Identification of a promoter region in the CG beta gene cluster

The tumor suppressor p53 induces expression of the pregnancy-supporting human chorionic gonadotropin (hCG) CGB7 gene

Successful pregnancy requires a functionally normal blastocyst encountering a receptive maternal endometrium. Interestingly, the cell cycle regulator and tumor suppressor p53 has been reported to support reproduction in mice by regulating the expression of the leukemia inhibitory factor gene in the maternal endometrium. However, in humans the hormonal system orchestrating successful pregnancy is considerably different from rodents. Particularly, the primate-specific dimeric glycoprotein hormone human chorionic gonadotropin (hCG) is essential for blastocyst implantation and maintenance of early human pregnancy. Here we provide evidence that p53 selectively induces expression of the hCGbeta7 (CGB7) gene. None of the other CGB genes was found to be regulated by p53. We show that expression of the CGB7 gene is upregulated upon p53 induction in human HFF, HCT116 and DLD1 cells as well as in cell preparations enriched in human primary first-trimester trophoblasts. The increase in CGB7 levels upon doxorubicin treatment is lost after siRNA-directed knockdown of p53. Furthermore, we describe CGB7 as a direct transcriptional target gene of p53 by identifying a p53-responsive element in the CGB7 promoter using reporter assays, electrophoretic mobility shift assays and chromatin immunoprecipitations. With these results we provide a new link between p53 transcriptional activity and human reproduction.

The evolution and genomic landscape of CGB1 and CGB2 genes

The origin of completely novel proteins is a significant question in evolution. The luteinizing hormone (LHB)/chorionic gonadotropin (CGB) gene cluster in humans contains a candidate example of this process. Two genes in this cluster (CGB1 and CGB2) exhibit nucleotide sequence similarity with the other LHB/CGB genes, but as a result of frameshifting are predicted to encode a completely novel protein. Our analysis of these genes from humans and related primates indicates a recent origin in the lineage specific to humans and African great apes. While the function of these genes is not yet known, they are strongly conserved between human and chimpanzee and exhibit three-fold lower diversity than LHB across human populations with no mutations that would disrupt the coding sequence. The 5'-upstream region of CGB1/2 contains most of the promoter sequence of hCGbeta plus a novel region proximal to the putative transcription start site. In silico prediction of putative transcription factor binding sites supports the hypothesis that CGB1 and CGB2 gene products are expressed in, and may contribute to, implantation and placental development.

Development of human chorionic gonadotropin subunit-beta promoter-based toxic gene therapy for testicular cancer

OBJECTIVES

To develop a new toxic gene therapy using the tissue-specific human chorionic gonadotropin-beta (hCG-beta) promoter for testicular cancer. Although most patients presenting with disseminated testicular tumor are cured through the use of chemotherapy with or without surgery, those patients with relapse after initial therapy present a difficult clinical problem. The serum tumor marker hCG-beta is frequently elevated in patients with testicular cancer, and the pretreatment and post-treatment levels of serum hCG-beta are highly predictive of treatment outcome.

METHODS

Human testicular embryonal carcinoma cell line, NEC 8, a human prostate cancer cell line, PC-3, and a human bladder cancer cell line, WH, were used in this study. A transient expression experiment was used to analyze the activity of a 729-bp hCG-beta promoter in all three cell lines. A recombinant adenovirus carrying thymidine kinase (Ad-hCG-beta-TK) under control of the hCG-beta promoter was generated. The tissue-specific activity of Ad-hCG-beta-TK was tested in vitro and in vivo.

RESULTS

The hCG-beta promoter had significantly greater activity in the hCG-beta-producing cell line (NEC 8) than in the non-hCG-beta-producing cell lines (PC-3 and WH). In vitro, Ad-hCG-beta-TK with acyclovir significantly inhibited NEC 8 growth but not PC-3 or WH cell growth. In vivo, Ad-hCG-beta-TK with acyclovir significantly inhibited NEC 8 subcutaneous tumor growth in nude mice.

CONCLUSIONS

In this study, we explored the possibility of developing a new therapeutic agent to target and induce the killing of testicular germ cell tumor selectively by using tissue-specific hCG-beta promoters.

