Cloning and sequence analysis of a rat liver cDNA encoding hydroxysteroid sulfotransferase

Human dehydroepiandrosterone sulfotransferase: molecular cloning of cDNA and genomic DNA

Human tissues contain at least three well-characterized cytoplasmic sulfotransferase (ST) enzymes, dehydroepiandrosterone (DHEA) ST and two of phenol ST (PST). DHEA ST catalyzes the sulfation of DHEA and other steroids. We cloned and expressed two cDNAs for human liver DHEA ST. The cloning strategy involved the design of PCR primers directed against two conserved domains in ST proteins. These primers were used to generate a specific PCR product that was then used successfully to clone cDNAs for DHEA ST from a human liver cDNA library. Two cDNAs were isolated that were approximately 1.1 and 1.8 kb in length. These two clones had identical open reading frames. Both cDNAs produced enzymatically active DHEA ST protein in a mammalian expression system. Northern blot analysis confirmed the presence of 1.1 and 1.8 kb transcripts in human liver. cDNAs for a number of eukaryotic enzymes have now been cloned, and they share significant sequence homology. These ST cDNAs appear to fall into distinct groups on the basis of amino acid sequences of the proteins that they encode, thus demonstrating that the enzymes comprise a gene superfamily. We have also isolated, a genomic clone for human DHEA ST that contains approximately 3 kb of 5'-flanking sequence, exon 1 and 1.7 kb of intron 1. Characterization of the structure and regulatory elements of this gene should help to elucidate mechanisms involved in the regulation of DHEA ST in humans.

Androgen and estrogen sulfotransferases of the rat liver: physiological function, molecular cloning, and in vitro expression

Cloning of the androgen and estrogen sulfotransferases has allowed studies on their spatiotemporal regulation and physiological function. These two enzymes appear to be involved in regulating target cell sensitivity for the androgenic and estrogenic steroids. Recombinant androgen sulfotransferase produced in insect Sf9 cells through a baculoviral expression vector is capable of transferring the sulfate from PAPS (phosphoadenosine phosphosulfate) to 3 alpha, 3 beta, 17 alpha, and 17 beta hydroxyl groups of a number of steroid substrates indicating a broad range of substrate specificity.

Characterization of expressed human phenol-sulfating phenol sulfotransferase: effect of mutating cys70 on activity and thermostability

The cDNA for human liver phenol-sulfating phenol sulfotransferase (P-PST) has been cloned and the active enzyme expressed in Cos cells and bacteria. Analysis of the sequence identified two cysteine residues, one of which is highly conserved in the phenol sulfotransferase gene family. Previous studies with the pure human liver enzyme suggested that the conserved cysteine may be involved in binding substrates. Bacterial expression of P-PST with the cysteine converted to a serine indicates that the cysteine is not essential for activity or substrate binding, however, the mutant enzyme is significantly more sensitive to thermal inactivation.

Age- and sex-related changes of sulfotransferase activities in the rat

Temporal and gender-related changes of sulfotransferase activities in the rat were studied using alcoholic, amine and phenolic compounds as substrates. Alcohol and amine sulfotransferase activities in the rat exhibited different temporal and sex-related changes of those for phenol. Formation of sulfoconjugates in vivo correlated well with in vitro sulfotransferase activities in the rat liver.

Molecular cloning of three sulfotransferase cDNAs from mouse liver

Sulfate conjugation plays an important role in the biotransformation of not only xenobiotics but also many endogenous substances. Sulfotransferases, the enzymes that are responsible for this process, exist as a superfamily of genes. It has long been recognized that significant species differences exist among drug and carcinogen metabolizing enzymes such as cytochrome P450. Species differences in both regulation and catalytic activities of sulfotransferases may also exist. To investigate this, we conducted cDNA cloning and cDNA expression studies of sulfotransferase in the mouse. Three sulfotransferase cDNA clones were isolated from a female B6CBA mouse liver. Two of the clones, mSTa1 and mSTa2, were highly homologous to each other. Alignment of mSTa1 and mSTa2 cDNAs' nucleotide sequences with those of other sulfotransferase cDNAs revealed the greatest sequence identity with the rat STsmp cDNA. This analysis suggests that mSTa1, mSTa2 and rSTsmp cDNAs are derived from orthologous genes belonging to the alcohol/hydroxysteroid sulfotransferase gene family. The third clone, mSTp1 showed high identity to rSTp, hSTp1, hSTp3, and rSTp1C1, suggesting that mSTp1 belongs to the phenol family.

