA domain 1, has been determined. The c-erbA gene has an exon-intron structure characteristic of the eukaryotic split genes. The c-erbA domain 1 is composed of at least eight exons and seven introns. Analysis of the sequence data reveals a long open reading frame of 239 amino acid residues that share highly significant homology with the viral protein. Our results show that the viral erbA oncogene is a truncated form of its cellular homologue. In fact the cellular gene is 42 nucleotides longer at its 5' coding extremity. The presence of a gag-specific (17/20) nucleotide stretch in this region favours the hypothesis of a homologous recombination event between the cellular erbA and the gag gene of a parental retrovirus. We have also sequenced 1400 bp of DNA lying 5' to the long open reading frame in search of the transcription initiation sites for the c-erbA messenger RNAs. Our findings and interpretations are presented here.

Domain structure of the glucocorticoid receptor protein

The purified rat liver glucocorticoid receptor protein was analyzed by limited proteolysis and amino acid sequence determination. The NH2 terminus appears to be blocked. The steroid-binding domain, defined by a unique tryptic cleavage site, corresponds to the COOH-terminal part of the protein with the domain border in the region of residue 518. The DNA-binding domain, defined by a region with chymotryptic cleavage sites, is immediately adjacent to the steroid-binding domain and reflects another domain border in the region of residues 410-414. The results described at the protein level in this report confirm functional data previously obtained by mutations at the genetic level.

The chicken c-erbA proto-oncogene is preferentially expressed in erythrocytic cells during late stages of differentiation

We analyzed the expression of the c-erbA proto-oncogene in different tissues of chicken embryos. c-erbA transcripts were found at low levels in the lung, kidney, liver, and heart and in high amounts in embryonic blood cells. Nuclease mapping assays proved that these transcripts were true c-erbA transcripts. In situ hybridization on fractionated embryonic blood cells showed that c-erbA transcripts were predominantly found in erythroblasts, particularly during the final step of differentiation. Life span analysis of c-erbA mRNAs revealed their relative instability, demonstrating that the high level of c-erbA transcripts in embryonic erythroblasts was not the result of passive accumulation. These results suggest that the c-erbA genes play some role in erythrocyte differentiation.

Regulation of inducible and tissue-specific gene expression

Molecular genetics approaches have been used to identify and characterize cis-acting DNA sequences required for eukaryotic gene regulation. These sequences are modular in nature, consisting of arrays of short (10- to 12-base pair) recognition elements that interact with specific transcription factors. Some transcription factors have been extensively purified and the corresponding genes have been cloned, but the mechanisms by which they promote transcription are not yet understood. Positive and negative regulatory elements that function only in specific cell types or in response to extracellular inducers have been identified. A number of cases of inducible and tissue-specific gene expression involve the activation of preexisting transcription factors, rather than the synthesis of new proteins. This activation may involve covalent modification of the protein or an allosteric change in its structure. The modification of regulatory proteins may play a central role in the mechanisms of eukaryotic gene regulation.

Expression of the v-erbA oncogene in chicken embryo fibroblasts stimulates their proliferation in vitro and enhances tumor growth in vivo

In contrast to uninfected chicken embryo fibroblasts (CEFs), CEFs infected with a retroviral vector that carries the v-erbA gene of avian erythroblastosis virus displayed new properties. These included limited anchorage-independent growth in soft agar, growth without latency in serum-supplemented medium, ability to overcome quiescence induced by serum deprivation, growth at low cell density, and an extended life span in vitro. Furthermore, when explanted in vivo onto the chorioallantoic membrane of chicken embryo, the transformed CEFs expressing v-erbA in addition to v-erbB exhibited a high proliferative rate, giving rise to fibrosarcoma tumors that were ten times larger than those developed from transformed CEFs expressing v-erbB alone. All these data show that CEFs expressing the v-erbA oncogene display activated growth and suggest that the v-erbA product interferes with the mechanisms regulating the growth and/or differentiation of primary CEFs.

