Aryl-(SULT1A1), estrogen-(SULT1E1), and hydroxysteroid-(SULT2A1) sulfotransferases (SULTs) are active determinants of xenobiotic detoxication and hormone metabolism in the adult human liver. To investigate the role of these conjugating enzymes in the developing human liver, the ontogeny of immunoreactive SULT1A1, SULT1E1, and SULT2A1 expression was characterized in a series of 235 pre-and postnatal human liver cytosols ranging in age from early gestation to a postnatal age of 18 years. Interindividual variability in expression levels was apparent for all three SULTs in pre-and postnatal liver samples. Expression of the three SULTs displayed distinctly different developmental profiles. Semiquantitative Western blot analyses indicated that SULT1A1 and SULT2A1 immunoreactive protein levels were readily detectable in the majority of developmental human liver cytosols throughout the prenatal period. Whereas SULT1A1 expression did not differ significantly among the various developmental stages, SULT2A1 expression increased during the third trimester of gestation and continued to increase during postnatal life. By contrast, SULT1E1, a cardinal estrogen-inactivating enzyme, achieved the highest levels of expression during the earliest periods of gestation in prenatal male livers, indicating a requisite role for estrogen inactivation in the developing male. The present analysis suggests that divergent regulatory mechanisms are responsible for the differential patterns of hepatic SULT1A1, SULT1E1, and SULT2A1 immunoreactive protein levels that occur during pre-and postnatal human development, and implicates a major role for sulfotransferase expression in the developing fetus.

The effects of rifampicin treatment on SULT2A1 mRNA expression were evaluated in 23 preparations of primary cultured human hepatocytes. In contrast to the consistently occurring induction of CYP3A4, a prototypical pregnane X receptor (PXR) target gene, rifampicin treatment increased SULT2A1 mRNA levels in 12 of the hepatocyte preparations, but it produced little change or even suppression in the others. Transient transfection of HepG2 cells with a series of reporter constructs implicated two SULT2A1 5Ј-flanking regions as containing rifampicin-responsive information. Each of these regions contained a hepatocyte nuclear factor 4 (HNF4) binding site (at nucleotide [nt] Ϫ6160 and Ϫ54), as demonstrated by in vitro binding and site-directed mutagenesis. HNF4␣ bound to the HNF4-54 region of the endogenous SULT2A1 gene, as indicated by chromatin immunoprecipitation. Cotransfection of HepG2 cells with pregnane X receptor (PXR) dose-dependently suppressed reporter expression from SULT2A1 constructs containing the HNF4 sites, and rifampicin treatment augmented the suppression. Rifampicin treatment concentration-dependently suppressed SULT2A1 reporter expression at the same concentrations that progressively induced expression from a PXR-responsive CYP3A4 reporter, whereas higher rifampicin concentrations reversed the SULT2A1 suppression. The suppressive effect of rifampicin was diminished, whereas the activating effect was augmented, in HepG2 cells with RNA interference-mediated PXR knockdown. These results suggest that HNF4␣ plays a central role in the control of SULT2A1 transcription and that rifampicin-liganded PXR suppresses SULT2A1 expression by interfering with HNF4␣ activity. By contrast, the rifampicin-inducible SULT2A1 expression that occurs in many human hepatocyte preparations seems to be mediated through a PXR-independent mechanism.

ABSTRACT:To determine whether the dexamethasone (DEX)-inducible hepatic sulfotransferase gene expression that has been described in the rat is conserved in humans, the effects of DEX treatment on hydroxysteroid sulfotransferase (SULT2A1) and aryl sulfotransferase (SULT1A1) gene expression were investigated in primary cultured human hepatocytes. Hepatocytes were prepared from nontransplantable human livers by collagenase perfusion of the left hepatic lobe, and cultured in Williams' medium E that was supplemented with 0.25 U/ml insulin. As reported in the rat, DEX treatment produced concentration-dependent increases in SULT2A1 mRNA and protein expression, with maximum increases observed at concentrations of DEX that would be expected to activate the pregnane X receptor (PXR) transcription factor. In contrast to the rat, in which DEX-inducible SULT1A1 expression has been demonstrated, SULT1A1 expression in primary cultured human hepatocytes was not measurably increased by DEX. In transient transfections conducted in primary cultured rat hepatocytes, the PXR ligands DEX and pregnenolone-16␣-carbonitrile significantly induced transcription of human and rat SULT2A reporter gene constructs. Cotransfection of either the human or rat SULT2A reporter gene with a PXR dominant negative construct significantly reduced DEX-inducible transcription. These results underscore that while certain features of rat hepatic sulfotransferase gene regulation are conserved in humans, important differences exist across species. The findings also implicate a role for the PXR transcription factor in DEXinducible rat and human SULT2A gene expression.The cytosolic aryl sulfotransferase (SULT1A1 2 ) and hydroxysteroid sulfotransferase (SULT2A1) conjugating enzymes catalyze the transfer of a ϪSO 3 H moiety from the physiological sulfate donor 3Ј-phosphoadenosine-5Ј-phosphosulfate to the appropriate phenolic or hydroxysteroid substrates, respectively (Jakoby et al., 1980). In drug metabolism, sulfate conjugation is recognized as a double-edged sword. As a rule, sulfate conjugates are more polar than the parent substrate and hence, more amenable to excretion and elimination. However, the production of unstable sulfate conjugates can lead to the focused generation of genotoxic species and carcinogen activation.In both rats and humans, SULT1A1 and SULT2A1 enzymes are abundantly expressed in the liver, which is the seat of drug metabolism in mammalian species Falany et al., 1995). Human SULT2A1 is also expressed in the fetal (Parker et al., 1994) and adult adrenal gland (Comer and Falany, 1992), the adult small intestine (Her et al., 1996), and gastric mucosa (Tashiro et al., 2000). Relative to SULT2A1, human SULT1A1 is more extensively expressed in extra-hepatic tissues. SULT1A1 detoxifies common phenolic pharmaceuticals, such as acetaminophen (Larrey et al., 1986) and troglitazone (Honma et al., 2001), and metabolizes the hypotensive and hypertrichotic drug minoxidil to its pharmacologically active form (Falany and Kerl, 1990). The well described g...