Estrogen memory effect in human hepatocytes during repeated cell division without hormone.

Transient stimulation of target tissues by sex steroids can cause long-lasting changes that may facilitate or alter responses to subsequent hormonal treatment. How these altered characteristics are propagated during cell division in the absence of the stimulating hormone is unknown. The human hepatocarcinoma cell line HepG2 was used as a model to examine the effects of estrogen on the synthesis of serum apolipoproteins in vitro. Treatment with low concentrations of estrogen for 24 to 48 hours resulted in long-lasting alterations in the kinetics with which the cells responded to subsequent stimulation with estrogen. Manifestation of this memory effect was correlated quantitatively with the induction and propagation of a moderate-affinity, nuclear, estrogen-binding protein with the characteristics of a type II estrogen receptor. The data indicate that transient exposure of these cells to estrogen can induce changes in their response characteristics and composition of nuclear proteins that are inherited by daughter cells grown in the absence of hormone for more than ten generations.

DNA-PK phosphorylation sites on Oct-1 promote cell survival following DNA damage.

Octamer transcription factor-1 (Oct-1) has recently been shown to function as a stress sensor that promotes cell survival subsequent to DNA damage. Here, we show that the survival signal imparted by Oct-1 following exposure to ionizing radiation (IR) is dependent upon DNA-dependent protein kinase (DNA-PK)-dependent phosphorylation of a cluster of 13 specific ser/thr residues within the N-terminal transcriptional regulatory domain of Oct-1. Although IR treatment did not affect the recruitment of Oct-1 to the histone H2B promoter, the recruitment of RNA polymerase II, TATA-binding protein and histone H4 acetylation were strongly reduced, consistent with a decrease in Oct-1 transcriptional regulatory potential following IR exposure. Ser/Thr-Ala substitution of 13 sites present in Oct-1 transcriptional regulatory domain eliminated Oct-1 phosphorylation subsequent to IR exposure. Further, these substitutions prevented Oct-1 from rescuing the survival of IR-treated Oct-1-/- murine embryonic fibroblasts, providing a direct link between DNA-PK-dependent phosphorylation and the contribution of Oct-1 to cell survival. These results implicate Oct-1 as a primary effector in a DNA-PK-dependent cell survival pathway that is activated by double-stranded DNA breaks.

Association of autoantibodies with Ku and DNA repair proteins in connective tissue diseases.

OBJECTIVE: To analyse the autoimmune response to DNA damage response factors in systemic autoimmune rheumatic disease (SARD) patients and to determine their association with autoantibodies to Ku antigen. METHODS: We have screened the serum of 239 patients suffering from SARD, including systemic lupus erythematosus, systemic sclerosis and rheumatoid arthritis to detect the occurrence of autoantibodies to Ku and four other DNA damage response factors that form macromolecular complexes with Ku using an immunoprecipitation assay. RESULTS: We identified samples positive for autoantibodies to Ku (20.5%), DNA-dependent protein kinase catalytic subunit (DNA-PKcs, 8.4%) and poly(ADP-ribose) polymerase (5.9%), and report for the first time autoantibodies directed against two additional DNA repair proteins, Werner (6.3%) and Mre11 (9.6%). Remarkably, we found a striking correlation between the production of antibodies to Ku and the other four Ku-binding factors. Sixty-five percent of anti-Ku-positive sera were found to contain at least one of the four anti-DNA repair antibodies vs only 10% of the anti-Ku-negative sera. CONCLUSION: Our results suggest that the autoantibodies directed against Ku are elicited by macromolecular protein complexes containing Ku and the associated DNA damage proteins. The presence of autoantibodies directed against macromolecular complexes known to play roles in the DNA damage response provides evidence that B-cell responses to latent or persistent DNA damage may be present at the onset or during the development of autoimmunity in certain SARDs.

Long-term effects of estrogen on avian liver: estrogen-inducible switch in expression of nuclear, hormone-binding proteins.

