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J W Funder

Publications and source records attributed to J W Funder.

At least 73 records · Page 4Linked to original sources
PubMed1995

Several homozygous mutations in the gene for 11 beta-hydroxysteroid dehydrogenase type 2 in patients with apparent mineralocorticoid excess.

Four deleterious mutations are described in the gene for HSD11B2, which encodes the type 2 isoenzyme of 11 beta-hydroxysteroid dehydrogenase (11 beta HSD2). In seven families with one or more members affected by apparent mineralocorticoid excess, this disorder is shown to be the result of a deficiency in 11 beta HSD2. Surprisingly, the patients are all homozygous for their mutation. This results from consanguinity in two families and possibly from endogamy or a founder effect in four of the other five families. The absence of compound heterozygotes remains to be investigated.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1995

The R337C mutation generates a high Km 11 beta-hydroxysteroid dehydrogenase type II enzyme in a family with apparent mineralocorticoid excess.

The 11 beta-hydroxysteroid dehydrogenase type II enzyme (11 beta HSD2) inactivates glucocorticoids in the kidney and thus permits aldosterone to occupy the non-selective mineralocorticoid receptor in epithelial tissues. We have recently described a C to T transition in the HSD11B2 gene which results in an arginine to cysteine mutation (R337C) in the 11 beta HSD2 enzyme in a consanguineous family with three siblings suffering from Apparent Mineralocorticoid Excess (AME). In the present study we have examined the metabolism of cortisol in mammalian cells transfected with plasmids expressing the wild type and mutant enzymes. In whole cells the Km of the normal enzyme was 110nM, while the enzyme containing the R337C mutation displayed a Km of 1010nM. Further experiments revealed that the mutant was totally inactive in cell free preparations, suggesting that it has additional properties which may compromise its activity in whole cells.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1995

Steroids, hypertension and cardiac fibrosis.

Though we normally think of mineralocorticoid receptors as mediating aldosterone action on the kidney and other epithelia, the same receptors are found at comparable levels in non-epithelial tissues such as hippocampus and heart. In all tissues mineralocorticoid receptors have identical, high affinity for aldosterone, corticosterone and cortisol. In tissues such as the heart and hippocampus they are unprotected by the enzyme 11 beta hydroxysteroid dehydrogenase, which converts glucocorticoids to inactive 11-keto congeners; in such tissues mineralocorticoid receptors are thus overwhelmingly occupied by glucocorticoids, reflecting their much higher circulating levels. The epithelial effects of mineralocorticoid receptors and glucocorticoid receptors appear relatively uncomplicated, paralleling findings in cotransfection systems (corticosterone and cortisol, as well as aldosterone, are agonist in mineralocorticoid receptors; activated mineralocorticoid receptors and activated glucocorticoid receptors equivalently transactivate gene expression). In non-epithelial tissues, most notably the brain, the actions (and possible interactions) of mineralocorticoid receptors and glucocorticoid receptors appear much more complex, and are yet to be established in detail. We have recently confirmed and extended the findings of Weber and his colleagues that administration of aldosterone or deoxycorticosterone to uninephrectomized rates drinking 1% NaCl solution for 8 weeks is followed by interstitial and perivascular cardiac fibrosis. Whether or not the effect of corticosteroids on cardiac fibrosis reflects direct actions on cardiac muscle, or other cellular constituents of the heart, there appears to be significant interplay between mineralocorticoid receptors and glucocorticoid receptors, and possible roles for agonist and antagonist occupancy of both receptor types.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Apparent mineralocorticoid excess.

Apparent mineralocorticoid excess is a congenital syndrome of sodium retention and hypertension with suppressed renin and aldosterone and normal cortisol levels. Patients with the syndrome have, however, highly abnormal levels of urinary cortisol to cortisone metabolites, indicating a reduced or absent activity of 11 beta-hydroxysteroid dehydrogenase 2, the enzyme responsible for conversion of cortisol to receptor-inactive cortisone. Very recently, the gene for 11 beta-hydroxysteroid dehydrogenase 2 was cloned, and mutations leading to absent or markedly reduced enzyme activity were found in 10 or 11 patients to date.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1994

Enzymatic regulation of ligands.

Enzymes are clearly important for the biosynthesis of steroid hormones and in their conversion to inactive metabolites for excretion. More recently, in addition to these roles in tissues of origin and disposal, it has become clear that enzymes also have important roles--for steroid and thyroid hormones, and for vitamin A derivatives--in both tissues of passage and target tissues. These actions may be reversible or essentially irreversible, and may activate or inactivate signals, thus affecting both the intensity and specificity of hormone action. In this paper, the involvement of 11 beta-hydroxysteroid dehydrogenase in adrenal steroid action is presented as a case study.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1994

Enzymes and receptors: challenges and future directions.

