Pituitary-specific repression of placental members of the human growth hormone gene family. A possible mechanism for locus regulation

Obesity and regulation of human placental lactogen production in pregnancy

The four genes coding for placental members of the human (h) growth hormone (GH) family include two that code independently for placental lactogen (PL), also known as chorionic somatomammotrophin hormone, one that codes for placental growth hormone (PGH) and a pseudogene for which RNA but no protein product is reported. These genes are expressed preferentially in the villus syncytiotrophoblast of the placenta in pregnancy. In higher primates, the placental members, including hPL and PGH, are the result of multiple duplication events of the GH gene. This contrasts with rodents and ruminants, where PLs result from duplication of the prolactin (PRL) gene. Thus, unlike their mouse counterparts, the hPL and PGH hormones bind both lactogenic and somatogenic receptors with varying affinity. Roles influenced by nutrient availability in both metabolic control in pregnancy and maternal behaviour are supported. However, the effect maternal obesity has on the activation of placental members of the hGH gene family, particularly the expression and function of those genes, is poorly understood. Evidence from partially humanised hGH/PL transgenic mice indicates that both the remote upstream hPL locus control region (LCR) and more gene-related regulatory regions are required for placental expression in vivo. Furthermore, a specific pattern of interactions between the LCR and hPL gene promoter regions is detected in term placenta chromatin from women with a normal body mass index (BMI) in the range 18.5-25 kg m^-2 by chromosome conformation capture assay. This pattern is disrupted with maternal obesity (class II BMI > 35 kg m^-2 ) and associated with a > 40% decrease in term hPL RNA levels, as well as serum hPL but not PRL levels, during pregnancy. The relative importance of the chromosomal architecture and predicted properties for transcription factor participation in terms of hPL production and response to obesity are considered, based on comparison with components required for efficient human pituitary GH gene expression.

Effects of 17β-Estradiol on growth-related genes expression in female and male spotted scat (Scatophagus argus)

Growth hormone (GH) is the most important endocrine factor to regulate somatic growth. Spotted scat (Scatophagus argus) is a famous marine aquaculture species in China with a typical sexual growth dimorphism in which females grow faster and larger than males. In this study, gh messenger RNA (gh mRNA) and GH protein expression were examined in the pituitary glands of female and male spotted scat. Based on qPCR analysis, gh mRNA was mainly expressed in the pituitary gland, and weakly in the gonads and hypothalamus. Furthermore, gh mRNA expression in the pituitary gland was significantly higher in females at stages II-IV than in males at stages III-V. In addition, gh mRNA was highly expressed in the ovary and testis during mature development stages. In this study, spotted scat GH polyclonal antibody was produced. Western blot analysis showed that the molecular weight of spotted scat GH was about 21 KDa. Immunohistochemistry (IHC) in pituitary glands showed that GH was mainly expressed in the proximal pars distal (PPD) and a few cells were distributed in the rostral pairs distal (RPD). After injecting 17β-Estradiol (E₂) in vivo, gh mRNA expression was significantly up-regulated in the pituitary gland, whereas igf1 and ghr1 mRNA levels were down-regulated in the liver, which might regulate gh mRNA expression in the pituitary gland. These results provide valuable insight into the molecular mechanisms of E₂ regulating gh expression in spotted scat.

Expression of growth hormone gene in the baboon eye

The human growth hormone (GH) locus is comprised by two GH (GH1 and GH2) genes and three chorionic somatomammotropin (CSH1, CSH2 and CSH-L) genes. While GH1 is expressed in the pituitary gland, the rest are expressed in the placenta. However, GH1 is also expressed in several extrapituitary tissues, including the eye. So to understand the role of this hormone in the eye we used the baboon (Papio hamadryas), that like humans has a multigenic GH locus; we set up to investigate the expression and regulation of GH locus in adult and fetal baboon ocular tissues. We searched in baboon ocular tissues the expression of GH1, GH2, CSH1/2, Pit1 (pituitary transcription factor 1), GHR (growth hormone receptor), GHRH (growth hormone releasing hormone), GHRHR (growth hormone releasing hormone receptor), SST (somatostatin), SSTR1 (somatostatin receptor 1), SSTR2 (somatostatin receptor 2), SSTR3 (somatostatin receptor 3), SSTR4 (somatostatin receptor 4), and SSTR5 (somatostatin receptor 5) mRNA transcripts and derived proteins, by qPCR and immunofluorescence assays, respectively. The transcripts found were characterized by cDNA cloning and sequencing, having found only the one belonging to GH1 gene, mainly in the retina/choroid tissues. Through immunofluorescence assays the presence of GH1 and GHR proteins was confirmed in several retinal cell layers. Among the possible neuroendocrine regulators that may control local GH1 expression are GHRH and SST, since their mRNAs and proteins were found mainly in the retina/choroid tissues, as well as their corresponding receptors (GHRH and SSTR1-SSTR5). None of the ocular tissues express Pit1, so gene expression of GH1 in baboon eye could be independent of Pit1. We conclude that to understand the regulation of GH in the human eye, the baboon offers a very good experimental model.

Human placental growth hormone in normal and abnormal fetal growth

Human placental growth hormone (PGH), encoded by the growth hormone (GH) variant gene on chromosome 17, is expressed in the syncytiotrophoblast and extravillous cytotrophoblast layers of the human placenta. Its maternal serum levels increase throughout pregnancy, and gradually replaces the pulsatile secreted pituitary GH. PGH is also detectable in cord blood and in the amniotic fluid. This placental-origin hormone stimulates glyconeogenesis, lipolysis and anabolism in maternal organs, and influences fetal growth, placental development and maternal adaptation to pregnancy. The majority of these actions are performed indirectly by regulating maternal insulin-like growth factor-I levels, while the extravillous trophoblast involvement indicates a direct effect on placental development, as it stimulates trophoblast invasiveness and function via a potential combination of autocrine and paracrine mechanisms. The current review focuses on the role of PGH in fetal growth. In addition, the association of PGH alterations in maternal circulation and placental expression in pregnancy complications associated with abnormal fetal growth is briefly reviewed.

