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P J Fuller

Publications and source records attributed to P J Fuller.

At least 19 recordsLinked to original sources
PubMed2000

Rapid upregulation of serum and glucocorticoid-regulated kinase (sgk) gene expression by corticosteroids in vivo.

The molecular mechanisms by which corticosteroids regulate epithelial sodium transport remain to be fully elucidated. Expression of the serum and glucocorticoid-regulated kinase (sgk) has recently been reported to be regulated acutely by corticosteroids in the amphibian A6 cell line and in cortical collecting tubule cells in vitro. In order to extend this observation to a mammalian system in vivo, the acute response of the sgk gene to a single parenteral dose of aldosterone or dexamethasone was examined in the rat kidney and distal colon. The sgk mRNA levels were significantly elevated by both steroids by 30 min in the distal colon, reaching a peak at 2 h. A more modest increase in sgk mRNA levels was also seen in the kidney in response to both steroids. In both tissues, sgk mRNA has a very short half-life. As for other corticosteroid-regulated genes, the response appears to be mediated by both the mineralocorticoid and glucocorticoid receptors. The response to aldosterone in the distal colon in the presence of cycloheximide was superinduced, strongly suggesting that this is a primary response. The responses to both adrenalectomy and carbenoxolone sodium treatment suggest that the observed responses to corticosteroids can occur in the physiological range of endogenous circulating corticosteroids. These studies provide strong evidence that sgk is an aldosterone-induced gene in vivo in a mammalian system.

Aldosterone↗
PubMed2000

Acute differential regulation by corticosteroids of epithelial sodium channel subunit and Nedd4 mRNA levels in the distal colon.

The molecular mechanisms by which corticosteroids affect fluid and electrolyte balance have yet to be fully elucidated. The apical amiloride-sensitive electrogenic epithelial sodium channel (ENaC) has been shown to have a central role in corticosteroid-mediated sodium transport in the distal colon. The acute response of the alpha-, beta- and gammaENaC subunit genes to a single parenteral dose of aldosterone or dexamethasone was examined in the rat distal colon in vivo. The response of the Nedd4 gene, whose product is involved in channel turnover, was also examined. Whilst the alphaENaC and Nedd4 genes showed no significant response to either steroid, both the beta- and gammaENaC mRNA levels were increased acutely by both aldosterone and dexamethasone. The gammaENaC mRNA appears to have a very short half-life. Use of the highly selective glucocorticoid receptor agonist RU28362 confirmed that the response was mediated by both the mineralocorticoid and glucocorticoid receptors.

Adrenal Cortex Hormones↗
PubMed2000

Mineralocorticoid action.

The physiology of mineralocorticoid action, particularly with respect to epithelial sodium transport, is well defined. A full understanding of the molecular basis of mineralocorticoid action has however proven to be more elusive. In the last decade insights into structural and functional aspects of the mineralocorticoid receptor combined with emerging details of the components of the mediators of the sodium flux has resulted in a clearer picture. This review focuses on two aspects of these new developments; the mineralocorticoid receptor and putative aldosterone induced proteins.

Aldosterone↗
PubMed2000

Humoral factors in intestinal adaptation.

The small bowel has a remarkable ability to adapt after injury, inflammation or resection. It has long been suggested that humoral factors, particularly enteroglucagon, epidermal growth factor, neurotensin and growth hormone/insulin-like growth factor I, might stimulate bowel growth. Of particular interest is the recent finding that glucagon-like peptide 2 (GLP-2), a product of the gene encoding proglucagon, exerts a trophic effect on the intestinal epithelium via a specific G-protein-coupled receptor. GLP-2 and/or these other trophic peptides might prove to have a role in the treatment of bowel diseases associated with structural or functional loss of the small bowel.

Adaptation, Physiological↗
PubMed2000

Specificity in mineralocorticoid versus glucocorticoid action.

The mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR) share considerable structural and functional homology. Overlapping effects on epithelial sodium transport are observed in vivo; in vitro, both are able to bind and transactivate through a common hormone response element. This has led several investigators to suggest that specificity is conferred primarily by prereceptor mechanisms, and we have addressed this question using both in vitro and in vivo approaches. Although the MR has been regarded as less transcriptionally active than the GR in vitro, significant differences are observed when epithelial rather than fibroblast cell lines are used. These differences are mediated by the N-termini of the receptors. Activation of intracellular signaling pathways differentially modulates MR- versus GR-mediated transactivation. Although these studies identify mechanisms by which specificity may be achieved, they do not prove that this occurs in vivo. Such studies have been limited by an absence of MR-regulated genes. Known candidate aldosterone-responsive genes have been examined in the rat distal colon; the time course and the specificity of the response to a single parenteral dose of corticosteroid has been characterized. The epithelial sodium channel beta and gamma subunit genes are both up-regulated within 60 minutes by either MR or GR activation. Similar responses are observed for the serum and glucocorticoid-regulated kinase and channel-inducing factor genes. All four genes show clear and rapid up-regulation of their mRNA levels by aldosterone, which is paralleled by GR-mediated up-regulation of expression. While they are indeed aldosterone-responsive genes, genes that are uniquely aldosterone-regulated remain to be identified.

Animals↗
PubMed2000

The distribution of cells containing estrogen receptor-alpha (ERalpha) and ERbeta messenger ribonucleic acid in the preoptic area and hypothalamus of the sheep: comparison of males and females.

We have used in situ hybridization to compare the distributions of estrogen receptor alpha (ERalpha) and ERbeta messenger RNA (mRNA)-containing cells in the preoptic area and hypothalamus of ewes and rams. Perfusion-fixed brain tissue was collected from luteal phase ewes and intact rams (n = 4) during the breeding season. Matched pairs of sections were hybridized with sheep-specific, 35S-labeled riboprobes, and semiquantitative image analysis was performed on emulsion-dipped slides. A number of sex differences were observed, with females having a greater density of labeled cells than males (P < 0.001) and a greater number of silver grains per cell (P < 0.01) in the ventromedial nucleus for both ER subtypes. In addition, in the retrochiasmatic area, males had a greater (P < 0.05) cell density for ERalpha mRNA-containing cells than females, whereas in the paraventricular nucleus, females had a greater density (P < 0.05) of ERalpha mRNA-containing cells than males. There was a trend (P = 0.068) in the arcuate nucleus for males to have a greater number of silver grains per cell labeled for ERalpha mRNA. In both sexes, there was considerable overlap in the distributions of ERalpha and ERbeta mRNA-containing cells, but the density of labeled cells within each nucleus differed in a number of instances. Nuclei that contained a higher (P < 0.001) density of ERalpha than ERbeta mRNA-containing cells included the preoptic area, bed nucleus of the stria terminalis, and ventromedial nucleus, whereas the subfornical organ (P < 0.001), paraventricular nucleus (males only, P < 0.05), and retrochiasmatic nucleus (females only, P < 0.05) had a greater density of ERalpha than ERbeta mRNA-containing cells. The anterior hypothalamic area and supraoptic nucleus had similar densities of cells containing both ER subtypes. The lateral septum and arcuate nucleus contained only ERalpha, whereas only ERbeta mRNA-containing cells were seen in the zona incerta. The sex differences in the populations of ER mRNA-containing cells in the ventromedial and arcuate nuclei may explain in part the sex differences in the neuroendocrine and behavioral responses to localized estrogen treatment in these nuclei. Within sexes, the differences between the distributions of ERalpha and ERbeta mRNA-containing cells may reflect differential regulation of the actions of estrogen in the sheep hypothalamus. Low levels of ERbeta mRNA in the preoptic area and ventromedial and arcuate nuclei, regions known to be important for the regulation of reproduction, suggest that ERbeta may not be involved in these functions.

Animals↗
PubMed2000

Estrogen receptor isoform gene expression in ovarian stromal and epithelial tumors.

The factors involved in the pathogenesis of ovarian cancers remain unclear, and the response of these tumors to hormonal therapy is limited. The identification of a second estrogen receptor gene (ERbeta), expressed predominantly in ovarian granulosa cells, led us to explore its possible role in ovarian cancer, particularly in granulosa cell tumors (GCT). Several isoforms of ERbeta have been identified. We sought to define the patterns of both ERalpha and ERbeta gene expression in a panel of ovarian tumors consisting of GCT and serous and mucinous cystadenocarcinomas as well as in normal ovary. Expression was determined by RT-PCR using gene- and isoform-specific primers and probes combined with Southern blot analysis of the PCR products. Widespread expression of ERalpha was observed in all tumor types, but at relatively low levels. ERbeta is expressed predominantly in GCT, with lower levels in mucinous tumors and very low levels in serous tumors. The ERbeta2 splice variant previously reported in rodents was not observed. Only very low levels of the exon 5, exon 6, and exon 5/6 deletion variants were detected. The C-terminal truncation variant ERbeta(cx), however, exhibited widespread expression across all the tumor types. As ERbeta(cx) has been shown to be a ligand-independent antagonist of ERalpha action, the relative ratios of ERbeta(cx), ERalpha, and ERbeta may influence the response of a tumor to antiestrogen therapy.