In many ways, the present paper will cover much of the same ground as those that precede it. As its title suggests, it is an overview--in part to highlight various aspects of the areas which have been discussed, and in part to put a personal view of where the most fruitful avenues for exploration over the next two years lie. It is very clearly not a comprehensive summary of the topic; given the delightful unpredictability of biological advance, there is every likelihood such predictions may prove substantially wrong. On the other hand, nothing ventured, nothing won; and so with this caveat, there follows one man's reckoning of the directions for the immediate future.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1994

Arginine vasopressin (AVP) causes the reversible phosphorylation of the myristoylated alanine-rich C kinase substrate (MARCKS) protein in the ovine anterior pituitary: evidence that MARCKS phosphorylation is associated with adrenocorticotropin (ACTH) secretion.

We have recently shown that AVP causes a protein kinase C (PKC)-dependent increase in ACTH release and biosynthesis in ovine anterior pituitary cells. In these cells, AVP also causes the translocation of PKC from the cytosol to the cell membrane which is maximal at 5 min, but the intracellular events distal to protein kinase C activation that underlie ACTH secretion have not been well characterized to date. Since the MARCKS protein has been implicated in neurosecretion and is phosphorylated by PKC in synaptosomes, studies were carried out to determine whether AVP might cause MARCKS phosphorylation in the ovine anterior pituitary, and to determine whether this phenomenon might be temporally correlated with PKC translocation and the release of ACTH. When cytosolic fractions of rat brain, ovine anterior pituitary, and cultured ovine anterior pituitary cells were incubated with purified PKC, several proteins were phosphorylated including those in the region of 83-85 kDa. After precipitation of the proteins with 40% acetic acid, the 83-85 kDa phosphoproteins were selectively recovered in the acid soluble phase. Phosphopeptide maps of either the 83 or 85 kDa proteins were generated with Staphylococcus aureus V8 protease and revealed 13 and 9 kDa phosphopeptides, which are characteristic of the authentic MARCKS protein. An identical phosphopeptide map was also obtained when the MARCKS protein was selectively extracted from intact 32P-labeled anterior pituitary cells. MARCKS phosphorylation was markedly increased when ovine anterior pituitary cells were exposed to 1 microM phorbol 12-myristate 13-acetate (PMA). When the cells were exposed to 1 microM AVP, MARCKS phosphorylation increased at 15 s and reached the maximal plateau value at 30 s. MARCKS phosphorylation then started to diminish at 2 min, and baseline levels were attained by 10 min. In the same cells, AVP stimulated ACTH release in a biphasic manner-during the first 30 s, there resulted a rapid burst of ACTH secretion that was followed by a slower, but sustained rate of secretion. We conclude that: (1) AVP causes a rapid, and reversible, phosphorylation of the MARCKS protein in the ovine anterior pituitary; (2) since the AVP-induced increase in MARCKS phosphorylation occurs much earlier in these cells than does PKC trans-location, MARCKS phosphorylation may provide a more sensitive index of the onset of PKC activation than the translocation assay; (3) the close temporal association between MARCKS phosphorylation and the rapid early release of ACTH suggests that MARCKS phosphorylation may be involved in the initial intracellular events that underly exocytosis of the hormone.

Adrenocorticotropic Hormone↗
PubMed1994

A comparative study of the role of adenylate cyclase in the release of adrenocorticotropin from the ovine and rat anterior pituitary.

The interaction between corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) is important in the regulation of adrenocorticotropin (ACTH) release from the anterior pituitary (AP). CRF exerts its effect on the AP by activating the adenylate cyclase (AC) complex whereas AVP increases the turnover of phosphatidylinositol. In the rat and in man, CRF is the most potent ACTH secretagogue whereas AVP alone is only a weak agonist. Since recent studies in the sheep indicate a reversal of this order of potency, these studies were undertaken to test the hypothesis that a functional alteration of the AC in the ovine corticotrope might limit the ability of CRF to release ACTH from these cells. When rat AP cells were incubated with CRF, a dose-dependent increase in AC activity was observed. This effect was potentiated either by AVP or PMA, although neither agent alone altered AC activity. In contrast, CRF alone, or in combination with AVP or PMA, did not increase AC activity in ovine AP cells. Both cholera toxin (CT) and pertussis toxin (PT) caused a dose-dependent release of ACTH from rat and ovine AP cells, but the amount of ACTH released from the ovine AP cells by both agents was relatively reduced. In the ovine cells, however, AVP acted synergistically with CT or PT to markedly increase the release of ACTH to levels which approached those obtained when the rat AP cells were exposed to CT or PT alone. Forskolin increased AC activity in AP cells of both species, but to a much lower extent in ovine cells than in the rat cells. However, when the ovine cells were exposed to AVP, the AC response to forskolin became similar to the response observed in the rat cells when incubated with forskolin alone. Forskolin also released significantly less ACTH from the ovine AP cells, but AVP also acted synergistically with forskolin to greatly enhance the amount of ACTH released from these cells. Finally, 8-bromo-cyclic AMP produced a similar release of ACTH from both ovine and rat AP cells. We conclude that: (1) the decreased ability of CRF to increase ACTH release from the ovine AP reflects a net decrease in AC activity and cannot be ascribed to an ovine corticotropic resistance to cAMP; (2) the decreased activity of the ovine corticotropic AC complex may in turn reflect functional alterations at the level of both the G proteins and the catalytic subunit; (3) since AVP causes protein kinase C substrate phosphorylation in the ovine AP, AVP may increase AC activity in this tissue by phosphorylating the G proteins and/or the catalytic subunit.