Molecular cloning and functions of rat liver hydroxysteroid sulfotransferases catalysing covalent binding of carcinogenic polycyclic arylmethanols to DNA

Three sulfotransferases (STs) catalysing the metabolic activation of potent carcinogenic polycyclic arylmethanols were purified from female Sprague-Dawley (SD) rat liver cytosol without loss of their enzyme activities in the presence of Tween 20 used for preventing the enzymes from aggregation during purification and identified as hydroxysteroid sulfotransferases (HSTs). All the purified HSTs, STa, STb, and STc, with different electric charges had an apparently equal size of subunit (30.5 kDa) and cross-reacted with polyclonal antibody raised against STa. Our study on molecular cloning of cDNA libraries from two female SD rat livers indicated that both contained cDNA inserts coding for 5 different HST subunits, consisting of 284-285 amino acid residues (M(r), 33,084-33,535) and sharing strong amino acid sequence identity (> 83%). Of the 5 HST subunits, two had an identical amino acid sequence except for only one amino acid residue, and the other two contained only 6 amino acid substitutions in their sequences.

Structural similarity and diversity of sulfotransferases

In the present study, four new forms of aryl sulfotransferase cDNAs have been isolated and their structures determined. A compilation of primary structures of 16 different sulfotransferases, including enzymes metabolizing endogenous chemicals and xenobiotics, showed a considerable extent of similarity among bacterial, plant and mammalian species, and indicates that these enzymes constitute a supergene family. Aryl sulfotransferase and estrogen sulfotransferase are shown to belong to a single gene family (ST1) which consists of at least four subfamilies, whereas, based on the sequence similarity, hydroxysteroid sulfotransferases constitute a distinct family (ST2). Little or no clear similarity was observed between the primary structures of enzymes N-sulfating aminosugars and those sulfating hydrophobic chemicals such as phenols, alcohols or amines, indicating that both types of enzymes diverged early in their evolutionary history. Two regions in the C-terminal parts are, however, conserved among all enzymes examined, which suggests a possibly essential role of these sites for the binding of a PAPS cofactor or for sulfate transfer.

Cloning and expression of cDNA encoding human placental estrogen sulfotransferase

Using two oligoprimers derived from the bovine placental estrogen sulfotransferase sequence, we amplified a probe for human placental estrogen sulfotransferase. Using this probe to screen a human placental cDNA library constructed in lambda gt11, we isolated a cDNA clone of 1.3 kb encoding human estrogen sulfotransferase. DNA analysis predicts a protein of 295 amino acids with a calculated molecular weight of 34,199. Alignment of the amino acid sequence with other sulfotransferases indicates that human placental estrogen sulfotransferase shares 68.6, 68.2 and 65.9% similarity with bovine placental, guinea pig adrenocortical, and rat liver estrogen sulfotransferase, respectively. It shows also 95.6, 57.6, 85.3, and 54.2% similarity to human phenol, human DHEA, rat phenol, and rat hydroxysteroid sulfotransferase, respectively. Transfection of expression vectors encoding human estrogen sulfotransferase and dehydroepiandrosterone (DHEA) sulfotransferase in human adrenal adenocarcinoma SW-13 cells indicates that estrogen sulfotransferase transforms estrone more specifically, whereas DHEA sulfotransferase is more specific for DHEA and pregnenolone.