The stimulation of chicks or embryos with estrogen results in transient, hepatic expression of the vitellogenin gene, as well as long-term, propagatable alterations in the rapidity with which the gene can be reactivated. We examined the possibility that nuclear, type II estrogen-binding sites are involved in this long-term change in response characteristics. We demonstrate that the primary induction kinetics of type II sites in embryos and chicks correlated with the expression of the vitellogenin gene and that once their induction was triggered by estrogen, they accumulated, were propagated, and persisted for months after withdrawal of the hormone. We also show that their accumulation in the embryo was accompanied by prolonged expression of both the vitellogenin and very low-density apolipoprotein II genes, in the absence of elevated levels of type I receptor, and that the type II sites, like the classical receptor, appear to be preferentially associated with active or potentially active chromatin. Finally, we describe a regulatory mechanism, tested by computer modelling, that simulated the behavioral characteristics of these nuclear estrogen-binding sites and which may explain their role in mediating the long-term effects of estrogen.

Ku antigen-DNA conformation determines the activation of DNA-dependent protein kinase and DNA sequence-directed repression of mouse mammary tumor virus transcription.

Mouse mammary tumor virus (MMTV) transcription is repressed by DNA-dependent protein kinase (DNA-PK) through a DNA sequence element, NRE1, in the viral long terminal repeat that is a sequence-specific DNA binding site for the Ku antigen subunit of the kinase. While Ku is an essential component of the active kinase, how the catalytic subunit of DNA-PK (DNA-PKcs) is regulated through its association with Ku is only beginning to be understood. We report that activation of DNA-PKcs and the repression of MMTV transcription from NRE1 are dependent upon Ku conformation, the manipulation of DNA structure by Ku, and the contact of Ku80 with DNA. Truncation of one copy of the overlapping direct repeat that comprises NRE1 abrogated the repression of MMTV transcription by Ku-DNA-PKcs. Remarkably, the truncated element was recognized by Ku-DNA-PKcs with affinity similar to that of the full-length element but was unable to promote the activation of DNA-PKcs. Analysis of Ku-DNA-PKcs interactions with DNA ends, double- and single-stranded forms of NRE1, and the truncated NRE1 element revealed striking differences in Ku conformation that differentially affected the recruitment of DNA-PKcs and the activation of kinase activity.

Hormonal induction of transfected genes depends on DNA topology.

Plasmids containing the hormone regulatory element of mouse mammary tumor virus linked to the thymidine kinase promoter of herpes simplex virus and the reporter gene chloramphenicol acetyltransferase of Escherichia coli respond to glucocorticoids and progestins when transfected into appropriate cells. In the human mammary tumor cell line T47D, the response to progestins, but not to glucocorticoids, is highly dependent on the topology of the transfected DNA. Although negatively supercoiled plasmids respond optimally to the synthetic progestin R5020, their linearized counterparts exhibit markedly reduced progestin inducibility. This is not due to changes in the efficiency of DNA transfection, since the amount of DNA incorporated into the cell nucleus is not significantly dependent on the initial topology of the plasmids. In contrast, cotransfection experiments with glucocorticoid receptor cDNA in the same cell line show no significant influence of DNA topology on induction by dexamethasone. A similar result was obtained with fibroblasts that contain endogenous glucocorticoid receptors. When the distance between receptor-binding sites or between the binding sites and the promoter was increased, the dependence of progestin induction on DNA topology was more pronounced. In contrast to the original plasmid, these constructs also revealed a similar topological dependence for induction by glucocorticoids. The differential influence of DNA topology is not due to differences in the affinity of the two hormone receptors for DNA of various topologies, but probably reflects an influence of DNA topology on the interaction between different DNA-bound receptor molecules and between receptors and other transcription factors.

Developmental regulation of specific protein interactions with an enhancerlike binding site far upstream from the avian very-low-density apolipoprotein II gene.

