Identification of a new class of steroid hormone receptors

Transcriptional activities of the orphan nuclear receptor ERR alpha (estrogen receptor-related receptor-alpha)

Estrogen receptor-related receptor alpha (ERR alpha) is an orphan nuclear receptor closely related to the estrogen receptor (ER), whose expression covers various stages of embryonic development and persists in certain adult tissues. We show that ERR alpha binds as a homodimer on a specific target sequence, the SFRE (SF-1 response element), already known to respond to the orphan nuclear receptor SF-1. Target sequences that are related to the SFRE and that discriminate between ERR alpha and SF-1 were identified. We have also analyzed the transcriptional properties of the ERR alpha originating from various species. All ERR alpha orthologs act as potent transactivators through the consensus SFRE. ERR alpha activity depends on the putative AF2AD domain, as well as on a serum compound that is withdrawn by charcoal treatment, suggesting the existence of a critical regulating factor brought by serum.

Redox-dependent regulation of nuclear import of the glucocorticoid receptor

A number of transcription factors including the glucocorticoid receptor (GR) are regulated in a redox-dependent fashion. We have previously reported that the functional activity of the GR is suppressed under oxidative conditions and restored in the presence of reducing reagents. In the present study, we have used a chimeric human GR fused to the Aequorea green fluorescent protein and demonstrated that both ligand-dependent and -independent nuclear translocation of the GR is impaired under oxidative conditions in living cells. Substitution of Cys-481 for Ser within NL1 of the human GR resulted in reduction of sensitivity to oxidative treatment, strongly indicating that Cys-481 is one of the target amino acids for redox regulation of the receptor. Taken together, we may conclude that redox-dependent regulation of nuclear translocation of the GR constitutes an important mechanism for modulation of glucocorticoid-dependent signal transduction.

Identification of two hERR2-related novel nuclear receptors utilizing bioinformatics and inverse PCR

Identification of novel nuclear receptors based on the highly conserved DNA-binding domain (DBD) has previously depended mainly on low stringency hybridization of cDNA libraries and degenerate PCR. Establishment of the expressed sequence tag (EST) database in recent years has provided an alternative approach for the discovery of novel members of gene families. The rate-limiting step is the conversion of ESTs to full-length cDNA. This article describes the identification of two novel nuclear receptors (hERRbeta2 and hERRgamma2) related to human estrogen-receptor-related receptor 2 (hERR2) by mining the EST database and retrieving of full-length cDNA via inverse PCR on subdivided primary cDNA library pools. The deduced protein sequences of hERRbeta2 and hERRgamma2 contain 500 and 458 amino acid (aa) residues respectively. Sequence analysis revealed that hERRbeta2 and hERRgamma2 respectively share 95% and 77% overall aa sequence identity with hERR2. However, the extra C-terminal domain in hERRbeta2 and extra N-terminal domain in hERRgamma2 are not present in the closely related hERR2 or mouse ERR2 (mERR2). Extensive sequence verification revealed that hERR2 previously reported as a human gene is actually a rat gene, whereas hERRbeta2 is the true human ortholog of hERR2 and mERR2. Tissue distribution studies showed that hERRgamma2 was expressed in a broader panel of tissues at a higher level than hERRbeta2. hERRbeta2 was mapped to cytogenetic locus 14q24.3 approximately -14q31, a region containing multiple loci involved in genetic diseases, including Alzheimer and diabetes. hERRgamma2 was mapped to 1q32. Given the high sequence homology between hERRbeta2 and mERR2, the two receptors may have similar biological function in vivo.

The Nuclear Receptor Superfamily Has Undergone Extensive Proliferation and Diversification in Nematodes

The nuclear receptor (NR) superfamily is the most abundant class of transcriptional regulators encoded in the Caenorhabditis elegans genome, with >200 predicted genes revealed by the screens and analysis of genomic sequence reported here. This is the largest number of NR genes yet described from a single species, although our analysis of available genomic sequence from the related nematode Caenorhabditis briggsae indicates that it also has a large number. Existing data demonstrate expression for 25% of theC. elegans NR sequences. Sequence conservation and statistical arguments suggest that the majority represent functional genes. An analysis of these genes based on the DNA-binding domain motif revealed that several NR classes conserved in both vertebrates and insects are also represented among the nematode genes, consistent with the existence of ancient NR classes shared among most, and perhaps all, metazoans. Most of the nematode NR sequences, however, are distinct from those currently known in other phyla, and reveal a previously unobserved diversity within the NR superfamily. In C. elegans, extensive proliferation and diversification of NR sequences have occurred on chromosome V, accounting for > 50% of the predicted NR genes.

[The sequence data described in this paper have been submitted to the GenBank data library under accession nos.AF083222–AF083225 and AF083251–AF083234.]

Genetic control of extraembryonic cell lineages studied with tetraploid<–>diploid chimeric concepti

The first differentiation event during mammalian embryogenesis is the commitment of blastomeres to the trophectoderm cell lineage. Much remains to be learned about the genetic control of this first cell lineage commitment and the subsequent events underlying the differentiation of all extraembryonic cell lineages. Because of the unique features of intrauterine embryonic development, the study of embryogenesis in lower organisms has shed little light on mammalian extraembryonic lineage differentiation. Rather, two major methods in developmental genetics have contributed to our understanding of genetic control of extraembryonic cell lineages. First, abnormalities in extraembryonic tissues have been described in many genetically engineered mutant mouse lines. However, the histological description of these abnormalities does not demonstrate whether the observed defect is the primary cause of embryonic lethality. Second, tetraploid<–>diploid aggregation experiments have been used to generate chimeric concepti with distinct genotypes in the extraembryonic tissues and the embryo proper. This experimental approach has provided the definitive demonstration of the crucial role of several transcription factors, growth factors and cytoskeleton proteins in extraembryonic tissue formation. The present review summarizes the origin of tetraploid<–>diploid aggregation experiments and it usefulness for the study the genetic control of extraembryonic cell lineages.Key words: tetraploid, aggregation, chimera, extraembryonic cell lineages, placenta.

Isolation and characterization of an estrogen binding protein which may integrate the plethora of estrogenic actions in non-reproductive organs

A putative estrogen receptor (pER) from mouse liver has been characterized. The heterodimer protein (81-84 kDa) consists of two covalently bound subunits (61-67 and 17-27 kDa) with following characteristics: sedimentation constant--4.9 S; IP--4.8; dissociation constant (Kd) for estradiol-17beta binding--0.7 nmol; binding sites--0.746 pmol/mg protein; relative binding affinity--estradiol-17beta--100, estrone--80 and estriol--30; specificity--does not bind, other natural steroids, synthetic estrogens, antiestrogens and bioflavonoids. Importantly, immunosuppressants, neuroleptic and carcinogens influence 3H-estradiol-17beta binding to pER. Interestingly, pER is a serine phosphatase and this may have relevancy to estrogen action in Alzheimer's disease. The polyclonal anti-pER antibody does not react with estrogen receptors (ER). ER antibody does not react with pER. Remarkably, anti-pER antibody reacts with calcineurin, a brain phosphatase and anti-calcineurin antibody reacts with pER. Immunohistochemical analyses showed that pER is undetectable in reproductive organs (except ovary). It is localized on the plasma or the nuclear membranes in some, in cytoplasm and/or nucleus in other cells of non-reproductive organs (skeletal, neural, vascular, hair and retina), and in tumors (mammary, endometrial and prostate cancers, and prostatic hyperplasia). The information presented justifies the proposition that pER may mediate the estrogenic actions in non-reproductive organs.