Long-range looping of a locus control region drives tissue-specific chromatin packing within a multigene cluster

The relationships of higher order chromatin organization to mammalian gene expression remain incompletely defined. The human Growth Hormone (hGH) multigene cluster contains five gene paralogs. These genes are selectively activated in either the pituitary or the placenta by distinct components of a remote locus control region (LCR). Prior studies have revealed that appropriate activation of the placental genes is dependent not only on the actions of the LCR, but also on the multigene composition of the cluster itself. Here, we demonstrate that the hGH LCR 'loops' over a distance of 28 kb in primary placental nuclei to make specific contacts with the promoters of the two GH genes in the cluster. This long-range interaction sequesters the GH genes from the three hCS genes which co-assemble into a tightly packed 'hCS chromatin hub'. Elimination of the long-range looping, via specific deletion of the placental LCR components, triggers a dramatic disruption of the hCS chromatin hub. These data reveal a higher-order structural pathway by which long-range looping from an LCR impacts on local chromatin architecture that is linked to tissue-specific gene regulation within a multigene cluster.

Expression of Placental Members of the Human Growth Hormone Gene Family Is Increased in Response to Sequential Inhibition of DNA Methylation and Histone Deacetylation

The genes coding for human (h) chorionic somatomammotropin (CS), hCS-A and hCS-B, and placental growth hormone (GH-V), hGH-V, are located at a single locus on chromosome 17. Efficient expression of these placental genes has been linked to local regulatory (5′ P and 3′ enhancer) sequences and a remote locus control region (LCR), in part, through gene transfer in placental and nonplacental tumor cells. However, low levels of endogenous hCS/GH-V transcripts are reported in the same cells compared with term placenta, suggesting that chromatin structure, or regulatory region accessibility, versus transcription factor availability contributes to the relatively low levels. To assess individual hCS-A, CS-B, and GH-V gene expression in placental and nonplacental tumor cells and the effect of increasing chromatin accessibility by inhibiting DNA methylation and histone deacetylation using 5-aza-2′-deoxycytidine (azadC) and trichostatin A (TSA). Low levels of hCS-A, CS-B, and GH-V were detected in placental and nonplacental tumor cells compared with term placenta. A significant >5-fold increase in activity was seen in placental, but not nonplacental, cells transfected with hybrid hCS promoter luciferase genes containing 3′ enhancer sequences. Pretreatment of placental JEG-3 cells with azadC resulted in a >10-fold increase in hCS-A, CS-B, and GH-V RNA levels with TSA treatment compared with TSA treatment alone. This effect was specific as reversing the treatment regimen did not have the same effect. An assessment of hyperacetylated H3/H4 in JEG-3 cells treated with azadC and TSA versus TSA alone revealed significant increases consistent with a more open chromatin structure, including the hCS 3′ enhancer sequences and LCR. These observations suggest that accessibility of remote and local regulatory regions required for efficient placental hGH/CS expression can be restricted by DNA methylation and histone acetylation status. This includes restricting access of the hCS 3′ enhancer sequences to available placental enhancer transcription factors.

Immunoglobulin isotype isolated from human placental extract does not interfere in complement-mediated bacterial opsonization within the wound milieu

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Human placental extract has many applications as a wound healer.

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Immunoglobulin G is a key glycoprotein present in human placental extract.

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Placental IgG (25.2 ± 3.97 μg/ml) did not exert anti-complementary effects.

The wound healing potency of an aqueous extract of placenta can be evaluated through the presence of numerous regulatory components. The presence of glycans was detected by thin layer chromatography and fluorophore-assisted carbohydrate electrophoresis. Mass spectrometric analysis revealed the existence of multiple fragments of immunoglobulin G (IgG). IgG was present in the extract at a concentration of 25.2 ± 3.97 μg/ml. IgG possesses anti-complementary activity by diverting the complement activation from target surface. Thus, effect of placental IgG on complement–bacteria interaction was investigated through classical and alternative pathway and the preparation was ascertained to be safe with respect to their interference in the process of bacterial opsonization.

Tissue specific CTCF occupancy and boundary function at the human growth hormone locus

The robust and tissue-specific activation of the human growth hormone (hGH) gene cluster in the pituitary and placenta constitutes an informative model for analysis of gene regulation. The five-gene hGH cluster is regulated by two partially overlapping sets of DNase I hypersensitive sites (HSs) that constitute the pituitary (HSI, II, III and V) and placental (HSIII, IV, and V) locus control regions (LCRs). The single placenta-specific LCR component, HSIV, is located at −30 kb to the cluster. Here we generate a series of hGH/BAC transgenes specifically modified to identify structural features of the hGH locus required for its appropriate placental expression. We find that placental specificity is dependent on the overall multigene configuration of the cluster whereas the distance between the cluster and its LCR impacts the level of placental expression. We further observe that a major function of the placental hGH LCR is to insulate the transgene locus from site-of-integration effects. This insulation activity is linked to placenta-specific occupancy of the chromatin architectural protein, CTCF, at HSIV. These data reveal a remarkable combination of structural configurations and regulatory determinants that must work in concert to insure robust and tightly controlled expression from a complex multigene locus.