Expression of the avian very-low-density apolipoprotein II (apoVLDLII) gene is completely dependent on estrogen and restricted to the liver. We have identified binding sites for nonhistone nuclear proteins located between -1.96 and -2.61 kilobases. One of these sites, located at -2.6 kilobases (designated site 1), was found to span an MspI site that becomes demethylated between days 7 and 9 of embryogenesis, the stage of development at which competence to express the apoVLDLII gene begins to be acquired. Levels of the factor(s) involved were high at day 7 of embryogenesis, decreased two- to threefold by days 9 to 11, and continued to decline more slowly until hatching. Furthermore, the mobility of the complex formed underwent a well-defined shift between days 11 to 13 embryogenesis. Methylation interference studies showed that modification of the outer guanosines of the MspI site resulted in marked inhibition of the formation of the protein-DNA complex. Competition studies, fractionation of nuclear extracts, and tissue distribution indicated that the factor was not the avian homolog of hepatocyte nuclear factor 1, nuclear factor 1, or CCAAT/enhancer-binding protein (C/EBP). However, site 1 could complete for binding to an oligonucleotide, previously shown to be recognized by C/EBP, in a nonreciprocal fashion. These studies demonstrate that the sequence recognized by the protein includes a C/EBP consensus sequence but that elements in addition to the core enhancer motif are essential for binding.

Discrimination between NL1- and NL2-mediated nuclear localization of the glucocorticoid receptor.

Glucocorticoid receptor (GR) cycles between a free liganded form that is localized to the nucleus and a heat shock protein (hsp)-immunophilin-complexed, unliganded form that is usually localized to the cytoplasm but that can also be nuclear. In addition, rapid nucleocytoplasmic exchange or shuttling of the receptor underlies its localization. Nuclear import of liganded GR is mediated through a well-characterized sequence, NL1, adjacent to the receptor DNA binding domain and a second, uncharacterized motif, NL2, that overlaps with the ligand binding domain. In this study we report that rapid nuclear import (half-life [t1/2] of 4 to 6 min) of agonist- and antagonist-treated GR and the localization of unliganded, hsp-associated GRs to the nucleus in G0 are mediated through NL1 and correlate with the binding of GR to pendulin/importin alpha. By contrast, NL2-mediated nuclear transfer of GR occurred more slowly (t1/2 = 45 min to 1 h), was agonist specific, and appeared to be independent of binding to importin alpha. Together, these results suggest that NL2 mediates the nuclear import of GR through an alternative nuclear import pathway. Nuclear export of GR was inhibited by leptomycin B, suggesting that the transfer of GR to the cytoplasm is mediated through the CRM1-dependent pathway. Inhibition of GR nuclear export by leptomycin B enhanced the nuclear localization of both unliganded, wild-type GR and hormone-treated NL1(-) GR. These results highlight that the subcellular localization of both liganded and unliganded GRs is determined, at least in part, by a flexible equilibrium between the rates of nuclear import and export.

Developmental effects of ectopic expression of the glucocorticoid receptor DNA binding domain are alleviated by an amino acid substitution that interferes with homeodomain binding.

