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

The sequence motif CGTCA is critical for binding of a group of cellular transcription factors (ATF, CREB, E4F, and EivF) and for activation of certain Ela-inducible and cyclic AMP (cAMP)-inducible promoters. We have tested different promoter elements containing the CGTCA motif (referred to here as ATF-binding sites) for the ability to function as Ela or cAMP response elements. The adenovirus E4 promoter and the cellular vasoactive intestinal peptide (VIP) promoter responded differently to Ela and cAMP, demonstrating that the activating potential of ATF-binding sites within these promoters is not equivalent. While particular ATFbinding sites were sufficient for the activity of both the E4 (Ela inducibility) and VIP (cAMP inducibility) enhancers, these two enhancers had contrasting effects on Ela-and cAMP-inducible transcription. Thus, the relationship between Ela-and cAMP-inducible transcription is not simply explained by the action of these two inducers through the same promoter elements.Transcriptional activation of eucaryotic genes often allows specific gene expression in response to a variety of physiological and viral inducing agents. Activation occurs, in part, through binding of cellular transcription factors to specific sites within the affected promoter (for reviews, see references 13, 33, 34, and 42) and through protein-protein interactions between activators (35, 38, 51). In this way genes can be targeted for activation according to the particular array of factor-binding sites present in their control regions. It is now apparent that this simple view is unable to explain certain aspects of structure-function relationships for inducible promoters. Of salient interest is the fact that multiple factors (or promoter elements) with similar or identical DNA-binding specificity (or sequence) have different activation potential (12,16,19,25,41,45,48). The subtle mechanisms underlying control of the above factors are central to understanding differential gene activation.Promoter elements containing the sequence motif CGTCA (referred to throughout this paper as ATF-binding sites) have been shown to be critical for Ela inducibility of certain adenovirus early viral promoters (3,7,22,26,27,44) and for cyclic AMP (cAMP)-mediated activation of many neuropeptide promoters (5,9,11,15,28,36,37,43,47). As is the case with other eucaryotic transcriptional control elements (see above), a complex set of activator proteins bind directly to ATF sites (7,10,19,22,31,36 matostatin promoter (36). Of the above polypeptides, CREB (which is likely to correspond to ATF-43) has been directly implicated in activation of the somatostatin promoter by cAMP (36, 50), and ATF (19) and EivF (7) have been shown to function as transcriptional activators in vitro. Beyond this, the functional relationship between polypeptides that bind to ATF sites is unknown. The inability to distinguish most (but not all [7,39]) ATF-binding sites containing the invariant CGTCA motif (2,7,20,23,27,31) together with the effect of mutations on binding of nucl...

Section: Resultsmentioning

confidence: 99%

Distinguishable promoter elements are involved in transcriptional activation by E1a and cyclic AMP.

Lee¹,

Fink²,

Goodman³

et al. 1989

“…Nuclear transcription assays have denmonstrated that thyroid hormones have direct effects on the transcription of both the a(-and 1B-subunit genes in pituitary thyrotropes (40). In addition, cyclic AMP (cAMP) increases the transcription rate of the axand ,B-chorionic gonadotropin genes in placental cells (21), and the cAMP responsiveness of the ox-subunit gene has been shown by gene transfer experiments to reside in its 5'-flanking sequences (8,21,41 mally involved in transcription in order to modify their activity.In the current studies we analyzed two elements important for the expression of the human a-subunit getne. The 5'-flanking region contains a cAMP-responsive enhancer which participates in tissue-specific expression yet mediates cAMP responsiveness in a non-tissue-specific manner.…”

mentioning

confidence: 99%

“…Nuclear transcription assays have denmonstrated that thyroid hormones have direct effects on the transcription of both the a(-and 1B-subunit genes in pituitary thyrotropes (40). In addition, cyclic AMP (cAMP) increases the transcription rate of the axand ,B-chorionic gonadotropin genes in placental cells (21), and the cAMP responsiveness of the ox-subunit gene has been shown by gene transfer experiments to reside in its 5'-flanking sequences (8,21,41). Although cAMP is known to activate cAMP-dependent protein kinase by binding to its regulatory subunit, little is known about the mechanisms by which cAMP influences gene expression.…”

mentioning

confidence: 99%

Tissue-specific enhancer of the human glycoprotein hormone alpha-subunit gene: dependence on cyclic AMP-inducible elements.