A role for estrogen-related receptor alpha in the control of mitochondrial fatty acid beta-oxidation during brown adipocyte differentiation

Little is known about the factors involved in the brown adipocyte gene regulatory program. In contrast to the white adipocyte, the brown adipocyte is characterized by abundant mitochondria and high level expression of mitochondrial fatty acid beta-oxidation enzymes. Previous studies in transgenic mice have shown that the brown adipose-enriched expression of a key beta-oxidation enzyme, medium chain acyl-coenzyme A dehydrogenase (MCAD), requires cis-acting elements located within the proximal promoter region of the MCAD gene. The levels of mRNA encoding MCAD and several other beta-oxidation cycle enzymes were coordinately induced during differentiation of brown adipocytes in culture. Expression of transgenes comprised of MCAD gene promoter fragments fused to chloramphenicol acetyltransferase reporters in differentiating brown adipocytes revealed that a known nuclear receptor response element (NRRE-1) was required for the transcriptional induction of the MCAD gene during brown adipocyte differentiation. Electrophoretic mobility shift assays and antibody recognition studies identified distinct brown adipocyte differentiation stage-specific, NRRE-1-protein complexes; the orphan nuclear receptors, chicken ovalbumin upstream promoter transcription factors I and II, were identified as major the NRRE-1 binding proteins in the pre-adipocyte, whereas the estrogen-related receptor alpha (ERRalpha) bound NRRE-1 in extracts prepared from differentiated brown adipocytes. DNA binding studies performed with a series of NRRE-1 mutant probes indicated that ERRalpha was capable of binding two distinct sites within NRRE-1, each of which conform to the known ERRalpha monomeric binding consensus. The expression of ERRalpha paralleled NRRE-1 binding activities and MCAD expression during brown adipocyte differentiation, cardiac development, and among a variety of adult mouse tissues. These results identify a new class of ERRalpha target genes and implicate ERRalpha and chicken ovalbumin upstream promoter transcription factor in the control of a pivotal metabolic pathway during brown adipocyte differentiation.

Chromosomal mapping of the human and murine orphan receptors ERRalpha (ESRRA) and ERRbeta (ESRRB) and identification of a novel human ERRalpha-related pseudogene

The estrogen-related receptors ERRalpha and ERRbeta (formerly ERR1 and ERR2) form a subgroup of the steroid/thyroid/retinoid receptor family. ERRalpha and ERRbeta are homologous to the estrogen receptor and bind similar DNA targets; however, they are unable to activate gene transcription in response to estrogens. We have used interspecific backcross analysis to map the murine Estrra locus to chromosome 19 and Estrrb to mouse chromosome 12. Using fluorescence in situ hybridization, we have mapped the human ESRRA gene to chromosome 11q12-q13 and the human ESRRB gene to chromosome 14q24.3. In addition, we report the isolation of a processed human ERRalpha pseudogene mapping to chromosome 13q12.1. To our knowledge, this represents the first report of a pseudogene associated with a member of the nuclear receptor superfamily.

The orphan nuclear receptor estrogen-related receptor alpha is a transcriptional regulator of the human medium-chain acyl coenzyme A dehydrogenase gene

Estrogen-related receptor alpha (ERR alpha) is an orphan member of the superfamily of nuclear hormone receptors. ERR alpha was initially isolated based on its sequence homology to the estrogen receptor but is not activated by classic estrogens. To identify possible physiologic functions for this orphan receptor, we cloned the mouse ERR alpha cDNA and used it to characterize the expression of ERR alpha transcripts and to identify potential ERR alpha target genes. RNA in situ hybridization studies detect ERR alpha transcripts in an organ-specific manner through mid- to late embryonic development, with persistent high-level expression in brown adipose tissue and intestinal mucosa. In the adult mouse, ERR alpha is most highly expressed in kidney, heart, and brown adipocytes, tissues which preferentially metabolize fatty acids. Binding site selection experiments show that ERR alpha preferentially binds to an ERR alpha response element (ERRE) containing a single consensus half-site, TNAAGGTCA. An ERRE is present in the 5'-flanking region of the gene encoding medium-chain acyl coenzyme A dehydrogenase (MCAD), a key enzyme involved in the mitochondrial beta-oxidation of fat. The MCAD nuclear receptor response element 1 (NRRE-1) interacts in vitro with ERR alpha expressed in COS-7 cells. Supershift experiments show that endogenous ERR alpha present in nuclear extracts obtained from a brown fat tumor cell line (HIB) interacts with NRRE-1. In the absence of its putative ligand, ERR alpha does not activate the MCAD promoter in transient transfection studies; however, a VP16-ERR alpha chimera activates natural and synthetic promoters containing NRRE-1. In addition, ERR alpha efficiently represses retinoic acid induction mediated by NRRE-1. These results demonstrate that ERR alpha can control the expression of MCAD through the NRRE-1 and thus may play an important role in regulating cellular energy balance in vivo.

Mouse estrogen receptor beta forms estrogen response element-binding heterodimers with estrogen receptor alpha

The recent discovery that an additional estrogen receptor subtype is present in various rat tissues has advanced our understanding of the mechanisms underlying estrogen signaling. Here we report on the cloning of the cDNA encoding the mouse homolog of estrogen receptor-beta (ER beta) and the functional characterization of mouse ER beta protein. ER beta is shown to have overlapping DNA-binding specificity with that of the estrogen receptor-alpha (ER alpha) and activates transcription of reporter gene constructs containing estrogen-response elements in transient transfections in response to estradiol. Using a mammalian two-hybrid system, the formation of heterodimers of the ER beta and ER alpha subtypes was demonstrated. Furthermore, ER beta and ER alpha form heterodimeric complexes with retained DNA-binding ability and specificity in vitro. In addition, DNA binding by the ER beta/ER alpha heterodimer appears to be dependent on both subtype proteins. Taken together these results suggest the existence of two previously unrecognized pathways of estrogen signaling; I, via ER beta in cells exclusively expressing this subtype, and II, via the formation of heterodimers in cells expressing both receptor subtypes.

Placental abnormalities in mouse embryos lacking the orphan nuclear receptor ERR-beta

Classical endocrine studies have shown that steroid hormones are required for the maintenance of pregnancy and placental viability. The oestrogen-receptor-related receptor beta (ERR-beta) is an orphan member of the superfamily of nuclear hormone receptors. Although ERR-beta is homologous to the oestrogen receptor and binds the oestrogen response element, it is not activated by oestrogens. Expression of ERR-beta during embryogenesis defines a subset of extra-embryonic ectoderm that subsequently forms the dome of the chorion, suggesting that ERR-beta may be involved in early placental development. Homozygous mutant embryos generated by targeted disruption of the Estrrb gene have severely impaired placental formation, and die at 10.5 days post-coitum. The mutants display abnormal chorion development associated with an overabundance of trophoblast giant cells and a severe deficiency of diploid trophoblast. The phenotype can be rescued by aggregation of Estrrb mutant embryos with tetraploid wild-type cells, which contribute exclusively to extra-embryonic tissues. Our results indicate that ERR-beta has an important role in early placentation, and suggest that an inductive signal originating from or modified by the chorion is required for normal trophoblast proliferation and differentiation.