Steroid hormone receptors are distinguished from other members of the nuclear hormone receptor family through their association with heat shock proteins and immunophilins in the absence of ligands. Heat shock protein association represses steroid receptor DNA binding and protein-protein interactions with other transcription factors and facilitates hormone binding. In this study, we investigated the hormone-dependent interaction between the DNA binding domain (DBD) of the glucocorticoid receptor (GR) and the POU domains of octamer transcription factors 1 and 2 (Oct-1 and Oct-2, respectively). Our results indicate that the GR DBD binds directly, not only to the homeodomains of Oct-1 and Oct-2 but also to the homeodomains of several other homeodomain proteins. As these results suggest that the determinants for binding to the GR DBD are conserved within the homeodomain, we examined whether the ectopic expression of GR DBD peptides affected early embryonic development. The expression of GR DBD peptides in one-cell-stage zebra fish embryos severely affected their development, beginning with a delay in the epibolic movement during the blastula stage and followed by defects in convergence-extension movements during gastrulation, as revealed by the abnormal patterns of expression of several dorsal gene markers. In contrast, embryos injected with mRNA encoding a GR peptide with a point mutation that disrupted homeodomain binding or with mRNA encoding the DBD of the closely related mineralocorticoid receptor, which does not bind octamer factors, developed normally. Moreover, coinjection of mRNA encoding the homeodomain of Oct-2 completely rescued embryos from the effects of the GR DBD. These results highlight the potential of DNA-independent effects of GR in a whole-animal model and suggest that at least some of these effects may result from direct interactions with homeodomain proteins.

Recruitment of octamer transcription factors to DNA by glucocorticoid receptor.

Glucocorticoid receptor (GR) and octamer transcription factors 1 and 2 (Oct-1/2) interact synergistically to activate the transcription of mouse mammary tumor virus and many cellular genes. Synergism correlates with cooperative DNA binding of the two factors in vitro. To examine the molecular basis for these cooperative interactions, we have studied the consequences of protein-protein binding between GR and Oct-1/2. We have determined that GR binds in solution to the octamer factor POU domain. Binding is mediated through an interface in the GR DNA binding domain that includes amino acids C500 and L501. In transfected mammalian cells, a transcriptionally inert wild-type but not an L501P GR peptide potentiated transcriptional activation by Oct-2 100-fold above the level that could be attained in the cell by expressing Oct-2 alone. Transcriptional activation correlated closely with a striking increase in the occupancy of octamer motifs adjacent to glucocorticoid response elements (GREs) on transiently transfected DNAs. Intriguingly, GR-Oct-1/2 binding was interrupted by the binding of GR to a GRE. We propose a model for transcriptional cooperativity in which GR-Oct-1/2 binding promotes an increase in the local concentration of octamer factors over glucocorticoid-responsive regulatory regions. These results reveal transcriptional cooperativity through a direct protein interaction between two sequence-specific transcription factors that is mediated in a way that is expected to restrict transcriptional effects to regulatory regions with DNA binding sites for both factors.

Glucocorticoid receptor homodimers and glucocorticoid-mineralocorticoid receptor heterodimers form in the cytoplasm through alternative dimerization interfaces.

Steroid hormone receptors act to regulate specific gene transcription primarily as steroid-specific dimers bound to palindromic DNA response elements. DNA-dependent dimerization contacts mediated between the receptor DNA binding domains stabilize DNA binding. Additionally, some steroid receptors dimerize prior to their arrival on DNA through interactions mediated through the receptor ligand binding domain. In this report, we describe the steroid-induced homomeric interaction of the rat glucocorticoid receptor (GR) in solution in vivo. Our results demonstrate that GR interacts in solution at least as a dimer, and we have delimited this interaction to a novel interface within the hinge region of GR that appears to be both necessary and sufficient for direct binding. Strikingly, we also demonstrate an interaction between GR and the mineralocorticoid receptor in solution in vivo that is dependent on the ligand binding domain of GR alone and is separable from homodimerization of the glucocorticoid receptor. These results indicate that functional interactions between the glucocorticoid and mineralocorticoid receptors in activating specific gene transcription are probably more complex than has been previously appreciated.

AF-2-dependent potentiation of CCAAT enhancer binding protein beta-mediated transcriptional activation by glucocorticoid receptor.

