Differential expression of the human gonadotropin alpha gene in ectopic and eutopic cells

The onconeural antigen cdr2 is a novel APC/C target that acts in mitosis to regulate c-myc target genes in mammalian tumor cells

Cdr2 is a tumor antigen expressed in a high percentage of breast and ovarian tumors and is the target of a naturally occurring tumor immune response in patients with paraneoplastic cerebellar degeneration, but little is known of its regulation or function in cancer cells. Here we find that cdr2 is cell cycle regulated in tumor cells with protein levels peaking in mitosis. As cells exit mitosis, cdr2 is ubiquitinated by the anaphase promoting complex/cyclosome (APC/C) and rapidly degraded by the proteasome. Previously we showed that cdr2 binds to the oncogene c-myc, and here we extend this observation to show that cdr2 and c-myc interact to synergistically regulate c-myc-dependent transcription during passage through mitosis. Loss of cdr2 leads to functional consequences for dividing cells, as they show aberrant mitotic spindle formation and impaired proliferation. Conversely, cdr2 overexpression is able to drive cell proliferation in tumors. Together, these data indicate that the onconeural antigen cdr2 acts during mitosis in cycling cells, at least in part through interactions with c-myc, to regulate a cascade of actions that may present new targeting opportunities in gynecologic cancer.

Rapid Maturation of Glycoprotein Hormone Free α-Subunit (GPHα) and GPHαα Homodimers

The dynamics of glycoprotein hormone α-subunit (GPHα) maturation and GPHαα homodimer formation were studied in presence (JEG-3 choriocarcinoma cells) and absence (HeLa cells) of hCGβ. In both cases, the major initially occurring GPHα variant in [35S]Met/Cys-labeled cells carried two N-glycans (Mr app = 22 kDa). Moreover, a mono-N-glycosylated in vivo association-incompetent GPHα variant (Mr app = 18 kDa) was observed. In JEG-3 cells the early 22-kDa GPHα either associated with hCGβ, or showed self-association to yield GPHαα homodimers, or was later converted into heavily glycosylated large free GPHα (Mr app = 24 kDa). Micro-preparative isolation of intracellular GPHαα homodimers of JEG-3 cells and their conversion by reduction revealed that they consisted of 22-kDa GPHα monomers and not of large free GPHα. In HeLa cells, the large free GPHα variant was not observed, whereas GPHαα homodimers were present. Intracellularly, early GPHαα homodimers (35 kDa) and late variants (JEG-3: 44 kDa, HeLa: 39 kDa) were found. Both cell types secreted 45 kDa GPHαα homodimers. Large free GPHα and GPHαα homodimers were more rapidly sialylated than hCG αβ-heterodimers indicating a sequestration mechanism in the secretory pathway. In GPHαα homo- as well as hCG αβ-heterodimers the subunit interaction site, located on loop 2 of GPHα (amino acids 33–42), became immunologically inaccessible indicating similar spatial orientation of GPHα in both types of dimers. The studies demonstrate the formation, in vivo dynamics of GPHαα homodimers, and the pathways of the cellular metabolism of variants of GPHα, monoglycosylated GPHα and large free GPHα.

Silencing of the gene for the alpha-subunit of human chorionic gonadotropin by the embryonic transcription factor Oct-3/4