Adult↗
PubMed1999

Structural determinants of aldosterone binding selectivity in the mineralocorticoid receptor.

The structural determinants of aldosterone binding specificity in the mineralocorticoid receptor (MR) have not been determined. The MR has greatest sequence identity with the better characterized glucocorticoid receptor (GR), which is reflected in their overlapping ligand binding specificities. There must be subtle sequence differences that can account for the MR-specific binding of aldosterone and the shared binding of cortisol. To characterize ligand binding specificity, chimeras were made between the human MR and GR ligand-binding domains (LBDs). Three points were chosen as break points to generate a total of 16 different constructs. These chimeric LBDs were placed in a human GR expression vector containing the GR DNA-binding and N-terminal domains and assayed by co-transfection into CV-1 cells with the mouse mammary tumor virus-luciferase reporter plasmid. Binding of [(3)H]aldosterone and [(3)H]dexamethasone was also measured. All of the constructs that are potently activated by aldosterone contain amino acids 804-874 of the MR. The results of the ligand binding experiments using [(3)H]aldosterone were consistent with the transactivation assay. Cortisol activation of the chimeras was surprisingly complex. Constructs that are activated by cortisol contain either amino acids 804-874 and 932-984 of the MR or amino acids 598-668 and 726-777 of the GR. However, all of the chimeras retained the ability to bind the synthetic glucocorticoid [(3)H]dexamethasone, and cortisol was able to displace [(3)H]dexamethasone binding, suggesting that the differential effects of cortisol on transcriptional activation are caused by an effect that occurs downstream of ligand binding. These results identify a subregion of the MR LBD that confers specificity of aldosterone binding, which contrasts with cortisol binding where differential effects between chimeras appear to be mediated by interactions distal to ligand binding.

Aldosterone↗
PubMed1999

Inhibin subunit gene expression in ovarian cancer.

OBJECTIVE(S): Granulosa cell tumors (GCT) and mucinous cystadenocarcinoma of the ovary are associated with elevated circulating levels of immunoreactive inhibin. Measurement of serum inhibin levels provides a useful tumor marker in the management of ovarian tumors. Inhibin is a dimeric ovarian glycoprotein hormone consisting of one alpha and one of two beta subunits. The beta subunits can dimerize to form activin. Activin is bound and its action modulated by another gonadal peptide, follistatin. In this study the patterns of expression of the three inhibin subunit genes, the follistatin gene, and the activin receptor type II gene have been determined. METHODS: Gene expression was analyzed in RNA prepared from 16 primary ovarian tumors using reverse transcriptase-polymerase chain reaction (RT-PCR). Gene-specific primes were used for RT-PCR; the products were analyzed by Southern blot analysis with gene-specific 32P-labeled probes. RESULTS: Widespread expression of these genes was found in all of the tumor types examined. Abundant expression of the inhibin alpha subunit gene was observed in the GCT and to a lesser extent in the mucinous and serous tumors. beta subunit expression was also present in the GCT and to a lesser extent in the other tumors. Widespread expression of both the activin receptor type II and the follistatin genes was also observed. CONCLUSIONS: Expression of the inhibin subunit genes in GCT and some epithelial tumors confirms that these tumors are the source of the increased immunoreactive inhibin seen in the circulation of patients with ovarian tumors. Expression of the activin receptor type II and follistatin genes suggests a paracrine role for activin in these tumors which may be modulated by follistatin, particularly in the GCT.

Activin Receptors, Type II↗
PubMed1999

mRNA levels of dipeptidyl peptidase IV decrease during intestinal adaptation.

