Antisense oligomers of cfos and cjun block glucocorticoid stimulation of thyrotropin-releasing hormone (TRH) gene expression in cultured anterior pituitary cells

Structural and Functional Analysis of the Differential Effects of c-Jun and v-Jun on Prolactin Gene Expression

The protooncogene c-Jun and its oncogenic isoform v-Jun are members of the activator protein 1 family of transcription factors that have been shown to have differential transcriptional effects that are both promoter specific and cell type specific. Previously, we have demonstrated that whereas c-Jun inhibits pituitary-specific rat prolactin (rPRL) promoter activity, expression of v-Jun stimulates the rPRL promoter in GH4 pituitary cells. In this report, we have conducted an extensive structure-function analysis of c-Jun vs. v-Jun to determine which regions of these proteins are responsible for their differential transcriptional effects in this pituitary model system. We show that isoform-specific responses are mediated by complex interactions between the delta-domain, serine 243, and the amino-terminal transcriptional activation domains. Thus, in contrast to previous reports, no single domain is responsible for the differential transcriptional activities of c-Jun and v-Jun. Mutation of c-Jun serine 243 to phenylalanine and replacement of the c-Jun amino terminus with the corresponding region from v-Jun, thereby removing the delta-domain, are necessary and sufficient to confer a functional switch from the c-Jun-inhibitory to the v-Jun-activating phenotype. Thus, we propose that isoform-specific subdomains in c-Jun and v-Jun dictate discrete interactions with distinct protein partners, which underlie the differential Jun-dependent transcriptional responses of the rPRL promoter.

Cellular distribution and regulation of ghrelin messenger ribonucleic acid in the rat pituitary gland

Ghrelin, a 28-amino-acid acylated peptide, strongly stimulates GH release and food intake. In the present study, we found that ghrelin is expressed in somatotrophs, lactotrophs, and thyrotrophs but not in corticotrophs or gonadotrophs of rat pituitary. Persistent expression of the ghrelin gene is found during postnatal development in male and female rats, although the levels significantly decrease in both cases from pituitaries of 20-d-old rats onward, but at 60 d old, the levels were higher in male than female rats. This sexually dimorphic pattern appears to be mediated by estrogens because ovariectomy, but not orchidectomy, increases pituitary ghrelin mRNA levels. Taking into account that somatotroph cell function is markedly influenced by thyroid hormones, glucocorticoids, GH, and metabolic status, we also assessed such influence. We found that ghrelin mRNA levels decrease in hypothyroid- and glucocorticoid-treated rats, increase in GH-deficient rats (dwarf rats), and remain unaffected by food deprivation. In conclusion, we have defined the specific cell types that express ghrelin in the rat anterior pituitary gland. These data provide direct morphological evidence that ghrelin may well be acting in a paracrine-like fashion in the regulation of anterior pituitary cell function. In addition, we clearly demonstrate that pituitary ghrelin mRNA levels are age and gender dependent. Finally, we show that pituitary ghrelin mRNA levels are influenced by alteration on thyroid hormone, glucocorticoids, and GH levels but not by fasting, which indicates that the regulation of ghrelin gene expression is tissue specific.

The expression of the growth hormone secretagogue receptor ligand ghrelin in normal and abnormal human pituitary and other neuroendocrine tumors

Ghrelin is a recently identified endogenous ligand of the GH secretagogue (GHS) receptor. It was originally isolated from the stomach, but has also been shown to be present in the rat hypothalamus. It is a 28-amino acid peptide with an unusual octanoylated serine 3 at the N-terminal end of the molecule, which is crucial for its biological activity. Synthetic GHSs stimulate GH release via both the hypothalamus and the pituitary, and the GHS receptor (GHS-R) has been shown by us and others to be present in the pituitary. We investigated whether ghrelin messenger ribonucleic acid (mRNA) and peptide are present in the normal human hypothalamus and in normal and adenomatous human pituitary. RNA was extracted from pituitary tissue removed at autopsy and transsphenoidal surgery (n = 62), and ghrelin and GHS-R type 1a and 1b mRNA levels were investigated using real-time RT-PCR. Both ghrelin and GHS-R mRNA were detected in all samples. Corticotroph tumors showed significantly less expression of ghrelin mRNA, whereas GHS-R mRNA levels were similar to those in normal pituitary tissue. Gonadotroph tumors showed a particularly low level of expression of GHS-R mRNA. Immunohistochemistry, using a polyclonal antibody against the C-terminal end of the ghrelin molecule, revealed positive staining in the homolog of the arcuate nucleus in the human hypothalamus and in both normal and abnormal human pituitary. Pituitary tumor ghrelin peptide content was demonstrated using two separate RIA reactions for the N-terminal and C-terminal ends of the molecule. Both forms were present in normal and abnormal pituitaries, with 5 +/- 2.5% octanoylated (active) ghrelin (mean +/- SD) present as a percentage of the total. We suggest that the presence of ghrelin mRNA and peptide in the pituitary implies that the locally synthesized hormone may have an autocrine/paracrine modulatory effect on pituitary hormone release.

Activation of the parapyramidal region in the ventral medulla stimulates gastric acid secretion through vagal pathways in rats

Neurons synthesizing thyrotropin-releasing hormone, substance P and serotonin in the medullary caudal raphe nuclei project to the dorsal vagal complex and play a role in the central vagal regulation of gastric function. Neurons in the parapyramidal region in the ventral medulla share similar biochemical coding and projections as those in the caudal raphe nuclei. The role of the parapyramidal region in the autonomic regulation of gastric acid secretion was investigated in urethane-anesthetized rats. Unilateral microinjection of kainate into the parapyramidal region at 10, 15 and 20 ng induced a dose-related stimulation of gastric acid secretion (net increases: 22.2+/-11.2, 40.5+/-8.5 and 89.8+/-19.4 micromol/60 min, respectively), while injection of vehicle had no effect (net change: -0.1+/-1.4 micromol/60 min). Time-course studies showed a nine-fold peak increase over basal at 30 min after parapyramidal injection of kainate (20 ng) and acid secretion returned to basal level at 70 min. Microinjections of kainate (15-20 ng) outside the parapyramidal region or into the parapyramidal region in vagotomized rats had no effect. Exposure to cold (4 degrees C) for 2 h, which is known to induce vagally mediated gastric secretory and motor responses through medullary thyrotropin-releasing hormone pathways, increased the number of Fos-positive cells in the caudal, middle and rostral parts of the parapyramidal region to 4.3+/-0.4, 9.4+/-0.9 and 18.4+/-1.6/section, respectively, compared with 0.1+/-0. 1, 0.1+/-0.0 and 0.7+/-0.6/section, respectively, in rats maintained at room temperature. Most of the Fos-labeled cells co-expressed pro-thyrotropin-releasing hormone messenger RNA signal and/or were serotonin immunoreactive. These data show that chemical activation of neurons in the parapyramidal region results in a vagal-dependent stimulation of gastric acid secretion and that acute cold exposure activates parapyramidal neurons containing pro-thyrotropin-releasing hormone and/or serotonin, suggesting a potential role of the parapyramidal region, in addition to the caudal raphe nuclei, as medullary sites involved in the vagal regulation of gastric function.