Placental lactogen is expressed but is not translated into protein in breast cancer

Introduction

Several studies reported that the pregnancy-specific hormone placental lactogen (hPL) is expressed at both mRNA and protein levels in breast cancer. The overall objective was to establish hPL, the product of the CSH1 and CSH2 genes, as a biomarker for breast cancer.

Methods

CSH expression was determined at the mRNA level in breast cancer cell lines (BCC) and primary carcinomas by real-time and conventional PCR and the products verified as CSH1 by sequencing. Expression of hPL protein was examined by western blots and immuno-histochemistry, using commercial and custom-made polyclonal and monoclonal antibodies.

Results

Variable levels of CSH mRNA were detected in several BCC, and in some primary tumors. We detected a protein, slightly larger than recombinant hPL by western blotting using several antibodies, leading us to postulate that it represents an hPL variant (‘hPL’). Furthermore, some monoclonal antibodies detected ‘hPL’ by immunohistochemistry in breast carcinomas but not in normal breast. However, further examination revealed that these antibodies were non-specific, as efficient suppression of CSH mRNA by shRNA did not abolish the ‘hPL’ band. Custom-made monoclonal antibodies against recombinant hPL detected hPL of the correct size in placental lysate and hPL-overexpressing BCC, but not in unmodified cells or primary carcinomas. hPL protein was detected only when mRNA was increased several thousand fold.

Conclusions

We call into question previous reports of hPL expression in breast cancer which relied on mRNA levels as surrogates for protein and/or used improperly validated antibodies to measure hPL protein levels. Our data suggests that an inhibitory mechanism(s) prevents translation of CSH mRNA in breast cancer when not highly expressed. The mechanism by which translation of CSH mRNA is inhibited is intriguing and should be further investigated.

Identification of functional CCAAT/enhancer-binding protein and Ets protein binding sites in the human chorionic somatomammotropin enhancer sequences

The human chorionic somatomammotropin (CS) A and B genes (listed as CSH1 and CSH2 in the HUGO database) are highly expressed in placenta. A 241 bp potent enhancer, nucleotides (nts) 1-241, located at the 3' end of the CS-B gene (CS-Benh) stimulates promoter activity specifically in placental trophoblast cells in vitro. Strong activity is exerted by a 23 bp element within the CS-Benh (nts 117-139), shown to interact with transcription enhancer factor (TEF) members of the transcription enhancer activator (TEA) DNA-binding domain-containing family. An identical TEF element is present in the homologous (97.5%) CS-Aenh; however, a few nucleotide differences suppress its activity. Previously, we identified regulatory sequences distinct from the TEF element within an 80 bp modulatory domain (nts 1-80) in the CS-Benh. Using structural and functional assays we now show that CCAAT/enhancer-binding protein (C/EBP) binding sites exist in the 80 bp modulatory domains of both enhancers, and an Elk-1 binding site exists in the modulatory domain of the CS-Aenh. C/EBPα or C/EBPβ strongly repressed CSp.CAT activity but stimulated CSp.CAT.CS-Benh activity. In contrast, the equivalent CS-A enhancer sequences were unable to relieve promoter repression. Elk-1 overexpression also resulted in differential effects on the CS-Aenh versus CS-Benh. Finally, we provide evidence for the association of C/EBPβ with the CS-A and CS-B genes in human placental chromatin, including differential involvement of C/EBPβ with the CS-Aenh versus the CS-Benh, and therefore consistent with the notion that these are regions of regulatory significance in vivo. We conclude that members of the C/EBP and Ets families can differentially modulate CS-Benh and CS-Aenh activity.

Epigenetic activation of the human growth hormone gene cluster during placental cytotrophoblast differentiation

The hGH cluster contains a single human pituitary growth hormone gene (hGH-N) and four placenta-specific paralogs. Activation of the cluster in both tissues depends on 5' remote regulatory elements. The pituitary-specific locus control elements DNase I-hypersensitive site I (HSI) and HSII, located 14.5 kb 5' of the cluster (position -14.5), establish a continuous domain of histone acetylation that extends to and activates hGH-N in the pituitary gland. In contrast, histone modifications in placental chromatin are restricted to the more 5'-remote HSV-HSIII region (kb -28 to -32) and to the placentally expressed genes in the cluster, with minimal modification between these two regions. These data predict distinct modes of hGH cluster gene activation in the pituitary and placenta. Here we used cell culture models to track structural changes at the hGH locus through placental-gene activation. The data revealed that this process was initiated in primary cytotrophoblasts by histone H3K4 di- and trimethylation and H4 acetylation restricted to HSV and to the individual placental-gene repeat (PGR) units within the cluster. Later stages of transcriptional induction were accompanied by enhancement and extension of these modifications and by robust H3 acetylation at HSV, at HSIII, and throughout the placental-gene regions. These data suggested that elements restricted to HSIII-HSV regions and each individual PGR might be sufficient for activation of the hCS genes. This model was tested by comparing hCS transgene expression in the placentas of mouse embryos carrying a full hGH cluster to that in placentas in which the HSIII-HSV region was directly linked to the individual hCS-A PGR unit. The findings indicate that the HSIII-HSV region and the PGR units, although targeted for initial chromatin structural modifications, are insufficient to activate gene expression and that this process is dependent on additional, as-yet-unidentified chromatin determinants.