CG is required for maintenance of the corpus luteum during pregnancy in higher primates. As CG is a heterodimeric molecule, some form of coordinated control must be maintained over the transcription of its two subunit genes. We recently found that expression of human CG beta-subunit (hCGbeta) in JAr human choriocarcinoma cells was almost completely silenced by the embryonic transcription factor Oct-3/4, which bound to a unique ACAATAATCA octameric sequence in the hCGbeta gene promoter. Here we report that Oct-3/4 is also a potent inhibitor of hCG alpha-subunit (hCGalpha) expression in JAr cells. Oct-3/4 reduced human GH reporter expression from the -170 hCGalpha promoter in either the presence or absence of cAMP by about 70% in transient cotransfection assays, but had no effect on expression from either the -148 hCGalpha or the -99 hCGalpha promoter. Unexpectedly, no Oct-3/ 4-binding site was identified within the -170 to -148 region of the hCGalpha promoter, although one was found around position -115 by both methylation interference footprinting and electrophoretic mobility shift assays. Site-directed mutagenesis of this binding site destroyed the affinity of the promoter for Oct-3/4, but did not affect repression of the promoter. Therefore, inhibition of hCGalpha gene transcription by Oct-3/4 appears not to involve direct binding of this factor to the site responsible for silencing. When stably transfected into JAr cells, Oct-3/4 reduced the amounts of both endogenous hCGalpha mRNA and protein by 70-80%. Oct-3/4 is therefore capable of silencing both hCGalpha and hCGbeta gene expression. We suggest that as the trophoblast begins to form, reduction of Oct-3/4 expression permits the coordinated onset of transcription from the hCGalpha and hCGbeta genes.

Human chorionic gonadotropin-beta subunit gene expression in cultured human fetal and cancer cells of different types and origins

BACKGROUND

The authors' previous investigations using living cultured human cancer cells and cells isolated from cancer tissues, analytical flow cytometry, and monoclonal antibodies directed to epitopes located in five different sites of the human chorionic gonadotropin (hCG) molecule, identified the presence of membrane-associated hCG, its subunits and fragments, by cells from all cancers, irrespective of type and origin, indicating that the expression of these sialoglycoproteins is a common phenotypic characteristic of cancer. Although benign neoplasms do not express these compounds, cultured human embryonic and fetal cells also express the same materials. To corroborate these findings, five fetal cell lines and 28 cancer cell lines were randomly selected from those previously studied, to determine the presence of translatable levels of hCG-beta (hCG beta) mRNA.

METHODS

All cell lines were grown under identical conditions. Determination of hCG beta mRNA was made by extracting the total RNA from the cells, followed by synthesis of cDNA with RNase H- reverse transcriptase and polymerase chain reaction amplification using specific hCG beta-luteinizing hormone-beta (hLH beta) primers. The presence of amplified hCG beta cDNA was corroborated by hybridization of the product with an hCG beta-specific oligonucleotide and Southern blot analyses of the hybridization products. Gestational choriocarcinoma cells and HeLa adenocarcinoma of cervical cells, known producers of biologically active hCG, were positive control subjects, and human pituitary cells were used as negative control subjects.

RESULTS

The results showed single and multiple hCG beta gene activation by the fetal cells and the different types of cancer, indicating that at any given time, there is the possibility of activation of as many as four genes of the six genes of the hCG beta-hLH beta gene cluster, even though alternative gene splicing cannot be ruled out.

CONCLUSIONS

In addition to the authors' previous findings, the results of these studies support the concept that cancer is a problem of development and differentiation, and, to the authors' knowledge, prove definitively for the first time that synthesis and expression of hCG, its subunits, and its fragments, is a common biochemical denominator of cancer, providing the scientific basis for studies of its prevention and/or control by active and/or passive immunization against these sialoglycoproteins.

Effects of hydroxyurea and cyclic adenosine monophosphate/protein kinase A inhibitors on the expression of the human chorionic gonadotropin alpha subunit and c-myc genes in choriocarcinoma

We have previously shown that treatment of choriocarcinoma cells with methotrexate or hydroxyurea leads to both cessation of cell growth, accompanied by repression of c-myc oncogene expression, and induction of genes associated with the placental phenotype, including both subunits of human chorionic gonadotropin (hCG) and placental alkaline phosphatase. Since the genes induced by these antimetabolites are also cyclic AMP inducible, we hypothesized that these antimetabolites may cause activation of the cyclic AMP/protein kinase A pathway, suppressing genes associated with cellular proliferation and inducing placental gene expression. Three inhibitors of the cyclic AMP/protein kinase A pathway were assayed for their ability to inhibit the induction of the human chorionic gonadotropin alpha gene by hydroxyurea, and none of these inhibitors eliminated this induction. In addition, blockade of the cyclic AMP/protein kinase A pathway did not reverse the suppression of c-myc by hydroxyurea. The results of the inhibitor studies suggest that hydroxyurea acts independently of the protein kinase A pathway to stimulate gene expression, and that suppression of c-myc is insufficient to cause the induction of the human chorionic gonadotropin alpha gene by hydroxyurea.

