Immunochemical characterisation of a dehydroepiandrosterone sulfotransferase in rats and humans

Abstract

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.Sulfation is an important pathway of metabolism for a host of xenobiotics (e.g. drugs, carcinogens, environmental chemicals) and endogenous compounds (e.g. steroid hormones, bile acids, neurotransmitters and small peptides j, which in general (though not always) reduces the biological activity of compounds through the attachment of a polar sulfate group to various hydroxyl and amine groups [l, 21. These reactions are catalysed by a family of sulfotransferase isozymes (ST), present in the cytosolic fraction of the liver and other tissues. In rats, a number of subfamilies of ST have been discovered, which exhibit enzyme activities towards different classes of substrate, including phenol ST, hydroxysteroid ST and estrone ST, and it is believed, based on protein-purification experiments and the sex differences in the expression of the different activities, that each of these subfamilies comprises a number of different ST enzymes with distinct but overlapping substrate specificities Abbreviations. DHEA, dehydroepiandrosterone ; DHEA-S, dehydroepiandrosterone sulfate ; ST, sulfotransferase; PAdoPS, 3'-phosphoadenosine 5'-phosphosulfate; FITC, fluorescein isothiocyanate; PAdoP, adenosine 3',5'-diphosphate. Dehydroepiandrosterone (DHEA) is an important steroid hormone, and its sulfate ester (DHEA-S) is the major circulating steroid. The exact physiological role(s) of DHEA (and DHEA-S) still remains unclear, although it has been established that DHEA-S is a good substrate for steroid biosynthesis [18-201, and much speculation has appeared regarding the observed anticancer [21], anti-obesity [22] and antidiabetic [2...

Rat, but not human, sulfotransferase activates a tamoxifen metabolite to produce DNA adducts and gene mutations in bacteria and mammalian cells in culture

“…This may explain the liver specificity of the carcinogenic effect, as rHSTa is primarily a hepatic enzyme (16)(17)(18) and reactive sulfuric acid conjugates may not be readily transferred from one cell to another owing to their charge. For example, 1-hydroxymethylpyrene, a compound which is activated by SULTs, forms DNA adducts in SULT-proficient, parenchymal liver cells, but not in neighbouring, SULT-deficient, Kupffer cells in the rat (30).…”

“…Therefore, if α-hydroxytamoxifen is activated by SULT, then SULT2 enzymes are the most likely candidates. In the rat, hydroxysteroid sulfotransferase a (rHSTa) is the predominant SULT2 form; rHSTa is highly expressed in the liver, whereas in all other tissues that have been investigated its expression is very low or not detectable (16)(17)(18). In humans only a single SULT2 form, hHST is known (16).…”

Novel lipoidal derivatives of pregnenolone and dehydroepiandrosterone and absence of their sulfated counterparts in rodent brain

“…In some studies, the enzyme was not detected in human (11,12), mouse (13), or rat (12) brain, although some groups have found the enzyme in rat (14,15) and in frog (16) brain. Other studies have reported a very low hydroxysteroid sulfotransferase activity in rat (17) and human (18) brain.…”

Investigation of the Localization of Dehydroepiandrosterone Sulphotransferase in Adult Rat Kidney

“…However, as DHEA-ST is distributed across the liver lobule [16], with perhaps higher activity found in periportal hepatocytes than perivenous [12], the activity in liver homogenate would be expected to be high as more cells express the enzyme in comparison to the kidney. The liver is the main site for endogenous and xenobiotic metabolism generally within the body, and the high activity of this phase II enzyme might also, therefore, be expected.…”

“…Expression was only noted in liver and adrenals, with none being observed in kidney. The only previous report of DHEA-ST in rat kidney was made by Sharp et al [16]who postulated that it might represent a different isoform of sulphotransferase, since immunological studies showed a band of different molecular weight from the sulphotransferase isolated from the liver. In the rat kidney, DHEA also modulates expression of the cytochrome P-450 isoform [17].…”