Purification of a human placental cholesteryl ester hydrolase

Bile salt-stimulated lipase from human milk binds DC-SIGN and inhibits human immunodeficiency virus type 1 transfer to CD4+ T cells

A wide range of pathogens, including human immunodeficiency virus type 1 (HIV-1), hepatitis C virus, Ebola virus, cytomegalovirus, dengue virus, Mycobacterium, Leishmania, and Helicobacter pylori, can interact with dendritic cell (DC)-specific ICAM3-grabbing nonintegrin (DC-SIGN), expressed on DCs and a subset of B cells. More specifically, the interaction of the gp120 envelope protein of HIV-1 with DC-SIGN can facilitate the transfer of virus to CD4+ T lymphocytes in trans and enhance infection. We have previously demonstrated that a multimeric LeX component in human milk binds to DC-SIGN, preventing HIV-1 from interacting with this receptor. Biochemical analysis reveals that the compound is heat resistant, trypsin sensitive, and larger than 100 kDa, indicating a specific glycoprotein as the inhibitory compound. By testing human milk from three different mothers, we found the levels of DC-SIGN binding and viral inhibition to vary between samples. Using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blotting, and matrix-assisted laser desorption ionization analysis, we identified bile salt-stimulated lipase (BSSL), a Lewis X (LeX)-containing glycoprotein found in human milk, to be the major variant protein between the samples. BSSL isolated from human milk bound to DC-SIGN and inhibited the transfer of HIV-1 to CD4+ T lymphocytes. Two BSSL isoforms isolated from the same human milk sample showed differences in DC-SIGN binding, illustrating that alterations in the BSSL forms explain the differences observed. These results indicate that variations in BSSL lead to alterations in LeX expression by the protein, which subsequently alters the DC-SIGN binding capacity and the inhibitory effect on HIV-1 transfer. Identifying the specific molecular interaction between the different forms may aid in the future design of antimicrobial agents.

Regulation of pathways determining cholesterol availability in the baboon placenta with advancing gestation

Low density lipoprotein (LDL) is accepted as the primary source of cholesterol for progesterone biosynthesis in the primate placental syncytiotrophoblast. We hypothesized that the syncytiotrophoblast may, however, derive significant amounts of cholesterol from sources in addition to the LDL pathway, especially during early pregnancy or when faced with a paucity of lipoprotein-cholesterol. To test this, alternate cholesterol-providing pathways were assessed in placentae at early (Days 60-61), mid (Days 98-102), and late (Days 160-167) gestation in the baboon (Papio sp., term approximately 184 days). Expression of LDL receptor mRNA transcripts in an enriched fraction of syncytiotrophoblast cells was approximately 13-fold greater (P < 0.05) in mid and late gestation than in early pregnancy, although no differences were observed in whole villous tissue. The abundance of transcripts for 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the enzyme responsible for de novo cholesterol synthesis, remained unchanged in syncytiotrophoblast cells; however, HMG-CoA reductase activity declined approximately 2-fold from early to late pregnancy (P < 0.01), with a commensurate decline in immunoreactive HMG-CoA reductase protein. Activities for acyl-coenzyme A:cholesterol acyl transferase (ACAT), a rate-limiting enzyme for cholesterol esterification, were greater (P < 0.05) at early and mid pregnancy in placental homogenates than in those from late pregnancy, while ACAT-1 mRNA concentrations and cholesterol ester hydrolase activity remained unchanged. These results, taken together, suggest that although de novo synthesis has the potential to provide a measure of the cholesterol used for placental progesterone production during early baboon pregnancy, its contribution declines with advancing gestational age as LDL receptor-derived cholesterol becomes the major source of substrate. Changes in LDL receptor mRNA abundance suggest differences in mechanisms regulating cholesterol homeostasis in steroidogenically active syncytiotrophoblasts vs. proliferative nonendocrine cell types in the placenta.

