Human placental steroid sulphatase--purification and monospecific antibody production in rabbits

Down-regulation of messenger ribonucleic acid encoding an importer of sulfoconjugated steroids during human chorionic gonadotropin-induced follicular luteinization in vivo

Members of the organic anion transporting polypeptide (SLCO/OATP) superfamily are capable of importing anionic compounds across the lipid bilayer in a sodium-independent manner. Member 2B1 has been shown to transport few substrates, two of which are dihydroepiandrosterone-3-sulfate (DHEA-S) and estrone-3-sulfate. Steroid sulfatase (STS) catalyses the hydrolysis of these steroids into their unconjugated counterparts. The objective of this study was to investigate the regulation of SLCO2B1 and STS mRNAs during human chorionic gonadotropin (hCG)-induced ovulation/luteinization. The equine SLCO2B1 cDNA was cloned and shown to encode a 709-amino acid protein (OATP2B1) that is highly conserved when compared to mammalian orthologs. RT-PCR/Southern blot analyses were performed to study the regulation of SLCO2B1 and STS transcripts in equine preovulatory follicles isolated between 0 and 39h after hCG treatment. Results showed high levels of SLCO2B1 mRNA expression before hCG, with a marked decrease observed in follicles obtained 24-39h post-hCG (P<0.05). Analyses of isolated granulosa and theca interna cells identified high mRNA expression in both cell types prior to hCG treatment, with granulosa cells showing a more rapid SLCO2B1 mRNA down-regulation. No significant change in STS mRNA was observed in intact follicle walls. However, when both cell types were isolated, a significant decrease in STS mRNA was observed in granulosa cells 24-39h post-hCG. Collectively, these results demonstrate that the hCG-dependent induction of follicular luteinization is accompanied by the down-regulation of SLCO2B1 and STS transcripts. Considering that OATP2B1 can import sulfoconjugated DHEA and estrogens, and that STS can remove the sulfonate moiety from these steroids, their down-regulation in luteinizing preovulatory follicles may provide an additional biochemical basis for the decrease in ovarian 17beta-estradiol biosynthesis after the LH surge.

Three‐Dimensional Structures of Sulfatases

The sulfatase family of enzymes catalyzes the hydrolysis of sulfate ester bonds of a wide variety of substrates. Nine human sulfatase proteins and their genes have been identified, many of which are associated with genetic disorders leading to reduction or loss of function of the corresponding enzyme. A catalytic cysteine residue, strictly conserved in prokaryotic and eukaryotic sulfatases, is modified posttranslationally into a formylglycine. Hydroxylation of the formylglycine residue by a water molecule forming the activated hydroxylformylglycine (a formylglycine hydrate or a gem-diol) is a necessary step for sulfatase activity of the enzyme. Crystal structures of three human sulfatases, arylsulfatases A and B (ARSA and ARSB) and C, also known as steroid sulfatase or estrone/dehydroepiandrosterone sulfatase (ES), have been determined. In addition, the crystal structure of a homologous bacterial arylsulfatase from Pseudomonas aeruginosa (PAS) is also available. While ARSA, ARSB, and PAS are water-soluble enzymes, ES has a hydrophobic domain and is presumed to be bound to the endoplasmic reticulum membrane. This chapter compares and contrasts four sulfatase structures and revisits the proposed catalytic mechanism in light of available structural and functional data. Examination of the ES active site reveals substrate-specific interactions previously identified in another steroidogenic enzyme. Possible influence of the lipid bilayer in substrate capture and recognition by ES is described. Finally, mapping the genetic mutations into the ES structure provides an explanation for the loss of enzyme function in X-linked ichthyosis.

Mutations in X-linked ichthyosis disrupt the active site structure of estrone/DHEA sulfatase

X-linked ichthyosis is an inherited genetic disorder of the skin that results from steroid sulfatase (STS) deficiency. Seven critical point mutations have been previously reported for the STS gene, six leading to amino acid substitutions and one to a premature termination of the polypeptide chain. The three-dimensional structure of the full-length human enzyme has been recently determined. Amino acid substitutions due to point mutations in X-linked ichthyosis are mapped onto the three-dimensional structure of human STS. In each case, the substitution appears to cause disruption of the active site architecture or to interfere with the enzyme's putative membrane-associating motifs crucial to the integrity of the catalytic cleft, thereby providing an explanation for the loss of STS activity.