Human estrogen receptor-like 1 (ESRL1) gene: genomic organization, chromosomal localization, and promoter characterization

Estrogen receptor-like 1a (ESRL1a; same as estrogen receptor-related orphan receptors, ERR1) belongs to a subfamily of the nuclear receptor superfamily. We have previously shown that human ESRL1a modulates estrogen responsiveness of the lactoferrin gene promoter in transiently transfected endometrial carcinoma RL95-2 cells. In this study, we cloned and characterized the human ESRL1 gene. Through the fluorescence in situ hybridization method, the ESRL1 gene was localized to the centromere region of chromosome 11q12. Partial sequencing, restriction mapping, and PCR analysis revealed that the ESRL1 gene consists of seven exons and is approximately 20 kb in length. We found that the smallest exon (exon 3) contains 117 bp and the largest exon (exon 7) has 1032 bp. The smallest intron (intron 5) is only 88 bp long and the largest intron (intron 2) is 8 kb long. All introns have the conserved GT and AG dinucleotides present at the donor and acceptor sites, respectively. Like the estrogen receptor, the highly conserved DNA-binding domain of hESRL1a is encoded by exon 2 and exon 3, and the intron/exon junctions (2 and 3) are well conserved between the two genes. Primer extension analysis revealed multiple transcription initiation start sites in human uterine (HeLa, HEC, and RL95-2) cell lines. However, one major initiation start site was found by RNase protection assay. The hESRL1a mRNA is differentially expressed in various human tissues. The nucleotide sequence adjacent to the transcription start sites of the ESRL1 lacks the typical TATA and CAAT boxes but is GC rich and contains 10 consensus Sp1-binding elements and two E boxes. The region that contains these transcription factor-binding elements showed a high level of promoter activity when transiently transfected into RL95-2 cells.

Characterization of the Retinoid Binding Properties of the Major Fusion Products Present in Acute Promyelocytic Leukemia Cells

The bcr1- and bcr3- promyelocytic leukemia/retinoic acid receptor α (PML/RARα) are the two major fusion proteins expressed in acute promyelocytic leukemia (APL) patients. These proteins, which are present in different lengths of PML (amino acids 1-552 and 1-394, respectively), contain most of the functional domains of PML and RARα, bind all-trans-retinoic acid (t-RA), and act as t-RA–dependent transcription factors. T-RA is an effective inducer of clinical remission only in patients carrying the t(15; 17) and expressing the PML/RARα products. However, in APL patients achieving complete remission with t-RA therapy the bcr3-PML/RARα product has been found associated with a poorer prognosis than bcr1-PML/RARα. In the present study we have investigated the structural and functional properties of the bcr3-PML/RARα in comparison to the previously characterized bcr1-PML/RARα. In particular, we have measured the binding properties of the two endogenous ligands t-RA and 9-cis-RA to both of these isoforms. T-RA binding analysis of nuclear and cytosolic extracts prepared from bcr3-PML/RARα APL patients and from bcr3-PML/RARα COS-1 transfected cells indicates that this protein is present only as high-molecular-weight nuclear complexes. Using saturation binding assays and Scatchard analyses we found that t-RA binds with slightly less affinity to the bcr3-PML/RARα receptor than to bcr1-PML/RARα or RARα (Kd = 0.4 nmol/L, 0.13 nmol/L or 0.09 nmol/L, respectively). Moreover, two different high-affinity 9-cis-RA binding sites (Kd = 0.45 and 0.075 nmol/L) were detectable in the bcr3-PML/RARα product but not in the bcr1-PML/RARα product (Kd = 0.77 nmol/L). By competition binding experiments we showed that 9-cis-RA binds with higher specificity to the bcr3-PML/RARα isoform than to the bcr1-PML/RARα or RARα. Consistent with these data, the binding of 9-cis-RA to the bcr3-PML/RARα product resulted in increased transcriptional activation of the RA-responsive element (RARE) TRE, but not of the βRARE, in transiently transfected COS-1 cells. These results provide evidence indicating that preferential retinoid binding to the different PML/RARα products can be measured.

Characterization of the Retinoid Binding Properties of the Major Fusion Products Present in Acute Promyelocytic Leukemia Cells

The bcr1- and bcr3- promyelocytic leukemia/retinoic acid receptor α (PML/RARα) are the two major fusion proteins expressed in acute promyelocytic leukemia (APL) patients. These proteins, which are present in different lengths of PML (amino acids 1-552 and 1-394, respectively), contain most of the functional domains of PML and RARα, bind all-trans-retinoic acid (t-RA), and act as t-RA–dependent transcription factors. T-RA is an effective inducer of clinical remission only in patients carrying the t(15; 17) and expressing the PML/RARα products. However, in APL patients achieving complete remission with t-RA therapy the bcr3-PML/RARα product has been found associated with a poorer prognosis than bcr1-PML/RARα. In the present study we have investigated the structural and functional properties of the bcr3-PML/RARα in comparison to the previously characterized bcr1-PML/RARα. In particular, we have measured the binding properties of the two endogenous ligands t-RA and 9-cis-RA to both of these isoforms. T-RA binding analysis of nuclear and cytosolic extracts prepared from bcr3-PML/RARα APL patients and from bcr3-PML/RARα COS-1 transfected cells indicates that this protein is present only as high-molecular-weight nuclear complexes. Using saturation binding assays and Scatchard analyses we found that t-RA binds with slightly less affinity to the bcr3-PML/RARα receptor than to bcr1-PML/RARα or RARα (Kd = 0.4 nmol/L, 0.13 nmol/L or 0.09 nmol/L, respectively). Moreover, two different high-affinity 9-cis-RA binding sites (Kd = 0.45 and 0.075 nmol/L) were detectable in the bcr3-PML/RARα product but not in the bcr1-PML/RARα product (Kd = 0.77 nmol/L). By competition binding experiments we showed that 9-cis-RA binds with higher specificity to the bcr3-PML/RARα isoform than to the bcr1-PML/RARα or RARα. Consistent with these data, the binding of 9-cis-RA to the bcr3-PML/RARα product resulted in increased transcriptional activation of the RA-responsive element (RARE) TRE, but not of the βRARE, in transiently transfected COS-1 cells. These results provide evidence indicating that preferential retinoid binding to the different PML/RARα products can be measured.

NMR spectroscopic studies of the DNA-binding domain of the monomer-binding nuclear orphan receptor, human estrogen related receptor-2. The carboxyl-terminal extension to the zinc-finger region is unstructured in the free form of the protein

Unlike steroid and retinoid receptors, which associate with DNA as dimers, human estrogen related receptor-2 (hERR2) belongs to a growing subclass of nuclear hormone receptors that bind DNA with high affinity as monomers. A carboxyl-terminal extension (CTE) to the zinc-finger domain has been implicated to be responsible for determining the stoichiometry of binding by a nuclear receptor to its response element. To better understand the mechanism by which DNA specificity is achieved, the solution structure of the DNA-binding domain of hERR2 (residues 96-194) consisting of the two putative zinc fingers and the requisite 26-amino acid CTE was analyzed by multidimensional heteronuclear magnetic resonance spectroscopy. The highly conserved zinc-finger region (residues 103-168) has a fold similar to those reported for steroid and retinoid receptors, with two helices that originate from the carboxyl-terminal ends of the two zinc fingers and that pack together orthogonally, forming a hydrophobic core. The CTE element of hERR2 is unstructured and highly flexible, exhibiting nearly random coil chemical shifts, extreme sensitivity of the backbone amide protons to solvent presaturation, and reduced heteronuclear (1H-15N) nuclear Overhauser effect values. This is in contrast to the dimer-binding retinoid X and thyroid hormone receptors, where, in each case, a helix has been observed within the CTE. The implications of this property of the hERR2 CTE are discussed.