Evolving concepts in the mechanism of steroid action: current developments

The mechanisms of steroid action remain a poorly understood enigma. Although much effort has focused on the steroid receptor as a mediator of the steroid's effect in the cell, we are only beginning to understand the structure of steroid receptors. Development of monoclonal antibodies directed against both the steroid-binding "receptors" and receptor-associated proteins has allowed novel approaches to the problem. They were important in determining the nucleotide sequences of several receptor genes and subsequently the amino acid sequence of three receptors. Surprisingly, receptors contain amino acid sequences common to v-erb-A, a potentiator of oncogenic transformation. Two receptor-associated proteins have been found and their relationship to the receptors suggests the possibility of additional functions of receptors in addition to binding deoxyribonucleic acid. Thus the role of the receptor in the mechanism of steroid action is evolving from the "two-step mechanism" to one that includes the recently discovered receptor-associated proteins.

Amplification of the neu (c-erbB-2) oncogene in human mammmary tumors is relatively frequent and is often accompanied by amplification of the linked c-erbA oncogene

We investigated alterations in the structure and expression of oncogenes in mammary tumors and mammary tumor-derived cell lines. In 16 of 95 samples, we detected amplification of the human neu oncogene, also known as c-erB-2, accompanied by overexpression in the tumors from which intact RNA could be isolated. In 10 of these DNAs, the linked oncogene c-erbA was also amplified, whereas another gene on human chromosome 17, p53, was present in normal copy numbers. Overexpression of c-erbA could not be detected in the tumors analyzed. The relatively high frequency of neu amplification points to a functional role in human breast cancer. Coamplification of the c-erbA oncogene could contribute to this disease as well but is most likely fortuitous.

Estrogen stimulates growth of mammary tumor cells ZR-75 without activation of S6 kinase and S6 phosphorylation. Difference from epidermal growth factor and alpha-transforming growth-factor-induced proliferation

Growth of the human mammary tumor cell line ZR-75-1 is stimulated by epidermal growth factor (EGF) and alpha-type transforming growth factor (alpha TGF), as well as by estradiol (E2). The role of activation of S6 kinase and S6 phosphorylation in the EGF(alpha TGF)-induced and E2-induced growth was investigated. Maximal effects on growth are observed at 10 nM EGF or alpha TGF. EGF as well as alpha TGF treatment of serum-starved cells leads to rapid activation of S6 kinase; the activity is increased about tenfold after 30 min of EGF treatment and declines with the time reaching about 25% of the maximal activity after 2 h of EGF treatment. Similar to the growth response, S6 kinase is activated at lower doses of EGF than alpha TGF and shows a maximal response at 10 nM for both growth factors. In contrast to this finding the incubation of serum-starved cells with E2 over a concentration range between 1 pM and 10 nM and times from 30 min to 4 h does not lead to increased S6 kinase activity. On investigating whether this lack of response to E2 is due to desensitization of the system by induction of alpha TGF it was found that preincubation of cells with alpha TGF for 2-6 h desensitizes them to reactivation of S6 kinase by alpha TGF, whereas preincubation with E2 does not. When S6 phosphorylation is monitored over times from 1 h to 6 h, it is observed that EGF leads to increased S6 phosphorylation, whereas E2 does not. The rate of onset of protein synthesis in the first 2 h of stimulation, when EGF-induced S6 phosphorylation is maximal, is more rapid with EGF than with E2. The results suggest that different pathway are involved in E2-induced and EGF(alpha TGF)-induced proliferation.

Antisense RNA of proto-oncogene c-fos blocks renewed growth of quiescent 3T3 cells

Mouse 3T3 cells were transformed with an antisense c-fos gene fused to a mouse mammary tumor virus promoter. In transformants that integrated a large number of antisense c-fos sequences, the usual large increase in c-fos mRNA and protein following stimulation of quiescent cells by platelet-derived growth factor was blocked in the presence of dexamethasone. These cells subsequently also failed to show the stimulation of DNA synthesis normally induced by platelet-derived growth factor. Appropriate expression of c-fos appears to be a prerequisite for reentry of quiescent cells into the cell cycle.

Colocalization of DNA-binding and transcriptional activation functions in the human glucocorticoid receptor

Using a combination of a transient expression assay and in vitro mutagenesis, we showed previously that the human glucocorticoid receptor (hGR) is composed of a series of discrete functional domains. Here we report the effects of selective deletion of each of these domains on hGR ability to activate transcription of the MTV-CAT fusion gene. Deletion of the immunogenic domain or the entire amino-terminal half of the protein reduces but does not abolish the ability of the hGR to induce transcriptional activation. Somewhat surprisingly, deletion of the steroid-binding domain engenders a constitutively active receptor, revealing that this domain normally represses receptor function. However, the central, cysteine-rich region contains all the information required for both DNA binding and trans-activation. Taken together, these data delineate a core domain in the hGR spanning 88 amino acids that determines both DNA-binding and transcriptional activation functions. This physical linkage distinguishes the glucocorticoid receptor from other described eukaryotic regulatory proteins, where these two functions have been shown to be separable.