Structure of human estrone sulfatase suggests functional roles of membrane association

Estrone sulfatase (ES; 562 amino acids), one of the key enzymes responsible for maintaining high levels of estrogens in breast tumor cells, is associated with the membrane of the endoplasmic reticulum (ER). The structure of ES, purified from the microsomal fraction of human placentas, has been determined at 2.60-A resolution by x-ray crystallography. This structure shows a domain consisting of two antiparallel alpha-helices that protrude from the roughly spherical molecule, thereby giving the molecule a "mushroom-like" shape. These highly hydrophobic helices, each about 40 A long, are capable of traversing the membrane, thus presumably anchoring the functional domain on the membrane surface facing the ER lumen. The location of the transmembrane domain is such that the opening to the active site, buried deep in a cavity of the "gill" of the "mushroom," rests near the membrane surface, thereby suggesting a role of the lipid bilayer in catalysis. This simple architecture could be a prototype utilized by the ER membrane in dictating the form and the function of ER-resident enzymes.

Purification, characterization and crystallization of human placental estrone/dehydroepiandrosterone sulfatase, a membrane-bound enzyme of the endoplasmic reticulum

Estrone (E1)/dehydroepiandrosterone (DHEA) sulfatase (ES/DHEAS) catalyzes the hydrolysis of E1 and DHEA-sulfates releasing unconjugated steroids. ES is a component of the three-enzyme system that has been implicated in intracrine biosynthesis of estradiol, hence, proliferation of hormone dependent breast tumors. ES is bound to the membrane of the endoplasmic reticulum, presumably through multiple transmembrane and other membrane anchoring segments. The highly hydrophobic nature of the enzyme has so far prevented its purification to homogeneity in quantities sufficient for crystallization. We report here the purification, biochemical characterization and crystallization of the full-length, active form of the enzyme from the membrane bound fraction of human placenta. Our results demonstrate that the key to successful purification and growth of diffraction quality crystals of this difficult membrane bound enzyme is the exploitation of optimal solubilization and detergent conditions to protect the structural and functional integrity of the molecule, thereby preventing nonspecific aggregation and other instabilities. This work paves the way for the first structural study of a membrane bound human sulfatase and subsequent rational design of inhibitors for use as anti-tumor agents.

Characterization of point mutations in patients with X-linked ichthyosis. Effects on the structure and function of the steroid sulfatase protein

X-linked ichthyosis is the result of steroid sulfatase (STS) deficiency. While most affected individuals have extensive deletions of the STS gene, point mutations have been reported in three patients (1). In this study, we identify an additional three point mutations and characterize the effects of all six mutations on STS activity and expression. All six are unique single base pair substitutions. The mutations are located in a 105-amino acid region of the C-terminal half of the polypeptide. Five of the six mutations involve the substitutions of Pro or Arg for Trp372, Arg for His444, Tyr for Cys446, or Leu for Cys341. The other mutation is in a splice junction and results in a frameshift causing premature termination of the polypeptide at residue 427. All the affected residues are conserved to some degree within the sulfatase family. The six mutations were reproduced in normal STS cDNA and transiently expressed in STS-deficient cells. All six mutant vectors direct the expression of STS protein that lacks enzymatic activity. The mutant polypeptides show a shift in mobility on SDS-PAGE and resistance to proteinase K digestion when translated in the presence of dog pancreas microsomes, indicating glycosylation and normal translocation.

A "soluble" form of sterol sulphate sulphohydrolase from cell nuclei of human placenta tissue--examinations with oestrone sulphate as substrate

DN-ase digestion of the nuclear envelope-chromatin complex of the cell nuclei preparations from human placenta, released a soluble form of sterolsulphohydrolase. The enzyme revealed three pH optima, at 4.0, 6.2 and 7.4. The Km value was 4.16 +/- 1.44 x 10(-5) M. The molecular mass determined by gel filtration on Bio-gel A 15 m was 406 kDa. The enzyme is sensitive to -SH group reacting reagents such as cysteine, p-chloromercuribenzoate and iodoacetamide. Oxidized and reduced forms of NAD, FAD, dithiothreitol and glutathione moderately inhibited enzyme activity. Ascorbic acid (reduced and oxidized) exerted slight activation. The enzyme was insensitive to phosphate ions.

Biochemical and immunological characterization of X-linked ichthyosis

An immunoquantification protocol based on an enzyme-linked immunosorbent assay was developed to measure the abundance of the microsomal enzyme steroid sulphatase (STS). The two-step sandwich immunoassay is sufficiently sensitive to detect 100-200 pg purified steroid sulphatase in a 50-microliters sample. The steroid sulphatase content in fibroblast, leukocyte and placental extracts correlates with the steroid sulphatase activity in these extracts. No steroid sulphatase protein was found in approximately 350 micrograms plasma proteins from a normal person. In three of four X-linked ichthyosis patients a complete gene deletion was found by Southern hybridization with the full-length STS cDNA as probe. Neither steroid sulphatase protein nor enzymatic activity was found in fibroblast extracts of these three patients. In a fibroblast extract of another X-linked ichthyosis patient, which had a normal Southern blotting pattern, no immunoreactive protein was detected. Residual activity of steroid sulphatase was also not found after prolonged incubation of this fibroblast extract with the natural substrate oestrone sulphate.