BACKGROUND: Glucagon-like peptide 2 (GLP-2) has recently been shown to be a potent enterotrophic factor that may mediate mucosal hyperplasia during intestinal adaptation. The intestinal brush-border protease dipeptidyl peptidase IV (DPP IV) cleaves GLP-2 to an inactive form. It has been postulated that DPP IV activity limits the enterotrophic activity of GLP-2 in rats and humans. Massive small bowel resection (MSBR) in rats is an animal model of intestinal adaptation that has been used successfully to characterize factors involved in the modulation of adaptation. METHODS: Total RNA was extracted from normal terminal ileum or terminal ileum post-MSBR from Sprague-Dawley rats which were sacrificed 2, 4, and 7 days postresection. A partial rat DPP IV clone was isolated by reverse transcription polymerase chain reaction, and Northern blot analysis of rat DPP IV mRNA levels in normal small bowel and small bowel post-MSBR was performed. RESULTS: Within normal small bowel, DPP IV mRNA levels were greatest in the terminal ileum; levels in the duodenum and jejunum were approximately 50% of those in the terminal ileum. DPP IV mRNA levels decreased in terminal ileum post-MSBR 2, 4, and 7 days after resection. CONCLUSION: The decreased DPPIV gene expression suggests a novel mechanism by which the effects on mucosal growth of GLP-2 may be further enhanced, and further that GLP-2 may be a more useful therapeutic agent in humans than currently anticipated.

Adaptation, Physiological↗
PubMed1999

Cushing's syndrome secondary to ectopic ACTH secretion from metastatic breast carcinoma.

Breast carcinoma is a rare cause of ectopic ACTH syndrome. There are only two previously reported cases in which ACTH secretion is documented. We describe the case of a 56-year-old woman who presented with clinical and biochemical features of ectopic ACTH syndrome in the setting of metastatic breast carcinoma. Despite aggressive management of her ectopic ACTH syndrome, her course was complicated by opportunistic infection, respiratory failure and death. Immunostaining of the breast metastases for ACTH was positive and in situ hybridization revealed proopiomelanocortin gene expression. This is the first reported case of ectopic ACTH syndrome associated with metastatic breast cancer in which the technique of in situ hybridization has been used to confirm the breast cancer metastases as the source of ectopic ACTH secretion.

ACTH Syndrome, Ectopic↗
PubMed1999

Acute regulation by corticosteroids of channel-inducing factor gene messenger ribonucleic acid in the distal colon.

The molecular mechanisms by which corticosteroids affect fluid and electrolyte balance are unclear. Though glucocorticoid-responsive genes have been identified, genes regulated by aldosterone have not. CHIF (channel-inducing factor gene) is a recently identified gene that is up-regulated in the distal colon by chronic corticosteroid exposure, is expressed in the kidney, and induces a K+-specific current in Xenopus oocytes. The predicted protein shows similarity to gammaNa.K-ATPase, phospholemman, and Mat-8; all seem to be involved in ion transport. CHIF thus presents as a potential aldosterone target gene. In this study, CHIF expression was examined in rats in the acute timeframe of 0.5-4 h after corticosteroid administration. CHIF messenger RNA showed up-regulation by both mineralocorticoid and glucocorticoid receptor agonists in the distal colon, which was not diminished by cycloheximide. Corticosteroid regulation was not observed in the kidney. Basal and induced expression was absent in the lung and in all gastrointestinal tissues except colon, with expression increasing proximal to distal. CHIF is the first gene to show acute regulation by aldosterone and thus encodes a candidate aldosterone-induced protein. In addition, gammaNa.K-ATPase gene expression was found to be very low in colon and significantly higher in kidney. Regulation by corticosteroids was not evident in either tissue.

Adrenal Cortex Hormones↗
PubMed1999

[Inhibin and ovarian cancer].

Previous observations from our laboratory have demonstrated that the levels of immunoreactive inhibin (ir-inh) are elevated in almost all patients with granulosa cell tumors and in the majority of postmenopausal women with mucinous ovarian cancers. The present report confirms these findings in a larger group of post-menopausal women. Immunohistochemistry for the inhibin alpha. beta A and beta B sununits shows predominantly epithelial staining in granulosa cell tumors and in the majority of mucinous cancers. Serous cystadenocarcinomas also frequently show positive staining. Studies seeking to identify G alpha i-2 or FSH receptor mutations have provided negative results in contrast to other reports. Further studies of the roles of the inhibin-related family of peptides in ovarian cancer diagnosis and monitoring are clearly indicated.

Adenocarcinoma, Mucinous↗
PubMed1998

Tissue distribution of rat glucagon receptor and GLP-1 receptor gene expression.