Mutations that inactivate a yeast transcriptional regulatory protein cluster in an evolutionarily conserved DNA binding domain

The protein encoded by the GAL4 gene of the yeast Saccharomyces cerevisiae binds to DNA upstream of several genes and activates transcription. To try to understand these processes, we have undertaken a genetic analysis of GAL4. Here we report that nearly all missense mutations in GAL4, selected in vivo to lack function of the protein, cluster in the small region of the gene that encodes the DNA binding domain. About half of these mutations alters a cysteine-rich region of the protein highly homologous to several eukaryotic DNA binding proteins; the other half alters some of the 20 amino acids adjacent to the cysteine-rich region. Nearly all of the missense mutations that alter the DNA binding domain abolish the DNA binding activity of GAL4 protein measured in vitro. In contrast, nearly all of the mutations that alter the 3' 95% of the gene that encodes the transcription activation function are nonsense or frameshift mutations. These results support the idea that the conserved cysteine-rich sequence motif is directly involved in binding of several eukaryotic transcriptional regulatory proteins to DNA.

Molecular cloning and characterization of rat estrogen receptor cDNA

A cDNA clone of rat uterus estrogen receptor (ER) has been isolated and sequenced. This clone contains a complete open reading frame encoding 600 amino acid residues which is 5 and 11 amino acids larger than the corresponding molecules of human and chicken, respectively. The molecular weight of this protein is calculated to be 67,029. When this clone was ligated to the pSV2 vector and transfected into COS7 cells, a protein was produced that had the same affinity to estrogen as rat uterus ER. This sequence shows 88% homology with human ER; 528 amino acids are identical and 14 amino acids are conservative substitutions. The comparison of rat, human and chicken ER sequences indicate the presence of three highly conserved regions suggesting that these regions play important roles in ER function. The putative DNA-binding domain is completely identical in rat, human and chicken. The C-terminal half region which is thought to be the estrogen binding domain is also highly conserved and is rich in hydrophobic amino acid residues. Southern blot analysis of genomic DNA with ER cDNA as a probe has shown that related sequences are present in the genome.

[Clinical relevance of glucocorticoid receptors in the treatment of lymphoid neoplasias]

A generalized view on the mechanism of steroid hormone action is presented with special emphasis on glucocorticoids and their lymphocytolytic effects. The present knowledge on the structure and function of glucocorticoid receptors is reviewed. Following hormone binding, the receptor complex is activated to a form which is able to interact with chromatin or DNA. Several types of receptor mutants have been obtained in an animal cell culture system which allows selection of cell variants. The biochemical analysis of these mutants helped to establish a domain model of receptor structure. The quantitative effect of receptor numbers and hormone activity on lymphocytolysis is described in a cell culture model system and the results are discussed in view of the rational treatment of lymphoid neoplasia with glucocorticoids. The clinical experience with glucocorticoids alone and in combination therapy with cytostatic drugs is summarized. Our special emphasis is on acute lymphoblastic leukemia and malignant lymphoma as patients with these diseases can now be treated with remarkable success rates.

Complete amino acid sequence of the human progesterone receptor deduced from cloned cDNA

A lambda gt10 library containing DNAs complementary to messenger RNAs from human breast cancer T47-D cells was constructed and screened with a cDNA probe encoding the rabbit progesterone receptor. Four overlapping clones have been sequenced. The open reading frame corresponds to a protein of 933 amino acids with a molecular weight of 98,868 Da. The cysteine rich basic region supposed to be involved in DNA binding is completely homologous in the human and rabbit receptors, whereas the C-terminal end, where hormone binding is thought to take place, differs by a single amino acid change. The human progesterone receptor is characterized, as is the rabbit receptor, by the very high proline content of its N-terminal region. When mRNAs from either human breast cancer cell lines T47-D and MCF-7 or from normal human uterus tissue were blotted and probed with the cloned cDNA, four main bands were observed (5100, 4300, 3700, and 2900 nucleotides).