Biochemistry of cytosolic sulfotransferases involved in bioactivation

Numerous studies have indicated that two classes of cytosolic STs are involved in the bioactivation of procarcinogens and drugs to reactive electrophiles, especially in rodent tissues. These two classes of STs are the hydroxysteroid STs, which are involved in the conjugation of hydroxymethyl PAHs, and the phenol STs involved in the sulfation of alkenylbenzenes and N-hydroxyarylamines. Purification studies of rat liver STs have clearly indicated that specific isoforms of hydroxysteroid and phenol STs are capable of sulfating procarcinogens in vitro. Rat liver STa and BAST I are structurally similar hydroxysteroid STs, which have been shown to sulfate and bioactive HMBA. Molecular cloning studies of the rat hydroxysteroid STs indicate that these enzymes are probably part of a family of closely related genes. The single human hydroxysteroid ST that has been characterized is very similar to the rat enzymes, but its role in the bioactivation of hydroxymethyl PAHs has not been established. Phenol STs have been demonstrated to have an important role in the bioactivation of alkenylbenzenes and N-hydroxyarylamines. Purification of rat phenol STs has identified several different forms, but only some appear to be involved in bioactivation of procarcinogens. Four isoforms (HAST I and II, AST III and IV) are apparently responsible for the majority of N-hydroxyarylamine sulfation. The relationship between these enzymes has not been established but they may represent similar enzymes. Different isoforms of rat phenol ST are also involved in the bioactivation of procarcinogens and drugs. However, the role of these phenol STs, PST-1, Mx-ST, and paracetamol ST, in carcinogenesis requires further study. In human tissues, only two phenol STs, P-PST and M-PST, have been identified. The role of these enzymes or unidentified STs in the sulfation of N-hydroxyarylamine procarcinogens has not yet been established. Initial reports of the molecular cloning and expression of the rat and human phenol ST genes will provide a valuable mechanism for the characterization of roles of the individual enzymes in bioactivation.

Genomic structure of rat liver aryl sulfotransferase IV-encoding gene

This report contains the first description of the genomic structure for a sulfotransferase (ST). The gene (ASTIV) encodes rat hepatic aryl ST IV, also known as tyrosine-ester ST (EC 2.8.2.9). A phage genomic clone containing 70% of the 3' AST gene coding sequence was isolated after screening a rat genomic library with an ASTIV cDNA. The remaining 5' sequence was determined from a PCR product obtained from rat genomic DNA and ASTIV cDNA-specific primers. ASTIV spans 3.5 kb and contains eight exons and seven introns. The fourth intron of this gene contains sequences homologous to rodent B1 repetitive elements and an Alu repeat found in rat. An alignment of the primary structures of ten different ST revealed several conserved regions, as well as a putative binding site for the cofactor for enzymatic sulfation reactions, 3'-phosphoadenosine-5'-phosphosulfate.

Developmental changes in the isoelectric variants of rat hepatic hydroxysteroid sulphotransferase

Major isoenzymes of androsterone-sulphating sulphotransferase (AD-ST) were isolated from liver cytosols of weanling and young adult female rats and their isoelectric properties were compared. On chromatofocusing the enzyme activity of young adults was eluted over a wider range of pH than was that of weanling rats. The activity at pH 7.8-7.2 (fraction I) is obvious at both ages, whereas the activity eluted over the pH 6.6-5.5 range (fraction II) is much lower in weanlings than in young adults. The AD-ST activities eluted in fractions I and II were separately purified by 3'-phosphoadenosine 5'-phosphate-agarose affinity chromatography at both ages. Two-dimensional gel electrophoresis of the isolated enzyme revealed several subunits with distinct pI values, but with the same molecular mass, namely 30 kDa. The relative levels of the pI 6.7 and pI 7.2 subunits are high and the relative level of the pI 6.1 is low in fraction I. In fraction II, the levels of pI 6.1 and pI 6.7 subunits are high and the level of the pI 7.2 subunit is low. There is no significant difference in the relative levels of the pI variants in each fraction between weanlings and young adults. The N-terminal amino acid sequences of the pI variants are identical within the area determined, irrespective of animal age or pI values. These results demonstrate that the pI variants of AD-ST are derived from the same precursor by post-translational modification or that they are products of closely related, but distinct, genes. The pI 6.1 and 6.7 subunits presumably increased during the development from the weanling stage to adulthood, resulting in the increase in acidic form(s) of AD-ST (fraction II) in adult females.

Steroid sulfation Current concepts

Formation of steroid sulfates is catalyzed by sulfotransferase enzymes that are widely distributed and frequently of high specificity. Steroid sulfates cannot be described as being active hormones, but some serve in tissue sites as precursors of active steroids formed by enzymic cleavage of the sulfate group by sulfatase enzymes. There is increasing evidence that intracellular sulfation and desulfation can play a role in regulating the availability of active steroid hormones near target sites. There are strong indications for this regulation in the uterine compartment, in the liver, and in mammary cancer cells.