In vitro effect of synthetic progestogens on estrone sulfatase activity in human breast carcinoma

The effect of progesterone and nine synthetic progestogens on the activity rate of microsome estrone sulfatase obtained from human breast carcinoma tissues was studied. The progestogens were classified into three groups: group I with a strict inhibitor effect: demegestone and chlormadinone acetate; group II with a strict activator effect: medroxyprogesterone acetate, quingestanol acetate, lynestrenol and progesterone and group III with a nonsignificant effect: dydrogesterone, promegestone, norgestrel and danazol. Demegestone was the most potent inhibitor and medroxyprogesterone acetate and quingestanol acetate had the highest activator effect. The effect of Triton X-100, a nonionic detergent, was also tested. This detergent consistently increased the microsome estrone sulfatase activity. A comparison was made between the effects of demegestone, medroxyprogesterone acetate and danazol on estrone sulfatase activity measured with or without Triton X-100 in the incubation medium. The presence of the detergent modified the progestogen action. Our results suggest that synthetic progestogens can influence the estrone sulfatase activity measured in human breast carcinoma tissues. However, the effect of progestogens was dependent on experimental conditions. Progestogens such as demegestone and chlormadinone acetate which inhibited estrone sulfatase activity in intact preparations, can reduce the intracellular production of biological active estrogen via the sulfatase pathway.

Human placental sterylsulfatase: immunocytochemical and biochemical localization

Human placental sterylsulfatase was localised in situ by light and electron microscope immunocytochemical techniques as well as in homogenate and tissue extract fractions by enzyme assays. Light microscope observations on frozen sections of term and preterm placenta revealed sterylsulfatase immunoactivity primarily in the syncytiotrophoblast. Electron microscope observations confirmed the light microscope findings; in addition, they showed that the sulfatase is present in the endoplasmic reticulum of endothelial cells, too. In the syncytiotrophoblast, the enzyme was detectable in the cytoplasmic membrane of the nuclear evelope, in the membranes of the rough endoplasmic reticulum, in the plasma membrane with predominant localisation in coated pits, and in the membranes of endosomes and multivesicular bodies; little or no reactivity was detectable over the membranes of the Golgi complex and of lysosomes. Sterylsulfatase immunoactivity was absent in placentas with hereditary sterylsulfatase deficiency. The observations indicate that human placental sterylsulfatase is normally present in the membranes of compartments along the secretory pathway and the endocytic route of cells lining the fetal and maternal blood. Homogenates of normal term placenta as well as membrane vesicle preparations obtained by extraction of trophoblast tissue with isotonic saline were fractionated by differential centrifugation; the fractions were assayed for specific activities of sterylsulfatase and several marker enzymes of cellular topography. In agreement with our immunocytochemical findings, the results of these biochemical localisation experiments indicate the repeatedly described association of the placental sterylsulfatase with microsomal membranes but also point to the presence of the enzyme's activity in the microvillous plasma membrane of the syncytiotrophoblast. This localisation of sterylsulfatase may have functional implications in the placental uptake of circulating steroid sulfates.

Characterization of rat and human steroid sulfatases

Rat and human steroid sulfatases were purified from liver and placenta, respectively, by the same procedure. The rat and human enzymes were solubilized with Triton X-100, and purified by immunoaffinity chromatography with a monoclonal antibody showing high binding activities to both the enzymes. They were further purified by high-pressure anion-exchange chromatography to compare their structural and catalytic properties. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that both enzymes had a molecular weight of 62,000. The enzymes had similar amino acid compositions and amino-terminal amino acid sequences. Significant differences of the optimum pH, Michaelis constant and maximum velocity were observed between these enzymes. The optimum pH of each enzyme varied from 6.0 to 8.0, depending on substrates and with or without Triton X-100. In detergent-free media, steroid sulfates competitively inhibited the ability of these enzymes to hydrolyze 4-nitrophenyl sulfate. In media containing Triton X-100, on the other hand, the inhibition types of the steroid sulfates on the hydrolyzing activities of the rat and human enzymes were noncompetitive- and mixed-types, respectively.

