Charles A. Strott

Cholesterol sulfate in human physiology: what's it all about?

Cholesterol sulfate is quantitatively the most important known sterol sulfate in human plasma, where it is present in a concentration that overlaps that of the other abundant circulating steroid sulfate, dehydroepiandrosterone (DHEA) sulfate. Although these sulfolipids have similar production and metabolic clearance rates, they arise from distinct sources and are metabolized by different pathways. While the function of DHEA sulfate remains an enigma, cholesterol sulfate has emerged as an important regulatory molecule. Cholesterol sulfate is a component of cell membranes where it has a stabilizing role, e.g., protecting erythrocytes from osmotic lysis and regulating sperm capacitation. It is present in platelet membranes where it supports platelet adhesion. Cholesterol sulfate can regulate the activity of serine proteases, e.g., those involved in blood clotting, fibrinolysis, and epidermal cell adhesion. As a result of its ability to regulate the activity of selective protein kinase C isoforms and modulate the specificity of phosphatidylinositol 3-kinase, cholesterol sulfate is involved in signal transduction. Cholesterol sulfate functions in keratinocyte differentiation, inducing genes that encode for key components involved in development of the barrier. The accumulating evidence demonstrating a regulatory function for cholesterol sulfate appears solid; the challenge now is to work out the molecular mechanisms whereby this interesting molecule carries out its various roles.

Plasma Progesterone and 17-hydroxyprogesterone in normal men and children with congenital adrenal hyperplasia

Plasma 17-hydroxyprogesterone (17-OHP) concentrations in normal men averaged 0.094 mug/100 ml. Studies using suppressive doses of androgens and glucocorticoids showed that 90% of the 17-OHP originated from the Leydig cell. The 17-OHP production rate was 1.8 mg/24 hr. Plasma 17-OHP has a marked circadian variation, the 8 p.m. values being only 40% of the 8 a.m. values. Plasma luteinizing hormone measured in the same samples did not vary. The adrenal cortex has the capacity to synthesize and secrete 17-OHP and progesterone since adrenocorticotrophic hormone (ACTH) caused a fourfold increase in these plasma steroids. In children with congenital adrenal hyperplasia, plasma 17-OHP levels were 50-200 times those of normal men and plasma progesterone was increased 6- to 10-fold over normal men.

Cushing's syndrome caused by bronchial adenomas

Abstract Two cases of Cushings syndrome caused by ACTH secreting bronchial adenomas are reported. In one ACTH was demonstrated in the tumor by bioassay and in the other by radioimmunoassay. In one patient the adenoma was found at autopsy, in the other the adenoma was discovered at the time Cushings syndrome was recognized. In this latter patient Cushings syndrome disappeared after resection of the tumor. Careful search for such a tumor should be made in every patient thought to have pituitary Cushings syndrome in order to select the most appropriate therapy. Presently available functional studies such as dexamethasone suppression and the response to metyrapone do not distinguish between these patients and those with Cushings syndrome due to excessive pituitary secretion of ACTH.

Oxysterols are substrates for cholesterol sulfotransferase

Oxysterols constitute a class of cholesterol derivatives that exhibit broad biological effects ranging from cytotoxicity to regulation of nuclear receptors. The role of oxysterols such as 7-ketocholesterol (7-KC) in the development of retinal macular degeneration and atheromatous lesions is of particular interest, but little is known of their metabolic fate. We establish that the steroid/sterol sulfotransferase SULT2B1b, known to efficiently sulfonate cholesterol, also effectively sulfonates a variety of oxysterols, including 7-KC. The cytotoxic effect of 7-KC on 293T cells was attenuated when these cells, which do not express SULT2B1b, were transfected with SULT2B1b cDNA. Importantly, protection from 7-KC-induced loss of cell viability with transfection correlated with the synthesis of SULT2B1b protein and the production of the 7-KC sulfoconjugate (7-KCS). Moreover, when 7-KCS was added to the culture medium of 293T cells in amounts equimolar to 7-KC, no loss of cell viability occurred. Additionally, MCF-7 cells, which highly express SULT2B1b, were significantly more resistant to the cytotoxic effect of 7-KC. We extended the range of oxysterol substrates for SULT2B1b to include 7α/7β-hydroxycholesterol and 5α,6α/5β,6β-epoxycholesterol as well as the 7α-hydroperoxide derivative of cholesterol. Thus, SULT2B1b, by acting on a variety of oxysterols, offers a potential pathway for modulating in vivo the injurious effects of these compounds.