An intracellular role for pancreatic bile salt-dependent lipase: evidence for modification of lipid turnover in transfected CHO cells

Pancreatic bile salt-dependent lipase (BSDL) hydrolyzes cholesteryl esters, triglycerides and phospholipids. BSDL is also capable of transferring free fatty acid to cholesterol. BSDL has been detected in many cells including fetal and tumor cells, hepatocytes, macrophages and eosinophils and in tissues such as adrenal glands and testes. The enzyme may be secreted or located within subcellular compartments such as the endoplasmic reticulum or the cytosol. Although the role of the secreted enzyme is well documented, that of the intracellular form(s) is still hypothetical. In the present study, we addressed the effects of BSDL on cell lipid metabolism. For that purpose, the cDNA of rat BSDL was transfected into CHO K1 cells (CHO K1-BSDL clone) which were then loaded with [3H]oleic acid. The results demonstrate that the transfected BSDL is secreted; in spite of that, a large fraction of catalytically active BSDL is found in cell lysate. The lipid metabolism of transfected cells is affected and BSDL induces an enhanced incorporation of [3H]oleic acid in cholesteryl esters whereas fatty acid incorporation in phosphatidylcholine is decreased. These effects were particularly important in the cytosol of transfected cells where transfected BSDL preferentially locates. These data suggested that BSDL could be implicated in the cycle of the cellular homeostasis of cholesterol which is particularly affected in tumoral cells leading to cholesteryl ester storage within cytosolic lipid droplets.

Pancreatic carboxyl ester lipase: a circulating enzyme that modifies normal and oxidized lipoproteins in vitro

Pancreatic carboxyl ester lipase (CEL) hydrolyzes cholesteryl esters (CE), triglycerides (TG), and lysophospholipids, with CE and TG hydrolysis stimulated by cholate. Originally thought to be confined to the gastrointestinal system, CEL has been reported in the plasma of humans and other mammals, implying its potential in vivo to modify lipids associated with LDL, HDL (CE, TG), and oxidized LDL (lysophosphatidylcholine, lysoPC). We measured the concentration of CEL in human plasma as 1.2+/-0.5 ng/ml (in the range reported for lipoprotein lipase). Human LDL and HDL3 reconstituted with radiolabeled lipids were incubated with purified porcine CEL without or with cholate (10 or 100 microM, concentrations achievable in systemic or portal plasma, respectively). Using a saturating concentration of lipoprotein-associated CE (4 microM), with increasing cholate concentration there was an increase in the hydrolysis of LDL- and HDL3-CE; at 100 microM cholate, the present hydrolysis per hour was 32+/-2 and 1.6+/-0.1, respectively, indicating that CEL interaction varied with lipoprotein class. HDL3-TG hydrolysis was also observed, but was only approximately 5-10% of that for HDL3-CE at either 10 or 100 microM cholate. Oxidized LDL (OxLDL) is enriched with lysoPC, a proatherogenic compound. After a 4-h incubation with CEL, the lysoPC content of OxLDL was depleted 57%. Colocalization of CEL in the vicinity of OxLDL formation was supported by demonstrating in human aortic homogenate a cholate-stimulated cholesteryl ester hydrolytic activity inhibited by anti-human CEL IgG. We conclude that CEL has the capability to modify normal human LDL and HDL composition and structure and to reduce the atherogenicity of OxLDL by decreasing its lysoPC content.

Cloning and sequence analysis of a Streptomyces cholesterol esterase gene

Streptomyces lavendulae H646-SY2 produces cholesterol esterase (CHE; EC 3.1.1.13) extracellularly. A genomic library of the strain, prepared in plasmid pUC119, was screened with probes based on the amino acid sequence of the protein. A plasmid, designated as pKX101 and identified by hybridization with the probes, contained a 2.7-kb insert from Streptomyces DNA. We determined the 17-N-terminal amino acid sequence of mature CHE and the nucleotide sequence of the 0.9-kb segment containing the CHE gene (che). We found that the N-terminal of the mature CHE was Ala39 and an open reading frame consisting of 681 bp starts at ATG and ends at TGA, suggesting that a precursor and a mature CHE consist of 227 and 189 amino acids, with a calculated relative molecular mass of 24,362 and 20,650, respectively. The leader peptide extends over 38 amino acids and has the characteristics of a signal sequence, including basic amino acids near the N-terminus and a hydrophobic core near the signal cleavage site.

Temperature lability and cAMP-dependent protein kinase activation of cholesteryl ester hydrolase as a function of age in developing rat testis

Cholesteryl ester hydrolase (CEH) was measured at 32 degrees C and 37 degrees C, and with and without cofactors for stimulation of cyclic AMP-dependent protein kinase, in 104,000 X g supernatants from rats aged 14-365 days. Activity at the two temperatures was also partially resolved by cation exchange FPLC. Total specific activity of CEH was relatively constant, with or without addition of cofactors, from 14 to 47 days, during which time temperature labile CEH was a very small fraction of total CEH activity. At later times, 51-150 days, activity was increased as much as two-fold, both with and without cofactors, with most of the increase occurring in the temperature labile fraction. Activation of temperature stable and temperature labile activities, where present, by protein kinase cofactors could be demonstrated in all age groups, but was highly variable as a function of age and protein concentration used in the assay. Apparent induction of temperature labile activity over the interval 47-51 days coincides with reported increases in testosterone synthesis and first appearance of spermatozoa in the testis. This and other lines of evidence suggest unique roles for these enzymes in regulation of availability of free cholesterol for testosterone and membrane synthesis, respectively.