Adenylyl Cyclases↗
PubMed1994

Arginine vasopressin (AVP) causes the reversible phosphorylation of the myristoylated alanine-rich C kinase substrate (MARCKS) protein in the ovine anterior pituitary: evidence that MARCKS phosphorylation is associated with adrenocorticotropin (ACTH) secretion.

We have recently shown that AVP causes a protein kinase C (PKC)-dependent increase in ACTH release and biosynthesis in ovine anterior pituitary cells. In these cells, AVP also causes the translocation of PKC from the cytosol to the cell membrane which is maximal at 5 min, but the intracellular events distal to protein kinase C activation that underlie ACTH secretion have not been well characterized to date. Since the MARCKS protein has been implicated in neurosecretion and is phosphorylated by PKC in synaptosomes, studies were carried out to determine whether AVP might cause MARCKS phosphorylation in the ovine anterior pituitary, and to determine whether this phenomenon might be temporally correlated with PKC translocation and the release of ACTH. When cytosolic fractions of rat brain, ovine anterior pituitary, and cultured ovine anterior pituitary cells were incubated with purified PKC, several proteins were phosphorylated including those in the region of 83-85 kDa. After precipitation of the proteins with 40% acetic acid, the 83-85 kDa phosphoproteins were selectively recovered in the acid soluble phase. Phosphopeptide maps of either the 83 or 85 kDa proteins were generated with Staphylococcus aureus V8 protease and revealed 13 and 9 kDa phosphopeptides, which are characteristic of the authentic MARCKS protein. An identical phosphopeptide map was also obtained when the MARCKS protein was selectively extracted from intact 32P-labeled anterior pituitary cells. MARCKS phosphorylation was markedly increased when ovine anterior pituitary cells were exposed to 1 microM phorbol 12-myristate 13-acetate (PMA). When the cells were exposed to 1 microM AVP, MARCKS phosphorylation increased at 15 s and reached the maximal plateau value at 30 s. MARCKS phosphorylation then started to diminish at 2 min, and baseline levels were attained by 10 min. In the same cells, AVP stimulated ACTH release in a biphasic manner - during the first 30 s, there resulted a rapid burst of ACTH secretion that was followed by a slower, but sustained rate of secretion. We conclude that: (1) AVP causes a rapid, and reversible, phosphorylation of the MARCKS protein in the ovine anterior pituitary; (2) since the AVP-induced increase in MARCKS phosphorylation occurs much earlier in these cells than does PKC trans-location, MARCKS phosphorylation may provide a more sensitive index of the onset of PKC activation than the translocation assay; (3) the close temporal association between MARCKS phosphorylation and the rapid early release of ACTH suggests that MARCKS phosphorylation may be involved in the initial intracellular events that underly exocytosis of the hormone.

Adrenocorticotropic Hormone↗
PubMed1994

Corticosteroid receptors and the central nervous system.

In mammalian systems, the physiological mineralocorticoid is aldosterone (aldo), and the physiological glucocorticoid cortisol (F), or corticosterone (B) in rats and mice. Receptors (MR) with high affinity for aldo, B and F are found in both epithelia and the central nervous system (CNS); receptors (GR) with lower affinity for F and B, and still lower for aldo, are found in essentially all cells. Both MR and GR bind to and activate canonical pentadecamer response elements in transfected cells and in epithelia, wherein MR aldo, B and F all act as agonists. In vivo, in epithelial cells a low Km, NAD-dependent, 11 beta hydroxysteroid dehydrogenase (11 beta OHSD) converts B and F, but not aldo, to receptor-inactive 11-keto congeners, thus allowing aldo to occupy epithelial MR and produce sodium retention. The CNS differs markedly in terms of MR/GR in a number of ways: (i) most but not all MR in the CNS are functionally unprotected, despite the presence of a low Km, NADP-preferring 11 beta OHSD, so that they operate as high-affinity GR; (ii) in such CNS 'MR', aldo antagonizes the effects of B, and vice versa, in contrast with epithelia; (iii) also in contrast with epithelia, activated GR in the CNS do not mimic activated MR, suggesting considerable if not total specificity at the response element level. These differences suggest that glucocorticoids have two distinct domains of action in the CNS, mediated by 'MR' at low B/F concentrations, and GR at higher concentrations; secondly, they suggest that the nuclear recognition and response elements mediating these effects are other than canonical pentadecamer sequences.