Laboratory tests in the diagnosis of hyperparathyroidism in hypercalcemic patients.

Abstract The results of tests of serum phosphate concentration or urine calcium or phosphate excretion, either under controlled conditions or after infusion of calcium or phosphate, were examined f...

Crystal structure of human cholesterol sulfotransferase (SULT2B1b) in the presence of pregnenolone and 3'-phosphoadenosine 5'-phosphate. Rationale for specificity differences between prototypical SULT2A1 and the SULT2BG1 isoforms.

The gene for human hydroxysteroid sulfotransferase (SULT2B1) encodes two peptides, SULT2B1a and SULT2B1b, that differ only at their amino termini. SULT2B1b has a predilection for cholesterol but is also capable of sulfonating pregnenolone, whereas SULT2B1a preferentially sulfonates pregnenolone and only minimally sulfonates cholesterol. We have determined the crystal structure of SULT2B1a and SULT2B1b bound to the substrate donor product 3′-phosphoadenosine 5′-phosphate at 2.9 and 2.4 Å, respectively, as well as SULT2B1b in the presence of the acceptor substrate pregnenolone at 2.3 Å. These structures reveal a different catalytic binding orientation for the substrate from a previously determined structure of hydroxysteroid sulfotransferase (SULT2A1) binding dehydroepiandrosterone. In addition, the amino-terminal helix comprising residues Asp19 to Lys26, which determines the specificity difference between the SULT2B1 isoforms, becomes ordered upon pregnenolone binding, covering the substrate binding pocket.

Molecular cloning, expression, and characterization of human bifunctional 3'-phosphoadenosine 5'-phosphosulfate synthase and its functional domains.

The universal sulfonate donor, 3′-phosphoadenosine 5′-phosphosulfate (PAPS), is synthesized by the concerted action of ATP sulfurylase and adenosine 5′-phosphosulfate (APS) kinase, which in animals are fused into a bifunctional protein. The cDNA for human PAPS synthase (hPAPSS) along with polymerase chain reaction products corresponding to several NH2- and COOH-terminal fragments were cloned and expressed in COS-1 cells. A 1–268-amino acid fragment expressed APS kinase activity, whereas a 220–623 fragment evinced ATP sulfurylase activity. The 1–268 fragment and full-length hPAPSS (1–623) exhibited hyperbolic responses against APS substrate with equivalent K m values (0.6 and 0.4 μm, respectively). The 1–268 fragment demonstrated Michaelis-Menten kinetics against ATP as substrate (K m 0.26 mm); however, full-length hPAPSS exhibited a sigmoidal response (apparent K m 1.5 mm) suggesting cooperative binding. Catalytic efficiency (V max/K m ) of the 1–268 fragment was 64-fold higher than full-length hPAPSS for ATP. The kinetic data suggest that the COOH-terminal domain of hPAPSS exerts a regulatory role over APS kinase activity located in the NH2-terminal domain of this bifunctional protein. In addition, the 1–268 fragment and full-length hPAPSS were overexpressed in Escherichia coli and column purified. Purified full-length hPAPSS, in contrast to the COS-1 cell-expressed cDNA construct, exhibited a hyperbolic response curve against ATP suggesting that hPAPSS is perhaps modified in vivo.