Immunochemical characterisation of a dehydroepiandrosterone sulfotransferase in rats and humans

A member of the rat liver hydroxysteroid sulfotransferase (ST) enzyme family metabolising dehydroepiandrosterone (DHEA) was purified from female rats and used to raise rabbit polyclonal antibodies. Characterisation of this antibody preparation demonstrated that it was specific for DHEA ST, and recognised a single 30-kDa protein on immunoblot analysis of rat liver cytosol which was expressed preferentially in female rat liver, and immunohistochemical localisation of the protein in female rat liver determined that DHEA ST was distributed homogeneously in the cytoplasm of hepatocytes. Examination of the extrahepatic expression of this protein showed it to be located predominantly in the liver, although a small amount of enzyme activity was found in the kidney which was not apparently subject to the same sex difference as the hepatic activity. Immunological analysis suggested that this activity was not due to the action of DHEA ST, but to another, unidentified ST isozyme. The antibody cross-reacted strongly with adult human liver DHEA ST, recognising a protein of 35 kDa on immunoblotting. Using this antibody preparation, the distribution of DHEA ST in mid-trimester human fetal tissues was examined, and it was shown that the enzyme is expressed in the adrenal and liver, but not to any significant extent in the kidney or lung. This antibody therefore provides a powerful tool for investigating the function of DHEA ST.

Purification and immunochemical characterization of a male-specific rat liver oestrogen sulphotransferase

Sulphation of oestrogens represents an important regulatory mechanism for these biologically active compounds. We have characterized and purified a form of rat liver sulphotransferase (ST), existing as a 32,500 Da monomer, which sulphates oestrogens, and have used this preparation to produce antibodies against oestrogen ST. The enzyme was active against oestrone, oestriol and beta-oestradiol, but not towards androgens. Using the antibody as a probe for immunoblotting, it was determined that the enzyme is expressed solely in male rats, and predominantly in the liver. Of the tissues examined, the only major extrahepatic tissue found to have any oestrogen ST was the brain (although the levels were very low), indicating that there might be a role for the sulphation of oestrogens in the brain. Examination of human liver and platelet cytosols by immunoblotting showed that the antibody recognized two major proteins of 32 and 34 kDa, which were presumed to correspond to the two principal phenol ST isoenzymes present in man.

Molecular cloning of cDNA encoding the phenol/aryl form of sulfotransferase (mSTp1) from mouse liver

The cDNA sequence of the mouse liver phenol/aryl form of sulfotransferase (mSTp1) has been determined. The cloned cDNA consists of 1269 base pairs (bp) and contains an 897 nucleotide open reading frame (ORF) beginning at nucleotide 65, which encodes a 298 amino acid polypeptide of 34.7 kDa. Alignment of mSTp1 to other sulfotransferases shows overall identities of 87% to r-STp, 37% to r-STa, 48% to r-STe, 51% to b-STe, and 37% to h-STa, at the deduced amino acid level.

Cloning and expression of human liver dehydroepiandrosterone sulphotransferase

Dehydroepiandrosterone sulphotransferase (DHEA-ST) catalyses the 3'-phosphoadenosine 5'-phosphosulphate-dependent sulphation of a wide variety of steroids in human liver and adrenal tissue and is responsible for most, if not all, of the sulphation of bile acids in human liver. This report describes the isolation, characterization and expression of a cDNA which encodes human liver DHEA-ST. The DHEA-ST cDNA, designated DHEA-ST8, was isolated from a Uni-Zap XR human liver cDNA library and is composed of 1060 bp and contains an open reading frame encoding a 285-amino-acid protein with a molecular mass of approx. 33765 Da. Translation of DHEA-ST8 in vitro generated a protein identical in molecular size with that of DHEA-ST. Expression of DHEA-ST8 in COS-7 cells produces an active DHEA-ST protein which is capable of sulphating DHEA, has the same molecular mass as human liver DHEA-ST and is recognized by rabbit anti-(human liver DHEA-ST) antibodies. Northern-blot analysis of human liver RNA detects the presence of three different size transcripts; however, Southern-blot analysis of human DNA suggests that only one gene may be present in the genome. These results describe the cloning of a human ST which has an important role in the sulphation of steroids and bile acids in human liver and adrenals.