Flow cytometry method for the analysis of membrane-associated human chorionic gonadotropin, its subunits, and fragments on human cancer cells

A quantitative flow cytometry method for the analysis of membrane-associated human chorionic gonadotropin (hCG), its subunits, and fragments on human cancer cells was developed using a double-antibody reaction; a flow cytometry with a 2-W argon laser, standard settings, and filters for fluorescein isothiocyanate use; commercially available software; and the ectopic hCG producer CCL 2 HeLa cells from the American Type Culture Collection (ATCC) as a cell control to standardize the reagents and for overall quality control. Twenty-two monoclonal antibodies (MoAb) and immunoglobulin G fractions from three rabbit polyclonal antisera were tested for effects of antibody concentration (titration), reproducibility at different levels of epitope expression, and variability of epitope expression to select appropriate primary antibodies. Based on the results of the various tests, three polyclonal immunoglobulin G antibodies and a panel of nine MoAb directed to epitopes located in five different regions on the hCG molecule were selected as first antibodies. Their specificity was determined by using two unrelated MoAb of the same isotype at the same concentration to replace the primary MoAb and by a competition experiment. The unrelated MoAb also were used for the selection of the appropriate control fluorescence profile needed for the software. The unique characteristics of this method were: the use of living cells, standardized reagents, internal and external quality control, and the highest sensitivity, which could detect as few as 10(3) molecules of fluorochrome per cell. Serial analyses of the ATCC CCL 2 HeLa cells and two of its variants and of the eutopic hCG producer JEG-3 choriocarcinoma cells revealed the expression of membrane-associated epitopes of intact hCG, its subunits, and fragments by a high percentage of the cells, indicating that the expression of these sialoglycoproteins by these two different types of cancer cells is a common phenotypic characteristic.

A cell line that produces the glycoprotein hormone alpha-subunit contains specific nuclear factors similar to those present in thyrotropes

A unique characteristics of thyrotrope-specific gene expression is the coordinated expression and regulation of the alpha- and beta-subunits of TSH. A cell line (alpha TSH) derived from the transplantable mouse thyrotropic tumor MGH101A, which no longer expresses the TSH beta-subunit gene but continues to secrete large amounts of alpha-subunit, was used as a model to study alpha-subunit gene expression independent from the TSH beta-subunit gene and was compared with the expression in TSH-secreting TtT97 tumors. Transient transfection studies showed a striking similarity in the activity of 5' deletions of the mouse alpha-subunit gene promoter in both alpha TSH and TtT97 cells and localized two regions important for expression that spanned 100 base pairs, from -480 to -417 and from -417 to -381. These regions were found to have no activity in nonthyrotrope pituitary GH4 cells and L-cell fibroblasts. Analysis of the alpha-subunit 5' flanking DNA interactions with alpha TSH and TtT97 nuclear extracts showed two DNase I protected sequences, from -474 to -452 and from -447 to -400, both of which colocalized with the functionally important regions. Gel retardation analysis demonstrated the specificity of these interactions, and a similar migration of the DNA-protein complexes suggested that protein factors were similar in the two cell types. We conclude that the nuclear factors necessary for alpha-subunit expression in thyrotropes are retained in alpha TSH cells. Moreover, since alpha TSH cells do not express the TSH beta-subunit gene, the factors that determine the expression of the alpha-subunit may not be sufficient for TSH beta-subunit gene expression.