Expression of the estrogen-related receptor 1 (ERR-1) orphan receptor during mouse development

We studied the expression of the estrogen-related receptor 1 (ERR-1) during mouse embryonic development. ERR-1 is expressed at very early stages in ES cells and at E8.5 in the mesodermal cells of the visceral yolk sac. ERR-1 continues to be expressed later in mesodermal tissues and particularly in heart and in skeletal muscles. This expression persists during all the embryonic development and in adult stage. ERR-1 transcripts level increases during muscle differentiation. Accordingly, we show that ERR-1 expression increases during the myoblast to myotube transition in differentiating C2 myoblastic cells. ERR-1 has also been detected in the nervous system during embryonic development. At E10.5, a high level of ERR-1 transcripts can be observed in differentiated cells of the intermediate zone of the spinal cord which also suggests a role of ERR-1 in the differentiation of the nervous system. The same is observed in the telencephalon vesicules at E13.5. Later, at E15.5 and E17.5, expression persists in the spinal cord but decreases dramatically in the central nervous system. Moreover, ERR-1 expression increases during skin formation and is detected in the stratum spinosum which contains differentiated Malpighian cells. Finally, we also observed ERR-1 in endodermal derivatives such as the epithelium of intestine and urogenital system. The DNA target of ERR-1 has been identified to be the SF-1/FTZ-F1 responsive element (SFRE) and we show in this paper that SF-1/FTZ-F1 and ERR-1 bind to and activate transcription independently through the SFRE element. Our study suggests that ERR-1 may be implicated in numerous physiological or developmental functions, particularly in the muscle, the central and peripheral nervous system and the epidermis. Interestingly, in these various systems ERR-1 expression is correlated with post-mitotic cells stage, suggesting that ERR-1 may play a role in the differentiation process.

Direct modulation of simian virus 40 late gene expression by thyroid hormone and its receptor

Transcription of the late genes of simian virus 40 (SV40) is repressed during the early phase of the lytic cycle of infection of primate cells by the binding of cellular factors, called IBP-s, to the SV40 late promoter; repression is relieved after the onset of viral DNA replication by titration of these repressors (S. R. Wiley, R. J. Kraus, F. R. Zuo, E. E. Murray, K. Loritz, and J. E. Mertz, Genes Dev. 7:2206-2219, 1993). Recently, we showed that IBP-s consists of several members of the steroid/thyroid hormone receptor superfamily (F. Zuo and J. E. Mertz, Proc. Natl. Acad. Sci. USA 92:8586-8590, 1995). Here, we show that the thyroid hormone receptor TRalpha1, in combination with retinoid X receptor alpha (RXRalpha), is specifically bound at the transcriptional initiation site of the major late promoter of SV40. This binding repressed transcription from the SV40 late promoter by preventing the formation of pre-initiation complexes. Addition of the thyroid hormone 3,5,3'-L-triiodothyronine (T3) resulted in reversal of this repression in cotransfected CV-1 cells. Interestingly, repression did not occur when this thyroid response element (TRE) was translocated to 50 bp upstream of the major late initiation site. Binding of TRalpha1/RXRalpha heterodimers to this TRE induced bending of the promoter DNA. We conclude that hormones and their receptors can directly affect the expression of SV40, probably by affecting protein-protein and protein-DNA interactions involved in the formation of functional preinitiation complexes.

ER beta: identification and characterization of a novel human estrogen receptor

A novel estrogen receptor (hereinafter referred to as ER beta) was cloned using degenerate PCR primers. A comparison of the amino acid sequence of ER beta with the "classical' ER (ER alpha) shows a high degree of conservation of the DNA-binding domain (96%), and of the ligand-binding domain (58%). In contrast, the A/B domain, the hinge region and the F-domain are not conserved. Northern blot analysis revealed that ER beta is expressed in human thymus, spleen, ovary and testis. Transient transfections of an ER beta expression construct together with an ERE-based reporter construct in CHO cells clearly demonstrated transactivation of ER beta by 17 beta-estradiol. In addition, the ER alpha antagonist ICI-164384 is a potent antagonist for ER beta as well. Interestingly, the level of transactivation by 17 beta-estradiol is higher for ER alpha than for ER beta, which may reflect suboptimal conditions for ER beta at the level of the ligand, responsive element or cellular context.

Cloning of a novel receptor expressed in rat prostate and ovary

We have cloned a novel member of the nuclear receptor superfamily. The cDNA of clone 29 was isolated from a rat prostate cDNA library and it encodes a protein of 485 amino acid residues with a calculated molecular weight of 54.2 kDa. Clone 29 protein is unique in that it is highly homologous to the rat estrogen receptor (ER) protein, particularly in the DNA-binding domain (95%) and in the C-terminal ligand-binding domain (55%). Expression of clone 29 in rat tissues was investigated by in situ hybridization and prominent expression was found in prostate and ovary. In the prostate clone 29 is expressed in the epithelial cells of the secretory alveoli, whereas in the ovary the granuloma cells in primary, secondary, and mature follicles showed expression of clone 29. Saturation ligand-binding analysis of in vitro synthesized clone 29 protein revealed a single binding component for 17beta-estradiol (E2) with high affinity (Kd= 0.6 nM). In ligand-competition experiments the binding affinity decreased in the order E2 > diethylstilbestrol > estriol > estrone > 5alpha-androstane-3beta,17beta-diol >> testosterone = progesterone = corticosterone = 5alpha-androstane-3alpha,17beta-diol. In cotransfection experiments of Chinese hamster ovary cells with a clone 29 expression vector and an estrogen-regulated reporter gene, maximal stimulation (about 3-fold) of reporter gene activity was found during incubation with 10 nM of E2. Neither progesterone, testosterone, dexamethasone, thyroid hormone, all-trans-retinoic acid, nor 5alpha-androstane-3alpha,I7beta-diol could stimulate reporter gene activity, whereas estrone and 5alpha-androstane-3beta,17beta-diol did. We conclude that clone 29 cDNA encodes a novel rat ER, which we suggest be named rat ERbeta to distinguish it from the previously cloned ER (ERalpha) from rat uterus.

In situ hybridization study of messenger RNA for estrogen receptor and immunohistochemical detection of estrogen and progesterone receptors in the human ovary

The expression of estrogen and progesterone receptors (ER and PR), as well as the presence of messenger RNA for estrogen receptor (ER-mRNA), were analyzed by immunohistochemistry and in situ hybridization, respectively, in the ovary of 25 healthy eumenorrheic women. Ovarian biopsies were taken in different phases of the menstrual cycle during laparotomy or operative laparoscopy performed for extraovarian benign diseases. A total of 126 follicles (105 primordial, 13 preantral and eight antral) and 50 corpora lutea (eight active and 42 atretic) was analyzed. Granulosa cells stained positively for ER, PR and ER-mRNA in 13.3, 9.5 and 17.1% of primordial follicles, respectively. The proportions of preantral and antral follicles with ER-positive granulosa cells were 23.1 and 37.5%, respectively; these follicles were positive for PR in 23.1 and 37.5% of cases, and for ER-mRNA in 30.7 and 37.5% of cases, respectively. For thecal cells, 38.5% of preantral and 37.5% of antral follicles were PR-positive, but no more than 25% stained positive for ER and ER-mRNA. Active corpora lutea stained positive for ER, PR and ER-mRNA in 50, 62.5 and 50% of cases, respectively. Corpora albicantes always stained negative. In all subjects the stroma surrounding both follicles and corpora lutea contained several fibroblast-like cells which stained positive for ER, PR and ER-mRNA. Oocytes and blood vessels stained negative in all cases. This study supports the hypothesis that estrogens and progesterone play a role in the intraovarian regulation of follicle growth from the first steps of follicle development, and participate in the regulation of corpus luteum.