Sterol ester hydrolase in Fusarium oxysporum

Two electrophoretically different forms of sterol ester hydrolase (EC 3.1.1.13) were obtained from the cytoplasmic extract of the mycelia of Fusarium oxysporum. The entities, estimated at 60,000 (I) and 15,000 (II) molecular weights, were obtained in Sephadex G100 column chromatography of the ammonium sulfate precipitate from the cytoplasmic extract. A third form III, 75,000 MW, was obtained from the culture filtrate. The activity of the enzyme was increased by Triton X-100 and was not inhibited by p-chloromercuribenzoate (PCMB), a sulfhydryl reagent. The enzymes I and II were inhibited differentially by NaCl. The optimal activities of forms I, II and III occurred at pH 4.8, pH 8.0 and pH 7.0, respectively. The apparent Km values of 7.7 X 10(-5), 8.3 X 10(-5) and 10.5 X 10(-5), respectively, indicate a similar order of affinity for cholesteryl oleate at pH 7.1. The rate of hydrolysis of cholesteryl esters were in the order: linoleate greater than oleate greater than valerate greater than butyrate greater than acetate. Cholesteryl benzoate and palmitate were not hydrolyzed. The properties of the microbial enzyme are discussed in relation.

Two cholesterol ester hydrolases. Distribution in rat tissues and in cultured human fibroblasts and monkey arterial smooth muscle cells

Hydrolytic activity against acetone-dispersed [4-14C]cholesterol oleate has been assayed as a function of pH in seven parenchymal tissues, blood cells, and plasma of the rat, as well as in cultured human fibroblasts and monkey (Macaca nemestrina) arterial smooth muscle cells. Both acid and neutral hydrolytic activities were present in all of these except rat plasma. The pH optima were in all cases close to pH 4.5 and pH 6.8. Acid activity was quite constant from tissue to tissue, while neutral activity varied greatly, being greatest in adrenal, testis, and adipose tissue. Subcellular fractionation of human fibroblasts allowed demonstration that activities at pH 4.5 and pH 6.8 were concentrated in different fractions, apparently lysosomal and polysomal, respectively. It appears most cell types, including fibroblasts and smooth muscle cells, contain two separate enzymes capable of hydrolyzing cholesterol esters. The neutral pH polysomal enzyme, which is especially prominent in certain tissues, may have a function related to the specialized roles of these tissues.

Purification and control of bovine adrenal cortical cholesterol ester hydrolase and evidence for the activation of the enzyme by a phosphorylation

A procedure for the purification of cholesterol ester hydrolase from bovine adrenal cortical 105000 x g supernatant is described. Preincubation of a crude enzyme extract with [gamma-32P]ATP followed by purification resulted in the isolation of a phosphorylated preparation of cholesterol ester hydrolase. The phosphorylated cholesterol ester hydrolase appeared to be composed of 4 subunits, each having a molecular weight of 41000 +/- 280, only one of which may be phosphorylated. Preincubation of the crude enzyme preparation with [alpha-32P]ATP followed by purification did not produce a phosphorylated preparation of cholesterol ester hydrolase. Cyclic-AMP-dependent protein kinase, cyclic AMP, ATP and magnesium ions were required for activation of purified cholesterol ester hydrolase in vitro and the time course of activation closely paralleled the time course of phosphorylation of the enzyme. The addition of ATP, cyclic AMP and magnesium ions to the bovine adrenal cortical 105000 x g supernatant produced a 2.5-fold stimulation in cholesterol ester hydrolase activity. This stimulation was abolished if protein kinase inhibitor was added prior to the addition of ATP cyclic AMP and magensium ions. The addition of magnesium ions or calcium ions to a crude preparation of cholesterol ester hydrolase was found to inhibit activity; however the same additions made to a purified preparation of cholesterol ester hydrolase were not inhibitory. The decrease in cholesterol ester hydrolase activity on incubation with magnesium ion was accompanied by a loss of 32P radioactivity from the protein. Preincubation of a crude preparation of cholesterol ester hydrolase with alkaline phosphatase resulted in a deactivation of cholesterol ester hydrolase. It is suggested that bovine adrenal cortex cholesterol ester hydrolase is activated by a phosphorylation catalysed by a cyclic-AMP-dependent protein kinase. Deactivation of cholesterol ester hydrolase is accomplished by dephosphorylation catalysed by a phosphoprotein phosphatase, dependent on magnesium or calcium ions.