Molecular cloning of the alcohol/hydroxysteroid form (hSTa) of sulfotransferase from human liver

A cDNA encoding the human alcohol/hydroxysteroid sulfotransferase (h-ST-a), which catalyzes the sulfo-conjugation of many drugs and hormones, was isolated from a human liver cDNA library using a rat STa (rSTa) cDNA probe. The cDNA, designated as hSTa, consists of 1069 base pairs (bp) and contains an 855-nucleotide open reading frame beginning at nucleotide 65, which encodes a 285 amino acid polypeptide of 33.76 kDa. A second cDNA clone (1563 bp) was truncated 5' at nucleotide 231 (lacking the first 15 amino acids) with identical coding region, however, it had a much longer 3' untranslated region (UTR). Both clones contained a short segment of poly(A)+ tail. Northern blot analysis of an adult human liver showed that there are at least 2 mature mRNA with sizes ranging from approximately 1.1 kb to 1.7 kb, verifying the authenticity of the obtained cDNA clones. From the sequence alignment, the hSTa shares 62%/74%, 39%/59%, 35%/48%, 36%/54% identity with rSTa, rSTp (phenol), rSTe (estrogen), and bovine STe (bSTe) at the deduced amino acid and DNA levels, respectively, indicating that there are at least three subfamilies (alcohol, phenol and estrogen) of genes that encode for sulfotransferases in mammals.

Immunochemical characterization of developmental changes in rat hepatic hydroxysteroid sulfotransferase

A major isoenzyme of hepatic androsterone-sulfating sulfotransferase (AD-ST) was purified from adult female rats. The activity was purified 122-fold over that found in the cytosol and showed a single protein band with a subunit molecular mass of 30 kDa after sodium dodecyl sulfate polyacrylamide gel electrophoresis. The purified enzyme exhibited four isoelectric variants of subunits on denaturing isoelectrofocusing gels (pI = 5.8, 6.1, 6.7 and 7.2). Rabbit antiserum raised against the enzyme specifically detected AD-ST polypeptide in rat liver cytosol. Immunoblot analysis of liver cytosol from female and male rats at various ages showed good correlation between the levels of AD-ST activity and AD-ST polypeptide. Significant levels of AD-ST activity and polypeptide were detected in senescent male rats, though normal adult male rats have very low levels of AD-ST activity and protein. The relative content of the isoelectric variants of AD-ST were different in liver cytosol of weanling and adult females, indicating that age- and gender-related alterations of hepatic AD-ST activity are primarily determined by the levels of AD-ST polypeptide and the relative amounts of the four isoelectric variants of the enzyme.

Differential localization of sulfotransferase isoenzymes in rat liver

Liver sections prepared from male and female rats were immunohistochemically stained with the antisera against phenol sulfotransferase G (P-STG), an isoenzyme of phenol ST as well as androsterone-sulfating ST (AD-ST), an isoform of hydroxysteroid ST. Localization of these isoenzymes in liver is sex-dependent and is markedly different between the two. P-STG is preferentially localized in the hepatocytes proximal to the central vein in females, whereas it is present in all the hepatocytes throughout the liver in males. On the other hand, AD-ST is evident in the hepatocytes proximal to the portal triad in males, while in females it is synthesized and localized in all the hepatocytes. The polarized sex-related localization of these ST isoenzymes appears to correlate with differential hormonal regulation of the enzymes.

Molecular characterization of two plant flavonol sulfotransferases

cDNA clones coding for flavonol 3- and 4'-sulfotransferases (STs) were isolated by antibody screening of a cDNA expression library produced from poly(A)+ RNA extracted from terminal buds of Flaveria chloraefolia. Sequence analysis revealed full-length cDNA clones with open reading frames of 933 and 960 base pairs, which encode polypeptides containing 311 and 320 amino acids, respectively. This corresponds to a molecular mass of 36,442 Da for the 3-ST and 37,212 Da for the 4'-ST. Expression of these clones in Escherichia coli led to the synthesis of beta-galactosidase-ST fusion proteins having the same substrate and position specificities as those for the 3- and 4'-flavonol ST enzymes isolated from the plant. Comparison of the deduced amino acid sequence of the two clones revealed an overall identity of 69% in 311 amino acid residues. The two flavonol STs of F. chloraefolia also shared significant sequence similarities with steroid and aryl STs found in animal tissues and with the senescence marker protein 2 isolated from rat liver, suggesting an evolutionary link between plant and animal STs.