Nuclear orphan receptor as a repressor of glucocorticoid receptor transcriptional activity

Nuclear orphan receptors belong to the superfamily of ligand-activated transcription factors that show a close structural relationship and sequence homology. Ligands and functions of most of the orphan receptors have not yet been identified. The first nuclear orphan receptors that were cloned displayed a high degree of amino acid identity with the human estrogen receptor and were termed estrogen receptor-related (ERR) 1 and 2. In the present study, we show that ERR2 functions as a potent repressor of transcriptional activity mediated by the glucocorticoid receptor (GR). Transient transfection of different cell lines with a steroid-responsive reporter plasmid and receptor expression plasmids revealed that transcriptional activity mediated by GR in response to agonists was strongly suppressed by coexpression of ERR2. The orphan receptor displayed no promoter activity when expressed without GR. The inhibitory activity of ERR2 is cell-specific and also receptor-specific because transactivation mediated by the progesterone receptor is unaffected by ERR2. Our observations provide evidence that the nuclear orphan receptor ERR2 acts as an endogenous modulator of GR transcriptional activity.

Suppression of the human erythropoietin gene expression by the TR2 orphan receptor, a member of the steroid receptor superfamily

A DNA response element, TR2RE-EPO (5'-TCTGACCTCTCGACCTAC-3') has been identified in the 3-minimal hypoxia-inducible enhancer of the human erythropoietin gene for the TR2 orphan receptor, an androgen-repressed transcription factor and a member of the steroid/thyroid hormone receptor superfamily. Electrophoretic mobility shift assay showed a specific binding with high affinity (Kd = 0.14 nM) between the TR2 orphan receptor and the TR2RE-EPO. Our data further indicated that this specific binding is not due to the homo-dimerization of the TR2 orphan receptor. In addition, reporter gene expression using chloramphenicol acetyltransferase assay demonstrated that the TR2 orphan receptor may suppress the expression of the chloramphenicol acetyltransferase activities via the TR2RE-EPO in the hypoxic/normoxic human hepatoma HepG2 cells. Finally, our in situ hybridization data also indicated that the TR2 orphan receptor and the erythropoietin transcripts can be co-expressed in mouse kidney and liver. Together, our data suggest that the human erythropoietin gene could represent the first human target gene regulated directly by the human TR2 orphan receptor.

Estrogen-related receptor, hERR1, modulates estrogen receptor-mediated response of human lactoferrin gene promoter

We have shown previously that estrogen-stimulated transcription from the human lactoferrin gene in RL95-2 endometrium carcinoma cells is mediated through an imperfect estrogen response element (ERE) at the 5 -flanking region of the gene. Upstream from the ERE, a DNA sequence (-418 to -378, FP1) was selectively protected from DNase I digestion by nuclear extracts from endometrial and mammary gland cell lines. In this report, using the electrophoresis mobility shift assay, site-directed mutagenesis, and DNA methylation interference analyses, we show that three different nuclear proteins bind to the FP1 region (C1, C2, and C3 sites). The nuclear receptor, COUP-TF, binds to the C2 site. Mutations in the C1 binding region abolish C1 complex formation and reduce estrogen-dependent transcription from the lactoferrin ERE. When the imperfect ERE of the lactoferrin gene is converted to a perfect palindromic structure, the enhancing effect of the C1 binding element for estrogen responsiveness was abolished. We isolated a complementary DNA (cDNA) clone from an RL95-2 expression library that encodes the C1 site-binding protein. The encoded polypeptide maintains 99% amino acid identity with the previously described orphan nuclear receptor hERR1. A 2.2-kilobase mRNA was detected in RL95-2 cells by the newly isolated cDNA but not by the first 180 base pair of the published hERR1 sequence. By Western analysis, a major 42-kDa protein is detected in the RL95-2 nuclear extract with antibody generated against GST-hERR1 fusion protein. Finally, we show that the hERR1 interacts with the human estrogen receptor through protein-protein contacts.

The efficacy of 9-cis retinoic acid in experimental models of cancer

9-cis retinoic acid (9-cis RA) is a retinoid receptor pan-agonist that binds with high affinity to both retinoic acid receptors (RARs) and retinoid X receptors (RXRs). Using a variety of in vivo and in vitro cancer models, we present experimental data that 9-cis RA has activity as a potential chemotherapeutic agent. Treatment of the human promyelocytic leukemia cell line HL-60 with 9-cis RA decreases cell proliferation, increases cell differentiation, and increases apoptosis. Induction of apoptosis correlates with an increase in tissue transglutaminase (type II) activity. In vivo, 9-cis RA induces complete tumor regression of an early passage human lip squamous cell carcinoma xenograft. Finally, 9-cis RA inhibits the anchorage-independent growth of the human breast cancer cell lines MCF-7 and LY2 (an antiestrogen-resistant MCF-7 variant). Transient co-transfection assays indicate that 9-cis RA inhibits estrogen receptor transcription of an ERE-tk-LUC reporter through RAR or RXR receptors. These data suggest that retinoid receptors can antagonize estrogen-dependent transcription and provides one possible mechanism for the inhibition of cell growth by 9-cis RA in breast cancer cell lines. In summary, these findings present evidence that 9-cis RA has a wide range of activities in human cancer models.

Expression of a novel member of estrogen response element-binding nuclear receptors is restricted to the early stages of chorion formation during mouse embryogenesis

Members of the nuclear hormone receptor gene family of transcription factors have been shown to be expressed in characteristic patterns during mouse organogenesis and postnatal development. Using an RT-PCR based screening assay, we have identified nuclear receptors expressed in embryonal carcinoma stem cells. One of the cDNAs characterized, mERR-2, was found to be expressed exclusively during a narrow developmental window in trophoblast progenitor cells between days 6.5 and 7.5 post coitum (p.c.). From 8.5 days p.c. and onwards, the mERR-2 gene activity evaded detection as analysed by in situ hybridization. We also show that the mERR-2 gene product and the estrogen receptor share a common target DNA-sequence recognition specificity unique among members of the gene family. Furthermore, efficient homodimerization and DNA-binding of the orphan receptor mERR-2 was found to be dependent on interaction with the heat shock protein 90, a molecular chaperone hitherto recognized to interact only with the steroid hormone receptor subgroup of nuclear receptors. Based on our results we suggest that the mouse orphan receptor mERR-2 has the potential to regulate overlapping gene networks with the estrogen receptor and may participate in signal transduction pathways during a short developmental period coinciding with the formation of the chorion.

Antisense oligonucleotide to NOR-1, a novel orphan nuclear receptor, induces migration and neurite extension of cultured forebrain cells

We previously identified a novel orphan nuclear receptor referred to as NOR-1 from rat forebrain cells. This study examined the role of NOR-1 in primary cultured forebrain cells by selectively inhibiting NOR-1 expression by addition of antisense oligonucleotide to the culture media. Treating cells with the antisense oligomer resulted in the following dramatic morphological changes: (i) cell migration, (ii) extension of processes, and (iii) formation of cellular aggregates. Immunocytochemistry for microtubule-associated protein 2 revealed that the processes were filled with neurites growing from neuronal cells. These findings suggest that NOR-1 may be involved in the molecular mechanisms regulating neural differentiation.