Identification of the promoter region of the rat protein phosphatase 2A alpha gene

We have cloned a genomic fragment containing the promoter region of the rat protein phosphatase 2A alpha gene (PP-2A alpha). A 1.6 kb fragment of the 5' flanking region was sequenced. Three major transcriptional initiation sites were identified by the primer extension method using rat liver mRNA and found to be located 225, 222 and 220 bases upstream of the translational initiation site, respectively. Bacterial chloramphenicol acetyltransferase (CAT) assay revealed that a 503 bp SmaI fragment containing the transcriptional initiation sites had promoter activity, which was stronger than that of the SV40 early promoter on the pSV2CAT plasmid when introduced into NIH3T3 cells. Deletion of a 119 bp SacII fragment decreased its promoter activity considerably. The promoter region has an extremely high GC content and does not contain either a 'TATA box' or a 'CAAT box' suggesting that this promoter can be classified as that of a 'house keeping' gene, although there is only one typical GC-box (GGGCGG) immediately preceding the transcriptional initiation sites. There is a 10 base pair palindrome, 5'-GTGACGTCAC-3', 26 base pairs upstream of the +1 transcriptional initiation site, which is highly conserved in many other genes, whose expression is regulated by cAMP. The promoter activity was shown to be increased by forskolin treatment (10 microM) in NIH3T3 cells.

DNA sequences required for expression of the LH beta promoter in primary cultures of rat pituitary cells

To begin analysis of the DNA sequences necessary for luteinizing hormone (LH) gene transcription, fusion genes containing the 5' flanking region of the rat LH beta or the human alpha-subunit gene linked to luciferase were transfected into primary cultures of rat pituitary cells. The LH beta-luciferase construct was expressed in the primary cultures at a level 50 times greater than a promoterless luciferase control plasmid. Little or no expression of the LH beta-luciferase construct was detected following transfection of MCF-7, JAR or GH3 tumor cell lines. Treatment of transfected cells with gonadotropin-releasing hormone resulted in a modest induction of LH beta-luciferase activity. Considerably higher levels of LH beta-luciferase activity were obtained with cultures from ovariectomized rats than were obtained with cultures from intact female rats. Analysis of 5' deletions of the LH beta-luciferase construct demonstrated that activity was well maintained even after substantial deletions. The shortest construct, which contained 75 base pairs of 5' flanking sequence had 38% of the activity of the longest which contained 1.7 kilobase pairs of flanking sequence. These findings demonstrate that transfection of primary cultures of rat pituitary cells may provide a useful system for analysis of the cis-acting sequences and trans-acting factors required for LH gene expression.

Human chorionic gonadotropin alpha and human cytomegalovirus promoters are extremely active in the fission yeast Schizosaccharomyces pombe

We have investigated the transcriptional activity of human cytomegalovirus, herpes thymidine kinase, human chorionic gonadotropin alpha, somatostatin, immunoglobulin kappa chain, alpha crystallin, albumin and interferon-beta promoters in the fission yeast Schizosaccharomyces pombe. Among these, the human cytomegalovirus, human chorionic gonadotropin alpha, and somatostatin promoters were found to be very active, approximately 11-, 9-, and 0.9-fold as active as the SV40 early promoter, respectively. The remainder of the promoters studied were weak, having only 10-20% of the SV40 promoter activity. Primer extension analysis showed that the strong promoters initiated transcription in S. pombe at the same sites as in mammalian cells, indicating the high similarity between both transcriptional systems.

