To study the mechanisms that activate expression of the atrial natriuretic factor (ANF) gene during pressure-induced hypertrophy, we have developed and characterized an in vivo murine model of myocardial cell hypertrophy. We employed microsurgical techniques to produce a stable 35-to 45-mmHg pressure gradient across the thoracic aorta of the mouse that is associated with rapid and transient expression of an immediate-early gene program (c-fos/cjun/junB/Egr-1/nur-77), an increase in heart weight/body weight ratio, and up-regulation of the endogenous ANF gene. These responses that are identical to those in cultured cell and other in vivo models of hypertrophy. To determine whether tissue-specific and inducible expression of the ANF gene can be segregated, we used a transgenic mouse line in which 500 base pairs of the human ANF promoter region directs atrial-specific expression of the simian virus 40 large tumor antigen (T antigen), with no detectable expression in the ventricles. Thoracic aortic banding of these mice led to a 20-fold increase in the endogenous ANF mRNA in the ventricle but no detectable expression of the T-antigen marker gene. This result provides evidence that atrial-specific and inducible expression of the ANF gene can be segregated, suggesting that a distinct set of regulatory cis sequences may mediate the up-regulation of the ANF gene during in vivo pressure overload hypertrophy. This murine model demonstrates the utility of microsurgical techniques to study in vivo cardiac physiology in transgenic mice and should allow the application of genetic approaches to identify the mechanisms that activate ventricular expression of the ANF gene during in vivo hypertrophy.In response to diverse stimuli, such as hypertension, valvular heart disease, and endocrine disorders, the myocardium adapts to increased workloads through the hypertrophy of individual muscle cells (for a review, see refs. 1 and 2). Although the signaling mechanisms that mediate the hypertrophic response of cardiac muscle cells remain unclear, transcriptional activation of cardiac target genes, including contractile proteins and embryonic markers, appears to play a pivotal role in this adaptive response (3, 4). In this regard, the reactivation of atrial natriuretic factor (ANF) gene expression in ventricular cells occurs in response to diverse hypertrophic stimuli (genetic, hormonal, volume overload, pressure overload, hypertension, etc.) in multiple species (5-11), including humans, and could be considered one of the conserved features of ventricular cell hypertrophy.To study the transcriptional regulation of cardiac genes, workers in our laboratory (3, 12, 13) and others (14-16) have extensively characterized cultured myocardial cell models in which several features of hypertrophy can be induced after stimulation with defined agents, such as a-adrenergic agonists (3, 12, 14-17) or endothelin 1 (13). In this model, the inducibility of a constitutively expressed contractile protein gene, myosin light chain 2 (MLC-2), is mediat...

Tissue-specific expression of the mammalian FTZ-F1 gene is essential for adrenal and gonadal development and sexual differentiation. The FTZ-F1 gene encodes an orphan nuclear receptor, termed SF-1 (steroidogenic factor-1) or Ad4BP, which is a primary transcriptional regulator of several hormone and steroidogenic enzyme genes that are critical for normal physiological function of the hypothalamic-pituitary-gonadal axis in reproduction. The objective of the current study is to understand the molecular mechanisms underlying transcriptional regulation of SF-1 gene expression in the pituitary. We have studied a series of deletion and point mutations in the SF-1 promoter region for transcriptional activity in alphaT3-1 and L/betaT2 (pituitary gonadotrope), CV-1, JEG-3, and Y1 (adrenocortical) cell lines. Our results indicate that maximal expression of the SF-1 promoter in all cell types requires an E box element at -82/-77. This E box sequence (CACGTG) is identical to the binding element for USF (upstream stimulatory factor), a member of the helix-loop-helix family of transcription factors. Studies of the SF-1 gene E box element using gel mobility shift and antibody supershift assays indicate that USF may be a key transcriptional regulator of SF-1 gene expression.

Tissue-specific expression of the mammalian FTZ-F1 gene is essential for adrenal and gonadal development and sexual differentiation. The FTZ-F1 gene encodes an orphan nuclear receptor, termed SF-1 (steroidogenic factor-1) or Ad4BP, which is a primary transcriptional regulator of several hormone and steroidogenic enzyme genes that are critical for normal physiological function of the hypothalamic-pituitary-gonadal axis in reproduction. The objective of the current study is to understand the molecular mechanisms underlying transcriptional regulation of SF-1 gene expression in the pituitary. We have studied a series of deletion and point mutations in the SF-1 promoter region for transcriptional activity in alphaT3-1 and L/betaT2 (pituitary gonadotrope), CV-1, JEG-3, and Y1 (adrenocortical) cell lines. Our results indicate that maximal expression of the SF-1 promoter in all cell types requires an E box element at -82/-77. This E box sequence (CACGTG) is identical to the binding element for USF (upstream stimulatory factor), a member of the helix-loop-helix family of transcription factors. Studies of the SF-1 gene E box element using gel mobility shift and antibody supershift assays indicate that USF may be a key transcriptional regulator of SF-1 gene expression.

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