The ligand binding domain of the human retinoic acid receptor gamma is predominantly alpha-helical with a Trp residue in the ligand binding site

Retinoic acid exerts its many biological effects by interaction with a nuclear protein, the retinoic acid receptor (RAR). The details of this interaction are unknown due mainly to the lack of sufficient quantities of pure functional receptor protein for biochemical and structural studies. We have recently subcloned the D and E domains of human RAR gamma for expression in Escherichia coli. Using nickel-chelation affinity chromatography with a polyhistidine amino-terminal tail, purification of the DE peptide with a pI of 5.18 was accomplished to greater than 98% purity. Scatchard analysis and fluorescence quenching techniques using the purified protein indicate a very high percentage of functional molecules ( > 95%) with a Kd for retinoic acid (t-RA) of 0.6 +/- 0.1 nM. Circular dichroism spectra of the purified domains predict a predominantly alpha-helical structure (approximately 56%) with little beta sheet present. No significant changes in these structural characteristics were observed upon binding of t-RA. Inspection of the amino acid sequence within these domains identified a single tryptophan residue at position 227. Modeling the amino acid sequence in this region as an alpha-helical structure indicates that this tryptophan is adjacent to alanine 234, which corresponds to alanine 225 in RAR beta that has previously been linked to the ligand binding site. Fluorescence of this tryptophan was quenched in a dose-dependent manner on the addition of t-RA, confirming that Trp-227 is within the ligand binding site. Tryptophan fluorescence quenching analysis also demonstrates that a single retinoic acid molecule is bound per receptor and suggests that receptor-ligand interactions occur within the amino-terminal portion of the predominantly alpha-helical ligand binding domain.

Genes involved in testicular development and function

The development of the testis requires the highly regulated expression of a series of genes. Many of the genes involved are transcription factors, such as steroid hormone receptors and growth factors. Investigators have used gene cloning, mutation analysis, transgenic mice, and gene-deletion studies to define the role of specific genes in testicular development and function. In the past 5 years, investigators have defined a gene on the Y chromosome, SRY, thought to be required for testis determination. This protein is a member of a larger family of related transcription factors. Expression of this gene triggers a cascade of events that leads to the development of the Sertoli cell, Leydig cells, and the testis. The development of the male phenotype is dependent on the presence and action of androgens, which exert their effect after combining with a receptor in the nucleus of the target cell that stimulates gene transcription. Defects in the androgen receptor gene lead to a full spectrum of morphological defects in the male. Interestingly, mutations in other members of the steroid receptor superfamily, such as the estrogen receptor gene, also affect male fertility. A number of "orphan" receptors (i.e., receptors whose ligans have not been identified) are also required for normal testicular development and function, as are several genes normally thought to be tumor-suppressor genes (e.g., Wilms' tumor-suppressor gene). In contrast, alpha-inhibin has been thought to be an endocrine hormone, yet it functions as a tumor-suppressor gene in the testis. Testicular development and normal spermatogenesis require the proper function and coordination of a large number of transcription factors, steroid hormone and orphan receptors, and growth factors. There are likely to be a large number of other, as yet unidentified genes that are necessary for male gonadal development.

Simian virus 40 late gene expression is regulated by members of the steroid/thyroid hormone receptor superfamily

Transcription of the late genes of simian virus 40 (SV40) is repressed during the early phase of the lytic cycle of infection of binding of cellular factors, called IBP-s, to the SV40 late promoter; repression is relieved after the onset of viral DNA replication by titration of these repressors. Preliminary data indicated that one of the major components of IBP-s was human estrogen-related receptor 1 (hERR1). We show here that several members of the steroid/thyroid hormone receptor superfamily, including testis receptor 2, thyroid receptor alpha 1 in combination with retinoid X receptor alpha, chicken ovalbumin upstream promoter transcription factors 1 and 2 (COUP-TF1 and COUP-TF2), as well as hERR1, possess the properties of IBP-s. These receptors bind specifically to hormone receptor binding sites present in the SV40 major late promoter. Recombinant COUP-TF1 specifically represses transcription from the SV40 major late promoter in a cell-free transcription system. Expression of COUP-TF1, COUP-TF2, or hERR1 in monkey cells results in repression of the SV40 late promoter, but not the early promoter, in the absence of the virally encoded large tumor antigen. Overexpression of COUP-TF1 leads to a delay in the early-to-late switch in SV40 gene expression during the lytic cycle of infection. Thus, members of this superfamily can play major direct roles in regulating expression of SV40. Possibly, natural or synthetic ligands to these receptors can serve as antiviral drugs. Our findings also provide the basis for the development of assays to screen for the ligands to testis receptor 2 and hERR1.

Gene expression of the androgen repressed rat TR2 orphan receptor: a member of steroid receptor superfamily

A full-length rat cDNA clone was obtained from the TR2 orphan receptor, a member of the steroid receptor superfamily, using cDNA library screening and 3' RACE-PCR technology. Under these conditions, only the TR2-11 form of the TR2 orphan receptor, the major form found in prostate, was identified. The overall amino acid homology between human and rat TR2-11 orphan receptors was near 90% with one amino acid difference in the DNA-binding domain sequence. Northern blot analysis identified multiple forms of the TR2 orphan receptor mRNAs expressed in human and rat prostates. Androgens repressed TR2 orphan receptor mRNA levels in human prostate LNCaP cells and rat ventral prostate. Polyclonal anti-TR2 orphan receptor antibodies raised from a unique TR2 orphan receptor 20 amino acid peptide were used to localize the TR2 orphan receptor in the nuclei of prostate and epididymis epithelium cells. Together, these data demonstrate that the TR2 orphan receptor can be expressed at mRNA and protein levels in the human and rat prostrates and may have some potential function in mediating androgen action in these tissues.

Identification of human TR2 orphan receptor response element in the transcriptional initiation site of the simian virus 40 major late promoter

A DNA response element (TR2RE-SV40) for the TR2 orphan receptor, a member of the steroid-thyroid hormone receptor superfamily, has been identified in the simian virus 40 (SV40) +55 region (nucleotide numbers 368-389, 5'-GTTAAGGTTCGTAGGTCATGGA-3'). Electrophoretic mobility shift assay, using in vitro translated TR2 orphan receptor with a molecular mass of 67 kilodaltons, showed a specific binding with high affinity (dissociation constant = 9 nM) for this DNA sequence. DNA-swap experiments using chloramphenicol acetyl-transferase assay demonstrated that androgen can suppress the transcriptional activities of SV40 early promoter via the interaction between this TR2RE-SV40 and the chimeric receptor AR/TR2/AR with the DNA-binding domain of the TR2 orphan receptor flanked by the N-terminal and androgen-binding domains of the androgen receptor. In addition, this TR2RE-SV40 can function as a repressor to suppress the transcriptional activities of both SV40 early and late promoters. Together, these data suggest the TR2RE-SV40 may represent the first identified natural DNA response element for the TR2 orphan receptor that may function as a repressor for the SV40 gene expression.

The hormone-binding domain of Oreochromis aureus estrogen receptor gene: homology comparison with other steroid binding receptors

Although the estrogen receptor gene of Oreochromis aureus (OaER) shows 85% homology to rainbow trout ER (rtER), the molecular organization of its exons and introns in the hormone-binding E domain is more closely related to the human ER gene. Comparison with other vertebrates yielded reduced homologies of 64-67%, probably due to evolutionary speciation. The E1 and E2 exons of OaER are interspersed by a short intron of 1.3 kb which is flanked by consensus splice sites. This is in sharp contrast to the 11 kb intron separating E1 and E2 exons of rtER which also displayed a rare GC donor junction. Three conserved cys at 83, 112 and 195, which are important for formation of 3-D ligand-binding pocket were found in OaER. However, the 4th conserved cys is replaced by a ser. This substitution which is the result of a single base mutation probably suggests different affinity for estrogen or transactivation of the OaER gene. Two overlapping steroid binding and receptor dimerization domains have been observed. The E domain of OaER and rtER has diversified significantly from that of other non-piscine vertebrates, such that they form a separate subgroup in the UPGMA tree of steroid receptors.