Molecular heterogeneity of steroid sulfatase deficiency: a multicenter study on 57 unrelated patients, at DNA and protein levels

Steroid sulfatase (STS) deficiency is the biochemical defect of X-linked ichthyosis (XLI), one of the most common X-linked disorders. We studied 57 European unrelated patients affected by STS deficiency. Twenty-eight patients were from Italy, 24 from the United Kingdom, 4 from The Netherlands, and 1 from Denmark. In two families XLI was associated with Kallmann syndrome (hypogonadotropic hypogonadism and anosmia). STS enzymatic activity was profoundly deficient in all cases. Direct DNA analysis, using cDNA and genomic probes from the STS gene and linked regions, demonstrated heterogeneity of the molecular defect. Forty-eight patients (84%) showed a deletion of the STS gene. In 44 cases the deletion also involved the STS flanking locus DXS237. In 1 patient a partial deletion of the STS gene was detected and in 9 patients no evidence of deletion was found. Locus DXS31 (probe M1A), previously mapped to Xp22.3-pter, was not deleted either in 24 patients with X-linked ichthyosis or in two families with X-linked ichthyosis associated with Kallmann syndrome. Consequently, the following loci order could be suggested: telomere--DXS31--(DXS237, STS)--Kallmann--centromere. Immunoblotting experiments, performed using anti-STS polyclonal antibodies, revealed the absence of cross-reacting material to STS in all cases tested, including 4 patients without evidence of deletions.

Ultrastructural localization of steroid sulphatase in cultured human fibroblasts by immunocytochemistry: a comparative study with lysosomal enzymes and the mannose 6-phosphate receptor

Immunocytochemistry was used to study the subcellular localization of steroid sulphatase in cultured human fibroblasts. Ultra-thin cryosections were incubated with antibodies raised against steroid sulphatase purified from human placenta and immune complexes were visualized with gold probes as electron dense markers. Steroid sulphatase was found in rough endoplasmic reticulum, Golgi cisternae and in the trans-Golgi reticulum, where it co-distributes with lysosomal enzymes and the mannose 6-phosphate receptor. The enzyme was not detected in lysosomes. Steroid sulphatase was also found at the plasma membrane and in the endocytic pathway (i.e. coated pits, endosomes and multivesicular endosomes). These may be the sites where sulphated oestrogen precursors are hydrolysed. Also here, it co-localizes with lysosomal enzymes and the mannose 6-phosphate receptor. It is concluded that microsomal steroid sulphatase and lysosomal enzymes share several cellular compartments.

Deletions of the steroid sulphatase gene in "classical" X-linked ichthyosis and in X-linked ichthyosis associated with Kallmann syndrome

We have studied 16 men, from 10 unrelated Italian families, affected by steroid suphatase (STS) deficiency, which is the basic defect of X-linked ichthyosis (XLI). The patients' clinical diagnoses were of either isolated ichthyosis or ichthyosis associated with Kallmann syndrome (KS) (hypogonadotropic hypogonadism and anosmia). DNA from patients and their relatives was analysed by Southern blotting followed by hydridization with an STS cDNA probe. None of the patients affected by either XLI or XLI/KS showed any hybridization signal, thus revealing a deletion in the STS gene. We suggest that a gene deletion may be the most common molecular defect involved in XLI and that the syndrome XLI/KS may be due to a deletion of both the STS and the KS loci.

Isolation and characterization of a steroid sulfatase cDNA clone: genomic deletions in patients with X-chromosome-linked ichthyosis

We have isolated several cDNA clones from a lambda gt11 expression library by screening with antibodies prepared against the microsomal enzyme steroid sulfatase, which is deficient in classical X-chromosome-linked ichthyosis patients. One of these clones (p422) has been assigned by mapping with a somatic cell hybrid panel and by in situ hybridization to Xp22.3. Clone p422 therefore has a coincident localization with the previously identified locus for steroid sulfatase expression in the region of the X chromosome escaping from inactivation. Twelve steroid sulfatase-deficient patients, including eight cases of classical ichthyosis, were found to be deleted for genomic sequences detected by the clone.

Studies on cross-reacting material to steroid sulphatase in fibroblasts from patients affected by different types of steroid sulphatase deficiency

Immunologically cross-reacting material to antibodies against steroid sulphatase has not been found in fibroblasts from patients with steroid sulphatase deficiency.

Rapid degradation of steroid sulfatase in multiple sulfatase deficiency

Pulse labeling followed by SDS-PAGE electrophoresis of immunoprecipitated [35S]methionine-labeled steroid sulfatase (STS) gave a single band of molecular weight 65,000 daltons. After a chase period of 18 hours the material appeared as molecular weight approximately 64,000. No labeled STS could be detected in fibroblasts from individuals with STS deficient X-linked ichthyosis. Pulse-chase labeling of normal and multiple sulfatase deficiency (MSD) fibroblasts showed a normal rate of synthesis of STS in MSD during a 3 hour pulse but during the chase the STS of MSD cells disappeared with a half-life of 4 to 6 hours until approximately 25% of the material remained after 24 hr. STS of normal cells had a half-life of 6 days. The material produced in MSD cells had the same molecular size as normal and had the same amount of endoglycosidase sensitive carbohydrate as normal. The defect in MSD thus seems to result in degradation after the addition of N-linked oligosaccharides.