Growth hormone locus expands and diverges after the separation of New and Old World Monkeys

While most mammals including the prosimians have a single copy of the growth hormone (GH) gene, anthropoids possess a cluster of GH-related genes. Throughout the evolution of the main anthropoid groups [New World Monkeys (NWM), Old World Monkeys (OWM), and apes], two features stand out of the GH loci. The first is the appearance of chorionic somatommamotropin hormone (CSH) genes within the OWM lineage and the second is the expansion of the loci intergenic regions in the OWM and apes. In relation with this loci expansion, the NWM possess intergenic regions of homogeneous lengths (3.5 kb). In contrast, heterogeneous lengths (6 and 13 kb) have been reported for species of the OWM. At the present, none of the OWM genomic GH loci organizations have been described. Here, we report the genomic organization of the GH locus in the rhesus monkey, this locus has six GH-related genes separated by five intergenic regions. The 5' end gene (GH-1) encodes for the pituitary GH and is followed by CSH-1, GH-2, CSH-2, CSH-3 and CSH-4 genes. The five intergenic regions have heterogeneous lengths and also present more or less the same Alu distribution as the human GH locus. To analyze the events that contributed to the extension of the intergenic regions of the GH locus and the emergence of the regulatory elements, the five GH locus intergenic regions of the spider monkey (NWM) were sequenced. The results of comparing the loci from both species suggest that the long intergenic regions (13 kb) of the rhesus GH locus share a common ancestor with the 3.5 kb intergenic regions of the spider monkey. However, the observed increased length of the former is due to an insertion (approximately 8.7 kb) at their 3' end. Interestingly in this insert, we discovered a DNA element resembling the enhancer of the CSH genes of the human GH locus. On the other hand, we observed that the short intergenic regions (6 kb) increased by a different recombination event.

Aspects of placental growth hormone physiology

Placental growth hormone (PGH) has been known for 20 years. Nevertheless, its physiology is far from understood. In this review, basal aspects of PGH physiology are summarised and put in relation to the highly homologous pituitary growth hormone (GH). During normal pregnancy, PGH progressively replaces GH and reach maximum serum concentrations in the third trimester. A close relationship to insulin-like growth factor (IGF)-I and -II levels is observed. Furthermore, PGH levels are positively associated to fetal growth. The potential importance of growth hormone receptors and binding protein for PGH effects is discussed. Finally, the review outlines current knowledge of PGH in pathological pregnancies.

Regulation of the human growth hormone gene family: possible role for Pit-1 in early stages of pituitary-specific expression and repression

The somatic cells of a multicellular organism contain an identical complement of genes that need to be expressed specifically and appropriately to allow the normal development and functions associated with an organism. In the eukaryotic cell nucleus, genes are packaged with nucleoprotein histones into chromatin. The human growth hormone (GH)/chorionic somatomammotropin (CS) gene family offers an excellent model to study the relationship between chromatin structure and transcription factor binding in terms of tissue-specific gene expression. The GH/CS gene family consists of five genes (GH-N, GH-V, CS-A, CS-B and CS-L), contained in a single locus on chromosome 17. Although they share approximately 94% sequence similarity, GH-N expression is restricted to pituitary somatotropes while the four placental GH/CS genes are expressed in the villus syncytiotrophoblast. Appropriate expression in vivo is dependent on remote sequences found 14-32 kb upstream of GH-N in the loci of adjacent genes, and these sequences are characterized by five (I-V) nuclease-hypersensitive sites (HS). Pituitary-specific factor Pit-1 binds at HS I/II and plays an essential role in chromatin remodeling and GH-N expression; however, the processes that lead to HS I/II accessibility are unknown. We discuss the possibility that Pit-1-driven remodeling at HS III may precede that at HS I/II in the pituitary. Also, in pituitary chromatin, all five GH/CS genes share similar nuclease sensitivity, suggesting that the conformation of the placental genes is not inhibitory to transcription. Given that the promoters of both GH-N and the placental GH/CS genes contain Pit-1-binding sites, possible mechanisms to restrict placenta GH/CS promoter activity in the pituitary are discussed, including active repression via P sequences located upstream of each of the placental GH/CS genes. Positively or negatively influencing those components known to be important for pituitary transcription may link epigenetic events to key transcription factors in the overall picture of tissue-specific control of gene expression.

Expansion and divergence of the GH locus between spider monkey and chimpanzee

Growth hormone (GH) has been previously described as showing distinct evolutionary stories between primates and other mammals. A burst of changes and successive amplification events took place in the primate lineage giving rise to a multigene family in the three Anthropoidea lineages. Polymerase chain reaction (PCR) was used to obtain the genes and the intergenic regions comprising the GH loci of the spider monkey (Ateles geoffroyi), a New-World primate, and of the chimpanzee (Pan troglodytes), an ape. The intergenic sequences of both species were screened by hybridization to detect copies of the Alu family, which have been implicated in the formation of the human GH locus. The GH locus of the spider monkey contains at least six GH-related genes, four of them were cloned. Likewise, five short intergenic sequences of approximately 3 kb were amplified and cloned. On the other hand, in the chimpanzee four new placental lactogen (PL) genes as well as four intergenic regions were amplified. Consequently, in this ape, six genes (two GHs, previously obtained, and four PLs) are clustered, separated by intergenic sequences of different lengths (two short ones of about 5 kb, and at least two long ones between 9 and 13 kb). The presence of Alu sequences within the intergenic regions of both GH loci corroborates the current hypothesis that they acted as a driving force for the locus expansion. GH sequence comparisons reveal that several gene-conversion events might have occurred during the formation of this genome region, which has undergone independent evolution in the three Anthropoidea branches. To establish the GH's evolutionary history may prove to be a difficult task due to these gene-conversion events.