The 'LXCXE' hydropathic superfamily of ligands for retinoblastoma protein: a proposal

The present study reports structural similarities between viral oncoproteins, growth factors belonging to the insulin family, members of the steroid/thyroid receptor superfamily, a D-type cyclin, the Elf-1 transcription factor and Bcl oncoproteins in regions that have been shown or proposed to mediate complex formation of these proteins with the tumor suppressor retinoblastoma protein (RB). This relationship predicts a common intracellular pathway for mitogenic signals and molecules promoting cell survival. Conversely, the structural evidence described here suggests that RB may play a central role both at the boundary between negative and positive cell growth regulation as well as in developmental decisions between cell death and cell survival.

Human resident peritoneal macrophages: phenotype and biology

Macrophages represent the primary line of host defences in the peritoneal cavity. In order to study the metabolic activity and maturation stage of human resident peritoneal macrophages (PM phi). peritoneal fluid (PF) was taken by Douglas puncture from healthy hyperstimulated infertile women undergoing oocyte retrieval for in vitro fertilization. Peritoneal fluid and macrophage culture fluids were studied for different inflammatory mediators such as interleukin-1 (IL-1), tumour necrosis factor (TNF) and interleukin-6 (IL-6). The level of macrophage colony-stimulating factor (M-CSF), which represents a macrophage proliferation and differentiation factor, was determined in the PF and in the serum. Furthermore, the macrophage phenotypic profile was analysed, in particular the expression of sex steroid hormone receptors. IL-1. IL-6 and TNF were detectable in the PF and in the culture supernatants of PM phi whether stimulated or not by IFN-gamma and LPS. The mean level of M-CSF in the PF was 6.37 +/- 2.02 ng/ml as measured by RIA; this level did not correlate with the concentration of PM phi. The mean PF-M-CSF level was 1.4-fold higher than in the sera as measured by a EIA. Oestrogen and progesterone receptors could not be demonstrated on the PM phi analysed, so that a direct relationship between the ovarian steroid concentration in these women and the function of PM phi was unlikely. As compared to peripheral blood monocytes (Mo). PM phi showed a phenotypic profile, with some more mature features, e.g. increased expression of CD14, CD68, FcRII, FcRIII, CR3, CR4 and MHC class II determinants. These results indicate that resident PM phi have acquired in vivo a certain differentiation and/or activation state under micro-environmental factors where cytokines secreted by the M phi themselves or by other cells such as the mesothelium may play important roles.

Human in vivo pharmacology of topical retinoids

All-trans retinoic acid is used topically for treating a variety of dermatologic conditions ranging from acne to photoaged skin. Although the clinical effects of retinoic acid treatment are often considerable, relatively little is known about the basic mechanisms underlying such effects. With the development of an in vivo human assay we have investigated the pleiotypic effects of topical retinoids from the histologic to the molecular. Histologically, retinoic acid induces epidermal proliferation and differentiation coupled with dermal fibroblast production of collagen. Immunologic effects include stimulation of the antigen-presenting capacity of Langerhans cells and induction of keratinocyte ICAM-1 expression. At the biochemical level, retinoic acid regulates transglutaminase and tyrosinase activities and activates protein kinase C. Both polar metabolites and stereoisomers of all-trans retinoic acid are also biologically active. Molecular biologic techniques have revealed that elevation of mRNA for cellular retinoic acid binding protein II is a retinoid-related event and that nuclear receptors such as retinoic acid receptors and retinoid X-receptors may transduce the retinoid response.

NER, a new member of the gene family encoding the human steroid hormone nuclear receptor

NER, a new member of the steroid hormone nuclear receptor (NR)-encoding gene family, was isolated from a human osteosarcoma SAOS/B10 cell line cDNA library. NER codes for a polypeptide of 461 amino acids which contains the conserved sequences of the DNA-binding and ligand-binding domains of typical steroid hormone NR. It has highest homology with the retinoic acid receptors: 55% at the DNA-binding domain and 38-40% at the ligand-binding domain. A single transcript of 2.3 kb was detected in all cells and tissues tested. Although no ligand was identified for NER-I, its wide distribution may indicate that this novel steroid hormone NR may play a basic role in cell function.

Isoform-specific amino-terminal domains dictate DNA-binding properties of ROR alpha, a novel family of orphan hormone nuclear receptors

Three isoforms of a novel member of the steroid hormone nuclear receptor superfamily related to the retinoic acid receptors have been identified. The three isoforms, referred to as ROR alpha 1, ROR alpha 2, and ROR alpha 3, share common DNA- and putative ligand-binding domains but are characterized by distinct amino-terminal domains generated by alternative RNA processing. An exon encoding a functionally important subregion of the amino-terminal domain of the ROR alpha 2 isoform resides on the opposite strand of a cytochrome c-processed pseudogene. Binding site selection using in vitro-synthesized proteins reveals that the ROR alpha 1 and ROR alpha 2 isoforms bind DNA as monomers to hormone response elements composed of a 6-bp AT-rich sequence preceding a half-site core motif PuGGTCA (RORE). However, ROR alpha 1 and ROR alpha 2 display different binding specificities: ROR alpha 1 binds to and constitutively activates transcription from a large subset of ROREs, whereas ROR alpha 2 recognizes ROREs with strict specificity and displays weaker transcriptional activity. The differential DNA-binding activity of each isoform maps to their respective amino-terminal domains. Whereas truncation of the amino-terminal domain diminishes the ability of ROR alpha 1 to bind DNA, a similar deletion relaxes ROR alpha 2-binding specificity to that displayed by ROR alpha 1. Remarkably, transfer of the entire amino-terminal region of ROR alpha 1 or amino-terminal deletion of ROR alpha 2 confers RORE-binding specificities to heterologous receptors. These results demonstrate that the amino-terminal domain and the zinc finger region work in concert to confer high affinity and specific DNA-binding properties to the ROR isoforms and suggest a novel strategy to control DNA-binding activity of nuclear receptors.

Antibody reactivity to an Epstein-Barr virus BERF4-encoded epitope occurring also in Asp-57 region of HLA-DQ8 beta chain. Childhood Diabetes in Finland Study Group

A five amino acids-long sequence (GPPAA) in the region of the 57th amino acid of HLA-DQ8 beta chain, which seems to be important in defining the risk for type 1 diabetes, occurs also in the BERF4-encoded EBNA3C protein of Epstein-Barr virus (EBV) in six successive repeats. The antigenicity of this region was analysed using synthetic peptides containing different modifications of the GPPAA sequence. Two of the seven individuals who had acute EBV infection produced antibodies against an EBV-derived peptide (GPPAAGPPAAGPPAA) paralleling the EBNA2 antibodies. These two cases also contracted type 1 diabetes immediately after the infection. High antibody levels against this peptide were found in a total of 12% of EBV+ individuals, and in most cases antibodies remained at high levels for several years. Human sera as well as affinity-purified antibodies specific for the GPPAAGPPAAGPPAA peptide reacted also with shorter peptide analogues (GPPAAGPPAA and GPPAA), as well as with peptides containing the surrounding motifs from DQ8 beta chains. However, none of these antibodies bound to denatured DQ8 beta chains in immunoblotting. The charge of the 57th amino acid modulated the antigenicity of this epitope, as peptides from Asp-57-negative DQ molecules were reactive, while peptides from Asp-57-positive DQ molecules were not. The responsiveness was seen in both HLA-DQ8-positive and -negative subjects as well as in type 1 diabetic individuals. The results suggest that some individuals who carry the GPPAA sequence in their HLA-DQ molecule recognize this epitope in EBV. This phenomenon may have potential importance in EBV-induced immune abnormalities, although cross-reactivity against DQ molecules could not be demonstrated in the present study.

