Differential placental hormone gene expression during pregnancy in a transgenic mouse containing the human growth hormone/chorionic somatomammotropin locus

The human (h) growth hormone/chorionic somatomammotropin (GH/CS) gene locus presents a unique model to gain insight into the molecular mechanisms that have allowed a closely related family of genes to be expressed in two distinct cell lineages/tissues: pituitary somatotrophs and placental syncytiotrophoblasts. However, studies of external factors that regulate gene expression have been somewhat limited by (i) a lack of human cell lines expressing endogenous GH or CS appropriately; and (ii) the fact that the GH/CS locus is unique to primates and thus does not exist in rodents. In the current study, a transgenic (171 h GH/CS-TG) mouse was generated containing the intact hGH/CS gene cluster and hGH locus control region (LCR) in a 171-kilobase DNA fragment. Pituitary and placental-specific expression of hGH/CS RNA was detected at embryonic day (E) 18.5. Immunostaining of hGH was seen in somatotrophs of the anterior pituitary beginning in late gestation. The presence of hCS protein was detected in the placental labyrinth in trophoblasts functionally analogous to the syncytiotrophoblast of the chorionic villi. This pattern of gene expression is consistent with the presence of essential components of the hGH/CS LCR. Transcript levels for hCS-A, hCS-B and placental hGH-variant increased in 171 hGH/CS-TG placenta during gestation (E11.5-E18.5), as previously observed in human placental development. Throughout gestation, hCS-A RNA levels were proportionately higher, accounting for 91% of total CS RNA by E18.5, comparable to term human placenta. Finally, the previous correlation between the transcription factor AP-2alpha and hCS RNA expression observed in developing primary human cytotrophoblast cultures, was extended to pregnancy in the 171 hGH/CS-TG mouse. The 171 hGH/CS-TG mouse thus provides a model to investigate hGH/CS gene expression, including in pregnancy.

Role for early growth response-1 protein in alpha(1)-adrenergic stimulation of fibroblast growth factor-2 promoter activity in cardiac myocytes

Fibroblast growth factor-2 (FGF-2), a mitogenic, angiogenic, and cardioprotective agent, is released from the postnatal heart by a mechanism of transient remodelling of the sarcolemma during contraction. Both release of FGF-2 and its synthesis can be increased with adrenergic stimulation. We reported previously that FGF-2 synthesis can be regulated at the transcriptional level by alpha-adrenergic stimulation of cultured neonatal rat cardiac myocytes as well as in the adult mouse heart. Examination of the proximal promoter region of both human and rat FGF-2 gene sequences revealed binding sites for the early growth response-1 (Egr-1) protein. Using gel mobility shift assays, we observed a transient increase in a complex between nuclear extracts from neonatal rat cardiac myocytes treated with inducers of Egr-1, including the alpha-adrenergic agonist phenylephrine, angiotensin II, and phorbol ester, and a consensus Egr-1 DNA element. A similar complex was seen with the FGF-2 promoter region -7/+42 as the DNA probe, but not when the Egr-1 element at nucleotides +3/+31 was disrupted. Participation of Egr-1 protein in the complex was confirmed by competition with Egr-1 DNA elements and antibodies. With deletion analysis and transfection of neonatal rat cardiac myocytes, the alpha-adrenergic response was localized to nucleotides -110/+42 of the FGF-2 gene in the context of a hybrid FGF-2/luciferase reporter gene, -110FGFp.luc. Overexpression of Egr-1 increased -110FGFp.luc gene expression, whereas mutation of its Egr-1 element at nucleotides +3/+31 abolished alpha-adrenergic responsiveness. These data indicate that Egr-1 is involved in the alpha-adrenergic stimulation of the FGF-2 promoter region in neonatal cardiac myocytes.

alpha1-Adrenergic stimulation of FGF-2 promoter in cardiac myocytes and in adult transgenic mouse hearts