Adrenal Cortex Hormones↗
PubMed1994

Hormone-nuclear receptor interactions in health and disease. Mineralocorticoid resistance.

Mineralocorticoid resistance, or pseudohypoaldosteronism (PHA), is a rare cause of salt wasting in young children. It may be inherited as an autosomal dominant or recessive trait, it may occur sporadically or, rarely, it may develop secondary to other conditions. It is characterized by episodes of dehydration and hyponatraemia in the face of high aldosterone levels. In most cases, after a short period of salt supplementation no further ill effects are experienced. The condition is of great interest because it provides insights into both the mechanisms by which salt and water balance are controlled and the actions of aldosterone. This article reviews the normal physiology of aldosterone, with particular reference to its biosynthesis and its actions in specific target tissues. Current knowledge regarding the molecular mechanisms involved in aldosterone action is discussed in some detail. The clinical features of PHA are reviewed and diagnostic issues and clinical management considered. Finally, current views regarding the pathophysiology of the condition are presented. Here, considerable uncertainty remains. Whilst in many cases of PHA there is greatly reduced binding of aldosterone to its receptor, the underlying abnormality is yet to be identified; in particular, in spite of strong reasons for suspecting a defect or defects in the mineralocorticoid receptor, there is so far no direct evidence to support this hypothesis. The article concludes with a discussion of other possible explanations for the underlying abnormality in PHA.

Animals↗
PubMed1994

Aldosterone and cardiac fibrosis: in vitro studies.

OBJECTIVE: Increased cardiac collagen is seen in uninephrectomised rats made hypertensive by aldosterone infusion and high salt, with the possibility of a direct effect of aldosterone at the level of the cardiac fibroblast. The aim of this study was to examine the effects of aldosterone, glucocorticoids, and angiotensin II on collagen production in a series of rat cardiac fibroblast cultures. METHODS: Cardiac fibroblast cultures were established from neonatal and adult rats of Sprague-Dawley, WKY, and SHR strains, with collagen synthesis measured by incorporation of [3H]proline into collagen. Cells were grown alone or co-cultured with cardiomyocytes, and exposed to aldosterone, glucocorticoids, or angiotensin II for 24-28 h before determination of [3H]proline incorporation. RESULTS: Aldosterone did not affect production of collagen; in contrast, angiotensin II increased, and the glucocorticoid agonist RU28362 suppressed, collagen production in cultured cardiac fibroblasts in the various rat strains. CONCLUSIONS: Aldosterone does not exert a direct effect on collagen synthesis in rat cardiac fibroblasts grown in culture. The increased cardiac collagen observed in vivo in aldosterone treated, salt loaded rats may thus represent secondary effects of aldosterone in this model.

Aldosterone↗
PubMed1994

Differential glucocorticoid effects on catecholamine responses to stress.

There have been relatively few studies of the relationships between glucocorticoid and catecholamine responses to stress. We have therefore determined plasma levels of adrenocorticotropic hormone (ACTH), cortisol (F), norepinephrine (NE), and epinephrine (Epi) in four intact sheep treated with cortisol, dexamethasone (DM), or saline (S) and subjected to both audiovisual (barking dog) and insulin-induced hypoglycemic stress. In control sheep, exposure to both stressors resulted in acute rises in ACTH, F, Epi, and NE, with the rises after insulin being greater than those after dog stress. Pretreatment with DM blocked the ACTH and F responses to stress. Both DM and F markedly attenuated the Epi response to hypoglycemia, whereas the rises in NE after each stress and those of Epi after dog stress were unaffected by steroid treatment. In a second experiment with six sheep treated with S or DM only and subjected to the same stressors in reverse order, the same results were obtained, excluding a confounding effect of prior stress. We conclude that 1) the poststress release of NE, presumably primarily from extra-adrenal sources, is largely steroid independent; 2) the mechanism of release of Epi from the adrenal medulla in response to audiovisual stress is different from that after hypoglycemia; and 3) this may reflect different inputs from central glucocorticoid receptors to splanchnic outflow in the two situations.

Adrenocorticotropic Hormone↗