We report glucocorticoid-dependent induction of transcription from the herpes simplex virus thymidine kinase gene promoter proximal regulatory region in the absence of glucocorticoid response elements and independent of the ability of glucocorticoid receptor (GR) to bind DNA. Examination of the thymidine kinase promoter localized glucocorticoid responsiveness to a binding site for CCAAT enhancer-binding proteins (C/EBPs). Further analysis indicated that GR specifically potentiated the induction of transcription by C/EBP beta, but not C/EBP alpha or delta, and that full induction could be obtained by the ligand-binding domain (LBD) of GR alone. C/EBP beta, but not C/EBP alpha or delta, reciprocally potentiated transcriptional activation by DNA-bound GR LBD. However, C/EBP beta was unable to increase activation by a GR LBD with a short C-terminal truncation, indicating that the functional interaction between the two factors was dependent upon the GR AF-2. Surprisingly, despite the specificity in functional effects, all three C/EBPs bound indistinguishably to GR in GST pull-down and immunoprecipitation assays. Indeed, several nuclear receptors, including the estrogen (ER alpha), progesterone, retinoic acid (RAR), and androgen receptors, displayed a similar potential to bind C/EBPs. Previous reports have demonstrated that ER alpha and RARs repress transcriptional activation by C/EBP beta in ways that were dependent on their related AF-2 functions. Therefore, the GR AF-2 may encode functional features that distinguish the transcriptional regulatory potential of GR from that of ER and RAR. Finally, C/EBP binding mapped to the GR DNA-binding domain, which was not required for functional interaction with C/EBP beta. Thus, the potentiation of C/EBP beta-mediated transcription by GR would appear to require the presence of an intermediary factor.

Determinants of subcellular distribution of the glucocorticoid receptor.

Glucocorticoid receptor (GR) exchanges between an active nuclear form and a complexed inactive, steroid-sensitive cytoplasmic form. Using a semi-quantitative indirect immunofluorescence assay to measure the kinetics of subcellular redistribution of GR in response to challenge during G(o), we have found that the ability to bind DNA is an important determinant for localization and tight binding of GR to the nucleus. The transfer of GR DNA-binding mutants to the nucleus after treatment with hormone agonists and antagonists was markedly reduced. Further, mutant receptors localized to the nucleus were only weakly associated with the nuclear compartment as they were released into cytosol upon hypotonic lysis of the cell membrane. Moreover, after agonist withdrawal, GR redistributed to the cytoplasm more rapidly when unable to bind DNA. By contrast, withdrawal of the hormone antagonist RU486 was found to yield a form of wild type GR that was completely unable to redistribute to the cytoplasm. However, this did not appear to result from a block in nuclear export as selective inactivation of nuclear import with energy inhibitor released RU486-withdrawn GRs from the nucleus at the same rates as agonist-withdrawn receptors. In addition, GR mutants unable to bind DNA, which retained a significant presence in the cytoplasm both during and after antagonist treatment, also failed to redistribute. The effect of RU486 treatment did not appear to be mediated through a block in reassociation of GR into a steroid-responsive form as RU486-withdrawn wild type receptors retained full potential to activate transcription from a glucocorticoid-responsive promoter after a second challenge with hormone. Therefore, reassociation of GR into a steroid-responsive form appears to be independent of signals important for the retention of GR in the cytoplasm.

Extraction of DNA-binding proteins from cryogenically preserved cells.

We demonstrate that DNA-binding protein extracts can be effectively prepared directly from tissue culture cells preserved under liquid nitrogen without returning the cells to culture. We prepared DNA-binding protein extracts directly upon thawing of T47D, Jurkat and CAC-L153S cell lines after storage in liquid nitrogen for periods of up to one year. Our results show that DNA binding of a repressor of mouse mammary tumor virus transcription in these extracts is indistinguishable from binding activity in similar extracts prepared from cells maintained in culture.

5 alpha-Reductase type 1 is localized to the outer nuclear membrane.

