Growth hormone (GH) exerts sexually dimorphic effects on liver gene transcription that are regulated by the temporal pattern of pituitary GH release, which is intermittent in male rats and nearly continuous in females. To investigate the influence of these GH secretory patterns on intracellular hepatocyte signaling, we compared the pattern of liver nuclear protein tyrosine phosphorylation in male and female rats. An M(r) approximately 93,000 polypeptide, p93, was found to be tyrosine phosphorylated to a high level in male but not female rats. GH, but not prolactin, rapidly stimulated p93 tyrosine phosphorylation in hypophysectomized rats. Intermittent plasma GH pulses triggered repeated p93 phosphorylation, while continuous GH exposure led to desensitization and a dramatic decline in liver nuclear p93. p93 was cross-reactive with two monoclonal antibodies raised to mammary Stat 5, whose tyrosine phosphorylation is stimulated by prolactin. Intermittent GH pulsation translocated liver Stat 5/p93 protein from the cytosol to the nucleus and also activated its DNA binding activity, as demonstrated using a mammary Stat 5-binding DNA element derived from the beta-casein gene. p93 is thus a liver-expressed, Stat 5-related DNA binding protein that undergoes tyrosine phosphorylation and nuclear translocation in response to intermittent plasma GH stimulation and is proposed to be an intracellular mediator of the stimulatory effects of GH pulses on male-specific liver gene expression.

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Intermittent plasma growth hormone (GH) pulses, which occur in male but not female rats, activate liver Stat 5 by a mechanism that involves tyrosine phosphorylation and nuclear translocation of this latent cytoplasmic transcription factor (Waxman, D. J., Ram, P. A., Park, S. H., and Choi, H. K. (1995) J. Biol. Chem. 270, 13262-13270). We demonstrate that physiological levels of GH can also activate Stat 1 and Stat 3 in liver tissue, but with a dependence on the dose of GH and its temporal plasma profile that is distinct from Stat 5 and with a striking desensitization following a single hormone pulse that is not observed with liver Stat 5. GH activation of the two groups of Stats leads to their selective binding to DNA response elements upstream of the c-fos gene (c-sis-inducible enhancer element; Stat 1 and Stat 3 binding) and the ␤-casein gene (mammary gland factor element; liver Stat 5 binding). In addition to tyrosine phosphorylation, GH is shown to stimulate phosphorylation of these Stats on serine or threonine in a manner that either enhances (Stat 1 and Stat 3) or substantially alters (liver Stat 5) the binding of each Stat to its cognate DNA response element. These findings establish the occurrence of multiple, Stat-dependent GH signaling pathways in liver cells that can target distinct genes and thereby contribute to the diverse effects that GH and its sexually dimorphic plasma profile have on liver gene expression. Growth hormone (GH)1 regulates a large number of metabolic and other processes in the liver, primary through its effects on gene transcription. GH exerts both stimulatory and inhibitory effects on the expression of a wide range of liver gene products, including cytochrome P450 (1, 2), glutathione S-transferase (3), and sulfotransferase enzymes involved in steroid and drug metabolism (4), in addition to several cellsurface receptors (5, 6), including GH receptor (7). Hepatic secretory products, such as insulin-like growth factor 1, serine protease inhibitor Spi 2.1 (8), and various urinary proteins (9, 10), are also expressed in a GH-dependent manner. Studies carried out in rodents demonstrate that many, although not all, of the effects of GH on liver gene expression are sex-dependent. This sex dependence is a direct consequence of a striking differential response of individual target genes to GH, depending on whether hepatocytes are stimulated by the intermittent plasma pulses of GH that are characteristic of adult male rats or whether the cells are exposed to GH on a more continual basis, as occurs in adult female rats. Prototypic examples of this sex-dependent GH regulation are the cytochrome P450 genes CYP2C11 and CYP2C12, which are transcribed in a male-and female-specific manner, respectively, in adult rat liver in direct dependence on the plasma GH profile (11,12). By contrast, other effects of GH, in particular the acute stimulation of insulin-like growth factor 1 (13), c-fos (14), and serine protease inhibitor (Spi 2.1) gene expression in liver (8), exhibit little or no sex dependence...

Cytolytic hemolysin, a gene product of vvhA, is a putative virulence factor of the pathogenic bacterium Vibrio vulnificus. We have previously shown that hemolysin production is repressed by adding glucose to culture media and that production can be restored by adding cAMP. In this study, hemolysin activity and the level of vvh transcript were determined to reach a maximum in late exponential phase and were repressed when cells entered stationary phase. Northern blot and primer extension analyses revealed that vvhA is cotranscribed with a second gene, vvhB, located upstream of vvhA. Transcription of the vvhBA operon begins at a single site and is under the direction of a single promoter, P vvh . A crp null mutation decreased hemolysin production and the level of vvhBA transcript by reducing the activity of P vvh , indicating that the P vvh activity is under the positive control of cAMP receptor protein (CRP). A direct interaction between CRP and the regulatory region of the vvhBA operon was demonstrated by gel-mobility shift assays. The CRP binding site, centered at 59.5 bp upstream of the transcription start site, was mapped by deletion analysis of the vvhBA promoter region and confirmed by DNase I protection assays. These results demonstrate that the vvhBA expression is activated by CRP in a growth-dependent manner and that CRP exerts its effects by directly binding to DNA upstream of P vvh .