Activation of the human GH gene cluster: roles for targeted chromatin modification

The cluster of genes encoding the human growth hormone (GH) contains an array of five highly related genes. From 5' to 3' these are: GHN, CSL (encoding chorionic somatomammotropin-like gene), CSA, GHV (encoding GH-variant gene) and CSB. These five genes are expressed in mutually exclusive tissue distributions, GHN in pituitary somatotropes and the remaining four genes in placental villous syncytiotrophoblasts. The onset of GH expression during development is dependent upon epigenetic modifications at the GH locus under the control of its distal locus control region (LCR). A clear understanding of these normal epigenetic controls on the expression of GH could lead to new insights into the development and treatment of isolated GH deficiency in children. This review focuses on the role of the LCR in histone hyperacetylation at the GH locus and subsequent effects on the tissue-specific activation of these genes.

Human placental growth hormone--a review

Placental growth hormone (PGH) is the product of the GH-V gene, predominantly expressed in the syncytiotrophoblast layer of the human placenta. PGH differs from pituitary growth hormone by 13 amino acids and possesses one glycosylation site. It has high somatogenic and low lactogenic activities. In the maternal circulation from 12-20 weeks up to term, PGH gradually replaces pituitary growth hormone, which becomes undetectable. PGH is secreted by the placenta in a non-pulsatile manner. This continuous secretion appears to have important implications for physiological adjustment to gestation and especially in the control of maternal IGF1 levels. PGH secretion is regulated in vitro and in vivo by glucose. Lower maternal levels of PGH are observed in pregnancies with fetal growth retardation. PGH is one example of a trophoblast hormone, which allows maternal metabolic adaptation to pregnancy. In addition, our recent data on its expression in invasive extravillous trophoblasts suggest that the physiological role of PGH might also include a direct influence of this hormone on placental development via an autocrine or paracrine mechanism.

An unusual member of the human growth hormone/placental lactogen (GH/PL) family, the testicular alternative splicing variant hPL-A2: recombinant expression revealed a membrane-associated growth factor molecule

The human growth hormone/placental lactogen (GH/PL) gene cluster consists of five highly-related genes (GH-N, GH-V, PL-L, PL-A, PL-B). This evolutionarily young gene cluster codes for an array of mRNAs and proteins, such as the major 22 k forms (hGH-N/V, identical PL-A and B), 20 k and 17.5 k hGH-N and the recently described 25 k hGH-Delta4, a presumably chimeric molecule. In addition, two longer alternatively spliced, (intron D retaining) mRNAs isoforms, termed PL-A2 and GH-V2, have been described in placenta and testis. To elucidate the role of hPL-A2 in male reproduction and pregnancy, testicular PL-A2 cDNA was cloned in a complementary overlapping 2-way RT-PCR approach to analyze translation, localization and structure/function of this unusual member of the GH/PL growth factor family. Analysis of insect mRNA revealed that intron D-retaining PL-A2 cDNA was expressed without splicing in the baculovirus expression system. Thus, PL-A2 mRNA does not represent a nuclear intermediate splicing product simply co-isolated with the mature RNA, but is a stable mRNA isoform generated by placental/testis-specific splicing factors. Recombinant protein was present in whole cell extracts, and no secreted protein was detected in the supernatant. Immunologically, the N-terminus of the 230 amino acid protein is similar to 22 k hPL-A/B, as determined by hPL-specific monoclonal antibodies. In contrast, the C-terminus shares a hydrophobic region presumably responsible for membrane insertion. By the use of confocal microscopy recombinant hPL-A2 was localized in the cell membrane. Thus, hPL-A2 might exert its function by modulating GH/PL actions or act as an independent growth-regulatory molecule itself and its functions in male reproduction and embryonic development remain to be investigated.

Targeted recruitment of histone acetyltransferase activity to a locus control region

Locus control regions (LCRs) are capable of activating target genes over substantial distances and establishing autonomously regulated chromatin domains. The basis for this action is poorly defined. Human growth hormone gene (hGH-N) expression is activated by an LCR marked by a series of DNase I-hypersensitive sites (HSI-III and HSV) in pituitary chromatin. These HSs are located between -15 and -32 kilobases (kb) relative to the hGH transcription start site. To establish a mechanistic basis for hGH LCR function, we carried out acetylation mapping of core histones H3 and H4 in chromatin encompassing the hGH cluster. These studies revealed that the entire LCR was selectively enriched for acetylation in chromatin isolated from a human pituitary somatotrope adenoma and in pituitaries of mice transgenic for the hGH locus, but not in hepatic or erythroid cells. Quantification of histone modification in the pituitary revealed a dramatic peak at HSI/II, the major pituitary-specific hGH LCR determinant (-15 kb), with gradually decreasing levels of modification extending from this site in both 5'- and 3'-directions. The 5'-border of the acetylated domain coincided with the 5' most hGH LCR element, HSV (-34 kb); and the 3'-border included the expressed hGH-N gene, but did not extend farther 3' into the placenta-specific region of the gene cluster. These data support a model of LCR function involving targeted recruitment and subsequent spreading of histone acetyltransferase activity to encompass and activate a remote target gene.