The subcellular distribution of the two isozymes of 5 alpha-reductase has been controversial. To resolve this issue which could provide clues about the respective functions of the two isozymes, two antisera were generated, one which was specific for the Type 1 5 alpha-reductase and one which recognized both isozymes. In COS cells transfected separately with the Type 1 or Type 2 cDNA, both isozymes were detected on Western blots at an M(r) of 26,000. Subfractionation of the COS cells resulted in the partitioning of both isozymes between the crude nuclear and cytosolic fractions, while cytoimmunofluorescence localized both reductases to the nuclear periphery. In rat liver homogenate, the 5 alpha-reductase was also detected at M(r) 26,000. The 5 alpha-reductase immunoreactivity was increased after castration of the animals with no further effect when castrated animals were treated with androgens. Although the rat liver expresses only the Type 1 5 alpha-reductase, the 5 alpha-reductase was distributed about equally between crude nuclear and cytosolic subfractions; this distribution could be shifted to the cytosolic fractions with harsher homogenization procedures. Further extensive subfractionation and extraction studies identified the rat liver Type 1 5 alpha-reductase as an integral membrane protein present in the outer nuclear membrane of the nuclear envelope and in rough endoplasmic reticulum. Thus, the subfractionation and cytoimmunofluorescence studies are consistent with the localization of the Type 1 5 alpha-reductase to the outer nuclear membrane of the nuclear envelope which is continuous with and indistinguishable from the endoplasmic reticulum. This study is the first to localize rat liver Type 1 5 alpha-reductase to the nuclear envelope to which the prostatic 5 alpha-reductase activity previously had been localized. We conclude that, contrary to previous tissue distribution studies, but consistent with investigations in transfected cells, both isozymes are similarly localized to the nuclear periphery.

Regulation of activin type-II receptor mRNA levels in rat hypothalamus by estradiol in vivo.

A solution-hybridization S1-nuclease protection assay was used to evaluate the expression of messenger RNAs for the activin beta A subunit and type II activin receptor in adult rat brain. Results indicate the presence of beta A subunit mRNA in both hypothalamus and brainstem, with approximately two-fold higher levels in brainstem. Levels of activin type II receptor mRNA were similar in the hypothalamus of young virgin and 15-day lactating females, and in females in which pups were removed after a 5-day lactation period. Male rats castrated prepubertally (30 days p.n.) had approximately 220% higher (P < 0.05) hypothalamic activin type II receptor mRNA levels than postpubertal, 3-month old age-matched sham controls. Two month treatment of castrate rats with estradiol (200 ng/g, i.p. every 2 days) reduced hypothalamic activin type II receptor mRNA expression to control levels; the same dose of testosterone had no effect. The expression of the hypothalamic activin type II receptor gene may be estrogen-regulated in vivo.

Nuclear factor binding to a DNA sequence element that represses MMTV transcription induces a structural transition and leads to the contact of single-stranded binding proteins with DNA.

NRE1 is a DNA sequence element in the long terminal repeat of mouse mammary tumor virus through which viral transcription is repressed. In addition to double-stranded DNA binding, both upper- and lower-stranded NRE1 binding activities occur in nuclear extracts. All three binding activities appear to be important for transcriptional effects. We report that occupancy of NRE1 within linear double-stranded NRE1 induces a structural transition in upstream flanking DNA that is facilitated by Mg2+. This transition was reflected by the striking DNase I sensitivity of the DNA. As Mg2+ concentration was increased, discrete DNase I hypersensitivity on one face of the DNA progressed to complete degradation of template. On the DNA face opposite the DNase I hypersensitivity, Mg2+ promoted regularly spaced cleavage by the single-strand-specific cleavage agents KMnO4 and S1 nuclease. Induction of degradation by DNase I occurred independently of MMTV sequences flanking NRE1, because nuclear extract-dependent DNase I sensitivity was conferred to an unrelated DNA fragment by introduction of a 23-bp NRE1-containing oligonucleotide. UV protein-DNA cross-linking revealed that addition of Mg2+ to a double-stranded NRE1 DNA binding assay induced conversion from a double- to a single-stranded protein-DNA cross-linking pattern. Thus, nuclear factor binding to NRE1 induces changes in DNA topology that promote the direct contact of single-stranded NRE1 binding factors with DNA.