A novel nuclear receptor superfamily member in Xenopus that associates with RXR, and shares extensive sequence similarity to the mammalian vitamin D3 receptor

We report the isolation of xONR1, a novel member of the nuclear receptor superfamily from Xenopus laevis. xONR1 shares a high degree of amino acid sequence identity with the mammalian receptor for 1 alpha, 25-dihydroxy vitamin D3, particularly within the DNA-binding domain, although it does not bind this ligand. xONR1 DNA binding is stimulated by association with retinoid X receptor gamma (RXR gamma).

Drug design with a new type of molecular modeling based on stereochemical complementarity to gene structure

Why certain chemical structures and not others are present in nature has been a recurring question raised by scientists since the first organic natural products were characterized. Of equal interest has been elucidating what structural features within any given class of organic molecules are responsible for biological activity. Historically, the lack of satisfactory answers to both questions has relegated the development of biologically active molecules either to serendipity or to exhaustive synthesis and biological testing of large numbers of compounds. This frustration is particularly evident in the pharmaceutical industry where the development of drug agonists and antagonists is often time consuming, tedious and expensive. Fortunately, this picture is beginning to change as more information is derived from modern molecular modeling techniques including characterization of the active sites in enzymes and the ligand binding sites in receptors. Over the past 15 years another approach has emerged based upon a series of discoveries made in our laboratories with molecular models. Namely, many biologically active small molecules have been found to possess complementary stereochemical relationships with gene structure. These relationships have proven useful in understanding constraints imposed by nature on the structures of small molecules and in correlating structure with activity among certain classes of compounds. Recently, computer graphics and energy calculations have confirmed salient observations lending credence to what promises to be a powerful and rapidly evolving technology for designing new safe and effective drugs.

Retinoic acid induction of major histocompatibility complex class I genes in NTera-2 embryonal carcinoma cells involves induction of NF-kappa B (p50-p65) and retinoic acid receptor beta-retinoid X receptor beta heterodimers

Retinoic acid (RA) treatment of human embryonal carcinoma (EC) NTera-2 (NT2) cells induces expression of major histocompatibility complex (MHC) class I and beta-2 microglobulin surface molecules. We found that this induction was accompanied by increased levels of MHC class I mRNA, which was attributable to the activation of the two conserved upstream enhancers, region I (NF-kappa B like) and region II. This activation coincided with the induction of nuclear factor binding activities specific for the two enhancers. Region I binding activity was not present in undifferentiated NT2 cells, but binding of an NF-kappa B heterodimer, p50-p65, was induced following RA treatment. The p50-p65 heterodimer was produced as a result of de novo induction of p50 and p65 mRNAs. Region II binding activity was present in undifferentiated cells at low levels but was greatly augmented by RA treatment because of activation of a nuclear hormone receptor heterodimer composed of the retinoid X receptor (RXR beta) and the RA receptor (RAR beta). The RXR beta-RAR beta heterodimer also bound RA responsive elements present in other genes which are likely to be involved in RA triggering of EC cell differentiation. Furthermore, transfection of p50 and p65 into undifferentiated NT2 cells synergistically activated region I-dependent MHC class I reporter activity. A similar increase in MHC class I reporter activity was demonstrated by cotransfection of RXR beta and RAR beta. These data show that following RA treatment, heterodimers of two transcription factor families are induced to bind to the MHC enhancers, which at least partly accounts for RA induction of MHC class I expression in NT2 EC cells.

Retinoic acid induction of major histocompatibility complex class I genes in NTera-2 embryonal carcinoma cells involves induction of NF-kappa B (p50-p65) and retinoic acid receptor beta-retinoid X receptor beta heterodimers

Retinoic acid (RA) treatment of human embryonal carcinoma (EC) NTera-2 (NT2) cells induces expression of major histocompatibility complex (MHC) class I and beta-2 microglobulin surface molecules. We found that this induction was accompanied by increased levels of MHC class I mRNA, which was attributable to the activation of the two conserved upstream enhancers, region I (NF-kappa B like) and region II. This activation coincided with the induction of nuclear factor binding activities specific for the two enhancers. Region I binding activity was not present in undifferentiated NT2 cells, but binding of an NF-kappa B heterodimer, p50-p65, was induced following RA treatment. The p50-p65 heterodimer was produced as a result of de novo induction of p50 and p65 mRNAs. Region II binding activity was present in undifferentiated cells at low levels but was greatly augmented by RA treatment because of activation of a nuclear hormone receptor heterodimer composed of the retinoid X receptor (RXR beta) and the RA receptor (RAR beta). The RXR beta-RAR beta heterodimer also bound RA responsive elements present in other genes which are likely to be involved in RA triggering of EC cell differentiation. Furthermore, transfection of p50 and p65 into undifferentiated NT2 cells synergistically activated region I-dependent MHC class I reporter activity. A similar increase in MHC class I reporter activity was demonstrated by cotransfection of RXR beta and RAR beta. These data show that following RA treatment, heterodimers of two transcription factor families are induced to bind to the MHC enhancers, which at least partly accounts for RA induction of MHC class I expression in NT2 EC cells.

Modulation of mammary carcinoma cell phenotype and keratin expression patterns by retinoic acid

Immunohistochemical and biochemical procedures were used to study the influence of retinoic acid (RA) on cellular expression and distribution of cytokeratins (CKs) in feline mammary carcinoma cells. These cells were grown in vitro as established cell lines (K248C and K266) and in vivo as xenografts in athymic mice. The results were compared with the distribution of CKs in normal feline mammary gland and in a series of invasive mammary carcinomas previously probed with a panel of monoclonal antibodies specific for individual CKs. Coexpression of CKs of both major mammary gland cell types (myoepithelial cells, MECs, CKs 5/14 positive, and luminal epithelial cells, LECs CKs8/18 positive) by K248C and K266 cells, suggested a stem cell-like character of both cell lines. RA increased CK19 expression in both cell lines and CK19 was also present in tumors developed in nude mice from both RA untreated (CK19 negative) and RA-treated (CK19 positive) K248C and K266 cells. In addition, RA had cell line specific effects as well. RA treatment induced differentiation of K248C cells to more mature LEC-like cells and this change was accompanied by the loss of the MEC keratins CKs 5/14. Under the same culture conditions however, RA treatment did not induce morphological changes in the K266 cell line and the expression of CKs 5/14 was not significantly reduced. These findings suggest that the modulation of CK19 and CKs 5/14 expression observed in mammary carcinoma cells upon RA treatment might be regulated through different pathways.

The orphan receptors NGFI-B and steroidogenic factor 1 establish monomer binding as a third paradigm of nuclear receptor-DNA interaction

We examined in detail the DNA interaction of the nuclear receptors NGFI-B and steroidogenic factor 1 (SF-1) by using a series of gain-of-function domain swaps. NGFI-B bound with high affinity as a monomer to a nearly linear DNA molecule. The prototypic zinc modules interacted with a half-site of the estrogen receptor class, and a distinct protein motif carboxy terminal to the zinc modules (the A box) interacted with two A/T base pairs 5' to the half-site. SF-1 bound in the same manner as NGFI-B, with an overlapping but distinct sequence requirement 5' to the half-site. The key features that distinguished the NGFI-B and SF-1 interactions were an amino group in the minor groove of the SF-1 binding sequence and an asparagine in the SF-1 A box. These results define a common mechanism of NGFI-B and SF-1 DNA binding, which may underlie a competitive mechanism of gene regulation in steroidogenic tissues that express these proteins. This monomer-DNA interaction represents a third paradigm of DNA binding by nuclear receptors in addition to direct and inverted dimerization.