Structure and transcriptional regulation of the ovine placental lactogen gene

Ovine placental lactogen (oPL), a member of the growth hormone/prolactin gene family, is produced by chorionic binucleate cells at the maternal-fetal interface, and is thought to modulate metabolic processes and enhance fetal growth. We have determined that the oPL gene contains five exons and four introns, and the transcriptional start site was mapped 91 bp 5' of the initiation codon (AUG). An additional 4.5 kb of 5'-flanking sequence was sequenced and used for transient transfection analysis in human (BeWo) and rat (Rcho-1) choriocarcinoma cell lines to examine trophoblast cell-specific activity. Trophoblast cell-specific transactivation of the reporter gene was conferred by the proximal 1. 1 kb of oPL gene 5'-flanking sequence. Transfection of deletion constructs derived from the 1.1 kb of 5'-flanking sequence resulted in varying profiles of transactivation between the two choriocarcinoma cell lines, but maximal activation in both cell lines resided within the proximal 383 bp of oPL gene 5'-flanking sequence. DNase I protection analysis using ovine chorionic binucleate cell nuclear protein, identified 19 footprints within the 1.1-kb sequence, six of which are located within the 383-bp region. Electrophoretic mobility-shift assays and mutational analysis identified two functional GATA (-67, -102) sequences as transactivators of the oPL gene. However, a previously undefined element (GAGGAG) residing at -338 and -283 is required for full transactivation, and mutation of either significantly reduces reporter activity. In addition, an AP-2 site (-58) and an E-box (-163) were identified and may coordinate oPL transactivation. Transcriptional regulation of human and rodent PL genes has been previously characterized, and our results indicate that tissue-specific regulation of oPL expression may result from cis-acting elements in common with human and rat genes expressed within the placenta. However, our data indicate that regulation of oPL also results from novel cis-acting elements.

The testis-specific expression pattern of the growth hormone/placental lactogen (GH/PL) gene cluster changes with malignancy

Growth hormone (GH) and placental lactogen (PL) gene transcription patterns in testicular germ cell tumors (GCT) and normal testicular tissue were comparatively investigated to identify GH/PL gene products associated with the development of GCT. This was done by nondiscriminative reverse transcriptase-polymerase chain reaction (RT-PCR), amplifying all major transcripts of any of the 5 GH/PL genes--GH-N(ormal), GH-V(ariant), PL-A, PL-B, PL-L(ike)--and subsequent analytical restriction enzyme analyses of 5'-end radioactively labeled cDNA. Surprisingly, all nonseminomatous GCT (NSGCT; n = 9) expressed GH-N, PL-A/B, and PL-L transcripts (9 of 9). Seminoma (n = 7) showed a distinctly unique pattern of GH-N and PL-A/B. GH-V products, which are hallmarks of the normal healthy testis, were not detected in any testicular cancer specimen (0 of 16). The fact that both seminomatous and NSGCT showed alterations in the same gene cluster indicates a pathogenetic relationship. Two choriocarcinoma cell lines of conceptus origin, BeWo and JAR, clearly differing from the male counterparts, exhibited a placental-derived pattern of PL-A/B and GH-V. Obviously, profound differences exist between conceptus and male germ cell GH/PL gene cluster transcription. In summary, the unique testicular pattern of GH/PL gene expression changes significantly and in directed ways with malignancy. Loss of GH-V gene expression in testicular GCT compared with normal testis and loss (seminoma) or mutation (NSGCT) of PLL gene products might have significance in terms of the relationship between these tumors and for testicular GCT development.

Physical linkage of the human growth hormone gene family and the thyroid hormone receptor interacting protein-1 gene on chromosome 17

A P1 cloned insert of about 85.5 kilobases (kb) was isolated, containing four members of the human growth hormone/chorionic somatomammotropin (GH/CS) gene family and the thyroid hormone receptor interacting protein (TRIP-1) gene. The presence of the CS-like, CS-A, GH-variant and, most downstream, CS-B gene was confirmed by DNA blotting and sequence analysis. The TRIP-1 gene was detected 40 kb downstream of the CS-B gene and in the reverse transcriptional orientation to all the GH/CS genes. The TRIP-1 gene is highly homologous to the SUG-1 gene in yeast and is evolutionarily conserved among several species. Based on the common location of the GH and TRIP-1 (or homologue) genes on the same chromosome in the human, pig and rat genomes, we suggest that these loci are physically linked. Previously, it was reported that a muscle-specific sodium channel (SCN4A) gene is located immediately upstream of the pituitary growth hormone (GH-N) gene, and is linked to the GH gene locus in both humans and rats. This suggests a further linkage between the SCN4A, GH and TRIP-1 loci. Also, deoxyribonuclease hypersensitive sites have been reported in and around these loci and were associated with an important locus control region for the GH/CS genes. Unlike the GH/CS genes, we show, using reverse transcriptase-polymerase chain reaction that the TRIP-1 gene is expressed ubiquitously and, through RNA blotting, as a 1.4-kb transcript. This implies an open and active chromatin structure. The possible effect of this structure on the adjacent human GH/CS gene locus is discussed.

Growth hormone and placental lactogen: biology, medicine and biotechnology

Molecular cloning gave us access to the gene members of the human growth hormone and placental lactogen multigene family. Genomic sequencing provided clues for the understanding of the origin, functioning and regulation of this family. It has also allowed us to develop new diagnostic approaches for deficiencies of these hormones and to make new biotechnological contributions.

Human placental growth hormone

Placental growth hormone is the product of the GH-V gene specifically expressed in the syncytiotrophoblast layer of the human placenta. Placental growth hormone differs from pituitary growth hormone by 13 amino acids. It has high somatogenic and low lactogenic activities. Assays by specific monoclonal antibodies reveal that in the maternal circulation from 15 to 20 weeks up to term placental growth hormone gradually replaces pituitary growth hormone, which becomes undetectable. It is secreted by the placenta in a nonpulsatile manner. This continuous secretion appears to have important implications for physiologic adjustment to gestation and especially in the control of maternal insulin-like growth factor-I levels. Placental growth hormone secretion is inhibited by glucose in vitro and in vivo and is significantly decreased in the maternal circulation in pregnancies with intrauterine growth restriction. Placental growth hormone does not appear to have a direct effect on fetal growth because this hormone is not detectable in the fetal circulation. However, the physiologic role might also include a direct influence on placental development through an autocrine or paracrine mechanism, as suggested by the presence of specific growth hormone receptors in this tissue.