Activation of PARP-1 in response to bleomycin depends on the Ku antigen and protein phosphatase 5.

Poly (ADP-ribose) polymerase-1 (PARP-1) has an important role in the cellular response to a broad spectrum of DNA lesions. PARP-1 is strongly activated in response to double-stranded DNA breaks (DSBs), yet its contribution to the DSB response is poorly understood. Here we used bleomycin, a radiomimetic that generates DSBs with high specificity to focus on the response of PARP-1 to DSBs. We report that the induction of PARP-1 activity by bleomycin depends on the Ku antigen, a nonhomologous-DNA-End-Joining factor and protein phosphatase 5 (PP5). PARP-1 activation in response to bleomycin was reduced over 10-fold in Ku-deficient cells, whereas its activation in response to U.V. was unaffected. PARP-1 activation was rescued by reexpression of Ku, but was refractory to manipulation of DNA-dependent protein kinase or ATM. Similarly, PARP-1 activation subsequent to bleomycin was reduced 2-fold on ablation of PP5 and was increased 5-fold when PP5 was overexpressed. PP5 seemed to act directly on PARP-1, as its basal phosphorylation was reduced on overexpression of PP5, and PP5 dephosphorylated PARP-1 in vitro. These results highlight the functional importance of Ku antigen and PP5 for PARP-1 activity subsequent to DSBs.

Organization, sequence and nuclease hypersensitivity of repetitive elements flanking the chicken apoVLDLII gene: extended sequence similarity to elements flanking the chicken vitellogenin gene.

Analysis of nuclease hypersensitivity of regions flanking the estrogen-dependent, chicken apoVLDLII gene has revealed an hepatic, DNaseI hypersensitive site whose sensitivity is influenced by both the developmental stage and sex of the bird. The site is located 3.0kb upstream from the gene, in a block of middle repetitive elements. Contact hybridization studies indicate that the block consists of contiguous copies of two elements with reiteration frequencies of 500-1000 and 10,000-30,000 copies per haploid genome. Sequencing of 1.8kb spanning the repeats has revealed that the higher frequency element is a member of the CR1 family. The adjacent lower frequency repeat can also be found next to another member of the CR1 family located in the 3' flanking region of the vitellogenin gene. The hypersensitive site has been mapped to one of the two most highly conserved regions of the CR1 element. This region displays homology with a silencer sequence recently identified in a CR1 element flanking the chicken lysozyme gene.

Generation of C127-derived cell lines expressing estrogen or progesterone receptors for studying gene regulation on bovine papilloma virus minichromosomes.

To study regulation of transcription by multiple steroid hormones we have stably introduced expression vectors for human estrogen and rabbit progesterone receptors into the genome of the murine fibroblast cell line C127. These cells express functional endogenous glucocorticoid receptor and support bovine papilloma virus minichromosomes, a useful system for studying the role of chromatin structure on gene expression. Three clones containing progesterone receptor integrates and six containing estrogen receptors integrates were selected and characterized. All three progesterone and four of the estrogen receptors containing cell lines expressed functional receptors that were able to transactivate transcription from a mouse mammary tumor virus and Xenopus vitellogenin promoter, respectively, in steroid-specific manner. Levels of steroid binding varied between 38 and 890 fmol/mg protein for progesterone receptor, and between 22 and 94 fmol/mg protein for estrogen receptor. The observed dissociation constants of 1.8-2.5 nM (Organon.2058) and 0.75-2.8 nM (17 beta-Estradiol) are consistent with previously reported values for wild type rabbit progesterone receptor and the estrogen receptor derivative employed. Finally, we demonstrate that transcription of a mouse mammary tumor virus construct in a novel nontransforming bovine papilloma virus vector is regulated by both progestin and glucocorticoid agonists in line C127PR9.