The regulation of glucose metabolism by glucagon and GLP-1 is well established, but novel functions for these and other proglucagon-derived peptides are less well defined. This paper highlights the diversity of both GLP-1 and glucagon activity by studying the tissue distribution of glucagon and GLP-1 receptor gene expression by both Southern blot analysis of RT-PCR products and nuclease protection assays. By Southern blot analysis of RT-PCR products, GLP-1 receptor mRNA was detected in lung, hypothalamus, hippocampus, cerebral cortex, kidney, pancreas, and throughout the gastrointestinal tract. Glucagon receptor expression was detected in liver, kidney, spleen, thymus, adrenal glands, pancreas, cerebral cortex, lung, and throughout the gastrointestinal tract. Nuclease protection assay revealed glucagon receptor expression to be highest in liver and kidney, whereas GLP-1 receptor expression was only detected by protection assay in lung, stomach, and large bowel. Despite previous evidence that other receptors for proglucagon-derived peptides may exist, no evidence of novel receptors or multiple isoforms of the glucagon and GLP-1 receptors was found, indicating that the two cloned receptors may mediate all the effects of proglucagon-derived peptides, or that novel receptors may share less homology with the glucagon and GLP-1 receptors than previously anticipated.

Animals↗
PubMed1998

Inhibin and ovarian cancer.

Previous observations from our laboratory have demonstrated that the levels of immunoreactive inhibin (ir-inh) are elevated in almost all patients with granulosa cell tumours and in the majority of postmenopausal women with mucinous ovarian cancers. The present manuscript confirms these findings in a larger group of postmenopausal women. Immunohistochemistry for the inhibin alpha, betaA and betaB subunits shows predominantly epithelial staining in granulosa cell tumours and in the majority of mucinous cancers. Serous cystadenocarcinomas also frequently show positive staining. Studies seeking to identify G alpha(i-2) or FSH receptor mutations have provided negative results in contrast to other reports. Further studies of the roles of the inhibin-related family of peptides in ovarian cancer diagnosis and monitoring are clearly indicated.

Aged↗
PubMed1998

Cautionary note on the use of end-labelling DNA fragments for detection of apoptosis.

The gastrointestinal epithelum undergoes a continual process of cell renewal which is partly regulated by apoptosis. The process of growth and differentiation is greatly enhanced in the terminal ileum after massive small bowel resection, a well-established model of intestinal adaptation. We have applied the terminal deoxynucleotidyl transferase (TdT)-mediated UTP nick end-labelling (TUNEL) method to establish the role of apoptosis in intestinal adaption in terminal ileum of control animals after small bowel resection. Healing skin wound and lymph node were used as positive control tissue for apoptotic cells. We report that considerable inter-animal variation was observed in the intestinal tissue. We believe that caution is required in the interpretation of TUNEL staining in intestinal tissue and in its use as a specific marker for apoptosis in this setting.

Animals↗
PubMed1998

Intracellular signaling pathways confer specificity of transactivation by mineralocorticoid and glucocorticoid receptors.

The glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR) bind similar ligands and target genes in vitro yet have distinct roles in vivo. With a single exception, known mechanisms conferring specificity have been limited to prereceptor mechanisms. These alone cannot account for specificity, particularly at a transcriptional level. These studies aimed to determine whether receptor-specific transcriptional regulation via physiological modulators of cellular signaling pathways, and MR-, as well as GR-specific interactions, could be demonstrated. By comparing modulation of GR- and MR-mediated transactivation in renal LLC-PK1 cells, we have identified several activators of intracellular signaling pathways that discriminate between the GR and the MR and demonstrate that differential regulation occurs at relatively specific points in the signaling pathway. The phosphatase inhibitor, okadaic acid, and the protein kinase G activator, sodium nitroprusside, stimulate only GR-mediated transactivation, in contrast to modulators of other protein kinase pathways that act in parallel on both receptors. The GR-specific effect of okadaic acid is observed only at doses where both phosphatases 1 and 2A are inhibited. MR-specific modulators include a centrally active alpha-2 adrenergic agonist and the thyroid receptor. Comparison of the interaction between the thyroid receptor and the GR, or the MR, distinguish two types of repression, only one of which is receptor-specific. These studies identify several signal transduction pathways that can differentially activate either the MR or the GR at a transcriptional level and might play physiological roles in conferring MR- or GR-specific regulation.

Adrenergic alpha-Agonists↗