A central role for Ets-2 in the transcriptional regulation and cyclic adenosine 5'-monophosphate responsiveness of the human chorionic gonadotropin-beta subunit gene

Ets-2 has an important role in controlling the differentiation of the placenta. Here we show by truncation and mutational analysis that two closely spaced Ets-2 binding sites in the proximal promoter of the human chorionic gonadotropin beta5 (hCGbeta5) gene constitute a major enhancer for hCGbeta gene expression in JAr and JEG-3 human choriocarcinoma cells and in mouse NIH3T3 cells. Contrary to a previous report, we also demonstrate that the ability of Ets-2 to enhance transcription is subject to control by the Ras/MAPK pathway, although this relationship is less easily demonstrable in JAr and JEG-3 choriocarcinoma cells than in the 3T3 cells because the former already possess a fully activated MAPK pathway and contain Ets-2 phosphorylated at threonine residue at T72. Coexpression of Ets-2 and activated Ras in 3T3 cells led to activation of MAPK/ERK kinase 1/2, phosphorylation of Ets-2 at T72, and an approximately 120-fold up-regulation of reporter gene expression from a short (-175) hCGbeta promoter. Fold activation in JAr and JEG-3 cells was rather less (20- to 30-fold), but basal activity was much higher. These effects on promoter activity were largely reversed in presence of the MAPK inhibitor PD98059, which prevents ERK1/2 activation, and partially reversed by mutating T72 on Ets-2. We finally show that the ability of 8-bromoadenosine-cAMP to stimulate hCGbeta promoter activity in JAr and JEG-3 cells occurs with a short promoter lacking the upstream elements previously considered to be essential for cAMP activation of the gene and, through mutational analysis, confirm that the major cAMP effects on the hCGbeta promoter are mediated through the proximal Ets-2 enhancer. The data are consistent with the hypothesis that Ets-2 has a general and possibly essential role in controlling the activity of genes associated with trophectoderm differentiation.

Predictive value of hormone measurements in maternal and fetal complications of pregnancy

Intrauterine tissues (placenta, amnion, chorion, decidua) express hormones and cytokines that play a decisive role in maternal-fetal physiological interactions. The excessive or deficient release of some placental hormones in association with gestational diseases may reflect an abnormal differentiation of the placenta, an impaired fetal metabolism, or an adaptive response of the feto-placental unit to adverse conditions. This review is focused on the applicability of hormone measurements in the risk assessment, early diagnosis, and management of pregnancies complicated by Down's syndrome, fetal growth restriction, preeclampsia, preterm delivery, and diabetes mellitus. Combined hormonal tests or the combination of hormones and ultrasound may achieve reasonable sensitivity, but research continues to simplify the screening programs without sacrificing their accuracy. Only in a few instances is there sufficient evidence to firmly recommend the routine use of hormone tests to predict maternal and fetal complications, but the judicious use of selected tests may enhance the sensitivity of the risk assessment based solely on clinical and ultrasound examination.

Gene for porcine pregnancy-associated glycoprotein 2 (poPAG2): its structural organization and analysis of its promoter

The pregnancy-associated glycoproteins (PAG) are abundant secretory products of the placental trophectoderm of ungulate species. They are structurally related to pepsin, having the capability to bind peptides. However, many cannot function as enzymes due to amino acid substitutions in and around the catalytic site. Here, we demonstrate that pigs, like cattle and sheep, but unlike equids, have multiple PAG genes. One of the transcribed porcine PAG (poPAG) genes, the one for poPAG2, was cloned. It had a nine-exon organization similar to that of other mammalian aspartic proteinase genes with an atypical TATA sequence. A total of 1.2 kbp upstream from exon 1 was sequenced. This region shared identity (> 65%) with the promoter regions of the bovine (bo) PAG1, boPAG2 and equine (eq) PAG genes, but not with other aspartyl proteinase genes, including that of pepsinogen A. Nor were there clear similarities to the promoters of other genes with trophoblast-specific expression. Of the different poPAG2 promoter constructs tested in transfection experiments in two human (JAr and JEG3) and one rat (Rcho) choriocarcinoma cell lines, only the shortest (-149 bp) was required to provide full expression of a luciferase reporter. Although this short promoter was not active in Cos-1 and L-929 cells, it was active in CHO cells, a transformed non-trophoblast hamster ovarian cell line. Co-transfection of Ets2 elevated the activity of this short promoter approximately six-fold in JAr cells, but, disruption of the two putative Ets sites did not alter the ability of Ets2 to transactivate the promoter. In the non-trophoblast cell lines, Ets2 failed to elicit any response. Ets2 responsiveness may be a common feature of most or all trophoblast-expressed genes, although in the case of poPAG2, the effect may be indirect.