Enhancement by theophylline of the butyrate-mediated induction of choriogonadotropin alpha-subunit in HeLa cells. II. Effect of both agents on mRNA turnover

In the accompanying paper it was demonstrated that among several methylxanthine phosphodiesterase inhibitors, only theophylline significantly increased production of the glycoprotein hormone alpha-subunit in HeLa cells, and that this action was synergistic with that of sodium butyrate. A correlation between alpha-subunit induction and cAMP concentrations was not evident. In this report we characterized the effect of these two drugs on the metabolism of alpha-subunit mRNA. Sodium butyrate decreased the apparent half-life of mRNAs encoding alpha-subunit, beta 2-microglobulin, and alpha-tubulin, as well as that of total poly(A)+ RNA and rRNA. Theophylline produced a two- to threefold increase in the apparent half-life of alpha-subunit mRNA but had no effect on the turnover of beta 2-microglobulin, alpha-tubulin, or total poly(A)+ mRNA. An inverse correlation was noted between the apparent half-life of the mRNA and the degree of destabilization elicited by butyrate. It is concluded that alpha-subunit induction by theophylline is in large part due to mRNA stabilization, and that the concerted effect of theophylline and butyrate results from inhibition by theophylline of the butyrate-mediated destabilization of alpha-subunit mRNA combined with the elevation in alpha-subunit gene transcription known to be produced by the fatty acid.

Enhancement by theophylline of the butyrate-mediated induction of choriogonadotropin alpha-subunit in HeLa cells. I. Lack of correlation with cAMP

The glycoprotein hormone common alpha-subunit can be induced in HeLa and other nontrophoblastic tumor cell lines by sodium butyrate. This report demonstrates that production of alpha-subunit can be further modulated by theophylline, especially in conjunction with butyrate. This synergism was not observed with other phosphodiesterase inhibitors such as xanthine, caffeine, theobromine, or methylisobutylxanthine. Induction by a combination of the short chain fatty acid plus the methylxanthine results from a decrease in the lag time after effector addition as well as a change in the rate of subunit accumulation. The increase in alpha-subunit is correlated with an increase in the levels of alpha-subunit mRNA, suggesting that induction is manifest at a pretranslational stage. The production of alpha-subunit was only marginally affected in cultures treated with 8-Br-cAMP or forskolin. Intracellular levels of cAMP were increased approximately threefold by methylisobutylxanthine, twofold by theophylline, fourfold by forskolin, and about 50% by butyrate, yet significant induction was achieved only by butyrate and theophylline. Taken together, these data suggest that the synergism between butyrate and theophylline is not mediated by cAMP.

Regulation of the transfected human glycoprotein hormone alpha-subunit gene by dexamethasone and thyroid hormone

A chimeric plasmid, (-1,500)h alpha CAT, containing approximately 1,500 bp of 5'-flanking DNA of the human glycoprotein hormone alpha-subunit gene directing the expression of the bacterial chloramphenicol acetyl transferase (CAT) gene, was transfected transiently into rat pituitary-derived GH3 cells. (-1,500)h alpha CAT expression was stimulated 5- to 20-fold by dexamethasone and 3- to 5-fold by 8-bromo-cAMP (8-Br-cAMP), and was inhibited by 50% by L-triiodothyronine (T3). Thus, suppression by T3 in this system was similar to that seen in pituitary thyrotropes. Induction of (-1,500)h alpha CAT expression by dexamethasone was antagonized by T3 but was unaffected by 8-Br-cAMP. However, T3 augmented the stimulation of (-1,500)h alpha CAT activity by 8-Br-cAMP. Deletants containing less than 346 bp of 5'-flanking alpha DNA showed a stepwise decrease in induction by dexamethasone, suggesting that multiple sequence elements located in this region are required for full induction of h alpha CAT activity. Deletion analysis also indicated that a thyroid hormone response element is located between 207 and 172 bp of the alpha gene transcriptional start site. Our finding of induction of alpha expression by dexamethasone in pituitary cells contrasts with the inhibition of alpha gene activity by glucocorticoids which has previously been shown in placental cells. Therefore, these data indicate that cell-type-specific factors play an important role in the modulation of alpha gene transcription.