Molecular basis of symbiotic host specificity in Rhizobium meliloti: nodH and nodPQ genes encode the sulfation of lipo-oligosaccharide signals

The symbiosis between Rhizobium and legumes is highly specific. For example, R. meliloti elicits the formation of root nodules on alfalfa and not on vetch. We recently reported that R. meliloti nodulation (nod) genes determine the production of acylated and sulfated glucosamine oligosaccharide signals. We now show that the biochemical function of the major host-range genes, nodH and nodPQ, is to specify the 6-O-sulfation of the reducing terminal glucosamine. Purified Nod factors (sulfated or not) from nodH+ or nodH- strains exhibited the same plant specificity in a variety of bioassays (root hair deformations, nodulation, changes in root morphology) as the bacterial cells from which they were purified. These results provide strong evidence that the molecular mechanism by which the nodH and nodPQ genes mediate host specificity is by determining the sulfation of the extracellular Nod signals.

Age and gender-related gene expression of hydroxysteroid sulfotransferase-a in rat liver

Hepatic hydroxysteroid sulfotransferase-a (HST-a) gene expression was examined in young male (age 22-26 days) and female rats (age 22-30 days), and in older male (age 42-45 days) and female (age 49-55 days) rats. Northern and slot blot analyses of poly(A)+RNA revealed that HST-a was differentially expressed with respect to both age and gender with female rats expressing higher levels of HST-a in both age groups. Hepatic HST-a mRNA levels were approximately 4 to 6-fold higher in females compared to males in both age groups examined. HST-a expression increased with age in both male and female rats. HST-a expression was approximately 8 to 10-fold higher in 42-45 day old males relative to 22-26 day old males. HST-a mRNA levels were approximately 3 to 7-fold higher in 49-55 day old females relative to females in the 22-30 day age group. These data suggest that HST-a gene expression is transcriptionally controlled and that HST-a regulation is subject to hormonal and developmental modulation.

Age- and sex-related differences in activation of the carcinogen 7-hydroxymethyl-12-methylbenz[a]anthracene to an electrophilic sulfuric acid ester metabolite in rats. Possible involvement of hydroxysteroid sulfotransferase activity

Metabolic activation of 7-hydroxymethyl-12-methylbenz[a]anthracene (HMBA) and related hydroxymethyl polycyclic aromatic hydrocarbons to electrophilic and mutagenic sulfuric acid esters has been demonstrated previously (Watabe et al., In: Xenobiotic Metabolism and Disposition (Eds. Kato R, Estabrook RW and Cayen MN), pp. 393-400. Taylor & Francis, London, 1989). In the present study, the rat hepatic sulfotransferase activity catalyzing the formation of such reactive sulfuric acid esters was inhibited strongly by dehydroepiandrosterone, a typical substrate hydroxysteroid sulfotransferases (HSSTs). Pentachlorophenol, a potent phenol sulfotransferase inhibitor, had little effect in this regard. A marked sex difference was observed for the hepatic cytosolic sulfotransferase activity for HMBA in rats. This sex difference was age-related; no significant difference was observed in preweanling rats, whereas in adult rats female rat liver showed a much higher enzyme activity. These age- and sex-related differences in the sulfonation of HMBA reflect the regulation of HMBA sulfotransferase activity by gonadal hormones as previously demonstrated with HSSTs. Thus, pretreatment with estradiol benzoate significantly enhanced the sulfotransferase activity for HMBA in both male and female rats, (P less than 0.01 and P less than 0.05 respectively), whereas testosterone propionate pretreatment decreased this activity. Castration of male rats increased the HMBA sulfotransferase activity 2- to 3-fold compared with that in control animals. By contrast, ovariectomy reduced the enzyme activity 38% in females. These results imply that rat liver HSST activity is responsible for the sulfonation of HMBA. Intraperitoneal injection of HMBA (0.25 mumol/g body wt) into infant rats produced benzylic DNA adducts in the liver which were chromatographically identical with those obtained from incubations of HMBA with deoxyguanosine and deoxyadenosine in the presence of hepatic cytosolic sulfotransferase activity. Intraperitoneal administration of sodium 7-sulfooxymethyl-12-methylbenz[a]anthracene resulted in much higher levels of these adducts and the deoxycytidine adduct in the liver DNA than did an equimolar amount of the parent hydroxymethyl hydrocarbon. The levels of hepatic benzylic DNA adducts formed from HMBA were reduced markedly by pretreatment of rats with dehydroepiandrosterone, a strong inhibitor of hepatic sulfotransferase activity for this hydrocarbon.