Delegeane¹,

Ferland²,

Mellon³

1987

412

222

We identified and characterized elements which confer tissue specificity and cyclic AMP (cAMP) responsiveness to the human glycoprotein a-subunit gene. An enhancer containing an 18-base-pair repeat conferred cAMP responsiveness in a non-tissue-specific fashion. DNase I protection assays revealed DNA-binding factors that bound to this element in both placental and nonplacental cells. It also enhanced the a-subunit promoter in a tissue-specific manner but had a negligible effect on a heterologous promoter. A unique element found upstream of this enhancer had no independent activity but, in combination with the cAMP-responsive enhancet-, distinctly increased the tissue-specific activity of both the a-subunit promoter and a heterologous promoter. A factor that bound to this upstream element was found in placental but not nonplacental cells. We conclude that this novel element acts, perhaps through a specific trans-acting factor, in concert with a cAMP-responsive enhancer to confer tissue specificity to the a-subunit gene.The a-subunit gene of human glycoprotein hormones is expressed coordinately with each of four separate ,B-subunit genes. Their combined products comprise the four glycoprotein hormones: chorionic gonadotropin, luteinizing hormone, follicle-stimulating hormone, and thyroid-stimulating hormone (14,36). These hormones direct the synthesis of several classes of hormones and control aspects of reproductive and metabolic function. They are produced in three separate cell types: placental trophoblasts produce chorionic gonadotropin, pituitary gonadotropes produce folliclestimulating hormone and luteinizing hormone and pituitary thyrotropes produce thyroid-stimulating hormone (36). In each of these cell types, production of the a subunit is regulated differently in coordination with the a subunit with which it becomes associated (16,33,37). For example, thyroid-stimulating hormone expression is induced by thyrotropin-releasing hormone and inhibited by thyroid hormones, while luteinizing hormone and follicle-stimulating hormone are induced by gonadotropin-releasing hormone and inhibited by estrogens (12). Thus, the a-subunit gene must contain regulatory sequences which direct its expression in several different tissues and mediate its differential hormonal responsiveness.Some information is available concerning the mechanisms which control these complex responses. Nuclear transcription assays have denmonstrated that thyroid hormones have direct effects on the transcription of both the a(-and 1B-subunit genes in pituitary thyrotropes (40). In addition, cyclic AMP (cAMP) increases the transcription rate of the axand ,B-chorionic gonadotropin genes in placental cells (21), and the cAMP responsiveness of the ox-subunit gene has been shown by gene transfer experiments to reside in its 5'-flanking sequences (8,21,41 mally involved in transcription in order to modify their activity.In the current studies we analyzed two elements important for the expression of the human a-subunit getne. The 5'-flanking region conta...

“…The molecular basis for placenta-specific expression of the human and equine a-subunit genes has been studied by transfection of human placental trophoblast cell lines that express human chorionic gonadotropin (10,54). The human gene contains a composite enhancer, positioned within 180 bp of the mRNA start site, that confers placental specificity.…”

mentioning

confidence: 99%

GATA-binding proteins regulate the human gonadotropin alpha-subunit gene in the placenta and pituitary gland.

Steger¹,

Hecht²,

Mellon³

1994

173

106

The human glycoprotein hormone ot-subunit gene is expressed in two quite dissimilar tissues, the placenta and anterior pituitary. Tissue-specific expression is determined by combinations of elements, some ofwhich are common and others of which are specific to each tissue. In the placenta, a composite enhancer confers specific expression. It contains four protein-binding sites: two cyclic AMP (cAMP) response elements that bind CREB, a trophoblast-specific element that binds TSEB, and a sequence motif, AGATAA, that matches the consensus binding site for a family of transcription factors termed the GATA-binding proteins. In pituitary gonadotropes, the cAMP response elements remain important for expression, TSEB is absent, and elements further upstream participate in tissue-specific expression. Here we establish a regulatory role for the GATA element in both the placenta and pituitary by demonstrating that a mutation of this element decreases ot-subunit gene expression 15-fold in JEG-3 human placental cells and 2.5-fold in otT3-1 mouse pituitary gonadotropes. In JEG-3 cells, human GATA-2 (hGATA-2) and hGATA-3 are highly expressed and both proteins bind to the ot-subunit gene GATA element. In otT3-1 cells, the GATA motif is bound by mouse GATA-2 (mGATA-2) and an mGATA-4-related protein. Cotransfection of hGATA-2 or hGATA-3 into otT3-1 cells activates the ft-subunit gene threefold. These studies establish a role for the GATA-binding proteins in placental and pituitary ft-subunit gene expression, significantly expanding the known target genes of GATA-2, GATA-3, and perhaps GATA-4.