CRE-binding proteins interact cooperatively to enhance placental-specific expression of the glycoprotein hormone alpha-subunit gene

The 18-bp direct repeat occurring between positions -146 and -111 in the 5'-flanking region of the human alpha-subunit gene serves two functions: it mediates the transcriptional effect of cAMP and it acts in conjunction with an adjacent cis-acting element (URE) to confer properties of placental-specific expression to the alpha-subunit promoter. Functional activity of the URE and CRE requires binding of a trans-acting factor; each element binds a different factor. Analysis of saturation isotherms provides good evidence that cooperativity is involved in binding of CREB to the 18-bp direct repeat. This cooperativity could account for the synergistic effect of two CRE on both basal and cAMP-stimulated transcription. It remains to be determined whether heterotropic cooperativity is involved in binding of trans-acting factors to the URE and CRE. A major difference between the 5'-flanking region of the human alpha-subunit gene and comparable regions from bovine, rat, and mouse alpha-subunit genes is that the latter contain a single CRE homolog which appears incapable of binding the trans-acting factor that binds to the human alpha CRE. Lack of a functional CRE provides at least one explanation for inactivity of the bovine alpha-subunit promoter in choriocarcinoma cells and probably in bovine placenta as well. Yet, the same bovine promoter-regulatory region that lacks a functional CRE is capable of conferring pituitary-specific expression to the CAT gene in transgenic mice (data not shown). This suggests that the CRE is not required for pituitary-specific expression of the bovine alpha-subunit gene. Instead, another cis-acting element(s) must confer this property to the alpha-subunit promoter. While it is tempting to suggest that bovine, rat, and mouse alpha-subunit genes are not regulated by cAMP because of their inactive CRE homolog, it is also quite possible that other CRE are located further upstream. Accordingly, it will be of interest to obtain additional 5'-flanking sequence and determine whether functional homologs of the human alpha CRE are present in the bovine, rat, and mouse alpha-subunit genes, or whether another class of cis-acting elements provide cAMP-responsiveness.

Regulation of low-density-lipoprotein-receptor mRNA by insulin in human hepatoma Hep G2 cells

The low-density-lipoprotein (LDL)-receptor mRNA content of human hepatoma (Hep G2) cells has been estimated from densitometric scans of autoradiograms obtained following the hybridisation of Northern blots of a poly(A)-rich RNA fraction with a 32P-labelled cDNA probe for the LDL-receptor gene. The recovery of beta-actin mRNA was used to correct for losses occurring during the preparation of the poly(A)-rich RNA. The content of LDL-receptor mRNA was reduced when the cells were pre-incubated in medium containing foetal calf serum, 25-hydroxycholesterol, or LDL, compared to that measured in cells which had been pre-incubated in medium containing lipoprotein-deficient serum (LPDS). When insulin (100 mU/ml) was included in pre-incubation medium containing LPDS, the amount of LDL-receptor mRNA increased approximately twofold. The level of beta-actin mRNA was not significantly increased by insulin treatment. Addition of insulin to incubation medium containing LPDS also overcame the suppressive effect of exogenous LDL on the cellular content of mRNA for the LDL receptor. These findings suggest that one action of insulin in these cells may be to promote transcription of the LDL-receptor gene by a mechanism that can override the sterol regulatory pathway.

Effects of adenine nucleotides on choriogonadotropin alpha and beta subunit synthesis

The alpha subunit of human chorionic gonadotropin (CG) contains a discrete cAMP response element in the 5' flanking region of the gene. Since cAMP also stimulates the synthesis of the CG beta subunit the presence of a cAMP cis element in the CG beta gene was examined. Deletion mutants bearing various lengths of CG beta 5' region in front of the chloramphenicol acetyl transferase (CAT) gene were transfected in placental tumor cells. No discrete cAMP response element could be identified. Unexpectedly we also observed that AMP and adenosine not only stimulated CAT activity driven by CG beta promoter sequences but also enhanced synthesis of CG alpha and beta subunits in cultured choriocarcinoma cells. GMP, CMP, guanosine, and cytosine were inactive at comparable concentrations. These data suggest that the response of the CG alpha and beta genes to the non-cyclic adenine derivatives occurs by a mechanism that differs from cAMP.