A multigene family encoding several "finger" structures is present and differentially active in mammalian genomes

Mouse genomic DNA contains multiple copies of sequences homologous to the Drosophila "Krüppel," a member of the "gap" class of developmental control genes of the fruit fly. The most interesting aspect of the homologous region is that, like Xenopus TFIIIA, it contains multiple finger-like folded domains capable of binding to nucleic acids. We have isolated six individual phages from a mouse genomic library on the basis of their DNA homology to Krüppel finger-coding probes, and describe here the DNA sequence and expression of two such clones containing finger-like structures. Upon differentiation of mouse teratocarcinoma cell line F9 with retinoic acid and cAMP, the expression of both genes was drastically reduced, and in one instance was undetectable. Each of the several other eukaryotic DNAs analyzed contained multiple copies of homologous genes with putative finger structures, indicating the presence of a finger-containing multigene family in higher organisms.

Expression of oncogenes in human tumours with special reference to the head and neck region

A major recent advance in cancer research has been in the field of oncogenes. Oncogenes are genes with a proven cancer association and which appear to be particularly implicated in cellular regulation and proliferation. The oncogenic potential of specific cellular genes has now been recognised and this has influenced current thinking concerning the initiation of carcinogenesis. The specific role of an oncogene is still incompletely understood but research with one particular oncogene (ras) has demonstrated that it can be involved in more than one stage of multi-step carcinogenesis. New techniques are being developed and evaluated to determine the expression of specific oncogenes in normal and neoplastic tissues, with a view to using them in future diagnostic immuno-histopathological methods. This review describes the concept of oncogenes and discusses their role in the development of neoplasia. The results of the expression of various oncogenes in human malignancies with special reference to the head and neck regions are discussed. Finally, the future prospects of this research field are examined their and its possible implications in cancer therapy.

The amino-terminal sequence of the 85-90K nonhormone binding component of the molybdate-stabilized estradiol receptor from calf uterus

The first six N-terminal amino acid residues of the 85-90K non-estrogen binding component of the calf uterine, molybdate-stabilized estradiol receptor have been determined by Edman degradation. After affinity chromatography of the stabilized receptor oligomer, the 85-90K unit was purified to homogeneity by preparative gel electrophoresis using electroelution for protein recovery. Inverse-gradient high performance liquid chromatography provided the 85-90K protein suitable for amino-terminal sequence analysis.

Antisense RNA of proto-oncogene c-fos blocks renewed growth of quiescent 3T3 cells

Mouse 3T3 cells were transformed with an antisense c-fos gene fused to a mouse mammary tumor virus promoter. In transformants that integrated a large number of antisense c-fos sequences, the usual large increase in c-fos mRNA and protein following stimulation of quiescent cells by platelet-derived growth factor was blocked in the presence of dexamethasone. These cells subsequently also failed to show the stimulation of DNA synthesis normally induced by platelet-derived growth factor. Appropriate expression of c-fos appears to be a prerequisite for reentry of quiescent cells into the cell cycle.

Glucocorticoid receptor mutants that are constitutive activators of transcriptional enhancement

Glucocorticoids, a class of steroid hormones, associate specifically with intracellular receptors, facilitating a conformational change that converts the receptor in vitro to a DNA-binding protein and in vivo to a nuclear species that activates a class of transcriptional enhancers termed glucocorticoid response elements (GREs). The DNA sequences recognized specifically by the hormone-receptor complex correspond directly to those required for GRE enhancement. The structural transition that accompanies steroid binding, 'receptor transformation', has been monitored by changes in receptor chromatographic properties, accessibility to monoclonal antibodies, association with other receptor subunits or with heterologous proteins, and aqueous two-phase partition coefficient. However, the significance of the structural change for the biological activity of the receptor is not understood. We have used cloned rat glucocorticoid-receptor coding sequences to produce and characterize a novel class of receptor mutants that elicit GRE enhancer function in transfected cells even in the absence of hormone. The constitutive activity of those receptor derivatives, together with mapping studies that distinguish between the DNA- and hormone-binding domains of the receptor, imply that the conformational change corresponding to receptor transformation may simply unmask pre-existing functional domains for DNA binding, enhancer activation, or both.