Site of stimulation of aldosterone biosynthesis by angiotensin and potassium

Studies were undertaken to determine what part of the aldosterone biosynthetic pathway is stimulated by angiotensin and potassium. The availability of a method for isolating the early portion of the aldosterone pathway and a new method for measuring plasma deoxycorticosterone permitted the design of experiments to determine whether angiotensin and potassium stimulate the pathway before deoxycorticosterone. To eliminate ACTH-dependent steroid synthesis, the experiments were performed in subjects receiving constant dosage of dexamethasone. To minimize the intra-adrenal conversion of deoxycorticosterone to corticosterone, all subjects also received constant dosage of metyrapone. Plasma deoxycortisol was measured as an index of the activity of the zona fasciculata. In the absence of changes in plasma deoxycortisol, one may infer that changes in plasma deoxycorticosterone represent changes in function of zona glomerulosa, the site of aldosterone formation. Under these conditions, human subjects responded both to angiotensin and to potassium with significant increases in plasma deoxycorticosterone but without significant increases in plasma deoxycortisol. In contrast, small doses of ACTH given under similar conditions never induced increases in plasma deoxycorticosterone without simultaneously inducing large increases in plasma deoxycortisol. It is concluded that the aldosterone-stimulating effects of angiotensin and potassium are, at least in part, consequences of stimulation of the biosynthetic pathway at some point before the formation of deoxycorticosterone so as to increase the availability of aldosterone precursors.

Refractory cushing’s disease caused by multinodular ACTH-cell hyperplasia

A patient with pituitary-dependent hypercortisolism, unresponsive to resection of nodules in the anterior lobe, is described. Histochemical stains of the nodules showed multiple, focal, cellular expansions of the fibrovascular stroma. Transitions between normal and expanded adenohypophysial acini were present. Immunoperoxidase stains for ACTH and other pituitary hormones revealed that these multiple foci contained an excess of ACTH-positive cells. Less than 10% of the cells in these foci were negative for ACTH and positive for other hormones. Serial sections showed that these foci of predominantly ACTH-producing acini were not connected. Clinical, morphological, and immunohistochemical data indicated that ACTH-cell hyperplasia caused Cushings disease in this patient. Pathologic study of individual cases should concentrate on determining whether hyperplasia or adenoma exist at the time of surgical exploration of the pituitary gland, since this determination is important to proper treatment. Tentative criteria to recognize ACTH-cell hyperplasia are: 1. Multiple foci of ACTH laden cells. 2. A minor subpopulation of cells of alternate hormone series. 3. Expansion without destruction of acini in the adenohypophysis.

SITE-SELECTED MUTAGENESIS OF A CONSERVED NUCLEOTIDE BINDING HXGH MOTIF LOCATED IN THE ATP SULFURYLASE DOMAIN OF HUMAN BIFUNCTIONAL 3'-PHOSPHOADENOSINE 5'-PHOSPHOSULFATE SYNTHASE

3′-Phosphoadenosine-5′-phosphosulfate (PAPS) synthase is a bifunctional protein consisting of an NH2-terminal APS kinase and a COOH-terminal ATP sulfurylase. Both catalytic activities require ATP; the APS kinase domain involves cleavage of the β-γ phosphodiester bond of ATP, whereas the ATP sulfurylase domain involves cleavage of the α-β phosphodiester bond of ATP. Previous mutational studies have suggested that β-γ phosphodiesterase activity involves a highly conserved NTP-binding P-loop motif located in the adenosine-5′-phosphosulfate kinase domain of PAPS synthases. Sequence alignment analysis of PAPS synthases and the superfamily of TagD-related nucleotidylyltransferases revealed the presence of a highly conserved HXGH motif in the ATP sulfurylase domain of PAPS synthases, a motif implicated in the α-β phosphodiesterase activity of cytidylyltransferases. Thus, site-selected mutagenesis of the HXGH motif in the ATP sulfurylase domain of human PAPS synthase (amino acids 425–428) was performed to examine this possibility. Either H425A or H428A mutation produced an inactive enzyme. In contrast, a N426K mutation resulted in increased enzymatic activity. A G427A single mutant resulted in only a modest 30% reduction in catalytic activity, whereas a G427A/H428A double mutant produced an inactive enzyme. These results suggest an important role for the HXGH histidines in the ATP sulfurylase activity of bifunctional PAPS synthase and support the hypothesis that the highly conserved HXGH motif found in the ATP sulfurylase domain of PAPS synthases is involved in ATP binding and α-β phosphodiesterase activity.