Effects of 8-bromo-cAMP on expression of endocrine functions by cultured human trophoblast cells. Regulation of specific mRNAs

There is little information on the molecular events underlying the effects of cAMP on human chorionic gonadotropin (hCG) and particularly steroidal hormone production in normal trophoblasts. We examined the effects of 8-bromo-cAMP on mRNAs encoding two components of the cholesterol side-chain cleavage system, cytochrome P-450scc and adrenodoxin, and the alpha- and beta-subunits of hCG in cultured cytotrophoblasts. cAMP caused an increase in all of these mRNAs within 24 h, whereas actin mRNA declined. alpha-hCG mRNA increased first, followed by adrenodoxin, beta-hCG and cytochrome P-450scc mRNAs. The effects of 8-bromo-cAMP on alpha- and beta-hCG, adrenodoxin, and cytochrome P-450scc mRNAs, in cytotrophoblasts and JEG-3 choriocarcinoma cells, required the catalytic unit of protein kinases since H-7, a kinase inhibitor, blocked the increase in the mRNAs and prevented the stimulation of hCG and progesterone secretion. 8-Bromo-cAMP promoted a rapid increase in alpha-hCG mRNA in cytotrophoblasts in the presence of cycloheximide, an inhibitor of protein synthesis. In cytotrophoblasts, cycloheximide reduced basal and 8-bromo-cAMP-stimulated adrenodoxin mRNA abundance. In contrast, basal and cAMP-stimulated adrenodoxin mRNA was augmented by cycloheximide in JEG-3 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Possible induction of fatty acid cyclooxygenase in mouse osteoblastic cells (MC3T3-E1) by cAMP

Prostaglandin E2 (PGE2), a bone-resorption factor, was essentially the sole arachidonate metabolite in an osteoblastic cell line cloned from mouse calvaria (MC3T3-E1). When the cells were cultured in the presence of 2% newborn bovine serum, 1 microM epinephrine markedly stimulated PGE2 synthesis from endogenous arachidonic acid. The PGE2 synthesis commenced after a lag phase of 1-2 h, and reached a maximum at about 3 h after the addition of epinephrine. The effect of epinephrine was inhibited by propranolol, and epinephrine could be replaced by isoproterenol, suggesting beta-adrenergic stimulation of PGE2 production. A rapid increase in intracellular cAMP was observed upon the addition of epinephrine. When the intracellular cAMP level was raised using cholera toxin or forskolin, the PGE2 synthesis was also stimulated. The enhanced PGE2 synthesis was attributed to an increased level of cyclooxygenase, which was shown by immunoprecipitation of the enzyme using anti-cyclooxygenase antibody. Inhibitors of transcription and translation suppressed the epinephrine-dependent increase in cyclooxygenase activity. These findings suggest induction of cyclooxygenase involving cAMP via an as yet unclarified mechanism.

Effect of pyrimidine deoxynucleosides and sodium butyrate on expression of the glycoprotein hormone alpha-subunit and placental alkaline phosphatase in HeLa cells