Cellular localization of the human chorionic gonadotropin beta-subunit in transgenic mouse placenta

CG is a human placental glycoprotein expressed in first-trimester trophoblasts. To examine the regulation of the CGbeta-subunit in an in vivo model, we previously constructed transgenic mice containing the CGbeta gene cluster and demonstrated its expression in the placenta. Here, we determine the cell type responsible for CGbeta synthesis in the mouse by immunohistochemical and in situ hybridization analyses. Unexpectedly, the protein and messenger RNA were not detected in trophoblast or elsewhere in the chorioallantoic placenta but in the parietal endoderm, a separate extraembryonic component of the placenta. The identity of this CGbeta-producing layer was confirmed by the presence of laminin A, a known protein of the parietal endoderm extracellular matrix. However, we observed heterogeneity, with respect to synthesis of laminin A and CGbeta; parietal endoderm cells expressing CGbeta at high levels synthesized less laminin A, and vice versa. The absence of CGbeta production in trophoblasts of the transgenic mouse demonstrates a lack of transcriptional equivalence between rodent and human trophoblasts. The data are consistent with the hypothesis that, in human placenta, one or more transcriptional factors coevolved as members of the CGbeta gene cluster underwent duplication.

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.

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

The transcription factor Oct-3/4 may be important in maintaining embryonic cells in an undifferentiated state. It is probably down-regulated at about the time that human chorionic gonadotropin (hCG) is first expressed in embryonic trophectoderm. Here we report that Oct-3/4 strongly inhibits the hCGbeta subunit (hCGbeta) promoter in JAr choriocarcinoma cells. Oct-3/4 reduced chloramphenicol acetyltransferase (CAT) reporter expression from the -305hCGbeta promoter by about 90% in transient co-transfection assays, but had no effect on expression from the -249hCGbeta promoter. The -305/-249 hCGbeta fragment specifically bound synthetic Oct-3/4 protein as measured in electrophoretic mobility shift assays, and the Oct-3/4-binding site was localized around -270 by methylation interference footprinting. Site-directed mutagenesis of this binding site abolished Oct-3/4 repression. When stably transfected into JAr cells, Oct-3/4 reduced the amounts of both endogenous hCGbeta messenger RNA and hCG protein to less than 10% of controls. We suggest that silencing of Oct-3/4 in trophectoderm is a prerequisite for hCG up-regulation in early human embryos at the time of maternal recognition of pregnancy.

Multiple promoter elements in the human chorionic gonadotropin beta subunit genes distinguish their expression from the luteinizing hormone beta gene

The beta subunit of human chorionic gonadotropin (CG beta) is encoded by a cluster of six genes, which have developed through gene duplication from an ancestral LH beta gene. Despite approximately 90% sequence homology between the CG beta and LH beta promoters, the CG beta gene is expressed in the placenta, whereas the LH beta promoter is active only in the pituitary. The CG beta gene uses a TATA-less promoter that is located upstream of the transcriptional start site used by the homologous LH beta gene. The purpose of this study was to use the high degree of homology among members of the CG beta gene cluster and between the CG beta and LH beta promoters to localize regulatory elements that confer CG beta expression in the placenta. The 5'-flanking regions of the different CG beta genes were cloned and expressed in JEG-3 placental cells. Naturally occurring sequence variations were correlated with promoter activity and used to identify candidate regulatory elements. Exchanges of homologous sequences in the CG beta 5 and LH beta proximal identified three separate regions between -362 and +104 that are necessary for full basal expression of the CG beta promoter. Site-directed mutagenesis of four evolutionarily divergent sequences near the CG beta transcription start site confirmed the importance of multiple distinct regulatory elements as each of these mutations resulted in an 80% decrease in promoter activity.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.