Both pituitary and placental growth hormone transcripts are expressed in human peripheral blood mononuclear cells (PBMC)

The hGH-V gene codes for a variant of human pituitary growth hormone (hGH-N) named placental growth hormone (hPGH). hPGH shares 93% amino acid identity with hGH-N. Until now the hGH-V gene was considered to be exclusively expressed in human placenta, where it replaces maternal circulating hGH-N at the end of pregnancy. In this study we investigated by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis hGH-N, and hGH-V, gene expression in PBMC in men, women and pregnant women. We have demonstrated that hGH-N and hGH-V transcripts are simultaneously produced by PBMC in both men and women as well as pregnant women. The PBMC of a PIT-1-negative woman expressed only the hGH-V transcript, but not the hGH-N one as expected. In conclusion, hGH-V mRNA is expressed by cells other than the syncytiotrophoblast, is not regulated by PIT-1, and may be involved in immune regulation, as is pituitary GH.

The rat growth hormone and human cellular retinol binding protein 1 genes share homologous NF1-like binding sites that exert either positive or negative influences on gene expression in vitro

High levels of expression for the rat growth hormone (rGH) gene are restricted to the somatotroph cells of the anterior pituitary. Previously, we have shown that rGH cell-specific repression results in part from the recognition of negatively acting silencers by a number of nuclear proteins that repress basal promoter activity. Examination of these silencers revealed the presence of binding sites for proteins that belong to the NF1 family of transcription factors. Indeed, proteins from this family were shown to bind the rGH proximal silencer (designated silencer-1) in in vitro assays. Furthermore, this silencer site is capable of repressing chloramphenicol acetyltransferase (CAT) gene expression driven by an heterologous promoter (that of the mouse p12 gene), even in pituitary cells. Recently, we identified in the 5' untranslated region of the gene encoding human cellular retinol binding protein 1 (hCRBP1) a negative regulatory element (Fp1) that also bears an NF1 binding site very similar to that of rGH silencer-1. However, although deletion of Fp1 in the hCRBP1 gene yielded increased CAT activity, pointing toward a negative regulatory function exerted by this element, its insertion upstream of the p12 basal promoter results in an impressive positive stimulation of CAT gene expression. By exploiting NaDodSO4 gel protein fractionation and renaturation, we identified a 40-kD nuclear protein (designated Bp1) present in GH4C1 cells that binds very strongly to rGH silencer-1 but only weakly to hCRBP1 Fp1. Similarly, we also detected a 29-kD nuclear factor (designated Bp2) that recognizes exclusively the Fp1 element as its target site, therefore suggesting that different, but likely related, proteins bind these homologous elements to either activate or repress gene transcription. Although they bind DNA through the recognition of the NF1-like target sequence contained on these elements, competition and supershift experiments in electrophoretic mobility shift assays provided evidence that neither of these proteins belong to the NF1 family.

Organ-specific expression pattern of the human growth hormone/placental lactogen gene-cluster in the testis

In addition to testosterone, the essential paracrine factor for spermatogenesis, a number of potential auto/paracrine regulatory substances such as beta-endorphins, enkephalins, chorionic gonadotropin beta, growth hormone-releasing hormone (GHRH) and insulin-like growth factor I (IGF-I) have been identified in the testis of various mammalian species. The latter findings prompted us to investigate a possible eutopic production of GH, placental lactogen (PL) and PRL in human testes. Specific expression of testicular GH/PL mRNA (n = 20) was shown by reverse transcription-polymerase chain reaction (RT-PCR) using a pair of primers designed to non-selectively amplify any transcript of the five GH/PL genes (GH-N, GH-V, PL-A, PL-B, PL-L). In contrast to the classical sites of production, the pituitary (exclusively GH-N transcripts) and the placenta (PL-A/B > 99%, GH-V < 1%), radioactive semiquantitative restriction enzyme analysis of the PCR-products revealed, that the testis has its own organ-specific pattern of GH/PL gene expression: PL-A/B > GH-V > or = PL-L = GH-N. All three organs express the single PRL gene, and testis and placenta show the alternative splice variant GH-V2. Immunological analyses by immunofluorometric assays for hPL-A/B, hGH-N and hPRL, demonstrated significant amounts of protein hormones in all testicular cytosolic homogenates (means: hPL 1.0 ng/g, hGH 5.1 ng/g and hPRL 58.7 ng/g tissue wet weight). Most noteworthy, hPL serum levels in an elderly age-matched healthy subjects (n = 18) were < 0.02 ng/ml. The concept of purely endocrine functions of placental and pituitary-derived GH/PL needs to be reassessed, since human testicular synthesis of these molecules suggest auto/paracrine functions in the male reproductive tract.