Localization of minoxidil sulfotransferase in rat liver and the outer root sheath of anagen pelage and vibrissa follicles

The precise biochemical mechanism and site(s) of action by which minoxidil stimulates hair growth are not yet clear. Minoxidil sulfate is the active metabolite of minoxidil, with regard to smooth muscle vasodilation and hair growth. Formation of minoxidil sulfate is catalyzed by specific PAPS-dependent sulfotransferase(s) and minoxidil-sulfating activities have been previously reported to be present in liver and hair follicles. One of these minoxidil-sulfating enzymes has been purified from rat liver (rat minoxidil sulfotransferase, MST) and a rabbit anti-MST antibody has been prepared. Using this anti-MST antibody, we have immunohistochemically localized minoxidil sulfotransferase in the liver and anagen hair follicles from rat. In rat pelage and vibrissa follicles, this enzyme is localized within the cytoplasm of epithelial cells in the lower outer root sheath. Although the immunolocalization of MST might not necessarily correlate with the MST activity known to be present in anagen follicles, the results of this study strongly suggest that the lower outer root sheath of the hair follicle may serve as a site for the sulfation of topically applied minoxidil.

Purification and immunochemical characterization of a rat liver sulphotransferase conjugating paracetamol

Paracetamol sulphotransferase (ST) was purified 250-fold from male rat liver, and the pure enzyme used to elicit antibodies in rabbit. The enzyme was active towards paracetamol at pH 9.0, as well as towards several commonly used drugs, and formed sulphates at both O- and N-atoms. Comparison of the substrate specificity of paracetamol ST with that of aryl sulphotransferases isolated by other workers suggested that we have purified a previously unknown isoenzyme of rat liver ST, although the difficulties of characterization of STs based on their substrate specificities is noted. The antibody preparation recognized only one polypeptide (Mr = 35,000) on immunoblot analysis of rabbit liver cytosol, corresponding to purified paracetamol ST. Analysis of the tissue distribution of this protein demonstrated that its expression was restricted to the liver, as was the enzyme activity. The observed sex difference in paracetamol ST (males greater than females) was determined by immunoblot analysis to be the result of reduced enzyme protein levels in females. In human liver cytosol, the antibody recognized two polypeptides, probably corresponding to M- and P-phenol STs, suggesting significant sequence similarity between rat and human phenol sulphotransferases.

cDNA cloning of the hydroxysteroid sulfotransferase STa sharing a strong homology in amino acid sequence with the senescence marker protein SMP-2 in rat livers

A cDNA encoding hydroxysteroid sulfotransferase a (STa), which catalyzes activation of carcinogenic polycyclic hydroxymethyl-arenes, was isolated from a lambda gtll cDNA expression library constructed from poly(A)+RNA of a female Sprague-Dawley (SD) rat liver. The cDNA, designated as ST-40, consisted of 1,015 base pairs which had an open reading frame of 852 base pairs encoding the entire rat STa subunit of 284 amino acids. The nucleotide base sequence of the ST-40 cDNA shared a strong homology of 94.4% with that of ST-20 cDNA encoding a hydroxysteroid ST which had been reported by us. The deduced amino acid sequence of STa had a homology of 73.7% with that of an SD rat liver senescence marker protein (SMP-2) consisting of 282 amino acid residues. However, STa was found to share a much stronger homology of 92% on the average with SMP-2 in their four specific regions corresponding to about 60% of the total sequences, indicating SMP-2 to be an isozyme of hydroxysteroid ST.