Fibroblast growth factor (FGF-2), a mitogenic, angiogenic, and cardioprotective agent, is reported to be released from the postnatal heart by a mechanism of transient remodeling of the sarcolemma during contraction. This release can be increased with adrenergic stimulation. RNA blotting was used to assess whether FGF-2 synthesis in neonatal rat cardiomyocytes might also be regulated by adrenergic stimulation. FGF-2 RNA levels were increased after treatment with norepinephrine for 6 h or with the alpha-adrenergic agonist phenylephrine for 48 h. To assess an effect on transcription, neonatal rat cardiomyocytes were transfected with a hybrid rat FGF-2 promoter/luciferase gene (-1058FGFp.luc) and treated with norepinephrine or phenylephrine for 6 or 48 h, respectively. FGF-2 promoter activity was increased two- to sevenfold in an alpha1-specific manner. Putative phenylephrine-responsive elements (PEREs) were identified at positions -780 and -761 relative to a major transcription initiation site. However, deletion analysis of -1058FGFp.luc showed that the phenylephrine response was independent of the putative PEREs, cell contraction, and Ca2+ influx. In transgenic mice expressing -1058FGFp.luc, a significant three- to sevenfold stimulation of FGF-2 promoter activity was detected in the hearts of two independent lines 6 h after intraperitoneal administration of phenylephrine (50 mg/kg). This increase was still apparent at 24 h but was not detected at 48 h posttreatment. Analysis of FGF-2 mRNA in normal mouse hearts revealed accumulation of the 6.1-kb transcript at 24 h. Control of local FGF-2 synthesis at the transcriptional level through adrenergic stimulation may be important in the response to injury as well as in the maintenance of a healthy myocardium.

An A/G-rich motif in the rat fibroblast growth factor-2 gene confers enhancer activity on a heterologous promoter in neonatal rat cardiac myocytes

We have cloned the rat fibroblast growth factor-2 (FGF-2) promoter region including 1058 base pairs (bp) of 5'-flanking DNA. Complete sequencing of this promoter region revealed a 74 bp domain between nucleotides-793 and-720 that was greater than 97% A/G-rich. A repeat of the sequence 5'-AGGGAGGG-3' separated by 11 bp was located at the core of this domain. A 37 bp A/G-rich oligonucleotide containing these AGGG-repeat sequences was synthesised, and tested for function on a minimal herpes simplex virus thymidine kinase (TK) promoter, fused to the firefly luciferase gene (TKp.luc), in transiently transfected neonatal rat cardiac myocytes. Promoter activity was stimulated approximately 3 fold in the presence of AGGG-repeat sequences. This effect was neither tissue or species-specific since TK promoter activity was increased approximately 11 fold in both rat and human glial tumor cells. Four specific complexes (Cl-4) were detected between neonatal rat heart nuclear proteins and the 37 bp A/G-rich oligonucleotide by gel mobility shift assay. Competition with excess unlabelled 37 bp A/G-rich oligonucleotide revealed that two complexes represented very high affinity/specificity interactions (C2 > C4) while Cl and C3 were of lower affinity. As a result, competition with up to a 25 fold molar excess of 37 bp A/G-rich oligonucleotide led to the loss of C2 and C4, and a corresponding and transient increase in the levels of Cl and C3, which themselves were reduced with more competitor oligonucleotide. The AGGG-repeat resembles the 5'-gGGGAGGG-3' sequence previously implicated in the response of the atrial natriuretic factor promoter to the alpha-adrenergic agonist, phenylephrine. Although an additional 1.5 fold increase in TK promoter activity was detected in the presence of the 37 bp A/G-rich oligonucleotide with phenylephrine treatment of transfected myocytes, this effect was not statistically significant. Furthermore, there was no difference in the gel mobility shift (Cl-4) pattern obtained with the 37 bp A/G-rich oligonucleotide and nuclear protein isolated from neonatal rat cardiac myocytes grown in the presence or absence of norepinephrine. These data suggest that the A/G rich sequences in the rat FGF-2 gene 5'-flanking DNA, including the AGGG-repeat, are able to confer stimulatory activity on a promoter in a tissue- and species-independent manner, but alone are not able to induce a significant phenylephrine response in neonatal rat cardiac myocytes.