Nuclease sensitivity of the human growth hormone-chorionic somatomammotropin locus in pituitary and placenta suggest different mechanisms for tissue-specific regulation

The five human growth hormone (GH) and chorionic somatomammotropin (CS) genes are located at a single locus on chromosome 17. These genes share extensive nucleotide sequence similarity (approximately 94%) even in their flanking DNA, yet GH-N is expressed efficiently in the pituitary under the control of the pituitary-specific factor GHF-1/Pit-1 and the remaining CS-A, CS-B, CS-L and GH-V genes are transcriptionally active in the placenta. Despite this specificity in vivo, a truncated CS-A promoter can bind GHF-1/Pit-1 and allow CS-A promoter activity in pituitary cells in vitro. With a view to assessing whether the placental genes of the GH/CS locus possess a different chromatin structure in the pituitary and are, thus, less transcriptionally active than the GH-N gene, we have compared the DNAase I sensitivity of GH/CS in isolated pituitary and placenta cell nuclei. Our data indicate that these genes are equally sensitive in isolated human pituitary nuclei. By contrast, the CS-A, CS-B and CS-L genes were significantly (P < 0.05) more sensitive than the GH-N gene in isolated human placenta nuclei. Although just not significant, the GH-V gene was slightly more sensitive than the GH-N gene. This pattern was also seen with nuclei from human choriocarcinoma BeWo and JEG-3 cells, which express low and extremely low levels of CS RNA, respectively, but was distinct from the pattern observed in the non placental human cervical carcinoma HeLa cell line. These data indicate that the inactivity of the CS genes in the pituitary does not correlate with a 'closed' chromatin structure. However, they are consistent with a role for a more 'open' chromatin conformation in placenta-specific expression, but not necessarily high levels of transcriptional activity.

Control of growth hormone synthesis

A large body of research, primarily in the rodent and human species, has elucidated many of the details regarding the control of GH synthesis and release. Cell type-specific transcriptional control has been identified as the main mechanism of the somatotroph-specific expression of GH. The recent detailed analysis in rodents and humans of a highly specific transcriptional activator protein, PIT-1, has opened several new areas of study. This is especially true for research in the farm animal species, where PIT-1 has been cloned and its binding elements on the GH gene are being investigated in a number of economically important species. Genetic and biochemical analyses of PIT-1 and other GH regulators have shown the central role of PIT-1 not only in the cell-autonomous stimulation of GH gene transcription, but also in the participation of PIT-1 in the response at the GH gene to exogenous hormones such as RA and TH. PIT-1 has been implicated in the proliferative development of the pituitary itself, in the maintenance of anterior pituitary cell types once cell types are defined, and in the mechanism by which the hypothalamic signal for GH release is transduced. However, PIT-1 by itself does not activate the GH gene, so that additional unknown factors exist that need to be identified to fully understand the cell type-specific activation of the GH gene. In addition, GH gene regulatory elements acting through well-characterized systems such as TH have seemingly different effects; the specific context of the regulatory elements relative to the promoter elements appear to be crucial. These contextual details of GH gene regulation are not well understood for any species and need to be further studied to be able to make predictions for particular elements and regulatory mechanisms across species. The regulation of the pulsatile secretion of GH by GHRH and SRIH is reasonably well understood after the cloning and analysis of the two releasing factors and their receptors. Modification or manipulation of the pathways involved in the regulation of GH secretion is a potential means of enhancing the lean tissue growth of meat animals. However, further understanding of the systems controlling the in vivo release of GH is needed before such manipulations are likely to be productive. Several other research questions regarding the control of GH expression and release remain to be answered. What is the biochemical connection between exogenous signal transduction (i.e., GRH/GHRH-R, TR, ER, RAR) and PIT-1 at the GH gene? Are there additional coactivators or repressors of GH that respond to cAMP levels? Do ubiquitous regulatory factors such as GHF-3 and Zn-15, identified thus far only in the rat, exist in humans or livestock? Zn-15 is expected to be found in many mammalian species, because its recognition sequence between the PIT-1 binding sites is highly conserved across mammals (Figure 2). What is the mechanism causing GH levels to drop during aging? Does PIT-1 expression decrease during the lifespan of animals? Is it possible to increase GH gene expression within target tissues by directing the expression of PIT-1 to these tissues via transgenesis, or are other factors limiting in peripheral tissues so that the lack of PIT-1 expression is not the deciding factor? Finally, is there genetic variation in the expression of GHRH and/or SRIH or in their respective receptors? These questions are relevant to and could be investigated in several of the livestock species.

Role of the transcription factor C/EBP beta in expression of a rat pregnancy-specific glycoprotein gene

Pregnancy-specific glycoproteins (PSGs), which are the major placental proteins, and the carcinoembryonic antigens comprise a subfamily within the immunoglobulin superfamily. To understand the molecular mechanisms underlying the control of PSG expression, we characterized the promoter elements of a rodent PSG gene, rnCGM3, and showed that DNA elements at nucleotides -326 to -185 (PI) relative to the translation start site of rnCGM3 function as a promoter. The rnCGM3 PI promoter contains two placental factor binding sites, PISI and PISII. Both are transcription activation elements. In the present report, we screened a placental expression cDNA library with a rnCGM3-PISII probe (nucleotides -263 to -233) encompassing two overlapping palindromes (TGTTGCTCAACATGTTG) and demonstrated that the PISII-binding factor is C/EBP beta, a leucine zipper family of transcription factor. Gel mobility-shift and transient expression analyses showed that C/EBP beta and C/EBP isoforms, C/EBP alpha and C/EBP delta, bind to the PISII element and trans-activate rnCGM3 gene expression. Deletion of PISII from the rnCGM3 PI promoter greatly reduced the basal as well as the C/EBP-activated rnCGM3 expression. Gel supershift assays demonstrated that C/EBP beta is the placental isoform that binds to the PISII site rnCGM3. Moreover, C/EBP beta is expressed in high levels in the placenta, ovary, liver, lung, heart, and spleen, in contrast to C/EBP alpha, which is expressed primarily in the liver and only low levels in the placenta. Our results demonstrate that C/EBP beta is one of the transcription factors that positively regulate rnCGM3 expression during 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)