Production of the glycoprotein hormone common alpha-subunit and placental alkaline phosphatase activity can be modulated in HeLa cells by a variety of deoxynucleosides. Dose response curves for thymidine (Thd), fluorodeoxyuridine (FdUrd), bromodeoxyuridine (BrdUrd) and iododeoxyuridine (IdUrd) demonstrate that, in general, alkaline phosphatase was increased by lower concentrations of inducer than was alpha-subunit. The deoxynucleosides were not as effective as sodium butyrate as inducers of either protein. Whereas Thd and the halogenated dUrd derivatives enhanced protein expression, deoxycytidine (dCyd) had negative effects. Induction by deoxynucleosides of both alkaline phosphatase and alpha-subunit was inhibited by dCyd, but induction of alkaline phosphatase by butyrate was more sensitive to dCyd inhibition than was the butyrate-mediated induction of alpha-subunit. These results suggest that the two proteins are not regulated in a coordinate manner. Reversal of alkaline phosphatase induction by dCyd was not observed in cells preincubated with sodium butyrate for 6-24 h before the addition of dCyd, indicating that the deoxynucleoside interferes with an early event in the butyrate-mediated response. Combinations of butyrate with Thd, BrdUrd or IdUrd were synergistic with respect to the induction of HeLa-alpha. It is concluded that incorporation of the deoxynucleosides into DNA may not be required for the synergistic response since 2',5'-dideoxythymidine was an effective as Thd. Cytoplasmic dot hybridizations demonstrate that a primary effect of the various effectors is to increase the steady-state levels of alpha-subunit mRNA. There was a good correlation between alpha-subunit accumulation and corresponding levels of alpha-mRNA, suggesting that regulation occurs at a pretranslational site. Although the mechanism(s) is not understood, these data provide evidence that nucleosides or their derivatives can significantly affect gene expression.

Expression and cAMP-mediated regulation of the human gonadotropin alpha subunit gene in transfected mouse L-cells

Expression of the dimeric glycoprotein hormone, human chorionic gonadotropin (HCG), occurs either eutopically in placental trophoblast cells and trophoblastic tumor cells (choriocarcinoma) or ectopically in nontrophoblastic tumor cells. However, regulation of constitutive HCG-subunit mRNA production appears to differ in trophoblastic and nontrophoblastic cells, as evidenced by the fact that cAMP analogs and agonists enhance eutopic but not ectopic HCG-subunit mRNA synthesis. In the present study, we compared the effects of cAMP on HCG alpha-subunit expression in human choriocarcinoma cells and in nontrophoblastic mouse L-cells stably transfected with the HCG alpha-subunit gene. Constitutive levels of alpha-subunit expression in transfected mouse L-cells were equivalent to or exceeded those found in choriocarcinoma cells as determined by Northern blot analysis and indirect immunofluorescence for alpha-subunit protein. However, cAMP-mediated induction of alpha-subunit gene expression was retained in nontrophoblastic L-cells and closely paralleled that observed in human choriocarcinoma cells. These findings indicate that cells distinctly nontrophoblastic in origin may share the necessary cellular factors for cAMP-mediated induction of alpha-subunit gene expression. Failure of ectopic HCG-producing tumor cells to be stimulated by cAMP may thus be the result of deletion or mutation of such factors.

Regulation of low density lipoprotein receptor and cytochrome P-450scc mRNA levels in human granulosa cells

hCG and 8-bromo-cAMP increase the levels of the mRNAs encoding the LDL receptor and cytochrome P-450scc in human granulosa cells. The increment in these mRNAs occurs rapidly after stimulation (within hours). Actin mRNA levels are not changed by hCG and 8-bromo-cAMP treatment. The tropic hormone effects on LDL receptor mRNA are observed even in the presence of 25-hydroxycholesterol and aminoglutethimide, which by themselves suppress LDL receptor mRNA. Actinomycin D blocks the hCG and 8-bromo-cAMP promoted augmentation of LDL receptor mRNA, suggesting that the tropic factors act to increase transcription of this gene. Treatment of cells with cycloheximide increases LDL receptor mRNA levels, and the stimulatory response to hCG and 8-bromo-cAMP is enhanced in the presence of cycloheximide. This indicates that tropic hormones act to increase LDL receptor mRNA levels without requiring synthesis of intermediary proteins and suggests that some short-lived protein may actually be reducing LDL receptors mRNA levels in these cells. We conclude that gonadotropins increase steroidogenesis in human granulosa cells, in part, by increasing expression of mRNAs encoding specific proteins involved in cholesterol metabolism.