Purification and properties of aortic cholesteryl ester hydrolase

The enzyme(s) present in acetonedried powder of rat and rabbit aortas, which catalyzes the synthesis and hydrolysis of cholesteryl ester, was purified partially by acid precipitation, acetone fractionation, O-(diethylaminoethyl) cellulose chromatography, and Sephadex G-100 filtration. The synthetic activity was purified by 120-fold (rat) and 140-fold (rabbit). Purification of hydrolytic activity was 90-fold (rat) and 103-fold (rabbit). Cholesteryl ester hydrolase activity was separated from nonspecific esterase by column chromatography. Both synthetic and the hydrolytic activities are apparently the functions of one enzyme. The mol wt of the enzyme was estimated to be 140,000 dalton as determined by Sephadex G-200 gel filtration. The extracts of the acetone-dried powders of aortas of both species contained an inhibitor of synthetic activity. The inhibitor was nondialyzable and was precipitated at pH 5.7. Both activities were found to be fairly nonspecifc with regard to sterol and fatty acids. With oleic acid, the relative rates of sterol ester synthesis were: cholesterol, 100; cholestanol, 94; desmosterol, 35; coprostanol, 24; ergosterol, 20; and beta-sitosterol, 19. Epicholesterol was not esterified. Oleic acid was most active in cholesteryl ester synthesis, the relative rates being: oleic greater than linoleic greater than arachidonic greater than palmitic greater than stearic greater than butyric. The rate of hydrolysis was maximum with cholesteryl linoleate followed by oleate, linolenate, palmitate, stearate, and laurate in decreasing order.

The effect of dietary rape-seed oil on cholesterol-ester metabolism and cholesterol-ester-hydrolase activity in the rat adrenal

The effects of stock diet and stock diet supplemented by olive oil and rape seed on rat adrenal cholesterol ester metabolism have been studied. Rats fed rape seed oil failed to gain weight at the same rate as rats fed olive oil. A prominent feature of the rats fed rape seed oil was an accumulation of high concentrations of cholesterol erucate in the adrenal lipid droplets. When these rats were subjected to an ether stress no percentage decrease in the amount of cholesterol erucate was observed. Adrenal cholesterol ester hydrolase activity was higher in rats fed the olive oil and rape seed oil diets than rats fed the stock diet. In rats fed stock or olive oil diets, a ten-minute ether anaesthesia stress resulted in a two-fold increase in activity of adrenal cholesterol ester hydrolase. Cofactor addition of ATP, cyclic AMP and MgCl-2 in vitro resulted in a stimulation of cholesterol ester hydrolase to a similar activity in both quiescent and ether-stressed rats. By contrast rats fed the rape seed oil diet gave no significant stimulation of cholesterol ester hydrolase activity when given an ether stress or when cofactors were added in vitro. Cholesterol erucate was hydrolysed at only 25% to 30% of the rate of cholesterol oleate in vitro in all groups of animals. Oleic acid added in vitro gave an inhibition of cholesterol ester hydrolase activity in rats fed stock diet while erucic acid activated the enzyme. The accumulation of cholesterol erucate in the adrenal when rats are fed rape seed oil could be due to the reduced ability of cholesterol ester hydrolase to hydrolyse this ester.

Cholesterol ester hydrolase in human red blood cells

1. Cholesterol ester hydrolytic activity (sterol-ester hydrolase EC 3.1.1.13) was detected in human red blood cells. Enzyme activity appeared confined to the cell membrane and was most marked in washed preparations of red cell ghosts. 2. Hydrolytic activity was stimulated by the anti-oxidants D-alpha-tocopherol and butylated hydroxytoluene. Marked inhibition was produced by erythrocyte hemolysate, sodium taurocholate, and Triton X-100. 3. Optimal pH for the reaction was 5.4--5.7. 4. Because red cell cholesterol is all unesterified, it is speculated that the hydrolase serves to maintain the erythrocyte membrane free of esterified cholesterol.